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Measurement of in situ lateral stress during full-displacement penetration tests Sully, John Paul 1991

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MEASUREMENT OF IN SITU LATERAL STRESS DURING FULL-DISPLACEMENT PENETRATION TESTS by JOHN PAUL SULLY M.Sc. and DIC, Imperial C o l l e g e , U n i v e r s i t y of London, 1981 A THESIS SUBMITTED IN THE REQUIREMENTS DOCTOR OF PARTIAL FULFILLMENT OF FOR THE DEGREE OF PHILOSOPHY i n THE FACULTY OF GRADUATE STUDIES (Department of C i v i l Engineering) 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 1991 ©John Paul S u l l y , 1991 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 The University of British Columbia Vancouver, Canada Date l O - O ^ - ^ l A . DE-6 (2/88) ABSTRACT The t h e s i s considers the problem of the i n s i t u measurement of h o r i -z o n t a l s t r e s s w i t h s p e c i f i c reference to the use of f u l l displacement probes. I t i s g e n e r a l l y accepted that c o r r e c t measurement of the h o r i z o n t a l s t r e s s i n s i t u should be performed under c o n d i t i o n s of no disturbance s i n c e , depending on the s o i l c h a r a c t e r i s t i c s , even small amounts of disturbance can s i g n i f i -c a n t l y a l t e r the i n s i t u c o n d i t i o n s . The s e l f - b o r i n g pressuremeter i s w i d e l y acknowledged to be the best a v a i l a b l e instrument f o r measuring h o r i z o n t a l s t r e s s but recent research has shown the data obtained to be very s e n s i t i v e to the e f f e c t s of probe i n s t a l l a t i o n . On the other hand f u l l displacement probes cause repeatable degrees of disturbance and.the induced s t r e s s e s and pore pressures may provide a means of b a c k f i g u r i n g the i n i t i a l pre-p e n e t r a t i o n i n s i t u s t r e s s c o n d i t i o n . The t h e s i s presents the r e s u l t s of a d e t a i l e d programme of i n s i t u t e s t i n g using both s e l f - b o r i n g and f u l l - d i s p l a c e m e n t probes during which measurements of both s t r e s s and pore pressure have been performed. In a d d i t i o n these measurements have been performed at v a r i o u s l o c a t i o n s on the f u l l - d i s p l a c e m e n t probes to evaluate the s t r e s s d i s t r i b u t i o n . Both p l a t e -l i k e and c y l i n d r i c a l probes have been used i n the study. Reference p r o f i l e s of l a t e r a l s t r e s s have been e s t a b l i s h e d f o r each of the research s i t e s based on both i n s i t u and l a b o r a t o r y t e s t r e s u l t s . The s t r e s s e s measured by the f u l l - d i s p l a c e m e n t probes and the i n t e r p r e t e d i n s i t u c o n d i t i o n s are compared to the reference p r o f i l e s . The data suggest t h a t i n s o f t to s t i f f c l a y and sands r e l i a b l e estimates of the reference l a t e r a l s t r e s s p r o f i l e can be obtained from the large s t r a i n measurements using semi-e m p i r i c a l techniques which are based on the r e s u l t s of p u b l i s h e d case h i s t o r i e s . C e r t a i n index parameters are a l s o shown to provide c o n s i s t e n t i n d i c a t o r s of the v a r i a t i o n i n K Q s t r e s s s t a t e as obtained from the reference t e s t s . Using both c a l i b r a t i o n chamber and f i e l d data both the cone r e s i s t a n c e and pore pressure gradient around the t i p are shown to be dependent on the i n s i t u h o r i z o n t a l s t r e s s . T h e o r e t i c a l approaches f o r e v a l u a t i n g the s t r e s s e s around f u l l -displacement probes are considered and c a v i t y expansion formulations are a p p l i e d to measurements i n both sand and c l a y . The data c l e a r l y show the inadequacy of the t h e o r e t i c a l approaches to consider the unloading t h a t occurs around the penetrometer t i p . The degree of unloading i s shown to be a f u n c t i o n of both s o i l and probe c h a r a c t e r i s t i c s . TABLE OF CONTENTS Page ABSTRACT i i TABLE OF CONTENTS i i i LIST OF TABLES v i i i LIST OF FIGURES x LIST OF SYMBOLS x x i ACKNOWLEDGEMENTS x x v i i 1. INTRODUCTION 1 1.1 Background 1 1.2 In S i t u Stress State 3 1.3 Laboratory Techniques f o r E v a l u a t i n g K Q 9 1.4 Conditions f o r In S i t u Measurement of H o r i z o n t a l Stress ... 12 1.5 Research Objectives 14 1.6 Thesis Layout 15 2. LATERAL STRESS FROM FULL-DISPLACEMENT PROBES: CONSIDERATIONS ... 16 2.1 I n t r o d u c t i o n 16 2.2 C o r r e l a t i o n of S o i l Behaviour at Varying S t r a i n Levels ... 22 2.3 Stress and Pore Pressure D i s t r i b u t i o n Around F u l l -Displacement Probes 29 2.4 A p p l i c a t i o n of C a l i b r a t i o n Chamber Results to In S i t u Measurements 36 2.5 Conclusions 41 3. DETAILS OF EQUIPMENT AND TEST PROCEDURES • 43 3.1 I n t r o d u c t i o n 43 3.2 Index Parameter Test Equipment 43 3.2.1 Piezocone Penetrometer 45 3.2.2 In S i t u ( F i e l d ) Vane 46 3.2.3 Seismic Cone Penetrometer 46 3.2.4 Laboratory Index Tests 49 3.3 F u l l Displacement Probes: Cones 50 3.3.1 L a t e r a l Stress Cone (LSC) 50 3.3.1.1 UBC LSC 50 Design Considerations 52 D e t a i l s of LS Module 53 Laboratory C a l i b r a t i o n of LSC 55 H y d r o s t a t i c C a l i b r a t i o n of LS Module 57 F r i c t i o n - L a t e r a l Stress Cross Talk 57 C a l i b r a t i o n f o r Temperature E f f e c t s 59 E v a l u a t i o n of Base l i n e D r i f t 60 F i e l d T e s t i n g Procedures 61 3.3.1.2 Berkeley (UCB) LSC 62 3.3.2 Seismic Cone Pressuremeter (SCPM) 64 3.4 Full-Displacement Probes: P l a t e s 64 3.4.1 Dilatometer (DMT) 64 - i i i -TABLE OF CONTENTS (Continued) Page 3.4.2 T o t a l Stress C e l l (TSC) 65 D e t a i l s of TSC 65 Pressure and Temperature C a l i b r a t i o n 68 I n s t a l l a t i o n Procedure 72 3.5 S e l f - B o r i n g Probes 73 3.5.1 S e l f - B o r i n g Pressuremeter (SBPM) 73 D e t a i l s of SBPM Design 73 Membrane and Lantern C h a r a c t e r i s t i c s 75 D e t a i l s of J e t t i n g System 76 C a l i b r a t i o n of Transducers 78 I n s t a l l a t i o n Procedure 80 3.5.2 S e l f - B o r i n g Load C e l l (SBLC) 81 3.6 L a t e r a l Stress Oedometer 82 3.6.1 D e t a i l s of LS Oedometer 82 3.6.2 C a l i b r a t i o n of Transducers 83 4, GEOLOGY AND GEOTECHNICAL CHARACTERISTICS OF RESEARCH SITES 87 4.1 I n t r o d u c t i o n 87 4.2 G e o l o g i c a l H i s t o r y of the Lower Mainland 89 4.3 Laing Bridge South, Richmond 90 4.3.1 S i t e D e s c r i p t i o n 90 4.3.2 Test i n g Programme 92 4.3.3 Geotechnical C h a r a c t e r i s t i c s 93 4.4 McDonald Farm, Richmond 95 4.4.1 S i t e D e s c r i p t i o n 95 4.4.2 Te s t i n g Programme 98 4.4.3 Geotechnical C h a r a c t e r i s t i c s 98 4.5 Lower 232nd S t r e e t , Langley 102 4.5.1 S i t e D e s c r i p t i o n 102 4.5.2 Te s t i n g Programme 102 4.5.3 Geotechnical C h a r a c t e r i s t i c s 102 4.6 Strong P i t , Aldergrove 109 4.6.1 S i t e D e s c r i p t i o n 109 4.6.2 Test i n g Programme I l l 4.6.3 Geotechnical C h a r a c t e r i s t i c s 112 4.7 200th S t r e e t , Langley 117 4.7.1 S i t e D e s c r i p t i o n 117 4.7.2 Te s t i n g Programme 119 4.7.3 Geotechnical C h a r a c t e r i s t i c s 120 5. COMPARISON OF MEASURED STRESSES AND PORE PRESSURES 123 5 .1 I n t r o d u c t i o n 123 5.2 Measured Pore Pressures i n Fine Grained S o i l s 124 5.2.1 P e n e t r a t i o n Pore Pressures i n Clays 124 McDonald Farm 125 L r . 232 Str e e t 127 - i v -TABLE OF CONTENTS (Continued) Page Strong P i t 134 5.2.2 L a t e r a l Stress Measurements i n Clays 139 McDonald Farm . 139 Lr . 232 S t r e e t 141 Strong P i t 148 5.2.3 I n i t i a l E f f e c t i v e L a t e r a l Stresses i n Clays 151 5.3 Measured Pressures i n Coarse Grained S o i l s 161 5.3.1 P e n e t r a t i o n Pore Pressures i n Sands 161 McDonald Farm 161 Laing Bridge South 165 5.3.2 L a t e r a l Stress Measurements i n Sands 167 McDonald Farm 169 Laing Bridge South 173 5.3.3 I n i t i a l E f f e c t i v e L a t e r a l Stresses i n Sands .. 175 5.4 D i s s i p a t i o n of I n i t i a l Pressures 180 5.4.1 D i s s i p a t i o n of Excess Pore Pressures 180 LS-CPTU 183 DMT and TSC 190 5.4.2 D i s s i p a t i o n of I n i t i a l L a t e r a l Stress 194 T o t a l Stress C e l l 195 L a t e r a l Stress Cone 197 5.5 L a t e r a l Stress Oedometer Results .• 199 5.6 Stress Dependent Parameters 202 5.6.1 Shear Wave V e l o c i t y Measurements 205 Lr 232 St. ; 206 200th St 208 Laing Bridge South 208 5.6.2 Comparison of V e l o c i t y Ratios 211 5.7 D i s c u s s i o n and Conclusions 216 5.7.1 Equipment and Test i n g Methods 216 5.7.2 S o i l Response to Probe I n s t a l l a t i o n 221 6. EVALUATION OF FIELD MEASUREMENTS 228 6.1 I n t r o d u c t i o n 228 6.2 Reference Stress Conditions at Research S i t e s 229 6.2.1 McDonald Farm 229 6.2.2 Laing Bridge South 232 6.2.3 Strong P i t 234 6.2.4 L r . 232 St 241 6.2.5 200th St 247 6.2.6 Conclusions 247 6.3 Stress H i s t o r y Parameters from CPTU 249 6.3.1 I n t r o d u c t i o n 249 6.3.2 K Q from CPT i n Sand 250 6.3.3 OCR from P e n e t r a t i o n Pore Pressures i n Clay 255 - v -TABLE OF CONTENTS (Continued) Page 6.3.4 Effect of Lateral Stress on Penetration Pore Pressures 262 6.3.5 Conclusions 267 6.4 Interpretation of Cone Data by Cavity Expansion Theory .... 267 6.4.1 Introduction 267 6.4.2 Undrained Cavity• Expansion in Clay 268 Cylindrical Cavity Theory - Randolph et a l . (1979) 271 Comparison with Field Data at Research Sites 273 McDonald Farm 274 Lr. 232 St 277 Strong Pit 279 6.4.3 Drained Cavity Expansion in Sand 281 6.5 Empirical Approaches to Evaluation K Q 286 6.5.1 Dilatometer Correlations for K 287 DMT Correlations in Sand 288 DMT Correlations in Clay 290 6.5.2 LS Cone Correlations for K 291 LS-CPTU Correlations in Clay 291 LS-CPTU Correlations in Sand 295 6.5.3 Full Displacement Pressuremeter Correlations 298 6.5.4 Indexing K 0 by Shear Wave Velocity Measurements .. 301 6.5.5 Correlations with Undrained Shear Strength 304 6.6 Conclusions 306 7. CONCLUDING COMMENTS 311 7.1 Overview 311 7.2 Equipment Details 315 7.3 Suggestions for Future Research 317 APPENDICES A - IN SITU MEASUREMENT OF LATERAL STRESS - A CRITICAL REVIEW 321 A.l Introduction ; 322 A.2 Self-Boring Pressuremeter Test (SBPMT) 322 A.2.1 Estimation of Lateral Stress by L i f t - o f f Methods 326 A.2.2 Estimation of Lateral Stress by Graphical Methods 330 A.2.3 Computer Aided Procedures for Determining Lateral Stress 331 A.2.4 Empirical Methods for Evaluating Lateral Stress 333 A.2.5 Conclusions 333 A.3 Total Stress Cell (TSC) 335 A.4 Dilatometer Test (DMT) 341 A.4.1 DMT in Sand 348 A.4.2 DMT in Clay 357 A.5 Hydraulic Fracture Test (HFT) 363 A.6 Lateral Stress Cone Penetration Test (LS-CPTU) 370 A.7 Piezo-Lateral Stress Cell (PLSC) 380 A.8 Pre-Bored Pressuremeter Test (PBPMT) 385 A.9 Push-In Pressuremeter Test (PIPMT) 388 - v i -TABLE OF CONTENTS (Continued) Page A.10 F u l l Displacement Pressuremeter Test (FDPMT) 390 A. 11 Stepped Blade Test (SBT) 396 A. 12 Tapered Blade Test (TBT) 403 A. 13 F i e l d Vane Test (FVT) 403 A. 14 S e l f - B o r i n g Load C e l l (SBLC) ... 410 A. 15 Cone P e n e t r a t i o n Test (CPT/CPTU) 413 A. 16 In S i t u Shear Wave V e l o c i t y Measurements 419 A. 17 E l e c t r i c a l Methods 426 A. 18 Push-In L a t e r a l S tress Tool (LAST) 427 B - EVALUATION OF STRESS DISTRIBUTION AROUND FULL DISPLACEMENT PROBES 430 B. l I n t r o d u c t i o n 431 B.2 Theories f o r C y l i n d r i c a l Probes 432 B.2.1 Bearing Capacity Methods 433 B.2.2 C a v i t y Expansion Methods (CEM) 434 B.2.2.1 Undrained CEM 435 B.2.2.2 Drained CEM 446 B.2.3 F i n i t e Element Methods 451 B.2.4 S t r a i n Path A n a l y s i s 453 B.3 Theories f o r F l a t Probes 455 B.4 Comparison w i t h F i e l d Measurements 459 C - REFERENCES 461 - v i i -LIST OF TABLES Page Table 3.1 Summary of i n s i t u t e s t equipment used and general c h a r a c t e r i s t i c s of s t r e s s measurement systems 44 3.2 C a l i b r a t i o n data f o r UBC LS piezocone 51 3.3 I n i t i a l c a l i b r a t i o n data f o r spade c e l l s (before i n s t a l l a t i o n ) 70 3.4 C a l i b r a t i o n data f o r SBLC 82 4.1 Research s i t e s f o r i n s i t u measurement of l a t e r a l s t r e s s .... 87 4.2 F i e l d . t e s t i n g programme at Laing Bridge South 92 4.3 Legend f o r t e s t i n g programme at research s i t e s 93 4.4 F i e l d t e s t i n g programme at McDonald Farm 99 4.5 F i e l d t e s t i n g programme at Lower 232nd St r e e t 104 4.6 Oedometer t e s t r e s u l t s f o r h o r i z o n t a l l y - c u t undisturbed samples, Lower 232nd S t r e e t 108 4.7 Oedometer t e s t r e s u l t s f o r v e r t i c a l l y - c u t undisturbed samples, Lower 232nd S t r e e t 109 4.8 F i e l d t e s t i n g programme at Strong P i t 114 4.9 Oedometer t e s t r e s u l t s f o r undisturbed samples, Strong P i t .. 115 4.10 F i e l d t e s t i n g programme at 200th S t r e e t 120 4.11 Oedometer t e s t r e s u l t s f o r undisturbed samples, 200th S t r e e t (Crawford, 1989) 122 5.1 LS-Oedometer Results on Undisturbed Clayey Samples from Research S i t e s 199 5.2 Base l i n e and C a l i b r a t i o n Changes f o r T o t a l Stress C e l l s A f t e r I n s t a l l a t i o n and Removal at Strong P i t (modified a f t e r S u l l y and Campanella, 1989) 218 6.1 D e t a i l s of In S i t u Measurements f o r E v a l u a t i o n of K Q and PPSV Parameters ( S u l l y and Campanella, 1991) 265 - v i i i -LIST OF TABLES (Continued) Page A . l R e s ults of experience w i t h DMT f o r p r e d i c t i n g s t r e s s h i s t o r y parameters (modified from Schmertmann, 1986) 347 A.2 Review of DMT data i n c l a y s f o r e v a l u a t i o n of r e v i s e d K D~K 0 c o r r e l a t i o n 360 A. 3 Summary of l a b o r a t o r y r e s u l t s f o r V determination - slope of V -a r e l a t i o n s h i p s f o r dry sand (modified a f t e r Stokoe et a l . , 1985) 424 B. l T o t a l s t r e s s e s due to undrained expansion of a c y l i n d r i c a l c a v i t y 440 B.2 E f f e c t i v e s t r e s s e s due to undrained c y l i n d r i c a l c a v i t y expansion 441 - i x -LIST OF FIGURES Page Figure 1.1 T y p i c a l e f f e c t i v e s t r e s s paths f o r ID c o n s o l i d a t e d s o i l (modified a f t e r Wroth, 1985) 5 1.2 V a r i a t i o n s of K A, ( K Q ) N C and Kp as a f u n c t i o n of <f>' 7 1.3 Change i n ( K Q ) N C w i t h time a f t e r d e p o s i t i o n 11 2.1 Comparison of l i f t - o f f pressure from SBPM and h o r i z o n t a l chamber s t r e s s f o r (a) c o n d i t i o n s of i d e a l i n s t a l l a t i o n , and (b) i n s t a l l a t i o n by s e l f - b o r i n g (data from B e l l o t t i et a l . , 1987) 19 2.2 Comparison of measured h o r i z o n t a l s t r e s s from s e l f - b o r e d and f u l l displacement pressuremeters (adapted from Howie, 1991) 21 2.3 E f f e c t of v a r y i n g on SBPM pressure expansion curve according to Hughes (1989) i n t e r p r e t a t i o n 22 2.4 Influence of v a r i a b l e s f o r undrained SBPM i n c l a y ( a f t e r J e f f e r i e s et a l . , 1988) 23 2.5 Chart f o r determining G Q from G* measured during SBPM unload-reload loop ( a f t e r Byrne et a l . , 1990) 24 2.6 L i q u i d l i m i t versus A and a ( a f t e r S h e r i f and S t r a z e r , 1973) 26 2.7 CC data f o r q c-G 0 c o r r e l a t i o n ( a f t e r B a l d i et a l . , 1989) 28 2.8 I d e a l i z e d change of l a t e r a l s t r e s s c o e f f i c i e n t , K, caused by f u l l displacement probes ( S u l l y and Campanella, 1989) 31 2.9 Pore pressure d i s t r i b u t i o n i n satura t e d c l a y s during CPTU based on f i e l d measurements ( a f t e r Robertson et a l . , 1986) ... 33 2.10 E v a l u a t i o n of K Q from K D based on CC data ( a f t e r Jamiolkowski and Robertson, 1988) 39 2.11 Comparison of CC data indexing t e s t s by (a) r e l a t i v e d e n s i t y , or (b) s t a t e parameter 40 3.1 Nomenclature used f o r d i f f e r e n t pore pressure measurement l o c a t i o n s (based on S u l l y , Campanella and Robertson, 1988) ... 45 - x -LIST OF FIGURES (Continued) Pag 3.2 D e t a i l s of vane cone f o r generating crosshole shear wave s i g n a l s 48 3.3 C o n f i g u r a t i o n f o r downhole and crosshole shear wave v e l o c i t y measurements 48 3.4 D e t a i l s of UBC l a t e r a l s t r e s s cone (Campanella, S u l l y , G r eig and J o l l y , 1990) 54 3.5 D e t a i l s of UBC data a c q u i s i t i o n system (modified a f t e r Greig et a l . , 1987) (Campanella, S u l l y , Greig and J o l l y , 1990) 56 3.6 H y d r o s t a t i c pressure c a l i b r a t i o n of LS module (Campanella, S u l l y , Greig and J o l l y , 1990) 58 3.7 E v a l u a t i o n of cross t a l k on LS channel due to a x i a l f r i c t i o n load (Campanella, S u l l y , Greig and J o l l y , 1990) 59 3.8 Temperature s e n s i t i v i t y of LS b a s e l i n e (Campanella, S u l l y , Greig and J o l l y , 1990) 60 3.9 Schematic i l l u s t r a t i o n of the l a t e r a l s t r e s s measuring system, Berkeley LSC Model I I I ( a f t e r Tseng, 1989) 63 3.10 Components of S o l i n s t t o t a l pressure c e l l (modified a f t e r S o i l Instruments L t d . , 1987) 66 3.11 T y p i c a l temperature and pressure c a l i b r a t i o n f o r t o t a l s t r e s s c e l l ( Sully,and Campanella, 1989) 69 3.12 I n i t i a l temperature dependence of b a s e l i n e pressure f o r a l l spade c e l l s used i n t h i s study ( S u l l y and Campanella, 1989) .. 70 3.13 O r i g i n a l and r e v i s e d l a n t e r n design f o r UBC SBPM (Campanella and Stewart, 1990) 76 3.14 Types of j e t t i n g arrangement used w i t h UBC SBPM (Campanella and Stewart, 1990) 77 3.15 C a l i b r a t i o n data f o r s t r a i n arms and pressure transducers - SBPM ; 79 3.16 LS oedometer w i t h top and bottom p l a t e s f o r c a l i b r a t i o n of s t r a i n gauges 84 - x i -LIST OF FIGURES (Continued) Page 3.17 Nonlinear response of l a t e r a l s t r e s s transducers to a x i a l l oading 85 3.18 E f f e c t of a x i a l load on c a l i b r a t i o n c h a r a c t e r i s t i c s of LS transducers . 86 4.1 L o c a t i o n of UBC geotechnical research s i t e s 88 4.2 Laing Bridge South - general s i t e d e t a i l s 91 4.3 Layout of t e s t s at Laing Bridge South 94 4.4 Geotechical data f o r Laing Bridge South deposits 96 4.5 McDonald Farm - general s i t e d e t a i l s 97 4.6 Layout of t e s t s at McDonald Farm 100 4.7 Geotechnical data f o r McDonald Farm deposits . . 101 4.8 Lower 232nd S t r e e t - general s i t e d e t a i l s 103 4.9 Layout of t e s t s at Lower 232nd S t r e e t 105 4.10 C l a s s i f i c a t i o n and index t e s t r e s u l t s f o r Lower 232nd S t r e e t . . 106 4.11 Results of i n s i t u vane shear t e s t s - Lower 232nd S t r e e t 107 4.12 P r o f i l e of OCR determined from l a b o r a t o r y oedometer and f i e l d vane t e s t s - Lower 232nd S t r e e t (Campanella, S u l l y and Robertson, 1988) 109 4.13 G Q p r o f i l e from downhole SCPT - Lower 232nd S t r e e t (Campanella, Baziw and S u l l y , 1989) 110 4.14 Strong P i t - general s i t e d e t a i l s and layout of t e s t l o c a t i o n s 113 4.15 C l a s s i f i c a t i o n and index t e s t r e s u l t s f o r Strong P i t 116 4.16 Undrained vane s t r e n g t h r a t i o p r o f i l e - Strong P i t 116 4.17 Downhole Shear wave v e l o c i t y p r o f i l e - Strong P i t 117 4.18 200th S t r e e t - general s i t e d e t a i l s 118 4.19 Layout of t e s t s at 200th S t r e e t 119 - x i i -LIST OF FIGURES (Continued) Page 4.20 Geotechnical data f o r 200th S t r e e t 121 5.1 Comparison of pore pressures measured at d i f f e r e n t l o c a t i o n s on p e n e t r a t i n g cones i n normally c o n s o l i d a t e d c l a y s i l t 126 5.2 Pore pressures measured at three l o c a t i o n s during CPTU at L r . 232 S t r e e t (Campanella, S u l l y and Robertson, 1988) 128 5.3 E f f e c t of f i l t e r s i z e on u 2 pore pressure response f o r s o f t NC cohesive s o i l (Campanella, S u l l y and Robertson, 1988) 129 5.4 Comparison of u 3 pore pressure p r o f i l e s from LS-CPTU at L r . 232 S t r e e t (Campanella, S u l l y and Robertson, 1988) 131 5.5 Comparison of measured pore pressures at L r . 232 S t r e e t f o r (a) c y l i n d r i c a l probes, and (b) f l a t probes 132 5.6 Comparison of measured pore pressures at Strong P i t f o r (a) c y l i n d r i c a l probes, and (b) f l a t probes 135 5.7 Comparison of pore pressures measured at the u x l o c a t i o n w i t h p l a s t i c and ceramic f i l t e r elements i n OC c l a y s i l t 138 5.8 Comparison of l a t e r a l pressures measured using c y l i n d r i c a l and f l a t probes i n NC f i n e grained s o i l s at McDonald Farm .... 140 5.9 Measured l a t e r a l s t r e s s e s at L r . 232 S t r e e t from (a) LS cone, and (b) f l a t penetrometer l i f t - o f f values 142 5.10 L a t e r a l s t r e s s measurements at L r . 232 S t r e e t using c y l i n d r i c a l and f l a t penetrometers 145 5.11 F l a t penetrometer data from Strong P i t i l l u s t r a t i n g (a) d i r e c t i o n a l DMT p 0 v a l u e s , and (b) v a r i a t i o n i n DMT l i f t - o f f pressures i n N-S d i r e c t i o n 149 5.12 L a t e r a l s t r e s s measured using f u l l displacement probes at Strong P i t ( S u l l y and Campanella, 1990) 150 5.13 I n i t i a l e f f e c t i v e l a t e r a l s t r e s s v a r i a t i o n from v a r i o u s i n s i t u probes i n s o f t c l a y s i l t at McDonald Farm 154 5.14 I n i t i a l e f f e c t i v e l a t e r a l s t r e s s r e s u l t s from L r . 232 S t r e e t 157 5.15 I n i t i a l e f f e c t i v e l a t e r a l s t r e s s r e s u l t s from Strong P i t 160 - x i i i -LIST OF FIGURES (Continued) Page 5.16 ^Penetration pore pressures i n granular s o i l s at McDonald Farm using d i f f e r e n t l a t e r a l s t r e s s cones 162 5.17 P e n e t r a t i o n pore pressures at Laing Bridge South 166 5.18 Comparison of f r i c t i o n sleeve measurements i n sand at va r i o u s l o c a t i o n s behind the penetrometer t i p 168 5.19 L a t e r a l s t r e s s measurements i n sand at McDonald Farm 170 5.20 L a t e r a l s t r e s s measurements i n sand at Laing Bridge South ... 174 5.21 E f f e c t i v e l a t e r a l s t r e s s p r o f i l e s i n sand from measurements at McDonald Farm 176 5.22 E f f e c t i v e l a t e r a l s t r e s s p r o f i l e s i n sand from measurements at Laing Bridge South 177 5.23 S o i l - s t e e l i n t e r f a c e f r i c t i o n angles i n sand from LS-CPTU ... 179 5.24 Pore pressure d i s s i p a t i o n i n s t i f f c l a y at Strong P i t 185 5.25 Normalized pore pressure p l o t s f o r Strong P i t data: (a) uncorrected, and (b) c o r r e c t e d f o r i n i t i a l r e d i s t r i -b u t i o n e f f e c t s 186 5.26 D e t a i l s of the root-time method f o r e v a l u a t i n g pore pressure d i s s i p a t i o n data 188 5.27 V a r i a t i o n i n c^ values at v a r i o u s stages along p r e d i c t e d d i s s i p a t i o n curves 191 5.28 TSC measurements i n s t i f f c l a y at Strong P i t 193 5.29 D i s s i p a t i o n of measured pressures a f t e r TSC i n s t a l l a t i o n .... 194 5.30 V a r i a t i o n of oc^  and f3 f o r TSC r e s u l t s at c l a y s i t e s 196 5.31 LS cone i n i t i a l s t r e s s d i s s i p a t i o n at s t i f f c l a y s i t e 198 5.32 E f f e c t of b a s e l i n e c o r r e c t i o n s on i n t e r p r e t e d LS-oedometer data 201 5.33 LS-oedometer r e s u l t s from t e s t 2 (block sample) - Strong P i t 203 - x i v -LIST OF FIGURES (Continued) Page 5.34 LS-oedometer r e s u l t s from t e s t 1 (block sample) - L r . 232 St 204 5.35 Downhole and crosshole shear wave v e l o c i t y p r o f i l e s at L r . 232 St 207 5.36 Downhole and crosshole shear wave v e l o c i t y p r o f i l e s f o r 200th St 209 5.37 Downhole and crosshole shear wave v e l o c i t y p r o f i l e s f o r Laing Bridge South . 210 5.38 R a t i o of crosshole and downhole shear wave v e l o c i t i e s from f i e l d measurements at L r . 232 St. and 200th St 212 5.39 Crosshole shear wave v e l o c i t y r a t i o s from f i e l d measurements 213 5.40 T h e o r e t i c a l dependence of ( V s ) A / ( V s ) j on K 0 215 6.1 K Q v a r i a t i o n at McDonald Farm from SBPM and l a b o r a t o r y -based c o r r e l a t i o n s 231 6.2 K Q p r o f i l e s f o r Laing Bridge South based on SBLC r e s u l t s and laboratory-based c o r r e l a t i o n s 233 6.3 Measured and c o r r e c t e d pressures f o r TSC 1538 at Strong P i t . . 234 6.4 Evaluated s t r e s s p r o f i l e s f o r Strong P i t based on f i e l d and l a b o r a t o r y measurements ( S u l l y and Campanella, 1989) .... 237 6.5 P r o f i l e of s t r e s s h i s t o r y r e l a t e d parameters f o r the clayey s i l t at Strong P i t ( S u l l y and Campanella, 1989) 238 6.6 KQ v a r i a t i o n at Strong P i t from TSC and LS oedometer r e s u l t s 239 6.7 V a r i a t i o n of OCR w i t h depth at L r . 232 St. (Campanella, S u l l y and Robertson, 1989) 241 6.8 Time dependence of o^gQ at L r . 232 St 243 6.9 Measured s t r e s s p r o f i l e s at L r . 232 St 244 6.10 KQ p r o f i l e s from l a b o r a t o r y and f i e l d measurements -Lr . 232 St 245 6.11 Stress h i s t o r y data f o r 200th St 8- xv -LIST OF FIGURES (Continued) Page 6.12 E f f e c t of s t r e s s s t a t e on q c measured i n c a l i b r a t i o n chamber t e s t s ( a f t e r Houlsby and Hitchman, 1988) 251 6.13 C o r r e l a t i o n between A and D r based on c a l i b r a t i o n chamber t e s t data 253 6.14 P r e d i c t e d K c p T values f o r McDonald Farm and Laing Bridge South 254 6.15 V a r i a t i o n i n pore pressure d i f f e r e n c e , PPD, due to over-c o n s o l i d a t i o n r a t i o ( S u l l y , Campanella and Robertson, 1988b) 258 6.16 Comparison of OCR p r e d i c t e d from PPD w i t h reference p r o f i l e at L r . 232 St 259 6.17 PPD-OCR c o r r e l a t i o n f o r OCR > 15 ( S u l l y , Campanella and Robertson, 1988b) 260 6.18 Comparison of PPD parameters using u x and u 2 or u 3 f o r h e a v i l y o v e r c o n s o l i d a t e d Taranto c l a y ( S u l l y , Campanella and Robertson, 1988a) 261 6.19 PPSV-K Q trends f o r Strong P i t and L r . 232 St. ( S u l l y and Campanella, 1990) 264 6.20 PPSV-K 0 c o r r e l a t i o n f o r c l a y s from p u b l i s h e d f i e l d data ( S u l l y and Campanella, 1991) 266 6.21 G r a p h i c a l c o n s t r u c t i o n f o r G, S and from Houlsby and Withers unloading a n a l y s i s ( a f t e r Houlsby and Withers, 1988) 274 6.22 Measured and c a l c u l a t e d pressures i n NC c l a y s i l t at McDonald Farm 275 6.23 Measured and c a l c u l a t e d pressures i n s e n s i t i v e c l a y s i l t at L r . 232 St 278 6.24 Measured and c a l c u l a t e d pressures i n s t i f f OC clayey s i l t at Strong P i t 280 6.25 ^max~^D r a t i ° s f° r p u b l i s h e d data on sand (modified a f t e r S u l l y and Campanella, 1989) 283 6.26 Comparison of f i e l d measurements of l a t e r a l s t r e s s w i t h p r e d i c t e d values from c y l i n d r i c a l c a v i t y expansion i n sand .. 285 - xv i -LIST OF FIGURES (Continued) Page 6.27 Kpj^p. p r o f i l e s i n sand 289 6.28 KQ M T p r o f i l e s i n f i n e grained s o i l s 292 6.29 K ^ g p r o f i l e s i n f i n e grained s o i l s from c y l i n d r i c a l c a v i t y f o r m u l a t i o n ( S u l l y and Campanella, 1990) 294 6.30 K ^ g f a c t o r s f o r sand research s i t e s (Campanella, S u l l y , G r eig and J o l l y , 1990) 296 6.31 L a t e r a l s t r e s s a m p l i f i c a t i o n f a c t o r f o r sands t e s t e d (Campanella, S u l l y , Greig and J o l l y , 1990) 297 6.32 V a r i a t i o n of K as determined from shear wave v e l o c i t y measurements i n the l a b o r a t o r y and i n s i t u 305 6.33 Estimated K values by means of i n s i t u f i e l d vane data 307 A . l D e t a i l s of the B r i t i s h - t y p e SBPM 324 A.2 I d e a l i z e d p-e responses f o r SBPMT 327 A.3 Methods f o r e v a l u a t i n g h o r i z o n t a l s t r e s s from SBPMT (adapted from Lacasse and Lunne, 1982) 329 A.4 Influence of v a r i a b l e s f o r undrained SBPMT i n c l a y ( a f t e r J e f f e r i e s et a l . , 1988) 332 A.5 C o r r e l a t i o n between overread and S u f o r spade c e l l s i n c l a y (adapted from Tedd et a l . , 1989) 338 A.6 R e l a t i o n s h i p between K^SQ and OCR from published data 340 A.7 E f f e c t of l i n e a r e x t r a p o l a t i o n on derived p 0 value from DMT 344 A.8 Comparisons of the M a r c h e t t i (1980) and Schmertmann (1983) c o r r e l a t i o n s f o r K Q from DMT data 349 A.9 M a r c h e t t i (1985) g r a p h i c a l form f o r K r , - K - q c / o v r e l a t i o n s h i p m odified using Robertson and Campanella (1983) qc_<j>' c o r r e l a t i o n ( a f t e r Robertson, 1986) 350 A.10 E v a l u a t i o n of K from KQ based on CC data ( a f t e r Jamiolkowski and Robertson, 1988) 353 - x v i i -LIST OF FIGURES (Continued) Page A.11 Measured p 0 and p x values from CC t e s t s to show (a) dependence on h o r i z o n t a l e f f e c t i v e s t r e s s , and (b) i n s e n s i t i v i t y to v e r t i c a l e f f e c t i v e s t r e s s 354 A.12 C o r r e l a t i o n of p 0 and p x f o r v a r i o u s sand t e s t e d i n the CC 355 A.13 KQ-KQ c o r r e l a t i o n f o r DMT i n c l a y ( a f t e r Powell and Uglow, 1988) 358 A. 14 T y p i c a l data from a h y d r a u l i c f r a c t u r e t e s t 365 A.15 V a r i a t i o n s i n deduced o^ w i t h time from HFT ( a f t e r Tavenas et a l . , 1975) 368 A.16 E f f e c t of length of the piezometer t i p on c a l c u l a t e d K Q values from HFT (modified a f t e r Lefebvre et a l . , 1981) 370 A.17 Schematic d e t a i l s of l a t e r a l s t r e s s sensing cone penetro-meter Model I I developed at Berkeley ( a f t e r Huntsman, 1985) 372 A.18 G r a p h i c a l r e p r e s e n t a t i o n of KTC/KQ from l a t e r a l s t r e s s cone t e s t s i n CC ( a f t e r Jamiolkowski and Robertson, 1988) .. 377 A.19 Schematic d e t a i l s of the Berkeley Model I I I LSSCP ( a f t e r Masood, 1990) 378 A.20 D e t a i l s of the piezo l a t e r a l s t r e s s c e l l ( a f t e r Morrison, 1984) 382 A.21 T y p i c a l v a r i a t i o n of pressures measured using PLSC i n Boston Blue Clay ( a f t e r B a l i g h et a l . , 1985) 384 A.22 E f f e c t of borehole c o n d i t i o n s on PBPM r e s u l t s ( a f t e r Tavenas et a l . 1975) 386 A. 23 KprjpM and OCR p r o f i l e s i n a s e n s i t i v e c l a y 391 A.24 D e t a i l s of the UBC seismic cone pressuremeter ( a f t e r Campanella and Robertson, 1986) 393 A.25 Measured l i m i t pressure as a f u n c t i o n of D r and ( a f t e r Schnaid and Houlsby, 1990) 395 A.26 Estimated and measured al values from FDPM t e s t s i n CC ( a f t e r Schnaid and Houlsby, 1990) 395 - x v i i i -LIST OF FIGURES (Continued) Page A.27 D e t a i l s of stepped blade and s t r e s s i n t e r p o l a t i o n method ( a f t e r Handy et a l . , 1982) 397 A.28 T y p i c a l l o g pressure - thickness p l o t from SBT and i n f e r r e d s o i l response ( a f t e r Handy et a l . , 1990) 400 A.29 D e t a i l s of the tapered blade ( a f t e r M i t c h e l l , 1988) 404 A.30 Shear s t r e s s d i s t r i b u t i o n on the c y l i n d r i c a l surface described by a r o t a t i n g vane - a comparison of v a r i o u s t h e o r i e s ( a f t e r Chandler, 1988) 406 A.31 Undrained s t r e n g t h r a t i o s f o r d i f f e r i n g K Q c o n d i t i o n s as given by Eqs. (A. 56) and (A.58) 408 A.32 S e l f - b o r i n g load c e l l w i t h c u t t e r d e t a i l ( a f t e r Dalton and Hawkins, 1982) 411 A.33 R e s ults of SBLC i n s t i f f c l a y a f t e r two complete r o t a t i o n s of probe (20° steps) at a depth of 5m ( a f t e r Dalton and Hawkins, 1982) 412 A.34 Change i n K due to cone p e n e t r a t i o n i n sand ( a f t e r Robertson, 1982) 415 A.35 Influence of D r and chamber boundary c o n d i t i o n s on fg -Qft r e l a t i o n s h i p from CC t e s t data (modified a f t e r Huntsman 1985) 416 A.36 K Q from sleeve f r i c t i o n measurements during CPT ( a f t e r Masood, 1990) 418 A. 37 D i r e c t i o n s of wave propagation and p a r t i c l e motion f o r shear waves i n crosshole and downhole t e s t s (modified a f t e r Stokoe et a l . , 1985) 421 A. 38 R e l a t i o n s h i p between K Q and e l e c t r i c a l index (A*.f) f o r NC c l a y s ( a f t e r Meegoda and Arulanandan, 1986) 428 B. l Assumed f a i l u r e p a t t e r n at penetrometer t i p ( a f t e r B a l i g h , 1975) 438 B.2 Stress paths f o r c a v i t y expansion i n an e l a s t i c - p l a s t i c s o i l ( a f t e r Bouckovalas and Marr, 1981) 442 - x i x -LIST OF FIGURES (Continued) Page B.3 E f f e c t of s t r a i n s o f t e n i n g on e f f e c t i v e s t r e s s path during c a v i t y expansion ( a f t e r Bouckovalas and Marr, 1981) AA3 B.4 Stress f i e l d on cone and s p h e r i c a l c a v i t y expansion i n t e r -p r e t a t i o n of CPTU data ( a f t e r Konrad and Law, 1987) AA5 B.5 K g values from instrumented p i l e load t e s t s i n normally c o n s o l i d a t e d sand ( a f t e r Meyerhof, 1976) A52 B.6 S t r a i n contours around a 60° cone penetrometer ( a f t e r Teh, 1987) A56 B.7 Comparison of s t r a i n path and c a v i t y expansion s t r e s s e s 20D above t i p ( a f t e r Teh, 1987) A57 B.8 Panel r e p r e s e n t a t i o n of cone and dilatometer t i p s ( a f t e r Huang, 1989) A58 - xx -LIST OF SYMBOLS ID One dimensional 3D Three dimensional a,b Regression c o e f f i c i e n t s A Dilatometer f i r s t reading A T „ L a t e r a l s t r e s s a m p l i f i c a t i o n f a c t o r L i u AA.AB Dilatometer c o r r e c t i o n values B Dilatometer second reading BAT Piezometer probe B^ Pore pressure parameter B^ Temperature c o e f f i c i e n t C. Shear wave v e l o c i t y constant i n a n i s o t r o p i c s t r e s s plane CA Rate of secondary compression CEM C a v i t y expansion method C c Compression index CC C a l i b r a t i o n chamber, c y l i n d r i c a l c a v i t y c' Drained ( e f f e c t i v e s t r e s s ) shear s t r e n g t h parameter cc C y l i n d r i c a l c a v i t y ( s u b s c r i p t ) C Dilatometer t h i r d reading CCW Counterclockwise c. C o e f f i c i e n t of h o r i z o n t a l c o n s o l i d a t i o n n Cj Shear wave v e l o c i t y constant i n i s o t r o p i c s t r e s s plane CPM(T) Cone pressuremeter ( t e s t ) CPT(U) Cone p e n e t r a t i o n t e s t (with pore pressure measurement) cv Constant volume c C o e f f i c i e n t of v e r t i c a l c o n s o l i d a t i o n v CW Clockwise C 0,C 1,C 2 Regression constants D Diameter of c y l i n d r i c a l penetrometer DAS Data a c q u i s i t i o n system DH Downhole DH-XH Downhole-crosshole DMT Dilatometer ( t e s t ) D R e l a t i v e d e n s i t y (%) - x x i -LIST OF SYMBOLS (Cont'd) d e D E s E FD FDPM(T) f s FVT G ,G o max G ,G GHH GVH H HFT HSC r r k K A K KCOR h ur DMT FVT LS K LS Diameter of pressure diaphragm Void r a t i o Pressure c e l l s t i f f n e s s Dilatometer modulus S o i l s t i f f n e s s Young's modulus of e l a s t i c i t y -F u l l displacement F u l l displacement pressuremeter ( t e s t ) Sleeve f r i c t i o n on p i l e or penetrometer F i e l d vane t e s t Shear modulus Maximum (small s t r a i n ) shear modulus Unload-reload modulus from pressuremeter G i n v e r t i c a l plane from SCPT max c Small s t r a i n shear modulus of a n i s o t r o p i c plane H o r i z o n t a l H y d r a u l i c f r a c t u r e t e s t H o r i z o n t a l s t r e s s cone M a t e r i a l index from DMT R i g i d i t y index Reduced r i g i d i t y index C o e f f i c i e n t of p e r m e a b i l i t y A c t i v e pressure c o e f f i c i e n t C o e f f i c i e n t of l a t e r a l s t r e s s K estimated from e m p i r i c a l c o r r e l a t i o n s H o r i z o n t a l s t r e s s index from DMT F a c t o r i z e d value of Passive pressure c o e f f i c i e n t K estimated from DMT data o K estimated from FVT data o K estimated from LS-CPTU data o K q estimated from LS-CPTU data using t o t a l s t r e s s approach - x x i i -LIST OF SYMBOLS (Cont'd) KLAB K l » K 2 L LBS LL LS LSC LSSCP LS-CPTU LS-FS in M M r MDF na,nb,nt NC N h N P Au OC OCR OCR max OD.OED P ( P ' ) P 0 » P i » P 2 Po ( P « } a v ( P 0 ) O M P a PBPM(T) P cc PfCp£> K estimated from LS oedometer results o K determined from oedometer tests on oriented samples Distance behind penetrometer tip Laing Bridge South Liquid limit (%) Lateral stress Lateral stress cone Lateral stress sensing cone penetrometer Lateral stress piezocone test Lateral stress sleeve f r i c t i o n Exponent for K Q-OCR relationship ID constrained modulus Rebound factor McDonald Farm Exponents for V - o 1 relationships Normally consolidated Cone resistance stress factor Pressuremeter empirical parameter Excess pore pressure factor Overconsolidated Overconsolidation ratio Maximum past OCR at greatest unloading. Oedometer (test) Pressure (effective) Corrected DMT readings L i f t - o f f pressure Average l i f t - o f f pressure L i f t - o f f pressure from PBPM Atmospheric pressure Prebored pressuremeter (test) Cylindrical cavity expansion limit pressure Final mean stress (effective) - x x i i i -LIST OF SYMBOLS (Cont'd) PI PIPM(T) P L ' P L PL PM(T) PPD PPSV P sc r r o R P RDMT RI R2 SBLC SBPM SBT SCPT SPT STR SVC S t s u u r t t x l t H o r i z o n t a l y i e l d pressure from PMT I n i t i a l mean s t ress ( e f f e c t i v e ) P l a s t i c i t y index P u s h - i n pressuremeter (test) L i m i t pressure P l a s t i c l i m i t Pressuremeter (test) Pore pressure d i f f e r e n c e parameter Pore pressure s t ress dependent parameter S p h e r i c a l c a v i t y expansion l i m i t pressure Cone bearing r e s i s t a n c e Dilatometer bearing r e s i s t a n c e Radius of c a v i t y or probe, c o e f f i c i e n t of c o r r e l a t i o n I n i t i a l c a v i t y radius Radius of p l a s t i c zone Research dilatometer Receiver 1 of XH SCPT Receiver 2 of XH SCPT S e l f - b o r i n g load c e l l S e l f - b o r i n g pressuremeter Stepped blade tes t Seismic cone penet ra t ion t e s t Standard penet ra t ion tes t Strong P i t source vane cone S e n s i t i v i t y Undrained shear s t rength Peak undrained shear s trength Residual undrained shear s t rength Blade t h i c k n e s s , time T r i a x i a l Time for end of primary c o n s o l i d a t i o n - x x i v -LIST OF SYMBOLS (Cont'd) T TBT T I TR TSC u u o u c u. u. 1 u t u upper lower U(t) UBC UCB V V f s (VLS>M V s ( V A w W N W T XH in a a A Temperature, DMT t h r u s t , vane torque Tapered blade t e s t In s i t u e q u i l i b r i u m temperature Reference temperature T o t a l s t r e s s c e l l Pore pressure E q u i l i b r i u m pore pressure C r i t i c a l pore pressure Crack opening pressure I n i t i a l pore pressure during p e n e t r a t i o n Pore pressure at time t during d i s s i p a t i o n P e n e t r a t i o n pore pressures at d i f f e r e n t l o c a t i o n s around a probe Upper pore pressure on UCB LS cone Lower pore pressure on UCB LS cone Degree of pore pressure d i s s i p a t i o n at time t U n i v e r s i t y of B r i t i s h Columbia U n i v e r s i t y of C a l i f o r n i a at Berkeley V e r t i c a l R e l a t i v e sleeve f r i c t i o n v o l t age Corrected r e l a t i v e l a t e r a l s t r e s s v o l tage Measured r e l a t i v e l a t e r a l s t r e s s v o l tage Shear wave v e l o c i t y Shear wave v e l o c i t y i n a n i s o t r o p i c plane Shear wave v e l o c i t y i n i s o t r o p i c plane Moisture content N a t u r a l water content Depth to water t a b l e Crosshole Gauge zero reading Regression c o e f f i c i e n t , r e d u c t i o n f a c t o r Anisotropy f a c t o r Disturbance f a c t o r - xxv -LIST OF SYMBOLS (Cont'd) a p Modulus r a t i o ST a. i I n i t i a l s t r e s s measurement at t = l Power decay constant T o t a l (saturated) u n i t weight Id Dry u n i t weight Unit weight of water 5 S o i l - s t e e l i n t e r f a c e angle of f r i c t i o n A H o r i z o n t a l s t r e s s f a c t o r Au Pore pressure increment, excess pore pressure Aa Stress increment € h H o r i z o n t a l s t r a i n e V V e r t i c a l s t r a i n M Poisson's r a t i o X E m p i r i c a l c o e f f i c i e n t p Bulk d e n s i t y % B a s e l i n e t o t a l pressure at reference temperature H o r i z o n t a l s t r e s s ( e f f e c t i v e ) a (a') V e r t i c a l s t r e s s ( e f f e c t i v e ) V V o^(CC) E f f e c t i v e h o r i z o n t a l chamber pressure °hm Maximum past h o r i z o n t a l c o n s o l i d a t i o n pressure a m Measured t o t a l blade pressure, mean normal s t r e s s a j_ Octahedral s t r e s s oct °TSC Temperature c o r r e c t e d net t o t a l blade pressure o' vm Maximum past v e r t i c a l c o n s o l i d a t i o n pressure a i ' ° 2 ' ° 3 T o t a l p r i n c i p a l s t r e s s e s X Shear s t r e s s T v h Shear s t r e s s on penetrometer surface ( f g ) P-e M i c r o s t r a i n <*> Shear s t r e n g t h parameter *' cv Drained constant volume f r i c t i o n angle Drained t r i a x i a l angle of f r i c t i o n Drained plane s t r a i n angle of f r i c t i o n ps - x x v i -ACKNOWLEDGEMENTS The author i s g r a t e f u l to Dr. R.G. Campanella f o r h i s encouragement and a s s i s t a n c e throughout the p e r i o d of t h i s research. Discussions and sugges-t i o n s from Drs. Byrne, Fannin, Finn and Vaid are g r a t e f u l l y acknowledged. The a s s i s t a n c e of Dr. J.M.O. Hughes to improve the s e l f - b o r i n g pressuremeter i n s t a l l a t i o n technique and Dr. A.B. Huang w i t h the s e l f - b o r i n g load c e l l i s much appreciated. Dr. T. Masood a s s i s t e d w i t h the l a t e r a l s t r e s s cone t e s t -in g at McDonald Farm as p a r t of a UBC/University of C a l i f o r n i a at Berkeley cooperative t e s t i n g programme. The t e c h n i c a l support of Scott Jackson, A r t Brookes, Harald Schrempp, Jim Greig and Glenn J o l l y has been i n v a l u a b l e i n performing the research t e s t s reported h e r e i n . Discussions w i t h colleagues i n the geotechnical group and a s s i s t a n c e w i t h f i e l d work are g r a t e f u l l y acknowledged, i n p a r t i c u l a r Don G i l l e s p i e , John Howie, Ian Hers, Ross Hitchman, Ilmar Weemees and Dan Zavoral. The author would a l s o l i k e to extend h i s thanks to Dr. P. Robertson f o r c r i t i c a l l y reviewing Chapters 1 and 2. Thanks a l s o to K e l l y Lamb f o r t y p i n g the t e x t and to Richard Brun f o r producing some of the f i g u r e s . F i n a n c i a l support was i n i t i a l l y provided by the Science and Engineering Research C o u n c i l (UK) i n the form of a NATO Overseas F e l l o w s h i p . Subsequent funding from the U n i v e r s i t y of B r i t i s h Columbia Graduate Fellowship Programme and INTEVEP, S.A. i s g r a t e f u l l y acknowledged. A s p e c i a l thanks to my w i f e Carmen f o r her support and understanding and to my sons P a u l , Peter and Thomas f o r being such great guys. - x x v i i -1 CHAPTER 1 1. INTRODUCTION 1.1 Background In s i t u t e s t i n g has r e c e n t l y undergone r a p i d advances both i n terms of the v a r i e t y of techniques and methods of i n t e r p r e t a t i o n . In the e a r l y 1970's s e l f - b o r i n g pressuremeters (SBPM) were introduced to the geotechnical commun-i t y f o l l owed by cone penetrometers (CPT) capable of measuring pore pressures (Torstensson, 1975; Baguelin et a l . , 1972; Hughes, 1973; Wissa et a l . , 1975) and the f l a t expandable dilatometer (DMT, M a r c h e t t i , 1975). The t r a d i t i o n a l o b j e c t i v e s of s o i l p r o f i l i n g f o r s i t e c h a r a c t e r i z a t i o n became more e a s i l y a t t a i n a b l e as experience w i t h the near continuous logging cone p e n e t r a t i o n t e s t (CPT) and DMT methods was acquired. S o i l behaviour type charts were produced based on samples obtained from contiguous borehole i n v e s t i g a t i o n s which, when a p p l i e d at other s i t e s , allowed considerable s t r a t i g r a p h i c a l d e t a i l to be i n f e r r e d i n d i r e c t l y (Jones and Rust, 1982; Senneset and Janbu, 1984; Robertson et a l . , 1985; Olsen and F a r r , 1986) without recourse to more t r a d i t i o n a l procedures ( i . e . , sample recovery and i n s p e c t i o n ) . With the trend towards increased i n s i t u e v a l u a t i o n of s o i l parameters, i n t e r p r e t a t i o n techniques were developed and used to o b t a i n estimates of s o i l behaviour f o r engineering design (Robertson and Campanella, 1984). Theore-t i c a l and e m p i r i c a l procedures were presented f o r d e r i v i n g s t r e n g t h and s t i f f n e s s parameters (Durgunoglu and M i t c h e l l , 1975; Schmertmann, 1976; Sanglerat, 1979; Robertson and Campanella, 1983; B a l d i et a l . , 1986). For i n s i t u t e s t s where s p e c i f i c parameters were being sought, t h e o r e t i c a l i n t e r p r e -t a t i o n techniques gave c o n s i s t e n t (but not n e c e s s a r i l y c o r r e c t ) parameter values. E m p i r i c a l procedures, sometimes l o o s e l y based on theory, were 2 adopted to o b t a i n s i m i l a r parameters from the logging methods; the r e s u l t s g e n e r a l l y being very e r r a t i c . As the f i e l d of i n s i t u t e s t i n g developed, i t became apparent th a t a co n s i s t e n t form of a n a l y s i s of i n s i t u t e s t r e s u l t s could only be achieved i f the f o l l o w i n g data were a v a i l a b l e : (a) i d e n t i f i c a t i o n of s o i l types i n p r o f i l e , (b) d e t a i l s of the i n s i t u s t r e s s s t a t e of the s o i l , (c) i n f o r m a t i o n p e r t a i n i n g to the s t r e s s h i s t o r y of the s o i l d e p o s i t , (d) deformation c h a r a c t e r i s t i c s ( s t r e s s - s t r a i n response), and (e) flow and 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 . Topics (a) , (c) and (e) have r e c e i v e d considerable a t t e n t i o n and va r i o u s techniques e x i s t f o r e v a l u a t i n g the r e q u i r e d i n f o r m a t i o n (Torstensson, 1972; B a l i g h and Levadoux, 1980; Jamiolkowski et a l . , 1985; Teh, 1987; Campanella and Robertson, 1988). The advances have been made p o s s i b l e through the p r e s e n t a t i o n of case h i s t o r i e s whereby i n s i t u t e s t r e s u l t s have been c a l i b r a t e d a g a i n s t b e h a v i o u r measured i n the l a b o r a t o r y ( i n c l u d i n g c a l i b r a t i o n chambers) or i n the f i e l d . Topics (b) and (d) are p r e s e n t l y the subject of i n t e n s i v e research and have many s i m i l a r a s s o c i a t e d problems. The d i r e c t measurement of i n s i t u h o r i z o n t a l s t r e s s and modulus i s s e n s i t i v e to disturbance, whether s t r e s s or s t r a i n r e l a t e d . E r r o r s i n measurement can be c r u c i a l f o r both parameters. Furthermore, while s p e c i f i c t e s t methods e x i s t f o r determining i n s i t u s t r e s s and modulus, considerable d i s c u s s i o n e x i s t s as to how to best measure each one and the v a l i d i t y of what i s a c t u a l l y being measured. Equipment charac-t e r i s t i c s and method of i n s e r t i o n are extremely important and may so d i s r u p t the i n i t i a l i n ground c o n d i t i o n s t h a t d i r e c t measurement i s not f e a s i b l e . 3 For e v a l u a t i o n of the i n s i t u s t r e s s s t a t e , i n p a r t i c u l a r the h o r i z o n t a l s t r e s s , i t i s g e n e r a l l y accepted amongst e x p e r i m e n t a l i s t s t h a t i n - p l a c e measurement i s p r e f e r r e d wherever p o s s i b l e . The i n s i t u s t a t e of s t r e s s i s considered i n the f o l l o w i n g s e c t i o n . 1.2 In S i t u Stress State The three components that define the i n s i t u s t r e s s s t a t e at any depth w i t h i n a s o i l deposit f o r l e v e l ground c o n d i t i o n s are the v e r t i c a l and h o r i -z o n t a l s t r e s s e s and the e q u i l i b r i u m pore pressure. I f h y d r o s t a t i c c o n d i t i o n s e x i s t , the e q u i l i b r i u m pore pressure, Uq, can be c a l c u l a t e d i f the depth to the water t a b l e i s known; otherwise i n s i t u p i e z o m e t r i c measurements are n e c e s s a r y . The t o t a l v e r t i c a l s t r e s s , o , i s u s u a l l y computed from v e r t i c a l e q u i l i b r i u m of the u n i t s o i l column t a k i n g i n t o account the v a r i a t i o n of s o i l d e n s i t y throughout the p r o f i l e . No computational procedure e x i s t s to eva l u -a t e t he t o t a l h o r i z o n t a l s t r e s s , o^, and i f measurements are not a v a i l a b l e , c o r r e l a t i o n s ( u s u a l l y based on l a b o r a t o r y t e s t data) are employed. For a normally c o n s o l i d a t e d (NC) or overconsolidated (OC) s o i l the r e l a t i o n s h i p between the e f f e c t i v e v e r t i c a l and h o r i z o n t a l s t r e s s e s i s given by: a,-u 0/ K = _A_° = J l 0 -u a v o v where K i s termed the c o e f f i c i e n t of l a t e r a l s t r e s s (Donath, 1891; Terzaghi, 1925) . For the l e v e l ground s i t u a t i o n where and o^ are p r i n c i p a l e f f e c -t i v e s t r e s s e s , and where c o n s o l i d a t i o n occurs under c o n d i t i o n s of no l a t e r a l s t r a i n , the r a t i o of the s t r e s s e s i s termed the c o e f f i c i e n t of l a t e r a l s t r e s s a t r e s t and i s denoted K . Where the ground surface i s not h o r i z o n t a l , the o p r i n c i p a l s t r e s s d i r e c t i o n s are r o t a t e d . In t h i s case °^ a[ a n d a ^ ° 3 ( f o r a 4 NC s o i l ) and the l a t e r a l s t r e s s c o e f f i c i e n t , by d e f i n i t i o n , i s not K q but K. To det e r m i n e K i t would be necessary to evaluate o at d i f f e r e n t d i r e c t i o n s o J so that the p r i n c i p a l s t r e s s e s and t h e i r d i r e c t i o n could be c a l c u l a t e d . In most cases i n engineering, K i s the r e q u i r e d parameter and measurement of the h o r i z o n t a l s t r e s s i s the o b j e c t i v e . I n a d v e r t e n t l y t h i s i s o f t e n designated K . o At the UBC research s i t e s where t e s t s have been performed, the ground surfaces are e s s e n t i a l l y h o r i z o n t a l and so the s t r e s s r a t i o obtained r e f e r s t o K q . Where a s l i g h t s u r f a c e g r a d i e n t e x i s t s , K has been assumed t o represent K Q. A unique s t r e s s - r a t i o r e l a t i o n s h i p e x i s t s f o r a p a r t i c u l a r homogeneous i s o t r o p i c s o i l under c o n d i t i o n s of v i r g i n or f i r s t time l o a d i n g . The one-dimensional (ID) normally c o n s o l i d a t e d value of K can be estimated based J o on the Jaky (1944) expression (derived from l a b o r a t o r y t e s t s ) : ( V N C - ( 1 + f where <j>' i s the drained f r i c t i o n angle of the s o i l determined i n the t r i a x i a l shear apparatus. In more general use, Eq. (1.2) i s s i m p l i f i e d t o : (K ) == 1 - s i n * ' (1.3) o NC The s t r e s s path AB i n F i g . 1.1 corresponds to the above s i t u a t i o n . Upon ID unloading of an i d e a l e l a s t i c s o i l the s t r e s s path should f o l l o w BA and the ID o v e r c o n s o l i d a t e d K q v a l u e would be the same as f o r v i r g i n l o a d i n g . In r e a l i t y K i n c r e a s e s as the o v e r c o n s o l i d a t i o n r a t i o (OCR) increases and the o s o i l f o l l o w s s t r e s s path BCD when unloaded. The o v e r c o n s o l i d a t i o n r a t i o , l-sincfr' l+sin<f>1 (1.2) 5 OCR, i s defined as the r a t i o of the maximum e f f e c t i v e past pressure experi-enced by the s o i l (a' ) to the present v e r t i c a l e f f e c t i v e s t r e s s ( a ' ) , i . e . vm v OCR = a' /a' vm v (1.4) In F i g . 1 .1 , the e f f e c t i v e s t r e s s at p o i n t B corresponds to o' while t h a t at vm any p o i n t a l o n g the unloading or r e l o a d i n g curves corresponds to o^. At C, (K q)Q£ = 1 which u s u a l l y corresponds to an OCR of about 4. Further unloading to D promotes passive f a i l u r e w i t h both OCR and K q i n c r e a s i n g . CT V = C J H , ' (Ko=1) F i g . 1.1 T y p i c a l e f f e c t i v e s t r e s s paths f o r ID c o n s o l i d a t e d s o i l (modified a f t e r Wroth, 1975). D u r i n g r e l o a d i n g a l o n g p a t h DEFB the (K ) n r value decreases becoming e q u a l t o ( K q ) ^ somewhere between F and B. As pointed out by Wroth (1975), a t p o i n t s C and E the s o i l has the same OCR but d i f f e r e n t (K )^_, values. K o OC o i s thus s t r e s s path dependent. 6 Where i n f o r m a t i o n regarding the i n s i t u h o r i z o n t a l s t r e s s e s i s not a v a i l a b l e , e s t i m a t e s of (K )„_ can be obtained from p u b l i s h e d data r e l a t i n g o NC K q and OCR ( B r o o k e r and I r e l a n d , 1965; Mayne and Kulhawy, 1982). Several a t t e m p t s at r e l a t i n g (K ) a n d OCR have been s u g g e s t e d on the b a s i s of l a b o r a t o r y data, the most popular being that suggested by Schmidt (1966): (KoW- ( V N C ( 0 C R ) C X ( 1 - 5 ) where a i s e s s e n t i a l l y constant f o r a p a r t i c u l a r s o i l and v a r i e s from 0.42 f o r low p l a s t i c i t y c l a y s to 0,32 f o r h i g h p l a s t i c i t y c l a y s (Wroth and Houlsby, 1985). Mayne and Kulhawy (1982) reviewed p u b l i s h e d data and confirmed the v a l i d i t y of Eq. (1.5) f o r uncemented c l a y s during ID primary unloading. Schmidt (1966) suggested t h a t : a = s i n * ' (1.6) which was a l s o confirmed by Mayne and Kulhway (1982) using a much l a r g e r data base. The c o e f f i c i e n t o f p a s s i v e e a r t h p r e s s u r e , K^, i s an upper l i m i t on (K ) where: o OC U s i n ^ P 1 - s m f S i m i l a r l y , the c o e f f i c i e n t of a c t i v e e a r t h pressure, K^, where: K. = l=Si2£. ( 1 . 8 ) A l+smcf)1 i s a lower l i m i t f o r (K )„.,. For a p u r e l y f r i c t i o n a l loose to medium-dense o NC s o i l , the v a r i a t i o n o f K. , (K ) _ and K p as a f u n c t i o n of <j>' are shown i n A OWL* IT F i g . 1.2. K F i g . 1.2 V a r i a t i o n of K^, ( K Q ) N C and K p as a f u n c t i o n of <f>' Mayne and Kulhawy (1982) evaluated s o i l response during ID r e l o a d i n g and suggested t h a t : (K ) * = (K )„_ (-°^f—) + M ° 0 C ° N C OCR 1 _ a r max 1 " ( ^ - ) 'OCR max (1.9) where (K )„„ i s the ID overconsolidated l a t e r a l s t r e s s c o e f f i c i e n t during the o OC f i r s t c y c l e of r e l o a d i n g , OCR i s the maximum value of o v e r c o n s o l i d a t i o n J & max r a t i o experienced by the s o i l (point D i n F i g . 1.1) and: M r f . ( l - s i n ^ ) = | ( K o ) N C (1.10) At any p o i n t d u r i n g the r e l o a d i n g phase, o^ i n c r e a s e s so t h a t w h i l e o ^ remains constant the OCR i s decreasing u n t i l a value of u n i t y i s again a t t a i n e d when the r e l o a d i n g reaches p o i n t B. The a p p l i c a t i o n of Eq. (1.9) i s d i f f i c u l t i n a f i e l d s i t u a t i o n s i n c e g e n e r a l l y OCR i s not known. max 8 The above r e l a t i o n s h i p s have been de r i v e d from l a b o r a t o r y t e s t data on both undisturbed and r e c o n s t i t u t e d samples. Most of the data f o r undisturbed s o i l r e l a t e s to c l a y due to the problems a s s o c i a t e d w i t h recovery of q u a l i t y samples i n sand. Because the s t r e s s c o n d i t i o n s and the e f f e c t s of d i s t u r b -ance i n the undisturbed samples at the s t a r t of the t e s t are unknown, the K Q values so defined are incremental i n nature and i t has been suggested t h a t they provide a lower bound to the f i e l d s i t u a t i o n . Aging i n the f i e l d may a l s o cause d i f f e r e n c e s w i t h the l a b o r a t o r y measured values. Furthermore, the s t r e s s h i s t o r y r e l a t i o n s h i p s have been evaluated f o r the c o n d i t i o n of simple mechanical o v e r c o n s o l i d a t i o n . Stress h i s t o r y c h a r a c t e r i s t i c s can be i n f l u -enced by many f a c t o r s , some q u a n t i f i a b l e , many not. Schmertmann (1985) d i s c u s s e s many of the n o n - t a n g i b l e f a c t o r s t h a t may i n f l u e n c e K q , i . e . cementation, d e p o s i t i o n environment, t e c t o n i c environment, s t r a i n h i s t o r y , s t r e s s h i s t o r y , environmental f a c t o r s , d e s s i c a t i o n , aging, e t c . The e f f e c t of any of the above, s i n g u l a r l y or i n combination, w i l l cause the in-ground K q v a l u e t o d e v i a t e m a r k e d l y from t h a t p r e d i c t e d based on the l a b o r a t o r y d e r i v e d r e l a t i o n s h i p s . I t i s a l s o to be expected t h a t these r e l a t i o n s h i p s w i l l be i n e r r o r f o r c o n d i t i o n s other than l e v e l ground. Hence where p o s s i b l e the h o r i z o n t a l s t r e s s should be measured i n s i t u . 1.3 Laboratory Techniques f o r E v a l u a t i n g K Q Schmertmann (1985) l i s t e d seven techniques f o r l a b o r a t o r y determination of K q , a p p l i c a b l e m a i n l y t o c o h e s i v e s o i l s . More r e c e n t techniques are inc l u d e d i n the f o l l o w i n g l i s t : • T r i a x i a l t e s t u s i n g i n d i r e c t or bu r e t t e method (Bishop and E l d i n , 1953) 9 • T r i a x i a l t e s t w i t h l a t e r a l s t r a i n i n d i c a t o r (Bishop and Henkel, 1957) • T r i a x i a l t e s t , c a p i l l a r y pressure measurement (Skempton, 1961; Burland and Maswoswe, 1982) • K q t r i a x i a l c e l l (Campanella and Va i d , 1972) • H o r i z o n t a l and v e r t i c a l oedometer t e s t s (Zeevaert, 1953; Poulos and Davis, 1972) • P r o p o r t i o n a l loading t e s t s i n t r i a x i a l c e l l (Andrawes and El-Sohby, 1973) • H y d r a u l i c f r a c t u r i n g ( A l - S h a i k h - A l i , 1977) • T r i a x i a l d e v i a t o r s t r e s s method (Chang et a l . , 1977) • L a t e r a l s t r e s s d i r e c t shear t e s t (Dyvik et a l . , 1987) • L a t e r a l s t r e s s oedometer (Dyvik et a l . , 1985; Senneset, 1989) For granular s o i l s , these t e s t s are u s u a l l y performed on specimens formed i n the l a b o r a t o r y . A l s o inherent i n the above procedure i s the assumption that the K q v a l u e i s uniquely r e l a t e d to o v e r c o n s o l i d a t i o n r a t i o , at l e a s t during ID unloading. This has been questioned by J e f f e r i e s et a l . (1987) f o r recent o f f s h o r e d e p o s i t s . For the Beaufort Sea sediments s t u d i e d , i t may be that p h y s i o c h e m i c a l p r o c e s s e s c o n t r i b u t e to the higher than expected K q v a l u e s , although some doubt a l s o e x i s t s as to the a c t u a l OCR values used f o r the s i t e . Undrained shear strengths measured i n the Beaufort Sea sediments, which are u s u a l l y r e l i a b l e i n d i c e s f o r e s t i m a t i n g s t r e s s h i s t o r y , i n d i c a t e OCR values higher than obtained from l a b o r a t o r y c o n s o l i d a t i o n t e s t s . The e f f e c t s o f secondary c o m p r e s s i o n and a g i n g on K q a r e a r e a s o f i n t e r e s t i n geotechnics. Schmertmann (1983) f i r s t r a i s e d the question; Jamiokowski et a l . (1985) reviewed a v a i l a b l e data and concluded that no d e f i n i t e change i n K q occurs w i t h time. I t i s the a u t h o r ' s o p i n i o n t h a t K i n NC s o i l s (K < 1) increases w i t h o o 10 g e o l o g i c time t o a value of u n i t y and that i n OC s o i l s (K Q > 1) a r e d u c t i o n to u n i t y occurs. The i n d i c a t i o n s f o r t h i s v a r i a t i o n from p u b l i s h e d data are discussed i n the f o l l o w i n g paragraph. For any s o i l , the v a r i a t i o n of K q dur-ing l oading and unloading w i l l be c o n t r o l l e d by the s t r e s s - s t r a i n charac-t e r i s t i c s of the m a t e r i a l . Based on a c o n s i d e r a t i o n of p o s t - d e p o s i t i o n h i s t o r y , one might conclude: • I n the s l u r r y form, a t the moment of d e p o s i t i o n , K q i s not e a s i l y d e f i n e d (may be c l o s e t o u n i t y as f o r a l l non-viscous f l u i d s ) since both a' and oJ" are very small v h J • A f t e r d e p o s i t i o n and w i t h b u r i a l , the K value approaches (K ).Tr, over o o NC a short p e r i o d of time, where K = 1 - s i n * o • As the s o i l becomes p r o g r e s s i v e l y b u r i e d , the l a t e r a l s t r a i n c o n d i t i o n i s modified and s t r e s s r e d i s t r i b u t i o n as a r e s u l t of a n i s o t r o p i c hard-e n i n g o c c u r s so t h a t K i n c r e a s e s t o a v a l u e of u n i t y . T h i s i s to o c o n s i s t e n t w i t h s t r e s s measurements i n NC sedimentary rocks u n a f f e c t e d by major t e c t o n i c a c t i v i t y (Brown and Hoek, 1978; Hergert, 1988). The s u g g e s t e d v a r i a t i o n of (K ).T„ w i t h time a f t e r d e p o s i t i o n i s i l l u s t r a t e d o NL i n F i g . 1.3. SBPM data from the Beaufort Sea presented by Graham and J e f f e r i e s (1986) concur w i t h the idea of K q reducing from u n i t y to l-sincf)' during the i n i t i a l p e r i o d a f t e r d e p o s i t i o n . Tests performed i n a h y d r a u l i c sand f i l l one month a f t e r placement gave K q values around 1. Values measured one year l a t e r gave K q values i n b e t t e r agreement w i t h the Jaky expression. The C a/C c concept p r o p o s e d by M e s r i and Godlewski (1977) can a l s o be a p p l i e d t o e v a l u a t i n g K v a r i a t i o n s . Mesri and Castro (1987) show that K 11 SLURRY CONDITION r- RATE OF CHANGE DEPENDENT ' ON SOIL TYPE AND DEPOSITION ENVIRONMENT TO CONDITION Ko»l OVER GEOLOGIC TIME FOR NC STATE WITH INCREASING DEPTH OF BURIAL. j S-AM = f ( C * /Cc) i 1 1 B -fp TIME where: t = time for.end of primary c o n s o l i d a t i o n F i g . 1.3 Change i n w i t h time a f t e r d e p o s i t i o n . i n c r e a s e s w i t h time f o r NC s o i l s and t h a t the C /C method can be used to a c adjust l a b o r a t o r y values to the f i e l d c o n d i t i o n . However, much more f i e l d and l a b o r a t o r y d a t a a r e r e q u i r e d t o e v a l u a t e the time dependence of K q i n both NC and OC s o i l s . I r r e s p e c t i v e of the problems that may e x i s t w i t h the f i e l d a p p l i c a t i o n o f l a b o r a t o r y determined K q v a l u e s , the use of l a b o r a t o r y data i s one of the few checks a v a i l a b l e on measured f i e l d data. C a l i b r a t i o n chamber (CC) t e s t i n g i s a la r g e s c a l e form of l a b o r a t o r y t e s t i n g . The a p p l i c a t i o n of CC r e s u l t s to the i n t e r p r e t a t i o n of i n s i t u measurements i s considered i n Chapter 2. 1.4 Conditions f o r the In S i t u Measurement of H o r i z o n t a l Stress As d i s c u s s e d e a r l i e r , the i d e a l measurement of o^ i n s i t u r e q u i r e s that no disturbance i s imparted to the s o i l and that the measurements are made Ko 12 under conditions of no l a t e r a l s t r a i n . Other considerations also e x i s t . Ideal c r i t e r i a for measuring the true i n s i t u would include: • i n s t a l l a t i o n of measuring apparatus with no l a t e r a l movement of s o i l , either inward or outward, = 0 • no shear stresses applied to the s o i l resulting from f r i c t i o n between the s o i l and instrument during i n s e r t i o n , T ^ = 0 • no induced pore pressures during or after probe in s e r t i o n , • measurement of o^ obtained by i n f i n i t e s i m a l ( i d e a l l y zero) expansion/ contraction of probe, • no change i n a^, o^ or due to measurement procedure, • very sensitive measuring system for stress and pore pressure, and • universal i n s t a l l a t i o n technique applicable for any s o i l type. I d e a l l y , the measurement of K q i s a zero s t r a i n condition (by d e f i n i -t i o n ) . However, t h i s requirement i s impossible to a t t a i n with presently available equipment where measurements are obtained at some minimal displace-ment. For t h i s reason, the measurement of K can be considered a small-' o s t r a i n technique. The importance of the above conditions varies according to s o i l type, i.e . s o i l s t i f f n e s s i s important i n determining the effect of stress or s t r a i n r e l i e f . In general, the s t i f f e r the s o i l the more severe the effects of i n s t a l l a t i o n become. I t i s worth considering these ideal conditions i n r e l a t i o n to the established techniques for measuring the i n s i t u l a t e r a l stress. The most widely used f i e l d techniques for measuring the i n s i t u l a t e r a l stress are: - self-boring pressuremeter (SBPM) - self-boring load c e l l (SBLC) 13 - hydraulic fracture test (HFT) - push-in total stress cells (TSC) The individual test techniques and data interpretation are not con-sidered here as detailed comments are contained later in the thesis. In relation to the seven ideal requirements listed above the following observa-tions are made: • The main problem associated with the self-boring probes i s the disturbance caused during installation, the effects of which are indeterminate. • Even i f ideal installation of a self-boring probe were possible, the shear-ing at the probe-soil interface would modify the near-field stress distribution to various degrees depending on the characteristics of the s o i l being penetrated. Furthermore, only in normally consolidated soils would the effective l i f t - o f f pressure represent the in-situ horizontal effective stress. In overconsolidated s o i l s , the l i f t - o f f pressure would correspond to an effective horizontal yield stress, indicative of the maximum past horizontal pressure to which the s o i l had been subjected. • Both the HFT and TSC techniques require the installation of a probe or blade into a disturbed s o i l . The change in the in situ stress regime i s corrected for in an arbitrary manner. Notwithstanding this, the i n i t i a l stress f i e l d i s modified and the results may be ambiguous. The development of non-destructive techniques such as in situ shear wave velocity measurements may satisfy the conditions for the idealized require-ments listed above. However, the evaluation rather than direct measurement of from these techniques w i l l depend on the uncertainty of any parameter relationships involved, i . e . the dependence of V g on both structure and stress. Similar conditioning relationships w i l l also prevail for the inter-14 p r e t a t i o n of f u l l - d i s p l a c e m e n t s t r e s s and pore pressure measurements. This i s discussed l a t e r i n t h i s t h e s i s . 1.5 Research Objectives The s e l f - b o r i n g pressuremeter i s considered by many to be the best low displacement method f o r measuring o^ i n s i t u . However, the e f f e c t s of bo r i n g disturbance, equipment c h a r a c t e r i s t i c s and shear s t r e s s e s induced at the s o i l - i n s t r u m e n t i n t e r f a c e and v a r i a t i o n s i n t e s t procedure cause problems i n the i n t e r p r e t a t i o n o f J a m i o l k o w s k i e t a l . , 1985; Mair and Wood, 1987). The problem i s the determination of the o f t e n e r r a t i c disturbance that has occurred during probe i n s e r t i o n and a d j u s t i n g / e v a l u a t i n g the data accord-i n g l y . The a p p l i c a t i o n o f f u l l d i s p l a c e m e n t probes t o es t i m a t e o^ has been developed w i t h the idea of inducing l a r g e yet repeatable degrees of disturbance to the s o i l and then c o r r e c t i n g f o r the r e s u l t i n g e f f e c t s of the i n s e r t i o n on the measurement of o^. T h i s methodology r e l a t e s the two d i f f e r i n g s o i l responses according to the induced s t r a i n l e v e l , i . e . t h a t the measurements of s t r e s s or pore pressure during f u l l - d i s p l a c e m e n t p e n e t r a t i o n t e s t i n g are c o n t r o l l e d to some degree by the pr e - p e n e t r a t i o n h o r i z o n t a l e f f e c t i v e s t r e s s . Furthermore, depending on the loa d i n g c o n d i t i o n s and the i n t e r p r e t a t i o n technique employed to evaluate the pr e - p e n e t r a t i o n l a t e r a l s t r e s s , the b a c k - c a l c u l a t i o n technique i s l i n k e d to both the i n i t i a l s t r e s s s t a t e and the s t r e s s - s t r a i n response of the s o i l under the a p p l i e d l o a d i n g . The c o r r e c t i o n technique i s based on e m p i r i c a l or semi-empirical c o r r e l a t i o n s . The o b j e c t i v e of t h i s research i s to evaluate the s o i l response during the i n s t a l l a t i o n of f u l l displacement probes. Comparisons of the h o r i z o n t a l 15 s t r e s s e s measured i n both sand and c l a y by v a r i o u s types of probe w i l l be made to evaluate the f a c t o r s c o n t r o l l i n g s o i l response to both s e l f - b o r i n g and f u l l displacement i n s t a l l a t i o n . The d i s t r i b u t i o n of s t r e s s e s and pore pressures around the d i f f e r e n t penetrometers are a l s o considered. The measur-ed s t r e s s e s are a l s o i n t e r p r e t e d w i t h the o b j e c t i v e of p r e d i c t i n g the i n s i t u p r e - p e n e t r a t i o n s t r e s s . The o b j e c t i v e i s to see i f i t i s p o s s i b l e to i n t e r -p r e t the l a r g e s t r a i n measurements i n order to b a c k - c a l c u l a t e the i n i t i a l l a t e r a l s t r e s s c o n d i t i o n and i f so, how s e n s i t i v e these techniques are to the a l g o r i t h m used and s o i l parameters employed i n the model. Reference values of h o r i z o n t a l s t r e s s (see Chapter 6 f o r d i s c u s s i o n ) are determined by both f i e l d measurements and l a b o r a t o r y t e s t s f o r comparative purposes. Index parameters are d e fined as i n d i c a t o r s f o r p r o f i l i n g v a r i a t i o n s i n the s t r e s s h i s t o r y . 1.6 Thesis Layout The c o n d i t i o n s induced during the i n s t a l l a t i o n of f u l l displacement probes are considered i n Chapter 2 and r e l a t i o n s h i p s are presented which l i n k s o i l behaviour at small and l a r g e s t r a i n s . The s t r e s s d i s t r i b u t i o n around a p e n e t r a t i n g probe i s considered i n terms of the c o n t r o l l i n g i n f l u e n c e of the p r e - p e n e t r a t i o n s t r e s s s t a t e and c a v i t y expansion methods are used -to evaluate the measured s t r e s s e s and pore pressures during f u l l - d i s p l a c e m e n t p e n e t r a t i o n t e s t i n g . Laboratory methods f o r measuring and/or indexing the l a t e r a l s t r e s s c o n d i t i o n s are b r i e f l y discussed. The equipment used during the i n s i t u and l a b o r a t o r y t e s t i n g program i s discussed i n Chapter 3 and the research s i t e s described i n Chapter A. Chapters 5 and 6 present the r e s u l t s and i n t e r p r e t a t i o n of the f i e l d and l a b o r a t o r y t e s t s performed. These r e s u l t s are discussed and concluding comments presented i n Chapter 7. 16 C H A P T E R 2 2. L A T E R A L S T R E S S FROM F U L L - D I S P L A C E M E N T P R O B E S ; C O N S I D E R A T I O N S 2.1 I n t r o d u c t i o n T h e e v a l u a t i o n o f i n s i t u h o r i z o n t a l s t r e s s c a n b e c l a s s i f i e d i n t o f o u r m a i n g r o u p s a c c o r d i n g t o t h e t y p e o f m e a s u r e m e n t m a d e : 1) D i r e c t m e t h o d s 2) S e m i - d i r e c t o r b a c k - e x t r a p o l a t i o n m e t h o d s 3) I n d i r e c t m e t h o d s 4) E m p i r i c a l m e t h o d s D i r e c t m e t h o d s i n c l u d e t e s t s p e r f o r m e d u s i n g t h e s e l f - b o r i n g p r e s s u r e -m e t e r a n d s e l f - b o r i n g l o a d c e l l . D i r e c t m e t h o d s s u f f e r f r o m t h e o f t e n l a r g e e f f e c t s o f e v e n s m a l l d e g r e e s o f d i s t u r b a n c e , t h e c o n s e q u e n c e s o f w h i c h b e c o m e m o r e i m p o r t a n t a s t h e s o i l s t i f f n e s s i n c r e a s e s . S e m i - d i r e c t o r b a c k - e x t r a p o l a t i o n m e t h o d s . D e v e l o p m e n t s i n t h i s a r e a i n c l u d e t h e s t e p p e d b l a d e a n d w e d g e b l a d e , b o t h o f w h i c h r e q u i r e a d d i t i o n a l c a l i b r a t i o n o r c o r r e l a t i o n s a t s p e c i f i c s i t e s p r i o r t o g e n e r a l u s e . I n d i r e c t m e t h o d s a r e u s e d w h e r e b y a l a t e r a l s t r e s s v a l u e i s m e a s u r e d d u r i n g o r a f t e r t h e i n s t a l l a t i o n o f a f u l l - d i s p l a c e m e n t p r o b e . I n s o m e c a s e s , t h e d i s s i p a t i o n o f s t r e s s a n d p o r e p r e s s u r e i n d u c e d d u r i n g i n s e r t i o n c a n b e m o n i t o r e d w i t h t i m e s o t h a t a n e q u i l i b r i u m v a l u e f o r t h e i n s e r t e d p r o b e c a n b e o b t a i n e d . E a c h o f t h e f u l l - d i s p l a c e m e n t m e t h o d s , i . e . l a t e r a l s t r e s s c o n e , c a u s e s s i g n i f i c a n t b u t r e p e a t a b l e d i s t u r b a n c e t o t h e s o i l . E m p i r i c a l m e t h o d s a r e a n i m p o r t a n t s o u r c e o f i n f o r m a t i o n f o r e v a l u a t i n g t h e s t r e s s h i s t o r y o f s o i l d e p o s i t s . E x i s t i n g c o r r e l a t i o n s a r e g e n e r a l l y 17 d e r i v e d from l a b o r a t o r y or c a l i b r a t i o n chamber data and modified to i n c o r p o r -a t e f i e l d p a r a m e t e r s , an example of t h i s being the dilatometer K q c o r r e l a -t i o n s presented by B a l d i et a l . (1986). A c r i t i c a l review of the current methods a v a i l a b l e f o r measuring or indexing the s t a t e of l a t e r a l s t r e s s i s given i n Appendix A. As discussed e a r l i e r i n Chapter 1, i t i s very d i f f i c u l t w i t h p r e s e n t l y a v a i l a b l e equipment to o b t a i n a measurement of the tru e i n s i t u h o r i z o n t a l s t r e s s , o^. A d d i t i o n a l u n c e r t a i n t y a r i s e s as to the choice of a reference value against which measured values can be evaluated. In many comparisons of t h i s type, the r e s u l t s from the s e l f - b o r i n g pressuremeter t e s t (SBPMT) are taken as the reference v a l u e s , even though t h i s technique has been shown t o be u n r e l i a b l e , e s p e c i a l l y i n sands and s t i f f c l a y s (Jamiolkowski et a l . , 1985; Hawkins et a l . , 1990). Many of the problems a s s o c i a t e d w i t h the SBPM as a method f o r measuring o^ have been a t t r i b u t e d to the i n s e r t i o n of the probe i n t o the ground, i . e . disturbance during d r i l l i n g (Hughes, 1973; Denby, 1978; Ghionna et a l . , 1982; Benoit, 1983). Other e f f e c t s due to membrane and equipment compliance, t e s t procedures, e t c . , have a l s o been recognized (Dalton and Hawkins, 1982; Howie et a l . , 1990; Mair and Wood, 1987). These are reviewed b r i e f l y i n Appendix A. In an attempt to evaluate q u a l i t a t i v e l y the e f f e c t s of disturbance during the SBPM d r i l l i n g process i n sand, B e l l o t t i et a l . (1987) performed two types of SBPMT i n a c a l i b r a t i o n chamber (CC). The " i d e a l i n s t a l l a t i o n " of the probe was a t t a i n e d by p l a c i n g the probe i n the centre of the CC before sample formation and subsequently a i r - p l u v i a t i n g the sample i n t o the chamber to o b t a i n the r e q u i r e d r e l a t i v e d e n s i t y . S e l f - b o r e d c o n d i t i o n s were a t t a i n e d by d r i l l i n g the probe i n t o the already p l u v i a l l y deposited sand. A l l PM t e s t s were conducted s t r a i n c o n t r o l l e d . The chamber s t r e s s e s h e l d constant 18 on b o t h b o u n d a r i e s of the chamber (Ao = Ao, = 0). The l i f t - o f f s t r e s s f o r v n each s t r a i n arm, p Q , was determined from v i s u a l i n s p e c t i o n of the e a r l y p a r t of the expansion curve. The r e s u l t s of the two types of t e s t are summarized i n F i g . 2.1. For i d e a l i n s t a l l a t i o n , n o t i c e a b l e d i f f e r e n c e s e x i s t between p from the ' r o SPBM and o^ a p p l i e d to the chamber. S i g n i f i c a n t s c a t t e r a l s o e x i s t s between the l i f t - o f f s t r e s s f o r each of the three s t r a i n arms, which may be due i n p a r t to i n d i v i d u a l s t r a i n arm compliance. The f a c t t h a t most of the data g i v e s p Q > o^ may i n d i c a t e the existence of s t r e s s concentrations around the r i g i d probe induced during the ID c o n s o l i d a t i o n stage. Based on a s i n g l e t e s t using the s e l f - b o r i n g load c e l l (SBLC) B e l l o t t i et a l . (1987) suggest th a t no induced s t r e s s c o n c e n t r a t i o n occurs f o r the i d e a l i n s t a l l a t i o n case. Huntsman (1985) evaluated the e f f e c t of s t r e s s concentrations around a l a t e r a l s t r e s s cone as a r e s u l t of a p p l i e d chamber s t r e s s e s and suggested th a t the measured s t r e s s , o, would approximate t o : o = 1.5 a, + 0.04 o (2.1) n v From the l i m i t e d p u b l i s h e d data, i t would a l s o appear the SBLC underestimates the t r u e l a t e r a l s t r e s s (Charles and Watts, 1987; Tedd and Charles, 1983; Penman and C h a r l e s , 1985). I r r e s p e c t i v e of the i n d i v i d u a l arm s c a t t e r , f o r i d e a l i n s t a l l a t i o n the average p Q v a l u e s a r e r e a s o n a b l y c o n s i s t e n t f o r o^ < 200 kPa. I n d i v i d u a l s t r a i n arm s c a t t e r increases as the r e l a t i v e d e n s i t y and s t r e s s l e v e l i n c r e a s e . From F i g . 2.1(a) i t would appear t h a t even f o r the case of i d e a l i n s t a l l a t i o n p gives v a r i a t i o n of o, between -10% and +50%. B e l l o t i et a l . o n (1987) do, however, provide more c o n s i s t e n t data a f t e r modifying the PM s t r a i n arm design. 19 5 0 0 -. 4 0 0 -o CL CD 3 3 0 0 -in CD 2 0 0 -< 1 0 0 -Data f r o m Bellotti et a l . ( 1987 ) using Cambr idge Mark 8 SBPM in CC with Ticino sand . (a) IDEAL INSTALLATION u 0 = 0 kPa + 10% 1:1 -^o% o o o o o A rm 1 o D • n o A rm 2 A A i i A A rm 3 • • • • • Average — I 1 I 1 1 1 1 r 0 1 0 0 2 0 0 3 0 0 4 0 0 Hor izonta l s t ress in c h a m b e r (kPa) 5 0 0 5 0 0 -4 0 0 -D CD 3 3 0 0 -cn CD 2 0 0 -< 1 0 0 -Data f r o m Bellotti et a l . ( 1987 ) using Cambr idge Mark 8 SBPM + 1 0 % -in CC with Ticino s and . / (b) INSTALLATION BY SELP BORING u 0 = 6 - 7 kPa 1:1 -1 096 / / ' o o o o o A rm 1 • n D a D A rm 2 A A A * & A rm 3 • • • • • Average 0 1 0 0 2 0 0 3 0 0 4 0 0 5 0 0 Hor izonta l s t ress in c h a m b e r (kPa) Fig. 2.1 Comparison of l i f t - o f f pressures from SBPM and horizontal chamber stress for (a) conditions of ideal i n s t a l l a t i o n , and (b) i n s t a l l a -t i o n by self-boring (data from B e l l o t t i et a l . , 1987). 20 Figure 2.1(b) i n d i c a t e s t h a t f o r the s e l f - b o r e d i n s t a l l a t i o n , intended t o be i n d i c a t i v e of the f i e l d s i t u a t i o n , i n almost a l l cases (p ) i s l e s s ' *o av than o^. Using only the average p Q , B e l l o t t i et a l . (1987) quote: ° a V = 0.47 ± 0.28 (2.2) o h(CC) The s c a t t e r i n the i n d i v i d u a l s t r a i n arm data i s s i m i l a r to t h a t f o r the i d e a l i n s t a l l a t i o n . Based on the above, i t would appear t h a t the mechanical design of the SBPM s t r a i n arms i s inadequate f o r determining a c c u r a t e l y the small s t r a i n response r e q u i r e d f o r measuring the t r u e i n s i t u l i f t - o f f pressure, even under i d e a l c o n d i t i o n s . Even under c o n t r o l l e d l a b o r a t o r y c o n d i t i o n s , s i g n i f i c a n t disturbance occurs as a r e s u l t of s e l f - b o r i n g . Considerable doubt must t h e r e f o r e e x i s t w i t h respect to the v a l i d i t y of data obtained i n the f i e l d , e s p e c i a l l y at the low s t r a i n p o r t i o n of the expansion curve. This i s evidenced by the f i e l d data presented by Robertson (1982) and Howie (1991) f o r pressuremeter t e s t s i n sand. A comparison of determined by various types of pressuremeter i s shown i n F i g . 2.2. The s c a t t e r i n the SBPM data i s l a r g e r than that a s s o c i a t e d w i t h three types of f u l l - d i s p l a c e -ment pressuremeter. The reduced s c a t t e r produced by f u l l - d i s p l a c e m e n t probes suggests t h a t l a t e r a l s t r e s s measurements of t h i s type may provide a more r e l i a b l e b a s i s from which to evaluate the i n s i t u p r e - p e n e t r a t i o n h o r i z o n t a l s t r e s s . The usefulness of t h i s technique would depend on: • A l i n k between small s t r a i n and large s t r a i n behaviour of s o i l . This r e q u i r e s some interdependence on the two extremes of s o i l response. 21 Fig. 2.2 Comparison of measured horizontal stress from self-bored and full-displacement pressuremeters (adapted from Howie, 1991). 22 0"hi<crh2<o-h3 (orh')3 Cavity strain F i g . 2.3 E f f e c t of v a r y i n g o^ on SBPM pressure expansion curve according to ,•> Hughes (1989) i n t e r p r e t a t i o n . • Development of i n t e r p r e t a t i o n techniques f o r f u l l - d i s p l a c e m e n t mea-surements to provide repeatable and r e l i a b l e estimates of s o i l parameters. These two p o i n t s are considered s e p a r a t e l y below. 2.2 C o r r e l a t i o n of S o i l Behaviour at Varying S t r a i n Levels Several types of i n t e r p r e t a t i o n technique e x i s t whereby the complete pressure-expansion curve obtained from the SBPM t e s t i s u t i l i z e d f o r para-meter d e t e r m i n a t i o n . Hughes (1989) employs a four parameter model (G, t o^, v) t o evaluate SBPM f i e l d data i n sand whereby the i n f l u e n c e of o^ i s to define the o v e r a l l p o s i t i o n of the curve referenced to the s t r e s s o r i g i n ( F i g . 2.3). J e f f e r i e s (1988)- uses both the loa d i n g and unloading phases of 23 the t e s t to i n t e r p r e t data i n c l a y . The curve shape and p o s i t i o n i s deter-m i n e d by G, S^, o^, and u ( F i g . 2.4). These methods, which have been reported to give good esitmates of the c o n d i t i o n i n g parameters (Appendix A.2.3), i l l u s t r a t e the e f f e c t of o^ throughout the expansion curve, i . e . both at small and la r g e s t r a i n . Both techniques have been developed to overcome the e f f e c t s on the e a r l y p a r t of the PM expansion curve caused by disturbance during s e l f - b o r i n g i n s t a l l a t i o n . R A D I A L S T R A I N F i g . 2.4 Influence of v a r i a b l e s f o r undrained SBPMT i n c l a y ( a f t e r J e f f e r i e s et a l . , 1988) Byrne et a l . (1990) demonstrate the interdependence of la r g e s t r a i n parameters on the i n i t i a l s t a t e of s o i l by l i n k i n g G*, the unload-reload modulus from PM t e s t s , to the small s t r a i n maximum shear modulus, G (G ) o max fo r a wide range of loading and unloading c o n d i t i o n s . G* i s a parameter measured at any p a r t i c u l a r c a v i t y s t r a i n ; consequently i t depends on both the 24 s t r e s s and v o i d r a t i o changes induced i n the s o i l during expansion. G* and G are r e l a t e d through the f a c t o r a which was determined from the r e s u l t s of o P a f i n i t e element e l a s t i c p l a s t i c a n a l y s i s i n c o r p o r a t i n g n o n l i n e a r e l a s t i c b e h a v i o u r d u r i n g u n l o a d i n g ( F i g . 2.5). G q values from SBPMT unload-reload G* 1.8 .6 0.6 0.4- -0 .2- -(4er r) f, " r > F o c . > 0 . 0 0.0-1 1 ! 1 1 1 1 ! i 1 1 1 1 2 3 4 5 6 7 8 9 10 II IE ' W W . F i g . 2.5 Chart f o r determining G q from G* measured during SBPM unload-reload loop ( a f t e r Byrne et a l . , 1990). l o o p s (G^y) and r e s o n a n t column t e s t s (G, u ) i n d i c a t e the requirement to HH V ri a p p l y a d i s t u r b a n c e f a c t o r (a^) and an a n i s o t r o p y f a c t o r (a^) to o b t a i n good agreement between two modulus measurements. The moduli are r e l a t e d according t o : G R H (SBPM) = ot D[a pG*(SBPM)] (2.3) 25 a = G*/G (from F i g . 2.5) o (2.4) and otp i s used t o c o r r e c t the SBPM G* f o r disturbance e f f e c t s . For seismic crosshole data: where c o n s i d e r s t h e a n i s o t r o p i c s t r e s s c o n d i t i o n s f o r the r e s p e c t i v e moduli. Byrne et a l . (1990) a l s o show t h a t : Hence the above equations suggest t h a t the modulus G* at any value of c a v i t y s t r a i n can be r e l a t e d to the small s t r a i n value G and th a t both values are r e l a t e d to the i n s i t u s t r e s s c o n d i t i o n . This i s a l s o confirmed by the l a b o r a t o r y s t u d i e s performed at UBC. Negussey (1984) showed th a t the i n i t i a l unloading modulus i n t r i a x i a l compression, performed at any a x i a l s t r a i n v a l ue, corresponded w e l l w i t h the small s t r a i n low amplitude modulus determined i n the resonant column t e s t . The three cases described above demonstrate the l i n k between small and lar g e s t r a i n behaviour based on t h e o r e t i c a l / a n a l y t i c a l c o n s i d e r a t i o n s . In geotechnical engineering, where the use of r e l a t i o n s h i p s based on experience i s widespread, many g e n e r a l l y h e l d tenets a l s o demonstrate t h i s same l i n k between parameters d e t e r m i n e d at d i f f e r e n t s t r a i n l e v e l s . The Jaky (1944) e x p r e s s i o n which r e l a t e s K q to the la r g e s t r a i n f r i c t i o n angle was described i n Chapter 1. For c l a y s , various authors have s u c c e s s f u l l y r e l a t e d GVH " GHH a A (2.5) (2.6) o 26 p l a s t i c i t y index (PI) to(K )„_ i n a very e m p i r i c a l manner. Brooker and o NC Ir e l a n d (1965) , Alpan (1967) and Massarsch (1979) suggested r e l a t i o n s h i p s of the form: (K )„_ = A + B(PI) (2.7) o NC where A and B are constants determined from l a b o r a t o r y t e s t s on var i o u s s o i l s . S h e r i f and St r a z e r (1973) r e l a t e K to the l i q u i d l i m i t as: o K = X + a(OCR-l) (2.8) o where X and a are determined from F i g . 2.6. O BROOKER (CHICAGO CLAY) <> BROOKER (LONDON CLAY) • SHERIF (SEATTLE CLAY) • •• (GOOSE LAKE CLAY) A " (BEARPAW SHALE) • NEYER " » A " (WEALD CLAY) • SKEMPTOM (EOCENE CLAY) X + 05© 3 SHERIF. OBLAS 60,70,80,90 AND 100% , RESPECTIVELY, CLAY/SAND BY WEIGHT ^< 10 <3 0.1 X C U R V E (X'1.0 WHEN LL>WO%) - o - ~CST © o O a C U R V E 20 40 60 60 LIQUID LIMIT, L L (%) 100 (after Sh»rif) F i g . 2.6 L i q u i d l i m i t vs X and a ( a f t e r S h e r i f and S t r a z e r , 1973). 27 The dependence of the normalized strength r a t i o (S^/o^) on the overcon-s o l i d a t i o n r a t i o (OCR) i n c lays i s a f u r t h e r example of the interdependence of small and large s t r a i n behaviour . C r i t i c a l s tate s o i l mechanics (Wroth, 1984) and the SHANSEP p r i n c i p l e (Ladd et a l . , 1977) i n d i c a t e t h a t : ' V v ' o C " ' V V ' N C ( ° C R ) A ( 2 - 9 ) where A i s the p l a s t i c volumetr ic s t r a i n r a t i o . OCR i s def ined as : OCR = o' / a ' (2.10) vm v where i s the maximum past e f f e c t i v e v e r t i c a l pressure experienced by the s o i l and a ' i s the i n s i t u v e r t i c a l e f f e c t i v e s t r e s s , o' can be considered v . vm as a small s t r a i n e l a s t i c response which occurs during r e l o a d i n g to the maximum p a s t p r e s s u r e e x p e r i e n c e d by the s o i l and thus i n d i c a t e s a change from e l a s t i c to p l a s t i c s t r a i n s , whereas i s a l a r g e s t r a i n ( p l a s t i c ) r e s p o n s e . M e s r i (1989) has shown t h a t f o r many c l a y s S u / a ^ i s equal to 0.22. Windisch and Wong (1990) suggest a value of 0.27 f o r eastern Canada marine c l a y s . I f S /a' = (S / o ' ) „ _ , i t fol lows t h a t : J u vm u v NC S (-7) = (S / o ' ) „ _ (OCR) (2.11) ° v OC which agrees with E q . (2.9) when A = 1. The t y p i c a l range of reported values for A i s from 0.8 to 1.35 (Jamiolkowski et a l . , 1985), with an average of around 0.98. For most s o i l s , these constants can be used i n E q . (2.9) to provide r e l i a b l e estimates of OCR from i n s i t u f i e l d vane strengths (Mayne and M i t c h e l l , 1988). Through OCR, can a lso be r e l a t e d to K Q. 28 Calibration chamber tests have provided another means by which s o i l response at small and large s t r a i n can be compared. Results have shown that cone penetration resistance (q ) i n sands can be correlated to G since both r ^c o parameters are governed e s s e n t i a l l y by Dr and a' (Robertson, 1982; B e l o t t i et a l . , 1986; Rix, 1984; Jamiolkowski and.Robertson, 1988). F i e l d data obtained i n Po River sand generally confirm the trends suggested by CC res u l t s . Figure 2.7 demonstrates the well-defined relationship between qc and Go obtained from CC tests. The f i e l d data from Po River and Gioia Tauro sands and gravel are i n good agreement with the trends from CC tests. I t has also been demonstrated that the cone penetration resistance i s almost completely governed by i n sand and that the relationship i s of the form (Houlsby and Hitchman, 1988): ,RANGE FOR PLUVIALLY DEPOSITED TICINO SAND, G 0 FROM R.C. TESTS, q c FROM CC TESTS AAD PO RIVER SAND • GIOIA TAURO SAND WITH GRAVEL OCR = 1 OCR = 10 • IN kPa 200 300 500 1000 _ 2000 3000 Mc Fig. 2.7 CC data for q -G correlation (after Baldi et a l . , 1989) c o 29 where A v a r i e s according to the sand s t a t e . In c o n c l u s i o n , i t appears t h a t the la r g e s t r a i n response of s o i l may be i n f l u e n c e d to a great extent by the small s t r a i n p r o p e r t i e s and th a t back-c a l c u l a t i o n may be a f e a s i b l e approach f o r e v a l u a t i n g one extreme of s o i l response from the other. The c o r r e l a t i o n s presented above have a l s o been a p p l i e d to s o i l types ranging from c l a y to sand although the i n d i v i d u a l c o r r e l a t i o n s are s o i l - t y p e s p e c i f i c . 2.3 Stress and Pore Pressure D i s t r i b u t i o n Around Full-Displacement Probes Se c t i o n 2.2 has considered the l i n k between s o i l behaviour at small and large s t r a i n s and shown that many c o r r e l a t i o n s e x h i b i t i n g t h i s interdepend-ence are i n widespread use. As s t a t e d i n Se c t i o n 2.1, the usefulness of the c o r r e l a t i o n of la r g e s t r a i n behaviour to small s t r a i n p r o p e r t i e s a l s o r e q u i r e s a method(s) of i n t e r p r e t a t i o n which can provide repeatable and r e l i -able estimates of the parameters of i n t e r e s t . In terms of i n s i t u measure-ment of l a t e r a l s t r e s s , i t i s important to i d e n t i f y the f a c t o r s which a f f e c t the measured values so that a meaningful i n t e r p r e t a t i o n can be made. Hence in f o r m a t i o n regarding the s t r e s s and pore pressure d i s t r i b u t i o n around f u l l displacement penetrometers i s r e q u i r e d f o r d i f f e r e n t s t r e s s and pore pressure measuring l o c a t i o n s and d i f f e r i n g probe geometries. This i s considered i n t h i s s e c t i o n . F u l l displacement l a t e r a l s t r e s s sensing probes were developed to induce repeatable degrees of disturbance; the problem then becomes one of r e l a t i n g the measured l a t e r a l s t r e s s to the pre - p e n e t r a t i o n value as opposed to ev a l u -a t i n g whether or not the s o i l had been d i s t u r b e d as i s the case during SBPM 30 i n s t a l l a t i o n . The idea of p r e d i c t i n g small s t r a i n behaviour from l a r g e s t r a i n parameters has been considered above. In the i d e a l case f o r undrained p e n e t r a t i o n , the p e n e t r a t i o n l a t e r a l s t r e s s , o A , measured by a f u l l - d i s p l a c e m e n t probe r e s u l t s from two compon-ents : o.„ = o, + Ao (2.13) no where: a, = i n s i t u t o t a l h o r i z o n t a l s t r e s s ho Aa = t o t a l s t r e s s increment caused by i n s e r t i o n In any p a r t i c u l a r s o i l , the magnitude of the t o t a l s t r e s s increment caused by i n s e r t i o n i s made up of both s t r e s s and pore pressure components and can be expected to be r e l a t e d to the displacement caused during p e n e t r a t i o n of a probe. The i d e a l i z e d change i n the l a t e r a l s t r e s s c o e f f i c i e n t (defined i n terms of an e f f e c t i v e s t r e s s r a t i o ) f o r v a r i o u s i n s i t u t e s t i n g probes i s shown s c h e m a t i c a l l y i n F i g . 2.8. Although t h i s s i m p l i f i e d r e p r e s e n t a t i o n i s i n s t r u c t i v e , i t i s , however, complicated by the f a c t that f o r each t e s t method the s t r e s s / s t r a i n paths are very d i f f e r e n t and even under undrained c o n d i t i o n s no s i n g l e curve e x i s t s . The r e l a t i v e p o s i t i o n s of the t e s t s are a l s o very s u b j e c t i v e and dependent on i n d i v i d u a l probe c h a r a c t e r i s t i c s . A review of methods p r e s e n t l y a v a i l a b l e f o r e v a l u a t i n g the s t r e s s d i s t r i b u t i o n around f u l l displacement probes i s given i n Appendix B. Many of the techniques have been s p e c i f i c a l l y developed f o r p i l e s but can be e q u a l l y used f o r i n s i t u t e s t i n g r e s u l t s . S o l u t i o n s e x i s t f o r both drained and undrained c o n d i t i o n s during i n s e r t i o n . P e n e t r a t i o n of a probe i n c l a y gives r i s e to excess pore pressure as the s o i l i s d i s p l a c e d both v e r t i c a l l y and l a t e r a l l y . C a v i t y expansion methods 31 EARTH PRESSURE COEFFICIENT LEGEND » SPT- Standard penetration test FDPMT' Full-displacement pressuremeter test DMT : Dilatometer test CPT= Cone penetration test TSC : Total stress cell SBPMT 'Self-bored pressuremeter test K 0 ( SBPMT) NEGATIVE RELATIVE DISPLACEMENT POSITIVE RELATIVE DISPLACEMENT IN SITU (at rest) F i g . 2.8 I d e a l i z e d change of l a t e r a l s t r e s s c o e f f i c i e n t , K, caused by f u l l -displacement probes ( S u l l y and Campanella, 1989). i n d i c a t e t h a t the magnitude of the excess pore pressure depends on the l o c a t i o n o f the pore pressure measurement and on s o i l parameters (G, o^, S^, S t, OCR, e t c . ) . This i s confirmed by the more rig o r o u s s t r a i n path approach described by B a l i g h (1986). In terms of s o i l response to undrained l o a d i n g , the excess pore pressure (Au) components c l o s e to the probe ( p l a s t i c zone) are: Au = Ao . + Au oct s (2.14) 32 where Ao . i s the change i n octahedral s t r e s s and Au i s the pore pressure o c t & s c r r e s u l t i n g from shear. C a v i t y expansion methods consider the shear r e l a t e d pore pressures i n an e m p i r i c a l manner (V e s i c , 1972). In the s t r a i n path method ( B a l i g h , 1986) , shear induced pore pressures are r e l a t e d to a y i e l d shear s t r a i n . In both cases: Au = o ' /x (2.15) s where a' i s a defined s t r e s s term and x i s a defined pore pressure parameter. Comparison of Eqs. (2.13) to (2.15) i n d i c a t e s the dependence of the measured pore pressure on the i n s i t u p r e - p e n e t r a t i o n s t r e s s . A l s o , at a p a r t i c u l a r s t r e s s l e v e l , the t h e o r e t i c a l s o l u t i o n s suggest t h a t the magnitude of Au i n s a t u r a t e d c l a y s depends p r i m a r i l y on and to a l e s s e r extent on G. I t has a l s o been e s t a b l i s h e d t h a t a gradient of pore pressure e x i s t s around a p e n e t r a t i n g cone (Robertson et a l . , 1986) and t h a t the gradient can be q u a l i t a t i v e l y r e l a t e d to changes i n normal and shear s t r e s s e s as the s o i l moves around the cone t i p ( B a l i g h , 1986; S u l l y et a l . , 1988). As suggested by F i g . 2.9, measurement of the gradient around a p e n e t r a t i n g cone should provide i n f o r m a t i o n r e l a t e d to the s t r e s s d i s t r i b u t i o n during undrained p e n e t r a t i o n i n c l a y . The trends i n the data i n d i c a t e that the s o i l i s unloaded as i t passes the t i p and that the e f f e c t of the unloading i s more pronounced as the s o i l s t i f f n e s s i n c r e a s e s . For CPTU i n c l e a n sands, the p e n e t r a t i o n process can be considered as drained and no l a r g e excess pore pressures are generated. G i l l e s p i e (1990) demonstrates t h a t , i r r e s p e c t i v e of r e l a t i v e d e n s i t y , f o r < 200 kPa, the excess pore pressures behind the t i p are zero or negative of s t a t i c e q u i l i b -rium and r e s u l t from the r a p i d unloading t h a t occurs due to the cone geometry 33 u « u0 F i g . 2.9 Pore pressure d i s t r i b u t i o n i n s a t u r a t e d c l a y s during CPTU based on f i e l d measurements ( a f t e r Robertson et a l . , 1986). i n t h i s r e g i o n . Pore pressures on the face of the cone are approximately equal to h y d r o s t a t i c i f f i l t e r c o m p r e s s i b i l i t y e f f e c t s are not present. Consequently, i n sands p e n e t r a t i o n pore pressures provide very l i t t l e i n f o r -m a t i o n r e g a r d i n g s t r e s s changes along the probe. Cone r e s i s t a n c e (q £) and sleeve f r i c t i o n ( f g ) are g e n e r a l l y more u s e f u l parameters f o r e v a l u a t i n g sand response during p e n e t r a t i o n . Campanella and Robertson (1981) and Hughes and Robertson (1985) examined the p o s s i b l e v a r i a t i o n of l a t e r a l s t r e s s around a p e n e t r a t i n g cone w i t h respect to changes i n measured sleeve f r i c t i o n . Tests i n sand show a marked increase i n f between 10 cm and 25 cm behind the t i p ( f o r 10 cm2 cone). For s l a r g e r d i s t a n c e s (greater than 25 cm, or 7D, where D i s the cone diameter), •f i s e s s e n t i a l l y c o n s t a n t . For a c o n s t a n t s o i l - s t e e l f r i c t i o n angle, a s i m i l a r d i s t r i b u t i o n f o r can be determined. Hughes and Robertson (1985) 34 suggested the existence of high s t r e s s g r a d i e n t s , s i m i l a r to the pore pressure gradients described e a r l i e r f o r c l a y s , as the cone t i p approaches and passes an element of s o i l . S o i l i s thus unloaded as i t passes the t i p of the penetrometer. The shoulder of the cone t i p , where t h i s t r a n s i t i o n from loading to unloading behaviour occurs represents a s i n g u l a r i t y . A n a l y s i s using the s t r a i n path method i n c l a y s has shown th a t ( B a l i g h and Levadoux, 1980; Teh and Houlsby, 1988): • D i f f i c u l t i e s e x i s t i n modelling s o i l response at the cone shoulder where l a r g e s t r e s s / p o r e pressure g r a d i e n t s e x i s t . • At the t r a n s i t i o n p o i n t , the v e r t i c a l s t r a i n (e^) i s c l o s e to zero. Below t he t i p e i s compressive, becoming s l i g h t l y t e n s i l e behind the t i p . • Along the s h a f t , r a d i a l , c i r c u m f e r e n t i a l and shear s t r a i n contours are con c e n t r i c about the cone a x i s , s i m i l a r to the c o n d i t i o n of an expand-ing c y l i n d r i c a l c a v i t y . No a n a l y s i s has been performed to define the s t r a i n contours t h a t occur f o r pe n e t r a t i o n i n sand, but s i m i l a r s t r a i n contours to those p r e d i c t e d f o r c l a y could be expected. I t must be noted t h a t the s t r a i n p a t t e r n w i l l not change much f o r d i f f e r e n t s o i l s . The induced s t r e s s e s and pore pressures, however, w i l l depend very much on the p r o p e r t i e s of the s o i l being penetrated. Levadoux and B a l i g h (1980) and Teh (1987) p r e d i c t the existence of pore pressure gradients i n s o f t c l a y . Simple c a v i t y expansion methods suggest a r a t i o of 4/3 between the s t r e s s e s and pore pressures at the t i p and behind the t i p , independent of OCR, i f the same G and S values are a p p l i e d to both 35 the s p h e r i c a l and c y l i n d r i c a l c a v i t y formulations. Coop (1987), May (1987) and G i l l e s p i e (1990) compare the t h e o r e t i c a l d i s t r i b u t i o n of pore pressures determined by the s t r a i n path method w i t h f i e l d data and obtained notable d i f f e r e n c e s even f o r NC and l i g h t l y OC c l a y s . The d i s t r i b u t i o n s shown i n F i g . 2.9 suggest t h a t departure from the t h e o r e t i c a l s o l u t i o n increases as OCR i n c r e a s e s . Measurements i n c a l i b r a t i o n chambers ( B a l d i et a l . , 1986; Huntsman, 1985) suggest that the l a t e r a l s t r e s s a c t i n g on the f r i c t i o n sleeve l o c a t e d immediately behind the t i p i s low compared to that on the t i p and approxi-mates to the p r e - p e n e t r a t i o n h o r i z o n t a l s t r e s s f o r loose sand. This i s confirmed by l i m i t e d f i e l d data ( J e f f e r i e s et a l . , 1987). As the sand becomes denser, s t r e s s a m p l i f i c a t i o n e f f e c t s occur. This i s reviewed f u r t h e r i n Appendix A f o r the v a r i o u s types of f u l l - d i s p l a c e m e n t l a t e r a l s t r e s s probes. However, at l o c a t i o n s f u r t h e r up the s h a f t no d i r e c t i n f o r m a t i o n i s a v a i l a b l e . T h e o r e t i c a l s o l u t i o n s i n d i c a t e a constant l a t e r a l s t r e s s c o n d i t i o n behind the t i p ( V e s i c , 1972; Carter et a l . , 1986). M a r c h e t t i (1979) suggests t h a t the disturbance caused during f l a t p l a t e p e n e t r a t i o n ( i . e . dilatometer) i s l e s s than that a s s o c i a t e d w i t h a cone, simply based on the lower apex angle at the t i p (20° f o r the DMT as opposed to 60° f o r the CPT) . Studies by B a l i g h (1975) on the p e n e t r a t i o n of long wedges confirm t h i s observation. However, the model t e s t s reported by B a l i g h (1975) are 2D i n nature and are misleading s i n c e the 3D e f f e c t s of cone pene-t r a t i o n are not considered. Cone p e n e t r a t i o n i s axisymmetric and f a c i l i t a t e s i ncreased unloading e f f e c t s ; the g e n e r a l l y a v a i l a b l e f l a t penetrometers can-not be considered as i n f i n i t e l y long and thus the deformation may l i e some-where between the 2D and 3D i d e a l i z a t i o n s . The width to t h i c k n e s s r a t i o of the f l a t penetrometer may n o t i c e a b l y a f f e c t the s t r e s s measured at the centre 36 of the blade i f s t r e s s concentrations due to edge e f f e c t s are s i g n i f i c a n t . No f i e l d or l a b o r a t o r y data are a v a i l a b l e concerning t h i s . A 3D s t r a i n path method has been developed by Huang (1989) which permits a complete e v a l u a t i o n of the f l a t p l a t e p e n e t r a t i o n problem (see Appendix B.3). Huang (1989) concludes t h a t the d i f f e r e n c e s between the s t r a i n f i e l d s f o r cone and p l a t e penetrometers are more than expected s o l e l y from apex angle v a r i a t i o n s . S t r a i n l e v e l s around f l a t p l a t e s appear to be lower than those obtained w i t h cones, but are much more complicated due to the f i n i t e width of the p l a t e . The r e s u l t s of the a n a l y s i s do, however, suggest t h a t the s t r e s s behind the t i p f o r a cone should be higher than behind a DMT t i p due to the l a r g e r disturbance induced during i n s e r t i o n . This corroborates e a r l i e r r e s u l t s obtained by Davidson and Boghrat (1983) from l a b o r a t o r y measurements i n sand. Approximate a n a l y s i s of f l a t p l a t e p e n e t r a t i o n problems has sometimes been performed by r e p r e s e n t i n g the blade as an equivalent c y l i n d r i c a l c a v i t y , or by use of the e l a s t i c s o l u t i o n presented by Finn (1963). Several methods e x i s t to evaluate the s t r e s s d i s t r i b u t i o n around p e n e t r a t i n g probes. The v a l i d i t y of each approach depends on both s o i l and probe c h a r a c t e r i s t i c s and these e f f e c t s are examined i n Chapter 6. 2.4 A p p l i c a t i o n of C a l i b r a t i o n Chamber Results to In S i t u Measurements Performing f i e l d t e s t s i n large c a l i b r a t i o n chambers where sample char-a c t e r i s t i c s and boundary s t r e s s e s can be c o n t r o l l e d has provided i n v a l u a b l e i n s i g h t i n t o the dominant modes of s o i l response measured by f u l l -displacement penetrometers. Many of the recent advances i n i n t e r p r e t a t i o n techniques have been made p o s s i b l e by r e s u l t s from CC t e s t s ( B a l d i et a l . , 1982, 1988). I t i s not the o b j e c t i v e of t h i s s e c t i o n to provide a review of 37 CC procedures and developments, r a t h e r to discuss some of the l i m i t a t i o n s i n v o l v e d when t r y i n g to evaluate l a t e r a l s t r e s s e s from CC measurements. I t i s recognized t h a t chamber s i z e and boundary c o n d i t i o n s a f f e c t the r e s u l t s obtained and c o r r e c t i o n s to measured data need to be made. These c o r r e c t i o n s are w e l l e s t a b l i s h e d f o r cone r e s i s t a n c e i n clean sands and have been derived from comparisons of r e s u l t s obtained i n d i f f e r e n t s i z e chambers (Pa r k i n and Lunne, 1982; P a r k i n , 1988). Very l i t t l e i n f o r m a t i o n e x i s t s f o r other measured parameters. For measuring l o c a t i o n s behind the t i p , the s t a n d a r d q c c o r r e c t i o n may not be a p p l i c a b l e s i n c e the boundary w i l l have a d i f f e r e n t e f f e c t on the s o i l during unloading than during i n i t i a l l o a d i n g . P a r k i n (1988) evaluates sleeve f r i c t i o n data i n cle a n s i l i c a sand obtained at the Norwegian Geotechnical I n s t i t u t e (NGI) and suggests t h a t f o r a 10 cm2 cone: f = A (q ) 1 , 6 (2.16) s c The r e l a t i o n s h i p i s dependent on the s i z e of the cone being used, thus a l s o suggesting that q c and f are i n f l u e n c e d d i f f e r e n t l y by the a p p l i e d CC bound-ary c o n d i t i o n s . Masood (1990) compares the DMT bearing r e s i s t a n c e and l i m i t pressure (q^ and p x) from DMT t e s t s i n the Berkeley CC and concludes that the two parameters are i n f l u e n c e d i n a d i f f e r e n t way by s o i l c o m p r e s s i b i l i t y . As a r e s u l t q ^ / P i would vary depending on s o i l type, D^  and chamber s i z e . Masood (1990) suggests t h a t both p Q (DMT) and o^s obtained from l a t e r a l s t r e s s cone t e s t s (LS-CPTU) are a f f e c t e d by chamber s i z e but i n s u f f i c i e n t data are a v a i l a b l e to c l a r i f y the exact dependence. The author attempted a review of pub l i s h e d CC data to evaluate the e f f e c t of chamber s i z e on measured parameters at d i f f e r e n t l o c a t i o n s on a probe. I n s u f f i c i e n t data d i d 38 not permit any conclusions to be drawn. J e f f e r i e s et a l . (1987) assume th a t the q /o T„ r a t i o measured d u r i n g l a t e r a l s t r e s s cone t e s t s i n a CC i s a c LS constant value f o r a p a r t i c u l a r chamber s i z e . They then apply the same CC c o r r e c t i o n f a c t o r s t o b o t h o T „ and q to account f o r chamber s i z e e f f e c t s . LS ^c I n t u i t i v e l y t h i s would appear to be i n c o r r e c t and i s confirmed i n p a r t by the data presented by Masood (1990). The a p p l i c a t i o n of c o r r e l a t i o n s obtained from CC t e s t s to a f i e l d s i t u a -t i o n should be performed w i t h care. C e r t a i n w e l l e s t a b l i s h e d r e l a t i o n s h i p s , i . e . <1C-Dr a n d q c~* are a v a i l a b l e and work w e l l provided s o i l c o m p r e s s i b i l i t y i s considered (Robertson and Campanella, 1983). However, i n some s i t u a t i o n s the CC d e r i v e d c o r r e l a t i o n s can be i n e r r o r . B a l d i et a l . (1986) developed a r e l a t i o n s h i p between K q , and q c / ° v from CC t e s t s which was found to over-p r e d i c t the i n s i t u (see Appendix A.4.1). The CC r e l a t i o n s h i p was r e v i s e d based on f i e l d data i n Po R i v e r sand. The f i e l d c a l i b r a t e d r e l a t i o n s h i p suggested by B a l d i et a l . (1986) i s compared i n F i g . 2.10 against a s i m i l a r CC d e r i v e d f u n c t i o n presented by Jamiolkowski and Robertson (1988). The CC derived equation suggests t h a t K q i s very s e n s i t i v e to v a r i a t i o n s i n and hence not very u s e f u l f o r e v a l u a t i n g K q from measurements of and q^. The f i e l d c o r r e l a t i o n suggests a more acceptable interdependence of the parameters. I f the B a l d i et a l . (1986) r e l a t i o n s h i p i s assumed to be c o r r e c t (since i t i s f i e l d c a l i b r a t e d ) , then the d i f f e r e n c e i n the t r e n d f o r the two r e l a t i o n s h i p s shown i n F i g . 2.10 would suggest that CC t e s t s are unable to c o r r e c t l y simulate the i n s i t u s t r e s s response of granular s o i l s at l o c a t i o n s behind the penetrometer t i p where the s o i l has undergone some degree of unloading. As discussed e a r l i e r , t h i s may r e s u l t from the loading/unloading s t r e s s paths and the e f f e c t s of the chamber boundary on parameters undergoing 39 F i g . 2.10 E v a l u a t i o n of K from K Q based on CC data ( a f t e r Jaraiolkowski and Robertson, 1988?. s t r e s s / s t r a i n r e v e r s a l . F a b r i c , environmental f a c t o r s and other i n s i t u e f f e c t s not modelled i n the chamber may a l s o be important f a c t o r s . As a f i n a l p o i n t , the i n t e r p r e t a t i o n of CC data f o r sand i s o f t e n indexed using the s t a t e parameter (\jj) approach (Been and J e f f e r i e s , 1985). T h i s i s i d e a l f o r CC t e s t s where both o^ and v o i d r a t i o are known. A p p l i c a -t i o n of the s t a t e parameter approach to i n s i t u data appears promising but r e q u i r e s f u r t h e r c o n f i r m a t i o n . As suggested by Sladen (1989) , the method may n e c e s s i t a t e a d d i t i o n a l s p e c i a l i z e d i n s i t u t e s t s to confirm the v o i d r a t i o s evaluated on the b a s i s of CPT data, i . e . nuclear d e n s i t y ( T j e l t a et a l . , 1985; S u l l y and E c h e z u r i a , 1988) or e l e c t r i c a l r e s i s t i v i t y (Zuidberg et a l . , 1987) t e s t s . Furthermore, an a p r i o r i knowledge of a, i s r e q u i r e d . AO Data presented by Huntsman (1985) for CC tests using a lateral stress cone penetrometer are shown in Fig. 2.11. The range of chamber stresses (q^ A, 10-t s 0.1 Monterey #0 sand (BC1) Lateral stress cone data from CC (Huntsman, 1985) (a) o o o o 0 0 0 o °o o o o o OQ ooo A L S = 0"Ls '/cr h ' 20 40 60 80 Relat ive d e n s i t y , DR% 100 Monterey #0 sand (BC1) Lateral stress cone data from CC (Huntsman, 1985) o o o o o o o o o (b) 1 I I 1 1 1 1 — 0.20 -0.15 -0.10 -0.05 -0.00 S t a t e p a r a m e t e r , Fig. 2.11 Comparison of CC data indexing tests by (a) relative density, and (b) state parameter. and o^) used i n the study varied between 100 kPa and 500 kPa, hence the results are valid for the depths of interest common to most geotechnical problems. More specifically, stress measurements performed as part of this research have been conducted to maximum depths of 30 m where attains a value of about 300 kPa. The amplification of lateral stress, A^, is plotted against D r and \|). The scatter in the two plots is identical and leads to the conclusion that for f i e l d measurements D is a suitable index parameter and can be used for comparative purposes. 41 2.5 Conclusions The p o i n t s discussed above have emphasized the f o l l o w i n g important aspects which r e l a t e to the a p p l i c a t i o n of f u l l - d i s p l a c e m e n t . t e s t methods f o r determination of the i n s i t u h o r i z o n t a l s t r e s s : • Behaviour of s o i l at large s t r a i n i s governed to a s i g n i f i c a n t degree by small s t r a i n p r o p e r t i e s or c o n d i t i o n s . • A n a l y t i c a l techniques e x i s t by which the l a r g e s t r a i n parameters can be i n t e r p r e t e d to provide estimates of the c o n t r o l l i n g small s t r a i n c o n d i t i o n s . • A v a i l a b l e i n t e r p r e t a t i o n techniques, i r r e s p e c t i v e of complexity, a l l r e l y to some degree on e m p i r i c a l i n f e r e n c e s . The methods may be o v e r l y s e n s i t i v e to the a r b i t r a r i l y chosen s o i l parameters used i n the models. • L i m i t e d p u b l i s h e d data are a v a i l a b l e , e s p e c i a l l y i n sand, f o r evalu a t -in g the d i s t r i b u t i o n of s t r e s s around f u l l - d i s p l a c e m e n t probes. • Data from c a l i b r a t i o n chamber t e s t i n g have been instrumental i n the development of s p e c i f i c i n t e r p r e t a t i o n techniques f o r f u l l - d i s p l a c e -ment t e s t i n g . More im p o r t a n t l y , the idea that f u l l - d i s p l a c e m e n t t e c h -niques could be used to evaluate small s t r a i n parameters developed d i r e c t l y as a r e s u l t of CC r e s u l t s . • The d i r e c t a p p l i c a t i o n of CC de r i v e d r e l a t i o n s h i p s to a f i e l d s i t u a -t i o n has to be performed w i t h c a u t i o n as s a l i e n t p o i n t s r e l a t e d to the f i e l d response cannot be represented i n chamber s t u d i e s . • S i m i l a r l y , the above i s tr u e w i t h respect to data from l a b o r a t o r y t e s t s on both undisturbed and r e c o n s t i t u t e d samples. However, i n l a b o r a t o r y t e s t s the problems of boundary e f f e c t s are not so pronounced as f o r a f u l l - d i s p l a c e m e n t t e s t i n a CC. The main concerns 42 are r e l a t e d to the i n i t i a l s t r e s s e s i n the sample and the e f f e c t s of disturbance, aging and other secondary f a c t o r s on measured K q values. • Laboratory t e s t s do provide important i n f o r m a t i o n regarding p o s s i b l e l i m i t s f o r f i e l d K values. o • For most s o i l s under l a b o r a t o r y c o n d i t i o n s of ID unloading there appears t o be a strong dependence between K q and OCR. This r e l a t i o n -ship has a l s o been demonstrated between OCR and K q from f i e l d measure-ments . 43 CHAPTER 3 3. DETAILS OF EQUIPMENT AND TEST PROCEDURES 3.1 I n t r o d u c t i o n Several types of f u l l - d i s p l a c e m e n t and s e l f - b o r i n g probe have been used during t h i s research w i t h the o b j e c t i v e of comparing s t r e s s and pore pressure measurements f o r : • Probes of v a r y i n g magnitudes of displacement, i . e . d i f f e r e n t degrees of disturbance. • Probes of v a r y i n g geometry, i . e . c y l i n d r i c a l or p l a t e - l i k e . • D i f f e r i n g l o c a t i o n s along probe length. A summary of the general c h a r a c t e r i s t i c s of the probes used i s given i n Table 3.1 which a l s o gives d e t a i l s on the method of l a t e r a l s t r e s s measurement. The equipment described i n t h i s chapter has not been designed by the w r i t e r but was a v a i l a b l e f o r t h i s research. In some cases minor m o d i f i c a t i o n s were made to improve equipment response and data q u a l i t y . As o u t l i n e d i n Appendix A, r e s u l t s of more general t e s t s such as p i e z o -cone soundings (CPTU) and i n s i t u f i e l d vane t e s t s (FVT) can a l s o be used as l a t e r a l s t r e s s i n d i c a t o r s . These t e s t s are only discussed very b r i e f l y i n the next s e c t i o n as they now represent a general s t a t e of p r a c t i c e f o r i n s i t u t e s t i n g . 3.2 Index Parameter Test Equipment B r i e f d e t a i l s of equipment used to define index parameters are given below. For index t e s t equipment, no d i r e c t h o r i z o n t a l s t r e s s measurement i s obtained, r a t h e r a parameter i s recorded which can be r e l a t e d to i n s i t u l a t e r a l s t r e s s or s t r e s s h i s t o r y . Table 3.1 Summary of In Situ Test Equipment Used and General Characteristics of Stress Measurement Systems Probe Type Dimensions of Measuring Location Condition Used for Lateral Stress Measurement Stress-Displacement Measurement Technique Distance Behind Tip to Stress Measurement Location UBC Lateral Stress Cone 15 cmJ 44mm OD Negligible movement Strain gauged section of underreamed f r i c t i o n sleeve, 20 mm long 16.6D UCB Lateral Stress Cone 10 cm2 35.7 mm OD S t i f f measuring system - n e g l i -gible movement Lateral stress on 25mm long f r i c t i o n sleeve transmitted to inner s t r a i n gauged diaphragm ID and 7.5D UBC Seismic Cone Pressuremeter 15 cmJ 44 mm OD [1] Membrane l i f t -off Total pressure e l e c t r i c a l transducer and 3 s t r a i n -gauged feeler arms 29.8D [3] Dilatometer 95 mm x 14 mm 60 mm diameter membrane Back extrapola-tion from 0.05 mm displacement Pneumatic pressure trans-ducer and single membrane displacement sensor 6.8t [2] Total Stress C e l l 100 mm x 6 mm Negligible dia-phragm movement Pressure transmitted by o i l to hydraulic pressure transducer (pressure sensi-tive area 185 mm x 79 mm) 30.8t [1] Self-Boring Pressuremeter 73 mm OD L/D = 6 Membrane l i f t -off Total and ef f e c t i v e stress e l e c t r i c a l transducers and 3 strain-gauged feeler arms 5.6D [3] Self-Boring Load C e l l 80.4 mm OD 44.4 mm diameter load c e l l Maximum load c e l l deflection of 9 um at 280 kPa Two bending web ( e l e c t r i -cal) load c e l l s 3.5D [4] UBC Research Dilatometer 95 mm x 14 mm 60 mm diameter membrane Membrane l i f t -off Effective stress e l e c t r i c a l transducer and s t r a i n -gauged feeler arm 7.14t [2] [1] Using distance to centre of pressure sensitive area and t = 6 mm [2] Ratio calculated using blade thickness of 14 mm [3] Using distance to middle of PM section [4] To centre of stress c e l l s . 45 3.2.1 Piezocone Penetrometer Two types of b a s i c piezocone are a v a i l a b l e at UBC; the Hogentogler equipment and UBC designed equipment, both of which comply w i t h the ASTM CPT standard. Test procedures have been elaborated upon by Campanella and Robertson (1988) and G i l l e s p i e (1990) and w i l l not be discussed f u r t h e r . As o u t l i n e d i n Appendix A, pore pressures during CPTU can be measured at va r i o u s l o c a t i o n s around a cone. The f o l l o w i n g nomenclature i s used i n t h i s t h e s i s to denote the measurement l o c a t i o n ( F i g . 3.1): r o p e n e t r o m e t e r s h a f t f r i c t i o n s l e e v e L I shoulder-cone f a c e D u. beh ind t ip t i p L = d i s t a n c e beh ind cone apex D = d i a m e t e r o f c o n e F i g . 3.1 Nomenclature used f o r d i f f e r e n t pore pressure measurement l o c a t i o n s (based on S u l l y , Campanella and Robertson, 1988) u x denotes the pore pressure measured on the face of the cone. No d i s t i n c t i o n i s made between pore pressures measured at the cone apex 46 or along the face since the v a r i a t i o n i s r e l a t i v e l y unimportant ( F i g . 2.9). • u 2 denotes the pore pressure measured immediately behind the cone t i p , u s u a l l y at a distance of 5 mm behind the shoulder. • u 3 denotes the pore pressure measured at the back end of the f r i c t i o n s leeve. A l l pore pressures were measured using 5 mm h i g h , polypropylene f i l t e r s , except where s t a t e d . 3.2.2 In S i t u ( F i e l d ) Vane Two types of vane equipment were used during t h i s study: • N i l c o n vane borer i n s t a l l e d using a p o r t a b l e j a c k i n g frame. Three d i f f e r e n t s i z e d tapered vanes are a v a i l a b l e depending on s o i l s t r e n g t h . • Geonor vane borer i n s t a l l e d by pushing w i t h UBC Geotechnical Research V e h i c l e (GRV). D i f f e r e n t s i z e d r e c t a n g u l a r vanes are a v a i l a b l e w i t h a height to diameter r a t i o of 2. The undrained shear s t r e n g t h of the s o i l i s obtained from the torque r e q u i r e d to r o t a t e the vane. Peak and remolded strengths were determined at each t e s t depth. A l l t e s t procedures employed were those s t i p u l a t e d i n ASTM D2573/D2573M. 3.2.3 Seismic Cone Penetrometer The UBC seismic cone penetrometer i s e s s e n t i a l l y a standard cone u n i t which has an accelerometer l o c a t e d 20 cm behind the t i p (Campanella et a l . , 47 1986). The accelerometer i s o r i e n t e d to be s e n s i t i v e to h o r i z o n t a l l y p o l a r -i z e d waves which are generated by s t r i k i n g the support pads of the GRV w i t h a hammer. S t r i k i n g the opposite sides of the pad generates two r e v e r s e l y p o l a r i z e d shear waves. The shear wave a r r i v a l times can be determined using e i t h e r the reverse p o l a r i t y (cross over) technique or the c r o s s - c o r r e l a t i o n procedure (Campanella, Baziw and S u l l y , 1985) and the shear wave v e l o c i t y c a l c u l a t e d using the pseudo i n t e r v a l method. Shear wave v e l o c i t y determina-t i o n s were u s u a l l y performed at 0.5 m or 1.0 m depth i n t e r v a l s . By s t r i k i n g each s i d e of the pad t w i c e , ei g h t separate v e l o c i t y determinations can be obtained. The seismic cone i s u s u a l l y employed as a downhole technique, that i s the h o r i z o n t a l l y p o l a r i z e d wave t r a v e l s down from the surface to the cone which i s l o c a t e d at some known depth. The d i r e c t i o n of p a r t i c l e motion ( h o r i z o n t a l ) i s perpendicular to the d i r e c t i o n of wave t r a v e l ( v e r t i c a l ) . This i s r e f e r r e d to a VH shear wave. The e x i s t i n g downhole c o n f i g u r a t i o n was modified to permit crosshole shear wave v e l o c i t i e s to be c a l c u l a t e d . To shoot c r o s s h o l e , a separate h o r i z o n t a l l y - d i s p l a c e d source at the same depth as the r e c e i v e r cone i s r e q u i r e d . A 15 cm2 vane cone was designed so th a t both HV and HH shear waves could be generated. In a d d i t i o n , two r e c e i v e r s are necessary to permit accurate i n t e r v a l time measurement. D e t a i l s of the vane cone are given i n F i g . 3.2 and the f i e l d t e s t c o n f i g u r a -t i o n s c h e m a t i c a l l y shown i n F i g . 3.3 The downhole-crosshole (DH-XH) t e s t procedure c o n s i s t e d of: • performing DH seismic cone t e s t at 1 m depth i n t e r v a l s at l o c a t i o n of source vane cone (SVC) using a 10 cm2 cone w i t h no f r i c t i o n reducer • the 15 cm 2 vane cone (source) i s then i n s t a l l e d i n t h i s hole to a depth of 1 m, measured to the centre of the vane s e c t i o n . 48 F i g . 3.2 D e t a i l s of vane cone f o r generating crosshole shear wave s i g n a l s , S O U R C E H O L E F O R C R O S S - H O L E S I G N A L S 1 D O W N , R E C E I V E R # 1 I N S T A L L E D R E C E I V E R # 2 I N S T A L L E D U S I N G C O N E T R A I L E R U S I N G R E S E A R C H V E H I C L E R1 R2 " ( A r r o w s i n d i c a t e S H E A R B E A M C W * - * C C W a i r e c t i o n o f n a r n m e r ^ T O D A S 1 S O U R C E F O R =T"p b l o w t o a n v i l ) / D O W N H O L E S I G N A L • S T A N D A R D C O N E R O D S H V S H E A R W A V E 7T* V H S H E A R -W A V E - A C C E L E R O M E T E R -T O D A S 2 G R O U N D S U R F A C E U B C 10cm S E I S M I C P I E Z O C O N E H H S H E A R W A V E F i g . 3.3 C o n f i g u r a t i o n f o r downhole and crosshole shear wave v e l o c i t y measurements 49 • two r e c e i v e r cones (RI and R2) were i n s t a l l e d along a common l i n e at known distances from the source h o l e . Downhole shear wave v e l o c i t i e s were determined at the r e c e i v e r (R2) i n s t a l l e d using the GRV; the other r e c e i v e r (RI) was i n s t a l l e d using the UBC In S i t u Group t r a i l e r and downhole v e l o c i t i e s were not determined at t h i s l o c a t i o n . • a l l three cones (source and two r e c e i v e r s ) were penetrated i n t o the s u b s o i l at 0.5 m i n t e r v a l s . At each depth, the f o l l o w i n g shear wave tr a c e s were recorded: - downhole t r a c e s from l e f t and r i g h t h i t s on f r o n t pad of t r u c k (VH) at R2 l o c a t i o n - crosshole t r a c e s from v e r t i c a l up and down h i t s generated by s t r i k -i ng on source cone a n v i l (HV). Traces recorded at both r e c e i v e r s (RI and R2). - crosshole t r a c e s from clockwise and a n t i c l o c k w i s e h i t s generated by l a t e r a l l y s t r i k i n g vane cone a n v i l (HH). Traces recorded at both r e c e i v e r s (RI and R2). where the f i r s t l e t t e r i n the (**) i n d i c a t e s the d i r e c t i o n of wave t r a v e l and the second l e t t e r i n d i c a t e s the d i r e c t i o n of p a r t i c l e motion (H = h o r i z o n t a l ; V = v e r t i c a l ) . M u l t i p l e h i t s f o r each stage were used to check r e p e a t a b i l i t y . As f o r the downhole technique, i t was p o s s i b l e to c a l c u l a t e shear wave v e l o c i t i e s from crosshole measurements using both the crossover and c r o s s - c o r r e l a t i o n techniques w i t h d i g i t a l l y f i l t e r e d s i g n a l s . The h o r i z o n t a l spacing between the cones f o r the crosshole set-up was between 2 m and 3 m. 3.2.4 Laboratory Index Tests Laboratory index t e s t s were performed on both d i s t u r b e d and undisturbed samples obtained at each of the research s i t e s where i n s i t u t e s t s were 50 c a r r i e d out. The purpose of the t e s t s was to provide d e t a i l s of s o i l type c h a r a c t e r i s t i c s , index p r o p e r t i e s and s t a t e . Index parameters are u s e f u l f o r d e f i n i n g v a r i a t i o n s i n the s o i l p r o f i l e and f o r a i d i n g the i n t e r p r e t a t i o n of i n s i t u t e s t d a t a . C e r t a i n i n d i c e s can a l s o be used to estimate (K )„_, as o NC discussed i n Chapter 2. The f o l l o w i n g t e s t s were performed: - g r a i n s i z e determinations by dry and wet s i e v i n g - hydrometer t e s t s - n a t u r a l water content determinations - determination of l i q u i d and p l a s t i c l i m i t s - unconfined compression t e s t s - standard incremental oedometer t e s t s on both h o r i z o n t a l l y - and v e r t i c a l l y - c u t samples The r e s u l t s of these t e s t s are discussed i n Chapter 4. 3.3 Full-Displacement Probes: Cones D i r e c t l a t e r a l s t r e s s measurements using c y l i n d r i c a l axisymmetric penetrometers were obtained using two pieces of equipment designed and b u i l t at UBC, namely a l a t e r a l s t r e s s piezocone and a seismic cone pressuremeter. A second l a t e r a l s t r e s s cone designed and b u i l t at the U n i v e r s i t y of C a l i f o r n i a at Berkeley was a l s o used at the UBC research s i t e s and i s b r i e f l y d escribed here. 3.3.1 L a t e r a l Stress Cone (LSC) 3.3.1.1 UBC LSC The l a t e r a l s t r e s s (LS) piezocone designed and b u i l t at UBC comprises two separated measurement systems; a standard UBC piezocone u n i t followed by 51 a l a t e r a l s t r e s s module (Campanella, S u l l y , Greig and J o l l y , 1990). The 8 channel cone has a t i p area of 15 cm 2, a f r i c t i o n sleeve are of 225 cm2 and allows the simultaneous measurement of the f o l l o w i n g parameters: - cone r e s i s t a n c e , q c (bar) - pore pressure on the face, u l f or behind the t i p , u 2 (m of water) - sleeve f r i c t i o n , f (bar) - pore pressure behind the f r i c t i o n s l eeve, u 3 (m of water) - temperature (°C) The above channels operate over a 7.5 V range. The c a l i b r a t i o n f a c t o r s f o r each channel are given i n Table 3.2. The l a t e r a l s t r e s s module, which e s e n t i a l l y c o n s i s t s of an instrumented f r i c t i o n s l e e v e , i s l o c a t e d 0.69 m behind the t i p shoulder and permits the f o l l o w i n g values to be recorded: - sleeve f r i c t i o n , LS-FS (bar) - pore pressure, u^g (m of water) - l a t e r a l s t r e s s , o ^ (kPa) - temperature (°C) Table 3.2 C a l i b r a t i o n Data f o r UBC LS Piezocone. Channel No. Parameter Un i t s C a l i b r a t i o n Factor 1 Cone r e s i s t a n c e bar 0.13 bar/mV 2 Sleeve f r i c t i o n bar 0.013 bar/mV 3 Lower pore pressure m of water 0.23 kPa/mV 4 Upper pore pressure m of water 0.23 kPa/mV 5 Temperature °C * 6 LS-FS bar 0.013 bar/mV 7. LS-PP m of water 0.23 kPa/mV 8 °LS kPa 1.44 kPa/mV *Temperature i n degrees c e l s i u s i s obtained from ( V r p x 4 ) - l l where V j i s the voltage measured from a r e s i s t a n c e temperature device (RTD) 52 Even though two temperature sensors are l o c a t e d i n the LSC, only the temperature at the l a t e r a l s t r e s s module p o s i t i o n i s recorded when the cone i s being used i n t h i s format. The transducer ranges are again 7.5 V f o r a l l the channels except the l a t e r a l s t r e s s channel which operates on 1 V f u l l s c a l e . The choice of l o c a t i o n f o r the l a t e r a l s t r e s s module r e q u i r e s some comment. Design Considerations Previous s t u d i e s i n t o s o i l behaviour have demonstrated that l a r g e g r a d i -ents of both s t r e s s and pore pressure e x i s t around a p e n e t r a t i n g cone and that these gradients are r e l a t e d p r i m a r i l y to the geometry of the equipment. In e f f e c t , the s i n g u l a r i t y at the base of the cone t i p causes a l a r g e normal s t r e s s r e d u c t i o n to occur as the s o i l passes the shoulder. The extent of the re d u c t i o n has been experimentally evaluated w i t h respect to pore pressures but l i t t l e i n f o r m a t i o n e x i s t s w i t h respect to l a t e r a l s t r e s s r e d u c t i o n and the r e l a t i v e importance of s t r e s s r e d i s t r i b u t i o n and creep. For sands, i n d i r e c t evidence based on the v a r i a t i o n of averge sleeve f r i c t i o n , f g , w i t h distance suggests t h a t at approximately 12D (D = diameter of cone) behind the t i p , the l a t e r a l s t r e s s should be e s s e n t i a l l y constant f o r any p a r t i c u l a r r e l a t i v e d e n s i t y . Location of the l a t e r a l s t r e s s sensor c l o s e to the t i p would r e q u i r e measurements i n an area of h i g h l y v a r i a b l e s t r e s s . Furthermore, at t h i s l o c a -t i o n dimensional t o l e r a n c e s may have unacceptable e f f e c t s on the measured valu e s , i . e . , a s l i g h t l y undersized f r i c t i o n sleeve w i l l promote a l a r g e r s t r e s s r e d u c t i o n whereas an o v e r s i z e d sleeve w i l l reduce the unloading e f f e c t . S t r a i n r a t e changes near the t i p and r o t a t i o n of p r i n c i p a l s t r e s s e s may a l s o be important. This a s i d e , both Huntsman (1985) and J e f f e r i e s et a l . 53 (1987) present data where the l a t e r a l s t r e s s measured during cone p e n e t r a t i o n by a sensor l o c a t e d ID behind the t i p correspond remarkably w e l l to r e s u l t s of s e l f - b o r i n g pressuremeter t e s t s . This i s s u r p r i s i n g c o n s i d e r i n g the disturbance caused by i n s e r t i o n of the cone and may w e l l r e s u l t from the loose nature of the s o i l s t e s t e d . The l o c a t i o n of the sensor cl o s e to the t i p i s advantageous where reference t e s t s are performed i n c a l i b r a t i o n chambers. C a l i b r a t i o n of an upper s t r e s s sleeve i s not p o s s i b l e due to the l i m i t e d p e n e t r a t i o n distance r e s u l t i n g from chamber s i z e . No CC f a c i l i t y e x i s t s at UBC and consequently i t was planned to c a l i b r a t e the l a t e r a l s t r e s s cone i n i t i a l l y i n the l a b o r a t o r y and then i n the f i e l d at s i t e s where the K c o n d i t i o n was known. J o As such, the geometry of the cone i n terms of sensor l o c a t i o n was not a r e s t r i c t i o n . F i n a l l y , w i t h a view to developing some k i n d of t h e o r e t i c a l i n t e r p r e t a -t i o n , i t i s reasonable to expect t h a t data obtained away from the t i p may more c l o s e l y represent c o n d i t i o n s of c y l i n d r i c a l c a v i t y expansion (Appendix B) . S tress changes near the t i p may cuase s i g n i f i c a n t d e v i a t i o n from the c a v i t y expansion c o n d i t i o n . D e t a i l s of LS Module For the UBC l a t e r a l s t r e s s piezocone the sensor i s l o c a t e d 0.69 m (15.6 D) behind the cone shoulder ( F i g . 3.4). The l a t e r a l s t r e s s sleeve i s 88 mm long and 44 mm i n diameter (surface area of 121.6 cm 2), w i t h a w a l l t h i c k n e s s of 3 mm. At the centre of the s l e e v e , a 20 mm long s e c t i o n has a reduced w a l l t hickness of 1 mm. An arrangement of s t r a i n gauges i s o r i e n t e d at t h i s l o c a t i o n to measure the hoop s t r e s s i n the s e c t i o n induced by the l a t e r a l 54 ( NOT TO SCALE ) u L S pore pressure transducer Lateral stress friction sleeve Lateral stress sensor Temperature sensor Cone electronics LATERAL STRESS MODULE u 3 pore pressure transducer Friction sleeve ( 225cm ) u 2 pore pressure j interchangeable pore pressure J filter locations 6 0 ° 15cm2 tip > PIEZOCONE UNIT F i g . 3.4 D e t a i l s of UBC l a t e r a l s t r e s s cone (Campanella, S u l l y , Greig and J o l l y , 1990). 55 s t r e s s a c t i n g on the sleeve. Several d i f f e r e n t gauge arrangements were t e s t e d to optimize the l a t e r a l s t r e s s response and minimize both temperature and f r i c t i o n cross t a l k e f f e c t s . A f u l l bridge c o n f i g u r a t i o n i s mounted on the sleeve. Each arm of the bridge c o n s i s t s of two 1000 ohm s t r a i n gauges. The a c t i v e arms are l o c a t e d on the t h i n w a l l e d s e c t i o n of the sleeve whereas the i n a c t i v e arms are on the t h i c k e r s e c t i o n The current design remains temperature s e n s i t i v e to some degree and consequently a platinum RTD sensor has been i n s t a l l e d i n the sleeve to a l l o w f o r temperature compensation c o r r e c t i o n s to both the l a t e r a l s t r e s s and sleeve f r i c t i o n measurements. The d i f f e r e n t i a l s i g n a l s from the l a t e r a l s t r e s s gauges are a m p l i f i e d i n the cone to give a f u l l s c a l e output of 1 v o l t f o r an e x t e r n a l h y d r o s t a t i c pressure of approximately 1440 kPa. The analog s i g n a l s are converted at the surface to a 12 b i t r e p r e s e n t a t i o n of t h e i r voltage g i v i n g a s e n s i t i v i t y of 4.9 mV or 7.4 kPa of l a t e r a l s t r e s s . The IBM PC based data a c q u i s i t i o n system (UBC DAS) c o n s i s t s of an analog to d i g i t a l (A/D) converter, depth c o n t r o l l e r board, counter timer board and a b a t t e r y backed-up power supply (Greig et a l . , 1987). A schematic layout of the UBC DAS i s shown i n F i g . 3.5. The data a c q u i s i t i o n program i n t e r f a c e s the various components of the system to provide a means of c o l l e c t i n g and s t o r i n g the data. Data storage i s e i t h e r on f l oppy or hard d i s k . The program operates i n two modes: cone p e n e t r a t i o n and d i s s i p a t i o n . The change to d i s s i p a t i o n mode i s automatic when p e n e t r a t i o n i s h a l t e d . Laboratory C a l i b r a t i o n of LSC Laboratory c a l i b r a t i o n of the load c e l l s and pore pressure transducers f o r the piezocone u n i t were performed according to standard procedures Z80 Counter / T i m e r Boa rd D e p t h P u l s e e CMOS 6805 Depth Cont ro l l e r Board i t I t i t IBM PC Compati ble Mi crocompu ter I n t e r n a l B u t Ex». C L K >• D i s p I o y Mo ni tor DT280I 12 bi t A/ D Converter Hydrau lie Valve Switch A n o l o g a S i g n a l e Keyboard Pr i n t e r P lotter Interface Unit 1 15 V Power Supply for LS Module Depth Encoder Reaction Cylinders Load Switch j Loading Head Latera l Stress Module I 5 cn r CPTU V ON Figure 3.5 Details of UBC data acquisition system (modified after Greig et a l . , 1987) 57 adopted at UBC ( G i l l e s p i e , 1990). Only the l a b o r a t o r y c a l i b r a t i o n of the l a t e r a l s t r e s s module i s considered here. Due to the nature of the design of the LS module i t was necessary to c a l i b r a t e the module f o r the f o l l o w i n g c o n d i t i o n s : • h y d r o s t a t i c a l l y a p p l i e d c o n f i n i n g pressure • l a t e r a l s t r e s s cross t a l k on f r i c t i o n sleeve due to a x i a l loads. • temperature s e n s i t i v i t y • time-dependent s t a b i l i t y of a l l channels. During each of the c a l i b r a t i o n s performed, a l l e i g h t cone channels were monitored to ensure the absence of channel i n t e r f e r e n c e . H y d r o s t a t i c C a l i b r a t i o n of LS Module To c a l i b r a t e the bridge output f o r a p p l i e d h y d r o s t a t i c pressure a s p e c i a l sleeve was f i t t e d over the LS module and connected to a dead weight pressure t e s t e r . Pressure increments of 20 p s i (^138 kPa) were used up to a maximum of 250 p s i (1724 kPa) maintaining a constant temperature throughout. H y d r o s t a t i c loading and unloading sequences were performed f o r c o n d i t i o n s of zero a x i a l load. The r e s u l t s are shown i n F i g . 3.6 which give a c a l i b r a t i o n f a c t o r of 0.000695 V/kPa or 1440 kPa/V, w i t h l i t t l e or no h y s t e r e s i s e f f e c t s and no b a s e l i n e d r i f t over f u l l s c a l e c y c l i n g . The f a c t o r was independent of temperature f o r the range of a p p l i c a t i o n (6-20°C). F r i c t i o n - L a t e r a l Stress Cross Talk A x i a l loading of the f r i c t i o n sleeve causes an output voltage on the l a t e r a l s t r e s s channel due to the Poisson e f f e c t . For the s t r a i n gauge arrangement employed, i n c r e a s i n g sleeve f r i c t i o n on the LS sleeve causes a negative o f f s e t on the l a t e r a l s t r e s s channel. 58 -1.50 LS - CPTU : Calibration of lateral stress sleeve Temperature = 22.6 C D I -3.00 0 400 800 1200 1600 Applied Pressure (kPa) 2000 Fig. 3.6 Hydrostatic pressure c a l i b r a t i o n of LS module (Campanella, Sully, Greig and J o l l y , 1990). The cone was set up i n a frame so that the a x i a l l y applied load was . transferred by s p l i t rings to the LS f r i c t i o n sleeve. Data for both the l a t e r a l stress and sleeve f r i c t i o n channels were recorded by means of an HP7090A measurement p l o t t i n g system. The load-unload was performed under zero confining pressure over a period of approximately 1 minute with readings taken every 0.1 sec. Linear regression of the data gave gradients of -0.2136 and -0.2150 for loading and unloading (Fig. 3.7). A correction factor of 0.53 i s applied to the slope i n Fig. 3.7 which takes into account the d i f f e r -ence between the a x i a l load d i s t r i b u t i o n imposed for the laboratory c a l i b r a -t i o n and actual f i e l d conditions. An average value was used to correct the l a t e r a l stress data according to the equation: 59 - 2 . 6 co -+-> o > CO CO CD CO CD -M D - 3 . 1 --3.6 — i 1 1 1 1 1 1— FS—LS cross talk calibration • for LS-CPTU module ' 0 R e p r e s e n t a t i v e d a t a p o i n t s 8 on ly s h o w n . o F a c t o r = ( A L S / A F S ) * 0 . 8 0 7 • • • • • Loading 0 0 0 0 0 Unloading -0.5 0 . 5 1.5 2 .5 Applied friction load (volts) 3 .5 Fig. 3.7 Evaluation of cross t a l k on LS channel due to a x i a l f r i c t i o n load (Campanella, Sully, Greig and J o l l y , 1990). (VLS>C = {\s\ + [ ° - 1 1 3 5 * V f s ] ( 3 - X ) where: ( V L S ) ^ = corrected r e l a t i v e l a t e r a l stress voltage (VTr,)„ = measured r e l a t i v e l a t e r a l stress voltage LS M V^ . = r e l a t i v e sleeve f r i c t i o n voltage fs ° Calibration for Temperature Effects To evaluate the temperature s e n s i t i v i t y of the LS module, the whole cone was immersed i n a bath of ice water and was l e f t to warm to room temperature 60 over a 24 hour period during which time readings on a l l channels were taken every minute. The results for the l a t e r a l stress channel are shown i n Fig. 3.8. The temperature co e f f i c i e n t ( B ^ ) ^ for the LS channel was calculated to be +3.6 mV/°C on cooling. (Similarly, temperature coef f i c i e n t s were also evaluated for the other channels.). Evaluation of Baseline D r i f t During the l a t t e r part of the temperature c a l i b r a t i o n , when the system had arrived at an equilibrium condition with the ambient temperature, co •2.80 -i 1 1 r i 1 r co - 4 — ' o > CO CO CD - 2 . 8 5 LS-CPTU Temperature calibration - 12 May 1989 Temperature sensor located in lateral stress sleeve. Every 10th data point shown - 2 . 9 0 -D CD O - 2 . 9 5 -3.00 i r 10.0 n 1 1 1 r 15.0 Temperature (C) ~i r 20.0 Fig. 3.8 Temperature s e n s i t i v i t y of LS baseline (Campanella, Sully, Greig and J o l l y , 1990). 61 continued monitoring allowed b a s e l i n e d r i f t on each channel to be evaluated. For a l l e i g h t channels of the piezocone and LS module, the time dependent d r i f t (measured over a 16 hour period) was found to be n e g l i g i b l e . The c a l i b r a t i o n f a c t o r s obtained as o u t l i n e d above have been i n c o r p o r a -ted i n t o the data a c q u i s i t i o n program so t h a t the output i s given i n c o r r e c t e d engineering u n i t s . The uncorrected raw data can be accessed i f r e q u i r e d . F i e l d T e s t i n g Procedures P r i o r to performing the LS-CPTU, a l l pore pressure measuring systems were de-aired and satura t e d w i t h g l y c e r i n . S a t u r a t i o n techniques used at UBC have been discussed e x t e n s i v e l y by G i l l e s p i e (1990) and w i l l not be considered here. The LS piezocone was placed i n a c o l d water bath to b r i n g the probe temperature to an estimated e q u i l i b r i u m ground temperature. A l l connections to the data a c q u i s i t i o n system (DAS) were made and the cone momentarily suspended j u s t above the ground (zero load on a l l channels). Baseline v o ltage readings were taken on a l l channels. Having completed the b a s e l i n e procedure, the cone was then pushed to a depth of 2 m (or j u s t below the water t a b l e ) and p e n e t r a t i o n h a l t e d w h i le the cone came i n t o temperature e q u i l i b r i u m w i t h the ground. A f t e r a wait of approximately 15 minutes, the sounding was commenced. A l l t e s t s were performed i n accordance w i t h the I n t e r n a t i o n a l Reference Procedure o u t l i n e d i n ISOPT-1. A second set of b a s e l i n e voltages on a l l 8 channels was a l s o recorded on completion of the sounding. The two sets of b a s e l i n e provided a check on the temperature c o r r e c t i o n s a p p l i e d i n the data r e d u c t i o n software. 62 3.3.1.2 Berkeley (UCB) LSC The UBC LSC described above was developed f o l l o w i n g the o r i g i n a l Berkeley design f o r the model I I l a t e r a l s t r e s s sensing cone penetrometer, i . e . the measurement of hoop s t r a i n i n a c i r c u l a r underreamed s e c t i o n on the f r i c t i o n sleeve. The Berkeley LSC (Model I I ) i s described i n Appendix A ( F i g . A.17). A subsequent v e r s i o n (Model I I I ) was developed by Tseng (1989) and employed by Masood (1990) f o r e v a l u a t i n g in-ground l a t e r a l s t r e s s e s (Appendix A, F i g . A. 19). The Berkeley (UCB) LSC was used at McDonald Farm as p a r t of a cooperative research program between the U n i v e r s i t i e s of B r i t i s h Columbia and C a l i f o r n i a (at Berk e l e y ) . The UCB Model I I I LSC measures the l a t e r a l s t r e s s i n a d i f f e r e n t manner than the e a r l i e r Model I I probe. The l a t e r a l s t r e s s s e c t i o n i s 25 mm long and c o n s i s t s of a two-ring arrangement: an outer a c t i v e r i n g and an inner p a s s i v e r i n g , both being f a b r i c a t e d w i t h s t a i n l e s s s t e e l . Four i d e n t i c a l a r c i f o r m s t e e l pieces 1.3 mm t h i c k are j o i n e d by a polyurethane compound to form the outer f l e x i b l e r i n g . The f l e x i b l e r i n g i s formed over the r i g i d i n n e r passive r i n g which contains a s t r a i n gauged s t a i n l e s s s t e e l diaphragm. The 6.3 mm diameter t h i n - w a l l e d diaphragm performs as a pressure transducer. A sealed rubber membrane i s o l a t e s the inner and outer r i n g s . The c a v i t y between the membrane and the inner r i n g i s f i l l e d w i t h de-aired water. The s a t u r a t i o n of the pressure c a v i t y i s v i t a l to the performance of the measuring system. A schematic i l l u s t r a t i o n of the l a t e r a l s t r e s s measuring system i s shown i n F i g . 3.9. Two l a t e r a l s t r e s s measurement s e c t i o n s are incorp o r a t e d i n t o the UCB cone; one l o c a t e d ID and the other 7.5D behind the cone t i p . The DAS f o r the cone was a l s o developed at UCB and e s s e n t i a l l y c o n s i s t s of an AT compatible 63 EUctronics S.ction UPPER UTERAL STRESS SENSING SECTION =OROUS STONE T O ! UPPER PIEZOMETER IOWER U T E R » L STRESS SENSING SECTION POROUS RING fOR LOWER PIEZOMETER F i g . 3.9 Schematic i l l u s t r a t i o n of the l a t e r a l s t r e s s measuring system, Berkley LSC Model I I I ( a f t e r Tseng, 1989). microcomputer i n t e r f a c e d w i t h the downhole cone e l e c t r o n i c s . The f o l l o w i n g channels are recorded during a sounding: - t i p r e s i s t a n c e (MPa) - sleeve f r i c t i o n (kPa) - lower l a t e r a l s t r e s s at ID behind t i p (kPa) - upper l a t e r a l s t r e s s at 7.5D behind t i p (kPa) - lower pore pressure (kPa) - upper pore pressure (kPa) - temperature (°C) 64 A l l c o r r e c t i o n s to the b a s i c f i e l d data are performed by the DAS and the output i s given i n engineering u n i t s . 3.3.2 Seismic Cone Pressuremeter (SCPM) The seismic cone pressuremeter (SCPM) developed at UBC has been used at s e v e r a l of the Lower Mainland research s i t e s considered during t h i s study. A d e s c r i p t i o n of the equipment and t e s t procedures followed w i t h the SCPM have been reported by Hers (1989) and Howie (1991). A review of f u l l displacement pressuremeters i s given i n Appendix A. Schematic d e t a i l s of the probe are shown i n F i g . A,24. The pressuremeter s e c t i o n i s mounted behind a 15 cm2 piezocone u n i t . The exact diameter of the PM u n i t was measured to average 43.6 mm. When compared to the cone diameter of 44 mm, t h i s would suggest that the PM s e c t i o n i s s l i g h t l y undersized. This has important consequences i n r e l a t i o n to the l i f t - o f f s t r e s s e s measured w i t h the probe. This i s discussed l a t e r i n the t h e s i s . SCPM t e s t s were performed at 1 m i n t e r v a l s at s e v e r a l of the research s i t e s . D e t a i l s of the t e s t procedures and data i n t e r p r e t a t i o n have been discussed by Hers (1989) and Howie (1991). For t h i s study, the pressuremeter l i f t - o f f and l i m i t pressures were of primary i n t e r e s t . 3.4 Full-Displacement Probes; P l a t e s 3.4.1 Dilatometer (DMT) D e t a i l s of the dilatometer equipment and t e s t procedures are given i n Appendix A. Data r e d u c t i o n and d e f i n i t i o n of DMT index parameters are a l s o o u t l i n e d . The DMT t e s t s performed were i n accordance w i t h the suggested ASTM procedure (Schmertmann, 1986). The data a c q u i s i t i o n system used at UBC 65 d i f f e r s s l i g h t l y from t h a t normally s u p p l i e d w i t h the DMT. The standard dilatometer control/readout box incorporates a pneumatic 0-40 bar pressure gauge. A second low range gauge (0-5 bar) can a l s o be i n c l u d e d to measure low l i f t - o f f pressures and to a c c u r a t e l y monitor pore pressure changes v i a the c l o s u r e reading. In the modified UBC system the pneumatic gauges have been replaced by a CEC flush-mounted e l e c t r o n i c transducer w i t h a f u l l s c a l e range of 0-200 bar. For low pressures (< 20 bar) the gain on the a m p l i f i e r s can be switched to provide b e t t e r s i g n a l d e f i n i t i o n . The sampling r a t e f o r the c i r c u i t r y was i n i t i a l l y 2 Hz, but t h i s has been increased to 4 Hz. Rates of pressure increase during a t e s t have to be c o n t r o l l e d so that the sampling r a t e a c c u r a t e l y captures the A, B and C readings. This i s a l s o true f o r the c a l i b r a t i o n constants AA and AB. Using the new system, t e s t data have been found to be very repeatable. The e l e c t r o n i c system a l s o i n c l u d e s a pressure-value hold f a c i l i t y at each of the standard displacements during expansion/ c o n t r a c t i o n , i . e . , 0.05 mm, 1.1 mm and c l o s u r e . In t h i s way, t r u e readings at each p a r t i c u l a r displacement are obtained, r a t h e r than e s t i m a t i n g the value from a moving gauge p o i n t at each sounding of the buzzer. 3.4.2 T o t a l Stress C e l l (TSC)  D e t a i l s of TSC The spade-shaped push-in t o t a l pressure c e l l s (TSC) used f o r t h i s research were purchased from S o l i n s t Canada L t d . The spade c e l l i s a p l a t e 6.4 mm t h i c k w i t h a pressure c e l l of dimensions 100 mm x 200 mm. The rectangular o i l - f i l l e d chamber i s formed of two t h i n s t e e l sheets welded at the edges. The pressure s e n s i t i v e area i s welded to a support p l a t e . The c a v i t y so formed i s p r e s s u r i z e d to maintain p l a t e s e p a r a t i o n . The welded p l a t e s are strengthened by a s o l i d metal s t r i p which i s welded on the c e l l 66 perimeter. The o i l pressure i n the chamber i s connected v i a a short length of s t e e l tube to a pneumatic transducer l o c a t e d on a connector boss behind the support p l a t e ( F i g . 3.10). A ceramic porous d i s c i s a l s o l o c a t e d on the support p l a t e and connected h y d r a u l i c a l l y to a second pneumatic transducer which i s tandem mounted behind the f i r s t . Both transducers are pr o t e c t e d w i t h i n a s t e e l sleeve adaptor which connects the spade c e l l t o the i n s t a l l a -t i o n rod. TWIN TUBING PNEUMATIC TRANSDUCER FOR PRESSURE CELL CONNECTOR BOSS 200 mm SUPPORT PLATE PLATE WELD 'AND STIFFENER PNEUMATIC TRANSDUCER FOR PIEZOMETER ACTIVE PART OF PRESSURE CELL F i g . 3.10 Components of S o l i n s t t o t a l pressure c e l l ( a f t e r S o i l Instruments L t d . , 1987). A pre-set b a s e l i n e (zero value) and c a l i b r a t i o n i s s u p p l i e d f o r each c e l l by the manufacturer. The zero reading corresponds to the o i l pressure i n the chamber. The manufacturers recommend an i n i t i a l storage l i f e t o check th a t no b a s e l i n e changes occur. Twin nylon tubes, sheathed i n polythene, are attached to the compression f i t t i n g s l o c a t e d on each of the pneumatic transducers. Quick r e l e a s e coup-67 l i n g s are attached to one of the nylon tubes at the other end of the twin t u b i n g . The quick r e l e a s e couplings are used to connect the down pressure-l i n e .to the pressure readout box. The twin tubing l i n e s are u s u a l l y cut at lengths determined by the depth to which the spade c e l l i s to be i n s t a l l e d . The c e l l and pore pressure measurements are taken using a p o r t a b l e pneu-matic readout box. The readout u n i t contains a compressed n i t r o g e n pressure b o t t l e . With the quick r e l e a s e coupling connected to the readout box, the pressure v a l v e i s opened and g r a d u a l l y i n c r e a s i n g pressure i s a p p l i e d to the transducer. When the a p p l i e d pressure j u s t exceeds the pressure i n the c e l l , the diaphragm i n the transducer d e f l e c t s and vents the a p p l i e d pressure to the r e t u r n l i n e (the second nylon tube). The readout box then measures the gas pressure r e q u i r e d to j u s t maintain a continuous flow through the d i a -phragm chamber. The same technique i s used f o r reading both the o i l chamber and pore pressure transducers. The pressures are measured at the surface by a Druck e l e c t r o n i c transducer w i t h a 0 to 2000 kPa range. R e s o l u t i o n of the transducer i s ±0.05% f u l l s c a l e , i . e . ± 1 kPa. P r i o r to i n s t a l l a t i o n i n the f i e l d , minor m o d i f i c a t i o n s were made to the c e l l s and c a l i b r a t i o n checks made. Because the c e l l s are o i l - f i l l e d and sealed, the d i f f e r i n g temperature c h a r a c t e r i s t i c s of the c e l l components w i l l cause the b a s e l i n e to be s e n s i t i v e to v a r i a t i o n s i n temperature. This i s recognized by the manufac-t u r e r but no data have been presented to evaluate the e f f e c t s . Furthermore, f o r none of the case s t u d i e s reported i n the l i t e r a t u r e are the pressure c e l l data c o r r e c t e d f o r temperature e f f e c t s . To provide data on the in-ground ambient temperature and i t s v a r i a t i o n during the p e r i o d when the c e l l s are i n s t a l l e d , platinum RTD temperature sensors were i n s t a l l e d i n s e v e r a l of the c e l l s . The RTD sensors were i n s t a l l e d adjacent to the compression f i t t i n g s 68 on the connector boss ( F i g . 3.10). The e l e c t r i c a l cables from the sensor were taken up through the r e t u r n pressure l i n e attached to the pressure c e l l transducer. The presence of the t h i n wires d i d not r e s t r i c t the venting a c t i o n r e q u i r e d f o r diaphragm movement during readout. Pressure and Temperature C a l i b r a t i o n Temperature and h y d r o s t a t i c pressure c a l i b r a t i o n s were performed i n the l a b o r a t o r y p r i o r to f i e l d i n s t a l l a t i o n . For t h i s purpose a t e s t i n g chamber was constructed. Each c e l l was placed i n the chamber w i t h a RTD temperature sensor attached to the midpoint of the pressure s e n s i t i v e c e l l area. The chamber was then water f i l l e d and sealed. An e x t e r n a l pressure source was used to vary the chamber c o n f i n i n g pressure. Temperature v a r i a t i o n s were achieved by immersing the complete chamber i n a temperature bath. The s t a b i l i z e d temperature f o r each set of pressure c a l i b r a t i o n s was measured by the RTD sensor on the face of the blade. A temperature range of 0-20°C was used f o r both c o o l i n g and warming c y c l e s . T y p i c a l l y , a s e r i e s of c e l l and porewater pressures were taken at nominal chamber (confining) pressures of 0, 50, 100, 150 and 200 kPa f o r loading and unloading c y c l e s . The r e s u l t s of the pressure and temperature c a l i b r a t i o n f o r one of the purchased spade c e l l s are shown i n F i g . 3.11. From the r e s u l t s of the c a l i b r a t i o n i t i s evident t h a t : • the t o t a l s t r e s s c e l l s have an i n t e r n a l pressure at zero a p p l i e d s t r e s s which has to be subtracted from the a c t u a l reading to give the s t r e s s increase r e s u l t i n g from the increase i n e x t e r n a l pressure. • an o f f s e t i n the i n t e r n a l c e l l zero pressure occurs (baseline d r i f t ) as the temperature of the blade changes. This concurs w i t h r e s u l t s presented f o r other types of pressure c e l l ( F e l i o and Bauer, 1986). 69 400- T r 350-T S C 1 5 4 2 o Q_ CD 300-3 CD S 250-o 200-X ) ~0 ^ 150-D CD 100-+ + + + + 0 kPa 40 kPa ««««» 82 kPa 127 kPa 180 kPa • * i 50- " i — r 5.0 T r 10.0 15.0 T e m p e r a t u r e ( ° C ) i r 20.0 Fig. 3.11 Typical temperature and pressure calibration for total stress c e l l (Sully and Campanella, 1989). • the offset resulting from temperature change i s essentially independ-ent of the applied stress. This facilitates easy f i e l d correction for temperature effects since the correction does not vary with the recorded in-ground stress. The temperature d r i f t for a l l the blades purchased i s shown i n Fig. 3.12 for the condition of zero applied chamber pressure. The temperature coefficient, B T, for the cells i s listed in Table 3.3. Temperature coefficients of up to 1.35 kPa/°C were measured although average values are around 0.5 kPa/°C. 70 200-190-L?180" £l70 13 CO CO <D Q_ CD D 150--i—r ~ i — i — i — i — i — i — r ~i 1 1 1 1 1 r T e m p e r a t u r e d e p e n d e n c e o f m e a s u r e d t o t a l b l a d e s t r e s s f o r z e r o a p p l i e d ce l l p r e s s u r e CD 140-***** TSC1542 •••••TSC1541 TSC1540 poooo TSC 1539 °°°°° TSC1538 ***** TSC1537 130-" i 1 1—j 1 — r 5 ~i I i i i i 1—i 1 1 r 10 15 20 o , Temperature ( °C) Fig. 3.12 I n i t i a l temperature dependence of baseline pressure for a l l spade c e l l s used i n th i s study (Sully and Campanella, 1989). Table 3.3 I n i t i a l Calibration Data for Spade Cells (Before Installation) Spade C e l l Reference Baseline Factor, B.j. Number Temperature Pressure, (kPa/°C on (°C) (kPa) cooling) TSC 1350 2.2 130 0.45 TSC 1537 9.5 156 1.35 TSC 1538 8.0 179 0.58 TSC 1539 10.2 138 0.14 TSC 1540 9.3 146 0.14 TSC 1541 10.5 135 0.48 TSC 1542 9.1 139 0.91 TSC 1580 9.2 232 0.67 TSC 1581 9.9 160 0.95 71 Since temperature changes of 10°C or more may occur between the l a b o r a t o r y and f i e l d environments the temperature c o r r e c t i o n s become a p p r e c i a b l e , e s p e c i a l l y where low s t r e s s e s are being measured. C a l i b r a t i o n measurements were c a r r i e d out on the pressure c e l l s before i n s t a l l a t i o n and again a f t e r the c e l l s had been recovered from the ground. The l a t t e r c a l i b r a t i o n was used f o r data i n t e r p r e t a t i o n . The b a s e l i n e pressure f o r the i n d i v i d u a l TSC's given i n Table 3.3 i s governed by the a r b i t r a r y choice of the reference temperature. A l l temperature c o r r e c t i o n s to the measured blade pressures were made w i t h respect to the e q u i l i b r i u m ground temperature, as measured by the RTD temperature sensor i n s t a l l e d on the c e l l . A s u f f i c i e n t number of c e l l s were instrumented so t h a t a repre-s e n t a t i v e temperature p r o f i l e could be obtained at each s i t e ( u s u a l l y from 3 or 4 c e l l s ) . At depths where blades were not instrumented f o r temperature, the ground temperature was estimated by i n t e r p o l a t i o n from other temperature measurements. Thus, the measured blade pressures from i n s i t u measurements can be c o r r e c t e d according t o : = 0 m - ° b - [ ( V T I ) B T ] (3.2) where: a, TSC temperature c o r r e c t e d net t o t a l blade pressure (kPa) o m measured t o t a l blade pressure (kPa) o, b b a s e l i n e t o t a l pressure at reference temperature (kPa) T. R reference temperature (°C) in-ground temperature (°C) B, T c e l l pressure c a l i b r a t i o n f a c t o r f o r temperature (kPa/°C) 72 S i m i l a r b a s e l i n e readings were a l s o determined f o r the pneumatic pore pressure tranducers; these transducers were not found to be temperature s e n s i t i v e . I n s t a l l a t i o n Procedure T o t a l s t r e s s c e l l s of the push-in type are normally i n s t a l l e d i n the base of an e x i s t i n g borehole; t h i s reduces the r i s k of damaging the c e l l . Due to costs i n v o l v e d i n the boring o p e r a t i o n , and the a v a i l a b i l i t y of an a l t e r n a t i v e technique, minor m o d i f i c a t i o n s were made to the spade c e l l s to f a c i l i t a t e i n s t a l l a t i o n using the UBC Geotechnical Research V e h i c l e . This i n v o l v e d machining of a s t e e l sleeve adaptor to connect the spade c e l l to the i n s t a l l a t i o n rods. The adaptor a l s o serves as a p r o t e c t i v e housing f o r the pneumatic transducers. One end of the adapter was screwed onto the c e l l connector boss ( F i g . 3.10) w h i l e the other accepted the AWL casing (44.7 mm OD, 4.6 mm w a l l t hickness) t h a t was used to push the spade c e l l i n t o the ground. High b u c k l i n g s t r e n g t h rods were r e q u i r e d to avoid rod damage due to the h i g h loads r e q u i r e d to push the c e l l assembly - most of the r e s i s t a n c e r e s u l t i n g from the l a r g e r diameter sleeve adaptor. U n l i k e the borehole problem, where the spade c e l l i s only advanced 0.5 to 1.0 m below the base, the use of the UBC GRV r e q u i r e d the c e l l s to be pushed from ground l e v e l to t h e i r f i n a l intended depth. To avoid b u c k l i n g and breakage of the rods, i t was decided to use AWL casing f o r i n s t a l l a t i o n . The 35 mm rod ID a l s o permitted easy passage of the two l i n e s of twin tubing from the c e l l to the surface. The TSC blade i s most s u s c e p t i b l e to breakage, under a x i a l l o a d i n g , where the twin p l a t e s are welded to the support p l a t e . To reduce the a x i a l loads on the pressure c e l l , i t was decided to prepush a dummy p l a t e to a 73 f i n a l depth 0.5 to 1.0 m above the re q u i r e d depth p r i o r to i n s t a l l i n g the TSC. In t h i s way the TSC was only pushed i n v i r g i n s o i l f o r a depth of 0.5 to 1.0 in. The dummy push was performed using the dil a t o m e t e r and standard DMT readings were taken every 0.2 m (Thrust, p 0 , p a , p 2 ) . A f t e r i n s t a l l a t i o n of the TSC the l a t e r a l s t r e s s and pore pressure were monitored w i t h time u n t i l a s t a b l e f i n a l e q u i l i b r i u m value was obtained. 3.5 S e l f - B o r i n g Probes Two types of s e l f - b o r i n g probes were used during t h i s study, namely a pressurementer (SBPM) and a load c e l l (SBLC) . While the i n t e n t i o n of the t h e s i s i s t o e v a l u a t e a l t e r n a t i v e methods f o r e v a l u a t i n g o^ i n s i t u , i t was f e l t t hat some comparison w i t h SBPM data would be d e s i r a b l e at some of the s i t e s s t u d i e d . Previous s t u d i e s performed at UBC using SBPM data have been performed i n a s s o c i a t i o n w i t h Dr. J.M.O. Hughes using h i s probe. Recently a UBC SBPM has been designed (Campanella et a l . , 1990) and was used during t h i s study. Tests w i t h the s e l f - b o r i n g load c e l l were conducted i n conjunction w i t h Dr. A.B. Huang (Clarkson U n i v e r s i t y , U.S.A.) using a Cambridge i n s i t u probe (Camkometer) operated by him. The two types of probes are b r i e f l y described below. Further d e t a i l s of the general methods and i n t e r p r e t a t i o n techniques are given i n Appendix A. 3.5.1 S e l f - B o r i n g Pressuremeter (SBPM)  D e t a i l s of SBPM Design The UBC SBPM design i s based on the equipment developed by Hughes (1973) ( F i g . A .l) w i t h improvements i n the areas of instrumentation/data p r o c e s s i n g , membrane and l a n t e r n c h a r a c t e r i s t i c s and i n s t a l l a t i o n techniques (Campanella 74 et a l . , 1990). The o v e r a l l length of the probe i s 1.43 m w i t h an e x t e r n a l diameter of 73 mm. The monocell probe has an expandable membrane L/D r a t i o of 6. Three strain-gauged c a n t i l e v e r f e e l e r arms t r a c k membrane movement at the centre of the PM s e c t i o n during i n f l a t i o n . A i r pressure f o r probe expansion i s s u p p l i e d by a small compressor l o c a t e d at ground surface. The SBPM i s i n s t a l l e d using the UBC GRV by a combination of pushing and s e l f - b o r i n g ( j e t t i n g w i t h d r i l l i n g mud). The instrumentation i n the SBPM system c o n s i s t s of 5 transducers, downhole e l e c t r o n i c s w i t h A/D converter and m i c r o c o n t r o l l e r , a 12V DC power supply and a p o r t a b l e personal computer. The transducers i n the probe comprise 3 c a n t i l e v e r - t y p e s t r a i n arm sensors and two pressure sensors. Each transducer has a separate a m p l i f i e r which permits f u l l use of the A/D converter f o r each channel. The s t r a i n arms monitor the membrane displacement using a f u l l - b r i d g e gauge arrangement to measure arm bending. The three s t r a i n arms are mounted at 120° at the centre of the i n f l a t a b l e membrane. The e f f e c t i v e operating range of each arm i s 8 mm which corresponds to a r a d i a l c a v i t y s t r a i n of about 22%. One of the pressure transducers i s used to monitor the a i r pressure i n s i d e the probe ( i n f l a t i o n pressure) while the other measures the d i f f e r e n t i a l pressure between the i n t e r n a l a i r pressure an the e x t e r n a l pore pressure. This d i f f e r e n t i a l corresponds to the e f f e c t i v e pressure exerted by the s o i l . The d i f f e r e n c e between the two pressure measurements gives the porewater pressure. The e f f e c t i v e s t r e s s transducer i s mounted on the SBPM membrane and moves w i t h i t during expansion. A small porous f i l t e r mounted i n the transducer c a v i t y keeps s o i l away from the diaphragm but permits the tra n s m i s s i o n of pore pressures. The wires from the transducers are passed to the surface i n s i d e the 6.4 mm OD a i r r e t u r n l i n e . For the pressure sensors and displacement transducers, 12 and 13 b i t r e s o l u t i o n are used, respect-75 i v e l y . This gives a r e s o l u t i o n of. 4 microns f o r the s t r a i n arms and 2 kPa f o r the pressure sensors. The s i g n a l s are converted to ASCII format and then sent to the surface PC v i a an RS232 s e r i a l l i n k . The data a c q u i s i t i o n program converts the raw data to engineering u n i t s and provides a r e a l - t i m e data l i s t i n g f o r a l l channels and a l s o a g r a p h i c a l r e p r e s e n t a t i o n i n terms of the pressure-displacement response f o r e i t h e r any one or a l l of the three s t r a i n arms. Membrane and Lantern C h a r a c t e r i s t i c s Commercially a v a i l a b l e Gooch rubber t u b i n g , 58 mm diameter and 1 mm i n th i c k n e s s i s used f o r the membrane m a t e r i a l . This was p r e f e r r e d to t h i c k e r more robust membranes which u s u a l l y have higher membrane c o r r e c t i o n and compliance f a c t o r s , o f t e n being n o n l i n e a r , and which sometimes show marked h y s t e r e t i c behaviour. Expansion of the probe i n a i r w i t h a Gooch membrane gave a b i l i n e a r envelope. Y i e l d occurs at about 2% r a d i a l s t r a i n at a pressure of 17 kPa. Expanding from 2% to 22% r a d i a l s t r a i n the pressure remains e s s e n t i a l l y constant w i t h l i t t l e or no h y s t e r e s i s . The low value of membrane c o r r e c t i o n , i . e . 17 kPa, i s i d e a l f o r t e s t i n g i n s o f t s o i l . Problems were experienced w i t h the i n i t i a l l a n t e r n design which c o n s i s t e d of a s e r i e s of 24 overlapping s t r i p s 16 mm wide and 540 mm long. The s t r i p s were h e l d i n place by r i v e t t i n g to a r i n g at each end of the l a n t e r n . Frequent blow-out of the membrane occurred at pressures ranging from 400 kPa to 600 kPa. A modified design, using overlapping spot welded 16 mm wide s t r i p s prevented any f u r t h e r blow-outs. D e t a i l s of the o r i g i n a l and r e v i s e d l a n t e r n designs are shown i n F i g . 3.13. 76 ORIGINAL DESIGN REVISED DESIGN F i g . 3.13 O r i g i n a l and r e v i s e d l a n t e r n design f o r UBC SBPM (Campanella et a l . , 1990). D e t a i l s of J e t t i n g System S e l f - b o r i n g pressuremeters are f r e q u e n t l y i n s t a l l e d by means of a c u t t i n g technique w i t h d r i l l i n g mud being f l u s h e d through the system to remove the broken-up s o i l . Hughes et a l . (1984) suggested the use of j e t t i n g i n cohesionless s o i l s and low-strength c l a y s and t h i s system has been adopted at UBC. Two types of j e t t i n g arrangement were used f o r the f i e l d s t u d i e s ; a c e n t r a l j e t t i n g system as shown i n F i g . 3.14(a) and a "showerhead" system as i n F i g . 3.14(b). The advantage of the c e n t r a l rod system i s t h a t the p o s i t i o n of the e x i t p o i n t s ( j e t s ) can be adjusted r e l a t i v e to the c u t t i n g shoe edge, although the adjustment can only be made while the probe i s above ground. The j e t holes are 2.4 mm i n diameter w i t h v a r y i n g o r i e n t a t i o n s (see 77 CENTRALIZING-WING GUIDE (3 total) (a) Central j e t t i n g rod arrangement (b) Showerhead arrangement Fig. 3.14 Types of j e t t i n g arrangement used with UBC SBPM (Campanella et a l . , 1990). 78 F i g . 3.14). For the showerhead setup the j e t t i n g holes are 40 mm from the c u t t i n g shoe which can cause problems i n s t i f f / d e n s e s o i l s s i n c e the j e t s o n l y s t a r t to break up the m a t e r i a l a f t e r the s o i l i s penetrated by t h i s d i s t a n c e . The i n t e r n a l spaces f o r both j e t t i n g arrangements l i m i t s the maximum p a r t i c l e s i z e that w i l l pass up the probe to about 10 mm. C a l i b r a t i o n of Transducers The s t r a i n arms were c a l i b r a t e d using a micrometer to provide a r e l a t i o n between measured displacement and s t r a i n arm output v o l t a g e . With the membrane removed the s t r a i n arms are at t h e i r maximum d e f l e c t i o n . By pushing back the arms to the zero s t r a i n p o s i t i o n and mounting a micrometer screw over each arm i n t u r n , the r e q u i r e d c a l i b r a t i o n was performed. The s t r a i n arm c a l i b r a t i o n was found to be l i n e a r w i t h very l i t t l e h y s t e r e s i s . The c a l i b r a t i o n f a c t o r s obtained i n t h i s way were introduced i n t o the data a c q u i s i t i o n system. D e t a i l s of the i n d i v i d u a l arm c a l i b r a t i o n s are given i n F i g . 3.15. The pressure transducers were c a l i b r a t e d by p l a c i n g the probe i n s i d e a c a l i b r a t i o n chamber and applying known increments of pressure. This was performed i n two ways: - i n f l a t i o n of the probe i n the empty chamber - i n f l a t i o n of the probe i n a w a t e r - f i l l e d chamber, where the water pressure could a l s o be v a r i e d . A l l pressure c a l i b r a t i o n s were performed using a dead weight t e s t e r . The pressure transducer c a l i b r a t i o n data are shown i n F i g . 3.15 and the f a c t o r s so-determined were a l s o i n c o r p o r a t e d i n t o the data a c q u i s i t i o n program. 79 400 1000-D CL 750 (0 <u I— 500 Q-T J <D as 250 2 I I I I I I I I I I I I I I I I ' SBPM pressure tranducer calibration : 16-10-89 Slope = 0.834 (Pressure applied external to membrane with lontern on) New cal. factor for effective stress transducer is equal to 0.834 x old factor = 0.351 i i | i i i i | i i i i_ \ i ' i i | i i i ' 250 500 750 1000 Applied pressure (kPa) 1250 F i g . 3.15 C a l i b r a t i o n data f o r s t r a i n arms and pressure transducers - SBPM. 80 I n s t a l l a t i o n Procedure P r i o r to i n s t a l l a t i o n i n the f i e l d , the transducer operation was checked and one-point c a l i b r a t i o n s performed. The f i l t e r used i n the e f f e c t i v e s t r e s s transducer was saturat e d under vacuum using g l y c e r i n . To o b t a i n a re g u l a r c y l i n d r i c a l shape of the membrane (with the same diameter as the probe), p i s t o n r i n g compressors were tightened over the l a n t e r n and l e f t i n place f o r 24 hours p r i o r to i n s t a l l a t i o n . The SBPM i s i n s t a l l e d i n a prebored hole which i s opened by pushing a lar g e diameter cone to a depth of about 2m - 3m. The probe i s assembled and connected to the DAS i n the f i e l d , at which time the p i s t o n r i n g compressors are removed and the e f f e c t i v e s t r e s s transducer c a v i t y s a t u r a t e d and the f i l t e r p o s i t i o n e d . With the probe suspended i n the prebored h o l e , b a s e l i n e readings are taken on a l l transducers. The s e l f - b o r i n g process then begins by f i r s t c i r c u l a t i n g d r i l l i n g mud u n t i l the prebored hole i s f i l l e d and the f l u i d e x i t s at the ground surface. A s y n t h e t i c d r i l l i n g mud (WDS120L) i s mixed at the surface and forced down the centre of standard cone rods by a h y d r a u l i c a l l y operated r o t a r y mud pump capable of achie v i n g pressures up to 2500 kPa. The cables e x i t i n g the SBPM are taped to the si d e of the pushing rods. The d r i l l i n g mud passes down the push rods and i s then channelled to the j e t s from a c e n t r a l j e t t i n g rod w i t h i n the PM body. I n i t i a l f i e l d t r i a l s w i t h the UBC SBPM were conducted w i t h the a s s i s t -ance of Dr. J.M.O. Hughes. The pushing f o r c e and r a t e of p e n e t r a t i o n were monitored and v a r i e d c ontinuously according to s o i l type. At p a r t i c u l a r depths, u s u a l l y at 0.5 m i n t e r v a l s , p e n e t r a t i o n was h a l t e d and the PM membrane expanded and then unloaded. 81 3.5.2 S e l f - B o r i n g Load C e l l (SBLC) The s e l f - b o r i n g load c e l l used during t h i s study was on loan from Dr. A.B. Huang (Clarkson U n i v e r s i t y , U.S.A.) who was i n v o l v e d i n the i n i t i a l t e s t s e r i e s . Subsequent t e s t s were performed by the w r i t e r . The SBLC i s the o r i g i n a l camkometer designed at Cambridge U n i v e r s i t y (Hughes, 1973) l a t e r described by Dalton and Hawkins (1982). The SBLC has a passive measuring system i n the sense t h a t i t does not have an expandable membrane. The probe i s f i t t e d w i t h two flush-mounted bending web load c e l l s (C and D) l o c a t e d on opposite sides of the probe near i t s midheight. The probe diameter i s 80.4 mm and the load c e l l s have a diameter of 44.4 mm. Deformation of the pressure c e l l s produces an e l e c t r i c a l output p r o p o r t i o n a l to the d i f f e r e n c e between the e x t e r n a l a p p l i e d pressure (on the c e l l surface) an the i n t e r n a l gas pressure which i s c o n t r o l l e d by a surface r e g u l a t o r . Two pore pressure sensors (A and B) are a l s o l o c a t e d at the midpoint of the probe inbetween the pressure c e l l s and these are a l s o referenced to the i n t e r n a l gas pressure. D e t a i l s of the probe are shown i n F i g . A.32 (Appendix A). The probe i s i n s t a l l e d by s e l f - b o r i n g using a c e n t r a l c u t t e r i n the shoe of the instrument and a c i r c u l a t i n g s l u r r y which removes the s o i l c u t t i n g s to the s u r f a ce. The same d r i l l i n g mud a d d i t i v e (WDS120L) was used as f o r the SBPM. The SBLC readings were taken i n voltages and then c o r r e c t e d i n spread-sheet f i l e s to provide data i n engineering u n i t s . I t was not p o s s i b l e to connect the probe d i r e c t l y to one of the UBC data a c q u i s i t i o n systems due to fundamental d i f f e r e n c e s i n system designs - the SBLC was o r i g i n a l l y designed i n the e a r l y 1970's. The channel ranges were 200 mV f u l l s c a l e f o r the pore pressure transducers and 10 V (amplified) f o r the s t r e s s c e l l s . For c a l i b r a -t i o n purposes, a s p e c i a l l y designed sleeve was placed over the probe which 82 could be p r e s s u r i z e d when connected to a pressure t e s t e r . The r e s u l t s given i n Table 3.4 were obtained from the l a b o r a t o r y c a l i b r a t i o n t e s t s . Only voltages from t o t a l s t r e s s transducers C and D were a m p l i f i e d . Table 3.4 C a l i b r a t i o n Data f o r SBLC Transducer Range C a l i b r a t i o n Constant Pore pressure A Pore pressure B T o t a l s t r e s s C T o t a l s t r e s s D 0-200 mV 0-200 mV ± 10V ± 10V 109.4 kPa/mV 118.6 kPa/mV 67.59 kPa/V 67.28 kPa/V The i n s t a l l a t i o n procedure f o r the probe was very s i m i l a r to that used f o r the SBPM except that a c u t t e r head w i t h c i r c u l a t i n g f l u i d was used i n s t e a d of simple j e t t i n g . Tests were performed at 0.5 m depth i n t e r v a l s . On reaching the p r e s c r i b e d depth, readings on a l l transducers were taken u n t i l e q u i l i b r i u m values were obtained. This u s u a l l y r e q u i r e d a wait of about 20 minutes. The r e s u l t s of the t e s t s are presented i n Chapter 5. 3.6 L a t e r a l Stress Oedometer 3.6.1 D e t a i l s of LS Oedometer The LS oedometer t e s t i s performed i n e x a c t l y the same way as a standard incremental t e s t except t h a t the oedometer r i n g i s now instrumented to measure hoop deformation. The c e n t r a l area of the r i n g has a reduced w a l l t hickness (0.5 mm) which i s gauged to measure hoop s t r a i n s i n the same way as does the l a t e r a l s t r e s s cone f r i c t i o n sleeve. By c a l i b r a t i o n , the hoop s t r a i n i s r e l a t e d to a t o t a l r a d i a l s t r e s s a c t i n g on the i n s i d e of the instrumented r i n g . A lo a d increment r a t i o of 1 was used f o r both loading and 83 unloading. Each t e s t comprised an i n i t i a l r e l o a d i n g phase, subsequent l o a d -in g under NC c o n d i t i o n s and then unloading. The v e r t i c a l load was a p p l i e d v i a a B e l l o f r a m a i r loading p i s t o n and measured using a c a l i b r a t e d load c e l l . Displacements were measured using a d i a l gauge i n d i c a t o r reading to 0.001 mm. A maximum v e r t i c a l s t r e s s of 1200 kPa was used during loading which was unloaded i n c r e m e n t a l l y to between 25 kPa and 50 kPa. Data f o r each load increment were recorded on a displacement-root time p l o t . Void r a t i o s at the end of 24 hours were used to p l o t the e-log r e l a t i o n s h i p s . 3.6.2 C a l i b r a t i o n of Transducers The c a l i b r a t i o n of the v e r t i c a l load c e l l was performed using a s t r a i n i n d i c a t o r box according to standard UBC p r a c t i c e and gave a c a l i b r a t i o n f a c t o r of 0.0327 kg/pe. The l a t e r a l s t r e s s , transducer was c a l i b r a t e d by s e a l i n g the i n s i d e area of the r i n g using an upper and lower p l a t e h e l d together by a c e n t r a l rod. The c e n t r a l rod was f i x e d to the lower p l a t e and passed through the upper p l a t e . A screw was l i g h t l y t i g h t e n e d against the top p l a t e to h o l d the p l a t e s against the oedometer r i n g . 0-rings s e a l s were l o c a t e d on both p l a t e s ( F i g . 3.16). A pressure l i n e was connected to the assembled u n i t and 5 p s i (34.47 kPa) increments were a p p l i e d . The output from the LS gauges was monitored i n terms of m i c r o s t r a i n (pe). A maximum c e l l pressure of 75 p s i (517.11 kPa) was a p p l i e d . M i c r o s t r a i n measurements were a l s o taken during unloading. The c a l i b r a t i o n pressures were monitored and a p p l i e d u s i n g a Druck DPI 600 d i g i t a l pressure i n d i c a t o r w i t h 300 p s i maximum, reading to 0.01 p s i . During the c a l i b r a t i o n i t became apparent t h a t the s t r a i n gauges would be s e n s i t i v e to a x i a l l o a d (the a x i a l load being simulated by t i g h t e n i n g the screw nut to var y i n g degrees) . In the t e s t s i t u a t i o n , the a x i a l load w i l l 84 F R O M A IR P R E S S U R E S U P P L Y S W A G E - L O C K C O N N E C T I O N P E R S P E X S L E E V E T O P R O T E C T > S T R A I N G A U G E S S C R E W N U T C A L I B R A T I O N T O P P L A T E O - R I N G S E A L S T R A I N - G A U G E D C E N T R A L R O D T H I N W A L L E D S E C T I O N O N O E D O M E T E R R I N G C A L I B R A T I O N B O T T O M P L A T E Fig. 3.16 LS oedometer with top and bottom plates for c a l i b r a t i o n of s t r a i n gauges. result from shear along the s o i l - r i n g interface as the sample compresses. The nonlinearity of the a x i a l load response of the LS transducers i s shown i n Fig. 3.17. The c a l i b r a t i o n i n terms of load was obtained by placing weights on the top of the oedometer ring and monitoring the LS gauge output. As suggested e a r l i e r , i t i s also possible to apply an a x i a l load by tightening the screw nut of the c a l i b r a t i o n unit. This produces a ue baseline s h i f t on the LS transducers but no actual load estimate i s possible. The effect of varying the a x i a l load by screw tightening i s i l l u s t r a t e d i n Fig. 3.18. It appears that the effect of a x i a l load on the LS transducer i s such that i t not only causes a baseline s h i f t but also a change i n c a l i b r a t i o n 85 CO 1100 1080-1060-1040-1020-1000H o 980 4 °°, 960-940-920-900 Unloading Loading Axial load calibration LS oedometer i—i—i—i—i—i—i—i—i—i i i i i i 0 5 10 15 Axial Load (kg) i — i — r 20 F i g . 3.17 Nonlinear response of l a t e r a l s t r e s s transducers to a x i a l loading. f a c t o r . The b a s e l i n e s h i f t s i n F i g . 3.18 of 78 pe, 400 pe, and 777 ue, a r i s e from t i g h t e n i n g the screw nut that holds the upper and lower c a l i b r a t i o n p l a t e s i n p o s i t i o n . I t appears that a change i n the c a l i b r a t i o n f a c t o r only occurs once a b a s e l i n e s h i f t of around 400 pe occurs. This e f f e c t w i l l have to be considered when i n t e r p r e t i n g the r e s u l t s obtained. D e t a i l s of the t e s t s performed and f i n a l r e s u l t s are given i n Chapter 5. 3500 100 Applied pressure (psi) Fig. 3.18 Effect of a x i a l load on c a l i b r a t i o n characteristics of LS transducers. 87 CHAPTER 4 4. GEOLOGICAL AND GEOTECHNICAL CHARACTERISTICS OF RESEARCH SITES 4.1 I n t r o d u c t i o n The i n s i t u t e s t equipment described i n Chapter 3 has been u t i l i z e d at s e v e r a l research s i t e s i n the Lower Mainland of B r i t i s h Columbia where the s o i l s are s u i t a b l e f o r i n s i t u t e s t i n g . The f i v e main research s i t e s l i s t e d i n Table 4.1 provided t e s t data i n s o i l s ranging from s o f t NC c l a y s to sands and s t i f f OC c l a y s and s i l t s . A d d i t i o n a l data from other UBC research s i t e s have been used to supplement the main data. The l o c a t i o n of a l l the UBC research s i t e s i s shown on F i g . 4.1. A d e s c r i p t i o n of the g e o l o g i c a l and d e p o s i t i o n environment f o r each research Table 4.1 Research S i t e s f o r In S i t u Measurement of L a t e r a l Stress S i t e A b b r e v i a t i o n Used i n Text L o c a t i o n S o i l Type McDonald Farm MDF Sea I s l a n d , Richmond Sand & s o f t c l a y s i l t Laing Bridge South LBS Sea I s l a n d , Richmond Sand & s o f t c l a y s i l t Lower 232nd S t r e e t L r . 232 St. Langley Soft to f i r m NC & OC clayey s i l t (overcon-s o l i d a t i o n p r i n c i p a l l y due to d e s s i c a t i o n ) Strong P i t STR Aldergrove Firm to s t i f f OC clayey s i l t (overcon-s o l i d a t i o n due to unloading 200th S t r e e t -#88th Ave. 200th St. Langley Soft to s t i f f NC & OC clayey s i l t (overcon-s o l i d a t i o n due to minor unloading and d e s s i c a t i o n Figure 4.1 Location of UBC geotechnical research s i t e s . 89 area i s given below followed by d e t a i l e d s i t e i n f o r m a t i o n i n terms of s o i l s present and b a s i c geotechnical parameters. The t e s t i n g programme performed at each s i t e i s a l s o described. 4.2 G e o l o g i c a l H i s t o r y of the Lower Mainland The g e o l o g i c a l h i s t o r y of the Lower Mainland has been s t u d i e d by Blunden (1973) and Clague and Luternauer (1982). The Fraser R i v e r e s s e n t i a l l y c o n t r o l s the d e p o s i t i o n environments throughout the r e g i o n . The s u r f i c i a l d eposits of the lowland are of Quarternary age and a t t a i n thicknesses of up to 300 m, o v e r l y i n g P l e i s t o c e n e g l a c i a l deposits and T e r t i a r y freshwater sediments. The Quarternary s o i l s were deposited during periods of the l a s t g l a c i a t i o n being i n f l u e n c e d a l s o by the contemporaneous i s o s t a t i c and e u s t a t i c f l u c t u a t i o n s . As a consequence of the complex d e p o s i t i o n e n v i r o n -ment, the sediment types range from g l a c i a l to d e l t a i c and demonstrate considerable h e t e r o g e i e t y both l a t e r a l l y and v e r t i c a l l y . The development of the Fraser River d e l t a began about 11,000 years ago once the i c e had r e t r e a t e d from the area. At t h i s time the present l o c a t i o n of Richmond was some 40 km out to sea and subject to d e p o s i t i o n of f i n e sediments discharged i n t o the sea by the Fraser R i v e r . Due to the l a r g e volume of sediments s u p p l i e d to the r i v e r by the r e t r e a t i n g i c e sheet, the d e l t a expanded r a p i d l y and a t t a i n e d i t s almost present p o s i t i o n about 5,000 years ago. Continued development was slowed by an 11 m r i s e i n sea l e v e l . The Richmond area was now only 10 km out to sea and s l i g h t l y coarser s e d i -ments were being deposited. Between 5,000 years ago and the present the d e l t a grew to i t s present p o s i t i o n as the sea rose a f u r t h e r metre. As the d e l t a f r o n t approached Richmond sands were deposited over the f i n e r grained c l a y s and s i l t s . Recent s i l t and c l a y overbank deposits were deposited 90 during annual f l o o d i n g of the r i v e r as d e l t a growth continued. The d e l t a i s s t i l l growing at rat e s of between 2.5 ra/yr and 8.5 ra/yr (depending on the depth of water). Being p o s t - g l a c i a l , the Holocene s o i l s have not been i c e - l o a d e d and are g e n e r a l l y normally c o n s o l i d a t e d . The g e n e r a l i z e d s o i l p r o f i l e f o r the low-land area c o n s i s t s of f i n e grained marine sediments o v e r l a i n by granular marine, d e l t a i c and t i d a l f l a t deposits and then by f i n e overbank deposits ( W a l l i s , 1979). To the east of the Fraser River d e l t a i s the upland area where the Langley-Cloverdale b a s i n i s l o c a t e d . The sediments are P l e i s t o c e n e g l a c i a l and p o s t - g l a c i a l . The e a r l i e r g l a c i a l deposits c o n s i s t s of dense sands and gr a v e l s . The o v e r l y i n g p o s t - g l a c i a l sediments have a glaciomarine o r i g i n having been deposited during a p e r i o d when the Fraser R i v e r became dammed by i c e . The s o f t c l a y s i l t s are known l o c a l l y as Capilano or Fort Langley sediments. Horizons of interbedded sand are common throughout, the frequency of which dies out towards the west. 4.3 Laing Bridge South, Richmond 4.3.1 S i t e D e s c r i p t i o n The s i t e i s l o c a t e d on the east s i d e of Sea I s l a n d ( F i g . 4.1) and i s reached by means of the Arthur Laing Bridge to the nort h . The s i t e i s bounded to the north and east by McConachie Way overpass and by A i r p o r t Way to the south and west ( F i g . 4.2). The s i t e i s approximately 340 m long and 70 m wide and reasonably l e v e l . An average slope of 0.5° dipping to the northwest was measured. Surface drainage features on the s i t e are v i s i b l e . A main drainage d i t c h which runs p a r a l l e l to A i r p o r t Way suggested a groundwater l e v e l about 1.2 m below 91 ground surface. The ground i s covered by low grass. The study area had p r e v i o u s l y been p a r t of the land i n c o r p o r a t e d f o r the c o n s t r u c t i o n of McConachie Way overpass and has a regraded surface r e l i e f w i t h p o s s i b l e f i l l placement. 92 Overbank deposits w i t h some f i l l comprise the s u r f i c i a l s o i l s to a depth of 2 m which are u n d e r l a i n by 18 m of f i n e to medium sand. At 20 m a t r a n s i -t i o n to a s o f t normally c o n s o l i d a t e d c l a y s i l t begins. The s i l t a t t a i n s thicknesses of 40 m to 45 m at t h i s l o c a t i o n (Le C l a i r , 1988). 4.3.2 Tes t i n g Programme Two t e s t areas are i n d i c a t e d on F i g . 4.2. The t e s t i n g programme at each l o c a t i o n i s o u t l i n e d i n Table 4,2. The legend used to denote each p a r t i c u l a r t e s t i s i n d i c a t e d i n Table 4.3 and the layout of the t e s t s at each l o c a t i o n i s shown i n F i g . 4.3, Table 4.2 T e s t i n g Programme at Laing Bridge South Test Performed/Equipment I n s t a l l e d Date Designation Comments Test Area 1 Hogentogler CPTU, u 2 to 29.7m UBC #7, U j &. u 2 to 29.7m Dilatometer (#89) to 21m Dilatometer (#74) to 29.8m Dutch sampler to 4.75m SPT i n hollow stem auger to 23.7m Seismic CPTU, UBC #7, u 2 & u 3 to 17, UBC Seismic cone pressuremeter to 7, 9m Om UBC Seismic cone pressuremeter to 14m Dilatometer (#74) to 19.2m L a t e r a l s t r e s s cone to 23.5m 24/09/87 C87--LBS2 24/09/87 C87--LBS3 28/09/87 D87--LBS1 01/10/87 D87--LBS2 08/10/87 S87- -LBS1 08/10/87 SPT--LBS1 15/10/87 C87--LBS4 05/11/87 SCPMLBS1 04/12/87 SCPMLBS2 31/08/87 D88--LBS3 05/09/87 LBS- -LBS1 Subsquent t e s t by Howie (1987) U 2 « U 3 - U L S Test Area 2 Seismic CPTU, UBC #7, u 1 &. u 3 to 20m L a t e r a l s t r e s s cone to 25.90m S e l f - b o r i n g load c e l l to 6.5m S e l f - b o r i n g load c e l l to 5.5m S e l f - b o r i n g load c e l l to 8.5m Sesmic CPTU, UBC #7 to 20m Seismic CPTU, UBC #7 &. #8 to 10m 19/09/88 20/07/89 23/07/90 24/07/90 27/07/90 21/08/90 22/08/90 C88-LBS5 LS2-LBS CAM1-LBS CAM2-LBS CAM3-LBS C90-LBS6 C90-LBS7 u„ u 3 » U L S Downhole and crosshole 93 Table A.3 Legend f o r Test i n g Programme at Research S i t e s Symbol Test Performed o CPTU ( i n c l u d i n g seismic CPTU) DMT (arrow i n d i c a t e s d i r e c t i o n of membrane) • LS-CPTU (using UBC equipment) IS LS-CPTU (using UCB equipment) • SBPM ® SBLC • D e l f t or Swedish sampler + Seismic cone pressuremeter t e s t (SCPMT) 9 Screw p l a t e t e s t X FVT TSC (long a x i s denotes o r i e n t a t i o n of blade) © R e s i s t i v i t y cone BAT probes oo-o Crosshole and downhole seismic CPTU (3 soundings D r i l l h o l e w i t h SPT ( c a l i b r a t e d hammer) A j Dynamic cone 4.3.3 Geotechnical C h a r a c t e r i s t i c s Based on the r e s u l t s of the i n i t i a l i n s i t u and l a b o r a t o r y t e s t s performed, the index p r o p e r t i e s and b a s i c geotechnical parameters have been defined. These are b r i e f l y presented here and w i l l be used l a t e r f o r i n t e r p r e t a t i o n of the more s o p h i s t i c a t e d i n s i t u t e s t s c a r r i e d out. TO LAMP STANDARD N I5.8m TO CULVERT TEST AREA 1 X N I 2 3 ® ® ® T E S T A R E A 2 T V v v 7-+