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Thixotropy and flow properties of fine grained soils
Ackermann, E.
https://publications-cnrc.canada.ca/fra/droits
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https://nrc-publications.canada.ca/eng/view/object/?id=6d6165a8-b9a3-410e-860c-9020e1c2e635 https://publications-cnrc.canada.ca/fra/voir/objet/?id=6d6165a8-b9a3-410e-860c-9020e1c2e635
N A T I O N A L RESEARCH COUNCIL OF CANADA
TRANSLATION TT
-
150THIXOTROPY AND
FLOW
PROPERTIES OFF I W G R A I N E D SOILS ( T h i x o t r o p i e und F l i e s s e i g e n s c h a f t e n f e i n k b r n i g e r Bbden) 3r. E r n s t Ackerrnann GLI
t
t
ingen R e p r i n t from "Geologische ~ u n d s c h a u " V O ~ .36,
1948.
T r a n s l a t e d byH.
A . G . Nathan T h i s i s t h e Tenth of the S e r i e s of T r a n s l a t i o n s Prepared f o r t h e D i v i s i o n of B u i l d i n g Research 0 ttawa A p r i l , 1950PREFACE
The s o i l s of Canada i n c l u d e a l a r g e p r o p o r t i o n of f i n e - g r a i n e d sediments, the d e p o s i t i o n of which was a s - s o c i a t e d w i t h g l a c i a l a c t i o n . Some of t h e s e s o i l s have most p e c u l i a r p r o p e r t i e s which have a l r e a d y caused a g r e a t d e a l of t r o u b l e i n t h e use of the s o i l s , even i n d i r e c t l y , f o r e n g i n e e r i n g purposes. They a r e , t h e r e f o r e , under d e t a i l e d study by the D i v i s i o n of B u i l d i n g Research which h a s been p r i v i l e g e d t o use t h e s o i l s exposed i n t h e bed of S t e e p Rock Lake, O n t a r i o ( i n iron-mining o p e r a t i o n s ) f o r t h i s purpose
.
The somewhat s t r a n g e phenomenon of t h i x o t r o p y i s one s o i l c h a r a c t e r i s t i c which h a s a l r e a d y a t t r a c t e d t h e a t - t e n t i o n of t h o s e working on t h i s problem. The l i t e r a t u r e d e a l i n g with t h e t h i x o t r o p i c p r o p e r t i e s of s o i l s i s meagre t o a d e g r e e , b u t d e s p i t e t h i s , t h e work of D r . E r n s t Acker- inann of GBttingen, was known t o be o u t s t a n d i n g . D r .
Ackermann k i n d l y agreed t o t h e w r i t e r ' s r e q u e s t t h a t h i s most r e c e n t paper i n t h i s f i e l d might be t r a n s l a t e d i n t o E n g l i s h by t h e Council i n o r d e r t o make i t more g e n e r a l l y a v a i l a b l e . The D i v i s i o n i g t h e r e f o r e p l e a s e d t o have been a b l e t o a r r a n g e f o r t h i s t r a n s l a t i o n by M r . Nathan;
i t
l o o k s forward t o f o l l o w i n g up, w i t h Canadian s o i l s , some of t h e i n t e r e s t i n g work h e r e i n d e s c r i b e d by D r . Ackermann. 9 t h August, 1950, Ottawa. Robert F. Legget, D i r e c t o r , D i v i s i o n of B u i l d i n g Research.
THIXOTROPY AND FLOW PROPERTIES OF FINE GRAINED SOILS
.;:- ) T h i x o t r o p i c Phenomena i n L a b o r a t o r y E x p e r i m e n t s
I f c l a y i s s t i r r e d up w i t h a p p r o x i m a t e l y a n e q u a l amount o f w a t e r i n a t e s t t u b e and t h e l a t t e r t h e n s l o w l y t u r n e d u p s i d e down, t h e c l a y p a s t e s t i c k s t o t h e bottom of t h e t u b e . I f , how- e v e r , t h e t u b e i n t h i s p o s i t i o n i s j o l t e d , pushed o r s h a k e n by t a p p i n g , t h e c l a y p a s t e f l o w s down. A f t e r a s h o r t r e s t p e r i o d , t h e s u s p e n s i o n s t i f f e n s a g a i n s o t h a t on t u r n i n g t h e t u b e r i g h t - s i d e up t h e s u s p e n s i o n no l o n g e r f l o w s . The p r o c e s s
may
be r e - p e a t e d a s o f t e n a s d e s i r e d . Such i s o t h e r m a l , r e v e r s i b l e v i s - c o s i t y changes o f c o n c e n t r a t e d s u s p e n s i o n s o f v e r y f i n e p a r t i c l e s 3: ) P r e s e n t e d a t t h e m e e t i n o f t h e f e l l o w s of t h e " G e o l o g i s c h e V e r e i n i g u n g " , A p r i l ,19
7 . ( D r a f t r e c e i v e d by t h e e d i t o r , s p r i n g , 1947. ) 3;-<:- ) T h i x o t r o p y , which was d i s c o v e r e d i n 1923 by c o l l o i d o - c h e m i c a l r e s e a r c h of S z e g v a r i and S c h a l e c k ( l ) , up t o t h e p r e s e n t h a s s c a r c e l y b e e n t a k e n i n t o a c c o u n t i n s o i l p h y s i c s and g e o l o g y . D i f f e r e n c e s i n s t r e n g t h between u n d i s t u r b e d and remoulded c l a y s were f o r t h e f i r s t t i m e d e s c r i b e d i n 1922 by t h e G e o t e c h n i c a l Commission of t h e Swedish S t a t e Railway ( 2 ) .I n 1937 H v o r s l e v i d e n t i f i e d t h e s e d i f f e r e n c e s a s t h i x o t r o p i c phenomena. I n S w i t z e r l a n d c e r t a i n c h a n g e s i n t h e p r o p e r t i e s o f f r e s h w a t e r l i m e s t o n e s were d e f i n e d a s t h i x o t r o p i c phenomena by R . K a e f e l i
( 3 ) ,
v . h!oos(4)
and R . F. R u t s c h( 5 ) .
I n1945
Ackermann ( 6 a ) proved t h i x o t r o p y o f Norwegian c l a y s (known i n N3rway a s " k v i k k l e i r " ) . The dependence o f t h e i r s t r e n g t h on t h e e l e c t r o l y t e c o n t e n t was shown by I . Th. R o s e n q u i s t( 7 ) .
fl d e t a i l e d e x p l a n a t i o n of t h e v a r i o u s p r o b l e m s a s s o c i a t e d w i t h t h i x o t r o p y i s h a r d l y p o s s i b l e w i t h i n t h e l i m i t e d scope o f t h i s p a p e r . I t was t h e r e f o r e n e c e s s a r y t o o m i t some e x - amples which m i g h t have s e r v e d t o c l a r i f y t h e g e o l o g i c a l a s p e c t s o f t h i x o t r o p y t o r e a d e r s n o t v e r y f a m i l i a r w i t h t h e s u b j e c t . The p r e s e n t r e p o r t on f l o w p r o p e r t i e s and t h e i r d e - pendence on g e o l o g i c a l l y i m p o r t a n t f a c t o r s i s b a s e d c h i e f l y on t h e s t u d y of p o s t g l a c i a l c l a y s i n Norway w i t h s p e c i a l r e f e r e n c e t o t h e i r b e h a v i o u r i n t h e n a t u r a l s t a t e .
a r e c a J l e d t h i x o t r o p y . The e x p e r i m e n t d e s c r i b e d i s a p a r t i c u l a r l y c l e a r example o f t h i x o t r o p y a s i t was o b s e r v e d when t h e phenomena was d i s c o v e r e d . The t e r n " t h i x o t r o p y " h a s s i n c e b e e n e x t e n d e d t o i n c l u d e r e v e r s i b l e v i s c o s i t y c h a n g e s i n m e c h a n i c a l l y d i s - t u r b e d c l a y p a s t e s
( e ) "
and moving f l u i d s( 9 ) .
T h i x o t r o p y i s a b o r d e r - l i n e nhenomenon f o r w h i c h a s y e t t h e r e i s no s a t i s f a c t o r y t h e o r e t i c a l e x p l a n a t i o n . I n a t h i x o - t r o p i c s y s t e m " s o l i d - l i q u i d " , t h e s o l i d p a r t i c l e s do n o t come i n t o immediate c o n t a c t s i n c e t h e y a r e s u r r o u n d e d by a n e n v e l o p e o f w a t e r which s e p a r a t e s them. I n t h e g e l s t a t e t h e p a r t i c l e s b u i l d up a s t r u c t u r e w h i c h i s v e r y l o o s e . I n t h i s s t r u c t u r e t h e f o r c e s l i n k i n g t h e p a r t i c l e s a r e e x t r e m e l y s m a l l . Upon t h e s l i g h t e s t m e c h a n i c a l a g i t a t i o n ( j o l t i n g , s h a k i n g ) t h e s t r u c t u r e b r e a k s down ( s o l s t a t e ) , b u t a f t e r t h e m e c h a n i c a l s t r e s s c e a s e s i t i s r e f o r m e d w i t h i n a c e r t a i n t i m e . O f t h e numerous f a c t o r s a f f e c t i n g t h i x o t r o p y t h e f o l - l o w i n g a r e l i s t e d h e r e : t y p e and c o n c e n t r a t i o n o f t h e d i s p e r s e p h a s e , g r a i n s i z e , g r a i n s h a p e , t y p e o f c l a y m i n e r a l s and i n t e r - c h a n g e a b l e i o n s , and t h e e l e c t r o l y t e c o n t e n t .T h i x o t r o ~ i c Phenomena d u r i n g S o i l Movements i n Norwav
The t h i x o t r o p i c change o f s t a t e " s t i f f - l i q u i d - s t i f f f 1 shown by t h e t e s t c a n a l s o be o b s e r v e d i n f i n e - g r a i n e d s o i l s i n t h e n a t u r a l s t a t e . I n t h e p o s t g l a c i a l v a r v e d c l a y s which r o s e above s e a l e v e l owing t o t h e c o n t i n e n t a l e l e v a t i o n o f S c a n d i - n a v i a , t h e r e i s an i r r e g u l a r o c c u r r e n c e o f q u i c k c l a y . I n t h e s e c l a y s c a t a s t r o p h i c movements o f t h e s o i l a r e f r e q u e n t .
On many o c c a s i o n s t h e s o l i d wooded ground o f a v a l l e y o r of a t e r r a c e h a s been o b s e r v e d f i r s t t o wobble a n d t h e n t o b u r s t w i t h f r i g h t f u l n o i s e , w i t h c l a y e y mud p o u r i n g o u t o f i t
and f l o w i n g d o w n h i l l ( c f . 1 0 b, p. 2 0 , 2 6 ) . B l o c k s o f s u r f a c e d r y - c r u s t w i t h r o o t e d t r e e s f l o a t on t h e p a s t y q u i c k c l a y l i k e i c e f l o e s on a r i v e r and p e o p l e and h o u s e s a r e c a r r i e d away f o r m i l e s ( c f . 1 0 a , p .
5
f f . , and 11). C o n t r a r y t o t h e o b s o l e t e c o n c e p t o f a p e r m a n e n t l i q u i d s t a t e o f s u c h mud m a s s e s , t h e G e o t e c h n i c a l Commission o f t h e Swedish S t a t e R a i l w a y ( c f . 2 , p . 1 7 ) f o u n d t h a t q u i c k c l a y s have no l i q u i d c o n s i s t e n c y when t h e s o i l i s a t r e s t b u t become l i q u i d a s soon a s i t i s i n m o t i o n .The same o b s e r v a t i o n was made when movements r e s e m b l i n g s m a l l s c a l e ground r u p t u r e s o c c u r r e d i n t h e L e r k e d a l r a i l w a y c u t c
2% )
t i n g n e a r Trondhjem." When t h e u p p e r l a y e r s were dredged o u t t h e q u i c k c l a y s , l i k e t h e s o f t - p l a s t i c c l a y s , remained s t a t i o n a r y . Only when t h e e q u i l i b r i u m o f t h e masses was t o o much d i s t u r b e d by s i n k i n g t h e f l o o r o f t h e c u t t i n g t o a d e p t h o f s e v e n m e t r e s d i d t h e ground b r e a k , t h e r u p t u r e s b e i n g c o n f i n e d t o a narrow zone o f q u i c k c l a y . On August 21,
194.4,
a s a n i n d i c a t i o n of t h e impending f i r s t r u p t u r e , a c l e a v a g e t a p e r i n g o f f o b l i q u e l y towards t h e u p p e r edge o f t h e y o u t h s l o p e a p p e a r e d i n t h e 2 . 5 m . t h i c k d r y - c r u s t . R ' i t h i n s e v e r a l h o u r s t h e c l e a v a g e widened by s e v e r a l d e c i m e t r e s . The f o l l o w i n g day a 28 m. wide s e c t i o n o f t h e s l o p e which hadbeen s e p a r a t e d by t h i s c l e a v a g e s l i d down a p p r o x i m a t e l y f o u r m e t r e s , t i l t i n g backwards i n t h e d i r e c t i o n o p p o s i t e t o t h e s l i d i n g s u r f a c e . I t t h e n moved a p p r o x i m a t e l y n i n e m e t r e s i n t o t h e c u t t i n g . I n t h e u p p e r p a r t o f t h e moving e a r t h b l o c k a d d i t i o n a l g a p i n g c l e a v a g e s a p p e a r e d i n t h e d r y - c r u s t . The lower p a r t s o f t h e s o i l c o n s i s t i n g of s a n d y q u i c k c l a y w i t h low s a l t c o n t e n t became p a s t y and poured o u t i n t h e form o f a v i s c o u s mud o n t o t h e 20 m . wide f l o o r o f t h e c u t t i n g a t t h e f o o t o f t h e s l o p e ( s o i l p h y s i c a l i n d i c e s , Table I , No.
4
and7 ) .
The d r y - c r u s t ( a p p r o x i m a t e l y 1 1/2 m . t h i c k ) of t h e s l o p e s u r f a c e r u p t u r e d and s p l i t i n t o s m a l l e r b l o c k s on t o p of t h e f l o w i n g mud. %hen walked upon t h e n e x t d a y , t h e s e b l o c k s were p r e s s e d i n t o t h e mud. Flow b u l g e ss i m i l a r t o t h o s e o f l a v a w i t h c o r d e d - f o l d e d s u r f a c e formed i n some p l a c e s on t h e mud s u r f a c e . These b u l g e s remained i n t h e r a p i d l y f o r m i n g s u r f a c e d r y - c r u s t o f one c e n t i m e t r e t h i c k n e s s . Under t h i s d r y - c r u s t t h e c l a y was s o f t , l i k e p u d d i n g . When knocked w i t h t h e s o l e o f t h e f o o t t h e c l a y became t h i c k - f l o w i n g and f l o w e d u n d e r i t s own w e i g h t . During a r e s t p e r i o d o f ap- p r o x i m a t e l y f o u r weeks
i t
a g a i n became s t r o n g enough t h a t c a r e - f u l d i g g i n g and d r e d g i n g became p o s s i b l e .l?,%en t h e e q u i l i b r i u m o f t h e s l i d i n g mass had been o v e r l y d i s t u r b e d by d r e d g i n g a f a i r l y l a r g e a r e a o f t h e maFses of d i s c h a r g e d q u i c k f l a y , c l e a v a g e s o f
e
m. w i d t h a p p e a r e d on December 1,19&.
On t h e f o l l o w i n g day w i t h i n t h e a r e a o f t h e f i r s t ground r u p t u r e , a n o t h e r15
m . wide s t r i p o f ground r u p t u r e d . 5elow t h e d r y c r u s t , which was t a n g e n t i a l l y s l i c e d i n t o s e v e r a l t i l t i n g b l o c k s , t h e c e n t r e o f t h e m a r s e s o f t h e f i r s t f l o w s l i d e became p a s t y a g a i n , , s h i f t i n g i n p l a s t i c f l o w u n t i l i t r e a c h e d a p o i n t u n d e r t h e b a s e of t h e f o u n d a t i o n t r e n c h and c a u s e d t h e b a s e t o b u l g e up by a p p r o x i m a t e l y one m e t r e w i t h i n a week. -2 ) on which a r e p o r t was r e c e i v e d t h r o u g h t h e c o u r t e s y o f D r .H.
hceixner.
A t t h e p e r i p h e r y o f t h e b u l g e d - u p m a s s e s , c l e a v a g e s h a v i n g a w i d t h up t o 30 c e n t i m e t r e s a p p e a r e d . D u r i n g t h i s minor movement o f t h e ground t h e q u i c k c l a y d i d n ~ t pour o u t on t h e s u r f a c e . A f t e r a n o t h e r r e s t p e r i o d o f a b o u t f o u r weeks t h e q u i c k c l a y had become s t r o n g enough t h a t i t c o u l d be removed w i t h o u t l i q u e f a c t i o n o c c u r r i n g .
The L e r k e d a l q u i c k c l a y s which became l i q u i d f i r s t and t h e n s o l i d a g a i n a r e f o r t h e most p a r t q u i t e syrupy and d i f f e r i n t h i s r e s p e c t from t h e g e n e r a l l y l e s s v i s c o u s q u i c k c l a y s o f m a j o r s o i l - f l o w c a t a s t r o p h e s . But by means of t h e s o i l - p h y s i c a l methods g i v e n below i t c o u l d be p r o v e d t h a t t h e q u i c k c l a y s which become s y r u p y a r e a l s o t h i x o t r o p i c
a able
I , No.6
and9 ) .
I m ~ o r t a n t P r o ~ e r t i e s of Norwegian E l u e C l a s s
n u r i n g t h e r e t r e a t o f t h e c o n t i n e n t a l g l a c i a t i o n , p u l - v e r i z e d m a t t e r c a r r i e d i n t o t h e s e a by t h e g l a c i a l w a t e r s was de- p o s i t e d i n t h e c o a s t a l r e g i o n s o f Norway a s a n u n s t r a t i f i e d b l u e mud. These d e p o s i t s , r e f e r r e d t o a s " b l u e c l a y " , v a r y i n t h e i r g r a i n - s i z e d i s t r i t , u t i o n between f a t c l a y and f i n e s a n d w i t h low c l a y c o n t e n t . According t o e l u t r i a t i o n a n a l y s e s ( c f . T a b l e I ) t h e s e d e p o s i t s c o n t a i n c h i e f l y p a r t i c l e s o f 2-20 p d i a m e t e r , and, a c c o r d i n g t o t h e n o m e n c l a t u r e o f C o r r e n s ( 1 2 ) , a r e t h u s t o be c l a s s i f i e d a s c o a r s e c l a y s o r s i l t s ( ~ i g . 2 ) . P a r t i c l e s o f d i a m e t e r C 2/1 were o b t a i n e d f r o m a sandy c o a r s e c l a y (No. 7 6 , c f . F i g . 2 ) a t t h e f o o t of Raa moraine by e l u t r i a t i o n a n a l y s i s . P h o t o g r a p h q o f t h e s e p a r t i c l e s t a k e n w i t h t h e a i d o f a n e l e c t r o n m i c r o s c o p e " show t h a t t h i s f i n e - c l a y f r a c t i o n f o r t h e most p a r t c o n s i s t s of p a r t i c l e s o f
1/5
t o 1 / 2 0 p d i a m e t e r . Hence e v e n s o i l s w i t h a low p e r c e n t a g e of c l a y - s i z e s may c p n t a i n a r e l a t i v e l y l a r g e number o f g r a i n s o f v e r y s m a l l d i a m e t e r . T h i s i s s i g n i f i c a n t f o r t h e t h i x o t r o p i c b e h a v i o u r o f r e l a t i v e l y c o a r s e - g r a i n e d s e d i - ments ( f i n e s a n d s ) . M i n e r a l c o n t e n t and c o l o u r o f t h e b l u e c l a y s v a r y w i t h t h e p e t r o g r a p h i c c o m p o s i t i o n o f t h e i r r e g i o n o f o r i g i n( 1 3 ) .
A s t h e f i n e n e s s of g r a i n i n c r e a s e s t h e c o n t e n t o f f e l d s p a r and q u a r t z d e c r e a s e s , w h i l e t h e c o n t e n t o f mica and c l a y - m i n e r a l s i n - c r e a s e c o n s i d e r a b l y . C l a y - m i n e r a l s c a p a b l e o f s w e l l i n g and$ 1
t h r o u g h t h e c o u r t e s y o f D r . Helmcke, who u s e d Siemens andh a v i n g a l o o s e l y - b o u n d l a y e r - l a t i c e s u c h a s t h a t o f m o n t m o r i l l o - n i t e a r e l a c k i n g i n b l u e c l a y
'?.
A s t h e S - v a l u e s e s t a b l i s h e d byF
E n d e l l( 1 5 )
show, t h e b a r e exchange c a p a c i t y o f sampleq t a k e n n e a r Koss and Oslo i s s i m i l a r t o t h a t o f t h e D a n i s h c l a y s ( r i c h i n sodium) l i s t e d ky c e i f e r t , E h r e n b e r g e t a 1( 1 6 ) .
The normal p l a s t i c b l u e c l a j l i e s u n d e r a s u r f a c e d r y - c r u s t o f a n a v e r a g e t h i c k n e s s o f two t o t h r e e m e t r e s . I t c o n t a i n s i n a d d i t i o n t o ? o r e w a t e r ( f r o m2 5
t o75
p e r c e n t by w e i g h t ) , a c o n s i d e r a b l e amount o f i t s o r i g i n a l w a t e r c o n t e n t and s e a s a l t s i n s o l u t i o n . I n g e n e r a l , b l u e c l a y c o n t a i n s 50 p e r c e n t w a t e r and may be r e g a r d e d a s a s u s p e n s i o n . D e s p i t e i t s h i g h w a t e r c o n t e n t b l u e c l a y u s u a l l y h a s a s o f t - p l a s t i c o r l i q u i d - p l a s t i c c o n s i s t e n c y ( F i g .3 ) .
When kneaded o r s t i r r e d i t l o s e s most o fi t s s t r e n g t h and becomes a v i s c o u s , do ~ h ) p a s t e I t t e n d s t o p l a s t i c f l o w o n l y when s u b j e c t e d t o p r e s s u r e . I n normal t l u e c l a y t h e r e i s a n i r r e g u l a r o c c u r r e n c e o f q u i c k c l a y . If t y p i c a l q u i c k c l a y i s t h o r o u g h l y s t i r r e d , i t s s t r e n g t h d e c r e a s e s s o ~ u c h t h a t i t t e c o m e s a t h i c k - f l o w i n g p a q t e , i . e . , a ~ a s t e which f l o w s from a n i n c l i n e d g l a g s t u b e u n d e r i t s own w e i g h t a l o n e Between t h i s q u i c k c l a y which become- t h i c k - f l o w i n g a n d t h e normal s o f t - p l a s t i c b l u e c l a y t h e r e a r e i n t e r - 3 e d i a t e f o r m s s u c h a s q u i c k c l a y s which become s y r u p y . I n t h e l a t t e r c a s e , i n a d d i t i o n t o t h e f o r c e o f g r a v i t y , m e c h a n i c a l a g i t a t z u n i s r e q u i r e d t o make t h e p a s t e f l o w , f o r i n s t a n c e , con- t i n u o u s v i t r a t i o n s ( k n o c k i n g , s h a k i n b ) a r e r e q u i r e d f o r t h e q u i c k c l a y t o f l o w o r t r i c k l e f r o t h e i n c l i n e d g l a ~ s t u b e - - l i k e v i s c o u s s y r u p . Thlck-flow i n & q u i c k c l a y s a r e w i d e l y mown from numerous l a n d s l i d e c a t a s t r o p k e s . Howev r , q u l c k c l a v s which t e n d t o ue- come s y r u p y a r e r e f e r r e d t o i n Norway a s b l 8 t l e l r ( s o f t c l a y ) a n d a r e f r e q u e n t l y c o n s i d e r e d " k v i k k a g t i g " ( " a p t t o f l o w " i , e . , c l a y s w i t h i n h e r e n t f l o w d a n g e r ) . They a r e n o t c l a s s i f i e d a s " k v i k k l e i r " ( q u i c k c l a y ) a l t h o u g h t h e y , t o o , p a r t i c i p a t e i n s o l 1 f l o w s and t h e i r slow movements a r e a n i m p o r t a n t f a c t o r c a u s i n g daaage t o c o n s t r u c t i o n
-:: )
Neitk.er Norwegian n o r German r e s e a r c h s u c c e e d e d i n d e t e c t i n g c l a y - m i n e r a l s w i t h l o o s e l y - b o u n d l a y e r - l a t t i c e i n b l u e c l a y . Acknowledgment: The X - r a y o p t l c a l and c o l l o i d o - c h e m i c a l i n - v e s t i g a t i o n s were c a r r i e d o u t by P r o f . I?'. C o r r e n s and D r . K.
Proof of T h i x o t r o p y by Means of t h e S t i f f n e s s L i m i t I n o r d e r t o o b t a i n a n i n d e x comparable t o t h e A t t e r b e r g l i m i t s o f c o n s i s t e n c y ( 1 7 ) i.t i s a d v a n t a g e o u s t o modify t h e v o i d r a t i o ( ~ r e n z v ~ e r t ) s u g g e s t e d by H . Winkler
( 9 ) , i
. e . , t h e r a t i o : volume of l i q u i d t o volume of s o l i d . Py n e g l e c t i n g t h e s p e c i f i c g r a v i t y , which i s i n c l u d e d i n t h e v o i d r a t i o , t h e f f s t i f f e n i n g l i m i t f 1 i s o b t a i n e d ( F i g .3 ) .
The s t i f f e n i n g l i m i t g i v e s i n p e r c e n t by w e i g h t t h e w a t e r c o n t e n t a t which, a f t e r a s t i f f e n i n g time of e x a c t l y one m i n u t e , a t h o r o u g h l y s t i r r e d , f i n e g r a i n e d , t h i x o - t r o p i c s o i l s t i l l f l o w s under i t s own w e i g h t i n a t u b e o f 11 mm. d i a m e t e r ( cf.
p .1 7
and 1 8 ).
The f o l l o w i n g method ( " i n v e r t e d t u t e method") i s u s e d t o d e t e r m i n e t h e s t i f f e n i n g l i m i t . A f t e r d e t e r m i n a t i o n o f t h e w a t e r c o n t e n t , wet c l a y ( i f p o s s i b l e i n t h e n a t u r a l - w e t s t a t e ) c o n t a i n i n g 1 gm. d r y s u b s t a n c e i s mixed d r o p by d r o p w i t h d i s - t i l l e d w a t e r i n a t e s t - t u b e o t 11 ( t o
15)
mm. i n n e r d i a m e t e r . The s i z e of t h e d r o p s i s measured ~ i t h a p i p e t t e . A t t h e t e r m i n a t i o n of t h e t e s t the t o t a l w a t e r c o n t e n t i s checked by w e i g h i n g . T h i s i s n e c e s s a r y i f a c a l i b r a t e d p i p e t t e of 1c c .
c a p a c i t y i s n o t a v a i l a b l e . Such a p i p e t t e i s o f c o u r s e u s e f u l s i n c e t h e amount of w a t e r added can be r e a d d i r e c t l y i n c c . A f t e r t h e f i r s t d r o p h a s been added t h e n a t u r a l - w e t c l a y i s c a r e f u l l y s t i r r e d w i t h a g l a s s r o d of 2 mm. t h i c k n e s s f o r a t l e a s t 20 m i n u t e s and a f t e r e a c h ad- d i t i o n a l d r o p f o r t e n m i n u t e s . Tlje s t i r r e d c l a y - w a t e r m i x t u r e i s l e f t t o r e s t w i t h o u t t h e r o d ".
A f t e r e x a c t l y one minute t h etube
i s r a p i d l y t u r n e d u p s i d e down i n o r d e r t o d e t e r m i n e w h e t h e r t h e p a s t e f l o w s down t h e t u b e w a l l s under i t s own w e i g h t . T h i s f l o w t e s t i s r e p e a t e d e v e r y t i m e a d r o p i s added, t h e p a s t e s t i r r e d and t h e s e t t i n g time of one minute o b s e r v e d . When t h e p a s t e b e g i n s t o f l o w t h e s t i f f e n i n g l i m i t h a s j u s t been e x c e e d e d . The w a t e r c o n t e n t (minus t h e l a s t d r o p ) a t which t h e s t i r r e d c l a y i s j u s t on t h e verge o f f l o w i n g a f t e r e x a c t l y one m i n u t e ' s r e s t and i s l i q u i d when s t i r r e d i s t h e s t i f f e n i n g l i m i t . The w a t e r c o n t e n t t h u s d e t e r m i n e d i s checked i n e a c h c a s e by two a d d i t i o n a l t e s t s .LOW s t i f f e n i n g l i m i t s ( i n most c a s e s 30 t o
60
p e r c e n t )i n d i c a t e weak t h i x o t r o p y and h i g h l i m i t s ( m o s t l y o v e r 100 p e r c e n t )
-::- )
The e x p e r i m e n t a l method s u g g e s t e d h e r e d i f f e r s from t h a t r e - comnended i n t h e f i r s t German v e r s i o n and a p p r o x i m a t e s t h e method g i v e n by P . G . H . Boswell. ( 3 5 ) .
a h i g h d e g r e e o f t h i x o t r o p y . A t h i g h s t i f f e n i n g l i m i t s t h e c h a n g e s i n t h i x o t r o p i c p r o p e r t i e s a r e more d i s t i n c t l y pronounced and s h o r t e r s t i f f e n i n g t i m e s may be e x p e c t e d . The f a c t o r s which b r i n g a b o u t c o n s o l i d a t i o n a r e u n i f o r m l y d i s t r i b u t e d i n t h e whole system
( 1 8 ) .
T h e r e f o r e , t h e v o i d r a t i o , and t h u s t h e s t i f f e n i n g l i m i t i s n o t changed by t h e q u a n t i t y o f t h e sample o r i t s h e i g h t i n t h e t e s t t u b e .
The s t i f f e n i n g l i m i t s a r e c o m p a r a t i v e f i g u r e s f o r e s t i - m a t i n & t h e t h i ~ o t ~ r o p i c p r o p e r t i e s of' f i n e - g r a i n e d s o i l s and a p p l y
o n l y t o s m a l l s a m p l e s . ';"he? t h e s e v a l u e s a r e e v a l u a t e d i t must be remembered t h a t a s o i l which i s a p t t o f l o w and which h a s t h e w a t e r c o n t e n t o f t h e s t i f f e n i n g l i m i t s t i f f e n s u n d e r t h e w e i g h t o f t h e q u a n t i t y chosen h e r e , b u t s t i l l f l o w s u n d e r t h e l a r g e r w e i g h t , e
.g.
a s a n p l e s t i f f e n i n g i n a p r e s e r v i n g j a r . \'!hen s u b j e c t e d t o i n c r e a s e d s h e a r i n g s t r e s s e s t h e q u i c k s o i l h a s a r e l a t i v e l y lower v i s c o s i t y . T h e r e f o r e t h e w a t e r c o n t e n t of t h e s t i f f e n i n g l i m i t c a n n o t be u s e d a s a c o n s t a n t v a l u e f o r e s t i m a t i n g t h e b e h a v i o u r o f l a r g e : n a s s e s of s o i l . The s t i f f e n i n g l i m i t c o u l d be u s e d a s a means t o p r o v e t h a t t h e g l a c i a l b l u e c l a y s and q u i c k c l a y s o c c u r r i n g i n Norway ( i . e . , from f a t c l a y t o f i n e s a n d w i t h low c l a y c o n t e n t ) a r e t h i x o t r o p i c ( c f . T a b l e I ) . A method i s g i v e n below f o r m e a s u r i n g t h e c h a n g e s i n v i s c o s i t y and s t r e n g t h o c c u r r i n g when t h i x o t r o p i c s o i l s a r e d i s t u r b e d and t h e n l e f t t o s e t t l e . T h i s method may a l s o be u s e d t o p r o v e t h i x o t r o p y (p.14. ).
Dependence of T h i x o t r o p i c Phenomena on t h e Ip!ater C o n t e n t
The " n a t u r a l w a t e r c o n t e n t " a s t h e c r i t e r i o n of t h e con- c e n t r a t i o n of t h e d i s p e r s e p h a s e g r e a t l y a f f e c t s t h e f l o w p r o - p e r t i e s o f n a t u r a l s o i l s . I n a d d i t i o n t o t h e c o n t e n t o f e l e c t r o - l y t e , o r g a n i c s u b s t a n c e , e t c . , i t d e t e r m i n e s t h e c o n s i s t e n c y a s d e f i n e d by A t t e r b e r g ( 1 7 ) . To A t t e r b e r g ' s s t a t e s o f c o n s i s t e n c y a n o t h e r s t a t e must be a d d e d , namely t h a t produced by t h e change i n c o n s i s t e n c y o f q u i c k c l a y s o'cserved i n l a b o r a t o r y e x p e r i m e n t s a s w e l l a s i n n a t u r e .
I f t h e w a t e r c o n t e n t o f a c l a y i s h i g h e r t h a n t h e l i q u i d l i m i t
"1
t h e n t h e c l a y i s n o t i n a p e r m a n e n t - l i q u i d s t a t e,
b u t i n +:- )The l i q u i d l i m i t i s t h e w a t e r c o n t e n t a t which a sample o f
8
rnm.h e i g h t f l o w s t o g e t h e r a l o n g a 2 mm. wide g r o o v e i n C a s a g r a n d e ' s a p p a r a t u s f o r a d i s t a n c e o f 1 3 mm. when s u b j e c t e d t o 2 5 blows.
a l a t e n t - l i q u i d o r q u a s i - s o l i d s t a t e , i . e . , t h e c l a y c a n tem- p o r a r i l y become l i q u i d . The l i q u i d s t a t e c a u s e d by v i b r a t i o n s o r s t i r r i n g i s r e p l a c e d by a q u a s i - s o l i d s t a t e a f t e r a c e r t a i n r e s t p e r i o d o r time o f s t i f f e n i n g . The b e h a v i o u r o f t h e c l a y i s t h i x o t r o p i c o r " q u i c k " ( 6 b )
.
Hence between t h e p e r m a n e n t - p l a s t i c and p e r m a n e n t - l i q u i d c o n s i s t e n c i e s d e f i n e d by A t t e r b e r g t h e r e i s t h e q u i c k c o n s i s t e n c y , i . e . , a q u a s i - s o l i d s t a t e w i t h p o s s i b l e temporary l i q u e f a c t i o n by mere m e c h a n i c a l a c t i o n ( F i g .3 ) .
The d u r a t i o n o f t h i x o t r o p i c l i q u e f a c t i o n and t h e minimum v i s c o s i t y depend on t h e d e g r e e of t h i x o t r o p y .The " s t i f f e n i n g l i m i t " i s s u g g e s t e d a s t h e boundary be- tween q u i c k and l i q u i d c o n s i s t e n c i e s . Hence t h e n e g a t i v e v a l u e s of t h e c o e f f i c i e n t of f l o w d a n g e r , f , g i v e t h e " q u i c k c o n s i s t e n c y " of a s o i l i n t h e n a t u r a l s t a t e o r i t s "tendency t o flow": f = l i q u i d l i m i t minus w a t e r c o n t e n t s t i f f e n i n g l i m i t minus l i q u i d l i m i t The n e g a t i v e v a l u e s of t h e c o n s i s t e n c y f a c t o r s i n t r o d u c e d by S c h e i d i g ( 2 0 ) may a l s o be used i f s u i t a b l e . S i n c e t h e l i q u e f a c t i o n of q u i c k s o i l s depends on t h e s u p p l y o f a c e r t a i n amount o f e n e r g y , s o i l s i n d e c l i v i t i e s h a v i n g q u i c k c o n s i s t e n c y may f o r a l o n g time have a n a p p a r e n t s t a b i l i t y u n t i l t h e whole mass o f s o i l suddenly becomes t e m p o r a r i l y l i q u i d t h r o u g h v i b r a t i o n s , o v e r l o a d , e x c e s s i v e p r e s s u r e i n t h e p o r e w a t e r o r o t h e r d i s t u r b a n c e s .
I f t h e w a t e r c o n t e n t i n c r e a s e s beyond t h e s t i f f e n i n g
l i m i t , t h e time o f s t i f f e n i n g i s e x t e n d e d . These t h i x o t r o p i c v i s - c o s i t y changes a l s o o c c u r when p a s t y - l i q u i d mud i s d i s t u r b e d .
C,%ere t h e s t a t e o f l i q u i d c o n s i s t e n c y s h o u l d b e g i n i s y e t t o be s e t t l e d .
R e l a t i o n s h i p between Flow P r o p e r t i e s o f Norwegian Blue C l a y s and Content of Clay S i z e s and Water
I n n a t u r a l s o i l s t h i x o t r o p y i s c o n f i n e d t o f i n e - g r a i n e d s o i l s . When t h e s t r u c t u r e of n o n - c o n s o l i d a t e d , l o o s e - p a c k e d , m o i s t s o i l s i s d i s t u r b e d , t h i x o t r o p y becomes e v i d e n t by p a r t i a l l y r e - v e r s i b l e v i s c o s i t y changes, i r r e s p e c t i v e o f t h e c o n s i s t e n c y of t h e s o i l ( p l a s t i c , q u i c k o r l i q u i d ) . T h e r e f o r e a d i s t i n c t i o n must be made between q u i c k o r t h i x o t r o p i c c o n s i s t e n c y and t h i x o t r o p i c p r o - p e r t i e s , o r between " a b i l i t y t o f low" and " a p t n e s s t o f low". The
two t e r m s s u g g e s t e d h e r e c a n n o t be c o n f i n e d t o t h i x o t r o p i c s o i l s a l o n e , s i n c e , a s w i l l be shown below, danger o f flow a190 o c c u r s i n
non- t h i x o t r o p i c s o i l s . S o i l s a p t t o f l o w ( f ' f 3 i e s s g e f ~ h r l i c h " ) a r e t h o s e which,
a t
t h e waber c o n t e n t of t h e n a t u r a l s t a t e , may become l i q u i d i f t h e r e a r e p o s s i b i l i t i e s o f f l o w i n g away.S o i l s a b l e t o f l o w ( " f l i e s s t a u g l i c h r ' ) may become a p t t o f l o w upon a b s o r p t i o n of s u f f i c i e n t w a t e r o r d e c r e a s e i n e l e c t r o l y t e c o n t e n t . Assuming t h a t t h e t h i x o t r o p i c b e h a v i o u r i s a f u n c t i o n o f g r a i n s i z e a n d g r a i n - s i z e d i s t r i b u t i o n , d i s r e g a r d i n g f o r t h e t i m e b e i n g t h e e f f e c t o f e l e c t r o l y t e c o n t e n t and t a k i n g t h e Norwegian q u i c k c l a y s ( f o r w h i c h a c o n t e n t o f homogeneous c l a y m i n e r a l s may be assumed a s a r u l e ) a s a n e x a m p l e , t h e n i t f o l l o w s f r o m t h e s t i f - f e n i n g l i m i t ( c f . T a b l e I ) t h a t t h e d e g r e e o f t h i x o t r o p y i n c r e a s e s a s t h e c l a y c o n t e n t i n c r e a s e s . T h i s was p r o v e d f o r m i n e r a l powders by W i n k l e r i n
1938
( c f .9 ) .
The d e p e n d e n c e o f o t h e r s o i l - p h y s i c a l p r o p e r t i e s on t h e c o l l o i d a l c o n t e n t was p o i n t e d o u t by Z n d e l l , Loos e t a l .( 1 5 ) .
F a t c l a y w i t h a h i g h c o n t e n t o f c l a y - s i z e s must ab- s o r b a g r e a t d e a l o f w a t e r b e f o r e i t c a n l i q u e f y . I t s l i q u i d l i m i t i s i n t h e c a s e o f Norwegian c l a y s g e n e r a l l y above 4 0 p e r c e n t . F a t c l a y h a s an a v e r a g e t o h i g h d e g r e e o f t h i x o t r o p y ( s t i f - f e n i n g l i m i t above6 5 ) ,
w h e r e a s a l e a n c o a r s e c l a y ( s i l t ) , w h i c h h a s a p p r o x i m a t e l y t h e same e l e c t r o l y t e c o n t e n t and c o n t a i n s t h e same c l a y m i n e r a l s , c a n a b s o r b b u t l i t t l e w a t e r o n a c c o u n t o f i t s low c o n t e n t o f c l a y s i z e s . I t k e g i n s t o become s y r u p y a t w a t e r c o n t e n t s a s low a s 20 p e r c e n t and i t s s t i f f e n i n g l i m i t ( l o w e r t h a n 1 0 0 ) i n d i c a t e s weak t h i x o t r o p y . I f t h e e x a m p l e s shown i n F i g u r e4
a r e compared a t a w a t e r c o n t e n t o f 20 p e r c e n t i t c a n be s e e n t h a t t h e f i n e c l a y i s s o l i d , t h e c o a r s e c l a y p l a s t i c a n d t h e c l a y e y f i n e s a n d l i q u i d . The l a t t e r h a s t h e g r e a t e s t t e n d e n c y a n d a b i l i t y t o f l o w . The a b i l i t y t o f l o w i s i n v e r s e l y p r o p o r t i o n a l t o t h e t h i x o t r o p y.
Because o f i t s h i g h deg,ree o f t h i x o t r o p y , a f i n e c l a y--
w i t h a n optimum c o n t e n t of w a t e r and e l e c t r o l y t e r e q u i r e d f o r t h e t h i x o t r o p i c l i q u e f a c t i o n--
may become more h i g h l y l i q u i d a n d t h u s more a p t t o f l o w t h a n a c o a r s e c l a y . The c r i t e r i o n f o r t h e d a n g e ro f f l o w i s t h e d e g r e e o f v i s c o s i t y i n t h e l i q u i d s t a t e ( E l v a l u e o f t h e S w e d i s h c o n e t e s t s ) . The c r i t e r i o n f o r t h e a b i l i t y t o f l o w i s t h e minimum w a t e r c o n t e n t a t w h i c h l i q u e f a c t i o n o f a s o i l c a n o c c u r . C a s a g r a n d e ( 2 1 a ) d e f i n e d t h i s by t h e l i q u i d l i m i t . T h i s , v i z . t h e minimum w a t e r c o n t e n t , i s l o w e r f o r loam and c l a y e y f i n e s a n d t h a n f o r c l a y and e v e n - g r a i n e d f i n e s a n d c o n t a i n i n g no c l a y .
The a b i l i t y t o f l o w i n c r e a s e s a s t h e c l a y c o n t e n t i n - c r e a s e s . A c c o r d i n g l y a more f r e q u e n t o c c u r r e n c e o f t h e d a n g e r o f f l o w must be e x p e c t e d f o r c o a r s e c l a y s , loams and c l a y e y f i n e s a n d s on a c c o u n t of t h e i r g r a i n - s i z e d i s t r i b u t i o n a n d t h e i r low w a t e r - a b s o r p t i o n c a p a c i t y ( F i g .
s ) .
Flow P r o p e r t i e s o f Sandy S o i l s
As c a n be s e e n from T a b l e I (No.
14,
1 7 , 2 0 ) t h e t h i x o - t r o p i c a b i l i t y t o f l o w a l s o e x t e n d s t o c o h e s i v e s o i l s composed p r e p o n d e r a n t l y o f sand and c a n be found e v e n i n f i n e s a n d s c o n - t a i n i n g c o a r s e c l a y w i t h few c l a y - s i z e s ( i . e . , a few p e r c e n t , c f . T a b l e I No. 2 ,3 ) .
I n c o n f o r m i t y w i t h t h i s , F r e u n d l i c h andJ u l i u s k u r g e r ( 2 2 ) proved d i s t i n c t t h i x o t r o p y f o r t h e q u i c k s a n d from Knott End, F l e e t w o o d . T h i s q u i c k s a n d c o n t a i n e d o n l y 2 . 1 p e r c e n t c l a y . The l o e s s of D e r e n t u r g which, a c c o r d i n g t o H . J u n g , c o n t a i n s a p p r o x i m a t e l y
3
p e r c e n t m o n t r n o r i l l o n i t e a l s o hap- p e n s t o be t h i x o t r o p i c .However, a i n c e s a n d s u s u a l l y show pronounced d i l a t a n c y ; $ ) and t h e d i a m e t e r o f t h e i r g r a i n s i s above t h e l i m i t ( o f
S p
)up t o which Brownian movements a r e s t i l l marked. The o b s e r v e d t h i x o t r o p y seems s u r p r i s i n g . A c c o r d i n g t o F r e u n d l i c h
( 8 )
a d - d i t i o n s o f s m a l l q u a n t i t i e s ( a p p r o x i m a t e l y 2 t o4
p e r c e n t ) o f a c o l l o i d which promotes t h i x o t r o p y a r e s u r f i c i e n t t o e n v e i o p ~ t h e l a r g e r p a r t i c l e s s o t h a t t h e l o o s e p a c k i n g r e q u i r e d f o r t h e t h i x o t r o p y i s c r e a t e d . Loose p a c k i n g , a s i t i s c h a r a c t e r i z e d by a h i g h p o r o s i t y e x c e e d i n g t h e " c r i t i c a l p o r o s i t y " o f Casagrande ( 2 3 ),
was r e c o g n i z e d a s e a r l y a s 1925 by v . T e r z a g h i ( 2 4 ) a s one of t h e i n d i s p e n s a t l e c o n d i t i o n s f o r t h e o c c u r r e n c e o f q u i c k s a n d phenomena, e s p e c i a l l y o f flovr s l i d e s due t o s e t t l e m e n t . A c c o r d i n g t o R . C l o s -sop and A . Yi. Skempton (25'), v. T e r z a g h i assumes a honeycomb s t r u c t u r e s i m i l a r t o t h a t assumed by Casagrande ( 2 1 b ) f o r c l a y s . A . Zucken ( 2 6 ) assumed a s i m i l a r s t r u c t u r e f o r t h i x o t r o p i c s u s -
p e n s i o n s , t h o u e h i n a somewhat d i f f e r e n t way. The t y p e of s t r u c t u r e i s c o n t r o v e r s i a l . However, s i n c e t h e l a r g e p a r t i c l e s a r e e n v e l o p e d by t h e s m a l l e r ones i t i s s a f e t o assume t h a t t h e p h y s i c o - c h e m i c a l p r o p e r t i e s of t h e l a r g e r p a r t i c l e s a r e r e p l a c e d by t h o s e o f t h e s m a l l p a r t i c l e s w i t h marked e f f e c t on t h e boundary a r e a s .
The few a v a i l a b l e i n v e s t i g a t i o n s show t h a t n o t a l l t h e f l o w i n g o r s i m i l a r s a n d s ( " T r i e b - , F l i e s s - o d e r Schwimmsandet' ) h i t h e r t o d e s i g n a t e d a s q u i c k s a n d s a r e t h i x o t r o p i c . The a p t n e s s
-- - -- -
<:-) D i l a t a n c y o r Osborne H e y n o l d t s phenomenon ( c o n t o r t e d d i l a t i o n i n t h e s e n s e o f S a n d e r ) i s a s s o c i a t e d w i t h c l o s e p a c k i n g . When b e i n g walked upon, wet s e a sand becomes d r y s i n c e t h e g r a i n s a r e d i s p l a c e d t o a l o o s e p a c k i n g . When t h e p r e s s u r e c e a s e s t h e g r a i n s r e v e r t t o t h e i r c l o s e p a c k i n g and t h e s a n d becomes wet a g a i n .
of s u c h s a n d s t o f l o w d e p e n d s on f a c t o r s o t h e r t h a n t h o s e making t h i x o t r o p y p o s s i b l e . These unknown f a c t o r s ( p e r h a p s u n i f o r m g r a i n s i z e , mica c o n t e n t ) have y e t t o be d i s c o v e r e d . I t i s sug- g e s t e d , t h e r e f o r e , t h a t t h e t e r m q u i c k s a n d be C o n f i n e d t o c l e a r l y t h i x o t r o p i c s a n d s . N o n - t h i x o t r o p i c s a n d s which a r e a p t t o f l o w s h o u l d be c l a s s i f i e d a c c o r d i n g t o t h e c a u s e s o f t h i s a p t n e s s , f o r example a s " d r i f t s a n d s " ( ' ' T r i e b s a n d e " ) i n t h e c a s e o f e v i d e n t f l o w p r e s s u r e and a s " f l o a t i n g sands'' ("Schwimrnsande" ) i f t h e w a t e r c o n t e n t i s h i g h . I n s u c h s a n d s t h e p a c k i n g i s s u f f i c i e n t l y l o o s e t o c r e a t e a t e n d e n c y t o f l o w . However, t h e t r u e t h i x o t r o p i c s t r e n g t h c y c l e , which d e p e n d s on c o n s t a n t w a t e r c o n t e n t , i s n o t p o s s i b l e . Danger o f f l o w
--
o r t e n d e n c y t o f l o w--
i s a c h a r a c - t e r i s t i c n o t o n l y o f t h i x o t r o p i c s o i l s b u t a l s o o f l o o s e l y p a c k e d s o i l s w h i c h . u p o n d i s t u r b a n c e o f t h e i r s t r u c t u r e become l i q u i d by a s p o n t a n e o u s d e c l i n e i n s t r e n g t h a n d m u s t y i e l d w a t e r a n d r e - v e r t t o c l o s e p a c k i n g i n o r d e r t a become s o l i d a g a i n . F o r many " f l o a t i n g s a n d s " , and a l s o i n t h e c a s e o f c o a r s e r s o i l s w h i c h a r e a p t t o f l o w ( s u c h a s s l i d e r o c k , m a t e r i a l o f mud f l o w , e t c . ) , l o o s e p a c k i n g i n a d d i t i o n t o s a t u r a t i o n w i t h w a t e r i s , a c c o r d i n g t o v . T e r z a g h i (21!), t h e c o n d i t i o n f o r t h e s p o n t a n e o u s s e t t l e m e n t i n i t i a t i n g t h e f l o w p r o c e s s . Loose pack- i n g i s characterized by h i g h p o r o s i t i e s , which, a c c o r d i n g t o L a n g e r ( 2 7 ) amount t o x o r e t h a n4 7
p e r c e n t i n t h e f l o a t i n g s a n d s o f Y p r e s . T h i s i s a v e r y h i g h v a l u e a s compared w i t h t h a t f o r t h e low p o r o s i t i e s o f t h e c l a y e y q u i c k s a n d s g i v e n i n T a b l e I (No. 2 ) . A s m e n t i o n e d above, t h e t h i x o t r o p i c a b i l i t y t o f l o w o f t h e s a n d y q u i c k c l a y s i n c r e a s e s w i t h d e c r e a s i n g c o n t e n t o f c l a y - s i z e s and t h e r e s u l t i n g c o a r s e n i n g of g r a i n a s w e l l a s t h e d i m i - n i s h e d w a t e r - a b s o r p t i o n c a p a c i t y . On t h e o t h e r hand, a s was shown by v . T e r z a g h i ( 2 8 ) , t h e m o b i l i t y o f c o a r s e r s o i l s d e c r e a s e s a s t h e g r a i n s i z e i n c r e a s e s . A t t h e same t i m e t h e p e r m e a b i l i t y i n c r e a s e s s o t h a t c o a r s e s a n d s c a n g i v e o f f p o r e w a t e r more r a p i d - l y , t h e r e b y s h o r t e n i n g t h e s t a t e s o f l i q u e f a c t i o n and r e s o l i d i - f i c a t i o n . I n sandy s o i l s t h e a b i l i t y t o f l o w t h u s i n c r e a s e s a s t h s c o a r s e n e s s o f g r a i n i n c r e a s e s and t h e u n i f o r m i t y o f g r a i n s i z e d e c r e a s e s . Hence a maximum a b i l i t g t o f l o w r e s u l t s f o r t h e f i n e s a n d s , e s p e c i a l l y f o r t h e c l a y e y o n e s ( F i g .5').
I t t h u s becomes e v i d e n t why q u i c k s a n d s a r e g e n e r a l l y known, w h e r e a s q u i c k c l a y s , w i t h a few e x c e p t i o n s , h a v e r e m a i n e d unknown o r f o rt h e o r e t i c a l r e a s o n s h a v e n o t b e e n s u s p e c t e d a s s u c h owing t o t h e c o h e s i v e f o r c e s a c t i n g i n them ( h . G l o s s o p a n d A . In]. Skempton,
1941,
p . 2 1 ) . S i l t s which a r e a p t t o f l o w and h a v e o t h e r p r o p e r - t i e s t h a n t h o s e o f t h e Norwegian c l a y s h a v e been d e s c r i b e d by R . F. L e g g e t , Canada ( 2 9 ) .The t h r e s h o l d v a l u e of t h e a b i l i t y t o f l o w f o r c o a r s e c l a y s a n d f i n e s a n d s h a s a p a r a l l e l phenomenon i n t h e s o i l s o f s i m i l a r g r a i n - s i z e d i s t r i b u t i o n which A . C a s a g r a n d e f o u n d t o t-e p a r t i c u l a r l y a p t t o f r e e z e . P r e s u m a b l y c e r t a i n p r o p e r t i e s i m - p o r t a n t f o r b o t h phenomena, s u c h a s l c o s e p a c k i n g and permea- b i l i t y , a r e p a r t i c u l a r l y p r o n o u n c e d i n t h e s e s o i l s . I n t h e s e n s e o f s u c h c l o s e r e l a t i o n s h i p s t h e c r e s c e n t - s h a p e d s h e l l i n g o f f r o z e n s o i l s ( l i k e s h e l l i n g of s o d s ) o c c u r r i n g i n Norwegian b l u e - c l a y d e p o s i t s i s o b s e r v e d w i t h r e m a r k a b l e f r e q u e n c y i n t h e r e g i o n s h a v i n g a t e n d e n c y t o l a n d s l i d e s . I n f l u e n c e o f t h e E l e c t r o l y t e C o n t e n t on t h e Tendency o f Norwegian Blue C l a y s t o Flow I n c e r t a i n t h i x o t r o p i c s y s t e m s , e . g . c l a y e y s o i l s , t h e e l e c t r o l y t e c o n t e n t a f f e c t s t h e t h i x o t r o p y
.
F o r a g i v e n amount of e l e c t r o l y t e t h e d e g r e e o f t h i x o t r o p y i n c r e a s e s a s t h e d e g r e e o f f i n e n e s s o f t h e g r a i n i n c r e a s e s(9).
Even a v e r y s l i g h t i n - c r e a s e o f a weak e l e c t r o l y t e c o n c e n t r a t i o n i s s u f f i c i e n t t o i n - c r e a s e t h e t h i x o t r o p y . On c h e c k i n g t h e c h a n g e s i n s t r e n g t h R o s e n q u i s t('0
f o u n d t h a t a t h r e s h o l d v a l u e r e s u l t e d a t a3
p e r c e n t a d d i t i o n o f NaC1, i . e . , a t a c o n c e n t r a t i o n w h i c h , s t r a n g e l y enough, c o r r e s p o n d s t o t h e s a l t c o n t e n t o f s e a w a t e r . Ty a d d i n g sodium c h l o r i d e R o s e n q u i s t s u c c e e d e d i n i n c r e a s i n g t h e s t r e n g t h of q u i c k c l a y s so t h a t t h e y l o s t t h e i r t e n d e n c y t o f l o w . But they- r e v e r t e d t o t h e l a t t e r s t a t e a s soon a s t h e s a l t c o n t e n t was removed b y e l e c t r o d i a l y s i s . These e x p e r i m e n t s c o n f i r m e d G .Holmson's a s s u m p t i o n t h a t t h e t e n d e n c y t o f l o w i n h e r e n t i n c e r - t a i n Norwegian q u i c k c l a y s c a n b e a t t r i b u t e d t o t h e i r r e l a t i v e d e f i c i e n c y i n s a l t ( l o b )
.
S i r r . i l a r l y , when H . X e i x n e r c h e m i c a l l y examined p o r e w a t e r s , which h a d b e e n pumped i n t h e L e r k e d a l by means o f L . C a s a g r a n d e ' s n e t h o d o f e l e c t r i c d r a i n a g e ( 3 0 ) a zoneo f minimum s a l t c o n t e n t was f o u n d i n t h e r e g i o n o f t h e rr'oving q u i c k c l a y s . I n a g r e e m e n t w i t h t h e s e f i n d i n g s a q u i c k c l a y from .Moss was f o u n d t o have a lovier b a s e exchange c a p a c i t y t h a n t h a t o f a b l u e c l a y f r o m O s l o .
Viith r e s p e c t t o t h e o r i g i n of t h e Norwegian q u i c k c l a y s
i t i s e v i d e n t from t h e i r l i q u i d l i m i t s , which a c c o r d i n g t o T a b l e I a r e l o w e r t h a n
56
p e r c e n t , t h a t d u r i n g t h e i r d e p o s i t i o n t h e b l u e c l a y s w i t h t h e c o n s i d e r a b l y h i g h e r m o i s t u r e c o n t e n t s of n e w l y formed a u d s had a t f i r s t l i q u i d o r q u i c k c o n s i s t e n c y . Even a f t e r t h e l o s s o f w a t e r due t o s y n a e r e s i s t h e q u i c k c o n s i s t e n c y r e m a i n e d c o n s t a n t i n t h e l a y e r s n e a r t h e s u r f a c e( 3 1 ) .
9wing t o t h e p r e s - s u r e o f o v e r l y i n g s t r a t a t h e b e g i n n i n g o f d i a g e n e s i s c a u s e d a c l o s e r p a c k i n g w i t h a d e c r e a s e of p o r e and m o i s t u r e c o n t e n t s : t h e b l u e c l a y o b t a i n e d p l a s t i c c o n s i s t e n c y .A s t h e d i a g e n e s i s p r o g r e s s e s t h e l a t t e r s t a t e h a s been u n d e r g o i n g v a r i o u s l o c a l changes i n r e c e n t t i m e s . A d r y - c r u s t of
s o l i d c o n s i s t e n c y i s forming a t t h e s u r f a c e o f b l u e c l a y s r a i s e d above t h e sea l e v e l ( F i g .
6 ,
1 ) . Under bogs t h e b l u e c l a y i s b e i n g i n f i l t r a t e d by humic a c i d and t h i s , t o g e t h e r w i t h t h e r e - s u l t i n g j n c r e a s e i n w a t e r c o n t e n t , i s c a u s i n g a d e t e r i o r a t i o n o f i t s c o n s i s t e n c y . According t o R o s e n q u i s t( 7 )
t h e s a l t c o n t e n t of b l u e c l a y n e a r b a s e o r embedded l a y e r s o f g r a v e l c a n be l e a c h e d o u t by t h e e f f e c t o f s u b t e r r a n e a n w a t e r s f l o w i n g i n the g r a v e l . As a m a t t e r o f f a c t q u i c k c l a y s formed by such l e a c h - i n g p r o c e s s e s a r e f r e q u e n t l y e n c o u n t e r e d on t o p o f base l a y e r s of g r a v e l ( ~ i g .6 ) .
However, t o what e x t e n t f a c t o r s o t h e r t h a n the l e a c h - i n g p r o c e s s ( a s a s e c o n d a r y c a u s e of t h e t e n d e n c y t o f l o w ) con- t r i b u t e t o t h e formation o f Norwegian q u i c k c l a y s i s n o t y e t known. As t h e e l e c t r o l y t e c o n c e n t r a t i o n d e c r e a s e s t h e i n t e n s i t y of t h e f o r c e s a c t i n g between t h e p a r t i c l e s changes, w h i l e t h e d i s t a n c e between t h e p a r t i c l e s and t h e w a t e r c o n t e n t r e m a i n un- ,
changed. The i n v a r i a b l e w a t e r e n v e l o p e s c a n n o t be e q u a l l y ab- s o r b e d by t h e weakened i o n e n v e l o p e s : " e x c e s s w a t e r " , a s d e s c r i b e d by R o s e n q u i s t
( 7 ) ,
i s formed. Thus, i f t h e w a t e r c o n t e n t i s c o n s t a n t , a p l a s t i c c l a y c a n become a q u i c k c l a y because o f d e c r e a s i n g e l e c t r o l y t e c o n c e n t r a t i o n . D e p o s i t i o n S t r e n g t h and T h i x o t r o p i c Changes i n S t r e n g t h I n 1937 H v o r s l e v( 1 9 )
i n v e s t i g a t e d samples o f s o i l i n t h e remoulded s t a t e w i t h r e s p e c t t o t h e t h i x o t r o p i c r e g a i n i n s t r e n g t h . The v a l u e s o b t a i n e d by d e t e r m i n a t i o n of t h e Casagrande f l o w c u r v e s and from t h e Swedish cone t e s t s ( 2 ) were found t o be a t v a r i a n c e . The l a t t e r method, however, i s e s p e c i a l l y s u i t e d t o c o m p a r a t i v e i n v e s t i g a t i o n s of s o i l i n t h e u n d i s t u r b e d n a t u r a l s t a t e of d e p o s i t i o n and of t h e i r changes i n s t r e n g t h i n t h e r e - moulded s t a t e.
I t i s a known f a c t t h a t on b e i n g kneaded p l a s t i c c l a y s become s o f t e r and q u i c k c l a y s l i q u i d . Although i n p l a s t i c c l a y s t h e d e c r e a s e i n s t r e n g t h i s c o n s i d e r a b l e t h e y remain p l a s t i c . I n q u i c k c l a y s , however, t h e l o s s of s t r e n g t h i s g r e a t e r . I t i s so e x t e n s i v e t h a t t h e ( q u a s i - ) s o l i d c o n s i s t e n c y even changes t o t h e ( t e m p o r a r i l y ) l i q u i d o n e . With t h e i n d i c e s u s e d i n t h e Swedish cone t e s t s t h e l o s s of s t r e n g t h i s e x p r e s s e d by t h e f o l l o w i n g r a t i o :
Hj
( r e l a t i v e s t r e n g t h i n t h e u n d i s t u r b e d s t a t e ) H; ( r e l a t i v e s t r e n g t h i n t h e remoulded s t a t e )The r a t i o H3/:11 g e n e r a l l y r e s u l t s i n v a l u e r l o w e r t h a n
50
f o r p l a s t i c b l u e c l a y s and i n v a l u e s between 50 and 300 f o r qurick c l a y s . Hence i n q u i c k c l a y s t h e v i s c o s i t y d i m i n i s h e s i n t h e l i q ; i d s t a t e t o a - m e r e f r a c t i o n ( 1 t o - 1 ) o f t h e i n i t i a l d e -F
m
p o s i t i o n s t r e n g t h . The extreme l o s s e s o f - s t r e n g t h a r e c o n f i n e d t o h i g h l y t h i x o t r o p i c q u i c k c l a y s h a v i n g a g r e a t amount of e x c e s s w a t e r . I n t h e u n d i s t u r b e d s t a t e o f d e p o s i t i o n c l a y s have a " d e p o s i t i o n s t r e n g t h " , H3, which i s r e l a t i v e l y h i g h , e v e n f o r q u i c k c l a y s . By s t i r r i n g o r o t h e r m e c h a n i c a l d i s t u r b a n c e of t h e s t r u c t u r e t h e s t r e n g t h s u d d e n l y d e c r e a s e s t o t h e s t r e n g t h i n t h e remoulded s t a t e , 31. I m m e d i a t e l y a f t e r t h e s t i r r i n g c e a s e s t h e s t r e n g t h i n c r e a s e s a g a i n . D u r i n g t h e t h i x o t r o p i c s t i f f e n i n g i t i n c r e a s e s a t a d e c r e a s i n g r a t e and g r a d u a l l y a p p r o a c h e s a " t h i x o - t r o p i c f i n a l s t r e n g t h " , H t . I n Norwegian c l a y s t h i s s t r e n g t h(H
) i s g e n e r a l l y o b t a i n e d a f t e r f o u r weeks when i t i s n e a r l y a s g r e a k a s t h e s t r e n g t h a f t e r a r e s t p e r i o d o f one y e a r ( 3 2 ) . Compared w i t h t h e q u i c k c l a y s , p l a s t i c c l a y s l o s e a s m a l l e r p a r t o f t h e de- p o s i t i o n s t r e n g t h by t h e f i r s t d i s t u r b a n c e of t h e s t r u c t u r e and r e g a i n a l a r g e r ? a r t of t h e l o s t s t r e n g t h by t h e t h i x o t r o p i c s t i f f e n i n g . As E a u g l s t e s t s show, t h e t h i x o t r o p i c f i n a l s t r e n g t hHt
i s r e l a t e d t o t h e v i s c o s i t y i n t h e remoulded s t a t e and c a n be e s t i m a t e d from i t w i t h good a p p r o x i m a t i o n . I f s t i f f e n e d q u i c k c l a y i s r e p e a t e d l y l i q u i f i e d , t h e s t r e n g t h t e n d s i n e a c h c a s e t o w a r d s t h e t h i x o t r o p i c f i n a l v a l u e . Hence, t h e t h i x o t r o p i c s t r e n g t h c y c l e i s c l o s e d n o t upon t h e f i r s t l i q u e f a c t i o n b u t o n l y a f t e r r e p e a t e d l i q u e f a c t i o n s . The o r i g i n a l , h i g h e r d e p o s i t i o n s t r e n ~ t h i s presumably due t o a n i n c r e a s e i n t h e a d h e s i o n f o r c e s d u r i n g t h e l o n g t i m e e l a p s e d s i n c e t h e de- p o s i t i o n of t h e q u i c k c l a y . For t h e n a t u r a l s o i l s t h e c o n c e p t of " r e v e r s i b l e " t h i x o t r o p i c v i s c o s i t y change must be m o d i f i e d s o t h a t t h e t r e n d c a u s e d by t h e s t i f f e n i n g i s n o t t h e d e p o s i t i o n s t r e n g t h b u t m e r e l y t h e c o n s i d e r a b l y l o w e r t h i x o t r o p i c f i n a l s t r e n g t h . The c h a n g e s i n s t r e n g t h o f n a t u r a l s o i l s show e s - s e n t i a l l y t h e same b e h a v i o u r f o r p l a s t i c and t h i x o t r o p i c con- s i s t e n c i e s . The change of s t a t e , s t i f f - l i q u i d - s t i f f , which i s c h a r a c t e r i s t i c o f q u i c k s o i l s h a s tieen m o d i f i e d t o a l e s s marlred change i n s t r e n g t h f o r t h e p l a s t i c r a n g e . However, by t h e sub- s e q u e n t i n c r e a s e i n s t r e n g t h t h e m o d i f i e d change a l s o p r o v e s t o be a t h i x o t r o p i c phenomenon. A s i s now g e n e r a l l y known, p l a s t i cs o i l s l o s e t h e i r s t r e n g t h when t h e y a r e d i s t u r b e d . T h i s was f i r s t shown by A . C a s a g r a n d e . T h i s l o s s i n s t r e n g t h i s a l s o a t h i x o t r o p i c phenomenon.
Quick S o i l s . , S o i l s w i t h I n h e r e n t Flow Tendency and Flowing S o i l s Too l i t t l e i s known a b o u t t h e v a r i o u s f a c t o r s which de- t e r m i n e t h e t e n d e n c y t o f l o w o f f i n e - g r a i n e d s o i l s a s f a r a s t h e i r i n t e r r e l a t i o n s h i p s a r e c o n c e r n e d . I t would be u s e f u l f o r f u t u r e i n v e s t i g a t i o n s t o d e f i n e c l e a r l y t h e c o n c e p t s and t e r m s u s e d i n t h i s f i e l d . I t i s t h e r e f o r e s u g g e s t e d t h a t t h e t e r m " a p t t o f l o w " s h o u l d k,e employed o n l y a s a g e n e r a l term and t h a t t h e p r e f i x
" q u i c k " s h o u l d be r e s e r v e d f o r s o i l s which, w i t h t h e w a t e r c o n t e n t o f t h e n a t u r a l s t a t e , e v i d e n t l y have q u i c k o r t h i x o t r o p i c con-
s i s t e n c y .
Quick s o i l s i n t h i s s e n s e a r e f i n e - g r a i n e d s o i l s which,
i n
t h e n a t u r a l s t a t e , when s u b j e c t e d t o m e c h a n i c a l d i s t u r b a n c e o f t h e i r s t r u c t u r e o n l y-
w i t h o u t any change i n t h e i r w a t e r con-t e n t
