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UBC Theses and Dissertations

Development of a correlation between rotary drill performance and controlled blasting powder factors Leighton, John Charles 1982

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DEVELOPMENT OF A CORRELATION BETWEEN ROTARY DRILL PERFORMANCE AND CONTROLLED BLASTING POWDER FACTORS by JOHN CHARLES LEIGHTON B . A . S c , The 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 , 1978 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPL IED SCIENCE i n THE FACULTY OF GRADUATE STUDIES Depa r tmen t o f M i n i n g and M i n e r a l P r o c e s s E n g i n e e r i n g We a c c e p t t h i s t h e s i s as c o n f o r m i n g t o t h e r e q u i r e d s t a n d a r d THE UNIVERSITY OF BRIT ISH COLUMBIA A u g u s t 1982 © John C h a r l e s L e i g h t o n , 1982 In presenting t h i s thesis i n p a r t i a l f u l f i l m e n t of the requirements for an advanced degree at the University of B r i t i s h Columbia, I agree that the Library s h a l l make i t f r e e l y available for reference and study. I further agree that permission for extensive copying of t h i s thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. I t i s understood that copying or publication of t h i s thesis for f i n a n c i a l gain s h a l l not be allowed without my written permission. John C h a r l e s L e i g h t o n Department of MIVMV I3 The University of B r i t i s h Columbia 1956 Main Mall Vancouver, Canada V6T 1Y3 Date DE-6 (.3/81) - i i -ABSTRACT Despite the a v a i l a b i l i t y of e s t a b l i s h e d , soph is t i ca ted methods fo r p l a n -ning and designing stable slopes in rock , comparatively l i t t l e a t ten t ion i s usua l ly paid to the problems of car ry ing out the excavat ion . B l a s t i n g should be c a r e f u l l y planned to obtain optimum fragmentation as well as s teep , s table p i t wal ls f o r a minimum s t r i p p i n g r a t i o . The p r i n c i p a l d i f f i c u l t y fac ing a b l a s t designer i s the lack of p r i o r information about the many c r i t i c a l b l a s t i n g c h a r a c t e r i s t i c s of the rock mass. The common prac t i ce of t r i a l -and-er ror b l a s t i n g w i l l eventual ly lead to a s u i t a b l e d e s i g n , but t h i s must be repeated time a f t e r time in va r iab le geology. Th is f requent ly r e s u l t s in many b l a s t damaged slopes with decreased s t a b i l i t y and increased safety hazards. For t h i s research p r o j e c t , an extensive study was undertaken to develop a concise background knowledge on s t a t e - o f - t h e - a r t b l a s t i n g technology. A f i e l d research program at Afton Mine examined the r e l a t i o n s h i p between charac-t e r i s t i c rock mass features and b l a s t performance f o r a p p l i c a t i o n in optimal b l a s t i n g des ign . Due to the complex i n t e r - r e l a t i o n s h i p s of the many rock mass p r o p e r t i e s , the development of a comprehensive rock b l a s t i n g model i s not f e a s i b l e . A p r a c t i c a l approach to the problem was achieved by c l a s s i f y i n g each rock type with a s i n g l e Rock Qua l i ty Index value which can be obtained from monitoring the performance of a rotary b las tho le d r i l l . A se r ies of c o n t r o l l e d b l a s t i n g tes ts revealed a strong c o r r e l a t i o n between the Rock i Qua l i ty Index and Powder Factor values over a broad range of geologica l c o n d i -t i o n s . The c o r r e l a t i o n was found to be s u f f i c i e n t l y r e l i a b l e to enable the p red ic t ion of optimum Powder Factors f o r perimeter b las ts in prev ious ly untest -ed rock types. This Rock Qua l i ty Index and Powder Factor c o r r e l a t i o n provides a p r a c t i c a l — i i i — approach to s o l v i n g the problems of s i t e s p e c i f i c b l a s t i n g des ign . Without the costs of add i t iona l equipment or s p e c i a l l y t ra ined personne l , the d r i l l i n g can provide a cont inual supply of d a t a , r e f l e c t i n g changes in the rock mass and permit t ing the s e l e c t i o n of an economical Powder Fac tor . The ul t imate goals of t h i s simple c o r r e l a t i o n system are opt imizat ion of f ragmentat ion, e l im ina t ion of unacceptable b l a s t damage, preservat ion of inherent rock s t r e n g t h , and maximization of slope s t a b i l i t y . - iv -TABLE OF CONTENTS Page ABSTRACT i i TABLE OF CONTENTS iv LIST OF TABLES v i i i LIST OF FIGURES i x LIST OF PLATES x i ACKNOWLEDGEMENTS x i i i CHAPTER 1 INTRODUCTION 1 1.1 References 12 CHAPTER 2 EXPLOSIVES AND BLASTING MATERIALS 13 2.1 Proper t ies of Explos ives 19 2.1.1 Strength 19 2.1.2 V e l o c i t y of Detonation 20 2.1.3 Power 22 2.1.4 Br isance 23 2 .1 .5 S e n s i t i v i t y 23 2.1.6 Density 24 2.1.7 Detonation Pressure 26 2.1.8 Water Resistance 29 2.1.9 Considerat ions f o r Se lec t ing an Explosive 29 2.2 Explos ives Used on th is Research Project 32 2.2.1 Ammonium Ni t ra te / Fuel O i l (AN/FO) 32 2.2.2 S l u r r i e s 38 2 .2 .3 Primers 39 2.2.4 Detonating Cord 40 2 .2 .5 E l e c t r i c B l a s t i n g Caps 41 2.2.6 B l a s t i n g Machine 41 - v -Page 2.2.7 P l a s t i c Borehole L ine r 41 2.3 References 43 CHAPTER 3 ROCK MASS DETONICS 44 3.1 The Breakage Process in Homogeneous Rock 48 3.1.1 Bench B l a s t i n g 48 3.1.2 Crater B l a s t i n g 59 3.1.3 Pre-Shear B l a s t i n g 60 3.2 The Influence of Rock Mass Proper t ies on the Rock Breakage 66 Process 3.2.1 In -S i tu Dynamic Rock Strength 67 3.2.2 Presence o f S t ructura l Features 69 3.2.3 Po isson 's Ratio 7.4 3.2.4 Young's Modulus 76 3.2.5 Internal F r i c t i o n 76 3.2.6 Rock Density 77 3.2.7 Seismic Wave V e l o c i t y 77 3.2 .8 Water Content 79 3.2.9 In -S i tu Stress 79 3.3 References 82 CHAPTER 4 THE INFLUENCE OF BLASTING ON SLOPE STABILITY 84 4.1 E f f e c t of Physical B l a s t i n g Forces 87 4.2 E f f e c t of Ground V ibra t ions 93 4.3 References 103 CHAPTER 5 DESIGN CONSIDERATIONS FOR CONTROLLED BLASTING 104 5.1 Se lec t ing a Cont ro l l ed B l a s t i n g Technique 107 5.1.1 Pre-Shear B l a s t i n g 108 5.1.2 Cushion B l a s t i n g 111 5.1.3 Buf fer B l a s t i n g 113 - v i -Page 5.2 B l a s t i n g Design Parameters 115 5.2.1 B las tho le Diameter 115 5.2.2 Explosive Type 118 5.2.3 S u b - D r i l l Depth 118 5.2.4 Stemming 119 5.2.5 Optimum Charge 121 5.2.6 Powder Factor and Burden Volume 122 5.2.7 B las tho le Pattern 122 5.2.8 Front Row Considerat ions 123 5.2.9 I n i t i a t i n g and F i r i n g Sequence 125 5.3 B las t Evaluat ion and Opt imizat ion 129 5.3.1 During Detonation 129 5.3.2 A f t e r Detonation 129 5.4 References 133 CHAPTER 6 EXPERIMENTAL STUDIES AND FIELD WORK 134 6.1 Background Information on Afton Mine 138 6.1.1 Regional Information 138 6.1.2 H i s t o r i c a l Summary 141 6.1.3 Summary of S i t e Geology 143 6.2 Development of the Rock Qua l i ty Index 150 6.2.1 Mechanical Theory of D r i l l Performance 151 6.2.2 E s t a b l i s h i n g Rock Qua l i ty Index Values 154 6.3 Development of an Improved Perimeter B las t Design 162 6.3.1 Former B l a s t i n g Methods 162 6.3.2 Design of an Improved Perimeter B l a s t i n g Method 164 6.4 Development of the Powder Factor C o r r e l a t i o n 172 6.4.1 E s t a b l i s h i n g Powder Factor Values 172 6.4.2 Data Ana lys is and Results 176 - v i i -Page 6.4.3 Test ing the RQI/Powder Factor C o r r e l a t i o n 177 6.4.4 Suggested Further Research 181 6.5 P r a c t i c a l App l i ca t ions of Results 183 6.6 References 185 CHAPTER 7 CONCLUSIONS 188 BIBLIOGRAPHY 192 APPENDICES : I GLOSSARY OF BLASTING TERMINOLOGY 202 II BASIC PROPERTIES OF EXPLOSIVES AND BLASTING MATERIALS USED BY 215 AFTON OPERATING CORPORATION III DATA LOGS AND PLOTS USED TO DETERMINE ROCK QUALITY INDEX VALUES 224 IV DESIGN EXAMPLE FOR THE NEW PERIMETER BLAST AND COMPARISON OF 237 DE-COUPLING METHODS V EXPLOSIVE LOAD TABLES FOR PERIMETER BLASTS 242 VI CONVERSION TABLES FOR IMPERIAL AND S . I . UNITS 252 EPILOGUE 254 - v i i i -LIST OF TABLES Table Page 1 B las tho le Diameter, Volume and Cost 117 2 C l i m a t i c Data, Kamloops A i r p o r t 140 3 Descr ip t ion of Domains 148 4 Hardness of Rock Types Using Jennings' Hardness C l a s s i f i c a t i o n 149 5 D r i l l i n g Machine S p e c i f i c a t i o n s 157 6 Rock Qua l i ty Index Values 160 7 Summary of RQI/Powder Factor C o r r e l a t i o n 179 - ix -LIST OF FIGURES Figure Page 1.0-1 E f f e c t of P i t Slope Angle on Volumes of Waste and Ore in a Hypothet ical Open P i t 3 1.0-2 E f f e c t of P i t Slope Angle on S t r i p p i n g Ratio f o r the Hypo-t h e t i c a l Open P i t of F igure 1.0-1 4 1.0-3 E f f e c t of Fragmentation on Cost of Mining 6 2 .0- 1 General C l a s s i f i c a t i o n s of B l a s t i n g Compounds 15 2 .1 - 1 Test Methods f o r Determining Confined and Unconfined V e l o c i t i e s of Detonation 21 2.1-2 Re la t ionsh ip of S e n s i t i v i t y to S p e c i f i c Grav i ty and Charge Diameter 25 2.1-3 Detonation Pressure as a Function of S p e c i f i c Gravi ty and Detonation V e l o c i t y 27 2.1-4 Factor N v s . S p e c i f i c Grav i ty f o r Borehole Pressure Est imat ion 28 2 .1 - 5 Some Re la t ive Ingredients and Proper t ies of Explosives 30 2 .2- 1 Confined Detonation V e l o c i t y of AN/F0 v s . Borehole Diameter 34 2.2-2 E f f e c t of Water Content on the Detonation V e l o c i t y of AN/F0 37 3.1-1 Comparison of B las tho le Conf igurat ions in Crater and Bench B l a s t i n g 49 3.1-2 I n i t i a l Radial F rac tur ing Mechanism on an Element of Rock 51 3.1-3 Plan View of Stage 1 of Rock Breakage Process 52 3.1-4 B las tho le Cross -Sec t ion in the Plane of a Radial Crack During Stage 1 of the Rock Breakage Process 53 3.1-5 Plan View of Stage 2 of Rock Breakage Process 56 3.1-6 Plan View of Stage 3 of Rock Breakage Process 58 3.1-7 Comparison Between Removed Volumes in Bench B l a s t i n g and Crater B l a s t i n g With Ident ical Charges and Burdens 61 3.1-8 I n i t i a t i o n of Pre-Shear F rac tur ing Mechanism on an Element of Rock Between Two Simultaneously Detonated Blastho les 63 3 .1 - 9 Propagation of Pre-Shear Fracture Due to the In teract ion of Two Shock Waves 64 3.2- 1 Empir ica l Re la t ionsh ip Between Powder F a c t o r , Fracture Frequency and J o i n t Shear Strength at Bouga inv i l l e Copper 75 - X -Figure Page 3.2-2 Empir ical Re la t ionsh ip Between Powder Factor and In -S i tu Seismic V e l o c i t y at Kennecott Copper 78 3.2-3 The Inf luence of an In -S i tu Stress F i e l d on a Pre-Shear Line With Various B las tho le Spacings 81 4.2-1 Peak P a r t i c l e V e l o c i t y versus Scaled Distance 96 4.2-2 P a r t i c l e V e l o c i t i e s and Damage Induced at Given Distances by P a r t i c u l a r Charges 99 4.2-3 The E f f e c t of Increasing the Number of Delays f o r Reducing B l a s t i n g V ibra t ions at Da Ye Mine, China 100 5.2-1 Bench B l a s t i n g Terminology and Design Parameters 116 5.2-2 Rock Breakage at the Bottom of a B las tho le due to Sub-D r i l l i n g 120 5.2-3 Various Patterns Commonly Used in Perimeter B l a s t i n g 124 5.2-4 Design Parameters f o r the C r i t i c a l Front Row Burden 126 5.2- 5 Various F i r i n g Sequences Commonly Used in Perimeter B l a s t i n g 127 5.3- 1 C h a r a c t e r i s t i c Features of a Successful Perimeter B las t 130 6.1-1 Locat ion Map f o r Afton Mine 139 6.1-2 Regional Geology at Afton Mine 142 6 .1 - 3 P i t Plan Showing Domain Boundaries at Afton Mine (August 1981) 147 6.2- 1 Rock Qua l i ty Index Values f o r Each Domain Ranked in Order of Increasing Qua l i ty 161 6.3- 1 Former Perimeter B las t Pattern at Afton Mine 163 6.3-2 New Perimeter B las t Pattern at Afton Mine 166 6.3-3 Comparison of D r i l l h o l e Densi t ies on Old and New Perimeter B las t Patterns 167 6.3- 4 Plan of New Perimeter B las t F i r i n g Sequence 169. 6.4- 1 Proposed C o r r e l a t i o n Between Rock Qua l i ty Index and Powder Factor 178 - xi -LIST OF PLATES Except where noted, a l l photographs were taken by the author. Plate . Page 1 Underblast ing r e s u l t s in b l o c k y , poor ly fragmented rock and t i g h t d igging c o n d i t i o n s . Broken shovel t e e t h , s t ra ined shovel c a b l e s , truck t i r e damage and increased loading times add s i g n i f i c a n t delays and costs to the mining opera t ion . 7 2 Overb last ing can severe ly weaken rock s l o p e s , r equ i r ing expen-s ive and time consuming s t a b i l i z a t i o n measures. Rockbol ts , s h o t c r e t e , s teel straps and mesh were used on the upper rock face in t h i s photo, cont ras t ing dramat ica l ly with the c l e a n , w e l l - b l a s t e d face below. 8 3 The C . I . L . t ruck t ranspor ts and d e l i v e r s bulk AN/FO s a f e l y and e a s i l y . On s i t e , i t mixes the fuel o i l with the ammonium n i t r a t e p r i l l s and e jects the f i n i s h e d mixture pneumatical ly through the black hose at the rear of the t ruck . 35 4 Loading AN/FO into a b las tho le i s a f a s t and easy procedure. Th is p a r t i c u l a r hole contained water, was pumped out and had a p l a s t i c l i n e r i n s e r t e d . Two primers are used to ensure deton-a t ion in wet h o l e s , as ind ica ted by the two Primacord downlines. 36 5 Plan view of a b l a s t h o l e showing Stage 1 f r a c t u r i n g mechanisms in a homogeneous rock block as i l l u s t r a t e d in Figure 3 .1 -3 . Note the d i s t o r t e d b las tho le surrounded by an in tense ly crushed zone and the rad ia l f r a c t u r e pa t te rn . 54 6 View of f r a c t u r e plane p a r a l l e l to a s ing le b las tho le in a homogeneous rock b lock . Surface texture c l e a r l y ind ica tes t h i s to be a t e n s i l e f r a c t u r e . Note rad ia l nature of t e n s i l e f rac tu re pattern as i l l u s t r a t e d in Figure 3 .1 -4 . Excessive f rac tu re at toe of hole is probably due to loca t ion of the primer charge. 55 7 Pre-Shear b l a s t i n g created a s ing le f rac tu re plane to produce th is c l e a n , smooth rock face along a highway. The presence of i n t a c t h a l f - b l a s t h o l e s ind ica tes a minimum of damage to the rock behind the pre-shear p lane. 65 8 Th is exposed b las tho le c l e a r l y reveals the e f f e c t of an i n t e r s e c t i n g j o i n t . Note the shape of the crushed zone and the d i s t i n c t l y open j o i n t caused by the pneumatic wedging of escaping high pressure explosion gases. 70 9 The e f f e c t of a major j o i n t p a r a l l e l and adjacent to the b l a s t -hole can be seen at the centre of th is photo. The r e f l e c t e d t e n s i l e wave in teracted with the j o i n t to cause overbreak along the well def ined j o i n t p lane. Premature gas re lease into the j o i n t reduced the b las tho le pressure such that a substant ia l port ion of rock along the b las tho le f a i l e d to break; out . 72 - xi i -P late Page 10 The presence of non-shattered h a l f - b l a s t h o l e s and several smooth shear faces ind ica te that t h i s rock face was not overb las ted . This photo i l l u s t r a t e s that s teep , outward d ipping rock s t ruc ture w i l l u l t imate ly control the f i n a l appearance of a rock face . In t h i s c a s e , the primary concern in the b l a s t design i s to keep such overbreak to a minimum. 73 11 Tension cracks outs ide the p i t perimeter reveal the extent of the large p i t wall f a i l u r e i n i t i a t e d by care less b l a s t -i n g . Although t r iggered by gas pressure damage, continued movement was caused by a combination of high groundwater l e v e l s and b l a s t i n g v i b r a t i o n s . 91 12 Cushion b l a s t i n g was used to create t h i s c l e a n , low main-tenance rock face in the very weak and h ighly f rac tured Kami oops Volcanic format ion. 112 13 An a e r i a l view of the Afton Mine s i t e , November 1980. 144 14 View across A f t o n ' s p i t looking west. The var ious geolog-i c a l uni ts wi th in the p i t are c l e a r l y seen by the d i f f e r e n t coloured zones. 146 15 One of the two Bucyrus E r i e 40-R d r i l l s used at Afton Mine. 156 16 A l l b las tho les were d r i l l e d with 230 mm. (9 inch) diameter t r i - c o n e b i t s with ch ise l -shaped tungsten carbide i n s e r t s . 158 17 The new perimeter b l a s t design during detonat ion. As the pattern f i r e s from l e f t to r i g h t , the varying dust plume heights i l l u s t r a t e the e f f e c t of the delay sequence. 171 18 The tes t b l a s t of Plate 17 produced t h i s muck p i l e which i l l u s t r a t e s the features of a successfu l b l a s t . Note the evenness of throw, i n d i c a t i n g a good f ront row charge. 173 19 A c lose up view of the muck p i l e toe area . Note the r e l a t i v e l y uniform fragmentation and the lack of rock debr is beyond the toe . The slope of th is muck face is i d e a l . 174 20 A c lose up view on top of the muck p i l e . Note the s l i g h t r i s e of the evenly fragmented c res t and the s l i g h t dip along the back of the berm. The area appears uniform without c ra te rs or humps. 175 21 A handful of f r e e - f l o w i n g AN/FO. Safe handling i s one of the important c h a r a c t e r i s t i c s of a b l a s t i n g agent. 217 22 A 25 ki logram bag of Hydromex T - 3 . This w i l l be hand loaded in to wet b las tho les because of i t s exce l len t water r e s i s t a n c e . 219 23 A Procore III Primer t i e d onto the end of a Reinforced Primacord downline i s ready f o r lowering into a b l a s t h o l e . 222 - x i i i -ACKNOWLEDGEMENTS The author wishes to express h is grat i tude to his research s u p e r v i s o r , Mr. C O . Brawner, f o r his encouragement, comments and guidance throughout t h i s research p r o j e c t . Thanks are a lso extended to the other f a c u l t y members of the Department of Mining and Mineral Process Engineering f o r t h e i r general support and encouragement. At Afton Operating Corpora t ion , the author wishes to express his appre-c i a t i o n to Mike L ipkewich, Mine Manager, f o r his i n t e r e s t and w i l l i n g n e s s in permit t ing t h i s research to be done at Afton Mine. Fred Mason, P i t Super-intendent , and Hans Geertsema, General P i t Foreman, deserve spec ia l thanks f o r t h e i r comments and guidance throughout the development and t e s t i n g of the new b l a s t i n g des igns . Valuable ass is tance in the geologica l work was provided by Doug Stewart , Chief Engineer; A l l a n Reed, Teck Explora t ion Engineer; and Ian O l i v e r , P i t G e o l o g i s t . The i n t e r e s t and pat ience of a l l the b l a s t i n g crew members was great ly appreciated during the experimental s tages . The i r input with respect to p r a c t i c a l problems encountered in the f i e l d contr ibuted to the value of t h i s thes is as a u s e f u l , working;document. Thanks t o : Mike S h i e l d s , Pat S t a l l a r d , B i l l Kaczanowski, Dean Blanchard , Michael Godard, Barry McDonald, and Jim S e i b a l . F inanc ia l support from the National Science and Engineering Research Council of Canada and from the Freder ick Armand McDiarmid Scholarships was grea t ly apprec ia ted . CHAPTER ONE INTRODUCTION - 2 -1 . 0 INTRODUCTION Achiev ing a s a t i s f a c t o r y leve l of slope s t a b i l i t y i s the most important cons idera t ion f o r a geotechnical engineer designing large sca le surface excav-at ions in rock. Unfor tunate ly , rock i s f a r from being an ideal engineering m a t e r i a l , possessing h igh ly complex c h a r a c t e r i s t i c s which of ten change over very short d i s t a n c e s . D i f fe ren t rock types can span a broad range of s t rengths , be h ighly f rac tured or broken, and can be intermixed with other substances such as c lay gouge or hard i n f i l l i n g . Even the loca l environment can add fu r ther compl icat ions by the presence of water, l o c a l seismic a c t i v i t y , and weathering upon exposure. The design of a rock slope must take in to account the degree of s t a b i l i t y that i s necessary. In the f i e l d of c i v i l eng ineer ing , rock cuts demand a high degree of s t a b i l i t y along t ranspor ta t ion c o r r i d o r s , in habitated a r e a s , or in high cost i n s t a l l a t i o n s such as hydro-power p r o j e c t s . Minor f a i l u r e s or r o c k f a l l s cannot be to le ra ted f o r the safety of the i n s t a l l a t i o n s or the people working and t r a v e l l i n g beneath the s l o p e s . For t h i s reason, a conserv-a t i ve approach i s genera l ly accepted in rock slopes designed f o r c i v i l p r o j -ects where the consequences of minor i n s t a b i l i t y can j u s t i f y the higher cap i ta l costs of c o n s t r u c t i o n . However, in the open p i t mining i n d u s t r y , there i s the add i t iona l economic incent ive to maintain the steepest s tab le slope angle f o r the minimum s t r i p p i n g r a t i o . 1 Every degree of reduced p i t wall angle represents a substant ia l amount of l o s t p r o f i t . Th is is more true than ever now that lower grade deposi ts are being developed and open p i t s are excavated to greater depths. See Figures 1 . 0 - 1 and 1 . 0 - 2 . For these reasons, the mining industry cannot a f fo rd the higher costs of absolute slope s t a b i l i t y . P i t slope design has evolved over the years to the point where a c e r t a i n amount of i n s t a b i l i t y ( i . e . l o c a l -i zed bench c res t f a i l u r e ) is a c t u a l l y allowed f o r in order to achieve the maximum poss ib le overa l l slope angle . - 3 -9 0 0 m. H Y P O T H E T I C A L CIRCULAR O P E N PIT AND O R E B O D Y 250 H 0 -I 1 1 1 1 1 — 20° 3 0 ° 4 0 ° 5 0 ° 6 0 ° 7 0 ° PIT S L O P E " A N G L E FIGURE 1.0-1 ' E F F E C T OF PIT SLOPE ANGLE ON VOLUMES OF WASTE AND ORE IN A HYPOTHETICAL OPEN PIT (after Stewart and K e n n e d y 1 ) - 4 -0 •! 1 ; 1 1 1 —i 20° 30° 40° 50° 60° 70° PIT S L O P E A N G L E FIGURE 1 . 0 - 2 « EFFECT OF PIT SLOPE ANGLE ON STRIPPING RATIO FOR THE HYPOTHETICAL OPEN PIT OF FIGURE I.O-l ( a f t e r Stewart and Kennedy 1 ) - 5 -Such design prac t ices require d e t a i l e d knowledge of the rock mass prop-e r t i e s to be able to design within these c l o s e r t o l e r a n c e s . The geotechnical engineer w i l l have to spend considerable e f f o r t to produce a s a f e , f e a s i b l e and economic des ign . Much time w i l l usua l ly be spent on the f i e l d mapping, s t r u c t u r a l geologic s t u d i e s , surface and subsurface hydrology, determination of strengths and e f f e c t i v e f r i c t i o n angles of d i s c o n t i n u i t i e s , and f i n a l l y , checking s t a b i l i t y with the a i d of mathematical and a n a l y t i c a l models. Unfor tunate ly , the engineer often f a i l s to recognize the c r i t i c a l importance of problems involved in t r a n s l a t i n g the design "on paper" to a slope "in rock" . The great care taken f o r the design must be continued into the excavation stage i f the optimum stab le slope i s to be r e a l i z e d . Construct ion in rock usua l ly requires b l a s t i n g which, by i t s very nature , i s a h ighly des t ruc t i ve force demanding carefu l c o n t r o l . Since b l a s t i n g i s the f i r s t step in the mining process , achiev ing successfu l fragmentation has an important e f f e c t on a l l the downstream ore hand l ing arid processing a c t i v -i t i e s . Rock which is underblasted can add s i g n i f i c a n t headaches and costs to a mining opera t ion . See Figure 1.0-3 and Plate 1. At the same t ime, the f i n a l rock s l o p e , having been designed to f a i r l y c lose t o l e r a n c e s , must not be subjected to excessive forces which could a l t e r the rock mass strength proper t ies and lead to ser ious i n s t a b i l i t y . Thus, overb las t ing w i l l a lso cause extra problems and often r e s u l t in very expensive and time consuming so lu t ions to regain slope s t a b i l i t y . See Plate 2. This problem of s a t i s f y i n g two apparent ly opposite tasks simultaneously i s the dilema faced by a b l a s t des igner . He must always s t r i v e to f i n d the optimal point between fragment-a t ion and s t a b i l i t y where the operat ing costs are minimized. Over the past 20 y e a r s , considerable progress has been made in the study of e x p l o s i v e s , rock mass d e t o n i c s , and b l a s t i n g techniques. Much of t h i s information was reviewed f o r t h i s thes is and has been summarized in Chapters 2 through 5 to provide the background necessary f o r understanding rock b l a s t -- 6 -FIGURE 1.0-3 • E F F E C T OF FRAGMENTATION ON COST OF MINING ( after Hoek 8 Bray2 ) - 7 -PLATE I Underblast ing r e s u l t s in b locky , poorly fragmented rock and t igh t d igging c o n d i t i o n s . Broken shovel t e e t h , s t ra ined shovel c a b l e s , truck t i r e damage and increased loading times add s i g n i f i c a n t delays and costs to the mining opera t ion . - 8 -P L A T E 2 Overblast ing can severe ly weaken rock s l o p e s , requ i r ing expensive and time consuming s t a b i l i z a t i o n measures. Rockbol ts , s h o t c r e t e , s teel straps and mesh were used on the upper rock face in t h i s photo, cont ras t ing dramat ica l ly with the c l e a n , w e l l - b l a s t e d face below. - 9 -ing p r i n c i p l e s . Despite the a v a i l a b i l i t y of a good body of l i t e r a t u r e , much of the mining industry s t i l l tends to regard b l a s t i n g as more of an a r t than a s c i e n c e . Consequently, there are many cases where a good p i t s lope design has been ruined by poor b l a s t i n g p r a c t i c e s , r e s u l t i n g in c o s t l y r e - s t a b i l i z a -t ion programs. More and more mines are gradual ly r e a l i z i n g the importance of apply ing up-to-date b l a s t i n g t e c h n o l o g y . 3 - 1 0 Good references and experienced personnel are now a v a i l a b l e f o r designing the geometric b l a s t i n g parameters (hole depth, subgrade, burden, s p a c i n g , c o l l a r ) , choosing the r igh t exp los ive type , and s e l e c t i n g a delayed f i r i n g sequence. Yet , even in operat ions using recognized c o n t r o l l e d b l a s t i n g techniques, there are numerous cases where the b l a s t i n g has damaged the rock s l o p e s . Th is i s due to one s i g n i f i c a n t unknown f a c t o r : What i s the optimum amount of explos ive to place in each b l a s t h o l e which w i l l provide good fragmentation and leave the f i n a l wall in tac t? This parameter i s commonly re la ted to the powder f a c t o r . T y p i c a l l y , in open p i t mining, the explos ive type , the perimeter b las t geometry and the f i r i n g sequence are f i x e d as standard p rac t i ce throughout the p i t , leav ing the powder f a c t o r as the only remaining design v a r i a b l e . Although i t has long been recognized that the optimum powder f a c t o r i s l a r g e l y dependent on the nature of the rock mass, t h i s c r i t i c a l r e l a t i o n s h i p i s extremely complex, incorporat ing many of the rock mass p r o p e r t i e s . Conse- : quent ly , i t has remained poorly understood and r a r e l y documented. In p r a c t i c e , the optimum powder f a c t o r i s usua l ly a r r i v e d at by a t r i a l -and-error procedure. Due to fears of delaying the mining operat ion by under-b l a s t i n g , t h i s procedure tends to promote the use of excessive powder fac to rs to ensure necessary f ragmentat ion. Obv ious ly , considerable damage can be i n f l i c t e d to the slope before a s a t i s f a c t o r y value i s a r r i v e d a t , r e s u l t i n g - 10 -in faces with high r a v e l l i n g potent ia l or sometimes t r i g g e r i n g more massive slope f a i l u r e s . Due to the sequence of p i t excavat ion , th is tends to leave the most unstable faces at the top of the cut s l o p e . When the excavation encounters v a r i a t i o n s in the rock mass, or moves into a d i f f e r e n t geologic u n i t , the problems of t r i a l - a n d - e r r o r ! b.lasting begin aga in . There is c l e a r l y a need to e s t a b l i s h a r e l i a b l e , working c o r r e l a t i o n between the proper t ies of a rock mass and an optimum powder f a c t o r i f one hopes to a t t a i n s a t i s f a c t o r y and economical b l a s t i n g r e s u l t s . Th is c o r r e l a -t ion should be r e l a t i v e l y simple so that the non-geotechnical man- in- the-f i e l d could use i t in regular b l a s t i n g p r a c t i c e . I d e a l l y , the system should be able to account f o r a l l the key rock mass proper t ies which a f f e c t b l a s t i n g and should be able to provide s u f f i c i e n t data f o r a ho le -by-ho le explos ive des ign . To date there has been l i m i t e d success in achiev ing such a c o r r e l a t i o n system between powder fac to rs and rock mass c o n d i t i o n s . Two authors , Broadbent 1 1 and A s h b y 1 2 , have es tab l i shed r e l a t i o n s h i p s between powder fac to rs and s i n g l e rock mass f e a t u r e s , but these tend to be s i t e s p e c i f i c . Due to t h e . l a r g e number of key rock mass proper t ies i n v o l v e d , a q u a l i t a t i v e type of rock mass index, s i m i l a r to those now in use by tunnel design engineers , would best be able to provide an overa l l value f o r c o r r e l a t i o n with powder f a c t o r s . This thes is contains the r e s u l t s of research work on t h i s subject as part of a Masters of Appl ied Science degree program which commenced in Sept-ember 1980. Fol lowing a year of background i n v e s t i g a t i o n , an experimental program of f i e l d t e s t i n g was c a r r i e d out over 6 months in 1981 at an open p i t copper mine operated by Afton Operating Corporat ion near Kamloops, B . C . Afton Mine proved to be an exce l l en t t e s t i n g f a c i l i t y due to i t s broad range of geologic c o n d i t i o n s . As a r e s u l t of the f i e l d research program, a good c o r r e l a t i o n was estab-1 ished between c o n t r o l l e d b l a s t i n g powder f a c t o r s and rock mass proper t ies based on the performance of rotary b las tho le d r i l l s . The ul t imate goals of t h i s simple c o r r e l a t i o n system are opt imiza t ion of f ragmentat ion, e l im ina t ion of unacceptable b l a s t damage, preservat ion of inherent rock s t r e n g t h , and maximization of slope s t a b i l i t y . - 12 -1 REFERENCES ) STEWART, R.M. & KENNEDY, B . A . : The Role of Slope S t a b i l i t y in the Economics, Design and Operation of Open P i t Mines. Proceedings, F i r s t Internat ional Conference on S t a b i l i t y in Open P i t Mi ni g , Vancouver, B . C . AIME, 1971. ) HOEK, E. & BRAY, J . W . : Rock Slope Engineer ing , Chapter 11 - B l a s t i n g . Second E d i t i o n , IMM, 1977. ) HOLMBERG, R. & MAKI, K . : Case Examples of B l a s t i n g Damage and i t s Influence on Slope S t a b i l i t y . P r o c e e d i n g s , T h i r d Internat ional Confer-ence on S t a b i l i t y in Surface Min ing , Vancouver, B . C . , AIME, 1982. ) BAXTER, C.W.: Cont ro l l ed B l a s t i n g on a Production Scale at Thunderbird Mine. Mining Eng ineer ing , V o l . 24, No. 11, November 1972. ) BROWN, C. & BIGANDO, J . : P r e s p l i t t i n g and Smooth Wall B l a s t i n g in La Cananea P i t . Mining Eng ineer ing , V o l . 24, No. 9, September 1972. ) DAVIS, D . J . : How Delay B l a s t i n g Has Been Modif ied to El iminate Cutof fs and Improve Fragmentation at K a i s e r ' s Open P i t Coal Mines. Proceedings, CIM Operators Conference, Kamloops, B . C . , October 1978. ) DIMOCK, R.R. & CLAYTON, G . D . : Kennecott 's Delayed B l a s t i n g Technique Cuts C o s t s , Improves P i t S t a b i l i t y . Mining Engineer ing , V o l . 29, No. 4 , A p r i l 1977. ) JOHNSTON, S . G . : B l a s t i n g Advances at Hammersley I ron. Mining Magazine, V o l . 128, No. 8, August 1973. ) MARCONA MINING CORPORATION: How Marcona Uses C a r e f u l l y Cont ro l led B las t ing Techniques. World Min ing, V o l . 28, No. 10, September 1975. ) MORASH, B . J . : Control B l a s t i n g For Slope S t a b i l i t y at the Adams Mine. CIM B u l l e t i n , V o l . 71, No. 793, May 1978. ) BROADBENT, C D . : Pred ic tab le B l a s t i n g With In S i tu Seismic Surveys. Mining Eng ineer ing , V o l . 26, No. 4 , 1974. ) ASHBY, J . P . : Production B l a s t i n g and Development of Open P i t S lopes . Proceedings, Th i rd Internat ional Conference on S t a b i l i t y in Surface Min ing , Vancouver, B . C . , AIME, 1982. - 13 -CHAPTER TWO EXPLOSIVES AND BLASTING MATERIALS - 14 -2.0 EXPLOSIVES AND BLASTING MATERIALS Explosives are perhaps the most thoroughly studied of a l l compounds and are a vast science unto themselves. A chemical explos ive can be def ined as a compound or a mixture of compounds which, when i n i t i a t e d by heat , impact, f r i c t i o n , or shock, undergoes a very r a p i d , s e l f - p r o p a g a t i n g , exothermic d e c o m p o s i t i o n . 1 Th is decomposition produces more stable products , usua l ly gases, which occupy a much la rger volume than the explosive in i t s o r i g i n a l c o n f i g u r a t i o n . The intense heat generated by the explos ive react ion continues to rap id ly expand the gaseous products to such an extent that they exert enormous pressure on t h e i r surroundings. The work done by an explosive depends p r imar i l y on the amount of heat given o f f during the e x p l o s i o n . As shown in Figure 2 . 0 - 1 , explosives are broadly c l a s s i f i e d as mechanical , chemical or nuc lear . Since the mining and const ruc t ion i n d u s t r i e s use chemical explosives e x c l u s i v e l y , t h i s w i l l be the only group considered in t h i s t h e s i s . Chemical explos ives can be sub-d iv ided in to high explosives or low e x p l o s i v e s . High explos ives "detonate", i n d i c a t i n g that the react ion is moving through the explos ive f a s t e r than the speed of sound in the unreacted e x p l o s i v e . Low explosives " d e f l a g r a t e " , a react ion slower than the speed of sound. A l l com-mercial explos ives a v a i l a b l e today, except black powder, are high e x p l o s i v e s . High explos ives are f u r t h e r s u b - d i v i d e d . i n t o primary and secondary explo-s i v e s . Primary explos ives are r e l i a b l y detonated by spark , f lame, and impact, but are too s e n s i t i v e f o r use in conventional i n d u s t r i a l a p p l i c a t i o n s . Charac-t e r i z e d by high densi ty ( s . g . of 3 to 5 ) , these extremely powerful products are genera l ly used as m i l i t a r y explos ives and as explos ive base ingredients in secondary explos ive formula t ions . Secondary explos ives are s t i l l very powerful but are l ess s e n s i t i v e , requ i r ing a detonating wave of considerable magnitude f o r successfu l i n i t i a t i o n . V i r t u a l l y a l l commercially a v a i l a b l e explos ives belong in t h i s secondary high explos ive category . BLASTING COMPOUNDS EXPLOSIVES MECHANICAL CHEMICAL NUCLEAR HIGH EXPLOSIVES LOW EXPLOSIVES PRIMARY SECONDARY DYNAMITES GELATINS BLASTING AGENTS DRY SLURRY i FIGURE 2 . 0 - 1 : GENERAL CLASSIFICATIONS OF BLASTING COMPOUNDS - 16 -Despite the large var ie ty of formulat ions and brand names, secondary explos ives can be s p l i t in to the two general groupings o f dynamites and g e l a -t i n s . O r i g i n a l l y , s t r a i g h t dynamites cons is ted of n i t r o g l y c e r i n ' and k i e s e l -guhr, a porous and i n e r t va r ie ty of s i l i c a . L a t e r , sodium n i t r a t e was mixed with n i t r o g l y c e r i n to increase the power of the e x p l o s i v e . The i r use has great ly diminished in recent years due to high costs and high s e n s i t i v i t y to 'shock and f r i c t i o n . The most widely used car t r idged explos ives in the f i e l d today are ammonia dynamites, sometimes re fe r red to as extra dynamites. Ammonia dynamites are s i m i l a r in composit ion to s t r a i g h t dynamites except that ammonium n i t r a t e replaces a large por t ion of n i t r o g l y c e r i n and sodium n i t r a t e . Manufactured in both high and low d e n s i t i e s , ammonia dynamites are l ess expensive and considerably less s e n s i t i v e to shock and f r i c t i o n . Ge la t ins are tough, rubbery or p l a s t i c - t e x t u r e d compositions with the d i s t i n g u i s h i n g feature of good water r e s i s t a n c e . As with dynamites, ge la t ins have a va r i e ty of fo rmula t ions . B l a s t i n g Ge la t in is the most powerful explo-s ive commercial ly a v a i l a b l e , composed of n i t r o c e l l u l o s e , a lso known as gun-c o t t o n , added to a very high percentage of n i t r o g l y c e r i n . S t ra ight g e l a t i n has a grea t ly reduced n i t r o g l y c e r i n content and i s the equivalent of a s t r a i g h t dynamite in the dynamite^category. Ammonium n i t r a t e i s used to replace some of the n i t r o g l y c e r i n and sodium n i t r a t e to produce ammonia g e l a t i n and semi-g e l a t i n , which are r e s p e c t i v e l y comparable to high and low densi ty ammonia dynamites. Although the wide va r i e ty of commercially a v a i l a b l e explos ives have d i f f e r e n t chemical composi t ions, they a l l contain f i v e basic funct iona l i ngred ien ts : 1) Explos ive bases 2) Combustibles 3) Oxygen c a r r i e r s - 17 -4) Antacids 5) Absorbants An explos ive base i s a s o l i d or l i q u i d which, upon the a p p l i c a t i o n of s u f f i c i e n t heat or shock, breaks down into gaseous products with an accompany-ing re lease of heat e n e r g y , 1 Combustibles and oxygen c a r r i e r s are added to an explos ive to achieve oxygen balance. A combustible combines with excess oxygen in an explos ive mixture to prevent the formation of ni t rogen ox ides . An oxygen c a r r i e r assures complete ox idat ion of the carbon in the explos ive mixture to prevent the formation of carbon monoxide. An antac id is added to an explos ive to increase s t a b i l i t y in storage and an absorbant i s used, when needed, to absorb l i q u i d explos ive b a s e s . 1 Achieving complete oxygen balance during detonation is an important , but ra re ly s t r e s s e d , aspect in the optimal performance of an e x p l o s i v e . The formation of n i t rogen oxides or carbon monoxide, in add i t ion to being undes i r -able because of t h e i r fumes, r e s u l t s in a lower heat of explosion than does the formation of carbon dioxide and n i t rogen . A lower heat of explosion means a lower energy output , reducing the e f f i c i e n c y of the explos ive and the b l a s t -i n g . Except f o r n i t r o g l y c e r i n and ammonium n i t r a t e , v i r t u a l l y a l l explosives are oxygen-de f i c ien t . The s e n s i t i v i t y , strength and power of explos ives reaches a maximum at per fect oxygen balance. The fo l lowing two examples, each using an explos ive formulated with ammonium n i t r a t e and t r i n i t r o t o l u e n e ( T . N . T . ) , i l l u s t r a t e the e f f e c t of oxygen balance. One e x p l o s i v e , 80/20 Amatol , detonates according to the fo l lowing reac-t i o n : 2 21Nh\N0 3 + 2 C H 3 C 6 H 2 ( N 0 2 ) 3 — 1 4 C 0 2 + 47H 20 + 24N 2 This explos ive contains enough oxygen f o r complete ox idat ion and the react ion has a heat of explosion of approximately 1000 c a l . / g r a m of o r i g i n a l e x p l o s i v e . - 18 -For 60/40 Amatol , the detonation react ion i s : 2 17Nh\N0 3 + 2CH3C6H2(N02)3 — - 17C0 + 11C0 2 + 36H20 + 8H 2 + 23N 2 This explos ive i s 25% d e f i c i e n t in oxygen, producing a s i g n i f i c a n t quant i ty of carbon monoxide and with a r e s u l t i n g heat o f explosion o f approximately 880 c a l . / g r a m . Thus, i t i s evident that a lack of oxygen r e s u l t s in a decrease in the heat of e x p l o s i o n , reducing the e f f i c i e n c y of the e x p l o s i v e . In general p r a c t i c e , the term "explos ive" is usua l ly used as a c o l l e c t i v e term to inc lude any substance used in b l a s t i n g . This terminology has led to some misunderstanding when deal ing with b l a s t i n g agents. T e c h n i c a l l y , these widely used b l a s t i n g compounds are not e x p l o s i v e s , belonging to a completely separate c l a s s i f i c a t i o n as represented in Figure 2 .0 -1 . Some r e f e r -ences have added to the confusion by c l a s s i f y i n g b l a s t i n g agents as t e r t i a r y high e x p l o s i v e s , presumably because they require a powerful shock wave f o r i n i t i a t i n g t h e i r detonat ion . This i s completely i n c o r r e c t . A b l a s t i n g agent i s any mater ia l or mixture , c o n s i s t i n g o f a fue l and o x i d i z e r , intended f o r b l a s t i n g , not otherwi.se c l a s s i f i e d as an explos ive and in which none of the ingredients is c l a s s i f i e d as an e x p l o s i v e , provided that the f i n i s h e d product cannot be detonated by means of a No. 8 b l a s t i n g c a p . 1 A b l a s t i n g agent cons is ts p r i m a r i l y of inorganic n i t r a t e s and carbonaceous fue ls and may contain a d d i -t iona l substances such as powdered aluminum or f e r r o s i l i c o n . However, the add i t ion of an explos ive ingredient changes the c l a s s i f i c a t i o n of the mixture from a b l a s t i n g agent to an e x p l o s i v e . Due to the complexity of modern explos ives and b l a s t i n g agents , fu r ther d e t a i l e d d i s c u s s i o n of t h e i r chemical and physical components and react ions i s unwarranted wi th in t h i s t h e s i s . Instead, i t i s more important to examine those performance proper t ies of exp los ives which are c r i t i c a l to the under-standing of an e x p l o s i v e ' s behaviour and i t s i n t e r a c t i o n with a rock mass. - 19 -2.1 PROPERTIES OF EXPLOSIVES 2.1.1 Strength: The strength of an explos ive may be def ined as i t s a b i l i t y to d isp lace the conf in ing medium, or as the amount of energy released by the e x p l o s i o n . 3 Strength is synonymous with work and i s measured by the b a l l i s t i c mortar t e s t . Th is i s an empir ical t es t f o r comparing e x p l o s i v e s , measuring the a b i l i t y of 10 grams of exp los ive to d e f l e c t a heavy s tee l m o r t a r . 4 Throughout t h i s t h e s i s , the strength of an explos ive or b l a s t i n g agent i s expressed as a per-centage of the strength of g rav i ty - loaded ammonium n i t r a t e / f u e l o i l (AN/FO). It should be noted that some ra t ing systems use the strength of T . N . T . as the standard value f o r compari t ive purposes. The two ra t ings commonly used are Re la t ive Weight Strength (RWS), which compares explos ives on a weight b a s i s , and Rela t ive Bulk Strength (RBS), which compares explos ives on a volume b a s i s . The weight strength and bulk strength are re la ted by s p e c i f i c g rav i ty or d e n s i t y . owe * - i • Weight of AN/FO x 100% RWS of Explos ive = - — Equivalent Weight of Explos ive D D C , r , . Volume of AN/FO x 100% RBS of Explos ive = — Equivalent Volume of Explosive RBS _ S p e c i f i c Gravi ty of Explosive RWS S p e c i f i c Grav i ty of AN/FO (0.84) The term "strength" has been t r a d i t i o n a l l y used by explos ives manufact-urers to descr ibe var ious grades of e x p l o s i v e s . Although i t i s now out -da ted , the term i s s t i l l so common in industry that an understanding of strength ra t ings i s important f o r anyone working in the f i e l d of b l a s t i n g . When dynamites were only a mixture of n i t r o g l y c e r i n and an iner t f i l l e r such as k i e s e l g u h r , a 60% dynamite (conta in ing 60% n i t r o g l y c e r i n by weight) was 3 times as strong as a 20% dynamite. However, present day dynamites contain ac t ive ingredients instead of i ne r t substances, adding s u b s t a n t i a l l y to the - 20 -energy of the e x p l o s i v e . Consequently, a 60% dynamite s t i l l contains 60% n i t r o g l y c e r i n , but i t i s much less than 3 times the strength of 20% dynamite. Nowadays, the pers is tence of the archaic "strength" term causes considerable confusion and misunderstanding. It must be remembered that the "percent" labe ls on dynamites r e f e r only to the n i t r o g l y c e r i n content and no longer s i g n i f y any r e l a t i v e strength va lues . Another drawback to the strength l a b e l s i s due to the nature of the b a l l i s t i c mortar t e s t . This tes t takes no account of other important explo-s ive proper t ies such as the v e l o c i t y of detonat ion. There fore , the term "strength" i s inaccurate and mis lead ing , bearing l i t t l e r e l a t i o n to the c a p a b i l i t y of an explos ive to break rock. It seems to have pers is ted over the years only by i t s s i m p l i c i t y of a p p l i c a t i o n . In genera l , strength rat ings w i l l only apply when comparing two explos ives with s i m i l a r v e l o c i t i e s of detonation and should otherwise be avoided. 2.1.2 V e l o c i t y of Detonation: Mentioned in the d i s c u s s i o n of strength r a t i n g s , the v e l o c i t y of deton-at ion may be the most important s i n g l e property to consider when ra t ing an e x p l o s i v e . This may be quoted as e i t h e r a conf ined or unconfined va lue . The conf ined detonation v e l o c i t y i s a measure of the speed at which the detonation wave t r a v e l s through a column of explos ive wi th in a borehole or other conf ined space. Th is i s usua l l y measured with high speed photography, recording the time i n t e r v a l s f o r the l i g h t - e m i t t i n g detonation wave f ront to pass between r e g u l a r l y spaced holes in a s tee l t u b e . 5 The unconfined v e l o c i t y ind ica tes the detonation speed when the exp los ive i s detonated in the open or unconfined s t a t e . Th is i s measured by detonating the explos ive from e i t h e r end while i t res ts on a steel p l a t e , and l a t e r recording the p o s i t i o n of a notch formed in the s tee l where the opposing detonation waves c o l l i d e . See Figure 2 . 1 - 1 . Since explos ives are usua l ly under some degree of confinement, the conf ined - 2 1 -Ports in tube wall-Light emitting from detonation wave front Blasting cap V//\V/\V/\V AVAX//W A\//W A\//\YAV/ A Undetonated explosive 1— Steel tube MEASUREMENT OF THE CONFINED VELOCITY OF DETONATION Detonation waves collide Blasting cap :)IMJ)i!b)'))^;\^i)M^i^(^i(i( Blasting cap V///////// ////////'////W//////// //////// steel plate length L, impact notch forms cord length L 2 L Initiation point •—Detonating cord with velocity of detonation = Vc UNCONFINED VELOCITY OF DETONATION = Vc L 2 - L, FIGURE 2.1-1 « TEST METHODS FOR DETERMINING CONFINED AND UNCONFINED VELOCITIES OF DETONATION - 22 -value i s the more s i g n i f i c a n t . However, manufacturers usua l ly quote the uncon-f i n e d value because i t i s an eas ie r tes t to perform and there i s no standard borehole diameter to use f o r confined t e s t s . Since unconfined v e l o c i t i e s are genera l ly 70 to 80 percent of conf ined v e l o c i t i e s , i t i s important to know the condi t ions under which the manufacturer made h is v e l o c i t y measurement. The detonation wave v e l o c i t y of an explos ive i s dependent o n : 1 1 ) the densi ty of the explos ive 2) the ingredients in the explos ive 3) the p a r t i c l e s i z e of the ingredients 4) the charge diameter 5) the degree of confinement Decreased p a r t i c l e s i z e , increased charge diameter, and increased confinement a l l tend to increase the detonation v e l o c i t y . Ve loc i ty w i l l decrease with charge diameter u n t i l , at the e x p l o s i v e ' s c r i t i c a l diameter, propagation i s no longer assured and m i s f i r e s are l i k e l y . With car t r idged explos ives the conf ined v e l o c i t y i s seldom at ta ined because complete confinement is usua l ly imposs ib le . The v e l o c i t y of detonation i s a very s i g n i f i c a n t f a c t o r in assessing the a b i l i t y of an explos ive to break or move rock. A high v e l o c i t y explos ive has greater br isance or shat te r ing a b i l i t y and i s p re fe r rab le in hard or b r i t -t l e rock. A low v e l o c i t y explos ive r e l i e s more on i t s expanding gas pressures f o r a "heaving" a c t i o n , provid ing s a t i s f a c t o r y r e s u l t s in a s o f t or h ighly f rac tured rock at lower c o s t s . 2 .1.3 Power: The s t r i c t d e f i n i t i o n of power i s the rate of doing work. For an explo-s i v e , power depends on both strength and detonating v e l o c i t y - the amount of energy re leased and the speed of r e l e a s e . In general terms, "power" i s used to ind ica te the e f fec t i veness of detonation of an e x p l o s i v e , such as - 23 -i t s potent ia l to penetrate or sha t te r . 2 .1.4 Br isance : B r i s a n c e , a unique c h a r a c t e r i s t i c of e x p l o s i v e s , i s the extreme shat te r ing e f f e c t r e s u l t i n g from almost instantaneous decomposit ion. Although there i s no prec ise d e f i n i t i o n , the br isance of an explos ive is genera l ly accepted as being proport ional to the product of i t s load d e n s i t y , react ion zone pres-s u r e , and detonating v e l o c i t y . 3 Explos ive decomposition proceeds as a s e l f -susta in ing wave, t r a v e l l i n g at high v e l o c i t y , which is enveloped by extreme pressures . On contact with surrounding m a t e r i a l , the wave d e l i v e r s momentary shocks of t e r r i f i c i n t e n s i t y , which induce the shat te r ing e f f e c t . 2.1.5 S e n s i t i v i t y : S e n s i t i v i t y i s a measure of the impulse magnitude required to s t a r t an explos ive r e a c t i o n . Explos ives w i l l be s e n s i t i v e to varying degrees of impact, f r i c t i o n , heat , or spark. Primary high explos ives are very s e n s i t i v e , r e q u i r -ing l i t t l e energy to propagate an explos ive r e a c t i o n . Secondary high exp los-ives are l ess s e n s i t i v e while b l a s t i n g agents are the l eas t s e n s i t i v e . The s e n s i t i v i t y of an explos ive determines the method by which a charge may be detonated, the minimum charge diameter, and the safety with which the explos ives may be handled. While s e n s i t i v e explosives can be r e l i a b l y deton-ated by a No. 6 b l a s t i n g cap , r e l a t i v e l y i n s e n s i t i v e compounds such as b l a s t -ing agents must be i n i t i a t e d by a powerful , s e n s i t i v e primer charge conta in ing a high explos ive such as T . N . T . or P . E . T . N . ( P e n t a e r y t h r i t o l t e t r a n i t r a t e ) . The shock wave t r a v e l s through the explos ive c rea t ing loca l f r i c t i o n between the g r a i n s , i n i t i a t i n g secondary d e t o n a t i o n . 6 As an exp los ive i s compressed to higher d e n s i t i e s to develop greater bulk s t r e n g t h , the exp los ive becomes less s e n s i t i v e u n t i l i t becomes t o t a l l y i n s e n s i t i v e or "dead-pressed". In cases where the charge diameter i s l ess than the hole diameter, a phenomenon known as the "channel e f f e c t " can de-- 24 -s e n s i t i z e an exp los ive and lead to m i s - f i r e s . The high pressure gas wave t r a v e l l i n g up the a i r space ahead of the e x p l o s i v e ' s detonation wave f ront may compress the explos ive to i t s dead-pressed s t a t e , ex t inguish ing the deton-a t i o n . Highly s e n s i t i v e explos ives w i l l detonate when used in small diameter charges. As the s e n s i t i v i t y of the explosive i s reduced, the diameter of the charge must be increased . The r e l a t i o n s h i p of s e n s i t i v i t y to densi ty i s i l l u s t r a t e d in Figure 2 .1 -2 . 2.1.6 Densi ty: The densi ty of an explos ive i s usua l ly expressed in terms of s p e c i f i c g r a v i t y , the r a t i o o f the dens i ty of the explos ive to the dens i ty of water under standard c o n d i t i o n s . O c c a s i o n a l l y , i t i s expressed in terms of a c a r t -r idge count which represents the number of \ \ by 8 inch car t r idges in a 50 pound box. Th is term i s archaic and i s c l e a r l y of no value when deal ing with bulk explos ives or b l a s t i n g agents. For these products , the densi ty i s often expressed as the kilograms of exp los ive per metre of charge length in a given s i z e borehole. With only a few except ions , the denser explos ives genera l ly give the higher detonation v e l o c i t i e s and pressures required in hard , dense rock. A dense explosive a lso permits maximum u t i l i z a t i o n of the borehole d r i l l e d which i s an important economic f a c t o r with the high costs of hard rock d r i l l i n g . In e a s i l y fragmented rock where l i t t l e explos ive energy i s needed, a low densi ty explos ive w i l l s u f f i c e . Not only are the low densi ty explos ives genera l ly less expensive, but they w i l l f i l l more of the h o l e , prov id ing a bet ter pressure d i s t r i b u t i o n upon detonat ion. The densi ty of an explos ive i s important i f the b l a s t s i t e w i l l be in wet or high groundwater c o n d i t i o n s . An explos ive with a s p e c i f i c grav i ty l ess than 1.0 or a c a r t r i d g e count greater than 140 w i l l f l o a t in the borehole. - 25 -— i 1 1 1 1 1 r 0.8 0.9 1.0 I.I 1.2 1.3 1.4 SPECIFIC GRAVITY FIGURE 2 .1-2 > RELATIONSHIP OF SENSITIVITY TO SPECIFIC GRAVITY AND CHARGE DIAMETER - 26 -2.1.7 Detonation Pressure: Detonation pressure i s an important c h a r a c t e r i s t i c of an explos ive but i s seldom mentioned in technica l data sheets or b l a s t e r s ' handbooks. The detonation pressure i s a measure of the pressure in the detonation wave. This d i r e c t l y con t ro ls the amplitude of the s t ress pulse produced in the rock by an e x p l o s i v e . The r e f l e c t i o n of t h i s s t ress pulse at a f ree face i s an import-ant mechanism in rock breakage. Detonation pressure is a funct ion of the detonation v e l o c i t y and densi ty of an explos ive but t h e i r r e l a t i o n s h i p i s complex and depends on the ingredients of the e x p l o s i v e . The fo l lowing approx-imat ion, i l l u s t r a t e d in F igure 2 . 1 - 3 , i s one of several that can be made: 1 p = 4 .5xl0 ' ! *x D x C 2 1.0 + 0.8 x D where: P = detonation pressure in MPa D = s p e c i f i c g rav i ty C = detonation v e l o c i t y in m . / s e c . Sometimes i t i s p re fe r rab le to use the borehole pressure f o r b l a s t i n g s t u d i e s . The borehole pressure i s the peak e f f e c t i v e pressure ac t ing behind the detonation head on the c y l i n d r i c a l surface area of the borehole . It i s approximately one ha l f of the detonation pressure and can be estimated b y : 7 B p = N x D x C 2 13470 where: BP = borehole pressure in MPa D = s p e c i f i c g rav i ty C = detonation v e l o c i t y in m . / s e c . N = f a c t o r obtained from Figure 2.1-4 As can be seen, the detonation and borehole pressures are much more dependent on detonation v e l o c i t y than on s p e c i f i c g r a v i t y . - 27 -0 J 1 1 1 T r— 0.8 1.0 1.2 1.4 1.6 SPECIFIC GRAVITY FIGURE 2.1-3 • DETONATION PRESSURE AS A FUNCTION OF SPECIFIC GRAVITY AND DETONATION VELOCITY - 28 -0.8 1.0 1.2 1.4 1.6 1.8 2.0 S P E C I F I C G R A V I T Y FIGURE 2 . 1 - 4 = FACTOR N vs. SPECIFIC GRAVITY FOR BOREHOLE P R E S S U R E ESTIMATION (after C o l d e r 7 ) - 29 -2 . 1 . 8 Water Resis tance: The water res is tance of an explos ive is a measure of i t s a b i l i t y to wi th-stand exposure to water without d e t e r i o r a t i n g or l o s i n g s e n s i t i v i t y . Water res is tance ra t ings range from " N i l " , f o r use in dry h o l e s , to " E x c e l l e n t " , used when groundwater i s perco la t ing through the borehole or when the explo-s ive i s exposed to standing water f o r prolonged per iods . In genera l , ge la t ins o f f e r the best water res is tance with low-densi ty dynamites and dry b l a s t i n g agents having l i t t l e or none. Emission of brown n i t rogen-ox ide fumes from a b l a s t often means that the explos ive has deter iora ted from exposure to water and ind ica tes that a change should be made in the choice of exp los ive or b l a s t -ing procedures. 2 . 1 . 9 Considerat ions For Se lec t ing An E x p l o s i v e : When s e l e c t i n g an explos ive fo r a s p e c i f i c b l a s t i n g p r o j e c t , a l l of the above c h a r a c t e r i s t i c s w i l l have to be assessed to d i f f e r i n g degrees. P r e d i c t -ing the behaviour of an explos ive demands an apprec ia t ion of the in te rp lay of i t s s t reng th , detonating v e l o c i t y , power and b r i s a n c e . Such fac to rs as safety and cost are obviously important, but f o r e f fec t i veness a lone , an explo-s i v e ' s v e l o c i t y of detonation i s the governing f a c t o r . The schematic diagram presented in F igure 2 . 1 - 5 summarizes the i n t e r - r e l a t i o n s h i p s of the most important exp los ive p r o p e r t i e s . There are a va r i e ty of t r a d e - o f f s which must be considered when s e l e c t i n g an e x p l o s i v e , but f o r every given b l a s t i n g job there is an explosive or b l a s t -ing agent that w i l l perform bes t . To s e l e c t the most s u i t a b l e e x p l o s i v e , the b l a s t e r must def ine the physica l s i t e condi t ions such as : 1 ) the hardness and densi ty of the rock 2) geo log ica l and geophysical c h a r a c t e r i s t i c s 3) moisture condi t ions - 30 -co UJ I-rr UJ O. o cc CL Decreasing water resistance - H Decreasing detonation velocity i I—H Decreasing density i H CO UJ > CO o _J 0_ X UJ CO o UJ co 3 O UJ to I CO z UJ Q UJ CC CO 2 c c c c ^ 3 o o o a> 9) a> Q> ID cn cn _^ a E c x : • ~ a? ' ^ i cn f__ o CO as o ^_ ECD Am a> a> mi tp III! 1 C amil riami o c >, c yn >> >» t: a >. Q Q in 0 ) O c o a> — CD -x : 7 3 £ T 3 £ "cn o> o u O o 1 o -c E s E -t— .2» E o £ Z CO x < _i < a> _ 3 CO c a> cn o cn c in o >> Q a> u c o in a> a> o cn c tn o (D O c Decreasing nitroglycerin content — H Increasing ammonium nitrate content Decreasing cost O CO UJ I-or UJ o_ o or o_ o z: < CO \-z UJ Q UJ or CP 2 Ul > I— < _J UJ or UJ :> o CO LO I cvi or u -•31 -4) a v a i l a b l e v e n t i l a t i o n and must a lso decide on what the optimum r e s u l t s a r e , i n c l u d i n g : 5) degree of fragmentation 6) height and displacement of muck p i l e 7) cond i t ion of f i n a l face Knowing these f a c t o r s , the b l a s t e r can decide which explos ive proper t ies are important in h is p a r t i c u l a r s i t u a t i o n . - 32 -2.2 EXPLOSIVES USED ON THIS RESEARCH PROJECT Three d i f f e r e n t types of b l a s t i n g compounds, a l l manufactured by Canadian Industr ies Limited ( C . I . L . ) , were used during the f i e l d experiments c a r r i e d out at Afton Mine. The major i ty of t es t b las ts used bulk- loaded AN/FO, a common dry b l a s t i n g agent. On occasions when groundwater condi t ions prevented the use of AN/FO, i t was necessary to go to a s l u r r y explos ive fo r i t s improv-ed water r e s i s t a n c e . Most commonly, pre-packaged Hydromex T-3 was used, but bulk- loaded Powergel A was t r i e d in two of the b l a s t s . The purpose of t h i s sec t ion i s to provide greater technica l de ta i l fo r the explos ives and detonating mater ia ls used throughout the f i e l d experiments. 2.2.1 Ammonium N i t ra te / Fuel O i l (AN/FO): Dry b l a s t i n g agents were patented in Sweden in 1867 but t h e i r f u l l pot-e n t i a l was not r e a l i z e d u n t i l the development of AN/FO in the mid-1950's . It qu ick ly replaced dynamites and g e l a t i n s in many a p p l i c a t i o n s . Although much of the b l a s t i n g f i e l d i s becoming dominated by s l u r r i e s , AN/FO is s t i l l the most widely used b l a s t i n g agent in s o f t e r rock format ions. AN/FO c o n s i s t s of ammonium n i t r a t e p r i l l s and fuel o i l and, when the mixture is proper ly ba lanced, detonates with the fo l lowing chemical r e a c t i o n : 8 3NH 4N0 3 + CH 2 — * 7H20 + C0 2 + 3N 2 From the l e f t s ide of the equation one can c a l c u l a t e that an oxygen balanced AN/FO contains 94.5% ammonium n i t r a t e and 5.5% fuel o i l . These proport ions are usua l l y 94% and 6% in p r a c t i c e , with the extra fuel o i l ensuring int imate combination with the ammonium n i t r a t e . Not being c a p - s e n s i t i v e , AN/FO must be i n i t i a t e d by a high explos ive primer such as 75% ammonia g e l a t i n , composition B (a mixture of T . N . T . and R . D . X . ) , or p e n t o l i t e (a mixture of equal parts of T . N . T . and P . E . T . N . ) . Since i n i t i a t i o n s e n s i t i v i t y increases with confinement and decreases with - 33 -greater charge diameters, the s i z e of the primer must be increased appropr i -a t e l y in large diameter ho les . Depending on the densi ty and p a r t i c l e s i z e of the ammonium n i t r a t e , the s p e c i f i c g rav i ty of AN/FO var ies from 0.75 to 0 . 9 5 . 9 Dens i t ies in the bore-hole can be increased with e jec to r type pneumatic l o a d e r s , but AN/FO reaches a "dead-pressed" state at a s p e c i f i c g rav i ty of 1.2 and w i l l not detonate. The v e l o c i t y of detonation of AN/FO increases with borehole diameter to an upper l i m i t of about 4200 m . / s e c . Figure 2.2-1 shows the r e l a t i o n s h i p between the conf ined detonation v e l o c i t y and the borehole diameter at two s p e c i f i c g r a v i t i e s of AN/FO. The p r i n c i p a l advantages of AN/FO are i t s safety in t r a n s p o r t a t i o n , s t o r -age and hand l ing , as well as the ease of loading and low pr ice compared to other e x p l o s i v e s . See Plates 3 and 4. Bulk- loaded AN/FO has the fu r ther advantage of completely f i l l i n g the borehole , leav ing no v o i d s . 1 0 This d i r e c t coupl ing to the borehole wal ls assures a more e f f i c i e n t use of explos ive energy than can be obtained with car t r idged e x p l o s i v e s . AN/FO is an ideal b l a s t i n g mater ia l f o r weak or h ighly f rac tured rock masses where more heaving ac t ion and l e s s br isance is requ i red . Since weaker rock usua l l y requires r e l a t i v e l y low explos ive l o a d s , the low densi ty of AN/FO means that more of the borehole i s f i l l e d and the heaving forces are bet ter d i s t r i b u t e d . The most ser ious disadvantage with AN/FO i s i t s complete lack of water res is tance other than that suppl ied by external p r o t e c t i o n . As shown in Figure 2 .2 -2 , AN/FO w i l l f a i l to detonate with a moisture content as low as 9%. When a wet borehole i s encountered, water i s usua l ly pumped from the h o l e , a p l a s t i c s leeve l i n e r i n s e r t e d , and the AN/FO loaded into the l i n e r . This procedure i s tedious and slow but i s the only a l t e r n a t i v e without switching to a s l u r r y or other water r e s i s t a n t e x p l o s i v e . Although AN/FO w i l l withstand prolonged periods of s torage , i t can deter -- 34 -FIGURE 2 . 2 - 1 CONFINED DETONATION VELOCITY OF AN/FO vs. BOREHOLE DIAMETER ( after Dick 1 ) - 35 -P L A T E 3 The C . I . L . truck t ransports and d e l i v e r s bulk AN/FO s a f e l y and e a s i l y . On s i t e , i t mixes the fuel o i l with the ammonium n i t r a t e p r i l l s and e jects the f i n i s h e d mixture pneumatical ly through the black hose at the rear of the t ruck . - 36 -P L A T E 4 Loading AN/FO into a b las tho le i s a f a s t and easy procedure. This p a r t i c u l a r hole contained water, was pumped out and had a p l a s t i c l i n e r i n s e r t e d . Two primers are used to ensure detonation in wet h o l e s , as ind icated by the two Primacord downlines. - 37 -FIGURE 2.2-2 = EFFECT OF WATER CONTENT ON THE DETONATION VELOCITY OF AN/FO - 38 -io ra te under ce r ta in c o n d i t i o n s . In a warm and humid environment, the ammon-ium n i t r a t e p r i l l s w i l l eventual ly become lumpy and mushy, leading to caking and a loss in s e n s i t i v i t y . Another cause of d e t e r i o r a t i o n i s the " c y c l i n g e f f e c t " which occurs when the AN/FO is cyc led through 0°C or 32°C more than once. Th is causes the p r i l l s to swell and contract and eventual ly c rumble . 8 The basic proper t ies of AN/FO, as used at Afton Mine, are summarized in Appendix II. 2.2.2 S l u r r i e s : S l u r r i e s are the most recent development in explos ive formulat ions and trends ind ica te that they w i l l eventual ly become the most widely used of a l l b l a s t i n g m a t e r i a l s . Sometimes c a l l e d water g e l s , s l u r r i e s contain high prop-or t ions of ammonium n i t r a t e , part of which i s in an aqueous s o l u t i o n . S lur ry explosives contain c a p - s e n s i t i v e ingredients and the mixture i t s e l f may be c a p - s e n s i t i v e . The ammonium n i t r a t e and s e n s i t i z e r mixture is thickened and ge l led with a gum to give considerable water r e s i s t a n c e . Developed in 1958, Hydromex T-3 was the f i r s t commercial s l u r r y a v a i l a b l e in Canada. It i s a mixture of ammonium n i t r a t e , T . N . T . , water and minor amounts of other i n g r e d i e n t s . 1 1 It has a low s e n s i t i v i t y to shock, f r i c t i o n and impact, making i t safe in handling and use. Only high strength primers can ensure cons is tent i n i t i a t i o n . Unl ike AN/FO, Hydromex T-3 has a high densi ty and a high v e l o c i t y of detonat ion. The consistency of the s l u r r y ranges from f l u i d near 38°C to r i g i d at f r eez ing temperatures. At Afton Mine, Hydromex T-3 was used instead of AN/FO only when i t was impossible to pump out a wet b las tho le or when the hole recharged with water too r a p i d l y . Since i t was genera l ly not required in l a r g e , bulk q u a n t i t i e s , the Hydromex was suppl ied in 25 k g . , 203 mm. (8 inch) diameter bags which were i n d i v i d u a l l y hand loaded. As more wet b las tho les were encountered in some areas of the open p i t - 39 -during summer 1981, the labor ious hand!loading of Hydromex T-3 caused a s i g n i f -icant drop in b l a s t product ion . This ind icated that a bulk- loaded s l u r r y may be needed as the p i t deepens and encounters more groundwater. Two t r i a l b l a s t s were made with Powergel A , a bu lk , t ruck- loaded s l u r r y e x p l o s i v e . This explosive i s a m e t a l l i z e d , T . N . T . - b a s e d s l u r r y explos ive with a lower densi ty and lower v e l o c i t y of detonation than Hydromex T - 3 . Powergel A i s c a p - s e n s i t i v e yet i s s t i l l safe to handle. It has the advantages of f a s t , easy loading and, l i k e AN/FO, provides d i r e c t borehole coupl ing f o r more e f f i c i e n t use of the explos ive e n e r g y . 1 2 Neither Hydromex T-3 nor Powergel A can be considered as equivalent sub-s t i t u t e s fo r AN/FO due to t h e i r higher d e n s i t i e s and detonation v e l o c i t i e s . Both explosives are much more expensive than AN/FO and were se lec ted s t r i c t l y f o r t h e i r water r e s i s t a n t p r o p e r t i e s . The basic proper t ies of Hydromex T-3 and Powergel A , as used at Afton Mine, are summarized in Appendix II. 2 .2.3 Primers: A primer i s any high power, high v e l o c i t y explos ive compound capable of i n i t i a t i n g detonation of low s e n s i t i v i t y b l a s t i n g agents or e x p l o s i v e s . The primers themselves can be detonated d i r e c t l y by b l a s t i n g caps or detonat-ing c o r d . Procore III pr imers , which are except iona l ly powerful , are used at A f t o n . Each primer weighs 450 grams (1 l b . ) and c o n s i s t s of T . N . T . cast around a Pento l i te c o r e . 1 3 Two holes are provided in each primer to al low the uni t to be threaded onto a downline of detonating c o r d . The Procore primers provide very r e l i a b l e i n i t i a t i o n of both AN/FO and Hydromex T - 3 , being e s p e c i a l l y designed f o r large diameter b l a s t h o l e s . These primers are designed f o r safe hand l ing , being much less s e n s i t i v e to shock, f r i c t i o n or impact in normal use than conventional high e x p l o s i v e s . - 40 -They are completely waterproof and w i l l not de te r io ra te during extended s t o r -age. Thei r performance is unaffected by temperature changes or by immersion in proper ly formulated b l a s t i n g agent composi t ions, even fo r an extended per iod . Procore primers are very high explos ives and should be t reated with appro-pr ia te care during handling and loading opera t ions . Any pieces a c c i d e n t l y broken o f f these primers or powdered fragments should be cleaned up and prompt-l y destroyed. If l e f t on the ground, these pieces could become admixed with g r i t , making them more s e n s i t i v e and a poss ib le hazard to the b l a s t i n g opera-t i o n . See Appendix II. 2 .2.4 Detonating Cord: Primacord i s a detonating cord c o n s i s t i n g of a high explosive core of P . E . T . N , contained within a re in forced waterproof cover ing . It has a very high v e l o c i t y of detonation and i s r e l a t i v e l y i n s e n s i t i v e to detonation by f r i c t i o n or ordinary shock. It i s unaffected by s t ray currents or other forms of extraneous e l e c t r i c i t y , and is an extremely safe method of i n i t i a t i n g high explosives or b l a s t i n g agents. Although l i g h t in weight , i t possesses good t e n s i l e strength and i s extremely easy to handle and connect up in a b l a s t . It absorbs water very s lowly , even from a cut end, but should the cord become soaked with water, i t w i l l s t i l l detonate s a t i s f a c t o r i l y i f i n i t i a t e d from a dry e n d . 4 The v io lence and speed of i t s explosion is s u f f i c i e n t to ensure detonation of high explosives of normal s e n s i t i v i t y in contact with i t . Primacord comes in several types , each possessing: the sameibasic detonat-ing p r o p e r t i e s , but with d i f f e r i n g degrees of strength and toughness. Afton Mine uses the heavy, ye l low, re in forced Primacord f o r a l l t runk l ines and down-l i n e s wi thin the b l a s t i n g pattern where the cord may be subjected to abras ion . A' lower cost detonating c o r d , red E -Cord , i s used f o r the 1ongi t runkl ine from the b las t ing cap to the b l a s t pa t te rn . See Appendix II. - 41 -2.2.5 E l e c t r i c B las t ing Caps: An e l e c t r i c b l a s t i n g cap usua l ly cons is ts of a metal she l l with two wires leading in from one end. The ends of these leg wires are connected wi th in the device by a very f i n e bridge wire of high r e s i s t a n c e . This heats to incan-descence on the passage of an e l e c t r i c current of s u f f i c i e n t i n t e n s i t y , i g n i t -ing a heat s e n s i t i v e loose charge. A l l C . I . L . e l e c t r i c detonators are suppl ied with aluminum f o i l or polythene shunts as a protect ion against st ray c u r r e n t s . A " s t a t i c short" is a lso incorporated in to t h e i r make-up as a protect ion against s t a t i c c h a r g e s . 4 Although caps are a v a i l a b l e with a va r i e ty of short or long delay elements, Afton Mine uses the instantaneous e l e c t r i c b l a s t i n g caps. See Appendix II. 2 .2.6 B las t ing Machines: B las t ing machines are s m a l l , portable un i ts to provide current fo r f i r i n g b las ts e l e c t r i c a l l y where a l te rna te power sources are not r e a d i l y a v a i l a b l e . Afton Mine uses the C . I . L . 10-Shot B l a s t i n g Machine, designed f o r use where only a few caps are to be f i r e d in a p a r t i c u l a r b l a s t . It i s powered by two standard "D" s i z e f l a s h l i g h t ba t te r ies which charge heavy-duty meta l l i zed paper capac i tors to a potent ia l of approximately 200 v o l t s . 1 1 * Its rated capaci ty i s 10 E .B . Caps connected in a s i n g l e s e r i e s with a maximum c i r c u i t res is tance (caps plus lead wires) of 40 ohms. See Appendix II. 2 .2.6 P l a s t i c Borehole L i n e r : When wet boreholes are encountered, they have to be pumped dry i f AN/FO i s to be loaded. These holes must then be l i n e d with a tubular p l a s t i c sleeve to provide a c l e a n , dry contact in the borehole . P l a s t i c l i n e r s are recommended pr imar i l y f o r use in v e r t i c a l holes in open-cut work where the b l a s t i n g agent can be poured in to the borehole . When pneumatic loading i s used, the p l a s t i c l i n e r increases the hazard of s t a t i c e l e c t r i c i t y b u i l d - u p . More tox ic fumes are a lso generated when l i n e r s are - 42 -used. A var ie ty of l i n e r s are a v a i l a b l e , but few are completely f ree of defects or p in -ho les which may leak water into the AN/FO. Thus, even when l i n e r s are used, i t i s best to load and f i r e wi th in one s h i f t instead of leav ing holes loaded f o r several days. The p l a s t i c l i n e r used at Afton Mine is a cont inuously extruded sleeve of 10 m i l . p l a s t i c , coming on a 183 m. (600 f t . ) r o l l . With a l a y - f l a t dimen-sion of 394 mm. (15-1/2 i n c h e s ) , i t has a 250 mm. (9-7/8 inches) diameter bore which i s s l i g h t l y l a rger than the 230 mm. (9 inch) borehole diameter. The end of the sleeve is fo lded and t i e d shut a f t e r p lac ing a small amount of b a l l a s t into the tube to ensure that i t w i l l s ink to the bottom of the ho le . Although the fo lded and t i e d end may not be as water - t ight as the more expensive heat -sealed method, i t provides s u f f i c i e n t protect ion f o r the dura-t ion of one s h i f t . Despite the high groundwater condi t ions at A f t o n , no mis-f i r e s were recorded during the f i e l d experiments. See Appendix II. - 43 -2.3 REFERENCES 1) DICK, Richard A . : Factors in Se lec t ing and Applying Commercial Explosives and B l a s t i n g Agents. Information C i r c u l a r 8405, U.S. Department of the I n t e r i o r , Bureau of Mines, 1968. 2) MANON, J . J . : The Chemistry and Physics of E x p l o s i v e s . Engineering and Mining J o u r n a l , V o l . 177, No. 12, December 1976.-3) MANON, J . J . : E x p l o s i v e s : The i r C l a s s i f i c a t i o n and C h a r a c t e r i s t i c s . Engineering; and Mining J o u r n a l , V o l . 177, No. 10, October 1976. 4) CANADIAN INDUSTRIES LTD. : C . I . L . B l a s t e r s ' Handbook, Sixth E d i t i o n . Explosives Technical Marketing S e r v i c e s , 1968. 5) JOHANSSON, C H . & PERSSON, P . A . : Detonics of High E x p l o s i v e s . Swedish Detonic Research Foundat ion, Academic P r e s s , 1970. 6) COOK, M.A.: The Science of High E x p l o s i v e s . Reinhold Publ ish ing Corp-o r a t i o n , 1958. 7) CALDER, P . : P i t Slope Manual, Chapter 7 - Perimeter B l a s t i n g . CANMET (Canada Centre fo r Mineral and Energy Technology) , May 1977. 8) MATTS, T . : B l a s t i n g and Handling E x p l o s i v e s . Presented at "Slope S t a b i l i t y f o r the Transportat ion Industry" , Vancouver, B . C . , 1981. A l l the fo l lowing references are brochures prepared by Canadian Industr ies L t d . , Explosives Technical Marketing S e r v i c e s : 9) Information Report No. 117: P r i l l e d Ammonium N i t ra te 10) Information Report No. 150: Bulk AN/FO 11) Information Report No. 136: Hydromex 12) Information Report No. 151: Bulk S lur ry Explos ives 13) Information Report No. 119: Pento-Mex and Procore Primers 14) Information Report No. 137: C . I . L . 10-Shot B l a s t i n g Machine - 44 -CHAPTER THREE ROCK MASS DETONICS - 45 -3.0 ROCK MASS DETONICS As descr ibed in Chapter Two, explos ives have several s p e c i f i c p r o p e r t i e s , a v a i l a b l e in a va r ie ty of combinat ions, which are c a r e f u l l y created by prec ise chemical formulat ions . Through decades of t e s t i n g and ana lys is in c o n t r o l l e d laboratory c o n d i t i o n s , t h e i r detonating c h a r a c t e r i s t i c s and behaviour in c y l i n d r i c a l holes have become well understood and documented. However, the mechanisms of rock mass fragmentation i n i t i a t e d by explosives have remained r e l a t i v e l y obscure. Even though rock b l a s t i n g comprises the most important i n d u s t r i a l use of e x p l o s i v e s , there has yet to be developed a comprehensive theory that completely expla ins how explosives break r o c k . 1 The poor understanding of fragmenting mechanisms can be a t t r ibu ted to several f a c t o r s . F i r s t , the de ta i l ed physical processes leading to the end r e s u l t are h ighly complex and occur in such a short time that observat ion becomes d i f f i c u l t . Second, the opaqueness of rock masks the in terna l fragment-ing a c t i o n , permit t ing only surface observat ions . T h i r d , the large des t ruc -t i v e forces involved in a b l a s t make s e n s i t i v e instrumentat ion almost impos^ s i b l e . Four th , the geologica l make-up of rock masses var ies g r e a t l y , r e s u l t -ing in d i f f e r e n t fragmentation c h a r a c t e r i s t i c s from one b l a s t s i t e to another. Furthermore, each rock mass in i t s e l f i s h ighly heterogeneous with included d i s c o n t i n u i t i e s which in f luence the d i s t r i b u t i o n of t rans ien t s t resses created by explosive detonat ion. C l e a r l y , the study of rock mass detonics i s a compl icated , s p e c i a l i z e d f i e l d of s tudy, prompting U l f Langefors , an eminent Swedish b l a s t i n g exper t , to s t a t e : "Fragmentation in rock b l a s t i n g i s one of the most important of the remaining problems in the sphere of t e c h n i c s . " 2 In an e f f o r t to reduce the complexity of the overa l l problem to a manage-able working l e v e l , most of the experimental and t h e o r e t i c a l work done on rock mass detonics has dea l t with rock as a homogeneous and i s o t r o p i c m a t e r i a l . - 46 -Although th is does not represent the heterogeneous real wor ld , fu r ther progress in understanding b l a s t i n g mechanisms w i l l only be poss ib le i f and when the mechanisms in homogeneous mater ia ls are unders tood. 3 Many d i f f e r e n t mater ia ls have been used fo r model b l a s t i n g experiments but p lex ig lass i s the most popular . In add i t ion to i t s uniform c h a r a c t e r i s -t i c s , p l e x i g l a s s i s t ransparent , permit t ing observat ion of fragmenting pro-cesses wi thin the specimen. Although p l e x i g l a s s i s more d u c t i l e than most r o c k s , the f rac ture pattern at high rates of loading appears to be i d e n t i c a l with that in rock. 1* Test b l a s t patterns can be d r i l l e d in to p l e x i g l a s s blocks and small explos ive charges placed in the ho les . The detonation i s then f i lmed with the a id of high speed cine-cameras capable of up to 100,000 frames per second. A frame by frame study reveals the d e t a i l s of detonat ion , the movement of shock waves, and the f r a c t u r i n g sequences. P lex ig lass model b l a s t i n g has been performed by many researchers , with some p a r t i c u l a r l y good photographs publ ished by Langefors and K i h l s t r o m 2 , Kutter and Fa i rhurs t 1 * , C o o k 5 , and Johansson and P e r s s o n 5 . Other b l a s t i n g models have included underwater b las ts f o r shock wave studies and the use of lead blocks f o r measuring volumetr ic displacement. Since none of these mater ia ls have the same proper t ies or moduli i as rock , some b l a s t i n g tests have a lso been done with large blocks of homogeneous rock. Notable r e s u l t s have been publ ished by Noren 7 and by Bergmann et a l 8 - 1 0 with large in tac t blocks of g r a n i t e . From such t e s t i n g work, some ideas have emerged about key rock fragment-ing mechanisms. At t h i s t ime, there have been three major theor ies put forward, each developed by independent research groups. One is known as the "shock wave theory" , championed p r imar i l y by the U.S. Bureau of Mines and descr ibed in l i t e r a t u r e by H i n o 1 1 . This theory s t resses impedance mismatch, re lease wave scabbing or f ragmentat ion, and other shock wave concepts developed from fundamental work on impact loading of metals and c o m p r e s s i b i l i t y of s o l i d s - 47 -at extremely high pressures . Another concept , known as the "energy theory" , i s widely accepted in the Soviet Union and best descr ibed in pub l ica t ions by C o o k 5 ' 1 2 . Th is descr ibes rock breakage as a s t ress r e l i e f fo l lowing the i n i t i a l t r a n s f e r of the b l a s t energy into potent ia l energy by powerful compression under the sustained pressure of the detonation products and the great i n e r t i a of the burden. The t h i r d theory of rock b l a s t i n g i s the " rad ia l cracking theory" of the Swedish Detonics Research group which has some overlap with both the "shock wave" and "energy" t h e o r i e s . It s t resses the importance of shear wave f r a c t u r e during the ear ly stages of shock wave propagat ion, r a d i a l cracking therea f te r and f i n a l l y concentr ic s t ress r e l i e f . This t h i r d theory i s the one with which t h i s author is most f a m i l i a r and which formed the bas is of any f i e l d b l a s t i n g experiments. The next seer t ion of t h i s chapter o u t l i n e s the fragmentation mechanics of homogeneous, i s o t r o p i c rock as explained by the Swedish theory. Once these bas ic p r i n c i p l e s have been covered, the in f luences of inhomogeneous rock proper t ies w i l l be d i s c u s s e d . - 48 -3 . 1 THE BREAKAGE PROCESS IN HOMOGENEOUS ROCK In surface b l a s t i n g , there are b a s i c a l l y two d i f f e r e n t b l a s t i n g c o n f i g -u ra t ions . In one c a s e , the b las tho le is completely surrounded by rock with the mouth of the b las tho le at the only f ree s u r f a c e . This conf igura t ion i s known as c r a t e r b l a s t i n g and i s used f o r s ink ing cuts or ramp c u t s . At Afton Mine, i t was a lso used f o r most production b l a s t s in the centra l por t ion of the p i t . In the other c a s e , the rock mass has an add i t iona l f ree surface near the b las tho le and p a r a l l e l to i t . Referred to as bench b l a s t i n g or f ree face b l a s t i n g , i t i s used at Afton f o r a l l p i t perimeter b l a s t s . These two conf igura t ions are compared in Figure 3 . 1 - 1 . Although the same detonics p r i n c i p l e s are involved in each case , the behaviour of the b las ts and the end r e s u l t s are qui te d i f f e r e n t . 3 . 1 . 1 Bench B l a s t i n g : This i s the most important surface b l a s t i n g mode, forming the basis of a l l p r e c i s e , c o n t r o l l e d b l a s t i n g methods. Any reference book.on b l a s t i n g techniques w i l l s t ress the importance of b l a s t i n g to a f ree face p a r a l l e l to the b l a s t h o l e . To bet ter understand the mechanics i n v o l v e d , i t i s d e s i r -able to consider a s i n g l e explos ive charge which is f u l l y coupled with the b l a s t h o l e . Such a conf igura t ion may be l ikened to a th ick -wa l led c y l i n d e r . When the explosive i s detonated, i t changes extremely rap id ly into very hot , high pressure gases occupying the same volume as the o r i g i n a l exp los ive ( i . e . the b las tho le volume). This sudden a p p l i c a t i o n of the sustained explo-sion pressure causes the b las tho le i t s e l f to expand and thus generate an . intense s t r a i n in the surrounding rock. Measurements ind ica te the s t r a i n r a t e to be between 250 mm./sec. and 500 m m . / s e c . 1 3 The c y l i n d r i c a l l y expanding s t r a i n wave often exceeds the e l a s t i c l i m i t of the so f te r rocks . As the volume is compressed, f rac tu re occurs through - 49 -G S C R A T E R B L A S T CONFIGURATION Nearest free surface is perpendicular to blasthole axis . •6.S. 1 1 B E N C H B L A S T CONFIGURATION Nearest free surface is parallel to blasthole axis. FIGURE 3.1-1 : COMPARISON OF BLASTHOLE CONFIGURATIONS IN CRATER AND BENCH BLASTING - 50 -the co l l apse of i n t e r c r y s t a l l i n e and in te rg ra in s t r u c t u r e , completely pu lver -i z i n g the rock immediately surrounding the b l a s t h o l e . The extent of t h i s crushed zone increases with both the detonation pressure of the charge and the degree of coupl ing in the ho le . As the outgoing s t r a i n wave extends into the rock , t r a v e l l i n g at 3000 to 5000 metres per second, i t sets up tangent ia l s t resses which create f i n e cracks extending r a d i a l l y and p a r a l l e l to the b las tho le a x i s . See Figure 3 .1 -2 . The f i r s t of these rad ia l cracks develops in 1 to 2 m i l l i s e c o n d s . 1 3 The ; ac t ions during th is f i r s t stage of the breakage process are i l l u s t r a t e d in Figures 3.1-3 and 3.1-4 and in Plates 5 and 6. During the f i r s t s tage , the pressure assoc ia ted with the outgoing shock wave is p o s i t i v e . When the shock wave reaches the f ree face of the bench i t w i l l r e f l e c t , causing the pressure to f a l l r a p i d l y to negative v a l u e s , c rea t ing a tension wave. This wave t r a v e l s back into the rock and, because t h i s material i s less r e s i s t a n t to tension than to compression, fu r ther f a i l u r e cracks w i l l develop under the t e n s i l e s t r e s s . If the r e f l e c t e d wave i s s u f f i c i e n t l y i n t e n s e , i t may cause scabbing or s p a l l i n g at the f ree f a c e . See Figure 3 .1 -5 . However, t h i s scabbing e f f e c t i s considered to be of minor importance in rock breaking. It has been c a l c u l -ated that the explosive load would have to be e ight times that normally r e q u i r -ed in order to cause f a i l u r e of the rock by r e f l e c t e d shock wave a l o n e . 1 4 The p r i n c i p a l i n t e r a c t i o n between the rad ia l crack system of the f i r s t stage and the r e f l e c t e d t e n s i l e wave was studied by F i e l d and Ladegaard-P e d e r s e n 1 5 . They not iced that two primary rad ia l cracks would extend to a greater d istance from the b las tho le than a l l other cracks and had a d i r e c t i o n of about 45° to the f ree f a c e . The material in f ront of the b las tho le would tend to break out along these major c r a c k s . In a s e r i e s of model sca le tes ts in p l e x i g l a s s , they not iced that the r e f l e c t e d t e n s i l e wave increases the t e n s i l e s t ress at the t i p of those Stage 1 cracks tangent ia l to the curved FIGURE 3.1- 2 : INITIAL RADIAL FRACTURING MECHANISM ON AN ELEMENT OF ROCK ( after Mercer 1 5 ) - 52 -Expanding Shock Wave FIGURE 3.1-3 « PLAN VIEW OF STAGE 1 ROCK BREAKAGE PROCESS ( a f t e r L a n g and F a v r e a u 1 4 ) - 53 -6 S Expanding Shock Wave Crushed Zone Note = Shape of shock wave front will vary slightly depending on relative values of Detonation Velocity and Shock Wave Velocity. Ridge - like Traces of Tensile Fracture Path Point of Detonation Initiation FIGURE 3.1-4 ' BLASTHOLE CROSS-SECTION IN THE PLANE OF A RADIAL CRACK DURING STAGE 1 OF THE ROCK BREAKAGE PROCESS - 54 -P L A T E 5 P l a n v i e w o f a b l a s t h o l e s h o w i n g S t a g e 1 f r a c t u r i n g mechanisms i n a homogeneous r o c k b l o c k a s i l l u s t r a t e d i n F i g u r e 3.1 - 3 . N o t e t h e d i s t o r t e d b l a s t h o l e s u r r o u n d e d by an i n t e n s e l y c r u s h e d zone and t h e r a d i a l f r a c t u r e p a t t e r n . - 55 -P L A T E 6 View of f rac tu re plane p a r a l l e l to a s i n g l e b las tho le in a homogeneous rock b lock . Surface texture c l e a r l y ind ica tes t h i s to be a t e n s i l e f r a c t u r e . Note rad ia l nature of t e n s i l e f rac ture pattern as i l l u s t r a t e d in Figure 3.1 -4 . Excessive f rac ture at toe of hole probably due to loca t ion of primer charge. - 56 -FIGURE 3.1-5 ! PLAN VIEW OF STAGE 2 OF ROCK BREAKAGE PROCESS - 57 -wave f r o n t . See Figure 3 .1 -5 . There fore , those cracks forming an angle of 40° to 80° to the normal of the f ree face are given; a greater propagation v e l o c i t y . They w i l l t rave l ahead of the other cracks and, by re laxa t ion of the surrounding m a t e r i a l , w i l l reduce the v e l o c i t y of these. This theory a c t u a l l y provides a p l a u s i b l e explanat ion f o r e a r l i e r observat ions that the break-out angle increases with increasing, burden and with increas ing bench height as reported by Persson, Ladegaard-Pedersen and K i h l s t r o m 1 6 . Throughout the f i r s t and second stages of the breakage process , the func-t ion of the shock wave energy is to induce numerous small f rac tures around the b l a s t h o l e . However, the shock wave energy t h e o r e t i c a l l y amounts to only 5 to 15% of the to ta l exp los ive e n e r g y . 3 This s t rongly suggests that the shock wave i s not d i r e c t l y responsib le f o r any s ign i f icant 'amount of rock breakage, but merely provides the bas ic cond i t ion ing f o r the t h i r d stage of the process . In t h i s l a s t s tage , the actual rock breakage is a slower a c t i o n . Under the in f luence of the exceedingly high q u a s i - s t a t i c pressure of the explosion gases, the primary rad ia l cracks are r a p i d l y enlarged under the combined e f f e c t s of t e n s i l e s t ress induced by rad ia l compression and by pneumatic wedg-i n g . As gases escape through the rad ia l cracks and stemming, and as the mass in f ron t o f the b l a s t h o l e y i e l d s and moves forward, the high compressive s t resses wi thin the rock unload in much the same way as a compressed c o i l spr ing being suddenly r e l e a s e d . 1 4 The e f f e c t of unloading induces high tension s t resses wi thin the mass which complete the breakage process . The rock i s then acce lera ted forwards and upwards by the ac t ion of the explos ive gases. See Figure 3 .1-6 . The heaving pressure of these gases ac t ing on the b las tho le burden causes the fragmented rock mass to be d isp laced into a muckpile with a shape depending on the proper t ies of the explosive and the rock. Experimental measurements have shown that the time in te rva l between det-onation and the s t a r t of motion of the f ree face i s between 5 and 10 times - 58 -FIGURE 3.1-6 PLAN VIEW OF STAGE 3 OF ROCK BREAKAGE PROCESS (after Lang and Favreau 1 4 ") - 5 9 -the shock wave t rave l time from the b las tho le to the f ree sur face . A f t e r t h i s time i n t e r v a l there i s a rapid a c c e l e r a t i o n to the f i n a l breakout v e l o -c i t y . This phenomenon was f i r s t not iced by Noren 7 in f u l l sca le grani te b las ts where the time in te rva l between detonation and f ree face motion was found to be 7 times the shock t rave l t ime. This was a point of great concern due to i t s imp l ica t ions in the sequencing of mult i -rowed delayed b l a s t pa t te rns . The processes involved were l a t e r explained in a mathematical model developed by J o h a n s s e n 3 ' 1 7 which accounted f o r expansion of the gases into s p e c i f i c crack volumes created by the i n i t i a l high compressive s t r e s s e s . This model a l s o predic ted the same delay in te rva l of 7 times the shock t rave l time between detonation and the s t a r t of face movement. From the knowledge of rock and explos ive behaviour , bet ter models of the b l a s t i n g process can be postu la ted . As ind ica ted by J u s t 1 8 , the a p p l i c a -t ion of s c i e n t i f i c p r i n c i p l e s may a l low an engineer to design, a b l a s t which w i l l produce a des i red fragmentation and shape of muckpile to s u i t the p a r t i -c u l a r loading equipment to be used. 3.1.2 Crater B l a s t i n g : The important e f f e c t of a f ree surface on the fragmentation process i s qui te c l e a r in the case of bench b l a s t i n g . In c r a t e r b l a s t i n g , with the only f ree surface being perpendicular to the b las tho le a x i s , the e f f e c t i s l ess s i g n i f i c a n t . Around the b l a s t h o l e , the fragmenting process cannot go beyond the Stage 1 phase discussed f o r bench b l a s t i n g . Without a f ree face to provide l a t e r a l r e f l e c t i o n , the i n i t i a l compressive s t ress wave continues to expand out into the rock un t i l i t d i s s i p a t e s at some considerable d istance from the b l a s t h o l e . This r e s u l t s in a r a d i a l pattern of extensive cracks p a r a l l e l to the b las tho le a x i s . The compressive s t ress wave only gets r e f l e c t e d back into the rock near - 60 -the mouth of the hole at the upper f ree s u r f a c e . However, t h i s t e n s i l e wave has much less e f f e c t than in the case o f bench b l a s t i n g because the wave f ront i s perpendicular to the rad ia l cracks formed in Stage 1. Even though the cracks extend to the s u r f a c e , they are not instrumental in breaking loose much rock. Consequently, c ra te r b l a s t i n g r e s u l t s in a small amount of fragmented mater ial and a large volume of rock mass which has been cracked in a l l d i r e c -t i o n s . Th is l a t t e r point i s of c r i t i c a l concern when consider ing b l a s t i n g e f f e c t s on the ul t imate s t a b i l i t y of an excavated f a c e . There fore , c ra te r b l a s t i n g must always be avoided when t ry ing to e s t a b l i s h a f i n a l wall or slope in' rock. In g e n e r a l , c r a t e r b l a s t i n g i s a h igh ly i n e f f i c i e n t use of explos ives and borehole l ength . In t es t b l a s t s with i d e n t i c a l charge s i z e s and the same distance to the nearest f ree f a c e , bench b l a s t i n g removed 10 times the volume as d id c r a t e r b l a s t i n g . 3 See Figure 3 .1 -7 . I t ' s only p r a c t i c a l a p p l i c a t i o n i s f o r s ink ing cuts or ramp c u t s . 3 .1.3 Pre-Shear B l a s t i n g : F a l l i n g in to ne i ther of the two basic conf igura t ions examined so f a r , t h i s important b l a s t i n g technique deserves a separate d i s c u s s i o n . B las tho les f o r a pre-shear l i n e a r e ; l i k e those in a c r a t e r b l a s t with the only f ree surface at the mouth of the b l a s t h o l e . However, pre-shear b l a s t -ing requires the b las tho les to be much c l o s e r together f o r maximum contro l of the rock f r a c t u r i n g act ion and to enable the use of l i g h t e r explos ive . charges. Up to t h i s p o i n t , the d iscuss ion of rock mass detonics has deal t with the modes of ac t ion around s i n g l e b l a s t h o l e s . The unique mechanics of pre-shear b l a s t i n g involves the i n t e r a c t i o n of mu l t ip le b las tho les detonated simultaneously to produce a s i n g l e , c lean f rac ture along an en t i re l i n e of - 61 -S i d e V i e w TGS B E N C H B L A S T I N G C R A T E R B L A S T I N G P l a n V i e w FIGURE 3.1-7 •  COMPARISON BETWEEN REMOVED VOLUMES IN BENCH BLASTING AND CRATER BLASTING WITH DENTICAL CHARGES AND BURDENS (a f te r Persson, Lundborg 8 J o h a n s s o n 3 ) - 62 -pre-shear h o l e s . C l e a r l y , the necessary t e n s i l e forces must be created in some way other than r e f l e c t i o n from a f ree f a c e . For ease of i l l u s t r a t i o n , the i n t e r a c t i o n between two pre-shear holes is examined. When the two shock waves simultaneously t rave l out from the b l a s t h o l e s , the rock at the mid-point between the holes i s subjected to t h e i r combined compressive f o r c e s . As descr ibed by the laws of e l a s t i c i t y , t h i s very high compression sets up tangent ia l shear s t resses which cause an i n i t i a l f rac ture to form on the pre-shear l i n e . See Figure 3.1-8. As the two shock waves meet, t h e i r compressive components p a r a l l e l to the pre-shear l i n e oppose each other while the normal components combine to form a t e n s i l e force perpendicular to the pre-shear l i n e . See Figure 3.1-9. This t e n s i l e fo rce acts on the i n i t i a l f r a c t u r e and causes i t to r a p i d l y prop-agate in both d i r e c t i o n s , in te rcept ing the o r i g i n a l b l a s t h o l e s . Since the f r a c t u r e process employs the summation of forces from two comp-ress ive shock waves, the force in each wave can be below that required f o r the threshold of r o c k ' f r a c t u r e . Thus, small charges in each b las tho le are s u f f i c i e n t to produce the s i n g l e pre-shear f rac tu re while not shat te r ing the f i n a l rock face behind the intended l i n e of excavat ion . See Plate 7. For t h i s reason, pre-shear b l a s t i n g is i d e a l ; f o r producing clean s tab le faces in many rock types when used in conjunct ion with c o n t r o l l e d bench b l a s t -ing techniques. - 63 -Expanding Shock Waves P L A N VIEW FIGURE 3.1-8 • INITIATION OF PRE-SHEAR FRACTURING MECHANISM ON AN ELEMENT OF ROCK BETWEEN TWO SIMULTANEOUSLY DETONATED BLASTHOLES - 64 -S t r e s s P L A N V IEW FIGURE 3.1-9 • PROPAGATION OF PRE-SHEAR FRACTURE DUE TO THE INTERACTION OF TWO SHOCK WAVES - 65 -PLATE 7 Pre-Shear b l a s t i n g created a s i n g l e f rac tu re plane to produce th is c l e a n , smooth rock face along a highway. The presence of in tac t h a l f - b l a s t h o l e s ind ica tes a minimum of damage to the rock behind the pre-shear plane. - 66 -3.2 THE INFLUENCE OF ROCK MASS PROPERTIES ON THE ROCK BREAKAGE PROCESS The important processes in rock b l a s t i n g are reasonably well understood and are r e l a t i v e l y simple wi thin homogeneous mater ia ls such as p l e x i g l a s s or large rock b l o c k s . However, in real rock b l a s t i n g , the s i t u a t i o n i s much more complicated and m u l t i - f a c e t t e d . There are many d i f f e r e n t types of rock b l a s t i n g operat ions in which any one of the d i f f e r e n t simple mechanisms may predominate. A real rock mass is usua l ly s t rongly inhomogeneous and a n i s o t r o p i c with regions of high and low strength wi th in the f r a c t u r i n g range of one b l a s t h o l e . The rock normally contains a complicated network of both large and f i n e cracks and f i s s u r e s . Although most of these w i l l be n a t u r a l l y occurr ing s t ructures in the rock , some may have been produced by a previous b l a s t i n g round or the neighbouring charge in the same round. A rock mass may have planes of easy f rac tu re or iented in any conceivable way r e l a t i v e to the f ree face and the axis of the b l a s t h o l e . The f ree face i t s e l f w i l l normally be qui te i r r e g u l a r . A fu r ther cons idera t ion i s the combined e f f e c t and i n t e r a c t i o n of charges in several h o l e s , f i r e d simultaneously or at delayed time i n t e r v a l s . C l e a r l y , the basic knowledge presented on b l a s t i n g mechanisms up to t h i s point is not s u f f i c i e n t f o r a complete and d e t a i l e d understanding of detonics in a real rock mass. Although the e f f e c t s of ind iv idua l rock mass features are becoming bet te r understood, i t i s doubtful whether a comprehensive and i n t e r a c t i v e rock mass detonics model w i l l ever be developed. Perhaps t h i s i s why b l a s t i n g has been regarded as an ar t rather than a sc ience f o r so long . Undoubtedly, many of the o ld "powder monkeys" were a r t i s t s in t h e i r own r i g h t , subconsciously taking every advantage of known j o i n t s and headings within t h e i r ind iv idua l q u a r r i e s . To date , the most successfu l s c i e n t i f i c e f f o r t s have been in empir ical rather than t h e o r e t i c a l r e l a t i o n s , based on r e a l rock b l a s t i n g experiments - 6 7 -and incorporat ing those major features of the process known to be important. Through t h i s type of work, the fo l lowing rock mass proper t ies have been iden-t i f i e d as those having s i g n i f i c a n t e f f e c t s on b l a s t i n g mechanisms. 3.2.1 In -S i tu Dynamic Rock Strength: Although the t e s t i n g of rock strength has been done as standard procedure f o r many decades, t h i s heading points out two very important q u a l i f i c a t i o n s in determining strength values which w i l l be meaningful f o r b l a s t i n g . Upon detonation of the explos ive charge, the rock at the b las tho le wall i s subjected to the intense detonation pressure over a per iod of about 0.05 m i l l i s e c o n d s . Since the strength of rock increases with the rate, o f ! l o a d i n g , i t i s important to r e a l i z e that ne i ther standard Uniax ia l Compressive Strength tes ts nor T r i a x i a l tes ts can poss ib ly produce a useful strength value f o r rock under such a dynamic loading r a t e . 3 Unfor tunate ly , a simple c o r r e l a t i o n i s not a v a i l a b l e s ince the rate at which strength increases with loading rate •varies with rock type. Weaker rocks and those with" lower t e n s i l e strengths show a greater r e l a t i v e strength increase with increas ing loading ra te . To date , s t rength / load ing rate r e l a t i o n s h i p s have not been accura te ly d e f i n e d , e s p e c i a l l y f o r loading periods less than 1 m i l l i s e c o n d . One of the major problems in b l a s t i n g opt imizat ion l i e s in the uncerta inty of the proper t ies and behaviour of rocks under the extremely dynamic condi t ions assoc ia ted with explos ive a t t a c k . 1 9 A s o p h i s t i c a t e d technique f o r obta in ing dynamic rock strength has been developed in Switzer land by Young and Dubugnon 2 0 . The i r i n v e s t i g a t i o n s used a r e f l e c t e d shear wave to study the dynamic f a i l u r e of l imestone under cont -r o l l e d laboratory condi t ions with care fu l instrumentat ion. However, any v a l i d rock strength t e s t i n g should be made i n - s i t u rather than in the labora tory . It i s abso lu te ly impossible f o r a reasonably s ized laboratory specimen to proper ly represent the volume of rock wi th in a b l a s t -- 68 -h o l e ' s zone of i n f l u e n c e . By making i n - s i t u measurements, the e f f e c t s of weathering or of any observed s t ruc ture on the rock strength can be assessed . If rock specimens were t rans fe r red to a l a b o r a t o r y , the weakest port ions would f a l l apart so that only the strongest parts of the rock would get t e s t e d . 2 1 The i n - s i t u dynamic strength of rock depends on more than jus t the strength of the i n t a c t rock. A strong rock type can be s i g n i f i c a n t l y weakened by weathering, groundwater, a l t e r a t i o n , the presence of s t r u c t u r a l d i s c o n t i n u i t i e s , or f rac tures due to previous b l a s t i n g . The i n - s i t u t e s t i n g of rock types should c o n s i s t of determining both the dynamic t e n s i l e strength and the dynamic compressive s t rength . The dyn-amic compressive strength i s determined by s e t t i n g o f f charges having var ious borehole pressures ranging upwards from the s t a t i c compressive strength of the rock. The burden/hole diameter r a t i o should be roughly the same as that to be used f o r the designed b l a s t , s ince the apparent compressive strength of the rock mass var ies with the burden/hole diameter r a t i o . The i n - s i t u dynamic compressive strength of the rock mass w i l l be equal to the maximum borehole pressure which does not cause crushing around the b l a s t h o l e . Since t e n s i l e f r a c t u r i n g usua l ly accounts f o r the greater part of f r a g -mentat ion, the dynamic t e n s i l e strength is a lso important, e s p e c i a l l y f o r pre-shear ing c a l c u l a t i o n s . Its value is determined by d r i l l i n g o f f several sets of holes at var ious spac ings . The la rges t spacing which s t i l l al lows a good pre-shear crack to form between the holes can determine an accurate f i g u r e f o r the dynamic t e n s i l e strength by s u b s t i t u t i n g into the fo l lowing e q u a t i o n : 2 1 T = r x BP 500 x S - r where: T BP S r Dynamic T e n s i l e Strength (MPa) Borehole radius (mm.) Borehole pressure (MPa) Borehole spacing (metres) - 69 -3.2.2 Presence of S t ructura l Features: One of the most obvious features of a rock mass i s the presence of such s t ruc tu ra l d i s c o n t i n u i t i e s as f a u l t s , j o i n t s and bedding. When these features in tercept a b las tho le or pass near to one, they w i l l r a d i c a l l y in f luence the sequence of events out l ined in Sect ion 3 .1 . The in f luence of d i s c o n t i n u i t i e s w i l l p r imar i l y depend on t h e i r s p a t i a l d e n s i t y , t h e i r c o n t i n u i t y through the rock mass, and whether they are t i g h t l y c losed or open. The type of i n f i l l i n g , i f any is present , w i l l a lso have some e f f e c t . Upon detonat ion , a j o i n t passing through the b las tho le w i l l tend to act as an extension of the ho le . The i n i t i a l high pressure gases w i l l flow into the j o i n t , c rea t ing considerable crushing at the b las tho le wall and causing pneumatic wedging to p r e f e r e n t i a l l y expand the j o i n t . See Plate 8. If the j o i n t i s very cont inuous, the wedging e f f e c t can cause d is rup t ion f o r a great d istance in a l l d i r e c t i o n s . At the same t ime, gas leakage into the j o i n t w i l l reduce the pressure a v a i l a b l e in the b las tho le f o r the normal fragmenta-t ion process . When bedding or near ly hor izonta l j o i n t s occur in bench b l a s t i n g , t h i s pneumatic wedging e f f e c t i s often responsib le f o r unexpectedly large d istances of throw. Due to the p r e - e x i s t i n g planes of p r e f e r e n t i a l gas t r a v e l , the rock w i l l separate along these planes r e s u l t i n g in blocky fragmentat ion. F iner f i s s u r e s through the b las tho le wall w i l l not n e c e s s a r i l y cause such e f f e c t s as they may c lose up under the large ax ia l and tangent ia l pressures in the ea r l y stages of shock propagat ion. Large , open j o i n t s p a r a l l e l to the b las tho le may cause r e f l e c t i o n of the shock wave before i t reaches the f ree sur face . This w i l l r e s u l t in more intense fragmentation of the mater ia l c l o s e r to the b las tho le and even in terna l scabbing at the j o i n t . The rad ia l cracks w i l l not cut through the j o i n t open-i n g . Instead, the gas pressure w i l l expand into the j o i n t and cause unexpect-edly large break-out boulders which may reach fa r beyond the intended excava-- 70 -P L A T E 8 This exposed b las tho le c l e a r l y reveals the e f f e c t of an i n t e r s e c t i n g j o i n t . Note the shape of the crushed zone and the d i s t i n c t l y open j o i n t caused by the pneumatic wedging of escaping high pressure explosion gases. - 71 -t ion l i m i t . Narrow or t i g h t j o i n t s p a r a l l e l to the borehole may be too th in to cause r e f l e c t i o n of the shock wave but w i l l separate under the in f luence of the returning t e n s i l e wave. Th is may reduce the i n t e r a c t i o n with the es tab l i shed r a d i a l cracks and can prevent the rock from breaking out around the b l a s t h o l e . 3 See Plate 9. If a , j o i n t has been i n f i l l e d with d i f f e r e n t m a t e r i a l s , i t provides an acoust ic impedance d i s c o n t i n u i t y . 1 The more near ly the impedance of the i n f i l l material matches that of the adjacent rock , the greater the energy transmit ted and the l e s s e r re f rac ted or r e f l e c t e d . The o r i e n t a t i o n of s t ruc ture r e l a t i v e to the bench face or p i t slope grea t ly a f f e c t s the in f luence of the b l a s t on the f i n a l w a l l . When the s t r u c -tures are hor izonta l or p a r a l l e l to the f i n a l w a l l , a clean smooth face can r e a d i l y be ach ieved. Problems usua l ly a r i s e when the s t ruc tures are undercut by the excavat ion . Even in good b l a s t s which create clean faces and no excess f r a c t u r e s , s t ruc tures d ipping s teeply out of the wall w i l l u l t imate ly contro l the appearance of the f i n a l f a c e . See Plate 10. For t h i s reason, i t i s .. important to sca le a f i n a l face immediately upon completion of muck excavat ion . Such problems of undercutt ing s t ruc tures should be avoided by proper design of the p i t s lope . Although many open p i t mines may have large port ions of the p i t wi thin one rock type, the b l a s t i n g c h a r a c t e r i s t i c s w i l l change around the p i t p e r i -meter as the o r i e n t a t i o n of the wall s h i f t s r e l a t i v e to the p r i n c i p a l d i s c o n t -i n u i t i e s . Th is was h igh l igh ted in a study at the Smallwood Mine where the b l a s t i n g engineer worked in conjunct ion with the p i t geo log is t in a se r ies of b l a s t i n g t e s t s . 2 2 The j o i n t spacing or densi ty of natural f rac tures is another s i g n i f i c a n t f a c t o r in a b l a s t . C l o s e l y spaced j o i n t s in a hard rock type w i l l cause i t to behave l i k e a low strength m a t e r i a l . Within some orebodies and h ighly - 72 -P L A T E 9 The e f f e c t of a major j o i n t p a r a l l e l and adjacent to the b las tho le can be seen at the centre of th is photo. The r e f l e c t e d t e n s i l e wave in teracted with the j o i n t to cause overbreak along the well def ined j o i n t p lane. Premature gas re lease into the j o i n t reduced the b las tho le pressure such that a substant ia l port ion of rock along the b las tho le f a i l e d to break out . - 73 -P L A T E 10 The presence of non-shattered h a l f - b l a s t h o l e s and several smooth shear faces ind ica te that t h i s rock face was not overb las ted . This photo i l l u s t r a t e s that s teep , outward dipping rock s t ructure w i l l u l t imate ly control the f i n a l appearance of a rock face . In th is case , the primary concern in the b l a s t design is to keep such overbreak to a minimum. - 74 -sheared f a u l t zones, the rock i s a lready d issec ted to an acceptable fragment-at ion gradation requ i r ing only the gas pressure act ion of the b las t to loosen the rock. Much of the rock at Bouga inv i l l e Copper Mine f a l l s into t h i s d e s c r i p t i o n . Since the s p a t i a l densi ty of the j o i n t i n g appeared!to be a major v a r i a b l e in b l a s t i n g around the p i t , a r e l a t i o n s h i p was es tab l ished by John A s h b y 2 3 between f r a c t u r e frequency observed in core and b l a s t i n g powder f a c t o r s . See Figure 3 .2 -1 . It must be noted that such a c o r r e l a t i o n i s s i t e s p e c i f i c s ince i t involves only one of the many rock p r o p e r t i e s . A separate set of c o r r e l -a t ion curves would be required f o r each d i f f e r e n t rock type. Although there i s no cons idera t ion f o r the r e l a t i v e o r i e n t a t i o n of s t ruc tu ra l features to the p i t w a l l , the densi ty of natural fragmentation i s such that t h i s aspect becomes inconsequent ia l . Ashby's approach in e s t a b l i s h i n g an empir ica l c o r r e l a t i o n with a dominant rock mass feature may be one of the most e f f e c t i v e means cur ren t l y a v a i l a b l e to overcome the l i m i t e d understanding of complex s t r u c t u r a l in f luences on rock mass d e t o n i c s . 3.2.3 Po isson 's Rat io : The nature of f a i l u r e induced by b l a s t i n g changes with the e l a s t i c constant of the rock. Rocks possessing the lowest Po isson 's Ratio (a) f a i l d i r e c t l y by a b r i t t l e f r a c t u r e process while those having a high value f a i l mainly by p l a s t i c means. D iv id ing rocks into those that normally exh ib i t p l a s t i c or b r i t t l e behav-iour may be misleading because the nature of f a i l u r e depends upon the loading ra te . At a high loading r a t e , b r i t t l e f a i l u r e i s poss ib le even in mater ia ls that normally deform p l a s t i c a l l y . Both the s t a t i c and dynamic values of a increase with c o n f i n i n g pressure with the dynamic value being the lower of the two. - 75 -POWDER FACTOR* Gravity Loaded ANFO Blasting Gelatine t o E 3 Kg/tonne c o •a >> lb/s.ton c o E a CO T> >. .^ a 0.8-0.3- 1.3- 0.6-0.6. 1.0-0.7- 1.2" 1.1" 0.5 0.5-0.9-0.6- 1.0-0.5-0.8-0.7-0.5-0.2^  3.8- 0.1.-0.6-O . V . J . ; -1.6-0.3 0.3- 0.5-0.3- 35- o.u-0.1-3.<l-0.2-0.2J 0.3-0.2- 3.3" 0.1-0. H 0.2-0. 1-Powder Factor = 0.56y*tan lj>+ I) (kg ANF0/m3) 3 / F f a c t u r e F r e q u e n c y where y= insitu density of rock 4> = basic friction angle i = roughness angle Friction angle / < < £ + 0 Fractures/meter * y = 2.5 tonnes/m3 I L 12 H 16 18 20 22 7k 26 28 Fractures/foot FRACTURE FREQUENCY FIGURE 3.2-1 : EMPIRICAL RELATIONSHIP BETWEEN POWDER FACTOR, FRACTURE FREQUENCY AND JOINT SHEAR STRENGTH AT BOUGAINVILLE COPPER (after A s h b y " ) - 76 -For t h i s reason, the v e l o c i t y of detonation of the explos ive and the peak b las tho le pressure should be increased as Po isson 's Ratio decreases in the 0.5 to 0.2 range to achieve acceptable fragmentat ion. The approximate range f o r a f o r most common rock types is 0.2 to 0 . 3 . 1 9 3.2.4 Young's Modulus: Both the s t a t i c and dynamic Young's Modulus increases with conf in ing pressure . The dynamic e l a s t i c modulus f o r some rocks could be up to 20% greater than that of the s t a t i c c a s e , even under moderate con f in ing pressures . The e f f e c t i v e Young's Modulus of a rock mass with open j o i n t s or c a v i t i e s i s less than i t s i n t r i n s i c Young's Modulus. 3.2.5 Internal F r i c t i o n : As the explosion-generated s t r a i n wave radiates out into the rock , some of i t s mechanical energy i s converted in to heat due to wave transmission r e s i s -tance wi thin the rock mass. This in terna l f r i c t i o n gives an i n d i c a t i o n of a r o c k ' s a b i l i t y to attenuate s t r a i n waves. In massive rock bod ies , fragment-at ion decreases with an increase in in terna l f r i c t i o n . In rock which exh ib i ts a dense network of natural cracks and planes of weakness, the wastage of s t r a i n energy has been demonstrated by L a n g 2 4 where fragmentation depends almost e n t i r e l y upon the gas pressure ac t ion of the e x p l o s i v e . Internal f r i c t i o n var ies considerably with rock type , increas ing with p o r o s i t y , permeabi l i ty and j o i n t i n g of the r o c k . 1 9 Attenuat ion increases considerably across a f a u l t or shear zone. Internal f r i c t i o n p a r a l l e l to the bedding can be ha l f that normal to the bedding. If pores are f i l l e d with water, the maximum pore pressure r i s e during passage of the s t r a i n wave i s several times greater than i f they conta in gas. Unfor tunate ly , most in terna l f r i c t i o n values have been determined in the laboratory using rock c o r e s . I n -s i tu determination of s t r a i n wave at tenu-at ion would provide a much more accurate i n d i c a t i o n of a r o c k ' s s u s c e p t i b i l i t y - 77 -to s t r a i n wave f r a c t u r i n g mechanisms. 3.2.6 Rock Densi ty: The d e n s i t i e s and strengths of rocks can usua l ly be well c o r r e l a t e d . In genera l , low densi ty rocks can be most e a s i l y deformed and require r e l a -t i v e l y low powder f a c t o r s f o r successfu l f ragmentat ion. Dense rocks usua l ly require f u l l y coupled powerful e x p l o s i v e s , e s p e c i a l l y i f such rocks have a massive s t r u c t u r e . Even i f the rock i s s a t i s f a c t o r i l y f r a c t u r e d , the broken mass requires a minimum displacement f o r good d i g g a b i l i t y . Denser rocks w i l l cause a decrease in muck displacement simply due to the increased load of the burden. This can be compensated f o r by increas ing b las tho le diameter, reducing the pa t te rn , or changing to an explos ive with a higher borehole pressure . For v e r t i c a l b las tho les which are deep and/or in very dense rock , the weight of over ly ing rock w i l l impede muck displacement and may cause problems at grade leve l such as unbroken toes and high f l o o r s . 3.2.7 Seismic Wave V e l o c i t y : The seismic wave v e l o c i t y represents the speed at which the shock wave t r a v e l s through the rock mass. It i s usua l ly used i n - s i t u on geophysical surveys to determine depth of overburden or broken rock. However, the seismic wave v e l o c i t y a lso r e f l e c t s some of- the other import-ant rock mass p r o p e r t i e s . Rocks which have a higher seismic v e l o c i t y are genera l ly observed to be s t ronger , while those which are weakened by weather-i n g , a l t e r a t i o n , f r a c t u r i n g due to dense j o i n t i n g or previous b l a s t i n g have a lower v e l o c i t y . In research work at Kennecott Copper Corpora t ion , Carl Broadbent 2 5 deve l -oped a r e l a t i o n s h i p between seismic wave v e l o c i t i e s and powder fac to rs required to achieve acceptable fragmentat ion. See Figure 3 .2 -2 . Th is i s s i m i l a r to the empir ical approach used by A s h b y 2 3 , but seismic v e l o c i t y may be the bet ter - 78 -or o h-o < or LU o o CL a> c c o 0 . 2 5 -0 . 2 0 -0 . 15 0 . 1 0 0 . 0 5 + c o (A -ri 0.5 0.4! 0.3 0.2 0.1 . . 2 <S s o CO So • Good or Excn» Froflmontotion O Poor Fragmentation 10 1 2 1 4 f t . /sec. (x 1000) 0 m V s e c . (x 1000) SEISMIC VELOCITY FIGURE 3 .2-2 • EMPIRICAL RELATIONSHIP BETWEEN POWDER FACTOR AND IN-SITU SEISMIC VELOCITY AT KENNECOTT COPPER (after B r o a d b e n t " ) - 79 -rock mass property f o r c o r r e l a t i o n because i t i s a f fec ted by several other p r o p e r t i e s . This r e l a t i o n s h i p i s probably not u n i v e r s a l , but i t should apply wi th in g e o l o g i c a l l y cons is ten t a r e a s . 2 5 3.2.8 Water Content: In most r o c k s , water sa tura t ion markedly increases the v e l o c i t y of propa-gat ion of e l a s t i c waves owing to the f i l l i n g of pores and f i s s u r e s with water. Thus s t resses and water content are inherent c h a r a c t e r i s t i c s of a rock mass which reduce the e f f e c t s of j o i n t i n g on the e l a s t i c proper t ies of the s o l i d rock. F l u i d s in a porous rock decrease f r i c t i o n between gra in s u r f a c e s , decreas-ing the y i e l d s t reng th . Increased water content appears to reduce energy absorpt ion and thus makes breakage by explos ive energy e a s i e r . Unfor tunate ly , the at tenuat ion of the explosion-generated s t r a i n wave by the water annulus around the charge tends to e l iminate the benef i ts of water wi th in the s t r a t a . 1 9 The advantages of water wi th in the rockmass w i l l only be r e a l i z e d with f u l l y coupled explos ives having s p e c i f i c g r a v i t i e s greater than 1.0. 3.2.9 In -S i tu S t r e s s : Although t h i s feature i s most commonly encountered in underground b l a s t -i n g , i t has been s i g n i f i c a n t in some surface b l a s t i n g opera t ions . The presence of p r e - e x i s t i n g s t ress cracks c ross ing the b las tho le i s one e f f e c t of high s t a t i c s t r e s s e s . These in f luence the b l a s t performance in the same way as other s t r u c t u r a l d i s c o n t i n u i t i e s . The second e f f e c t i s due to the s t ress concentrat ion i t s e l f . In the presence of a g r a v i t a t i o n a l and/or t e c t o n i c s t ress f i e l d , the f r a c t u r e pattern i s in f luenced by the non-uniform s t ress condi t ion around the b l a s t h o l e . Some of the cracks which s t a r t to grow in rad ia l d i r e c t i o n s may evenuta l ly curve o f f in to the d i r e c t i o n of the s t a t i c s t r e s s f i e l d . This phenomenon is most v i s i b l e when attempting to e s t a b l i s h a s t r a i g h t pre-shear f rac tu re as i n v e s t -- 80 -igated by N i c h o l l s and D u v a l ! 2 6 . See Figure 3 .2 -3 . When the s t ress f i e l d acts in a d i r e c t i o n normal to p r e - e x i s t i n g c r a c k s , i t can be s u f f i c i e n t l y intense to prevent extension of these c r a c k s , but at the same t ime, a s s i s t in forming long new cracks in the d i r e c t i o n of the s t ress f i e l d . It should be appreciated that such ground s t resses can e x i s t only well within the rock mass. There w i l l be a surface layer of f r a c t u r e d , l a r g e l y s t ress r e l i e v e d rock over the tops and faces of a l l benches. Front row burdens w i l l probably not be in f luenced by even high s t ress f i e l d s but the e f f e c t must be expected to increase towards the back row of the b l a s t pa t te rn . FIGURE 3 .2 -3 « THE INFLUENCE OF AN IN-SITU STRESS FIELD ON A PRE-SHEAR LINE WITH VARIOUS BLASTHOLE SPACINGS (a f te r N icho l l s and D u v a l l * ' ) - 82 -REFERENCES ASH, Richard L . : The Influence of Geological D i s c o n t i n u i t i e s on Rock B l a s t i n g . Ph.D. T h e s i s , U n i v e r s i t y of Minnesota, 1973. LANGEFORS, U. & KIHLSTROM, B . : The Modern Technique of Rock B l a s t i n g . Th i rd E d i t i o n , Halsted P r e s s , 1978. PERSSON, P . A . , LUNDBORG, N. & JOHANSSON, C . H . : The Basic Mechanisms in Rock B l a s t i n g . Proceedings, Second Congress of the Internat ional Soc ie ty of Rock Mechanics, Beograd, 1970. KUTTER, H.K. & FAIRHURST, C : On the Fracture Process in B l a s t i n g . Internat ional Journal of Rock Mechanics & Mining S c i e n c e , V o l . 8, 1971. COOK, M.A. : The Science of Industr ia l E x p l o s i v e s . Publ ished by IRECO Chemicals , S a l t Lake C i t y , 1974. JOHANSSON, C H . & PERSSON, P . A . : Detonics of High E x p l o s i v e s . Swedish Detonics Research Foundat ion, Academic P r e s s , 1970. NOREN, C . H . : B l a s t i n g Experiments in Grani te Rock. Quarter ly of the Colorado School of Mines, V o l . 15, No. 3 , 1956. BERGMANN, O . R . , RIGGLE, J.W. & WU, F . C . : Model Rock B l a s t i n g - E f f e c t of Explosive Proper t ies and Other Var iab les on B l a s t i n g R e s u l t s . Inter-nat ional Journal of Rock Mechanics, Mining Science & Geomechanics Abs t r -a c t s , V o l . 10, 1973. BERGMANN, O . R . , WU, F . C & EDL, J . : Model Rock B l a s t i n g Measures E f f e c t of Delays and Hole Patterns on Rock Fragmentation. Engineer ing and Min-ing J o u r n a l , V o l . 175, No. 6, June 1974. BERGMANN, O . R . , WU, F . C & EDL, J . : Model Rock B l a s t i n g Measures E f f e c t of Delays and Hole Patterns on Rock Fragmentation. Proceedings, F i r s t Conference on Explos ives and B l a s t i n g Techniques, P i t t s b u r g h , Pennsylvania , February 1975. HINO, Kumao: Fragmentation of Rock Through B l a s t i n g and Shock Wave Theory of B l a s t i n g . Quar ter ly of the Colorado School of Mines, V o l . 51, No. 3 , 1956. COOK, M.A. , COOK, V . C , CLAY, R . B . , KEYES, R.T. & UDY, L . L . : Behaviour of Rock During B l a s t i n g . T r a n s a c t i o n s , S o c i e t y . o f Mining Engineers , V o l . 235, December 1966. MERCER, J . K . : Some Aspects of B l a s t i n g P h y s i c s . Quarry Management and Products , V o l . 7, No. 12, December 1980. LANG, L . C . & FAVREAU, R . F . : A Modern Approach to Open P i t B las t Design and A n a l y s i s . CIM B u l l e t i n , V o l . 65, No. 722, June 1972. FIELD, J . E . & LADEGAARD-PEDERSEN, A . : The Importance of the Ref lected St ress Wave in Rock B l a s t i n g . Internat ional Journal of Rock Mechanics and Mining S c i e n c e , V o l . 8, 1971. - 83 -PERSSON, P . A . , LADEGAARD-PEDERSEN, A. & KIHLSTROM, B.: The Influence of Borehole Diameter on the Rock B l a s t i n g Capacity of an Extended Explo-s ive Charge. Internat ional Journal of Rock Mechanics & Mining S c i e n c e , V o l . 6, 1969. JOHANSSON, C . H . : Rock Motion in Bench B l a s t i n g . Swedish Detonic Research Foundat ion, Report DL 27, 1968. JUST, G . D . : Rock Fragmentation in B l a s t i n g . CIM B u l l e t i n , V o l . 72, No. 803, March 1979. HAGAN, T . N . & HARRIES, G . : The E f f e c t of Rock Proper t ies on B l a s t i n g Resu l ts . Chapter 4 of the A u s t r a l i a n Mineral Foundation Workshop Course Manual, D r i l l i n g and B l a s t i n g Technology, A d e l a i d e , 1977. YOUNG, C. & DUBUGNON, 0 . : A Ref lected Shear Wave Technique f o r Determin-ing Dynamic Rock Strength . Internat ional Journal of Rock Mechanics, Mining Science & Geomechanics A b s t r a c t s , V o l . 14, 1977. CALDER, P . : P i t Slope Manual, Chapter 7 - Perimeter B l a s t i n g . CANMET (Canada Centre f o r Mineral and Energy Technology) , May 1977. BELLAND, J . M . : St ructure as a Control in Rock Fragmentation. CIM B u l l e t i n , V o l . 59, No. 647, March 1966. ASHBY, J . P . : Production B l a s t i n g and Development of Open P i t S lopes . Proceedings, Th i rd Internat ional Conference on S t a b i l i t y in Surface Min ing , Vancouver, B . C . , AIME, 1982. LANG, L . C . : B l a s t i n g Frozen Iron Ore at Knob Lake. Canadian Mining J o u r n a l , V o l . 87, No. 8, August 1966. BROADBENT, C D . : Pred ic tab le B l a s t i n g With In -S i tu Seismic Surveys. Mining Eng ineer ing , V o l . 26, No. 4 , A p r i l 1974. NICHOLLS, H.R. & DUVALL, W. I . : P r e - S p l i t t i n g Rock in the Presence of a S t a t i c St ress F i e l d . Report of Invest igat ions 6843, U.S. Department of the I n t e r i o r , Bureau of Mines, 1966. - 84 -CHAPTER FOUR THE INFLUENCE OF BLASTING ON SLOPE STABILITY - 85 -4.0 THE INFLUENCE OF BLASTING ON SLOPE STABILITY Designing f o r optimum slope s t a b i l i t y i s one of the most important a p p l i -cat ions of rock mechanics to surface excavat ions. During the past two decades, rock slope engineers have been able to design s t a b l e , economical excavations of e v e r - i n c r e a s i n g sca le and complexity due to advances in geologic data gath-e r i n g , core recovery and o r i e n t a t i o n , shear strength t e s t i n g of d i s c o n t i n u i t i e s , and monitoring of pore water pressures . A few engineers have a lso attempted to use s t a t i s t i c a l means f o r incorporat ing uncerta inty into slope s t a b i l i t y a n a l y s i s . Through the improved capaci ty and a v a i l a b i l i t y of desktop micro-computers, i t i s now poss ib le to e a s i l y handle large volumes of geologica l and hydro log ica l da ta , to produce, with conf idence , slope angles of optimum s t a b i l i t y wi th in ranges of a few degrees. Many of the rock mass proper t ies incorporated into a good slope design are those which have been determined from care fu l laboratory t e s t i n g of in tac t rock specimens. If a rock slope engineer i s to produce a t r u l y optimal slope d e s i g n , then he c l e a r l y must depend on these rock mass proper t ies being present wi th in the f i n a l rock s l o p e . Any subsequent changes in these proper t ies cont -r i b u t i n g to an o v e r a l l decrease in the competancy of the rock mass w i l l r e s u l t in a l ess s tab le rock s l o p e . Unfor tunate ly , most engineers involved in rock slope design are not f a m i l i a r with b l a s t i n g mechanics and f a i l to r e a l i z e the important in f luence of b l a s t i n g on the s t a b i l i t y of t h e i r designed s l o p e s . 1 Even good b l a s t i n g can a f f e c t the inherent rock proper t ies and may lead to minor changes in a n t i -c ipa ted slope s t a b i l i t y . At b e s t , the b l a s t designer can only hope to contain the b las t damage within the mass of rock to be excavated and to minimize any de le te r ious e f f e c t s in the surrounding rock. At t h i s point in t ime, the a b i l i t y of engineers to design s tab le rock slopes i s more advanced than the a b i l i t y to construct them when b l a s t i n g i s requ i red . - 86 -There are two p r i n c i p a l means by which b l a s t i n g can adversely in f luence slope s t a b i l i t y . The most obvious i s through i n s u f f i c i e n t contro l of the physical exp los ive forces and the expanding gases, c rea t ing excessive d i s r u p -t ion of the rock mass. The other e f f e c t i s that of substant ia l ground v i b r a -t ions caused by detonating a large quant i ty of explosive in a s i n g l e i n s t a n t . These two types of b l a s t induced damage are d iscussed separa te ly . - 87 -4.1 EFFECT OF PHYSICAL BLASTING FORCES Highly des t ruc t i ve forces are necessary when attempting to fragment and d isp lace rock , but they must be constra ined or c o n t r o l l e d through the a p p l i c a -t ion of spec ia l b l a s t i n g techniques in order to minimize t h e i r e f f e c t beyond the perimeter of the des i red excavat ion . In the previous chapter , the behaviour of b l a s t i n g forces; and t h e i r physical e f f e c t s were d iscussed with respect to t h e i r a b i l i t y to produce well fragmented muck, p a r t i c u l a r l y near a f ree f a c e . This sect ion examines the e f f e c t of those same forces on the f i n a l rock slope and t h e i r in f luence on ul t imate slope s t a b i l i t y . Although the en t i re perimeter b l a s t pattern must be c o r r e c t l y designed and f i r e d to produce minimal wall damage, a t tent ion w i l l be focussed on the row of l i n e holes which form the c r i t i c a l i n te r face between the muck and the f i n a l w a l l . One of the d i f f i c u l t i e s in achiev ing both good muck and an in tac t face i s the f a c t that i n i t i a l f r a c t u r i n g mechanisms extend r a d i a l l y in a l l d i r e c -t ions from the b l a s t h o l e . Since s u f f i c i e n t explosive i s required to break the l i n e hole burden, i t i s i n e v i t a b l e that some crack ing of the f i n a l wall w i l l take place adjacent to the b las tho le p o s i t i o n s . This increase in f r a g -mentation of the rock slope surface reduces the competancy of the f i n a l face and can lead to i n s t a b i l i t y . The degree of damage w i l l depend on the amount of explos ive in the b l a s t h o l e , i t s d i s t r i b u t i o n , and i t s f r a c t u r i n g a b i l i t y ( i . e . v e l o c i t y of de tonat ion) . If proper ly c o n t r o l l e d , t h i s f r a c t u r i n g does not usua l ly extend f o r s i g n i f i c a n t d is tances into the f a c e , r e s u l t i n g in a r a v e l l i n g type of f a i l u r e as opposed to large sca le mass f a i l u r e . Although r a v e l l i n g may not represent a major loss of overa l l wall ang le , i t s t i l l presents a ser ious safety hazard to men and equipment working below. Even a small piece of rock can gain s u f f i c i e n t speed on a high p i t s lope to do ser ious damage. For th is reason, i t i s good p r a c t i c e to sca le any f i n a l rock faces to remove weakened material - 88 -before i t becomes a hazard. If the b las tho le contains a large amount of e x p l o s i v e , the cracks can e a s i l y extend f a r into the rock face to i n t e r s e c t e x i s t i n g natural d i s c o n t i n -u i t i e s . Th is deeper penetrat ion produces more blocky f a i l u r e s which cannot be removed by s c a l i n g , present ing a more ser ious problem. Such damage is l i k e l y to cause the loss of bench c r e s t s , reducing the e f f e c t i v e capac i ty of the bench to catch material f a l l i n g from above. A concentrat ion of excessive cracking in the rock slope surface not only weakens the face from a s t r u c t u r a l aspect , but leaves i t open to fu r ther degradation by the subsequent weathering act ions of water and i c e . Water from both p r e c i p i t a t i o n and subsurface seepage c o l l e c t i n g in open f rac tu res i s well known f o r i t s a b i l i t y to s e r i o u s l y reduce slope s t a b i l i t y . In Canada, and other countr ies with co ld winter c l i m a t e s , a f reez ing f ron t can penetrate in to the rock f o r considerable d i s t a n c e s . The water f reez ing in the near-surface f rac tu res causes " i c e - j a c k i n g " and can r e s u l t in a s i g n i f i c a n t amount of s p a l l i n g and r o c k f a l l . Over a per iod of several y e a r s , t h i s phenomenon can cause large volumes of rock to s p a l l , gradual ly reducing a well-benched p i t wall into a r e l a t i v e l y continuous rubble slope and reducing the overa l l slope angle . Although some rock f r a c t u r i n g i s unavoidable simply due to the charge prox imi ty , several steps can be taken in the b l a s t i n g design to minimize t h i s e f f e c t . A common approach i s to increase the s p a t i a l d ispers ion of the explo-s ive along the l i n e hole row. By doubling the number of l i n e h o l e s , each b las tho le w i l l contain only ha l f the usual amount of explos ive f o r the same powder f a c t o r . This p r i n c i p l e i s most c l e a r l y seen in pre-shear b l a s t i n g where very c lose hole spacing is used f o r maximum face c o n t r o l . The explos ives user must ensure that the spa t i a l d i s t r i b u t i o n of the explos ive is proper f o r the soundness and smoothness of the f i n a l surface that is d e s i r e d . 2 Minimizing rock face damage can a lso be achieved through s e l e c t i n g an - 89 -explos ive with the lowest v e l o c i t y of detonation capable of producing the des i red fragmentat ion. The higher v e l o c i t y explos ives are only necessary where rock s t ructure i s massive and more f r a c t u r i n g is requ i red . Further improvements can be made by de-coupl ing the charge from the b las tho le w a l l . By leav ing an annulus of a i r between the explos ive and the rock , the detonation wave i s p a r t i a l l y attenuated before i t i s t ransmit ted in to the rock , reducing i t s shat te r ing e f f e c t . On t h i s research p r o j e c t , some e x p e r i -ments were made on f u l l y coupl ing the charge to the f ront or muck s ide of the b l a s t h o l e , there-by increas ing the degree of de-coupl ing from the back of the b l a s t h o l e . Th is work i s de ta i l ed in Sect ion 6 .3 .2 . Immediately fo l lowing these f r a c t u r i n g mechanisms around the b l a s t h o l e , the rap id ly expanding high pressure gases provide the other major physical b l a s t i n g f o r c e . These pressures are usua l ly the more ser ious problem, even i f the face f r a c t u r i n g is under c o n t r o l , because they can d is rupt the rock mass f o r considerable d istances into the f i n a l w a l l . The e f f e c t of the expanding gases i s most ser ious in a rock mass with a high natural f r ac tu re frequency and very continuous j o i n t p lanes. These d i s c o n t i n u i t i e s provide planes of easy t rave l f o r the gas pressures , causing pneumatic wedging to p r e f e r e n t i a l l y open and extend the j o i n t s . This act ion causes rock block separat ion and can r e s u l t in a to ta l loss of cohesion along the j o i n t s , an important f a c t o r in maintaining slope s t a b i l i t y . Since cohesion i s a d i f f i c u l t value to a s s e s s , rock slope engineers may be prudent to assume a zero value f o r bench design when they cannot be conf ident about the q u a l i t y of the b l a s t i n g opera t ions . Another c r i t i c a l s t a b i l i t y f a c t o r , the angle of f r i c t i o n a l s l i d i n g r e s i s -tance (cj>), can a lso be adversely a f fec ted by the d i s r u p t i v e forces of the expanding gases. In ter -b lock shearing may cause $ to s h i f t from i t s peak toward i t s res idua l v a l u e , or <p could be v i r t u a l l y e l iminated through d i r e c t loss of i n t e r - b l o c k contact at shallow depths. - 90 -Due to the l a rger zone of in f luence of the penetrat ing gas pressures , rock slope damage can occur well wi thin the f i n a l w a l l , causing large sca le and moderately deep-seated p i t " s l o p e f a i l u r e s . If such damage weakens an area at the toe of an e x i s t i n g high p i t w a l l , subsequent i n s t a b i l i t y could involve the f u l l height of the rock s l o p e . As mentioned in the case of face f r a c t u r i n g above, newly expanded j o i n t s may permit groundwater and seepage forces to fu r ther contr ibute to a reduct ion in s t a b i l i t y . Such a s i t u a t i o n occurred at the s t a r t of the research work at Afton Mine while the o ld b l a s t i n g prac t ices were s t i l l in use. A large p i t wall f a i l u r e was t r iggered by a s i n g l e blast-when^entrapped gas pressures t r a v e l l e d over 40 metres along a major shear p lane , opening i t up, breaking cohes ion , and causing strength loss by planar shear ing . Subsequent inf low of seeping groundwater worsened the s i t u a t i o n and acce lera ted the s l i d e mass which event-u a l l y grew to involve a 35 metre high port ion of the p i t wall and extended f a r beyond the intended p i t per imeter . See Plate 1 1 . The extra cost of monit-o r i n g , r e - s t a b i l i z i n g and extra waste s t r i p p i n g was ample j u s t i f i c a t i o n f o r embarking on a b l a s t improvement program. The key to preventing rock slope damage from expanding gases i s to al low re lease of the excess pressures as soon a f t e r detonation as p o s s i b l e , before they can t rave l in to the rock mass f o r any s i g n i f i c a n t d i s t a n c e . Th is i s best achieved by making sure that b l a s t pattern burdens, e s p e c i a l l y on the l i n e hole row, are small enough to prevent the b l a s t from becoming "choked". By prov id ing f u l l re lease of the rock burden on a h o l e , the excess gases w i l l n a t u r a l l y vent forward into the muck and not back into the f i n a l s lope . This reinfo'rces the importance of always b l a s t i n g to a f ree face instead of c r a t e r b l a s t i n g , e s p e c i a l l y on perimeter pa t te rns . Further improvements can be made by l igh ten ing or e l im ina t ing the stemming in the b l a s t h o l e , thereby provid ing f u l l gas pressure venting immediately a f t e r the necessary s t r a i n pulse has been transmit ted in to the rock. This - 91 -PLATE II Tension cracks outside the p i t perimeter reveal the extent of the large p i t wall f a i l u r e i n i t i a t e d by care less b l a s t i n g . Although t r iggered by gas pressure damage, continued movement was caused by a combination of high groundwater l e v e l s and b l a s t i n g v i b r a t i o n s . - 92 -may leave s l i g h t l y t i g h t e r muck in f ront of the f i n a l f a c e , but i t should s t i l l be diggable and provide a c leaner f i n a l rock s lope . Through understanding the geologica l s i t e condi t ions important f o r main-ta in ing slope s t a b i l i t y , i t should be poss ib le to plan and execute a good perimeter b l a s t pattern where the physical b l a s t i n g forces w i l l have a minimal e f f e c t on the f i n a l rock f a c e . Unfor tunate ly , very l i t t l e p r a c t i c a l work has been done on t h i s problem to date , p r imar i l y due to the complex inf luences of geologic f e a t u r e s . The importance of t a i l o r i n g b l a s t designs to i n - s i t u rock mass condi t ions f o r opt imiz ing rock slope s t a b i l i t y forms the centra l theme of the f i e l d research and t h i s t h e s i s . - 93 -4.2 EFFECT OF GROUND VIBRATIONS In recent y e a r s , the problems of physical b l a s t i n g forces have been over-shadowed by the amount of a t ten t ion paid to studies on the v i b r a t i o n a l e f f e c t s of b l a s t i n g . Th is i s l a r g e l y due to the f a c t that wave phenomenon can be s c i e n t i f i c a l l y monitored and understood through the known laws of p h y s i c s . Unl ike physica l b l a s t i n g e f f e c t s , v i b r a t i o n a l wave e f f e c t s are somewhat independent of the frequency and o r i e n t a t i o n of d i s c o n t i n u i t i e s , making i t s l i g h t l y e a s i e r to model t h e i r in f luence on slope s t a b i l i t y wi th in any s ing le rock type. In the case of the physical f o r c e s , the concern f o r rock mass damage focussed mainly on the rock immediately adjacent to the b l a s t which was to become the f i n a l s l o p e . The e f f e c t s of ground v ib ra t ions cover a much la rger area around the e n t i r e b l a s t zone because of the shock wave's a b i l i t y to t ravel over great d is tances through a s o l i d rock mass while maintaining much of i t s source energy. Thus, a r e l a t i v e l y minor b l a s t may adversely a f f e c t the nearby e x i s t i n g slopes and p o s s i b l y lead to problems i f they are already in a state of marginal s t a b i l i t y . Furthermore, the convoluted geology common to the ore zones of many open p i t s can a f f e c t the complex r e f l e c t i o n s and r e f r a c t i o n s of waves such that they can focus in unexpected l o c a t i o n s . A f t e r the primary shock f ron t has passed beyond the shattered and f rac tured zone of rock around the b l a s t h o l e , i t t r a v e l s in the form of e l a s t i c waves and v i b r a t i o n s . Th is energy takes on d i f f e r e n t forms which t rave l at d i f f e r e n t v e l o c i t i e s and cause d i f f e r e n t types of deformation to occur in the rock. The f a s t e s t wave, a Primary or P wave, i s a compressive wave deforming the rock in a rad ia l d i r e c t i o n . The slower Secondary or S wave is a shear wave causing deformation of the r o c k a t r igh t angles to the d i r e c t i o n of wave t r a v e l . The P and S waves are both known as body waves because they t rave l wi thin the rock mass and are responsib le f o r any in terna l v i b r a t i o n a l damage. When the body waves a r r i v e at ground s u r f a c e , new waves are generated - 94 -inc lud ing a group which t rave ls along the s u r f a c e . These surface waves, which are slower than e i t h e r of the body waves, are known as Rayleigh or R waves. The i r motion i s qui te d i f f e r e n t from that of the body waves, being character -ized by la rger ampl i tudes, lower f r e q u e n c i e s , and a lower propagation v e l o c i t y . 2 The R waves are very important s ince they propagate along the surface of the earth and because t h e i r amplitude decays more slowly with d istance t r a v e l l e d than e i t h e r the P or S waves. 3 This i s e s p e c i a l l y true i f the groundwater tab le i s c lose to surface and the rock mass i s sa tura ted . The R waves contain s i g n i f i c a n t l y more energy than the body waves and are of concern fo r v i b r a t i o n e f fec ts on sur face"s lope s t a b i l i t y . The wide v a r i a t i o n in geometrical and geologica l s i t e condi t ions preclude the s o l u t i o n of ground v i b r a t i o n problems by means of elastodynamic equat ions. The most r e l i a b l e p red ic t ions are given by empir ical r e l a t i o n s h i p s based on the r e s u l t s of several monitored b l a s t s . An ear ly study of t h i s nature was made in 1957 by Edwards and Northwood1* during const ruct ion of the S t . Lawrence Seaway. Of a l l the va r iab les examined, they found that the peak p a r t i c l e v e l o c i t y of the ground motion cor re la ted best to b u i l d i n g damage. Peak p a r t i c l e v e l o c i t y is the maximum v e l o c i t y of p a r t i c l e motion during the passage of the seismic wave beneath the p a r t i c l e . This d iscovery prompted the U.S. Bureau of Mines to review i t s own records , r e s u l t i n g in the same conclus ion and in the development of the fo l lowing s c a l i n g law f o r p a r t i c l e v e l o c i t y versus scaled d istance between the b las t and the point of i n t e r e s t : 5 where: V = peak p a r t i c l e v e l o c i t y ( i n . / s e c . ) d = d istance from shot to observat ion point ( f t . ) W = charge weight per delay ( l b s . ) K = constant depending on charge d i s t r i b u t i o n and the material type (var ies from 45 to 450) - 95 -and where: x = va r iab le depending on material type and whether the l o n g i t u d i n a l , v e r t i c a l or t ransverse component i s being measured. As a general r u l e , the long i tud ina l and v e r t i c a l components are approximately equal and the t ransverse component i s considerably smal ler than the other two, so that usua l ly the long i tud ina l or v e r t i c a l v e l o c i t i e s are used. Accord-ing to the U . S . B . M . , the exponent x var ies from -1 .5 to -1 .9 f o r these compon-ents with -1 .7 being a good average . 5 If the charges were s p h e r i c a l , charge weight would vary as the cube of the radius of the sphere, t h e o r e t i c a l l y d i c t a t i n g the use of cube root s c a l i n g . However, in most bench b las ts the loaded b las tho les are more representat ive of c y l i n d r i c a l charges with the charge Weight varying as the square of the c y l i n d e r r a d i u s . Thus, i t has been found convenient; toi use square root s c a l i n g f o r p red ic t ion of the widest range.bf b l a s t i n g c o n d i t i o n s . Based on his a n a l y s i s of several hundred thousand b l a s t i n g v i b r a t i o n s , O r i a r d 2 has recent ly publ ished a graph showing peak p a r t i c l e v e l o c i t y versus scaled d i s t a n c e . See Figure 4 . 2 - 1 . Expressed mathemat ical ly , t h i s r e l a t i o n -ship is almost i d e n t i c a l to the e a r l i e r U .S .B .M. v e r s i o n : V = H x[-A-l 6 x k l , k2,k3 where: V = peak p a r t i c l e v e l o c i t y ( i n . / s e c . ) H = v e l o c i t y in te rcept at uni ty sca led d istance D = d istance from shot to observat ion point ( f t . ) W = charge weight per delay ( l b s . ) k T= fac to rs represent ing the v a r i a t i o n s in e x p l o s i v e s , confinement, s p a t i a l d i s t r i b u t i o n , geology and other parameters of i n t e r e s t The slope of -1 .6 represents the a t tenuat ion . Although i t i s not the same at a l l s i t e s nor the same f o r a l l wave types , t h i s slope shows s u r p r i s i n g accuracy f o r most s i t u a t i o n s . 2 With increas ing s p a t i a l d i s p e r s i o n , t h i s p lo t shows a l i n e which has - 96 -FIGURE 4 . 2 - 1 : PEAK PARTICLE VELOCITY V E R S U S SCALED DISTANCE ( after Or iard* ) - 97 -a f l a t t e r slope and a lower in tercept va lue . If the charge quant i ty is d i s t r i b u t e d over a large a r e a , then the c l o s e s t port ion of the e l a s t i c zone can be adjacent to only a port ion of the to ta l charge per delay and the e f f e c t s at c lose distances cannot reach predic ted l e v e l s . 6 The e f f e c t of charge confinement i s a lso noted on the graph. I f a charge i s buried too deeply to break out to s u r f a c e , the explos ive charge w i l l produce maximum v i b r a t i o n . If the charge i s too c lose to the s u r f a c e , energy re lease into the atmosphere produces less energy in the form of e l a s t i c waves. This fu r ther re in fo rces the importance f o r b l a s t i n g to a f ree face and using minimal burdens in order to avoid backslope damage. Beyond these general r e l a t i o n s , i t i s an unfortunate f a c t that the p lo t of Figure 4.2-1 i s s t i l l inadequate f o r p r e d i c t i n g peak p a r t i c l e v e l o c i t i e s f o r b l a s t planning purposes. Although based on an unusual ly large amount of f i e l d da ta , i t cannot account f o r the h ighly s i t e s p e c i f i c condi t ions e x i s t -ing on any i n d i v i d u a l b l a s t i n g problem. The complex geologica l s e t t i n g which acts as the wave t ransmi t t ing medium has a strong in f luence on the a t tenua t ion , frequency and displacement c h a r a c t e r i s t i c s of a seismic wave. For example, hard massive rock w i l l be charac ter i zed by smal ler displacements and higher f r e q u e n c i e s , whereas s o i l w i l l be charac ter i zed by la rger displacements and lower f r e q u e n c i e s . 6 S i t e condi t ions can a lso a f f e c t seismic wave at tenuat ion by geometric spread ing , s e l e c t i v e s c a t t e r i n g , absorpt ion and d i s p e r s i o n . 2 Both the at tenuat ion and the wave form c h a r a c t e r i s t i c s are in f luenced by such geologica l f a c t o r s as l a y e r i n g , j o i n t i n g and water content , as well as the small sca le e l a s t i c proper t ies of the medium. In c e r t a i n regions under la in by prominent hor izonta l layers of sedimentary rock , i t has been noted that surface waves appear to be more prominent and p e r s i s t to greater distances than i s t y p i c a l f o r regions that are more heterogeneous and geometr ica l ly complex. For these reasons, the peak p a r t i c l e v e l o c i t i e s induced by b l a s t i n g cannot be r e a l i s t i c a l l y predicted and should be measured by o n - s i t e monitoring - 98 -to obtain the true va lues . A fu r ther d i f f i c u l t y a r i s e s from i n t e r p r e t i n g the p r a c t i c a l impl ica t ions of peak p a r t i c l e v e l o c i t y va lues . Although i t has long been acknowledged that they genera l ly c o r r e l a t e to rock mass damage, there i s very l i t t l e hard data dea l ing with any s p e c i f i c r e l a t i o n s h i p s . Perhaps the best work done in th is respect i s the of t -quoted research by Langefors and K i h l s t r o m 7 who produced a general i n d i c a t i o n of damage thresholds in r e l a t i o n to charge weight per delay and d is tance from the b l a s t . See Figure 4 .2 -2 . This p lo t was deve l -oped from the U .S .B .M. equation using values of K=200 and x=-1.5 based on guide l ines by O r i a r d 6 . It must be noted that t h i s f i g u r e should only be used f o r very general guidance. When v i b r a t i o n damage i s a ser ious problem f o r a p a r t i c u l a r mine s i t e , proper values of K and x must be determined from f i e l d measured peak p a r t i c l e v e l o c i t y data . However, the general r e l a t i o n of F igure 4.2-2 i s s u f f i c i e n t to i l l u s t r a t e one of the e a s i e s t and most e f f i c i e n t ways to contro l excessive b l a s t i n g v i b r a -t i o n s . This f i g u r e ind ica tes that the detonation of 200 kilograms of explos ive per delay w i l l cause rock breakage up to 20 metres from the b las tho le while the detonation of 2000 kilograms per delay w i l l extend t h i s d istance to approx-imately 70 metres. C l e a r l y , the use of an increased number of delays to l i m i t the amount of exp los ive detonated at any one time i s an extremely important and simple method of l i m i t i n g damage to the f i n a l rock s lope . The important i n t e r - r e l a t i o n s h i p s between the number of d e l a y s , the leve l of v i b r a t i o n , and the movements of an unstable slope were well demonstrated in an extensive 3 year study at the Da Ye Mine, one of the la rges t open p i t operat ions in the People 's Republic of C h i n a . 8 One of the several experimental methods examined f o r s t a b i l i t y contro l involved increas ing the number of delays wi th in a cons is ten t perimeter b l a s t pa t te rn . The r e s u l t s , shown in Figure 4 . 2 - 3 , c l e a r l y ind ica te the e f fec t i veness of decreasing the charge per de lay . Through repeated t e s t i n g , peak p a r t i c l e v e l o c i t y measurements at the unstable slope - 99 -FIGURE 4 . 2 - 2 » PARTICLE VELOCITIES AND DAMAGE INDUCED AT GIVEN DISTANCES BY PARTICULAR CHARGES (af ter Langefors S K i h l s t r o m 7 ) - 100 -FIGURE 4 . 2 - 3 • THE EFFECT OF INCREASING THE NUMBER OF DELAYS FOR REDUCING BLASTING VIBRATIONS AT DA YE MINE, CHINA (after L i a o S Q i n 9 ) - 101-ind icated the c r i t i c a l threshold of movement and determined the maximum permiss ib le charge per de lay . Delays are such important elements in c o n t r o l l e d surface b l a s t i n g that they are now r e a d i l y a v a i l a b l e in a broad va r i e ty of periods and types . Des-. p i t e t h e i r increased a v a i l a b i l i t y , many mining operat ions s t i l l f a i l to take advantage of them, l a r g e l y due to concerns about t h e i r extra cost and the add i t iona l time required to t i e them into a b l a s t i n g pa t te rn . It i s a lso important to s e l e c t the cor rec t type of delay f o r the p a r t i c u l a r s i t e c o n d i t i o n s . In many cases where s u f f i c i e n t delays are being i n s t a l l e d , inappropr iate periods are being used due to lack of a t tent ion to rock motion and displacement charac-t e r i s t i c s . The f u l l benef i ts of a well delayed b l a s t can only become apparent a f t e r being proper ly appl ied into a well designed b l a s t i n g pa t te rn . A good case study at Kennecott Copper Corporat ion examines the s h i f t i n g from a time-consuming and expensive pre-shear b l a s t i n g system to a mul t ip le delayed buf fer b l a s t with economical s a v i n g s . 9 A f t e r a p p l i c a t i o n of the new system, the cost of delays was found to be minimal compared to pre-shear ing and the same minimal wall damage was achieved by reducing the v i b r a t i o n a l shock energy transmit ted into the surrounding s l o p e s . A fu r ther example can be found at the Adams Mine where the in t roduct ion of a delayed pattern became an essen t ia l part of m i n i n g . 1 0 Preserving s t a b i l i t y and steep wal ls with reduced overbreak and reduced s t r i p p i n g paid f o r the system cost many times over . As d iscussed in t h i s s e c t i o n , many s i t e s p e c i f i c va r iab les have complex in f luences on b l a s t induced v i b r a t i o n l e v e l s , making i t d i f f i c u l t to f u l l y understand the kinematics invo lved . However, a d e t a i l e d s c i e n t i f i c understand-ing i s not r e a l l y necessary in order to contro l the v i b r a t i o n a l e f f e c t s which adversely in f luence slope s t a b i l i t y . When used in combination with an approp-r i a t e c o n t r o l l e d b l a s t i n g technique, to be d iscussed in the; next chapter , the a v a i l a b i l i t y of a wide va r i e ty of delay devices permits a good b l a s t e r - 1 0 2 -to e l iminate such s t a b i l i t y problems by simple lowering the maximum charge per de lay . - 103 -4.3 REFERENCES 1) BRAWNER, C O . : The Three Major Problems in Rock Slope S t a b i l i t y in Canada. Proceedings, Second Internat ional Conference on Surface Min ing , Minneap-o l i s , AIME, 1968. 2) ORIARD, L . L . : The Influence of B l a s t i n g on Slope S t a b i l i t y ; S ta te -o f -t h e - A r t . Proceedings, Th i rd Internat ional Conference on S t a b i l i t y in Surface Min ing , Vancouver, B . C . , AIME, 1982. 3) HOEK, E. & BRAY, J . W . : Rock Slope Engineer ing , Chapter 11 - B l a s t i n g . Second E d i t i o n , IMM, 1977. 4) EDWARDS, A . T . & N0RTHW00D, T . D . : Experimental Studies of the E f f e c t s of B l a s t i n g on S t r u c t u r e s . The Engineer , September 1960. 5) BAUER, A. & CALDER, P . N . : The Influence and Evaluat ion of B l a s t i n g on S t a b i l i t y . Proceedings, F i r s t Internat ional Conference on S t a b i l i t y in Open P i t M in ing , Vancouver, B . C . , AIME, 1971. 6) ORIARD, L . L . : B l a s t i n g E f f e c t s and The i r Control in Open P i t Min ing. Proceedings, Second Internat ional Conference on S t a b i l i t y in Open P i t M in ing , Vancouver, B . C . , AIME, 1972. 7) LANGEFORS, U. & KIHLSTROM B . : The Modern Technique of Rock B l a s t i n g . Th i rd E d i t i o n , Halsted P r e s s , 1978. 8) LIAO Xian-Kuei & QIU J i a - K u e i : The Technique of Reducing Ground V i b r a -t ions Near A Slope During B l a s t i n g . The Changsha Ins t i tu te of Mining and Meta l lu rgy , The People 's Republic of Ch ina , 1978. 9) DIMOCK, R.R. & CLAYTON, G . D . : Kennecott 's Delayed B l a s t i n g Technique Cuts C o s t s , Improves P i t S t a b i l i t y . Mining Engineer ing , V o l . 29, No. 4, A p r i l 1977. 10) MORASH, Barry J . : Control B l a s t i n g f o r Slope S t a b i l i t y at the Adams Mine. CIM B u l l e t i n , V o l . 71, No. 793, May 1978. - 104 -CHAPTER FIVE DESIGN CONSIDERATIONS FOR CONTROLLED BLASTING - 105 -5.0 DESIGN CONSIDERATIONS FOR CONTROLLED BLASTING The previous chapters have presented a f a i r l y complete summary of the d i f f e r e n t f i e l d s forming the basic components an the science of b l a s t i n g . With a thorough understanding of a l l the aspects d i s c u s s e d , and an apprec ia t ion of t h e i r i n t e r - r e l a t i o n s h i p s , a b l a s t i n g engineer has a l l the techn ica l back-ground necessary to produce a good, optimal b l a s t i n g des ign . However, the p r i n c i p a l chal lenge has been, and w i l l probably continue to be , the t a i l o r i n g of the b l a s t design to i n - s i t u geologica l condi t ions when provided with very l i m i t e d per t inent s i t e data . It i s t h i s aspect which introduces the "art" of b l a s t i n g into the overa l l des ign . Combining both the "sc ience" and the "art" of rock b l a s t i n g can be a complex procedure and i s genera l ly performed best by those b l a s t i n g engineers with the broadest f i e l d exper ience. Apart from the s i t e s p e c i f i c problems, a b las t design i s composed of several parameters and v a r i a b l e s , many of which are inter -dependent . These are d iscussed in t h i s chapter . Although they are presented in a c e r t a i n sequence, t h i s i s not to suggest that t h i s i s the only way to undertake a b l a s t des ign . Various b l a s t e r s w i l l have t h e i r own approach to the problem and the sequencing of t h i s chapter simply r e l e c t s t h i s author 's pre fer rence . It would be d i f f i c u l t to develop a universal formula approach due to the way in which s i t e v a r i a t i o n s a l t e r the importance of d i f f e r e n t design parameters. No matter which approach i s used to a r r i v e at an i n i t i a l scheme, b l a s t des ign-ing is an i t e r a t i v e process where constant adjustments can be expected as f i e l d condi t ions and s i t e plans change. The key is to get as c lose as pos-s i b l e to the optimal design at the s t a r t so that any subsequent changes are minor. The sequence of b l a s t design steps presented here is that used by the author when approaching a new s i t e with l i t t l e or no information a v a i l a b l e on the b l a s t i b i l i t y c h a r a c t e r i s t i c s . The premise of t h i s system is to c a l c u l -ate the maximum poss ib le charge per b l a s t h o l e , and then to plan the b las tho le - 106 -pattern based on a powder f a c t o r value f o r the rock mass. This approach genera l ly produces the most economical b las t design through f u l l u t i l i z a t i o n of each b las tho le and by keeping the d r i l l i n g costs to a minimum. However, the success of t h i s approach depends upon some p r i o r knowledge of a s u i t a b l e powder f a c t o r f o r the p a r t i c u l a r rock mass in ques t ion . To date t h i s has been the main stumbling block to producing an optimal b l a s t design and i s why i t has been se lec ted as the focus of t h i s research p r o j e c t . If the powder f a c t o r is known f o r a p a r t i c u l a r rock mass, the b l a s t design procedure becomes an economic exerc ise in opt imiz ing the balance between d r i l l i n g costs and explos ive c o s t s . - 107 -5.1 SELECTING A CONTROLLED BLASTING TECHNIQUE In order to minimize the damage to the f i n a l wall and to achieve optimum slope s t a b i l i t y , i t i s essen t ia l that some form of c o n t r o l l e d b l a s t i n g be used f o r p i t perimeter b l a s t s . However, a r b i t r a r i l y implementing any c o n t r o l -led b l a s t i n g technique w i l l not guarantee good r e s u l t s s ince each of the recog-nized methods has s p e c i a l , unique c h a r a c t e r i s t i c s . It i s important to ca re -f u l l y s e l e c t the technique which i s most appropriate f o r the s i t e condi t ions and w i l l produce the best r e s u l t s at the greatest economy. Of the several f a c t o r s which must be considered when s e l e c t i n g a b l a s t i n g technique, perhaps the most important i s the nature of the rock mass to be b l a s t e d . Th is would include the degree of j o i n t i n g (from massive to h ighly f r a c t u r e d ) , the c o n t i n u i t y of the j o i n t s , and the cond i t ion of the j o i n t s ( c l o s e d , opened or i n f i l l e d ) . The strength and e l a s t i c proper t ies of the i n t a c t rock must a lso be assessed s ince hard , b r i t t l e rocks demand d i f f e r e n t b l a s t i n g techniques from those employed in s o f t , f r i a b l e rocks . It i s a lso important to consider the type of r e s u l t s which are des i rab le and most economic. Some of the c o n t r o l l e d b l a s t i n g techniques are capable of producing p r e c i s e , sculptured rock f a c e s , but require a l o t of c a r e f u l l y d r i l l e d b l a s t h o l e s , adding s i g n i f i c a n t cost to the p r o j e c t . While t h i s degree of contro l may be necessary in some c i v i l engineering a p p l i c a t i o n s , i t can r a r e l y be j u s t i f i e d in a mining operat ion where a modif ied approach or a less p r e c i s e technique may be more appropr ia te . The type and s i ze of d r i l l i n g equipment a v a i l a b l e is another major c o n s i d -eraton in the s e l e c t i o n process . Cer ta in techniques require f a i r l y small b las tho le diameters and the a b i l i t y to d r i l l the holes at prec ise angles . D r i l l i n g accuracy and speed may a lso a f f e c t the amount of rock which can be d r i l l e d o f f per s h i f t . This may require the use of a d i f f e r e n t d r i l l type from that used in the large sca le production b l a s t s , increas ing the i n i t i a l c a p i t a l expenditure on equipment. - 108 -Depending on s i t e l o c a t i o n , other fac to rs f o r cons idera t ion could include the presence of groundwater or seepage, the types of explos ives that can be s u p p l i e d , and the s k i l l or experience of a v a i l a b l e b l a s t i n g personnel . High groundwater l e v e l s or seepage rates w i l l necess i ta te the use of b las tho le l i n e r s or high densi ty s l u r r y e x p l o s i v e s . More remote mining s i t e s may have d i f f i c u l t y ge t t ing the spec ia l explos ive products necessary f o r some c o n t r o l l e d b l a s t i n g methods, while a lack of t ra ined personnel may make i t d i f f i c u l t to implement a more complex b l a s t i n g program. These fac to rs can s t r i n g e n t l y l i m i t the techniques which can be cons idered . Each of the above mentioned fac to rs has d i f f e r i n g degrees of importance in the var ious b l a s t i n g methods, but a l l must be considered together when making a s e l e c t i o n . This sec t ion w i l l now d iscuss the p r i n c i p a l recognized c o n t r o l l e d b l a s t i n g techniques and w i l l o u t l i n e the condi t ions under which each of them can be most favourably a p p l i e d . 5.1.1 Pre-Shear B l a s t i n g : Pre-shear ing or p r e - s p l i t t i n g is a technique which i s used very exten-s i v e l y and s u c c e s s f u l l y in c i v i l engineer ing excavations in competent rock and less commonly in open p i t mining. This technique involves d r i l l i n g a l i n e of small diameter holes to conform with the desi red l i n e of break. These holes are usua l ly 65 to 125 mm. diameter, using tracked percussive equipment capable of d r i l l i n g at the des i red face angle . Genera l l y , the recommended hole spacing i s approximately 12 times the hole diameter, but c l o s e r spacing may have to be used where complex rock s t ruc ture requires greater c o n t r o l . 1 It i s a lso recommended that the explos ive diameter be ha l f the hole d i a -meter and the load d i s t r i b u t e d so that only ha l f the hole length i s loaded. The charge should be decoupled from the rock by leav ing an a i r space between the charge and the b las tho le w a l l . This is usua l ly achieved by p lac ing the - 109 -charge in a tube of smal ler diameter than the hole and center ing t h i s tube in the b las tho le with some form of s p a c e r . 2 The row of pre-shear holes is f i r e d before the main charge and the r e i n -f o r c i n g e f f e c t of the c l o s e l y spaced h o l e s , together with an e s s e n t i a l l y i n f i n -i t e burden, r e s u l t s in the formation of a clean f rac tu re running from one hole to the next . The detonic p r i n c i p l e s of t h i s ac t ion have already been discussed in Sect ion 3 .1 .3 . The main charge i s then f i r e d using an appropr i -ate number of delays to prevent v i b r a t i o n a l damage to the rock s lope . Upon excavat ion , a good pre-shear face i s charac ter i zed by a clean face running across the p a r a l l e l h a l f - b l a s t h o l e s as i l l u s t r a t e d in Plate 7. The extra costs involved in the denser d r i l l i n g pattern of pre-shear ing can be o f f s e t by the reduced excavation costs brought about by the e l imina t ion of overbreak. This a lso leads to the advantages of increased s a f e t y , savings on s c a l i n g operat ions and r e a l i z a t i o n of the steepest s tab le slope angle . In a mining opera t ion , the requirement f o r small diameter angled holes may mean that add i t iona l d r i l l s have to be purchased j u s t f o r the pre-shear ho les . Although t h i s is necessary f o r the best r e s u l t s , some mines are loathe to take on the costs of extra d r i l l i n g equipment. If only the large diameter production b las tho le r igs are a v a i l a b l e , a rough form of pre-shear ing can s t i l l be c a r r i e d out but some experimentation may be required to achieve an acceptable r e s u l t . The main problem involves get t ing proper d i s t r i b u t i o n of the l i g h t exp los ive charge within the l a rger ho le . This usua l ly involves the time consuming process of p lac ing the explos ive in smal ler cardboard tubes which are centred in the b l a s t h o l e . In g e n e r a l , pre-shear ing with large diameter holes can only be attempted in competent rock and the c h a r a c t e r i s t i c pattern of h a l f - b l a s t h o l e s is r a r e l y v i s i b l e on the f i n a l f a c e . For a number of years i t was commonly thought that the pre-shear f rac ture protected the rock behind i t from v i b r a t i o n s induced by the main b l a s t . This i s now known not to be the case s ince these v i b r a t i o n s are induced by compres-- 1 1 0 -s ive s t r a i n waves which are unable to not ice a pre-shear f rac tu re unless i t i s greater than 1 0 mm. a c r o s s . However, th is f rac ture plane can provide a vent path f o r the expanding explos ive gases, preventing rad ia l cracks from propagating across the pre-shear l i n e . When pre-shear b l a s t i n g i s s u c c e s s f u l , the r e s u l t s can be spec tacu la r . However, t h i s has tended to r e s u l t in an o v e r s e l l i n g of the technique into rock mass condi t ions which are not appropr ia te . Pre-shear ing can a c t u a l l y cause more harm than good i f appl ied in h ighly f rac tured rock masses, e s p e c i -a l l y where the j o i n t s are open, cont inuous, and i n c l i n e d to the pre-shear l i n e . Th is is because the pre-shear b l a s t i s completely "choked" such that the expanding gases are trapped and w i l l r e a d i l y t rave l out in to the j o i n t s . This weakens the f i n a l slope and can r e s u l t in extensive overbreak because f r a c t u r i n g w i l l fo l low the j o i n t s rather than the pre-shear l i n e . G e n e r a l l y , pre-shear b l a s t i n g works well in any rock type as long as the s t ructure i s f a i r l y massive with t i g h t , well spaced j o i n t s . It should not be used in a rock mass with a high natural f rac ture frequency. Results can be equal ly good in both hard and so f t rock i f the proper explosive i s used but the smoothness of the f i n a l wall a c t u a l l y depends on the d r i l l i n g accuracy as much as any other f a c t o r . Many mines present ly employing pre-shear b l a s t i n g are doing so with t h e i r f u l l s i ze rotary d r i l l s on reduced hole spac ings. Although the end r e s u l t i s usua l ly acceptab le , much bet ter control can be achieved with smal ler d i a -meter d r i l l s such as those used, at La Cananea Mine in M e x i c o . 3 Unfor tunate ly , many mines look only at the d r i l l i n g costs and not the slope s t a b i l i t y b e n e f i t s , r e j e c t i n g the use of a small d r i l l f o r p r e - s h e a r i n g . However, on s i t e s where small diameter d r i l l s are in use , they are found to be valuable f o r a wide range of odd jobs in add i t ion to t h e i r pre-shear d r i l l i n g . - Ill -5.1.2 Cushion B l a s t i n g : Cushion b l a s t i n g , sometimes re fe r red to as s lash ing or tr imming, requires exact ly the same b las tho le pattern as fo r pre-shear ing with c l o s e l y spaced holes d r i l l e d along the f i n a l breakage plane. The only d i f fe rence between the two methods i s the detonation sequence. In cushion b l a s t i n g , the main port ion of the perimeter b l a s t is usua l ly f i r e d and excavated f i r s t . This leaves a great ly reduced burden on the f i n a l row of c l o s e l y spaced h o l e s , permit t ing the use of l i g h t , decoupled charges and rapid re lease of b l a s t i n g energy. The f i r i n g of t h i s f i n a l row trims o f f the remaining rock , producing a c l e a n , low maintenance face very s i m i l a r to that of a pre-shear b l a s t . See Plate 12. Cushion b l a s t i n g can be appl ied in cases where the s i t e i s g e o l o g i c a l l y unsui tab le f o r pre -shear ing but where good face contro l i s requ i red . It can be used in weak rock masses with a high i n t e n s i t y of natural f r a c t u r i n g because the excess explos ive gases e a s i l y vent out in to the l i g h t burden without damaging the backslope. As a fu r ther advantage, l a rger s i zed production d r i l l i n g equip-ment can be used with reasonable success s ince i t i s not necessary to achieve the unique rock f r a c t u r i n g ac t ion of pre -shear ing between the ho les . The p r i n c i p a l disadvantage to cushion b l a s t i n g in a mining operat ion i s the d i f f i c u l t y caused in sequencing the d r i l l i n g , b l a s t i n g and excavating opera t ions . The f i n a l row of holes often have to be d r i l l e d a f t e r the f ront por t ion of the b l a s t has been f i r e d , e s p e c i a l l y in weak or h ighly f rac tured rock , otherwise they would tend to cave or become c u t - o f f . A l s o , sequencing f o r the shovel can be awkward s ince i t must excavate most of the b las t at one stage and then return a few days l a t e r to excavate the f i n a l trimming. For these reasons, many mines have adopted a modif ied form of cushion b l a s t i n g where the cushion hole row is detonated on the l a s t delay of the main por t ion of the b l a s t . However, i f t h i s approach i s used, i t i s important to use a long enough f i n a l delay to al low a q u a s i - f r e e face to develop on - 1 1 2 -PLATE 12 C u s h i o n b l a s t i n g was u s e d t o c r e a t e t h i s c l e a n , l o w m a i n t e n a n c e r o c k f a c e i n t h e v e r y weak and h i g h l y f r a c t u r e d Kamloops V o l c a n i c f o r m a t i o n . - 113 -the cushion row. Otherwise, t h i s modif ied method w i l l produce a s i m i l a r r e s u l t to good q u a l i t y buf fe r b l a s t i n g , but at l e s s e r economy. Thus, the schedul ing headaches in an e f f i c i e n t l y operated open p i t with high equipment u t i l i z a t i o n w i l l often d i s q u a l i f y true cushion b l a s t i n g as a p r a c t i c a l s o l u t i o n . However, t h i s method w i l l continue to be very valuable in the f i e l d of c i v i l engineering and should not be overlooked when faced with i s o l a t e d t rouble spots' of bad rock wi th in an open p i t opera t ion . 5.1.3 Buf fer B l a s t i n g : Buf fer b l a s t i n g i s the most simple and economical method of c o n t r o l l e d b l a s t i n g , accounting f o r i t s use throughout the mining indust ry . It does not require the c l o s e l y spaced, angled , small diameter b las tho les as in pre-shear or cushion b l a s t i n g , thereby reducing d r i l l i n g costs and speeding up the en t i re opera t ion . Th is method simply requires a modi f ica t ion to the burden, spacing and exp los ive load on the l a s t row in the perimeter b l a s t pa t te rn . In t h i s row, f u l l s i z e production holes are d r i l l e d v e r t i c a l l y at some o f f s e t d istance from the f i n a l d i g l i n e . The aim is to reduce groundshock from the b l a s t , but c l e a r l y there is a l i m i t to the s i z e of the o f f s e t d istance before unacceptable digging condi t ions are created at the f i n a l d i g l i n e . The burden and spacing f o r the buf fe r row are simply reduced to 0.5 to 0.8 times that of the adjacent production row. The f i n a l buf fe r row is f i r e d with the rest of the perimeter b l a s t , using f a i r l y long delay elements to ensure that i t f i r e s l a s t and towards a f ree f a c e . E s s e n t i a l l y , buf fe r b l a s t i n g is a form of c o n t r o l l e d backbreak along the f i n a l row. The smal ler burden and reduced spacing permits l i g h t e r charges f o r bet ter contro l of the f r a c t u r i n g and l i t t l e time i s required before the optimum o f f s e t d istance becomes apparent. T y p i c a l l y , the buf fer holes are placed with t h e i r bases at or near the projected toe of the f i n a l s lope . - 114 -The p r i n c i p a l advantages of buf fer b l a s t i n g include the a b i l i t y to d r i l l v e r t i c a l holes with the main production d r i l l s and the f i r i n g of the en t i re pattern in one stage instead of two. While the smoothness of the f i n a l face cannot be compared with that obtained by pre-shear or cushion b l a s t i n g , t h i s i s usua l ly compensated f o r by savings in d r i l l i n g and b l a s t i n g procedures. It may produce minor c r e s t f r a c t u r i n g or backbreak, but the amount of damage i s much less than would be produced by the main production b l a s t i f no c o n t o l -led b l a s t i n g was used at a l l . 4 Buffer b l a s t i n g works well over a broad range of rock mass c o n d i t i o n s , but extra care in design is required when working with hard or massive rock in order t o avoid coarse f ragmentat ion, high p i t f l o o r s and excessive back-b r e a k . 5 S i m i l a r l y , care i s required when deal ing with weak, incompetent rock which i s suscept ib le to extensive backbreak and s t a b i l i t y problems. When dea l ing with these extremes in rock mass c o n d i t i o n s , buf fer b l a s t i n g may not be economical or w i l l probably have to be used in conjunct ion with some other c o n t r o l l e d b l a s t i n g technique such as p r e - s h e a r i n g . 4 G e n e r a l l y , the f l e x i b i l i t y in the design of a buf fer b l a s t method as well as i t s ease of implementation has made i t popular throughout the wor ld. Case studies have descr ibed i t s successfu l a p p l i c a t i o n at the Bong Mine in L i b e r i a 6 and some fur ther development work has been done at the Adams Mine 7 in Ontario where experiments have attempted to re f ine the technique. - 115 -5.2 BLASTING DESIGN PARAMETERS A b l a s t design is made up of several parameters which work together to produce the f i n a l des i red r e s u l t s . However, changing any one of the parameters can d r a s t i c a l l y a l t e r the outcome of the b l a s t . This f a c t makes i t d i f f i c u l t to t r u l y optimize each parameter s ince the number of poss ib le v a r i a t i o n s and combinations are fa r too numerous f o r actual f i e l d t e s t i n g in each of the d i f f e r e n t rock zones. This sec t ion w i l l examine each of the b l a s t design parameters in r e l a t i o n to t h e i r in f luence upon the b las t behaviour and t h e i r in f luence upon the amount of damage to the surrounding, i n t a c t rock. These parameters are presented in a sequence which might be used when undertaking a b l a s t design at a new s i t e where no previous b l a s t i b i l i t y data i s a v a i l a b l e . Refer to F igure 5.2-1 f o r an i l l u s t r a t i o n of the terms and parameters d i s c u s s e d . 5.2.1 B las tho le Diameter: In recent years there has been a tendency in open p i t work to d r i l l b l a s t -holes of increas ing diameter. This tendency has been f a c i l i t a t e d by develop-ment of large e l e c t r i c rotary machines, improvements in b i t technology and extensive use of bu lk , s i te -mixed e x p l o s i v e s . The cost benef i ts to be gained by increas ing the diameter of the b las tho le are shown in Table 1. Although the cost per l i t r e suggests that there i s fu r ther benef i t to be gained by going to very large h o l e s , there i s an upper l i m i t . Since e f f e c t i v e charge u t i l i z a t i o n i s achieved with a burden at 40 . t imes. the hole diameter, large holes w i l l r e s u l t in a burden with the same dimensions as the bench he ight . This proport ion i s very i n e f f i c i e n t and Persson 8 suggests that the b las tho le diameter be l i m i t e d by the fo l lowing r e l a t i o n : B las tho le Diameter < B e n c h H e i 9 h t 40 Large diameter b las tho les a lso contain too high an explos ive concentrat ion f o r proper damage c o n t r o l , leading to excessive f r a c t u r i n g of the remaining FIGURE 5.2-1 = BENCH BLASTING TERMINOLOGY AND DESIGN PARAMETERS - 117 -TABLE I BLASTHOLE DIAMETER, VOLUME AND COST Hole Diameter Inches Mi l l imet res 1 2 3 4 6 10 15 20 25.4 50.8 76.2 101.6 152.4 254.0 381.0 508.0 Hole Volume  1 i t r e s / m . 0.51 2.03 4.56 8.11 18.2 50.7 114.0 203.0 Hole Cost* ( in grani te) $/m. $ / l i t r e 1.0 2.0 3.1 4.1 6.1 10.1 15.2 20.3 2.0 1.0 0.67 0.50 0.33 0.20 0.13 0.10 * 1975 c o s t s , a f t e r Persson £ - 118 -rock. As the explos ive impact i n t e n s i f i e s , a i r b l a s t problems are increased and f l y r o c k has been known to t ravel up to 1 k i l o m e t r e . 9 A b l a s t i n g engineer has to compromise between the apparent cost savings of large b las tho les and the problems r e s u l t i n g from them. The engineer would be well advised to inves t iga te the matter extremely thoroughly and to d iscuss h is recommendations with b l a s t i n g engineers at other mines with s i m i l a r rock types and production requirements before committing management to the high cap i ta l cost investment in something as important as a d r i l l r i g . 2 5 . 2 . 2 Explos ive Type: The cons idera t ions f o r the s e l e c t i o n of an appropr iate explos ive type have already been d e t a i l e d in Sect ion 2 . 1 . 9 . For large sca le opera t ions , s e l e c t i o n s should be l i m i t e d to bulk explo-s ives f o r easy s torage , t r a n s p o r t , handling and l o a d i n g . As discussed in the chapter on e x p l o s i v e s , compatible detonating mater ia ls and b l a s t i n g acces-sor ies must a lso be chosen to develop a complete b l a s t i n g system. Explosive manufacturers and supp l ie rs are best able to advise on some of these d e t a i l s . In g e n e r a l , rock which i s already weakened by a high i n t e n s i t y of natural f r a c t u r i n g requires more heaving ac t ion than breaking a c t i o n , making AN/FO a s u i t a b l e c h o i c e . As the rock becomes harder and more massive, explos ives with higher d e n s i t i e s and detonation v e l o c i t i e s w i l l provide the required f r a c t u r i n g power. 5 . 2 . 3 S u b - D r i l l Depth: It i s necessary to extend the b las tho les to a c e r t a i n depth below the intended f l o o r of the excavation in order to completely break the rock between the b las tho les down to the required l e v e l . Poor fragmentation at bench grade can lead to very expensive shovel operat ion due to delays and can leave a hummocky surface which i s very hard on haulage truck suspension and s tee r ing systems. - 119 -Breakage usua l ly pro jects from the base of the bottom charge in the form of an inverted cone with the s ides i n c l i n e d at an angle of 15° to 25° to the h o r i z o n t a l . 2 See Figure 5 .2-2 . The breakage angle w i l l vary with rock strength and o r i e n t a t i o n of dominant s t ruc tu ra l f e a t u r e s . In h o r i z o n t a l l y bedded or well j o i n t e d rock i t i s often unnecessary to employ heavy toe loads or subgrade d r i l l i n g s ince the rock has a large radius of rupture under these condi t ions and w i l l break out more e a s i l y . In mult i -row b l a s t i n g , the breakage cones i n t e r s e c t to give a reasonably even t r a n s i t i o n from broken to undamaged rock. Experience has shown that a s u b - d r i l l depth of 0.2 to 0.3 times the d istance to the adjacent b las tho le is usua l ly adequate to ensure e f f e c t i v e digging at bench g r a d e . 2 In the p i t perimeter b l a s t s , c e r t a i n b las tho les w i l l be on top of the underly ing bench c res t p o s i t i o n . In these holes the s u b - d r i l l depth should be reduced or even e l iminated to avoid damaging and d e s t a b i l i z i n g the future bench. S i m i l a r l y , s u b - d r i l l i n g should be minimized in b las tho les along the f i n a l d i g l i n e to avoid c rea t ing a weakened toe zone on the bench above. In areas with known seepage or ponding problems, e s p e c i a l l y adjacent to haulage ramps, s l i g h t l y increased s u b - d r i l l depths can help to improve d r a i n a g e . 4 A fur ther reason f o r over -est imat ing s u b - d r i l l depth i s to al low f o r minor b las tho le caving which i n e v i t a b l y fo l lows the removal of the d r i l l stem. Although the amount of caving w i l l vary with geologic and hydraul ic c o n d i t i o n s , a shortened hole can lead to poor b l a s t performance and a rough bench g r a d e . 1 0 It i s much e a s i e r to br ing an o v e r d r i l l e d hole back to i t s proper depth with a few scoops of d r i l l cu t t ings than i t i s to t ry blowing out a shortened ho le . •j 5.2.4 Stemming: The upper unloaded port ion of the b l a s t h o l e , known as the c o l l a r , i s usua l ly b a c k f i l l e d with some form of granular material known as stemming. - 1 2 0 -yr Ground Surfoce f Bench Grade — .—• T Sub- Drill Depth — \ ~~ -FIGURE 5.2-2 = ROCK BREAKAGE AT THE BOTTOM OF A BLASTHOLE DUE TO SUB-DRILLING (after Hoek S Bray 2) - 121 -The use of stemming i s a genera l ly accepted procedure f o r conta in ing the . i n i t i a l b l a s t energy and d i r e c t i n g the explos ive e f f o r t in to the rock. Too l i t t l e stemming w i l l a l low the explosion gases to vent prematurely and w i l l generate f l y r o c k and a i r b l a s t problems as well as reduce b l a s t e f f e c t i v e n e s s . 9 Too much stemming means the explos ive load i s too low in the hole and w i l l produce c o a r s e , blocky muck on the upper l ayer of the b l a s t . The stemming height var ies from 12 times the charge diameter in hard competent rock with s t a t i c compressive strength > 210 MPa to 22 times the charge diameter in s o f t e r rock with a s t a t i c compressive strength of approx-imately 100 MPa. The stemming can be increased up to 30 diameters f o r s o f t incompetent rock with a s t a t i c compressive strength of 35 MPa. 4 Frequent open j o i n t s w i l l require a la rger c o l l a r s ince th is type of rock i s more apt to c r a t e r at the s u r f a c e . Although stemming should c o n s i s t of well graded granular mater ial (10 to 15 mm. crushed r o c k ) , d r i l l cu t t ings are almost u n i v e r s a l l y used because they are the most convenient and cheapest mater ial a v a i l a b l e . 5.2.5 Optimum Charge: The optimum charge i s simply the amount of exp los ive which w i l l a t t a i n maximum u t i l i z a t i o n of the b l a s t h o l e . Once the above parameters are known, the optimum charge may be c a l c u l a t e d by mu l t ip ly ing the a v a i l a b l e hole capac i ty by the explos ive dens i ty : D 2 Optimum Charge = y x TT x - x (H + SD - C) 4 where: y = exp los ive densi ty ( kg . /m . 3 ) : . D = b las tho le diameter (m.) H = bench height (m.) SD = s u b - d r i l l depth (m.) C = c o l l a r height (m.) The higher the densi ty or bulk s t rength , the greater the explos ive energy - 122 -that can be contained within the b l a s t h o l e . In add i t ion to c a l c u l a t i n g the optimum charge, i t i s advisable to e s t i -mate maximum and minimum charges from minimum and maximum stemming requirements. 5.2.6 Powder Factor and Burden Volume: Powder f a c t o r is a very useful r a t i o of the quant i ty of exp los ive r e q u i r -ed to fragment a c e r t a i n volume of rock and is usua l ly expressed as k g . / m . 3 or kg . / tonne . However, i f the b l a s t designer is faced with a s i t e where no previous b l a s t i n g tes ts have been done, then i t i s l i k e l y that he w i l l not have any idea of an appropr iate powder f a c t o r f o r the geologica l condi t ions present . Experienced b l a s t e r s are often able to estimate a f a i r l y c lose i n i t i a l v a l u e , but even they may have to make a few tes t b las ts before c l o s i n g in on the cor rec t va lue . To date , i t has been d i f f i c u l t to guess a cor rec t i n i t i a l powder f a c t o r due to the complex in f luences of so many rock mass p r o p e r t i e s . This research pro jec t has concentrated on improving powder f a c t o r p r e d i c t a b i l i t y before a l o t of rock slope damage is caused by overloaded tes t b l a s t s . The r e s u l t s are d e t a i l e d in Chapter 6. Once a powder f a c t o r value has been s e l e c t e d , the volume of rock burden on each b las tho le can be simply c a l c u l a t e d by d i v i d i n g the powder f a c t o r into the optimum charge: Burden Volume = Optimum Charge Powder Factor It i s often convenient to convert the b las tho le burden from a volume to a surface area value by d i v i d i n g i t by the bench he ight . 5.2.7 B las tho le Pat tern: E s t a b l i s h i n g a b las tho le pattern requires the determination of hole spac-ings along each row and the burdens in f ront of the rows. I f the surface area of the b las tho le burden is known, then the required values of burden - 123 -and spacing can e a s i l y be c a l c u l a t e d a f t e r s e l e c t i n g an appropr iate burden to spacing r a t i o . Although there are many poss ib le pa t te rns , there are a few basic con f igur -at ions which are most accepted. See Figure 5 .2 -3 . With a burden to spacing r a t i o of 1:1, the square pattern i s the s implest to lay out . However, b l a s t i n g tes ts c a r r i e d out in both the f i e l d and the laboratory have shown that i t i s important to reduce the burden and to l e t the spacing i n c r e a s e . 1 1 ' 1 2 In p r a c t i c e , many mines use rectangular patterns with burden to spacing r a t i o s of 1:2. A bet ter charge d i s t r i b u t i o n is achieved by the use of the staggered pattern where the holes are located at the apices of e q u i l a t e r a l t r i a n g l e s . This type of pattern is known in c rys ta l lography as the hexagonal c lose packed system and represents the most per fec t d i s t r i b u t i o n of points wi th in a mass. This staggered pattern has a burden to spacing r a t i o of 1:1.15 and i s most appropr iate in b l a s t i n g weak o r h igh ly j o i n t e d rock. In hard competent rock , bet ter fragmentation can be achieved by using the "Swedish" pa t te rn . Burden to spacing r a t i o s ranging from 1:4 up to 1:8 have been used s u c c e s s f u l l y . 8 It should be noted that the burden and spacing values as l a i d out on a g r id bas is of rows and columns are known as the e f f e c t i v e burden and e f f e c t - , t i v e spac ing . This i s because the actual burden and spacing values during detonation may be a l t e red due to the choice of delayed f i r i n g sequence. Once the e f f e c t i v e burden and spacing values have been determined, the prev ious ly c a l c u l a t e d s u b - d r i l l depths should be checked to make sure they w i l l be adequate. It i s bet ter ,to i t e r a t e while in the design stage than engaging in c o s t l y b l a s t i n g t e s t s . 5.2.8 Front Row Cons idera t ions : Successful movement of the f ront row burden i s essent ia l f o r the success of the overa l l b las t and deserves spec ia l a t t e n t i o n . Excessive charge leads - 124 -T-T—T—~) y-Tr-n—pr i i i—ro--pr T n r S Q U A R E P A T T E R N Burden /Spac ing Ratio = h i 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 n — r ~ r r r j — » — ^ n—r " u — r T 7 S T A G G E R E D P A T T E R N B u r d e n / S p a c i n g Ratio = I = 1.15 o o o o o o o o o o o o o o o o~" o o T~J~^\~i ' I—T—n^j | n — r T ^ T n r-|— \ > I T T SWEDISH P A T T E R N B u r d e n / S p a c i n g Ratio = l ; 4 FIGURE 5 . 2 - 3 • VARIOUS PATTERNS COMMONLY USED PERIMETER BLASTING (after Hoek 8 B r a y z ) - 125 -to blow outs and f l y r o c k at the f ree f a c e , r e s u l t i n g in a hazard to equipment and a wastage of e x p l o s i v e . Too small a charge w i l l not i n i t i a t e the necessary motion of the burden, r e s u l t i n g in a choking of the b l a s t on subsequent rows. A cor rec t f ront row charge i s a key to economic b l a s t i n g . However, the i r r e g u l a r i t y of the f ront burden and bench face makes accurate charge c a l c u l a t i o n s d i f f i c u l t . If v e r t i c a l b las tho les are being used and the bench face i s i n c l i n e d as a r e s u l t of the shove l ' s d igging ang le , the f ron t row burden w i l l vary with depth as i l l u s t r a t e d in Figure 5 .2-4. For t h i s reason, the mean burden i s the cor rec t value to use in f ront row charge design c a l c u l a t i o n s . The slope of the bench face can a lso be deal t with by using a higher energy toe load in the f ront holes to ensure re lease at the bench toe . A l t e r -n a t i v e l y , the b las tho les could be i n c l i n e d to provide a more uniform burden. If the f ree face i s uneven with l a rger burdens at c e r t a i n p o i n t s , extra holes known as easer holes can be placed in the excess m a t e r i a l . However, t h i s i s a time consuming p rac t i ce and should be avoided by provid ing very c l e a r dig l i m i t l i n e s f o r the shovel opera tors . 5.2.9 I n i t i a t i n g and F i r i n g Sequence: The s e l e c t i o n of a good i n i t i a t i o n and f i r i n g sequence i s a most v i t a l step in designing a successfu l b l a s t . 1 3 By s t r a t e g i c a l l y loca t ing a number of delay elements wi thin the b l a s t p a t t e r n , the b l a s t e r w i l l not only reduce the v i b r a t i o n a l damage d iscussed in Sect ion 4 . 2 , but w i l l improve the e f f i c i -ency of the b l a s t by ensuring each b las tho le w i l l detonate towards a f r e s h l y created f ree f a c e . Although there are several standard f i r i n g sequences as shown in Figure 5 .2 -5 , a great deal of freedom and o r i g i n a l i t y can be used, e s p e c i a l l y when designing f o r s p e c i f i c b l a s t s i t e c o n f i g u r a t i o n s . T r a d i t i o n a l l y , b l a s t s were f i r e d row-by-row, but as bench b l a s t patterns became longer , the charge weight per delay became excess ive . As a r e s u l t , - 126 -FIGURE 5 . 2 - 4 » DESIGN PARAMETERS FOR THE CRITICAL FRONT ROW BURDEN - 1 2 7 -vi \ r i f-i pi | j — r ~ i ; — — r ~ 7 — r ROW- B Y - R O W FIRING SEQUENCE r r r r — r i / i 17"x^nnp~T--T-7--rT~7—7 ALONG-THE-ROW FIRING SEQUENCE V E E ' CUT AND EN E C H E L O N FIRING S E Q U E N C E FIGURE 5 . 2 - 5 = VARIOUS FIRING SEQUENCES COMMONLY USED IN PERIMETER BLASTING (a f ter Hoek a B r a y 2 ) - 128 -row-by-row f i r i n g was modif ied to along-the-row f i r i n g where each row is broken into shorter segments. However, the number of rows f i r e d per b l a s t should not exceed 4 to 6 in order to prevent the f i n a l rows from becoming choked. An a l t e r n a t i v e method is to f i r e the b las t en eche lon , thereby reducing the maximum number of holes per delay to twice the number of rows in the pat-t e r n . It should be noted that the burden to spacing r a t i o created by t h i s f i r i n g method i s considerably l ess than the e f f e c t i v e burden to spacing r a t i o . For example, a square pattern with an e f f e c t i v e r a t i o of 1:1 w i l l have a r a t i o of 1:2 upon detonat ion. Th is can provide bet ter fragmentation without the cost of extra d r i l l i n g . En echelon f i r i n g can be i n i t i a t e d from a f ree end of the bench or by s t a r t i n g with a "Vee" cut in the centre of the pa t te rn . The length of delay i n t e r v a l s i s usua l ly d ic ta ted by loca l ground c o n d i -t ions and t h e i r behaviour during the b l a s t . For a surface delayed system, i n t e r v a l s from 2 to 6 m i l l i seconds per metre of burden are t y p i c a l . 1 1 * Gener-a l l y , the longest delay element that can be used between f i r i n g l i n e s without leading to c u t o f f s in undetonated holes w i l l produce the best r e s u l t s . This longer time ensures that a good q u a s i - f r e e face has had time to develop in f ront of each succeeding detonat ion. In weak fragmented rock where hole cu to f fs can be a problem, down-the-hole delay systems may provide greater s e c u r i t y and permit in ter - row delays of 50 to 100 m i l l i s e c o n d s . The i n i t i a t i n g of a l l charges i s c r i t i c a l to the success of the en t i re b l a s t . Care must be taken when planning the surface layout of detonating cord so that there i s more than one poss ib le f i r i n g path to each ho le . A great va r i e ty of i n i t i a t i n g and f i r i n g methods have been t e s t e d 1 5 s ince they are a key f a c t o r in; achiev ing optimum;fragmentation with minimal damage to the surrounding rock. - 129 -5.3 BLAST EVALUATION AND OPTIMIZATION B las t evaluat ion is a very important step in the overa l l design process. It i s only by care fu l study and ana lys is of the b l a s t i n g r e s u l t s that i t i s poss ib le to make proper adjustments f o r working towards b l a s t op t im iza t ion . Observations made both during and a f t e r detonation are valuable in assess ing the b l a s t behaviour. 5.3.1 During Detonat ion: Since the actual detonation happens so q u i c k l y , the use of high speed c ine cameras are r e a l l y necessary to be able to do any d e t a i l e d study of the b l a s t m o t i o n . 1 6 Unfor tunate ly , such studies are expensive and are reserved f o r spec ia l p r o j e c t s . However, a l o t of useful information can be gleaned by an experienced observer . The onset of movement of the f ront burden can usua l ly be seen and the observer should watch f o r an evenness of l i f t and the presence of any f l y r o c k . Lack of c l e a r motion may ind ica te inadequate f ront row charges, r e s u l t i n g in a choked b l a s t . A l s o , the rhythmic sound of the r a p i d l y f i r i n g delayed charges provides an audib le check f o r any m i s f i r e s in the pa t te rn . The appearance o f orange-brown ni t rogen dioxide fumes ind ica tes excess o x i d i z e r or d e f i c i e n t f u e l . Nitrogen oxides are sometimes emitted by ammonium n i t r a t e compounds in broken or wet ground. This could mean that l i n e r bags w i l l be necessary to protect the e x p l o s i v e . Black smoke i s i n d i c a t i v e of an explos ive too r i c h in fue l or d e f i c i e n t in o x i d i z e r . The appearance of abnormal smoke should be fol lowed by a check into the mixing of the explos ives and the implacement in the ground. 5.3.2 A f t e r Detonation: When the dust and fumes have d i s p e r s e d , the b l a s t i n g engineer can assess the success of a b l a s t by walking over and around the b l a s t i n g area to c l o s e l y inspect the shape and d e t a i l s of the muck p i l e . See Figure 5 .3 -1 . FIGURE 5.3-1 • CHARACTERISTIC FEATURES OF A SUCCESSFUL PERIMETER BLAST - 1 3 1 -The f ront row should have moved out even ly , but not too f a r . Excessive throw i s not necessary and only adds to the amount of c o s t l y cleanup time required before the excavating equipment can move i n . The fragmentation should appear to be even and cons is ten t across the face of the muck p i l e . There should be a s l i g h t and even l i f t along the c r e s t of the muck p i l e . Since most bench heights are designed f o r e f f i c i e n t shovel o p e r a t i o n , low muck p i l e s represent low p roduc t i v i t y and high cost c leanup. The upper surface of the muck should look evenly fragmented and not hum-mocky. F l a t areas are c l e a r signs of m i s f i r e s . This could be caused by poor surface t i e - i n s or a r e s u l t of long delays leading to b las tho le c u t o f f s . Isolated surface c ra te rs w i l l i nd ica te excessive hole charge or i n s u f f i -c i e n t stemming. An area of several surface c ra te rs or humped up ground is usua l ly a s ign that the area became choked during the f i r i n g sequence. This could be caused by inadequate charges or by short delays which do not permit f ree faces to form or by too many holes f i r i n g together s imul taneously . The back area of the muck should be character i zed by a s l i g h t drop , i n d i c a t i n g a good forward movement to the f ree f a c e . C lear tension cracks should be v i s i b l e in f ron t of the f i n a l d i g l i n e . Any v i s i b l e cracking on surface (behind the f i n a l d i g l i n e d e f i n i t e l y ind ica tes damage to the backslope and a wastage o f e x p l o s i v e . This could be due to overs ize hole charges, exces-s ive stemming, or excessive burden on the c r i t i c a l f i n a l row. In genera l , an e f f e c t i v e forward movement and ro ta t ion of the b lasted rock mass towards a f ree face i s the best i n d i c a t i o n of a s a t i s f a c t o r y b l a s t . Observations during the excavating stage are a lso important. Fragmenta-t ion should be reasonably even throughout the b l a s t without the need f o r any secondary d r i l l i n g and b l a s t i n g . The muck should not be too t igh t in order to permit an economical d igging r a t e . Coarse or blocky ground in the upper l ayer usua l ly ind ica tes overs ized c o l l a r s and excessive stemming, although well def ined hor izonta l bedding can produce s i m i l a r r e s u l t s . Coarse or blocky - 1 3 2 -ground at the bottom of the b l a s t may ind ica te i n s u f f i c i e n t s u b - d r i l l i n g or the need f o r higher energy toe charges in the b l a s t h o l e s . Apart from the general c h a r a c t e r i s t i c s seen throughout the b l a s t a r e a , any unusual i s o l a t e d features which may seem i n e x p l i c a b l e can 'o f ten beconnected to l o c a l i z e d geologica l changes. The presence of weak shear zones or hard i n t r u s i v e s t r i n g e r s which were i n v i s i b l e before excavating should be noted and t h e i r presence expected on the next! bench below. Upon completion of the excavat ion , the f i n a l face should be c l o s e l y exam-ined f o r any damage such as backbreak or open f r a c t u r e s . A l s o , long term observat ions of any r a v e l l i n g tendency may ind ica te the degree of damage i n f l i c t e d on the rock s lope . Once the b l a s t eva luat ion i s complete, the b l a s t i n g engineer must decide whether the r e s u l t s are s a t i s f a c t o r y . If not , i t may be necessary to embark on a s e r i e s of modi f ica t ions and b l a s t i n g tes ts in order to a r r i v e at an optimum des ign . Wherever p o s s i b l e , only one va r iab le should be changed at a time:.and the b l a s t r e s u l t s c a r e f u l l y documented with notes and photographs f o r comparison with other t es t b l a s t s . With the large number of design parameters a v a i l a b l e f o r adjustment, the opt imizat ion procedure can become complex. The best way to modify the b l a s t i s to s e l e c t the parameter which i s the eas ies t to a d j s u t , such as the powder f a c t o r . By holding the geometric parameters constant and varying only the powder f a c t o r , i t should be poss ib le to optimize each b l a s t on a s i t e -s p e c i f i c basis s ince powder f a c t o r var ies most d i r e c t l y with the rock mass p r o p e r t i e s . The c r i t i c a l eva luat ion of the muck p i l e shape, fragmentation and digging condi t ions of each b l a s t is an essent ia l part of every b l a s t i n g opera t ion . Although t h i s evaluat ion is time consuming and therefore expensive, the cost of t h i s eva luat ion i s usua l ly j u s t i f i e d in the development of an e f f i c i e n t , optimized b l a s t i n g s y s t e m . 2 - 133 -4 REFERENCES ) BAUER, A. & CALDER, P . N . : The Influence and Evaluat ion of B las t ing on S t a b i l i t y . Proceedings, F i r s t Internat ional Conference on S t a b i l i t y in Open P i t M in ing , Vancouver, B . C . , AIME, 1971. ) HOEK, E. & BRAY, J . W . : Rock Slope Engineerng, Chapter 11 - B l a s t i n g . Second E d i t i o n , IMM, 1977. ) BROWN, C . C . & BIGANDO, J . : P r e s p l i t t i n g and Smooth Wall B l a s t i n g in La Cananea P i t . Mining Engineer ing , V o l . 24, No. 9, September 1972. ) CALDER, P . N . : P i t Slope Manual, Chapter 7 - Perimeter B l a s t i n g . CANMET (Canada Centre f o r Mineral and Energy Technology) , CANMET Report 77-14, May 1977. ) LANG, L . C . : Buf fer B l a s t i n g Techniques in Open P i t Mines. Proceedings, Second Open P i t Operators Conference, October 1978. ) LANG, L . C . : Mining I tabar i te in the Bong Range in L i b e r i a . Canadian Mining J o u r n a l , V o l . 86, No. 11, November 1965. ) CALDER, P.N. & MORASH, B . J . : P i t Wall Control at Adams Mine. Mining Congress J o u r n a l , V o l . 57, No. 8, August 1971. ) PERSSON, P . A . : Bench D r i l l i n g - An Important F i r s t Step in the Rock Fragmentation Process . A t l a s Copco Bench D r i l l i n g Symposium, Stockholm, 1975. ) LUNDBORG, N . , PERSSON, A . , LADEGAARD-PEDERSEN, A. & HOLMBERG, R.: Keeping the L i d on F lyrock in Open P i t B l a s t i n g . Engineering and Mining J o u r n a l , V o l . 176, No. 5, May 1975. ) COLLINS, J . L . , GALIBOIS, A . & MONETTE, H . : O v e r d r i l l i n g of Open P i t B l a s t h o l e s . CIM B u l l e t i n , V o l . 64, No. 710, June 1971. ) BHANDARI, S . : Improved Fragmentation by Reduced Burden and More Spacing in B l a s t i n g . Mining Magazine, V o l . 132, No. 3, March 1975. ) BHANDARI, S . : Burden and Spacing Re la t ionships in the Design of B l a s t i n g Pat terns . Proceedings, Sixteenth Symposium on Rock Mechanics, Minneapolis 1975. ) HAGAN, T . N . : I n i t i a t i o n Sequence - V i t a l Element of Open P i t B las t Design Proceedings, Sixteenth Symposium on Rock Mechanics, Minneapol is , 1975. ) WRIGHT, F . D . : M i l l i s e c o n d Delay B l a s t i n g of Bench Rounds. Mining Congress J o u r n a l , V o l . 39, No. 6, June 1953. ) LANG, L . C . : Delay B l a s t i n g Techniques in Open P i t Mines. Proceedings, AIME Annual Meet ing, Chicago, February 1981. ) PAGE, A . P . : High Speed Photographic Study, Gran is le Copper L im i ted . Internal Report , Dupont of Canada L i m i t e d , Explosives D i v i s i o n , October 1978. - 134 -CHAPTER SIX EXPERIMENTAL STUDIES AND FIELD WORK - 135 -6.0 EXPERIMENTAL STUDIES AND FIELD WORK As pointed out in the previous chapters , the powder f a c t o r i s one of the most c r i t i c a l but l e a s t understood parameters in c o n t r o l l e d b l a s t i n g des ign . O f ten , i t i s the major design va r iab le s ince many mining operat ions prefer to keep t h e i r perimeter b l a s t geometry and f i r i n g sequence constant throughout the p i t f o r ease of p lann ing , surveying and d r i l l i n g . While i t has been r e a l -ized f o r many years that the powder f a c t o r value p r i n c i p a l l y depends on the cond i t ion and proper t ies of the rock mass, the r e l a t i o n s h i p is uncertain due to the number of extremely complex i n t e r - r e l a t i o n s h i p s i n v o l v e d , as d iscussed in Sect ion 3 .2 . An optimum powder f a c t o r is usua l ly found a f t e r a s e r i e s of t r i a l - a n d -e r ro r b l a s t s , but t h i s procedure is not economical s ince the des i re to ensure adequate fragmentation usua l ly leads to excessive powder f a c t o r values and consequently damages the ul t imate p i t s l o p e . A r e l i a b l e c o r r e l a t i o n between the rock mass proper t ies and a powder f a c t o r value would lead to great savings by opt imiz ing the b l a s t i n g and by reducing the costs involved with slope stab-i l i t y problems. Since open p i t s usua l ly encompass several d i f f e r e n t geologica l zones or domains, such a c o r r e l a t i o n would permit continued monitoring of changes in the rock mass and b l a s t opt imizat ion in each domain. The f i r s t p r a c t i c a l attempt to answer t h i s problem was made by Carl Broadbent 1 at Kennecott Copper Corporat ion where he developed; a r e l a t i o n s h i p between seismic wave v e l o c i t i e s and powder f a c t o r s . See Sect ion 3 .2 .7 . More r e c e n t l y , John Ashby 2 developed a r e l a t i o n s h i p at Bouga inv i l l e Copper between natural f r a c t u r e frequency and powder f a c t o r s . See Sect ion 3 .2 .2 . While both t h e i r e f for ts- are steps in the r i g h t d i r e c t i o n , each of these c o r r e l a t i o n s involve only one of the many rock mass p r o p e r t i e s , m a k i n g t h e i r a p p l i c a t i o n very s i t e s p e c i f i c . A separate set of c o r r e l a t i o n curves would have to be es tab l ished in each d i f f e r e n t rock type. For th is research p r o j e c t , i t was decided that the approach of e s t a b l i s h -- 1 3 6 -ing empir ical c o r r e l a t i o n s with dominant rock mass features was probably the most e f f e c t i v e way to overcome the l i m i t e d understanding of the complex rela--t ionsh ips between rock mass proper t ies and powder f a c t o r s . However, in c o n t i n - ; uing with t h i s research , i t was decided not to se lec t another s i n g l e rock mass property s ince t h i s would a lso produce a c o r r e l a t i o n too s p e c i f i c in s i t e a p p l i c a b i l i t y . Instead, i t was decided to attempt to e s t a b l i s h a powder f a c t o r c o r r e l a t i o n with some measure of rock q u a l i t y , thereby taking account of a large number of the key rock mass proper t ies invo lved . This approach was insp i red by the techniques used by tunnel design engin-e e r s . The problems they face are h ighly analagous to those faced by b l a s t i n g engineers , s ince each i s attempting to gain knowledge about rock condi t ions and proper t ies concealed wi th in the mass to be excavated. To a id in overcoming t h i s c r i t i c a l problem, tunne l l ing engineers have devised several d i f f e r e n t systems of rock mass c l a s s i f i c a t i o n , used to ind ica te the type of t u n n e l l i n g condi t ions or support requirements which may be e n c o u n t e r e d . 3 ' 4 These c l a s s -i f i c a t i o n systems, based on d r i l l i n g r e s u l t s and the ana lys is of recovered c o r e , produce a q u a l i t y ra t ing which can be assessed in l i g h t of past tunne l -l i n g exper ience. To date , B ien iawsk i ' s C . S . I . R . Geomechanics C l a s s i f i c a t i o n and Bar ton 's N .G. I . Tunnel l ing Qual i ty Index have been s u c c e s s f u l l y appl ied in a wide var ie ty of rock mass condi t ions around the wor ld , c l e a r l y i n d i c a t i n g t h e i r a b i l i t y to overcome the problem of s i t e s p e c i f i c r e s t r i c t i o n s . 3 ' 1 * Based on the success of these systems, i t was f e l t that some s i m i l a r sor t of rock q u a l i t y c l a s s i f i c a t i o n could be equal ly well app l ied to the problems of open p i t b l a s t des ign . U l t i m a t e l y , i t was hoped that such a rock q u a l i t y i n d i c a t o r could be cor re la ted to optimum powder fac to rs fo r economcial , c o n t r o l l e d p e r i -meter b l a s t i n g . C l e a r l y , the research f o r th is pro ject could not be c a r r i e d out in any-thing less than a f u l l s c a l e , operat ing open p i t mine. An agreement was made with Afton Operating Corpora t ion , permit t ing the research program to take - 137 -place at Afton Mine which was in need of an improved b l a s t i n g program. Afton Mine proved to be an ideal f a c i l i t y f o r t h i s research pro ject f o r several reasons. F i r s t , the p i t encompassed a broad range of geo log ica l c o n d i -t ions from very weak sediments to hard and massive v o l c a n i c s , making i t pos-s i b l e to obtain rock q u a l i t y measurements from one extreme to the other . Second, the a c t i v e l y mined area of the p i t was small ' enough to ensure that a good number of perimeter b l a s t s , in a l l rock types , could take place during the per iod of f i e l d research . T h i r d , the mine had lacked a D r i l l i n g and B l a s t -ing Foreman f o r some t ime, permit t ing the author to take an a c t i v e and d i r e c t r o l e in planning and executing the b l a s t i n g opera t ions . The f i e l d research was c a r r i e d out at the mine s i t e from the beginning of May to the end of October 1981. In order to achieve the f i n a l o b j e c t i v e , the work was done in f i v e separate phases: 1) E s t a b l i s h i n g a Rock Qua l i ty Index (RQI) value f o r each geologica l domain in the p i t . 2) Designing a new and proper perimeter b l a s t i n g method. 3) Executing tes t b las ts to determine the optimum powder f a c t o r va lues . 4) Der iv ing a c o r r e l a t i o n between RQI values and powder f a c t o r va lues . 5) Tes t ing the proposed c o r r e l a t i o n with fu r ther t es t b l a s t s . The remainder of t h i s chapter d iscusses each of these phases in d e t a i l . Upon completion of the work at the mine s i t e , an Open P i t B l a s t i n g Manual was prepared f o r Afton Operating C o r p o r a t i o n . 5 - 138 -6.1 BACKGROUND INFORMATION ON AFTON MINE 6.1.1 Regional Information: Afton Mine is located a longside the Trans-Canada Highway, 420 km. by road from Vancouver and only 13 km. west of Kamloops, a c i t y of 60,000 people in the south-centra l i n t e r i o r of B r i t i s h Columbia. See Figure 6 .1 -1 . The area i s c e n t r a l l y located at the confluence of the North and South Thompson r i v e r s , and i s served by three major highway a r t e r i e s , by both Canadian P a c i f i c and Canadian National Rai lways, and by P a c i f i c Western A i r l i n e s . The regional economy has min ing, f o r e s t r y , a g r i c u l t u r e and tourism as i t s main i n d u s t r i e s . As a r e s u l t , Kamloops i s a v i t a l commercial and i n d u s t r i a l c e n t r e , well able to serve the neighbouring mining indust ry . The loca l pros-p e r i t y and conveniences of c i t y l i v i n g r e s u l t in low s t a f f turnover which i s an important f a c t o r to the operat ion of Afton Mine. The area i s in the centre of the i n t e r i o r p la teau , bounded by the Coast Mountains to the west and the Monashee Mountains to the eas t . The cl imate i s part of the s e m i - a r i d , co ld steppe formation and supports extensive natural growth of ponderosa pine and bunchgrass. The major c l i m a t i c s t a t i s t i c s , as recorded at the Kamloops a i r p o r t weather s t a t i o n , are l i s t e d in Table 2. At an e leva t ion of 640 m. above sea l e v e l , Afton Mine i s about 300 m. higher than the a i r p o r t , but d i f fe rences between the weather at the two loca t ions are minor. Afton may rece ive s l i g h t l y l ess p r e c i p i t a t i o n , but the proport ion occur r ing as snow would be greater . Winter temperatures at the mine can be 5° to 10°C coo le r than the a i r p o r t , permit t ing a f a i r l y deep f r o s t penetrat ion over the months of sustained sub- f reez ing c o n d i t i o n s . As a r e s u l t , l a te Febru-ary and March are the times of most c r i t i c a l slope s t a b i l i t y as meltwater bu i lds up behind the frozen p i t f a c e s . G e o l o g i c a l l y , Afton Mine i s located in the Quesnel Trough, a 30 to 60 km. wide b e l t of Lower Mesozoic v o l c a n i c s , enclosed between o lder rocks and much FIGURE 6.1-1 • LOCATION MAP FOR AFTON MINE - 140 -TABLE 2 CLIMATIC DATA, KAMLOOPS AIRPORT (Based on 30 years of record) MEAN MEAN MEAN NUMBER OF MONTH TEMPERATURE PRECIPITATION^) DEGREE-DAYS BELOW 0°C January - 6.1 °C 31.6 mm. 217.6 February - .1.3 16.0 81.5 March 3.5 9.7 15.9 A p r i l 9.1 10.4 0.0 May 14.1 18.0 0.0 June 18.0 29.9 0.0 Ju ly 20.8 22.5 0.0 August 19.8 27.5 0.0 September 14.9 24.4 0.0 October 8.4 15.2 0.9 November 1.6 22.0 34.4 December - 2.8 32.3 127.5 Annual T o t a l s : - 259.5 mm. 477.8 deg.-days (*) Rain plus Snow Equivalent Data Obtained From: Environment Canada, Climate Information S e r v i c e s , 1200 West 73rd Avenue, Vancouver, B . C . - 141 -invaded by ba tho l i ths and l e s s e r i n t r u s i o n s . 6 Afton l i e s in the southern part of the t rough, known as the N ico la B e l t , which continues near ly 200 km. southward to i t s terminat ion at the U.S. border and contains the important copper mines of Highland V a l l e y , Craigmont, Copper Mountain and the former Hedley gold camp. In the v i c i n i t y of A f t o n , the Iron Mask d i s t r i c t i s part of a major s t r u c -ture extending northwestward across the Nicola B e l t . See Figure 6 .1-2 . In the southern por t ion of t h i s s t r u c t u r e , the 18 km. long Iron Mask Pluton and the smal ler Cherry Creek Pluton are important f ea tu res . S i g n i f i c a n t known copper occurrences in the d i s t r i c t are a l l in the p lu tons , mainly c lose to the p lu ton ic margins. 6.1.2 H i s t o r i c a l Summary: (from Carr and Reed 6) Except in an o ld prospect p i t near i t s east end, the Afton orebody was hidden by T e r t i a r y and P le is tocene cover up to 27 metres th ick and by a s a l t pond. Numerous small mines occur in the d i s t r i c t and near ly 200,000 tonnes of mater ial was mined between 1891 and 1928. Old workings on the Afton prop-er ty date from t h i s ear ly p e r i o d , and the orebody i t s e l f l i e s pa r t l y on a Crown-granted c la im staked in 1904. Axel Berglund f i r s t staked the Afton claims in 1949. Subsequent d r i l l -ing programs explored the area of the o ld Pothook s h a f t , where modest reserves of 0.6% copper were i n d i c a t e d . Test ing the property widely with scat tered h o l e s , DDH 70-4 encountered pers is ten t low-grade copper m inera l i za t ion near the o ld prospect p i t by the highway. In 1971, when C F . M i l l a r resumed exp lor -a t ion f o r Afton Mines L t d . , he percussion d r i l l e d on a g r i d around t h i s hole and so discovered the Afton orebody. Development of the orebody was begun in 1972 with extensive d r i l l i n g cont inuing to the-end of 1974. Decision f o r production was announced in 1975. The Stage 1 P i t contained 31 m i l l i o n tonnes of ore grading 1.0% copper, - 142 -FIGURE 6 .1 -2 : REGIONAL GEOLOGY AT AFTON MINE ( f r o m Carr and R e e d 6 ) - 143 -0.58 ppm. gold and 4.19 ppm. s i l v e r at a c u t o f f of 0.25% copper and a waste-to-ore r a t i o of 4 . 2 : 1 . Excavation of the Stage 1 P i t was completed at the end of June 1981 and the expanded Stage 2 P i t , 70 metres deep at completion of the f i e l d research program, w i l l u l t imate ly reach a depth of 280 metres at a waste- to-ore r a t i o of 7:1. Open p i t ore reserves are s u f f i c i e n t to main-ta in m i l l production un t i l 1988. The ore is m i l l e d at 8500 tonnes per day, prov id ing a m e t a l l i c concentrate grading about 97% copper and a f l o t a t i o n concentrate grading about 50% copper. About 87% of the copper i s recovered in m i l l i n g . A unique feature of Afton Mine i s the o n - s i t e top blown rotary converter ( T . B . R . C . ) smelter which prod-uces b l i s t e r copper exceeding 99% in p u r i t y . P la te 13 i s an a i rphoto mosaic made in November 1980, prov id ing a d e t a i l -ed view of the e n t i r e Afton Mine s i t e . 6.1.3 Summary of S i t e Geology: Much of the mater ial in t h i s sect ion was prepared by Doug Stewart, A f t o n ' s Chief Engineer , f o r a paper prev ious ly wr i t ten on th is research p r o j e c t . 7 The Afton deposi t i s about 520 metres long and i s e s s e n t i a l l y t a b u l a r , s t r i k i n g N70°W and dipping at 5 5 ° S . The orebody i s d iv ided into two d i s t i n c t -l y d i f f e r e n t zones: a br ight red supergene zone which comprises 80% of the o r e , and a pale grey hypogene zone forming the remainder . 8 The supergene zone extends to a depth of 400 metres and contains m e t a l l i c copper and cha lco -c i t e . The under ly ing hypogene material contains borni te and c h a l c o p y r i t e . The Afton orebody occurs at the northwestern extremity of the Iron Mask P lu ton , a vo lcan ic d i o r i t i c mass which was intruded into the o lder N ico la V o l c a n i c s . D i o r i t e i s the predominant rock type and, with the v o l c a n i c s , i s f lanked to the north by a deep graben s t ructure which i s occupied by younger (Ter t i a ry ) sediments and v o l c a n i c s . The p i t t ransgresses the east-west s t r i k -ing graben s t ructure so that the north wall i s wi th in the younger sediments P L A T E 13 An a e r i a l view of the Afton Mine s i t e , November 1980. - 145 -and vo lcan ics while the remaining p i t i s wi th in d i o r i t e and o lder v o l c a n i c s . Minor occurrences of magnetite v e i n s , a n d e s i t e , serpent ine , and porphyry l a t i t e s are found in the d i o r i t e s and Nico la V o l c a n i c s . The widely var iab le geologica l zones can be c l e a r l y seen in the panoramic view of Plate 14. Var ie ty in the c h a r a c t e r i s t i c s of these rock masses i s provided not only by t h e i r l i t h o l o g y , but by intense a l t e r a t i o n , j o i n t i n g , and f a u l t i n g . The degree of a l t e r a t i o n has been such that d i o r i t e s and vo lcan ics are often macro-s c o p i c a l l y d i f f i c u l t to i d e n t i f y . Near-surface a l t e r a t i o n of f e ldspars to s e r i c i t e and k a o l i n , abundant c h l o r i t e , c a l c i t e , ep ido te , s a u s s u r i t i z a t i o n of f e l d s p a r s , and pi s o l i t i c a l t e r a t i o n to c h l o r i t e in basa l ts a l l ind ica te that a l t e r a t i o n has been s i g n i f i c a n t . Within the orebody, the pervasive d e v e l -opment of supergene ore with s c a l e s , g ranu les , p lates and dendri tes of nat ive copper ind ica tes that the processes of a l t e r a t i o n have long been a c t i v e . J o i n t i n g i s well developed and most of the rocks within the open p i t break r e a d i l y in to blocks smal ler than 600 mm. (2 f t . ) a c r o s s . S t r i ke f a u l t s are s t rongly developed and, together with obl ique f a u l t s and l i t h o l o g i c a l changes, have served to form the well es tab l i shed boundaries of the p i t s t ruc tu ra l domains. See Figure 6.1-3 and Table 3. J o i n t and f a u l t condi t ions vary throughout the p i t with f r i c t i o n angles of about 30° f o r j o i n t s and 21° f o r f a u l t s and s h e a r s . 9 * 1 0 However, f r i c t i o n angles as low as 13° have been determined f o r some d i s c o n t i n u i t i e s with c l a y gouge present on t h e i r s u r f a c e s . Back analyses of f a i l u r e s suggest that cohesion on the f a i l u r e plane was i n i t i a l l y about 24 kPa. (500 p s f . ) . The unconfined compressive strengths vary from about 7 MPa. (1000 p s i . ) in the T e r t i a r y Sediments to over 207 MPa. (30,000 p s i . ) in the dac i te and are depend-ent on the degree of a l t e r a t i o n of the rock. See Table 4. The geology at Afton has been descr ibed in de ta i l by Carr and Reed . 6 PLATE 14 View across A f t o n ' s p i t looking west. The var ious geological un i ts wi th in the p i t are c l e a r l y seen by the d i f f e r e n t coloured zones. FIGURE 6 .1-3 » PIT PLAN SHOWING DOMAIN BOUNDARIES AT AFTON MINE (August 1981) - 148 -TABLE 3 DESCRIPTION OF DOMAINS DOMAIN ROCK TYPES DESCRIPTION II III "IV A & B IV A - Py V VI VII VIII VIII A Iron Mask D i o r i t e N ico la Volcanics Iron Mask D i o r i t e Iron Mask D i o r i t e Iron Mask D i o r i t e Iron Mask D i o r i t e Grey D i o r i t e T e r t i a r y Volcanics T e r t i a r y Sediments T e r t i a r y Volcanics Heavi ly sheared, ep ido te , c h l o r i t e , hematite Magnetite dykes, ep ido te , serpent ine , c a l c i t e Intensely sheared, c l a y gouge, b recc ia Minor dykes, minor a l t e r a t i o n , c h l o r i t e , c a l c i t e P y r i t e m i n e r a l i z a t i o n , moderately a l t e r e d , epidote Some v o l c a n i c s , ep idote , hematite, c h l o r i t e Minor a l t e r a t i o n , some c h l o r i t e , epidote Conformable and unconformable, a n d e s i t e , l a t i t e Mudstone, s h a l e , a rkose , c l a y gouge Dacite as l o p o l i t h s , dykes, s i l l s , very hard - 149 -TABLE 4 HARDNESS OF ROCK TYPES USING JENNINGS'1 HARDNESS CLASSIFICATION ROCK TYPE Mudstone Shale Dacite N i c o l a Vo lcan ics Grey D i o r i t e Hematite P y r i t i c D i o r i t e SCALE OF HARDNESS RI - 2 R2 R5 R4 R2 - 3 R3 R3 APPROXIMATE RANGE OF UNCONFINED COMPRESSIVE STRENGTH ( p . s . i . ) 500 1,000 16,000 8,000 3,000 4,000 4,000 1,500 4,000 32,000 16,000 7,000 8,000 7,000 (MPa.) 3 7 110 55 21 28 28 10 28 228 110 48 55 48 - 150 -6.2 DEVELOPMENT OF THE ROCK QUALITY INDEX In an open p i t opera t ion , an ideal measure of i n - s i t u rock q u a l i t y would be one which could be e a s i l y obtained without add i t iona l costs and personnel , and one which would provide a complete, unbiased coverage of the e n t i r e p i t a rea . None of the i n - s i t u rock mass c l a s s i f i c a t i o n methods cur ren t l y a v a i l a b l e f u l f i l l a l l of these requirements. This research pro ject set out to s a t i s f y as many of these c r i t e r i a as p o s s i b l e . The approach involved the study of rotary d r i l l performance in the broad v a r i e t y of rock types at A f t o n , and the development of index values based on the d r i l l i n g data . If the r e s u l t i n g rock mass index values appeared to be reasonable , then work would continue with the b l a s t i n g tes ts in order to determine optimum powder fac to rs f o r c o r r e l a t i o n purposes. The use of rotary d r i l l s as the p r i n c i p a l monitoring too ls was decided upon f o r several reasons. F i r s t , data c o l l e c t e d from production b las tho le d r i l l i n g provides inexpensive , comprehensive coverage of the p i t because a l l rock mined must be d r i l l e d before being b l a s t e d . Since most mines already keep b las tho le d r i l l i n g records , a rock q u a l i t y measure can be based on the data a l ready a v a i l a b l e and no add i t iona l personnel or equipment are requ i red . Second, the b las tho le wall represents the most c r i t i c a l point of i n t e r a c t i o n between the explos ive and the rock. For th is reason, the b las tho le p o s i t i o n i s the most valuable l o c a t i o n from which to obtain some measure of rock q u a l i t y . T h i r d , a large body o f l i t e r a t u r e i s a v a i l a b l e on the performance mech-an ics of large rotary d r i l l s , suggesting that they w i l l r e f l e c t many of the rock mass proper t ies important to b l a s t i n g . This is pa r t l y because the cu t -t i n g act ion of a d r i l l b i t i s a dynamic rock f r a c t u r i n g act ion in i t s e l f . In order to understand the de r iva t ion of a rock q u a l i t y measurement from rotary d r i l l performance, i t i s necessary to b r i e f l y examine some of the theory of d r i l l i n g mechanics. - 151 -6.2.1 Mechanical Theory of D r i l l Performance: As presented by T e a l e 1 2 , the rotary d r i l l i n g act ion i s accomplished by a combination of two d i s t i n c t , separate a c t i o n s . F i r s t , rock is broken by indentat ion where the c u t t i n g edges of the b i t are cont inuously pushed into the rock by the weight on the b i t . Second, a combination of b r i t t l e shear f a i l u r e and crushing of the rock is caused by l a t e r a l movement of the b i t as the cones r o l l over the bottom of the hole during b i t r o t a t i o n . The e f f i c -iency of t h i s cu t t ing and f r a c t u r i n g act ion i s not only a funct ion of b i t wear, but depends to a large degree on the design and geometry of the o r i g i n a l b i t . 1 3 Opera t iona l ly speaking, the d r i l l penetrat ion rate i s a prime cons idera -t ion s ince i t w i l l govern the economics of d r i l l i n g . Th is plays an important part in b l a s t designing where an optimal balance must be found between the d r i l l i n g and explos ive c o s t s . Thus, a low penetrat ion rate may lead to fewer b l a s t h o l e s , n e c e s s i t a t i n g more explos ive per hole and r e s u l t i n g in the undes i r -able aspects of excessive ground rupture , a i r b l a s t and f l y r o c k as d iscussed in Chapter 5. The importance of the penetrat ion rate has prompted many authors to study the rotary d r i l l i n g act ion and to develop mathematical models f o r p r e d i c t i o n purposes. Th is is a complex problem with many d i f f e r e n t va r iab les i n v o l v e d , but the var ious authors , inc lud ing F i s h 1 4 , T s o u t r e l i s 1 5 , B a u e r 1 6 and Markman 1 7 , genera l ly agree that penetrat ion rate (R) is re la ted to the fo l lowing f a c t o r s : 1) Axia l thrust or weight (W) on the b i t . This i s a lso re la ted to the hydrau l ic down pressure (P) . 2) Rotat ion speed (RPM). 3) Diameter (D) of the d r i l l h o l e and b i t . 4) Uniaxia l compressive strength (a c ) of the rock. 5) Shear strength (T) of the rock. - 152 -6) Abrasiveness (a) of the rock. 7) Geometry of the b i t . 8) F lush ing at the b i t . Using these parameters, the same authors proposed the fo l lowing experi-mental equat ions: F i s h 1 4 : R = f(RPM,x ,bit hardness,a) x -°c where f i s a funct ion not e x p l i c i t l y de f ined . T s o u t r e l i s 1 5 : R = RPM x (W - W0) x A D oc - a where A , B and W0 are experimental constants B a u e r 1 6 : R = RPM x — x 6 1 " 2 8 1 o 9 an D 300 Markman 1 7 : 1 = (13790 x a c x x + 12 x a c x x + 1 ? A x R \ RPM x M v/W7 (1 + .0055 a) x K d x K h where and are b i t geometry c o e f f i c i e n t s . Unfor tunate ly , most of these equations require the use of var ious experi-mental constants in order to include parameters such as wear res is tance of the b i t , rod d e s i g n , f l u s h i n g c o n d i t i o n s , and rock s t ruc tu ra l p r o p e r t i e s . Th is makes these equations impract ica l f o r any general use. With the exception of Markman's equat ion , which i s n o n - l i n e a r , the pene-t r a t i o n rate (R) i s shown to be proport ional to the ax ia l pressure on the b i t (W) and to the ro ta t ion speed (RPM), and i s shown to decrease as the uniax ia l compressive strength of the rock (a c) i nc reases . Rock abrasiveness and b i t geometry are a lso included e x p l i c i t l y in Markman's equat ion. In 1975, M a t h i s 1 8 examined a l l four of the above equat ions, noted t h e i r general s i m i l a r i t i e s , and der ived a s i m p l i f i e d general equation fo r penetra-t ion ra te : - 153 -R = RPM x W x f ( a c ) x K where: f ( a c ) decreases as a c i n c r e a s e s . K is a constant that depends on experimental condi t ions and the d r i l l i n g equipment used. With t h i s s i m p l i f i e d equat ion , Mathis fu r ther noted that by keeping the d r i l l i n g procedure and RPM constant , as they often are in p r a c t i c e , the only remaining measurable va r iab les were penetrat ion rate (R) and weight (W) on the b i t . Put t ing both these va r iab les on one side of the equation ind icated that the r a t i o of weight to penetrat ion rate would r e f l e c t v a r i a t i o n s in rock q u a l i t y . This r a t i o was proposed as the Rock Qual i ty Index as f o l l o w s : R Q J = Weight on D r i l l B i t (W) Penetrat ion Rate (R) Since both of the required parameters are measured e a s i l y during d r i l l i n g of ind iv idua l b l a s t h o l e s , i t should be poss ib le to obtain a comprehensive assessment of rock mass q u a l i t y . D r i l l operators at most mines a l ready keep records of- d r i l l i n g parameters f o r the evaluat ion of d r i l l b i t l i f e and performance. Procedures vary from mine to mine, but t y p i c a l parameters recorded f o r each b las tho le include depth ( d ) , d r i l l i n g time ( t ) , hydrau l ic down pressure (P ) , and RPM. The <•. hydrau l ic down pressure (P) is proport ional to the weight on the b i t (W), d i f f e r i n g only by the f a c t o r of b i t area in contact with the rock. There fore , f o r a given s i z e and type of b i t , and taking | - as penetrat ion r a t e , the RQI can be more p r a c t i c a l l y c a l c u l a t e d a s : R Q J _ Hydraul ic Down Pressure Penetrat ion Rate or - 154 -This measure of rock mass q u a l i t y appeared to meet a l l the requirements out l ined at the beginning of t h i s sect ion and i t s ease of c a l c u l a t i o n would permit the tabu la t ion of a very large number of b las tho les within the l i m i t e d f i e l d time a v a i l a b l e . As a r e s u l t , the RQI was se lec ted as the basis f o r rock mass c l a s s i f i c a t i o n and was u l t imate ly used f o r c o r r e l a t i o n to powder f a c t o r s . 6.2.2 E s t a b l i s h i h g Rock Qua! i ty Index Values: Shor t ly a f t e r the o r i g i n a l idea of RQI was proposed, i t was' assessed during the summer of 1975 in a research pro ject by L i t t l e . 1 9 He c a l c u l a t e d several RQI v a l u e s , p lo t ted and contoured them on p i t p l a n s , and attempted to c o r r e l a t e the maps to l i t h o l o g y , s t ruc tu ra l geology and rock strength f o r the purpose of open p i t slope des ign . However, he found the index to be u n r e l i a b l e , p r i n c i p a l l y due to poor recording techniques by the d r i l l e r s , and the lack of s e n s i t i v i t y to changes over small areas made i t d i f f i c u l t to determine domain boundaries. Thus, f o r the purpose of slope design and s t a b i l i t y e v a l u a t i o n , L i t t l e f e l t that the use of the RQI system could not be j u s t i f i e d s ince geo log ica l mapping provided him with bet ter in format ion. A f t e r t h i s study, no other researchers d id any fu r ther work with the RQI concept . Despite t h i s unfavourable r e p o r t , i t was decided to revive the RQI con-cept fo r the current research into powder f a c t o r c o r r e l a t i o n , c h i e f l y because of i t s s i m p l i c i t y and ease of p r a c t i c a l a p p l i c a t i o n . However, learn ing from L i t t l e ' s f i n d i n g s , some important changes were made: 1) Concerted e f f o r t was put into improving the q u a l i t y and accuracy of d r i l l performance records . 2) Rather than using the RQI to determine domain boundar ies, i t was simply used to c l a s s i f y the rock q u a l i t y within the domain boundaries already es tab l i shed by conventional mapping. - 155 -3) The ind iv idua l areas assessed f o r RQI values were kept large enough to minimize e f f e c t s of b i t wear, s h i f t changes, e t c . A l l the d r i l l i n g at Afton Mine was c a r r i e d out by two e l e c t r i c - p o w e r e d , track-mounted Bucyrus E r i e 40-R d r i l l s . See Plate 15 and Table 5. These d r i l l s are equipped with the maximum permissib le s i z e of 230 mm. (9 inch) diameter t r i - c o n e b i t s with ch ise l -shaped tungsten carbide i n s e r t s . See Plate 16. For tuna te ly , Afton had good d r i l l records going back fo r several years as well as good geolog ica l and b las tho le p lans . This provided a large amount of data to compile the pre l iminary RQI va lues . Deta i led geologic mapping in the ear ly production stages had es tab l ished the we l l -de f ined geologica l and s t ruc tu ra l domains as shown in Figure 6 .1 -3 . As mining progressed, the pos i t ions of the domain boundaries were c o n t i n u a l l y updated on the master p i t plans through d a i l y mappings by the p i t g e o l o g i s t . These domain boundaries were reta ined f o r the RQI assessment and b l a s t i n g tes ts in order to develop a c o r r e l a t i o n system compatible with e x i s t i n g p i t planning work. The same rock mass features which determined these slope design domains, inc lud ing slope face o r i e n t a t i o n , are those which a f f e c t the b l a s t i n g behaviour of the rock. A l s o , each domain provided a large enough area to obtain reasonable, average RQI va lues . Although not t e c h n i c a l l y d i f f i c u l t , e s t a b l i s h i n g the RQI values f o r each domain was a l o n g , tedious procedure requ i r ing about a month of data t a b u l a t i o n . For each bench l e v e l , the d e t a i l e d plans showing a l l the b las tho le numbers and pos i t ions were l a i d over the geologica l p lans . Within each domain, every b las tho le number was located among the o r i g i n a l d r i l l e r s ' log sheets to deter -mine the hydrau l ic down pressure (P) , the hole depth (d ) , and the d r i l l i n g time (t) f o r that p a r t i c u l a r b l a s t h o l e . The task was complicated by the fac t that the d r i l l e r s seldom d r i l l e d the holes in the same sequence as they had been numbered by the surveyors . This tabu la t ion process was done f o r each PLATE 15 One of the two Bucyrus E r i e 40-R d r i l l s used at Afton Mi - 157 -TABLE 5 DRILLING MACHINE SPECIFICATIONS 2 0 D r i l l Type: Bucyrus E r i e 40-R, track-mounted Power Source: E l e c t r i c Hole Diameter Range: 171 - 230 mm. ( 6 1 - 9 inches ) Rotat ion Speed Range: 0 - 7 7 RPM Maximum Torque: 7,186 Nm. ( 5300 f t . - l b s . ) Maximum Pull-down Force: 222 kN ( 25 tons ) Maximum Feed Rate: 1.5 m./min. ( 5 f t . / m i n . ) Maximum Ext rac t ion Rate: 31.2 m./min. ( 102 f t . / m i n . ) - 158 -PLATE 16 A l l b las tho les were d r i l l e d with 230 mm. (9 inch) diameter t r i - c o n e b i t s with ch ise l -shaped tungsten carbide i n s e r t s . - 159 -domain and repeated over bench numbers 2100, 2070, 2040 and 2010. In genera l , RQI values were found to be cons is ten t from one bench leve l to the next wi thin each domain. In a l l , data was c o l l e c t e d and RQI values c a l c u l a t e d f o r some 6000 b l a s t h o l e s . In order to s e l e c t a s i n g l e determinative RQI value f o r each domain, the values from a l l four bench l e v e l s were combined and p lot ted to examine the nature of t h e i r d i s t r i b u t i o n . See Appendix III. Genera l l y , each p lo t showed a d i s t i n c t i v e centra l peak f lanked by a smal ler number of higher and lower va lues . Th is was f e l t to be s u f f i c i e n t j u s t i f i c a t i o n fo r simply s e l e c t -ing the mean or average RQI value to represent each domain. The f i n a l r e s u l t s are shown in Table 6 and Figure 6 .2 -1 . The r e l a t i v e p o s i t i o n of these values agreed with the ranking estimated by s i t e g e o l o g i s t s , provid ing s u f f i c i e n t confidence to continue onto the next phase of the research p r o j e c t . - 160 -TABLE 6 ROCK QUALITY INDEX VALUES DOMAIN ROCK QUALITY INDEX p s i - m i n . / f t . MPa-min./m. I 345 7.8 II 360 8.2 IV A 245 5.5 ' IV A - Py 290 6.5 IV B 325 7.4 V 290 6.5 VI 270 6.1 VII 380 8.6 VIII 150 3.4 VIII A 380 8.6 - 1 6 1 -FIGURE 6.2-1 • ROCK QUALITY INDEX VALUES FOR EACH DOMAIN RANKED IN ORDER OF INCREASING QUALITY - 162 -6.3 DEVELOPMENT OF AN IMPROVED PERIMETER BLAST PATTERN At the time when f i e l d research commenced at A f t o n , the b l a s t i n g methods in use did not conform to acceptable p r a c t i c e . Before any of the important powder f a c t o r t es t b l a s t s could beg in , a new design was required f o r A f t o n ' s perimeter b l a s t s because c o n t r o l l e d b l a s t i n g techniques were not prev ious ly used. 6.3.1 Former B l a s t i n g Methods: Due to the conf ined condi t ions of mining the "doughnut" shape of the expanded Stage 2 p i t , i t was often d i f f i c u l t to maintain a s u f f i c i e n t amount of broken muck f a r enough ahead of the shove ls . Consequently, the main p i t production b l a s t s were almost always completely choked due to the lack of an a v a i l a b l e f ree f a c e . Apart from being extremely i n e f f i c i e n t , these heavi ly loaded choked b l a s t s were usua l ly f i r e d with a minimum of delays and the entrap-ped gas pressures were forced to expand out into A f t o n ' s h ighly f rac tured rock f o r great d i s t a n c e s . As mentioned in Sect ion 4 . 1 , v i s i b l e rock mass d i s r u p t i o n propagated from; a product ion b l a s t , through the perimeter b l a s t zone, and into the f i n a l w a l l , t r i g g e r i n g a large sca le slope f a i l u r e . See Plate 11. Th is problem was p a r t l y because the width of the perimeter b las t zone was too narrow, permit t ing the heavy production b l a s t s . t o take place fa r too c l o s e to the p i t w a l l . The extensive backbreak was often such that the shovels were able to d ig well into the perimeter zone without i t having been b l a s t e d . The o r i g i n a l perimeter pattern cons is ted of one row of buf fe r l i n e holes and one row of r e g u l a r l y spaced production ho les . See Figure 6 .3 -1 . Each row had a f u l l production burden of 6.1 m. (20 f t . ) which was too heavy to permit proper movement and ro ta t ion of the rock during the b l a s t , impeding vent ing of gas pressures . If exp los ive loads of s u f f i c i e n t quant i ty to achieve f u l l burden movement were used, they would have i n f l i c t e d ser ious damage to - 1 6 3 -1 .1 m Final Digline I -H h - 3 m . o o o o o o o o o o o o o Buffer Hole Row Cr*- 6.1 m.-MD . 3 m. i—'•7^r-r<-'nrT~<-"TTr l- \ — L J d—Ji > ' _ ' _ ' ' yil O First Production Row —pry'-*~i j r'-^rrrr'-T' A P L A N Last Row of Main Production Blast Scale = 1=400 Final Digline S E C T I O N A - A FIGURE 6.3-I •• FORMER PERIMETER BLAST PATTERN AFTON MINE - 164 -the f i n a l wall and probably produced f l y r o c k . Furthermore, the f i r s t produc-t ion row was d i r e c t l y over the p o s i t i o n of a future bench c r e s t . The sub-d r i l l depth of 1.2 m. (4 f t . ) was r e s u l t i n g in the f r a c t u r i n g and weakening of these future c r e s t s , reducing the ul t imate e f fec t i veness of the benches. This perimeter pattern was usua l ly f i r e d by the simple row-by-row method with no delays along the rows. The excessive charges per delay occur r ing on longer bench patterns set up s i g n i f i c a n t v i b r a t i o n s which r a t t l e d windows in the engineering o f f i c e s h a l f a ki lometre away from the nearest rim of the p i t . A l l of these fac to rs contr ibuted to overbreak and severedamage :to the rock s t ructure in several areas of the f i n a l p i t . Continued monitoring of the large wall f a i l u r e , mentioned above, showed an a c c e l e r a t i o n of movement in the f a i l u r e mass when fu r ther b l a s t i n g took place in that quadrant of the p i t . As part of the geotechnical program at the mine, contours were e s t a b l i s h -ed around the f a i l u r e showing the maximum poss ib le charge per de lay . Much of t h i s work was done by Br ian H i l l , a summer student who developed th is top ic f o r his undergraduate t h e s i s . 2 1 6.3.2 Design of an Improved Perimeter B las t Method: Due to the t i g h t mining l ayou t , i t was impossible to improve the s i t u a -t ion with respect to the choked production b l a s t s . However, a s i g n i f i c a n t increase in the number of delays on these b l a s t s kept the v ib ra t iona l problems under bet ter c o n t r o l . A l l new b l a s t design work was conf ined to the perimeter b l a s t s , fo l lowing the gu ide l ines presented in Chapter 5. An example of the b l a s t design c a l c u l a t i o n i s presented in Appendix I V V Pre-shear ing was ru led out due to A f t o n ' s h ighly f r a c t u r e d , weak rock and the f a c t that only the large diameter d r i l l s were a v a i l a b l e . Cushion b l a s t i n g would have produced the best r e s u l t s but the sequencing of the d r i l l -i n g , b l a s t i n g and excavation was too compl icated. Furthermore, Bucyrus E r i e - 165 -40-R d r i l l s are incapable of d r i l l i n g the angled holes necessary f o r c rea t ing the bench face angle . Instead, i t was f e l t that buf fer b l a s t i n g would y i e l d good r e s u l t s in the h ighly f rac tured rock , as long as very l i g h t explos ive loads were used adjacent to the f i n a l w a l l . The new buf fer b l a s t design is shown in F igure 6 .3 -2 . The f i r s t p r i o r i t y of the new design was to increase the overa l l width of the perimeter b l a s t zone to bet ter protect the f i n a l wall from the main production b l a s t s . This was accomplished by adding another row to the p e r i -meter b l a s t pattern and by increas ing the distance out to the nearest row of the main b l a s t , taking advantage of the f r e e - d i g g i n g in the considerable overbreak caused by the choked b l a s t s . It was grea t ly hoped that the digging could continue f o r another 3 metres, thereby reducing the mean burden on the f ron t row to 4.8 m. (16 f t . ) . However, a c r e s t burden of 6.1 m. (20 f t . ) had to be maintained to s a t i s f y the d r i l l e r s while they manoeuvred along the second production row. A l s o , the former burden- to-spacing r a t i o of 1:1 was reduced to 1:1.33 by shr ink ing the burden on both the buf fer l i n e holes and the f i r s t production row to 4.6 m. (15 f t . ) . This is a much more favourable r a t i o , permit t ing be t te r movement and ro ta t ion of the burden at lower charges. A staggered pattern would have been d e s i r a b l e , but the surveyors and d r i l l e r s were not prepared to accept a departure from the g r i d system. Although t h i s new pattern appears to require a l o t of extra d r i l l i n g , the b las tho le densi ty wi thin the perimeter zone i s a c t u a l l y reduced by 9% from 4.04 holes/100 m2 on the o ld pattern to 3.67 holes/100 m2 on the new pa t te rn . This is l a r g e l y due to the extra 2.7 m. (9 f t . ) between the second production row and the l a s t row of the main production b l a s t . See Figure 6 .3 -3 . With the reduced burdens on the buf fe r l i n e h o l e s , the required charges of bulk- loaded AN/FO would j u s t f i l l the subgrade port ion of the ho le . To get bet ter exp los ive d i s t r i b u t i o n up the hole and to protect the f i n a l w a l l , - 166 -Final Digline i —\ | * -3 .m . O O O O O O b O O O O O O Buffer Hole Row 4.6 m. 4.6 m. O*- 6.1 m.-K) 6.1 m. 8.8 ml 1 \i n ' i f — r n r r First Production Row Second Production Row 1 — m rrmr *- B P L A N Last Row of Main Production Blast S c a l e ' 1-400 Final Digline "To. 6 m. Sc a le ' 1-200 S E C T I O N B - B FIGURE 6.3-2 • NEW PERIMETER BLAST PATTERN AT AFTON MINE Final Digline Final Digline. O 6.1 m O O O Q O 6.1 m. 0 6.1 m. I R I Dr i l lho le r Density = 4 . 0 4 holes/100sq.m. O L D P A T T E R N f 4.6 m. 4.6 m. 8.8 m. 6.1 m. -5 O (j) O O O O O Drillhole Density = 3 . 6 ? holes/100 sq.m. N E W P A T T E R N cn —i FIGURE 6.3-3 » COMPARISON OF DRILLHOLE DENSITIES ON OLD AND NEW PERIMETER B L A S T PATTERNS - 168 -the explos ive was de-coupled from the back of the hole and f u l l y coupled to the f ront of the ho le . A new and inexpensive technique was devised f o r de-coupl ing by using conventional p l a s t i c b las tho le l i n e r s manufactured to h a l f the b las tho le diameter. These turned out to be one t h i r d the cost of the waxed, cardboard tubes normally used. See Appendix IV. Furthermore, the use of these l i n e r s d id not upset the rout ine of the b l a s t i n g crew since they involved the same i n s t a l l a t i o n procedures as r e g u l a r , f u l l - s i z e d l i n e r s . The only d i f f i c u l t y with the smal ler diameter l i n e r s was the increased blow-back pressure caused by the pneumatic AN/FO loader . However, by reducing t h i s pressure on the pumper t ruck , the loading rout ine was evenuta l ly worked out . The most important change f o r improving b l a s t performance and reducing p i t slope damage was the new f i r i n g sequence with i t s increased number of de lays . Th is minimized the amount of explos ive detonating at any i n s t a n t , reducing harmful v i b r a t i o n waves, e s p e c i a l l y in areas of s e n s i t i v e slope stab-i l i t y . In contrast to the former b l a s t i n g method, the engineer ing o f f i c e personnel were usua l ly unable to t e l l when the b l a s t was f i r e d . The f i r i n g sequence i s designed to be easy to lay out and can be continued along any length of berm. See Figure 6 .3 -4 . The system involves a v a r i a t i o n of en echelon f i r i n g s ince most of A f t o n ' s perimeter b l a s t s had a f ree end as well as a f ree f ront f a c e . This f i r i n g pattern cont r ibutes to greater d r i l l i n g economy and b l a s t e f f i c i e n c y s ince the d r i l l - p a t t e r n burden of 4.6 m. is reduced to a detonating burden of 2.5 m. Expressed another way, the e f f e c t i v e burden- to-spacing r a t i o of 1:1.33 is reduced to 1:2.2. As a fu r ther benef i t of t h i s f i r i n g sequence, the obl ique d i r e c t i o n of muck heave is p re fe r rab le to throwing i t out into the shovel a rea . When comb-ined with a proper ly c o n t r o l l e d f ron t row charge, t h i s f a c t o r e l iminates c o s t l y c lean-up time before moving the shovel back to the digging f a c e . The success of t h i s new perimeter b l a s t design was proved in i t s f i r s t FIGURE 6.3-4= PLAN OF NEW PERIMETER BLAST FIRING SEQUENCE - 170 -t es t b l a s t on June 26th. From that point on i t was es tab l i shed as the stand ard perimeter b l a s t design at Afton Mine. See Plate 17. This l e f t the powd f a c t o r as the only remaining b l a s t design var iab le to be se lec ted f o r each d i f f e r e n t rock group. For the convenience of the b l a s t i n g crew, a set of tables was produced, r e l a t i n g the required b las tho le loads to powder f a c t o r values f o r each of the th ree 'exp los ives used at A f t o n . See Appendix V. Once the new perimeter b l a s t design was in use , i t was poss ib le to pro-ceed to the next phase of t es t b las ts to determine optimum powder f a c t o r s in each geolog ica l domain. - 171 -P L A T E 17 The new perimeter b l a s t design during detonat ion. As the pattern f i r e s from l e f t to r i g h t , the varying dust plume heights i l l u s t r a t e the e f f e c t of the delay sequence. - 172 -6.4 DEVELOPMENT OF THE POWDER FACTOR CORRELATION 6.4.1 E s t a b l i s h i n g Powder Factor Values: In order to decide upon the optimum powder fac to rs f o r each rock group, i t was necessary to car ry out a program of t e s t b l a s t s with the new pattern in each of the p i t domains. Only in those b las ts y i e l d i n g good r e s u l t s could the powder f a c t o r used be accepted as the cor rec t value f o r that p a r t i c u l a r domain. C l e a r l y , many of the ea r l y t e s t s contr ibuted no f i n a l v a l u e s , but each one helped to focus more rap id ly towards an optimal powder f a c t o r on subsequent b l a s t s . The c r i t e r i a used f o r i d e n t i f y i n g a s a t i s f a c t o r y b l a s t were d iscussed in de ta i l in Sect ion 5.3. Before a powder f a c t o r could be se lected as the optimum value f o r i t s p a r t i c u l a r rock type , a l l of these c r i t e r i a had to be met: 1) Uniform, moderate movement of the toe burden without f l y r o c k rubble . 2) A s l i g h t r i s e along the muck p i l e c r e s t . 3) No surface c r a t e r i n g or f l a t a reas . 4) A s l i g h t drop along the buf fe r l i n e h o l e s . 5) No broken ground beyond the f i n a l d i g l i n e . 6) No digging problems. 7) Uniform fragmentat ion. 8) A c lean f i n a l wall with minimum r a v e l l i n g p o t e n t i a l . The f i n a l t es t b l a s t in the T e r t i a r y Volcanics of Domain VII , shown during detonation in P late 17, was a p a r t i c u l a r l y good example of a l l the features of a successfu l b l a s t . This i s i l l u s t r a t e d in Plates 18, 19 and 20. Based on a q u a l i t a t i v e evaluat ion process , the assessment of a successful b l a s t i s a h ighly sub ject ive procedure. Unl ike the determination of RQI v a l u e s , the f i n a l s e l e c t i o n of an optimum powder f a c t o r was based on the author 's - 173 -PLATE 18 The tes t b l a s t of Plate 17 produced t h i s muck p i l e which i l l u s t r a t e s the features of a successful b l a s t . Note the evenness of throw, i n d i c a t i n g a good f ront row charge. - 1 7 4 -PLATE 19 A c lose up view of the muck p i l e toe area . Note the r e l a t i v e l y uniform fragmentation and the lack of rock debr is beyond the toe . The slope of th is muck face is i d e a l . - 1 7 5 -PLATE 2 0 A c lose up view on top of the muck p i l e . Note the s l i g h t r i s e of the evenly fragmented c res t and the s l i g h t dip along the back of the berm. The area appears uniform without c ra ters or humps. - 176 -own judgement and experience a f t e r having witnessed many b las ts over the course of the f i e l d research program. Test b l a s t s continued as long as p o s s i b l e in order to obtain the maximum number of data points in the l i m i t e d time a v a i l -a b l e . 6.4.2 Data Ana lys is and Resu l ts : Towards the end of the f i e l d research p e r i o d , f i n a l powder f a c t o r values had been c o l l e c t e d from f i v e of the domains. Although fur ther b l a s t i n g tes ts were s t i l l required in the remaining domains, i t was f e l t that s u f f i c i e n t data was a v a i l a b l e f o r an i n i t i a l attempt to c o r r e l a t e the powder fac to rs with t h e i r respect ive RQI va lues . The f i n a l values f o r powder f a c t o r and RQI were p lo t ted and a simple regress ion a n a l y s i s was made using one of the l i b r a r y rout ines of the Hewlett-Packard 9845 computer. A f t e r attempts to f i t d i f f e r e n t types of curves to the p l o t , the a n a l y s i s ind icated the best f i t to be a natural logar i thmic curve with a c o e f f i c i e n t of determination of 0.98. This strong c o r r e l a t i o n is des-c r ibed by the fo l lowing equat ion: In (Powder Factor) = R Q I " 2 4 , 9 7.1 where: Powder Factor i s in kg. / tonne RQI is in MPa-min./metre By convert ing the uni ts (see Appendix V I ) , the c o r r e l a t i o n becomes: In (Powder Factor) = R Q I " 8 8 5 315 where: Powder Factor i s in l b s . / s . t b n RQI is i s p s i - m i n . / f t . . In using t h i s c o r r e l a t i o n , i t must be remembered that the powder f a c t o r quoted i s f o r AN/FO and the RQI i s based on a Bucyrus Er ie 40-R d r i l l with a 230 mm. (9 inch) diameter carbide t ipped t r i - c o n e b i t . - 177 -With the remaining time in the f i e l d program r a p i d l y drawing to a c l o s e , t h i s c o r r e l a t i o n was used as a guide to pred ic t l i k e l y powder fac to rs f o r the b l a s t tes ts in the remaining domains. Th is proved to be the f i r s t t es t of the RQI/Powder Factor c o r r e l a t i o n and the subsequent tes t b las ts were s u c c e s s f u l . The f i n a l powder f a c t o r data points served to re in fo rce the a c c -uracy of the c o r r e l a t i o n curve as shown in F igure 6 .4 -1 . At the end of the f i e l d program, a new b l a s t i n g manual was produced fo r Afton Mine. This included a large master p i t plan showing a l l the geologica l domains with t h e i r corresponding RQI and powder f a c t o r va lues . Th is data i s summarized in Table 7. Since the plan pos i t ions of the d i f f e r e n t rock zones w i l l s h i f t with deepening excavat ion , the p i t geo log is t must keep th is plan up to date along with h is regular geo log ica l sheets . Should the rock q u a l i t y condi t ions change s i g n i f i c a n t l y with depth, RQI values tabulated from the d a i l y d r i l l logs should r e f l e c t t h i s , i n d i c a t i n g a corresponding change in powder f a c t o r to maintain optimal b l a s t performance. 6.4.3 Test ing the RQI/Powder Factor C o r r e l a t i o n : The use of the pre l iminary curve to s u c c e s s f u l l y p red ic t powder fac to rs in the l a s t domains already provided a good i n i t i a l t es t fo r the proposed c o r r e l a t i o n . However, two more cha l lenging tes ts of the RQI system occurred in the F a l l of 1981. In September, two production b l a s t s in Domain II f a i l e d to break down to bench grade and had large boulders mixed in with the muck. It was impos- . s i b l e f o r the shovel to excavate t h i s a r e a , causing major production delays and n e c e s s i t a t i n g secondary d r i l l i n g and b l a s t i n g . At A f t o n ' s request , the author returned to the mine s i t e to examine the s i t u a t i o n . Upon c l o s e r i n s p e c t i o n , the problem was a t t r i b u t e d to several hard veins of magnetite e r r a t i c a l l y located wi th in the N ico la Volcanics of Domain II. It was suspected that the same condi t ions could be encountered in the ad jo in ing - 178 -t o n n e P O W D E R F A C T O R FIGURE 6.4-1 : PROPOSED CORRELATION B E T W E E N ROCK QUALITY INDEX AND POWDER FACTOR 179 TABLE 7 SUMMARY OF POWDER FACTOR/RQI CORRELATION DOMAIN I II IV A IV A - Py IV B V VI VII VIII VIII A IX POWDER FACTOR I b s . / s . ton kg. / tonne ROCK QUALITY INDEX 0.18 0.19 0.13 0.15 0.17 0.15 0.14 0.20 0.10 0.20 0.25 0.090 0.095 0.065 0.075 0.085 0.075 0.070 0.100 0.050 0.100 0.125 p s i - m i n . / f t , 345 360 245 290 325 290 270 380 150 380 450 MPa-min./m. 7.8 8.2 5.5 6.5 7.4 6.5 6.1 8.6 3.4 8.6 10.2 Imperial U n i t s : In (Powder Factor) = R ^ " 8 8 5 315 S. I. U n i t s : In (Powder Factor) = R Q I " 2 4 - 9 7.1 - 180 -b l a s t pa t te rn . Examination of the d r i l l logs f o r t h i s b l a s t s i t e revealed several holes with s i g n i f i c a n t l y higher RQI v a l u e s , c l e a r l y r e f l e c t i n g the presence of fu r ther magnetite v e i n s . By using higher explos ive charges in those p a r t i c u l a r b l a s t h o l e s , as d ic ta ted by the RQI/Powder Factor c o r r e l a t i o n , the b l a s t was successfu l and no hard toes remained. This event demonstrated the a b i l i t y of the d r i l l s and the RQI to ind ica te i s o l a t e d changes wi th in the rock mass. From t h i s , i t i s conceivable that improved techniques in the recording of d r i l l performance data may permit the s e l e c t i o n of powder fac to rs on a ho le -by -ho le b a s i s . A f t e r the f i e l d work was completed, i t was learned that an automatic d r i l l data recording device i s a v a i l a b l e from Totco Mining and Industr ia l Instrumentation which may be able to provide the necessary accuracy f o r more re f ined RQI measurements. The most c r i t i c a l t es t of the RQI concept came in October when a large zone of d a c i t e , l a b e l l e d Domain IX, appeared at the base of the l a r g e , unstable s lope f a i l u r e re fer red to e a r l i e r . Completely unl ike any other rock type in A f t o n ' s p i t , the dac i te was very hard and qui te massive, requ i r ing a f a i r l y heavy explos ive load f o r proper f ragmentat ion. In add i t ion to the problem of c l e a n l y excavating the d a c i t e , there were grave concerns about the e f f ec ts of the heavier impact on the wall f a i l u r e above. However, i t was f e l t that the large number of delays wi thin the new perimeter b l a s t pattern would be s u f f i c i e n t to minimize any disturbance of the s l i d e . There was no c l e a r data on an appropr iate powder f a c t o r f o r the dac i te s ince the only b l a s t prev ious ly attempted did not succeed in completely f r a g -menting the massive s t r u c t u r e . Having l i t t l e e lse to go on , i t was decided that th is s i t u a t i o n could provide a c r u c i a l tes t of the RQI/Powder Factor C o r r e l a t i o n and the chance to see i f the curve could be extrapolated into higher RQI v a l u e s . Although there were only 43 b las tho les wi th in the d a c i t e , a rough RQI of 10.2;'MPa-min./m. (450 p s i - m i n . / f t . ) was ca lcu la ted and the corresponding powder f a c t o r of 0.125 kg. / tonne (0.25 l b s . / s . t o n ) determined. - 181 -See Table 7. A few boulders were shaken loose on the already weakened upper s l o p e , but no s i g n i f i c a n t movement was recorded on the f a i l u r e mass and the dac i te was b lasted out s u c c e s s f u l l y . The r e s u l t s of t h i s b l a s t provided a fu r ther data point f o r the proposed c o r r e l a t i o n and ind icated that i t was poss ib le to extend the e x i s t i n g curve in to the realm of more competent rock masses. Since th is l a s t o c c a s i o n , there have been no fu r ther tes ts on the l i m i t a -t ions or a p p l i c a b i l i t y of the proposed RQI/Powder Factor c o r r e l a t i o n . 6 . 4 . 4 Suggested Further Research: Before i t w i l l be poss ib le to con f iden t ly apply t h i s c o r r e l a t i o n outside A f t o n ' s open p i t , a more r igorous s e r i e s of tes ts should be c a r r i e d out . The idea l t e s t i n g program would involve repeat ing t h i s e n t i r e research pro jec t in other mines with i d e n t i c a l d r i l l i n g equipment and b i t s i z e . A comparison of the r e s u l t s from each mine would be needed to provide d e f i n i t i v e evidence as to the v a l i d i t y of the e x i s t i n g c o r r e l a t i o n on a un iversa l b a s i s . Should such a program prove s u c c e s s f u l , then i t would be worthwhile to begin estab- : l i s h i n g s i m i l a r c o r r e l a t i o n s f o r other d r i l l type and b i t combinations. At t h i s t ime, such an extensive t e s t i n g program is beyond the l i m i t s of the cur -rent research p r o j e c t , but i t is hoped that work w i l l be continued in th is area by future researchers . Smaller sca le research projects could be done on fu r ther refinement of the Rock Qua l i ty Index. By d r i l l i n g a large number of holes wi thin a s i n g l e , uniform rock type , i t should be poss ib le to develop bet ter s t a t i s t i c a l para-meters on RQI value d i s t r i b u t i o n s and to assess the s i g n i f i c a n c e of b i t wear e f f e c t s . a s the number of holes d r i l l e d inc reases . A separate d r i l l i n g program should be c a r r i e d out with an automatic d r i l l data recording d e v i c e , such as the one mentioned above, to tes t i t s a b i l i t y to improve data q u a l i t y . This could then be fol lowed by a se r ies of c a r e f u l l y - 182 -c o n t r o l l e d b l a s t i n g tes ts to assess the f e a s i b i l i t y of ho le -by -ho le powder f a c t o r s e l e c t i o n . Some pre l iminary experiments were c a r r i e d out at Afton in an attempt to e s t a b l i s h a c o r r e l a t i o n between the RQI values and the seismic v e l o c i t i e s in each domain. Due to poor equipment and lack of t ime, these experiments were not completed. A much more extensive and proper ly c o n t r o l l e d f i e l d pro-gram i s necessary to tes t t h i s hypothes is , but such a c o r r e l a t i o n could provide an i n t e r e s t i n g cross-check with the ear ly work done by Broadbent . 1 In genera l , i t i s hoped that the ideas presented in t h i s research project w i l l prove to be of p r a c t i c a l value in operat ing mines, thereby prov id ing a considerable amount of fu r ther data f o r improvements and refinements to the present ly proposed RQI/Powder Factor c o r r e l a t i o n . - 183 -6.5 PRACTICAL APPLICATIONS OF RESULTS From the o u t s e t , the author was determined to approach th is research pro ject in a p r a c t i c a l manner such that any r e s u l t s could be r e a d i l y appl ied by p r a c t i s i n g engineers and thus be of maximum b e n e f i t . It i s f e l t that th is basic ob jec t ive has been met in e s t a b l i s h i n g the Rock Qual i ty Index c l a s s i f i -ca t ion and in the proposed RQI/Powder Factor c o r r e l a t i o n . The concept of the RQI can be e a s i l y implemented, taking advantage of e x i s t i n g d r i l l performance data and without the need f o r extra equipment or s p e c i a l l y t ra ined personnel . This system i s p a r t i c u l a r l y valuable in p i ts with several domains of widely varying l i t h o l o g y , permit t ing a constant monit-or ing of the rock mass c o n d i t i o n s . In non-g lac ia ted parts of the wor ld , where open p i ts are excavated through extensive zones of weathered rock , the RQI would be an e x c e l l e n t i n d i c a t o r of changing and improving rock q u a l i t y c o n d i -t ions as the p i t approached the lower leve l of the weathering hor i zon . Due to the s i m p l i c i t y of the RQI system, the author is o p t i m i s t i c that i t w i l l be of p r a c t i c a l value in t h i r d world na t ions . By extending the RQI concept to a c o r r e l a t i o n with powder f a c t o r s , a h ighly p r a c t i c a l method is a v a i l a b l e f o r overcoming one of the major problems in c o n t r o l l e d b l a s t i n g des ign . Although fur ther t e s t i n g w i l l be necessary to determine whether the proposed c o r r e l a t i o n i s u n i v e r s a l l y a p p l i c a b l e , the important r e s u l t of th is research i s to show that a comprehensive program can c e r t a i n l y be developed within a s ing le open p i t opera t ion . With p r i o r knowledge of rock mass condi t ions obtained from d r i l l i n g da ta , i t i s now pos-s i b l e to determine the optimal explos ive charge which w i l l produce the des i red fragmentation with minimal p i t slope damage. This has been a major ob jec t ive of rock slope engineers fo r many y e a r s . As the importance of th is system becomes apparent , the author hopes that the present d r i l l data recording t e c h -niques w i l l improve, .permit t ing a greater refinement of RQI c a l c u l a t i o n s and - 184 -ul t imate ly leading to a ho le -by -ho le powder f a c t o r des ign . The potent ia l economic benef i ts could be s u b s t a n t i a l . Although t h i s research pro ject concentrated mainly on the aspect of b l a s t o p t i m i z a t i o n , there was some evidence that a good c o r r e l a t i o n may e x i s t between RQI and ore m i l l i n g r a t e s . This p o s s i b i l i t y was examined b r i e f l y , but a major d i f f i c u l t y was presented by the v a r i a t i o n s in ore storage time on the s t o c k p i l e between excavating and m i l l i n g . However, the v a r i a t i o n s in m i l l i n g rate were of s u f f i c i e n t importance to the m i l l operators that some form of RQI c o r r e l a t i o n would be very va luab le . It i s a lso hoped that the background knowledge accumulated on rock b l a s t -ing and d iscussed in the four previous chapters has been presented in a manner which w i l l make p r a c t i c a l cont r ibu t ions to the understanding and a p p l i c a t i o n of modern b l a s t i n g techniques. - 185 -6.6 REFERENCES 1) BROADBENT, C D . : Pred ic tab le B l a s t i n g With In S i tu Seismic Surveys. Mining Eng ineer ing , V o l . 26, No. 4, A p r i l 1974. 2) ASHBY, J . P . : Production B l a s t i n g and Development of Open P i t S lopes . Proceedings, Th i rd Internat ional Conference on S t a b i l i t y in Surface Min ing , Vancouver, B . C . , AIME, 1982. 3) HOEK, E. & BROWN, E . T . : Underground Excavations in Rock, Chapter 2 -C l a s s i f i c a t i o n of Rock Masses. F i r s t E d i t i o n , IMM, 1980. 4) ONTARIO MINISTRY OF TRANSPORTATION & COMMUNICATIONS: Tunne l l ing Technol -ogy. Research and Development D i v i s i o n , May 1976. 5) LEIGHTON, J . C . : Open P i t B l a s t i n g Manual. Internal Report , Afton Operating Corpora t ion , Kamloops, B . C . , August 1981. 6) CARR, J . M . & REED, A . J . : A f ton : A Supergene Copper Deposi t . CIM Specia l Volume No. 15, Porphyry Deposits of the Canadian C o r d i l l e r a . 7) LEIGHTON, J . C , BRAWNER, C O . & STEWART, D. : Development of a Cor re la t ion Between Rotary D r i l l Performance and Cont ro l led B l a s t i n g Powder Fac to rs . CIM B u l l e t i n , V o l . 75, No. 844, August 1982. 8) REED, A . O . : S t ruc tura l Geology of the Afton Copper-Gold Mine, Kamloops, B . C . , and i t s Inf luence on Pi twal l Slope S t a b i l i t y . Proceedings, 82nd Annual Meeting of CIM, Toronto, A p r i l 1980. 9) TRENHOLME, B . S . : A Pre l iminary Slope S t a b i l i t y Invest igat ion and Ana lys is of the South and East Walls of the Open P i t at Afton Mines, B r i t i s h Columbia. B . A . S c . T h e s i s , Department of Geological Engineer ing , Un ivers i ty of B r i t i s h Columbia, 1979. 10) TAYLOR, R . S . : Report on S t a b i l i t y Analyses of the Afton Open P i t Mine Based on Data Gathered During 1979. M.Eng. T h e s i s , Department of Mining and Mineral Process Eng ineer ing , U n i v e r s i t y of B r i t s h Columbia, 1980. 11) JENNINGS, J . E . : A Pre l iminary Theory f o r the- S t a b i l i t y of Rock S lopes . Unpublished in terna l r e p o r t , U n i v e r s i t y of Witwatersrand, 1968. 12) TEALE, R.: The Concept of S p e c i f i c Energy in Rock D r i l l i n g . In ternat ion-al Journal of Rock Mechanics & Mining S c i e n c e , V o l . 2 , 1965. 13) KULISHENKO, I.I., KOVALEV, V . I . , VASIL'CHENKO, V . F . & SOLOGUB, S . Y . : The Optimum B i t Geometry f o r Rotary D r i l l i n g of Boreholes . Soviet Mining S c i e n c e , V o l . 12, No. 6, 1976. 14) FISH, B . G . : The Basic Var iab les in Rotary D r i l l i n g . Mine and Quarry Engineer ing , V o l . 27, No. 1, January 1961, and Vol-. 27, No. 2, February 1961. 15) TSOUTRELIS, C . E . : Determination of the Compressive Strength of Rock In S i t u Using a Diamond D r i l l . In ternat ional Journal of Rock Mechanics and Mining -Science, V o l . 6 , No. 3, 1969. i - 186 -16) BAUER, A . : Open P i t D r i l l i n g and B l a s t i n g . Journal of the South A f r i c a n Ins t i tu te of Mining and Meta l lu rgy , V o l . . 7 1 , No. 6, 1971. 17) MARKMAN, L . D . : Formula f o r Rotary D r i l l i n g . Soviet Mining Sc ience , V o l . 7, No. 5, 1971. 18) MATHIS, C : Proposal of a Report on Rock Qual i ty Index Based on Rotary D r i l l Performances. Unpublished r e p o r t , Un ive rs i t y of A l b e r t a , March 1975. 19) LITTLE, T . E . : Evaluat ion of a Rock Qua l i ty Index Based on Rotary D r i l l Performance. B . A . S c . T h e s i s , Department of Geological Engineer ing , U n i v e r s i t y of B r i t i s h Columbia, 1976. 20) EDITORS, MINING MAGAZINE: Rotary Blasthole , D r i l l s . Mining Magazine, V o l . 142, No. 3, March 1980. 21) HILL, BRIAN: Invest igat ion of a Slope Displacement at Afton Operating Corpora t ion . B . S c . T h e s i s , Department of Mining Engineer ing , Queen's U n i v e r s i t y , 1982. - 188 -CHAPTER SEVEN CONCLUSIONS - 189 -7.0 CONCLUSIONS Rock b l a s t i n g is the v i t a l f i r s t step in any excavating or mining p r o j e c t . In the pas t , achiev ing good fragmentation was the sole cons idera t ion in b l a s t des ign , but in recent years rock slope engineers have drawn a t ten t ion to other key f a c t o r s , such as slope s t a b i l i t y , which are important to the overa l l safety and economy of a b l a s t i n g opera t ion . The p r i n c i p a l requirement is to conf ine the des t ruc t ive b l a s t energy to the des i red excavation while i n h i b i t i n g or preventing damage to the surrounding rock of the f i n a l p i t s l o p e . Although t h i s ob jec t ive has been grea t ly f a c i l i t a t e d by the development of var ious c o n t r o l l e d b l a s t i n g techniques, there are s t i l l c e r t a i n areas in b l a s t design which are poorly understood yet c r i t i c a l to achiev ing the des i red r e s u l t s . The most important area of uncer ta inty is that of the i n t e r - r e l a t i o n s h i p between b l a s t performance and the proper t ies of the rock mass being b l a s t e d . It has long been r e a l i z e d that the many geologica l features c h a r a c t e r i z -ing a p a r t i c u l a r rock mass have d i r e c t in f luences on the b l a s t i n g r e s u l t s . Although the con t r ibu t ion of c e r t a i n features is p a r t i a l l y known, i t is t h e i r . i n t e r - a c t i o n together which con t ro ls the rock f r a c t u r i n g process . Since the complexity of problem p r o h i b i t s the development of a comprehensive rock b l a s t -ing theory , t h i s study examined t h e . p o s s i b i l i t y of apply ing a s i n g l e rock mass c l a s s i f i c a t i o n which would take account of those rock mass proper t ies most important to b l a s t i n g . Based on the performance of a rotary d r i l l , t h i s c l a s s i f i c a t i o n , known as the Rock Qua l i ty Index, has been found to bear a strong c o r r e l a t i o n to the powder f a c t o r , a major v a r i a b l e in s i t e s p e c i f i c b l a s t i n g des ign . As a r e s u l t of the background study and f i e l d work on t h i s research pro-j e c t , the fo l lowing conclus ions have been made: 1) The ac t ion of a rotary d r i l l i s a f fec ted by major rock mass proper t ies and s t r u c t u r a l geology, causing i t to r e f l e c t the competancy of the - 190 -rock on a q u a l i t a t i v e b a s i s . Provided that the hydrau l ic down pressure and penetrat ion rate are c a r e f u l l y monitored when d r i l l i n g each b l a s t h o l e , the Rock Qual i ty Index can be c a l c u l a t e d and w i l l serve as a r e l i a b l e i n d i c a t o r of the rock mass c o n d i t i o n . The Rock Qua l i ty Index i s s e n s i t i v e to changing rock mass condi t ions from one b las tho le to the next. Improved monitoring methods may permit indexing on a ho le -by -ho le b a s i s . The p r a c t i c e of choked b l a s t i n g in rock with a high frequency of cont inuous, natural f rac tures w i l l r e s u l t in extensive ground rupture fo r considerable d istances beyond the intended excavation l i m i t s . P i t s lope movements caused by e x c e s s i v e , b las t - induced ground v i b r a -t ion can be minimized or e l iminated by using mul t ip le delays wi thin a b l a s t i n g pattern to reduce the maximum detonating charge per de lay . The care fu l design of the burden and charge weight along the f ront row of a b l a s t pattern i s a key element in successfu l perimeter b l a s t i n g . Provided a well planned c o n t r o l l e d b l a s t i n g design is used, the geo-metric parameters can be held constant and the powder f a c t o r kept as the only design v a r i a b l e , even when b l a s t i n g in a broad var ie ty of geologic c o n d i t i o n s . A strong c o r r e l a t i o n e x i s t s between the powder f a c t o r and the rock mass condi t ions as descr ibed by the Rock Qual i ty Index (RQI) at Afton Mine. For the p a r t i c u l a r d r i l l i n g equipment and explos ive type used, t h i s c o r r e l a t i o n can be def ined as f o l l o w s : In (Powder Factor) = R Q I " 2 4 , 9 7.1 where: Powder Factor i s in kg. / tonne RQI is in MPa-min./metre - 191 -9) A good b l a s t evaluat ion program is essent ia l in order to c o n t i n u a l l y maintain optimal b l a s t i n g performance as s i t e condi t ions or b l a s t i n g conf igura t ions change. 10) By understanding and apply ing the bas ic p r i n c i p l e s of c o n t r o l l e d rock b l a s t i n g , i t i s poss ib le to produce the des i red fragmentation and, at the same t ime, preserve the inherent rock mass proper t ies important to the s t a b i l i t y of the f i n a l rock s lope . 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Internat ional Journal of Rock Mechanics, Mining Science & Geomechanics A b s t r a c t s , V o l . 14, 1977. - 202 -APPENDIX I GLOSSARY OF BLASTING TERMINOLOGY - 203 -GLOSSARY OF BLASTING TERMINOLOGY Absorbant: a material used to absorb l i q u i d explos ive bases. Acoust ic Impedance D i s c o n t i n u i t y : a break in the continuum of the rock mass ( i . e . an open j o i n t or f a u l t ) which causes a drop in the shock wave energy. A i r b l a s t : a strong v i b r a t i o n a l shock wave propagating through the. a i r as a r e s u l t of a l a r g e , inadequately conf ined e x p l o s i o n . Along-the-Row F i r i n g : a method f o r detonating perimeter patterns where delay elements are used along the row in add i t ion to the i n t e r -row delays f o r b l a s t v i b r a t i o n reduc t ion . AN/FO: Standard abbrev ia t ion f o r Ammonium N i t r a t e / F u e l O i l . Th is i s a common bulk b l a s t i n g agent c o n s i s t i n g of 94% ammonium n i t r a t e p r i l l s and 6% d iese l f u e l . Inexpensive and safe to handle. A n t a c i d : an ingredient added to an explos ive formulat ion to increase s t a b i l i t y in s torage. At tenuat ion: the reduct ion of shock wave amplitude and energy as the wave propagates outward from the source po in t . Backbreak: d is tance of broken or f rac tured rock beyond the intended l i n e of excavat ion . See a lso Overbreak. B a l l i s t i c Mortar: an empir ica l t es t f o r comparing explos ive s t rengths , measur-ing the a b i l i t y of 10 grams of explos ive to d e f l e c t a heavy s tee l mortar. Bench B l a s t i n g : b l a s t i n g to two or more f ree s u r f a c e s . Bench Grade: usua l ly taken to be the e leva t ion at the toe of the bench f a c e . - 204 -B las tho le Cuto f f : the shearing o f f of an undetonated b l a s t h o l e , preventing detonat ion . Usual ly caused by damage from neighbouring b las tho les or shearing along f a i l u r e p lanes. B las tho le L i n e r : a tubular p l a s t i c s leeve used to protect explos ives of low water res is tance when the b las tho le i s wet. B l a s t i n g Agent: a b l a s t i n g m a t e r i a l , c o n s i s t i n g of a fuel and an o x i d i z e r , not c l a s s i f i e d as an explos ive and in which none of the ingred-ients i s an e x p l o s i v e . Cannot be detonated with a No. 8 cap. B l a s t i n g Machine: a s m a l l , portable device to provide current f o r f i r i n g b l a s t s e l e c t r i c a l l y where a l te rnate power sources are not r e a d i l y a v a i l a b l e . B l a s t i n g Records: records of b las tho le p a t t e r n , charge weights , f i r i n g sequence, and p o s t - b l a s t s i t e condi t ions f o r a b l a s t eva luat ion program. Borehole Pressure: the peak e f f e c t i v e pressure ac t ing behind the detonation head on the c y l i n d r i c a l surface area of the borehole. Breakout V e l o c i t y : v e l o c i t y imparted to the fragmented rock on the bench face as a r e s u l t of the b l a s t f o r c e s . B r i s a n c e : the extreme shat te r ing e f f e c t r e s u l t i n g from almost instantaneous decomposition of the explos ive upon detonat ion. Buf fer B l a s t i n g : the most simple and economical method of c o n t r o l l e d b l a s t i n g , i t requires a row of l i g h t l y loaded holes s l i g h t l y o f f s e t from the f i n a l d i g l i n e f o r reducing backbreak. Bulk E x p l o s i v e : an explos ive which i s produced and handled in large batch quan t i t i es and is usua l ly f r e e - f l o w i n g . T y p i c a l l y used on mine s i t e s where large volumes of explos ive are requ i red . - 205 -Burden to Spacing Ra t io : the r a t i o of e f f e c t i v e burden d iv ided by the e f f e c t -ive s p a c i n g , usua l ly quoted to charac te r i ze a b l a s t pa t te rn . Burden Volume: The volume of rock in f ront of a s ing le b las tho le = burden x spacing x bench he ight . Cap S e n s i t i v i t y : descr ibes the s e n s i t i v i t y of an explos ive to being i n i t i a t e d by a s i n g l e b l a s t i n g cap. Caving: r e f e r s to the co l l apse of an undetonated b l a s t h o l e . Usual ly caused by d r i l l stem removal or natural degradation as opposed to C u t o f f s . Channel E f f e c t : occurs when the explos ive column i s narrower than the b l a s t -hole diameter. A wave of a i r pressure t r a v e l s ahead of the detonating f r o n t , compressing the explos ive to i t s dead-pressed state and preventing complete detonation of the ho le . Charge Diameter: the diameter of the explos ive column. For bulk e x p l o s i v e s , t h i s is the same as the b las tho le diameter. Charge Weight: the quant i ty of explos ive in a s i n g l e b l a s t h o l e . Choked B l a s t : a b l a s t which is excess ive ly c o n f i n e d , preventing proper rock mass motion and re lease of the burden. C o l l a r : the unloaded upper port ion of the b l a s t h o l e . Cohesion: re fe rs to the cohesive component of i n t e r - b l o c k shearing res is tance wi thin a rock mass. Cont ro l l ed B l a s t i n g : methods of b l a s t i n g used to reduce the damage to surround-ing rock masses and s t r u c t u r e s . - 206 -Combustible: an explos ive ingredient which combines with excess oxygen to prevent the formation of n i t rogen ox ides . Coupl ing: the extent to which an explos ive charge is in d i r e c t contact with the rock wall of the b l a s t h o l e . Crater B l a s t i n g : b l a s t i n g with the only f ree surface being normal to and at the mouth of the b l a s t h o l e . Crest Burden: minimum distance measured on the bench surface from the f ront b las tho le to the c r e s t of the bench f a c e . Cushion B l a s t i n g : a c o n t r o l l e d b l a s t i n g method where the f i n a l row is f i r e d a f t e r the main por t ion of the perimeter pattern has been f i r e d and excavated. C y c l i n g E f f e c t : when AN/FO is cyc led through 0°C or 32°C more than once, the p r i l l s swell and c o n t r a c t , eventua l ly crumbl ing. Dead-Pressed: re fe rs to an explos ive which has been compacted to a densi ty where: i t w i l l no longer detonate. Delay: a device c o n s i s t i n g of a slow burning composition which provides a short break in the detonating sequence of a b l a s t pa t te rn . Densi ty: r e f e r r i n g to the densi ty of an e x p l o s i v e , usua l ly quoted as a s p e c i f i c g r a v i t y . Detonating Cord: a cord used f o r f i r i n g b l a s t patterns n o n - e l e c t r i c a l l y . The cord usua l ly c o n s i s t s of a core of PETN wrapped wi th in a re in forced waterproof c o v e r i n g . Detonation Burden: the burden on a b las tho le during the b las t pattern detona-t i o n . May be d i f f e r e n t from E f f e c t i v e Burden due to f i r i n g sequence. - 207 -Detonation Pressure: the pressure in the detonation wave of an explos ive in a b l a s t h o l e . Detonation Spacing: the spacing on a group of b las tho les during the b l a s t pattern detonat ion . May be d i f f e r e n t from E f f e c t i v e Spacing due to f i r i n g sequence. Detonics: the study of exp los ive detonat ion . D i g l i n e : the intended l i n e of ul t imate excavation at the back of a perimeter b l a s t pa t te rn . D i s c o n t i n u i t y : any break in the continuum of a rock mass. Includes f a u l t s , j o i n t s , bedding, shear zones, or f i s s u r e s . Downline: the length of detonating cord extending from the surface b l a s t pattern down the b las tho le to the primer charge. Down-the-Hole Delay System: a b l a s t i n g technique where a l l the delay elements are in the b las tho les adjacent to the pr imers. Used in s i t u a t i o n s where Cutof fs may occur . D r i l l C u t t i n g s : the conic p i l e of f i n e l y ground rock produced by the d r i l l when excavating a b l a s t h o l e . Dynamic Rock Strength: the strength of rock under very rapid loading condi t ions such as those encountered in b l a s t i n g . Dynamites: the o r i g i n a l formulat ion of high e x p l o s i v e s , c o n s i s t i n g p r imar i l y of n i t r o g l y c e r i n and an absorbant. Easer Hole: an extra hole placed between the f ront row and the bench c res t in loca t ions where bench face i r r e g u l a r i t y r e s u l t s in excessive f ron t row burden. - 208 -E f f e c t i v e Burden: the burden on a row of b las tho les measured perpendicular to the row as on a b las tho le p l a n . E f f e c t i v e Spacing: the spacing between, b las tho les along a row as measured on a b las tho le p l a n . E l e c t r i c B l a s t i n g Cap: a metal s h e l l with two wires leading in to one end used to i n i t i a t e the en t i re b l a s t f i r i n g sequence. En Echelon F i r i n g : a f i r i n g sequence where the b las tho les are f i r e d in groups at some angle to the bench face . Explos ive Base: a s o l i d or l i q u i d which breaks down into gaseous products with an accompanying re lease of heat energy. Forms the basic ingredient of exp los ive formula t ions . F i r i n g Sequence: the order in which a b las tho le pattern i s f i r e d , usua l ly employing a number of delay elements. F l y r o c k : rock which i s thrown through the a i r as a r e s u l t of excessive b l a s t i n g f o r c e s . Fragmentation: a q u a l i t a t i v e term r e f e r r i n g to the s i z e to which rock is broken by b l a s t i n g . There i s no genera l ly accepted s i ze or gradat ion . Free Face B l a s t i n g : see Bench B l a s t i n g . F r i c t i o n Angle: the dip angle to which i n t e r - b l o c k f r i c t i o n i s able to r e s i s t i n t e r - b l o c k shear ing . Usual ly denoted by <j>. G e l a t i n s : tough, rubbery or p l a s t i c - t e x t u r e d explos ive compositions which possess good water r e s i s t a n c e . Usual ly are high dens i ty . - 209 -Geologica l Domain: a zone in which a rock mass has cons is ten t proper t ies and s t ruc tu ra l features and has a slope with r e l a t i v e l y constant o r i e n t a t i o n . • Geometric B l a s t i n g Parameters: those b l a s t design parameters which are usua l ly c a l c u l a t e d by geometric .means and remain con-stant throughout much of the p i t . Includes burden, s p a c i n g , s u b - d r i l l and bench height . High E x p l o s i v e s : exp los ives which detonate, i n d i c a t i n g that the react ion moves through the explos ive f a s t e r than the speed of sound. High Toes: re fe rs to port ions of the rock mass which f a i l e d to break out down to intended bench grade, producing a hummocky f l o o r . Hydraul ic Down Pressure: the hydrau l ic pressure appl ied to a d r i l l stem f o r c -ing the b i t aga inst the bottom of the b l a s t h o l e . I c e - J a c k i n g : a weathering process where f reez ing water expands in near -sur face cracks and f i s s u r e s , f o r c i n g the rock to s p a l l o f f the f a c e . I n i t i a t i n g Trunk l ine : the long l i n e of detonating cord extending from the b l a s t i n g cap to the b l a s t pa t te rn . I n i t i a t i o n : the commencement of explos ive detonat ion. Internal F r i c t i o n : the res is tance to wave t ransmission within a rock mass, producing heat from the shock wave's mechanical energy. Leg Wires: the two f i n e wires which lead in to the metal she l l of an e l e c t r i c b l a s t i n g cap. Low E x p l o s i v e : exp los ives which d e f l a g r a t e , i n d i c a t i n g that the react ion moves through the explos ive slower than the speed of sound. - 2 1 0 -Maximum Instantaneous Charge: the la rges t amount of explos ive which detonates at any instant wi thin a mul t i -de layed f i r i n g sequence. Mean Burden: average d is tance from a f ron t row b las tho le to the nearest f ree f a c e . Usual ly used f o r f r o n t row burden c a l c u l a t i o n s . Muck: rock which has been fragmented by b l a s t i n g . Optimum Charge: the maximum amount of exp los ive which can be placed in a b l a s t h o l e , a l lowing f o r the necessary height of stemming. Optimum Powder Fac to r : the lowest powder f a c t o r which w i l l achieve des i red fragmentation and produce minimal damage to the surrounding rock mass. Overb las t ing : using excessive quan t i t i es of explos ive without regard fo r the r e s u l t i n g damage to the surrounding rock. Overbreak: the add i t iona l volume of rock which must be excavated due to severe Backbreak beyond the f i n a l d i g l i n e . Oxygen C a r r i e r : an explosive ingredient to ensure complete ox idat ion of the carbon in the explos ive mixture , preventing the formation of carbon monoxide. Peak P a r t i c l e V e l o c i t y : the maximum v e l o c i t y of p a r t i c l e motion during the passage of the seismic wave beneath the p a r t i c l e . Perimeter B l a s t : the b l a s t which takes place in the zone immediately adjacent to the f i n a l p i t s l o p e . Pneumatic Wedging: the ac t ion which causes loss of i n t e r - b l o c k contact due to the r a p i d l y expanding explos ive gases penetrat ing into - 211 -p r e - e x i s t i n g d i s c o n t i n u i t i e s . Po isson 's Ra t io : an e l a s t i c constant usua l ly denoted by a Powder Fac tor : a convenient r a t i o r e l a t i n g the required amount of explos ive to a un i t mass or volume of rock to be b l a s t e d . Power: used to ind ica te the potent ia l of an explos ive to penetrate or sha t te r . Pre-Shear B l a s t i n g : a c o n t r o l l e d b l a s t i n g method where the l i n e hole row i s f i r e d before the main port ion of the b l a s t , c rea t ing a we l l -de f ine d f rac tu re plane along the f i n a l f a c e . Primary E x p l o s i v e : the most s e n s i t i v e category of High E x p l o s i v e s , r e l i a b l y detonated by spark , flame or impact. Primary Wave: the f a s t e s t of the shock waves, i t i s a compressive wave which deforms the rock in a rad ia l d i r e c t i o n . Primer: any high power, high v e l o c i t y explos ive compound capable of i n i t i a t i n g detonation of low s e n s i t i v i t y b l a s t i n g agents or e x p l o s i v e s . Production B l a s t : a large sca le b l a s t wi th in the p i t operat ion which produces the muck on the required production s c a l e . Propagation V e l o c i t y : the speed with which a shock wave t rave ls through a m a t e r i a l . Quasi -Free Face: re fe rs to the imaginary ' f r e e ' planes which occur upon succeeding rows of a mul t i -de layed b l a s t , prov id ing r e l i e f f o r the next burden. Q u a s i - S t a t i c Pressure : the high gas pressure which remains r e l a t i v e l y constant wi th in the b las tho le over the very .-brief durat ion - 212 -of the detonic r e a c t i o n . R a v e l l i n g : the slow but steady degradation of a rock slope s u r f a c e , producing ta lus mater ial at the base of the s lope . Rayleigh Wave: the slow seismic waves which t rave l along ground s u r f a c e . Re la t ive Bulk Strength: a strength comparison between i d e n t i c a l volumes of an explos ive and a standard explos ive such as AN/FO. Re la t ive Weight St rength: a strength comparison between i d e n t i c a l weights of an explos ive and a standard explos ive such as AN/FO. Rock Qua l i ty Index (RQI): an index value which can r e f l e c t rock mass q u a l i t y , based on rotary d r i l l performance. Rock Slope Engineer ing: the p r a c t i c e of s i t e i n v e s t i g a t i o n , design and ana lys is f o r producing stable surface excavations in rock. Row-by-Row F i r i n g : a f i r i n g sequence where each row of the pattern is f i r e d one at a time with the only delays between the rows. Rupture Radius: the d is tance around a b las tho le which is broken or d isturbed by the detonation of an explos ive charge in that b l a s t h o l e . S c a l i n g : removing weakened or loosened rock from a face to avoid a safety hazard. Secondary B l a s t i n g : t h e • r e - d r i l 1 i n g and r e - f i r i n g of rock which was not prop-e r l y fragmented by the f i r s t b l a s t attempt. Secondary E x p l o s i v e : the l ess s e n s i t i v e category of High E x p l o s i v e s . - 213 -Secondary Wave: the seismic shear wave, causing deformation of the rock at r igh t angles to i t s d i r e c t i o n of t r a v e l . Seismic Wave V e l o c i t y : the speed with which the primary seismic wave t rave ls through the rock mass. S e n s i t i v i t y : a measure of the impulse magnitude required to s t a r t an explosive r e a c t i o n . S i t e S p e c i f i c Design: the adapting or modifying of a b l a s t design to s u i t the p a r t i c u l a r rock mass condi t ions at the b l a s t s i t e . S l u r r y : an ammonium n i t r a t e based explos ive in an aqueous s o l u t i o n , ge l led with a gum to give considerable water r e s i s t a n c e . S p a l l i n g : a f l a k i n g or scabbing act ion on the surface of the rock caused by the r e f l e c t i o n of the compressive shock wave at the f ree f a c e . Square Pat tern: a b l a s t pattern with a Burden to Spacing Ratio of 1:1. Staggered Pat tern: a b l a s t pattern with holes placed at optimum densi ty wi th -in the rock mass fo r a Burden to Spacing Ratio of 1:1.15. Stemming: the granular mater ial used to b a c k f i l l the unloaded c o l l a r of a b l a s t h o l e . D r i l l Cutt ings are usua l ly used. S t r i p p i n g Ra t io : the r a t i o of s t r i p p i n g (waste) volume to the volume of ore recovered in an open p i t mine. S t ruc tura l O r i e n t a t i o n : the o r i e n t a t i o n of a d i s c o n t i n u i t y plane in space. Usual ly def ined by s t r i k e and d i p , or by dip and dip d i r e c t i o n . S u b - D r i l l Depth: the depth of the b las tho le below f i n a l bench grade to prevent the formation of High Toes. - 214 -Surface Delay System: a b l a s t i n g method where a l l the delay elements are t i e d in to the surface t runk l ines of the b l a s t pa t te rn . Swedish Pat tern: a b l a s t i n g pattern f o r hard rock where the Burden to Spacing Ratio can be 1:4 or l e s s . Swe l l : the increase in rock volume from i t s p re -b las ted state to i t s f r a g -mented c o n d i t i o n . Toe Burden: the d is tance from the f ron t row b las tho les to the nearest f ree face measured at bench grade e l e v a t i o n . Trim B l a s t i n g : see Cushion B l a s t i n g . T r u n k l i n e s : the sur face pattern of detonating cord which l i n k s a l l the b l a s t -holes, together wi th in the b l a s t a r e a . Underb las t ing: using i n s u f f i c i e n t e x p l o s i v e , r e s u l t i n g in coarse fragmenta-t ion and p o s s i b l y leading to secondary b l a s t i n g . V e l o c i t y of Detonat ion: the speed with which the detonating wave propagates through the e x p l o s i v e . The conf ined value i s greater than the unconfined va lue . Water G e l s : see S lurry Water Res is tance: a ra t ing of an e x p l o s i v e ' s a b i l i t y to withstand exposure to water without d e t e r i o r a t i n g . Young's Modulus: the e l a s t i c modulus of a m a t e r i a l , usua l ly denoted by E. - 215 -APPENDIX II BASIC PROPERTIES OF EXPLOSIVES AND BLASTING MATERIALS USED AT AFTON OPERATING CORPORATION - 216 -AMMONIUM NITRATE / FUEL OIL (AN/FO) AN/FO i s a dry b l a s t i n g agent c o n s i s t i n g of 94% p r i l l e d ammonium n i t r a t e and 6% d iese l fuel o i l . It was the p r i n c i p a l explos ive used at Afton Mine and was suppl ied in bulk f o r easy t ransport and l o a d i n g . See Plate 21. Basic P r o p e r t i e s : S p e c i f i c Grav i ty 0.84 Density 840 k g . / m . 3 Rela t ive Weight Strength 100 Re la t ive Bulk Strength 100 Unconfined Detonation V e l o c i t y 2700 m . / s e c . Water Resistance Ni l Proper t ies in a 230 mm. (9 inch) Diameter Borehole: Density 34.5 kg . /m. of hole Estimated Detonation V e l o c i t y 4000 m . / s e c . Estimated Detonation Pressure 3600 MPa. Estimated Borehole Pressure 2400 MPa. Cost at Afton Mine (August 1981) = $ 33.09 / 100 kg. - 217 -P L A T E 21 A handful of f r e e - f l o w i n g AN/FO. Safe handling i s one of the important c h a r a c t e r i s t i c s of a b l a s t i n g agent. - 218 -HYDROMEX T-3 Hydromex T-3 i s a s l u r r y explos ive p r i n c i p a l l y composed of ammonium n i t r a t e , T . N . T . and water. At Afton Mine, i t was stocked in 203 mm. (8 inch) diameter bags, each conta in ing 25 kg. of the e x p l o s i v e . See Plate 22. Basic P r o p e r t i e s : S p e c i f i c Grav i ty 1.46 Density 1460 k g . / m . 3 Rela t ive Weight Strength 89 Re la t ive Bulk Strength 155 Unconfined Detonation V e l o c i t y 4600 m . / s e c . Water Resistance Exce l len t Propert ies in a 230 mm. (9 inch) Diameter Borehole: Density 60 kg . /m. of hole Estimated Detonation V e l o c i t y 5700 m . / s e c . Estimated Detonation Pressure 9850 MPa. Estimated Borehole Pressure 5100 MPa. Cost at Afton Mine (August 1981) = $ 180.00 / 100 kg. - 219 -PLATE 2 2 A 25 kilogram bag of Hydromex T - 3 . This w i l l be hand loaded into wet b las tho les because of i t s exce l len t water r e s i s t a n c e . - 220 -POWERGEL A Powergel A i s a s l u r r y explos ive s i m i l a r to Hydromex T - 3 . At Afton Mine i t was suppl ied in bulk f o r use on b l a s t patterns where most of the holes contained groundwater. Basic P r o p e r t i e s : S p e c i f i c Grav i ty 1.25 Density 1250 k g . / m . 3 Rela t ive Weight Strength 82 Re la t ive Bulk Strength 122 Unconfined Detonation V e l o c i t y 4500 m . / s e c . Water Resistance Exce l l en t Proper t ies in a 230 mm. (9 inch) Diameter Borehole: Density 51 kg. /m. of hole Estimated Detonation V e l o c i t y 5600 m . / s e c . Estimated Detonation Pressure 8800 MPa. Estimated Borehole Pressure 5000 MPa. Cost at Afton Mine (August 1981) = $ 92.60 / 100 kg. - 221 DETONATING MATERIALS Procore III Pr imers: (See Plate 23) Weight Water Resistance Cost at Afton Mine (August 1981) Reinforced Primacord: (See Plate 23) Weight Diameter T e n s i l e Strength Detonation V e l o c i t y Cost at Afton Mine (August 1981) E-Cord: Weight Diameter T e n s i l e Strength Detonation V e l o c i t y Cost at Afton Mine (August 1981) Instantaneous E l e c t r i c B l a s t i n g Caps: Leg Wire Length Leg Wire Diameter Resistance (Cap + Leg Wires) Cost at Afton Mine (August 1981) 450 grams each Good $ 2.95 each 25.3 gm./m. 5.1 mm. 1.11 kN. 6200 m . / s e c . $ 32.30 / 100 m. 17.9 gm./m. 4.1 mm. 1.0 kN. 6200 m . / s e c . $ 25.10 / 100 m. 3.0 m. 0.53 mm. 1.55 Ohms $ 73.30 / 100 caps - 222 -PLATE 2 3 A Procore III Primer t i e d onto the end of a Reinforced Primacord downline is ready fo r lowering in to a b l a s t h o l e . - 223 -DETONATING MATERIALS continued P l a s t i c B las tho le L i n e r : L a y f l a t Dimension Bore Diameter Wall Thickness Cost at Afton Mine 394 mm. 250 mm. 10 m i l . $ 63.25 / 183 m. r o l l - 224 -APPENDIX III DATA LOGS AND PLOTS USED TO DETERMINE ROCK QUALITY INDEX VALUES - 225 -DATA LOGS AND PLOTS USED TO DETERMINE ROCK QUALITY INDEX VALUES This appendix contains an example of the type of d r i l l e r s ' log sheets used at Afton Mine f o r recording the d r i l l performance parameters. This is fol lowed by the frequency d i s t r i b u t i o n p lots of the RQI v a l u e s , used to inves t iga te the nature of t h e i r d i s t r i b u t i o n wi th in each domain. The shape of these p lo ts provided s u f f i c i e n t j u s t i f i c a t i o n f o r using mean RQI values to represent each domain. Conlinental Explosives Ltd. 620 East Hastings Street. Vancouver. B.C. VGA 1 R V - 2 2 6 -Distributors of: SMITH —BLASTHOLE BITS DRILCO—STABILIZERS '—DRILL PIPE —SHOCK SUBS ^ 3 C O M P A N Y L O C A T I O N PIT 2 - / C o Z c - . ^ D R I L L M A K E ft M O D E L BIT SIZE-TYPE N O Z Z L E S I Z E C O M P R E S S O R M A K E ft M O D E L BIT S E R I A L N U M B E R • M A K E DATE ON 12- 7 7 7 DATE SHIFT HOLE/RUN NUMBER FEET DRILLED DRILLING TIME HYD. DOWN PRESSURE RPM AIR (PSI) ROCK TYPE COMMENTS SOFT MED. H A R D 3./o/77 / - •YO / f c 2..- ¥ 0 / , 3. V •Vice? / / i'-'c 7 f 6- s - t. < 7 )> / ' '/ I i X r / . ti S o • t I , / o 3-C! 1 , // J Z , I' / z 9o Zc3 / / c < r i— / 3 / ' — / / YZ /£ K> . — <-ft> Y - Z Lf,V — '\ > • 1 3 i/J-/f IfO 1 y — — - — - -7 — — -> - r t/zz.y x r — — • i 1 -^ Z Z < £ z r — — - - -< / z>f — / / z ' 1 / x<? - — / / z? -/ / » /'/ 923/ If. 6 z^ .-/ / X - e — 2.SW 7 ' ' * T O T A L ^ f £ <P DATE O F E T Y P E O F F A I L U R E — B E A R I N G S — C O N E S — 6 H I R T T A I L DR 1LLER / - 227 -m. R O C K Q U A L I T Y INDEX DOMAIN | No. of readings = 567 Mean RQI = 345 p S I ' " m i n -ft. n MPa-min. - 228 -DOMAIN II No. of readings = 34 2 Mean RQI = 3 6 0 p s i ~ m i n -ft. n n MPa-min. - 229 -DOMAIN IV A No. of readings = 3 96 Mean RQI = 2 4 5 p s i " m i n -ft. r. MPa-min. - 230 -c o l -<u CL o Z UJ ID o LU cr LU o z UJ or. O o o 7 0 6 0 H 5 0 4 0 30H 2 0 \0A I r 0 I 100 2 0 0 3 0 0 4 0 0 5 0 0 6 0 0 psi-min. ft. T 3 4 5 6 7 8 9 R O C K Q U A L I T Y INDEX T 1 r— 10 il 12 MPo-min. m. DOMAIN IV A - P y No. of readings = 3 36 Mean RQI = 2 9 0 = 6.5 psi-mm. ft. MPa-min. m. - 2 3 1 -7(H 6 0 A c CJ u a. 5 0 H > o z LU O LU CC LU a z LU rr o o o 4 0 H 30H 2 0 -10-0 100 2 0 0 3 0 0 4 0 0 5 0 0 6 0 0 5 6 7 8 9 R O C K Q U A L I T Y INDEX -i 1 r— 10 II 12 psi-min. ft. MPd-min. m. DOMAIN IV B No. of readings = 119 7 Mean RQI = 325 7.4 psi-mm. ft. MPa-min. m. - 232 -70A 60 H c OJ o _^ OJ CL > o z UJ O UJ or u. UJ z UJ or z> <_> o o 50 H 4 0 -30-20^ I0H 0 - I— 100 2 0 0 300 4 0 0 5 0 0 6 0 0 psi-min. ft. T - r -4 8 9 5 6 7 R O C K Q U A L I T Y I N D E X -t 1 r— 10 II 12 MPa-min. m. DOMAIN V No. of readings = 10 6 5 Mean RQI = 2 9 0 = 6.5 psi -mm. ft. MPa-min. m. - 233 -c Q> O i _ OJ Q. u 2 Ui 3 O UJ cr UJ o z UJ cr 3 O o o 70 A 60 A 5 0 4 0 A 3 0 20H 10 0 I r 0 I 100 2 0 0 3 0 0 4 0 0 5 0 0 6 0 0 P s i ' m i n -ft. T 3 4 5 6 7 8 9 R O C K Q U A L I T Y INDEX T , j— 10 II 12 MPo-min . m. DOMAIN VI No. of readings = 411 Mean RQI = 2 70 = 6.1 psi-mm. ft. MPa-min. m. - 234 -7 0 6 0 H c OJ o CL 5 0 -> o z UJ 3 o UJ rr UJ C J z UJ cr 3 O CJ o 4 0 H 3 0 H 2 0 -I0H 0 0 100 2 0 0 3 0 0 — J — 400 i 5 0 0 6 0 0 T 3 4 8 9 5 6 7 R O C K Q U A L I T Y INDEX i i i 10 II 12 psi-min. ft. MPa-min. m. DOMAIN VII No. of readings = 351 Mean RQI = 3 8 0 = 8.6 psi-mm. ft. MPa-min. m. - 235 -7 C H 6 0 H c OJ o C J C L 5 0 H >-o z LU 3 o UJ or LJ o z UJ or 3 O o o 4 0 -30H 2 0 ^ \0A 100 2 0 0 3 0 0 4 0 0 5 0 0 i i 1 — i 1 ' 1 • 1 1 1 1 1— 1 2 3 4 5 6 7 8 9 10 II 12 R O C K Q U A L I T Y INDEX 6 0 0 P s ' - m i n -ft. MPa - m i n . m . DOMAIN VIII No. of readings = 10 2 3 Mean R Q I = 150 = 3.4 psi -mm. ft. MPa-min. m. - 236 -c 0> u CL >-O z UI 3 o LU or LU o z UJ or 3 <_> O o 7 0 H 6 0 H 5 0 4 0 H 30H 20H 100 2 0 0 3 0 0 4 0 0 5 0 0 6 0 0 psi-mm. FT. I i •—1 1 i 1 1 ' 1 1 \ r - j— 0 1 2 3 4 5 6 7 8 .9 10 II 12 R O C K Q U A L I T Y INDEX MPo-min . m. DOMAIN VIII A No. of readings = 3 8 0 Mean R Q I = 3 8 0 = 8 .6 psi -min. ft. MPa-min. m. - 237 -APPENDIX IV DESIGN EXAMPLE FOR THE NEW PERIMETER BLAST and COMPARISON OF DE-COUPLING METHODS - 238 -DESIGN EXAMPLE FOR THE NEW PERIMETER BLAST A d e t a i l e d d iscuss ion of a l l the considerat ions f o r a c o n t r o l l e d b l a s t design are presented in Chapter F i v e . These gu ide l ines were used in the fo l lowing design f o r A f t o n ' s new perimeter b l a s t , although some external cons t ra in ts l i m i t e d the f l e x i b i l i t y of c e r t a i n design a s p e c t s . The F i e l d Parameters: Bench Height -- H = 9.1 m. (30 f t . ) B las tho le Diameter : = D = 230 mm. (9 i n . ) Rock Density = Yr = 0.37 m.3 / tonne (12 f t . 3 / S . T o n ) Powder Factor = PF = 0.085 kg. / tonne (0.17 l b s . / S . T o n ) Length of B l a s t = L = 61 m. (200 f t . ) Design C o n s t r a i n t s : Minimum hole spacing of 3.05 m. (10 f t . ) along buf fer l i n e row. Minimum c r e s t burden of 6.1 m. (20 f t . ) . Minimum row burdens of 3.7 m. (12 f t . ) . Staggered pattern not acceptab le . B las tho le Pat tern: To maintain a g r id p a t t e r n , use hole spacings twice that of the buf fer l i n e row. : . S = 6.1 m. (20 f t . ) Buf fer l i n e burden should be 20 times the b las tho le diameter, or between 0.6 and 0.8 times the production row burden: 20 x D = 20 x 230 mm. = 4.6 m. (15 f t . ) 0.6 x B = 0.6 x 6.1 m. = 3.7 m. (12 f t . ) 0.8 x B = 0.8 x 6.1 m. = 4.9 m. (16 f t . ) There fore , s e l e c t burdens f o r both rows to be = 4.6 m. (15 f t . ) Burden to Spacing Ratio = 1:1.33 - 239 -S u b - D r i l l Depths: For buf fer l i n e holes and f i r s t production row h o l e s , s e l e c t a minimal s u b - d r i l l depth of 0.61 m. (2 f t . ) to avoid damage to the future bench below. Shallow s u b - d r i l l should be a l r i g h t due to large radius of rup-ture in A f t o n ' s h igh ly fragmented rock. For second production row, assume a toe c r a t e r i n g angle of 2 0 ° . Sub-d r i l l depth w i l l be the greater o f : SD = (4.6 - (0 .61/ tan 2 0 ° ) ) x tan 20° = 1.07 m. (3.5 f t . ) or SD = (8.8 - (1 .83/ tan 2 0 ° ) ) x tan 20° = 1.4 m. (4.6 f t . ) There fore , s e l e c t s u b - d r i l l depth = SD = 1.5 m. (5 f t . ) Extra hole length w i l l al low f o r usual b las tho le cav ing . AN/FO Charge Design: ( re fe r to tables in Appendix V f o r quick reference) In Buf fer Line Holes: Charge Weight = ( B x S x H x P F ) / y r = (4.6 x 3.05 x 9.1 x 0.085)/0.37 = 29 kg. (64 l b s . ) per hole In F i r s t Production Holes: Charge Weight = (4.6 x 6.1 x 9.1 x 0.085)/0.37 = 59 kg. (130 l b s . ) per hole In Second Production Holes: Charge Weight = (8.8 x 6.1 x 9.1 x 0.085)/0.37 = 112 kg. (250 l b s . ) per hole F i r i n g Sequence: As shown in Figure 6.3-4 of Chapter S i x . - 240 -B las t Inventory Summary: Number of Buf fer L ine Holes = (L/3.05) + 1 - 2 1 Number of F i r s t Production Holes = (L /6 .1) + 1 = 11 Number of Second Production Holes = (L /6 .1 ) + 1 = 11 Total Explos ive Quanti ty Required = 2.49 tonnes (2.76 S.Tons) Number of 50 msec, delays = ( (L /6 .1 ) x 4) + 3 = 43 Number of 100 msec, delays = (L /6 .1 ) = 10 Duration of Detonation = ( (L /3 .05) + 2) x 0.05 = 1.1 seconds - 241 -COMPARISON OF METHODS FOR DE-COUPLING BUFFER LINE CHARGES Cardboard L iner Tubes: Suppl ied by Sono-Co L t d . , 877 C l i v e d e n , Annacis Is land . As c u r r e n t l y suppl ied to Brenda Mines: Main tubes: 20 f t . x 4-3/4" (4.714" i . d . ) x 1/8" w a l l . Waxed inner and outer ply plus water r e s i s t a n t s e a l e r . $ 3362.31 / 1000 tubes + $ 66.58 set -up charge. Couplers : 12" x 5-1/4" (5" i . d . ) x 1/8" w a l l . $ 366.25 / 1000 couplers + $ 66.58 set-up charge. Total Charge = $ 3861.72 / 1000 tubes = 19.3* / f t . = 63.32* / m. P l a s t i c P ipe: Suppl ied by - International P l a s t i c s , 12180 Vickers Way, Richmond. As suppl ied to Kidd Creek Mine: "Big 0" corrugated dra in pipe (the cheapest pipe a v a i l a b l e ) 4.61" o . d . , 4.0" i . d . , 74 l b s . / 2 5 0 f t . c o i l Cost = $ 85.00 / 250 f t . c o i l = 34* / f t . = 116* / m. P l a s t i c Borehole L i n e r : Suppl ied by L a y f i e l d P l a s t i c s , 12104 - 121A S t . , Edmonton. As suppl ied to Afton Mine: 7-1/2" l a y f l a t dimension, 4-3/4" bore , 8 m i l . wall t h i c k n e s s . Cost = $31.00 / 500 f t . r o l l = 6.2* / f t . = 20.3* / m. - 242 -APPENDIX V EXPLOSIVE LOAD TABLES FOR PERIMETER BLASTS - 243 -AN/FO REQUIREMENTS IN LBS./HOLE SECOND PRODUCTION ROW 5 FOOT SUBGRADE Hole Depth Powder Factor ( I b s . / S . ton) : eet) 0.10 0.11 0.12 0.13 0.14 0.15 0.16 0.17 0.18 0.19 0.20 0.21 0.2! 29 120 132 144 156 168 180 192 204 216 228 240 252 300 30 125 138 150 163 175 188 200 213 225 238 250 263 313 31 130 143 156 169 182 195 208 221 234 247 260 273 325 32 135 149 162 176 189 203 216 230 243 257 270 284 338 33 140 154 168 182 196 210 224 238 252 266 280 294 350 34 145 160 174 189 203 218 232 247 261 276 290 305 363 35 150 165 180 195 210 225 240 255 270 285 300 315 375 36 155 171 186 202 217 233 248 264 279 295 310 326 388 37 160 176 192 208 224 240 256 272 288 304 320 336 400 38 165 182 198 215 231 248 264 281 297 314 330 347 413 39 170 187 204 221 238 255 272 289 306 323 340 357 425 40 175 193 210 228 245 263 280 298 315 333 350 368 438 41 180 198 216 234 252 270 288 306 324 342 360 378 450 Rock Density = 12 f t . 3 / S . ton - 244 -AN/FO REQUIREMENTS IN LBS./HOLE FIRST PRODUCTION ROW 2 FOOT SUBGRADE Hole Depth Powder Factor ( I b s . / S . ton) (Feet) 0.10 0.11 0.12 0.13 0.14 0.15 0.16 0.17 0.18 0.19 0.20 0.21 0.25 26 60 66 72 78 84 90 96 102 108 114 120 126 150 27 63 69 75 81 88 94 100 106 113 119 125 131 156 28 65 72 78 85 91 98 104 111 117 124 130 137 163 29 68 74 81 88 95 101 108. 115 122 128 135 142 169 30 70 77 84 91 98 105 112 119 126 133 140 147 175 31 73 80 87 94 102 109 116 123 131 138 145 152 181 32 75 83 90 98 105 113 120 128 135 143 150 158 188 33 78 85 93 101 109 116 124 132 140 147 155 163 194 34 80 88 96 104 112 120 128 136 144 152 160 168 200 35 83 91 99 107 116 124 132 140 149 157 165 173 206 36 85 94 102 111 119 128 136 145 153 162 170 179 213 37 88 96 105 114 123 131 140 149 158 166 175 184 219 38 - 90 99 108 117 126 135 144 153 162 171 180 189 225 Rock Density = 12 f t . 3 / S . ton - 245 -AN/FO REQUIREMENTS IN LBS./HOLE BUFFER LINE ROW 2 FOOT SUBGRADE Hole Depth Powder Factor ( I b s . / S . ton) : eet) 0.10 0.11 0.12 0.13 0.14 0.15 0.16 0.17 0.18 0.19 0.20 0.21 0.2! 26 30 33 36 39 42 45 48 51 54 57 60 63 75 27 31 34 38 41 44 47 50 53 56 59 63 66 78 28 33 36 39 42 46 49 52 55 59 62 65 68 81 29 34 37 41 44 47 51 54 57 61 64 68 71 84 30 35 39 42 46 49 53 56 60 63 67 70 74 88 31 36 40 44 47 51 54 58 62 65 69 73 76 91 32 38 41 45 49 53 56 60 64 -68 71 75 79 94 33 39 43 47 50 54 58 62 66 70 74 78 81 97 34 ' 40 44 48 52 56 60 64 68 72 76 80 84 100 35 41 45 50 54 58 62 66 70 74 78 83 87 103 36 43 47 51 55 60 64 68 72 77 81 85 89 106 37 44 48 53 57 61 66 70 74 79 83 88 92 109 38 45 50 54 59 63 68 72 77 81 86 90 95 113 Rock Density = 12 f t . 3 / S . ton - 246 -BAGS OF HYDROMEX T-3 / HOLE SECOND PRODUCTION ROW 5 FOOT SUBGRADE Hole Depth AN/FO Powder Factor ( I b s . / S . ton) : eet) 0.10 0.11 0.12 0.13 0.14 0.15 0.16 0.17 0.18 0.19 0.20 0.21 0.25 29 2.5 2.5 3.0 3.0 3.5 3.5 4.0 4.0 4.5 4.5 5.0 5.0 6.0 30 2.5 3.0 3.0 3.5 3.5 4.0 4.0 4.5 4.5 5.0 5.0 5.5 6.5 31 2.5 3.0 3.0 3.5 3.5 4.0 4.0 4.5 5.0 5.0 5.5 5.5 6.5 32 3.0 3.0 3.5 3.5 4.0 4.0 4.5 4.5 5.0 5.0 5.5 6.0 7.0 33 3.0 3.0 3.5 3.5 4.0 4.5 4.5 5.0 5.0 5.5 5.5 6.0 7.0 34 3.0 3.5 3.5 4.0 4.0 4.5 4.5 5.0 5.5 5.5 6.0 6.0 7.5 35 3.0 3.5 3.5 4.0 4.5 4.5 5.0 5.0 5.5 6.0 6.0 6.5 7.5 36 3.0 3.5 4.0 4.0 4.5 4.5 5.0 5.5 5.5 6.0 6.5 6.5 8.0 37 . 3.5 3.5 4.0 4.0 4.5 5.0 5.0 5.5 6.0 6.0 6.5 7.0 8.0 38 3.5 3.5 4.0 4.5 4.5 5.0 5.5 5.5 6.0 6.5 6.5 7.0 8.5 39 3.5 4.0 4.0 4.5 5.0 5.0 5.5 6.0 6.0 6.5 7.0 7.5 8.5 40 3.5 4.0 4.5 4.5 5.0 5.5 5.5 6.0 6.5 7.0 7.0 7.5 9.0 41 3.5 4.0 4.5 5.0 5.0 5.5 6.0 6.0 6.5 7.0 7.5 7.5 9.0 Rock Density = 12 f t . 3 / S . ton - 247 -BAGS OF HYDROMEX T-3 / HOLE FIRST PRODUCTION ROW 2 FOOT SUBGRADE Hole Depth AN/FO Powder Factor ( I b s . / S . ton) r eet ) 0.10 0.11 0.12 0.13 0.14 0.15 0.16 0.17 0.18 0.19 0.20 0.21 0.25 26 1.0 1.5 1.5 1.5 1.5 2.0 2.0 2.0 2.0 2.5 2.5 2.5 3.0 27 1.5 1.5 1.5 1.5 2.0 2.0 2.0 2.0 2.5 2.5 2.5 2.5 3.0 28 1.5 1.5 1.5 1.5 2.0 2.0 2.0 2.5 2.5 2.5 2.5 3.0 3.5 29 1.5 1.5 1.5 2.0 2.0 2.0 2.0 2.5 2.5 2.5 3.0 3.0 3.5 30 1.5 1.5 1.5 2.0 2.0 2.0 2.5 2.5 2.5 2.5 3.0 3.0 3.5 31 1.5 1.5 2.0 2.0 2.0 2.0 2.5 2.5 2.5 3.0 3.0 3.0 3.5 32 1.5 1.5 2.0 2.0 2.0 2.5 2.5 2.5 3.0 3.0 3.0 3.0 4.0 33 1.5 1.5 2.0 2.0 2.0 2.5 2.5 2.5 3.0 3.0 3.0 3.5 4.0 34 1.5 > 2.0 2.0 2.0 2.5 2.5 2.5 3.0 3.0 3.0 3.5 3.5 4.0 35 1.5 2.0 2.0 2.0 2.5 2.5 2.5 3.0 3.0 3.0 3.5 3.5 4.0 36 1.5 2.0 2.0 2.5 2.5 2.5 3.0 3.0 3.0 3.5 3.5 3.5 4.5 37 2.0 2.0 2.0 2.5 2.5 2.5 3.0 3.0 3.0 3.5 3.5 3.5 4.5 38 2.0 2.0 2.0 2.5 2.5 3.0 3.0 3.0 3.5 3.5 3.5 4.0 4.5 Rock Density = 12 f t . 3 / S . ton - 248 -BAGS OF HYDROMEX T-3 / HOLE BUFFER LINE ROW 2 FOOT SUBGRADE Hole Depth AN/FO Powder Factor ( I b s . / S . ton) (Feet) 0.10 0.11 0.12 0.13 0.14 0.15 0.16 0.17 0.18 0.19 0.20 0.21 0.25 26 0.5 0.5 0.5 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.5 1.5 27 0.5 0.5 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.5 1.5 1.5 28 0.5 0.5 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.5 1.5 1.5 1.5 29 0.5 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.5 1.5 1.5 1.5 30 0.5 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.5 1.5 1.5 1.5 2.0 31 0.5 1.0 1.0 1.0 1.0 1.0 1.0 1.5 1.5 1.5 1.5 1.5 2.0 32 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.5 1.5 1.5 1.5 1.5 2.0 33 1.0 1.0 1.0 1.0 1.0 1.0 1.5 1.5 1.5 1.5 1.5 1.5 2.0 34 1.0 1.0 1.0 1.0 1.0 l . p 1.5 1.5 1.5 1.5 1.5 1.5 2.0 35 1.0 1.0 1.0 1.0 1.0 1.5 1.5 1.5 1.5 1.5 1.5 2.0 2.0 36 1.0 1.0 1.0 1.0 1.0 1.5 1.5 1.5 1.5 1.5 1.5 2.0 2.0 37 1.0 1.0 1.0 1.0 1.0 1.5 1.5 1.5 1.5 1.5 2.0 2.0 2.0 38 1.0 1.0 1.0 1.0 1.5 1.5 1.5 1.5 1.5 1.5 2.0 2.0 2.5 Rock Density = 12 f t . 3 / S . ton - 249 -COLLAR HEIGHTS FOR POWERGEL A SECOND PRODUCTION ROW 5 FOOT SUBGRADE Hole Depth AN/FO Powder Factor ( I b s . / S . ton) : eet) 0.10 0.11 0.12 0.13 0.14 0.15 0.16 0.17 0.18 0.19 0.20 0.21 0.2! 29 25 24 24 23 23 23 22 22 21 21 21 20 18 30 26 25 25 24 24 23 23 22 22 22 21 21 19 31 26 26 25 25 25 24 24 23 23 22 22 21 19 32 27 27 26 26 25 25 24 24 23 23 22 22 20 33 28 28 27 27 26 26 25 25 24 24 23 23 21 34 29 28 28 27 27 26 26 25 25 24 24 23 21 35 30 29 29 28 28 27 27 26 25 25 24 24 22 36 31 30 29 29 28 28 27 27 26 26 25 24 22 37 31 31 30 30 29 29 28 27 27 26 26 25 23 38 32 32 31 30 30 29 29 28 27 27 26 26 23 39 33 32 32 31 31 30 29 29 28 28 27 26 24 40 34 33 33 32 31 31 30 29 29 28 28 27 25 41 35 34 33 33 32 31 31 30 30 29 28 28 25 Rock Density = 12 f t . 3 / S . ton - 250 -COLLAR HEIGHTS FOR POWERGEL A FIRST PRODUCTION ROW 2 FOOT SUBGRADE Hole Depth AN/FO Powder Factor ( l b s . / S . ton) : eet) 0.10 0.11 0.12 0.13 0.14 0.15 0.16 0.17 0.18 0.19 0.20 0.21 0.2! 26 24 24 23 23 23 23 23 22 22 22 22 22 21 27 25 25 24 24 24 24 23 23 23 23 23 22 21 28 26 25 25 25 25 25 24 24 24 24 23 23 22 29 27 26 26 26 26 25 25 25 25 24 24 24 23 30 28 27 27 27 27 26 26 26 26 25 25 25 24 31 28 28 28 28 27 27 27 27 26 26 26 26 25 32 29 29 29 29 28 28 28 27 27 27 27 26 25 33 30 30 30 29 29 29 29 28 28 28 28 27 26 34 31 31 31 30 30 30 29 29 29 29 28 28 27 35 32 32 31 31 31 31 30 30 30 29 29 29 28 36 33 33 32 32 32 31 31 31 31 30 30 30 28 37 34 34 33 33 33 32 32 32 31 31 31 30 29 38 35 34 34 34 34 33 33 33 32 32 32 31 30 Rock Density = 12 f t . 3 / S . ton - 251 -COLLAR HEIGHTS FOR POWERGEL A BUFFER LINE ROW 2 FOOT SUBGRADE Hole Depth AN/FO Powder Factor ( I b s . / S . ton) (Feet) 0.10 0.11 0.12 0.13 0.14 0.15 0.16 0.17 0.18 0.19 0.20 0.21 0.25 26 25 25 25 25 25 24 24 24 24 24 24 24 23 27 26 26. 26 26 25 25 25 25 25 25 25 25 24 28 27 27 27 27 26 26 26 26 26 26 26 26 25 29 28 28 28 27 27 27 27 27 27 27 27 26 26 30 29 29 29 28 28 28 28 28 28 28 28 27 27 31 30 30 29 29 29 29 29 29 29 29 28 28 28 32 31 31 30 30 30 30 30 30 30 29 29 29 29 33 32 31 31 31 31 31 31 31 31 30 30 30 30 34 33 32 32 32 32 32 32 32 31 31 31 31 30 35 34 33 33 33 33 33 33 33 32 32 32 32 31 36 34 34 34 34 34 34 34 33 33 33 33 33 32 37 35 35 35 35 35 35 35 34 34 34 34 34 33 38 36 36 36 36 36 36 35 35 35 35 35 35 34 Rock Density = 12 f t . 3 / S . ton - 252 -APPENDIX VI CONVERSION TABLES FOR IMPERIAL AND S . I . UNITS - 253 -IMPERIAL UNITS CONVERSION FACTORS S . I . UNITS Lengths: Areas: Volumes: Mass: Force: Pressure: Densi ty : mil inch foot mi le square inches square fee t square miles square miles acres cubic inches cubic fee t ounces (Imp.) ga l lons (Imp.) pound short ton ounce pound p . s . i . inches of Hg l b s . / c u . foot c u . f t . / S . ton l b s . / S . ton 25.4 25.4 0.3048 1.609344 645.16 0.09290304 2.589988110 258.999 0.4046873 16387.064 0.02831685 28.4131 4.5460905 0.45359237 0.90718474 27801.38510 4.448221615 6894.757293 33.864 16.0185 0.031214 0.5000 micrometre (micron) mi 11 imetre metre ki lometre s q . m i l l imet res s q . metres s q . ki lometres hectares hectares c u . mi l l imet res c u . metres c u . centimetres 1 i t r e s kilogram tonne dyne newton pascal mi 11 ibar k g . / c u . metre c u . m./tonne kg. / tonne R . Q . I . : p . s . i . - m i n . / f t . 0.022620596 MPa-min./m. * Convert ing from Imperial to S . I . , mu l t ip ly by the conversion f a c t o r . * Convert ing from S . I . to Imper ia l , d i v ide by the conversion f a c t o r . 254 -- 255 -EPILOGUE You can convince some of the people a l l of the t ime. You can convince a l l of the people some of the t ime. But you c a n ' t convince a l l of the people a l l of the t ime! P h o t o b y : Ma rk S t o a k e s 

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