UBC Theses and Dissertations

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UBC Theses and Dissertations

Stability of the Kamloops silt bluffs Lum, Ken King Yee 1979

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STABILITY OF THE KAMLOOPS SILT BLUFFS by KEN KING YEEjLUM,, B A S c , U n i v e r s i t y o f B r i t i s h C o l u m b i a , 1975 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE i n THE FACULTY OF GRADUATE STUDIES Department of C i v i l E n g i n e e r i n g U n i v e r s i t y o f B r i t i s h Columbia We a c c e p t t h i s t h e s i s as c o n f o r m i n g t o t h e r e q u i r e d s t a n d a r d THE UNIVERSITY OF'BRITISH COLUMBIA March, 1979 c) Ken K i n g Yee Lum, 1979 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of Brit ish 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 representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. j Department of CIVIL ENGINEERING The University of Brit ish Columbia 2075 Wesbrook P l a c e Vancouver, Canada V6T 1 W 5 Date i i . ABSTRACT S t a b i l i t y problems a r e e n c o u n t e r e d w i t h i n t h e g I a c i o I a c u s t r i n e s i l t s o f t h e South Thompson V a l l e y near Kamloops, B r i t i s h C o l u mbia. F i e l d i n v e s t i g a t i o n s have been c a r r i e d . o u t e x a m i n i n g s l o p e f a i l u r e s , p i p i n g and c o l l a p s e f e a t u r e s t y p i c a l o f t h e a r e a . The s t r e n g t h p a r a m e t e r s , c o l l a p s e mechanism and t h e n a t u r e o f t h e c o h e s i o n of t h e s i l t were examined i n t h e l a b o r a t o r y . The s e n s i t i v i t y o f t h e s o i l t o s l i g h t i n p u t s of w a t e r has been examined i n d e t a i l from t h e s t r e n g t h and s t r u c t u r a l s t a b i l i t y a s p e c t s . A c o l l a p s e mechanism has been proposed f o r t h e l a c u s t r i n e s i l t . A l t h o u g h t h e c o l l u v i u m d e r i v e d from t h e l a c u s t r i n e s i l t i s known t o be h i g h l y c o l l a p s i b l e , o n l y p r e l i m i n a r y l a b o r a t o r y t e s t s have been performed on t h e c o l l u v i a l m a t e r i a l . The s h o r t and long term s t a b i l i t y o f t h e s l o p e s have b e e n . s t u d i e d w i t h c o n s i d e r a t i o n g i v e n t o t h e e f f e c t s o f urban development. Based on s t a b i l i t y c o n s i d e r a t i o n s , a p o s s i b l e z o n i n g scheme f o r urban development has been proposed. TABLE OF CONTENTS Page ABSTRACT i i LIST OF FIGURES v i - v i i i LIST OF TABLES i x CHAPTER 1. INTRODUCTION 1.1 I n t r o d u c t i o n 1 1.2 G e o l o g i c H i s t o r y 1-3 1.3 S u r f i c i a l Geology 3-4 1.4 CI imate 4 CHAPTER 2. FIELD RECONNAISSANCE 2.1 Problems Observed 5 2.1.1 P i p e s and S i n k h o l e s 5-7 2.1 .2 S l o p e S t a b i I i t y 8 2.2 S l o p e Geometry 8-12 2.3 J o i n t i n g 12-15 2.4 Soi I Sampl i n g 15-17 2.5 F i e l d Seepage S i m u l a t i o n 17-18 CHAPTER 3. BASIC SOIL PROPERTIES 3.1 Speci f i c G r a v i t y 19 3.2 G r a i n S i z e A n a l y s i s 19-21 3.3 M i n e r a l o g y 21-22 3.4 A t t e r b e r g L i m i t s & F i e l d M o i s t u r e C o n t e n t s 23 i V . Page CHAPTER 4. LABORATORY TESTS 4.1 S c a n n i n g E l e c t r o n M i c r o s c o p e S t u d i e s 24-28 4.2 U n c o n f i n e d Compression T e s t s 29-30 4.3 T r i a x i a l T e s t s 30-31 4.3.1 T r i a x i a l T e s t A p p a r a t u s 31-32 4.3.2 S a t u r a t i o n P r o c e d u r e 33-34 4.3.3 E x p e r i m e n t a l P r o c e d u r e 34-35 4.4 T r i a x i a l T e s t R e s u l t s and D i s c u s s i o n 35 4.4.1 S t r e s s - S t r a i n R e l a t i o n s h i p s 36-39 4.4.2 Volume Changes D u r i n g S h e a r i n g .... 40 4.4.3 S t r e n g t h Envelope (P-Q Diagram) ... 36-39 4.5 U n c o n v e n t i o n a l 'Dry' T r i a x i a l T e s t s 45 4.6 R e s u l t s and D i s c u s s i o n 45-50 4.7 C o n s o l i d a t i o n T e s t s 51-52 4.7.1 C o n s o l i d a t i o n A p p a r a t u s 52-53 4.7.2 S a t u r a t i o n P r o c e d u r e 53-54 4.7.3 E x p e r i m e n t a l P r o c e d u r e 54 4.8 C o n s o l i d a t i o n R e s u l t s and D i s c u s s i o n 54-57 4.8.1 Incremental Load T e s t 57-65 4.8.2 S t r a i n C o n t r o l l e d T e s t 66-70 4.8.3 D i s c u s s i o n o f Combined R e s u l t s .... 70-72 CHAPTER 5. STRUCTURAL STABILITY OF KAMLOOPS SILT 5.1 L i t e r a t u r e Review on Co I I a p s i b I e S o i l s ... 73 5.1.1 C o l l a p s i b l e Soi Is 73 Page 5.1.2 C o l l a p s e Mechanisms 73-76 5.1.3 E n g i n e e r i n g A p p l i c a t i o n s 76-77 5.2 C o l l a p s e Phenomenon o f Kamloops S i l t 78-80 5.3 C o l l a p s e Mechanism o f Kamloops S i l t 80-83 CHAPTER 6. SLOPE STABILITY 6.1 Frequency and E x t e n t 84 6.2 J o i n t i n g 84 6.3 Modes o f F a i l u r e 84-90 6.4 I n f l u e n z e o f Water 93 6.5 S t a b i l i t y A n a l y s i s o f Deep F a i l u r e s ...... 92-93 6.6 Long Term S t a b i l i t y 94-95 6.7 P o s s i b l e Zoning.Scheme 95-97 CHAPTER 7. SUMMARY AND CONCLUSIONS 98-101 APPENDIX I. SAMPLING SITES & SAMPLE DESCRIPTIONS . 103-107 APPENDIX I I . SAMPLE TRIMMING PROCEDURES 108-110 APPENDIX 111. APPARATUS COMPRESSIBILITY CORRECTIONS FOR THE CONSOLIDATION TEST 111-116 APPENDIX IV. CONSOLIDATION TESTS ON COLLUVIUM 117-119 REFERENCES .. 120-124 V i . LIST OF FIGURES FIGURES Page 1. T o p o g r a p h i c Map of t h e South Thompson V a l l e y .... 2 2. H o r i z o n t a l p i p e i n C o l l u v i u m 6 3. V e r t i c a l p i p e i n c o l l u v i u m 6 4. S i n k h o l e s on t h e bench s u r f a c e 7 5. I s o l a t e d s i n k h o l e w i t h i n t h e c o l l u v i u m 7 6. S l o p e f a i l u r e on t h e e a s t f a c e of Magazine Gul l y 9 7. Bench s l o p e f a c i n g South Thompson R i v e r 9 8. O b l i q u e a e r i a l View o f s t u d y a r e a 10 9. G e n e r a l s l o p e geometry 11 10. S t e r e o n e t p l o t o f j o i n t s 13 1 1 . Rose d i agram 14 12. Sampling s i t e l o c a t i o n 16 13. G r a i n s i z e d i s t r i b u t i o n c u r v e s 20 14. M i c r o p h o t o g r a p h , u n d i s t u r b e d s i l t , 400X 25 15. M i c r o p h o t o g r a p h , remolded s i l t , 400X 25 16. M i c r o p h o t o g r a p h , u n d i s t u r b e d s i l t , 1000X 26 17. M i c r o p h o t o g r a p h , remolded s i l t , 1000X 26 18. M i c r o p h o t o g r a p h , u n d i s t u r b e d s i l t , 1000X 27 19. M i c r o p h o t o g r a p h , u n d i s t u r b e d s i l t , 2000X 27 20. U n c o n f i n e d c o m p r e s s i o n , s t r e s s - s t r a i n c u r v e s ... 29 21. S c h e m a t i c diagram of t r i a x i a l a p p a r a t u s 32 22. S t r e s s - s t r a i n p l o t , ' o v e r c o n s o I i d a t e d ' s t a t e ... 37 23. S t r e s s - s t r a i n p l o t , ' n o r m a l l y c o n s o l i d a t e d ' .... 38 v i i . FIGURES Page 24. % .a-Volume v s . % s t r a i n , O.C. s t r e s s r e g i o n 41 25. * ^ Volume v s . % s t r a i n , N.C. s t r e s s r e g i o n 42 26. P-Q Diagram f o r Kamloops S i l t 43 27. P-Q Diagram f o r t h e O.C. s t r e s s r e g i o n 44 28. Mohr c i r c l e o f f a i l u r e a t v a r i o u s s a t u r a t i o n s .. 46 29. Shear s t r e n g t h v s . s a t u r a t i o n graph 47 30. Incremental Load C o n s o l i d a t i o n c u r v e 58 31. S t r u c t u r a l c o l l a p s e r a t e upon f l o o d i n g 60 32. A H vs Log t i m e p l o t f o r i n c r . load c o n s o l i d a t i o n 62 33. P l o t o f pore p r e s s u r e d i s s i p a t i o n and amount o f c o n s o l i d a t i o n w i t h t i m e 63 34. S t r a i n c o n t r o l l e d c o n s o l i d a t i o n c u r v e s 67 35. S w e l l p r e s s u r e vs t i m e graph 69 36. Composite c o n s o l i d a t i o n c u r v e s 71 37. P e r c e n t c o l l a p s e vs P p l o t 79 38. S l o p e f a i l u r e s near P r i t c h a r d 85 39. Columnar j o i n t i n g i n t h e l a c u s t r i n e s i l t 87 40. Column t o p p l i n g mode of f a i l u r e 88 41. B l o c k o r s l a b f a i l u r e mode 89 42. R o t a t e d i n t a c t b l o c k f a i l u r e 90 43. A p p r o x i m a t e s e t b a c k z o n i n g scheme 96 44. C o n s o l i d a t i o n a p p a r a t u s c o m p r e s s i b i l i t y , Curve A 114 45. C o n s o l i d a t i o n a p p a r a t u s c o m p r e s s i b i l i t y , Curve B 115 FIGURES P a g e 4 6 . C o n s o l i d a t i o n a p p a r a t u s c o m p r e s s i b i l i t y , C u r v e C 116 4 7 . C o n s o l i d a t i o n c u r v e s f o r c o l l u v i u m 119 i x . LIST OF TABLES TABLE Page I. Hydrometer A n a l y s i s R e s u l t s 20 I I . C o m p o s i t i o n of Kami oops S i l t 22 I I I . C o n s o l i d a t e d - d r a i n e d T r i a x i a l T e s t s 39 IV. 'Dry' T r i a x i a l T e s t R e s u l t s 50 V. ' C o n s o l i d a t i o n ' T e s t s of Kami oops S i l t 55 V I . R e s u l t s of t h e C o n s o l i d a t i o n T e s t s 56 V I I . Observed and C a l c u l a t e d S l o p e H e i g h t s U s i n g T a y l o r ' s C h a r t s 92 X. ACKNOWLEDGEMENTS I am i n d e b t e d t o my t h e s i s a d v i s o r , Dr. R.G. C a m p a n e l l a , Department o f C i v i l E n g i n e e r i n g , f o r h i s h e l p f u l s u g g e s t i o n s and g u i d a n c e . I would a l s o I i k e t o t h a n k t h e B r i t i s h Columbia Department o f Highways ( G e o t e c h -n i c a l and M a t e r i a l s T e s t i n g Branch) f o r t h e i r f i n a n c i a l a s s i s t a n c e and encouragement t h r o u g h o u t t h e c o u r s e o f t h i s t h e s i s . 1. CHAPTER 1  I NTRODUCTI ON 1 . 1 I n t r o d u c t i on G e o t e c h n i c a l problems a s s o c i a t e d w i t h t h e g I a c i o I a c u s t r i n e s i l t s o f t h e South Thompson V a l l e y have been examined. The a r e a o f s t u d y encompasses t h e s i l t b l u f f s on t h e n o r t h s i d e o f t h e South Thompson R i v e r , j u s t e a s t of Kamloops, B r i t i s h Columbia between Highway number 5 and Harper Road ( f i g . 1 ) . The problems o f s l o p e s t a b i l i t y , p i p i n g and s o i l c o l i a p s e e n c o u n t e r e d i n t h e s e m i - a r i d e n vironment i n v a r i a b l y r e l a t e t o e x c e s s i v e m o i s t u r e i n p u t s . T h i s r e p o r t examines t h e c o n t r a s t i n b e h a v i o u r o f t h e s i l t i n i t s n a t u r a l l y d r y s t a t e and i n i t s s a t u r a t e d c o n d i t i o n . I n v e s t i g a t i o n s i n v o l v e f i e l d r e c o n n a i s s a n c e and e x t e n s i v e l a b o r a t o r y t e s t i n g o f u n d i s t u r b e d s i l t samples. A p o s s i b l e c o l l a p s e mechanism i s p r o p o s e d . B a s i c s l o p e s t a b i l i t y c a l c u l a t i o n s a r e a l s o p r e s e n t e d a l o n g w i t h a proposed z o n i n g scheme f o r u r b a n i z a t i o n a I developments. 1.2 G e o l o g i c H i s t o r y The s i l t o f t h e South Thompson was d e p o s i t e d i n a g l a c i a l l a k e r e f e r r e d t o as Lake Thompson (Mathews, 1944) d u r i n g t h e l a s t deg I a c i a t i o n . R eceding i c e from t h e u p l a n d s l e f t an i c e tongue i n t h e main v a l l e y . The tongue s e p a r a t e d i n t h e v i c i n i t y o f Monte Creek ( f i g . 1 ) , t h e w e s t e r n lobe r e t r e a t i n g toward Kamloops Lake and t h e e a s t e r n one toward L i t t l e Shuswap Lake ( F u l t o n , 1965). D u r i n g t h e i n i t i a l r e c e d i n g s t a g e from t h e FIG 1 . T O P O G R A P H I C MA P OF T H E S O U T H T H O M P S O N V A L L E Y 3. a d j a c e n t u p l a n d s , maximum e r o s i o n , t r a n s p o r t a t i o n , and d e p o s i t i o n o c c u r r e d (up t o 20 f e e t / y e a r ) ( F u l t o n , 1965). Much o f t h e s i l t was d e r i v e d from t h e e r o s i o n o f t h e t i l l on t h e upla n d s a d j a c e n t t o t h e v a l l e y and e n t e r e d t h e Thompson V a l l e y i n t h e v i c i n i t y o f Kamloops. The c o a r s e p o r t i o n o f t h e t i l l was l e f t on t h e upland w h i l e t h e s i l t was c a r r i e d i n t o t h e v a l l e y . With t h e d r y i n g o u t o f Lake Thompson, d e s s i c a t i o n o f t h e s i l t s r e s u l t e d , f o l l o w e d by t h e i n c i s i o n o f t h e South Thompson R i v e r which r e s u l t e d i n t h e f o r m a t i o n o f a s i n g l e broad r i v e r t e r r a c e between 270 and 360 f e e t below t h e b e n c h - l i k e remnants o f t h e o r i g i n a l l a k e f l o o r ( R y der, 1971). G u l l y s formed w i t h i n t h e s i l t bench, d r a i n i n g i n t o t h e main r i v e r c h a n n e l . F u r t h e r e r o s i o n o f t h e l a c u s t r i n e s i l t l e f t t h e g u l l i e s f i l l e d w i t h a c o n s i d e r a b l e t h i c k n e s s o f c o l l u v i u m . Today, c o n t i n u i n g e r o s i o n i s r e s u l t i n g i n t h e f o r m a t i o n o f s e c o n d a r y g u l l i e s w i t h i n . t h e v a l l e y f i l l . 1.3 S u r f i c i a l Geology The main d e p o s i t w i t h i n t h e South Thompson R i v e r V a l l e y has been r e f e r r e d t o as t h e South Thompson S i l t s by F u l t o n ( 1 9 6 5 ) . These g l a c i o -l a c u s t r i n e s i l t s form w e l l - d e f i n e d benches on e i t h e r s i d e o f t h e South Thompson R i v e r near Kamloops. The s i l t i s c h a r a c t e r i z e d by v a r v i n g and l a m i n a t i o n s . Each r h y t h m i t e c o n s i s t s o f a t h i c k s i l t l a y e r on t o p o f a t h i n c l a y band. The c l a y bands v a r y from one i n c h o r l e s s i n t h i c k n e s s near t h e t o p o f t h e s e c t i o n t o h a l f an i n c h t o f o u r i n c h e s near t h e lower s e c t i o n . The s i l t bands grade from one i n c h a t t h e t o p o f t h e s e c t i o n t o 250 i n c h e s t h i c k a t t h e base ( F u l t o n , 1965). H o r i z o n t a l l a m i n a t i o n s p a r a l l e l t o t h e beddin g a r e e v i d e n t w i t h i n t h e s i l t bands. Throughout much o f t h e v a l l e y , t h e s i l t i s c o v e r e d by a brown l o e s s 4. capping , o n t h e bench s u r f a c e v a r y i n g between 6 i n c h e s t o 10 f e e t t h i c k . The o t h e r s o i l d e r i v e d from t h e l a c u s t r i n e s i l t i s t h e c o l l u v i a l m a t e r i a l which c o v e r s t h e s l o p e s below t h e near v e r t i c a l b l u f f f a c e o f t h e benches. G u l l y f l o o r s a r e a l s o f i l l e d by c o n s i d e r a b l e t h i c k n e s s e s o f t h e c o l l u v i u m . In t h e f i e l d , t h e c o l l u v i a l d e p o s i t s may be i d e n t i f i e d by i t s ' l a c k o f v a r v i n g ( a l t h o u g h l a m i n a t i o n s may be p r e s e n t ) and by t h e p r e s e n c e o f two w h i t e v o l c a n i c ash l a y e r s . These t e p h r a l a y e r s a r e t h o u g h t t o be Mazama (6600 y r s . B . P . ) and S t . Helen's Y (3200 y r s . B.P.) ( F u l t o n , I975). 1.4 C I i m a t e The s e m i - a r i d e n v i r o n m e n t o f t h e Kamloops r e g i o n has been summarized by Evans and Buchanan ( 1 9 7 6 ) : mean annual p r e c i p i t a t i o n 260.6 mm mean annual r a i n f a l l 186.9 mm mean annual s n o w f a l l 769.6 mm The hot summers r e a c h a mean t e m p e r a t u r e o f 20.8 °C i n J u l y w i t h d a i l y maximums o f 29 °C. Most o f t h e r a i n f a l l o c c u r s as summer showers d u r i n g t h i s p e r i o d . In December, Jan u a r y and F e b r u a r y , t e m p e r a t u r e s drop below f r e e z i n g . In e a r l y March, t e m p e r a t u r e s r i s e s u f f i c i e n t l y f o r r a p i d i c e and snowmelt c o n d i t i o n s . D u r i n g t h i s month, t h e w e t t e s t ground c o n d i t i o n s e x i s t - e s p e c i a l l y when combined w i t h t h e o c c a s i o n a l h i g h i n t e n s i t y shower. The v e g e t a t i v e c o v e r i s s p a r s e , c o n s i s t i n g m a i n l y o f sa g e b r u s h and bun c h g r a s s . 5. CHAPTER 2  FIELD RECONNAISSANCE A low l e v e l f l i g h t from Kamloops t o P r i t c h a r d and down t h e Okanagan V a l l e y t o P e n t i c t o n was i n i t i a l l y c a r r i e d out.-. T h i s was f o l l o w e d by a s e r i e s o f ground t r a v e r s e s , j o i n t mapping, a s o i l s a m p l i n g program and a f i e l d seepage t e s t . 2.1 Problems Observed 2.1.1 P i p e s and S i n k h o l e s Many p i p e s were found i n t h e c o l l u v i a l d e p o s i t s and a l t h o u g h l e s s numerous, t h e y e x i s t w i t h i n t h e g I a c i o I a c u s t r i n e s i l t . P i p e s e x i s t as s h a f t - l i k e v o i d s w i t h t h e i r axes near h o r i z o n t a l , near v e r t i c a l o r i n c l i n e d w i t h t h e s l o p e s , ( f i g 2'& 3 ) . P i p e o p e n n i n g s as l a r g e as 12 f e e t i n d i a m e t e r have been found. The o r i g i n o f t h e s e p i p e s has been a t t r i b u t e d t o ( I ) t h e p i p i n g p r o c e s s as a r e s u l t o f w a t e r e r o s i o n i n which s i l t p a r t i c l e s a r e d i s l o d g e d and c a r r i e d away by f l o w i n g w a t e r and/or (2) t h e c o l l a p s e o f t h e l o o s e s o i l s t r u c t u r e as a r e s u l t o f w e t t i n g . A r e l a t e d f e a t u r e i s t h e p r e s e n c e o f l a r g e ground d e p r e s s i o n s o r " s i n k h o l e s " found on t h e bench s u r f a c e . They o c c u r e i t h e r as i s o l a t e d d e p r e s s i o n s o r i n a l i g n m e n t w i t h g u l l i e s ( f i g 4 & 5 ) . These have been a t t r i b u t e d t o (1) t h e c a v i n g o f t h e ground above a s u b t e r r a n e a n p i p e o r (2) t o t h e c o l l a p s e o f s o i l s t r u c t u r e upon w e t t i n g , e i t h e r o f t h e near s u r f a c e s i l t o r a t depth f o l l o w e d by s u c c e s s i v e c a v i n g o f t h e o v e r l y i n g m a t e r i a l (Hardy, 1950; Evans & Buchanan, 1976; Nyland & M i l l e r , 1977). F i g u r e 2 . H o r i z o n t a l p i p e i n c o l l u v i u m i s a p p r o x i m a t e l y 12 f e e t i n d i a m e t e r . Note t h e p r e s e n c e of t h e t e p h r a l a y e r ( w h i t e , h o r i z o n t a l band). F i g u r e 3 . V e r t i c a l p i p e i n c o l l u v i u m near t h e base of a s t e e p b l u f f f a c e w i t h i n Magaz i ne GuI Iy. F i g u r e 5. A s i n g l e i s o l a t e d s i n k h o l e w i t h i n t h e c o l l u v i u m a t t h e b o t t o m o f M a g a z i ne GuI Iy. 8. 2.1.2 S l o p e S t a b i I i t y A l t h o u g h no major s l o p e f a i l u r e s a r e e v i d e n t w i t h i n t h e s t u d y a r e a , i n s t a b i l i t y does e x i s t on a s m a l l e r s c a l e . E v i d e n c e o f s h a l l o w s l a b f a i l u r e s and b l o c k f a i l u r e s can be seen on t h e near v e r t i c a l s l o p e s f a c i n g t h e South Thompson R i v e r and i n t h e s t e e p g u l l y w a l l s w i t h i n t h e l a c u s t r i n e d e p o s i t ( f i g . 6 ) . C o l l u v i a l s l o p e f a i l u r e s w i t h i n t h e s t u d y a r e a a r e a l s o o f s m a l l magnitude. However, o u t s i d e t h e s t u d y a r e a , on t h e s o u t h b l u f f s o f t h e Thompson V a l l e y , c o l l u v i a l s l o p e f a i l u r e s a r e o f g r e a t e r f r e q u e n c y and magnitude due t o u r b a n i z a t i o n a I d i s t u r b a n c e s such as under-c u t t i n g of t h e t o e o f s l o p e s . 2.2 S l o p e Geometry Near Kamloops, t h e s i l t o c c u r s i n benches on both s i d e s of t h e South Thompson R i v e r , s l o p i n g g e n t l y t o w a r d s t h e r i v e r a t an e l e v a t i o n o f 1600 t o 1500 f e e t . The bench t e r m i n a t e s a t an i r r e g u l a r s c a r p l i n e r u n n i n g a p p r o x i m a t e l y p a r a l l e l t o t h e r i v e r below which a s t e e p i r r e g u l a r b l u f f w a l l b r e a k s i n t o c o l l u v i a l s l o p e s ( f i g . 7 ) . Many s t e e p s i d e d g u l l i e s w i t h depths i n t h e o r d e r o f 300 f e e t d i s s e c t t h e benches p e r p e n d i c u l a r t o t h e r i v e r . One o f t h e s e g u l l i e s (Magazine G u M y M f i g . 8) was chosen as t h e d e t a i l s t u d y a r e a s i n c e i t c o n t a i n s some o f t h e s t e e p e s t and h i g h e s t s t a n d i n g b l u f f f a c e s , r e p r e s e n t i n g t h e l e a s t s t a b l e s l o p e s . From e i g h t s u r v e y e d s e c t i o n s w i t h i n Magazine G u l l y , t h e s l o p e geometry can be g e n e r a l i z e d i n t h e form g i v e n i n f i g u r e 9, c o n s i s t i n g o f a p p r o x i m a t e l y 100 f e e t o f l a c u s t r i n e s i l t a t a 70° s l o p e , b r e a k i n g i n t o a 35° s l o p e o f c o l l u v i u m t h a t g r a d e s i n t o a v e r y s l i g h t l y concave-up s u r f a c e which F i g u r e 6. E v i d e n c e o f a s l o p e f a i l u r e on t h e e a s t f a c e o f M a g a z i n e G u l l y . F i g u r e 7. The bench f a c i n g t h e S o u t h Thompson R i v e r c o n s i s t s o f a s t e e p i r r e g u l a r b l u f f w a l l w h i c h b r e a k s i n t o c o l l u v i a l s l o p e s . F i g u r e 8. O b l i q u e a e r i a l v i e w o f t h e d e t a i l s t u d y a r e a ( M a g a z i n e G u l l y ) l o o k i n g n o r t h . 7 70" S C A L E L.ACUSTRIA/£' SilT \ C O L L U N / I U M \ N \ FIG. 3 GENERAL SLOPE GEOMETRY WITHIN MAGAZINE GULLY 12. c o u l d be a p p r o x i m a t e d by a u n i f o r m s l o p e a n g l e of 28 from t h e h o r i z o n t a l . L i t t l e i s known about t h e depth o f c o l l u v i u m on t h e s l o p e s , however, a c r o s s - s e c t i o n g i v e n by Evans (I976) which was deduced from r e s i s t i v i t y and dynamic cone p e n e t r o m e t e r d a t a i n d i c a t e s depths o f 30 t o 60 f e e t a t t h e g u l l y bottom and 15 t o 30 f e e t midway down t h e c o l l u v i a l s l o p e s . The depth o f t h e l a c u s t r i n e s i l t d e p o s i t i s a l s o unknown but i t i s b e l i e v e d t h a t t h e s i l t e x t e n d s t o a minimum depth o f 500 f e e t and p o s s i b l y g r e a t e r t h a n 1300 f e e t i n depth ( F u l t o n , 1965). 2.3 J o i n t i ng A s m a l l j o i n t s u r v e y was c a r r i e d o u t by r u n n i n g t r a v e r s e s a l o n g t h e base o f t h e s t e e p b l u f f f a c e w i t h a B r u nton compass. As i n a l l j o i n t s u r v e y s , human b i a s and a c c e s s i b i l i t y problems must be kept i n mind. J o i n t o r i e n t a t i o n s were measure, m a i n l y from t h e e a s t f a c e o f Magazine G u l l y which t r e n d s a p p r o x i m a t e l y N o r t h - S o u t h . The s t e r e o n e t p l o t ( f i g . 10) shows t h e p o l e s o f j o i n t s p l o t t e d i n n o r t h e r n : h e m i s p h e r e p r o j e c t . i o r K o f . a WuIf net (Hoek & B r a y , l974).The j o i n t s a r e m a i n l y s t e e p l y d i p p i n g t o w a r d s t h e w e s t e r n s e c t o r . T h i s i s e x p e c t e d s i n c e j o i n t s d i p p i n g e a s t would r e p r e s e n t u n s t a b l e c o n d i t i o n s o n /the e a s t e r n b l u f f f a c e . S i n c e t h e j o i n t s a r e a l l near v e r t i c a l , a r o s e diagram i s p l o t t e d ( f i g . 11) w i t h r a d i a l l e n g t h s r e p r e s e n t i n g t h e number o f j o i n t s f a l l i n g w i t h i n each 10° s e c t o r o f t h e s t e r e o n e t . The r o s e diagram i n d i c a t e d t h a t f o u r major j o i n t s e t s e x i s t n e a r l y p e r p e n d i c u l a r t o t h e a l m o s t h o r i z o n t a l b e d d d i n g . Two major s e t s e x i s t a t s t r i k e s o f 30° and 120° w h i l e two weaker s e t s o c c u r a t a p p r o x i m a t e l y 0° and 90°. The c o m b i n a t i o n of t h e s e j o i n t s e t s forms t h e l o c a l columnar j o i n t i n g seen i n t h e f i e l d ( f i g . 39). T h i s t y p e o f 1 3 . X OF Jo»r*T$ S i t e s -F\6. / 0 STEReoKET P L O T O F TOIKTS 1 4 . S R A D I A L S C A L E ; I " = S P O L E S C1 FRoM. EASTEItK 6U>fF FA.CE. C i PRO»A SVTCS FIG. //• ROSE DIAGRAM columnar j o i n t i n g i s a l s o t y p i c a l o f t h e s i l t y l o e s s d e p o s i t s i n t h e Western U n i t e d S t a t e s . I t s h o u l d be r e a l i z e d t h a t t h i s j o i n t s u r v e y i s l i m i t e d t o a v e r y s p e c i f i c a r e a and may not a p p l y on a r e g i o n a l b a s i s . Many o f t h e j o i n t s a r e c o n t i n u o u s and near p l a n a r e x t e n d i n g t h e f u l l h e i g h t o f t h e b l u f f e x p o s u r e w i t h j o i n t s p a c i n g s o f about 4 t o 8 f e e t . W i t h i n t h e t o p 20 t o 30 f e e t o f t h e s e c t i o n , t h e j o i n t s a r e more c l o s e l y s p a c e d , becoming d i s c o n t i n u o u s f i s s u r e s . The o r i g i n o f t h e j o i n t i n g i s p r o b a b l y due t o s t r e s s r e l e a s e and s h r i n k a g e on d e s s i c a t i o n . Most j o i n t s show no s i g n s o f w e a t h e r i n g , but many a r e c o a t e d w i t h a brown weathered f i l m and a few show s i g n s o f s w e l l i n g and s l a k i n g a l o n g t h e f r a c t u r e I i ne. 2.4 S o i I Samp I i ng D i f f i c u l t i e s were e n c o u n t e r e d i n a t t e m p t s by t h e Department o f Highways t o r e t r i e v e i n t a c t u n d i s t u r b e d s i l t samples by S h e l b y Tubes. The samples o b t a i n e d by t h i s method were h i g h l y f r a c t u r e d . T h e r e f o r e , Sampling by backhoe o p e r a t i o n was employed. B l o c k samples were o b t a i n e d from two backhoe p i t s on t h e bench s u r f a c e a d j a c e n t t o Magazine g u l l y ( f i g . 12) a t a depth o f 4£ t o 51 f e e t . The b l o c k s were hand c a r v e d w i t h a s h a r p k n i f e , making use o f e x i s t i n g i n - s i t u f r a c t u r e s . D u r i n g s a m p l i n g , t h e weather was g e n e r a l l y c l o u d y w i t h b r i e f p e r i o d s o f s u n s h i n e . The t e m p e r a t u r e s reached 31°C w i t h a h u m i d i t y o f 15$ (June 29, 1976). To p r e v e n t m o i s t u r e l o s s , t h e s o i l samples were i m m e d i a t e l y wrapped w i t h " s a r a n wrap" i n t h e f i e l d and t r a n s p o r t e d t o t h e Kamloops l a b o r a t o r y f o r w a x i n g . The samples were t h e n t a k e n by c a r t o t h e U n i v e r s i t y o f B r i t i s h Columbia where t h e y were re-waxed w i t h a low 1 6 . p e r m e a b I i t y , p l i a b l e wax and s t o r e d i n a c o n s t a n t t e m p e r a t u r e l a b o r a t o r y e n v i ronment. P r i o r t o t h e backhoe o p e r a t i o n , s u r f a c e b l o c k samples were o b t a i n e d from two o t h e r l o c a t i o n s w i t h i n t h e l a c u s t r i n e d e p o s i t f o r s p e c i f i c g r a v i t y d e t e r m i n a t i o n s and p r e l i m i n a r y t e s t s t o a c e s s i t s t r i m m a b i l i t y and s p e c i a l equipment r e q u i r e m e n t s . In mid-May o f 1977, t h e s t u d y was f u r t h e r e xtended t o i n c l u d e t h e p r e l i m i n a r y c o n s o l i d a t i o n t e s t i n g o f c o l l u v i u m . Two waxed b l o c k samples o f c o l l u v i u m were s u p p l i e d by t h e Department of Highways ( G e o t e c h n i c a I Branch) i n Kamloops. The e n c l o s e d d e s c r i p t i o n s o f t h e l o c a t i o n o f t h e b l o c k s a r e i n c l u d e d i n Appendix I a l o n g w i t h t h e d e s c r i p t i o n of t h e l a c u s t r i n e samples and t h e i r s i t e l o c a t i o n s . 2.5 F i e l d Seepage S i m u l a t i o n A s m a l l t r e n c h was e x c a v a t e d 4 f e e t west o f t h e backhoe sample p i t #3 and f i I led w i t h w a t e r t o o b s e r v e t h e seepage r a t e and t o a t t e m p t t o cause p i p i n g and/or a s l o p e f a i l u r e t o o c c u r on t h e a d j a c e n t p i t f a c e . The s m a l l t r e n c h was c o n t i n u o u s l y f e d from a water t r u c k t o m a i n t a i n a p p r o x i m a t e l y 27 i n c h e s o f water a t t h e m i d p o i n t of t h e t r o u g h . The i n i t seepage under t h e l a r g e c a p i l l a r y head was 1.0 f t . ~ V m i n . d r o p p i n g t o about 0.9 f t . ^ / m i n . a f t e r one hour. The t r e n c h was t h e n a l l o w e d t o d r a i n c o m p l e t e l y and a s m a l l 2 i n c h d i a m e t e r i d e n t a t i o n ( p i p e ? ) was o b s e r v e d a t t h e c e n t r a l b a s e - l i n e of t h e west s i d e o f t h e t r e n c h . The t r e n c h was a g a i n f i l l e d , g i v i n g a seepage r a t e o f 0.7 f t . ^ / m i n . a f t e r a n o t h e r hour. The w a t e r l e f t i n t h e t r e n c h was t h e n c h a n n e l l e d away w i t h t h e backhoe t o d e t e r m i n e t h e p o s i t i o n o f t h e w e t t e d f r o n t . The f r o n t extended 3 f e e t t o e i t h e r s i d e o f t h e water t r e n c h edges and extended 4 f e e t and 6 f e e t below t h e t r e n c h f l o o r on t h e e a s t and west s i d e s r e s p e c t -i v e l y . The w e t t e d f r o n t d i d not e n chroach o n t o t h e p i t f a c e i n t h e t i m e a l l o t t e d as e x p e c t e d , t h u s no p i p i n g was e v i d e n c e d on t h i s f a c e . However, on t h e west s i d e o f t h e t r o u g h , t h e " p i p e " formed was l a r g e enough t o i n s e r t an arm i n t o . The " p i p e " was a v e r y low s t r e n g t h ' l i q u e f i e d ' c hannel e x t e n d i n g about 8 i n c h e s i n t o t h e f a c e and c u r v i n g t o p a r a l l e l t h e t r e n c h f a c e , h e a d i n g s o u t h f o r an unknown d i s t a n c e . C a l c u l a t i o n s show t h a t t h e e s t i m a t e d 160 f t . " ^ o f w a t e r pumped i n t o t h e t r e n c h c o u l d e a s i l y go i n t o t h e p a r t i a l f i l l i n g o f t h e v o i d s i n t h e s i l t . The t o t a l v o i d space w i t h i n t h e w e t t e d zone i s a p p r o x i m a t e l y 250 f t . ~ \ t h e r e f o r e t h e w a t e r i n p u t r e p r e s e n t s o n l y 64$ s a t u r a t i o n o f t h e s o i I . CHAPTER 3 BASIC SOIL PROPERTIES 3. 1 S p e c i f i c G r a v i t y S p e c i f i c g r a v i t y d e t e r m i n a t i o n s were c a r r i e d out i n t h e c o n s t a n t t e m p r a t u r e l a b o r a t o r y a c c o r d i n g t o t h e p r o c e d u r e o u t l i n e d i n Lambe (1951). A t o t a l o f seven t e s t s w i t h samples from f o u r d i f f e r e n t l o c a t i o n s r e s u l t e d i n s p e c i f i c g r a v i t i e s between 2.749 and 2.796 w i t h an a verage o f 2.77 f o r t h e l a c u s t r i n e s i l t . The h i g h s p e c i f i c g r a v i t y i s p r o b a b l y a t t r i b u t e d t o t h e p r e s e n c e o f mica i n t h e s i l t . S p e c i f i c g r a v i t i e s were a l s o d e t e r m i n e d f o r two c o l l u v i a l samples. The sample from t h e i n c i s e d c r e e k showed a s p e c i f i c g r a v i t y o f 2.60 and t h e sample from t h e w a l l o f a s m a l l p i p e had a s p e c i f i c g r a v i t y of 2.78. I t would seem t h a t t h e p r o p e r t i e s of t h e c o l l u v i u m i s not u n i f o r m and w i l l be h i g h l y dependent on i t s l o c a t i o n . 3.2 G r a i n S i z e A n a l y s i s Hydrometer a n a l y s i s of t h e l a c u s t r i n e s i l t from s i t e #3 was performed by t h e u n d e r g r a d u a t e s t u d e n t s a t U.B.C. under p r o f e s s o r and g r a d u a t e s t u d e n t s u p e r v i s i o n . The p r o c e d u r e as d e s c r i b e d i n Lambe (1951) was f o l l o w e d u s i n g sodium hexametaphosphate as t h e d e f l o c u I a t i n g a g e n t . Sample p r e p a r a t i o n i n c l u d e d m i x i n g t h e sample and d e f I o c u I a t i n g agent i n a b l e n d e r f o r 10 m i n u t e s . 21 . The d a t a i s p l o t t e d i n f i g u r e 13. T a b l e I summarizes t h e r e s u l t s . TABLE I. Average r e s u l t s o f t h e hydrometer a n a l y s i s o f t h e Kamloops s i l t ( l a c u s t r i n e s i l t ) from s i t e #3. % sand A% % s i I t % c l a y 1% D 1 Q 0.0027 mm D,n 0.0092 mm 50 C 3.4 u MIT c l a s s i f i c a t i o n : ' f a i r l y ' u n i f o r m c l a y e y s i l t . Data from Evans and Buchanan (1976) a g r e e s w i t h f i g u r e 13 even though a d e f I o c u I a t i n g agent was not added i n t h e i r t e s t i n g p r o c e d u r e . T h e i r g r a i n s i z e a n a l y s i s on t h e c o l l u v i u m i n d i c a t e s l i t t l e d i f f e r e n c e i n t h e p a r t i c l e s i z e d i s t r i b u t i o n as compared t o t h a t o f t h e l a c u s t r i n e s i l t s . T h i s s i m i l a r i t y s u g g e s t s l i t t l e s o r t i n g has r e s u l t e d and c o n s e q u e n t l y c o n f i r m s t h a t t h e s i l t was t r a n s p o r t e d o n l y a s h o r t d i s t a n c e p r i o r t o r e d e p o s i t i o n as c o l l u v i u m . 3.3 Mi n e r a l o g y M i n e r a l o g i c a I a n a l y s i s on t h e l a c u s t r i n e s i l t has been p r e s e n t e d by F u l t o n (I965) and Q u i g l e y ( I 9 7 6 ) . T a b l e s MA and MB shows a g e n e r a l agreement i n t h e a n a l y s i s . I t s h o u l d be r e a l i z e d however, t h a t F u l t o n a n a l y s e d t h e s i l t and sand f r a c t i o n s o p t i c a l l y w h i l e Q u i g l e y used X-ray powder a n a l y s i s on t h e whole sample ( i e . w i t h t h e c l a y f r a c t i o n i n c l u d e d ) . TABLE MA. COMPOSITION OF KAMLOOPS SILT MINERAL FULTON QUIGLEY ( o p t i c a M y) ( X - r a y powder) q u a r t z main c o n s t i t u e n t abundant f e 1 d s p a r major c o n s t i t u e n t moderate mi ca major c o n s t i t u e n t mi nor f e r r o m a g n e s i a n m i n e r a l s minor c o n s t i t u e n t mi nor TABLE MB. X-RAY DIFFRACTION OF CLAY FRACTION ONLY M1NERAL FULTON QUIGLEY montmor i 11 on i t e 35 - 40 % abundant i I I i te/mi ca 28 - 35 % moderate ch1 o r i t e 27 - 36 % m i nor - k a o L i n i t e - mi nor 23. 3.4 A t t e r b e r q L i m i t s and F i e l d Mois+ure C o n t e n t Data f o r a t t e r b e r g l i m i t s o f t h e s i l t has been p r e s e n t e d by Evans and Buchanan ( 1 9 7 6 ) . L i q u i d l i m i t s g i v e n ranged from 27$ t o 36.8$ w i t h an a v e r a g e o f 31.1$ and t h e p l a s t i c i t y index ranged from 1.9 t o 11.7$ w i t h an a v e r a g e o f 8.4$. On t h e p l a s t i c i t y c h a r t , t h i s d a t a would p l o t c l o s e t o t h e A - I i n e w i t h i n t h e same r e g i o n as t h e s i l t y l o e s s of t h e w e s t e r n U n i t e d s t a t e s s t u d i e d by G i b b s , Hi I f and H o l t z ( 1 9 6 0 ) . D u r i n g t h e summer, n a t u r a l w a t e r c o n t e n t s measured by Evans & Buchanan (1976) ranged from 0.2$.to 2.4$ near t h e s u r f a c e . Samples from t h e backhoe o p e r a t i o n a t a depth o f a p p r o x i m a t e l y 5 f e e t had a n a t u r a l w a t e r c o n t e n t o f 7-8$ i n June a t t h e t i m e o f s a m p l i n g . A w a t e r g r a d i e n t i s e x p e c t e d t o e x i s t w i t h depth but i t s a c t u a l v e r t i c a l v a r i a t i o n i s not known and s u b j e c t e d t o s e a s o n a l and l o c a l f l u c t u a t i o n s . The r e g i o n a l ground w a t e r t a b l e e x i s t s w e l l below t h e s l o p e s under c o n s i d e r a t i o n w i t h i n t h e s t u d y a r e a . However, i t i s h i g h l y p o s s i b l e t h a t p erched water t a b l e s d u r i n g r a p i d snowmelt and heavy r a i n f a l l above t h e c l a y seams w i t h i n t h e v a r v e d sequence e x i s t s . 24. CHAPTER 4 LABORATORY TESTS 4.1 S c a n n i n g E l e c t r o n M i c r o s c o p e S t u d i e s Three samples were s t u d i e d under t h e E t e c A u t o s c a n S c a n n i n g E l e c t r o n M i c r o s c o p e on t h e U n i v e r s i t y o f B r i t i s h C olumbia campus. The f i r s t two u n d i s t u r b e d samples o f t h e l a c u s t r i n e s i l t were scanned p a r a l l e l and p e r p e n d i c u l a r t o t h e b e d d i n g . . The t h i r d sample was a remolded sample viewed p e r p e n d i c u l a r t o t h e s e d i m e n t a t i o n d i r e c t i o n . The remolded sample was formed by a l l o w i n g a w e l l - m i x e d s l u r r y t o s l o w l y a i r d r y under l a b o r a t o r y c o n d i t i o n s . The i n i t i a l w a t e r c o n t e n t s a s s o c i a t e d w i t h t h e samples were c o n s i d e r e d low enough t h a t s t r u c t u r a l a l t e r a t i o n was n e g l i g i b l e d u r i n g t h e d r y i n g p r o c e s s ( t h e u n d i s t u r b e d samples had a w a t e r c o n t e n t o f 1.6% and t h e remolded sample was a t 1.9% w a t e r c o n t e n t ) . " D r y i n g " was -4 a c h i e v e d by s l o w l y a p p l y i n g a vacuum o f 10 t o r r t o t h e samples. The samples were t h e n c o a t e d w i t h a few hundred Angstroms o f c a r b o n ( g o l d -p a l l a d i u m c o a t i n g was a d v o i d e d s i n c e X-ray m i c r o - p r o b e a n a l y s i s was des i r e d ) . E l e c t r o n p h o t o m i c r o g r a p h s o f t h e s o i l a r e p r e s e n t e d i n f i g u r e s 14 t o 19. S t e r e o p a i r s ( not shown) o f t h e samples showed a s t r o n g h o r i z o n t a l p r e f e r e n c e i n o r i e n t a t i o n o f t h e p l a t t y p a r t i c l e s i n t h e u n d i s t u r b e d and remolded s i l t . S t r u c t u r a l l y , t h e r e a p p ears t o be l i t t l e d i f f e r e n c e between t h e remolded and u n d i s t u r b e d l a c u s t r i n e s i l t o t h e r t h a n t h e v o i d r a t i o d i f f e r e n c e s ( I . I 4 and 1.28 r e s p e c t i v e l y ) . F i g u r e 14. P h o t o m i c r o g r a p h o f t h e Kamloops s i l t , u n d i s t u r b e d sample, s i d e v i e w , a t 400X magn i f i c a t i on. F i g u r e 15. Kamloops s i l t , remolded sample, s i d e v i e w , 400X m a g n i f i c a t i o n . F i g u r e 16. P h o t o m i c r o g r a p h o f u n d i s t u r b e d K a m l o o p s S i l t a t 1000X m a g n i f i c a t i o n , v i e w e d p a r a l l e l t o t h e b e d d i n g . F i g u r e 17. P h o t o m i c r o g r a p h o f r e m o l d e d s i l t ( K a m l o o p s s i l t ) a t 1000X m a g n i f i c a t i o n , v i e w e d f r o m t h e s i d e , i e . p e r p e n d i c u l a r t o t h e s e d i m e n t a t i o n d i r e c t i o n . 27. F i g u r e 18. P l a n e view of t h e u n d i s t u r b e d Kamloops S i l t a t 1000X m a g n i f i c a t i o n . P a r t i c l e s 18A & 18B were s t u d i e d under t h e E l e c t r o n M i c r o p r o b e . F i g u r e 19. P l a n e view o f t h e u n d i s t u r b e d s i l t a t 1000X m a g n i f i c a t i o n . Peds 19A & 19B were s t u d i e d under t h e E l e c t r o n M i c r -probe. Note t h e c l a y b r i d g i n g formed by 19A. 28. A m i c r o p r o b e ( O r t e c M u l t i c h a n i e l A n a l y s e r , Model 6200) was used i n an a t t e m p t t o i d e n t i f y t h e m i n e r a l o g y of t h e p a r t i c l e s . But i n t e r p r e t a t i o n i s a l ways d i f f i c u l t when o n l y e l e m e n t a l d a t a can be o b t a i n e d and t h e q u a n t i t a t i v e d a t a b e i n g q u e s t i o n a b l e . The p a r t i c l e s 18A, 18B, 19A and 19B i n f i g u r e s 18 and 19 y i e l d t h e f o l l o w i n g e l e m e n t s , l i s t e d i n d e c r e a s i n g peak i n t e n s i t y . P a r t i c l e 18A: S i , A l , Fe, K, Mg, Na, T i P a r t i c l e 18B: S i , A l , Ca, Fe, K, Mg, Na, T i P a r t i c l e 19A: S i , A l , Mg, Fe, Ca, K, Na, T i , S P a r t i c l e 19B: S i , A l , Fe, Ca, S, Mg, K, T i The p l a t t y p a r t i c l e s i n t h e p h o t o m i c r g r a p h s a r e p r o b a b l y mica s h e e t s (eg. p a r t i c l e 18A i n f i g u r e 18). P a r t i c l e 18B may be f e l d s p a r . The c l u s t e r s o f 19A and 19B i n f i g u r e 19 a r e p o s s i b l y montmori I l o n i t e . Much o f t h e c l a y p r e s e n t i n t h e sample e x i s t s as c l u s t e r s o r peds, but a t t h e same t i m e , i t p r o v i d e s bonding w i t h t h e s i l t p a r t i c l e s i t c o n t a c t s . The p h o t o m i c r o g r a p h s a r e g e n e r a l l y a t t o o s m a l l a s c a l e f o r s m a l l b r i d g i n g c l a y s t r u c t u r e s t o be c l e a r l y v i s i b l e . C l o s e e x a m i n a t i o n of t h e l a r g e r s c a l e d photographs (eg. f i g u r e 19) c l e a r l y shows t h e t y p e o f b r i d g i n g p o s s i b l e between s i l t g r a i n s . S c a t t e r e d t h r o u g h o u t t h e sample a r e s i l i c e o u s d i a t o m s (me Ios i r a  g r a n u I a t a ) . T h i s common s p e c i e s i s a s s o c i a t e d w i t h f r e s h w a t e r l a k e s and t h e r e f o r e most l i k e l y d a t e s back t o t h e l a s t d e g I a c i a t i o n . F I G . 20 U N C 0 N F \NEO COMPfctSSloti ( A N I ^ Y OF S C * « W T ^ ( OF'K*«MU<>OPS S O T ' ) APPROX. PERPENDICULAR TO BE.DD.MC — ApPRox. P A R A L L E L TO tjEDOlUG 3 - 5 : 2 4 . JJO 3 - 5 - 2 5 - If 3-S.2C V 3 - S.17 3 - 5 2 8 69° 3 - 5--2? er 3 - - 5 \Z I 64° 3 - 5 . 2 3 8o° S T R A I N , C VD 30. 4.2 U n c o n f i n e d Compression T e s t To d e t e r m i n e whether s t r e n g t h a n i s o t r o p y e x i s t s f o r t h e l a c u s t r i n e s i l t , e i g h t samples were t e s t e d i n t h e motor d r i v e n u n c o n f i n e d c o m p r e s s i o n a p p a r a t u s . Four samples were s u b j e c t e d t o a x i a l loads p e r p e n d i c u l a r t o t h e b edding ( t 11°) and f o u r samples p a r a l l e l t o t h e b e d d i n g (+ 10°). A l l samples were trimmed from t h e same i n t a c t b l o c k from s i t e #3. The w a t e r c o n t e n t of t h e s i l t b l o c k was 6.8$. The samples were f a i l e d a t a c o n s t a n t s t r a i n r a t e o f 0.1"/min. o r a p p r o x i m a t e l y 3$ s t r a i n per m i n u t e . The s t r e s s - s t r a i n d a t a p l o t t e d i n f i g u r e 20 shows t h a t a s l i g h t 2 a n i s o t r o p y e x i s t s w i t h maximum s t r e n g t h s ( T ) o f 1.93 - 2.36 kg/cm f o r samples loaded p e r p e n d i c u l a r t o t h e b e d d i n g . A l t f a i l e d samples e x h i b i t e d a x i a l s p l i t t i n g which i s c h a r a c t e r i s t i c o f t h e f a i I ure mode o f b r i t t l e m a t e r i a l s i n u n c o n f i n e d c o m p r e s s i o n (Townsend, Sangrey & Walker, 1969; C o a t e s , , 1970). 4.3 T r i a x i a l T e s t To d e t e r m i n e t h e s t r e n g t h e n v e l o p e o f t h e s i l t , c o n s o l i d a t e d -d r a i n e d t r i a x i a l t e s t s were performed on s a t u r a t e d samples. The e f f e c t i v e c o n f i n i n g p r e s s u r e s used ranged from 0.05 kg/cm^ t o 3.0 kg/cm^ s a t u r a t i o n a p p a r a t u s and p r o c e d u r e i s d e s c r i b e d i n t h e f o l l o w i n g s e c t i o n s . S i n c e u n d r a i n e d t e s t s r e q u i r e 100$ s a t u r a t i o n f o r a c c u r a t e pore p r e s s u r e measurements, d r a i n e d t e s t s were used. The pore p r e s s u r e parameter, B, was measured a t v a r i o u s s t a g e s of s a t u r a t i o n u n t i l a B-vaIue o f 95$ o r g r e a t e r was r e a c h e d . T h i s p r o c e d u r e g e n e r a l l y r e q u i r e d from 3-7 days o f p e r c o l a t i o n under a s m a l l p r e s s u r e g r a d i e n t and h i g h b a c k p r e s s u r e s (see s e c t i o n 4.3.2). The sample was t h e n s u b j e c t e d t o i s o t r o p i c c o n s o l i d a t i o n f o r a p p r o x i m a t e l y 24 hours b e f o r e l o a d i n g t o f a i l u r e . 31 . A l l t e s t s were performed w i t h t h e d e v i a t o r s t r e s s a p p r o x i m a t e l y p e r p e n d i c u l a r t o t h e b e d d i n g . The bedding o r i e n t a t i o n was e v i d e n c e d by l a m i n a t i o n s on most o f t h e trimmed samples ( t h e t r i m m i n g p r o c e d u r e s a r e b r i e f l y o u t l i n e d i n Appendix I I ) . With t h e d e v i a t o r s t r e s s v e r t i c a l d u r i n g t e s t i n g , t h e l a m i n a t i o n s were measured t o range from 5° t o 24° o f f h o r i z o n t a l w i t h most sample bedding o r i e n t a t i o n s between 5° t o 12°. 4.3.1 T r i a x i a l T e s t A p p a r a t u s The c o n v e n t i o n a l t r i a x i a l c e l l was used i n which c y l i n d r i c a l samples 3" h i g h by 1.4V i n d i a m e t e r a r e s e a l e d from t h e c e l l f l u i d by d o u b l e r u b b e r membranes. A t h i n l a y e r o f s i l i c o n e l u b r i c a n t was a p p l i e d between t h e two r u b b e r membranes t o m i n i m i z e f r i c t i o n a l r e s i s t a n c e . A s c h e m a t i c diagram o f t h e a p p a r a t u s i s shown i n f i g u r e 21. The t o p and bottom d r a i n a g e l i n e s a r e c o n n e c t e d t o a " t r e e " c o n t a i n i n g a c a l i b r a t e d p i p e t t e , a b e l l o f r a m r e s e r v o i r and a Tyco Model AB pore p r e s s u r e t r a n s d u c e r . The c e l l p r e s s u r e i s a p p l i e d t h r o u g h a c l e a r l u c i t e r e s e r v o i r a t t a c h e d t o th e t o p o f t h e t r i a x i a l c e l l u n i t . The bottom and t o p d r a i n a g e l i n e s a r e c o n n e c t e d t o t h e s a t u r a t i o n - system. The v e r t i c a l d e f o r m a t i o n r a t e was p r e - s e t on t h e 5 Ton Wykeham F e r r a n c e Compression Machine t h r o u g h a s e t o f g e a r s . The d e f o r m a t i o n r a t e was checked by a d i a l gauge d u r i n g t h e t e s t . The' Load was measured by a b e r y l l i u m c opper diaphragm load c e l l p l a c e d above t h e l o a d i n g r o d . E l e c t r i c a l s i g n a l s from t h e load c e l l and p r e s s u r e t r a n s d u c e r were a u t o -m a t i c a l l y r e c o r d e d by t h e V i d a r A u t o d a t a E i g h t u n i t . Data r e d u c t i o n was c a r r i e d o u t by t r a n s f e r i n g t h e i n f o r m a t i o n o n t o computing c a r d s and f e d t o t h e main U.B.C. computer. C f L L L . 3 L \ = T ^ AIR. P R E S S U R E P O R E . P R E S S U R E . \ R W * S O U C E R . L ~ Z ] FIG. 2/ S C H E M A T I C O F T R I A X I A L A P P A R A T U S NJ 4.3.2 S a t u r a t i o n P r o c e d u r e In s a t u r a t i n g a sample, d e - a i r e d w a t e r i s f o r c e d from t h e bottom d r a i n a g e l i n e up t h r o u g h t h e sample and o u t t h e t o p d r a i n a g e l i n e . The bottom d r a i n a g e i s c o n n e c t e d t o a l u c i t e r e s e r v o i r c o n t a i n i n g a r u b b e r b e l l o f r a m . The d e s i r e d a i r p r e s s u r e i s a p p l i e d t o one s i d e o f t h e b e l l o f r a m f o r c i n g t h e wa t e r o u t t h e o t h e r s i d e o f t h e r e s e r v o i r i n t o t h e sample. The r u b b e r b e l l o f r a m s e r v e s t o p r e v e n t p r e s s u r i z e d a i r from d i s s o l v i n g i n t o t h e water i n t h e r e s e r v o i r and t o p r e v e n t a i r from e n t e r i n g t h e sample when t h e wa t e r i n t h e r e s e r v o i r i s d r a i n e d . The t o p d r a i n a g e l i n e o f t h e sample i s c o n n e c t e d t o a c l e a r l u c i t e r e s e r v o i r which h o l d s t h e water which has been f l u s h e d t h r o u g h t h e sample. T h i s r e s e r v o i r i s a l s o p r e s s u r i z e d . By c o n t r o l l i n g t h e p r e s s u r e s w i t h i n t h e b e l l o f r a m r e s e r v o i r and t h e o u t f l o w r e s e r v o i r , a s m a l l p r e s s u r e g r a d i e n t c o u l d be a p p l i e d t o t h e sample and s t i I I m a i n t a i n a h i g h b a c k p r e s s u r e . The a c t u a l s a t u r a t i n g g p r o c e d u r e c o n s i s t s o f two s t a g e s . S i n c e t h e sample i s e s s e n t i a l l y d r y , t h e sample i s f i r s t f l u s h e d w i t h w a t e r a p p l y i n g 2 2 a t o p p r e s s u r e o f 0.1 kg/cm and a base p r e s s u r e o f 0.2 kg/cm ( p r e s s u r e g r a d i e n t o f a p p r o x i m a t e l y 13 cm/cm). The c e l l p r e s s u r e i s m a i n t a i n e d 2 a t 0.5 kg/cm . T h i s p r o c e d u r e f o r c e s a i r o u t o f t h e t o p d r a i n a g e . 2 The f o l l o w i n g day, t h e c e l l p r e s s u r e i s s l o w l y i n c r e a s e d t o 4.00 kg/cm i n s m a l l i n c r e m e n t s s i m u l t a n e o u s l y w i t h t h e i n c r e m e n t a l i n c r e a s e o f t h e 2 t o p and bottom p r e s s u r e s t o 3.60 and 3.80 kg/cm r e s p e c t i v e l y . Each increment i s checked such fha't t h e e f f e c t i v e c o n f i n i n g s t r e s s a t t h e t o p 2 2 of t h e sample i s not g r e a t e r t h a n 0.5 kg/cm and not l e s s t h a n 0.2 kg/cm . The t o p and bottom p r e s s u r e s a r e r a i s e d i n i n c r e m e n t s which a s s u r e s t h a t 2 a p r e s s u r e g r a d i e n t o f 0.2 kg/cm a c r o s s t h e sample i s not exceeded. 34. F l u s h i n g i s c o n t i n u e d a t t h e above p r e s s u r e s u n t i l a B-vaIue o f 95$ o r g r e a t e r i s a c h i e v e d . The water c o n t e n t o f a l l samples were measured a f t e r t e s t i n g and c a l c u l a t i o n s show s a t u r a t i o n s o f e s s e n t i a l l y 100$ (47 - 48$ w a t e r c o n t e n t ) were a c h i e v e d . I n v a r i a b l y a few samples would show s a t u r a t i o n s e x c e e d i n g 100$ due t o e r r o r s i n t h e measurement o f sample voIume. 4.3.3 E x p e r i m e n t a l P r o c e d u r e A f t e r s a t u r a t i o n i s c o m p l e t e , t h e t o p d r a i n a g e i s c l o s e d and i t s pore p r e s s u r e m o n i t o r e d . The pore p r e s s u r e i s a l l o w e d t o r e a c h e q u i l i b r i u m and t h e n t h e sample was c o n s o l i d a t e d a t t h e d e s i r e d e f f e c t i v e p r e s s u r e . The t e s t t h e n f o l l o w s t h e c o n v e n t i o n a l c o n s o l i d a t e d - d r a i n e d p r o c e d u r e s o u t l i n e d by B i s h o p & H e n k e l , I974. The s t r a i n r a t e was s e l e c t e d on t h e b a s i s o f d i r e c t pore p r e s s u r e measurements under s i n g l e d r a i n a g e c o n d i t i o n s ( d r a i n a g e a t t h e t o p w i t h pore p r e s s u r e s m o n i t o r e d a t t h e base of t h e s a m p l e ) . A s t r a i n r a t e o f 0.15"/min. (0.5$/min.) produced no s i g n i f i c a n t r i s e i n pore p r e s s u r e w i t h i n t h e sample. However s i n c e o v e r c o n s o I i d a t e d samples were e x p e c t e d t o f a i l a t l e s s t h a n 2$ s t r a i n , t h e t i m e t o f a i l u r e would o n l y be 4 m i n u t e s . Thus, t o a l l o w s u f f i c i e n t t i m e t o m o n i t o r t h e b e h a v i o u r o f t h e s i l t , a much s l o w e r r a t e o f 0.0006"/min. was adopted. T h i s r e s u l t e d i n a t e s t i n g t i m e of/ a p p r o x i m a t e l y 1 hour. Thus, a l l o v e r c o n s o I i d a t e d samples were t e s t e d a t 0.0006"/min. W i t h i n t h e n o r m a l l y c o n s o l i d a t e d r e g i o n , sample #3.31 was s u b j e c t e d t o t h e same slow r a t e . S i n c e f a i l u r e was not reached u n t i l v e r y l a r g e s t r a i n s , s ubsequent n o r m a l l y c o n s o l i d a t e d samples (#3.34 and 3.35) were t e s t e d a t 0.015"/min. t o d e c r e a s e t h e t e s t i n g t i m e . I t was e v i d e n t from t h e Mohr e n v e l o p e p l o t t h a t t h e i n c r e a s e i n s t r a i n r a t e d i d not 35. a f f e c t t h e s o i l s t r e n g t h ( f r i c t i o n a n g l e ) . 2 V a r i o u s e f f e c t i v e c o n f i n i n g s t r e s s e s r a n g i n g from 0.05 t o 3.0 kg/cm were used t o d e f i n e t h e Mohr e n v e l o p e . The low c o n f i n i n g s t r e s s e s were employed i n an a t t e m p t t o d e t e r m i n e t h e c o h e s i o n i n t e r c e p t more a c c u r a t e l y . 2 At t h e lowest e f f e c t i v e c o n f i n i n g s t r e s s o f 0.05 kg/cm , s l i g h t f l u c t u a t i o n s i n t h e h e i g h t o f w a t e r i n t h e d r a i n a g e p i p e t t e due t o sample volume change d u r i n g s h e a r i n g would r e s u l t i n s i g n i f i c a n t changes i n t h e c o n f i n i n g e f f e c t i v e s t r e s s (eg. e x p u l s i o n o f 1 cm^ o f water would r e s u l t i n an 2 a d d i t i o n a l 12 cm. head of w a t e r o r 0.012 kg/cm i n t h e b a c k p r e s s u r e ) . T h e r e f o r e , a much l a r g e r l u c i t e t u b e (1 . 0 " I.D.) was employed as t h e d r a i n a g e r e s e r v o i r , s a c r i f i c i n g t h e v o l u m e t r i c a c c u r a c y t o a t t a i n a s t e a d y e f f e c t i v e c o n f i n i n g s t r e s s . The problem o f p o s s i b l e s w e l l i n g o f t h e sample a t such low c o n f i n i n g p r e s s u r e s d u r i n g f l u s h i n g and t e s t i n g c o u l d not be a d v o i d e d - we can o n l y assume t h a t s i n c e t h e magnitude o f s w e l l i n g i s s m a l l (as i n c o n s o l i d a t i o n sample #3.33) t h e s t r e n g t h may not be t o o g r e a t l y r educed. 4.4 TRIAXIAL TEST: RESULTS & DISCUSSIONS The r e s u l t s o f t h e e l e v e n t r i a x i a l t e s t s a r e l i s t e d i n t a b l e I I I . Water c o n t e n t s were measured on a I I samples a f t e r f a i l u r e had been a t t a i n e d . C a l c u l a t i o n s c o n f i r m t h a t samples were e s s e n t i a l l y s a t u r a t e d . I n v a r i a b l y , a few samples showed above 100$ s a t u r a t i o n which was a t t r i b u t e d t o e r r o r s i n measurements o f sample d i m e n s i o n s . The v o i d r a t i o s o f t h e t r i a x i a l samples ranged from 1.30 t o 1.39. As wi I I be seen l a t e r , t h e v o i d r a t i o s o b t a i n e d from t h e oedometer mold i s somewhat lower and deemed more re I i a b I e ( ( s e c t i o n 4.8). 36. 4.4.1 S t r e s s - s t r a i n R e l a t i o n s h i p s A few s t r e s s - s t r a i n r e l a t i o n s h i p s a r e p l o t t e d i n f i g u r e s 22 & 23. F i g u r e 22 p r e s e n t s t h e s t r e s s - s t r a i n b e h a v i o u r o f t h e s i l t i n t h e o v e r -c o n s o l i d a t e d s t r e s s f i e l d . As e x p e c t e d , a peak i n s t r e n g t h i s r e a l i z e d w i t h i n t h i s r e g i o n . Thus t h e peak s t r e s s c o n d i t i o n s have been d e f i n e d as t h e f a i l u r e c r i t e r i a . B e i n g a d r a i n e d t e s t , t h e maximum d e v i a t o r s t r e s s c o r r e s p o n d s t o t h e maximum p r i n c i p a l s t r e s s r a t i o c r i t e r i a . In a l l o v e r c o n s o I i d a t e d c a s e s , f a i l u r e had o c c u r r e d a t s t r a i n s o f 1.1$ o r l e s s (see t a b l e I I I ) . I t s h o u l d be noted however, t h a t e x c e s s i v e t r a v e l o f t h e l o a d i n g p l a t f o r m o f up t o 0.7$ s t r a i n due t o improper s e a t i n g p r i o r t o load b u i l d - u p w i t h i n t h e sample was r e g a r d e d as z e r o s t r a i n . T h i s s e a t i n g problem r e s u l t s from t i l t e d c o n t a c t o f t h e sample ends w i t h t h e l o a d i n g p l a t f o r m s . The o r i e n t a t i o n o f t h e f a i l u r e p l a n e s o f t h e s t r a i n e d samples ranged from 28° t o 32° away from t h e major p r i n c i p a l s t r e s s d i r e c t i o n 2 w i t h one e x c e p t i o n : a t t h e lowest c o n f i n i n g p r e s s u r e used (0.05 kg/cm ), t h e f a i l u r e mode resembled t h a t o f t h e u n c o n f i n e d c o m p r e s s i o n t e s t o f d r y b r i t t l e s i l t - i e . t h e f a i l u r e p l a n e was n e a r l y v e r t i c a l . W i t h i n t h e n o r m a l l y c o n s o l i d a t e d s t r e s s s t a t e s , t h e s t r e s s - s t r a i n c u r v e s e x h i b i t e d a r a p i d r i s e i n s t r e s s f o l l o w e d by s t e a d i l y i n c r e a s i n g s t r e n g t h w i t h r i s i n g s t r a i n up t o t h e t e s t e d range o f 35$ s t r a i n ( f i g . 2 3 ) . At such l a r g e s t r a i n s , t h e a r e a c o r r e c t i o n which assumes t h e sample deforms i n a r i g h t c y l i n d e r i s i n e r r o r and t h e s t r e s s e s on t h e f a i l u r e p l a n e i s i l l - d e f i n e d . S i n c e t h e s t r e s s - s t r a i n c u r v e s do not l e v e l o f f a t r e a s o n a b l e s t r a i n s , t h e f a i l u r e c r i t e r i a has been d e f i n e d as t h e s t r e n g t h o f t h e s o i l a t 20$ s t r a i n . In t h e f i e l d , s t r a i n s o f t h i s magnitude would most l i k e l y c o n t i n u e t o f a i l u r e . I . 8T FIG. ZZ S T R E S S - S T R A I N PLOT TlU/WlM_ TE.ST RESULTS , KM*L0OPS SiCT XOVEikCo»4i<»V»DNT&o' S T A T E L E G E N D ~* 3-1-3 -e 3 - / 4 X * 3 - / . Z T/ (X<,./cj). \.oo 0,20 ui 39. TABLE I I I . CONSOLIDATED-DRAINED TRIAXIAL TESTS T e s t # V o i d R a t i o oc °3 < + °3 2 or; + «< 2 S t r a i n a t Fa i I u r e 3.1 1 1 .38 - I . I00 2.429 1 .329 0.97$ 3.12 1 .41 - 0.200 1.115 0.915 0.75$ 3.13 1 .33 8° 0.493 1 .660 1 .167 1 .10$ 3. 14 1 .30 11° 1 .000 2.223 1 .223 0.81$ 3.21 1 .38 12° 0. 157 1 . 196 0.955 0.98$ 3.22 1 .30 24° 0.500 1 .421 0.921 1 .05$ 3.31 1 .33 15° 2.990 6.635 3.650 20.00$ ** 3.34 1 .34 17° 1 .440 3.324 1 .880 20.00?"-** 3.35 1 .34 11° 1 .90 4.313 2.409 20.00$ ** 4. 11 1 .39 5° 0.05 I 0.700 0.649 0.90$ 4. 12 1 .36 6° 1 . 12 2.463 1 .343 3.17$ n a t u r a l w a t e r c o n t e n t s : 7-8$ f i n a l w a t e r c o n t e n t s : 47-48$, e s s e n t i a l l y 100$ s a t u r a t i o n * i s t h e a n g l e between t h e bedding p l a n e and t h e & a x i s d i r e c t i o n ** samples 3.31, 3.34 and 3.35 a r e n o r m a l l y c o n s o l i d a t e d and f a i l u r e i s d e f i n e d a t 20$ s t r a i n ; a l l o t h e r samples a r e o v e r c o n s o I i d a t e d . 40. 4.4.2 Volume Changes D u r i n g S h e a r i n g Changes i n sample volume were measured d u r i n g s h e a r i n g by r e c o r d i n g t h e amount o f w a t e r e x p e l l e d from t h e sample i n t o t h e c a l i b r a t e d p i p e t t e . W i t h i n t h e o v e r c o n s o I i d a t e d r e g i o n , a g e n e r a l d e c r e a s e i n sample volume o c c u r r e d up t o t h e p o i n t o f f a i l u r e f o l l o w e d by sample d i l a t a n t c y ( f i g . 2 4 ) . Samples s h e a r e d i n t h e n o r m a l l y c o n s o l i d a t e d r e g i o n showed a d e c r e a s e i n b u l k volume w i t h i n c r e a s i n g s t r a i n w i t h no d i l a t a n t b e h a v i o u r o b s e r v e d ( f i g . 2 5 ) . 4.4.3 S t r e n g t h Envelope (P-Q Diagram) The f a i l u r e s t r e s s c o n d i t i o n s a r e p l o t t e d i n f i g u r e s 26 & 27 i n t h e form o f a i ( c ' - cr^ ) v e r s u s + o^) f a i l u r e e n v e l o p e . If oC i s t h e s l o p e a n g l e o f t h e b e s t l i n e drawn t h r o u g h such p o i n t s , i t can be shown t h a t s i n jd = tan<* where 0 i s t h e e f f e c t i v e a n g l e o f f r i c t i o n a l r e s i s t a n c e . S i m i l a r l y , i f 'a' i s t h e - cr^ ) i n t e r c e p t , t h e n c'=a/cos 0 (Lambe & Whitman, 1969). From f i g u r e 26, oC = 29° and t h e r e f o r e , 0= 33.7 w i t h i n t h e n o r m a l l y c o n s o l i d a t e d s t r e s s f i e l d . F i g u r e 27 r e p r e s e n t s t h e d a t a o f t h e o v e r c o n s o I i d a t e d r e g i o n p l o t t e d t o a l a r g e r s c a l e . Thus oC = 17 and a = 0.58 kg/cm . C o n v e r s i o n t o / o 2 Mohr e n v e l o p e parameters y i e l d s 0 = 17.8 and c' = 0.609 kg/cm . The e x i s t e n c e o f t h e o v e r c o n s o I i d a t e d r e g i o n i s no t e w o r t h y s i n c e t h e s i l t i s a g I a c i o I a c u s t r i n e d e p o s i t o f t h e l a s t d e g I a c i a t i o n , t h e r e f o r e , t h e maximum o v e r b u r d e n s t r e s s w i l l not c o n t a i n a component due t o w e i g h t o f o v e r l y i n g i c e . S i n c e s a m p l i n g depth was between 41 t o 5{ f e e t and i f we assume t h a t o n l y a few f e e t o f s i l t had been eroded away, t h e r e would be i n s u f f i c i e n t o v e r l y i n g m a t e r i a l t o produce t h e o v e r c o n s o I i d a t e d S T R A I N , £ i* 02. 0-4- o(> o.e> /-O IZ /.+ /•£> 0.7^ oa\ _J 1 1 1 1 F |<3. 2-4- % A\I0\-. \1$ £ % PoB. OC STttfcSS R£GIOt4 . 4 ^ 43. e f f e c t e x h i b i t e d by t h e s i l t samples. T h e r e f o r e , t h e o v e r c o n s o I i d a t e d b e h a v i o u r o f t h e s i l t c o u l d be due t o (1) c h e m i c a l c e m e n t a t i o n (2) n e g a t i v e pore w a t e r s t r e s s e s d e v e l o p e d d u r i n g d e s s i c a t i o n (3) p h y s i c o -c h e m i c a l changes and bond f o r m a t i o n o f t h e c l a y due t o d e s s i c a t i o n o r (4) a c o m b i n a t i o n o f t h e above. T h i s p o i n t w i l l be f u r t h e r d i s c u s s e d a f t e r e x a m i n i n g t h e c o n s o l i d a t i o n d a t a i n t h e next c h a p t e r . 4.5 U n c o n v e n t i o n a l 'Dry' T r i a x i a l T e s t s To d e t e r m i n e t h e e f f e c t o f water c o n t e n t on t h e s t r e n g t h of t h e s i l t , f o u r t r i a x i a l t e s t s were performed a t d i f f e r e n t w a t e r c o n t e n t s 2 w i t h a c o n s i s t e n t c e l l p r e s s u r e o f 0.50 kg/cm . The samples were s t r a i n e d a t a c o n s t a n t r a t e o f 0.0006 i n c h e s / m i n . Sample 3.22 was s a t u r a t e d by f l u s h i n g w i t h water and h i g h b a c k p r e s s u r e s . Sample 3.71 was t e s t e d a t i t s n a t u r a l w a t e r c o n t e n t and sample 3.72 was a i r - d r i e d under c o n s t a n t t e m p e r a t u r e l a b o r a t o r y c o n d i t i o n s f o r 30 days. Sample 3.73 was o v e n - d r i e d f o r 30 days under a c o n s t a n t t e m p e r a t u r e of 105°C. D u r i n g t e s t i n g of t h e o v e n - d r i e d sample, p r e c a u t i o n s were t a k e n t o m i n i m i z e a b s o r b t i o n o f w a t e r from t h e a i r . The t o p d r a i n a g e o f t h e t r i a x i a l a p p a r a t u s was c l o s e d and t h e bottom d r a i n a g e was p l a c e d i n a c o n t a i n e r of o v e n - d r i e d d e s s i c a n t p e l l e t s . The sample w e i g h t was d e t e r m i n e d t o be t h e same b e f o r e and a f t e r t e s t i n g , i n d i c a t i n g n e g l i g i b l e w a t e r was absorbed by t h e sample d u r i n g t e s t i n g . 4.6 R e s u l t s and D i s c u s s i o n s o f t h e 'Dry' T r i a x i a l T e s t s The t e s t r e s u l t s a r e p l o t t e d i n f i g u r e 28 as Mohr c i r c l e s o f f a i l u r e . From f i g u r e 29, i t i s e v i d e n t t h a t t h e s t r e n g t h i s s e n s i t i v e t o t h e 0 l 2. 3 A 5" 6 7 6 ? /0 // /2 /J 14- IS FIG.Z8 MOHR. C I R C L E O F F A I L U R E A T V A R I O U S S A T U R A T I O N S 8 7 6 2 " , /^fc/tt1- 5- 4-1 0 1 1 1 10 2.0 3o 4c So Co 70 So S A T U R A T I O N 5 /£ % Uo F I G . ZS SHEAFk S T P.ENi6TH VS- 5ATURAT\0Nf ( FOP* K M 4 U 0 O P S S\ l-T *) 48. degree o f s a t u r a t i o n , e s p e c i a l l y t o w a r d s t h e d r i e r s t a t e s . L u t t o n (1969) found a s i m i l a r b e h a v i o u r f o r V i c k s b u r g l o e s s under u n c o n f i n n e d c o m p r e s s i o n . A l s o , H o l t z & G i b b s (1951) r e p o r t e d a d i f f e r e n t Mohr e n v e l o p e e x i s t s f o r v a r i o u s s a t u r a t i o n s o f t h e Kansas and Nebraska l o e s s . The s t r e s s - s t r a i n d a t a shows a peak i n s t r e n g t h i n a l l f o u r samples 2 t e s t e d . Thus under t h e 0.50 kg/cm c o n f i n i n g p r e s s u r e , t h e samples were c o n s i d e r e d t o be w i t h i n t h e o v e r c o n s o I i d a t e d s t r e s s range. The i n c r e a s e i n s t r e n g t h e x h i b i t e d by p r o g r e s s i v e l y d r i e r samples may be due t o (1) t h e i n c r e a s e i n e f f e c t i v e c o n f i n i n g s t r e s s as a r e s u l t o f pore w a t e r m e n i s c i i t e n s i o n , (2) t h e i n c r e a s e i n i n t e r p a r t i c I e bonding o f c l a y p a r t i c l e s which may be p r e s e n t between s i l t g r a i n s , o r (3) a c o m b i n a t i o n o f t h e above. For i n t e r e s t , i f we assume t h e t o t a l i n c r e a s e i n s t r e n g t h t o be a t t r i b u t e d t o w a t e r m e n i s c i i t e n s i o n , t h e magnitude o f t h e n e g a t i v e pore w a t e r p r e s s u r e s can be c a l c u l a t e d from t h e Mohr f a i l u r e c r i t e r i a . E x p r e s s e d i n terms o f 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 , t h e c r i t e r i a i s : - cr. 3 C, - 3 s i n 0 = c'cos 0 2 2 where C.' and d' a r e p o s i t i v e f o r c o m p r e s s i o n . In terms of t o t a l s t r e s s e s : (cr + 4 - 2u) s i n 0 = c'cos.0 2 2 where u i s t h e pore p r e s s u r e , b e i n g n e g a t i v e i n t e n s i o n . T a b l e IV l i s t s t h e c a l c u l a t e d n e g a t i v e pore p r e s s u r e s t h a t would have t o d e v e l o p w i t h i n t h e samples t o e x h i b i t t h e s t r e n g t h s measured. 2 The p r e s s u r e d e f i c i e n c y o f 15 kg/cm f o r t h e o v e n - d r i e d sample i s o n l y an a p p a r e n t o r " e f f e c t i v e " v a l u e s i n c e t h e r e i s no f r e e water p r e s e n t 2 w i t h i n an o v e n - d r i e d sample. The n e g a t i v e pore p r e s s u r e o f 6.3 kg/cm a t 4.9$ s a t u r a t i o n i s i n t h e o r d e r o f magnitude e x p e c t e d f o r a s i l t . A i t c h i s o n and Donald ( 1956) showed t h a t f o r i d e a l s p h e r i c a l p a r t i c l e s , 2 n e g a t i v e pore p r e s s u r e s i n t h e o r d e r o f 3.5 kg/cm .can be a t t a i n e d f o r s i l t - s i z e d p a r t i c l e s and p r e s s u r e d e f i c i e n c i e s o f 30 kg/cm can be e a s i l y r e a l i z e d f o r c l a y s . 50. TABLE IV. 'Dry' T r i a x i a l T e s t Data & R e s u l t s T e s t # Water c o n t e n t s a t u r a t i on *3 °1 C m OC C a l c . 2 U kg/cm 3.22 47.8$ 100$ 0.5 2.341 1 .410 24° 0.921 0 3.71 7.71$ 16.1$ 0.5 6. 192 3.346 5° 2.846 -4.067 3.72 2.28$ 4.9$ 0.5 8.134 4.317 10° 3.817 -6.272 3.73 0.00$ 0.0$ 0.5 15.048 7.774 3° 7.274 -15.048 A l l s t r e s s v a l u e s i n kg/cm' 51. 4.7 C o n s o l i d a t i o n T e s t s C o n s o l i d a t i o n t e s t i n g o f s i l t s i s not c o n s i d e r e d s t a n d a r d o r c o n v e n t i o n a l . Compared t o c l a y s and s a n d s , l i t t l e i n f o r m a t i o n i s a v a i l a b l e c o n c e r n i n g t h e b e h a v i o u r o f s i l t s . Many r e s e a r c h e r s s t u d y i n g c o l l a p s i b l e s i l t s g e n e r a l l y p e r f o r m oedometer t e s t s w i t h t h e s i l t a t i t s n a t u r a l w a t e r c o n t e n t ( u s u a l l y low s a t u r a t i o n ) and' w i t h t h e oedometer mold f l o o d e d w i t h w a t e r . ( G i b b s & H o l t z , 1951; L u t t o n , 1969; Dudley, 1970; J e n n i n g s & K n i g h t , 1975). A l t h o u g h t h e t e r m ' c o n s o l i d a t i o n ' t e s t i s adopted i n t h i s r e p o r t , we a r e not d e a l i n g w i t h c o n s o l i d a t i o n i n i t s u s u a l meaning. C o n v e n t i o n a l l y , c o n s o l i d a t i o n i s r e f e r r e d t o as t h e e x p u l s i o n of pore w a t e r from t h e sample l e a d i n g t o c o m p r e s s i o n o f t h e sample. In t e s t s performed on s i l t s , t h e m a j o r i t y of t h e ' c o n s o l i d a t i o n ' t e s t s a r e on n o n - s a t u r a t e d samples and t h e r e f o r e s e t t l e m e n t s a r e due t o s t r u c t u r a l changes as t h e a i r o r a i r - w a t e r m i x t u r e i s e x p e l l e d from t h e s o i l . In p r o b i n g t h e s t r u c t u r e o f t h e Kamloops s i l t , v a r i o u s c o n s o l i d a t i o n t e s t s were p e r f o r m e d . Samp Ies were consoI 1 d a ted a t v a r i o u s w a t e r c o n t e n t s r a n g i n g from s a t u r a t e d t o a i r - d r i e d s t a t e s . To d e t e r m i n e t h e s t r u c t u r a l r e s p o n s e o f t h e s i l t t o t h e a d d i t i o n of f r e e i o n s , samples were f l o o d e d w i t h a s i m u l a t e d s e p t i c t a n k e f f l u e n t and a c i d i c w a t e r . A l s o , samples were remolded i n t o a s l u r r y and a l l o w e d t o d r y o u t b e f o r e t e s t i n g t o a s s e s s t h e e f f e c t o f r e m o l d i n g on s t r u c t u r a l s t a b i l i t y . I n c r emental load c o n s o l i d a t i o n was c a r r i e d o u t on seven of t h e 15 c o n s o l i d a t i o n t e s t s o f t h e l a c u s t r i n e s i l t . The o t h e r e i g h t l a c u s t r i n e s i l t samples were t e s t e d by t h e s t r a i n c o n t r o l l e d method (Byrne & O a k i , 1969). The c o n s t a n t s t r a i n r a t e t e s t was employed s i n c e i t had t h e 52. advantage o f p r o d u c i n g e - l o g P d a t a i n a much s h o r t e r t e s t i n g t i m e (one hour as compared t o t h e 6 days r e q u i r e d f o r i n c r e m e n t a l load t e s t s ) . A l s o , t h e r e i s t h e added advantage o f b e i n g a b l e t o a c h i e v e loads much l a r g e r t h a n t h o s e p o s s i b l e w i t h t h e i n c r e m e n t a l load a p p a r a t u s . Four c o l l u v i a l samples from t h e Kamloops a r e a were a l s o t e s t e d t o d e t e r m i n e t h e degree o f s t r u c t u r a l c o l l a p s e upon f l o o d i n g w i t h w a t e r ( a p p e n d i x I V ) . 4.7.1 C o n s o l i d a t i o n A p p a r a t u s Two s e t u p s were used i n t h e i n c r e m e n t a l load t e s t and two i n t h e s t r a i n c o n t r o l l e d t e s t . I n i t i a l l y , a l l c o n s o l i d a t i o n t e s t i n g was performed w i t h a 3 i n c h I. D. c o n s o l i d a t i o n r i n g and a s p e c i a l l y d e s i g n e d base f i t t e d i n t o a s t a n d a r d t r i a x i a l c e l l . T h i s a l l o w e d t h e sample t o be f l u s h e d w i t h water w h i l e m a i n t a i n i n g a h i g h b a c k p r e s s u r e t o a i d i n t h e s a t u r a t i o n p r o c e s s . S i n c e t h e assembly i s p l a c e d w i t h i n a t r i a x i a l c e l l , t h e load was a p p l i e d t h r o u g h a l o a d i n g r o d , on t o p o f which s i t s a load c e l l . For s t r a i n c o n t r o l l e d t e s t s , t h e load c e l l was s e a t e d a g a i n s t t h e r i g i d frame. For i n c r e m e n t a l load t e s t s , a r o l l i n g b e l l o f r a m a i r p i s t o n was a t t a c h e d t o t h e r i g i d frame and i t s l o a d i n g ram t r a n s f e r s t h e c o n s t a n t load t o t h e t r i a x i a l c e l l l o a d i n g r o d . At l a r g e l o a d s , t h e . c o m p r e s s i o n o f t h e l o a d i n g rod and load c e l l become s i g n i f i c a n t . Thus, t h e c o m p r e s s i o n o f t h e a p p a r a t u s had t o be t a k e n i n t o a c c o u n t when computing t h e sample d e f o r m a t i o n . The system c o m p r e s s i o n s ( c o r r e c t i o n c u r v e s ) a r e p r e s e n t e d i n append i x I I I. In subsequent t e s t s , s i n c e s a t u r a t i o n o f t h e sample was not n e c e s s a r y , a s i m p l e , more d i r e c t l o a d i n g s e t u p was adopted. For t h e s t r a i n c o n t r o l l e d t e s t s , t h e l o a d i n g rod and t r i a x i a l c e l l was ommitted and t h e c o n s o l i d a t i o n r i n g and porous s t o n e s were p l a c e d i n an open c o n t a i n e r . With t h i s a rrangement, t h e c o m p r e s s i o n o f t h e l o a d i n g rod was e l i m i n a t e d , but load c e l l d e f l e c t i o n was s t i l l e n c o u n t e r e d . Appendix I I I p r e s e n t s t h e c o r r e c t i o n s due t o system c o m p r e s s i b i l i t y . For t h e subsequent i n c r e m e n t a l load t e s t s , a s m a l l s i m p l e pneumatic system which was r e c e n t l y d e s i g n e d a t UBC was employed. With t h i s s y s t e m , 2 1 " d i a m e t e r samples were used. System c o m p r e s s i b i l i t y was e s s e n t i a l l y n e g l i g i b l e and t h e o n l y e x t r a n e o u s d e f l e c t i o n s p r e s e n t a r e due t o i n i t i a l s e a t i n g d e f l e c t i o n s which a r e i n t h e o r d e r o f 0.003 i n c h e s a t loads of 450 kg. Thus t h i s s i m p l e system e l i m i n a t e s t h e need f o r system c o m p r e s s i b i l i t y c o r r e c t i o n s due t o load c e l l and l o a d i n g rod d e f o r m a t i o n s . 4.7.2 S a t u r a t i o n P r o c e d u r e Two samples were s a t u r a t e d i n t h e t r i a x i a l c e l l a p p a r a t u s - one f o r a s t r a i n c o n t r o l l e d t e s t and one f o r an i n c r e m e n t a l load t e s t . The s a t u r a t i o n p r o c e d u r e i s s i m i l a r t o t h a t f o l l o w e d i n s a t u r a t i n g a t r i a x i a l 2 sample. C e l l p r e s s u r e s were s e t a t 4.00 kg/cm and base d r a i n a g e p r e s s u r e s 2 were h e l d a t 4.10 kg/cm . Thus, t h e d e - a i r e d w a t e r was pushed from t h e b e l l o f r a m r e s e r v o i r up t h e sample i n t o t h e c e l l r e s e r v o i r . S i n c e B - v a l u e s c o u l d not be measured i n t h i s a p p a r a t u s , t h e p e r c o l a t i o n was c o n t i n u e d f o r an extended p e r i o d o f 30 days i n an a t t e m p t t o i n s u r e s a t u r a t i o n o f t h e sample. 4.7.3 E x p e r i m e n t a l P r o c e d u r e In t h e i n c r e m e n t a l load t e s t s , t h e a p p l i e d loads were doubled each 24 hours ( A P / P = 1) p r o d u c i n g 1-day c o n s o l i d a t i o n c u r v e s . I n c r e a s e of t h e loads were a c h i e v e d by i n c r e a s i n g t h e a i r p r e s s u r e a p p l i e d t o t h e 54. l o a d i n g p i s t o n s . D e f o r m a t i o n o f t h e sample was measured by a d i a l gauge a t t a c h e d t o t h e a i r p i s t o n ' s l o a d i n g rod as r e f e r r e n c e d t o t h e f i x e d frame. D e f l e c t i o n s of t h e d i a l gauge were c o r r e c t e d f o r system c o m p r e s s i -b i l i t y when n e c e s s a r y t o o b t a i n t h e t r u e sample s e t t l e m e n t s . The s t r a i n c o n t r o l l e d c o n s o l i d a t i o n t e s t s were performed f o l l o w i n g t h e o u t l i n e by Byrne & Oaki ( 1 9 6 9 ) . The sample w i t h i n t h e oedometer mold i s s i m p l y s t r a i n e d a t a c o n s t a n t r a t e w h i l e t h e load i s b e i n g m o n i t o r e d by a load c e l l . Thus, h i g h loads can be a c h i e v e d s i n c e we a r e not l i m i t e d by t h e maximum h o u s e - l i n e p r e s s u r e s a v a i l a b l e t o t h e i n c r e m e n t a l load t e s t a p p a r a t u s . For s a t u r a t e d samples',the c h o i c e o f s t r a i n r a t e s i s g e n e r a l l y d e t e r m i n e d by l i m i t i n g t h e pore p r e s s u r e b u i l d - u p w i t h i n t h e samples t o 5-10$ o f t h e l o a d . In t h e c a s e o f t h e h i g h l y permeable s i l t , a s t r a i n r a t e o f 0.003 i n c h e s / m i n . produced an i n s i g n i f i c a n t r i s e i n pore p r e s s u r e w i t h i n t h e s a t u r a t e d sample. T h i s s t r a i n r a t e was adopted f o r most o f t h e s t r a i n c o n t r o l l e d t e s t i n g . 4.8 C o n s o l i d a t i o n T e s t R e s u l t s and D i s c u s s i o n Both i n c r e m e n t a l load and s t r a i n c o n t r o l l e d c o n s o l i d a t i o n t e s t s a r e l i s t e d i n t a b l e V. The c o l l u v i a l t e s t s which were performed a t a l a t e r d a t e a r e l i s t e d i n a p p e n d i x IV. V o i d r a t i o s o f t h e l a c u s t r i n e s i l t ranged from 1.26 t o 1.30 w i t h an a v e r a g e o f 1.28. A l l v o i d r a t i o s were c a l c u l a t e d b e f o r e t e s t i n g by m e a s uring t h e t o t a l sample w e i g h t , d i m e n s i o n s w i t h i n t h e mold and t h e w a t e r c o n t e n t o f t h e s i d e t r i m m i n g s of t h e sample. R e c a l l t h a t t h e v o i d r a t i o s c a l c u l a t e d from t r i a x i a l samples were s l i g h t l y h i g h e r due t o e r r o r s i n m e a suring t h e sample d i m e n s i o n s . However, w i t h t h e c o n s o l i d a t i o n r i n g , t h e d i m e n s i o n s c o u l d be measured a c c u r a t e l y by m e a s u r i n g t h e TABLE V. 'CONSOLIDATION' TESTS OF KAMLOOPS SILT T e s t # D e s c r i p t i o n Samp Ie Di am. S t r a i n Rate e o w$ S$ 3.32 s a t u r a t e d 3.0" 0.003"/min. 1 .260 43.1$ 100.0$ 3.33 s a t u r a t e d 3.0" i n c r . load 1 .279 36.0$ 99.7$ 3.41 d r y , rebounded, f l o o d e d 3.0" dry:0.015 f l o o d e d : .0.003"/min. 1 .273 40.0$ 86.8$ 3.42 f l o o d e d % 0.121 kg/cm 3.0" 0.003'/min. .1.291 - -3.43 f l o o d e d @ 0.329 kg/cm 3.0" 0.003"/min. 1 .283 46.2$ 99.8$ 3.44 dr y 3.0" 0.003"/min. 1 .306 2.97$ 6.3$ 3.45 3.51 dry moi s t 3.0" 3.0" 0.0001 1 i n./mi n. 0.003"/min. 1 .281 1 .301 2.44$ 22.8$ 5.3$ 48.6$ 3.62 dr y 2.5" i n c r . load 1 .277 7.15$ 15.3$ 3.R1 remoIded,dry, f l o o d e d § ^ 6.786 kg/cm 2.5" i n c r . load 1.141 1 .70$ S.= 4.1$ SJ=87.8$ 3.64 f l o o d e d @ „ 0.890 kg/cm 2.5" i n c r . load 1 .274 36.6$ 92.3$ 3.66 f l o o d e d % 0.845 kg/cm 2.5" i n c r . load 1 .269 36.1$ 93.8$ 3.67 dr y 2.5" 0.003"/min. 1 .263 6.54$ 14.3$ 3.R2 f l o o d e d § „ 0.889 kg/cm 2.5" i n c r . load 1 . 137 32.9$ 94.2$ 3.71 f l o o d e d w i t h 0.0 IM HCI 2.5" i n c r . load 1 .208 56. TABLE VI. RESULTS OF THE CONSOLIDATION TESTS T e s t # D e s c r i p t i o n "max. P " P kg/cm Compress i on Index, C c 3.62 u n d i s t u r b e d , d r y , S=15.3$ ..14.. -3.R1 remolded, dry 13 -~U 3.64 f l o o d e d w i t h w a t e r 5.9 0.303 ro O 3.66 f l o o d e d w i t h c h e m i c a l so Iut i on 4.5 0.271 menta I 3.33 s a t u r a t e d w i t h w a t e r 3.7 0.275 ncre 3.R2 remolded, f l o o d e d 2.1 0.151 3.71 f l o o d e d w i t h 0.01M HCI 2.4 0.222 3.45 u n d i s t u r b e d , d r y , S=5.3$ 26 -3.44 u n d i s t u r b e d , d r y , S-6.3% 26 -3.67 u n d i s t r u b e d , d r y , S=14.3$ 13 0.240 TD CD 3.41 3.51 d r y , S=14.4$ m o i s t , S=48.6$ 12 7.8 0.240 0.189 controI 3.43 f l o o d e d , S=99.8$ 6.2 0.215 c ro 3.33 s a t u r a t e d , S=100% 6.3 0.252 L. 4-Ifl 3.42 f l o o d e d , S=? 5.6 0.225 57. i n s i d e volume o f t h e mold i t s e l f . The v o i d r a t i o of t h e c o l l u v i u m was 1.07 and 1.35 f o r t h e two d i f f e r e n t : sample s i t e s . W h i l e t h e v o i d r a t i o o f t h e l a c u s t r i n e s i l t i s f a i r l y u n i f o r m , t h e v o i d r a t i o o f t h e c o l l u v i u m appears t o v a r y w i t h l o c a t i o n . I n i t i a l l y , t h e r e was c o n c e r n t h a t t h e s o i l squeezed o u t due t o l a r g e i n i t i a l h y d r a u l i c g r a d i e n t s a t t h e t o p o f t h e i n c r e m e n t a l load sample would be s i g n i f i c a n t and t h e r e f o r e would a l t e r t h e shape of t h e e - l o g p c u r v e . S i n c e t h e l a r g e g r a d i e n t s a r e n o n - e x i s t e n t i n s t r a i n c o n t r o l l e d t e s t s , t h e c o m p arison of t h e two s e t s o f d a t a may be a f f e c t e d by t h e l o s t o f s o i l i n t h e i n c r e m e n t a l load t e s t . The amount o f s o i l l o s t was measured a f t e r t h e c o m p l e t i o n o f 3 of t h e c o n s o l i d a t i o n t e s t s and i t was found t h a t t h e s o i l l o s t was l e s s t h a n 1 gram, r e p r e s e n t i n g l e s s t h a n ] % o f t h e s o i l sample w e i g h t and t h e r e f o r e was c o n s i d e r e d t o o smaI I f o r c o n c e r n . 4.8.1 Incremental Load R e s u l t s and D i s c u s s i o n s One-day i n c r e m e n t a l load t e s t s o f t h e l a c u s t r i n e s i l t were performed under v a r i o u s c o n d i t i o n s : 1. a t n a t u r a l m o i s t u r e c o n t e n t (#3.62) 2. f l o o d e d w i t h d e - a i r e d w a t e r (#3.64) 3. s a t u r a t e d sample (#3.33) 4. f l o o d e d w i t h s i m u l a t e d s e p t i c t a n k e f f l u e n t (#3.66) 5. f l o o d e d w i t h 0.01M HCI (#3.71) 6. a i r - d r i e d remolded sample (#3.R1) 7. f l o o d e d remolded sample (#3.R2) The e - l o g p c u r v e s of t h e t e s t s a r e p r e s e n t e d i n f i g u r e 30. Each c u r v e w i l l be d i s c u s s e d s e p a r a t e l y . 58. 59. 1. Sample a t n a t u r a l w a t e r c o n t e n t (#3'..62) At t h e w a t e r c o n t e n t o f 7.2$, t h e s i l t behaves as a h i g h l y i n c o m p r e s s i b l e 1 2 s o i l w i t h t h e ' e f f e c t i v e maximum p a s t p r e s s u r e ' o f 14 kg/cm . Upon 2 rebound t o 6.67 kg/cm , f l o o d i n g o f t h e sample w i t h d r i n k i n g w a t e r r e s u l t e d i n an a d d i t i o n a l 3.2$ ( A e/e ) d e c r e a s e i n b u l k volume. The o m a j o r i t y o f t h e c o l l a p s e o c c u r r e d w i t h i n t h e f i r s t hour ( f i g . 3 1 ) . 2. F l o o d e d sample (#3.64) 2 Sample 3.64 was c o n s o l i d a t e d t o 0.89 kg/cm and t h e n f l o o d e d w i t h d e - a i r e d d r i n k i n g w a t e r . Upon f l o o d i n g , no a d d i t i o n a l s e t t l e m e n t o c c u r r e d . F u r t h e r c o n s o l i d a t i o n i n i t s f l o o d e d s t a t e r e s u l t e d i n a much lower 2 maximum p a s t p r e s s u r e t h a n t h a t f o r t h e d r y sample (4.5 kg/cm as 2 compared t o 14 kg/cm f o r t h e sample c o n s o l i d a t e d a t n a t u r a l water c o n t e n t . 3. S a t u r a t e d Sample (3.33) The s a t u r a t i o n p r o c e d u r e was d e s c r i b e d i n s e c t i o n 4.7.2 The maximum 2 p a s t p r e s s u r e i s 3.7 kg/cm and t h e v i r g i n s l o p e (C ) i s s t e e p e r t h a n t h a t of t h e f l o o d e d sample. S i n c e t h e sample was s a t u r a t e d , t h e pore p r e s s u r e d i s s i p a t i o n c o u l d 1. A l t h o u g h t h e t e r m 'maximum p a s t p r e s s u r e ' o r maximum p r e c o n s o I i d a t i o n p r e s s u r e ' i s used i n t h e t e x t , t h e term i s used o n l y t o denote t h e l i m i t i n g p r e s s u r e , beyond' which d e f o r m a t i o n s i n c r e a s e c o n s i d e r a b l y ( i e . t h e t r a n s i t i o n t o ' v i r g i n ' c o m p r e s s i o n ) . T h i s p a r t i c u l a r p r e s s u r e v a l u e cannot be c o n s i d e r e d t o be a t r u e p r e c o n s o I i d a t i o n p r e s s u r e because i t v a r i e s w i t h t h e degree of s a t u r a t i o n and w i t h t h e t y p e o f l i q u i d s a t u r a t i n g t h e s o i l . F u r t h e r m o r e , t h e a b i l i t y o f t h e s o i l t o s u p p o r t loads a t s t r e s s e s below t h i s l i m i t i n g v a l u e may not be due t o p a s t s t r e s s h i s t o r y , but i s most l i k e l y due t o some t y p e o f i n t e r g r a n u l a r bonding such as c e m e n t a t i o n , c l a y b r i d g i n g o r c a p i l l a r y t e n s i o n . 61 . be m o n i t o r e d a l o n g w i t h . t h e s e t t l e m e n t upon a p p l i c a t i o n o f each load i n c r e m e n t . With each load i n c r e m e n t , a t l e a s t 50% o f t h e s e t t l e m e n t o c c u r e d w i t h i n t h e f i r s t 15 s e c o n d s . The s e t t l e m e n t v e r s u s l o g - t i m e c u r v e s ( f i g . 32) a r e s l i g h t l y concave up a t t h e s t a r t and a r e v e r y near t o b e i n g l i n e a r t owards t h e end o f each i n c r e m e n t . T h i s i m p l i e s t h a t a l a r g e p o r t i o n o f t h e s e t t l e m e n t i s due t o s e c o n d a r y c o n s o l i d a t i o n . F i g u r e 33 compares t h e pore p r e s s u r e a t t h e base of t h e sample ( d r a i n a g e a t t h e t o p o n l y ) t o t h e measured c o m p r e s s i o n f o r a g i v e n load i n c r e m e n t . A f t e r 5 m i n u t e s , pore p r e s s u r e s have e s s e n t i a l l y f u l l y d i s s i p a t e d but t h e s e t t l e m e n t s c o n t i n u e a t a l m o s t a c o n s t a n t r a t e (on a l o g - t i m e p l o t ) . T h e r e f o r e , a t s t a n d a r d load i n c r e m e n t s (<^P/P=1), c r e e p b e h a v i o u r c o n s t i t u t e s a s u b s t a n t i a l r o l e i n t h e 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 o f t h e w e t t e d s i l t . 4. F l o o d e d w i t h s i m u l a t e d s e p t i c t a n k e f f l u e n t (#3.66) In some s o i l s , t h e c o l l a p s e b e h a v i o u r i s dependent on whether t h e s o i l i s f l o o d e d w i t h d r i n k i n g w a t e r , sewage w a t e r o r an a c i d i c s o l u t i o n . ( R e g i n a t t o & F e r r e r o , 1973). S i n c e leakages from s e p t i c t a n k s c o u l d be a c o n c e r n , t h e c o l l a p s e c h a r a c t e r i s t i c s o f t h e s i l t i s d e t e r m i n e d by a s i m u l a t e d s e p t i c t a n k e f f l u e n t . T y p i c a l s e p t i c t a n k e f f l u e n t from Kal T e r r a c e , Vernon, B.C. i n 1972 were re p r o d u c e d i n a c h e m i c a l s o l u t i o n f o r i t s e x c h a n g e a b l e c a t i o n c o n c e n t r a t i o n s . S i n c e no s e p t i c t a n k c h e m i c a l • a n a l y s i s were r e a d i l y a v a i l a b l e from t h e Kamloops a r e a , i t was assumed t h a t t h e c o n c e n t r a t i o n s o b t a i n e d "from Kal T e r r a c e were i n t h e o r d e r o f magnitude e x p e c t e d i n t h e Kamloops r e g i o n . The e x c h a n g e a b l e c a t i o n s and t h e i r c o n c e n t r a t i o n s a r e : Ion: Ca Mg K Na C o n c e n t r a t i o n (ppm): 71 36 15 68 The pH o f t h e e f f l u e n t was a l s o d u p l i c a t e d as 7.8. F i g u r e 34 shows t h a t t h e c o n s o l i d a t i o n b e h a v i o u r i s not g r o s s l y d i f f e r e n t t o t h a t o f t h e samples f l o o d e d w i t h j u s t d r i n k i n g w a t e r from Vancouver, a l t h o u g h a s l i g h t d e c r e a s e i n maximum p a s t p r e s s u r e i s n o t e d . However, t h e p o s s i b l i t y o f f u r t h e r s e t t l e m e n t s on a much l o n g e r t i m e s c a l e t h a n t h a t r e a l i z e d i n t h e l a b o r a t o r y must be borne i n mind. A l s o , i t s h o u l d be noted t h a t e f f e c t s due t o c h e m i c a l s and o r g a n i c m a t t e r not d u p l i c a t e d i n t h e c h e m i c a l s o l u t i o n a r e not known. 5. F.looded w i t h 0.01M HCI (#3.71) It was noted t h a t a drop o f 0.5M HCI produced a s t r o n g r e a c t i o n on t h e s i l t ( a p p e n d i x I ) . Thus, a c o n s o l i d a t i o n t e s t was c a r r i e d out w i t h a s t r o n g s o l u t i o n of HCI (0.01M). The r e s u l t a n t c o n s o l i d a t i o n c u r v e e x h i b i t e d a more c o m p r e s s i b l e b e h a v i o u r t h a n t h e samples f l o o d e d w i t h 2 d r i n k i n g w a t e r . The maximum p a s t p r e s s u r e was 2.4 kg/cm as compared 2 t o 4.5 kg/cm f o r t h e s i l t f l o o d e d w i t h d o m e s t i c w a t e r . 6. A i r - d r i e d Remolded sample (#3.R1) The remolded sample was formed by m i x i n g t h e s i l t w i t h d i s t i l l e d w a t e r t o form a s l u r r y . The s l u r r y was t h e n a l l o w e d t o d r y i n "the c o n s t a n t t e m p e r a t u r e l a b o r a t o r y e n v i r o n m e n t f o r 30 days. The remolded sample was i n i t i a l l y c o n c e i v e d as an a t t e m p t t o r e - d u p l i c a t e t h e l a c u s t r i n e s i l t ' s 65 p r o p e r t i e s . However, from f i g u r e 30, we see t h a t t h e b e h a v i o u r of t h e u n d i s t u r b e d l a c u s t r i n e s i l t and t h e remolded sample a t t h e same wa t e r c o n t e n t does d i f f e r . The remolded sample w i t h i t s s a t u r a t i o n o f 4.1$ 2 e x h i b i t s a maximum p a s t p r e s s u r e o f 13 kg/cm w h i l e a l a c u s t r i n e s i l t t e s t e d a t a s i m i l a r s a t u r a t i o n (5.3$) has a much h i g h e r maximum p a s t 2 p r e s s u r e o f a p p r o x i m a t e l y 26 kg/cm . S i n c e t h e v o i d r a t i o o f t h e u n d i s t u r b e d Kamloops s i l t i s 1.28 w h i l e t h e v o i d r a t i o o f t h e remolded sample i s 1.14, t h e c o n s o l i d a t i o n c u r v e s have a l l been n o r m a l i z e d (e/e ) i n an a t t e m p t t o a c c o u n t f o r d i f f e r e n c e s i n t h e shapes o f t h e c o n s o l i d a t i o n c u r v e s due t o d i f f e r e n c e s i n i n i t i a l v o i d r a t i o s . 7. F l o o d e d Remolded Sample (#3.R2) In t h e f l o o d e d s t a t e , t h e maximum p a s t p r e s s u r e o f t h e remolded 2 sample i s 2.1 kg/cm w i t h C c=0.151 which i s s i m i l a r t o t h a t o f t h e sample f l o o d e d w i t h HCI. T h i s s i m i l a r i t y s u g g e s t s t h a t t h e same t y p e of bonding (eg. c a l c i u m c a r b o n a t e ) d e s t r o y e d by t h e HCI was a l s o d e s t r o y e d by r e m o l d i t h e s i l t and t h a t t h i s bonding was not r e c o v e r e d upon d r y i n g . 4.8.2 S t r a i n C o n t r o l l e d C o n s o l i d a t i o n - R e s u l t s & D i s c u s s i o n s E i g h t c o n s t a n t s t r a i n r a t e c o n s o l i d a t i o n t e s t s were performed a t v a r i o u s degrees o f s a t u r a t i o n : 1. l a b o r a t o r y a i r - d r i e d s t a t e (#3.44 & #3.35) 2. a t n a t u r a l water c o n t e n t (#3.41 & #3.67) 3. a t m o i s t c o n d i t i o n s , vi% = 23% (#3.51) 4. f l o o d e d s t a t e (#3.42 & #3.43) 5. s a t u r a t e d s t a t e (#3.32) F i g u r e 34 p r e s e n t s t h e d a t a i n an e / e Q v e r s u s log p p l o t . T a b l e VI (pg. 56 ) summarizes t h e 'maximum p a s t p r e s s u r e s ' and 'C ' o f t h e c o n s o I i dat i on t e s t s . 1. A i r - d r i e d s t a t e (#3.44, #3.45) Samples #3.44 and #3.45 were c o n s o l i d a t e d a t d i f f e r e n t s t r a i n r a t e s (0.003"/min. and 0.00011"/min. r e s p e c t i v e l y ) i n an a t t e m p t t o d e t e r m i n e t h e e f f e c t o f s t r a i n r a t e on t h e shape of t h e c o n s o l i d a t i o n c u r v e s . From f i g u r e 34, i t i s e v i d e n t t h a t t h e two c o n s o l i d a t i o n c u r v e s d i v e r g e a t h i g h e r s t r e s s e s , but i t i s b e l i e v e d t h a t a l a r g e p a r t o f t h i s d i f f e r e n c e i n 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 i s due t o t h e s l i g h t d i f f e r e n c e i n water c o n t e n t o f t h e samples r a t h e r t h a n due t o s t r a i n r a t e e f f e c t s . 2. At n a t u r a l w a t e r c o n t e n t (#3.41, #3.67) The s l i g h t i n c r e a s e i n wa t e r c o n t e n t from t h e a i r - d r i e d s t a t e ( w a t e r c o n t e n t o f a p p r o x i m a t e l y 3%) t o t h e n a t u r a l water c o n t e n t ( a p p r o x i m a t e l y 6.5$) produced a marked d e c r e a s e i n t h e maximum p a s t 67. p r e s s u r e o f t h e s i l t . The maximum p a s t p r e s s u r e d e c r e a s e d from 26 kg/cm' 2 t o 13 kg/cm . 3. M o i s t s t a t e (#3.51) The w a t e r c o n t e n t o f 23$ of t h e m o i s t sample was o b t a i n e d by p l a c i n g t h e trimmed sample between two w e t t e d porous s t o n e s . The water w i t h i n t h e porous s t o n e s were absorbed by t h e s i l t and d i s t r i b u t e d u n i f o r m l y t h r o u g h o u t t h e sample by a l l o w i n g t h e s i l t t o s t a n d f o r two days w i t h i n t h e t r i a x i a l c e l l . The t e s t r e s u l t i n d i c a t e s a f u r t h e r d e c r e a s e i n maximum p a s t p r e s s u r e as a consequence of i n c r e a s i n g t h e water c o n t e n t o f t h e s i l t . 4. F l o o d e d s t a t e s (#3.42, #3.43) With a c o n s t a n t s e a t i n g l o a d , t h e s o i l r e s p o n s e on f l o o d i n g was noted by t h e s w e l l i n g t e n d e n c i e s o f t h e sample a t low c o n f i n i n g s t r e s s e s 2 (0.2 kg/cm ) and s l i g h t c o l l a p s e a t h i g h e r s e a t i n g p r e s s u r e s o f 0.8 kg/cm' With a s t r a i n c o n t r o l l e d t e s t , a s m a l l s e a t i n g load i s a p p l i e d t o t h e sample and s w e l l i n g i s p r e v e n t e d by c o n f i n i n g t h e s o i l between r i g i d l o a d i n g p l a t f o r m s . Upon f l o o d i n g , t h e r e s p o n s e of t h e sample can be m o n i t o r e d by t h e heave p r e s s u r e s measured by t h e load c e l l . F i g u r e 35 p r e s e n t s t h e s t r e s s r e s p o n s e of t h e s o i l w i t h t i m e a f t e r f l o o d i n g o f t h e sample. I n i t i a l l y , t h e r e i s a s l i g h t r a p i d drop i n p r e s s u r e f o l l o w e d by a r a p i d p r e s s u r e i n c r e a s e . The i n i t i a l drop i s p o s s i b l e due t o t h e l a r g e inward g r a d i e n t produced upon f l o o d i n g . The b u i l d - u p i n p r e s s u r e may be a r e s u l t of t h e d e s t r u c t i o n o f c a p i l l a r y t e n s i o n and t h e s w e l l i n g o f t h e montmori I l o n i t e w i t h i n t h e s i l t . •\8 -IT % .14 uJ >/3] llAVTlM. SEATING R 6 . 35 SWELL PRESSURE A FLOOOED SAMPV-E. (*3A2.) " LpacL cell o-cacracu - it . oz kq ' - £ .0044- y»/c*r-- inrh'*t £COTITM //>I/= *UaiK« /c~-• SO /OO 20O 70 The c o n s o l i d a t i o n c u r v e s o f t h e f l o o d e d samples from t h e s t r a i n c o n t r o l l e d t e s t c l o s e l y a p p r o x i m a t e s t h e c u r v e s o b t a i n e d from t h e i n c r e -mental load t e s t s o f f l o o d e d samples. 5. S a t u r a t e d s t a t e (#3.32) The s a t u r a t i o n p r o c e d u r e of t h i s sample has been d e s c r i b e d i n s e c t i o n 4.7.2. The r e s u l t a n t d a t a shows l i t t l e d i f f e r e n c e i n c o n s o l i d a t i o n b e h a v i o u r between a f l o o d e d and s a t u r a t e d sample. Thus i t i s p o s s i b l e t h a t t h e s l i g h t l y h i g h e r c o m p r e s s i b i l i t y o f t h e s a t u r a t e d sample t e s t e d i n t h e i n c r e m e n t a l load p r o c e d u r e i s due t o a c o m b i n a t i o n of s t r u c t u r a l d i s t u r b a n c e due t o i n i t i a l sample s w e l l and t h e shock d i s t u r b a n c e by sudden pore p r e s s u r e i n c r e a s e s a t t h e b e g i n n i n g of each load increment ( C r a w f o r d , 1964). 4.8.3 D i s c u s s i o n of Combined R e s u l t s F i g u r e 36 p l o t s t h e i n c r e m e n t a l load d a t a and s t r a i n c o n t r o l l e d c o n s o l i d a t i o n d a t a o n t o one g r a p h . The v o i d r a t i o s have a l l been n o r m a l i z e d t o m i n i m i z e t h e e f f e c t s of v a r i a n c e s i n i n i t i a l v o i d r a t i o s . F u r t h e r m o r e , a l l c u r v e s a r e s h i f t e d t o t h e same r e f e r e n c e p o i n t where t h e n o r m a l i z e d v o i d r a t i o i s u n i t y a t t h e f i e l d o v e r b u r d e n p r e s s u r e . S i n c e t h e samples were o b t a i n e d from a depth of a p p r o x i m a t e l y 5 f e e t , t h e 2 n o r m a l i z e d v o i d r a t i o s o f a l l samples s h o u l d be u n i t y a t 0.2 kg/cm o f o v e r b u r d e n p r e s s u r e . T h i s s h i f t i n g o f a l l t h e c u r v e s a c c o u n t s f o r e r r o r s i n d e f i n i n g t h e i n i t i a l s e a t i n g p o s i t i o n o f t h e samples. F i g u r e 36 c l e a r l y r e v e a l s t h e e f f e c t o f w a t e r c o n t e n t on t h e c o m p r e s s i o n c h a r a c t e r i s t i c s of t h e s i l t . The s i l t i s h i g h l y s e n s i t i v e t o changes i n 72. m o i s t u r e c o n t e n t - e s p e c i a l l y a t low degrees o f s a t u r a t i o n . In t h e a i r -d r i e d s t a t e o f 5.3$ s a t u r a t i o n , t h e maximum p a s t p r e s s u r e i s e x t r e m e l y 2 h i g h (26 kg/cm ). In t h e f l o o d e d and s a t u r a t e d s t a t e s , t h e p r e c o n s o I i d a t i o n 2 p r e s s u r e drops t o a p p r o x i m a t e l y 6 kg/cm . Samples which a r e s t r u c t u r a l l y a l t e r e d by r e m o l d i n g o r by ponding w i t h 0.01M HCI e x h i b i t s maximum 2 p a s t p r e s s u r e s o f 2.1 and 2.4 kg/cm r e s p e c t i v e l y . Upon w e t t i n g by ponding o f t h e r e l a t i v e l y d r y s o i l , a t h i g h s e a t i n g l o a d s , a d e c r e a s e i n b u l k volume r e s u l t s . The d e c r e a s e i n b u l k volume does not f o l l o w t h e c l a s s i c a l c o n s o l i d a t i o n t h e o r i e s but i n s t e a d i n v o l v e s a c o l l a p s e o f i n t e r g r a n u I a r s t r u c t u r e which can o c c u r i n a b r i e f p e r i o d of t i m e . The f o l l o w i n g terms have been a p p l i e d t o t h i s b e h a v i o u r : c o l l a p s e , c o l l a p s i n g s o i l , near s u r f a c e s u b s i d e n c e , s u b s i d e n c e , h y d r o -c o m p a c t i o n , and h y d r o c o n s o l i d a t i o n ( D u d l e y , 1970). F u r t h e r d i s c u s s i o n o f t h e c o l l a p s e b e h a v i o u r o f t h e Kamloops s i l t i s p r e s e n t e d i n t h e f o l l o w i n g c h a p t e r a l o n g w i t h a b r i e f l i t e r a t u r e re v i ew. 73. CHAPTER 5 STRUCTURAL INSTABILITY OF THE KAMLOOPS SILT 5.1 LITERATURE REVIEW ON COLLAPSIBLE SOILS 5.1.1 Co I Iaps i bIe Soi Is C o l l a p s i b l e s o i l s have been found i n v a r i o u s forms t h r o u g h o u t t h e w o r l d . In g e n e r a l , t h e y have been l o c a t e d i n a r i d r e g i o n s and due t o t h e i n c r e a s i n g u t i l i z a t i o n o f t h e s e a r e a s i n r e c e n t y e a r s t h e r e has been a growing awareness o f t h e problem. The t y p e s o f s o i l s t h a t d i s p l a y a c o l l a p s i n g b e h a v i o u r v a r y tremen-d o u s l y . They can be a i r d e p o s i t e d , w a t e r d e p o s i t e d , r e s i d u a l o r man made and g e n e r a l l y c o n s i s t o f s i l t and f i n e sand f o r m i n g a l o o s e open s t r u c t u r e . In many c a s e s , t h e s o i l d e p o s i t w i l l c o l l a p s e under i t s own w e i g h t when s a t u r a t e d . T h i s c o n d i t i o n has been termed " t r u l y c o l l a p s i b l e " by R e g i n a t t o & F e r r e r o ( 1 9 7 3 ) . Other s o i l s w i l l e x h i b i t c o l l a p s e upon w e t t i n g o n l y when s u f f i c i e n t l y h i g h s t r e s s e s a r e a p p l i e d t o t h e s o i l s t r u c t u r e . These have been termed " c o n d i t i o n a l l y c o l l a p s i b l e " s i n c e t h e e x t e r n a l l y a p p l i e d p r e s s u r e l e v e l g overns whether c o l l a p s e w i l l o c c u r o r n o t . 5.1.2 C o l l a p s e Mechanisms The mechanisms i n v o l v e d i n t h e c o l l a p s e phenomena have been sum-m a r i z e d by Dudley (1970 ) . The b a s i c c o n c e p t i s t h a t o f open s t r u c t u r e of b u l k y shaped g r a i n s h e l d t o g e t h e r by some bonding m a t e r i a l o r f o r c e . T h i s bonding must be s u s c e p t i b l e t o removal o r r e d u c t i o n by t h e i n t r o -d u c t i o n of a d d i t i o n a l w a t e r , a l l o w i n g t h e g r a i n s t o s l i d e i n t o t h e v a c a n t s p a c e s . The t h r e e commonly proposed mechanisms were summarized by Dudley (1970) : 1. Capi I l a r y T e n s i o n In many c a s e s , t h i s t e m p o r a r y s t r e n g t h i s due t o c a p i l l a r y t e n s i o n w i t h i n t h e p a r t i a l l y s a t u r a t e d s o i l . G e n e r a l l y , t h e s o i l g a i n s s t r e n g t h u n t i l a c e r t a i n s a t u r a t i o n i s reached and s a t u r a t i o n s e x c e e d i n g t h i s o p t i m a l v a l u e r e s u l t s i n a d e c r e a s e i n s o i l s t r e n g t h . For s i l t and f i n e s and, t h e peak e f f e c t i v e s t r e s s v a l u e u s u a l l y e x i s t s a t m o i s t u r e c o n t e n t s l e s s t h a n s a t u r a t i o n and above 10$ m o i s t u r e ( A i t c h i s o n & Donald, 1956). When t h e s o i l i s f l o o d e d t o near s a t u r a t i o n , t h e c a p i l l a r y t e n s i o n s a r e d e c r e a s e d o r d e s t r o y e d , t h u s r e d u c i n g t h e e f f e c t i v e s t r e s s which reduces t h e i n t e r g r a n u I a r s h e a r s t r e n g t h , t h u s a l l o w i n g t h e g r a i n s t o c o l l a p s e i n t o a more s t a b l e arrangement (Moore & M i l l a r , 1971). 2. C l a y C o a t i n g s and C l a y B u t t r e s s e s With l a r g e p a r t i c l e s , t h e b u l k o f t h e i n t e r g r a n u I a r f o r c e s may c o n s i s t o f c a p i l l a r y f o r c e s . The magnitude o f t h e c a p i l l a r y f o r c e s i n c r e a s e s w i t h d e c r e a s i n g p a r t i c l e s i z e . However, f o r c l a y s i z e d p a r t i c l e s t h e f o r c e s o f r e p u l s i o n , Van der Waals and m o l e c u l a r a t t r a c t i o n become much more s i g n i f i c a n t . Thus, w i t h more and more c l a y p a r t i c l e s p r e s e n t i n t h e s o i l , t h e e f f e c t o f c a p i l l a r y f o r c e s may become p r o p o r t i o n a l l y l e s s as t h e e l e c t r o - c h e m i c a l f o r c e s become r e l a t i v e l y more pro m i n e n t . A number o f p o s s i b l e s t r u c t u r a l arrangements become p o s s i b l e , depending on t h e g e o l o g i c o r i g i n s and h i s t o r y o f t h e s o i l . When t h e c l a y i s formed by w e a t h e r i n g i n p l a c e (by a u t h i g e n e s i s ) , a t h i n c l a y c o a t i n g may e x i s t around t h e i n d i v i d u a l s i l t g r a i n s . Under d e s s i c a t e d c o n d i t i o n s , t h i s s t r u c t u r e c o u l d have c o n s i d e r a b l e s t a b i l i t y ; but w i t h t h e a d d i t i o n o f w a t e r , t h e c l a y p l a t e s may t e n d t o s w e l l and s e p a r a t e t o some e x t e n t , t h e r e b y p r o d u c i n g a l o s s o f s t r e n g t h . An a l t e r n a t e s t r u c t u r a l arrangement c o u l d be formed i f t h e c l a y p a r t i c l e s were o r i g i n a l l y suspended i n w a t e r . As t h e d e p o s i t s d r i e d , t h e c l a y p l a t e s a r e drawn i n t o t h e i n t e r p a r t i c l e c o n t a c t a r e a o f t h e l a r g e r g r a i n s . The e v a p o r a t i o n p r o c e s s would c o n c e n t r a t e t h e d i s s o l v e d i o n s i n t h e f l u i d c a u s i n g t h e c l a y p l a t e s t o f l o c c u l a t e i n t o a b u t t r e s s arrangement. Upon t h e a d d i t i o n o f w a t e r , t h e ion c o n c e n t r a t i o n would d e c r e a s e c a u s i n g an i n c r e a s e i n r e p u l s i v e f o r c e between t h e c l a y p l a t e s r e s u l t i n g i n a d e c r e a s e o f i n t e r g r a n u I a r s u p p o r t . As t h e g r a i n s i z e s d e c r e a s e i n t o t h e s m a l l e r c l a y s i z e s , t h e c a p i l l a r y f o r c e s c o n t r i b u t e a l e s s e r p o r t i o n o f t h e t o t a l f o r c e s p r e s e n t as t h e e l e c t r o - c h e m i c a l f o r c e s i n c r e a s e i n magnitude. However, c a p i l l a r i t y between c l a y p l a t e s would s t i l l be i m p o r t a n t ( D u d l e y , 1970). Barden, McGown & C o l l i n s ( 1 9 7 3 ) : a l s o s t r e s s t h e d i f f i c u l t y o f d i s t i n g u i s h i n g between t h e p o r t i o n o f t h e s t r e n g t h due t o c a p i l l a r y f o r c e s and t h a t due t o c l a y i n t e r p a r t i c I e bonds: "There a r e c l e a r l y many p o s s i b l e v a r i a t i o n s i n t h e s t r u c t u r a l arrangement of t h e c l a y p l a t e s between t h e q u a r t z g r a i n s . The n a t u r e o f t h e c l a y bonding i s c o m p l i c a t e d , and i t i s never c l e a r how much i s due t o e l e c t r o - c h e m i c a l e f f e c t s and how much t o c a p i l l a r y e f f e c t s . The i m p o r t a n t p o i n t i s t h a t i n most c a s e s  t h e lower t h e w a t e r c o n t e n t of t h e c l a y t h e g r e a t e r t h e bond s t r e n g t h . " p. 51. 3. Chemical Cementing Agent S t r u c t u r a l i n s t a b i l i t y may r e s u l t from t h e l o s s i n s t r e n g t h o f a cementing a g e n t . The r a t e o f s t r u c t u r a l weakening would depend on t h e n a t u r e and c o n c e n t r a t i o n o f i o n s w i t h i n t h e incoming w a t e r as w e l l as t h e n a t u r a l d i s s o l u t i o n r a t e o f ' t h e c h e m i c a l cementing a g e n t . In g e n e r a l t h e s t r e n g t h breakdown o f t h e c h e m i c a l cementing agent due t o i n f i l t r a t i n w a t e r i s a s l o w e r p r o c e s s t h a n s t r e n g t h l o s s due t o c a p i l l a r y t e n s i o n d i s s i p a t i o n and t h e c o l l a p s e o f c l a y b u t t r e s s e s . In r e c e n t y e a r s t h e r e have been a number o f e l e c t r o n m i c r o s c o p e s t u d i e s performed on v a r i o u s c o l l a p s i b l e s o i l s . Barden, McGown & C o l l i n s (1973) and C o l l i n s & McGown (1974) have shown m i c r o p h o t o g r a p h s s u p p o r t i n g t h e e x i s t e n c e o f t h e g e n e r a l c o l l a p s e s t r u c t u r e s mentioned above. For some s o i l s , t h e c o l l a p s e phenomena i s s t r o n g l y dependent on t h e c h a r a c t e r i s t i c s o f t h e l i q u i d s a t u r a t i n g t h e s o i l . F or example, l o e s s i a l s o i l s i n t h e Cordoba r e g i o n o f A r g e n t i n a f r e q u e n t l y e x h i b i t e d more s e t t l e m e n t f o r c a s e s o f r u p t u r e d sew.age p i p e s t h a n f o r c a s e s o f w e t t i n g w i t h p l a i n w a t e r ( R e g i n a t t o & F e r r e r o , 1973). These s o i l s e x h i b i t even more s u b s i d e n c e when f l o o d e d w i t h a c i d i c w a t e r . 5.1.3 E n g i n e e r i n g A p p l i c a t i o n s The p r a c t i c a l problem f a c i n g t h e e n g i n e e r i n v o l v e s t h e d i f f i c u l t t a s k o f p r e d i c t i n g t h e pr e s e n c e o f t h e s e c o l l a p s i n g s o i l s . Many in d e x e s a r e proposed f o r p r e d i c t i n g t h e o c c u r r e n c e o f c o l l a p s e based on n a t u r a l v o i d r a t i o s v s . v o i d r a t i o s a t t h e i r l i q u i d l i m i t and on d r y d e n s i t i e s 77. o f t h e s o i l ( M a r k i n , 1971; G i b b s & B a r a , 1967; D e n i s o v , 1961; Dud Iey,1970). However, i t i s commonly agreed t h a t t h e i n d i c e s a r e not c o m p l e t e l y r e l i a b l e f o r d i f f e r e n t i a t i n g between c o l l a p s i b l e and n o n - c o l l a p s i b l e s o i l s ( D u d l e y , 1970; Evans & Buchanan, 1976). To o b t a i n q u a n t i t a t i v e i n f o r m a t i o n on t h e amount o f c o l l a p s e , t h e doubl e oedometer t e s t p r e s e n t e d by J e n n i n g s & K n i g h t (1957) i s commonly used. In t h i s t e s t , two s i m i l a r samples a r e t e s t e d ; one a t f i e l d m o i s t u r e c o n t e n t , and one s a t u r a t e d . The t o t a l c o l l a p s e due t o s a t u r a t i o n under a c e r t a i n load can be d e t e r m i n e d s i m p l y by c o n s i d e r i n g t h e change i n v o i d r a t i o between t h e two c u r v e s . However, as t h e t e s t s do not c o m p l e t e l y r e p r o d u c e f i e l d c o n d i t i o n s , c o r r e c t i o n f a c t o r s based on e x p e r i e n c e i n t h e a r e a must be a p p l i e d t o t h e t e s t d a t a t o p r e d i c t t h e c o l l a p s e t h a t w i l l o c c u r i n t h e f i e l d ( D u d l e y , 1970; J e n n i n g s & K n i g h t , 1975). In some c a s e s , t h e e n g i n e e r i s a l s o c o n c e r n e d w i t h t h e t i m e r e q u i r e d f o r c e r t a i n p o r t i o n s o f t h e t o t a l c o l l a p s e t o o c c u r . As a r u l e , however, t h e d u r a t i o n s measured i n t h e l a b o r a t o r y a r e much s h o r t e r t h a n t h a t which i s e x p e r i e n c e d i n t h e f i e l d ( R a b i n o v i c h & U r i n o v , 1974). U s u a l l y s e t t l e -ments due t o c o l l a p s e i n i n c r e m e n t a l load t e s t s s t a b i l i z e a f t e r s e v e r a l hours ( f i g . 31) whereas t h e c o l l a p s e o f s o i l s under f o u n d a t i o n s o f b u i l d i n g s sometimes c o n t i n u e s f o r s e v e r a l months. F u r t h e r m o r e , t h e t y p e o f t e m p o r a r y bonding t h a t e x i s t s i n t h e s o i l would be e x p e c t e d t o govern t h e r a t e o f c o l l a p s e . In t h e case of'cap i I I a r y s u c t i o n t h e drop i n s t r e n g t h w i l l be immediate; i n t h e c a s e o f t h e b r i d g i n g c l a y , r a t h e r s l o w e r ; and i n t h e c a s e o f c h e m i c a l cementing i t might be v e r y s low (Barden McGown & Col I i n s , 1973). 5.2 COLLAPSE PHENOMENON OF THE KAMLOOPS SILTS The g I a c i o I a c u s t r i n e s i l t under s t u d y i s a c o n d i t i o n a l l y c o l l a p s i b l e s o i l as d e f i n e d by R e g i n a t t o & F e r r e r o ( 1 9 7 3 ) . Whether o r not t h e s o i l s t r u c t u r e w i l l undergo c o l l a p s e when f l o o d e d w i t h w a t e r i s dependent on i t s p r e s e n t s t r e s s s t a t e . At v e r y low c o n f i n i n g p r e s s u r e s , t h e s o i l e x h i b i t s h e a v i n g when f l o o d e d ; and a t h i g h e r s t r e s s l e v e l s , c o l l a p s e o c c u r s . T h i s t y p e o f b e h a v i o u r i s a l s o found i n some dry c l a y s ( J e n n i n g s & K n i g h t , 1975). For Kamloops s i l t , t h e a c t u a l c r i t i c a l c o n f i n i n g p r e s s u r e where no volume change r e s u l t s due t o f l o o d i n g l i e s between 2 2 0.2 kg/cm and 0.8 kg/cm . The heave e x h i b i t e d a t lower s t r e s s e s i s p o s s i b l y due t o t h e s w e l l i n g of t h e montmori I l o n i t e ( a p p r o x i m a t e l y 3-4$ o f t h e s o l i d s ; Q u i g l e y , 1976) and/or t h e d i s s i p a t i o n o f c a p i l l a r y f o r c e s which may be p r e s e n t w i t h i n t h e s o i l . 2 The 'maximum p r e c o n s o I i d a t i o n p r e s s u r e ' i s a p p r o x i m a t e l y 26 kg/cm 2 f o r t h e a i r - d r i e d s t a t e and 6 kg/cm f o r t h e f l o o d e d s t a t e . T h e r e f o r e , v e r y l i t t l e s u b s i d e n c e due t o w e t t i n g would be e x p e c t e d t o o c c u r a t 2 s t r e s s e s l e s s t h a n 6 kg/cm (see f i g . 3 7 ) . The c o l l a p s e i s a p p r o x i m a t e l y 2 2% a t 6 kg/cm . For t h e s t r e s s l e v e l s commonly e n c o u n t e r e d i n f o o t i n g d e s i g n s and most e n g i n e e r i n g p r oblems, t h e Kamloops s i l t i s not a problem s o i l from t h e c o l l a p s e a s p e c t s i n s p i t e o f i t s h i g h i n - s i t u v o i d r a t i o ( f i g . 3 7 ) . However, t h e l e a c h i n g o f t h e s o i l by a c i d i c w ater w i l l cause a d d i t i o n a l s u b s i d e n c e . The 'maximum p a s t p r e s s u r e ' f o r t h e s i l t f l o o d e d 2 w i t h 0.01M HCI i s 2.4 kg/cm . At t h i s s t r e s s , t h e l a b o r a t o r y c o l l a p s e i s a p p r o x i m a t e l y 2%. At h i g h e r s t r e s s e s , s e t t l e m e n t problems may a r i s e e s p e c i a l l y when d i f f e r e n t i a l s e t t l e m e n t s c o u l d e a s i l y r e s u l t due t o l o c a l f l o o d i n g by a c i d i c s o l u t i o n s . A l t h o u g h t h e a c i d i c c o n c e n t r a t i o n s 19. 80. e n c o u n t e r e d i n t h e f i e l d due t o water p e r c o l a t i n g t h r o u g h t o p s o i I and decayed v e g e t a t i o n a r e much s m a l l e r t h a n t h e l a b o r a t o r y c o n c e n t r a t i o n , t h e long t e r m e f f e c t o f r e d u c i n g t h e s i l t ' s s t r u c t u r a l s t a b i l i t y i s s t i I I p r e s e n t . 5.3 COLLAPSE MECHANISM In o r d e r t o u n d e r s t a n d t h e b e h a v i o u r o f t h e s i l t , an a t t e m p t must be made t o i s o l a t e t h e c o l l a p s e mechanism i n v o l v e d . Based on t h e e x t e n s i v e l a b o r a t o r y t e s t r e s u l t s , a h y p o t h e s i s i s proposed. I t a ppears t h a t t h e s t r e n g t h e x h i b i t e d by t h e s i l t i n i t s n a t u r a l d r y s t a t e i s not t h e r e s u l t o f any one s i n g l e f a c t o r , r a t h e r , i t i s a complex i n t e r a c t i o n o f c a p i l l a r y t e n s i o n , i n t e r p a r t i c I e c l a y a t t r a c t i o n and c h e m i c a l c e m e n t a t i o n . T h e o r e t i c a l c o m p u t a t i o n s p r e s e n t e d w i t h r e g a r d t o c a p i l l a r y s t r e s s e s by A i t c h i s o n & Donald (1956) i n d i c a t e s t h a t f o r u n s a t u r a t e d s i l t s (0.02mm t o 0.002mm), t h e e f f e c t i v e s t r e s s e s may be i n 2 2 t h e range o f 0.35 kg/cm t o 3.5 kg/cm . In c l a y s , c a p i l l a r y s t r e s s e s 2 as much as 100 kg/cm may be r e a l i z e d . For t h e Kamloops s i l t , t h e p o s s i b l e e f f e c t i v e s t r e s s due t o c a p i l l a r y f o r c e s as c a l c u l a t e d from t h e s t r e n g t h 2 d a t a ( t a b l e IV, p.50 ) j s 6.3 kg/cm f o r a w a t e r c o n t e n t o f 2.28$ and 2 15.0 kg/cm f o r an oven d r i e d sample (making t h e g r o s s a s s u m p t i o n t h a t c a p i l l a r y f o r c e s may e x i s t i n an o v e n - d r i e d sample (p.49 ). The magnitude o f t h e s e s t r e s s e s a r e c e r t a i n l y w i t h i n reason as compared t o t h e i d e a l i z e d v a l u e s , e s p e c i a l l y when c o n s i d e r a t i o n i s g i v e n t o t h e pr e s e n c e o f c l a y w i t h i n t h e s o i l . However, i t has been shown t h a t peak e f f e c t i v e s t r e s s due t o c a p i l l a r y t e n s i o n f o r s i l t s o c c u r between 10$ m o i s t u r e c o n t e n t and 100$ s a t u r a t i o n ( D u d l e y , 1970; A i t c h i s o n & Dona l d , 1956). 81 . C a p i l l a r y t e n s i o n i s c o n s i d e r e d n o n - e x i s t e n t i n t h e o v e n - d r i e d s t a t e . As t h e wa t e r c o n t e n t o f t h e s o i l i n c r e a s e s , c a p i l l a r y t e n s i o n a l s o i n c r e a s e s u n t i l a t a c e r t a i n w a t e r c o n t e n t , t h e m e n i s c i i f o r c e s a r e a t a maximum. R a i s i n g t h e water c o n t e n t f u r t h e r r e s u l t s i n a d e c r e a s e i n c a p i l l a r y f o r c e and c o n s e q u e n t l y r e s u l t s i n a d e c r e a s e i n e f f e c t i v e s t r e s s w i t h i n t h e s o i l which i s r e f l e c t e d by a d e c r e a s e i n s o i l s t r e n g t h . Thus, f o r a s o i l whose bonding s t r e n g t h i s s o l e l y due t o c a p i l l a r y f o r c e s , we would e x p e c t an i n c r e a s e i n s t r e n g t h w i t h i n c r e a s i n g water c o n t e n t u n t i l some optimum w a t e r c o n t e n t i s r e a c h e d . Beyond t h i s m o i s t u r e l e v e l , t h e s t r e n g t h would drop a g a i n . A s e r i e s o f t r i a x i a l t e s t s were performed ( s e c t i o n 4.5, p. 45 ) a t t h e same c o n f i n i n g s t r e s s but a t v a r i o u s w a t e r c o n t e n t s t o d e t e r m i n e i f c a p i l l a r y f o r c e s were s o l e l y r e s p o n s i b l e f o r t h e s i l t ' s s t r e n g t h . The r e s u l t a n t s t r e n g t h d a t a ( f i g . 29, p. 47 ) shows t h a t t h e s o i l s t r e n g t h i n c r e a s e s w i t h c o n t i n u a l l y d e c r e a s i n g w a t e r c o n t e n t ; r e a c h i n g maximum s t r e n g t h i n t h e o v e n - d r i e d s t a t e . In l i g h t o f t h e above d i s c u s s i o n , t h i s b e h a v i o u r r u l e s o u t t h e p o s s i b i l i t y t h a t t h e bonding s t r e n g t h i s due s o l e l y t o c a p i l l a r y f o r c e s between s i l t g r a i n s . The r e s u l t s o f i n c r e a s i n g s t r e n g t h w i t h c o n t i n u a l l y d e c r e a s i n g w a t e r c o n t e n t i n d i c a t e s t h a t i n t e r p a r t i c I e c l a y i s m a i n l y r e s p o n s i b l e f o r t h e s i l t ' s bonding s t r e n g t h ( B a r d e n , McGown & C o l l i n s , 1973). Thus, i t i s h y p o t h e s i s e d t h a t t h e b u l k o f t h e s i l t ' s d r y s t r e n g t h i s l a r g l e y due t o i n t e r p a r t i c I e ( c l a y ) f o r c e s ; t h a t i s , t h e second s o u r c e o f te m p o r a r y bonding p r e s e n t e d by Dudley ( 1 9 7 0 ) ( s e c t i o n 5.1.2) i s e x p e c t e d t o a p p l y t o t h e s o i l under s t u d y . The p r e s e n c e o f c l a y between s i l t g r a i n s produces i n t e r p a r t i c l e a t t r a c t i v e f o r c e s such as Van der Waals' f o r c e s and London f o r c e s . Any wa t e r p r e s e n t i n t h e s o i l w i l l m i g r a t e t o p a r t i c l e c o n t a c t s upon b e i n g d r i e d and w i l l r e s u l t i n c a p i l l a r y f o r c e s t o be p r e s e n t a l s o . At lower w a t e r c o n t e n t s , t h e c l a y p l a t e s come c l o s e r and c l o s e r t o g e t h e r , f o r m i n g s t r o n g e r i n t e r p a r t i c I e bonds. Upon f l o o d i n g o f a d r y sample, t h e menisci.i a r e broken and t h e ion c o n c e n t r a t i o n between c l a y p l a t e s d e c r e a s e . The r e d u c t i o n o f ion c o n c e n t r a t i o n w i t h i n t h e pores d e c r e a s e s t h e a t t r a c t i v e f o r c e between c l a y p l a t e s r e s u l t i n g i n s e p a r a t i o n o f c l a y p a r t i c l e s and l o s s o f i n t e r g r a n u l a r s t r e n g t h . The d e s t r u c t i o n o f m e n i s c i i f o r c e s i s a l s o accompanied by a l o s s o f e f f e c t i v e s t r e s s r e s u l t i n g i n a f u r t h e r d e c r e a s e of i n t e r g r a n u l a r s t r e n g t h . M i c r o -s h e a r i n g between g r a i n s can o c c u r under s u f f i c i e n t s t r e s s l e v e l s l e a d i n g t o s t r u c t u r a l c o l l a p s e . Thus, i t i s t h e c l a y a t t r a c t i v e f o r c e s which p r o v i d e s t h e b u l k o f t h e s t r e n g t h w i t h c a p i l l a r y f o r c e s c o n t r i b u t i n g t o an unknown f r a c t i o n o f t h e t o t a l s o i l s t r e n g t h . S e a r c h i n g f o r more e v i d e n c e t h a t i n t e r p a r t i c I e c l a y i s t h e major s o u r c e o f bonding s t r e n g t h , t h e e l e c t r o n s c a n n i n g m i c r o s c o p e was employed t o " v i s u a l l y " s t u d y t h e s i l t . A l t h o u g h e l e c t r o n m i c r o p h o t o g r a p h s do not show t h e p r e s e n c e o f c l a y c o n n e c t o r s between most p a r t i c l e s , c l a y b r i d g e s f r e q u e n t l y o c c u r ( f i g . 19, p. 27 ) and may be s u f f i c i e n t t o h o l d t h e s i l t p a r t i c l e s t o g e t h e r i n an open l o o s e s t r u c t u r e ( s e c . 4.1). The e l e c t r o - c h e m i c a l e f f e c t o f i n c r e a s i n g w a t e r c o n t e n t i s r e f l e c t e d not o n l y i n t h e d e c r e a s e o f s o i l s t r e n g t h but a l s o i n t h e s i l t ' s 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 ( f i g . 3 6 ) . With i n c r e a s i n g water c o n t e n t , t h e s o i l e x h i b i t s lower s h e a r s t r e n g t h and d e c r e a s i n g "maximum p r e -c o n s o l i d a t i o n p r e s s u r e " ( s e c . 4.8.3). For some s o i l s , t h e magnitude of s t r u c t u r a l c o l l a p s e i s s t r o n g l y i n c r e a s e d by f l o o d i n g t h e s o i l w i t h sewage w a t e r ( R e g i n a t t o & F e r r e r o , 83. 1973). In t h e case o f Kamloops s i l t , a sample f l o o d e d w i t h s i m u l a t e d sewage wa t e r e x h i b i t e d no a p p r e c i a b l e d i f f e r e n c e i n c o n s o l i d a t i o n b e h a v i o u r as compared t o a sample f l o o d e d w i t h d i s t i l l e d w a t e r ( s e c . 4.8.1). However, f l o o d i n g w i t h a HCI s o l u t i o n produced a marked d e c r e a s e i n s o i l s t r e n g t h . The r e s u l t a n t a d d i t i o n a l c o l l a p s e i s p r o b a b l y due t o t h e breakdown of some form o f cementing agent — namely c a l c i u m c a r b o n a t e . ( Q u i g l e y , I976, r e p o r t s a p p r o x i m a t e Iy 5% c a I c i u m c a r b o n a t e i n t h e s i l t ; Hardy, I960, r e p o r t s 5-6% c a l c i u m c a r b o n a t e ) . Thus, a s m a l l p o r t i o n o f t h e s o i l s t r e n g t h i s due t o c h e m i c a l c e m e n t a t i o n . F u r t h e r s u p p o r t i n g e v i d e n c e t h a t c h e m i c a l c e m e n t a t i o n does e x i s t was .-.obtained by r e m o l d i n g t h e s i l t i n t o a s l u r r y and a l l o w i n g t h e sample t o dry s l o w l y b e f o r e t e s t i n g ( s e c . 4.8.1). If c h e m i c a l c e m e n t a t i o n does e x i s t , t h e n r e m o l d i n g a sample i n t o a s l u r r y w i l l d e s t r o y t h e c h e m i c a l bonding between s i l t g r a i n s . Upon slow d r y i n g , t h e c l a y i n t e r p a r t i c I e f o r c e s s h o u l d t a k e e f f e c t i n bonding t h e s i l t p a r t i c l e s t o g e t h e r and g i v e t h e sample i t s c o h e s i v e s t r e n g t h . T h i s was indeed t h e c a s e . In t h e c o n s o l i d a t i o n t e s t , a d r i e d remolded sample behaved i n a s i m i l a r manner t o t h e u n d i s t u r b e d s i l t i n t h e d r y s t a t e . However, i n i t s f l o o d e d s t a t e , t h e c o n s o l i d a t i o n c u r v e o f t h e remolded sample a p p r o x i m a t e d t h a t o f t h e sample f l o o d e d w i t h HCI ( f i g . 3 0 ) . T h i s s u g g e s t s t h a t r e m o l d i n g o f t h e s i l t has i r r e v e r s i b l y d e s t r o y e d t h e c a l c i u m c a r b o n a t e bonds. In summary, a l l t h e e v i d e n c e i n d i c a t e s t h a t t h e b u l k o f t h e s i l t ' s c o h e s i v e s t r e n g t h i s a r e s u l t o f t h e p r e s e n c e o f i n t e r s t i t i a l c l a y . C a p i l l a r y t e n s i o n and c h e m i c a l c e m e n t a t i o n a l s o c o n t r i b u t e t o a p o r t i o n o f t h e t o t a l bonding s t r e n g t h . Upon f l o o d i n g w i t h w a t e r , i t i s t h e d e c r e a s e i n bonding s t r e n g t h which r e s u l t s i n s t r u c t u r a l c o l l a p s e when t h e s o i l i s under a s u f f i c i e n t l y l a r g e l o a d . 84. CHAPTER 6  SLOPE STABILITY 6.1 Frequency & E x t e n t F i e l d e v i d e n c e o f p a s t s l o p e f a i l u r e s a l o n g t h e South Thompson V a l l e y a r e v e r y l i m i t e d i n number and s i z e w i t h i n t h e l a c u s t r i n e d e p o s i t . The two a d j a c e n t s l i d e s near P r i t c h a r d r e p r e s e n t t h e o n l y r e c e n t , major s l o p e f a i l u r e s ( f i g . 3 8 ) . Here, t h e o v e r s t e e p e n i n g o f t h e s l o p e s by t h e u n d e r c u t t i n g a c t i o n o f t h e South Thompson R i v e r i s a major f a c t o r . G e n e r a l l y , t h e e f f e c t o f r i v e r e r o s i o n i s not d'irecif l y f e I t a t t h e t o e of t h e s i l t b I u f f s . The b l u f f s i n t h e i r n a t u r a l s t a t e appear c o n d i t i o n a l l y s t a b l e a l t h o u g h on a long t e r m b a s i s , s m a l l l o c a l s i l t f a l l s c o u l d cause slow r e c e s s i o n o f t h e bench edge. 6.2 J o i nt i ng As d e s c r i b e d i n s e c t i o n 2.3, t h e l a c u s t r i n e s i l t i s h i g h l y j o i n t e d w i t h major j o i n t s e t s a t a n g l e s o f a p p r o x i m a t e l y 60 and 30 degrees t o t h e s t r i k e o f t h e b l u f f f a c e w i t h i n Magazine G u l l y . A t h i r d s e t s t r i k e s p a r a l l e l t o t h e b l u f f f a c e and a f o u r t h s e t e x i s t s p e r p e n d i c u l a r t o t h e b l u f f f a c e . L o c a l l y , t h e s e j o i n t s e t s form t h e columnar t y p e j o i n t i n g p a t t e r n s commonly seen i n t h e f i e l d . 6.3 Modes of Fa i I u res In h i g h l y j o i n t e d s l o p e s , i n v a r i a b l y j o i n t i n g g o v e r n s t h e f a i l u r e modes e v i d e n c e d i n t h e f i e l d . Two major t y p e s o f s i l t f a l l s ( s h a l l o w f a i l u r e s ) 85. F i g u r e 38. S l o p e f a i l u r e s caused by o v e r s t e e p e n i n g as a r e s u l t o f r i v e r e r o s i o n of t h e t o e . (Near P r i t c h a r d , on t h e South Thompson R i v e r , l o o k i n g n o r t h ) . 86. a r e u s u a l l y o b s e r v e d : 1. Co Iumn T o p p I i ng Lo c a l columnar j o i n t i n g such as t h o s e seen i n f i g u r e 39 p r o v i d e t h e s e t t i n g f o r column t o p p l i n g f a i l u r e s . When t h e o v e r t u r n i n g moment i s i n c r e a s e d (eg. by c l e f t w a t e r p r e s s u r e s ) o r when t h e s t a b i l i z i n g moment i s reduced ( eg. by a d e c r e a s e o f s o i l s t r e n g t h as a r e s u l t o f w e a t h e r i n g o r w e t t i n g ) , columnar t o p p l i n g may r e s u l t . The s i l t columns commonly break up on impact and " f l o w s " down t h e c o l l u v i a l s l o p e s as l o o s e d e b r i s ( f i g . 4 0 ) . 2. B l o c k Fa i I u res Most of t h e f i e l d i n s t a b i l i t y e x i s t s as l o c a l b l o c k o r s l a b f a i l u r e s . The g e n e r a l geometry c o n s i s t s o f a s i l t b l o c k o r wedge bounded by j o i n t s u r f a c e s f a i l i n g a l o n g a s h e a r s u r f a c e i n c l i n e d o u t o f t h e s l o p e f a c e ( f i g . 4 1 ) . The l a t e r a l and r e a r j o i n t s u r f a c e s p r o v i d e s l i t t l e ( i f any) t e n s i l e s t r e n g t h . The b u l k o f t h e r e s i s t a n c e t o f a i l u r e i s due t o s h e a r r e s i s t a n c e on t h e i n c l i n e d p o t e n t i a l f a i l u r e s u r f a c e . Decrease i n t h i s s t r e n g t h due t o w e a t h e r i n g o r i n t r o d u c t i o n o f water w i l l r e s u l t i n a s l i d i n g f a i l u r e o f t h e b l o c k . The s i z e o f t h i s i n s t a b i l i t y i s u s u a l l y l i m i t e d t o o n l y a few hundred c u b i c y a r d s o f s o i l . A s i m i l a r mechanism f r e q u e n t l y e n c o u n t e r e d i s f a i l u r e by r o t a t i o n o f i n t a c t b l o c k s . The base o f t h e b l o c k r o t a t e s out w h i l e t h e upper end o f t h e b l o c k moves downwards a l o n g t h e r e a r j o i n t s u r f a c e . R o t a t e d i n t a c t b l o c k s s i m i l a r t o t h a t i n f i g u r e 42 a r e f r e q u e n t l y o b s e r v e d i n t h e f i e l d . 87. 88. FIG • 40 DI*\6RAMAPTIC REPRESENTATIOK OF THE COLUMN T 0 P P L I H 6 MODE OP F A I L U R E 89. F I G . 4-1 DIA6RAMATIC RERESEKTTATIOK OF 01 BLOCK OR. SLfcfc FArfLUft£ MODS M o 12) BLOCK ROTATIOKM- FAILURE MODE F i g u r e 42. R o t a t e d i n t a c t b l o c k w i t h i n Magazine G u l l y . 6.4 I n f I u e n c e o f Water S t a b i l i t y of t h e s l o p e s appears t o be s t r o n g l y r e l a t e d t o w a t e r i n f i l t r a t i o n as s u g g e s t e d by t h e c o r r e l a t i o n of t h e known p a s t f a i l u r e s d u r i n g peak r a i n and snowmelt c o n d i t i o n s . In t h e long term c o n d i t i o n , w a t e r causes w e a t h e r i n g a l o n g j o i n t s . C o n t i n u e d p e r c o l a t i o n by r a i n w a t e r can c o n c e i v a b l y remove t h e d i s s o l v a b l e c h e m i c a l c e m e n t a t i o n such as c a l c i u m c a r b o n a t e . Thus, t e n s i l e r e s i s t a n c e may be d e s t r o y e d by t h e w e a t h e r i n g p r o c e s s . S w e l l i n g and s l a k i n g of t h e s o i l near t h e j o i n t s may o c c u r under low c o n f i n i n g s t r e s s e s , r e s u l t i n g i n a weak p l a n e which i s s u s c e p t i b l e t o s l i p p a g e . The i n t r o d u c t i o n o f w a t e r i n t o t h e s o i l w i l l have an immediate e f f e c t on s t a b i l i t y by: 1. d e c r e a s i n g t h e s h e a r s t r e n g t h of t h e s i l t ( i n terms o f e f f e c t i ve s t r e s s e s ) . G i b b s , Hi If & H o l t z (1960) a l s o found t h a t a d i f f e r e n t Mohr e n v e l o p e ( i n terms o f e f f e c t i v e s t r e s s e s ) e x i s t s f o r v a r y i n g degrees of s a t u r a t i o n o f t h e Nebraska-Kansas l o e s s . At low d e grees o f s a t u r a t i o n , a s l i g h t i n c r e a s e i n w a t e r c o n t e n t o f a few p e r c e n t t o t h e Kamloops s i l t w i l l cause a d r a m a t i c l o s s i n s o i l s t r e n g t h as a r e s u l t of c l a y - w a t e r i n t e r a c t i o n w i t h i n t h e s i l t . 2. I n c r e a s i n g t h e h y d r o s t a t i c f o r c e s on t h e c r a c k s and j o i n t s w i t h i n t h e s o i I. 3. i n c r e a s i n g t h e u n i t w e i g h t o f t h e s o i l . A l t h o u g h t h i s f a c t o r i s t h e l e a s t s i g n i f i c a n t , i n c r e a s e i n u n i t w e i g h t of t h e s o i l can d e c r e a s e t h e f a c t o r o f s a f e t y of t h e s l o p e s when s t a b i l i t y depends on c o h e s i o n as w e l l as t h e i n t e r n a l f r i c t i o n a n g l e o f t h e s o i l . 92. 6.5 S t a b i l i t y A n a l y s i s o f Deep F a i l u r e s S i n c e t h e s t r e n g t h o f t h e s i l t i s h i g h l y dependent on t h e m o i s t u r e regime, t h e f i e l d s t r e n g t h p arameters may v a r y as t h e m o i s t u r e c o n t e n t i n c r e a s e s w i t h d e p th. Thus, t h e a c t u a l o p e r a t i v e s t r e n g t h p a r a m e t e r s a r e not w e l l d e f i n e d . A n a l y s i s must the n proceed based on t h e weakest p o s s i b l e s t r e n g t h o f t h e u n d i s t u r b e d s o i l - t h a t i s , a p p l i c a t i o n o f t h e s t r e n g t h d a t a o b t a i n e d from s a t u r a t e d t r i a x i a l s amples. S i n c e t h e s o i l s t r e n g t h i s not w e l l known, d e t a i l e d s t a b i l i t y a n a l y s i s i s not j u s t i f i e d . Hence, t h e usage o f T a y l o r ' s s t a b i l i t y c h a r t s w i l l s u f f i c e f o r t h e n e a r l y homogeneous s o i l . T a b l e VII p r e s e n t s t h e o b s e r v e d b l u f f h e i g h t s i n t h e f i e l d a l o n g w i t h t h e c r i t i c a l s l o p e h e i g h t s as c a l c u l a t e d from T a y l o r ' s c h a r t s ( T a y l o r , 1948, p. 4 5 9 ) . TABLE VII COMPARISON OF THE OBSERVED AND CALCULATED SLOPE HEIGHTS USING TAYLOR'S CHARTS. Measured s l o p e a n g l e ( i ) Observed H e i g h t C a l c u l a t e d H e i g h t (H ) 75° 122' 108' **•* 66° 45' 126' 71.5° 70'. 114' 59.5° 38' 121 ' 66° 70' 127' 79.3° 93' 99' 70.6° 139' 102' *** f a c t o r o f s a f e t y i s l e s s t h a n one. 93. I t can be r e a d i l y seen from t a b l e VII t h a t u s i n g i n - s i t u d e n s i t i e s c o u p l e d w i t h s a t u r a t e d s t r e n g t h d a t a , t h e f a c t o r o f s a f e t y of t h e s i I t b l u f f s can be l e s s t h a n u n i t y . If j o i n t i n g i s a l s o c o n s i d e r e d , t h e s l o p e s would be even more c r i t i c a l . Thus, t h i s s i m p l e a n a l y s i s shows t h a t s h o u l d t h e s i l t b l u f f s be s u f f i c i e n t l y w e t t e d , deep s l o p e f a i l u r e s may r e s u I t . 94. 6.6 Long-Term S t a b i I i t y In t h e long term c o n d i t i o n , e r o s i o n a l p r o c e s s e s such as b l o c k f a l l s w i l l proceed u n t i l t h e a n g l e o f repose i s a c h i e v e d . From t h e t r i a x i a l d a t a , t h i s i s d e t e r m i n e d t o be a p p r o x i m a t e l y 33° ( b e i n g somewhat dependent on o u r c h o i c e o f t h e f a i l u r e c r i t e r i a ) . In t h e f i e l d , c o l l u v i a l s l o p e s e x i s t s a t an average a n g l e o f 35°. W i t h o u t c o m p l i c a t i n g f a c t o r s such as removal o f t o e s u p p o r t and added l o a d s , e q u i l i b r i u m w i l l e x i s t a t t h i s a n gIe. In t h e e v e n t of r e a c h i n g c o n d i t i o n s which a p p r o x i m a t e s t h e p a r a l l e l f l o w o f w a t e r down a s a t u r a t e d s l o p e , t h e i n f i n i t e s l o p e a n a l y s i s c o u l d be a p p l i e d . In t h e c a s e o f t h e s i l t b l u f f s , t h e s t a b l e a n g l e ( i ) c o u l d be found from i = t a n " 1 (( / / * t ) t a n 0 ) = 16° (Lambe & Whitman, 1969, p. 364) A l t h o u g h t h e i n f i n i t e s l o p e a n a l y s i s i s based on a s s u m p t i o n s which may never be f u l l y r e a l i z e d i n t h e f i e l d s i t u a t i o n , n e v e r t h e l e s s , i t r e p r e s e n t s t h e lower bound f o r i n s t a b i l i t y . In p r a c t i c e , t h e a s s u m p t i o n s o f s a t u r a t e d s l o p e and t h e seepage o f w a t e r p a r a l l e l t o t h e s l o p e may never be met e x a c t l y but i n t h e e v e n t o f heavy r a i n and s n o w n e l t c o u p l e d w i t h sewer main r u p t u r e s , t h e above c o n d i t i o n s may be l o c a l l y a p p r o x i m a t e d . From t h e p r e c e e d i n g rough a n a l y s i s , t h e ' s a f e ' s l o p e a n g l e l i e s between 16°- 33° f o r t h e long t e r m c o n d i t i o n . In t h i s long t e r m c a s e , o n l y t h e f r i c t i o n a l r e s i s t a n c e i s c o n s i d e r e d t o be m o b i l i z e d and c e m e n t a t i o n and o t h e r forms o f .cohesion a r e c o n s i d e r e d t o be n o n - e x i s t e n t . Thus, even 95. under t h e c o n d i t i o n s o f p e r c o l a t i o n o f a weak a c i d i c s o l u t i o n t h r o u g h t h e s o i l , t h e above l i m i t s s t i l l a p p l y from t h e s l i d i n g f a i l u r e a s p e c t -a l t h o u g h s t r u c t u r a l c o l l a p s e may o c c u r under loaded f o u n d a t i o n s . 6.7 P o s s i b l e Zoning Scheme One p o s s i b l e z o n i n g scheme f o r urban development i s based on t h e a n g l e of r e p o s e (33°) and t h e l i m i t i n g lower bound s l o p e a n g l e f o r i n s t a -b i l i t y (16°). C o n s i d e r i n g an i d e a l i z e d s e c t i o n ( f i g . 43) c o n s i s t i n g o f 100 v e r t i c a l f e e t o f b l u f f f a c e a t 70° and 200 f e e t o f c o l l u v i . a l s l o p e a t 33°, an a p p r o x i m a t e s a f e s e t b a c k and f o r e s e t c o u l d be d e l i n e a t e d . E x t e n s i o n o f t h e a n g l e o f repose t o t h e t o p o f t h e s e c t i o n r e s u l t s i n a s e t b a c k o f a p p r o x i m a t e l y 100'. W i t h i n t h i s 100' o f t h e c l i f f edge, s t r u c t u r e s o f any form s h o u l d be c o n s i d e r e d u n s a f e . Between 100' and 400', a c o n t r o l o f t h e t y p e o f s t r u c t u r e s t o be e r e c t e d s h o u l d be e n f o r c e d . Temporary s t r u c t u r e s such as s t o r a g e sheds may be a l l o w e d . The zone beyond 400' i s c o n s i d e r e d s a f e f o r u r b a n i z a t i o n a I developments such as h o u s i n g p r o j e c t s ; a l t h o u g h i n d u s t r i a l use may have t o be f u r t h e r removed from t h e c l i f f edge. The s e t b a c k d i s t a n c e s a r e based on a b l u f f f a c e o f 100' h i g h and s l o p e g e o m e t r i e s as g i v e n i n t h e i d e a l i z e d s e c t i o n o f f i g u r e 43. The a c t u a l : z o n i n g would r e q u i r e t h e p r e p a r a t i o n o f t o p o g r a p h i c maps o f t h e a r e a . The f o r e s e t a t t h e base of t h e s l o p e s may be d e l i n e a t e d w i t h a s i m i l a r approach s i n c e s o i l removed a t t h e t o p of t h e b l u f f must a c c u m u l a t e on t h e c o l l u v i a l s l o p e s . Small s i I t f a l l s which may f r e q u e n t l y o c c u r w i l l not be e x p e c t e d t o f l o w p a s t i t s p r e s e n t t o e p o s i t i o n s i n c e t h e d e b r i s wi I I s p r e a d o v e r a l a r g e a r e a b e f o r e i m p i n g i n g on t h e t o e o f t h e s l o p e . FIG. 4 3 APPROXIMATE SETBKCK ZONIMG SCUtrtE 97. Thus a f o r e s e t o f 100' may be s u f f i c i e n t under d r y c o n d i t i o n s . However, when s a t u r a t e d c o n d i t i o n s e x i s t s , t h e 400' f o r e s e t g u i d e l i n e may be a p p l i e d i f we c o n s i d e r t h a t t h e s o i l removed a t t h e t o p i s c o m p l e t e l y t r a n s f e r r e d t o t h e lower h a l f o f t h e s l o p e as shown i n f i g u r e 43. T h i s f o r e s e t n a t u r a l l y assumes t h e advance o f t h e t o e i n a g r a d u a l p r o c e s s and not a r e s u l t o f a h i g h v e l o c i t y mass f a i l u r e , i n which c a s e , t h e s i l t ' s momentum may r e s u l t i n t h e d e b r i s from s p r e a d i n g f u r t h e r downs I ope. CHAPTER 7 SUMMARY AND CONCLUSIONS In t h e a t t e m p t t o u n d e r s t a n d t h e b e h a v i o u r of t h e g l a c i o l a c u s t r i n e s i l t , e x t e n s i v e l a b o r a t o r y t e s t i n g has been employed. The s i l t was found t o be e x t r e m e l y s e n s i t i v e t o m o i s t u r e i n p u t s . The lower t h e w a t e r c o n t e n t , t h e g r e a t e r t h e s o i l s t r e n g t h . Thus, a d i f f e r e n t Mohr e n v e l o p e of f a i l u r e ( i n terms of e f f e c t i v e s t r e s s e s ) e x i s t s f o r each degree of s a t u r a t i o n . In t h e s i l t ' s f u l l y s a t u r a t e d s t a t e , c o n s o l i d a t e d d r a i n e d 2 t r i a x i a l t e s t s y i e l d a c o h e s i o n i n t e r c e p t o f 0.609 kg/cm and a f r i c t i o n a n g l e (0) o f 17.8° f o r t h e o v e r c o n s o I i d a t e d s t r e s s range. W i t h i n t h e n o r m a l l y c o n s o l i d a t e d s t r e s s f i e l d , t h e i n t e r n a l f r i c t i o n a n g l e i s 33°. The above s t r e n g t h parameters were o b t a i n e d by a x i a l l o a d i n g ( d e v i a t o r s t r e s s d i r e c t i o n ) p e r p e n d i c u l a r t o t h e bedding p l a n e . A l t h o u g h t h e s o i l s t r e n g t h i s a n i s o t r o p i c , t h e v a r i a t i o n has been shown t o be s m a l l . The s e n s i t i v i t y of t h e s i l t t o m o i s t u r e c o n t e n t i s a l s o r e f l e c t e d i n t h e s o i l ' s s t r u c t u r a l s t a b i l i t y , and hence, i n i t s b e h a v i o u r i n t h e c o n s o l i d a t i o n a p p a r a t u s . In t h e s i l t ' s n a t u r a l l y dry s t a t e , ponding by w ater r e s u l t s i n s o i l heave a t low c o n f i n i n g p r e s s u r e s w h i l e s t r u c t u r a l c o l l a p s e o c c u r s under h i g h e r s t r e s s l e v e l s . The s l i g h t heave i s p r o b a b l y due t o s w e l l i n g of t h e 3-4$ montmori I I o n i t e w i t h i n t h e s o i l w h i l e t h e c o l l a p s e mechanism r e v o l v e s around t h e p h y s i c o - c h e m i c a l b e h a v i o u r of t h e c l a y - w a t e r system w i t h i n t h e s o i l . I n t e r g r a n u I a r bonding by Van der Waals' f o r c e s , London f o r c e s and o t h e r a t t r a c t i v e f o r c e s of t h e c l a y p l a t e s c o n s t i t u t e s t h e b u l k of t h e 99. bonding s t r e n g t h e x h i b i t e d by t h e s i l t i n i t s n a t u r a l l y d r y s t a t e . The c l a y may e x i s t as b r i d g e s and c o n n e c t o r s o r as t h i n c o a t i n g s a t s i l t g r a i n c o n t a c t s . Upon f l o o d i n g t h e s o i l w i t h w a t e r , t h e ion c o n c e n t r a t i o n o f t h e bounded water l a y e r d e c r e a s e s and t h e c l a y p l a t e s t e n d t o s e p a r a t e s l i g h t l y , r e s u l t i n g i n a d e c r e a s e o f i n t e r g r a n u l a r bonding s t r e n g t h . 2 Under s u f f i c i e n t l y h i g h s t r e s s l e v e l s (above 6 kg/cm ), m i c r o s h e a r i n g between g r a i n s o c c u r , l e a d i n g t o s t r u c t u r a l c o l l a p s e o f t h e l o o s e open network (e = 1.28). C a p i l l a r y f o r c e s must n e c e s s a r i l y e x i s t i n a m o i s t s o i l and m e n i s c i i f o r c e s between c l a y - c l a y and c l a y - s i l t c o n t a c t s may be s u b s t a n t i a l a l t h o u g h t h e a c t u a l p o r t i o n o f t h e bonding s t r e n g t h due t o c a p i l l a r y f o r c e s i s not known. S i n c e s t r u c t u r a l c o l l a p s e i s i n s i g n i f i c a n t 2 below s t r e s s l e v e l s of 6 kg/cm , c o l l a p s e as a r e s u l t o f f l o o d i n g i s not a problem under s t r e s s e s commonly e n c o u n t e r e d i n e n g i n e e r i n g p r a c t i c e . 2 However, a d d i t i o n a l c o l l a p s e w i l l r e s u l t as s t r e s s e s as low as 2.4 kg/cm when t h e s o i l i s f l o o d e d w i t h a c i d i c w a t e r . The d i s s o l u t i o n of c a l c i u m c a r b o n a t e (5-6% by w e i g h t ) by t h e a c i d i c s o l u t i o n leads t o t h e f u r t h e r l o s s of i n t e r g r a n u l a r bonding s t r e n g t h . Under t h e p r e s e n t n a t u r a l c o n d i t i o n s o f t h e s i l t b l u f f s , l i m i t e d s l o p e f a i l u r e s a r e e v i d e n t i n t h e f i e l d . Where t h e y do o c c u r , t h e y e x i s t as s m a l l s h a l l o w b l o c k f a i l u r e s . These f a i l u r e s have been o b s e r v e d t o c o r r e s p o n d t o peak r a i n f a l l and snowmelt c o n d i t i o n s . Thus under usual c o n d i t i o n s , l a r g e mass f a i l u r e s a r e not e x p e c t e d t o o c c u r . However, i n t r o d u c t i o n o f e x c e s s i v e w a t e r i n t o t h e s l o p e s as a r e s u l t of urban-i z a t i o n a l d i s t u r b a n c e s , o r a b n o r m a l l y wet c l i m a t i c c o n d i t i o n s , can p o s s i b l y lead t o l a r g e s c a l e s l o p e f a i l u r e s . The f a i l u r e mechanism and i t s c o r r e s p o n d i n g f a c t o r of s a f e t y a r e dependent on t h e j o i n t i n g system. 100. Four, near v e r t i c a l j o i n t s e t s w i t h i n t h e d e t a i l s t u d y a r e a forms a l o c a l c o l u m n a r - t y p e j o i n t i n g p a t t e r n . S l o p e f a i l u r e s may be bonded l a t e r a l l y by c o m b i n a t i o n s o f t h e j o i n t s e t s ( t r e n d i n g a p p r o x i m a t e l y 0°, 30°, 90°, and 120°). A s i m p l e a n a l y s i s has i n d i c a t e d t h a t l a r g e s c a l e f a i l u r e s can o c c u r under s a t u r a t e d s t a t e s . However, s i n c e t h e s o i l s t r e n g t h ( a t 40-50$ s a t u r a t i o n ) drops t o n e a r l y t h e s t r e n g t h l e v e l of t h e s a t u r a t e d s o i l , f i e l d s a t u r a t i o n s d u r i n g u n u s a l l y wet c o n d i t i o n s may reduce t h e s o i l s t r e n g t h s u f f i c i e n t l y t o induce f a i l u r e . A long term z o n i n g p r o p o s a l f o r u r b a n i z a t i o n a I developments may be based on t h e a n g l e o f repose (33°) and on t h e s a f e s l o p e a n g l e c a l c u l a t e d from an i n f i n i t e s l o p e a n a l y s i s (16°). The a r e a between t h e p r e s e n t c l i f f edge and t h e 33° p r o j e c t i o n o f t h e c o l l u v i a l s l o p e s s h o u l d be c o n s i d e r e d u n s a f e f o r s t r u c t u r e s o f any form. T h i s zone i n c l u d e s t h e p r o b a b l e f a i l u r e p l a n e assumed i n T a y l o r ' s a n a l y s i s . In t h e long term s i t u a t i o n , m a t e r i a l removed from t h e upper s e c t i o n must c o l l e c t a t t h e lower p a r t o f t h e s l o p e s . Assuming t h e m i d - h e i g h t o f t h e s l o p e p r o f i l e remains f i x e d , t h e s o i l i s eroded from t h e upper s e c t i o n and d e p o s i t e d i n t h e lower s e c t i o n , a m a r g i n a l l y s a f e zone c o u l d be d e l i n e a t e d between t h e 16° s l o p e p r o j e c t i o n and t h e 33° p r o j e c t i o n . C o n s t r u c t i o n w i t h i n t h i s r e g i o n s h o u l d be r e s t r i c t e d t o t e mporary s t r u c t u r e s such as s m a l l s t o r a g e sheds. The a r e a beyond t h e 16° p r o j e c t i o n may be c o n s i d e r e d s a f e f o r h o u s i n g developments. However, c a u t i o n must be e x e r c i s e d i n t h e s u r r o u n d i n g a r e a s e x h i b i t i n g e v i d e n c e of s i n k h o l e s and p i p e s . N a t u r a l l y , c e r t a i n c o n t r o l s must be e n f o r c e d w i t h i n a l l u r b a n i z e d a r e a s . C o n t r o l o f r u n o f f and d r a i n a g e s must be o b s e r v e d t o p r e v e n t t h e d e c r e a s e o f s o i l s t r e n g t h w i t h w e t t i n g , as w e l l as t o p r e v e n t t h e f o r m a t i o n of " l i q u i f i e d p i p e s " such as t h e one formed i n t h e f i e l d seepage t e s t . U n d e r c u t t i n g of t h e s l o p e s by roads and e x t e n d i n g p r o p e r t y l i m i t s by removal of s o i l from t h e base of t h e s l o p e s must be p r o h i b i t e d o r s t r i c t l y c o n t r o l l e d . APPENDICES APPENDIX 1 : SAMPLING SITES AND SAMPLE DESCRIPTIONS APPENDIX 2 : SAMPLE TRIMMING PROCEDURES APPENDIX 3 : COMPRESSIBILITY CORRECTIONS OF THE CONSOLIDATION APPARATUS APPENDIX 4 : CONSOLIDATION TESTING OF COLLUVIUM APPENDIX 1 SAMPLING SITES AND SAMPLE DESCRIPTIONS APPENDIX 1 SAMPLING SITES AND SAMPLE DESCRIPTIONS A. G I a c i o - I a c u s t r i n e Samples S i t e #\: One b l o c k sample was o b t a i n e d from t h e base o f t h e b l u f f f a c e r u n n i n g p a r a l l e l t o t h e South Thompson R i v e r near t h e E a s t e r n I n d i a n R e serve boundary. T h i s near s u r f a c e sample was t r a n s p o r t e d unwaxed and was c o n s e q u e n t l y used f o r s p e c i f i c g r a v i t y measurements o n l y . The s i l t had l a m i n a t i o n s o f c o a r s e and medium s i l t s i z e d p a r t i c l e s w i t h s h i n n y f l a k e s ( p o s s i b l y mica) l y i n g a p p r o x i m a t e l y p a r a l l e l t o t h e lam-i n a t i o n s . The sample showed s i g n s o f w e a t h e r i n g , r e f l e c t e d by t h e p r e s e n c e of s m a l l (0.1mm - 1mm) d a r k p a t c h e s t h roughout t h e sample. When t h e s i l t was p l a c e d i n w a t e r , r a p i d s l a k i n g o c c u r e d p a r a l l e l t o t h e l a m i n a t i o n s , f o l l o w e d by t h e breakdown o f t h e sample t o a c o h e s i o n l e s s mass. S i t e #2: A s m a l l b l o c k sample was o b t a i n e d from t h e Western b l u f f of Magazine G u l l y b e s i d e a r e c e n t s i l t f a l l . The unwaxed sample was used f o r s p e c i f i c g r a v i t y d e t e r m i n a t i o n s and p r e l i m i n a r y c o n s o l i d a t i o n t e s t i n g t o a c e s s t h e a p p a r a t u s r e q u i r e m e n t s such as load c e l l c a p a c i t y . The sample i s a medium f i n e s i l t e x h i b i t i n g t h e same w e a t h e r i n g 105. p a t t e r n s as sample b l o c k #1, but l a c k i n g v i s i b l e l a m i n a t i o n s . When submerged i n w a t e r , s l a k i n g r e s u l t e d . SITE #3 & #4: S i t e s 3 & 4 a r e backhoe sample s i t e s on t h e bench s u r f a c e b e s i d e Magazine G u l l y ( f i g . 12). At both s i t e s , t h e brown l o e s s c o v e r was 1 - \{ f e e t t h i c k and samples were o b t a i n e d from a depth of A{ t o 5{ f e e t . Samples were hand c a r v e d w i t h a s h a r p k n i f e , f o l l o w i n g e x i s t i n g j o i n t s where p o s s i b l e . J o i n t i n g g e n e r a l l y c o n s i s t e d of d i s c o n t i n u o u s f r a c t u r e s . Many o f t h e s e p l a n e s showed a r u s t y - b r o w n w e a t h e r i n g s u r f a c e . J o i n t o r i e n t a t i o n s were noted and p l o t t e d i n t h e s t e r e o n e t of f i g u r e 10. At s i t e #4, many unweathered f r a c t u r e s u r f a c e s e x i s t e d and t h e s e a r e l i k e l y due t o d i s t u r b a n c e s by t h e s c r a p p i n g a c t i o n o f t h e backhoe. T h i s made l a r g e i n t a c t samples d i f f i c u l t t o o b t a i n . At s i t e #3, t h e s i l t remained i n t a c t and f r e e o f d i s t u r b a n c e by t h e backhoe. As a consequence, much o f t h e samples were o b t a i n e d from s i t e #3. The b l o c k samples o b t a i n e d a r e u n d i s t u r b e d g I a c i o I a c u s t r i n e s i l t . A t s i t e #3, t h i s was c o n f i r m e d by t h e p r e s e n c e of a 3/4" t h i c k d e s s i c a t e d d a r k grey c l a y seam a t a depth o f 4 f e e t . T h i s n e a r l y h o r i z o n t a l c o n t i n u o u s l a y e r r e p r e s e n t s p a r t of t h e v a r v e d sequence which i s c h a r a c -t e r i s t i c o f t h e l a c u s t r i n e d e p o s i t s . At s i t e #4, a c l a y seam of 1" t h i c k n e s s a l s o e x i s t e d above t h e sampled h o r i z o n . A l l samples were marked i n t h e f i e l d as t o t h e s i t e number and o r i e n t a t i o n ( t o p and b o t t o m ) . The o r i e n t a t i o n was f u r t h e r c o n f i r m e d . i n t h e l a b o r a t o r y by t h e d i s t i n c t p r e s e n c e of t h i n l a m i n a t i o n s i n t h e trimmed samples. 106. The l i g h t b u f f c o l o r e d samples e x h i b i t e d s i m i l a r w e a t h e r i n g p a t c h e s as t h e s i l t b l o c k from s i t e #1. Rapi d s l a k i n g was a l s o o b s e r v e d when t h e s i l t was submerged i n w a t e r . When t h e s i l t was w e t t e d w i t h a drop o f 0.5M HCI, t h e sample e f f e r v e s c e d and l e f t a c r a t e r l i k e p i t t e d s u r f a c e . However, a drop o f 0.01M HCI produced no o b s e r v a b l e r e a c t i o n . B. C o l l u v i a l Samples ( s i t e s #5 & #6) Two c o l l u v i a l b l o c k samples were s u p p l i e d by t h e G e o t e c h n i c a l and M a t e r i a l s Branch o f t h e Department o f Highways i n Kamloops t o exte n d t h e s t u d y t o t h e p r e l i m i n a r y l a b o r a t o r y i n v e s t i g a t i o n o f t h e 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 o f t h e c o l l u v i u m . Both samples a r r i v e d a t U.B.C. as waxed b l o c k s . D e s c r i p t i o n s o f t h e sample l o c a t i o n s were i n c l u d e d . SITE #5: S i t e #5 was d e s c r i b e d as " t h e s i d e o f an i n c i s e d c r e e k a t t h e bottom o f Magazine G u l l y , 5 f e e t s o u t h o f p r o f i l e l i n e B". The c o l l u v i a l sample was a medium b r o w n i s h - g r e y s i l t w i t h abundant r o o t s and r o o t h o l e s t h r o u g h o u t t h e sample. I r r e g u l a r fragments o f i n t a c t l a c u s t r i n e s i l t ( l i g h t b u f f c o l o r ) a r e s c a t t e r e d w i t h i n t h e b l o c k . The p i e c e s o f l a c u s t r i n e s i l t ranged from 1mm t o 2 cm a c r o s s and formed s h a r p c o n t a c t s w i t h t h e m a t r i x m a t e r i a l . The sample was d e f i n i t e l y weaker i n s t r e n g t h t h a n t h e l a c u s t r i n e s i l t samples o f s i t e s 3 & 4. No l a m i n a t i o n s were v i s i b l e i n t h e sample. When p l a c e d i n w a t e r , t h e sample s l o w l y l o s t i t s c o h e s i v e s t r e n g t h , a l t h o u g h t h e r o o t s h e l d t h e main mass t o g e t h e r . When wette d w i t h a drop o f 0.5M HCI, t h e sample e x h i b i t e d t h e same e f f e r v e s c e n t 107. c h a r a c t e r i s t i c s as t h e l a c u s t r i n e s i l t w i t h perhaps s l i g h t l y more v i g o r . SITE #6: T h i s c o l l u v i a l sample was d e s c r i b e d as b e i n g t a k e n from t h e w a l l o f a 1 f t . d i a m e t e r p i p e near an ash l a y e r by t h e f o r k i n t h e road w i t h i n Magaz i ne GuI Iy. The medium-fine s i l t had a medium b r o w n i s h - g r e y c o l o r and c o n t a i n e d f l e c k s o f w h i t e powder ( a s h ? ) . The s t r e n g t h i s a l s o much weaker t h a n t h e l a c u s t r i n e s i l t and c o n t a i n e d l e s s r o o t s and r o o t h o l e s t h a n t h e p r e v i o u s c o l l u v i a l sample. No fragments o f l a c u s t r i n e s i l t was p r e s e n t w i t h i n t h e sample. When submerged i n water o r w e t t e d w i t h 0.5M HCI, t h e r e a c t i o n s were s i m i l a r t o t h a t of t h e sample from s i t e #5. APPENDIX 2 SAMPLE TRIMMING PROCEDURE 109. APPENDIX 2 SAMPLE TRIMMING PROCEDURE A. T r i a x i a l Sample Trimming The f i n a l c y l i n d r i c a l t r i a x i a l samples a r e a p p r o x i m a t e l y 3' h i g h by 1.4' i n d i a m e t e r . Due t o t h e b r i t t l e n a t u r e o f t h e s i l t , c a r e f u l , time-consumming t r i m m i n g o f t h e sample i s mandatory t o p r e v e n t c h i p p i n g . To o b t a i n a t r i a x i a l sample, t h e waxed s i l t b l o c k i s unwrapped and c u t i n t o s m a l l e r r e c t a n g u l a r s e c t i o n s . These s m a l l e r b l o c k s a r e u s u a l l y c u t a t l e a s t 2" l a r g e r t h a n t h e f i n a l sample d i m e n s i o n s i n o r d e r t o e n s u r e minimal d i s t u r b a c n c e o f t h e f i n a l sample. The main b l o c k i s c u t w i t h a f l e x i b l e , wide s e t 30" Swedish saw b l a d e (10 t e e t h t o t h e i n c h ) . The frame i s removed s i n c e i t s added w e i g h t and r i g i d i t y t e n d s t o cause o c c a s s i o n a l f r a c t u r i n g o f t h e sample. The s m a l l b l o c k i s t h e n f u r t h e r trimmed w i t h a s h a r p k n i f e t o t h e r e q u i r e d sample d i a m e t e r i n t h e t r i m m i n g box. The l a m i n a t i o n s o f t h e s i l t becomes d i s t i n c t l y v i s i b l e under t h i s p r o c e d u r e . To o b t a i n t h e c o r r e c t sample h e i g h t i s s l i g h t l y more d i f f i c u l t s i n c e f i n e t r i m m i n g of t h e ends by a k n i f e t e n d s t o cause c h i p p i n g a t t h e edges. Slow s c r a p p i n g motions of a t h i n w i r e saw does e l i m i n a t e t h i s problem and s q u a r e edges can be o b t a i n e d . 1 10. B. Sample Trimming P r o c e d u r e o f C o n s o l i d a t i o n Samples The s i l t b l o c k i s trimmed w i t h a s h a r p k n i f e i n t h e t r i m m i n g a p p a r a t u s t o w i t h i n 1/16 t o 1/8 i n c h e s o f t h e i n s i d e d i a m e t e r o f t h e c o n s o l i d a t i o n r i n g . The s h a r p edged r i n g i s the n p l a c e d on t o p o f t h e sample. The s i l t o u t s i d e t h e c o n t a c t a r e a i s f u r t h e r shaven t o n e a r l y t h e e x a c t r i n g d i m e n s i o n , t a k i n g c a r e not t o o v e r t r i m . The c o n s o l i d a t i o n r i n g i s the n pushed 1/8" a t a t i m e w h i l e t h e a r e a i m m e d i a t e l y beneath t h e r i n g ' s c u t t i n g edge i s trimmed t o a l m o s t t h e e x a c t r i n g s i z e . The sample s i z e had t o be v e r y near t h a t o f t h e c o n s o l i d a t i o n r i n g ' s i n s i d e d i a m e t e r b e f o r e a d v a n c i n g t h e c o n s o l i d a t i o n r i n g i n t o t h e sample t o p r e v e n t c h i p p i n g of t h e b r i t t l e s i l t which would r e s u l t i n v o i d s between t h e r i n g and t h e sample i t s e l f . Even when much c a r e i s t a k e n t o e n s u r e minimal c h i p p i n g , when t r i a l samples where i m m e d i a t e l y e x t r u d e d from t h e r i n g a f t e r t r i m m i n g f o r i n s p e c t i o n , t h e r a r e v o i d may e x i s t between t h e r i n g and t h e sample i t s e l f due t o b r i t t l e f r a c t u r i n g . The l o s t i n s o i l was however v e r y minimal and t h e volume of t h e sample l o s t r e p r e s e n t e d l e s s t h a n \% of t h e t o t a l sample volume. APPENDIX 3 APPARATUS COMPRESS IBILTY CORRECTIONS FOR CONSOLIDATION TESTS 112. APPENDIX 3 APPARATUS COMPRESS IBITY CORRECTIONS FOR CONSOLIDATION TESTS The c o m p r e s s i o n o f t h e c o n s o l i d a t i o n a p p a r a t u s c o n t r i b u t e d a s i g n i -f i c a n t p e r c e n t a g e o f t h e measured c o m p r e s s i o n o f t h e sample. Where a p p l i c a b l e , t h e a p p a r a t u s c o m p r e s s i o n i s t h e r e s u l t o f d e f o r m a t i o n o f the. l o a d i n g r o d , l o a d i n g c e l l o r s e a t i n g problems a s s o c i a t e d w i t h s l i g h t warps i n t h e porous s t o n e s e t c . A. C o r r e c t i o n Curve A ( f i g . 44) T h i s c u r v e a p p l i e s t o t h e system c o m p r e s s i b I i t y o f t h e a p p a r a t u s s e t u p w i t h t h e c o n s o l i d a t i o n r i n g mounted i n s i d e t h e t r i a x i a l c e l l . The m a j o r i t y o f t h e c o m p r e s s i o n c o r r e c t i o n i s due t o t h e c o m b i n a t i o n o f t h e d e f o r m a t i o n o f t h e 1/8" d i a m e t e r by 8" l o n g , s t a i n l e s s s t e e l l o a d i n g rod and t h e d e f o r m a t i o n o f t h e b e r y l l i u m copper diaphragm load c e l l . L i t t l e s t r a i n i s a t t r i b u t e d t o improper s e a t i n g s i n c e t h e c o r r e c t i o n c u r v e i s l i n e a r t h r o u g h t h e o r i g i n . T h i s c o r r e c t i o n c u r v e a p p l i e s t o c o n s o l i d a t i o n t e s t s 3.22, 3.33, 3.41, 3.42, 3.43, 3.44, 3.45 and 3.51. B. C o r r e c t i o n Curve B ( f i g . 45) The c o r r e c t i o n c u r v e o f f i g u r e 48 a p p l i e s t o t e s t 3.67 o n l y s i n c e a more d i r e c t l o a d i n g s e t u p was used which e x c l u d e d t h e l o a d i n g rod and t r i a x i a l c e l l . The l a r g e s t r a i n s r e q u i r e d f o r load b u i l d u p i n d i c a t e s s e a t i n g problems. When t h e porous s t o n e s were examined c l o s e l y , a s l i g h t warp was n o t i c e d i n t h e t o p porous s t o n e . 113. C. C o r r e c t i o n Curve C ( f i g . 46) The e x t e n s i o n o f t h i s s t u d y t o i n c l u d e c o l l u v i u m r e q u i r e d a t h i r d l a y o u t which i s s i m i l a r t o t h a t o f t h e a p p a r a t u s used i n d e v e l o p i n g t h e c o r r e c t i o n c u r v e B e x c e p t t h a t a d i f f e r e n t load c e l l was used. With t h i s s e t o f equipment, a s l i g h t h y s t e r e s i s was measured when l o a d i n g and u n l o a d i n g . When a p p l y i n g t h e c o r r e c t i o n s , o n l y t h e l o a d i n g c u r v e was a p p l i e d . The d a t a of samples 5.10 and 5.11 were a d j u s t e d by t h i s c o r r e c t i o n c u r v e . 114. 1 15. N 116. » APPENDIX 4 CONSOLIDATION TESTS ON COLLUVIUM 1 18. APPENDIX 4 CONSOLIDATION TESTS ON COLLUVIUM From t h e hand specimens, i t i s r e a d i l y e v i d e n t t h a t t h e c o l l u v i u m i s not u n i f o r m from one l o c a t i o n t o t h e next (see a p p e n d i x 1 ) . L a b o r a t o r y t e s t s o f t h e two c o l l u v i a l samples a l s o r e s u l t s i n s i g n i f i c a n t d i f f e r e n c e s o f p r o p e r t i e s : S i t e #5 S i t e #6 s p e c i f i c g r a v i t y ( G ) 2.60 2.78 wat e r c o n t e n t (w$) 6.9$ 9.2$ v o i d r a t i o (e ) 1.07 1.35 o The c o n s o l i d a t i o n c u r v e s f o r t h e c o l l u v i u m a r e p r e s e n t e d i n f i g u r e 47. I t i s a p p a r e n t t h a t t h e "maximum p a s t p r e s s u r e s " f o r c o l l u v i u m a r e much lower t h a n t h a t f o r t h e i n t a c t l a c u s t r i n e s i l t . F l o o d i n g by water causes l a r g e s e t t l e m e n t s even a t low l o a d s . S i n c e t h e t e s t i n g program was l i m i t e d , i t was not c o n f i r m e d whether t h e s o i l was t r u l y c o l l a p s i b l e o r n o t . 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