External Dynamics and Sediments; Thixotropy in Transported Fine-Grained Soils

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External Dynamics and Sediments; Thixotropy in Transported

Fine-Grained Soils

Ackermann, E.

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NATIONAL RESEiiF.CH COITNC I L

OF

_CfiFIADA T e c h n i c a l T r a n s l a t i o n TT-379 T i t l e : E x t e r n a l Dynamics and S e d i m e n t s ; T h i o x o t r o p y i n T r a n s ~ o r t e d F i n e - g r a i n e d S o i l s . ( x u s s e r e Dynamik und S e d i m e n t e ; T h i x o t r o p i e b e i Urnlagerungen f e i n k 6 r n i g e r S e d i m e n t e . ) A u t h o r : D r . E r n s t kckermann R e f e r e n c e : G e o l o g i s c h e Rundsc1:au

-

3 7 : 1 0 0 - 1 0 1 ,

1949.

T r a n s l a t e d b y : 14.11. G. Nathan

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E x t e r n a l Dynamics a n d S e d i n e n t s T h i x o t r o p y i n T r a n s p o r t e d F i n e - g r a i n e d S o i l s T h i x o t r o p y a f f e c t s t h e s l i d i n g a n d f l o w i n g movements of m o i s t c o h e s i v e s o i l s . However, a d i s t i n c t i o n m u s t be made a s t o w h e t h e r t h e t e m p o r a r y v i s c o s i t y c h a n g e known a s t h i x o t r o p y f i n a l l y r e s u l t s i n l i q u e f a c t i o n , a s i n t h e c a s e o f s o i l s i n t h e s t a t e o f t h i x o t r o p i c c o n s i s t e n c y ( e . g . g l ~ i c k s o i l s ) , o r w h e t h e r i t o n l y r e s u l t s i n a ( p a r t l y ) r e v e r s i b l e d e c r e a s e i n s t r e n g t h a s i n p l a s t i c s o i l s . The g r o u p of m a t e r i a l s a f f e c t e d by t h i x o t , r o p i c t r e a k - down o f t h e s t r u c t u r e a n d t h i x o t r o p i c movements e x t e n d s f r o m f a t c l a y t o s a n d w i t h low c l a y c o n t e n t a n d a l s o c o m p r i s e s d e - p o s i t s of c a l c a r e o u s rnilrl a s w e l l a s T i n e - - r a i n e d s o i l s c o n t a i n i n g o r g a n i c m a t t e r . L a y e r s of q u i c k c l a y w i t h i n h e r e n t florv d a n c e r c a n b e d e t e c t e d b e f o r e a n d a f t e r t h e movement o f t h e s o i l k y d e t e r m i n i n g t h e A t t e r b e r g l i m i t s , f r o m ?,he e x c e s s o f n a t u r a l ? . l a t e r c o n t e r i t a b o v e t h e l i q u i d l i m i t , and t h e n e g a t i v e v a l u e s o f t h e r e l a t i v e c o n s i s 5 e n c p f a c t o r , x i t h t h o a i d o f c o n v e n t i : ~ n & l s o i l - m e c h a n i c s e::perirnental m e t h o d s . Althout';h t h e q u i c k z o n e s embedtied i n r e c e n t l o o s e s o i l s a r e n o t v e r y t h i c k , t h e y p r o v i d e a b e t t e r s l i d i n g s u r f a c e ?or f l o w s l i d e s t h a n s o f t - p l a s t i c c l a y s . T h i s i s d u e t o t l i e f a c t t h a t t h e i n t e r n a l f r i c t i o n o f q u i c k c l a y s i n t h e ?.iriuicl s t a t e

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a p p r o a c h e s t h e v a l u e o f z e r o . The p a t h s o f s u c h movements a r e c u r v e d . The c o n f i g u r a t i o n i s s i m i l a r t o t h a t o f t y p i c a l w o u n d r u p t u r e s o r l a n d s l i d e s . I f t h i c k e r d e ~ o s i t s o f ? \ l i c k s o i l become l i q u i d a n d b r e a k t h r o u g h t h e e n v e l o p i n g l a y e r s t h e y may f l o w f o r m i l e s a l o n g t h e f l o o r s o f v a l l e y s o? _{b a s i n s f o r m e d by s e d i -} m e n t a t i o n , b e f o r e t h e y s e t t l e a n d s t i f ' f e n . I n

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r n i l l i o n c u b i c m e t e r s o f s o i l f l o w e d s e v e n k i l o m e t r e s

down t h e V a e r d a l i n two h o u r s . I n s u c h r a p i d f l o w i n g movements

t h e d r y c r u s t i s b r o k e n i n t o b l o c k s , w h i c h f l o a t s e p a r a t , e l ; r i n t h e c l a y e y m a t r i x . F r e q u e n t l y , f?-owing a n d s l i d i n g mo~rements a r e combined. The d r y c r u s t i s f a u l t e d by d i s p l a c e m e n t s , b u t t h e c o h e r e n c e b e t w e e n t h e t a n g e n t i a l l y s l i c e d b l o c k s i s m a i n t a i n e d . D u r i n g t h e l a n d s l i d e a t Lade ( n e a r T r o n d h j e m ) i n 1 9 4 4 t h e l i q u e f i e d q u i c k c l a y f l o w e d downwards u n d e r t h e d r y c:-ilst, w h i c h n d s s i n k i n g down i n t h e u p p e r r e g i o n o f t h e s l i d e . T h i s r e s ~ i l t e a i n t h e d r y c r u s t b e i n g r a i s e d a n d bul!?ed up i n t h e l o w e r r e g i o n o f t h e s l i d e . P r o c e s s and c o n f i q r r a t i o n o f t l i e f l o w i n g movements o f t h e s o i l a r e d e t e r m i n e d c h i e f l y by t h e t h i c k n e s s o f t h e l a y e r s i n v o l v e d a n d t h e v i s c o s i t y o f t h e q u i c k c l a y . The l i q u e f a c t i o n o c c u r s i r r e s p e c t i v e o f t h e w a t e r c o n t e n t . The movement i s c a u s e d by v i b r a + , i o n s d u e t o e a r t h q u a k e s , v o l c a n i c e x p l o s i o n s , b l a s t s , e t c . , a s w e l l a s by h v d r o s t a t i c p r e s s u r e

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c h a n g e s i n t h e p o r e ; v s t e r d u r i n g s p r i n g t i d e s , f l o o d s , e t c . I n c l i n a t i o n s o f nppro:timat,el.y 2 p e r c e n t a r e s u f f i c i e n t f o r t ? . e rnasses of s o i l t o f l o w o f f . . I f a c o h s s i v e s o i l i s i n t h e s t a t e o f p l a s t i c c o n s i s - t e n c y , t h e t h i x o t r o p i c c o n s i s t e n c y c h a n g e d o e s n o t r e s u l t i n l i q u e f a c t i o n b ~ i t i n a s p o n t a n e o u s t e r n p o r b r y deer-case i n s t r e n g t h . T h e r e ' o r e , s l i t l i n i ; rnovements, a s w e l l a s nlrl s t i c f l o w u n d e r p r e s s i l r e o c c u r 1,;illen t k e i n t e r n a l l l r - i c t i o n sr.lddenlv d e c r e a s e s . The t h i l c o t r o p y f a c i l i t a t e s t h e r e l e a s e a n d t h e p r o g r e s s o f t h e r ~ o v e m e n t . I n s u b a y u e o u s s l i d i n g s a n i n f l u e n c e o f : , h i x o t r o g y on t h e rnovernent c a n t:e assumed o n l y z"or p l a s t i c c l a y e v I - a y e r s

and. p e r h a p s a l s o f o r c i . ~ l c : ~ r e o u s l a y e r s . The f i n e s 5 r a t ; i f i c a t i o n i n !.jav:T zon.r?s shows t h a t t h e c o h r ? r e n c e o f t h e rim\-ine l a y e r s h a s

b e e n i : , a i n t a i n e b . T h i s i s incompat;ibLe w i t h t h i x o t r o p i c ILique-

f a c t i o n .

I n c o n t r a s t t o t h e r a p i d f l o w i n g o f l i q u e f i e d q u i c k c l a y s , c r e e p s l i d e s move s l o w l y and o n l y when s o a k e d e x c e s s i v e l y . T h e i r movement i s a r r e s t e d b y l o s s o f w a t e r a n d i s o n l y r e ~ r i v e d

by i t s r e c o v e r y . T h e s e c r e e p i n g movements a r e r e l a t e d t o

s o l i f l u c t i o n phenomena a s l , ! e l l a s m u d f l o w s and s i m i l a r t r a n s - p o r t a t i n n o f c l e t r i t a l m a t e r i a l ; : i t h hi,n;h T ; ~ a t c r c o n t e n t .

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ma:.

_{be c o n s i d e r e d model e x a m p l e s f o r} t h e s t u d y o f m a c r o s t r i ~ c t u r e s . T h i s a p p l i e s p a r t i c u l a r l y t o t h e b e h a v i o u r o f r i g i d l a y e r s on t o p o f a p l a s t i c a l l y d i s p l s c e d

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s u b s t r a t u m . E r o s i o n p r o c e s s e s a r e a c c e l e r a t e d by t h e s u d d e n movements o f l a r g e m a s s e s s o t h a t s p e c i a l m o r p h o l o g i c s t r u c t u r e s a r i s e . Normal s e q u e n c e s o f s t r a t a a r e a f f e c t e d by t h e f a c t t h a t f i n e - g r a i n e d s e d i m e n t s p r e c i p i t a t e d n e a r t h e c o a s t a r e t h i x o - t r o p i c a l l y l i q u e f i e d by t h e l o a d of r e c e n t d e p o s i t s o r by s l i d i n g of o v e r s t e e p d e c l i v i t i e s a n d t r a n s p o r t e d a s mud f l o w s t o r e g i o n s f u r t h e r r e m o t e f r o m t h e c o a s t . I n t h i s p r o c e s s , u n s t r a t i f i e d m a s s e s , p o s s i b l y c o n t a i n i n g f r a g m e n t s o f non- l i q u e f i e d s e d i m e n t s w h i c h h a v e b e e n d r a g g e d a l o n g , become em- bedded i n t h e f i n e - l a y e r e d s e d i m e n t s o f t h e n o r m a l s e q u e n c e o f s t r a t a .