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Estimating undrained shear strength of clay from cone penetration tests Greig, James William 1985

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ESTIMATING UNDRAINED SHEAR STRENGTH OF CLAY FROM CONE PENETRATION TESTS By JAMES WILLIAM GREIG B.A.Sc, The U n i v e r s i t y of B r i t i s h Columbia, 1981 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE in THE FACULTY OF GRADUATE STUDIES (Department of C i v i l E ngineering) We accept t h i s t h e s i s as conforming to the r e q u i r e d standard THE UNIVERSITY OF BRITISH COLUMBIA September 1985 © James W i l l i a m G r e i g , 1985 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of The University of British Columbia 1956 Main Mall Vancouver, Canada V6T 1Y3 Date O^+vUz^ / S~ /<?0±' DE-6(3/81) i i ABSTRACT T h i s paper d i s c u s s e s s e v e r a l proposed methods f o r e s t i m a t i n g u n d r a i n e d shear s t r e n g t h from cone p e n t r a t i o n t e s t s . T h i s c o r r e l a t i o n has been s t u d i e d i n the p a s t , however, most have f o c u s s e d o n l y on the cone b e a r i n g . In a d d i t i o n t o d i s c u s s i n g t h e s e t r a d i t i o n a l methods, t h i s paper e v a l u a t e s r e c e n t l y proposed methods of e s t i m a t i n g Su from CPT pore p r e s s u r e d a t a . The r e s u l t s of f i e l d vane and cone p e n e t r a t i o n t e s t s from f i v e lower m a i n l a n d s i t e s a r e p r e s e n t e d i n r e l a t i o n t o the d i f f e r e n t proposed c o r r e l a t i o n t e c h n i q u e s . The r e s u l t s show t h a t t h e r e i s no unique cone f a c t o r f o r e s t i m a t i n g Su from CPT f o r a l l c l a y s , however, a r e a s o n a b l e e s t i m a t e of Su can be made by comparing the p r e d i c t i o n s from s e v e r a l of the proposed methods. With l o c a l c o r r e l a t i o n s t h e s e t e c h n i q u e s can be q u i t e r e l i a b l e . The r e s u l t s a l s o show t h a t the e s t i m a t i o n of Su from CPT i s i n f l u e n c e d by v a r i o u s f a c t o r s r e l a t i n g t o : the c h o i c e of a r e f e r e n c e Su, cone d e s i g n , CPT t e s t p r o c e d u r e s and the s o i l c h a r a c t e r i s t i c s . In p a r t i c u l a r , the e s t i m a t i o n of Su from CPT i s s t r o n g l y i n f l u e n c e d by such s o i l parameters as s t r e s s h i s t o r y , s e n s i t i v i t y and s t i f f n e s s . I n c r e a s e s i n OCR and s e n s i t i v i t y were r e f l e c t e d by i n c r e a s e s i n the t r a d i t i o n a l cone f a c t o r s Nc and Nk. The use of pore p r e s s u r e d a t a appears t o be a p r o m i s i n g means of e s t i m a t i n g . S u from CPT. E x p r e s s i o n s have been developed t h a t p r e d i c t e x c e s s pore p r e s s u r e s based on c a v i t y e x p a n s ion t h e o r y and attempt t o i n c l u d e the e f f e c t s of s e n s i t i v i t y , s t r e s s h i s t o r y and s t i f f n e s s . In a d d i t i o n , comparisons between f r i c t i o n s l e e v e measurements and Su and a method f o r e s t i m a t i n g s e n s i t i v i t y from f r i c t i o n r a t i o s a r e p r e s e n t e d . L a s t l y , recommended p r o c e d u r e s f o r e s t i m a t i n g Su from CPT a r e g i v e n . i v TABLE OF CONTENTS ABSTRACT i i LIST OF TABLES v i i i LIST OF FIGURES ix ACKNOWLEDGEMENTS x i v CHAPTER 1. INTRODUCTION 1 1.1 I n s i t u Measurement of Undrained Shear Strength 1 1.2 Report O r g a n i z a t i o n 5 CHAPTER 2. EQUIPMENT 7 2.1 I n t r o d u c t i o n 7 2.2 Research V e h i c l e 7 2.3 Penetrometers 8 2.4 Data A c q u i s i t i o n Systems 11 2.5 F i e l d Vanes 14 CHAPTER 3. TEST PROCEDURES AND DATA REDUCTION 18 3.1 I n t r o d u c t i o n 18 3.2 C a l i b r a t i o n 18 3.3 S a t u r a t i o n 20 3.4 F i e l d Cone P e n e t r a t i o n T e s t i n g ... 21 3.5 CPT Data Reduction 23 3.5.1 Unwanted Data 23 3.5.2 Temperature C o r r e c t i o n s 24 3.5.3 Pore Pressure C o r r e c t i o n s 24 3.5.4 F r i c t i o n R a t i o 27 3.5.5 D i f f e r e n t i a l Pore Pressure R a t i o 27 3.6 F i e l d Vane T e s t i n g 28 3.7 Reduction of Vane Data 29 V CHAPTER 4. A REVIEW OF THE VANE SHEAR TEST 32 4.1 I n t r o d u c t i o n 32 4.2 E v a l u a t i o n of Undrained Strength 32 4.3 E f f e c t s of An i s o t r o p y 37 4.4 Rate E f f e c t s 41 4.5 Disturbance Due to Vane I n s e r t i o n 42 4.6 C o r r e c t i o n F a c t o r s 45 4.7 Summary 50 CHAPTER 5. A BRIEF REVIEW OF THE CONE PENETRATION TEST 51 5.1 I n t r o d u c t i o n 51 5.2 S o i l C l a s s i f i c a t i o n 52 5.3 S o i l P r o f i l i n g 54 5.4 Dynamic Pore Pressure Response 64 CHAPTER 6. METHODS OF CORRELATION BETWEEN CPT AND Su 67 6.1 I n t r o d u c t i o n 67 6.2 T r a d i t i o n a l Methods of C o r r e l a t i o n 68 6.3 Re c e n t l y Proposed Methods of C o r r e l a t i o n 76 6.3.1 Using E f f e c t i v e Bearing to Estimate Su 77 6.3.2 Use of Excess Pore Pressures and C a v i t y Expansion Theory 78 6.3.3 Use of Va r i o u s Pore Pressure Parameters and Cone F a c t o r s 80 6.4 Using F r i c t i o n Sleeve Measurements to Estimate Su .. 85 6.5 E v a l u a t i n g S t r e s s H i s t o r y from CPT 87 6.6 E s t i m a t i n g S e n s i t i v i t y 94 CHAPTER 7. FIELD PROGRAMME AND DISCUSSION OF RESULTS 95 7.1 I n t r o d u c t i o n 95 v i 7.2 McDonald Farm Research S i t e 95 7.2.1 General Geology and S i t e D e s c r i p t i o n 95 7.2.2 C o r r e l a t i o n s Between Su and CPT 98 7.3 B.C. Hydro Railway C r o s s i n g S i t e 106 7.3.1 General Geology and S i t e D e s c r i p t i o n 106 7.3.2 C o r r e l a t i o n s Between Su and CPT 107 7.4 Upper 232nd St. S i t e 114 7.4.1 General Geology and S i t e D e s c r i p t i o n 114 7.4.2 C o r r e l a t i o n s Between Su and CPT 115 7.5 Lower 232nd St. S i t e 123 7.5.1 General Geology and S i t e D e s c r i p t i o n 123 7.5.2 C o r r e l a t i o n s Between Su and CPT 125 7.6 Haney S l i d e S i t e 125 7.6.1 General Geology and S i t e D e s c r i p t i o n 125 7.6.2 C o r r e l a t i o n s Between Su and CPT 132 7.7 A Summary of the R e s u l t s f o r the F i v e Lower Mainland S i t e s 138 7.8 C o r r e l a t i o n s Between Su and Sleeve F r i c t i o n 146 7.9 E s t i m a t i n g S e n s i t i v i t y from CPT 146 CHAPTER 8. SUMMARY AND CONCLUSIONS 152 8.1 Summary of F a c t o r s I n f l u e n c i n g the E s t i m a t i o n of Su 152 8.2 Con c l u s i o n s 155 8.2.1 Accuracy of CPT Data 155 8.2.2 Infl u e n c e of Layer Boundaries 156 8.2.3 D e t e c t i o n of Thin Layers 156 8.2.4 E s t i m a t i n g Su From Cone Bearing 157 8.2.5 Using CPT Pore Pressure Data to Estimate Su 157 v i i 8.2.6 Use of F r i c t i o n Sleeve Measurements 158 8.3 Recommended Procedure for E s t i m a t i n g Su From CPT 159 8.3.1 Use of CPT Data Without Pore Pressures 159 8.3.2 Use of CPT Data With Pore Pressures 159 REFERENCES 161 APPENDIX A 1 67 v i i i LIST OF TABLES Table No. Table T i t l e Page 1.1 PERCEIVED APPLICABILITY OF INSITU TEST METHODS 2 6.1 SUMMARY OF CONE FACTORS (Nc) DETERMINED FOR DIFFERENT CLAY DEPOSITS 69 6.2 SUMMARY OF CONE FACTORS (Nk) FOR SCANDANAVIAN CLAYS 71 6.3 SUMMARY OF EXISTING THEORIES OF CONE PENETRATION IN CLAYS 7 3 7.1 SUMMARY OF THE FIELD PROGRAMME 97 7.2 SUMMARY OF MATERIAL PROPERTIES AT THE DIFFERENT SITES 97 7.3 SUMMARY OF CONE FACTORS FOR 5 LOWER MAINLAND SITES 139 7.4 SUMMARY OF CORRELATIONS WITH FRICTION SLEEVE DATA FOR 4 LOWER MAINLAND SITES 149 i x LIST OF FIGURES Fi g u r e No. Figure T i t l e Page 1.1 LIKELY VARIATION IN UNDRAINED STRENGTH RATIO AND THEIR HIERARCHY FOR VARIOUS TEST METHODS .. 2 2.1 SCHEMATIC DIAGRAM OF CONE PENETROMETERS USED FOR THIS REPORT 9 2.2 POROUS FILTER LOCATION AND TIP DESIGN 10 2.3 FIELD VANE SYSTEMS 15 2.4 NILCON FIELD VANE AND SLIP COUPLE 16 3.1 SATURATION PROCEDURE 22 3.2 TEMPERATURE AND PORE PRESSURE EFFECTS ON CONE BEARING 25 3.3 EXAMPLE OF A NILCON TEST RECORD 30 4.1 STANDARD ANALYSIS OF THE VANE SHEAR TEST 34 4.2 SHEAR STRESS DISTRIBUTION ON A PLANE MIDWAY BETWEEN VANE BLADES USING A 3D FINITE ELEMENT ANALYSIS 35 4.3 DISTRIBUTIONS OF EQUIVALENT SHEAR STRESS ON A VERTICAL AND A HORIZONTAL BLADE EDGE 35 4.4 VARIOUS VANE CONFIGURATIONS USED TO MEASURE STRENGTH ANISOTROPY 39 4.5 VANE SHEAR STRENGTHS ON PLANES AT VARIOUS ANGLES 39 4.6 PLOT OF RATIO OF UNDRAINED SHEAR STRENGTHS IN HORIZONTAL AND VERTICAL DIRECTIONS vs PLASITICITY INDEX 40 4.7 VARIATION WITH DEPTH OF UNDRAINED SHEAR STRENGTH AT DIFFERENT RATES OF ROTATION 43 4.8 CORRELATION BETWEEN SHEAR STRESS LEVEL AND TIME TO FAILURE FROM UNDRAINED TRIAXIAL COMPRESSION TESTS ON DRAMMEN CLAY 43 4.9 CORRECTION FACTOR FOR UNDRAINED SHEAR STRENGTH DETERMINED FROM FIELD VANE TESTS 47 4.10 EMPIRICALLY ESTABLISHED CORRECTION FACTORS FOR RESULTS OF VANE SHEAR TESTS 47 X 4.11 RATIO OF UNDRAINED SHEAR STRENGTH TO VANE SHEAR STRENGTH FOR THREE TYPES OF CLAY 48 4.12 VANE SHEAR TEST REDUCTION FACTOR AS A FUNCTION OF THE LIQUID LIMIT ACCORDING TO THE SWEDISH GEOTECHNICAL INSTITUTE 48 5.1 CPT SOIL BEHAVIOUR TYPE CLASSIFICATION CHART .. 53 5.2 UBC SIMPLIFIED CPT SOIL BEHAVIOUR TYPE CLASSIFICATION CHART FOR THE ELECTRONIC FRICTION CONE 53 5.3 SIMPLIFIED EXAMPLES OF CONE BEARING PROFILES SHOWING LIKELY AND POSSIBLE INTERPRETATIONS FOR SOIL TYPES AND CONDITIONS 55 5.4 CONE PENETROMETER BEARING RESPONSE IN A LAYERED MEDIA 58 5.5 COMPARISON BETWEEN A CPT BEARING PROFILE AND A CONTINUOUS SAMPLE LOG 60 5.6 RELATIVE PROPORTIONS OF THE 10cm2 CONE PENETROMETER, PROBABLE ZONE OF INFLUENCE FOR CPT, UBC STANDARD SAMPLING RATE AND LARGE, MEDIUM AND SMALL FIELD VANES 63 5.7 . CONCEPTUAL PORE PRESSURE DISTRIBUTION IN SATURATED SOIL DURING CPT BASED ON FIELD MEASUREMENTS 65 6.1 EMPIRICAL CONE FACTOR Nk vs DEPTH FOR DIFFERENT CLAY DEPOSITS 70 6.2 SUMMARY OF CONE FACTORS (Nk) FOR SCANDANAVIAN CLAYS 71 6.3 EFFECT OF RIGIDITY INDEX AND CONE ANGLE ON THE PENETRATION RESISTANCE OF CLAY 74 6.4 SELECTION OF SOIL STIFFNESS 75 6.5 PROPOSED METHOD FOR OBTAINING Su FROM EXCESS PORE PRESSURE MEASURED DURING CPT 79 6.6 PORE PRESSURE PARAMETER Bq vs OVERCONSOLIDATION RATIO 82 6.7 CONE FACTOR Nkt vs PORE PRESSURE PARAMETER Bq 83 6.8 PORE PRESSURE PARAMETER NAu vs PORE PRESSURE PARAMETER Bq 84 x i 6.9 CONE FACTOR Nk vs PORE PRESSURE PARAMETER Bq .. 86 6.10 NORMALIZED Su/P' RATIO vs OVERCONSOLIDATION R A T I O F O R U S E I N E S T I M A T I N G O C R 89 6.11 S T A T I S T I C A L R E L A T I O N B E T W E E N Cu/avo R A T I O A N D P L A S T I C I T Y I N D E X F O R N O R M A L L Y C O N S O L I D A T E D C L A Y S 89 6.12 E X T R A P O L A T I O N O F T H E Qc P R O F I L E A S A N A L T E R N A T I V E M E T H O D T O E S T I M A T E O V E R -C O N S O L I D A T I O N I N T H I C K , H O M O G E N E O U S C L A Y L A Y E R S 91 6.13 T H E E F F E C T O F D E N S E R O V E R L Y I N G M A T E R I A L O N T H E E X T R A P O L A T E D Qt P R O F I L E F O R A N O R M A L L Y C O N S O L I D A T E D C L A Y L A Y E R 93 7.1 G E N E R A L L O C A T I O N O F R E S E A R C H S I T E S 96 7.2 T Y P I C A L C P T P R O F I L E A T M c D O N A L D F A R M 99 7.3 P R O F I L E S F R O M 4 C P T S O U N D I N G S I N M C D O N A L D F A R M C L A Y E Y S I L T 100 7 . 4 F I E L D V A N E S T R E N G T H A N D S E N S I T I V I T Y P R O F I L E S A T Mc D O N A L D F A R M 100 7.5 Qc/Su A N D Qt/Su vs D E P T H A T M C D O N A L D F A R M 101 7.6 (Qc-cr,a )/Su A N D (Qt- <T,o )/Su vs D E P T H A T M C D O N A L D F A R M 102 7 . 7 (Qc-Ut)/Su A N D (Qt-Ut)/Su vs D E P T H A T M C D O N A L D F A R M 1 0 3 7.8 AU/Su vs D E P T H F O R D I F F E R E N T P O R O U S E L E M E N T L O C A T I O N S A T M C D O N A L D F A R M 1 0 4 7.9 Nkt, N A U and Nke vs Bq A T M c D O N A L D F A R M 105 7.10 T Y P I C A L C P T P R O F I L E A T B . C . H Y D R O R A I L W A Y S I T E 108 7.11 I N D E X P R O P E R T I E S , F I E L D V A N E S T R E N G T H A N D S E N S I T I V I T Y P R O F I L E S A T B . C . H Y D R O R A I L W A Y S I T E 108 7.12 Qc/Su A N D Qt/Su vs D E P T H A T B . C . H Y D R O R A I L W A Y S I T E 109 7.13 (Qc- Co )/Su and (Qt-^ )/Su vs D E P T H A T B . C . H Y D R O R A I L W A Y S I T E 110 x i i 7.14 (Qc-Ut)/Su AND (Q t ~ U t ) / S u vs DEPTH AT B.C. HYDRO RAILWAY SITE 111 7.15 AU/Su vs DEPTH AT B.C. HYDRO RAILWAY SITE 112 7.16 Nkt, NAU and Nke vs Bq AT B.C. HYDRO RAILWAY SITE 113 7.17 TYPICAL CPT PROFILE AT UPPER 232nd S t . SITE ... 116 7.18 FIELD VANE STRENGTH AND SENSITIVITY PROFILES AT UPPER 232nd S t . SITE 116 7.19 COMPARISON BETWEEN CONE BEARING, VANE SHEAR STRENGTH AND OVERCONSOLIDATION RATIO AT UPPER 232nd St. SITE 117 7.20 Qc/Su AND Qt/Su vs DEPTH AT UPPER 232nd St. SITE 118 7.21 (Q C - C T , O )/Su and (Qt-o-TCl )/Su vs DEPTH AT UPPER 232nd St. SITE 119 7.22 (Qc-Ut)/Su AND (Qt-Ut)/Su vs DEPTH AT UPPER 232nd St. SITE 120 7.23 AU/Su vs DEPTH AT UPPER 232nd St. SITE 121 7.24 Nkt, NAU and Nke vs Bq AT UPPER 232nd St. SITE 122 7.25 TYPICAL CPT PROFILE AT LOWER 232nd S t . SITE ... 124 7.26 FIELD VANE STRENGTH AND SENSITIVITY PROFILES AT LOWER 232nd S t . SITE 124 7.27 Qc/Su AND Qt/Su vs DEPTH AT LOWER 232nd St. SITE 126 7.28 (Qc -oVo )/Su and (Qt- cr,o )/Su vs DEPTH AT LOWER 232nd St. SITE 127 7.29 (Qc-Ut)/Su AND (Qt"Ut)/Su vs DEPTH AT LOWER 232nd S t . SITE 128 7.30 AU/Su vs DEPTH AT LOWER 232nd St. SITE 129 7.31 Nkt, NAU and Nke vs Bq AT LOWER 232nd St. SITE 130 7.32 TYPICAL CPT PROFILE AT HANEY SLIDE SITE 131 x i i i 7.33 FIELD VANE STRENGTH AND SENSITIVITY PROFILES AT HANEY SLIDE SITE 131 7.34 Qc/Su AND Qt/Su vs DEPTH AT HANEY SLIDE SITE 133 7.35 (Qc - C s o )/Su and (Qt-av„ )/Su vs DEPTH AT HANEY SLIDE SITE 134 7.36 (Qc-Ut)/Su AND (Qt~Ut)/Su vs DEPTH AT HANEY SLIDE SITE 135 7.37 AU/Su vs DEPTH AT HANEY SLIDE SITE 136 7.38 Nkt, NAU and Nke vs Bq AT HANEY SLIDE SITE 137 7.39 USE OF EXCESS PORE PRESSURE FOR ESTIMATING UNDRAINED SHEAR STRENGTH 140 7.40 Bq vs OCR FOR 5 LOWER MAINLAND SITES 142 7.41 Nkt vs Bq FOR 5 LOWER MAINLAND SITES 143 7.42 N AU vs. Bq FOR 5 LOWER MAINLAND SITES 144 7.43 Nke vs Bq FOR 5 LOWER MAINLAND SITES 145 7.44 VANE SHEAR STRENGTH vs SLEEVE FRICTION FOR 4 LOWER MAINLAND SITES 147 7.45 Su/Fs vs DEPTH FOR 4 LOWER MAINLAND SITES . .• 147 7.46 REMOLDED SHEAR STRENGTH vs SLEEVE FRICTION FOR 4 LOWER MAINLAND SITES 1 48 7.47 Sur/Fs vs DEPTH FOR 4 LOWER MAINLAND SITES 148 7.48 ESTIMATING SENSITIVITY FROM CPT 150 x i v ACKNOWLEDGEMENTS I would l i k e to express my g r a t i t u d e to my re s e a r c h s u p e r v i s o r s , Dr. R.G. Campanella and Dr. P.K. Robertson, f o r t h e i r e x c e l l e n t guidance and support d u r i n g the course of t h i s study. I would a l s o l i k e to thank Don G i l l e s p i e f o r h i s i n v a l u a b l e a s s i s t a n c e and many h e l p f u l s uggestions. Thanks are extended to C l i f f o r d Tsang, Michael Davies, Alex Sy and K a r l Mokkelboost f o r t h e i r h elp i n c o l l e c t i n g data. I am a l s o g r a t e f u l f o r the s k i l l f u l work of A r t Brookes and the many hours of a s s i s t a n c e with the computer equipment by Glenn J o l l y . S p e c i a l thanks go to my wife Karen f o r her pa t i e n c e and support during the p r e p a r a t i o n of t h i s t h e s i s . L a s t l y , I would l i k e to express my a p p r e c i a t i o n f o r the tremendous support from my parents, to whom t h i s t h e s i s i s de d i c a t e d . The N i l c o n f i e l d vane equipment was k i n d l y p rovided by Klohn Leonoff L t d . The f i n a n c i a l support provided by N.S.E.R.C. i s g r a t e f u l l y acknowledged. 1 CHAPTER 1 INTRODUCTION 1.1 I n s i t u Measurement of U n d r a i n e d Shear S t r e n g t h In r e c e n t y e a r s t h e r e has been a growing tendancy towards the use of i n s i t u t e s t i n g t e c h n i q u e s f o r e v a l u a t i n g e n g i n e e r i n g s o i l p a r a m e t e r s . Wroth 1984 a t t r i b u t e d t h i s growth t o the r a p i d i n c r e a s e i n the v a r i e t y and q u a l i t y of i n s i t u t e s t i n g i n s t r u m e n t s i n a d d i t i o n t o our b e t t e r u n d e r s t a n d i n g of the beha v i o u r of r e a l s o i l s and the subsequent r e a l i z a t i o n of some of the l i m i t a t i o n s and i n a d e q u a c i e s of c o n v e n t i o n a l l a b o r a t o r y t e s t i n g . The h i g h c o s t of o f f s h o r e g e o t e c h n i c a l i n v e s t i g a t i o n s and the d i f f i c u l t i e s a s s o c i a t e d w i t h the r e c o v e r y of u n d i s t u r b e d samples make the use of i n s i t u t e s t i n g t e c h n i q u e s p a r t i c u l a r l y a t t r a c t i v e . For r o u t i n e i n v e s t i g a t i o n s , s e l e c t i o n of b o r e h o l e l o c a t i o n s can be more e f f i c i e n t l y p l a n n e d by employing cone p e n e t r a t i o n t e s t s d u r i n g p r e l i m i n a r y i n v e s t i g a t i o n s . W ith l o c a l e x p e r i e n c e b o r e h o l e s may not even be n e c e s s a r y . The s o i l p r o p e r t y most o f t e n measured i n the f i e l d i s the un d r a i n e d shear s t r e n g t h (Su) of c l a y s (Schmertmann 1975, Wroth 1984). U n f o r t u n a t e l y , Su i s not a unique parameter as i t depends s i g n i f i c a n t l y on the type of t e s t used, the r a t e of s t r a i n and the o r i e n t a t i o n of the f a i l u r e p l a n e s ( R o b e r t s o n and Campanella 1983). Based on l i m i t e d t e s t d a t a and a s p e c u l a t i v e approach t o a n a l y s i s , Wroth 1984 i n d i c a t e d the l i k e l y v a r i a t i o n i n u n d r a i n e d s t r e n g t h r a t i o (Su/P') w i t h f r i c t i o n a n g l e and the h i e r a r c h y f o r v a r i o u s t e s t methods ( i l l u s t r a t e d i n f i g u r e 1.1). These i d e a s , he added, were support e d by t e s t r e s u l t s o b t a i n e d by Ghionna e t 2 (S U/C7 V) DSS FV KJC a) L i k e l y v a r i a t i o n (n u n d r a i n e d s t r e n g t h r a t i o f o r d i f f e r e n t t e s t methods b) L i k e l y h i e r a r c h y of u n d r a i n e d s t r e n g t h r a t i o f o r d i f f e r e n t t e s t methods TEST TYPES PM - P r e s s u r e meter K QTC- Kg c o n s o l 1 d a t e d t r i a x i a l c o mpression FV - F i e l d Vane DSS - D i r e c t s i m p l e shear Figure 1.1 LIKELY VARIATION IN UNDRAINED STRENGTH RATIO AND THEIR HIERARCHY FOR VARIOUS TEST METHODS (adapted from Wroth 1984) METHOD RATING Dynamic Cone c Static Cone: Mechan ical B Elec. Friction B Elec. Piezo B Elec. Piezo/Friction B Acoustic Probe c Dilatometer B Vane Shear A Standard Penetration Test C Resistivity Probe C Screw Plate B Impact Cone C Borehole Shear B Menard Pressuremeter B Self Boring Pressuremeter A Self Boring Devices: Lateral Penetrometer B Shear Vane A Plate Load Tests C A - High applicability B - Moderate applicability C - Limited applicability Table 1.1 PERCEIVED APPLICABILITY OF INSITU TEST METHODS (adapted from Campanella and Robertson 1982) 3 a l . 1983. F i g u r e 1.1 a l s o i l l u s t r a t e s the importance of documenting the source of u n d r a i n e d shear s t r e n g t h d a t a . There a re s e v e r a l methods a v a i l a b l e f o r measuring the un d r a i n e d shear s t r e n g t h of c l a y i n s i t u . Campanella and Robertson 1982 p r e s e n t e d a t a b l e l i s t i n g v a r i o u s i n s i t u t e s t methods and t h e i r p e r c e i v e d a p p l i c a b i l i t y . A l i s t of the methods r e l e v a n t t o the measurement of Su i s reproduced i n t a b l e 1.1. The s u i t a b i l i t y of each method i s i n d i c a t e d by a r a t i n g of A, B or C i n d i c a t i n g h i g h , moderate and l i m i t e d a p p l i c a b i l i t y , r e s p e c t i v e l y . Campanella and Robertson based t h e i r grade on a q u a l i t a t i v e e v a l u a t i o n of the c o n f i d e n c e l e v e l a s s e s s e d f o r each method. Of the e i g h t e e n e n t r i e s o n l y two d i f f e r e n t methods have a r a t i n g of h i g h a p p l i c a b i l i t y ; the shear vane (VST) and the s e l f b o r i n g p ressuremeter (SBPMT). T h e i r h i g h r a t i n g i s a r e s u l t of t h e i r b e i n g the o n l y t e s t s t h a t a l l o w a d i r e c t e v a l u a t i o n of Su. The SBPMT, however, i s a s p e c i f i c t e s t (as d e s c r i b e d by Campanella and Robertson 1982) b e i n g r e l a t i v e l y e x p e n s i v e and slow and not a l i k e l y c a n d i d a t e f o r r o u t i n e s o i l p r o f i l i n g . On the o t h e r hand, the vane shear t e s t or the f i e l d vane (FV) i s c u r r e n t l y the most common i n s i t u method f o r measuring u n d r a i n e d shear s t r e n g t h . The FV has proven t o be a r e l i a b l e and h i g h l y r e p e a t a b l e t e s t method. One of i t s main advantages i s the g r e a t d e a l of e x p e r i e n c e t h a t has been d e v e l o p e d over i t s l o n g h i s t o r y . However, i t does s u f f e r some s e r i o u s d i s a d v a n t a g e s . The VST i s i n c r e m e n t a l w i t h t e s t s u s u a l l y b e i n g conducted a t 1 meter i n t e r v a l s . The m a t e r i a l t ype i n which the t e s t i s performed must be s p e c u l a t e d from the t e s t r e s u l t s or must be c o n f i r m e d by an 4 a d j a c e n t b o r e h o l e . V e r t i c a l i t y i s not ensured nor can i t be measured, p a r t i c u l a r l y w i t h the N i l c o n equipment. To pre v e n t damage t o the vane b l a d e s , p r e b o r i n g i s u s u a l l y r e q u i r e d through c o a r s e g r a i n e d m a t e r i a l . There are nine e n t r i e s h a v i n g a r a t i n g of moderate a p p l i c a b i l i t y . Three of which would be c l a s s i f i e d as s p e c i f i c t e s t s ; b o r e h o l e shear, Menard p r e s s u r e m e t e r , and the l a t e r a l p e netrometer. Two are i n c r e m e n t a l t e s t s ; the d i l a t o m e t e r and the screw p l a t e . The r e m a i n i n g f o u r methods r e l a t e t o the s t a t i c cone (CPT). Of t h e s e , the e l e c t r i c p i e z o / f r i c t i o n cone i s the most p r o m i s i n g . P i e z o / f r i c t i o n cone p e n e t r a t i o n t e s t s p r o v i d e a c o n t i n u o u s p r o f i l e of cone b e a r i n g , s l e e v e f r i c t i o n and dynamic pore p r e s s u r e response. The t e s t has proved t o be r a p i d , h i g h l y r e p e a t a b l e and c o s t e f f i c i e n t . R o b e r t s o n and Campanella 1983 r e p o r t t h a t s i g n i f i c a n t advances i n r e s e a r c h , development and a p p l i c a t i o n s of cone p e n e t r a t i o n t e s t i n g have been made i n r e c e n t y e a r s . The a d d i t i o n of pore p r e s s u r e measurements has g r e a t l y i n c r e a s e d our u n d e r s t a n d i n g and p o t e n t i a l of the CPT. The t e s t i s u n e q u a l l e d i n i t s a b i l i t y t o d e f i n e s o i l l a y e r b o u n d a r i e s and q u a l i t a t i v e l y e v a l u a t e m a t e r i a l t y p e s . However, because of the complex b e h a v i o u r of s o i l s and the complex changes i n s t r e s s and s t r a i n around the cone t i p , s o i l p arameters are n e c e s s a r i l y d e t e r m i n e d from e m p i r i c a l and semi-e m p i r i c a l c o r r e l a t i o n s . The e s t i m a t i o n of u n d r a i n e d shear s t r e n g t h i s one such example. The c o r r e l a t i o n has been s t u d i e d by s e v e r a l r e s e a r c h e r s i n the p a s t , however, most have f o c u s s e d o n l y on the cone 5 b e a r i n g as a means of e s t i m a t i n g Su. The c o r r e l a t i o n s u s u a l l y employ a cone f a c t o r Nk or Nc whose v a l u e s have e x h i b i t e d a tremendous range (from 5 t o 70) but a r e o f t e n r e l a t i v e l y w e l l d e f i n e d at i n d i v i d u a l s i t e s . The advent of the p i e z o cone has p e r m i t t e d a s e m i - e m p i r i c a l approach u s i n g c a v i t y e x p a n sion t h e o r y and the dynamic pore p r e s s u r e response t o be used t o e s t i m a t e Su. Non-dimensional parameters based on the excess pore p r e s s u r e s g e n e r a t e d d u r i n g p e n e t r a t i o n have been found t o p r o v i d e a p r o m i s i n g means of i n t e r p r e t i n g CPT d a t a . 1.2 Report O r g a n i z a t i o n The r e s e a r c h d e s c r i b e d i n t h i s r e p o r t was undertaken i n an attempt t o b e t t e r understand the e f f e c t s of v a r i o u s s o i l p r o p e r t i e s on the many methods t h a t have been proposed f o r e s t i m a t i n g u n d r a i n e d shear s t r e n g t h from cone p e n e t r a t i o n t e s t s . In a d d i t i o n t o the t r a d i t i o n a l methods, r e c e n t l y proposed methods of e s t i m a t i n g Su from pore p r e s s u r e d a t a a r e d i s c u s s e d . Test r e s u l t s from f i v e lower m a i n l a n d s i t e s a r e p r e s e n t e d and compared t o r e s u l t s r e p o r t e d f o r o t h e r s i t e s . Because the f i e l d vane i s the most common method of e v a l u a t i n g Su, vane shear t e s t s were used as a r e f e r e n c e f o r t h i s s t u d y . T h i s r e p o r t p r e s e n t s the r e s u l t s of t h i s i n v e s t i g a t i o n and i s d i v i d e d i n t o the seven f o l l o w i n g c h a p t e r s : Chapter 2 d e s c r i b e s the equipment used f o r t h i s s t u d y . B r i e f d e s c r i p t i o n s of the U.B.C. r e s e a r c h v e h i c l e , the d i f f e r e n t cone p e n e t r o m e t e r s , the d a t a a c q u i s i t i o n systems and the f i e l d vane equipment are p r e s e n t e d . A summary of the v a r i o u s t e s t p r o c e d u r e s used i s p r e s e n t e d 6 i n c h a p t e r 3. In p a r t i c u l a r , a d e s c r i p t i o n o f t h e methods of c a l i b r a t i o n , s a t u r a t i o n and a c t u a l f i e l d t e s t i n g a r e g i v e n . In a d d i t i o n , d e t a i l s of t h e c one p e n e t r a t i o n and f i e l d vane d a t a r e d u c t i o n a r e p r e s e n t e d . S p e c i f i c d e t a i l s o f t h e two t e s t s a r e a l s o i n c l u d e d i n o t h e r c h a p t e r s , where a p p r o p r i a t e . A r e v i e w of t h e vane s h e a r t e s t (VST) i s g i v e n i n c h a p t e r 4. V a r i o u s methods of a n a l y z i n g vane t e s t r e s u l t s and some of t h e f a c t o r s t h a t a f f e c t s u c h r e s u l t s a r e d i s c u s s e d . C h a p t e r 5 p r e s e n t s a b r i e f r e v i e w o f t h e c one p e n e t r a t i o n t e s t . S u ch t o p i c s as s o i l c l a s s i f i c a t i o n , s o i l p a r a m e t e r i n t e r p r e t a t i o n , g e n e r a t i o n of dymanic p o r e p r e s s u r e and f a c t o r s a f f e c t i n g c one p e n e t r a t i o n t e s t r e s u l t s a r e d i s c u s s e d . C h a p t e r 6 r e v i e w s t r a d i t i o n a l e m p i r i c a l methods o f c o r r e l a t i n g cone p e n e t r a t i o n t e s t r e s u l t s w i t h t h e u n d r a i n e d s h e a r s t r e n g t h of c o h e s i v e m a t e r i a l s . In a d d i t i o n , r e c e n t l y p r o p o s e d t e c h n i q u e s u s i n g CPT p o r e p r e s s u r e d a t a a r e p r e s e n t e d . Methods f o r e s t i m a t i n g vane s e n s i t i v i t y and o v e r c o n s o l i d a t i o n r a t i o from CPT a r e a l s o d i s c u s s e d . C h a p t e r 7 d e s c r i b e s , i n d e t a i l , t h e f i e l d programme c o n d u c t e d f o r t h i s s t u d y and p r e s e n t s t h e r e s u l t s o f t h e f i e l d vane and cone p e n e t r a t i o n t e s t s . A c o m p a r i s o n i s made between t h e c o r r e l a t i o n s d i s c u s s e d i n c h a p t e r 6 and t h e measured v a l u e s . C h a p t e r 8 summarizes t h e i n v e s t i g a t i o n and p r e s e n t s c o n c l u s i o n s and s u g g e s t i o n s f o r f u r t h e r r e s e a r c h . 7 CHAPTER 2 EQUIPMENT 2.1 I n t r o d u c t i o n The d e s i g n of equipment i s an i m p o r t a n t a s p e c t of any t e s t . In o r d e r t o make a proper i n t e r p r e t a t i o n of the t e s t r e s u l t s the e f f e c t s and l i m i t a t i o n s of the a p p a r a t u s must be u n d e r s t o o d . S e v e r a l t y p e s of equipment were used f o r t h i s r e p o r t : f o u r t y p e s of cones, two data a c q u i s i t i o n systems, and two f i e l d vane b o r e r s . T h i s c h a p t e r b r i e f l y d e s c r i b e s the impo r t a n t d e t a i l s of the equipment used. 2.2 Research V e h i c l e The U.B.C. g e o t e c h n i c a l r e s e a r c h v e h i c l e was used f o r a l l cone p e n e t r a t i o n t e s t s performed f o r t h i s r e p o r t . The v e h i c l e , d e s c r i b e d i n d e t a i l by Campanella and Robertson 1981, i s a s e l f -c o n t a i n e d i n s i t u t e s t i n g u n i t h o u s i n g an h y d r a u l i c l o a d i n g system and both a n a l o g and d i g i t a l e l e c t r o n i c d a t a a c q u i s i t i o n systems. The l o a d i n g system c o n s i s t s of a p a i r of h y d r a u l i c p i s t o n s which a r e l o c a t e d s y m m e t r i c a l l y about the penetrometer and cone rods and are capable of a p p l y i n g a combined maximum l o a d of 160 kN. H y d r a u l i c c o n t r o l v a l v e s are used t o manually c o n t r o l p e n e t r a t i o n and a d j u s t a b l e f l o w c o n t r o l v a l v e s r e g u l a t e the r a t e of p e n e t r a t i o n . 8 2.3 Penetrometers Four t y p e s of cone penetrometers were used: 1) U.B.C. 5 channel 10 cm 2 b e a r i n g - f r i c t i o n p i e z o m e t e r - i n c l i n a t i o n - temperature cone (UBC#4) 2) U.B.C. 6 channel 10 cm 2 a m p l i f i e d b e a r i n g f r i c t i o n - piezometer - s e i s m i c - i n c l i n a t i o n temperature cone (UBC#6) 3) U.B.C. 5 channel 15 cm 2 b e a r i n g - f r i c t i o n -piezometer - i n c l i n a t i o n - temperature - s e i s m i c cone (UBC#5) 4) M o d i f i e d Hogentogler 10 cm 2 a m p l i f i e d b e a r i n g f r i c t i o n - piezometer - i n c l i n a t i o n - te m p e r a t u r e cone The f o u r cones are i l l u s t r a t e d i n f i g u r e 2.1 and t h e i r s i m i l a r i t i e s and important d i f f e r e n c e s a re d i s c u s s e d below. A l l f o u r cones have a 60° apex a n g l e , e q u a l end a r e a f r i c t i o n s l e e v e s , and r e l o c a t a b l e pore p r e s s u r e e l e m e n t s . The d i f f e r e n t porous element l o c a t i o n s a r e i n d i c a t e d i n f i g u r e 2.2. The m o d i f i e d H o g e n t o g l e r , UBC #4, and UBC #6 cones each have a 10 cm 2 p r o j e c t e d base area and a 150 cm 2 f r i c t i o n s l e e v e . The UBC #5 cone has a 15 cm 2 p r o j e c t e d base a r e a and a 225 cm 2 f r i c t i o n s l e e v e . The 10cm 2 cones use a f r i c t i o n r e d u c e r (an e n l a r g e d s e c t i o n of cone rod a p p r o x i m a t e l y 5 cm. i n l e n g t h ) a p p r o x i m a t e l y 1 meter behind the f r i c t i o n s l e e v e . The 15 cm 2 cone i s i t s own f r i c t i o n r e d u c e r . The t h r e e U.B.C. cones are s i m i l a r i n m e c h a n i c a l d e s i g n f e a t u r i n g independent t i p and f r i c t i o n l o a d c e l l s and e a s i l y r e p l a c a b l e pore p r e s s u r e t r a n s d u c e r s which a r e l o c a t e d j u s t b e h i n d the t i p . The U.B.C. d e s i g n p e r m i t s l o a d c e l l s and t r a n s d u c e r s of d i f f e r e n t c a p a c i t i e s t o be used t h e r e b y o p t i m i z i n g the s e n s i t i v i t y of the i n d i v i d u a l measurements. 9 Figure 2.1 - SCHEMATIC DIAGRAM OF CONE PENETROMETERS USED FOR THIS REPORT 10 1. Standard UBC filter b) Porous F i l t e r L o c a t i o n s gure 2 . 2 - POROUS FILTER LOCATIONS AND TIP DESIGN 11 The d e s i g n of the UBC #4 cone has been d e s c r i b e d i n g r e a t e r d e t a i l by Campanella and Robertson 1981. The UBC #6 cone i s a UBC #4 s t y l e cone m o d i f i e d t o i n c o r p o r a t e a geophone ( v e l o c i t y t r a n s d u c e r ) or an a c c e l e r o m e t e r and an a m p l i f i e r b o a r d . The UBC #5 cone c o n t a i n s a t r i a x i a l geophone package and i s d e s c r i b e d i n g r e a t e r d e t a i l by R i c e 1984. The s e i s m i c a s p e c t s of the U.B.C. cones a r e beyond the scope of t h i s r e p o r t . The reader i s r e f e r r e d t o R i c e 1984 and Campanella and Robertson 1984 f o r more d e t a i l s . The H o g e n t o g l e r d e s i g n i s known as a s u b t r a c t i o n cone. I t f e a t u r e s the b e a r i n g and f r i c t i o n l o a d c e l l s p l a c e d i n s e r i e s . The l o a d c e l l n e a r e s t the t i p r e c o r d s the cone b e a r i n g w h i l e the o t h e r l o a d c e l l measures both the b e a r i n g and f r i c t i o n . To determine the f r i c t i o n l o a d a d i f f e r e n t i a l a m p l i f i e r c i r c u i t i s used t o e l e c t r o n i c a l l y s u b t r a c t the two measurements. A s e r i o u s consequence of t h i s d e s i g n i s t h a t both l o a d c e l l s must be of comparable c a p a c i t y which can r e s u l t i n poor s e n s i t i v i t y and r e s o l u t i o n of the much lower ( t y p i c a l l y 0.5% t o 10% of b e a r i n g ) f r i c t i o n r e a d i n g s . The cone was o r i g i n a l l y d e s i g n e d w i t h an unequal end ar e a f r i c t i o n s l e e v e , however, the H o g e n t o g l e r cone used f o r t h i s r e p o r t was m o d i f i e d t o accommodate an e q u a l end ar e a f r i c t i o n s l e e v e . I n a d d i t i o n , the f r o n t end ( t i p end) d e s i g n was made s i m i l a r t o t h a t of a U.B.C. cone t o a l l o w f o r r e l o c a t a b l e pore p r e s s u r e elements. 2.4 Data A c q u i s i t i o n Systems Two d a t a a c q u i s i t i o n systems were used t o c o l l e c t the CPT da t a f o r t h i s r e p o r t . Data from the n o n - a m p l i f i e d cones were 12 r e c o r d e d on a s i x cha n n e l Watanabe s t r i p c h a r t r e c o r d e r . S i g n a l s from the a m p l i f i e d cones were r e c o r d e d u s i n g a H o g e n t o g l e r d i g i t a l data a c q u i s i t i o n system. Both systems used a 16 co n d u c t o r c a b l e and a 10 v o l t e x c i t a t i o n . The c a b l e was co n n e c t e d t o a j u n c t i o n box mounted i n the t r u c k d i r e c t i n g the s i g n a l s t o the a p p r o p r i a t e data c o l l e c t i o n system. The n o n - a m p l i f i e d s i g n a l s were r o u t e d through a s i g n a l c o n d i t i o n i n g box c o n t a i n i n g balance and a t t e n u a t i o n r e s i s t o r s . In o r d e r t o change ranges on the s t r i p c h a r t r e c o r d e r w i t h o u t i n t r o d u c i n g an o f f s e t v o l t a g e i n d i v i d u a l b a l a n c e r e s i s i t o r s were used t o z e r o each t r a n s d u c e r . V a r i a b l e a t t e n u a t i o n r e s i s t o r s p e r m i t t e d the c h a r t r e c o r d e r t o p l o t the d a t a d i r e c t l y i n e n g i n e e r i n g u n i t s . A more complete d e s c r i p t i o n of t h i s a n a l o g d a t a r e c o r d i n g system i s g i v e n by Campanella and Robertson 1981. The a m p l i f i e d cones were used i n c o n j u n c t i o n w i t h a d i g i t a l d a t a a c q u i s i t i o n system manufactured by H o g e n t o g l e r & Co., I n c . of G a i t h e r s b u r g , M a r y l a n d . A t y p i c a l H o g e n t o g l e r system c o n s i s t s o f : 1) 5 ch a n n e l a m p l i f i e d cone 2) 10 con d u c t o r c a b l e 3) d a t a c o l l e c t i o n and s t o r a g e u n i t 4) p r i n t e r 5) H e w l e t t Packard HP 7470A p l o t t e r Some m o d i f i c a t i o n s were made t o the system i n o r d e r t o accommodate the e x t r a d e v i c e s p r e s e n t i n the U.B.C. cones. ' I n t e r n a l components of the d i g i t a l d a t a c o l l e c t i o n u n i t i n c l u d e a power s u p p l y , a microcomputer, a 12 b i t a n a l o g t o d i g i t a l (A/D) c o n v e r t e r , ROM ( r e a d o n l y memory) based s o f t w a r e , and e l e c t r o n i c i n t e r f a c e c i r c u i t s . The e x t e r n a l components i n c l u d e a 16 c h a r a c t e r LED ( l i g h t e m i t t i n g d i o d e ) d i s p l a y and 13 alphanumeric touchpad, a d i g i t a l c a s s e t t e tape d r i v e , an a n a l o g s i n g l e c hannel t h e r m a l s t r i p c h a r t r e c o r d e r , a n a l o g BNC c o n n e c t o r s and s e r i a l and p a r a l l e l i n t e r f a c e p o r t s f o r use w i t h p e r i p h e r a l d e v i c e s . D u r i n g a sounding a l l parameters ( b e a r i n g , f r i c t i o n , f r i c t i o n r a t i o , pore p r e s s u r e , pore p r e s s u r e r a t i o , i n c l i n a t i o n and temperature) a re l i s t e d by the p r i n t e r . S i n c e the f r i c t i o n s l e e v e i s l o c a t e d behind the t i p t h e r e i s a l a g between the c u r r e n t depth of p e n e t r a t i o n and t h a t f o r which the d a t a i s l i s t e d on the p r i n t e r . Because of the l a g i n the p r e s e n t a t i o n of the d a t a the therm a l s t r i p c h a r t r e c o r d e r i s r e q u i r e d i n o r d e r t o d i s p l a y the i n s t a n t a n e o u s b e a r i n g . The r e c o r d i n g system i s t r i g g e r e d when m e t a l event markers pass a p r o x i m i t y s w i t c h . The event markers a r e e q u a l l y spaced on the c i r c u m f e r e n c e of a rubber wheel which i s p l a c e d i n c o n t a c t w i t h the cone r o d s . As the rods a r e advanced the event wheel r o t a t e s thereby t r i g g e r i n g the system. Three s a m p l i n g r a t e s were a v a i l a b l e : 2.5 cm.; 5 cm.; and 10 cm. The d i g i t a l d a t a c o l l e c t e d f o r t h i s r e p o r t were sampled e v e r y 2.5 cm. G r a p h i c a l p r e s e n t a t i o n of the d a t a i s p r o v i d e d by a p l o t t i n g r o u t i n e s t o r e d i n ROM and the HP 7470A p l o t t e r . The program p l o t s each v a r i a b l e t o f i x e d s c a l e s , some of which a re i n a p p r o p r i a t e f o r the range of d a t a c o l l e c t e d i n s o f t s o i l s . To overcome t h i s problem the a u t h o r has w r i t t e n a f l e x i b l e g r a p h i c s r o u t i n e (CONEPLOT) t o be used on a microcomputer. In a d d i t i o n , CONEPLOT makes the n e c e s s a r y c o r r e c t i o n s ( d i s c u s s e d i n c h a p t e r 3) t o the d a t a p r i o r t o p l o t t i n g . 1 4 2.5 F i e l d Vanes Two types of f i e l d vanes were used; the N i l c o n vane b o r e r and the Geonor f i e l d vane. They d i f f e r p r i m a r i l y i n t h e i r method of r e c o r d i n g and i n t h e i r method of vane i n s e r t i o n . Both vane b o r e r s use s i m i l a r vanes. The two systems are i l l u s t r a t e d i n f i g u r e 2.3. The N i l c o n b o r e r c o n s i s t s of a torque l o a d i n g / r e c o r d i n g u n i t mounted on a j a c k i n g frame, 20 mm. vane r o d s , and a s p e c i a l s l i p c o u p l e . R e a c t i o n i s p r o v i d e d by augers l o c a t e d i n the c o r n e r s of the frame base. The l o a d i n g head a p p l i e s the torque t h r o u g h a c l u t c h assembly and a d e f l e c t i o n arm s c r i b e s the t o r q u e - r o t a t i o n c u r v e on a wax paper d i s k . To d e t e r m i n e the. t o r q u e r e q u i r e d t o overcome rod f r i c t i o n the s l i p c o u p l e , p l a c e d j u s t b e h i n d the vane, p e r m i t s 15° of rod r o t a t i o n b e f o r e t r a n s f e r r i n g the l o a d t o the vane. The f r i c t i o n can be d e t e r m i n e d from the t e s t r e c o r d . The s l i p c o u p l e i s i l l u s t r a t e d i n f i g u r e 2.4. The vane i s advanced u s i n g a manual crank and a c h a i n d r i v e n yoke. The vane rods a r e pushed d i r e c t l y i n t o the ground w i t h o u t ' a p r o t e c t i v e c a s i n g or s h e a t h . The c a p a c i t y of the l o a d i n g system i s 9900 Newtons f o r p e n e t r a t i o n and 113 Newton-meters f o r t o r q u e . The Geonor vane i s housed w i t h i n a p r o t e c t i v e m e t a l sheath d u r i n g p e n e t r a t i o n . A b a l l screw mechanism i s used t o advance the s h e a t h and the c a s i n g t h a t f o l l o w s i t t o a depth j u s t above t h a t d e s i r e d f o r the t e s t . An i n n e r s e t of rods are then used t o push the vane t o the r e q u i r e d d e p t h . To a p p l y and r e c o r d the l o a d a torque head i s c o n n e c t e d t o the top of the c a s i n g . A a) Geonor System b) N i l c o n System F i g u r e 2.3 - FIELD VANE SYSTEMS cn a) F i e l d Vane and S l i p Couple b) S l i p Couple D e t a i l Figure 2.4 - NILCON FIELD VANE AND SLIP COUPLE 1 7 d e f l e c t i o n n e e d l e and f o l l o w e r i n d i c a t e the maximum t o r q u e on an a r b i t r a r y s c a l e . There i s no permanent r e c o r d of the t e s t . C a l i b r a t i o n c h a r t s p r o v i d e the c o r r e l a t i o n between the s c a l e r e a d i n g and the u n d r a i n e d s t r e n g t h . 18 CHAPTER 3 TEST PROCEDURES AND DATA REDUCTION 3 .1 I n t r o d u c t i o n Another i m p o r t a n t a s p e c t of any t e s t i s the procedure by which i t i s conducted. The use of non - s t a n d a r d methods can make the i n t e r p r e t a t i o n of the r e s u l t s d i f f i c u l t , i f not i m p o s s i b l e . I t i s i m p o r t a n t t o f o l l o w a r i g o r o u s s e t of t e s t p r o c e d u r e s t o a c h i e v e r e p e a t a b l e t e s t s and t o g a i n c o n f i d e n c e i n the r e s u l t s . In t h i s r e s p e c t , cone p e n e t r a t i o n can be thought of as h a v i n g four d i s t i n c t s t e p s ( G i l l e s p i e 1981): c a l i b r a t i o n ; s a t u r a t i o n ; f i e l d t e s t i n g ; and d a t a r e d u c t i o n . T h i s c h a p t e r d e s c r i b e s the t e s t p r o c e d u r e s used f o r the cone p e n e t r a t i o n and the f i e l d vane t e s t s performed f o r t h i s r e p o r t . 3.2 C a l i b r a t i o n To m a i n t a i n a h i g h l e v e l of a c c u r a c y the v a r i o u s i n s t r u m e n t s were p e r i o d i c a l l y c a l i b r a t e d . In a d d i t i o n t o c h e c k i n g the l i n e a r i t y and s t a b i l i t y of the i n s t r u m e n t , the i n f l u e n c e of each c h a n n e l on the o t h e r cone c h a n n e l s ( c r o s s t a l k ) was r e c o r d e d . The cone l o a d c e l l s were c a l i b r a t e d i n the r e s e a r c h v e h i c l e u s i n g a c o n f i g u r a t i o n i d e n t i c a l t o t h a t used d u r i n g f i e l d t e s t i n g . F o r the n o n - a m p l i f i e d cones i t was of prime importance t o c a l i b r a t e the cone u s i n g the same 16 conductor c a b l e used d u r i n g a so u n d i n g . The vane t o r q u e r e c o r d e r s were c a l i b r a t e d i n the l a b o r a t o r y u s i n g a hanging weight and p u l l e y assembly. 19 A 7 ton l o a d i n g frame and a 10 ton h i g h q u a l i t y r e f e r e n c e l o a d c e l l were used f o r c a l i b r a t i o n of the b e a r i n g and f r i c t i o n l o a d c e l l s . A p r e s s u r e chamber h y d r a u l i c a l l y c o n n e c t e d t o a dead weight p r e s s u r e t e s t e r was used t o c a l i b r a t e the pore p r e s s u r e t r a n s d u c e r s . Large volume c o n s t a n t t emperature water baths s e r v e d as r e f e r e n c e s f o r the t h e r m i s t o r s and the i n c l i n o m e t e r s were c a l i b r a t e d a g a i n s t an a d j u s t a b l e s e t square and p r o t r a c t o r . The o u t p u t s from the r e f e r e n c e l o a d c e l l and the n o n - a m p l i f i e d cone c h a n n e l s were m o n i t o r e d on a 6 d i g i t m u l t i m e t e r h a v i n g a 1 m i c r o v o l t r e s o l u t i o n and were r e c o r d e d on a s i x cha n n e l s t r i p c h a r t r e c o r d e r . Data from the a m p l i f i e d cones were l i s t e d d i r e c t l y i n e n g i n e e r i n g u n i t s on the p r i n t e r . C a l i b r a t i o n a d j u s t m e n t s f o r the U.B.C. cones, when r e q u i r e d , were r e l a t i v e l y easy t o make compared t o those f o r the Hogentogler cone. The n o n - a m p l i f i e d cones r e q u i r e d o n l y changes i n the a t t e n u a t i o n r e s i s t o r s e t t i n g s . Changes t o the c a l i b r a t i o n of the UBC #6 cone were made by a d j u s t i n g the i n d i v i d u a l g a i n p o t e n t i o m e t e r s . The Hogentogler system uses f i x e d g a i n r e s i s t o r s and f i x e d c a l i b r a t i o n c o n s t a n t s s t o r e d i n ROM making c a l i b r a t i o n a d j u s t m e n t s d i f f i c u l t . I t was found t h a t the c a l i b r a t i o n of the cones d i d not change a p p r e c i a b l y u n l e s s they were l o a d e d near c a p a c i t y . There was no s i g n i f i c a n t c r o s s t a l k i n any of the cones. Campanella and Robertson 1982 r e p o r t t h a t when the cone i s s u b j e c t e d t o an a l l round p r e s s u r e the measurement of f r i c t i o n and b e a r i n g i s commonly i n e r r o r . For f r i c t i o n , u nbalanced f o r c e s due to unequal end areas of the f r i c t i o n s l e e v e r e s u l t i n a net f o r c e . T h e r e f o r e , o n l y e q u a l end ar e a cones were used f o r t h i s r e p o r t . 20 Even w i t h an e q u a l end a r e a s l e e v e , however, a net f r i c t i o n l o a d can e x i s t i f the pore p r e s s u r e d i s t r i b u t i o n around the s l e e v e i s uneven. Be i n g a t o t a l s t r e s s element the t i p s h o u l d r e c o r d a b e a r i n g e q u a l t o the a l l round p r e s s u r e . A c l o s e e x a m i n a t i o n of any cone w i l l r e v e a l t h a t some t r a n s f e r of the l o a d t a k e s p l a c e r e s u l t i n g i n a r e c o r d e d t i p s t r e s s l e s s than the a p p l i e d p r e s s u r e . C o r r e c t i o n s f o r these pore p r e s s u r e e f f e c t s can be made and a r e d i s c u s s e d i n more d e t a i l i n s e c t i o n 3.5.3. Campanella and Robertson 1981 a l s o p o i n t e d out t h a t l o a d c e l l s a r e o f t e n temperature dependent. U s i n g l a r g e volume c o n s t a n t temperature water bat h s the cones were c a l i b r a t e d f o r t e mperature. A f t e r r e a c h i n g t e m p e r a t u r e e q u i l i b r i u m i n the b ath the cones were q u i c k l y l o a d e d from z e r o l o a d t o near working c a p a c i t y . The UBC #6 cone was the o n l y one used t h a t was s i g n i f i c a n t l y s e n s i t i v e t o t e m p e r a t u r e . The data from t h i s cone were c o r r e c t e d u s i n g the p r o c e d u r e s d e s c r i b e d i n s e c t i o n 3.5.2. An a d j u s t a b l e set square was used t o c a l i b r a t e the i n c l i n o m e t e r s . The cones were p l a c e d on the set square and the output of the i n c l i n o m e t e r s were m o n i t o r e d as the a n g l e of i n c l i n a t i o n was changed. Because a l l p e n e t r a t i o n t e s t s performed f o r t h i s r e p o r t were near v e r t i c a l c o r r e c t i o n s were unnecessary. 3.3 S a t u r a t i o n For proper i n t e r p r e t a t i o n of the pore p r e s s u r e p r o f i l e s complete s a t u r a t i o n of the p i e z o m e t e r t i p was e s s e n t i a l . P r i o r to each sounding the porous element and the c a v i t y between the f i l t e r and the t r a n s d u c e r were c a r e f u l l y s a t u r a t e d w i t h g l y c e r i n . Because i t d e v e l o p s a h i g h a i r e n t r y t e n s i o n and i s 21 m i s c i b l e w i t h w a t e r , g l y c e r i n has been used as a s a t u r a t i n g f l u i d at U.B.C. f o r s e v e r a l y e a r s . In p r e p a r a t i o n f o r s a t u r a t i o n a cup was p l a c e d over the i n v e r t e d cone and s e a l e d w i t h an o-r i n g . With the f i l t e r , t i p , and a c c e s s screw removed, the cup was f i l l e d w i t h g l y c e r i n . A i r bubbles were e x p e l l e d by i n j e c t i n g the c a v i t y w i t h g l y c e r i n from a hypodermic s y r i n g e . When no more bubbles c o u l d be seen the f i l t e r was put i n t o p l a c e and the screw and t i p were r e p l a c e d . F i g u r e 3.1 i l l u s t r a t e s the s a t u r a t i o n system used. 3.4 F i e l d Cone P e n e t r a t i o n T e s t i n g P r i o r t o s a t u r a t i n g the cone and a f t e r a l l o w i n g the e l e c t r o n i c systems t o warm up, each c h a n n e l (except f o r temperature) was checked by a p p l y i n g s m a l l l o a d s t o the cone. A f t e r s a t u r a t i o n the cone was a t t a c h e d t o the f i r s t cone rod and hung from the l o a d i n g chuck f o r a l i g n m e n t . When the cone was p r o p e r l y a l i g n e d i t was lowered t o j u s t above the ground s u r f a c e and h e l d t h e r e u n t i l the cone came i n t o e q u i l i b r i u m w i t h the s u r r o u n d i n g a i r t e m p e r a t u r e . Once i n e q u i l i b r i u m , the e x c i t a t i o n v o l t a g e was checked and the cone c h a n n e l s were z e r o e d . For the a m p l i f i e d cones the b a s e l i n e r e a d i n g s were t a k e n . P e n e t r a t i o n began a f t e r the z e r o l o a d i n f o r m a t i o n was r e c o r d e d . A l l t e s t s were performed a t a p e n e t r a t i o n r a t e of 2 cm/s. Rod changes o c c u r r e d a t one meter i n t e r v a l s d u r i n g which time pore p r e s s u r e d i s s i p a t i o n s were r e c o r d e d . An i m p o r t a n t d e t a i l i n the t e s t p r o c e d u r e was t o check the z e r o e s f o r each c h a n n e l a f t e r the c o m p l e t i o n of a h o l e . To do t h i s , the e l e c t r o n i c s were l e f t on as the rods were withdrawn. 22 F i g u r e 3.1 - S A T U R A T I O N P R O C E D U R E 23 A f t e r removing the cone from the h o l e i t was h e l d v e r t i c a l l y j u s t above the ground s u r f a c e i n o r d e r t o r e c o r d the z e r o l o a d i n f o r m a t i o n . Zero s h i f t s were o c c a s i o n a l l y e n c o u n t e r e d . The t h e r m i s t o r data i n d i c a t e d t h a t the s h i f t s were p r i m a r i l y due t o temperature changes. C o r r e c t i o n s were made t o the data t o account f o r the temperature e f f e c t s . 3.5 CPT Data R e d u c t i o n The method of da t a r e d u c t i o n was dependent upon the type of dat a a c q u i s i t i o n system used. The d i g i t a l l y c o l l e c t e d d a t a was t r a n s f e r r e d from the Ho g e n t o g l e r u n i t t o an IBM XT microcomputer f o r m a n i p u l a t i o n and p l o t t i n g . The a n a l o g r e c o r d s were d i g i t i z e d u s i n g a g r a p h i c s t a b l e t and the U.B.C. mainframe computer. In a d d i t i o n t o c o r r e c t i n g f o r te m p e r a t u r e and pore p r e s s u r e e f f e c t s , the data r e q u i r e d m a n i p u l a t i o n t o e l i m i n a t e i n c o r r e c t d a t a a t rod breaks and s p u r i o u s d a t a due to e l e c t r i c a l power s p i k e s . For i n t e r p r e t a t i o n of the d a t a v a r i o u s parameters a l s o needed t o be c a l c u l a t e d . A d i s c u s s i o n of the d i f f e r e n t c o r r e c t i o n s a p p l i e d t o the d a t a and the v a r i o u s c a l c u l a t e d parameters f o l l o w s . 3.5.1 Unwanted Data At each rod break the a n a l o g d a t a r e c o r d e d the drop i n b e a r i n g l o a d as the l o a d i n g head was l i f t e d o f f the r o d s . T h i s d a t a was s i m p l y i g n o r e d d u r i n g d i g i t i z i n g . Due t o power surges and f o r o t h e r e l e c t r i c a l reasons the d i g i t a l system o c c a s i o n a l l y r e c o r d e d s p u r i o u s d a t a . A t e x t e d i t o r was used t o remove t h e s e d a t a from the r e c o r d . 24 3.5.2 Temperature C o r r e c t i o n s Because the cones had been c a l i b r a t e d f o r the e f f e c t s of tem p e r a t u r e , c o r r e c t i o n s t o the d a t a were e a s i l y made. The temperature c a l i b r a t i o n s i n d i c a t e d t h a t the l o a d c e l l s underwent a z e r o s h i f t r a t h e r than a change i n t h e i r c a l i b r a t i o n . For the most p a r t , o n l y b e a r i n g v a l u e s were a f f e c t e d . To c o r r e c t the an a l o g d a t a , the depth a x i s was s i m p l y s h i f t e d the a p p r o p r i a t e amount d u r i n g d i g i t i z i n g . The d i g i t a l d a t a were c o r r e c t e d u s i n g a program (CPTCORR) which a d j u s t e d the d a t a f o r each c h a n n e l a c c o r d i n g t o the l o a d c e l l temperature c a l i b r a t i o n , the r e c o r d e d t e m p e r a t u r e , and the b a s e l i n e t e m p e r a t u r e . Temperature c o r r e c t i o n s were q u i t e s u b s t a n t i a l i n s o f t s o i l s as i n d i c a t e d i n f i g u r e 3.2. 3.5.3 Pore P r e s s u r e C o r r e c t i o n s Both b e a r i n g and f r i c t i o n measurements were a f f e c t e d by pore p r e s s u r e . As d i s c u s s e d p r e v i o u s l y , the b e a r i n g l o a d c e l l does not r e c o r d a l l of the pore p r e s s u r e a c t i n g on the t i p and the f r i c t i o n s l e e v e r e a d i n g s can be i n e r r o r because of end area e f f e c t s . B e a r i n g The c o n f i g u r a t i o n of the f r i c t i o n s l e e v e and b e a r i n g l o a d c e l l l e a d s t o an i n c o r r e c t i n t e r p r e t a t i o n of the s t r e s s a p p l i e d to the t i p due t o pore p r e s s u r e . A l t h o u g h the l o a d c e l l r e c o r d s the c o r r e c t f o r c e a c t i n g on i t , i t i s i n c o r r e c t l y assumed t o be a c t i n g over an a r e a e q u a l t o t h a t of the t i p area (10 cm 2 or 15 cm 2 depending on the cone used). An e x a m i n a t i o n of f i g u r e 2.1 Figure 3.2 - TEMPERATURE AND PORE PRESSURE EFFECTS ON CONE BEARING 26 i n d i c a t e s t h a t the e f f e c t i v e a r e a of the l o a d c e l l i s l e s s than t h a t of the t i p because of the presence of the f r i c t i o n s l e e v e . The b e a r i n g l o a d due t o s o i l s t r e s s i s , however, c o r r e c t l y i n t e r p r e t e d . D u r i n g c a l i b r a t i o n the cone i s s u b j e c t e d t o an a l l round p r e s s u r e t o determine the r a t i o of the t o t a l a p p l i e d p r e s s u r e t h a t i s r e c o r d e d by the t i p . T h i s r a t i o has been termed 'the net area r a t i o ' by Campanella and Robertson 1981. One needs o n l y t o add t o the r e c o r d e d p r e s s u r e t h a t f r a c t i o n which was not r e c o r d e d . Campanella and Robertson term the c o r r e c t e d b e a r i n g , Qt, and c a l c u l a t e i t a c c o r d i n g t o the f o l l o w i n g e x p r e s s i o n : Qt=Qc+(1-a)-U 3.1 where Qt = c o r r e c t e d b e a r i n g Qc = r e c o r d e d b e a r i n g a = net a r e a r a t i o U = pore p r e s s u r e measured be h i n d the t i p To p r o p e r l y c o r r e c t the b e a r i n g the pore p r e s s u r e must be r e c o r d e d behind the t i p . I f pore p r e s s u r e s a r e measured on the f a c e they must be c o n v e r t e d t o an e q u i v a l e n t b e h i n d the t i p pore p r e s s u r e b e f o r e c a l c u l a t i n g Qt. S e c t i o n 5.4 d e s c r i b e s how one might make t h i s c o n v e r s i o n . Pore p r e s s u r e c o r r e c t i o n s were s i g n i f i c a n t i n s o f t n o r m a l l y c o n s o l i d a t e d s o i l s as shown i n f i g u r e 3.2. F r i c t i o n I f the two ends of the f r i c t i o n s l e e v e a r e of d i f f e r e n t c r o s s s e c t i o n a l a r e a s the pore p r e s s u r e s w i l l a p p l y a net f o r c e on the s l e e v e . Depending upon which end i s l a r g e r , the net f o r c e may i n c o r r e c t l y be a t t r i b u t e d t o s o i l f r i c t i o n or i t may s u b t r a c t from the a c t u a l f r i c t i o n . I n the l a t t e r -case, n e g a t i v e f r i c t i o n v a l u e s have been obs e r v e d . Even i f the ends of the 27 f r i c t i o n s l e e v e are of e q u a l a r e a , a net f o r c e can r e s u l t i f the pore p r e s s u r e d i s t r i b u t i o n about the s l e e v e i s not u n i f o r m . The d i s t r i b u t i o n of pore p r e s s u r e s about the cone i s d i s c u s s e d i n s e c t i o n 5.4. 3.5.4 F r i c t i o n R a t i o F r i c t i o n r a t i o (Rf) i s a c a l c u l a t e d parameter t h a t i s used as an i n d i c a t o r of s o i l b e h a v i o u r t y p e . I t i s a d i m e n s i o n l e s s r a t i o and i s d e f i n e d a s : The e x a c t l o c a t i o n of where the f r i c t i o n a c t s i s unknown, however, i t i s u s u a l l y assumed t o a c t a t the c e n t e r of the s l e e v e , a p p r o x i m a t e l y 1Ocm beh i n d the t i p . The H o g e n t o g l e r u n i t assumes the f r i c t i o n / b e a r i n g o f f s e t t o be 1Ocm and a u t o m a t i c a l l y makes t h i s adjustment when r e c o r d i n g the d a t a . Because the d i g i t a l d a t a i s r e c o r d e d a t d i s c r e t e i n t e r v a l s the f r i c t i o n r a t i o s a r e e a s i l y c a l c u l a t e d . The a n a l o g b e a r i n g , f r i c t i o n and pore p r e s s u r e r e c o r d s a r e d i g i t i z e d a c c o r d i n g t o the peaks and v a l l e y s i n t h e i r r e s p e c t i v e r e c o r d s and, t h u s , the t h r e e parameters a r e not n e c e s s a r i l y d i g i t i z e d a t c o r r e s p o n d i n g d e p t h s . The f r i c t i o n r a t i o s were c a l c u l a t e d a t the depths of the o f f s e t f r i c t i o n v a l u e s u s i n g l i n e a r l y i n t e r p o l a t e d b e a r i n g v a l u e s . Rf=Fs«100% Q 3.2 where Fs Q s l e e v e f r i c t i o n cone b e a r i n g Qc or Qt 3.5.5 D i f f e r e n t i a l Pore P r e s s u r e R a t i o A l t h o u g h pore p r e s s u r e i s an i n d i c a t i o n of s o i l t y p e , 28 Campanella and Robertson 1981 suggested that d i f f e r e n t i a l pore pressure was more fundamental. The d i f f e r e n t i a l pore pressure i s d e f i n e d as: AU=Ud-Ue 3.3 where Ud = the dynamic pore pressure ( i . e . that measured during a sounding) Ue = e q u i l i b r i u m pore pressure An e q u i l i b r i u m pore pressure p r o f i l e can be determined by conducting complete pore pressure d i s s i p a t i o n s at s e l e c t e d depths. As a f i r s t approximation, a h y d r o s t a t i c d i s t r i b u t i o n i s o f t e n assumed. Campanella and Robertson 1981 r e p o r t that the d i f f e r e n t i a l pore pressure r a t i o (AU/Q) i s a good i n d i c a t o r of s o i l type and p o s s i b l y s t r e s s h i s t o r y . The d i f f e r e n t i a l pore pressure r a t i o s c a l c u l a t e d from the analog records were done so at the depths of the pore pressure measurements using l i n e a r l y i n t e r p o l a t e d bearing v a l u e s . 3.6 F i e l d Vane T e s t i n g The Geonor f i e l d vane t e s t s at McDonald Farm (Richmond, B.C.) were performed by the N a t i o n a l Research C o u n c i l (NRC), D i v i s i o n of B u i l d i n g Research under the s u p e r v i s i o n of the author. Vane t e s t s were conducted at 1 meter i n t e r v a l s with remolded t e s t s being performed at each t e s t depth a f t e r 20 turns of the vane rods. The N i l c o n vane t e s t s were performed by the author and a s s i s t a n t s . The m a j o r i t y of the t e s t s were performed at 0.5 meter i n t e r v a l s at shallow depths ( <l0m ) and at 1 meter i n t e r v a l s at g r e a t e r depths. Remolded t e s t s were u s u a l l y performed at a l t e r n a t e t e s t s depths a f t e r 20 turns of the vane rods. A l l vane t e s t s were conducted at a s t r a i n r a t e 29 a p p r o x i m a t e l y e q u a l t o t h e g e n e r a l l y a c c e p t e d s t a n d a r d r a t e o f 6° p e r m i n u t e . Because t h e s l i p c o u p l e was d e s i g n e d t o r e t u r n t h e vane t o t h e c o r r e c t p o s i t i o n a f t e r 1 meter of p e n e t r a t i o n , s p e c i a l a t t e n t i o n was p a i d t o r o t a t i n g t h e vane r o d s t o r e g a i n t h e 15° s l i p b e f o r e a d v a n c i n g t h e v a n e . Two t o t h r e e vane t e s t s were r e c o r d e d on a s i n g l e wax d i s k . To a v o i d c o n f u s i o n i t was v e r y i m p o r t a n t t o document e a c h t e s t r e c o r d on t h e d i s k i m m e d i a t e l y f o l l o w i n g a t e s t . 3.7 R e d u c t i o n of Vane D a t a A l l u n d r a i n e d s t r e n g t h s were d e t e r m i n e d u s i n g t h e s t a n d a r d e x p r e s s i o n : Su= 6T 3.4 7TTD 3 where Su = u n d r a i n e d s h e a r s t r e n g t h T = a p p l i e d t o r q u e D = d i a m e t e r o f t h e vane T h i s e x p r e s s i o n a p p l i e s o n l y f o r a vane h a v i n g a h e i g h t t o d i a m e t e r r a t i o of 2. T h e r e has been much d i s c u s s i o n by r e s e a r c h e r s (see c h a p t e r 4) as t o t h e c o r r e c t i n t e r p r e t a t i o n o f t h e vane t e s t , however, most e n g i n e e r s use t h e above e x p r e s s i o n . C o r r e l a t i o n c h a r t s b a s e d on t h e above e x p r e s s i o n were u s e d t o d e t e r m i n e t h e u n d r a i n e d s t r e n g t h from t h e peak r e a d i n g s on t h e Geonor e q u i p m e n t . An example of a N i l c o n t e s t r e c o r d i s shown i n f i g u r e 3.3. The r a d i a l d i s t a n c e f r o m t h e o u t e r z e r o l i n e m u l t i p l i e d by a c a l i b r a t i o n c o n s t a n t (K) g i v e s t h e a p p l i e d t o r q u e . The d i s t a n c e s Mf and Mp r e p r e s e n t t h e r o d f r i c t i o n and t h e peak a p p l i e d t o r q u e , r e s p e c t i v e l y . The v a l u e (Mf-Mp)«K r e p r e s e n t s t h e t o r q u e 30 Su = (Mf - Mp) x K x a where: Su - u n d r a i n e d s t r e n g t h Mf - as shown i n f i g u r e Mp - as shown i n f i g u r e K - t o r q u e head s p r i n g c o n s t a n t a - vane c o n s t a n t (6/(77rD 3)) F i g u r e 3.3 - EXAMPLE OF A NILCON TEST RECORD 31 a p p l i e d to the vane and i s s u b s t i t u t e d f o r T i n equation 3.4. The determination of undrained s t r e n g t h i s s e n s i t i v e to the a b i l i t y to a c c u r a t e l y d e f i n e the rod f r i c t i o n . I t i s t h e r e f o r e important to use the l a r g e s t p o s s i b l e vane to maximize the output on the d i s k . 32 CHAPTER 4 A REVIEW OF THE VANE SHEAR TEST 4.1 Introduct ion The f i e l d vane t e s t was in t r o d u c e d i n Sweden 60 years ago (Bjerrum and F l o d i n 1960) and has been used by engineers in i t s present form s i n c e 1948 (Cadling and Odenstad 1950). Because of i t s s i m p l i c i t y , r e p e a t a b i l i t y and r e l a t i v e l y low c o s t of o p e r a t i o n i t has found wide spread use i n p r a c t i c e . A great d e a l of experience has been gained with i t s use i n the design of sl o p e s , embankments, foundations and other e n g i n e e r i n g s t r u c t u r e s . I t has only been i n the l a s t decade or two that engineers have begun to c r i t i c a l l y study the vane shear t e s t ; Aas 1965, F l a a t e 1966, Bjerrum 1972 and 1973, Arman et a l . 1975, Schmertmann 1975, Donald et a l . 1977, Menzies and M e r r i f i e l d 1980, Wroth 1984 and o t h e r s . These s t u d i e s have l e d to a b e t t e r a p p r e c i a t i o n of some of the f a c t o r s that i n f l u e n c e the vane t e s t , however, the a b i l i t y to i n c o r p o r a t e a l l of these f a c t o r s and other u n q u a n t i f i a b l e s o i l c h a r a c t e r i s t i c s i n t o the a n a l y s i s of the vane i s s t i l l incomplete. In l i g h t of t h i s r e l a t i v e l y recent r e s e a r c h i t i s f e l t that a b r i e f review of the main f a c t o r s i n f l u e n c i n g vane r e s u l t s i s a p p r o p r i a t e . 4.2 E v a l u a t i o n of Undrained Shear Strength The t r a d i t i o n a l method of i n t e r p r e t i n g the vane t e s t assumes that f a i l u r e occurs over the c y l i n d r i c a l s u r f a c e c i r c u m s c r i b e d by the vane with the shear s t r e s s being u n i f o r m l y 33 d i s t r i b u t e d on the top, bottom, and s i d e s of the c y l i n d e r . The m a t e r i a l i s assumed to be i s o t r o p i c ; the peak shear s t r e s s being equal to the undrained s t r e n g t h , Su. These b a s i c assumptions lead to e x p r e s s i o n 4.1, the d e r i v a t i o n of which i s shown i n f i g u r e 4.1. Su= 6M 4.1 TTD 2H(3+D/H) where Su - undrained shear s t r e n g t h M - measured peak torque D - diameter of vane H - height of vane ( c o n s i s t e n t u n i t s ) The most commonly used vane, and that which i s the recommended standard a c c o r d i n g to ASTM (ASTM D2573), has a height to diameter r a t i o (H/D) of 2. E x p r e s s i o n 4.1 thereby reduces to the standard e x p r e s s i o n shown e a r l i e r as 3.4 and repeated here: Su= 6M 3.4 7TTD3 I t i s equation 3.4 that i s i m p l i e d i n the method of vane i n t e r p r e t a t i o n d e s c r i b e d by ASTM D2573 and in the manuals accompanying vane equipment. I t has r e c e n t l y been showen by Donald et a l . 1977 and Menzies and M e r r i f i e l d 1980 that the d i s t r i b u t i o n of shear s t r e s s i s l i k e l y to be non-uniform, p a r t i c u l a r y on the ends of the vane. Using a three dimensional l i n e a r e l a s t i c f i n i t e element f o r m u l a t i o n , Donald et a l . d e r i v e d the s t r e s s d i s t r i b u t i o n shown in f i g u r e 4.2 f o r a plane midway between the blades. T h e i r r e s u l t s i n d i c a t e that a uniform d i s t r i b u t i o n of shear s t r e s s i s a reasonable assumption on the v e r t i c a l plane, however, the shear s t r e s s e s on the h o r i z o n t a l plane increase from zero at the a x i s of r o t a t i o n to a maximum at the blade 34 On End (Horizontal Plane) On V e r t i c a l Surface dMQ=r rdrd0«r dMv=rv dA «R f d M a = T a j V d r d S Ma = r a R_32jr 3 r a =Su at peak Me = 7 r D 3 S u 12 JdMv = i;R 2/ H; S"dSdh o o Mv=rv R22TTH TV =Su at Peak Mv = irDJHSu 2 M=M v +2M e M=SuirD 2H(3+D) 6 H F i g u r e 4.1 - STANDARD ANALYS IS OF THE VANE SHEAR TEST 35 Figure 4.2 - SHEAR STRESS DISTRIBUTION ON A PLANE MIDWAY BETWEEN VANE BLADES USING A 3D FINITE ELEMENT ANALYSIS (adapted from Donald et a l . 1977) a - v e r t i c a l blade edge _ hor izontal blade edge Note: shear s t resses have been scaled to g ive equal torque Figure 4.3 - DISTRIBUTIONS OF EQUIVALENT SHEAR STRESS ON A VERTICAL AND A HORIZONTAL BLADE EDGE (adapted from Menzies and Merrifield 1980) 36 edge. Menzies and M e r r i f i e l d i n s t r u m e n t e d a vane w i t h c l o s e f i t t i n g s t r a i n gauged c a n t i l e v e r s a l o n g the top edge of one bl a d e and a l o n g the v e r t i c a l edge of a n o t h e r . They used t h i s vane to perform t e s t s i n a f i n e sand and i n an o v e r c o n s o l i d a t e d c l a y . T h e i r r e s u l t s , shown i n f i g u r e 4.3, appear t o be s i m i l a r t o those of Donald et a l . i n d i c a t i n g t h a t the d i s t r i b u t i o n a l o n g the t o p of the blade i s indeed non-uniform. I t i s encouraging t o see the agreement between the a n a l y t i c a l a n a l y s i s and the f i e l d t e s t i n g , however, one might expect the e l a s t i c a n a l y s i s t o a d e q u a t e l y p r e d i c t the b e h a v i o u r of an o v e r c o n s o l i d a t e d c l a y and, t h u s , i t would be v e r y i n t e r e s t i n g t o see r e s u l t s from t e s t s i n a s o f t n o r m a l l y c o n s o l i d a t e d c l a y . As Wroth 1984 p o i n t s o u t , the r e s u l t s j u s t p r e s e n t e d suggest t h a t the shear s t r e s s d i s t r i b u t i o n on the h o r i z o n t a l p l a n e s can be approximated by the e x p r e s s i o n : n •T = R where T - shear s t r e s s T M - maximum shear s t r e s s R - r a d i u s of vane r - r a d i a l d i s t a n c e from a x i s of r o t a t i o n U s i n g t h i s d i s t r i b u t i o n e x p r e s s i o n 4.1 becomes Su= 2M(3+n) 4.3 TTD2H( (3+n)+D/H) For the u s u a l case where H/D=2, e q u a t i o n 4.3 reduces t o : Su= 2(3+n)M 4.4 TTD3 (2) (3.5+n) Based on the r e s u l t s of Menzies and M e r r i f i e l d 1980, Wroth 1984 r e p o r t e d t h a t n i s a p p r o x i m a t e l y 5. E x p r e s s i o n 4.4 t h e r e b y y i e l d s : Su= 16M 4.5 177TD3 37 Comparing equation 4.5 to 3.4 there i s an almost 10% underestimation of the undrained shear s t r e n g t h using the standard a n a l y s i s i f one accepts that n i s 5. Seve r a l other assumptions are made i n the a n a l y s i s of the vane and are d i s c u s s e d in the f o l l o w i n g s e c t i o n s : 1) S t r e s s c o n d i t i o n s remain unchanged d u r i n g vane i n s e r t ion 2) the s o i l around the vane remains undisturbed 3) shearing takes p l a c e under undrained c o n d i t i o n s 4) the shear s t r e n g t h i s f u l l y m o b i l i z e d ( s i m u l t a n -eously) on a l l s u r f a c e s 5) the s o i l i s i s o t r o p i c with r e s p e c t to s t r e n g t h 6) there i s no p r o g r e s s i v e f a i l u r e 4.3 E f f e c t s of A n i s o t r o p y The e f f e c t of a n i s o t r o p y i s one of the most commonly s t u d i e d aspects of the vane t e s t . The r e s i s t a n c e to shear can be separated i n t o the c o n t r i b u t i o n s by each s u r f a c e of the c y l i n d e r . Denoting the shear s t r e n g t h on the h o r i z o n t a l s u r f a c e as Sh and that on the v e r t i c a l face as Sv e q u i l i b r i u m i s s a t i s f i e d by the equation: _2M_ = Sv + Sh-D 4.6 7rD 2H (3+n)H Equation 4.6 i n d i c a t e s that f o r the standard vane (H/D=2) the v e r t i c a l face c o n t r i b u t e s 86% to 94% of the shear r e s i s t a n c e f o r values of n=0 (uniform shear d i s t r i b u t i o n ) and n=5, r e s p e c t i v e l y . In other words, the vane t e s t i s s t r o n g l y dominated by the a v a i l a b l e s t r e n g t h on the v e r t i c a l plane. By using vanes of v a r i o u s p r o p o r t i o n s s e v e r a l researchers have s t u d i e d the e f f e c t s of a n i s o t r o p y ; Aas 1965 and 1967, Eide 1968, B l i g h t 1970, Wiesel 1973, Bjerrum 1973, Richardson et a l . 38 1975, Donald et a l . 1977, and Poplin et a l . 1978. At least two torque measurements using vanes of different H/D ratios are required at each test depth to solve for Sh and Sv in equation 4.6. Wiesel 1973 recommends using vanes of equal diameter but different lengths to eliminate the problem of the peak strengths not being simultaneously mobilized on the horizontal and vertical planes. Richardson et a l . 1975 used diamond shaped vanes (figure 4.4) to determine the anisotropy on planes at various angles. The results from their tests are shown in figure 4.5 and they indicate that the greatest strengths are observed on the vertical plane and the minimum strengths occur on the horizontal planes. They reported that the strengths observed on planes at various angles describe an ellipse having Sv as the radius on the major axis and Sh the radius on the minor axis. Bjerrum 1973 plotted the ratio of Sh/Sv for several clays against their plasticity index concluding that the ratio decreases with increasing pl a s t i c i t y . In his state of the art address Bjerrum 1973 presents a rationale as to why this relationship should exist. Richardson et a l . 1975 added their data to Bjerrum's figure and this is shown in figure 4.6. The trend of decreasing Sh/Sv ratio with increasing PI was also observed, however, they suggest that Bjerrum's curve should be adjusted. Donald et a l . 1977 attempted to analyse the effect of anisotropy by recording the f u l l torque-rotation curves for vanes of various H/D ratios but of equal diameters. From two curves they inferred the side resistance (and thus the end resistance) by multiplying the difference between the two curves 39 © © F i g u r e 4.4 - VARIOUS VANE CONFIGURATIONS USED TO MEASURE STRENGTH ANISOTROPY (adapted from R i c h a r d s o n e t a l . 1975) Vane sheer strength ( kg /cm) 0. O P S OIO 0 J 5 0 20 0_25 F i g u r e 4.5 - VANE SHEAR STRENGTHS ON PLANES AT VARIOUS ANGLES (adap t e d from R i c h a r d s o n e t a l . 1975) 40 Symbol 1 2 .3 CO .C tn 1 1 Cloy Manglerud (Silty Quick) Lierstranda ( — do—) KjeU a s ( Quick ) Lean Drammen (Silty Sens) Plastic Drammen Loan Drammen ( D«ep ) Bangkok ( Eioe ) "I Reference Bjerrum (1973) do — do . do — do — do d o — Ska-Eck^(Avg.&xribJctt)Wiesel (1973). Bangpli ( Silty- Sens ) Memon (1973) © Bjerrum'* Relationship * 7 O 40 60 Plasticity Index (%) 80 100 F i g u r e 4 . 6 - PLOT OF RATIO OF UNDRAINED SHEAR STRENGTHS IN HORIZONTAL AND V E R T I C A L DIRECTIONS VS P L A S T I C I T Y INDEX ( a d a p t e d f r o m R i c h a r d s o n e t a l . 1975) 41 by the ratio of the length of the f i r s t vane to the difference in the lengths of the two vanes. Their analysis indicated that the ends reached their peak strengths before the sides which would mean that the peak torque would be dominated by the strength of the vertical plane even more than considered previously. However, their a b i l i t y to reasonably estimate the Sh/Sv ratio met with limited success suggesting that this method is unreliable. Most methods used to estimate the Sh/Sv ratio assume a uniform distribution of stress on both planes. As shown earlier, this may be a reasonable assumption on the vertical planes but is probably not very accurate for the horizontal planes. This assumption has a significant effect on the Sh/Sv ratio. By solving expression 4.3 simultaneously for tests that have recorded different torques T, and T 2, used vanes of different diameters D, and D 2, and different vane heights H, and H2 i t can be shown that: Sh = (3+n)0 4.7 Sv = 2T, - fD,| 0 4.8 where 0= / 2T2 - 2T, \ H2H, ^ D , 2 H , TTD^H" j'H,D 2-H 2D 1 The value of n does not affect the estimation of Sv but i t does have a significant effect on Sh. 4.4 Rate Effects It has been commonly found that the undrained shear strength is dependent upon the rate of shear; Aas 1965, Flaate 1966, Blight 1968, Bjerrum 1972, Berre and Bjerrum 1973, Wiesel 42 1973. T h i s e f f e c t i s i l l u s t r a t e d i n f i g u r e s 4.7 and 4.8. F i g u r e 4.7 shows the v a r i a t i o n i n undrained s t r e n g t h with depth at d i f f e r e n t r a t e s of vane r o t a t i o n whereas f i g u r e 4.8 shows the c o r r e l a t i o n between shear s t r e s s l e v e l and time to f a i l u r e f o r undrained t r i a x i a l compression t e s t s e s t a b l i s h e d by Berre and Bjerrum 1973 f o r Drammen c l a y . Bjerrum 1972 s t a t e s that the ra t e e f f e c t i s a s s o c i a t e d with the cohesive component of shear and that there are good reasons to assume that the rate e f f e c t should i n c r e a s e with i n c r e a s i n g p l a s t i c i t y of the c l a y . Tests by Aas 1965, F l a a t e 1966, Torstensson 1977, and Kimura and S a i t o h 1983 i n d i c a t e that the shear s t r e n g t h can vary with the time delay between vane i n s e r t i o n and the s t a r t of sh e a r i n g . In the r e s u l t s presented by F l a a t e 1966 a time delay of only 15 minutes l e d to an increase in the undrained s t r e n g t h by more than 10%. This e f f e c t i s r e l a t e d to the d i s s i p a t i o n of the pore pressures generated during i n s e r t i o n of the vane r e s u l t i n g in the c o n s o l i d a t i o n of the surrounding c l a y . B l i g h t 1968 proposed a method by which the p r e s e l e c t i o n of a t e s t d u r a t i o n can be made to ensure that the vane t e s t in s i l t y s o i l s i s conducted under undrained c o n d i t i o n s . 4.5 Disturbance Due to Vane I n s e r t i o n I t i s g e n e r a l l y assumed that the s o i l remains undisturbed during vane i n s e r t i o n , however, i t has been documented that high pore pressures can be generated and that the i n s e r t i o n of the blades can p a r t i a l l y d e s t r o y the n a t u r a l s o i l s t r u c t u r e . Both of these e f f e c t s can r e s u l t i n a measured undrained shear s t r e n g t h l e s s than the a c t u a l i n s i t u v a l u e . 43 SHEAR STRENGTH, kN/m 2 0 10 20 30 F i g u r e 4 . 7 - V A R I A T I O N WITH DEPTH OF UNDRAINED SHEAR STRENGTH AT D I F F E R E N T RATES OF ROTATION ( a d a p t e d f r o m W i e s e l 1973) F i g u r e 4 . 8 - CORRELATION BETWEEN SHEAR STRESS L E V E L AND T IME TO F A I L U R E FROM UNDRAINED T R I A X I A L COMPRESSION T E S T S ON DRAMMEN CLAY ( a d a p t e d f r o m B e r r e a n d B j e r r u m 1973) 4 4 L a R o c h e l l e e t a l . 1 9 7 3 p e r f o r m e d t e s t s u s i n g f o u r d i f f e r e n t t h i c k n e s s e s o f v a n e b l a d e s t o e v a l u a t e t h e e f f e c t o f d i s t u r b a n c e d u e t o v a n e i n s e r t i o n . B y p l o t t i n g t h e m e a s u r e d S u v a l u e s a g a i n s t t h e v a n e p e r i m e t e r r a t i o ( r a t i o o f 4 t i m e s t h e b l a d e t h i c k n e s s e t o t h e v a n e p e r i m e t e r - 4 e / 7 r D ) h e w a s a b l e t o e x t r a p o l a t e t h e r e s u l t s t o e s t i m a t e t h e s h e a r s t r e n g t h c o r r e s p o n d i n g t o a z e r o b l a d e t h i c k n e s s . H i s r e s u l t s i n d i c a t e d t h a t t h e d i s t u r b a n c e d u e t o t h e i n s e r t i o n o f t h e s t a n d a r d v a n e r e d u c e d t h e a p p a r e n t s t r e n g t h b y a b o u t 16%. I t i s i m p o r t a n t t o n o t e t h a t L a R o c h e l l e w a s t e s t i n g C h a m p l a i n c l a y , a h i g h l y s e n s i t i v e a n d b r i t t l e g l a c i a l m a r i n e c l a y c h a r a c t e r i s e d b y c h e m i c a l b o n d s b e t w e e n t h e c l a y e y p l a t e l e t s . C l a y s f r o m t w o d i f f e r e n t s i t e s w e r e u s e d f o r h i s s t u d y ; o n e h a v i n g a n a v e r a g e s e n s i t v i t y o f 5 0 , t h e o t h e r h a v i n g a n a v e r a g e s e n s i t i v i t y o f 2 0 . H e p r e s e n t e d t h e r e s u l t s f o r o n l y t h e m o s t s e n s i t i v e s i t e a n d s t a t e d t h a t t h e r e s u l t s f r o m t h e o t h e r s i t e w e r e n o t a s m a r k e d . T h i s s u g g e s t s t h a t t h e e f f e c t s o f v a n e i n s e r t i o n ' a r e p r o b a b l y n o t a s s i g n i f i c a n t i n l e s s b r i t t l e a n d l e s s s e n s i t i v e s o i l s . K i m u r a a n d S a i t o h 1 9 8 3 i n s t r u m e n t e d a l a b o r a t o r y v a n e a n d a t r i a x i a l c e l l w i t h p o r e p r e s s u r e t r a n s d u c e r s t o i n v e s t i g a t e t h e e f f e c t s o f v a n e i n s e r t i o n . T h e y f o u n d t h a t h i g h p o r e p r e s s u r e s i n t h e o r d e r o f 75% o f t h e c o n s o l i d a t i o n p r e s s u r e w e r e g e n e r a t e d d u r i n g v a n e i n s e r t i o n . T h e y a l s o f o u n d t h a t t h e p o r e p r e s s u r e c h a n g e s d u r i n g v a n e r o t a t i o n w e r e v e r y s m a l l . E v i d e n c e o f t h e g e n e r a t i o n o f h i g h p o r e p r e s s u r e s a n d t h e i r s u b s e q u e n t d i s s i p a t i o n c o n f i r m s t h a t t h e t i m e d e l a y b e t w e e n v a n e i n s e r t i o n a n d t h e s t a r t o f r o t a t i o n c a n b e a c o n t r o l l i n g f a c t o r i-n t h e m e a s u r e d u n d r a i n e d s t r e n g t h . 45 Flaate 1966 also indicated that an unknown degree of disturbance can be caused by so i l sticking to the vane blades thereby increasing the area ratio of the vane (ratio of the actual vane blade area to the projected area of the vane 7rD2) for tests at other depths. 4.6 Correction Factors Several papers appear in the literature in which attempts have been made to correlate the results of vane shear tests to those obtained from laboratory tests. These laboratory tests have included unconfined compression, consolidated undrained, K0 consolidated undrained, direct shear and simple shear among others. Rightly so, no single correlation has been established between the vane and laboratory tests which would help in 'correcting' the vane strength. The discrepencies are not surprising since the failure mechanism of the vane test is unlike that of any other test. More importantly, however, is the fact that there are many examples of vane tests producing non-conservative stability calculations. Back calculations from actual failures should yield the true insitu undrained strength and i t has been found that in many cases the vane strength overpredicted the value at failure. This problem has led to the concept of applying correction factors to the vane strength. Bjerrum 1972 reviewed 14 known failures (FS=1) and discovered that the theoretical factors of safety differed from 1 and varied with the plasticity index of the clay. He therefore introduced a correction factor, n, with which the vane strength 46 s h o u l d be m u l t i p l i e d b e f o r e i t i s i n t r o d u c e d i n t o a s t a b i l i t y a n a l y s i s . B j e r r u m ' s c o r r e c t i o n f a c t o r i s i l l u s t r a t e d i n f i g u r e 4 . 9 . He s p e c u l a t e d t h a t t h e d i s c r e p a n c y was d u e p r i m a r i l y t o r a t e e f f e c t s a n d s o i l s t r e n g t h a n i s o t r o p y . He d i d c o n s i d e r t h a t p r o g r e s s i v e f a i l u r e may a l s o be a c o n t r i b u t i n g f a c t o r b u t he c o n c l u d e d t h a t i t i s o n l y a m i n o r o n e . B j e r r u m 1973 a t t e m p t e d t o s e p a r a t e t h e two e f f e c t s a n d t h i s i s shown i n f i g u r e 4 . 1 0 . He i n t r o d u c e d two f a c t o r s M R a n d M 3 r e p r e s e n t i n g t h e f a c t o r s f o r r a t e e f f e c t s a n d a n i s o t r o p y r e s p e c t i v e l y a n d s t a t e d t h a t t h e s h e a r s t r e n g t h t o be u s e d i n a s t a b i l t y a n a l y s i s s h o u l d b e : S u f = S u v M r M a 4 . 9 w h e r e S u f - f i e l d Su Suv - v a n e Su MR - c o r r e c t i o n f a c t o r f o r r a t e e f f e c t s MA - c o r r e c t i o n f a c t o r f o r a n i s o t r o p y B j e r r u m 1973 p o i n t s o u t t h a t LLT ( f i g u r e 4 . 1 0 ) r e p r e s e n t s a c o r r e c t i o n f a c t o r f o r c a s e s w h e r e t h e m i n i m u m f a c t o r o f s a f e t y w i l l be r e a c h e d i n a m a t t e r o f w e e k s o r m o n t h s a f t e r c o n s t r u c t i o n . A d i f f e r e n t v a l u e may be r e q u i r e d f o r s h o r t e r t i m e p e r i o d s . He a l s o i n d i c a t e s t h a t t h e v a l u e o f M A w i l l v a r y a l o n g t h e e x p e c t e d f a i l u r e s u r f a c e d e p e n d i n g on i t s i n c l i n a t i o n a n d c a n be e s t i m a t e d f r o m f i g u r e 4 . 1 1 . A z z o u z e t a l . 1983 p r o p o s e d a new f i e l d v a n e c o r r e c t i o n c u r v e t o be u s e d i n t h e d e s i g n o f e m b a n k m e n t s t o a c c o u n t f o r t h e i r t h r e e d i m e n s i o n a l mode o f f a i l u r e . The S w e d i s h G e o t e c h n i c a l I n s t i t u t e ( S G I ) u s e s a r e d u c t i o n f a c t o r n b a s e d on t h e l i q u i d l i m i t (W| ) o f t h e s o i l . The SGI c o r r e c t i o n c u r v e i s c o m p a r e d t o B j e r r u m ' s c u r v e ( a s p l o t t e d a g a i n s t W | ) i n f i g u r e 4 . 1 2 . 47 F i g u r e 4 . 9 - CORRECTION FACTOR FOR UNDRAINED SHEAR STRENGTH DETERMINED FROM F I E L D VANE T E S T S ( a d a p t e d f r o m B j e r r u m 1972) F i g u r e 4 . 1 0 - E M P I R I C A L L Y E S T A B L I S H E D CORRECTION FACTORS FOR RESULTS OF VANE SHEAR T E S T S ( a d a p t e d f r o m B j e r r u m 1973) 48 0.0-1—.—.—.—.—.—I—,—,—,—,—,— 90' 60* 30* 0* 30* 60* 90* | PASSIVE " ACTIVE m. OFCIAV Ip IH.) it f. »« t>» Om tOW PLASTIC 10 O.SO 0.0 3 JO' '1 0.30 MEDIUM PLASTIC S 0 a«s 0.15 1 5* 1.8 o.ts HIGHLY PLASTIC 100 a so 0.30 10* 2.0 O.SO F i g u r e 4 . 1 1 - R A T I O O F U N D R A I N E D S H E A R S T R E N G T H T O V A N E S H E A R S T R E N G T H F O R T H R E E T Y P E S O F C L A Y ( a d a p t e d f r o m B j e r r u m 1 9 7 3 ) F i g u r e 4 . 1 2 - V A N E S H E A R T E S T R E D U C T I O N F A C T O R A S A F U N C T I O N O F T H E L I Q U I D L I M I T A C C O R D I N G T O T H E S W E D I S H G E O T E C H N I C A L I N S T I T U T E ( a d a p t e d f r o m H e l e n e l u n d 1 9 7 7 ) 49 Helenelund 1977 presents s e v e r a l d i f f e r e n t methods f o r reducing the undrained shear s t r e n g t h of c l a y . Some engineers are opposed to the a p p l i c a t i o n of c o r r e c t i o n f a c t o r s to vane s t r e n g t h s . Schmertmann 1975, a f t e r reviewing the d i f f e r e n t f a c t o r s a f f e c t i n g the vane t e s t , s t a t e d that any engineer who d e s i r e d to apply these s t a t e - o f - t h e - a r t c o r r e c t i o n s would probably be at a l o s s as how to use h i s p a r t i c u l a r Suv data and he termed t h i s the "current c o r r e c t i o n c r i s i s " . Kenney and Folkes 1979 con s i d e r e d the problem of s o f t Canadian s o i l s and t h e i r unique behaviour and concluded that i n the absence of s u f f i c i e n t e m p i r i c a l i n f o r m a t i o n , i t would be f o o l hardy to accept the approach of equation 4.9. Th i s w r i t e r has observed that c o r r e c t i o n f a c t o r s are o f t e n a p p l i e d without regard to the problem at hand and how i t r e l a t e s to the c o n d i t i o n s f o r which the c o r r e c t i o n f a c t o r s were introduced. For example, i t does not seem c o r r e c t to apply Bjerrum's c o r r e c t i o n to f i e l d vane data when i t i s to be compared to CPT r e s u l t s . Bjerrum's c o r r e c t i o n i s used to reduce the measured s t r e n g t h to account f o r the e f f e c t s of the r e l a t i v e l y high rate of s t r a i n a s s o c i a t e d with the VST. However, the rate of s t r a i n d u r i n g cone p e n e t r a t i o n i s g r e a t e r than that in a vane t e s t . I f anything, the s t r e n g t h should be i n c r e a s e d . Although the e f f e c t s of a n i s o t r o p y should vary along the expected f a i l u r e plane, depending on i t s o r i e n t a t i o n , a s i n g l e c o r r e c t i o n f a c t o r i s o f t e n a p p l i e d to vane s t r e n g t h data. 50 4.7 Summary The use of the fi e l d vane test has a long history and engineers have attained a great deal of experience in the interpretation of VST results. Recent work has shown, however, that the standard method of analysis is likely incorrect. Laboratory studies and finite element analyses suggest that the distribution of shear stress is not uniform, particularly on the ends of the vane. It has also been shown that the vertical face contributes up to 90% of the shear resistance. Using vanes of various shapes and dimensions to study the effects of strength anisotropy, tests indicate a trend of decreasing Sh/Sv with increasing plasticity. The calculation of this ratio, however, is highly sensitive to the assumed shear stress distribution on the ends of the vane. Field vane results are dependent upon the rate of strain with greater strengths being measured at higher rates of strain. Delays between vane insertion and the start of shearing also influence VST results due to the consolidation of the surrounding soil that takes place as the pore pressures induced during vane insertion dissipate. Because of these problems and due to our lack of complete understanding of the VST, some consider the test to be nothing more than a strength index test (Schmertmann 1975). Despite this feeling, the VST is s t i l l used extensively because i t is a quick, inexpense and highly repeatable method of determining undrained shear strength. 51 CHAPTER 5 A BRIEF REVIEW OF THE CONE PENETRATION TEST 5.1 Introduct ion The cone p e n e t r a t i o n t e s t i s unequalled in i t s a b i l i t y to i n d e n t i f y s o i l l a y e r boundaries and q u a l i t a t i v e l y evaluate m a t e r i a l types. Because of the complex behaviour of s o i l s and the complex changes in s t r e s s and s t r a i n around the cone t i p , c o r r e l a t i o n s between CPT data and m a t e r i a l parameters are n e c e s s a r i l y e m p i r i c a l . However, the h i g h l y repeatable nature of the t e s t has l e d to a great deal of c onfidence i n the v a r i o u s c o r r e l a t i o n s . Comprehensive reviews of the use and i n t e r p r e t a t i o n of cone p e n e t r a t i o n t e s t s have been presented by Schmertmann 1978, Robertson and Campanella 1984, Wroth 1984, Campanella et a l . 1985 and Jamiolkowski et a l . 1985. Although Schmertmann's re p o r t i s p r i m a r i l y concerned with the i n t e r p r e t a t i o n and a p p l i c a t i o n of mechanical cone data, there are many good d i s c u s s i o n s that are a p p l i c a b l e to e l e c t r o n i c cone data. These reviews have d i s c u s s e d such t o p i c s as equipment d e s i g n , t e s t procedures, i n t e r p r e t a t i o n techniques, a p p l i c a t i o n s to g e o t e c h n i c a l design and the f a c t o r s a f f e c t i n g t e s t r e s u l t s and t h e i r i n t e r p r e t a t i o n . Hence, t h i s review w i l l present only some of the important aspects of cone p e n e t r a t i o n t e s t i n g that are r e l e v a n t to the e s t i m a t i o n of undrained shear s t r e n g t h and cone t e s t i n g i n c l a y s . 52 5.2 S o i l C l a s s i f i c a t i o n The c u r r e n t method of i n t e r p r e t i n g s o i l type from CPT i s based on the cone bearing (Qc) and the f r i c t i o n r a t i o ( R f ) . Experience has shown that high bearing values and low f r i c t i o n r a t i o s are a s s o c i a t e d with coarse g r a i n e d noncohesive m a t e r i a l s and lower bearing values and i n c r e a s i n g f r i c t i o n r a t i o s are a s s o c i a t e d with f i n e grained cohesive m a t e r i a l s of i n c r e a s i n g p l a s t i c i t y . Douglas and Olsen 1981 d e s c r i b e t h e i r work i n developing the c l a s s i f i c a t i o n c h a r t i l l u s t r a t e d i n f i g u r e 5.1. They consi d e r that the c h a r t e s s e n t i a l l y c o n s i s t s of three zones of d i f f e r e n t s o i l type: c o h e s i o n l e s s coarse grained s o i l s , d u c t i l e f i n e g r a i n e d s o i l s and mixed s o i l s . T h e i r c h a r t i n d i c a t e s the e f f e c t of v a r i o u s s o i l i n d i c e s on the penetrometer response. From a p r a c t i c a l p o i n t of view, Douglas and Olsen's c h a r t i s not a very easy one to use. F i g u r e 5.2 shows a s i m p l i f i e d v e r s i o n used by U.B.C. for i n t e r p r e t i n g CPT data. Douglas and Olsen c o r r e c t l y i n d i c a t e that cone p e n e t r a t i o n t e s t s r e f l e c t an aggragate behaviour of the s o i l and that a more ap p r o p r i a t e d e s c r i p t i o n f o r s o i l c l a s s i f i c a t i o n i s s o i l behaviour type rather than j u s t s o i l type. The cone responds to an i n t e r a c t i o n of the s o i l composition, f a b r i c , l o c a l s t r e s s c o n d i t i o n s and s o i l behaviour w i t h i n a zone of i n f l u e n c e that extends ahead and behind the cone ( d i s c u s s e d i n more d e t a i l i n s e c t i o n 5.3). I t should a l s o be p o i n t e d out that the c l a s s i f i c a t i o n c h a r t s developed to date are a l l based on u n c o r r e c t e d cone bearing Qc. T h i s i s not a s e r i o u s problem i n coarse g r a i n e d m a t e r i a l s (except perhaps o f f s h o r e ) , however, i t may be of 53 F R I C T I O N RAT 13 ['/.) Figure 5.1 CPT SOIL BEHAVIOUR TYPE CLASSIFICATION CHART (adapted from Douglas and Olsen 1981) Figure 5.2 UBC SIMPLIFIED CPT SOIL BEHAVIOUR TYPE CLASSIFICATION CHART FOR THE ELECTRONIC FRICTION CONE 54 s i g n i f i c a n c e when i n t e r p r e t i n g data from soundings i n m a t e r i a l s t h a t tend to generate high excess pore p r e s s u r e s . These m a t e r i a l s g e n e r a l l y have low cone bearings and p l o t i n the lower l e f t p o r t i o n of the c h a r t . Future c l a s s i f i c a t i o n c h a r t s should be based on c o r r e c t e d b e a r i n g Qt. Since most c l a s s i f i c a t i o n c h a r t s have been developed from soundings that are g e n e r a l l y l e s s than 30m, i n t e r p r e t a t i o n of data from deep soundings may a l s o present a problem. The e f f e c t of high overburden pressure i s to i n c r e a s e the cone bearing, consequently, a c l a y from a deep sounding may be i n t e r p r e t e d as a sand. I t i s recommended that f u t u r e c l a s s i f i c a t i o n c h a r t s use normalized parameters. Several p r o p o s a l s have been made to i n c l u d e pore pressure data i n the i n t e r p r e t a t i o n of s o i l types (Jones et a l . 1981, Senneset et a l . 1982, Jones and Rust 1982 and Senneset and Janbu 1984). However, u n t i l a standard i s developed for the pore pressure element l o c a t i o n ( s ) the acceptance of a c l a s s i f i c a t i o n system based on pore pressure i s u n l i k e l y . 5.3 S o i l P r o f i l i n g An e v a l u a t i o n of m a t e r i a l type and i t s s t r e s s h i s t o r y can o f t e n be obtained by c o n s i d e r i n g the e n t i r e bearing p r o f i l e . Some m a t e r i a l s are c h a r a c t e r i z e d by t y p i c a l p r o f i l e shapes. Schmertmann 1978 presented some s i m p l i f i e d examples of t y p i c a l p r o f i l e s and i n d i c a t e d the l i k e l y and p o s s i b l e i n t e r p r e t a t i o n s . These examples are reproduced i n f i g u r e 5.3. Of s p e c i a l i n t e r e s t f o r t h i s r e p o r t are the t y p i c a l shapes of bearing p r o f i l e s i n c l a y d e p o s i t s . F i g u r e 5.3a i n d i c a t e s t hat the t i p r e s i s t a n c e i n 55 Figure 5.3 SIMPLIFIED EXAMPLES OF CONE BEARING PROFILES SHOWING LIKELY AND POSSIBLE INTERPRETATIONS FOR SOIL TYPES AND AND CONDITIONS (adapted from Schmertmann 1978) 56 a normally consolidated clay deposit typically increases linearly with depth (if groundwater conditions are hydrostatic). An extrapolation of the profile should extend through the origin (this idea is modified in section 6.4). Robertson and Campanella 1983 report that for most young clays where overconsolidation has been caused by erosion or dessication, the cone bearing may remain constant or may decrease with depth until the depth where the deposit is normally consolidated. This can be seen in the CPT profile shown in figure 7.3. For aged clays where the OCR is constant with depth, the tip resistance may continue to stay constant with depth. It has also been found that the friction ratio for some fine grained soils may decrease with increasing overburden stress (Robertson and Campanella 1983). Evidence of this can be seen in the various CPT profiles presented in chapter 7. This result may lead to d i f f i c u l t y when interpreting deep soundings. Penetration tests performed in a multilayered media by Treadwell 1976 indicated that a transition zone exists at layer boundaries within which the tip resistance is affected by the soil properties of an adjacent layer. It was observed that the tip resistance is significantly influenced by the material ahead and behind the tip. Treadwell considers that this transition zone consists of upper and lower parts; the upper portion being the depth over which the tip resistance is influenced by the next layer and the lower portion being the distance that the tip must advance beyond the layer interface for i t s resistance not to be affected by the overlying material. Treadwell reports that the upper portion of the transition zone typically begins 3 to 4 57 cone diameters above the layer interface. The • lower portion appears to depend on density, depth and the relative stiffness between the two layers. With regards to the lower portion of the transition zone, he found that the transition was made quickly (in 3 to 5 diameters) when penetrating from a dense layer to a loose layer. However, when penetrating from a loose layer to a dense layer the transition zone was significantly larger, increasing in size with increasing depth. These effects are illustrated in figure 5.4. It can be seen that at a shallow depth the tip resistance in the dense material is almost equal to that for a uniformly dense deposit, however, at greater depth the cone bearing does not attain its f u l l resistance. On the other hand, the tip resistance in the loose layers is equal to or slightly greater than that in a uniformly loose material. Similar work by Schmertmann 1978 shows that the influence of the soil layer interface is felt from a distance of 5 to 10 cone diameters on either side of the layer boundary. Schmertmann found that the greater the difference in strength and compress.ibilty between the layer to be sensed and the adjacent soi l the thinner the layer that can be detected. He added that the smaller the cone diameter the more sensitive the tip is to local variations with depth. These effects are of great importance when interpreting strength parameters from CPT data. It must be recognized that the cone bearing w i l l not reach its f u l l resistance in thin layers of sand. This can lead to d i f f i c u l t y when estimating such parameters as relative density, modulus and friction angle. On the other hand, much thinner layers of clay are required to 58 Figure 5.4 CONE PENETROMETER BEARING RESPONSE IN A LAYERED MEDIA (adapted from Treadwell 1976) 59 record the true b e a r i n g . When e s t i m a t i n g shear s t r e n g t h of cohesive m a t e r i a l s in s t r a t i f i e d d e p o s i t s , i t i s best to use the minimum bearing values ( i . e . the v a l l e y s in the bearing record) rather than an average l i n e drawn through the p r o f i l e s i n c e the l o c a l v a r i a t i o n s i n bearing are a r e f l e c t i o n of the non-cohesive m a t e r i a l s . These r e s u l t s r a i s e the q u e s t i o n as to how t h i n a l a y e r cone p e n e t r a t i o n t e s t s can d e t e c t . A recent report by Davies 1985 r e v e a l s that t h i s can be of i n t e r e s t i n the i d e n t i f i c a t i o n of shear planes. Schmertmann's r e s u l t s suggest that a l a y e r must be at l e a s t 10 to 20 cone diameters t h i c k (36cm to 72cm for a 10cm2 cone) to a t t a i n f u l l p e n e t r a t i o n r e s i s t a n c e . C l e a r l y , p e n e t r a t i o n t e s t s can d e t e c t l a y e r s t h i n n e r than 36cm, however, the i n t e r p r e t a t i o n of m a t e r i a l parameters may be s e r i o u s l y a f f e c t e d . The a b i l i t y of CPT to d e f i n e s o i l l a y e r s i s i l l u s t r a t e d i n f i g u r e 5.5. A p o r t i o n of a CPT b e a r i n g p r o f i l e i s presented a l o n g s i d e a c o n t i n u o u s l y sampled borehole l o g obtained at the B.C. Hydro rai l w a y c r o s s i n g s i t e ( d e s c r i b e d i n chapter 7). The borehole log i s based s o l e l y on a v i s u a l c l a s s i f i c a t i o n of the sampled a f t e r i t had been extruded from the sample tube and s p l i t i n h a l f lengthwise. The complete bearing/continuous sample log i s i n c l u d e d i n appendix A, and r e f e r e n c e w i l l be made to i t i n the f o l l o w i n g d i s c u s s i o n . The m o d i f i e d Hogentogler cone (see chapter 2) was used f o r the CPT and a GMF 67mm diameter continuous sampler was used f o r the borehole. The CPT was performed 1m from the borehole. During l o g g i n g of the borehole sample only l a y e r s of t h i c k n e s s 1cm or g r e a t e r were recorded as 5. 0 (A L a +> a E D_ U l a 7. 5 CONE BEARING Qt (bar) CONTINUOUS BOREHOLE LOG 14 g r e y s i l t y c l a y , o c c a s i o n a l s a n d l e n s e f i n e sand 1 g r e y s i I t y c l a y l a y e r e d s i l t y c l a y and s i l t y f i n e s a n d ( l a y e r s a p p r o x . 1cm) ^ f i n e s a n d ) g r e y s 1 1 t y c l a y I s i l t y f i n e s a n d / l a m i n a t e d s i l t y f i n e s a n d and s i l t y c l a y g r e y s i l t y c1 a y f i ne sand g r e y s 11ty c1 ay s i l t y f ine s a n d g r e y s i 1ty c l a y CTi O Figure 5 . 5 COMPARISON BETWEEN A CPT BEARING PROFILE AND A CONTINUOUS SAMPLE LOG 61 individual layers. It is quite clear from figure 5.5 that layers of the order 10cm thick were easily detected by the tip resistance. There are some examples of thinner layers, possibly as thin as 1cm thick being detected. This can be seen in the layered s i l t y clay and s i l t y fine sand at 5.58m in figure 5.5. The layers of sand were approximately 1cm thick, alternating with layers of s i l t y clay. The increased bearing, however, may be a result of the influence of several thin sand layers that are relatively close together. Had there been only a single sand layer the response of the bearing may not of been as pronounced. The detection of layers less than 10cm thick can also be seen at depths of approximately 9.47m (figure A.1c - inclined sand lense), 11.52m (figure A.1d - sandy clay) and 13.5m (figure A.1e - s i l t y fine sand). A pore pressure profile should be of considerable help in detecting different layers, unfortunately, the standard Hogentogler porous element used for the CPT at this site had a very small average pore size (approximately* 20 microns) which tended to . clog, resulting in a poor pore pressure response (Hogentogler & Co. has since changed the material for their porous elements, the new material having an average pore size of 120 microns). The detection of thin layers is complicated by the sampling rate used during CPT. The profile presented in figure 5.5 was sampled at the U.B.C. standard rate of 2.5cm. Although thin layers may be detected at this rate, many can easily be missed. The a b i l i t y to confidently identify thin layers also depends upon the relative stiffness between the thin layer and the 62 surrounding m a t e r i a l . For example, i t may be d i f f i c u l t to i d e n t i f y a t h i n c l a y l a y e r w i t h i n a s i l t d e p o s i t s i n c e a small drop in the cone bearing may be a t t r i b u t e d to the n a t u r a l v a r i a b i l i t y of the s i l t . On the other hand, a t h i n cemented sand l a y e r may e a s i l y be d e t e c t e d . F i g u r e 5.6 i l l u s t r a t e s the r e l a t i v e p r o p o r t i o n s of the 10cm2 cone, the l i k e l y t r a n s i t i o n zone r e q u i r e d to a t t a i n f u l l p e n e t r a t i o n r e s i s t a n c e and the standard U.B.C. sampling r a t e . For comparison, the three commonly used s i z e s of f i e l d vanes are a l s o shown. Es t i m a t i n g the t h i c k n e s s of a l a y e r (as opposed to d e t e c t i n g a t h i n l a y e r ) i s h i g h l y dependent upon the sampling r a t e . I t can be shown that the e s t i m a t i o n of l a y e r t h i c k n e s s f o r l a y e r s t h i n n e r than the sampling r a t e i s h i g h l y s p e c u l a t i v e and can often be i n e r r o r . Sampling at d i s c r e t e i n t e r v a l s can a l s o l e a d to subdued peaks i n the CPT p r o f i l e . One s o l u t i o n might be to d i g i t i z e a continuous record o b t a i n e d from a s t r i p c h a r t recorder. However, t h i s author's experience has shown that the r e s o l u t i o n of the d i g i t i z i n g pad can be of the same order as the minor v a r i a t i o n s of i n t e r e s t i n the CPT p r o f i l e and that the minor v a r i a t i o n s are o f t e n ignored during the d i g i t i z i n g process. The pore pressure p r o f i l e can be of c o n s i d e r a b l e use i n d e t e c t i n g s t r a t i g r a p h i c d e t a i l s . Robertson 1985 i n d i c a t e s that a f u l l y s a t u r a t e d piezometer cone can u s u a l l y respond to pore pressure changes w i t h i n a t i p advancement of 5mm at the standard r a t e or p e n e t r a t i o n of 2cm/sec. However, i f the t h i n l a y e r s are d i s c o n t i n u o u s the drainage c o n d i t i o n s may be such that pore pressure response i s i n h i b i t e d . The same sampling rate problems 63 PROBABLE ZONE OF INFLUENCE FOR CONE BEARING 10D V 10cm2 60° cone 55 x 110mm 65 x 130mm 10D 80 x 160mm STANDARD NILCON AND GEONOR FIELD VANES STANDARD UBC SAMPLING RATE (2.5cm) Figure 5.6 RELATIVE PROPORTIONS OF THE 10cm* CONE PENETROMETER, PROBABLE ZONE OF INFLUENCE FOR CPT, UBC STANDARD CPT SAMPLING RATE AND LARGE, MEDIUM AND SMALL FIELD VANES 64 occur f o r both the r e c o r d i n g of dynamic pore p r e s s u r e s and t i p r e s i stance. 5.4 Dynamic Pore P r e s s u r e Response The r e c o r d i n g of dynamic pore pressures d u r i n g cone p e n e t r a t i o n s i g n i f i c a n t l y improves the use, i n t e r p r e t a t i o n and a p p l i c a t i o n of the e l e c t r i c cone. The measurement of pore pressure a i d s i n s o i l l a y e r i d e n t i f i c a t i o n and can be used to e s t a b l i s h e q u i l i b r i u m groundwater c o n d i t i o n s , i n d i c a t e s t r e s s h i s t o r y , evaluate c o n s o l i d a t i o n c h a r a c t e r i s t i c s and estimate s o i l p e r m e a b i l i t y and undrained shear s t r e n g t h . A comprehensive review of the uses and i n t e r p r e t a t i o n of dynamic pore p r e s s u r e s and the f a c t o r s that a f f e c t t h e i r measurement i s presented by Robertson and Campanella 1984 and Campanella et a l . 1985. The two main f a c t o r s a f f e c t i n g the measurement of pore pressures a r e : s a t u r a t i o n and porous element l o c a t i o n . Complete s a t u r a t i o n of the pore pressure measuring system i s e s s e n t i a l i n order to record high q u a l i t y and r e p e a t a b l e data. The importance of s a t u r a t i o n has been d i s c u s s e d i n chapter 3 of t h i s r e p o r t . The pore pressure response i s h i g h l y i n f l u e n c e d by the porous element l o c a t i o n . A conceptual pore p r e s s u r e d i s t r i b u t i o n around the cone i s i l l u s t r a t e d i n f i g u r e 5.7 and c l e a r l y shows the dramatic e f f e c t that the element l o c a t i o n has on the measured response. Campanella et a l . 1985 e x p l a i n that the t i p i s i n a zone of maximum compression and shear, u n l i k e the area immediately behind the t i p which i s i n a zone of normal s t r e s s r e l i e f . The l a r g e normal s t r e s s e s dominate the pore pressure response on the face and, thus, h i g h p o s i t i v e pore p r e s s u r e s are 65 n o HEAVILY . o.c I CLAY ! I N.C. CLAY I i « LIGHTLY O.C. SENSITIVE CLAY HEAVILY -^O.C. CLAY /\N.C. CLAY 10 COMPACT SILT (dilative) j.—LOOSE SILT V» (compressible) SILT DENSE FINE , SANO I — I — L _ 4 I 10 15 u /u „ 15 Figure 5.7 CONCEPTUAL PORE PRESSURE DISTRIBUTION IN SATURATED SOIL DURING CPT BASED ON FIELD MEASUREMENTS (after Campanella et a l . 1985) 6 6 generally recorded. Large shear stresses dominate the response behind the tip and the recorded pore pressures more closely reflect the volume change characteristics of the s o i l . The fact that tremendously different pore pressures are recorded on the face than behind the tip is of significance when correcting the bearing for pore pressure effects. Pore pressures must be recorded behind the tip to properly correct the bearing. If pore pressures are recorded at other locations then an estimate of the ratio of behind the tip to on the face pore pressure must be made before adjusting the bearing data. A similar but much less dramatic situation may occur when correcting friction data. Figure 5.7 indicates that the pore pressure at the top of the friction sleeve is different from that at the bottom. This can lead to an incorrect friction measurement as the imbalance of pore pressures produces a net force on the friction sleeve. The excess pore pressure is commonly presented as a normalized value and has been found to be a rough indicator of stress history. Robertson and Campanella 1984 l i s t four A U different definitions and suggest that Q ffo be adopted as a standard. This particular definition has been termed Bq by Senneset et a l . 1982. Work by Gillespie 1981 showed that predicted pore pressure response using cavity expansion theory compared well with measured values. Pore pressures generated on the face were best predicted using spherical cavity expansion whereas pore pressures generated behind the tip and up the sleeve were best predicted using cylindrical cavity expansion. 67 CHAPTER 6 METHODS OF CORRELATION BETWEEN CPT AND Su 6.1 Introduct ion T h i s chapter d i s c u s s e s the d i f f e r e n t methods that have been proposed for c o r r e l a t i n g CPT r e s u l t s with undrained shear s t r e n g t h . T h i s t o p i c has been s t u d i e d by s e v e r a l r e s e a r c h e r s i n the past, however, most have focussed only on the cone b e a r i n g as a means of e s t i m a t i n g Su. These have been termed the " t r a d i t i o n a l methods" by t h i s author and they u s u a l l y employ a cone f a c t o r Nk or Nc whose values have e x h i b i t e d a tremendous range but are often r e l a t i v e l y w e l l d e f i n e d at i n d i v i d u a l s i t e s . V arious t h e o r e t i c a l cone f a c t o r s have a l s o been proposed by d i f f e r e n t r e s e a r c h e r s . Recently proposed methods make use of excess pore pressures measured duri n g p e n e t r a t i o n . Senneset et a l . 1982 proposed the use of ' e f f e c t i v e ' b e a r i n g f o r e s t i m a t i n g Su. A semi-empirical approach based on c a v i t y expansion theory has been adopted by Campanella et a l . 1985 and v a r i o u s pore pressure parameters and cone f a c t o r s have been used by Lunne et a l . 1985 i n an attempt to f i n d a s a t i s f a c t o r y c o r r e l a t i o n technique. Several r e s e a r c h e r s have a l s o proposed the use of f r i c t i o n measurements to estimate Su. T h i s chapter concludes with a p r e s e n t a t i o n of some proposed methods of e v a l u a t i n g the s t r e s s h i s t o r y of a d e p o s i t from CPT and a method f o r e s t i m a t i n g s e n s i t i v i t y from f r i c t i o n r a t i o s . 6 8 6.2 T r a d i t i o n a l Methods of C o r r e l a t i o n The undrained shear strength of c l a y has t r a d i t o n a l l y been evaluated from cone bearing data u s i n g a bearing c a p a c i t y type equation of the form: Qc = Su Nk + cr 6.1 where Qc i s the cone b e a r i n g Nk i s the cone f a c t o r cr i s a measure of i n s i t u s t r e s s V a r i o u s forms of i n s i t u s t r e s s have been used; t o t a l v e r t i c a l s t r e s s , t o t a l h o r i z o n t a l s t r e s s and o c t a h e d r a l s t r e s s . The i n s i t u s t r e s s i s sometimes ignored, i n which case the cone f a c t o r i s u s u a l l y d e f i n e d as Nc. A wide range of values f o r Nk and Nc have been r e p o r t e d by Brand et a l . 1974, Schmertmann 1975, Lunne et a l . 1976 Schmertmann 1978, B a l i g h et a l . 1979, Lunne and K l e v i n 1981 and Jamiolkowski et a l . 1982. It was noted i n chapter 1 that Su i s not a unique parameter as i t i s dependent on the type of t e s t used. T h i s may p a r t l y e x p l a i n the wide range i n re p o r t e d cone f a c t o r s s i n c e many d i f f e r e n t types of t e s t s have been used to e s t a b l i s h a r e f e r e n c e Su. Table 6.1 summarizes Nc cone f a c t o r s f o r v a r i o u s c l a y s from around the world and i l l u s t r a t e s the wide range of repo r t e d v a l u e s . B a l i g h et a l . 1979 presented a p l o t of Nk against depth fo r nine d i f f e r e n t c l a y s (reproduced i n f i g u r e 6.1), the values f o r Nk ranging from 5 to 28. The lowest and highest values of Nk were recorded f o r m a t e r i a l s of h i g h p l a s t i c i t y and high s e n s i t i v i t y (St>40), r e s p e c t i v e l y . The curves which e x h i b i t e d a dec r e a s i n g cone f a c t o r with depth correspond to d e p o s i t s where s e n s i t i v i t y decreased with depth. T a b l e 6.2 presents a summary of m a t e r i a l p r o p e r t i e s and cone f a c t o r s f o r some Scandanavian R e f e r e n c e C l a y Avg Cone C l a y P r o p e r t i e s F a c t o r 1 W% W1% P I % Su. kPa Sens i 11v1ty Thomas ( 19G5) London C l a y 18 20-30 80-85 50 49-285* -Ward e t a l . ( 1965) London C l a y 15.5 22-26 60-7 1 36-43 206-510* -Melgh & C o r b e t t (1969) A r a b i a n G u l f C l a y 16 30-47 38-62 20-35 4.9-39" 5 Ladanyl 6 Eden (1969) Leda C l a y ( G l o u c e s t e r ) 7.5 50-57 50 23 25" 30 - 50 Ladanyf & Eden (1969) Leda C l a y (Ottawa) 5.5 7.2-84 40 20 56" 10 - 35 Pham ( 1972) Bangkok C l a y ( C i t y ) 16 60-70 70-80 40-50 12.8-28.5" 5 - 7 Anagnostopou1os (1974) P a t r a s C l a y 17 30 35 18 29.4-68.7* 1 . 5 - 3 Brand et a l . ( 1974) Bangkok C l a y ( B a n g p l i ) 19 60-130 60-130 60-120 12.8-37.3" 5 - 7 Brand et a l . ( 1974) Weathered Bangkok C l a y ( B a n g p l i ) 14 100-130 100-135 60-80 12.8-19.6" 6 - 8 Author Richmond C l a y e y S i l t 11.9 23-40 25-42 3-20 45-94" 2 - 7 Author Langley C l a y 14.4 27-53 32-59 16-34 19-80" 2 - 19 Author Haney C l a y 14.2 40-45 44 18 33-96" 3 - 13 1 - cone f a c t o r c a l c u l a t e d from Qc/Su * - u n c o n f l n e d compression " - f i e l d vane T a b l e 6 . 1 - S U M M A R Y OF G O N E F A C T O R S ( N c ) D E T E R M I N E D F O R D I F F E R E N T C L A Y D E P O S I T S ( r e v i s e d f r o m B r a n d e t a l . 1 9 7 4 ) F i g u r e 6.1 - EMPIRICAL CONE FACTOR Nk v s DEPTH FOR D I F F E R E N T CLAY D E P O S I T S ( a d a p t e d f r o m B a l i g h e t a l . 1979) 71 Tart Ospth Rang* Plasticity Con* Factor titi (m) Tf(t7m2) y%> Sensitivity "k Sundland 4-9 2-2.5 22-28 10-15 17-18 Drammen 9-14 2-4.5 - 1 0 ~2 20 14-22 2.5-4 ~10 3-4 15.5 Dansvigj gats 5-10 2-3 20-25 6-9 14-15 Drammen 11-30 24 10-11 2-4 14-16 80rresens gats 5.5-12 3-2 - 1 5 15-25 16-20 Drammen 12-30 1.3-2.5 ~ 5 50-160 20-24 Ons«ly 1-9 1.2-1.4 20-30 5-10 16-18 10-20 1.8-4.8 35-40 4-7 13-18 Ska-Edeby 1-4 0.6-1.2 45-80 6-10 8-9 4-12 0.8-2.0 30-50 10-15 10-12 GfHeborg 3-10 1.5-2.5 50-60 15-24 13.5-14.5 10-21 2.5-4.2 50-55 13-19 13-14 21-30 4.5-5.5 ~40 13-17 13-14 T a b l e 6 . 2 - SUMMARY O F C O N E F A C T O R S ( N k ) F O R S C A N D A N A V I A N C L A Y S ( a d a p t e d f r o m L u n n e e t a l . 1 9 7 6 ) z o Z rr O i-u < z o u 20 15 10 >50 V 3-4 O10-25 1 0 o 1 5 " ~2 * A 5-10 Range in Sensitivity Cn 2-4 • 6-9 LEGEND: O SUNDLAND 0 DANVIKS GT V E. B0RRESENSGT a ONS0Y + G0TEBORG X SKA-EOEBY 4-7 A + 13-17 15-24 • + 13-19 x 10-15 x 6-10 10 20 30 40 50 60 PLASTICITY, I % F i g u r e 6 . 2 - SUMMARY O F C O N E F A C T O R S ( N k ) F O R S C A N D A N A V I A N C L A Y S ( a d a p t e d f r o m L u n n e e t a l . 1 9 7 6 ) 7 2 c l a y s . T h e s e c o n e f a c t o r s w e r e p l o t t e d a g a i n s t p l a s t i c i t y i n d e x b y L u n n e e t a l . 1 9 7 6 a s s h o w n i n f i g u r e 6 . 2 . T h e r e a p p e a r s t o b e a g e n e r a l t r e n d o f d e c r e a s i n g c o n e f a c t o r w i t h i n c r e a s i n g P I . F o r a g i v e n P I t h e r e i s a l s o a t r e n d o f i n c r e a s i n g N k w i t h i n c r e a s i n g s e n s i t i v i t y . B a l i g h e t a l . 1 9 7 9 p r e s e n t e d a r e v i e w o f e x i s t i n g t h e o r i e s o f c o n e p e n e t r a t i o n i n c l a y s a n d r e p o r t e d t h a t t h e r e a r e b a s i c a l l y t h r e e d i f f e r e n t a p p r o a c h e s : p l a n e - s t r a i n s l i p - l i n e s o l u t i o n , e x p a n s i o n o f c a v i t i e s , o r s t e a d y p e n e t r a t i o n a n a l y s i s . T h e p l a i n - s t r a i n s l i p - l i n e a p p r o a c h t r e a t s c o n e p e n e t r a t i o n a s a b e a r i n g c a p a c i t y p r o b l e m w h e r e t h e m a t e r i a l i s i n a s t a t e o f i n c i p i e n t f a i l u r e . V a r i o u s s h a p e a n d d e p t h f a c t o r s h a v e b e e n p r o p o s e d t o d e t e r m i n e a n a p p r o p r i a t e c o n e f a c t o r . T h e s e c o n d m e t h o d i s b a s e d o n t h e e x p a n s i o n o f c y l i n d r i c a l o r s p h e r i c a l c a v i t i e s ; t h e o r i e s w h i c h h a v e b e e n d e s c r i b e d b y G i b s o n a n d A n d e r s o n 1 9 6 1 , V e s i c 1 9 7 2 a n d L a d a n y i 1 9 7 2 . T h e s t e a d y p e n e t r a t i o n a p p r o a c h i s a c o m b i n a t i o n o f t h e f i r s t t w o m e t h o d s . A s u m m a r y o f t h e d i f f e r e n t c o n e p e n e t r a t i o n t h e o r i e s i s p r e s e n t e d i n t a b l e 6 . 3 . U s i n g t h e s t e a d y p e n e t r a t i o n a p p r o a c h , B a l i g h e t a l . 1 9 7 5 d e m o n s t r a t e d t h e e f f e c t o f r i g i d i t y i n d e x G / S u ( a p a r a m e t e r c e n t r a l t o c a v i t y e x p a n s i o n t h e o r y ) a n d c o n e a n g l e o n t h e p e n e t r a t i o n r e s i s t a n c e o f c l a y s . T h i s e f f e c t i s s h o w n i n f i g u r e 6 . 3 a n d i t c l e a r l y i l l u s t r a t e s t h a t N k i n c r e a s e s w i t h i n c r e a s i n g s o i l s t i f f n e s s . A n e s t i m a t e o f t h e r i g i d i t y i n d e x c a n b e m a d e f r o m t h e c u r v e s p r e s e n t e d b y L a d d e t a l . 1 9 7 7 ( f i g u r e 6 . 4 ) . N o t e , h o w e v e r , t h a t L a d d ' s c u r v e s a r e i n t e r m s o f E u a n d n o t G u ( G = E / 2 ( 1 + f ) ) . L o w v a l u e s o f G / S u c o r r e s p o n d t o h i g h l y p l a s t i c Type o f Approach R e f e r e n c e q - N k a + p Ex p r e s f l l n n f o r Nk Nk f o r 2 6 - 60' p o C/s - 100 u C/s - 400 u Bearing Capacity T e n a g h l (1943) Heverhof (1951) (nltape f a c t o r ) (depth f a c t o r ) x 5.14 9.25 l a n e 0 vo Bearing Capacity H l t c h e l l and Dorgunoglu (1973) (shaoe f a c t o r ) ( d e p t h f a c t o r ) x (2.57 + 2 S + co t 6) 9.63 anme a vo Bearing Capacity M eyerhof (1961) (1.09 to 1.15) x (6.28 + 2 4 + c o t <5) 10.2 • ame a vo a o tt ' c N <x K U u -rt > Blehop et a l (1945) 1.33(1 + t n C/s ) u . 7.47 9.30 u n s p e c i f i e d C l b a o n (1950) 1.33(1 + l n c / e ) + c o t 6 u 9.21 11.03 a vo V e a l c (1975,1977) 1.33(1 + I n C/s u) + 2.57 10.04 11.87 °oct A l A w k a t l (1975) ( c o r r e c t i o n f a c t o r ) x (1 + I n C/a u) 10.65 13.28 °oct i • •a M a •> d « c o u U H U> P. U B a l l g h (1975) 1.2(5.71 + 3.33 i + c o t 6) + (1 * I n C/» u) 11.02 + 5.61 -16.63 11.02 + 6.99 -18.01 "ho T a b l e 6 . 3 - SUMMARY O F E X I S T I N G T H E O R I E S O F C O N E P E N E T R A T I O N I N C L A Y S ( a d a p t e d f r o m B a l i g h e t a l . 1979) F i g u r e 6 . 3 - E F F E C T O F R I G I D I T Y I N D E X A N D C O N E A N G L E ON T H E P E N E T R A T I O N R E S I S T A N C E O F C L A Y ( a d a p t e d f r o m B a l i g h e t a l . 1 9 7 5 ) 7 5 2000 1000 800 600 400 & 2 0 0 100 80 60 40 20 No. DESCRIPTION cu/p' Port smouf h CL C l a y PI»15 if-IO LL«35 Boston c L Cloy LL«4I P l * 2 2 •20 •20 •27 29 •26 •24 Bangkok CH Cloy L L ' 6 5 P I * 4 ! 4 Maine CH OH Clay LL«65PI*38 _ AGS CH Clay 0 LL»7I P 1 - 4 0 At ehaf alayo 6 CH Clay L L * 9 5 Pl = 75 _ Taylor River P e a t w =50 0 % CKo U simple shear tests all soils normally c ons oil d ate d 0-2 0 4 0-6 0-8 APPLIED SHEAR STRESS RATIO T h / c u F i g u r e 6 . 4 - S E L E C T I O N O F S O I L S T I F F N E S S ( a d a p t e d f r o m L a d d e t a l . 1 9 7 7 ) 76 m a t e r i a l s . T h i s dependence on s o i l s t i f f n e s s e x p l a i n s the trend of d ecreasing Nk with i n c r e a s i n g PI observed i n the data from Lunne et a l . 1976 ( f i g u r e 6.2). 6.3 Recently Proposed Methods of C o r r e l a t i o n The data presented i n the pre v i o u s s e c t i o n c l e a r l y i n d i c a t e that c o r r e l a t i o n s between cone bearing and Su are h e a v i l y i n f l u e n c e d by such s o i l c h a r a c t e r i s t i c s as s o i l s t i f f n e s s and s e n s i t i v i t y . In a d d i t i o n , the c o r r e l a t i o n s are a f f e c t e d by s t r e s s h i s t o r y , s t r e n g t h a n i s o t r o p y and s e v e r a l f a c t o r s r e l a t i n g to cone design d e t a i l s . Many of these f a c t o r s have not or can not be i n c o r p o r a t e d i n t o the t r a d i t i o n a l methods of c o r r e l a t i o n and are the l i k e l y reasons for the tremendous range i n repor t e d cone f a c t o r s . The dependence on these f a c t o r s i n d i c a t e s that there can not be a unique cone f a c t o r that i s a p p l i c a b l e to a l l c l a y s . These p r o p e r t i e s are d i f f i c u l t to q u a n t i f y and e q u a l l y d i f f i c u l t to i n c o r p o r a t e i n t o a n a l y s e s . S t r e s s h i s t o r y i s g e n e r a l l y expressed as o v e r c o n s o l i d a t i o n r a t i o but such f a c t o r s as aging, e f f e c t s of secondary compression and creep are n e c e s s a r i l y omitted. S o i l s t i f f n e s s i s u s u a l l y expressed as a r i g i d i t y index, G/Su. S e n s i t i v i t y i s commonly expressed in terms of the vane s e n s i t i v i t y and r e f l e c t s the s t r u c t u r e and f a b r i c of the cohesive m a t e r i a l . As has been mentioned s e v e r a l times throughout t h i s r e p o r t , the consequences of c e r t a i n cone design d e t a i l s must be considered when a n a l y z i n g CPT data. I t i s now becoming widely accepted that bearing values must be c o r r e c t e d f o r pore pressure 7 7 e f f e c t s . H o w e v e r , r e s u l t s p r e s e n t e d i n c h a p t e r 5 i n d i c a t e t h a t t h e r e c o r d i n g o f p o r e p r e s s u r e s a t l o c a t i o n s o t h e r t h a n t h e t i p c a n c r e a t e p r o b l e m s i n m a k i n g t h e p r o p e r c o r r e c t i o n s . A g r e a t d e a l o f a t t e n t i o n m u s t a l s o b e p a i d t o d e t a i l s i n t e s t p r o c e d u r e s , i n p a r t i c u l a r , t h e s a t u r a t i o n p r o c e d u r e a n d t h e c h e c k i n g o f z e r o e s b e f o r e a n d a f t e r p e n e t r a t i o n . Z e r o o f f s e t s c a n o f t e n b e c a u s e d b y t e m p e r a t u r e i n s t a b i l i t y . B e c a u s e b e a r i n g v a l u e s a r e t y p i c a l l y l o w i n n o r m a l l y c o n s o l i d a t e d c l a y s , n u m e r i c a l l y s m a l l e r r o r s i n t h e b e a r i n g m a y a c t u a l l y b e q u i t e s u b s t a n t i a l ( s e e f i g u r e 3 . 2 ) . A n o t h e r p r o b l e m i s t h a t t h e t i p l o a d c e l l i s u s u a l l y w o r k i n g i n t h e r a n g e o f 2% t o 5% o f c a p a c i t y a n d , t h e r e f o r e , t h e r e s o l u t i o n o f t h e d a t a r e c o r d i n g s y s t e m m a y b e i n a d e q u a t e . O n t h e o t h e r h a n d , t h e p o r e p r e s s u r e t r a n s d u c e r i s g e n e r a l l y w o r k i n g n e a r c a p a c i t y a n d m a y b e m o r e r e l i a b l e a n d c o n s i s t e n t t h a n t h e b e a r i n g v a l u e s . F o r t h e s e r e a s o n s , r e c e n t l y p r o p o s e d c o r r e l a t i o n m e t h o d s m a k e s i g n i f i c a n t u s e o f p o r e p r e s s u r e d a t a a l l o w i n g c o r r e l a t i o n s t o b e b a s e d o n s e m i - e m p i r i c a l m e t h o d s s u c h a s c a v i t y e x p a n s i o n t h e o r y . T h e s e n e w m e t h o d s m a k e a n a t t e m p t t o i n c o r p o r a t e s t r e s s h i s t o r y , s o i l s t i f f n e s s a n d s e n s i t i v i t y i n t o t h e i r a n a l y s e s . 6 . 3 . 1 U s i n g E f f e c t i v e B e a r i n g t o E s t i m a t e S u S e n n e s e t e t a l . 1 9 8 2 r e c o m m e n d e d t h e u s e o f e f f e c t i v e b e a r i n g ( Q c ' ) f o r e s t i m a t i n g S u . E f f e c t i v e b e a r i n g i s d e f i n e d a s Q c ' = Q c - U t 6 . 2 7 8 a n d S u i s t o b e d e t e r m i n e d u s i n g a n e f f e c t i v e c o n e f a c t o r N c ' a n d t h e e x p r e s s i o n S u = Qc_l 6 . 3 N c ' T h e y s u g g e s t e d t h a t a n a v e r a g e v a l u e o f N c ' = 9 ( ± 3 ) s h o u l d b e u s e d . I t h a s b e e n n o t e d e a r l i e r t h a t t h e d y n a m i c p o r e p r e s s u r e c a n o f t e n b e g r e a t e r t h a n t h e r e c o r d e d b e a r i n g w h i c h i s i m p o s s i b l e s i n c e t h e t i p i s a t o t a l s t r e s s e l e m e n t . C o n e b e a r i n g m u s t b e c o r r e c t e d f o r p o r e p r e s s u r e e f f e c t s i n o r d e r t o u s e t h i s m e t h o d . T h e c o n e f a c t o r N c 1 w a s l a t e r d e f i n e d a s N k e b y L u n n e e t a l . 1 9 8 5 a n d i s d i s c u s s e d i n g r e a t e r d e t a i l i n s e c t i o n 6 . 3 . 3 . 6 . 3 . 2 T h e U s e o f E x c e s s P o r e P r e s s u r e s a n d C a v i t y E x p a n s i o n T h e o r y A n e s t i m a t e o f u n d r a i n e d s h e a r s t r e n g t h c a n b e m a d e f r o m e x c e s s p o r e p r e s s u r e d a t a u s i n g t h e c h a r t s s h o w n i n f i g u r e 6 . 5 . T h e s e c h a r t s w e r e p r e s e n t e d b y C a m p a n e l l a e t a l . 1 9 8 5 a n d w e r e b a s e d o n e x p r e s s i o n s d e v e l o p e d b y M a s s a r c h a n d B r o m s 1 9 8 1 . I n a s t u d y o f p i l e d r i v i n g i n c l a y s l o p e s M a s s a r c h a n d B r o m s p r e s e n t e d e x p r e s s i o n s f o r t h e d i s t r i b u t i o n o f p o r e p r e s s u r e s w i t h i n t h e p l a s t i c z o n e a d j a c e n t t o a s p h e r i c a l o r c y l i n d r i c a l c a v i t y : s p h e r i c a l M J = _ 4 l n / G \ + 2 A f - 0 . 6 6 7 6 . 4 S u 3 \ S u / c y l i n d r i c a l _AU = A l n ( J L J + 1 . 7 3 A f - 0 . 5 7 7 6 . 5 S u 3 \ S u / T h e s e e q u a t i o n s i n c o r p o r a t e t h e e f f e c t s o f o v e r c o n s o l i d a t i o n a n d s e n s i t i v i t y b y u s i n g S k e m p t o n ' s p o r e p r e s s u r e p a r a m e t e r , A f . T h e e f f e c t o f s o i l s t i f f n e s s i s a l s o i n c l u d e d b y u s i n g t h e r i g i d i t y i n d e x G / S u . 7 9 S a t u r a t e d C l a y s A p p r o x i m a t e Af Range Very s e n s i t i v e t o q u i c k 1.5 - 3.0 Nor m a l l y c o n s o l i d a t e d 0.7 - 1.3 L i g h t l y o v e r c o n s o l i d a t e d 0.3 - 0.7 H i g h l y o v e r c o n s o l i d a t e d -0.5 - 0 F i g u r e 6.5 - PROPOSED METHOD FOR OBTAINING Su FROM EXCESS PORE PRESSURE MEASURED DURING CPT ( a f t e r Campanella e t a l . 1985) 80 Because measured pore pressures are also dependent on the porous element location, two charts are shown in figure 6.5 reflecting the different porous element locations and the corresponding equation. The face of the cone is often considered to be in a zone of spherical cavity expansion whereas the region behind the tip is thought to be in a zone of cylindrical cavity expansion. Typical values for Af are given below the charts. A review of the two charts reveals that they describe, qualitatively, the expected pore pressure response. The diagonal lines correspond to different values of Af. Although Af is a parameter associated with tria x i a l testing, its value should adequately reflect the volume change characteristics of the soil for the purposes of correlation. Sensitive soils tend to generate high pore pressures when sheared and, therefore, have a corresponding high Af value. On the other hand, heavily overconsolidated materials are often dilative and this is reflected by a negative Af value. Given a value for soil stiffness, the charts indicate that AU/Su increases as Af increases, as would be expected. It has been mentioned several times that pore pressure response is also dependent on the soil stiffness, with s t i f f e r soils generating greater pore pressures. This expected behaviour is also predicted in figure 6.5. 6.3.3 Use of Various Pore Pressure Parameters and Cone Factors A different approach was adopted by Lunne et a l . 1985 for correlating pore pressure data with undrained shear strength. A l t Using Senneset's pore pressure parameter Bq ( Q Q-,,) they found 81 that i t had a rough correlation with overconsolidation ratio. Other dimensionless parameters were defined and attempts were made to correlate these parameters with Bq as a means of isolating stress history. It was stated in section 5.4 that many researchers have observed that Bq is a rough indicator of stress history. With this in mind, Lunne et a l . 1985 plotted values of Bq versus OCR for different North Sea clays (figure 6.6) and concluded that Bq generally decreased with increasing OCR. This conclusion appears to be valid; however, the data define a relatively wide band. This is not surprising since Bq should also be affected by soi l stiffness and sensitivity. For a given value of sensitivity the upper part of the band should represent materials of high stiffness (low PI) and the lower part of the band should represent less s t i f f materials (high PI). Three dimensionless parameters were defined; Nkt, NAU and Nke: Nkt = Qt - cr,o 6.6 — s n — N AU = _AU_ Su Nke = Qt - Ut Su Lunne et a l . plotted these dimensionless parameters against Bq in an attempt to isolate stress history. Figure 6.7 shows Nkt (the traditional cone factor) plotted against Bq. The high degree of scatter might be expected since i t has been shown that Nkt varies with sensitivity and stiffness in addition to OCR. Plotting N A U against Bq (figure 6.8) provides a more promising correlation as data appear to define a narrow band. Lunne et a l . 6.7 6.8 8 2 1.0 3 < b I ci" 0.8 er CD tr Ld r-U 2 < < LU CC z> CO CO u rr CL Ld or o CL 0.6 0.4 0.2 e v.. v. 1 i i i i f Jmax A u , u m e , - « o : i _ J 1 I 1_ I 2 4 6 8 10 OVERCONSOLIDATION RATIO , OCR F i g u r e 6 . 6 - P O R E P R E S S U R E P A R A M E T E R B q v s O V E R C O N S O L I D A T I O N R A T I O ( a d a p t e d f r o m L u n n e e t a l . 1985) 8 3 F i g u r e 6 . 7 - CONE FACTOR N k t v s PORE PRESSURE PARAMETER Bq ( a d a p t e d f r o m L u n n e e t a l . 1985) 8 4 3 3 «3 rr o H u if LU rr to cn LU rr o_ rr o o. 12 i -8 LOW PI S< / / ' / HIGH PI 'vo i i i Umax V J I 0 . 4 0 . 8 1.2 PORE PRESSURE PARAMETER. B q = 1.6 Au F i g u r e 6 . 8 - PORE PRESSURE PARAMETER NAU VS PORE PRESSURE PARAMETER Bq ( a d a p t e d f r o m L u n n e e t a l . 1985) 8 5 r e c o m m e n d e d u s i n g a n a v e r a g e l i n e t o e s t i m a t e S u w i t h u p p e r a n d l o w e r b o u n d s b e i n g d e f i n e d b y t h e o u t e r e d g e s o f t h e b a n d . T h i s a u t h o r s u g g e s t s t h a t t h e b a n d a c u t a l l y r e p r e s e n t s v a r y i n g d e g r e e s o f s o i l s t i f f n e s s w i t h t h e u p p e r a n d l o w e r l i n e c o r r e s p o n d i n g t o m a t e r i a l s o f l o w a n d h i g h P I r e s p e c t i v e l y . T h e m o s t p r o m i s i n g c o r r e l a t i o n i s s h o w n i n f i g u r e 6 . 9 w h e r e a n ' e f f e c t i v e ' c o n e f a c t o r N k e i s p l o t t e d a g a i n s t B q . T h i s a u t h o r c a u t i o n s t h a t t h e c a l c u l a t i o n o f N k e c a n p r e s e n t s o m e p r o b l e m s . L u n n e e t a l . s t r e s s t h a t c o r r e c t e d b e a r i n g m u s t b e u s e d w h e n c a l c u l a t i n g N k e . I n a d d i t i o n , t h e y c o r r e c t l y i n d i c a t e t h a t p o r e p r e s s u r e s m e a s u r e d o n t h e f a c e ( F P P ) m u s t b e c o n v e r t e d t o a n e q u i v a l e n t b e h i n d t h e t i p p o r e p r e s s u r e ( B T P P ) . T h e r e i n l i e s a p r o b l e m . L u n n e e t a l . a d o p t e d a s i n g l e c o n v e r s i o n v a l u e ( k ) o f 0 . 8 f o r c o n v e r t i n g F P P t o B T P P ( i . e . B T P P = 0 . 8 » F P P ) f o r p e n e t r a t i o n t e s t s i n d i f f e r e n t c l a y t y p e s . F i g u r e 5 . 7 c l e a r l y s h o w s t h a t a u n i q u e v a l u e o f k d o e s n o t e x i s t . A s i d e f r o m t h e d i f f i c u l t i e s o f c o r r e c t i n g f o r p o r e p r e s s u r e e f f e c t s , t h e p r o b l e m s o f l o w b e a r i n g v a l u e s p r e v i o u s l y d i s c u s s e d m a y e x i s t . H o w e v e r , L u n n e e t a l . l i k e l y d i d n o t e x p e r i e n c e t h i s p r o b l e m b e c a u s e o f t h e g r e a t d e p t h o f w a t e r u n d e r w h i c h t h e t e s t s w e r e m a d e . B e c a u s e o f t h e s e p r o b l e m s , t e s t s o n l a n d m a y r e s u l t i n a g r e a t e r d e g r e e o f s c a t t e r t h a n w a s f o u n d f o r t h e o f f s h o r e t e s t s . D e s p i t e t h e p r o b l e m s , c o r r e l a t i o n s b e t w e e n N k e a n d N AU d o s h o w c o n s i d e r a b l e p r o m i s e . 6 . 4 U s i n g F r i c t i o n S l e e v e M e a s u r e m e n t s t o E s t i m a t e S u S o m e r e s e a r c h e r s h a v e p r o p o s e d t h e u s e o f f r i c t i o n s l e e v e m e a s u r e m e n t s t o e s t i m a t e u n d r a i n e d s h e a r s t r e n g t h . B e g e m a n 1 9 6 5 86 16 r -e E 3 12 UJ of 8 o r-O < LL. L U 4 O U A 2* ^ 2 * \ \ 0.4 0.8 1.2 1.6 Au PORE PRESSURE PARAMETER,Bq = F i g u r e 6 . 9 - CONE FACTOR Nk v s PORE PRESSURE PARAMETER Bq ( a d a p t e d f r o m L u n n e e t a l . 1985) 8 7 s u g g e s t e d t h a t t h e f r i c t i o n m e a s u r e m e n t , F s , s h o u l d b e a p p r o x i m a t e l y e q u a l t o S u . D r n e v i c h e t a l . 1 9 7 4 p r e s e n t e d s o m e r e s u l t s f r o m t e s t s u s i n g a m e c h a n i c a l f r i c t i o n c o n e a n d c o n s o l i d a t e d u n d r a i n e d t r i a x i a l t e s t s . T h e y c o n c l u d e d t h a t t h e f r i c t i o n m e a s u r e m e n t s w e r e s l i g h t l y g r e a t e r t h a n t h e u n d r a i n e d s h e a r s t r e n g t h . T h e y c i t e d w o r k b y C l e v e l a n d 1971 a n d W e s l e y 1 9 6 7 t h a t s h o w e d s i m i l a r r e s u l t s , i n d i c a t i n g t h a t F S = ( 1 . 1 9 -1 . 2 8 ) « S u . S c h m e r t m a n n 1 9 7 8 c o n s i d e r e d F s t o b e a n a v e r a g e b e t w e e n p e a k s t r e n g t h a n d r e m o l d e d s t r e n g t h . R o b e r t s o n a n d C a m p a n e l l a 1 9 8 4 s u g g e s t e d t h a t t h e f r i c t i o n m e a s u r e m e n t i s e q u a l t o t h e r e m o l d e d s t r e n g t h . I t s e e m s u n l i k e l y t h a t t h e f r i c t i o n m e a s u r e m e n t s h o u l d b e g r e a t e r t h a n t h e u n d r a i n e d s h e a r s t r e n g t h o f t h e s o i l . C o n s i d e r i n g t h e e x t e n t o f r e m o l d i n g t h a t m u s t t a k e p l a c e d u r i n g p e n e t r a t i o n , t h i s a u t h o r s u g g e s t s t h a t F s s h o u l d r e f l e c t a v a l u e c l o s e t o t h e r e m o l d e d s t r e n g t h o f t h e s o i l , p a r t i c u l a r y i n s e n s i t i v e m a t e r i a l s . I t i s i m p o r t a n t t o n o t e t h a t a l l o f t h e a b o v e c o n c l u s i o n s , e x c e p t f o r t h a t b y R o b e r t s o n a n d C a m p a n e l l a , w e r e b a s e d o n e x p e r i e n c e w i t h t h e m e c h a n i c a l f r i c t i o n c o n e . F r i c t i o n m e a s u r e m e n t s m a d e w i t h t h i s t y p e o f c o n e a r e u s u a l l y r e l a t i v e l y h i g h b e c a u s e o f t h e e n d b e a r i n g o n t h e f r i c t i o n s l e e v e . T h e f r i c t i o n m e a s u r e m e n t s a r e , t h e r e f o r e , n o t a t r u e r e f l e c t i o n o f t h e s t r e s s o n t h e f r i c t i o n s l e e v e . T h i s p r o b l e m d o e s n o t o c c u r w i t h t h e e l e c t r i c f r i c t i o n c o n e ; h e n c e , o n e m u s t b e c a u t i o u s w h e n u s i n g e x i s t i n g c o r r e l a t i o n s b e t w e e n F s a n d S u . 6 . 5 S t r e s s H i s t o r y A n e s t i m a t i o n o f t h e e x t e n t o f o v e r c o n s o l i d a t i o n o f a c l a y 88 d e p o s i t can be made using CPT r e s u l t s . Schmertmann 1978 proposed two methods f o r e s t i m a t i n g the o v e r c o n s o l i d a t i o n r a t i o and maximum past pressure of c l a y . The f i r s t method made use of a c o r r e l a t i o n between normalized undrained shear s t r e n g t h r a t i o and o v e r c o n s o l i d a t i o n r a t i o from l a b o r a t o r y t e s t s . The second method employed a g r a p h i c a l technique to estimate OCR. Using data from Ladd and Foott 1974 and Koutsoftas and F i s c h e r 1976, Schmertmann presented a c o r r e l a t i o n of the r a t i o of the cur r e n t normalized undrained shear s t r e n g t h (normalized with e f f e c t i v e overburden pressure; Su/P') to the normalized undrained shear s t r e n g t h for the normally c o n s o l i d a t e d m a t e r i a l , (Su/P')/(Su/P')nc, with o v e r c o n s o l i d a t i o n r a t i o (on a lo g a r i t h m i c s c a l e ) . T h i s c o r r e l a t i o n i s i l l u s t r a t e d in f i g u r e 6.10. Ladd et a l . 1977 suggested that the curve i n f i g u r e 6.10 can be represented by the f o l l o w i n g e x p r e s s i o n : (Su / P') = OCR m 6.9 (Su / P*)nc with m=0.8. Wroth 1984 presented a t h e o r e t i c a l argument based on C r i t i c a l State S o i l Mechanics theory as to why t h i s c o r r e l a t i o n should e x i s t . He i n d i c a t e d that the theory r e l a t e s the exponent, m, with p h y s i c a l p r o p e r t i e s of c l a y ; i n p a r t i c u l a r , m i s the volumetric s t r a i n r a t i o . Based on the curve i n f i g u r e 6.10 and the undrained shear s t r e n g t h determined from the cone b e a r i n g , Schmertmann suggested using an average normally c o n s o l i d a t e d Su/P' of 0.33 to estimate OCR. Robertson and Campanella 1983 s l i g h t l y m o d i f i e d Schmertmann's method by suggesting that the undrained shear s t r e n g t h can a l s o be estimated from the dynamic pore pressure p r o f i l e and that the normally c o n s o l i d a t e d Su/P' be e s t a b l i s h e d 8 9 1 1.9 2 1 4 5 • 7 i > 10 OCR = Overconsolidation Ratio = max. past a1. present (0^= p') g u r e 6 . 1 0 - N O R M A L I Z E D S u / P * R A T I O v s O V E R C O N S O L I D A T I O N R A T I O F O R U S E I N E S T I M A T I N G O C R ( a d a p t e d f r o m S c h m e r t m a n n 1 9 7 8 ) -0 20 40 60 80 100 120 P L A S T I C I T Y . I N D E X P I % F i g u r e 6 . 1 1 - S T A T I S T I C A L R E L A T I O N B E T W E E N C u / a v o R A T I O AND P L A S T I C I T Y I N D E X F O R N O R M A L L Y C O N S O L I D A T E D C L A Y S 90 using the well known (but controversial) Skempton correlation between (Su/P')nc and plasticity index shown in figure 6.11. However, Robertson and Campanella's method does require a knowledge of PI. This author further suggests that the normally consolidated Su/P' can be determined from the cone bearing or pore pressure profile. As described earlier in section 5.3, the tip resistance is linearly increasing with depth in normally consolidated clay deposits with hydrostatic groundwater conditions. From the linearly increasing portion of the cone bearing profile or the corresponding portion of the pore pressure profile an estimate of (Su)nc can be made using one of the methods previously described. Hence, from this value and from an estimate of the effective overburden pressure (Su/P')nc can be calculated. If the overconsolidated and the normally consolidatd material have the same origin (i.e. are the same deposit) this (Su/P')nc value can be applied in the overconsolidated material. Using this method an estimate of PI is not required (except possibly for estimating Su from the pore pressure profile). Schmertmann 1978 offered an alternative method for estimating OCR in sufficiently thick and homogeneous clay layers. By extrapolating the linearly increasing Qt profile to the intersection of the depth axis (Qt=0) one can define the highest probable past ground surface. The difference in elevation between this surface and the existing ground surface suggests past erosion and overconsolidation due to this depth of material. This method is shown in figure 6.12. For a homogeneous normally consolidated material this extrapolation should pass 91 extrapolated past surface if c Q » 0 and q c 0 • estimate of removed overburden depth causing overconsolidation a. Oessicated "clay crust" layer, ignore (can also occur below GWT) b. Homogeneous clay layer interrupted by: c Silt or sand lenses, ignore d. Sand layer, bottom of clay Note: If log b' obtained here, then signal that this layer not same clay as b above. F i g u r e 6 . 1 2 - EXTRAPOLATION OF THE Qc P R O F I L E AS AN ALTERNATIVE METHOD TO E S T I M A T E OVER-CONSOLIDATION IN T H I C K , HOMOGENEOUS CLAY LAYERS ( a d a p t e d f r o m S c h m e r t m a n n 1978) 92 through the o r i g i n . However, the u n i t weight of the m a t e r i a l o v e r l y i n g the c l a y d e p o s i t and the p o s i t i o n of the water t a b l e can a f f e c t the l o c a t i o n of the i n t e r s e c t i o n of the e x t r a p o l a t e d Qt p r o f i l e and the depth a x i s . In order to determine the depth of e r o s i o n , the e x i s t i n g ground s u r f a c e should be r e p o s i t i o n e d by r e p l a c i n g the o v e r l y i n g m a t e r i a l with an e q u i v a l e n t depth of the normally c o n s o l i d a t e d m a t e r i a l on the b a s i s of bouyant weight. F i g u r e 6.13 shows the bearing p r o f i l e from one the s i t e s used by the author and d i s c u s s e d in g r e a t e r d e t a i l i n chapter 7. The s i t e c o n s i s t s of an upper 2m l a y e r of organic s i l t y c l a y 7=18.4 kN/m3) which i s u n d e r l a i n by approximately 11m of loose to dense sand (avg. 7=20 kN/m 3). Below 13m i s a 2m t r a n s i t i o n l a y e r of s i l t y sand to c l a y e y s i l t f o l l o w e d by a t h i c k d e p o s i t of normally c o n s o l i d a t e d c l a y e y s i l t (avg. 7=18.8 kN/m 3). The water t a b l e i s at a depth of 1m. The e f f e c t of the p o s i t i o n of the water t a b l e and the denser o v e r l y i n g m a t e r i a l i s to cause the p o i n t of i n t e r s e c t i o n to be at an e l e v a t i o n g r e a t e r than the e x i s t i n g ground s u r f a c e . An e q u i v a l e n t depth of the normally c o n s o l i d a t e d m a t e r i a l would be 17.5m; 2.5m above e x i s t i n g ground s u r f a c e . The e x t r a p o l a t e d Qt p r o f i l e i n f i g u r e 6.13 i n t e r s e c t s the depth a x i s approximately 2m above the e x i s t i n g ground s u r f a c e . Because the c l o s u r e angle, a., i n d i c a t e d i n f i g u r e 6.12 i s t y p i c a l l y s m a l l , t h i s method of e s t i m a t i n g OCR i s s e n s i t i v e to the e x t r a p o l a t i o n of the bearing p r o f i l e . Very e r r a t i c b e a r i n g values i n the l i n e a r l y i n c r e a s i n g p o r t i o n of the p r o f i l e or i n s u f f i c i e n t l y t h i c k d e p o s i t s make the e x t r a p o l a t i o n of the p r o f i l e d i f f i c u l t . T h e r e f o r e , the author recommends us i n g the d i s p l a c e d ground surface 30 F i g u r e 6.13 - THE EFFECT OF DENSER OVERLYING MATERIALS ON THE EXTRAPOLATED Qt PROFILE FOR A NORMALLY CONSOLIDATED CLAY LAYER 94 f i r s t method for e s t i m a t i n g OCR from cone p e n e t r a t i o n t e s t s . 6.6 S e n s i t i v i t y S e n s i t i v i t y i s d e f i n e d as the r a t i o of undrained shear s t r e n g t h of undisturbed c l a y to undrained shear s t r e n g t h of t o t a l l y remolded c l a y . I t s value i s dependent upon the t e s t method used. However, the most common value quoted i s that obtained from f i e l d or l a b o r a t o r y vane t e s t s . Schmertmann 1978 proposed a method f o r o b t a i n i n g a rough estimate of the vane s e n s i t i v i t y f o r the Begemann mechanical cone. Robertson and Campanella 1983 proposed a s i m i l a r method for use with the e l e c t r i c cone: St = J_0_ 6.10 Rf% T h i s method i m p l i e s that the s t r e s s on the f r i c t i o n sleeve i s c l o s e to the remolded shear s t r e n g t h of the s o i l . Equation 6.10 a l s o ignores the e f f e c t of overburden p r e s s u r e . 95 CHAPTER 7 FIELD PROGRAMME AND DISCUSSION OF RESULTS 7.1 Introduction The f i e l d programme consisted of cone penetration and f i e l d vane shear tests at five lower mainland s i t e s : 1) McDonald Farm 2) B.C. Hydro Railway Crossing 3) Upper 232nd St. 4) Lower 232nd St. 5) Haney Slide The general locations of the si t e s are shown in figure 7.1 and a summary of the f i e l d tests conducted for t h i s investigation i s presented in table 7.1. A summary of the material properties for the different s i t e s is given in table 7.2. This chapter presents the test results from each s i t e and discusses them in rel a t i o n to the various correlation methods described in chapter 6. A summary compares the results from the five s i t e s . In addition, correlations between f r i c t i o n sleeve measurements and vane shear strength are presented. Lastly, estimating vane s e n s i t i v i t y from CPT data i s discussed. 7.2 McDonald Farm Research Site 7.2.1 General Geology and Site Description McDonald Farm i s located at the northern edge of Sea Island in the municipality of Richmond. The island i s one of several that make up the Fraser River delta. The general geology consists of d e l t a i c d i s t r i b u t a r y channel f i l l and overbank 7.1 GENERAL LOCATION OF RESEARCH S I T E S SITE CPT CPT DATE CONE VST VST DATE VANE TYPE PROFILE 1 Apr 1 1 15 1981 UBC MA 1 Sept 27 1983 GEONOR MCDONALD FARM 2 Ju 1 y 23 1982 UBC #4 2 Sept 29 1983 GEONOR RICHMOND 3* Aug. 04 1982 UBC #4 4 Jan. 26 1984 UBC #6 5 May 05 1984 UBC #6 B.C. HYDRO RAILWAY 1 Nov. 04 1982 UBC MA 1 Feb. 15 1984 NILCON SITE LANGLEY 2 Oct . 24 1982 MOD. HOG. 232nd St. - Upper 1 Dec. 08 1983 UBC 15cm' 1 Feb. 10 1984 NILCON LANGLEY (UBC *5) 2 Feb. 10 1984 NILCON 232nd St. - Lower 1 Nov 17 1984 UBC #4 1 Nov. 17 19S4 NILCON LANGLEY 2 duly 17 1984 UBC #6 2 dan. 1 1 1984 NILCON 3 dan. 20 1984 NILCON HANEY SLIDE SITE 1 dune 22 1984 UBC MG 1 dune 22 1984 NILCON • pore pressure measured on face T a b l e 7.1 SUMMARY OF THE F I E L D PROGRAMME SITE S.G. Wl Wp Wn PI St range avg range avg range avg range avg range avg MCDONALD FARM 2.8 25-42 35 22-25 24 23-40 34 3-20 15 2- 7 5 B.C. HYDRO RAIL. SITE 2.8 32-59 42 16-27 21 27-53 45 16-34 24 7- 10 9 232nd St. SITE 2.8 40 20 42-47 45 19 2-19 1 1 HANEY SLIDE SITE 2.8 44 26 40-45 42 18 3-13 6 S.G. « s p e c i f i c g r a v i t y Wl' " l i q u i d l i m i t (%) Wp » p l a s t i c l i m i t (X) Wn « natural water content ('/.) PI '= p l a s t i c i t y index (%) St = s e n s i t i v i t y T a b l e 7 . 2 SUMMARY OF MATERIAL P R O P E R T I E S A T THE D I F F E R E N T S I T E S 98 d e p o s i t s which o v e r l i e p o s t g l a c i a l e s t u a r i n e and marine sediments (Armstrong 1978). A t y p i c a l CPT p r o f i l e from the s i t e i s p r e s e n t e d i n f i g u r e 7.2 and shows t h a t the g e n e r a l s t r a t i g r a p h y c o n s i s t s o f : 0-2m s o f t o r g a n i c s i l t y c l a y 2-13m l o o s e t o dense c o a r s e sand; some l a y e r s of f i n e sand 13-I5m f i n e sand, some s i l t ; t r a n s i t i o n zone l5-300*m s o f t n o r m a l l y c o n s o l i d a t e d c l a y e y s i l t T h i s r e p o r t i s concerned o n l y w i t h the c l a y e y s i l t below 15m. C o r r e c t e d b e a r i n g and dynamic pore p r e s s u r e p r o f i l e s from f o u r soundings i n the c l a y e y s i l t a r e shown i n f i g u r e 7.3. Note t h a t h i g h e r pore p r e s s u r e s were r e c o r d e d f o r the p r o f i l e where the pore p r e s s u r e s were measured on the f a c e . These p r o f i l e s i l l u s t r a t e the r e p e a t a b i l i t y of CPT and t h a t both cone b e a r i n g and pore p r e s s u r e i n c r e a s e l i n e a r l y w i t h depth i n a n o r m a l l y c o n s o l i d a t e d m a t e r i a l . Note i n f i g u r e 7.2 t h a t the f r i c t i o n r a t i o tends t o decrease w i t h d e p t h . U n d r a i n e d shear s t r e n g t h and vane s e n s i t i v i t y p r o f i l e s from two VST soundings a r e shown i n f i g u r e 7.4. The u n d r a i n e d shear s t r e n g t h i n c r e a s e s l i n e a r l y w i t h depth (Su/P'=0.34) and the. s e n s i t i v i t y i s r e l a t i v e l y c o n s t a n t w i t h depth (avg. St=5). 7.2.2 C o r r e l a t i o n s Between Su and CPT The r e s u l t s of the v a r i o u s c o r r e l a t i o n t e c h n i q u e s f o r McDonald Farm a r e shown i n f i g u r e s 7.5 through 7.9. P l o t s of Qc/Su and Qt/Su vs depth ( f i g u r e 7.5) p r o v i d e a f a i r l y r e a s o n a b l e e s t i m a t e of Su. The s c a t t e r i s reduced when c o r r e c t e d 100 CONE BEARING Ot (bar) PORE PRESSURE U < b a r ) -I-F i g u r e 7.3 PROFILES FROM 4 CPT SOUNDINGS IN MCDONALD FARM CLAYEY SILT UNDRAINED SHEAR STRENGTH Su (ViPo) 20 40 60 BO VANE SENSITIVITY St IS 20 LEGEND VST 1 • VST 2 (a) (b> F i g u r e 7.4 FIELD VANE STRENGTH AND SENSITIVITY PROFILES AT MCDONALD FARM 101 Nc Oc / Su Nc Ot / Su (a) (to) LEGEND a CPT 1 - VST 1 & 2 & CPT 2 - VST 1 & 2 o CPT 3 - VST 1 & 2 • CPT 4 - VST 1 & 2 igure 7.5 Qc/Su AND Qt/Su vs DEPTH AT MCDONALD FARM 102 N k (Qe - SICV) / Su 10 15 20 •ao €EO BO * A ° •flflo BUO, B ffl • to 43*20 D D < ° A O D IS AO ri? & DD ^ O -• AO 1 1 1— (a) L E G E N D • CPT 1 - VST 1 & 2 A CPT 2 - VST 1 & 2 O CPT 3 - VST 1 & 2 * CPT 4 - VST 1 & 2 F i g u r e 7.6 (Qc-cr,o )/Su A N D (Qt-<r„ )/Su vs D E P T H A T M C D O N A L D F A R M 103 N k e <Qt - Ut> / Su 15 20H 25 30 - c • • - - CO c DO ° C ? o D fi 0 D r f o D D ° o ft <fc B 8 0 0 °a °o ° D 0 O B % D D ° 0 tP 0 ° ° o ° o D 0 (a) (b) LEGEND • CPT 1 - VST 1 & 2 O CPT 2 - VST 1 £. 2 * CPT 4 - VST 1 & 2 Fi g u r e 7.7 (Qc-Ut)/Su AND (Qt-Ut)/Su vs DEPTH AT MCDONALD FARM 1 04 15-20-25-30-N<MJ Olt - Uo) / Su P.P. BEHIND THE TIP S 10 15 _1 I 1— a -B o ' . ° 8 . B a -a -i i i A u » u 20 r3 I I I nt " m a . V OJt. - Uo) / Su P. P. ON THE TIP (a) (b) LEGEND LEGEND D CPT 1 a CPT 2 O CPT 4 * CPT 5 VST 1 & 2 VST 1 & 2 VST 1 & 2 VST 1 & 2 o CPT 3 - VST 1 & 2 Figure 7.8 AU/Su vs DEPTH FOR DIFFERENT POROUS ELEMENT LOCATIONS AT McDONALD FARM CONC FACTOR - M.I CQt - SICV) / Su in c ft) PORE PRESSURE F A C T O R - Ntu (Ut. - U«J / Su z z E» C 0> a z < 01 CO > -3 2 n a o z > sr1 a > 2 O r> • n n n TJ TJ TJ - 3 -3 -3 N i - » I I I < < < w w w -3 -3 -3 fr> (?•• tr» N> N> t o f W PJ z a •» a • ~ JO . c in •n I S m ' c in < • tn " C X s m , ~ Tl o > f X < w i .1, r <&-<< tr -0 1 1 1 1 1 1 0 i 1 J _ ,i „ C O N E F A C T O R - Nk, tat - uo / Su s in . c i» #c .Of £ -i i * • i ' • • ' i SO I 1 06 b e a r i n g , Qt, i s used. An even b e t t e r e s t i m a t e can be made i f overburden s t r e s s i s i n c l u d e d as shown i n f i g u r e 7.6. A g a i n , the s c a t t e r i s reduced when Qt i s used. F i g u r e 7.7a i l l u s t r a t e s the n e c e s s i t y f o r u s i n g c o r r e c t e d b e a r i n g when employing Senneset's e f f e c t i v e b e a r i n g approach. A f a i r l y u n i f o r m cone f a c t o r i s a t t a i n e d u s i n g t h i s method, however, the s c a t t e r appears to be s l i g h t l y g r e a t e r than t h a t o b s e r v e d f o r the t r a d i t i o n a l methods ( f i g u r e s 7.5b and 7.6b). The use of excess pore p r e s s u r e p r o v i d e s a v e r y good means of e s t i m a t i n g Su as shown i n f i g u r e 7.8 where AU/Su i s p l o t t e d a g a i n s t d e p t h f o r two d i f f e r e n t porous element l o c a t i o n s . P l o t s of Nkt, N A U and Nke vs Bq are shown i n f i g u r e 7.9. There i s no d i s c e r n i b l e c o r r e l a t i o n , except p o s s i b l y f o r Nke vs Bq, as the d a t a t e n d t o c l u s t e r i n one a r e a . T h i s i s due t o the s m a l l v a r i a t i o n i n Bq, which might be e x p e c t e d s i n c e the m a t e r i a l i s n o r m a l l y c o n s o l i d a t e d and i t s p r o p e r t i e s are f a i r l y u n i f o r m . In s e c t i o n 7.7 the data are compared t o t h o s e from the o t h e r s i t e s where the range i n Bq i s g r e a t e r . 7.3 B.C. Hydro R a i l w a y C r o s s i n g S i t e 7.3.1 G e n e r a l Geology and S i t e D e s c r i p t i o n T h i s s i t e i s l o c a t e d a t the base of a 5m c u t a d j a c e n t t o the T r ans Canada Highway i n L a n g l e y . I t i s s i t u a t e d a p p r o x i m a t e l y 100m west of the B.C. Hydro r a i l w a y o v e r p a s s . The s i t e i s l o c a t e d a t the e a s t e r n e x t e n t of t h e C a p i l a n o sediments which c o n s i s t of r a i s e d d e l t a s , i n t e r t i d a l and beach d e p o s i t s and g l a c i o m a r i n e sediments (Armstrong 1978). The CPT p r o f i l e i n 1 07 f i g u r e 7.10 shows t h a t the s i t e s t r a t i g r a p h y i s : 0-2.5m mixed g r a v e l and sand f i l l 2.5-10 m l i g h t l y o v e r c o n s o l i d a t e d s i l t y c l a y w i t h o c c a s i o n a l s i l t y sand l a y e r s l0-30*m n o r m a l l y c o n s o l i d a t e d s i l t y c l a y w i t h o c c a s i o n a l s i l t y sand l a y e r s A d e t a i l e d l o g from a c o n t i n u o u s l y sampled b o r e h o l e ( t o 14.4m) i s p r o v i d e d i n appendix A. P r o f i l e s of index p r o p e r t i e s and u n d r a i n e d s t r e n g t h and s e n s i t i v i t y from l a b o r a t o r y and f i e l d vane t e s t s a r e shown i n f i g u r e 7.11. Note t h a t the l a b o r a t o r y v a l u e s tend t o be l e s s than the i n s i t u v a l u e s i n d i c a t i n g p o s s i b l e sample d i s t u r b a n c e or s i z e e f f e c t s . The p l a s t i c i t y index d e c r e a s e s s l i g h t l y w i t h depth. S e n s i t i v i t y does not v a r y much and has an average v a l u e of 9. The u n d r a i n e d s t r e n g t h i n c r e a s e s w i t h depth h a v i n g Su/P'=0.31 i n the n o r m a l l y c o n s o l i d a t e d r e g i o n . 7.3.2 C o r r e l a t i o n s Between Su and CPT The r e s u l t s of the v a r i o u s c o r r e l a t i o n methods are shown i n f i g u r e s 7.12 through 7.16. The cone f a c t o r , Nc (Qc/Su or Qt/Su; f i g u r e 7.12), i n i t i a l l y d e c r e a s e s w i t h d e p t h t o a depth of 10m. Below t h i s , Nc tends t o i n c r e a s e w i t h d e p t h . A s i m i l a r t r e n d i s observed f o r Nk ((Qc-cr,o)/Su or (Qt-cr, 0)/Su; f i g u r e 7.13). Note the s i g n i f i c a n t r e d u c t i o n i n s c a t t e r when c o r r e c t e d b e a r i n g i s used. The i n i t i a l d e c r e ase i n Nc and Nk may be a r e s u l t of the d e c r e a s i n g o v e r c o n s o l i d a t i o n of the c l a y . The subsequent i n c r e a s e i n cone f a c t o r w i t h depth may be a r e f l e c t i o n of the decrease i n p l a s t i c i t y and the s l i g h t i n c r e a s e i n s e n s i t i v i t y of the m a t e r i a l w i t h depth. 1 0 8 F i g u r e 7 . 1 0 T Y P I C A L C P T P R O F I L E A T B . C . H Y D R O R A I L W A Y S I T E MOISTURE CONTENT (X) a D » : 0 - • • • D * V o n . Su ChPol 10 30 30 40 SO V o n . S . n . l t l v l t y (b) •oa a a a a a L E G E N D (a) A P l a s t i c L i m i t A. •_ i qu i d L i m i t O N a t u r a l M o i s t u r e Conten t (b) tk F i e l d Vane (Peak) O F i e l d Vane (Remolded) O Lab Vane (Peak) * Lab Vane (Remolded) (c) A F i e l d Vane • Lab Vane F i g u r e 7 . 1 1 I N D E X P R O P E R T I E S , F I E L D V A N E S T R E N G T H A N D S E N S I T I V I T Y P R O F I L E S A T B . C . H Y D R O R A I L W A Y S I T E 1 09 Nc Oo / Su Nc Ot / Su ( b ) LEGEND • CPT 1 a CPT 2 F i g u r e 7.12 Qc/Su AND Qt/Su vs DEPTH AT B.C. HYDRO RAILWAY SITE 1 10 Nk <Qc - S1CV) / Su Nk 10 _L_ IS A a A • a O A a A • a • A • A • A • A • A • 20 (Qt - SIGV) / Su (a) LEGEND • CPT 1 A CPT 2 F i g u r e 7.13 (Qc-cr„ )/Su and ( Q t - O i . )/Su vs DEPTH AT B.C. HYDRO RAILWAY S I T E 111 Nke COc - UO / So Nke <0t - U O / Su (a) (b) LEGEND o CPT 1 a CPT 2 Figure 7.14 (Qc-Ut)/Su AND (Qt-Ut)/Su vs DEPTH B.C. HYDRO RAILWAY SITE 1 12 ait - u.) / Su P.P. BEHIND TIP L E G E N D • C P T 1 * C P T 2 F i g u r e 7 . 1 5 A U / S u v s D E P T H A T B . C . H Y D R O R A I L W A Y S I T E COME FACTOR - Nkt COt - SIGV) / Su 1 c CTi W Z > t-H r r tr1 -£z X > c ty. t-H Q) -3 = D3 O. Z < 01 CO > •3 CO r> o TJ TJ -3 -3 to — o w z a . 1*1 « C X m H n x PORE PRESSURE FACTOR - NAu (Ut - U%3 / Su t> • t> • * r» > : tr ' • I 1 1 1-CONE FACTOR - Hum COt - UO / Su X X a » o O . » X c m v5 r» X ci x < -»—e--i i i— 1 1 4 Two d i s t i n c t c u r v e s a r e o b s e r v e d i n f i g u r e 7.14b where the r a t i o of e f f e c t i v e b e a r i n g t o Su (Nke) i s p l o t t e d a g a i n s t depth. The s e p a r a t i o n between the two c u r v e s might r e f l e c t the problem of a c c u r a c y d i s c u s s e d i n s e c t i o n 6.3.3; two s i m i l a r numbers, Qt and Ut, are s u b t r a c t e d t o a t t a i n a s m a l l number which may be prone t o e r r o r . However, t h e t r e n d s i n the c u r v e s are s i m i l a r and suggest t h a t the use of e f f e c t i v e b e a r i n g works w e l l i n n o r m a l l y c o n s o l i d a t e d d e p o s i t s . The cone f a c t o r tends t o i n c r e a s e w i t h i n c r e a s i n g OCR. T h i s i s as e x p e c t e d s i n c e Qt s h o u l d i n c r e a s e and Ut (measured be h i n d the t i p ) s h o u l d decrease w i t h i n c r e a s i n g OCR. The v a l u e of AU/Su i n c r e a s e s w i t h depth as shown i n f i g u r e 7.15. A g a i n , t h i s might be a r e f l e c t i o n of the decrease i n p l a s t i c i t y and the s l i g h t i n c r e a s e i n s e n s i t i v i t y w i t h depth. A l t h o u g h the d a t a a r e s c a t t e r e d , t h e r e appears t o be a d i s t i n c t k i n k i n the c u r v e above 5m. A n o t i c a b l e decrease i n AU/Su i s observed because of the lower excess pore p r e s s u r e i n the o v e r c o n s o l i d a t e d m a t e r i a l . C o n s i s t e n t t r e n d s are observed f o r N A U and Nke vs Bq i n f i g u r e 7.16, the l a t t e r h a v i n g the l e a s t s c a t t e r . No c o r r e l a t i o n i s o b s e r v e d f o r Nkt vs Bq. 7.4 Upper 232nd S t . S i t e 7.4.1 G e n e r a l Geology and S i t e D e s c r i p t i o n T h i s s i t e i s l o c a t e d a t the 232nd S t . e x i t of the Trans Canada Highway i n L a n g l e y . I t i s a p p r o x i m a t e l y 1km e a s t of the B.C. Hydro r a i l w a y s i t e . Two s i t e s have been d e s i g n a t e d at the 232nd S t . i n t e r c h a n g e ; the upper and lower s i t e s . The lower s i t e 1 15 i s d i s c u s s e d i n s e c t i o n 7.5. The upper s i t e i s s i t u a t e d on a compacted c l a y f i l l t h a t forms the approach f o r the 232nd S t . ove r p a s s . The s i t e l i e s a t the western e x t e n t of the F o r t L a n g l e y F o r m a t i o n . T h i s f o r m a t i o n has r e c o r d e d a t l e a s t t h r e e advances and r e t r e a t s of a v a l l e y g l a c i e r and c o n s i s t s of i n t e r b e d d e d marine, g l a c i o m a r i n e and g l a c i a l sediments (Armstrong 1978). A CPT p r o f i l e from the upper s i t e i s shown i n f i g u r e 7.17 and the f i e l d vane p r o f i l e s a r e shown i n f i g u r e 7.18. Note t h a t the cone b e a r i n g c l e a r l y i n d i c a t e s the o v e r c o n s o l i d a t i o n of t h e upper 7m. The s t a t i g r a p h y c o n s i s t s o f : 0-2.5m compacted c l a y f i l l ; o r g a n i c 2.5-7.5m o v e r c o n s o l i d a t e d s i l t y c l a y 7.5-20*m n o r m a l l y c o n s o l i d a t e d s i l t y c l a y w i t h o c c a s i o n a l sand l e a s e ; i n c r e a s i n g i n sand c o n t e n t w i t h depth The cone b e a r i n g i s compared w i t h the f i e l d vane r e s u l t s and the o v e r c o n s o l i d a t i o n r a t i o i n f i g u r e 7 .19 . The OCR was c a l c u l a t e d u s i n g the f i r s t method d e s c r i b e d i n s e c t i o n 6.5. Note how b o t h the cone b e a r i n g and vane s t r e n g t h d e c r e a s e w i t h depth i n the o v e r c o n s o l i d a t e d m a t e r i a l . Both i n c r e a s e l i n e a r l y w i t h depth i n the n o r m a l l y c o n s o l i d a t e d r e g i o n (Su/P'=0.23). 7.4.2 C o r r e l a t i o n s Between Su and CPT The r e s u l t s f o r the upper 232nd S t . s i t e a r e shown i n f i g u r e s 7.20 t h r o u g h 7.24. The cone f a c t o r Nc e x h i b i t s c o n s i d e r a b l e s c a t t e r and g e n e r a l l y i n c r e a s e s w i t h depth ( f i g u r e 7.20). I t does appear t h a t Qc/Su i n i t i a l l y d e c r e a s e s w i t h depth r e f l e c t i n g the decrease i n OCR, however, t h i s i s not obser v e d f o r Qt/Su. There i s s i g n i f i c a n t l y l e s s s c a t t e r f o r Nk vs de p t h 1 1 6 FiiCTiai RATIO oirrrjxxriM. p.p. imutMim • f CD RATIO i i v s t pacrtu: 7 0 0 3 0 I 0 F i g u r e 7.17 TYPICAL CPT PROFILE AT UPPER 232nd S t . SITE UNOR AINED SHEAR STRENGTH Su CKPoJ 10-1 3 -20-23-30-50 VANE SENSITIVITY St 100 0 2 4 S 8 10 12 14 IB IB 20 (a) _ l I F i g u r e 7.18 FIELD VANE STRENGTH AND SENSITIVITY PROFILES AT UPPER 232nd S t . SITE 1 1 7 L E G E N D a. V S T 1 a V S T 2 F i g u r e 7 . 1 9 C O M P A R I S O N B E T W E E N C O N E B E A R I N G , V A N E S H E A R S T R E N G T H A N D O V E R C O N S O L I D A T I O N R A T I O A T U P P E R 2 3 2 n d S t . S I T E 1 1 8 Nc Oo / Su Nc Q t / S u (a) (b) LEGEND A VST 1 D VST 2 Figu r e 7.20 Qc/Su AND Qt/Su vs DEPTH AT UPPER 232nd S t . SITE 119 Nk <0e - SICV) / Su Nk (Qt - SICV) / Su (a) LEGEND • V S T 1 A V S T 2 F i g u r e 7.21 ( Q c - t j , . ) / S u a n d ( Q t - a , . ) / S u v s DEPTH AT UPPER 232nd S t . S I T E 120 Nke <Ot - Ut) / Su (a) (b) LEGEND • VST 1 & VST 2 F i g u r e 7.22 (Qc-Ut)/Su AND ( Q t - U t ) / S u vs DEPTH AT UPPER 232nd S t . SITE 121 N A U ( l i t - Us) / Su 10 13 20 OA DA. • A A Q A A o a L E G E N D • VST 1 & VST 2 F i g u r e 7.23 AU/Su vs DEPTH AT UPPER 232nd S t . SITE CONC FACTOR - Nkt COt - SIGV) / £u C PORE PRESSURE FACTOR CUt - U«J / Su KAu to M Z UJ rO rr 3 -Q j Z CO r> rr c Cu CO 3 ra z < tn M > -3 G TJ TJ W » t> O < < CO CO -3 -3 ro — tr1 ra O ra z a CONE FACTOR - Nk« COt - Ut) / Su 221 123 ( f i g u r e 7.21). Nk i n i t i a l l y d e c r e a s e s w i t h depth t o a p p r o x i m a t e l y 8m where the m a t e r i a l i s e s s e n t i a l l y n o r m a l l y c o n s o l i d a t e d . Below 8m, Nk i n c r e a s e s w i t h i n c r e a s i n g s e n s i t i v i t y . F i g u r e 7.22a c l e a r l y i l l u s t r a t e s t he need t o c o r r e c t b e a r i n g data f o r pore p r e s s u r e e f f e c t s when u s i n g the e f f e c t i v e b e a r i n g approach as the val u e of Nke i s n e g a t i v e which, of c o u r s e , i s . i m p o s s i b l e . A d r a m a t i c d e c r e a s e i n Nke w i t h d e c r e a s i n g OCR can be seen i n f i g u r e 7.22b. In the n o r m a l l y c o n s o l i d a t e d range Nke i n c r e a s e s w i t h i n c r e a s i n g s e n s i t i v i t y . N f l U (AU/Su) vs depth i s shown i n f i g u r e 7.23 and i s observed t o i n c r e a s e d r a m a t i c a l l y w i t h depth i n the o v e r c o n s o l i d a t e d s i l t y c l a y . A g a i n , a f a i r l y c o n s i s t e n t t r e n d i s obser v e d f o r N A U and Nke vs Bq. There does n o t , however, appear t o be a c o r r e l a t i o n between Nkt and Bq. 7.5 Lower 232nd S t . S i t e 7.5.1 G e n e r a l Geology and S i t e D e s c r i p t i o n The lower s i t e i s s i t u a t e d s l i g h t l y above highway l e v e l and about 5m below the e l e v a t i o n of the upper s i t e . The near s u r f a c e m a t e r i a l i s o v e r c o n s o l i d a t e d due t o d e s s i c a t i o n . A t y p i c a l CPT p r o f i l e i s shown i n f i g u r e 7.25 and the f i e l d vane r e s u l t s a r e shown i n f i g u r e 7.26. The u n d r a i n e d shear s t r e n g t h p r o f i l e g e n e r a l l y i n c r e a s e s w i t h depth (Su/P'=0.23) but t a k e s a c u r i o u s jump a t a depth of 15m. T h i s i n c r e a s e i n Su i s l i k e l y due t o the i n f l u e n c e of sand l e n s e s . 124 F i g u r e 7 . 2 6 F I E L D VANE STRENGTH AND S E N S I T I V I T Y P R O F I L E S AT LOWER 2 3 2 n d S t . S I T E 125 7 . 5 . 2 C o r r e l a t i o n s Between Su a n d CPT R e s u l t s f o r t h e l o w e r 232nd S t . s i t e a r e shown i n f i g u r e s 7 . 2 7 t h r o u g h 7 . 3 1 . The t r a d i t i o n a l c o n e f a c t o r s , Nc and Nk ( f i g u r e s 7 . 2 7 and 7 . 2 8 r e s p e c t i v e l y ) show c o n s i d e r a b l e s c a t t e r e v e n t h o u g h t h e s c a t t e r i s r e d u c e d when Q t i s u s e d . The g e n e r a l t r e n d i s c o n s i s t e n t w i t h t h e r e s u l t s f r o m t h e o t h e r s i t e s ; Nc o r Nk i n c r e a s i n g w i t h i n c r e a s i n g s e n s i t i v i t y . T h e r e i s a d e c r e a s e i n Nc a n d Nk between 13m and 17m due t o t h e u n r e a l i s t i c a l l y h i g h Su v a l u e s . T h e p l o t o f Nke v s d e p t h i n f i g u r e 7 . 2 9 b shows c o n s i d e r a b l e s c a t t e r ; a g a i n l i k e l y due t o t h e i n f l u e n c e o f t h e s a n d l e n s e s on t h e m e a s u r e d p o r e p r e s s u r e s . The p l o t of N A U v s d e p t h i n f i g u r e 7 . 3 0 i n d i c a t e s t h e same t r e n d s o b s e r v e d a t t h e o t h e r s i t e s . C o n s i s t e n t t r e n d s a r e a l s o o b s e r v e d f o r N Au a n d Nke v s Bq i n f i g u r e 7 . 3 1 . 7 . 6 Haney S l i d e S i t e 7 . 6 . 1 G e n e r a l G e o l o g y a n d S i t e D e s c r i p t i o n T h e H a n e y S l i d e s i t e i s l o c a t e d a p p r o x i m a t e l y 30km e a s t ' o f V a n c o u v e r a l m o s t d i r e c t l y b e l o w t h e town c e n t r e o f H a n e y . The s i t e i s a remnant o f t h e Haney s l i d e o f J a n u a r y 3 0 , 1880 . I t f e a t u r e s a hummocky t o p o g r a p h y made u p o f t h e s l i d e b l o c k s f rom t h e r e t r o g r e s s i v e f a i l u r e ( D a v i e s 1 9 8 5 ) . T h e g e n e r a l g e o l o g y c o n s i s t s o f i n t e r b e d d e d m a r i n e , g l a c i o m a r i n e and g l a c i a l s e d i m e n t s o f t h e F o r t L a n g l e y F o r m a t i o n . T h e C P T p r o f i l e f r o m a s o u n d i n g a d j a c e n t t o t h e FV b o r i n g i s shown i n f i g u r e 7 . 3 2 . The s o i l p r o f i l e c o n s i s t s o f : 1 26 Nc Oo / Su Nc at / su o4 13 20 30 10 13 20 23 o ° cP * cB A. A°-D Vs. -A -A. on • * CO m A • A D O «A* A rtl A» U oa J ' 1 L~ (a) (t>) LEGEND • CPT 1•- V S T 1 A> CPT 1 ~ V S T 3 O CPT 2 - V S T 1 • C P T 2 - V S T 3 F i g u r e 7 . 2 7 Q c / S u AND Q t / S u v s DEPTH AT LOWER 232nd S t . S I T E 1 27 Nk <0o - SICV) / Su 3 10 13 20 1 • /„. • _o °. 8 o . r ° C ? B O A A ° 3 - B A i ' J -° a > A O _ a? • A • O "-^ ° A 0 0 * o a -1 o a _ _ i i - J 10 13 20 23 30 Nk «0t - SICV) / Su 3 10 13 CA D -• O^  DiAOO * C C * A - 0 B f i OJ . a A A» • o - A3. O • A - ° A ° - A ° ° a oo 20 (a) (b) LEGEND • CPT 1 - VST 1 a. CPT 1 - VST 3 o CPT 2 - VST 1 • CPT 2 - VST 3 F i g u r e 7.28 (Qc- cr,0 )/Su and (Qt-cr,» )/Su vs DEPTH AT LOWER 232nd S t . SITE 1 28 Nke Nke LEGEND • CPT 1 - V S T 1 a. CPT 1 - V S T 3 O CPT 2 - V S T 1 • C P T 2 - V S T 3 F i g u r e 7 . 2 9 ( Q c - U t ) / S u AND ( Q t - U t ) / S u v s DEPTH AT LOWER 232nd S t . S I T E 1 29 NAU CUt - Ua> / Su 0 5 10 13 20 l I I I 0 4 1 1 B •• 3- - B - * eft « D A 0 a - p A ' f £ A . 10- 5- £A . 2 0 . D A ° *> m 13- •ao w CTc* -A D O -f2 ° ,S° - A D O - A ° ° ^ 0 0 CL Ul a 20-25-**. i i i H I n» V * °> ID An • 1 1 1 LEGEND • CPT 1 - V S T 1 & CPT 1 - V S T 3 O CPT 2 - V S T 1 * CPT 2 - V S T 3 F i g u r e 7 . 3 0 A U / S u v s DEPTH AT LOWER 232nd S t . S I T E i < U I M 14-10-O o (a) (b) 8 i i i 6« •»«..-«. 1 1 1 1 1 r— .4 .8 .8 1 1.2 1.4 PORE PRESSURE PARAMETER -(Ut - U«) / (Dt - SICV) 1.8 3 1 20 14 Si )2 5> u p B or o a . H 2 H 0 * 1 — 1 1 T " ~ l 1 Pi *>° -0. . c?A 0 * 0 . A o f -CD e o iii|ii<l "... Ii .4 .6 .8 I 1.2 1.4 l . i PORE PRESSURE PARAMETER - Bq (Ut - U.) / (Qt - SICV) - I 1 1 1 r .4 .8 .8 I 1.2 PORE PRESSURE PARAMETER - Bq (Ut - U.) / (Qt - SICV) CO O LEGEND • CPT 1 - VST 1 a. CPT 1 - VST 3 O CPT 2 - VST 1 • CPT 2 - VST 3 Figu r e 7.31 Nkt, N*u and Nke 232nd St. SITE vs Bq AT LOWER 131 PORE P R E S S U R E F R I C T I O N B E A R I N G F R I C T I O N D I F F . P . P . (m. o f w a t e r ) ( B A R ) Ot ( B A R ) RATIO (%) RATIO ( A U / Q t ) F i g u r e 7 . 3 2 T Y P I C A L CPT P R O F I L E AT HANEY S L I D E S I T E UNDRAINED SMEAR STRENGTH VANE SENSITIVITY Su CkPo) St F i g u r e 7 . 3 3 F I E L D VANE STRENGTH AND S E N S I T I V I T Y P R O F I L E S AT HANEY S L I D E S I T E 1 32 0-2m f i l l 2 - 3m s a n d 3 - 30*m s a n d y s i l t t o s i l t y c l a y w i t h numerous t h i n f i n e s a n d l a y e r s U n d r a i n e d s h e a r s t r e n g t h a n d v a n e s e n s i t i v i t y p r o f i l e s f r o m t h e two V S T s o u n d i n g s a r e shown i n f i g u r e 7 . 3 3 . T h e Su p r o f i l e i n c r e a s e s o n l y s l i g h t l y w i t h d e p t h ( d i s r e g a r d i n g t h e d a t a o b v i o u s l y i n f l u e n c e d by s a n d l e n s e s ) w i t h an a v e r a g e S u / P ' = 0 . 6 i n d i c a t i n g an o v e r c o n s o l i d a t e d m a t e r i a l . The OCR r a n g e s f r o m 9 n e a r t h e s u r f a c e t o a p p r o x i m a t e l y 2 . 5 a t a d e p t h o f 20m. OCR was c a l c u l a t e d u s i n g t h e f i r s t me thod d e s c r i b e d i n s e c t i o n 6 . 5 . S e n s i t i v i t y d o e s n o t v a r y much h a v i n g an a v e r a g e v a l u e o f 6 . 7 . 6 . 2 C o r r e l a t i o n s Between Su and CPT The r e s u l t s o f t h e v a r i o u s c o r r e l a t i o n t e c h n i q u e s f o r t h e Haney S l i d e s i t e a r e shown i n f i g u r e s 7 . 3 4 t h r o u g h 7 . 3 8 . The c o n e f a c t o r s Nc and Nk ( f i g u r e s 7 .34 a n d 7 . 3 5 ) t e n d t o i n c r e a s e s l i g h t l y w i t h d e p t h a n d be somewhat s c a t t e r e d . On t h e o t h e r h a n d , t h e p l o t o f Nke v s d e p t h i n f i g u r e 7 . 3 6 b i s u n i f o r m w i t h d e p t h w h i c h i s c o n s i s t e n t w i t h t h e s e n s i t i v i t y p r o f i l e . N 4 U v s d e p t h ( f i g u r e 7 . 3 7 ) a p p e a r s t o be s c a t t e r e d , h o w e v e r t h i s i s l i k e l y d u e t o t h e i n f l u e n c e o f t h e s a n d l a y e r s on t h e p o r e p r e s s u r e r e s p o n s e . A c o n s i s t e n t t r e n d i s o b s e r v e d f o r N A U v s Bq i n f i g u r e 7 . 3 8 b . A l t h o u g h t h e Nke d a t a i s c l u s t e r e d , t h e y do seem t o be i n l i n e w i t h what h a s b e e n o b s e r v e d a t t h e o t h e r s i t e s . 133 Nc Oc / Su 10 _L_ IS _J 20 0 A * A A * A A * 8 a 4 • • (a) (b) LEGEND • VST 1 A VST 2 F i g u r e 7 . 3 4 Qc/Su AND Qt/Su vs DEPTH AT HANEY SLIDE SITE 1 34 Nk COc - SICV) / Su Nk «Dt. - SICV) / Su (b) LEGEND a VST 1 A VST 2 F i g u r e 7 . 3 5 (Qc-*. )/Su and (Qt- t r , . )/Su vs DEPTH AT HANEY SLIDE SITE 1 35 Nice (Oe - Ut> / So Nke <0t - UU / Su (a) (b) LEGEND Q VST 1 A VST 2 F i g u r e 7.36 (Qc-Ut)/Su AND ( Q t - U t ) / S u vs DEPTH AT HANEY SLIDE SITE 1 3 6 L E G E N D • V S T 1 A V S T 2 F i g u r e 7.37 A U / S u v s D E P T H A T H A N E Y S L I D E S I T E CDHC FACTO* - Nkt (Ot - SICV) / Sw in c fD PORE PRESSURE FACTOR - Htu CUt - U«) / Su LO 00 UJ Z i-i rr D -PJ Z tn r> *-< c -3 PJ D) D Qi Z < w to > •-3 > Z PJ «3 o O < < CO CO -3 -3 ro —• PJ a Rl z a TJ D - X c in r» TJ i a m C In a . * in ~ c X N in ~ X « -D > r> X > 1 z m in i m n x < " I B X TJ D X c m r» TJ 1 X m c in O) • in ~£ ~ t B • D > f X > t X m in — n n x < *- i a <fiZE> •O * • D t» CONE FACTOR - Nk* COt - Ut) / Su c £ J 1 1 I I 1 1 1——I 1 LZi 1 38 7 .7 A Summary o f t h e R e s u l t s f o r t h e F i v e Lower M a i n l a n d S i t e s A summary o f t h e v a r i o u s c o n e f a c t o r s f o r t h e f i v e l o w e r m a i n l a n d s i t e s i s p r e s e n t e d i n t a b l e 7 . 3 . An a v e r a g e v a l u e f o r a l l t h e s i t e s i s g i v e n f o r e a c h c o r r e l a t i o n m e t h o d . V a l u e s f o r ( Q c - U t ) / S u h a v e been p u r p o s e l y l e f t o u t . T h e r e s u l t s h a v e shown t h a t t h e r e c a n n o t be a s i n g l e c o n e f a c t o r t h a t i s a p p l i c a b l e t o a l l c l a y s . A l l t h e c o r r e l a t i o n t e c h n i q u e s were i n f l u e n c e d by t h e s t r e s s h i s t o r y and most n o t a b l y , t h e s e n s i t i v i t y o f t h e d e p o s i t . T h e d e p e n d a n c e upon s o i l s t i f f n e s s was n o t r e a d i l y a p p a r e n t e x c e p t a t t h e B . C . H y d r o r a i l w a y s i t e , h o w e v e r , t h i s i s p r o b a b l y b e c a u s e t h e r a n g e i n p l a s t i c i t y f o r t h e f i v e s i t e s was n o t g r e a t . The s c a t t e r i n t h e c o r r e l a t i o n s u s i n g c o n e b e a r i n g was r e d u c e d when t h e b e a r i n g was c o r r e c t e d f o r p o r e p r e s s u r e s a n d when o v e r b u r d e n s t r e s s was a c c o u n t e d f o r . T h e s c a t t e r i n t h e d a t a was a l s o c a u s e d by many o t h e r c o n t r i b u t i n g f a c t o r s ; among them were t h e e f f e c t s o f a n i s o t r o p y , v a r i a t i o n s i n s t r a i n r a t e , s t r e s s p a t h s , p r o g r e s s i v e f a i l u r e i n t h e v a n e t e s t s , d i s t u r b a n c e due t o i n s e r t i o n o f t h e i n s t r u m e n t s a n d t h e i n f l u e n c e o f s a n d l e n s e s on t h e v a n e t e s t r e s u l t s a n d t h e CPT b e a r i n g a n d p o r e p r e s s u r e m e a s u r e m e n t s . The u s e o f p o r e p r e s s u r e d a t a a p p e a r s t o be a p r o m i s i n g means o f e s t i m a t i n g u n d r a i n e d s h e a r s t r e n g t h . F i g u r e 7 . 3 9 shows a c o m p a r i s o n be tween p r e d i c t e d a n d m e a s u r e d Su f o r t h e n o r m a l l y c o n s o l i d a t e d c l a y e y s i l t a t t h e M c D o n a l d F a r m s i t e . T h e p r e d i c t e d Su was b a s e d on t h e m e t h o d by C a m p a n e l l a e t a l . 1985 , w h i c h i s d e s c r i b e d i n s e c t i o n 6 . 3 . 2 . E x c e l l e n t a g r e e m e n t was f o u n d f o r t h e p r e d i c t i o n s f r o m t h e p o r e p r e s s u r e s m e a s u r e d N c N k N k e SITE St' PI • 0c Ot Qc-O"»o ot -cr , 0 Ot-Ut AU' A l l ' Su Su Su Su Su Su Su MCDONALD FARM 5 15 11.9 13.9 6. 1 8 . 1 3 . 5 7.4 B . a B.C. HYDRO RAILWAY 9 24 15.4 18.9 11.6 14.3 6.3 10. 3 UPPER 232nd St. 8 19 1 1 .0 13.3 5.8 8. 1 2.5 8.9 LOWER 232nd St. 14 19 16.7 18.3 9.8 11.3 5.9 8.9 HANEY SL I D E 6 18 14 . 2 15.0 16.0 12.7 5.4 8.6 ALL S I T E S 14.2 16 .0 8 . 5 10.3 4 . 7 8.6 1 - average s e n s i t i v i t y 2 - average p l a s t i c i t y index 3 - pore pressure measured behind the t i p 4 - pore pressure measured on the face T a b l e 7.3 S U M M A R Y O F C O N E F A C T O R S F O R 5 L O W E R M A I N L A N D S I T E S 1 40 UNDRAINED SHEAR STRENCTH Su (hPa) L X t-a. u a MCDONALD FARM UNDRAINED SHEAR STRENGTH Su <KPa) • t. a t» 9 E a. ui a 100 LEGEND A Vane Su D P r e d i c t e d Su F i g u r e 7.39 USE OF EXCESS PORE PRESSURE FOR ESTIMATING UNDRAINED SHEAR STRENGTH 141 b e h i n d t h e t i p ( c y l i n d r i c a l c a v i t y e x p a n s i o n a p p r o a c h ) as w e l l as f o r t h o s e measured on t h e f a c e ( s p h e r i c a l c a v i t y e x p a n s i o n a p p r o a c h ) . F i g u r e s 7.40 t h r o u g h 7.43 show t h e a p p r o a c h a d o p t e d by Lunne e t a l . 1985 a p p l i e d t o a l l f i v e o f t h e l o w e r m a i n l a n d s i t e s . The v a r i a t i o n of Bq w i t h OCR i s i l l u s t r a t e d i n f i g u r e 7.40 and shows t h a t t h e p o r e p r e s s u r e p a r a m e t e r d e c r e a s e s w i t h i n c r e a s i n g OCR. T h e r e i s c o n s i d e r a b l e s c a t t e r i n t h e d a t a i n d i c a t i n g t h a t Bq i s not s o l e l y a f f e c t e d by s t r e s s h i s t o r y . The p l o t of Nkt vs Bq f o r a l l f i v e s i t e s i n f i g u r e 7.41 i n d i c a t e s t h a t t h e r e i s no d i s c e r n i b l e c o r r e l a t i o n between Nkt and Bq. A more p r o m i s i n g c o r r e l a t i o n i s t h a t between N A U and Bq shown i n f i g u r e 7.42. A r e g r e s s i o n a n a l y s i s o f t h e d a t a i n d i c a t e s a c o r r e l a t i o n c o e f f i c i e n t • of 0.69. The b e s t c o r r e l a t i o n was between Nke and Bq as shown i s f i g u r e 7.43. A c o r r e l a t i o n c o e f f i c i e n t of 0.81 was d e t e r m i n e d f r o m the d a t a f o r t h e f i v e s i t e s . T h i s w r i t e r a g a i n p o i n t s o u t t h e d i f f i c u l t i e s one may have i n c a l c u l a t i n g Qn, ( Q t - U t ) . B e a r i n g and p o r e p r e s s u r e v a l u e s a r e v e r y s i m i l a r i n s o f t n o r m a l l y c o n s o l i d a t e d s o i l s and a l o s s of a c c u r a c y i n t h e b e a r i n g c a n s i g n i f i c a n t l y a f f e c t t h e c a l c u l a t i o n of Nke. T h i s s h o u l d not p r e s e n t a p r o b l e m , however, s i n c e a p r u d e n t e n g i n e e r i s u n l i k e l y t o r e l y on a s i n g l e c o r r e l a t i o n method, p a r t i c u l a r l y when t h e r e a r e s e v e r a l t e c h n i q u e s a v a i l a b l e . 142 T — i — i — i — r <r m i > or u Iii i - u i u i z I < cc *> < a a. u i s K Ul 0 U) 3 Ul CC I CL •> Ui 3 CC ~ a a. B IT* A F H H • ^ H H A J " .6 H .2 H OA H H r4 q "0 i i i Hf7 ~ r 10 O V E R C O N S O L I O A T I O N R A T I O - O C R LEGEND O McOONALO FARM A B.C HYDRO RAIL SITE Q 232nd St- UPPER 232nd St- LOVER H HANEY SLIDE F i g u r e 7.40 Bq vs OCR FOR 5 LOWER MAINLAND SITES 1 4 3 PORE PRESSURE PARAMETER - Bq (Ut - U«> / CQt SICV) LEGEND O HcOONALO FARM A B.C. HYDRO RAIL SITE D 232nd St. UPPER • 232nd St. LOWER H HANEY SLICE F i g u r e 7 . 4 1 N k t v s B q F O R 5 L O W E R M A I N L A N D S I T E S 1 44 3 < 3 Z W I N tr n a a (j < i u. z ~ a u 20-18-16-14-12-10-B-4-2-a i i i V A • • * D • • — r . 6 l 1.2 D _ D a a 1 a a • • — i — 1.4 1.6 P O R E P R E S S U R E P A R A M E T E R -<Ut - U o ) / ( Q t - S1GV) Bq LEGEND: O . HcOONALO FARM A B.C. HYORO RAIL SITE 0 232nd St. UPPER • 232rvd St. LOVER H HANEY SLIOE F i g u r e 7 . 4 2 N i u v s B q F O R 5 L O W E R M A I N L A N D S I T E S 1 4 5 LEGEND, o MCDONALD FARM A B.C. HYDRO RAIL S I T E 0 232nd St. UPPER • 232nd St. LOVER H HANEY SLIDE F i g u r e 7 . 4 3 N k e v s B q F O R 5 L O W E R M A I N L A N D S I T E S 1 46 7 . 8 C o r r e l a t i o n s Between S u a n d S l e e v e F r i c t i o n F i g u r e s 7 .44 and 7 . 4 5 c o m p a r e f r i c t i o n s l e e v e m e a s u r e m e n t s t o peak v a n e s h e a r s t r e n g t h , S u . F i g u r e s 7 . 4 6 a n d 7 . 4 7 c o m p a r e s l e e v e f r i c t i o n t o r e m o l d e d s h e a r s t r e n g t h , S u r . F i g u r e 7 . 4 4 shows t h a t a r e a s o n a b l e e s t i m a t e o f Su c a n be made u s i n g S u / F s = 5 . 3 , h o w e v e r , t h e r e i s c o n s i d e r a b l e d e v i a t i o n f r o m t h i s r e l a t i o n s h i p , p a r t i c u l a r l y a t s h a l l o w d e p t h s ( f i g u r e 7 . 4 5 ) . T h i s may be p a r t l y due t o t h e low s t r e s s e s t h a t t h e f r i c t i o n s l e e v e e x p e r i e n c e s . A t s h a l l o w d e p t h s t h e t o t a l f o r c e on t h e s l e e v e i s a r o u n d 4 kg t o 10 kg w h e r e a s t h e c a p a c i t y o f t h e f r i c t i o n l o a d c e l l i s 1500 k g . F i g u r e s 7 . 4 6 a n d 7 . 4 7 i n d i c a t e t h a t t h e f r i c t i o n measurement i s c l o s e r t o t h e r e m o l d e d s h e a r s t r e n g t h o f t h e s o i l . N e g l e c t i n g t h e s c a t t e r a t s h a l l o w d e p t h s , t h e a v e r a g e r a t i o o f S u r t o F s i s 1. A summary o f S u / F s a n d S u r / F s f o r t h e d i f f e r e n t s i t e s i s g i v e n i n t a b l e 7 . 4 . 7 . 9 E s t i m a t i n g S e n s i t i v i t y f r o m CPT I t was r e p o r t e d i n s e c t i o n 6 . 6 t h a t a r o u g h e s t i m a t e o f s e n s i t i v i t y c o u l d be made f r o m S t = J_0_ 6 . 1 0 Rf% F i g u r e 7 . 4 8 a shows a p l o t o f S t « R f t (Rf c a l c u l a t e d u s i n g c o r r e c t e d b e a r i n g Qt ) a g a i n s t d e p t h f o r f o u r o f t h e s i t e s w i t h an a v e r a g e v a l u e o f 8 . 1 . A g a i n t h e r e i s some s c a t t e r a t s h a l l o w d e p t h s . N e g l e c t i n g t h i s , t h e b e s t e s t i m a t e o f S t c a n be made f r o m 6 / R f t . Su / F» too 80-60-40 20-i " i o • — - r — — - i D od o o ° o °o H o H D H _ A A A • • o a A D LEGEND o MCDONALD FARM A B.C. HYDRO RAIL S I T E 0 2 3 2 n d St. UPPER H HANEY SLIOE II L a a E C *» o, 0 a 10 20 30 . Slaeva F V I c t J o n F a (kPo) 40 50 F i g u r e 7.44 V A N E S H E A R S T R E N G T H v s S L E E V E F R I C T I O N F O R 4 L O W E R M A I N L A N D S I T E S 10-15-20-25-30-2 4 6 8 10 _ J I I I B B a H A a H a o o o o o o o o o o o o o o I LEGEND O HcOONALO FARM A B.C. HYDRO RAIL SITE • 2 3 2 n d St. UPPER H HANEY SLIDE F i g u r e 7.45 S u / F s v s D E P T H F O R 4 L O W E R M A I N L A N D S I T E S Sur- / Fm CD O O HcOONALO FARM F i g u r e 7 . 4 6 R E M O L D E D S H E A R S T R E N G T H v s S L E E V E F R I C T I O N F O R 4 L O W E R M A I N L A N D S I T E S B.C. HYDRO RAIL SITC 232nd St. UPPER HANEY SLIOe F i g u r e 7 . 4 7 S u r / F s v s D E P T H F O R 4 L O W E R M A I N L A N D S I T E S 1 4 9 SITE St' PI ' Su Sur St Rft' Ot- 0",0 Fs Fs Fs F s . St MCDONALD FARM 5 15 5. 1 1 .0 6. 1 10. 8 B.C. HYDRO RAILWAY 9 24 5.2 0.67 8.4 9. 1 UPPER 232nd St. 8 19 5.7 0.60 9 . 2 16. 5 HANEY SLIDE 6 18 5. 1 0.92 12.0 9 0 ALL SITES 5.3 0.84 8. 1 12 1 1 - average s e n s i t i v i t y 2 - average p l a s t i c i t y index 3 - f r i c t i o n r a t i o c a l c u l a t e d using corrected cone bearing Qt T a b l e 7 . 4 S U M M A R Y O F C O R R E L A T I O N S W I T H F R I C T I O N S L E E V E D A T A F O R 4 L O W E R M A I N L A N D S I T E S c *> a. a a St * Rft 10 IS (Ot - SICV)/<Fa»St > H 10-15-20-25-30-• ° • . a HA o H • a A A o A • H O O O O o o o o o o o o o o o 8 _ J 20 25 LEGEND O McDQNALO FARM. A B.C. HYDRO RAIL SITE • 232nd St. UPPER H HANEY SHOE c »> a. a • 10 IS 20 25 3D 10 i IS 20 H A H °P H H O O O O O O O O O O O O 8 • • o LEGEND o HcOONALO FARM A B.C. HYDRO RAIL SITE • 232nd St. UPPER H HANEY SLIOE l a ) (b) F i g u r e 7 . 4 8 E S T I M A T I N G S E N S I T I V I T Y F R O M C P T 151 E x p r e s s i o n 6 . 1 0 n e g l e c t s t h e e f f e c t o f o v e r b u r d e n s t r e s s . A s s u m i n g F s i s c l o s e t o S u r i t may be p o s s i b l e t o e s t i m a t e S t f r o m S t = Qn 7.1 N s t - P s where S t - s e n s i t i v i t y N s t - f a c t o r f o r e s t i m a t i n g S t Qn - n e t b e a r i n g ; Q t - U t F s - s l e e v e f r i c t i o n A p l o t o f Q n / ( F s - S t ) f o r f o u r s i t e s i s shown i n f i g u r e 7 . 4 8 b h a v i n g an a v e r a g e v a l u e o f 11 ( n e g l e c t i n g s c a t t e r ) . H o w e v e r , t h e r e i s c o n s i d e r a b l y more s c a t t e r u s i n g t h i s m e t h o d t h a n t h e r e i s u s i n g S t = 6 / R f t . A summary o f t h e s e two m e t h o d s i s g i v e n i n t a b l e 7 . 4 . 1 52 CHAPTER 8 SUMMARY AND CONCLUSIONS 8.1 Summary o f F a c t o r s I n f l u e n c i n g t h e E s t i m a t i o n o f Su T h i s p a p e r h a s d i s c u s s e d t h e r e s u l t s o f f i e l d vane and c o n e p e n e t r a t i o n t e s t s f r o m f i v e l o w e r m a i n l a n d s i t e s i n r e l a t i o n t o s e v e r a l p r o p o s e d m e t h o d s o f e s t i m a t i n g S u f r o m C P T . The r e s u l t s h a v e shown t h a t t h e r e i s no u n i q u e m e t h o d f o r e s t i m a t i n g Su f r o m CPT f o r a l l c l a y s . F u r t h e r m o r e , t h e e s t i m a t i o n o f Su f rom CPT i s h e a v i l y i n f l u e n c e d by v a r i o u s f a c t o r s r e l a t i n g t o : 1) m a t e r i a l t y p e and s o i l c h a r a c t e r i s t i c s 2) c o n e d e s i g n a n d CPT t e s t p r o c e d u r e s 3) t h e c h o i c e o f a r e f e r e n c e S u The c h o i c e o f a r e f e r e n c e Su i s s i g n i f i c a n t b e c a u s e Su i s n o t a u n i q u e p a r a m e t e r . I t d e p e n d s on t h e t y p e o f t e s t u s e d , t h e r a t e o f s t r a i n a n d t h e o r i e n t a t i o n o f t h e f a i l u r e p l a n e s . T h e l i k e l y v a r i a t i o n i n Su f o r v a r i o u s t e s t m e t h o d s was i l l u s t r a t e d i n c h a p t e r 1 and was t h e r e a s o n f o r s e l e c t i n g a s i n g l e t e s t m e t h o d ( f i e l d v a n e ) a s a r e f e r e n c e f o r t h i s i n v e s t i g a t i o n . T h e u s e o f d i f f e r e n t r e f e r e n c e s h e a r s t r e n g t h s a l s o makes c o m p a r i s o n s b e t w e e n r e s u l t s r e p o r t e d i n t h e l i t e r a t u r e d i f f i c u l t . The u n d r a i n e d s h e a r s t r e n g t h d e t e r m i n e d f r o m f i e l d v a n e t e s t s i s a l s o i n f l u e n c e d by s e v e r a l f a c t o r s s u c h a s s t r e n g t h a n i s o t r o p y , r a t e e f f e c t s , s o i l d i s t u r b a n c e , d e l a y s be tween v a n e i n s e r t i o n a n d t h e s t a r t o f s h e a r i n g , t h e a s s u m e d s h e a r s t r e s s d i s t r i b u t i o n a n d t h e m e t h o d o f a n a l y s i s . R e c e n t work h a s shown t h a t t h e s t a n d a r d a n a l y s i s i s l i k e l y i n c o r r e c t . H o w e v e r , w i t h 153 o u r p r e s e n t l a c k o f c o m p l e t e u n d e r s t a n d i n g o f t h e VST i t i s b e s t t h a t we c o n t i n u e t o u s e t h e m e t h o d f o r w h i c h we h a v e t h e g r e a t e s t e x p e r i e n c e ; u s i n g a v a n e o f H/D=2 a n d a n a l y s i n g t h e d a t a u s i n g t h e s t a n d a r d e q u a t i o n : E s s e n t i a l t o t h e c o r r e l a t i o n o f Su w i t h CPT i s c o n f i d e n c e a n d a c c u r a c y i n t h e CPT d a t a . One must u n d e r s t a n d t h e l i m i t a t i o n s o f t h e i n s t r u m e n t a n d t h e i r e f f e c t s on t h e t e s t r e s u l t s . The c o n e b e a r i n g c a n s u f f e r a c c u r a c y p r o b l e m s i n s o f t n o r m a l l y c o n s o l i d a t e d c l a y s b e c a u s e t h e t i p l o a d c e l l i s o f t e n o n l y s t r e s s e d f r o m 1% t o 3% o f i t s c a p a c i t y . A f u r t h e r l o s s o f a c c u r a c y c a n o c c u r i f p o r e p r e s s u r e e f f e c t s on t h e c o n e b e a r i n g a n d s l e e v e f r i c t i o n a r e n e g l e c t e d . I t i s a l s o e s s e n t i a l t h a t z e r o l o a d r e a d i n g s be c h e c k e d b e f o r e and a f t e r a p r o f i l e i n o r d e r t o d e t e r m i n e w h e t h e r d r i f t s h a v e o c c u r r e d i n t h e e l e c t r o n i c s . D r i f t s due t o t e m p e r a t u r e h a v e b e e n o b s e r v e d ; t h e e f f e c t s o f w h i c h c a n be s u b s t a n t i a l a s was shown i n c h a p t e r 3 . C o m p l e t e a n d p r o p e r s a t u r a t i o n o f t h e p o r e p r e s s u r e m e a s u r i n g s y s t e m i s r e q u i r e d t o e n s u r e h i g h q u a l i t y p o r e p r e s s u r e d a t a . C h a p t e r 5 i l l u s t r a t e d t h a t p o r e p r e s s u r e s m e a s u r e d a t d i f f e r e n t l o c a t i o n s on t h e c o n e c a n be r a d i c a l l y d i f f e r e n t d e p e n d i n g on t h e t y p e o f m a t e r i a l i n w h i c h t h e t e s t i s m a d e . T h i s b e h a v i o u r must be r e c o g n i z e d i n o r d e r t o p r o p e r l y make p o r e p r e s s u r e c o r r e c t i o n s a n d t o c o m p a r e CPT r e s u l t s . P o r e p r e s s u r e c o r r e c t i o n s t o b e a r i n g must be made u s i n g p o r e p r e s s u r e s m e a s u r e d b e h i n d t h e t i p . D e s p i t e t h e s e p r o b l e m s , t h e c o n e p e n e t r a t i o n t e s t h a s p r o v e d t o be u n e q u a l l e d i n i t s a b i l i t y t o i d e n t i f y s o i l l a y e r 154 b o u n d a r i e s a n d q u a l i t a t i v e l y e v a l u a t e m a t e r i a l t y p e s . L a y e r s a s t h i n a s 1 cm h a v e been d e t e c t e d by t h e c o n e b e a r i n g , h o w e v e r , t h e e s t i m a t i o n o f l a y e r t h i c k n e s s i s c o m p l i c a t e d by t h e s a m p l i n g r a t e . S i g n i f i c a n t t o t h e e s t i m a t i o n o f u n d r a i n e d s h e a r s t r e n g t h i s t h e i n f l u e n c e t h a t t h e s u r r o u n d i n g l a y e r s h a v e on t h e t i p r e s i s t a n c e . A z o n e o f i n f l u e n c e e x t e n d s a b o u t 5 t o 10 c o n e d i a m e t e r s a h e a d a n d b e h i n d t h e t i p d e p e n d i n g on t h e r e l a t i v e s t i f f n e s s o f t h e l a y e r s . T h i s e f f e c t c a n c a u s e a b e a r i n g v a l u e t o be r e c o r d e d t h a t d o e s n o t t r u e l y r e p r e s e n t t h e m a t e r i a l b e i n g t e s t e d . H o w e v e r , t h i s e f f e c t i s more p r o n o u n c e d i n s t i f f e r s o i l s t h a n i n s o f t l a y e r s . T h e e s t i m a t i o n o f Su f r o m CPT a p p e a r s t o be s t r o n g l y i n f l u e n c e d by s u c h s o i l p r o p e r t i e s a s s t r e s s h i s t o r y , s e n s i t i v i t y a n d s t i f f n e s s . The r e s u l t s p r e s e n t e d i n c h a p t e r 7 i n d i c a t e d t h a t i n c r e a s e s i n OCR a n d s e n s i t i v i t y were r e f l e c t e d by i n c r e a s e s i n t h e t r a d i t i o n a l c o n e f a c t o r s Nc a n d N k . A t t h e B . C . H y d r o r a i l w a y s i t e t h e c o n e f a c t o r s a l s o i n c r e a s e d w i t h d e c r e a s i n g p l a s t i c i t y i n d e x ( w i t h OCR a n d s e n s i t i v i t y e s s e n t i a l l y c o n s t a n t ) . C o n s i d e r a b l e s c a t t e r was o f t e n o b s e r v e d b u t was m i n i m i z e d when p o r e p r e s s u r e e f f e c t s a n d o v e r b u r d e n s t r e s s were a c c o u n t e d f o r . I t i s c l e a r t h a t t h e r e i s no u n i q u e v a l u e f o r t h e t r a d i t i o n a l c o n e f a c t o r Nk t h a t i s a p p l i c a b l e t o a l l c l a y s . The u s e o f p o r e p r e s s u r e d a t a a p p e a r s t o be a p r o m i s i n g means o f e s t i m a t i n g Su f r o m C P T . E x p r e s s i o n s h a v e been d e v e l o p e d t h a t p r e d i c t t h e e x c e s s p o r e p r e s s u r e s b a s e d on c a v i t y e x p a n s i o n t h e o r y . T h e y a t t e m p t t o i n c l u d e t h e e f f e c t s o f s e n s i t i v i t y a n d s t r e s s h i s t o r y t h r o u g h t h e u s e o f S k e m p t o n ' s p o r e p r e s s u r e 1 55 p a r a m e t e r A f . The e f f e c t s o f s o i l s t i f f n e s s i s i n c l u d e d by u s i n g t h e r i g i d i t y i n d e x G / S u . A s p h e r i c a l c a v i t y e x p a n s i o n a p p r o a c h s h o u l d be u s e d f o r p o r e p r e s s u r e s m e a s u r e d on t h e f a c e a n d a c y l i n d r i c a l a p p r o a c h f o r t h o s e m e a s u r e d b e h i n d t h e t i p . The method o f C a m p a n e l l a e t a l . 1985 a p p e a r s t o work w e l l , p a r t i c u l a r l y i n n o r m a l l y c o n s o l i d a t e d d e p o s i t s . C o r r e l a t i o n s be tween NAU a n d Bq a n d Nke a n d Bq l o o k p r o m i s i n g a n d s h o u l d be i n v e s t i g a t e d f u r t h e r w i t h d a t a f r o m o t h e r s i t e s . 8 . 2 C o n c l u s i o n s T h i s s e c t i o n p r e s e n t s t h e most i m p o r t a n t c o n c l u s i o n s r e g a r d i n g t h e f a c t o r s t h a t a f f e c t t h e e s t i m a t i o n o f S u f r o m C P T . 8 . 2 . 1 A c c u r a c y o f CPT D a t a A t t e n t i o n t o t h e f o l l w i n g d e t a i l s i n t e s t a n d d a t a r e d u c t i o n p r o c e d u r e s a r e e s s e n t i a l i n - o r d e r t o o b t a i n m e a n i n g f u l r e s u l t s . i ) b e a r i n g must be c o r r e c t e d f o r p o r e p r e s s u r e a n d t e m p e r a t u r e e f f e c t s i i ) f r i c t i o n m e a s u r e m e n t s must be c o r r e c t e d f o r t h e e f f e c t s o f u n e q u a l end a r e a s a n d t e m p e r a t u r e i i i ) p o r e p r e s s u r e s must be m e a s u r e d b e h i n d t h e t i p i n o r d e r t o p r o p e r l y c o r r e c t t h e b e a r i n g a n d f r i c t i o n f o r p o r e p r e s s u r e e f f e c t s i v ) a l l c o n e c h a n n e l s s h o u l d be c a l i b r a t e d f o r t e m p e r a t u r e e f f e c t s v ) c o m p l e t e s a t u r a t i o n o f t h e p o r e p r e s s u r e m e a s u r i n g 156 s y s t e m i s e s s e n t i a l v i ) p o r o u s e l e m e n t s s h o u l d h a v e an a v e r a g e p o r e s i z e o f a t l e a s t 100 m i c r o n s t o p r e v e n t c l o g g i n g v i i ) z e r o l o a d r e a d i n g s must be c h e c k e d b e f o r e a n d a f t e r a p r o f i l e t o d e t e c t z e r o s h i f t s 8 . 2 . 2 I n f l u e n c e o f L a y e r B o u n d a r i e s i ) t h e c o n e b e a r i n g i s i n f l u e n c e d by s u r r o u n d i n g s o i l l a y e r s , however t h i s e f f e c t i s more s i g n i f i c a n t i n c o a r s e g r a i n e d m a t e r i a l s i i ) t h e c o n e b e a r i n g w i l l n o t r e a c h i t s f u l l r e s i s t a n c e i n t h i n ( l e s s t h a n f r o m 5 t o 10 c o n e d i a m e t e r s t h i c k ) l a y e r s o f s a n d i i i ) t h i n n e r l a y e r s o f c l a y a r e r e q u i r e d t o r e c o r d t h e t r u e b e a r i n g i v ) t h e v a l l e y s i n t h e b e a r i n g r e c o r d s h o u l d be u s e d f o r e s t i m a t i n g t h e u n d r a i n e d s t r e n g t h i n c o h e s i v e d e p o s i t s 8 . 2 . 3 D e t e c t i o n o f T h i n L a y e r s i ) l a y e r s o f t h e o r d e r 10cm t h i c k a r e e a s i l y d e t e c t e d by t h e t i p r e s i s t a n c e i i ) i t may be p o s s i b l e t o d e t e c t l a y e r s a s t h i n a s 1cm, h o w e v e r , t h e m a t e r i a l p r o p e r t i e s o f t h i s t h i n l a y e r w o u l d h a v e t o be c o n s i d e r a b l y d i f f e r e n t f r o m t h e s u r r o u n d i n g s o i l t o be d e t e c t e d 157 i i i ) e s t i m a t i n g t h e t h i c k n e s s o f a l a y e r i s h i g h l y d e p e n d e n t on t h e s a m p l i n g r a t e i v ) t h e e s t i m a t i o n o f l a y e r t h i c k n e s s f o r l a y e r s t h i n n e r t h a n t h e s a m p l i n g r a t e i s h i g h l y s p e c u l a t i v e a n d c a n o f t e n be i n e r r o r v ) s a m p l i n g a t d i s c r e t e i n t e r v a l s c a n a l s o l e a d t o s u b d u e d p e a k s i n t h e CPT p r o f i l e 8 . 2 . 4 E s t i m a t i n g Su f r o m Cone B e a r i n g i ) t h e e s t i m a t i o n o f Su f r o m CPT i s s t r o n g l y i n f l u e n c e d by s t r e s s h i s t o r y , s e n s i t i v i t y a n d s t i f f n e s s i i ) i n c r e a s e s i n OCR a n d s e n s t i v i t y r e s u l t e d i n i n c r e a s e s i n t h e t r a d i t i o n a l c o n e f a c t o r s Nc and Nk i i i ) t h e c o n e f a c t o r s a l s o i n c r e a s e d w i t h d e c r e a s i n g p l a s t i c i t y i n d e x ( i . e . i n c r e a s i n g s o i l s t i f f n e s s ) i v ) s c a t t e r i n t h e c o n e f a c t o r was m i n i m i z e d when - p o r e p r e s s u r e e f f e c t s a n d o v e r b u r d e n s t r e s s were a c c o u n t e d f o r v ) t h e r e i s no u n i q u e v a l u e f o r t h e t r a d i t i o n a l c o n e f a c t o r Nk t h a t i s a p p l i c a b l e t o a l l c l a y s 8 . 2 . 5 U s i n g CPT P o r e P r e s s u r e D a t a t o E s t i m a t e S u i ) t h e u s e o f p o r e p r e s s u r e d a t a a p p e a r s t o be a p r o m i s i n g means o f e s t i m a t i n g Su f r o m CPT i i ) t h e m e t h o d o f C a m p a n e l l a e t a l . 1985 ( f i g u r e 6 . 5 ) a p p e a r s t o work w e l l , p a r t i c u l a r l y i n n o r m a l l y 158 c o n s o l i d a t e d d e p o s i t s i i i ) when u s i n g a c a v i t y e x p a n s i o n a p p r o a c h , s p h e r i c a l c a v i t y e x p a n s i o n m e t h o d s s h o u l d be u s e d f o r p o r e p r e s s u r e s m e a s u r e d on t h e f a c e a n d c y l i n d r i c a l c a v i t y e x p a n s i o n f o r t h o s e m e a s u r e d b e h i n d t h e t i p i v ) t h e p o r e p r e s s u r e p a r a m e t e r Bq d e c r e a s e w i t h i n c r e a s i n g OCR, b u t t h e r e i s no u n i q u e r e a l t i o n s h i p . b e t w e e n Bq a n d OCR s i n c e Bq i s a l s o a f u n c t i o n o f s e n s i t i v i t y a n d s o i l s t i f f n e s s v ) t h e r e i s no d i s c e r n i b l e r e l a t i o n be tween Nkt a n d Bq v i ) t h e r e a p p e a r s t o be f a i r l y c o n s i s t e n t r e l a t i o n s h i p s b e t w e e n N A U and Bq a n d b e t w e e n Nke a n d Bq v i i ) t h e b e s t c o r r e l a t i o n i s b e t w e e n Nke a n d B q , h o w e v e r , u n l e s s c a r e f u l a t t e n t i o n i s p a i d t o t h e d e t a i l s d i s c u s s e d i n s e c t i o n 8 . 2 . 1 c o n s i d e r a b l e e r r o r i n t h e c a l c u l a t i o n o f Nke c a n r e s u l t 8 . 2 . 6 Use o f F r i c t i o n S l e e v e M e a s u r e m e n t s C o m p a r i s o n s be tween f r i c t i o n s l e e v e m e a s u r e m e n t s a n d Su i n d i c a t e t h a t t h e s l e e v e f r i c t i o n i s c l o s e t o t h e r e m o l d e d s h e a r s t r e n g t h S u r , p a r t i c u l a r l y i n s e n s i t i v e s o i l s . E s t i m a t e s o f s e n s i t i v i t y ( f i e l d v a n e ) were b e s t made u s i n g S t = _ 6 Rf t% where t h e f r i c t i o n r a t i o R f t h a s been c a l c u l a t e d u s i n g b e a r i n g a n d f r i c t i o n c o r r e c t e d f o r p o r e p r e s s u r e e f f e c t s . 159 8 . 3 Recommended P r o c e d u r e s f o r E s t i m a t i n g Su f r o m CPT The f a c t t h a t Su a n d CPT c o r r e l a t i o n s c a n be a f f e c t e d by many v a r i o u s p a r a m e t e r s i n d i c a t e s t h a t a s i n g l e m e t h o d c a n n o t work i n a l l c l a y t y p e s . The e n g i n e e r s h o u l d n o t r e l y on a s i n g l e m e t h o d b u t i n s t e a d s h o u l d u s e a v a r i e t y o f m e t h o d s t o d e t e r m i n e t h e b e s t e s t i m a t e o f S u . Where p o s s i b l e , i t i s b e s t t h a t l o c a l c o r r e l a t i o n s be u s e d . The f o l l o w i n g d e s c r i b e s recommended p r o c e d u r e s f o r e s t i m a t i n g Su f r o m C P T . 8 . 3 . 1 Use o f CPT D a t a W i t h o u t P o r e P r e s s u r e s I t i s n o t recommended t h a t CPT d a t a be u s e d t h a t d o e s n o t i n c l u d e p o r e p r e s s u r e s . T h e v a r i a t i o n i n Nc a n d Nk i s t o o g r e a t a n d w i t h o u t p o r e p r e s s u r e s t h e r e i s no a l t e r n a t e method f o r c o n f i r m i n g t h e a p p r o p r i a t e c o n e f a c t o r . An e s t i m a t e o f t h e a p p r o p r i a t e c o n e f a c t o r w o u l d h a v e t o be made f r o m t a b l e s 6 . 1 , 6 . 2 , o r 7 . 3 o r f r o m f i g u r e s 6 . 1 , 6 . 2 , o r 7 . 4 1 . An k n o w l e d g e o f P I , s e n s i t i v t y a n d OCR w o u l d be h e l p f u l . S e n s i t i v i t y c a n be e s t i m a t e d f r o m t h e f r i c t i o n r a t i o a n d OCR c a n be e s t i m a t e d f r o m t h e s i t e g e o l o g y o r t h e c o n e b e a r i n g . 8 . 3 . 2 Use o f CPT D a t a W i t h P o r e P r e s s u r e s To make u s e o f a c o m b i n a t i o n o f t h e v a r i o u s p r o p o s e d m e t h o d s o f c o r r e l a t i o n an i t e r a t i v e a p p r o a c h c a n be u s e d . 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" I n t e r p r e t a t i o n o f Cone P e n e t r a t i o n T e s t s : P a r t s 1 a n d 2 " , C a n a d i a n G e o t e c h n i c a l J o u r n a l , V o l . 2 0 , N o . 4 , p p . 718 - 7 4 5 . R o b e r t s o n , P . K . a n d R . G . C a m p a n e l l a , 1984 . " G u i d e l i n e s F o r U s e and I n t e r p r e t a t i o n o f t h e E l e c t r o n i c C o n e P e n e t r a t i o n T e s t " , S o i l M e c h a n i c s S e r i e s N o . 6 9 , D e p a r t m e n t o f C i v i l E n g i n e e r i n g , U n i v e r s i t y o f B r i t i s h C o l u m b i a , V a n c o u v e r , C a n a d a . 166 S c h m e r t m a n n , J . H . , 1975 . " M e a s u r e m e n t o f I n - S i t u S h e a r S t r e n g t h " , P r o c e e d i n g s o f t h e S p e c i a l t y C o n f e r e n c e on I n -S i t u M e a s u r e m e n t o f S o i l P r o p e r t i e s , A S C E , R a l e i g h , N o r t h C a r o l i n a , V o l . 2 , p p . 5 7 - 1 3 8 . S c h m e r t m a n , J . H . , 1978 . " G u i d e l i n e s f o r Cone P e n e t r a t i o n T e s t P e r f o r m a n c e a n d D e s i g n " , F e d e r a l H i g h w a y s A d m i n i s t r a t i o n , R e p o r t F H W A - T S - 7 8 - 2 0 9 , W a s h i n g t o n , D . C . S e n n e s e t , K . , N . J a n b u a n d G . S v a n o , 1982 . " S t r e n g t h a n d D e f o r m a t i o n P a r a m e t e r s f r o m Cone P e n e t r a t i o n T e s t s " , P r o c e e d i n g s o f t h e S e c o n d E u r o p e a n Sympos ium on P e n e t r a t i o n T e s t i n g , A m s t e r d a m , p p . 863 - 8 7 0 . S e n n e s e t , K. and N . J a m b u , 1984 . " S h e a r S t r e n g t h P a r a m e t e r s O b t a i n e d f r o m S t a t i c Cone P e n e t r a t i o n T e s t s " , A - 8 4 - 1 , I n s t i t u t e o f G e o t e c h n i c s a n d F o u n d a t i o n E n g i n e e r i n g , The N o r w e i g i a n I n s t i t u t e o f T e c h n o l o g y , T r o n d h e i m , N o r w a y . T o r s t e n s o n , B . A . , 1973 . " T i m e - D e p e n d e n t E f f e c t s i n t h e F i e l d Vane T e s t " , P r o c e e d i n g s o f t h e I n t e r n a t i o n a l Sympos ium on S o f t C l a y , B a n g k o k , p p . 3 8 7 - 3 9 7 . T r e a d w e l l , D . D . , 1976 . "The I n f l u e n c e o f G r a v i t y , P r e s t r e s s , C o m p r e s s i b i l i t y a n d L a y e r i n g on S o i l R e s i s t a n c e t o S t a t i c P e n e t r a t i o n " , P h . D . T h e s i s , U n i v e r s i t y o f C a l i f o r n i a , B e r k e l e y . V e s i c , A . S . , 1972 . " E x p a n s i o n o f C a v i t i e s i n I n f i n i t e S o i l M a s s e s " , J o u r n a l o f t h e S o i l M e c h a n i c s and F o u n d a t i o n E n g i n e e r i n g D i v i s i o n , A S C E , V o l . 9 8 , SM3, p p . 2 6 5 - 2 9 0 . W e s l e y , L . D . , 1 9 6 7 . "The D u t c h P e n e t r o m e t e r a n d I t s Use i n I n d o n e s i a " , P r o c e e d i n g s , S o u t h e a s t A s i a n R e g i o n a l C o n f e r e n c e on S o i l E n g i n e e r i n g , B a n g k o k , p p . 2 2 3 - 2 3 0 . W i e s e l , C . E . R . , 1973 . "Some F a c t o r s I n f l u e n c i n g I n - S i t u V a n e T e s t R e s u l t s " , P r o c e e d i n g s o f t h e E i g h t h I n t e r n a t i o n a l C o n f e r e n c e on S o i l M e c h a n i c s a n d F o u n d a t i o n E n g i n e e r i n g , V o l . 2 . , p p . 4 7 5 - 4 7 9 . W r o t h , C P . , 1984 . " T h e I n t e r p r e t a t i o n o f I n - S i t u S o i l T e s t s " , W r i t t e n V e r s i o n o f t h e 1984 R a n k i n e L e c t u r e . 1 67 A P P E N D I X A C O M P A R I S O N B E T W E E N A C P T B E A R I N G P R O F I L E A N D A C O N T I N U O U S S A M P L E L O G CONE BEARING Qt (bar) CONTINUOUS BOREHOLE LOG 20 B.C. HYDRO RAIL S I T E LANGLEY B. C. START OF CONTINUOUS BOREHOLE fine to coarse sand grey silty clay •silty fine to medium sand grey silty clay sandy clay grey silty clay grey silty clay, some fine sand flne sand grey silty clay, occasional sand lense Figure A.la COMPARISON BETWEEN A CPT BEARING PROFILE AND A CONTINUOUS SAMPLE LOG CONE BEARING Qt (bar) CONTINUOUS BOREHOLE LOG 20 g r a y s i l t y c l a y , o c c a s i o n a l sand tense f i n s sand g r a y s i l t y c l a y B.C. HYDRO R A I L S I T E LANGLEY B.C. l a y e r e d a l l t y c l a y and s i l t y f i n e sand ( l a y e r s approx. 1cm) f i n e aand g r e y a l 1 t y c l a y VC-i l I t y f Ine s a n d l a m i n a t e d s i l t y f i n e sand and s i l t y c l a y g r e y a l l t y c l a y f i n e sand g r e y a l l t y c l a y a l I t y f Ine aand g r e y s i l t y c l a y Figure A.lb COMPARISON BETWEEN A CPT BEARING PROFILE AND A CONTINUOUS SAMPLE LOG CONE BEARING Qt (bar) • B. C. HYDRO R A I L S I T E LANGLEY 9. C. 20 CONTINUOUS BOREHOLE LOG g r e y s i l t y cI a y g r e y s i l t y c l a y . I n c r e a s i n g In s a n d c o n t e n t w i t h d e p t h i n t e r b e d d e d f i n e s i l t y s a n d and 5.My c l a y s i l t y f I n e s a n d g r e y f i n e s a n d g r e y s i l t y cI ay s i l t y s a n d , some c l a y g r e y s l I t y c l a y , some f i n e s a n d l e n s e s g r e y s l 1 t y c l a y g r e y s i l t y c l a y and f i n e s a n d s a n d l e n s e . s l i g h t l y i n c l i n e d . g r e y s 1 1 ty c 1 av f f n e s f l t y sand, some c l a y g' ey 5 f 1 t y c l a y g r e y s u t y snnd g r e y s i l t y c l a y — g r e y s i l t y c l a y g r e y s i l t y sand, l i t t l e c l a y Figure A.Ic COMPARISON BETWEEN A CPT BEARING PROFILE AND A CONTINUOUS SAMPLE LOG 10. 0 u L fj a E 0. UJ a 12. 5 CONE BEARING Ot (bar) B. C. HYDRO RAIL SITE LANGLEY B.C. • CONTINUOUS BOREHOLE LOG 20 g r e y s f 1 ty c 1 ay, o c c a s 1ona 1 f t ne sancl I a y e r — g r e y s i l t y c l a y " -g r e y s i l t y c l a y , some f i n e s a n d p a r t i n g s g r e y s1J t y c l a y g r e y s i l t y c1 ay, some f 1 n e s a n d p a r t i n g s f i n e t o medium sandy c l a y g r e y s i l t y c l a y , some s i l t y f i n e s a n d g r e y s i l t y c l a y . I n c l i n e d s a n d l a y e r 1cm t h i c k g r e y s 1 1 t y c l a y sandy c l a y , s a n d c o n t e n t i n c r e a s i n g w i t h d e p t h f \ ne sa n d . t r a c e s i l t s11 t y fIne s a n d g r e y s i l t y c1 ay l a m i n a t e d g r e y s f l t y c l a y and f i n e s a n d s 1 1 t y s a n d . some she 1 I f r a g m e n t s g r e y s i l t y c l a y Figure A.Id COMPARISON BETWEEN A CPT BEARING PROFILE AND A CONTINUOUS SAMPLE LOG Figure A.le COMPARISON BETWEEN A CPT BEARING PROFILE AND A CONTINUOUS SAMPLE LOG 

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