@prefix vivo: . @prefix edm: . @prefix ns0: . @prefix dcterms: . @prefix skos: . vivo:departmentOrSchool "Applied Science, Faculty of"@en, "Civil Engineering, Department of"@en ; edm:dataProvider "DSpace"@en ; ns0:degreeCampus "UBCV"@en ; dcterms:creator "Vaid, Yoginder Pal"@en ; dcterms:issued "2011-06-09T22:03:14Z"@en, "1968"@en ; vivo:relatedDegree "Master of Applied Science - MASc"@en ; ns0:degreeGrantor "University of British Columbia"@en ; dcterms:description """An apparatus has been designed to investigate the mechanical behaviour of soils under plane strain. Provision has also been made to consolidate specimens under condition of no lateral yield prior to their shear; thus simulating the consolidation state in natural sedimentary deposits. The apparatus is suited for testing both sands and clays, including undisturbed clay samples from standard size bore hole samplers. The design permits a variety of stress paths to be followed during shear. An experimental procedure for testing both sands and clays has been developed and some test results are described. The results obtained show a general confirmation of existing information on the behaviour of soils under plane strain."""@en ; edm:aggregatedCHO "https://circle.library.ubc.ca/rest/handle/2429/35337?expand=metadata"@en ; skos:note "A PLANE STRAIN APPARATUS FOR SOILS by Y o g i n d e r P a l V a i d B . S c . E n g i n e e r i n g , P a n j a b U n i v e r s i t y , C h a n d i g a r h , I n d i a P o s t G r a d . D i p l o m a , U n i v e r s i t y o f R o o r k e e , R o o r k e e , I n d i a A THES I S SUBMITTED IN PART IAL FULF ILMENT OF THE REQUIREMENTS FOR THE DEGREE OF ' M . A . S c . i n t h e D e p a r t m e n t o f C i v i l E n g i n e e r i n g 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 UNIVERS ITY OF BR IT ISH COLUMBIA O c t o b e r , 1968 In p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f t h e r e q u i r e m e n t s . f o r a n . a d v a n c e d d e g r e e a t t h e 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 , I a g r e e t h a t the. L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and S t u d y . I f u r t h e r a g r e e . t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s , f o r s c h o l a r l y p u r p o s e s may be g r a n t e d b y t h e Head o f my • D e p a r t m e n t • o r b y h.i's r e p r e s e n t a t i v e s . I t i s u n d e r s t o o d t h a t c o p y i n g o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l n o t be a l l o w e d w i t h o u t my. w r i t t e n , p e r m i s s i o n . D e p a r t m e n t o f O'vif *^'>Ketrirfr-The Up i v e r s i t y o f Br i t i s h Columb i a V a n c o u v e r 8, C a n a d a D a t e N\"0Vlr*}>ZT 6y ( i i ) ABSTRACT. An a p p a r a t u s h a s b e e n d e s i g n e d t o i n v e s t i g a t e t h e m e c h a n i c a l b e h a v i o u r o f s o i l s u n d e r p l a n e s t r a i n . P r o v i s i o n h a s a l s o b e e n made t o c o n s o l i d a t e s p e c i m e n s u n d e r c o n d i t i o n o f no l a t e r a l y i e l d p r i o r t o t h e i r s h e a r ; t h u s s i m u l a t i n g t h e c o n s o l i d a t i o n s t a t e i n n a t u r a l s e d i m e n t a r y d e p o s i t s . The a p p a r a t u s i s s u i t e d f o r t e s t i n g b o t h s a n d s a n d c l a y s , i n c l u d i n g u n d i s t u r b e d c l a y s a m p l e s f r o m s t a n d a r d s i z e b o r e h o l e s a m p l e r s . The d e s i g n p e r m i t s a v a r i e t y o f s t r e s s p a t h s t o be f o l l o w e d d u r i n g s h e a r . An e x p e r i m e n t a l p r o c e d u r e f o r t e s t i n g b o t h s a n d s and c l a y s h a s b e e n d e v e l o p e d a n d some t e s t r e s u l t s a r e d e s c r i b e d . The r e s u l t s o b t a i n e d show a g e n e r a l c o n f i r m a t i o n o f e x i s t i n g i n f o r m a t i o n on t h e b e h a v i o u r o f s o i l s u n d e r p l a n e s t r a i n . ( i i i ) TABLE OF CONTENTS Page CHAPTER 1 INTRODUCTION . l CHAPTER 2 REVIEW OF L ITERATURE . . . . 6 F a i l u r e C r i t e r i a 6 T y p e s o f S h e a r T e s t s 13 T e s t R e s u l t s 16 Some S i g n i f i c a n t F e a t u r e s o f T y p e s . o f A p p a r a t u s E m p l o y e d i n t h e above I n v e s t i g a t i o n s . . . . . . . . . 24 CHAPTER 3 DESCRIPTION OF THE APPARATUS 3 0' S i z e 32 F r i c t i o n l e s s E n d P l a t e s 32 L a t e r a l P r e s s u r e D i a p h r a g m s . . . . . . . 34 Vo lume Change and P r e s s u r e M e a s u r e m e n t s 36 L o a d i n g E q u i p m e n t 36 CHAPTER 4 EXPERIMENTAL PROCEDURE . . . . . . . . . 40 P r e p a r a t i o n o f C l a y S amp l e s 4 0 P r e p a r a t i o n o f S a t u r a t e d Sand S a m p l e s . . kl CHAPTER 5 CHARACTER IST ICS OF THE APPARATUS . . . . 51 M e a s u r e m e n t o f A x i a l L o a d 51 M e a s u r e m e n t o f P r e s s u r e s . 52 ( i v ) TABLE OF CONTENTS ( C o n t ' d . ) Page M e a s u r e m e n t o f A x i a l D e f o r m a t i o n . . . . 53 K - C o n s o l i d a t i o n 53 o S a t u r a t i o n o f t h e S p e c i m e n s 6 0 U n i f o r m i t y o f D e f o r m a t i o n s 61 S h e a r S t a g e . 6 3 Measu remen t o f • ^ CHAPTER 6 SOME EXPERIMENTAL RESULTS 6 6 The T e s t P r o g r a m 6 6 T e s t R e s u l t s - c l a y 7 0 T e s t R e s u l t s - s a n d 8 5 CHAPTER 7 SUMMARY AND CONCLUSIONS 9 4 L I S T OF REFERENCES • 9 6 APPENDIX 1 P r o c e d u r e f o r M a k i n g R u b b e r , M e m b r a n e s . . 102 APPENDIX 2 M e a s u r e m e n t o f B - v a l u e s 104 ( v ) L I S T OF F.'GURES F i g u r e Page 2.1 R i g h t s e c t i o n s o f f a i l u r e s u r f a c e s by an o c t a h e d r a l p l a n e 11 3.1 P r i n c i p a l s t r e s s e s u n d e r p l a n e s t r a i n . . . . 31 3.2 E x p l o d e d v i ew o f t h e p l a n e s t r a i n a p p a r a t u s . 33 3.3 L a t e r a l p r e s s u r e d i a p h r a g m s . . . . . . . . . 35 3.4 S c h e m a t i c l a y o u t o f vo lume change and p r e s s u r e m e a s u r e m e n t s . . . . 37 3.5 S c h e m a t i c d i a g r a m o f t h e l o a d i n g e q u i p m e n t . . 3 8 4 .1 T r i m m i n g a p p a r a t u s f o r c l a y s p e c i m e n s . . . . 41 4 .2 R u b b e r membrane s t r e t c h e d on s l e e v e f o r i n s t a l l i n g c l a y s a m p l e s 43 4 . 3 A c l a y s amp le i n p a l c e 46 4 .4 Sample a s s e m b l y i n t h e l o a d i n g f r ame 46a 4 . 5 Sand s p e c i m e n u n d e r p r e p a r a t i o n 48 » 5.1 C o m p l i a n c e o f l a t e r a l p r e s s u r e d i a p h r a g m s . . 5 7 5.2 C o m p a r i s o n o f p r e s s u r e v o i d r a t i o r e l a t i o n s h i p f r o m p l a n e s t r a i n a p p a r a t u s and s t a n d a r d r i n g c o n s o l i d o m e t e r 5 8 5 .3 U n i f o r m v e r t i c a l s e c t i o n a l o n g t h e l e n g t h o f a d e f o r m e d p l a n e s t r a i n s p e c i m e n , (a ) i n a x i a l e x t e n s i o n , (b) i n a x i a l c o m p r e s s i o n .62 6.1 D e v i a t o r s t r e s s v s . a x i a l s t r a i n f o r c o n s o l i d a t e d u n d r a i n e d p l a n e s t r a i n t e s t s on Haney c l a y . . . . . . . . . . ?3 6 .2 P r i n c i p a l e f f e c t i v e s t r e s s r a t i o v s . a x i a l s t r a i n f o r c o n s o l i d a t e d u n d r a i n e d p l a n e s t r a i n t e s t s on Haney c l a y . . . . 74 ( v i ) L I S T OF FIGURES ( C o n t ' d . ) Page 6 .3 P o r e p r e s s u r e v s . a x i a l s t r a i n f o r c o n -s o l i d a t e d u n d r a i n e d p l a n e s t r a i n t e s t s on Haney c l a y 77 6 .4 P o r e p r e s s u r e p a r a m e t e r A v s . a x i a l s t r a i n f o r c o n s o l i d a t e d u n d r a i n e d p l a n e s t r a i n t e s t s on Haney c l a y 8 0 6 .5 E f f e c t i v e s t r e s s p a t h s f o r c o n s o l i d a t e d u n d r a i n e d p l a n e s t r a i n t e s t s on Haney c l a y 8 3 6 . 6 D e v i a t o r s t r e s s v s . a x i a l s t r a i n f o r d r a i n e d p l a n e s t r a i n t e s t s on d e n s e O t t a w a s a n d . . . . . . 86 6 . 7 E f f e c t i v e s t r e s s r a t i o v s . a x i a l s t r a i n f o r d r a i n e d p l a n e s t r a i n t e s t s on dense O t t a w a s a n d 87 6 .8 V o l u m e t r i c v s . a x i a l s t r a i n f o r d r a i n e d p l a n e s t r a i n t e s t s on d e n s e O t t a w a s a n d . . . . . 89 6 .9 E f f e c t i v e s t r e s s p a t h s f o r d r a i n e d s t r a i n t e s t s on dense O t t a w a p l a n e s a n d . . . . 91 ( v i i ) LIST OF TABLES Page Table I Results o f one dimensional c o n s o l i d a t i o n t e s t on undisturbed Haney c l a y . . . . 7 0 a. Table I I Results of c o n s o l i d a t e d undrained plane s t r a i n shear t e s t s on normally loaded undisturbed Haney c l a y 1J> a. Table I I I Results of drained plane s t r a i n shear t e s t s on dense Ottawa sand 9 I a Table A2-1 Measurement of B-values f o r an undisturbed specimen of Haney c l a y . . 104 ( v i i i ) LIST OF SYMBOLS ?oct °oct i f Shearing strength c\" E f f e c t i v e cohesion / ( 2 . 2 ) which i s known as the Mohr-Coulomb f a i l u r e c r i t e r i o n . In equation ( 2 . 2 ) , c\" and \" are r e s p e c t i v e l y the apparent cohesion and angle o f i n t e r n a l f r i c t i o n o f the s o i l w i t h respect to e f f e c t i v e s t r e s s e s . When expressed i n terms o f p r i n c i p a l s t r e s s e s , the Mohr-Coulomb f a i l u r e c r i t e r i o n i s : 8 io'-a') = (a n-a.) = 2c'cos' + (a_'+a*) s i n $ * ( 2 . 3 ) 1 3 x j 1 -3 where o£ and a r e r e s p e c t i v e l y t h e m a j o r and t h e m i n o r 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 a t f a i l u r e . F o r g r a n u l a r s o i l s and n o r m a l l y l o a d e d c l a y s c o h e s i o n c\" e q u a l s z e r o and e q u a t i o n ( 2 . 3 ) becomes ( 0 ^ - 0 - 3 ) = (a£+aj)sin(|) ( 2 . 3 a ) M o h r - C o u l o m b f a i l u r e c r i t e r i o n i m p l i e s t h a t t h e i n t e r m e d i a t e p r i n c i p a l e f f e c t i v e s t r e s s , 0 ^ , does n o t i n f l u e n c e t h e e x t r e m e v a l u e s o f t h e p r i n c i p a l s t r e s s e s 0 ^ and 0 3 a t t h e p o i n t o f f a i l u r e . Two o t h e r f a i l u r e c r i t e r i a c o n s i d e r e d a p p l i c a b l e t o s o i l s , f o l l o w the o c t a h e d r a l s h e a r t h e o r y . T h e s e a r e t h e e x t e n d e d T r e s c a and t h e e x t e n d e d von M i s e s c r i t e r i a , w h i c h t a k e a c c o u n t o f t h e i n f l u e n c e o f t h e i n t e r m e d i a t e p r i n c i p a l e f f e c t i v e s t r e s s , 0 ^ , on f a i l u r e s t r e n g t h . F o r c o h e s i o n l e s s s o i l s and n o r m a l l y l o a d e d c l a y s , i . e . , c o n -s i d e r i n g c\" - 0 , t h e s e c r i t e r i a may be w r i t t e n as f o l l o w s : E x t e n d e d T r e s c a : o.'+o' + 0 o ( 0 f - 0 3 > = at-^-j £ ) = c t 0 o C t ( 2 . 4 ) E x t e n d e d von M i s e s : 9 T o c t 2 = ( a £ - a 2 ) 2 + ( c J 2 - ° 3 ) 2 + ( ( 7 3 ^ 1 ) 2 = 2 a 2 a o c t 2 ( 2 ' 5 ) 9 where a * o c t and T o c t a r e r e s p e c t i v e l y t h e o c t a h e d r a l n o r m a l e f f e c t i v e and s h e a r s t r e s s e s and a i s a s t r e n g t h p a r a m e t e r . mean n o r m a l e f f e c t i v e s t r e s s and d e s i g n a t e d by a\". F o r an t e n d e d T r e s c a and e x t e n d e d von M i s e s c r i t e r i a c o i n c i d e . The f o r m o f E q u a t i o n s ( 2 . 4 ) and ( 2 . 3 a ) i s n o t a n a l y t i c ; i t v i o l a t e s t h e r u l e t h a t t h e manne r i n w h i c h t h e 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 a r e l a b e l l e d 1, 2 , 3 s h o u l d n o t a f f e c t , t h e f o r m o f f a i l u r e c r i t e r i a ( Fung 19 6 6 ) . H o w e v e r , E q u a t i o n s ( 2 . 4 ) and ( 2 . 3 a ) c a n be made a n a l y t i c as f o l l o w s : i t i s o b s e r v e d t h a t any one o f t h e d i f f e r e n c e s j a £ — | > |a^-o^ | , | ^3 —cr£ 1 n a s a v a l u e otaoct ^ n e x t e n d e d T r e s c a a n d (,a^+a^) sin^\" i n M o h r - C o u l o m b c r i t e r i a . Hence t h e s e two C r i t e r i a may be w r i t t e n a s , E x t e n d e d T r e s c a : O c t a h e d r c l n o r m a l e f f e c t i v e s t r e s s , i s a l s o c a l l e d t h e m [ ( a £ - a 2 - ) 2 - a 2 a 0 ' c t 2 ] x C ( a 2 ' - a 3 ) 2 - a 2 a ( ; c t 2 ] x x C ^ - a ^ - a 2 ^ 2 ] = 0 ( 2 . 4 a ) M o h r - C o u l o m b : ( 2 . 3 b ) 10 Equations (2.3b), (2.4a) and (2.5) represent pyramid shaped s u r f a c e s , with apex at the o r i g i n , i n the p r i n c i p a l e f f e c t i v e s t r e s s space w i t h coordinates a^, a^j a^• These surfaces are symmetrical with respect to the space d i a g o n a l , a£ = = a g • T n e r i g h t s e c t i o n s of pyramids formed by planes p e r p e n d i c u l a r to the space diagonal(the o c t a h e d r a l planes) are r e s p e c t i v e l y ( f i g . 2.1) i r r e g u l a r hexagons (equal s i d e s but not p a r a l l e l ) f o r the Mohr-Coulomb, r e g u l a r hexagons f o r the extended Tresca and c i r c l e s f o r extended von Mises c r i t e r i a . The s i z e of the r i g h t s e c t i o n s depends on the magnitude of the mean normal e f f e c t i v e s t r e s s and strength parameters of the s o i l , ' or a. A x i a l l y symmetric st a t e s of s t r e s s (a^ = c^ o r ^\\ ~ which correspond r e s p e c t i v e l y to the conventional t r i a x i a l compression and extension t e s t s , y i e l d f a i l u r e p o i n t s which are l o c a t e d on the adjacent r a d i a l l i n e s of a 60° s e c t o r (points a and b or b\" i n f i g . 2.1). The shape-of the f a i l u r e surface between these extreme l i m i t s of the magnitude of > can be i n v e s t i g a t e d o n l y under nonsymmetrical s t a t e s of s t r e s s . Because of the symmetry of the r i g h t s e c t i o n s of f a i l u r e s u r f a c e s , i t i s s u f f i c i e n t to e s t a b l i s h e x p e r i m e n t a l l y o n l y a 60° s e c t o r such as a to bb*. One obvious procedure to e s t a b l i s h the v a l i d i t y of any f a i l u r e c r i t e r i o n , i s to determine whether the values o f the r e l e v a n t s t r e n g t h parameters c\", or a are i n f a c t dependent on the s t a t e of s t r e s s at f a i l u r e . Mohr-11 F ig . 2-1 - R i ? M sections °-f jo.Wu.re. S U T ^ Q C « S by An 12 C o u l o m b c r i t e r i o n has o f t e n b e e n a d v o c a t e d f o r s o i l s and i t s p a r a m e t e r s c\", <|>'are. d i r e c t l y a p p l i c a b l e t o t h e s o l u t i o n o f p r a c t i c a l p r o b l e m s o f s t a b i l i t y . T h i s c o n c l u s i o n has been drawn on t h e s t r e n g t h o f i n f o r m a t i o n f r o m t h e t r i a x i a l t e s t r e s u l t s , where t h e same <{>\" i s o f t e n o b t a i n e d i n c o m -p r e s s i o n and e x t e n s i o n t e s t s . T h e r e f o r e , t h e r e s u l t s o f s t r e n g t h t e s t s u n d e r n o n s y m m e t r i c a l s t a t e s o f s t r e s s a l s o a r e o f t e n e x p r e s s e d i n t e r m s o f M o h r - C o u l o m b c r i t e r i o n and i t s p a r a m e t e r s c\" and (J>'-. T h e n a c o m p a r i s o n o f t h e s e p a r a -m e t e r s w i t h t h e c o r r e s p o n d i n g p a r a m e t e r s u n d e r . t r i a x i a l c o m p r e s s i o n c o n d i t i o n s (a^ = a £ ) i n d i c a t e s w h e t h e r i n f l u e n c e s t h e f a i l u r e s t r e n g t h . An a l t e r n a t i v e way t o i n -v e s t i g a t e t h e v a l i d i t y o f any f a i l u r e c r i t e r i o n i s t o p l o t t e s t r e s u l t s on t h e o c t a h e d r a l p l a n e i n t h e p r i n c i p a l e f - ' f e c t i v e s t r e s s s p a c e and e x a m i n e w h i c h o f t h e r i g h t s e c t i o n s t h e y f i t mos t c l o s e l y . S p e c i f i c a t t e m p t s t o f o r m u l a t e c o n s t i t u t i v e r e l a t i o n s f o r s o i l s i n t h e s u b f a i l u r e r e g i o n have n o t met w i t h much s u c c e s s , b e c a u s e o f t h e c o m p l e x n a t u r e o f s o i l s i n v o l v i n g a n i s o t r o p y , n o n l i n e a r i t y , i n e l a s t i c i t y and t i m e d e p e n d e n c e . T h e s i m p l e r r e l a t i o n s h i p s t h a t m i g h t be a p p l i -c a b l e t o many m e t a l s ( i n w h i c h t h e v o l u m e t r i c s t r a i n i s a • f u n c t i o n o n l y o f mean n o r m a l s t r e s s , and o c t a h e d r a l s h e a r s t r a i n a f u n c t i o n o f o c t a h e d r a l s h e a r s t r e s s o n l y ) a r e n o t a p p l i c a b l e i n g e n e r a l t o s o i l s . S h e a r s t r e s s e s may c a u s e vo lume i n c r e a s e o r d e c r e a s e i n s o i l s a t c o n s t a n t mean n o r m a l 13 s t r e s s . S t u d y o f s t r e s s - s t r a i n r e s p o n s e o f s o i l s h a s , t h e r e f o r e , b e e n m a i n l y c o n f i n e d t o a g r a p h i c a l f o r m . Some s u c c e s s f u l a t t e m p t s , h o w e v e r , have been made ( H e n k e l S Wade 1 9 6 6 , S h i b a t a £ K a r u b e 1965 ) t o e x p r e s s p o r e p r e s s u r e change ( w h i c h a r e r e l a t e d t o t e n d e n c y t o vo lume c h a n g e ) i n c o n s o l i d a t e d u n d r a i n e d t e s t s on c l a y s , as a s i m p l e f u n c t i o n o f o c t a h e d r a l n o r m a l and s h e a r s t r e s s e s . T y p e s o f S h e a r T e s t s A n o n s y m m e t r i c a l o r t h r e e d i m e n s i o n a l s t a t e o f s t r e s s u n d e r p l a n e s t r a i n i s r e a l i s e d i n a d i r e c t s h e a r box t e s t . H o w e v e r , as a r e s e a r c h t o o l t h i s t e s t has many s h o r t -c o m i n g s w h i c h make t h e m e c h a n i c s o f s h e a r d i f f i c u l t t o i n t e r p r e t . I n d e t e r m i n a c y o f t h e s t r e s s f i e l d , n o n u n i f o r m i t y o f s t r a i n s l e a d i n g t o p r o g r e s s i v e f a i l u r e , p r e s e l e c t i o n o f t h e f a i l u r e p l a n e a n d r o t a t i o n o f p r i n c i p a l a x e s a r e some o f t h e s e r i o u s l i m i t a t i o n s o f t h e t e s t . The r e s u l t s f r o m t h i s t e s t , t h e r e f o r e , c a n n o t be m e a n i n g f u l l y u t i l i z e d t o i n v e s t i g a t e s o i l b e h a v i o u r u n d e r p l a n e s t r a i n c o n d i t i o n s . An i n d e p e n d e n t c o n t r o l o f a l l t h e t h r e e p r i n c i p a l s t r e s s e s on t h e f a c e s o f a p r i s m a t i c s p e c i m e n o f s o i l has been u s e d b y some i n v e s t i g a t o r s ( K j e l l m a n 1 9 3 6 , L o r e n z e t a l 1 9 6 5 , L o m i z e a n d K r y z h a n o v s k y 1 9 6 7 , and Ko and S c o t t 1 9 6 7 a ) . The t y p e s o f a p p a r a t u s e m p l o y e d f o r t h i s h a v e , i n g e n e r a l , a l l r i g i d o r . a l l f l e x i b l e b o u n d a r i e s t o t r a n s m i t s t r e s s e s t o 14 t h e s a m p l e . In mos t s o i l s , h o w e v e r , d e f o r m a t i o n s r e s u l t i n g b o t h d u r i n g c o n s o l i d a t i o n and d u r i n g s u b s e q u e n t s h e a r may be s u f f i c i e n t l y l a r g e t o c a u s e i n t e r f e r e n c e o f s u c h b o u n d a r i e s a t common e d g e s . C o n s e q u e n t l y , t h e use o f t h e s e a p p a r a t u s i s l i m i t e d t o t h o s e s o i l s w h i c h r e q u i r e v e r y s m a l l d e f o r m a t i o n s t o f a i l u r e . H o w e v e r , a p l a n e s t r a i n a p p a r a t u s i n w h i c h one s e t o f o p p o s i t e b o u n d a r i e s i s . f l e x i b l e (Wood 195 8 , C o r n f o r t h 1 9 6 4 , H e n k e l and Wade 1 9 6 6 , Duncan and S e e d 1966 ) h a s been s u c c e s s f u l l y u s e d t o s t u d y f a i l u r e c o n d i t i o n s u n d e r p l a n e d e f o r m a t i o n . The s i m p l e s h e a r a p p a r a t u s ( Roscoe 1953 ) a l s o i m p o s e s a p l a n e d e f o r m a t i o n b o u n d a r y c o n d i t i o n on a p r i s m a t i c s p e c i m e n o f s o i l . T h i s a p p a r a t u s has t h e a d v a n t a g e t h a t i t p r o d u c e s v e r y u n i f o r m d i s p l a c e m e n t s on t h e b o u n d a r i e s o f t h e s p e c i m e n , b u t t h i s u n i f o r m i t y i s o b t a i n e d a t t h e c o s t o f a v e r y c o m p l e x s t r e s s f i e l d . T h e t e s t ha s p r i m a r i l y been u s e d t o s t u d y t h e y i e l d i n g o f s o i l s . The r e s u l t s f r o m t h i s a p p a r a t u s h a v e n o t g e n e r a l l y b e e n i n t e r p r e t e d i n t e r m s o f t h e c o n v e n t i o n a l s t r e n g t h p a r a m e t e r s c T and (j>\". A n o t h e r c l a s s o f t e s t s w h i c h a im a t s i m u l a t i n g a n o n s y m m e t r i c a l s t a t e o f s t r e s s on t h e s p e c i m e n , u t i l i z e s o l i d and h o l l o w c y l i n d r i c a l s a m p l e s , where f a i l u r e i s c a u s e d by a x i a l t o r s i o n c o u p l e d w i t h a x i a l l o a d . In t h e s e t e s t s a p a r t f r o m t h e i n h o m o g e n i t y o f s t r e s s - s t r a i n f i e l d s due t o r i g i d end c a p s , s t r e s s e s and s t r a i n s a r e n o t u n i f o r m i n t h e r a d i a l a n d t a n g e n t i a l d i r e c t i o n s , b e c a u s e where t o r s i o n a l 15 moment i s used to induce f a i l u r e , shear s t r a i n s vary with the distance from the centre o.- r o t a t i o n . In hollow c y l i n d e r s , however, the nonuniformity of t o r s i o n a l s t r a i n i s minimised. In hollow c y l i n d e r t e s t s f a i l u r e can a l s o be induced w i t h -out t o r s i o n i f independent c o n t r o l i s e x e r c i s e d on pressures i n s i d e and out s i d e of the bore. Stresses and s t r a i n s , how-ever, s t i l l remain nonuniform as the two p r i n c i p a l s t r e s s e s , r a d i a l and t a n g e n t i a l , vary throughout the th i c k n e s s of the c y l i n d e r . F a i l u r e s t a r t s at e i t h e r the i n s i d e or outside of the bore, depending on s t r e s s path t o f a i l u r e , and progresses towards the opposite side along the t h i c k n e s s . This leads to a progressive f a i l u r e . Hence i n t e r p r e t a t i o n of t e s t r e s u l t s from the above types of t e s t s appears d i f -f i c u l t with most s o i l s . Furthermore, hollow c y l i n d e r t e s t cannot be used w i t h undisturbed s o i l s . When e v a l u a t i n g the t e s t r e s u l t s of various i n -v e s t i g a t o r s i t i s , t h e r e f o r e , imperative to recognise the l i m i t a t i o n s o f the t e s t type i n respect of i t s producing a r e l a t i v e l y homogeneous s t a t e o f s t r e s s or s t r a i n i n the e n t i r e specimen. From the foregoing d i s c u s s i o n i t appears tha t t e s t s i n v o l v i n g p r i s m a t i c specimens may not s u f f e r from s t r e s s - s t r a i n inhomogenity to as la r g e an extent as the hollow c y l i n d e r t e s t s , o r sol-id c y l i n d e r t e s t s with t o r s i o n . 16 T e s t R e s u l t s Mos t o f t h e i n v e s t i g a t i o n s c o n c e r n i n g s o i l b e h a v i o u r u n d e r n o n s y m m e t r i c a l s t a t e s o f s t r e s s h a v e been c o n f i n e d t o c o h e s i o n l e s s s o i l s . I n f o r m a t i o n on c l a y s i s v e r y l i m i t e d and c o v e r s o n l y n o r m a l l y l o a d e d r e m o l d e d c l a y s . H a r d l y any r e s u l t s have been r e p o r t e d on u n d i s t u r b e d c l a y s . I t h a s been f o u n d by some i n v e s t i g a t o r s ( B i s h o p 8 E l d i n 195 3 , K i r k p a t r i c k 195 7 , C o m f o r t h 1 9 6 4 , Wu e t a l 1963 ) t h a t t h e v a l u e o f was t h e same u n d e r t r i a x i a l c o m -p r e s s i o n a n d e x t e n s i o n - t h u s s u p p o r t i n g t h e M o h r - C o u l o m b c r i t e r i o n . In c o n t r a s t H a b i b ( 1 9 5 3 ) , P e l t i e r ( 1957 ) and H a y t h o r n t h w a i t e (1960 ) showed l o w e r v a l u e s w h e r e a s Broms 8 C a s b a r i a n (1965 ) showed h i g h e r v a l u e s o f cf>' i n e x t e n s i o n . In a s e t o f t r i a x i a l c o m p r e s s i o n and e x t e n s i o n t e s t s on a s a n d i n w h i c h b o t h l o c a l a n d o v e r a l l d e f o r m a t i o n o f t h e s a m p l e s were m e a s u r e d , Roscoe e t a l ( 1963 ) c o n c l u d e d , t h a t a l t h o u g h t h e a n a l y s i s o f t h e t e s t r e s u l t s on t h e b a s i s o f o v e r a l l d e f o r m a t i o n s s u p p o r t s M o h r - C o u l o m b c r i t e r i o n , u s i n g t h e l o c a l s t r e s s e s i n t h e c e n t r a l p o r t i o n o f t h e s p e c i m e n s , t h e f a i l u r e c r i t e r i o n i s f o u n d t o a p p r o a c h t h e e x t e n d e d T r e s c a o r e x t e n d e d von M i s e s c r i t e r i o n . B i s h o p ( 1 9 6 6 ) , h o w e v e r , a r g u e d t h a t t h e e x t e n d e d T r e s c a o r e x t e n d e d von M i s e s c r i t e r i a c a n n o t r e p r e s e n t t h e b e h a v i o u r o f d e n s e c o h e s i o n -l e s s m a t e r i a l s ( o r c' - 0 m a t e r i a l s ) h a v i n g a c o m p r e s s i o n o f more t h a n 3 6 . 9 ° . Above t h i s l i m i t i n g v a l u e o f t}»', 17 t h e r i g h t s e c t i o n s o f f a i l u r e s u r f a c e s f o r t h e s e c r i t e r i a p r o j e c t i n t o t h e n e g a t i v e o r t e n s i l e e f f e c t i v e s t r e s s s p a c e , w h i c h o b v i o u s l y i s m e a n i n g l e s s f o r a c \" - 0 m a t e r i a l . S i m . M a r c o n c l u s i o n s were drawn by B a r d e n and K h a y a t t ( 1 9 6 6 ) . T e s t s on p r i s m a t i c s p e c i m e n s o f s a n d l o a d e d by a l l r i g i d b o u n d a r i e s and f a i l e d u n d e r n o n s y m m e t r i c a l s t a t e s o f s t r e s s have b e e n r e p o r t e d by K j e l l m a n ( 1 9 3 6 ) . He o b s e r v e d a s i z e a b l e i n c r e a s e (up t o 8 ° ) i n t h e v a l u e o f (J>'for a d e n s e s a n d u n d e r s t r e s s s t a t e s a £ > > compa red t o t h e t r i -a x i a l c o m p r e s s i o n s t a t e , = 0 3 . U s i n g K j e l l m a n ' s a p p a r a t u s J a c o b s o n (195 7) d rew s i m i l a r c o n c l u s i o n s ; he f o u n d t h a t t h e v a l u e o f ' f o r s a n d s i n c r e a s e d as t h e t e s t d e p a r t e d f r o m t h e s y m m e t r i c c o m p r e s s i o n (a^ = a^) s t a t e o f s t r e s s and became as much as 6 ° h i g h e r when t h e o t h e r l i m i t o f s y m m e t r i c e x t e n s i o n (a^ = cr£) was a p p r o a c h e d . In a s i m i l a r a p p a r a t u s L o r e n z e t a l ( 1965 ) made a s t u d y o f s t r e s s s t r a i n r e s p o n s e o f a d r y s a n d u n d e r p l a n e s t r a i n . - T h e y r e p o r t e d an a l m o s t c o n s t a n t v a l u e o f i r r e s p e c t i v e o f t h e i n i t i a l p o r o s i t y o f s a n d . F u r t h e r m o r e , t h e y d i d n o t o b s e r v e any v o l u m e e x -p a n s i o n d u r i n g s h e a r , e v e n f o r t h e l o w e s t i n i t i a l p o r o s i t y . The t e s t s r e p o r t e d were made a t m o d e r a t e p r e s s u r e s . T h e s e o b s e r v a t i o n s a r e a p p a r e n t l y i n c o n f l i c t w i t h t h o s e f r o m t h e c o n v e n t i o n a l t r i a x i a l t e s t s . A l l f l e x i b l e p r i n c i p a l s t r e s s b o u n d a r i e s on t h e f a c e s o f a p r i s m a t i c s p e c i m e n were u s e d by Ko and S c o t t (1967a ) a n d L o m i z e £ K r y z h a n o v s k y ( 1 9 6 7 ) , f o r t h e s t u d y o f 18 deformation and strength c h a r a c t e r i s t i c s o f sands, under nonsymmetrical s t a t e s of s t r e s s . Scott and Ko found l a r g e v a r i a t i o n i n the value o f 4)\" obtained i n t h e i r t e s t device under s t r e s s s t a t e corresponding to = 0 g , when compared to that obtained i n the conventional t r i a x i a l t e s t . Un-f o r t u n a t e l y , an a r b i t r a r y d e f i n i t i o n o f f a i l u r e was used to analyse t e s t r e s u l t s , because t e s t s could not be c a r r i e d to the usual d e f i n i t i o n of f a i l u r e due to extremely l i m i t e d deformations p o s s i b l e i n the t e s t device. T h e i r r e s u l t s showed that the value o f increased by 4° to 8° (depending on i n i t i a l p o r o s i t y ) as the s t r e s s s t a t e s departed from symmetric compression, ~ o^> towards nonsymmetrical s t a t e s and f i n a l l y reached the other l i m i t , the symmetric e x t e n s i o n , °2 = a i a n c^ Scott 196 8). The shape of f a i l u r e surface on an o c t a h e d r a l plane was found to be curved and d i d not f i t any o f the f a i l u r e c r i t e r i a discussed above. Lomize and Kryzhanovsky a l s o found that the value of was s i g n i f i c a n t -l y i n f l u e n c e d by a^. An increase of as much as 9° to 22° i n the value of was observed when the state of s t r e s s was v a r i e d from that of symmetric compression to the intermediate nonsymmetrical s t a t e s and f i n a l l y taken to the other l i m i t of symmetry, = a£. Their experimental r e s u l t s d i d not . favour any o f the commonly accepted c r i t e r i o n of f a i l u r e . Consequently they formulated a new f a i l u r e c r i t e r i o n , which p o s t u l a t e d , t h a t at f a i l u r e TQ ^ i s not d i r e c t l y p r o p o r t i o n a l to a\" (as assumed i n Extended von Mises c r i t e r i o n ) but i s oct 19 a c o m p o s i t e f u n c t i o n o f °QC^. ^nd ( a^a^a^ ) , t h e t h i r d i n -v a r i a n t o f t h e s t r e s s t e n s o r . \" h i s s u g g e s t i o n f a v o u r s the p o s t u l a t e o f Newmark ( 1 9 6 0 ) , who c o n s i d e r e d t h a t t he f o r m u -l a t i o n o f f a i l u r e c o n d i t i o n m i g h t i n v o l v e a l l t h e t h r e e i n v a r i a n t s o f t h e s t r e s s t e n s o r : i . ^ . . , a ' . . . T +. and ' ' OCT' OCt S t u d i e s on t h e b e h a v i o u r o f c o h e s i o n l e s s m a t e r i a l s u n d e r p l a n e s t r a i n c o n d i t i o n s have been done u s i n g l o n g r e c t a n g u l a r s p e c i m e n s w i t h one p a i r o f f l e x i b l e l o a d i n g b o u n d a r i e s ( L e u s s i n k and W i t t k e 1 9 6 3 , L e u s s i n k 1 9 6 5 , C o r n f o r t h 1 9 6 4 , M a r s a l 1 9 6 5 ) . B o t h t h e o r e t i c a l and e x p e r i m e n t a l r e s u l t s show t h a t t h e s t r e n g t h u n d e r p l a n e s t r a i n e x c e e d s t h e c o r r e s p o n d i n g t r i a x i a l v a l u e . The d i f f e r e n c e i n e q u i -v a l e n t \" v a r i e s w i t h d i f f e r e n t i n v e s t i g a t o r s . C h r i s t e n s o n ( 1 9 6 1 ) , C o r n f o r t h (1964) and L e u s s i n k (1965 ) r e p o r t e d an i n c r e a s e i n t h e v a l u e o f ' f o r s a n d s f r o m 2 ° t o 4 ° , whe reas M a r s a l ( 1965 ) showed an i n c r e a s e o f as much as 1 3 ° f o r a c o m p a c t e d r o c k f i l l m a t e r i a l . U n d e r p l a n e s t r a i n , vo lume c h a n g e s and s t r a i n a t f a i l u r e were f o u n d t o be a b o u t one t h i r d o f t h o s e o b s e r v e d u n d e r t h e c o r r e s p o n d i n g t r i a x i a l c o n d i t i o n s ( C o r n f o r t h 19 6 4 , F i n n , Wade and Lee 1 9 6 7 ) . H o w e v e r , t h e r a t e o f v o l u m e c h a n g e a t f a i l u r e was o b s e r v e d t o be a l m o s t t h e same i n t h e two t y p e s o f t e s t s , f o r t h e same i n i t i a l p o r o s i t y ( C o r n f o r t h 1 9 6 4 ) . In t o r s i o n t e s t s on s o l i d s a n d c y l i n d e r s ( H a b i b 1953 ) and on h o l l o w c y l i n d e r s o f a r e m o l d e d s i l t 20 (Haythornthwaite I 9 6 0 , 1963 ) i t was found t h a t considerable departure from the Mohr-Coulomb c r i t e r i o n occurred under s t r e s s s t a t e s a-^ > >'O-^' ^ v a ^ u e °f <{>' w a s reported to be 1 1 ° higher than the t r i a x i a l compression value by Habib ( 1 9 5 3 ) . Using hollow c y l i n d r i c a l sand samples, K i r k p a t r i c k ( 1957 ) observed an increase of about 2 ° i n the value of under c o n d i t i o n s approximating plane s t r a i n , whereas Whitman and Luscher ( 1962 ) reported a 6 ° i n c r e a s e . S i m i l a r c o n c l u s i o n s were drawn f o r sands by Wu, Loh and Malvern (1963 ) , when f a i l u r e occurred under a^ ' > °2 > a3 s t a ' t e s °f s t r e s s . I t , t h e r e f o r e , appears t h a t the l i t e r a t u r e todate p o i n t s out a sense of disagreement on the v a l i d i t y of the Mohr-Coulomb f a i l u r e c r i t e r i o n . There does not appear to be a general acceptance o f t h i s c r i t e r i o n even under t h e r a x i a l l y symmetric compression and extension s t a t e s of s t r e s s i n the conventional t r i a x i a l t e s t . Under nonsymmetrical s t a t e s of s t r e s s i n c l u d i n g the case of plane s t r a i n there seems a general agreement on the strengt h o f sand being higher when compared to the conventional t r i a x i a l compression value. However, the magnitude of the d i f f e r e n c e v a r i e s g r e a t l y with d i f f e r e n t i n v e s t i g a t o r s . This could be a t t r i b u t e d p a r t l y to the p e c u l i a r i t i e s of the t e s t devices and a r b i t r a r y d e f i n i t i o n s of f a i l u r e i n some cases. Where attempts have been made to e s t a b l i s h f a i l u r e surface f o r sands, i t has been g e n e r a l l y found that the surface does not favour any one o f the f a i l u r e 21 c r i t e r i a d i s c u s s e d a b o v e . I t seems r e a s o n a b l e t o e x p e c t t h e vo lume c h a n g e and s t r a i n a t f a i l u r e u n d e r p l a n e d e f o r m a t i o n t o be s m a l l e r t h a n the c o r r e s p o n d i n g t r i a x i a l v a l u e s . U n d e r p l a n e s t r a i n , t h e s a n d g r a i n s h a v e a more r e s t r i c t e d movement u n d e r i m p o s e d s h e a r s t r e s s e s c o m p a r e d t o t h e s y m m e t r i c s t a t e s o f s t r e s s , t h e r e b y c a u s i n g l e s s s l i p p a g e p a s t e a c h o t h e r a n d c o n s e q u e n t l y l e s s vo lume change a t any s t a g e o f s h e a r i n g p r o c e s s . H o w e v e r , t h e r e i s a d i s a g r e e m e n t on t h e s i g n o f vo lume c h a n g e s d u r i n g s h e a r . L o r e n z e t a l ( 1965 ) d i d n o t o b s e r v e any n e t e x p a n s i o n i n s h e a r u n d e r p l a n e d e f o r m a t i o n i r r e s p e c t i v e o f t h e i n i t i a l p o r o s i t y i n c o n t r a s t t o t h e p a r a l l e l o b s e r v a t i o n s by C o r n f o r t h (1964 ) a n d F i n n , Wade and Lee ( 1 9 6 7 ) . F o r a dense s a n d u n d e r n o n s y m m e t r i c a l s t a t e s o f s t r e s s e s , Ko and S c o t t ( 1 9 6 7 b ) d i d n o t o b s e r v e any c o m p r e s s i o n i n t h e e a r l y s t a g e s o f s h e a r i n c o n t r a s t t o t h e c o n v e n t i o n a l t r i a x i a l c o m p r e s s i o n t e s t . Thus t h e r e i s a n e e d t o f u r t h e r c l a r i f y t h e s t r e s s - s t r a i n r e l a t i o n s and f a i l u r e c o n d i t i o n s f o r s a n d s u n d e r s t r e s s s t a t e s o t h e r t h a n t h o s e i n t h e c o n v e n t i o n a l t r i a x i a l t e s t . O t h e r f e a t u r e s o f s i g n i f i c a n t i n t e r e s t may be t h e i n f l u e n c e o f s t r e s s p a t h t o f a i l u r e , a n i s o t r o p y i n c o n s o l i d a t i o n and r o t a t i o n o f p r i n c i p a l a x e s . T h e s e v a r i a b l e h a v e r e c e i v e d l i t t l e a t t e n t i o n u n d e r n o n s y m m e t r i c a l s t a t e s o f s t r e s s . B e h a v i o u r o f s a t u r a t e d , r e m o l d e d n o r m a l l y l o a d e d c l a y s i n n o n s y m m e t r i c a l s t r e s s f i e l d u s i n g p r i s m a t i c 2 2 s p e c i m e n s was s t u d i e d by S h i b a t a and K a r u b e ( 1965 ) and i n p l a n e s t r a i n by H e n k e l £ Wade (196 6 ) , U s i n g i s o t r o p i c c o n s o l i d a t i o n and s t r e s s p a t h t o f a i l u r e as (o^-cfg) = c o n s t , S h i b a t a £ K a r u b e (1965) showed t h a t t he r e l a t i v e v a l u e o f o\"2 i n f l u e n c e d t h e s t r e s s - s t r a i n r e s p o n s e ; an i n c r e a s e i n (o^-cfg) r e s u l t e d i n a l i n e a r d e c r e a s e i n f a i l u r e s t r a i n . T h e i r r e s u l t s showed t h a t Moh r-Cou lomb c r i t e r i o n u n d e r -e s t i m a t e d t h e s t r e n g t h o f c l a y s u n d e r n o n s y m m e t r i c a l s t r e s s s t a t e s . H e n k e l and Wade (1966 ) p e r f o r m e d t e s t s on K 0 -c o n s o l i d a t e d s a m p l e s , a n d f o u n d t h a t \" was l a r g e r by a b o u t 1 . 2 ° and f a i l u r e s t r a i n o n l y a t h i r d when c o m p a r e d to t h e c o r r e s p o n d i n g t r i a x i a l c o n d i t i o n s . M e a s u r e m e n t o f showed t h a t t h e r a t i o c r a £ s t a y s c o n s t a n t d u r i n g s h e a r a t t h e e n d o f K Q - c o n s o l i d a t i o n v a l u e . B o t h S h i b a t a £ K a r u b e (1965) and H e n k e l £ Wade (1966) f o u n d t h a t p o r e p r e s s u r e s d u r i n g s h e a r were g o v e r n e d by o c t a h e d r a l s t r e s s e s a n d s u g g e s t e d t h e f o l l o w i n g r e l a t i o n s : Au = A a o c t + a o c t f ( A T o c t V A a o c t ) ( 2 . 6 ) S h i b a t a £ K a r u b e •: . ,. ( 2 . 7 ) H e n k e l £ Wade A u = A a o c t + a A x o c t where Au i s t h e c h a n g e i n p o r e p r e s s u r e and A T o c ^ - and A a o c t a r e c n a n S e s i- n o c t a h e d r a l s h e a r and n o r m a l s t r e s s r e s p e c t i v e l y ; f s t a n d s f o r \" f u n c t i o n o f \" a n d \" a \" i s a p o r e p r e s s u r e p a r a m e t e r . S h i b a t a £ K a r u b e (1965 ) f o u n d t h a t b e l o w a c e r t a i n c r i t i c a l v a l u e o f A t _ _ t , Au was a f u n c t i o n 23 o f A°\" + o n l y and h e n c e i n d e p e n d e n t o f Ax OCX j - x o c t F o r r e m o l d e d n o r m a l l y c o n s o l i d a t e d c l a y s , h o l l o w c y l i n d e r t e s t s by Wu, L o h , and M a l v e r n (1963 ) s u p p o r t t he v a l i d i t y o f Moh r-Cou lomb f a i l u r e c r i t e r i o n i n t h r e e d i m e n -s i o n a l e f f e c t i v e s t r e s s s p a c e . In c o n t r a s t , i n s i m i l a r t e s t s by Broms and C a s b a r x a n ( 1 9 6 5 ) , t h e r e l a t i v e v a l u e o f o\"^ was shown t o i n f l u e n c e t h e v a l u e o f cb' t o a c o n s i d e r -a b l e e x t e n t . S t a r t i n g f r o m t h e s y m m e t r i c c o m p r e s s i o n s t a t e o f s t r e s s , i n c r e a s i n g t h e v a l u e o f r e s u l t e d i n an i n c r e a s e i n t h e v a l u e o f cb\" w h i c h a p p r o a c h e d 7 ° h i g h e r a t t h e o t h e r e x t r e m e l i m i t o f cr^* x n e s y m m e t r i c e x t e n s i o n s t a t e . F o r a n o r m a l l y c o n s o l i d a t e d r e m o l d e d k a o l i n i t e , Broms and Ratnam (1963 ) a l s o n o t e d an i n c r e a s e i n cb** v a l u e by a b o u t 4- 1/2 ° u n d e r n o n s y m m e t r i c a l s t a t e s o f s t r e s s when c o m p a r e d t o t h e t r i a x i a l c o m p r e s s i o n v a l u e . T h u s , f o r r e m o l d e d n o r m a l l y c o n s o l i d a t e d c l a y s a g r e e m e n t on t h e . v a l i d i t y o f M o h r - C o u l o m b f a i l u r e c r i t e r i o n i s l a c k i n g . U n f o r t u n a t e l y , t h e e x i s t i n g i n f o r m a t i o n i s e x t r e m e l y l i m i t e d and i t i s n o t p o s s i b l e t o draw e v e n a g e n e r a l p i c t u r e o f t h e s t r e s s - s t r a i n and s t r e n g t h c h a r a c t e r -i s t i c s o f c l a y s u n d e r n o n s y m m e t r i c a l s t a t e s o f s t r e s s . A g a i n , t h e i n f l u e n c e o f a n i s o t r o p y i n c o n s o l i d a t i o n , s t r e s s p a t h t o f a i l u r e and r o t a t i o n o f p r i n c i p a l a x e s have been g i v e n l i t t l e c o n s i d e r a t i o n , a l t h o u g h i n t h e f i e l d t h e s e s i t u a t i o n s a r e o f t e n e n c o u n t e r e d . 24 Some S i g n i f i c a n t F e a t u r e s o f T y p e s o f A p p a r a t u s E m p l o y e d i n t h e Above I n v e s t i g a t i o n s S o i l t e s t i n g u n d e r t h r e e d i m e n s i o n a l s t a t e s o f s t r e s s c o n s t i t u t e s a h i g h l y s p e c i a l i s e d r e s e a r c h f i e l d . The m e c h a n i c a l d i f f i c u l t i e s e n c o u n t e r e d i n t h e d e s i g n o f s u i t a b l e t e s t i n g e q u i p m e n t a r e numerous and t h e o p e r a t i o n o f a p p a r a t u s g e n e r a l l y i n v o l v e d . Such t y p e s o f t e s t s a r e e v i d e n t l y n o t s u i t e d f o r r o u t i n e p u r p o s e s , y e t t h e y a r e e s s e n t i a l t o c l a r i f y c e r t a i n a s p e c t s o f t h e m e c h a n i c a l b e h a v i o u r o f s o i l s w h i c h c a n n o t be a t t e m p t e d i n t h e c o n v e n -t i o n a l t y p e s o f a p p a r a t u s . I t i s n o t i n t e n d e d h e r e t o p r e s e n t t h e d e t a i l s a b o u t t h e v a r i o u s t y p e s o f e q u i p m e n t so f a r e m p l o y e d f o r s o i l t e s t i n g u n d e r n o n s y m m e t r i c a l s t a t e s o f s t r e s s . The e m p h a s i s o f d i s c u s s i o n w i l l be p l a c e d on the p r i n c i p l e s i n v o l v e d i n s u c h t y p e s o f t e s t i n g and on t h e m a j o r d i f f i -c u l t i e s i n h e r e n t i n t h e t e c h n i q u e . I t i s p r o p o s e d ; t o d i s c u s s o n l y t h o s e a p p a r a t u s w h i c h a r e d e s i g n e d t o t e s t p r i s m a t i c s p e c i m e n s . F o r r e a s o n s s t a t e d e a r l i e r , use o f p r i s m a t i c s p e c i m e n s i n i n v e s t i g a t i n g s o i l b e h a v i o u r u n d e r n o n s y m m e t r i c a l s t a t e s o f s t r e s s a p p e a r s s u p e r i o r t o t h e use o f h o l l o w o r s o l i d c y l i n d r i c a l s p e c i m e n s . K j e l l m a n (1936 ) and L o r e n z e t a l (1965 ) u s e d c u b i c s a m p l e s • ' l o a d e d on a l l f a c e s by r i g i d b o u n d a r i e s . Such an a r r a n g e m e n t p u t s s e r i o u s r e s t r i c t i o n s on t h e p e r m i s s i b l e d e -f o r m a t i o n s . As a c o n s e q u e n c e o n l y dense c o h e s i o n l e s s 25 m a t e r i a l s r e q u i r i n g s m a l l f a i l u r e s t r a i n c o u l d be t e s t e d t o f a i l u r e . L o r e n z e t a l ( 1965 ) e m p l o y e d s t r a i n gauge b l o c k s t o measu re t h e i n t e r m e d i a t e p r i n c i p a l s t r e s s i n t h e i r p l a n e s t r a i n t e s t s , b u t were n o t s u r e o f t h e m e a s u r e d v a l u e s , a p -p a r e n t l y due t o i m p e r f e c t i o n s o f t h e t e s t d e v i c e . The use o f a l l f l e x i b l e l o a d i n g b o u n d a r i e s on c u b i c s a m p l e s o f s a n d , as r e p o r t e d by Ko and S c o t t ( 1967a ) and L o m i z e and K r y z h a n o v s k y ( 1 9 6 7 ) , ha s t h e a d v a n t a g e o f p r o v i d i n g p r a c t i c a l l y t r u e p r i n c i p a l s t r e s s l o a d i n g b o u n d a r -i e s , and as a r e s u l t s h o u l d a p p r o a c h a homogeneous s t a t e o f s t r e s s a n d s t r a i n t h r o u g h o u t t h e e n t i r e s p e c i m e n . How-e v e r , s o i l s r e q u i r i n g l a r g e d e f o r m a t i o n s d u r i n g c o n s o l i d a t i o n and s u b s e q u e n t s h e a r c a n n o t be t e s t e d t o f a i l u r e b e c a u s e o f t h e i n t e r f e r e n c e o f f l e x i b l e b o u n d a r i e s a t common e d g e s , w h i l e u n d e r d i f f e r e n t p r e s s u r e s . The d e v i c e s , t h e r e f o r e , a p p e a r t o h a v e a l i m i t e d p o t e n t i a l . . Ko and S c o t t (196 7a) made u s e o f a r i g i d s e p a r a t i n g f r ame t o k e e p t h e f l e x i b l e membrane b o u n d a r i e s f r o m i n t e r f e r i n g w i t h e a c h o t h e r . A s i g n i f i c a n t p o r t i o n o f t h i s f r a m e ( a b o u t 1/4 \" ) p r o j e c t s i n t o a p p r o x i m a t e l y 3.5 i n c h c u b i c s a m p l e a l o n g a l l t h e e d g e s . I t c a n be e x p e c t e d , t h e r e f o r e , t h a t t h e f r a m e m i g h t c a r r y a s i g n i f i c a n t p o r t i o n o f t he a p p l i e d s t r e s s e s , c a u s i n g t h e s t r e s s and s t r a i n f i e l d s t o be f a r f r o m homogeneous ( G r e e n 1 9 6 7 , B e l l 1 9 6 8 , A r t h u r 6 M e n z i e s 1 9 6 8 ) . : T h i s may a l s o e x p l a i n t h e u n u s u a l l y h i g h v a l u e s o f s a n d , Ko and S c o t t o b t a i n e d i n t h e i r t e s t d e v i c e , f o r s y m m e t r i c c o m p r e s s i o n 26 s t a t e o f s t r e s s , when c o m p a r e d t o t h o s e o b t a i n e d i n a c o n -v e n t i o n a l t r i a x i a l c o m p r e s s i o n t e s t . In f a c t , t h e s t r e s s -s t r a i n c u r v e s r e p o r t e d a r e s t e e p l y r i s i n g e v e n a t t h e p o i n 1 ; o f d e f i n e d f a i l u r e and show no s i g n o f f l a t t e n i n g o u t a t t h e s t r a i n s t h e t e s t s were t e r m i n a t e d . L o m i z e and K r y z h a n o v s k y ( 1 9 6 7 ) , on t h e o t h e r h a n d , d i d n o t s t a t e how t h e y g o t o v e r t h e p r o b l e m o f k e e p i n g f l e x i b l e r u b b e r membrane b o u n d a r i e s f r o m i n t e r f e r i n g w i t h e a c h o t h e r w h i l e u n d e r d i f f e r e n t p r e s s u r e s . In t h e t e s t i n g d e v i c e s e m p l o y e d f o r i n v e s t i g a t i n g s o i l b e h a v i o u r u n d e r p l a n e s t r a i n , l o n g r e c t a n g u l a r s p e c i m e n s a r e o f t e n u s e d . In g e n e r a l one p a i r o f l o a d i n g b o u n d a r i e s was made f l e x i b l e (Wood 195 8, C o r n f o r t h 1 9 6 4 , H e n k e l and Wade 1 9 Q 6 , L e u s s i n k and W i t t k e 1 9 6 3 , M a r s a l 1 9 6 5 , Duncan and Seed 1 9 6 6 ) . T h e s e r e c t a n g u l a r s p e c i m e n s h a d t h e h e i g h t -w i d t h r a t i o b e t w e e n 2 and 3 , as i n a c o n v e n t i o n a l t r i a x i a l s p e c i m e n , and l e n g t h much l a r g e r -than t h e w i d t h . C o n d i t i o n o f z e r o d e f o r m a t i o n was m a i n t a i n e d i n t h e l o n g i t u d i n a l d i r e c t i o n o f t h e s p e c i m e n by means o f one p a i r o f r i g i d e n d p l a t e s h e l d a t a f i x e d d i s t a n c e a p a r t . F r i c t i o n a l d r a g be tween t h e s e p l a t e s and t h e s p e c i m e n was k e p t t o a min imum by u s i n g p o l i s h e d p l a t e s w i t h a t h i n l a y e r o f s i l i c o n e g r e a s e be tween p l a t e and s a m p l e membrane . I f l e n g t h t o w i d t h r a t i o o f t h e s a m p l e i s l a r g e , a c o n d i t i o n o f p l a n e d e f o r m a t i o n i s c l o s e l y a p p r o a c h e d n e a r t h e c e n t r e o f t h e s p e c i m e n . Thus t he end e f f e c t s o f f r i c t i o n b e t w e e n p l a t e 27 and samp le membrane a r e m i n i m i s e d . . H o w e v e r , t h e e n d f r i c t i o n d o e s i n f l u e n c e t h e m e a s u r e d v a l u e o f v e r t i c a l s t r e s s on h o r i z o n t a l f a c e s , and s h o u l d be c o r r e c t e d a c c o r d i n g l y . No a t t e m p t s were made t o measu re f r i c t i o n d i r e c t l y . C o r r e c t i o n t o t h e v e r t i c a l d e v i a t o r s t r e s s was a p p l i e d on t h e b a s i s o f work done i n m o v i n g t h e s p e c i m e n a l o n g t h e e n d p l a t e s (Wood 1 9 5 8 ) . G e n e r a l l y a p r e s s u r e c e l l was u s e d t o e n c l o s e t h e s p e c i m e n ( s i m i l a r t o t h a t f o r a t r i a x i a l t e s t ) and t h e f l u i d p r e s s u r e f u r n i s h e d one o f t h e p r i n c i p a l s t r e s s e s . F o r d r y c o h e s i o n l e s s m a t e r i a l s , vacuum o n p o r e s p a c e s e r v e d t o p r o v i d e t h e c o n f i n i n g p r e s s u r e and no s e p a r a t e c e l l was n e c e s s a r y . ^ - c o n s o l i d a t i o n was a c h i e v e d ( C o r n f o r t h 1964 , H e n k e l a n d Wade 1966 ) t h r o u g h t h e use o f a n u l l d e v i c e s i m i l a r t o t h e l a t e r a l s t r a i n i n d i c a t o r ( B i s h o p and H e n k e l 1 9 6 2 ) . F o r c l a y s , t h i s t e c h n i q u e n e c e s s i t a t e d i n t e r m i t t e n t and s l o w i n c r e a s e o f b o t h c e l l and d e v i a t o r p r e s s u r e , a n d , b e c a u s e o f t h e l a r g e s i z e s p e c i m e n s ( 1 6 \" x 4 \" x 2 \" ) , t o o k as l o n g a s one t o t h r e e weeks t o c o n s o l i d a t e . The s h e a r s t a g e o f t h e t e s t s u n d e r p l a n e s t r a i n c o n d i t i o n s , c o n s i s t e d o f i n c r e a s i n g t h e v e r t i c a l l o a d on t h e r e c t a n g u l a r l o a d i n g c a p . I t i s e s s e n t i a l t o p r e v e n t c o m p l e t e l y t h e r o t a t i o n o f t h e l o a d i n g c a p t o k e e p i t f r o m i n t e r f e r i n g w i t h t h e r i g i d e n d p l a t e s d u r i n g i t s v e r t i c a l movement . T h i s was a c h i e v e d by Wood ( 1 9 5 8 ) , C o r n f o r t h (1964 ) and H e n k e l and Wade ( 1 9 6 6 ) , by l o a d i n g t h e c a p a t t h e two 28 q u a r t e r p o i n t s . No s u c h a r r a n g e m e n t a p p e a r s t o have been a d o p t e d by Duncan and Seed ( 1 9 6 o ) . I n p l a n e s t r a i n a p p a r a t u s t h e m e a s u r e m e n t o f i n t e r m e d i a t e p r i n c i p a l s t r e s s , , i n t he l o n g i t u d i n a l d i r e c t i o n o f s p e c i m e n was done by t h e use o f a n u l l t e c h n i q u e s i m i l a r i n p r i n c i p l e t o t h a t u s e d i n p o r e w a t e r p r e s s u r e m e a s u r e m e n t s (Wood 195 8, C o r n f o r t h 1 9 6 4 , H e n k e l £ Wade 1 9 6 6 , L e u s s i n k and W i t t k e 1 9 6 3 ) . The r i g i d end p l a t e s m a i n t a i n i n g p l a n e d e f o r m a t i o n were c o n n e c t e d t h r o u g h f o u r s y m m e t r i c a l l y p l a c e d t i e b a r s . One o f t h e end p l a t e s i n c o r p o r a t e d a w a t e r p r e s s u r e c e l l , w i t h a f l e x i b l e r u b b e r d i a p h r a g m w h i c h was c o n n e c t e d t o t h e n u l l i n d i c a t o r . T h i s t y p e o f a r r a n g e m e n t has a f i n i t e f l e x i b i l i t y and t h e c o n d i t i o n o f z e r o s t r a i n had t o be m a i n t a i n e d by c o n t i n u o u s l y a d j u s t i n g t h e m e r c u r y t h r e a d o f t h e n u l l i n d i c a t o r t o a c c o u n t f o r t h e e l o n g a t i o n o f t i e r o d s , l e a d s e t c . u n d e r p r e s s u r e c h a n g e s . T h i s i s a t e d i o u s p r o c e d u r e when t h e s h e a r t e s t i s o f a l o n g d u r a t i o n (12 d a y s f o r 1 6 \" x 4 \" x 2 \" c l a y s a m p l e ; H e n k e l and Wade 1 9 6 6 ) . I t a p p e a r s , t h e r e f o r e , t h a t s o i l t e s t i n g i n a n o n s y m m e t r i c a l s t r e s s f i e l d may i n v o l v e some f o r m i d a b l e p r o b l e m s . . S p e c i a l box s h a p e d membranes a r e n e e d e d t o e n c l o s e t h e s p e c i m e n s i f e d g e s o f t h e s p e c i m e n a r e t o be r e a s o n a b l y s h a r p . The a p p a r a t u s p r e f e r a b l y s h o u l d be a d a p t a b l e f o r t e s t i n g t o f a i l u r e b o t h s a n d s and c l a y s . In p l a n e s t r a i n a p p a r a t u s l o n g s p e c i m e n s a r e p r e f e r a b l e t o o f f s e t t h e e f f e c t o f e n d f r i c t i o n , b u t t o o b i g a s i z e i s 29 d i f f i c u l t to handle, makes the t e s t i n g times u n n e c e s s a r i l y long and i s i m p r a c t i c a l f o r undisturbed c l a y because o f l i m i t a t i o n on s i z e o f tube samplers. S e t t i n g up a satu-r a t e d r e c t a n g u l a r c l a y specimen i f always a problem, as i t i s d i f f i c u l t to get a i r out from between the sample and the membrane. Very close t o l e r a n c e s are needed i n machin- .. ing the moving boundaries to prevent t h e i r i n t e r f e r e n c e w i t h other r i g i d boundaries. Use o f water pressure c e l l s and t i e rods to ho l d end p l a t e s at f i x e d distance apart i n a plane s t r a i n apparatus, n e c e s s i t a t e s a cumbersome manual c o n t r o l with a p r e c a l i b r a t e d n u l l device. K Q c o n s o l i d a t i o n stage i s unusually prolonged as the st r e s s e s have to be brought on the sample g r a d u a l l y . In the plane s t r a i n device to be described h e r e i n , an attempt has been made to incor p o r a t e some improvements over the devices c u r r e n t l y i n use. Some s i g n i f i c a n t innova-t i o n s aimed at were: the use o f no n r o t a t i n g l o a d i n g cap, f a s t e r K - c o n s o l i d a t i o n , d i r e c t measurement o f f r i c t i o n o ' between the end p l a t e s and the deforming sample, measurement of through the use o f end p l a t e s with b u i l t i n lo a d c e l l s and f l e x i b i l i t y i n l o a d i n g path to f a i l u r e . A reasonably convenient sample s i z e was employed which reduced t e s t i n g time f o r c l a y s o f even low p e r m e a b i l i t y to l e s s than 3 days. 30 CHAPTER 3 DESCRIPT ION OF THE APPARATUS The a p p a r a t u s t o be d e s c r i b e d was d e s i g n e d t o i m p o s e a c o n d i t i o n o f p l a n e s t r a i n d u r i n g s h e a r o f a r e c -t a n g u l a r s p e c i m e n o f s o i l ( f i g . 3 . 1 ) . P r i v i s i o n was a l s o made t o c o n s o l i d a t e t h e s p e c i m e n s a n i s o t r o p i c a l l y u n d e r c o n d i t i o n s o f no l a t e r a l y i e l d (K o r one d i m e n s i o n a l c o n -s o l i d a t i o n ) . No p r e s s u r e c e l l was u s e d ; i n s t e a d , f l e x i b l e w a t e r f i l l e d r u b b e r d i a p h r a g m s s e a l e d on p e r s p e x p l a t e s were e m p l o y e d ' t o f u r n i s h t h e l a t e r a l p r i n c i p a l s t r e s s . The f l e x i b l e d i a p h r a g m s u p p o r t p l a t e s were c l a m p e d t o t h e r i g i d e n d p l a t e s w h i c h m a i n t a i n z e r o d e f o r m a t i o n i n t h e l o n g i t u d i n a l d i r e c t i o n o f t h e s p e c i m e n . B o t h l o n g i t u d i n a l and l a t e r a l d e f o r m a t i o n s d u r i n g c o n s o l i d a t i o n were c o m p l e t e l y p r e v e n t e d by t h e end p l a t e s and by m a i n t a i n i n g a c o n s t a n t vo lume o f w a t e r i n t h e l a t e r a l p r e s s u r e d i a p h r a g m s . P e r s p e x was u s e d f o r m a k i n g t h e e n d p l a t e s and the f l e x i b l e d i a p h r a g m s u p p o r t p l a t e s i n t h e i n i t i a l d e s i g n i n o r d e r t o o b t a i n a c l e a r v i e w o f t h e . s p e c i m e n d u r i n g a l l s t a g e s o f t e s t a n d , h e n c e t o be a b l e t o d e t e c t any u n u s u a l h a p p e n i n g l i k e i n t e r f e r e n c e o f b o u n d a r i e s o r r u b b e r membranes . 31 °1 =o e,= o F»g- 3 1 — P-rinci'^al s+T«sses u n d e r JJ lane de-foTrncxH ton 32 S i z e The s p e c i m e n i s 4 i n c h e s l o n g , 1 i n c h w ide and 2 t o 2 1/2 i n c h e s h i g h . The l e n g t h - w i d t h r a t i o was c h o s e n t o m i n i m i s e t h e e f f e c t o f e n d f r i c t i o n on s a m p l e b e h a v i o u r . The h e i g h t - w i d t h r a t i o was t h e same as t h a t u s e d , i n t h e c o n -v e n t i o n a l t r i a x i a l s p e c i m e n s . S p e c i m e n s o f u n d i s t u r b e d c l a y s c o u l d be c o n v e n i e n t l y t r i m m e d f r o m s t a n d a r d 5 i n c h d i a m e t e r t h i n ' w a l l e d t u b e s a m p l e r s . F r i c t i o n l e s s End P l a t e s T h e s e p l a t e s f o r c e p l a n e d e f o r m a t i o n on t h e s p e c i m a n , b o t h d u r i n g t h e c o n s o l i d a t i o n and s h e a r s t a g e s o f t h e t e s t . T h e y were made o f p e r s p e x and t h e f a c e s i n c o n t a c t w i t h t h e s p e c i m e n e n d s were h i g h l y p o l i s h e d . A t h i n l a y e r o f s i l i c o n e g r e a s e was u s e d on t h e p o l i s h e d f a c e s t o r e d u c e f r i c t i o n a l d r a g be tween t h e s a m p l e membrane and t h e p l a t e s . The c o e f f i c i e n t o f f r i c t i o n b e t w e e n t h e s amp l e and t h e e n d p l a t e s i s t h e n q u i t e s m a l l ( C o r n f o r t h 1 9 6 4 , B l i g h t 196 3 , Wood 1 9 5 8 , Duncan a n d S e e d 1 9 6 6 ) , u s u a l l y o f t h e o r d e r o f 0 . 0 2 . The end p l a t e s were h e l d i n p o s i t i o n a t f i x e d d i s t a n c e a p a r t by h o l d i n g them t o t h e f l e x i b l e d i a p h r a g m s u p p o r t p l a t e s ( f i g . 3 . 2 ) . -4-02»-end fifties assembly-34 L a t e r a l Pressure Diaphragms I t was proposed to e x e r c i s e a completely inde-pendent c o n t r o l over the v e r t i c a l and l a t e r a l s t r e s s e s a c t i n g on the specimen, L a t e r a l pressure diaphragms p r e s s i n g against the side s o f the specimen were used to provide the l a t e r a l p r i n c i p a l s t r e s s . These diaphragms c o n s i s t e d of shallow, box shaped, water f i l l e d , t h i n rubber membranes (0.012\" to 0.015\" t h i c k ) sealed by rubber 0-rings on the faces o f perpex p l a t e s ( f i g . 3.2). The diaphragms were connected through short 1/8\" outside diameter saran tubes to a volume change and pressure measuring device. In order to prevent the p r e s s u r i s e d diaphragms from squeezing out past the opening between the diaphragm p l a t e s and the l o a d i n g cap or base p e d e s t a l , the clearance between the diaphragm p l a t e s and cap or base was kept at 0.00 8 inches on each s i d e . Pressures up to 100 p . s . i . were used i n these diaphragms but there was no tendency f o r them to squeeze i n between the sample and end p l a t e s o r out of the opening between the diaphragm support p l a t e s and cap or base. To reduce t h e i r volume compliance (Volume change under u n i t pressure change) the l a t e r a l pressure diaphragms were s t i f f e n e d by H-shaped m i l d s t e e l s t i f f n e r s , on faces away from, the sample ( f i g . 3.3). 35 ® o ® o ® o ® s d t-t-Jl-1-OH U-36 Vo lume Changes and P r e s s u r e ' M e a s u r e m e n t s A s c h e m a t i c l a y o u t o f t h e e q u i p m e n t f o r vo lume c h a n g e s and p r e s s u r e m e a s u r e m e n t s i s shown i n f i g . 3 . 4 . S h o r t 1/8\" o u t s i d e d i a m e t e r s a r a n t u b i n g d r a i n a g e l i n e s f r o m t o p and b o t t o m o f t h e s amp l e l e d t o a vo lume c h a n g e and p r e s s u r e m e a s u r i n g d e v i c e w h i c h h a d a c a l i b r a t e d p i p e t t e f o r m e a s u r i n g vo lume c h a n g e s and a s t r a i n gauge t r a n s d u c e r f o r m e a s u r i n g p r e s s u r e . D r a i n a g e l e a d s f r o m t h e l a t e r a l p r e s s u r e d i a p h r a g m s l e d t o a n o t h e r s i m i l a r d e v i c e . Vo lume c h a n g e s were m e a s u r e d by o b s e r v i n g t h e movement o f t h e c o l o u r e d k e r o s e n e - w a t e r i n t e r f a c e i n t h e c a l i b r a t e d p i p e t t e , g r a d u a t -ed t o r e a d t o t h e n e a r e s t 0 . 0 1 - c c . To a c h i e v e s a t u r a t i o n o f t h e s a m p l e s a b a c k p r e s s u r e was a p p l i e d by r e g u l a t i n g t h e a i r p r e s s u r e on t h e B e l l o f r a m s e a l w h i c h was u s e d t o p r e v e n t d i f f u s i o n o f a i r t h r o u g h t h e d r a i n a g e l i n e s . A s i m i l a r s e a l was u s e d a t t h e a i r - w a t e r i n t e r f a c e where l a t e r a l d i a p h r a g m p r e s s u r e was a p p l i e d . A l l p r e s s u r e s were m e a s u r e d on the w a t e r s i d e o f t he B e l l o f r a m s e a l s u s i n g t h e t r a n s d u c e r s . L o a d i n g E q u i p m e n t A s c h e m a t i c a r r a n g e m e n t o f t h e l o a d i n g e q u i p m e n t i s shown i n f i g . 3 . 5 . The r e c t a n g u l a r s a m p l e l o a d i n g cap was s c r e w e d t o t h e l o a d i n g r o d w h i c h was g u i d e d i n i t s 37 38 A n t i To+c?-!'('oin guide •0 r »i 0 T O L o a d i n g b l a i ^ o r m &TacKef -for dial gauge - T h o m p s o n l i n e a r ba l l bush ings - T o f > c i r c u l a r j s l a f e ~ Locxd iVsg -rod - Loa -=1 ii'ig cab - Botl'ovn c i r c u l a r f>late - Spacer -i-eei. A IT b i sf on F i g . 3 - 5 _ S c h e w a f i ' c d i a g r a m o.f Hhe l o a d i n g e ^ a i b m e n - f 39 v e r t i c a l m o t i o n by two Thompson l i n e a r b a l l b u s h i n g s . I t was p r e v e n t e d f r o m r o t a t i n g a b o u t i t s v e r t i c a l a x i s by means o f an a n t i r o t a t i o n g u i d e ( f i g . 3.5). The p i s t o n g u i d e b u s h i n g s were m o u n t e d a t t h e c e n t r e o f a t h i c k c i r c u l a r p l a t e ( t o p p l a t e ) w h i c h c o u l d be l o c a t e d p a r a l l e l and c e n t r a l l y o v e r t h e c i r c u l a r :base p l a t e by means o f t h r e e u p r i g h t r o d s h a v i n g s h o u l d e r s a t t h e i r u p p e r e n d s . The b a s e p e d e s t a l was a t t a c h e d c e n t r a l l y o v e r t h e b a s e c i r c u l a r p l a t e . Thus t h e l o a d i n g p i s t o n c o u l d be g u i d e d i n i t s v e r t i c a l m o t i o n i n t h e same v e r t i c a l p l a n e as t h e b a s e p e d e s t a l . V e r t i c a l l o a d on t h e s amp l e d u r i n g c o n s o l i d a t i o n was a p p l i e d by means o f an a i r p i s t o n t h r o u g h t h e l o a d i n g y o k e . S h e a r i n g o f t h e s a m p l e c o u l d be done w i t h s t r a i n c o n t r o l l e d , s t r e s s c o n t r o l l e d o r s t r e s s - s t r a i n c o n t r o l l e d t y p e s o f l o a d i n g s . T h i s was a c h i e v e d by m o u n t i n g a s t r a i n d r i v e i n p a r a l l e l w i t h t h e a i r p i s t o n . T h i s a r r a n g e m e n t a l s o p e r m i t t e d a f l e x i b i l i t y o f l o a d i n g p a t h t o f a i l u r e ; f a i l u r e i n a x i a l c o m p r e s s i o n o r a x i a l e x t e n s i o n c o u l d be i n d u c e d u n d e r b o t h s t r e s s o r s t r a i n c o n t r o l l e d l o a d i n g . The v e r t i c a l l o a d was m e a s u r e d by a b e r y l l i u m c o p p e r d i a p h r a g m l o a d c e l l h a v i n g a f u l l r e s i s t a n c e b r i d g e . V e r t i c a l d e -f o r m a t i o n o f t h e s amp l e was m e a s u r e d on t h e p i s t o n r o d by means o f a 0 . 0 0 0 1 i n c h d i a l g a u g e , t h u s e l i m i n a t i n g any c o n t r i b u t i o n f r o m t h e d e f o r m a t i o n o f t h e l o a d c e l l . 40 CHAPTER 4 EXPERIMENTAL PROCEDURE P r e p a r a t i o n o f S amp l e s 1• U n d i s t u r b e d C l a y S amp l e s were t r i m m e d f r o m b l o c k s o f c l a y w h i c h h a d b e e n s e a l e d and s t o r e d i n a h u m i d r o o m , and c u t t o t h e s i z e 4 \" x l \" x 2 1/4\" u s i n g a s p e c i a l l y c o n s t r u c t e d t r i m m i n g a p p a r a t u ( f i g . 4 . 1 ) . Wa te r c o n t e n t s we re d e t e r m i n e d f r o m t h e t r i m m i n g s f r o m l a t e r a l f a c e s o f t h e s a m p l e s . A p r o c e d u r e was d e v e l o p e d t o make r u b b e r membranes r e q u i r e d t o e n c l o s e t h e s amp l e and f o r use as l a t e r a l p r e s s u r e d i a p h r a g m s . The p r o c e d u r e t o make t h e r u b b e r membranes i s d e s c r i b e d i n d e t a i l i n A p p e n d i x 1. To p r o v i d e some s t r e t c h , t h e l i n e a r d i m e n s i o n s o f t h e samp le membrane were made a b o u t 4% s m a l l e r t h a n n e c e s s a r y t o e n c l o s e t h e s a m p l e , t o p and b o t t o m p o r o u s s t o n e s , a n d s t a i n l e s s s e a l i n g p l a t e s ( f i g . 3 . 2 ) . B e f o r e p r e p a r i n g t h e p l a n e s t r a i n s p e c i m e n , t h e v o l u m e c h a n g e a n d p r e s s u r e m e a s u r i n g d e v i c e s were c a r e f u l l y d e a i r e d . L a t e r a l p r e s s u r e d i a p h r a g m s were a s s e m b l e d u n d e r d e a i r e d w a t e r i n a t a n k so as n o t t o e n t r a p any a i r i n t h e 42 s y s t e m . T h e i r c o n n e c t i o n s t o t h e vo lume change and p r e s s u r e m e a s u r i n g d e v i c e was a l s o made u n d e r w a t e r . The l a t e r a l d i a p h r a g m s were t h e n c o a t e d w i t h a t h i n l a y e r o f s i l i c o n e g r e a s e , champed t o g e t h e r f a c e t o f a c e a n d p l a c e d u n d e r p r e s s u r e u n t i l l r e q u i r e d , i n o r d e r t o p r e v e n t any d i f f u s i o n o f a i r t h r o u g h t h e r u b b e r membranes . T h e r e was no t e n d e n c y f o r t h e d i a p h r a g m s t o b u r s t w i t h f r e q u e n t u s e . In f a c t t h e same d i a p h r a g m s were u s e d f o r a l l t h e t e s t s made so f a r . F o r p r e p a r i n g t h e p l a n e s t r a i n s p e c i m e n , t h e t o p and b o t t o m p o r o u s s t o n e s were b o i l e d i n w a t e r f o r a b o u t 10 m i n u t e s and l e t c o o l t o room t e m p e r a t u r e . One e n d o f t h e box s h a p e d s a m p l e membrane was s e a l e d t o t h e b a s e p e d e s t a l b y . m e a n s o f t h e l o w e r s t a i n l e s s s e a l i n g p l a t e . The b o t t o m d r a i n a g e l i n e was c o n n e c t e d t o a s m a l l p e r s p e x r e s e r v o i r f i t t e d w i t h a n e e d l e v a l v e a n d a vacuum l i n e , D e a i r e d w a t e r was r u n f r o m t h e r e s e r v o i r i n t o t h e s e a l e d membrane and b u i l t up t o a d e p t h o f a b o u t one i n c h . C a r e was t a k e n t o e l i m i n a t e any a i r b u b b l e s t r a p p e d b e t w e e n t h e membrane and t h e s e a l i n g p l a t e . The membrane was s t r e t c h e d open a t t h e t o p e n d , a n d t h e l o w e r p o r o u s s t o n e q u i c k l y t r a n s f e r r e d o n t o t h e s t a i n l e s s p l a t e , Any e x c e s s w a t e r was drawn b a c k i n t o t h e r e s e r v o i r l e a v i n g t h e p o r o u s s t o n e b a r e l y s u b -m e r g e d . A r e c t a n g u l a r s l e e v e a b o u t 1/4\" h i g h e r t h a n t h e t o p o f t h e p o r o u s s t o n e was p l a c e d a r o u n d t h e b a s e p e d e s t a l and t h e s amp l e membrane s t r e t c h e d o p e n and t u r n e d b a c k on t h e s l e e v e ( f i g . 4 . 2 ) . W a t e r was a g a i n r u n f r o m t h e p e r s p e x 4 3 Fig. 4-2 - K u b J ? e r m e m b r a n e i n s t a l l i n g c | a y s f r e a c h e d o n s k e v e f o r s p e c i m e n 44 r e s e r v o i r t i l l i t s t a y e d a b o u t 1/4\" above t h e t o p o f p o r o u s s t o n e . The c l a y s amp l e was t r i m m e d , w e i g h e d and c a r e f u l l y p o s i t i o n e d ( u n d e r t h e s m a l l d e p t h o f w a t e r ) o v e r t h e p o r o u s s t o n e . \" The t o p p o r o u s s t o n e w h i c h was k e p t s c r e w e d t o t h e s e a l i n g p l a t e was p o s i t i o n e d on t h e t o p o f t he s a m p l e . The r e c t a n g u l a r s l e e v e was t h e n moved up s l o w l y and t h e membrane s i m u l t a n e o u s l y \" s l i d o f f \" c a r e f u l l y t i l l i t s u p p e r e n d r e a c h e d t h e t o p o f t h e u p p e r s e a l i n g p l a t e . Any e x c e s s w a t e r be tween t h e s amp l e and t h e membrane was q u i c k l y r emoved by r o l l i n g t h e w a t e r o f f i n t h e upward d i r e c t i o n u s i n g two c i r c u l a r r o d s w h i c h were w o r k e d up s i m u l t a n e o u s l y a l o n g t h e o p p o s i t e s i d e s o f t h e s a m p l e . By t h i s t e c h n i q u e t h e membrane c o u l d be p l a c e d w i t h o u t d e f o r m i n g t h e s a m p l e a n d no a i r was t r a p p e d be tween t h e s a m p l e and t h e membrane . ( F l o o d i n g w i t h w a t e r as d e s c r i b e d above may i n v o l v e some s u r f a c e s o f t e n i n g i n a medium t o s t i l l c l a y , b u t was n e c e s s a r y i n o r d e r t o o b t a i n a s a t u r a t e d s a m p l e . F u l l s a t u r a t i o n i s an e s s e n t i a l r e q u i r e m e n t f o r t h e c o n s o l i d a t e d -u n d r a i n e d t e s t s i f p o r e p r e s s u r e s a r e t o be r e l i a b l e ) . . The t o p c i r c u l a r p l a t e w i t h i t s l o a d i n g cap m o u n t i n g was s l i p p e d i n t o p o s i t i o n o v e r t h e u p r i g h t r o d s . The membrane was t h e n s e a l e d a t i t s u p p e r end be tween t h e s e a l i n g p l a t e and t h e l o a d i n g cap w h i c h h a d t h e t o p d r a i n a g e l e a d c o n n e c t e d t o a n o t h e r p e r s p e x r e s e r v o i r . A s m a l l vacuum ( abou t 3 i n c h e s o f m e r c u r y ) was a p p l i e d t o b o t h p e r s p e x r e s e r v o i r s a n d t h e i r n e e d l e v a l v e s o p e n e d t o remove any e x c e s s w a t e r t h r o u g h t h e 45 d r a i n a g e l i n e s . F i g . 4 . 3 shows a c l a y s a m p l e i n p l a c e . The samp le was a l l o w e d t o r e m a i n u n d e r t h i s vacuum w h i l e t h e r e s t o f t h e e q u i p m e n t was a s s e m b l e d . The membrane and l o a d i n g cap were c o a t e d l i b e r a l l y w i t h s i l i c o n e ' g r e a s e and t h e a s s e m b l y t a k e n t o t h e l o a d i n g p l a t f o r m . The end p l a t e s a n d t h e l a t e r a l p r e s s u r e d i a p h r a g m s were a s s e m b l e d a r o u n d t h e s a m p l e and t h e b o l t s t i g h t e n e d . The c l e a r a n c e be tween t h e cap o r b a s e and t h e r e c t a n g u l a r o p e n i n g f o r m e d by l a t e r a l p r e s s u r e d i a p h r a g m s and t h e e n d p l a t e s was a d j u s t e d t o be t h e same on a l l s i d e s by u s i n g a f e e l e r g a u g e . The box f o r m e d by t h e l a t e r a l d i a p h r a g m s and t h e e n d p l a t e s , r e s t e d on f o u r s h o r t s p a c e r b l o c k s p o s i t i o n e d on t h e b o t t o m c i r c u l a r p l a t e , a r o u n d t h e b a s e p e d e s t a l . ( I t i s p r o p o s e d t o r e p l a c e t h e s e s p a c e r b l o c k s by l o a d c e l l s , i n o r d e r t o measu re t h e amount o f l o a d t r a n s -f e r r e d i n f r i c t i o n be tween t h e s amp l e a s s e m b l y and t h e s u r -r o u n d i n g l a t e r a l d i a p h r a g m s a n d e n d p l a t e s b o x ) . The l o a d c e l l was s c r e w e d o n t o t h e t o p e n d o f t h e l o a d i n g r o d and d i a l gauge p o s i t i o n e d a g a i n s t a b r a c k e t c l a m p e d to t h e same 2 r o d . A p r e s s u r e o f 0 .5 k g / c m was t h e n s i m u l t a n e o u s l y a p p l i e d i n t h e v e r t i c a l and l a t e r a l d i r e c t i o n s t h r o u g h t h e a i r p i s t o n and t h e v o l u m e change a n d p r e s s u r e m e a s u r i n g d e v i c e r e s p e c t i v e l y . The d r a i n a g e l i n e s were r emoved f r o m t h e p e r s p e x r e s e r v o i r s and a i r f r e e c o n n e c t i o n s made t o t h e vo lume c h a n g e and p r e s s u r e m e a s u r i n g d e v i c e w i t h w a t e r d r i p p i n g f r o m b o t h e n d s . F i g . 4 . 4 shows t h e s a m p l e a s s e m b l y i n the l o a d i n g frame. 2. Saturated Sand Samples The procedure f o r s e t t i n g up a sand sample was s i m i l a r to that f o r a c l a y specimen up to the stage o f p l a c -i n g the lower porous stone. A r e c t a n g u l a r forming jacket was employed f o r making the sample by d e p o s i t i n g sand under water. This jacket could be s p l i t i n two l o n g i t u d i n a l halves and was l i n e d i n s i d e with porous p l a s t i c which was connected to a vacuum lead. The membrane was p u l l e d against the sides of j a c k e t by appl y i n g vacuum to the porous p l a s t i c and keeping the top end o f membrane st r e t c h e d out by a t h i n r e c t a n g u l a r frame so that a s e a l was obtained around the top periphery o f the j a c k e t ( f i g . 4 . 5 ) . Sand was b o i l e d i n water i n a long necked f l a s k and l e t c o o l under vacuum overnight. The f l a s k was then f i l l e d w i t h water to the top and a s p e c i a l hollowed out stopper w i t h a glass tube stem was put on sec u r e l y . A d d i t i o n a l water was added to f i l l the stem to the top. F r e s h l y b o i l e d water cooled to room temperature was then poured i n t o the sample space i n s i d e the forming j a c k e t so as to f i l l i t to the top. The f l a s k was i n v e r t e d (the s o i l allowed to f i l l the neck and the stem), clamped on a r i n g stand and p o s i t i o n e d over the centre of the water f i l l e d j a c k e t . When the e x i t t i p o f the flask'was submerged under water i n the j a c k e t , sand flowed out of the f l a s k and was replaced by water,. For preparing loose Samples', the sand was allowed to f a l l f r e e l y i n t o the jac k e t without d i s t u r b i n g o r moving the f l a s k i n t h i s process. When vhe sand f i l l e d the jac k e t to the d e s i r e d depth and came i n contact w i t h the e x i t t i p , flow a u t o m a t i c a l l y stopped. At t h i s point the f l a s k was moved back and f o r t h on the bench top to l e v e l o f f the top of the sample. The r i n g stand w i t h the f l a s k was then removed and very c a r e f u l l y and-slowly the top s t a i n l e s s s e a l i n g p l a t e was pushed i n t o the jacket and against the sand. Only bottom drainage was used f o r sand samples and so the top porous stone was omitted from the assembly. While h o l d i n g the s e a l i n g p l a t e i n p o s i t i o n the membrane was brought very c a r e f u l l y over the s e a l i n g p l a t e . Extreme care was taken so as not to entrap any a i r between the p l a t e and the membrane. The membrane was then sealed at the top with the l o a d i n g cap, by b r i n g i n g the top p l a t e i n p o s i t i o n over the upright rods. A vacuum of about 8\" of mercury was a p p l i e d through the bottom drainage l i n e and the forming j a c k e t was c a r e f u l l y removed. Dense samples were prepared i n e s s e n t i a l l y the same manner as loose samples, except that during formation the base p l a t e was v i b r a t e d continuously. This was accomplish-ed by p r e s s i n g a v i b r a t i n g t o o l against the base p l a t e . When the s e a l i n g p l a t e was seated on the top the base was v i b r a t e d again to den s i f y the top l a y e r s o f sand and take 50 out any s e a t i n g i r r e g u l a r i t y . A f t e r the forming j a c k e t was removed, the height of the sample was recorded to the nearest 0.0 01\" using a reference d i a l i n d i c a t o r . Length and width were c a l c u l a t e d from the in n e r dimensions of the forming jacket making due c o r r e c t i o n f o r the th i c k n e s s o f rubber membrane. Further procedure i n s e t t i n g up of sample i n the l o a d i n g device was the same as f o r the c l a y specimens. 51 CHAPTER 5 CHARACTERISTICS OF THE APPARATUS Measurement of A x i a l Load The load c e l l used f o r the measurement of a x i a l force, on the sample had a r a t e d c a p a c i t y of 300 kg. I t was accompanied by an e l e c t r i c a l readout device and the system was c a l i b r a t e d against dead weights. The c a l i b r a t i o n was found to be l i n e a r with l o a d , and the a x i a l s t r e s s on the 2 sample could be estimated to the nearest 0.001 kg/cm . The l o a d c e l l had n e g l i g i b l e zero d r i f t over a long p e r i o d of usage. The p i s t o n f r i c t i o n i n the guide bushings f o r the l o a d i n g rod was i n s i g n i f i c a n t since no s e a l s were r e q u i r e d . However, during the v e r t i c a l deformation of the sample the f r i c t i o n a l drag between the sample and l a t e r a l diaphragms and end p l a t e s may r e q u i r e a small c o r r e c t i o n to the measured a x i a l f o r c e . The magnitude of t h i s c o r r e c t i o n w i l l depend on the e f f e c t i v e n e s s of the l u b r i c a t i o n between the moving and the s t a t i o n a r y v e r t i c a l boundaries, and also the i n t e n -s i t y of normal pressure between them. With s i l i c o n e grease 52 a s t h e l u b r i c a n t , i t was f e l t t h a t t h e f r i c t i o n b e t w e e n t h e r u b b e r d i a p h r a g m s and t h e s amp le membrane s h o u l d be s m a l l , s i n c e t h e c o e f f i c i e n t o f f r i c t i o n s h o u l d be l e s s t h a n 0 .02 w h i c h i s t h e m e a s u r e d v a l u e be tween p e r s p e x and s a m p l e membrane ( C o r n f o r t h 1 9 6 4 , B l i g h t 1 9 6 3 ) . I t i s h o w e v e r , p r o p o s e d t h a t i n t he f u t u r e d e s i g n t h e s i d e f r i c t i o n a l f o r c e w i l l be d i r e c t l y m e a s u r e d and t h e a x i a l l o a d c o r r e c t e d a c c o r d i n g l y . T h i s w i l l be done by s u p p o r t i n g t h e e n d p l a t e s and d i a p h r a g m s a s s e m b l y on l o a d c e l l s i n s t e a d o f s p a c e r b l o c k s u s e d i n t h e p r e s e n t i n v e s t i g a t i o n s . The a x i a l f o r c e w i l l t h e n be c o r r e c t e d a t a l l s t a g e s o f t h e t e s t t o a c c o u n t f o r t h e p o s s i b i l i t y o f a v a r y i n g f r i c t i o n a l f o r c e . M e a s u r e m e n t o f P r e s s u r e s The e l e c t r i c a l t r a n s d u c e r s u s e d f o r t h e m e a s u r e -ment o f p r e s s u r e s were o f t h e b o n d e d s t r a i n gauge t y p e made by D a t a S e n s o r s I n c . They were p l a c e d as c l o s e t o t h e a p p a -r a t u s as p o s s i b l e t o k e e p d r a i n a g e l e a d s s h o r t and m i n i m i s e t h e c o m p l i a n c e o f t h e s y s t e m s . The t r a n s d u c e r s h a d a r a n g e o f 0-150 p . s . i . a b s o l u t e and a r a t e d c o m p l i a n c e o f 0 . 0 0 0 2 7 c u b i c i n c h e s f o r 100 p s i c h a n g e i n p r e s s u r e . . T h e y were a l s o a c c o m p a n i e d by an e l e c t r i c a l r e a d o u t d e v i c e and t h e s y s t e m was c a l i b r a t e d a g a i n s t a d e a d w e i g h t t e s t e r . The c a l i b r a t i o n was f o u n d l i n e a r w i t h p r e s s u r e , and p r e s s u r e c h a n g e s o f 2 0 . 0 0 1 k g / c m c o u l d be d e t e c t e d . The t r a n s d u c e r m e a s u r e s p r e s s u r e on an a b s o l u t e s c a l e and a b a r o m e t e r was i n s t a l l e d 53 so t h a t t h e p r e s s u r e s c o u l d be r e f e r r e d t o a t m o s p h e r i c ( gauge ' p r e s s u r e s ) . . The u n d r a i n e d l a t e r a l d i a p h r a g m s d u r i n g t h e one d i m e n s i o n a l c o n s o l i d a t i o n o f t h e s p e c i m e n s f o r m e d a c l o s e d s y s t e m a n d , t h e r e f o r e , a f f e c t e d by t e m p e r a t u r e v a r i a t i o n s ( C a m p a n e l l a 196 8 ) . The e x p e r i m e n t a l s e t up was t h e r e f o r e made i n a c o n s t a n t t e m p e r a t u r e r oom. The maximum v a r i a t i o n i n t e m p e r a t u r e d u r i n g t h e t e s t was t h e r e b y l i m i t e d t o _ + 0 . 5 ° C . Any v a r i a t i o n s i n p o r e w a t e r p r e s s u r e s due t o t e m p e r a t u r e c h a n g e s were p r a c t i c a l l y e l i m i n a t e d by t h i s p r o c e d u r e . M e a s u r e m e n t o f A x i a l D e f o r m a t i o n ' A s t a n d a r d 0 . 0 0 0 1 \" d i a l gauge was u s e d t o m e a s u r e a x i a l d e f o r m a t i o n o f the s a m p l e . The d e f o r m a t i o n was m e a s u r e d on t h e l o a d i n g p i s t o n a n d t h u s any c o n t r i b u t i o n f r o m t h e l o a d m e a s u r i n g c e l l was e l i m i n a t e d . K - C o n s o l i d a t i o n The l a t e r a l p r e s s u r e d i a p h r a g m s were d e s i g n e d t o p r e v e n t any l a t e r a l d e f o r m a t i o n o f t h e s a m p l e d u r i n g c o n s o -l i d a t i o n by m a i n t a i n i n g a c o n s t a n t vo lume o f w a t e r i n thera. H o w e v e r , when a v e r t i c a l s t r e s s was a p p l i e d t o t h e s a m p l e w i t h t h e l a t e r a l d i a p h r a g m s i n t h e u n d r a i n e d c o n d i t i o n , t h e p r e s s u r e r e s p o n s e i n t h e l a t e r a l d i a p h r a g m s amoun ted t o o n l y a b o u t 20% o f t h e a p p l i e d v e r t i c a l p r e s s u r e a t l o w p r e s s u r e 54 l e v e l s , and rose to about 40% at higher pressure l e v e l s . This was due to the volume compliance of the diaphragms under a change i n pressure. I f the l a t e r a l diaphragms had zero compliance and were kept undrained, they, i n conjunction w i t h the end p l a t e s , would form a system l i k e a one dimensional consolidometer. Thus under a v e r t i c a l pressure increment on an undrained saturated specimen the pressure response i n such undrained l a t e r a l diaphragms would be t h e o r e t i c a l l y equal to the v e r t i c a l increment. U n f o r t u n a t e l y , i t i s impossible to have a system p e r f e c t l y r i g i d and some com-p l i a n c e i n the l a t e r a l diaphragms had to be. t o l e r a t e d . The r e l a t i v e l y h i g h compliance o f the l a t e r a l pressure system was due to the use of perspex f o r the diaphragm support p l a t e m a t e r i a l . I t i s proposed to make the l a t e r a l pressure system more r i g i d i n the future design by r e p l a c i n g the perspex diaphragm support p l a t e s w i t h t h i c k s t a i n l e s s s t e e l p l a t e s , s t i f f e n e d more e f f e c t i v e l y . Nondisplacement valves and pressure transducers w i l l be mounted r i g h t on the diaphragm p l a t e s , thus d i s p e n s i n g w i t h any drainage leads c o n t r i b u t i n g to compliance., In the present i n v e s t i g a t i o n s i t was, t h e r e f o r e , decided to adopt the f o l l o w i n g procedure to achieve K Q c o n s o l i d a t i o n . Instead o f b u i l d i n g up the v e r t i c a l pressure under c o n d i t i o n s of undrained l a t e r a l diaphragms, equal increments of l a t e r a l and v e r t i c a l pressure were a p p l i e d to the undrained sample simultaneously. This step i s equi v a l e n t 55 to a p p l y i n g a v e r t i c a l pressure increment i n the presence o f i n f i n i t e l y s t i f f compliance l a t e r a l diaphragms which would r e g i s t e r ah equal pressure i n c r e a s e . Just before the con-s o l i d a t i o n of the sample was commenced the diaphragms were made undrained by s h u t t i n g o f f the n->ndisplacement valve on the volume change and pressure measuring device. The opposite diaphragms were kept interconnected so that both had equal pressure i n them at any stage of the t e s t . As the sample c o n s o l i d a t e d under a constant t o t a l v e r t i c a l s t r e s s , the pressure i n the diaphragms g r a d u a l l y decayed. Because of t h e i r f i n i t e compliance, they contained s l i g h t l y excess amounts o f water corresponding to the pressure, change i n them at any i n s t a n t a f t e r the s t a r t o f c o n s o l i d a t i o n . Consequently, at the end of c o n s o l i d a t i o n , the sample would experience a very small compressive l a t e r a l s t r a i n which i s p r o p o r t i o n a l to the volume compliance of the diaphragms between the i n i t i a l and the f i n a l pressures i n them. To prevent any l a t e r a l s t r a i n i n g o f the sample i n order to achieve t r u l y one dimensional c o n s o l i d a t i o n , the p i p e t t e o f the volume change and pressure measuring device was used to e x t r a c t from the l a t e r a l diaphragms the predetermined amount o f water at any instantaneous pressure. The adjustments were made i n such a way that at no time during c o n s o l i d a t i o n di d the l a t e r a l diaphragms contain an excess volume o f water of more than 0.01 c c . By t h i s technique the specimen could be c o n s o l i d a t e d to p r a c t i c a l l y a true one dimensional con-56 d i t i o n ; t h e maximum l a t e r a l s t r a i n was t h e n l e s s t h a n 0 .0 00 07 f o r an i n i t i a l l y 2 1/4 i n c h h i g h s p e c i m e n . F i g . 5.1 shows t h e vo lume c o m p l i a n c e o f t h e l a t e r a l p r e s s u r e d i a p h r a g m s a g a i n s t p r e s s u r e when m e a s u r e d w i t h d i a p h r a g m s c l a m p e d f a c e t o f a c e . T h e s e m e a s u r e m e n t s i n c l u d e d t h e c o n t r i b u t i o n f r o m t h e s h o r t s a r a n d r a i n a g e l i n e s as w e l l as t h e vo lume change and p r e s s u r e m e a s u r i n g d e v i c e . In t h e t e s t s on a n o r m a l l y c o n s o l i d a t e d u n d i s t u r b e d c l a y t o be d e s c r i b e d l a t e r , t h e p r e s s u r e i n u n d r a i n e d l a t e r a l 2 2 d i a p h r a g m s d r o p p e d f r o m 6 .5 k g / c m t o a b o u t 4 . 0 leg/cm d u r i n g c o n s o l i d a t i o n o f t h e s a m p l e . F rom f i g . 5.1 t h i s c o r r e s p o n d s t o a p p r o x i m a t e l y 0 .3 c c . o f vo lume c o m p l i a n c e . I f d u r i n g c o n s o l i d a t i o n , a d j u s t m e n t s a r e n o t made f o r vo lume c o m p l i a n c e o f t h e l a t e r a l d i a p h r a g m s , t h e i n i t i a l l y 2 1/4 i n c h h i g h s a m p l e w o u l d e x p e r i e n c e a l a t e r a l c o m p r e s s i v e s t r a i n o f a p p r o x i m a t e l y 0 . 0 0 2 . H o w e v e r , w i t h t h e p r o p o s e d i m p r o v e -ment i n t h e d e s i g n o f t h e l a t e r a l - p r e s s u r e s y s t e m i t i s e x -p e c t e d t h a t i t s much s m a l l e r vo lume c o m p l i a n c e u n d e r a s i m i l a r p r e s s u r e d r o p w i l l y i e l d p r a c t i c a l l y a z e r o l a t e r a l s t r a i n c o n d i t i o n . Any a d j u s t m e n t s f o r vo lume c o m p l i a n c e d u r i n g c o n s o l i d a t i o n o f t h e s p e c i m e n s w i l l t h e n be u n n e c e s s a r y . A s t a n d a r d one d i m e n s i o n a l c o n s o l i d a t i o n t e s t w i t h l o a d i n c r e m e n t r a t i o o f one was p e r f o r m e d on an u n d i s t u r b e d c l a y i n t h e new a p p a r a t u s . D u r i n g t h e c o n s o l i d a t i o n p r o c e s s , t h e l a t e r a l d i a p h r a g m s were k e p t u n d r a i n e d and no a l l o w a n c e was made f o r t h e i r c o m p l i a n c e by p e r i o d i c a l l y d r a w i n g o u t w a t e r . F i g . 5.2 shows a t y p i c a l p l o t o f v o i d r a t i o , e , v s . 5 7 fe 1-5 op I : 1 _ J 1 1 — i — I I I I 1 u _ — ' 1 — i — L 0-1 0-2 0-3 0-4 0-5 0-6 0-7 08 0? H> 2 3 4 . iP 6 T log 0 f c Fig . 5-2 - C o « \\ | > a - r i w r \\ of pressure void . T < X T I ' O ' xela+fonsVu\\> f-rom C o n s o l rdovwc^T-59 log of v e r t i c a l c o n s o l i d a t i o n pressure, o\"^c, obtained from the t e s t along w i t h the corresponding curve obtained i n a standard r i n g consolidometer. I t may be noted that the r e s u l t s from the new apparatus agree c l o s e l y with tho.3e from a standard consolidometer. S l i g h t d i f f e r e n c e i n the p o s i t i o n of the two curves was due p a r t l y to s l i g h t l y d i f f e r e n t i n i t i a l void r a t i o s o f the specimens, and p a r t l y to squeez-i n g out of c l a y under higher pressures, past the clearance between the porous d i s c and r i n g i n the r i n g c o n s o l i d a t i o n 2 t e s t . At the end of c o n s o l i d a t i o n under cx =7.2 kg/cm , l c the sample had undergone a l a t e r a l compressive s t r a i n of only 0.006 which amounted to 3% of the v e r t i c a l s t r a i n . Height change of the sample at any time during c o n s o l i d a t i o n was found p r o p o r t i o n a l to the volume of water drained at that time. This i n d i c a t e s the u n i f o r m i t y of the small l a t e r a l s t r a i n the sample underwent at any stages of the c o n s o l i d a -t i o n process. C o e f f i c i e n t of c o n s o l i d a t i o n , c v , determined e i t h e r from height change w i t h time, or volume drained with time during any c o n s o l i d a t i o n increment, gave the same r e s u l t . For the same v e r t i c a l c o n s o l i d a t i o n pressure a > l c the value o f c y found from the t e s t i n the new apparatus agreed c l o s e l y w i t h that found from the standard r i n g con-s o l i d a t i o n t e s t . 60 S a t u r a t i o n o f t he S p e c i m e n s D u r i n g t h e p r o c e s s o f b u i l d i n g up v e r t i c a l and l a t e r a l s t r e s s e s on t h e u n d r a i n e d samp le b e f o r e t h e c o m -mencement o f c o n s o l i d a t i o n , a t e s t was made t o c h e c k s a t u -r a t i o n o f t h e s a m p l e s . F o r an u n d r a i n e d s o i l s p e c i m e n t h e c h a n g e i n p o r e p r e s s u r e u n d e r p l a n e s t r a i n c o n d i t i o n s can be e x p r e s s e d b y an e q u a t i o n s i m i l a r t o S k e m p t o n ' s f o r t h e t r i a x i a l c o n d i t i o n s ( B i s h o p a n d H e n k e l 1 9 6 2 ) : Au = B [Aa g + A ( A o 1 - A a 3 ) ] ( 5 . 1 ) where Au i s t h e i n c r e m e n t i n p o r e p r e s s u r e due t o i n c r e m e n t s Ao\"2 and* Aa^ i n 03 and r e s p e c t i v e l y . A a n d B a r e e m p i r i c a l p o r e p r e s s u r e p a r a m e t e r s u n d e r p l a n e s t r a i n c o n d i t i o n s . F o r a f u l l y s a t u r a t e d s o i l B = 1, as u n d e r t r i a x i a l c o n d i t i o n s . E q u a l i n c r e m e n t s o f Aa^ and Ao\"g were a p p l i e d t o t h e samp le by i n c r e a s i n g t h e l a t e r a l and v e r t i c a l p r e s s u r e s and t h e i n c r e a s e Au i n p o r e p r e s s u r e was r e c o r d e d . U n d e r t h i s l o a d i n g c o n d i t i o n , B = A u / A a 3 ( 5 . 2 ) I n t h e t e s t s o n c l a y s a m p l e s a B v a l u e o f o v e r 96% was. m e a s u r e d . To f u r t h e r i n c r e a s e t h e d e g r e e o f s a t u r a t i o n s a m p l e s were l e f t u n d r a i n e d u n d e r f u l l c o n s o l i d a t i o n 61 s t r e s s e s f o r about 12 hours before the s t a r t of c o n s o l i d a -t i o n process. Since the t o t a l s t r e s s e s a p p l i e d to the sample before c o n s o l i d a t i o n were of larg e magnitude, high pore pressures were generated which helped any a i r present to go i n t o s o l u t i o n . A t a b l e showing the measurements o f B value f o r a t y p i c a l t e s t on c l a y i s in c l u d e d i n Appendix 2. Uni f o r m i t y of Deformations As the samples could be con s o l i d a t e d one dimensional-l y , the deformations were e s s e n t i a l l y uniform throughout p r i o r to shear. In the t e s t s to be described l a t e r , normally con-s o l i d a t e d undisturbed c l a y specimens f a i l e d E (a-^ -o\" ^ ) m a x 3 ^ n undrained shear under a x i a l compression at a s t r a i n o f about 0.75%. Drained dense sand specimens f a i l e d at about 2% a x i a l s t r a i n . At such small f a i l u r e s t r a i n s l i t t l e non-uni f o r m i t y of deformation should a r i s e , A x i a l extension f a i l u r e s occurred at higher a x i a l s t r a i n s . S t r a i n c o n t r o l l e d shear t e s t s i n a x i a l compression were continued a f t e r the peak was d e f i n e d , u n t i l l about 6% a x i a l s t r a i n o r u n t i l l maximum o c c u r r e < 3 . An examination o f the specimens at the end of the t e s t showed that they had bulged o r contracted symmetrically at the. c e n t r e , i . e . , b u l g i n g o r c o n t r a c t i o n was the same at a l l v e r t i c a l s e c tions along the e n t i r e l e n g t h of the specimens ( f i g . 5.3). This suggests that the f r i c t i o n on the end p l a t e s i s n e g l i g i b l e f o r both sand and c l a y t e s t e d , and that h a r d l y any nonuniformity of deformation would r e s u l t i n the l o n g i t u d i n a l d i r e c t i o n o f the specimens F i g . 5-3 _ U«ifoTW v c r K c a l secfi ' o n o.le-nf \"Ike U n g t k of- «, «lcfarmed: J>lan«. s^xaiv\\ s^ >eci'««eir» . i n c»>i*«l e x t e n s i o n ^ J i n a x i a l cor*J>resj ion. . 63 due to the presence of the end p l a t e s . In the present i n v e s t i g a t i o n s no p r o v i s i o n was made to introduce f r i c t i o n l e s s ei.d platens on top and bottom of the specimen i n order to increase the homogenity of the s t r e s s and s t r a i n f i e l d s during shear. However, the design could e a s i l y be adapted to incorporate t h i s improve-ment. This may be p a r t i c u l a r l y important i n case o f sands, whose drained strength i s i n f l u e n c e d to a great extent by the rate o f volume change t a k i n g place at f a i l u r e . In drained t r i a x i a l t e s t s on sands the rat e of volume change at f a i l u r e has been found to be dependent on the degree of end r e s t r a i n t (Barden 6 Khayatt 1966). However, there i s some d i f f e r e n c e o f opi n i o n on t h i s conclusion (Bishop £ Green 1965). Shear Stage The v e r t i c a l l o a d i n g Bellofram a i r p i s t o n gave a s u f f i c i e n t l y r a p i d response under s t r a i n r ates experienced during the t e s t s . The house supply pressure was passed v i a a d j u s t a b l e p r e c i s i o n r e g u l a t o r s , and b u i l t to the de s i r e d value at various i n l e t s as re q u i r e d . The r e g u l a t o r s held the pressures w i t h i n +0.5% of the i n i t i a l l y set values. The constant s t r a i n rate d r i v e which was mounted above and i n p a r a l l e l w i t h the a i r p i s t o n ( f i g . 3.5) made i t p o s s i b l e to f o l l o w a v a r i e t y of s t r e s s paths to f a i l u r e * 64 A s t r e s s c o n t r o l l e d a x i a l compression t e s t could be made by usin g the a i r p i s t o n to apply p e r i o d i c l o a d i n g increments while m a i n t a i n i n g constant pressure i n l a t e r a l diaphragms, whereas an a x i a l extension t e s t could be made by i n c r e a s i n g the l a t e r a l diaphragm pressure under constant a x i a l s t r e s s . A s t r a i n c o n t r o l l e d a x i a l compression or extension t e s t c o u l d be performed by making the s t r a i n d r i v e push or p u l l on the middle yoke crossbar ( f i g . 3.5) thereby i n c r e a s i n g or decreasing the a x i a l l o a d . A combined s t r e s s - s t r a i n c o n t r o l l e d t e s t could also be made by using a i r p i s t o n f o r s t r e s s c o n t r o l i n the i n i t i a l stages o f the t e s t , and then s w i t c h i n g over to s t r a i n c o n t r o l l a t e r on. This k i n d o f t e s t e l i m i n a t e s the disadvantage of r a p i d l o a d i n g on the sample i n the conventional constant s t r a i n rate t e s t , and al s o provides post peak i n f o r m a t i o n which cannot be obtained i n a conventional s t r e s s c o n t r o l l e d t e s t . In the s t r a i n c o n t r o l l e d t e s t s so f a r made, a • constant rate o f s t r a i n was not completely obtained. At the s t a r t of sh e a r i n g , the s t r a i n r a t e was l e s s than the c a l i b r a t -.ed value and approached the c a l i b r a t e d value around the peak d e v i a t o r s t r e s s . This behaviour was due to the f i n i t e deformations o f the yoke rods above the d r i v i n g point ( f i g . 3.5) under v a r y i n g v e r t i c a l f o r c e . Consequently, the de-formation t r a n s f e r r e d to the sample amounted to the a l g e b r a i c d i f f e r e n c e between the movement of the s t r a i n d r i v e and the deformation of the yoke rods. This drawback w i l l be removed 65 i n the future design by mounting the s t r a i n r a t e d r i v e so as to push or p u l l d i r e c t l y on the top crossbar o f the yoke. Measurement o f In the i n v e s t i g a t i o n s reported h e r e i n , no attempt was made to measure cr^' ^ n \"*-^ e f u - t u : r e however, the design of the end p l a t e s w i l l be modified to in c l u d e load c e l l s . 66 CHAPTER 6 SOKE EXPERIMENTAL RESULTS The Test Program The tests to be described were performed to es t a b l i s h the f e a s i b i l i t y of v a l i d testing with the new apparatus. Tests were performed on a l o c a l undisturbed' clay and on uniform Ottawa sand (A.S.T.M. standard C-190, 20-30 sieve s i z e ) . the properties of clay tested have been described in d e t a i l by Byrne (1966). It i s known l o c a l l y as Haney clay, and i s thought to have been deposited i n a marine environment and subsequently leached by rain water causing i n s e n s i t i v e clay structure. Haney clay has a natural water content of about 41%, l i q u i d l i m i t of 44% and p l a s t i c l i m i t of 26%. I t i s medium s t i f f when sampled and has a s e n s i t i v i t y of about 12. Preconsolidation pressure 2 i s about 2.2 kg/cm . The following types of tests were performed: 1. Consolidation Tests One dimensional consolidation tests were performed on specimens of Haney clay to determine the value of K . 6 7 To achieve one dimensional c o n s o l i d a t i o n , l a t e r a l s t r a i n i n g of the samples was completely prevented by a d j u s t i n g the volume of water i n the l a t e r a l diaphragms f o r zero compliance. Some t e s t s were also performed to determine the i n f l u e n c e of small l a t e r a l s t r a i n s on the measured value of s t r e s s r a t i o , aq /a., , at the end of c o n s o l i d a t i o n . A small ' 3c l c ' ex t e n s i o n a l l a t e r a l s t r a i n was imposed on the sample by withdrawing an amount of water from the l a t e r a l diaphragms i n excess o f tha t which corresponded to zero compliance. Whereas a small compressive l a t e r a l s t r a i n was imposed on the sample when no adjustments were made f o r compliance of l a t e r a l diaphragms during the c o n s o l i d a t i o n process. The l o n g i t u d i n a l s t r a i n was zero i n a l l cases because of the presence of r i g i d end p l a t e s . 2. Shear Tests The f o l l o w i n g three types of shear t e s t s were per-formed on c l a y specimens c o n s o l i d a t e d to e s s e n t i a l l y i d e n t i c -a l s t r e s s e s . a. AC-1 K , normally c o n s o l i d a t e d specimen, sheared under o plane s t r a i n c o n d i t i o n , using s t r a i n c o n t r o l l e d a x i a l com-p r e s s i o n , while m a i n t a i n i n g constant l a t e r a l diaphragm pressure. T h i s t o t a l s t r e s s path i s r e p r e s e n t a t i v e o f the s t r e s s c o n d i t i o n s under the centre l i n e of a s t r i p loaded area (A6' R i s of no consequence as long as Aa-, > Aa_). 68 b. AC-2 K q , normally c o n s o l i d a t e d specimen, sheared under plane s t r a i n c o n d i t i o n , u s i n g s t r e s s c o n t r o l l e d a x i a l com-pres s i o n by decreasing l a t e r a l diaphragm pressure, while m a i n t a i n i n g constant a x i a l l o a d . This t o t a l s t r e s s path i s r e p r e s e n t a t i v e of s t r e s s c o n d i t i o n s behind a long r e -t a i n i n g w a l l under a c t i v e e a r t h pressure c o n d i t i o n s . c. AE K q , normally c o n s o l i d a t e d specimens, sheared under plane s t r a i n c o n d i t i o n , using s t r a i n c o n t r o l l e d a x i a l e x t e n s i o n , while m a i n t a i n i n g constant l a t e r a l diaphragm pressure. This t o t a l s t r e s s path i s r e p r e s e n t a t i v e of s t r e s s c o n d i t i o n s under the centre l i n e of a long rectangu-l a r excavation. Under t h i s s t r e s s path the p r i n c i p a l axes are r o t a t e d through 9 0°. The same three types o f t e s t s were performed on dense sand, w i t h the d i f f e r e n c e that the c o n s o l i d a t i o n was done under equal v e r t i c a l and l a t e r a l diaphragm pressures. In other words c o n d i t i o n o f zero s t r a i n during c o n s o l i d a -tions-was f u l f i l l e d i n l o n g i t u d i n a l d i r e c t i o n o n l y . Pre-vention of l a t e r a l s t r a i n of the sample was not attempted, as the s t r e s s change during c o n s o l i d a t i o n i n undrained l a t e r a l diaphragms occurred immediately upon opening the drainage valve on the specimen, g i v i n g no time f o r volume of water to be adjusted f o r zero compliance. However, 69 w i t h the proposed improvement i n the design o f l a t e r a l pressure diaphragms, i t w i l l be p o s s i b l e to c o n s o l i d a t e sand specimens also under c o n d i t i o n s of one dimensional s t r a i n . A l l c l a y samples were c o n s o l i d a t e d to the same v e r t i c a l e f f e c t i v e c o n s o l i d a t i o n pressure, c r ^ c , of a p p r o x i -mately 6 kg/cm', which would e f f e c t i v e l y take them i n t o the normally loaded zone. C o n s o l i d a t i o n l a s t e d f o r a p e r i o d of approximately 36 hours and specimens were l e f t undrained f o r another 12 hours (to l e t secondary compression generate major part of i t s pore pressures and cause e q u a l i z a t i o n throughout the specimen) before commencement of shear. In sand samples only high i n i t i a l d e n s i t y was used. This was done f o r convenience o f reproducing the same i n i t i a l v o id r a t i o i n the three types o f t e s t s . Only drained t e s t s were made on saturated samples w i t h volume change measurements. Test types AC-2 and AE were made by c o n s o l i d a t i n g the samples to higher v e r t i c a l and l a t e r a l e f f e c t i v e s t r e s s e s than were used f o r t e s t type AC-1. This was done to get approximately same value of (c^+c^)/2 at f a i l u r e i n a l l types of t e s t s , and thus e l i m i n a t e any i n f l u e n c e o f mean normal e f f e c t i v e s t r e s s on the measured value of (Beer De 1965 , Barden'and Khayatt 1966 ). Clay samples were sheared undrained with pore pressure measurements. Rate o f s t r a i n or r a t e of l o a d i n g was slow enough i n order to achieve f u l l e q u a l i s a t i o n of 70 pore pressures. Time to f a i l u r e was evaluated (using the measured values of c o e f f i c i e n t of c o n s o l i d a t i o n o f the samples during c o n s o l i d a t i o n stage) as suggested by Bishop and Henkel (1962) and B l i g h t (1963). Sand samples were sheared at a constant r a t e of s t r a i n or constant rate of l o a d i n g so as to cause f a i l u r e i n about one hour. This time to f a i l u r e was chosen f o r convenience of r e c o r d i n g data at s u i t a b l e time i n t e r v a l s and o b t a i n enough readings f o r p l o t t i n g t e s t data. Test Results - Clay Stress Ratio o\"gc/a-]_c a f t e r C o n s o l i d a t i o n The r e s u l t s from c o n s o l i d a t i o n of f i v e specimens are summarised i n t a b l e I. Specimens PS-C2 to PS-C4 were c o n s o l i d a t e d s t r i c t l y under one dimensional c o n d i t i o n . The r e s u l t i n g s t r e s s r a t i o , a3./ai., = K , was 0.55 and was es-OC J-'— o s e n t i a l l y the same f o r a l l three t e s t s . In specimen PS-C1, inducing a small amount of l a t e r a l e x t e n s i o n a l s t r a i n caused a s l i g h t drop i n the value of s t r e s s r a t i o to 0.53. Inducing a small l a t e r a l compressive s t r a i n i n sample PS-C5 als o r e s u l t e d i n a s l i g h t drop i n the s t r e s s r a t i o to 0.54. The observed small drop i n s t r e s s r a t i o f o r compressive l a t e r a l s t r a i n when compared to K Q value, was probably due to the d i f f e r e n c e i n procedure f o r c o n s o l i d a t i o n of specimen PS-C5 and r e s t o f the specimens. During one dimensional 70, ! * 1 3 « 0 o o o . . o 1 3 t | T -t- c wi (5 0 c •> ^ 0 V) q \\ to to K> ro Ki X u «; K 0 c o C 1 • < o CM' to K> CD _£ -+-V •s 1 I 5 o > 00 to Kl VD o C o -X o -3 ~o s: o 11 «« rO «\\ h- «o in in o 0\\ to 10 ** lO N to t\\ l« o c cy | Q O • t-c \"o 1-w> \"6 L. \"tf t-T-6 « U K o (J o Z •5 o =: O 0 w i r-l •r -•- -*-rt tf c c 2 ° z o 1-w - 1 62 CM O v% Kl O » ° P r—--—--—__>; PS-C3 E 3 0 bn q .. •? 1 1 •• 1 A '/ S-e 12. -10 - 8 - 6 - A x t a l S + T a m - jp>«rccnr Fi$ 6-1 _ Pcvicvtor stress VS. a.*tal 5.rTa.in for cortsoWdatea und-ra«necA f>lane sfrain Teste on Haney day • 7? a-r « * 5 i f « c4 o o » t o ? Jo is o cO fe l J4 1 \"E 3 S tfl to ti> ro •p' KJ to c < N «• to i rJ-|0 1 • K> C CH 1 w 00 i VO O i 1 1 0 b* 1 & •4-«< N 0\\ <* 10 oo CO VN b\"1 vi fO vo tr> *N V *t 00 10 to VO V9 In r>4 vo civ i vo U l l- to m VO m + 10 b*. Os 10 |0 •O to lt> b* 0 VO 0 OA vt\\ o vo o vi) tf C * C P u 0 K o A . .4-<5 0 i 0 •3 »-« d A . 0 «i f >\\ -C -t-1 < N 0 < U J < T < CM «J 1 « 0 I-u (A C C «t a h u Cy T5 C 6 ^ u o C o 41 .c Q \\J V v. M C J C J J -t- \\ 0 \\ / 0 u V V e c t \"5 i -H i «o «( X K 8 6 C _0 u ii XV-• d < < in < s 3 15 6 -15 O I-3 -T3 ff c o 74 i 75 c o n s e q u e n t l y b o t h (a . .-a . ) and ( c K ' / a ' ) _^ o c c u r r e d a t t h e I d max J- 3 max same s t r a i n . I t may be n o t e d t h a t t h e r e was h a r d l y any d i f f e r e n c e • i n s t r e s s - s t r a i n b e h a v i o u r o f s p e c i m e n s u n d e r s t r e s s p a t h s AC-1 and A C - 2 . In none o f t h e s t r a i n c o n t r o l l e d s h e a r t e s t s was an a p p a r e n t f a i l u r e p l a n e o b s e r v e d and f a i l u r e o c c u r r e d by a g e n e r a l p l a s t i c f l o w . In s t r e s s c o n t r o l l e d p l a n e s t r a i n c o m p r e s s i o n t e s t , A C - 2 , h o w e v e r , s u d d e n f a i l u r e on a s i n g l e r u p t u r e p l a n e was i n e v i t a b l e . S t r e n g t h C h a r a c t e r i s t i c s S p e c i m e n s P S - C 1 , PS-C2 a n d PS-C5 h a d p r a c t i c a l l y t h e same ( a 1 - a „ ) ( t a b l e I I ) . T h e s e s p e c i m e n s were c o n -s o l i d a t e d u n d e r e s s e n t i a l l y i d e n t i c a l ° \" ^ c » b u t i n s p e c i m e n s PS-C1 and P S - C 5 , t h e s t r e s s r a t i o ° \" 3 c / t f l c a t t h e end o f c o n s o l i d a t i o n was s l i g h t l y d i f f e r e n t c o m p a r e d t o t h e s t r e s s r a t i o K Q o f s p e c i m e n PS-C2 . T h i s s u g g e s t s t h a t f o r t h e same 0\"^c> t h e u n d r a i n e d s t r e n g t h o f c l a y i n a x i a l c o m p r e s s i o n was n o t a f f e c t e d by s l i g h t d i f f e r e n c e i n t h e i r a 3 C / a i c « F u r t h e r m o r e , t h e u n d r a i n e d s t r e n g t h was t h e same b o t h u n d e r i n c r e a s i n g and d e c r e a s i n g a x i a l c o m p r e s s i o n . The a v e r a g e v a l u e o f t h e r a t i o o f h a l f t h e p e a k d e v i a t o r s t r e s s t o t h e m a j o r c o n s o l i d a t i o n s t r e s s , su/-o*^ , f o r a x i a l c o m p r e s s i o n f a i l u r e was 0 . 3 0 . In c o n t r a s t f a i l u r e o f an e s s e n t i a l l y i d e n t i c a l s p e c i m e n P S - C 3 , u n d e r a x i a l e x t e n s i o n r e s u l t e d i n a much l o w e r ( 0 . 2 1 ) v a l u e o f t h i s 76 r a t i o . T h i s k i n d o f s t r e n g t h l o s s i s r e g a r d e d a s t h e r e s u l t o f r e o r i e n t a t i o n o f t h e p r i n c i p a l axes ( L a d d 1 9 6 5 , Broms and C a s b a r i a n 1 9 6 5 , Duncan and S e e d 1 9 6 6 ) . I t i s i n t e r e s t i n g t o n o t e t h a t ( a ^ / a 3 ) m a x w a s same i r r e s -p e c t i v e o f t h e t o t a l s t r e s s p a t h t o f a i l u r e . P o r e P r e s s u r e s F o r s p e c i m e n s c o n s o l i d a t e d t o e s s e n t i a l l y i d e n t i c a l s t r e s s e s , t h e p o r e p r e s s u r e s g e n e r a t e d d u r i n g s h e a r d e p e n d t o a g r e a t e x t e n t on t h e t o t a l s t r e s s p a t h t o f a i l u r e ( f i g . 6 . 3 ) . U n d e r i n c r e a s i n g a x i a l c o m p r e s s i o n , A C - 1 , t h e p o r e p r e s s u r e i n c r e a s e d t h r o u g h o u t t h e s h e a r i n g p r o c e s s , b u t a p p r o a c h e d an a l m o s t c o n s t a n t v a l u e a t ^ l ^ ^ m a x ' U P t o ^ a i \" a 3 ^ m a x ^ e P o r e P r e s s u r e b u i l d up i n t h i s t e s t was due t o i n c r e a s e i n b o t h mean n o r m a l and s h e a r i n g s t r e s s e s , and a l s o t o a b r e a k d o w n o f s e n s i t i v e s o i l s t r u c t u r e u n d e r i n c r e a s i n g s h e a r i n g s t r a i n s ( C r a w f o r d 1 9 5 9 , H i r s c h f e l d 1 9 6 0 ) . C o n t i n u e d i n c r e a s e i n p o r e p r e s s u r e a f t e r ( a , - a q ) was s o l e l y due t o s t r u c t u r a l c o l l a p s e o f J- ° max s o i l . U n d e r d e c r e a s i n g a x i a l c o m p r e s s i o n , A C - 2 , t h e p o r e p r e s s u r e i n i t i a l l y d e c r e a s e d , b u t s t a r t e d t o i n c r e a s e a f t e r a b o u t 0 . 1 % a x i a l c o m p r e s s i o n , w i t h t h e r e s u l t t h a t t h e n e t c h a n g e a t f a i l u r e was p o s i t i v e . T h i s t e s t was s i m i l a r t o AC-1 i n t h a t i t i n v o l v e d i n c r e a s e i n s h e a r tl 78 s t r e s s e s on t h e s p e c i m e n ; h o w e v e r , t h e mean n o r m a l s t r e s s c o n t i n u o u s l y d e c r e a s e d . . I n i t i a l d e c r e a s e i n p o r e p r e s s u r e w a s , t h e r e f o r e , a s s o c i a t e d w i t h d o m i n a t i n g i n f l u e n c e o f d e c r e a s e i n mean n o r m a l s t r e s s e s c o m p a r e d t o t h a t o f i n -c r e a s e i n s h e a r i n g s t r e s s e s . P r o g r e s s i v e s t r a i n i n g u n d e r l o a d i n g i n c r e m e n t s r e s u l t e d i n s t r a i n d e p e n d e n t p o r e p r e s s u r e s ( s t r u c t u r a l b r e a k d o w n , c a u s i n g r i s e i n p o r e p r e s s u r e s ) . F o r an i n s e n s i t i v e o r a r e m o l d e d c l a y t h e p o r e p r e s s u r e i n t h i s t y p e o f t e s t g e n e r a l l y d e c r e a s e s t h r o u g h o u t t h e t e s t and n e t c h a n g e a t f a i l u r e i s n e g a t i v e ( B i s h o p and H e n k e l 1 9 6 2 ) . U n d e r a x i a l e x t e n s i o n , A E , t h e i n i t i a l p o r e p r e s s u r e r e s p o n s e was s i m i l a r t o t h a t u n d e r a x i a l c o m p r e s s i o n , A C - 2 , b u t a t a g i v e n a x i a l s t r a i n t h e d e c r e a s e i n p o r e p r e s s u r e was much l a r g e r f o r A E . F u r t h e r s t r a i n i n g c a u s e d t h e p o r e p r e s s u r e t o r i s e , b u t a t a much s l o w e r r a t e t h a n u n d e r p a t h A C - 2 , and was h a r d l y c h a n g i n g a r o u n d f a i l u r e ( i . e . ( a i - a 3 ) m a x ^ • As s o o n as f a i l u r e was p a s s e d p o r e p r e s s u r e s t a r t e d b u i l d i n g up o n c e more a t a f a s t e r r a t e . T h i s s t r e s s p a t h l i k e A C - 2 , i n v o l v e s a c o n t i n u o u s d e c r e a s e i n mean n o r m a l s t r e s s b u t u n l i k e A C - 2 , c a u s e d a r e l e a s e o f c o n s o l i d a t i o n s h e a r s t r e s s i n t h e i n i t i a l s t a g e s . T h i s r e l e a s e o f s h e a r s t r e s s m i g h t be t h e r e a s o n f o r a g r e a t e r i n i t i a l d r o p o f p o r e p r e s s u r e when c o m p a r e d t o t h a t u n d e r AC-2 i n w h i c h s h e a r i n g s t r e s s e s c o n t i n u o u s l y i n c r e a s e d . 79 I t i s l i k e l y that w i t h i d e n t i c a l i n i t i a l s t r e s s c o n d i t i o n s and under no change i n o\"m, an a n i s o t r o p i c a l l y normally con-s o l i d a t e d c l a y develops l a r g e r p o s i t i v e pore pressures under i n c r e a s i n g than decreasing sh?;ar s t r e s s e s . Furthermore, under AE the r a t e o f decrease of a i n the i n i t i a l stages m ° o f the t e s t s was 3 to 4 times g r e a t e r than that under AC-2, which may be another cause o f r a p i d and l a r g e r drop i n pore pressure under AE when compared to t h a t under AC-2. A slower b u i l d up i n pore pressure a f t e r the i n i t i a l drop may be due to the compensating i n f l u e n c e of decreasing mean normal s t r e s s e s (causing pore pressure drop), i n c r e a s i n g shearing s t r e s s e s and s t r u c t u r a l breakdown of s o i l (causing pore pressure i n c r e a s e ) . An a c c e l e r a t e d r i s e i n pore pressure a f t e r the peak d e v i a t o r s t r e s s was apparently due to an i n -crease i n the mean normal s t r e s s combined w i t h s t r u c t u r a l breakdown of s o i l . F i g . 6.4 shows the v a r i a t i o n o f pore pressure parameter A (Eq. 5.1) with a x i a l s t r a i n f o r the three s t r e s s paths. For a saturated specimen, B = 1 and, t h e r e f o r e , equation 5.1 becomes Au = Aa„ + A(Aa 1-Aa q) (6.1) Under a x i a l extension decreased to zero and path, AE, the shearing s t r e s s e s then increased i n the opposite f i r s t 80 81 d i r e c v i o n u n t i l l f a i l u r e was r e a c h e d . The change i n p o r e p r e s s u r e due t o s h e a r i n g s t r e s s e s w i l l , h o w e v e r , d e p e n d on t h e t o t a l change i n s h e a r i n g s t r e s s e s , i . e . , ( A c ^ - A a ^ ) , where Aa a n d Aa s t a n d f o r c h a n g e s i n a x i a l and l a t e r a l a a t o t a l p r i n c i p a l s t r e s s e s r e s p e c t i v e l y . To t a k e a c c o u n t o f t h i s f a c t , e q u a t i o n ( 6 . 1 ) was w r i t t e n i n t h e f o l l o w i n g f o r m : Au = Aa^ + A ( A a a - A a j l ) ( 6 . 2 ) I t may be s e e n i n f i g . 6 .4 t h a t l i k e p o r e p r e s s u r e s , p o r e p r e s s u r e p a r a m e t e r A a l s o depends on t h e t o t a l s t r e s s p a t h t o f a i l u r e . I n p a r t i c u l a r t h e v a r i a t i o n o f A w i t h a x i a l s t r a i n , u n d e r a x i a l e x t e n s i o n , A E , b e a r s no r e s e m b l a n c e t o i t s c o r r e s p o n d i n g v a r i a t i o n u n d e r a x i a l c o m p r e s s i o n a n d i t s v a l u e a t f a i l u r e was f o u n d d i f f e r e n t u n d e r t h e t h r e e t o t a l s t r e s s p a t h s i n v e s t i g a t e d ( t a b l e ''.I). T h i s i m p l i e s t h a t A v a l u e f r o m t h e a^ i n c r e a s i n g a x i a l c o m p r e s s i o n p l a n e s t r a i n t e s t c a n n o t be u s e d t o e s t i m a t e p o r e p r e s s u r e s i n s i t u a t i o n s where t o t a l s t r e s s p a t h t o f a i l u r e u n d e r p l a n e s t r a i n i s d i f f e r e n t . I t , t h e r e f o r e , a p p e a r s t h a t p o r e p r e s s u r e p a r a -m e t e r A i s v e r y s e n s i t i v e t o c h a n g e i n t o t a l s t r e s s p a t h to f a i l u r e ( H e n k e l 1 9 6 0 ) . T h i s s e n s i t i v i t y seems v e r y p r o n o u n c e d p a r t i c u l a r l y when s h e a r o c c u r s u n d e r n o n s y m m e t r i c a l s t a t e s o f s t r e s s and i n w h i c h r o t a t i o n o f p r i n c i p a l a x e s may 82 a l s o .be i n v o l v e d . However, f o r undrained shear under non-symmetrical st a t e s of s t r e s s , the changes i n pore pressures have been shown to be b e t t e r expressed i n terms of changes i n o c tahedral normal and shearing s t r e s s e s (Equation 2.7). The pore pressure parameter \"a\" i n equation (2.7) has then been found to be r e l a t i v e l y unaffected by the v a r i a t i o n i n t o t a l s t r e s s path to f a i l u r e i n the undrained t r i a x i a l t e s t s (Henkel 1960). In the present i n v e s t i g a t i o n s no measurements were made o f o^j but i t i s i n t e r e s t i n g to note that the use o f equation ( 2 . 7 ) , assuming at f a i l u r e equal to.(a£+ag)/2 gives approximately the same value o f pore pressure parameter \"a\" (=0.9 8) at ( a i ~ a 3 ) m a x i r r e s p e c t i v e of the t o t a l s t r e s s path to f a i l u r e i n plane s t r a i n . E f f e c t i v e S t r e s s Paths F i g . 6 . 5 shows e f f e c t i v e s t r e s s paths followed i n \\\\a^-o^)/2 vs. (a£+ap/2 s t r e s s plane by e s s e n t i a l l y i d e n t i c a l samples i n the three types of t e s t s . E f f e c t i v e s t r e s s paths under a x i a l compression AC-1 and AC-2 are s i m i l a r and almost i d e n t i c a l up to (a,-a-)^ .^ Under a x i a l e x t e n s i o n , the s t r e s s path followed i s very d i f f e r e n t when compared to those under a x i a l compression. This i s apparently due to the r e l e a s e o f c o n s o l i d a t i o n d e v i a t o r s t r e s s , ( a i c ~ a 3 C ) » from the sample i n the i n i t i a l stages of the t e s t . F i g . 6 . 5 a l s o shows the e f f e c t i v e s t r e s s path f o r an i s o t r o p i c a l l y 83 84 c o n s o l i d a t e d s p e c i m e n o f t h e same c l a y , u n d e r a x i a l c o m -p r e s s i o n s h e a r . I t i s i n t e r e s t i n g t h a t t he s t a r t i n g p o i n t s o f p l a n e s t r a i n s t r e s s p a t h s l i e : o n t h e p a t h o f t h e i s o -t r o p i c a l l y c o n s o l i d a t e d t r i a x i a l s p e c i m e n . I t i s s e e n t h a t t h e p l a n e s t r a i n c o m p r e s s i o n s t r e s s p a t h s a l w a y s l i e above t h a t f o r t h e i s o t r o p i c t r i a x i a l s p e c i m e n . T h i s f a c t i m p l i e s t h a t i t i s n o t p o s s i b l e t o p r e d i c t p l a n e s t r a i n s t r e s s p a t h s o f a n i s o t r o p i c a l l y c o n s o l i d a t e d s p e c i m e n f r o m t e s t s o n l . i s o t r o p i c a l l y c o n s o l i d a t e d t r i a x i a l s p e c i m e n s . T h i s phenomenon i s i n a g r e e m e n t w i t h t h e o b s e r v a t i o n s o f o t h e r i n v e s t i g a t o r s ( H e n k e l and Sowa 1 9 6 3 , L a d d 1 9 6 5 ) , who r e -p o r t e d t h a t s t r e s s p a t h s o f a n i s o t r o p i c a l l y c o n s o l i d a t e d t r i a x i a l s p e c i m e n s c o u l d n o t be p r e d i c t e d f r o m t h o s e o f i s o t r o p i c a l l y c o n s o l i d a t e d s p e c i m e n s . S i n c e (a.T/cr£) _ v was t h e same u n d e r a x i a l com-X 6 max p r e s s i o n AC-1 a n d a x i a l e x t e n s i o n A E , t h e f a i l u r e e n v e l o p c o r r e s p o n d i n g t o maximum o b l i q u i t y i s . i n d e p e n d e n t o f t h e t o t a l s t r e s s p a t h t o f a i l u r e . A s s u m i n g c ' = 0 f o r t h e s e n o r m a l l y c o n s o l i d a t e d s p e c i m e n s , t h e c a l c u l a t e d v a l u e o f <}>' a t ( a . - o . ) v was 2 8 . 3 ° and a t (On '/a^) v ' was 3 3 . 5 ° . 1 3 max ± 6 max The c o r r e s p o n d i n g v a l u e s f r o m c o n v e n t i o n a l t r i a x i a l t e s t s on i s o t r o p i c a l l y c o n s o l i d a t e d s p e c i m e n s o f t h e same c l a y , was 2 6 . 6 ° and 3 1 . 8 ° r e s p e c t i v e l y ( S n e a d 1 9 6 8 ) . T h i s i n -c r e a s e i n v a l u e u n d e r p l a n e s t r a i n c o n d i t i o n s o v e r $ ' v a l u e s u n d e r t r i a x i a l c o n d i t i o n s o f 1 . 7 ° i s o f t h e same o r d e r o f m a g n i t u d e as r e p o r t e d by H e n k e l and Wade (1966 ) 85 f o r r e m o l d e d Wea ld c l a y . T e s t R e s u l t s - Sand Sand s a m p l e s were c o n s o l i d a t e d u n d e r e q u a l a x i a l (a^) and l a t e r a l Cc^') e f f e c t i v e s t r e s s e s w i t h z e r o s t r a i n i n t h e l o n g i t u d i n a l d i r e c t i o n . C o n s e q u e n t l y t h e l o n g i t u d i -n a l s t r e s s w o u l d be t h e m i n o r p r i n c i p a l e f f e c t i v e s t r e s s a t t h e end o f c o n s o l i d a t i o n . H o w e v e r , a t f a i l u r e ( ( a .-a 0 ) _ ) t h e l o n g i t u d i n a l s t r e s s i n a l l t y p e s o f s h e a r t e s t s w o u l d c o r r e s p o n d t o t h e i n t e r m e d i a t e p r i n c i p a l e f f e c t i v e s t r e s s , and 0.\"/, a . ' w o u l d c o n s t i t u t e t h e m a j o r and m i n o r p r i n c i p a l a JO e f f e c t i v e s t r e s s s y s t e m . In t h e s e i n v e s t i g a t i o n s , s i n c e no m e a s u r e m e n t s were made o f t h e l o n g i t u d i n a l s t r e s s , t h e s t r e s s v a r i a b l e s d u r i n g s h e a r t e s t s on s a n d were e x p r e s s e d i n t e r m s o f , and o ^ \" . 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 I n f i g . 6 .6 a r e p l o t t e d t h e a b s o l u t e v a l u e o f d e v i a t o r s t r e s s , |o* - a 0 | , and i n f i g . 6 . 7 a'/a^ {a\"f a\" f o r e x t e n s i o n t e s t ) v s . a x i a l s t r a i n , f o r e s s e n t i a l l y i d e n t i c a l s p e c i m e n s s h e a r e d u n d e r d i f f e r e n t s t r e s s p a t h s . S p e c i m e n s PS-S2 and PS-S3 h a d s t i f f e r s t r e s s - s t r a i n c u r v e s , a p p a r e n t -l y due t o t h e i r b e i n g c o n s o l i d a t e d t o h i g h e r i n i t i a l s t r e s s e s when c o m p a r e d t o s p e c i m e n PS-S I . F a i l u r e o f s p e c i m e n s i n a x i a l c o m p r e s s i o n was w i t h a c h a r a c t e r i s t i c 87 88 p e a k a n d a t l ow a x i a l s t r a i n s . T h i s b e h a v i o u r i s i n a g r e e -ment w i t h t h e r e s u l t s o f C o r n f o r t h ( 1 9 6 4 ) . F a i l u r e i n a x i a l e x t e n s i o n o c c u r r e d a t a r e l a t i v e l y l a r g e r a x i a l s t r a i n and a s h a r p p e a k d i d n o t e x i s t . No a p p a r e n t f a i l u r e p l a n e c o u l d be s e e n i n any o f t h e s p e c i m e n s . A l s o no n e c k i n g o c c u r r e d i n t h e e x t e n s i o n t e s t . Vo lume C h a n g e s d u r i n g S h e a r A l l s a m p l e showed a n e t e x p a n s i o n o r d i l a t i o n a t f a i l u r e . T h i s was mos t l i k e l y due t o t h e f a c t t h a t t h e y we re i n i t i a l l y a t maximum d e n s i t y and t e s t s were p e r f o r m e d a t r e l a t i v e l y l o w p r e s s u r e s . U n d e r i n c r e a s i n g a a x i a l a ' c o m p r e s s i o n , A C - 1 , t h e s a m p l e d e c r e a s e d i n vo lume i n i t i a l l y b u t e x p a n d e d c o n t i n u o u s l y t h e r e a f t e r ( f i g . 6 . 8 ) . T h i s k i n d o f vo lume c h a n g e b e h a v i o u r i s i n a g r e e m e n t w i t h t h e o b s e r v a -t i o n s o f o t h e r i n v e s t i g a t o r s ( C o r n f o r t h 1 9 6 4 ; F i n n , Wade and Lee 1 9 6 7 ) . U n d e r d e c r e a s i n g a a x i a l c o m p r e s s i o n a n d u n d e r a x i a l e x t e n s i o n , a n e t c o m p r e s s i o n o f t h e s a m p e l was n e v e r r e a l i s e d p r o b a b l y due t o c o n t i n u o u s l y d e c r e a s i n g mean n o r m a l e f f e c t i v e s t r e s s e s i n b o t h t h e s e t e s t s . The i n t e r -e s t i n g a s p e c t t o n o t e i s t he w i d e l y d i f f e r e n t r a t e s o f v o l u m e c h a n g e a t f a i l u r e ( ( c i-a „ )- ) i n t e s t t y p e AE when to 1 3 max c o m p a r e d t o t y p e s AC-1 and A C - 2 . I n a l l t y p e s o f t e s t s maximum r a t e s o f v o l u m e change o c c u r r e d n e a r f a i l u r e ; t h i s a g r e e s w i t h r e s u l t s o f C o r n f o r t h ( 1 9 6 4 ) . 90 E f f e c t i v e S t r e s s P a t h s D r a i n e d s t r e s s p a t h s on ( a - a )/2 v s . (.c'+o') / 2 1 3 1 3 s t r e s s p l a n e f o r t e s t s where one o f t h e 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 i s h e l d c o n s t a n t a r e s t r a i g h t l i n e s a t ^ 4 5 ° t o t h e (c'+0/2 a x i s ( f i g . 6 . 9 ) . F o r t h e t h r e e e s s e n t i a l l y i d e n t i c a l . s p e c i m e n s t a k e n t o f a i l u r e u n d e r A C - 1 , AC-2 and A E , t h e s t r e s s p a t h s do n o t t e r m i n a t e on a common f a i l u r e e n v e l o p e . T a b l e I I I shows t h a t s h e a r i n g r e s i s t a n c e o f t h e s e e s s e n t i a l l y i d e n t i c a l s a m p l e s o f s a n d d i f f e r e d by a b o u t 4 ° i n ' was f o u n d a b o u t 3 ° s m a l l e r i n p l a n e s t r a i n e x t e n s i o n c o m p a r e d t o p l a n e s t r a i n c o m -p r e s s i o n . T h i s a p p a r e n t l y d e f i e s t h e c o n c l u s i o n s drawn f r o m t r i a x i a l c o m p r e s s i o n and e x t e n s i o n t e s t s , where t h e same * h a s b e e n f o u n d by a number o f i n v e s t i g a t o r s ( B i s h o p and E l d i n 1 9 5 3 , K i r k p a t r i c k 1 9 5 7 , C o r n f o r t h 1 9 6 4 , Wu e t a l 1 9 6 3 ) . In t h e d a t a p u b l i s h e d by R o s c o e e t a l ( 1963 ) i t was shown t h a t f o r d e n s e s a n d s p e c i m e n s w i t h t h e same i n i t i a l v o i d r a t i o s , t h e r a t e o f vo lume change a t f a i l u r e i n t r i -91 5>l. tin 00 < tn 6 __ .0 i 1 i Oo in rfl co in vo1 '•0 * S3 > <5 _ Z O Oo 1 in t~ Co 1 «-1 0 e a 0 b > — 00 wo + 0 S +• co cs + •'- - V x •— K ti eo 00 10 4 1 « 00 M- s-in 4 w 0 £ V tn 10 K. 4 eo •«* 4 r f 5 o\" .£ > to VP vn ON VO vp in ve m •» 0< v» 1*? VI -t-• • <: CM V> < 10 < * i 0 3 vn • A. «s \\A 1 J? m vO 1 •> vV E _2 o > > _ < 5 I c tn vv M 0 c c vi 6 V-u cv S 0 w t-u Cv TJ c c4 c • J 0 O c VI 0 .s «r» «bi >- V c C 6 Si-XL. f Q H - V -4-* it V C Of * —* I Cf .£ V. Ckl . A \"0 < ~<$ 3 •/> cv K ci I VJ Ui \"TJ z d ri E O a c5 -rr \"5 t-3 : VI V -Q 0-92 a x i a l compression was about 4 0 to 5 0% g r e a t e r than i n t r i -a x i a l extension. Yet under c o n d i t i o n s o f plane s t r a i n , the r a t e o f volume change at f a i l u r e under a x i a l compression was about 2 1/2 times g r e a t e r than under a x i a l extension ( t a b l e I I I and f i g . 6.8). The much lower rate of volume change at f a i l u r e i n extension than compression under plane s t r a i n c o n d i t i o n s when compared to the conventional t r i -a x i a l c o n d i t i o n , may e x p l a i n the observed d i f f e r e n c e i n cb' between plane s t r a i n compression and extension t e s t s . * To the w r i t e r ' s knowledge no extension t e s t s under c o n d i t i o n s of plane s t r a i n have been reported i n the l i t e r a t u r e . I t i s , t h e r e f o r e , not p o s s i b l e to compare the observed behaviour. A standard t r i a x i a l compression t e s t was per-formed on the same sand at c l o s e l y the same i n i t i a l v o i d r a t i o as i n the plane s t r a i n t e s t s . The rat e of volume * I t i s i n t e r e s t i n g to note t h a t , a p p l i c a t i o n of Rowe's energy equation (Rowe, Barden and Lee 1964) f o r c o r r e c t i n g the s t r e s s r a t i o , a^Va^, at f a i l u r e , gives approximately the same value o f ' i s measured i n t r i a x i a l compression and extension by many i n v e s t i g a t o r s , the reason may be the compensating rates of volume change at f a i l u r e i n the two types of t e s t s . I f Roscoe's energy equation (Roscoe and S c h o f i e l d 1963) i s a p p l i e d to the plane s t r a i n t e s t data (using s t r e s s para-meters t = (0-^-03)72, s = (a£+ag)/2 and s t r a i n parameters 6v = £-^+£2, <5e = £,-£3 a n < 3 n e g l e c t i n g e l a s t i c s tored energy), i t i s also i n t e r e s t i n g to f i n d that approximately the same value of parameter M (=0.42) i s found i n compression and extension t e s t s on sand. 93 c h a n g e a t f a i l u r e was f o u n d t o be a l m o s t t h e same as i n t h e p l a n e s t r a i n i n c r e a s i n g cr_ a x i a l c o m p r e s s i o n t e s t , C l A C - 1 . The v a l u e o f . <*>\" f o r t h e t r i a x i a l t e s t was 3 8 . 5 ° , c o m p a r e d t o a p p r o x i m a t e l y 4 4 ° f o r a x i a l c o m p r e s s i o n t e s t s u n d e r p l a n e s t r a i n c o n d i t i o n s . The i n c r e a s e i n tf)\" v a l u e u n d e r p l a n e s t r a i n c o m p r e s s i o n o v e r t h e t r i a x i a l c o m p r e s s i o n v a l u e was 5 . 5 ° and o f t h e same o r d e r o f m a g n i t u d e as r e -p o r t e d by C o r n f o r t h ( 1 9 6 4 ) . The c o m p a r a b l e r a t e s o f vo lume c h a n g e i n t h e two t e s t s a r e a l s o i n a g r e e m e n t w i t h t h e o b -s e r v a t i o n s o f C o r n f o r t h ( 1 9 6 4 ) . 94 CHAPTER 7 SUMMARY AND CONCLUSIONS A new apparatus f o r shear t e s t i n g o f s o i l s under plane s t r a i n has been described. The main advantages claimed f o r t h i s apparatus over those used by other i n v e s t i g a t o r s , are: ( i ) Convenient and r e l a t i v e l y r a p i d c o n s o l i d a t i o n of samples under c o n d i t i o n s o f no l a t e r a l y i e l d p r i o r to shear; ( i i ) Permits a v a r i e t y of t o t a l s t r e s s path to f a i l u r e ; ( i i i ) No pressure chamber with f l u i d i s used around the specimen, thereby e l i m i n a t i n g any leakage i n t o the specimen e s p e c i a l l y f o r long term t e s t s . Further improvements to be inco r p o r a t e d i n the future design have been i n d i c a t e d . These include the measurements of intermediate p r i n c i p a l s t r e s s , f r i c t i o n on end p l a t e s , and use of f r i c t i o n l e s s end p l a t t e n s . Test technique has been described. From the plane s t r a i n t e s t s performed, both on a normally c o n s o l i d a t e d undisturbed c l a y and a sand, a general confirmation o f the form of previous r e s u l t s has been obtained. The value 95 of (j)'* was found l a r g e r under c o n d i t i o n s of plane s t r a i n when compared to the conventional t r i a x i a l c o n d i t i o n s . A reasonably c o n s i s t e n t p i c t u r e of the m a t e r i a l behaviour was observed from the t e s t r e s u l t s i n the apparatus. I t was, t h e r e f o r e , concluded that the apparatus was capable of y i e l d i n g the i n f o r m a t i o n d e s i r e d . 96 REFERENCES Ar t h u r , J.R.F. and Menzies, B.K., (1968) \"Correspondence\", Geotechnique, V o l . X V I I I , No. 2, p. 271-272. Barden, L. and Khayatt, A.J., (1966) \"Increment S t r a i n Rate Ratios and Strength of Sand i n the T r i a x i a l Test\", Geotechnique, V o l . XVI, No. 4, p. 338-357. Barden, L. and McDermott, J.W., (1965) \"The Use of Free Ends i n T r i a x i a l T e s t i n g of Clays\", Journal of S o i l Mechanics and Foundation D i v i s i o n , ASCE, Vo l . 91, SM6, p. 1-23. Beer, E. De (1965) \"Influence o f the mean normal s t r e s s on the shearing strength of sand\", Proc. 6th I n t . Conf. on S.M.F.E., Montreal, Vol. 1, p. 165-169. B e l l , J.M. (1968), \"Correspondence\", Geotechnique, V o l . X V I I I , No. 2, p. 267-271. Bishop, A.W. (1966), \" S i x t h Rankine Lecture: The str e n g t h of s o i l s as engineering m a t e r i a l s \" , Geotechnique, V o l . XVI, No. 2, p. 91-126. Bishop, A.W. and E l d i n , A.K. (1953), \"The e f f e c t o f s t r e s s h i s t o r y on the r e l a t i o n between and p o r o s i t y i n sand\", Proceedings, T h i r d I n t e r n a t i o n a l Conference on S.M.F.E., Z u r i c h , V o l . 1, p. 100-105. Bishop, A.W. and Henkel, D.J. (1962), \"The measurement o f s o i l p r o p e r t i e s i n the t r i a x i a l t e s t \" , Edward Arnold, Second E d i t i o n . Bishop, A.W. and Green, G.E. (1965) \"The i n f l u e n c e of end r e s t r a i n t on the compression strength of a cohesionless s o i l \" , Geotechnique, V o l . XV, No. 3, p. 243-265. Bjerrum, L. and Simons N.E. (196 0) \"Comparison of shear s t r e n g t h c h a r a c t e r i s t i c s of normally c o n s o l i d a t e d c l a y s \" , ASCE, research conference on shear s t r e n g t h o f cohesive s o i l s , Boulder, Colorado, p. 711-724. 97 B l i g h t , G . E . (196 3) \" T h e e f f e c t o f n o n u n i f o r m p o r e p r e s s u r e s on l a b o r a t o r y m e a s u r e m e n t s o f t h e s h e a r s t r e n g t h o f s o i l s \" , S y m p o s i u m , l a b o r a t o r y s h e a r t e s t i n g o f s o i l s , O t t a w a , A S T M , S . T . P . 3 6 1 . B l i g h t , G . E . ( 1965 ) \" S h e a r s t r e s s and p o r e , p r e s s u r e s i n t r i a x i a l t e s t i n g \" , J o u r n a l o f t h e s o i l m e c h . a n d f o u n a . d i v . , A S C E , V o l . 9 1 , S . M . 6 , p . 2 5 - 3 9 . B r o m s , B .B . and C a s b a r i a n , A . 0 . ( 1965 ) \" E f f e c t o f r o t a t i o n o f p r i n c i p a l s t r e s s a x e s and o f t h e i n t e r m e d i a t e p r i n c i p a l s t r e s s on t h e s h e a r s t r e n g t h \" , P r o c e e d i n g s , 6 t h I n t n . C o n f . on S . M . F . E . , M o n t r e a l , V o l . I, p . 1 7 9 - 1 8 3 . B r o m s , B .B . and J a m a l , A . K . ( 1965 ) \" A n a l y s i s o f t h e t r i a x i a l t e s t - c o h e s i o n l e s s s o i l s \" , P r o c e e d i n g s , 6 t h I n t n . C o n f . on S . M . F . E . , M o n t r e a l , V o l . I, p . 1 8 4 - 1 8 7 . B r o m s , B .B . and R a t n a m , M.V. ( 1963 ) \" S h e a r s t r e n g t h o f a n i s o t r o p i c a l l y c o n s o l i d a t e d c l a y s \" , J o u r n a l o f s o i l m e c h . and f o u n d , d i v . A S C E , V o l . 8 9 , S . M . 6 , p . 1-26. B y r n e , P .M . ( 1966 ) \" E f f e c t i v e s t r e s s p a t h s i n a s e n s i t i v e c l a y \" , M .A . S c . T h e s i s , U . B . C . Campane J . l a , R .G . a n d M i t c h e l l , J . K . ( 1968 ) \" I n f l u e n c e o f t e m p e r a t u r e v a r i a t i o n s on s o i l b e h a v i o u r \" , J o u r n a l o f s o i l m e c h . and f o u n d , d i v . A S C E , V o l . 9 4 , No . SM3, p. 7 0 9 - 7 3 4 . C a s a g r a n d e , A . and P o u l o s , S . J . ( 1964 ) \" I n v e s t i g a t i o n s o f s t r e s s d e f o r m a t i o n and s t r e n g t h c h a r a c t e r i s t i c s o f . c o m p a c t e d c l a y \" , H a r v a r d s o i l m e c h . s e r i e s No . 7 4 , H a r v a r d U n i v . , C a m b r i d g e , M a s s . C h r i s t e n s e n , N . H . ( 1961 ) \" M o d e l t e s t s on p l a n e a c t i v e e a r t h p r e s s u r e s i n s a n d s \" , D a n i s h G e o t e c h n i c a l I n s t i t u t e B u l l e t i n N o . 1 0 . C o r n f o r t h , D . H . ( 1964 ) \"Some e x p e r i m e n t s on t h e i n f l u e n c e o f s t r a i n c o n d i t i o n s on t h e s t r e n g t h o f s a n d \" , G e o t e c h n i q u e , V o l . X I V , No . 2 , p . 1 4 3 - 1 6 6 . C r a w f o r d , C B . ( 1959 ) \" T h e i n f l u e n c e o f r a t e o f s t r a i n on e f f e c t i v e s t r e s s e s i n a s e n s i t i v e c l a y \" , P a p e r s on s o i l s , A S T M , S . T . P . N o . 2 5 4 . D u n c a n , J . M . and S e e d , H .B , ( 1966 ) \" S t r e n g t h v a r i a t i o n a l o n g f a i l u r e s u r f a c e s i n c l a y \" , J o u r n a l o f s o i l m e c h a n i c s and f o u n d a t i o n d i v . A S C E , V o l . 9 2 , S . M . 6 , p . 8 1 - 1 0 4 . 98 F i n n , W . D . L . , Wade, N . H . and L e e , K . L . (1967 ) \" V o l u m e c h a n g e s i n t r i a x i a l and p i a n e s t r a i n t e s t s \" , J o u r n a l o f s o i l m e c h . and f o u n d , d i v . , A S C E , V o l . 9 3 , S .M . 6J p . 2 9 7 - 3 0 8 . F u n g , Y . C . ( 1 9 6 5 ) \" F o u n d a t i o n s o f s o l i d m e c h a n i c s \" , P r e n t i c e H a l l I n c . , New J e r s e y . G r e e n , G . E . , ( 1967 ) \" C o r r e s p o n d e n c e \" , G e o t e c h n i q u e , V o l . X V I I , N o . 3, p . 2 9 5 . H a b i b , M.P . (195 3) \" I n f l u e n c e o f t h e v a r i a t i o n o f t h e a v e r a g e p r i n c i p a l s t r e s s upon t h e s h e a r i n g s t r e n g t h o f s o i l s \" , P r o c e e d . 3 r d I n t . C o n f . on S . M . F . E . , Z u r i c h , p . 1 3 1 - 1 3 6 . H a y t h o r n t h w a i t e , R .M. ( 1960 ) \" S t r e s s a n d s t r a i n i n s o i l s \" , P r o c e e d . 2nd s ympos ium on n a v a l s t r u c t u r a l m e c h a n i c s , Pe rgamon p r e s s , p . 1 8 5 - 1 9 3 . H a y t h o r n t h w a i t e , R .M. ( 1963 ) \" D i s c u s s i o n \" , J o u r n a l o f s o i l m e c h . and f o u n d , d i v . , A S C E , V o l . 8 9 , No . SM4. H e n k e l , D . J . ( 1960 ) \" T h e s h e a r s t r e n g t h o f s a t u r a t e d r e m o l d e d c l a y s \" , A S C E , r e s e a r c h c o n f e r e n c e on s h e a r s t r e n g t h o f c o h e s i v e s o i l s , B o u l d e r , C o l o r a d o , p . 5 3 3 - 5 5 4 . H e n k e l , D . J . a n d Sowa, V . A . , ( 1963 ) \" T h e i n f l u e n c e o f s t r e s s h i s t o r y on s t r e s s p a t h s i n u n d r a i n e d t r i a x i a l t e s t s on c l a y \" , S ympos ium on l a b o r a t o r y s h e a r t e s t i n g o f s o i l s , A . S . T . M . , STP 3 6 1 . H e n k e l , D . J . a n d Wade, N . H . ( 1966 ) \" P l a n e s t r a i n t e s t s on a s a t u r a t e d r e m o l d e d c l a y \" , J o u r n a l o f s o i l mech . and f o u n d , d i v . A S C E , V o l . 9 2 , S . M . 6 , p . 6 7 - 8 0 . H i r s c h f e l d , R . C . , ( 1960 ) \" D i s c u - s i o n , S e s s i o n 4 \" , A S C E , r e s e a r c h c o n f e r e n c e on s h e a r s t r e n g t h o f c o h e s i v e s o i l s , B o u l d e r , C o l o r a d o , p . 1 0 7 3 - 1 0 7 9 . J a c o b s o n , B. ( 1 9 5 7 ) , \"Some f u n d a m e n t a l p r o p e r t i e s o f s a n d \" , P r o c e e d . 4 t h I n t . C o n f . on S . M . F . E . , L o n d o n , V o l . 1. K i r k p a t r i c k , W . M . , (195 7) \" C o n d i t i o n s f o r f a i l u r e o f s a n d s \" , P r o c e e d . 4 t h I n t . C o n f . on S . M . F . E . , L o n d o n , V o l . 1 , p . 1 7 2 - 1 7 8 . K j e l l m a n , W . , ( 1 9 3 6 ) \" R e p o r t on an a p p a r a t u s f o r consumate i n v e s t i g a t i o n s o f t h e m e c h a n i c a l p r o p e r t i e s o f s o i l s \" , P r o c e e d . 1 s t I n t . C o n f . on S . M . F . E . , C a m b r i d g e , M a s s . , V o l . 2 , p . 1 6 - 2 0 . 99 K o , H . Y . a n d S c o t t , R . F . , ( 1967a ) \" A new s o i l t e s t i n g a p p a r a t u s \" , G e o t e c h n i q u e , V o l . X V I I , N o . 1, p . 4 0 - 5 7 . K o , H . Y . a n d S c o t t , R . F . ( 1967b ) \" D e f o r m a t i o n o f s a n d i n s h e a r \" , J o u r n a l o f s o i l m e c h . and f o u n d , d i v . , A S C E , V o l . 9 3 , S . M . 5 , p . 2 8 3 - 3 1 0 . K o , H . Y . a n d S c o t t , R . F . ( 1968 ) \" D e f o r m a t i o n o f s a n d a t f a i l u r e \" , J o u r n a l o f s o i l m e c h . and f o u n d , d i v . A S C E , V o l . 9 4 , S . M . 4 , p . 8 8 3 - 8 9 8 . L a d d , C . C , ( 1964 ) \" S t r e s s s t r a i n m o d u l u s o f c l a y i n u n d r a i n e d s h e a r \" , J o u r n a l o f s o i l mech . and f o u n d , d i v . A S C E , V o l . 9 0 , S . M . 5 , p . 1 0 3 - 1 3 2 . L a d d , C . C , ( 1 9 6 5 ) \" S t r e s s - s t r a i n b e h a v i o u r o f a n i s o t r o -p i c a l l y c o n s o l i d a t e d c l a y s d u r i n g u n d r a i n e d s h e a r \" , P r o c e e d . 5 t h I n t . c o n f . on S . M . F . E . , M o n t r e a l , V o l . 1 , p . 2 8 2 - 2 8 6 , L e e , K . L . and S e e d , H . B . ( 1964 ) \" D i s c u s s i o n \" , J o u r n a l o f s o i l m e c h . and f o u n d , d i v . A S C E , V o l . 9 0 , S . M . 6 , p . 1 7 3 - 1 7 5 . L e u s s i n k , H. and W i t t k e , W. (1963 ) \" D i f f e r e n c e i n t r i a x i a l and p l a n e s t r a i n s h e a r s t r e n g t h \" , S y m p o s i u m , L a b o r a t o r y s h e a r t e s t i n g o f s o i l s , O t t a w a , A S T M , STP l o . 3 6 1 , p . 7 7 - 8 9 . L e u s s i n k , H. (1965 ) \" C o n t r i b u t i o n t o p a n e l d i s c u s s i o n , D i v . 2 \" , P r o c e e d . 6 t h I n t . C o n f . on S . M . F . E . , M o n t r e a l , V o l . 3, p . . L o m i z e , G.M . and K r y z h a n o v s k y , A . L . (1967 ) \" O n t h e s t r e n g t h o f s a n d \" , P r o c e e d , o f t he G e o t e c h n i c a l C o n f . O s l o , V o l . 1, p . 2 1 5 - 2 1 9 . L o r e n z , H . , N e u m e u e r , H. a n d G u d e h u s , G . , (1965 ) \" T e s t s c o n c e r n i n g c o m p a c t i o n and d i s p l a c e m e n t s p e r f o r m e d on s a m p l e s o f s a n d i n t he s t a t e o f p l a n e d e f o r m a t i o n \" , P r o c e e d . 6 t h I n t . C o n f . on S . M . F . E . , M o n t r e a l , V o l . 1 , p . 2 9 3 - 2 9 6 . M a r s a l , R . J . , ( 1 9 6 5 ) \" D i s c u s s i o n s D i v . 2 \" , P r o c e e d . 6 t h I n t . C o n f . on S . M . F . E . , M o n t r e a l , ' V o l . 3. M o r e t t o , 0 . , ( 1965 ) \" G e n e r a l r e p o r t , D i v . 2 \" , P r o c e e d . 6 t h I n t . C o n f . on S . M . F . E . , M o n t r e a l , V o l . 3. 100 Newmark, N .M . ( 1960 ) \" F a i l u r e h y p o t h e s e s f o r s o i l s \" , A S C E , R e s e a r c h c o n f e r e n c e on s h e a r s t r e n g t h o f c o h e s i v e s o i l s , B o u l d e r , C o l o r a d o , p . 1 7 - 3 2 . O l s o n , R . E . a n d C a m p b e l l , L . M . ( 1 9 6 4 ) , \" D i s c u s s i o n \" , J o u r n a l o f s o i l m e c h . and f o u n d , d i v . A S C E , V o l . 9 0 , S . M . 6 , p . 1 6 7 - 1 7 3 . P e l t i e r , M.R. ( 1 9 5 7 ) , \" E x p e r i m e n t a l i n v e s t i g a t i o n s on t h e i n t r i n s i c r u p t u r e c u r v e o f c o h e s i o n l e s s s o i l s \" , P r o c e e d . 4 t h I n t . C o n f . on S . M . F . E . , L o n d o n , V o l . 1, p . 1 7 9 - 1 8 2 . R o s c o e , K . H . ( 1 9 5 3 ) , \" A n a p p a r a t u s f o r a p p l i c a t i o n f o s i m p l e s h e a r t o s o i l s a m p l e s \" , P r o c e e d . 3 r d I n t . C o n f . on S . M . F . E . , Z u r i c h , V o l . 1, p . 1 8 6 - 1 9 1 . R o s c o e , K . H . , S c h o f i e l d , A . N . and T h u r a i r a j a h , A . ( 1 9 6 3 ) , \" A n e v a l u a t i o n o f t e s t d a t a f o r s e l e c t i n g a y i e l d c r i t e r i o n f o r s o i l s \" , S ympos ium on L a b o r a t o r y s h e a r t e s t i n g o f s o i l s , O t t a w a , ASTM. STP No . 3 6 1 , p . 1 1 1 - 1 2 8 . R o s c o e , K . H . and S c h o f i e l d , A . N . ( 1963 ) \" M e c h a n i c a l b e h a v i o u r o f an i d e a l i s e d wet c l a y \" , P r o c e e d . E u r o p e a n C o n f . on s o i l m e c h . , V o l . 1 , p. 4 7 - 5 4 . Rowe, P.W. a n d B a r d e n , L. ( 1964 ) \" I m p o r t a n c e o f f r e e e n d s in* t r i a x i a l t e s t i n g \" , J o u r n a l s o i l mech . and f o u n d , d i v . A S C E , V o l . 9 0 , S . M . I , p . 1-27 . Rowe, P .W. , B a r d e n , L. and L e e , I .K . ( 1964 ) \" E n e r g y c o m p o n e n t s t r i a x i a l c e l l and d i r e c t s h e a r t e s t s \" , G e o t e c h n i q u e , V o l . X I V , N o . 3 , p . 2 4 7 - 2 6 1 . S h i b a t a , T . a n d K a r u b e , D. ( 1965 ) \" I n f l u e n c e o f t h e v a r i a t i o n o f t h e i n t e r m e d i a t e p r i n c i p a l s t r e s s on t h e m e c h a n i c a l p r o p e r t i e s o f n o r m a l l y c o n s o l i d a t e d c l a y s \" , P r o c e e d . 6 t h I n t . C o n f . on S . M . F . E . , M o n t r e a l , V o l . 1 , p . 3 5 9 - 3 6 3 . S n e a d , D . E . ( 1968 ) \" C r e e p s t u d i e s on an u n d i s t u r b e d s e n s i t i v e c l a y \" , F o r t h c o m i n g P h . D . t h e s i s , U . B . C . W h i t m a n , R .V . and L u s c h e r , U. ( 1962 ) \" B a s i c e x p e r i m e n t s i n t o s o i l s t r u c t u r e i n t e r a c t i o n \" , J o u r n a l o f s o i l m e c h . and f o u n d , d i v . A S C E , V o l . 8 8 , S . M . 6 , p . 1 3 5 - 1 6 7 . 101 •Wood, C . C . ( 1958 ) \" S h e a r s t r e n g t h and vo lume c h a n g e c h a r a c t e r i s t i c s o f c o m p a c t e d s o i l s u n d e r c o n d i t i o n s o f p l a n e s t r a i n \" , P h . D . t h e s i s , U n i v . o f L o n d o n . Wu, T . H . , L o h , A . K . and M a l v e r n , L . E . ( 1 9 6 3 ) \" S t u d y o f f a i l u r e e n v e l o p e o f s o i l s \" , J o u r n a l o f s o i l mech . and f o u n d , d i v . A S C E , V o l . 8 9 , N o . S . M . I , p . 14 5-181 . 102 APPENDIX 1 \"PROCEDURE FOR MAKING RUBBER MEMBRANES\" The r u b b e r membranes u s e d f o r t h e d i a p h r a g m s and t h e s a m p l e were made i n t h e l a b o r a t o r y by a s i n g l e d i p p r o c e s s . Compounded n a t u r a l r u b b e r l a t e x ( V u l t e x , l - F - 5 5 0 1 N a t u r a l ) made by t h e G e n e r a l L a t e x C o . o f C a n a d a , B r a m p t o n , O n t a r i o , was u s e d . D i p p i n g m o l d s were made o f a l u m i n u m and t h e s u r f a c e s o f m o l d s were f i n i s h e d t o a smoo th p o l i s h . B e f o r e d i p p i n g t h e m o l d i n t o l a t e x , i t was c l e a n e d t h o r o u g h l y w i t h a d e t e r g e n t , d r i e d a n d t h e n g i v e n a d i p i n a c o a g u l a n t . The c o a g u l a n t u s e d was a s o l u t i o n o f c a l c i u m n i t r a t e t e t r a h y d r a t e i n e t h y l a l c o h o l . The c o n c e n t r a t i o n o f t h e s a l t i n a l c o h o l g o v e r n s t h e t h i c k n e s s o f t h e l a t e x f i l m d e p o s i t on t h e m o l d . By t r i a l i t was f o u n d t h a t a 15% (by w e i g h t ) c o n c e n t r a t i o n o f t h e s a l t i n a l c o h o l w o u l d g i v e a f i l m t h i c k n e s s o f 0 . 0 1 0 \" t o 0 . 0 1 2 \" i n a s i n g l e d i p . The m o l d c o a t e d w i t h wet c o a g u l a n t was d i p p e d s l o w l y i n t o t h e l a t e x . C a r e was t a k e n n o t t o c r e a t e o r e n t r a p any a i r b u b b l e s i n t h i s . p r o c e s s . A f t e r a b o u t 2 t o 3 m i n u t e s o f d w e l l t i m e i n t h e l a t e x , t h e m o l d was w i t h d r a w n a t s u c h a r a t e t h a t t h e e x c e s s l a t e x w o u l d f l o w b a c k i n t o t h e t a n k 103 o f l a t e x and n o t c a u s e any r u n n i n g o n t h e s u r f a c e o f d e -p o s i t e d f i l m . T h e f i l m on t h e m o l d was a l l o w e d t o d r y a t room t e m p e r a t u r e ( a b o u t 7 0 ° ) f o r a b o u t 16 h o u r s . I t was t h e n c u r e d i n t h e o v e n f o r a b o u t 1 h o u r a t 1 0 0 - 1 1 0 ° C . When t h e m o l d c o o l e d down, t h e o u t s i d e o f t h e membrane was d u s t e d w i t h t a l c . I t was t h e n s t r i p p e d o f f t h e m o l d as more t a l c was a p p l i e d t o i t s i n n e r s u r f a c e . Membranes made i n t h i s m a n n e r s e e m e d ' t o g i v e no s i g n s o f d e t e r i o r a t i n g o v e r l o n g p e r i o d s o f u s a g e . In f a c t one s a m p l e membrane c o u l d be u s e d f o r 4 t o 5 t e s t s . The same d i a p h r a g m membranes s e r v e d f o r t h e e n t i r e t e s t i n g p r o g r a m . 104 APPENDIX 1 M E A S U R E M E N T OF B- VALUES S a m p l e numbeT P S - C 2 I n i t i a l . s t r e s s e s , °Z = 0-5 Kg/cm* U = 0-422 ,.• Verfi'c.a.1 Pressure Lcteral Dia.bWfa.grrt Pressure kg/a? AOJ POT2 p r e ssu re B -Value . ASi. ALL , 1475 • 7 1 • 4 S 5 -91 1730 2136 lozo o-5 0-5 • 4 9 4 •922 2o5>5 2704 0-5 0-5 - 4 9 4 • 988 2460 32 72. 3122 \\o i-O / o /•o 3 ( 9 0 4 4 0 8 4255 Tabic A2 - I M«*saTemen\\$ of B- Values =Jor a n und isfurbed s'j»