Studies on shrinking and swelling of Leda clay and of a Prairie clay

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NATIONAL RESEARCH COUNCIL CANADA

D I V I S I O N OF B U I L D I N G RESEARCH

S T U D I E S ON SHRINKING AND SWELLING OF LEDA CLAY AND OF A P R A I R I E CLAY

by B. P. W a r k e n t i n I n t e r n a l R e p o r t N o . 226 of t h e D i v i s i o n of B u i l d i n g R e s e a r c h OTTAWA O c t o b e r 1 9 6 1

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PREFACE

Shallow foundations on clay a o i l s a r e o f t e n subjected t o s e r i o u s d i f f e r e n t i a l movements. These movements, which a r e due t o volume changes i n the c l a y , may occur over long periods of time o r they may be seasonal. They a r e c l o s e l y associated with fundamental p r o p e r t i e s of the s o i l and with environmental changes of t h e s o i l

in

n a t u r e .

The Division of Building Research i s engaged i n f i e l d s t u d i e s of the environmental changes of two d i s t i n c t and important Canadian c l a y s

-

t h e Leda c l a y of Eastern Canada and the highly p l a s t i c c l a y of t h e .Prairies. The arrangement with MacDonald College, McGill University, f o r D r . Warkentin, A s s i s t a n t Professor, A g r i c u l t u r a l Physics Department, t o spend t h e summer of 1959 with t h e Division was t h e r e f o r e

e s p e c i a l l y welcomed since he had an i d e a l background t o extend the l a b o r a t o r y s t u d i e s of swelling and shrinking of t h e s e

c l a y s which had a l r e a d y been s t a r t e d . This work r e s u l t e d i n a j o i n t publication (Reference 1 9 ) . This r e p o r t records

a d d i t i o n a l t e s t r e s u l t s and describes t h e techniques developed by D r . Warkentin during h i s term with the Division. I t

i l l u s t r a t e s t h e value of co-operative research of t h i s nature.

Ottawa

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TABLE OF CONTENTS

VOLUME CHANGE MECHANISMS 1. Shrinkage

2. S w e l l i n g

3.

S h r i n k i n g a n d S w e l l i n g Cycles

EXPERIMENTAL MAmIALS

AND

METHODS

SHRINKAGE CHARACTERISTICS 1. Leda Clay 2. P r a i r i e Clays SWELLING CIURACTERISTICS 1. Leda Clay 2. P r a i r i e Clays CONCLUSIONS

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STIJDIES ON SHRLVKING AND SWELLING OF LEDA CLAY AJD OF A P R A I H I E

CLAY

B.

P.

Warlcentin

'1Zli.s work w a s u n d e r t a k e n t o s t u d y t h e volume changes a s s o c i a t e d w i t h m o i s t u r e c o n t e n t c h a n g e s , a n d t o d e t e r m i n e

t h e f a c t o r s t h a - t c o n t r o l t h e volume t o which s o i l s w i l l s w e l l on w e t t i n g a f t e r d r y i n g .

S h r i n k i n g and s w e l l i n g c h a r a c t e r i s t i c s depend upon t h e m i n e r a l s p r e s e n t i n t h e c l a y and upon t h e i r o r i e n t a t i o n o r r e s p e c t i v 2 arrangement. a l e exchangeable i o n a s s o c i a t e d

w i t h t h e c l a y , -the s a l t c o n c e n t r a t i o n , a n d a n y o r g a n i c o r i n o r g a n i c m a t e r i a l s which c a n bond between c l a y

p a r t i c l e s a l s o i n f l u e n c e volume changes, e s p e c i a l l y s w e l l i n g on w e t t i n g . With t h e s e p r o p e r t i e s a s v a r i a b l e s i n sample p r e p a r a t i o n , d i m e n s i o n a l shrinlcage a n d r e s w e l l i n g have been measured i n samples of two c l a y s o i l s .

VOLUME CHANGE MECIIANISMS

1. Shrinkage

S h r i n k a g e of c l a y s on d r y i n g has been measured i n numerous ways. E a r l y a t t e m p t s were made t o measure l i n e a r

s h r i n k a g e , from which volume shrinlrage w a s c a l c u l a t e d ( 1 0 ) .

I h p e r i m e n t a l p r e c i s i o n was improved by m e a s u r i n g t h e volume of a sample, a t v a r i o u s m o i s t u r e c o n t e n t s d u r i n g d r y i n g ,

by d i s p l a c e m e n t of mercury i n a s p e c i a l pycnometer b o t t l e

( 7 ) .

Methods i n v o l v i n g d i s p l a c e m e n t of mercury a r e c u r r e n t l y u s e d i n slnrinl~age measurements. Volume c a n a l s o b e - o b t a i n e d b y

d i s p l a c e m e n t i n w a t e r u s i n g p a r a f f i n ( 1 2 ) o r p l a s t i c

( 5 )

c o a t i n g s t o p r e v e n t e n t r y of w a t e r . Another method i n v o l v e s f i l l i n g s o i l p o r e s w i t h k e r o s e n e ( 1 6 ) . S h r i n k a g e has been d e t e r m i n e d r e c e n t l y by m e a s u r i n g l i n e a r dimensions of t h e m a g n i f i e d image of a s o i l cube p r o j e c t e d on a s c r e e n

( 4 ) .

Most of t h e c o n c e p t s of s h r i n k a g e a r e b a s e d on t h e work of H a i n e s

( 7

), who measured volumes of remoulded c l a y

specimens by d i s p l a c e m e n t of mercury i n a s p e c i a l pycnometer b o t t l e . For remoulded c l a y b l o c k s h e d e f i n e d t h r e e s t a g e s of s h r i n k a g e . During t h e f i r s t i n c r e m e n t s of w a t e r l o s s from a s a t u r a t e d c l a y , t h e d e c r e a s e i n volume e q u a l s t h e volume of w a t e r l o s t . %is has been termed "normal s h r i n k a g e " . m e sample becomes u n s a t u r a t e d below a c e r t a i n w a t e r c o n t e n t a n d t h e volume d e c r e a s e on f u r t h e r d r y i n g i s l e s s t h a n t h e

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volume of w a t e r l o s t . T h i s h a s been termed " r e s i d u a l shrinkage". Below t h e range of r e s i d u a l s h r i n k a g e , t h e c l a y w i l l l o s e w a t e r w i t h no f u r t h e r d e c r e a s e i n volume. This i s t h e t h i r d s t a g e i n s h r i n k a g e .

The moisture c o n t e n t a t which t h e s o i l becomes

u n s a t u r a t e d h a s been i n t e r p r e t e d a s t h e p o i n t a t which t h e s o i l p a r t i c l e s i n t e r a c t t o s e t up a s t r u c t u r e t h a t can r e s i s t s h r i n k a g e . If t h e sample volume i s p l o t t e d a g a i n s t moisture c o n t e n t , b o t h normal and r e s i d u a l s h r i n k a g e , e x c e p t f o r some t r a n s i t i o n p o i n t s , can o f t e n be approximated by s t r a i g h t l i n e s , and t h e i n t e r s e c t i o n of t h e s e two l i n e s i s

c a l l e d t h e "shrinkage l i m i t f f . I n some r e f e r e n c e s t h e

shrinlrage l i m i t i s d e f i n e d a s t h e p o i n t where t h e e x t e n s i o n of t h e normal shrinkage l i n e i n t e r s e c t s t h e w a t e r c o n t e n t a x i s

( 9 ) .

The shrinkage l i m i t s o d.efined does n o t have

p h y s i c a l s i g n i f i c a n c e because t h e t r a n s i t i o n r e g i o n may o c c u r o v e r a

5

t o 1 0 p e r c e n t w a t e r c o n t e n t change. It i s a

p l o t t i n g convenience. A more s i g n i f i c a n t p o i n t would be t h e w a t e r c o n t e n t a t which s h r i n k a g e f i r s t d e v i a t e s from normal s h r i n k a g e , i . e . t h e p o i n t a t which u n s a t u r a t i o n occurs. T h i s p o i n t may o f t e n be d i f f i c u l t t o determine p r e c i s e l y .

Clods t a k e n from s u r f a c e s o i l s t h a t have s t r u c t u r e i n t h e ~ g r i c u l t u r a l s e n s e and have undergone s e v e r a l w e t t i n g and d r y i n g c y c l e s o f t e n show no range of normal s h r i n k a g e ;

t h e degree of u n s a t u r a t i o n i n c r e a s e s p r o g r e s s i v e l y a s t h e c l o d d r i e s o u t ( 1 2 ) . These c l o d s have 3 wide range of void s i z e s and d i f f e r from s u b s u r f a c e s o i l , ? i n t h a t t h e y have a g r e a t e r percentage of v o i d s which become u n s a t u r a t e d a t v e r y low moisture t e n s i o n s . Water i s h e l d i n t h e s e v o i d s

by s u r f a c e t e n s i o n f o r c e s r a t h e r t h a n by t h e f o r c e s a s s o c i a t e d w i t h s w e l l i n g of t h e s o i l . S t i r k ( 1 6 ) found t h a t t h e f i r s t

increments of water l o s s from c l o d s of s u r f a c e s o i l were accompanied by a volume change l e s s t h a n t h e volume of w a t e r l o s t . He terms t h i s ' ' s t r u c t u r a l shrinkage", A s more w a t e r

i s l o s t , normal shrinkage occurs.

The s h r i n k a g e c h a r a c t e r i s t i c s of a s o i l depend upon g r a i n s i z e d i s t r i b u t i o n , t y p e of c l a y , and s t r u c t u r e o r arrangement of p a r t i c l e s . I n g e n e r a l , c l a y s t h a t have a h i g h n a t u r a l w a t e r c o n t e n t e x h i b i t t h e g r e a t e s t t o t a l

s h r i n k a g e and t h e g r e a t e s t normal and r e s i d u a l s h r i n k a g e . Kaolin e x h i b i t s l i t t l e o r no r e s i d u a l s h r i n k a g e whereas montmori l l o n i t e h a s a h i g h r e s i d u a l s h r i n k a g e

.

S i l t

-

and s a n d - s i z e p a r t i c l e s i n a s o i l i n c r e a s e t h e r e s i d u a l s h r i n k a g e and a l s o t h e amount of w a t e r l o s t over t h e low w a t e r c o n t e n t range where no shrinkage occurs. The arrangement of p l a t e - shaped p a r t i c l e s i n c l a y s would a l s o be expected t o i n f l u e n c e

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t h e amount of r e s i d u a l s h r i n k a g e .

Shrinkage o f a s o i l mass r e s u l t s from t e n s i o n i n t h e pore w a t e r . With l o s s o f t h e f i r s t i n c r e m e n t s of w a t e r a c u r v e d i n t e r f a c e i s formed i n t h e p o r e , w i t h l o w e r p r e s s u r e on t h e convex s i d e . Water moves from t h e i n s i d e o f t h e s o i l

mass t o t h e a r e a s of t h e c u r v e d i n t e r f a c e a n d t h e s o i l mass s h r i n k s . Shrinkage i s r e s i s t e d by p a r t i c l e i n t e r a c t i o n , e i t h e r o s m o t i c f o r c e s of r e p u l s i o n e x e r t e d when l i q u i d w a t e r s e p a r a t e s t h e p a r t i c l e s o r i n t e r p a r t i c l e c o n t a c t . Normal s h r i n k a g e ends when t e n s i o n i n t h e p o r e w a t e r becomes g r e a t enough t o empty t h e l a r g e s t p o r e s a n d a l l o n a i r t o e n t e r t h e sample. R e s i d u a l s h r i n k a g e e n d s when i n t e r p a r t i c l e c o n t a c t p r e v e n t s any f u r t h e r s h r i n k a g e of t h e s o i l mass.

The s o i l m o i s t u r e t e n s i o n o r s u c t i o n of t h e s o i l a t

which t h e v a r i o u s s t a g e s o f s h r i n k a g e o c c u r depends upon p a r t i c l e - s i z e d i s t r i b u t i o n a n d s o i l t y p e a s w e l l a s upon s t r u c t u r e o r a r r a n g e m e n t o f t h e p a r t i c l e s . Only a l i m i t e d number of e x p e r i m e n t s have been r e p o r t e d where s h r i n k a g e c h a r a c t e r i s t i c s have been r e l a t e d t o s o i l s u c t i o x . R e s u l t s show t h a t t h e s h r i n k a g e l i m i t f o r s u b s o i l s a n d remoulded c l a y s o i l s o c c u r s a t a s u c t i o n g r e a t e r t h a n t h a t c o r r e s p o n d i n g t o t h e permanent w i l t i n g p e r c e n t a g e , which i s g e n e r a l l y t a k e n

a s pF 4.2. pF i s d e f i n e d a s t h e l o g of s o i l s u c t i o n e x p r e s s e d i n cm of w a t e r ( 1 4 ) . For two A u s t r a l i a n c l a y s , Holmes ( 8 )

r e p o r t e d v a l u e s of pP 5.1 a n d

5.5

a t t h e s h r i n k a g e l i m i t , and pP

5.7

a n d >6.0 viliere s h r i n k a g e c e a s e d . For London c l a y Croney and Coleman

( 3 )

showed a p2 of 1 . 4 a t t h e s h r i n k a g e

l i m i t . S t i r k ( 1 6 ) found v a l u e s between pF 4.2 and 4.9

a t t h e commencement 01f r e s i d u a l s h r i n k a g e f o r s o i l s which c r a c k e d on d r y i n g . For s u r f a c e s o i l s i n which l a r g e r p o r e s predominate, t h e pF a t t h e s h r i n k a g e l i m i t s h o u l d d e c r e a s e . T h i s i s i n d i c a t e d i n t h e v a l u e s r e p o r t e d by S t i r k f o r non- c r a c k i n g s o i l s . The pP a t t h e commencement of r e s i d u a l s h r i n k a g e v a r i e s from (2.0 t o 4.2. S e v e r a l d i f f e r e n t mechanisms a r e i n v o l v e d i n w a t e r u p t a k e by a drry s o i l . The w a t e r a d s o r b e d al; low v a p o u r p r e s s u r e s e x i s t s a s w a t e r m o l e c u l e s i n s p e c i f i c a r r a n g e m e n t on t h e s u r f a c e of t h e c l a y p a r t i c l e s , and a s w a t e r o f h y d r a t i o n of t h e exchangeable i o n s (1). 'Khen t h e s e f i r s t l a y e r s of w a t e r a r e p r e s e n t a n d j o i n e d t o form c u r v e d i n t e r f a c e s i n a r e a s of c o n t a c t , t h e s p a c e s between s o i l p a r t i c l e s can be f i l l e d by c a p i l l a r i t y . I n s u r f a c e s o i l s w i t h l a r g e v o i d s , t h i s may a c c o u n t f o r most o f t h e w a t e r absorbed. I n s u b s o i l s where v o i d s a r e s m a l l a n d f i l l e d w i t h w a t e r even a t h i g h s u c t i o n s , most of t h e w a t e r u p t a k e w i l l be

(8)

accompanied by a volume change. The s w e l l i n g o r i n c r e a s e i n volume of c l a y r e q u i r e s a f o r c e s e p a r a t i n g t h e p a r t i c l e s ,

sometimes t o l a r g e d i s t a n c e s . Hydration f o r c e s a r e r e s p o n s i b l e f o r t h e i n i t i a l s e p a r a t i o n ; l a r g e r d i s t a . n c e s probably r e s u l t from an osmotic f o r c e . The i n c r e a s e d c o n c e n t r a t i o n of i o n s

between t h e c l a y p l a t e s a t t r a c t s w a t e r between t h e c l a y p a r t i c l e s and f o r c e s them a p a r t ( 1 7 ) . The amount of s w e l l i n g i n c r e a s e s w i t h i n c r e a s e d s u r f a c e a r e a of t h e c l a y , which r e s u l t s more from t h i n n e r plate-shaped p a r t i c l e s t h a n from s m a l l e r

p a r t i c l e s . Swelling i s g r e a t e s t w i t h monovalent exchangeable i o n s , and d e c r e a s e s a s t h e valence of t h e i o n i n c r e a s e s .

The l i m i t of s w e l l i n g depends upon t h e magnitudes of t h e osmotic f o r c e c a u s i n g i t , t h e f o r c e s a s s o c i a t e d w i t h t h e s t r u c t u r e which r e s i s t p a r t i c l e s e p a r a t i o n , and t h e o r i e n t a t i o n of p a r t i c l e s . Swelling and s w e l l i n g p r e s s u r e a r e h i g h e r i n low-svtelling c l a y s f o r random o r i e n t a t i o n of p a r t i c l e s t h a n f o r p a r a l l e l o r i e n t a t i o n ( 1 5 ) . The r e v e r s e i s t r u e , however, f o r h i g h - s w e l l i n g c l a y s a s shown by measurements w i t h sodium

m o n t m o r i l l o n i t e (18). T h i s h i g h e r s w e l l i n g volume f o r more n e a r l y p a r a l l e l p a r t i c l e o r i e n t a t i o n may be due t o one o r more

of t h e following r e a s o n s . F i r s t l y , t h e f o r c e s of a t t r a c t i o n a r e g e n e r a l l y a s s o c i a t e d w i t h t h e edges of t h e c l a y p l a t e s , because of t h e presence of p o s i t i v e l y charged s i t e s o r

exposed hydroxyl i o n s , Secondly, t h e d i f f u s e l a y e r of exchangeable i o n s , which i s t h e s e a t of t h e osmotic f o r c e

of r e p u l s i o n , i s i r r e g u l a r l y developed a t t h e edges because of t h e d i s t r i b u t i o n of n e g a t i v e charges i n t h e c r y s t a l l a t t i c e .

I n random edge-to-face o r i e n t a t i o n , t h e n , t h e f o r c e of a t t r a c t i o n

i s l a r g e r and t h e f o r c e of r e p u l s i o n s m a l l e r t h a n i n p a r a l l e l o r i e n t a t i o n . F i n a l l - y , t h e f o r c e of r e p u l s i o n depends upon t h e a r e a over which i n t e r a c t i o n i s t a k i n g p l a c e . For a n edge-to-face arrangement t h i s a r e a i s much lower than f o r t h e f a c e - t o - f a c e arrangement of p a r a l l e l o r i e n t a t i o n .

Swelling may a l s o be l i m i t e d by "cementing" m a t e r i a l s i n t h e s o i l such a s i r o n and aluminium o x i d e s and calcium o r magnesium c a r b o n a t e s ( 2 0 ) . The o x i d e s o f t e n e x i s t a s h y d r a t e d

s h o r t c h a i n polymers o r

a s

g e l s , On d r y i n g t h e y become i r r e v e r s i b l y dehydrated, and i f t h e y occur a t a p o i n t where t h e y a r e i n c o n t a c t w i t h two p a r t i c l e s a bond i s formed from p a r t i c l e , t o o x i d e , t o p a r t i c l e , The presence e s p e c i a l l y of i r o n s a l t s d e c r e a s e s s w e l l i n g . If a h i g h s w e l l i n g c l a y i s

d r i e d a f t e r t h e a d d i t i o n of i r o n s a l t s , i t s s w e l l i n g p r o p e r t i e s a r e g r e a t l y reduced. This may be due t o i r o n bonding between c l a y p a r t i c l e s , o r t o i r o n adsorbed on t h e c l a y s u r f a c e

changing t h e p r o p e r t i e s which c o n t r o l s w e l l i n g . On t h e basis

of v a l e n c e , t r i v a l e n t i r o n , a s exchangeable i o n , would a l s o be expected t o produce l i m i t e d s v ~ e l l i n g ,

3. Shrinlcing and Swelling Cycles

-

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r e a c h e s a volume on s w e l l i n g t h a t d i f f e r s from t h e volume it had a t t h e same w a t e r c o n t e n t on s h r i n k i n g ( 2 ) . U s u a l l y t h e volume i s h i g h e r on s w e l l i n g , i n d i c a t i n g e n t r a p p e d a i r . I t i s a l s o p o s s i b l e t h a t t h e sample w i l l c o n t a i n l e s s a i r a f t e r s w e l l i n g . The f i n a l volume a t t a i n e d on s w e l l i n g i s u s u a l l y d i f f e r e n t from t h e o r i g i n a l volume of t h e sample. This w i l l depend

upon t h e f a c t o r s t h a t c o n t r o l s w e l l i n g . If t h e r e i s a n e t d e c r e a s e i n volume a f t e r one c y c l e of d r y i n g and w e t t i n g , t h e second c y c l e u s u a l l y shows a f u r t h e r volume d e c r e a s e . E v e n t u a l l y a n e q u i l i b r i u m i s r e a c h e d where t h e volume changes accompanying w e t t i n g and d r y i n g a r e r e v e r s i b l e ( 1 0 ) . Some change i n s t r u c t u r e o c c u r s d u r i n g s h r i n k i n g a n d s w e l l i n g , a s shown by t h e h y s t e r e s i s l o o p when s u c t i o n i s p l o t t e d a g a i n s t w a t e r c o n t e n t and by t h e f i n a l . w a t e r c o n t e n t which, a f t e r s w e l l i n g , i s o f t e n lower t h a n t h e i n i t i a l w a t e r c o n t e n t ( 3 , 8 ) . The h y s t e r e s i s of u n s a t u r a t e d s o i l s may be caused by c a p i l l a r y e f f e c t s b u t i n s a t u r a t e d c l a y s where w a t e r uptake r e s u l t s i n swell-ing, i t i s probably due t o

p l a s t i c r e a d j u s t m e n t of t h e c l a y p a r t i c l e s ( 1 4 ) . m e a r e a of t h e h y s t e r e s i s l o o p r e p r e s e n t s t h e energy l o s t p e r c y c l e of w e t t i n g and d r y i n g ( 8 ) , used i n p a r t i c l e rearrangement.

EXPERIMEIJTAL MATERIALS

-

LKD METHODS

Tho g e o l o g i c a l l y d i f f e r e n t c l a y s were chosen f o r t h i s s t u d y of t h e volume change c h a r a c t e r i s t i c s on w e t t i n g and drying. A sample of Leda c l a y from O t t a w a was chosen a s

r e p r e s e n t a t i v e of t h e marine-deposited sediments of t h e Champlain Sea, and two samples from Nanitoba were used a s r e p r e s e n t a t i v e of l a c u s t r i n e d e p o s i t s of g l a c i a l Lake Agassiz on t h e P r a i r i e s . Engineering s o i l t e s t r e s u l t s f o r t h e samples a r e g i v e n i n Table I. The Leda c l a y w a s a p p a r e n t l y d e p o s i t e d i n s a l t w a t e r w i t h s a l t c o n c e n t r a t i o n s u b s e q u e n t l y reduced by l e a c h i n g ( 6 ) . I t r e t a i n s a w a t e r c o n t e n t c h a r a c t e r i s t i c of c l a y s t h a t s e t t l e o u t i n a f l o c c u l a t e d s t r u c t u r e , w i t h a h i g h f l o c volume o r h i g h w a t e r c o n t e n t caused by t h e p a r t i c l e arrangement i n which edge-to-face c o n t a c t of p a r t i c l e s i s dominant ( 1 3 ) .

X - r a y - d i f f r a c t i o n a n a l y s i s of t h e Leda c l a y shows t h a t p a r t of t h e c l a y - s i z e f r a c t i o n c o n s i s t s of i l l i t e a n d c h l o r i t e . The remainder c o n s i s t s of non-clay m i n e r a l s such

as q u a r t z , f e l d s p a r and amphibole. m e ( 2 ~ f r a c t i o n h a s a

s u r f a c e a r e a by g l y c o l a d s o r p t i o n of 90 m2/gm, and a n

exchange c a p a c i t y of 20 me/100 gm w i t h calcium a s dominant exchangeable c a t i o n (18). The c l a y m i n e r a l a n a l y s i s , exchange c a p a c i t y , and n a t u r e of exchangeable i o n s i n d i c a t e a m a t e r i a l w i t h l i m i t e d osmotic s w e l l i n g .

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The P r a i r i e c l a y s were d e p o s i t e d i n f r e s h w a t e r where a more p a r a l l e l arrangement of p a r t i c l e s on s e t t l i n g

o u t would be expected. The c l a y from Seven S i s t e r s c o n s i s t s l a r g e l y of m o n t m o r i l l o n i t e and i l l i t e

,

w i t h some i n t e r s t r a t i - f i e d m i n e r a l s mhich have a b a s a l r e f l e c t i o n between 1 0

and

1 4 8.

S u r f a c e a r e a by g l y c o l a d s o r p t i o n of t h e ( 2 ~

f r a c t i o n i s 380 m2/gm, and t h e exchange c a p a c i t y i s 40 me/100 gm ( 1 8 ) . A m i n e r a l a n a l y s i s of

45

p e r c e n t i l l i t e , 40 p e r c e n t mon-trnorillonite, 3 per c e n t c a l c i t e , and 2 p e r c e n t o r g a n i c m a t t e r h a s a l s o been r e p o r t e d f o r a sample from t h e Seven

S i s t e r s ' s i t e (11). The presence of m o n t m o r i l l o n i t e i n d i c a t e s ~ t h a t osmotic s w e l l i n g would be h i g h .

Measurement of volume change i n c l a y samples p r e s e n t s c e r t a i n d i f f i c u l t i e s . I n most l i q u i d s t h e volume cannot be measured by displacement because t h e y w i l l wet t h e s o i l .

Displacement i n mercury h a s been used, b u t t h i s r e q u i r e s e x t e n s i v e h a n d l i n g of t h e sample which r e s u l t s i n b r e a k i n g

when t h e sample i s dry and i n remoulding when i t i s s u f f i c i e n t l y wet t o be p l a s t i c . There i s a l s o t h e problem of mercury

becoming contaminated v e r y q u i c k l y w i t h s o i l , and t h e g e n e r a l u n d e s i r a b i l i t y of prolonged h a n d l i n g of mercury because of t h e h e a l t h h a z a r d . Volume c a l c u l a t e d from measured l i n e a r dimensions l a c k s s u f f i c i e n t p r e c i s i o n due t o t h e i r r e g u l a r shape of t h e sample. This method a l s o r e q u i r e s a l a r g e sample, where d r y i n g and w e t t i n g m u s t be c a r r i e d o u t slowly t o p r e v e n t l a r g e m o i s t u r e g r a d i e n t s . I f t h e s o i l i s c o a t e d t o a l l o w volume measuremerlt by displacement i n w a t e r , t h e

sample can be used only once.

Wafer-shaped c l a y samples a b o u t 1

1/4

by 1

1/4

by 3/16 i n . were c u t w i t h a w i r e saw and p l a c e d i n p r o t e c t i v e h o l d i n g frames so t h a t t h e r e q u i r e d h a n d l i n g would n o t damage

t h e sample. Use of t h i n samples d e c r e a s e d t h e time r e q u i r e d f o r w e t t i n g and d r y i n g , and a l s o decreased warping on drying.

The samples were s u p p o r t e d i n t h e h o l d e r s t o a l 1 . 0 ~ d r y i n g from b o t h f a c e s . Crosses were s c r a t c h e d on one f a c e of t h e c l a y wafer a t t h e mid-point n e a r each s i d e . The d i s t a n c e between t h e s e c r o s s e s was measured w i t h a t r a v e l l i n g

microscope t o t h e n e a r e s t 0.031 i n . F i g u r e 1 shows a p l a n of sample and h o l d e r .

Samples were allowed t o a i r - d r y a t a c o n s t a n t temperature of 20

+

1 ° C . Rate of d r y i n g was reduced by c o n f i n i n g t h e

samples i n a small space. Dimensions and weight were measured p e r i o d i c a l l y d u r i n g t h e d r y i n g p e r i o d of t h r e e days t o one week. These were n o t e q u i l i b r i u m v a l u e s , b u t w i t h t h e slow-

drying r a t e and t h i n samples, m o i s t u r e g r a d i e n t s through t h e sample would n o t be l a r g e .

No at-tempt was made t o g e t r e a d i n g s a t v a r i o u s i n t e r m e d i a t e w a t e r c o n t e n t s d u r i n g w e t t i n g . L i n e a r dimensions and w a t e r

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c o n t e n t were measured a f t e r t h e sample h a d been i n c o n t a c t w i t h w a t e r from t h r e e t o f i v e days. Water u p t a k e c o n t i n u e d beyond t h i s t i m e b u t a t a v e r y slow r a t e . The samples h a d t o be m o i s t e n e d c a r e f u l l y t o p r e v e n t c r a c k i n g on w e t t i n g . They were u s u a l l y p l a c e d i n t h e humid room f o r two d a y s , t h e n moistened w i t h w e t f i l t e r p a p e r f o r s e v e r a l d a y s , and t h e n p l a c e d on a wet f i l t e r p a p e r i n c o n t a c t w i t h w a t e r j u s t below t h e l e v e l of t h e sample.

Many of t h e s a m p l e s , b o t h u n d i s t u r b e d a n d remoulded, were n o t c o m p l e t e l y s a t u r a t e d . . No e a s y e x p e r i m e n t a l method

of removing t h e a i r was found, a n d t h e s a m p l e s were u s e d a s t h e y o c c u r r e d . I t w a s r e c o g n i z e d t h a t t h e a i r p r e s e n t c o u l d i n f l u e n c e s h r i n k a g e and e s p e c i a l l y s w e l l i n g , b u t no a t t e m p t

w a s made t o measure t h e d e g r e e o f s a t u r a t i o n . The o n l y

sanlples from which a i r w a s a b s e n t were t h o s e c o n s o l i d a t e d a t

2 kg/cm2. m e c l a y

a-t

f l u i d c o n s i s t e n c y was f i r s t p u t u n d e r

vacuum a f t e r which t h e w a t e r c o n t e n t was d e c r e a s e d u n d e r low p r e s s u r e i n a n u l t r a - f i l t r a t i o n c e l l u n t i l t h e sample w a s f i m enough

t o be h a n d l e d . I t was t h e n p l a c e d i n t o tlie c o n s o l i d a t i o n r i n g .

Dry d e n s i t y o r volume w e i g h t on oven-dry samples was d e t e r m i n e d by irnmcrsion i n mercury. A s p e c i a l . pycnorneter b o t t l e of c l e a r p l a s - t i c w i t h a t o p which c o u l d be i n s e r t e d t o a c o n s t a n t d e p t h , a s shown i n P i g . 1, was u s e d f o r t h e s e measurements. IITnc? bot-L1.c was weighed when f i l l e d w i t h mercury, and t h e n w i t h t h e c l a y sa:nple p l u s mercury. From t l ~ e s e

w e i g h i n g s t h e volume of t h e sample was c a l c u l a t e d .

1. Leda Clay

The d i m e n s i ~ n a l s h r i n k a g e c u r v e s of two t y p i c a l samples of u n d i s t u r b e d Leda c l a y a r e shown i n P i g . 2. W i t h i n e x p e r i m e n t a l v a r i a t i o n , v e r t i c a l shrinlrage and h o r i z o n t a l s h r i n k a g e a r e e q u a l . The s h r i n k a g e l i m i t i s a t 27 p e r c e n t w a t e r c o n t e n t ; t o t a l l i n e a r s I ~ r i n l r a g e i s 1 5 t o 17 p e r c e n t n i t l i 1 p e r c e n t r e s i d u a l s h r i n k a g e . R e r ~ ~ o u l d i n g u n d i s t u r b e d c l a y r e s u l t s i n a d e c r e a s e of

-clie shrinlrage l i m i t from 27 t o 20 p e r c e n t w a t e r . !his i n d i c a t e s a breakdor~rn oi" t h e s-truc-t;ilre p r e s e n t i n t'ne

u n d i s t u r b e d c l a y , a l l o w i n g t h e p a r t i c l e s t o be a r r a n g e d i n t o a more dense s t r u c t u r e b e f o r e t h e y d e v e l o p s u f f i c i ' m t r e s i s t a n c e t o s h r i n k a g e t o c a u s e u n s a - t u r a t i o n of t h e sample. The

remoulded samples h a d a d r y d e n s i t y o r volume w e i g h t of 1 . 7 7 m / c c compared viith 1 . 6 4 f o r t h e u n d i s t u r b e d samples.

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The v a r i a b i l i t y i n measured s h r i n k a g e f o r d i f f e r e n t samples was l a r g e . For remoulded samples t o t a l shrinlcage i n two d i r e c t i o n s d i f f e r e d a s much a s 1 1/2 p e r c e n t f o r a t o t a l s h r i n k a g e of 1 0 p e r c e n t . Die s a m p l e s showing t h e g r e a t e s t v a r i a b i l i t y were t h o s e o:E h i g h w a t e r c o n t e n t s which were s o s o f t t h a t t h e y were s l i g h t l y deformed by h a n d l i n g .

m e i n i t i a l p o i n t on t h e s l r i n l c a g e c u r v e f o r t h e

u n d i s t u r b e d samples w a s o f t e n above a l i n e on which s u b s e q u e n t r e a d i n g s f e l l . T h i s may have r e s u l t e d from sample d i s t u r b a n c e

d u r i n g c u t t i n g , o r p a r t i a l d e h y d r a t i o n a t tlie s u r f a c e b e f o r e measurements were made.

m e r e w a s no s i g n i f i c a n t d i f f e r e n c e between h o r i z o n t a l a n d v e r t i c a l s h r i n k a g e of t h e u n d i s t u r b e d s a m p l e s , i n d i c a t i n g t h a t any p r e c o n s o l i d a t i o n l o a d h a d n o t e x e r t e d a n o v e r - a l l o r i e n t i n g e f f e c t on t h e c l a y p a r t i c l e s . I n o t h e r s a m p l e s o f Leda c l a y , some from g r e a t e r d e p t h , measured v e r t i c a l s h r i n k a g e d i d e x c e e d h o r i z o n t a l s h r i n k a g e . !The r e s u l t s a r e summarized i n Table 11. m e r a t i o of h o r i z o n t a l t o v e r t i c a l shrin1:age s h o u l d be a measure o f t h e l o u d t o which t h e c l a y h a s been s u b j e c t e d , b u t t h e measurements a r e p r o b a b l y n o t s u f f i c i e n t l y p r e c i s e f o r u s e i n t h i s c o n n e c t i o n . R e s u l t s o b t a i n e d from sarnples c o n s o l i d a t e d i n t h e l a b o r a t o r y showed t h a t o r i e n t a t i o n of p a r t i c l e s o f Leda c l a y can be i n d u c e d t o produce p r e f e r e n t i a l s h r i n k i n g a n d s w e l l i n g i n one d i r e c t i o n . F i g .

3

shows t h e s h r i n k a g e c u r v e s f o r

remoulded specimens of sample

83-33

from which cementing

m a t e r i a l s h a d been removed p r i o r t o c o n s o l i d a t i o n a t 2 kg/cn2. 'Ihe l o a d w a s a p p l i e d s l o w l y a n d c o n s o l i d a t i o n p r o c e e d e d o v e r a p e r i o d of two weeks. V e r t i c a l shrinlcage w a s s l i g h t l y g r e a t e r t h a n h o r i z o n t a l shrinlcage. The w a t e r c o n t e n t a t t h e shrinlcage l i m i t w a s 2G t o 27 p e r c e n t , a n i n c r e a s e from 20 p e r c e n t f o r t h e remoulded sample t o a v a l u e comparable w i t h t h e u n d i s t u r b e d sample, T h i s i n d i c a t e s a r e a r r a n g e m e n t c a u s e d by t h e c o n s o l i d a t i o n l o a d o r a time-dependent r e a r r a n g e m e n t s ~ l c h a s ' o c c u r s i n

t h i x o t r o p i c s t r e n g t h r e g a i n .

For a sample of remoulded c l a y c o n s o l i d a t e d a t 46 kg/cm* t o a f i n a l w a t e r c o n t e n t o f 25 p e r c e n t , t h e h o r i z o n t a l s h r i n k a g e on f u r t h p r d r y i n g exceeded v e r t i c a l s h r i n k a g e , b u t on r e w e t t i n g s w e l l i n g w a s much g r e a t e r i n t h e v e r t i c a l d i r e c t i o n , I n t h e c o n s o l i d a t i o n a p p a r a t u s t h e l o a d i s a p p l i e d i n t h e v e r t i c a l d i r e c t i o n , a n d t h e p l a t e - s h a p e d p a r t i c l e s a r e o r i e n t e d p e r p e n d i c u l a r t o t h e l o a d . 'fie d i s t a n c e between c l a y p a r t i c l e s i n t h e v e r t i c a l d i r e c t i o n i s r e d u c e d , b u t l i t L l e c o n s o l i d a t i o n o c c u r s a l o n g t h e h o r i z o n t a l a x i s . F u r t h e r s h r t n k a g e c a n tlien t a k e p l a c e i n a h o r i z o n t a l d i r e c t i o n a s t h e p a r t i c l e e d g e s a p p r o a c h e a c h o t h e r .

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2. P r a i r i e C l a y s V e r t i c a l s h r i n k a g e exceeded h o r i z o n t a l s h r i n k a g e by a f a c t o r of a l m o s t 2 f o r t h e Winnipeg c l a y a n d 3 f o r t h e Seven S i s t e r s c l a y ( P i g s . 4 and

5 ) .

S h r i n k a g e c u r v e s f o r t h e s e s o i l s d i f f e r from t h o s e f o r Leda c l a y n o t b e c a u s e of a much l a r g e r p r e c o n s o l i d a t i o n l o a d b u t because of t h e d i f f e r e n t c l a y m i n e r a l s a n d d e p o s i t i o n c o n d i t i o n s . To-tal volume s h r i n k a g e i s a b o u t t h e same f o r t h e Leda a s f o r t h e

P r a i r i e c l a y s because t h e i r i n i t i a l w a t e r c o n t e n t s a r e s i m i l a r . B b l e I11 summarizes t h e r e s u l t s of a l l shrinlcage d e t e r m i n a t i o n s .

Dimensional s h r i n k a g e w i t h d e c r e a s e i n w a t e r c o n t e n t i s n o t l i n e a r . !l&e s l o p e of t h e s h r i n k a g e c u r v e i n d i c a t e s t h a t v e r t i c a l s h r i n k a g e i s r e l a t i v e l y g r e a t e r a t h i g h wa-ter c o n t e n t , a n d h o r i z o n t a l s h r i n k a g e g r e a t e r a t t h e s h r i n k a g e l i m i t . T h i s r e s u l t s from p r e f e r r e d o r i e n t a t i o n o f p a r t i c l e s p a r a l l e l t o t h o h o r i z o n t a l a x i s . The f o r c e o f r e p u l s i o n between p a r t i c l e s i s g r e a t e s t normal t o t h e f l a t s u r f a c e s , and hence tlie v e r t i c a l i n t e r p a r t i c l e d i s - t a n c e i s l a r g e r t h a n t h e h o r i z o n t a l when t h e c l a y i s d e p o s i t e d . Removal o f t h e f i r s t i n c r e m e n t s of w a t e r i s %hen accompanied by a g r e a t e r v e r t i c a l s h r i n k a g e . O r i e n t a t i o n of p a r t i c l e s i n t h e n a t u r a l c l a y i s n o t cornglete, however, a n d much of t h e measured

h o r i z o n t a l s h r i n k a g e may be due t o f l a t s u r f a c e s of c l a y p a r t i c l e s a p p r o a c h i n g e a c h o t h e r .

The w a t e r c o n t e n t a t t h e s h r i n k a g e l i m i t c a n n o t be d e t e r m i n e d w i t h a c c u r a c y because d i m e n s i o n a l change i s n o t l i n e a r l y dependent upon w a t e r l o s s . If d i m e n s i o n a l s h r i n k a g e i s c o n v e r t e d t o volume sllrinlrage, t h e u s u a l normal a n d

r e s i d u a l s h r i n k a g e l i n e s can be drawn t o f i n d a s h r i n k a g e l i m i t o f 20 p e r c e n t f o r t h e Seven S i s t e r s c l a y a n d

17

p e r c e n t f o r t h e Winnipeg c l a y . A d e f i n i t e change i n s l o p e of t h e u r i d i m e n s i o n a l s h r i n k a g e c u r v e s a l s o o c c u r s n e a r t h e s h r i n k a g e l i m i t . For t h e Winnipeg c l a y t h i s i s

a t 1 7

p e r c e n t f o r b o t h h o r i z o n t a l a n d v e r t i c a l s h r i n k a g e , b u t f o r t h e Seven S i s t e r s c l a y it o c c u r s a t 23 p e r c e n t f o r v e r t i c a l s h r i n k a g e a n d 18 p e r c e n t f o r h o r i z o n t a l shrinlcage. There i s l i t t l e r e s i d u a l s h r i n k a g e i n t h e h o r i z o n t a l d i r e c t i o n . Comparison of t h e s e two c l a y s i n d i c a t e s t h a t a s t h e r a t i o of v e r t i c a l t o h o r i z o n t a l s h r i n k a g e i n c r e a s e s due t o g r e a t e r p a r t i c l e o r i e n t a t i o n t h e s h r i n k a g e l i m i t f o r h o r i z o n t a l s h r i n k a g e d e c r e a s e s .

! h e w a t e r c o n t e n t of a remoulded sample of Seven S i s t e r s c l a y a t t h e s h r i n k a g e l i m i t w a s

17

p e r c e n t ; t h e amount of r e s i d u a l s h r i n k a g e w a s r e l a t i v e l y h i g h . Because of t h e u n c e r t a i n t y i n d e t e r m i n i n g s h r i n k a g e l i m i t s f o r t h e undi.-:i;urbed m a t e r i a l s , i t i s n o t p o s s i b l e t o i n f e r d i f f e r e n c e s

i n al-i-angement of p a r t i c l e s between u n d i s t u r b e d a n d remoulded samples from s h r i n k a g e l i m i t a n d r e s i d u a l shrinlrage v a l u e s .

(14)

SWELLING CHARACTERISTICS

Leda c l a y d i d n o t r e g a i n t h e o r i g i n a l w a t e r c o n t e n t o r dimensions on r e w e t t i n g a f t e r d r y i n g . Both t h e w a t e r c o n t e n t t o which a sample w a s d r i e d a n d t h e sample t r e a t m e n t i n f l u e n c e d t h e amount of r e g a i n .

Water c o n t e n t r e g a i n f o r samples of Leda c l a y t r e a t e d i n d i f f e r e n t ways i s shown i n F i g . 6. There i s c o n s i d e r a b l e s c a t t e r i n t h e measured v a l u e s , b u t b ? o l i m i t i n g c o n d i t i o n s a r e e v i d e n t . !he u n d i s t u r b e d samples show a n a l m o s t l i n e a r d e c r e a s e i n w a t e r r e g a i n e d w i t h d e c r e a s i n g w a t e r c o n t e n t t o which t h e sample i s d r i e d . !he samples, w i t h cementing m a t e r i a l s removed show a c o n s t a n t w a t e r u p t a k e u n t i l d r i e d t o 1 0 p e r c e n t w a t e r . Then wa-ter u p t a k e d e c r e a s e s s h a r p l y t o t h a t of t h e oven-dry sample. The remoulded sample f a l l s between t h e s e two p a t t e r n s , b u t r e s e m b l e s t h e u n d i s t u r b e d

sample more c l o s e l y . The s t r u c t u r e h a s n o t been d e s t r o y e d a s c o m p l e t e l y i n remoulded samples a s i n t h o s e which were

s l u r r i e d and c h e m i c a l l y t r e a t e d t o remove cementing m a t e r i a l s . The w a t e r c o n t e n t r e g a i n e d by t h e s e samples r e p r e s e n t e d a n e q u i l i b r i u m a t t r i b u t a b l e t o t h e c l a y m i n e r a l s , whereas t h e h i g h e r w a t e r c o n t e n t of t h e u n d i s t u r b e d samples was c a u s e d by s t r u c t u r e .

Sample dimensions a f t e r s w e l l i n g a r e shown i n F i g .

7

where t h e i n f l u e n c e of remoulding on s w e l l i n g i s emphasized. Dimensional r e g a i n i s d e c r e a s e d moi-e by ovendrying t h a n w a t e r c o n t e n t r e g a i n . B l i s d i f f e r e n c e i s due t o c a p i l l a r y u p t a k e of w a t e r which d o e s n o t i n c r e a s e volume. I n c o n j u n c t i o n w i t h t h e s h r i n k a g e c u r v e s , t h e s e r e s u l t s i n d i c a t e t h a t t h e i m p o r t a n t f a c t o r i n d i m e n s i o n a l r e g a i n i s w a t e r c o n t e n t a t t h e time t h e sample i s r e w e t t e d . The i n f l u e n c e of d r y i n g a n d remoulding on p a r t i c l e o r i e n t a t i o n which e x p l a i n s t h e s e s w e l l i n g r e s u l t s h a s been d i s c u s s e d

( 1 9 ) .

Regain d e c r e a s e d s l i g h t l y a f t e r a s e c o n d c y c l e of d r y i n r e w e t t i n g b u t was of t h e o r d e r of t h e e x p e r i m e n t a l p r e c

f

s i o n . and A d i f f e r e n t method of measurement would be r e q u i r e d t o s t u d y t h i s a s p e c t of d i m e n s i o n a l r e g a i n .

The Leda c l a y samples w i t h cementing m a t e r i a l s removed and c a l c i u m s u b s t i t u t e d a s exchangeable i o n were t h e o n l y o n e s t h a t d i d n o t c r a c k on wet-ting. None of t h e s e samples brolce u p on w e t t i n g , whereas some samples from a l l o t h e r

methods of p r e p a r a t i o n were l o s t b e c a u s e of r a p i d c r a c k i n g on w e t t i n g .

(15)

e a s i l y on w e t t i n g t o be s t u d i e d by t h e s e methods. S w e l l i n g i n w a t e r c o n t i n u e d u n t i l t h e sample w a s s o f t a n d b egan t o d i s p e r s e . S w e l l i n g i n sodium ch1orid.e s o l u t i o n s w a s l o w e r ; a t

0.5

molar N a C l no s v i e l l i n g w a s measured.

On r e w e t t i n g a f t e r o v e n d r y i n g , remoulded s a m p l e s cracked. i n t o s m a l l crumbs l e s s t h a n 1

mm

i n d i a m e t e r which were v e r y d i f f i c u l t t o r e w e t .

Water c o n t e n t a n d dimension changes on d r y i n g a n d wel;ting c o n s o l i d a t e d Leda c l a y a r e g i v e n i n Table I V . 'When a c o n s o l i d a t e d sample w a s d r i e d , t h e g r e a t e s t s h r i n k a g e was i n t h e h o r i z o n t a l d i r e c t i o n p e r p e n d i c u l a r t o t h e c o n s o l i d a t i o n l o a d . Subsequent w e t t i n g produced g r e a t e r s w e l l i n g i n t h e v e r t i c a l d i r e c t i o n . If t h e c o n s o l i d a t e d sample w a s s a t u r a t e d w i t h w a t e r b e f o r e d r y i n g , t o t a l s w e l l i n g w a s g r e a t e r a s w a s t h e r a t i o of v e r + t i c a l t o h o r i z o n t a l s v ~ e l l i n g . During c o n s o l i d a t i o n some o r i e n t a t i o n of p a r t i c l e s o c c u r s , p e r p e n d i c u l a r t o t h e c o n s o l i d a t i o n l o a d . T h i s can be c o n s i d e r e d a s s h r i n k a g e i n t h e v e r t i c a l d i l - e c t i o n . On s u b s e q u e n t d r y i n g h o r i z o n t a l s h r i n k a g e c a n o c c u r more r e a d i l y . On w e t t i n g , however, t h e s w e l l i n g f o r c e i s e x e r t e d normal t o t h e p l a n e of o r i e n t a t i o n , a n d s w e l l i n g o c c u r s p r e f e r e n t i a l l y i n t h e v e r t i c a l d i r e c t i o n . 2. P r a i r i e Clays Measurements of volume a n d w a t e r c o n t e n t r e g a i n of u n d i s t u r b e d samples of P r a i r i e c l a y s were d i f f i c u l t t o o b t a i n because of e x t e n s i v e c r a c k i n g . 1Jndistu1:bed s a m p l e s developed h o r i z o n t a l c r a c k s u n l e s s d r i e d v e r y s l o w l y , a n d most c r a c k e d

on r e w e t t i n g .

Water c o n t e n t f o r t h e P r a i r i e c l a y s a f t e r w e t t i n g i s p l o t t e d i n P i g . 8. Water c o n t e n t r e g a i n d e c r e a s e s a l m o s t l i n e a r l y w i t h d e c r e a s i n g w a t e r c o n t e n t t o which 'the sample i s d r i e d . The s l o p e s of t h e s e l i n e s i n d i c a t e t h a t t h e d e c r e a s e i s g r e a t e r f o r t h e remoulded samples t h a n f o r t h e u n d i s t u r b e d ones.

On w e t t i n g t h e w a t e r c o n t e n t i n c r e a s e d above t h e v a l u e s f o r t h e n a t u r a l s t a t e of t h e sample e x c e p t when t h e w a t e r

c o n t e n t h a d been r e d u c e d t o air-Ciry o r oven-dry b e f o r e w e t t i n g . I n c o n t r a s t t o some of t h e Leda c l a y samples, o v e n d r y i n g t h e

P r a i r i e c l a y h a d no added i n f l u e n c e on r e n e t t i n g c h a r a c t e r i s t i c s . Removal of i r o n o x i d e s a n d cal-bonates i n c r e a s e d r e g a i n o n l y

s l i g h t l y above t h a t of t h e remoulded samples; t h i s d i f f e r e n c e shows u p f o r t h e o v e n - d r i e d sample.

Dimensional r e g a i n shovis t h e same c h a r a c t e r i s t i c s a s w a t e r c o n t e n t r e g a i n ( P i g .

9).

The u n d i s t u r b e d samples s w e l l

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beyond t h e o r i g i n a l d i m e n s i o n s , w i t h s w e l l i n g g r e a t e r i n t h e v e r t i c a l d i r e c t i o n t h a n i n t h e h o r i z o n t a l . Remoulding l e s s e n s t h e amount of r e g a i n . The remoulded s a m p l e s wi%h a l o w e r

d e g r e e of p a r t i c l e o r i e n t a t i o n showed a s m a l l e r r e g a i n . S w e l l i n g a s a f u n c t i o n of p a r t i c l e o r i e n t a t i o n a n d c l a y m i n e r a l f o r t h e s e s a m p l e s h a s been d i s c u s s e d ( 1 9 ) . CONCLUSIONS 1. Both c l a y s e x h i b i t e d a l a r g e s h r i n k a g e on a i r d r y i n g . T o t a l volume d e c r e a s e e x p r e s s e d on t h e b a s i s o f t h e o r i g i n a l volume w a s 35 p e r c e n t . !be Leda c l a y showed e q u a l h o r i z o n t a l a n d v e r t i c a l s h r i n k a g e , w h i l e t h e v e r t i c a l s h r i n k a g e of t h e P r a i r i e c l a y s exceeded t h e h o r i z o n t a l by a f a c t o r o f 2 t o 3. 2. S h r i n k a g e c h a r a c t e r i s t i c s changed on r e m o u l d i n g b e c a u s e of t h e change i n p a r t i c l e o r i e n t a t i o n . 3 . !be p a r t i c l e s of Leda c l a y c o u l d b e o r i e n t e d by c o n s o l i d a t i o n o f a sample, a s shown by s u b s e q u e n t s h r i n k i n g a n d s w e l l i n g c h a r a c t e r i s t i c s .

4.

S w e l l i n g a n d w a t e r c o n t e n t r e g a i n o f . t h e c l a y s depended upon sample t r e a t m e n t a n d w a t e r c o n t e n t t o which t h e c l a y w a s d r i e d . Both o f t h e s e i n f l u e n c e s c o u l d be e x p l a i n e d a s r e s u l t i n g from d i f f e r e n c e s i n p a r t i c l e o r i e n t a t i o n . For t h e Leda c l a y , n o n - p a r a l l e l o r i e n t a t i o n r e s u l t e d i n h i g h e r r e g a i n . !he P r a i r i e c l a y showed t h e c h a r a c t e r i s t i c s of

a

h i g h - s w e l l i n g c l a y , a n d s w e l l i n g w a s g r e a t e s t f o r p a r a l l e l p a r t i c l e o r i e n t a t i o n . 5. Cementing m a t e r i a l s i n t h e c l a y h a d a n e g l i g i b l e i n f l u e n c e on s w e l l i n g of t h e s e c l a y s . It i s a p l e a s u r e t o e x p r e s s a p p r e c i a t i o n t o t h e N a t i o n a l R e s e a r c h C o u n c i l , a n d t o t h e members o f t h e s t a f f c o n c e r n e d w i t h this work. !be D i v i s i o n of B u i l d l n g R e s e a r c h a n d t h e D i r e c t o r , M r . R.F. L e g g e t , p r o v i d e d t h e o p p o r t u n i t y o f working i n t h e S o i l Mechanics S e c t i o n l a b o r a t o r i e s . !be work was

d i s c u s s e d a t a l l s t a g e s w i t h many members o f t h e s t a f f ,

e s p e c i a l l y M r . C.B. Crawford, Head o f t h e S o i l Mechanics S e c t i o n a n d M r . M. Bozozuk.

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1. B a r s h a d , I s a a c . A d s o r p t i v e a n d s w e l l i n g p r o p e r t i e s of c l a y - w a t e r s y s t e m s . P r o c . 1st N a t . Conf. on C l a y s a n d Clay P t i n e r a l s , 1 9 5 2 , C a l i f . Dept. of N a t . R e s o u r c e s , M v . Mines, B u l l . 1 6 9 , 1955, p. 70-77-

2. Bozozuk, M.. Volume changes measured i n Leda c l a y .

-

I n Proc. Ibvelf-th Can. S o i l Mech. Conf., N a t . Res.

C o u n c i l , A s s o c i a t e Committee on S o i l a n d Snow Mechanics, Tech. Memo. No. 59, 1 9 5 9 , p. 53-54.

3

Croney, D., a n d Coleman, J. D. S o i l s t r u c t u r e i n r e l a t i o n t o s o i l s u c t i o n ( p F ) . J o u r . S o i l S c i . , Vol. 5 , 1 9 5 4 , p. 75-84.

4

.

Croney, D., Coleman, J . E . , a n d R u s s a m , K. The s u c t i o n a n d s w e l l i n g p r o p e r t i e s o f some B r i t i s h c l a y s . B r i t i s h Road Research S t a t i o n . Unpublished hlirneo. N a t e r i a l , 1953.

5. Davidson, S t e v e E. Volume-weight ( b u l k d e n s i t y ) d e t e r m i n a t i o n i n t h e l a b o r a t o r y o f c l o d s c o a t e d w i t h Dow Saran r e s i n . U.S. Dept. Agric. S o i l

Survey Lab. R e l t s v i l l e

,

unpublished-Mimeo. M a t e r i a l , 1957. 6. Eden, W.

J . ,

a n d Crawford, C.B. G e o t e c h n i c a l p r o p e r t i e s of Leda c l a y i n t h e O t t a w a a r e a . P r o c . F o u r t h I n t

.

C O I ? ~ ' . S o i l Mech. Foundation l h g i n e e r i n g , London, l a , 1 9 5 7 , p. 22-27. 7. H a i n e s , W.B. The volume-changes a s s o c i a t e d w i t h v a r i a t i o n s of w a t e r c o n t e n t i n s o i l . J o u r . A g r i c . S c i . , Vol. 13, 1923, p.296-510. 8. Holmes, J . W . Water s o r p t i o n a n d s w e l l i n g o f c l a y b l o c k s . J o u r . S o i l S c i . , Vol. 6 , 1 9 5 5 , p. 200-208. 9. Hough, B.K. B a s i c s o i l s e n g i n e e r i n g , Ronald P r e s s

Co.

,

Nevi York. 1 9 57.

10

.

Keen, B.A. 'Jlhe p h y s i c a l p r o p e r t i e s of s o i l s . Lon&mans Green a n d Co., London. 1931.

11. Lambe, T. W i l l i a m , a n d T!iart-in, R. T o r r e n c e

.

Composition a n d e n g i n e e r i n g p r o p e r t i e s o f s o i l s ( I V ) . P r o c . Highway Res. Bd. Vol. 35, 1 9 5 6 , P. 661-667.

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L a u r i t z e n , C.W. Apparent s p e c i f i c volume a n d s h r i n k a g e c h a r a c t e r i s t i c s of s o i l m a t e r i a l . S o i l S c i . , Vol. 6 5 , 1 9 4 8 , p. 155-179.

R o s e n q v i s t , I.

Th.

Physico-chemical p r o p e r t i e s o f s o i l s : S o i l - w a t e r s y s t e m s . J o u r . S o i l Mech.

Foundation Div., Proc. Amer. Soc. C i v i l E n g i n e e r s , Vol. 8 5 , 1959, P. 31-53.

S c h o f i e l d , R.K. The pP of t h e w a t e r i n s o i l . W a n s . ! b i r d I n t . Cong. S o i l S c i . Vol. 2 , 1935, p. 37-48. Seed, H.B., a n d Chan. C.K. S t r u c t u r e a n d s t r e n g t h

c h a r a c t e r i s t i c s of compacted c l a y s . J o u r . S o i l Mech. Foundation Div., P r o c . Amer. Soc. C i v i l E n g i n e e r s , Vol. 8 5 , 1959, 7. 87-128.

S t i r k . G.B. Some a s p e c t s of s o i l s h r i n k a g e a n d t h e e f f e c t o f c r a c k i n g upon w a t e r e n t r y i n t o t h e s o i l . A u s t . J o u r . Agric. Res., Vol. 5 , 1 9 5 4 ? p. 279-290.

Warkentin, B.P. ! b e mechanism of volume c h a n g e s i n cl.ays.

9

Proc. Twelfth Can. S o i l 1Vlech. Conf., N a t . Res. C o u n c i l , A s s o c i a t e Committee on S o i l a n d Snow Mechanics, Tech. Memo., No. 59, 1 9 5 9 , p. 44-45. Warkentin, B .P. Unpublished r e s u l t s . S o i l P h y s i c s L a b o r a t o r y , Macdonald C o l l e g e . 1960. Warkentin, B.P., a n d Bozozuk, bl. S h r i n k i n g a n d s w e l l i n g p r o p e r t i e s of two Canadian c l a y s . P r o c . F i f t h I n t . Conf. S o i l NIech. F o u n d a t i o n Z n g i n e e r i n g , P a r i s , 1961. W i n t e r k o r n , H.F.

,

a n d T s c h e b o t a r i o f f

,

G ; T. S e n s i t i v i t y of c l a y s t o r e m o u l d i n g a n d i t s p o s s i b l e c a u s e s . Highway Res. Bd. P r o c . , Vol. 27, 1947, p. 435-442.

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TABLE

I

PROPZRTIES OF CLAY SAIKPLES

Sam21 e No. 83-27 83-33 5 0 - 1 4 1 4 88 -3 88-11 M i n e 1-a 1 Density, gm/cc 2.65 2.78 2.79 2.8C 2.EO

-

P l a s t i c L i m i t , / 5t 0 26 2

5

2 8 4 1 35 Clay Le da Leda Le da P r a i r i e (Seven S i s t e r s ) P r a i r i e ('llinnipeg ) l\Tatural V a t s r C o n t e n t , $ 6 5 65 75 6 2 54 Grain S i z e s , -$ S i l t Clay 30 7 0 48 5 2 30 70 20 8 0

5

95 Depth, f t 1 6 1 9 18 1 4 1 3 L i q u i d L i m i t , $ 55 66 70 1 0 4 1 0 6 Naxirnum P r e c o n s o l i d a t i o n Load, T.S.F. 1 . 9 2. ( 2 ,- 2 . 5 0 . 5 1 . 0

(20)

VERTICAL

AND

HORIZONTAI; SHRIXKAGE

FOR LEDA CLAY

Shrinkage

-

Air-dry

dimension

as ;$

of o r i g i n a l dimension

V e r t i c a l

H o r i z o n t a l

84.5

84.7

86.9

86.5

86.3

86.8

87.4

87.3 8 6 . 3

88.1

87.9

88.4

84.2

86.3

81.1

82.5

89.5

90.6

88.4

90.1

88.6

93.7 I n i t i a l

Water

Content,

%

66

64

64 -

-

47

41 Sam p l e

83-27

II 11 t l

94-5

It

50-141-C

tt

C o n s o l i d a t e d

a t 2 kg/cm2 tr

C o n s o l i d a t e d

a t

46

kg/cm2

and w e t t e d t o

s a t u r a t i o n

Depth,

f t

1 6

42

17

-18j

17

-18$

(21)

s m w y OF SHRINLIAGZ CHARACTERISTICS OF THZ CLAYS Sample Clay Weatment P r a i r i e Undisturbed

-

Winnipeg

-

v e r t i c a l

-

h o r i z o n t a l P r a i r i e Undisturbed

-

Seven S i s t e r s

-

v e r t i c a l

-

h o r i z o n t a l P r a i r i e Remoulded

-

Seven S i s t e r s I n i t i a l Water Content,

%

Le da Undisturbed

1

65

1

27

1

1 6 0.6 Remou l d e d

1

l 2 0 . 5 Water Content a t s h r i n k a g e l i m i t ,

%

Cementing ma-

I,,,

t e r i a l s removed" ^ 47

I

a washed w i t h 1

M

CaC12, e x c e s s s a l t removed by p r e s s u r e f i l t r a t i o n .

L i n e a r s h r i n k a g e e x p r e s s e d a s $ of oven-dry dimension of sample Normal Residual shrinkage s h r i n k a g e -

-:--% t r e a t e d t o remove i r o n and alumi

urn

o x i d e s and c a r b o n a t e s , s a t u r a t e d w i t h calcium a s exchangeable ioll,

2

and c o n s o l i d a t e d a t 2 kg/cn

.

Volume s h r i n k - age

-

cc/100 cc o r i g i n a l volume

(22)

TABLE I V

WAmR CONTENT AND DIP~SIONAL REGAIN OF COPTSOLIDA!FED SAMPLES OF LEDA CLAY Sequence of t r e a t m e n t s Remoulded Leda c l a y c o n s o l i d a t e d a t 46 kg/cm2 A i r - d r i e d S a t u r a t e d Remoulded Leda c l a y c o n s o l i d a t e d a t 46 kg/cm2 S a t u r a t e d A i r - d r i e d S a t u r a t e d Leda c l a y w i t h cementing agen-tsmmoved and l e a c h e d w i t h C a C l c o n s o l i d a t e d a t 2 kgFcm2 Oven-dried S a t u r a t e d Leda c l a y w i t h cementing a g e n t s removed and l e a c h e d w i t h CaCl2 c o n s o l i d a t e d a t 2 kg/cm2 S a t u r a t e d A i r - d r i e d Water C o n t e n t ,

%

25 2

31

25 4 1 2 30 47 0 29 Dimensions o f samples a s

,%

i n c r e a s e o v e r d r y dimension V e r t i c a l H o r i z o n t a l 1.9 3.2 0 0 8.3 4.5 0.5 3.2 12.9 6.8 0 0 8.1 3.0 a

-

b

-

a

-

b 13.2 11.6 11.2 10.6 0 0 0 0 4 . 8 .

2.7

2.6 2.2

(23)

SAMPLE HOLDER SOIL SAMPLE CLEAR PLASTIC CYLINDER CROSS-SECTION OF PYCNOMETER BOTTLE FOR DETERMINING DRY DENSITY

FIGURE I

(24)

WATER CONTENT Oh

F I G U R E 2

(25)

(26)

-

UNDISTURBED SAMPLE, VERTICAL DIRECTION

-

SAMPLE NO. 8 8 - 9

-

REMOULDED

-

(VERTICAL &

_-

-

UNDISTURBED SAMPLE,

-

+

noRIzoNTPiL ,plREcT,oN I

-

0 10 2 0 30 40 5 0 60 70

WATER CONTENT (PER CENT DRY WEIGHT OF SOIL)

iz!GURE

4 SHRIIN<AGE

CURVES

FOR PRAIRIE CLAY

FROM

(27)

FIGURE

5

(28)

I? -1

-

REMOULDED SAMPLE, MATERIALS REMOVED I N I T I A L W = 4 0 O/! SAMPLE NO. 83- 27

GrJATER CONTENT TO WHICH SAMPLE W A S DRIED

(PER CENT OF DRY VdElGHT OF SOIL)

FIGURE

6 VIAYER

CONTENT REGAIN FOR LEDA CLAY SAMPLES

(29)

WATER CONTENT TO WHICH SAMPLE WAS DRIED O/o

FIGURE

7 DIMENSIONAL REGAIN OF LEDA CLAY SAMPLES ON

WETTING AFTER DRYING

(30)

WATER CONTENT TO WHICH SAMPLE WAS DRIED O/o

F I G U R E

8

(31)

-

_-I

a

2 VERTICAL DIMENSION, UNDISTURBED SAMPLE -ZE!wlENTING MATERIALS HORIZONTAL DI?:4ENSION UNDISTURBED SAMPLE REMOULDED SAMPLE SAMPLE NO. 88-9 Z