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Strain rate behaviour of Saint-Jean-Vianney clay Robertson, Peter K. 1975

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STRAIN RATE BEHAVIOUR OF SAINT - JEAN - VIANNEY CLAY by PETER K. ROBERTSON B . S c , U n i v e r s i t y of Nottingham, 1972. A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE i n the Department of CIVIL 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 May, 1975. In presenting th i s thes i s in pa r t i a l fu l f i lment of the requirements fo r an advanced degree at the Un ivers i ty of B r i t i s h Columbia, I agree that the L ibrary sha l l make i t f r e e l y ava i l ab le for reference and study. I fur ther agree that permission for extensive copying of t h i s thes i s for scho lar ly purposes may be granted by the Head of my Department or by his representat ives. It i s understood that copying or pub l i ca t i on of th i s thes i s f o r f i nanc ia l gain sha l l not be allowed without my wr i t ten permiss ion. Department of CIVIL L x IG l^EFKlIva. The Univers i ty of B r i t i s h Columbia Vancouver 8, Canada Date A p r i l 1975 ABSTRACT A s e r i e s of constant r a t e of s t r a i n compression t e s t s and creep rupture t e s t s have been performed on undisturbed, i s o t r o p i c a l l y c o n s o l i d a t e d quick c l a y from the Saint-Jean-Vianney regi o n , Quebec Province, Canada. Both drained and undrained t e s t s were performed i n conventional t r i a x i a l equipment. A l s o included i s the data obtained from a s e r i e s of Ko c o n s o l i d a t i o n t e s t s performed by Dr.Y.P.Vaid at U.B.C. Saint-Jean-Vianney c l a y , h e r e a f t e r r e f e r r e d t o as S.J.V. c l a y , i s a s t i f f , h e a v i l y overconsolidated, cemented c l a y , from the s i t e of the Saint-Jean-Vianney s l i d e of 1971. The t e s t i n g of t h i s , very s t i f f , cemented c l a y proved to be very d i f f i c u l t due t o i t ' s very s t i f f and b r i t t l e nature, combined with i t ' s lenses of s i l t and f i n e sand. The c o n s o l i d a t i o n t e s t i n g showed tha t the p r e c o n s o l i d a t i o n pressure could vary from 7.5 Kg/cm to 12 Kg/cm depending on the s t r a i n r a t e of the t e s t . Snead (1970) and Campanella and Vaid (1972) performed s i m i l a r creep t e s t s on a l o c a l c l a y , known as Haney c l a y . The a n a l y s i s of the creep tests:performed on S.J.V. c l a y showed s i m i l a r r e l a t i o n s h i p s to those reported by Snead and, Campanella and Vaid, but because of the extremely s t i f f nature of t h i s c l a y the s c a t t e r i i i o f "th*2* resu 1 t s was more than- -that renor-ted f o r Haney c l a y . The t e s t i n g i n d i c a t e d a p o s s i b l e s t r e s s - s t r a i n -s t r a i n r a t e r e l a t i o n s h i p mav e x i s t a l o n ^ w i t h a nossxble d r a i n e d f a i l u r e c r i t e r i o n . The r e s u l t s o b t a i n e d fror" t h i s r e s e a r c h were very dependant on the bonding of t h i s c l a y , and i n d i c a t e that the bond s t r e n g t h appears to be a f u n c t i o n of s t r a i n r a t e , i v TABLE OF CONTENTS CHAPTER Page 1 INTRODUCTION 1.1 I n t r o d u c t i o n 1 1 .2 Review of L i t e r a t u r e 2 Creep and Creep Rupture 2 Quick Clays of Eastern 10 1 .3 Scope 18 2 LABORATORY TESTING 2.1 D e s c r i p t i o n of S o i l Tested 21 2 . 2 D e s c r i p t i o n of Apparatus 23 2 . 3 Experimental Proceedure 25 Sample P r e p a r a t i o n 25 Constant Rate of S t r a i n Compression Tests 26 Creep Tests 27 3 EFFECTS OF STRAIN RATE ON CONSOLIDATION 30 4 RESULTS AND DISCUSSION OF CONSTANT RATE OF STRAIN COMPRESSION TESTS 4 . 1 Undrained Constant ra t e of S t r a i n Compression Tests 3^ 4 . 2 Drained Constant Rate of S t r a i n Compression Tests J ^Q CHAPTER Page 5 RESULTS AND DISCUSSION OF CREEP TESTS 5.1 Undrained Creep Tests 52 5 . 2 Drained Creep Tests 61 5 . 3 S t r e s s - S t r a i n - S t r a i n Rate R e l a t i o n s 65 5 . 4 E f f e c t i v e S t r e s s Conditions 70 6 SUMMARY AND CONCLUSIONS 73 BIBLIOGRAPHY 75 APPENDIX I C a l c u l a t i o n of S t r a i n Rates 78 I I Sketches of F a i l e d Samples 80 LIST OF TABLES. v i Table Page I P h y s i c a l p r o p e r t i e s of undisturbed S.J.V. c l a y . 22 I I Summary of t e s t i n f o r m a t i o n f o r s t r a i n c o n t r o l l e d compression t e s t s . 2 8 I I I Summary of t e s t i n f o r m a t i o n f o r the creep t e s t s . 29 IV Summary of r e s u l t s of s t r a i n c o n t r o l l e d compression t e s t s . 51 V Summary of r e s u l t s of creep t e s t s . 66 V l l LIST OF FIGURES. Figure Page 1. A t y p i c a l s t r a i n - t i m e curve f o r normally c o n s o l i d a t e d Haney c l a y under sustained d e v i a t o r s t r e s s . ( A f t e r Snead, 1970) 4 2 . Logarithm of a x i a l s t r a i n r a t e versus Log. elapsed time f o r normally con-s o l i d a t e d undrained creep t e s t s on Haney c l a y . ( A f t e r Snead, 1970) 5 3. Minimum s t r a i n r a t e against t o t a l rupture l i f e . ( A f t e r Snead, 1970) 7 4 . R e l a t i o n s h i p between time to rupture and current s t r a i n r a t e . ( A f t e r Snead, 1970) 9 5. E f f e c t i v e s t r e s s c o n d i t i o n s at creep rupture and minimum creep r a t e . ( A f t e r Campanella & Va i d , 1972) 11 6. Area of Eastern Canada where Leda c l a y i s found. 13 7 . Schematic of the development of cementation bonds and f r i c t i o n a l strengths and the observed composite shapes. ( A f t e r Conlon, I 9 6 6 ) 15 v i i i F i g ure Page 8. T y p i c a l Mohr-Coulomb p l o t f o r con-s o l i d a t e d drained t r i a x i a l t e s t s on Leda c l a y . ( A f t e r Conlon ,1966) ^ 9. T y p i c a l compression l o g pressure curves f o r various r a t e s of l o a d i n g . ( A f t e r Crawford, 196?) l g 10. Schematic layout of lo a d i n g , d i s -placement, pressure and volume change measuring system. 24 11. Change i n v o i d r a t i o against v e r t i c a l e f f e c t i v e s t r e s s f o r Ko c o n s o l i d a t i o n t e s t s on undisturbed S.J.V. Clay at .;•„',:".: c..r:.:, d i f f e r e n t s t r a i n r a t e s . -^ 1 12. P l o t of the c o e f f i c i e n t of c o n s o l i d a t i o n against v e r t i c a l e f f e c t i v e s t r e s s f o r Ko c o n s o l i d a t i o n t e s t s on undisturbed S.J.V. c l a y at d i f f e r e n t s t r a i n r a t e s . -33 13. I s o t r o p i c t r i a x i a l constant r a t e of s t r a i n undrained t e s t s on top l a y e r of undisturbed S.J.V. c l a y . ^5 14. Change i n pore pressure during constant r a t e of s t r a i n undrained, undrained compression t e s t s on top l a y e r of undisurbed S.J.V. c l a y . ^5 IX F i g u r e Page 15. I s o t r o p i c t r i a x i a l constant r a t e of s t r a i n undrained t e s t s on lower l a y e r of undisturbed S.J.V. c l a y . JQ 16. Change i n pore pressure during constant r a t e of s t r a i n , undrained compression t e s t s on lower l a y e r of undisturbed S.J.V. c l a y . 39 17. I s o t r o p i c t r i a x i a l constant r a t e of s t r a i n drained t e s t on undisturbed S.J.V. c l a y . 2^ 18. Volumetric s t r a i n d u r i n g constant r a t e of s t r a i n drained t e s t on undisturbed S.J.V. c l a y . i±2 19. I s o t r o p i c t r i a x i a l constant r a t e of s t r a i n undrained/drained t e s t on undisturbed S.J.V. c l a y . 44 20. Volumetric s t r a i n and change i n pore pressure during undrained/drained t e s t on undisturbed S.J.V. c l a y . 45 21. Comparision between drained and undrained i s o t r o p i c t r i a x i a l constant r a t e of s t r a i n t e s t s on undisturbed S.J.V. c l a y . 45 X F i g u r e Page 2 2 . T y p i c a l s t r e s s path f o r s t r a i n c o n t r o l l e d undrained compression t e s t s . 48 2 3 . E f f e c t i v e s t r e s s c o n d i t i o n f o r s t r a i n c o n t r o l l e d compression t e s t s at peak and f i n a l d e v i a t o r c o n d i t i o n s . 49 24. Creep r a t e behaviour f o r i s o t r o p i c a l l y c o n s o l i d a t e d , undisturbed S.J.V. c l a y under symmetric l o a d i n g . 53 2 5 . R e l a t i o n s h i p between rupture l i f e and minimum creep r a t e f o r i s o t r o p i c a l l y c o n s o l i d a t e d undisturbed S.J.V. c l a y . 55 2 6 . R e l a t i o n s h i p between minimum creep r a t e and remaining time to rupture f o r i s o t r o p i c a l l y c o n s o l i d a t e d undisturbed S.J.V. c l a y . 56 2 7 . Some t y p i c a l curves f o r T e r i a r y creep r a t e a g a i n s t remaining time t o ruptu r e , t t r , f o r i s o t r o p i c a l l y c o n s o l i d a t e d undisturbed S.J.V. c l a y . 58 28. R e l a t i o n s h i p between minimum creep r a t e and s t r e s s l e v e l f o r both l a y e r s of the block sample of S.J.V. c l a y . 59 X I 60 62 Figure Page 2 9 . R e l a t i o n s h i p between peak d e v i a t o r s t r e s s and s t r a i n r a t e f o r undrained s t r a i n c o n t r o l l e d t e s t s on both l a y e r s of the block sample of S.J.V. c l a y . 3 0 . V a r i a t i o n of creep stren g t h w i t h time to rupture f o r i s o t r o p i c a l l y con-s o l i d a t e d S.J.V. c l a y . 3 1 . Creep r a t e behaviour f o r i s o t r o p i c a l l y c o n s o l i d a t e d drained creep t e s t s on undisturbed S.J.V. c l a y . 3 2 . R e l a t i o n s h i p between s t r a i n r a t e and s t r a i n f o r some of the undrained S.J.V. c l a y . 3 3 . Comparison of observed s t r e s s - s t r a i n behaviour i n undrained constant s t r a i n r a t e compression t e s t s w i t h t h a t p r e d i c t e d from undrained creep t e s t s . 69 3 4 . E f f e c t i v e s t r e s s c o n d i t i o n s a t minimum creep r a t e f o r the undrained creep t e s t s on undisturbed S.J.V. c l a y . 71 64 67 x i i LIST OF SYMBOLS ^ 1 , 2 , 3 P r i n c i p a l t o t a l s t r e s s e s °"'l,2,3 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 Ko C o e f f i c i e n t of earth pressure at r e s t D e v i a t o r s t r e s s (crj - cr^) t Elapsed time t m Time to minimum s t r a i n r a t e t r T o t a l rupture l i f e t t r Time t o rupture £ s Secondary creep s t r a i n r a t e km Minimum s t r a i n r a t e tr Shear s t r e s s cr' E f f e c t i v e s t r e s s *1 Time t o f a i l u r e c V C o e f f i c i e n t of c o n s o l i d a t i o n u Pore pressure A & B Skempton's pore pressure parameters A f Pore pressure parameter at f a i l u r e x i i i ACKNOWLEDGEMENTS The w r i t e r would l i k e to thank h i s research s u p e r v i s o r , Dr.R.G. Campanella f o r h i s guidance during t h i s research. He f u r t h e r wishes t o express h i s a p p r e c i a t i o n to Dr.P.M. Byrne f o r h i s va l u a b l e suggestions. The w r i t e r a l s o wishes t o express h i s g r a t i t u d e t o Dr.Y.P. Vaid f o r h i s continued i n t e r e s t and advice throughout t h i s research. 1 CHAPTER 1 INTRODUCTION 1.1 I n t r o d u c t i o n . At present, 1975 , L i m i t Design i s used f o r most s o i l mechanics problems i n v o l v i n g the s t r e n g t h and s t a b i l i t y of slopes. Although p r o v i d i n g a means f o r design against t o t a l c o l l a p s e , i t does not estimate the magnitude of a n t i c i p a t e d deformations, e s p e c i a l l y w i t h respect to time. The i n f l u e n c e of time on s t r e s s / s t r a i n r e l a t i o n s has been observed under f i e l d c o n d i t i o n s by many, i n c l u d i n g H a e f e l i ( 1953)• S a i t o and Uezawa (1961) and S u k l j e ( 1 961 ) . They r e p o r t c o n t i n u a l movements t a k i n g place i n n a t u r a l slopes i n which the t o t a l s t r e s s e s are remaining n e a r l y constant. These time dependent shearing deformations have given the engineer many d i f f i c u l t i e s as he i s unable to p r e d i c t r e l i a b l y the long term behaviour. This problem i s p a r t i c u l a r y true of slopes i n the very s e n s i t i v e c l a y s of Eastern Canada. Such s l i d e s as the one t h a t occurred a t S a i n t - Jean - Vianney, Quebec, on May 4 t h , 1971. where an estimated 9x10 cubic yards of m a t e r i a l moved from an area of approximately 3 5 0 , 0 0 0 square yards, Tavenas ( 1 971 ) . 2 With the a v a i l a b i l i t y of a block sample from t h i s a c t u a l s l i d e s i t e , i t was f e l t there was an i d e a l oppurtunity f o r anc'-investigation i n t o the s t r a i n r a t e behaviour of t h i s very s t i f f , very s e n s i t i v e , h e a v i l y over c o n s o l i d a t e d c l a y . 1.2 Review of L i t e r a t u r e . T h i s l i t e r a t u r e review w i l l present the p e r t i n e n t i n f o r m a t i o n on creep and creep rupture and al s o a general review of the c h a r a c t e r i s t i c s of the very s e n s i t i v e c l a y s of eastern Canada. Creep and Creep Rupture. Casagrande and Wilson (195D have shown that some types of b r i t t l e undisturbed c l a y s and c l a y shales continuously deform under sustained l o a d , and t h a t f a i l u r e u l t i m a t e l y occurs under a sustained load a p p r e c i a b l y l e s s than the s t r e n g t h i n d i c a t e d by a normal undrained compression t e s t . V i a l o r and S k i b i t s h y (1957) i n v e s t i g a t e d the e f f e c t of creep i n f r o z e n s o i l s and showed the existence of a upper y i e l d s t r e n g t h defined as the maxium sustained shearing s t r e s s which would not cause f a i l u r e w i t h time. Snead (1970) performed creep t e s t s on a undrained normally c o n s o l i d a t e d undisturbed s e n s i t i v e c l a y , c a l l e d Haney c l a y , u s i n g the conventional t r i a x i a l apparatus. A t y p i c a l s t r a i n time curve i s 3 given i n F i g . l . He observed that the s t r a i n rate i n i t i a l l y decreased, reached a minimum, and then increased gradually proceeding to rupture. He could not f i n d a stage when the s t r a i n rate was constant, as found f o r metal, concrete and p l a s t i c . Snead concluded that once a minimum s t r a i n rate i s reached, the sample w i l l eventually rupture and f a i l u r e can be considered to have occurred. He also confirmed the existence of an upper y i e l d strength. Snead (1970) obtained a log log pl o t of s t r a i n rate and time, as shown i n F i g . 2, by performing a series of creep rupture tests with d i f f e r e n t sustained shearing stresses using the conventional t r i a x i a l apparatus. A l l the samples were i s o t r o p i c a l l y con-solidated to anC.effective stress of 75 p s i (approximately 5 .25 Kg/cm ). Figure 2 shows that f o r deviator creep stresses greater thn 43.4 p s i , the s t r a i n rate i n i t i a l l y decreased, reached a minimum then increased rapidly proceeding to rupture. For the sample with a deviator stress of 42.8 p s i the curve appears to be proceeding towards the l i n e of minimum s t r a i n rates but changes i t s course and continues p a r a l l e l to the l i n e of minimum s t r a i n rates. Thus i t would appear that the stress l e v e l of 42.8 p s i was below the upper y i e l d strength of that sample. Snead used the existence of a minimum s t r a i n rate as a f a i l u r e c r i t e r i o n , since i f a AXIAL STRAIN PERCENT TT S I K o /* JO i i 0 o m o ?-0 < TV P f> IA 3 2 L m s r\ * 3 H I r. 3! AXIAL STRAIN RATE (% / W j o p r 31 < 7-o ? 3 o 2 o ?-3 0 -D o • o 1-v 3 o •n r o1 -I *1 2. r O m 1 2 o o 4 b m m Co o T i c 5 S3 m 6 sample reached a minimum s t r a i n r a t e the sample would e v e n t u a l l y rupture. S a i t o and Uezawa (1961) performed t r i a x i a l compression t e s t s on fo u r Japanese s o i l s and proposed a l i n e a r r e l a t i o n s h i p between the l o g of secondary s t r a i n r a t e and the l o g ; o f the t o t a l time t o rupture. Snead (1970) found t h a t a secondary creep stage d i d not e x i s t f o r Haney c l a y , and suggested t h a t the secondary s t r a i n r a t e measured by S a i t o and Uezawa was approximately equal t o the minimum s t r a i n r a t e c a l c u l a t e d by him. Snead a l s o found t h a t a l i n e a r r e l a t i o n s h i p e x i s t e d between the l o g of minimum s t r a i n r a t e "£ . " and the ° mm t o t a l rupture l i f e " t ". Snead and S a i t o ' s r e s u l t are shown on Figur e 3« S a i t o and Uezawa proposed that the • r e l a t i o n s h i p between " t " and " ^ m £ n " i s unique f o r a l l s o i l s , whereas Snead suggested the r e l a t i o n s h i p was s i m i l a r f o r other s o i l s but not n e c e s s a r i l y unique f o r a l l s o i l s . S a i t o used t h i s r e l a t i o n s h i p t o p r e d i c t the occurrence of time to slope f a i l u r e s i n 19&5 w i t h reasonable accuracy. Snead on the other hand proposed a method of p r e d i c t i n g the time t o slope f a i l u r e f o r t e r t i a r y creep stage. Snead (1970) defined the "time to rupture" as the elapsed time from the i n s t a n t considered u n t i l f a i l u r e and obtained a l i n e a r r e l a t i o n -ship between l o g of time t o rupture " t t " and curren t 8 s t r a i n r a t e , "£", as shown i n F i g u r e . 4 . S a i t o ( I 9 6 9 ) a l s o proposed a method f o r p r e d i c t i n g slope f a i l u r e during t e r t i a r y creep. I n t h i s method he assumed a r e l a t i o n s h i p between " t t " and "£" s i m i l a r to Figure 4 , to o b t a i n an expression f o r s t r a i n by mathematical i n t e r g r a t i o n . He found reasonable agreement between the p r e d i c t e d and observed time of occurrence of slope f a i l u r e . Campanella and Vaid (1972 and 1973) t e s t e d Haney c l a y under constant shear s t r e s s i n ; Ko c o n s o l i d a t e d t r i a x i a l , i s o t r o p i c a l l y c o n s o l i d a t e d t r i a x i a l and Ko c o n s o l i d a t e d plane s t r a i n . I n comparing the r e s u l t s they found t h a t the general shapes of the curves found by Snead were repeated but were s h i f t e d s l i g h t l y . They found t h a t the conventional i s o t r o p i c t r i a x i a l t e s t would give an unconservative estimate of rupture l i f e or remaining time t o rupture by a f a c t o r of about 4 , i f the r e a l s i t u a t i o n corresponded t o Ko c o n s o l i d a t i o n or plane s t r a i n . Snead (1970) and Campanella and Vaid (1972) both found a unique r e l a t i o n s h i p between s t r e s s , s t r a i n and s t r a i n r a t e , s i m i l a r t o t h a t found by Lubahn and F e l g a r , ( I 9 6 I ) f o r metals. Both r e s t r i c t e d i t s use to samples t e s t e d undrained at constant temperature f o r c o n t i n u a l l y i n c r e a s i n g compressive a x i a l s t r a i n s , and not h e a v i l y overconsolidated. This r e l a t i o n s h i p means that creep t e s t curves can he obtained from s t r e s s -s t r a i n curves at d i f f e r e n t s t r a i n r a t e s i f the samples have the same c o n s o l i d a t i o n h i s t o r y , thus creep t e s t s and constant s t r a i n r a t e t e s t s are complementary to each other f o r o b t a i n i n g s t r e s s - s t r a i n - time p r o p e r t i e s . Campanella and Vaid (1972) analyzed the r e s u l t s of t h e i r creep rupture t e s t s i n terms bf e f f e c t i v e s t r e s s e s . They obtained the same l i n e a r f a i l u r e envelope f o r both creep rupture and f a i l u r e i n con-v e n t i o n a l s t r a i n r a t e undrained t e s t s . This p l o t i s shown i n Figure 5. From t h i s they could assume that the r h e o l o g i c a l component of shear r e s i s t a n c e appeared to be n e g l i g i b l e f o r t h a t s o i l . The e f f e c t i v e s t r e s s c o n d i t i o n at the i n s t a n t when the creep r a t e s t a r t e d t o increase was a l s o shown on F i g u r e 5. and a l i n e a r envelope passing through the o r i g i n appears t o define t h i s onset of i n s t a b i l i t y . This envelope of minimum s t r a i n r a t e s occurs at a lower shearing r e s i s t a n c e than t h a t defined by creep rupture and since a l l samples which reach t h i s s t r e s s e v e n t u a l l y f a i l , Campanella and Vaid f e l t i t was more appropriate to use the envelope defined by the minimum creep r a t e s as a f a i l u r e c r i t e r i o n . Quick Clay of Eastern Canada. These c l a y s are commonly found i n the v a l l e y s CfKSGP RATE. (ftFTETZ. <Lfirt*PAfj£LLfit V*ib; AVERAGE FROM CON TESTS ~ -FAILURE EN 1VENTI0NAL IVELOPE SHEAR ^^^^ * LINE ^ — + CREEP • MINIMI RUPTURE DATA M CREEP RATE DATA 1 1 1 2 3 4 5 6 12 of the St. Lawrence and Ottawa R i v e r s i n eastern Canada, as shown i n Fig u r e 6 . I t ' s g e n e r a l l y agreed t h a t they were deposited i n a marine or b r a c k i s h environment during a b r i e f post - g l a c i a l p e r i o d of i s o s t a t i c depression and marine i n v a s i o n . Most of these c l a y s now have a low pore water s a l t c o n c e n t r a t i o n of l e s s than 2 g / l which would i n d i c a t e t h a t much of the s a l t water has been leached away by p e r c u l a t i n g f r e s h ground water. Recent work by Gadd (1962) suggests t h a t the c l a y may have f i r s t been deposited i n a marine environ-ment then the land rose and the c l a y s were redeposited i n t o f r e s h water. I f t h i s were so, some e x p l a i n a t i o n must be found f o r t h e i r open s t r u c t u r e and s e n s i t i v i t y . Crawford (1967) proposed t h a t the s t r u c t u r e may have been due to f l o c c u l a t i o n caused by r e s i d u a l c a t i o n s remaining even a f t e r washing by the f r e s h water. The s e n s i t i v e f i n e - grained sediments of t h i s area are normally c a l l e d "Leda" c l a y i n engineering l i t e r a t u r e . The Leda c l a y s , l i k e other s e n s i t i v e c l a y s , are thought to have a card house f a b r i c because of t h e i r environment during d e p o s i t i o n . The s t a b i l i t y of such a very open s t r u c t u r a l arrangement i s p a r t l y governed by the geometry of the arrangement and p a r t l y by the s t r e n g t h of the cohesive bonds at the i n t e r p a r t i c l e contact p o i n t s . The cohesive bonds are b a s i c a l l y due to two 13 types of bonding, one due to i o n i c and Van der Waals forces of a t t r a c t i o n and the other caused by cementing a c t i o n of chemical p r e c i p i t a t e s , mainly ferrous oxides and calcium carbonates. The p r i n c i p l e d i f f e r e n c e between the two types i s that during shearing the f i r s t type i s at l e a s t p a r t l y redeveloped when new contact p o i n t s are e s t a b l i s h e d , whereas the second type i s not. In a d d i t i o n to cohesive bonds a f r i c t i o n a l r e s i s t a n c e i s a v a i l a b l e at each load bearing contact. C.onion (1966) and Kenney and Bjerrum ( I 9 6 7 ) proposed an idea t h a t the combination of the cohesive bonds and the f r i c t i o n a l r e s i s t a n c e could e x p l a i n the unusual s t r e s s s t r a i n curves produced by these quick c l a y s , F i g u r e 7 . The mineral s k e l e t o n i s r e l a t i v e l y f l e x i b l e , so t h a t the deformation i s of an e l a s t i c nature up to a c e r t a i n " c r i t i c a l s t r e s s " , where the maximum r e s i s t a n c e of the s t r u c t u r a l arrangement i s reached. At t h i s p o i n t bonded contacts between p a r t i c l e s begin to f a i l throughout the s t r u c t u r e and i t s a b i l i t y t o r e s i s t shear s t r e s s e s i s g r e a t l y reduced, l e a d i n g t o a rearrangement of p a r t i c l e s t o c a r r y the e f f e c t i v e s t r e s s and shear f o r c e s by s l i d i n g r e s i s t a n c e . I t ' s only when a l l e f f e c t i v e s t r e s s e s are t r a n s m i t t e d through contact p o i n t s which are s l i d i n g , t h a t the a v a i l a b l e f r i c t i o n a l r e s i s t a n c e i s f u l l y m o b i l i s e d . This c o n d i t i o n i s only reached when the s t r u c t u r e i s so d i s t u r b e d and 15 CEHE1TATI0H IOND FRICTION OBSERVED COMPOSITE SHAPE Sale M fine O F T H E - 2>B^EI.OPME:NT O F 16 the p a r t i c l e s so rearranged t h a t a l l movements are due to s l i d i n g of p a r t i c l e s over each other i n the plane of shearing. This type of behaviour produces an unusual f a i l u r e envelope, as i l l u s t r a t e d i n Figu r e 8. Below the p r e c o n s o l i d a t i o n pressure the peak st r e n g t h i s much higher than the f u l l y m o b i l i s e d f r i c t i o n envelope. This type of f a i l u r e envelope makes a n a l y s i s of s t a b i l i t y problems very d i f f i c u l t , e s p e c i a l l y w i t h n a t u r a l slopes. Recent i n v e s t i g a t i o n s , Crawford ( I 9 6 7 ) and M i t c h e l l ( I 9 6 9 ) , have i n d i c a t e d t h a t e f f e c t i v e s t r e s s a n a l y s i s using the method of s l i c e s f o r a f i r s t f a i l u r e g ives a reasonable answer, although the i n f l u e n c e of the f i e l d pore pressure has been found t o be of g r e a t e s t importance. But i t i s d i f f u l t to p r e d i c t the water c o n d i t i o n s i n the f i e l d . A l s o the f a i l u r e s a a r e of a progr e s s i v e nature. There have been many such f a i l u r e s of n a t u r a l slopes i n eastern Canada, some, such as the s l i d e on the Toulnustouc R i v e r , Quebec i n 1 9 6 2 . This was a pr o g r e s s i v e s l i d e which occurred on a n a t u r a l slope of only a few degrees. The s l i d e i n v o l v e d 5x10^ cubic yards of s o i l ' . Another majyor s l i d e occurred i n 1971 at Sa i n t - Jean Vianney, Quebec. This s l i d e destroyed 40 homes and k i l l e d 31 people. An estimated 9x10^ cubic yards of m a t e r i a l moved during the s l i d e . The s l i d e commenced w i t h i n the c r a t e r of a much l a r g e r land s l i d e t h a t occurred about 500 years ago, and a f t e r complete 17 —I . i u >! 1 I | _ 4o 9o IZO 'ko 3.0O ZO-O <j- 0 . T7Picr>z_ rrloHA.- c o u t o m f l PLOT <>(>. 18 l i q u e f a c t i o n t r a v e l l e d down the R i v i e r e aux Vases at a speed of approximately 16 miles/hour. Both these s l i d e s occurred i n May when the water t a b l e was at i t ' s highest. Because of the ridged s t r u c t u r e of Leda c l a y s , they have a low index of recompression, but when the load - c a r r y i n g c a p a c i t y of the s t r u c t u r e i s exceeded the compression index i s very high. This r e s u l t s i n a sharply defined " p r e c o n s o l i d a t i o n pressure". Crawford ( I 9 6 7 ) found that d i f f e r e n t p r e c o n s o l i d a t i o n pressures could be obtained by t e s t i n g the samples at d i f f e r e n t r a t e s of l o a d i n g . Results of these t e s t s are shown i n Figure 9 . 1.3 Scope There i s an obvious need f o r more research i n t o these quick c l a y s to obta i n a b e t t e r understanding of t h e i r s t r e s s - s t r a i n r e l a t i o n s h i p , e s p e c i a l l y w i t h respect to the i n f l u e n c e of time. In t h i s study an attempt has been made to look at the e f f e c t of s t r a i n r a t e on the h e a v i l y o v e r c o n s o l i d a t i o n c l a y from the S a i n t - Jean - Vianney s l i d e area. A l l the samples were i s o t r o p i c a l l y c o n s o l i d a t e d to an a l l round e f f e c t i v e s t r e s s of 0 . 4 Kg/cm . This meant tha t the samples had an o v e r c o n s o l i d a t i o n r a t i o of around 2 5 . Since there are widespread areas where Leda c l a y deposites are s u b s t a n t i a l l y overconsolidated, i t was f e l t t hat t e s t s i n 19 1 10 EFFECTIVE STRESS (Kc/CM 2 ) O F -Lo^b/fNJC - f /VFTEa CA.AUJf^OfZ^ t h i s study should be on h e a v i l y overconsolidated samples. I t was decided to i s o t r o p i c a l l y c o n s o l i d a t e the samples because of the ease of usi n g the more conventional equipment and because the r e s u l t s obtained from the creep t e s t s would s t i l l produce curves of e s s e n t i a l l y the same shape as i f t e s t e d w i t h Ko c o n s o l i d a t i o n . A l s o the r e s u l t s were t o be st u d i e d i n a more q u a l i t a t i v e r a t h e r than q u a n t i t a t i v e manor. Undrained s t r a i n c o n t r o l l e d t e s t s and creep t e s t s were performed along w i t h a group of drained . s t r a i n c o n t r o l l e d t e s t s and creep t e s t s . The' e f f e c t of s t r a i n r a t e on the c o n s o l i d a t i o n of S a i n t - Jean - Vianney c l a y was a l s o i n v e s t i g a t e d by performing Ko c o n s o l i d a t i o n t e s t s . 21 CHAPTER 2 LABORATORY TESTING 2.1 D e s c r i p t i o n of S o i l Tested. The c l a y used i n t h i s t e s t i n g programme was obtained from the s i t e of the S a i n t - Jean - Vianney s l i d e i n Quebec, and was sampled f o r Dr. P. LaRochelle of L a v a l U n i v e r s i t y , Quebec by the Quebec Hydro i n June 1971. The sample was a block sample, 10"xl0"x8" hi g h , which had been given many coatings of wax and was stored i n a moist room u n t i l r e q u i r e d . This c l a y i s normally r e f e r r e d to as Leda c l a y but i n t h i s t e x t w i l l from here a f t e r be r e f e r r e d to as S.J.V. c l a y , a f t e r the area from which i t came. This c l a y was b e l i e v e d to have been deposited i n a b r a c k i s h or marine environment during a b r i e f post - g l a c i a l p e r i o d of i s o s t a t i c depression and marine i n v a s i o n . Subsequent l e a c h i n g by p e r c o l a t i n g f r e s h ground water has been one of the reasons f o r the c l a y s l a r g e s e n s i t i v i t y . Cementation at p a r t i c l e contacts has a l s o been p o s t u l a t e d as a major cause f o r the l a r g e s e n s i t i v i t y , Crawford (1967) and Kenney ( 1 9 6 7 ) . Table 1 shows i t s t y p i c a l p h y s i c a l p r o p e r t i e s . TABLE 1 PHYSICAL PROPERTIES OF UNDISTURBED S.J.V. CLAY. L i q u i d L i m i t 36% P l a s t i c L i m i t 20% P l a s t i c i t y Index 16% N a t u r a l Water Content ^2% + 1% Degree of S a t u r a t i o n 100% S p e c i f i c G r a v i t y of S o l i d s 2 . 7 5 Percent f i n e r than 2 microns 50$ Unconfined compressive Strength 6 . 5 Kg/cm S e n s i t i v i t y around 100 A c t i v i t y P.I. ' 0 . 3 2 %<2yU. 2 Maximum past pressure around 10 Kg/cm 23 2 • 2 D e s c r i p t i o n of the Apparatus. The main piece of apparatus used i n t h i s study-was a conventional t r i a x i a l c e l l , i n which c y l i n d r i c a l samples 3 inches high by 1.4, inches diameter were i s o t r o p i c a l l y c o n s o l i d a t e d . A schematic layout of the measuring system i s shown i n F i g u r e 10. Drainage l i n e s from the top and bottom of the sample were connected to a device which contained a c a l i b r a t e d p i p e t t e and d i f f e r e n t i a l pressure transducer f o r measuring volume changes and a pressure transducer f o r measuring the pore pressure at the base of the sample. The back pressure was a p p l i e d through the graduated p i p e t t e . The c e l l pressure was a p p l i e d through a seperate p l a s t i c water r e s e r v o i r which a l s o had a pressure transducer a t t a c t e d . Both systems contained a s i x foot length o f " O.D. 8 saran t u b i n g i n order to prevent d i f f u s i o n of a i r i n t o the system. The v e r t i c a l deformations were measured by a l i n e a r D.C. d i f f e r e n t i a l transformer (L.V.D.T.) connected t o the l o a d i n g rod of the t r i a x i a l c e l l . The load was measured by a b e r y l l i u m copper diaphragm load c e l l placed above the l o a d i n g rod. S i g n a l s from a l l the transducers, load c e l l s and transformers were fed i n t o a V i d a r D i g i t a l Data A q u i s i t i o n System. Test data was acquired simultaneously an a magnetic tape and a p r i n t e r . The Magnetic tape was then used as an input data f i l e w hile reducing t e s t 24 data w i t h the I.B.M. 360/67 computer at U.B.C. Data acquired on the p r i n t e r helped to keep t r a c k of s a t i s f a c t o r y progress of the experiments. The high speed automatic r e c o r d i n g was p a r t i c u l a r l y u s e f u l t o enable accurate measurements i n the i n i t i a l and f i n a l rupture stages of both the creep and the constant r a t e of s t r a i n t e s t s . 2 . 3 . Experimental Procedure. Sample P r e p a r a t i o n . Because of the extremely s t i f f nature of the c l a y , sample p r e p a r a t i o n was very d i f f i c u l t . The trimming was done w i t h a sharp k n i f e removing only a small s e c t i o n at a time. The samples were found t o c o n t a i n numerous, very t h i n , s i l t lens which had almost zero shear s t r e n g t h i n the h o r i z o n t a l d i r e c t i o n , such t h a t when the ends of the sample were trimmed there was a tendency f o r the sample to shear along one of these s i l t l e n s es. Thus much care was taken i n the trimming of the ends of each sample. I t was found t h a t the trimming was aided by preparing the sample i n the moist room, t h i s a l s o helped obtain B values nearer to u n i t y . A l l the samples were i s o t r o p i c a l l y c o n s o l i d a t e d f o r a p e r i o d of 2k hours, w i t h drainage from both top and bottom of the sample, t o an a l l round e f f e c t i v e 26 s t r e s s of approximately 0.4 Kg/cm^. C o n s o l i d a t i o n was done against a back pressure of 3.6. Kg/cm . Normally the sample would have been l e f t undrained f o r 12 hours to allow any secondary compression to take p l a c e , but because the samples were so h e a v i l y over c o n s o l i d a t e d i t was f e l t unnecessary t o do t h i s . The f i r s t t e s t performed was l e f t , however f o r 12 hours undrained, a f t e r c o n s o l i d a t i o n , but the change.'iin pore pressure was n e g l i g i b l e , so i t was f e l t reasonable to omit t h i s step f o r the remaining t e s t s . A l l the t e s t s performed were c a r r i e d out i n a constant temperature environment i n order t o e l i m i n a t e the i n f l u e n c e of temperature as a v a r i a b l e . Constant-Rate of S t r a i n Compression Tests. For the undrained constant r a t e of s t r a i n compression t e s t s , the valve l e a d i n g to the p i p e t t e was closed a f t e r c o n s o l i d a t i o n and the s t r a i n r a t e mechanism s t a r t e d , such t h a t the pore pressure being recorded was from both the top and bottom of the sample, see Figure 10. For the drained constant r a t e of s t r a i n compression t e s t s , the valve between the pore pressure transducer and the p i p e t t e was c l o s e d , such t h a t there was drainage from the top of the sample and pore pressure measurements from the base, see Fig u r e 10. The drainage and pore pressure arrangements were the same as f o r the constant r a t e of s t r a i n t e s t s . The re q u i r e d load was a p p l i e d through a r o l l i n g b e l l o f r a m p i s t o n mounted above the t r i a x i a l c e l l , see Fi g u r e 1 0 . The d e s i r e d l e v e l of creep s t r e s s was "instantaneously" a p p l i e d by connecting the l o a d i n g p i s t o n t o a preset a i r pressure through a 3 way v a l v e . As the sample s t r a i n s under the creep s t r e s s , the increase i n area causes the s t r e s s t o decrease s l i g h t l y , but i t was found t h a t the s t r a i n s encountered were so small very l i t t l e adjustment was r e q u i r e d i n order to maintain a constant creep s t r e s s . A summary of a l l the t e s t i n f o r m a t i o n i s shown i n T a b l e l l a n d J I I . 28 TABLE I I SUMMARY OF TEST INFORMATION FOR STRAIN  CONTROLLED COMPRESSION TESTS UNDRAINED MEAN EFFECTIVE TEST INITIAL NO. W/C % CONSOLIDATED W/C % INITIAL HEIGHT ( i n s . ) VOID RATIO e CONSOL. STRESS 3 Kg/cm2 STRAIN RATE fo/min £ UD1 41.2 41 . 3 2.976 1.157 0.49 1 . 6 x l 0 " 3 UD2 41.4 41 . 5 2 .553 1.161 0.41 2 . 8 x l 0 _ 1 UD3 41 . 3 41.4 2 .557 1.156 0 .40 2 . 0 x l 0 " 2 UD4 42.2 42 . 6 3.121 1.192 0.40 2 . 8 x l 0 _ 1 UD5 42.1 42.4 3.156 1.186 0 .63 -4 7.2x10 UD6 42 . 3 42 . 6 3.202 1.19^ 0.40 2. 0 x l 0 " 2 DRAINED DR.T1 42.4 42 . 9 3.190 1.201 0.42 -4 7.5x10 ^ UD/DR 42.2 42.8 3.170 1.198 0 .39 7.5X10"2 4" 29 TABLE III SUMMARY OF TEST INFORMATION  FOR THE CREEP TESTS UNDRAINED MEAN EFFECTIVE TEST INITIAL NO. W/C % CONSOLIDATED w/c % INITIAL HEIGHT (ins.) INITIAL VOID RATIO CONSOL. STRESS Kg/cm^ APPLIED STRESS, Kg/cm2 CR.T1 43.4 44.1 2.745 1 .235 0.45 4 . 7 1 CR.T2 41.1 42 .5 3.146 1.200 0.42 4 . 3 2 CR.T3 42 .5 44.1 3.041 1 .234 0.42 4.22 CR.T4 42.1 42 .5 3.199 1.190 0 . 4 3 6 . 3 0 CR.T5 c 44.2 45 .7 3 . 2 3 1 1.280 0.47 5.97 CR.T6 42 .5 43.0 3.268 1 .205 0.46 5.74 CR.T6A 4 3 . 6 4 3 . 9 3.177 1.211 0 . 4 9 5 . 8 5 CR.T7 43.2 43.8 3.197 1.216 0 . 4 3 5 . 5 0 CR.T8 42.2 42.8 3.197 1.197 0.45 5.17 DRAINED DR.CR1 42.2 42.8 2.713 1.197 0.42 4 . 9 DR.CR2 42.2 42 .7 2.918 1 . 194 0.39 3 . 8 30 CHAPTER 3 EFFECTS OF STRAIN RATE  ON CONSOLIDATION The c o n s o l i d a t i o n r e s u l t s shown h e r e i n were obtained from Ko c o n s o l i d a t i o n t e s t s performed by Dr.Y.P.Vaid on S.J.V. c l a y at U.B.C. The t e s t s were performed i n a Ko t r i a x i a l c e l l , d e t a i l s of which have been presented elsewhere, Campanella and Vaid (1972). The samples were subjected to Ko one dimensional c o n s o l i d a t i o n under s t r a i n c o n t r o l l e d l o a d i n g w i t h drainage permitted from the top and pore pressure recorded at the bottom of the specimen. Four t e s t s were performed at s t r a i n r a t e s ranging from 1 . 1 3 x 1 t o 1.95xlO~' s t r a i n r a t e / s e c . One t e s t was performed using the standard incremental c o n s o l i d a t i o n method. Figure 11 shows the r e s u l t s of these f i v e t e s t s on a change i n v o i d r a t i o to l o g v e r t i c a l e f f e c t i v e s t r e s s p l o t . The curves c l e a r l y show th a t the apparent p r e c o n s o l i d a t i o n pressure v a r i e s from 12Kg/cm f o r the fastest t e s t to 7«5Kg/cm f o r the slowest t e s t . The standard incremental method gives an apparent pre-c o n s o l i d a t i o n pressure of around llKg/cm . These sharply defined p r e c o n s o l i a t i o n pressures are a c l e a r i n d i c a t i o n of the sudden break-down of the r i g i d s t r u c t u r e of S.J.V. Clay. This sudden S . 3 - . V / . C A « V i ^ T T > | FFe=-CerN/T , S T £ / W R A T E ' S . breakdown i s c l e a r l y very s t r a i n r a t e dependant and makes the " c o r r e c t " p r e c o n s o l i d a t i o n pressure extremely d i f f i c u l t to obtained. F i g u r e 12 shows the change i n the c o e f f i c i e n t of c o n s o l i d a t i o n , Cv f o r three of the t e s t s . There appears to be no d i r e c t r e l t i o n s h i p between v a r y i n g s t r a i n r a t e s and Cv, but the range of values was q u i t e l a r g e . The importance of o b t a i n i n g a v a l i d pre-c o n s o l i d a t i o n pressure i s very apparent. I f the r a t e of l o a d i n g i n the f i e l d i s slow, a standard incremental t e s t could give a very unconservative r e s u l t . The la r g e range i n C v could a l s o produce a very erroneous estimate f o r time f o r c o n s o l i d a t i o n to take p l a c e . L a t e r a l s t r a i n s were measured throughout the t e s t s and showed that reasonably good Ko c o n d i t i o n s e x i s t e d f o r the f a s t e r t e s t s , but i n the very long t e s t s there was a small amount of leakage l e a d i n g to l a t e r a l s t r a i n s of around 2 . 0 % . 33 FKj- ,42.. fVoT OF TWGT Coe-FF/C/eWT OF CGNSOAtlJi^TJOtJ A O j i W s X /ERTicKVi- GTFFe-cTi ST/geTiS Fo£-CHAPTER 4 RESULTS AND DISCUSSION OF CONSTANT  RATE OF STRAIN COMPRESSION TESTS 4 . 1 UNDRAINED CONSTANT RATE OF STRAIN  COMPRESSION TESTS. Figu r e s 13 and 14 show the r e s u l t s of the f i r s t set of three undrained s t r a i n c o n t r o l l e d compression t e s t s at d i f f e r e n t s t r a i n r a t e s . F i g u r e 13 c l e a r l y shows that there was a 2jfo increase i n d e v i a t o r s t r e s s w i t h over 100 times increase i n s t r a i n r a t e . The f i r s t p a r t of the curves shows t h a t the d i s t o r t i o n was of a l i n e a r nature. The e f f e c t of s t r a i n r a t e i n t h i s l i n e a r range "before peak d e v i a t o r s t r e s s was q u i t e small i n comparison to the p o i n t at which peak occurred. I t would appear that any bonding t h a t e x i s t s w i t h i n the c l a y i s not very s t r a i n r a t e dependant, expect i n r e l a t i o n to the p o i n t at which the bonds a c t u a l l y break. This p o i n t of f a i l u r e , or peak d e v i a t o r s t r e s s , was reached at between 0.58 and 0 . 7 0 percent s t r a i n , which i s an extremely small s t r a i n . This small s t r a i n l e v e l at peak d e v i a t o r s t r e s s would be expected f o r such a s t i f f , over-c o n s o l i d a t e d and bonded c l a y . The s t r a i n s measured a f t e r peak are r e l a t i v i l y meaningless because shear was t a k i n g place along a s i n g l e f a i l u r e surface. This type of f a i l u r e mechanism Fl(j./&. / s o r A o ^ / d TAlfiXnAL. <u>siS>TfrNT ZATer OF S T f c ^ / A / UA/ r j«.^/N/ e "D o iv/ TOP J~rtye& O F UrJT>\&T~UR.<5EV> - S . 3 " . / <^o4y. 3 6 37 i s to be expected i n an o v e r c o n s o l i a t e d c l a y , s i n c e when i t i s sheared i t tends to d i l a t e and so when f a i l u r e occurs i t w i l l appear, along a s i n g l e f a i l u r e s u r f a c e . F i g u r e 14 shows how the pore pressure q u i c k l y rose t o almost equal the c e l l pressure then r a p i d l y decrease to a negative value. This r i s e i n pore pressure meant t h a t , at peak d e v i a t o r s t r e s s , the samples were e s s e n t i a l l y under zero e f f e c t i v e c o n f i n i n g s t r e s s . This r e s u l t e d i n some' of the samples showing signs of v e r t i c a l s p l i t t i n g due to t e n s i l f a i l u r e , see Appendix I I . This a l s o suggests t h a t j u s t about a l l of the compressive stre n g t h of these samples was due to cementation bonding. The block from which the samples came was so shaped t h a t the samples used f o r the f i r s t three undrained s t r a i n c o n t r o l l e d compression t e s t s and the f i r s t three creep t e s t s were from the top h a l f of the block w h i l s t the. remaining samples were from the lower h a l f . F i g u r e s 15 and 16 show the r e s u l t s of the undrained s t r a i n c o n t r o l l e d compression t e s t s on the lower l a y e r of the block, and i t can be c l e a r l y seen that there was a 28$ increase i n s t r e n g t h at t h i s second l a y e r t o t h a t of the f i r s t l a y e r , even though the samples were only inches apart v e r t i c a l l y . No complete ex p l a n a t i o n can be given f o r t h i s , except t h a t the c o n c e n t r a t i o n of s i l t lenses d i d appear to be F)Cj. IS. l£>oT&oPic T&\AX\>°>L- coslST/^JT OF s r z A i r f uHT>tLicvs/e& TESTS, OA/ /CtfwerQ. LAi<cPt O F U.MT>l&Ti^&.@>&2> S .3". / . CUJ^Y. 3 9 coiAAP&ersLs/osJ TESTES < W LCUIEQ lAy&z. 40 higher i n the top l a y e r . F i g u r e 15 a l s o shows th a t there was s t i l l the 2$% increase i n streng t h w i t h over 100 times increase i n s t r a i n r a t e . The t e s t UD5 appears to be much s t i f f e r p r i o r to peak than the other t e s t s . T h i s could have been j u s t sample v a r i a b i l i t y or more probably due to the unusually l a r g e s e a t i n g load a p p l i e d during c o n s o l i d a t i o n , see t a b l e IV. This e x t r a s e a t i n g load may have e f f e c t e d the samples i n i t i a l s t i f f n e s s but not i t ' s s t r e n g t h , which i s dependant on the bonding. Fig u r e 16 again shows how the pore pressure rose q u i c k l y to equal the c e l l pressure and then a f t e r peak dropped r a p i d l y t o a negative value. Again t h i s suggest t h a t j u s t about a l l the streng t h of these samples was due to cementation bonding and tha t the bond strength appears t o be a f u n c t i o n of s t r a i n r a t e . 4.2 DRAINED CONSTANT RATE OF STRAIN  COMPRESSION TESTS. Figu r e s 1? and 18 show the r e s u l t s of the s t r a i n c o n t r o l l e d drained compression t e s t s , ran at the slowest s t r a i n r a t e . As expected from the r e s u l t s 6'f the undrained compression t e s t s , the r e d u c t i o n i n strengt h a f t e r peak was much gr e a t e r , due t o the d i l a t i o n e f f e c t s (Swelling) of t h i s h e a v i l y overconsolidated c l a y . F i g u r e 18 shows t h i s d i l a t i o n e f f e c t , where up Fiq. 'T hoT&DplC TAtrtXlAL.. Cofi/^Wfi/T AATtT O F ST/ZA/f\S T t s T OKI 42 43 to peak the sample was c o n t r a c t i n g s l i g h t l y , whereas a f t e r peak i t r a p i d l y d i l a t e d . The f a i l u r e at peak was so r a p i d t h a t i t was e s s e n t i a l l y undrained around the f a i l u r e zone. A f t e r these r e s u l t s i t was decided to perform a t e s t where the sample was s t r a i n e d undrained up t o i t ' s peak and then drainage allowed t o occur. The r e s u l t s of t h i s UN/DR. t e s t are shown i n F i g u r e s 19 and 20. The l o s s i n d e v i a t o r s t r e s s a f t e r peak was very marked, more so than the drained t e s t . The r e s u l t s a l s o showfthat the drained and undrained peak d e v i a t o r s t r e s s e s were almost the same but at d i f f e r e n t s t r a i n s . Figure 20 shows the v a r i a t i o n of pore pressure, measured at the base, plus volumetric s t r a i n a gainst a x i a l s t r a i n . This p l o t shows the sharp decrease i n pore pressure a f t e r drainage was allowed to occur, combined w i t h an i n i t i a l s mall decrease i n volume followed by a steady increase i n volume. Fig u r e 21 shows a comparison of the undrained/ drained t e s t w i t h the drained t e s t and one of the undrained t e s t (UD5), a l l of which were performed at the same l e v e l i n the block sample. The f i n a l s trength i n the drained c o n d i t i o n i s c l e a r l y much lower than the undrained s t a t e due t o the increase i n water content. Since there i s normally water a v a i l a b l e i n the f i e l d t h i s l a r g e l o s s i n s t r e n g t h could take place a f t e r an i n i t i a l undrained f a i l u r e . F i TeS"T" ON/ a/VbrsTU^^Tj JS.3~.-V. CL/V/. 45 V * O 5 t lu ^0-5 " £2. J "4 f S 0 o t ••f s 8 /*/ Pezzer /°*e^s.u.«.e ?>U.R.IKJCJ KNb&^/VtFo / DA^i/Veli T€TS.7~ OAs/ 0 1 2 - 3 AXIAL S T O A 7 ^ / £ . CoAs/'S.mN/T ^ ^-TE" OF= STR*/*/ TESTS 47 F i g u r e 22 shows the e f f e c t i v e s t r e s s path on a modified Mohr p l o t f o r one of the undrained s t r a i n c o n t r o l l e d compression t e s t s (UD2). The s t r e s s path shows how the e f f e c t i v e s t r e s s e s w i t h i n the sample q u i c k l y climb and r i s e up c l o s e l y t o the l i m i t of t r i a x i a l t e s t i n g (<y - o ). The s t r e s s e s continue to r i s e up c l o s e l y to t h i s l i n e . u n t i l peak d e v i a t o r s t r e s s , where upon the s t r e s s e s drop back sharply. A f t e r t h i s sharp drop the s t r e s s e s begin to climb again and then f a l l to a lower s t r e s s c o n d i t i o n . A l l the undrained s t r a i n c o n t r o l l e d compression t e s t s followed t h i s same p a t t e r n except f o r the p o i n t at whichpeak d e v i a t o r s t r e s s was reached. F i g u r e 23 shows the r e s u l t s of a l l the s t r a i n c o n t r o l l e d compression t e s t s on the modified Mohr p l o t . This shows how a l l the p o i n t s of peak d e v i a t o r s t r e s s l i e on or very c l o s e to the l i m i t of t r i a x i a l t e s t i n g , i t a l s o shows tha t the f i n a l d e v i a t o r s t r e s s c o n d i t i o n l i e s on a l i n e a r envelope passing through the o r i g i n t h a t r i s e s at around 33° to the a b s i s s a f o r a value of ^ = 4 0 ° . This value appears to agree w e l l w i t h the " r e s i d u a l f r i c t i o n envelope" found by Conlon (1966) and shown i n F i g u r e 8. F i g u r e 23 i m p l i e s that the s t r e n g t h of t h i s bonded c l a y i s dependant on e f f e c t i v e s t r e s s e s which i s c o n t r a r y to the concept of a bonded s t r u c t u r e . This would i n d i c a t e t h a t t r i a x i a l t e s t i n g f o r a bonded 4 8 c l a y at such a low s t r e s s l e v e l i s i n e f f e c t i v e i n ob t a i n i n g the complete f a i l u r e envelope. A l s o p l o t t e d on Fig u r e 23 are the peak and f i n a l d e v i a t o r s t r e s s c o n d i t i o n s f o r the drained t e s t . These p o i n t s l i e on a l i n e t h a t r i s e s at 4 5 ° from the i n i t i a l s t r e s s c o n d i t i o n , which would be expected f o r a drained t e s t . The f i n a l d e v i a t o r s t r e s s c o n d i t i o n l i e s very c l o s e to the r e s i d u a l f r i c t i o n envelope produced from the undrained t e s t s . A summary of a l l the r e s u l t s f o r the s t r a i n c o n t r o l l e d compression t e s t s i s shown i n t a b l e IV. This t a b l e shows that the peak d e v i a t o r s t r e s s , , was reached at s t r a i n s ranging from 0.40 t o 0 . 7 0 $ f o r the undrained t e s t s , and 0 . 2 6 ^ f o r the drained t e s t . These very small s t r a i n s were reached i n times ranging from 5 | minutes to 860 minutes f o r the undrained.tests and 961 minutes f o r the drained t e s t . The pore pressure parameter at f a i l u r e , A f, f o r the undrained t e s t s , were a l l around - 0 . 5 i which was as expected f o r an over-c o n s o l i d a t e d c l a y . 51 TABLE IV SUMMARY OF RESULTS OF STRAIN  CONTROLLED COMPRESSION TESTS. UNDRAINED TEST No. STRAIN RATE £ %/min PEAK °k 2 Kg/cm FINAL (>3fo)2 Kg/cm STRAIN AT PEAK %/min TIME TO PEAK MINS PORE PRESSURE PARAMETER AT PEAK or Af. °-UD1 1.6xl0 : 7-3 4 . 7 0 3 . 1 0 0 . 5 8 420 - 0 . 7 4 UD2 2.8x10' -1 5.80 4 . 2 0 0 . 7 0 5 . 5 - 0 . 5 6 UD3 2.0x10' -2 5 . 3 5 3 . 7 5 0 . 6 8 57 - 0 . 5 5 UD4 2.8x10' -1 7 . 4 5 4.40 0 . 6 8 6 . 7 -o.6o UD5 7 . 2 x 1 0 ' -4 5.80 3 . 6 0 0.40 860 - 0 . 5 4 UD6 2 . 0 x 1 0 ' -2 6 . 9 0 N / A 0 . 6 5 54 - 0 . 5 8 DRAINED TEST No. STRAIN RATE t fo/min -4 PEAK % Kg/cm FINAL 2 ^ Kg/cm STRAIN TIME AT PEAK TO PEAK fo/min MINS VOLUME CHANGE crrr DR.T : 7 . 5 x 1 0 ' 6 . 2 5 2 . 5 5 0 . 2 6 961 0 . 2 6 UD/DR 7 . 5 x 1 0 ' -4 6 . 5 0 2 . 3 0 0 . 5 2 945 N/A CHAPTER 5 RESULTS AND DISCUSSION OF CREEP TESTS. 5.1 UNDRAINED CREEP TESTS Figure 24 i s a p l o t of a x i a l creep r a t e against time, i n minutes, and shows th a t i n i t i a l l y the creep r a t e i s very f a s t , hut w i t h time decreases to a minimum, where upon i t begins to increase r a p i d l y again, l e a d i n g t o f a i l u r e . These curves d i f f e r from those found by Snead (1970) and Campanella and Vaid ( 1 9 7 2 ) , i n that i n i t i a l l y a l l the t e s t s f o l l o w more c l o s e l y the same l i n e of decreasing creep r a t e . T h i s agrees w e l l with the r e a c t i o n obtained from the s t r a i n c o n t r o l l e d compression t e s t s p r i o r to peak, since they a l l tended to f o l l o w the same s t r e s s - s t r a i n l i n e . R e s u l t s of a l l the creep t e s t s have been p l o t t e d on Figure 24. I t i s i n t e r e s t i n g t o see t h a t even though the samples t e s t e d from the top l a y e r of the block (CR.T . 1 ,2 and 3 ) , which had lower strengths, s t i l l l i e along the same i n i t i a l l y decreasing creep r a t e l i n e . R e s ults from Figure 24 suggest that the onset of an a c c e l e r a t i n g creep r a t e i n d i c a t e s impending f a i l u r e , s ince as long as the creep r a t e i s i n c r e a s i n g , f a i l u r e i s i n e v i t a b l e . However, s u f f i c i e n t warning concerning rupture was u s u a l l y present, since elapsed time u n t i l rupture (rupture l i f e ) was g e n e r a l l y around io I I L X to /<x> 54 twice the elapsed time up t o the p o i n t when the creep r a t e s t a r t e d a c c e l e r a t i n g (minimum creep r a t e ) . F i g u r e 25 shows the rupture l i f e , t , f o r each s t r e s s l e v e l p l o t t e d against the corresponding minimum creep rate,£ min, on a l o g - l o g s c a l e . T h i s p l o t shows th a t there e x i s t s a reasonable s t r a i g h t l i n e r e l a t i o n s h i p between the rupture l i f e and the minimum creep r a t e , r e g a r d l e s s of s t r e s s l e v e l . I n long term t e s t s , the rupture l i f e could be estimated from t h i s r e l a t i o n s h i p as soon as the minimum creep r a t e has occurred. U n f o r t u n a t e l y the width of e r r o r bands are extremely l a r g e , which shows that f o r a given minimum creep r a t e , rupture l i f e could vary by as much as a f a c t o r of 5 . Since, f o r n a t u r a l slopes i n the f i e l d , the s t a r t of creep i s not u s u a l l y known, a p l o t of minimum creep r a t e against remaining timetto:'rupture: i s ; shown i n Figure 2 6 , f o r a l l the creep t e s t s . Again a reasonable s t r a i g h t l i n e a r r e l a t i o n s h i p i s shown w i t h the same e r r o r band as F i g u r e 2 5 . This r e l a t i o n s h i p would i n d i c a t e that once the minimum creep r a t e has been reached, and i t s value found, an estimate of the remaining time to rupture can be obtained. But again, s i n c e i t would be d i f f i c u l t t o obta i n the p o i n t of minimum creep r a t e i n the f i e l d , a p l o t of t e r t i a r y , or a c c e l e r a t i n g creep r a t e a g a i n s t remaining time to rupture, t t r , has been 55 o 1 ( 1 o \ o \ / "ft FoA. I So TA o fit c *L L V co hJsoL I &*T£-fc 56 -1 -a. i -V -5" 10 I F/ 7 fceMAlNltiCf TIME TO AuPTUAC f /*/A/U.T<ES F F 57 p l o t t e d i n Figure 2 7 , f o r three of the creep t e s t s . The s c a t t e r of the p o i n t s was extremely l a r g e when a l l the t e s t s were p l o t t e d , so the data was seperated i n t o i t s i n d i v i d u a l t e s t s and seperate l i n e s p l o t t e d f o r each, of which only three.are shown i n Figure 2 7 . Campanella and Vaid (1972) obtained a s i n g l e l i n e f o r a l l t h e i r t e s t s at d i f f e r e n t s t r e s s l e v e l s , u n l i k e the seperate l i n e s obtained here. P a r t of the reason f o r t h i s disagreement could be due to the d i f f i c u l t y of o b t a i n i n g reasonable data f o r t h i s quick c l a y i n the t e r t i a r y creep r a t e range, a l s o the f a c t t h a t s t r a i n s measured near to rupture are meaningless due t o the movement along a s i n g l e f a i l u r e plane. I t was apparent from Figure 24 that as the creep s t r e s s l e v e l increased the rupture l i f e p r o g r e s s i v e l y decreased. F i g u r e 28 shows the r e l a t i o n s h i p between creep s t r e s s and the corresponding minimum creep r a t e f o r both l a y e r s of the block sample. Both l i n e s appeart;to be p a r a l l e l although the data a v a i l a b l e f o r the top l a y e r was obviously l i m i t e d . F i g u r e 29 shows the same p l o t , but w i t h the s t r e s s l e v e l s at peak d e v i a t o r s t r e s s p l o t t e d f o r a l l the undrained s t r a i n c o n t r o l l e d compression t e s t s , the dotted l i n e s on the p l o t are the creep data as from F i g u r e 28. Although the data i s a l i t t l e s c a t t e r e d there does appear to be a trend that would i n d i c a t e the"existance of a p o s s i b l e 58 10 -! 5 5" -Z-0: * /o Si hi / 0 \ cAT. -- © © 1 ) i /o loo 1 LtfJ t AH^wTBS. . F/t^ . 0.J-. Sows T 7 P « C A L - curves. F 0 £ 59 10 -1 -Z 10 •ft* 10 i i J i i ! i | j i / / / 1 . . . . . i / i I ! 1 -? - -! °/ 4 ^ ! i I i i j 1 ;-' \ t j 1 ! | i ' / ! 1 0 / 0 oe.T. i $2 Cv i 1 i 1 ) / r. «,s,<,,i 4-o So V-^ 7 0 Ri\TE /Ws/2> S773CS5 fcD/C 6 0 T H U4ye«S 60 r e l a t i o n s h i p between s t r a i n r a t e and s t r e s s r e g a r d l e s s of the t e s t i n g method. Figu r e 30 shows a p l o t of s t r e s s l e v e l a gainst lo g time to rupture f o r the creep t e s t s performed on the bottom l a y e r of the block sample. At higher s t r e s s l e v e l s the creep strength shows e s s e n t i a l l y a l i n e a r decrease w i t h l o g rupture l i f e . At lower s t r e s s l e v e l s , however, the decrease i n creep s t r e n g t h was much slower w i t h time t o rupture and the form of the curve seems to i n d i c a t e the existence of a long term y i e l d s t r e n g t h below which creep rupture w i l l not occur. This i s u s u a l l y termed the upper y i e l d s t r e n g t h . There are v a r i o u s methods of e s t i m a t i n g the upper y i e l d s t r e n g t h from creep t e s t r e s u l t s , but because of the l i m i t e d number of t e s t s performed here, no r e a l i s t i c value can be obtained. These methods r e q i r e a l a r g e number of t e s t s t o be performed, which i s not always p o s s i b l e , but i f two s t r a i n c o n t r o l l e d compression t e s t s are performed at d i f f e r e n t , very slow s t r a i n r a t e s and give the same st r e n g t h , then that strength can be regarded as the upper::/ y i e l d s t r e n g t h . 5 . 2 DRAINED CREEP TESTS. One drained creep t e s t was performed, DR.CR1, but due t o the problems w i t h the a v a i l a b i l i t y of the V i d a r D i g i t a l Data A q u i s i t i o n very l i t t l e I cow 63 i n f o r m a t i o n was obtained to f u l l y a n a l y s i s the r e s u l t s . F igure 31 shows a p l o t of a x i a l s t r a i n r a t e against time, and the curve f o r DR.CR1 i s shown, as p l o t t e d from the a v a i l a b l e data. I t can be seen from Fi g u r e 31 t h a t the curve f o r t h i s drained t e s t followed very much the same p a t t e r n as the undrained t e s t s . Another drained t e s t was performed, DR.CR2, i n which the a p p l i e d s t r e s s l e v e l was much lower than th a t a p p l i e d i n DR.CR1. I t i s i n t e r e s t i n g to see that the curve at the lower s t r e s s l e v e l p l o t s above t h a t of the higher s t r e s s l e v e l curve, which i s contrary t o the undrained creep curves. A f t e r 3000 minutes of loa d i n g f o r DR.CR2, the pore pressure was boosted by 0.1 Kg/cm to t r y and simulate a r i s e i n the watertable i n n a t u r a l slopes. I t can be seen from Fi g u r e 31 t h a t t h i s increase i n pore pressure caused an immediate increase i n s t r a i n r a t e , which a f t e r a p e r i o d of time reached a maximum and then began to decrease again. This continued f o r another 3000 minutes where the pore pressure was again boosted by 0.1 Kg/cm , but again, due to problems w i t h the a v a i l a b i l i t y of the V i d a r and a l s o the f a c t t h a t the s t r a i n measured remained p r a c t i c a l l y constant, the curve has been terminated. The t e s t was, however, kept running f o r another 3000 minutes, i n which time i t was observed t h a t the s t r a i n remained almost constant but the sample was sucking i n water. 6 4 10 > I tt * /O I /o (!) \ \ A a - o V f /cro /crc~o r 1=1 1 > f t r % / N / e " b C f o T B " " 3 T E S T ' S <W 65 This i n d i c a t e s t h a t the compression due to the s t r e s s l e v e l was being e x a c t l y compensated by the s w e l l i n g due to the boost i n pore pressure. A f t e r a t o t a l time of 9000 minutes the pore pressure was again boosted by 0.1 Kg/cm , which put the sample under an e f f e c t i v e 2 s t r e s s of 0 . 1 Kg/cm . The t e s t was then continued f o r another 3000 minutes, a f t e r which time the sample had s t i l l not f a i l e d . This i n d i c a t e s how the stren g t h of the sample i s dependant almost completely on the bonding which appears to be independant of e f f e c t i v e s t r e s s . Table V shows a summary of the r e s u l t s of the creep t e s t s . CR.T3 and CR.T8 have been omitted since they d i d not f a i l . Table V a l s o shows that the s t r a i n reached at minimum s t r a i n r a t e ranged from 0.40 to 0.4-9 percent. 5 . 3 STRESS-STRAIN-STRAIN RATE RELATIONS. Campanella and Vaid (1972) had found that f o r a given c o n s o l i d a t i o n h i s t o r y there e x i s t s a unique s t r e s s - s t r a i n - s t r a i n r a t e law th a t could be used to c o r r e l a t e the r e s u l t s of creep and constant s t r a i n r a t e t e s t s . F i g u r e 32 shows the constant s t r e s s creep rupture curves f o r some of the undrained t e s t s on a l o g s t r a i n r a t e versus s t r a i n p l o t . A constant s t r a i n r a t e t e s t i s a l s o shown on t h i s p l o t by a h o r i z o n t a l l i n e TABLE V SUMMARY OF RESULTS OF  CREEP TESTS. UNDRAINED APPLIED MEAN EFFECTIVE MINIMUM STRAIN RUPTURE TEST No. STRESS (Kg/cm ) CONSOL. STRESS J*™/ 2 Kg/cm STRAIN RATE %/min AT a £ • < LIFE, miKs CR.T1 4.71 0.45 1.8xl0"3 0.40 40 CR.T2 4.32 0.42 1.2xl0"i|' 0.42 300 CR.T4 6.30 0.43 2.7xl0" 2 0.42 10 CR.T5 5.97 0.47 1.5xl0"3 0.455 50 CR.T6 5.74 0.46 4.6xl0" 4 0.46 135 CR.T6A 5.85 0.49 -4 2.1x10 ^ 0.47 120 CR.T7 5.50 0.43 8.9xlO~5 0.49 1050 67 corresponding to the value of the s t r a i n r a t e used. I f the s t r e s s i s assumed uniquely r e l a t e d to the c u r r e n t s t r a i n and s t r a i n r a t e , then the p o i n t s of i n t e r s e c t i o n of the constant s t r a i n r a t e t e s t w i t h the creep curves would give a set of values d e f i n i n g the s t r e s s - s t r a i n curve f o r t h a t p a r t i c u l a r constant s t r a i n r a t e used. The s t r e s s - s t r a i n curve determined from a constant s t r a i n r a t e t e s t , having the same c o n s o l i d a t i o n h i s t o r y as t h a t used f o r the creep t e s t s , i s shown i n Figure 33• The p r e d i c t e d s t r e s s - s t r a i n curve from the s e r i e s of creep curves i s a l s o shown "by the c i r c l e s . I t can be seen t h a t reasonable agreement e x i s t s , except t h a t the p r e d i c t e d p o i n t s are s h i f t e d t o one side by approximately 0.1%. Because of the very small range of s t r a i n s encountered w i t h t h i s c l a y , t h i s s h i f t could w e l l have been caused by a nonuniformity i n the s e a t i n g loads. Snead ( 1970) and Campanella and Vaid ( 1972) both r e s t r i c t e d the use of a unique s t r e s s s t r a i n - s t r a i n r a t e r e l a t i o n s h i p to s o i l s t e s t e d undrained at constant temperature and not h e a v i l y overconsolidated, where as these r e s u l t s would i n d i c a t e that t h i s r e l a t i o n s h i p could s t i l l be a p p l i e d t o a h e a v i l y overconsolidated and bonded c l a y . 6 9 / X 3 FlCy.S^b. CCMPARISQISI OP 0%SE3$Verh #ATET ccnvv^e^S'c»N/ TESTS CQ £€? TESTES. 70 5 . 4 EFFECTIVE STRESS CONDITIONS. Figure 34 shows the e f f e c t i v e stress conditions of the undrained creep tests at the instant of minimum creep rate on a modified Mohr p l o t . A l l the points l i e very close to the l i n e of l i m i t f o r t r i a x i a l ; t e s t i n g , where the e f f e c t i v e confining stress, cr^, equals zero. Comparison of t h i s plot with the equivalent p l o t f o r the undrained s t r a i n controlled compression te s t s , Figure 2 3 , shows that the instant of peak deviator stress i s also defined by the same envelope. These points could have f a l l e n onto t h i s same l i n e simply because the tests had a l l reached t h e i r l i m i t for t r i a x i a l t e s t i n g , that i s , the pore pressure equalled the c e l l pressure. But i n the undrained/drained s t r a i n controlled compression t e s t , where the drainage valve was opened just a f t e r peak deviator stress, the e f f e c t i v e stress within the sample was not zero at peak, but t h i s point s t i l l p lots very close to the envelope. This indicates that there could be a single envelope fo r peak deviator stress i n the s t r a i n controlled compression tests and minimum creep rate i n the creep t e s t s . Campanella and Vaid (1972) found that the l i n e a r envelope defined by the instant of minimum creep rate occurred at a lower shearing resistance than that defined by the s t r a i n controlled compression t e s t s . / / / Al*vtu OF __ / Ti / /O /o 1 / / / / / / / 1 THE UM'bR.&fM&b CfiLSEP TfeS 7S 72 This d i f f e r e n c e i n r e s u l t s i s c h i e f l y due to the f a c t that the r e s u l t s h e r e i n are f o r a h e a v i l y overconsolidated, cemented c l a y , whereas those obtained by Campanella and Vaid were f o r a normally c o n s o l i d a t e d c l a y . 73 CHAPTER 6 SUMMARY AND CONCLUSIONS The t e s t i n g of t h i s very s t i f f , s e n s i t i v e c l a y was very d i f f i c u l t since the a x i a l s t r a i n s t o f a i l u r e were very s m a l l , a l l l e s s than 1 percent. Based on the u n a x i a l constant s t r e s s creep rupture t e s t s and the s t r a i n c o n t r o l l e d compression t e s t s c e r t a i n conclusions can be drawn. There appears to e x i s t a l i n e a r r e l a t i o n s h i p between l o g minimum creep r a t e and l o g rupture l i f e and a l s o l o g minimum creep r a t e and l o g remaining time to rupture. A l i n e a r r e l a t i o n s h i p was a l s o noted between l o g current creep r a t e during t e r t i a r y creep and the remaining time to ruptu r e , although very l i t t l e r e l i a n c e can be placed on s t r a i n s measured near t o creep rupture. A . l i n e a r r e l a t i o n s h i p between l o g minimum creep r a t e and s t r e s s l e v e l and a p o s s i b l e l i n k between s t r e s s and s t r a i n r a t e f o r both s t r a i n c o n t r o l l e d compression t e s t s and creep t e s t s appears to e x i s t . There i s some i n d i c a t i o n t h a t a s t r e s s -s t r a i n - s t r a i n r a t e r e l a t i o n s h i p may e x i s t f o r t h i s over-c o n s o l i d a t e d , cemented c l a y . R e sults from the Ko c o n s o l i d a t i o n t e s t s , performed by Dr. Y.P.Vaid, show tha t the apparent pre-c o n s o l i d a t i o n pressure v a r i e s over a very l a r g e range, i f t e s t e d at d i f f e r e n t s t r a i n r a t e s . I n c o n c l u s i o n , the r e s u l t s obtained i n t h i s research were very dependant on the bonding t h a t e x i s t e d i n t h i s c l a y , and t h a t the bond strength appeared to be a f u n c t i o n of the s t r a i n r a t e . BIBLIOGRAPHY Bishop,A.W., Henkel.D.J., ( 1 9 6 2 ), "The measurement of s o i l p r o p e r t i e s i n the t r i a x i a l t e s t . " Edward A r n o l d , Second E d i t i o n . Campanella,R.G., and R.C.Gupta, ( 1 966 ) , " E f f e c t of S t r u c t u r e on Shearing r e s i s t a n c e of a s e n s i t i v e Clay." S o i l Mechanics S e r i e s No. 6 U.B.C. Campanella,R.G., and Y.Vaid,( 1 9 7 2 ), "Creep rupture of a saturated N a t u r a l Clay." S o i l Mechanics S e r i e s No. 16 U.B.C. Campanella,R.G., and Y.Vaid, ( 1 9 7 3 ) , " T r i a x i a l and Plane S t r a i n Creep Rupture of an undisturbed Clay," S o i l Mechanics S e r i e s No. 2 1 , U.B.C. Casagrande.A., and S.Wilson,(1951), " E f f e c t of r a t e of l o a d i n g on strength of c l a y s and shales at constant water content." Geotechnique, V o l . I I , No. 3i June 1951. Conlon.R.J., ( I 9 6 6 ) , "Landslide on the Toulnustouc R i v e r , Quebec." Canadian Geotechnical J o u r n a l , V o l . Crawford,C.B., ( 1 9 5 9 ) . "The i n f l u e n c e of r a t e of s t r a i n on e f f e c t i v e s t r e s s e s i n s e n s i t i v e c l a y . " ASTM, STP. No. 2 5 4 . Crawford,C.B., ( 1 9 6 8 ) , "Quick Clays of Eastern Canada." Engineering Geology, Amsterdam, pp. 2 3 9 - 2 6 5 . Gadd.N.R., ( 1 9 6 2 ) , " S u r f i c i a l geology of Ottawa map-area Ontario and Quebec." Geol. Surv. Can., Paper, 6 2 ( 1 6 ) : 4 pp. Ha e f e l i . R . , ( 1 9 5 3 ) , "Creep problems i n S o i l s , Snow and I c e . " Proceedings, 3 r d . I n t . Conf. on s o i l Mech. and Found. Eng., V o l . I l l , pp. 2 3 8 - 2 5 1 , 1 9 5 3 . 76 11. Henkel,D.J., (1957). " I n v e s t i g a t i o n of two long term f a i l u r e s i n London c l a y slopes at Wood and N o r t h o l t . " Proceedings 4th I n t . Conf. on S.M. and Found. Eng., V o l . 1 1 , p. 315, 1957. 12. Kenney.T.C, and L.Bjerrum, (1972), " E f f e c t of st r u c t u r e on the shear behaviour of Normally c o n s o l i d a t e d Quick Clays." Canadian Geotechnical V o l . 9 . No. 3 1972. 1 3 . L o i s e l l e , A . , M.Massiera, and U.R.Sainani, (1970) "A Study of the Ce'mtation Bonds of the S e n s i t i v e c l a y s of the Ontardes R i v e r Region." Can. Geotechnical J o u r n a l , V o l . 8. 14. Lubahn.J.D. and R.P.Felgar, (1961), " P l a s t i c i t y and creep of metals." J.Wiley and Sons Inc., New York, p. 6 0 0 . 15. Mallawaratchie.D.P., (1970), "Plane s t r a i n creep rupture of a saturated undisturbed c l a y . " M.A.Sc. Thesis U.B.C. 16. M i t c h e l l , J . K . , A.Singh, and R.G.Campanella, ( I 9 6 9 ) "Bonding:,: E f f e c t i v e s t r e s s e s , and strengt h of s o i l s . " Jour, of S.M. and Found. Div. ASCE, V o l . 95, S.M.5, pp. 1219-1246. 17. Saito,M., and H.Uezawa, (1961), " F a i l u r e of s o i l due t o creep." Proceeding of the 5th I n t . Conf. on S.M. and F.E., P a r i s , V o l . I pp. 315-318. 18. Saito,M., ( I 9 6 9 ) , "Forecasting time of slope f a i l u r e by t e r t i a r y creep." Proc. 7th I n t . Conf. on S.M. and F.E., Mexio, V o l . I I , pp. 677-683. 19. Sead,D. (1970), "Creep s t u d i e s on an undisturbed s e n s i t v e c l a y . " Ph.D. Thesis, U.B.C. 20. S u k l j e , (1961), "A l a n d s l i d e due to long term creep." Proceedings 5th I n t . Conf. on S.M. and F.E. VOL I I , p. 727, 1961. 77 21. Tavenas,F., J.Y.Changnon, and P.LaRochelle, (1971), "The Saint-Jean-Vianney L a n d s l i d e : Observations and eyewitnesses Accounts." Can. Geotechnical J o u r n a l , V o l . 8 pp. 463-478. 2 2 . Townsend,D.L., D.L.Sangrey, and I.K.Walker,( I 9 6 9 ) "The B r i t t l e Behaviour of n a t u r a l l y cemented s o i l s . " Proc, 7th I n t . Conf. S.M. and F.E. Mexio pp. 411-417. 2 3 . V i a l o r . S . , and A . S k i b i t s k y , (1957), " R h e o l o g i c a l processes i n f r o z e n s o i l s and dense c l a y . " Proc. 4th I n t . Conf. on S.M. and F.E., V o l . I , p 121. 1957. 78 APPENDIX I CALCULATION OF STRAIN RATES The s t r a i n rates were computed by using the s t r a i n log time plot as shown i n Figure A l . A smooth curve was drawn through the s t r a i n - l o g time points plotted from the "raw" data. The technique to calculate s t r a i n rates assumes a l i n e a r change i n s t r a i n f o r f i n i t e time i n t e r v a l s . The s t r a i n rate at a given time " t " was determined by subtracting the value of the s t r a i n at (t-At) from the value at t+At and divided by time i n t e r v a l At (Figure A l ) . That i s the s t r a i n at B (Figure Al) was taken to be: _ S t r a i n ordinate at C - s t r a i n ordinate at A time AC (natural scale) I I I APPENDIX I I SKETCHES OF FAILED SAMPLES UD5 UD£> 

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