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An investigation to evaluate the relationship between rock quality index (RQI) and powder factor for… LeBel, J. R. Guy 1984

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AN INVESTIGATION TO EVALUATE THE RELATIONSHIP, BETWEEN ROCK QUALITY INDEX (RQl) AND POWDER FACTOR FOR SURFACE MINING by J.R. GUY LEBEL B . A . S c , L a v a l U n i v e r s i t y , 1981 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE i n THE FACULTY OF GRADUATE STUDIES Department of 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 required s t a n d a r d THE UNIVERSITY OF BRITISH COLUMBIA June 1984 (cT) J.R. GUY LEBEL, 1984 I n p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f t h e r e q u i r e m e n t s f o r an a d v a n c e d d e g r e e a t t h e 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 , I a g r e e t h a t t h e L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e a n d s t u d y . I f u r t h e r a g r e e t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y p u r p o s e s may be g r a n t e d by t h e h e a d o f my d e p a r t m e n t o r b y h i s o r h e r r e p r e s e n t a t i v e s . I t i s u n d e r s t o o d t h a t c o p y i n g o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l n o t be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . D e p a r t m e n t o f M i n i n g and M i n e a l P r o c e s s E n g i n e e r i n g 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 1956 Main Ma l l V a n c o u v e r , Canada V6T 1Y3 A u g u s t 13, 1984 i i ABSTRACT The d e t e r m i n a t i o n of t h e b l a s t a b i l i t y of t h e r o c k mass i s a p r o b l e m t h a t f a c e s b l a s t i n g e n g i n e e r s on a d a i l y b a s i s . The c o s t l y t r i a l and e r r o r a p p r o a c h may e v e n t u a l l y l e a d t o a s u i t a b l e d e s i g n , a l t h o u g h c o n s t a n t v a r i a t i o n s i n t h e r o c k mass p r o p e r t i e s presume t h a t t h i s a p p r o a c h i s c o n s t a n t l y i n p r o g r e s s . S h o r t l y a f t e r t h e p u b l i c a t i o n , a t UBC, of t h e L e i g h t o n r e p o r t on t h e c o r r e l a t i o n between t h e Rock Q u a l i t y Index (RQI) and t h e c o n t r o l l e d powder f a c t o r d e f i n e d a t A f t o n Mine, t h i s r e s e a r c h p r o j e c t was e s t a b l i s h e d i n o r d e r t o d e t e r m i n e t h e e x t e n t of s u c h c o r r e l a t i o n . The Rock Q u a l i t y Index i s o b t a i n e d from r o t a r y b l a s t h o l e d r i l l p e r f o r m a n c e d a t a . D e f i n e d as a s i n g l e n u m e r i c a l e s t i m a t i o n of t h e r o c k mass p r o p e r t i e s , t h e RQI r e f l e c t s v a r i a t i o n s i n t h e r o c k q u a l i t y . I t i s a s i m p l e and p r a c t i c a l a p p r o a c h t o b l a s t d e s i g n b a s e d on an e m p i r i c a l r e l a t i o n s h i p . At E q u i t y S i l v e r , L o r n e x and G r e e n h i l l s M i n e s , d a t a were g a t h e r e d and e v a l u a t e d i n o r d e r t o c o n f i r m t h e r e l a t i o n s h i p and d e t e r m i n e t h e f a c t o r s t h a t i n f l u e n c e o r c o n t r o l i t s d e f i n i t i o n . I t was f o u n d t h a t many f a c t o r s a c t u a l l y a f f e c t t h e d e t e r m i n a t i o n of t h e r e l a t i o n s h i p . They a r e e a s i l y d i v i d e d i n two c a t e g o r i e s , t h e f a c t o r s r e l a t e d t o t h e d r i l l i n g mechanism o r t o t h e b l a s t i n g p r o c e s s . The a c c u r a c y of t h e d r i l l i n g d a t a was of c o n c e r n t o L e i g h t o n and a d r i l l p e r f o r m a n c e r e c o r d e r was u s e d a t two o f t h e l o c a t i o n s i n o r d e r t o o b t a i n a c c u r a t e d a t a . T h i s r e s e a r c h p r o j e c t p e r m i t s t h e c o n c l u s i o n t h a t t h e b a s i c i d e a of a c o r r e l a t i o n between Rock Q u a l i t y Index and t h e r o c k mass b l a s t a b i l i t y i s r i g h t . The c o r r e l a t i o n i s , a t t h i s t i m e , s i t e s p e c i f i c due t o t h e d i f f e r e n c e i n t h e RQI v a l u e s o b t a i n e d from v a r i o u s d r i l l i n g e q u i p m e n t and a l s o due t o t h e s p e c i f i c b l a s t i n g c o n d i t i o n s . S i n c e many v a r i a b l e s a r e f o u n d t o a f f e c t b o t h t h e d r i l l i n g and b l a s t i n g mechanisms, b a s i c g u i d e l i n e s a r e p r o p o s e d i n o r d e r t o a s s u r e t h e s u c c e s s of f u r t h e r r e s e a r c h on t h e Rock Q u a l i t y I n d e x . Optimum b l a s t i n g i s t h e key t o i m p roved s l o p e s t a b i l i t y , h i g h e r s t r i p p i n g r a t i o , h i g h p r o d u c t i v i t y and r e d u c e d m a i n t e n a n c e c o s t . However, optimum b l a s t i n g i s a c h i e v e d o n l y w i t h a w e l l e s t a b l i s h e d r o c k mass c h a r a c t e r i z a t i o n p r ogram. i v TABLE OF CONTENTS Page ABSTRACT i i TABLE OF CONTENTS i v L I S T OF TABLES i x L I S T OF FIGURES x ACKNOWLEDGEMENTS xv CHAPTER 1 INTRODUCTION 1 1.1 The 1980-1982 R e s e a r c h P r o j e c t 5 1.2 The 1982-1984 R e s e a r c h P r o j e c t 9 1 .3 R e f e r e n c e s 12 CHAPTER 2 ROCK FRAGMENTATION 13 2.1 Review of Rock F a i l u r e Mechanisms 16 2.1.1 Rock Mass C h a r a c t e r i s t i c s 16 2.1.2 The C o u l o m b - N a v i e r T h e o r y o f F a i l u r e 16 2.1.3 The Mohr T h e o r y o f F a i l u r e 17 2.1.4 The G r i f f i t h T h e o r y o f F a i l u r e 18 2.1.5 Hoek and Brown E m p i r i c a l F a i l u r e 21 Cr i t e r i o n 2.2 D r i l l i n g , B l a s t i n g , G r i n d i n g 26 2.3 R e f e r e n c e s 29 CHAPTER 3 THE DRILLING PROCESS 31 3.1 T r i c o n e R o t a r y B i t s 34 3.1.1 J o u r n a l A n g l e and Skew A n g l e 38 3.1.2 T e e t h and C a r b i d e I n s e r t s 40 3.1.3 Bear i n g s 43 V Page 3.1.4 Gage D e s i g n and S h i r t t a i l P r o t e c t i o n 46 3.1.5 A i r c o u r s e s 48 3.2 P e n e t r a t i o n of B r i t t l e Rocks 51 3.2.1 S t r e s s e s B e n e a t h t h e I n d e n t o r 51 3.2.1.1 The I n d e n t o r Geometry 54 3.2.1.2 I n d e x i n g 58 3.2.2 T o o l P e n e t r a t i o n M o d e l s 58 3.2.2.1 P a u l and S i k a r s k i e P e n e t r a t i o n 60 Model 3.2.2.2 Bauer and C a l d e r P e n e t r a t i o n 62 Model 3.2.2.3 P a r i s e a u and F a i r h u r s t P e n e t r a - 65 t i o n M o d e l s 3.3 S p e c i f i c E n e r g y 69 3.4 Rock Mass D r i l l a b i l i t y 72 3.4.1 D r i l l i n g T e s t s 72 3.4.2 A n a l y s i s of t h e M e c h a n i c a l P r o p e r - 73 t i e s of t h e Rock 3.5 T r i c o n e R o t a r y D r i l l i n g 79 3.5.1 D r i l l i n g P a r a m e t e r s 79 3.5.1.1 The Weight on t h e B i t 79 3.5.1.2 The R o t a r y Speed 82 3.5.1.3 The A i r P r e s s u r e and Volume 82 3.5.1.4 The T o r q u e 84 3.5.2 D r i l l i n g E q u a t i o n s 84 3.6 Rock Q u a l i t y Index 88 3.7 Summary 92 v i Page 3.8 R e f e r e n c e s 93 CHAPTER 4 THE BLASTING PROCESS 97 4.1 T h e o r y of B l a s t i n g 103 4.1.1 Gas E x p a n s i o n T h e o r y 103 4.1.2 S t r e s s Wave T h e o r y 105 4.1.3 P r a c t i c a l B l a s t i n g T h e o r y 107 4.2 The M a j o r F a c t o r s A f f e c t i n g F r a g m e n t a - 108 t i o n 4.2.1 Rock Mass P r o p e r t i e s 108 4.2.1.1 S t r u c t u r a l G e o l o g y 108 4.2.1.2 F a i l u r e B e h a v i o u r 117 4.2.2 D e s i g n P a r a m e t e r s 120 4.2.3 The D e s i g n Powder F a c t o r 137 4.3 Rock Mass B l a s t a b i l i t y 142 4.3.1 V i s u a l D e t e r m i n a t i o n o f t h e Rock 142 Mass B l a s t a b i l i t y 4.3.2 C h a r a c t e r i z a t i o n o f t h e Rock Mass 143 by G e o p h y s i c Methods 4.3.3 C o r r e l a t i o n of t h e B l a s t a b i l i t y w i t h 144 one or more Rock Mass P r o p e r t i e s , M e a s u r e d i n L a b o r a t o r y o r I n - S i t u 4.3.4 D e t e r m i n a t i o n o f t h e B l a s t a b i l i t y 149 by S m a l l C r a t e r T e s t s 4.3.5 C h a r a c t e r i z a t i o n o f t h e Rock Mass 154 f r o m t h e P e r f o r m a n c e of P r o d u c t i o n R o t a r y D r i l l s 4.4 Summary 159 4.5 R e f e r e n c e s 165 v i i Page CHAPTER 5 F I E L D RESEARCH PROJECT 171 5.1 D r i l l P e r f o r m a n c e R e c o r d e r i n t h e M i n i n g 175 I n d u s t r y 5.2 E q u i t y S i l v e r Mine ^ 185 5.2.1 Summary of t h e G e o l o g y 185 5.2.2 The B l a s t i n g P r o c e d u r e s a t E q u i t y 190 „ S i l v e r 5.2.3 De v e l o p m e n t o f t h e C o r r e l a t i o n 192 Between RQI and Powder F a c t o r 5.2.4 A n a l y s i s o f t h e R e s u l t s 198 5.3 L o r n e x Mine 200 5.3.1 Summary of t h e G e o l o g y 200 5.3.2 The B l a s t i n g P r o c e d u r e s a t L o r n e x 204 5.3.3 Development o f t h e C o r r e l a t i o n 206 Between RQI and Powder F a c t o r 5.3.4 A n a l y s i s o f t h e R e s u l t s 211 5.4 G r e e n h i l l s Mine 212 5.4.1 Summary of t h e G e o l o g y 212 5.4.2 The B l a s t i n g P r o c e d u r e s a t 217 G r e e n h i l l s 5.4.3 Development o f t h e C o r r e l a t i o n 218 Between RQI and Powder F a c t o r 5.4.4 A n a l y s i s o f t h e R e s u l t s 224 5.5 D i s c u s s i o n and I n f e r e n c e s 225 5.5.1 A c c u r a c y of t h e I n p u t D a t a 225 5.5.2 D r i l l P e r f o r m a n c e R e c o r d e r s 226 5.5.3 D r i l l i n g P r o c e d u r e s 228 5.5.4 B l a s t i n g P r o c e d u r e s 231 v i i i Page 5.5.5 Rock Mass C o n d i t i o n s and P r o p e r t i e s 233 5.5.6 C o r r e l a t i o n s w i t h t h e Rock Q u a l i t y 234 Index 5.6 S u g g e s t e d F u r t h e r R e s e a r c h 236 5.7 R e f e r e n c e s 240 CHAPTER 6 CONCLUSIONS 242 BIBLIOGRAPHY 246 APPENDICES I BIT COMPARISON 260 I I RELATIONSHIP BETWEEN DOWN PRESSURE AND APPLIED 262 WEIGHT I I I POSSIBLE BENEFITS FROM IMPROVED FRAGMENTATION 266 IV REVIEW OF T.E. L I T T L E REPORT ON RQI 268 V MODIFICATION OF BLASTING METHODS 273 i x L I S T OF TABLES T a b l e 1 A p p r o x i m a t e R e l a t i o n s h i p Between Rock Mass Q u a l i t y and M a t e r i a l C o n s t a n t s 2 E f f e c t on O v e r s i z e F r a g m e n t a t i o n of B l a s t -h o l e S p a c i n g , S, J o i n t S p a c i n g , S j , and O v e r s i z e S p e c i f i c a t i o n , M 3 L e v e l s o f B l a s t i n g Damage Commonly O b s e r v e d on P i t W a l l s 4 Rock P r o p e r t i e s E q u i t y S i l v e r Mine 5 Summary o f RQI V a l u e s a t E q u i t y S i l v e r Mine 6 C o r r e l a t i o n Between RQI and Powder F a c t o r a t E q u i t y S i l v e r Mine 7 Summary o f RQI V a l u e s and Rock S t r e n g t h a t L o r n e x M i n e 8 Rock P r o p e r t i e s G r e e n h i l l s Mine 9 Summary o f RQI V a l u e s a t G r e e n h i l l s Mine 10 C o r r e l a t i o n Between RQI and Powder F a c t o r a t G r e e n h i l l s Mine 11 R e l a t i o n s h i p Between Rock Q u a l i t y Index and R o t a r y B i t D i a m e t e r X L I S T OF FIGURES F i g u r e 1.1-1 Rock Q u a l i t y Index V a l u e s f o r E a c h Domain Ranked i n O r d e r of I n c r e a s i n g Q u a l i t y 1.1-2 P r o p o s e d C o r r e l a t i o n Between Rock Q u a l i t y Index and Powder F a c t o r a t A f t o n Mine 2.1-1 G r a p h i c a l R e p r e s e n t a t i o n of Mohr T h e o r y o f ^ S t r e s s C o n d i t i o n s f o r F a i l u r e of I n t a c t Rock 2.1-2 Mohr C i r c l e s f o r F a i l u r e o f Specimen of Q u a r t z i t e T e s t e d by Hoek 2.1- 3 G r a p h i c a l R e p r e s e n t a t i o n of Hoek and Brown F a i l u r e C r i t e r i o n 2.2- 1 C o m p a r i s o n of E n e r g y R e q u i r e m e n t f o r V a r i o u s F r a g m e n t a t i o n P r o c e s s e s 3.1-1 Development H i s t o r y o f R o t a r y Rock B i t s 3.1-2 R o l l e r B i t Improvement 3.1-3 N o m e n c l a t u r e o f R o t a r y B i t 3.1-4 T r i c o n e B i t O f f s e t 3.1-5 V a r i o u s I n s e r t Shapes Commonly Used i n B l a s t H o l e Rock B i t s 3.1-6 R e s u l t s of R o l l e r B e a r i n g T e s t s 3.1-7 E f f e c t o f S i d e L o a d s on B i t B e a r i n g s 3.1- 8 C r o s s - S e c t i o n a l View of a J e t B i t 3.2- 1 S t r e s s P r o f i l e on C o n t a c t S u r f a c e and o n . A x i s of Symmetry 3.2-2 M e d i a A f t e r S e c o n d a r y F a i l u r e Has O c c u r e d 3.2-3 C h a r a c t e r i s t i c F o r c e - P e n e t r a t i o n C u r v e s f o r C h a r c o a l G r a y G r a n i t e Under S t a t i c B i t L o a d i n g x i 3.2-4 A v e r a g e F o r c e - P e n e t r a t i o n C u r v e s f o r C a r t h a g e M a r b l e as O b t a i n e d w i t h 30 and 60 D e g r e e S h a r p B i t - T e e t h a t A t m o s p h e r i c P r e s s u r e f o r V a r i o u s I n d e x i n g D i s t a n c e s 3.2-5 T h e o r e t i c a l F o r c e - P e n e t r a t i o n C u r v e f o r B r i t t l e C r a t e r Model 3.2-6 Rock P e n e t r a t i o n C o n s t a n t v s U n i a x i a l C o m p r e s s i v e S t r e n g t h 3.2-7 Assumed S t r e s s F i e l d f o r " F a l s e - N o s e " S i t u a t i o n 3.4-1 E s t i m a t e d D r i l l i n g R a te o f New Hughes T r i -cone Rock B i t a t 60 r e v / m i n as D e t e r m i n e d by M i c r o b i t D r i l l i n g R a t e T e s t s 3.4-2 E s t i m a t e d R e l a t i v e I n c r e a s e i n P e n e t r a t i o n R a t e V e r s u s Number o f Weakness P l a n e s p e r M e t r e D r i l l - H o l e 3.4- 3 C o r r e l a t i o n of D r i l l i n g P e r f o r m a n c e w i t h Rock C h a r a c t e r i s t i c s 3.5- 1 D r i l l i n g C o n d i t i o n s 3.5- 2 R e l a t i o n s h i p Between Rock C o m p r e s s i v e S t r e n g t h , P e n e t r a t i o n R a t e , Weight and RPM 3.6- 1 D r i l l i n g R a t e v s . Weight p e r I n c h o f B i t D i a m e t e r 4.0-1 E f f e c t o f F r a g m e n t a t i o n on C o s t of M i n i n g 4.0- 2 O u t p u t f o r D i f f e r e n t S h o v e l T r u c k Combina-t i o n S i n g l e C r u s h e r , Good C o n d i t i o n s and Po o r D i g g i n g 4.1- 1 I n t e r a c t i o n of S t r a i n Wave w i t h P r o p a g a -t i n g C r a c k 4.2- 1 I l l u s t r a t i o n of t h e E f f e c t o f Rock S t r u c -t u r e on C r a t e r F o r m a t i o n 4.2-2 I l l u s t r a t i o n of t h e E f f e c t of Rock S t r u c -t u r e on C r a t e r F o r m a t i o n 4.2-3 I l l u s t r a t i o n of t h e E f f e c t of Rock S t r u c -t u r e on C r a t e r F o r m a t i o n x i i Page 4.2-4 S p e c t r u m of Rock B e h a v i o u r 118 4.2-5 T r e n d s of F r a g m e n t a t i o n Index, F c , w i t h 123 L/B and S/B R a t i o s 4.2-6 S c h e m a t i c of t h e E f f e c t o f D e c r e a s i n g t h e 125 B u r d e n on S i m i l a r C h a r g e s F i r e d i n Rock 4.2-7 E f f e c t o f Water C o n t e n t on t h e D e t o n a t i o n 127 V e l o c i t y of AN/FO 4.2-8 R a t i o s a t Benches 129 4.2-9 E f f e c t o f D e l a y Time Between S h o t h o l e s on 133 A v e r a g e Fragment S i z e 4.2-10 B l a s t h o l e / I n i t i a t i o n P a t t e r n s w i t h B=S f o r 134 S h o t s F i r e d t o an Open F a c e 4.2-11 P l o t o f P a r t i c l e V e l o c i t i e s I n d u c e d a t 136 G i v e n D i s t a n c e s by P a r t i c u l a r C h a r g e s 4.2-12 S h o v e l P r o d u c t i o n on a Y e a r l y B a s i s a t One 139 O p e r a t i o n V e r s u s E x p l o s i v e C o n s u m p t i o n i n Rock o f 20,000 p s i C o m p r e s s i v e S t r e n g t h 4.2- 13 A P l o t o f Ground V i b r a t i o n v s Powder F a c t o r 140 M e a s u r e d From a S e r i e s of P r o d u c t i o n B l a s t s a t a L a r g e Open P i t Mine Showing t h e A b r u p t I n c r e a s e of t h e L e v e l o f G r ound V i b r a t i o n as t h e Powder F a c t o r i s D e c r e a s e d 4.3- 1 U n i a x i a l C o m p r e s s i v e S t r e n g t h v s Powder 145 F a c t o r 4.3-2 A c o u s t i c V e l o c i t y v s Powder F a c t o r 147 4.3-3 F r a c t u r e F r e q u e n c y v s Powder F a c t o r 148 4.3-4 B l a s t a b i l i t y F a c t o r v s E q u i v a l e n t RQD 150 4.3-5 V a r i a t i o n of B r o k e n Rock Volume w i t h t h e 151 D e p t h of Embedment f o r a C o n c e n t r a t e d C h arge 4.3-6a Optimum D e p t h R a t i o v s S t r a i n E n e r g y F a c t o r 153 4.3-6b B l a s t a b i l i t y F a c t o r v s S t r a i n E n e r g y F a c t o r 153 4.3-6c E x p l o s i v e C o n s u m p t i o n vs S t r a i n E n e r g y 153 F a c t o r x i i i Page 4.3- 7 P r o p o s e d C o r r e l a t i o n Between Rock Q u a l i t y 158 Index and Powder F a c t o r a t A f t o n Mine 4.4- 1 F e a t u r e s of a S a t i s f a c t o r y B l a s t 163 5.0- 1 L o c a t i o n s of t h e M i n e s Where t h e RQI S t u d i e s 173 Were C a r r i e d Out 5.1- 1 E f f e c t o f Mean D i s c o n t i n u i t y S p a c i n g on 177 a) E a s e of B l a s t i n g , b) P e n e t r a t i o n R a t e 5.1-2 R e c o r d e d C h a r t ( L o r n e x ) 179 5.1-3 Computer P l o t of t h e D i f f e r e n c e Between 182 RQI-LOGS and RQI-REC as a F u n c t i o n of RQI-LOGS 5.1- 4 H i s t o g r a m o f t h e A v e r a g e D i f f e r e n c e Between 183 RQI-LOGS and RQI-REC as a F u n c t i o n of RQI-LOGS 5.2- 1 S c h e m a t i c H i s t o r i c a l G e o l o g y , E q u i t y S i l v e r 186 Mine 5.2-2 E q u i t y S i l v e r M i n e , 1260m Bench G e o l o g y 191 5.2-3 Rock Q u a l i t y Index V a l u e s f o r E a c h Domain 195 Ranked i n O r d e r o f D e c r e a s i n g Q u a l i t y , E q u i t y S i l v e r Mine 5.2- 4 P r o p o s e d C o r r e l a t i o n Between Rock Q u a l i t y 197 Index and Powder F a c t o r a t E q u i t y S i l v e r Mine 5.3- 1 L o r n e x Open P i t Mine 201 5.3-2 L o w e r - H e m i s p h e r e , E q u a l - A r e a S t e r e o g r a p h i c 203 P r o j e c t i o n s of S t r u c t u r e s Mapped i n t h e L o r n e x Open P i t 5.3-3 Rock Q u a l i t y Index i n D i f f e r e n t Domains o f 208 L o r n e x Mine 5.3- 4 R e l a t i o n s h i p Between Rock Q u a l i t y Index and 210 G r i n d i n g R ate a t L o r n e x 5.4- 1 G r e e n h i l l s Mine S t a t i g r a p h y 213 5.4-2 G r e e n h i l l s Cougar P i t 214 x i v Page 5.4-3 Rock Q u a l i t y Index V a l u e s f o r E a c h Domain 221 Ranked i n O r d e r of D e c r e a s i n g Q u a l i t y , G r e e n h i l l s 5.4- 4 P r o p o s e d C o r r e l a t i o n Between Rock Q u a l i t y 223 Index and Powder F a c t o r a t G r e e n h i l l s Mine 5.5- 1 I n f l u e n c e of T r i c o n e R o t a r y B i t Wear on 230 P e n e t r a t i o n R ate X V ACKNOWLEDGEMENTS The a u t h o r f i r s t w i s h e s t o thank h i s r e s e a r c h s u p e r v i s o r , P r o f e s s o r C O . Brawner, f o r h i s d e d i c a t i o n , u n l i m i t e d s u p p o r t and p e r t i n e n t a d v i c e . The f a c u l t y members of t h e Department 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 a r e a l s o t h a n k e d f o r t h e i r e n c o u r a g e m e n t . I n a d d i t i o n , t h e a u t h o r has a p p r e c i a t e d t h e i n v o l v e m e n t o f t h e f o l l o w i n g m i n i n g c o m p a n i e s and t h e a s s i s t a n c e and c o o p e r a t i o n o f t h e i r e m p l o y e e s t o w a r d t h i s r e s e a r c h p r o j e c t : - E q u i t y S l i v e r M i n e s L t d . - L o r n e x M i n i n g C o r p . - G r e e n h i l l s Mine (Westar M i n i n g L t d . ) V a l u a b l e t e c h n i c a l a s s i s t a n c e was p r o v i d e d by Don G i b s o n and Don Cameron of G e o l o g r a p h P i o n e e r , C h r i s P a q u e t t e o f S I I , Doug Young and E r i c P r e z i o z i o f D r e s s e r I n d u s t r i e s , A l a n Bauer of Queen U n i v e r s i t y and J a c k H a r b o u r n e of Prime E x p l o s i v e s . T h a n k s t o M.C. C h a r t r a n d f o r h e r e n c o u r a g e m e n t . The a u t h o r w i s h e s t o a c k n o w l e d g e t h e f i n a n c i a l s u p p o r t from t h e B.C. S c i e n c e C o u n c i l w h i c h made t h e p r o j e c t p o s s i b l e . The Cy and E m e r a l d Keyes Fund S c h o l a r s h i p , t h e D r . G.M. F u r n i v a l S c h o l a r s h i p (Westmin R e s o u r c e s L t d . ) and t h e L t . E r i c S. D i t m a r s S c h o l a r s h i p were a l s o v e r y much a p p r e c i a t e d d u r i n g t h e two y e a r s t h e a u t h o r s p e n t a t U.B.C. 1 CHAPTER 1 2 1.0 INTRODUCTION Open p i t s l o p e s t a b i l i t y i s g o v e r n e d by t h r e e major f a c t o r s : s t r u c t u r a l g e o l o g y , g r o u n d w a t e r and b l a s t i n g . They d i f f e r i n t h e s e n s e t h a t mine o p e r a t o r s have b e t t e r c o n t r o l o v e r b l a s t i n g t h a n t h e y do w i t h t h e f i r s t two. However, when c a r e f u l e n g i n e e r i n g i s u s e d when d e s i g n i n g a p i t s l o p e , v e r y l i t t l e i s g e n e r a l l y a v a i l a b l e d u r i n g t h e e x c a v a t i o n o f t h e same s l o p e . A l t h o u g h b l a s t i n g has became more a s c i e n c e t h a n an a r t , many m i n i n g o p e r a t i o n s a r e s t i l l b r e a k i n g t h e r o c k i n e f f i c i e n t l y . In some c a s e s , t h e w i l l i n g n e s s o f t h e b l a s t i n g e n g i n e e r t o m i n i m i z e p r o d u c t i o n downtime l e a d s him t o t h e u t i l i z a t i o n o f a h i g h powder ( e n e r g y ) f a c t o r , t h e r e f o r e c a u s i n g damage t o t h e r o c k mass o u t s i d e t h e p i t p e r i m e t e r w i t h a r e s u l t i n g f l a t t e r s l o p e a n g l e . On t h e o t h e r hand, when u r g e d t o keep t h e d i r e c t b l a s t i n g c o s t s t o a minimum, t h e b l a s t i n g e n g i n e e r w i l l o f t e n u n d e r l o a d t h e b l a s t h o l e s and c h o k e d b l a s t s w i l l o c c u r . In a d d i t i o n t o t h e p i t w a l l damage, t o u g h d i g g i n g c o n d i t i o n s r e d u c e p r o d u c t i v i t y and i n c r e a s e equipment m a i n t e n a n c e . T h e r e f o r e , t h e r e i s a major e c o n o m i c i n c e n t i v e t o w a r d t h e a c h i e v e m e n t of optimum b l a s t i n g p r a c t i c e . S t e e p e r and s t a b l e p i t w a l l s and w e l l f r a g m e n t e d muck p i l e s r e p r e s e n t r e d u c e d s t r i p p i n g r a t i o and o p e r a t i n g c o s t s . Many mine o p e r a t o r s have r e a l i z e d t h e s i t u a t i o n and u n d e r s t o o d t h e f a c t t h a t a more p r o f i t a b l e b a l a n c e s h e e t does not g e n e r a l l y c o i n c i d e w i t h t h e minimum b l a s t i n g c o s t s . C o n s e q u e n t l y , t h e y a r e p l a n n i n g b l a s t 3 o p t i m i z a t i o n p r o g r a m s . B l a s t i n g o p t i m i z a t i o n s t a r t s w i t h t h e c h a r a c t e r i z a t i o n o f t h e r o c k mass. The b l a s t i n g e n g i n e e r must d e t e r m i n e t h e b l a s t a b i l i t y of t h e r o c k and a l l o c a t e t o i t a c e r t a i n powder ( e n e r g y ) f a c t o r . However, b e c a u s e of t h e inhomogeneous n a t u r e of t h e r o c k , t h e d e t e r m i n a t i o n of b l a s t a b i l i t y i s a v e r y d i f f i c u l t t a s k . C o n s e q u e n t l y , b l a s t o p t i m i z a t i o n p r o g r a m s a r e g e n e r a l l y p e r f o r m e d as c o s t l y t r i a l and e r r o r p r o c e s s e s . N e v e r t h e l e s s , s e v e r a l methods have been p r o p o s e d i n o r d e r t o d e t e r m i n e r o c k mass b l a s t a b i l i t y and t h e r e f o r e r e d u c e t h e e x t e n t of t h e t r i a l and e r r o r a p p r o a c h . A l l a r e h a n d i c a p p e d by m a j o r drawbacks s u c h as t h e method i s c o s t l y , i t r e q u i r e s s k i l l e d p e r s o n e l o r s p e c i a l e q u i p m e n t ; o r i t may be i n a c u r a t e , t o o g e n e r a l o r s i t e s p e c i f i c ; o r f i n a l l y , t h e method i s j u s t n o t p r a c t i c a l i n a m i n i n g o p e r a t i o n . A r e s e a r c h p r o j e c t , d i r e c t e d by P r o f e s s o r C O . Brawner of t h e 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 D e p a r t m e n t of U n i v e r s i t y of B r i t i s h C o l u m b i a , h a s been d i r e c t e d t o w a r d t h e d e t e r m i n a t i o n o f a s i m p l e and p r a c t i c a l method of a s s e s s i n g t h e r o c k mass b l a s t a b i l i t y . The p r o p o s e d method i s n o t b a s e d on any p a r t i c u l a r r o c k mass p r o p e r t y but r a t h e r u t i l i z e s t h e t r i c o n e r o t a r y b i t as a t e s t i n g t o o l t o e v a l u a t e a measure o f t h e s t r e n g t h o f t h e r o c k mass, and t h e r e f o r e t a k e s i n t o a c c o u n t a l l r o c k mass p r o p e r t i e s as a w h o l e . I t i s b e l i e v e d t h a t t h e l a r g e body o f d a t a a v a i l a b l e f r o m t h e b l a s t h o l e d r i l l l o g s c o u l d be i n t e r p r e t e d t o y i e l d a u s e f u l i n d i c a t i o n of t h e r o c k mass 4 b l a s t a b i l i t y . T h e s e d a t a a r e a l r e a d y c o l l e c t e d f o r o t h e r p u r p o s e s by t h e d r i l l e r and c o n s e q u e n t l y does n o t r e q u i r e any a d d i t i o n a l e x p e n s e . I t c o n s i s t s of t h e p e n e t r a t i o n r a t e ( h o l e d e p t h and d r i l l i n g t i m e ) and t h e w e i g h t on t h e b i t (down p r e s s u r e ) . From t h e s e d a t a , t h e Rock Q u a l i t y Index (RQI) i s d e f i n e d a s : RQI = W/PR = Wt/d - P t / d where W = w e i g h t on t h e b i t PR = p e n e t r a t i o n r a t e t = d r i l l i n g t i m e d = h o l e d e p t h P = h y d r a u l i c down p r e s s u r e and w i t h W = f ( P ) + C t e V e r y good r e s u l t s were o b t a i n e d by John C. L e i g h t o n a t A f t o n Mine when c o r r e l a t i n g RQI and optimum d e s i g n powder f a c t o r f o r p e r i m e t e r b l a s t s . 5 1.1 THE 1980 TO 1982 RESEARCH PROJECT T h i s s e c t i o n b r i e f l y summarizes t h e r e p o r t s p u b l i s h e d by L e i g h t o n i n 1 9 8 2 1 " 3 . The f i r s t f i e l d p r o g r a m was p e r f o r m e d a t A f t o n Mine d u r i n g t h e summer of 1981. In a p e r i o d o f o v e r s i x months, L e i g h t o n s t a n d a r d i z e d and o p t i m i z e d t h e c o n t r o l l e d b l a s t i n g p r o c e d u r e t o t h e e x t e n t where t h e powder ( e n e r g y ) f a c t o r was t h e o n l y d e s i g n v a r i a b l e l e f t w h i l e m o n i t o r i n g t h e d r i l l p e r f o r m a n c e i n n i n e g e o l o g i c a l domains o f t h e p i t ( F i g u r e 1.1-1). The s t a t i s t i c a l a n a l y s i s of t h e RQI d i s t r i b u t i o n w i t h i n e a c h domain showed t h a t t h e a v e r a g e v a l u e was r e p r e s e n t a t i v e o f t h e d i s t r i b u t i o n . The g r a p h shown i n F i g u r e 1.1-2 was t h e n d e r i v e d , r e p r e s e n t i n g t h e optimum d e s i g n powder ( e n e r g y ) f a c t o r f o r p e r i m e t e r b l a s t i n g i n e a c h domain v e r s u s t h e RQI a l l o c a t e d t o t h e p a r t i c u l a r domain a t A f t o n M i n e . The f o l l o w i n g i s a q u o t a t i o n o f t h e f i r s t two c o n c l u s i o n s r e p o r t e d by L e i g h t o n 1 : " 1) The a c t i o n o f a r o t a r y d r i l l i s a f f e c t e d by major r o c k mass p r o p e r t i e s and s t r u c t u r a l g e o l o g y , c a u s i n g i t t o r e f l e c t t h e competancy of t h e r o c k on a q u a l i t a t i v e b a s i s . " " 2) P r o v i d e d t h a t t h e h y d r a u l i c down p r e s s u r e and p e n e t r a t i o n r a t e a r e c a r e f u l l y m o n i t o r e d when d r i l l i n g e a c h b l a s t h o l e , t h e Rock Q u a l i t y Index can be c a l c u l a t e d and w i l l s e r v e as a r e l i a b l e i n d i c a t o r of t h e r o c k mass c o n d i t i o n . " 6 c E i s. c E i (?) o_ 8-350-300-x U J Q Z >-_ l <t ID O o o oc 6-4-3-2.26-1-250-200-150-I00 J O Q < i > O Q O Q i Z < o Q z < o o I < I > z < o Q m i > z < O Q Z o Q < O O i > z < o Q C D > z < o Q DOMAINS FIGURE 1.1 —I - ROCK QUALITY INDEX VALUES FOR EACH DOMAIN RANKED IN ORDER OF INCREASING QUALITY. ( after Leighton1) 7 FIGURE 1.1-2= PROPOSED CORRELATION BETWEEN ROCK QUALITY INDEX AND POWDER FACTOR AT AFTON MINE, (after Leighton1) 8 I t was a l s o s p e c i f i e d t h a t t h e r e l a t i o n s h i p was, a t t h i s t i m e , o n l y v a l i d f o r t h e p a r t i c u l a r b i t d e s i g n and d r i l l i n g e q u i pment ( c h i s e l shape WC, BE 40R). F i n a l l y , L e i g h t o n l e f t t h e d i s c u s s i o n open on t o p i c s r e l a t e d t o t h e e f f e c t o f b i t wear on RQI, t h e use of a d r i l l p e r f o r m a n c e r e c o r d e r as a means of o b t a i n i n g more a c c u r a t e d a t a and t h e p o s s i b i l i t y of u s i n g t h e RQI t o p r e d i c t g r i n d i n g r a t e . L e i g h t o n c o n s i d e r e d t h e r e l a t i o n s h i p may be s i t e s p e c i f i c and i t s h o u l d be e v a l u a t e d a t e a c h m i n i n g p r o j e c t . 9 1.2 THE 1982 TO 1984 RESEARCH PROJECT T h i s r e s e a r c h p r o j e c t was u n d e r t a k e n i n September 1982 f o l l o w i n g t h e p u b l i c a t i o n o f L e i g h t o n ' s t h e s i s r e p o r t 1 . The o b j e c t i v e s were t h e f o l l o w i n g : 1) e v a l u a t e t h e v a l i d i t y of t h e c o r r e l a t i o n 2) d e f i n e t h e l i m i t s o f a p p l i c a b i l i t y ( i f any) 3) i n v e s t i g a t e t h e i n f l u e n c e o f m a j o r p a r a m e t e r s i ) t h e l e v e l o f a c c u r a c y o f t h e d r i l l i n g d a t a i i ) t h e d i f f e r e n t d r i l l i n g e q u i p m e n t s i i i ) t h e d i f f e r e n t b l a s t d e s i g n s i v ) t h e r o c k mass b e h a v i o u r d u r i n g d r i l l i n g & b l a s t i n g B a c k e d by an e x t e n s i v e l i t e r a t u r e r e v i e w , t h e f i e l d p r o g r a m was p e r f o r m e d d u r i n g t h e summer o f 1983 i n t h r e e open p i t o p e r a t i o n s i n B r i t i s h C o l u m b i a . The a u t h o r o b t a i n e d , f r e e o f c h a r g e , a d r i l l p e r f o r m a n c e r e c o r d e r f r o m t h e G e o l o g r a p h P i o n e e r Company. The t h r e e mines where f i e l d t e s t i n g was p e r f o r m e d were : 1) E q u i t y S i l v e r Mine (5 weeks) The E q u i t y S i l v e r Mine i s a s i l v e r - a n t i m o n y - g o l d p r o p e r t y l o c a t e d i n n o r t h e r n B r i t i s h C o l u m b i a . They a r e u s i n g 200 mm (7 7/8 i n c h ) and 229 mm (9 i n c h ) d i a m e t e r b i t s on B u c y r u s E r i e 40-R d r i l l s . B e n c h e s a r e 5 m (16.4 f t ) h i g h . The i n t e n s i t y of i n -s i t u f r a c t u r i n g i s h i g h l y v a r i a b l e . The b l a s t r e s u l t s were g e n e r a l l y r a t e d from f a i r t o good. S i m p l e m o d i f i c a t i o n s of t h e 10 b l a s t d e s i g n were im p l e m e n t e d d u r i n g t h e r e s e a r c h p r o j e c t . A d r i l l p e r f o r m a n c e r e c o r d e r was i n s t a l l e d on t h e 229 mm (9 i n c h ) d i a m e t e r d r i l l . 2) L o r n e x Mine (5 weeks) The L o r n e x Mine i s a l a r g e c o p p e r p r o d u c e r l o c a t e d i n t h e c e n t r a l p a r t o f t h e p r o v i n c e . They a r e u s i n g 250 mm (9 7/8 i n c h ) d i a m e t e r b i t s on f i v e BE 45-R d r i l l s . At t h i s s i t e , a l t h o u g h f r a c t u r i n g i s i n t e n s e , t h e d e g r e e o f a l t e r a t i o n a l s o m o d i f i e s t h e s t r e n g t h of t h e r o c k mass. The b l a s t d e s i g n s were not optimum and m o d i f i c a t i o n s were p r o p o s e d . The d r i l l p e r f o r m a n c e r e c o r d e r was a l s o u s e d a t t h i s s i t e . 3) G r e e n h i l l s Mine (3 weeks) The Westar M i n i n g G r e e n h i l l s p r o p e r t y i s a new c o a l mine l o c a t e d i n s o u t h e a s t e r n B r i t i s h C o l u m b i a . They a r e u s i n g 270 mm (10 5/8 i n c h ) d i a m e t e r b i t s on Reed SK-60II d r i l l s . The c h a r a c t e r i s t i c s of t h e d i f f e r e n t beds of s e d i m e n t a r y r o c k s between t h e c o a l seams s u g g e s t t h a t d i f f e r e n t powder ( e n e r g y ) f a c t o r s c o u l d be u s e d from seam t o seam. N e v e r t h e l e s s , t h e w e l l managed b l a s t i n g p r o c e d u r e was d e s i g n e d t o p r o d u c e a f i n e muck p i l e f o r t h e medium s c a l e h y d r a u l i c s h o v e l s . C a l i b r a t i o n p r o b l e m s r u l e d o u t t h e i n s t a l l a t i o n of t h e d r i l l p e r f o r m a n c e r e c o r d e r . 11 D a t a f r o m a p p r o x i m a t e l y 1200 b l a s t h o l e s were r e v i e w e d from e a c h s i t e . The f i r s t p a r t of t h i s t h e s i s c o n t a i n s t h r e e c h a p t e r s . E a c h c o v e r s a p a r t i c u l a r a s p e c t of t h e l i t e r a t u r e r e v i e w t h a t was u n d e r t a k e n . C h a p t e r Two i s d i r e c t e d t o w a r d t h e u n d e r s t a n d i n g of t h e r o c k mass f a i l u r e b e h a v i o u r and a n a l y s e s t h e d i f f e r e n t p a r a m e t e r s t h a t i n f l u e n c e f r a c t u r e d e v e l o p m e n t . The d i f f e r e n t f a i l u r e c r i t e r i a a r e a l s o r e v i e w e d . C h a p t e r T h r e e i s c o n c e r n e d w i t h t h e d r i l l i n g p r o c e s s . The p r i n c i p a l o b j e c t i v e b e i n g t o r e v i e w a l l t h e f a c t o r s t h a t i n f l u e n c e t h e p e n e t r a t i o n r a t e , f r o m t h e r o c k mass p r o p e r t i e s t h r o u g h t h e o p e r a t i n g p a r a m e t e r s . The r e l a t i o n s h i p between t h e t h e o r e t i c a l a n a l y s i s and t h e p r a c t i c a l d r i l l i n g p r o c e s s i s a l w a y s p r e s e n t . The l a s t c h a p t e r of t h i s f i r s t p a r t d e a l s w i t h t h e b l a s t i n g p r o c e s s . The f a c t o r s t h a t i n f l u e n c e t h e e x p l o s i v e c o n s u m p t i o n a r e p r e s e n t e d i n d e t a i l . The r o c k mass b e h a v i o u r d u r i n g t h e b l a s t i n g p r o c e s s i s a l s o c o v e r e d . The s e c o n d p a r t o f t h i s t h e s i s p r e s e n t s t h e p r o c e d u r e s , r e s u l t s , r e c o m m e n d a t i o n s and c o n c l u s i o n s of t h e f i e l d r e s e a r c h p r o g r a m . 1 2 1.3 REFERENCES 1. LEIGHTON, J . C . ; Development of a C o r r e l a t i o n Between R o t a r y D r i l l P e r f o r m a n c e and 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 , M a s t e r ' s D e g r e e T h e s i s , U.B.C., A u g u s t 1982 2. LEIGHTON, J . C . ; BRAWNER, C O . ; STEWART, D.; Development of a C o r r e l a t i o n Between R o t a r y D r i l l P e r f o r m a n c e and  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 , C.I.M. B u l l e t i n , A u g u s t 1982 3. LEIGHTON, J . C . ; P r e d i c t i n g Powder F a c t o r s f r o m R o t a r y D r i l l P e r f o r m a n c e f o r C o n t r o l l e d B l a s t i n g , 14th C a n a d i a n Rock M e c h a n i c s Symposium, V a n c o u v e r , 1982 1 3 CHAPTER 2 '14 2.0 ROCK FRAGMENTATION The f r a c t u r e of r o c k i s a p r i m e c o n s i d e r a t i o n i n m i n i n g 1 " 6 . W h i l e t h e d e s i g n o f u n d e r g r o u n d o p e n i n g s i n r o c k a t t e m p t t o e l i m i n a t e f r a c t u r e s , o t h e r m i n i n g p r o c e s s e s l i k e d r i l l i n g , b l a s t i n g and g r i n d i n g a r e d i r e c t e d t o w a r d t h e f a i l u r e of t h e r o c k mass. I t i s f o u n d a p p r o p r i a t e t o r e v i e w t h e p r i n c i p a l t h e o r i e s of f a i l u r e o f b r i t t l e r o c k , t h e i n f l u e n c e o f t h e r o c k mass p r o p e r t i e s on t h e d i f f e r e n t f r a c t u r e p r o c e s s e s and t h e s i m i l i t u d e between them p r i o r t o t h e d e t a i l e d a n a l y s i s of d r i l l i n g and b l a s t i n g a c t i o n on t h e r o c k mass. F i r s t , b r i t t l e f a i l u r e s h o u l d be d e f i n e d . Q u o t i n g Hoek 7 : " B r i t t l e f a i l u r e i s s a i d t o o c c u r when t h e a b i l i t y of t h e r o c k t o r e s i s t l o a d d e c r e a s e s w i t h i n c r e a s i n g d e f o r m a t i o n . " However, t h e d e f o r m a t i o n i s u s u a l l y minimum, t h u s l e a d i n g t o sudden f a i l u r e . W i t h i n t h e p u b l i s h e d t h e o r i e s o f f a i l u r e , Mohr's a p p r o a c h i s t h e more a c c e p t e d and p r a c t i c a l . He p r e d i c t s f a i l u r e on any p l a n e when t h e s h e a r s t r e s s e x c e e d s t h e combined e f f e c t o f c o h e s i o n and f r i c t i o n ( e f f e c t i v e n o r m a l s t r e s s t i m e s t h e t a n g e n t of t h e f r i c t i o n a n g l e ) on t h a t p a r t i c u l a r p l a n e . The G r i f f i t h c o n c e p t b r i d g e s t h e gap between t h e o r e t i c a l and r e a l s t r e n g t h of t h e r o c k mass. I t i s l a t e r r e v i e w e d i n o r d e r t o o b t a i n a b e t t e r e x p l a n a t i o n of a c t u a l r e s u l t s . F i n a l l y , Hoek and Brown d e v e l o p e d an e m p i r i c a l f a i l u r e c r i t e r i o n t h a t p r e d i c t s t h e f r a c t u r e b e h a v i o u r of b o t h t h e r o c k mass and i n t a c t r o c k 15 s p e c i m e n . The s t r u c t u r a l c h a r a c t e r i s t i c s of t h e r o c k on b o t h l a r g e and s m a l l s c a l e a r e e x p e c t e d t o p r o d u c e l o c a l a n o m o l i e s i n t h e s t r e s s d i s t r i b u t i o n . The s t r e s s c o n c e n t r a t i o n i s a f u n c t i o n o f t h e n o r m a l s t r e s s a p p l i e d , t h e f r i c t i o n a l r e s i s t a n c e and t h e c o h e s i o n o f t h e p l a n e o f weakness. 1 6 2.1 REVIEW OF ROCK FAILURE MECHANISMS 2.1.1 Rock Mass C h a r a c t e r i s t i c s Under s t r e s s , r o c k b e h a v i o u r d i f f e r s from o t h e r e n g i n e e r i n g m a t e r i a l s . T h i s i s due t o t h e f a c t t h a t t h e r o c k i s u s u a l l y n e i t h e r homogeneous nor i s o t r o p i c . H e t e r o g e n e i t y o c c u r s on b o t h s m a l l and l a r g e s c a l e . F r a c t u r e p r o p a g a t i o n i s a f u n c t i o n of r o c k mass p r o p e r t i e s s u c h as t h e p o s i t i o n o f t h e d i s c o n t i n u i t i e s i n s p a c e , t h e b o u n d a r i e s between d i f f e r e n t r o c k t y p e s , t h e v a r i a t i o n i n t h e m a g n i t u d e and o r i e n t a t i o n of i n - s i t u s t r e s s f i e l d , e t c . On a s m a l l e r s c a l e , c r y s t a l s t r u c t u r e v a r i a t i o n s , v o i d s , i n c l u s i o n s , g r a i n b o u n d a r i e s and p r e f e r r e d o r i e n t a t i o n o f m i n e r a l c o n s t i t u e n t s w i l l i n f l u e n c e t h e s t a b i l i t y o r c o n t i n u i t y of f r a c t u r e g r o w t h . G e o l o g i c a l h i s t o r y a l s o a f f e c t s r o c k mass p r o p e r t i e s and t h u s i t s b e h a v i o u r , and makes e a c h s i t e d i f f e r e n t . (Ex. W e a t h e r i n g ) The b r i t t l e n e s s o f t h e r o c k i s m a i n l y c a u s e d by t h e v a r i a t i o n s of t h e p h y s i c a l p r o p e r t i e s of i t s c o n s t i t u e n t s and i n t e r n a l s t r u c t u r a l i m p e r f e c t i o n s . B r i t t l e n e s s and weakness o f t h e r o c k a r e g e n e r a l l y a s s o c i a t e d w i t h i t s h e t e r o g e n e i t y . 2.1.2 The C o u l o m b - N a v i e r T h e o r y of F a i l u r e The C o u l o m b - N a v i e r t h e o r y p r e d i c t s t h a t f a i l u r e w i l l o c c u r i n a m a t e r i a l when t h e maximum s h e a r s t r e s s a t one p o i n t r e a c h e s a c r i t i c a l v a l u e , i . e . , t h e s h e a r s t r e n g t h of t h e m a t e r i a l . 17 M o r e o v e r , i t i s p r e d i c t e d t h a t t h e f a i l u r e p l a n e w i l l b i s e c t t h e a n g l e between t h e maximum and minimum s t r e s s e s . T h i s l a t t e r s t a t e m e n t i s not v e r i f i e d by e x p e r i m e n t . I t i s a l s o p o s s i b l e t o d e m o n s t r a t e from t h i s t h e o r y t h a t t h e s h e a r s t r e n g t h i n t e n s i o n e q u a l s t h e s h e a r s t r e n g t h i n c o m p r e s s i o n , a s i t u a t i o n t h a t n e v e r o c c u r s i n b r i t t l e m a t e r i a l . N a v i e r p r o p o s e d t o m o d i f y t h i s t h e o r y . He p o s t u l a t e s t h a t t h e n o r m a l s t r e s s a c t i n g on t h e f a i l u r e p l a n e i n c r e a s e s t h e s h e a r s t r e n g t h o f t h e r o c k p r o p o r t i o n a l l y t o i t s m a g n i t u d e . He i n t r o d u c e s t h e c o e f f i c i e n t of i n t e r n a l f r i c t i o n . The C o u l o m b - N a v i e r t h e o r y p r e d i c t s t h a t t h e c o m p r e s s i v e s t r e n g t h i s l a r g e r t h a n t h e t e n s i l e s t r e n g t h , b ut a t a r a t i o l ower t h a n i n d i c a t e d by e x p e r i m e n t . 2.1.3 The Mohr T h e o r y o f F a i l u r e The Mohr t h e o r y p r e d i c t s t h a t a m a t e r i a l w i l l f r a c t u r e when t h e s h e a r s t r e s s on t h e f a i l u r e p l a n e has r e a c h e d a l i m i t i n g v a l u e , a f u n c t i o n of t h e n o r m a l s t r e s s on t h i s p l a n e , o r i f t h e l a r g e s t t e n s i l e p r i n c i p a l s t r e s s e q u a l s t h e t e n s i l e s t r e n g t h o f t h e m a t e r i a l . The r e l a t i o n s h i p between t h e s h e a r s t r e s s and t h e n o r m a l s t r e s s has t o be d e t e r m i n e d e x p e r i m e n t a l l y and i s r e p r e s e n t e d by t h e e n v e l o p e o f f a i l u r e . The C o u l o m b - N a v i e r f a i l u r e c r i t e r i o n i s r e p r e s e n t e d on a Mohr d i a g r a m w i t h a s t r a i g h t l i n e e n v e l o p e , and i s a s p e c i a l c a s e o f t h e Mohr t h e o r y . Note t h a t s e d i m e n t a r y r o c k s l i k e l i m e s t o n e and s a n d s t o n e a r e i l l u s t r a t e d w i t h a c u r v e d Mohr e n v e l o p e whereas 18 more b r i t t l e r o c k s l i k e g r a n i t e and q u a r t z i t e p o s s e s s s t r a i g h t e n v e l o p e s . The Mohr c r i t e r i o n a l s o p r e d i c t s t h e d i r e c t i o n o f t h e f a i l u r e p l a n e and t h e s t a t e o f s t r e s s i n t h e m a t e r i a l a t f a i l u r e . ( F i g u r e 2.1-1) 2.1.4 The G r i f f i t h T h e o r y o f F a i l u r e The C o u l o m b - N a v i e r and t h e Mohr t h e o r i e s c o n s i d e r t h e f a i l u r e on a m a c r o s c o p i c s c a l e , whereas t h e G r i f f i t h t h e o r y a p p r o a c h e s t h e f a i l u r e on a m i c r o s c o p i c s c a l e t o e x p l a i n r o c k mass b e h a v i o u r . In 1921, G r i f f i t h p u b l i s h e d a t h e o r y t h a t i s l a t e r u s e d t o e x p l a i n t h e low s t r e n g t h o f t h e r o c k s compared t o t h e t h e o r e t i c a l s t r e n g t h o f p e r f e c t c r y s t a l s . He h y p o t h e s i z e d t h a t f r a c t u r e o f b r i t t l e m a t e r i a l s i s due t o h i g h t e n s i l e s t r e s s e s i n d u c e d a t t h e e x t r e m i t i e s of s m a l l , r a n d o m l y o r i e n t e d m i c r o s c o p i c c r a c k s . The c r a c k s c r e a t e a s t r e s s c o n c e n t r a t i o n t h a t overcome t h e t h e o r e t i c a l s t r e n g t h o f t h e m a t e r i a l even t h o u g h t h e a p p l i e d s t r e s s i s much l o w e r . G r i f f i t h p o s t u l a t e s t h a t no f o r c e i s c a r r i e d a c r o s s t h e c r a c k s . He a l s o assumed t h a t c r a c k s were e q u a l l y o r i e n t e d i n s p a c e . F a i l u r e o c c u r r e d when t h e c r a c k h a v i n g th e w o r s t o r i e n t a t i o n r e a c h e d a s t r e s s v a l u e l a r g e r t h a n t h e s t r e n g t h of t h e m a t e r i a l o r a l i m i t i n g v a l u e o f l o c a l s t r a i n e n e r g y . However, t h e G r i f f i t h t h e o r y f a i l s t o e x p l a i n some e x p e r i m e n t a l r e s u l t s . F i r s t , t h e c r i t e r i o n p r e d i c t s an i n c r e a s e of t h e t r i a x i a l c o m p r e s s i v e s t r e n g t h w i t h an i n c r e a s e d c o n f i n i n g p r e s s u r e , but 19 FIGURE 2.1-1 « GRAPHICAL REPRESENTATION OF MOHR THEORY OF STRESS CONDITIONS FOR FAILURE OF INTACT ROCK! (after Hoek and Brown^) 20 many s c i e n t i s t s o b s e r v e d a l a r g e r a u g m e n t a t i o n o f s t r e n g t h t h a n p r e d i c t e d . A l s o , w i t h t h e p r e s e n c e of p o r e p r e s s u r e , t h e G r i f f i t h c r i t e r i o n p r e d i c t s t h a t t h e s t r e n g t h o f t h e r o c k w i l l i n c r e a s e . A g a i n , t h e t h e o r y u n d e r e s t i m a t e s t h e r e a l i n c r e a s e . F i n a l l y , t h e G r i f f i t h t h e o r y i n d i c a t e s t h a t t h e c o m p r e s s i v e s t r e n g t h s h o u l d be e i g h t t i m e s t h e t e n s i l e " S t r e n g t h of t h e r o c k . E x p e r i m e n t s r e p o r t e d v a l u e s of c o m p r e s s i v e s t r e n g t h t o t e n s i l e s t r e n g t h r a t i o between 5 and 22. Even when a n i s o t r o p i c d i s t r i b u t i o n of t h e G r i f f i t h c r a c k s i s c o n s i d e r e d , t h e t h e o r y d o e s n o t seem t o be i n a c c o r d a n c e w i t h e x p e r i m e n t s . M c C l i n t o c k and W a l s h 8 d e v e l o p e d t h e i d e a t h a t i t i s p o s s i b l e f o r t h e c r a c k s t o c l o s e and t h u s c a r r y n o r m a l and s h e a r s t r e s s e s due t o f r i c t i o n . T h e s e s t r e s s e s w i l l i n c r e a s e t h e s t r e n g t h o f t h e r o c k by r e d u c i n g t h e s t r e s s c o n c e n t r a t i o n a t t h e ends of t h e c r a c k s . S i m i l a r l y , f l u i d under p r e s s u r e i n t h e p o r e s w i l l m o d i f y t h e s t r e s s d i s t r i b u t i o n i n t h e r o c k . T h i s m o d i f i e d t h e o r y p r e d i c t s a c o m p r e s s i v e t o t e n s i l e s t r e n g t h r a t i o o f 10. F r a c t u r e p r o p a g a t i o n e x p l a i n e d by t h i s t h e o r y i s d e s c r i b e d by W a l s h and B r a c e 9 . The f r i c t i o n a l f o r c e r e s i s t i n g s h e a r between c r a c k s u r f a c e s i s p r o p o r t i o n a l t o t h e n o r m a l f o r c e t r a n s m i t t e d a c r o s s t h e s e s u r f a c e s . N o n - u n i f o r m s t r e s s i n t h e r o c k d e v e l o p s l o c a l s t r e s s e s a t m i c r o c r a c k t i p s t h a t e v e n t u a l l y e x c e e d t h e s t r e n g t h of t h e s u r r o u n d i n g m a t e r i a l s . The c r a c k b e g i n s t o grow, but o n l y t o a l e n g t h i n t h e o r d e r of magn i t u d e of t h e g r a i n s i z e , and s t o p s when i t i n t e r s e c t s o t h e r c r a c k s . 21 The d i r e c t i o n o f p r o p a g a t i o n i s g e n e r a l l y p a r a l l e l t o t h e maximum c o m p r e s s i v e s t r e s s . I f t h e l o a d i s i n c r e a s e d , o t h e r l e s s f a v o r a b l y o r i e n t e d m i c r o c r a c k s w i l l be i n i t i a t e d o r r e -i n i t i a t e d . However, no s i n g l e c r a c k grows c a t a s t r o p h i c a l l y and p r o d u c e s a m a c r o s c o p i c f r a c t u r e , b u t under s u f f i c i e n t s t r e s s , r e g i o n s o f h i g h c r a c k d e n s i t y w i l l c r e a t e a m a c r o s c o p i c s h e a r p l a n e . The G r i f f i t h f a i l u r e c r i t e r i o n may be r e p r e s e n t a t e d by a p a r a b o l i c Mohr e n v e l o p . As m o d i f i e d by M c C l i n t o c k and W a l s h , t h e G r i f f i t h t h e o r y of f a i l u r e i s r e p r e s e n t e d by a s t r a i g h t e n v e l o p e on a Mohr d i a g r a m . 2.1.5 Hoek and Brown E m p i r i c a l F a i l u r e C r i t e r i o n Hoek s t u d i e d c r a c k i n i t i a t i o n and p r o p a g a t i o n and c o n c l u d e d t h a t b o t h t h e o r i g i n a l and m o d i f i e d G r i f f i t h t h e o r i e s were s a t i f a c t o r y when d e a l i n g w i t h t h e r o c k mass, but l e s s a c c u r a t e when d e s c r i b i n g t h e f a i l u r e o f i n t a c t l a b o r a t o r y s p e c i m e n s 1 0 ( F i g u r e 2 . 1 - 2 ) . N e v e r t h e l e s s t h e s e t h e o r i e s were t h e s t a r t i n g p o i n t i n t h e d e v e l o p m e n t o f t h i s e m p i r i c a l f a i l u r e c r i t e r i o n . Hoek and Brown d e r i v e d t h e i r f a i l u r e c r i t e r i o n by t r i a l and e r r o r . They e x p e r i m e n t e d w i t h c u r v e f i t t i n g i n o r d e r t o c o r r e l a t e b o t h t h e o r i g i n a l G r i f f i t h t h e o r y , under t e n s i l e s t r e s s , a n d t h e f a i l u r e d a t a p r o d u c e d under c o m p r e s s i v e s t r e s s s i t u a t i o n s . In s p i t e o f t h e a b s e n c e of a f u n d a m e n t a l r e l a t i o n s h i p between t h e e m p i r i c a l c o n s t a n t s i n c l u d e d i n t h e 22 Modified Griffith theory O i l U I . I L U LJULi I " I i i I i i i -50 0 100 200 300 400 500 600 EFFECTIVE NORMAL STRESS 0~:MPa FIGURE 2.1-2 t MOHR CIRCLES FOR FAILURE OF SPECIMENS OF QUARTZITE TESTED BY HOEK. ENVELOPES INCLUDED IN THE FIGURE ARE CALCULATED BY MEANS OF THE ORIGINAL AND MODIFIED GRIFFITH THEORIES OF BRITTLE FRACTURE, (after Hoek10) 23 c r i t e r i o n and any p h y s i c a l c h a r a c t e r i s t i c of t h e r o c k , t h e c r i t e r i o n a d e q u a t e l y p r e d i c t s r o c k f r a c t u r e b e h a v i o u r . The c r i t e r i o n d e f i n e s t h e m a g n i t u d e of t h e major p r i n c i p a l s t r e s s a t f a i l u r e as a f u n c t i o n o f t h e m i n o r p r i n c i p a l s t r e s s , t h e u n i a x i a l c o m p r e s s i v e s t r e n g t h o f i n t a c t s p e c i m e n s o f t h e r o c k mass and two e m p i r i c a l c o n s t a n t s . ( F i g u r e 2.1-3) I t i s assumed t h a t t h e i n t e r m e d i a t e p r i n c i p a l s t r e s s has no i n f l u e n c e on t h e f a i l u r e mechanism and t h a t t h e major and minor p r i n c i p a l s t r e s s e s a r e a l w a y s t h e e f f e c t i v e s t r e s s e s , o b t a i n e d by c o n s i d e r i n g t h e p o r e or j o i n t p r e s s u r e i n t h e r o c k . The e m p i r i c a l f a i l u r e c r i t e r i o n o f t h e r o c k mass i s r e l a t e d w i t h b o t h CSIR and NGI r o c k mass c l a s s i f i c a t i o n s y s t e m s , t h u s p e r m i t t i n g t h e e v a l u a t i o n of t h e e m p i r i c a l c o n s t a n t s . (See T a b l e 1) 24 T Trlaxial compression cr,' = o-3+VmCta3+sq:2 •Ocm Uniaxial compression tTcs = \ / serf CO CO LU CC \-co * r r u U n i a x i a l *—^tension CT-t = '/2 CTc(m-\/m2+4s) i l L -0.5 0.5 L5 MINOR PRINCIPAL STRESS O3' 2.0 Mohr envelope (Cot^ '-Cospf , ' )^ 0.5 1.0 1.5 2.0 2.5 3D EFFECTIVE NORMAL STRESS 0~' FIGURE 2.1 -3 • GRAPHICAL REPRESENTATION OF HOEK AND BROWN FAILURE CRITERION, (after Hoek10) 25 TABLE 1 APPROXIMATE RELATIONSHIP BETWEEN ROCK 7 MASS QUALITY AND MATERIAL CONSTANT (after Hoek and Brown ) Empirical failure criterion Oj " 03 + /mo c03 + s o c t " A 0 c ( " / 0 - T )B where T - i(m - Jm* +~Tt) U J t S < » -1 < 1/1 t-X in u >-o a: c£ u u i c i I - u i < a . z o O _ l C D U J ui oc > u < U J < <_> 0 > I "g.3 1^ o OC — tn X X I— u — o - J DC 1- >-— o oc < t o u i u _ i a . o < a oc h- _ J V) UJ </i >- > 3 oc U J <u O U O l l J c u i u 6 <_> u >- < -tS < 2 -I > B z o oc < "a U l DC O U l t ? oc H o -1 Q < V ) 0 . O (0 1 .< >- t-_ l U l o >-a . oc o a U l 1/1 z 3 — a S£ o o — v> u i z u u o ll. J cc . a •8 i3 1/1 1 I SC U J < U Z H O — U l o c a : 1 >- U l _ l O Z O Z — o . < - I _ l • l/l < u l Z J I-z a in — u i v 5 2 CC u C J 0 — u U l ( J — l / l — X OC _ l 0 . < - I oc o < a u oc r £ 8 * .** 0>+> 0 -W C N O « H »Q » 3 INTACT ROCK SAMPLES Laboratory eize specimens free from joints CSIR rating 100 NCI rating 500 m - 7.0 s - 1.0 A - 0.816 B - 0.658 T - -O.HO m - 10.0 s - 1.0 A - 0.918 B - 0.677 > T - -0.099 m - 15-0 s - 1.0 A - 1. 0***» B - 0.692 T - -0.067 tn - 17.0 s - 1.0 A - 1.086 B - O.696 T - -0.059 m - 25.0 s - 1.0 A - 1.220 B - 0.705 T - -0.0^0 VERY GOOD QUALITY ROCK MASS Tightly interlocking undis turbed rook with unueather ed joints at ±3m. CSIR rating 85 NGI rating 100 m - 3.5 s - 0.1 A - 0.651 B = 0.679 T - -0.028 m - 5.0 s - 0.1 A - 0.739 B = 0.692 T - -0.020 m - 7.5 s - 0.1 A - 0.81(8 B - 0.702 T = -0.013 m - 8.5 s - 0.1 A - 0.883 B •» 0.705 T = -0.012 m - 12.5 5 = 0.1 A - 0.998 B - 0.712 T - -0.008 GOOD QUALITY ROCK MASS Freeh to slightly weathered rock, slightly distux-bed with joints at 1 to 3m. CSIR rating 65 NGI rating 10 m - 0.7 s - 0.001) A - 0-369 B = 0.669 T - -0.006 m - 1.0 s - 0.00<i A - 0.1127 B - 0.683 T - -O.OOli m - 1.5 s - 0.00*1 A - 0.501 B - 0.695 T - -0.003 m - 1.7 s - 0.00«l A - 0.525 B - 0.698 T - -O.O02 m - 2.5 s - 0.00*1 A - 0.603 B - 0.707 T - -0.002 FAIR QUALITY ROCK MASS Several sets of moderately weathered joints spaaed at 0.3 to lm. CSIR. rating kU NGI rating 1.0 m » 0.1*1 s » 0.0001 A - 0.198 B - .0.662 T - -0.0007 m - 0.20 s - 0.0001 A - 0.23^ B - 0.675 T - -0.0005 m » 0.30 s - 0.0001 A - 0.280 B - 0.688 T - -0.0003 m - 0.3k s - 0.0001 A - 0.295 B r 0.691 T - -0.0003 m - 0.50 s - 0.0001 A = 0.3'*6 B - 0.700 T - -0.0002 POOR QUALITY ROCK MASS numerous weathered joints at 30 to 500mm with some gouge - clean waste rook. CSIR rating 23 NGI rating 0.1 m = 0.0't s = 0.00001 A = 0.115 B - 0.6*16 T - -0.0002 tn - 0.05 s = 0.000O1 A •» 0.129 B - 0.655 T - -0.0002 m » 0.08 s - 0.00001 A - 0.162 B - 0.672 T » -0.0001 tn «= 0.09 s - O.OOOOI A » 0.172 B - 0.676 T - -0.0001 tn - 0. 13 s - 0.00001 A - 0.203 B - 0.686 T - -0.0001 VERY POOR QUALITY ROCK MASS Numerous heavily weathered joints spaced < SOnrn with gouge - waste with fines. CSIR rating 3 NGI rating 0.01 tn - 0.007 S » 0 A - 0.0*12 B - 0.53*1 T - 0 m - 0.010 s - 0 A - 0.050 B - 0.539 T - 0 m - 0.015 s - 0 A - 0.061 B - 0.5^6 T » 0 in - 0.017 S - O A - 0.065 B - O.S>iB T - 0 m - 0.025 S - 0 A - 0.078 B - 0.556 T - 0 26 2.2 DRILLING, BLASTING AND GRINDING In t h e m a j o r i t y o f m i n i n g o p e r a t i o n s , t h e r e d u c t i o n of t h e r o c k mass t o a s u i t a b l e s i z e f o r l o a d i n g and h a n d l i n g i s done t h r o u g h d r i l l i n g and b l a s t i n g . A t t h e p l a n t , t h e s i z e r e d u c t i o n o f t h e r o c k f r a g m e n t s below a c e r t a i n l i m i t f a c i l i t a t e s e x t r a c t i o n of v a l u a b l e components o r c h e m i c a l a c t i o n . In a l l c a s e s , a u n i f o r m s i z e of t h e p r o d u c t i s t h e b e s t . However, d r i l l i n g , b l a s t i n g and g r i n d i n g p r o d u c e a range o f f r a g m e n t s i z e s . T h i s i s r e l a t e d t o t h e f a c t t h a t e n e r g y i s t r a n s m i t t e d t o t h e r o c k by c o m p r e s s i o n under c o n c e n t r a t e d l o a d . T h i s c o n c e n t r a t e d l o a d p r o d u c e s a non-homogeneous s t r e s s f i e l d and e n e r g y d i s t r i b u t i o n w h i c h r e s u l t i n a n o n - e f f i c i e n t f r a g m e n t a t i o n p r o c e s s and a n o n - u n i f o r m s i z e o f f r a g m e n t s . In t h e z o n e s o f h i g h s t r e s s , f a i l u r e of t h e r o c k under c o m p r e s s i o n p r o d u c e s a v e r y f i n e , p o w d e r - l i k e m a t e r i a l . At low-s t r e s s l e v e l s , t h e f a i l u r e i s of a b r i t t l e t y p e , r e s u l t i n g i n l a r g e r f r a g m e n t s . The s i z e of t h e f r a g m e n t s i s a f u n c t i o n of t h e d e g r e e of h e t e r o g e n e i t y on a s m a l l s c a l e and of t h e i n t e n s i t y of j o i n t i n g on a l a r g e r s c a l e . The e n e r g y c o n s u m p t i o n i n t h e f r a g m e n t a t i o n p r o c e s s i s a f u n c t i o n o f t h e r e l a t i v e amount o f f i n e s p r o d u c e d and t h e i r d e g r e e o f f i n e n e s s 1 1 " 1 3 . I t s h o u l d be r e a l i s e d t h a t t h e r e l a t i v e e n e r g y u s e d i n d r i l l i n g r o c k s e x c e e d s t h e e n e r g y u s e d t o b l a s t t h e same r o c k ( F i g u r e 2 . 2 - 1 ) . T h i s s t a t e m e n t i s w e l l u n d e r s t o o d when one i m a g i n e s how t h e s i z e of t h e r o c k specimen 27 I I I l I I 0,01 0,1 I 10 100 1000 SIZE (mm) 1 - DIAMOND CUTTING 2 - PERCUSSIVE DRILLING 3 - ROLLER BIT BORING 4 - GYRATORY CRUSHING 5 - EXPLOSIVES FIGURE 2.2-1 » COMPARISON OF ENERGY REQUIREMENTS FOR VARIOUS FRAGMENTATION PROCESSES, (after Page12) 28 t o be b r o k e n i n f l u e n c e s i t s s t r e n g t h . As t h e s i z e i s r e d u c e d , t h e i m p e r f e c t i o n s i n t h e s t r u c t u r e a r e r e d u c e d and t h e m a t e r i a l i n c r e a s e s i n s t r e n g t h and, t h e r e f o r e , needs more e n e r g y t o c o n t i n u e t h e s i z e r e d u c t i o n . N e v e r t h e l e s s , i t i s i m p o r t a n t t o n o t e t h a t t h e e n e r g y c o n s u m p t i o n i n a l l t h e r o c k b r e a k a g e p r o c e s s e s i s a l s o a f u n c t i o n of a number of o t h e r p a r a m e t e r s s u c h as t h e i n d e n t o r ' s g eometry i n d r i l l i n g a nd t h e d e p t h o f t h e c h a r g e or p r e s e n c e of a f r e e f a c e i n b l a s t i n g . The optimum c o n d i t i o n s o f d r i l l i n g and b l a s t i n g a r e t h e ones t h a t need t h e l e a s t amount o f e n e r g y t o p r o d u c e a g i v e n s e t of r e s u l t s . The f o l l o w i n g c h a p t e r s w i l l d e a l w i t h t h e a n a l y s i s o f t h e f r a g m e n t a t i o n p r o c e s s e s i n d r i l l i n g and i n b l a s t i n g . 29 2.3 REFERENCES 1. CLAUSING, D.P.; C o m p a r i s i o n o f G r i f f i t h ' s T h e o r y w i t h Mohr's F a i l u r e C r i t e r i a , 3 r d Symposium on Rock M e c h a n i c s , Q u a r t e r l y o f t h e C o l o r a d o S c h o o l of M i n e s , N3, J u l y 1959 2. TANDANAND, S.; P r i n c i p l e s o f D r i l l i n g , SME, M i n i n g E n g i n e e r i n g Handbook, Cummins and G i v e n e d i t o r s , AIME, 1973 3. FAIRHURST, C;CORNET, F. ; Rock F r a c t u r e and F r a g m e n t a t i o n , 22nd U.S. Symposium on Rock M e c h a n i c s , M a s s a c h u s e t t s I n s t i t u t e o f T e c h n o l o g y , C ambridge, M a s s a c h u s e t t s , J u l y 1981 4. RATIGAN, J . L . ; An E x a m i n a t i o n of t h e T e n s i l e S t r e n g t h of B r i t t l e Rock, 2 3 r d U.S. Symposium on Rock M e c h a n i c s , Goodman e d i t o r , AIME, 1982 5. OBERT, L.; DUVALL, W.I.; Rock M e c h a n i c s and t h e D e s i g n o f S t r u c t u r e s i n Rock, John W i l e y & Sons, e d i t o r , 1967 6. MORRISON, R.G.K.; A P h i l o s o p h y of Ground C o n t r o l , D e p t . o f M i n i n g and M e t a l l u r g i c a l E n g i n e e r i n g , M c G i l l U n i v e r s i t y , M o n t r e a l , 1976 7. HOEK, E . ; BROWN, E.T.; U n d e r g r o u n d E x c a v a t i o n i n Rock, I n s t i t u t i o n o f M i n i n g & M e t a l l u r g y , London, 1980 8. McCLINTOCK, F.A.; WALSH, J.B.; F r i c t i o n on G r i f f i t h C r a c k s i n Rock Under P r e s s u r e , 4 t h N a t i o n a l C o n g r e s s A p p l i e d M e c h a n i c s , B e r k e l e y , 1962; pages 1015 - 1021 9. WALSH, J.B.; BRACE, W.F.; M e c h a n i c s of Rock D e f o r m a t i o n , 30 Rock M e c h a n i c s Symposium, S i k a r s k i e e d i t o r , ASME, 1973 10. HOEK, E.; S t r e n g t h o f J o i n t e d Rock M a s s e s , G e o t e c h n i q u e , V33, N3, 1983; pages 187 - 223 11. KHALAF, F.; ABOUZEID, A.Z.M.; A n a l o g y Between I n d e n t a t i o n and B l a s t i n g T e s t s on B r i t t l e R o c k s , 2 1 s t U.S. Symposium on Rock M e c h a n i c s , U n i v e r s i t y o f M i s s o u r i - R o l l a , May 1980 12. PAGE, C.H.; B l a s t i n g and Comminution, u n p u b l i s h e d r e p o r t , S t e f f e n , R o b e r t s o n and K i r s t e n 13. YOUNG, C.; Rock F r a g m e n t a t i o n - Needs and P o s s i b i l i t i e s , Rock f r a g m e n t a t i o n s e s s i o n o f t h e 17th U.S. Symposium on Rock M e c h a n i c s , U n i v e r s i t y o f U t a h , U t a h E n g i n e e r i n g E x p e r i m e n t S t a t i o n , 1976 31 CHAPTER 3 32 3.0 THE DRILLING PROCESS D r i l l i n g i s t h e i n i t i a l o p e r a t i n g s e q u e n c e i n open p i t m i n i n g . I t i s a l s o one o f t h e h i g h e s t o p e r a t i n g c o s t s i n v o l v e d and c o n s e q u e n t l y t h e d r i l l i n g p r o c e s s i s o p t i m i z e d a c c o r d i n g l y t o t h e s i t e c o n d i t i o n s . D i f f e r e n t c o m b i n a t i o n s of b i t d e s i g n s and o p e r a t i n g p a r a m e t e r s a r e t e s t e d i n o r d e r t o d e f i n e t h e one t h a t m i n i m i z e s t h e o v e r a l l c o s t s and m a x i m i z e s t h e p e n e t r a t i o n r a t e . The r o t a r y d r i l l s f a c e t h e u n d i s t u r b e d r o c k mass and, w i t h t h e - knowledge of t h e p r i n c i p l e s o f t r i c o n e r o t a r y d r i l l i n g , u s e f u l r o c k mass d a t a c a n be d e r i v e d from d r i l l p e r f o r m a n c e . The use of a t r i c o n e r o t a r y b i t as a v a l i d r o c k t e s t i n g t o o l i s n o t new, a l t h o u g h u n t i l r e c e n t l y , s c i e n t i s t s were r e s t r i c t i n g t h e f i e l d of a p p l i c a t i o n t o t h e p r e d i c t i o n o f t h e d r i l l a b i l i t y o r a b r a s i v e n e s s . The f i r s t p a r t of t h i s c h a p t e r i s t h e r e f o r e an o v e r v i e w o f t h e t r i c o n e b i t d e s i g n c o n s i d e r a t i o n s . T h e s e d e s i g n c o n s i d e r a t i o n s a r e not b a s i c a l l y a p u r e m e c h a n i c a l p r o b l e m c o n t r o l l e d by t h e s i z e and s t r e n g t h o f t h e d i f f e r e n t b i t components and t h e s t r e s s e s a p p l i e d on them. The r o c k mass f a i l u r e b e h a v i o u r i n f l u e n c e s t h e b i t d e s i g n and t h e o v e r a l l d r i l l i n g p r o c e s s , whereas t h e s t r e s s e s a r e v e r y l a r g e . In o r d e r t o u n d e r s t a n d t h e a c t i o n of a t r i c o n e r o t a r y b i t on t h e r o c k mass, i t i s n e c e s s a r y t o r e v i e w t h e t h e o r e t i c a l mechanisms o f r o c k p e n e t r a t i o n by a s i n g l e t o o t h . D i f f e r e n t models have been p r o p o s e d and a r e p r e s e n t e d i n t h e s e c o n d 33 s e c t i o n o f t h i s c h a p t e r . A d i s c u s s i o n on t h e c o n c e p t o f s p e c i f i c e n e r g y i n d r i l l i n g f o l l o w s . In a d d i t i o n , t h e s t u d y o f t h e f a c t o r s t h a t i n f l u e n c e r o c k mass d r i l l a b i l i t y i s of p r i m e i m p o r t a n c e i n t h i s r e s e a r c h p r o j e c t . F o r t u n a t e l y , a l a r g e number o f s c i e n t i s t s have been c o n c e r n e d w i t h t h e d e t e r m i n a t i o n of t h e r o c k mass d r i l l a b i l i t y and a wide body of l i t e r a t u r e i s a v a i l a b l e . T h e s e f a c t o r s a r e of two t y p e s : t h e m e c h a n i c a l p r o p e r t i e s of t h e r o c k mass b e i n g d r i l l e d and t h e f a c t o r s r e l a t e d t o t h e p a r t i c u l a r d r i l l i n g t o o l u s e d and t h e o p e r a t i n g p a r a m e t e r s . The d r i l l a b i l i t y s e c t i o n i s f o l l o w e d by a r e v i e w of t h e t r i c o n e r o t a r y d r i l l i n g i n p r a c t i c e . T h i s f i f t h s e c t i o n a l s o c o v e r s d r i l l i n g f o r m u l a s . F i n a l l y , t h e c h a p t e r c o n c l u d e s w i t h a d i s c u s s i o n on t h e Rock Q u a l i t y I n d e x . 34 3.1 TRICONE ROTARY BITS Howard R. Hughes p a t e n t e d t h e f i r s t r o t a r y r o c k b i t on A u g u s t 10, 1909. T h i s i n v e n t i o n was l a t e r i m p r o v e d t o become one o f t h e most e c o n o m i c a l r o c k p e n e t r a t i n g t o o l s . ( F i g u r e 3.1-1) R o l l e r cone b i t improvements were s t e a d y o v e r t h e p a s t t wenty y e a r s b e c a u s e of s i g n i f i c a n t d e s i g n o p t i m i z a t i o n of t h e c u t t i n g s t r u c t u r e m a t e r i a l s and o f t h e b e a r i n g s . Today, c a r b i d e i n s e r t b i t s w i t h i n c r e a s e d r a t e o f p e n e t r a t i o n and l o n g e r l i f e have l a r g e l y r e p l a c e d m i l l e d - t o o t h b i t s ( F i g u r e 3 . 1 - 2 ) . The p r i n c i p a l l i m i t a t i o n i n t h e d e s i g n o f a r o l l e r cone b i t i s t h e s p a c e . The s i z e o f e v e r y p i e c e i s d e t e r m i n e d by t h e d i a m e t e r of t h e h o l e and t h e s i z e o f o t h e r components. In most c a s e s , one p a r t c a n o n l y be made l a r g e r i f a n o t h e r p a r t ( o r p a r t s ) i s r e d u c e d i n s i z e . The s e l e c t i o n of t h e optimum d i m e n s i o n s r e s u l t s i n a s e r i e s o f compromises u n t i l t h e v a r i o u s e l e m e n t s a r e p r o p e r l y b a l a n c e d t o g i v e t h e b e s t o v e r - a l l p e r f o r m a n c e . M a n u f a c t u r e r s c l a i m t h a t t h e b i t d e s i g n i s m a i n l y b a s e d on p a s t e x p e r i e n c e . The f u n d a m e n t a l s o f m e c h a n i c a l d e s i g n a r e s e l d o m u s e d . The s e v e r e c o n d i t i o n s i n w h i c h r o c k b i t s work f o r c e a l l p a r t s t o w i t h s t a n d l a r g e r s t r e s s e s , i n r e l a t i o n t o t h e u l t i m a t e s t r e n g t h of t h e m a t e r i a l , t h a n t h e ones commonly e n c o u n t e r e d i n o t h e r m e c h a n i c a l d e s i g n s 3 . A l s o , t h e s i m p l i c i t y of t h e d e s i g n i s t h e key t o r e l i a b i l i t y . F i g u r e 3.1-3 shows a t r i c o n e r o t a r y b i t u s e d i n t h e b l a s t h o l e i n d u s t r y . The i m p o r t a n c e o f e a c h m a j o r component, r e l a t e d t o t h e r a t e of IMPORTANCE OF DEVELOPMENT (arbitrary scale) CD O CO cn o m 01 > OJ H O o c o m 0 1 on CD 0> ro O T " O T o 03 O o o l — I — i — I — r FIRST ROTARY ROCK BIT SELF-CLEANING CONES UNITIZED BIT BODY FIRST TRI-CONE BITS "CONE OFFSETS AND SPECIFIC TYPES -HARD ROCK \ BITS -SOFT F O R M A T I O N BITS -TUNGSTEN CARBI - J E T BITS - S E A L E D BEARINGS -SHAPED INSERTS AVAILABLE -SOFT INSERTS, JOURNAL BEARINGS" co cn 37 MAIN AIR A R M BLEED HOLE ROLLER BEARING PILOT PIN AIR HOLE TO PILOT PIN AIR HOLE TO BALL RACE APPLIED HARDMETAL SHIRTTAIL COMPACTS ARM JOURNAL ROLLER BEARING OUTER BALL RACE FLANGE INNER BALL RACE FLANGE! WATER SEPARATOR SNAP RING AIR SCREEN A.P.I.R. TOOL JOINT RUBBER FLAPPER ASS'Y. CHECK VALVE SCREEN TUBE ASS'Y. "0"RING NAIL LOCK RETAINING PIN JET NOZZLE GAGE COMPACT CUTTING STRUCTURE INSERTS BALL BEARING PILOT BUSHING APPLIED HARDMETAL APPLIED HARDMETAL THRUST BUTTON CONE TUNGSTEN CARBIDE NSERTS JOURNAL ANGLE FIGURE 3.1-3 » NOMENCLATURE OF ROTARY BIT. (after Dresser Industries4) 38 p e n e t r a t i o n and t h e l i f e of t h e b i t , i s d e s c r i b e d i n t h e f o l l o w i n g s e c t i o n s . 3.1.1 J o u r n a l A n g l e and Skew A n g l e Bottom h o l e a c t i o n i s a f u n c t i o n of t h e p o s i t i o n of t h e j o u r n a l on t h e arm. The p o s i t i o n o f t h e j o u r n a l i n r e l a t i o n t o t h e h o r i z o n t a l p l a n e d e f i n e s t h e j o u r n a l a n g l e . The v a r i a t i o n o f t h e j o u r n a l p o s i t i o n w i t h t h e a x i s of t h e b i t i s t h e skew a n g l e or o f f s e t . The most b a s i c d e s i g n e l e m e n t o f a t r i c o n e r o c k b i t i s t h e j o u r n a l a n g l e a l s o t e r m e d p i n a n g l e . F o r any g i v e n b i t d i a m e t e r , t h e cone s i z e i s a f u n c t i o n of t h e j o u r n a l a n g l e . The c o ne d i a m e t e r d e c r e a s e s w i t h an i n c r e a s e i n t h e j o u r n a l a n g l e . S o f t r o c k b i t s g e n e r a l l y have a low j o u r n a l a n g l e . A n o t h e r v a r i a t i o n o f t h e j o u r n a l p o s i t i o n i s t h e o f f s e t . I t i s d e f i n e d as t h e h o r i z o n t a l d i s t a n c e between a v e r t i c a l p l a n e t h r o u g h t h e a x i s o f t h e j o u r n a l and t h e b i t a x i s . ( F i g u r e 3.1-4) The skew a n g l e i s t h e a n g l e s u b t e n d e d by t h e o f f s e t and a p r e - s e l e c t e d p o i n t on t h e j o u r n a l a x i s . T h i s o f f s e t i s d e s i g n e d f o r s o f t t o medium r o c k b i t s t o p r o v i d e a g o u g i n g and s c r a p i n g a c t i o n . T h i s s l i g h t s l i d i n g movement of t h e cone i n c r e a s e s t h e d r i l l i n g r a t e o r , r e d u c e s t h e t h r u s t r e q u i r e m e n t f o r a g i v e n d r i l l i n g r a t e . However, t h e amount of o f f s e t i s a f u n c t i o n of t h e r o c k f o r m a t i o n b e c a u s e skewed c o n e s r e s u l t i n a c c e l e r a t e d c a r b i d e wear i n a b r a s i v e f o r m a t i o n s and i n t r o d u c e s i d e l o a d t o 39 DIRECTION OF ROTATION FIGURE 3.1-4-TRICONE BIT OFFSET, (after Hughes Tool Co.3) 40 t h e b e a r i n g s . 3.1.2 T e e t h and C a r b i d e I n s e r t s T u n g s t e n c a r b i d e i n s e r t b i t s were i n t r o d u c e d i n 1951 t o d r i l l e x t r e m e l y h a r d and a b r a s i v e f o r m a t i o n s t h a t were v e r y c o s t l y t o d r i l l w i t h c o n v e n t i o n a l s t e e l t o o t h b i t s . The c u t t i n g s t r u c t u r e of a t u n g s t e n c a r b i d e i n s e r t b i t r e s i s t s a b r a s i o n and h i g h c o m p r e s s i v e l o a d s . Components of c y l i n d r i c a l s i n t e r e d t u n g s t e n c a r b i d e , p r e s s e d i n t o m a c h i n e d h o l e s i n a l l o y s t e e l c o n e s form t h e t e e t h of t h i s t y p e of b i t . The c o s t d i f f e r e n t i a l between a t u n g s t e n c a r b i d e b i t and a s t e e l - t o o t h e d b i t i s o f f s e t by t h e i n c r e a s e d f o o t a g e . N e v e r t h e l e s s , a f t e r l a b o u r , d r i l l b i t s c o n s t i t u t e t h e most s i g n i f i c a n t c o s t component o f l a r g e d i a m e t e r b l a s t h o l e d r i l l i n g . The f i r s t c a r b i d e i n s e r t s u t i l i z e d were h e m i s p h e r i c a l ended b e c a u s e o f t h e i n h e r e n t s t r e n g t h o f t h i s s h a p e . T h i s shape i s s t i l l t h e b e s t f o r h a r d e s t f o r m a t i o n s . I n f o r m a t i o n g a i n e d by t e s t i n g a l a r g e number o f b i t s p e r m i t m a n u f a c t u r e r s t o u p g r a d e t h e i r d e s i g n . I n s e r t s h a p e , s p a c i n g and p o s i t i o n i n g a r e f u n c t i o n s o f t h e r o c k t y p e t o be d r i l l e d . V e r y p r o f i t a b l e b l a s t h o l e b i t p e r f o r m a n c e has been a c h i e v e d w i t h shaped c a r b i d e i n s e r t s ( F i g u r e 3.1-5). T u n g s t e n c a r b i d e b i t s a r e now u s e d i n a wide r a n g e o f r o c k f o r m a t i o n s . In A p p e n d i x 1, d i f f e r e n t m a n u f a c t u r e r s models a r e l i s t e d as a f u n c t i o n o f t h e r o c k f o r m a t i o n . 41 I \ | Z7 \ | ~ 7 CONICAL TOP INSERT ROUND TOP INSERT FIGURE 3.I-5' VARIOUS INSERT SHAPES COMMONLY USED BLAST HOLE ROCK BITS, (qfter Toll5) 42 H a r d r o c k b i t : As p r e v i o u s l y s p e c i f i e d , h e m i s p h e r i c a l l y shaped end c o m p a c t s were f o u n d t h e most e f f i c i e n t and d u r a b l e i n h a r d r o c k d r i l l i n g . The compact nose p r o j e c t i o n o v e r t h e cone s u r f a c e i s s m a l l and p e r m i t s t h e compact t o r e s i s t h i g h impact l o a d w i t h o u t b r e a k i n g . T h e r e i s no o f f s e t on t h e s e b i t s so t h e c o n e s r o t a t e on a t r u e r o l l i n g movement and t h u s , a b r a s i v e wear i s m i n i m i z e d . The c o m p a c t s a r e c l o s e l y s p a c e d on t h e c o n e s and p e n e t r a t i o n i s o b t a i n e d by a c r u s h i n g - c h i p p i n g a c t i o n on t h e r o c k . The r o c k f a i l s under p u r e i m p a c t and i n d e n t a t i o n of t h e c u t t e r e l e m e n t s 6 . Medium-hard r o c k b i t : The t u n g s t e n c a r b i d e i n s e r t s i n t h i s t y p e of b i t p o s s e s s a b u l l e t s h a p e d c o n i c a l end w i t h more compact p r o j e c t i o n . The r a t e o f p e n e t r a t i o n o f t h e s e b i t s i s f a s t e r t h a n t h e b a l l n o s e d compact b i t s i n t h e medium-hard f o r m a t i o n . M e d i u m - s o f t r o c k b i t : In t h i s c a s e , t h e c h i s e l s h a p e d i n s e r t b i t was f o u n d t h e most s u c c e s s f u l l d e s i g n i n t h e s o f t e r p l a s t i c f o r m a t i o n s . The c o n e s of t h e s e b i t s a r e s l i g h t l y skewed t o i n c r e a s e t h e r a t e of p e n e t r a t i o n and t h e s c r a p i n g - g o u g i n g a c t i o n s l o w l y r e p l a c e s t h e c r u s h i n g - c h i p p i n g t y p e o f r o c k b r e a k a g e f o u n d w i t h h a r d e r f o r m a t i o n r o c k b i t s . S o f t r o c k b i t : The t e e t h of a s o f t f o r m a t i o n t r i c o n e r o t a r y b i t a r e b r o a d and t h i n , deep and w i d e l y s p a c e d 5 . In 1933, t h e d e v e l o p m e n t 43 of r o l l e r c o n e b i t s w i t h i n t e r - f i t t i n g t e e t h made p o s s i b l e t h e use of l o n g e r t e e t h w i t h o u t a c o r r e s p o n d i n g r e d u c t i o n of t h e cone s i z e . Thus, s o f t f o r m a t i o n b i t s c a n e f f i c i e n t l y u t i l i z e l o n g e r c a r b i d e on t h e c o n e s , a l l o w i n g f o r more wear. A l s o , s i n c e t h e t e e t h p e n e t r a t e t h e r o c k d e e p e r , skew i s needed t o d i s l o d g e t h e r o c k more e a s i l y . P r o v i d e d w i t h l o n g l a s t i n g b e a r i n g s , t h e t u n g s t e n c a r b i d e compact b i t s have been u s e d w i t h s u c c e s s i n t h e s o f t e s t f o r m a t i o n s . In summary, t h e s p a c i n g and t h e l e n g t h o f t h e compacts i n c r e a s e w i t h an i n c r e a s e d s o f t n e s s o f t h e f o r m a t i o n . The number of c o m p a c t s i n c r e a s e s as t h e f o r m a t i o n h a r d n e s s i n c r e a s e s . Even i f t h e t o t a l number of com p a c t s has t o be h i g h so e a c h t o o t h l o a d i s n o t t o o l a r g e , t h e number must be few enough t o make s u r e t h a t when t h e t e e t h become worn, a s u f f i c i e n t u n i t l o a d w i l l s t i l l be a p p l i e d t o t h e f o r m a t i o n and p r o v o k e f a i l u r e 3 . F i n a l l y , t h e nose shape i n c r e a s e s i n r o u n d n e s s as t h e f o r m a t i o n becomes h a r d e r . 3.1.3 B e a r i n g s The b e a r i n g s a r e i m p o r t a n t p a r t s i n a t r i c o n e r o t a r y b i t . They t r a n s m i t t h e w e i g h t t o t h e i n s e r t s a t t h e r o c k c o n t a c t . Tough d r i l l i n g c o n d i t i o n s w i l l r a p i d l y s h o r t e n t h e b e a r i n g l i f e , and t h u s , l e a d t o t h e f a i l u r e o f t h e e n t i r e b i t . The b e a r i n g l i f e i s a f u n c t i o n of t h e i n t e n s i t y o f t h e u n i t l o a d s t r a n s m i t t e d by t h e b i t and t h e n a t u r e of t h e b o t t o m h o l e 44 e n v i r o n m e n t . R o l l e r cone b i t s a r e o c c a s i o n a l l y s u b j e c t e d t o l a r g e dynamic l o a d i n g w h i c h l o w e r t h e b i t l i f e s u b s t a n t i a l l y . However, t h e e n v i r o n m e n t was f o u n d t o have a much g r e a t e r i n f l u e n c e on t h e l i f e of t h e b e a r i n g s t h a n t h e dynamic l o a d i n g d o e s 7 . In some m i n i n g o p e r a t i o n s , water i s i n j e c t e d i n t o t h e a i r c i r c u l a t i o n l i n e t o a v o i d t h e f o r m a t i o n o f d u s t p a r t i c l e s . M e d l o c k 8 d e m o n s t r a t e d t h e e f f e c t o f w ater on b e a r i n g l i f e and h i s r e s u l t s a r e shown i n F i g u r e 3 . 1 - 6 . He f o u n d t h a t c l e a n , d r y a i r was t h e b e s t c i r c u l a t i o n f l u i d f o r maximum b e a r i n g l i f e and a l s o , t h a t t h e l i f e i n c r e a s e s w i t h t h e r a t e of a i r f l o w . The d i f f e r e n t b e a r i n g segments a r e shown i n F i g u r e 3 . 1 - 3 . They have s p e c i f i c f u n c t i o n s , b u t a g a i n , c ompromises must be made u n t i l a l l e l e m e n t s a r e w e l l b a l a n c e d . The r a d i a l l o a d i n g c a u s e d by t h e w e i g h t on t h e b i t i s t a k e n by t h e r o l l e r b e a r i n g s and by t h e nose f r i c t i o n b e a r i n g . The number and s i z e of r o l l e r s i s a f u n c t i o n o f t h e b e a r i n g p i n r o l l e r r a c e . A maximum number o f r o l l e r s r e d u c e s t h e u n i t l o a d i n g and t h u s , t h e s p a l l i n g and wear. On t h e o t h e r hand, t h e d i a m e t e r of t h e r o l l e r s must be l a r g e enough t o s u p p o r t t h e l o a d . The same d e s i g n c o n s i d e r a t i o n s h o l d f o r t h e b a l l b e a r i n g s , but i n t h i s c a s e , a n o t h e r c o n s t r a i n t has t o be f u l f i l l e d . The t h i c k n e s s of t h e s i d e s of t h e b a l l r a c e must be o f an a p p r o p r i a t e t h i c k n e s s t o r e s i s t b r e a k a g e . T h i s i s due t o t h e f a c t t h a t even i f t h e b a l l b e a r i n g s c a r r y some of t h e r a d i a l l o a d , e s p e c i a l l y i f some wear has o c c u r r e d on t h e end of t h e p i l o t p i n , t h e i r most i m p o r t a n t f u n c t i o n i s t o h o l d t h e c o n e s on 45 FIGURE 3.1-6' RESULTS OF ROLLER BEARING TESTS, (after Medlock8) 46 t h e arm j o u r n a l s . The nose b e a r i n g w h i c h r e s i s t s o u t w a r d t h r u s t i s made of a p i l o t p i n , h a r d f a c e d w i t h a s p e c i a l a l l o y and g r o u n d smooth, f i t t e d i n t o a b u s h i n g s i n c e no s p a c e i s a v a i l a b l e f o r a n o t h e r row of r o l l e r s . The b u s h i n g i s an a n t i f r i c t i o n m e t a l l i n i n g made o f s t a i n l e s s s t e e l . In o r d e r t o keep t h e u n i t l o a d t o a minimum on t h i s a r r a n g e m e n t of f r i c t i o n b e a r i n g , a l a r g e d i a m e t e r o f a d q u a t e l e n g t h i s r e q u i r e d . 3.1.4 Gage D e s i g n and S h i r t t a i l P r o t e c t i o n In t h e r e c e n t y e a r s , gage d e s i g n has been i m p r o v e d i n o r d e r t o m i n i m i z e p r e m a t u r e wear of t h e t r i c o n e b i t . The i n f l u e n c e o f gage wear on t h e b i t p e r f o r m a n c e i s i m p o r t a n t . The d u l l n e s s o r b r e a k a g e o f gage com p a c t s makes r o c k d r i l l i n g a l o n g t h e w a l l o f th e h o l e i n e f f i c i e n t . T h i s c a u s e s t h e t h r e e c o n e s t o e n c o u n t e r i n w a r d p r e s s u r e s a s shown on f i g u r e 3.1-7. The p r e s s u r e comes from t h e w e i g h t a p p l i e d on t h e b i t i n c o m b i n a t i o n w i t h t h e r o u n d e d gage. The r e s u l t i n g f o r c e i s d i r e c t e d t o w a r d t h e c e n t e r of t h e b i t . However, b i t b e a r i n g s a r e d e s i g n e d t o w i t h s t a n d o u t w a r d t h r u s t p r o d u c e d under n o r m a l d r i l l i n g c o n d i t i o n s . The p r e s e n c e o f i n w a r d t h r u s t on t h e b i t c r e a t e s l a r g e p r e s s u r e s on the i n n e r b e a r i n g s and s p e e d s up wear u n t i l c o m p l e t e f a i l u r e . The a b r a s i v e wear t h a t o c c u r s on gage i n s e r t s a l s o a f f e c t s t h e b i t s h i r t t a i l . T u n g s t e n c a r b i d e i n s e r t s a r e u s e d t o d e l a y r a p i d wear o f t h e l o w e r p a r t o f t h e s h i r t t a i l . W i t h o u t heavy FIGURE 3.1-7- EFFECT OF SIDE LOADS ON BIT BEARINGS, (after Dresser Industries4) 48 p r o t e c t i o n t h e c h a n c e s a r e t h a t t h e r o l l e r b e a r i n g s c o u l d e v e n t u a l l y be e x p o s e d and a l l o w e d t o d r o p o u t , b r e a k i n g t h e b i t . 3.1.5 A i r c o u r s e s A i r c o u r s e s a r e passageways f o r t h e c i r c u l a t i n g a i r . A l t h o u g h a p p r o x i m a t e l y t wenty p e r c e n t o f t h e t o t a l c o m p r e s s e d a i r i s d i v e r t e d t h r o u g h t h e b e a r i n g s f o r c o o l i n g and c l e a n i n g p u r p o s e s , t h e a i r i s f i r s t u s e d t o f l u s h t h e c u t t i n g s from t h e h o l e b o t t o m t o t h e s u r f a c e . The i m p o r t a n c e o f c u t t i n g r e m o v a l on d r i l l i n g p e r f o r m a n c e w i l l be d e s c r i b e d i n s e c t i o n 3.5.1. A t t h i s p o i n t , o n l y t h e c i r c u l a t i o n of a i r t h r o u g h t h e b i t i s c o n s i d e r e d . T r i c o n e r o t a r y b i t s a r e d i f f e r e n t i a t e d i n t o two t y p e s as f a r as t h e a i r c i r c u l a t i o n i s c o n c e r n e d : 1 . C o n v e n t i o n a l b i t s w h i c h d i r e c t t h e a i r r i g h t above t h e c o n e s . 2. J e t b i t s w h i c h d i r e c t t h e a i r o n t o t h e h o l e b o t tom, between t h e c o n e s . C o n v e n t i o n a l b i t s have l o n g been s t a n d a r d , b u t t h e y a r e now r e p l a c e d by t h e j e t b i t s . The p r i n c i p a l d i s a d v a n t a g e s r e l a t e t o t h e f a c t t h a t t h e f l u s h i n g medium i s p a s s e d a r o u n d t h e c o n e s b e f o r e i t r e a c h e s t h e h o l e b o t tom, t h u s r e d u c i n g i t s a b i l i t y t o move t h e c u t t i n g s and, i n many c a s e s , c a u s i n g s e v e r e e r o s i o n o f th e cone s h e l l and t e e t h a t h i g h v e l o c i t y . J e t b i t s have t h r e e n o z z l e s on t h e p e r i p h e r y of t h e b i t body t h r o u g h w h i c h t h e a i r 49 r u n s d i r e c t l y t o t h e h o l e b o t t o m . T h i s d e s i g n g i v e s s u p e r i o r c l e a n i n g o f t h e c h i p s and m i n i m i z e s t h e s a n d b l a s t i n g e f f e c t on t h e c u t t i n g s t r u c t u r e . F i g u r e 3.1-8 shows a c r o s s s e c t i o n a l view o f t h e a i r c p u r s e s of a j e t b i t . T h r o u g h t h e b e a r i n g s , t h e a i r f i r s t r u n s t h r o u g h s c r e e n s or f i l t e r s a t t h e e n t r a n c e s t o t h e b e a r i n g d i v e r s i o n . T h i s p r e v e n t s t h e b e a r i n g s f r o m b e i n g c l o g g e d w i t h d e b r i s c a r r i e d i n t h e a i r . Then t h e a i r i s d i s c h a r g e d i n t h e nose o f t h e cone and i n t h e b a l l r a c e , c o o l i n g t h e b e a r i n g s and k e e p i n g them f r e e o f f o r e i g n m a t e r i a l . F i n a l l y t h e a i r e s c a p e s t h r o u g h t h e cone o p e n i n g s , b e h i n d t h e gage. The major p a r t of t h e a i r volume f l o w s t h r o u g h t h e n o z z l e s t h a t a r e o f a d j u s t a b l e d i a m e t e r . 50 NOZZLE FIGURE 3.1-8' CROSS SECTIONAL VIEW OF A JET BIT. (after Steinke9) 51 3.2 PENETRATION OF BRITTLE ROCK D r i l l i n g w i t h t r i c o n e r o t a r y b i t s c a u s e s t h e r o c k t o b r e a k by t h e c o m b i n a t i o n o f c r u s h i n g - c h i p p i n g a c t i o n s . I f t h e b i t i s l o a d e d under s u f f i c i e n t w e i g h t , c o m p r e s s i v e s t r e s s d e v e l o p e d a t t h e end o f t h e t u n g s t e n c a r b i d e i n s e r t s overcomes t h e m a t e r i a l ' s c o m p r e s s i v e s t r e n g t h . The r o c k d i r e c t l y below t h e i n s e r t i s c r u s h e d i n a f i n e p o w d e r - l i k e m a t e r i a l , whereas t h e s t r e s s c o n c e n t r a t i o n a r o u n d t h e c r u s h e d zone u l t i m a t e l y d e v e l o p s d i s c r e t e f r a c t u r e s . The p r o p a g a t i o n o f t h e s e f r a c t u r e s t o t h e i n t e r s e c t i o n of t h e h o l e bottom forms t h e d r i l l i n g c h i p s . T h i s l a t e r mode of f a i l u r e i s a s s o c i a t e d w i t h t h e t e n s i l e o r s h e a r mode. Even t h o u g h t h e s e s t r e s s e s a r e dynamic i n n a t u r e , i t has been d e m o n s t r a t e d t h a t t h e y a r e a p p l i e d s l o w l y enough t o be s i m u l a t e d by s t a t i c l o a d i n g c o n d i t i o n s . Thus, t r i c o n e r o t a r y d r i l l i n g c a n be s i m u l a t e d as an i n d e n t a t i o n p r o c e s s . The knowledge of t h e r o c k p e n t r a t i o n p r o c e s s has been d e v e l o p e d t h r o u g h e x p e r i m e n t a l and m a t h e m a t i c a l r e s e a r c h . The f a c t o r s t h a t a f f e c t t h e m e c h a n i c s o f r o c k p e n e t r a t i o n a r e t h e a p p l i e d f o r c e , t h e s t r e n g t h p r o p e r t i e s of t h e r o c k and t h e geom e t r y of th e t o o t h 1 0 . D i f f e r e n t p e n e t r a t i o n m o d els has been p r o p o s e d . A l t h o u g h t h e y i n c l u d e d some s i m p l i f i c a t i o n s , t h e y c o n t r i b u t e t o th e u n d e r s t a n d i n g of t h e d r i l l i n g p r o c e s s . 3.2.1 S t r e s s e s B e n e a t h t h e I n d e n t o r 52 The f o r c e a p p l i e d by t h e i n s e r t c r e a t e s a complex s t r e s s f i e l d b e n e a t h i t t h a t i s e s s e n t i a l l y c o m p r e s s i v e . The s t r e s s d i s t r i b u t i o n i s a f u n c t i o n of t h e d e s i g n of t h e i n d e n t o r and t h e r o c k c o n d i t i o n s (smooth v s . i r r e g u l a r ) . T a n d a n a n d 1 1 p r o p o s e d a s i m p l i f i e d m a t h e m a t i c a l a p p r o a c h t o d e f i n e t h e s t r e s s c o n d i t i o n u n der a s p h e r i c a l i n d e n t o r ( F i g u r e 3 . 2-1). At t h e s u r f a c e , t h e r a d i a l , t a n g e n t i a l and v e r t i c a l s t r e s s e s a r e i n c o m p r e s s i o n . However-, t h e r a d i a l s t r e s s e s c hange i n t o t e n s i o n a t t h e b o u n d a r y between t h e i n s e r t and t h e r o c k and i s t h e l a r g e s t t e n s i l e s t r e s s ( t o p r i g h t ) . The l a r g e s t c o m p r e s s i v e s t r e s s i s t h e v e r t i c a l s t r e s s , i n d u c e d a t t h e c e n t e r of t h e c o n t a c t s u r f a c e and e q u a l t o t h e l o a d on t h e i n s e r t . H e r e , t h e r o c k f a i l s i n t h e c r u s h i n g mode ( i e . , t r i - a x i a l c o m p r e s s i o n ) . The maximum s h e a r s t r e s s i s f o u n d on t h e z a x i s a t a p o i n t d e p e n d e n t on t h e v a l u e o f P o i s s o n ' s r a t i o o f t h e i n d e n t e d m a t e r i a l ( z / a = 0 . 5 ) . S i k a r s k i e 1 2 has p u b l i s h e d a d e s c r i p t i o n of a wedge p e n e t r a t i n g t h e r o c k i n q u a s i - s t a t i c c o n d i t i o n s and t h e f o r m a t i o n of c h i p s : i ) I n i t i a l l y , f o r m a t i o n of c r u s h e d m a t e r i a l a t wedge t i p w i t h i n c r e a s i n g a p p l i e d f o r c e , i i ) P r i m a r y f r a c t u r e f orms and e x t e n d s i n t o v i r g i n m a t e r i a l w i t h i n c r e a s i n g a p p l i e d f o r c e , i i i ) D u r i n g t h e c r u s h i n g p h a s e , s t r e s s e s a r e i n c r e a s i n g i n t h e s u r r o u n d i n g m a t e r i a l mass, u n t i l , a t some p o i n t , s e c o n d a r y f r a c t u r e s a r e i n i t i a t e d . 53 FIGURE 3.2-1 - STRESS PROFILE ON CONTACT SURFACE AND ON AXIS OF SYMMETRY, (after Tandanand" ) 54 i v ) T h e s e f r a c t u r e s grow i n a s t a b l e manner w i t h i n c r e a s i n g l o a d u n t i l c r a c k i n s t a b i l i t y i s r e a c h e d , whereupon r a p i d c r a c k g r o w t h ( w i t h l i t t l e o r no i n c r e a s e i n f o r c e ) e x t e n d s t h e f r a c t u r e t o t h e f r e e s u r f a c e . A c h i p i s f o r m e d . Two t y p e s of f a i l u r e a r e s a i d t o o c c u r b e n e a t h an i n d e n t o r . I m m e d i a t l y a r o u n d t h e t i p of t h e i n s e r t , t h e r o c k i s c r u s h e d i n t r i - a x i a l c o m p r e s s i o n . T h i s t y p e o f f a i l u r e p r o d u c e s powder-l i k e m a t e r i a l and does n o t o p t i m i z e t h e use of e n e r g y a v a i l a b l e ( i e . , volume of b r o k e n m a t e r i a l / u n i t of e n e r g y ) . The s e c o n d t y p e o f f a i l u r e i s t h e t e n s i l e f a i l u r e . Away from t h e zone of t r i - a x i a l c o m p r e s s i o n , t h e c o n f i n e m e n t d e c r e a s e s and t h e r o c k p o s s e s s e s a more b r i t t l e b e h a v i o u r . I f t h e t e n s i l e s t r e s s i s l a r g e enough, c r a c k i n i t i a t i o n o c c u r s . The volume of m a t e r i a l s u b m i t t e d t o t r i - a x i a l s t r e s s c a n be r e d u c e d by m o d i f y i n g t h e i n d e n t o r g e o m e t r y o r by r e d u c i n g t h e l a t e r a l c o n f i n e m e n t . 3.2.1.1 The I n d e n t o r Geometry F i g u r e 3.2-2 shows t h e g r a p h i c a l r e p r e s e n t a t i o n of a model d e v e l o p e d by R e i c h m u t h 1 3 . On t h e b a s i s of p u r e l y e l a s t i c a n a l y s i s , he has d e r i v e d t h e f o l l o w i n g r e l a t i o n s h i p : Tan /3 > (TT - 2 U ) / ( 2 + TTU) Tan p <= (TT - 2 U ) / ( 2 + TTU) Where ft = s e m i - i n c l u d e d wedge a n g l e . U = c o e f f i c i e n t of f r i c t i o n between t h e t o o t h and t h e r o c k . 55 SECONDARY FAILURE ZONE OF TRIAXIAL COMPRESSION SECONDARY FAILURE • (chip removed* ZONE OF TRIAXIAL COMPRESSION INITIAL FAILURE INITIAL FAILURE FOR WIDE ANGLE WEDGES FOR NARROW ANGLE WEDGES 2a 2b FIGURE 3.2-2-- MEDIA AFTER SECONDARY FAILURE HAS OCCURED. (after Reichmuth13) 56 In t h e c a s e 2a, t h e s t r e s s d i s t r i b u t i o n i s e f f e c t i v e l y l o c a l i z e d i n a r e g i o n below t h e t o o t h , c a u s i n g c o n s i d e r a b l e c r u s h i n g and c o m p a c t i o n o f t h e r o c k and i n h i b i t i n g t h e f o r m a t i o n of c h i p s 1 4 . The i n t e n s i t y o f t h e c o m p r e s s i v e s t r e s s , t r a n s m i t t e d from t h e i n s e r t t o t h e i n t a c t r o c k t h r o u g h t h e c r u s h e d zone, d e c r e a s e s as t h e wedge a n g l e i n c r e a s e s . In a d d i t i o n , t h e p r e f e r e n t i a l g r o w t h o r i e n t a t i o n o f t h e s e c o n d a r y c r a c k s i s s t e e p e r and t h e f r i c t i o n a l f o r c e s t e n d t o e x e r t g r e a t e r r e s t r a i n t on t h e m a t e r i a l under a w i d e r wedge a n g l e . C o n v e r s e l y , w i t h a s h a r p e r wedge, as i n c a s e 2b, s e c o n d a r y f r a c t u r e s a r e p r o d u c e d c l o s e r t o t h e f r e e s u r f a c e and c h i p s a r e f o r m e d . In t h i s c a s e , v e r y l i t t l e c o m p a c t i o n and c r u s h i n g o f t h e r o c k i s d e v e o p e d i n t h e t o o t h ' s noze a r e a . From t h e a b o v e , i t i s c o n c l u d e d t h a t t h e f o r c e r e q u i r e d t o o b t a i n a g i v e n p e n e t r a t i o n d e p t h i n c r e a s e s r a p i d l y w i t h an i n c r e a s e i n t h e wedge a n g l e . E x p e r i m e n t s have c o n f i r m e d t h i s c o n c l u s i o n 1 5 ( f i g u r e 3 . 2 - 3 ) . M o r e o v e r , t h e s e e x p e r i m e n t s a l s o i l l u s t r a t e d t h a t t h e r e was a change i n t h e f a i l u r e b e h a v i o u r of t h e r o c k when wedge a n g l e were i n c r e a s e d o v e r 75 t o 90 d e g r e e s , i n a c c o r d a n c e w i t h t h e R e i c h m u t h m o d e l . W i t h a s h a r p wedge, r o c k i s b e l i v e d t o behave i n a b r i t t l e manner whereas w i t h a l a r g e r wedge a n g l e , t h e r o c k b e h a v i o u r i s more d u c t i l e . As a r e s u l t , i n s e r t shape has a much g r e a t e r e f f e c t on d r i l l i n g r a t e f o r d r i l l s w h i c h a r e l o a d l i m i t e d ( r o l l e r - b i t ) b e c a u s e a l a r g e i n s e r t w i l l n o t p e n e t r a t e as deep as a s h a r p one, r e s u l t i n g i n a 57 BIT PENETRATION, Inches FIGURE 3,2-3= CHARACTERISTIC FORCE-PENETRATION CURVES FOR CHARCOAL GRAY GRANITE UNDER STATIC BIT LOADING. ( after Reichmuth13) 58 r e d u c e d d r i l l i n g r a t e 1 6 . A l t h o u g h s m a l l wedges a r e more e f f i c i e n t , l a r g e r wedge a n g l e s a r e u s e d t o keep wear w i t h i n r e a s o n a b l e l i m i t s . 3.2.1.2 I n d e x i n g The i n t e r a c t i o n o f a b i t t o o t h w i t h a p r e v i o u s l y formed c r a t e r i s r e f e r e d t o as i n d e x i n g . When an i n s e r t i s l o a d e d a d j a c e n t t o a p r e v i o u s l y formed c r a t e r , t h e t e n s i l e f r a c t u r e g e n e r a l l y p r o g r e s s e s t o w a r d i t s d i r e c t i o n and t h e c h i p b r e a k s i n t o t h e c r a t e r . T y p i c a l f o r c e - d i s p l a c e m e n t c u r v e s a r e shown i n f i g u r e 3.2-4 f o r i n d e x e d t o o t h p e n e t r a t i o n . In g e n e r a l , t h e a v e r a g e s l o p e of a f o r c e - d i s p l a c e m e n t c u r v e d e c r e a s e s w i t h d e c r e a s i n g i n d e x i n g d i s t a n c e . I n d e x i n g i s more e f f i c i e n t b e c a u s e of t h e r e d u c e d p r o p o r t i o n o f c r u s h e d m a t e r i a l formed p e r u n i t volume o f b r o k e n r o c k . The optimum i n d e x i n g d i s t a n c e may be as g r e a t as f i v e t i m e s t h e p e n e t r a t i o n d e p t h . In a r e s e a r c h p r o j e c t c o n d u c t e d by G n i r k and C h e a t h a m 1 8 , t h e optimum i n d e x i n g d i s t a n c e was r e l a t e d t o t h e w i d t h o f t h e i n s e r t and t h e p e n e t r a t i o n d e p t h . T h i s i s o f i m p o r t a n c e i n d e t e r m i n i n g t h e optimum s p a c i n g of i n d i v i d u a l i n s e r t on a r o l l e r - b i t and f o r t h e s e l e c t i o n o f t h e t o o t h a n g l e f o r v a r i o u s r o c k t y p e s . 3.2.2 T o o l P e n e t r a t i o n M o d e l s T h e o r e t i c a l a n a l y s i s of b r i t t l e r o c k p e n e t r a t i o n by a r i g i d t o o l , a l t h o u g h s i m p l i f i e d , a r e t h e b a s i s of our u n d e r s t a n d i n g o f 59 - 2/3=30° PENETRATION (In.) FIGURE 3.2-4'AVERAGE FORCE PENETRATION CURVES FOR CARTHAGE MARBLE AS OBTAINED WITH 30 AND 60 DEGREE SHARP BIT-TEETH AT ATMOSPHERIC PRESSURE FOR VARIOUS INDEXING DISTANCES (after Cheatham and Gnirk17) 60 t h e d r i l l i n g p r o c e s s . T h i s p a r a g r a p h w i l l r e v i e w f o u r of them. 3.2.2.1 P a u l and S i k a r s k i e P e n e t r a t i o n M odel The r o c k p e n e t r a t i o n model p r o p o s e d by P a u l and S i k a r s k i e 1 9 p r e d i c t s t h e g r o s s b e h a v i o u r of r o c k under a l o a d e d i n s e r t a t s h a l l o w d e p t h . In t h i s m o d e l , i t i s assumed t h a t ; i ) The Mohr-Coulomb c r i t e r i o n i s s a t i s f i e d e v e r y w h e r e on t h e f a i l u r e p l a n e a t t h e i n s t a n t of f a i l u r e , i i ) The f r a c t u r e s o c c u r a l o n g p l a n e s e x t e n d i n g f r o m t h e i n s e r t t i p t o t h e f r e e s u r f a c e a t an i n c l i n a t i o n ( t o t h e s u r f a c e ) o f : ii = TT/4 - (/3 + <(>)/2 w i t h 0 = h a l f i n c l u d e d wedge a n g l e <t> = a n g l e o f i n t e r n a l f r i c t i o n i i i ) The f o r c e p e n e t r a t i o n c u r v e s a r e l i n e a r d u r i n g t h e c r u s h i n g p h a s e o f p e n e t r a t i o n , i v ) The r o c k i s c o n s i d e r e d as a m a t e r i a l w h i c h e x h i b i t s b o t h c r u s h i n g n e a r t h e i n s e r t t i p and t h e f o r m a t i o n of c h i p s on b o t h s i d e s of t h e p e n e t r a t i n g wedge, a l t h o u g h t h e model a n a l y s i s o m i t s t h e c r u s h e d z o n e . The f o r c e p e n e t r a t i o n c u r v e s p r e d i c t e d by t h e model a r e shown i n f i g u r e 3.2-5 f o r b o t h c o n s t a n t l o a d and c o n s t a n t r a t e . The a c t u a l l o a d i n g c o n d i t i o n s on a wedge a r e somewhere between t h e s e two e x t r e m e c o n d i t i o n s . The c h i p s a r e formed when t h e c r u s h i n g c u r v e s i n t e r s e c t t h e f a i l u r e l i n e . The c r u s h i n g c u r v e s 61 WEDGE PENETRATION FIGURE 3.2-5' THEORETICAL FORCE-PENETRATION CURVE FOR BRITTLE CRATER MODEL. (after Paul and Sikarskie19) 62 s l o p e k i s e x p e r i m e n t a l l y d e t e r m i n e d whereas t h e f a i l u r e l i n e s l o p e i s g i v e n by: K = 2 S 0 sin/3 (1 - s i n 0 ) / (1 - sin(/3 + tf>)) where S 0 = U n i a x i a l c o m p r e s s i v e s t r e n g t h |3 = S e m i - i n c l u d e d wedge a n g l e <t> = A n g l e of i n t e r n a l f r i c t i o n The a s s u m p t i o n s o f p l a n a r c h i p s u r f a c e and s i m u l t a n e o u s f r a c t u r e can be v i e w e d as an upper bound t y p e o f s o l u t i o n and t h e r e f o r e , t h e p e n e t r a t i o n d e p t h p r e d i c t e d by t h i s model i s t h e m i n i m a l d e p t h t h a t c a n be o b t a i n e d a t a g i v e n l o a d . T h i s model i s c o n s e r v a t i v e . M o r e o v e r , t h e c r u s h i n g p h a s e o f t h e p e n e t r a t i o n p r o c e s s i s n o t an e x a c t b r i t t l e f r a c t u r e p r o b l e m . The p u l v e r i z e d n a t u r e o f t h e m a t e r i a l and t h e h i g h h y d r o s t a t i c s t r e s s e s i n t h e v i c i n i t y o f t h e wedge t i p make t h e m a t e r i a l behave more o r l e s s p l a s t i c a l l y . The model p r e d i c t s t h e c e s s a t i o n of c h i p f o r m a t i o n when t h e s e m i - i n c l u d e d t o o t h a n g l e e x c e e d s ( TT/2 - <j> ). Cheatham and G n i r k 1 7 n o t e d t h a t s i n c e most r o c k s e x h i b i t on a n g l e of f r i c t i o n of a p p r o x i m a t i v e l y 30 d e g r e e s , t h e above e x p r e s s i o n i m p l i e s t h a t o n l y c r u s h i n g w i l l o c c u r f o r a t o o t h a n g l e o f a p p r o x i m a t i v e l y 120 d e g r e e s . However, t h e o b s e r v e d range o f v a l u e f o r numerous v a r i e t i e s of r o c k i s 75 t o 90 d e g r e e s . 3.2.2.2 Bauer and C a l d e r P e n e t r a t i o n M o d e l 63 The r o c k p e n e t r a t i o n model p r o p o s e d by Bauer and C a l d e r 2 0 i s b a s e d on t h e s t u d y o f i n d e n t o r p e n e t r a t i o n i n r o c k . They c o n c l u d e d f r o m a s e r i e s o f i n d e n t a t i o n t e s t s t h a t , f o r i n d e n t o r s s h a p e s commonly employed i n d r i l l i n g , t h e f o r c e - p e n e t r a t i o n r e l a t i o n i s e i t h e r l i n e a r o r becomes l i n e a r as p e n e t r a t i o n p r o c e e d s . In a d d i t i o n , i t was a p p a r e n t t h a t t h e i n d e n t o r s " s e a t " t h e m s e l v e s on a s h e l l o f v e r y c o m p a c t e d m a t e r i a l as t h e a p p l i e d l o a d i n c r e a s e s . I t r e s u l t s t h a t t h e i n s e r t - r o c k c o n t a c t a r e a a l s o becomes c o n s t a n t a s p e n e t r a t i o n p r o c e e d s . T h e r e f o r e , dF/dh = Ka where F = t o t a l a p p l i e d f o r c e on i n d e n t o r K = r o c k p e n e t r a t i o n c o n s t a n t A = h o r i z o n t a l p r o j e c t i o n o f i n d e n t o r a r e a a t d e p t h h K i s s i m p l y t h e s l o p e o f t h e f o r c e - p e n e t r a t i o n c u r v e when i t becomes l i n e a r , d i v i d e d by t h e c o n t a c t a r e a ( i e . , t h i s c o n s t a n t i s n o t e q u a l t o K or k of t h e P a u l & S i k a r s k i e m o d e l ) . F i g u r e 3.2-6 shows a p l o t o f t h e u n i a x i a l c o m p r e s s i v e s t r e n g t h v e r s u s K. The c o r r e l a t i o n i s e x c e l l e n t . The v a l u e o f K f o r d i f f e r e n t s h a p e s o f i n d e n t o r i s g i v e n by t h e f o l l o w i n g e q u a t i o n s : i ) c o n s t a n t a r e a i n d e n t o r s : K = F/hA i i ) wedges: K = F / ( L t a n ( a / 2 ) h 2 ) where L = l e n g t h of wedge a = i n c l u d e d a n g l e of wedge (2/3) FIGURE 3.2-6 ROCK PENETRATION CONSTANT VS UNIAXIAL COMPRESSIVE STRENGTH, (after Bauer and Colder20) 65 i i i ) h e m i s p h e r e s : K = F / ( 7 r h 2 ( r - h/3) ) f o r h <= r i v ) c o n e s : K = 3F/(T T h t a n 2 ( a / 2 ) ) The t o t a l p e n e t r a t i o n o b t a i n e d when an i n d e n t o r i s f o r c e d i n t o r o c k i n r o t a r y d r i l l i n g i s made of two p a r t s . F i r s t l y , a p o r t i o n c a u s e d by t h e i n d e n t o r p e n e t r a t i o n , u s u a l l y l e s s t h a n 10% ( t e r m e d h ) , and s e c o n d l y a p o r t i o n c a u s e d by t h e s t r e s s f r a c t u r e b e n e a t h t h e i n d e n t o r t i p ( t e r m e d d ) . The v a l u e of d i.s o b t a i n e d from t h e f o l l o w i n g e q u a t i o n s : i ) l i n e l o a d ( c y l i n d r i c a l e n v e l o p e of d i a m e t e r d c a u s e d by a wedge) d = F(1 - s i n 0 ) ( w - 1 ) / ir Sc s i n 0 i i ) p o i n t l o a d ( s p h e r i c a l e n v e l o p e o f d i a m e t e r d c a u s e d by a cone or a s p h e r e ) d = 3F(1 - s i n ^ M w - 1 ) / 47r S C sintf> where F = a p p l i e d l o a d Sc = u n i a x i a l c o m p r e s s i v e s t r e n g t h 0 = a n g l e of i n t e r n a l f r i c t i o n w = t a n 2 (45 + (0/2) ) In p r a c t i c e , however, t h e d e p t h of r o c k f a i l u r e due t o t h e s t r e s s f i e l d b e n e a t h t h e i n d e n t o r c o u l d be as low as 0.4d due t o i n d e n t o r geometry or i n d e x i n g e f f e c t s . 3.2.2.3 P a r i s e a u and F a i r h u r s t P e n e t r a t i o n M o d e l s The r o c k p e n e t r a t i o n models p r o p o s e d by P a r i s e a u and 66 F a i r h u r s t 2 1 a r e d e r i v e d f r o m t h e a p p l i c a t i o n o f p l a s t i c i t y a n a l y s i s i n wedge p e n e t r a t i o n of r o c k . The most p r a c t i c a l a p p r o a c h i s t h e one t h a t c o n s i d e r s t h e e x i s t a n c e of a f a l s e - n o s e composed of f i n e l y c r u s h e d m a t e r i a l a t t h e apex o f t h e wedge ( s e e F i g u r e 3 . 2 - 7 ) . P e n e t r a t i o n t e s t s c o n f i r m t h e e x i s t e n c e of s u c h a z o n e . The f o r c e - d i s p l a c e m e n t c h a r a c t e r i s t i c f o r t h i s c o n d i t i o n i s g i v e n by t h e f o l l o w i n g e q u a t i o n : F/hbSo = T a n / 3 / ( T a n 0 Tan/x) [e x p ( 7rTan0) - Tan 2,u] and t h u s h = F / MbSo where F = a p p l i e d f o r c e b = b i t c o n t a c t edge (= c t e = u n i t y ) So = u n i a x i a l c o m p r e s s i v e s t r e n g t h M = Tan/3/(TanQTanu) [ e x p ( r r T a n 0 ) - T a n 2 / u 3 /3 = s e m i - i n c l u d e d wedge a n g l e <j> = a n g l e of i n t e r n a l f r i c t i o n M = TT/4 - <j>/2 In t h i s model, however, t h e p l a s t i c r e g i o n e x t e n d s from t h e b i t f a c e t o t h e r o c k s u r f a c e . I t i s l i k e l y t h a t i n p r a c t i c e , t h e p l a s t i c r e g i o n i s o f f i n i t e d i m e n s i o n and doe s n o t e x t e n d t o t h e r o c k s u r f a c e . Then b r i t t l e f a i l u r e as w e l l a s p l a s t i c f a i l u r e a c c o m p a n i e s p e n e t r a t i o n . They a p p r o a c h e d t h i s p r o b l e m by a s s u m i n g a n o n - l i n e a r f a i l u r e c r i t e r i o n . B e c a u s e t h e Coulomb e n v e l o p e i s f o r many r o c k s a l i n e a r a p p r o x i m a t i o n of what i s i n f a c t a n o n - l i n e a r f a i l u r e e n v e l o p e , t h e y e x a m i n e d a p a r a b o l i c FIGURE 3.2-7'ASSUMED STRESS FIELD FOR 'FALSE NOSE'SITUATION, (after Pariseau and Fairhurst21) 68 t y p e of f a i l u r e c r i t e r i o n . They d e r i v e d t h e f o l l o w i n g r e l a t i o n s h i p : F/hbSo = S i n 0 o T a n / 3 / S i n 0 [ l / 2 S i n 0 + (Sin(20+/3) )/Sin/3] + ( T o T a n / 3 ) / ( 2 S o S i n 0 o ) M and t h u s , h = F/M'bSo where F = a p p l i e d f o r c e b = b i t c o n t a c t edge ( = c t e = u n i t y ) So = u n i a x i a l c o m p r e s s i v e s t r e n g t h To = u n i a x i a l t e n s i l e s t r e n g t h To <= 0 4>0 = i n c l i n a t i o n of t h e y i e l d e n v e l o p t o t h e S - a x i s a t t h e p o i n t i t t o u c h e s t h e u n i a x i a l c o m p r e s s i v e s t r e n g t h s t r e s s c i r c l e 0 = v a r i a b l e = f(am) am = 1/2 ( a , + a 3 ) a, = major p r i n c i p a l s t r e s s a 3 = m i n o r p r i n c i p a l s t r e s s /3 = s e m i - i n c l u d e d wedge a n g l e M' =" [ ( S i n 0 o T a n / 3 ) / S i n 0 ] [ l / 2 S i n 0 + S i n ( 20 + /3) / S i n/3 ] + ( T o T a n / 3 / 2 S o S i n 0 o ) 6 = IT/2 + 1/2(0O " 0) + l / 2 ( C o t 0 o - Cot0) The p r o b l e m w i t h t h i s e q u a t i o n i s t h e f a c t t h a t 0 i s a f u n c t i o n of t h e m a j o r and minor p r i n c i p a l s t r e s s e s e n c o u n t e r e d i n t h e a r e a o f p l a s t i c b e h a v i o u r ( i e : b e n e a t h t h e i n d e n t o r ) . T h i s v a l u e i s o b t a i n e d by knowing t h e e q u a t i o n of t h e f a i l u r e e n v e l o p and t h e m a g n i t u d e of t h e s t r e s s e s . 69 3.3 S P E C I F I C ENERGY The c o n c e p t of s p e c i f i c e n e r g y can be a p p l i e d t o a l l f r a g m e n t a t i o n p r o c e s s e s as shown i n f i g u r e 2.2-1, i t i s d e f i n e d as t h e e n e r g y r e q u i r e d t o f r a c t u r e a c e r t a i n volume o f r o c k . The amount of e n e r g y r e q u i r e d t o f r a c t u r e t h e r o c k i s d e pendent on t h e f r a g m e n t s s i z e and t h e f r a g m e n t a t i o n p r o c e s s . I n d r i l l i n g , i t i s a q u a n t i t y t h a t depends not o n l y on t h e s t r e n g t h o f t h e r o c k , but a l s o on d r i l l i n g p a r a m e t e r s s u c h as t h e g eometry o f t h e b i t , t h e s i z e of t h e h o l e , t h e c u t t i n g r e m o v a l method, e t c . The s p e c i f i c e n e r g y i n d r i l l i n g c o n s i d e r s a l l t h e modes of f a i l u r e o c c u r i n g a t t h e r o c k - b i t i n t e r f a c e and t h e t o t a l e n e r g y l o s s e s . D u r i n g t h e d r i l l i n g p r o c e s s , t h e r o c k i s i n i t i a l l y b r o k e n and c h i p s a r e f ormed, but b e c a u s e p e r f e c t c l e a n i n g c o n d i t i o n n e v e r o c c u r s , t h e r o c k i s r e g r o u n d . Such e f f e c t i m p l i e s t h a t a c e r t a i n amount of e n e r g y i s a l s o consumed i n a c o m m i n u t i o n p r o c e s s and t h e r e f o r e , t h e s p e c i f i c e n e r g y i n d r i l l i n g i s a c o l l e c t i v e measure of t h e s p e c i f i c e n e r g i e s r e q u i r e d f o r c r u s h i n g , c h i p p i n g and g r i n d i n g t h e r o c k 2 2 . The c o n c e p t of s p e c i f i c e n e r g y i n d r i l l i n g has been i n t e n s i v e l y s t u d i e d by T e a l e 2 3 . He p o s t u l a t e d t h a t , f o r a g i v e n t o o l , t o e x c a v a t e a g i v e n volume of r o c k , a c e r t a i n t h e o r e t i c a l minimum q u a n t i t y of e n e r g y w i l l be r e q u i r e d . T h i s amount of e n e r g y w i l l be a f u n c t i o n of t h e n a t u r e o f t h e r o c k mass, and t h e d i f f e r e n c e between t h e t h e o r e t i c a l r e q u i r e m e n t s and t h e r e a l p r o c e s s w o u l d be a measure of t h e work d i s s i p a t e d i n t h e 70 c o m m u n i t i o n p r o c e s s , i n f r i c t i o n between t h e t o o l and t h e r o c k a n d / o r i n m e c h a n i c a l l o s s e s i n t h e s y s t e m . In o t h e r words, t h i s d i f f e r e n c e i s a measure of t h e e f f i c i e n c y of t h e p r o c e s s . In t r i c o n e r o t a r y d r i l l i n g , t h e s p e c i f i c e n e r g y r e a c h e s v e r y h i g h v a l u e s a t low t h r u s t s . T h i s i s c a u s e d by t h e f a c t t h a t below a c e r t a i n v a l u e , t h e t h r u s t w i l l be i n a d e q u a t e t o f o r c e t h e t o o l i n t o t h e r o c k . As t h e volume o f r o c k e x c a v a t e d w i l l t e n d t o w a r d z e r o , a f i n i t e amount o f work w i l l s t i l l be done t o overcome f r i c t i o n . But as t h e t h r u s t i n c r e a s e s , t h e s i z e of p a r t i c l e s b r o k e n a l s o i n c r e a s e s and t h e f r i c t i o n l o s s w i l l c o n s t i t u t e a r a p i d l y d e c r e a s i n g p o r t i o n o f t h e t o t a l e n e r g y i n p u t . T h e r e f o r e , t h e s p e c i f i c e n e r g y w i l l d e c r e a s e . N e v e r t h e l e s s , a t h i g h t h r u s t v a l u e s , t h e t o o l i s h e a v i l y p u s h e d i n t o t h e r o c k and c l o g s . The r e d u c t i o n i n t h e e f f i c i e n c y o f t h e p r o c e s s w i l l c a u s e t h e s p e c i f i c e n e r g y t o r i s e a g a i n . The l o w e s t v a l u e o b t a i n e d i s a measure o f t h e maximum m e c h a n i c a l e f f i c i e n c y of t h a t p a r t i c u l a r t o o l i n t h e p a r t i c u l a r o p e r a t i n g c o n d i t i o n s i n t o a g i v e n r o c k . T h i s q u a n t i t y i s i n t h e o r d e r o f m a g n i t u d e of t h e u n i a x i a l c o m p r e s s i v e s t r e n g t h of t h e r o c k . T e s t s p e r f o r m e d by T e a l e 2 3 showed t h a t t h e r a t i o o f minimum s p e c i f i c e n e r g y t o u n i a x i a l c o m p r e s s i v e s t r e n g t h r a n g e s between 0.8 and 1.6. A l t h o u g h T e a l e n o t e d t h a t t h e u n i a x i a l c o m p r e s s i v e s t r e n g t h i s n ot an a b s o l u t e measure of t h e r o c k s t r e n g t h n o r p o s s e s s e s p h y s i c a l s i m i l a r i t y w i t h t h e d r i l l i n g p r o c e s s , he s u g g e s t e d t h a t t h e r e must be some k i n d of r e l a t i o n s h i p between t h e two. 71 However M e l l o r 2 4 p u b l i s h e d t h e r e s u l t s o f r e s e a r c h i n w h i c h he e x a m i n e d t h e v a l i d i t y o f t h e use o f t h e u n i a x i a l c o m p r e s s i v e s t r e n g t h as a n o r m a l i z i n g f a c t o r f o r t h e s p e c i f i c e n e r g y i n f r a g m e n t a t i o n p r o c e s s . He p o i n t e d out t h a t t h e u n i a x i a l c o m p r e s s i v e s t r e n g t h i s a c t u a l l y p r o p o r t i o n a l t o t h e s p e c i f i c e n e r g y i n b r e a k i n g t h e r o c k i n u n i a x i a l c o m p r e s s i o n ( i e . , S.E.ucs oc * 10~ 3) and t h e r e f o r e c an be u s e d as a n o r m a l i z i n g f a c t o r . Even t h o u g h , a c c o r d i n g t o T e a l e , t h e r a t i o of minimum s p e c i f i c e n e r g y / u n i a x i a l c o m p r e s s i v e s t r e n g t h i s a r o u n d one f o r optimum o p e r a t i n g c o n d i t i o n s , i n p r a c t i c e , t h e v a l u e s range from 0.3 t o 3. 72 3.4 ROCK MASS DRILLABILITY D r i l l a b i l i t y c a n be d e f i n e d a s t h e r e s i s t a n c e o f t h e r o c k t o p e n e t r a t i o n . U n f o r t u n a t e l y , t h e r e a r e as many d r i l l a b i l i t y i n d e x e s as t h e r e a r e d r i l l a b i l i t y t e s t s . T h i s r e s u l t s i n a wide d i v e r g e n c e on norms and i n c o n f u s i o n 2 5 . D r i l l a b i l i t y i n d e x e s a r e u s e d t o p r e d i c t t h e d r i l l i n g p e r f o r m a n c e in' a g i v e n r o c k mass. However, on t h i s r e s e a r c h p r o j e c t , we a r e u s i n g t h e d r i l l i n g p e r f o r m a n c e t o d e f i n e an i n d e x of t h e r o c k mass f a i l u r e p r o p e r t i e s . F o r t h i s r e a s o n , t h e r e v i e w of t h e f a c t o r s c o n t r o l l i n g d r i l l a b i l i t y has been u n d e r t a k e n and p r e s e n t e d i n t h i s p a r a g r a p h . Two g e n e r a l methods e x i s t t o d e t e r m i n e t h e r o c k mass d r i l l a b i l i t y : 1) D r i l l i n g t h e r o c k 2) A n a l y s i s o f t h e m e c h a n i c a l p r o p e r t i e s o f t h e r o c k 3.4.1 D r i l l i n g T e s t s T h i s method has been u s e d by many s c i e n t i s t s . The p r o c e d u r e i s g e n e r a l l y c l o s e t o t h e f o l l o w i n g . A t y p i c a l d r i l l -b i t a r r a n g e m e n t i s s e l e c t e d . The r o c k i s d r i l l e d u n d e r s t r i c t c o n d i t i o n s ( t h r u s t , rpm) u p - s i d e down t o o b t a i n p e r f e c t c l e a n i n g c o n d i t i o n s . The b i t wear, d r i l l i n g t i m e o r e n e r g y i n p u t a r e m o n i t o r e d f o r a g i v e n d r i l l e d d e p t h and e v e n t u a l l y r e s u l t as a d r i l l a b i l i t y i n d e x . In some o c c a s i o n s , t h e i n d e x i s r e l a t e d , w i t h d i f f e r e n t d e g r e e s of s u c c e s s , w i t h p h y s i c a l p r o p e r t i e s of 73 t h e r o c k . D r i l l a b i l i t y i n d e x e s d e r i v e d from t h i s method depend not o n l y on t h e r o c k p r o p e r t i e s , b u t a l s o on t h e equipment u s e d and t h e o p e r a t i n g c o n d i t i o n s . A l t h o u g h t h e p r o c e d u r e i s l o g i c a l , t h e e x p e r i m e n t a l c o n d i t i o n s have t o c l o s e l y s i m u l a t e t h e f i e l d c o n d i t i o n s t o r e s u l t i n a r e l i a b l e d r i l l a b i l i t y s c a l e . In open p i t d r i l l i n g , d r i l l a b i l i t y t e s t s a r e g e n e r a l l y p e r f o r m e d by b i t m a n u f a c t u r e r s . E v e n t h o u g h some c o m p a n i e s promote t h e i n d e n t a t i o n t e s t o t h e r s a r e u s i n g a more e m p i r i c a l a p p r o a c h c a l l e d t h e m i c r o b i t t e s t . D e t a i l s o f t h e t e s t p r o c e d u r e a r e g i v e n i n t h e l i t e r a t u r e 2 6 . The main f a c t o r i n t h i s a p p r o a c h i s t h a t t h e r e s u l t s o f t h i s t e s t a r e c o r r e l a t e d w i t h o t h e r m i c r o b i t d r i l l a b i l i t y r e s u l t s of r o c k f o r m a t i o n s on w h i c h f u l l s i z e b i t s have been u s e d . F i g u r e 3.4-1 i s a c h a r t showing an e m p i r i c a l c o r r e l a t i o n o f known f o r m a t i o n s w i t h m i c r o b i t d a t a . The d r i l l i n g r a t e o b t a i n e d from t h i s c h a r t i s m o d i f i e d by e x p e r i m e n t a l f a c t o r s (0.5 t o 0.7) t o r e f l e c t t h e a v e r a g e d r i l l i n g r a t e f o r t h e l i f e o f t h e b i t . In g e n e r a l , t h e r e s u l t s of t h i s t e s t a r e c o n s e r v a t i v e . As a m a t t e r of f a c t , i t s h o u l d be n o t e d t h a t t h e r e s u l t s a r e a s good as t h e d e g r e e of r e p r e s e n t a t i v i t y o f t h e t e s t e d s p e c i m e n o v e r t h e whole r o c k mass. In a d d i t i o n , no a l l o w a n c e i s made f o r t h e a b r a s i v e n e s s o f the r o c k . 3.4.2 A n a l y s i s of t h e M e c h a n i c a l P r o p e r t i e s of t h e Rock One o f t h e f i r s t d r i l l a b i l i t y i n d e x e s was t h e Moh's s c a l e . A c c o r d i n g t o P r o t o d y a k o n o v 2 5 , a d r i l l a b i l i t y s c a l e b a s e d on 74 FIGURE 3.4-1 ESTIMATED DRILLING RATE OF NEW HUGHES TRICONE ROCK BITS AT 60 rev/min. AS DETER-MINED BY MICROBIT DRILLING RATE TESTS, (after Rollow26) 75 s t a n d a r d i z e d method o f m e a s u r i n g t h e m e c h a n i c a l p r o p e r t i e s of r o c k s i s a more r a t i o n a l a p p r o a c h . D i f f e r e n t t e c h n i q u e s e x i s t t o measure t h e s t r e n g t h o f t h e r o c k : 1) R e s i s t a n c e t o d e s t r u c t i o n by e l e m e n t a r y s t r e s s e s ( c o m p r e s s i o n , t e n s i o n , s h e a r ) 2) R e s i s t a n c e t o l o c a l d e s t r u c t i o n ( h a r d n e s s , i n d e n t a t i o n ) 3) R e s i s t a n c e t o b r e a k a g e ( g r i n d a b i l i t y ) The u n i a x i a l c o m p r e s s i v e s t r e n g t h o f t h e r o c k shows a s i g n i f i c a n t c o r r e l a t i o n w i t h p e r c u s s i v e d r i l l a b i l i t y 2 7 a l t h o u g h i t i s not a l w a y s r e l i a b l e i n t r i c o n e r o t a r y d r i l l i n g . R o l l o w 2 6 gave t h e example of V i r g i n i a d o l o m i t e and G r a y g r a n i t e , b o t h a t 214 MPa (31000 p s i ) , where t h e d r i l l i n g r a t e , u nder t h e same l o a d , i s t h r e e t i m e s g r e a t e r i n d o l o m i t e t h a n i n g r a n i t e . A l t h o u g h no c l o s e r e l a t i o n s h i p e x i s t s between c o m p r e s s i v e s t r e n g t h and d r i l l i n g r a t e , a r e l a t i o n e x i s t s between t h e w e i g h t on t h e b i t (W) and t h e c o m p r e s s i v e s t r e n g t h 2 " . . T a n d a n a n d 1 1 s u g g e s t e d t h a t t h e poor c o r r e l a t i o n i s due t o t h e f a c t t h a t t h e m a g n i t u d e o f s t r a i n i n v o l v e d i n t h e f a i l u r e p r o c e s s i n d r i l l i n g i s not p r o p o r t i o n a l w i t h t h e f a i l u r e s t r a i n c a u s e d i n u n i a x i a l c o m p r e s s i o n b e c a u s e t h e two modes o f f a i l u r e a r e d i f f e r e n t . I t i m p l i e s t h a t t h e e l a s t i c p r o p e r t i e s of t h e r o c k a r e t o be c o n s i d e r e d t o o . He p r o p o s e d t h e s h o r e s c l e r o s c o p e h a r d n e s s t e s t t o measure t h e amount of e l a s t i c and i n e l a s t i c d e f o r m a t i o n s o f t h e r o c k . O t h e r s s u g g e s t e d i n d e n t a t i o n t e s t s i n o r d e r t o o b t a i n a q u a n t i t a t i v e h a r d n e s s c l a s s i f i c a t i o n t h a t r e l a t e s t o t h e 76 r e s i s t a n c e o f t h e r o c k t o b i t t o o t h p e n e t r a t i o n . R e s u l t s from t h i s t e s t can be u s e d w i t h a t h e o r e t i c a l e x p r e s s i o n o f t h e d r i l l i n g r a t e ( s e e s e c t i o n 3 . 5 ) . The d r i l l a b i l i t y i s a l s o d e p e n d e n t on t h e s t r u c t u r a l c h a r a c t e r i s t i c s o f t h e r o c k mass. A c o a r s e - g r a i n e d s t r u c t u r e i s e a s i e r t o d r i l l and c a u s e s l e s s wear t h a n a f i n e - g r a i n e d s t r u c t u r e 2 9 . In a d d i t i o n , t h e d e g r e e and t y p e o f f r a c t u r i n g , a l t e r a t i o n , c e m e n t i n g m a t e r i a l and t h e a n g l e a t w h i c h t h e d i s c o n t i n u i t y p l a n e s a r e d r i l l e d a f f e c t d r i l l p e r f o r m a n c e . F i g u r e 3.4-2 shows t h e i n c r e a s e i n p e n e t r a t i o n r a t e i n r e l a t i o n t o t h e number of weakness p l a n e s f o r a p e r c u s s i v e d r i l l . One o f t h e r o c k mass p r o p e r t i e s t h a t r e f l e c t s t h e m e c h a n i c a l b e h a v i o u r and t h e i n t e n s i t y of f r a c t u r i n g i s t h e s o n i c v e l o c i t y . G s t a l d e r and R a y n a l 3 1 p u b l i s h e d a r e l a t i o n s h i p between t h e d r i l l i n g p e n e t r a t i o n r a t e , t h e Young's M o d u l u s and t h e s o n i c v e l o c i t y ( F i g 3 . 4 - 3 ) . The good c o r r e l a t i o n s u g g e s t s t h a t t h e d r i l l p e r f o r m a n c e c a n r e f l e c t t h e f a i l u r e b e h a v i o u r o f t h e r o c k . F i n a l l y , a d r i l l a b i l i t y i n d e x was p r o p o s e d 2 7 o v e r t h i r t y y e a r s ago and was d e f i n e d a s : K = dS / d(W/D 2) where K = d r i l l a b i l i t y S = p e n e t r a t i o n r a t e ( i n / m i n ) W = w e i g h t ( l b ) D = d i a m e t e r ( i n ) I t i s i n t e r e s t i n g t o n o t e t h e s i m i l a r i t y between K and t h e RQI. 77 2 4 6 8 10 12 WEAKNESS PLANES PER METRE DRILLED FIGURE 3.4-2'ESTIMATED RELATIVE INCREASE IN PENETRATION RATE VERSUS NUMBER OF WEAKNESS PLANES PER METRE DRILL-HOLE ( after Blindheim30) 78 E i or o 8 4 -SOFT ROCK BIT SMF-T i i WEIGHT ON BIT: i i (a) TONNES _ 2 TONNES 1 1 0 8 MED. HARD BIT W4T T 2000 4000 6000 0 2000 0 4000 6000 YOUNG'S MODULUS-Kg/mm^ I 4T V - T - , 1 (c) 2T -« ^ 1 2000 4000 6000 8000 2000 4000 6000 8000 SONIC VELOCITY-m/sec. FIGURE 3.4-3'CORRELATION OF DRILLING PERFORMANCE WITH ROCK CHARACTERISTICS, (after Gstalder and Raynal31) 79 3.5 TRICONE ROTARY DRILLING In t r i c o n e r o t a r y d r i l l i n g , t h e e n e r g y i s t r a n s m i t t e d t o t h e b i t - r o c k i n t e r f a c e v i a a l o a d e d r o t a t i n g p i p e . F l u s h i n g a i r i s s u p p l i e d t h r o u g h t h e d r i l l p i p e t o remove c u t t i n g s a t t h e h o l e bottom and t r a n s p o r t them t o t h e s u r f a c e . The major p a r a m e t e r s i n t h i s p r o c e s s a r e t h e w e i g h t o r t h r u s t on t h e b i t (W), t h e r o t a r y s p e e d (RPM), t h e t o r q u e (T) and t h e a i r p r e s s u r e and volume. T h e s e p a r a m e t e r s a r e i n t e r - r e l a t e d and i t i s not p o s s i b l e t o d e f i n e t h e optimum o p e r a t i n g c o n d i t i o n f o r a g i v e n s i z e and t y p e of b i t i n a g i v e n r o c k t y p e . T r i a l t e s t s must be p e r f o r m e d . N e v e r t h e l e s s , t h e u n d e r s t a n d i n g o f t h e i n f l u e n c e of one p a r a m e t e r o v e r t h e o t h e r s o r i t s e f f e c t s on t h e p e n e t r a t i o n r a t e or d r i l l i n g c o s t s would c e r t a i n l y r e d u c e t h e e x t e n t of t h e t e s t s . 3.5.1 D r i l l i n g P a r a m e t e r s 3.5.1.1 The Weight on t h e B i t A c c o r d i n g t o F i s h 3 2 , t h e t h r u s t i s one o f t h e most i m p o r t a n t v a r i a b l e s i n t h e d r i l l i n g p r o c e s s . I t i s a p p l i e d on t h e b i t by h y d r a u l i c p r e s s u r e t h r u c y l i n d e r s o r by o t h e r m e c h a n i c a l p r o c e s s e s . C o n s e q u e n t l y , t h e h y d r a u l i c p r e s s u r e r e a d i n g i s t h e p r e s s u r e i n t h e s y s t e m and s i n c e e v e r y m a n u f a c t u e r has a d i f f e r e n t p r e s s u r e t o w e i g h t r a t i o , i t i s recommended t o use t h e w e i g h t r a t h e r t h a n t h e down p r e s s u r e when 80 c o m p a r i n g d r i l l p e r f o r m a n c e s . A p p e n d i x II g i v e s t h e r e l a t i o n s h i p s between p r e s s u r e r e a d i n g and w e i g h t on t h e b i t f o r s e v e r a l d r i l l r i g m o d e l s . The i n t e n s i t y of t h e l o a d i n g a t t h e b i t - r o c k i n t e r f a c e d e f i n e s f o u r t y p e s of d r i l l i n g c o n d i t i o n s as shown i n f i g u r e 3.5-1 and d e s c r i b e d i n s e c t i o n 3.3 : 1) a b r a s i v e p h a s e : t h e f o r m a t i o n i s worn away 2) f a t i g u e p h a s e : t h e f o r m a t i o n i s l o a d e d s e v e r a l t i m e b e f o r e r o c k f a i l u r e o c c u r s 3) s p a l l i n g p h a s e : s u f f i c i e n t amount of w e i g h t c a u s e s t h e f o r m a t i o n t o f r a c t u r e r e a d i l y 4) f o u n d e r p h a s e : e x c e s s w e i g h t b u r i e s t h e c a r b i d e s t o f u l l d e p t h A l t h o u g h t h e r a t e o f p e n e t r a t i o n i n c r e a s e s p r o p o r t i o n a l l y t o W**a (where 1<=a<=2), i t s h o u l d be n o t e d t h a t t h e r e l a t i o n s h i p i s o n l y v a l i d d u r i n g optimum c o n d i t i o n s . In t h e f o u n d e r p h a s e o r when t h e h o l e i s i m p r o p e r l y c l e a n e d , i n c r e a s i n g t h e w e i g h t w i l l not i n c r e a s e t h e p e n e t r a t i o n r a t e . In p r a c t i c e , t h e w e i g h t s u s e d on t u n g s t e n c a r b i d e b i t s r a n g e from 0.7 t o 1.4 t o n n e s p e r c e n t i m e t e r (2 t o 4 t o n s p e r i n c h ) o f b i t d i a m e t e r . The s t r o n g e r t h e r o c k mass, t h e h i g h e r t h e l o a d . I f s u f f i c i e n t l o a d i s n e e ded t o overcome t h e c o m p r e s s i v e s t r e n g t h of t h e r o c k , e x c e s s i v e w e i g h t can c a u s e i n s e r t b r e a k a g e and r e d u c e b e a r i n g l i f e a l t h o u g h b e a r i n g s a r e l a r g e r and s t r o n g e r i n h a r d f o r m a t i o n t r i c o n e b i t s . In a s t u d y p e r f o r m e d a t a mine s i t e i n L a b r a d o r , i t was r e c o g n i s e d t h a t t h e t h r u s t on t h e b i t was t h e most 81 UJ o < rr »-u z UJ CL i» / I / S O F T ' FORMATION * s / / / / r /ME / FO / r I :DIUM RMATIO s / / / FORMATION / KEY -ABRASION PHASE -FATIGUE PHASE -SPALLING PHASE -FOUNDERING PHASI L 1 — WEIGHT ON BIT FIGURE 3.5-1 DRILLING CONDITIONS (after Dresser Industries4) 82 i m p o r t a n t p a r a m e t e r i n t r i c o n e r o t a r y d r i l l i n g . 3.5.1.2 The R o t a r y Speed The r a t e o f p e n e t r a t i o n of a r o c k b i t i s g e n e r a l l y i n c r e a s e d , when r o t a t i n g s p e e d i s i n c r e a s e d , by a r a t i o s l i g h t l y l e s s t h a n 1:1 up t o t h e l i m i t s o f p r o p e r h o l e c l e a n i n g 5 * 3 3 . The f a c t o r s t h a t d e t e r m i n e t h e maximum r o t a r y s p e e d a r e t h e b e a r i n g ' s wear, t h e i n s e r t b r e a k a g e and t h e d r i l l r i g l i m i t a t i o n s . B e a r i n g l i f e i s i n v e r s e l y p r o p o r t i o n a l t o r o t a r y s p e e d . A l t h o u g h t u n g s t e n c a r b i d e i s a v e r y h a r d and wear r e s i s t a n t m a t e r i a l , i t i s a l s o b r i t t l e and i n s e r t s can be s u b j e c t e d t o e x c e s s i v e b r e a k a g e a t h i g h r o t a r y s p e e d . In h a r d f o r m a t i o n s , t h e p r a c t i c e i s t o d e c r e a s e t h e r o t a r y s p e e d as t h e w e i g h t i s i n c r e a s e d . The o p p o s i t e i s a l s o t r u e ( F i g u r e 3 . 5 - 2 ) . In p r a c t i c e , r o t a r y s p e e d i n a l m o s t c o n s t a n t a t a g i v e n mine s i t e o r w i t h i n t h e d o m a i n s . 3.5.1.3 The A i r P r e s s u r e and Volume The c o n t r o l l a b l e f a c t o r of a i r i s a i r ' p r e s s u r e , m o d i f i e d by c h a n g i n g t h e j e t n o z z l e s of t h e b i t . The s i t u a t i o n i s t h e f o l l o w i n g : by u s i n g s m a l l s i z e n o z z l e s , t h e a i r p r e s s u r e i n c r e a s e s , f o r c i n g more a i r t o f l o w t h r o u g h t h e b e a r i n g s . T h i s p r o c e d u r e w i l l g e n e r a l l y e x t e n d t h e b e a r i n g s l i f e . However, t h e a i r volume i s r e d u c e d and p o o r b a i l i n g v e l o c i t y w ould r e s u l t . The p o o r b a i l i n g v e l o c i t y w i l l c a u s e p o o r b o t t o m h o l e 83 SELECTING THE RIGHT BIT I+ ++ + + -H- + + RHYOLITE V+ -f1 + -t V+ + WWW WWW r» /"* I I I P T H H W H W H W W W I : x x x X x « x SCH I S T x x x x x x x x x o o o o o ROCK COMPRESSIVE STRENGTH (psl 8 8 g § S 9. °, 8. o Q in q in O 8 I500H _ 2000-w C 3 a 2300-Ul 2 < a t m 3000-4000-^  ^ B B B B B „ 1 B B B B *mmu ' « B B mi. • B B B k : ' ' B B B B B B ' ' ' B B B B B 0000 X o z - 6000 UJ Q. I-X o UJ a ° s s 7000 8000 •120 110 •100 90 2 a. 80 9000 in N g ESTIMATED PENETRATION (feet/hr) FIGURE 3 . 5 - 2 ' RELATIONSHIP BETWEEN ROCK COMPRESSIVE STRENGTH, PENETRATION R A T E . WEIGHT AND RPM (afler Steinke 9 ) ' 8 4 c o n d i t i o n s , t h e r e f o r e e x c e s s i v e wear of t h e b i t components and d e c r e a s e i n t h e d r i l l i n g e f f i c i e n c y a t a g i v e n t h r u s t . On t h e o t h e r hand, h i g h b a i l i n g v e l o c i t y can c a u s e cone e r o s i o n and e xtreme wear t o o * ( s a n d b l a s t i n g ) . The optimum b a i l i n g v e l o c i t y i s a f u n c t i o n o f t h e h o l e c o n d i t i o n s ( r o u g h o r smooth w a l l ) , t h e r o c k d e n s i t y , t h e t y p e o f c u t t i n g s ( s h a p e , wet o r d r y ) , e t c . In any c a s e , w i t h h i g h p e n e t r a t i o n r a t e , t h e b a i l i n g v e l o c i t y has t o be i n c r e a s e d i n o r d e r t o c l e a r t h e g e n e r a t e d c u t t i n g s . 3.5.1.4 The T o r q u e The t o r q u e i s not e x a c t l y an o p e r a t i n g p a r a m e t e r . I t i s t h e a p p l i c a t i o n o f t h e t h r u s t a n d - t h e r o t a t i o n of t h e t o o l on t h e r o c k mass t h a t p r o d u c e t h e t o r q u e i n t h e s y s t e m . In t r i c o n e r o t a r y d r i l l i n g , w i t h t r u e r o l l i n g b i t s , v e r y l i t t l e t o r q u e i s d e v e l o p e d . However, a h i g h t o r q u e may be d e v e l o p e d by a b i t w i t h i n t e n s e wear of t h e gage s t r u c t u r e 3 . In s o f t f o r m a t i o n s , t h e r o c k i s d r i l l e d by t h e s c r a p i n g - g a u g i n g e f f e c t o f t r i c o n e b i t t e e t h and t h e i n t e n s i t y o f t h i s a c t i o n i s r e l a t e d w i t h t h e t o r q u e d e v e l o p e d 3 " . N o r m a l l y , d r i l l s a r e d e s i g n e d t o s u s t a i n t o r q u e between 1.6 t o 3.2 j o u l e s p e r 10 Kg (10 t o 20 f t - l b s p e r 100 l b s ) o f t h r u s t , a l t h o u g h t h i s amount i s s e l d o m n e e e s s a r y 6 . The t o r q u e d e v e l o p e d i s d i r e c t l y p r o p o r t i o n a l t o t h e p e n e t r a t i o n r a t e . 3.5.2 D r i l l i n g E q u a t i o n s 85 Many t h e o r e t i c a l and e m p i r i c a l d r i l l i n g e q u a t i o n s have been p u b l i s h e d i n t h e p a s t t h i r t y y e a r s . Many o t h e r s w i l l p r o b a b l y be p u b l i s h e d i n t h e f u t u r e . In t h i s p a r a g r a p h , some of t h e p r o p o s e d d r i l l i n g e q u a t i o n s a r e r e v i e w e d i n o r d e r t o summarize t h e d r i l l i n g p r o c e s s . The s i m p l e s t d r i l l i n g e q u a t i o n s a r e : M a u r e r 1 6 PR = ( d V / d t ) / A where PR = p e n e t r a t i o n r a t e , V = volume, t = t i m e , A = a r e a of t h e h o l e M o r r i s 1 0 PR = Np where N = r o t a r y s p e e d , p = p e n e t r a t i o n p e r r e v o l u t i o n A l t h o u g h t h o s e e q u a t i o n s a r e s i m p l e and t h e o r e t i c a l l y t r u e , t h e i r a p p l i c a b i l i t y r e q u i r e a more d e t a i l e d e v a l u a t i o n o f t h e d r i l l i n g p r o c e s s . The t h e o r e t i c a l a p p r o a c h i s b a s e d on t h e s t r e s s c o n c e n t r a t i o n and f a i l u r e of t h e r o c k b e n e a t h i n d i v i d u a l l o a d e d i n s e r t s . U n f o r t u n a t e l y , t h e c o m p l e x i t y of t h e e q u a t i o n s i n c r e a s e s q u i c k l y due t o t h e number of v a r i a b l e s t h a t have t o be c o n s i d e r e d . M a u r e r 1 6 PR = K(NW 2/A)**s 86 where s = 1 = good c l e a n i n g s = 1/2 = p o o r c l e a n i n g K = r o c k mass c o n s t a n t W = w e i g h t on t h e b i t N = r o t a r y s p e e d A = a r e a o f t h e h o l e The f o l l o w i n g e q u a t i o n s assume p e r f e c t c l e a n i n g c o n d i t i o n s . M o r r i s 1 0 PR = Nb (p'/E) (W/0.08C) where b 1 .8 and c o n v e r t s b i t r o t a r y s p e e d t o c one r o t a r y s p e e d . C = t o t a l number of i n s e r t s p e r b i t . (p'/E) = r o c k p e n e t r a t i o n f a c t o r f r o m i n d e n t a t i o n h a r d n e s s t e s t s . G n i r k and C h e a t h a m 1 8 PR = 0.l56mNl (w/D) 2 ( ( W / w n t l a p ) 2 - 75.69) where m = number of p e n e t r a t i o n s p e r r e v o l u t i o n N = r o t a r y s p e e d 1 = l e n g t h of c u t t i n g edge of a s i n g l e b i t - t o o t h ( i n c h ) W = a p p l i e d w e i g t h ( l b s ) D = b i t d i a m e t e r ( i n c h ) nt = number of b i t - t e e t h e f f e c t i v e l y i n c o n t a c t w i t h t h e r o c k a t t h e b o t t o m of t h e d r i l l h o l e a t any i n s t a n t w = b i t - t o o t h f l a t w i d t h ( i n c h ) 87 ap = c o m p r e s s i v e s t r e n g t h of t h e r o c k a t d i f f e r e n t i a l p r e s s u r e p ( p s i ) Some s c i e n t i s t s have p r e f e r r e d a more p r a c t i c a l a p p r o a c h and d e r i v e d e m p i r i c a l d r i l l i n g e q u a t i o n s . T h e s e a r e u s u a l l y a more u s e f u l t o o l i n e n g i n e e r i n g e s t i m a t e : Bauer and C a l d e r 2 0 PR = ((61 - 2 8 1 o g 1 0 S c ) W N) / (250 D) where Sc = u n i a x i a l c o m p r e s s i v e s t r e n g t h W = a p p l i e d w e i g h t N = r o t a r y s p e e d D = h o l e d i a m e t e r C u n n i n g h a m 2 6 PR = N (W**a) / 0.424. od**1.5 where ad = d r i l l i n g s t r e n g t h a = f ( a d ) and > 1.1 N = r o t a r y s p e e d W = a p p l i e d w e i g h t The d e r i v a t i o n o f t h e Cunningham e q u a t i o n i s r e v i e w e d i n d e t a i l i n t h e f u t u r e s e c t i o n b e c a u s e o f i t s s i m i l a r i t y w i t h t h e Rock Q u a l i t y I n d e x . 88 3 . 6 ROCK QUALITY INDEX I t has been shown, i n t h i s c h a p t e r t h a t t h e p e n e t r a t i o n r a t e i s a f u n c t i o n of t h e o p e r a t i n g p a r a m e t e r s , t h e b i t d e s i g n a.od t h e r o c k p r o p e r t i e s . The g e n e r a l r e l a t i o n s h i p i s e x p r e s s e d a s : PR = W**a * (RPM)**b * f ( r o c k mass p r o p e r t i e s , d r i l l i n g p r o c e d u r e s ) However, a t a g i v e n mine s i t e , t h e d r i l l i n g p r o c e d u r e i s g e n e r a l l y c o n s t a n t . In a d d i t i o n , t h e v a r i a t i o n i n r o t a r y s p e e d a r e l i m i t e d , when compared w i t h t h e v a r i a t i o n i n t h e a p p l i e d w e i g h t on t h e b i t , t h e l a t e s t b e i n g t h e p r i n c i p a l o p e r a t i n g p a r a m e t e r . The g e n e r a l r e l a t i o n s h i p c a n t h e r e f o r e be e x p r e s s e d a s : PR = W**a * f ( r o c k mass p r o p e r t i e s ) and f ( r o c k mass p r o p e r t i e s ) = (W**a)/PR T h i s was t h e c o n c l u s i o n d e r i v e d by M a t h i s 3 5 . H e . d e f i n e d t h e Rock Q u a l i t y Index a s : RQI = W/PR In a r e s e a r c h p r o j e c t c o n d u c t e d by C u n n i n g h a m 2 6 and d i r e c t e d t o w a r d t h e e x p r e s s i o n o f a s i m p l e r e l a t i o n s h i p between t h e d r i l l i n g p a r a m e t e r s , i t was f o u n d t h a t an e m p i r i c a l r e l a t i o n s h i p was a more w o r k a b l e a p p r o a c h t h a n a t h e o r e t i c a l one. A l t h o u g h t h e r e i s no i n d i c a t i o n t h a t Cunningham r e v i e w e d 89 t h e work of M a t h i s , t h e c o n c l u s i o n s a r e q u i t e s i m i l a r . The r e l a t i o n s h i p e x p r e s s e d by Cunningham was g i v e n i n s e c t i o n 3.5 and i s r e p e a t e d h e r e : PR = K(W**a)N where N = r o t a r y s p e e d W = w e i g h t a,K = c o n s t a n t PR = p e n e t r a t i o n r a t e and i f N i s k e p t c o n s t a n t : PR = K(W**a) Then, b a s e d on t h e g e n e r a l r e l a t i o n s h i p between t h e c o m p r e s s i v e s t r e n g t h and t h e w e i g h t r e q u i r e d t o d r i l l a f o r m a t i o n a t a s p e c i f i c r a t e , Cunningham c o n s t r u c t e d a f a m i l y o f l i n e s r e l a t i n g t h e p e n e t r a t i o n r a t e and t h e a p p l i e d w e i g h t ( F i g u r e 3 . 6 - 1 ) . T h o s e l i n e s a r e t e r m e d l i n e s o f e q u a l d r i l l i n g s t r e n g t h (ad e x p r e s s e d i n t h o u s a n d o f P S I ) . The d r i l l i n g s t r e n g t h i s t r e a t e d as a s i n g l e p h y s i c a l p r o p e r t y o f t h e f o r m a t i o n d r i l l e d and has l i t t l e meaning i n any o t h e r c o n t e x t . I t i s a n u m e r i c a l e x p r e s s i o n o f t h e r o c k mass b e h a v i o u r d u r i n g t h e d r i l l i n g p r o c e s s , w i t h t r i c o n e b i t s . Cunningham t h e n e x p r e s s e d K and a as f u n c t i o n s o f ad, and t h e r e l a t i o n s h i p became: PR = W**a / 0.424(ad**1.5) w i t h a = (0.178254 l n ( a d ) + 1.09793) 1.1 <= a <= 1.9 In a d d i t i o n , t h e d r i l l i n g s t r e n g t h , w h i c h i s d e r i v e d from 90 WEIGHT PER INCH BIT DIAMETER / 1000 (LB/ IN) FIGURE 3.6-1 = DRILLING RATE VS WEIGHT PER INCH OF BIT DIAMETER, (after Cunnihaham28) 91 d r i l l i n g t e s t s , c an be a p p r o x i m a t e d by t h e u n i a x i a l c o m p r e s s i v e s t r e n g t h when t h e t e s t s a r e not p e r f o r m e d . The work by Cunningham t h e r e f o r e c o n f i r m s t h e s i m p l e r e l a t i o n s h i p p r o p o s e d by M a t h i s . The W/PR r a t i o g u a n t a t i v e l y e x p r e s s e s t h e v a r i a t i o n i n r o c k q u a l i t y . The p r a c t i c a l a d v a n t a g e s of t h e Rock Q u a l i t y Index a r e numerous. The i n d e x i s q u i c k l y and e a s i l y o b t a i n e d w i t h o u t a d d i t i o n a l c o s t s o r p e r s o n n e l and p r o v i d e an u n b i a s e d c o v e r a g e of t h e e n t i r e p i t a r e a , s i n c e a l l r o c k must be d r i l l e d b e f o r e b e i n g b l a s t e d . The m a t h e m a t i c a l d e t e r m i n a t i o n o f t h e RQI i s a l s o v e r y s i m p l e and e a s y t o u n d e r s t a n d b e c a u s e o f i t s e m p i r i c a l n a t u r e . T h i s i s an i m p o r t a n t c o n s i d e r a t i o n when d e a l i n g w i t h t h e p r a c t i c a l a p p l i c a t i o n of t h e i n d e x i n t h e f i e l d . 92 3.7 SUMMARY T r i c o n e r o t a r y d r i l l i n g i s a complex r o c k b r e a k a g e p r o c e s s . I t i s i n f l u e n c e d by t h e t o o l d e s i g n , o p e r a t i n g p a r a m e t e r s m a i n l y W and r o c k mass p r o p e r t i e s . The t h e o r e t i c a l optimum d r i l l i n g c o n d i t i o n c o r r e s p o n d s t o t h e l e a s t amount o f e n e r g y p e r u n i t volume o f b r o k e n r o c k . However, i n p r a c t i c e , t h e optimum d r i l l i n g c o n d i t i o n i s d e t e r m i n e d by a c o s t e v a l u a t i o n of t h e p r o c e s s . DC = ROC + B/L where DC = d r i l l i n g c o s t s ( $ / f t ) B = b i t c o s t ($) L = l i f e of b i t ( f t ) ROC = d r i l l o p e r a t i n g c o s t ( $ / f t ) w i t h ROC = f ( m a c h i n e c o s t , o p e r a t o r wages, e f f e c t i v e d r i l l i n g r a t e ) I t i s p o s s i b l e t h a t t h e p r a c t i c a l optimum d r i l l i n g c o n d i t i o n does not c o i n c i d e w i t h t h e t h e o r e t i c a l optimum. N e v e r t h e l e s s , t h e r o c k mass p r o p e r t i e s a r e r e f l e c t e d on t h e d r i l l p e r f o r m a n c e and t h e e s t a b l i s h m e n t of t h e Rock Q u a l i t y Index p r o v i d e a u s e f u l method o f r o c k mass c h a r a c t e r i z a t i o n . 93 3.8 REFERENCES 1. ESTES, J.C.; S e l e c t i n g t h e P r o p e r R o t a r y Rock B i t , J o u r n a l of P e t r o l e u m T e c h n o l o g y , V23, November 1971 2. 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PARISEAU, W.G.; FAIRHURST, C ; The F o r c e - P e n e t r a t i o n C h a r a c t e r i s t i c f o r Wedge P e n e t r a t i o n i n t o Rock, I n t e r n a t i o n a l J o u r n a l Rock Mech. M i n . S c i . , V o l . 4, pp. 165, 1967 22. TANDANAND, S.; UNGER, F.H.; D r i l l a b i l i t y D e t e r m i n a t i o n - a D r i l l a b i l i t y Index f o r P e r c u s s i o n D r i l l s , USBM, r e p o r t o f i n v e s t i g a t i o n 8073, 1975 23. TEALE, R.; The C o n c e p t o f S p e c i f i c E n e r g y i n Rock D r i l l i n g , I n t e r n a t i o n a l J o u r n a l Rock Mech. M i n . S c i . V o l . 2, pp. 57, 1965 24. MELLOR, M.; N o r m a l i z a t i o n of S p e c i f i c E n e r g y V a l u e s , I n t e r n a t i o n a l J o u r n a l Rock Mech. M i n . S c i . , V o l . 9, pp. 661, 1972 25. PROTODYAKONOV, M.M.; M e c h a n i c a l P r o p e r t i e s and D r i l l a b i l i t y o f R o c k s , P r o c e e d i n g s 5 t h Symposium on Rock M e c h a n i c s , F a i r h u r s t e d i t o r , Pergamon P r e s s , 1963 26. ROLLOW, A.G.; E s t i m a t i n g D r i l l a b i l i t y i n t h e L a b o r a t o r y , 96 P r o c e e d i n g s 5 t h Symposium on Rock M e c h a n i c s , F a i r h u r s t e d i t o r , Pergamon P r e s s , 1963 27. WHITE, C.G.; A Rock D r i l l a b i l i t y Index, Q u a r t e r l y o f t h e C o l o r a d o S c h o o l o f M i n e s , V 64, N 2, 1969 28. CUNNINGHAM, R.A.; An E m p i r i c a l A p p r o a c h f o r R e l a t i n g D r i l l i n g P a r a m e t e r s , J o u r n a l of P e t r o l e u m T e c h n o l o g y , J u l y , 1978 29. A t l a s Copco Manual, P u b l i s h e d by A t l a s Copco, 4 t h e d i t i o n , Sweden, 1982 30. BLINDHEIM, O.T.; D r i l l a b i l i t y P r e d i c t i o n s i n H a r d Rock T u n n e l l i n g , T u n n e l l i n g '79, IMM, 1979 31. GSTALDER, S.; RAYNAL, J . ; Measurements o f Some M e c h a n i c a l P r o p e r t i e s of Rocks and T h e i r R e l a t i o n s h i p t o Rock  D r i l l a b i l i t y , J o u r n a l o f P e t r o l e u m T e c h n o l o g y , A u g u s t 1966 32. FISH, B.G.; The B a s i c V a r i a b l e s i n R o t a r y D r i l l i n g , M i ne and Q u a r r y E n g i n e e r i n g , V 27, N 1 and N 2, 1961 33. WILLIAMSON, T.N.; R o t a r y D r i l l i n g , S u r f a c e M i n i n g , S e c t . 6.3, P f l e i d e r e d i t o r , AIME, 1972 34. A u t o m a t i c R e c o r d e r of D r i l l i n g P a r a m e t e r s , G e n e r a l P r e s e n t a t i o n , P u b l i s h e d by J e a n L u t z , S.A., F r a n c e 35. MATHIS, C ; P r o p o s a l of a R e p o r t on Rock Q u a l i t y Index B a s e d on R o t a r y D r i l l P e r f o r m a n c e s , U n p u b l i s h e d p a p e r , U n i v e r s i t y Of A l b e r t a , M a r c h 1975 97 CHAPTER 4 98 4.0 THE BLASTING PROCESS The q u a l i t y of t h e b l a s t i n g r e s u l t s i n f l u e n c e s t h e p r o d u c t i v i t y o f t h e m i n i n g o p e r a t i o n . I d e a l l y , t h e b l a s t e d r o c k s h o u l d be w e l l f r a g m e n t e d and h e a v e d i n o r d e r t o maximize t h e p r o d u c t i o n c a p a b i l i t i e s o f t h e l o a d i n g and h a u l i n g e q u i p m e n t , t h e c r u s h e r and t h e m i l l ( a u t o g e n o u s ) . The f o l l o w i n g q u o t a t i o n i s f r o m Hagan and M e r c e r 1 : "Mine management o f t e n c o n c e n t r a t e d on m i n i m i z i n g t h e c o s t of i n d i v i d u a l o p e r a t i n g f u n c t i o n w i t h o u t c o n s i d e r i n g t h e e f f e c t s of s u c h c o s t r e d u c t i o n on d e p e n d e n t o p e r a t i o n s . A l l t o o o f t e n , e x p l o s i v e s c o s t s a p p e a r as a s i n g l e e n t r y i n t h e m i n i n g c o s t s t a t e m e n t , and undue s i g n i f i c a n c e i s a t t a c h e d t o them. E x p l o s i v e s c o s t , b l a s t i n g c o s t s o r even t o t a l b r e a k i n g c o s t s must n o t be c o n s i d e r e d i n i s o l a t i o n . Management s h o u l d use o n l y t o t a l p r o d u c t i o n c o s t s as a b a s i s f o r d e t e r m i n i n g t h e c o s t - e f f e c t i v e n e s s of an i n d i v i d u a l o p e r a t i o n s u c h as b l a s t i n g . " ( F i g u r e 4.0-1) In a d d i t i o n , t h e r o c k s l o p e a n g l e has t o be e v a l u a t e d . A s h o v e l d i g g i n g a w e l l f r a g m e n t e d and d i s p l a c e d r o c k mass i s t w i c e as p r o d u c t i v e as a s h o v e l d i g g i n g a p o o r l y f r a g m e n t e d and t i g h t muck p i l e ( F i g u r e 4 . 0 - 2 ) . The t r u c k p r o d u c t i v i t y i s a l s o i n c r e a s e d , wear and t e a r on e v e r y p i e c e of e q u ipment i s r e d u c e d . In a p p e n d i x I I I i s a l i s t o f p o s s i b l e b e n e f i t s of i m p r oved f r a g m e n t a t i o n . Mine o p e r a t o r s s h o u l d a c k n o w l e d g e t h a t l a r g e e q u i p m e n t a r e d e s i g n e d t o h a n d l e l a r g e r volume o f 99 FIGURE 4.0-1« EFFECT OF FRAGMENTATION ON COST OF MINING. (after Hoek a Bray2 ) 100 1000 £ 800 c t LU Q. 600 to D < ° , 400 O 200 POOR DIGGING — 5 Shovels ^ 0 0 * e S S : s : ^ X ^ \ o v e 1 s 3 Shovels — 2 Shovels 1 Shovel 1 1 1 1 1 1 1 1 1 6 8 10 12 TRUCK FLEET SIZE 16 18 1000 800 cc 600 UJ Q-CO < 400 o GOOD DIGGING 3 or 4 Shovels 6 8 10 12 TRUCK FLEET SIZE 14 16 FIGURE 4.0-2 ' OUTPUT FOR DIFFERENT SHOVEL TRUCK COMBI-NATIONS SINGLE CRUSHER, GOOD CONDITIONS AND POOR DIGGING, (after Bauer3) 101 m a t e r i a l s , not l a r g e r s i z e o f f r a g m e n t s . N e v e r t h e l e s s , optimum b l a s t i n g r e s u l t s a r e o b t a i n e d o n l y when t h e b l a s t i n g e n g i n e e r u n d e r s t a n d s t h e r e l a t i o n s h i p s between t h e r o c k mass p r o p e r t i e s and t h e w e l l - b a l a n c e d r a t i o s o f b l a s t h o l e d i s t a n c e s , bench h e i g h t s , s u b d r i l l i n g and stemming, c h a r g e l e n g t h s and e x p l o s i v e s t r e n g t h s . A more s c i e n t i f i c a p p r o a c h t o t h e b l a s t i n g p r o c e s s c a n r e s u l t i n an i n c r e a s e i n p r o d u c t i v i t y and t h e r e f o r e p r o f i t a b i l i t y . In t h e f i r s t p a r t of t h i s r e s e a r c h p r o j e c t , p u b l i s h e d by L e i g h t o n " , t h e b l a s t i n g p r o c e s s has been a p p r o a c h e d f r o m t h e t h e o r e t i c a l s t a n d p o i n t . H i s l i t e r a t u r e s e a r c h has r e s u l t e d i n two c h a p t e r s on t h e r o c k mass d e t o n i c and on t h e d e s i g n c o n s i d e r a t i o n s f o r c o n t r o l l e d b l a s t i n g . The o b j e c t i v e s of t h e p r e s e n t r e p o r t a r e s u c h t h a t t o a c e r t a i n e x t e n d , r e p e t i t i o n w i l l be a v o i d e d . F o r t u n a t e l y , t h e f i e l d o f b l a s t i n g c a n s t i l l be a p p r o a c h e d w i t h d i f f e r e n t c o n c e p t s . B e c a u s e of t h e i m p o r t a n c e o f t h e r o c k mass f r a g m e n t a t i o n of t h e m i n i n g o p e r a t i o n s , t h e a u t h o r has d e c i d e d t o r e v i e w t h e b l a s t i n g p r o c e s s by r e l a t i n g t h e p r i n c i p a l p a r a m e t e r s t o t h e t h e i r e f f e c t s on t h e d e g r e e of f r a g m e n t a t i o n and i n d i r e c t l y , on t h e e n e r g y r e q u i r e m e n t . In t h i s c h a p t e r , two b l a s t i n g t h e o r i e s w i l l be r e v i e w e d i n o r d e r t o d e m o n s t r a t e how c o n t r o v e r s i a l t h i s s u b j e c t i s . The c o r e o f t h e c h a p t e r w i l l be c o n c e r n e d w i t h t h e major f a c t o r s a f f e c t i n g f r a g m e n t a t i o n . The d e s i g n powder f a c t o r and i t s i n f l u e n c e on t h e m i n i n g o p e r a t i o n i s a s u b j e c t of p r i m e 1 02 i m p o r t a n c e . However, i n some i n s t a n c e s , t h e m i n i n g o p e r a t i o n s d i c t a t e v a r i a t i o n s i n t h e powder f a c t o r . A p a r t i c u l a r p a r a g r a p h w i l l d e a l w i t h t h e d e s i g n powder f a c t o r a p p r o a c h . F i n a l l y , a r e v i e w of t h e r o c k mass b l a s t a b i l i t y i n d e x c o m p l e t e s t h i s c h a p t e r . 1 03 4.1 THEORY OF BLASTING The p e r f e c t e x p l a n a t i o n of t h e r o c k f r a g m e n t a t i o n p r o c e s s d u r i n g b l a s t i n g , s u p p o r t e d by an a c c u r a t e m a t h e m a t i c a l model t h a t p r e d i c t s r e s u l t s f o r any c o n d i t i o n s , i s s t i l l t o be a c h i e v e d . T h i s f i e l d i s c o n f u s e d and c o n t r a d i c t o r y l i t e r a t u r e i s a b u n d a n t . The b l a s t i n g t h e o r i e s were g r o u p e d i n two c l a s s e s as a f u n c t i o n of t h e r e l a t i v e i m p o r t a n c e a c c o r d e d t o t h e r o l e of t h e s t r e s s waves o r t h e e x p a n d i n g g a s e s i n t h e f r a g m e n t a t i o n p r o c e s s . A l l of them were o b t a i n e d when w o r k i n g i n homogenous m a t e r i a l s , p l e x i g l a s s o r i n r o c k s p e c i f i c a l l y c h o s e n t o be as f r e e as p o s s i b l e of major d i s c o n t i n u i t i e s . However, i n most l a r g e s c a l e p r o d u c t i o n b l a s t s , m a s s i v e and j o i n t f r e e r o c k s a r e v e r y s e l d o m e n c o u n t e r e d . 4.1.1 Gas E x p a n s i o n T h e o r y T h i s t h e o r y i s w e l l d e s c r i b e d i n t h e l i t e r a t u r e by L a n g e f o r s and K i h l s t r o m 5 . The c h e m i c a l e n e r g y o f t h e e x p l o s i v e i s q u i c k l y l i b e r a t e d and t r a n s f o r m e d i n t o h i g h p r e s s u r e g a s e s . The g a s e s c a u s e a v e r y r a p i d e x p a n s i o n of t h e b o r e h o l e volume. T h i s sudden e x p a n s i o n i s e v e n t u a l l y s t o p p e d by t h e e l a s t i c r e s i s t a n c e o f t h e r o c k , but i t has n o n e t h e l e s s g e n e r a t e d a s t r o n g c o m p r e s s i v e s t r a i n wave, w h i c h t h e n t r a v e l s t h r o u g h t h e r o c k mass, c a u s i n g l i m i t e d damage 6. The wave v e l o c i t y i s a f u n c t i o n of t h e d e n s i t y and t h e g e o s t r u c t u r a l p r o p e r t i e s o f t h e 1 04 r o c k mass. I t r a n g e s between 3000 and 4500 m e t e r s p e r s e c o n d (10,000 - 15,000 f p s ) , b e i n g f a s t e r i n dense and m a s s i v e r o c k . As t h e c o m p r e s s i v e wave t r a v e l s t h r o u g h t h e medium, from t h e b l a s t h o l e , i t s e t s up t a n g e n t i a l t e n s i l e s t r e s s e s t h a t c r e a t e r a d i a l c r a c k i n g . T h e s e c r a c k s t r a v e l a t a s p e e d of a b o u t 0.4 t i m e s t h e v e l o c i t y o f t h e c o m p r e s s i v e wave. At t h e f r e e f a c e , t h e c o m p r e s s i v e wave i s r e f l e c t e d back t o w a r d s t h e b o r e h o l e as a t e n s i l e s t r e s s wave. S l a b b i n g of t h e r o c k s u r f a c e may o c c u r . T h o s e f i r s t two s t a g e s of r o c k b r e a k i n g p r o c e s s a r e a f f e c t e d by t h e shock wave. But L a n g e f o r d s and K i h l s t r o m b e l i e v e t h a t t h e shock wave e n e r g y a c c o u n t s o n l y f o r 5 t o 15 % of t h e t o t a l t h e o r e t i c a l e x p l o s i v e e n e r g y and i s d i s t r i b u t e d a l l a r o u n d t h e b l a s t h o l e . I t s u p p o s e s t h a t o n l y 1/3 o f t h e wave e n e r g y i s a c t u a l l y u s e d t o b r e a k a d e f i n i t e b u r d e n . T h u s , t h e shock wave, w h i l e not b e i n g r e s p o n s i b l e f o r t h e a c t u a l b r e a k a g e of t h e medium, s e t s up t h e s t a g e f o r t h e e x p a n d i n g g a s e s . The f i n a l p a r t o f t h e b r e a k i n g p r o c e s s i s done by t h e p r e s s u r i z e d g a s e s r u s h i n g i n t o t h e r a d i a l c r a c k s , wedging them open. The r o c k i n f r o n t o f t h e b o r e h o l e t h e n y e i l d s and moves f o r w a r d . However, as t h e f r o n t a l s u r f a c e moves f o r w a r d , t h e p r e s s u r e i s r e d u c e d b ut t e n s i o n i s m a i n t a i n e d and t h e r a d i a l c r a c k s c o n t i n u e t o grow. When t h e b u r d e n i s optimum, s e v e r a l c r a c k s w i l l r e a c h t h e f r e e f a c e and t h e c o m p l e t e l o o s e n i n g of th e r o c k mass o c c u r s . B l a s t i n g g e n e r a l l y u s e s a b o u t 30% o f t h e t o t a l e x p l o s i v e e n e r g y j u s t i n p h y s i c a l l y moving t h e r o c k 7 . 105 4.1.2 S t r e s s Wave T h e o r y T h i s t h e o r y was f i r s t d e v e l o p e d by t h e USBM i n t h e 1950's. L a t e r , i t was d e m o n s t r a t e d t h a t a c r a t e r c a n be formed s o l e l y by s t r a i n wave b r e a k a g e 8 . However, d u r i n g t h e l a s t 15 y e a r s , t h i s m t h e o r y was s e c o n d t o t h e e x p a n d i n g g a s e s t h e o r y . R e c e n t work by W i n z e r and R i t t e r 9 may soon l e a d t o an i m p r o v e d s t r a i n wave t h e o r y o f r o c k b r e a k a g e . They o b s e r v e d t h a t even as a s m a l l p e r c e n t a g e o f t h e e x p l o s i v e e n e r g y , t h e s t r a i n wave, i n c o n j u n c t i o n w i t h t h e r o c k mass s t r u c t u r a l d e f e c t s , p l a y s a c o n s i d e r a b l y g r e a t e r r o l e t h a n p r e v i o u s l y t h o u g h . F i r s t , t h e t a n g e n t i a l t e n s i l e s t r a i n s c a u s e d by t h e c o m p r e s s i v e wave p r o d u c e t h e r a d i a l c r a c k s . A l s o , as t h e c o m p r e s s i v e wave r e a c h e s t h e f r e e f a c e w i t h s u f f i c i e n t e n e r g y , i t i s r e f l e c t e d t o w a r d t h e b l a s t h o l e a s a t e n s i l e s t r e s s wave. The t e n s i l e s t r e s s e s c an i n i t i a t e o r r e - i n i t i a t e c r a c k s . A c c o r d i n g t o t h e G r i f f i t h t h e o r y , t h e t e n s i l e s t r e s s w i l l have i t s maximum e f f e c t when t a n g e n t i a l t o t h e t i p o f t h e c r a c k . T h i s i s e q u a l l y v a l i d f o r t h e m i c r o c r a c k s o r t h e r a d i a l c r a c k s . F i g u r e 4.1-1 shows t h a t t h e a n g l e s u b t e n d e d by t h e c r a c k s t a n g e n t i a l t o t h e r e f l e c t e d s t r a i n wave i s 1 3 8 . 2 ° . B l a s t i n g e x p e r i m e n t s have shown c r a t e r s a v e r a g i n g 135° and c o n f i r m , t o a c e r t a i n e x t e n t , t h e G r i f f i t h t h e o r y d u r i n g t h e b l a s t i n g p r o c e s s . A l s o , i t has been o b s e r v e d t h a t t h e f i r s t v i s i b l e c r a c k s i n t h e r o c k g e n e r a l l y a p p e a r e d not d i r e c t l y i n f r o n t of t h e b l a s t h o l e , but t o one o r b o t h s i d e s o f i t 1 0 . They a l s o n o t e d t h a t t h e Mirror image of charge Angle subtended by crater, 138.2° Crack propagating at 0,38 of sound velocity of rock. FIGURE 4.1-1'INTERACTION OF STRAIN WAVE WITH PROPAGATING CRACK, (after Harries10) 107 f r a g m e n t s i n m o t i o n from t h e f r e e f a c e c o n t i n u e t o b r e a k - u p , due t o s t r e s s waves t r a p p e d i n t h e b l o c k as i t i s d e t a c h e d from t h e f a c e . 4.1.3 P r a c t i c a l B l a s t i n g T h e o r y At t h e p r e s e n t t i m e , t h e b l a s t i n g p r o c e s s i s e x p l a i n e d by b o t h t h e o r i e s . K u t t e r and F a i r h u r s t 1 1 have d e m o n s t r a t e d t h a t optimum r e s u l t s a r e o b t a i n e d o n l y when t h e two mechanisms a r e p r e s e n t . They have w e l l d e s c r i b e d e a c h of them by u s i n g l a b o r a t o r y methods. But i n t h e f i e l d , t h e h i g h l y d e s t r u c t i v e n a t u r e o f b l a s t i n g and t h e s h o r t i n t e r v a l d u r i n g w h i c h i t o c c u r s make a c c u r a t e measurement a t e c h n o l o g i c a l c h a l l e n g e . F o r t u n a t e l y , a s more s o p h i s t i c a t e d i n s t r u m e n t s a r e b e i n g d e v e l o p e d , s c i e n t i s t s w i l l a c q u i r e more q u a n t i t a t i v e d a t a on t h e b l a s t i n g p r o c e s s . T h i s w i l l e v e n t u a l l y improve o u r knowledge of t h i s f r a g m e n t a t i o n mechanism. 108 4.2 THE MAJOR FACTORS AFFECTING FRAGMENTATION F r a g m e n t a t i o n o f t h e r o c k mass by e x p l o s i v e s i s a c h i e v e d by t h e o p t i m i z a t i o n of a c o n s i d e r a b l e number o f d e s i g n p a r a m e t e r s . However, t h e r o c k mass i s g e n e r a l l y f r a c t u r e d and t h i s i m p o r t a n t p r o p e r t y c a n n o t be c o n t r o l l e d by t h e b l a s t i n g e n g i n e e r . T h u s , h i s d e s i g n has t o be p l a n n e d i n c o n j u n c t i o n w i t h t h e s t r u c t u r a l p r o p e r t i e s of t h e r o c k mass. T h i s s e c t i o n w i l l examine i n d e t a i l t h e p r i n c i p a l d e s i g n p a r a m e t e r s and r o c k mass p r o p e r t i e s i n r e l a t i o n w i t h t h e i r i n f l u e n c e on t h e f r a g m e n t a t i o n p r o c e s s . A l t h o u g h t h e a u t h o r w ould p r e f e r t o a v o i d t h e o v e r l a p p i n g w i t h p a r t one of t h i s r e s e a r c h p r o j e c t " , some o f t h e s e f a c t o r s have t o b e - r e v i e w e d i n o r d e r t o h i g h l i g h t t h e i r i m p o r t a n c e on t h e b l a s t i n g p r o c e s s and t h e i r i n f l u e n c e on t h e r e s u l t s o f t h i s p r o j e c t . 4.2.1 Rock Mass P r o p e r t i e s Many a u t h o r s have d i s c u s s e d t h e r o c k mass p r o p e r t i e s and t h e i r r e l a t i o n s h i p w i t h t h e f r a g m e n t a t i o n d u r i n g b l a s t i n g . T h r o u g h out t h i s r e s e a r c h p r o j e c t , two of them have a p p e a r e d t o overshadow t h e o t h e r s . T h e r e a r e t h e g e o - s t r u c t u r a l c h a r a c t e r i s t i c s and f a i l u r e b e h a v i o u r of t h e r o c k mass. 4.2.1.1 S t r u c t u r a l G e o l o g y The e f f e c t s of t h e r o c k s t r u c t u r e on t h e b l a s t i n g p r o c e s s 109 and t h e f r a g m e n t a t i o n can be g r o u p e d i n two c a t e g o r i e s : m i c r o -s c a l e and m a c r o - s c a l e e f f e c t s . The m i c r o - f i s s u r e s have been s t u d i e d by D a l l y e t a l 1 2 i n l a b o r a t o r y t e s t s . They c o n c l u d e d t h a t f l a w s i m p r o v e d f r a g m e n t a t i o n i n two d i f f e r e n t ways. F i r s t , t h e r e a r e a c t i n g as c r a c k i n i t i a t i o n s i t e s by t h e p a s s a g e of t h e r e f l e c t e d t e n s i l e wave. S e c o n d l y , t h e f l a w s enhance b r a n c h i n g by r e d u c i n g t h e e n e r g y r e q u i r e m e n t t o d r i v e t h e c r a c k s . M i c r o -f i s s u r e s a l s o i n f l u e n c e t h e e l a s t i c b e h a v i o u r of t h e r o c k mass. P r e f e r e n t i a l l y o r i e n t e d m i c r o - s t r u c t u r e s i n d u c e l a r g e v a r i a t i o n s i n t h e r o c k p r o p e r t i e s t h a t c a n be r e v e a l e d by wave v e l o c i t y a n i s o t r o p y . N e v e r t h e l e s s , m a c r o - f i s s u r e s a r e t h e most i m p o r t a n t b l a s t i n g v a r i a b l e as d e g r e e o f f r a g m e n t a t i o n i s c o n c e r n e d . They o v e r r i d e any o f t h e p h y s i c a l and m e c h a n i c a l p r o p e r t i e s o f t h e r o c k 1 3 . The e x i s t i n g b e d d i n g and j o i n t i n g p l a n e s , i n c o n j u n c t i o n w i t h t h e f r a c t u r e p a t t e r n r e s u l t i n g from t h e p r e v i o u s b l a s t s , have a l r e a d y d e f i n e d t h e f r a g m e n t a t i o n l i m i t s . The b l a s t h o l e , i n many c a s e s , i s s u r r o u n d e d by a network o f c r a c k s t h a t w i l l s e r v e as t h e l e a s t r e s i s t a n c e p a t h f o r t h e d e v e l o p m e n t and p r o p a g a t i o n of t e n s i l e or s h e a r f a i l u r e . D u r i n g t h e b l a s t i n g p r o c e s s , t h e s e c r a c k s a r e e x t e n d e d t o g r e a t l e n g t h , and t h e f o r m a t i o n of new c r a c k s i n t h e i r immediate v i c i n i t y i s s u p p r e s s e d b e c a u s e of t h e a b s e n c e o f t e n s i l e s t r e s s d e v e l o p m e n t 1 " . Even where a new r a d i a l c r a c k i s d e v e l o p e d , i t t e r m i n a t e s p r e m a t u r e l y where i t i n t e r s e c t s a p r e - e x i s t i n g c r a c k . T h i s l a t t e r s t a t e m e n t i s e s p e c i a l l y t r u e when t h e s e p r e - e x i s t i n g 110 c r a c k s have been widened by g a s e s from b l a s t h o l e s on p r e v i o u s d e l a y p e r i o d s . In t h o s e c a s e s , t h e b l a s t l o o s e n s t h e b l o c k s and t h rows them i n t o t h e muck p i l e w i t h v e r y l i t t l e improvement i n t h e f r a g m e n t a t i o n . A n o t h e r e f f e c t of t h e m a c r o - s t r u c t u r e i s t h e gas e x p a n s i o n i n major j o i n t s w h i c h i n t e r s e c t t h e b l a s t h o l e w a l l . T h i s l e a d s t o p r e m a t u r e v e n t i n g of t h e g a s e s and f l y r o c k s o r s t a b i l i t y p r o b l e m s , d e p e n d i n g on t h e d i r e c t i o n of t h e wedging mechanism. D e s p i t e t h e c o n s t r a i n t s b r o u g h t o v e r t h e f r a g m e n t a t i o n c o n t r o l by t h e r o c k mass d i s c o n t i n u i t i e s , t h e b l a s t i n g e n g i n e e r must be c a p a b l e t o p r o d u c e th e most e c o n o m i c a l and p r a c t i c a l d e s i g n . T h i s i s g e n e r a l l y done by t h e s e l e c t i o n of t h e o r i e n t a t i o n o f t h e e f f e c t i v e f a c e s r e l a t i v e t o dominant j o i n t p l a n e s , b e d d i n g p l a n e s , e t c 1 . The e a s i e s t d i r e c t i o n t o b l a s t i s a l o n g t h e s t r i k e of t h e major s e t o f d i s c o n t i n u i t i e s . The f r a g m e n t a t i o n i s n o t g e n e r a l l y as f i n e as i t would be i n o t h e r d i r e c t i o n s , but i t a l l o w s t h e use of a r e d u c e d powder ( e n e r g y ) f a c t o r . The r e s u l t i n g c r a t e r shape i s i n f l u e n c e d by t h e 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 and a r e a s of p o o r f r a g m e n t e d r o c k w i l l l i k e l y o c c u r when t h e s p a c i n g between t h e b l a s t h o l e s i s t o o l a r g e ( F i g u r e 4 . 2 - 1 ) . S m a l l e r d i a m e t e r and r e d u c e d s p a c i n g s h o u l d c o r r e c t t h i s p r o b l e m . When t h e d i r e c t i o n of b l a s t i n g i s a t r i g h t a n g l e s t o t h e major r o c k j o i n t s , i t g e n e r a l l y r e q u i r e s more e n e r g y t o move t h e r o c k but t h e f r a g m e n t a t i o n w i l l i m p r o v e 1 5 " 1 6 . In some i n s t a n c e s , t h e b u r d e n would need t o be r e d u c e d i n o r d e r t o 111 PREDOMINANT FRACTURING ALMOST PARALLEL TO DIRECTION OF BLASTING FIGURE 4.2-I' ILLUSTRATIONS OF THE EFFECT OF ROCK STRUCTURE ON CRATER FORMATION, (after Bauer3) 1 1 2 a s s u r e t h e t o t a l b r e a k a g e o f e a c h s l a b . B l a s t i n g down-dip w i l l o f t e n r e s u l t i n e x c e s s i v e back b r e a k and l a r g e t o e b u r d e n , e s p e c i a l l y when t h e d i p r a n g e s from 40 t o 60 d e g r e e s . The d e v e l o p m e n t o f t h e f a c e a t an a n g l e g r e a t e r o r e q u a l a t 45 d e g r e e t o t h e d i p d i r e c t i o n w i l l r e d u c e t h e b a c k b r e a k . However, when t h e d i p i s g r e a t e r t h a n 70 d e g r e e s , c a r e f u l b l a s t i n g p r o d u c e s s t a b l e and s t e e p s l o p e s . B l a s t i n g u p - d i p w i l l be e a s i e r b e c a u s e of a r e d u c e d t o e b u r d e n . But i n t h e c a s e where t h e t o e b u r d e n s h o u l d be e q u a l , b l a s t i n g down-dip i s e a s i e r t h a n b l a s t i n g u p - d i p 3 ( F i g u r e 4 . 2 - 2 ) . When d e a l i n g w i t h q u a s i - h o r i z o n t a l b e d d i n g p l a n e s , a t t e n t i o n s h o u l d be p a i d t o t h e c o l l a r a r e a where p o o r f r a g m e n t a t i o n may o c c u r a l t h o u g h b o t t o m d e t o n a t i o n p e r m i t s a h e l p f u l b u i l d - u p o f t h e shock wave t o w a r d t h e c o l l a r . P o c k e t c h a r g e s a r e sometime n e c e s s a r y and w i l l i n c r e a s e d r a m a t i c a l l y t h e b l a s t i n g c o s t s . P o c k e t c h a r g e s would a l s o be needed i n t h e s i t u a t i o n where h a r d r o c k beds l i e between s o f t r o c k seams, w i t h i n t h e h e i g h t o f t h e b e n c h . I f column c h a r g e s a r e u s e d , p r e m a t u r e v e n t i n g t h r o u g h t h e s o f t beds w i l l r e s u l t i n poor f r a g m e n t a t i o n o f t h e h a r d b a n d s 1 7 ( F i g u r e 4 . 2 - 3 ) . C o a t e s and G y e n g e 1 8 have a t t e m p t e d a r e v i e w of t h e r e l a t i o n s h i p s between t h e b l a s t h o l e s p a c i n g S, j o i n t s p a c i n g S j and o v e r s i z e s p e c i f i c a t i o n M. T a b l e 2 shows how t h e r e a r e i n t e r - r e l a t e d . R e v i e w i n g t h e s e s i t u a t i o n s , c a s e s 2,3 and 5 a r e u n l i k e l y t o o c c u r as t h e s p a c i n g of t h e b l a s t h o l e s i s l e s s t h a n th e maximum s p e c i f i e d o v e r s i z e . The f o l l o w i n g d i s c u s s i o n i s 1 13 -FACE REDUCTION OF BURDEN PREDOMINANT FRACTURING AT RIGHT ANGLES TO DIRECTION OF BLASTING PLAN LESS DIFFICULT DUE TO SMALLER TOE BURDEN LARGE TOE /•BURDENS, EASIER DIRECTION SECTION FIGURE 4.2-2' ILLUSTRATIONS OF THE EFFECT OF ROCK STRUCTURE ON CRATER FORMATION, (after Bauer3) 1 1 4 I HORIZONTAL FRACTURING ^Soft ilHord SIMILAR TO (I) -EXCEPT AT THE -COLLAR Soft I Hard Soft POCKET CHARGE I Hard mm FIGURE 4.2-3' ILLUSTRATIONS OF THE EFFECT OF ROCK STRUCTURE ON CRATER FORMATION, (after Bauer3) 1 1 5 TABLE 2 EFFECT ON OVERSIZE FRAGMENTATION OF BLASTHOLE SPACING, S, JOINT SPACING, S j , AND OVERSIZE SPECIFICATION, M 18 (after Coates and Gyenge ) Case Sy.S Sj:M S:M Fragmentation Sensitive to Powder Factor ? % Oversize 1 Sj >S Sj >M S >M Yes Medium 2 Sj >S Sj >M S <M Yes Low 3 Sj >S Sj <M S <M Yes Low 4 Sj <s Sj >M S >M No High $ Sj <s Sj <M S <M No Low . 6 Sj <s Sj <M S >M No Low 1 16 q u o t e d from C o a t e s and G y e n g e 1 8 . "Of t h e t h r e e l i k e l y c a s e s , c a s e 1 i s of low p r o b a b i l i t y a s t h e j o i n t s p a c i n g S j , i s g r e a t e r t h a n t h e s p a c i n g o f t h e b l a s t h o l e s , S. However, i f i t o c c u r e d , t h e p r o b l e m o f o b t a i n i n g f r a g m e n t a t i o n c o u l d be e a s i l y r e s o l v e d w i t h e i t h e r t h e c o n v e n t i o n a l use of l a r g e r d i a m e t e r b l a s t h o l e s , c o r r e s p o n d i n g l y l a r g e s p a c i n g and above a v e r a g e powder f a c t o r . In c a s e 4, where t h e r e p r e s e n t a t i v e j o i n t s p a c i n g , S j , i s l e s s t h a n t h a t of t h e b l a s t h o l e s , S, b u t g r e a t e r t h a n t h e maximum s i z e of muck, M, t h e p r o b l e m of a l a r g e p e r c e n t a g e o f o v e r s i z e f r a g m e n t s i s not u s u a l l y s o l v a b l e by i n c r e a s i n g t h e powder f a c t o r . Reduced s i z e o f h o l e s and s p a c i n g a t t h e same powder f a c t o r c a n be e f f e c t i v e , a l t h o u g h i t m i g h t be more e x p e n s i v e t h a n a c c e p t i n g t h e c o s t o f s e c o n d a r y b r e a k a g e w i t h t h e same c o n v e n t i o n a l p a t t e r n . C ase 6, w h i c h r e p r e s e n t s t h e i d e a l s i t u a t i o n of t h e r e p r e s e n t a t i v e j o i n t s p a c i n g S j , b e i n g l e s s t h a n t h e maximum s p e c i f i e d s i z e of muck M, p e r m i t t h e use of l a r g e r d i a m e t e r b l a s t h o l e s , l a r g e s p a c i n g and low powder f a c t o r s . " The a u t h o r s a r e n o t w i t h o u t s p e c i f y i n g t h a t t h i s t a b l e c a n be u s e d o n l y as a means o f q u i c k e v a l u a t i o n of t h e s i t e s i t u a t i o n . O t h e r v a r i a b l e s l i k e t h e v a r i a t i o n of j o i n t s p a c i n g and t h e i r d e g r e e o f c e m e n t a t i o n a r e a l s o i m p o r t a n t i n r e l a t i o n t o t h e p r o d u c t i o n of o v e r s i z e f r a g m e n t s . F i n a l l y , as t h e f r e q u e n c y of d i s c o n t i n u i t i e s and p l a n e s of weakness d e c r e a s e s , a h i g h e r e n e r g y f a c t o r w i l l be u s e d i n o r d e r 117 t o c r e a t e a l a r g e r number of f r a c t u r e s . T h i s i s g e n e r a l l y done by g e n e r a t i n g a more p o w e r f u l s t r a i n wave, as p r o d u c e d by h i g h d e n s i t y s l u r r i e s . 4.2.1.2 F a i l u r e B e h a v i o u r The f a i l u r e b e h a v i o u r and e n e r g y a b s o r p t i o n p r o p e r t y of t h e r o c k mass l a r g e l y i n f l u e n c e s t h e f r a g m e n t a t i o n p r o c e s s 1 1 . The p h y s i c a l p r o p e r t i e s o f t h e m a t e r i a l t h a t r e l a t e t o t h e a b i l i t y of t h e m a t e r i a l t o a b s o r b , s t o r e and r e l e a s e e n e r g y a r e of t h e utmost i m p o r t a n c e . The modulus o f E l a s t i c i t y i s a measure of t h e b r i t t l e n e s s of t h e r o c k . G e n e r a l l y , r o c k s w h i c h show a h i g h modulus of E l a s t i c i t y a l s o have a h i g h c o m p r e s s i v e s t r e n g t h and so a r e h a r d e r t o b r e a k 1 9 . In a d d i t i o n , t h e i r d e f o r m a t i o n a t f a i l u r e i s minimum. A b e t t e r e v a l u a t i o n of t h e b r i t t l e n e s s i s g i v e n by t h e a n a l y s i s o f t h e s t r e s s - s t r a i n c u r v e of t h e r o c k i n u n i a x i a l c o m p r e s s i o n t o f a i l u r e . F i g u r e 4.2-4 shows s u c h c u r v e s from b r i t t l e r o c k t o c r e e p i n g r o c k s . I t was f o u n d by L a n g 2 1 t h a t t h e e l a s t i c b r i t t l e b e h a v i o u r was a s s o c i a t e d w i t h t h e shock wave t y p e o f f a i l u r e o f t h e r o c k d u r i n g b l a s t i n g . The more b r i t t l e t h e r o c k mass, t h e h i g h e r i s t h e f r a c t u r i n g e f f e c t i v e n e s s o f t h e s t r a i n wave. In t h i s t y p e of f a i l u r e mode, t h e r o c k s t o r e s a l a r g e amount o f e n e r g y and r e l e a s e s i t v i o l e n t l y . The f r a g m e n t a t i o n i s g e n e r a l l y good. In l e s s b r i t t l e r o c k s , however, p l a s t i c d e f o r m a t i o n o c c u r s and a c o n s i d e r a b l e amount of e n e r g y w i l l be a b s o r b e d d u r i n g t h i s 1 18 BRITTLE' BRITTLE DUCTILE. TRANSITION DUCTILE TYPICAL STRAIN BEFORE FRACTURE OR FAULTING (PERCENT) < I 1-5 2-8 5-10 > 10 COMPRESSION cr, > o-2 = O3 CT, V A // EXTENSION <r3< <r, = cr 2 i l 3 TYPICAL STRESS-STRAIN CURVES FRACTURE TYPE I :ELASTIC EXAMPLES TYPE m : PLASTIC ELASTIC TYPE APLAST IC ELASTIC • PLASTIC TYPE ^ELASTIC PLASTIC TYPEJZHELASTIC PLASTIC CREEP BASALT TYPE PLASTIC ELASTIC PLASTIC \^ SCHIST SILTSTONE ROCK-SALT SANDSTONE MARBLE FIGURE 4.2-4'SPECTRUM OF ROCK BEHAVIOUR, (after Hendron20) 119 s t a g e 2 2 i n s t e a d o f b e i n g u s e d f o r t h e f r a g m e n t i o n o f t h e r o c k mass. F a i l u r e of t h e s e t y p e s o f r o c k , d u r i n g b l a s t i n g , i s a s s o c i a t e d w i t h t h e s h e a r i n g a c t i o n o f t h e e x p a n d i n g g a s e s p u s h i n g t h e b u r d e n and c a u s i n g o u t w a r d d e f o r m a t i o n . The r e s u l t of a s h e a r t y p e f a i l u r e i s a c o a r s e f r a g m e n t a t i o n w i t h l a r g e b l o c k s and s l a b s . T h i s s i t u a t i o n o f t e n prompts mine o p e r a t o r s t o d e c l a r e t h a t a g i v e n r o c k t y p e w i t h i n t h e i r p i t i s e a s y t o d r i l l but u n e a s y t o b l a s t . T h i s may g e n e r a l l y be e x p l a i n e d when l o o k i n g t o t h e d r i l l i n g p r a c t i c e i n s o f t t o medium f o r m a t i o n s , where t h e l o n g p r o j e c t i o n i n s e r t s or t e e t h s c r a p e and s h ave t h e r o c k r a t h e r t h a n making i t f a i l under c o n c e n t r a t e d s t r e s s f i e l d s l i k e i n h a r d r o c k s ( s e e c h a p t e r 3 ) . When d e a l i n g w i t h t h o s e t y p e s o f r o c k , t h e b l a s t i n g e n g i n e e r must c o n s i d e r t h a t t h e r o c k mass w i l l e x p e r i m e n t l i t t l e , i f any, o f t h e p r e - c o n d i t i o n i n g e f f e c t o f t h e s t r a i n wave on t h e b u r d e n . B e c a u s e t h e f r a g m e n t a t i o n i s t h e r e f o r e e n t i r e l y done by t h e e x p a n d i n g g a s e s , t h e o p t i m i z a t i o n of gas r e t e n t i o n by t h e use o f an a d q u a t e l e n g t h and t y p e of stemming m a t e r i a l 2 3 , t h e c a r e f u l p l a n n i n g of t h e i n i t i a t i o n p a t t e r n so t h a t any two f r e e f a c e s a r e e q u i d i s t a n t from t h e b l a s t h o l e and by making s u r e t h a t t h e r a t e o f y e i l d a t t h e p o i n t o f minimum b u r d e n i s not t o o g r e a t , s h o u l d r e s u l t i n i m p r o v e d f r a g m e n t a t i o n i n t h o s e "uneasy t o b r e a k " r o c k s 1 . The a t t e n u a t i o n of t h e s t r a i n wave e n e r g y , w i t h i n t h e b u r d e n d i s t a n c e , l a r g e l y r e d u c e s t h e e x p l o s i v e p o t e n t i a l t o c r e a t e t e n s i l e s t r e s s e s . The a t t e n u a t i o n of t h e s t r a i n wave v a r i e s i n v e r s e l y w i t h t h e d i s t a n c e t o t h e power of 1.4 i n s t r o n g 120 e l a s t i c r o c k s whereas v a l u e s up t o 2.5 a r e u s e d i n l e s s b r i t t l e r o c k s 2 " . A t t e n u a t i o n o f t h e s t r a i n wave a l s o o c c u r s i n t h e j o i n t e d r o c k mass a l t h o u g h t h e p r e s e n c e of g r o u n w a t e r w i l l l a r g e l y r e d u c e t h i s e f f e c t . N e v e r t h e l e s s , as t h e i n t e n s i t y of f r a c t u r i n g o f t h e r o c k mass i n c r e a s e s , t h e l e s s b r i t t l e i s t h e f a i l u r e b e h a v i o u r o f t h e r o c k mass. 4.2.2 D e s i g n P a r a m e t e r s T h i s p a r a g r a p h e x a m i n e s t h e i m p o r t a n c e of t h e c h a r g e d i s t r i b u t i o n on t h e d e g r e e of f r a g m e n t a t i o n . The g e o m e t r i c r e l a t i o n s h i p s between t h e d i f f e r e n t d e s i g n p a r a m e t e r s have t o be b a l a n c e d i n o r d e r t o a l l o c a t e t h e e x p l o s i v e e n e r g y , a c r o s s t h e p a t t e r n , a c c o r d i n g t o t h e work t o be done. T h i s i s , a f t e r t h e s t r u c t u r a l p r o p e r t i e s o f t h e r o c k mass, t h e s e c o n d most i m p o r t a n t f a c t o r i n d e t e r m i n i n g f r a g m e n t a t i o n . The d e s i g n p a r a m e t e r s t h a t w i l l be d i s c u s s e d i n t h e f o l l o w i n g p a g e s have been c l a s s i f i e d by t h e a u t h o r i n a s y s t e m t h a t e m p h a s i s e s t h e d e g r e e of c o n t r o l t h e b l a s t i n g e n g i n e e r e x p e r i e n c e d o v e r t h e s e p a r a m e t e r s . CATEGORY 1: BLASTHOLE DIAMETER AND BENCH HEIGHT The p a r a m e t e r s of c a t e g o r y one a r e t h e b l a s t h o l e d i a m e t e r and t h e b e n c h h e i g h t . G e n e r a l l y , t h e b l a s t i n g e n g i n e e r does' not c o n t r o l t h e s e p a r a m e t e r s . T h e r e have been f i x e d by t h e t y p e of equipment bought t o match mine d e s i g n , p r o d u c t i o n r e q u i r e m e n t s , 121 r e g u l a t i o n s a n d / o r d i l u t i o n c o n s t r a i n t s 2 5 . D e s i g n p r o p o s a l s t h a t i n c l u d e a m o d i f i c a t i o n of t h e b l a s t h o l e d i a m e t e r o r b e n c h h e i g h t would n o t be r e c e i v e d w i t h e n t h u s i a s m a t upper management l e v e l . However, t h e b l a s t i n g e n g i n e e r must u n d e r s t a n d t h e i n f l u e n c e of t h e s e p a r a m e t e r s on t h e f r a g m e n t a t i o n p r o c e s s and on o p e r a t i n g c o s t s . D r i l l i n g c o s t s a r e r e d u c e d when t h e b l a s t h o l e d i a m e t e r i s i n c r e a s e d 2 6 . However, t h e r e i s an upper l i m i t i n t h e b l a s t h o l e s i z e . T h i s l i m i t i s r e a c h e d when t h e e f f e c t i v e b u r d e n e q u a l s 40 t i m e s t h e b l a s t h o l e d i a m e t e r o r e q u a l s t h e bench h e i g h t . In s u c h c a s e s , t h e f r a g m e n t a t i o n i s g e n e r a l l y c o a r s e r b e c a u s e of t h e p o o r d i s t r i b u t i o n of t h e e x p l o s i v e a c r o s s t h e p a t t e r n and t h e l a r g e c o l l a r r o c k volume. T h u s , a t a g i v e n s i t e , an i n c r e a s e i n t h e e n e r g y f a c t o r must come w i t h an i n c r e a s e i n t h e b l a s t h o l e d i a m e t e r i n o r d e r t o m a i n t a i n t h e d e g r e e of f r a g m e t a t i o n 1 . The use of l a r g e d i a m e t e r b l a s t h o l e s a l s o r e s u l t s i n an u n e c o n o m i c a l use o f t h e b l a s t h o l e volume. In a d d i t i o n , p i t w a l l i n s t a b i l i t y i s more l i k e l y t o o c c u r when l a r g e p o n c t u a l c h a r g e s a r e u s e d . N e v e r t h e l e s s , t h e i n f l u e n c e o f t h e b l a s t h o l e d i a m e t e r on t h e d e g r e e o f f r a g m e n t a t i o n i s s u b o r d i n a t e d t o t h e s t r u c t u r a l c h a r a c t e r i s t i c s o f t h e r o c k mass. Where p r o n o u n c e d j o i n t p l a n e s d i v i d e t h e b u r d e n i n t o l a r g e b l o c k s , good f r a g m e n t a t i o n w i l l be a c h i e v e d o n l y when each b l o c k i s i n t e r c e p t e d by a b l a s t h o l e . In t h e i n t e n s e l y f r a c t u r e d r o c k mass, f r a g m e n t a t i o n i s s t r u c t u r a l l y c o n t r o l l e d and t h e use of l a r g e r d i a m e t e r b l a s t h o l e s c a u s e s 122 r e l a t i v e l y s m a l l r e d u c t i o n i n t h e d e g r e e of f r a g m e n t a t i o n . The g e o m e t r i c r e l a t i o n s h i p s between t h e b l a s t h o l e d i a m e t e r , b e n c h h e i g h t and ( e f f e c t i v e ) b u r d e n a r e w e l l documented. P e r s s o n 2 6 and B e r g m a n n 2 7 s u g g e s t a b u r d e n / b l a s t h o l e d i a m e t e r r a t i o of 30 t o o b t a i n good r e s u l t s w i t h i n a c o s t e f f e c t i v e d e s i g n . A l t h o u g h t h e s e may be s l i g h t l y more e x p e n s i v e , medium s i z e d i a m e t e r b l a s t h o l e s g i v e b e t t e r b r e a k a g e s i n c e t h e c h a r g e i s b r o u g h t up h i g h e r i n t h e b l a s t h o l e . S m i t h and A s h 2 8 have s t u d i e d t h e g e o m e t r i c r e l a t i o n s h i p between b l a s t i n g p a r a m e t e r s . They showed t h a t t h e f r a g m e n t a t i o n was i m p r o v e d when bench h e i g h t was i n c r e a s e d from one t o v a l u e s o v e r two t i m e s t h e ( e f f e c t i v e ) b u r d e n , e v e r y t h i n g e l s e b e i n g t h e same ( F i g u r e 4.2-5 ) . T h i s i s e x p l a i n e d by t h e b e n d i n g c o n d i t i o n s d e v e l o p e d w i t h i n t h e b u r d e n d u r i n g t h e b l a s t i n g p r o c e s s . They o b s e r v e d c o a r s e f r a g m e n t a t i o n , b a c k b r e a k and t o e f o r m a t i o n i n s i t u a t i o n s where H/Be was e q u a l t o one. CATEGORY 2: BURDEN, SPACING AND EXPLOSIVE PROPERTIES The p a r a m e t e r s of c a t e g o r y two a r e t h e s p a c i n g / b u r d e n r a t i o and t h e e x p l o s i v e p r o p e r t i e s . The b l a s t i n g e n g i n e e r has more c o n t r o l o v e r t h e s e v a r i a b l e s a l t h o u g h e c o n o m i c c o n s t r a i n t s e v e n t u a l l y narrow t h e r a n g e of a l t e r n a t i v e s . The b u r d e n and s p a c i n g a r e o f t e n c o n s i d e r e d as t h e p r i n c i p a l b l a s t d e s i g n v a r i a b l e s . T h e r e a r e i m p o r t a n t , i n d e e d , but t h e i n i t i a t i o n 1 23 FIGURE 4.2-5« TRENDS OF FRAGMENTATION INDEX, F c , WITH L/B AND S/B RATIOS, (after Smith and Ash28) 1 24 s e q u e n c e c a n t o t a l l y a l t e r t h e d r i l l i n g p a t t e r n . C o n s e q u e n t l y , b u r d e n and s p a c i n g a r e r e f e r r e d t o as e f f e c t i v e b u r d e n (Be) and e f f e c t i v e s p a c i n g (Se) when r e l a t e d t o t h e b l a s t i n g p r o c e s s . The e f f e c t i v e b u r d e n i s d e f i n e d as t h e s h o r t e s t d i s t a n c e between t h e b l a s t h o l e and t h e e f f e c t i v e f r e e f a c e a t t h e i n s t a n t t h e c h a r g e d e t o n a t e s 2 9 . T h e r e i s an optimum e f f e c t i v e b u r d e n f o r w h i c h t h e volume of w e l l f r a g m e n t e d r o c k i s maximum ( F i g u r e 4.2-6 ) . When t h e e f f e c t i v e b u r d e n i s t o o l a r g e , t h e a t t e n u a t i o n o f t h e s t r a i n e n e r g y r e s u l t s i n l e s s d e v e l o p e d r a d i a l c r a c k s and uneven p r e - c o n d i t i o n i n g of t h e r o c k mass. The e x p a n d i n g g a s e s v e n t i n t o a network of c r a c k s i n a d e q u a t e f o r e f f i c i e n t f r a g m e n t a t i o n and g e n e r a l l y e s c a p e by e j e c t i n g t h e stemming m a t e r i a l . The s u b s e q u e n t h o l e s w i l l t h u s f a c e an a g g r a v a t e d s i t u a t i o n ( c h a i n r e a c t i o n ) . T h e r e f o r e , t h e f i r s t row b u r d e n s h o u l d be c a r e f u l l y d e s i g n e d . When t h e e f f e c t i v e b u r d e n i s l e s s t h a n optimum, s t r a i n wave f r a c t u r i n g i n c r e a s e s . T h i s u s u a l l y r e s u l t s i n p r e m a t u r e v e n t i n g of t h e e x p a n d i n g g a s e s t h r o u g h t h e b u r d e n and p r o b l e m s s u c h as f l y r o c k s and a i r b l a s t s . However, mine o p e r a t o r s a r e g e n e r a l l y d e a l i n g w i t h t o o l a r g e r a t h e r t h a n t o o s m a l l e f f e c t i v e b u r d e n . The s p a c i n g d i m e n s i o n i s a f u n c t i o n of t h e b u r d e n and B a u e r 3 s u g g e s t s Se/Be r a t i o between 2 and 5. T h i s g e o m e t r i c r e l a t i o n s h i p e x e r c i s e s a dominant c o n t r o l o v e r r a d i a l c r a c k i n g and t h e optimum i s t h e r e f o r e d e p e n d i n g upon t h e r o c k mass s t r u c t u r e . F i n a l l y , on t h e p r a c t i c a l a s p e c t of d r i l l i n g and b l a s t i n g , 125 BURDEN 4 \ Doming of ^ the surface a) COMPLETLY CONTAINED, ONLY FAILURE IS PUL-VERISATION NEAR THE CHARGE AND RADIAL TENSILE FAILURE RUNNIG OUT FROM IT. b) START OF SURFACE FAILURE BURDEN NOT BROKEN.SOME DOMING OF THE SURFACE. c) SURFACE AND SUB-SURFACE FAILURE ALMOST MEET THERE WILL BE A SHELF OF UNBROKEN ROCK BETWEEN THE TWO, DOMING OR SURFACE BULGING. d) FULL CRATER, BURDEN COMPLETLY BROKEN OUT. SURFACE AND SUBSURFACE FAILURES RUN THROUGH TO THE SURFACE. . e)'FULL CRATER, LOWER ' VOLUME THAN OPTIMUM •• FINE FRAGMENTATION NOISE, FLYROCK, BOWL 7 SHAPED CRATER. FIGURE 4.2-6'SCHEMATIC OF THE EFFECT OF DECREASING THE BURDEN ON SIMILAR CHARGES FIRED IN ROCK; ( after Bauer3) 126 mine o p e r a t o r s s h o u l d e m p h a s i z e t h e f o l l o w i n g d r i l l i n g p r a c t i c e : i n c a s e of c a v e - i n , t h e d r i l l e r s h o u l d a t t e m p t h i s new h o l e on t h e s p a c i n g r a t h e r t h a n t h e b u r d e n d i m e n s i o n s . T h i s i s n o t a l w a y s done and t h e r e s u l t i s t h a t t h e a d j a c e n t h o l e s become o u t of b a l a n c e d u r i n g t h e d e t o n a t i o n p r o c e s s . The s e l e c t i o n o f t h e e x p l o s i v e i s a f u n c t i o n o f t h e r e l a t i v e c o s t a l t e r n a t i v e s , t h e e x p l o s i v e p r o p e r t i e s , t h e r o c k mass p r o p e r t i e s and t h e e x p e c t e d r e s u l t s . ' E x p l o s i v e s a r e g e n e r a l l y b u l k - d e l i v e r e d on t h e p a t t e r n t o m i n i m i z e t r a n s p o r t a t i o n and h a n d l i n g c o s t s . In s u c h a form, s l u r r i e s - a r e a b o u t t w i c e a s e x p e n s i v e a s ANFO. U t i l i z a t i o n of p r e - p a c k s l u r r i e s o r c u s t o m p r o d u c t s has t o be ke p t t o a minimum. They a r e v e r y e x p e n s i v e p r o d u c t s . In a d d i t i o n , h o l e pumping and l i n i n g p r o c e d u r e s c a n p e r m i t t h e use o f ANFO i n wet h o l e s and r e d u c e t h e t o t a l b l a s t i n g c o s t . The r e d u c t i o n i n s t r e n g t h o f ANFO w i t h i n c r e a s i n g w ater c o n t e n t i s shown i n F i g u r e 4.2-7. In t h e f i e l d , wet ANFO w i l l be e v e n t u a l l y i n d i c a t e d by o r a n g e -y e l l o w smoke d u r i n g b l a s t i n g . I t i s i m p o r t a n t t o n o t e t h a t , g i v e n t h e i m p o r t a n c e of b l a s t i n g r e s u l t s on downstream o p e r a t i o n s , t h e r e d u c t i o n of o n l y 20% o f t h e ANFO e f f i c i e n c y makes s l u r r i e s an e c o n o m i c a l a l t e r n a t i v e 3 0 . The e x p l o s i v e s e l e c t i o n p r o c e s s a l s o has t o c o n s i d e r t h e r o c k mass p r o p e r t i e s . M a s s i v e r o c k f o r m a t i o n w i l l r e q u i r e a maximum o f s t r a i n e n e r g y as p r o v i d e d by h i g h d e n s i t y s l u r r i e s whereas h i g h l y f i s s u r e d r o c k mass w i l l need a maximum o f b u b b l e e n e r g y from t h e e x p a n d i n g g a s e s as p r o v i d e d by ANFO. P r a c t i c a l l y , mine 127 3500 UJ a. £5 H UJ 5 < a * E . E < i E >- — o o _J Ul > z o Si z g U J o 3000 -2500 -2000 -NO DETONATION 1 2 4 6 8 WATER CONTENT t % BY WEIGHT) 10 FIGURE 4.2-7'EFFECT OF WATER CONTENT ON THE DETONATION VELOCITY OF AN/ FO. (after Leighton4) 1 28 o p e r a t o r s a r e u s i n g ANFO as much as p o s s i b l e u n t i l s e r i o u s p r o b l e m s a n d / o r d e t a i l e d c o s t s t u d i e s d e m o n s t r a t e t h e a d v a n t a g e s of s l u r r y e x p l o s i v e s . C o m p l e t e d i s c u s s i o n o f e x p l o s i v e s e l e c t i o n i s g i v e n i n t h e l i t e r a t u r e 3 1 " 3 5 . The b l a s t i n g e n g i n e e r s h o u l d a c k n o w l e d g e t h a t f o r e a c h b l a s t i n g s i t u a t i o n , t h e r e i s an optimum e x p l o s i v e . CATEGORY 3: SUBDRILLING AND COLLAR HEIGHT The p a r a m e t e r s of c a t e g o r y t h r e e a r e t h e s u b d r i l l i n g and c o l l a r h e i g h t . T h e s e two p a r a m e t e r s a r e u s u a l l y d e f i n e d as a f u n c t i o n o f t h e e f f e c t i v e b u r d e n ( F i g u r e 4 . 2 - 8 ) . P a g e 1 7 s u g g e s t s a s u b d r i l l i n g h e i g h t r a n g i n g between 0.0 and 0.5 Be, B u c h t a 3 6 s u g g e s t s an i n t e r v a l f r o m 0.1 t o 0.4 Be whereas Hoek 2 s u g g e s t s 0.2 t o 0.3 Be. T h i s wide r a n g e of d e s i g n c r i t e r i a s i g n i f i e s t o t h e b l a s t i n g e n g i n e e r t h e i m p o r t a n c e of p e r f o r m i n g h i s own t e s t s i n t h e d i f f e r e n t domains i n t h e p i t . ' The r o l e o f s u b d r i l l i n g i s t o b r e a k t h e r o c k a t g r a d e between t h e b l a s t h o l e s . Thus a c c o r d i n g t o H a g a n 2 9 optimum s u b d r i l l i n g i s f u n c t i o n o f t h e s t r u c t u r a l and d e n s i t y c h a r a c t e r i s t i c s of t h e r o c k , t h e t y p e of e x p l o s i v e ( i e . , e n e r g y p e r f o o t of b l a s t h o l e ) , t h e b l a s t h o l e d i a m e t e r , t h e e f f e c t i v e b u r d e n , e t c . Where t h e t i m e i n t e r v a l between t h e d r i l l i n g and t h e b l a s t i n g o f t h e b l a s t h o l e i s l o n g , i t i s a good p r a c t i c e t o d r i l l a c e r t a i n e x t r a d i s t a n c e f o r s l u d g e o r d r i l l c u t t i n g s w h i c h may a c c u m u l a t e i n t h e b o t t o m of t h e b l a s t h o l e . However, o v e r - d r i l l i n g s h o u l d 1 29 «» 3 0 -«A v. <U ••-£ h-x o Ul X X o z Ul CD Floor 2 0 -10--5-Charge height is about one-half the bench height / Subdrilled zone c E E CO Column zone Bottom exp osive charge 10 20 BURDEN (meters) FIGURE 4.2-8 • RATIO AT BENCHES (after Buchta 130 be m i n i m i z e d . I t may c o s t up t o $ 750,000/year i n l a r g e o p e r a t i o n s . In s u c h c a s e s , b l a s t h o l e s must be b a c k f i l l e d t o p r o p e r d e p t h t o a v o i d a d v e r s e e f f e c t s l i k e e x c e s s i v e g r o u n d v i b r a t i o n s and p o o r c o l l a r l o a d . On t h e o t h e r hand, i n s u f f i c i e n t s u b d r i l l i n g c a u s e s a h i g h p i t f l o o r and b l a s t i n g i n t h o s e c o n d i t i o n s e v e n t u a l l y r e s u l t s i n more t o e s on e a c h s u c c e s s i v e s h o t . Some o p e r a t o r s 2 7 i n c r e a s e t h e s u b d r i l l i n g on t h e f r o n t row o f m u l t i - r o w b l a s t t o improve d i s p l a c e m e n t . T h i s p r a c t i c e s e v e r l y damages t h e n e x t b e n c h and c a r e f u l d e s i g n of t h e f r o n t row b u r d e n i s a b e t t e r a l t e r n a t i v e . F i n a l l y , i n p e r i m e t e r b l a s t s o r i n h i g h l y f r a c t u r e d r o c k mass, t h e s u b d r i l l i n g can be r e d u c e d t o n o t h i n g . The c o l l a r h e i g h t s h o u l d be k e p t between 0.7 and 1.0 Be. The stemming l e n g t h has t o be l o n g enough t o r e s i s t t h e p r e m a t u r e v e n t i n g of t h e e x p a n d i n g g a s e s and f o r c e them t o p u s h ou t t h e b u r d e n . P r e m a t u r e v e n t i n g t h r o u g h t h e stemming column r e s u l t s i n a waste of e x p l o s i v e e n e r g y and a s s o c i a t e d p r o b l e m s s u c h as p o o r f r a g m e n t a t i o n , t o e s and a b s e n c e of a f r e e f a c e f o r t h e s u b s e q u e n t b l a s t h o l e , e t c . On t h e o t h e r hand, a t o o l o n g c o l l a r h e i g h t may c r e a t e b l o c k y f r a g m e n t a t i o n i n t h e t o p p a r t of t h e b e n c h . Even t h o u g h d r i l l c u t t i n g s a r e not t h e b e s t stemming m a t e r i a l 2 3 , t h e r e a r e g e n e r a l l y u s e d b e c a u s e t h e r e a r e t h e c h e a p e s t m a t e r i a l a v a i l a b l e . CATEGORY 4: DELAY INTERVAL, INITIATION SEQUENCE AND DESIGN POWDER FACTOR 131 The p a r a m e t e r s of c a t e g o r y f o u r a r e t h e d e l a y i n t e r v a l , t h e i n i t i a t i o n s e q u e n c e and t h e d e s i g n powder f a c t o r . T h e s e a r e t h e p a r a m e t e r s on w h i c h t h e b l a s t i n g e n g i n e e r e x e r t s t o t a l c o n t r o l . V a r i a t i o n s i n t h e i n i t i a t i o n s e q u e n c e have no s i g n i f i c a n t e f f e c t on t h e d r i l l i n g and b l a s t i n g c o s t s , b u t , w i t h i t s i n f l u e n c e on t h e d e g r e e o f f r a g m e n t a t i o n , c a n r e d u c e t h e t o t a l p r o d u c t i o n c o s t . The o r i g i n a l i t y of t h e d e l a y p a t t e r n d e s i g n i s o n l y l i m i t e d by t h e q u a l i t y of t h e b l a s t i n g crew. The d e g r e e of f r a g m e n t a t i o n , i n o p e n ' p i t bench b l a s t i n g , i s s t r o n g l y d e p e n d e n t on t h e a v a i l a b i l i t y of e f f e c t i v e f r e e f a c e and on t h e Se/Be r a t i o . B o t h a r e c o n t r o l l e d by t h e d e l a y i n t e r v a l and i n i t i a t i o n s e q u e n c e . The e f f e c t i v e f r e e f a c e i s c r e a t e d , i n m u l t i - r o w b l a s t s , by a l l o w i n g s u f f i c i e n t movement o f t h e b u r d e n t o t a k e p l a c e p r i o r t o t h e i n i t i a t i o n of t h e c h a r g e s i n t h e n e x t row. I f t h e d e l a y i n t e r v a l i s t o o s h o r t , t h e f o l l o w i n g row i s o v e r l o a d e d by t h e p r e v i o u s b u r d e n . The r e s u l t s a r e p o o r f r a g m e n t a t i o n , t i g h t muck p i l e , t o e p r o b l e m s , b a c k b r e a k s and f l y r o c k s c a u s e d by c r a t e r i n g . The s h o t becomes c h o k e d . I f t h e d e l a y i n t e r v a l i s t o o l o n g , c u t - o f f s a r e l i k e l y t o o c c u r , u n l e s s a l o n g p e r i o d down t h e h o l e i n i t i a t i o n s y s t e m i s u s e d . T h u s , t h e b e s t d e l a y i n t e r v a l i s t h e l o n g e s t t h a t can be u s e d w i t h o u t c u t - o f f p r o b l e m s . I t i s g e n e r a l l y d e p e n d a n t upon t h e r o c k mass c h a r a c t e r i s t i c s , h i g h l y f i s s u r e d r o c k mass b e i n g more p r o n e t o l i n e d i s r u p t i o n . In e x p e r i m e n t s c a r r i e d by Bergmann e t a l 3 7 , d i f f e r e n t d e l a y i n t e r v a l s between a d j a c e n t h o l e s a l o n g one row were t e s t e d i n r e g a r d t o f r a g m e n t a t i o n 1 32 o p t i m i z a t i o n ( F i g u r e 4 . 2 - 9 ) . I t s u g g e s t s t h a t d e l a y i n t e r v a l between 3 and 6 m i l l i s e c o n d p e r meter (1 and 2 ms/f) o f e f f e c t i v e b u r d e n , t h i s w ould be a good s t a r t i n g p o i n t when d e s i g n i n g a row p e r row b l a s t w i t h no down t h e h o l e i n i t i a t i o n s y s t e m . The b l a s t i n g e n g i n e e r must c o n s i d e r t h a t s i m u l t a n e o u s i n i t i a t i o n o f h o l e s ( a l o n g one row) p r o d u c e s a more u n i f o r m s t r e s s d i s t r i b u t i o n i n t h e r o c k , r e s u l t i n g i n a s m a l l e r number of w e l l d e f i n e d f r a c t u r e s and t h e r e f o r e p o o r e r f r a g m e n t a t i o n . Optimum f r a g m e n t a t i o n d e pends on t h e f u l l d e v e l o p m e n t o f t h e c r a c k network a r o u n d e a c h h o l e b e f o r e t h e c h a r g e i n t h e n e x t h o l e i s d e t o n a t e d . F o r a s e q u e n t i a l b l a s t , A n d r e w s 3 8 s u g g e s t s d e l a y r a t i o o f 9 ms/m (3 ms/f) of Be between h o l e s a l o n g t h e .row, w i t h an upper l i m i t o f 15 ms/m (5 ms/f) o f Be i n m a s s i v e o r i n f r e q u e n t l y j o i n t e d r o c k ; and a d e l a y i n t e r v a l between t h e rows e q u a l t o two o r t h r e e t i m e s t h e d e l a y r a t i o u s e d between t h e h o l e s i n a row. The e f f e c t i v e s p a c i n g / e f f e c t i v e b u r d e n r a t i o a l s o i n f l u e n c e s f r a g m e n t a t i o n , as s t a t e d p r e v i o u s l y . Many mines use a s q u a r e d r i l l i n g p a t t e r n b e c a u s e i t i s e a s y t o l a y - o u t and s i m p l e t o d r i l l . T h e r e f o r e , VI i n i t i a t i o n p a t t e r n s h o u l d be c o n s i d e r e d ( F i g u r e 4.2-10). However, i t i s o f t e n more s i m p l e t o t i e - u p t h e s q u a r e p a t t e r n i n V r a t h e r t h a n i n V1. In a l l c a s e s , t h e V and V1 p a t t e r n s g i v e b e t t e r f r a g m e n t a t i o n t h a n i n - l i n e p a t t e r n s b e c a u s e of t h e m o d i f i c a t i o n o f t h e b e nch h e i g h t / e f f e c t i v e b u rden r a t i o . T hese two p a t t e r n s a l s o c a u s e a d d i t i o n a l b r e a k a g e w i t h i n - f l i g h t c o l l i s i o n 3 9 . 1 33 65 o Ul N CO 5 0 -2 52 35 n- 30 ui o 25 rr ui 20 < J I L • = Square pattern, 13-in. burden, 13-ln. spacing. A = Rectangular pattern I, 11.0-in. burden, 15.5-in. spacing. O = Rectangular pattern II, 9.2-in. burden, 18.4-in. spacing. Best commercial delays J L (according to Langefors) I I I I I I I L 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 DELAY RATIO, MILLISECONDS PER FT. OF BURDEN 1.8 FIGURE 4.2-9'EFFECT OF DELAY TIME BETWEEN SHOTHOLES ON AVERAGE FRAGMENT SIZE. THE SAME POWDER FACTOR WAS USED FOR ALL SHOTS, (after Bergman 8 all37) 1 34 FACE FACE i — • • "— — —- - — ' - -0 • * • * • • - • 7 . - - • • - -A 0 D A 0 c • o • -#—---m • • • #-—-m • a — - • • • — - - • B I E I 2 2 • o -• -•—---• • -•- • -• • a -a • •--—a a — - • • ° (a) SQUARE IN-LINE F R 8 (b)STAGGERED IN-LINE0 ° C \ <g*X / / "/ AT^ 0»X ~fF ~f J^Jf \ \ \ A / / /1 \ \ \ \ /i / / / • V \ N * B e \ / y - 4 k 3Y 2V V J J J J \ \ V n \ i A A A A \ * J» cv—'D ;K f / % t V \ -V / / A $ . \ Y ^ - i - - " / /» . B Y R B Q (c) SQUARE V (d)STAGGERED V A > ^ \ 2 C A 2,. ' > " A \ < 8 " < ^ < \ D ^ ' > ' V ' ' 8 6 \ ? \ \ / / / j B (e) SQUARE VI F R B (f)STAGGERED VI D ° » .^G «2 •! »0 •! «2 ,J» [• \m H»5 -•• a-' «5 ,J» ,^a -a r j* D 7 |0 7 ^--"'Ifi 7 10 "~ ~ ~ ; . : ^ (g) SQUARE V2 F (h) STAGGERED V2 SQUARE PATTENS STAGGERED PATTENS Pattens Se/Be Pattens Se/Be 1. in-line 1.0 I. in-line 1.0 2. V 2.0 2. V 1.25 3. VI 5.0 3. VI 3.25 4 V2 quasi 10.0 4. V2 quasi 7.25 FIGURE 4.2-10' BLASTHOLE/ INITIATION PATTENS WITH FIRE TO AN OPEN FACE, (after Hagan39j B = S FOR SHOTS 135 D e l a y i n t e r v a l and i n i t i a t i o n s e q u e n c e a l s o i n f l u e n c e t h e p i t s l o p e s t a b i l i t y by r e d u c i n g t h e amount of e x p l o s i v e f i r e d s i m u l t a n e o u s l y and by d i r e c t i n g t h e b l a s t t o w a r d a f r e e f a c e . F i g u r e 4.2-11 shows t h e i m p o r t a n t r e l a t i o n s h i p between t h e i n s t a n t a n e o u s c h a r g e i n i t i a t i o n and damages a t d i s t a n c e f r o m t h e b l a s t . On t h i s f i g u r e , v a l u e s of K = 200 and B = -1.5 have been u s e d t o s o l v e t h e f o l l o w i n g e q u a t i o n : V = K (R/W**-2)**/3 (USBM) W i t h V = p a r t i c l e v e l o c i t y W = w e i g h t of e x p l o s i v e d e t o n a t e d p e r d e l a y R = r a d i a l d i s t a n c e f r o m t h e p o i n t o f d e t o n a t i o n K,/3 = c o n s t a n t s ( s i t e s p e c i f i c ) T h i s f i g u r e s h o u l d be u s e d as a g e n e r a l t o o l t o d e t e r m i n e t h e maximum c h a r g e p e r d e l a y as t h e b l a s t p a t t e r n moves t o w a r d t h e p i t l i m i t s . The b l a s t i n g e n g i n e e r must remember t h a t t h e v a l u e s of K and B a r e s i t e s p e c i f i c and t h a t o n l y a v e r a g e v a l u e s a r e g i v e n h e r e . Those c o n s t a n t s a r e e a s i l y d e t e r m i n e d i n t h e f i e l d by u s i n g s e i s m o g r a p h . B e c a u s e of i t s i n t r i n s i c i m p o r t a n c e i n t h e b l a s t i n g p r o c e s s and i n t h e f i e l d of t h i s i n v e s t i g a t i o n , t h e d e s i g n powder f a c t o r i s c o v e r e d i n a p a r t i c u l a r p a r a g r a p h . 136 Distance from blast - metres I I • i ' • i i 1 1 « 1 • , 5 10 2 0 50 1 0 0 2 0 0 5 0 0 1 0 0 0 5000 2 0 0 0 0 Distance from blast - feet FIGURE 4.2-11 PLOT OF PARTICLE VELOCITIES INDUCED AT GIVEN DISTANCES BY PARTICULAR 2, CHARGES (after Hoek and Bray) 1 37 4.2.3 The D e s i g n Powder F a c t o r The powder f a c t o r i s t h e most w i d e s p r e a d and y e t most m i s u n d e r s t o o d s t a t i s t i c i n t h e f i e l d of b l a s t i n g . A l t h o u g h many o p e r a t o r s c o n s i d e r t h e powder f a c t o r as an a c c o u n t i n g t o o l , numbers o f them a r e now u s i n g i t as an e f f i c i e n t d e s i g n q u a n t i t y . I t p e r m i t s a good u n d e r s t a n d i n g o f t h e b l a s t i n g p r o c e s s , c o n s i s t e n t r e s u l t s and c o n t r o l l e d p r o d u c t . The f a c t t h a t d i f f e r e n t e x p l o s i v e s p o s s e s s d i f f e r e n t e n e r g y c o n t e n t l e a d s t o t h e n o r m a l i z a t i o n of t h e powder f a c t o r . T h i s i s done by m u l t i p l y i n g t h e w e i g h t o f e x p l o s i v e u s e d by i t s r e l a t i v e w e i g h t s t r e n g t h ( e n e r g y ) f a c t o r . The w e i g h t s t r e n g t h f a c t o r of s t r a i g h t ANFO i s a r b i t r a r e l y f i x e d a s 100. The b l a s t i n g e n g i n e e r t h e r e f o r e r a t i o n a l i z e s t h e l o a d i n g p r o c e d u r e by d e t e r m i n i n g t h e q u a n t i t y and t y p e of e x p l o s i v e t o be p o u r e d i n e a c h h o l e i n o r d e r t o keep t h e e n e r g y d i s t r i b u t i o n as u n i f o r m a s p o s s i b l e . The d e s i g n powder f a c t o r d o e s t a k e i n t o a c c o u n t o n l y t h e bu r d e n volume of t h e b l a s t h o l e and t h u s , i s g e n e r a l l y h i g h e r t h a n t h e a c c o u n t i n g powder f a c t o r t h a t i n c l u d e f r e e d i g g i n g and o v e r b r e a k . However, t h e b l a s t i n g e n g i n e e r i s s t i l l f a c i n g t h e p r o b l e m o f d e t e r m i n i n g t h e optimum powder f a c t o r f o r e a c h d i f f e r e n t b l a s t i n g domain i n t h e p i t . The scope of t h i s r e s e a r c h p r o j e c t i s t o s i m p l i f y t h e t r i a l and e r r o r p r o c e d u r e by d e f i n i n g a r e l i a b l e r e l a t i o n s h i p between t h e powder f a c t o r and t h e Rock Q u a l i t y I n d e x . T h e r e i s an optimum powder f a c t o r f o r e a c h r o c k mass and 1 38 b l a s t i n g c o n d i t i o n s . W i t h e v e r y t h i n g kept c o n s t a n t , f r a g m e n t a t i o n i m p r o v e s as t h e powder f a c t o r i s i n c r e a s e d u n t i l a miximum i s r e a c h e d ( F i g u r e 4 .2-12). I n c r e a s i n g t h e powder f a c t o r f u r t h e r t h e n e v e n t u a l l y c a u s e s t h e f r a g m e n t a t i o n t o d e t e r i o r a t e 1 0 and i s a waste of e x p l o s i v e e n e r g y . However, i t has been shown t h a t i f t h e powder f a c t o r i s r e d u c e d by a b o u t 20% from t h e optimum v a l u e , i n a g i v e n open p i t , t h e g r o u n d v i b r a t i o n l e v e l c a n be i n c r e a s e d by a f a c t o r of 2 o r 3 3 8 ( F i g u r e 4.2-13). T h i s r e d u c t i o n i n t h e powder f a c t o r c a n be o b t a i n e d w i t h o u t i n t e n t i o n when ANFO i s s i d e - i n i t i a t e d by a p r i m a c o r d d o w n l i n e . In t h i s c a s e t h e e n e r g y o u t p u t i s r e d u c e d . However, i n p e r i m e t e r b l a s t i n g , t h e g e n e r a l r u l e i s t h a t t h e powder f a c t o r i s r e d u c e d i n o r d e r t o m a i n t a i n t h e i n t e g r e t y o f t h e f i n a l w a l l . T h e r e f o r e t h e b l a s t i n g e n g i n e e r s h a l l d e s i g n t h e s h o t by u s i n g t h e maximum a d v a n t a g e o f d o w n - t h e - h o l e d e l a y s s y s t e m s i n o r d e r t o c r e a t e e f f e c t i v e f r e e f a c e s and c o u n t e r b a l a n c e t h i s i n c r e a s e i n t h e g r o u n d v i b r a t i o n l e v e l . The r e d u c t i o n , i n t h e powder f a c t o r , on a t r i m p e r i m e t e r s h o t i s i n th e r a n g e of 35 t o 50 p e r c e n t 1 9 + * 0 . A wide p r a c t i c e i n open p i t m i n i n g i s t h e c h o k e d b l a s t i n g s i t u a t i o n . The s h o t i s s a i d t o be c h o k e d when i t d e a l s w i t h t h e f i r i n g o f r o c k i n t o p r e v i o u s l y - s h o t muck w h i c h l i e s d i r e c t l y a g a i n s t t h e v e r t i c a l " f r e e f a c e " . T h e r e i s a number of a d v a n t a g e s and d i s a d v a n t a g e s r e l a t e d t o t h i s p r a c t i c e . Some o p e r a t o r s a r e c o n c e r n e d w i t h t h e c o s t o f moving equipment i n and out b e c a u s e of f l y r o c k h a z a r d s . O t h e r s want t o m i n i m i z e t h e 139 0.4 0.5 0.6 0.7 0.8 EXPLOSIVE CONSUMPTION (lbs/ton EQUIVALENT AN/FO) FIGURE 4.2-I2' SHOVEL PRODUCTION ON A YEARLY BASIS AT ' ONE OPERATION VERSUS EXPLOSIVE CONSUMP-TION IN ROCK OF 20,000 PSI COMPRESSIVE STRENGTH, (after Bauer3) 140 0.5 0.6 POWDER FACTOR-1b/LT FIGURE 4.2-l3 = A PLOT OF GROUND VIBRATION VS POWDER FACTOR MEASURED FROM A SERIES OF PRODUCTION BLASTS AT A LARGE OPEN PIT MINE SHOWING THE ABRUPT INCREASE OF THE LEVEL OF GROUND VIBRATION AS THE POWDER FACTOR IS DECREASED, (after Andrews38) 141 movement o f d r i l l i n g e quipment o r t o a c c u m u l a t e b l a s t e d r e s e r v e s i n t h e p i t . F u r t h e r a d v a n t a g e i s t h e i n c r e a s e i n s a f e t y when d r i l l i n g c l o s e t o t h e c r e s t of t h e b e n c h . Mine o p e r a t o r s may a l s o p r a c t i c e c h o k e d b l a s t i n g b e c a u s e o f t h e w i d t h of t h e o r e b o d y i n r e l a t i o n t o t h e p r o d u c t i o n r e q u i r e m e n t s . I t c a n a l s o be t h e r e s u l t o f b l e n d i n g r e q u i r e m e n t s o r s i m p l y i n a d e q u a t e mine p l a n n i n g . In any c a s e , o p e r a t o r s w i l l f a c e t h e f o l l o w i n g d i s a d v a n t a g e s . F i r s t , i f t h e r e i s no n a t u r a l p a r t i n g a t t h e p i t f l o o r t o a s s i s t r o c k d i s p l a c e m e n t a t t h e t o e r e g i o n , i t may r e s u l t i n an uneven p i t f l o o r . The s e c o n d d i s a d v a n t a g e s i s t h e h i g h e r g r o u n d v i b r a t i o n l e v e l c a u s e d by c h o k e d b l a s t s and i t s e f f e c t on s l o p e s t a b i l i t y . F i n a l l y , c h o c k e d s h o t s n e c e s s i t a t e an i n c r e a s e d powder f a c t o r i n o r d e r t o keep t h e d e g r e e o f f r a g m e n t a t i o n c o n s t a n t . B a u e r " 0 s u g g e s t s a f a c t o r of 1.1 w h i l e H a g a n 2 9 a c k n o w l e d g e s an o v e r a l l f r a g m e n t a t i o n r e d u c t i o n and t h e need f o r an i n c r e a s e i n e n e r g y r e q u i r e m e n t b u t he does n o t p r o p o s e any n u m e r i c a l v a l u e . In h i s o p i n i o n , t h e f r a c t u r i n g mechanisms w h i c h r e l y on t h e s t r a i n wave a r e not i n f l u e n c e d by t h e b u f f e r r o c k s . O n l y t h e b r e a k a g e mechanisms t h a t r e q u i r e d i s p l a c e m e n t a r e a l t e r e d . L a n g " 1 p r o p o s e s l o n g e r d e l a y i n t e r v a l s i n o r d e r t o m a i n t a i n t h e f r a g m e n t a t i o n and o b t a i n s a t i s f y i n g r e s u l t s . 142 4.3 ROCK MASS BLASTABILITY The c h a r a c t e r i z a t i o n o f t h e r o c k mass i n r e g a r d w i t h b l a s t i n g and t h e d e t e r m i n a t i o n of t h e optimum powder f a c t o r u n d e r s p e c i f i c b l a s t i n g c o n d i t i o n s a r e t h e main s u b j e c t s of t h i s p r o j e c t . The e v a l u a t i o n o f t h e b l a s t a b i l i t y of t h e r o c k mass has been a t t e m p e d by many s c i e n t i s t s d u r i n g t h e l a s t 20 y e a r s . T h i s s e c t i o n w i l l r e v i e w and c r i t i q u e t y p i c a l r e l a t i o n s h i p s d e v e l o p e d r e c e n t l y . The d e t e r m i n a t i o n o f r o c k mass b l a s t a b i l i t y c a n be o b t a i n e d by t h e f o l l o w i n g methods: 1) v i s u a l d e t e r m i n a t i o n of t h e b l a s t a b i l i t y . 2) g e o p h y s i c s , by u s i n g s p e c i a l b o r e h o l e s o r d r i l l e d p r o d u c t i o n b l a s t h o l e s . 3) c o r r e l a t i o n w i t h one o r more r o c k p r o p e r t i e s , measured i n l a b o r a t o r y , i n - s i t u o r b o t h . 4) b l a s t a b i l i t y i n d e x d e r i v e d f r o m s m a l l s c a l e c r a t e r t e s t s . 5) r o c k mass c h a r a c t e r i z a t i o n w i t h p r o d u c t i o n r o t a r y d r i l l s . 4.3.1 V i s u a l D e t e r m i n a t i o n of t h e Rock Mass B l a s t a b i l i t y T h i s method i s f a r from optimum and r e q u i r e s a c e r t a i n amount of s i t e s p e c i f i c e x p e r i e n c e o r a g r e a t d e a l of e x p e r i e n c e i n a wide r a n g e o f r o c k mass. T h i s i s t h e method g e n e r a l l y u s e d i n W e s t e r n Canada. By t r i a l and e r r o r , t h e b l a s t i n g e n g i n e e r hopes t h a t he w i l l e v e n t u a l l y d e f i n e t h e optimum powder f a c t o r 143 i n e a c h and e v e r y domains on t h e p r o p e r t y . I t i s a s l o w p r o c e s s . T r i a l s h o t s have t o be c a r e f u l l y m o n i t o r e d and e v a l u a t e d . S e v e r a l s h o t s of e v e r y t e s t e d d e s i g n must be p e r f o r m e d b e f o r e a l t e r a t i o n o f any p a r a m e t e r s . T h i s method a s k s f o r a d e t a i l e d f i l i n g s y s t e m and t h e use of p h o t o g r a p h s a r e s t r o n g l y recommended. However, when t h e v a r i a b i l i t y i n t h e r o c k mass p r o p e r t i e s i s h i g h , t h e o p e r a t i o n i s c o n t i n u a l l y p e r f o r m i n g t e s t b l a s t s . The c o s t o f s u c h p r o c e d u r e on t h e downstream u n i t o p e r a t i o n s a r e - v e r y h i g h . M o r e o v e r , t h e damage c a u s e d t o t h e f i n a l w a l l a n d / o r t h e d e s i g n of a c o n s e r v a t i v e s l o p e a n g l e a r e even more c o s t l y . T h i s i s t h e s i t u a t i o n we want t o o p t i m i z e . 4.3.2 C h a r a c t e r i z a t i o n of t h e Rock Mass By G e o p h y s i c s Methods These methods a r e w e l l known o f e x p l o r a t i o n g e o l o g i s t s and g e o p h y s i s t s . U s i n g s p e c i a l e q u ipment and s k i l l t e c h n i c i a n s , i t i s p o s s i b l e t o o b t a i n d a t a on t h e r o c k mass t o be b l a s t e d . T h o s e d a t a a r e p r e s e n t e d i n t h e form of l o g s t h a t show v a r i a t i o n s i n r o c k mass p r o p e r t i e s s u c h as s o n i c v e l o c i t y , d e n s i t y , r e s i s t i v i t y , e t c . T h i s t y p e o f i n f o r m a t i o n c a n be u s e f u l , i n i d e n t i f y i n g s o f t e r o r h a r d e r l a y e r s o f r o c k s a l o n g t h e b l a s t h o l e l e n g t h . B a s ed on t h i s i n f o r m a t i o n , t h e b l a s t i n g e n g i n e e r c a n d e t e r m i n e t h e l o c a t i o n of t h e c h a r g e , b o o s t e r and p r i m e r and o p t i m i z e f r a g m e n t a t i o n or r e d u c e wastage o f e x p l o s i v e e n e r g y . T h e s e d a t a can h a r d l y be u s e d as b l a s t a b i l i t y i n d e x b e c a u s e of t h e i r r e l a t i o n s h i p w i t h o n l y one, r a r e l y a few, r o c k 144 mass p r o p e r t i e s , u n l e s s s e v e r a l d i f f e r e n t l o g s a r e u s e d . The p r i n c i p a l c o n s i d e r a t i o n i n t h e s e methods i s c o s t . They a r e e x p e n s i v e . In a d d i t i o n , as t h e v a r i a b i l i t y of t h e m a t e r i a l i n c r e a s e s , i n t h e s t r i k e a n d / o r d i p d i r e c t i o n , t h e amount of d a t a needed f o r e a c h d a i l y s h o t w i l l h a r d l y be b a l a n c e d by t h e c o s t e f f i c i e n t b l a s t d e s i g n t h a t would r e s u l t . The use of t h e s e methods can n o t be j u s t i f i e d i n open p i t p r o d u c t i o n b l a s t i n g . 4.3.3 C o r r e l a t i o n o f t h e B l a s t a b i l i t y w i t h One o r More Rock  Mass P r o p e r t i e s , M e a s u r e d In L a b o r a t o r y o r I n - S i t u T h i s i s t h e f i e l d where most of t h e work has been done. V a r i o u s a t t e m p t s have been made t o r e l a t e t h e b l a s t a b i l i t y of t h e r o c k mass w i t h p r o p e r t i e s s u c h a s Young's M o d u l u s , u n i a x i a l c o m p r e s s i v e s t r e n g t h , t e n s i l e s t r e n g t h , e t c . One o f t h e f i r s t b l a s t a b i l i t y i n d e x was t h e u n i a x i a l c o m p r e s s i v e s t r e n g t h / t e n s i l e s t r e n g t h r a t i o . A low v a l u e i n d i c a t e s a p l a s t i c b e h a v i o u r whereas a h i g h v a l u e i n d i c a t e s a b r i t t l e b e h a v i o u r . Munoz-C a s a y u s 4 2 has p u b l i s h e d a r e l a t i o n s h i p between t h e r o c k u n i a x i a l c o m p r e s s i v e s t r e n g t h and t h e powder f a c t o r ( F i g u r e 4 . 3 - 1 ) . T h o s e t y p e s o f r e l a t i o n s h i p a r e g e n e r a l l y p o o r due t o t h e f a c t t h a t r o c k p r o p e r t i e s were measured i n s t a t i c l a b o r a t o r y t e s t s and, i n a d d i t i o n do not c o n s i d e r t h e s t r u c t u r a l p r o p e r t i e s of t h e r o c k mass. O t h e r e x p e r i m e n t s were c a r r i e d on t h e s i t e . Rock mass p r o p e r t i e s s u c h as s o n i c v e l o c i t y were r e l a t e d w i t h t h e powder 1 45 ro O 40 * tsd 35 •— x. h-o 30 z UJ cc \-(/) 25 Ul > if) 20 </) Ul tr Q_ o 15 o _ l < X 10 < z 5 h 0.2 0.3 0.4 0.5 0.6 P0WDED FACTOR ( Ib/S.ton) 0.7 FIGURE 4.3-1! UNIAXIAL COMPRESSIVE STRENGTH VS POWDER FACTOR.( after Munoz-Casayus42) 1 46 f a c t o r . V e l o c i t i e s t e n d t o d e c r e a s e as t h e number o f f r a c t u r e s i n t h e r o c k mass i n c r e a s e . The v e l o c i t y i s a l s o r e d u c e d i n r o c k mass showing a p l a s t i c b e h a v i o u r , a c c o r d i n g l y w i t h a r e d u c t i o n i n t h e modulus o f e l a s t i c i t y . F i g u r e 4.3-2 shows t h e r e l a t i o n s h i p s d e v e l o p e d by H e i n e n and D i m o c k * 3 of K e n n e c o t t Coppor C o r p o r a t i o n and by B r o a d b e n t . B e c a u s e b o t h v e l o c i t y and b l a s t a b i l i t y a r e f u n c t i o n s o f t h e same r o c k mass c h a r a c t e r i s t i c s , t h e r e a r e d i r e c t l y r e l a t e d . T h i s method has few d i s a d v a n t a g e s : 1. S o f t m a t e r i a l ; shows v e l o c i t i e s 600 m/s (2000 f p s ) h i g h e r t h a n n o r m a l when f r o z e n . 2. S h o o t i n g s e i s m i c l i n e s must be done when t h e e q u ipment i n t h e a r e a i s not o p e r a t i n g due t o b a c k g r o u n d n o i s e . 3. The p r e s e n c e o f h a r d a n o m a l i e s below t h e m i n i n g l e v e l s u r v e y e d c o u l d r e s u l t i n v e l o c i t i e s h i g h e r t h a n n o r m a l . H e i n e n and Dimock c l a i m e d t h a t t h e c o s t o f t h e s e i s m o g r a p h and t h e s e i s m i c s u r v e y s p e r f o r m e d a r e i n s i g n i f i c a n t compared t o t h e c o s t s a v i n g s t o t h e o p e r a t i o n . However, i f o n l y one s e i s m i c l i n e s u r v e y p e r 120 m e t e r s (400 f t ) i s s u f f i c i e n t i n a r e a s of u n i f o r m s t r u c t u r e , 4 t i m e s more a r e needed i n a r e a s of h i g h v a r i a b i l i t y . When t h e f r a c t u r e p r o c e s s i s b e l i e v e d t o be s t r u c t u r a l l y c o n t r o l l e d , r e l a t i o n s h i p s between t h e i n t e n s i t y o f f r a c t u r a t i o n and powder f a c t o r ( F i g u r e 4.3-3) or b l a s t a b i l i t y i n d e x 147 0.6 c o (A \ JQ tr u. rr ui Q S 0.4 0.3 0.2 AVERAGE OF /* / / / / i BLASTS / ' (D / * / / / / / ' / t i © : HEINEN AND DIMOCK i / / / / / / i (|): BROAD BE NT 1 VELOCITY BROKEN ROCK " J 1 A IUJ / S|£ / 5l§ I UJIt I I I I 1 I I 1 3 4 5 6 7 8 ACOUSTIC VELOCITY (1000 ft/s) 10 FIGURE 4.3-2' ACOUSTIC VELOCITY VS POWDER FACTOR, (after Heinen and Dimock 4 3) 0.3 h b 0.4h 0.1 h FRACTURE FREQUENCY 90 FRACTURES/METRE 26 2,8 FRATURES/F00T FIGURE 4.3-3 • FRACTURE FREQUENCY VS POWDER FACTOR.(after Ashby3 0) 1 49 ( F i g u r e 4.3-4) have been d e v e l o p e d . F i n a l l y , an o r i g i n a l a p p r o a c h has been t a k e n by C h r i s t e n s e n and O l s e n " 6 t o e v a l u a t e t h e r e s i s t a n c e t o b l a s t i n g i n t u n n e l l i n g . I n t h e f i e l d t h e y e v a l u a t e t h e b l a s t i n g r e s u l t s by m e a s u r i n g t h e a d v a n c e i n p e r c e n t a g e of d r i l l e d d e p t h as a f u n c t i o n of a g i v e n n o r m a l i z e d c h a r g e . Then, u s i n g r e g r e s s i o n a n a l y s i s , t h e y r e l a t e d t h e r o c k ' s s o n i c v e l o c i t y , t e n s i l e s t r e n g t h and d e n s i t y , m e asured i n t h e l a b o r a t o r y and t h e j o i n t i n g i n t e n s i t y t o t h e f i e l d b l a s t a b i l i t y i n d e x . They c l a i m e d a c o r r e l a t i o n c o e f f i c i e n t of 0.9367. T h i s example was r e v i e w e d t o p o i n t out how a r o c k mass c l a s s i f i c a t i o n s y s t e m c o u l d be d e v e l o p e d t o e v a l u a t e t h e r o c k mass b l a s t a b i l i t y . 4.3.4 D e t e r m i n a t i o n of t h e B l a s t a b i l i t y by S m a l l S c a l e  C r a t e r T e s t s The most l o g i c a l method o f d e t e r m i n i n g t h e b l a s t a b i l i t y o f t h e r o c k mass i s c e r t a i n l y by b l a s t i n g i t . E x p e r i m e n t s were c a r r i e d out by Bauer e t a l " 7 a t I.O.C. They d e v e l o p e d a r o c k mass b l a s t a b i l i t y i n d e x b a s e d on t h e optimum d e p t h r a t i o and t h e s t r a i n e n e r g y f a c t o r computed from c r a t e r t e s t s . In c r a t e r t e s t s , a s p h e r i c a l c h a r g e , a p p r o x i m a t e d by a l e n g t h t o d i a m e t e r r a t i o l e s s t h a n 6, i s d e t o n n a t e d a t d i f f e r e n t d e p t h s and t h e s c a l e d c r a t e r volume i s p l o t t e d as a f u n c t i o n o f t h e s c a l e d d e p t h of embedment ( F i g u r e 4 . 3 -5). The maximum volume o c c u r s a t t h e optimum d e p t h o f embedment Zo. The 1 50 1.6 1.5 1.4 1.3 1.2 K = 1.96-0.27 Ln(ERQD) I.I 2 i.o ac. P 0.9 o >- 0.8 m 0.7 3 0.6 CD 0.5 0.4 0.3 0.2 0.1 0.0 CORRECTION FACTORS FOR ESTIMATING JOINT STRENGTH ESTIMATION OF QUALITY ALTERATION FACTOR STRONG MEDIUM WEAK VERY WEAK 1.00 0.90 0.80 0,70 JL I * 0 10 20 30 40 50 60 70 80 90 ERQD =RQD* ALTERATION FACTOR 100 FIGURE 4.3-4 : BLASTABILITY FACTOR VS EQUIVALENT RQD. (after Borquez 4 5 ) 151 FIGURE 4.3-5 ! VARIATION OF BROKEN ROCK VOLUME WITH DEPTH OF EMBEDMENT FOR A CONCENTRATED CHARGE, (after Coates and Gyenge18) 1 52 e x p l o s i v e i s c o m p l e t e l y c h o k e d and d o e s not p r o d u c e any c r a t e r a t t h e c r i t i c a l d e p t h , Zc. T h e s e r e l a t i o n s a r e e x p r e s s e d by t h e f o l l o w i n g e q u a t i o n s : Zc = E ( W ) * * l / 3 Zo = A O E ( W ) * * 1 / 3 w i t h Zc = c r i t i c a l d e p t h Zo = optimum d e p t h E = s t r a i n e n e r g y f a c t o r ( r o c k mass c o n s t a n t ) W = c h a r g e w e i g h t Ao = optimum d e p t h r a t i o = Zo/Zc On t h i s b a s i s , t h e y d e f i n e d t h e b l a s t a b i l i t y as AoE. D u r i n g t h i s r e s e a r c h , t h e y a l s o c o n f i r m e d t h e e x i s t a n c e of two t y p e s of f a i l u r e d u r i n g b l a s t i n g : b r i t t l e and s h e a r ( p l a s t i c ) . F i g u r e 4.3-6a shows how t h e s t r a i n e n e r g y f a c t o r (E) c a n be u s e d t o p r e d i c t t h e t y p e o f f a i l u r e . M o v i n g t o t h e l e f t , r o c k s g e t s o f t e r ( p l a s t i c ) and c o n v e r s e l y g o i n g t o t h e r i g h t t h e y g e t h a r d e r ( b r i t t l e ) . The most i n t e r e s t i n g r e s u l t , however, i s t h e r e l a t i o n s h i p between t h e b l a s t a b i l i t y i n d e x and t h e s t r a i n e n e r g y f a c t o r ( F i g u r e 4.3-6b). T h i s f i g u r e shows t h a t a t b o t h e x t r e m e v a l u e s of E, t h e m a t e r i a l shows v e r y low b l a s t a b i l i t y and t h u s r e q u i r e s more e n e r g y p e r t o n of r o c k . F i n a l l y , t h e y d e v e l o p e d a r e l a t i o n s h i p between t h e powder f a c t o r and t h e s t r a i n e n e r g y f a c t o r ( F i g u r e 4 . 3 - 6 c ) . T h a t r e l a t i o n s h i p i s t a k i n g i n t o a c c o u n t t h e two major c h a r a c t e r i s t i c s t h a t i n f l u e n c e t h e b l a s t i n g r e s u l t s , t h e s t r u c t u r a l p r o p e r t i e s and t h e f a i l u r e 153 1.0 0.8 • >\, f \* A o 0 - 6 0.4 0.2 _SHEAR FAILURE BRITTLE FAILLURE DRILLING COST ——»-°C i i i i l l ) 1 2 3 4 5 6 F I G U R E 4.3-6a•• O P T I M U M D E P T H R A T I O , A © V S S T R A I N E N E R G Y F A C T O R , E (after Bauer et al 4 7) A 0 E 2 FIGURE-4.3-6b- B L A S T A B I L I T Y F A C T O R , 0 E , V S S T R A I N E N E R G Y F A C T O R , E (after Bauer et al47) 0.9 5 0.8 o £j 0.7 £ 0.6 oT Q 5 -P £ o-4 2 03 LU 0.2 a £ 0,1 o SOFT ROCKS HARD -BRITTLE ROCKS « 3.0 3,5 4.0 4.5 F I G U R E 4.3-6C ' P O W D E R F A C T O R V S S T R A I N E N E R G Y F A C T O R , E (after Bauer et al 4 7) 1 54 b e h a v i o u r . However, t h e d e t e r m i n a t i o n of t h e s t r a i n e n e r g y f a c t o r i s a l o n g and c o s t l y p r o c e s s . A l t h o u g h t h e r o c k c h a r a c t e r i z a t i o n methods, p r o p o s e d up t o now i n t h i s p a r a g r a p h , n u m e r i c a l l y e v a l u a t e t h e b l a s t a b i l i t y of t h e r o c k mass, t h e i r a c c u r a c y i s as v a r i a b l e a s t h e d e g r e e o f h o m o g e n e i t y of t h e r o c k . In a d d i t i o n , a l l r e q u i r e a d d i t i o n a l o p e r a t i o n s s u c h as r o c k t e s t i n g , s e i s m i c v e l o c i t y measurement, s t r u c t u r a l mapping o r c r a t e r t e s t s . 4.3.5 C h a r a c t e r i z a t i o n of t h e Rock Mass from t h e P e r f o r m a n c e  of P r o d u c t i o n R o t a r y D r i l l s S i n c e e v e r y h o l e has t o be d r i l l e d b e f o r e b e i n g b l a s t e d , t h e b l a s t i n g e n g i n e e r s h o u l d t a k e a d v a n t a g e o f a l l t h e i n f o r m a t i o n a v a i l a b l e a t t h i s s t a g e t o o p t i m i z e h i s d e s i g n . The c o s t s a r e minimum and t h e d a t a a r e numerous, so t h e r e i s no draw back i n r o c k mass t h a t p r e s e n t h i g h d e g r e e of i n h o m o g e n e i t y . In h a r d b r i t t l e r o c k , t h e r e i s a s i m i l i t u d e between t h e f a i l u r e i n d r i l l i n g ( r o l l e r - b i t , p e r c u s s i v e ) and i n b l a s t i n g . In b o t h c a s e s , t h e r o c k f a i l s under c o n c e n t r a t e d , n o n - u n i f o r m s t r e s s e s . C l o s e t o t h e v i c i n i t y o f t h e a p p l i e d f o r c e , t h e r o c k c o m p r e s s i v e s t r e n g t h i s overcome and t h e r o c k i s f i n e l y c r u s h e d . Away from t h a t zone, t h e r o c k f a i l s i n a b r i t t l e manner where t h e t e n s i l e s t r e s s r e a c h e s t h e t e n s i l e s t r e n g t h . The i n f l u e n c e of t h e s t r u c t u r a l p r o p e r t i e s on d r i l l i n g and b l a s t i n g i s more complex. M i c r o - s c a l e d i s c o n t i n u i t i e s i n f l u e n c e d r i l l i n g 155 p e r f o r m a n c e by a c t i n g as weakness p l a n e s s u c h as m a c r o - s c a l e d i s c o n t i n u i t i e s i n f l u e n c e b l a s t i n g . In b o t h c a s e s , t h e f a i l u r e mechanism i s i m p r o v e d . However, t h e i n f l u e n c e o f macro-d i s c o n t i n u i t i e s on d r i l l i n g p e r f o r m a n c e and t h e o v e r a l l e f f e c t of m i c r o - f i s s u r e s on b l a s t a b i l i t y need a more d e t a i l e d i n v e s t i g a t i o n . I t i s b e l i e v e d t h a t , f r o m a c e r t a i n l e v e l of i n t e n s i t y , m a c r o - s c a l e d i s c o n t i n u i t i e s improve d r i l l i n g p e r f o r m a n c e . M i c r o - f l a w s a r e s a i d t o i mprove f r a g m e n t a t i o n . The f i r s t a t t e m p t t o c o r r e l a t e t h e Rock Q u a l i t y Index w i t h t h e r o c k mass b e h a v i o r was p e r f o r m e d by T.E. L i t t l e " 8 i n 1975. On t h i s r e s e a r c h p r o j e c t , t h e c h a r a c t e r i z a t i o n o f t h e r o c k mass u s i n g b l a s t h o l e d r i l l s p e r f o r m a n c e was d i r e c t e d t o w a r d t h e d e s i g n o f s t a b l e p i t s l o p e . The i d e a was t h a t t h e RQI w o u l d p r o v i d e u s e f u l d a t a on t h e f u t u r e b e h a v i o u r o f t h e r o c k s l o p e , when b e i n g c o r r e l a t e d w i t h l i t h o l o g y , s t r u c t u r a l g e o l o g y and r o c k s t r e n g t h . In s u c h c a s e , t h e g e o t e c h n i c a l e n g i n e e r i n g d e p a r t m e n t , by m o n i t o r i n g t h e d r i l l p e r f o r m a n c e , would o b t a i n a q u a n t i t a t i v e measure of t h e r o c k q u a l i t y , d e t e r m i n e c r i t i c a l a r e a s and implement r e m e d i a l m e a s u r e s . The s t u d y was p e r f o r m e d i n t h r e e open p i t mines i n B r i t i s h C o l u m b i a . However, t h e r e p o r t c o n c l u d e d t h a t t h e Rock Q u a l i t y Index was not r e l i a b l e enough f o r p r e d i c t i n g t h e s l o p e b e h a v i o u r . F i r s t , t h e a c c u r a c y of t h e d a t a i n p u t was d e f i n e d as n o t s u f f i c i e n t enough t o p e r m i t v a l u a b l e i n t e r p r e t a t i o n of t h e r o c k mass b e h a v i o u r . L i t t l e a l s o f o u n d t h a t t h e RQI was p r i m a r i l y r e l a t e d t o t h e r o c k s t r e n g t h but n o t t o a c t u a l s t r u c t u r e . 1 56 H i g h e r v a l u e s o f RQI were e n o u n t e r e d i n h a r d c o m p e tent r o c k s w h i l e l o w e r v a l u e s were c o r r e l a t e d w i t h f a u l t z o n e s . U n f o r t u n a t e l y , h a r d dyke r o c k s , a t one s i t e , showed a h i g h RQI even t h o u g h t h e f r a c t u r i n g was i n t e n s e . The r e p o r t s t a t e d t h a t t h e r e was no d i r e c t r e l a t i o n s h i p between RQI v a l u e s and g e o l o g y . F i n a l l y , d i f f e r e n t RQI v a l u e s were o b t a i n e d i n a d j a c e n t b l a s t h o l e s when d r i l l e d w i t h d i f f e r e n t d r i l l m o d e l s e q u i p p e d w i t h d i f f e r e n t b i t s i z e s , a l t h o u g h , a t one s i t e , d i f f e r e n t d i a m e t e r h o l e s y i e l d e d t h e same RQI when d r i l l e d by t h e same d r i l l m o d e l . M o r e o v e r , i t was f o u n d t h a t s t e e l t o o t h b i t s p r o d u c e h i g h e r RQI t h a n t u n g s t e n c a r b i d e i n s e r t b i t s , a s p r e d i c t e d by t h e t h e o r y . A d e t a i l e d r e p o r t of t h e c o n c l u s i o n s of t h i s r e s e a r c h p r o j e c t a r e g i v e n i n A p p e n d i x IV. L i t t l e s u g g e s t e d t h a t , b e c a u s e o n l y major t r e n d s a r e d e t e c t e d by t h e RQI, i t s a p p l i c a t i o n t o s l o p e d e s i g n was l i m i t e d . The use o f a d r i l l p e r f o r m a n c e r e c o r d e r would p r o d u c e b e t t e r q u a l i t y i n p u t d a t a , b u t a t h i g h e r c o s t and i n c r e a s e d c o m p l e x i t y . He c o n c l u d e d t h a t b a s i c g e o t e c h n i c a l d a t a g a t h e r i n g methods t h e r e f o r e r e m a i n t h e b e s t a l t e r n a t i v e . However, L i t t l e b e l i e v e d t h a t t h e Rock Q u a l i t y Index would be a u s e f u l t o o l i n p r e d i c t i n g e n e r g y r e q u i r e m e n t s i n d r i l l i n g , b l a s t i n g and g r i n d i n g . No o t h e r r e s e a r c h was done on t h e Rock Q u a l i t y Index u n t i l L e i g h t o n " r e v i v e d t h i s c o n c e p t i n t h e c u r r e n t r e s e a r c h p r o j e c t . B a s e d on L i t t l e ' s c o n c l u s i o n s , t h r e e major m o d i f i c a t i o n s were d e r i v e d : 157 1) Improve q u a l i t y and a c c u r a c y o f d r i l l p e r f o r m a n c e r e c o r d s . 2) R a t h e r t h a n u s i n g t h e RQI t o d e t e r m i n e domain b o u n d a r i e s , i t was s i m p l y u s e d t o c l a s s i f y t h e r o c k q u a l i t y w i t h i n t h e domain b o u n d a r i e s a l r e a d y e s t a b l i s h e d by c o n v e n t i o n a l methods. 3) Keep domain a r e a s l a r g e enough t o m i n i m i z e e f f e c t o f b i t wear, s h i f t c h a n g e s , d r i l l e r b i a s , e t c . L e i g h t o n t h e n d e v e l o p e d a r e l a t i o n s h i p between t h e Rock Q u a l i t y Index and t h e c o n t r o l l e d powder f a c t o r a t A f t o n Mine ( F i g u r e 4 . 3 - 7 ) . H i s s t u d y showed t h a t t h e p e r f o r m a n c e of t h e b l a s t h o l e d r i l l s r e f l e c t s t h e r o c k mass p r o p e r t i e s and s t r u c t u r a l g e o l o g y ; t h a t , when c a r e f u l l y m o n i t o r e d , t h e h y d r a u l i c down p r e s s u r e and p e n e t r a t i o n r a t e w o u l d p r o d u c e an i n d e x of t h e r o c k mass c o n d i t i o n and t h a t t h e a v e r a g e RQI v a l u e w i t h i n e a c h domain was r e p r e s e n t a t i v e of t h e d i s t r i b u t i o n . The v e r y e n c o u r a g i n g r e s u l t s have prompted t h e d e v e l o p m e n t of a c o n t i n u i t y of t h e r e s e a r c h p r o j e c t . The r e p o r t of t h e p r e s e n t i n v e s t i g a t i o n i s p r o d u c e d i n t h e f o l l o w i n g c h a p t e r s . 158 12 -10-8 -0-L c E (A a 500 _ Imperial - 400 300 200 100 S.I.: in (powder factor)=R Q ' 7 ~ 2 4 ' 9 In (powder factor) = RQI-885 315 0.025 0.050 Q075 OJOO POWDER FACTOR 0.125 kg.ANFO Tonne FIGURE4.3-7' PROPOSED CORRELATION BETWEEN ROCK QUALITY INDEX AND POWDER FACTOR AT AFTON MINE.(after Leighton4) 159 4.4 SUMMARY The a u t h o r would l i k e t o e m p h a s i z e t h e f a c t t h a t t h e b l a s t i n g p r o c e d u r e d i r e c t l y i n f l u e n c e s t h r e e o t h e r a s p e c t s of any open p i t m i n i n g o p e r a t i o n : t h e s l o p e s t a b i l i t y , t h e p r o d u c t i v i t y and t h e equipment m a i n t e n a n c e . The d i r e c t b l a s t i n g c o s t i s v e r y s m a l l compared w i t h t h e a c t u a l t o t a l o p e r a t i o n c o s t s . T h e r e f o r e , a s l i g h t i n c r e a s e i n t h e b l a s t i n g c o s t c an be j u s t i f i e d by o v e r a l l s a v i n g s t h a t w i l l r e s u l t . The optimum e n e r g y f a c t o r t o be u s e d i n a g i v e n domain i s a f u n c t i o n o f a wide r a n g e o f p a r a m e t e r s . T h i s i s t h e r e a s o n why t h e d e s i g n powder f a c t o r a p p r o a c h i s s u c c e s s f u l . Mine o p e r a t o r s a l w a y s a p p r e c i a t e s t a n d a r d p r a c t i c e s b u t few o f them a p p l y i t t o b l a s t i n g . The d e s i g n powder f a c t o r a p r o a c h r e s u l t s i n u n i f o r m e x p l o s i v e d i s t r i b u t i o n w i t h i n t h e p a t t e r n a n d / o r t h e domains when t h e b l a s t p a t t e r n e x t e n d s o v e r t h e domain b o u n d a r i e s . I t i s a l s o i m p o r t a n t t o c o n s i d e r t h e w e i g h t s t r e n g t h o f t h e e x p l o s i v e u t i l i z e d and e x p r e s s t h e powder f a c t o r c o n s i s t a n t l y on a r e l a t i v e e n e r g y b a s i s i n t h e i n d u s t r y ( i e . , r e l a t i v e t o ANFO, w e i g h t s t r e n g t h = 100). Good r e c o r d s of b l a s t p r o c e d u r e s a r e v e r y i m p o r t a n t . They p e r m i t one t o r e v i e w and a p p r e c i a t e t h e d e s i g n m o d i f i c a t i o n s . The use o f a p o l a r o i d camera t o o b t a i n a s e t of b l a c k and w h i t e p h o t o g r a p h s o f t h e b l a s t r e s u l t s c an be j u s t i f i e d . The b l a s t i n g f i l e a l s o c o n t a i n s : 1) - p l a n view of b l a s t p a t t e r n ( bench p l a n ) 160 - t y p e of e x p l o s i v e s - e x p l o s i v e l o a d and d e s i g n powder f a c t o r -- f r o n t row -- p r o d u c t i o n rows — b u f f e r r o w ( s ) - n e t powder f a c t o r ( t o t a l b l a s t volume i n c l u d i n g f r e e d i g g i n g ) - d e l a y p a t t e r n and i n i t i a t i o n s e q uence - d r i l l i n g r e c o r d s - c h o k e d or f r e e f a c e d 2) - l o c a t i o n o r domain - s h o r t d e s c r i p t i o n of t h e g e o l o g i c a l f e a t u r e s — r o c k t y p e , f r a c t u r e i n t e n s i t y , a l t e r a t i o n — m a j o r s d i s c o n t i n u i t i e s i n r e l a t i o n w i t h t h e d i r e c t i o n of b l a s t i n g -- g r o u n d w a t e r (number of wet h o l e s , pumped h o l e s , s l u r r y h o l e s , e t c . ) 3) - b l a s t e v a l u a t i o n form and p h o t o g r a p h s E x c e s s i v e Good F a i r Poor N i l Throw L i f t ( h e a v e ) F r a g m e n t a t i o n 161 P r e s e n t O c c a s i o n a l N i l C r a t e r i n g T o e ( s ) O v e r s i z e s S h o t g u n s V e r y Good F a i r Tough D i g g i n g M i s f i r e Number E x p l a n a t i o n Smoke C o l o r 4) - P i t w a l l c o n d i t i o n s 1 t o 5 ( s e e T a b l e 3) 5) - Remarks S i n c e good b l a s t i n g r e s u l t s seems t o v a r y f r o m one s i t e t h e n e x t , f r o m one e v a l u a t o r t o t h e o t h e r , r a t i n g h as t o be d e f i n e d r e l a t i v e t o a c e r t a i n s t a n d a r d . F i g u r e 4.4-1 shows f e a t u r e s o f a s a t i s f a c t o r y p r o d u c t i o n b l a s t . The f o l l o w i n g c r i t e r i a must be met: 162 TABLE 3 LEVELS OF BLASTING DAMAGES COMMONLY OBSERVED ON PIT 30 WALLS ( a f t e r Ashby ) Observed Conditions of the Wall Arbitrary Damage Level Joints & Blocks Dip Angle Appearance and Condition of Face Digging Condition at Face (E l e c t r i c Shovel) Slight Moderate 3 Heavy Joints closed, i n f i l l i n g s t i l l welded. Weak j o i n t i n -f i l l i n g i a broken, occas-ional blocks and joints s l i g h t l y displaced. ' Some joints dislocated and displaced. >75° cir c u l a r sections of wall control holes seen. >65° Face is smooth, some hole sec-tions seen. Minor cracks. >65° Minor spalls from face. Radial cracking seen. Scars of shovel teeth seen in softer formation, further digging not pr a c t i c a l . Some free digging possible, but teeth "chatter." Free digging possible for <1.5m « 5 f t ) with some effort. 4 Severe Face shattered, >55' joints dislocated. Face irregular, Some blocks some spalls, some backbreak cracks. Free digging possible for <3m « 1 0 f t ) . 5 Blocks dislocated Extreme and disoriented. Blast-induced fines or crushing observed. 55°>37° Face highly irregular, heavy spalling from face. Large back-break cracks. Extensive free digging possible for >3m (>10 f t ) . FIGURE 4.4-1 •  FEATURES OF A SATISFACTORY BLAST, (after Hoek and Bray2) 1 64 1) U n i f o r m , m o derate movement o f t h e t o e burden w i t h o u t f l y r o c k r u b b l e . 2) A s l i g h t r i s e a l o n g t h e muck p i l e c r e s t . 3) No s u r f a c e c r a t e r i n g or f l a t a r e a s . 4) A s l i g h t d r o p a l o n g t h e l a s t row o f h o l e s ( b u f f e r h o l e s c o n t r o l l e d b l a s t ) 5) No b r o k e n g r o u n d beyond t h e f i n a l d i g l i n e . 6) No d i g g i n g p r o b l e m s . 7) U n i f o r m f r a g m e n t a t i o n . 8) A c l e a n w a l l w i t h minimum r a v e l l i n g p o t e n t i a l . A p p e n d i x V l i s t s a s i m p l e b l a s t m o d i f i c a t i o n p r o c e d u r e . 165 4.5 REFERENCES 1. 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ASHBY, J.P.; P r o d u c t i o n B l a s t i n g and D e velopment of Open P i t S l o p e s , P r o c e e d i n g s , 3 r d I n t e r n a t i o n a l C o n f e r e n c e on S t a b i l i t y i n S u r f a c e M i n i n g , Brawner E d i t o r , AIME, 1982 31. DICK, R.A.; F a c t o r s i n S e l e c t i n g and A p p l y i n g C o m m e r c i a l E x p l o s i v e s and B l a s t i n g A g e n t s , USBM 1968 ( i n f . c i r c . 8405) 32. MANON, J . J . ; How t o S e l e c t an E x p l o s i v e o r B l a s t i n g A gent f o r a S p e c i f i c J o b , E n g i n e e r i n g and M i n i n g J o u r n a l , May, 1977 33. THORNBY, G.M.; FUNK, A.G.; A l u m i n i z e d B l a s t i n g A g e n t s , P r o c e e d i n g s o f t h e 7 t h c o n f e r e n c e on b l a s t i n g and 169 e x p l o s i v e t e c h n i q u e s , S o c i e t y o f E x p l o s i v e s E n g i n e e r s , P h o e n i x , 1981 34. MOHANTY, B.; E n e r g y , S t r e n g t h and P e r f o r m a n c e , and T h e i r I m p l i c a t i o n s i n R a t i n g C o m m e r c i a l E x p l o s i v e s , P r o c e e d i n g s of t h e 7 t h c o n f e r e n c e on b l a s t i n g and e x p l o s i v e t e c h n i q u e s , S o c i e t y of E x p l o s i v e s E n g i n e e r s , P h o e n i x , 1981 35. DRURY, F.C.; WESTMAAS, D.J.; C o n s i d e r a t i o n s A f f e c t i n g t h e S e l e c t i o n and Use of Modern C h e m i c a l E x p l o s i v e , P r o c e e d i n g s o f t h e 4 t h c o n f e r e n c e on b l a s t i n g and e x p l o s i v e t e c h n i q u e s , S o c i e t y o f E x p l o s i v e s E n g i n e e r s , L o u i s i a n a , 1978 36. BUCHTA, L.; Open P i t B l a s t i n g - How t o Improve R e s u l t s , W o r l d M i n i n g , June 1982 37. 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LANG, L.C.; B u f f e r B l a s t i n g T e c h n i q u e s i n Open P i t M i n e s , S e c o n d O p e n - p i t O p e r a t o r s C o n f e r e n c e and T h i r d A n n u a l M e e t i n g of CIM D i s t r i c t S i x , O c t o b e r 1978 42. MUNOZ-CASAYUS, J.M.; A p p r o c h e T e c h n i q u e de l a D e t e r m i n a t i o n des P a r a m e t r e s de S a u t a g e dans l e s M i n e s a C i e l O u v e r t , 3eme S e s s i o n d ^ E t u d e s u r l e s T e c h n i q u e s de S a u t a g e , L a v a l U n i v e r s i t y , 1980 43. HEINEN, R.H.; DIMOCK, R.R.; The Use o f S e i s m i c Measurements t o D e t e r m i n e t h e B l a s t a b i l i t y of Rock, P r o c e e d i n g s of t h e 2nd c o n f e r e n c e on e x p l o s i v e and b l a s t i n g t e c h n i q u e , S o c i e t y o f E x p l o s i v e s E n g i n e e r s , L o u i s v i l l e , 1976 44. BROADBENT, C.; P r e d i c t a b l e B l a s t i n g w i t h I n - S i t u S e i s m i c S u r v e y s , M i n i n g E n g i n e e r i n g , SME, A p r i l 1974 45. BORQUEZ, G.U.; E s t i m a t i n g D r i l l i n g and B l a s t i n g C o s t s - An A n a l y s i s and P r e d i c t i o n M o d e l , E n g i n e e r i n g and M i n i n g J o u r n a l , J a n u a r y 1981 46. CHRISTENSEN, J.B.; OLSEN, R.S.; On t h e R e s i s t a n c e t o B l a s t i n g i n T u n n e l i n g , P r o c e e d i n g s , 2nd C o n g r e s s I n t . S o c . Rock. Mech., B e l g r a d e , 1970 47. BAUER, A., e t a l ; How I.O.C. P u t s C r a t e r R e s e a r c h t o Work, E n g i n e e r i n g and M i n i n g J o u r n a l , September 1965 48. L I T T L E , T.E.; E v a l u a t i o n o f a Rock Q u a l i t y Index Based on R o t a r y D r i l l P e r f o r m a n c e , B.A.Sc. T h e s i s , D e p t . of G e o l o g i c a l E n g i n e e r i n g , U.B.C., 1976 171 CHAPTER 5 1 72 5.0 FI E L D RESEARCH PROJECT D u r i n g t h e summer of 1983, t h e c o r r e l a t i o n between t h e Rock Q u a l i t y Index and t h e powder f a c t o r was t e s t e d i n t h r e e mine s i t e s of B r i t i s h C o l u m b i a ( F i g u r e 5 . 0 - 1 ) . T h i s c h a p t e r , w h i c h r e p o r t s t h e f i n d i n g s of t h e f i e l d work, i s d i v i d e d i n t o s i x m a j o r s s e c t i o n s . The f i r s t s e c t i o n r e v i e w s t h e i n v e s t i g a t i o n p e r f o r m e d w i t h t h e d r i l l p e r f o r m a n c e r e c o r d e r on i m p r o v e d d a t a q u a l i t y . The n e x t t h r e e s e c t i o n s p r e s e n t t h e r e s u l t s o f t h e r e s e a r c h p r o j e c t a t t h e t h r e e mine s i t e s . The l a s t two c o v e r t h e d i s c u s s i o n , i n f e r e n c e s and f u r t h e r r e s e a r c h . At t h e s i t e s , t h e Rock Q u a l i t y Index was c o m p i l e d f o r e v e r y b l a s t h o l e , w i t h i n t h e b l a s t i n g d o m a i n s , from t h e b i t p e r f o r m a n c e r e c o r d s ( d r i l l e r l o g s ) a n d / o r from t h e r e c o r d e d c h a r t s . A c c o r d i n g t o t h e work o f L e i g h t o n 1 , t h e mean o r a v e r a g e v a l u e was t a k e n a s r e p r e s e n t a t i v e o f t h e RQI d i s t r i b u t i o n o f t h e doma i n s . E f f o r t s were made t o keep t h e b l a s t i n g domains l a r g e enough, a l t h o u g h t h i s was not a l w a y s p o s s i b l e . The a u t h o r d i d not r e s t r i c t t h e d e t e r m i n a t i o n o f t h e r o c k mass b l a s t a b i l i t y o n l y t o p e r i m e t e r b l a s t i n g . A c c o r d i n g t o A s h b y 2 , c o n t r o l l e d b l a s t i n g s t a r t s w i t h p r o d u c t i o n b l a s t i n g . As a m a t t e r of f a c t , many o p e r a t o r s c o n s i d e r t h a t t h e y a r e d o i n g w a l l c o n t r o l b l a s t i n g when t h e y s h o o t a f o u r row p a t t e r n , a l o n g t h e p e r i m e t e r , w i t h d o w n - t h e - h o l e d e l a y s . In t h e m a j o r i t y of t h e c a s e s , t h e damage t o t h e f i n a l w a l l were a l r e a d y c r e a t e d by the l a s t p r o d u c t i o n b l a s t s i n t h e a r e a , i n c l u d i n g t h e ones on 173 FIGURE 5.0-h LOCATIONS OF THE MINES WHERE THE RQI STUDIES WERE CARRIED OUT. 174 t h e p r e v i o u s b e n c h e s . C o n s e q u e n t l y , i t was f e l t t h a t t h e RQI a p p r o a c h s h o u l d a l s o be a p p l i e d t o p r o d u c t i o n b l a s t i n g . M o r e o v e r , t h e e x t e n t of t h e c o r r e l a t i o n was t e s t e d o v e r a wide r a n g e o f r o c k mass w i t h v a r i o u s c o m b i n a t i o n s o f d r i l l m o d e l / b i t s i z e . B l a s t p e r f o r m a n c e s were r a t e d as u n d e r l o a d e d , optimum and o v e r l o a d e d . 0 1 75 5.1 DRILL PERFORMANCE RECORDERS IN THE MINING INDUSTRY D r i l l p e r f o r m a n c e r e c o r d e r s a r e b e i n g u s e d i n t h e m i n i n g i n d u s t r y f o r many y e a r s and a r e h i g h l y r e l i a b l e . The i n s t a l l a t i o n of a r e c o r d e r t o m o n i t o r b l a s t h o l e d r i l l p e r f o r m a n c e i s a c o s t - s a v i n g i n v e s t m e n t i n m i n i n g o p e r a t i o n s . I n t r o d u c e d a s a d r i l l i n g t o o l , t h e r e a r e g e n e r a l l y w e l l a c c e p t e d by t h e p e r s o n n e l . A d r i l l p e r f o r m a n c e r e c o r d e r p r o v i d e s t h e mine o p e r a t o r w i t h a permanent r e c o r d of t h e d r i l l i n g p r o c e d u r e and t h u s p e r m i t s c o m p r e h e n s i v e d r i l l i n g o p t i m i z a t i o n p r o g r a m s . The p r i n c i p a l d r i l l i n g p a r a m e t e r s t h a t c an be m o n i t o r e d a r e t h e b i t d e p t h , p u l l d o w n t h r u s t or w e i g h t , r o t a r y s p e e d , d e v e l o p e d t o r q u e and p e n e t r a t i o n r a t e . In a d d i t i o n , o t h e r p a r a m e t e r s s u c h as t h e v e r t i c a l a c c e l e r a t i o n of t h e d r i l l p i p e c an a l s o be m o n i t o r e d . The p r i n c i p a l a d v a n t a g e s o f d r i l l p e r f o r m a n c e r e c o r d e r s a r e : 1 ) t o a s s i s t t h e d r i l l e r t o c o n t r o l t h e o p e r a t i o n 2) t o be u s e d as an i n s t r u c t i o n a l t o o l f o r t h e t r a i n i n g of new o p e r a t o r s 3) t o p e r m i t a s s e s m e n t o f t h e d r i l l i n g c r ews 4) t o p r o v i d e e a r l y w a r n i n g o f m e c h a n i c a l f a i l u r e 5) t o a v o i d o v e r - d r i l l i n g 6) t o c h a r a c t e r i z e t h e r o c k mass b e i n g d r i l l f o r g e o l o g i c a l l o g g i n g , b l a s t o p t i m i z a t i o n o r g r i n d i n g r a t e e v a l u a t i o n p u r p o s e s The f i r s t f o u r a d v a n t a g e s a r e w e l l c o v e r e d i n t h e 176 l i t e r a t u r e 3 and w i l l n o t be r e v i e w e d h e r e . The f i f t h p o i n t i s e a s y t o u n d e r s t a n d . In m a j o r open p i t o p e r a t i o n s , t h e c o s t of o v e r - d r i l l i n g i s i n e x c e s s o f t h e c o s t of i n s t a l l a t i o n of a d r i l l p e r f o r m a n c e r e c o r d e r i n e a c h d r i l l r i g . The a p p l i c a t i o n o f a d r i l l p e r f o r m a n c e r e c o r d e r t o t h e d r i l l i n g c h a r a c t e r i z a t i o n o f t h e r o c k mass i s more r e c e n t . Hagan" s u g g e s t e d t h e use of d r i l l p e r f o r m a n c e r e c o r d e r s i n s u r f a c e c o a l m i n i n g where t h e o v e r b u r d e n s t r a t a c o n s i s t s of a d j a c e n t beds of h i g h l y v a r i a b l e s t r e n g t h . He p r o p o s e d t h e m o n i t o r i n g of t h e p e n e t r a t i o n r a t e a n d / o r t h e t o r q u e a l o n g t h e b l a s t h o l e d e p t h t o o p t i m i z e t h e b l a s t e n g i n e e r i n g . A l t h o u g h he a c k n o w l e d g e d t h e f a c t t h a t v a r i a t i o n s i n t h e p e n e t r a t i o n r a t e r e f l e c t t h e r e l a t i v e e a s e w i t h w h i c h t h e v a r i o u s b l o c k s can be f r a g m e n t e d by b l a s t i n g and t h e optimum d i s t r i b u t i o n o f e x p l o s i v e s and stemming m a t e r i a l s w i t h i n t h e b l a s t h o l e , he c o n s i d e r e d t h a t a c o m p a r i s o n o f p e n e t r a t i o n r a t e s w i l l not u s u a l l y r e f l e c t t h e r e l a t i v e e a s e o f b l a s t i n g r o c k s w h i c h e x h i b i t e q u a l r o c k s u b s t a n c e s t r e n g t h but d i s s i m i l a r mean s p a c i n g s between d i s c o n t i n u i t i e s ( F i g u r e 5.1-1) O t h e r methods a r e a l s o a v a i l a b l e t o c h a r a c t e r i z e t h e r o c k mass. The S o c i e t e N a t i o n a l e des P e t r o l e s d ' A q u i t a i n e ( F r a n c e ) has d e v e l o p e d a dynamic t h e o r y b a s e d on t h e c r e a t i o n , by t h e t r i c o n e b i t , of l o n g i t u d i n a l v i b r a t i o n s and t h e t r a n s m i s s i o n o f t h e s e v i b r a t i o n s t h r o u g h t h e d r i l l s t e m 5 . By a n a l y s i n g t h e v i b r a t i o n s a t t h e t o p of t h e d r i l l p i p e , i t i s p o s s i b l e t o o b t a i n d a t a on t h e r o c k b e i n g d r i l l e d . The i n f o r m a t i o n i s 177 O.I 0.2 0.3 0.4 MEAN SPACING BETWEEN DISCONTINUITIES (m) 0.5 FIGURE 5.l-l= EFFECT OF MEAN DISCONTINUITY SPACING ON A) EASE OF BLASTING B) PENETRATION RATE (after Hagan4) 1 78 r e l a t e d t o t h e h a r d n e s s c h a r a c t e r i s t i c s of t h e r o c k . T h i s l o g g i n g method was a b l e t o p i c k - u p t h i n , h a r d s t r e a k s t h a t a r e o b s c u r e d i n t h e a v e r a g i n g p r o c e s s i n v o l v e d i n t h e s o n i c l o g . The a p p l i c a t i o n o f t h i s t e c h n i q u e t o t h e b l a s t h o l e i n d u s t r y t o p e r m i t t h e p r e d i c t i o n of e x p l o s i v e c o n s u m p t i o n has n o t y e t been d e m o n s t r a t e d . However, t h e i n s t r u m e n t a t i o n i s a v a i l a b l e i n N o r t h A m e r i c a and r e a d y t o t e s t 6 . In t h i s r e s e a r c h p r o j e c t , a l t h o u g h t h e c h a r a c t e r i z a t i o n of t h e r o c k mass i s b a s e d on p a r a m e t e r s t h a t a r e n o r m a l l y c o l l e c t e d by t h e mine management, i t was d e c i d e d t o i n v e s t i g a t e t h e e f f e c t of t h e a c c u r a c y o f t h e d a t a i n p u t on t h e RQI. L e i g h t o n 1 has s u g g e s t e d t h a t t h e q u a l i t y o f t h e d a t a i n p u t w o u l d be i m p r o v e d when u s i n g a d r i l l p e r f o r m a n c e r e c o r d e r . At two o f t h e t h r e e m i n i n g s i t e s , i t was p o s s i b l e t o a t t a c h a " G e o l o g r a p h " pen r e c o r d e r model MOR I I I t o one o f t h e B u c y r u s E r i e d r i l l s . The i n s t r u m e n t r e c o r d e d , on a c h a r t , t h e v a r i a t i o n s o f t h e a p p l i e d w e i g h t on t h e b i t and t h e b i t d e p t h a s a f u n c t i o n o f t i m e ( F i g u r e 5 . 1 - 2 ) . The o b t a i n e d d a t a were u s e d t o compute t h e Rock Q u a l i t y I n d e x ; t h e n t e r m e d RQI-RECORDER and t o compare i t w i t h t h e RQI-LOGS computed from t h e d r i l l e r l o g s . Many i n t e r e s t i n g o b s e r v a t i o n s a r e d e r i v e d f r o m t h i s i n v e s t i g a t i o n . A. From a p r a c t i c a l p o i n t o f v i e w , t h e i n t e r p r e t a t i o n o f t h e c h a r t s i s l e n g t h l y . The d r i l l i n g t i m e i s g e n e r a l l y w e l l r e c o r d e d and s i m p l e t o c o m p i l e . The a p p l i e d w e i g h t , p r i n c i p a l v a r i a b l e i n t h e d r i l l i n g p r o c e s s , p r o d u c e s a FIGURE 5.1-2 : RECORDED CHART ( Lornex) 180 g r a p h t h a t i s l e s s e a s y t o i n t e r p r e t . E s t i m a t i o n o f an a v e r a g e v a l u e i n t r o d u c e s a b i a s . The d e t e r m i n a t i o n of t h e d r i l l e d d e p t h , f r o m t h e c h a r t s , i s v e r y d i f f i c u l t and c o n s e q u e n t l y , i t was p r e f e r r e d t o use t h e d e p t h r e c o r d e d by t h e d r i l l e r s on t h e b i t p e r f o r m a n c e l o g s . When t h e d r i l l i n g p r o c e d u r e i s not c o n t i n u o u s w i t h i n a g i v e n b l a s t h o l e , t h e g r a p h p r o d u c e d i s h i g h l y i r r e g u l a r . M o r e o v e r , i f t h e d r i l l e r moved t h e d r i l l p i p e w i t h o u t b r i n g i n g t h e d r i l l p e r f o r m a n c e r e c o r d e r t o a s t a n d - b y p o s i t i o n , t h e d r i l l e d d e p t h was r e c o r d e d i n t h e upward d i r e c t i o n t o o . C a v i n g s i t u a t i o n s a l s o p r o d u c e d a wide v a r i a t i o n i n t h e a p p l i e d w e i g h t . In t h e s e c o n d i t i o n s , t h e combined e f f e c t s made t h e d a t a u s e l e s s . B. T e c h n i c a l l y , t h e d r i l l p e r f o r m a n c e r e c o r d e r i s a v e r y u s e f u l p i e c e of equipment on a d r i l l r i g . Many d r i l l e r s have a p p r e c i a t e d t h e p r e s e n c e o f t h e d e p t h meter and t h e a v a i l a b i l i t y of a g r a p h i c a l r e p r e s e n t a t i o n o f t h e i r d r i l l i n g p r a c t i c e . C o n c e r n i n g t h e Rock Q u a l i t y Index, c o m p a r i s o n of t h e c o m p i l e d d a t a shows t h a t t h e RQI-LOGS a r e s l i g h t l y h i g h e r t h a n t h e RQI-RECORDER. RQI v a l u e s c o m p i l e d from t h e d r i l l p e r f o r m a n c e l o g s o v e r e s t i m a t e t h e t o u g h n e s s of t h e r o c k . T h i s i s due t o t h e f a c t t h a t most of t h e d r i l l e r s r e c o r d e d t h e l a r g e r down p r e s s u r e a p p l i e d w h i l e , i n r e a l i t y , t h e a v e r a g e down p r e s s u r e o v e r a g i v e n ^ b l a s t h o l e i s g e n e r a l l y l o w e r . In a d d i t i o n , t h e d r i l l i n g t i m e i s r o u n d e d t o t h e n e a r e s t f i v e m i n u t e s by t h e 181 m a j o r i t y of t h e d r i l l e r s . The r e l a t i o n s h i p between RQI-LOGS and RQI-RECORDER i s n o t a s i m p l e one. F i g u r e 5.1-3 i s a p l o t of t h e d i f f e r e n c e between RQI-LOGS and RQI-RECORDER as a f u n c t i o n of RQI-LOGS. I t seems t h a t t h e a v e r a g e d i f f e r e n c e i n c r e a s e w i t h t h e v a l u e o f RQI-LOGS up t o a peak and them seems t o be r e d u c e d s l i g h t l y . The r e l a t i o n s h i p i s b e t t e r r e p r e s e n t e d on t h e h i s t o g r a m of f i g u r e 5.1-4. I t s u g g e s t s t h a t t h e o v e r e s t i m a t i o n , or b i a s , f r o m t h e d r i l l e r l o g s i s a f u n c t i o n of t h e r o c k q u a l i t y i t s e l f . However, a n a l y s i s o f t h e r e s u l t s f r o m E q u i t y S i l v e r mine shows t h a t t h e r a t i o RQI-LOGS/RQI-RECORDER i s c o n s t a n t from a domain t o t h e o t h e r , a l t h o u g h t h e f o u r domains c o n s i d e r e d were a l l o c a t e d RQI v a l u e s r a n g i n g from 36 t o 44. D r i l l p e r f o r m a n c e r e c o r d e r s a c c u r a t e l y m o n i t o r t h e d r i l l i n g p r o c e d u r e . However, from t h e a u t h o r ' s e x p e r i e n c e , t h e use o f a d r i l l p e r f o r m a n c e r e c o r d e r i n r e l a t i o n w i t h t h e g a t h e r i n g of v a l u a b l e d a t a f o r t h e d e t e r m i n a t i o n o f t h e Rock Q u a l i t y Index s h o u l d be s i m p l i f i e d t o a p o i n t where t h e manual c o m p i l a t i o n o f t h e d a t a becomes s u p e r f l o u s . In a d d i t i o n , t h e s y s t e m s h o u l d combine an a u t o m a t i c c o n t r o l d e v i c e t h a t w i l l b r i n g t h e r e c o r d e r on s t a n d - b y when t h e d r i l l p i p e i s moved up. F o r example, a c o m p u t e r i z e d m o n i t o r i n g s y s t e m t h a t i n t e g r a t e s RQI f r o m i n s t a n t a n e o u s p e n e t r a t i o n r a t e and w e i g h t d a t a c o l l e c t e d a t r e g u l a r t i m e i n t e r v a l s d u r i n g t h e d r i l l i n g p r o c e s s ( i e . , A t = l 5 , 30, 60 s e c ) . The d a t a c o u l d be s t o r e d 182 o o o o o o U J o z Ul oc ui u. u. o si o d ( 0 o 6 ro O H o ro i O d c E I vi O d - i - d I to o d o CM o d I o d I D.D i 0.0 0 CD rm 0 ° © C D 0 m CD o CD ° Q CD CD 00 O . Q 0 0 _ J j , ( | | I 20.0 40.0 60.0 80.0 < . < • _J I L l "1 lbs-min , 100.0 — — ( t l O O O ) _, kg-mln 30.0 60.0 RQI 90.0 LOGS 120.0 150.0 m. (tlOOO) FIGURE 5.1-3 ; COMPUTER PLOT OF THE DIFFERENCE BETWEEN RQI-LOGS AND RQJ.-REC AS A FUNCTION OF RQI-LOGS 183 o U J oc I o DC I O O o DC U J O z U J oc Ul u. u. Q U J O < Ul 3 8 O o o o £ i c 1 I (ft 28-24-20-16-8-20-| 18-16-14-12-10-8-6-4-2-0-•2 J 0 20 30 40 50 60 70 80 90 Ibs-mln ft. {XI000) 30 60 90 FIGURE 5.1-4= HISTOGRAM OF THE AVERAGE DIFFERENCE BETWEEN RQI-LOG AND RQI-REC AS A FUNCTION OF RQI-L0G. 1 84 on d i s k e t t e s o r t a p e s i n a f o r m a t t h a t i s c o m p a t i b l e w i t h an o f f i c e m i c r o - c o m p u t e r . 185 5.2 EQUITY SILVER MINE 5.2.1 Summary of t h e G e o l o g y The E q u i t y S i l v e r Mine i s l o c a t e d 35Km (22 m i l e s ) s o u t h e a s t o f t h e town o f H o u s t o n , B.C., and a p p r o x i m a t e l y 580 a i r Km (360 m i l e s ) n o r t h - n o r t h e a s t of V a n c o u v e r . The e l e v a t i o n o f t h e mine s i t e i s a p p r o x i m a t e l y 1300 m (4265 f t ) . The d e p o s i t i s d i v i d e d i n t o two z o n e s , t h e Main zone and t h e S o u t h e r n T a i l z o n e . M i n i n g o f t h e S o u t h e r n T a i l o r e b o d y commenced i n A p r i l 1980 w i t h m i l l f e e d r a t e of 5500 t o n n e / d a y (6060 S . t o n / d a y ) I t was s c h e d u l e d t o be mined out by t h e end o f 1983. The g e o l o g y has been d e s c r i b e d by C yr e t a l 7 . The d e p o s i t o c c u r s i n an i n l i e r o f s e d i m e n t a r y , p y r o c l a s t i c and v o l c a n i c r o c k s b e l i e v e d t o be o f c r e t a c e o u s a g e . S t r a t a s t r i k e 010 d e g r e e s and d i p 45 d e g r e e s west. The s e d i m e n t a r y r o c k s a r e i n t r u d e d by a q u a r t z m o n z o n i t e s t o c k on t h e west s i d e a n d a g a b b r o - m o n z o n i t e complex on t h e e a s t s i d e . C o p p e r - s i l v e r -a n t i m o n y - g o l d m i n e r a l i z a t i o n forms an e l o n g a t e w e s t - d i p p i n g t a b u l a r zone between t h e s t o c k s . P o s t m i n e r a l i z a t i o n a n d e s i t i c and q u a r t z l a t i t i c d y k e s c r o s s c u t t h e c r e t a c e o u s r o c k s and t h e g a b b r o - m o n z o n i t e complex. F i g u r e 5.2-1 shows t h e r e g i o n a l g e o l o g y o f t h e a r e a a s d e s c r i b e d a b o v e . The p y r o c l a s t i c u n i t o v e r l i e s t h e c l a s i c u n i t and has a maximum t h i c k n e s s of 975 m (3200 f t ) . The r o c k s c o n s i s t o f i n t e r c a l a t e d s u b a e r i a l t u f f s , b r e c c i a s and r e w o r k e d p y r o c l a s t i c d e b r i s a l l s h owing wide g r a i n 1 86 I. JURASSIC - LOWER CRETACEOUS North South Skeeno Arch Bowser Basin Nechaho Trough Topley Intrusions Zone of Crustal Weakness Deposition af Marine Claslics (Clastic Division) 100 2. UPPER CRETACEOUS North Nechako Trough South Deposition of "Goosly Sequence" 0 i_ _Volconic FIOK_—_-_ 0:'. '•Sedimentary- Volcanic v.-. i - . Pyrcjclosllc .+ w O i, 0 9 •* M 0 f l l O jlU» *•* *:*.Clasticn-.;:r;*: 10 20 _t i Km East • « « * ! Gobbro- £r> Monzonite Complex */j 4. PRESENT West Quartz Monzonite Volcanics Stock East 0 i_ 6 Km FIGURE 5.2-1 : SCHEMATIC HISTORICAL GEOLOGY, EQUITY SILVER MINE (after Pease9) 187 s i z e v a r i a t i o n . The d i s t i n c t i o n between d u s t , a s h and l a p i l l i t u f f i s b a s e d on t h e maximum p a r t i c l e d i a m e t e r s of 0.5mm, 5.0mm and 50mm (0.02, 0.20, 2.0 i n c h ) r e s p e c t i v e l y . D r a m a t i c p a r t i c l e s i z e v a r i a t i o n s o v e r r e l a t i v e l y s h o r t d i s t a n c e has been o b s e r v e d 9 . T h e r e i s an o c c u r e n c e o f d y k e s o f s e v e r a l d i f f e r e n t c o m p o s i t i o n s on t h i s p r o p e r t y . They a r e c l a s s e d i n t o two m a j o r s g r o u p s , f i n e g r a i n e d a n d e s i t e and f e l d s p a r p o r p h y r y . In t h e S o u t h e r n T a i l d e p o s i t , f e l d s p a r p o r p h y r y d y k e s s t r i k e n o r t h -s o u t h and d i p s l i g h t l y s t e e p e r t h a n t h e o r e h o r i z o n . W i d t h r a n g e s from 6 t o 10 m (20 t o 30 f t ) . T h e r e a r e a l s o many a n d e s i t e d y k e s t h r o u g h o u t t h e S o u t h e r n T a i l d e p o s i t and t h e y a r e g e n e r a l l y narrow and e r r a t i c . The dyk e s a r e n o t m i n e r a l i z e d . The s t r u c t u r e o f t h e d e p o s i t i s r e l a t i v e l y s i m p l e s i n c e t h e r e g i o n has n o t been e x p o s e d t o i n t e n s e d e f o r m a t i o n s . T h e r e a r e no l a r g e s c a l e f a u l t s on t h e p r o p e r t y . T a b u l a r i n form w i t h a s t r i k e o f 025 d e g r e e s , t h e d e p o s i t d i p s 30 t o 50 d e g r e e s w e s t e r l y . The s t r i k e l e n g t h of t h e o r e zone i s about 750 m e t r e s (2460 f t ) w i t h a down d i p e x t e n s i o n of more t h a n 300m (980 f t ) . The o r e zone t h i c k n e s s v a r i e s f r o m 15 t o 30 m (50 t o 100 f t ) . The p y r o c l a s t i c d i v i s i o n , i n c l u d i n g t h e d u s t t u f f s , i s c h a r a c t e r i z e d by a r e t i c u l a t e f r a c t u r e p a t t e r n . The f r a c t u r e i n t e n s i t y v a r i e s g r e a t l y b u t i t g e n e r a l l y i n c r e a s e s c l o s e r t o th e m i n e r a l i z e d a r e a s . The a s h t u f f s a r e l e s s f r a c t u r e d t h a n t h e d u s t t u f f s ( T a b l e 4 ) . The m i n e r a l i z a t i o n o f t h e S o u t h e r n T a i l d e p o s i t i s TABLE 4 ROCK PROPERTIES EQUITY SILVER MINE ROCK TYPE HARDNESS APPROXIMATE RANGE OF UNIAXIAL COMPRESSIVE STRENGTH (MPa) (psi) DENSITY (g/cc) RQD Quartz L a t i t e R4-R5 Dyke 89-166 13000-24000 2.58 48% 62% of the data between 41-70% Dust Tuff R4 55-111 8000-16000 2.78 29% 55% of the data l e s s than 30% Ash T u f f R3 27-55 4000-8000 2.78 35% 55% of the data between 21-50% M i n e r a l i z e d T u f f R2-R3 20-62 3000-9000 3.00 in c r e a s i n g with grade 10% 60% of the data l e s s than 30% 189 s t r u c t u r a l l y c o n t r o l l e d . S u l f i d e s were d e p o s i t e d as open s p a c e f i l l i n g s and t h e i r abundance i n c r e a s e d w i t h t h e i n t e n s i t y of f r a c t u r i n g . P y r i t e and a r s e n o p y r i t e a r e t h e most common m i n e r a l s i n t h e d e p o s i t . However, t h e p r i n c i p a l c o p p e r m i n e r a l i s c h a l c o p y r i t e w h i l e t e t r a h e d r i t e i s t h e p r i n c i p a l s i l v e r m i n e r a l . The o r e o c c u r s as v e i n s and d i s s e m i n a t i o n o f m a s s i v e s u l f i d e s p r e s e n t a s l o c a l p o d s . The o r e b o d y i s narrow and t h e m i n e r a l i z a t i o n i s e r r a t i c , l e a d i n g t o wide v a r i a t i o n s i n g r a d e o v e r s h o r t d i s t a n c e s . In a d d i t i o n , t h e w e s t e r n w a l l o f t h e p i t was more s u b j e c t e d t o a l t e r a t i o n t h a n t h e e a s t e r n w a l l . 190 5.2.2 The B l a s t i n g P r o c e d u r e s a t E q u i t y S i l v e r A t E q u i t y S i l v e r , t h e m i n i n g equipment was s e l e c t e d t o o p e r a t e w i t h 10 meter (33 f t ) b e n c h e s . However, due t o d i l u t i o n c o n s t r a i n t s , t h e bench h e i g h t was r e d u c e d t o 5 m e t r e s (16 f t ) e x c l u d i n g t h e 1.5m (5 f t ) s u b d r i l l d e p t h . In a d d i t i o n , a s t h e p i t f l o o r became c l o s e r t o t h e d e s i g n e d p i t l i m i t , t h e number o f w o r k i n g f a c e s was r e d u c e d and c h o k e d b l a s t s became more f r e q u e n t . D u r i n g t h i s r e s e a r c h p r o j e c t , many o f t h e b l a s t s were o r i e n t e d e a s t - w e s t ( a c r o s s t h e p i t ) , w i t h t h e b l a s t i n g t a k i n g p l a c e i n t h e s t r i k e d i r e c t i o n . In s u c h c o n d i t i o n s , c o n t r o l l e d b l a s t i n g i s n o t p e r f o r m i n g w e l l , e s p e c i a l l y i n t h e h i g h l y b r o k e n r o c k mass. M o r e o v e r , d e s i g n e d i n t h i s c o n f i g u r a t i o n , a g i v e n b l a s t p a t t e r n w i l l i n c l u d e many d i f f e r e n t r o c k t y p e s ( s e e F i g u r e 5.2-2) . The b l a s t p a t t e r n s were 5 m by 5 m (16 f t by 16 f t ) w i t h t h e 229 mm (9 i n c h ) d i a m e t e r b l a s t h o l e s and 4 m by 5 m (13 f t by 16 f t ) w i t h t h e 200 mm (7 7/8 i n c h ) d i a m e t e r h o l e s . The b l a s t g e o m e t r y was t h e r e f o r e v e r y d i s a d v a n t a g e o u s . B e c a u s e t h e l o a d i n g p r a c t i c e was b a s e d on t h e c o l l a r h e i g h t , w h i c h , i n r e t u r n , was f u n c t i o n of t h e h o l e d i a m e t e r , t h e powder f a c t o r , w i t h i n a g i v e n p a t t e r n , was h i g h l y v a r i a b l e as t h e r o c k d e n s i t y d i f f e r s f r o m one r o c k t y p e t o t h e n e x t . In a d d i t i o n , t h e v a r i a t i o n s i n h o l e d e p t h due t o c a v i n g , c a u s e d by t h e h i g h d e g r e e of f r a c t u r i n g o f t h e r o c k mass and t h e g r o u n d w a t e r , were a f f e c t i n g t h e e n e r g y d i s t r i b u t i o n w i t h i n a g i v e n r o c k t y p e . The 191 7200 N 7000 N 6800 N 6600 N ASH TUFF DUST TUFF QUARTZ LATITE DYKE MINERALIZED TUFF 0 250 ^ ft 0 50 100 m FIGURE 5.2-2= EQUITY SILVER MINE 1260m BENCH GEOLOGY, scale 1=5000 192 g r o u n d w a t e r has a l s o a more d i r e c t i n f l u e n c e on e n e r g y d i s t r i b u t i o n . The u t i l i z a t i o n o f b u l k ANFO was sometimes r e s t r i c t e d by t h e amount o f g r o u n d w a t e r . When t h e b l a s t h o l e s c a n n o t be p r o p e r l y l i n e d w i t h p l a s t i c s l e e v e s , s l u r r y e x p l o s i v e s were u s e d . C o n s e q u e n t l y , e n e r g y d i s t r i b u t i o n was s e l d o m u n i f o r m w i t h i n t h e b l a s t p a t t e r n s . In o r d e r t o m i n i m i z e t h e p o s s i b l e damage t o t h e p i t w a l l s , t h e row p e r row i n i t i a t i o n s y s t e m was m o d i f i e d t o a h o l e p e r h o l e d e l a y s equence on a V1 p a t t e r n . T h e r e f o r e , t h e amount o f e x p l o s i v e d e t o n a t i n g on t h e same d e l a y was r e d u c e d , t h e g e o m e t r i c r a t i o s were i m p r o v e d a s w e l l as t h e d i s p l a c e m e n t and f r a g m e n t a t i o n o f t h e muck p i l e . N e v e r t h e l e s s , t h e r e s u l t s were s t i l l n o n - u n i f o r m . 5.2.3 D e v e l o p m e n t o f t h e C o r r e l a t i o n Between RQI and Powder  F a c t o r The d i f f e r e n t b l a s t i n g domains w i t h i n t h e p i t were d i f f e r e n t i a t e d by t h e f o l l o w i n g c h a r a c t e r i s t i c s : 1. Rock t y p e : d u s t t u f f , a s h t u f f , q u a r t z l a t i t e dyke, m i n e r a l i z e d a s h t u f f , m i n e r a l i z e d d u s t t u f f , q u a r t z p o r p h y r y d y k e . 2. D e g r e e of a l t e r a t i o n : t h e t u f f s were a l s o d i v i d e d i n t o e a s t and west w a l l z o n e s , a c c o r d i n g t o t h e d e g r e e o f a l t e r a t i o n . At E q u i t y , some domains d i d not c o v e r v e r y l a r g e a r e a s due t o t h e w i d t h o f t h e p i t a t t h e 1260 m (4134 f t ) e l e v a t i o n . 1 93 C o n s e q u e n t l y , d a t a were l i m i t e d , e s p e c i a l l y i n t h e n o r t h e r n end o f t h e p i t ( a s h t u f f ) . The RQI v a l u e s were c o m p i l e d , i n a g i v e n d omain, f o r t h e d i f f e r e n t b i t d i a m e t e r and f o r t h e r e c o r d e d d a t a ( T a b l e 5, F i g u r e 5 . 2 - 3 ) . In t h e S o u t h e r n T a i l p i t , two BE 40-R d r i l l s were o p e r a t i n g . One was d r i l l i n g 229 mm (9 i n c h e s ) d i a m e t e r b l a s t h o l e s whereas t h e o t h e r one was d r i l l i n g 200 mm (7 7/8 i n c h e s ) d i a m e t e r b l a s t h o l e s . A l t h o u g h t h e y were g e n e r a l l y o p e r a t i n g on d i f f e r e n t b l a s t p a t t e r n s , i t o c c u r r e d , i n a few o c c a s i o n s t h a t b o t h were d r i l l i n g s i d e by s i d e on t h e same p a t t e r n . I t was o b s e r v e d t h a t , f o r a g i v e n s e t o f r o c k c o n d i t i o n s , t h e RQI c o m p i l e d from t h e s m a l l e r s i z e b l a s t h o l e s was, i n t h e a v e r a g e , 0.60 t i m e s t h e RQI c o m p i l e d from t h e 229 mm (9 i n c h ) d i a m e t e r b l a s t h o l e s . T h i s o b s e r v a t i o n has t o be a n a l y s e d w i t h L i t t l e ' s 1 3 f i n d i n g s on t h e e f f e c t o f b i t s i z e and d r i l l model on RQI. S i n c e t h e b l a s t i n g p r o c e d u r e s were v a r i a b l e s , o n l y t h e c h o k e d p r o d u c t i o n b l a s t s p e r f o r m e d a l o n g t h e s t r i k e d i r e c t i o n p r o v i d e d s u f f i c i e n t d a t a t o p e r m i t a n a l y s i s . However, t h e c o n d i t i o n s w i t h i n t h i s g r o u p of b l a s t s were n o t c o n s t a n t , c h a n g e s i n t h e d e l a y and i n i t i a t i o n s e q u e n c e b e i n g t e s t e d . B l a s t r e s u l t a n a l y s i s and c o m p i l a t i o n of t h e powder f a c t o r s were p e r f o r m e d , t a k i n g i n t o a c c o u n t t h e d i f f e r e n t r o c k t y p e s / d o m a i n s w i t h i n t h e p a t t e r n . T a b l e 6 summarizes t h e r e s u l t s . The optimum powder f a c t o r s were t h e n compared w i t h t h e Rock Q u a l i t y Index a l l o c a t e d t o e a c h domain ( F i g u r e 5 . 2 - 4 ) . TABLE 5 SUMMARY OF RQI VALUES AT EQUITY SILVER DOMAINS ROCK QUALITY INDEX RQI (229mm-•9 inch) RQI (200mm-7 7/8 inch) RQI-REC^15 (229rnm-9 ini kg-min/m lbs- m i n / f t kg-min/m Lbs-min/ft kg-min/m lbs-min, (*1000) (*1000) (*1000) (*1000) (*1000) (*1000 I Dust Tuff, east 61.0 40.9 35.6 23.9 50.2 33.7 II Dust Tuff, west 55.8 37.5 34.7 23.3 41.1 27.6 III" Ash Tuff, east 75.3 50.6 IV Ash Tuff, west 66.1 44.4 30.8 2 0 . 7 ( 2 ) V Quartz L a t i t e Dyke 65.6 44.1 37.5 25.2 51.3 34.5 VI > Mineralized DT, east 54.3 36.3 32.9 22.1 43.9 29.5 VII Mineralized DT, west 31.5 21.2 VIII M i n e r a l i z e d AT, east 77.7 52.2 IX M i n e r a l i z e d AT, west 72.6 48.8 X Quartz Porphyry Zone 33.0 22.2 (1) Recorder (2) One pattern only (3) 12 data p o i n t s only 195 FIGURE 5.2-3' ROCK QUALITY INDEX VALUES FOR EACH DOMAIN RANKED IN ORDER OF DECREASING ORDER, EQUITY SILVER. 196 TABLE 6 CORRELATION BETWEEN RQI AND  POWDER FACTORS AT EQUITY SILVER MINE DOMAINS ROCK QUALITY INDEX (229nim-9 inch) kg-min/m (*1000) lbs-min/ft (*1000) POWDER FACTOR (choked) kg/tonne lbs/s.ton I II III IV V VI VII VIII IX X 61.0 55.8 75.3 66.1 65.6 54.8 53.6 77.7 72.6 54.9 40.9 37.5 50.6 44.4 44.1 36.8 (36.0) 52.2 48.8 (36.9) 0.105 0.100 0.110 0.110 0.095 0.095 0.095 0.21 0.20 0.22 0.22 0.19 0;19 0.19 no optimum powder f a c t o r a l l o c a t e d to domains I I I , VIII, IX 197 _ O © o 0 o 1 * c E i i 75 r 60 x UJ o _i < O o o or o c 0> E E o> 30 CVJ CVJ 15 CH- 0. 0.025 0.050 0.075 0,100 ENERGY FACTOR 0.125 0.30 - S.ton 0.150 kg Tonne FIGURE 5.2-4' PROPOSED CORRELATION BETWEEN ROCK QUALITY INDEX AND POWDER FACTOR AT EQUITY SILVER MINE. 198 5.2.4 A n a l y s i s of t h e R e s u l t s No r e a l o p t i m i z a t i o n of t h e powder f a c t o r was p e r f o r m e d a t E q u i t y S i l v e r . The optimum powder f a c t o r s l i s t e d were d e t e r m i n e d f rom t h e e v a l u a t i o n o f t h e b l a s t r e s u l t s and c a l c u l a t e d f r o m t h e b l a s t r e p o r t s . Due t o t h e v a r i a t i o n s i n t h e b l a s t i n g p r o c e d u r e , t h e e v a l u a t i o n of t h e r e s u l t s and t h e c o m p a r i s o n between t h e powder f a c t o r s was d i f f i c u l t . C o n s e q u e n t l y , i t was d e c i d e d t h a t o n l y t h e p r o d u c t i o n c h o k e d b l a s t s would be c o n s i d e r e d f o r t h i s r e s e a r c h p r o j e c t . O t h e r t y p e s o f b l a s t p e r f o r m e d a t E q u i t y S i l v e r d u r i n g t h e d a t a g a t h e r i n g p e r i o d were p e r i m e t e r , ramp c o n s t r u c t i o n and c u t s i n k i n g b l a s t s . - The few p e r i m e t e r b l a s t s p e r f o r m e d were v e r y good. In g e n e r a l , t h e b l a s t i n g p r o c e d u r e i n r e g a r d t o t h e s l o p e s t a b i l i t y was i m p r o v e d as d e s i g n g u i d e l i n e s were s p e c i f i e d . One o f t h e p e c u l i a r i t i e s of t h e b l a s t i n g p r o c e d u r e a t E q u i t y S i l v e r , i s t h e f a c t t h a t t h e b l a s t i n g r e s u l t s a r e v e r y d e p e n d e n t on t h e c o l l a r / c h a r g e r a t i o . W i t h 6.5 m (21.3 f t ) h o l e s on 5 m (16 f t ) b e n c h e s , a s l i g h t v a r i a t i o n i n t h e c h a r g e l e n g t h makes t h e r a t i o change v e r y r a p i d l y . I n c r e a s i n g t h e powder f a c t o r by i n c r e a s i n g t h e c h a r g e ( l e n g t h ) w i l l c a u s e t h e stemming column t o be r e d u c e d and t h e r e f o r e , t o be more e a s i l y e j e c t e d , t h u s r e d u c i n g t h e e x p l o s i v e c o n f i n e m e n t and e f f i c i e n c y . The e x a m i n a t o n of t h e RQI v a l u e s a l l o c a t e d t o e a c h domain shows t h a t t h e e a s t e r n s i d e o f t h e p i t , c o r r e s p o d i n g t o t h e l e s s a l t e r e d r o c k s a t bench e l e v a t i o n , p o s s e s s e s h i g h e r RQI t h a n t h e 199 w e s t e r n d o m a i n s . T h i s s u g g e s t s t h a t t h e RQI i s s e n s i t i v e t o t h e d e g r e e o f a l t e r a t i o n . However, i t was o b s e r v e d t h a t g r o u n d w a t e r l e v e l s were h i g h e r c l o s e t o t h e e a s t w a l l . Due t o t h e a b s e n c e of s u f f i c i e n t b l a s t r e s u l t o b s e r v a t i o n s , no r e l a t i o n s h i p between t h e RQI and t h e powder f a c t o r were o b t a i n e d i n t h e n o r t h e r n p a r t o f t h e p i t . In a d d i t i o n , t h e RQI v a l u e s a l l o c a t e d t o t h o s e domains a r e d e r i v e d f r o m a s m a l l e r g r o u p o f d a t a , and s h o u l d n o t be c o n s i d e r e d as a c c u r a t e as t h e ones o b t a i n e d i n t h e s o u t h e r n and c e n t r a l p a r t o f t h e p i t where two b e n c h e s were mined out d u r i n g t h e d a t a g a t h e r i n g p e r i o d . The i n t e r p r e t a t i o n of t h e d a t a r e l a t e d t o t h e s e domains y i e l d s F i g u r e 5.2-4. I t shows t h a t t h e r e i s a t r e n d between t h e r o c k mass b l a s t a b i l i t y and t h e Rock Q u a l i t y Index as p r e d i c t e d by L e i g h t o n 1 . 200 5.3 LORNEX MINE 5.3.1 Summary of t h e G e o l o g y The L o r n e x copper-molybdenum d e p o s i t i s s i t u a t e d i n t h e H i g h l a n d V a l l e y of B r i t i s h C o l u m b i a , 74 Km (46 m i l e s ) s o u t h w e s t of Kamloops. The e l e v a t i o n o f t h e mine s i t e i s a p p r o x i m a t e l y 1060 m (3478 f t ) . B ecause o f t h e low g r a d e , t h e L o r n e x o r e b o d y has t o be m i n e d on a l a r g e s c a l e t o be p r o f i t a b l e . F u l l p r o d u c t i o n s t a t e d i n 1972 and d u r i n g t h e summer of 1983, t h e d e s i g n e d m i l l f e e d r a t e was 75300 t o n n e / d a y (83000 s . t o n / d a y ) . The s t r i p p i n g r a t i o i s a r o u n d 2.2 : 1.0. The g e o l o g y has been d e s c r i b e d by Waldner e t a l 1 0 . The d e p o s i t i s . e n t i r e l y w i t h i n t h e Skeena Q u a r t z D i o r i t e (SQD) zone, a s l i g h t l y p o r p h y r i c , medium t o c o a r s e - g r a i n e d r o c k . The o r e zone i s a p p r o x i m a t e l y 2100 m (6890 f t ) l o n g and 750 m (2460 f t ) wid e . The d e p o s i t i s b e l i e v e d t o p l u n g e 30 t o 40 d e g r e e s t o w a r d t h e n o r t h w e s t t o a d e p t h i n e x c e s s of 750 m (2460 f t ) . The o r e b o d y i s t r u n c a t e d on t h e west s i d e by t h e L o r n e x f a u l t s t r i k i n g n o r t h e r l y w i t h v a r i a b l e westward d i p . On t h e s o u t h e a s t end of t h e p r o p e r t y , a p r e - m i n e r a l q u a r t z p o r p h y r y dyke t r e n d s n o r t h w e s t e r l y . In some a r e a , c o n t a c t s of t h e dyke a r e not w e l l d e f i n e d b e c a u s e of t h e a l t e r a t i o n of a d j o i n i n g Skeena Q u a r t z D i o r i t e . The west p a r t of t h e p i t i s w i t h i n t h e B e t h s a i d a G r o n o d i o r i t e Zone ( F i g u r e 5 . 3 - 1 ) . The p r e d o m i n e n t s u l p h i d e m i n e r a l s a r e c h a l c o p y r i t e , FIGURE 5.3-1: LORNEX OPEN PIT MINE, scale 3/4"=l000' 202 b o r n i t e , m o l y b d e n i t e and p y r i t e . They o c c u r p r i m a r i l y as f r a c t u r e f i l l i n g s w i t h q u a r t z and as f r a c t u r e c o a t i n g s , v e i n s a v e r a g e 5 t o 15 m i l l i m e t e r s (0.2 i n c h e s t o 0.6 i n c h e s ) i n w i d t h , r a n g i n g f r o m a h a i r l i n e t o more t h a n a m e t e r . S t r i k e l e n g t h may e x c e e d 200 m e t e r s (656 f t ) . M i n e r a l i z a t i o n a t L o r n e x i s c o n t r o l l e d by f r a c t u r e d e n s i t y and d i s t r i b u t i o n . S t r u c t u r a l mapping has p r o d u c e d o v e r 11000 d a t a p o i n t s p l o t t e d on F i g u r e 5.3-2. The t h r e e m a j o r a t t i t u d e s f o r copper-molybdenum v e i n s a r e d o m i n a n t i n d i s t i n c t z o n e s of t h e o r e b o d y , a l t h o u g h , i n t h e c e n t r a l and w e s t e r n z o n e s , t h e r e i s an o v e r l a p of a l l t h r e e v e i n a t t i t u d e s , r e s u l t i n g i n h i g h e r g r a d e s . In a d d i t i o n , two p o s t -m i n e r a l f r a c t u r e s y s t e m s have been r e c o g n i z e d i n t h e p i t . F o u r t y p e s o f h y d r o t h e r m a l a l t e r a t i o n a s s o c i a t e d w i t h s u l p h i d e m i n e r a l i z a t i o n o c c u r i n t h i s d e p o s i t . The most i m p o r t a n t one i s t h e a r g i l l i c a l t e r a t i o n from w h i c h r e s u l t s t h e p r e s e n c e of s e r i c i t e , k a o l i n i t e , m o n t m o r i l l o n i t e and c h l o r i t e . In g e n e r a l , g r a d e i n c r e a s e s w i t h an i n c r e a s i n g i n t e n s i t y of a r g i l l i c a l t e r a t i o n and o r i g i n a l r o c k s t r e n g t h d e c r e a s e s w i t h an i n c r e a s i n g d e g r e e of any t y p e o f h y d r o t h e r m a l a l t e r a t i o n . The p o r p h y r y dyke i s l e s s a f f e c t e d by a l t e r a t i o n . The f o l l o w i n g s t a t e m e n t s on t h e L o r n e x d e p o s i t a r e q u o t e d from W aldner e t a l 1 0 "1. The p r i n c i p a l s u l p h i d e s f o r m a c o n c e n t r i c p a t t e r n w i t h b o r n i t e i n t h e c e n t e r , c h a l c o p y r i t e o u t s i d e b o r n i t e and m o l y b d e n i t e zone o v e r l a p p i n g p o r t i o n s of t h e b o r n i t e and c h a l c o p y r i t e z o n e s . P y r i t e forms a h a l o a r o u n d t h e o r e Cu-Mp VEINS FRACTURES FAULTS 3a 1 3b r ~ " ^ ^ 3c 1— MOST PROMINENT MOST PROMINENT MOST PROMINENT Cu-Mo VEIN TRENDS FRACTURE TRENDS FAULT TRENDS N22°E/55° S.E. N64 0E/57°S.E. N90°E/58°S. N32°E /54°S.E. N8S°W/62°S.W. N440V//66°S.W. N08°W/68°S.W. N68°W/69°S.W. N86°W/52° S.W. N08°W/ 64° S.W. N2 1 °W/ 46° S.E. N63°W/57° S:W. POLES TO 5835 VEINS POLES TO 3152 FRACTURES POLES TO 1564 FAULTS CONTOURS AT 2, 4. 5, 8, 12% PER 1% AREA CONTOURS AT 2 ,3 ,4% PER 1% AREA CONTOURS AT 2 .3 ,4 ,5% PER 1% AREA FIGURE 5.3-2 : LOWER HEMISPHERE , EQUAL AREA STEREOGRAPHIC PROJECTIONS OF STRUCTURES MAPPED IN THE 10 LORNEX OPEN PIT (after Waldner et al. ) 204 Zone. 2. C opper g r a d e s and t o t a l s u l p h i d e c o n t e n t d e c r e a s e o u t w a r d from t h e c o r e of t h e o r e b o d y t o i t s p e r i p h e r y . 3. S u l p h i d e and a l t e r a t i o n z o n e s a r e deep i n t h e n o r t h and s h a l l o w i n t h e s o u t h e r n p o r t i o n s of t h e o r e b o d y , i n d i c a t i n g a 30 t o 40 d e g r e e n o r t h w e s t p l u n g e . 4. Zones o f m o derate t o i n t e n s e a r g r i l l i c a l t e r a t i o n c o r r e s p o n d t o h i g h e r g r a d e s . " 5.3.2 B l a s t i n g P r o c e d u r e s a t L o r n e x At L o r n e x , a v a s t q u a n t i t y o f m a t e r i a l i s moved e v e r y day. I t i s one o f t h e l a r g e s t t r u c k and s h o v e l o p e r a t i o n s i n Canada and t h e r e f o r e numerous l a r g e s i z e u n i t s of e q uipment a r e u s e d . A t t h e t i m e t h e r e s e a r c h p r o j e c t was t a k i n g p l a c e , t h e m i n i n g method was s t r a i g h t f o r w a r d . The s t a g e one p i t h a v i n g been e x c a v a t e d , t h e y were p u s h i n g back t h e e a s t and s o u t h w a l l s . M i n i n g was a c c o m p l i s h e d on s e v e r a l b e n c h e s t o o b t a i n optimum b l e n d i n g c a p a c i t y and t o m a i n t a i n t h e s t r i p p i n g r a t i o . P r o d u c t i o n b l a s t s were c h o k e d most o f t h e t i m e w h i l e t h e p e r i m e t e r b l a s t s f r e e - f a c e d o n l y on t h e e a s t e r n w a l l . In t h e o r e zone o f t h e s o u t h e r n p a r t o f t h e p i t , a l l t h e b l a s t s were c h o k e d , even a t w a l l c o n t a c t . B l a s t p a t t e r n s were r a n g i n g f r o m 8.5 m by 8.5 m (28 f t by 28 f t ) i n t h e waste r o c k on t h e e a s t w a l l t o 11 m by 11 m (36 f t by 36 f t ) i n t h e s o f t o r e z o n e s . S u b d r i l l i n g , on t h e 12.2 m 205 ( 4 0 f t ) b e n c h e s , was a l s o v a r i a b l e , b e i n g n o n e x i s t a n t i n t h e s o f t o r e z o n e s . The b l a s t r e s u l t s were g e n e r a l l y r a n g i n g f r o m p o o r t o f a i r . The powder f a c t o r c a l c u l a t i o n d i d n o t c o n s i d e r t h e w e i g h t s t r e n g t h of t h e e x p l o s i v e s u s e d (ANFO, AL-ANFO, S l u r r i e s ) . T h e r e f o r e , t h e e n e r g y d i s t r i b u t i o n w i t h i n t h e p a t t e r n was n o t u n i f o r m . In a d d i t i o n , d r i l l i n g was n o t a c c u r a t e and v a r i a t i o n s o f t h e b u r d e n , s p a c i n g and d e p t h d i m e n s i o n s were f r e q u e n t l y n o t e d . F i n a l l y , y e l l o w / o r a n g e smoke was common, i n d i c a t i n g wet ANFO o r non-optimum mix. The p r o d u c t i o n b l a s t s , s h o t i n - l i n e or on a V p a t t e r n were g e n e r a l l y c h o k e d , but when t h e y were f r e e - f a c e d , i t was o b s e r v e d t h a t t h e y c h o k e d t h e m s e l f due t o t h e low e n e r g y f a c t o r a n d / o r t h e s h o r t 25 ms d e l a y p e r i o d between t h e rows. D u r i n g t h e r e s e a r c h p r o j e c t , i t was shown t h a t t h e p r a c t i c e o f u s i n g two d o w n l i n e s of r e i n f o r c e d p r i m a c o r d i n a 250 mm (9 7/8 i n c h e s ) b l a s t h o l e was p r o d u c i n g s i d e i n i t i a t i o n of t h e e x p l o s i v e column and c o n s e q u e n t l y was a v e r y i n e f f e c t i v e use of t h e e x p l o s i v e e n e r g y a v a i l a b l e . The d e s i g n of t h e w a l l c o n t r o l b l a s t s was p o o r . The l a s t 6 m (20 f t ) o f t h e p a t t e r n , c l o s e s t t o t h e w a l l , were a l l o c a t e d a h i g h e r e n e r g y f a c t o r t h a n t h e r e s t of t h e p a t t e r n . The i n i t i a t i o n was p e r f o r m e d by a d o w n - t h e - h o l e s y s t e m p e r m i t t i n g l o n g e r d e l a y s between t h e rows of t h e V p a t t e r n . However, b e c a u s e of t h e g e n e r a l u n d e r l o a d e d c o n d i t i o n s o f t h e r o c k mass, the d i s p l a c e m e n t was n o t s u f f i c i e n t and t h e b l a s t s were c h o k i n g t h e m s e l v e s . V i b r a t i o n s and c r a c k p r o p a g a t i o n t o w a r d t h e r o c k s l o p e s were damaging. The w a l l s d i d not l o o k good. D e s i g n 206 m o d i f i c a t i o n s c o n c e r n i n g e n e r g y d i s t r i b u t i o n were s u g g e s t e d . I t s h o u l d be n o t e d t h a t t h r e e H e r c u d e t t e s t b l a s t s were p e r f o r m e d a t L o r n e x d u r i n g t h i s r e s e a r c h p r o j e c t . The v e r y good r e s u l t s o b t a i n e d were p a r t l y due t o t h e s y s t e m , but a l s o t o t h e w e l l e n g i n e e r e d d e s i g n . 5.3.3 Development o f t h e C o r r e l a t i o n Between RQI and Powder  F a c t o r I t was n o t p o s s i b l e t o d e r i v e a c o r r e l a t i o n between t h e Rock Q u a l i t y Index and t h e powder f a c t o r a t L o r n e x . The main r e a s o n b e i n g t h e l a c k of u s e f u l b l a s t i n g d a t a . A p p r o x i m a t i v e l y h a l f of t h e b l a s t s m o n i t o r e d were s i d e i n i t i a t e d . On t h e e a s t w a l l , b l a s t r e s u l t s were i m p r o v i n g as m i n i n g p r o g r e s s e d t o w a r d t h e s o u t h end, but t h e s a t i s f a c t o r y r e s u l t s d e s c r i b e d i n c h a p t e r f o u r were n o t r e a c h e d . B l a s t s were u n d e r l o a d e d . The c o m p i l a t i o n of t h e RQI v a l u e s was done from t h e d r i l l e r l o g s and t h e r e c o r d e d c h a r t s . Of t h e f i v e B u c y r u s 45-R d r i l l s , t h r e e were g e n e r a l l y o p e r a t i n g on any g i v e n s h i f t . A l t h o u g h some s t e e l t o o t h b i t s were u s e d i n t h e s o f t o r e z o n e s , no d r a m a t i c v a r i a t i o n i n t h e Rock Q u a l i t y Index from t h e WC i n s e r t b i t s were o b s e r v e d . However, i t i s a p o t e n t i a l s o u r c e of i n t e r p r e t a t i o n e r r o r . The domains were d e f i n e d from a) Rock t y p e s : Skeena Q u a r t z D i o r i t e (SQD) o r Q u a r t z P o r p h y r y (QPP) b) Degree o f a l t e r a t i o n of t h e Skeena Q u a r t z D i o r i t e 207 Some of t h e domains, e s p e c i a l l y on t h e e a s t w a l l , were l i m i t e d i n s u r f a c e t o one or two b l a s t p a t t e r n s . In t h e s o u t h e r n end o f t h e p i t , t h e a r e a s were l a r g e r . B e c a u s e no o t h e r d r i l l i n g d a t a from t h e p r e v i o u s months were a n a l y s e d , t h e q u a n t i t y of d a t a i s a f u n c t i o n o f t h e domain a r e a . A l t h o u g h no c o r r e l a t i o n was d e r i v e d w i t h t h e powder f a c t o r , t h e r e i s a good c o r r e l a t i o n between t h e Rock Q u a l i t y Index and t h e d e g r e e o f a l t e r a t i o n of t h e Skeena Q u a r t z D i o r i t e ( F i g u r e 5.3-3, T a b l e 7 ) . In a d d i t i o n , i n t h e o r e z o n e s of t h e s o u t h e r n end o f t h e p i t , a c o r r e l a t i o n was e s t a b l i s h e d between t h e RQI and t h e g r i n d a b i l i t y o f t h e r o c k ( F i g u r e 5 . 3 - 4 ) . A p l a n o f t h e p r e v i o u s bench was s u p e r i m p o s e d o v e r t h e b l a s t h o l e p l a n and t h e g r i n d i n g r a t e a l l o c a t e d t o an o r e b l o c k on t h e p r e c e e d i n g b e n c h was d i r e c t l y compared w i t h t h e a v e r a g e RQI on t h e b l o c k ' s p r o j e c t i o n , 12.2 m (40 f t ) d e e p e r . The same e x e r c i s e was a l s o p e r f o r m e d on a l a r g e r s c a l e . FIGURE 5.3-3: ROCK QUALITY INDEX IN DIFFERENT DOMAINS OF LORNEX MINE. TABLE 7 SUMMARY OF RQI VALUES AND ROCK STRENGTH AT LORNEX MINE DOMAINS II SQD massive to weakly a l t e r e d SQD altered and fractured III SQD moderate a r g i l l i c a l t e r a t i o n IV SQD weak to intense a r g i l l i c a l t . V QPP weakly altered VI SQD Intense a r g i l l i c a l t e r a t i o n VII SQD moderate to intense a r g i l l i c a l t . VIII QPP weakly altered IX SQD moderate to intense a r g i l l i c a l t . (1) from point-load tests ROCK QUALITY INDEX (250mm-9 7/8inch) D r i l l e r logs Recorder kg-min/m lbs-min/ft kg-min/m lbs-min/ft (*1000) (*1000) (*1000) (*1000) 49.3 33.6 29.6 26.3 24.9 20.4 24.0 28.4 26.3-33.1 22.6 19.9 17.7 16.7 13.7 16.1 19.1 17.7 40.6 29.8 24.6 24.1 27.3 20.0 16.5 16.2 ESTIMATED ( 1 ) UNIAXIAL COMPRESSIVE STRENGTH (MPa) 261 111 179 132 50 (psi) 37800 16100 26000 19200 7200 M O o o * II 30F o 025 o E i cn X — II ~ 00 • o> < I Is 15 20 15 10 • 9 B L A S T HOLES AVERAGE A 25 B L A S T H O L E S AVERAGE 4 » 0-1- 10 12 14 20 13 15 GRINDING RATE 17 19 21 TONNE HR moo) FIGURE 5.3-4= RELATIONSHIP BETWEEN ROCK QUALITY INDEX AND GRINDING RATE AT LORNEX. 21 1 5.3.4 A n a l y s i s o f t h e R e s u l t s I t i s i m p o s s i b l e t o d e r i v e a c o r r e l a t i o n when one s i d e of t h e r e l a t i o n s h i p i s m i s s i n g . N e v e r t h e l e s s , t h e r o c k mass i n domain I r e q u i r e s more e x p l o s i v e s t h a n t h e r o c k mass i n t h e s o u t h e r n o r e z o n e s , i n a c c o r d a n c e w i t h t h e g e n e r a l r e l a t i o n s h i p . The f a c t t h a t t h e Rock Q u a l i t y Index i s s e n s i t i v e t o t h e v a r i a t i o n s of t h e s t r e n g t h p r o p e r t i e s of t h e r o c k mass i s c o n f i r m e d by t h e c o r r e l a t i o n between t h e RQI and t h e d e g r e e of a l t e r a t i o n . The more a l t e r e d t h e r o c k mass, t h e l e s s e r t h e RQI. T h i s c o u l d be o f i n t e r e s t i n r o c k s l o p e e n g i n e e r i n g , i n o r d e r t o m o n i t o r t h e v a r i a t i o n s i n r o c k q u a l i t y w i t h d e p t h . The s e c o n d i n t e r e s t i n g r e l a t i o n s h i p , a l t h o u g h v e r y a p p r o x i m a t i v e a t t h i s t i m e , i s t h e v a r i a t i o n of t h e g r i n d a b i l i t y w i t h t h e Rock Q u a l i t y I n d e x . I t i s n o t a c o i n c i d e n c e , b o t h b e i n g f r a g m e n t a t i o n p r o c e s s e s . In t h i s r e s e a r c h p r o j e c t , t h e g r i n d a b i l i t y r a t i n g was o b t a i n e d from t h e p r e v i o u s bench and t r a n s f e r e d d i r e c t l y one bench down. The mine g e o l o g i s t w i l l i n v e s t i g a t e t h i s s u b j e c t i n more d e t a i l . 212 5.4 GREENHILLS MINE 5.4.1 Summary of t h e G e o l o g y The W e s t a r Minin'g G r e e n h i l l s Mine i s l o c a t e d 35km (22 m i l e s ) n o r t h of t h e town o f Sparwood, i n t h e e a s t K o o t e n a y r e g i o n of s o u t h e a s t e r n B r i t i s h C o l u m b i a . The p i t e l e v a t i o n i s p r e s e n t l y 2000m (6562 f t ) a l t h o u g h t h e c o a l l o a d o u t f a c i l i t i e s , s h o p s and o f f i c e s a r e a t l o w e r e l e v a t i o n s . The p r o p e r t y i s d i v i d e d i n s e v e r a l z o n e s o r p i t s , a l o n g t h e r i d g e , i n o r d e r t o ex p o s e a s u f f i c i e n t t o n n a g e of c o a l . The f i r s t s h i p m e n t was s e n t i n A u g u s t 1982 and t h e p r o j e c t l i f e i s e s t i m a t e d a t 20 y e a r s . The a c t u a l y e a r l y p r o d u c t i o n r a n g e between 2.8 and 3.0 M t o n n e s (2.2 t o 3.3 M s . t o n ) o f c l e a n c o a l a l t h o u g h i t can be expanded t o 4.0 M t o n n e s / y e a r (4.4 M s . t o n / y e a r ) . Out o f t h e 29 seams i d e n t i f i e d on t h e p r o p e r t y , f o u r o f them, 1, 7, 10 and 16 a r e major and g e n e r a l l y c o n t i n u o u s t h r o u g h o u t t h e p r o p e r t y . A c c o r d i n g t o B r i t c h 1 1 , t h e m a j o r s t r u c t u r e i s a b r o a d open s y n c l i n e w h i c h p l u n g e s g e n t l y t o t h e n o r t h . The l i m b s of t h e s y n c l i n e d i p between 20 t o 40 d e g r e e s on t h e west l i m b and f r o m 20 t o 60 d e g r e e s on t h e e a s t l i m b . R e g i o n a l and l o c a l f a u l t i n g a r e a l s o p r e s e n t . A g e n e r a l o u t l o o k of t h e s t a t i g r a p h y i s g i v e n i n F i g u r e 5.4-1. D u r i n g t h e r e s e a r c h p r o j e c t , d a t a g a t h e r i n g has been c o n c e n t r a t e d i n t h e Cougar p i t where seams 16 t o 29 a r e e x p o s e d on t h e west l i m b ( F i g u r e 5 . 4 - 2 ) . One o f t h e major f e a t u r e s o f t h e Cougar p i t i s t h e p r e s e n c e of c r o s s f a u l t s 213 SANDSTONE SILTSTONE »**«»* MUDSTONE mm COAL co O UJ o Ul or c_> o CO CO < or "3 Z g < CE O U. > < z UJ h-o o z II si u. ELKMEMBER SANDSTONE SILTSTONE MUDSTONE 60 m + COAL BEARING MEMBER SANDSTONE SILTSTONE MUDSTONE COAL 550 m MOOSE MOUNTAIN MEMBER CHERT SANDSTONE l2-25rn SANDSTONE SILTSTONE SHALE 245 m + 600-H»»*u vl& E L K MEMBER 500 2-7 m 5-llm 400 3 0 0 -5-Mm j£C<S 7 - l l m SEAM 29 SEAM 28 SEAM 27 SEAM 25-26 SEAM 22 SEAM 20 SEAM I 9 SEAM I 8 SEAM I6-I6L SEAM 13 SEAM 11 SEAMIO-IOL 200-SEAM 9 ™F3 SEAM 9-1 SEAM 9-2 SEAM 7 100' 10-16 m \ SEAM 5 SEAM 3 SEAM I SEAM M MOOSE MTN MEMBER FIGURE 5.4-1 = GREENHILLS MINE STATIGRAPHY (after Britch") 214 6 50 lOOm FIGURE 5.4-2= GREENHILLS COUGAR PIT scale 1=5000 215 s t r i k i n g e a s t e r l y and d i p p i n g 70° t o t h e s o u t h . The f a u l t e d a r e a s e x h i b i t o x i d i z e d m a t e r i a l s of v e r y low s t r e n g t h . In a d d i t i o n , t h e s e d i m e n t a r y s e q u e n c e i s s l i g h t l y a l t e r e d and t h e r o c k mass i s more f r a c t u r e d . In t h e n o r t h e r n p a r t of t h e Cougar p i t , t h e r o c k shows a more competent b e h a v i o u r . T a b l e 8 shows t h e d i f f e r e n t s t r e n g t h p a r a m e t e r s of t h e r o c k s . i TABLE 8 ROCK PROPERTIES GREENHILLS MINE ROCK TYPE HARDNESS APPROXIMATE RANGE OF UNIAXIAL COMPRESSIVE STRENGTH (MPa) (psi) DENSITY (q/cc) SHEAR STRENGTH OF DISCONTINUITY Sandstone Siltstone Mudstone R4 R3-R4 R2-R3 115-155 40-152 60-99 17000-23000 6000-22000 9000-14000 2 . 7 0 2 . 7 0 2 . 7 0 28 33.5 31 217 5.4.2 The B l a s t i n g P r o c e d u r e s a t G r e e n h i l l s At G r e e n h i l l s mine, b l a s t s a r e d e s i g n e d t o p r o d u c e a f i n e and e v e n l y f r a g m e n t e d muck p i l e f o r optimum l o a d i n g c o n d i t i o n s and h i g h p r o d u c t i v i t y . B e c a u s e o f t h e n a t u r e o f t h e o p e r a t i o n and t h e g e o l o g y of t h e mine, a l l b l a s t s a r e d i r e c t e d t o w a r d a f r e e f a c e . However, as t h e d i p a n g l e o f t h e beds i s r e d u c e d , a d d i t i o n a l r o w ( s ) o f h o l e s a r e r e q u i r e d a t t h e t o e l o c a t i o n t o improve f r a g m e n t a t i o n and d i s p l a c e m e n t . At t h e p r e s e n t t i m e , no p e r i m e t e r b l a s t has been s h o t , t h e o p e r a t i o n b e i n g a t t h e t o p o f the r i d g e and t h e r e f o r e f a r away from t h e f i n a l w a l l . B e n c h e s a r e d e s i g n e d 14 m e t r e s (46 f t ) h i g h . B l a s t h o l e s 270 mm (10 5/8 i n c h e s ) i n d i a m e t e r a r e d r i l l e d t o a d e p t h o f 15.5 m e t r e s (51 f t ) on a s t a g g e r e d 7.0 by 8.1 m (23 f t by 26.5 f t ) p a t t e r n l a i d - o u t by t h e s u r v e y o r s . C a v i n g o c c u r s a t bench c r e s t a r e a s and b l a s t h o l e s a r e t h e n r e d r i l l e d . E ven t h o u g h t h e d e s i g n powder f a c t o r a p p r o a c h i s u s e d , t h e r e a l powder f a c t o r may be i n c r e a s e d by t h e p r e s e n c e o f f i l l e r h o l e s added, when needed, w i t h i n t h e p a t t e r n a n d / o r by t h e p r e s e n c e of b l a s t h o l e s d e e p e r t h a n 15.5 m e t r e s (51 f t ) . In b o t h c a s e s , t h e r e i s no burden volume a l l o c a t e d t o t h e e x t r a e x p l o s i v e l o a d . However, w i t h f r e e d i g g i n g , t h e o v e r a l l powder f a c t o r i s g e n e r a l l y s l i g h t l y l e s s t h a n t h e n e t d e s i g n powder f a c t o r . The e x p l o s i v e u s e d i s s t r a i g h t ANFO. I n i t i a t i o n i s by t h e NONEL s y s t e m w h i c h e l i m i n a t e s s i d e i n i t i a t i o n . D e l a y s between the rows a r e kept t o 50 ms t o a v o i d t h e p r o b a b i l i t y of 218 d i s r u p t i o n o f t h e e x p l o s i v e column a l o n g t h e w e l l d e f i n e d p a r t i n g p l a n e s between t h e d i f f e r e n t s e d i m e n t a r y b e d s . The d e s i g n powder f a c t o r i s e v a l u a t e d by t h e d r i l l and b l a s t foreman b a s e d on t h e g e o l o g y , h i s e x p e r i e n c e on t h e p r e v i o u s b e n c h e s , t h e d r i l l p e r f o r m a n c e and t h e c u t t i n g s . In t h e h a r d z o n e s , s u c h as t h e competent s a n s t o n e beds of t h e 16 and 20 u p p e r seams h a n g i n g w a l l s , i n t h e n o r t h e r n p a r t of Cougar p i t , t h e powder f a c t o r i s p r e s e n t l y f i x e d t o 0.55 kg/m 3 (0.41 l b s / s . t o n ) down from t h e 0.59 kg/m 3 (0.44 l b s / s : t o n ) u s e d d u r i n g t h e 1983 summer. D u r i n g t h e same b l a s t o p t i m i z a t i o n p r o g r a m , t h e powder f a c t o r a l l o c a t e d t o t h e s o f t a r e a s , s u c h as t h e f a u l t e d z o n e s i n th e s o u t h e r n Cougar p i t , was r e d u c e d t o 0.47 kg/m 3 (0.35 l b s / s . t o n ) . B l a s t r e s u l t s a r e s t i l l v e r y good. 5.4.3 Development o f t h e C o r r e l a t i o n Between RQI and Powder  F a c t o r At G r e e n h i l l s , c o a l i s mined on b e n c h e s i n a sequence t h a t s t a r t s from t h e e a s t (seam 29) westward. The m i n a b l e seams i n Cougar P i t a r e seams 29, 28, 27, 25-26, 22, 20 u p p e r , 20 l o w e r , 18 and 16. The waste r o c k t h a t l i e s between t h e seams a r e c a l l e d a c c o r d i n g t o t h e number of t h e f o l l o w i n g seam ( i e . , t h e 16 seam h a n g i n g w a l l i s t h e waste t h a t has t o be moved t o g a i n a c c e s s t o t h e 16 seam). The b l a s t i n g domains a r e t h e r e f o r e v e r y d i f f e r e n t f r o m one t o t h e n e x t , as a f u n c t i o n of t h e r o c k t y p e s and d e g r e e o f f r a c t u r i n g o f t h e s e d i m e n t a r y s e q u e n c e . The 219 n a t u r e of t h e domains r e m a i n s c o n s t a n t from one b e n c h t o t h e n e x t . However, t h e p r e s e n c e o f f a u l t s i n t h e s o u t h e r n p a r t of th e p i t s l i g h t l y d i s t u r b s t h e c o n t i n u i t y o f t h e c o a l seams i n t h e s t r i k i n g d i r e c t i o n , and i n c r e a s e s t h e i n t e n s i t y o f f r a c t u r i n g and a l t e r a t i o n o f t h e r o c k s . T h e r e f o r e , a d i f f e r e n t i a t i o n i s done, when n e c e s s a r y , between t h e n o r t h e r n and s o u t h e r n domains. A r e a s o f t h e domains were g e n e r a l l y l a r g e . A l s o , as t h e r e c o r d e r was n o t o p e r a t i n g , d r i l l i n g d a t a from t h e p r e v i o u s bench were a n a l y s e d ; t h e d r i l l i n g and b l a s t i n g r e c o r d s p e r m i t t e d e a s y i n t e r p r e t a t i o n . The a l l o c a t i o n o f t h e RQI t o t h e d i f f e r e n t d o mains i s summarized i n t h e f o l l o w i n g pages ( T a b l e 9, F i g u r e 5 . 4 - 3 ) . S i n c e t h e b l a s t i n g p r o c e d u r e s a t G r e e n h i l l s a r e k e p t c o n s t a n t and t h e powder f a c t o r i s t h e o n l y v a r i a b l e , e v a l u a t i o n of b l a s t r e s u l t s was made s i m p l e . As t h e o p p o s i t e o f L o r n e x Mine, G r e e n h i l l s b l a s t s a r e d e s i g n e d t o p r o d u c e a e v e n l y f r a g m e n t e d , w e l l d i s p l a c e d muck p i l e t h a t o p t i m i z e s t h e p r o d u c t i v i t y of t h e l o a d i n g e q u i p m e n t . T h e r e f o r e , no b l a s t r e s u l t s were c o n s i d e r e d u n d e r l o a d e d . T a b l e 10 and F i g u r e 5.4-4 d e s c r i b e t h e r e l a t i o n s h i p between RQI and e n e r g y f a c t o r d e r i v e d from t h e d a t a g a t h e r e d . I t i s i n t e r e s t i n g t o n o t e t h a t t h e powder f a c t o r has been r e d u c e d a t G r e e n h i l l s s i n c e t h e r e s e a r c h p r o j e c t t o o k p l a c e . S i n c e G r e e n h i l l s e x p r e s s e s t h e e x p l o s i v e c o n s u m p t i o n i n kg/m 3, t h i s u n i t i s a l s o i n c l u d e d i n t h e t a b l e . 220 TABLE 9  SUMMARY OF RQI VALUES AT GREENHILLS MINE DOMAINS ROCK QUALITY INDEX (270mm-10 5/8 inch) I Seam 28 HW I I Seam 21 HW I I I Seam 25-26 HW IV Seam 22 HW V Seam 20up HW north VI Seam 20up HW south V I I Seam 201w HW north V I I I Se; HW south IX Seair. . HW north X Seam 16 HW south kg-min/m (* 100.0) 32.3 33.6 37.4 29.2 62.9 39.7 39.1 25.9 48.7 42.1 lbs-min/ft .rC*1000) 21.7 22.6 25.1 19.6 42.3 26.7 26.3 17.4 32.7 28.3 221 O O o o o o c i I 75-1 50-i 60- 40-o E •'ton t o < O I 30-E E * O o r-O CM or — 30- 20-15- 10-5 o o 0 X 0- o Q O O o Q o o o < o o o Q z o o o DOMAINS FIGURE 5.4-3' ROCK QUALITY INDEX VALUES FOR EACH DOMAIN RANKED IN ORDER OF DECREASING QUALITY, GREENHILLS, 222 TABLE 10  CORRELATION BETWEEN RQI AND POWDER FACTORS AT GREENHILLS MINE DOMAINS ROCK QUALITY INDEX (270mm-10 5/8inch) kg-min/m (*1000) lbs-min/ft (*1000) POWDER FACTOR kg/tonne kg/m~ lbs/s.ton I II III IV V VI VII VIII IX X 32.3 33.6 37.4 29.2 62.9 39.7 39.1 25.9 48.7 42.1 21.7 22.6 25.1 19.6 42.3 26.7 26. 3 17.4 32.7 28.3 0.155 0.155 0.160 0.150 0.195 0.160 0.160 0.150 0.175 0.165 0.42 0.42 0.43 0.41 0.53 0.43 0.43 0.41 0.47 0.45 0. 31 0.31 0.32 0.30 0. 39 0.32 0.32 0.30 0.35 0.33 223 x -~r 1.1 _J o '31 o o o o o o E I 75-60- 40-45- 3 0 30 15- 10-0-L 0 - 20 050 lbs S.ton 0.150 0.175 0.200 ENERGY FACTOR 0.225 0.250 FIGURE 5.4-4-PROPOSED CORRELATION BETWEEN ROCK QUALITY HMDEX AND POWDER FACTOR AT GREENHILLS MINE. 224 5.4.4 A n a l y s i s of t h e R e s u l t s The d e t e r m i n a t i o n of a good c o r r e l a t i o n a t G r e e n h i l l s i s due t o t h r e e f a c t o r s : t h e domains b o u n d a r y were w e l l d e f i n e d , t h e d r i l l i n g d a t a were numerous enough w i t h i n e a c h o f t h e domains and t h e b l a s t i n g p r o c e d u r e was k ept c o n s t a n t . However, as f o r t h e o t h e r s i t e s , t h e powder f a c t o r s were no t r e a l l y o p t i m i z e d . The v a l u e s a l l o c a t e d t o e a c h domain a r e t h e minimum powder f a c t o r t h a t s t i l l y i e l d s good b l a s t i n g r e s u l t s . T h e r e f o r e , i t i s not known i f t h e powder f a c t o r s c a n be f u r t h e r r e d u c e d . The two domains, d e s c r i b e d by t h e d r i l l and b l a s t foreman as t h e t o u g h e s t t o b l a s t showed t h e h i g h e s t Rock Q u a l i t y I n d e x . The domains a r e d e s c r i b e d as c o m p e t ent s a n d s t o n e and c ompetent s i l t s t o n e w i t h s a n d s t o n e . The f a u l t e d end o f t h e s e two domains, e a s i e r t o b l a s t , p o s s e s s lower RQI. The r e l a t i o n s h i p d e v e l o p e d a t t h i s s i t e between t h e Rock Q u a l i t y Index and t h e powder f a c t o r i s s t i l l a t an e a r l y s t a g e of d e v e l o p m e n t . F u r t h e r t e s t i n g and d a t a e v a l u a t i o n a r e s u g g e s t e d i n o r d e r t o f i n e - t u n e t h e c o r r e l a t i o n . The r e s u l t s however a r e v e r y e n c o u r a g i n g . 225 5.5 DISCUSSION AND INFERENCES 5.5.1 A c c u r a c y of t h e I n p u t D a t a In p r e v i o u s s t u d i e s on Rock Q u a l i t y Index, t h e a c c u r a c y of t h e i n p u t d a t a was c o n s i d e r e d a major f a c t o r i n t h e e s t a b l i s h m e n t of a v a l i d r o c k mass c h a r a t e r i z a t i o n i n d e x . At A f t o n M i n e , t h e d e t e r m i n a t i o n o f domain b o u n d a r i e s by c o n v e n t i o n a l methods and t h e e v a l u a t i o n o f t h e Rock Q u a l i t y Index w i t h i n t h e s e domain has y i e l d e d good r e s u l t s . The domain a r e a s were l a r g e and t h e d r i l l i n g d a t a numerous. However, L e i g h t o n 1 was c o n c e r n e d by t h e h i g h d e g r e e of v a r i a t i o n i n t h e RQI i n a d j a c e n t b l a s t h o l e s . In t h i s r e s e a r c h p r o j e c t , t h e a u t h o r o b s e r v e d maximum v a r i a t i o n s r a n g i n g between 50 t o 200 % w i t h a common d e p a r t u r e r a n g i n g between 25 t o 140 %. T h i s h i g h d e g r e e o f v a r i a b i l i t y s u g g e s t s t h a t a c o n s i d e r a b l e amount of d a t a i s n e e d e d i n o r d e r t o make t h e a v e r a g e o r peak v a l u e r e p r e s e n t a t i v e of t h e d i s t r i b u t i o n . T h e s e a r e n o t a l w a y s a v a i l a b l e . The v a r i a t i o n s a r e n o t o n l y c a u s e d by t h e inhomogeneous n a t u r e o f t h e r o c k mass, b ut a l s o by t h e d r i l l i n g p r a c t i c e and t h e d e d i c a t i o n of t h e d r i l l i n g crew i n r e p o r t i n g t h e o p e r a t i o n a l p a r a m e t e r s . G e n e r a l l y , t h e d r i l l i n g t i m e i s r e p o r t e d t o t h e n e a r e s t f i v e m i n u t e s , sometimes g e n e r o u s l y r o u n d e d - u p t o t h e upper l i m i t . The down p r e s s u r e i s u s u a l l y s p e c i f i e d a s t h e maximum r e a d i n g ( i e . , 4.1 MPa (600 p s i ) w h i l e most of t h e h o l e was d r i l l e d a t 3.4 MPa (500 p s i ) ) o r as a range 226 3.4 MPa t o 4.1 MPa (500 - 600 p s i ) . The h o l e d e p t h i s a c c u r a t e most o f t h e t i m e a l t h o u g h some d r i l l e r s p r e f e r t o d r i l l a few more f e e t t o be on t h e s a f e s i d e ( e s p e c i a l l y i n c a v i n g g r o u n d ) . I f t h e Rock Q u a l i t y Index a p p r o a c h t o r o c k mass c h a r a c t e r i z a t i o n i s t o be i m p l e m e n t e d a t one s i t e , t h e d r i l l i n g crew must be aware of t h e i n f l u e n c e of t h e i r r e p o r t s on t h e d e c i s i o n making p r o c e s s t h a t f o l l o w s . The a u t h o r b e l i e v e s t h a t no r e a l p r o b l e m s would be e n c o u n t e r e d . In t h e p r e s e n t r e s e a r c h p r o j e c t , i t was b e l i e v e d t h a t t h e d r i l l p e r f o r m a n c e r e c o r d e r w o u l d p r o v i d e v e r y a c c u r a t e d a t a so t h a t t h e q u a n t i t y needed i n e v e r y domain would be d r a m a t i c a l l y r e d u c e d . The RQI v a l u e s c o m p i l e d a t E q u i t y S i l v e r and L o r n e x were computed o n l y from t h e d a t a g a t h e r e d d u r i n g t h e p e r i o d of t i m e t h e a u t h o r s p e n t a t e a c h s i t e , c o n s i d e r i n g t h a t t h e RQI o b t a i n e d f r o m t h e r e c o r d e r would b a c k -up t h e e s t a b l i s h m e n t o f t h e c o r r e l a t i o n . At G r e e n h i l l s , t h e RQI was c o m p i l e d f r o m d r i l l i n g d a t a o b t a i n e d f r o m r e c o r d s up t o s i x months o l d and c o v e r i n g two b e n c h e s i n a l m o s t e v e r y domain o f t h e C o u gar p i t . A c c u r a t e and e x t e n s i v e d a t a a r e i m p o r t a n t . I t seems t h a t t h e q u a n t i t y c o m p e n s a t e s f o r t h e wide v a r i a t i o n s . 5.5.2 D r i l l P e r f o r m a n c e R e c o r d e r s The use of a d r i l l p e r f o r m a n c e r e c o r d e r p a r t l y r e d u c e s t h e d e g r e e of v a r i a t i o n of t h e d r i l l i n g d a t a . The RQI v a l u e s c o m p i l e d f r o m t h e r e c o r d e d c h a r t s do n o t i n c l u d e t h e u n c e r t a i n i t i e s c a r r i e d by t h e d r i l l e r ' s method o f r e p o r t i n g t h e 227 o p e r a t i n g p a r a m e t e r s . However, t h e r e a r e s t i l l some e x t e r n a l f a c t o r s , r e d u c i n g t h e a c c u r a c y of t h e RQI, t h a t a r e r e c o r d e d . F o r example, t h e b i t wear, t h e d i f f e r e n c e i n b a i l i n g v e l o c i t y a n d / o r p r e s s u r e between t h e d r i l l , s l i g h t v a r i a t i o n s i n t h e d r i l l i n g p r a c t i c e , e t c . In a d d i t i o n , t h e use of a c h a r t r e c o r d e r may add a new s o u r c e o f b i a s . When t h e a p p l i e d w e i g h t on t h e b i t v a r i e s c o n s t a n t l y a l o n g t h e b l a s t h o l e d e p t h , t h e e s t i m a t i o n o f t h e ( a v e r a g e ) a p p l i e d w e i g h t f o r t h a t p a r t i c u l a r b l a s t h o l e i n c l u d e s an e s t i m a t o r b i a s . In t h e w o r s t c a s e s , t h e d a t a were n o t i n c l u d e d i n t h e d a t a f i l e . One o t h e r p r o b l e m t h a t was e x p e r i e n c e d i s t h e d e t e r m i n a t i o n of t h e b l a s t h o l e number c o r r e s p o n d i n g t o t h e r e c o r d e d d a t a . On t h e c h a r t s , t h e d r i l l e r s were r e q u i r e d t o r e g i s t e r t h e f i r s t and l a s t b l a s t h o l e number o f t h e s h i f t . N e v e r t h e l e s s , i t was sometimes d i f f i c u l t t o r e l a t e a l l t h e h o l e s d r i l l e d w i t h t h e r e c o r d s a v a i l a b l e . F i n a l l y , t h e d r i l l e r s were a s k e d t o w r i t e t h e b l a s t h o l e number b e s i d e s t h e r e c o r d e d d a t a . The a u t h o r f e e l s t h a t t h e r e a r e many i n c e n t i v e s t o t h e i n s t a l l a t i o n of a d r i l l p e r f o r m a n c e r e c o r d e r on b l a s t h o l e d r i l l r i g s . However, i f t h e i n s t a l l a t i o n o f s u c h a d e v i c e i s made w i t h t h e i d e a o f g a t h e r i n g r o c k mass c h a r a c t e r i z a t i o n d a t a , a c o m p u t e r i z e d s y s t e m t h a t would c o m p i l e , s t o r e and r e l e a s e t h e i n f o r m a t i o n s h o u l d be d e v e l o p e d . In t h e mean t i m e , mine o p e r a t o r s c a n p r o v i d e t h e d r i l l i n g crew w i t h a $10.00 p o c k e t c a l c u l a t o r and t e a c h them how t o compute t h e Rock Q u a l i t y I n d e x . In t h e o f f i c e , d a t a would be e a s i l y f i l e d on a computer by t e c h n i c i a n s . The i n v e s t i g a t i o n of t h e use o f a d r i l l 228 p e r f o r m a n c e r e c o r d e r s h o u l d be c o n t i n u e d i n o r d e r t o p e r m i t t h e d e v e l o p m e n t o f t h e optimum s y s t e m . They a r e d e f i n i t i v e l y u s e f u l i n e l i m i n a t i n g t h e d r i l l e r ' s b i a s . However, i f t h e q u a l i t y o f t h e d a t a i s i m p o r t a n t , t h e q u a n t i t y o f v a l u a b l e d a t a i s as i m p o r t a n t when c h a r a c t e r i z i n g t h e r o c k mass. 5.5.3 D r i l l i n g P r o c e d u r e s D r i l l i n g e f f i c i e n c y i n f l u e n c e s t h e Rock Q u a l i t y I n d e x . I t i s p o s s i b l e , w i t h i n a g i v e n o p e r a t i o n , t h a t t h e e f f i c i e n c y of t h e v a r i o u s d r i l l i n g u n i t s v a r i e s due t o t h e d r i l l e r a n d / o r t h e c o n d i t i o n s of t h e e q u i p m e n t . The e f f e c t of t h e d r i l l i n g c r ews has a l r e a d y been c o v e r e d and t h e r e f o r e , t h i s p a r a g r p h w i l l r e v i e w t h e b a s i c m e c h a n i c a l f a c t o r s . The c o n d i t i o n o f t h e d r i l l s , s u c h as t h e age o r wear of t h e components i s an o t h e r i m p o r t a n t f a c t o r i n t h e e s t a b l i s h m e n t of c o r r e l a t i o n s w i t h t h e Rock Q u a l i t y I n d e x . Many o p e r a t i o n s pay much more a t t e n t i o n t o t h e m a i n t e n a n c e o f t r u c k s and s h o v e l s t h a n t o t h e d r i l l m a i n t e n a n c e . C o m p r e s s o r s and r o t a r y m o t o r s s h o u l d be c h e c k e d and compared i n o r d e r t o d e t e r m i n e i f t h e d r i l l s a r e o p e r a t i n g a t t h e same l e v e l o f e f f i c i e n c y . G e n e r a l l y , d r i l l s of t h e same model bought a t d i f f e r e n t t i m e s w i l l n ot p e r f o r m e q u a l l y . The same i s t r u e w i t h d i f f e r e n t m a n u f a c t u r e r u n i t s . The c o m p a r i s o n of t h e Rock Q u a l i t y Index i n u n i t s of w e i g h t r a t h e r t h a n p r e s s u r e e l i m i n a t e s t h e d i f f e r e n c e s i n t h e r e l a t i o n s h i p s between h y d r a u l i c s y s t e m p r e s s u r e and 229 a p p l i e d w e i g h t w h i c h a r e v a r i a b l e s f r o m one d r i l l model ( m a n u f a c t u r e r ) t o t h e o t h e r . I t i s a l s o s u g g e s t e d t o c a l i b r a t e t h e p r e s s u r e gage i n t h e c a b i n t o e n s u r e a c c u r a t e r e a d i n g s when no d r i l l p e r f o r m a n c e r e c o r d e r i s u s e d . A v e r y i m p o r t a n t q u e s t i o n was l e f t open by L e i g h t o n 1 i n h i s r e p o r t . He wondered how t h e wear o f t r i c o n e b i t s does i n f l u e n c e t h e p e n e t r a t i o n r a t e , o t h e r v a r i a b l e s kept c o n s t a n t . T h i s q u e s t i o n was i n v e s t i g a t e d by t h e a u t h o r . A l t h o u g h v e r y a p p r o x i m a t i v e , F i g u r e 5.5-1 i l l u s t r a t e s t h e t h r e e s i t u a t i o n s t h a t may a r i s e . The v a r i a t i o n s o f t h e p e n e t r a t i o n r a t e a r e a f u n c t i o n o f t h e t y p e of wear. B i t m a u f a c t u r e r s c l a i m t h a t under n o r m a l d r i l l i n g c o n d i t i o n s , c a r b i d e i n s e r t b i t s w i l l n o t show any r e d u c t i o n i n t h e p e n e t r a t i o n r a t e u n t i l t h e v e r y l a s t h o u r s . N e v e r t h e l e s s , t h e g r a p h s u g g e s t s t h a t some v a r i a t i o n s w i l l o c c u r . T h e r e f o r e , t h e c o m p i l a t i o n o f numerous d r i l l i n g d a t a i n e v e r y domain i s recommended t o smooth o f f t h e s e v a r i a t i o n s i n RQI • F i n a l l y , t h e c o m p a r i s o n of t h e RQI v a l u e s a t E q u i t y S i l v e r M i ne, o b t a i n e d from t h e d i f f e r e n t d i a m e t e r b l a s t h o l e s and a r e v i e w of t h e L i t t l e ' s 1 3 f i n d i n g s prompt t h e f o l l o w i n g q u e s t i o n : would a g i v e n r o c k mass y e i l d t o t h e same RQI when d r i l l e d w i t h d i f f e r e n t d i a m e t e r b i t s i f t h e d e g r e e o f d r i l l i n g e f f i c i e n c y i s kept c o n s t a n t . T h i s i s a v e r y complex p r o b l e m r e l a t e d t o t h e th e d e t e r m i n a t i o n of t h e l e v e l o f d r i l l i n g e f f i c i e n c y and optimum d r i l l i n g c o n d i t i o n s . The d r i l l i n g g u i d e l i n e s p r o v i d e d by t h e b i t m a n u f a c t u r e r s and c o n c e r n i n g t h e a p p l i e d w e i g h t p e r 230 TIME OR FOOTAGE 0 : CUTTER SHAPE CHANGES (more Blunt) (g) : CUTTER SHAPE STAYS CONSTANT WITH TIME CUTTER AND CONE MATRIX WEAR EQUALLY (normal) (D :CONE MATRIX WEARS FASTER THAN CUTTERS FIGURE 5.5-h INFLUENCE OF TRICONE ROTARY BIT WEAR ON PENETRATION RATE (after Paquette12) 231 i n c h o f b i t d i a m e t e r a r e b a s e d on e x p e r i e n c e . A c c o r d i n g t o B u r k e 1 4 , t h e y y i e l d a c o n s t a n t p e n e t r a t i o n r a t e , a l t h o u g h t h e p e n e t r a t i o n r a t e may i n c r e a s e as t h e d i a m e t e r i s r e d u c e d . He ad d e d : "With t h e e x c e p t i o n of v e r y h a r d f o r m a t i o n s , t h e p e n e t r a t i o n r a t e i s g e n e r a l l y l i m i t e d o n l y by t h e . b a i l i n g c a p a c i t y o f t h e d r i l l i n g e q u i p m e n t . " As t h e d i a m e t e r of t h e b l a s t h o l e i s r e d u c e d , t h e b a i l i n g v e l o c i t y i n c r e a s e s and t h e c u t t i n g r e m o v a l p r o c e s s i s g e n e r a l l y i m p r o v e d . T h e r e f o r e , a s t h e b i t d i a m e t e r i s r e d u c e d , t h e Rock Q u a l i t y Index d e c r e a s e s a c c o r d i n g l y ( T a b l e 1 1 ) . F u r t h e r r e s e a r c h i s s u g g e s t e d i n o r d e r t o o b t a i n a r e l a t i o n s h i p t h a t would p e r m i t c o n v e r s i o n of RQI v a l u e s o b t a i n e d from d i f f e r e n t b i t d i a m e t e r s . The i n v o l v e m e n t of a b i t m a n u f a c t u r e r company and i t s r e s e a r c h f a c i l i t i e s w o u l d be a p p r e c i a t e d . 5.5.4 B l a s t i n g P r o c e d u r e s I t has been shown, i n c h a p t e r f o u r , how t h e v a r i a t i o n s i n b l a s t d e s i g n i n f l u e n c e t h e optimum d e s i g n powder f a c t o r . T h i s f i e l d r e s e a r c h p r o j e c t has d e m o n s t r a t e d t h i s f a c t . The e s t a b l i s h m e n t of a c o r r e l a t i o n between RQI and optimum d e s i g n powder f a c t o r s i s o n l y p o s s i b l e when t h e b l a s t d e s i g n r e m a i n s c o n s t a n t . V a r i a t i o n s i n t h e d e s i g n p a r a m e t e r s i n f l u e n c e t h e r e s u l t s and make i m p o s s i b l e t h e e v a l u a t i o n of t h e b l a s t p e r f o r m a n c e on a c o n s t a n t b a s i s . N e v e r t h e l e s s , i t i s b e l i e v e d t h a t a c o r r e l a t i o n c an be o b t a i n e d f o r any b l a s t d e s i g n a s l o n g 232 TABLE 11 RELATIONSHIP BETWEEN ROCK QUALITY INDEX AND ROTARY BIT DIAMETER BIT DIAMETER APPLIED WEIGHT PENETRATION RATE 311mm - 12 1/4 inches i reduced I 152mm - 6 inches reduced I 1 com;I ant or s l i g h t increase i 233 a s t h e y a r e k e p t c o n s t a n t w i t h i n a g i v e n domain. Choked b l a s t i n g s h o u l d be a v o i d e d . I t i s i n e f f i c i e n t and damages t h e w a l l s . T h e r e a r e v e r y few o c c a s i o n s where i t becomes t h e o n l y s o l u t i o n . The d e s i g n powder f a c t o r c o n c e p t s h o u l d be u n d e r s t o o d and i m p l e m e n t e d . W a l l c o n t r o l b l a s t i n g p r o c e d u r e s t a r t s w i t h t h e p r o d u c t i o n b l a s t s . Even i f t h e p r e s e n t w a l l s a r e c o n s i d e r e d i n t e r i m p i t w a l l s , s t r i p p i n g e x p e n s e s can be p o s t p o n e d by p r o d u c i n g more s t a b l e and s t e e p e r w a l l s . In a d d i t i o n , i t p e r m i t s t h e d e v e l o p m e n t and t e s t i n g of good w a l l c o n t r o l b l a s t i n g p r o c e d u r e s . 5.5.5 Rock Mass C o n d i t i o n s and P r o p e r t i e s The Rock Q u a l i t y Index r e f l e c t s r o c k mass p r o p e r t i e s and i t s f a i l u r e b e h a v i o u r . A r e v i e w of t h e work on RQI shows t h a t t h e s t r e n g t h o f t h e r o c k c o r r e l a t e s w i t h t h e RQI. In a d d i t i o n , t h e RQI v a l u e s a r e r e d u c e d i n h i g h l y f r a c t u r e d r o c k m a s s e s . W i t h i n a p r e d e t e r m i n e d b l a s t i n g domain, t h e Rock Q u a l i t y Index can be c o r r e l a t e d w i t h t h e optimum d e s i g n powder f a c t o r . I t w o u l d be of i n t e r e s t t o s t o r e RQI d a t a i n a g e o l o g i c a l m o d e l . Then, by u s i n g g e o s t a t i s t i c a l r o u t i n e s , s u c h as v a r i o g r a m s o r a v e r a g i n g m e t h o d s 1 5 , a more c o m p l e t e p i c t u r e of t h e r e l a t i o n s h i p s between t h e Rock Q u a l i t y Index and t h e r o c k mass p r o p e r t i e s c o u l d be o b t a i n e d . In t h i s r e s e a r c h p r o j e c t , two r o c k mass c o n d i t i o n s have been n o t i c e d f o r t h e i r e f f e c t on RQI. In i n t e n s e l y f r a c t u r e d 234 r o c k masses, t h e d r i l l i n g t i m e may i n c r e a s e s l i g h t l y due t o c a v i n g g r o u n d and t h e r e f o r e i n c r e a s e t h e RQI v a l u e s w h i l e t h e e x p l o s i v e r e q u i r e m e n t s r e d u c e w i t h t h e i n c r e a s e i n t h e d e g r e e o f f r a c t u r i n g . The s e c o n d f a c t o r i s g r o u n d w a t e r . I t a f f e c t s t h e 41 RQI i n two d i f f e r e n t ways. In h i g h l y b r o k e n r o c k s , t h e g r o u n d w a t e r i n c r e a s e s t h e i n t e n s i t y o f c a v i n g . F i n a l l y , g r o u n d w a t e r a f f e c t s t h e b a i l i n g c a p a c i t y of t h e d r i l l when a column o f w a t e r s t a n d s o v e r t h e b i t a t t h e b o t t o m o f t h e h o l e . In b o t h c a s e s , t h e g r o u n d w a t e r c h a n g e s t h e p e n e t r a t i o n r a t e and i n c r e a s e s t h e Rock Q u a l i t y I n d e x . 5.5.6 C o r r e l a t i o n s w i t h t h e Rock Q u a l i t y Index A r e l a t i o n s h i p between RQI and t h e d e s i g n powder f a c t o r e x i s t s . I t c a n be e s t a b l i s h e d i n any o p e r a t i o n i f t h e b a s i c g u i d e l i n e s a r e f o l l o w e d . At t h i s t i m e , t h e c o r r e l a t i o n s a r e s i t e s p e c i f i c i n a s e n s e t h a t i t i s not p o s s i b l e t o compare t h e RQI v a l u e s o f d i f f e r e n t o p e r a t i o n s nor t h e powder f a c t o r s a p p l i e d t o d i s t i n c t b l a s t d e s i g n s . As more d a t a a r e o b t a i n e d , a r a n g e o f r e l a t i o n s h i p s s h o u l d d e v e l o p . A c o r r e l a t i o n was a l s o e s t a b l i s h e d a t L o r n e x Mine between t h e RQI and t h e g r i n d i n g r a t e of t h e o r e . However, i t a p p e a r s t h a t t h e a c c u r a c y of t h e r e l a t i o n s h i p i s a l s o a f u n c t i o n of t h e domain a r e a . T h i s c o n s t r a i n t has t o be e v a l u a t e d w i t h t h e d e g r e e of p r e c i s i o n r e q u i r e d by t h e m i l l i n g o p e r a t i o n . F i n a l l y , v a r i a t i o n s i n t h e Rock Q u a l i t y Index i n a d j a c e n t 235 h o l e s a r e l a r g e enough t h a t i t s u g g e s t s t h a t a h o l e p e r h o l e l o a d i n g a p p r o a c h may not be p r a c t i c a l . N e v e r t h e l e s s , a c o m p a r i s o n of t h e b l a s t a v e r a g e RQI w i t h t h e Rock Q u a l i t y Index a l l o c a t e d t o t h e domain c o u l d l e a d t o a b e t t e r l o a d i n g p r a c t i c e on a day t o day b a s i s . However i t s h o u l d be remembered t h a t many d r i l l i n g f a c t o r s i n f l u e n c e t h e RQI, t h e r e f o r e c a r e must be use d when t h e d a t a a r e few. 236 5.6 SUGGESTED FURTHER RESEARCH The r e s u l t s o b t a i n e d i n t h e r e s e a r c h p r o j e c t e s t a b l i s h e d i n t h e 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 o f U.B.C. a r e i n t e r e s t i n g enough t o p e r m i t t h e c o n t i n u a t i o n of t h e r e s e a r c h on Rock Q u a l i t y I ndex. In t h i s s e c t i o n , t h e a u t h o r w i s h e s t o summarize t h e b a s i c g u i d e l i n e s t h a t w o u l d p e r m i t t h e d e f i n i t i o n of a f r u i t f u l c o r r e l a t i o n between t h e Rock Q u a l i t y Index and t h e d e s i g n powder f a c t o r . A l s o i n c l u d e d a r e t h e p o i n t s t h a t r e q u i r e f u r t h e r i n v e s t i g a t i o n . I t s h o u l d n e v e r be f o r g o t t e n t h a t t h e Rock Q u a l i t y Index a p p r o a c h t o r o c k mass c h a r a c t e r i z a t i o n has t o re m a i n s i m p l e and p r a c t i c a l . G u i d e l i n e s f o r t h e e s t a b l i s h m e n t of a c o r r e l a t i o n between RQI and d e s i g n powder f a c t o r s 1) The f a c t o r s t h a t i n f l u e n c e t h e d e t e r m i n a t i o n of t h e Rock Q u a l i t y Index and t h e optimum d e s i g n powder f a c t o r have t o be w e l l u n d e r s t o o d . The a u t h o r b e l i e v e s t h a t t h i s t h e s i s r e p o r t r e v i e w e d t h e s e f a c t o r s and t h e i r i n f l u e n c e on t h e d r i l l i n g and b l a s t i n g mechanisms i n d e t a i l . - The RQI i s a f f e c t e d by a) t h e o p e r a t o r s k i l l and h o n e s t y i n p r o d u c i n g a c c u r a t e r e p o r t s b) t h e d r i l l i n g p a r a m e t e r s i ) w e i g h t , r o t a r y s p e e d and c o m p r e s s o r c a p a b i l i t i e s , 237 a l t h o u g h t h e l a s t two s h o u l d e v e n t u a l l y r e m a i n a l m o s t c o n s t a n t , i i ) t h e b i t d e s i g n and wear. c) t h e r o c k mass p r o p e r t i e s i ) s t r u c t u r a l : m i c r o and macro s c a l e , i i ) f a i l u r e b e h a v i o u r : u n i a x i a l c o m p r e s s i v e s t r e n g t h , Young's Modulus and P o i s s o n r a t i o . d) t h e q u a n t i t y and q u a l i t y o f t h e d a t a . The optimum e n e r g y f a c t o r i s i n f l u e n c e d by a) t h e m i n i n g method i ) d i r e c t i o n of b l a s t i n g i n r e l a t i o n t o t h e major d i s c o n t i n u i t i e s , i i ) p r e s e n c e or a b s e n c e o f f r e e f a c e s . b) t h e b l a s t d e s i g n p a r a m e t e r s i ) r a t i o s o f h o l e d i a m e t e r , b e nch h e i g h t , b u r d e n , s p a c i n g , s u b d r i l l i n g . i i ) d e l a y s and i n i t i a t i o n s e q u e n c e , i i i ) e x p l o s i v e p r o p e r t i e s . c) t h e r o c k mass p r o p e r t i e s i ) s t r u c t u r a l : m i c r o and macro s c a l e , i i ) f a i l u r e b e h a v i o u r : u n i a x i a l c o m p r e s s i v e s t r e n g t h , Young's Modulus and P o i s s o n r a t i o . In t h e f i e l d , t h e f o l l o w i n g p r o c e d u r e i s s u g g e s t e d : a) D e f i n e b l a s t i n g d omains. 238 b) S t a n d a r d i z e b l a s t i n g p r o c e d u r e s and d e f i n e t h e optimum d e s i g n powder f a c t o r . c ) A v e r a g e RQI d a t a f o r t h e l a s t t h r e e b e n c h e s i n e v e r y domain. C o n s i d e r c h a n g e s i n d r i l l i n g p r a c t i c e and e q u i p m e n t . E n c o u r a g e d r i l l e r s t o pay a t t e n t i o n t o t h e i r r e p o r t s . d) P l o t RQI v s powder f a c t o r . Look a t t h e p o s s i b i l i t y o f f u r t h e r o p t i m i z a t i o n of t h e powder f a c t o r a c c o r d i n g t o t h e r e l a t i o n s h i p . 3) Mine o p e r a t o r s t h a t p o s s e s s good d r i l l i n g and b l a s t i n g r e c o r d s have an a d v a n t a g e . They s h o u l d u n d e r s t a n d t h e i n f l u e n c e of optimum b l a s t i n g p r a c t i c e on t h e o p e r a t i o n and s l o p e s t a b i l i t y . T h e i r f a m i l i a r i t y w i t h t h e d e s i g n powder f a c t o r a p p r o a c h i s a good a s s e t . F u r t h e r i n v e s t i g a t i o n on t h e methods o f c o m p a r i s o n of RQI v a l u e s o b t a i n e d from d i f f e r e n t o p e r a t i o n s i s needed i n o r d e r t o e s t a b l i s h a b a s i c o r g e n e r a l r e l a t i o n s h i p . The d e v e l o p m e n t o f a c o m p u t e r i z e d d r i l l p e r f o r m a n c e r e c o r d e r and t h e i r use on b l a s t h o l e d r i l l r i g s would s i m p l i f y t h e e s t a b l i s h m e n t of a l a r g e d a t a b a s e . I f s u c h a d a t a base i s a l r e a d y a v a i l a b l e , i t would be i n t e r e s t i n g t o p e r f o r m s i m p l e g e o s t a t i s t i c r o u t i n e s i n o r d e r t o o b t a i n o t h e r c o r r e l a t i o n s between t h e Rock Q u a l i t y Index and t h e r o c k mass p r o p e r t i e s . M o r e o v e r , on a l o n g t e r m b a s i s , t h e use of moving a v e r a g e t e c h n i q u e s c o u l d p e r m i t t o e v a l u a t i o n of 239 t h e t r e n d s i n Rock Q u a l i t y Index and p r e d i c t t h e optimum d e s i g n powder f a c t o r t h a t would be r e q u i r e d on f u t u r e b e n c h e s . 240 5.7 REFERENCES 1. LEIGHTON, J.C.; D evelopment o f a C o r r e l a t i o n Between R o t a r y D r i l l P e r f o r m a n c e and C o n t r o l l e d Powder F a c t o r s , M a s t e r ' s D e g r e e T h e s i s , U n i v e r i s t y o f B r i t i s h C o l u m b i a , A u g u s t , 1982 2. ASHBY, J. P . ; P r o d u c t i o n B l a s t i n g and t h e Development o f Open P i t S l o p e s , P r o c e e d i n g s , 3 r d I n t e r n a t i o n a l C o n f e r e n c e on S t a b i l i t y i n S u r f a c e M i n i n g , Brawner e d i t o r , AIME, 1982 3. SCARTACCINI, T.E.; B l a s t H o l e D r i l l R e c o r d e r U t i l i z a t i o n , P r o c e e d i n g s , F a l l M e e t i n g o f t h e S o c i e t y o f M i n i n g E n g i n e e r s of AIME, S t . L o u i s , M i s s o u r i , 1970 4. HAGAN, T.N.; R e i d , I.W.; P e r f o r m a n c e M o n i t o r i n g o f P r o d u c t i o n B l a s t h o l e D r i l l s - A Means of I n c r e a s i n g  B l a s t i n g E f f i c i e n c y , P r o c e e d i n g s , 2nd S u r f a c e M i n i n g and Q u a r r y i n g Symposium, B r i s t o l , E n g l a n d , O c t o b e r 1 983 5. LUTZ, J . , e t a l ; I n s t a n t a n e o u s L o g g i n g B a s e d on a Dynamic T h e o r y of D r i l l i n g , J o u r n a l o f P e t r o l e u m T e c h n o l o g y , V24, J u n e , 1972 6. M anuel d v I n f o r m a t i o n : V i b r a l o g , P u b l i s h e d by J e a n L u t z , S.A. ( F r a n c e ) . A v a i l a b l e ( i n E n g l i s h ) from S o l r o c C o n s u l t a n t s I n c , S a i n t - L a u r e n t , P.Q. H4T 1E3 7. CYR, J.B.; e t a l ; G e o l o g y and M i n e r a l i z a t i o n a t E q u i t y S i l v e r M ine, H o u s t o n , B.C., P r o c e e d i n g s , 8 t h CIM D i s t r i c t S i x M e e t i n g , S m i t h e r s , B.C., 1983 241 8. PEASE, R.B.; G e o l o g i c a l M a p p i n g , 1982 F i e l d S e a s o n , E q u i t y S i l v e r Mine P r o p e r t y , u n p u b l i s h e d r e p o r t 9. ROTHERHAM, D.C.; G e o l o g y and Ore R e s e r v e s o f t h e Sam G o o s l y S i l v e r - C o p p e r D e p o s i t s Volume I , 1979, u n p u b l i s h e d r e p o r t 10. WALDNER, G.D.; e t a l ; L o r n e x , P o r p h y r y D e p o s i t s o f t h e C a n a d i a n C o r d i l l e r a , p a p e r 13, CIM s p e c i a l volume no. 15, 1976 11. BRITCH, C ; The G r e e n h i l l s S u r f a c e C o a l M i n i n g P r o j e c t , CIM B u l l e t i n , M a r c h 1981 12. PAQUETTE, C ; P e r s o n a l C o m m u n i c a t i o n , A u g u s t , 1983 13. L I T T L E , T.E.; E v a l u a t i o n o f a Rock Q u a l i t y Index B a s e d on R o t a r y D r i l l P e r f o r m a n c e , B.A.Sc. t h e s i s , D e p t . o f G e o l o g i c a l E n g i n e e r i n g , 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 , 1976 14. BURKE, J.R.; P e r s o n a l C o m m u n i c a t i o n , J u n e , 1984 15. RAYMOND, G.; Ore E s t i m a t i o n P r o b l e m s i n an E r r a t i c a l l y M i n e r a l i z e d O r ebody, CIM B u l l e t i n , J u n e , 1979 242 CHAPTER 6 243 6.0 CONCLUSIONS The e x c a v a t i o n o f a r o c k s l o p e u s i n g d r i l l i n g and b l a s t i n g methods i s an e n g i n e e r i n g t a s k . The i n f l u e n c e o f t h e b l a s t r e s u l t s on t h e s l o p e s t a b i l i t y and t h e t o t a l o p e r a t i n g c o s t s i s s u c h t h a t e f f o r t s have t o be made t o r e a c h t h e optimum b l a s t d e s i g n . However, no r o c k b l a s t i n g t h e o r y can t a k e i n t o a c c o u n t . a l l t h e v a r i a b l e s i n c l u d e d i n t h e d e s i g n p r o c e s s o f an open p i t b l a s t . C o n s e q u e n t l y , t h e o p t i m i z a t i o n p r o c e s s i s a v e r y d i f f i c u l t t a s k . The Rock Q u a l i t y Index i s a s i m p l e r o c k mass c l a s s i f i c a t i o n s y s t e m t h a t r e f l e c t s t h e r o c k mass p r o p e r t i e s as a w h o l e . O b t a i n e d from t h e b l a s t h o l e r o t a r y d r i l l s , i t i s p r a c t i c a l and n o t e x p e n s i v e . C o r r e l a t i o n between t h e Rock Q u a l i t y Index and t h e d e s i g n powder f a c t o r can be e s t a b l i s h e d e a s i l y when t h e r i g h t p r o c e d u r e i s f o l l o w e d . F i r s t , t h e powder f a c t o r has t o be t h e o n l y b l a s t d e s i g n v a r i a b l e l e f t , t h e o t h e r s b e i n g h e l d c o n s t a n t w i t h i n t h e p i t . S e c o n d l y , s i n c e t h e RQI i s a l s o d e p e n d e n t upon t h e d r i l l i n g p r a c t i c e and t h e d r i l l i n g e q u i p m e n t , t h e s e f a c t o r s must be m a i n t a i n e d c o n s t a n t . P r a c t i c a l l y , t h i s i s n o t p o s s i b l e and t h e r e f o r e , a q u a n t i t y of a c c u r a t e d r i l l i n g d a t a i s needed and a v e r a g e d . A t t h i s p o i n t , t h e o n l y p a r a m e t e r s l e f t a r e t h e r o c k mass p r o p e r t i e s . As t h e i n t e r a c t i o n of t h e r o c k mass p r o p e r t i e s i n f l u e n c e t h e b l a s t i n g r e s u l t s , t h e same p r o p e r t i e s a f f e c t t h e d r i l l p e r f o r m a n c e . C o n s e q u e n t l y , an e m p i r i c a l r e l a t i o n s h i p can be d e f i n e d . I t a l s o a p p e a r s t h a t a c o r r e l a t i o n between Rock 244 Q u a l i t y Index and g r i n d a b i l i t y can a l s o be d e t e r m i n e d . B a s e d on two y e a r s o f r e s e a r c h on t h e s u b j e c t , t h e f o l l o w i n g c o n c l u s i o n s a r e p r e s e n t e d : 1) A c o r r e l a t i o n between t h e Rock Q u a l i t y Index and t h e optimum d e s i g n powder f a c t o r e x i s t s . At t h i s p o i n t , c o r r e l a t i o n s a r e d e f i n e d f o r t h e d i f f e r e n t d r i l l i n g and b l a s t i n g p r a c t i c e s , as l o n g as t h e r e a r e m a i n t a i n e d c o n s t a n t t h r o u g h o u t t h e p i t . 2) I t a p p e a r s t h a t a c o r r e l a t i o n c a n be e s t a b l i s h e d w i t h t h e r o c k mass g r i n d a b i l i t y a l t h o u g h t h e g r i n d i n g r a t e i s a l s o a f u n c t i o n o f t h e s i z e of t h e f r a g m e n t s i n t h e muck p i l e . 3) A c c u r a t e m o n i t o r i n g of t h e d r i l l i n g p a r a m e t e r s i s n e e d e d . The d o w n p r e s s u r e r e a d i n g s s h o u l d be r e c o r d e d i n u n i t s of a p p l i e d w e i g h t . 4) C o n s i d e r a b l e d a t a a r e needed i n o r d e r t o be r e p r e s e n t a t i v e o f t h e r o c k mass p r o p e r t i e s w i t h i n e a c h domain. 5) G r o u n d w a t e r and c a v i n g b l a s t h o l e s i n f l u e n c e t h e Rock Q u a l i t y I n d e x . 6) Rock Q u a l i t y Index d a t a c o u l d be s t o r e d w i t h i n t h e g e o l o g i c a l computer model t o f a c i l i t a t e a n a l y s i s . 7) D r i l l p e r f o r m a n c e r e c o r d e r s a r e a u s e f u l d r i l l i n g t o o l . However, when us e d i n c o n j u n c t i o n w i t h RQI d a t a g a t h e r i n g p r o g r a m s , r e c o r d e d c h a r t s s h o u l d be r e p l a c e d by d i g i t a l i n f o r m a t i o n . 245 Even w i t h i m p r o v e d m o n i t o r i n g , a h o l e p e r h o l e l o a d i n g a p p r o a c h may n o t be p r a c t i c a l . B l a s t i n g p r o c e d u r e s : i ) The RQI a p p r o a c h t o r o c k mass c h a r a c t e r i z a t i o n has t o be made i n c o n j u n c t i o n w i t h t h e d e s i g n powder f a c t o r a p p r o a c h t o b l a s t e n g i n e e r i n g , i i ) C o n t r o l l e d b l a s t i n g commences w i t h p r o d u c t i o n b l a s t s . i i i ) S e q u e n t i a l b l a s t i n g t e c h n i q u e s i m p r o v e s l o p e s t a b i l i t y . i v ) Choked b l a s t s d e c r e a s e t h e s l o p e s t a b i l i t y and t h e b l a s t p e r f o r m a n c e , v) B l a s t e v a l u a t i o n s a r e a l s o p a r t o f t h e b l a s t e n g i n e e r ' s t a s k . 246 BIBLIOGRAPHY 247 BIBLIOGRAPHY 1. 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WINZER, S.R.; RITTER, A.P.; The R o l e o f S t r e s s Waves and D i s c o n t i n u i t i e s i n Rock F r a g m e n t a t i o n : A St u d y of  F r a g m e n t a t i o n i n L a r g e L i m e s t o n e B l o c k s , 2 1 s t U.S. Symposium on Rock M e c h a n i c s , U n i v e r s i t y o f M i s s o u r i -R o l l a , 1980 107. YOUNG, C ; Rock F r a g m e n t a t i o n - Needs and P o s s i b i l i t i e s , Rock F r a g m e n t a t i o n s e s s i o n o f t h e 17th U.S. Symposium on Rock M e c h a n i c s , U n i v e r s i t y o f U t a h , U t a h E n g i n e e r i n g E x p e r i m e n t S t a t i o n , 1976 2 6 0 4> APPENDIX I 261 APPENDIX I BIT COMPARISON S o f t r o c k Hughes HH33 Reed M52J S e c u r i t y S8M S m i t h Q4 M e d i u m - s o f t r o c k Hughes HH44 Reed M62 S e c u r i t y M8M S m i t h Q5 V a r e l AMC8 Medium-hard r o c k Hughes HH77 Reed M73 - M74 S e c u r i t y H8M S m i t h Q7 V a r e l QMCS Ha r d r o c k Hughes HH99 Reed M83 S e c u r i t y H10M S m i t h Q9 V a r e l QMCH 262 APPENDIX II 2 63 APPENDIX I I RELATIONSHIP BETWEEN DOWN PRESSURE AND A P P L I E D WEIGHT MANUFACTURER AND MODEL MAXIMUM PULLDOWN HYDRAULIC PRESSURE WEIGHT RATIO FACTOR B u c y r u s E r i e 30-R Bucyrus E r i e 40-R B u c y r u s E r i e 45-R 30,000 l b s @ 1,000 l b s . g a g e p r e s s u r e 50,000 l b s , 70,000 l b s . @ 1,300 l b s . g a g e p r e s s u r e S e r i e s 45 m o t o r 21 x gage p r e s s u r e + 3,800 l b s . S e r i e s 60 m o t o r 27 x gage p r e s s u r e + 3,800 l b s . S e r i e s 45 m o t o r 57 x gage p r e s s u r e + 7,000 l b s . S e r i e s 60 m o t o r 72 x gage p r e s s u r e + 7,000 l b s . 45 x g a g e p r e s s u r e + 10,000 l b s . B a c y r u s E r i e 50-4 Bacyrus E r i e 60-R & Bucyrus E r i e 61-R 75,000 l b s , 110,000 l b s . @ 1,200 l b s . gage p r e s s u r e S e r i e s 45 m o t o r 49 x gage p r e s s u r e + 9 , 0 0 0 l b s . , 60 m o t o r 62 x gage p r e s s u r e + 9,000 l b s . , 75 m o t o r 82 x g a g e p r e s s u r e + 9,000 l b s . 80 x g a g e p r e s s u r e + 14,000 l b s . G a r d n e r - D e n v e r GD-60 60,000 l b s . The a c t u a l weight on the b i t can be read from the h y d r a u l i c gage on the G D - 6 0 , G D - 8 0 , G D - 1 2 0 and the GD-13 0. Gardner-Denver 80,000 l b s . GD-80 Same a s GD-60 Gardner-Denver 12 0,000 l b s . GD-120 Same a s GD-60 G a r d n e r - D e n v e r GD-130 130,000 l b s . Same a s GD-60 264 M a r i o n M-4 M a r i o n M-5 C h i c a g o P n e u m a t i c T-650 C h i c a g o P n e u m a t i c T-750 C h i c a g o P n e u m a t i c C-850 C h i c a g o P n e u m a t i c C-950 C h i c a g o P n e u m a t i c C-975 R o b b i n s RR 10-S R o b b i n s RR 11 R o b b i n s RRT-50 R o b b i n s RRT-60 R o b b i n s RRT-7 0 105,000 l b s . @ 3,500 l b s . g a g e p r e s s u r e 120,000 l b s . @ 3,500 l b s g a g e p r e s s u r e 30,000 l b s . @ 2,300 l b s . g a g e p r e s s u r e 50,000 l b s . @ 2,300 l b s . gage p r e s s u r e 60,000 l b s . @ 2,300 l b s . g a g e p r e s s u r e 90,000 l b s . @ 2,700 l b s . g a g e p r e s s u r e 100,000 l b s . @ 3,200 l b s . g age p r e s s u r e 65,000 l b s . 70,000 l b s . 50,000 l b s . 60,000 l b s . 70,000 l b s . 24.3 x gage p r e s s u r e + 20,000 l b s . H y d r a u l i c g a g e i n d i c a t e s a c t u a l w e i g h t o n t h e b i t 28.6 x gage p r e s s u r e + 20,000 l b s . H y d r a u l i c g age i n d i c a t e s a c t u a l w e i g h t o n t h e b i t 13. x g a g e p r e s s u r e 21.75 x g a g e p r e s s u r e 26 x gage p r e s s u r e 33 x g a g e p r e s s u r e 31.25 x g a g e p r e s s u r e 30.6 x g a g e p r e s s u r e + 6,000 l b s . 30.6 x g a g e p r e s s u r e + 7,500 l b s . 30.6 x g a g e p r e s s u r e + 5,000 l b s . 30.6 x g a g e p r e s s u r e + 6,000 l b s . 3 0.6 x g a g e p r e s s u r e + 8,000 l b s . 265 R o b b i n s H100 H o r i z o n t a l D r i l l Schramm T985H Schramm T64HB Schramm C985H Schramm C9120 80,000 l b s . 38,000 l b s . @ 2,000 l b s . gage p r e s s u r e 30,000 l b s . @ 2,000 l b s . gage p r e s s u r e 50,000 l b s . @ 2,500 l b s . gage 50,000 l b s . @ 2,500 l b s . gage p r e s s u r e 41.28 x gage p r e s s u r e + 3,000 l b s . 19. x gage p r e s s u r e 15, x gage p r e s s u r e 20 x gage p r e s s u r e 20 x gage p r e s s u r e 266 APPENDIX I I I 267 APPENDIX I I I PO S S I B L E BENEFITS FROM IMPROVED FRANGMENTATION I n c r e a s e d s h o v e l c a p a c i t y R e d u c e d s h o v e l m a i n t e n a n c e : — p a r t l y due t o l o n g e r b u c k e t a n d t e e t h l i f e b e c a u s e t h e s h o v e l w o u l d n o t be a b u s e d i n d i g g i n g o v e r s i z e d b o u l d e r s o n h a r d b o t t o m s I n c r e a s e d t r u c k c a p a c i t y ( r e d u c e d l o a d i n g t i m e ) R e d u c e d t r u c k m a i n t e n a n c e : — p a r t l y d u e t o f i n e r m a t e r i a l f l o w s b e t t e r -- p a r t l y due t o l a r g e o v e r s i z e b o u l d e r s n o t s t r i k i n g t h e bo d y I n c r e a s e d c r u s h e r c a p a c i t y R e d u c e d c r u s h e r m a i n t e n a n c e I n c r e a s e d m i l l c a p a c i t y D e c r e a s e d o r e l i m i n a t e d s e c o n d a r y b r e a k i n g c o s t D e c r e a s e d p i t c l e a n - u p c o s t s D e c r e a s e d t r u c k t i r e w e a r : -- p a r t l y b e c a u s e f i n e r m a t e r i a l s p r o v i d e b e t t e r t r a v e l s u r f a c e s D e c r e a s e d v e h i c l e c o s t f r o m b e t t e r p i t f l o o r s ( p i c k - u p s , m a i n t e n a n c e t r u c k s , e t c . ) 268 ( APPENDIX IV 269 APPENDIX I V  REVIEW OF T.E. L I T T L E REPORT ON RQI S h o r t l y a f t e r b e i n g p r o p o s e d , t h e c o n c e p t o f R o c k Q u a l i t y I n d e x was i n v e s t i g a t e d i n r e g a r d w i t h i t s a p p l i c a b i l i t y t o t h e d e s i g n o f o p e n p i t s l o p e by L i t t l e . RQI v a l u e s w e r e c o n t o u r e d a n d a t t e m p t s w e r e made t o c o r r e l a t e c o n t o u r p a t t e r n s w i t h m e c h a n i c a l a n d p h y s i c a l p r o p e r t i e s o f t h e r o c k . The s t u d i e s w e r e c a r r i e d o u t a t E n d a k o , K a i s e r and G i b r a l t a r m i n e s d u r i n g t h e summer o f 1975. I t was f o u n d t h a t s e v e r a l i n d e p e n d a n t v a r i a b l e s c a n h a v e an i n f l u e n c e o n RQI v a l u e s . 1. C o n c l u s i o n s o f t h e E n d a k o M i n e f i e l d w o r k : i ) R e c o r d e d d r i l l i n g d a t a : L i t t l e o b s e r v e d t h a t t h e a c c u r a c y o f c a l c u l a t e d v a l u e s o f RQI i s t o t a l l y d e p e n d a n t o n t h e a c c u r a c y o f r e c o r d e d d a t a d a t a o n d r i l l b i t p e r f o r m a n c e r e c o r d s ( d r i l l e r l o g s ) . I t was n o t e d t h a t t h e RQI c o n t o u r s t e n d t o r e l a t e w i t h t h e movements o f t h e d r i l l s . D r i l l b i t p e r f o r m a n c e r e c o r d s , show t h a t f o r many w o r k s h i f t s , t h e same d r i l l i n g p a r a m e t e r s h a v e b e e n a l l o c a t e d t o a l l h o l e s d r i l l e d i n one s h i f t . I n a d d i t i o n , d r i l l i n g t i m e was r e c o r d e d t o t h e n e a r e s t f i v e m i n u t e s a n d t h e h y d r a u l i c down p r e s s u r e t o t h e n e a r e s t 50 t o 100 p s i . i i ) D r i l l t y p e a n d s i z e : A t E n d a k o , B u c y r i u s BE 40-R d r i l l i n g 9 i n c h e s d i a m e t e r h o l e s a n d M a r i o n M-4 d r i l l i n g 9 7/8 i n c h e s d i a m e t e r h o l e s w e r e u s e d . 2 7 0 A c o m p a r i s o n o f a d j a c e n t h o l e s d r i l l e d w i t h t h e d i f f e r e n t d r i l l i n g e q u i p m e n t shows t h a t t h e RQI ( 9 " ) was e q u a l t o 0 . 6 - 0 . 7 RQI (9 7 / 8 " ) . I t was c o n c l u d e d t h a t t h e RQI v a r i e s s i g n i f i c a n t l y w i t h t h e t y p e o f d r i l l u s e d , i i i ) L i t h o l o g y a n d s t r u c t u r a l g e o l o g y : G e n e r a l l y , h i g h e r RQI v a l u e s o c c u r e d i n t h e v i c i n i t y o f d y k e c h a r a c t e r i z e d a s a h i g h l y f r a c t u r e d r o c k m a s s , b u t h a v e . a h i g h c o m p r e s s i v e s t r e n g t h . L o w e r v a l u e s w e r e e n c o u n t e r e d i n a f a u l t z o n e a r e a w h e r e t h e r o c k i s g e n e r a l l y w e l l f r a c t u r e d , a l t e r e d a n d h a s a l o w c o m p r e s s i v e s t r e n g t h . I t was c o n c l u d e d t h a t t h e RQI a p p e a r e d t o be r e l a t e d t o t h e r o c k s t r e n g t h w h i c h may o r may n o t c o r r e l a t e w i t h t h e l i t h o l o g y o r s t r u c t u r e . L i t t l e a l s o t r i e d t o r e l a t e r o c k h a r d n e s s a n d d e g r e e o f f r a c t u r i n g w i t h RQI w i t h o u t s u c c e s s . I I . C o n c l u s i o n o f t h e K a i s e r M i n e f i e l d w o r k : i ) R e c o r d e d d r i l l i n g d a t a : I t was o b s e r v e d t h a t h i g h v a r i a t i o n s i n t h e h y d r a u l i c down p r e s s u r e a n d r o t a r y s p e e d a r e due t o t h e p r e s e n c e o f a l t e r n a t i n g b e d s o f s a n d s t o n e and s i l t s t o n e a b o v e t h e c o a l seam. I n a d d i t i o n , t h e d r i l l i n g t i m e f o r h o l e s d e e p e r t h a n . . . 40 f e e t i n c l u d e d t h e t i m e r e q u i r e d t o a d d a s e c o n d p i e c e o f d r i l l s t e e l . T h i s p r a c t i c e r e d u c e s t h e r e a l p e n e t r a t i o n r a t e a n d t h e r e f o r e i n c r e a s e d t h e RQI. 271 i i ) B i t d e s i g n and s i z e : E x t r e m e l y h i g h v a l u e s o f RQI were o b t a i n e d i n a r e a s where s t e e l t o o t h b i t s were u s e d . The RQI f o r s t e e l t o o t h b i t s r a n g e d f r o m 1.5 t o 8.0 t i m e s t h e RQI f o r i n s e r t b i t s . L i t t l e a l s o o b s e r v e d t h a t , e v e n t h o u g h a l l b l a s t h o l e s were-d r i l l e d by t h e same model o f d r i l l , t h e RQI v a l u e s o b t a i n e d f o r t h e 9 7/8 i n c h d i a m e t e r b i t s d i d n o t d i f f e r s i g n i f -i c a n t l y f r o m t h o s e o b t a i n e d w i t h t h e 12 1/4 i n c h e s d i a m e t e r b i t s . i i i ) L i t h o l o g y and s t r u c t u r a l g e o l o g y : A r e a s o f h i g h RQI were c o r r e l a t e d w i t h z o n e s o f h a r d s a n d -s t o n e s . I n a d d i t i o n , a g e n e r a l t r e n d o f t h e RQI s u b p a r t a l l e l w i t h t h e s t r u c t u r a l g e o l o g i c a l s t r i k e was n o t e d . Low RQI v a l u e s were a l s o e n c o u n t e r e d i n f a u l t e d a r e a s . I I I . C o n c l u s i o n s f r o m t h e G i b r a l t a r M i n e f i e l d work i ) R e c o r d e d d r i l l i n g d a t a : A t G a b r a l t a r , t h e h y d r a u l i c down p r e s s u r e was r e c o r d e d a s a s t a n d a r d r a n g e ( i e . , 500 - 100 p s i ) w h i l e t h e a c t u a l v a l u e was p r o b a b l y a r o u n d 650 p s i . . i i ) D r i l l t y p e and s i z e : As f o r Endako M i n e , two m o d e l s o f d r i l l were u s e d : BE 45R (9 7/8") and M a r i o n M4 (12 1/4") C o m p a r i s o n o f RQI v a l u e s showed t h a t t h e RQI (9 7/8) was e q u a l t o 0.5 t o 0.7 t i m e s t h e RQI (12 1 / 4 ) . 272 i i i ) L i t h o l o g y a n d s t r u c t u r a l g e o l o g y : H i g h RQI v a l u e s w e r e r e c o r d e d i n a r e a s o f l o w p e r c e n t a g e o f b r o k e n a nd f a u l t e d r o c k . I n a r e a s w h e r e t h e i n t e n s i t y o f f r a c t u r a t i o n i n c r e a s e d , t h e RQI v a l u e s w e r e g e n e r a l l y l o w e r , i n d i c a t i n g a r e l a t i o n b e t w e e n RQI a n d t h e d e g r e e o f f r a c t u r i n g o f t h e r o c k . Summary o f L i t t l e ' s C o n c l u s i o n s 1 - i n t e r p r e t a t i o n s a r e l i m i t e d by t h e r e l i a b i l i t y o f t h e d a t a i n p u t . - some t i m e s , t h e RQI i s r e l a t e d t o d r i l l movement more t h a n t o a n y o t h e r f a c t o r s . - a v e r a g i n g t e c h n i q u e s c o m p e n s a t e d f o r t h e i n a c c u r a t e d a t a , b u t t h e s e t e c h n i q u e s masked t h e r e a l c h a n g e s i n r o c k q u a l i t y . 2 - RQI i s p r i m a r i l y r e l a t e d t o r o c k s t r e n g t h , h o w e v e r , f a u l t e d a r e a s a n d i n t e n s e l y f r a c t u r e d r o c k s showed a l o w RQI. - t h e r e i s no d i r e c t r e l a t i o n s h i p b e t w e e n RQI a n d g e o l o g y . 3 - l a r g e r b i t s o n l a r g e r d r i l l s p r o d u c e h i g h e r RQI ( n o t e t h a t t h e d r i l l m o d e l s w e r e d i f f e r e n t ) . - d i f f e r e n t s i z e b i t s o n t h e same t y p e o f d r i l l p r o d u c e d s i m i l a r RQI v a l u e s . - s t e e l t o o t h b i t s p r o d u c e d RQI v a l u e s up t o 8.0 t i m e s a s h i g h a s t h o s e f o r t u n g s t e n c a r b i d e i n s e r t b i t s . 273 APPENDIX V 274 APPENDIX V  MODIFICATION OF BLASING METHODS When i t i s e v i d e n t t h a t u n s a t i s f a c t o r y r e s u l t s a r e b e i n g o b t a i n e d f r o m a p a r t i c u l a r b l a s t i n g m e t h o d a n d t h a t t h e m e t h o d s h o u l d be m o d i f i e d , t h e b l a s t i n g e n g i n e e r may h a v e t o embark o n a s e r i e s o f t r a i l s i n o r d e r t o a r r i v e a t a n o p t i m u m d e s i g n . A s w i t h a n y t r i a l s , c a r e f u l d o c u m e n t a t i o n o f e a c h b l a s t i s e s s e n t i a l a n d , w h e n e v e r p o s s i b l e , o n l y one v a r i a b l e a t a t i m e s h o u l d be c h a n g e d . The f o l l o w i n g s e q u e n c e o f t e s t w o r k i s a n i l l u s t r a t i o n o f t h e t y p e o f e x p e r i m e n t w h i c h w o u l d be c a r r i e d o u t t o e v a l u a t e t h e c o s t e f f e c t i v e n e s s o f u s i n g a h i g h e r e n e r g y e x p l o s i v e . S i m i l a r t e s t s e q u e n c e s c o u l d be c a r r i e d f o r e a c h o f t h e o t h e r f a c t o r s w h i c h a r e r e l e v a n t i n a p a r t i c u l a r s i t u a t i o n . R a t i o n a l i z a t i o n : a. Document p r e s e n t p o w d e r f a c t o r s o n a n e q u i v a l e n t e n e r g y b a s i s u s i n g t h e w e i g h t s t r e n g t h s o f v a r i o u s e x p l o s i v e s c o m p a r e d t o t h a t o f t h e e x p l o s i v e i n c u r r e n t u s e . W e i g h t s t r e n g t h d a t a s h o u l d be o b t a i n e d f r o m t h e e x p l o s i v e s m a n u f a c t u r e r i f t h e s e a r e n o t a l r e a d y a v a i l a b l e . E v a l u a t i o n : b. F o r a b l a s t w i t h t h e e x p l o s i v e c u r r e n t l y i n u s e , d o c u m e n t t h e b e h a v i o u r o f t h e b l a s t d u r i n g i n i t i a t i o n a n d t h e c o n d i t i o n o f t h e r e s u l t i n g muck p i l e . 2 75 c. Document r a t e a n d c o n d i t i o n s o f d i g g i n g . d. Document f r a g m e n t a t i o n b a s e d u p on t h e r a t i o o f o v e r s i z e d m a t e r i a l r e q u i r i n g s e c o n d a r y b l a s t i n g t o t h e t o t a l b l a s t t o n n a g e . e. d o c u m e n t d r i l l i n g a n d b l a s t i n g c o s t s . E x p e r i m e n t a t i o n : f . S e l e c t a s i m i l a r a r e a o f g r o u n d and c a r r y o u t a b l a s t w i t h a h i g h e r p owder f a c t o r w h i c h i s o b t a i n e d by u s i n g a h i g h e r e n e r g y e x p l o s i v e e . g . by i n c r e a s i n g t h e a l u m i n u m c o n t e n t o f a s l u r r y . E v a l u a t i o n : g. Document t h e r e s u l t s a s f o r s t e p s b t o e. h. C a r r y o u t a c o s t - b e n e f i t s t u d y . i . R e p e a t t h e e x p e r i m e n t b e f o r e p r e p a r i n g a s t a t e m e n t t o mange-ment s u g g e s t i n g a m o d i f i c a t i o n o r a r e t e n t i o n o f t h e e x i s t i n g m e t h o d . I t s h o u l d a l s o be n o t e d t h a t i t i s now p o s s i b l e t o s i m u l a t e b l a s t p e r f o r m a n c e on a c o m p u t e r . T h i s a p p r o a c h e l i m i n a t e s a l o n g t r i a l a n d e r r o r p r o c e s s a n d p e r m i t s one t o n a r r o w t h e f i e l d o f p o s s i b l e m o d i f i c a t i o n s i n r e g a r d t o a t a r g e t o b j e c t i v e ( i e . , r e d u c t i o n o f f l y r o c k s , t o e s , e t c . ) . The m o s t p u b l i c i z e d s y s t e m i n N o r t h /America i s a v a i l a b l e t h r o u g h R.F. F a v r e a u o f t h e R o y a l M i l i t a r y C o l l e g e i n S t . - J e a n , Q uebec. 

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