UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

Rock slope stability and design of granite lake open pit with the application of vacuum drainage : Gibraltar… Pakalnis, Rimas Thomas 1982

Your browser doesn't seem to have a PDF viewer, please download the PDF to view this item.

Notice for Google Chrome users:
If you are having trouble viewing or searching the PDF with Google Chrome, please download it here instead.

Item Metadata

Download

Media
831-UBC_1982_A7 P35.pdf [ 23.32MB ]
Metadata
JSON: 831-1.0081083.json
JSON-LD: 831-1.0081083-ld.json
RDF/XML (Pretty): 831-1.0081083-rdf.xml
RDF/JSON: 831-1.0081083-rdf.json
Turtle: 831-1.0081083-turtle.txt
N-Triples: 831-1.0081083-rdf-ntriples.txt
Original Record: 831-1.0081083-source.json
Full Text
831-1.0081083-fulltext.txt
Citation
831-1.0081083.ris

Full Text

ROCK SLOPE STABILITY AND DESIGN OF GRANITE LAKE OPEN PIT WITH THE APPLICATION OF VACUUM DRAINAGE GIBRALTAR MINES LTD., McCLEESE LAKE, B.C. by RIMAS THOMAS PAKALNIS B. 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 , 1979 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE i n THE FACULTY OF GRADUATE STUDIES DEPARTMENT OF MINING AND MINERAL PROCESS ENGINEERING We accept t h i s t h e s i s as conforming t o the r e q u i r e d s t a n d a r d THE UNIVERSITY OF BRITISH COLUMBIA May, 1982 (5) Rimas P a k a l n i s , 1982 In presenting t h i s thesis i n p a r t i a l f u l f i l m e n t of the requirements for an advanced degree at the University of B r i t i s h Columbia, I agree that the Library s h a l l make i t f r e e l y available for reference and study. I further agree that permission for extensive copying of t h i s thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. I t i s understood that copying or publication of t h i s thesis for f i n a n c i a l gain s h a l l not be allowed without my written permission. Department of Mining and Mineral Process Engineering The University of B r i t i s h Columbia 1956 Main Mall Vancouver, Canada V6T 1Y3 Date March 30,1982 E-6 (3/81) ABSTRACT Volume 1 o f the t h e s i s e v a l u a t e s the r o c k s l o p e s t a b i l -i t y o f the South W a l l of the G r a n i t e Lake open p i t of G i b r a l t a r Mines L t d . S t r e n g t h , s t r u c t u r e and groundwater i n f o r m a t i o n was g a t h e r e d which was comprised l a r g e l y o f 3.4 k i l o m e t e r s of l i n e mapping d a t a (3064 s t r u c t u r e s ) , p r e v i o u s r e p o r t s and i n t e r p r e t a t i o n . The study i n d i c a t e d t h a t deep-s e a t e d f a i l u r e s encompassing the e n t i r e p i t w a l l were not p r o b a b l e . I t was found t h a t f a i l u r e s were r e s t r i c t e d t o bench (27 m) s i z e , and c o n s e q u e n t l y d i c t a t e d a d e s i g n where-by catchment berms of s u f f i c i e n t w i d t h were determined. T h i s i n d i c a t e d an o v e r a l l w a l l angle of 38° w i t h i s o l a t e d areas e x h i b i t i n g s t e e p e r s l o p e s . Steeper s l o p e s would be p o s s i b l e under the f o l l o w i n g c o n d i t i o n s : (a) L o c a l d r a i n a g e be a p p l i e d (b) C o n t r o l b l a s t i n g be i n c o r p o r a t e d (c) A h i g h e r p r o b a b i l i t y o f r a v e l l i n g be a c c e p t e d . In a d d i t i o n Volume I I of the t h e s i s examines the bene-f i t s a c h i e v e d by employing vacuum h o r i z o n t a l d r a i n a g e . H o r i z o n t a l d r a i n s were i n s t a l l e d under vacuum i n a mine s l o p e . The b e n e f i t a r i s e s from an i n c r e a s e d h y d r a u l i c g r a d -i e n t due t o e x h a u s t i n g t o a n e g a t i v e a t m o s p h e r i c p r e s s u r e . The p r o t o t y p e was based on the w e l l known c i v i l e n g i n e e r i n g d e - w a t e r i n g p r a c t i c e , w e l l p o i n t i n g . R e s u l t s showed t h a t a vacuum of 457 mm o f mercury was o b t a i n a b l e i n a f r a c t u r e d m o d e r a t e l y permeable rock s l o p e . Immediate drawdown o f the water t a b l e o c c u r r e d r e s u l t i n g i n a t o t a l o f 1.1 m o f drop o c c u r r i n g a f t e r 59 minutes o f o p e r a t i o n . Flow i n c r e a s e d from 0 1/s t o 0.2 1/s d i s c h a r g i n g from the h o r i z o n t a l d r a i n s when the vacuum was a p p l i e d . I t was found t h a t drawdown c o n t i n u e d t o o ccur w i t h the water l e v e l d r o p p i n g below the d r a i n e l e v a -t i o n . The system developed may be employed as a d e p r e s s u r i -z a t i o n t o o l f o r s l o p e s t a b i l i z a t i o n p r o j e c t s . The above was f u r t h e r r e i n f o r c e d t h rough l a b o r a t o r y and n u m e r i c a l m o d e l l i n g i v TABLE OF CONTENTS Page ABSTRACT TABLE OF CONTENTS LIST OF TABLES LIST OF ILLUSTRATIONS ACKNOWLEDGEMENTS VOLUME I 1- 1 . INTRODUCTION 1 SCOPE OF STUDY 1 1-2. GEOLOGIC SETTING 4 MINING HISTORY 4 GENERAL GEOLOGY 6 MINE GEOLOGY 10 1-3. DESCRIPTION OF INVESTIGATION 13 GEOLOGIC MAPPING 13 FABRIC ANALYSIS 18 EXAMINATION OF DRILL DATA 19 GROUNDWATER INVESTIGATION 19 STRENGTH DETERMINATION 20 STABILITY INVESTIGATION 20 1-4. STRUCTURE ANALYSIS 26 MAJOR STRUCTURES 26 DOMAIN DELINEATION BY SECTOR 27 DOMAIN DELINEATION BY BENCH 33 DOMAIN DELINEATION BY FAULTS 33 ASSESSMENT OF DOMAIN BOUNDARIES EMPLOYING CUMULATIVE SUMS TECHNIQUE . . . 33 G.B.A.S. CORRELATION 47 FAULTS OR FAULT SHEARS 51 ROCK FABRIC 58 FABRIC ANALYSIS 58 FRACTURE INTENSITY AND INFILL 59 ANALYSIS OF CORE 61 JOINT DATA 68 1-5. DETERMINATION OF STRENGTH PARAMETERS 79 COMPRESSIVE STRENGTH OF INTACT ROCK . . . 79 FRICTION ANGLE 81 BACK-ANALYSIS 84 i i i v v i v i i x i cont' d TABLE OF CONTENTS (cont'd) Page 1-6. GROUNDWATER INVESTIGATION 87 HYDROLOGIC INVESTIGATION 87 1- 7 . DESIGN 95 STABILITY ANALYSIS 95 MAJOR FAILURES 98 INVESTIGATION OF KINEMATICALLY POSSIBLE FAILURE MODES 98 INVESTIGATION OF PLANAR AND WEDGE FAILURES 102 ANALYSIS OF JOINT LENGTH AND ROCK BRIDGE 114 INTERPRETATION 118 BENCH DESIGN 118 1-8. SUMMARY 124 GEOLOGY 124 STRUCTURE ANALYSIS 124 CONTROL BLASTING 125 STRENGTH PARAMETERS 127 GROUNDWATER 128 DESIGN 128 1- 9. RECOMMENDATIONS 130 APPENDIX I - FACTOR OF SAFETY DETERMINATION. . . . 131 APPENDIX I I - BERM WIDTH DESIGN 136 REFERENCES 192 v i LIST OF TABLES Table VOLUME I Page I. 1. DISCODAT DISCONTINUITY DATA 17 I . 2 . CUMSUM ANALYSIS 28 I . 3 . SUMMARY OF ATTITUDES OF MAJOR FAULTS ON THE SOUTH WALL OF GRANITE LAKE 57 I . 4 . ATTITUDE OF JOINT SETS 69 I . 5 . UNCONFINED COMPRESSIVE TEST RESULTS 81 I . 6 . SUMMARY OF SHEAR STRENGTH RESULTS 83 I . 7 . BACK-ANALYSIS RESULTS 85 I . 8. STABILITY ANALYSIS OF MAJOR FAILURES 100 I . 9 . EQUILIBRIUM ANALYSIS EMPLOYING HOEK'S CHARTS . 108 I . 10 . STATISTICAL ANALYSIS - SECTOR IA I l l I. 11 . CUMULATIVE PERCENT OF FAILURES PLUNGING FLATTER THAN Bco (UN-DEWATERED CASE) 112 I . 12 . CUMULATIVE PERCENT OF FAILURES PLUNGING FLATTER THAN Bw (DEWATERED CASE) 113 I. 13 . ULTIMATE WALL DESIGN 119 I . 14 . RECOMMENDED ULTIMATE WALL DESIGN 122 VOLUME I I I I . 1. COST SUMMARY 32 v i i LIST OF ILLUSTRATIONS F i g u r e VOLUME 1 P a g e I . 1. LOCATION MAP OF GIBRALTAR MINES LTD 5 1.2. REGIONAL GEOLOGY 7 I. 3. GENERALIZED GEOLOGIC MAP GIBRALTAR MINE AREA 8 I. 4A,B STRUCTURAL MODEL OF GIBRALTAR AREA 11 1.5. PHOTOGRAPHIC COLLAGE OF THE SOUTH WALL OF GRANITE LAKE PIT 14 1.6. VARIATION OF STRIP RATIO WITH SLOPE ANGLE . . 15 1.7. STUDY AREA 16 I. 8. POSSIBLE MODES OF FAILURE 21 1.9. FAILURES CONTROLLED BY MINOR AND MAJOR DISCONTINUITIES 22 1.10. CONTOUR MAPS OF SEISMIC ACTIVITY 24 1.11. IDENTIFICATION OF STRUCTURAL SETS (STEREONET) 29 1.12. DOMAIN DELINEATION BY SECTORS 30 1.13. STRUCTURAL DATA BY SECTOR (STEREONET) . . . . 31 1.14. JOINT SET NUMBER VS OCCURRENCE - SECTOR . . . 32 1.15. DOMAIN DELINEATION BY BENCH (STEREONET) . . . 34 1.16. JOINT SET NUMBER VS OCCURRENCE - BENCH . . . 35 1.17. PLAN SHOWING MAJOR STRUCTURES 36 I.18A DOMAIN DELINEATION BY MAJOR STRUCTURES - FAULT 1/2 (STEREONET) 37 I.18B DOMAIN DELINEATION BY MAJOR STRUCTURES - FAULT 2/3 (STEREONET) 38 I .180 DOMAIN DELINEATION BY MAJOR STRUCTURES - FAULT 3/4 (STEREONET) 39 I.18D DOMAIN DELINEATION BY MAJOR STRUCTURES - FAULT 4/5 (STEREONET) 40 I.18E DOMAIN DELINEATION BY MAJOR STRUCTURES - FAULT 5/6 (STEREONET) 41 I.18F DOMAIN DELINEATION BY MAJOR STRUCTURES - FAULT 6/7 (STEREONET) 42 I.18G DOMAIN DELINEATION BY MAJOR STRUCTURES - FAULT >7 (STEREONET) 43 1.19. PLOT OF STRUCTURAL SET VS FAULT BOUNDARY - ALL BENCHES 44 1.20. PLOT OF STRUCTURAL SET VERSUS FAULT BOUNDARY - 1135m BENCH (G) 45 1.21. PLOT OF THE OCCURRENCE OF 'G' SET AS A BOUNDARY IS CROSSED FOR EACH BENCH LEVEL . 46 1.22. PLOT OF STRIKE VS LOCATION FOR 'G' SET ALONG ' D' BENCH 48 1.23. PLOT OF CUMSUM OF STRIKE VS LOCATION FOR ' G' SET ALONG 1135m BENCH (G) 48 cont ' d v i i i LIST OF ILLUSTRATIONS (cont'd) F i g u r e Page I . 24. G.B.A.S. LEVEL PLAN 1149m BENCH (F) 49 I. 25A EVALUATION OF INTENSITY OF THE GRANITE CREEK STRUCTURE EMPLOYING FIELD AND G.B.A.S. INFORMATION 50 I . 25B EVALUATION OF INTENSITY OF THE SUNSET STRUCTURE EMPLOYING FIELD AND G.B.A.S. INFORMATION 50 I. 26. PLAN SHOWING DOMAIN BREAKDOWN - PRESENT PIT . 52 I . 27. LOWER HEMISPHERE PLOT SHOWING FAULTS AND FAULT SHEARS 53 I. 28A,B,C PHOTOGRAPHS OF MAJOR BOUNDARIES 54,55,56 I. 29. FABRIC ANALYSIS (STEREONET) 60 I. 30A,B,C ASSESSMENT OF ROCK MASS - GRANITE LAKE PHOTOGRAPH 62,63,64 I. 31. FRACTURE MAP OF SOUTH WALL OF GRANITE LAKE . 65 I. 32. INFILL MAP OF SOUTH WALL OF GRANITE LAKE . . 66 I. 33. PERCENTAGE OF BROKEN AND FAULTED DRILL CORE . 67 I . 34A STRUCTURAL SETS WITHIN RESPECTIVE DOMAINS - ABOVE 1163m BENCH (E) (STEREONET) 70 I. 34B STRUCTURAL SETS WITHIN RESPECTIVE DOMAINS - BELOW 1163m BENCH (E) (STEREONET) 71 I. 35A,B,C MINOR STRUCTURES ALONG THE SOUTH WALL . . . . 72,74,75 I. 36. JOINT SETS ALONG THE SOUTH WALL OF GRANITE LAKE PIT 78 I. 37. CONDITIONS THAT MUST PREVAIL TO CAUSE INSTABILITY 80 I. 38. RESIDUAL STRENGTHS FOR QUARTZ DIORITE SAMPLES 82 I . 39. FRICTION ANGLE VS DEPTH 82 I. 40. BACK-ANALYSIS OF FAILURES ALONG THE SOUTH WALL OF GRANITE LAKE 86 1.41. PRECIPITATION RECORD 88 I . 42. SECTION ANALYSED BY FINITE ELEMENT 90 I . 43. SOUTH WALL GRANITE LAKE (1981) - FINITE ELEMENT MESH 91 I . 44. FLOW PATTERN OF STUDY AREA (1981) 92 I. 45. FLOW PATTERN OF STUDY AREA - HORIZONTAL DRAIN 92 I. 46. COMPARISON OF DEPRESSURIZATION METHODS . . . 93 I. 47. COMPARISON OF UN-DEWATERED CONDITIONS FOR: a) 1974 93 b) 1981 93 I. 48. SLOPE GEOMETRY RELATIONSHIPS 96 cont ' d i x LIST OF ILLUSTRATIONS (cont'd) F i g u r e Page 1.49. EXTRAPOLATION OF DOMAIN BOUNDARIES TO ULTIMATE LIMITS 97 I . 50A MAJOR STRUCTURES BELOW 1163m BENCH (E) . . . 99 I. 50B MAJOR STRUCTURES ABOVE 1163m BENCH (E) . . . 99 1.51. STEREO-PLOTS DENOTING FAILURE TYPE 101 1.52. RANGE OF STRUCTURAL POPULATIONS TO BE INVESTIGATED - SECTOR IA 103 I. 53A ANALYSIS OF POTENTIAL FAILURES BELOW THE 1135m BENCH (E) 104 I.53B ANALYSIS OF POTENTIAL FAILURES ABOVE THE 1135m BENCH (E) 105 1.54. GREAT CIRCLES REPRESENTING STRUCTURAL DISCONTINUITIES - SECTOR IA 107 1.55. FREQUENCY PLOT OF OCCURRENCE OF WEDGES PLUNGING FLATTER THAN Bco 110 1.56. PROBABILITY OF JOINT LENGTH BEING EXCEEDED . 115 1.57. REQUIRED ROCK BRIDGE VS SLOPE HEIGHT TO ACHIEVE A F.S. = 1.2 116 1.58. EVALUATION OF ROCK BRIDGE 117 1.59. BERM WIDTH DESIGN 120 1.60. RECOMMENDED ULTIMATE SLOPE DESIGN - SOUTH WALL OF GRANITE LAKE 123 1.61. PLOT OF PARTICLE VELOCITIES INDUCED AT GIVEN DISTANCES FOR PARTICULAR CHARGE WEIGHTS 126 VOLUME I I I I . 1. INFLUENCE OF WATER PRESSURE ON STABILITY 2 11.2. RESULTANT INCREASE IN SLOPE ANGLE DUE TO TOTAL DEPRESSURIZATION 3 11.3. RECOMMENDED DEPRESSURIZATION TECHNIQUES FOR VARIOUS MASS PERMEABILITIES 4 I I . 4. SLOPE DRAINAGE SYSTEMS 5 I I . 5. VACUUM PRINCIPLE 7 I I . 6. VACUUM WELLPOINTING APPLIED ON 5 M LIFTS 7 I I . 7. STUDY AREA - GRANITE LAKE 10 I I . 8. GRANITE LAKE TEST AREA 11 I I . 9A. TEST AREA WITH INSTALLED VACUUM SYSTEM (PHOTO) 12 I I . 9B. 'NAPCO' PERCUSSION DRILL (PHOTO) 12 I I . 9C. 'NAPCO' DRILLING HORIZONTAL DRAINS (PHOTO) 12 11.10. SCHEMATIC REPRESENTATION OF VACUUM SYSTEM 13 11.11. PIEZOMETER CONSTRUCTION 14 11.12. HORIZONTAL DRAIN CONSTRUCTION 16 11.13. PACKER SYSTEM 16 II.1 4 A . PACKERS EMPLOYED TO FORM SEAL (PHOTO) 18 I I . 1 4 B . HORIZONTAL DRAIN PRIOR TO INSTALLATION (PHOTO) . . . 18 I I . 1 4 C . NITROGEN CANNISTER TO INFLATE PACKER (PHOTO) . . . . 18 X LIST OF ILLUSTRATIONS (cont'd) FIGURE Page I I . 1 5 A . GROUT SYSTEM (PHOTO) 19 I I . 15B. GROUT PUMPED INTO DRAIN HOLE (PHOTO) 19 I I . 1 5 C , BENTONITE SURFACE SEAL (PHOTO) 19 II . 1 6 A . VACUUM PUMP (PHOTO) 20 I I . 1 6 B . INSTALLED VACUUM SYSTEM (PHOTO) 20 II . 1 7 A . DRAIN CONNECTED TO HEADER PIPE (PHOTO) 22 I I . 1 7 B . STOP-COCK TO DIRECT AIR FLOW (PHOTO) 22 I I . 1 7 C . VACUUM GAUGE (PHOTO) 22 II . 1 8 A . RECHARGE POND (PHOTO) 23 I I . 1 8 B . DISCHARGE TO TEST AREA (PHOTO) 23 11.19. PIEZOMETER NEST 24 11.20. GRAVITY FLOW THROUGH HORIZONTAL DRAIN (PHOTO) . . . 26 11.21. SEEPAGE THROUGH DISCONTINUITY (PHOTO) 26 11.22. WATER LEVEL VERSUS TIME 29 II . 2 3 A . HORIZONTAL DRAIN MODEL WITHOUT SAND (PHOTO) . . . . 34 I I . 2 3 B . HORIZONTAL DRAIN AND PIEZOMETERS (PHOTO) 34 I I . 2 3 C . HORIZONTAL DRAIN MODEL WITH SAND (PHOTO) 34 11.24. PLAN VIEW OF DRAINAGE MODEL 35 11.25. CROSS-SECTION OF DRAINAGE MODEL 36 11.26. FLOW PROFILE - NO HORIZONTAL DRAIN 37 11.27. FLOW PROFILE - HORIZONTAL DRAIN 37 II . 2 8 A . RECHARGE POND (PHOTO) 38 I I . 2 8 B . DISCHARGE THROUGH DRAINS (PHOTO) 38 I I . 2 8 C . VACUUM PUMP AND CHAMBER 38 II.29A. DRAINAGE UNDER GRAVITY - NO VACUUM (PHOTO) 39 II.29B. DRAINAGE UNDER GRAVITY - NO VACUUM (PHOTO) 40 II.30A. DRAINAGE UNDER VACUUM (PHOTO) 42 II.30B. DRAINAGE UNDER VACUUM (PHOTO) 43 11.31. PLOT OF DRAWDOWN VERSUS TIME UNDER a) G r a v i t y 44 b) Vacuum Drainage 44 11.32. PHREATIC SURFACE VERSUS TIME 45 11.33. DEPENDENCE OF SHEAR STRENGTH ON DISPLACEMENT . . . . 47 11.34. INCREASED HYDRAULIC GRADIENT UNDER VACUUM 47 II.35A. SEEPAGE FORCES REDUCING STABILITY 48 II.3 5 B . SEEPAGE FORCES INCREASING STABILITY 48 ACKNOWLEDGEMENTS The author would l i k e t o e x p r e s s h i s a p p r e c i a t i o n t o the management of G i b r a l t a r Mines L t d . , McLeese Lake, B.C., f o r p r o v i d i n g f i n a n c i a l a s s i s t a n c e , d a t a , a c c e s s t o i t s m i n i n g f a c i l i t i e s , and r e v i e w o f the m a n u s c r i p t . S p e c i a l g r a t i t u d e i s extended t o Jim Balmer, George B a r k e r , and Gary Bysouth of t he Geology Department a t G i b r a l t a r Mines. The a u t h o r would l i k e t o thank t h e B r i t i s h Columbia S c i e n c e C o u n c i l f o r i t s f i n a n c i a l a s s i s t a n c e , f o r w i t h o u t whose h e l p i t would not have been p o s s i b l e t o under t a k e t h e t a s k o f p r o v i n g the p r a c t i c a l i t y o f vacuum a s s i s t h o r i z o n t a l d r a i n s . The a u t h o r i s i n d e b t e d t o P r o f e s s o r C. 0. Brawner, the T h e s i s D i r e c t o r , f o r h i s c o n t i n u e d g u i d a n c e , encouragement and c o n s t r u c t i v e c r i t i c i s m t h r o u g h o u t t h i s s t u d y . A d d i t i o n a l t hanks goes t o C o r r i n e L a n g e l o o and Mike Hammond f o r t h e i r h e l p i n p r e p a r i n g t h i s m a n u s c r i p t . Review o f the m a n u s c r i p t and s u g g e s t i o n s from Chuck Brawner, J i m Balmer, A l l a n Moss, and Anna Hammer proved t o be i n v a l u a b l e . 1 VOLUME I ROCK SLOPE STABILITY AND DESIGN OF GRANITE LAKE OPEN PIT CHAPTER 1-1 INTRODUCTION T h i s study was unde r t a k e n t o e v a l u a t e the roc k s l o p e s t a -b i l i t y o f the South W a l l o f the G r a n i t e Lake p i t o f G i b r a l t a r Mines L t d . G i b r a l t a r Mines L t d . i s l o c a t e d i n the so u t h c e n t r a l p o r t i o n o f B r i t i s h Columbia, a p p r o x i m a t e l y 370 k i l o m e t e r s n o r t h e a s t o f Vancouver, Canada. G i b r a l t a r Mines c o n s i s t s o f t h r e e open p i t s : Gib E a s t , P o l l y a n n a and G r a n i t e Lake. The t o t a l mine p r o d u c t i o n i s a p p r o x i m a t e l y 38,000 tonnes per day of copper and molybdenum o r e . Stage I o f m i n i n g o f the G r a n i t e Lake p i t was completed i n 1978 and m i n i n g i s s c h e d u l e d t o r e -commence i n 1983. The o b j e c t i v e o f t h i s t h e s i s i s : (a) t o recommend an u l t i m a t e s t a b i l i t y d e s i g n f o r Stage I I o f m i n i n g o f the G r a n i t e Lake d e p o s i t , and (b) t o e v a l u a t e the a p p l i -c a t i o n o f vacuum h o r i z o n t a l d r a i n a g e t o improve s l o p e s t a b i l -i t y . The d e s i g n i n c o r p o r a t e s a ' F a c t o r o f S a f e t y - P r o b a b i l i t y Approach' [1] which would y i e l d t he f o l l o w i n g f o r each d e s i g n s e c t o r t h a t was d e l i n e a t e d from the a n a l y s e s : (a) O v e r - a l l w a l l a n g l e (b) Bench f a c e a n g l e (c) Bench w i d t h Scope o f Study 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 g e n e r a l l y d i c t a t e t he f a i l u r e modes t h a t c o n t r o l w a l l s t a b i l i t y . A s t e e p e n i n g o f the w a l l a n g l e by one degree can save m i l l i o n s o f d o l l a r s i n d e f e r r e d 2 s t r i p p i n g (Chapter I«3) . I t i s f o r t h i s reason t h a t one must un d e r s t a n d the f a c t o r s i n f l u e n c i n g s t a b i l i t y . The p r o j e c t c o n s i s t e d o f the f o l l o w i n g phases: A. ROCK SLOPE STABILITY ANALYSIS BASED ON THE INTERPRETATION OF STRUCTURAL GEOLOGY (1) A n a l y s i s o f e x i s t i n g s t r u c t u r a l d a t a t h a t had been c o l l e c t e d by mine p e r s o n n e l (2) E x a m i n a t i o n o f e x i s t i n g c o r e (3) D e t a i l e d mapping conducted by the auth o r t o d e t e r -mine : (a) D i s c o n t i n u i t y o r i e n t a t i o n (b) C o n t i n u i t y o f s t r u c t u r e (c) F r a c t u r e d e n s i t y and i n f i l l (d) S u r f a c e roughness on d i s c o n t i n u i t i e s (4) R e d u c t i o n o f f i e l d d a t a by computer t o determine the d i s c o n t i n u i t y maxima and d i s t r i b u t i o n (5) A n a l y s i s o f l a b o r a t o r y shear s t r e n g t h d a t a (6) Back a n a l y s i s o f e x i s t i n g f a i l u r e s t o c a l c u l a t e f i e l d shear s t r e n g t h parameters (7) A n a l y s i s o f e x i s t i n g f a u l t s and o t h e r p o s s i b l e domain b o u n d a r i e s (8) P i t s l o p e d e s i g n based on the k i n e m a t i c a n a l y s i s o f 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 B. GROUNDWATER INFLUENCE ON STABILITY AUGMENTED BY VACUUM HORIZONTAL DRAINAGE The vacuum d r a i n a g e r e s u l t e d i n the d r a i n s e x h a u s t i n g a t a n e g a t i v e a t m o s p h e r i c p r e s s u r e . H o r i z o n t a l d r a i n s are an a c c e p t e d s l o p e d e p r e s s u r i z a t i o n t e c h n i q u e [ 2 ] [ 3 ] , however, the f i r s t a p p l i c a t i o n o f vacuum a s s i s t d r a i n a g e was proposed by Brawner [ 2 ] . The b e n e f i t o f augmenting h o r i z o n t a l d r a i n s by a p p l y i n g a vacuum a r i s e s from an i n c r e a s e d h y d r a u l i c g r a d i -e n t . A l a b o r a t o r y model was a l s o c o n s t r u c t e d and p l a c e d un-der vacuum i n o r d e r t o observe the e f f e c t s on the system. The f o l l o w i n g areas were t o be i n v e s t i g a t e d : (1) The a b i l i t y t o c r e a t e a vacuum i n the rock s l o p e (2) The e f f e c t s o f vacuum on s l o p e d e p r e s s u r i z a t i o n and r e s u l t a n t f l o w r a t e s (3) The p r a c t i c a l i t y o f d e v e l o p i n g the system The f o r e g o i n g s t u d y was supplemented w i t h n u m e r i c a l m o d e l l i n g which i n c o r p o r a t e d f i n i t e element t e c h n i q u e s . T h i s t h e s i s summarizes the f o r e g o i n g a n a l y s i s and r e s u l t s t o p r o -duce a 'Slope S t a b i l i t y D esign a t G r a n i t e Lake Open P i t With the A p p l i c a t i o n o f Vacuum Drainage'. 4 CHAPTER 1-2 GEOLOGIC SETTING The G i b r a l t a r Mine i s l o c a t e d i n the s o u t h - c e n t r a l p o r -t i o n o f B r i t i s h Columbia ( F i g i - l ) . Access t o the mine i s p r o -v i d e d by a 15 k i l o m e t e r paved highway t h a t c o n n e c t s w i t h the main n o r t h - s o u t h Highway 97 a t McLeese Lake, which i s 45 k i l o -meters n o r t h o f W i l l i a m s Lake. The area i s o f moderate t o p o g r a p h i c r e l i e f , w i t h e l e v a -t i o n s r a n g i n g between 1070 and 1250 meters. Annual p r e c i p i -t a t i o n averages 500 mm w i t h a i r t e m p e r a t u r e s r a n g i n g from a summer maximum of +35°C t o a w i n t e r minimum o f -35°C. The f o l l o w i n g b r i e f d i s c u s s i o n o f the g e o l o g i c h i s t o r y o f the G i b r a l t a r Mine s i t e i s t a k e n from the works o f Drummond, Ten-nant and Young (1974). M i n i n g H i s t o r y G i b r a l t a r Mines L t d . c o n s i s t s o f t h r e e open p i t s : Gib E a s t , P o l l y a n n a and G r a n i t e Lake. The t o t a l d a i l y p r o d u c t i o n i s i n excess o f 38,000 tonnes g r a d i n g 0.37 p e r c e n t copper and 0.016 molybdenum s u l p h i d e o r e . G i b r a l t a r has been i n produc-t i o n s i n c e 1972, w i t h m i n i n g p r e s e n t l y (1981) b e i n g c o n f i n e d t o the Gib E a s t ore zone. The G r a n i t e Lake p i t was mined be-tween the y e a r s 1973 and 1977 w i t h recommencement s c h e d u l e d t o o c c u r i n 1983. The ore r e s e r v e s as o f December 31, 1971, employing a c u t - o f f grade o f 0.25 p e r c e n t copper, were: FIGURE!*! = LOCATION MAP OF GIBRALTAR MINES LTD. 6 Zone M e t r i c Tonnes Copper ( P e r c e n t ) Gib E a s t 136,000,000 0 . 372 G r a n i t e Lake 109,000,000 0 . 373 P o l l y a n n a 73,000,000 0 . 360 Gib West 8,000,000 0.4 TOTAL 326,000,000 0.371 ( p l u s 0.016 p e r c e n t MoS, ) The o v e r a l l s t r i p r a t i o i s 2.15 tonnes o f waste t o one tonne o f ore mined. The G i b r a l t a r Mine i s l o c a t e d on the w e s t e r n s l o p e o f G r a n i t e Mountain. The o l d e s t r o c k s are l o c a t e d i n t h i s a r e a (FigI-2) and c o n s i s t o f r e g i o n a l l y metamorphosed se d i m e n t a r y and v o l c a n i c r o c k s b e l o n g i n g t o the Cache Creek group o f Permian Age. The G r a n i t e Mountain a r e a c o n t a i n s b a t h o l i t h i c i n t r u s i v e s . The b a t h o l i t h s are composed of g r a n o d i o r i t e , q u a r t z d i o r i t e and g n i e s s i c v a r i e t i e s o f t h e above. The G i b r a l t a r d e p o s i t s are found i n the G r a n i t e Mountain p l u t o n . I t appears t o be one o f a s t r i n g o f b a t h o l i t h s which f a l l a l o n g a n o r t h - s o u t h l i n e on the e a s t e r n s i d e o f the F r a s e r R i v e r f a u l t system. T h i s f a u l t i s a r e g i o n a l o c c u r r e n c e and i s shown i n FigI-2. The G i b r a l t a r Mine i s composed o f the f o l -l o w i n g rock u n i t s (FigI-3): G e n e r a l Geology 9 B 8 LEGEND PLEISTOCENE and RECENT Till ,grovtl, tand, and clay MIOCENE 8 PLIOCENE Botalt EOCENE ond/or OLIGOCENE 8o»alt,tuff, bracda, conglomerate, ihalt, and sandstone PALEOCENE ond/or EOCENE Rhyolltt, daclte, tuff, and breccia PERMIAN CACHE CREEK GROUP Chart, orglll lit., limestone, and graywocke INTRUSIONS ID JURASSIC-CRETACEOUS Gronodiorlte, dlorltt, quartz dioritt and related grwiiiii | 6 as] LD CD 7 ' I 8 ' ••• •:..\ M or 9 u* fir* i V x Gibral tor McL*'»M":Lol(t 1 TA* \ e i jl. ••.WIIMomt Lake.. I 7 . H45' I" 7 « \ \ - i - r -30 Iff I22'00 10 ZO km FIGURE 1-2 : REGIONAL GEOLOGY V3UV 3NIIAI UV11VU8I9 dVlAI 01901039 Q3ZinVd3N39 : £ - I3df l9 ld (1) White Quartz D i o r i t e : T h i s u n i t i s composed o f q u a r t z ( 3 0 % ) , s a u s s u r i t i z e d p l a g i o c l a s e w i t h a l -b i t i c rims (4-5%), q u a r t z and a l b i t i c p l a g i o c l a s e ( 2 5 % ) , and a t r a c e o f c h l o r i t e ( 1 - 2 % ) . (2) Q u a r t z - F e l d s p a r Prophyry: C o n t a i n s p h e n o c r y s t s o f q u a r t z (30%) and a l b i t i c p l a g i o c l a s e (10%) i n an a p h a n i t i c m a t r i x composed of q u a r t z , a l b i t i c p l a g -i o c l a s e and t r a c e s o f carbon t e , m u s c o v i t e and z o i s i t e . (3) A p l i t e : An i n t r u s i v e f i n e - g r a i n e d u n i t e x h i b i t i n g a sugary t e x t u r e . (4) Hornblende D a c i t e : An e x t r e m e l y f i n e - g r a i n e d c h l o r i t i z e d r o c k which i s found o n l y i n the Gib E a s t ore zone. T h i s r o c k , u n l i k e t h e above, had been i n t r u d e d a f t e r m i n e r a l i z a t i o n has o c c u r r e d . A h y p o t h e s i s r e g a r d i n g the development o f the G i b r a l t a r d e p o s i t i s as f o l l o w s : (1) The G r a n i t e Mountain p l u t o n i n t r u d e d the Cache Creek group of r o c k s d u r i n g J u r a s s i c - C r e t a c e o u s t i m e . (2) The r e s u l t a n t d e f o r m a t i o n s had produced s i m u l t a n e o u s development of r e g i o n a l f o l i a t i o n and r e g i o n a l green-s c h i s t f a c i e s type o f metamorphic assemblages w i t h -i n the q u a r t z d i o r i t e o f the G r a n i t e Mountain p l u t o n . (3) Upon f u r t h e r d e f o r m a t i o n , a q u a r t z f e l d s p a r p o r p h y r y i n t r u d e d the p l u t o n which has r e s u l t e d i n a s t r u c -t u r a l l y more competent c o r e . (4) The above i n t r u s i o n i n d u c e d a f r a c t u r e p a t t e r n around the QFP c o r e . T h i s f r a c t u r e system was im-posed on t h e e x i s t i n g r e g i o n a l f o l i a t i o n which r e -s u l t e d i n a c o n d u i t system f o r f u r t h e r s u l p h i d e m i g r a t i o n . (5) Movements along the Fraser R i v e r f a u l t system had up-l i f t e d the G r a n i t e Mountain p l u t o n . R e l a t i v e l y down-dropped a r e a s , which encompass a l l o f the G i b r a l t a r d e p o s i t s , were s u b s e q u e n t l y f i l l e d by g l a c i a l t i l l and g r a v e l . The above h y p o t h e s i s i s summarized by Figuresl-4A andKB which d e p i c t a s t r u c t u r a l model of the G i b r a l t a r a r e a . The w e s t e r n boundary o f the i n f e r r e d s t r u c t u r a l b l o c k i s the F r a s e r f a u l t system. The two double l i n e s r e p r e s e n t the r e g i o n a l f o l i a t i o n w i t h the secondary f r a c t u r e system en-v e l o p i n g the p o r p h y r y c o r e . The e l l i p t i c a l shape o f the zone i n which the G i b r a l t a r d e p o s i t s occur, suggest t h a t the r e g i o n a l f o l i a t i o n had a c t e d as a s t r u c t u r a l c o n t r o l . T h i s a x i s o f the m i n e r a l i z e d zone p a r a l l e l s the t r e n d o f t h e f o l -i a t i o n . Mine Geology The rock a t G r a n i t e Lake i s a h i g h l y f r a c t u r e d and j o i n t -ed q u a r t z d i o r i t e . There are two main s t r u c t u r e s which have been i d e n t i f i e d as c o n t r o l l i n g the grade and a t t i t u d e o f the d e p o s i t . These are the Sunset and G r a n i t e Creek s t r u c t u r e s . 11 S T R U C T U R A L M O D E L OF G I B R A L T A R A R E A r Regional KJ Foliation Fraser Fault System Regional Foliation FIGUREI4A: INFERRED STOCKWORK DEVELOPED AROUND THE PORPHYRY-BEARING CORE Pollyanna Fault Granite Lake Structure Fraser Fault System FIGURE T-4B LOCATION OF THE COPPER-MOLYBDENUM DEPOSITS WITHIN THE DEVELOPED STOCKWORK The Sunset zone s t r i k e s n o r t h w e s t - s o u t h e a s t and d i p s a p p r o x i m a t e l y 35°SW. The G r a n i t e Creek zone s t r i k e s e a s t - w e s t and d i p s s h a l l o w l y t o the s o u t h . The f r a c t u r e i n -t e n s i t y w i t h i n the Sunset zone i s g e n e r a l l y g r e a t e r than t h a t found w i t h i n the G r a n i t e Creek, w i t h the g r e a t e s t i n t e n s i t y o c c u r r i n g where the two i n t e r s e c t . The dominant s t r u c t u r e found i n the G r a n i t e Lake p i t i s the G r a n i t e Creek s t r u c t u r e , w h i l e the Sunset s t r u c t u r e i s more p r e v a l e n t i n the Gib E a s t and P o l l y a n n a p i t s . The f a u l t s a l o n g the South Wall o f Gran-i t e Lake are g e n e r a l l y p a r a l l e l the F r a s e r f a u l t system, d i p -p i n g s t e e p l y towards the west. A p h o t o g r a p h i c c o l l a g e o f the st u d y a r e a i s shown by F i g u r e l - 5 . 13 CHAPTER 1-3 DESCRIPTION OF INVESTIGATION Slope s t a b i l i t y i s an i n t e g r a l p a r t o f s e l e c t i n g a p r o p e r p i t d e s i g n . The u l t i m a t e o b j e c t i v e i n a m i n i n g o p e r a t i o n i s t o excavate as much ore out o f the ground as p o s s i b l e w h i l e m i n i m i z i n g the c o s t o f the a s s o c i a t e d waste s t r i p p i n g . F i g u r e 6 shows the dependence o f s t r i p r a t i o on the o v e r a l l s l o p e a n g l e . [5] C O . Brawner (1977) [6] s u g g e s t s t h a t f o r deep p i t s , sav-i n g s i n the o r d e r o f 15 t o 20 m i l l i o n d o l l a r s can be r e a l i z e d f o r each degree t h a t the p i t s l o p e can be steepened. The s t a b i l i t y a n a l y s i s i s an i n t e g r a t e d s t u d y i n c o r p o r a t i n g g eology, r o c k s t r e n g t h , groundwater p r e s s u r e s and m i n i n g p r o -cedures. The f o l l o w i n g s e c t i o n s d e s c r i b e the a n a l y s e s t h a t were performed i n o r d e r t o a r r i v e a t a s t a b l e p i t s l o p e d e s i g n . G e o l o g i c a l Mapping G e o l o g i c mapping was conducted on a l l a c c e s s i b l e exposed f a c e s on the South W a l l o f the G r a n i t e Lake p i t ( F i g I - 7 ) . Map-p i n g r e q u i r e d the r e c o r d i n g o f a l l s t r u c t u r e s g r e a t e r than 6 m (20 f t ) i n l e n g t h and p e n e t r a t i n g e i t h e r beyond the t o e or c r e s t o f the mapped bench (13.5 m h e i g h t ) . The s t r u c t u r e t y p e , s i z e o f d i s c o n t i n u i t y , f r a c t u r e i n t e n s i t y , f r a c t u r e i n f i l l i n g , g e o l -ogy, water and r o c k hardness were r e c o r d e d , i n a d d i t i o n t o the d i s c o n t i n u i t y o r i e n t a t i o n (TableJ-1.0) . A t o t a l o f 3064 s t r u c -14 ^ UJ UJ UJ UI O O FIGURE 5: PHOTOGRAPHIC COLLAGE OF THE SOUTH WALL OF THE GRANITE LAKE PIT FIGURE 5 HYPOTHETICAL OPEN PIT AND OREBOOY FIGUREF6: VARATION OF STRIP RATIO WITH SLOPE ANGLE ( A F T E R S T E W A R T Q KENNEDY) C5D 16 FIGURE I-?1 STUDY AREA S C A L E 1 : 4 8 0 0 T a b l e l - l .0 D i s c o d a t D i s c o n t i n u i t y Data Type a) Bedding BG a) b) Cleavage CL b) c) F a u l t FL c) d) J o i n t JN d) e) J o i n t Set JS e) f ) F a u l t Shear FS f ) g) V e i n VN S i z e o f D i s c o n t i n u i t y g r e a t e r t h a n 27 m M 14 m - 27 m L 6 m - 14 m K 20 cm - 60 cm J 2 cm - 20 cm I Less t h a n 2 cm H ROCK MASS CLASSIFICATION F r a c t u r e I n t e n s i t y (1) Very Low - s p a c i n g 2m (2) Low - s p a c i n g 60 cm - 2 m (3) M o d e r a t e l y 20 cm - 60 cm (4) S t r o n g l y 7 cm - 20 cm (5) I n t e n s e l y under 7 cm F r a c t u r e I n f i l l i n g A) 80-100% fractures open very loosely held B) 60-100% fractures open loosely held C) 40-60% fractures open held moderately t i g h t D) 20-40% fractures open t i g h t l y held E) 0-20% fractures open very t i g h t l y held Geology Water Hardness a) A i r A a) No p o s s i b i l i t y of water flow 1 a) D i f f i c u l t to move with pick- 1.5 MPa S5 b) C a l c i t e Z b) Dry with no evidence of water 2 b) crumbles under firm blow- 3 MPa RI c) C h l o r i t e K c) Dry with past evidence i e . rust 3 c) shallow indentation by firm blow of d) Gouge G d) Damp with no free water present 4 geological harrmer- 10 MPa R2 e) P y r i t e P e) Seepage, no continuous flow 5 d) specimen fractured by 1 blow-- 25 MPa R3 f ) Quartz Q f) Continuous flow 6 e) specimen requires 2/4 blows- 80 MPa R4 g) Quartz Diori t e QZD f) specimen requires many blows-- 200 MPS5 From P i t Slope Manual [7] t u r e s were r e c o r d e d encompassing n i n e benches, each approximate-l y 650 m i n l e n g t h . Standard d e t a i l l i n e mapping t e c h n i q u e s [7] were employed w i t h d a t a r e d u c t i o n b e i n g conducted w i t h the use o f the 'Discodat Computer Package' [ 7 ] , F e d e r a l Depart-ment of Energy, Mines and Resources. I t must be noted t h a t s t r i k e and d i p were r e c o r d e d f o r each s t r u c t u r e w i t h d i p d i -r e c t i o n = s t r i k e + 90°. Major s t r u c t u r e s were d e f i n e d as those p l a n a r f e a t u r e s which c o u l d be t r a c e d f o r a t l e a s t two or t h r e e benches. Geo-l o g i c i n f o r m a t i o n , o b t a i n e d from p r i o r mapping conducted by mine p e r s o n n e l , was employed t o r e i n f o r c e the o v e r a l l g e o l o g i c model as a c c u r a t e l y as p o s s i b l e . A composite g e o l o g i c a l map was con-s t r u c t e d t o show the l o c a t i o n and s p a t i a l r e l a t i o n s h i p o f the major s t r u c t u r e s . Bench f a c e a n g l e s o f e x i s t i n g s i n g l e and double benches were r e c o r d e d throughout the s o u t h w a l l t r a v e r s e . The e v a l u a t i o n was u n d e r t a k e n on the i n t e r i m w a l l s o f the G r a n i t e Lake p i t s i n c e u l t i m a t e p i t w a l l s were not exposed a t the time of the s t u d y . F a b r i c A n a l y s i s F i e l d mapping e n a b l e d a s t r u c t u r a l model t o be d e v e l o p e d whereby d e s i g n s e c t o r s were compared i n terms of t h e i r i n h e r e n t c h a r a c t e r i s t i c s such a s : r o c k hardness, water c o n t e n t , i n f i l l t y p e , and the d i s c o n t i n u i t y s i z e and s p a c i n g . A r o c k mass as-sessment was performed whereby the f r a c t u r e i n t e n s i t y and the degree of i n f i l l were r e c o r d e d . T h i s e n a b l e d one t o j u s t i f y i n c o r p o r a t i n g a c o h e s i o n v a l u e i n t o the w a l l d e s i g n . 19 E x a m i n a t i o n o f D r i l l Data Logs from Diamond D r i l l h o l e s , l o c a t e d w i t h i n the u l t i m a t e p i t l i m i t s , were examined t o a s s e s s whether s t r u c t u r e s l o c a t e d on the p r e s e n t w a l l would e x i s t a t u l t i m a t e d i m e n s i o n s . The d r i l l l o g s r e c o r d e d c o r e r e c o v e r y which e n a b l e d a r e a s o f poor ground t o be i d e n t i f i e d . However, the c o r e was not a v a i l a b l e t o be logged g e o t e c h n i c a l l y . The Geology Department of G i b r a l t a r Mines L t d . r e c o r d e d the p r o d u c t i o n d r i l l h o l e assays f o r each i n d i v i d u a l bench. The c o n t o u r e d a s s a y s assume a p a r a l l e l i n g t r e n d t o the two ore c o n t r o l l i n g s t r u c t u r e s ; the G r a n i t e Lake and Sunset. T h i s en-a b l e d the a u t h o r t o determine where the i n d i v i d u a l ore s t r u c -t u r e s were the s t r o n g e s t and how they v a r i e d l a t e r a l l y . Groundwater I n v e s t i g a t i o n A h y d r o l o g i c assessment of the G r a n i t e Lake p i t was con-f i n e d t o : (a) C o n d u c t i n g f i n i t e element s t u d i e s on the s o u t h w a l l f l o w regime w i t h r e f e r e n c e t o d e p r e s s u r i z a t i o n by the use o f h o r i z o n t a l d r a i n s . (b) I n s t a l l i n g a vacuum h o r i z o n t a l d r a i n system t o e v a l -uate i t s p r a c t i c a l i t y . A s t u d y [8] i n t o the f e a s i b i l i t y o f d e w a t e r i n g G r a n i t e Lake p r o v i d e d i n f o r m a t i o n f o r the above s i t e i n v e s t i g a t i o n . 20 S t r e n g t h D e t e r m i n a t i o n The U n i v e r s i t y of A l b e r t a [9] had conducted l a b o r a t o r y d i -r e c t shear t e s t s on t e n q u a r t z d i o r i t e samples i n o r d e r t o determine the peak and r e s i d u a l f r i c t i o n a n g l e s . U n c o n f i n e d compressive s t r e n g t h s were a l s o determined from u n i a x i a l t e s t s on s i x NX s i z e c o r e samples. The above d i s c o n t i n u i t y s t r e n g t h i n f o r m a t i o n was supplemented by t h e back a n a l y s i s o f e l e v e n bench s i z e f a i l u r e s . These f a i l u r e s were i n v e s -t i g a t e d f o r the d e t e r m i n a t i o n o f mass shear s t r e n g t h p a r a -meters . S t a b i l i t y I n v e s t i g a t i o n The above i n p u t parameters enabled p o s s i b l e f a i l u r e modes to be e v a l u a t e d (Fig I - 8 ) , s i n c e s l o p e f a i l u r e s i n c r y s t a l l i n e r o c k s g e n e r a l l y occur a l o n g 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 . S t r u c -t u r e s such as major f a u l t s were c o n s i d e r e d i n d i v i d u a l l y , because they are g e n e r a l l y c o n t i n u o u s over a l a r g e a r e a . The f a u l t bounded f a i l u r e s are o f a much l a r g e r s i z e and, as a consequence, r e q u i r e a d i f f e r e n t d e s i g n c r i t e r i a t han t h a t employed f o r bench c o n f i n e d f a i l u r e s (FigI-9). The minor s t r u c t u r e s must be ana-l y z e d s t a t i s t i c a l l y as they are o f h i g h f r e q u e n c y and s p a t -i a l d i s t r i b u t i o n . T h e i r i n f l u e n c e on d e s i g n i s r e s t r i c t e d t o minor f a i l u r e s f o r they are g e n e r a l l y d i s c o n t i n u o u s over t h e st u d y a r e a . PLANE SHEAR STEP PATH FIGUREI-8: POSSIBLE MODES OF FAILURE 22 FIGURE 1-9: FA I LURES CONTROLLED BY MINOR AND MAJOR DISCONTINUITIES G e o l o g i c s t r u c t u r a l d a t a from the d e t a i l l i n e mapping p r o -gram was p r o c e s s e d , p l o t t e d and c o n t o u r e d on e q u a l a r e a lower hemisphere s t e r e o g r a p h i c p r o j e c t i o n s [ 1 0 ] . T h i s was a c c o m p l i s h ed by the use o f the ' D i s c o d a t ' computer package. The s t r u c -t u r a l a n a l y s i s e n a b l e d the south W a l l t o be d i v i d e d i n t o s t r u c -t u r a l domains i n which the d i s c o n t i n u i t y p o p u l a t i o n s were s t a t -i s t i c a l l y s i m i l a r . The South W a l l was f u r t h e r s u b d i v i d e d w i t h r e f e r e n c e t o s i m i l a r w a l l o r i e n t a t i o n s , i n o r d e r t o e s t a b l i s h d e s i g n s e c t o r s f o r a p a r t i c u l a r domain. A c o n v e n t i o n a l s t a b i l -i t y a n a l y s i s [10] was performed on each d e s i g n s e c t o r which es-t a b l i s h e d p o t e n t i a l f a i l u r e modes and, as a r e s u l t , d e t e r -mined a recommended s l o p e geometry. A s t a t i s t i c a l f a c t o r o f s a f e t y - p r o b a b i l i t y [1] approach was employed whereby a q u a n t i t a t i v e assessment o f the r e l a t i v e o c c u r r e n c e o f f a i l u r e s was d e t e r m i n e d f o r a range o f o v e r a l l s l o p e a n g l e s . Berms were d e s i g n e d so t hey would be o f a s u f f i c i e n t w i d t h [11] i n o r d e r t o r e t a i n m a t e r i a l from minor bench f a i l u r e s . Major f a i l u r e s , which encompassed two or more 27 m double benches, were d e l i n e a t e d and t h e u l t i m a t e s l o p e d e s i g n was based on e n s u r i n g o v e r a l l w a l l s t a b i l i t y . Groundwater was c o n s i d e r e d i n the s t a b i l i t y a n a l y s i s as a major c o n t r i b u t o r t o i n s t a b i l i t y [ 1 2 ] . The e f f e c t o f employing h o r i z o n t a l d r a i n s as a d e p r e s s u r i z i n g method was compared t o the drawdown which would r e s u l t i f deep w e l l s were employed. S e i s m i c i t y was not c o n s i d e r e d t o be a problem, (FigI-10), due t o the remoteness CONTOUR MAP OF A C C E L E R A T I O N S A S  A P E R C E N T OF g WITH A 100 Y E A R R E T U R N P E R I O D F O R W E S T E R N CANADA FIGUREI-IO: CONTOUR MAPS OF SEISMIC ACTIVITY FROM MILNE ET AL [13] 25 o f the s t u d y s i t e from a c t i v e ' s e i s m i c a r e a s . Milne et a l (1978) i n -d i c a t e s t h a t a 1000-year r e t u r n p e r i o d e x i s t s f o r a 0.1 g earthquake and a 100-year p e r i o d f o r a 0.03 g s e i s m i c event [ 1 3 ] . T h i s c o r r e s p o n d s t o a m o d i f i e d M e r c a l l i i n t e n s i t y o f IV whereas r o c k f a l l s b e g i n t o o c c u r when the i n t e n s i t y r e a c h -es V I I [ 1 4 ] . 26 CHAPTERt-4 STRUCTURE ANALYSIS The s t r u c t u r e a n a l y s i s w i l l be d i s c u s s e d i n two s e c t i o n s : Major S t r u c t u r e s and Rock F a b r i c . Major S t r u c t u r e s a r e d e f i n e d as discontinuities h a v i n g a t r a c e l e n g t h o f g r e a t e r t h a n two bench h e i g h t s (28 m). The Rock F a b r i c a re those s t r u c t u r e s t h a t a re d i s c o n t i n u o u s but have a h i g h f r e q u e n c y o f o c c u r r e n c e . The min-imum t r a c e l e n g t h o f the s e secondary d i s c o n t i n u i t i e s are 6 m. Major S t r u c t u r e s The i n i t i a l s t age i n a s t a b i l i t y a n a l y s i s r e q u i r e d t h a t the s o u t h w a l l o f G r a n i t e Lake be broken i n t o s t r u c t u r a l l y s i m-i l a r domains. The i n d i v i d u a l domains behave as a s t r u c t u r a l unit of which the characteristics d i f f e r from a d j a c e n t domains. De-l i n e a t i n g the d i v i s i o n s r e q u i r e d a d e t a i l e d i n v e s t i g a t i o n i n t o the l a t e r a l v a r i a t i o n s t h a t e x i s t e d w i t h i n s t r u c t u r a l p o p u l a -t i o n s as a domain boundary was c r o s s e d . A n a l y s e s performed were as f o l l o w s : (1) The South W a l l was a r b i t r a r i l y segmented i n t o 150 m (500 f t ) l a t e r a l b l o c k s encompassing the f u l l p i t h e i g h t . (2) The south w a l l was a n a l y z e d bench by bench i n o r d e r t o d e t e c t v e r t i c a l v a r i a t i o n s i n s t r u c t u r a l s e t s . (3) The major f a u l t s were de t e r m i n e d t h r o u g h mapping and photo l i n e a r s and a n a l y z e d as domain b o u n d a r i e s . A n a l y t i c a l t e c h n i q u e s supplemented th e above o b s e r v a t i o n s i n o r d e r t o d e t e c t t r e n d v a r i a t i o n s a t domain b o u n d a r i e s . The g e n e r a t i o n o f a l l 3064 s t r u c t u r e s onto one s t e r e o n e t e n a b l e d the d e l i n e a t i o n o f e i g h t j o i n t p o p u l a t i o n s ( F i g l - l l ) , r a n g i n g from 'A' t h r o u g h 'H'. The i n d i v i d u a l benches were i d e n -t i f i e d as f o l l o w s : A L e v e l - 1218 m ( 3995 f t ) B L e v e l - 1204 m ( 3950 f t ) D L e v e l - 1177 m ( 3860 f t ) E L e v e l - 1163 m ( 3815 f t ) F L e v e l - 1149 m ( 3770 f t ) G L e v e l - 1135 m ( 3725 f t ) H L e v e l - 1122 m ( 3680 f t ) I L e v e l 1108 m ( 3635 f t ) Domain D e l i n e a t i o n by S e c t o r F i g 12 shows the south w a l l o f G r a n i t e Lake broken i n t o s i x 150 m wide segments. The s t r u c t u r a l d a t a f o r each s e c t o r was e v a l u a t e d i n o r d e r t o a s s e s s any l a t e r a l v a r i a t i o n w i t h i n the study a r e a . FigureI-13 i s a composite diagram o f the g e n e r a t e d s t e r e o n e t s from the above a n a l y s i s . A c o m p a r a t i v e approach was employed whereby the j o i n t s e t number was p l o t t e d a g a i n s t oc-c u r r e n c e f o r each i n d i v i d u a l s e c t o r (FigI-14). D e v i a t i o n s i n t r e n d s were r e l a t e d t o major f e a t u r e s l o c a t e d i n the v i c i n i t y o f the s e c t o r boundary. These major f e a t u r e s are d i s c u s s e d i n a l a t t e r s e c t i o n . TableI-2 .0  Cumsum A n a l y s i s FAULT 7 6 5 4 3 2 1 A BENCH B BENCH XX XX • XX XX D BENCH XX XX XX XX E BENCH XX XX F BENCH - Set Doesn ' t E x i s t -G BENCH - Set Doesn ' t E x i s t -H BENCH X X XX XX LEGEND XX - Very S t r o n g Presence X - S t r o n g Presence 3064 STRUCTURES N 331° L 270* FIGURE I-ll: IDENTIFICATION OF STRUCTURAL SETS 30 FIGURE I-.2-D0MAIN DELINEATION BY SECTORS FIGUREI-I2 S C A L E 1 : 4 8 0 0 3 1 NO. OF OBSERVATIONS: 22 SECTOR I NO. OF OBSERVATIONS: 404 SECTOR 2 NO. OF OBSERVATIONS: 759 SECTOR 3 NO. OF OBSERVATIONS : 757 SECTOR 4 NO. OF OBSERVATIONS: 870 SECTOR 5 NO. OF OBSERVATIONS: 2 52 SECTOR 6 FIGUREH3: STRUCTURAL DATA BY SECTOR FIGUREH3 32 SECTOR SECT 6 SECT. S SECT. 4 SECT. 3 SECT. 2 SECT. I J S A J S B J S C cr UJ 03 Z I-UJ V) JSr JSp 5 LEGEND I - > 3 % C O N C E N T R A T I O N l /2 -> l % C O N C E N T R A T I O N 0 - NO O C C U R R E N C E FIGURE:m- JOINT SET NUMBER VS. OCCURRENCE - SECTOR Domain D e l i n e a t i o n by Bench The study a r e a was s e p a r a t e d i n t o s t r u c t u r a l domains en-compassing i n d i v i d u a l benches. Figure 1-15 i s a composite o f the g e n e r a t e d s t e r e o n e t s from the above a n a l y s i s w i t h a s i m i l a r c o m p a r a t i v e approach employed, as d i s c u s s e d p r e v i o u s l y ( F i g l l 6 ) Domain D e l i n e a t i o n by F a u l t s Seven major f a u l t s were l o c a t e d w i t h i n the p i t a r e a as i n d i c a t e d by a l a t t e r s e c t i o n ( F i g l - 1 7 ) . A s t e r e o p l o t o f a l l s t r u c t u r e s bounded by the above f a u l t s were g e n e r a t e d w i t h a d d i t i o n a l d e l i n e a t i o n performed on a bench s c a l e ( F i g I T 8 ) . A s i m i l a r c o m p a r a t i v e approach t o t h a t p r e v i o u s l y d i s c u s s e d was employed whereby: (1) The presence o f p a r t i c u l a r s t r u c t u r a l s e t s as a f a u l t boundary was c r o s s e d , were a n a l y z e d ( F i g s 1-19, 1-20) . (2) A p l o t o f the o c c u r r e n c e o f 'G1 s e t as a f a u l t boundary was crossed for each individual bench (Fig 121). The above a n a l y s e s i n d i c a t e d t h a t f a u l t s c o u l d p o s s i b l y be employed as domain b o u n d a r i e s s i n c e v a r i a t i o n i n s t r u c -t u r a l s e t s were e v i d e n t as a major s t r u c t u r e was c r o s s e d . Assessment o f Domain Bo u n d a r i e s Employing  C u m u l a t i v e Sums Technique T h i s i s a s t a t i s t i c a l t e c h n i q u e [15] which a n a l y z e s t r e n d s above or below a p a r t i c u l a r r e f e r e n c e v a l u e . T h i s 34 N N N ^ ^ ^ ^ ^ N ^ ^ ^ ^ ^ ^ NO. OF OBSERVATIONS: 131 A NO O F OBSERVATIONS :32l B NO.OF OBSERVATIONS : 459 D NO O F OBSERVATIONS : 292 E N N ^ ^ ^ ^ ^ ^ N " ^ ^ ^ ^ ^ NO. O F OBSERVATIONS : 462 p NO. O F 08SERVATI0NS ;526 Q NO. O F OBSERVATIONS «39 8 H NO. O F 08SERVATI0NS :475 1 FIGUREH5 • DOMAIN DELINEATION BY BENCH FIGURE1I5 X o z I u z B E N C H x o z 5 3 m x o X X X u z lli o 5 z J S , J S g J S f m 3 UJ </> r-2 O "3 JSr JS« J S , JS i o-f~ LEGEND I - >3% CONCENTRATION 1/2- >l% CONCENTRATION 0 - NO OCCURRENCE FIGUREH6- JOINT SET NUMBER VS. OCCURRENCE-B ENCH 36 FIGUREH7;PLAN SHOWING MAJOR STRUCTURES F I G U R E I I 7 SCALE 1:2400 37 NO. OF 0BSERVATI0NS:706 | ALL BENCHES NO OF OBSERVATIONS: 68 | A BENCH NO.OF OBSERVATIONS : 141 | B BENCH NO OF OBSERVATIONS: 790 D BENCH NO. OF OBSERVATIONS : 61 | E BENCH | NO. OF OBSERVATIONS: 116 | F BENCH NO. OF OBSERVATIONS 1162 | G BENCH NO. OF OBSERVATIONS*. 78 H BENCH FIGURE 1)8A: DOMAIN DELINEATION BY MAJOR STRUCTURES — FAULT 1/2 FIGURE II8 A 38 N NO. OF OBSERVATIONS:622 [ALL BENCHES NO OF OBSERVATIONS :57 | B BENCH NO.OF OBSERVATIONS : 75 0 BENCH NO OF OBSERVATIONS: 151 E BENCH NO. OF OBSERVATIONS :68 F BENCH NO.OF OBSERVATIONS: 178 G BENCH NO. OF OBSERVATIONS: 91 BENCH NO. OF OBSERVATIONS*. 0 FIGURE.U8B: DOMAIN DELINEATION BY MAJOR STRUCTURES— FAULT 2 / 3 FIGURE H8B 40 N ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ N N ^ ^ ^ ^ ^ ^ ^ NO. OF OBSERVATIONS: 349 | ALL BENCHES NO OF OBSERVATIONS: 51 A BENCH NO.OF OBSERVATIONS : 41 B BENCH NO OF OBSERVATIONS: 67 | D BENCH N N N | C M NO. OF OBSERVATIONS :29 I E BENCH NO.OF OBSERVATIONS:78 1 F BENCH NO. OF OBSERVATIONS:61 | G BENCH NO. OF OBSERVATIONS*. 22 | 1 BENCH i FIGUREH8Di DOMAIN DELINEATION BY MAJOR STRUCTURES— FAULT 4 / 5 1 FIGUREH8 D I I I 42 N N N (^^^^^ N 1 1 Q 0 Q 1 NO. OF OBSERVATIONS: 461 ALL BENCHES NO OF OBSERVATIONS: 10 B BENCH NO.OF OBSERVATIONS : 104 D BENCH NO OF OBSERVATIONS: 33 F BENCH N ( ' ) N ^ ^ ^ ^ NO. OF OBSERVATIONS :30 G BENCH NO.OF OBSERVATIONS.* 103 H BENCH NO. OF OBSERVATIONS: 181 1 BENCH NO. OF OBSERVATIONS*. F I G U R E . H 8 F : DOMAIN DELATION BY MAJOR FAULTS— FAULT 6 / 7 FIGURE I-I8F t NO. OF OBSERVATIONS: 496 ALL BENCHES NO. OF OBSERVATIONS : 58 D BENCH NO. OF OBSERVATIONS: 94 F BENCH NO. OF OBSERVATIONS : 127 H BENCH NO. OF OBSERVATIONS: 217 I BENCH NO. OF OBSERVATIONS: FIGURE.I-'8G DOMAIN DELINEATION BY MAJOR FAULTS FAULT 7-h FIGUREB8G 3 FAULT BOUNDARY 10 h 2 J S H 0 LEGEND (I) ONE IF J . S . EXISTS > 3 % P K . CONC. (0) Z E R O IF J.S. D O E S NOT E X I S T (1/2) ONE H A L F IF J . S . P K . C O N O I % FIGURE r-19: PLOT OF STRUCTURAL SET VS. FAULT BOUNDARY - ALL BENCHES 45 • i FAULT 2 FAULT 3 r FAULT 4  n O c z > FAULT 5 ^ FAULT 6 FAULT 7 1-o-1-JSg Ch 1 J S C o cr QQ 1 z o-1-w 1 10 1 Z 0-5 i J S F 0-1-0-1-J S H o-1' LEGEND l->3% CONCENTRATION l/2->l% CONCENTRATION 0 - NO OCCURRENCE FIGURE 120: PLOT OF STRUCTURAL SET VS. FAULT BOUNDARY -1135 m BENCH (G) ft FAULT BOUNDARY 2 < D ALL L E G E N D I - > 3 % C O N C E N T R A T I O N 1/2- > l % C O N C E N T R A T I O N 0 - NO O C C U R R E N C E FIGURE 1-21 = PLOT OF THE OCCURRENCE OF 'G' SET AS A BOUNDARY IS CROSSED FOR EACH BENCH LEVEL approach i s p a r t i c u l a r l y a p p l i c a b l e i n a n a l y z i n g changes i n s t r u c t u r e o r i e n t a t i o n t h a t o c c u r a t domain b o u n d a r i e s . T h i s t e c h n i q u e was employed a l o n g the South W a l l o f G r a n i t e Lake whereby s t r i k e v a r i a t i o n s w i t h i n the 'G' s e t (253 - 300° s t r i k e ) were a n a l y z e d on i n d i v i d u a l benches 'A' th r o u g h ' I ' . Figures 1-22 andT23 show t y p i c a l r e s u l t s when cumsums were a p p l i e d on the 1177 m (D) bench. Table 1-2 summarizes t h e above i n -v e s t i g a t i o n which r e v e a l s t h a t f a u l t s 'one' th r o u g h 'seven' are i n d i c a t e d by the cumsums a n a l y s i s . Cumsum had f u r t h e r d e l i n e a t e d f a u l t 1.5 ( F i g 1-17) which, upon f u r t h e r i n v e s t i g a -t i o n , was e a s i l y l o c a t e d on t h e South W a l l . G.B.A.S. C o r r e l a t i o n G i b r a l t a r Mines L t d . r e c o r d s assay v a l u e s (G.B.A.S.) f o r a l l p r o d u c t i o n d r i l l h o l e s , and c o n t o u r s t h i s i n f o r m a t i o n on l e v e l p l a n s . The r e s u l t a n t c o n t o u r s strongly p a r a l l e l (Figi-24) the dominant ore c o n t r o l l i n g s t r u c t u r e s , t h e Sunset and G r a n i t e Creek s t r u c t u r e s . A domain breakdown o f f a u l t s was performed whereby the o c c u r r e n c e o f the G r a n i t e Creek (A) and Sunset (C) s t r u c t u r e s were q u a n t i f i e d f o r each l e v e l , conse-q u e n t l y , o b t a i n i n g a p l o t o f t h e i r i n t e n s i t i e s as one t r a v e r -ses i n a v e r t i c a l d i r e c t i o n . 'G.B.A.S.' ena b l e s a s i m i l a r approach t o be employed by a n a l y z i n g l e v e l p l a n s and a s s e s s i n g where the i n d i v i d u a l ore s t r u c t u r e s e x i s t (FigsI-25A andI-25B). 48 290 -t r* -* -f b • H 280 -L U </) r-Z O + -* 270 -L L . O L U 1 1 1 1 1 1 1 i i D2 03 04 0^ 06 07 08 09 010 LOCATION (1177 m BENCH-D) DM be! E t-260 -L D t M 250 " it X SCALE M2400 FIGURE 122-'PLOT OF STRIKE V S . LOCATION FOR "G" SET BO-i ALONG "D" BENCH 70-+ 1 60- 7 30- / + 40- / S o 30-H L U to 20-H Z o '°-O +• / \ FL7 •/ \ FL6 FL5 FL4 FL3 7 FL2 Fl \ \ \ \ \ \ \ I 1 \ \ L 1.3 ^ 0 -o: L O -10-L L o 5 -20-5? § -30-O -40-\D2 / 6i 1 0,4 D5 ' 06 D7| IDS 69 DIO ) DM \ J 1 LOCATION (1177m BENCH-D) / A i » / * 1 1 1 / SLOPE OF CURVE INDICATES THE * \ j - l / / AMOUNT OF DEVIATION FROM THE MEAN \ 1 1 * A \ / { Z T 0" > -50- \ / "* I / \ " * / \ 1 1 / \ * / -6 0. \ | ^^/" , \ ^/ SCALE P2400 j * F I G U R E D PLOT OF CUMSUM OF STRIKE VS. LOCATION FOR "G"SET ALONG 1135m BENCH (D) GRANITE LAKE STRUCTURE SUNSET STRUCTURE TT" ntcouCMCY or oci FMOJCMCT Of OCCU*UtE»C£ « I AS 5 8 LOCATION* 9£HCM L E V C L m% | 3"H -n,i 5 FIG. 2 5 A LEGEND STRUCTURE STRUCTURE mcouCNcr or OCCUMMCNCC «.I .A.S. m' r LOCATION . M M C H U V C L FIG. 2 5 B IS NOT PRESENT (G.B.A.S.) EXISTS (G.B.A.S.) - P E R C E N T RECORDED = no. Gronite /Sunset joints within boundary total Granite/Sunset joints along South Wall FIGUREf-25: EVALUATION OF INTENSITY OF THE GRANITE AND SUNSET STRUCTURES EMPLOYING FIELD AND G.B.A.S. INFORMATION O The above c o r r e l a t e s w e l l w i t h g e o l o g i c a l i n f o r m a t i o n whereby the G r a n i t e Creek zone i s e v i d e n t below the 1163 m l e v e l ( E ) , w i t h the Sunset r e c o r d e d a t e i t h e r e x t r e m i t y o f the p i t . T h i s a n a l y s i s i n d i c a t e s t h a t a f u r t h e r domain i s r e q u i r e d , s e p a r a t i n g the south w a l l above and below t h e 1163 m l e v e l ( FigI-26 ) . F a u l t s or F a u l t Shears FigureI-27 shows the s t e r e o p l o t o f a l l f a u l t s and f a u l t s h ears r e c o r d e d on the south w a l l o f G r a n i t e Lake. A l l ma-j o r s t r u c t u r e s were p l o t t e d on Figure i-17. T able 1-3 summarizes the major f a u l t b o u n d a r i e s which were d e l i n e a t e d by the p r e -v i o u s a n a l y s i s , i n a d d i t i o n , photographs o f each i n d i v i d u a l f a u l t are shown i n FigureI-28. The f a u l t s p r e d o m i n a n t l y s t r i k e between 120 - 197° and d i p 34 - 90° towards the west. I t i s i n t e r e s t i n g t o note t h a t t h e s e s t r u c t u r e s p a r a l l e l the F r a s e r f a u l t system which s u g g e s t s t h a t t hey were p o s s i b l y formed by movement a l o n g t h i s system. The G r a n i t e Creek boundary ( L e v e l E) has a d i s c o n t i n u o u s e f f e c t on F a u l t s 3 and 4 which r e s u l t e d i n t h e i r r o t a t i o n and/or s t e e p e n i n g w i t h i n t h e G r a n i t e Creek zone. F a i l u r e s were r e s t r i c t e d t o bench r a v e l -l i n g w i t h the e x c e p t i o n o f a t o p p l i n g mode e x i s t i n g i n the v i c i n i t y o f F a u l t 1. T h i s i s p r i m a r i l y because o f the f a v o u r a b l e o r i e n t a t i o n o f the f a u l t s w i t h r e s p e c t t o the s o u t h w a l l I t i s a l s o i n t e r e s t i n g t o note t h a t F a u l t 3B i s o f a low con-c e n t r a t i o n , as i n d i c a t e d by Figure 127. The boundary f a u l t s were i n c o r p o r a t e d i n the d e s i g n a n a l y s i s s i n c e t hey would 52 FIGUREI-26: PLAN SHOWING DOMAIN BREAKDOWN — PRESENT PIT FIGUREI-26 S C A L E 1 : 2 4 0 0 92 STRUCTURES FIGUREJ'27: LOWER HEMISPHERE PLOT SHOWING FAULTS AND FAULT SHEARS FIGURE 2 8 A : PHOTOGRAPHS OF MAJOR DOMAIN BOUNDARIES FIGURE 2 8 B : P H O T O G R A P H S O F M A J O R B O U N D A R I E S 56 Tablel-3 Summary o f A t t i t u d e s o f Major F a u l t s on South W a l l o f G r a n i t e Lake BENCH FL 1.0 FL 1.5 FL 2 FL 3 FL 4 FL 5 FL 6 FL 7 A -3995 L e v e l 130/34W B 3950 L e v e l 165/90 195/67W 160/48W 130/43W 162/90 D 3860 L e v e l 153/67W 198/67W 158/82W 302/35E 210/59W 158/90 155/23W obtained E 3815 L e v e l 180/90 307/30E 185/80W 127/-47W 140/35W from Average Above 159/78W 189/78W 130/34W 305/33E 197/69W 144/48W 142/34W h i s t o r i -G r a n i t e Creek & c a l data 158/82W F 3770 L e v e l 153/70W 145/65W 120/35W G 3725 L e v e l 20/78E 190/88W 137/75W 100/44W H 3680 L e v e l I 3635 L e v e l 18/79E 205/90 03/85E TRACE Average Below 153/70W 20/78E 197/89W 03/85E 137/75W 122/55W 120/35W G r a n i t e Creek Ul form major f a i l u r e s g o v e r n i n g the e n t i r e w a l l . The f a u l t s w hich were l e s s c o n t i n u o u s (92 obs) were a n a l y z e d as a f f e c t -i n g bench s i z e f a i l u r e s . Rock F a b r i c A t o t a l o f e i g h t s t r u c t u r a l s e t s were r e c o g n i z e d t o e x i s t on the South W a l l o f G r a n i t e Lake ( F i g l - l l ) . The i d e n -t i f i c a t i o n 'A' a p p l i e s t o the s t r o n g e s t and 'H' t o the weak-e s t s e t . F a b r i c A n a l y s i s The f o l l o w i n g o b s e r v a t i o n s were made c o n c e r n i n g the south w a l l : (1) 3064- s t r u c t u r e s were r e c o r d e d . (2) 0.7% (22 o b s e r v a t i o n s ) o f a l l s t r u c t u r e s were r e -cord e d as j o i n t s . (3) 95% (2907) o f a l l s t r u c t u r e s were r e c o r d e d as j o i n t s e t s . (4) 75% (2294) o f a l l s t r u c t u r e s were r e c o r d e d as h a v i n g a r o c k hardness c l a s s i f i c a t i o n o f 'R4', ( g r e a t e r than 80 MPa). (5) 1.2% (38) o f a l l s t r u c t u r e s i n d i c a t e d h a v i n g a low s t r e n g t h ( l e s s than 25 MPa). These low s t r e n g t h s t r u c t u r e s were r e s t r i c t e d t o f a u l t a r e a s . 59 (6) 2.4% (76) o f a l l s t r u c t u r e s were f i l l e d w i t h e i t h e r c a l c i t e , c h l o r i t e o r gouge. The remainder were e i t h e r c l o s e d o r had no t r a c e o f i n f i l l . 35% (1073) o f a l l s t r u c t u r e s r e c o r d e d i n d i c a t e d d r y c o n d i t i o n s . 65% (1991) o f a l l s t r u c t u r e s showed r u s t o r water f l o w a t one time o r an o t h e r , but not e v i d e n t p r e -s e n t l y . 0.4% (12) o f a l l s t r u c t u r e s r e c o r d e d showed s i g n s o f water f l o w . These water f l o w i n g s t r u c t u r e s were r e s t r i c t e d t o major f a u l t s . a. 6% (169) o f a l l s t r u c t u r e s r e c o r d e d were l e s s t han 13 m i n l e n g t h . b. 89% (2732) o f a l l s t r u c t u r e s r e c o r d e d were 13 m t o 27 m i n l e n g t h ( F i g 129). c. 5% (156) o f a l l s t r u c t u r e s r e c o r d e d were more tha n 27 m i n l e n g t h . a. 2.3% (72) o f a l l j o i n t s e t s r e c o r d e d were o f a s p a c i n g o f 2 cm or l e s s . b. 94% (2880) o f a l l j o i n t s e t s r e c o r d e d were o f a s p a c i n g 2 cm t o 20 cm. c. 0.6% (19) o f a l l j o i n t s e t s r e c o r d e d were o f a s p a c i n g 20 cm - 61 cm. F r a c t u r e I n t e n s i t y and I n f i l l D e t a i l e d mapping a l o n g t h e South W a l l o f G r a n i t e Lake i n c l u d e d an assessment o f the roc k mass (Table 1-1). The f r a c -t u r e i n t e n s i t y was denoted as a r a t i n g from one t o f i v e , where one r e p r e s e n t e d a low f r a c t u r i n g ( s p a c i n g g r e a t e r than 1.8 m), and f i v e , a v e r y s t r o n g l y f r a c t u r e d f a c e ( s p a c i n g l e s s than 7 cm) . (7) (8) (10) (11) 60 NO. OF OBSERVATIONS: 169 SIZE 6-13 m NO. OF OBSERVATIONS: 2 7 3 2 SIZE 13—27 m NO. OF OBSERVATIONS: 156 SIZE >27m NO. OF OBSERVATIONS : 72 SPACING < 2cm NO. OF OBSERVATIONS: 19 SPACING 2 0 — 6 1 c m NO. OF OBSERVATIONS: 2880 SPACING 2 —20cm FIGUREI-29: FABRIC ANALYSIS (TOTAL STRUCTURES REVIEWED = 3064) F1GUREI29 The f r a c t u r e i n f i l l was r a t e d 'A' t h rough 'E', whereby 'A' i n d i c a t e d t h a t the f r a c t u r e s were h e l d v e r y l o o s e l y t o -g e t h e r (80 - 100% o f f r a c t u r e s are open), and 1E' e x h i b i t e d v e r y t i g h t l y h e l d f r a c t u r e s (0 - 20% o f f r a c t u r e s were open), ( F i g 1-30). The above e n a b l e d h a z a r d a r e a s t o be d e t e c t e d s i n c e a r a t i n g o f '5A' would denote a v e r y f r a c t u r e d f a c e , f r e e o f i n f i l l . The degree o f i n f i l l would enable an assessment o f a v a l u e o f c o h e s i o n t o be a p p l i e d . A f r a c t u r e and i n f i l l i n t e n s i t y map was employed (Figs 1-31 and 32) t o d e l i n e a t e h a z a r d a r e a s . Areas o f h i g h f r a c t u r e i n -t e n s i t y and low i n f i l l were found t o be c o n c e n t r a t e d on the w e s t e r n and e a s t e r n e x t r e m i t i e s o f the South W a l l , t h e s e co-i n c i d e w i t h the i n t e r s e c t i o n s o f the Sunset and G r a n i t e Creek s t r u c t u r e s . The f r a c t u r e i n t e n s i t y was r a t e d as h i g h below the 'E' bench (3815 f t ) , which was c o n f i n e d t o the G r a n i t e Creek zone. High amounts of i n f i l l were present within the top two benches, t h i s conforms t o Freeze [ 1 6 ] , whereby i t i s g e n e r a l -l y a c c e p t e d t h a t w e a t h e r i n g i s most predominant i n the f i r s t 15 m, r e s u l t i n g from s i l i c a b e i n g d i s s o l v e d and d e p o s i t e d w i t h i n f r a c t u r e s . A n a l y s i s o f Core A p l o t o f the p e r c e n t a g e of f a u l t e d and broken c o r e from diamond d r i l l h c l e s i s shown i n FigureI-33. The g e o l o g i s t s a t FRACTURE INTENSITY = 4 INF1LL= B FRACTURE INTENSITY = 5 INFILL= D FIGURE 30A : ASSESSMENT OF ROCK MASS — GRANITE LAKE 65 FIGUREK5I- FRACTURE MAP OF SOUTH WALL OF GRANITE LAKE FIGURED I SCALE 1 : 2 4 0 0 66 FIGUREI-32: INFILL MAP OF SOUTH WALL OF GRANITE LAKE FIGUREI-32 SCALE 1:24 00 G i b r a l t a r have, t h r o u g h t h e i r e x p e r i e n c e , r e c o g n i z e d t h a t a c o r e r e c o v e r y o f 70% or l e s s would p r o v i d e a h a l o e f f e c t around known f a u l t s . T h i s may be employed t o r e c o g n i z e f a u l t s t h a t o t h e r w i s e would not be d e t e c t e d . The c o n t o u r map r e p r e s e n t s the p e r c e n t a g e o f c o r e , showing a r e c o v e r y o f under 70% w i t h i n a d r i l l h o l e . The p l o t i n d i c a t e s t h a t the g r e a t e s t degree o f f r a c t u r i n g i s c o n f i n e d t o t h e w e s t e r n and e a s t e r n e x t r e m i t i e s o f the s o u t h w a l l . T h i s i s s i m i l a r t o the c o n c l u s i o n s d e r i v e d from the f r a c t u r e / i n f i l l a n a l y s i s . Figurel33 suggests t h a t t h e degree o f broken and f a u l t e d r o c k d i m i n i s h e s i n i n t e n s i t y toward the u l t i m a t e p i t l i m i t s . J o i n t Data J o i n t s e t s are the dominant s t r u c t u r e s which p r e v a i l / a l o n g the s o u t h w a l l , v a r y i n g i n i n t e n s i t y from a maximum i n s e t 'A' t o a minimum i n s e t 'H'. Lower hemisphere Schmidt p l o t s were employed t o determine the peak and range o f each j o i n t p o p u l a t i o n w i t h i n t h e i r r e s p e c t i v e domains (FigI-34). A t t i t u d e s o f the p r i n c i p a l s e t s are summarized i n TableI-4 w i t h the f o l l o w i n g c l a s s i f i c a t i o n system employed. (1) J o i n t Set A ( G r a n i t e Lake S t r u c t u r e ) T h i s i s t h e most p r e v a l e n t s t r u c t u r e a l o n g the s o u t h w a l l . The s e t s t r i k e s e a s t - w e s t (90 - 120° A z) and d i p s s h a l l o w l y towards the s o u t h (10 - 40°). The s t r u c t u r e i s most i n t e n s e below the 3815 (E) bench. F i g u r e I-35A i s a photograph o f s e t A. TABLEI4: ATTITUDE OF JOINT SETS 69 NOTE- % / N O = % C O N C E N T R A T I O N O F S T R U C T U R E S IN A 1% A R E A F O R T H E A V E R A G E P E A K ORIENTATION O F T H E POPULATION, N O = % X NO. O F OBSERVATIONS STRIKE=DIP D I R E C T I O N — 9 0 ° D O M A I N NO O F O B S I I A I I I B I V B V A V I A 2 4 3 3 3 7 V I I I A 4 3 8 S5 J O I N T S E T A S E T S T R I K E D I P % / N O 96 34 1 7 / 4 7 6 7 61 3 / 8 9 0 4 2 1 5 / 1 6 1 1 0 37 1 8 / 1 9 114 114 6 7 6 / 5 34 1 9 / 1 6 Al A2 A 3 A4 A5 A6 A7 A10 A l l 102 124 114 132 125 84 85 120 61 5 6 6 8 5 5 58 5 0 4 3 20 2 7 3 / 7 4/10 4 / 1 0 3 / 7 6 / 1 5 4 / 1 0 9 / 2 2 4 / 1 0 3 / 7 A 1 0 9 9 29 1 3 / 1 4 114 121 7 0 48 7 / 2 0 48 7 / 2 4 6 3 / 9 1 0 6 104 1 0 7 7 0 A 1 0 105 61 4 / 5 3 3 9 / 1 1 35 9 / 1 1 37 1 4 / 1 7 9 2 / 2 92 92 4 3 3 3 8 / 7 4 / 3 A l 9 5 4 7 1 1 / 1 8 A2 105 42 1 1 / 1 8 A3 120 4 5 1 1 / 1 8 A4 7 3 4 0 9 / 1 4 112 8 0 62 39 1 2 / 2 3 35 4 / 8 4 0 4 / 8 92 4 9 1 7 / 1 7 114 4 9 1 8 / 1 8 92 35 1 0 / 1 0 121 36 1 4 / 1 4 A 1 0 A l l 118 5 9 4 / 5 1 0 0 37 1 0 / 8 8 2 4 0 . 5 / 6 84 2 6 1 0 / 1 2 1 2 3 3 0 4 / 4 127 55 4 / 1 4 106 42 1 4 / 4 9 A I O A l l 140 10 7 / 8 158 18 6 / 7 55 51 70 4 7 81 44 94 34 6 5 6 0 104 18 3 / 1 3 3 / 1 3 4 / 1 8 5 / 2 2 3 / 1 3 6 / 2 6 98 6 6 "Sji 108 4 0 1 6 / 9 92 18 2 5 / 1 5 J O I N T S E T B S E T S T R I K E D I P % / N O B l 2 1 7 4 7 3 / 8 71 7 / 7 B l 2 0 9 84 7 / 6 B l 2 0 8 B2 2 1 7 B3 2 2 5 B4 2 0 6 6 9 2 / 5 6 3 3 / 7 6 5 2 / 5 4 6 B l 2 1 0 B2 2 0 4 8 3 8 / 2 7 6 5 7 / 2 4 B l 2 0 9 6 2 5 / 1 4 B 2 2 0 7 75 6 / 1 7 B3 2 0 4 86 4 / 1 1 B l 2 1 4 71 5 / 6 B l 2 0 4 5 6 9 / 8 B2 2 1 6 62 1 0 / 9 B3 2 2 6 6 3 4 / 3 B l . 2 1 7 7 3 6 / 1 0 B2 2 1 0 55 3 / 5 B3 1 9 9 53 3 / 5 B4 2 2 0 41 2 / 3 B I O 2 0 3 29 3 / 5 B l 214 81 3 / 6 B2 2 0 8 54 2 / 4 B3 2 0 6 43 2 / 4 B l 1 9 6 B2 2 2 0 5 3 7 / 7 5 3 7 / 7 B1-. 199 68 1 2 / 1 5 B2 2 0 6 B3 2 0 2 B4 2 1 6 6 9 1 3 / 1 6 4 0 4 / 5 111 4 4 B l 2 0 0 8 3 B 2 2 1 6 5 5 2 / 7 2 / 7 B l 2 1 9 8 / 9 B l 2 1 7 75 4 / 1 8 B2 2 0 6 6 9 4 / 1 8 B3 2 1 5 6 9 5 / 2 2 B4 198 75 2 / 9 J O I N T S E T C S E T S T R I K E D I P % / N O CI 1 3 9 4 9 8 / 2 2 CIO 155 24 6 / 1 7 153 52 9 / 1 0 164 36 5 / 5 CI 139 4 9 8 / 7 CIO 155 24 6 / 5 144 6 3 4 / 1 0 C I 165 88 2 / 6 CI 1 5 8 6 5 9 / 1 1 C I , 162 6 8 9 / 8 164 78 2 / 4 , 154 6 0 7 / 7 144 62 5 / 1 7 157 64 4 / 1 4 1 5 2 3 3 2 / 7 144 5 7 3 / 1 3 146 34 4 / 1 8 142 5 2 8 / 5 J O I N T S E T D ni D2 2 1 4 71 7 / 7 2 3 2 6 6 7 / 7 DI 2 4 0 78 2 / 6 DI 2 5 3 5 7 4 / 5 DI 2 4 8 72 6 / 5 2 4 3 5 9 4 / 6 DI 2 4 9 7 3 4 / 8 D2 2 3 8 6 5 4 / 8 D3 2 3 0 54 4 / 8 2 5 0 62 5 / 6 2 4 6 55 4 / S 2 4 6 6 8 6 / 7 2 3 6 62 8 / 9 2 3 0 6 9 7 / 8 2 4 0 4 2 2 / 2 2 4 8 44 4 / 1 8 " 2 3 6 61 57T 2 4 8 46 8 / S 1 J O I N T S E T E J O I N T S E T F J O I N T S E T G J O I N T S E T H S E T S T R I K E D I P % / N O S E T S T R I K E D I P % / N O S E T S T R I K E D I P % / N O S E T S T R I K E D I P % / N O E l 183 7 0 1 0 / 2 8 F I 3 6 0 75 4 / 1 1 G l 2 8 9 5 6 7 / 1 9 111 3 0 9 76 3 / 8 H2 3 2 7 S 7 3 / 8 E l 194 76 2 / 2 F I 32 7 7 4 / 4 G l 2 8 2 82 3 / 3 H I 3 1 2 56 2 / 2 E l 1 8 3 7 0 1 0 / 8 F I 3 6 0 75 4 / 3 G l 2 8 9 5 6 7 / 6 HI 3 0 9 76 3 / 2 112 3 2 7 5 7 3 / 2 E l 182 79 4 / 1 C ) F I 0 6 6 5 4 / 1 0 G l 2 8 2 3 5 4 / 1 0 HI 3 2 9 56 4 / 1 0 G2 2 7 2 31 4 / 1 0 G3 2 7 0 4 3 4 / 1 0 G4 2 7 6 4 6 3 / 7 G5 254 84 4 / 1 0 G6 2 4 4 9 0 3 / 7 G7 2 6 7 35 4 / 1 0 G8 2 S 9 7 5 3 / 7 E l 1 8 0 7 3 7 / 2 4 F I 2 5 7 7 4 / 1 3 HI 3 0 3 7 7 3 / 1 0 E2 1 7 2 44 5 / 1 7 F 1 0 0 8 25 2 / 7 E l 1 9 0 4 8 2 / 6 1 F i 04 78 2 / 6 G i 2 9 3 35 8/23 H i -J3T" ST" 2/6 E 2 1 6 8 6 5 2 / 6 G2 2 8 2 44 8 / 2 3 H2 3 2 0 7 0 3 / 9 E 3 185 7 9 2 / 6 G3 2 8 3 5 5 3 / 9 r.m ™<1 ? R • ; / i 4 E l 190 8 0 5 / 6 F I 4 9 62 4 / 5 G 1 0 3 0 0 26 2 / 2 E 2 174 64 8 / 1 0 F 2 4 0 5 3 4 / 5 E 3 1 8 0 5 8 7 / 9 F 3 12 5 2 2 / 2 E l 1 7 0 71 9 / 8 F 1 0 26 2 8 2 / 2 G l 2 5 9 74 6 / 5 HI 3 3 4 7 0 4 / 3 E 2 1 7 5 74 6 / 5 G 1 0 2 8 2 31 4 / 3 H2 3 2 5 76 4 / 3 E 3 1 8 2 62 5 / 4 H3 3 2 4 6 6 4 / 3 H4 3 0 8 6 0 4 / 3 115 3 1 8 4 8 4 / 3 1110 3 1 0 34 4 / 3 E l 165 5 6 6 / 1 0 F I 0 3 88 2 / 3 11 3 2 7 6 5 3 / 5 E2 186 33 4 / 6 F 2 36 58 2 / 3 E 3 191 6 8 3 / 5 F 3 12 4 7 2 / 3 E 1 0 1 7 0 26 4 / 6 F I 5 2 54 4 / 8 G l 2 5 7 7 7 3 / 6 11 3 2 0 6 6 5 / 9 F 2 15 74 3 / 6 G2 2 5 7 6 8 3 / 6 12 3 2 8 5 6 3 / 6 F 1 0 4 4 2 0 2 / 4 G 1 0 2 8 0 34 2 / 4 13 3 2 4 4 3 3 / 6 14 3 5 6 72 2 / 4 15 3 5 8 5 0 3 / 6 E l 1 7 7 6 8 2 / 2 F I 2 3 76 3 / 3 11 315 84 6 / 6 12 3 0 3 37 4 / 4 13 3 5 2 70 3 / 3 E l 1 7 7 6 8 2/2 F I 2 3 76 3 / 3 11 3 1 5 84 6 / 6 12 3 0 3 3 7 4 / 4 * 13 3 5 2 70 3 / 3 31 2 6 3 5 3 2/2 U 324 68 8 / 1 0 1 32 2 7 8 8 7 3 / 4 E l 1 8 9 6 7 2 / 7 F I 42 56 4 / 1 4 31 2 6 0 75 3 / 1 0 1 1 311 4 9 2 / 7 E 2 1 6 7 44 2 / 7 F 2 2 8 61 4 / 1 4 2 3 5 6 62 3 / 1 0 F 3 0 3 0 34 4 / 1 4 F I 1 8 5 2 2/2 ( u 2 7 4 7 5 5 / 6 1 1 3 2 0 64 2/2 F2 5 8 82 8 / 9 2 3 5 0 72 4 / 5 F 1 0 5 6 3 0 2/2 E l 1 9 3 62 2/9 FI I S 6 3 2 / 9 C 1 2 9 7 75 2/9 E2 178 4 8 2 / 9 F2 3 9 4 8 3 9 / 3 TABLEI-4 71 N ^ ^ ^ ^ ^ ^ N x . y N ^ ^ ^ ^ ^ i N ( O 1 NO. OF OBSERVATIONS: 106 1 B NO OF OBSERVATIONS: 243 NB NO.OF OBSERVATIONS : 285 III B NO OF OBSERVATIONS: 86 IV B N • b N N NO. OF OBSERVATIONS : 182 V B NO. OF OBSERVATIONS" 125 V1 B NO. OF OBSERVATIONS'• 114 VI 1 B NO. OF OBSERVATIONS*. 59 VIII B FIGUREI-34B: STRUCTURAL SETS WITHIN THEIR RESPECTIVE DOMAINS ABOVE 1163m BENCH (E) FIGUREP34B (2) J o i n t Set B T h i s s t r u c t u r e ranges i n s t r i k e from 200 t o 225° and d i p s s t e e p l y towards the no r t h w e s t . T h i s s e t , by i t s e l f , does not r e s u l t i n f a i l u r e , however, i n c o m b i n a t i o n w i t h s o u t h - e a s t e r l y (H) d i p p i n g s t r u c -t u r e s , p o t e n t i a l wedge f a i l u r e s r e s u l t (FigI\35A). (3) J o i n t Set C (Sunset S t r u c t u r e ) T h i s s t r u c t u r e s t r i k e s n o r t h w e s t - s o u t h e a s t (135 -155°) and d i p s 30 t o 50° towards the southwest. A subset w i t h i n s e t C e x i s t s whereby i t has a s i m i -l a r s t r i k e , however, d i p s s t e e p l y (50 - 70°) t o -wards the southwest (FigI-35B). The Sunset S t r u c -t u r e appears to be o f the g r e a t e s t i n t e n s i t y a l o n g the e x t r e m e t i e s o f the South W a l l . (4) J o i n t Set D T h i s i s a weaker developed s t r u c t u r e s t r i k i n g 230 -250° and d i p p i n g towards the northwest a t a st e e p i n c l i n a t i o n , 45 - 70°. T h i s s t r u c t u r e i n combina-t i o n w i t h e a s t e r n d i p p i n g s t r u c t u r e s forms wedges which are c r i t i c a l f o r s l o p e s t a b i l i t y a l o n g t h e south w a l l , (FigI-35B). (5) J o i n t Set E T h i s s t r u c t u r e ranges i n s t r i k e from 170 - 195° d i p p i n g s t e e p l y towards the west, 45 - 80°. These j o i n t s g e n e r a l l y run p a r a l l e l t o the major w e s t e r -l y d i p p i n g f a u l t s i n the a r e a . 74 F IGURE 35B MINOR S T R U C T U R E S A LONG THE SOUTH WALL JOINT SET G AND SET H REVERSE STRUCTURES FIGURE 35C : MINOR STRUCTURES ALONG THE SOUTH WALL J o i n t Set F T h i s j o i n t s e t ranges i n s t r i k e from 0 - 60° and d i p s towards the e a s t between 30 - 80°. T h i s s t r u c t u r e , even though o f a low c o n c e n t r a t i o n , d i p s i n an e a s t e r l y d i r e c t i o n which combines w i t h w e s t e r l y d i p p i n g j o i n t s t o form wedges which are c r i t i c a l f o r w a l l s t a b i l i t y . FigureI-35B shows Set F i n c o m b i n a t i o n w i t h s e t D t o form a wedge. J o i n t Set G (Reverse G r a n i t e Creek) T h i s s t r u c t u r e i s o f a low c o n c e n t r a t i o n . However, i t p r e v a i l s t h r o u g h o u t the South W a l l . The s t r u c -t u r e s t r i k e s 245 - 280° and d i p s towards t h e n o r t h between 30 - 50°. A subset o f s e t G e x i s t s w i t h s i m i l a r s t r i k e and d i p p i n g s t e e p l y towards the n o r t h (50 - 80°). T h i s s t r u c t u r e i s c o n j u g a t e i n d i p t o the G r a n i t e Creek and forms the c r i t i c a l d e s i g n s e t f o r most o f the So u t h Wall, s i n c e i t p a r a l l e l s the study a r e a d i p p i n g northwards i n t o the p i t a r e a . The s t r u c t u r e tends t o be s t r o n g e s t i n i n t e n s i t y below the 3815 (E) bench, (FigI-35C). J o i n t Set H (Reverse Sunset S t r u c t u r e ) T h i s i s the weakest developed s t r u c t u r e , s t r i k i n g 300 - 330° and d i p p i n g s t e e p l y towards the e a s t 5 0 - 8 0 . T h i s s t r u c t u r e i s c o n j u g a t e i n d i p t o the Sunset s t r u c t u r e , therefore contributing towards c r i t -i c a l wedge g e o m e t r i e s (FigI-35C). The c o n t i n u i t y o f the j o i n t s a re g e n e r a l l y r e -s t r i c t e d t o one double bench (27 m), w i t h s e t s 'A' and 'B' e x h i b i t i n g much l o n g e r l e n g t h s , ( F i g l - 2 9 ) . The G r a n i t e Creek and Sunset s t r u c t u r e s have been i d e n t i f i e d by Diamond D r i l l i n g t o e x i s t a t u l t i -mate dimensions. FigureJl8 indicates that v e r t i c a l con-t i n u i t y e x i s t s between s e t s . I t i s t h e r e f o r e sug-g e s t e d t h a t the s t r u c t u r e s which have been a n a l y z e d f o r Stage 1 o f G r a n i t e Lake may be employed f o r the d e s i g n o f Stage I I . FigureI-36 summarizes the s t r u c t u r a l s e t s r e l a t i v e t o the t r e n d o f the South W a l l . 79 CHAPTER1-5 DETERMINATION OF STRENGTH PARAMETERS Slope i n s t a b i l i t y a l o n g a d e f i n e d p l a n e r e q u i r e s the existence of the following two conditions: (a) ' The f a i l u r e s u r f a c e must d a y l i g h t , and (b) The f a i l u r e s u r f a c e must be i n c l i n e d s t e e p e r t h a n the f r i c t i o n angle of the material (FigI-37). (Assuming no Wab3~ Pressure). C o hesion i s a bond between two s u r f a c e s t h a t must be broken i n o r d e r f o r r e l a t i v e movement t o o c c u r . However, be-cause of the i n f l u e n c e o f g e o l o g i c s t r u c t u r e , t h i s was not p r e -s e n t a l o n g the South W a l l o f G r a n i t e Lake and t h e r e f o r e , was not c o n s i d e r e d (FigI-32). Compressive S t r e n g t h o f I n t a c t Rock Index t e s t s performed on the q u a r t z d i o r i t e i n d i c a t e d a r o c k hardness e x c e e d i n g 'R4-', which i s e q u i v a l e n t to about 80 MPa. T h i s v a l u e was q u a l i t a t i v e l y d e t e r m i n e d by r e c o r d i n g the number o f blows r e q u i r e d by a p i c k i n o r d e r t o f r a c t u r e the sample ( T a b l e l - l . 0) . T h i s v a l u e c o r r e l a t e s w e l l w i t h l a b o r a t o r y t e s t s conducted by The U n i v e r s i t y o f A l b e r t a [9] whereby u n c o n f i n e d compressive s t r e n g t h s ranged from 100 MPa t o 165 MPa f o r t h e s i x c o r e samples t e s t e d (TableI-5). A s t r e n g t h o f 100 MPa would suggest a v e r t i c a l w a l l 1200 m h i g h would be s t a b l e s i n c e the compressive s t r e n g t h o f the r o c k , due t o overburden l o a d i n g , would not be exceed-ed (overburden l o a d = 25 x v e r t i c a l (KPa) Depth (m)). T h i s FAILURE CRITERIA (DRY SLOPE) C A S E I B>0 DOES NOT DAYLIGHT S T A B L E C A S E 2 B^>0 D O E S DAYLIGHT U N S T A B L E CASE 3 S w < 0 DOES NOT DAYLIGHT S T A B L E DOES DAYLIGHT S T A B L E CRITERIA FOR SLIDING: FAILURE SURFACE (# w ) M U S T DDAYLIGHT AND 2) BE INCLINED S T E E P E R T H A N T H E FRICTION A N G L E (0 ) FIGUREI-37:CONDITIONS THAT MUST PREVAIL TO CAUSE INSTABIL ITY 81 however, i s not r e a l i s t i c s i n c e the p i t s l o p e i s a f r a c t u r e d medium where f a i l u r e i s c o n t r o l l e d by d i s c o n t i n u i t i e s r a t h e r t h a n by rock s t r e n g t h . T a ble 1-5.0  Unc o n f i n e d Compressive Test R e s u l t s ( A f t e r E i s e n s t e i n [9]) SAMPLE NO. ROCK TYPE LENGTH DIAMETER UNCONFINED (cm) (cm) COMPRESSIVE STRENGTH (MPa) 1 Quartz D i o r i t e 6 . 47 2 . 69 120 2 Quartz D i o r i t e 6 , .46 2 .  69 103 3 Quartz D i o r i t e 8 . 64 2 , . 69 138 4 Quartz D i o r i t e 6 . 43 2 , . 69 166 5 Quartz D i o r i t e 6 . , 96 2 . 69 127 6 Quartz D i o r i t e 10 . 14 2 . 69 120 F r i c t i o n Angle D i r e c t shear t e s t s were conducted on t e n q u a r t z d i -o r i t e samples by The U n i v e r s i t y o f A l b e r t a [ 9 ] . Peak and r e s i d u a l s t r e n g t h s were determined i n d i c a t i n g v a l u e s o f 39 and 27 degrees r e s p e c t i v e l y ( T a ble 1-6 and F i g 1-38). The samples were p r i m a r i l y c o n f i n e d t o j o i n t s e t 'A' from the Gib E a s t P i t , however, the ro c k type i s s t r u c t u r a l l y s i m i l a r t o t h a t o f G r a n i t e Lake and t h e r e f o r e was employed i n t h e s t a b i l i t y assessment o f the st u d y a r e a . FIGUREB9 : FRICTION ANGLE VS. DEPTH TABLEf-6 SUMMARY OF SHEAR STRENGTH RESULTS SAMPLE JOINTSET PEAK STRENGTH (kg/cm ) GB1 GB2 GB3 GB4 GB5 GB6 GB7 GB8 GB9 GB10 GRN.CRK GRN.CRK GRN.CRK GRN.CRK GRN.CRK GRN.CRK GRN.CRK REVERSE GRN.CRK GRN.CRK GRN.CRK P P 0.757o +0.86 1.282a +0.24 0.975a + 0.51 0.538a(- 0.08) 0.840a +0.33 0.825a + 0.33 0.766a +0.59 0.948a + 0.42 1 . 180a + 0.11 0.478a + 0.70 RESIDUAL STRENGTH (kg/cm 2) PEAK 0 RESIDUAL 0 0 .416a(- 0.11) 0.513a(- 0.09) 0.762a(- 0.16) 0.440a + 0.96 0.573a(- 0.13) 0 . 627a(- 0.21) 0.537a(- 0.02) 0.302a + 0.03 0.465a(- 0.05) 0.370a + 0.09 37 . 1 52 . 0 44 . 3 28 . 2 40 .0 39 . 5 37 . 5 43 . 4 O 49 . 6 o 25 . 6 22 . 6 27 . 2 37 . 3 23 . 9 29 . 8 32 . 1 28 ,2 16 . 8 24 . 9 20 . 3 MEAN 39 . 7 26 . 2 oo 84 The peak f r i c t i o n a n g l e was found t o i n c r e a s e w i t h depth as was e x p e c t e d , due t o a d e c r ease i n the w e a t h e r i n g [ 1 8 ] , ( F i g 1-39) . Back A n a l y s i s A t o t a l o f e l e v e n wedge and p l a n a r f a i l u r e s were ana-l y z e d on t h e s o u th w a l l o f G r a n i t e Lake t o determine a f i e l d v a l u e f o r the peak f r i c t i o n a n g l e . The f a i l u r e s were c o n f i n e d t o a s i n g l e bench and were p r e d o m i n a n t l y of a wedge geometry. The a n a l y s i s approach i s o u t l i n e d i n Appendix 1 w i t h the f o l l o w i n g assumptions employed: (1) A f a c t o r o f s a f e t y o f 1.0 e x i s t e d a t f a i l u r e -c o n v e n t i o n a l e q u i l i b r i u m a n a l y s i s . (2) C ohesion = 0 (3) Slope was d r y - the assumption i s v a l i d s i n c e f a i l u r e s were c o n f i n e d t o a s i n g l e bench where the f a c e s would be d r a i n e d ( r e f e r t o groundwater s e c t i o n ) . The a n a l y s i s i n d i c a t e d t h a t the f r i c t i o n a n g l e ranged from 24.6 t o 51.3 degrees e x h i b i t i n g a mean of 39.1 - 10 de-grees (Tablep7 and FigI-40). A v a l u e o f 27 degrees was employed f o r d e s i g n purposes as i n d i c a t e d by l a b o r a t o r y and back a n a l y s i s r e s u l t s . T h i s v a l u e i s c o n s e r v a t i v e c o n s i d e r i n g t h a t most o f t h e f a i l u r e s a n a l y z e d i n d i c a t e d h i g h e r f r i c t i o n a n g l e s , however, under p r e s e n t b l a s t i n g c o n d i t i o n s a lower f r i c t i o n a n g l e was deemed n e c e s s a r y by the a u t h o r . ( R e f e r : C o n t r o l B l a s t i n g ) . 85 TABLE 1-7 BACK ANALYSIS RESULTS FAILURE MODE ORIENTATION PLANE A ORIENTATION PLANE B FRICTION ANGLE WEDGE 095/45SW 030/52NW * 25. 6° WEDGE 055/50NW 323/59SW 36 . 6° WEDGE 180/41W 98/45SW 49 1° WEDGE 340/42SW 62/46SE * 24 6° WEDGE 310/40NE 20/64NW 37 4° WEDGE 292/40NE 210/51NW 33 7° WEDGE 05/48SE 308/73NE 35 5° WEDGE 253/71NW 356/75NE 51 .0° WEDGE 331/64NE 242/65NW 51 .3° WEDGE 310/64NE 200/82NW 51 .3° PLANAR 312/34NE 34 .0° P o s s i b l e f a i l u r e due t o b l a s t i n g 4 in tn or .<3 UJ o z UJ o. OC 3 o o o 2-^ u. o >-o z UJ o UJ or u. I J Io 2 0 2 5 30 "35 4 0 45~ FRICTION A N G L E (DEGREES) FIGURE 140! BACK ANALYSIS OF-FAILURE5 ALONG THE SOUTH WALL OF GRANITE LK. Co cn CHAPTERI-6 GROUNDWATER INVESTIGATION T h i s c h a p t e r i s d i v i d e d i n t o two s e c t i o n s : I H y d r o l o g i c I n v e s t i g a t i o n o f the South W a l l o f G r a n i t e Lake, and I I The Assessment o f the B e n e f i t s and P r a c t i c a l i t y o f Employing Vacuum H o r i z o n t a l D r a i n s . Refer to S t a b i l i t y Design of Granite Lake with the Ap-p l i c a t i o n o f Vacuum Drainage' Volume I I . I H y d r o l o g i c I n v e s t i g a t i o n T h i s s e c t i o n summarizes a d e - w a t e r i n g s t u d y [8] t h a t was conducted by G i b r a l t a r Mines L t d (1974). In a d d i t i o n , a f i n i t e element a n a l y s i s was un d e r t a k e n by the au t h o r whereby f l o w regimes were determined f o r t he South W a l l . Annual p r e c i p i t a t i o n a t the mine s i t e i s a p p r o x i m a t e l y 500 mm, o f which 165 mm f a l l s as snow ( F i g l " 4 l ) . The de-w a t e r i n g s t u d y c o n c l u d e d t h a t : (1) mass p e r m e a b i l i t y was c o n t r o l l e d by the s o u t h -w e s t e r l y d i p p i n g s t r u c t u r e s ( S u n s e t ) , (2) p e r i p h e r a l w e l l s c o u l d be employed t o de-water p i t a r e a s , (3) r e g i o n a l groundwater f l o w was from n o r t h e a s t t o southwest, and (4) g o u g e - f i l l e d f a u l t s a c t as impermeable b a r r i e r s t o t he r e g i o n a l f l o w . 88 12.5 -, REFERENCE: MEAN GIBRALTAR MINE MAX. 1972-1974 MIN . F1GURE14I • PRECIPITATION RECORD 89 The r o c k mass h y d r a u l i c parameters a r e h i g h l y v a r i a b l e and r e f l e c t t h e v a r i a t i o n i n t h e degree o f f r a c t u r i n g , o x i d -a t i o n and a l t e r a t i o n w i t h i n t h e v a r i o u s d e p o s i t s . Pump — 6 t e s t s i n d i c a t e d mass p e r m e a b i l i t i e s r a n g i n g between 10 and — 8 — 5 10 m/sec, t r a n s m i s s i b i l i t i e s between 3.2 x 10 t o 7.9 x -4 10 m/s, and the s t o r a g e f a c t o r , 0 t o .014. F i n i t e element s t u d i e s were conducted on the South W a l l o f G r a n i t e Lake. A n o r t h - s o u t h s e c t i o n was c o n s t r u c t e d i n the v i c i n i t y o f W e l l S i t e #1 (FigI-42). The s t u d y s e c t i o n was d i s c r e t i z e d i n t o f i n i t e elements as shown by F i g u r e l - 4 3 . The employment of 1981 s t a t i c water l e v e l s , o b t a i n e d from W e l l #1 and t h a t o f G r a n i t e Lake e n a b l e d a f l o w regime t o be g e n e r a t -ed (FigI-44). I t i s i n t e r e s t i n g t o note t h a t t h e G r a n i t e Lake sump was a t 1116 m, however, the computer a n a l y s i s i n -d i c a t e d t h a t a seepage f a c e e x i s t e d below the 1149 m bench ( F ) . T h i s c o r r e l a t e s w e l l w i t h f i e l d o b s e r v a t i o n s ( F i g I - 5 ) , whereby f l o w i n g water was r e c o r d e d on the lower benches (G t o I ) . F i g u r e T 4 5 shows the r e s u l t a n t f l o w p a t t e r n t h a t e x i s t s upon employing h o r i z o n t a l d r a i n s . The l e n g t h o f the d r a i n i s 49 m which i s e q u i v a l e n t t o o n e - h a l f th e p i t h e i g h t which i s a suggested l e n g t h by C.0. Brawner [ 1 2 ] . The b e n e f i t o f t h i s form o f d r a i n a g e a r i s e s from d e p r e s s i n g t h e water t a b l e w e l l beyond the i n f l u e n c e o f bench s c a l e f a i l u r e s . I t was d e t ermined i n the d e s i g n c h a p t e r t h a t bench f a i l u r e s are c r i t i c a l t o the s t a b i l i t y o f t h e s t u d y a r e a . A comparison between the e f f e c t s o f employing w e l l d e - w a t e r i n g and h o r i -z o n t a l d r a i n s i s shown i n FigureI-46. A water l e v e l drawdown I2l9m_ WELL I 1204m. 1177m 149m. rWATER LEVEL 1974 rWATER LEVEL 1981 _ l204m(B) 1177m (D) —PIT BOTTOM 1974 _ 1163 m (E) _U49m(F ) _M22m(H) ^ |||6m I 198 m FIGURE 1431 SOUTH WALL OF GRANITE LAKE (1980— FINITE ELEMENT MESH FIGURE I-44FLQW PATTERN OF STUDY AREA (1981) (AFTER FINITE ELEMENT STUDIES) 1108m r» 49 m H •J-SLOPE HEIGHT FIGUREI45 FIQW PATTERN OF STUDY A R F A — HORIZONTAL DRAIN 93 .WELL I , - l204m(B) 177m (D) H49m(F) H22m(H) 1116m -HOSmdl FIGUREI46 : COMPARISON OF DEPRESSURIZATION METHODS WELL I I2l9m_ I204m_ irTTm 204m (B) Il77m-PIT BOTTOM 1974 1122m ( H) 1163m = WATER L E V E L 1981 • Il08m(l) 198m FIGUREI47 'COMPARISON OF UNDE WATER ED CONDITIONS 1974 8» 1981 o f 28 m, by deep w e l l d e - w a t e r i n g , i s r e q u i r e d i n o r d e r t o d e - p r e s s u r i z e s l o p e s i n the v i c i n i t y o f the 1149 m bench ( F ) , however, the 1122 m bench (H), would s t i l l remain s a t u r a t e d . T h e r e f o r e , t o ensure d e - p r e s s u r i z a t i o n , w e l l d e - w a t e r i n g would r e q u i r e t h a t the water l e v e l be lowered below the p i t bottom. H o r i z o n t a l d r a i n s , however, r e s u l t i n t o t a l de-p r e s s u r i z a t i o n a t the l e v e l o f the d r a i n . Water l e v e l f o r 1974 and 1981 e n a b l e d f l o w p r o f i l e s t o be g e n e r a t e d ( F i g l - 4 7 ) . The f o l l o w i n g was c o n c l u d e d : (1) t h e p h r e a t i c s u r f a c e was lowered by 28 m as a r e -s u l t o f 69 m o f v e r t i c a l e x c a v a t i o n o f the G r a n i t e Lake p i t , (2) employing the p r e v i o u s o b s e r v a t i o n , the water l e v e l would be lowered an a d d i t i o n a l 22 m as the p i t i s e x c a v a t e d t o u l t i m a t e l i m i t s (1053 m l e v e l ) . CHAPTERI-7 DESIGN The p r e v i o u s c h a p t e r s e n a b l e d a r o c k model t o be d e v e l o p -ed which would s u b s e q u e n t l y be employed t o g e n e r a t e a s l o p e s t a b i l i t y d e s i g n . T y p i c a l i n s t a b i l i t y modes have been o u t -l i n e d i n FigureI-8, however, th e s t u d y a r e a was found t o be prone t o wedge, p l a n a r and a c o m b i n a t i o n t h e r e o f , r e s u l t i n g i n a r a v e l l e d s l o p e . Major f a i l u r e s encompassing t h r e e or more benches were a n a l y z e d under d i f f e r e n t d e s i g n c r i t e r i a t h an t h a t o f bench s c a l e f a i l u r e s . A d e s i g n was based on m i n i n g t h e South W a l l under c o n t r o l l e d c o n d i t i o n s , w i t h ade-quate a c c e s s a v a i l a b l e f o r the removal o f f a i l u r e s caught on berms, (Appendix I I ) . The parameters which govern s l o p e geometry (Figl'48) are d i c t a t e d by t h e r o c k model, o p e r a t i o n a l and government r e -s t r i c t i o n s . The subsequent a n a l y s i s r e q u i r e s t h a t the apparent plunge o f a f a i l u r e mode d i p s t e e p e r t h a n 27 degrees and f l a t t e r t h a n 60 degrees. The lower bound on the above r e s t r i c t i o n i s due t o the r e s i d u a l f r i c t i o n a n g l e and the upper i s a l i m i t p l a c e d on the o v e r a l l s l o p e a n g l e due t o o p e r a t i o n a l and government r e g u l a t i o n r e q u i r e m e n t s . S t a b i l i t y A n a l y s i s Domain b o u n d a r i e s , d e t e r m i n e d i n Chapterl-4, were e x t r a -p o l a t e d t o u l t i m a t e l i m i t s as shown i n Figurel-4-9. The South F1GUREI-48: SLOPE GEOMETRY RELATIONSHIPS 97 FI6UREI-49: EXTRAPOLATION OF DOMAIN BOUNDARIES TO ULTIMATE LIMITS FIGUREI49 - — S C A L E 1=2400 W a l l was f u r t h e r d e l i n e a t e d i n t o s e c t o r s h a v i n g s i m i l a r w a l l o r i e n t a t i o n s (FigI-49). T h e r e f o r e , each s e c t o r was c h a r a c t e r -i z e d by s i m i l a r s t r u c t u r a l i n f o r m a t i o n as w e l l as a s i m i l a r w a l l t r e n d . The p r o j e c t i o n o f major s t r u c t u r e s r e s u l t e d i n the d e l i n e a t i o n o f s e c t o r s w i t h m i n i m a l a r e a s and i t i s f o r t h i s r e a s o n t h a t they were i n c o r p o r a t e d i n t o a d j a c e n t l a r g e r s e c t o r s . Major F a i l u r e s The a n a l y s i s o f the e i g h t major f a u l t s and t h e i n t e r -a c t i o n t h e r e o f was performed and i t was c o n c l u d e d t h a t major f a i l u r e s encompassing t h r e e o r more benches are not geometrically possible (FigI-50). TableI-8-sunrnarizes the above and o u t l i n e s a r e a s o f p o t e n t i a l i n s t a b i l i t y . Toe s u p p o r t i s s u p p l i e d by domain 'A' and as a r e s u l t , major f a i l u r e s a re v e r y u n l i k e l y . A ro c k b r i d g e o f l e s s than 3% ( 2 m ) i s r e q u i r e d i n o r d e r t o p r e v e n t f a i l u r e i n domain 'B', ( Refer - Rock B r i d g e ) . A major f a i l u r e was obser v e d i n the v i c i n i t y o f F a u l t 1 by the ev i d e n c e o f massive t e n s i o n c r a c k s and l a r g e v e r t i c a l d i s -placements. T h i s f a i l u r e , (domain I B ) , was p r e d i c t e d by the above a n a l y s i s , however, i t does not d a y l i g h t a t the p r e s e n t o v e r a l l w a l l a n g l e (4-8 d e g r e e s ) . I n v e s t i g a t i o n o f K i n e m a t i c a l l y P o s s i b l e F a i l u r e Modes FigureI-51 o u t l i n e s the c r i t e r i a [10] r e q u i r e d f o r i n -s t a b i l i t y w i t h i n a ro c k s l o p e . R o t a t i o n a l f a i l u r e i s t h e FIGUREl-50: MAJOR STRUCTURES BELOW 1163m BENCH (DOMAIN A) AND MAJOR STRUCTURES ABOVE 1163m BENCH (DOMAIN B) TABLE 1-8 STABILITY ANALYSIS OF MAJOR FAILURES DOMAIN STRUCTURE 1 STRUCTURE 2 WEDGE INTERSECTION - K i n e m a t i c - COMMENTS S t r i k e Dip S t r i k e Dip Azimuth Plunge Apparent Plunge A No P o s s i b l e F a i l u r e Mode T o p p l i n g by F X 6 i n S e c t o r VIIA3 B FU 197 69 I F l l . 5 189 78 354 44 44° f a i l u r e n o t p o s s i b l e F.S. g r e a t e r t h a n 2 i i 159 78 J>Xl. 5 189 78 352 78 84 Affects IB Involves minimal volime F^3 305 33 33 33° Affects IV B Minimal area affected Does not e x i s t below Level ' E' 101 Great circle representing/ e lope face a. C i r c u l a r f a i l u r e i n o v e r b u r d e n s o i l , w a s t e r o c k o r h e a v i l y f r a c t u r e d r o c k w i t h no i d e n t i f i a b l e s t r u c t u r a l p a t t e r n . crest of slope crest of si Great c i r c l e representing _ e lope face Direction of sliding Great circle representing b. P l a n e f a i l u r e i n r o c k w i t h h i g h l y Plane corresponding to centre o r d e r e d s t r u c t u r e s u c h as s l a t e . of pole concentration crest of slope Great c i r c l e representing slope face :— Direction of s l i d i n g . Great c i r c l e s representing ,, , , ., ^ . . ... planes corresponding to c. Wedqe f a i l u r e on two i n t e r s e c t i n g r K. ... .. . . . centres of pole concentrations a i s c o n t i n u i t i e s . r crest of slope Great c i r c l e representing slope face • Great c i r c l e representing planes corresponding to centre of pole concentration. d. T o p p l i n g f a i l u r e i n h a r d r o c k w h i c h can f o r m c o l u m n a r s t r u c t u r e s e p a r a t e d by s t e e p l y d i p p i n g d i s c o n t i n u i t i e s . FlgUREI6l:$TERgO-PL0TS DENOTING FAILURE T Y P E ^ ^ M 102 o n l y f a i l u r e geometry which can be d e l e t e d from the i n v e s t i g a -t i o n s i n c e a random s c a t t e r i n g o f s t r u c t u r a l i n f o r m a t i o n does not o c c u r w i t h i n the st u d y a r e a (FigI-34-). R a v e l l i n g f a i l u r e s are p r e s e n t a l o n g t h e South W a l l r e s e m b l i n g r o t a t i o n a l modes which are the r e s u l t o f p l a n a r and wedge f a i l u r e s . A f a c t o r o f s a f e t y o f 1.2 f o r a c o m p l e t e l y s a t u r a t e d , 500m (55°) w a l l s l o p e was c a l c u l a t e d assuming t h a t r o t a t i o n a l f a i l u r e [10] was p o s s i b l e . T h i s was based on the f o l l o w i n g : (1) S t r e n g t h o f i n t a c t r o c k = 120 MPa (2) Rock q u a l i t y d e s i g n a t i o n = 60% (3) J o i n t s p a c i n g = 2 0 - 6 0 cm (4) Groundwater c o n d i t i o n = Moderate f l o w The a n a l y t i c a l approach i s o u t l i n e d by Hoek [ 1 9 ] . I n v e s t i g a t i o n o f P l a n a r and Wedge F a i l u r e s The peak o r i e n t a t i o n s f o r each i n d i v i d u a l domain (Ta b l e l - 4 ) , were p l o t t e d on s t e r e o n e t s (FigI-52). K i n e m a t i c f a i l u r e modes were determined based on the f o l l o w i n g c r i t e r i a : (1) Apparent plunge o f p o t e n t i a l f a i l u r e i s g r e a t e r than 27 degrees, and (2) P o t e n t i a l f a i l u r e d i p s i n t o p i t a r e a . The s c a t t e r o f s t r u c t u r a l p o p u l a t i o n s are r e p r e s e n t e d by i n d i v i d u a l sub-groups (FigI-53) which i n c o r p o r a t e a range o f j o i n t o r i e n t a t i o n s . A c o n v e n t i o n a l e q u i l i b r i u m a n a l y s i s was employed on t h e above k i n e m a t i c a l l y p o s s i b l e f a i l u r e modes (Ap-pe n d i x I ) . T h i s a n a l y s i s employed t h e f o l l o w i n g as i n p u t p a r a -meters : (1) C o h e s i o n = 0 KPa (2) F r i c t i o n Angle = 27 degrees 275 OBSERVATIONS F1GUREI52:RANGE OF STRUCTURAL POPULATIONS TO BE INVESTIGATED —SECTOR IA 104 C , F / ^ - M ^ R.L5 2 7 ° FRICTION ANGLE DI N CIO F l | El FL 1.5^ N E2 | El FIO DOMAIN IA DOMAIN 11A D O M A I N III A DOMAIN I V A DOMAIN V A D O M A I N V I A D O M A I N VII A DOMAIN VII IA FIGUREI-53A: ANALYSIS OF POTENTIAL FAILURES BELOW THE 1135m BENCH FIGUREJ53A 105 N { FLI.5 2 7 ° Fl FRICTION A N G L E 6 0 ° W A L L I S L O P E N Fl E3 DOMAIN I B DOMAIN 11 B DOMAIN 1MB DOMAIN I V B DOMAIN V B D O M A I N VI B D O M A I N VI IB DOMAIN VIIIB FIGUREI-53 B ANALYSIS OF POTENTIAL FAILURES ABOVE THE 1135 m BENCH FIGURE 1-53 B A f a c t o r o f s a f e t y g r e a t e r than 2.0 would i n d i c a t e s t a -b i l i t y under c o m p l e t e l y s a t u r a t e d c o n d i t i o n s . A f a c t o r o f s a f e t y g r e a t e r t h a n 1.2 i n d i c a t e d s t a b l e c o n d i t i o n s under d r y con-d i t i o n s (Appendix I ) . An example o f the above a n a l y s i s i s shown by FigureI-5<4, whereby k i n e m a t i c a l l y p o s s i b l e f a i l u r e modes were r e c o r d e d f o r s e c t o r IA. E q u i l i b r i u m a n a l y s e s were conducted on the l a t t e r i n o r d e r t o determine a f a c t o r o f s a f e t y (TableI-9). S t a t i s t i c a l A n a l y s i s Due t o t h e v a r i a b i l i t y i n the f r e q u e n c y o f the o c c u r r e n c e o f s t r u c t u r a l s e t s , a s t a t i s t i c a l a n a l y s i s was employed. The d e s i g n w i l l be based on a l l o w i n g f o r 10% i n s t a b i l i t y which w i l be caught on catchment berms, d e s i g n p r o b a b i l i t i e s f o r v a r i o u s p i t s i n w e s t e r n Canada and the U n i t e d S t a t e s a re i n d i c a t e d be-low : P r o b a b i l i t y o f F a i l u r e L o c a t i o n 10% C a s s i a r P i t , Columbia [20] B r i t i s h 15% Mt. Tolman P i t , Washington [21] 20% I s l a n d Copper P i t , B r i t i s h Columbia [1] The a n a l y s i s t h a t was performed i s as f o l l o w s : (1) A w e i g h t i n g was a s s e s s e d (TableI-10) each s t r u c -t u r a l s e t : W e i g h t i n g = % Peak Value X Number o f S t r u c t u r e s Recorded W i t h i n S e c t o r 107 N F1GUREP54: GREAT CIRCLES REPRESTING STRUCTURAL SETS -SECTOR I A TABLEI-9 EQUILIBRIUM ANALYSIS EMPLOYING HOEK'S CHARTS ( S e c t o r IA) WEDGE DIP DIP A DIP DIP DIREC PLANE A PLANE B A 1 Cl & Gl 44 44 0" 240 2 Gl & BI 44 47 3 270 3 DI & E l 52 78 26 239 4 Gl & E l 44 78 34 270 5 BI & E l 47 78 31 217 6 HI & BI 47 57 10 217 7 Gl & DI 44 52 8 270 8 HI & B2 57 76 19 349 9 F l & A2 58 61 3 25 10 A2 & F2 61 78 17 67 11 H10 & A2 30 61 31 325 12 H10 & D2 30 80 50 325 13 Gl & F2 44 78 34 270 14 H10 & F2 30 78 48 325 15 H10 & Gl 30 44 14 325 16 Gl & F l 44 58 14 270 17 F l & F2 58 78 20 25 18 H10 & B2 30 76 46 325 19 DI & B2 52 76 24 239 20 DI & F l 52 58 6 239 21 H10 & F l 30 58 28 325 22 H10 & DI 30 52 22 325 23 DI & HI 52 57 5 239 24 B2 & B3 76 90 14 220 25 Gl & B3 44 90 46 270 26 DI & B3 52 90 38 239 27 HI & B3 57 90 33 349 28 F 1 & Gl 44 70 26 270 29 F 1.5 & DI 52 78 26 239 30 F 1.5 & B2 76 78 2 220 31 F 1.5 & Gl 44 78 34 270 32 F 1.5 & HI 57 78 21 349 DIP DIREC. A DIP A B F.S. B DIREC. 360 120 1.25 1.25 1.3 217 53 0.67 0.63 0.67 187 52 1.00 0.30 0.66 187 83 1.00 0.15 0.59 187 30 2.18 1.30 1.77 349 132 1.50 1.20 1.37 239 31 1.50 0.65 1.61 220 129 1.10 0.80 0.97 67 42 0.34 0.34 0.35 48 19 2.70 2.00 2.39 67 258 3.50 1.58 2.33 248 77 1.78 0.12 0.97 48 222 2.00 1.15 1.60 48 277 1.75 0.05 0.92 270 55 1.55 0.20 0.89 25 245 1.25 0.90 1.10 48 23 2.40 1.60 2.04 220 105 1.80 0.35 1.10 220 19 2.90 2.00 2.50 25 214 1.90 1.70 1.80 25 300 1.90 0.28 1.10 239 86 1.60 0.40 1.00 349 119 1.05 1.90 0.99 199 21 1.45 1.20 1.35 199 71 1.30 0.25 0.79 199 40 1.45 0.95 1.22 199 150 1.80 1.25 1.55 153 117 1.20 0.60 0.90 20 219 1.50 1.10 1.30 20 200 2.30 2.30 2.30 20 250 1.10 0.40 0.80 20 329 1.60 1.00 1.30 A l l k i n e m a t i c wedges h a v i n g a f a c t o r o f safety-l e s s t h a n 2.0 were a s s e s s e d a w e i g h t i n g e q u i v a -l e n t t o the sum o f each i n d i v i d u a l s t r u c t u r a l s e t ( T a b l e l - l l ) . Wedges h a v i n g an apparent plunge l e s s t h a n ' i? w' ( T a b le 11) were summed i n o r d e r t o o b t a i n a cumu-l a t i v e f r e q u e n c y p l o t v e r s u s plunge a n g l e (FigI-55). The r e s u l t a n t c u r v e r e p r e s e n t e d the u n d r a i n e d s i t -u a t i o n . A s i m i l a r a n a l y t i c a l approach was p e r f o r m -ed f o r a de-watered s l o p e where wedges h a v i n g a f a c -t o r o f s a f e t y l e s s than 1.2 were r e c o r d e d (TableI-12) APPARENT PLUNGE OF KINEMATIC ALLY POSSIBLE WEDGES ( degrees FIGUREI-55: FREQUENCY PLOT OF OCCURRENCE OF WEDGES PLUNGING FLATTER THAN Bw TABLE MO STATISTICAL ANALYSIS SECTOR T A - 275 obs S t r u c t u r a l Set Peak P e r c e n t W e i g h t i n g A l 18% 50 (275 x .18) A2 3 8 B l 3 8 B2 7 19 B3 6 17 CI 7 19 DI 4 11 D2 2 6 E l 4 11 FI 2 6 F2 4 11 Gl 3 8 HI 2 6 H10 2 6 F l l 4 F i l l . 5 4 112 TABLE M l CUMULATIVE PERCENT OF FAILURES PLUNGING FLATTER THAN B o i UN-DEWATERED CASE S e c t o r IA APPARENT PLUNGE Bui (Degrees) CUMULATIVE NUMBER OF WEDGES PLUNGING SHALLOWER THAN Boi STRUCTURAL SETS F.S. < 2.0 TOTAL PERCENT (%) (6) (8) 27 14 3 (14/528 ) HI & BI 30 115 22 B2 & HLO, B2 & DI Fl & DI, Fl & HLO, DI & HLO 32 134 25 BI & El 36 149 28 FiL.5 & DI 37 172 33 B3 & HI 38 222 42 F2 & GL, F2 & HLO HLO & GL 40 253 48 Fl & Gl, DI & HI 41 293 55 D2 & HLO, B3 & DI 42 305 58 FJ!l.5 & Gl 43 330 63 B3 & GL 44 338 64 Gl 45 363 69 HL & B2 46 382 72 Gl & El 49 408 77 BI & Gl, Fj>1.5 & HL 50 425 80 FL & F2 51 447 85 DI & El 52 473 90 D2 & Fl, F l l & Gl 54 492 93 GL & DI 60 528 100 B3 & B2 TABLE 1-12 CUMULATIVE PERCENT OF FAILURES PLUNGING FLATTER THAN B to DEWATERED CASE S e c t o r IA APPARENT PLUNGE Bto (Degrees) CUMULATIVE NUMBER OF WEDGES PLUNGING SHALLOWER THAN Bto STRUCTURAL SETS F.S. < 1.2 TOTAL CUMULATIVE PERCENT (%) ( 1 9 ) ( 6 ) ( 6 ) ( 6 ) 30 37 7 (37/528) B2 & H10, FI & H10 38 68 13 F2 & H10, H10 & Gl 40 99 19 FI & Gl, DI & HI 41 139 26 D2 & H10, B3 & DI 42 151 29 Fi.1.5 & Gl 43 176 33 B3 & Gl 44 184 35 Gl 45 209 40 HI & B2 46 228 43 Gl & E l 49 244 46 Bl & Gl 51 266 50 DI & E l 52 294 56 A2 & FI, Fh- & Gl 114 A n a l y s i s o f J o i n t Length and Rock B r i d g e I t was determined t h a t the r e v e r s e G r a n i t e Creek i s the most c r i t i c a l s t r u c t u r a l s e t t o e x i s t a l o n g the South W a l l . I t has a j o i n t l e n g t h l e s s than 27 m. The s t a t i s t i c a l d i s -t r i b u t i o n o f j o i n t l e n g t h s t e n d t o f o l l o w a n e g a t i v e expun-e n t i a l c u r v e [22] o f the form: Y% = 1 0 0 e ~ a x where a = 1 Y% = c u m u l a t i v e p e r c e n t f r e q u e n c y x x = j o i n t l e n g t h x = mean v a l u e o f t r a c e l e n g t h F i g u r e 156 shows the p r o b a b i l i t y o f a c h i e v i n g a t r a c e l e n g t h f o r a p a r t i c u l a r mean j o i n t l e n g t h . Employing a mean t r a c e l e n g t h o f 27 m would suggest a 3% p r o b a b i l i t y o f a-c h i e v i n g a 100 m l o n g j o i n t . I t a l s o s u g g e s t s t h a t a 200 m l o n g j o i n t , which would a f f e c t t h e e n t i r e p i t w a l l , would have a minimal p r o b a b i l i t y o f o c c u r r e n c e . Figuret-57 suggests t h a t l e s s than 3% ro c k b r i d g e i s r e q u i r e d i n o r d e r t o p r e v e n t s l i d i n g a l o n g p a r a l l e l j o i n t s . The a n a l y t i c a l approach i s o u t l i n e d i n FigureI-58 whereby the degree o f roc k b r i d g e r e q u i r e d t o a c h i e v e a f a c t o r o f s a f e t y o f 1.2 was c a l c u l a t e d . The South W a l l o f G r a n i t e Lake would r e q u i r e 6 m ( 3 % o f 200 m) o f roc k b r i d g e i n o r d e r t o p r e v e n t s t e p p l a n a r f a i l u r e . The r e v e r s e G r a n i t e Creek i s composed o f a p p r o x i m a t e l y 40 s t r u c t u r e s (FigT42) per 500 m l o n g bench o r a r o c k b r i d g e e q u i v a l e n t t o 13 m. Assuming a c o n s e r v a t i v e j o i n t l e n g t h o f 27 m one would have s u f f i c i e n t r o c k b r i d g e t o ensure s t a b i l i t y a g a i n s t s t e p f a i l u r e . IOOH X - MEAN TRACE LENGTH (m ) FIGUREI-56: PROBABILITY OF JOINT LENGTH BEING EXCEEDED 11 6 3 1 0 50 I00 I50 200 SLOPE HEIGHT (m) FIGUREI-57-' REQUIRED ROCK BRIDGE VERSUS SLOPE HEIGHT TO ACHIEVE A F.S.= I.2 117 F.S. = R-L(Cm+<3-n-Tan0m)4-(l-R)-L(Cj-h^n Ton^j) T WHERE: R= % ROCK BRIDGE = LENGTH INTACT ROCK ALONG FAILURE PLANE| LENGTH OF FAILURE PLANE L= LENGTH OF FAILURE PLANE Cm = COHESIVE STRENGTH OF INTACT ROCK = 0.16 X U.C.S. T221 = 19 KPa <fn= NORMAL STRESS ON INCLINED PLANE ^rn= INTERNAL ANGLE OF FRICTION FOR QUARTZ DIORITE = 4 0 ° • o : Cj = COHESION ALONG JOINT SURFACE = 0 KPa fa FRICTION ANGLE ALONG JOINT = 2 7 ° T= DRIVING FORCE ALONG INCLINED PLANE FIGUREI58:EVALUATI0N OF ROCK BRIDGE C221 INTERPRETATION The f r e q u e n c y p l o t (FigI-55) r e l a t e s the p r o b a b i l i t y o f f a i l u r e t o the apparent plunge o f the f a i l u r e s u r f a c e . The apparent plunge i s the a n g l e f l a t t e r t han which the s l o p e f a c e must d i p , i n o r d e r f o r the f a i l u r e s u r f a c e not t o day-l i g h t (FigI-37). T a b l e 1-13 l i s t s the o v e r a l l s l o p e a n g l e f o r each i n d i v i d u a l s e c t o r t h a t i s r e q u i r e d i n o r d e r t o not un-d e r c u t 10 and 20 p e r c e n t o f a l l p o t e n t i a l f a i l u r e s ( p l a n a r and wedge). F a i l u r e a l o n g the South W a l l i s r e s t r i c t e d t o b e n c h - s i z e i n s t a b i l i t y and as a consequence, berms of ade-quate w i d t h dimensions must be d e s i g n e d t o be a b l e t o r e t a i n a l l f a i l e d m a t e r i a l . Slope a n g l e s under d r a i n e d c o n d i t i o n s were a l s o determined, i n d i c a t i n g an i n c r e a s e i n o v e r a l l a n g l e o f 0 t o 19degrees (TableI-13). Bench Design Berm w i d t h s were d e s i g n e d t o c o n t a i n l o c a l f a i l u r e s . [Appendix I I ] . Design c h a r t s (FigI-59) were dev e l o p e d , r e -l a t i n g t h e r e q u i r e d berm w i d t h t o the c o n t a i n e d f a i l u r e v o l -ume f o r a range o f apparent p l u n g e s . Employing a 10% proba-b i l i t y o f f a i l u r e , s e v e r a l s e c t o r s e x i s t whereby p o t e n t i a l wedges plunge f l a t t e r t h a n the a n g l e o f repose o f t h e s l o p e (TableI-13). F a i l u r e s are r e s t r i c t e d t o bench s i z e and, as a r e s u l t , s l o p e s w i l l u l t i m a t e l y r a v e l t o the a n g l e o f r e -pose o f the broken m a t e r i a l . A bench break-back a n g l e o f 67 degrees was c o n s i s t e n t l y o b s e r v e d w i t h i n the s t u d y a r e a . 1 1 9 TABLE 1-15 ULTIMATE WALL DESIGN SECTOR WALL SLOPE DICTATED BY KINEMATICS FAILURE MODE 10% P r o b a b i l i t y 20% P r o b a b i l i t y IA 28 (30°) 30 (35°); HI & BI, B2 & H10 DI & H10, B2 & DI, F l & DI, F l & H10 II A 37 (53°) 37 (53°) H2 & E l I I I A 43 (43°) 43 (43°) E2 & HI IVA 28 (28°) 35 (35°) BI & G10, F3 & DI VA 1 33 (37°) 34 (38°) B3 & HI, F3 & DI VA 2 30 (56°) 38 (57°) DI & F3, F l & B2 VIA 37 (37°) 38 (48°) H2 F l & H2 VIIA 34 (46°) 40 (47°) B2 & H2 V I I I A 41 (41°) 43 (44°) DI & C2 IB 48 (48°) 48 (48°) HI & E l , F 1.5 & HI II B 31 (32°) 33 (34°) HI & B4, E l & G2, HI & G2, F l & B2, G2 F 1.5 & G2, F 2B & Gl, E l & C l , E l & HI, F l & G7, G7 & B2, BI & Gl I I I B 32 (33°) 34 (35°) Gl & C l , Gl & E l , Cl & HI, F 3 & BI, Cl & E3, E l & H2, H2 & C l , Gl & BI, Gl & F l , F 3 & DI IVB 32 (32°) 34 (34°) F 3 & DI, G10 & B3, F 3 & B3, H10 & DI, H10 & B3, H10 & Gl, F 3 VB 33 (38°) 38 (41°) D2 & G10, H5 & D3, H5 & BI, H5 & G10, F2 & D3, F2 & G10, F2 & BI, BI & G10 VIB 33 (33°) 41 (43°) B3 & HI, B4 & HI VIIB 39 (41°) 43 (48°) D5 & H2, E l & DI, D5 & HI, F 7 & D5 V I I I B 30 (30°) 31 (31°) Cl & Gl B r a c k e t e d f i g u r e s - d r a i n e d s i t u a t i o n 120 F I G U R E 59A: V A R I A T I O N O F C R O S S S E C T I O N A L W I T H DIP O F F A I L U R E P L A N E FIGURE 59 B : VARIATION O F B E R M W I D T H R E O U I R E D T O C A T C H F A L E D F I G U R E 59C: G E O M E T R I C R E L A T I O N S H I P O F O V E R A L L S L O P E A N G L E , B E R M W I D T H F O R F A I L U R E S I N V O L V I N G A S I N G L E 27m HIGH B E N C H ( H ) M A T E R I A L W I T H D I P ' O F F A I L U R E P L A N E F O R F A J L U R * A N D B E N C H F A C E F O R A 27m HIGH B E N C H I N V O L V J N G A S I N G L E 27m H I G H B C N C H FIGURET59?!INTERRELATIONSHIP OF SLOPE GEOMETRY AND FAILURE GEOMETRY-27m BENCH FIGUREI-59 A F T E R PITEAU C20U 121 FigureI-60 and T a b l e M 4 summarize the recommended s t a b i l -i t y d e s i g n f o r the South W a l l o f G r a n i t e Lake, based on the f o l l o w i n g c r i t e r i a : (a) bench h e i g h t = 27.4 m (b) bench f a c e a n g l e = 67 degrees (c) minimum o v e r a l l s l o p e a n g l e = 38 degrees (d) p r o b a b i l i t y o f f a i l u r e = 10 p e r c e n t (e) minimum bench w i d t h = 9 m (B.C. Government R e g u l a t i o n ) . TABLE 1-14 RECOMMENDED ULTIMATE WALL DESIGN RECOMMENDED RECOMMENDED BENCH FACE BENCH REMARKS DOMAIN OVERALL BENCH ANGLE HEIGHT DOMINANT MODES SLOPE WIDTH (M) (M) IA 38 (38) 23 (23) 67 27 .4 Wedge f a i l u r e j o i n t s . S e t s B & H, B & D, F & D, D & H. II A 38 (53) 23 (9) 67 27 .4 Wedge f a i l u r e H & E. I I I A 43 (43) 18 (18) 67 27.4 Wedge f a i l u r e E & H. IVA 38 (38) 23 (23) 67 27 .4 Wedge f a i l u r e B & G. VA1 38 (38) 23 (23) 67 27 .4 Wedge f a i l u r e D & F, F & B. VA2 38 (56) 23 (8) 67 27 .4 Wedge f a i l u r e D & F, F & B. VIA 38 (38) 23 (23) 67 27 .4 P l a n a r H g, Wedge F & H. VI I A 38 (46) 23 (15) 67 27 .4 Wedge B & H. V I I I A 41 (41) 20 (20) 67 27 .4 Wedge D & C. IB 48 (48) 13 (13) 67 27 .4 Wedge H & E, F£1.5 & H. I I B 38 (38) 23 (23) 67 27 .4 Wedge f a i l u r e H & B , E & G , H & G , F & B, G P l a n a r , Fj[l . 5 & G. I I I B 38 (38) 23 ( 23 ) 67 27 . 4 Wedge G & C , G & E , G & H , FJ?3 & B. IVB 38 (38) 23 (23) 67 27 .4 Wedge FJ03 & D, G & B. VB 38 (38) 23 (23) 67 27 .4 Wedge D & G. VIB 38 (38) 23 (23) 67 27 .4 Wedge B & H. (...) Represents Dewatered SLope 123 FIGUREi"-6Q-RECOMMENDED ULTIMATE SLOPE DESIGN —SOUTH WALL OF GRANITE LAKE FIGUREl-60 S C A L E 1 = 2 4 0 0 CHAPTER 1-8 124 SUMMARY The f o l l o w i n g i s a b r i e f summary of the r e s u l t s o f the i n v e s t i g a t i o n conducted on the South W a l l o f G r a n i t e Lake. Geology Quartz d i o r i t e i s t h e main r o c k type t h a t e x i s t s a l o n g the South W a l l o f G r a n i t e Lake. The ore body i s a p o r p h y r y type w i t h m i n e r a l i z a t i o n c o n f i n e d t o two major o r e - c o n t r o l l i n g s t r u c t u r e s ; the Sunset and G r a n i t e Creek. The Sunset zone s t r i k e s n o r t h w e s t - s o u t h e a s t and d i p s a p p r o x i m a t e l y 35°SW. The G r a n i t e Creek zone s t r i k e s e a s t - w e s t and d i p s s h a l l o w l y towards the s o u t h . S t r u c t u r e A n a l y s i s The a u t h o r r e c o r d e d a t o t a l o f 3064 s t r u c t u r e s , which were p r e d o m i n a n t l y j o i n t s h a v i n g a t r a c e l e n g t h ' under 27 m. Major s t r u c t u r e s w i t h i n the s t u d y a r e a were g e n e r a l l y s t e e p l y d i p -p i n g and d i d not a t t r i b u t e ' t o deep-seated w a l l f a i l u r e . The South W a l l was d i v i d e d i n t o s i x t e e n domains, each h a v i n g unique s t r u c t u r a l p r o p e r t i e s . The domain b o u n d a r i e s con-s i s t e d o f f a u l t s and a major ore-waste c o n t a c t a t t h e 3815 f t l e v e l . A t o t a l o f e i g h t major j o i n t p o p u l a t i o n s were de-125 l i n e a t e d , whereby the Sunset and G r a n i t e Creek were found t o be o f the g r e a t e s t c o n c e n t r a t i o n . These s t r u c t u r e s p l u n g -ed a t a p p r o x i m a t e l y 30° towards the south and, c o n s e q u e n t l y d i d n o t c o n t r i b u t e t o i n s t a b i l i t y . Conjugate s t r u c t u r e s t o the above e x i s t , which are o f a l i m i t e d c o n c e n t r a t i o n , d i p -p i n g towards the n o r t h . D e s ign o f the South W a l l was con-t r o l l e d by the r e v e r s e Sunset and G r a n i t e Creek s t r u c t u r e s . C o n t r o l B l a s t i n g The v a l u e o f 0 , the f r i c t i o n a n g l e , ranges from 27° t o a h i g h of 41°. P r i o r t o movement o c c u r r i n g a l o n g the d i s -c o n t i n u i t i e s , the u n d u l a t i o n s and a s p e r i t i e s on the s u r f a c e s a c t t o i n c r e a s e the shear s t r e n g t h o f the ro c k mass. Hydro-s t a t i c and b l a s t i n g f o r c e s t e n d t o reduce the f a c t o r o f s a f e -t y , [ 2 ] , r e s u l t i n g i n movement and the s h e a r i n g o f a s p e r i t -i e s . T h i s c o n s e q u e n t l y reduces t h e shear s t r e n g t h o f the roc k mass. Attempts s h o u l d be made t o l i m i t b l a s t v i b r a -t i o n s t o the f i n a l w a l l by l i m i t i n g t he k i l o g r a m s o f e x p l o -s i v e per d e l a y and i n c r e a s i n g the d e l a y between rows. T h i s s e c t i o n i s a g e n e r a l d i s c u s s i o n o f t h e immediate problems t h a t e x i s t i n the p r e s e n t b l a s t i n g p r a c t i c e s con-d u c t e d a t the G i b r a l t a r Mine. Smooth w a l l b l a s t i n g i s con-d u c t e d a t the s i t e , whereby 2700 kg o f e x p l o s i v e s per d e l a y are d e t o n a t e d 18 m from the f a c e . T h i s v a l u e would r e s u l t i n a peak p a r t i c a l v e l o c i t y e x c e e d i n g 250 cm/sec (100 i n / s e c ) a t t he p i t f a c e (FigI-61). C.O. Brawner [23] s u g g e s t s a v a l u e o f 100 cm/sec (4-0 i n / s e c ) , 6 m (20 f t ) b e h i n d the f a c e , 126 FIGUREI-6I:- PLOT OF PARTICLE VELOCITIES INDUCFD AT GIVEN DISTANCES FOR PARTICULAR CHARGE WEIGHTS (AFTER BRAWNER)I"2~] 127 s h o u l d be the d e s i g n peak p a r t i c a l v e l o c i t y i n o r d e r t o l i m i t r o c k breakage. A c c o r d i n g t o the above c r i t e r i a , t h e k i l o g r a m s per d e l a y s h o u l d be l i m i t e d t o 500. An i n c r e a s e d time i n t e r v a l between d e l a y s i s suggested. A v a l u e o f 10.9 t o 21.8 m i l l i s e c o n d s per meter o f burden i s recommended as a d e l a y i n t e r v a l between c o n s e c u t i v e rows, (Tansey [ 2 4 ] ) . A t y p i c a l p a t t e r n a t G r a n i t e Lake i s 5.5 x 7.9 m (18 x 26 f t ) , which would suggest a d e l a y between 60 t o 119 m i l l i s e c o n d s , p r e s e n t l y 25 m i l l i s e c o n d d e l a y s are em-p l o y e d a t G i b r a l t a r Mines. The above c r i t e r i a i s based on h a v i n g s u f f i c i e n t time f o r t h e f r o n t row t o move f o r w a r d b e f o r e the f i r i n g o f the n e x t c o n s e c u t i v e row. T h i s would reduce the e f f e c t s o f choke b l a s t i n g [ 2 5 ] , and t h e r e -f o r e , m i n i m i z e shock t o t h e f i n a l w a l l . Strength Parameters Ten d i r e c t shear t e s t s were performed on q u a r t z d i o r i t e samples by t h e U n i v e r s i t y o f A l b e r t a (1974). A f r i c t i o n a n g l e r a n g i n g between 27 and 41 degrees was found t o e x i s t a l o n g j o i n t s u r f a c e s . B a c k - a n a l y s i s o f e l e v e n f a i l u r e s a-l o n g the South W a l l o f G r a n i t e Lake i n d i c a t e d a f r i c t i o n angle o f 39°±10°. The degree o f i n f i l l p r e s e n t w i t h i n the s t u d y a r e a was r e c o r d e d and g e n e r a l l y found t o be non-e x i s t e n t , c o n s e q u e n t l y , c o h e s i o n was a s s e s s e d a v a l u e o f 0 KPa. The c ompressive s t r e n g t h o f t h e i n t a c t r o c k was d e t e r -mined t h r o u g h l a b o r a t o r y t e s t i n g ( U n i v e r s i t y o f A l b e r t a , 1974) t o range from 100 MPa t o 165 MPa. Groundwater The s t u d y a r e a has a mass p e r m e a b i l i t y r a n g i n g between g g 10 and 10 m/sec. The p h r e a t i c s u r f a c e i s w i t h i n 42 m o f the s u r f a c e d i s c h a r g i n g on the 1149 m (3770 f t ) bench. I n -s t a b i l i t y a l o n g t h e South W a l l i s c o n f i n e d t o bench f a i l u r e s , and as a consequence, d e p r e s s u r i z a t i o n w i t h i n t h e v i c i n i t y o f the immediate s l o p e i s r e q u i r e d . T h i s would be a c h i e v e d t h r o u g h the use o f h o r i z o n t a l d r a i n s . D e s i g n I t was c o n c l u d e d from the s t u d y t h a t i n s t a b i l i t y a l o n g the South W a l l i s r e s t r i c t e d t o b e n c h - s i z e f a i l u r e s (wedge and p l a n a r ) . C o n s e q u e n t l y , berms were d e s i g n e d o f s u f f i -c i e n t w i d t h t o be a b l e t o r e t a i n t h e f a i l e d m a t e r i a l . A p r o b a b i l i t y f a c t o r o f s a f e t y a n a l y s i s was employed, whereby the f r e q u e n c y o f i n s t a b i l i t y was q u a n t i t a t i v e l y a s s e s s e d . T h i s e n a b l e d a d e s i g n t o be d e v e l o p e d whereby 90 p e r c e n t o f a l l k i n e m a t i c a l l y p o s s i b l e f a i l u r e modes would be s t a b l e . The r e v e r s e G r a n i t e Creek and Sunset s t r u c t u r e s were found t o c o n t r o l the s t a b i l i t y o f the South W a l l . Employing a 10 p e r c e n t p r o b a b i l i t y o f f a i l u r e , s e v e r a l s e c t o r s e x i s t where-by p o t e n t i a l wedges plunge f l a t t e r t h a n the a n g l e o f repose. F a i l u r e s are c o n f i n e d t o b e n c h - s i z e and c o n s e q u e n t l y , t h e South W a l l w i l l u l t i m a t e l y r a v e l t o the a n g l e o f repose o f t h e broken m a t e r i a l . I t i s f o r t h i s r e a s o n t h a t the South W a l l o f G r a n i t e Lake was g e n e r a l l y d e s i g n e d a t 38°. P r e s e n t -l y (1981), t h e South W a l l o f G r a n i t e Lake has an o v e r a l l w a l l a n g l e between 45 and 50 degrees. T h i s s l o p e can be c o n s i d e r e d t o be a t e s t w a l l s i n c e r a v e l l i n g p r e s e n t l y en-compasses much o f the p i t ( F i g E 5 ) . 130 CHAPTER!9 RECOMMENDATIONS The f o l l o w i n g a r e recommendations t h a t have e v o l v e d from t h e s t a b i l i t y i n v e s t i g a t i o n o f the South W a l l o f G r a n i t e Lake. (1) Slope a n g l e s d e t e r m i n e d i n ChapterI-7 be employed and up-dated as more s t r u c t u r a l and h y d r o l o g i c a l i n f o r m a t i o n becomes a v a i l a b l e . (2) H o r i z o n t a l d r a i n s be i n s t a l l e d w i t h i n the s t u d y a r e a t o enable l o c a l d e p r e s s u r i z a t i o n . They s h o u l d be i n s t a l l e d a t the base o f the p i t w i t h l e n g t h s of t h e o r d e r o f 60 m. The a c t u a l s p a c i n g s h a l l be determined-by p r a c t i c e , however, i n i t i a l l y t h e y s h o u l d be l i m i t e d t o 10 m i n water b e a r i n g zones. (3) B l a s t i n g s t u d i e s be un d e r t a k e n i n o r d e r t o develop a b l a s t i n g p r a c t i c e which w i l l l i m i t damage t o the f i n a l w a l l . (4) Slope movement m o n i t o r i n g program be employed which w i l l warn a g a i n s t impending f a i l u r e s . (5) The i n p u t d a t a t o t h e above d e s i g n be c o n t i n u a l l y up-dated t h r o u g h s i m i l a r a n a l y t i c a l t e c h n i q u e s as employed i n t h i s s t u d y . (6) Any f u t u r e c o r e l o g g i n g s h o u l d r e c o r d : (a) RQD (b) r e c o v e r y (c) f r a c t u r e a n g l e t o v e r t i c a l i f diamond d r i l l h o l e i s a p p r o x i m a t e l y v e r t i c a l (d) i n f i l l t y p e and degree (e) p o i n t l o a d t e s t s ( f ) s t r u c t u r a l d a t a s h o u l d be o r i e n t e d i f an angl e h o l e i s employed [ 2 6 ] . APPENDIX I FACTOR OF SAFETY DETERMINATION AFTER HOEK [10] Wedge s tab i l i t y charts for f r i c t i o n only If the cohesive strength of the planes A and B is zero and the slope is fu l ly drained, equation 77 reduces to F = A .Tan* A + B.Tan<t>g (96) The dimensionless factors A and B are found to depend upon the dips and dip directions of the two planes and values of these two factors have been computed for a range of wedge geometries and the results are presented as a series of charts on the following pages. In order to i l lus t ra te the use of these charts, consider the following example : dipO d i p di rectiono f r i c t ion ang1e° Plane A ko 165 35 Plane B 70 285 20 D i fferences 30 120 Hence, turning to the charts headed "Dip difference 30°" and reading off the values of A and B for a difference in dip direction of 120°, one finds that A - 1.5 and B = 0.7 Substitution in equation 96 gives the factor of safety as F » 1.30. The values of A and B give a direct indication of the contribution which each of the planes makes to the total factor of safety. Note that the factor of safety calculated from equation 96 is independent of the slope height, the angle of the slope face and the incl inat ion of the upper slope surface. This rather surprising result arises because the weight of t h e wedge occurs in both the numerator and denominator of the factor of safety equation and, for the f r i c t i o n only case, this term cancels out, leaving a dimensionless rat io which defines the factor of safety (see equation 89 on page 202). This s impl i f icat ion is very useful in that it enables t h e user of these charts to carry out a very quick check on t h e stab i l i ty of a slope on the basis of the dips and dip directions of the discontinuities in the rock mass into which the slope has been cut. A-example of such an analysis Is presented later in this chapter. Many t r i a l calculations have shown that a wedge having a factor of safety in excess of 2.0, as obtained from the f r i c t i o n only st a b i l i t y charts, is unlikely.to f a i l under even the most severe combination of conditions to which the slope is likely to be subjected. Consider the example discussed on pages 207 to 209 in which the factor of safety for the worst conditions (zero cohesion and maximum water pressure) is 0.62. This Is 50% of the factor of safety of 1.2l» for the fr i c t i o n only case. Hence, had the factor of safety for the f r i c t i o n only case been 2.0, the factor of safety for the worst conditions would have been 1.0, assuming that the ratio of the factors of safety for the two cases remains constant. On the basis of such t r i a l calculations, the authors suggest that the f r i c t i o n only s t a b i l i t y charts can be used to define those slopes which are adequately stable and which can be ignored In subsequent analyses. Such slopes, having a factor of safety in excess of 2.0, pass into category 3 in the chart presented in Figure 6 on page 1**. Slopes with a factor of safety, based upon f r i c t i o n only, of less than 2.0 must be regarded as potentially unstable and pass into category k of Figure 6, i.e. these slopes require further detailed examination.. In many practical problems involving the design of the overall slopes of an open pit mine or the cuttings for a highway, it will be found that these f r i c t i o n only st a b i l i t y charts provide a l l the Information which is required. It is frequently possible, having identified a potentially dangerous slope, to eliminate the problem by a slight re-alignment of the pit benches or of the road cutting. Such a solution is clearly only feasible i f the potential danger is recognised before excavation of the slope Is started and the main use of the charts is during the site investigation and preliminary planning stage of a slope project. Once a slope has been excavated, these charts will be of limited use since it will be f a i r l y obvious i f the slope is unstable. Under these conditions, a more detailed study of the slope will be required and use would then have to be made of the method described on pages 203 to 208 or of one of the methods described in Appendix I. In the authors' experience, relatively few slopes require this detailed analysis and the reader should beware of wasting time on such an analysis when the simpler methods presented in this chapter would be adequate. A f u l l s t a b i l i t y analysis may look very impressive in a report but, unless It has enabled the slope engineer to take positive remedial measures, it may have served no useful purpose. WEDGE STABILITY CHARTS FOR FRICTION ONLY Plane B Note : The f lat ter of the two planes is always called plane A. Factor of Safety F = A.Tan<f>A + B.Tam)>B A/B CHART - DIP DIFFERENCE 0 DEGREES DIFFERENCE IN DIP DIRECTION - DECREES 135 A CHART - DIP D IFFERENCE 30 DECREES 2 ° < 6 6 8 86 100 120 140 160 180 360 340 320 300 280 260 240 220 200 DIFFERENCE IN DIP DIRECTION - DEGREES B CHART - DIP D I F F E R E N C E 30 DEGREES < 2.0 1.0 0.5 360 340 320 300 280 260 240 220 200 D I F F E R E N C E IN DIP DIRECTION - DEGREES APPENDIX I I BERM WIDTH DESIGN AFTER PITEAU [20] Surface mining DO NOT COPY LEAVES 137-hO. Select berm width to contain local failures Dennli C. Martin and Dougl»» R. Plteau, D. R. Piteau Associates Ltd STABILITY ANALYSES for open pit slope design must consider the possibility of the failure of individual benches as well as the failure of the overall slope. In many cases, the probability of overall slope failure along major faults or weak zones may prove to be small, while the design of individual benches against excessive failure may be the controlling factor for design of the overall slope. Small failures can cause major disruptions to pit operations and can limit accessibility. A graphical method for design of individual benches to control small failures is described here. Considerations for basic slope design In rock slopes, instability occurs as a result of failure along structural discontinuities, such as bedding planes, joints, geological contacts, and faults. Instability seldom occurs in homogeneous material unless the rock is weathered or soft. The most important single factor in stability analyses and design of rock slopes is the determination and evaluation of the orientation, geometry, and spatial distribution of discontinuities in the slopes. This process should be followed by evaluation of possible alternative angles of the proposed pit slopes relative to the orienta-tion of the discontinuities. Slope control may be accomplished by designing the slope so that no failure can occur or by excavating the pit under controlled conditions, with the slope designed for adequate access, while minor failures are caught on berms and removed as needed. The first solution is usually too conservative to be economical. The second solution requires a thorough consideration of slope geometry. Parameters that govern the geometry of a slope are bench height H, berm width /, and bench face angle /}. (See Fig. 1.) Normally, these parameters are determined by the strength and nature of the material of the slope", the size and type of equipment to be used, and mining regulations. Bench height should provide a safe working slope. For a given slope, higher benches permit wider berms. In general, berms should be designed wide enough to entrap falling debris and provide access for cleanup. Inclined bench faces reduce the likelihood of high stresses near bench crests and minimize tension cracks and overhangs. Problems of rockfall are thus reduced, and the safety of the slope is increased. Slope and failure geometry are related The volume of material in a bench failure is inversely proportional to either the dip of a plane failure or the plunge of a wedge failure. The volume varies with bench height. The shallower the dip or plunge of a failure, the greater the volume of material involved. Calculation of E/MJ-June 1977 Benchei at this mine in British Columbia were designed to contain the wedge failures predicted by stability analysis. 1 the cross-sectional area of a potential bench failure provides an estimate of the volume of failed material per unit width of berm. For plane failures, the slumped material on the berm is assumed to form a uniform debris slope with a triangular cross section. Slumped material from a wedge failure is assumed to form an approximately conical debris slope. This slope extends outward across the berm along the projection of the line of intersection. It is assumed that the maximum extent of slumped material from a wedge failure will occur along the projection of the line of intersection and will have a triangular cross section —similar to that of a plane failure —of unit width along the line of intersection. Therefore, calculation of the cross-sectional area of a wedge failure along the line of intersection provides an estimate of the maximum volume of material, per unit width, that could slump onto the berm. The vertical cross-sectional area A of a failure taken parallel to the direction of dip of the failure plane—or parallel to the line of intersection of a wedge failure—is calculated in Fig. 2 using the formula: 139 Fig. 3-Interrelationship of slope geometry and failure geometry, 45-ft benches (38° natural angle of repose of debris) _, ABatter luce 1 ».7(J\~ ibor J^ote Defoliations m baud «* jEfl^  - yvtwn Star amount of laDmf mttidiina » «oo>i . t - to lit 'di. 4Wi P » n # t t J •3r *tjpt"irf repose, tht f r f i * ^ ' * * * formuli -wis u » d ' 30 60 90 Dip or plunge of lailure 0to in degrees (A) Variation of cross-sectional area with dip or plunge of a failure involving a single 45-foot-high bench. 0 30 60 90 Dip or plunge of failure 0 U in degrees (B) Variation of minimum berm width required to catch failed material with dip or plunge of the lailure. 20 30 40 50 60 Overall slope angle 6 in degrees (C) Geometric relationship of overall slope angle, berm width, and batter face angle. where H = bench height, 0 = bench face angle, and 0U - the dip or plunge of the failure. Cross-sectional area of a potential bench failure is used to calculate the minimum berm width /,„, required to catch all failed material (Fig. 2). It is assumed that the failed material comes to rest at its natural angle of repose r, usually 35° to 40*. The formula used for calculation of the minimum berm width, from trigono-metric relationships, is: 4-2A sin r cos r + (sin r)' 2) tan (/3U - r ) Rg. 4-lnterrelationship of slope geometry and failure geometry, 90-ft benches (38° natural angle of repose of debris) 7.000 6,000 k n i a f t r W a ^ 5.000f-4.0001-3,00Cr S 2.000r-i.oooR 30 60 90 Dip or plunge of failure 0u in degrees (A) Variation of cross-sectional area with dip or plunge of a failure involving a single 90-foot-high bench. 0 30 60 90 Dip or plunge of failure fu in degrees IB) Variation of minimum berm width required to catch failed material with dip or plunge ol the failure. 20 30 40 SO 60 70 Overall slope angle B in degrees (0 Geometric relationship of overall slope angle, berm width, and batter face angle. 140 Fig. 5—Probability of wedge spillover for various slope angles 1 50 40 30 at I M B i i 20 10 >i»*0 ft, Xfry »tbp««; noT - M o w M r t u n ; ; ! ^ - ? , . i frRjoenfly e h t n d if tfebrwr - to Imu ttiam ifftctWt u ? 9v A f i l l ' - J t - i fcJ-'V- I, LisJ 20 30 40 50 60 70 Overall slope angle in degrees 80 In cases where the a m o u n t o f f a i l ed m a t e r i a l is geome t r i ca l l y too la rge to be c o m p l e t e l y caugh t on the b e r m (for a pa r t i cu la r b e n c h h e i g h t ) , i t is a s s u m e d that the s l u m p angle is less than r. T h e r e q u i r e d b e r m w i d t h is then ca lcu la ted on the a s s u m p t i o n that a s imp le t r i ang le o f s l umped m a t e r i a l ex tends f r o m the crest o f the bench . In this case , the m i n i m u m b e r m w id th is ca l cu la ted as: / =2± 3 ) T h e b u l k i n g (swel l ) fac to r — a n inc rease in the v o l u m e o f ma te r i a l du r i ng fa i l u re — i s not c o n s i d e r e d . B u l k i n g is a comp lex factor re la ted to rock t ype , f r a c t u r e in tens i ty , and the mechan i sm of rock f a i l u r e . B u l k i n g c a n increase v o l u m e by as m u c h as 5 0 % . F o r c o n d i t i o n s where E q . 2 app l ies (e.g., steeply d i p p i n g f a i l u r e s ) , the m i n i m u m b e r m w id th is increased o n l y by the s q u a r e root o f the b u l k i n g fac tor . O n the o the r h a n d , w h e r e E q . 3 app l ies (e.g. , for sha l low fa i l u res ) , the r e l a t i o n s h i p is d i rec t l y p ropo r t i ona l , and the requ i r ed m i n i m u m b e r m w i d t h can be 1.5 t imes the m i n i m u m b e r m w i d t h d e t e r m i n e d by that equa t ion . D e p e n d i n g on the t ype a n d s ize o f f a i l u re , b u l k i n g m a y be an impo r t an t f ac to r to be i nco rpo ra ted in to the ca lcu la t ions . T h e f a c t o r c a n be d e t e r m i n e d expe r imen ta l l y by c o m p a r i n g un i t we igh t s o f in -s i tu a n d o f fa i led rock ma te r i a l . M i n i m u m b e r m w i d t h is used to c a l c u l a t e the ove ra l l s lope ang le for the p a r t i c u l a r b e n c h he igh t and bench face ang le that are assumed in the a n a l y s i s . Acknow ledgemen t : T h e t e c h n i q u e desc r i bed here w a s deve loped in c o n j u n c t i o n w i t h pi t s lope s tab i l i t y analyses a n d des ign w o r k at the mines o f C y p r u s A n v i l M i n i n g C o r p . a n d C a s s i a r A s b e s t o s C o r p . T h e authors w i s h to t h a n k pe rsonne l o f the two mines for thei r ass i s tance . Graphs of bench and failure geometry F o r a p a r t i c u l a r b e n c h he igh t , the i n t e r r e l a t i o n s h i p of c ross-sec t iona l a rea A, m i n i m u m b e r m w i d t h / ,« , , a n d overa l l s lope ang le 8 c a n be presented on th ree g r a p h s . T h e g raphs show the v a r i o u s b e n c h face ang les a n d d i ps , or p lunges o f the f a i l u r e T h e re la t i onsh ips for benches 45 ft h igh a n d 90 ft h i g h a re g r a p h e d in F i g s . 3 a n d 4, r espec t i ve l y . Des ign g raphs for a spec i f i c b e n c h he igh t c a n be used to de te rmine the s ize o f a po ten t i a l f a i l u re , i n c l u d i n g the b e r m w id th and ove ra l l s lope a n g l e necessary to c o n t a i n the bench fa i l u re . F i g . 4 i l l us t ra tes a t y p i c a l e x a m p l e w i t h 90 - f t -h igh benches a n d 80* b e n c h face ang les . In th is case, the geo log i c s t r u c t u r e i n d i c a t e d that p lane fa i lu res cou ld deve lop , d i p p i n g at 60* . F i g . 4 shows that the m i n i m u m b e r m w i d t h r e q u i r e d to ca t ch such fa i l u res is 48 ft, a n d the r esu l t i ng o v e r a l l a l l owab le s lope ang le is abou t 54* . T h e a m o u n t o f f a i l u re tha t w o u l d have to be c l e a n e d u p is a p p r o x i m a t e l y 1,600 c u ft per ft w i d t h o f the f a i l u re ( F i g . 4 a ) . I f the n u m b e r a n d s ize o f fa i l u res per un i t l eng th o f b e n c h c a n be es t ima ted , the to ta l a m o u n t o f c l e a n u p o f f a i l e d m a t e r i a l c a n be c a l c u l a t e d . T h e a c c o m p a n y i n g g r a p h s a s s u m e that m i n i m a l b a c k -break o f the bench crests w i l l deve lop . P r o p e r c on t r o l o f b las t ing and i n c l i n e d bench faces w i l l r educe b a c k b r c a k . W h e r e access is r e q u i r e d a l o n g b e r m s , b e r m w i d t h shou ld be inc reased to pe rm i t e q u i p m e n t passage past fa i lu res . W h e r e d i scon t i nu i t i e s a re l a rge a n d i nvo l ve more than one b e n c h , the o v e r a l l s lope a n g l e m a y have to be f la t tened. Graphical analysis applied to B.C. mine T h e a p p l i c a t i o n o f the a n a l y t i c a l t e c h n i q u e d e s c r i b e d here proved e x t r e m e l y use fu l at a m i n e in no r t he rn B r i t i s h C o l u m b i a . A t th is m i n e , a n a l y s i s was m a d e o f the upper 700 - f t - h i gh sec t i on o f a n 1 ,100- f t -h igh h a n g i n g -w a l l s lope o f a r g i l l i t i c r ock . N u m e r o u s po ten t i a l wedge fa i l u res , f o rmed by the c o m b i n a t i o n o f two j o in t sets, con t ro l l ed s lope g e o m e t r y a n d the s t a b i l i t y o f the benches. (See photo . ) G r a p h i c a l t e c h n i q u e w a s used w i t h p r o b a b i l i t y theory to de te rm ine the o p t i m u m b e n c h g e o m e t r y r equ i r ed to con ta in a reasonab le n u m b e r o f wedge fa i l u res u p o n the be rms . T h e p l unge o f the wedges v a r i e d m a t h e m a t i c a l l y as a n o r m a l d i s t r i b u t i o n abou t the m e a n p l unge v a l u e . P r o b a b i l i t y techn iques were a p p l i e d to assess the l i k e l i -hood o f unstab le wedges o c c u r r i n g whose p l u n g e w o u l d be greater than that d e t e r m i n e d b y p r o b a b i l i t y c r i t e r i a . T h e p robab i l i t y o f a n u n s t a b l e w e d g e s p i l l i n g over a b e r m , for a p a r t i c u l a r o v e r a l l s lope a n g l e , was de ter -m i n e d as shown in F i g . 5 . M i n e m a n a g e m e n t was then in a pos i t ion to e v a l u a t e a l t e r n a t i v e s lope d e s i g n s . A more comp le te d i s c u s s i o n o f the techn ique desc r ibed here is presented in " S l o p e S t a b i l i t y A n a l y s i s a n d D e s i g n B a s e d on P r o b a b i l i t y T e c h n i q u e s at C a s s i a r M i n e , " 1 9 7 7 ) C I M B u l l e t i n b y D . R . P i t e a u a n d D . C . M a r t i n . Q 141 REFERENCES [1] PITEAU, D.R.: I s l a n d Copper Design, Utah Mines L t d . U n p u b l i s h e d r e p o r t - paper t o f o l l o w . [2] BRAWNER, CO.: Advances i n Rock Mechanics, P r o c e e d i n g s o f the T h i r d Congress o f t h e I n t e r n a t i o n a l S o c i e t y f o r Rock Mechanics, Denver, 1974. [3] CANMET: The P i t Slope Manual, Chapter 4: Groundwater, Supply and S e r v i c e s , Ottawa, Canada, '1976. [4] DRUMMOND, A.D., S.J. Tennant and R.J. Young: The I n t e r -r e l a t i o n s h i p o f R e g i o n a l Metamorphism, Hydrothermal A l -t e r a t i o n and M i n e r a l i z a t i o n a t G i b r a l t a r Mines Copper D e p o s i t i n B.C., CIMM B u l l e t i n , F e b r u a r y , 1973. [5] STEWART, R.M. and B.A. Kennedy: The Role o f S l o p e S t a b -i l i t y i n the Economics, Design and O p e r a t i o n o f Open P i t M i n i n g , P r o c . 1 s t Symposium on S t a b i l i t y i n Open P i t M i n i n g , Vancouver, 1970. P u b l i s h e d by AIME, New York, 1971. [6] BRAWNER, CO.: Open P i t Slope S t a b i l i t y Around t h e World. CIMM B u l l e t i n , J u l y , 1977. [7] CANMET: The P i t Slope Manual, Chapter 2: S t r u c t u r a l Geology, Supply and S e r v i c e s , Ottawa, Canada, 1976. [8] CARPENTER, T.L.: Deep Dewatering a t G i b r a l t a r Mine. C a r p e n t e r , CIMM, A p r i l , 1980. [9] EISENSTEIN,T: Case H i s t o r i e s o f Slope F a i l u r e s a t G i b r a l t a r Mines. Mines Branch, Supply and S e r v i c e s , Ottawa, Canada, 1975. [10] HOEK, E. and J.W. Bray: Rock Sl o p e E n g i n e e r i n g . I n -s t i t u t e o f M i n i n g and M e t a l l u r g y , London,' England, 1977. [11] MARTIN, C D and D.R. P i t e a u : S e l e c t Berm Width t o Con-t a i n L o c a l F a i l u r e s . EMJ, June, 1977. [12] BRAWNER, CO.: The I n f l u e n c e and C o n t r o l o f Groundwater i n Open P i t M i n i n g . F i f t h Canadian Symposium on Rock Mechanics, T o r o n t o , 1968. [13] MILNE, W.G., R.P. R i d d i h o u g h , G.A. McMechan and R.D. Hynoman: S e i s m i c i t y o f Western Canada. Canadian j o u r -n a l o f E a r t h S c i e n c e s , J u l y , 1978. [14] WHITMAN, V.R.: I n f l u e n c e o f Earthquakes on S t a b i l i t y . C i v i l E n g i n e e r i n g Department, M a s s a c h u s e t t s I n s t i t u t e o f Technology, S h o r t Course Notes, 1975. [15] PITEAU, D.R.: Cum u l a t i v e Sums Technique. S t a b i l i t y o f Rock S l o p e s , 13th Symposium on Rock Mechanics, 1971. [16] FREEZE, R.A. and J.A. Ch e r r y : Groundwater. P r e n t i c e H a l l , Englewood C l i f f s , New J e r s e y , U.S.A., 1979. [17] PITEAU, D.R.: Report on t h e I n v e s t i g a t i o n o r P r o d u c t i o n D r i l l i n g I n f o r m a t i o n f o r the Assessment o f Rock Q u a l i t y . Mines Branch, Department o f Energy, Mines and Resources, Canada, 1976. [18] DEERE, D.V. and F.D. P a t t o n : S t a b i l i t y o f S l o p e s i n R e s i d u a l S o i l s . S t a t e - o f - t h e - A r t Paper, S e s s i o n I I , 4 t h Panamerican Cong: S o i l Mechanics and F o u n d a t i o n E n g i n e e r i n g , P u e r t o R i c o , 1971. [19] HOEK, E.: A n a l y s i s o f Slope S t a b i l i t y i n Very H e a v i l y J o i n t e d or Weathered Rock Masses. T h i r d I n t e r n a t i o n a l Symposium 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 , Vancouver, B.C., 1981. [20] PITEAU, D.R. and D.C. M a r t i n : S e l e c t Berm Width t o C o n t a i n L o c a l F a i l u r e s . EMJ, June, 1977. [21] CALL, R.: Mt. Tolman Design. U n p u b l i s h e d r e p o r t , 1980. [22] ROBERTSON, A.MacG.: The D e t e r m i n a t i o n o f the S t a b i l i t y o f S l o p e s i n J o i n t e d Rock With P a r t i c u l a r R e f e r e n c e s t o the D e t e r m i n a t i o n o f S t r e n g t h Parameters and Mechanisms o f F a i l u r e . PhD T h e s i s , U n i v e r s i t y o f W i t w a t e r s r a n d , 1977 . [23] BRAWNER, CO.: Course Notes, Rock Slope 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 Columbia, 1981. [24] TANSEY, D.O.: The Du Pont S e q u e n t i a l B l a s t i n g System. CIM B u l l e t i n , J u l y 1979. [25] CANMET: The P i t Slope Manual, Chapter 7: P e r i m e t e r B l a s t i n g , Supply and S e r v i c e s , Ottawa, Canada, 1976. [26] CALL, R., J . S a v e l y and R. P a k a l n i s : A Simple Core O r i e n t i n g Technique, T h i r d I n t e r n a t i o n a l Symposium 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 , Vancouver, B.C., 1981. VOLUME I I APPLICATION OF VACUUM DRAINAGE CHAPTER I I - 1 INTRODUCTION Groundwater has a d e t r i m e n t a l e f f e c t on s l o p e s t a b i l i t y i n terms o f i n c r e a s e d h y d r a u l i c p r e s s u r e s . FigureTf-1 d e p i c t s a r o c k s l o p e w i t h a f a i l u r e p l a n e bounded by a t e n s i o n c r a c k . I t i s shown by the above f i g u r e t h a t water p r e s s u r e reduces the shear s t r e n g t h a l o n g the f a i l u r e p l a n e by p r o d u c i n g the u p l i f t f o r c e . In a d d i t i o n , water w i t h i n a t e n s i o n c r a c k c r e a t e s h o r i z o n t a l h y d r o s t a t i c p r e s s u r e s which c o n t r i b u t e t o i n s t a b i l i t y . Brawner [1] suggests t h a t the f r i c t i o n a l r e s i s -t a nce would decrease by 37 p e r c e n t due t o the buoyant u p l i f t o f t he groundwater f o r average d e n s i t y r o c k (S.G. = 2.65). The importance o f water p r e s s u r e c o n t r o l i s shown by FigureIT-2 whereby Hoek [2] r e l a t e s the r e s u l t a n t i n c r e a s e i n s l o p e a n g l e , due t o complete d e p r e s s u r i z a t i o n o f a s a t u r a t e d s l o p e t o the p r i m a r y f a c t o r s which determine t h e s l o p e a n g l e . F i g u r e d r e l a t e s mass p e r m e a b i l i t i e s t o recommended water p r e s s u r e c o n t r o l methods ( F i g 4 ) , i n o r d e r o f i n c r e a s i n g c o s t . The i n f o r m a t i o n i s condensed from Brown [3] and Skempton [ 4 ] . The d e s i g n o f Granite Lake Pit(Volume I) i n d i c a t e d t h a t f a i l u r e s were r e s t r i c t e d t o bench volume and as a consequence, l o c a l d e p r e s s u r i z a t i o n i n the form o f h o r i z o n t a l d r a i n s were recom-mended . FigureIT'3 shows t h a t vacuum w e l l p o i n t i n g i s a v i a b l e method f o r d r a i n i n g lower p e r m e a b i l i t y s o i l s , ( f i n e s i l t s ) . F= CA+(WCos6/p - U-V Sinl/p) T a n ^ W SinVp + VCos<yp W H E R E B Y : C= cohesion on failure plane W= weight of failure block kJ p= inclination of failure p lane 0 = friction angle on failure plane U = buoyant force of water V = l a t e r a l f o r c e e x e r t e d by water within tension crack FIGURE n-1 INFLUENCE OF WATER PRESSURE ON SLOPE STABILITY C/ *H C= effective cohesion 0= effective friction angle H = slope height y = unit weight of rock FIGURETX-2 RESULTANT INCREASE IN S L O P E ANGLE DUE TO  TOTAL DEPRESSURIZATION (AFTER HOEK) [>] 146 SOIL TYPE CLAYS SILTS SANDS PERMEABILITY RANGE K<IO"cm/s l 6 c m / s < K <IO*cm/s K > IO*cm/s PARTICLE SIZE .C ) 0 2 m m . ( )6mm 2 1 UNAIDED DRAINAGE HORIZONTAL DRAINS VACUUM DRAINAGE WELLPOINTING I/. \ •- •. •• W E L L S DRAINAGE ADITS UNLOADING . - . •. •. '. •. -.1 dHJ DEPRESSURIZATION POSSIBLE RGURE n-3: RECOMMENDED DEPRESSURIZATION  TECHNIQUES FOR VARIOUS MASS PERMEABILITIES (AFTER BROWN[3J a SKEMPTON [4] ) Surface drain to col lect run-off before it can enter the top of open tension cracks. This drain should be well graded and must be kept clear Potential tension crack position-Slope surface immediately behind crest should be graded to prevent pools of surface water gathering during heavy rain Col 1ector dra in-Horizontal hole to drain potential — ^ fai lure surface Potential tension crack Sub-surface dra inage gal 1ery / / ^ Fan of d r i l l holes to y increase drainage efficiency of sub-surface gal lery. Col 1ector draIn FIGURE. UPSLOPE DRAINAGE SYSTEMS ( A F T E R HC€K) [2] 148 Vacuum w e l l p o i n t i n g [5] i s a proven system f o r d e - w a t e r i n g s a t u r a t e d s o i l s . I t employs the p r i n c i p l e whereby a column of water, e x h a u s t i n g t o a vacuum, i s a b l e t o be r a i s e d 10.3m (MSL) (33.9 f t ) . T h i s i s due t o the p r e s s u r e e x e r t e d by t h e a t -mosphere onto the s u r f a c e o f the l i q u i d o u t s i d e o f the en-c l o s e d a r e a (FiglT-5). W e l l p o i n t s ( F i g l t 6 ) are s m a l l d i a m e t e r w e l l s t h a t are f u l l y i s o l a t e d from the atmosphere o t h e r t h a n a t the p o i n t where the water e n t e r s the system. An a i r sep-a r a t i o n chamber c o n t i n u o u s l y removes a i r from th e system w i t h the water b e i n g d i s c h a r g e d so as not t o i n t e r f e r e w i t h t h e vacuum u n i t . The maximum depth o f l o w e r i n g a water t a b l e w i t h one stage o f w e l l p o i n t s i s a p p r o x i m a t e l y 5 m [ 5 ] . T h i s d i f f e r s from the above (10.3 m) due t o the i m p o s s i b i l i t y o f p r o d u c i n g : (1) a t o t a l vacuum, and (2) a f r i c t i o n l e s s f r e e d r a i n a g e system. T h i s t h e s i s (Volume I I ) e v a l u a t e s the p r a c t i c a b i l i t y o f d e v e l o p i n g a vacuum h o r i z o n t a l d r a i n . The vacuum a s s i s t e d d r a i n would r e s u l t i n an i n c r e a s e d h y d r a u l i c g r a d i e n t due t o e x i t p r e s s u r e s b e i n g below a t m o s p h e r i c . A d d i t i o n a l b e n e f i t s would a r i s e from i n c r e a s e d r a t e s o f d r a i n a g e , t h e a b i l i t y o f d e p r e s s u r i z i n g lower p e r m e a b i l i t y m a t e r i a l s , and b e i n g a b l e t o de-water below the l e v e l o f the d r a i n s . Vacuum d r a i n a g e be-low a f a i l u r e s u r f a c e would change the d i r e c t i o n o f t h e seep-age f o r c e s so t h a t t h e y would a c t a p p r o x i m a t e l y p e r p e n d i c u l a r t o the f a i l u r e p l a n e and as a consequence, i n c r e a s e s t a b i l i t y . 14 9 T H J . vacuum (0. atm.) atmospheric pressure (10330 Kg/m2) WHEREBY-H= height of water column H= atmosheric pressure (10530Kg/m ) density of water(IOOOKg/m2) = 10.3 m (at mean sea level) FIGURE T-E-5 : VACUUM PRINCIPLE original water table FIGUREn-6: VACUUM WELLPOINTING APPLIED ON 5 m. LIFTS The study i n c o r p o r a t e d a p r o t o t y p e vacuum d r a i n t h a t was developed and i n s t a l l e d a t the G r a n i t e Lake p i t . The p e r f o r -mance of the system was m o n i t o r e d i n o r d e r t o a s s e s s : (1) drawdown r a t e s w i t h and w i t h o u t vacuum, (2) the amount o f vacuum that could be created, and (3) the p r a c t i c a l i m p l i c a t i o n s o f employing a vacuum t o a s s i s t d r a i n a g e . The above s t u d y was f u r t h e r r e i n f o r c e d t h r o u g h l a b o r a t o r y and n u m e r i c a l model l i n g whereby the r e l a t i v e b e n e f i t s o f vacuum a s s i s t e d d r a i n a g was determined. CHAPTEREI-2 LOCATION AND PROGRAM LAYOUT OF VACUUM PROTOTYPE A vacuum system has been developed by the auth o r t h a t can be i n s t a l l e d a t o p e r a t i n g open p i t mines. The p r o t o t y p e was i n s t a l l e d on the e a s t w a l l o f G r a n i t e Lake p i t o f G i b r a l -t a r Mines L t d . (FigIF7) and t e s t e d f o r a p e r i o d o f two weeks under f i e l d c o n d i t i o n s d u r i n g May 1981. The purpose o f the t e s t was t o determine: (1) Whether a vacuum can be developed i n a f r a c t u r e d medium. (2) What e f f e c t vacuum has on the groundwater regime. The a r e a s e l e c t e d ( F i g 8) has an average h y d r a u l i c con-d u c t i v i t y o f 10 m/sec which c o r r e l a t e d w e l l w i t h v a l u e s ob-t a i n e d i n an e a r l i e r groundwater s t u d y [ 6 ] . The s t u d y a r e a was l i m i t e d t o a 13.7 m bench as i n d i c a t e d by FigureIF9A. A 'Napco' (FigH9B &U9C) p r e c u s s i o n d r i l l was employed t o d r i l l t h r e e 15.2 m - 7.6 mm di a m e t e r v e r t i c a l h o l e s spaced a p p r o x i m a t e l y 15.2 m a p a r t f o r the i n s t a l l a t i o n o f p i e z o m e t e r s . The Napco was employed due t o i t s a v a i l a b i l i t y a t the p r o p e r -t y . Three h o r i z o n t a l d r a i n h o l e s were i n c l i n e d a t +2% and d r i l l e d from the bench below t o be l o c a t e d midway between the p r e v i o u s l y d r i l l e d p i e z o m e t e r s . The p i e z o m e t e r s were subse-q u e n t l y m o n i t o r e d t o determine the e f f e c t o f the h o r i z o n t a l d r a i n s . The second stage r e q u i r e d the system t o be p l a c e d under vacuum w i t h s i m u l t a n e o u s m o n i t o r i n g b e i n g conducted. FIGURE rj>9B:"NAPCO" DRILLING HORIZONTAL DRAINS .ary p iezometer FIGUREn-HO:SCHEMATIC REPRESENTATION OF VACUUM SYSTEM 156 NORTH PIFZOMETER •7-B E N T O N I T E *«6(T ^ G R A V E L 3m • SAWCUTS 0 . 9 n FIG.IIA CENTRE PIEZOMETER 1.9 cm dia. 1151.Im i isaom em d.a. GRND. E L E V . -i • V ; i i - -% .' > _ ^ G R A V £ L Xk %' E tN rt - SAWCUTS t,2 m T 0 . 3 m J C A p FIG.IIB SOUTH PIEZOMETER 1.9 cm dia. / ,5 gn til- . G R N D . E L E V . r5 SAWCUIS o.»» Ow 13m 3m FIG. IIC FIGURE III: PIEZOMETER CONSTRUCTION 157 P i e z o m e t e r I n s t a l l a t i o n I n i t i a l l y i t was proposed t o d r i l l t h r e e v e r t i c a l and t h r e e i n c l i n e d p i e z o m e t e r s p o s i t i o n e d so as t o o b t a i n a 3-d i m e n s i o n a l r e p r e s e n t a t i o n o f t h e water t a b l e (FigH-10). T h i s p l a n was abandoned due t o extreme d i f f i c u l t i e s a r i s i n g from inadequate f l u s h i n g o f the d r i l l c u t t i n g s . Three h o l e s were e v e n t u a l l y d r i l l e d t o 1.5 m below the top o f the subsequent bench. A 19 mm d i a m e t e r PVC p i p e was i n s e r t e d i n each d r i l l h o l e t o s e r v e as an open s t a n d p i p e p i e z o m e t e r . A b e n t o n i t e s e a l was i n s t a l l e d i n two o f the cases r e s u l t i n g i n a 3 m t e s t r e g i o n compared t o a 15.2 m t e s t s e c t i o n i n the c e n t r a l p i e z o m e t e r (Fig 'T I - NA, 11B & 11C). H o r i z o n t a l D r a i n I n s t a l l a t i o n The 'Napco' was employed t o d r i l l t he h o r i z o n t a l h o l e s which were spaced on a 12.2 m p a t t e r n t o be l o c a t e d between the p r e v i o u s l y d r i l l e d p i e z o m e t e r s . The d r a i n h o l e s were o f 76 mm d i a m e t e r i n c l i n e d a t +2% t o a l l o w f o r g r a v i t y d r a i n a g e and f l u s h i n g . Two h o l e s were d r i l l e d (FigI-12) t o 21.3 m and one t o 18.3 m. The l i m i t a t i o n was governed by the d r i l l c a -p a b i l i t i e s . A p a c k e r / g r o u t arrangement was employed t o en-sure t h a t a s u f f i c i e n t l y c l o s e d medium would be d e v e l o p e d (Figt-13). The outer 6.1 m of the' slope face was assumed to be highly f r a c t u r e d . T h i s v a l u e was d e t e r m i n e d t h r o u g h d i s c u s s i o n s w i t h mine p e r s o n n e l . CAP 4 -I 139,6m etev. perforated JI39.5m Pnth 1 1137,4 m | , , .-Il37.|m j-|-|l37,2m Pcen |-Il36.9rr| Pslh N acker \ grouted V 'sec tion co* 7.6 cm^ | j . l 3 9 . 3 m | | I 137m | | 1136,6m NORTH CENTER SOUTH FIGUREn-l2H0RIZONTAL DRAIN CONSTRUCTION FIGUREHH3:PACKER SYSTEM 159 Packer and Grout I n s t a l l a t i o n Schedule 80 48 mm O.D p e r f o r a t e d p i p e 38 mm I.D. w i t h 0.2 mm s l o t s was employed w i t h i n the vacuum zone. The pack-e r was an expandable rubber membrane e n v e l o p i n g a b l a n k PVC p i p e whose dimensions were 1 . 5 m x 69 mm O.D (FigIEi4-A) . The r e m a i n i n g 4.6 m w i t h i n t h e f r a c t u r e d zone was composed o f a b l a n k s e c t i o n o f PVC p i p e (FigI-14B) which was enveloped by a cement g r o u t . I t i s d e s i r a b l e t h a t an e x p a n s i v e cement be employed, i e , 10% e n d e r b l a s t - N . The packer was i n f l a t e d by means o f a n i t r o g e n c a n i s t e r (Fign-14C) which r e q u i r e s approx-i m a t e l y 3 1/hole o f gas. The e n t i r e d r a i n , i n c l u d i n g p e r f o r -a t i o n , packer and g r o u t s e c t i o n s were i n s e r t e d p r e - f a b r i c a t e d i n t o the d r a i n h o l e . The g r o u t u n i t c o n s i s t e d o f a g r o u t pump and mix tank as shown i n Figureni5A. Cement was pumped i n t o the c o l l a r o f the d r a i n h o l e and a i r was exhausted from a tube t e r m i n a t i n g a t the j u n c t i o n between the packer and g r o u t s e c -t i o n (FigJJ19B). I t was found t h a t a b e n t o n i t e s u r f a c e pack a i d e d the development o f a more complete s e a l (FigII15C). Vacuum System A w e l l p o i n t d e - w a t e r i n g system F i g u r e f l l 6 A andII16B, was employed with the well points being horizontal instead of v e r t i c a l . The vacuum pump was c a p a b l e o f e x h a u s t i n g 12 1/sec o f a i r and p r o d u c i n g 0.7 m. (mercury) o f vacuum a t mean sea l e v e l . A header system was employed whereby the t h r e e d r a i n s were a t -ta c h e d t o the vacuum pump thr o u g h v a l v e s e n a b l i n g a vacuum FIGUREffl4A: PACKERS EMPLOYED TO FORM S E A L 161 FIGUREU>I5A; GROUT S Y S T E M FIGUREDH5B : GROUT PUMPED INTO DRAIN HOI F F I G U R E H H 5 C : BENTONITE S U R F A C E S E A L FIGURE TJH6A VACUUM PUMP F I G U R E T X H 6 B INSTALLED V A C U U M S Y S T E M t o be a p p l i e d i n d i v i d u a l l y o r i n c o m b i n a t i o n w i t h each o t h e r (Fign.-17A & 17B). The exhausted water f l o w can be measured s i n c e f l o w t o the pump i s e x i t e d t h r o u g h a p o r t (FigK-16A). The vacuum i s m o n i t o r e d t h r o u g h the r e a d i n g o f a gauge (Figft-17C) a t t a c h e d t o the pump. The pump was a d i e s e l d r i v e n s e l f - c o n t a i n e d u n i t c a p a b l e o f e x h a u s t i n g a c o n s t a n t volume. R e s u l t s P r e l i m i n a r y P r e p a r a t i o n I t was soon r e a l i z e d t h a t upon i n s t a l l a t i o n o f the p i e -zometers t h a t the water t a b l e was w e l l b e h i n d the s l o p e . The south p i e z o m e t e r i n d i c a t e d the p h r e a t i c s u r f a c e was 15.2 m below the s u r f a c e . T h i s was not e x p e c t e d s i n c e seepage was p r e s e n t a l o n g the 1149 m l e v e l i n the v i c i n i t y o f the t e s t a r e a , w i t h an a r t e s i a n d r i l l h o l e p r e s e n t on t h e 1387 m l e v e l b e h i n d the t e s t s l o p e . The t h r e e d r a i n h o l e s d i d not e x h i b i t any water f l o w . The s l o p e was the n r e c h a r g e d by em-p l o y i n g a s i p h o n and r e d i r e c t i n g f l o w from a c o n d u i t 3 bench-i es above the c r e s t o f the t e s t a r e a . F i v e days (Fig]J.-18A andTJ-I 18B) o f re c h a r g e were r e q u i r e d , t o t a l i n g about 150000 l i t r e s w i t h a maximum d i s c h a r g e o f 0.76 1/s b e i n g d i v e r t e d from the c o n d u i t . T h i s r e s u l t e d i n r a i s i n g t h e water t a b l e t o l e v e l s i i n d i c a t e d by Figure][-19. The h o r i z o n t a l d r a i n s d i d not e x h i b i t a c o n t i n u o u s f l o w . However, upon f l o o d i n g i n the v i c i n i t y o f the n o r t h p i e z o -i meter, water d i d p e r i o d i c a l l y f l o w t h rough the n o r t h d r a i n 164 FIGUREILI7-A- DRAIN C O N N E C T E D T O HEADER PIPE FIGUREIH7B : " S T O P - C O C K " T O DIRECT AIR F L O W F IGUREIF I7C i V A C U U M G A U G E 165 FIGURES ISA.: RECHARGE POND FIGURE TJI8B: D ISCHARGE TO T E S T A R E A (FigH20) w i t h a g r e a t e r d i s c h a r g e e m i t t e d from a f r a c t u r e between p i e z o m e t e r s n o r t h and c e n t r a l ( F i g H 2 l ) . T h i s f r a c -t u r e has a d i p d i r e c t i o n o f 248 degrees and a d i p o f 60 de-grees and r e s u l t e d i n i t b i s e c t i n g t he t e s t a r e a . Because o f t h i s , the water t a b l e c o u l d not be r a i s e d s u b s t a n t i a l l y i n the v i c i n i t y o f the n o r t h e r n p i e z o m e t e r . I t was q u e s t i o n e d whether a vacuum c o u l d be devel o p e d s i n c e the t e s t a rea was not f u l l y s a t u r a t e d p r i o r t o r e -c h a r g i n g as i s n o r m a l l y the case i n c o n v e n t i o n a l w e l l p o i n t d e - w a t e r i n g . The t e s t a r e a was moderate t o h i g h l y f r a c t u r e d w i t h about 40 t o 60 p e r c e n t i n f i l l w i t h the dominant s t r u c -t u r e as i n d i c a t e d above. Vacuum T e s t 1 The pump was t e s t e d upon i n s t a l l a t i o n t o ensure t h a t i t was t r o u b l e f r e e s i n c e i t was t o be l e f t a t the mine s i t e f o r a two-week p e r i o d . I n i t i a l l y t he n o r t h d r a i n was p l a c e d un-der vacuum r e s u l t i n g i n 0 mm o f mercury b e i n g r e c o r d e d on the vacuum gauge. I t was e v i d e n t t h a t the packer had become de-f l a t e d s i n c e i t r e c o r d e d z e r o a i r p r e s s u r e . The c e n t r a l and so u t h e r n d r a i n i n d i v i d u a l l y r e c o r d e d a vacuum o f 380 mm o f mercury. P r i o r t o engaging the vacuum pump the water t a b l e , r e l -a t i v e t o the south d r a i n , was as f o l l o w s (FigTJ_19): FIGUREB2I t S E E P A G E THROUGH DISCONTINUITY 168 1. N o r t h p i e z o - w a t e r t a b l e 1.7 m below south d r a i n . 2. C e n t r e p i e z o - w a t e r t a b l e 0.49 m below south d r a i n . 3. South p i e z o - w a t e r t a b l e 2.3 m below south d r a i n . The r e s u l t o f a p p l y i n g vacuum t o the s o u t h e r n d r a i n h o l e where i n i t i a l l y no water f l o w e d , was as f o l l o w s : 1. 381 mm o f vacuum o b t a i n e d . 2. Flow i n c r e a s e d from 0 1/s t o 0.2 1/s which was c o n s t a n t f o r 15 minutes w h e r e a f t e r no f l o w o c c u r r e d . 3. A f f e c t on p i e z o m e t e r s : (a) P south - water t a b l e dropped 0.15 m. (b) P c e n t r e - water t a b l e dropped 0.15 m. (c) P n o r t h - no e f f e c t . I t must be noted t h a t f o u r hours p r i o r t o t h e t e s t 5400 l i t r e s o f water had been p l a c e d i n t h e v i c i n i t y o f t h e c e n t r a l p i e z o m e t e r . T h i s had r e s u l t e d i n ponding t o o c c u r w i t h a r i s -i n g t r e n d i n the water t a b l e (Figtt22A). The n o r t h e r n p i e z o -meter was not a f f e c t e d s i n c e i t was s e p a r a t e d from the s o u t h d r a i n by the southwest d i p p i n g s t r u c t u r e . T e s t Methodology F u r t h e r t e s t i n g comprised the f o l l o w i n g p r o c e d u r e s : 1. The water l e v e l was r a i s e d above t h e d r a i n h o l e s . 2. The t e s t was run i n s t a g e s : (a) Vacuum on south d r a i n . (b) Vacuum on s o u t h and c e n t r a l . (c) Vacuum on s o u t h , c e n t r a l and n o r t h d r a i n s . 3. Continuous m o n i t o r i n g o f p i e z o m e t e r s d u r i n g the t e s t . 4. The t e s t was conducted u n t i l : (a) No e f f e c t on the water t a b l e was n o t i c e d . (b) No water was pumped th r o u g h the vacuum pump. 5. Continuous m o n i t o r i n g o f the vacuum gauge and e x i t f l o w from the vacuum pump was conducted. A problem w i t h the above procedure was t h a t i t r e q u i r e d f i v e days t o r e p l e n i s h the s u p p l y o f water t o the t e s t a rea i n o r d e r t o r a i s e t h e water l e v e l above the d r a i n s . Vacuum T e s t 2 D u r i n g t h i s t e s t 0.6 1/s o f water was c o n t i n u o u s l y r e -c h a r g i n g the t e s t a r e a . ( i ) Stage: South D r a i n Engaged The i n i t i a l t e s t was conducted when the water l e v e l s were as i n d i c a t e d by FigureII-19: (a) South p i e z o m e t e r water l e v e l 0.6 m below s o u t h d r a i n . (b) C e n t r e p i e z o m e t e r water l e v e l 2.8 m above the south d r a i n . (c) N o r t h p i e z o m e t e r water l e v e l 0.18 m above the south d r a i n . The south d r a i n c o u l d m a i n t a i n a vacuum o f 178 mm, the c e n t r e 165 mm, and the n o r t h 381 mm o f vacuum. The n o r t h d r a i n was r e - i n f l a t e d which r e s u l t e d i n the i n c r e a s e d vacuum. The lower v a l u e s f o r t h e c e n t r a l and s o u t h e r n d r a i n s were p o s s i b l y due t o the f l u s h i n g a c t i o n d u r i n g the f i r s t t r i a l . IMCH II39H O 1138-1 < > w 1137-1136 11354 1134 WATER LEVEL VS. TIME SUMMARY FIGS22C 12 0 0 M A Y 4 MAY 5 M A Y 6 T I M E piezometer writer piezometer north > ^ (13 centfol drain !•»«' touffi Oroin l»**t plozomcttr south irol droin W I IT7-V i o> h droin Stvrl W A T E R I F V E L V S . T I M E  T E S T - I FIG.H22A 12 CD 15 00 MOO TIME — MAT 3 f96t — <HOURS> 13 00 16 OO W A T E R L E V E L V S . T I M E  T E S T - 2 FIG.H22B 0.6 * / . confirwoui rtcfiari II CO 12 00 13 00 MOO 13 00 TIWC — U AT 10 1981— (HOURS) 16 00 (7 00 FIGUREIT-22: WATER L E V E L VERSUS TIME o 171 The p a c k e r s were f u l l y i n f l a t e d i n both the c e n t r e and s o u t h d r a i n . The h i g h e r water l e v e l s d i d not r e s u l t i n a c o n t i n u -ous water f l o w under g r a v i t y d r a i n a g e w i t h no vacuum a p p l i e d . Figurell-22B shows t h e immediate e f f e c t r e s u l t i n g from ap-p l y i n g the vacuum and the r e s u l t s a re summarized below: 1. 178 mm o f vacuum c r e a t e d on the south d r a i n . 2. Flow i n c r e a s e d from 0 1/s t o 0.3 1/s which was c o n s t a n t f o r 32 minutes w h e r e a f t e r no f l o w o c c u r r e d . 3. A f f e c t on p i e z o m e t e r s : (a) P s o u t h water t a b l e dropped 0.9 m i n 70 minutes w h e r e a f t e r i n f l o w was g r e a t e r than o u t f l o w . (b) P c e n t r e - water t a b l e dropped 1.1 m i n 59 minutes w h e r e a f t e r i n f l o w was g r e a t e r than o u t f l o w . (c) P n o r t h - no e f f e c t , i n f l u e n c e o f d i s c o n t i n u i t y . ( i i ) South and C e n t r e D r a i n Engaged Vacuum was a p p l i e d i n a d d i t i o n t o t h e c e n t r a l d r a i n upon d e t e r m i n i n g t h a t f u r t h e r d r a i n a g e was not p o s s i b l e . At t h i s p o i n t the water t a b l e was as f o l l o w s : (a) P s o u t h water l e v e l 1.7 m below D-centre, 1.4 m below D-south. (b) P c e n t r e water l e v e l 2.0 m above D-centre, 2.3 m above D-south. The f o l l o w i n g was observed: 1. An 89 mm vacuum r e s u l t e d from the combined d r a i n a g e . 2. Flow i n c r e a s e d from 0 1/s t o 0.02 1/s which was c o n s t a n t f o r f i v e minutes w h e r e a f t e r no f l o w o c c u r r e d . 3. Recharge was g r e a t e r than d i s c h a r g e i n P c e n t r a l w i t h the r e s u l t i n a r i s i n g water t a b l e . 172 4. P n o r t h was u n a f f e c t e d due t o d i s c o n t i n u i t y . 5. P s o u t h i n d i c a t e d a drop of 0.05 m i n the water t a b l e , a f t e r 41 minutes th e water t a b l e began t o r i s e . ( i i i ) N o r t h , C e ntre and South D r a i n Engaged The water t a b l e c o n t i n u e d t o r i s e , i n d i c a t i n g t h a t the recharge was g r e a t e r than the d i s c h a r g e w i t h the t h r e e d r a i n s engaged. The combined vacuum was 63 mm w i t h f l o w i n c r e a s i n g from 0 1/s t o 0.03 1/s which was c o n s t a n t f o r f i f t e e n minutes w h e r e a f t e r no f l o w o c c u r r e d . The c o n c l u s i o n was t h a t the vacuum was too low t o o b t a i n drawdown. The above i s summarized by Figure][-22C . Cost o f I n s t a l l a t i o n T h i s p r o t o t y p e can be w i t h u n i t c o s t s lower than d i c a t i o n i s g i v e n i n T a b l e a p p l i e d t o an expanded p i t s c a l e t h a t e s t i m a t e d , however, an i n -TABLE Hi COST SUMMARY (1981) ITEM COST/UNIT AMOUNT P e r f o r a t e d PVC P i p e $ 9 60/m $ 518 00 Blank PVC P i p e 7 33/m 198 00 Pa c k e r s £• M i s c . 282 00/Hole* 846 00 Grout Equipment - R e n t a l & O p e r a t i o n - M a t e r i a l s 298 50 00/Hole* .00/Hole* 1045 00 Vacuum Pump - R e n t a l - I n s t a l l a t i o n - M a t e r i a l s , i e , p i p e 525 133 67 .00/Week .00/Hole* .00/Hole* 1920 00 P i e z o m e t e r s & M i s c . 3 . 44/m 557 00 TOTAL $5084 . 00 * Based on number o f d r a i n h o l e s d r i l l e d . 174 CHAPTERI-3 MODEL TESTING A l a b o r a t o r y model was c o n s t r u c t e d (FigJ£-23A, I-23B andf-230) h a v i n g dimensions 120 cm x 215 cm x 45 cm h i g h (Fig.1-24). H o r i z o n t a l d r a i n s , f i f t y c e n t i m e t e r s i n l e n g t h , were i n s t a l l e d which were composed o f a 15 cm p e r f o r a t e d segment o f 0.6 cm ID PVC p i p e . The model was f i l l e d w i t h 30 mesh sand which _2 had a p e r m e a b i l i t y o f 10 cm/sec. A 1:1 s l o p e was c o n s t r u c t e d w i t h a r e c h a r g e and d i s c h a r g e pond 45 and 15 cm i n h e i g h t , r e s p e c t i v e l y (FigI-25). P i e z o m e t e r s (0.6 cm ID) were i n s t a l l e d i n o r d e r t o m o n i t o r the e f f e c t o f d r a i n a g e on the water t a b l e . N u m e r i c a l m o d e l l i n g was employed t o s i m u l a t e the above super-imposed water l e v e l s (Figl-26 andI-27). R e s u l t s o f Model T e s t i n g A c o n s t a n t r e c h a r g e o f 1 1/min was found (Figl-28A) t o produce the above in d u c e d water t a b l e c o n d i t i o n s . Water l e v -e l s were r e c h a r g e d t o t h e base s i t u a t i o n p r i o r t o e n a c t i n g d r a i n a g e . D i s c h a r g e under g r a v i t y i s shown i n FigureH.-28B. Vacuum a s s i s t d r a i n a g e r e q u i r e d t h a t the i n d i v i d u a l d r a i n s be connected t o a h o l d i n g chamber t h a t was p l a c e d under vacuum (Fig i I 2 8 C ) . A c o m p a r a t i v e s t u d y between vacuum a s s i s t and g r a v i t y d r a i n a g e was conducted by m o n i t o r i n g the drawdown r a t e s w i t h i n the i n d i v i d u a l p i e z o m e t e r s . Figuresrj-29A andrj-29B are a s e r i e s o f photographs exposed ev e r y two minutes showing the e f f e c t t h a t g r a v i t y d r a i n a g e has on the p h r e a t i c s u r f a c e . 175 FIGURE E-23A-H0RIZ0NTAL DRAIN MODEL (WITHOUT SAND) FIGUREH-23B HORIZONTAL DRAIN AND PIEZOMETERS FIGURE.U-23C HORIZONTAL DRAIN MODEL (WITH SAND) DISTANCE (cm) OJ cn o to o o HEADPOND m N •V O l •v m O N m N 0"OJ DRAIN HOLE / crest of slope toe of slope — O N TAILPOND H E A D P O N D 1 I : i i i i j O 15 135, 150 165 200 215 DISTANCE (cm) SCALE i:12 F I G U R E D CROSS-SECTION OF DRAINAGE MODEL H=l5cm c m FIGURE 26 FLOW PROFILE—NO HORIZONTAL DRAIN FIGUREI27 : FLOW PROFILE — HORIZONTAL DRAIN S i m i l a r l y , the e f f e c t s o f vacuum a s s i s t d r a i n a g e are shown by FiguresH30A andl30B. I t was a l s o o b s e r v e d t h a t 23 cm (Mercury) o f vacuum was produced. F i g u r e I 3 1 q u a n t i f i e s t h e above t e s t d a t a i n the form o f a graph w h i c h r e l a t e s drawdown v e r s u s time f o r each i n d i v i d u a l d r a i n a g e s i t u a t i o n . F i g u r e l 3 2 i s a p l o t o f the p h r e a t i c s u r -f a c e a t d i f f e r e n t time i n t e r v a l s f o r each i n d i v i d u a l d r a i n s i t u a t i o n . The base case was the same both f o r g r a v i t y and vacuum a s s i s t d r a i n a g e and i s r e p r e s e n t e d by T = 0. I t i s shown by the above t h a t d r a i n a g e i s i n c r e a s e d by employing a vacuum p a r t i c u l a r l y w i t h i n the f i r s t 60 seconds of a p p l i c a t i o n . P i e z o m e t e r No. 2, which c o i n c i d e s w i t h the p e r f o r a t e d s e c t i o n o f the h o r i z o n t a l d r a i n , i n d i c a t e d the g r e a t e s t drawdown. FigureH31 shows t h a t vacuum d r a i n a g e r e -s u l t e d i n a t w o - f o l d i n c r e a s e i n the r a t e o f drawdown. F1GURE130B 1 DRAINAGE UNDER VACUUM T I M E ( M I N U T E S ) 2 4 6 8 10 12 14 16 "3 J i i I 1 1 1 1 1-FIGUREI-31 : PLOT OF DRAWDOWN V S . T l ME UNDER*, a) gravity drainage b) vacuum drainage LOCATION OF PIEZOMETER * 1 •» N * N M * S * P » i 5 5. FIGUREE32. PHREATIC SURFACE VS. TIME 18 CHAPTER II-4 PRACTICAL IMPLICATIONS The p r o t o t y p e t h a t was d e v e l o p e d i s a p p l i c a b l e t o a p i t d e p r e s s u r i z a t i o n system s i n c e i t i s a s e l f - c o n t a i n e d u n i t t h a t has been t e c h n i c a l l y proven by use i n the w e l l p o i n t i n d u s t r y t h roughout the p a s t t h i r t y y e a r s . The system has a p p l i c a t i o n i n the f o l l o w i n g a r e a s : 1. H o r i z o n t a l d r a i n s are e f f e c t i v e i n r o c k s h a v i n g a mass p e r m e a b i l i t y g r e a t e r than 10 5 cm/s. Vacuum a s s i s t d r a i n a g e i s a b l e t o draw m a t e r i a l s o f lower p e r m e a b i l i -t i e s as i n d i c a t e d by w e l l p o i n t i n g (10 cm/s). 2. The system tends t o a c c e l e r a t e the r a t e o f drawdown which i s an i m p o r t a n t f a c t o r i n s t a b i l i z i n g a c t i v e s l i d e s . ,The reason b e i n g t h a t w i t h i n c r e a s e d d e f o r m a t i o n due t o s l i d e movement, the shear s t r e n g t h i s r e d u c e d ( F i g 33). Consequently vacuum a s s i s t drainage results i n less strength loss. 3. Vacuum a s s i s t d r a i n a g e e n a b l e s an i n d i v i d u a l d r a i n t o e x h i b i t a w i d e r zone of i n f l u e n c e . T h i s i s p a r t l y due t o an i n c r e a s e d e f f e c t i v e mass p e r m e a b i l i t y s i n c e the c a p i l l i a r y [4-] e f f e c t s w i t h i n j o i n t s i s l a r g e l y overcome due t o the i n c r e a s e d h y d r a u l i c g r a d i e n t (Figfl.34). In a d d i t i o n , the water t a b l e i s a b l e t o be drawn an a d d i -t i o n a l 5 m below the l e v e l o f the d r a i n . The consequence o f t h e above i s t h a t fewer d r a i n s would have t o be i n -s t a l l e d i n o r d e r t o produce s i m i l a r b e n e f i t s t o t h a t o f g r a v i t y d r a i n s . 188 residual shear strength SHEAR DISPLACEMENT FIGUREH3-3.DEPENDANCE OF SHEAR STRENGTH ON DISPLACEMENT CASE I CASE 2 ASSUME NO VACUUM (P4=latm.) ASSUME VACUUM ASSIST H AT POINT A= P2-latm. HAT POINT A= P2-Oatm. CONSEQUENCE \ GRADIENT IS GREATER'.CASE2 FIGURE J-34-.INCREASED HYDRAULIC GRADIENT UNDER VACUUM 189 U N S T A B L E B L O C K FIGURE 135A . SEEPAGE FORCES REDUCING STABILITY U N S T A B L E B L O C K FIGURE ff35B:SEEPAGE FORCES INCREASING STABILITY Vacuum ass i s t drainage may be employed i n sub-surface g a l l e r i e s i n o r d e r t o a s s i s t d r a i n a g e i n the s t a b i l i z i n g of major s l i d e s . Vacuum d r a i n a g e r e - d i r e c t s seepage f o r c e s so t h a t they a c t p e r p e n d i c u l a r t o the f a i l u r e s u r f a c e . T h i s i s shown by FiguresE35A andK35B whereby the d r a i n i s below the f a i l u r e p l a n e . The consequence i s t h a t the normal l o a d a c t i n g on the f a i l u r e p l a n e i s i n c r e a s e d and, as a r e s u l t the shear s t r e n g t h o f the m a t e r i a l i s i n c r e a s e d . ( F i g . I 1) . Vacuum a s s i s t d r a i n a g e may be employed i n d e p r e s s u r i z a -t i o n of waste embankments, t a i l i n g s dams, s o i l l a n d s l i d e s and underground b a c k f i l l . 191 CHAPTER I I - 5 SUMMARY AND CONCLUSION I t i s e v i d e n t from f i e l d and l a b o r a t o r y o b s e r v a t i o n s t h a t : 1. A vacuum can be c r e a t e d i n a f r a c t u r e d media. 381 mm (Mercury) of vacuum was c r e a t e d a t G i b r a l t a r Mines L t d . 2. Vacuum a s s i s t d r a i n a g e i n c r e a s e d the r a t e o f drawdown. L a b o r a t o r y i n v e s t i g a t i o n s suggest a t w o - f o l d r a t e o f i n -c r e a s e . 3. Vacuum d r a i n a g e r e s u l t s i n immediate drawdown. Labora-t o r y i n v e s t i g a t i o n s i n d i c a t e t h a t the g r e a t e s t drawdown o c c u r s i n the f i r s t minute o f o p e r a t i o n . 4. Vacuum d r a i n a g e e n a b l e s a drawdown below the l e v e l o f the h o r i z o n t a l d r a i n s . T h i s was shown by f i e l d i n v e s t i -g a t i o n s whereby vacuum a s s i s t e d h o r i z o n t a l d r a i n s , l o c a t e d 2.3 m above the water t a b l e , had the subsequent e f f e c t o f l o w e r i n g the p h r e a t i c s u r f a c e by 15 cm. 5. A d i r e c t r e l a t i o n s h i p e x i s t e d between the amount o f vacuum and the subsequent drawdown. I t was c o n c l u d e d from the st u d y t h a t vacuum h o r i z o n t a l d r a i n s are a v i a b l e t e c h n i c a l a d d i t i o n t h a t can e f f i c i e n t -l y augment g r a v i t y systems through : 1. r e d u c i n g the p i e z o m e t r i c head and c o n s e q u e n t l y s t a b i l i z i n g s o i l s l o p e s , rock s l o p e s and underground b a c k f i l l . 2. i t can be employed f o r s t a b i l i z i n g l a r g e s l i d e s by p l a c i n g d r a i n a g e g a l l e r i e s under vacuum. REFERENCES [1] BRAWNER, CO.: The I n f l u e n c e and C o n t r o l o f Groundwater i n Open P i t M i n i n g . F i f t h Canadian Symposium on Rock Mechanics, U n i v e r s i t y o f Toronto, 1968. [2] HOEK, E. and J.W. Bray: Rock Slope E n g i n e e r i n g . R e v i s e d Second E d i t i o n , I n s t i t u t i o n o f m i n i n g and M e t a l l u r g y , London, 1977. [3] BROWN, A.: The I n f l u e n c e and C o n t r o l o f Groundwater i n Large S l o p e s . T h i r d I n t e r n a t i o n a l Symposium i n Open P i t M i n i n g , Vancouver, B.C., 1981. [4] SKEMPTON, A. and R. Gl o s s o p : P a r t i c l e S i z e i n S i l t s and Sands. J o u r n a l o f the I n s t i t u t i o n o f C i v i l E n g i n e e r s , Volume 25, London, 1945 . [5] TERZAGHI, K. and R. Peck: S o i l Mechanics i n E n g i n e e r i n g P r a c t i c e . W i l e y , New York, 1948. [6] CARPENTER, T.L.: Deep W e l l Dewatering a t G i b r a l t a r Mines. CIMM B u l l e t i n , A p r i l , 1980. 

Cite

Citation Scheme:

        

Citations by CSL (citeproc-js)

Usage Statistics

Share

Embed

Customize your widget with the following options, then copy and paste the code below into the HTML of your page to embed this item in your website.
                        
                            <div id="ubcOpenCollectionsWidgetDisplay">
                            <script id="ubcOpenCollectionsWidget"
                            src="{[{embed.src}]}"
                            data-item="{[{embed.item}]}"
                            data-collection="{[{embed.collection}]}"
                            data-metadata="{[{embed.showMetadata}]}"
                            data-width="{[{embed.width}]}"
                            data-media="{[{embed.selectedMedia}]}"
                            async >
                            </script>
                            </div>
                        
                    
IIIF logo Our image viewer uses the IIIF 2.0 standard. To load this item in other compatible viewers, use this url:
https://iiif.library.ubc.ca/presentation/dsp.831.1-0081083/manifest

Comment

Related Items