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Empirical open stope design in Canada Potvin, Yves 1988

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EMPIRICAL OPEN 8TOPE DESIGN IN CANADA  By YVES POTVIN B . A . S c , U n i v e r s i t e LAVAL, Quebec 1982 M . A . S c . , U n i v e r s i t y o f B r i t i s h C o l u m b i a , 1985 A THESIS  SUBMITTED I N PARTIAL FULFILLMENT OF  THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY in THE FACULTY OF GRADUATE STUDIES DEPARTMENT OF MINING AND MINERAL PROCESS ENGINEERING We a c c e p t t h i s to  t h e s i s as  the required  conforming  standard  THE UNIVERSITY OF BRITISH COLUMBIA NOVEMBER 1988 @  Yves P o t v i n ,  1988  In  presenting  this  degree at the  thesis in  University of  partial  fulfilment  of  this  department  or  thesis for by  his  or  requirements  for  an advanced  British Columbia, I agree that the Library shall make it  freely available for reference and study. I further copying of  the  agree that permission for extensive  scholarly purposes may be her  representatives.  It  is  granted by the understood  that  head of copying  my or  publication of this thesis for financial gain shall not be allowed without my written permission.  Department of  KtKtii^C £ hiotfc*) PROCESS E/Q'  The University of British Columbia 1956 Main Mall Vancouver, Canada V6T 1Y3 Date  n F . f i n / f t - n  hft<tctt  \ \R<\ C  ABSTRACT  This  thesis  stability  in  fundamental mechanics  addresses  open  aspects design  characterization properties The  and  mining  t o be  of  open  o f underground  methods.  considered stopes.  There  i n an  The  components  affecting  the rock  are  three  engineering  first  o f the rock mass t o i d e n t i f y  excavation  aspect  rock  i s the  and q u a n t i f y the mass  behaviour.  second aspect i s the e f f e c t o f the s t r e s s f i e l d s on the rock  mass  that  zones  may  result  of relaxation  physical the  stope  the t o p i c  condition  size,  regard  geometry  i n zones i n stope  of high  walls.  of the problem and r e l a t i v e  The t h i r d  stress  aspect  orientation  o f openings  field.  or  i s the  and i s d e f i n e d p r i m a r i l y  t o t h e rock mass and the s t r e s s  of these t h r e e fundamental  compressive  by  with  The i n t e r a c t i o n  a s p e c t s c o n s t i t u t e s t h e problem  t o be  investigated. The reliable that  the  predict geological  model  the  of  the  study  i s to  develop  a  (based on the above t h r e e aspects)  stability  settings.  of  open  An e m p i r i c a l  stopes  in  approach  was  typical chosen  t h e development o f the model, because o f t h e complexity of problem  parameters more  objective  geomechanical  can  Canadian for  principal  and  the  difficulty  with p r e c i s i o n .  reliable  since  they  in  Empirical make  use  estimating  the  input  methods are l i k e l y  t o be  of  past  experience.  A  c o n s i d e r a b l e amount o f e f f o r t has been spent i n b u i l d i n g a broad data  base  which  includes  more ii  than  250  case  histories  of  unsupported The large  and supported stopes from 34 Canadian  application number  calibration  of  of  the  model  representative  of each  in  the  mines.  b a c k - a n a l y s i s of  case  histories  a  allowed  of the f a c t o r s composing the model.  Since  the model's p r e d i c t i o n corresponds very w e l l t o the a c t u a l stope behaviour  in  empirically The  most  case  histories,  the  model  is  considered  verified.  effect  stability  of e x t e r n a l  that  are  not  factors related  (parameters to  the  affecting  geotechnical  g e o m e t r i c a l c o n d i t i o n s ) have a l s o been i n v e s t i g a t e d . of  applicability  guidelines based  on  of  the  systematic  of b l a s t i n g ,  in  case  include  of  there  are  been  effect  time no  limit  d e f i n e d and  rough  past  quantified,  of  blasting of  in  concern  activities  i n v e s t i g a t e d stope.  iii  in  the  has  actual  i n open the  proposed  experience. been  More r e s e a r c h i s r e q u i r e d  i s not mining  c o m p i l a t i o n of  although not  histories.  the  effect  has  or  The  f o r the d e s i g n of c a b l e support systems are  effect 18  cable b o l t i n g  stope  observed  i n order t o  modelwhile  stope  imediate  The  mining, area  of  the when the  TABLE OF CONTENTS  PAGE ABSTRACT  i i  LIST OF TABLES.  .  xi  LIST OF FIGURES  xiii  ACKNOWLEDGEMENTS  xxi  CHAPTER 1  INTRODUCTION  1  1.1  DEFINITION OF THE PROBLEM  1  1.2  OBJECTIVE OF THE PROJECT  4  1.3  CONTENTS OF THE THESIS  6  CHAPTER 2 2.1  2.2  REVIEW OF OPEN STOPE MINING PRACTICES  . . . .  INTRODUCTION  8 8  2.1.1  D e f i n i t i o n o f open stope mining  . . . . . . .  2.1.2  A p p l i c a t i o n s o f open stope mining  CLASSIFICATION OF OPEN STOPE MINING METHODS  8 9  . . . .  14  2.2.1  Mining d i r e c t i o n  14  2.2.2  Use o f p i l l a r s and b a c k f i l l  15  2.2.3  D r i l l h o l e diameter  20  2.2.4  Classification  o f open stope mining  . . . . .  21  2.3  DESCRIPTION OF OPEN STOPING PRE-PRODUCTION DEVELOPMENT  21  2.4  DESCRIPTION OF OPEN STOPE MINING AND SEQUENCING  24  with no b a c k f i l l  . .  2.4.1  Open stopirig  2.4.2  Open s t o p i n g w i t h b a c k f i l l  25  2.4.3  Stope and f i l l  32  mining iv  25  2.5  2.6  2.7  LONGHOLE OPEN STOPING  35  2.5.1  Longhole d r i l l i n g  37  2.5.2  Longhole b l a s t i n g  2.5.3  Longhole r e t r e a t i n g methods  . . . . . . .  39 39  BLASTHOLE OPEN STOPING  41  2.6.1  Blasthole  drilling  43  2.6.2  Blasthole  blasting  45  2.6.3  Blasthole  r e t r e a t i n g methods  46  SUMMARY AND CONCLUSIONS  CHAPTER 3  51  STRESS  56  3.1  INTRODUCTION  56  3 .2  PRE-MINING STRESS  58  3.3  STRESS MEASUREMENT  60  3.3.1  Method 1; F l a t j a c k  60  3.3.2  Method 2; H y d r a u l i c f r a c t u r i n g  61  3.3.3  Method 3; O v e r c o r i n g techniques  62  3.3.4  C o m p i l a t i o n o f s t r e s s measurements  64  3.4  INDUCED STRESS AND STRESS DISTRIBUTION  66  3.4.1  Components o f s t r e s s  68  3.4.2  Two d i m e n s i o n a l s t a t e o f s t r e s s  3.4.3  Two d i m e n s i o n a l c l o s e d  .  71  form s o l u t i o n o f simple  e x c a v a t i o n shape 3.5  72  NUMERICAL MODELLING  78  3.5.1  Continuum approach  79  3.5.2  Discontinuum approach v  ,  83  3.6  SUMMARY AND CONCLUSIONS  CHAPTER 4  . . .  84  FAILURE CRITERIA  87  4.1  INTRODUCTION  87  4.2  INTACT ROCK MATERIAL FAILURE CRITERIA  88  4.2.1  88  4.2.1.1  U n i a x i a l compressive s t r e n g t h  4.2.1.2  M u l t i a x i a l compressive s t r e n g t h  4.2.1.3  Uniaxial t e n s i l e strength  4.2.2 4.2.3 4.3  4.4  Laboratory t e s t i n g . . . .  89  . . .  91 92  A n a l y t i c a l approach  93  E m p i r i c a l approach  94  SHEAR FAILURE CRITERION ALONG AN EXISTING DISCONTINUITY  94  4.3.1  Shear s t r e n g t h  96  4.3.2  F r i c t i o n angle  .  98  JOINTED ROCK MASS FAILURE CRITERION  4.5 SUMMARY AND CONCLUSIONS  CHAPTER 5  101 .  104  REVIEW OF EXISTING DESIGN METHODS FOR UNDERGROUND OPENINGS  108  5.1  INTRODUCTION  108  5.2  ROCK MASS CLASSIFICATION DESIGN CHARTS  109  5.2.1  B i e n i a w s k i RMR system  109  5.2.2  Barton e t a l . system  5.2.3  D i s c u s s i o n o f the Q and RMR systems  5.3  LAUBSCHER S GEOMECHANICS 1  .  I l l 115  CLASSIFICATION OF JOINTED  ROCK MASSES  120 vi  5.4  5.5  5.6  5.3.1  D e s c r i p t i o n o f the model  121  5.3.2  Open stope d e s i g n a p p l i c a t i o n  128  5.3.3  D i s c u s s i o n o f the method  130  MATHEWS' OPEN STOPE DESIGN METHOD  131  5.4.1  D e s c r i p t i o n o f t h e method  131  5.4.2  D i s c u s s i o n o f the method  138  NUMERICAL MODELLING DESIGN  142  5.5.1  Open stope d e s i g n a p p l i c a t i o n  142  5.5.2  D i s c u s s i o n o f the method  144  SUMMARY AND CONCLUSIONS  CHAPTER 6  146  OPEN STOPE FAILURE MECHANISMS  149  6.1  INTRODUCTION  149  6.2  NATURE OF THE ROCK MASS  149  6.3  INTACT ROCK BEHAVIOUR  155  6.4  DISCRETE BLOCK BEHAVIOUR  6.5  JOINTED ROCK MASS BEHAVIOUR  158  6.6  SUMMARY AND CLASSIFICATION OF FAILURE MECHANISMS . .  160  CHAPTER 7  . . .  DEVELOPMENT OF THE GEOMECHANICAL MODEL . . . .  156  166  7.1  INTRODUCTION  166  7.2  THE BLOCK SIZE FACTOR  169  7.2.1 7.3  Estimation of block s i z e  STRESS FACTOR  169 . . . . .  174  7.3.1  E f f e c t o f compression  174  7.3.2  Open stope p a r a m e t r i c study  17 6  vii  7.3.2.1  General concept of the p a r a m e t r i c study  7.3.2.2  Longitudinal  7.3.2.3 7.4  177  open s t o p i n g p a r a m e t r i c  study  179  T r a n s v e r s e open s t o p i n g p a r a m e t r i c study  187  EFFECT OF JOINT ORIENTATION  195  7.4.1  The c r i t i c a l  198  7.4.2  E f f e c t of anisotropy  7.4.3  Shear s t r e n g t h o f the c r i t i c a l  joint factor  200 joint  . . . .  202  7.5  THE GRAVITY FACTOR  2 02  7.6  EFFECT OF STOPE SIZE AND SHAPE  203  7.7  CALCULATION OF THE MODIFIED STABILITY NUMBER AND  7.8  PRESENTATION OF THE MODIFIED STABILITY GRAPH . . . .  205  SUMMARY  207  CHAPTER 8  DATA BASE AND MODEL CALIBRATION  210  8.1  INTRODUCTION  210  8.2  DATA COLLECTION  212  8.3  DATA BASE  213  8.4  8.3.1  Description  o f the main data base  8.3.2  Description  o f t h e complementary data base  CALIBRATION OF THE FACTORS  214 .  219  COMPOSING THE MODIFIED  STABILITY NUMBER  219  8.4.1  Block s i z e r a t i n g  224  8.4.2  Stress factor rating  225  8.4.3  Joint orientation  229  8.4.4  The g r a v i t y  factor rating  factor rating viii  231  8.5  THE MODIFIED STABILITY GRAPH  232  8.6  DESIGN PHILOSOPHY  233  8.7  POSSIBILITY OF USING STASTISTICS  237  8.8  SUMMARY  238  CHAPTER 9  CABLE BOLT SUPPORT IN OPEN STOPE  9.1  INTRODUCTION  9.2  DESIGN CONCEPT  9.3  9.4  9.5  240 240 .  242  9.2.1  Prereinforcement  242  9.2.2  S t i f f n e s s o f t h e support system  244  CABLE BOLT SUPPORT SYSTEMS IN CANADIAN OPEN STOPE MINES 247 9.3.1  Cable b o l t p a t t e r n s f o r open stope backs  . .  247  9.3.2  Cable b o l t p a t t e r n s f o r open stope w a l l s  . .  251  . . . .  257  DEVELOPMENT OF CABLE BOLT DESIGN GUIDELINES 9.4.1  Design a n a l y s i s o f c a b l e b o l t support data  .  9.4.2  Density of b o l t i n g  264  9.4.3  Cable b o l t l e n g t h  266  9.4.4  Bolting  factor  2 69  9.4.5  Cable b o l t o r i e n t a t i o n  269  SUMMARY  CHAPTER 10  257  271  EXTERNAL FACTORS; BLASTING. BACKFILL AND TIME  EFFECT  274  10.1  INTRODUCTION  274  10.2  BLASTING EFFECT  274  10.2.1  Case h i s t o r i e s o f b l a s t induced damage . . . ix  275  10.3  10.2.2  B l a s t m o n i t o r i n g and p r e d i c t i o n  o f b l a s t damage 276  10.2.3  O p t i m i z a t i o n o f b l a s t d e s i g n f o r w a l l s t a b i l i t y 279  EFFECT OF BACKFILL IN ADJACENT STOPES 10.3.1  E f f e c t of b a c k f i l l  10.3.2  283  i n l i m i t i n g w a l l s and back  exposure  285  Case h i s t o r i e s analyses  287  10.4  THE TIME EFFECT  292  10.5  SUMMARY AND CONCLUSION  294  CHAPTER 11  SUMMARY AND CONCLUSION  297  11.1  SUMMARY  297  11.2  APPLICABILITY OF THE DESIGN METHOD  301  11.3  INDUSTRY BENEFITS OF THIS STUDY  302  11.4  FUTURE WORK  3 04  11.5  CONCLUDING REMARKS  305  REFERENCES  APPENDIX I  APPENDIX I I  307  OREBODY DIAGRAMS AND ROCK MECHANICS  DATA  . .  311  DESCRIPTION OF THE BOUNDARY ELEMENT PROGRAMS 2D: BITEM AND 3D: BEAP  333  APPENDIX I I I PLOT OF INDUCED STRESSES FOR DIFFERENT GEOMETRIES AND K RATIO  X  339  LIST OF TABLE PAGE TABLE 2.1 backfill,  Approximate v a l u e of ore f o r mines u s i n g and mines u s i n g permanent p i l l a r s .  19  TABLE 2.2 Comparison of the mining sequence used w i t h the proposed open stope c l a s s i f i c a t i o n system.  54  TABLE 4 . 1 Values o f the c o n s t a n t A from t h e M u r r e l l i n t a c t rock f a i l u r e c r i t e r i o n , and B from the Hoek i n t a c t rock f a i l u r e c r i t e r i o n , f o r f i v e rock m a t e r i a l s . ( A f t e r B i e n i a w s k i , 1984)  95  TABLE 4.2 Values of Hoek and Brown c o n s t a n t s m and s f o r 105 d i s t u r b e d and u n d i s t u r b e d rock masses. TABLE 5.1 B i e n i a w s k i CSIR geomechanics c l a s s i f i c a t i o n of 112 j o i n t e d rock mass. ( A f t e r Hoek and Brown) TABLE 5.2 Barton c l a s s i f i c a t i o n of i n d i v i d u a l parameters i n the NGI t u n n e l l i n g q u a l i t y index, (cont)  116  TABLE 5.3 The e x c a v a t i o n support r a t i o (ESR) f o r d i f f e r e n t underground openings a p p l i c a t i o n s . ( A f t e r Hoek and Brown 198 0)  117  TABLE 5.4 Assessment of j o i n t c o n d i t i o n s f o r the Laubscher geomechanic c l a s s i f i c a t i o n of j o i n t e d rock mass. ( A f t e r Laubscher, 1976)  122  TABLE 5.5 Summary of the f i v e b a s i c parameters o f the Laubscher geomechanic c l a s s i f i c a t i o n of j o i n t e d rock mass. ( A f t e r Laubscher, 1976)  12 5  TABLE 5.6 Adjustment f a c t o r f o r the number of j o i n t s i n c l i n e d away from v e r t i c a l . ( A f t e r Laubscher, 1976)  127  TABLE 5.7 Adjustment f a c t o r f o r the e f f e c t of b l a s t i n g . A f t e r Laubscher, 1976)  127  TABLE 5.8 Summary of the p o s s i b l e adjustment f a c t o r s . ( A f t e r Laubscher, 1976)  12 7  TABLE 5.9 Adjustment f a c t o r f o r the i n c l i n a t i o n of the designed stope s u r f a c e . ( A f t e r Laubscher, 1976)  129  TABLE  8.1  Background  i n f o r m a t i o n f o r the main data base. 215  xi  TABLE 8.2 Input parameters from the main data base necessary f o r open stope d e s i g n b a c k - a n a l y s i s .  218  TABLE 8.3 Background i n f o r m a t i o n f o r the complementary data base.  220  TABLE 8.4 Input parameters from the complementary data base necessary f o r open stope d e s i g n b a c k - a n a l y s i s .  222  TABLE 8.5 R e l a t i o n s h i p between the r e l a t i v e b l o c k s i z e f a c t o r (RQD/Jn / h y d r a u l i c r a d i u s ) , and rock mass behaviour.  226  TABLE 9.1 Background i n f o r m a t i o n f o r the data base of case h i s t o r i e s t h a t have used support.  2 58  TABLE 9.2 Input parameters f o r the data base of case h i s t o r i e s t h a t have used support.  260  TABLE 10.1 R e l a t i o n s h i p between the peak p a r t i c l e v e l o c i t y and the r e s u l t i n g c o n d i t i o n on rock s t r u c t u r e . ( A f t e r A t l a s Powder company, 1987)  280  TABLE 10.2 R e l a t i o n s h i p between the peak p a r t i c l e v e l o c i t y , the rock mass q u a l i t y and the r e s u l t i n g s t a b i l i t y of a stope.  280  TABLE 11.1 Importance of d i l u t i o n on the DCF Bawden, 1988)  xii  ROR.  (After  303  LIST OF FIGURES PAGE FIGURE 1.1 P i e diagram showing t h e p r o p o r t i o n o f mines having l e s s than 10% d i l u t i o n , between 10% and 20% d i l u t i o n , between 20% and 35% d i l u t i o n and above 35% d i l u t i o n . ( A f t e r P a k a l n i s , 1986) FIGURE  2.1  Range o f orebody d i p s i n open stope mining.  2  11  FIGURE 2.2 Range o f rock mass q u a l i t y (expressed i n terms o f the Q index) i n open stope backs.  12  FIGURE 2.3 Range o f rock mass q u a l i t y (expressed i n terms o f the Q index) i n hanging w a l l s .  13  FIGURE 2.4 Graph o f the orebody rock mass q u a l i t y (expressed i n terms o f the Q i n d e x ) , v e r s u s the orebody width, f o r l o n g i t u d i n a l open stope mines.  16  FIGURE 2.5 Graph o f the orebody rock mass q u a l i t y (expressed i n terms o f the Q i n d e x ) , v e r s u s the orebody width, f o r t r a n s v e r s e open stope mines.  16  FIGURE 2.6 Graph o f the stope w a l l s rock mass q u a l i t y (expressed i n terms o f the Q i n d e x ) , v e r s u s t h e stope w a l l s area, f o r open stope mines, u s i n g a " f u l l l e n s " longitudinal extraction.  18  FIGURE 2.7 C l a s s i f i c a t i o n system f o r open stope mining methods a p p l i e d t o Canadian mines.  22  FIGURE 2.8 I d e a l i z e d i s o m e t r i c drawing l e n s " open stope mining method.  o f the " f u l l  26  FIGURE 2.9 I d e a l i z e d i s o m e t r i c drawing r e t r e a t open stope mining method.  o f the s u b - l e v e l  27  FIGURE 2.10 I d e a l i z e d i s o m e t r i c drawing o f the l o n g i t u d i n a l l o n g h o l e open stope mining method, with permanent p i l l a r s .  28  FIGURE 2.11 I d e a l i z e d i s o m e t r i c drawing o f the t r a n s v e r s e b l a s t h o l e open stope mining method, u s i n g the " l e a p f r o g " sequence o f e x t r a c t i o n .  30  FIGURE 2.12 I d e a l i z e d i s o m e t r i c drawing o f the l o n g i t u d i n a l b l a s t h o l e open stope mining method, having s m a l l primary stopes and l a r g e secondary s t o p e s .  31  xiii  FIGURE 2.13 L o n g i t u d i n a l s e c t i o n o f a b l a s t h o l e open stope mining method, u s i n g the ( 1 - 5 - 9 ) sequence of extraction.  33  FIGURE 2.14 I d e a l i z e d i s o m e t r i c drawing o f t h e l o n g i t u d i n a l open stope mining method, u s i n g the "stope and f i l l " sequence o f e x t r a c t i o n .  34  FIGURE 2.15 Plan view showing the "panel mining" 36 sequence o f e x t r a c t i o n , ( a f t e r Alexander and Fabjanczyck, 1981) FIGURE 2.16 T y p i c a l longhole d r i l l i n g patterns i n Canadian open stope mines.  employed  38  FIGURE 2.17 Graph o f the maximum area o f rock t o be broken by i n d i v i d u a l d r i l l h o l e (burden x s p a c i n g ) , v e r s u s h o l e diameters.  40  FIGURE 2.18 I d e a l i z e d i s o m e t r i c drawing o f t h e l o n g i t u d i n a l l o n g h o l e open stope mining method, u s i n g a f u l l face r e t r e a t .  42  FIGURE 2.19 Typical blasthole d r i l l i n g i n Canadian open stope mines.  44  patterns  employed  FIGURE 2.20 I l l u s t r a t i o n o f the l o a d i n g procedure f o r l a r g e diameter b l a s t h o l e s .  47  FIGURE 2.21 I d e a l i z e d i s o m e t r i c drawing showing the "mass b l a s t " r e t r e a t f o r b l a s t h o l e open stope mining method.  49  FIGURE 2.22 Cross s e c t i o n o f the v e r t i c a l c r a t e r r e t r e a t method used i n b l a s t h o l e open stope mining, showing an i n i t i a l b l a s t , and the remnant crown b l a s t .  50  FIGURE 2.23 Cross s e c t i o n o f the i n v e r s e bench b l a s t i n g method used i n narrow b l a s t h o l e open stope mining.  52  FIGURE 3.1 Analogy o f a f l o w i n g stream o b s t r u c t e d by 57 three bridge p i e r s , representing stress streamlines around underground openings. ( A f t e r Hoek and Brown, 1980) FIGURE 3.2 surface.  Plot of v e r t i c a l stresses against ( A f t e r Hoek and Brown, 1980)  depth below  65  FIGURE 3.3 V a r i a t i o n o f r a t i o o f average h o r i z o n t a l s t r e s s t o v e r t i c a l s t r e s s w i t h depth below s u r f a c e . ( A f t e r Hoek and Brown, 1980)  65  FIGURE  67  3.4  V a r i a t i o n o f r a t i o o f average h o r i z o n t a l xiv  s t r e s s t o v e r t i c a l s t r e s s w i t h depth below s u r f a c e , from Canadian s h i e l d measurements. ( A f t e r Herget, 1987) FIGURE 3.5 S t r e s s components a c t i n g on a s u r f a c e element. ( A f t e r Hoek and Brown, 1980)  69  FIGURE 3.6 S t r e s s components a c t i n g on a c u b i c a l element. ( A f t e r Hoek and Brown, 1980)  69  FIGURE 3.7 K i r s h equations f o r the s t r e s s e s i n the m a t e r i a l surrounding a c i r c u l a r h o l e i n a s t r e s s e d e l a s t i c orebody. ( A f t e r Hoek and Brown, 1980)  74  FIGURE 3.8 V a r i a t i o n i n the r a t i o o f t a n g e n t i a l s t r e s s OQ t o t h e v e r t i c a l a p p l i e d s t r e s s pz w i t h r a d i a l d i s t a n c e r along h o r i z o n t a l a x i s f o r K=0. ( A f t e r Hoek and Brown, 1980)  76  FIGURE 3.9 D e f i n i t i o n o f nomenclature f o r an e l l i p t i c a l e x c a v a t i o n with axes p a r a l l e l t o the f i e l d s t r e s s e s . ( A f t e r Brady and Brown, 1985)  76  FIGURE 3.10 Idealized numerical m o d e l l i n g .  80  s k e t c h showing the p r i n c i p l e o f  FIGURE 4.1 T y p i c a l s t r e s s s t r a i n r e l a t i o n s h i p d u r i n g the 90 t e s t i n g o f an unconfined e l a s t i c specimen i n compression. FIGURE 4.2 I d e a l i z e d sketch showing a rock specimen submitted t o t r i a x i a l compression.  97  FIGURE 4.3 G r a p h i c a l r e p r e s e n t a t i o n o f t h e Mohr c i r c l e and f a i l u r e envelope. ( A f t e r Hoek and Brown, 198 0)  97  FIGURE 4.4 I d e a l i z e d sketch showing the s h e a r i n g along a d i s c o n t i n u i t y s u r f a c e having an exaggerated roughness. ( A f t e r Brady and Brown, 1985)  99  FIGURE 4.5 G r a p h i c a l r e p r e s e n t a t i o n o f the peak and r e s i d u a l f r i c t i o n angle. ( A f t e r Brady and Brown, 1985)  99  FIGURE 4.6 T y p i c a l d i s c o n t i n u i t y roughness p r o f i l e f o r the e v a l u a t i o n o f the JRC index. ( A f t e r Barton and Choubey, 1977)  102  FIGURE 5.1 R e l a t i o n s h i p between the stand-up time o f an unsupported underground e x c a v a t i o n span and the CSIR Geomechanics C l a s s i f i c a t i o n . ( A f t e r B i e n i a w s k i , 1973)  113  FIGURE 5.2 R e l a t i o n s h i p between the maximum e q u i v a l e n t dimension (De) of an unsupported underground e x c a v a t i o n and t h e NGI t u n n e l l i n g q u a l i t y index Q. ( A f t e r Barton  118  xv  L i e n and Lunde, 1974) FIGURE 5.3 Diagram f o r the e v a l u a t i o n o f t h e j o i n t s p a c i n g parameter i n the Laubscher m o d i f i e d geomechanics c l a s s i f i c a t i o n system. ( A f t e r Laubscher, 1976)  123  FIGURE 5 . 4 R e l a t i o n s h i p between the a d j u s t e d rock mass r a t i n g and h y d r a u l i c r a d i u s o f a stope s u r f a c e . ( A f t e r Laubscher, 197 6)  129  FIGURE 5.5 R e l a t i o n s h i p between the s t a b i l i t y number and h y d r a u l i c r a d i u s o f a stope s u r f a c e . ( A f t e r Mathews e t a l , 1980).  133  FIGURE 5.6 Graph f o r the e s t i m a t i o n o f f a c t o r A. ( A f t e r Mathews e t a l , 1980).  135  FIGURE 5.7 Graph o f t h e s t r e s s induced on t h e major s u r f a c e o f a stope v e r s u s the r a t i o o f opening dimensions. ( A f t e r Mathews e t a l , 1980).  13 6  FIGURE 5.8 Graph o f the s t r e s s induced on the minor s u r f a c e o f a stope v e r s u s the r a t i o o f opening dimension. ( A f t e r Mathews e t a l , 1980).  137  FIGURE 5.9 Sketch f o r the e s t i m a t i o n o f the rock d e f e c t o r i e n t a t i o n f a c t o r B. ( A f t e r Mathews e t a l , 1 9 8 0 ) .  139  FIGURE 5.10 Graph f o r the e s t i m a t i o n o f t h e stope s u r f a c e i n c l i n a t i o n f a c t o r C ( A f t e r Mathews e t a l , 1980) .  14 0  FIGURE 6.1 Triangular chart shape. ( A f t e r Folk, 1968).  152  f o r the e s t i m a t i o n o f b l o c k  FIGURE 6.2 I d e a l i s e d diagram showing the t r a n s i t i o n from i n t a c t rock t o a h e a v i l y j o i n t e d rock mass with i n c r e a s i n g sample s i z e . ( A f t e r Hoek and Brown, 1980)  154  FIGURE 6.3 F a i l u r e mechanism o f i n t a c t rock submitted t o compressive s t r e s s .  154  FIGURE 6 . 4 F a i l u r e mechanism of i n t a c t rock i n s t a t e of stress relaxation.  154  FIGURE 6.5 F a i l u r e mechanism o f d i s c r e t e b l o c k s f o r an 157 i s o t r o p i c rock m a t e r i a l submitted t o compressive s t r e s s . FIGURE 6.6 F a i l u r e mechanism o f d i s c r e t e b l o c k s f o r an 157 i s o t r o p i c rock m a t e r i a l i n a s t a t e o f s t r e s s r e l a x a t i o n . xv i  FIGURE 6.7 F a i l u r e mechanism o f d i s c r e t e b l o c k s f o r an a n i s o t r o p i c rock m a t e r i a l having elongated b l o c k s o r i e n t e d p a r a l l e l t o the stope s u r f a c e and submitted t o a compressive s t r e s s .  157  FIGURE 6.8 F a i l u r e mechanism of d i s c r e t e b l o c k s f o r an a n i s o t r o p i c rock m a t e r i a l having elongated b l o c k s o r i e n t e d p a r a l l e l t o the stope s u r f a c e i n a s t a t e o f stress relaxation.  157  FIGURE 6.9 F a i l u r e mechanism o f d i s c r e t e b l o c k s f o r an a n i s o t r o p i c rock m a t e r i a l having elongated b l o c k s o r i e n t e d p e r p e n d i c u l a r t o the stope s u r f a c e and submitted t o compressive s t r e s s .  159  FIGURE 6.10 F a i l u r e mechanism of d i s c r e t e b l o c k s f o r an a n i s o t r o p i c rock m a t e r i a l having elongated b l o c k s o r i e n t e d p e r p e n d i c u l a r t o the stope s u r f a c e i n a state of stress relaxation.  159  FIGURE 6.11 F a i l u r e mechanism o f j o i n t e d rock mass f o r an i s o t r o p i c m a t e r i a l submitted t o compressive s t r e s s .  159  FIGURE 6.12 F a i l u r e mechanism o f j o i n t e d rock mass f o r an i s o t r o p i c rock m a t e r i a l i n a s t a t e o f s t r e s s relaxation.  159  FIGURE 6.13 F a i l u r e mechanism of j o i n t e d rock mass f o r an a n i s o t r o p i c rock m a t e r i a l having elongated b l o c k s o r i e n t e d p a r a l l e l t o the stope s u r f a c e and submitted t o a compressive s t r e s s .  161  FIGURE 6.14 F a i l u r e mechanism o f a j o i n t e d rock mass 161 f o r an a n i s o t r o p i c rock m a t e r i a l having elongated b l o c k s o r i e n t e d p a r a l l e l t o the stope s u r f a c e i n a s t a t e o f stress relaxation. FIGURE 6.15 F a i l u r e mechanism o f j o i n t e d rock mass f o r an a n i s o t r o p i c rock m a t e r i a l having elongated b l o c k s o r i e n t e d p e r p e n d i c u l a r t o the stope s u r f a c e and submitted t o compressive s t r e s s .  161  FIGURE 6.16 F a i l u r e mechanism o f j o i n t e d rock mass f o r an a n i s o t r o p i c rock m a t e r i a l having elongated b l o c k s o r i e n t e d p e r p e n d i c u l a r t o t h e stope s u r f a c e i n a s t a t e of s t r e s s r e l a x a t i o n .  161  FIGURE 6.17 open stope  163  C l a s s i f i c a t i o n o f the f a i l u r e mechanisms i n mining.  FIGURE 6.18 a) failure.  Sketch showing the g r a v i t y f a l l mode of xvii  165  FIGURE 6.18 b) failure.  Sketch showing t h e s l i d i n g mode o f  FIGURE 6.18 c) Sketch showing t h e s l a b b i n g mode o f f a i l u r e . FIGURE  7.1  and b u c k l i n g  V i s u a l i z a t i o n o f t h e geomechanical  model.  165 165 168  FIGURE 7.2 Sketch showing t h e measurement o f j o i n t s along a scan l i n e . ( A f t e r P r i e s t and Hudson, 1976)  17 2  FIGURE 7.3 R e l a t i o n s h i p between RQD and t h e average number o f d i s c o n t i n u i t i e s p e r meter. ( A f t e r P r i e s t and Hudson, 1976)  172  FIGURE 7.4 Graph f o r t h e e s t i m a t i o n of t h e compressive stress factor.  17 5  FIGURE 7.5 D e f i n i t i o n o f t h e aspect r a t i o and K r a t i o used i n t h e e s t i m a t i o n o f t h e induced s t r e s s a c t i n g on a stope s u r f a c e .  178  FIGURE  7.6  FIGURE 7.7 horizontal  Longitudinal  open stope t y p i c a l dimensions.  181  Longitudinal plane.  open stope s t r e s s : hanging w a l l  182  FIGURE 7.8 Back and HW h o r i z o n t a l seam width. FIGURE 7.9 Longitudinal v e r t i c a l plane.  stresses:  e f f e c t of  open stope s t r e s s : hanging w a l l  183 185  FIGURE 7.10 stresses.  Longitudinal  open stope s t r e s s : back  18 6  FIGURE 7.11 stress.  Longitudinal  open stope s t r e s s : abutment  188  FIGURE 7.12 study.  Summary o f t h e l o n g i t u d i n a l  parametric  FIGURE 7.13 T r a n s v e r s e open stope dimensions i n terms o f stope l e n g t h ( L ) .  expressed  FIGURE 7.14 T r a n s v e r s e stope boundary s t r e s s e s : abutment w a l l . FIGURE 7.15 wall.  T r a n s v e r s e stope boundary s t r e s s e s :  xviii  189 191 192  pillar  194  FIGURE end.  7.16  T r a n s v e r s a l stope boundary s t r e s s e s :  stope  196  FIGURE  7.17  Summary o f the t r a n s v e r s e p a r a m e t r i c  study.  197  FIGURE  7.18  I l l u s t r a t i o n o f the c r i t i c a l  concept.  199  FIGURE  7.19  Influence of j o i n t o r i e n t a t i o n .  joint  201  FIGURE 7.20 I n f l u e n c e o f g r a v i t y f o r s l a b b i n g and g r a v i t y f a l l modes o f f a i l u r e .  204  FIGURE 7.21 failure.  I n f l u e n c e o f g r a v i t y f o r s l i d i n g mode o f  204  FIGURE  The m o d i f i e d  206  7.22  stability  graph.  M o d i f i e d s t a b i l i t y graph showing the case FIGURE 8.1 h i s t o r i e s of h i g h compressive s t r e s s .  228  FIGURE 8.2 M o d i f i e d s t a b i l i t y graph showing the case h i s t o r i e s of s t r e s s r e l a x a t i o n .  230  M o d i f i e d s t a b i l i t y graph showing the case FIGURE 8.3 h i s t o r i e s i n c l u d e d i n the main data base.  229  FIGURE 8.4 M o d i f i e d s t a b i l i t y graph showing the case h i s t o r i e s i n c l u d e d i n the t o t a l data base.  234  FIGURE 9.1 a) Uniform c a b l e b o l t p a t t e r n i n s t a l l e d open stope o v e r c u t s .  in  248  FIGURE 9.1 b) Uniform c a b l e b o l t p a t t e r n i n s t a l l e d i n open stope o v e r c u t s and supplemented with s h o r t r e b a r .  248  FIGURE 9.2 Cable b o l t support system u s i n g i n c l i n e d c a b l e s and two phases o f overcut development f o r prereinforcement.  250  FIGURE 9.3 Cable b o l t support l a c e d support p a t t e r n .  250  system u s i n g an i n t e r -  FIGURE 9.4 Cable b o l t support system designed overcuts containing a small p i l l a r ( s ) .  for  FIGURE 9.5 Uniform c a b l e b o l t p a t t e r n i n s t a l l e d open stope w a l l .  i n an  250 252  FIGURE 9.6 C r e a t i o n o f a rock beam i n the hanging w a l l by i n s t a l l i n g a l o c a l i z e d high d e n s i t y o f c a b l e b o l t s .  253  FIGURE  255  9.7  Cable b o l t support xix  system f o r a hanging  wall,  installed  FIGURE 9.8 walls.  from a p a r a l l e l b o l t i n g  drift.  Cable b o l t support system s t a b i l i z i n g p i l l a r  256  FIGURE 9.9 The m o d i f i e d s t a b i l i t y graph f o r supported case h i s t o r i e s .  263  FIGURE 9.10 R e l a t i o n s h i p between the d e n s i t y o f b o l t i n g v e r s u s the r e l a t i v e b l o c k s i z e f a c t o r (RQD/Jn) / hydraulic radius.  265  FIGURE 9.11 R e l a t i o n s h i p between t h e c a b l e b o l t l e n g t h and h y d r a u l i c r a d i u s o f a stope s u r f a c e .  268  FIGURE 9.12 The m o d i f i e d s t a b i l i t y graph showing b o l t i n g f a c t o r f o r each o f the "supported" case histories.  the  270  FIGURE 10.1 The m o d i f i e d s t a b i l i t y graph showing h i s t o r i e s t h a t had s i g n i f i c a n t b l a s t i n g e f f e c t .  case  277  FIGURE 10.2 R e l a t i o n s h i p between t h e r e d u c t i o n i n rock mass q u a l i t y and the peak p a r t i c l e v e l o c i t y o r i g i n a t i n g from a b l a s t . ( A f t e r Page, 1987)  281  FIGURE 10.3 The e f f e c t o f r e d u c i n g the burden on a charge o f c o n s t a n t energy. ( A f t e r A t l a s powder company, 1987)  282  FIGURE 10.4 The e f f e c t o f d e l a y i n g d e t o n a t i o n decks on the r e s u l t i n g wave p a c k e t s . ( A f t e r S p r o t t , 1986)  284  FIGURE 10.5 I d e a l i z e d i s o m e t r i c view o f t h e mining and b a c k f i l l o f a f o u r stope b l o c k .  286  FIGURE 10.6 I d e a l i z e d i s o m e t r i c view o f the mining b l o c k a t Mine #19 o f the data base.  288  FIGURE 10.7 The m o d i f i e d s t a b i l i t y graph showing e f f e c t o f b a c k f i l l i n a d j a c e n t stopes.  the  290  FIGURE 10.8 The m o d i f i e d s t a b i l i t y graph showing the time e f f e c t on seventeen case h i s t o r i e s from the data base.  293  FIGURE l l . l design.  299  The s t a b i l i t y graph method f o r open stope  xx  ACKNOWLEDGEMENTS The author wishes t o thank the p r i n c i p a l sponsors o f t h i s p r o j e c t , NSERC, Centre De Technologie Noranda and F a l c o n b r i d g e Ltd as w e l l as the t h i r t y f o u r mining o p e r a t i o n s t h a t have p r o v i d e d data and e x p e r t i s e . M a r t i n Hudyma and Dr W i l l Bawden are a l s o acknowledged f o r t h e i r s i g n i f i c a n t c o n t r i b u t i o n i n t h i s r e s e a r c h work. The a s s i s t a n c e p r o v i d e d by the t e c h n i c a l commitee formed by Dr Hamish M i l l e r p r o j e c t s u p e r v i s o r , Ken Mathews, A l l a n Moss, Dr Rimas P a k a l n i s , Chuck Brawner, A l l a n Reed and Andy Mular was g r e a t l y a p p r e c i a t e d . Acknowledgement goes t o the f o l l o w i n g persons f o r t h e i r continuous support and encouragement d u r i n g my graduate s t u d i e s ; Wendy Cumming-Potvin, Jacques P o t v i n , Jeanine P o t v i n , Audrey Cumming and Antonio de Conceicao Ramos.  xx i  CHAPTER 1 INTRODUCTION T h i s t h e s i s addresses stability stope from  i n open stope mining methods. The  mining large,  of  operations r e l i e s non-entry  Considering each  the t o p i c of underground e x c a v a t i o n  the  high  on  high p r o d u c t i v i t y  excavations cost  e f f i c i e n c y of open  and  mechanized  a s s o c i a t e d with  the  stope, the economic i n c e n t i v e t o produce  large  open  stopes  i s tremendous.  On  the  resulting equipment.  development  of  a s m a l l e r number o t h e r hand,  the  consequences of exceeding the maximum p o s s i b l e stope  dimensions  can  may  be  disastrous.  large  remedial  production,  Instability  costs  for  around  ground  actual  a  stopes  rehabilitation,  cause  delay  Canadian  performance  terms of d i l u t i o n .  mine survey of  open  I t was  done by  stope found  fatalities.  design that  Pakalnis was  forty  (1986),  suffering  confirmed to  seven  1.1  35%  dilution  (figure  open  stope  dimensions  specifically  in  p e r c e n t of  1.1).  the need f o r a r e l i a b l e e n g i n e e r i n g d e s i g n  optimize  Canadian  more than  the  investigated  the open stope mines had more than 20% d i l u t i o n with twenty percent  of  l o s s of mining equipment, l o s s of ore r e s e r v e s and  at the extreme, mine worker i n j u r i e s or In  open  one This  technique  adapted  to  geotechnical conditions.  DEFINITION OF THE PROBLEM  There are t h r e e fundamental 1  aspects t o be c o n s i d e r e d i n an  DILUTION -  OPEN STOPING METHODS DATA BASE -  15 MINES  FIGURE l . l P i e diagram showing the p r o p o r t i o n o f mines having l e s s than 10% d i l u t i o n , between 10% and 20% d i l u t i o n , between 20% and 35% d i l u t i o n and above 35% d i l u t i o n . ( A f t e r P a k a l n i s , 1986)  2  engineering  rock  mechanics  characterization  and components  The  aspect  mass.  The  first  aspect  a f f e c t i n g the rock  i s the e f f e c t o f s t r e s s  mass  fields  o f openings, may  on the rock  r e s u l t i n zones o f h i g h  s t r e s s , o r zones o f r e l a x a t i o n .  Estimation  the  stress  (compressive  or  tensile)  acting  on  each  i s very  important  i n the d e s i g n procedure.  aspect  is  physical  condition  primarily  the by  the s i z e ,  openings w i t h physical  regard  condition  factors  blasting, backfill  should  factors  influence  i n adjacent  (time e f f e c t ) .  accounted  problem  consider  field.  include:  of  cable  geotechnical  of The  (at l e a s t i n d i r e c t l y ) For  the e f f e c t o f p r o d u c t i o n bolts,  the  influence  of  o f t h e openings  factors. of  the problem  these  t o be  three  fundamental  investigated.  Each  f o r i n the model by one or more f a c t o r s  calibrated  defined  and r e l a t i v e o r i e n t a t i o n  stopes and the l o n g e v i t y  interaction  constitutes  The t h i r d  In t h i s t h e s i s , these f a c t o r s w i l l be r e f e r r e d  t o as the e x t e r n a l The  also  stope  t o the type o f opening environment.  these  the  the  t o the rock mass and s t r e s s  inherent  open s t o p i n g ,  geometry  of  compressive  o f t h e magnitude of  surface  data.  behaviour.  R e d i s t r i b u t i o n o f t h e pre-mining s t r e s s f i e l d due t o the  creation  the  i s the  o f the rock mass t o i d e n t i f y and q u a n t i f y the  properties second  design.  through  case  parameters  The p r i n c i p a l  h i s t o r i e s . The that  can be  hypothesis  s t a t e d as f o l l o w s ; 3  factors  estimated  defended  aspects aspect i s  empirically  are based with  in this  on  on site  thesis i s  "  The  stability  quantifying  the  of  effect  of  open  stopes  rock mass,  can  stress  be  predicted  and  the  by  physical  c o n d i t i o n of the problem."  1.2  OBJECTIVE OF THE  The  PROJECT  objective  geomechanical S i n c e one  of  the  project  to  develop  model f o r the p r e d i c t i o n of open stope  of the major concerns  of t h i s  p r a c t i c a l d e s i g n t o o l f o r Canadian the  is  following  guidelines  study  a  stability.  i s to provide a  open s t o p i n g mine o p e r a t o r s ,  were  set  regarding  the  model  development: The  design  overall  stability  problems. and  the  method stope and  method  must of  be  a  capable  stope  in  of  predicting  terms  of  Instead of f o c u s s i n g on p r e c i s e identification  should  discrete  concentrate  dimensions, critical  of  less  stope  on  defining  dimensions  operating  calculations  block  conservative  the  falls,  the  conservative  stope  (beyond  dimensions which  open  s t o p i n g become i m p r a c t i c a l ) . The  model must be r e l i a b l e and consequently  sensitive parameters  to in  all  the  significant  underground  stope  i t must be  geotechnical  stability.  In  a d d i t i o n , i t i s important t h a t the d i f f e r e n t c o n d i t i o n s associated stope  with  geometry,  open  stope  mining 4  mining, sequence,  such  as  typical  blasting  and  artificial  support  (backfill  and  cable  bolts),  be  by mining  or  d i r e c t l y or i n d i r e c t l y accounted f o r . The  methodology must be e a s i l y understood  geological  engineers  on  site.  The  input  parameters  should r e l y mainly on o b s e r v a t i o n a l methods r a t h e r than expensive  testing,  lengthy  s t u d i e s and  sophisticated  equipment. The  d e s i g n method should be a p p l i c a b l e a t any  mining, short  i n c l u d i n g d u r i n g the f e a s i b i l i t y term  precision quality mining  and of  of  long  designs  the  is  input  progresses,  providing  term  at  parameters,  the  least  study and f o r  planning.  largely  method  a  Although function  which  should  approximate  stage of  the  of  the  improves  as  capable  of  be  answers  at  the  f e a s i b i l i t y study stage. The  approach  behaviour modes  must  and  of  the  control  The  model  reliability base. building  A  of  of  This  the  proper  representative  capable  failure.  understanding select  be  be  remedial  identifying will  ground  of  rock  mass  underground  provide  c o n d i t i o n s and  a c t i o n s i n case  a  better help  of  to  ground  problems.  is  based  and  its  i s t h e r e f o r e a f u n c t i o n of the e x t e n t of the  data  considerable a broad  data  on  an  amount  of  base which 5  empirical  effort  approach  has  been  i n c l u d e s more than  spent 250  in case  histories  of unsupported  mines.  Each  occasions)  mine  and  and  has  supported  been  case  stopes  visited  histories  from  34  Canadian  (sometimes  on  several  were  back-analyzed  from  d i s c u s s i o n s w i t h mine p e r s o n n e l , underground o b s e r v a t i o n s , rock mass  classification  relationships compilation  and  numerical  been  derived  experience  acquired  have  of  modelling. from in  Empirical  this  systematic  Canadian  open  stope  t o p r o v i d e a good  review  operations.  1.3  of  CONTENTS OF THE  The  first  open  stope  THESIS  t a s k of t h i s study was mining  applicability  of  classification  and  methods i n order t o d e f i n e the the  geomechanical  identification  of  model.  the  field  Definition,  principal  variations  i n open stope mining p r a c t i c e s are g i v e n i n chapter 2. 3,  4  and  5  fundamental pre-mining  aspects stress  distribution c h a p t e r 3. the  for  principal  rock  physical  literature of  and  stope  design  elastic  In chapter  s t o p i n g methods) are  (of  laws governing are  the  three  1.2). the  The stress  described  to  estimate  the  in and  rock mass  e x i s t i n g models which i n t e g r a t e  characteristics,  conditions  (ref. section  Chapter  of rock f a i l u r e c r i t e r i a  available 5 the  covering  behaviour  4 i s a review  techniques  mass  reviews  the p r i n c i p a l  linear  Chapter  properties. the  are  of  the  tunnels,  reviewed. 6  effect  of  stress  caving  methods  and  and  the open  The stope From  study  mining  of the f a i l u r e mechanisms a s s o c i a t e d with i s the i n i t i a l  the l i t e r a t u r e  review,  step  of the model  and more  open  development.  importantly  from  field  o b s e r v a t i o n s of a c t u a l f a i l u r e s , a c l a s s i f i c a t i o n of open stope failure  mechanisms  i s proposed  in  chapter  provides  g u i d e l i n e s f o r the s e l e c t i o n  factors  representing  conditions. estimation factor the  of  the  rock  Techniques  are  the  mass,  stress  chapter  8.  Chapter  external factors. of  effect)  the  chapter  and  10  focus  on  external  and  factors  visual  guidelines (9)  observational  is  the  field  the  each  base  and  are g i v e n i n  effects  of the  I t should be noted t h a t t h e i n v e s t i g a t i o n of (blasting,  i s v e r y b r i e f because a v a i l a b l e  technology develop  9  physical  data  method  7  of the  composing  The  o f the d e s i g n  and for  parameters  (except f o r the e x t e r n a l f a c t o r s ) .  Chapter  definition  recommended  geotechnical  empirical calibration  some  and  6.  on  observation their  allocated  methods  were  to more  cable  and  time  i n f o r m a t i o n , mine  were  effect  backfill  on  not  sufficient  stability..  bolt  effective,  site  support  A  to full  because  allowing  for a  g r e a t e r data base and more d e t a i l e d i n v e s t i g a t i o n r e g a r d i n g i t s effect  on s t a b i l i t y .  The c o n c l u s i o n of the study can be  i n c h a p t e r 11.  7  found  CHAPTER 2 REVIEW OF OPEN STOPE MINING PRACTICES  2.1  INTRODUCTION  There  a r e a wide v a r i e t y  o f mining  used f o r t h e e x t r a c t i o n o f underground has been p r a c t i c e d years  because  modifications modern  definition  stoping  such  and b l a s t i n g  efficient have  as new  techniques.  and a c l a s s i f i c a t i o n  mining methods. practices w i l l  Open s t o p i n g  of  as  equipment  result  and  of  improved  This chapter w i l l provide a o f the d i f f e r e n t  The p r i n c i p a l v a r i a t i o n s a l s o be d i s c u s s e d .  concepts developed  Several  a  i n this  open  T h i s review, based  thesis  stope  i n open stope mining  30 Canadian underground mines, w i l l h e l p t o c l a r i f y design  underground  and s a f e .  evolved  mining  can be  1930's. In recent  p o p u l a r method  i t i s cost  o f open  technology  drilling  the most  that  orebodies.  i n Canada s i n c e the e a r l y  i t has become  extraction  methods  and w i l l  on over  some of the d e f i n e the  f i e l d o f a p p l i c a t i o n o f the proposed d e s i g n method.  2.1.1  D e f i n i t i o n o f open stope mining There  open  are three c h a r a c t e r i s t i c  stope  mining  from  the  features  other  methods  that  distinguish  of  underground  extraction: Open s t o p i n g i s a non-entry method. production  has s t a r t e d ,  Consequently,  the stope does 8  not need  after t o be  e n t e r e d by  mine workers,  making t h i s  mining methods.  A l l the miner's  to  periphery,  the  stope  production  face.  Cut  of the  safest  a c t i v i t i e s are c o n f i n e d  away  and  one  fill,  from  the  dangerous  longwall,  room  and  p i l l a r and shrinkage s t o p i n g are e n t r y mining methods. The  stopes are kept open u n t i l the f i n a l dimensions  obtained.  The broken ore i s removed as stope  progresses. after  the  Since  completion  AVOCA  sequence, VCR  Stabilizing  keep  uses  and  of  stope  the  stope  backfill  methods  the  backfill  such  full  extraction  introduced  only  (delayed b a c k f i l l ) .  during  as  of  is  are  the  shrinkage  broken  extraction  and  ore,  sometimes  they  are  not  c o n s i d e r e d open stope methods. The underground e x c a v a t i o n s are designed t o be s t a b l e as opposed t o c a v i n g methods. be no  This implies that there w i l l  l a r g e u n s t a b l e r e l e a s e s of energy  due  t o a sudden  change i n the opening geometry caused by c a v i n g .  The  t h r e e c r i t e r i a above have a fundamental  on the d e s i g n of openings t h a t can be  2.1.2  and  on the degree  of  influence instability  tolerated.  A p p l i c a t i o n s o f open stope mining Open  certain  stope  types  mining of  i s more e f f i c i e n t  orebodies  Because open s t o p i n g r e l i e s  and  geological  on the g r a v i t y 9  when a p p l i e d  to  conditions.  flow of the ore  to  the stope  angle 50°  bottom,  o f repose to 55°).  t h e stope  o f the broken Figure  2.1  d i p should  be  ore m a t e r i a l  above the  (greater  shows the d i s t r i b u t i o n  than  of the  stope d i p s o f t h e mines i n the p r o j e c t data base.  Although  open s t o p i n g  i s more s u i t e d t o a s t e e p l y d i p p i n g  orebody,  it  be  can a l s o  (approximately oriented  successful  i n a shallow  l e s s than 30°).  sub-vertically,  dipping  orebody  However t h e stopes  must be  and t h e t h i c k n e s s  o f t h e orebody,  should be a t l e a s t 15 t o 20 meters. The because  orebody open  stoping  minimum width excessive  outline  should  be  relatively  i s not s e l e c t i v e .  In a d d i t i o n , a  o f 5 meters i s g e n e r a l l y necessary  dilution  from  wall  damage  regular,  created  t o avoid  by b l a s t i n g  v i b r a t i o n s and/or d r i l l h o l e d e v i a t i o n s . Open  stoping  dimensions. backfill process,  created, Figures strength  inside  at least a " f a i r " i n t h e stope  excavation  involves  large  Since t h e r e i s no major support  or p i l l a r s  required  country  usually  t o be s e l f  rock, and 2.2  the  2.3  (expressed  and w a l l s  supporting.  larger  are  efficient  show  system such as  during  the mining  t o "good" rock mass s t r e n g t h i s  back  the more and  the stope  opening  i n order  The more competent the the  stopes  open  that  stoping  the d i s t r i b u t i o n  i n terms o f the NGI  can will  o f rock  be be.  mass  'Q' index) f o r the  stope backs and the stope w a l l s o f the data  10  f o r the  base.  FIGURE 35  _.  0 - 10  2.1  OREBODY DIP IN OPEN STOPE MINING SUB-VERTICAL  MINING  ONLY :  10 - 20 20 - 30 30 - 40 40 - 50 50 - 60 60 - 70 70 - 80 80 - 90 OREBODY  DIP  FIGURE  2.2  ROCK MASS QUALITY IN OPEN STOPE BACKS FROM  30  34  CANADIAN  —r  0.1 - 0.5  OPEN  STOPE  MINES  —  0.5 - 1.0  1 - 5  5 ROCK  10 MASS  10 - 20 QUALITY  (Q')  20 - 40  40 - 80  80 +  FIGURE  ROCK MASS QUALITY M HANGING WALLS  2.3  FROM 30 28  -  26  -  0.1  -  0.5  0.5  -  1.0  1  -  5  34  CANADIAN :  5 ROCK  - 1 0 MASS  OPEN  10  STOPE  -  QUALITY  20  MINES  20 (Q")  -  40  40  -  80  80  +  2.2  CLASSIFICATION OF OPEN STOPE MINING METHODS  The  elements t h a t  form open stope mining methods are  numerous and v a r i a b l e .  Consequently, t h e r e a r e no two open  stoping applications  t h a t are e x a c t l y  classification  the t h r e e  uses  t h e same.  following  A proposed  specifications to  group t h e open stope mining methods: mining d i r e c t i o n use  of p i l l a r s ,  drill These  ( l o n g i t u d i n a l or and b a c k f i l l ,  h o l e diameter (longhole or b l a s t h o l e ) .  specifications  stope  transverse),  mining  development  have  methods,  been  chosen  because  and stope p r e p a r a t i o n  to c l a s s i f y  open  determine  the  they required,  the method of  r e t r e a t and the sequencing o f mining.  2.2.1  Mining d i r e c t i o n The  first  criterion  f o r the c l a s s i f i c a t i o n o f open  s t o p i n g methods i s the d i r e c t i o n o f mining. In l o n g i t u d i n a l mining,  the d i r e c t i o n  strike,  while  of  i n transverse  direction  perpendicular  direction  of retreat  orientation the  stope  Longitudinal to  usually open  mining,  is vertical  strike  the  retreat  strike.  (ie. crater  the  have t h e i r  I f the  retreat)  mining  longest  and t r a n s v e r s e  orebody  i s i n the  o f the two h o r i z o n t a l  distinguish  stopes  i s along  t o the orebody  o f the l o n g e s t  the orebody  retreat  axis of  direction.  axis  stopes  the  parallel  have  their  l o n g e s t h o r i z o n t a l dimension  In  general  development and bring  into  a c r o s s orebody.  longitudinal  open  stoping  i s therefore faster  production.  l o n g i t u d i n a l mining self-supporting.  The  and  requires  less  less  expensive  limiting  factor  for  i s the a b i l i t y of the stope backs t o be In  figure  2.4,  the  width  of  the  stope  backs mined l o n g i t u d i n a l l y has been p l o t t e d a g a i n s t the rock  mass  base.  strength  The  lines  width,  while  width  orebody.  single The  index  'Q'  represent  f o r the orebodies  p o i n t s denotes  be mined l o n g i t u d i n a l l y .  seen  orebodies that  orebodies,  mined  i n the  having  mine  with 2.4  NGI data  a  variable  a  constant  i s that  the  i s the orebody t h a t  can  A s i m i l a r graph has been prepared  transversely  transverse and  mines  t r e n d shown i n f i g u r e  b e t t e r the rock mass i s , the wider  for  to  mining  a minimum width  (figure is  of  2.5).  practiced  15 metres  I t can on  be  wider  i s needed  to  make i t e f f i c i e n t .  2.2.2  Use o f p i l l a r s and  backfill  Open stope mining methods have f o u r o p t i o n s r e g a r d i n g the use of p i l l a r s and full  backfill:  l e n s mining can be done without p i l l a r s  or  backfill permanent p i l l a r s can be l e f t unmined, which w i l l limit  the orebody recovery, but no b a c k f i l l 15  i s used,  0RE30DY  STRENGTH V S 0 R E 3 0 D Y LONGmjDINAL  WIDTH  MINING  10-  0 R E 3 O 0 Y WIOTK (In  m.trma)  FIGURE 2.4 Graph of the orebody rock mass quality (expressed in terms of the Q index), versus the orebody width, f o r longitudinal open stope mines. C R E 3 0 D Y S T R E N G T H V S O R E B O D Y WIDTH TRANSVERSAL. MINING  C R E 3 0 0 Y WIDTH (In  m.lroa)  FIGURE 2.5 Graph of the orebody rock mass quality (expressed in terms of the Q index), versus the orebody width, f o r transverse open stope mines. 16  p i l l a r s can be recovered  u s i n g cemented  backfill,  a v o i d the c r e a t i o n of p i l l a r s by sequencing stope and fill  operations.  The mass  ideal  open  surrounding  the  pillars  or b a c k f i l l  termed  "full  relatively  versus  of  the w a l l  diamond  dashed  ore  lenses.  area  used  points  i s a rough  enough method  and  is  rock  that  no  has been  possible  in  2.6  is a  graphical  competency  (NGI,  Q  in full  represent  i f the  This  Figure  rock  exist  i s strong  stoping"  the w a l l  shaped  line  orebody  open  square shaped p o i n t s the  conditions  are necessary.  lens  small  presentation  stoping  lens  index)  open stopes.  The  stopes t h a t were s t a b l e and  show  walls  criterion  that  caved.  The  f o r the f e a s i b i l i t y  of  full  l e n s open s t o p i n g , s i n c e most cases p l o t t i n g above the  line  were s t a b l e and most cases below the l i n e  stability  problems.  Often are  left  option  when f u l l to  of  mining,  experienced  l e n s mining  i s not p o s s i b l e ,  maintain  the  overall  mine  recovering  the  pillars  at  pillars  stability. a  later  i s a f u n c t i o n of the grade and v a l u e  The  stage  of  of the ore.  T h i s i s shown i n t a b l e 2.1, where the approximate v a l u e per ton  of ore i s i n d i c a t e d  and  f o r mines  value  that  i s relatively  recovery  left high,  i s justified.  f o r mines t h a t permanent  recovered  pillars.  the use of b a c k f i l l  I f the ore and  Permanent p i l l a r s are l e f t 17  pillars  pillar  i f the  WALL ROCK MASS STRENGTH VS WALL AREA F U L L L E N S LONGITUDINAL O P E N  10O  •> B •  a  tt  •  _ • i  11  H  •  STOPING  SB  •  mm m  a  •  ••  i  • •  •  •  •  10-  a  • mm mm  a  ——j^-.  •  •  •  r-  *  .  «  HI m  0.1 0  2000  4000  WALL A R E A ( s q u a r e •  S T A B L E WALLS  •  6000  metres) CAVED WALLS  FIGURE 2.6 G r a p h o f t h e s t o p e w a l l s r o c k mass q u a l i t y (expressed i n terms o f the Q i n d e x ) , v e r s u s t h e s t o p e w a l l s a r e a , f o r open s t o p e m i n e s , u s i n g a " f u l l l e n s " l o n g i t u d i n a l extraction.  MINES USING BACKFILL NORITA MATTAGAMI LAKE MINES GASPE WESMIN CORBET KIDD CREEK KIENA LOCKERBY LAC SHORTT GOLDEN GIANT LYON LAKE GECO BRUNSWICK CENTENNIAL SELBAIE - ZONE B FALCONBRIDGE  $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $  88 60 68 128 108 125 69 123 69 114 144 70 125 54 100 129  MEAN  $  98  MINES USING PERMANENT PILLARS •  Table 2.1  APPROXIMATE VALUE OF ORE ($US/ton)  APPROXIMATE VALUE OF ORE ($US/ton)  RUTTAN ALGOMA HEATH STEELE SELBAIE - ZONE A  $ $ $ $  43 25 92 47  MEAN  $  52  Comparison o f the v a l u e of ore ($US/ton) f o r mines u s i n g b a c k f i l l a g a i n s t mines u s i n g permanent p i l l a r s . (Mine grades from 1987 Canadian Mines Handbook, p r i c e of metals from January 1988 E n g i n e e r i n g and Mining Journal).  19  ore  v a l u e i s low.  maximum orebody In  be  stressed  problem  advantageous  ground,  and p i l l a r to  where  bursting  is  done  by  sequence  finished, filled the of  filling  and  a  mining  the  stope as soon  "stope and f i l l " filling  cycle.  stope the  a  r e c o v e r y i s expensive, i t can extraction  and  backfill  o p e r a t i o n s i n o r d e r t o a v o i d the c r e a t i o n of p i l l a r s . is  the  r e c o v e r y i s about 75% t o 80%.  heavily  potential  For mines l e a v i n g permanent p i l l a r s ,  immediately  stope  after  directly  as the b a c k f i l l  has  method i s dependent  This  mining  adjacent  to  is the  set.  Success of  on the  reliability  In a d d i t i o n i t does not have the  initial  h i g h r a t e of r e t u r n a s s o c i a t e d w i t h primary mining of stope and p i l l a r methods.  2.2.3  Drill  h o l e diameter  Originally, diameter  a l l open  drill  production  holes  blasting.  stope  51 In  to  mining 64  the  mm  methods (2  to  1970's,  2.5  large  b l a s t h o l e technology from open p i t mining was underground stoping and  open stope mining.  stoping.  than  the  small  and  more c o s t  diameter  drilling,  blasting  and  effective open  selective p r i o r to  methods of r e t r e a t  l o n g h o l e and b l a s t h o l e open stope mining w i l l 20  for  diameter  longhole  However, b l a s t h o l e open s t o p i n g i s l e s s  The  in)  introduced i n  and r e q u i r e s l a r g e r and more e x t e n s i v e development mining.  small  In g e n e r a l , b l a s t h o l e open  i s more h i g h l y mechanized  productive  used  be  of  described  i n s e c t i o n 2.5  2.2.4  and  2.6.  C l a s s i f i c a t i o n o f open stope mining The  classification  according  to  the  three  of  i n a flowchart,  using  option  are  stope  specifications  illustrated each  open  some mines are u s i n g more than one  The  rules  for  s t o p i n g method.  the  above  I t i s noteworthy  of  rock  mass  discussed  above,  strength  factors  such  and  the  as  ore the  a v a i l a b l e and mine management p h i l o s o p h y  due  There are optimum  Although some g u i d e l i n e s based on  geometry,  that  open s t o p i n g method  selection  is  Canadian mines  t o v a r i a t i o n s i n the orebody c h a r a c t e r i s t i c s . rigourous  methods,  discussed  f i g u r e 2.7.  also given.  mining  value type  open  orebody  have  of  no  been  equipment  o f t e n p l a y a major  r o l e i n the f i n a l mining method s e l e c t i o n .  2.3  DESCRIPTION OF OPEN STOPING PRE-PRODUCTION DEVELOPMENT  The mining  typical  development work necessary  ( e x c l u d i n g orepasses and  f o r open  ventilation  raise  stope  systems)  i s comprised of the f o l l o w i n g f o u r components. Development production  of  interlevel  levels  can  mechanized o p e r a t i o n , mechanized  mining  be  access.  Travel  done v i a ramps,  between  i n the  case of  or manways, f o r more t r a d i t i o n a l  operations.  Ramps  are  necessary  b l a s t h o l e open s t o p i n g because of the l a r g e equipment. 21  the a  less in  FIGURE  CANADIAN  OPEN  2.7  STOPE  LONGITUDINAL  YES  USE OF FILL  MINING DIRECTION  USE OF PILLARS  YES  NO  MINES  TRANSVERSAL  NO  YES  YES  USE OF FILL  NO  YES  USE OF PILLARS  USE OF FILL  DRILL H O L E I-i TYPE " CHADBOURNE INCO THOMPSON LOCKERBY STRATHCONA flUgrj0  CENTENNIAL FALCQNBRIDGE EAST NINE FRASER GECO INCD THOMPSON LAC SHORTT LOCKERBY MINES GASPE MINES SELBAIE STRATHCONA  FUN FLON GECO GOLDEN GIANT LYON LAKE VESTHIN  LITTLE STOBIE NIDBEC RUTTAN  ALGOHA HEATH STEELE RUTTAN  LONOBOLE  BLASTHOLE  LOBBBOLE  GOLDEN GIANT ONAPING  CHADBOURNE CORBET DOME NIDBEC ROSS RUTTAN SPRUCE POINT  CAMFLO LYON LAKE MATTABI NORITA RUTTAN  BLASTHOLE  LOmBOLE  BRUNSWICK MATTAGAM CORBET LAKE FRASER KDDD CREEK KIENA LOCKERBY MINES SELBAIE NORITA STOBIE STRATHCONA  BLASTHOLE INCO THOMPSON ODD CREEK  YES  NO  IUSE  FILL  OF  Development usually  of the d r i l l i n g  horizon.  located i n the footwall,  orebody  in  order  to  maintain  An  access  i s driven p a r a l l e l access  to  the  l o c a t i o n s a f t e r t h e e x t r a c t i o n has s t a r t e d . drilling  f o r longhole mining  parallel) The  drilling  number  stope  drifts  of d r i l l i n g  height  and  (horizontally)  i s done  from  t o the drilling  The p r o d u c t i o n one (or s e v e r a l  running t h e l e n g t h o f t h e stope.  drifts  the  drift,  depends  maximum  on t h e width  (vertically)  drill  hole  o f t h e stope.  on the  length,  and  B l a s t h o l e open  s t o p i n g g e n e r a l l y r e q u i r e s a f u l l overcut f o r t h e p r o d u c t i o n drilling  equipment.  The  overcut  i s approximately  four  metres h i g h and covers t h e e n t i r e top s u r f a c e o f the stope. Sometimes, s m a l l p i l l a r s  are l e f t  temporary support t o l a r g e stope Development developed in  o f t h e mucking  parallel  the footwall.  connected  cones  drifts  a role  less  traditional  A haulage  i s done  to  as chute  stoping.  track  15 t o 30 metres from  drawpoints  open undercut case, 23  trackless  development i s often  a t 10 t o  Collection  used  loading  V-cut  t o the c o l l e c t i o n  complicated  In t h i s  or  l o a d i n g systems.  similar  A fully  drift is  d r i f t by c r o s s c u t s spaced  s l u s h e r mucking  scram d r i f t s . open  The mucking  are suited  as w e l l  have  involve  horizon.  There a r e t h r e e types o f drawpoints.  which  equipment  backs.  t o t h e orebody, u s u a l l y  t o t h e haulage  15 metres.  i n t h e overcut t o p r o v i d e  work. with  scram  cones, but The  more  t h e V-cut  i s common i n b l a s t h o l e  the d r i l l i n g  overcut  of the  stope  below  above,  which  control  i s used  as  undercut  minimizes the  scooptrams  are  drawpoint  of  the  amount o f development.  necessary t o  enter  the  level Remote  stopes  and  remove the l a s t p o r t i o n o f broken ore. Development  of the s l o t  raise.  The  slot  raise  c r e a t e a f r e e face f o r the p r o d u c t i o n b l a s t s .  i s used t o Its location  i s v a r i a b l e depending on the p r e f e r r e d d i r e c t i o n of r e t r e a t . S l o t r a i s e s can be developed by c o n v e n t i o n a l s t a g i n g , Alimak raise  climber,  drop r a i s i n g  by r a i s e b o r i n g  2.4  and  i n h i g h l y mechanized  machines.  DESCRIPTION OF OPEN STOPE MINING AND  The  most  common  open  procedures can be d i v i d e d  stope  SEQUENCING  mining  in  the major  order  to  and  sequencing  i n t o two groups; methods t h a t do not  use b a c k f i l l and methods t h a t use b a c k f i l l . used,  mines  If backfill  i s not  concern i s the sequencing of stope e x t r a c t i o n  avoid  an  early  overstressing  of  the  permanent  pillars.  T h i s i s done by mining from the c e n t r e of the orebody  towards  the  abutments.  s t r a t e g i e s cart be  When  backfill  is  used,  different  f o l l o w e d t o o p t i m i z e the r e c o v e r y of p i l l a r s  or t o simply a v o i d the c r e a t i o n of p i l l a r s .  These o p t i o n s w i l l  be d i s c u s s e d  isometric  drawings  and r e f e r e n c e s t o the open stope mining c l a s s i f i c a t i o n  (section  2.2)  in this  s e c t i o n with i d e a l i z e d  and p r e - p r o d u c t i o n development  24  ( s e c t i o n 2.3)  w i l l be made.  2.4.1  Open s t o p i n g w i t h no b a c k f i l l The  full  most simple  and economic open stope mining  l e n s e x t r a c t i o n because i t has no b a c k f i l l  T h i s method ( i l l u s t r a t e d  method i s  and no p i l l a r s .  i n f i g u r e 2.8) can be a p p l i e d i n s m a l l  o r e b o d i e s o r i s o l a t e d l e n s e s p r o v i d i n g t h e rock mass q u a l i t y i s sufficient variation  f o r stope  surfaces  o f t h i s approach  to  be  self-supporting.  i s t h e open stope sub l e v e l  method shown i n f i g u r e 2.9.  bottom)  instead  o f overhand  methods o f r e t r e a t  retreat  Once again, no p i l l a r s or b a c k f i l l  are necessary but t h e method o f r e t r e a t i s underhand to  A  (from  bottom  f o r l o n g h o l e and b l a s t h o l e  (from t o p  to top). mining  The  will  be  f u r t h e r d i s c u s s e d i n s e c t i o n 2.5.3 and 2.6.3. When backfill, stope,  the value  o f t h e ore does  the use of  but t h e orebody i s t o o l a r g e t o be mined as a s i n g l e  permanent p i l l a r s  retreat  not j u s t i f y  towards  the  are l e f t pillar  and  development  i s located  the orebody  recovery, t h e p i l l a r s  but they need t o remain  (figure  2.10).  permanent  i n the p i l l a r s .  The stopes stope  access  In o r d e r t o maximize  a r e kept  t o a minimum  s t a b l e t o i n s u r e o v e r a l l mine  width  stability  and t o p r o t e c t t h e access t o the stope.  2.4.2  Open s t o p i n g w i t h When  backfill  is  backfill involved,  the  sequencing  of  stope  e x t r a c t i o n becomes p a r t o f an o v e r a l l s t r a t e g y f o r t h e optimum recovery pillars).  of  the  secondary  and  tertiary  stopes  (temporary  By d e f i n i t i o n , primary stopes a r e mined a g a i n s t rock 25  FIGURE 2.8 Idealized isometric drawing of the " f u l l lens" ooen stope mining method.  Stope Width  Stope Height  Distance Haulage— Orebody 7  p. . . Drowpomt Spacing  FULL LENS VERTICAL CRATER RETREAT April  88  JMH  o  FIGURE 2.9 retreat  I d e a l i z e d isometric drawing of the s u b - l e v e l open s t o p e m i n i n g method.  Ultimate Stope Height  Distance Between Sub—Levels  SUB--LEVEL RETREAT 0A71  Nov  87  MAW  JMH  «rv.  0  walls,  secondary  cemented  stopes are u s u a l l y mined a g a i n s t one  backfill  surrounded  by  secondary  stopes  wall  backfilled will  t e r t i a r y can be f i l l e d The "leap  most  frog"  widely  and  blasthole  open is  development  and  can  often  used  need  mining  frog  drill  c o n c e n t r a t e on  minimizing  drill  one  level  movement.  In f i g u r e  and  on  variation  longitudinal Firstly, to  of  the  blasthole  Otherwise,  open  frog"  of  stope  such  as  availability  of  figure  primary  mining  2.11), and  thus  tertiary  levels.  sequence,  the  tertiaries.  cemented b a c k f i l l  stopes w i l l  the f l e x i b i l i t y  applied figure  of mining.  observed t h a t the primary stopes are  than  expensive  to  2.12.  This w i l l  reduce  the amount of  but on the o t h e r hand, the primary  c o n t r i b u t e a much s m a l l e r tonnage  1-5-9  sequence,  It  significantly  i n the important  stage of mining. The  the  t h e r e i s stope e x t r a c t i o n on m u l t i p l e l e v e l s i n order  can a l s o be  first  leaving  transverse  factors  s t o p i n g i s shown on  i n c r e a s e the p r o d u c t i o n and  smaller  a  called  number of stopes,  (as shown on  "leap  and  2.11,  order  the  s t o p i n g are done s i m u l t a n e o u s l y on m u l t i p l e A  to  actual  depends  I f t h e r e are a s u f f i c i e n t  and  backfill,  i s commonly  applied  The  scheduling  primary  a stope and  pillar. is  usually  fill.  sequence  method. and  are  cemented  between mining  sequence  variable  stopes  Consequently,  a temporary  stoping  extraction  backfill.  stopes.  alternates  leap  tertiary  w i t h uncemented  the a d j a c e n t stope as traditional  and  or more  another v a r i a t i o n of 29  "leap frog"  FIGURE 2.11 I d e a l i z e d i s o m e t r i c drawing o f t h e t r a n s v e r s e b l a s t h o l e open s t o p e m i n i n g method, u s i n g t h e " l e a p f r o g " sequence of e x t r a c t i o n .  Primary Stope Length  Secondary Stope Length  TRANSVERSE BLASTHOLE  FIGURE 2.12 Idealized isometric drawing of the longitudinal blasthole open stope mining method, having small primary stopes and large secondary stopes.  Primary Stope Length  Secondary Stope Length  Footwall Access  LONGITUDINAL BLASTHOLE " Dec  87  0  sequence i s shown i n l o n g i t u d i n a l s e c t i o n  i n f i g u r e 2.13.  first,  stopes  for  fifth  the  and  first  are s t a r t e d  ninth  (thirteenth  t h r e e l e v e l s b e f o r e the middle  level  l e v e l and t e r t i a r y  (see stage 4,  follow  order  of  When mining of  stopes 3, 7,  stoping i s i n i t i a t e d  5, 6 of f i g u r e 2.13). extraction  are  ( 3-7-11)  11 begin on a t the  first  The main reasons t o stopes  i n the  same mining b l o c k from each other, and t o keep the l o c a l  mining  rate  this  level,  are e x t r a c t e d  stopes  (see stage 1, 2, 3 of f i g u r e 2.13).  stopes 1, 5, 9 reach the f i f t h the t h i r d  etc.)  The  to i s o l a t e  low.  2.4.3  Stope and f i l l The  principle  mining  of "stope and  fill"  i s t o mine and  backfill  a d j a c e n t stopes c o n s e c u t i v e l y i n a manner such t h a t no are  created.  extracted  A l l the  a g a i n s t one  stopes  (except the v e r y  backfill  wall  (secondary  first  pillars one)  are  mining).  This  method l o s e s the h i g h r a t e of r e t u r n of the primary mining, is  sometimes necessary  highly fill  stressed  ground.  t o achieve A mining  total  orebody  sequence u s i n g a stope  In  this  case,  the  retreat  i s done  towards the c e n t r e of the mining b l o c k , on one creates  development but  recovery i n and  method and a l o n g i t u d i n a l open s t o p i n g i s , shown i n f i g u r e  2.14.  This  but  may  stopes.  two  production  faces,  minimizes  from  stress  c o n c e n t r a t i o n problems  ends  l e v e l at a time. the  (only t h r e e accesses t o the orebody are  cause  both  in  amount  of  required),  the  central  T h i s s i t u a t i o n can be avoided by r e t r e a t i n g from  one  FIGURE  1-5-9 •  2.13  Mining m  11 1 % i Stage 1  Mining  Sequence H  Backfilled  '•-ry  i 1  Stage 2  UJII Stage 3.  Stage 4  Stage 5  Stage 6 33  'n-  FIGURE 2.14 Idealized isometric drawing of the longitudinal open stope mining method, using the "stope and f i l l " sequence of extraction.  Stope  Length  oil  Ore  Access  Pass  LONGITUDINAL BLASTHOLE DATE  HV. 1  DRAWN  Nov 87  JMH  o  I  end  of the  face w i l l  orebody t o the o t h e r . However, o n l y one be  available.  A third  option i s to  production  start  a s e t of  stopes a t the c e n t r e of the mining b l o c k and t o r e t r e a t towards both  of the abutments.  will  keep two  This w i l l  prevent  p r o d u c t i o n f a c e s but may  stress build  up  and  c r e a t e access problems  and l o n g ore tramming d i s t a n c e s . Stope and  has  into  and  fill  has  also  been  been rtamed panel mining.  a number of s m a l l stopes  figure  2.15).  varies  from  orebody  The  mine  and  The  are  mining  an  massive bursting  2.5  to  mine  and  i s largely  conditions.  backfilled expensive  block i s divided  board"  manner  with  mining that  I t uses  method. bad  fill  the  s m a l l stopes,  and  Almost  which  a l l the  makes  It is typically ground  stopes  upon  development.  cemented  have  dependent  (see  panel  used  conditions  in  and/or  problems.  LONGHOLE OPEN STOPING  Longhole  i s the  mining method. to  mining  orebodies  sequence of e x t r a c t i o n of i n d i v i d u a l  geological  orebodies  t o wider  i n a "chess  thus r e q u i r e s a l o t of pre-mining stopes  applied  64  oldest  most c o n v e n t i o n a l open  stope  I t i s c h a r a c t e r i z e d by s m a l l diameter h o l e s  m i l l i m e t r e ) which  retreating  and  practices.  influence  the  drilling,  Those p r a c t i c e s must be  blasting  adapted  (51 and  t o the  orebody geometry, g e o l o g i c a l c o n d i t i o n s and the l o c a t i o n of the drilling  drifts.  FIGURE 2.15 P l a n view showing t h e "panel m i n i n g " sequence o e x t r a c t i o n , ( a f t e r A l e x a n d e r and F a b j a n c z y c k , 1981)  2.5.1  Longhole d r i l l i n g Drilling  and  patterns  frequently  vary  from mine t o mine, stope t o stope  from row t o row.  types o f longhole  However, t h e r e  d r i l l i n g patterns.  a r e two b a s i c  In t h e r i n g p a t t e r n ,  each  row  has h o l e s d r i l l e d  a t 360° from a f i x e d set-up p o i n t  (figure  2.16  a and b ) , while  f a n p a t t e r n s have o n l y down h o l e s  (figure  2.16  c) .  advantage  between  The main sub-levels  length.  can be  In Canadian  of r i n g s  almost  shield  deviation  meters.  Consequently, t h e t y p i c a l  becomes e x c e s s i v e  using r i n g patterns fan  drilling,  i t i s only of the ring  fragmentation  originating  has  Also, holes  favorable  the distance  t h e maximum  i t has been a t hole  found  lengths  d i s t a n c e between  against  f o r wall  that  over 20  sub-levels  15  to  pattern from  20  meters.  i s that  One  of the  i t may  have bad  where  the r i n g s  the l o c a t i o n  i t can be seen on f i g u r e 2.16 a) t h a t t h i s ending  hole  i s approximately 30 t o 35 meters, while f o r  disadvantages  meet.  double  rock,  longhole  i s that  the  stability.  stope  walls,  When  pattern  which  t h e stope  i s not  i s wider,  d r i l l i n g d r i f t s may be l o c a t e d a t t h e hanging w a l l and f o o t w a l l limits.  "Contour h o l e s " a r e d r i l l e d p a r a l l e l t o t h e stope/waste  contacts, (figure  and g e n e r a l l y  2.16 c ) .  result  stope w a l l  In f a n d r i l l i n g , contour w a l l h o l e s  p o s s i b l e and poor fragmentation Typically,  i n better  t h e t o e spacing  stability are also  i s not a common problem. between h o l e s  i s greater  the row burden t o help t h e b l a s t break c l e a n e r and reduce  37  than  FIGURE 2.16 T y p i c a l longhole d r i l l i n g C a n a d i a n open s t o p e m i n e s .  a)  Ring P a t t e r n .  b)  patterns  Ring p a t t e r n with p a r a l l e l wall holes.  employed  c)  in  Fan p a t t e r n with p a r a l l e l wall holes.  backbreak.  The  determination  of  l o n g h o l e s depends upon the d r i l l of  the  and  ore.  F i g u r e 2.17  shows t h a t  (burden  the  * spacing)  2.5.2  the  h o l e diameter  i s based on  amount  of  burden  ore  and  spacing  and the hardness  a c t u a l longhole  to  be  broken  i n c r e a s e s w i t h the d r i l l  by  hole  patterns each  general,  2  to  4  rings  longhole production b l a s t . delay  and  delay.  frequently Longholes  alternately  diameter.  right  multiple  to  fans  are  fired  Each h o l e i s detonated  within up  or  a  holes ring  the  are  or  collar  during  on a  fired  on  fan  are  often  while  the  next  done t o a v o i d o v e r b l a s t i n g caused the d r i l l  2.5.3  same loaded  hole  is  This i s  by the h o l e s converging  near  drift.  Longhole r e t r e a t i n g methods The  stoping giving  conventional i s by  method  face.  The  staggered  first  the t h i r d t o be  development  of  slashing vertical  horizontal retreat.  sub-level  order  a  single  the  loaded t o a d i s t a n c e of 3 t o 5 meters from the c o l l a r .  then  hole  Longhole b l a s t i n g In  full  of  and one,  able  The retreat  retreat slices  into  retreat  can  method  i s f o l l o w by the next etc.  to s t a r t  in  (see f i g u r e  the be  area,  the  or  bottom  s u b - l e v e l above  production b l a s t i n g ,  and  T h i s i s done i n before  a l l the  However, a problem  a s s o c i a t e d w i t h staggered r e t r e a t i s t h a t the sharp 39  slot  open  staggered  advances  2.10).  i n the upper subs i s f i n i s h e d .  longhole  corners  FIGURE  8.0  BURDEN*SPAOLNG VS HOLE DIAMETER  2i7  FAN AND RING PATTERNS  -i  o.o H 50  1  ,  54  1  ,  58  1  1  62  1  1  1  66  HOLE DIAMETER (mm)  1  70  1  1  74  r  r 78  created  are  in  drawpoints  the  Another start  prone t o  caving,  and  loss  disadvantage as  soon as  The  full  is  the  the development and  is  toe  sub  some d r i l l  of the r e s t of the retreats  all  The  expected  holes.  i f stope  or  can  jeopardize  stope. the  sub-levels created  p r o g r e s s i v e l y and  Furthermore, f i l l i n g  possible  and  pillars  until  muck  problems  i s completed  2.18).  not  of  stability  then d i m i n i s h e d  problems are  extraction  the  lead to oversized  pillar  method  (figure  the stope e x t r a c t i o n . the  that  recovery  converging stopes are stability  of  bottom  face  simultaneously  which can  by  pillar  the  final  and  resequencing of  pillar  stage  problems  of  are  encountered. A  completely  f i g u r e 2.9. the  top  consists  from  each  Because the metres, mining which  method  of  retreat  is  shown  in  T h i s method, o f t e n c a l l e d s u b - l e v e l r e t r e a t , mines  sub-level  drilling done  different  this  first,  e x c l u s i v e l y of  sub-level,  distance method  development. makes  the  followed up  instead  between the  the  holes of  a  However,  most  ones and  at  sublevels  requires  sub-level  by  retreat  the  the  The  mucking  stope  is  bottom.  i s approximately  considerable of  below.  amount  i t is  method,  of  located  one  of  in  the  10  preore most  economic.  2.6  BLASTHOLE OPEN STOPING  B l a s t h o l e open s t o p i n g was 41  d e r i v e d by m o d i f y i n g  longhole  FIGURE 2.18 Idealized isometric drawing of the longitudinal longhole open stope mining method, using a f u l l face retreat. Primary Stope Length  Secondary Stope Length  Manway  Distance Between Sub-Levels  LONGITUDINAL LONGHOLE  mining  t o the use of l a r g e diameter  v i b r a t i o n s generated  drill  In r e c e n t years, new  r e t r e a t i n g techniques  operations  take  b l a s t h o l e open methods.  2.6.1  Blasthole d r i l l i n g principal  the use  of 100  production  one  characteristic  - 200  blasting  mm  blasting.  l a r g e diameter  advantage  stoping  mining  The  drilling,  of  of  the  ground  have been s u c c e s s f u l l y developed.  l a r g e equipment i s r e q u i r e d to d r i l l  makes  At f i r s t ,  by the b l a s t i n g of b i g h o l e s caused  c o n t r o l problems.  blasthole  holes.  Since  h o l e s , most  mechanization.  the  most  and  cost  This  efficient  of b l a s t h o l e open s t o p i n g i s  (4 t o 8 inch) diameter Because l a r g e h o l e s  drill  can be  holes f o r  drilled  with  more p r e c i s i o n over a long d i s t a n c e , the stope h e i g h t can be to  50  t o 60 metres.  between  rows  metres.  The  165  mm  metre  varies most  (6.5  inch)  burden  and  parallel,  from  ( f i g u r e 2.19 undercut.  The from  typical drill  fully  a).  approximately  2.4  blasthole d r i l l i n g  holes  spacing.  a  The  s p a c i n g between h o l e s and  and  The  a  square  holes  open o v e r c u t  are  metres  burden to  3.6  arrangement  has  p a t t e r n with drilled  mutually undercut  The h o l e s ' p r e c i s i o n can be surveyed  from the  can  fully  a l s o be  apply  to  inclined  stopes, except a l l the h o l e s w i l l be i n c l i n e d p a r a l l e l t o walls  ( f i g u r e 2.19  where most  of  the  rows are d r i l l e d  a 3  open  same p r i n c i p l e  to a  the  up  b).  stope  A v a r i a t i o n i s shown on f i g u r e 2.19  holes  have been kept  along the hanging w a l l . 43  vertical  and  c),  inclined  When d r i l l i n g  drifts  FIGURE  2.19  Canadian  Typical open  blasthole  stope  mines.  drilling  patterns  employed  in  are used one  i n s t e a d of a f u l l  shown  stability stope  in  figure  problems  walls,  2.19  d)  since  and  overcut,  a  must  a fan p a t t e r n such be  large holes  large  near the  is  f o r i r r e g u l a r orebodies,  how  ideal  the  drilling  definition. to  a  Shorter  vertical  temporary overcut  2.6.2  drilling  can  be  are  quantity  concentrated not  used.  adapted  explosive  parallel  small p i l l a r s  the  can  be  B l a s t h o l e open s t o p i n g but  to  pattern,  the  cause  f i g u r e 2.19  better  suit  e) shows  the  orebody  i n c l i n e d h o l e s sometimes have t o be in  order  which are l e f t  (see f i g u r e 2.19  to  added  drill  f o r the support  under of  the  f) .  Blasthole blasting Large  first  diameter  h o l e s are b l a s t e d u s i n g  two  methods.  The  approach i s s i m i l a r t o l o n g h o l e open s t o p i n g and i n v o l v e s  the  slashing  resulting  of  vertical  slices  in horizontal retreat  (full  stope  3 metres of  blast, fires  stemming.  The  full  t o a v o i d p l u g g i n g problems. one  or  two  rows  (of  3  height)  from the s l o t area.  are loaded w i t h a s e r i e s of 2 t o 4 metre charges or  may  blasted against  of  drift.  This  as  to  hole  The  is fired  holes  holes  separated by 2 i n the same  A t y p i c a l production 5  and  each)  at  a  blast time.  However, mass b l a s t s of s e v e r a l rows are not uncommon. The  second  horizontal slices, the  stope  retreat  or  approach  for  big  hole  causing v e r t i c a l r e t r e a t ,  towards the vertical  top.  block  This mining.  blasting  from the bottom of  i s known as v e r t i c a l A  breaks  single  crater  charge having  a  l e n g t h t o width r a t i o l e s s than 6 t o 1 i s l o c a t e d i n each h o l e , at  an  optimum d i s t a n c e  blasts,  the bottom  portion  h o r i z o n t a l ore s l i c e One  of  the  from the f r e e  face.  During p r o d u c t i o n  of a l l the h o l e s are f i r e d  and  the  i s cut.  major  concerns  of  many  operators,  in  using  l a r g e diameter h o l e s , i s the p o t e n t i a l b l a s t i n g damage t o stope walls. to  Several  reduce  control  blast  blasting  vibrations  t e c h n i q u e s have been developed  and  overbreak  in blasthole  open  stoping. The  amount  separating  of  explosives  the charge  into  in  the  hole  is  reduced  s h o r t columns s e p a r a t e d by  of an i n e r t m a t e r i a l or wooden a i r s p a c e r s ( f i g u r e D i l u t e d AN/Fo explosives, for wall  by  decks  2.20).  i s used t o reduce the s h a t t e r i n g power of the  and  i s especially  effective  i n perimeter holes  control.  The weight of e x p l o s i v e f i r e d per d e l a y i s reduced. Preshear the  h o l e s are used  desired  production  line blast  of  to create break.  effects  on  a plane  This  is  nearby  o f shear along used  to  development  reduce or  weak  walls. The  pressure  reduced  by  effects  decoupling  of the  cardboard or p l a s t i c tube  2.6.3  the  bulk  charge  (figure  explosive in  a  column  smaller  diameter  2.20).  B l a s t h o l e r e t r e a t i n g methods  As mentioned  i n s e c t i o n 2.6.2, b l a s t h o l e r e t r e a t can be 46  are  ~  Primacbrd  TRUNK LINE  "-4"Cardboard tubes  — E CORD DOWNLINE 5 FT. SAND STEMMING  A*—  Drill cuttings  AUSTIN PRIMER #5 S.P. DELAY  Primer  or crushed stone K^iU.  Mi  80 lb. TOVEX 448  -AN/FO  30 FT.  6  AUSTIN PRIMER #3 S.P. DELAY  •".-IS  AUSTIN PRIMER #1 S.P. DELAY  Wood  WOOD PLUG SUSPENDED ON POLY ROPE Decked  plug—.  — I 6.5"—!  Decoupled  Charges  •Primer  Charges  Detonating Cord Air  Spacer  FIGURE 2.20 I l l u s t r a t i o n of the l o a d i n g procedure f o r large diameter b l a s t h o l e s . 47  horizontal  (slashing)  for extraction slot  (full  the  horizontally retreat  i n horizontal  stope  enlarging  or v e r t i c a l  retreat include:  height)  slot  to  towards  can i n v o l v e  (crater retreat).  at  the  full  the o t h e r slashing  the opening of a  extremity  stope  of  width  extremity  The steps  the  and  stope,  retreating  o f the stope.  o f one o r two rows a t a time, or  the use o f mass b l a s t s .  The p r i n c i p l e o f mass b l a s t i n g  increase  the  t h e volume  available  of  f o r the s w e l l  blasts,  of the broken  l a s t h a l f o f the stope i s o f t e n blast  of  the  stope.  The  exposed  fly  rock  t o the b l a s t may  cause  main  remaining b l a s t h o l e Vertical spherical The  charges  i s blasted  slice  t o the stope  and mining  final  crown  blasted  found  that  i t is difficult  The  v i b r a t i o n and and the  cleanup. on the use o f  (three  crown  mass  is  blasting  backs  o f the stope  a s i x t o t e n metre  this  retreat,  (Lang  until  i s then  of  theory  successively  void  ore ( f i g u r e 2.21).  methods are based  and c r a t e r i n g  bottom h o r i z o n t a l  thick)  damage  retreat  greater  However, s i n c e the overcut  c o l l a r s may r e q u i r e  crater  a  advantage  i n horizontal  some  as  i s to  taken a t once i n the l a s t mass  technique i s i t s h i g h p r o d u c t i v i t y . is  The  is left  t o four  retreats (figure  a t once.  to crater blast  e t al.,1977). metre  vertically  2.22) .  The  Some mines  have  in thin  stopes.  A  v a r i a t i o n c a l l e d "inverse  bench b l a s t i n g " has been developed t o  alleviate  The c e n t r a l  brought  t h i s problem.  portion  o f the stope i s  up a couple o f rounds i n advance i n o r d e r t o c r e a t e  supplementary  f r e e face  f o r the p r o d u c t i o n b l a s t , and t o avoid 48  a  Develop  slot  raise.  Open s l o t  to f u l l  stope  width.  I  i  Mass b l a s t  S l a s h s e v e r a l rows o f blastholes into slot.  remaining ore.  FIGURE 2.21 Idealized isometric drawing showing the "mass b l a s t " r e t r e a t f o r blasthole open stope mining method. 49  3  6-10m  FIGURE 2.22 Cross s e c t i o n of the v e r t i c a l c r a t e r r e t r e a t method u s e d i n b l a s t h o l e o p e n s t o p e m i n i n g , s h o w i n g an i n i t i a l b l a s t , and t h e r e m n a n t c r o w n b l a s t . 50  blast  choking  conditions  (figure  2.23).  The  advantages  of  v e r t i c a l retreat are: it  does not need a f u l l  expensive and produces  stope h e i g h t s l o t r a i s e which i s heavy b l a s t i n g  vibrations,  i t uses s m a l l b l a s t s w i t h s m a l l charges, good  fragmentation  and low e x p l o s i v e s c o s t s are o f t e n  achieved, -  the back o f the o v e r c u t i s not exposed t o p r o d u c t i o n b l a s t s , the o p t i o n o f l e a v i n g broken wall  ore i n t h e stope f o r temporary  support i s p o s s i b l e . In t h i s case, t h e mining method  does not meet the open stope s p e c i f i c a t i o n d e f i n e d i n t h i s study. One p o t e n t i a l disadvantage o f v e r t i c a l r e t r e a t occurs i f a weak h o r i z o n t a l s t r u c t u r e i s p r e s e n t i n the rock mass. may  from  the face  problems and secondary  blasting.  2.7  be  detached  (overbreak),  Large b l o c k s  causing  mucking  SUMMARY AND CONCLUSIONS  Open  stoping  i s a s a f e non e n t r y mining  method.  It is  v e r y c o s t e f f i c i e n t because i t a l l o w s f o r f a s t e x t r a c t i o n , mechanization,  high  productivity  and  it  is  not  high  labour  i n t e n s i v e . However, open stope mining has some l i m i t a t i o n s .  It  is  in  not s e l e c t i v e ,  regular  orebodies.  and  consequently  Better results  i t i s more  a r e a l s o o b t a i n e d i n steep  o r e b o d i e s having a minimum t h i c k n e s s o f 5 metres. 51  efficient  At l e a s t a  FIGURE 2.23 C r o s s s e c t i o n o f t h e i n v e r s e b e n c h b l a s t i n g method u s e d i n n a r r o w b l a s t h o l e open s t o p e m i n i n g . 52  f a i r t o good rock mass s t r e n g t h f o r the ore and country rock i s a l s o necessary. There methods.  are s e v e r a l  major  variations  They have been c l a s s i f i e d  o f open stope  in this  mining  chapter according  to: the  d i r e c t i o n o f mining  ( l o n g i t u d i n a l or transverse),  the  use o f b a c k f i l l and p i l l a r s ,  and t h e b l a s t i n g p r a c t i c e s  (longhole or b l a s t h o l e ) .  The pre-mining development  r e q u i r e d i n open s t o p i n g can be  r e l a t i v e l y e x t e n s i v e and i s comprised o f : i n t e r l e v e l access (ramp o r manway), development  o f the d r i l l i n g h o r i z o n (access d r i f t ,  d r i l l i n g d r i f t or overcut), development  o f the mucking h o r i z o n (haulage d r i f t ,  drawpoints o r undercut, drawpoint and the s l o t r a i s e  Four number  of  sequences  general Canadian are  cross-cuts),  ( i f necessary).  mining open  sequences stope  compared  have  mines.  been  observed  In t a b l e  against ' the  open  2.2,  stope  in a these mining  c l a s s i f i c a t i o n proposed i n s e c t i o n 2.2.4. There  are  fundamental  blasthole  open s t o p i n g .  equipment  which  development  Longhole  has b e t t e r  costs.  differences uses  selectivity  between  l o n g h o l e and  s m a l l and c o n v e n t i o n a l and  lower  pre-mining  B l a s t h o l e i s the epitome o f b u l k mining  TABLE  2.2 Comparison of the mining sequence used with p r o p o s e d open s t o p e c l a s s i f i c a t i o n s y s t e m .  the  OPEN STOPE CLASSIFICATION SYSTEM LONGITUDINAL PILLARS FILL  TRANSVERSAL  NO PILLARS  NO FILL  FILL  PILLARS  NO PILLARS  FILL  FILL  NO FILL  BLAST LONG BLAST LONG BLAST LONG BLAST LONG BLAST LONG BLAST HOLE HOLE HOLE HOLE HOLE HOLE HOLE HOLE HOLE HOLE HOLE .1*.  o or  LEAP FROG  X  PERMANENT PILLAR  w co  DIRECTIONAL STOPE AND FILL  O  FULL LENS MINING PANEL MINING  X X  X  X  X  X  X  X X  X X  X  X  X X  methods stopes.  using  large  Blasthole  costs  than  more  efficient  explosives  large  equipment,  open s t o p i n g g e n e r a l l y has lower  longhole,  costs.  development,  due  to higher  blasting The  practices  larger  drilling which  production  g i v e s a v e r y high o v e r a l l p r o d u c t i v i t y .  55  and  large  production  productivity result  scale  of  in  and  lower  blasthole  CHAPTER 3 STRESS  3.1  INTRODUCTION  The  stress  acting  underground openings of the  stress  a t any p o i n t  i s a combination  and the d i s t u r b e d  medium.  The  i n t h e immediate  area of  o f t h e pre-mining  state  s t r e s s caused by c r e a t i n g v o i d s i n  resulting  "induced"  stress  field  i s often  r e p r e s e n t e d by stream l i n e s o f p r i n c i p a l s t r e s s t r a j e c t o r i e s i n the  d i r e c t i o n o f the maximum t r a c t i o n .  Figure  3.1 shows t h a t  i n the v i c i n i t y of e x c a v a t i o n s the l i n e s c o n c e n t r a t e i n c e r t a i n areas lines  and p a r t identify  condition  may  i n other zones have  locations.  of  high  various  Heavy  c o n c e n t r a t i o n s of  compressive  effects  on  stress.  opening  This  stability  a c c o r d i n g t o the problem geometry and the nature o f the rock. The state  absence  of  of r e l a x a t i o n  significant  stress  trajectory  i n t h e medium.  effect i n a jointed  lines  rock mass because i t p r o v i d e s  a summary o f background i n f o r m a t i o n stress,  governing  Understanding  the  around  magnitude  T h i s chapter i s  on: the o r i g i n o f the p r e -  how i t can be measured  i t s redistribution  to a  The r e l a x a t i o n w i l l have a  more freedom o f movement t o i n d i v i d u a l b l o c k s .  mining  corresponds  and  and the p r i n c i p a l laws underground orientation  openings. of  the  ( r e d i s t r i b u t e d ) p r i n c i p a l s t r e s s i s an e s s e n t i a l s t e p i n the 56  FIGURE 3.1 A n a l o g y o f a f l o w i n g s t r e a m o b s t r u c t e d by t h r e e b r i d g e p i e r s , r e p r e s e n t i n g s t r e s s s t r e a m l i n e s around underground openings. ( A f t e r Hoek and B r o w n , 1980)  57  stope  design  procedure. review  Brady & Brown  (1985), B i e n i a w s k i  Franklin  3.2  the  following  comprehensive  and  of  The  subject  by  discussion  Hoek  &  Brown  (1984), Herget  is  a  (1980) ,  (1987) and  Kim  (1987).  PRE-MINING STRESS  The result  pre-mining s t r e s s i s locked of  the  represented every  by  point  principal  geological  directions.  history.  The  p r i n c i p a l stresses in  stress  sub-vertical  i n t o the  and  orthogonal  in  Canadian  i n two  Because  mutually of  the  stress  confining  three the  e a r t h ' s c r u s t as  the  of s t r e s s are  The  at  Pre-mining  shield usually perpendicular  variability  often  rock mass  directions.  acts  in  the  sub-horizontal  of  domains, the pre-mining s t r e s s w i l l be s u b j e c t v a r i a t i o n s i n space.  regime i s  a  the to  rock  mass  unpredictable  f a c t o r s i n f l u e n c i n g the  in-situ  state  summarized below ( a f t e r Brady & Brown, 1985).  a) S u r f a c e Topography: Stress stress  measurements  have  i s approximately  demonstrated  equal  Consequently, major s u r f a c e and  valley will  underlying b)  influence  to  the  that  weight  irregularities the  the of  overburden.  such as  d i s t r i b u t i o n of  vertical  load  mountain in  the  rock mass.  Erosion: Erosion  or g l a c i a t i o n may  remove p a r t of the  c e r t a i n areas r e d u c i n g the v e r t i c a l 58  rock "crown" i n  in-situ stress.  Because  the h o r i z o n t a l s t r e s s i s l o c k e d i n the medium t h i s i s l i k e l y t o show h i g h h o r i z o n t a l - v e r t i c a l s t r e s s  situation ratio.  c) R e s i d u a l S t r e s s : The  residual  stress  i s a t t r i b u t a b l e t o chemical o r p h y s i c a l  p r o c e s s e s such as thermal expansion d u r i n g t h e c o o l i n g phase of  crust  formation.  stresses  are  local  Other  phenomena  recrystallization  causing  in a  changes i n t h e water content of a m i n e r a l  rock  residual mass  or  aggregation.  d) I n c l u s i o n s , Dikes and V e i n s : The  formation  extrusive,  of  inclusions  occurring after  orientation  in a  rock  the host  o f the i n c l u s i o n s  mass  are o f t e n  rock has s e t t l e d .  i s largely  i n f l u e n c e d by the  s t a t e of s t r e s s a t the moment of t h e i r f o r m a t i o n . be  composed  difference  of very  hard  in stiffness  o r very  weak  They may  materials.  between the i n c l u s i o n  stiff  inclusions  will  attract  stresses  The  and the host  rock may p r o v i d e a l o c a l rearrangement o f the s t r e s s Very  The  while  field. weak  i n c l u s i o n s w i l l be d e s t r e s s e d . e) T e c t o n i c S t r e s s e s : Tectonic  activity  regional  s c a l e and are u s u a l l y a s s o c i a t e d w i t h major  and  folding.  horizontal  may  modify  Their effect  the l o a d i n g  c o n d i t i o n s on a faults  i s t o i n c r e a s e both v e r t i c a l and  s t r e s s e s i n the s t i f f e r  components  o f the host  rock. f) F r a c t u r e s e t s and D i s c o n t i n u i t i e s : A triaxial  compressive  test 59  on a rock specimen may help t o  i n t e r p r e t t h e i n t e r a c t i o n between f r a c t u r e state of  of stress.  frequency and c o n t i n u i t y  rock mass d i s c o n t i n u i t i e s a r e a l l i n d i c a t o r s  s i t u stress  3.3  The o r i e n t a t i o n ,  formation and the  of the i n -  field.  STRESS MEASUREMENT  A distinct rock  mass  values  d e f i n i t i o n of stress  i s an  impossible  can be determined  measurement collaboration reviewed  with  task.  using  techniques.  a t every  However,  a number  Kim  and  t h e Commission  t h e p r i n c i p a l methods  point  representative  of d i f f e r e n t  Franklin  on  Testing  of s t r e s s  w i t h i n the  stress  (1987) Methods  measurements.  in have This  review i s summarized below.  3.3.1  Method 1 - F l a t j a c k The method  surface using  o f an e x c a v a t i o n a diamond  creation the  consists  of i n s t a l l i n g and c u t t i n g  saw, o r u s i n g  of t h i s s l o t w i l l  measuring  a slot  a series  pins  between the p i n s  of boreholes  r e l a x the m a t e r i a l  on t h e  .  The  on each s i d e and  r e l a t i v e movement can be recorded by t h e p i n s .  The s t r e s s  e x i s t i n g i n t h e rock can be estimated by measuring t h e p r e s s u r e required  by a f l a t j a c k t o b r i n g t h e p i n s back t o t h e i r o r i g i n a l  locations.  T h i s t e s t measures t h e s t r e s s i n o n l y one d i r e c t i o n  and  a minimum o f s i x measurements w i l l  the  stress tensor.  be necessary t o o b t a i n  Often, nine t e s t s a r e c a r r i e d out, t h r e e i n 60  the  roof,  three  properties  are  i n the not  wall  and  necessary  three  for  i n the  this  face.  test.  (1985) have i d e n t i f i e d t h r e e p r e r e q u i s i t e s  Elastic  Brady  &  Brown  for a successful  in-  s i t u s t r e s s determination using f l a t j a c k s : "(a)  a r e l a t i v e l y undisturbed surface the t e s t  (b)  an  of the opening c o n s t i t u t i n g  site;  opening geometry  relating  the  f o r which c l o s e d  far-field  stresses  form s o l u t i o n s  and  the  boundary  exist,  stresses;  and (c) a rock mass which behaves e l a s t i c a l l y , are r e c o v e r a b l e when the  i n that  displacements  s t r e s s increments i n d u c i n g  them are  reversed."  3.3.2  Method 2 - H y d r a u l i c The  hydraulic  determine  the  fracturing  f r a c t u r i n g i s the  pre-mining  stress  available.  The  by  i n which a f l u i d  packers,  only e x i s t i n g technique to  when  t e s t i s done i n p a r t  direct  of  a drillhole,  pressure i s applied.  pressures required  to generate, propagate,  fractures  at  related An  in  rock  t o the  inspection  the  test  existing stress of  the  that the  orientation the  of the  drillhole  principal  at  are (Kim  the  televiewer  The  61  not  isolated  "The  measured & Franklin,  test  horizon  fluid re-open  and  are  1987). using  a  w i l l h e l p determining  same d i r e c t i o n hydraulic  is  s u s t a i n and  principal stresses.  i s i n the  stress.  horizon field."  fractures  b o r e h o l e camera or an a c o u s t i c the  access  I t w i l l be (±  15°)  as  assumed one  f r a c t u r i n g measures  of the  maximum  and  perpendicular efficient  minimum  stresses  t o the d r i l l h o l e .  i n rock  material  homogeneous, e l a s t i c ,  3.3.3  principal  the  I t i s found  which  behaves  plane  t o be more  as  a  brittle,  i s o t r o p i c and non-porous media.  Method 3 - O v e r c o r i n g t e c h n i q u e s The  overcoring  popular  techniques  dimensional gauges  mounted  measurement because  state  (approximately  i t often  of s t r e s s  on  a  has become  cell  from  each  at least  the f u l l  measurement.  are inserted  38mm diameter)  one o f t h e most  obtains  in a  Strain  pilot  diameter  from  the excavation i s  The rock  specimen  containing  the c e l l  r e c o v e r e d by o v e r c o r i n g u s i n g a core b a r r e l approximately diameter.  During  is  removed from  be  allowed  gauges  t o expand.  T h i s deformation  combined  be used  the pre-mining determines  t h e process o f o v e r c o r i n g , t h e rock  available  150mm  specimen  with  i s measured by s t r a i n  the e l a s t i c  properties of  the  t o c a l c u l a t e t h e magnitude and d i r e c t i o n o f  stress.  the e l a s t i c  An o n - s i t e b i a x i a l t e s t on t h e specimen properties.  breakage o f t h e overcored invalidate  is  i t s i n s i t u c o n f i n i n g s t a t e o f s t r e s s and w i l l  and when  rock, w i l l  hole  stress a distance  one opening  recommended.  three  and f i x e d a t t h e l o c a t i o n o f t h e  s t r e s s measurement. To o b t a i n t h e pre-mining of  in  I t should  sample d u r i n g t h e t e s t  t h e measurement.  Three  types  be noted  that  i s l i k e l y to  of c e l l s  a r e widely  commercially.  - The USBM  drillhole  deformation 62  gauge  i s a re-usable  cell  that  measures  cantilevers measures  the  and  rock  deformation  adjustable  t h e maximum  length  and minimum  with  strain  contact  principal  plane p e r p e n d i c u l a r t o the b o r e h o l e .  gauge  pistons. stress  It  i n the  Consequently,  at least  t h r e e n o n - p a r a l l e l measurements a r e necessary t o o b t a i n the three dimensional necessary, maximum  i n s i t u s t a t e o f s t r e s s . S i n c e no glue i s  the c e l l  horizontal  measurements  up  works range  to  70  well  i n wet  i s less  than  metres  away  conditions. 30  have  metres been  The while  achieved  vertically. Both  t h e South  African  are  based  similar  on  (CSIR) and A u s t r a l i a n concepts.  Three  (CSIRO)  cells  rosettes,  each  c o m p r i s i n g t h r e e o r f o u r s t r a i n gauges a r e mounted i n t h r e e directions against  on a non r e c o v e r a b l e  the wall of the p i l o t  overcoring. orientation  Because such  that  Overcore  s i x independent  breakage  The c e l l  hole several  the rosettes  can be o b t a i n e d , each t e s t can tensor.  cell.  hours  i s glued prior to  are i n s t a l l e d strain  a t an  measurements  completely d e f i n e t h e s t r e s s  and a i r bubbles  i n t h e glue a t  the s t r a i n gauges l o c a t i o n s a r e two frequent sources of t e s t failure.  It  has  been  generally  found  that  stress  measurement  t e c h n i q u e s a r e expensive and a l l have experimental problems and inaccuracies.  The success  o f a s t r e s s measurement program i s  i n g e n e r a l dependent on t h e number o f t e s t s done.  The r a t e of  success  of  individual  tests  has  been  reported  to  be  approximately 50 t o 70%.  3.3.4 C o m p i l a t i o n o f s t r e s s measurements When  stress  estimation  can  measurement  be  measurements.  obtained  Hoek  is from  and  the v e r t i c a l  pressure  and  Horizontal where  K  stress  increases  Brown  have  vertical  of  listed  116  rough  previous stress  equal t o t h e overburden  with  s t r e s s i s o f t e n presented i s t h e average  a  T h i s data tends t o c o n f i r m  i s generally linearly  possible,  compilation  measurements from around t h e world. that  not  depth  ( f i g u r e 3.2).  i n t h e form o f a r a t i o K,  horizontal  stress  divided  by the  stress. K  =  Avq aH aV  On a p l o t o f K v e r s u s depth, i t can be seen t h a t t h e h o r i z o n t a l s t r e s s data i s q u i t e s c a t t e r e d by Hoek and Brown d e f i n e s ratio  K  at d i f f e r e n t  following  ( f i g u r e 3.3).  t h e minimum and maximum l i m i t s of the  depths  and  can be  described  by the  formulas:  100 depth  + (m)  0.3  <  K  <  1500 + depth (m)  This  p r o v i d e s a rough e s t i m a t i o n  also  shows  that  K tends  i s o s t a t i c stress conditions Herget  An envelope drawn  of the h o r i z o n t a l  to diminish  with  depth,  stress. where  It more  a r e found.  (1987) has compiled  Canadian s h i e l d .  0.5  54 s t r e s s  measurements from the  He concluded t h a t t h e v e r t i c a l s t r e s s i s 64  vtaricM. n u t it '  <0  8  »  «, - <*•  »  >0  »  W  TO  • 1 *  •  *  •  — - o. 017 1  •  « 4  \ •V  •  MIITtU IA -  •v  \  *  UMlTtO ttt.ni  *  CAMAO*  0  10*0 IAVIA  •  tCUTHC Ui ATIICA  n  0  •  •  \  OTKH  sooo FIGURE 3.2 surface.  P l o t of v e r t i c a l s t r e s s e s against (After Hoek and Brown, 1980)  VilTtOL. tTH.il  o  o.s  ' .0  i.;  :.o  •  ,-•»"«!  A  /  /  •  1  i  «  •  1  •  ! •* • !  (  ; / • / / . /  . /'1  •  »  [^o  •  J.S  T  •  *•  0  0  •  o  o •  • '/  •  •/ a'  •  »  •  o  •  IA  • A  « <  •  [  *  x  •  •  s  «  depth below  /  /  •  AUJTtAllA  /  *  IWlTlD ITATTl  1  A  CAMAM  0  ICAaOlflAViA  •  tOU7"(»» AfllU  3  OTxtt i[C(0af  /  i  FIGURE 3.3 V a r i a t i o n of r a t i o of average h o r i z o n t a l s t r e s s to v e r t i c a l s t r e s s with depth below s u r f a c e . (After Hoek and Brown, 1980)  approximately 0.0260 t o 0.0324 MPa p e r metre o f o v e r l y i n g rock. At  a depth  o f 0 t o 900 metres,  the average h o r i z o n t a l  stress  can be e s t i m a t e d by the f o l l o w i n g equation,  a  and  from  H  = 9.86 MPa + (0.0371 MPa * depth (m))  900  metres  t o 2200  metres,  t h e average  horizontal  stress i s , CT = 33.41 MPa + (0.0111 MPa * depth (m)). H  Herget's e q u a t i o n s show t h a t a t a t y p i c a l Canadian open s t o p i n g depth t h e minimum p r i n c i p a l compressive s t r e s s  i s v e r t i c a l and  the maximum and i n t e r m e d i a t e p r i n c i p a l s t r e s s e s  are h o r i z o n t a l .  Plotting  h i s data  stress/vertical similar  stress),  the  a  better  form  versus  t o those p r e v i o u s l y  obtained focus.  in  of  K  (average  depth,  Herget  horizontal  found  trends  i d e n t i f i e d by Hoek and Brown, but  "envelope"  definition  f o r h i s region  of  The lower and upper bounds f o r K i n the Canadian s h i e l d  are shown on f i g u r e 3.4. These  relationships  are  measurements are a v a i l a b l e .  very  useful  when  no  stress  I t i s important t o r e a l i z e  that  the pre-mining s t r e s s regime may d e v i a t e s i g n i f i c a n t l y from the estimations  proposed  by Hoek  and Brown  o r Herget  g e o l o g i c a l h i s t o r y or l o c a l e f f e c t s .  3.4  INDUCED STRESS AND STRESS DISTRIBUTION 66  due t o the  FIGURE 3.4 V a r i a t i o n o f r a t i o of average h o r i z o n t a l s t r e s s v e r t i c a l s t r e s s w i t h depth below s u r f a c e , from Canadian s h i e l d measurements. ( A f t e r Herget, 1987)  67  Stress creation  cannot  of  magnitudes The  new  loading  be  openings and  transferred  will  orientations  vicinity  conditions,  geometry,  will  the  opening  of  a function and  of  the  stress  openings.  of the the  the  original  stress  and  rock mass as a r e s u l t of l o a d i n g .  of these f a c t o r s w i l l  be  thus  verifiable  at the  reach a s t a t e of  The  equilibrium  e x c a v a t i o n boundary and  at  the  field. In  it  the  voids,  re-arrangement  be  interaction  far  in  a  stress distribution w i l l  s t r a i n behaviour of the  that  produce  through  order to  understand  how  a new  d i s t r i b u t i o n i s obtained,  i s necessary t o look at some d e f i n i t i o n s and  f o r c e , t r a c t i o n and  3.4.1  a  stress  small  surface  element  within  The  r e s u l t i n g f o r c e a c t i n g on the element due  and  induced  acting  stresses  normal  to  acting p a r a l l e l Now better  consider model  dimensional. surface  can  the  (v , z x  since  defined  surface r y) Z  the  by  (a )  (Figure  the  two  rock  t o the  three  and  z  mass.  pre-mining  components, shear  one  components  3.5).  c u b i c a l element which r e p r e s e n t s a  pre-mining  three  element are now  cube ( f i g u r e  be  a v e r y small  The  concepts of  s t r e s s i n a continuum.  Components o f Consider  the  state  components  of  of  stress  stress  a p p l i e d t o each of the  is  acting  s i x faces  three on of  3.6).  Assuming the cube i s v a n i s h i n g l y 68  small,  the components of  a the  FIGURE 3.5 (After  FIGURE 3.6 (After  S t r e s s components a c t i n g on a s u r f a c e Hoek and Brown, 1980)  element.  S t r e s s components a c t i n g on a c u b i c a l Hoek and Brown, 1980)  element.  69  s t r e s s on p a r a l l e l condition  of  simplification  the  xy  problem by  conjugate  =  definition  yx  r  of  T  the  at a p o i n t  be expressed  axes  their  arbitrary  of  T  °y  zx  T  x,  T  yz  three  allows  must  faces  rotational  cancel  = T  each  zy  dimensional  cube  of  be  with  T  xz'  to develop  z  T  then  yz  influenced  by  reference  i s required  as  functions  of  reference  the  relative  axes.  A  non-  t o have a base f o r  mathematical r e l a t i o n s h i p s t h a t  r o t a t i o n s with  of  stress:  cartesian set  the  reference  state  the c u b i c a l element) can  xy  y,  will  i n v a r i a n t under any  regard  t o the  will  reference  I f the a p p l i e d l o a d on a s u r f a c e element i s i n the same as  components  direction  the  will  principal  normal  of  the  disappear.  stress having  major)  lowest  =  complete  chosen  the  system  direction  (or  xz  °z'  magnitude  comparison and  axes.  stresses  components of s t r e s s are expressed  arbitrarily  orientation  be  shear  by the f o l l o w i n g s i x components of  S i n c e these an  and  considering only three  ( d e s c r i b e d by  °xi  of  equilibrium  the  Therefore, T  stress  This s a t i s f i e s  In order t o s a t i s f y the c o n d i t i o n s of  equilibrium,  The  translational of the  of the cube.  other.  faces becomes i d e n t i c a l .  This  direction.  the  highest  principal  stress  plane,  direction By  two  shear  stress  i s defined  convention,  magnitude and  the  is called  i s represented  as  a  the  stress  the  maximum  by  a^.  The  s t r e s s i s the minimum (or minor) p r i n c i p a l s t r e s s and i s  represented  by a . 3  a  2  i s the i n t e r m e d i a t e p r i n c i p a l s t r e s s and 70  r e p r e s e n t s the s t r e s s a c t i n g i n the d i r e c t i o n o r t h o g o n a l t o and  o3  The p r i n c i p a l  #  system  f o r which  Transformation  stresses provide a useful non-arbitrary  the components  equations  will  of s t r e s s  can be  expressed.  be r e q u i r e d i n order  t o change  the components o f s t r e s s from any a r b i t r a r y system o f r e f e r e n c e to  the  principal  transformation Brown  (1980;  stress  equations p  system  of  reference.  These  are b r i e f l y  discussed  i n Hoek and  89) and more d e t a i l s  are given  i n Brady and  Brown (1985; p 19).  3.4.2  Two dimensional s t a t e o f s t r e s s A  problem  considered assumption  in  can be only  i s valid  considerably two  only  dimensions.  very  The  long  In  i f the n e g l e c t e d  long compared with the two o t h e r s . is  simplified  i n one d i r e c t i o n  i f i t can be practice,  dimension  i s very  For example, a mining  compared  to i t s  this  raise  cross-section.  s t r e s s d i s t r i b u t i o n can be assumed t h e same f o r a l l c r o s s -  sections  of  dimensional opening The  that  raise  except  close  to  the  ends.  Three  problems have the l e n g t h s o f a l l t h r e e axes of the  i n the same order o f magnitude. simplification  dimensional plane  the  stress  problem  from a t h r e e dimensional problem t o a two can be  o r plane  a l l forces  (cross-section).  acting  made  strain  mathematically  conditions.  on a body  Consequently,  z  assuming  stress  means  a r e w i t h i n t h e same  plane  a , v  x z  Plane  by  , and T y  Z  a r e a l l equal  t o zero and t h e complete two dimensional s t a t e o f s t r e s s can be 71  expressed by a , x  where  plates  of  Oy, and r y X  plexiglass  ( f i g u r e 3.5).  P h o t o e l a s t i c models  are  loaded  biaxially  represent  a  p h y s i c a l example of plane s t r e s s c o n d i t i o n s . The  basic  process  of  assumption  of  plane  strain  e x c a v a t i o n , displacements  can  i s that occur  p l a n e normal t o the l o n g a x i s of the opening. all  during  the  only w i t h i n a The  f o r c e s are  assumed t o be p e r p e n d i c u l a r t o the l o n g a x i s and  invariable  along  this  stress  axis.  can  be  In the  case  simplified  to  of plane  only  three  strain,  the  components:  state a , x  of Oy  f  xy.  T  3.4.3  Two  d i m e n s i o n a l c l o s e d form s o l u t i o n o f simple  e x c a v a t i o n shape The plane  two  dimensional  stress  permitted  simplifications the  development  of  plane  of  strain  two  dimensional  c l o s e d form s o l u t i o n s f o r e x c a v a t i o n s having simple The  c o n d i t i o n s t o be  displacement loading  satisfied  distributions  conditions,  have  i n the s o l u t i o n  f o r s p e c i f i c problem been  identified  by  and  geometries.  of s t r e s s  and  geometries  and  Brady  and  Brown  (1985) as: a) The boundary c o n d i t i o n s f o r the problem. b) The d i f f e r e n t i a l equations of e q u i l i b r i u m . c) The c o n s t i t u t i v e equation f o r the m a t e r i a l . d) The The  two  single  strain compatibility  dimensional circular  solution  opening  in  equations. f o r the s i m p l e s t p o s s i b l e case, a a  perfect  elastic  medium,  was  proposed 3.7.  by  Kirsh  (1898).  The  equations are g i v e n on  They are expressed i n terms  tangential  stress  terms  the  of  (OQ),  major  and  o f : the r a d i a l s t r e s s  shear  principal  figure  (T &)  stress  stress  a  well  s  R  (cr^)  and  (a ) , r  as i n  the  minor  principal stress ( a ) . 3  Practical limited closed  mining  since  applications  few  of  the  Kirsh  equations  mine have a c i r c u l a r shape.  form s o l u t i o n  i s useful  i n examining  are  However, t h i s  c e r t a i n e f f e c t s of  e x c a v a t i o n s on s t r e s s d i s t r i b u t i o n .  a) Boundary s t r e s s : In the case of c i r c u l a r openings, the boundary o b t a i n e d when " r " (the p o i n t  of  i n t e r e s t measured from  c i r c l e centre) equals "a" (the c i r c l e r a d i u s ) . this equality a  r  and  i n equations 1, 2, and 3, g i v e s  shear  stress  r  r  equal  0  to  0.  component of s t r e s s a c t i n g a t the boundary the  tangential  stress,  which  s t r e s s can be  in  the  the  Substituting r a d i a l stress  Thus,  the  only  o f an opening i s case  of  circular  openings i s g i v e n by: o  Q  b) Zone of i n f l u e n c e  = P  z  {(1+K) -  2(1-K)cosineG}  of an opening:  The d i s t u r b a n c e e f f e c t on s t r e s s due t o e x c a v a t i o n s tends t o diminish  as  excavation  the  point  of  i n t e r e s t moves  further  from  i n t o the medium. The K i r s h equations can be  the used  t o determine the zone of i n f l u e n c e of a c i r c u l a r opening by 73  Vertical  applied  stress  p  2  J II I.I I . I I L  1  • i I 11 i 11 r  STRESS COMPONENTS AT POINT ( r , 6 )  Radial  O  Tangential  o  Shear  * i P {(1 + k) (1 - a / r-) * (1 - k) (1 - ka /r 2  2  * U /r")Zoi u  29]  • i P j ( ( 1 f k ) (1 + a / r ) - (1 - k)(1 + 3 a / r " ) C o s 29 J 2  g  2  u  - i P z ( - ( l - k)() - 2 a / r 2  T  2  z  r  2  - 3 a V r " ) S i n 26 )  PRINCIPAL STRESSES IN PLANE OF PAPER AT POINT ( r . 6 ) Maximum  o j » : (o  Minimum  o  Inclinations  2  -  H o  • r  * a.) 8 +  c  8  )  ( i ( o - o „ ) + T D' r 9 ro  +  2  -  l i f e  to radial d i r e c t i o n  r  -  o  j  6  2  +  T  2  )  5  r8  Tan 2a * 2 T g / ( o g - a ) r  r  FIGURE 3.7 K i r s h equations f o r the s t r e s s e s i n t h e m a t e r i a l s u r r o u n d i n g a c i r c u l a r h o l e i n a s t r e s s e d e l a s t i c orebody. ( A f t e r Hoek and Brown, 1980)  74  calculating at  the t a n g e n t i a l s t r e s s along the h o r i z o n t a l axes  different  distances  (r=a,  r=2a,  r=3a  etc.),  until  induced t a n g e n t i a l s t r e s s e f f e c t i v e l y becomes the vertical  stress P .  distance  of  case  F i g u r e 3.8  z  r=3a  from  the  another  will  be  the  components  cumulate  to  stresses  inside  openings.  An  may  result  the  can  i n wall  of one  stress  due  and  the  excavation  on  separated  I f the openings are c l o s e r , to  each  compressive  medium  In  at  the  excavation  s t r e s s e s or boundaries  will  tensile of  the  or  roof  instability  (due  t o t e n s i o n or  constants and  seen t h a t the  elastic  the  K i r s h equation.  no  influence  elastic  modulus) and  on  the s i z e of the constants  the opening  T h i s suggests the  underground e x c a v a t i o n s .  proposed  not  t h a t these of  excavation:  (poisson's  s i z e do  distribution  ratio  appear i n  factors  stress  However, t h i s does not deny  e f f e c t on the s t a b i l i t y of  i n 1977,  stress  stability.  and  Bray  effect  opening.  While i n s i d e the medium, an i n c r e a s e d  of e l a s t i c be  the  i n c r e a s e of t a n g e n t i a l s t r e s s a t the boundary  affect p i l l a r  c) E f f e c t It  of  produce h i g h e r  compression). may  of  n e g l i g i b l e when t h e i r c e n t e r s are  by a d i s t a n c e of a t l e a s t r=6a. the  pre-mining  shows t h a t t h i s occurs a t a  centre  of m u l t i p l e openings,  the  have  around their  openings.  a  s e t of  formulae  s i m p l i f i c a t i o n of the c l o s e d form s o l u t i o n , 75  representing a  f o r the  calculation  FIGURE 3.8 V a r i a t i o n i n the r a t i o of t a n g e n t i a l s t r e s s a to the v e r t i c a l a p p l i e d s t r e s s pz w i t h r a d i a l d i s t a n c e r along h o r i z o n t a l a x i s f o r K=0. ( A f t e r Hoek and Brown, 1980) Q  I ' 1  q=  W/H  FIGURE 3.9 D e f i n i t i o n o f nomenclature f o r an e l l i p t i c a l e x c a v a t i o n w i t h axes p a r a l l e l t o the f i e l d s t r e s s e s . ( A f t e r Brady and Brown, 1985)  of  the state  elliptical  of  stress  opening.  following  a a  point  The s t r e s s e s  A) and i n t h e r o o f the  at a  (point  on  t h e boundary  o f an  acting at the sidewall  (point  B) shown i n f i g u r e  3.9 are g i v e n by  equations:  = p (1 - K + 2q) = p (1 - K + (2W/P )^)  A  A  = p (K - 1 + 2K/q) = p (K - 1 + K(2H/P )^)  B  B  where: a  = induced s t r e s s a c t i n g a t a p o i n t A o f the e l l i p s e  A  boundary a  = induced s t r e s s a c t i n g a t a p o i n t  B  B o f the e l l i p s e  boundary, p =  minimum pre-mining s t r e s s ,  K =  r a t i o o f maximum over minimum pre-mining s t r e s s ,  q =  ratio  W =  e l l i p s e width,  H =  ellipse  P  A  o f the e l l i p s e width and h e i g h t ,  height,  = r a d i i o f c u r v a t u r e a t a p o i n t A o f the e l l i p s e boundary,  P  B  = r a d i i of curvature a t a point  B o f the e l l i p s e  boundary. These equations demonstrate t h a t curvature be.  ( P , P )< A  t  high  l a r g e r the s t r e s s e s  e  B  Consequently,  generate  n  stress  c o r n e r produces  the s m a l l e r  a  high  boundary  concentrations.  i n f i n i t e l y high 77  the r a d i u s  at t h i s point  curvature  will  (1/P) w i l l  Theoretically,  stresses.  of  a  The equations  sharp also  show t h a t the s t r e s s d i s t r i b u t i o n  i n the case of an e l l i p s e i s  a f u n c t i o n of the r a t i o of the axes and t h e i r o r i e n t a t i o n with regard  t o the  ellipse  is  principal  principal  oriented  stress  stresses.  in  a  the  more  When the  same  long axis  direction  favorable  stress  as  of  the  the  major  distribution  is  obtained.  These  two  understand  dimensional  the  stresses.  factors  However, they  mining  problems which  having  irregular  conditions functions,  the  non-linear,  otherwise  problem  domain  insufficiently  Consequently,  in  modelling  provide  can  be  described  for  distribution  the  by  because  differential is rock  practical a  to of  mass  mathematical equations  are  solution  stopes  boundary  inhomogeneous,  problems,  realistic  of  the  simple  or  non-linear  simple m a t h e m a t i c a l l y . "  most  useful  suitable to solve t y p i c a l  " T h i s may  partial  relations  the  are  v a r i o u s arrangements  governing  the  constitutive  are r a r e l y  involve  be  solutions  influencing  shapes.  cannot  elastic  Brown  only for  are the or  (1987).  numerical the  stress  distribution.  3.5  NUMERICAL MODELLING  There degrees  of  dimensional  are many types of numerical models having sophistication. problems,  Some models  assuming 78  plane  are  strain  different  limited or  plane  to  two  stress  conditions,  while  others  can  handle  geometries. A c c o r d i n g t o the mathematical development  of  numerical  models,  they  three  dimensional  concepts used are better  i n the  suited  to  a n a l y z e problems having s p e c i f i c c h a r a c t e r i s t i c s and behaviour. The  behaviour  different  of a  rock  approaches.  mass  can be  The continuum  modelled  approach  assuming  assumes the rock  t o be a continuous medium with few o r no s i g n i f i c a n t discontinuities. mass  t o be  an  rotating.  The discontinuum assemblage  approach this  of blocks  The a p p l i c a t i o n  problems i s s t i l l  i n i t s infancy.  The emphasis  m o d e l l i n g u s i n g a continuum  3.5.1 Continuum The  concept  i n figure  medium  subject  mining  stresses.  medium  to  assigned  of s l i d i n g  models  will  i n mining  the continuum  and best developed review  and  method a t  c o n c e n t r a t e on  approach.  approach  basic  illustrated  capable  Consequently,  of t h i s  geological  c o n s i d e r s the rock  o f discontinuum  i s by f a r most popular  time.  approach  two  to  load,  used  i n the  3.10.  loading  A  continuum  region  "R"  variety  i s defined  is  in a  c o n d i t i o n s r e p r e s e n t i n g the p r e -  A c c o r d i n g t o the a n t i c i p a t e d a  approach  of  rock  mass  response o f the  properties  may  be  t o the medium by means o f c o n s t i t u t i v e equations f o r  the m a t e r i a l .  B i e n i a w s k i (1984), suggested t h a t t h e p r o p e r t i e s  that  modelled  can  be  behaviours;  linear  include  elastic,  viscoelastic, elasto-plastic,  the non  following linear  constitutive  elastic,  elasto-visco-plastic,  linear  FIGURE 3.10 numerical  Idealized sketch modelling.  showing the p r i n c i p l e  80  anisotropic, hard  rock  dilatant,  mining,  thermal-dependant  linear  and  and  non-linear  stochastic.  elastic  In  media  are  u s u a l l y assumed. The  effect  creating inside  the  excavations the  equations.  stress  will  medium  differential  groups  on  or  distribution in  be  at  calculated  the  excavation  equations of e q u i l i b r i u m  and  Differential  on  methods  the  mathematical  approximate  the  i n t e g r a l methods r e q u i r e  problem boundary  only.  D i f f e r e n t i a l methods:  e n t i r e region  and  areas.  finite  originally  applied  to  elements.  The  elements.  nodal  forces  finer  the  and  The  be  mesh, the  constructed  powerful  and  the  compatibility  divided method  into  of  utilized.  for  the  transfer  along  the  forces  r e p r e s e n t e d by problem  two  entire  approximation at  methods  region  displacements  the  shapes  the  i s then  load  the  network  of  from  element  to  i n t e r a c t i o n s at the analyzed  as  a  nodes set  for a d i s c r e t i z e d region.  more a c c u r a t e the  p r e c i s i o n i s required can  using  d i f f e r e n t i a l methods d i v i d e  element  transmission  element i s completely the  boundary,  i n t o a mesh of elements having v a r i o u s  The  of  The  of  points  solution  domain w h i l e the  the  be  medium  discrete  strain  Continuum numerical models can  depending  a)  at  the  solution w i l l  be.  of The  When  i n c e r t a i n areas of the problem, the mesh  with s m a l l e r  v e r s a t i l e method  non-linear  elastic,  plastic  properties.  However, the  elements. that and  is  capable  of  heterogeneous  medium i s not 81  F i n i t e element i s a simulating material  assumed i n f i n i t e and  a  far  field  boundary  The  far field  completely  o f the r e g i o n  stress  satisfied  must be a r b i t r a r i l y  conditions,  which w i l l  in this  introduce  case,  defined.  may  not  inaccuracies  be  i n the  solution. The  finite  method.  Their  difference best  dynamic  problems".  statics  (Cundall,  b)  models  application They  also  use  i s in solving  are r a r e l y employed  differential "transient  or  f o r problems i n  1976).  Integral  methods:  Integral  methods r e q u i r e  contour of the e x c a v a t i o n i n s i d e the r e g i o n This  a  only  the  t o be d i s c r e t i z e d .  reduces the s i z e of the problem by an o r d e r of magnitude,  and makes them e s p e c i a l l y u s e f u l dimensional  problems.  In  boundary  e x c a v a t i o n boundaries are d i v i d e d models)  or  surface  elements  i n s o l v i n g complicated element  three  models,  the  i n t o l i n e a r (two dimensional  (three  dimensional  models).  The  i n f l u e n c e of s t r e s s e s from one element t o another i s c a l c u l a t e d using  i n t e g r a l equations.  region  can  boundary  be  extrapolated  element  infinite  Stresses  and  method  is  assumes  usually  homogeneous and i s o t r o p i c . models regions  d i v i d e the r e g i o n t o which  assigned.  This  hanging w a l l ,  from  a c t i n g anywhere i n s i d e the  the boundary the medium  applicable  when  infinite the  or  The semi  material  is  More s o p h i s t i c a t e d boundary element  "R"  i n t o p i e c e wise homogeneous  d i f f e r e n t l i n e a r material feature  solution.  i s useful  properties  sub-  can  be  i n mining a p p l i c a t i o n s when  ore and f o o t w a l l have v a s t l y d i f f e r e n t rock mass 82  characteristics. s i m p l e r t o use  The and  boundary  element  intrinsically  less  models  are  generally  c o m p l i c a t e d than  finite  element models. Another problems  integral  is  the  discontinuity discretized third be  order  practical  i s the width of the orebody to  model  purposes,  the  to  the  overall  give  reef  dimensions  are  can  be  with  of  accurate  the  each  problem  solution.  considered  discontinuity  associated  (seam), which must  size  two  components element  displacements between the two  combination  the elements  in  and  planes.  in For  parallel three  represent  Displacements  o f the displacement d i s c o n t i n u i t i e s  Discontinuum  the m a t e r i a l intermediate  approach  individual  structure cases  discontinuum. models  of a l l  i n the seam.  " When the rock s t r u c t u r e  that  an  the  s t r e s s e s a t unmined p o i n t s i n the seam are c a l c u l a t e d as a  linear  3.5.2  method,  displacement  The  Displacement  and  this  mining  i n t o a g r i d o f square two d i m e n s i o n a l elements.  planes.  relative  dimensional  for  is  the  In  employed  orebody  in relation  for  commonly  pseudo-three  model.  dimension  small  method  This  a continuum  the  behaviour  requires  adequately  i s l a r g e or s m a l l compared with  the  discontinuities  analysis tends  the use  is justified. to  be  that  of a method of  deformation responses  and  allows  f e a t u r e s o f discontinuum behaviour." 83  several  Stewart & Brown  of  a  analysis  load  for  In  of  the  specific (1984).  The their  most  deformation  extensional and  important  f e a t u r e s o f discontinuum  characteristics  o r by s l i d i n g ,  stiffness  interlocking  of  can  Consequently,  or i n d i v i d u a l  r e s u l t from t h e l o a d displacement  failure  and  discontinuum not  model  Brady  &  finite approach,  properly  method  relaxation determine during  block.  may  element,  boundary  applied  i n the  been  characteristics  (1987) "This  solve  between,  described method  Newton's  the  uses  laws  of  and the displacement  progressive,  large-scale  The t r a n s l a t i o n  can be determined each  to  the forces  discontinua."  Brown follows:  technique  the  have  t h e discontinuum  as  of blocks  t h e b a s i c p r i n c i p l e o f these methods do  Brown,1985).  element  on  difference  the  characteristics.  Although p o p u l a r methods such as f i n i t e element  rotational,  according t o the o r i e n t a t i o n , d i p  discontinuities.  of blocks  be  models are  The a p p l i c a t i o n  distinct  a  dynamic  motion  to  of, units  deformation  and r o t a t i o n  from t h e r e s u l t a n t f o r c e s  (after  of  at block centers and moments a c t i n g  of d i s t i n c t  element  method i n  Canadian mining problems i s c u r r e n t l y a t t h e r e s e a r c h stage.  3.6  SUMMARY AND CONCLUSIONS  The .aspects openings.  objective of stress The  of  this  chapter  i n the engineering  design  parameter 84  was  to  design  of greatest  review of  various  underground  interest  i s the  magnitude and  orientation  excavations.  The  redistribution process  of  principal principal orebody  the  and  is  stress  the  and  the  along the on  is  stress  generally  acting  result  field  and  shield,  pre-mining s t r e s s  the  by  the  minimum  the  maximum  principal stress Six  of  the  perpendicular  orebody s t r i k e .  around  caused  sub-vertical,  intermediate  the  stress the  Canadian  sub-horizontal  some i n f l u e n c e  geological  induced  pre-mining In  stress stress  the  induced  mining.  strike  horizontal had  of  of  to  the  is  sub-  f a c t o r s may field  have  during  the  history: surface  topography,  erosion, residual  stress,  i n c l u s i o n , dykes and tectonic  stresses,  f r a c t u r e s e t s and The at  veins,  discontinuities.  t h r e e methods used t o determine the pre-mining s t r e s s a  given  location  overcoring available,  are:  methods. relationships  measurements can  be  the When  and  the  Canadian  The  stress  3.3,  stress  based  on  the  hydro-fracturing  measurements compilation  used f o r rough e s t i m a t e s .  s t r e s s t e s t s around the world f i g u r e 3.2  flatjack,  s h i e l d by  Herget  d i s t r i b u t i o n around  (1987)  85  are  not  existing  are  of  shown i n  s t r e s s t e s t s done i n  i s shown i n f i g u r e  openings may  the pre-mining s t r e s s , u s i n g a c l o s e  of  and  Compilations  (Hoek & Brown, 1980)  w h i l e a summary of the  field  be  estimated  3.4. from  form s o l u t i o n f o r a simple  geometry,  or  using  numerical  practical applications. different  capabilities  modelling  more  complex  There are many models a v a i l a b l e and  limitations.  based on the continuum or discontinuum sub-divided  in  according  to  the  ( d i f f e r e n t i a l or i n t e g r a l methods).  86  They  can  be  having divided  approach of a n a l y s i s method  of  and  and  calculation  CHAPTER 4 FAILURE CRITERIA  4.1  INTRODUCTION  "A c r i t e r i o n mechanical  i s an a l g e b r a i c e x p r e s s i o n o f the  c o n d i t i o n under which a m a t e r i a l f a i l s by f r a c t u r i n g  or deforming can  of f a i l u r e  beyond some s p e c i f i e d  limit.  be i n terms o f l o a d , deformation,  parameters." Z.T. B i e n i a w s k i  follow  several  stress,  specification  strain  o r other  (1984).  Because o f the v a r i a b l e may  This  nature o f the rock mass,  possible  mechanisms.  failure  I f t h e rock  mass  c o n t a i n s v e r y few o r no d i s c o n t i n u i t i e s ,  t h e f a i l u r e mechanism  will  rock.  be c r a c k i n g o r c r u s h i n g o f i n t a c t  widely  spaced  sliding of  discontinuities  are p r e s e n t  jointed  rock mass  several,  i n t h e rock mass,  or shearing of large blocks i s p o s s i b l e .  a heavily  When  (discontinuities  In the case having  close  s p a c i n g ) , the mechanism o f f a i l u r e w i l l be a r a v e l l i n g o f s m a l l blocks.  Consequently,  reviewed shearing  in this failure  t h r e e types o f f a i l u r e c r i t e r i o n w i l l be  chapter: criterion  a j o i n t e d rock mass f a i l u r e  intact  rock  for geological  failure  criterion,  a  d i s c o n t i n u i t i e s , and  criterion.  The v a r i a b l e s t a t e o f s t r e s s t o which the rock mass can be submitted  also  adds  to  the  complexity  of  the  problem.  T y p i c a l l y , the rock mass a t the boundary o f e x c a v a t i o n s w i l l be submitted  t o a b i a x i a l s t r e s s c o n d i t i o n w h i l e f u r t h e r i n t o the 87  medium a t h r e e d i m e n s i o n a l s t a t e of s t r e s s i s l i k e l y t o e x i s t . Different criteria. direct  techniques  method  of  stress  conditions  are  laboratory Otherwise,  observing  the  conditions.  used  t o develop  can  behaviour  of  I f t h e specimen  representative  testing  of  provide  the useful  a n a l y t i c a l or empirical  used t o account  failure  rock  under  and  in-situ  conditions,  failure  relationships  loading  criteria. have  f o r t h e d i f f e r e n c e s between l a b o r a t o r y  t o be and i n -  conditions. The  and  been  Laboratory t e s t i n g of rock specimens c o n s t i t u t e s a  controlled  situ  have  criteria  will  stresses rj ) .  reviewed  be expressed  i n t h i s chapter a r e based on s t r e s s  i n terms  o f major  and minor p r i n c i p a l  (o~]_, 03) o r i n terms o f shear and normal s t r e s s e s ( r ,  The mathematical equations d e s c r i b i n g t h e f a i l u r e o f rock  n  are o f t e n normalized by d i v i d i n g each member o f t h e equation by the  uniaxial  This  compressive  provides  a base  strength  (CT ) .  o f t h e rock m a t e r i a l  f o r t h e comparison  of r e s u l t s  C  from  a  number o f t e s t s made on a v a r i e t y o f specimens under d i f f e r e n t conditions. applied  rock  Also,  t h e most  mechanics  common  will  be  laboratory  briefly  tests  discussed  used i n in  this  specimens  are  chapter.  4.2  INTACT ROCK MATERIAL FAILURE CRITERIA  4.2.1 In  Laboratory t e s t i n g the  case  of  intact 88  rock,  small  representative determination  of  the  of t h e i r  that  the s c a l e e f f e c t  have  been  developed  compressive  whole  properties  allows  laboratory  for).  determine  or  which  in a  i s accounted to  strength  medium,  multi-axial  procedures (unconfined)  (confined)  compressive  s t r e n g t h , as w e l l as the t e n s i l e s t r e n g t h o f i n t a c t  4.2.1.1  U n i a x i a l compressive  The u n i a x i a l simple  crushing.  compressive  strength provides a  t o compare the r e s i s t a n c e o f rock t o  I t i s the most widely  used  characteristic  mechanics and i t i s i n c l u d e d i n most a n a l y t i c a l failure core  criteria.  sample  a x i a l load.  I t can be estimated  (of a standard The suggested  core o r g r e a t e r .  rock.  s t r e n g t h (o"c, o r UCS)  (or unconfined)  and u s e f u l index  (provided  Testing  the u n i a x i a l  the  size  and e m p i r i c a l  by s u b m i t t i n g  and shape)  diameter  i n rock  a  drill  t o an i n c r e a s i n g  o f the sample i s 54 mm  (NX)  The core l e n g t h should be 2.5 t o 3 times the  diameter. The  value  of u n i a x i a l  from the p l o t the  load  strength before  o f the a x i a l  applied  strength  deformation  (figure  4.1).  failure.  The  I t i s represented  p o i n t , rock may  properties,  deformation  fail  which  under a g i v e n  load.  ultimate  compressive  by p o i n t B on f i g u r e or simply  greater  and  U n i a x i a l compressive  a l s o a l l o w s the c a l c u l a t i o n o f the deformation 89  versus  specimen can s u s t a i n  violently  means  can be d e r i v e d  o f t h e specimen  i s the peak l o a d t h a t the rock  Beyond t h i s elastic  compressive  4.1.  lose i t s permanent testing  characteristics  Strain  FIGURE 4.1 T y p i c a l s t r e s s s t r a i n r e l a t i o n s h i p d u r i n g the t e s t i n g o f an unconfined e l a s t i c specimen i n compression.  90  of  the rock: p o i s s o n ' s r a t i o , and e l a s t i c modulus.  modulus  i s the  deformation  slope  curve  rock's  capability  before  failure  ratio  of  the  slope  of the  of  the  (point A, to  pre-failure  f i g u r e 4.1).  deform  occurs.  The  axially  on  the  under  deformation  deformation  These  elastic  model  rock  based  on  sample  rock  modulus and  to  uniaxial  curve  curve.  record  characteristics  deformation  or  are  used  deformation.  the  often  in specific  The  v a l u e of  Confined  to  conditions consists  to  of a  inaccuracy  of m u l t i - a x i a l  (o^) necessary t o f a i l  confinement  applies  ( M u l t i a x i a l ) Compressive  objective  designed  determine be  deformation.  to numerically  failure  intact  criterion  rock  elastic rock  f o r the presence  of  discontinuities.  a x i a l load of  the  gauges must  radial used  the  by  Poisson's r a t i o are not a p p l i c a b l e t o j o i n t e d  geological  The  load  loading  divided  In o r d e r t o  masses u n l e s s they are m o d i f i e d t o account  4.2.1.2  the  Thus i t d e f i n e s the  the v a l u e of Poisson's R a t i o , d i a m e t r a l s t r a i n installed  on  elastic  Poisson's R a t i o i s d e f i n e d as  s l o p e of a x i a l radial  region  The  (a ).  The  3  testing  triaxial  better  the  which  situ  rock  compressive three  l o a d i n g a p i e c e of d r i l l  constant of t h i s  radial test  stress  i s that  i s t o determine  the  a rock specimen under a s t a t e  represent in  Strength  on  is  test  has  dimensional  submitted.  The  been stress test  core w h i l e o i l p r e s s u r e the  specimen.  in situ  horizontal  r a r e l y c o n s t a n t and v a r i e s from the normal d i r e c t i o n .  The  main  stress i s  A c c o r d i n g t o Brady and Brown (1985;p.102), the major e f f e c t s of i n c r e a s i n g c o n f i n i n g p r e s s u r e  are:  - the peak s t r e n g t h i n c r e a s e s , - there  is  ductile  a  transition  behaviour,  mechanisms  of  grain sliding - the  region  deformation - the post reduces  from  with  typically  the  deformation  brittle  introduction  including  to  of  cataclastic  fully plastic  flow  and  effects, i n c o r p o r a t i n g the  peak  of  the  axial  stress-  curve f l a t t e n s and widens,  peak drop and  i n stress  disappears  at  (to the r e s i d u a l high  values  of  strength) confining  stress.  A  biaxial  test  also  r e c t a n g u l a r or c u b i c a l leaving  the  exists  where  specimens i n two  specimen unconfined  i n the  load  is  applied  orthogonal third  to  directions,  direction.  This  test  r e p r e s e n t s the e x c a v a t i o n boundary c o n d i t i o n s b e t t e r than  the  uniaxial  experimental on the  and  triaxial  tests.  problems, the end  However,  among  other  e f f e c t s have a s t r o n g i n f l u e n c e  results.  4.2.1.3  U n i a x i a l t e n s i l e strength  Rock m a t e r i a l s i n g e n e r a l low  tensile  are  often  strength. not  (approximately  For t h i s reason,  necessary 0  to  are known t o have a  5 MPa)  since can 92  low be  relatively  t e n s i l e strength tests  tensile assumed.  strength  values  However, when a  greater  degree  strength test gripping the  o f accuracy  can be performed.  devices  a t each  application  measured  i s desirable,  at rupture  tensile  I t c o n s i s t s o f i n s t a l l i n g two  end o f the rock  of a t e n s i l e  a uniaxial  sample which  l o a d on t h e specimen.  i s the u n i a x i a l  tensile  allows  The l o a d  s t r e n g t h o f the  i n t a c t rock m a t e r i a l .  4.2.2  A n a l y t i c a l Approach Analytical  the  exact  mechanism  analytical  failure  one  developed  and  Walsh  which  approaches attempt  criterion  by G r i f f i t h  failure.  based  mathematically  The most  for intact  rock  application h i s crack  interesting  i s probably the  i n 1921, and m o d i f i e d  i n 1962. I t formed  has some  Griffith  o f rock  t o reproduce  by  McLintock  the b a s i s o f f r a c t u r e  mechanics  i n the study theory  on  o f rock  fracturing.  the energy  instability  concept. "A  crack  energy  will  extend  o f the system  decreases o r  only  of applied  the t o t a l forces  potential  and m a t e r i a l  remains c o n s t a n t w i t h an i n c r e a s e i n c r a c k  l e n g t h . " Brady and Brown The  when  (1985).  e x t e n s i o n o f c r a c k s w i l l occur i n plane compression i f : (o^ - a ) 2  2  - 8 To (tf! + a ) = 0 2  or  a  2  + To = 0  i f a  x  + 3a  i f a-^ + 3 a  2  2  > 0 < 0  where, To i s the u n i a x i a l t e n s i l e s t r e n g t h o f i n t a c t m a t e r i a l . Griffith shear  equations  and normal  can a l s o  be w r i t t e n  stresses acting 93  as f u n c t i o n s o f the  on the plane  c o n t a i n i n g the  crack: r  4.2.3  = 4 To  2  (cT  Empirical Bieniawski  failure  Q  Approach (1974) s t u d i e d  criteria  suitable  + T ) .  n  (Murrell,  for predicting  material. a  / a  A [a /a ] °-  =  c  where:  3  Hoek,  triaxial  found  them  of  intact  rock  written:  + 1  7 5  c  stress,  - minor p r i n c i p a l  stress,  OQ = u n i a x i a l compressive A = an e m p i r i c a l  strength,  constant.  Hoek f a i l u r e c r i t e r i o n f o r i n t a c t rock i s d e s c r i b e d r /a m  where:  T a  As  a  m  m  c  = B [a /a ] m  in  relationships. and  of  412  empirical  tested  The  4.1  = =  the  (a^-a )/2 3  {0^+02)/2  specimens  for  by:  0.1  (1974) proposed  Table  on  five  the e m p i r i c a l Murrel  p r a c t i c a l mining  and  different  rock  c o n s t a n t s A and Hoek  application  failure criterion for intact  because g e o l o g i c a l  empirical  of a n a l y t i c a l  rock  are  limited  d i s c o n t i n u i t i e s are p r e s e n t i n the rock mass  and p l a y an important  4.3  +  9  = mean normal s t r e s s ;  result  listed  °-  = maximum shear s t r e s s ;  types, B i e n i a w s k i B  c  empirical  and  strength  o-^ = major p r i n c i p a l a2  of two  1968),  r e l a t i o n s h i p can be  1  i  1965;  the  The M u r r e l l s  the a p p l i c a t i o n  r o l e i n excavation  stability.  SHEAR FAILURE CRITERION ALONG AN EXISTING DISCONTINUITY 94  Criterion a,  TABLE  <-<»,->  Norile Quart zite Sandstone Sillstone Mudstone  A A A A A  = = = = =  5.0 45 4.0 3.0 3.0  Ail types  A = 3.5  Error:  3.6°; 9 2% 5.8% 5.6% 6-1%  Prediction error: 10.4%  B= B= B= B= B=  0 80 0 78 0.75 0.70 0 70  B = 0.75  Error:  1.8% 3.2% 2.3% 4.2% 6.6%  Prediction error: 8.3%  4.1 V a l u e s o f t h e constant A from t h e M u r r e l l i n t a c t rock f a i l u r e c r i t e r i o n , and B from t h e Hoek i n t a c t rock f a i l u r e c r i t e r i o n , f o r f i v e rock m a t e r i a l s . ( A f t e r B i e n i a w s k i , 1984)  95  4.3.1  Shear The  strength  shear  usually  It  is  discontinuity the l o a d has  the  which  test  developed  comes  involves  to  from  shear  aligned  possible  the  Coulomb  T  Referring  to  function  of  stress  (cr )  the  =  force  loading  necessary  1/2  and  normal  to  induce  conditions. r e l a t i o n s h i p between  t o the d i s c o n t i n u i t y  (C),  (an) and  the  expressed  in  tan <p.  n  4.2,  compressive  acting  on  r  (o  1  -  CT ) 3  and  stress the  discontinuity: T  specimen  ( r ) , the cohesion of the rock m a t e r i a l  figure  the 3  specimens,  (0),  C + a  -  cost  It  component normal  angle  shear  major  of  i n the d i r e c t i o n of the shear s t r e s s .  (1776) proposed the f o l l o w i n g  the shear s t r e n g t h  and  specimen  as  a  measure  a  the  containing  to  on  of  strength  jointed  t o apply  large  as w e l l  The  drilling  i s used  of  is  d i r e c t shear  shear  laboratory.  diamond  box  The  the  c o l l e c t i o n of  movement under v a r i o u s normal  friction  stability  characteristics  determine  simultaneously  the s t r e s s  the  i n the  careful  A  discontinuity then  on  discontinuity  t o the d i s c o n t i n u i t y .  discontinuities  preparation.  is  a  (roughness, a l t e r a t i o n and i n f i l l i n g ) ,  been  stresses  along  r e g a r d i n g the  dependent  a c t i n g normal  geological of  developed  a controlling factor  blocks.  test  strength  s i n 2/3 96  a  n  can  (cr^)  specimen  be  and  the  confining  containing  the  FIGURE 4.2 I d e a l i z e d sketch showing a rock specimen submitted to t r i a x i a l compression.  — Tension  I  Ccapressisn ——  0  Normal stress  o  FIGURE 4.3 G r a p h i c a l r e p r e s e n t a t i o n of the Mohr c i r c l e and f a i l u r e envelope. ( A f t e r Hoek and Brown, 1980)  a  = 1/2  n  (a-L + a ) + 1/2  (o  3  1  - a ) 3  cos 2/3.  These r e l a t i o n s h i p s can a l s o be d i s p l a y e d on a c a r t e s i a n  system  of axes, where on i s r e p r e s e n t e d on the x - a x i s and T on the zaxis.  The  confining  circle  stress  defined  by  (a ) i s c a l l e d  the  axial  stress  the Mohr c i r c l e  3  (a^) and  ( f i g u r e 4.3).  By t e s t i n g  a d i s c o n t i n u i t y under d i f f e r e n t  conditions  u s i n g a shear box, a s e r i e s of Mohr c i r c l e s  determined.  This  forms  the  (o± and CT ) l o a d i n g 3  Mohr-Coulomb  failure  can be  envelope  ( f i g u r e 4.3). The where  u n c o n f i n e d compressive the  confining  failure  stress  strength  envelope  crosses  friction  characteristic conditions. envelope  axis  stress axis  (ie.  ( f i g u r e 4.3).  by  friction  (cp)  angle  because  it  is  is a  useful  independent  shear of  strength  the  loading  I t can be o b t a i n e d from t h e Mohr-Coulomb measuring  horizontal.  the angle  Physically,  several  angle o f a m a t e r i a l . has a major  the envelope factors  influence.  F i g u r e 4.4  induced a l o n g t h i s plane, depending  irregularities,  may  affect  shows  the  of the  exaggerated  When shear movement  on the s t i f f n e s s of the  they may s l i p on each o t h e r and cause  of t h e d i s c o n t i n u i t y o r may simply be crushed. 98  failure  makes with the  Among them the roughness  i r r e g u l a r i t i e s on a d i s c o n t i n u i t y s u r f a c e . is  shear  graph  F r i c t i o n angle The  surface  the  on t h i s  i s 0) , w h i l e the t e n s i l e s t r e n g t h can be read  where t h e envelope c r o s s e s the normal  4.3.2  i s shown  dilatancy  I t i s expected  1  FIGURE 4.4 I d e a l i z e d sketch showing t h e s h e a r i n g along a d i s c o n t i n u i t y s u r f a c e having an exaggerated roughness. ( A f t e r Brady and Brown, 1985)  FIGURE 4.5 G r a p h i c a l r e p r e s e n t a t i o n o f t h e peak and r e s i d u a l f r i c t i o n a n g l e . ( A f t e r Brady and Brown, 1985) 99  that  a combination  resisting  these  important  factor  the d i s c o n t i n u i t y .  chlorite  or  relatively quartz  phenomenon  happen  c r e a t i n g the  f o r c e a g a i n s t shear s t r e s s .  Another within  of  graphite  infilling  Weak  has  low f r i c t i o n  i s t h e presence  practically  angle,  has a  infilling  high  while  infilling  material  no  such  cohesion  hard  friction  of  material  angle  and such  and h i g h  as a as  shear  strength. It  i s important  to differentiate (0 res) f r i c t i o n  peak) and t h e r e s i d u a l of  friction  occurs.  i s measured  I t corresponds  material  tested.  movement w i l l strength  as  the i n i t i a l  t o t h e maximum  be d i m i n i s h e d u n t i l  friction.  and  angle  i s obtained.  The r e s i d u a l  (1977)  friction  displacement  s t r e n g t h o f the  the resistance to (minimum)  shear  This i s i l l u s t r a t e d  i n f i g u r e 4.5. proposed  an  alternative  joint  angle which g e n e r a l l y  varies  d i s c o n t i n u i t y ) t o 35°, i s assessed from the  between t h e Schmidt  weathered rock.  Choubey  (0  technique t o estimate the peak and r e s i d u a l angle o f  from 15° (weathered ratio  shear  t h e peak  The peak angle  shear  a residual  on a shear v e r s u s normal l o a d diagram  empirical  angle.  As s h e a r i n g p r o g r e s s e s ,  and f r i c t i o n  Barton  between  wall  hammer rebound  and t h e rebound  The peak angle o f f r i c t i o n  (r) measured  (R) measured  usually  ranges  70° and can be c a l c u l a t e d u s i n g the f o l l o w i n g  0 peak =  J  R  C  l o  9l0 100  (^-)  +  <Pr  on  from  on the intact 30° t o  relationship:  where:  JRC i s t h e j o i n t roughness c o e f f i c i e n t  estimated  u s i n g t h e roughness p r o f i l e c h a r t , f i g u r e 4.6, JCS  i s the j o i n t w a l l compressive  strength obtain  from a Schmidt hammer measurement, a  n  i s t h e normal l o a d ,  0  r  i s t h e r e s i d u a l angle o f f r i c t i o n ,  A rough e s t i m a t i o n o f t h e r e s i d u a l f r i c t i o n angle can a l s o be  obtained  e x p e r i m e n t a l l y by a simple t i l t  t e s t u s i n g a rock  specimen c o n t a i n i n g an uncemented d i s c o n t i n u i t y .  When r o t a t i n g  the specimen, t h e angle which i n i t i a t e s s l i d i n g c o n s t i t u t e s the residual  friction  angle,  assuming no c o h e s i o n and a low normal  force.  4.4  JOINTED ROCK MASS FAILURE CRITERION  An difficult involved.  exact  definition  of j o i n t e d  rock  t o o b t a i n because o f t h e complexity Chappell  redistribution  (1979)  of stress  as  and  (1987),  failure  mass  failure i s  o f t h e mechanism by  propagates  studying proposed  the an  e x p l a n a t i o n t h a t i s summarized below.  at  The  deformations  first.  They  of a blocky  accumulate  rock mass a r e i n f i n i t e s i m a l  t o form  i n i t i a t e small r o t a t i o n s of blocks.  finite  deformations  A r e d i s t r i b u t i o n of stress  r e s u l t s from these s m a l l r o t a t i o n s and i n t e n s i f i e s t h e 101  and  TYPICAL  ROUGHNESS  PROFILES  for JRC  1  2  H  h  range:  o-2  2  4-6  .1  8-10  h  5  6-8  10 - 12  12-14  14 -16  8  9  16 -18  \  18-20  10 10  3 l  i  l  t  I  1 cm  SCAII  FIGURE 4.6 T y p i c a l d i s c o n t i n u i t y roughness p r o f i l e f o r the e v a l u a t i o n of the JRC index. ( A f t e r Barton and Choubey, 1977) 102  development  of s t r e s s  gradients.  gradients  acting  transferred  a c r o s s the j o i n t s  the tendency  along  Moments,  interactive from  of blocks to rotate.  caused  block  by  stress  joints,  are  b l o c k t o b l o c k and enhance F u r t h e r deformations  of s l i p  and r o t a t i o n may c o n t i n u e u n t i l a s i n g l e b l o c k i s detached  from  the  mass  excavation  boundary,  and  the  s t r u c t u r e may o r may not c o l l a p s e . thrust  between  "hinges".  the b l o c k s  A hinge  rest  of  the  rock  The l o c a t i o n o f the l i n e o f  are d e f i n e d  by  t h e formation  of  i s a p o i n t o r s m a l l r e g i o n w i t h i n the rock  mass a t which the e f f e c t o f a f o r c e i s l o c a l i z e d t o t h a t small area  or  region.  stiffness  As  decreases.  each  hinge  i s formed,  the rock  mass  F a i l u r e o f the rock mass as a whole w i l l  occur when a s u f f i c i e n t number of hinges have been formed. The  difficulties  jointed  i n developing  failure  criterion  for a  rock mass are extreme because o f t h e numerous p o s s i b l e  mechanisms  involved  and  the  large  a s s o c i a t e d w i t h each mechanism. rock  a  mass  behaviour  has  are  Although  evolved  still  number  decade,  there  no  criteria  f o r rock masses t o date.  of  parameters  the understanding o f  considerably  universally  i n the  accepted  last  failure  The author b e l i e v e s t h a t due  t o t h e complexity o f the problem, only e m p i r i c a l approaches can approximate advanced  rock  mass  failure  behaviour.  criterion  for  e m p i r i c a l r e l a t i o n s h i p proposed °l/ C a  =  °2/ C a  +  The most w i d e l y jointed  by Hoek and Brown  ( 3 / C + s) ^ m a  a  103  rock  used  mass (1980):  and  i s an  where:  o-y and a  3  are the major and minor p r i n c i p a l s t r e s s e s  OQ i s the u n i a x i a l compressive m and of  strength  s are c o n s t a n t s which depend upon the p r o p e r t i e s  the  rock  and  upon the extent  t o which  i t has  broken b e f o r e being s u b j e c t e d t o the s t r e s s e s o±  The  purpose of t h i s c r i t e r i o n  strength factors CT ).  characteristics (m and  s) and  of  the  and  i s t o i n t e g r a t e the  principal  rock  empirical  mass i n t o  two  r e l a t e them t o s t r e s s c o n d i t i o n s (ay  In the Rankine L e c t u r e  3  been  and  (1983), Hoek d e s c r i b e d the m and s  f a c t o r s as f o l l o w s : "Constant  m  approximately  and  s  analogous  are  both  t o the  dimensionless  angle  of  and  friction,  are  0,  and  cohesion s t r e n g t h (C), of the c o n v e n t i o n a l Mohr-Coulomb criterion." the m  and  quality The  certain to  the  failure  Hoek and Brown have p r o v i d e d c r i t e r i o n t o e v a l u a t e s factors  using  rock  limitations  strength  very  index adverse  estimate  a  of will  for different  rock masses, based  mass  classification  rock  mass  cause  geological  classification  some  insensitivity  conditions.  representative  systems  value  as of  on  their  (table  4.2).  a  rock  m  and  Consequently, for  m  and  s,  mass s  to  i n order a  site  c a l i b r a t i o n w i t h back a n a l y s i s of known f a i l u r e s i s necessary.  4.5  SUMMARY AND  CONCLUSIONS  F a i l u r e c r i t e r i a are mathematical 104  expressions that define  ac n CI fci  *  a oj  - ~« i»  r»  *1  »  p  ft.  » » ft  bo  •»  82  O  Jf  Jj  p.  M  M  ft E  3  a O  o  •• •  * • p•  i  o o  C>  J" Q •  C.  O  •  «» O l  « •  O  o 8  o g  a  • i  8 P § 2  o o  •  c» o  » •  » •  o  o  •  3  *  •  § s » « i  o  a ^  « •  o  a i  o  • •  O  o«  a  a  •  8^  o o  a  •  •  Ot  •  I  I  o go  O C>  Ot  8"  Of  o •  a  " a  i  •  •  »  a  i^.  Oi  •  P o  i  •  •  0  o.  O  u»  Ot  O  ot  •  a  •  i  <• •  a •  C»  N*  O  U>  •  •  • •  o  Ot  C A  •  a  > •  i  *  •  •  Oi  •  . -  Ol  » •  a *  •  a  O  0*  o  M.  D  8  b a  Q  w  8  ** *  »  O  P n I*  •  4  t>  I  •  u • ^ - —j  ^4  •  •  .  . •  o  o  o  •  •  O  O  B •* •* -6 -o - o 0 t ft » a  ¥*• n < n »i . * • m  r?  ( A ( A  ft.  • •  <• a • <  ?  to  3 •  I  »  »1  O  SS.£ K  O r» B  O  i B. ^ n  >J «  c a  i  M> •» n •» T» ^3  O  fie " • • o o  H  0 3  M M  8  o  «e  rt n  •  •  M  n  IT  2-  CARBONATE ROCKS WITH WELL DEVELOPED CRYSTAL CLEAVACE dolomita,  limaatona and marbla  LITHIFIED ARCILLACEOUS I0CKS thai* and olaavaga)  mad*Urns, ailtatona, O O  o  o  »lat*  (normal to  ARENACEOUS ROCKS WITH STRONG CRYSTALS AND POORLY DEVELOPED CRYSTAL CLEAVACE  » a Ol  «_  Ot  »  a  •  a  ^t  Nl  r-  ^4  d  d  O  O  aandatona and quartmiLa  FINE CRAINED POLYHINERALLIC ICNEOUS CRYSTALLINE ROCKS ondstit*, rhyolita  dolsri ta,  diobaaa and  COARSE CRAINED POLYHINERALLIC ICNEOUS AND NET AMORPHIC CRYSTALLINE ROCKS  I** O  O.  O  r-  8"  Ot  C4  „  o,  C>  Ot  *—  o»  d  o  o  Otfhibolita, norite and  gobbro, gnaiaa, quarta-diorita  granita,  the of  l e v e l a t which induced s t r e s s t h e rock mass.  based  on  exceeds t h e b e a r i n g  capacity  The development of f a i l u r e c r i t e r i a  laboratory  testing,  analytical  or  empirical  t e c h n i q u e s . Three types o f f a i l u r e c r i t e r i o n s u i t a b l e rock  mining  failure  a r e reviewed  criterion,  geological  the  in this shearing  discontinuities  can be  f o r hard  chapter:  the i n t a c t  failure  criterion  and t h e j o i n t e d  r o c k mass  rock along  failure  criterion. In be  the case of i n t a c t rock m a t e r i a l ,  representative  of  the  whole  medium  d e t e r m i n a t i o n of the i n t a c t p r o p e r t i e s  small which  specimens can allows  i n the laboratory.  the Four  d i f f e r e n t t e s t s can be done i n order t o reproduce the f o l l o w i n g induced s t r e s s uniaxial  conditions: (or unconfined) compressive  t r i a x i a l compressive b i a x i a l compressive and The  uniaxial tensile  ultimate load  criterion,  stress,  stress, stress, stress.  a t r u p t u r e may be d i r e c t l y used as a f a i l u r e  o r as a parameter i n s i d e an a n a l y t i c a l o r  empirical  failure criterion. The  shear  strength  of geological  discontinuities  can be  e s t i m a t e d u s i n g the r e l a t i o n s h i p proposed by Coulomb; r= C + a By t e s t i n g loading and  n  t a n cj>  a specimen c o n t a i n i n g a d i s c o n t i n u i t y  conditions  under v a r y i n g  (T and a ) , the Mohr-Coulomb f a i l u r e envelop n  t h e f r i c t i o n angle can be assessed. 106  The  behaviour  complicated  and o n l y  its failure.  of  a  jointed  empirical  Oy/o-Q  empirical  = o /a 3  c  mass  relationships  The most advanced e m p i r i c a l  a j o i n t e d rock mass was developed  The  rock  is  extremely  can approximate  failure criterion for  by Hoek & Brown (1980) :  + (mo- /a 3  c  +s) %  c o n s t a n t s m and s, a r e estimated u s i n g rock mass  c l a s s i f i c a t i o n and need t o be c a l i b r a t e d on s i t e .  107  CHAPTER 5  REVIEW OF EXISTING DESIGN METHODS FOR UNDERGROUND OPENINGS  5.1  INTRODUCTION Design  and  methods  f o r mining  e x c a v a t i o n s a r e r e l a t i v e l y new  i t i s o n l y i n t h e 1980's t h a t  been w i d e l y mine  used  operators  similar  mining  design.  an e n g i n e e r i n g approach has  t o o p t i m i z e stope relied  dimensions.  essentially  on  their  c o n d i t i o n s and on t r i a l  and e r r o r  f o r stope  development o f t h e two major rock mass c l a s s i f i c a t i o n  systems.  by Barton  et a l .  Bieniawski  (1973),  quantifiable  parameters  rock  For the f i r s t  mass.  "common  ground"  experience reliable  (1974)  divided  time,  i n a variety  this  rock  provided  into  t h e necessary  the geotechnical  conditions,  f o r the p r e d i c t i o n  and develop  o f underground  stability.  There a r e s e v e r a l types o f underground openings functions  mass  t h e p r o p e r t i e s o f the  compile  of geological  models  and t h e RMR-system by the  characterizing  to systematically  empirical  excavation  which  rock  in  was the  Q-system  i n applied  experience  mechanics  The  A turning point  In t h e past,  such  as: e n t r y  mining  stopes,  fulfilling  non-entry  mining  stopes, mining d r i f t s ,  roadway t u n n e l s , h y d r o e l e c t r i c chambers,  nuclear  caverns  waste  storage  d e a l w i t h t h e problem their  physical  etc.  Although  a l l these  cases  o f c r e a t i n g an e x c a v a t i o n i n a rock mass,  c o n d i t i o n s and environment 108  are very  different.  Furthermore,  since  different, longevity  the  the d e s i g n  purpose  of  requirements  the  regarding  and the degree o f i n s t a b i l i t y  completely  different.  methods used  Bieniawski)  T h i s chapter w i l l  models  developed  and c a v i n g methods  for  the  are  excavation  review  the p r i n c i p a l  openings. tunnels  (Laubscher)  (Barton  t o t h e more r e l e v a n t open stope model proposed design  consisting  assist  reviewed  o f a combination  criterion. contributed  method  The to  the designer  the  adapted  by Mathews.  most  widely  The used,  o f numerical m o d e l l i n g and f a i l u r e  development  make  is  and  have been i n c l u d e d  i n t h i s review because some o f t h e i r concepts have been  fourth  also  t o l e r a b l e may a l s o be  i n the d e s i g n o f underground  Empirical  openings  of  numerical  the  models  i n forecasting  d i s t r i b u t i o n f o r d i f f e r e n t mining  desk-top more  computer  has  accessible,  and  the e f f e c t  of stress r e -  sequences.  5.2 ROCK MASS CLASSIFICATION DESIGN CHARTS  5.2.1 B i e n i a w s k i RMR Developed Council rock  Bieniawski  for Scientific  mass  competency varies  by  system  and  classification called  linearly  (1974)  Industrial  system  the  Research  defines  the rock mass r a t i n g  from  at  an  (RMR) .  0 t o 100 and r e l a t e s  South  African  (CSIR), index  of  The RMR  ROCK QUALITY ASSESSMENT 109  rock value  t o the q u a l i t a t i v e  assessment o f rock as f o l l o w s : RMR  this  The RMR  Very Poor Rock  20  0 21  40  Poor Rock  41  60  F a i r Rock  61  80  Good Rock  81  100  values  Very Good Rock  are c a l c u l a t e d  based  on f i v e  parameters  which  c h a r a c t e r i z e the rock mass. 1)  The  rock  number  quality  designation  of fractures  discussed  i n section  (RQD)  i n t h e rock 7.2.1.  i s a measure  mass and w i l l  of the  be  Bieniawski assigns a  further relative  r a t i n g f o r RQD v a r y i n g from 0 t o 20 . 2)  The for  uniaxial  compressive  the hardness  s t r e n g t h of i n t a c t  of the rock m a t e r i a l .  rock  accounts  The r a t i n g  for this  f a c t o r v a r i e s 0 t o 15 . 3) The r e l a t i v e 30.  This  taken  into  s p a c i n g of j o i n t s  characteristic account  by  i s given a r a t i n g  o f t h e rock  RQD  and  mass  from  5 to  i s indirectly  consequently  gives  joint  spacing a large r e l a t i v e weighting. 4) The c o n d i t i o n of j o i n t s r e p r e s e n t s the shear s t r e n g t h of the rock  mass d i s c o n t i n u i t i e s .  five  different  joint  A  descriptive  scale  including  c o n d i t i o n s i s p r o v i d e d t o determine  a  r a t i n g v a r y i n g from 0 t o 25. 5) The groundwater f a c t o r v a r i e s from 0  f o r severe  mining  water  problems.  10 f o r d r y c o n d i t i o n s t o  (In the case  of open  i n Canada, water r a r e l y has an e f f e c t on  110  stope  stability).  An  adjustment  r e s p e c t t o openings  f o r the  i s also included.  for a favorable orientation, unfavourable  joint  orientation  w i l l be 0  f a c t o r s a r e estimated u s i n g the c h a r t s i n  The rock mass r a t i n g  the  described  chart  The adjustment  with  The f i v e parameters and t h e i r  T a b l e 5.1 . ratings  jointing  and up t o a maximum o f -12 f o r an  orientation.  r e s p e c t i v e adjustment  of  above.  (RMR) i s c a l c u l a t e d by adding Bieniawski  f o r t u n n e l l i n g by r e l a t i n g the RMR  proposed  a  design  index t o t h e stand up  time o f t h e rock mass i n a number o f t u n n e l spans ( f i g u r e 5.1). However, t h e a p p l i c a b i l i t y limited  to  drift  of t h i s  design.  It  c h a r t t o mining has  been  found  should be extremely  c o n s e r v a t i v e f o r t h e d e s i g n o f non e n t r y s t o p e s .  5.2.2 Barton e t a l . Q system Barton, Geotechnical  Lien  and  Institute,  Lunde  developed  (1974)  to  1000  on  a  the  Norwegian  t h e NGI c l a s s i f i c a t i o n  d e f i n e s t h e rock mass q u a l i t y index Q. 0.001  of  logarithmic  The Q v a l u e v a r i e s  scale  and  i s related  q u a l i t a t i v e rock mass assessments as f o l l o w s : ROCK QUALITY ASSESSMENT E x c e p t i o n a l l y Poor  0. 001 - 0.01 0.01 - 0.1  Extremely  0.1 - 1  Very  Poor  Poor  1  - 5  Poor  5  - 10  Fair 111  which from to  A.  CLASSIFICATION  P A R A M E T E R S  A N D  THEIR  R A T I N G S  RANGES  PARAMETER  i  Poml load strength ndex  Strength ot intoct rock mater io(  Uniaxial compressive strength  Drill core quality  ROD  Spacing of joints 3  -100%  Rating  7  4  50"/.-75%  25%-50%  | |  17  13  8  )3m  0.3-lm  5 0 - 3 0 0 mm  30  25  20  10  25  Roung  20  Inflow per lOm  Ground waier  <25  0  0  3 < 50 mm  j  5  |  5  r  n  .  m  t h i c k  0  6  litres/min  | 25 - 1 2 5 litres/mm  0 0 - 0 2  j  j  > 125 litres/mm  )0  0.2-0.5  5  OR  R A T I N G  10  A D J U S T M E N T  Ratings  R O C K  F O R  Very  O R I E N T A T I O N S  Favourable  Fair  Unfavourable  -2  -5  -.0  -12  -2  -7  -15  -25  Slopes  0  -5  -25  -50  -60  C L A S S E S  D E T E R M I N E D  Class No,  1 Very  O F  M A S S  R O C K  *  , T T  II  Foir rock  II  45*-90*  JOINT  perpendicular  Very favourable  TABLE  #  Favourable  Very  poor rock  S T R I K E  to tunnel  A N D  DIP  10 mm. tor 0.5m spon  1 5 0 - 2 0 0 kPo  100 - ISO kPo  < .00 kPo  3 0 * - 35"  O R I E N T A T I O N S  axis  Dip  IN  Strike  agoinst  V  5 hours for 1.5 m span  i5°-4C  40"-45*  Drive  20 -45*  V rock  IV  III  200-300kPo  -  with dip  Dip  Poor  . week for 3 m span  to  Dip  < 20  .V  C L A S S E S  >45  O F  40—21  ...  Good rock  >300kPo  E F F E C T  RATINGS  60—41  10 yeors fcr 5m span 6 montns for 4 m soon  *  Strike  T O T A L  80—61  i  Cohesion of ihe rock moss  T H E  F R O M  good rock  No  Friction angle al the rock mass  Drive  Very unfavourable  o  OC—81  -  0  0  ^Weroge siond-up  6  j  4  Foundations  M A S S  ' Cioss  |  Tunnels  Description  T A B L E  J O I N T  7  favourable  Rating  M E A N I N G  "OR "OR Severe Moist only iWaier under moderate water problems (interstitial water) | pressure  Completely dry  Strike and dip orientations of joints  D.  12  None  length  Rating  C.  I  I  (25%  ,0-nt *ot*r  General conditions  B.  1  2  l-3m  (  Condition erf joints  5  251 3-10 1-3 MPo | MPo MPo  10-  25 - 5 0 MPo  ISIickensided surfaces Very rougn surfaces Soft gouge > 5 m m thek Sightly rough surfaces Slightly rough s u r f o c e s j * ^ Not continuous or Seporation (1 mm or Seporation < 1 mm No separation Joints open > 5mm Soft joint wall rock open l - 5 m m Hard joint wall rock Herd joint wall rock Continuous )Otnts j Continuous joints  4  tunnel  For this low range -untaiial compressive test is preferred  1-2 MPo  50 - 1 0 0 MPa  75% - 9 0 %  20  Rating  • 2 - 4 MPa  12  15  90%  MPo  100 - 2 0 0 MPo  > 2 0 0 MPo  Rating  2  4-8  ) 8 MPo  OF V A L U E S  (30*  T U N N E L L I N G  parallel  tunnel  Dtp  axis  0*-20°  dip  4 5"-90*  Dip  20*-45*  Fair  Unfavourable  irrespective of strike Dip  Very  45*-90"  unfavourable  Dip  20*  Fair  -45*  Unfavourable  5.1 Bieniawski CSIR geomechanics c l a s s i f i c a t i o n of jointed rock mass. (After Hoek and Brown, 1980). 112  Stand-up time (h)  FIGURE 5.1 R e l a t i o n s h i p between t h e s t a n d - u p t i m e u n s u p p o r t e d u n d e r g r o u n d e x c a v a t i o n s p a n and t h e Geomechanics C l a s s i f i c a t i o n . ( A f t e r B i e n i a w s k i ,  113  o f an CSIR 1973)  Good  10 - 50  Very Good  50 - 100  Extremely Good  100 - 500  Exceptionally  500 - 1000 Q i s c a l c u l a t e d using the following  Good  equation:  Q = ROD * J r * Jw Jn Ja SRF The and  quotient  size  (Jr/Ja)  (RQD/Jn) r e p r e s e n t s the degree o f f r a c t u r i n g  o f the b l o c k s  forming  the rock mass.  accounts f o r the shear s t r e n g t h  formed  by  jointing.  effect  of  stress  The q u o t i e n t  and  ground  water  The  quotient  of i n t e r l o c k i n g blocks  (Jw/SRF) accounts i n t h e rock  f o r the  mass.  The  i n d i v i d u a l f a c t o r s of the NGI c l a s s i f i c a t i o n a r e : 1)  RQD  -  the  7.2.1). 2)  Jn  -  rock  quality  designation  index  s e t number  quantifies  number o f j o i n t s e t s i n the rock mass. o f random j o i n t s .  the e f f e c t  Jn v a r i e s from 0.5 t o 20.  i r r e g u l a r i t i e s of f r a c t u r e surfaces. 0.5 t o 4, based on a d e s c r i p t i v e J a - the j o i n t  the j o i n t  J r may have a value of  can be  friction  angle  presence  of  surface.  J a v a r i e s from 0.75 t o 20 d e f i n e d  infilling  and  114  surface. the  the shape and  scale.  a l t e r a t i o n number, of  of the  I t a l s o i n c l u d e s the  3) J r - the j o i n t roughness number, c h a r a c t e r i z e s  4)  section  The e f f e c t o f RQD on Q v a r i e s from 1 t o 100.  the j o i n t  influence  (see  related  t o the  I t considers  condition  of  the  the joint  on a d e s c r i p t i v e  scale. 5)  Jw  -  the  presence  joint  reduction  of water p r e s s u r e  v a r i e s from 0.05 6) SRF  water  t o 1.0  factor,  i n the  accounts  rock mass.  for  This  factor  .  - the s t r e s s r e d u c t i o n f a c t o r i s an attempt t o take  account  the i n f l u e n c e of an underground s t r e s s f i e l d on  masses. factor the  However, was  i t should  proposed  be  noted  for tunnelling  s t r e s s e s c o n d i t i o n s induced  that  and  the  does not  into rock  original represent  around open stopes. The  parameters are d e s c r i b e d on t a b l e  Barton  the  six  5.2.  e t a l . have proposed a d e s i g n c h a r t  (figure  5.2),  i n which the maximum unsupported span i s a f u n c t i o n of Q and equivalent accounts  opening  dimension  for different  (De).  types  The  equivalent  an  dimension  of underground e x c a v a t i o n s  and  is  c a l c u l a t e d as f o l l o w s : De = opening ESR where ESR factor  span  i s g i v e n on Table 5.3  of  safety.  and  Nevertheless,  i s analogous t o an this  design  e m p i r i c a l l y developed  based on t u n n e l l i n g and c i v i l  case  is  histories  and  not  calibrated  for  inverse  chart  was  engineering  non  entry  stope  two  rock  mass  design.  5.2.3  D i s c u s s i o n o f t h e Q and RMR The  design  charts  c l a s s i f i c a t i o n systems have met 115  systems  for  these  with approval f o r t u n n e l  # (appro..) f  A DC* QUALITY DESIGNATION Very poor  1. Where KQO It reported or H i i u r « d et • 10 ( Including 0 1, • nomine) value o l 10 It uied to evaluate Q.  I  i. tooc  n  fair  SO  0. Cood  2. »Q0 Intervals of 5. 100, 1S, 90 etc are sufficiently accurate.  ?S )0  {•cedent  1. JOINT SlT NUHMK festive,  no or few Joint*  One joint set  Unaliertd Joint walls, Surface staining only  (25° • )5°>  Slightly altered joint M a l l s non-»oltcnlng mineral coalings, sandy particles, clay-frte disintegrated rock, etc  (25° - J0°)  S i l l y , or sandy-day coatings, S>M11 eley-fract ion (nontor lining)  (20° - 2$°)  Values of e , (he residual friction angle, ere inland ed es en approalaeie guide to the minerelogicel properties of the a Iteration products, 4f present. f  Soltenlng or low f r i c t i o n clay M i n e r a l coatings, i . e . keolinlta. mice. Also chlorite, t e U , gypiua and graphite t i c , and smell quant i t i e s of swelling clays. (Discontinuous coatings, I-2mm or less in thickness)  i  a° -  i6°)  b. Rook vail contacttornfor*  C. One Joint >et plui random  10 cms enear.  0. T«4 joint salt  Sandy particles, clay-free d i s integrated rock etc  C. Two joint t e n plus random Three Joint sett  1. For intersections use ( ) - 0 • J ) n  Three joint sets plus rendo*  2. For portels use (2.0 • J )  Four or more Joint sets, random, heavily jointed 'sugar cube*. etc Crushed rock, eerthlike  (2S« • J0°)  Strongly o*er-ton»olidetcd, nonsoftening clay M i n e r a l f i l l i n g s (continuous, « £**• thick) Medium or low owtr-r.om.olidatIon, softening, clay M i n e r a l f i l l i n g s , (continuous, * Smm thick)  (16° • 2 * ° l  (12° - 16°)  Stalling clay f i l l i n g s . I.e. monimorI Ilonlte (continuous, * S an thick ). Values of depend on percent of Spelling c l a y - t i l e particles, and access to water  ). JOINTftOuCHNi&SNUnOER  a. Rook wait oontaot and b . Rock Mil contact btfon 10 c m tKtar.  1.0 - 12.0  ( 4° -  12°)  o. Mo rook uall contact uHen Mktarmd.  A. 01SCOntInuoul joints 1. Hough or Irregular, undulating  5  C . linooch, undulet ing  2  0. Sllchenslded, undulating  IS  £. Hough o r irregular, planar  l-S  f. Smooth, planer  1.0  C. SIickensldad, planar  OS  0 . Ho rock vail contact  Zones or bands of disintegrated or crushed rock and clay (see C,H and J for clay conditions) 1. Add 1.0 If the mean spacing of the releaent Joint set it greeter than \m. 2. if * O.S can be used for planar, allckentldad joints hawing llnettlons, provided the Itneetlons are orientated for minimum tt renaih.  4.0 6.0 8.0 - 12.0  Zones or bands of s i l l y * or sandy clay, small d a y fraction, (non*softening) Thick, continuous tones or bands or clay ( see C, M end J for clay conditions)  10.0 - M . I n o - 20.0  (  4°  - 2k°)  ( 4 « - 2k<»l  u n e n ih^artd. S. JOINT WATER A L OUCH OK FACTOR  H. Zona containing city minerals t h i c k enough to prevent rock M«II  contect.  >  J . Sandy, grewelly or crushed tone thick enough t o prevent rock » e l I contact.  * (appro*.) f  a. Rock, uall oontaat. A. Tightly healed, hard, nonso'ttntng. Impermeable f i l l i n g  TABLE  appro*, water preisure Ug'/cm ) 3  1.0  * 1-0  0.44  1.0 • 2.S  C. Large inflow or high pressure In competent rock with unfilled joints  0.$  2 5 - 10.0  0. Large Inflow or high pressure , considerable outwesh of f i l l i n g s  0.3)  IS  I.e. « S H i / - I n . locally I. Medium Inflow or pressure, occasional out-ash of joint f i l l i n g s  I  JQlHl ALTERATION MUnttH  .  A. Ory excavations or minor Inflow,  t. exceptionally high Inflow or prei* sura at blasting, decaying with lime  0.2 • 0.1  f. Incept tonally high Inflow or pressure continuing without decay  0.1 - 0.0$  - 10.0  . Factors C to F era crude estimates. Increase J if drainage measures era installed.  > 10  5.2 Barton c l a s s i f i c a t i o n o f i n d i v i d u a l parameters i n the NGI t u n n e l l i n g q u a l i t y index. (After Hoek and Brown, 1980).  H  Special problem* caused by Ue formation are not considered.  i.  ITMSS  REDUCTION  FACTO*  U M b w e * *ot*J intubating *xoa9ation, ttkioh nsy of rook maM9 vhen t w t a Z it txoauafd. A.  Multiple clay  o c c u r r e n c e s o f weakness  or chemically  Surrounding I.  rock  dlsIntegrated  weakness  Icelly  disintegrated  C.  Single  weakness  Ically  disintegrated  ft.  Multiple  I.  Single  shear  (depth  o f excavation  loo*a  f.  tones  containing  loos*  (excavation  ( m y depth  In c o a p e t e n t  SftF  o r choer depth  clay,  In c o m p e t e n t  rock  tones  clay,  (excavation  rock  ion«t  tones  sheer  (dapth  very  fteduce  containing rock  tones  surrounding  Single  con ( f i n i n g  rock,  (any depth)  Single  shear  tones  loomtni^  COUMI  <  o r Chaerdepth  rock  •  (clay  these  (an  T  In c o m p e t e n t >  but do n o t  Intersect  the  )  rock  (clay  free),  rock  (clay  2.  Jointed  or  t rea),  'sugar  cube  for strongly virgin  1  4  o  K.  High  stress,  (uiually •ay  near  l o r face  > 200  fltran  200-10  very  tight  favourable  for  Nild  M.  HaavY  rock rock  (ewjsslve  burst  (aassive  rock) rock)  o  ESR  Q  _  0.66-0.J3  $-1.5 <2-5  0.J)-0.1b <0.16  c  (If  A.  Temporary mine openings  3 - 5  to  Q.So  e  When o  B.  Permanent mine o p e n i n g s , w a t e r t u n n e l s f o r hydro power ( e x cluding high pressure penstocks) p i l o t tunnels, d r i f t s and headings f o rlarge e x c a v a t i o n s .  1.6  and  c  and 0 . o o ,  c  •  c  t  unconflnad s t r e n g t h , and  tenslIe load)  strength and a  a r e the * e J o r  principal |  wall  (  and  and a i n o r  stresses.  C.  0.5-1 ).  burst  to 0 . 6 o  "  o t  (point O)  structure  to s t a b i l i t y ,  be unfavourable  0,  1.0  stability) L.  Excavation category  $ a  > 10, reduce  compressive  2-5  13-0.w  t  field  : U*en  to 0.&o .  t  where  (  U x stress,  o  «l/aj  p r e * La we  anisotropic  strati  10, reduce  and etrvea  o /o,  Hadlu*  excavation.  $4*0  depth)  b. Co*mp*t*nt rook. rook  J.  only  influence  free),  SO*)  j o i n t s , heavily  H.  the  tones  « $0*>)  of excevetlon open  SOX i f  shear  •Matured) Loose  values of  » y 2$ -  relevant  5QM)  5-10 10-20  Few c a s e  records  where d e p t h Is  width.  Suggest  crease  a. Squstning rock, plastic ,T-*v of incoe>atint rock undtr (nas u c h influtnom of high rock prssiurt  fro*  cases  available  o f crown  Surface  less  than SftF  span  SQueeilno, rock p r e s s u r e  Heavy s q u e e z i n g rock p r e s s u r e  p.  d. Smiling rock, ohtmizal fuelling aativity (Upending upon pnsmutm of w a t e r fllld Heavy  swelling swelling  TABLE  rock rock  pressure pressure  surge  treatment  and ra ilway  chambers,  access 1.3  stations,  major  tunnels,  civil  chambers, p o r t a Is, E.  Underground railway  5-10  TABLE  road and defence  in t e r s e c t ions.  n u c l e a r power  stations,  facilities,  10-20  5.2 Barton c l a s s i f i c a t i o n of i n d i v i d u a l parameters i n the NGI t u n n e l l i n g q u a l i t y index, (cont)  Power  railway  5-10 10-20  road  In-  i(tf  Add  rooms, w a t e r minor  tunnels, tunnels.  below  2 . 5 to $ f o r ( l e e H).  Storage plants,  sports  factories.  1.0  stations, and p u b l i c 0.8  5.3 The excavation support r a t i o (ESR) f o r d i f f e r e n t underground openings a p p l i c a t i o n s . (After Hoek and Brown 1980)  FIGURE 5.2 R e l a t i o n s h i p b e t w e e n t h e maximum e q u i v a l e n t d i m e n s i o n (De) o f an u n s u p p o r t e d u n d e r g r o u n d e x c a v a t i o n and t h e NGI t u n n e l l i n g q u a l i t y i n d e x Q. ( A f t e r B a r t o n L i e n and Lunde, 1974)  118  d e s i g n , but not i n mine d e s i g n . up  time,  other  which were developed  types  of  differences  openings,  between  The  typical  relatively  too  tunnelling  shape small  of in  and stand-  t o a d j u s t the d e s i g n c h a r t s f o r  are  between mining and t u n n e l l i n g 1)  F a c t o r s such as ESR  simplistic  and  to  mining.  overcome  The  the  differences  include:  tunnel the  i s long  other  i n one  direction  directions.  The  and  critical  v a r i a b l e t o be designed i n t u n n e l l i n g i s the r o o f width. the case  of stopes, the shape i s o f t e n near c u b i c a l  t h r e e dimensions  In  and a l l  (stope h e i g h t , stope width and stope length)  must be designed. 2)  Tunnels  are u s u a l l y  comprised The  of  effect  stress  isolated  panels of  openings.  Mining  containing several  excavating  multiple  stopes  openings  c o n c e n t r a t i o n s i n some areas and  l a y o u t s are and  pillars.  i s to  relaxation  produce i n other  areas. 3)  Pre-mining tunnels their near  stress  are  magnitudes  shallow  stability.  and  Mine  i n c r e a s e s with  stress  plays  openings  are  s u r f a c e , but are u s u a l l y  only  depth.  a minor  occasionally  Most role  in  excavated  found a t depth, where s t r e s s e s  play a c r u c i a l role i n s t a b i l i t y . 4) Tunnels are r e q u i r e d t o be s t a b l e f o r a l o n g p e r i o d of time. They are permanent openings. personnel  inside  them  during  c e r t a i n amount of i n s t a b i l i t y to  remain  open  for  a  Non-entry the  extraction  i s tolerable.  comparatively 119  mining stopes have no  short  process  and  a  Open stopes need period  of  time  (approximately 3 t o 18 months).  Consequently,  the  They are temporary  rock mass c l a s s i f i c a t i o n  f i n d t h e i r best a p p l i c a t i o n i n tunnel design. for  designing  answers. design  mining  Both  drifts,  Bieniawski  charts with  but  and  they  Barton  artificial  will  The to  the  supplemented  their  proposals  which  drifts.  competency  of  a  rock  mass  on  a  comparative  These form the base f o r o t h e r e m p i r i c a l d e s i g n methods  b e t t e r adapted  5.3  used  rock mass c l a s s i f i c a t i o n systems o f f e r a v i a b l e method  estimate  scale.  charts  They can be  design  are a l s o s u i t a b l e f o r t u n n e l and mining  design  give conservative  have  support  openings.  t o mining c o n d i t i o n s .  LAUBSCHER'S  GEOMECHANICS  CLASSIFICATION  OF  JOINTED  ROCK  MASSES  Laubscher classification experience southern  (1976) was systems  with  the f i r s t  f o r mining  chrysotile  Africa.  t o adapt  one  applications,  asbestos  caving  H i s m o d i f i c a t i o n of  the  of the t u n n e l based  on  his  operations  in  CSIR system  i s the  r e s u l t of the c l a s s i f i c a t i o n of more than 50,000 metres of mine development and wide  variety  including  open  drill of  core.  rock  T h i s r e s e a r c h was  conditions  p i t , cut  and  s t o p i n g and c a v i n g methods.  120  fill,  and  many  open  performed mining  stoping,  in a  methods shrinkage  5.3.1  D e s c r i p t i o n of the Model  Laubscher used the which  same f i v e b a s i c parameters as  Bieniawski,  are: -  RQD,  - i n t a c t rock - joint  strength,  spacing,  - c o n d i t i o n of  joints,  - groundwater. In  order  to  improve  characterize  the  rock  ability  masses,  of  he  the  CSIR  proposed  the  method  to  following  modifications: 1)  The  r e l a t i v e s i g n i f i c a n c e of  total  rating  effect 30% 2)  of  was  joint  diminished conditions  i n t a c t rock from  has  15%  been  strength,  to  10%,  increased  on  the  while  the  from  25%  to  of the t o t a l r a t i n g .  The  joint  condition  descriptive  scale  was  expanded  and  improved t o p r o v i d e a more d e t a i l e s t i m a t e f o r the e f f e c t of joint  roughness,  alteration  g u i d e l i n e s are given 3)  The  factor  changed.  in table  representing Laubscher  and  The  new  5.4.  joint  proposed  infilling.  spacing a  chart  has  been  (figure  totally  5.3)  accounts f o r m u l t i p l e  j o i n t systems, as w e l l  of i n d i v i d u a l j o i n t s .  T h i s f a c t o r i s a much b e t t e r i n d i r e c t  measure of the  r e l a t i v e s i z e of the b l o c k s  as the  which spacing  forming the  rock  mass m a t r i x . The  RQD  and  j o i n t water parameters have not been changed. 121  The  ASSESSMENTS  OF-JOINT  CONDITIONS  ( A d j u s t m e n t s a s combined p e r c e n t a g e s o f t o t a l p o s s i b l e r a t i n g o f 3 0 )  Parameter  A. J o i r . t expression: (large scale)  Description  Wavy u n i - d i r e c t i o n a l  99 90  Curved  89 SO  Straight  79 70 99  Straited E.  Jcint expression (small scale)  C. A l t e r a t i o n zone  84 60  Polished  59 50  Softer  than w a l l rock  99 70  Coarse  hard-sheared  99 90  Fine  soft-sheared  soft-sheared  cn o CO CO  hard-sheared  Coarse  TABLE  es  Smooth  Fine  D.' J o i r . t filling  Percentage adjustment  79 70 69 50  Gouge t h i c k n e s s  < Irregularities  49 35  Gouge t h i c k n e s s  > Irregularities  23 12  Flowing material > I r r e g u l a r i t i e s  11 0  5.4 Assessment of j o i n t geomechanics c l a s s i f i c a t i o n L a u b s c h e r , 1976) .  conditions f o r the Laubscher of j o i n t e d r o c k mass. (After  R A T I N G S  FOR  M U L T I - J O I N T  S Y S T E M S  MINIMUM SPACING , m OJ  0,OJ  0,01  0.1 MAXIMUM  EXAMPLE  : JOINT  SPACING  A: 0 , 1 m  B r O . S m  AB;15  A B C= 6  SPACING.  C = 0 . 6 m  t£  to  1,0  '0  Tl  D:  1.0m  ABDill  FIGURE 5.3 Diagram f o r the e v a l u a t i o n o f the j o i n t parameter i n the Laubscher m o d i f i e d geomechanics c l a s s i f i c a t i o n system. (After Laubscher, 1976)  123  spacing  five are  parameters  used by  Laubscher  summarized with t h e i r  total rating In  i s called  quantify  rock masses  a s s o c i a t e d r a t i n g s on t a b l e 5.5.  the i n - s i t u rock mass  o r d e r t o extend  to mining c o n d i t i o n s ,  to characterize  the a p p l i c a b i l i t y f i v e adjustment  The  rating.  of the  classification  f a c t o r s were developed t o  the sources of i n s t a b i l i t y t y p i c a l l y  found  i n mining  operations. 1)  Weathering decrease  Adjustment.  the  adjustment  overall  is  made  The  effect  competency on  three  of  of  of  the  the  Reductions of up t o 5% of the o r i g i n a l the of  intact  i s on  the  decrease of up t o 18%  joint  rock  RQD  of the j o i n t  The main with  condition  An  parameters.  v a l u e and  condition  i s to  mass.  in-situ  rock s t r e n g t h are suggested.  weathering  weathering  4%  of  influence  a  possible  rating  can  be  applied. 2)  Field to  and  Induced  account  for  instability  the  Laubscher  effect to  stress  which  trigger  f a i l u r e due t o an i n c r e a s e i n the component of s t r e s s  acting  t o the d i s c o n t i n u i t y .  decrease  relaxation,  the  total  in-situ  stabilizing  may  factor  shear  can  contribute  of  introduced a  potential  normal  or  Stresses.  Consequently, rating  or i n c r e a s e the r a t i n g  by  by 20%  the  24%  adjustment for stress  i f the j o i n t s  are  kept i n compression. 3) Change i n S t r e s s . situations  is  A phenomenon a s s o c i a t e d w i t h most mining  local  variation  in  c a v i n g mining methods the changes may  stress.  However,  have v e r y important  for  A  B  IOO -  Eating Description  1  2  X  Class  R.Q.D.Jfc Rating I . R . S . (MPa)  Very  ei  80  good  ICC- 91  Joint  A  61  B  60  Good  9C-76  -  65-56  55-46  5  A  B  40  41  -  A  21  45-36  35-26  25-16  Very poor  15-6  20  18  15  • 13  11  9  7  5  3  141-136  135-126  125-111  110-96  95-81  80-66  65-51  50-36  35-21  ' .10  9  8  7  6  5  4  3  2  spacing  R e f e r  T a b l e  B  2 0 - 0  Poor  Fair  75-66  2 Rating  -  4  3  3  A  5  -  0  C 20-6  5-0 0  1  II  3  4  Rating  jU  Condition of joints  4?  ^  '  S t a t i c a n g l e o f R e f e r T a b l e  u  Rating  Groundwater  5  Rating  TABLE  u  1  f r i c t i o III  —  I n f l o w p e r 10 m l e n g t h OR J o i n t water pressure Major p r i n c i p a l s t r e s s OR Completely dry  = 0  = 25  litres/^n  = 25 - 125  > 125  •>  5°  ^  u  litres/nun  litres/min ^  = 0,0  -  0,2  Moist  10  only  7  =  0,2 - 0,5  Moderate pressure  4 .  > 0,5 Severe problems  0  5.5 Summary o f t h e f i v e b a s i c p a r a m e t e r s o f t h e L a u b s c h e r g e o m e c h a n i c s c l a s s i f i c a t i o n o f j o i n t e d r o c k mass. ( A f t e r Laubscher, 1976).  125  influence,  since  large  volume  rock  falls  changes  i n geometry.  The adjustment  in-situ  rating  from  varies  change  i n stress  change  i n stress  conditions favours,  f a c t o r i s more r e l e v a n t 4)  Influence  geologic walls.  increase  stability.  and  I t appears  Dip O r i e n t a t i o n .  since  gravity  with  the w a l l s .  Laubscher  i s the most s i g n i f i c a n t f o r c e  a guide t o e s t i m a t e t h e adjustment  rating.  A  geological joint  difference  as  a  30%  structures The  suggested in this  o f the number He p r o v i d e d  ( t a b l e 5.6), which may be  decrease  d i s t i n c t i o n i s also  sets.  regard t o  t o the l i k e l i h o o d of  of j o i n t s i n c l i n e d away from the v e r t i c a l a x i s .  significant  o f the t o t a l  made when  the  in  adjustment  situ  predominant  are shear zones o r f a u l t s r a t h e r proposed  this  The r e l a t i v e  parameter, the adjustment should be a f u n c t i o n  as  that  on the s t a b i l i t y of rock  i s proportional from  possible  mining methods.  s t r u c t u r e has an i n f l u e n c e The adjustment  on the t o t a l  o f 20% when the  and i n c l i n a t i o n o f the opening  b l o c k s b e i n g detached that,  applicable  in drastic  40% f o r t h e worst  t o an  t o caving  of S t r i k e  orientation  minus  result  for a  than  relative  i n orientation of:  0° - 15° i s minus 24%, 15° - 45° i s minus 16%, 45° - 75" i s minus 8%. 5) B l a s t i n g to  Effects.  minimize  In the mining p r o c e s s , i t i s endeavoured  the e f f e c t  however, development  of b l a s t i n g  on  stope  stability,  o f new f r a c t u r e s and a c e r t a i n degree 126  No. o f defining joints  TABLE  No. o f f a c e s i n c l i n e d away f r o m v e r t i c a l and a d j u s t m e n t p e r c e n t a g e 70%  3 4  3 4  5  5  6  6  75%  80%  3 4  2 2  3 4  3  1 2,1  5.6 A d j u s t m e n t f a c t o r f o r t h e number o f j o i n t s e t s i n c l i n e d away f r o m v e r t i c a l . ( A f t e r L a u b s c h e r , 1 9 7 6 ) .  Adjustment,  Boring Smooth w a l l  %  100 blasting  97  Good  conventional  blasting  94  Poor  conventional  blasting  80  5.7 Adjustment Laubscher, 1976).  factor f o rthe effect ofblasting.  TOTAL P O S S I B L E  Parameter  R.Q.D.  I.R.S.  Weathering F i e l d and induced stresses Changes i n s t r e s s  95%  96%  S t r i k e and d i p orientation Blasting  TABLE  90%  2  Technique  TABLE  85%  REDUCTIONS  Joint spacing  Condition of j o i n t s 82% 120% to 76% 120% to 60%  70% 86%  93%  5.8 Summary o f t h e p o s s i b l e a d j u s t m e n t Laubscher, 1976). 127  (After  Total  75% 120% to 76% 120% t o 60% 70% 80%  factors.  (After  of shaking remains proposed  by  inevitable.  Laubscher  T a b l e 5.7  for different  shows the  excavating  adjustments  and  blasting  procedures. The  five  mining  related  adjustments  are  summarized  on  5.8.  They are expressed i n terms of a d j u s t e d r a t i n g s .  5.3.2  Open Stope Design A p p l i c a t i o n  Table  In a more r e c e n t p u b l i c a t i o n , D i e r i n g and Laubscher proposed  one  more m o d i f i c a t i o n  open stope d e s i g n . influences  in table A  Because the  the a c t i o n  stope i n c l i n a t i o n  of g r a v i t y  adjustments  t o adapt  inclination  of stope s u r f a c e s  in potential  were proposed  the method f o r  block  and are  failures, reproduced  5.9.  relationship  between  hydraulic  r a d i u s of stope  shown  figure  on  defined  factor  (1987)  as  the  the  total  adjusted  s u r f a c e s has  5.4.  The  ratio  of  hydraulic the  been  rating  developed  r a d i u s of  surface  area  and  a  the  and  is  surface i s  divided  by  its  perimeter:  H y d r a u l i c Radius =  The  hydraulic  r a d i u s accounts  of stope s u r f a c e s . beyond  4:1,  Stope S u r f a c e Area (m) Stope S u r f a c e Perimeter (m)  f o r the e f f e c t of s i z e and  As the r a t i o of spans  the h y d r a u l i c  r a d i u s remains  shape  on s u r f a c e i n c r e a s e s relatively  constant.  T h i s corresponds t o the most s t a b l e shape (long and narrow) f o r a stope plane of a g i v e n a r e a . 128  TABLE  Dip of surface  Adjustment, %  0-30° 30-50° 50-70° 70-30° 80-90°  80 85 90 95 100  5.9 Adjustment f a c t o r f o r the i n c l i n a t i o n of the designed stope s u r f a c e . ( A f t e r Laubscher, 1976).  O  10  20  30  40 SO AREA HYDRAULIC RADIUS = PERIMETER  SO  FIGURE 5.4 R e l a t i o n s h i p between the adjusted rock mass r a t i n g and h y d r a u l i c radius of a stope surface. ( A f t e r Laubscher, 1976) 129  The  stability  according regions  t o where are  artificial  5.3.3  of  each  stope  i t p l o t s on  defined,  support  open  as  the  well  plane  graph.  as  a  evaluated  Stable  transition  and  caving  zone  where  i s recommended.  modified  classification  overcomes most of the giving  a  reliable  adjustment  system developed by  shortcomings of the CSIR  characterization  factors  quantify  the  of  Although applicable biased  Laubscher to  most  towards of  has  methods  adjustment  calibrations  do  conditions.  Furthermore,  calibration Laubscher  data  not  required  not  induced  design  methods,  and  their  known.  of In  respective open  stoping  open  stoping  earlier  paper,  the an  remains  Consequently,  represent  extent  it  method  (1976) s t a t e d ,  should for  classification.  This  is  a  extraction.  factors  the  mining  The  excavations.  mining  of  masses.  of  develop  necessarily  base  "Large open stopes stope  to  underground  caving  the  tried  Laubscher  classification,  rock  effect  a l t e r a t i o n s to rock masses surrounding  the  be  D i s c u s s i o n of the method The  some  can  is  can  have caving  only be mined i n competent ground  a  hydraulic a  rock  radius  mass  20%  with  less that  than  and that  adjusted  11  overly  between c a v i n g and  simplistic  considering  open s t o p i n g mining methods. 130  the  differences  As w e l l , i t i s  not  i n agreement with  (figure lack  5.4).  by  this  specialists  method  having  a  on t h e d e s i g n  of this  f o r the s e l e c t i o n  As a r e s u l t ,  employed  proposed  Another major c r i t i c i s m  of guidelines  factors.  the l i n e s  system  o f proper  i s more  i n t h e NGI and CSIR  artificial  5.4  systems,  i s the  adjustment  efficient  considerable  e x p e r i e n c e i n c l a s s i f y i n g and d e s i g n i n g underground As  graph  Laubscher  when  amount  of  openings.  has developed  support p r o p o s a l s .  MATHEWS * OPEN STOPE DESIGN METHOD  In 1981, K. Mathews, E. Hoek, E. W y l l i e , and S.B.V. Stewart of  Golder  Associates  predicting  the  environments extension  introduced  stability  (below  of  a new e m p i r i c a l approach f o r open  1000 metres  o f t h e NGI rock  mass  stopes  depth).  i n deep This  classification  method  mining i s an  and has the  p o t e n t i a l t o recognize: i ) s t r e s s c o n t r o l l e d f a i l u r e i n open stopes, ii) iii)  s t r u c t u r a l f a i l u r e i n stopes, and  a  combination  o f both  stress  and  structural  failure.  5.4.1  D e s c r i p t i o n o f t h e method  Mathews e t a l . suggested  t h a t t h e s t a b i l i t y o f each plane i n  a stope should be analyzed s e p a r a t e l y . detailed  investigation  T h i s a l l o w s f o r a more  o f t h e rock mass, s t r u c t u r e o r i e n t a t i o n 131  and  stress conditions  a t an i n d i v i d u a l p l a n e .  a n a l y s i s , two parameters a r e developed. defined  as the s t a b i l i t y  quantifies major  the e f f e c t  influence  of  on stope  number,  The f i r s t parameter i s  "N".  The s t a b i l i t y  the g e o t e c h n i c a l stability.  factors  A high  corresponds t o s t a b l e ground c o n d i t i o n s , number corresponds  In the s t a b i l i t y  having  stability  w h i l e a low  t o u n s t a b l e ground c o n d i t i o n s .  number a  number  stability  The second  parameter i s the h y d r a u l i c r a d i u s which accounts f o r the e f f e c t of  s i z e and shape of the stope s u r f a c e .  also  used  by  Laubscher,  was  briefly  The h y d r a u l i c discussed  radius,  in  section  (5.3.2) . A  r e l a t i o n s h i p between the s t a b i l i t y  radius  was  figure  5.5).  assessed  derived  following three  and  by p l o t t i n g them on a semi-log  The s t a b i l i t y  according  number  to  o f the plane  where  i t plots  hydraulic graph (see  investigated  with  respect  can be t o the  zones:  - stable, - potentially  unstable,  - and p o t e n t i a l l y c a v i n g . These t h r e e defined and  zones are separated  based  on 26 case s t u d i e s  1 Australian) The  stability  by t r a n s i t i o n areas from t h r e e  and 29 case h i s t o r i e s from number  is  calculated  mines  1  with  * factor A * factor B * factor C  where, 132  (2 Canadian  literature.  formula: N = Q  and were  the  following  0.1 L. 0  1  5  1  :  1  »  10  15  20  25  Shape Factor, S = Area/Perimeter (m)  FIGURE 5.5 R e l a t i o n s h i p between t h e s t a b i l i t y number a n d h y d r a u l i c r a d i u s of a stope s u r f a c e . ( A f t e r Mathews e t 1980).  Q It  i s a m o d i f i c a t i o n o f t h e NGI rock  1  mass  classification.  c h a r a c t e r i z e s the rock mass competency by u s i n g  f i v e of the  s i x o r i g i n a l parameters i n Barton's NGI c l a s s i f i c a t i o n : Q' = RQD * J r * Jw Jn Ja The  stress  reduction  factor  classification  is  tunnelling  histories  case  ( r e f . Chapter 5.2.2)  not  SRF  included  proposed  because  and does  in  i t is  the  NGI  based  on  not e f f e c t i v e l y  represent  the e f f e c t o f s t r e s s i n open s t o p i n g . Factor  A  replaces  classification  to  the SRF i n the o r i g i n a l  more  accurately  quantify  NGI the  rock effect  s t r e s s e s a c t i n g on the exposed s u r f a c e s o f open stopes. estimated  using  f i g u r e 5.6.  This  intact  rock  strength  of  It is  f a c t o r i s a f u n c t i o n o f the  r a t i o o f i n t a c t rock s t r e n g t h t o induced the  mass  s t r e s s where:  i s represented  by t h e u n i a x i a l  compressive s t r e n g t h o f t h e rock and, the  induced  stress  stress  i s defined  acting parallel  as t h e maximum  t o t h e exposed  tangential  s u r f a c e a t the stope  boundary. The  uniaxial  laboratory by  testing  numerical  Mathews which  while  modelling.  e t a l . have  describe  isolated closed  compressive  strength  t h e induced  be  determined  s t r e s s i s best  by  estimated  When such models a r e not a v a i l a b l e ,  provided  the s t r e s s e s  openings.  can  two graphs  induced  These graphs  i n the roof  5.7  and 5.8  and w a l l s of  a r e an approximation  form s o l u t i o n f o r a two dimensional  134  figure  elliptical  of the opening.  1.0  o.e  o. Z o n e of potential instability  0  5  10  15  ffl/ffl  (T,  • •  Uniaxial compressive strength of intact rock Induced compressive stress  FIGURE 5.6 G r a p h f o r t h e e s t i m a t i o n o f f a c t o r A. ( A f t e r Mathews e t a l , 1980).  135  20  MAJOR SURFACES ' H ,  Can be shown in plan or section  Strike <T  Virgin S t r e t i  H l  Oioorom  10  o i?  2.0  CO  \  c o  '35 cn  \  15  \  ca  \  ,a  CD  a E o O •  c o c  K-0.5  *•  \  J _ i  \  \  ft  \  N  K.1.2  N \  6"  \  K-1.5  \  O  —  -1.0  1(  —  3--I  2:1  Rotio  .  A 1 of  opening  K-2.0  5 1  6 1  7 1  8:  dimensions  LEGEND Ti • Induced stress <Tv • V e r n c o l v i r g i n s t r e s s cr Hi * H o n r o n t o l virgin s t r e s s on s t r i k e ff H j ' H o r i z o n t a l v i r g i n s t r e s s n o r m o l _ t o strike CTnormal to Horizontal p l a n e , K • <TH /<rH, Oparallel to Verticol p l o n e , K ' < T H / c r v 2  2  surface surface  FIGURE 5.7 Graph o f t h e s t r e s s i n d u c e d on t h e m a j o r s u r f a c e a stope versus t h e r a t i o o f opening dimensions. ( A f t e r Mathews e t a l , 1980). 136  MINOR SURFACES Can be seen in section  ^ 1  Sin de  HOT iiontol plant  'H2  VifQin  ~ 3  Can be seen in plan  Dip g ro m  Strtst  8.0  CO  E o 6.0  ft /  /  4.0  / /  / /  /  y  2.0  .  ^  .—  ^  y  c o  K ; 0  '35  .  CO CD k_  a E o O  1:1  2:| Rotio  .  6  4:| of o p e n i n g  1  5 _  —  1  dimensions  8  1  LEG £ NO CTj Cv CHI  • • •  CT  • Horizontal  M j  Induced s t r e s s V e r t i c o l virgin stress H o r i z o n t o l v i r g i n s t r e s s on s t r i k e  Horizontol Vertical  plane,  virgin K  •  stresi  C V ^ / T H ,  p l a n e , K » <r ^C H  v  normal  to s t r i k e  1  ° ~ p a r a l l e l to s u r t a c e  J  ° " n o r m a l to s u r f a c e  FIGURE 5.8 Graph o f t h e s t r e s s induced on t h e minor s u r f a c e o f a stope v e r s u s t h e r a t i o o f opening dimension. ( A f t e r Mathews e t a l , 1980). 137  Factor  B  geological  accounts  structures  analysis.  for  the  orientation  i n t e r s e c t i n g the  Depending  upon  the  of  stope  relative  surface  orientation  s t r u c t u r e with r e s p e c t to the i n v e s t i g a t e d plane, reflect  favorable  intersection predominant factor  or  unfavourable  between  the  structure,  is  cases.  exposed used  in  figure  of  the  and  5.9  angle the  to  of  most  determine  B.  inherently gravity.  an  true  surface  under  factor B w i l l  The  Factor C i s a surface i n c l i n a t i o n f a c t o r .  tunnel  persistent  less  s t a b l e than w a l l s  Barton  wall  because of the  (1974) suggested  that  i s h y p o t h e t i c a l l y improved  horizontal  roof.  Since  Stope backs are  some  the  rock  five  minor  i n f l u e n c e of quality in a  times compared  instability  can  to be  tolerated  i n non-entry mining, Mathews e t a l . suggested t h a t a  vertical  open  horizontal  stope  roof.  wall  Figure  is  5.10  eight or  times  the  as  stable  f o l l o w i n g formula  as  an  should  be used to determine f a c t o r C: FACTOR  C  =  8  -  7  cosine  (angle  of  stope  plane  inclination).  This  factor describes  the  increased  potential for  instability  as a s u r f a c e becomes more h o r i z o n t a l .  5.4.2  D i s c u s s i o n of the method Despite  the  small  data  base  the  Mathews  o f f e r s s t r o n g p o t e n t i a l f o r open stope d e s i g n . 138  et  a l . method  Similarly  to  0. 5  ROCK  DEFECT  ORIENTATION  FACTOR  (B)  FIGURE 5.9 Sketch f o r t h e e s t i m a t i o n o f t h e rock d e f e c t o r i e n t a t i o n f a c t o r B. ( A f t e r Mathews e t a l , 1 9 8 0 ) .  10  0 I 0  1 20  40  £o  SO  90  4ng/e of £>/p fro/77 Mor/zon/a/ (degrees)  Factor  C »  8-7  Cosine fong/c  of cfip)  FIGURE 5.10 Graph f o r t h e e s t i m a t i o n o f t h e stope s u r f a c e i n c l i n a t i o n f a c t o r C ( A f t e r Mathews e t a l , 1 9 8 0 ) .  140  Laubscher,  they  classification be  based  system, and  method  instability  gravity these  or  ( Q,  an  existing  rock  conditions.  The  mass  combination  o r i g i n a t e from h i g h s t r e s s ,  incompetent  factors.  an  A , B , C ) a l l o w s f o r the p r e d i c t i o n  1  t h a t may  on  a d j u s t e d the parameters i n order to  more r e p r e s e n t a t i v e of mining  of the f o u r f a c t o r s of  their  Because  rock each  mass, factor  structure,  or  any  combination  of  is  well  developed  and  p r e s e n t e d g r a p h i c a l l y , the method i s easy t o apply i n p r a c t i c a l situations  and  can  be  used  successfully  by  mine engineers  on  site. After analysis has  found  important has  extensive  of case the  histories  method  factors  roughly  application  very  promising. the  these  a)  in  back author  the  most  of open stopes,  The  design  and  methodology  However t h i s method s t i l l  has  shortcomings:  As a r e s u l t of the s m a l l data base, the t h r e e zones d e f i n e d on The  the  stability  transition  which may of the b)  method  I t addresses  stability  factors.  i s a l s o p r a c t i c a l and e f f i c i e n t . some  this  i n mines a c r o s s Canada, the  affecting  calibrated  of  graph  too  vague  zone between s t a b l e and  f o r adequate  design.  c a v i n g i s very l a r g e  l e a d t o u n c e r t a i n p r e d i c t i o n and m i s i n t e r p r e t a t i o n  analysis.  The graphs proposed based  are  on  f o r the d e t e r m i n a t i o n of each f a c t o r are  experience,  analytical approximately  work. correct  b a s i c rock mechanics concepts Their  calibration  appears  and  some  to  f o r Canadian c o n d i t i o n s but should 141  be be  r e - e v a l u a t e d a g a i n s t a l a r g e r data base. c)  The  original  data  base i n c l u d e d o n l y seven  walls  which  a l l had  a  there  i s no  evidence  that  steep  cases  inclination.  the  method  of  stope  Consequently,  i s suitable  f o r the  d e s i g n of i n c l i n e d w a l l s . d)  The  effect  of  tensile  stress,  support have not been addressed e)  The method was 1000  5.5  and  artificial  i n t h i s method.  i n t e n d f o r mining  a t depth  below  meters.  NUMERICAL MODELLING DESIGN  Numerical design  of  flexible opening  m o d e l l i n g i s the most w i d e l y used method f o r the  a l l types and  of  capable  mass a t  boundary. methods,  Numerical  calculations selected This which  computers  is  are  openings.  The  method i s  in  m o d e l l i n g uses t h e o r e t i c a l  t o determine  points  predict  geotechnical  underground  of m o d e l l i n g a l l kinds of geometries  arrangements.  empirical  key  originally  blasting  inside  the  the  medium and  opposition to the  stability  parameters required  and to  stability  past  solve  the of  of the  a t the  and and rock  opening  previous empirical  excavations  experience. the  large  based  on  Digital number  of  c a l c u l a t i o n s i n v o l v e d i n numerical m o d e l l i n g .  5.5.1  Open stope d e s i g n a p p l i c a t i o n The  primary  function  of 142  numerical  modelling  is  to  calculate  the  excavations.  stress  This  distribution  theoretical  stress  around  solution  underground  may  be  used  in  d i f f e r e n t ways t o p r e d i c t e x c a v a t i o n s t a b i l i t y . The most simple approach induced  i s to r e l y stress  commonly when  on r u l e s of thumb t o a s s e s s the e f f e c t  around  openings.  assumed t h a t  the  induced  compressive  the  commonly used  i n the  A  hard  rock mass w i l l  stress  strength.  In  is  more  fail  than  no-tension  rock  mining, in  half  failure  i t is  compression  the  uniaxial  criteria  a n a l y s i s of low t e n s i l e  of  i s also  s t r e n g t h of rock  masses. More s o p h i s t i c a t e d f a i l u r e c r i t e r i a can be i n t e g r a t e d the  numerical  operation.  model  interactively  or  as  a  into  post  processing  The advantage of an i n t e r a c t i v e approach  i s t h a t as  the s t r e s s exceeds the rock mass s t r e n g t h ( d e f i n e d by a criterion),  the  failed  rock  i s (mathematically)  the opening  and  the a n a l y s i s c o n t i n u e s assuming a new  failure  detached  from  geometry  u n t i l a stable c o n f i g u r a t i o n i s obtained. The  post  distribution criterion. stresses  tensile  of s t r e s s  The have  potential  processing around  stability been  failure  approach  at  a fixed each  openings  s t r e s s can be d e f i n e d .  applicable  t o hard  i n chapter  4.  Numerical  the  final  geometry with a  failure  point  c a l c u l a t e d ) can  around  compares  be  i n the  estimated.  due t o compressive,  The p r i n c i p a l  rock open stope mining,  (where  Zones  of  shear or  failure  criteria  have been  reviewed  m o d e l l i n g can a l s o be very u s e f u l 143  medium  i n parametric  studies. the  one  By of  regarding  keeping  a l l input  parameters constant  particular interest,  assumptions  and  inaccuracies For  instance,  d i f f e r e n t opening shapes can be modelled with the one  producing  the  the i n p u t parameters can be minimized.  except f o r  most  The  favorable  optimization  application developed  of  stress distribution of  the  mining  parametric  i n which  e f f e c t on s t a b i l i t y .  sequence  studies.  high  being  used  is  A mining  design.  another  common  strategy  stress concentrations  The  for  can  be  have a minimum  c r e a t i o n of s t r e s s shadows to improve  s t a b i l i t y can a l s o be i n v e s t i g a t e d .  5.5.2  D i s c u s s i o n o f the method Numerical  estimating  modelling  the  excavations.  In  t e c h n i q u e has  the  input  specific  aspects  addition, contains  this  of  comparison  to  versatility  must stay  parameters  most  distribution  openings of a l l types. formulation  i s the  stress the  around  empirical  t o be  models,  general  and  failure each  method  has  criteria  problem's  is  to r e l y to  entirely  mathematically  on  the  for  the  conditions.  In  account  physical  Consequently, s i n c e numerical  properly  this  a p p l i c a b l e t o underground  very  complex  selected,  applied  histories. 144  and  and  impossible  models have no  i n c a l i b r a t i o n , the s o l u t i o n s can be m i s l e a d i n g not  underground  i n t r i n s i c assumptions which are p r a c t i c a l l y  to v e r i f y .  for  However, i n order t o be v e r s a t i l e , i t s  and of  s o p h i s t i c a t e d method  built-  i f the model i s  calibrated  against  case  "Clearly,  limitations  method  of  or  analysis  restricted  inadequacies  may  or m i s l e a d i n g ,  i n p u t data are d e f i n e d . "  a stress  a n a l y s i s problem  of  i n p u t of f o u r data t y p e s .  1)  Problem geometry: The usually  modelled.  dimensional  plane  assumed. on  the  The  Geology  be  well  the  (1987), the  i s dependent on the  reliability  applicability  defined Model  stress  or  but  too  complex  limitations plane  such  strain  to  of  the  mine  that  can  be  be  as  have  two  to  included  be  factor in  the  P r a c t i c a l experience and e n g i n e e r i n g judgement i s  and  behaviour  material strength:  i n the  approximation medium.  due In  calculated  form  t o the complexity  stress  and  result,  most  factors  characterizing of  models  jointing  rock lack the  and  rock  is still  numerical models and f a i l u r e 145  mass.  i s only an of  to  the and  interaction  criterion. the  Amongst  p o o r l y taken criterion.  mass  assumptions  failure  sensitivity  rock  variability  t o model the  mass  the  equations  modelling,  are necessary  geometry.  Expressing  of mathematical  numerical  simplifications  effect  to  (1984).  e s s e n t i a l t o d e f i n e a r e p r e s e n t a t i v e problem 2)  a  s i z e of the models i s a l s o a l i m i t i n g  portion  analysis.  of how  to  contour of a c t u a l e x c a v a t i o n s i n hard  well  accurately  results  irrespective  and D i e r i n g  of  is  the  Stewart and Brown  A c c o r d i n g t o Laubscher  rock  cause  inherent  into  of  As  a  important them, account  the by  3)  Loading  condition:  specific first  measured  rock The  4)  i s the  with  proportion  to  source  loading  pre-mining  a  certain  the  budget  can  arise  grouted  study  of  these  calibrated  adequately.  and  has  of numerical  two  the  different  yet  model:  rock  in  open  t o be  The  Based on  modelled,  can  (often  as  be in The  h y d r a u l i c or  anchors  and  stope  mining  blasting. remains  estimated  numerical models  the understanding  and  available  approach  according  of the problem to  between a continuum  t o the  relative  and c o n t i n u i t y of b l o c k s compared with the opening also  have  dimensional  model  to  decide  is  the  geometry of the problem. failure available  criterion  will  whether  most The  two  appropriate,  final  depend  a  on  size. a  based  computer  He  three on  c h o i c e of the model the  or  importance  or  the and  resources  (hardware and s o f t w a r e ) , as w e l l as the purpose of  the e x e r c i s e and the degree of p r e c i s i o n r e q u i r e d .  5.6  The  testing).  measured,  a d e s i g n e r must s e l e c t  discontinuum  will  a  forms of a r t i f i c i a l  s u r f a c e s , such and  which  accuracy  in  on  sources.  field  of  acting  a wide range of c a p a b i l i t i e s and have a wide range of  limitations. be  from  effects  new  from  invested  cables  relatively  offer  conditions  stress  degree  against excavation  fill,  Choice  loading  problem geometry o r i g i n a t e  source  second  The  SUMMARY AND  CONCLUSIONS  146  Systematic using  engineering  empirical  development design  of  charts  schemes, rock  et  fundamental  has  mass  of  been  underground made  al.  and  excavations  possible  classification  with  systems.  f o r the p r e d i c t i o n of t u n n e l  proposed by the authors (Barton  design  Reliable  s t a b i l i t y have been  of the p r i n c i p a l c l a s s i f i c a t i o n  Bieniawski).  d i f f e r e n c e s between  However,  systems  because  t u n n e l l i n g and  these c h a r t s are not a p p l i c a b l e f o r open stope M o d i f i c a t i o n of the two  the  open  of  the  stoping,  design.  c l a s s i f i c a t i o n systems, to b e t t e r  r e p r e s e n t mining c o n d i t i o n s , has been proposed by Laubscher Mathews e t  al.  interesting estimation remains  The  model developed by  concepts, of  the  strongly  but  it  adjustment  biased  lacks  factors  towards  Laubscher o f f e r s guidelines and  caving  more  mining  and some  for  the  importantly,  methods.  The  most s u i t a b l e e m p i r i c a l method f o r the design of open stopes the  one  proposed  principal  by  Mathews  et  al.  It  accounts  factors affecting  the  stability  the methodology i s p r a c t i c a l  and  easy t o use  appears  to  have a  conditions. data in  base.  The  calibration  main c r i t i c i s m  such  Also,  the  as  inclined  transition  for  the  open  stopes  and  i n the  field.  It  f o r Canadian  of t h i s  walls  open  stoping  approach i s i t s small  Consequently, i t s r e l i a b i l i t y  conditions  depth.  fair  of  is  remains t o be  and  stopes  at  zone between s t a b l e and  proven shallow caving  needs t o be b e t t e r d e f i n e d . The numerical  fourth  design  modelling.  method  reviewed  Numerical m o d e l l i n g 147  in  this  chapter  is a versatile  is tool  that  can be adapted  principal  t o a l l types of underground openings.  f u n c t i o n of numerical  stress distribution  modelling  i s to c a l c u l a t e  around underground e x c a v a t i o n s .  as a d e s i g n method, numerical m o d e l l i n g must r e l y c r i t e r i o n t o p r e d i c t ground s t a b i l i t y .  on a  Those f a i l u r e  post  processing  m o d e l l i n g may  step.  The  inaccuracies  of  the  When used failure  criterion  can be a p p l i e d i n t e r a c t i v e l y w i t h the s t r e s s c a l c u l a t i o n , a  The  or as  numerical  o r i g i n a t e from the: problem geometry, geology  and m a t e r i a l s t r e n g t h ,  loading condition, c h o i c e of numerical model. One  of the major disadvantages  of numerical m o d e l l i n g , compared  t o the e m p i r i c a l approaches i s t h a t i t does not have a b u i l t - i n calibration. selected,  Consequently, applied,  and  if  the  calibrated,  misleading.  148  model the  is  not  solution  properly can  be  CHAPTER 6 OPEN STOPE FAILURE MECHANISMS  6.1 INTRODUCTION  The  d i r e c t cause o f underground  failure  i s . t h e c r e a t i o n of  an opening, which by removing a volume o f rock a l s o removes i t s supporting This  effect  unsupported  on the rock mass a d j a c e n t t o the opening. rock mass i s submitted t o s t r e s s  from t h e pre-mining s t r e s s f i e l d by  excavation.  The e f f e c t  originating  and the induced s t r e s s  o f the r e s u l t i n g  stresses  caused around  openings can be looked a t i n terms o f zones o f compression and zones o f r e l a x a t i o n . The 20  stress  response and  relaxation  nature o f t h a t the  o f a medium  medium.  rock mass, opening  such  as rock mass t o compressive  i s extremely Consequently, geometry  complex  due  to  variable  the i n t e r a c t i o n between  and s t r e s s  conditions  define  the p o t e n t i a l f a i l u r e mechanisms.  6.2 NATURE OF THE ROCK MASS  The  nature  o f the rock mass  v a r i a b l e from one p o i n t  is intrinsically  i n the medium t o another.  complex and I t comprises  one o r more types o f rock m a t e r i a l  which are c h a r a c t e r i s t i c a l l y  discontinuous  presence  discontinuities.  due  to  the  of  geological  Brady and Brown (1985) proposed the f o l l o w i n g 149  d e f i n i t i o n f o r rock m a t e r i a l and rock masses: "Rock m a t e r i a l intact  rock  represented  i s the term  between  by a hand  used  t o d e s c r i b e the  discontinuities; specimen  examined i n the l a b o r a t o r y .  i t might  or piece  be  of d r i l l  core  The rock mass i s the t o t a l  i n s i t u medium c o n t a i n i n g bedding  planes, f a u l t s ,  joints,  f o l d s and o t h e r g e o l o g i c a l f e a t u r e s . "  The  most  joint. very  common  type  of g e o l o g i c a l d i s c o n t i n u i t y  I t i s a regular fracture little  process,  or  they  no  movement.  u s u a l l y occur  along  which  Because  of  i n near  other  random  blocks. the  discontinuities  The o r i e n t a t i o n  size  and  matrix.  shape  of  has been formation  sets,  having  t h e rock  blocks  s e t s and  material  and s p a c i n g o f t h e j o i n t individual  limited  sets define  i n the rock  exposure  o f underground  difficult  feet)  mass  openings,  rule, long  features  are  not  less  than  considered  the e f f e c t  approximately in  a  joint  how  t o assess due  j o i n t c o n t i n u i t y may have a major i n f l u e n c e on s t a b i l i t y . general  into  The c o n t i n u i t y o f g e o l o g i c a l f e a t u r e s determine Although  a  ( f o l i a t e d rock) t o  of i n t e r s e c t i n g j o i n t divide  w e l l t h e b l o c k s are d e f i n e d . to  their  parallel  s p a c i n g range v a r y i n g from a few c e n t i m e t e r s s e v e r a l meters. The combination  there  i s the  of  As a  1.5 meters (5 survey.  This  e l i m i n a t e s most f r a c t u r e s induced by b l a s t i n g . Major usually  discontinuities  such  have t o be d e a l t w i t h 150  as  faults  individually.  or  shear  zones  On the s c a l e of  open stopes, they r a r e l y take r e g u l a r p a t t e r n s and t h e i r on  stability  i s largely  nature o f the f i l l  a function of t h e i r  location  effect and the  m a t e r i a l and the amount o f movement t h a t has  taken p l a c e along the d i s c o n t i n u i t y . With  regard  characteristics blocks  forming  case  elongated of  of  whether the rock  blocky  shape)  likely  joint  to  be  discontinuities the  third  sets.  most  important  The importance of b l o c k  mass w i l l  anisotropic  be  isotropic (in  ( i n the  If  have one or two  the  s e t s have  w i l l be a n i s o t r o p i c .  critical.  Generally,  blocks  behaviour  formed  by  the with  be elongated  or p l a t y and  In t h i s case,  the r e l a t i v e  the stope  the s m a l l e r  of  similar  long dimensions compared  the shape w i l l  with  case  i s a function  have a c u b i c a l shape and the  of the b l o c k s  the  the  I f a l l the j o i n t  orientation  strike  of  The shape o f b l o c k s  isotropic.  dimension,  the behaviour  or  shapes).  s p a c i n g , the b l o c k w i l l is  two  the rock mass matrix.  or p l a t y  individual  stability,  of the rock mass are the s i z e and shape of the  shape determines the  to  surface w i l l  become  the d i f f e r e n c e i n d i p and  (the more p a r a l l e l ) the b l o c k s are t o the stope s u r f a c e ,  less  stable  perpendicular  to  the a  condition stope  will  surface  be. have  Blocks little  oriented effect  on  stability. Folk assistance  (1965) developed  a t r i a n g u l a r c h a r t t h a t may  i n e s t i m a t i n g b l o c k shape  t h a t b l o c k s are composed (closest spacing).  ( f i g u r e 6.1).  He  provide assumed  o f the t h r e e most frequent j o i n t  I f the s m a l l s i d e of t h e b l o c k s have a 151  sets  «0 30  PLATY  3 3  BLADED L-i  67  ELONGATE  FIGURE 6.1 T r i a n g u l a r c h a r t f o r the e s t i m a t i o n of b l o c k shape. ( A f t e r F o l k , 1968).  152  length side  "S",  the  intermediate  length  "L",  the t h r e e axes of the F o l k b l o c k shape c h a r t  are d e f i n e d by However,  S/L,  side  length  ( L - I ) / ( L - S ) and  underground  observation  " I " and  (S /LI) / 2  is  1  d e f i n e s whether  the  rock  mass  6.1).  sufficient  determine the g e n e r a l shape of the b l o c k matrix, adequately  larger  (figure  3  usually  the  to  which i n t u r n  i s expected  to  be  i s o t r o p i c or a n i s o t r o p i c . The regard  size  of the  to  excavation  discontinuities The  are  b l o c k s i s the most important  the  stability weakest  because  component  of  factor  with  geological  the  rock  mass.  s m a l l e r the b l o c k s are, the more d i s c o n t i n u i t i e s t h e r e  are  exposed per u n i t s u r f a c e area and the l e s s s t a b l e the rock mass surface  will  behaviour size  of  be.  Several  authors  have  suggested  that  of a rock mass i s l a r g e l y i n f l u e n c e d by the the  blocks  compared  with  the  surface  of  the  relative  rock  mass  exposed. F i g u r e 6.2  shows t h a t d i f f e r e n t exposures of the same rock  mass w i l l produce domains having very d i f f e r e n t and  behaviours.  i n the behaviour to  In t h i s  open stope  study,  characteristics  t h r e e major  of rock masses have been i d e n t i f i e d  trends  according  the r e l a t i v e s i z e of the b l o c k s composing the rock mass.  These  1.  I n t a c t rock  2.  Discrete block  3.  J o i n t e d rock mass three  types  behaviour  of  behaviour behaviour  behaviour  and  their  associated  f a i l u r e mechanisms w i l l be d i s c u s s e d i n the f o l l o w i n g s e c t i o n s . 153  FIGURE  6.2  TRANSITION FROM INTACT R O C K TO HEAVILY JOINTED R O C K M A S S (After H o e k & B r o w n , 1980)  Intact rock Single discontinuity Two discontinuities Several discontinuities Rock mass  FIGURE 6.3 F a i l u r e mechanism of i n t a c t rock submitted to compressive s t r e s s , f a i l u r e type l a ; r e f . f i g u r e 6.1*7  FIGURE 6 . 4 F a i l u r e mechanism of i n t a c t rock i n s t a t e o f s t r e s s relaxation, f a i l u r e type l b ; r e f . f i g u r e 6.17  154  6.3  INTACT ROCK BEHAVIOUR  The behave  rock as  matrix  intact  is  dimensions. few  surrounding  rock  similar  when  in  I t usually  underground  the r e l a t i v e  size occurs  or  excavations  size  larger  will  of the block  than  the  opening  i n a rock mass c o n t a i n i n g very  o r no d i s c o n t i n u i t i e s which i s not common i n Canadian  rock mines. be  mass  For stope d e s i g n , i n t a c t  homogeneous,  isotropic  and show  hard  rock i s o f t e n assumed t o elastic  deformation  under  s t r e s s e d but p r e - f a i l u r e c o n d i t i o n s . When t h e compressive faces  exceeds  develop parallel  s t r e s s a c t i n g p a r a l l e l t o the opening  t h e rock  mass  i n the d i r e c t i o n t o the stope  of  walls  strength, the  tensile  compressive  and back  cracks  forces, i e . 6.3).  (figure  phenomenon has been observed  and e x p l a i n e d by s e v e r a l  Griffith  and Walsh  Cook occur  (1924),  (1968),  Hoek  i n t h e form  cracks. induced  Several fractures,  MacLintock (1965).  (1962),  The compressive  such  as b l a s t i n g  random d i s c o n t i n u i t i e s  This  authors:  F a i r h u r s t and  failure  may  of s l a b b i n g o r b u c k l i n g along these factors  may  then  induced  vibration,  blast  o r changes i n s t r e s s  can a l s o c o n t r i b u t e t o i n i t i a t e t h e f a i l u r e . Another  commonly  observed  effect  of  s t r e s s o c c u r s i n sharp c o r n e r s o f e x c a v a t i o n s . been demonstrated The  deterioration  high  compressive  T h i s e f f e c t has  w i t h a c l o s e d form s o l u t i o n i n s e c t i o n of corners 155  may  continue  until  a  3.4.3.  smoother  p r o f i l e i s obtained. Intact  rock  relaxation. submitted  will  Rock to  respond  i s known  tensile  differently  t o have  forces.  very  Tensile  in  a  zone  of  low s t r e n g t h when cracks  may  develop  p e r p e n d i c u l a r t o the a c t i n g t e n s i l e s t r e s s and c r e a t e a zone o f relaxation.  Because  perpendicular  t o the s t r e s s  6.4),  major  rock  the alignment  falls  of  cracks  and t h e opening  solely  is  typically  boundary  (figure  cracks  are not  due t o t e n s i l e  common when d e a l i n g with open stope mining i n i n t a c t  rock.  6.4 DISCRETE BLOCK BEHAVIOUR  The  ground  i n which d i s c r e t e  j o i n t sets.  The s p a c i n g o f the j o i n t s e t s a r e r e l a t i v e l y blocks of a f a i r  or  less large  ( i n the order of several  from the r o o f o r s i d e w a l l s .  For an i s o t r o p i c  a cubical  shape),  t h e rock mass i s submitted t o a zone o f compressive  stress,  potential  failure  relaxation,  according (figure  to  6.6).  medium  (figure  isotropic two  (blocks having  may be induced  e x c a v a t i o n boundaries of  three  D i s c r e t e b l o c k f a i l u r e occurs when one o r more  b l o c k s a r e detached  if  size  contains  i s not  fractured  c u b i c meters).  typically  occurs  extensively  which produces  and  block f a i l u r e  6.5).  discrete  different  The simple  by s h e a r i n g wedges from the  modes: gravity  When submitted t o a s t a t e block gravity fall  failure fall  may or  i s the free  displacement o f a b l o c k under the t r a c t i o n o f i t s own 156  occur sliding  vertical  FIGURE 6.5 F a i l u r e mechanism of d i s c r e t e block for an isotropic rock material submitted to compressive s t r e s s , f a i l u r e type 2a; ref. figure 6.17  FIGURE 6.6 F a i l u r e mechanism of discrete block for an i s o t r o p i c rock material i n a state of stress relaxation, f a i l u r e type 2b; r e f . figure 6.17  FIGURE 6.7 F a i l u r e mechanism of discrete block for an anisotropic rock material having elongated blocks oriented p a r a l l e l to the stope surface and submitted to a compressive stress, f a i l u r e type 2c; ref. figure 6.17  FIGURE 6.8 F a i l u r e mechanism of discrete block for an anisotropic rock material having elongated blocks oriented p a r a l l e l to the stope surface in a state of stress relaxation, f a i l u r e type 2d; r e f . figure 6.17  157  gravitational geological  load.  d i s c o n t i n u i t i e s have a n e g l i g i b l e t e n s i l e  the d e t e r m i n a t i o n In s l i d i n g , of  Since t h e r e are no c o n f i n i n g s t r e s s e s and  of block s t a b i l i t y  the d r i v i n g  the  case  becomes p u r e l y  kinematic.  f o r c e i s a f u n c t i o n o f the i n c l i n a t i o n  the " c r i t i c a l " d i s c o n t i n u i t y In  strength,  of  (sliding plane).  anisotropic  rock  (elongated  or  platy  b l o c k s ) , the e x c a v a t i o n s t a b i l i t y w i l l be g r e a t l y i n f l u e n c e d by the  relative  opening  orientation  faces.  t o a stope  this  or s l i d i n g . On  perpendicular  because  t o the  only t h e two extreme  f a c e , on which the compressive of f a i l u r e .  c o n d i t i o n may  other to  hand, the  to s t a b i l i z e  the b l o c k s t o g e t h e r stability  regard  cases  I f submitted  produce g r a v i t y  stress  may  t o a zone of fall,  slabbing  F i g u r e 6.8, shows the s l a b b i n g mode o f f a i l u r e .  the  contribute  with  F i g u r e 6.7 shows elongated b l o c k s sub-  c r e a t e a b u c k l i n g type relaxation,  the b l o c k s  For s i m p l i f i c a t i o n ,  w i l l be d i s c u s s e d here. parallel  of  of  when  face,  the  perpendicular  the c o n f i n i n g e f f e c t  are  stress  rock mass by  subwill  clamping  In a zone o f r e l a x a t i o n , the  blocks no  blocks  compressive  the surrounding  ( f i g u r e 6.9).  shows the g r a v i t y f a l l  elongated  becomes  longer  purely  exists.  kinematic  Figure  6.10  and s l i d i n g modes o f f a i l u r e .  6.5 JOINTED ROCK MASS BEHAVIOUR  A jointed  rock  mass  i s a less  competent  which i s c h a r a c t e r i z e d by a h i g h frequency 158  type  o f ground  of j o i n t i n g  FIGURE 6.9 F a i l u r e mechanism o f d i s c r e t e b l o c k f o r an a n i s o t r o p i c rock material having elongated blocks oriented perpendicular to the stope s u r f a c e and s u b m i t t e d t o compressive s t r e s s , f a i l u r e type 2e; r e f . f i g u r e 6.17  FIGURE 6.10 F a i l u r e mechanism o f d i s c r e t e b l o c k f o r an a n i s o t r o p i c rock m a t e r i a l h a v i n g e l o n g a t e d blocks o r i e n t e d perpendicular to the stope s u r f a c e i n a s t a t e o f stress relaxation, f a i l u r e type 2f; r e f . f i g u r e 6.17  FIGURE 6.11 F a i l u r e mechanism o f j o i n t e d . r o c k mass f o r an i s o t r o p i c rock m a t e r i a l s u b m i t t e d t o compressive s t r e s s , f a i l u r e type 3a; r e f . f i g u r e 6.17  FIGURE 6.12 F a i l u r e mechanism o f j o i n t e o rock mass f o r an isotropic rock material i n a state of stress relaxation, f a i l u r e t y p e 3b; r e f . f i g u r e 6.17  159  producing  a  includes  three  relatively whether  mass  matrix  o r more  i t occurs results  of small  well  close spacing.  relaxation, will  rock  defined  blocks. joint  I t usually  sets  having  a  The f a i l u r e o f a j o i n t e d rock mass,  under  conditions  i n a ravelling  of  compression  of blocks.  or  Rock movement  c o n t i n u e u n t i l the p e r i p h e r a l b l o c k s a r e i n t e r l o c k e d and a  s t a b l e a r c h i s formed.  The amount o f d i l u t i o n c o n t a i n e d i n s i d e  the a r c h p r i o r t o f a i l u r e i s a f u n c t i o n o f t h e o r i g i n a l span.  When t h e c r i t i c a l  opening  span i s exceeded, a s t a b l e a r c h can no  l o n g e r be formed and r a v e l l i n g w i l l p r o g r e s s as a chimney u n t i l better  ground  c o n d i t i o n s a r e met or i n t h e extreme  situation,  i t w i l l extend t o s u r f a c e . The will  be  f a i l u r e mechanisms a s s o c i a t e d w i t h a j o i n t e d rock mass similar  t o those  previously described  b l o c k s , but on a s m a l l e r s c a l e .  f o r discrete  F i g u r e s 6.11 t o 6.16 show the  s i x b a s i c cases d i s c u s s e d f o r d i s c r e t e b l o c k f a i l u r e a p p l i e d t o a j o i n t e d rock mass.  6.6 SUMMARY AND CLASSIFICATION OF FAILURE MECHANISMS  The  open  stope  failure  mechanism  by t h e nature of the rock mass.  i s primarily  influenced  Based on t h e r e l a t i v e  s i z e of  the rock mass b l o c k s , compared with t h e opening dimensions, the rock  mass  jointed  will  rock  behave  mass.  as i n t a c t  Each  rock,  o f these  discrete  three  behaviour can be submitted t o a compressive 160  types  blocks  or a  o f rock  mass  o r t e n s i l e s t a t e of  FIGURE 6.13 F a i l u r e mechanism of jointed rock mass for an anisotropic rock material having elongated blocks oriented p a r a l l e l to the stope surface and submitted to a compressive stress, f a i l u r e type 3 c ; r e f . figure 6.17  FIGURE 6.15 F a i l u r e mechanism of jointed rock mass for an anisotropic rock material having elongated blocks oriented perpendicular to the stope surface and submitted to compressive stress. f a i l u r e type 3e; ref. figure 6.17  FIGURE 6.14 F a i l u r e mechanism of jointed rock mass for an anisotropic rock material having elongated blocks oriented p a r a l l e l to the stope surface in a state of stress relaxation, f a i l u r e type 3d; ref. figure 6.17  FIGURE 6.16 F a i l u r e mechanism of jointed rock mass for an anisotropic rock material having elongated blocks oriented perpendicular to the stope surface in a state of stress relaxation, f a i l u r e type 3 f ; ref. figure 6.17  stress creating six possible situations. It  has  orientation  been of  mechanism of  observed  the  blocks  failure. will  elongated,  relative  surface  the  also play  In the  mass behaviour the  that  likely  shape  an  important  relative  role in  case of compact b l o c k s  be  isotropic.  o r i e n t a t i o n with  becomes c r i t i c a l .  and  The  If  the  respect  the  the  rock  blocks  to the  are  stope  most f a v o r a b l e o r i e n t a t i o n , f o r  discontinuities  that  delineate  stope s u r f a c e .  P a r a l l e l o r i e n t a t i o n i s more l i k e l y t o produce  instability.  The  stope  mechanisms  failure  6.17  .  result 6.3  Fourteen from t h i s  to  6.16.  different  criteria  failure  described  are  different  shown  and  this  scenarios,  is  above  on  potential  classification Although  blocks,  the  perpendicular  to  diagram  failure  are  illustrated  five  in  open figure  situations  classification  only  classify  to  has  may  in figures fourteen  i n d i v i d u a l modes  of  f a i l u r e emerge: - gravity  fall,  - slabbing, - buckling, -  sliding,  -  shearing.  A v a r i a t i o n of these modes of i s h e a v i l y f r a c t u r e d , and in  a  r a v e l l i n g manner.  of view  failure  occurs  i f the  rock mass  the detachment of s m a l l b l o c k s When looked  at from a kinematic  occurs point  (which i s based p u r e l y on d i s c o n t i n u i t y o r i e n t a t i o n and  does not account f o r n o n - g r a v i t a t i o n a l loads or s t r e s s ) , 162  the  1  a)  1  b)  compression  2  a)  '  relaxation  2  b)  —  compression  2  c)  relaxation  2 d)  compression  2  relaxation  2 f)  compression  3  a)  '  relaxation  3  b)  I  compression  3  c)  —  relaxation  3  d)  compression  3  e)  relaxation  3  f)  Intact Rock  •Isotropic-  Discrete Block • o n g a t e d Block •Parallel to StopeSurface Anisotropic-  • o n g a t e d Block •Perpendicular to S t o p e Surface  I  Jointed Mass  I  e)  Isotropic-  Rock Elongated Block • Parallel to S t o p e Surface '  Anlsotroplc• o n g a t e d Block •Perpendicular to Stope Surface  '  FIGURE 6.17 C l a s s i f i c a t i o n of the f a i l u r e mechanisms i n open stope mining. 163  s h e a r i n g become a sub-case o f s l i d i n g buckling  and s l a b b i n g  failure.  Brown  analysis  mode o f f a i l u r e as d e s c r i b e d  (1980), o r with t h e f o l l o w i n g  diagrams. "critical  Referring joint"  to figure  are f i r s t  represents the persistent angle w i t h t h e stope If  a gravity  critical  technique i n v o l v i n g  6.18, the e x c a v a t i o n  sketched.  joint  mode o f f a i l u r e gravity the  vector critical  stays joint,  The  set oriented  will  simple and the  critical  joint  a t the shallowest  surface.  falls  directly  be g r a v i t y  fall  vector crosses the c r i t i c a l  potential  7 o f Hoek and  v e c t o r r e p r e s e n t e d by a v e r t i c a l  joint),  and the  can be determined by  i n chapter  from t h e approximate c e n t r e o f g r a v i t y the  fall,  can be approximated by a t o p p l i n g mode of  The p o t e n t i a l  stereographic  or gravity  for sliding  failure  inside  medium  the  slabbing  or b u c k l i n g  6 .18 c) .  164  of the block inside  arrow drawn (formed by  t h e opening, the  ( f i g u r e 6.18 a ) . joint  I f the  (see f i g u r e 6.18 b) ,  exists. without failure  I f the g r a v i t y intersecting can occur  the  (figure  jj&jj WALL  BACK  FIGURE  6.18  gravity  a)  fall  FIGURE  Sketch showing  mode of  6.18  c)  the  FIGURE  failure.  6.18  sliding  Sketch showing the failure.  165  b)  Sketch showing  mode of  failure.  s l a b b i n g and buckling mode of  the  CHAPTER 7 DEVELOPMENT OF THE GEOMECHANICAL MODEL 7.1  INTRODUCTION The  review of e x i s t i n g  excavation design development. rock  RMR  that  Because open  systems,  were  and  better  Laubscher adapted  mining  calibration Bawden  et  for al.  methodology Therefore,  and  i t has  Canadian 1988),  f o r the the  which  been  development  factors  shown  conditions  i t was  of  to  the in  to  design  conditions. developed f o r  possess  (Potvin  decided  described  mining  et  a  fair  al.,  1987;  the  same  follow  geomechanical  this  the  on the Q  proposed  specially  with  allow  Based  have  for  the Mathews e t a l . method was  stope  in their  d e s i g n methods s t a r t e d  of the rock mass competency.  indexes, Mathews  methods  methods f o r underground  shown an e v o l u t i o n  empirical  classification  characterization and  (chapter 5) has  Efficient  mass  empirical  chapter  model.  will  be  s i m i l a r t o the one used by Mathews e t a l . The  concept employed  i n the proposed geomechanical  model  i s based on t h r e e fundamental a s p e c t s of c r e a t i n g an e x c a v a t i o n in  a  rock  characteristics stress (3rd  mass. of  By the  defining  rock  mass  and  calibrating  (1st aspect) ,  the  the  induced  (2nd a s p e c t ) , and the p h y s i c a l c o n d i t i o n s of the problem  aspect) , w i t h a l a r g e  data base,  i t will  be p o s s i b l e  to  p r e d i c t whether an e x c a v a t i o n w i l l be s t a b l e or w i l l experience ground c o n t r o l problems.  This w i l l 166  c o n s t i t u t e the v e r i f i c a t i o n  of  the main h y p o t h e s i s  each  aspect  stability  can  be  (chapter  d e f i n e d by  of e x c a v a t i o n s .  The  1.2).  The  characteristics  relevant factors  affecting  of the  f a c t o r s w i l l be d e f i n e d based on  the study of open stope f a i l u r e mechanisms (chapter 6), and  the  w e i g h t i n g used i n e x i s t i n g models (chapter 5). A  rock  critical from  joint  to  The  i s c h a r a c t e r i z e d by  factors.  numerical  stress. and  mass  the  A compressive  modelling,  block  stress  represents  the  size  and  factor,  aspect  derived  of  induced  p h y s i c a l c o n d i t i o n s are d i v i d e d i n t o a stope  shape f a c t o r and a g r a v i t y f a c t o r , the l a t t e r b e i n g the  stope  surface  inclination.  d i s c u s s e d i n chapters 9 and The  the  External  factors  size  related will  be  10.  above f i v e f a c t o r s can be broken i n t o key g e o t e c h n i c a l  parameters. The  g e o t e c h n i c a l parameters can be estimated  from:  o b s e r v a t i o n s and measurements of f i e l d data, l a b o r a t o r y t e s t i n g of  rock  specimens  conceptualization  and  numerical  of  the  s u b d i v i d e d i n t o f a c t o r s and  and  This  chapter  its  role  techniques  best  parameters w i l l for  the  in  the  suited a l s o be  factors w i l l  philosophy design  will  was  method.  be  chosen  modelling.  model  showing  how  the  7.1  is  a  problem  is  parameters.  focus  on  the  potential f o r the  definition failure  of each  factor  mechanisms.  The  e s t i m a t i o n of the  discussed. explained to  Figure  The  calibration  i n chapter  integrate  a l l the  I t i s b e l i e v e d t h a t an  8.  procedure  An e m p i r i c a l  factors  into  a  e m p i r i c a l approach i s  the most a p p r o p r i a t e because of the complexity 167  geotechnical  of the problem  FIGURE  7.1  VISUALIZATION OF THE MODEL  EXCAVATION IN A ROCK MASS THREE ASPECTS OF THE PROBLEM  ROCK MASS CHARACTERISITCS  STRESS EFFECT  PHYSICAL CONDITIONS  oo  BLOCK SIZE FACTOR  CRITICAL JOINT FACTOR DIFFERENCE DIFFERENCE SHEAR IH DIP IN STRIKESTRENGTH  COMPRESSIVE STRESS FACTOR  STOPE INCLINATION FACTOR SLIDING OPTICAL  ORAIYY  SLABBING S70PE  JOINT SURFACE INQ IN ATI OH  EXTERNAL FACTORS  STOPE SIZE AND SHAPE FACTORS _  BLASTING CABLE BOLTING  HYDRAULIC  • RAWS,.  and  the  difficulty  parameters.  in  estimating  E m p i r i c a l methods are  representative  likely  t o be more  because they make use of p a s t experience.  input  reliable  However, they should  be a p p l i e d i n c o n d i t i o n s s i m i l a r t o the data base.  7.2  THE  BLOCK SIZE FACTOR  The  most  degree  of  matrix.  important  fracturing, The  mass w i l l  characteristic or  the  s m a l l e r the  be.  size  blocks  Consequently,  of  the  the  of the less  a  rock  mass i s i t s  blocks  forming  competent  parameter  the  the  rock  representing  the  b l o c k s i z e must have a l a r g e i n f l u e n c e i n the a n a l y s i s and have a  decreasing  value  as  the  rock mass i s more  fractured.  parameter s e l e c t e d t o q u a n t i f y the e f f e c t of b l o c k s i z e r a t i o of RQD/Jn which was system.  The  provides  a  exposures. and  thus  stability  ratio  useful  proposed  RQD/Jn scale  to  is  total  number.  easily  account  estimated  f o r the  possible relative  on  number  i n f l u e n c e of  Q-  site of  and joint  and a minimum of 4 00  0.5,  on  the  A c c o r d i n g t o the data base f o r Canadian open  stope mines, t h i s i n f l u e n c e i n p r a c t i c e ranges  7.2.1  i s the  by Barton i n the o r i g i n a l  I t has a maximum v a l u e of 200 a  The  from  1 to  90.  E s t i m a t i o n of b l o c k s i z e RQD  block having  and Jn are the two parameters r e q u i r e d t o estimate the  size  factor.  persistent  The  joint  Jn  value  s e t s and 169  represents  random j o i n t  the  effect  s e t s i n the  of rock  mass.  I t i s e a s i l y estimated u s i n g t a b l e 5.2.  a rock mass c o n t a i n i n g s e v e r a l j o i n t orientation)  will  be  less  stable  Kinematically,  s e t s (of v a r i a b l e d i p  than  a  rock  mass  and  having  a  s i m i l a r degree of f r a c t u r i n g but o n l y one p e r s i s t e n t j o i n t s e t . The  Jn  parameter  mass t h a t  allows  the  differentiation  i s h e a v i l y f r a c t u r e d by a f o l i a t i o n ,  relatively  competent  when  oriented  s u r f a c e , and a t o t a l l y incompetent variable joint The 1964)  Quality  widely  fractures.  drill  cores  core  equal  a  rock  which c o u l d  perpendicular  to  be  stope  rock mass c o n t a i n i n g s e v e r a l  sets.  Rock  is a  rock  between  to  used RQD  and  Designation technique  can  be  RQD  (developed  measuring  assessed  longer  than  100  mm  on  of i n t a c t  over  the  Deere,  frequency  indirectly  r e p r e s e n t s the percentage or  the  by  of  diamond  p i e c e s of  total  length  considered.  % RQD  RQD (NX), and  = 100%  should be measured on core of a t l e a s t  drilled  easy  lead  to  prior  * ( l e n g t h of core l o n g e r than 100 t o t a l length considered  to  with double estimate  incorrect  t o the RQD  b a r r e l rods.  with  little  assessment estimation.  Although  supplementary  i f the  core  mm)  54 mm RQD  diameter i s simple  cost,  it  may  i s p o o r l y cared f o r  T h i s becomes important  when the  rock i n v e s t i g a t e d i s weak or b r i t t l e . Another c r i t i c i s m the  borehole  of RQD  orientation.  i s the p o t e n t i a l b i a s r e l a t e d Effectively, 170  the  to  discontinuities  parallel result of  RQD  direct  t o t h e borehole  will  not be i n t e r s e c t e d ,  i n an o v e r e s t i m a t i o n o f RQD. should  Palmstrom  Consequently,  be v e r i f i e d a g a i n s t  underground (1982)  other  j o i n t surveys.  have proposed  which  will  t h e measure  techniques  Hudson & P r i e s t  based on (1976) and  methods t o c o r r e l a t e  RQD  with  underground j o i n t mapping, a) Hudson and P r i e s t method According  to  discontinuities  Hudson  and  i s assumed  Priest,  t o have  f o l l o w s some form o f s t a t i s t i c a l  a  the  range  spacing  of values  distribution.  of  which  Based on twenty  seven measurements i n t h r e e t u n n e l p r o j e c t s i n t h e U.K., Hudson and  Priest  found  discontinuity  that  the p r o b a b i l i t y  spacings  can  be  d e n s i t y d i s t r i b u t i o n of  approximated  the  negative  exponential d i s t r i b u t i o n : v -XX  f (x) = Ae where  x = individual discontinuity = discontinuity  frequency  = mean d i s c o n t i n u i t y Individual  discontinuity  spacing, 1/x,  spacing.  spacing  is  measured  s c a n l i n e underground as shown i n f i g u r e 7.2.  a  Hudson and P r i e s t  proposed t h e f o l l o w i n g r e l a t i o n s h i p between t h e frequency  along  discontinuity  and RQD: RQD = 100 e -0.1* ( 0 . l \ + 1)  When t h e d i s c o n t i n u i t y between  s p a c i n g frequency  6 and 16 p e r meter,  (X ) has a v a l u e  t h e above r e l a t i o n s h i p  ( f i g u r e 7.3) and can be approximated by: 171  i s linear  Oi&toncs from A to Iht iih dittomrutyifl,  Spacing valuestogiven OSl/o^-d,., tor i i ! • « (olD'SContirwly intersection points otong o (b)Sconiins (rneosuring tope^ on exposed straight line CAB) through the rock moss lock tool  FIGURE 7.2 S k e t c h showing t h e measurement o f j o i n t s a l o n g a s c a n l i n e . ( A f t e r P r i e s t a n d H u d s o n , 1976)  Linear approximation ROD** -  0  t 2  i 4  6  8  3.68* * 110.4  i i • i Si 10 12 14 16 18 20 22 21 26 28 30 Average number ol discontinuities per m, X  i  32  i 34  I  '  36  38  40  FIGURE 7.3 R e l a t i o n s h i p b e t w e e n RQD a n d t h e a v e r a g e number o f d i s c o n t i n u i t i e s p e r m e t e r . ( A f t e r P r i e s t a n d H u d s o n , 1976)  RQD  = -3.68X +  110.4  b) Palmstrom method Palmstrom based  on  joint  count  direct  proposed  underground  (Jv)  c u b i c metre RQD  (1982)  defining  of  an  the  area  of  inside  per  by a f a c t o r  volumetric  rock  Jv has  - 3.3  been r e l a t e d  to  Jv  (Jv)  can  be  mass where the  are  per  estimated  majority  represented.  The  of  by the  number  the d e l i n e a t e d area are counted  and  of the  square  metre).  This value  (# of j o i n t s per  i s transformed  c u b i c metre) by  (# into  multiplying  "K":  Jv  (# of j o i n t s / m )  provided and  * K = (# of  2  did  very not  few  give  details a  factor  K  will  vary  joints/m ) 3  on  how  this  criteria  on  how  appropriate K f o r a given s i t u a t i o n . "The  The  also  of j o i n t i n g per u n i t of s u r f a c e can be c a l c u l a t e d  volumetric units  derived  technique  relationship.  count  discontinuities  joints  Palmstrom  factor  = 115  joint  discontinuities frequency  surveys.  by the f o l l o w i n g  volumetric  persistent  joint  The  RQD The  alternative  i s an e s t i m a t i o n of the number of j o i n t s  i n rock mass.  empirically  an  with  He  factor to  K  was  choose  an  stated:  the  distribution  of  the  joints.  With an equal d i s t r i b u t i o n i n a l l t h r e e d i r e c t i o n s ,  will  1.15  be  surface  with  -  1.5  depending  respect  to  upon  joint  the  orientation  planes.  d i s t r i b u t i o n s , the K w i l l have g r e a t e r v a r i a t i o n . 173  For  of  K  the  unequal  Under normal  conditions, Palmstrom  however,  (1982).  i t has  been  found t h a t  k =  In p r a c t i c e a k f a c t o r of 1.0  1.25  -  1.35"  i s often  used  assuming t h a t the s u r f a c e mapped i s r e p r e s e n t a t i v e of the t h r e e dimensions.  7.3  STRESS FACTOR  7.3.1  E f f e c t o f compression The e f f e c t of a h i g h compressive s t r e s s on a rock mass may  result  i n c r u s h i n g or c r a c k i n g  existing combination these  discontinuities, of the  phenomena  of p r e c i s i o n  chosen  the  tangential boundaries  one  is  rock, s h e a r i n g along  rotating  of  blocks  complexity and  attempt  to  by  reproduce  induced scaled  Mathews parallel  against  s t r e n g t h of the rock mass ( C T ) . c  the  or  any  variability  i n the e m p i r i c a l model.  proposed  stresses (oy)  The  any  h i g h degree was  or  above.  negate  of i n t a c t  of  them with The  a  approach  et  a l . , where  to  the  the  excavation  uniaxial  compressive  T h i s suggests t h a t the  effect  of compressive s t r e s s i s p r o p o r t i o n a l t o the r e l a t i v e magnitude of the t a n g e n t i a l The  adjustment  same as Mathews 7.4. number  s t r e s s normalized w i t h i n t a c t rock s t r e n g t h .  factor  factor  1  I t has a t o t a l calculation.  minimum adjustment or l e s s than 2.0  f o r compressive A,  and  relative  can be  stress  i s roughly  estimated using  i n f l u e n c e of 10 i n the  The  only m o d i f i c a t i o n  of 0.1  when the r a t i o  of  made was o /oy c  figure  stability to  set a  i s equal t o  ( i n s t e a d of assuming automatic f a i l u r e 174  the  as  FIGURE 7 . 4 factor.  Graph f o r the e s t i m a t i o n of the compressive  175  stress  suggested in  by  chapter  Mathews e t a l . ) .  8.4.2.  The  uniaxial  d i s c u s s e d i n s e c t i o n 4.2.1. for  simple  open  stope  This w i l l  The  two  and  three  further discussed  compressive  strength (a )  was  c  (oy)  induced t a n g e n t i a l s t r e s s  configurations  can  numerical m o d e l l i n g or curves developed using  be  dimensional  be  determined  using  from a p a r a m e t r i c study  numerical  modelling  (section  7.3.2) .  7.3.2  Open stope numerical m o d e l l i n g p a r a m e t r i c study The d e t e r m i n a t i o n of induced s t r e s s around  be d i f f i c u l t  t o estimate a t mine s i t e s ,  open stopes can  because of the l a c k of  numerical m o d e l l i n g hardware and software f a c i l i t i e s . most  mining  operations  access t o two  possess  computers  and  sometimes  t o use  and  time  geometries  are  consuming t o run.  "three  dimensional"  mining,  the development of s t r e s s induced curves was  order  sites. 70  to  The  runs  have  dimensional models, t h r e e d i m e n s i o n a l models are  uncommon, d i f f i c u l t  in  Although  make  the  design  frequent  method  in  applicable  open  stope  necessary  at  curves presented below have been developed  of the t h r e e dimensional  Since  the  mine  based  on  boundary element code "BEAP"  and a number of runs u s i n g the two dimensional boundary element program in  "BITEM".  Appendix  plotted  2  A b r i e f d e s c r i p t i o n of both program i s g i v e n  and  i n terms  the of  the  significant  stress  acting  stope  design  i n the  middle  output, of  each  should be kept i n mind t h a t a number of assumptions  have  plane, i s reproduced It  most  i n Appendix 3.  176  been made i n t h i s p a r a m e t r i c study. are based  on open stopes seen  The stope geometries  i n more than  3 0 Canadian  used  mines.  However, t h e i r shapes have been i d e a l i z e d and v e r t i c a l d i p only has  been  considered.  serve as a rough three dimensional  7.3.2.1  Consequently,  curves  should  guide t o determining t h e s t r e s s around  simple  geometries.  General concept o f t h e p a r a m e t r i c study  The p r i n c i p a l s t r e s s e s act  ( f i g u r e 7.5).  these  induced  mining  transverse ratios,  ratio  stope  configurations, from  2) The induced value),  compressive  stress  will study.  longitudinal  t h e pre-mining  pre-  and  stress  i s o s t a t i c t o 1.5, 2.0 and 2.5 i n o f these  variations  on the will  scheme:  t h e induced  stress  can be assumed  stress.  s t r e s s may decrease  but never  These  i n two d i r e c t i o n s on each plane)  No s i g n i f i c a n t e f f e c t , equal t o t h e pre-mining  of the  parametric  into  while  The e f f e c t s  (acting  function  of t h i s  be analyzed a c c o r d i n g t o t h e f o l l o w i n g 1)  t o t h e stope  geometry.  are divided  "K", a r e v a r i e d  stresses  a  and t h e problem  geometries  three d i r e c t i o n s .  induced  i s primarily  the p r i n c i p a l v a r i a b l e s  problem  tangential  o f a stope,  The magnitude (and e f f e c t on s t a b i l i t y ) of  stresses  stress  constitute  all  induced on each s u r f a c e  i n two p e r p e n d i c u l a r d i r e c t i o n s  plane  The  the s t r e s s  reaches  (from t h e pre-mining  tension,  condition.  resulting  In t h i s  case,  s t r e s s w i l l have no n e g a t i v e e f f e c t on s t a b i l i t y 177  stress  i n a low t h e induced and can be  PLANE A -  ASPECT RATIO = L/H HORIZONTAL PLANE K RATIO = VERTICAL PLANE K RATIO = <J-\  0<\/$2  FIGURE 7 . 5 D e f i n i t i o n o f t h e a s p e c t r a t i o and K r a t i o used i n t h e e s t i m a t i o n o f t h e induced s t r e s s a c t i n g on a stope surface.  178  overlooked i n the d e s i g n a n a l y s i s . 3)  The  induced s t r e s s may  decrease and  possibly  reach  tension.  Induced s t r e s s curves w i l l be produced i n t h i s s i t u a t i o n , to predict  which  conditions  result  in  a  tensile  stress  environment. 4)  The  induced  stress  may  show a  s i g n i f i c a n t increase.  Once  again, induced s t r e s s curves w i l l be produced i n order to able  to  determine  the  magnitude  o±  of  for  the  be  design  analysis.  An  important  observation,  problems modelled acting  in  a  dimensions  of  the  K  to  the  ratio,  in this  given the  stope by  stress  acting perpendicular It  study,  direction  defined  induced  made on  aspect the  was is  mainly  investigated  t o the  direction generally  has  an  the  of the stress  guidelines  of for  the the  estimation  transversal  open  surface  In of  (of  the  the  figure  7.5),  and  acting  stress  stope  (figure  7.5).  acting  i n the  third  the  following  induced  induced  s i m p l i f i e s the  stress  sections, will  interest in longitudinal  open s t o p i n g p a r a m e t r i c study 179  parallel  pre-mining  stoping).  Longitudinal  stress the  i n s i g n i f i c a n t e f f e c t on  results.  f o r each stope  induced  by:  T h i s s i m p l i f i e s the o v e r a l l problem and  presentation  dimensional  affected  (see  and  surface  pre-mining  7.3.2.2  the  pre-mining s t r e s s  the  given  that  surface  i s assumed t h a t  stress.  most t h r e e  be and  The  g e o m e t r i c a l shape of l o n g i t u d i n a l  characterized  by  stope  and  height  Canadian  a  stope  width  length.  (longitudinal)  that  figure  7.6.  most  three  dimensional  longitudinal of  the  study  extreme  m o d e l l i n g was of and  nearby  the  data  has  models  used  i n Appendix 3. been  done  back  abutments.  be  The  using  considered n e g l i g i b l e  analyses.  The  three  r e p r e s e n t e d on f i g u r e 7.5  This stope  is  not  by plane A  most the  of the  for  the  modelling  BITEM. The  The  influence  f o r stope  wall  f o r the  stope  true  surfaces  the  are between  performed on i s o l a t e d stopes o n l y . can  base,  A summary of the output  found  geometries  stopes  stope  can be  to  stope geometries  l i m i t s d e f i n e d on important  i s s m a l l compared t o  According  open  stopes i s generally-  of  interest  are  (the stope w a l l ) , plane B  (the back) and plane C (the stope end).  Plane A, stope w a l l : i)  The  stress  induced  i n the h o r i z o n t a l  s i g n i f i c a n t decrease and may (L/H stope  < 1)  and  walls,  stress the  ratio  surface  direction will  be t e n s i l e f o r c e r t a i n geometry combinations. aspect  ratio  For  The  horizontal  induced  stress  on  estimated u s i n g the curves i n f i g u r e 7.7). v a r y i n g the stope width considered n e g l i g i b l e ii)  on the s t r e s s e s  (see f i g u r e  The s t r e s s induced v e r t i c a l l y 180  longitudinal  i s d e f i n e d by  (stope l e n g t h / s t o p e height) and K i s g i v e n by 7.7).  show a  0-^/02  plane The  A  L/H  (figure can  be  i n f l u e n c e of  i n plane A can  7.8).  i s s i m i l a r t o the h o r i z o n t a l  be  FIGURE  7.6  LONGITUDINAL O P E N S T O P E T Y P I C A L DIMENSIONS EXPRESSED IN TERMS OF STOPE WIDTH (W)  L = (1 TO 9)W  LP = (1 TO 5)W  FIGURE  0.7  LONGITUDINAL OPEN STOPE STRESS  7.7  HANGING WALL - HORIZONTAL PLANE -i  1:INF  1:7  1:5  1:4  1:3  1:2  1:1  2:1  STOPE ASPECT RATIO (LENGTH /  3:1  HEIGHT)  4  • HW / WIDTH = 5 A BACK / WIDTH a 5  STOPE ASPECT RATIO (LENGTH / HEIGHT) + HW / WIDTH a 1.0 O HW / WIDTH = 20 X BACK / WIDTH = 10 V BACK / WIDTH a 20  induced s t r e s s except the problem  i s r o t a t e d 90°.  The stope  aspect r a t i o remains  L/H, but the s i g n i f i c a n t s t r e s s r a t i o K  i s d e f i n e d by a / a .  F i g u r e 7.9 can be used t o estimate the  1  vertical  3  induced  stress.  Plane B, stope back: i)  The  induced  tangential  stress  acting  p e r p e n d i c u l a r t o the stope s t r i k e significant  increase.  not v a r y d r a s t i c a l l y the  wall  aspect  ratio  ratio.  Consequently,  (L/H) induced the  o f a-y/o  3  i s not n e c e s s a r i l y  o r narrower  assessed  from  does  curves  a  than  much  greater  a back  developed  for  this  (L/H) and  The stope  width  The i n f l u e n c e of stope width  negligible.  stopes,  f i g u r e 7.8.  7.10).  aspect  o f the curves was 1/4 the s i z e  t h e i n t e r m e d i a t e dimension.  wider  have  stress,  (see f i g u r e  f o r the development  however  will  are a f u n c t i o n o f the w a l l aspect r a t i o  the K r a t i o  of  stope width  compared with stope h e i g h t and l e n g t h ,  on the back  assumed  direction  (oy d i r e c t i o n ) may show a  Because the t y p i c a l  influence  situation  i n the  the e r r o r  When d e a l i n g with made  can be  As a g e n e r a l r u l e  roughly  , the narrower  the stope the h i g h e r the back and abutment s t r e s s e s w i l l be. ii)  The  induced  stress  ratio  acting  along  the  strike  d i r e c t i o n ) may show a s m a l l i n c r e a s e , but i t w i l l significant Consequently, stability  as  the  the a  2  induced  stress  acting  (a  2  not be as  across  strike.  induced s t r e s s can be overlooked i n the  a n a l y s i s of simple l o n g i t u d i n a l stope 184  backs.  FIGURE  LONGTTUDMAL OPEN STOPE STRESS  7.9  HANGING WALL - VERTICAL PLANE 0.7  -,  1:INF  —  1:5  1:4  1:3  1:2  1:1  2:1  3:1  4:1  STOPE ASPECT RATIO (LENGTH / HEIGHT)  5:1  7:1  INF:1  FIGURE  7  10  LONGITUDINAL OPEN STOPE STRESS BACK STRESSES  ASPECT RATIO (LENGTH / HEIGHT)  Plane C, stope end o r abutment:  i)  The a n a l y s i s o f induced s t r e s s is  similar  This  t o the a n a l y s i s  means t h a t  and  the K r a t i o  This  induced  estimated  to  ii)  1  may  figure  2  i n the back, aspect  ratio  but r o t a t e d 90".  used  i s L/H again,  f o r the induced h o r i z o n t a l have  a large  7.11.  The  of  varying  effect  the width  stress.  i n c r e a s e and can be o f v a r y i n g the  on the abutment w a l l induced s t r e s s  the e f f e c t  (described  is a /a  stress  using  stope width  the stope  i n an i s o l a t e d abutment w a l l  on  i s similar  the back  stress  above).  The induced s t r e s s a c t i n g v e r t i c a l l y may show some i n c r e a s e , but  i t will  not be as s i g n i f i c a n t  horizontal direction.  as the i n c r e a s e i n the  The i n f l u e n c e o f t h e induced  vertical  s t r e s s can g e n e r a l l y be overlooked i n t h e s t a b i l i t y  analysis  of l o n g i t u d i n a l stope ends.  A  summary  tangentially  of at  the  possible  longitudinal  stope  stress  conditions  boundaries  acting  i s found  in  f i g u r e 7.12.  7.3.2.3  T r a n s v e r s e open s t o p i n g p a r a m e t r i c study  The t y p i c a l g e o m e t r i c a l shape of t r a n s v e r s e open stopes i s a relatively height.  s m a l l stope  l e n g t h compared w i t h stope width and  A c c o r d i n g t o the data base, t h e stope dimensions o f 187  FIGURE  7  11  LONGITUDINAL OPEN STOPE STRESS ABUTMENT STRESSES  2.5  - i  ASPECT RATIO (LENGTH / HEIGHT)  FIGURE  7.12  SUMMARY OF T H E  LONGITUDINAL PARAMETRIC  CASE # 4 . S M figure  STUDY  7.10  CASE #1  CASE #4 >e figure 7.11 CASE #3.  „  B figure 7.7  CASE #3, •ee figure 7.9  PLANE  A  L CASE  #1  — no s i g n i f i c a n t i n c r e a s e in t h e i n d u c e d p r e - m i n i n g s t r e s s is a s s u m e d  CASE  #2  — induced  CASE  #3  — induced stress decreases significantly, the referenced figure  CASE  jfA  -  induced the  stress  stress  referenced  d e c r e a s e s , low  increases figure  189  stress,  compression  significantly,  see  see  is  assumed  most t r a n s v e r s e stopes 7.13.  A  summary  are w i t h i n  of the  output  the  limits  f o r the most  shown oh  figure  important  three  d i m e n s i o n a l models used i n the t r a n s v e r s e study can be found i n Appendix each for  3.  S i n c e the openings  may  have a l a r g e  o t h e r i n t r a n s v e r s e mining, a t l e a s t two the m o d e l l i n g .  interest  In f i g u r e 7.13,  have been l a b e l l e d ?  influence  on  stopes were used  the f o u r stope s u r f a c e s of  plane A  (abutment w a l l ) ,  plane B  ( p i l l a r w a l l ) , plane C (back) and plane D (stope end).  Plane A, abutment w a l l ; i ) The h o r i z o n t a l induced s t r e s s i n the abutment w a l l may a significant  i n c r e a s e depending  (W/H), and the K r a t i o of a / a • 1  the curves shown i n f i g u r e ii)  on the w a l l  aspect  7.14.  induced s t r e s s u s u a l l y shows a s l i g h t  but  reaches  geometry.  tension  Stress i n this  ratio  I t can be e s t i m a t e d u s i n g  2  The v e r t i c a l never  have  for  direction  a  typical can  be  decrease  transverse  overlooked i n  the a n a l y s i s .  Plane B, p i l l a r  wall;  i ) The h o r i z o n t a l induced s t r e s s i n the p i l l a r w a l l may major i n c r e a s e . Because a  2  The  important  stope aspect r a t i o  i s shadowed by the openings,  length r a t i o  is  However,  (Lo/Lp) w i l l  a major i n f l u e n c e on the c o n c e n t r a t i o n of h o r i z o n t a l 190  W/H.  the s t r e s s r a t i o K  has o n l y a s m a l l i n f l u e n c e on the induced s t r e s s . the opening l e n g t h t o p i l l a r  show a  have  TRANSVERSE OPEN STOPE  DIMENSIONS  E X P R E S S E D IN TERMS OF S T O P E L E N G T H (L)  FIGURE  7.13  FIGURE  7.14  TRANSVERSAL STOPE BOUNDARY STRESSES ABUTMENT / SIGMA1 DIRECTION  STOPE  WIDTH  /  STOPE  HEIGHT  stress.  The  curves  shown i n f i g u r e  e s t i m a t e the h o r i z o n t a l  ii)  The  vertical  according  to  transverse Consequently,  stress  aspect  stope  may  ratio  geometries  i t does  can  be  used  induced s t r e s s i n the p i l l a r  induced  the  7.15  not  drop  (W/H)  will  have  to  be  wall.  significantly  but, not  to  for  typical  reach  tension.  considered  in  the  analysis.  Plane C, stope back, i) The the  induced s t r e s s a c t i n g a c r o s s s t r i k e remained s i m i l a r to pre-mining  modelled.  stress  (oy)  f°  r  a  H  For the d e s i g n a n a l y s i s ,  the  transverse  v i r g i n stress  cases  (a-jj can  be assume i n the back. ii)  The  induced  similar  to  stress the  acting  pre-mining  stress  increase  for  Generally,  the induced s t r e s s  greater  than  stopes  along  the  stress  ignored i n the s t r e s s  Plane D, stope i ) The  having  (a ) 2  i n the  strike  magnitude  also  (cr ) •  width  i  back w i l l  n  e  Some  2  large nt  stay  direction,  is  and  seen. not can  be be  analysis.  end.  induced s t r e s s a c t i n g h o r i z o n t a l l y on the stope end  have s i g n i f i c a n t decrease. 01/02  a  the  i s greater  than  g r e a t e r than the width  2  may  In the v e r y extreme cases, when or  the  length  of  the  stope  is  ( l o n g i t u d i n a l geometry), t e n s i o n i s 193  FIGURE  7 . 1 5  TRANSVERSE STOPE - BOUNDARY STRESSES PILLAR WALL / K = 2.0  2.0  -i  0.0  —  0.25  .  0.50 STOPE WIDTH /  0.75 STOPE HEIGHT  possible cases,  (see  low  induced  figure  7.16).  compression stress  can  can  However  be  be  f o r most  assumed, and  disregarded  in  transverse  the  horizontal  the  stability  analysis. ii)  In  the  vertical  decrease,  but  i t does not  A  summary  tangentially  direction,  will  stay  the  induced  low  compression.  into  stress  may  Generally,  need t o be c o n s i d e r e d i n the  stress  of  conditions  the  possible  stress  also  analysis.  acting  at t r a n s v e r s e stope boundaries i s found i n  figure  7.17.  7.4  EFFECT OF JOINT ORIENTATION  The respect  r e l a t i v e o r i e n t a t i o n and to  surfaces,  each will  other  and  determine  d i p of p e r s i s t e n t  with the  respect  stability  to of  j o i n t s with  the  excavation  blocks  and  p o t e n t i a l modes of rock mass f a i l u r e .  Kinematic a n a l y s i s  stereographic  the  method f o r of  the  movement  projection  investigating  basic must  constitutes the  assumptions occur  Because i t does not  e f f e c t of j o i n t  of  this  according  to  account f o r new  type  many  applying  open  stoping  situations.  stereographic projection 195  of  existing fractures  or b l a s t i n g , k i n e m a t i c a n a l y s i s alone has in  most  This  using  commonly  used  orientation.  One  analysis  is  that  discontinuities. created  been found was  the  by  stress  unreliable  demonstrated  i n the back a n a l y s i s  by  of more  FIGURE  7. i6  TRANSVERSAL STOPE BOUNDARY STRESSES STOPE END / SIGMA2 DIRECTION  1.2  - i  1.1  -  00  2.0  4.0  STOPE WIDTH / STOPE LENGTH  6.0  FIGURE  7.17  SUMMARY OF THE T R A N S V E R S E  P A R A M E T R I C  S T U D Y  H  CASE #1 — no significant induced stress increase, pre—mining stress is assumed CASE #2 -  induced stress decreases, low compression is assumed  CASE #3 — significant induced stress decrease, see figure referenced CASE §4 -  significant induced stress increase, see figure referenced  197  than  60 case h i s t o r i e s .  predicted  block f a i l u r e s  The  stabilizing  can  explain  non  entry  block  The r e s u l t s  effect  o c c u r r e d i n stopes  of a j o i n t  some of these  mining  showed t h a t  cases.  methods  clamping  t e n cases of  t h a t were compressive  In a d d i t i o n ,  stress  the success of  are o f t e n not a f f e c t e d  f a i l u r e when the s i z e of the rock f a l l  stable.  by  isolated  i s not e x c e s s i v e .  Furthermore, n i n e cases of stopes t h a t e x p e r i e n c e d c a v i n g were p r e d i c t e d s t a b l e by s t e r e o g r a p h i c a n a l y s i s .  7.4.1  The c r i t i c a l A  more  joint  general  factor  type  of  analysis  that  would  account  indirectly  f o r the p o s s i b l e c r e a t i o n of new  fractures,  suitable.  In the c o l l e c t i o n and a n a l y s i s of case h i s t o r i e s , i t  was observed t h a t most cases of s t r u c t u r a l l y c o n t r o l l e d occurred the  along  joints  unstable  observation  greater  "critical"  stress  Furthermore,  the  parallel  or  stress  diminishes  while  respect to  reason  the d i f f e r e n c e  of having other of  joint  the b r i d g e  joint  sets  stress  shearing  joint  angle  (0).  along the c r i t i c a l  the normal  e f f e c t ) a l s o decreases.  with  failure  for  this  i n d i p (6)  shallow j o i n t and e x c a v a t i o n f a c e , the  t o the c r i t i c a l  acting  angle  principal  smaller  component  c o s i n e o f the c r i t i c a l shear  a shallow The  the  the p r o b a b i l i t y  blasting,  acting  surface.  i s that  between t h i s  having  i s more  stress  Consequently, 198  "B"  broken  (figure  is a  7.18).  the b l o c k  function  by  or  of the  T h i s i m p l i e s t h a t the joint  (which  i n c r e a s e s as (8)  has  a  stabilizing  the angle of the  199  critical a  j o i n t (9), or the s h a l l o w e s t d i f f e r e n c e  persistent  indication is  a  joint  s e t and t h e stope  i n d i p between  surface,  offers  a good  o f t h e p r o b a b i l i t y o f having s t r u c t u r a l f a i l u r e and  viable  means  of  accounting  f o r the e f f e c t  of j o i n t  orientation. An joint  adjustment i s shown  calibrated joint of  f o r the influence  figure a  7.19.  adjustment  joint  angle  o f 0.2  was  empirically  f o r a small  critical  ( i e . 1.0) f o r t h e i n f l u e n c e  (9) o f 90°.  o f 5 on t h e s t a b i l i t y  of the c r i t i c a l  The graph  (9), and no adjustment  a critical  influence  on  giving  angle  factor  This  number.  gives  Best  a total  results  were  o b t a i n e d with t h e model by s e t t i n g t h e adjustment f a c t o r t o 0.3 for  t h e common  face,  angle  7.4.2  case  of a j o i n t dipping  t o stope  (9 equals 0° t o 10°).  E f f e c t of anisotropy Because  t h e rock  mass may  o r i e n t a t i o n of the c r i t i c a l on  sub-parallel  stability.  The c r i t i c a l  be a n i s o t r o p i c ,  the r e l a t i v e  j o i n t w i l l a l s o have a g r e a t e f f e c t joint will  have a maximum e f f e c t  when i t s s t r i k e i s p a r a l l e l t o the stope s u r f a c e . w i l l diminish minimum effect  as t h e d i f f e r e n c e  i n t h e case of anisotropy  The e f f e c t  i n s t r i k e increases  of perpendicular i s included  critical  and w i l l be  joint.  i n t h e adjustment  This  factor for  j o i n t o r i e n t a t i o n by t h e dashed l i n e s i n f i g u r e 7.19, where the difference  in strike  i s shown  a t increments  o f 15°.  curves were developed based on the t r u e angle between the 200  These  FIGURE  7.19  Influence of Joint Orientation  Difference In Strike  0.1 1  1  1  1  r  1  i  1  r  10  20  30  40  50  60  70  80  90  Relative Difference in Dip Between the Critical Joint and Stope Surface  201  discontinuity  and  stope  surface  determined  by  stereographic  proj ections.  7.4.3  Shear s t r e n g t h of the c r i t i c a l Another  joint  is  "index" in  is  J r / J a proposed 5.2),  on  the  quickly  already  has  4.  the  The  critical  simple  Barton c l a s s i f i c a t i o n for  the  model  shear  (described because  it  of d i s c o n t i n u i t y c h a r a c t e r i s t i c s and site.  relative  i t s effect However  f o r Canadian  regarding  strength.  selected  on  weighted  to  sensitivity  i n the  been  estimated  In theory,  0.02  shear  observation  been  RQD/Jn. from  consideration  i t s associated  table  relies  important  joint  In  addition,  to  the  on  the  according  open s t o p i n g  its  block  size  stability to  the  effect  parameter  number ranges  data  conditions  has  base,  its  i s generally  less.  7.5  THE  GRAVITY FACTOR  Gravity Its  influence  failure. stope  mining  In  varies  were  according  the  fall  to  potential  blocks. mode  of  as:  gravity  fall,  slabbing,  shearing.  development  of  an  adjustment  mode can  be  with  stress plays  the  the  removable  the modes of f a i l u r e r e l a t e d t o open  identified  s l i d i n g and  shearing  gravity  d r i v i n g f o r c e a c t i n g on  In s e c t i o n 6.6,  buckling,  the  i s the  t r e a t e d as  202  factor for gravity,  a sub-case of  sliding  or  a major r o l e i n t r i g g e r i n g  instability.  Similarly,  buckling  can be c o n s i d e r e d as a sub  case o f s l a b b i n g which reduces the problem t o only t h r e e modes of  failure:  mode  of  gravity  failure  fall,  can  slabbing  be  and s l i d i n g .  determined  with  a  ( d e s c r i b e d i n s e c t i o n 6.6) o r by s t e r e o g r a p h i c The  effect  .slabbing,  of gravity,  i n the case  i s mainly dependent  plane.  For s l i d i n g ,  sliding  plane's  The p o t e n t i a l simple  diagram  analysis.  of g r a v i t y  on the i n c l i n a t i o n  fall  and  o f the stope  the e f f e c t o f g r a v i t y i s a f u n c t i o n of the  (critical  joint's)  inclination.  Consequently,  two g r a v i t y adjustment f a c t o r s a r e proposed. The f i r s t adjustment used  f o r the g r a v i t y  adjustment  f a c t o r i s shown i n f i g u r e 7.20 and i s  fall  and s l a b b i n g modes o f f a i l u r e .  a c c o r d i n g t o t h e stope  surface  inclination  The has a  maximum v a l u e o f 8.0 f o r v e r t i c a l w a l l s and a minimum v a l u e of 2.0  for horizontal  effect). of  less  o f 8.0 when  30°. joint  This exceeds  gravity  factor  and i s shown on f i g u r e  value  than  critical  (where  The second adjustment  failure  maximum  backs  i s used  7.21.  the c r i t i c a l  assumes t h a t the d r i v i n g  has  largest  i n s l i d i n g mode  The adjustment joint  the f r i c t i o n force.  the  inclination  is  angle o f the  The adjustment  decrease t o a minimum o f 2.0 as the c r i t i c a l  has a  joint  will  inclination  increases.  7.6  EFFECT OF STOPE SIZE AND SHAPE  As employed by Laubscher  (1976) and Mathews e t a l . (1980), 203  10  >  I  •  I  1  I  20  30  40  50  60  70  80  90  Inclination of Stope Plane FIGURE  I n f l u e n c e of g r a v i t y f o r s l a b b i n g and g r a v i t y modes of f a i l u r e .  7.20  fall  8 7o  6 -  I?  5-  % =6 4 <  3  o  110  20  30  40  50  60  70  80  90  Inclination of Critical Joint FIGURE  7.21  Influence  of g r a v i t y f o r s l i d i n g mode of 204  failure.  the h y d r a u l i c r a d i u s o f i n d i v i d u a l an  adequate  shape  parameter  o f the plane  quotient  t o account  radius  f o r the e f f e c t  under a n a l y s i s .  o f the stope  Hydraulic  stope s u r f a c e appears t o be  plane  favors  area  a long  o f s i z e and  I t i s calculated and stope  and narrow  plane shape  by the  perimeter. over  square  shape, a l l o w s the a n a l y s i s o f stope s u r f a c e plane by plane, and i s easy t o a s s e s s .  7.7  CALCULATION  OF  THE  MODIFIED  STABILITY  NUMBER  AND  PRESENTATION OF THE MODIFIED STABILITY GRAPH  The  calculation  o f the m o d i f i e d  stability  number  i s done  by m u l t i p l y i n g the e f f e c t s of the f o l l o w i n g f o u r f a c t o r s : s i z e , s t r e s s , j o i n t o r i e n t a t i o n and g r a v i t y . each  parameter  sections values  t o 7.5  typically  figures The  7.2  composing  required  the f a c t o r s  and i s shown  seen  f o r each  t o estimate  parameter  each  The e s t i m a t i o n of  has been  i n page  block  explained i n  207.  The range of  i s given,  parameter  and the  are referenced.  a p p l i c a t i o n o f the d e s i g n method i n b a c k - a n a l y z i n g the case  histories  collected  relationship  between  in this  the m o d i f i e d  hydraulic  radius. This  stability  graph  method  study,  (figure  and the m o d i f i e d  205  an  improved  number  and the  i s shown on the m o d i f i e d  The c a l i b r a t i o n  stability  chapter 8.  l e d to  stability  relationship 7.22).  has  graph w i l l  o f the design  be d i s c u s s e d i n  FIGURE  7.22  Modified Stability Graph 1000  ....Ki I in'! /»»:*: :<:°:¥: .^: : :V:;:V: : : :-TJ> :  o  :  100  :  ;  :  :  E ZJ  10 o  CO <D  ^=  1.0  O  0.1 0  5  10 Hydraulic  15 Radius  206  20 (m)  25  Effect of Stress  Block Size N*  (0.2-720)  1-90  REFERENCE  Table 5.2  7.8  Effect of Gravity  Jt. Shear Comp. Relax. Critical Jr/Ja Angle 9  RQD/Jn  =  Effect of Joint Orientation  (0.1-1) (1.0)  (0.2-1) (0.05-3)  Fig 7.4  Fig 7.19 Table 5.2  Slabbing  Sliding  (2-8)  (2-8)  Fig 7.20 Fig 7.21  SUMMARY  A geomechanical model f o r open stope d e s i g n i s proposed i n t h i s chapter. the to  modification specific  models  the  existing  and  was  inspired  estimation  of  five  conditions  below,  each  systems  by p r e c e d i n g  Barton e t a l . (1974), B i e n i a w s k i (1973),  and  factor  key  The model i s based  factors  the geometry i s composed  of  of  related open  to  the  stopes.  parameters  As  easy  to  site.  1. B l o c k s i z e f a c t o r :  can  rock mass c l a s s i f i c a t i o n  conditions,  by  e s t i m a t e on a mine  - RQD  adopted i n t h e model i s based on  (1976) and Mathews e t a l . (1980).  geotechnical shown  of  mining  proposed  Laubscher on  The methodology  (RQD/Jn)  measures the degree  of f r a c t u r i n g  i n the rock mass and  be  core  but  direct  estimated  from  underground  mapping  logging using  preferably  Hudson  &  Priest  from or  Palmstrom t e c h n i q u e s . - Jn  i s also  estimated  from  underground  mapping  and  account  f o r the number o f j o i n t s e t s p r e s e n t i n the r o c k mass. 2. E f f e c t of s t r e s s :  (a /aj_) c  207  a  i s usually  c  core.  When  obtain  this  by l a b o r a t o r y t e s t i n g  i s not p o s s i b l e  o  of  can be  c  drill  roughly  estimated u s i n g a Schmidt hammer o r t h e p o i n t l o a d t e s t . o± i s b e s t estimated by numerical m o d e l l i n g . 7.3.2, a s e r i e s parametric numerical  o f curves  study  based  on  modelling,  common l o n g i t u d i n a l  adjustment  two  constructed  and t h r e e  can be read  from  a  dimensional  on t h e curves f o r  and t r a n s v e r s e open s t o p i n g l a y o u t s  and a range o f pre-mining The  has been  In s e c t i o n  stress  ratios.  r a t i n g f o r s t r e s s can be read from  figure  7.4. Effect of j o i n t The  critical  having the  orientation:  joint  the smallest d i f f e r e n c e  stope  surface.  are t h e d i f f e r e n c e between surface. from The  the  by  the j o i n t s e t  i n d i p and s t r i k e  with  The two d e s i g n parameters r e q u i r e d i n d i p and t h e d i f f e r e n c e  critical  The r a t i n g  joint  and  i n strike  t h e designed  f o r the c r i t i c a l  joint  stope  i s assessed  f i g u r e 7.19. shear s t r e n g t h o f t h e c r i t i c a l  the r a t i o joint of  i s represented  of J r / J a .  while  j o i n t i s estimated by  J r q u a n t i f i e s t h e roughness o f t h e  t h e J a r e p r e s e n t s t h e degree o f a l t e r a t i o n  the j o i n t surface.  E f f e c t of gravity In  a gravity  fall  or slabbing s i t u a t i o n , 208  the e f f e c t of  gravity  i s estimated  surface, - The  using figure  effect  function movement  from the  of  of will  dip  occur.  design  7.20.  gravity  the  i n c l i n a t i o n of the  in of  a the  The  sliding joint  rating  is  situation along read  is  which from  a the  figure  7.21.  5.  Stope s i z e and  - The and  hydraulic shape  shape radius  and  is  p e r i m e t e r / a r e a of the  The  r e p r e s e n t s the e f f e c t of stope s i z e calculated  stope s u r f a c e  g e o t e c h n i c a l parameters are  techniques that  can  amount of p r a c t i c e . model can  be The  by  learned input  under  ratio  quickly,  but  data f o r the cost.  of  the  analysis.  l a r g e l y based on  then be c o l l e c t e d at low  209  the  observational  require  a  application  certain of  the  CHAPTER 8 DATA BASE AND 8.1  MODEL CALIBRATION  INTRODUCTION Much  complete  importance data  base  was  given  because  of  to the  the  empirical  study. The m a j o r i t y of the f i e l d work was summers  of  198 6  and  1987  Hudyma, MASc student. visited, methods  and was  data  by  the  More than  from  collected  form  the  o b j e c t i v e of the mine v i s i t s was  undertaken  author  mines data  comprises  cable bolted  175  cases  of unsupported  of  assisted  by  a  this  Marty  o p e r a t i o n s were  using  open  base.  A  stoping  principal histories  The t o t a l data base  stopes and  67  cases of  stopes. The a n a l y s i s of case h i s t o r i e s has  to understand  of  d u r i n g the  t o back a n a l y z e case  of open stope's s t a b i l i t y and i n s t a b i l i t y . now  nature  f o r t y mining  thirty-four to  construction  helped  f a i l u r e mechanisms found i n open stope mining  and  formed the b a s i s f o r the c a l i b r a t i o n of the d e s i g n method. The  calibration  accepted 1987). The  rock  procedure  engineering  used  design  the components of a widely methodology  f l o w c h a r t concept has been adapted  Brown,  f o r the e m p i r i c a l  development of the d e s i g n method as shown below:  210  (after  SITE CHARACTERIZATION D e f i n i t i o n o f geomechanical p r o p e r t i e s o f the host rock mass  GEOTECHNICAL MODEL FORMULATION Conceptualization of s i t e c h a r a c t e r i z a t i o n data  DESIGN ANALYSIS S e l e c t i o n and a p p l i c a t i o n o f mathematical and computational schemes f o r study o f t r i a l d e s i g n  ROCK MASS PERFORMANCE MONITORING Measurement o f the performance of the host rock mass d u r i n g and a f t e r e x c a v a t i o n  RETROSPECTIVE ANALYSIS Q u a n t i f i c a t i o n o f i n s i t u rock mass p r o p e r t i e s and i d e n t i f i c a t i o n o f dominant modes of rock mass response ( a f t e r Brown, 1987) The  site  defined in  the  characterization  (using the g e o t e c h n i c a l  i n chapter 7) f o r each case h i s t o r y has been field  with  the  assistance  of  mine  parameters performed  staffs.  The  formulation  of the  parameters  into  geotechnical  factors  representing  open stope i n s t a b i l i t y 7.1).  The  model c o n s i s t s the  (also described  Mathews e m p i r i c a l  the  model  stope This  calibration.  surface  was  The  method  that  section  1.3).  effect stope  predicts  of  The  each  factor  on  As  a  other  modifications  mass  performance  as  stable,  unstable  the  sub-objective  overall  the  stability  result,  of  new  have  stability  of of  analysis  accuracy  parameters  t o the  as  the  most  or  each  caved.  developing  openings  the  have  of  been  re-calibrated,  number and  a  (ref.  prediction  parameters  been  for  for  investigated the  of  figure  served as a g u i d e l i n e  retrospective  stability.  created,  the  i n chapter 7 and selected  the  sources  rock  classified  i s i n accordance w i t h  potential  method was  s u i t a b l e d e s i g n a n a l y s i s approach and  of grouping  and  s t a b i l i t y graph have  been proposed.  8.2  DATA COLLECTION  The visits was  c o l l e c t i o n of at  to  the  and  subsequently were  convenience  understand  practices  the  the  geological  a  selected  high  had  of  mine  extraction  investigated.  minimum:  data  for The  power  hammer.  spot  be  done d u r i n g  mine o p e r a t o r s . history  and  sequence.  in-depth  use  Direct  to  of  layouts,  mine  first  task  the  and  case  equipment  was  reduced  a  underground  mining  Areas of the mine were  study  light,  212  The  short  Brunton  histories  compass  observational  to and  the a  methods  such  as  rock  mass c l a s s i f i c a t i o n  and  used t o c h a r a c t e r i z e the rock mass. more  sophisticated  compressive  equipment  geological  mapping were  The parameters measured by  (pre-mining  stress  and  uniaxial  s t r e n g t h ) were p r o v i d e d by the mines from  existing  in-house or c o n s u l t a n t s t u d i e s .  8.3  DATA BASE  The  total  data  base  i s comprised  of  175  from Canadian open stope mining o p e r a t i o n s . the  data  stress case  base  i n c l u d e s : the  c o n d i t i o n and  histories.  estimate access  On  physical  for site  information i n the  c o n d i t i o n s a s s o c i a t e d with  the  some o c c a s i o n s ,  reason,  total  the  stress  i t was  accurate  has  also  been  The geomechanical  calibrated  with  complementary tables:  containing  data  one  calculation  the  of  not  the  t o the l a c k of  lack  of  background  for instance).  data,  and  a  i s less  included  p o s s i b l e to  For  i n t o a main data  complementary  accurate.  i n the  this  data  Data  from  complementary  data  model d e s c r i b e d i n chapter 7, w i l l  main  base.  providing the  the  been d i v i d e d  base c o n t a i n i n g i n f o r m a t i o n t h a t literature  or  measurements  data base has  c o n t a i n i n g the  histories  characterization,  characterization,  (no  base.  mass  The  a l l the parameters with c o n f i d e n c e due  information  base  rock  case  data  base  Each  data  the  rating 213  confirmed  information  parameters, and  using  base i s p r e s e n t e d  background  geotechnical  parameter  and  the  and  modified  the  be the  on  two  for  the  second  stability  number f o r each case h i s t o r y . calculation  of  the  stress,  critical  all  tables,  the  The  modified  joint  and  i n order  f o u r f a c t o r s i n v o l v e d i n the  stability  number  g r a v i t y ) are to  facilitate  (block  shown as the  size,  headings  on  identification  of  t h e i r r e l e v a n t parameters and background i n f o r m a t i o n .  8.3.1  D e s c r i p t i o n o f the main data base The  main data base i n c l u d e s 84 case h i s t o r i e s .  shows the first  background  three  Table  i n f o r m a t i o n f o r the main data base.  columns  identify  the  case  histories  by  8.1 The  a  mine  number (at the request of many o p e r a t i o n s , mine names have been kept  anonymous) ,  investigated. stress  a  case  and  the  stope  Column 4 i s the b l o c k s i z e f a c t o r  condition  is  given  column 6 f o r r e l a x a t i o n . stress  number  graph  (figures  possible  with  effects.  Four  in  characterization  5  for  T h i s i s determined 7.7  to  underground types  column  7.17)  visual  of background  and  (RQD/Jn).  The  compression  and  u s i n g the  are  in  stope  strike.  of  of the e f f e c t of j o i n t o r i e n t a t i o n .  s u r f a c e and  indication  Column 7  tends  critical The  to  joint,  be  anisotropic).  represented  by  The Jr/Ja,  the  difference  of the a n i s o t r o p y of  the rock mass (blocky rock tends t o be i s o t r o p i c w h i l e rock  stress  j o i n t and  column 8 i s the r e l a t i v e  Column 9 g i v e s an  where  r e q u i r e d f o r the  shows the d i f f e r e n c e i n d i p between the c r i t i c a l designed  induced  confirmed  observations data  surface  shear  strength  i s found  foliated of  the  i n column  10.  e f f e c t of g r a v i t y can be assessed from the d i p of the  TABLE  8.1  Background i n f o r m a t i o n  f o r t h e main d a t a base.  JOINT ORIENTATION FACTOR ; BLOCK ; | ; SIZE i ! j FACTOR I JHINE  :  1  »  1 (1)  ! ! j  (3)  ', !  1  HW WALL WALL HW HW HW HW HW END HW HW BACK BACK HW BACK BACK HW HW BACK BACK BACK BACK BACK WALL WALL HW HW BACK HW BACK BACK HW BACK BACK  ;! ;! !! ;! ;! ;! ;! ;! ;; ;! ;! ;! ! !! ;1 ;! !! ;! ;1 ;! ;! ; ; ;! ;! ! ;! i ! ;! !! ;! ;! ;! ;!  2  3 4 5  3 4 5  !  5  6  :  5  !  6  ! ! '. !  6 7 8 9  7 8 10 12  13 16 17 18 19  ! 9 ! ii ! ii  20 21 22  ! 12 i 12 I 12 | 12  23 24 25 26 27 28 29 30 31 32  ! 13 1 13 ! n ! 13 ! 13 ! 13 ! 13 !  1*  I 14 !  33 34 35  1*  ! 14 ! 15 ! is  36 53 54 55  ; 19  ! 19 ; 19  19 i ' 19 19  56  ; 20 ! 20  61 62  ! ! ! I  t  !  (2)  i ]  ! !  PLANE ! ! RQD  CASK  57  58 59  1  1  1 1  !  BACK 1J ! WALL BACK ; ! i WALL ; J WALL ! ! ; HW |! ! FW ;! t  "  STRESS FACTOR  1  : ',  (*)  (6)  <5)  ', :  o ) ',  ; ! COMP ! ; COMP ! | COMP  !  45  ! J  5 5  ! ! ; ; ! COMP  RELAX ! ! RELAX ! ! RELAX ! !  15  *o 40 40 6 4  ! ; [ COMP  RELAX i !  ! i s ', 25 ! ! COMP  RELAX ! ! RELAX ; !  i8 6  6  7  i! | ! COMP ! i COMP : I ! | COMP  1 1 8 1 1 90 90 90 90  !! ; ; 1 COMP ; ; COMP  7 7  7  7  7  7  !! !! ;! 29 J !  COMP COMP COMP COMP  !1 ;! ;; j! !; !!  COMP  6 6 29  29  4  29  29 4 1 1 7  7  |  It  15 30 15  !  ! COMP  ! J COMP ! i COMP ! COMP i ! ', COMP ; !  1 1  0 0  !  7  25 30 30 u ii H ii  BLOCK SHAPE  CRITICAL JOINT  RELAX j J DIP ! STRK ! DIFF J DIFF  ;! COMP  /Jn  ! JJ  I ! RELAX ! ! !  70 <> 50 40  ! RELAX ! ! ! RELAX 1 !  20 10 10 20  RELAX RELAX RELAX RELAX  30  ; ;  30 30  !  30  !! ;! J ! i!  0 10 20  ! ;  (10)  i  35 0 0 0  BLOCKY BLOCKY BLOCKY FOLIATED BLOCKY BLOCKY BLOCKY BLOCKY FOLIATED BLOCKY BLOCKY BLOCKY BLOCKY BLOCKY BLOCKY BLOCKY BLOCKY BLOCKY BLOCKY BLOCKY BLOCKY BLOCKY BLOCKY BLOCKY BLOCKY BLOCKY BLOCKY BLOCKY BLOCKY BLOCKY BLOCKY BLOCKY BLOCKY BLOCKY BLOCKY FOLIATED BLOCKY BLOCKY FOLIATED FOLIATED FOLIATED  ; ; ! ! ; ; ! ! ; !  3.0 1.0 1.0 1-5 1.0 1.0 10 1-5 0.8 0.6  !  45  ;  ! ;  85 85  ; ;  !  30  ;  45  !  1 !  90  !  90 90  :  60  !  7  ;; 1 ! !  90 90  ; ! ; ; ! ! ! ! 1 | !  I  2.0 0.25 0.25 1.0 1.0 1-5 1-5 1-5 1-5 2.0 2.0 2.0 2.0  ! ! ! ; ! ! ; ! !  21.5 .0 2.0 1.0 1.0 1.0 1.0 1-5 1.5 1.5 1.5  ! ! ! ! ! ! ! ! !  0 0 0 0 0 0 0 0 0  ! ! ! !  0 0 0 0 0 0  1 !  !  ! ! ; RELAX 1 ! :  0 20 10 10 10 0 10  ! ! ! ! !  !  0 0 0 0 0  90  : ! !  0 0 0  ! ! !  0 0 0  1 1 !  ;  1 1  90 90 90 90  so  ! ! ! !  I !  1  !  ! CRITICAL ; STOPE ! ! HYD. {i ASSESS. ! JNT DIP | PLANE D I P i 1 RADIUS !  !  !  1 !  BLOCKY/ ! J f FOLIATED ! /Ja  ; SLIDING  ! ! SIZE ! ! AND ! ! FREEFALL/ | ! SHAPE ; BUCKLING ! 1 FACTOR 1 !  (9)  90 90 90 30  J  i SHEAR ! STREN.  EFFECT OF GRAVITY  (8)  10 10 10 N/A N/A N/A N/A 0  J  t  7  !  RELAX i !  COMP COMP COMP COMP COMP  0 0  ! ! : :  [  25  1  1  1 !  1 J  ! ! !  I ! 1  01.5 .5 1-5 1-5 0.5 1.5 1-5  i !  (ti)  ?5 5  so 7 0  :  ; !  ; ! ! !  70 40 40 20  ; ; ; ;  !  65 65  ! ;  !  20  |  ! !  30 30  | ;  ;  30  ;  ',  30  ! !  90 BO  ; i  1 !  so  ! !  N/A N/A N/A  ; !  N/A  !  ;  ; |  I  1 20 !  i  80  ; ! !  10 10 10  ; i ! !  '!  90  J  '! !  10 8  ! ;  ! I !  90  !  II  70  7  o  ;  ! 1  (12)  :!  (14)  )!  (13)  90  ', 1  90  ; .'  90  !! ;! ;! |  ; ; STABLE ; 1 UNSTABLE ! J CAVE - i ! ; UNSTABLE 1 4 . 0 ; 1 STABLE I STABLE i 5i -. 2o I! I STABLE 8 . 5 ! | STABLE 4 . 7 ! ; UNSTABLE 9.1 ; ; UNSTABLE 8.3 ! 1 STABLE CAVE 5.8 ; ! 4.2 : STABLE 8 . 8 ; 1; STABLE 3.5 ; J UNSTABLE 1.8 ; ! STABLE 4.7 ! 1, STABLE STABLE s.s :' 2.1 ; I STABLE CAVE 10.5 i ; CAVE ii-3 !; CAVE 12.2 ! ; 4.11 ; STABLE STABLE -6 ; 1 7 . 6 ! 1 STABLE 9.0 ; 1 STABLE STABLE 16.6 ; ! 4 . 0 ! i STABLE 23.0 ! ! STABLE 1 0 . 7 J ', STABLE 1 0 . 5 | J • CAVE 9 . 0 ; ! STABLE 2 . 4 ; I STABLE CAVE 6.8 ! J 8.0 ; CAVE CAVE 1 9 . 0 : J1  5.0 8.9  7  1  !! ;; ;! 5 !! so ; ! 0 !! 0 :i 90 ; ; 0 !! 0 !! ! 55 55 ', ; 0 !! 0 !! 0 ;! 0 ;! 0 ;; 90 :! ' 90 : j 60 ; ! 90 ;! 0 i! 90 ;| 0 '. ; 20 1 ! 60 -| ! 0 !! 0 !! 0 i! 90 ! ! 0 ;! 90 ; : 90 ! ! ! 70 ! ! 70 7  5  7  1  7  1  1  1  3.7 8.4 4.5 -5 -5  i!  7  1  ,  1  STABLE STABLE STABLE  !! ! 1 STABLE STABLE !!  7  1  FAIL MODE  (15)  (16)  DISC. BLOCK JOINTED RM JOINTED RM JOINTED RM DISC. BLOCK DISC. BLOCK DISC. BLOCK JOINTED RM JOINTED RM JOINTED RH DISC. BLOCK DISC. BLOCK DISC. BLOCK DISC. BLOCK DISC. BLOCK DISC. BLOCK DISC. BLOCK JOINTED RM DISC. BLOCK DISC. BLOCK DISC. BLOCK JOINTED RM DISC. BLOCK JOINTED RM DISC. BLOCK DISC. BLOCK DISC. BLOCK INTACT ROCK DISC. BLOCK DISC. BLOCK JOINTED RM JOINTED RM INTACT ROCK DISC. BLOCK DISC. BLOCK JOINTED RM DISC. BLOCK DISC. BLOCK JOINTED RM DISC. BLOCK DISC. BLOCK  7  7  90 90  TYPE OF BEHAVIOUR  1  3a 3a 3d  3c 3b 2a  la  2a 2a 2a  3a  2a 2a 3d  1  Background i n f o r m a t i o n  8.1  TABLE  f o r t h e main d a t a base  JOINT ORIENTATION FACTOR BLOCK SIZE FACTOR  NE  CASE  PLANE  (1)  (2)  (3)  !  22 22 22 22 22 22 22 22 22 22 22 22 22 22 22 22 23 23 23 27 27 27 28 28 28 28 28 29 30 30 30 31 31 31 31 31 31 31 31 31 32 32 32  132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 155 , 156 157 158 159 161 164 165 166 170 171 172 173 174 175 176 177 178 1 180 183 ; 184  HW HW BACK BACK BACK BACK BACK BACK HW HW HW HW BACK  ! ! ! ! ! ; {; i ;! ',; ;; !! ;;  BACK' BACK BACK BACK HW  !l ;; ;! !! ;|  HW BACK BACK WALL HW. END FW BACK BACK WALL BACK  ; ;; ;; !] |; ;! ! ]! ;, i; |1  HW FW BACK BACK BACK BACK BACK  I  COMP  RQD /Jn  I  !  STRESS FACTOR  (4) 6 6 5  13 13 13 13 13 8  8 8 8  i  i | j ;; ;; !! I; !]  WALL BACK ;1! BACK ! BACK ; ; HW ; ; WALL ; 1 HW ;  1  8 8 8 8 11 5 5 15 15 15 16 16 9 10 8 3 14 14 9 18 18 18 18 18 18 18 18 18 6 16 6  !  (5)  CRITICAL JOINT  RELAX  [  (6)  DIP DIFF  ||  (7)  STRK DIFF  j  (8)  ; ; RELAX | i 10 ! 20 ! COMP ! 20 io i 0 i COMP j !! 30 ; COHP j 0 ! COMP ! !! 50 50 | | 0 0 ! COMP ! II 50 | 0 I COMP ! 50 | 0 ! COMP ! ; COMP ; II i o 50 | | 0 i COHP ; 0 i i o | ! COMP ! 0 II 4 | | COMP ! 0 !! 7 | 0 ! COMP ! !! i o | ! COMP ! 0 II io I 0 ! COHP I !! io ! COMP ! 0 II i o ', COHP ! 0 II o ) ! ! RELAX ;! o ! 0 ; COMP ; 0 II o | ; COMP ; 0 II io I 0 II io | 1 COMP ; ; ; RELAX ]; o ; 45 ; ! RELAX I; 10 ! 15  !1 I 11 1! 1  1 1  1; COHP COHP ; ; 1 COMP i ! COHP ;  !! II  io io  1II1  20o  1 COHP ! II 20 1! COHP !! RELAX !| 600  11  I| COHP JI RELAX U i! II COMP COMP 1I | COMP | 1I COHP COHP 1; 1| COMP COHP 1| I COHP j | COMP | ! COMP | ', COHP ;  II II  10 35 35 35  1I ;|  1 1I J1 | |  1 ! 35 11 35 | 1 1 20 !'. *5 | 1 ! *5 1 1 *5 1 ! 0 II 0 | 11 0 |  75 25 0 0 0 0 0 0 60 60 60 60 | 60 25 | 60 60 | 60 |0 | 0 0  BLOCK SHAPE  SHEAR STREN.  BLOCKY/ FOLIATED  /Ja  EFFECT OF GRAVITY  (9)  |  (10)  J  FOLIATED FOLIATED BLOCKY BLOCKY BLOCKY BLOCKY BLOCKY BLOCKY FOLIATED  i | J | | | i j !  1.0  | ! l ; |  FOLIATED FOLIATED 1J FOLIATED BLOCKY BLOCKY BLOCKY BLOCKY  1| | | |  BLOCKY 1 FOLIATED FOLIATED 1| BLOCKY BLOCKY  1|  BLOCKY BLOCKY BLOCKY BLOCKY BLOCKY BLOCKY  1 1 1 1 1|  FOLIATED BLOCKY 1| BLOCKY | FOLIATED BLOCKY BLOCKY BLOCKY  1I | |  BLOCKY BLOCKY  1|  BLOCKY BLOCKY BLOCKY  1J |  BLOCKY 1 FOLIATED I BLOCKY 1 FOLIATED 1  1.0 10  2.0 2.0 2.0 2.0  2.0 1.0 1.0 1.0 10  1.0 l.o 1.0 1.0 2.0 0.1 o.i 2.0 2.0 2.0 2.0 2.0 1.8 2.5 2.0 1.0 1.5  HYD. RADIUS  (11) 80  80 30 50  I j | • |  1|  |  70 70 70  1 1|  10 io 10 10  | ; | |  1|!! I  i l! |  || I! !|  1 1| 11| | || |  || ||  1 | j 11  1.5 15  !| |  1-5  i; |  1.5 1.5  1J|  1.0  STOPE PLANE DIP  ; |  1.5  .1-0 1-5  CRITICAL JNT DIP  1| J 1I  11 IJlI  1.5  FREEFALL/ BUCKLING  50 50 50 50 70  1.5 1-5 1.5  1.5  SLIDING  SIZE AND SHAPE FACTOR  1l1 J J  700 70 10 10 90  ! | |  1| | ; | |  80 80 80  1 1|  20  |  700 60 90 80  65 65 65 65  65 70 65  1| 1| 1 1 1 1! | I |  65 65 70  1 1|  90 80  | |  (12)  |  90 90 0 0 0 0 0 700 70 66 63 0 0 00 700 70 0 0 90 90 90 90 0 900 900 90 30 30 30 30 30 90 20 20 20 70 90 80  1  |i I  1 1 !1 1', 1 !I ! 1| 1I I 1| ! 1 1 || 1 1 || 1I 1 1| 1 |1 I1 1 1| | 1 1| | |1 1 1| 1| 1 1 1J !| 1I 1| ', I |1 1| !I 1J 1 1 1| 1| 1| 1 || 1  (13) 5.6 6.7 1-9  '2 1  2.4 2.9 3.1 3.0 7-5 8.1 5.3 5.7  1.9 1.8 2.1  2-3 5.0 9.0 11.3 10.0 6.7  18.0 9.7 5.6 8.4 3.4 7.6 20.0 8.6 9.9 9.9 12.5  15.0 15.9 7-7 5.4 11.6 7.3 9.9 l t6.9 .l 4.9 6.7  (cont).  ASSESS.  1  (14)  I STABLE | STABLE | STABLE | STABLE | STABLE | STABLE I STABLE I STABLE | STABLE | UNSTABLE | STABLE | STABLE I STABLE | STABLE 1| UNSTABLE UNSTABLE 1 1 1 I1  STABLE CAVE CAVE CAVE STABLE  | ]  STABLE STABLE  1|  STABLE STABLE  1| | I  STABLE CAVE CAVE CAVE  1 STABLE 1| UNSTABLE CAVE 1 CAVE | CAVE I STABLE | STABLE | UNSTABLE I STABLE | STABLE 1 UNSTABLE 1| UNSTABLE STABLE J STABLE  TYPE OF BEHAVIOUR  (15)  (16)  JOINTED RH JOINTED RM DISC. BLOCK DISC. BLOCK DISC. BLOCK  | | | |  DISC. BLOCK DISC. BLOCK DISC. BLOCK JOINTED RM JOINTED RH DISC. BLOCK JOINTED RM DISC. BLOCK DISC. BLOCK  1 ! | | | | ] { |  DISC. BLOCK DISC. BLOCK DISC. BLOCK JOINTED RH JOINTED RM DISC. BLOCK DISC. BLOCK JOINTED RM DISC. BLOCK DISC. BLOCK JOINTED RH DISC. BLOCK JOINTED RM JOINTED RH DISC. BLOCK JOINTED RH JOINTED RM JOINTED RM JOINTED RM JOINTED RM DISC. BLOCK DISC. BLOCK DISC. BLOCK DISC. BLOCK DISC. BLOCK DISC. BLOCK JOINTED RH DISC. BLOCK JOINTED RH  I 1  3c  2a 2a 3d 3c 2a  3a 3c 2a 3d 3a 3a 3a 2a | | | | |  2a 3c  critical  joint  (column  11) i n the case  of a s l i d i n g  failure  and by t h e i n c l i n a t i o n  (column  12) f o r the o t h e r modes o f f a i l u r e .  shape a r e accounted  o f the designed  f o r by h y d r a u l i c  mode of  stope Stope  radius,  surface s i z e and  column  13.  The  assessment o f the stope plane s t a b i l i t y i s g i v e n i n column 14. The  mode o f f a i l u r e  can be determined  using  figure  6.18 and  columns 4 t o 12. The  second  table  parameters necessary the  background  (8.2) c o n t a i n s  the c a l c u l a t e d  f o r the d e s i g n a n a l y s i s .  information  previously  8.1.  Column  17 i s the induced  7.4.  The magnitude  figure  estimated  from  direction  (longitudinal/  mining from  stress  figure  critical  figures  field.  7.19.  joint  7.7  The d i f f e r e n c e  necessary  i s given  gravity  t o read 8.1.  i n column  joint  factor  and p r e -  can be read  7.19  Column  a r e found i n  joint 19  o f the  shear  i s the  index  sliding  f a c t o r and i s e v a l u a t e d u s i n g f i g u r e 7.21 and column 11  of t a b l e  8.1.  Column 20 i s the g r a v i t y  modes o f f a i l u r e  and i s estimated w i t h  12 o f t h e background i n f o r m a t i o n t a b l e (col.  can be  i n d i p and s t r i k e figure  from  t o t h e mining  geometry  The c r i t i c a l 10.  (ay)  stress  stope  to table  calculated  according  transverse),  ( t a b l e 8.1).  identical  factor  o f induced  The c r i t i c a l  columns 7 and 8 o f t a b l e (Jr/Ja)  stress  t o 7.17  I t i s based on  described  Columns 2, 4, 10, 13 and 14 have been kept  input  13)  and stope  from t a b l e 8.1.  assessment  Finally,  f a c t o r used  f o r other  f i g u r e 7.20 and column (8.1).  Hydraulic  ( c o l . 14) a r e taken  radius  directly  the s t a b i l i t y number ( c o l . 21) i s 217  TABLE  8.2 I n p u t p a r a m e t e r s from t h e main d a t a base n e c e s s a r y f o r open s t o p e d e s i g n b a c k - a n a l y s i s . ;  ILOCX  : sizz CASE  j  :  ;  IQD  /Jn  (2) ' : <*> : is 23 :; 66 I  ;  :  4 S  !  6 7  \  8  i  7  !1 40 40  : !  i12o ;; ', ; it i ! 17 i i is 19 :: ! 20 ; ! I ii22 ;; i ! 23 1 ; '  40 6  |  13  !  24  25  !  ;  4  7  is 25 25 30 30 U ll 11  11  t7  17 22?6 ;! I ! 17 i  17  28  : !  25  :! ;  8 17  17  i 3i : : 9090 3332 !: : 90 30  I  3*  !;  i 36 :: ; 5* :! i ss : J 5576 :: ! 59 ; ;! 6i ; ;! |  35 53  ;  58  62  132 133 134  135 137 138 136  139 140 141 142  143  144 145 146  147  148 149  150 151 152  153 155 156 157 is8 159  161 116564 166  170  171 172 173 174  i7s 176  177 178 180 183 184  ;  .:  :! ;! ;  ; !: ;; ;; ;! : ;; :: i :: ;! ;: :: : ;; ; ; ;: : ; ! i !: ! ;: !! ; ;: ; :; ;: :: ; ! ;; : ;: ; ; ;! : j; i: ; ;: ; ;; ! !  ;  !  !  ;  !  90 6  6  29 29 294  29 294 171' 6 6  5 1313 1313 13 8 8 8 8 s s s s 15 15 15i6 169 io 8 8  11  8  3 14  u9 18 is is is 18 i< i> is 18  6  166  STRESS  J O I N T ORIENTATION  (REF. FIC.  CRITICAL  7.4)  (17)  JOINT (18)  1.0 0.2 0.1 1.0 1.0 1.0  0.65 0.20.25 0.2  1.0  1.0  0.3  0.4  1.0  1.0 1.0 0.1 0.1 1.0 0.1  1.0 1.0 1.0 1.0  1.0 1.0 1.0 1.0 1.0  1.0  1.0 1.0  1.0 1.0  0.2 0.2 0.2  0.15 0.85 0.6 0.4  0.2 0.2 0.2 0.2 0.2  0. 3 0.1 0.1  0.7 1.0 1.0  0.4  1.0 1.0 1.0 0.1 1.0 0.1  oa 1.0 0.1 1.0 1.0 1.0 1.0 1.0 1.0 1.0  1.0  0.2 0.2  0.2 0.3  0.2 1.0  0.3 0.3  0.3  0.2 0.2 0.2 0.6 0.6  0.6 0.6 0.6 0.3 0.3  0.2  0.2 0.2 0.2 0.2  0.2 0.2 0.2 0.2 0.2  0.2 0.5  0.2 1.0 0.2 0.2 0.2 0.2 0.8  0.2 0.2 0.8  0.8 0.8 0.8 0.8 0.3  0.5  0. 0 . 88 55 0.0.3 85  0.5 1.0 0.1 1.0  i.o i.o 1.5 i.o 1.0 i.o 1.5 o.i o.6 2.0  ;:  0.3 0.3  6.5  : :: 2.2.5s : | ; j :: i 5.0 : J 3.5 ;;  i.o ; i.o :; 1.5 1.5 i l.s :: 1.5 2.o ;  2.0 2.0 2.0 2.0  i.o i.o i.o i.o i.o i.o i.o i.o 2.0 o.i 0.1 2.0 2.0 2.0 2.0  2.0  3.0  ; ; ; ; ; : : :; :  2.0  i  ;  218  !  ::  IO.S  !  11.3  :: ;  12.2 4.1 7.6  7.6 9.0 i6.6 4.0 210.7 3.0 10.5  9.2.4o  6.8 a.o i9.o 3.7 8.4  4.5 7.5 7-s  5.6 6.7 1.9  2.1 2.4  2.9 3.1 3.0 78.1.5 5.3 5.7  1.9  i.s 2.1  2.3  : s.o ; | 9.0 6.2.0o :; ! 11.3  1.5  :  8.8  6.o  : :: ;: : ;; i ; :;  I.S  HYD.  3.3.00  3.0  :  IO.O  ::  6.7  a.o ; ;: : 8.0 i : 2.0 ', 2.o ; ;; s.o : 2.0 ! :: 8.o : : 2-8 i ; 2.8 2.8 :1 2.8 ;: ! 2.8 i : 2.5 ', ! 2.5 ; 2-5 : : 6.o : :: s.7.0o :; ;  B.O  ;;  !  N  ASSESS.  1  RADIUS  : : ; !  2.0 i 2.o ; i 2.0 ; ! 2.o : ! 5.0 i 1 >.o ; : 2.0 J I i.o ;; :i 2.0 2.3 ,' ! 5.0 ! :: 2.2.0o :: ; 2.0 ! ; a.o ; : 2.o ; :1 8.o : 8.0 ! ! 6.o :! i 4.0 : a.o : ! a.o ; 1 2.0 ', ', 2.o : 1 2. o :: ! 2.0 1 2.0 J 1 2.0 ;| ! 6.0 1: 6.o ; : s.s ; : 5.5 i 2.o ; | 2.2.00 !; ;: 2.0 2.0  ::  : ', | ! ! !  ;  !  i.8 2. s 2.0 i.o 1.5 i.s i.s 1.5 i.s i.s 1.5 i.s 1.5 1.5 i.o 1.5 i.o  ;  (i3> s.o 8.9 7.7 3.7 ! 1 7.1 a.o ; 1 14.0 8.0 ! ;: u.o 6.5 1 5.2 s.4.7s :: 6-5 i ! 9.1 7.0 ! 8.3 2.0 ! ! 5.8 2.o ; : 4.2 8.0 ! 2.0 : ! 3.5 2.0 ! ! l-> i 4.7 «.s >2.1.8 2.0 ;; ::  (20)  2.0  : : ; :  ;  1 ;  4-5  ; ; j :: ; ; : ; ; ;: ; : i ; : :;  ;| : :  FREEFALL/ SLABBING  :  i.s ;1  i.o i.o i.o i.o 1.5 i.s i.s i.s i.s o.s i.s 1.5 o.s i.s 1.5 i.o i.o i.o 2.0  ;  !  0.25 ; 0.25 ;  ;  0.5 0.5  3.0  0.2  0.2 1.0  SLIDINC  : <i9)  (10)  2.0 2.0  1.0 1.0  1.0 1.0 1.0 0.1  1  EFFECT  OF c u v m  /J«  0.2  0.3 0.3  0.6 0.5 0.4 0.4 0.3 1.0  Jc  0.3  0.6 0.9  0.2 1.0 1.0 1.0 1.0 1.0 1.0 0.1  i  2.0 J 2.0 ; 2.0 1  0.2 0.2  0.1 1.0 0.4 0.5 0.5 0.5 1.0  ) :  FACTOR  FACTOR  u.o 9.7 s.8.46 3.4  7.6 8.9.96  20.0 9.9  i2.s  15.0  is.9  7.7 5.4 u.6  7.9.9 3 u.i 6.4.99 6.7  (21) 228 0.7 0.3 7.8 320 320 260 18 0.7 5.5 42 1.1  1.1  144 2.4 6.6 15  15  6.6  (i*) : STABLE  1  UNSTABLE CAVE  ; ;  UNSTABLE  1  STABLE  ,'  STABLE  1  STABLE STABLE UNSTABLE  1 1 |  UNSTABLE  |  STABLE  1  CAVE  !  STABLE STABLE  t ;  UNSTABLE  |  STABLE  1  STABLE  ',  STABLE  1  STABLE  1  14 14  CAVE  14  CAVE  ;  CAVE  !  14  STABLE  1  6.9 20  STABLE  34 720 720 72 3.9 18  13  8.a  8.8 8.8  5.2 3.5 352 5.2 45 3100 9.4  0.2 19 16 13 1103 15 15 9.2 9.2 0.3 1.0 0.3 0.3 5.9 0.8 0.8 4.8 12  120 19 10 26 1.0  0.6 4.8  3.3 31 8.3 60 60 60 60 60 32 29 29 2109 5.812  !  !  STABLE  !  STABLE  ,'  STABLE  !  STABLE STABLE  j 1  STABLE  1  CAVE STABLE  : 1  STABLE  1  CAVE  !  CAVE  1  CA AB VL EE ST  J{  STABLE STABLE  1 !  SS T LE E TA AB BL  J[  STABLE  1  STABLE  !  S TA AB BL LE E ST STABLE  J1 |  STABLE STABLE  : ;  STABLE STABLE UNSTABLE  1 ! !  STABLE  :  STABLE STABLE  ; ;  STABLE  !  UN NS ST TA AB BL LE E U  1I  STABLE CAVE  1 ;  CAVE  :  CAVE  !  STABLE  !  STABLE STABLE  1 ;  STABLE  :  STABLE STABLE  1 ',  CAVE CAVE CAVE  1 : :  STABLE  ',  U NCS A TV AE BLE CAVE  I| !  CAVE  1  STABLE  1  STABLE UNSTABLE  ! |  ST TA AB BL LE E S  i!  UNSTABLE  i  U SNTS A TB AL BE L E II STABLE  1  c a l c u l a t e d by m u l t i p l y i n g columns  8.3.2  4,17,18, 10 and  D e s c r i p t i o n o f t h e complementary The  complementary  histories.  It  parameters)  built  base  displayed  on  table  on t a b l e  8.4.  As  which  8.3  using  comprised  the  same  of  91  case  principles  (and  The background  information  and the d e s i g n parameters are shown  mentioned  have  d a t a base  is  as the main data base.  is  histories  was  data  (19 or 20).  before,  some  degree  i t i s composed of  uncertainty  e v a l u a t i o n of one or more parameters, and d a t a from The  data  from  literature  Pakalnis  (1986).  of  stopes  open  originate  from  of  the PhD  case  in  the  literature.  thesis  of R.  A t o t a l of 68 w e l l documented case h i s t o r i e s a t the Ruttan  operation  i n n o r t h e r n Manitoba  (mine 21 o f the data base) have been s e l e c t e d from the P a k a l n i s study and form the m a j o r i t y of the complementary  8.4  data base.  CALIBRATION OF THE FACTORS COMPOSING THE MODIFIED STABILITY  NUMBER  The c a l i b r a t i o n of the f o u r f a c t o r s composing stability  number  gravity)  was  described  i n section  the c a l i b r a t i o n , factors  is  (block  size,  carried  out  8.1.  stress, following  Because  joint the  the m o d i f i e d  orientation design  of the e m p i r i c a l  and  approach nature of  the v a l u e o f the r a t i n g s a s s o c i a t e d w i t h the  completely  arbitrary.  However,  their  relative  w e i g h t i n g must be r e p r e s e n t a t i v e of the i n f l u e n c e o f the 219  TABLE  f o r t h e complementary data  Background i n f o r m a t i o n  8.3 base.  J O I N T ORIENTATION FACTOR  |HINE  O  II  (1)  (2)  21 21 21 21 21 21 21 21 21 21 21 21 21 21 21 21 21 21 21 21 21 21 21 ! 21  1! 2121 ! ! i !  21 21 21 21 21 21 21 21 21 21 21 21 21 1 21 ! 21  1 21 21  I ! ! ! !  CASE  t  21 21 21 21  64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 no  PLANE ;  ;  BLOCK SIZE  ;!  ;  FACTOR  ;;  !!  HW HW HW HW HW HW HW HW HW HW HW HW  ; ! ; ! ; ! ; ! ; ! ; ; ! ; ! | ; ; ! ; !  HW HW HW HW HW HW HW HW HW  I!  HW HW FW HW HW HW HW HW HW HW HW HW HW HW HW HW HW HW HW HW HW HW HW HW HW HW  1  11  ; ; ] ; ; ; ; ;  i  !  i ! ; i  ! ; i i 1 | 1 | 1 |  ] 1 !  j ! ; ; ; ; ] ; J | ] ; ; ; ! ; ; !! ; ! ; ; !! | !  t 1  i!  (4) 4 3 3 3  | !; i; i! !|  18 6 6  !| !! ;;  i 16 8 8 is  !! ii ;! !; i i  !  4  33 3 i i is 3 l-s is  11!! ;; i  :; ;; ;; : i  ' 1i  20 20 20 20  :; ;; ;; ;;  33 3 3  !; || ;! i i  3 1! 3 i i i i ! • ii 8i 3 3 3  1;;!  6  i; i! ii ii | i  6  !  6  I1 i  15 2. ! | 32 3  !!  11| ! ;;  CRITICAL  !  !! C0HP ! RELAX \ i J | | ! !  ) RQD ! /Jn  (3)  STRESS FACTOR  (5)  j  (6)  i ; ; ; ! ! ; ; ; ; ! i ! ; i ! ! ; i ;  RELAX RELAX RELAX RELAX RELAX RELAX RELAX RELAX RELAX RELAX RELAX RELAX RELAX RELAX RELAX RELAX RELAX RELAX RELAX RELAX  i ;  RELAX 1 RELAX !  ;! ! ; ; ; ; ; ; ! ; ; ! ! i ! ; ; ; l ; ;  1 RELAX ; ; RELAX ] ; ; ; ! ! |  RELAX I RELAX ; RELAX ; RELAX ; RELAX ! RELAX ]  i; ;  RELAX 1; RELAX RELAX ;  1 i i ; ; i ; ! ! ! !  RELAX RELAX RELAX RELAX RELAX RELAX RELAX RELAX RELAX RELAX RELAX  ; ] ! ; ; ! ; ; i ! ;  1 RELAX i i RELAX i i RELAX J  ! ! ! ! ! !  t !  JOINT DIP i DIFF |  STRK DIFF  (7) i  (8)  o o o o o o o 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0  0  0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0  ! i i ! i : i i ! i i ! ! i i  1 i i i  1  i i i i i  1! 1!  o o o o o o 0  o o o o o o o o oo ° 0  o o o o o o o o o  i i i i  o o o o o o  !  °  i i i i ! ! ! i ! i i i  o o ° o o o o o o o o o  BLOCK SHAPE BLOCKY/ FOLIATED  (9) FOLIATED FOLIATED FOLIATED FOLIATED FOLIATED FOLIATED FOLIATED FOLIATED FOLIATED FOLIATED FOLIATED FOLIATED FOLIATED FOLIATED FOLIATED FOLIATED FOLIATED FOLIATED FOLIATED FOLIATED FOLIATED FOLIATED FOLIATED FOLIATED FOLIATED FOLIATED FOLIATED FOLIATED FOLIATED FOLIATED FOLIATED FOLIATED FOLIATED FOLIATED FOLIATED FOLIATED FOLIATED FOLIATED FOLIATED FOLIATED FOLIATED FOLIATED FOLIATED FOLIATED FOLIATED FOLIATED FOLIATED  SHEAR STREN.  Jr /Ja  E F F E C T OF j SLIDING  i 1 CRITICAL | JNT DIP  (10)  i  1.5 1.5 0.8 0.8 0.8  i  '65  !  65  ! !  82 82  3.0  0.8 0.8 0.25 3.0 1.5 1.5 3.0 0.25 0.25 0.25 0.25 3.0 0.8 1.5 3.0 3.0 3.0  3.0  0.8  0.8 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25 2.0 1.0 1.0 1.0 0.25 0.25 0.25 2.0 0.8 0.8 1.0 1.0  1 ;1  (ID  82 55  ;  90 90  ! i I ;  25 90 55 55 60  ;  90  :  25  1  ; :  ; i i i  1i  !  I  | ! i ! i  1 1i i ! i i i ;  so so 60 65 62 55  65 66 66 90 90 52 52 65 65 65 65 28  90 90 65 60 60 60  !  63  i ! ! ! ! ! !  63 63 20 80 80 60 60  GRAVITY  SIZE AND  FRKEFALL/ BUCKLING  ! i SHAPE 1 i i FACTOR !  STOPE PLANE D I P  i ! HYD. i; i i RADIUS !  (12) 65 65 82 82 82 55 90 90 25 90 55 55 60 90 80 80 '5 60 65 62 55 65 66 66 90 90 52 52 65 65 65 65 78  90  90 65 60 60 60 63 63 63 70 80 80 60 60  ASSESS.  T Y P E OF BEHAVIOUR  FAIL MODE  (16)  !!  (13)  !!  (14)  (15)  ii  6.0 i2.o  !; ;!  3.o 9.o 12.0 i6.o 5.o 8.o i6.o  ; ;| J1 ;I ; ; ;1 ;i  STABLE CAVE STABLE  J O I N T E D RM J O I N T E D RH J O I N T E D RM J O I N T E D RM J O I N T E D RH J O I N T E D RH J O I N T E D RH J O I N T E D RH J O I N T E D RH D I S C . BLOCK D I S C . BLOCK J O I N T E D RM D I S C . BLOCK J O I N T E D RM J O I N T E D RM J O I N T E D RH J O I N T E D RH D I S C . BLOCK J O I N T E D RH J O I N T E D RH D I S C . BLOCK D I S C . BLOCK INTACT ROCK D I S C . BLOCK D I S C . BLOCK D I S C . BLOCK J O I N T E D RM J O I N T E D RM D I S C . BLOCK J O I N T E D RM J O I N T E D RM J O I N T E D RM J O I N T E D RM J O I N T E D RM J O I N T E D RH D I S C . BLOCK J O I N T E D RM J O I N T E D RM J O I N T E D RM D I S C . BLOCK J O I N T E D RM J O I N T E D RM D I S C . BLOCK J O I N T E D RM J O I N T E D RM J O I N T E D RM J O I N T E D RM  1; i i1 1 J ! ;; ;i |i !; ii ii i! iI i! ;i i; i! !! ii !i i; ;i ;i ;i :! :i ii ii ! :! !i !! J i ;i |i i! ;I i! ;! J ! ;! !! !! ;! ;! ;! ;!  1  7.0 2.0  no 5.o  14.0 6.0  10.0 n o 9.0 6.0 i3.o  IO.O  !  ;J ;; ;! ;!  ;!  !!  ;|  ;; |J ;; ;; ;  UNSTABLE UNSTABLE CAVE CAVE STABLE STABLE STABLE STABLE CAVE CAVE CAVE CAVE STABLE UNSTABLE CAVE  4.0  ;1  STABLE STABLE STABLE UNSTABLE  4.0  ;I  STABLE  3.0  ; 1;  2.0 7.0 9.0 16.0 8.0 3.0  ;i ! !! i! ;!  TA AB BL LE SS T E CAVE STABLE CAVE CAVE CAVE CAVE UNSTABLE CAVE STABLE STABLE UNSTABLE CAVE STABLE UNSTABLE CAVE STABLE CAVE CAVE UNSTABLE CAVE  i.o 12.0 n.o n.o  5.0  3.o 3.0 6.o i4.o 3.o 8.o no io.o  4.0  io.o 6.0 n.o  1  UNSTABLE CAVE  ;! |; i  iJ !  J! !; ;! !{ ;{ ;j !I ;! !; ;j • !; Ii !!  ;  3d 3d 3d 3d 3d 3d 3d  3d 3d 3d 3d 3d Id  2d  3d 3d 3d 3d 3d 3d 3d 3d 3d 3d 3d 3d 3d 3d 3d  TABLE  8.3 Background i n f o r m a t i o n base (cont). J O I N T ORIENTATION BLOCK SIZE FACTOR  |MINE n  CASE II  (O  (2)  21 ! 21 21 ! 21 ! 21 21 21 21 21 21 21 21 21 21 21 21  21 21  1! 21 21 ! 21  1 ! ! ! !  76 8 8 28 30  1! 3030  ! I ! !  ! ', ! '. ! ! ! ! ! ! !  32 32 32 16 16 16 16 16 16 16 16 16 17 17 17 17  111 112 113 114 US  116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 9 11 14 15 154 167 168 169 179 181 182 37 38 39 40 41 42 43 44 46 47 | 48 49 ! 50  STRESS FACTOR  ; RQD  ! COMP  !  /Jn  !  (3)  :!  («)  !  HW HW HW  j  ; : ! |!  2 2  j j  PLANE 1  HW HW HW HW HW HW HW HW HW HW HW HW HW HW HW HW HW HW WALL HW HW HW BACK HW HW BACK BACK BACK HW BACK BACK BACK BACK BACK BACK BACK BACK HW BACK BACK BACK BACK  1; | J 1 | ; ! ; [ ! ! J ; ; ! ; ;  1  1; | ; ;  | !  ; ! ; [ | : ; : ; ! ; !  2 3 33 4 1  i I  i l i l l l i 12 l l 12 5  ! I  9 9 16 9  ! ! ! ! i ! ! ! ', ! ! ! ; ! ! ! ; ! ; !  15 15 15 15 .15 45 45 45 30 15 14 14 14 30 9 9 9 9  ; ; ;  1 I !  ; ; ; ; ; ; ; I ; ; ; ;  (5)  j  I1 j j. ; ] ;  1j 11 j I j  COMP  !1 COMP ; ! ; ! I ; ', ] ', ! !  (7)  (8)  (9)  o o o o o o  0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0  FOLIATED FOLIATED FOLIATED FOLIATED FOLIATED FOLIATED FOLIATED FOLIATED FOLIATED FOLIATED FOLIATED FOLIATED FOLIATED FOLIATED FOLIATED FOLIATED FOLIATED FOLIATED FOLIATED FOLIATED FOLIATED BLOCKY BLOCKY BLOCKY BLOCKY BLOCKY FOLIATED BLOCKY BLOCKY BLOCKY BLOCKY BLOCKY BLOCKY BLOCKY BLOCKY BLOCKY BLOCKY BLOCKY BLOCKY BLOCKY BLOCKY BLOCKY BLOCKY BLOCKY BLOCKY  o  o o  o o o o o o o o o o  ! ; ! ! !  o o io io 6 o o  ; ; ! !  RELAX  ! ! ! ! | ! !  20 o 70 70 o 90 90 90  ;  90  ! ! !  90 o o  ;  90  ! !  90 90  ;  90  !  COHP COMP COHP COMP COMP COMP COMP COMP  COMP COMP COMP  BLOCKY/ FOLIATED  ! ! ! ! ! ! ! ! !  1!  RELAX  j  1!  BLOCK SHAPE  STRK DIFF  RELAX RELAX  COMP COHP  1 COMP  ; ! ; !  ;!  RELAX 1! RELAX RELAX ; RELAX ; RELAX ! RELAX RELAX | RELAX ; RELAX ', RELAX ! RELAX ', RELAX ; RELAX I RELAX ; RELAX I  j  ! J  (6)  ! ! DIP | DIFF  RELAX ! ! RELAX ; ! RELAX ; ! RELAX t ! RELAX i ! RELAX | ! RELAX ! ! RELAX i ! RELAX ! RELAX ; !  j I j  |  RELAX  CRITICAL JOINT  20  o o  f o r t h e complementary data E F F E C T OF GRAVITY  FACTOR SHEAR STREN.  Jr  !  /Ja  (10) 0.5 0.5 0.5 0.8 0.8 0.8 1.5  0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.8 0.25 0.25 0.25 2.0 0.6 0.5 0.5 2.0 1.5 1.5 1.5 1.5 1.5 1.5  i  1 ! ! ! ; !  1I J ! i i ! ! ! ! ! ! I I | ; | | ! ! ;  1!  SLIDING  FREEFALL/ BUCKLING  SIZE AND SHAPE FACTOR  CRITICAL JNT DIP  STOPE PLANE D I P  HYD. ;i ! ! RADIUS  ;! '  :!  (13)  !!  3.o  ;!  (11) 72 72 72 65 65 65 65 76 76 60 60 60 65 65 71 71 71 65 65 60 65 80 70 78 78 o 70  ! ! I  70 o 70 70 90  2.7 2.7 2.7  ;  90  ! !  90 90  1.3  ;  90  ! ! I ! |  90 o 0 o 90 90 90  2.6 1.3 1.3 1.3 1.3  2.0 2.0 2.0 2.0  J  ! ;  90  !  90  (12) 72 72 72 65 65 65 65 76 76 60 60 60 65 65 71 71 71 65 65 60 65 90 80 72 78 0 90 90 0 0 0 90  o o o o o o o o 90 o o o o  !! !! !! ;! !! i; ;! ;| !! ;! !! !; ;; ;; !; !| !! !! ! i! ;I |! ;i !!  1  1 !!  J  ; | I! !! !! :! !! | !! ;| !! !! !! ;! ', ; |! !! !| ', ,' !  1  1  B.O  14.0 2.0 s.o IO.O  io.o 6.0 9.0 i.o 2.0  u.o 6.0 io.o i.o 2.0 i3.o 7.0 12-0 4.0  ASSESS.  (14)  STABLE ! ! UNSTABLE ]; CAVE ] ! STABLE ; ; UNSTABLE ; ! 1I U SNTSAT BA LBEL E ] i UNSTABLE CAVE |J  ;  STABLE ! ,'1 UNSTABLE CAVE UNSTABLE CAVE STABLE UNSTABLE CAVE STABLE UNSTABLE  !i !; !! !! |I ;; ;| ;i !  3.0  1 UNSTABLE ; ; UNSTABLE  4.7 7.9 8.8  ; ! 1', ;!  8.8 5.2  !; 1! U NCSATVAEB L E  7.8 6.0 5.0  1! 1| ;!  4.1  ;i  4.o 4.9 2.7  !! | ! 1!  6.1  7.6 s.s 13.4 6.1 15.2 6.4 i3.i 7.3 5.0 9.9 6.8  STABLE STABLE CAVE  SS TT A A BB LL EE STABLE STABLE STABLE  SS T LE E TA AB BL ! ! UNSTABLE | ] UNSTABLE ; ! UNSTABLE | j UNSTABLE  i STABLE ! 1; U NCAVE ; J UNSTABLE ! J STABLE CAVE !; ! ! UNSTABLE ]]  J ;  CAVE CAVE  T Y P E OF BEHAVIOUR  FAIL MODE  (15)  (16)  J O I N T E D RM J O I N T E D RM J O I N T E D RM D I S C . BLOCK J O I N T E D RH J O I N T E D RM J O I N T E D RM J O I N T E D RH J O I N T E D RM J O I N T E D RM J O I N T E D RH J O I N T E D RM J O I N T E D RM J O I N T E D RH J O I N T E D RH J O I N T E D RM J O I N T E D RH D I S C . BLOCK J O I N T E D RH J O I N T E D RH J O I N T E D RH D I S C . BLOCK J O I N T E D RH J O I N T E D RH J O I N T E D RH D I S C . BLOCK J O I N T E D RM D I S C . BLOCK D I S C . BLOCK D I S C . BLOCK D I S C . BLOCK D I S C . BLOCK I N T A C T ROCK D I S C . BLOCK D I S C . BLOCK D I S C . BLOCK J O I N T E D RH D I S C . BLOCK J O I N T E D RH D I S C . BLOCK D I S C . BLOCK J O I N T E D RH D I S C . BLOCK J O I N T E D RM J O I N T E D RH  3d 3d 3d 3d 3d 3d 3d 3d 3d 3d 3d 3d 3d 3d 3d 3b 3a 2d  2a 2a  2a 3a 2a 3a 2a 3a 2a 3a 3a  TABLE  8.4 I n p u t p a r a m e t e r s from t h e c o m p l e m e n t a r y d a t a n e c e s s a r y f o r open s t o p e d e s i g n b a c k - a n a l y s i s . BLOCK SIZE  CASE'! ! RQD |1 (REF. » ! ', /Jn II FIG. 74) (2) ! ! 64 65 66 67  68 69 70 71 72 73 74  75 76 77 78 79 80 si 82 83 84 85 86 87 88 89  90  91  92  93 94 95 96 97 98 99 100 101 102 103  i ! !! ;! !: ;! ;; !! !1 ! : !! !! 1! !  1 i 1 ;  6 i i* 8 8  (17)  ;] |; :; i ;  ! | ;! !!  !',  11 !!  !! ; |  18 !! 3 1 1 3 1! 3 1 1 i l l  ! ; ] ;! ;! 18 1 1 ;I 3 i; ; 1 1-5 11 ; 1 18 1 1 ; 1 7 1| ;! 2° ! ! ; 1 20 1 | ; 1 20 1 1 !! 20 ; i ;! 3 1 1 ! 1 3 11 ; 1 3 11 ', I 3',1 ! 1 3 11 | ! 3 1] ; 1 111 ; 1 11 11 11 :1 ! ! 8 1 1 ! 1 ' 3 11 i ! 3 1 1 ! ! 3 ] 1 ! ! 6 1 1 6 i ; ;!  104 105 : 1  106 107 108 109 no in 112  (4) !! 4 4 3 3 3 is 6  ! ! ! i  | ! ; !  i  1 ! ! ! !  113  1I  us  :!  114 ; 1116 ; 1 117 us 119  | ! ;  121 122 123 124 125 126 127 128 129 130 131 9 ii  ; ! :  i  '•  120 ; 1  1 ' 1 i 1 !  ] ; ! | | ] 1 ! ! ', 1 ;I !! !1  6 1 1 15 1 1 2 1 1 2 1 1 3 1 1 3 1 l 2 ; l 2',l 2 1 1 3 1 1 3',|  11 11 111 1 1 1 111 111 111 111 111 1 1 1 1 1 1 111 12 1 1 6 1 1 1 11 i 1! n i l 3 4  5  JOINT ORIENTATION FACTOR  STRESS FACTOR  !;  i  EFFECT OF GRAVITY 1 SLIDING FREEFALL/ J 1 HTO. SLABBING ', 1 RADIUS  1 CRITICAL Jr /J» 1 JOINT  1 1 o !1 1 o 11 1 o 11 1 0 11 1 o 11 1 o ; 1 1 o 11 1 o ', ! 1 0 11 1 0 11 1 o 11 1 o ; 1 1 0 11 1 o ! 1 1 o 11 1 0 11 1 0 11 1 0 11 1 ! o 1 1 o ! 1 1 o 11 1 o 11 1 o I 1 1 o 11 1 0 11 1 0 11 1 0 11 1 o ! 1 1 o 11 1 o ', ', 1 o 11 1 o 11 1 o 11 1 o 11 1 0 11 1 o 11 1 o 11 1 0 11 1 0 11 1 I 0 1 1 0 11 1 o 11 1 0 11 1 0 11 1 ', 0 1 1 o 11 1 0 11 1 o 11 1 I o 1 1 0 11 1 0 11 1 o ! 1 1 0 11 1 0 11 1 o 11 1 0 11 1 0 11 1 I 0 1 1 0 11 1 0 11 1 o 11 1 0 11 1 o 11 1 o 11 1 o 11 1 o 1! 1 0 ', ', 1 0 11 0 3 11 1 o 11  1  (10)  (18)  0.3  1.5 1.5 0.8 0.8 0.8 3.0 0.8 0.8 0.25 3.0 1.5 1.5 3.0 0.25 0.25 0.25 0.25 3.0 0.8 1.5 3.0 3.0 3.0 3.0 0.8 0.8 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25 2.0  0.3 0.3 0-3 0.3 0.3 0.3 0-3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0-3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3  1.0 1.0 1.0 0.25 0.25 0.25 2.0 0.8 0.8 1.0 1.0  0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3  0.5 0.5  0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3  ; '  0.3 0.2 0.2  ' '  0.5 0.8 0.8 0.8 1.5 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.8 0.25 0.25 0.25 2.0 0.6  base  (19)  (20)  11  5.5 5.5  |! !i 7.0 1 ! 7.o ; !  7-0 4.5 8.0 8.0 6.5 8.0 4.5 4.5  1 1  4.5 4.5  ,' ! |i 5.0 1 ! 8.0 ! ! 7.0 ; ! 7.0 1 1 6.5 1 ! 5.0 ; ! 5.5 ', ', 5.0 1 1 4.5 1 1 5.5 1 ! ! ! 8.0 1 1 8.0 1 ! 4.0 1 1 4.0 1 ! 5.5 1 1 5.5 ', 1  1! 11 7.0 1 1 8.0 1 1 8.0 1 1 5.5 1 1 5.0 1 ! 5.0 | 5.0 1 1 5.5 1 ! 5.5 1 i 5.5 1 1 6.0 1 1 7.0 1 1 7.0 1 1 5.0 1 ! 5.0 1 1 6.0 1 1 6.0 1 1 6.0 1 1 5.5 1 1 5.5 ', ', 5.5 1 1 5.5 1 1 6.5 1 1 6.5 1 1 5.0 1 1 5.0 1 5.0 1 1 5.5 1 1 5.5 1 1 6.0 1 1 6.0 1 ! 6.0 ! ! 1 5.5 i I 5.0 1 1 5.5 1 ! 8.0 1 1 7.0 1 ! 5.5 5.5  !  1 1 1 1 1 1 1 1 1 1, 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1i 1 1 1 1 1 1 222  4.5  1! 11 1! J ', 1! 1 !  (13)  1  6  12 : 3  1  16 5  ; !  9 ! 12 ! 8 16 7 2 ii 5 1* 6 10 ii  1 1| 1 :  !  9 !  6 13 10 4 ! i 12 4 ] ii ! 3 1 n 1 2 ! 7 ]  9 |  16 1 8 ; 3 1 5 | 3 1 3 1  6 |  1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 91 1 1 2 1 13 1 61  14 3 8 13 10 4 10 6 12 3 8 14 2 8 10 10 6  10 ; 1 ! 2 l  13 1 7 1 12 1 4 ] 3' l  4.7 7.9  1 1  1 N 1 ASSESS. (21)  :  (u)  STABLE CAVE STABLE UNSTABLE CAVE UNSTABLE UNSTABLE 1 CAVE ! CAVE ! STABLE ,' STABLE 1 STABLE 1 STABLE 1 CAVE 1 CAVE 1 CAVE 1 CAVE ! STABLE 1 UNSTABLE 1 CAVE 1 STABLE 1 STABLE 1 STABLE UNSTABLE STABLE 1 STABLE 1 STABLE CAVE STABLE 1 CAVE 1 CAVE CAVE CAVE UNSTABLE CAVE STABLE STABLE UNSTABLE CAVE STABLE UNSTABLE CAVE STABLE CAVE CAVE UNSTABLE CAVE STABLE 1.8 UNSTABLE 1.8 CAVE 4.0 STABLE 4.0 UNSTABLE 4.0 UNSTABLE 10 STABLE 0.5 UNSTABLE 0.5 CAVE 0.4 STABLE 0.4 UNSTABLE 0.4 CAVE 0.4 UNSTABLE 0.4 CAVE 0.5 STABLE 0.5 UNSTABLE 0.5 CAVE 13 STABLE 2.5 UNSTABLE 0.4 UNSTABLE 0.4 UNSTABLE 12 STABLE 4.2 STABLE 10 10 5.0 5.0 5.0 73 12 12 0.5 115 16 16 81 1.8 1.6 1.6 0.5 81 4.0 3.4 73 35 81 81 38 38 0.9 0.9 1.2 1.2 1.2 1.2 0.5 0.6 0.6 26 4.5 4.5 4.5 2.5 2.5 2.5 54 3.4 3.4 4.5 4.5 1.8  TABLE  8.4 Input parameters from t h e complementary d a t a base n e c e s s a r y f o r open s t o p e d e s i g n b a c k - a n a l y s i s ( c o n t ) . BLOCK SIZE  CASE  RQD /Jn  t  (2)  l* is  ! ! ;  167 168 169 179  | ; ; |  181  ;  182 37 38 39  ; : ; !  40  ;  4i  ;  42  ;  43 46  ! J ;  47  |  48 49 50  ! : ;  44  (REF. FIG.  (4)  154  9  !',  1 1 ;;  9  !!  is  15 15  is  ;:  1i!; i:  15 ! 1 45 • ! i 45 ! ! 45 : i 30 i; is ;; 14 14  CRITICAL JOINT  7.4)  (17)  9  ie  JOINT ORIENTATION FACTOR  STRESS FACTOR  ;;  14 30  : i !; ;!  9 9 9 9  ;! ;! !! !!  (18)  i.o  o.i o.i i.o  ll ;i ! i ;; l! !: ;! i;  o.4 0.4 0.6 0.6 o.6  |! ;; | ] ;! ;;  o.s o.s  i; ;;  0.3  ;;  i.o o.i i.o  ;; ; i ;; ;|  0.4  ;;  1.0  o.i i.o i.o 0.3  0.3  Jr  EFFECT OF GRAVITY SLIDING  FREEFAU./ SLABBING  (19)  (20)  / J (10  0.2  6.0 7.0 2.0 8.0 8.0 2.0 2.0 2.0 8.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 8.0 2.0 2.0 2.0 2.0  0.3 0.3  0.2 0.2 0.3  0.85 0.85 0.3 1.0 1.0 1.0 1.0 1.0 0.3 0.3 0.3 0.3 1.0 1.0 1.0 1.0  223  HYD. RADIUS (13)  8.8 8.8 5.2  7.8 6 5 4.1 4 4.9 2.7 6.1 7.6  8.8 13.4 6.1 15.2 6.4 13.1 7.3 5 9.9  6.8  ASSESS.  (21) S.4 9.5 1.9 22 36 4.1  3.8 3.8 54 97 97 146 47 47 5.5 5.5 3.3 94 11 3.6 36 14  (14)  ,  CAVE CAVE UNSTABLE STABLE STABLE STABLE STABLE STABLE STABLE STABLE UNSTABLE UNSTABLE UNSTABLE UNSTABLE UNSTABLE CAVE UNSTABLE STABLE CAVE UNSTABLE CAVE CAVE  i n d i v i d u a l f a c t o r s on open stope s t a b i l i t y . or p r e - c a l i b r a t i o n of the f a c t o r s was A,  B  and  C  modification  of  the  and  original  calibration  the  e m p i r i c a l adjustment  process as new  effect  parameters on  of d i f f e r e n t  understood. detailed rating is  For  reason,  justification  scheme.  given  on  s e c t i o n s 7.2  8.4.1  this  how  the  t o 7.5,  Block s i z e The  rating  stope  ratings  advantage  contains Instead  joint of  prominent (1974),  the  each  the  were b e t t e r  to  provide  a  of each  parameter's  a brief  explanation  parameter  f o r the e f f e c t of b l o c k s i z e  i s that sets  set  shear  block  on-going  presented  in  determined.  and  i t avoids  having the  strength separately.  c o n f u s i o n when a  different shear  i n the  rock  shear  factor  been  mass, as  rock  The mass  characteristics.  characteristics  of  suggested  s t r e n g t h of the c r i t i c a l  size  (RQD/Jn) has  There are s e v e r a l advantages  shear  g r e a t e r i n f l u e n c e on s t a b i l i t y , The  The  rating  assigning  joint  an  stability  section,  of  have been  factor  method.  was  i t is difficult  in this  considering block size  main  factors  and  1  cases were analyzed and  kept unchanged from the Q-system. in  design  f o r the d e r i v a t i o n  However,  starting point  p r o v i d e d by Q  Mathews  of  The  joint,  the by  most Barton  which has  a  i s used.  RQD/Jn  can  also  be  used  in  the  c a l c u l a t i o n of a rough c r i t e r i o n t o i d e n t i f y the t h r e e types of rock  mass behaviour  rock mass).  I t was  (intact  rock,  discrete  mentioned i n s e c t i o n 6.2 224  block  and  jointed  t h a t the rock mass  behaviour i s dependent on the r e l a t i v e s i z e o f b l o c k s compared with the surface the  o f the rock mass exposed.  U s i n g t h i s concept,  q u o t i e n t o f the b l o c k s i z e f a c t o r RQD/Jn and the h y d r a u l i c  radius  o f the stope  discrete failure the  block  failure  (see t a b l e  failed  From  surface  table  and  8.5).  blocks could  8.5,  were c a l c u l a t e d 19  cases  For a j o i n t e d  jointed  rock  mass  Only the cases i n which the s i z e of  be v i s u a l l y estimated were  i t can be seen t h a t  f a i l u r e s have a (RQD/Jn / h y d r a u l i c 1.5.  of  f o r 10 cases of  included.  most d i s c r e t e  block  r a d i u s ) r a t i o g r e a t e r than  rock mass t h i s r a t i o i s s m a l l e r than 1.5.  S i n c e t h e r e i s no case o f i n t a c t rock f a i l u r e i n the data base, the  only  guide  to  (RQD/Jn / h y d r a u l i c which  i s 8.6.  identify radius)  This  this  behaviour  i s the  ratio for discrete  can be  used  as  a  block  rough  largest failure,  guideline  to  a n t i c i p a t e t h e t h r e e t y p i c a l open stope rock mass b e h a v i o u r s . Finally,  the  block  size  factor  estimation of a s u i t a b l e density  will  be  useful  of cable b o l t s .  f o r the  This  w i l l be  r a t i n g f o r the compressive s t r e s s f a c t o r i s a  function  f u r t h e r d i s c u s s e d i n chapter 9.4.2.  8.4.2  Stress The  of  factor rating  the r a t i o  of  the u n i a x i a l  (o /oy).  induced  stress  (o /oy)  and t h e compressive  c  c  The  compressive relationship  stress  rating  strength  and the  between the r a t i o comes  from  r u l e of  thumb adapted by Mathews e t a l . i n t o t h e o r i g i n a l f a c t o r A 225  TABLE  8.5  Relationship between the r e l a t i v e block size factor (RQD/Jn / h y d r a u l i c radius), and rock mass behaviour.  Discrete  Rock Mass Failure  RQD/Jn  Hyd. Radius  RQD/Jn /Hyd.  25  5.8  30  4.3  3.5  17  8.6  10.5  17  1.6  11.3  17  1.5  12.2  29  1.4  6.8  29  4.3  8.0  3.6  8  2.1  3.8  8  2.3  15  3.4  10.0  1.5  Radius  M e a n = 3.4  Jointed Rock Mass Failure RQD/Jn  Hyd. Radius  RQD/Jn  / /Hyd.  8  7.6  6  1.1  8.9  7  0.7  7.1  1.0  4  4.7  0.9  7  9.1  0.8  6  10.5  0.6  4  19.0  0.2  8  8.1  1.0  5  9.0  0.6  5  11.3  0.4  3  20.0  0.2  14  8.6  1.6  9  9.9  0.9  18  12.5  18  15.0  1.2  18  15.9  1.2  18  11.1  1.6  6  6.9  0.9  6  7.7  0.8 Mean=> 0.9  226  1.4  Radius  curve. except  This  relationship  were  stable  have  been  the  kept  roughly  t h e same,  f o r s e t t i n g a minimum r a t i n g o f 0.1 ( f i g u r e 7.4).  was j u s t i f i e d  8.1.  has been  by s e v e r a l because  plotted  cases  of t h e i r  of highly small  s t r e s s e d backs which  dimensions.  cases  i n figure  A c c o r d i n g t o the b a c k - a n a l y s i s o f a l l t h e case  histories,  A  calibration  m a j o r i t y o f case  stability  These  graph  factor  on the m o d i f i e d  This  appears  to  be  adequate  f o r the  histories.  The e f f e c t o f s t r e s s r e l a x a t i o n on the d e s i g n a n a l y s i s has also  been  walls  investigated.  of l o n g i t u d i n a l  Zones  of r e l a x a t i o n  stopes when the pre-mining  "K" i s approximately g r e a t e r than 1.5 t o 1. has  are created i n stress  ratio  Since i n t a c t  rock  a v e r y low t e n s i l e s t r e n g t h and j o i n t s have no s t r e n g t h i n  tension,  tensile  mass.  Instead,  induce  new  stress tensile  cracks  relaxation.  i s not l i k e l y stress  through  Inside t h i s  will  intact  to build open  rock  up i n a rock  existing creating  zone of r e l a x a t i o n  joints  or  zone  of  a  individual  blocks  have more freedom o f movement and become more s e n s i t i v e t o the a c t i o n of g r a v i t y , it  appears  that  because they are unconfined. tensile  stress  and  i t s associated  r e l a x a t i o n have an e f f e c t on stope s t a b i l i t y . been  investigated  Consequently,  u s i n g two dimensional  zone  of  T h i s e f f e c t has  and t h r e e  dimensional  numerical m o d e l l i n g (parametric study, s e c t i o n 7.3.2), with the intention  of  developing  an  adjustment  factor.  The  case  h i s t o r i e s o f stope s u r f a c e s i n a s t a t e o f s t r e s s r e l a x a t i o n has been p l o t t e d on the m o d i f i e d s t a b i l i t y 227  graph,  i n f i g u r e 8.2.  FIGURE  8.1  Modified S t a b i l i t y Graph Total Data Base: C a s e s of High Stress 9 case histories  «#H : X* :  ^  :  :X;x :x :X:v:x-* ''' :  -  yyyyy:^  :»;•;•;•;!;'!'!':':'!!>•'  ****  ym  •  —f&i-  0  5  10  Hydraulic  15  Radius (m)  • Stable Stope Surface • Unstable Stope Surface T Caved Stope Surface 228  20  25  It  can  be  seen  that  the data  does not  factor for stress relaxation,  since  analyzed  generally  case  histories  modified s t a b i l i t y Nevertheless, that  the  stress. shape  included effect  shape  stope  of the back-  i n accordance  with  the  the  surface)  of r e l a x a t i o n  stope the  surface  is  found  the  "theoretical"  most  tensile  r a d i u s (which account f o r the s i z e and  i n the model,  seven case h i s t o r i e s  of  influencing  Since hydraulic the  the assessment  adjustment  from the p a r a m e t r i c study i t has been  parameter  of  ah  graph.  relative  important  are  justify  and  the  effect  of  gravity  are  i t seems reasonable t o assume t h a t  i s i n d i r e c t l y taken i n t o account. (shown i n f i g u r e 8.2)  the  Ninety  of r e l a x e d w a l l s are  i n agreement w i t h t h i s h y p o t h e s i s .  8.4.3  Joint orientation  factor  The j o i n t o r i e n t a t i o n joint  parameter  shear  strength rating  system and factor. figure  the  shear  critical  strength c h a r a c t e r i s t i c s .  i s Jr/Ja  critical  7.19.  i s taken d i r e c t l y from  The  the  Q-  The  joint  chart  rating  was  can  be  constructed  estimated according  using to  the  principles:  total  influence  number c a l c u l a t i o n , influence equally  t o t a l r a t i n g depends on the  i s a l r e a d y c a l i b r a t e d w i t h r e s p e c t t o the b l o c k s i z e The  following The  and  rating  of  of the c r i t i c a l should be  gravity,  because  important f a c t o r s .  j o i n t on the  approximately they  are  Empirically, 229  two  stability  similar  t o the  approximately  i t has been found  FIGURE  8.2  Modified S t a b i l i t y G r a p h Total Data Base: Cases of S t r e s s Relaxation 97 case histories 1000  100 _Q  E Z3  10 O  00 TD  1.0 "O o  0.1 15  10  Hydraulic R a d i u s complementary d a t a base  «  main d a t a base ^ , , i L  O  L  o • Stable Stope Surface • • Unstable Stope Surface v • Caved Stope Surface 230  20  (m)  25  t h a t an i n f l u e n c e of 5 works w e l l . The  rating,  which  is a  critical  function  between  the  joint  and  minimum  (0.2) when the d i f f e r e n c e  of the d i f f e r e n c e the  stope  i n dip  surface,  is a  i n d i p i s shallow  (10° to  30°) . A slightly  better  the c r i t i c a l the  stope  case  (with  regard t o s t a b i l i t y )  joint i s sub-parallel  surface.  A  rating  occurs i f  (0° t o 10° d i f f e r e n c e )  o f 0.3  i s assigned  to  in this  situation. A  difference  dip  of  j o i n t s perpendicular  influence  on s t a b i l i t y  difference  difference  8.4.4  for  has  a  small  i s used.  surface  have no  i s accounted f o r by c o n s i d e r i n g dip,  which  between  i n dip  is  influenced  by  the  and  the  i n s t r i k e increases,  the  the c r i t i c a l  increases  the  and  the  joint  effect  of the  j o i n t r a t i n g decreases.  The g r a v i t y f a c t o r r a t i n g The g r a v i t y  factor rating  the  mode  increase as  t o the stope  As the d i f f e r e n c e  difference  critical  in  in strike  stope s u r f a c e . true  60°  ( t h i s i s g i v e n a r a t i n g of 1.0).  The e f f e c t o f a n i s o t r o p y true  approximately  on stope s t a b i l i t y and a r a t i n g of 0 . 8  influence Critical  in  sliding  of  i s estimated  failure.  gravity  figure  7.21  rating  will  the m o d i f i e d s t a b i l i t y number (by up t o a f a c t o r of 4)  the d i p of the s l i d i n g plane  sliding  The  using  is  less  likely  to  (critical  happen. 231  j o i n t ) decreases and If  the  dip  of  the  discontinuity  i s s m a l l e r than o r equal  maximum, because t h e f r i c t i o n  t o 30°, t h e r a t i n g i s a  angle o f a t y p i c a l  rock  joint i s  around 30°. When t h e mode o f f a i l u r e the  rating  stope  i s a function  surface.  influence walls  varies  As  i s by g r a v i t y f a l l  of the i n c l i n a t i o n  i n the s l i d i n g  from  2 t o 8.  or slabbing,  o f t h e designed  analysis,  the rating's  I t i s a maximum  for vertical  and a minimum f o r h o r i z o n t a l backs. The equation  d e r i v e t h e r a t i n g curve rating = 8 - 6  used t o  ( i n f i g u r e 7.20) i s g i v e n below: (cosine  (angle o f i n c l i n a t i o n ) ) .  T h i s r e l a t i o n s h i p d e s c r i b e s t h e i n c r e a s i n g e f f e c t o f g r a v i t y on stopes s u r f a c e d i p p i n g c l o s e r t o t h e h o r i z o n t a l .  8.5  THE MODIFIED STABILITY GRAPH  The  modified  stability  number  and h y d r a u l i c  radius  are  r e l a t e d g r a p h i c a l l y on a s t a b i l i t y graph, as i n the methodology proposed by Mathews e t a l . the  key parameters  combination hydraulic stable, that  radius  unstable  on one graph  stability (stope  number surface  o r caved  i n order (rock size  conditions.  had low d i l u t i o n ) a r e represented  shaped and  of  T h i s allows t h e p r e s e n t a t i o n o f a l l  points.  Case  histories  ground f a l l s causing  unstable.  that  t o determine mass  and  quality)  shape)  Stable  leads  stopes  what and to  (planes  on t h e graph by round  had experienced  dilution  o p e r a t i o n a l problems a r e c l a s s i f i e d as  They a r e shown on t h e graph by square shaped p o i n t s . 232  The  t r i a n g u l a r p o i n t s r e p r e s e n t case h i s t o r i e s t h a t had  ground c o n t r o l The  points  problems.  stability  data base  severe  graph  (84 p o i n t s ) .  located  i n f i g u r e 8.3, As  expected  i s a p l o t of the main  the graph  i n the upper l e f t c o r n e r  shows t h a t most  (good rock q u a l i t y  and  s m a l l stope s u r f a c e ) are s t a b l e w h i l e the cases p l o t t i n g i n the lower have  right  area  caved.  areas  A  (poor  rock  transition  i s r e p r e s e n t e d on  noticed  that  the  zone  around  that  expected.  modified  and  large  between  the graph  unstable  concentrate The  quality  by  cases  stable  (square  graph  surface) and  a grey band.  transition  stability  the  stope  points)  caved  I t can  be  tend  to  zone,  which  is  also  i s now  comprised  of a  s t a b l e area, a t r a n s i t i o n zone and a caved a r e a . In  the  complementary  next data  stability base  has  graph been  (figure  added  and  8.4),  the  confirms  r e l a t i o n s h i p p r e v i o u s l y d e f i n e d i n the m o d i f i e d s t a b i l i t y (figure  8.3).  T h i s new  zone between s t a b l e stability for  8.6  shallow  has  a reduced  graph  transition  c a v i n g areas which makes the m o d i f i e d  graph a more p r e c i s e d e s i g n t o o l and l e a v e s l e s s room  of  applicability at  and  mis-interpretation  warrant  relationship  the  the  of a n a l y s e s .  method  's  The  reliability  l a r g e data base i s a and  confirms  of the d e s i g n method f o r stope w a l l s , and  depth.  DESIGN PHILOSOPHY  233  the  stopes  FIGURE  8.3  Modified S t a b i l i t y Graph Main Data B a s e 84 case histories 1000  100 CD _Q  E Z3  ^  10  D -I-'  CO " O (D  b  1.0  o  0.1 0  5  10  15  Hydraulic • • •  Radius  Stable Stope Surface Unstable Stope Surface Caved Stope Surface 234  20  (m)  25  FIGURE  8.4  Modified Stability G r a p h Total Data Base 176 case histories 1000  100  E Z3  ^  10  O 00 "O CD  it: o  1.0  0.1 0  Hydraulic RadlUS ( m )  complementary d a t a base  15  10  \  /  main d a t a base  o • Stable Stope Surface • • Unstable Stope Surface v • Caved Stope Surface 235  20  25  The a  modified  reliable  tool  stability for  graph  ( f i g u r e 7.22)  predicting  open  stope  can be used  dimensions.  as The  f i n a l d e s i g n must c o n s i d e r the g e o t e c h n i c a l parameters i n v o l v e d in  the  calculation  should account Consequently, the  most  of  engineering  i s expected  or  schedule  when  and  stability  to  As  as  When mining is  no  instability  is  number but  required to  a general  increase  there  no  judgement  design.  i n t o the c a v i n g zone. lenses,  modified  also  f o r economic, s c h e d u l i n g and mining c o n s t r a i n t s .  efficient  dilution  the  the  rule,  the  design  can  be  in  amount of  plots  i n the v i c i n i t y  flexibility  determine  deeper  of other ore  the  tolerated,  production all  designs  should p l o t above the grey area, i n the s t a b l e zone. Sometimes i t i s not the  stable  zone.  practical  Because  of  or economical  the  non  entry  to d e s i g n i n  nature  s t o p i n g , stopes p l o t t i n g i n or below the grey area may viable. graph  The  has  author's  effect  control the  of  stope  time.  blasting  stope  is  In t h i s  techniques  emptied.  cable  bolts  is  discontinuities. mass  further  quality  discussed  limit  This  results  and in  the  be  stability  transition  zone  i t i s recommended  use  below The  to  immediately  the  after  transition  principal  movement  along  zone  a c t i o n of existing  i n a hypothetical increase in  stability  chapter  still  and  support.  to  the  to b a c k f i l l  Designing  requires a r t i f i c i a l  revised  open  s e n s i t i v e to b l a s t i n g  case,  and  the  inside  w i l l be v e r y  usually  rock  with  been t h a t when p l o t t i n g  (grey area) , the the  experience  of  9  236  number.  (cable  bolt  This support  will in  be open  stoping).  8.7  POSSIBILITY OF USING STATISTICS  Empirical r e s e a r c h and meaningful the  research  confirmatory  hypotheses  empirical r e a l i t y  proposed.  can  be  divided  research.  are  exploratory-  In c o n f i r m a t o r y  developed  when the  i s w e l l advanced and  For t h i s type  into  research,  understanding  of  a sounded theory i s  of r e s e a r c h the s t a t i s t i c a l  inference  allows f o r the e v a l u a t i o n of the p r o b a b i l i t y of e r r o r r e g a r d i n g e i t h e r the c o n f i r m a t i o n or i n f i r m a t i o n of the hypotheses. In t h i s to  thesis,  exploratory  limited.  research  This  problem  and  research.  the  Statistical  estimate  the  observations  because the due  relative  Therefore,  powerful  proposed h y p o t h e s i s  i s mainly  c o u l d be achieved  less  the  only  to  theoretical  the  scarcity  high of  a limited  background i s  complexity  applied  degree of  of  the  geomechanics sophistication  i n the model development. inference  than  in  in  exploratory  confirmatory  research  research,  although  is  used  e r r o r i n i n f e r r i n g knowledge t o a p o p u l a t i o n based  on  a sample.  The  quality  i n f e r e n c e i s h i g h l y dependant on the sampling to  i s more r e l e v a n t  obtain a s i g n i f i c a n t s t a t i s t i c a l  of  this  scheme.  to from  type  of  In order  i n f e r e n c e i n t h i s study,  a  random sample of the p o p u l a t i o n of a l l p o s s i b l e stopes would be required. stopes  (and  Due the  to  practical  assessment  considerations, of  their  the  stability)  sample used  is  of a  convenient sampling  sample  was  (in opposition to  based  possibility  on  for  the  safe  a  typicality  random of  measurements  sample).  the  of  stopes  the  The  and  the  geotechnical  parameters.  8.8  SUMMARY  The to  principal  predict  the  problems. design,  o b j e c t i v e of the proposed  stability  Because  the  empirical  of  of open stopes the  reliability  model, the  economic  of  the  i n terms of o p e r a t i n g  consequences  model  reliability  d e s i g n method i s  is  of  crucial.  i s largely  a  bad  For  a f u n c t i o n of the  e x t e n t of the data base.  In a d d i t i o n , the model i s expected  work  bounds  better  inside  the  defined  an  by  the  to  geotechnical  c o n d i t i o n s i n the data base. The  total  case h i s t o r i e s has  been  data  base  from  divided  of  unsupported  stopes  t h i r t y - f o u r Canadian mines. into  a  main  data  base  contains The  data base  (high  level  confidence) and a complementary data base (data from and data with a lower l e v e l of c o n f i d e n c e ) . was  used  f o r the  calibration  complementary data base was  of  the  175  of  literature  The main data base  design  method while  the  used  t o c o n f i r m the r e l i a b i l i t y  the  geomechanical  of  the method.  through the  The  calibration  the  b a c k - a n a l y s i s of  input  data  was  of  case  estimated 238  histories. on  site,  and  model For  was  done  each  case,  the  modified  stability  number  stability  graph.  assessment d i d of  the  calculated  For  not  the  f i t the  cases  predicting  model was  tool.  This  and  plotted  on  i n which the  actual  mis-interpretation  geomechanical  new  was  the  modified  stability  stope behaviour, the  were  investigated,  modified  i n order  to  procedure  resulted  i n the  graph causes  and  become a  the better  creation  parameters, the r e - c a l i b r a t i o n of e x i s t i n g parameters and  better  d e f i n i t i o n of the  stability  graph  zone between s t a b l e and  caving).  parameter  ( r e f . chapter  i n the  ( i n s e c t i o n 8.4)  model  w i t h regard  The  a  (a s m a l l e r t r a n s i t i o n  r a t i n g s a s s i g n e d t o each 7)  are  briefly  discussed  t o r e l e v a n t case h i s t o r i e s .  239  of  CHAPTER 9 CABLE BOLT SUPPORT IN OPEN STOPING  9.1  INTRODUCTION  Artificial become  an  operations  support,  important because  make underground rock  anchors  variety of  form  component  their  of  featuring  safer.  of  effect  There  different  rock  anchors,  a l l underground  stabilizing  workings  of functions.  grouted  i n the  has  mining  contributes to  are several  properties  and  types o f having  a  T h i s chapter focuses on the a p p l i c a t i o n  cable bolts  i n open stope mining.  Such a support  system may improve the competency o f a d i s t u r b e d rock mass t o a point  approaching  joint  movement  the u n d i s t u r b e d  and d i l a t i o n .  rock  This  quality  results  by  i n more  limiting stable,  p o s s i b l y l a r g e r and thus more e f f i c i e n t p r o d u c t i o n s t o p e s . effect larger the  of  increasing  stope  modified  t h e rock  dimensions stability  mass  stability  i s investigated graph  and case  resulting  The in  in this  chapter u s i n g  histories  o f supported  open s t o p e s . It gained  i s i n c u t and f i l l their  greatest popularity.  c a b l e b o l t s i n c u t and f i l l three  or  necessary  applications that cable bolts  four after  lifts, each  installation  o f long  backs has the advantage o f c o v e r i n g  which blast  The  have  reduces  the r e h a b i l i t a t i o n  and reduces 240  work  the cost of b o l t i n g .  Furthermore, blasting, the  since  the reinforcement  i t considerably  rock  mass induced  limits  i s installed  prior  to  t h e degree o f d i s t u r b a n c e i n  by b l a s t i n g .  This  concept  i s known as  pre-reinforcement. In mining  recent  years,  the Canadian,  i n d u s t r i e s have been  b o l t technology beginning, mining  (with  this  regard  i n a survey  of  using  stopes source  access  existed  i n stope  open. be  and  cable  bolts  success.  suffered  not w e l l Fabjanczyk t h a t 75%  backs,  when only  using  Another  i n hanging the d r i l l i n g  but  horizon  a low d e n s i t y  unfavourable  major  walls  This  was not  of cable  patterns  d i f f e r e n c e between  also  bolts  and  cable  c u t and  fill  i s t h a t open s t o p i n g u s u a l l y i n v o l v e s l a r g e r frequent  redistributions.  Although mining  The  bolts.  spans and has r a p i d changes i n geometry, c a u s i n g  stress  In the  overbreak.  o f the c a b l e  acute  As a r e s u l t ,  open s t o p i n g  stope  were  o f t e n A u s t r a l i a n mines  particularly  installed  orientations.  bolting)  had l i t t l e  f o r the i n s t a l l a t i o n  was  could  t o t r a n s f e r the c a b l e  o f the problems i n open s t o p i n g was the l a c k  problem  fully  Swedish  t o open stope mining.  to cable  technique  (1982) r e p o r t e d  of  and  because the fundamental d i f f e r e n c e s between the two  understood,  principal  attempting  from c u t and f i l l  methods  open  Australian  the a p p l i c a t i o n of cable  i s relatively  technique  new,  i s increasing.  bolts  the p o p u l a r i t y  of  i n open this  stope support  Among the t h i r t y - f o u r Canadian mines  v i s i t e d d u r i n g t h i s two year study 241  (1986 t o 1988), twenty mines  used  cable  bolts  approximately years  t o some  75%.  This  a rate  the progress  cable b o l t  made  i n recent  above and emphasizes  systems and r u l e s  the majority  mining.  no accepted g u i d e l i n e s f o r the design of thumb o r i g i n a l l y  c o n v e n t i o n a l rock b o l t s a r e sometimes s t i l l  explains  o f success of  f o r c a b l e b o l t a p p l i c a t i o n i n open stope  However, t h e r e are s t i l l  for  shows  with  t o overcome t h e problems mentioned  the p o t e n t i a l  of  extent,  o f the 25%  developed  applied.  This  o f the underdesigned  case  h i s t o r i e s , as w e l l as other cases t h a t seem t o be overdesigned. The bolt  different  support  chapter.  options  available  systems f o r open stopes w i l l be presented  The complex  interaction  ground c o n d i t i o n s and opening simplified  f o r the d e s i g n  empirical  manner  of cable in this  o f the c a b l e b o l t s with the  geometry w i l l using  be looked a t i n a  the open  stope  stability  model proposed i n p r e c e d i n g c h a p t e r s .  9.2  DESIGN CONCEPT  9.2.1  Prereinforcement O r i g i n a l l y the support p h i l o s o p h y was t o suspend the l o o s e  rock and  i n t h e p e r i p h e r y o f the e x c a v a t i o n t o t h e more competent undisturbed  layers  b e t t e r understanding  remote  support  the opening  of rock mass behaviour  has l e d t o a more e f f i c i e n t The  from  technique c a l l e d  surface.  A  and support systems prereinforcement.  concept o f p r e r e i n f o r c e m e n t c o n s i s t s o f i n s t a l l i n g the prior  to  excavating 242  the  rock  adjacent  to  the  excavation. of  the  rock  suggested is  principal effect  mass  to  small  i s t o l i m i t the  values.  Fuller  t h a t when p r e r e i n f o r c e d , the  limited  shear  The  to  and  less  than  dilation  preserves t h e i r  two  along  in-situ  and  (1978)  displacement  T h i s minimizes  geological  cohesion and  Cox  rock mass  millimeters.  existing  displacement  structures  f r i c t i o n angle.  The  the and rock  mass becomes " s e l f - s u p p o r t i n g . " Another  interesting  technique  is  reinforced  surface,  blasting  blasting  in  the  In  the  of  (after  prereinforcement  against  amount the  stress  geometry  the  done  addition,  surrounding  i n opening  is  reducing  vibrations.  changes change  that  advantage  of  damage  effect  field each  an  of  already caused  the  resulting  b l a s t ) can  sudden  from be  by  the  better  c o n t r o l l e d by a p r e r e i n f o r c e d rock mass. The  principal  technique  t o open stopes  installation. the  developed  two As  The  first,  i n a p p l y i n g the  opposed  sequence  to  is  f o r cable  bolt  open stope development i s l o c a t e d i n  mucking h o r i z o n followed  by  (overcut or d r i l l i n g  h o r i z o n s can  prereinforcement  i s the l a c k of access  Typically,  footwall.  horizon  limitation  the  (undercut, opening  drift(s))  .  drawpoints)  of  The  the  is  drilling  ore between the  then be r e t r e a t e d v e r t i c a l l y or h o r i z o n t a l l y .  cut  access  and  fill  mining,  available  to  at  install  no  time  cable  during bolts  this  in  the  attempted  by  o v e r c u t and undercut b e f o r e they are opened. However, the use installing  the  of p r e r e i n f o r c e m e n t  cable b o l t s  may  be  i n the overcut as soon as p o s s i b l e 243  a f t e r i t i s open. to  occur,  before  A c e r t a i n amount o f displacement  but i f c a r e f u l  the support  blasting  i s installed  i s used  the r o o f r e i n f o r c e d This  has  become  and t h e time  i s minimized,  back should be e f f e c t i v e l y supported.  i s expected  the open  most  commonly  procedure and i t has been proven  stope  The advantage o f having  f o r the heavy p r o d u c t i o n b l a s t i n g  the  delay  employed  cable  remains. bolting  effective.  About t h e concept o f p r e r e i n f o r c e m e n t , Hoek & Brown (1980) concluded "The  that:  principal  objective  i n the d e s i g n  of excavation  support i s t o h e l p the rock mass t o support i t s e l f . P r e placed  grouted  reinforcing  elements  are probably  the  most e f f e c t i v e means o f a c h i e v i n g t h i s o b j e c t i v e and the authors have no doubt t h a t the f u t u r e w i l l  see a g r e a t  i n c r e a s e i n t h i s support t e c h n i q u e . "  9.2.2 S t i f f n e s s o f t h e support The deform  stiffness  of a material represents  when submitted  deformation  before  system  to stress.  failing  Stiff  i t s capacity to  m a t e r i a l s show s m a l l  and are prone t o v i o l e n t  M a t e r i a l s having a low s t i f f n e s s may s u s t a i n l a r g e before collapsing. a  cable  according stiff,  bolt  failure.  deformations  In o r d e r t o o b t a i n the maximum advantage of  support  system,  i t s stiffness  t o the rock mass s t i f f n e s s .  the rock mass w i l l  be r e s t r a i n e d  must be  I f the support from deforming  designed i s too but the  energy u s u a l l y d i s s i p a t e d through deformation w i l l b u i l d up and  c o u l d cause the sudden f a i l u r e of the support  system.  if  compared with  the  stiffness  rock  mass  of the  support  stiffness,  the  i s very  low  stabilizing  However,  effect  may  the be  insignificant. The  stiffness  several cables 9.4.2  factors. are  and  9.4.3.  and  the  they  constitute  discussion can  on be  bolting inch) than  of  subject  in  Sometimes  bolts  on  points  the  discussed  a major  of  the  i s beyond the (Stheeman,  Canadian are  is  mines,  used with  length  grout  role  not  employed,  some  system.  and  A  full  scope of t h i s t h e s i s 1982;  Jeremic  general  be  used  16  mm  to  and  properly  s l i g h t l y rusted.  operators  will  designed  less the  density  double  the  to n o t i c e t h a t  i n s t a l l a t i o n of c a b l e s can have a l a r g e  strength.  cleaned  The  (5/8  reduce  When o n l y a low  I t i s important  Fuller  before  o t h e r hand, the bond s t r e n g t h w i l l  specially  of  because  (1983) r e p o r t e d  that  g r o u t - s t e e l bond can be damaged by d i r t or d e b r i s i f the are  on  i n sections  a water cement r a t i o  i n the h o l e .  i n each h o l e .  their  in  additives w i l l  slumping  c o n t r o l i n the  influence  w i l l be  dependent  Although t h e r e are c e r t a i n v a r i a t i o n s i n c a b l e  number of c a b l e s quality  is  b o l t i n g and  also play  elsewhere  diameter c a b l e s  cable  system  s t r e n g t h between the  steel  weakest  found  amount of grout  of  bonding  and  the  practices  0.5.  bolt  density  The  this  cable  f a c t o r s and  grout  D e l a i r e , 1983).  a  The  important  rock  and  of  their  installation.  the  cables On  i n c r e a s e when the c a b l e s  the are  " b i r d cage" type of c a b l e b o l t s have been  t o improve the g r o u t - c a b l e  245  bond but  are  not  w i d e l y used The  i n Canada a t t h i s  d e s i g n e r may  support  system  also  for  time.  a d j u s t the  specific  applications,  t e c h n i q u e s d u r i n g the i n s t a l l a t i o n . or  decrease the support  This  can  tensioned later  be  realized  that  i n most  by  be more e f f i c i e n t reinforcement  tensioned  the  increase  cable  i n zones of i s required.  bolts.  At  first,  i n a hanging  wall.  deformation T i l l m a n n and decrease  large  after  without  a  layers  of  only  in  of r e l a x e d rock  deformation  cable  losing  Worotnicki  practiced  together  bolt  i s expected,  system  i t s support  capable  capacity.  of  cable  bolts.  The  i n c l u d e s the i n s t a l l a t i o n of supplementary  anchors  artificially  cable  sections 246  of  the  i t is  of  high  Matthews,  (1983) d e s c r i b e d a debonding  stiffness  debonding  specific  stiffness.  amount  design  the  now  as clamping  - Decreasing the support  to  mass  i n most  is  sufficient  rock  S i n c e i t i s a time consuming technique and  such  desirable  the  was  tension  it  was  of  It  to n a t u r a l l y  applications  a  expansion  cases  redundant,  When  cable  different  These adjustments  where a d d i t i o n a l  achieved  the c a b l e s .  to  using  c a b l e b o l t s were a p p l i e d i n a l l s i t u a t i o n s .  excavation  cases  the  stiffness.  A s t i f f e r support system may relaxation  of  stiffness.  - I n c r e a s i n g the support  stress  stiffness  procedure procedure  (swages) and with  plastic  tubing  or p a i n t .  failure  due  T h i s minimizes  t o the  T i l l m a n n and  localised  the r i s k  of premature s t r a n d  movement of a j o i n t .  Matthews,  Worotnicki also reported a s u c c e s s f u l a p p l i c a t i o n  of t h i s technique i n the case of a h i g h l y s t r e s s e d crown p i l l a r where  lateral  expansion  case  histories  was  collected  excessive. for  this  However, none of study  used  the  the  above  debonding technique.  9.3  CABLE BOLT SUPPORT SYSTEMS IN CANADIAN OPEN STOPE MINES  Cable to  the  bolt  nature  support of  the  systems should be rock  mass t o  be  installed  supported,  according the  access  a v a i l a b l e and the s p e c i f i c f u n c t i o n of the support system. different  c a b l e b o l t p a t t e r n s observed  i n Canadian open  d u r i n g the data c o l l e c t i o n phase are i l l u s t r a t e d t o 9.8  and w i l l be d i s c u s s i n t h i s s e c t i o n .  length  and  d e n s i t y of  c a b l e s are  also  The  stopes  i n figures  9.1  Typical cable bolt  given.  However,  these  v a l u e s should not be used as d e s i g n g u i d e l i n e s s i n c e c a b l e b o l t systems  should  be  designed  according  to  the  rock  mass  c o n d i t i o n s and the p o t e n t i a l rock mass f a i l u r e mechanism.  9.3.1  Cable b o l t p a t t e r n s f o r open stope backs The  create  principle  of the system shown i n f i g u r e 9.1  a regular p a r a l l e l  of c a b l e s .  pattern with  a uniform  i s to  distribution  T h i s c o n s t i t u t e s the most commonly used  i s g e n e r a l l y a p p l i e d when the overcut i s f u l l y open. 247  a)  system  and  According  FIGURE 9.1 a) Uniform cable b o l t p a t t e r n i n s t a l l e d i n open s t o p e overcuts.  FIGURE 9.1 b) Uniform cable b o l t p a t t e r n i n s t a l l e d i n open s t o p e o v e r c u t s and supplemented w i t h short rebar.  to  the  data  base,  pattern  varies  bolting  i s designed  (cb/ m ) . reinforcing  10  to  at 0.1  bar  are  of  25  a  bolts,  and  with  this  density  of  c a b l e b o l t s per square metre  in  t o t h r e e metres  between  rebar/ m . with  a  the  high  T h i s i s shown i n f i g u r e 9.1  with  a  o b j e c t i v e i s to  density  of  short  l a y e r s with  b).  long  Some mines have  fan p a t t e r n s of c a b l e b o l t s i n the  attempt t o p r o v i d e a l o c a l i z e d w a l l support  grouted  cables  The  2  beam  the  t i e t h a t beam i n t o more competent  cable b o l t s . added  associated while  a s e t of two  installed  r e i n f o r c e d rock  cable  metres  to 0.4  i n t e n s i t y of about 0.7  create  also  from  length  In some cases,  2  pattern  the  s i d e w a l l s i n an  as the stopes above  are e x t r a c t e d . The of the is  concept  driven  first the  second  and  support  system  tries  of p r e r e i n f o r c e m e n t .  i n two  stages.  c a b l e b o l t s are  open s e c t i o n  (see  The  The  central  installed  figure  t o take  9.2).  better  overcut section  vertically  advantage  in this (C)  case  i s opened  i n the back of  Supplementary c a b l e b o l t s  are a l s o i n s t a l l e d a t an angle, over the s i d e s (S) t h a t w i l l  be  "slashed" during  At  the  second  stage  the  o n l y mine u s i n g t h i s design,  was  9 meters with  the  preceding  of  the  overcut  l e n g t h of c a b l e b o l t  a d e n s i t y of b o l t i n g  case,  2.7  metre  long  of 0.16 rebar  between the c a b l e s with a d e n s i t y of 0.44 Another m o d i f i c a t i o n of open stope on  f i g u r e 9.3.  development.  cb/ m . 2  were  rebar/  used As i n  utilized m. 2  roof b o l t i n g  i s shown  Cable b o l t s ( i n t h i s case s i x metres long)  i n s t a l l e d a t an i n c l i n a t i o n of 76° 249  in  are  i n one d i r e c t i o n f o r a given  FIGURE 9.2 Cable b o l t support system using inclined cables and two phases of overcut d e v e l o p m e n t f o r prereinforcement.  FIGURE 9.4 Cable b o l t support system designed f o r overcuts containing a small p i l l a r ( s ) .  row  while  opposite  in  the  next  direction.  interlaced  This  pattern  discontinuities  row  more  cables  are  inclined  alternate inclination  which  at  the  aims  at  angles.  The  density  temporary drilling  cable b o l t original wider  pillars  drifts  d e s i g n has  as  the  stope  is  i n these  cases  of b o l t i n g of 0.2  in  the  overcut,  development,  shown i n f i g u r e  9.4.  were very s m a l l but w i l l  extracted.  Once  again,  of p r e r e i n f o r c e m e n t . were roughly  or  The  The become  this  takes  bolt  length  10 metres w i t h  a density  m. 2  Cable b o l t p a t t e r n s f o r open stope w a l l s The  first  attempted  to  the  restricted  application  distribute  supported access,  necessarily  support. 2  cb/  left  are used as the d r i l l i n g  spans t o be supported  observed  m.  are  been done as  advantage of the concept  not  0.25  2  parallel  over  to  of  m. When  9.3.2  an  geological  b o l t i n g achieved i n t h i s type of d e s i g n v a r i e s from 0.2 cb/  the  produces  intersecting  favorable  in  was  Only  the  wall  cable  cables (figure  the d r i l l  produce  of  a  as  bolts  favourable  stope  uniformly  9.5).  h o l e s had  in  t o be bolt  as  Because fanned  with  such  design  and  the  possible of  the  which does  inclination  a low b o l t i n g d e n s i t y of approximately  achieved  walls  bolt  for  0.06  lengths  cb/ were  variable. The  approach  illustrated  in  figure  9.6  consists  c r e a t i n g a r e i n f o r c e d beam i n v e r t i c a l or i n c l i n e d w a l l s . 251  of This  FIGURE 9.5 U n i f o r m c a b l e b o l t p a t t e r n i n s t a l l e d i n an stope w a l l . 252  open  FIGURE 9.6 C r e a t i o n o f a r o c k beam i n t h e h a n g i n g w a l l i n s t a l l i n g a l o c a l i z e d high density of cable bolts. 253  can  be  done by  pattern  at  every  reinforcement one  stope  installing  cable bolts  sublevel.  i s to  limit  height.  The  bolt  most expensive  support  installed  system  from  length  supported  optimum.  (see  secondary figure  drift  fully  and  purpose from  the second  the  in this  9.7).  parallel  case  cable  The  to  the  concept  of  cable i n c l i n a t i o n i s  has  been used  drift  only o c c a s i o n a l l y  in  base.  i n t r a n s v e r s e b l a s t h o l e mining.  cables  of  running  a p p l i e d and  are  installed  angles t h a t h a l f of the p i l l a r left  bolts  only  example i n v o l v e d the support of p i l l a r w a l l s (or  stopes)  9.8,  cable  of  w a l l s i s when the c a b l e s are  figure  approach  two mines of the data last  form  Because of the h i g h c o s t of the b o l t i n g  development, t h i s  The  this  but c e r t a i n l y the most e f f i c i e n t  p r e r e i n f o r c e m e n t can be near  of  dimensions.  bolting  wall  of  f o r hanging  a  concept  d e n s i t y fan  the w a l l spans t o e f f e c t i v e l y  v a r i e s w i t h the stope w a l l The  The  i n a high  from  the  system  pillar  in  i s t o prevent order  undercut  at  such  i s supported by the stope on i t s  h a l f by the stope on  the  As shown i n  to  i t s right.  The  main  the detachment of b l o c k s  maintain  the  integrity  of  the  pillar. In cable  the bolt  reviewed, stiffness.  preceding support  as  well All  discussion,  systems as  these  the  and  the  their  concept  elements  principal  options  applications  have  of  must  o p t i m i z a t i o n process of a support system. 254  prereinforcement be  considered The remainder  in of  of  been and the  FIGURE 9.7 Cable b o l t support system f o r a hanging i n s t a l l e d from a p a r a l l e l b o l t i n g d r i f t . 255  wall,  FIGURE  9.8  Cable b o l t support system s t a b i l i z i n g 256  pillar  walls.  this  paper  will  characterizing length  9.4  on  cable bolt  the  design  support:  of  three  of c a b l e  bolts.  DEVELOPMENT OF CABLE BOLT DESIGN GUIDELINES  the  open stopes  data  supported  collected  the  data  of  gathering  program,  data.  the  66  case  on t a b l e s s i m i l a r t o those  Table  9.1  case h i s t o r i e s  g e o t e c h n i c a l parameters necessary  and  shows table  the 9.2  of  for  background contains  the  f o r the d e s i g n a n a l y s i s .  The  t h r e e p r i n c i p a l v a r i a b l e s of c a b l e b o l t d e s i g n of b o l t i n g , the l e n g t h of the c a b l e s and cable  histories  by c a b l e b o l t s were c a r e f u l l y documented.  i s presented  unsupported  information  are the  density  the o r i e n t a t i o n of the  bolts.  9.4.1  Design a n a l y s i s o f the c a b l e b o l t support The  use  of  the  graph)  empirical  q u a n t i f i c a t i o n of  bolts. length  in  geomechanical  stability  the  design the  model  (and  data the  analysis  allows  supporting  effect  modified for of  the cable  G u i d e l i n e s f o r the e s t i m a t i o n of b o l t d e n s i t y and will  be  derived  a n a l y s i s also provides the  variables  the d e n s i t y of b o l t i n g , the  and the r e l a t i v e o r i e n t a t i o n  During  The  focus  most  suitable  from  type  of  some a s s i s t a n c e i n the d e t e r m i n a t i o n  of  cable  bolt  the  analysis.  orientation  by  This  bolt  analyzing  the  p o s s i b l e f a i l u r e mechanisms. The m o d i f i e d  stability  numbers and h y d r a u l i c r a d i u s have 257  TABLE  9.1 Background i n f o r m a t i o n f o r t h e d a t a base o f case h i s t o r i e s t h a t have used s u p p o r t . JOINT ORIENTATION 1 ;  HIHE  CASE  ff  I (1)  (2)  1  251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 ! 272 ! 273 274 | 275  1 1 1 1 1 1 1 1 1  | ! ', !  2 2 2 2 2 2 2 3 3 3 4  ;  s  ! : ! : :  6 6 6 6 6 7 7 8 8  ;  I  ! :  1» I 9 ! >o  1!  276 277 278 279 280 281 282 284 285  PLANE  1  (3)  !  BACK BACK  1 i  ! BLOCK SIZE ! ;  !  FACTOR  !  RQD  ;  FACTOR  ;J  !;  /Jn  :  (*) i !  COMP  (5)  BACK  ! i COMP | J COHP ] ! COMP  BACK  ;  ',  is  :  HW  ;  !  25  !  ; ! ! !  IB  ! j  18 18 18  ; ! COMP ! ! COMP ! ; COMP  BACK  !  BACK  ',  ! ;  BACK  !  ;  is  BACK  ;  !  14  ;  14  BACK  ;  BACK  !  BACK  ;  BACK  ;  BACK  !  BACK  ;  ! ; ! ! ! ! ! !  6 4 6 6 4 6 6 6  WALL  !  BACK  ;  BACK  ;  BACK  ! !  BACK  ;  !  'o  BACK  !  6 6 6 6 6 4 4  7  ',  ;;  I ;! i! !  COMP COMP  STRK  BLOCKY/  !  DIFF  FOLIATED  (7) !  (8)  20  i ; :  20 40  !  40  ; ; ! ] ; : |  ;  COMP  1 !  ;  COMP  !  22  ;  COMP  !  COMP  ;  COHP  ! ! ! ! !  22 66 15 24  ;  COMP  ;  ;  RELAX  22 42  COMP  1!  24 *5  ;;  COMP  ;  90  !; !1 ;! !! !!  COMP  !  20 20 30 5 20 20 20 20 20 70  ;  END  ;  BACK  ;  BACK  !  BACK  !  BACK  ;  !  is  ! ',  BACK  ! ! ; ! ! !  15 25 9 8  ! ; COMP ! ! COMP ; ! J COMP  HW  i!  j  20 20 20 20 20 20 20 20  COMP  ;  BACK  SHAPE  DIP  ! ! ! RELAX ! ! ! ! !  COMP  END  ;  BLOCK  JOINT  DIFF  ;  COMP  BACK  ;  (6)  COMP  ! ! ! ! ! ! ;  BACK  ! ! I  25 25 25  BACK  RELAX  !  ! ! ! !  BACK  CRITICAL  !  !  j  !  i  COMP COMP  ! ; ! ! ! ! ! !  COMP COMP COMP  | ! COMP COMP  RELAX  FACTOR  !  i {  E F F E C T OF GRAVITY  !  STRESS  ! !  Q  !  15  ; ! !  1 !  ! ! ! ! ! ! ! ! ! ! ! ! !  1 ! 1 ! !  o o o 0  i  SHEAR  ;  1  STREN.  i  ! Jr ! /Ja  i  CRITICAL  J  !  JNT DIP  !  (ID  ;  !  (10)  :  BLOCKY  !  20  ;  J  0.75 0.75  !  BLOCKY  !  20  ;  BLOCKY  1  0.75  !  20  !  !  20  l  !  20  ;  !  20  !  !  20  ;  BLOCKY FOLIATED  o o o o o  BLOCKY BLOCKY BLOCKY BLOCKY  1 ! ! ; ! ;  BLOCKY  I  BLOCKY BLOCKY  ! ! ;  BLOCKY BLOCKY  0.753 3 3 3 3 3 0.5 0.5  ;  ',  STOPE PLANE  DIP  (12)  o o o o 90  o o o o o  20  ;  66 66  ; ;  0.7  !  42  ;  !  0.2  !  42  ;  ! ! !  0.7 0. 7 0.2  !  42  ;  20  !  42  !  20  i i  :  BLOCKY  ; ;  66  BLOCKY  !  l  FOLIATED  !  1.5  BLOCKY  BLOCKY BLOCKY BLOCKY  BLOCKY BLOCKY  ! I  i  !  20  ;  I t  1.5  ! ! ! ! !  o o o o o  FOLIATED BLOCKY  1.5 1-5 1.5 0.8  BLOCKY  ;  BLOCKY  o o o  BLOCKY  ! !  BLOCKY  ! !  BLOCKY  ;  1.5  ', ! ! !  i  ;  24  ! !  !  BLOCKY  75  ; | ;  BLOCKY  BLOCKY  1 ! 1 !  24 45 90  FOLIATED  o  20  20  BUCKLING  !  30  1 ! 1  !  ',  FREEFALL/  ; !  1 !  1  !  i  (9)  o o o o o o o o o o o o o o  o  SLIDING  25 25 20  o o 90  o o o o o o  20  ;  !  60 60  ; ;  90 55  ;  20  ;  0  !  20  ;  o.8  :  20  ;  o o  2 2 0.25 0.5 0.75  ',  20  !  0  !  20  ;  ! ! !  70 70 15  ; ! !  o o 70  o  J ; ! ;  SIZE  ;  AND  ;  SHAPE  ;  FACTOR  !  ; !  HYD.  J ;  RADIUS  i:  d3)  ;! ;! ;; ;!  8 8 5 6  1 !; ;  1  ! ;! ;! ;;  ! ; ! ;  ; ]  ;! ; :  1 !| ;  ;  !  !; :| ;; !! !! i! 1! St i! i! !I ',  1  !I !S |!  !!  5  |;  ASSESS.  ;  1  TYPE  OF  MODE  (15)  (16)  : ,'  (14)  4  ; !  CAVE  DISC.  BLOCK  4  ; !  CAVE  DISC.  BLOCK  3 4  |! !!  STABLE  DISC.  BLOCK  STABLE  DISC.  BLOCK  o  !j  STABLE  DISC.  BLOCK  ! ,'  STABLE  5 9 7  DISC.  BLOCK  STABLE  DISC.  BLOCK  i  I! ;!  STABLE  DISC.  BLOCK  6  ;i  STABLE  DISC.  BLOCK  !I  STABLE  DISC.  BLOCK  !|  STABLE  J O I N T E D RM  76 4 5  o  13 9 16 o 7 3 6 o  ;;  CAVE  J O I N T E D RM  ;I  STABLE  J O I N T E D RM  !i !!  STABLE  J O I N T E D RM  ;! ;;  CAVE  B  o  8 7 8 8 9  14  4 4 5 3 5 3  6 2 4 4 6 5 2 7  i  1 ; i  2  ; 1 ; 1 ; !  6 2  :j !!  STABLE CAVE STABLE STABLE STABLE STABLE STABLE  JOINTED  1 J O I N T E D RM J O I N T E D RM  3a 3a  JOINTED  RH  J O I N T E D RM DISC.  BLOCK  STABLE  DISC.  BLOCK  STABLE  J O I N T E D RM  ;  !!  1  STABLE STABLE  2 5  !! !!  STABLE  J O I N T E D RM  STABLE  DISC.  s  ;I  CAVE  1!  3a  J O I N T E D RM  i  2 7 3 6 4 l 7. 5 6. 3  2a 2a  RH  J O I N T E D RM  7  i  FAIL  BEHAVIOUR  J O I N T E D RM J O I N T E D RM BLOCK  J O I N T E D RM  STABLE  DISC.  !  STABLE  DISC.  BLOCK  !I !! ! |  STABLE  DISC.  BLOCK  STABLE  J O I N T E D RM  UNSTABLE  J O I N T E D RM  3a  BLOCK  3a  TABLE  9.1 Background i n f o r m a t i o n f o r t h e d a t a base h i s t o r i e s t h a t have u s e d s u p p o r t , ( c o n t ) . JOINT ORIENTATION  MINE  »  (1)  (2) 286 287 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 , 311 312 313 314 315 316 317 318  10 11 13 15 15 15 15 19 19 20 20 20 20 22 22 26 26 26 26 26 26 , 26  1 26 ! 26  ! 26 ! 26 ! 26 26  I  I  CASE  f  26 28 30 32 I  I  PLANE  BLOCK  !  STRESS  !  ;  SIZE  !  FACTOR  !!  !  FACTOR  1 RQD /Jn  !  !  (3) ! ! HW  ;  HW  ;  BACK BACK BACK BACK BACK  !  ! ! !  ! ; ! ! ; ! ! ! !  BACK  !  !  BACK  ! !  BACK  ;  BACK BACK BACK BACK BACK BACK BACK BACK BACK BACK BACK  | j ',  ! ! ; !  ! ; ! ;  ! ! | ; ; ! ! ! ! !  ;  BACK  ;  BACK  ;  !  ;  BACK  ! ; !  BACK  ;  BACK  ;  BACK  ;  BACK  !  HW  ;  BACK  ;  BACK  |  ! !  ! ! !  I !  I I  J  COMP  s !  6 6 6 6  !  WALL  ;  (4> ; ! (5) 30 i»  4  29 I?  ] !!  !! ;! ;; ;;  COMP COMP COMP COMP COMP RELAX  ;  !;  COMP  !1  COMP COMP  i;  COMP  >  ! ;  COMP  io 5 2 5 i 8  ; 1 COMP  j;  COMP  |!  COMP  ;! ;! ;! ;; !;  i1  15 : ;  25 20  ;; |;  5 ||  io  i;  20 ; ! 20 ; ; 9  14  n  (6) RELAX  !;  9 9 2  RELAX  RELAX  25 25 7  CRITICAL  BLOCK  JOINT  SHAPE  1 DIP  !  STRK  BLOCKY/  !  DIFF  !  DIFF  FOLIATED  J!  (2)  !  (8)  ! !  !  COMP COMP COMP COMP COMP COMP COMP COMP COMP COMP COMP COMP COMP  !  !;  RELAX COMP  !;  COMP  I  I  I  ! o ! ! o ! ! 20 ! ! o ! ! o ! ! o ! ! o i ! ! o 1 ! o ! : 20 ! ! 20 ! | 20 ! | 70 ! ! 10 ! 1 10 ! ; 20 ! ! 20 ! ! ?o ! ! 20 ! ! 20 ! ! 20 ! 1 20 ! I 20 ! ! 20 ! i 20 ! ! 20 ! | 20 ! 1 20 ! ! 20 ! J ! > 5 ! ! 60 ! ! 70 ! ii i I  |  |  FACTOR  E F F E C T OF GRAVITY  (9)  o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o  FOLIATED FOLIATED BLOCKY BLOCKY BLOCKY  ;  JNT DIP  ;  !  (10)  :  (ii)  :  ! !  0.75 1  J  ; | |  BLOCKY  !  BLOCKY  !  FOLIATED  !  FOLIATED FOLIATED  ! !  FOLIATED  !  FOLIATED  ; ;  BLOCKY  ;  2  1.5 1.5 1-5 1-5 0.5 1-5 1-5 2 2  1-5  i.s i.s I .o  i  !  1.0  io  BLOCKY  ; ; !  BLOCKY  ;  BLOCKY  ! ; ; ;  i.o i.o io I .o i.o i.o i.o i.o  ; ;  1.0 1.0  BLOCKY  ; ;  i.o i.s  BLOCKY  !  1-5  BLOCKY  BLOCKY BLOCKY BLOCKY BLOCKY BLOCKY BLOCKY  BLOCKY  i CRITICAL  !  BLOCKY  i  !  !  !  BLOCKY  SLIDING  ;  BLOCKY  BLOCKY  ;  ! Jr ! /Ja  BLOCKY  FOLIATED  i  1 SHEAR ! STREN.  SIZE  ;  ;  AND  ;  ;  i.s  i  ', !  !  !  ! !  !  !  i i ! !  ! !  70 90 20  ! !  i  ;  20 ! 20 !  90  i  o ! 20 : 20 ;  20 70  J  !  io ! io !  !  20  J  !  7o  !  1 1  20  i  ; !  ; ! ! ',  ! ;  20 ! 20 ;  20 ; 20 ! 20 ;  20 20  ; ',  20 ! 20 ; 20 ;  1 1 i  20  !  so ;  ! !  60 70  ; !  I I  |  BUCKLING  !  i  1 SHAPE i  ! ;  STOPE  20 ;  20  FREEPALL/  PLANE  DIP ! !  :i  (12) 70 90 0  20 20 20 20 90 o o o  o o o o o o o o o o o o o o  case  i !  J  ;  of  1  ! ji !:  FACTOR HYD. RADIUS  (13)  !! !| ;!  1!  !: !I !! !! ;1  ! !  !:  I: ; ',  ; ! !!  o o !! I I  FAIL MODE  STABLE  J O I N T E D RM  STABLE  DISC.  BLOCK  i;  STABLE  DISC.  BLOCK  CAVE  J O I N T E D RM  ;;  STABE  J O I N T E D RM  ;| !j  CAVE  J O I N T E D RM  STABLE  J O I N T E D RM  CAVE  J O I N T E D RM  6.2  ;!  ;  | ;! |; !! ;; !!  STABLE  DISC.  BLOCK  STABLE  DISC.  BLOCK  STABLE  DISC.  BLOCK  STABLE  DISC.  BLOCK  STABLE  DISC.  BLOCK  7 !!  STABLE  DISC.  BLOCK  7.7  i|  CAVE  J O I N T E D RM  5.6  i!  STABLE  J O I N T E D RM  |!  STABLE  DISC.  BLOCK  2.7 ; ;  STABLE  DISC.  BLOCK  9.0 3.9 8.0  4.  4.3  14  9.3  ! ; i  ;  7.1 ;  7.4  J O I N T E D RM  ;  CAVE  J O I N T E D RM  1 !  STABLE STABLE  | ',  8.4 8.6  ;i ;!  5.9 ; 1 I I  3a 3a 3b  3c  3a 3a  J O I N T E D RM  CAVE UNSTABLE  s.o ; 1  (16)  (15)  d4)  J ;  o ! 1 13.7 ; ! o !! io ! 1 o 1 ! 5.3 ; ! o i ! 6.9 ; !  65  TYPE OF BEHAVIOUR  io.o ; ;  11 12.7 ;j ! 146 ! !!  ASSESS.  ;  19.7  ; ! ii.4 ; ! s.o ; ; 20.8 9.2 ;| ; 1 19.0 ; ; 3.7 ! ! 5.3 ;!  | 1  3a  J O I N T E D RM  STABLE STABLE  DISC.  BLOCK  DISC.  BLOCK  DISC.  BLOCK  3a  J O I N T E D RM  CAVE  J O I N T E D RM  STABLE STABLE  DISC.  BLOCK  STABLE  DISC.  BLOCK  STABLE  J O I N T E D RM  UNSTABLE STABLE  i  DISC.  BLOCK  DISC.  BLOCK  3a  i  TABLE  9.2 Input parameters f o r t h e data base o f case t h a t have used s u p p o r t .  ; BLOCK ; ; STRESS ; 1 JOINT ORIENTATION \ ! FACTOR !! : S I Z E i ! FACTOR || |CASE  ;  i  :  !! oc/  ! RQD  !  /Jn !  (2)  :  (4)  ! 251  ! J !  25  1  252  ! 253 ! 254 ! 255  i 256 J 257  1 i  1!  ]  !  ! !  ! 261  | 262  1  ! J 25 [ ! 25  is 25  :I  0.25  !!  0.2  0.75  ;! J!  0.75  i  0.25  !!  0.2  0.75  ;!  o.i  !i  0.2  3.0  i.o  ;i  0.2  0.75  o. I  i!  0.2  3.0  |  ! !!  ;i ]  !  is  :;  o.i  ;  is  :!  o. I  ||  !  !  ; ; ! ; ; :  ;  18  is 14  14  1[i ;1 ] ;i ; ; ;!  4  ; | !i  j  6  |  |  1  |  i  6  | ;|  ! ! 268 269 : 270 ! 271 ! 272 ! 273 !  4 6 6 6 2 40 6  ;! ;! ;! :! !! !! ;  i  1 !  j  ti  0.2 0.2  i  j1 II  !  !  1  8 4  ;  1 9  CAVE  J !  2 o  i:  8 4  ;  CAVE  1  2 0  i;  5 3  1 9  ! ;  STABLE  2 o  i:  1!  6 4  2 2  STABLE  !  8o  ii  5 o  30  5 9  (24)  (25)  ;; ;; I; ;; ;; !;  REBAR CABLE REBAR CABLE REBAR CABLE  ;I! 1  REBAR CABLE  2.2 21 2.2 21 2.2 21 2.2 21  5.1  STABLE  1| ;  0.7 0.17 0.7 0.17 0.7 0.17 0.7 0.17  1|  CABLE  2 2  STABLE  1  ;; ;; ;; ;; ;; ;: i',  CABLE REBAR CABLE REBAR CABLE REBAR CABLE  1; ;;  REBAR CABLE  1! ;; ;] ;; ;; ;; ;; ;; ;; ;; ;; ;; ;; !; !; ;; !; ;; ;!  REBAR REBAR CABLE CABLE REBAR CABLE CABLE CABLE CABLE CABLE CABLE CABLE CABLE CABLE CABLE CABLE CABLE CABLE CABLE  ;;; 1 ;; ;: ;;  CABLE CABLE CABLE REBAR CABLE  3 8  ;! !  2 o  !!  6 7  j  2 2  STABLE  2 o  I|  7 1  ]  2 2  ] ',  ! ; ! ; ',  STABLE  i ; |  2 o  ;J  4 6  i  2 2  STABLE  ',  ; |  2 o  !;  5 o  ;  2 2  STABLE  !  2 6  ;  i  13 9  ;  0 7  2 6  :  1  16  o  !  0 7  !  ;  o.2  3.0  ;: !  o.i  ;!  0.4  o.s  o . i ;;  0.4  0.5  I  | ; i !  |  ;  ]  0.2  0.7  i!  0.1  |  !  0.4  0.2  i  0.35  '; !  0.2  0.7  0.77  J!  0.2  0.7  o.i i.o  ;! j|  0.2 1.0  0.2  ;; ;! ;!  0.85 0.2 0.2 0.2 0.5  !  0.2  1.0 1.5  i.o  1.5  [ ] !  j  j;  i.o  ;  ;I  0.36  j  2  4  ];  7 3  !  0 7  1I  !  2 o  ;!  6 o  ;  0 1  I  STABLE  ! | ] ! ] !  2 4  ;  i  8 o  ;  0 7  STABLE  24  !!  14 8  !  1 6  CAVE  2o  !!  i  ! ! ! ! !  2 2 2 2 2  i ;!  0 4 0 0 1 8 0  ;] ; ! j! | |! !! :! |! ;! ;! !! II  3.5  J  i i  !  o o o o o  ! ;| !: !;  7 8 4 5 5 6 2  8 9 4 3 3 2 6  ! ! ; ; | !  j  J  |  ! ; STABLE j | ] CAVE ; - ;  1 j  j i  !!  STABLE  1 2 5 2 1 0 4  1  1| ! | ! ;  1 |1  !  CAVE STABLE STABLE STABLE STABLE  ! i ! !  STABLE STABLE  1 ! [  II  i  BOLTING i; FACTOR ;;  BOLT LENGTH  (23)  i !  o. I  (i  2 o  BOLT DENSITY  (22)  3.0  J  i.o  i!  3.0 3.0  |  j  ii  0.2  ;!  (14)  2 o  ;!  0.1  (21)  (20)  !  ;  o.i  o.i o.i o.i  ;  i  i!  !! SUPPORT ;; TYPE  (i j)  1! 1i  i!  1J  ;!  ! !  1 ; i1  ASSESS.  i  ]|  ! ] !  I  1  (19)  N  ;  |  ! 264  »  do)  0.2  ;i  J ! ! !  (18)  ;  i!  6  ! 267  i!  01  o.s  !  266  (i2)  j|  ! 263  i  /J«  18  1;  | 265  JOINT  CABLE BOLT DATA  •j  | ! HYD. ; SLABBINC ! ; ; RADIUS ! ! ;1 SLIDING !; FREEFALL/  !  ! ]  258 ] 259 ', !  1 260  1  i:  Jr  ! ! CRITICAL  EFFECT OF GRAVITY  histories  i  I  I  I  5. i 5.1 5.1  i.o 9 2.7 9 2.7 9 2.7 9 2.7 9 2.7 2.4 6 24 2.4 6 24 3 18 3 18 3 18 30 3 18 18 10 3 6 9 3 2.4 6  0.16 0.44 0.16 0.44 0. 16 0.44 0.16 0.44 0.16 0.44 0.7 0.17 0.17 0.7 0.17 0.17 0.17 0. 17 0.17 0.17 0.17 0.17 0.05 0.17 0.17 0.23 0.04 0.2 0.2 0.3 0.7 0.7 0.24 i  i  •  i.7  ii  ii  |j ;;  ;; ;| ;; ;;  j [ ;;  1.7  ;! ;; |; ;; ;;  I .• 7  Ij ;i  1.7  1 1 ;;  1.7  6.8  ;; ; j ;;  j | 6.8  ;; ; [  3.6  !| ] |  3.6  : i  5.1  ! | || ! |  3.6  1|1|  4.2  ! | ||  0.4 0.6 1.1 2.8 2.1 3.0  i  ;j  11| | || | |  II  | |  I| II  TABLE  iCASE  O  I!  ! ! ! ! ! ! ! !  | ! 1  ;  9.2 Input parameters f o r t h e data base o f case t h a t have used s u p p o r t , ( c o n t ) .  BLOCK  STRESS  SIZE  FACTOR  RQD  !  ! 0c/  1  JOINT  EFFECT OF GRAVITY  ORIENTATION FACTOR  !  CRITICAL  Jr  !  «  I  /Jn  i!  oi  ;  JOINT  /Ja  ;  (2)  !  (*)  !:  d7)  !  (18)  (10)  !  274  !  «  !!  o.i  !  1.5  !  ! ! ! ! ! !  6 6 6 4 4 15  Ii ji  0.1 0.23  !  25  275 276 277 278 279 280 281 282 284 285 286 287 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317  ; sis  !  is  !  !  9  s  ! ! ! ! ! !  8 30 1?  !  6  6  6 6  ; !  4 29  !  i'  ! ! 1 ! ! !  !  ! ! !  ! ! ! | ! !  !  25 25 17 9 ' 2  io  5 2 5  i  8 15 25 20 5  io  !  20  !  20  ! ! !  9 >4 13  i; |! !! !!  !; ; !  !! ;! ;I ;! !! !! ;! !i !  ;  ;i !;  !!  !! ;! 1; !; ;!  ; ;| [! ;; !! !! ;! ;  !! !! |! !! !! ; ! ; ! !! !! !;  o.i o.i  0.2 0.6  o.s o.i  0.45 0.5 1.0  l .o i.o 0.6  l .o  1 .0  l .o 1.0 0.2  o.i  0.3  o.  I  0.3  0.1  o.i l .o 1.0  i.o i.o i.o  i -0 i.o 0.7 0.7  0.7  0.7 0.7 0.5 0.5  l .o o.i o.i  j ! ! | ! !  0.2  ! J  0.4 0.25 0.2 0.2 0.2 0.2 o.2 0.9 o.3 0.2 0.3 0.3 0.2 o.3 0.3 0.3  ;  0.3  ;  i  0.3 o.3  ;  0.2  | ! !  0.2 0.2 0.9 0.2 .0.2  ; |  :  i ! ! !  ;  I ! ;  0.2  ! !  0.2 0.9 o.2 0.2 o.2 0.2 0.2 o.2 0.2 0.2 0.2 0.2 0.2  ; !  ; i !  ;  ! ! ! ! i ;  0.2  !  0.8 o.9  :  1.5 1.5 1.5 0.8 0.8 2.0 2.0 0.25 0.5 0.75 0.75 1.0 2.0 1.5 1.5 1.5 1.5 0.5 1.5 1.5 2.0 2.0 1.5 1.8 1.8 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0  1.0 1.0 1.0 1.0 1.0 1.8 1.5 1.8  SLIDING  (19)  CABLE  !  FREEFALL/  | ;  HYD.  ;  SLABBING  ; ;  RADIUS  ;  ;!  d3)  !  (21)  1  0.4  !  (20) 2.0  |!  !  ! !  j! !!  !  1  4.6  !  2.0 2.0  ! ;  ;  !  2.0  !  !  2.0  !  !  2.0  ! !  l ;  2.0  ! !  5.0  BOLT  DATA  ;  !  histories  6.o  !  !  2.0  !  !  6.0  ; ! ; ; { ! ! ! ;! ;! ! !  !  [  s.o  ! !!  !  !  2.0  !  ;  !  ! ! ', ! !  ! ! ! | i  2.4 2.4 2.4 2.4 8.0  ;! i: ;; ;! |!  !  |  2.0  ; ;  ;  !  2.0  ;  !  !  2.0  |  ; 1  !  ;  2.0  ; :  !  !  2.0  1 1 !  2.0  I  ! ! i ;  2.0 2.0  !  !  2.0  |  !  2.0  !  !  2.0  !  !  2.0  !  !  2.0  !  !  2.0  !  !  2-0  !  !  2.0  !  ;  2.0  !  !  2.0  : ;; ; | |; |! | ! i! I! ! ! ; ! ; ; !! ! ! ; ! ; !  !  !  2.0  ! J  !  !  2.0  |  2.0  !  !  5.5  !  !  2.0  !  !  2.0  ;  ; ;! ; ! ; ;  4 2 4 6 5 2 7 2 3 4 7 6  7  ;  i  ;  2 s 5 7 6  i  5 3  io o  19 7 6 2 ll 4 8 o 20  8 9 2 19 o  ! ; ; ! !  ;  ! ]  !  ! ! ; 1  1! !  3 7  ;  5 3 9 o 3 9 8 o 4 7 7 7 s 6 4 3 2 7 14 9 3 12 7 14 6 7 i  !  8  o  7 4 13 7 10 5 3 6 9 8 4 8 6 5 9  ! !  ! ; ! ] ;  ! ! ;  ! !  ! |  ; ! ! ! ! ; : !  N  1.8 2.4 0.4 0.1 0.3 7.2 9.6 1.1 3.6 1.2  11 72 14 3.9 6.5 6.5 6.5 4.8 5.2 1.0 6.0 2.0 11 0.6 0.6 0.8 4.0 9.0 0.8 2.0 0.4 3.2  ASSESS.  (u) STABLE  !  ;!  j  ||  SUPPORT  ;  !!  (22)  ;  ;;  REBAR  |!  CABLE  TYPE  STABLE  1  ;;  CABLE  STABLE  !  ; |  CABLE  STABLE  !  !;  CABLE  STABLE  !  ;;  REBAR  CAVE  !  !!  REBAR  STABLE  !  ;;  REBAR  STABLE  ;  ;;  REBAR  STABLE  ;  ];  STABLE  !  1!  CABLE  I ;  ;;  REBAR  ;;  REBAR  STABLE  ;  ;!  CABLE  STABLE  ;  ;!  CABLE  UNSTABLE STABLE  CABLE  CAVE  J  ;;  CABLE  STABE  ;  ;;  CABLE  CAVE  i  ;;  CABLE  STABLE  ;  ;;  CABLE  BOLT  LENGTH  (23)  (24)  0.7 0.24 0.06 0.06 0.23 0.4 0.4 0.7 0.7 0.1 0.03 0.7 0.04 0.07 0.07 0.1 0. 1 0.1 0.1 0.02 0.15 0.23 0.27 0.2 0.21 0.22 0.22 0.33 0.33 0.37 0.22 0.19 0.28  CAVE  ;  !i  CABLE  STABLE  !  ;;  CABLE  ;;  CABLE  STABLE STABLE  1 ,'  ;;  CABLE  STABLE  J  ;;  CABLE  STABLE  i  ;;  CABLE  STABLE CAVE  I !  ;; !!  CABLE  STABLE  ;  !;  CABLE  STABLE  J  ;;  CABLE  STABLE  !  ; i  CABLE  CAVE  !  ;l  CABLE  UNSTABLE  |  ;;  CABLE  CAVE  ;  !i  CABLE  STABLE  !  ! !  CABLE  0.2  4.2  STABLE  ;  ;;  CABLE  7.0 5.6 1.4 2.8 4.0 4.0 18 3.4 4.2  STABLE  !  STABLE  J  CAVE  0.16 0.16 0.16 0.25 0.16 0.16 0.13 0.07 0.11 0.31  CABLE  !;  CABLE CABLE CABLE  !  ;1 ;;  STABLE  |  ;;  CABLE  STABLE  ;  ; i  CABLE  STABLE  !  ;;  CABLE  STABLE  j  ;;  CABLE  UNSTABLE  !  ;;  CABLE  STABLE  !  ;;  CABLE  BOLT  DENSITY  2.4 6 9 9 9 2.4 2.4 2.1 2.1 15 15 2.4 2.4 21 11 20 20 20 20 6 6  9 10 5 10 12 12 10 7.5 7.5 10 10 10 10 15 10 25 10 18 15 25 12 15 6  BOLTING FACTOR  (25) 3.0 0.5 0.5 2.1 1.1 1.1 1.5 1.5 1.7 0.4 0.7 0.1 1.5 0.8 1.9 1.9 1.9 1.9 0.1 0.9 2.1 2.7 1.0 2.1 2.7 2.7 3.3 2.5 2.8 2.2 1.9 2.8 2.0 2.4  1.6 4.0 2.5 2.9  2.4 3.3 0.9 1.7 1.9  been c a l c u l a t e d f o r a l l s i x t y - s i x  case h i s t o r i e s  ( t a b l e 9.2).  They have been p l o t t e d on the r e v i s e d s t a b i l i t y graph i n f i g u r e 9.9.  The assessment  divided  into  represented system  three  by round  failed  bad g r o u t i n g .  cases  groups. shaped  Stable  points.  stope  stope  planes  was  surfaces  are  Cases where the support The empty  f a i l e d cases where t h e cause was a t t r i b u t e d The square  where r a v e l l i n g  couple  bolted  a r e shown on the graph by t r i a n g l e s .  t r i a n g l e s represent to  o f the c a b l e  shaped  o f rock  of interesting  points  occurred  conclusions  a r e the unstable  between the c a b l e s .  can be d e r i v e d  from  A  figure  9.9. Most  case  between  histories  stable  stability general  graph  have  when i t was  plot  and  i n o r below  caving.  i s accurate  been  used  this  that  the dashed  other  attempts  the r e v i s e d  means t h a t c a b l e b o l t s i n stope  mine  operators  only  that  line have  cable  when p l o t t i n g  system had success  drawn  on  figure  been  reported  bolts  a r e an  when p l o t t i n g  9.9, w h i l e  twelve  unsuccessful. impractical  below the dashed  line  means  stable  case  was  heavily  bolted  with  This of  because o f the  combination o f bad ground c o n d i t i o n and l a r g e openings. only  zone  necessary.  below  support  Assuming  by open  Only one c a b l e b o l t support  suggests  the t r a n s i t i o n  three  The  different  sets of cables.  The  grey area o f the support 262  s t a b i l i t y graph  ( f i g u r e 9.9)  Modified Stability Graph Main Data Base 66 case histories  1000  CD  100  ^*-*-* V.'.'.v.vvv'VC**  _Q  ^  10  D CO  -a 1.0  T5  o  0.1  0  5  10  Hydraulic  15  Radius  20  25  (m)  • Stable Stope Surface • Unstable Stope Surface T Caved Stope Surface FIGURE 9.9 The histories.  modified  stability  263  graph  f o r supported case  shows t h e maximum unsupported stope s u r f a c e dimensions t h a t can be  opened  for different  c a b l e b o l t e d stope line.  geotechnical  conditions.  The maximum  s u r f a c e dimensions are d e f i n e d by the dashed  The i n c r e a s e i n p o s s i b l e stope dimensions can be roughly  estimated  for a  hydraulic  radius  given  stability  corresponding  number to  the  h y d r a u l i c r a d i u s a t the dashed l i n e . c a b l e b o l t i n g can then be  by  subtracting  grey  area  and  the the  The economical b e n e f i t of  estimated.  9.4.2 D e n s i t y o f b o l t i n g The along  purpose  existing  bolting ratio  should  of cable  discontinuities.  of  i s t o prevent Consequently  be r e l a t e d t o the frequency  of the block  radius  bolts  the  size  parameter  stope  the movement  the d e n s i t y of  of j o i n t i n g .  The  (RQD/Jn) and the h y d r a u l i c  surface  are  useful  parameters  in  r e p r e s e n t i n g the r e l a t i v e s i z e of b l o c k s . I t i s expected t h a t a higher  d e n s i t y of b o l t i n g ( c l o s e r spacing)  the b l o c k s i z e i s r e l a t i v e l y Figure hydraulic case  9.10  radius,  histories.  included  in this  shows  Only  o f the r a t i o  the d e n s i t y the cases  analysis.  be used when  small.  a plot  versus  should  of  (RQD/Jn) and  o f b o l t i n g used  involving  The convention  stope  backs  regarding  of the p o i n t s i s the same as the one i n t h e s t a b i l i t y figure  9.9.  Once again,  be made from t h i s The  several  interesting  i n the  the shape graph i n  observations  data.  f i r s t observation  i s the s c a t t e r o f t h e data. 264  are  This  can  FIGURE  9.10  Design Chart for Cable Bolt Density 0.40  0.35  0.30  H  0.25 H  0.20 H  0.15  0.10  0.05  0.00 1  2  3  4  5  6  (RQD/Jn) / Hydraulic Radius O Stable Stope Surface  •  Unstable Stope Surface  v Caved Stope Surface  implies that of  for similar  b o l t i n g used  cases  at  rock mass c o n d i t i o n s the  different  mines v a r i e d  must have been designed  trial The  and  exception,  line  indicates  cb/  with  used  only  i n open  cases  have been r e p o r t e d  s t a b l e out  density  i s s m a l l e r than  stope  y-axis  of a t o t a l  of  Consequently,  it  likely  f a c t o r (RQD/Jn  i n d i c a t e s the t r e n d of u s i n g a  bolting  plotting  size  of  0.75.  for  smaller  (RQD/Jn / h y d r a u l i c r a d i u s ) .  cases  the  T h i s suggest t h a t c a b l e b o l t s are not  band shown on f i g u r e 9.10  smaller  one  2  e f f e c t i v e when the r e l a t i v e b l o c k  higher  the  m.  / h y d r a u l i c radius)  most  that  minimum b o l t i n g d e n s i t y  t e n attempts.  The  others  This also r e f l e c t s well  zone between the v e r t i c a l dashed l i n e and  two  t o be  dashed  the  backs i s 0.1  only  while  Some  e r r o r approach used i n most cases.  horizontal  In the  greatly.  conservatively  have been n e a r l y underdesigned.  intensity  inside  appears  I t can  this  that  block  zone  a  be  size  (and  noted  that  are  conservative  stable. design  g u i d e l i n e f o r the d e n s i t y of b o l t i n g i s t o use the c e n t r e of that  zone.  This  corresponds  b o l t i n g used with success  9.4.3  Cable b o l t The  length  undisturbed numerical  to  the  average  density  of  i n s i m i l a r rock mass c o n d i t i o n s .  length of  ground  modelling  cable to  bolts  insure  a  should proper  reach  anchor.  a n a l y s i s , the d i s t u r b a n c e 266  f a r enough According  into to  e f f e c t of s t r e s s  i n the rock mass surrounding of  the r e l a t i v e  size  underground openings i s a f u n c t i o n  and shape  of i n d i v i d u a l  stope  surface.  Consequently, a rough r e l a t i o n s h i p i s expected t o e x i s t between the  h y d r a u l i c r a d i u s o f stope  bolt  used.  9.11,  These two parameters have been p l o t t e d on f i g u r e  f o r t h e cases  of supported  the f o l l o w i n g o b s e r v a t i o n s As  backs  i n the data  base, and  can be made.  i n t h e b o l t d e n s i t y p l o t , f i g u r e 9.11 shows t h a t t h e data  is quite scattered. be  s u r f a c e s and t h e l e n g t h o f c a b l e  Once again i t i s b e l i e v e d t h a t t h i s can  a t t r i b u t e d t o the l a c k o f g u i d e l i n e s f o r support  and  a trial  The  use o f c a b l e b o l t s i n very l a r g e open stope  had  little  design  and e r r o r process.  success.  s u r f a c e s has  I t can be seen on f i g u r e 9.11 t h a t f o r  h y d r a u l i c r a d i u s exceeding t e n , seven support  systems out of  nine have c o l l a p s e d . The  minimum  been  stope  installed  plane dimension i n which c a b l e b o l t s have  has  an  hydraulic  radius  of  approximately  three. The  minimum  cable b o l t  length  included  i n the data  base i s  t h r e e meters. T h i s was a r b i t r a r i l y decided p r i o r t o the data collection  i n order  to d i f f e r e n t i a t e  o t h e r kinds o f s h o r t e r rock A rough and c o n s e r v a t i v e plot  of cable  bolt  bolt  a c t i o n and  anchors.  g u i d e l i n e can be d e r i v e d  length  and  shown on f i g u r e 9.11 by the l i n e c a b l e d e s i g n approximately  cable  hydraulic  radius.  from the This i s  "L" which correspond  equal t o the span o f opening. 267  to a It  FIGURE 9.11  Design Chart for Cable Bolt Length 30  - i  1  Hydraulic Radius (m) o Stable Stope Surface  v Caved Stope Surface  also  constitutes  an approximate  average  o f what  Canadian  open stope o p e r a t o r s have been u s i n g w i t h success.  9.4.4  Bolting The  conditions  stabilizing and to  factor  open stopes have been d e f i n e d  9.11.  In t h e s t a b i l i t y  assume t h a t  should line  intensity  of b o l t i n g  as a stope  of figure  9.9.  factor.  surface  A practical  of b o l t i n g  has been  The b o l t i n g  multiplying  the density  b o l t length  (meter).  i n f i g u r e 9.9, 9.10,  graph a n a l y s i s  the i n t e n s i t y  increase  bolting  i n which c a b l e b o l t systems a r e capable of  (density  plots factor  factor  of b o l t i n g  below  bolting  factors  the  trend  impossible the  t h e dashed  t o account  for  from  area.  i s simply (bolts/  Figure  t h e support  data  the  and i s c a l l e d the calculated  by  square meter) and  When used on t h e support s t a b i l i t y  t h e grey  expected.  and length)  towards  developed  the b o l t i n g f a c t o r i s expected t o i n c r e a s e further  i t seems reasonable  graph,  as a case i s l o c a t e d  9.12  i s a plot  of the  base and roughly  shows  However, t h e s c a t t e r o f t h e data makes i t  t o draw recommended  design b o l t i n g  factor  l i n e s on  graph.  9.4.5  Cable b o l t The  design  orientation of  cable  bolt  orientation  is  a  three  d i m e n s i o n a l problem i n which t h e optimum s t r i k e and i n c l i n a t i o n must be d e f i n e d .  At t h e optimum o r i e n t a t i o n ,  system should develop a maximum s t r e n g t h 269  against  the cable the forces  bolt  FIGURE  9.12  Modified S t a b i l i t y G r a p h Bolting F a c t o r 66 case histories 1000  Hydraulic • • •  Radius  Stable Stope Surface Unstable Stope Surface Caved Stope Surface 270  (m)  acting  on  the cables.  These  forces  a r e dependant  p o t e n t i a l mode o f f a i l u r e o f t h e stope s u r f a c e . in  t h e case  the  cables  of gravity  fall  the p r i n c i p a l  are t e n s i l e .  oriented v e r t i c a l l y  The  cable  on the  For instance,  f o r c e s generated on  bolts  should  then  be  i n o r d e r t o maximise t h e t e n s i l e s t r e n g t h  acting against gravity. For along  a  sliding  mode  the potential  sliding  s t a b i l i t y problems. analytical shear  of f a i l u r e ,  Miller  model suggested  strength  plane  when  t h e shear  force  i s t h e one t h a t  acting  may  induce  (1984) based on a t h r e e dimensional that  cable bolts  installed  develop  a maximum  i n t h e same d i r e c t i o n  as the  shear plane but having an i n c l i n a t i o n o f 17° t o 27°. The slabbing  optimum  of b o l t i n g  o r b u c k l i n g mode o f f a i l u r e  foliation The  orientation  because  intention  case  dealing  with  i s p e r p e n d i c u l a r t o the  i t i s the d i r e c t i o n  in this  when  of p o t e n t i a l  i s t o clamp  movement.  the layers  o f rock  together. The  mode  stereographic  of  failure  projection  can  be  techniques  easily or a  determined simple  using  "sketching"  method d e s c r i b e d i n s e c t i o n 6.6.  9.5  SUMMARY  The use o f c a b l e b o l t support systems i n open stope mining has  become  increasingly  popular  and e f f i c i e n t .  problem o f a l a c k o f proper access f o r c a b l e b o l t 271  The o r i g i n a l installation  can be p a r t l y s o l v e d by u s i n g t h e support p a t t e r n s d e s c r i b e d i n section  9.3.1  i n t h e case  o f stope  backs and 9.3.2  f o r stope  concepts  f o r t h e o p t i m i z a t i o n of a  walls. Two support  important system  have  prereinforcement supporting  design also  been  contributes  and h e l p s  discussed.  to  t o minimize  opening  make  The  the  rock  the disturbance  surrounding  the  during  the  Consequently,  when d e s i g n i n g support  concept mass  self-  o f t h e rock  excavation  systems,  of  process.  prereinforcement  should be used whenever i t i s p o s s i b l e . The concept performance  of s t i f f n e s s can have a l a r g e i n f l u e n c e on the  o f a support  system.  In most a p p l i c a t i o n s  it  is  d e s i r a b l e t o match t h e s t i f f n e s s o f t h e support system w i t h the s t i f f n e s s o f t h e rock mass.  However,  forspecific  applications  i t might be u s e f u l t o i n c r e a s e o r decrease t h e s t i f f n e s s o f the cable  bolts.  This  can be done  using  special  cable  bolting  i n s t a l l a t i o n techniques such as p r e t e n s i o n i n g o r debonding. The t h r e e p r i n c i p a l bolt bolts  system  variables  t o be designed  are the density of b o l t i n g ,  and t h e i r  relative  orientations.  cable bolts  should be designed  of f a i l u r e .  When g r a v i t y f a l l  efficient  design  The o r i e n t a t i o n  of  o r s l a b b i n g a r e a n t i c i p a t e d , the In t h e case o f s l i d i n g ,  i s when t h e c a b l e s a r e i n s t a l l e d a t  an angle between 17° and 27° t o t h e shear Based  the length of cable  a c c o r d i n g t o t h e p o s s i b l e mode  c a b l e should be i n s t a l l e d v e r t i c a l l y . the most  i n a cable  on t h e c o m p i l a t i o n o f a c t u a l 272  direction. Canadian  experience,  some  rough  design  determination  guidelines  have  been  o f d e n s i t y and l e n g t h  proposed  of cable  f o r the  bolts.  I t has  been found t h a t a rough r e l a t i o n s h i p e x i s t s between the d e n s i t y of b o l t i n g Figure  and the r e l a t i v e s i z e o f b l o c k s formed by j o i n t i n g .  9.10 can be used t o estimate  bolting  an a p p r o p r i a t e d e n s i t y o f  according to the block s i z e factor  radius).  S i m i l a r l y , the l e n g t h o f c a b l e b o l t s has been r e l a t e d  t o t h e s i z e and shape o f t h e supported 9.11  (RQD/JN / h y d r a u l i c  can a s s i s t  i n the d e t e r m i n a t i o n  stope s u r f a c e and f i g u r e o f adequate  cable  bolt  length. It  i s important  been used proven. when  t o mention t h a t these g u i d e l i n e s have not  i n a c t u a l design  at this  time  and s t i l l  need t o be  N e v e r t h e l e s s , the g u i d e l i n e s appear t o be c o n s e r v a t i v e compared  with  some  past  experience  and  offer  i n t e r e s t i n g a l t e r n a t i v e t o the t r i a l and e r r o r p r o c e s s .  273  an  CHAPTER 10 EXTERNAL FACTORS: BLASTING, BACKFILL AND 10.1  TIME EFFECT  INTRODUCTION  The  effect  of  external factors  on  the  stability  of  open  stopes i s w e l l r e c o g n i z e d by rock mechanics engineers, although the  factors  are  hardly  ever measured, monitored  f o r i n a d e s i g n procedure. simplification and this  the  fact  that  mining  practices  the  effect  of  stopes  will  accounted  The p r i n c i p a l reason f o r t h i s  i s the l a c k of a c c e s s i b l e m o n i t o r i n g  chapter,  adjacent  or  be  have evolved  blasting,  discussed  time,  over-  technology  rapidly.  and  backfill  qualitatively,  based  o b s e r v a t i o n s of these e x t e r n a l f a c t o r s i n case h i s t o r i e s . number  of  r e l e v a n t case  hypotheses,  but  further  histories work and  is sufficient a  l a r g e r data  to  In in on The  formulate  base would  be  r e q u i r e d t o c o n f i r m some of them.  10.2  BLASTING EFFECT  The  principal  objective  of  a  blast  design  i s to obtain  good fragmentation a t the lowest p o s s i b l e c o s t , t o a v o i d missf i r i n g and t o minimize  the v i b r a t i o n r e l a t e d damage done t o the  rock w a l l s exposed t o the b l a s t . has  the  desirable  the  charge  and  effects  relieving  of the  The e x p l o s i v e energy r e l e a s e d  fracturing  the  h o l e burden.  274  rock mass In  a non  around optimum  blast,  this  increases, will  energy  may  a i r blasts  and  r e s u l t i n a decrease  w a l l s and may  the  design analysis  the  flyrock,  of the rock mass q u a l i t y  effect  of  blast  damage  in  and  map  the  a  i n the  case  walls  after  to production.  to  within This  o v e r - l o o k i n g the the  precision  will  excessive  be and  conditions. the  cases  true are  effect  and only  sensitivity i f the  similar  to  T h i s assumption shown on  the  of b l a s t  drilling  I t i s then  assumed,  of  the  design  practices  majority  of  the  i s o l a t e d by the s t a b i l i t y  10.2.1  effects case  Ruttan,  to in  of  blast  histories  Pakalnis  attributed included  method. are  data  not base  stability  graph,  figure on  8.4.  stability  analysis.  Case h i s t o r i e s o f b l a s t induced damage  The several  quality  f o r the m a j o r i t y of  However, i n s p e c i f i c cases, the e f f e c t of b l a s t i n g was  has  damage) i s i n c l u d e d  i s confirmed  modified  access  i n the  blasting  the  rock  production  t h a t the e r r o r made i n (over) e s t i m a t i n g the rock mass (due  stope  history  t h e r e i s no  begun. In g e n e r a l , the rock mass i s c l a s s i f i e d or mucking h o r i z o n , p r i o r  These  f o r by c l a s s i f y i n g the  However, i n p r a c t i c e ,  stopes  temperature  s t a b i l i t y problems.  should be accounted  mass a f t e r the b l a s t . enter  create  e x c e s s i v e ground v i b r a t i o n s .  cause p o t e n t i a l  Ideally,  to  also  damage  different  mines.  (1986)  blasting  this  at  induced  documented  for  study's  his  the  was  observed  For  instance  percent  entire  data  base  complementary  data  base).  275  in at  dilution (which On  is the  stability case  graph  (figure  10.1),  the s t a b i l i t y  numbers 70, 107, 121 and 12 6 i s s t a b l e ,  accordance  with  the actual  the d i l u t i o n induced The  effect  case h i s t o r i e s number have  ground part  of blasting  at least  was a l s o  base.  F o r a l l these  observed  Once again,  marginally  Blasting  t h e problem  technique  i s not i n cases,  i n four  other  (170, 171, 172, 175, see f i g u r e 10.1) from mine  falls. of  which  of  by b l a s t i n g was between 3% and 7%.  31 o f t h e data  been  assessment.  prediction  induced  since  stable,  stopes  have  that  should  suffered  large  damage i s suspected  this  mine  d e s c r i b e d i n s e c t i o n 2.6.3.  uses  as being  t h e mass  blast  The amount o f e x p l o s i v e  f i r e d s i m u l t a n e o u s l y i n t h e mass b l a s t i s s e v e r a l times g r e a t e r than t h a t o f r e g u l a r p r a c t i c e s . It  can surmised  that  other  cases  of blasting  induced  damage have o c c u r r e d but c o u l d not be i s o l a t e d by t h e s t a b i l i t y graph of  analysis  caving.  (figure  because b l a s t i n g  was not t h e predominant  cause  Cases 71, 78, 79, 82, 83, 109, 118, 119, 123, 124  10.1) from  t h e Ruttan  study  have a l l experienced  more  than 5% d i l u t i o n r e l a t e d t o b l a s t damage.  10.2.2  B l a s t m o n i t o r i n g and p r e d i c t i o n o f b l a s t damage  Significant using monitoring to  optimize  progress  t h e energy  made  i n recent  systems t o q u a n t i f y b l a s t  blast  design.  measuring t h e v i b r a t i o n of  has been  A  blast  induced  can be  years, i n damage and  monitored  waves c r e a t e d by t h e e x p l o s i o n .  by Some  r e l e a s e d by t h e b l a s t , t r a v e l s a t t h e speed of 276  FIGURE  10.1  Modified S t a b i l i t y G r a p h BLASTING DATA B A S E 18 case histories 1000  0.1 5  10  15  Hydraulic complementary d a t a base  Radius  main d a t a base  Stable Stope Surface • • Unstable Stope Surface v • Caved Stope Surface  ""^^  J  277  20  (m)  25  sound  into  the unbroken rock  i n t h e form  o f a p r e s s u r e wave.  There a r e t h r e e types o f wave motion: compressional, shear, and The  pressure  movement,  wave  can be  displacement  causes  limits,  shape  particles  t o a cork  of a p a r t i c l e  to  bobbing  move.  This  on water.  i s the distance t r a v e l l e d  The  from i t s  I f movements are w i t h i n t h e e l a s t i c l i m i t s o f  no breakage occurs  original  ground  compared  static position. rock,  raleigh.  and the m a t e r i a l w i l l  and volume.  breakage  occurs  recover to i t s  I f movements exceed  as the rock  mass  the e l a s t i c  i s pulled  apart i n  tension. The  particle  particles particle  have  velocity  moved.  vibrations,  can be determined velocity  i s the speed  By  measuring  the s i z e  and r e l a t e d  a t which  the ground  the v e l o c i t y  of  rock  and s t r e n g t h o f a p r e s s u r e wave t o damage c r i t e r i a .  can be measured by r e c o r d i n g audio  The p a r t i c l e  frequency  signals  from the b l a s t . The dynamic range necessary t o capture the peak amplitude  is  frequencies  in  over  the  order  1000 Hz.  of  50  inches  per  second  The peak p a r t i c l e v e l o c i t y  at  i s the  h i g h e s t v e l o c i t y v a l u e a t t a i n e d a t a g i v e n p o i n t and time, by a p a s s i n g wave.  The a n a l y s i s  of  the v i b r a t i o n  t r a c e a l l o w s the  d e t e r m i n a t i o n the peak p a r t i c l e v e l o c i t y . Rock levels  fracture  i s associated with  o f approximately  peak p a r t i c l e  25 t o 40 inches p e r second 278  velocity  o r higher,  depending 10.1. of  on the rock q u a l i t y and g e o l o g i c a l c o n d i t i o n s .  shows how  rock  Table  peak p a r t i c l e v e l o c i t y i s r e l a t e d t o the amount  damage.  Page  (1987)  proposed  a  slightly  refined  r e l a t i o n s h i p by a c c o u n t i n g f o r t h r e e types of rock mass q u a l i t y (table  10.2).  relationship percentage (Barton  Page  between  the  technology,  when  generate  MRMR  also  peak  r e d u c t i o n i n the  e t a l ) and  ultimately  has  empirically  particle  rock  better  the  quality  i n terms  of Q  (see f i g u r e  10.2).  This  understood  velocity  a  and  mass  (Laubscher)  developed  and  documented,  enough a c c u r a t e data t o develop a  b l a s t c o r r e c t i o n f a c t o r c a l i b r a t e d i n f u n c t i o n of the  may  reliable stability  graph d e s i g n method.  10.2.3  Optimization of b l a s t design f o r w a l l s t a b i l i t y  The if  the  low.  amount of damage caused by b l a s t i n g w i l l be ground v i b r a t i o n s  and  peak p a r t i c l e  velocity  minimized are  kept  T h i s can be achieved by o p t i m i s i n g : the b l a s t p a t t e r n and geometry, the charge weight per d e l a y , and the b l a s t  The  amount of burden,  the  relief  mining, size.  and  this Large  approximately o f t e n used  sequencing. as shown i n f i g u r e 10.3,  is critical  fragmentation of the rock mass. burden  is  diameter 3 metres,  largely  a  blastholes,  function typically  w h i l e a burden of 1.2  f o r s m a l l h o l e diameters. 279  of  In open the  stope  drillhole  have a burden t o 1.8  for  of  metres i s  The most common longhole  PPV in/s  Resulting condition on rock structure  10-12  falls of rock in unlined tunnels: no fracturing of intact rock  12-25  minor tensile slabbing will occur  25-100  strong tensile and some radial cracking will occur  >100 TABLE  complete break-up of rock mass  10.1 R e l a t i o n s h i p between t h e p e a k p a r t i c l e v e l o c i t y and t h e r e s u l t i n g c o n d i t i o n on r o c k s t r u c t u r e . (After Atlas Powder company, 1987)  ROCK MASS QUALITY  STABILITY  THRESHOLD DAMAGE LIMITS PPV mm/s in/s  MARGINAL  200  8  HIGH  600  25  MARGINAL  600  25  HIGH  2000  80  MARGINAL  100  4  HIGH  600  25  POOR  GOOD  UNFAVOURABLE JOINTING (Unstable Key Blocks) TABLE  10.2 R e l a t i o n s h i p between t h e p e a k p a r t i c l e v e l o c i t y , t h e r o c k mass q u a l i t y a n d t h e r e s u l t i n g s t a b i l i t y o f a stope.  280  1000  2000 P t i k  Partkle Velocity  3000  4000  mm/i  FIGURE 10.2 R e l a t i o n s h i p b e t w e e n t h e r e d u c t i o n i n r o c k mass q u a l i t y and t h e peak p a r t i c l e v e l o c i t y o r i g i n a t i n g f r o m a blast. ( A f t e r Page, 1987)  281  FIGURE  10.3  T H E E F F E C T OF REDUCBNG THE BURDEN ON A C H A R G E OF CONSTANT ENERGY TOP VIEW  co CO to  Overblast  Confined  rjaecck ch(fe aw rgece tios,n)  Cracks on face  (no relief)  (fly oiscek), nro ( f u l r e l i e f , good fragmentation) Optimum crater  and b l a s t h o l e d r i l l i n g p a t t e r n s have been d i s c u s s e d i n chapters 2.5.1  and 2.6.1. The  large  amount of e x p l o s i v e detonated a t one time a l s o has a  influence  particle  on  velocity).  empirical, estimate  site the  the  blast  The  cube  calibrated peak  vibrations root  The  cube r o o t  D/(W°' ))~ 3 3  scaling  at  can  a  be  the  stope  walls.  an  used  to "D",  "W".  m  equation i s u s e f u l  In  is  distance  t o estimate the  maximum amount of e x p l o s i v e per d e l a y t h a t can be used damaging  (peak  equation  which  velocity  a s s o c i a t e d w i t h the charge detonated VELOCITY = K(  scaling  relationship  particle  generated  blasthole  mining,  without  i t will  be  found t h a t the decking and d e c o u p l i n g of charges i s a p r a c t i c a l means of l o w e r i n g the b l a s t Finally, interval  sequencing  of  10.4  possibility shows  detonation,  a  detonations  and  detonations.  two  an  delay  was  of  idealized  wave packet a  wave  In the  peak p a r t i c l e v e l o c i t y the  of  the  blasting  too  packet  third  vibration  wave  wave packet of  the  delay  superposition.  from  an  a p r o p e r l y delayed  from  situation,  two  improperly  from the packet are superimposed  short.  This  could r e s u l t  EFFECT OF BACKFILL IN ADJACENT STOPES 283  isolated pair  in blast  of  delayed  the wave amplitude  damage.  10.3  and  between i n d i v i d u a l d e t o n a t i o n s must be l o n g enough t o  eliminate Figure  the  vibrations.  and  because induced  FIGURE 10.4 resulting  The e f f e c t o f d e l a y i n g d e t o n a t i o n d e c k s o n t h e wave p a c k e t s . ( A f t e r S p r o t t , 1986)  wave packet from one deck detonation  *\]—^/jM/vw— J-  -I  at  wave packets from two properly delayed decks to  CO  ^ll^f^ |:  V^Arw-  *  >  At  -id, At  resulting wave packet from two improperly delayed decks AX  2  AX  »  2  d  t  <  Xj At  The recover  present  trend  t h e orebody,  which  cemented b a c k f i l l w a l l s . thoroughly effect  i n open  stoping  i n most case  Although  backfill  totally  means mining  against  i t i s not intended t o review  the subject of b a c k f i l l  of  i s towards  ( i n adjacent  i n open stope stopes)  on  mining, the  the s t a b i l i t y  a n a l y s i s w i l l be i n v e s t i g a t e d . Backfill displacement confinement is  provides  passive  support  counter  o f the w a l l s towards t h e opening i n the d i r e c t i o n  sufficient,  i t can be  o f movement. assumed  that  acting  and g i v e s some  If this  confinement  the t o t a l  effective  opening  span i s l i m i t e d  10.3.1  E f f e c t o f b a c k f i l l i n l i m i t i n g w a l l s and back  Figure  10.5  with b a c k f i l l .  B) and the w a l l  by t h e b a c k f i l l .  illustrates  a  common  situation  exposure  when  mining  The mining b l o c k has f o u r stopes; stopes 1 and  3 are b a c k f i l l e d , not s t a r t e d y e t .  the  stope  2 i s empty and mining  i n stope  4 has  For the s t a b i l i t y a n a l y s i s o f the r o o f (plane (plane E) o f stope  2, two hypotheses  w i l l be  formulated: 1)  The s u r f a c e t o be designed  f o r the w a l l o f stope 2 i s the  s u r f a c e o f plane E, which i m p l i e s t h a t b a c k f i l l l i m i t s the exposure  2)  The designed  effectively  o f the b a c k f i l l e d w a l l s (plane D and F ) .  s u r f a c e o f t h e stope back i s the summation of  a l l t h e backs o f c o n s e c u t i v e b a c k f i l l e d 285  and empty stopes  286  (plane  A + plane  backfill  B + plane  i s not t i g h t  significant  effect  effectively  limit  if  C) .  enough  I t i s assumed  against  on confinement, the t o t a l  stope  t h e back  restricting  t o have a  and t h e r e f o r e does not back exposure.  a back c a v i n g occurs, p a r t o f t h e f a i l e d  backfill  t h a t the  most o f t h e emptied  However,  rock may s i t on  stope  back  (plane  B) .  It  should  be  noted  that  a  common  assumption  made i n  numerical m o d e l l i n g i s t o ignore t h e b a c k f i l l meaning s t r e s s i s not  t r a n s m i t t e d through  the  induced  oy  stress  t h a t medium. f o r each  In t h e d e t e r m i n a t i o n of  stope  surface, the b a c k f i l l e d  stopes w i l l be c o n s i d e r e d empty.  10.3.2  Case h i s t o r y  The with  analyses  i m p l i c a t i o n s o f t h e above h y p o t h e s i s w i l l be d e s c r i b e d  respect  transverse  t o case  histories  b l a s t h o l e mining  from  method  mine  #19, which  (ref. section  uses a  2.6).  An  i d e a l i z e d i s o m e t r i c view o f t h e mining b l o c k i s shown on f i g u r e 10.6.  The stope  dimensions  are i d e n t i c a l  on each l e v e l :  long, 23m wide and 60m h i g h f o r t h e bottom l e v e l , x  45m  f o r the top l e v e l .  indicated of  mining  and 11m x 23m  sequence  of e x t r a c t i o n i s  on t h e stopes by c i r c l e d numbers.  I t i s a variation  t h e leap  frog  sequence  o f a l l primary  The  11m  described  stopes  (stopes  i n s e c t i o n 2.4.2.  1 t o 18) was completed  with no s t a b i l i t y problems i n t h e r o o f o r w a l l s . 287  The  As shown  FIGURE 10.6 M i n e #19  Idealized isometric of the data base.  TRANSVERSE  B L A S T HOLE  view of  OPEN  STOPING  the  mining block  at  below, and  t h e back  57  (roof)  analysis  o f case h i s t o r i e s  a r e i n accordance  with  59  this  (hanging w a l l )  assessment (see  F i g u r e 10.7) .  RQD/Jn WALL #59  4  BACK #57  29  In  STRESS FACTOR  CRITICAL JOINT  Jr/Ja  GRAVITY FACTOR  1  0.3  0.5  8.0  4.84.5  Stable  0.2  0.2  1.5  2.0  3.5  Stable  of  the t e r t i a r y  the  mining  N  S  stopes  ASSESS MENT  3.7  (between  two  b a c k f i l l e d w a l l s ) , the hanging w a l l s o f stope 19 t o 34 remained s t a b l e but t h e backs experienced c o n s i d e r a b l e d e t e r i o r a t i o n and systematic tertiary  cable  backs.  bolt  This w i l l  regarding b a c k f i l l a)  Tertiary true  i n a l l the  allow the t e s t i n g of the hypothesis  (mentioned above).  hanging  and  support had t o be i n s t a l l e d  walls:  backfill  Supposing  effectively  that  limits  h y p o t h e s i s 1) i s the  stope  wall  dimensions t o t h e exposure o f t h e empty stope, t h e s t a b i l i t y number  and h y d r a u l i c  radius  of t e r t i a r y  walls  will  remain  i d e n t i c a l t o t h e ones c a l c u l a t e d f o r primary w a l l s , case #59 (see f i g u r e 10.7, case #59). T h i s i s i n accordance w i t h the stable t e r t i a r y wall and  the b a c k f i l l  exposure, would  then  assessment. does  not e f f e c t i v e l y  the h y d r a u l i c  be c a l c u l a t e d  based  I f h y p o t h e s i s 1) i s f a l s e  radius  limit  the  of t h e t e r t i a r y  on a hanging w a l l  walls  exposure o f a t  l e a s t t h r e e stope l e n g t h s (stope 19, 2 and 8 i n f i g u r e 289  wall  FIGURE  10.7  Modified Stability Graph cases of backfilled  stopes  1000  0.1  5  10 Hydraulic  15 Radius ( m )  o Stable Stope Surface • Unstable Stope Surface • Caved Stope Surface 290  20  25  10.6).  The  stability  new  number  hydraulic is still  zone  (see f i g u r e 10.7,  with  the  support  actual  radius 4.8.  This  be  plots  10.6  and  i n the  the  caving  case 59-) which i s not i n accordance  assessment.  hypothesis  would  Both  of  the  1) r e g a r d i n g the e f f e c t  above  analyses  of b a c k f i l l i n  adjacent walls.  b)  Tertiary that  backs:  backfill  The  hypothesis  does  not  2)  for tertiary  effectively  backs i s  limit  the  back  dimensions, and b a c k f i l l e d stopes should be c o n s i d e r e d empty i n the a n a l y s i s . will  The h y d r a u l i c r a d i u s of the t e r t i a r y  be c a l c u l a t e d  l e n g t h s and  back  f o r an exposure of t h r e e times the stope  the stope width.  The s t a b i l i t y  number remains  3.5 but the h y d r a u l i c r a d i u s i n c r e a s e s t o 6.8 which p l o t s i n the  caving  57 + ) .  zone  This  reported,  of the  stability  graph  i s i n accordance with  and  the need  2) was  10.7  the s t a b i l i t y  f o r cable b o l t  Supposing the h y p o t h e s i s  (figure  case  problems  support of the back.  incorrect  and the  backfill  e f f e c t i v e l y l i m i t s the stope backs, then the a n a l y s i s of the tertiary (case  backs  57) .  A  would stable  be  similar  to that  "prediction"  of primary backs  f o r the t e r t i a r y  backs  does not f i t the a c t u a l assessment. These cases.  hypotheses have However,  been  verified  monitoring,  f o r a number  instrumentation  and  of  other  more  case  h i s t o r i e s would be r e q u i r e d t o prove them s y s t e m a t i c a l l y .  291  10.4  THE TIME EFFECT  The two  time  effect  different  i n hard rock mining can be  perspectives.  The  first  considered i n  p e r s p e c t i v e i s when  t h e r e i s no mining a c t i v i t y i n the stope area t o c r e a t e dynamic loads  (such as  changes  i n stress  or b l a s t i n g  vibration).  In  t h i s case, the time e f f e c t w i l l be d i r e c t l y a s s o c i a t e d with the sources of rock mass a l t e r a t i o n  (mainly ground  open stope e x t r a c t i o n i s u s u a l l y r a p i d open  stope mines  time  effect  will  conditions. effect  i n the not  I t was  of time  be  possible  Since  ( l e s s than one year)  Shield  are u s u a l l y  significant  in  t o observed  this  dry,  dormant  was  absence  of time.  used and the stopes remained These cases are p l o t t e d  and the  mining of  i n some case h i s t o r i e s where open stope  (with no b a c k f i l l ) long p e r i o d  Canadian  water).  the  mining  open f o r a  in figure  10.8.  At the time of the b a c k - a n a l y s i s , the stopes had been open f o r more than  one  instability  year  had  (sometimes s e v e r a l  been  reported,  even  years)  and  no  though  their  a n a l y s i s p l o t t e d c l o s e t o the grey area (see f i g u r e The  second  perspective  of  the  time  s i g n s of stability  10.8).  effect  can  c o n s i d e r e d when t h e r e are mining a c t i v i t i e s  i n the area.  dynamic  premature  during  loads the  induced  stope  by  mining  extraction.  may  Most  cause of  the  case  292  The  failure  histories  i n s t a b i l i t y and c a v i n g i n c l u d e d i n the database can be  be  of  F I G U R E  1 0 . 8  Modified S t a b i l i t y G r a p h TIME EFFECT DATA BASE 17 c a s e histories 1000  •  •  i  .  Hydraulic  Radius  • Stable Stope Surface • Unstable Stope Surface T Caved Stope Surface 293  I  (m)  —  classified  in this  group.  Although  the s t a b i l i t y  of  stope  s u r f a c e s has shown r a p i d d e t e r i o r a t i o n with time, the p o s s i b l e sources exact  of i n s t a b i l i t y  quantification  impossible. stability  a r e numerous  of the  However,  and v a r i e d  ( s h o r t term)  when  the  time  design  problems, c a v i n g i s expected  which make an effect  analysis  nearly predicts  t o occur w i t h i n a s h o r t  p e r i o d of time and l i k e l y d u r i n g the e x t r a c t i o n p r o c e s s .  10.5 SUMMARY AND CONCLUSION  The stability on  effects  blasting,  the o b s e r v a t i o n of these  of  in the  minimized  by  per  development  effect,  stability design  t e c h n i q u e s are used.  weight  and  external factors  For the b l a s t i n g  reduction  accuracy  backfill  time  in  the  a n a l y s i s are d i s c u s s e d i n t h i s chapter and a r e based  histories. the  of  i t will  i s within  method,  in specific  the  unless  case  be assumed t h a t sensitivity  excessive  and  blasting  The amount of b l a s t induced damage can be  optimising  delay  and  of  blast  the  the  drilling  sequence  patterns,  of  charge  blasting.  the  measurement of the peak p a r t i c l e v e l o c i t y a s s o c i a t e d with  each  which  Ultimately,  this  can may  be  offer  related a means  techniques  The  allows  detonation,  monitoring  the  the  to  blast  induced  damage.  f o r the development  of a  b l a s t c o r r e c t i o n f a c t o r f o r the s t a b i l i t y graph d e s i g n method. The  presence  common s i t u a t i o n  of b a c k f i l l i n open stope  i n adjacent mining.  stopes  is a  very  I t i s suggested  that  the t h r e e f o l l o w i n g assumptions e f f e c t i n the s t a b i l i t y 1)  Stope are  can be used t o account f o r t h i s  analysis;  w a l l s are supported by b a c k f i l l  actually  exposed  and  t o empty openings  o n l y the s u r f a c e  should be c o n s i d e r e d  i n the c a l c u l a t i o n of the h y d r a u l i c r a d i u s . 2) Stope  backs  total  are not g e n e r a l l y supported by b a c k f i l l  surface  exposed  by  a l l the  consecutive  and  empty  the and  b a c k f i l l e d stopes should be c o n s i d e r e d i n the c a l c u l a t i o n of the h y d r a u l i c r a d i u s .  The  effect  of  time  on  stope  stability  can  be  assumed  n e g l i g i b l e when d e a l i n g w i t h stopes t h a t are remote from mining activities,  because  the  typically  dry  c o n d i t i o n s of  Canadian  open stope mines r e s u l t o n l y i n a slow d e t e r i o r a t i o n of  exposed  rock mass.  When stopes show a r a p i d d e t e r i o r a t i o n of s t a b i l i t y  with  i t i s generally  time,  vicinity nearly  of the stopes.  due  to  mining  activities  in  the  In these c o n d i t i o n s the time e f f e c t i s  impossible to d i f f e r e n t i a t e  from the e f f e c t s of dynamic  l o a d i n g due t o mining. The can  effect  make  the  prediction. effects  and  analysis. external case  of e x t e r n a l  factors in  the s t a b i l i t y  difference  between  stable  Consequently, attempt Although  factors  histories,  to the  a  and  analysis a  i t i s e s s e n t i a l t o understand  take  them  into  assumptions  account  i n the  r e g a r d i n g the  caving these design  effects  of  have not been confirmed by a l a r g e number of the  e x p l a n a t i o n s are 295  i n accordance  with  the  case  histories  undertaken which  of  the  data  base.  Future  work  t o improve the c o n f i d e n c e i n the above  will  contribute  to  the  predictions.  296  accuracy  of  the  should  be  assumptions, stability  CHAPTER 11 SUMMARY AND CONCLUSION 11.1  SUMMARY The  open  problem  stopes  in typical  geomechanics specific  o f opening  them  simplification,  to  i n this thesis  Canadian  investigation  type  submitting  investigated  focus  geological  t h e problem  settings.  on t h e e f f e c t  i n a variety  mining  i s the design of The  of creating  a  o f r o c k mass media and  related  dynamic  loads.  For  was s u b d i v i d e d i n t o t h r e e a s p e c t s :  the c h a r a c t e r i s t i c s o f t h e rock mass, the r e d i s t r i b u t i o n o f i n s i t u induced on t h e stope the p h y s i c a l  stress, or the stress  surfaces,  condition  o f t h e problem  including  stope geometry and i n c l i n a t i o n , c a b l e b o l t , backfill  and t h e e f f e c t o f time.  Each o f t h e above aspects i s d i v i d e d quantify  and  instability.  calibrate  based  factor  o f t h e problem  (hydraulic  parameters  Each  joint  f o r by t h e s t r e s s  on t h r e e dimensional  factors.  factors  i n order t o  sources  of  ground  The rock mass c h a r a c t e r i s t i c s a r e r e p r e s e n t e d by  i s accounted  condition  into  the possible  the b l o c k s i z e and t h e c r i t i c a l stress  blasting,  factor  (geotechnical  induced  t h e stope  the gravity  i s quantified or  The e f f e c t o f  f a c t o r , which i s  numerical m o d e l l i n g . includes  radius),  factors.  The p h y s i c a l size  and shape  f a c t o r and t h e e x t e r n a l by  geometrical) .  a  combination Most  of  of the  parameters  are  observational mapping  and  estimated  from  methods such the  study  field  investigation,  relying  as rock mass c l a s s i f i c a t i o n ,  of  mine  layouts.  The  on  joint  methodology  of  d e s i g n and the o r g a n i z a t i o n of the i n p u t data i s s i m i l a r t o the one  proposed  graphical shows  by  Mathews  et  p r e s e n t a t i o n of  how  the  al.  the  parameters  (1980).  open  stope  combine  into  Figure design  11.1  is a  method.  factors  and  It  how  the  s t a b i l i t y a n a l y s i s i s developed. The  main h y p o t h e s i s  open stopes rock  can  mass  surfaces  be  of  p r e d i c t e d by  characteristics,  and  the  verification  the  physical  study  i s : "The  stability  q u a n t i f y i n g the e f f e c t  the  stress  induced  c o n d i t i o n s of  the  at  of  of the  the  stope  problem".  The  of the h y p o t h e s i s  i n v o l v e s the a p p l i c a t i o n of the  model d e s c r i b e d i n f i g u r e 11.1  i n the b a c k - a n a l y s i s of a l a r g e  number  histories.  of  r e p r e s e n t a t i v e case  behaviour  corresponds  stability  graph,  I f the  actual  stope  t o the model's p r e d i c t i o n on the m o d i f i e d verified.  Figure  8.4  shows a p l o t of the t o t a l data base of unsupported  stopes.  The  clear  confirm  the  s e p a r a t i o n between  d e s i g n method bolt  the h y p o t h e s i s  will  stable  and  (and the hypothesis)  reinforcement.  The  effect  be  caving  cases  f o r stopes not u s i n g c a b l e of  external  factors  on  d e s i g n a n a l y s i s i s summarized as f o l l o w s : The of  stabilizing stope  modified  a c t i o n of c a b l e b o l t s a l l o w s the d e s i g n  dimensions, stability  below  graph  the  transition  (see f i g u r e  9.9).  area  of  However, a  minimum i n t e n s i t y of b o l t i n g i s necessary t o m a i n t a i n 298  the  the  663 B L O C K SIZE FACTOR  CRITICAL JOINT FACTOR  >  . O  2  it  JOIN NUMB 0.5 -  •4h  FFERENICE 1 IP ic STRIKI 0.2 - 1.0  o S  m -H  _°s lis s5>  •••• CO  to to  •-3 >  COMPRESSIVE STRESS FACTOR P  —  c  o  CO  i—i  SI  t—i  "ito  Q  >  >>  GRAVITY  CD O > Tl  FACTOR  -3.  O  =•3 m—  z: o  2 -n C ""I > m  -ui =d  a  O  -H  POTENTIAL EXTERNAL  FACTORS  o o  POTENTIAL EXTERNAL FACTOR z o ? > c O m * z 3 n  CO  o w o CO I—I  1 I  O -  O S  II S T O P E P L A N E SIZE AND S H A P E F A C T O R  Q  stability, increase (figure of  and  as  the  a case  9.12).  plots  further  i n open  is  within  is built  the  caving  to  zone  t o the a p p l i c a b i l i t y i s indicated  by  i s t o decrease the q u a l i t y of the  be assumed t h a t ,  effect  i s expected  9.9.  rock mass i n w a l l s exposed  this  into  stope mining  line in figure  The e f f e c t of b l a s t i n g  It w i l l  intensity  A practical limit  cable b o l t i n g  the dashed  necessary  f o r normal  into  the p r e c i s i o n  t o the e f f e c t of the blasting  blast.  practices,  the model's c a l i b r a t i o n ,  of the d e s i g n method.  and  This i s  supported by the good c o r r e l a t i o n o b t a i n e d between stope predictions  and  actual  data base  (see f i g u r e  excessive  blasting  analysis The  graph  stope assessments 8.4),  practices  (figure  l i m i t back  and  were  isolated  cases of in  the  i n a d j a c e n t stopes i s taken  into  account by two assumptions: exposure,  the f a c t t h a t  total  10.1).  e f f e c t of b a c k f i l l  wall  and  f o r the  the  backfill effectively limits  backfill  does  not  effectively  exposure.  The  e f f e c t of time, when t h e r e are no mining a c t i v i t i e s  in  the  investigated  negligible. in  No  the case h i s t o r i e s  stope  dynamic  is  not  loads  area,  can  s i g n s of i n s t a b i l i t y  been open f o r a p e r i o d a  stope  be  considered  have been  shown i n f i g u r e  10.8,  noticed  which have  of time exceeding one year.  isolated  from  associated 300  mining  with  When  activities,  mining  may  the  induce  premature  failure.  c o n d i t i o n s was stope have  life. been  The  stope  stand-up  time  in  e v a l u a t e d o n l y i n f u n c t i o n of the F i g u r e 8.4  stable  shows the  for their  full  case  APPLICABILITY OF THE  The for  d e s i g n method  entire  histories  stope  lives,  stopes t h a t have caved a t one time d u r i n g t h e i r  11.2  these  that  and  the  life.  DESIGN METHOD  proposed  in this  thesis  was  developed  open stope mining methods i n g e o l o g i c a l c o n d i t i o n s s i m i l a r  to  those encountered  is  better  50°),  suited  having  width  of  i n the Canadian  shield.  Open stope mining  t o steep d i p p i n g orebodies  a relatively  approximately  (dip g r e a t e r than  regular definition,  5 meters.  Because the  and  a minimum  stope  roof  and  w a l l s must be s e l f s u p p o r t i n g , a f a i r t o good rock mass q u a l i t y is  desirable  appendix in  the  used  1,  for  the  ore  the orebody  zone  and  the  country  rock.  shape of the open stope mine i n c l u d e d  data base has been drawn, along with the mining  and  w a l l and  In  the g e o t e c h n i c a l c h a r a c t e r i s t i c s  of the  method  ore,  hanging  footwall.  Open stope mining i s a non e n t r y mining method which means mine  workers  Consequently, as  long  as  are  not  exposed  a c e r t a i n degree adjacent not  mine  to  does  proposed  d e s i g n method w i l l  production  of i n s t a b i l i t y can be  workings  dilution  the  become e x c e s s i v e . be 301  non  are  not  The  face.  tolerated,  affected  calibration  and  the  of  the  c o n s e r v a t i v e i f used  with  e n t r y mining methods. Open stope mining a l s o i n v o l v e s f a s t e x t r a c t i o n in  significant  mining  related  dynamic l o a d i n g .  frequent changes i n stope dimensions, production blasts  may  p l a y an  resulting,  The  effect  stope geometry and  important  role  i n the  of  large  stability  of open stopes.  11.3  INDUSTRY BENEFITS FROM THIS STUDY  There  are  systematic  open  important  one  several stope i s the  potential  d e s i g n method proposed reduction  (1988) d e s c r i b e d the economical "If  we  crushing, hoisting 100m  x  assume b a s i c  $2.00/ton then,  30m,  milled  reduces  $100,000.00. of  secondary  blasting  the  may  stope  the  be  showing  the  orebody  (see t a b l e  Another  costs  large  stope  f o r mucking  and  haulage  and  which  the  the  if  c o s t s may lost."  the  serious be  Bawden  influence  of  Bawden follows: and  $1.00/ton f o r w a l l of say  i s h o i s t e d and stope  by  over  dilution  results  in  production  delays  and  incurred.  In the worst  (1988) a l s o  of d i l u t i o n  most  for milling  open stope hanging  profitability  the  The  dilution.  meter of w a l l d i l u t i o n  drawpoints,  using  here.  of $5.00/ton  Alternatively,  plugging  in  in  impact of d i l u t i o n as  for a "typical"  each  benefits  on  provided a the ROR  of a  case, table zinc  11.1).  benefit  of t h i s d e s i g n approach  i s in providing a  c l e a r understanding of the rock mass medium behaviour 302  and  TABLE  11.1 I m p o r t a n c e o f d i l u t i o n o n t h e DCF ROR. Bawden, 1988)  (After  Zinc Tomagt 2,500.000 torn Grade 20X Zn Mining Rata : 360,000 tpy  DILUTION  %  Tomaae Grade  U)  MK  20X  JOK  40X  2.500.000  2.780,000  3.130.000  3.570.000  4.170.000  20.OX  18.0X  16.0X  14.0X  12.0X  360,000  360,000  360.000  360.000  360.000  Nina L i f t , yr».  6.9  7.7  8.7  9.9  11.5  Natal Recovery  85X  BSX  85X  85X  85X  *7n/ton  340  304  272  238  204  Mining Rat*  o  OK  •Zn/yr  1.22*10®  1.OtalO  0.98x10  Nina Revenuee/yr (25c/lb)  $30.50x10*  $27.25x10*  All Nina Coata (U0/T)  $14.4x10*  Operating Proflta  O.SSxIO  0.73x10*  $24.S0x10  •21.25*10*  $18.36x10*  •14.4*10*  $14.4x10*  $14.4x10*  •14.4K10*  $16.10x10*  $12.85x10*  $10.10x10*  •6.85x10*  $3.9x10*  Taxes (50X of O.P.)  $a.osxio*  06.41x10*  •5.05x10*  $3.43x10*  $1.98x10*  Nat Profit  $8.05x10*  $6.43x10*  •5.05*10*  $3.43x10*  $1.98x10*  Capital Coat of Nina  $2.5x10*  •  -  •  -  18.9X  13.5X  0CF ROR  25.5X  8  S  8  6  6.0X  •1.5X  giving  the means f o r a n t i c i p a t i n g  failure  occur d u r i n g the stope e x t r a c t i o n . engineered  design  The  design  applied  with  design.  developed  success  in  work  Bawden, Nantel report l i s t e d  11.4  support  in better  components  as  is  during t h i s  several  Noranda  documented  Sprott  in  (1988) and  study  mines  Bawden  et  in a series  have  been  for  actual  al  (1988),  of  internal  i n the b i b l i o g r a p h y .  FUTURE WORK  The  future  concentrate has  and  result  may  environment.  concepts  This  This w i l l  of mine s t r u c t u r e and  w e l l as a s a f e r mining  mechanisms t h a t  been  made  blasting, been  on  the e f f e c t in  backfill  realized  histories. achieved  improvements  to  time  entirely  design  approach  of e x t e r n a l f a c t o r s .  accounting and  this  f o r the  effect  Some progress  of  cable  i n the d e s i g n a n a l y s i s .  based  on  the  should  bolts,  This  interpretation  of  has case  However, a much g r e a t e r degree of p r e c i s i o n can  i n accounting  m o n i t o r i n g programs.  f o r the  above e f f e c t s  with  be  systematic  In r e c e n t years, s i g n i f i c a n t p r o g r e s s  has  been made i n the development of e f f i c i e n t m o n i t o r i n g t o o l s f o r underground which  may  blasting lead  to  a  (peak  particle  blast  correction  velocity factor  measurements) in  the  design  analysis. The  range  of  efficiency  of  cable b o l t s  has  been d e f i n e d  and rough g u i d e l i n e s r e l a t i n g ground c o n d i t i o n s , stope s i z e 304  and  shape,  and  developed.  the  required  intensity  Once  again,  g r e a t e r data  a  monitoring  techniques  such  as  gauges can  improve the p r e c i s i o n  of  bolting base  cable b o l t s and  have  and  strain  reliability  the and  been  use  of  tension  of the  cable  b o l t design g u i d e l i n e s . There are a l s o a c e r t a i n amount of p e r s o n a l specifically c o u l d be  in  the  reduced  classification  i f an instrumented  rock mass e x i s t e d .  T h i s i s another  of  the  interpretation  rock  mass,  which  system f o r c l a s s i f y i n g important  the  area of r e s e a r c h  t h a t c o u l d improve a c t u a l stope d e s i g n .  11.5  CONCLUDING REM/ARKS  The use  of  very  actual  trend  computer  useful  i n rock mechanics  technology  in  and  investigating  i s towards a g r e a t e r  numerical the  effect  modelling. of  Although  stress,  i t is  b e l i e v e d t h a t rock mechanics r e s e a r c h should put more emphasis on  underground  of  the  of  the  observation, monitoring  rock mass, rock  the  classification  i n order t o b e t t e r understand  mass  medium.  element models, Barton "One  and  problem  that  Commenting  on  the  the use  behaviour of  finite  (1985) s t a t e d : arises  i s that  these  methods  are  so  s o p h i s t i c a t e d t h a t the people working w i t h them, i n my o p i n i o n , are  not  going  to  have t o much time  to  investigate  rock mass  properties." T h i s study was  l a r g e l y based 305  on o b s e r v a t i o n a l methods and  past the  experience. results  Historically,  of p r e v i o u s  mines have been designed  designs  in similar  ground c o n d i t i o n s .  I t i s the author's  o p i n i o n t h a t a v a s t amount of experience  knowledge  at  each  can b e n e f i t  from  industry  exists  experience. mining  By  operators,  comparison, ultimately  making  mine  site  and  the s y s t e m a t i c such  i t gives  i n c r e a s e s the c o n f i d e n c e reduce the o v e r a l l  the  a  entire  compilation  a compilation them  from  broader  and  mining of  this  a v a i l a b l e t o the data  i n t h e i r design,  base  for  and w i l l  d i l u t i o n u s u a l l y a s s o c i a t e d with  open s t o p i n g .  306  REFERENCES Barton, N., L i e n , R. and Lunde, J . 1974. Engineering classification o f rock masses f o r t h e d e s i g n o f t u n n e l support. Rock Mechanics 6, No. 4: 189-236. 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Die t h e o r i e b e d u r f n i s s e der f e s t i g k e i t s l e h r e . 797-807.  der e l a s t i z i t a t und V e i t . Ver. Deut. Ing.  Lang, L.C., Roach, R.J. and Osoko, M.N. 1977. r e t r e a t an important new mining method. Journal. September.  die 42,  Vertical crater Canadian Mining  Laubscher, D.H. 1976. Geomechanics c l a s s i f i c a t i o n of j o i n t e d rock masses - mining a p p l i c a t i o n s . Trans. I n s t . Min. M e t a l l . No.l, A1-A8. Mathews, K.E., Hoek, E., W y l l i e , D.C. and Stewart, S.B.V. 1980. P r e d i c t i o n o f s t a b l e e x c a v a t i o n s f o r mining at depths below 1000 metres i n hard rock. CANMET Report 802-1571. Matthews, M. , T i l l m a n , V.H. m o d i f i e d c a b l e b o l t system openings, Aust. I n s t . Min. N.S.W.  and W o r o t n i c k i , G. 1983. A f o r the support of underground M e t a l l . Conference, Broken H i l l ,  MacLintock, F.A. and Walsh, J.B. 1962. Friction c r a c k s under p r e s s u r e . Proc. 4th I n t . Con. App. 1021.  on G r i f f i t h Mech. 1015-  M i l l e r , D.R. 1984. Design of c a b l e r e i n f o r c e m e n t p a t t e r n s t o r e s i s t shear f a i l u r e i n open stope w a l l s . Stability in 309  Underground Mining I I , Lexington, Kentucky, Ed: A.B. C O . Brawner.  Swilski,  M u r r e l l , S.A.F. 1965. The e f f e c t l o f t r i a x i a l s t r e s s systems on the s t r e n g t h of rock a t atmospheric temperatures. Geophy. J . R. A s t r . Soc. 10, 231-281. P a k a l n i s , R.CT. 1986. E m p i r i c a l stope d e s i g n PhD. T h e s i s , U n i v e r s i t y of B r i t i s h Columbia.  at  Ruttan.  P a k a l n i s , R.CT. 1987. PCBEM u s e r ' s manual. Canada/Manitoba M i n e r a l Development Agreement, CANMET P r o j e c t No. 4-9147-1, Energy, Mines and Resources Canada, Ottawa. Palmstrom, A. 1982. The v o l u m e t r i c j o i n t count - a u s e f u l and simple measure of the degree of rock mass j o i n t i n g . Proc. 4th Con. I n t . Assoc. Eng. Geol. Volume V, New D e l h i , 221-228. P o t v i n , Y. , Hudyma, M. and M i l l e r , H.D.S. 1987. Progress r e p o r t of the i n t e g r a t e d mine d e s i g n p r o j e c t . Unpublished report. P r i e s t , S.D. and Hudson, J.A. 197 6. D i s c o n t i n u i t y spacings i n rock. I n t . J . Rock Mech. Min. S c i . 13, 135-148. Stewart, I . J . and Brown, E.T. 1984. A static relaxation method f o r the a n a l y s i s of e x c a v a t i o n s i n d i s c o n t i n u o u s rock. Design and performance of underground excavations: ISRM symposium, Cambridge. London: B r i t i s h G e o t e c h n i c a l S o c i e t y , 149-155. Stheeman, W.H. 1982. A p r a c t i c a l s o l u t i o n to cable b o l t i n g problems a t Tsumeb Mine. Can. I n s t . Min. M e t a l l . B u l l . , 75, No. 838, 65-77. Watson, J.O. and Cowling, R. 1985. A p p l i c a t i o n of t h r e e dimensional boundary element methods t o m o d e l l i n g of l a r g e mining excavations at depth. Proceedings of the 5th International Conference on Numerical Methods in Geomechanics. 1901-1910. Yu, Y.S., Toews, N.A. and Wong, A.S. 1983. MINTAB user's guide -a mining simulator f o r determining the elastic response of s t r a t a surrounding t a b u l a r mining excavations ( v e r s i o n 4.0, 1982). D i v i s i o n r e p o r t MRP/MRL 83-25 (TR) , Mining Research L a b o r a t o r i e s , CANMET, Energy, Mines and Resources Canada, Ottawa.  310  APPENDIX I OREBODY DIAGRAMS AND ROCK MECHANICS DATA  311  MINE No. I ORE  BANGING WALL  Rock T y p e : T v  -  Breccia  Bock Type:  2 . 9 t/m 80 MPa 46.1 CPa 0.26 1  312  Peridotite  MINE No. 2 QBE (LENS i t II Rock Typei T  °c E V  Q'  t u s s i v e Sulphide  UANCIWG HALL t ROOP Rock Typei  4.2 t/m? 200 MP* 61.0 CPs 0.3 7  ->  f  Andeslte 2.9 t/m* 109 MPa 63.0 CPs 0.2S 4  Y °t E w  0'  LENS  2  •115m-  OPEN  [t.VMK  ' I' •  '/<'//;//< A;;/  „ ,  i  .  1  Y o E v Q' t  -'/' '  ' ". »'  -,/,,;;"',*V•.'VHk':V$C  HANGING WALL * ROOP (LEWS 3) Rock Typei  ' •'/'„",'  ' '  A l t e r e d Andeslte  - 3.0 t/m* - 87 MPs - 84.0 CPs - 0.28 - 0.9  1  > •  ;s;-'---  MINE No. 3 o,= n Y  o,„-1.6vh  o, -th B  ORB Rock Typei t o K v  c  -  0' -  Maaalve S u l p h i d e 4.3 t/u* 116 MPa 39.0 CPa 0.11  6  N  200m  •pih 1050m  MINE No. 4  ORE FW Contact Typei T °c E v 0*  " • -  Late Granite Breccia 3.4 t>> 131 MPa SO.O GPa 0.26 18  HW Contact  HANGING WALL  rOOT  Rock Type:  Rock Typei  Dark N o r i t e  WALL  Dark Norite Breccia 3.2 t/m* 81 MPa 53.0 GPa 0.26 18  r e l a t e Gneiss 2.7 t/«« 141 MPa 58.8 CPa 0.28 J  E  V  MINE  No. 6  O R E  Rock Type: Breccia 4 Massive Sulphide  T V  0'  3 . 1 t/m 125 MPa 9 4 . 0 CPs 0.22 9 3  NORTH WALL Rock Type:  Y  2< v  0*  Norite  2 . 9 t/m 113 MPs 5 6 . 0 CPs 0.17 9 1  274m  SOOTH WALL Rock Type:  Granite  T  2< V  0"  Depth  1050 m  316  MINE No. 8  o,'yb  317  03  MINE No. 10  o , „ - 1 . 7 th  ORB  e -Th l o  Hock Typei  S i l i c e o u s Ore 3.0 t/m* 41 - »9 M P a 44 - SJ C P S 0.21 - 0.40  • 200m  LON0ITU0INAL LONOHOLE OPEN STOPES M  HANGING WALL Hock Typei Tf " o. » 0 S  Siliceous t/m* 60 MPs 6  i SedlMnt  SILL  100m  PILLAR  2Sm  2.8  N SU8LEVEL RETREAT STOPES  P0OT WALL Hock Typei  •,-»h  Siliceous  -  2.8  -  1 4 0  t/m* MI'S  Schist  CONTINUES TO 1000m  100m  w  MINE No. II MINED OUT (Ne Backfill)  /  f  MINED OUT (Ne Bockflll)  <—  PERMANENT PILLAR (No Grode) 200m  LONGITUDINAL LONGHOLE 62 m STOPE  LONGITUDINAL LONGHOLE OOm STOPE  LONGITUDINAL LONGHOLE STOPE  4*  _D«plh 925m -62m  • 30m-H — 200m ORE  0,-1.ISTO  Rock T y p e : y o E  t  »  v Q* -  I J o«-l.Syh  Porphyry 2.72 t/w* 148 MPa I B . 5 GPa 0.20 30  eio»1.7Yh  320  MINE  No. 13  MINE No. 14  322  MINE  No. 16  OR!  Surfoce  Rock Typei j o, B v 0*  Maaoive Sulphide  - 4.6 t/mi* - 176 MPa - 119.0 CPa - 0.24 m 20  HANGING WALL u> w  Hook Typei  Ouarti Porphyry  y - 2.9 t/a)' o , - 9 1 MPa K - 68.7 GPa v - 0.19 Q' - 42  850m  FOOT WALL Rock Typei y  o, E V Q«  C h l o r i t e Tuff  - 2.9 t/a? - 84 MPa - 68.5 GPa - 0.25 - 40  1  MINE No. 17 o,-yh  2.«th*  J.lyh*  'stress based on f o r a u l s by Oerget  LONGITUDINAL LONGHOLE OPEN STOPINO  870m  co  ro  JL -IBOOm-  HALL  ORE  Rock Typei Y  •  °c E  -  v O'  » .  Massive Sulphide 5.3 t/m* 100 HPa 103 GPa 0.31 19  Rock Typei T  -  "c E  " -  V  •  Q" -  Gnelaa 2.7 t/ai 52 MPa 105 CPa 0.20 IS  J  MINE  No. 18  A  ORE  .  Rock T y p e : y o E v Q* c  -  -  Maaalve S u l p h i d e 4 . 8 l/m* 285 MPa 65.5 GPa 0.10 15  TRANSVERSE OPEN  LONGHOLE STOPING  o„,-3.3th  MINE No. 19 o,-T»  MINEO  OUT A  BACKFILLED  TO SURFACE  • 150m •  •420m LONQITUOINAL  70m  to -o  SUB-LEVEL  LONOITUOINAJL  2-ISm  •US-LEVEL RETREAT  ReTRCAT  30m  TRANSVERSAL BLASTHOLE BTOPES  110m  760m  -210m. ORE Rock Typoi  Maaelve Sulphlda  O, 316 MP* E 232.2 GPa v - 0.16 0' - 44 N  NORTH WALL 190*1  SOOTH WALL (90*1  Rock Typai  Rock Typoi  E V  Baaaltle Tuff  a, B v 0'  -  Rhyolltlo Tuff 90 MPa 67.9 CPa 0.1S 2.2 N  MINE No. 20  328  MINE No. 21  TYPICAL MINE CROSS SECTION  LONGHOLE tc BLASTHOLE LONGITUDINAL OPEN STOPING  ORE Rock Type: Massive Sulphide Oc = 100 MPa E = 88 GPa V = 0.20 Q' = 10-20 HANGING WALL & FOOTWALL Rock Type: Quartz Meta Sediments CT = 50-135 MPa E = 50-75 GPa y = 0.12-0.34 Q' = 0.1-50  = 2.5 crv  C  329  MINE  No. 23  330  MINE No. 30  TYPICAL MINE CROSS SECTION  TRANSVERSE BLASTHOLE OPEN STOPING  ORE Rock Type: Massive Sulphide Y = 3.3 t / m Oc = 160 MPa E = 80 GPa V = 0.21 Q' = 22 3  1500m  HANGING WALL Rock Type: Rhyolite Y = 2.7 t / m or = 120-150 MPa E = 80 GPa 0.14 v = 13-30 5  CT =YH  c  V  CT = 0.8 CT,  Q' =  FOOTWALL Rock Type: Andesite/Diorite 3.0 t / m Y 160 MPa Oc 85 GPa E 0.23 V 14 Q'  2  0\ =  3  331  6+0.055H(m)  MINE No. 31  TYPICAL MINE CROSS  LONGITUDINAL LONGHOLE OPEN STOPING  ORE Y = 3.5 t / m  SECTION  3  Oc = 265 MPa E = 63 GPa Q' = 2 5 - 4 0 HANGING WALL Rock Type: TUFF Y = 2.8 t / m CTc = 195 MPa E = 44 GPa Q' = 2 5 - 4 0 3  FOOTWALL Rock Type: Iron Formation Y = 2.9 t / m CT = 275 MPa E = 51 MPa Q' = 2 5 - 4 0 3  850m  0~„ = 8+l.6YH(m) (isostatic)  C  3 32  OY^YH  APPENDIX I I D E S C R I P T I O N OF THE 2D:  BITEM  BOUNDARY E L E M E N T AND  333  3D:  BEAP  PROGRAMS  BITEM  The the  2D  direct  program  boundary  "BITE"  Carnegie-Mellon piece-wise  integral  developed  university  in  homogeneous  model  by  P.C.  1973.  e l a s t i c i t y  Scientific  and  Australia)  in  1978.  program  the  U.B.C.  mainframe  computer  by  R.  for  an  compatible  computer  by  CANMET  PCBEM  IBM  (Pakalnis  The that  one  shape.  It  integral long  into  explicit  solution  vary the  BITEM  then  modes  of  determined and  These  with  the  through  of  ends  iterations  is  at the when  less  to  field  to  the  perform  by  CSIRO  Organization, modified  (1983)  under  the  and  for  later  program  each  nodes  When the  name  334  the  medium's  be  in  of  defined  the  ). in  constant are  nodes  zero.  a l l  solution the  the  convergence  the is  stress  stress  boundary.  between  can  created,  at  the  An situ  or  becomes  which  influences  difference user  figure  boundary  procedure  excavation  (see  displacements  The  problems sectional  a l l  excavations  and  nodes  for  cross  of  can  boundary  node  other  a  constant  stresses  iterative  than  designed  represent  tractions  the  is a  boundaries. an  displacement  procedure  Pakalnis  by  position.  calculates a l l  and  connected  perpendicular  displacement  Research  at  on  to  analyses  discretization  is selected  conditions.  stress  the  segments  linearly  expanded  subsequently  technique  dimension  requires  surfaces  stress  was  based  1987).  boundary have  Industrial  is  Riccardella  I t was  (Commonwealth  The  "BITEM"  last  and This two  criterion.  Once a boundary  s o l u t i o n has been determined, s t r e s s e s  335  and  OPENING  TO  FIGURE 2 3 . I s o m e t r i c v i e w o f an o p e n i n g t h a t i s l o n g i n d i r e c t i o n a n d t h e d i s c r e t i z a t i o n o f t h e boundary u s e d two d i m e n s i o n a l m o d e l l i n g ( a f t e r Hudyma 1988b).  displacements determined  internal  using  relationships.  the A  more  to  the  boundary detailed  problem solution  boundary and  description  of  be  stress-strain the  i n t e g r a l t e c h n i q u e i s found i n Brady and Bray (1978).  337  can  boundary  BEAP  BEAP  is a  developed University  three  by J.A.C. (1987),  dimensional Diering  as a  boundary  element  PhD t h e s i s ,  at Pretoria  i n c o n j u n c t i o n w i t h CANMET, INCO  D i v i s i o n ) and GEMCOM (Pty.) L i m i t e d .  program  (Thompson  V e r s i o n 1.0, used i n t h i s  p r o j e c t , i s due f o r p u b l i c r e l e a s e i n t h e F a l l 1988. Excavation  boundaries  are generally  q u a d r i l a t e r a l elements (see f i g u r e to  an a r b i t r a r i l y  displacements  oriented  by  ) . The problem i s s u b j e c t field.  The s t r e s s and  on t h e boundary elements v a r y q u a d r a t i c a l l y and  a r e non-conforming. assumed t o v a r y displacements  stress  discretized  T h i s means d i s p l a c e m e n t s  according  and t r a c t i o n s a r e  to a quadratic polynomial,  and t h e  between a d j a c e n t elements a r e d i s c o n t i n u o u s .  The  r e s u l t i n g n u m e r i c a l model has some p o w e r f u l a b i l i t i e s i n m i n i n g related stress analysis,  including:  - t h e need f o r fewer elements t o d i s c r e t i z e an e x c a v a t i o n  than  o t h e r 3d boundary element models, - the a b i l i t y  t o accommodate up t o f i v e  zones w i t h  different,  material properties, - t h e use o f lumping - and t h e a b i l i t y  t o reduce d a t a s t o r a g e  t o determine  requirements,  s t r e s s e s and d i s p l a c e m e n t s  very  c l o s e t o an e x c a v a t i o n boundary. Further d e t a i l s  about BEAP can be found  D i e r i n g and Stacey  (1987).  338  i n D i e r i n g (1987) and  85  FIGURE 25. A t y p i c a l BEAP geometry showing the boundary of t h e e x c a v a t i o n s d e f i n e d by two dimensional q u a d r a t i c , nonconforming elements i n a t h r e e dimensional s t r e s s f i e l d ( a f t e r Hudyma 1988b).  339  APPENDIX I I I PLOT OF INDUCED STRESSES FOR DIFFERENT GEOMETRIES AND K RATIOS  340  23-^  x  H=40  L=120  Ct-28  f  05-29  2 - _ J >  ,1? VV^  $1  1 7 ^  5*  H=40  1=120  Oj-U.7 Ot-2ft  H=40 tf  L=120  0J<-1Z5  <*-  13 H=40 tf  1=120  0,-10 05-: ct-i© T4~3"  349  350  

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