Liquefaction study for the Little Jackfish Dyke

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Liquefaction study for the Little Jackfish Dyke / Étude de liquéfaction

concernant la digue Little Jack Fish

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S e r

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National Research

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construction

Liquefaction Study for the Little Jackfish

Dyke

by K.T. Law, J.H.S. Huang, and R. Zhu

ANALYZED

Reprinted from

Proceedings of the

12th International Conference on Soil Mechanics

and Foundation Engineering.

Rio de Janeiro, 13-18 August 1989

pp. 1971 -1 974

(IRC Paper No. 1658)

NRCC 31662

NRC

-

ClSTl

I

/

APR

2s

1991

'.,

1 I

B I S L I O T H ~ Q U E

I R C

C N R C

-

ICIIT

I

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Rksumk

Le

potentiel de liquaaction des dCp8ts granulaires dans la rkgion de la digue

Little Jackfish a kt6 Ctudik au moyen du p&nktrom&tre

ordinaire, du

pi6zocone, du dispositif

A

_{cisaillement simple cyclique et de la cellule triaxiale.}

L'6tude montre que la couche meuble sup6rieure de sable fin peut se liqu6fier

en deux endroits, tandis que les sols en d'autres endroits ne sont pas

liqukfiables. La methode, b a d e sur la notion de regime permanent, indique

qu'une rupture de la digue par koulement est peu vraisemblable.

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Liquefaction study for the Little Jackfish Dyke

Etude de liquefaction concernant la digue Little Jack Fish

K.T.LAW, Institute for Research in Construction, National Research Council of Canada, Canada

J.H.S.HUANG, Ontario Hydro, Toronto, Canada

R.ZHU, Institute of Water Conservancy and Hydro Electric Power Research Beijing, People's Republic of China

SYNOPSIS: The l i q u e f a c t i o n p o t e n t i a l o f t h e g r a n u l a r d e p o s i t s a t t h e L i t t l e J a c k f i s h d y k e s i t e was s t u d i e d u s i n g t h e s t a n d a r d p e n e t r o m e t e r , t h e p i e z o c o n e p e n e t r o m e t e r , t h e c y c l i c s i m p l e s h e a r d e v i c e and t h e t r i a x i a l c e l l . The s t u d y shows t h a t t h e t o p l o o s e f i n e s a n d l a y e r may l i q u e f y f o r t w o l o c a t i o n s w h i l e s o i l s a t o t h e r l o c a t i o n s a r e n o t l i q u e f i a b l e . The a p p r o a c h b a s e d o n t h e s t e a d y s t a t e c o n c e p t i n d i c a t e s t h a t a f l o w s l i d e f a i l u r e f o r t h e p r o p o s e d d y k e i s u n l i k e l y . INTRODUCTION The L i t t l e J a c k f i s h R I v e r i s l o c a t e d n o r t h o f L a k e N i p i g o n , O n t a r i o , Canada. The r i v e r i s a p p r o x i m a t e l y 48 km l o n g and d r o p s a b o u t 67 m i n e l e v a t i o n a l o n g i t s l e n g t h . A s t u d y i s c u r r e n t l y b e i n g u n d e r t a k e n b y O n t a r i o H y d r o t o d e v e l o p a b o u t 85% o f t h e a v a i l a b l e h y d r a u l i c h e a d i n a s i n g l e s t a g e . The c u r r e n t p r o p o s a l c a l l s f o r a new h y d r o e l e c t r i c g e n e r a t i n g s t a t i o n w i t h an i n s t a l l e d c a p a c i t y o f 1 3 2 MW. The d e s i g n p l a n t d i s c h a r g e w i l l be 283 m 3 / s e c w i t h a g r o s s h e a d o f 57.4 m. I n c o n j u n c t i o n w i t h t h i s d e v e l o p m e n t a m a i n dam, t w o b l o c k dams, 8 d y k e s and t w o c a n a l s w i l l be c o n s t r u c t e d . F o l l o w i n g a p r e l i m i n a r y i n v e s t i g a t i o n , i t was r e c o g n i z e d t h a t p o t e n t i a l 1 y t r o u b l e s o m e f o u n d a t i o n c o n d i t i o n s e x i s t e d a t t h e s i t e f o r d y k e 1. A d e t a i l e d g e o t e c h n i c a l s t u d y was s u b s e q u e n t l y c a r r i e d o u t . An i m p o r t a n t a s p e c t o f t h e s t u d y , w h i c h i s r e p o r t e d h e r e , i s an a s s e s s m e n t of t h e l i q u e f a c t i o n p o t e n t i a l o f t h e s i t e . S I T E CONDITIONS D y k e 1 w i l l be c o n s t r u c t e d a c r o s s a b r o a d v a l l e y . F o r a b o u t 435 m a l o n g t h e p r o p o s e d d y k e a l i g n m e n t t h e t e r r a i n of t h e v a l l e y s l o p e s g e n t l y and i s p a r t l y swampy. The s i m p l i f i e d s u b s o i l c o n d i t i o n s a r e shown i n F i g u r e 1.

I B r i e f l y , t h e s u b s o i l i s composed o f f o u r m a i n I c o m p r e s s i b l e l a y e r s o f v a r y i n g t h i c k n e s s . The

I _{t o p l a y e r i s muskeg, f o l l o w e d i n s e q u e n c e by} s i l t y f i n e sand, s i l t and v a r v e d c l a y . The d y k e w i l l b e a b o u t 5 0 0 m i n l e n g t h and w i l l h a v e a h e i g h t o f up t o a b o u t 20 m. I t w i l l c o n s i s t o f r o c k f i l l w i t h an i m p e r v i o u s c o r e and z o n e s o f f i l t e r m a t e r i a l s . I n t h e l o w e r p a r t s o f t h e v a l l e y t h e s u r f a c e o r g a n i c s o i l w i l l b e r e p l a c e d w i t h s a n d and g r a v e l . S e e p a g e t h r o u g h t h e s i l t and f i n e s a n d d e p o s i t s w i l l b e c o n t r o l l e d by a s l u r r y t r e n c h c u t o f f c o n s t r u c t e d b e l o w t h e i m p e r v i o u s c o r e and e x t e n d i n g t o t h e u n d e r l y i n g v a r v e d c l a y o r b e d r o c k . T h e r e i s l i t t l e r e c o r d e d i n f o r m a t i o n o n s i g n i f i c a n t h i s t o r i c a l e a r t h q u a k e e v e n t s i n n o r t h w e s t O n t a r i o w h e r e t h e p r e s e n t p r o j e c t i s l o c a t e d . T h e r e i s , h o w e v e r , some d e t e c t e d a c t i v i t y w i t h i n 750 km o f t h e s i t e . S u c h a l a r g e d i s t a n c e i m p l i e s o n l y m i n o r s i t e e f f e c t s b a s e d on t h e a t t e n u a t i o n e q u a t i o n s o f Hasegawa e t a l . ( 1 9 8 1 ) . The maximum c a l c u l a t e d p e a k h o r i z o n t a l g r o u n d a c c e l e r a t i o n ( a m a ) i s 0.0199 w h i c h i s r e l a t e d t o an e a r t h q u a k e o f 6.3 m a g n i t u d e ( M ) w h f c h o c c u r r e d on Keweenaw P e n i n s u l a i n M i c h i g a n i n 1906, a b o u t 350 km away f r o m t h e p r e s e n t s i t e . B a s e d on t h e 1 9 8 5 N a t i o n a l B u i l d i n g Code o f Canada, amax a t t h e s i t e 1 s 0.049 f o r a p r o b a b l l f t y o f e x c e e d a n c e o f 10% I n 50 y e a r s ( r e t u r n p e r i o d = 475 y r s . ) . T h i s a c c e l e r a t i o n i s a s s o c i a t e d w i t h a f r e q u e n c y o f 5 Hz. F o r d e s i g n p u r p o s e s , t h e r e f o r e . i t i s s a f e t o assume M = 6.5 a n d a m a x = 0.049 f o r t h i s s i t e . D E F I N I T I O N OF LIQUEFACTION T h e r e a r e t w o m a i n c o n c e p t s o f l i q u e f a c t i o n . The c o n c e p t o f Seed and Lee ( 1 9 6 6 ) i s b a s e d o n c y c l i c l o a d t e s t s . T h e y d e f i n e d i n i t i a l l i q u e f a c t i o n as t h e s t a t e when t h e p o r e w a t e r p r e s s u r e i s e q u a l t o t h e a p p l i e d c o n f i n i n g s t r e s s . C o m p l e t e l i q u e f a c t i o n i s d e f i n e d a s t h e c o m p l e t e l o s s o f r e s i s t a n c e o v e r a w i d e s t r a i n a m p l i t u d e . F o r l o o s e sand, t h e d e v e l o p m e n t o f i n i t i a l l i q u e f a c t i o n a n d c o m p l e t e 1 i q u e f a c t i o n h a p p e n a l m o s t s i m u l t a n e o u s l y . F o r d e n s e s a n d , c o m p l e t e 1 i q u e f a c t i o n may n o t t a k e p l a c e f o l l o w i n g i n i t i a l l i q u e f a c t i o n . A s t r a i n c r i t e r i o n i s t h e n u s e d by d e f i n i n g l i q u e f a c t i o n as t h e s t a t e when t h e c y c l i c l o a d p r o d u c e s a c e r t a i n d o u b l e s t r a i n a m p l i t u d e , t y p i c a l l y 5% t o 20%. T h i s c o n d i t i o n i s t e r m e d p a r t i a l l i q u e f a c t i o n by Seed and Lee ( 1 9 6 6 ) .

The o t h e r c o n c e p t o f l i q u e f a c t i o n comes f r o m t h e H a r v a r d s c h o o l o f t h o u g h t ( C a s a g r a n d e , 1 9 7 6 ) . L i q u e f a c t i o n i s d e f i n e d as t h e r e s p o n s e o f l o o s e s a t u r a t e d s a n d when s u b j e c t t o m o n o t o n i c , c y c l i c o r d y n a m i c l o a d i n g t h a t r e s u l t s i n s u b s t a n t i a l l o s s o f s t r e n g t h and, i n e x t r e m e c a s e s , l e a d s t o f l o w s l i d e s . T h i s s c h o o l o f t h o u g h t s u g g e s t s t h a t d u r i n g l i q u e f a c t i o n t h e mass o f s o i l t e n d s t o w a r d s t h e s t e a d y s t a t e w h e r e t h e mass i s c o n t i n u o u s l y d e f o r m i n g a t c o n s t a n t v o l u m e , c o n s t a n t n o r m a l e f f e c t i v e s t r e s s , c o n s t a n t s h e a r s t r e s s and

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PROPOSED M U HEADFOND WATER LEVEL 127 10

FIGURE 1 LAYER SILT WITH CUY SElMS _{SAND AND GRAVEL}

SIMRIFIED CROSS SECTION OF SITE AND FIELD TEST LOCATION-

-

GRANITIC GNEISS

c o n s t a n t r a t e o f s h e a r s t r a i n . P o u l o s e t a l . ( 1 9 8 5 ) e x t e n d e d t h i s c o n c e p t and i n t r o d u c e d t h e u n d r a i n e d s t e a d y s t a t e s t r e n g t h f o r a s s e s s i n g t h e l i k e l i h o o d o f a f l o w s l i d e . TEST PROGRAM S t a n d a r d p e n e t r a t i o n t e s t s (SPT) and p i e z o c o n e p e n e t r a t i o n t e s t s w e r e c o n d u c t e d i n t h e f i e l d a t l o c a t i o n s as shown i n F i g u r e 1. S a m p l i n g b y means o f a 76.2 mm d i a m e t e r O s t e r b e r g s a m p l e r was c a r r i e d o u t a t AJ37. The SPT was c a r r i e d o u t i n a c c o r d a n c e w i t h common N o r t h A m e r i c a n p r ? c t i c e . The p i e z o c o n e p e n e t r o m e t e r w i t h a 6 0

.

10 cm2 a r e a cone, m e a s u r e s t i p r e s i s t a n c e . s l e e v e f r i c t i o n and p o r e p r e s s u r e . ' The p o r e p r e s s u r e was m e a s u r e d t h r o u g h a 4 mm t h i c k c y l i n d r i c a l p o r o u s s t o n e l o c a t e d i m m e d i a t e l y a b o v e t h e c o n e . I n t h e l a b o r a t o r y , t h r e e t y p e s o f t e s t s w e r e c o n d u c t e d on t h e s i l t s a m p l e s t a k e n f r o m t h e s i t e : 1 ) r o u t i n e t e s t s t o d e t e r m i n e t h e b a s i c s o i l p r o p e r t i e s , 2 ) c y c l i c s i m p l e s h e a r t e s t s t o s t u d y t h e l i q u e f a c t i o n r e s i s t a n c e and 3 ) l o a d and s t r a i n r a t e c o n t r o l l e d t r i a x i a l t e s t s t o s t u d y t h e s t e a d y s t a t e c h a r a c t e r i s t i c s o f t h e s o i l . A S e i k e n c y c l i c s i m p l e s h e a r a p p a r a t u s was u s e d t o p e r f o r m t h e c o n s o l i d a t e d , u n d r a i n e d c y c l i c s i m p l e s h e a r t e s t s on u n d i s t u r b e d a n d r e c o n s t i t u t e d s a m p l e s . T h i s a p p a r a t u s h a s p r o v i s i o n s f o r d r a i n a g e c o n t r o l , a p p l i c a t i o n o f a c e l l ( h o r i z o n t a l ) p r e s s u r e and s h e a r i n g u n d e r a b a c k p r e s s u r e . W h i l e s h e a r i n g , t h e s o i l s a m p l e was c o n s t r a i n e d t o a c o n s t a n t a r e a by a r e m o v e d and t h e t e s t c e l l was a s s e m b l e d a n d f i l l e d w i t h e n o u g h w a t e r t o c o v e r t h e t o p c a p o n t h e s a m p l e . A t h i n l a y e r o f o i l was a d d e d t o p r e v e n t a i r f r o m e n t e r i n g i n t o t h e s o i l s a m p l e by p e r m e a t i n g t h r o u g h t h e w a t e r and t h e membrane. The s a m p l e was s a t u r a t e d b y p a s s i n g c a r b o n d i o x i d e t h r o u g h i t u n d e r a s m a l l c e l l p r e s s u r e t o d i s p l a c e t h e a i r i n t h e v o i d s p a c e a n d t h e n , by p a s s i n g d i s t i l l e d w a t e r t o r e p l a c e t h e c a r b o n d i o x i d e . Any t r a c e o f c a r b o n d i o x i d e t h a t r e m a i n e d i n t h e s a m p l e w o u l d d i s s o l v e i n t h e p o r e w a t e r when t h e b a c k p r e s s u r e o f a t l e a s t 3 0 0 kPa was a p p l i e d . TEST RESULTS The p e n e t r a t i o n r e s f s t a n c e ( N ) i n t e r m s o f number o f b l o w s per f o o t f r o m t h e SPT and t h e t i p r e s i s t a n c e (q,) i n ~ g / c n ~ f r o m t h e

p i e z o c o n e t e s t s may b e c o m p a r e d as a r a t i o . F o r t h e s f l t d e p o s i t , t h e a v e r a g e r a t i o o f q c / N

f o r e a c h l o c a t l o n 1 s shown f n T a b l e I. T a b l e I. q c / N r a t i o f o r s i l t d e p o s i t L o c a t i o n AJ34A PC2 PC3 AJ37 AJ50

q c /N 5.97 4.25 4.38 4.12 7.78 s t a c k o f t e f l o n - c o a t e d m e t a l s l i p r i n g s w h i c h h a v e an i n s i d e d i a m e t e r e q u a l t o t h e d i a m e t e r o f t h e r u b b e r membrane and t h e s a m p l e . s C o n s o l i d a t i o n f o r t h i s t e s t s e r i e s was m a n i s o t r o p i c w i t h t h e h o r i z o n t a l c o n s o l i d a t i o n L" 5 s s t r e s s e q u a l t o 0.45 o f t h e v e r t i c a l

_$2

_"

c o n s o l i d a t i o n s t r e s s ( o l , ) . T h i s r a t i o i s S%

A t l o c a t i o n s AJ34A and AJ50, an a r t e s i a n p r e s s u r e was o b s e r v e d . T h i s c o n d i t i o n c r e a t e d an u n s t a b l e b o t t o m o f t h e b o r e h o l e f o r t h e SPT. Hence, t h e m e a s u r e d p e n e t r a t i o n r e s i s t a n c e e r r e d o n t h e l o w s i d e . The p i e z o c o n e t e s t r e s u l t s w e r e n o t a f f e c t e d b y t h e a r t e s i a n p r e s s u r e . T h e r e f o r e , t h e r e s u l t i n g q c / N r a t i o f o r t h e s e t w o h o l e s i s t o o h i g h and i s d i s c a r d e d f o r e s t i m a t i n g t h e mean q c / N v a l u e o f t h e s i l t d e p o s i t f o r t h e w h o l e s i t e . T h i s v a l u e i s e q u a l t o 4.25. S i m i l a r c o m p a r i s o n on t h e f i n e s a n d l a y e r , shows t h a t t h e mean v a l u e o f q c / N i s a b o u t 5. The r e s p o n s e o f a t y p i c a l c y c l i c s i m p l e s h e a r t e s t on an u n d i s t u r b e d s i l t s a m p l e ( F i g . 2 ) r e s e m b l e s t h a t o f a d e n s e s a n d . I n t h e i n i t i a l s t a g e o f s h e a r i n g , t h e p o r e p r e s s u r e ( u ) s t e a d i l y i n c r e a s e d , t h e t o t a l v e r t i c a l p r e s s u r e f o r m a i n t a i n i n g c o n s t a n t s a m p l e t h i c k n e s s a p p r o x i m a t e l y e q u a l t o {fie c o e f f i c i e n t o f e a r t h

9

-5 0 - p r e s s u r e a t r e s t (K ) f o r t h e d e p o s i t . 30 Y B L o a d c o n t r o l l e d aXd s t r a ~ n r a t e c o n t r o l l e d _._;_; ₂₀ t r i a x i a l t e s t s w e r e a l s o c o n d u c t e d o n a W = u n d i s t u r b e d and r e c o n s t i t u t e d s a m p l e s . A V- 20

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40 s p e c i a l t r i a x i a l c e l l was b u i l t f o r t h e l o a d 2 !o

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60 c o n t r o l l e d t e s t s w i t h t h e v e r t i c a l l o a d b e i n g "7 = 80 a p p l i e d by means o f an a i r - p i s t o n . F o r t h e $ 0 s t r a i n r a t e c o n t r o l l e d t e s t s , an o r d i n a r y Y)

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.20 Urn c o m p a c t i n g m o i s t s o i l p a r t i c l e s ( 4 % m o i s t u r e ZL c o n t e n t ) i n a m o u l d m o u n t e d on t h e b a s e o f t h e -30 3 a s i m p l e s h e a r o r t r i a x i a l c e l l . The i n s i d e o f TIME

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t h e m o u l d was l i n e d w i t h a r u b b e r membrane f o r e n c l o s i n g t h e s a m p l e t h r o u g h o u t t h e t e s t . FIGURE 2

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d e c r e a s e d and t h e h o r i z o n t a l s t r a i n showed v e r y s m a l l c h a n g e . A t u e q u a l t o a b o u t 70% o f t h e h o r i z o n t a l c o n s o l i d a t i o n p r e s s u r e , t h e s a m p l e s t a r t e d t o d e f o r m a p p r e c i a b l y . The s a m p l e , h o w e v e r , d i d n o t c o l l a p s e e v e n a t many c y c l e s a f t e r 100% p o r e w a t e r p r e s s u r e was d e v e l o p e d . The i n i t i a l s h e a r i n g r e s p o n s e o f a r e c o n s t i t u t e d s a m p l e was s i m i l a r t o t h a t o f t h e u n d i s t u r b e d s a m p l e . A t 1 0 0 % p o r e w a t e r p r e s s u r e , h o w e v e r , t h e s a m p l e c o l l a p s e d q u i c k l y . 0.m I 10 100 1 OW EFFECTIVE MINOR PRINCIPAL STRESS, kPa

I I

SYMBOL a;, kPa 0 1 6 0 A 50 A100 I 1 0 0

Y

I I

I

50 100 5W

NUMBER OF CYCLES TO CAUSE LIQUEFACTION ec = Void retio sner mnarllastmon

FIGURE 3

LIQUEFACTION RESISTANCE vs NUMBER OF

CYCLES TO CAUSE LIQUEFACTION IN CYCLIC SIMPLE SHEAR TESTS

The l i q u e f a c t i o n r e s i s t a n c e n o r m a l i z e d b y o i o a t t h e b e g i n n i n g o f 1 0 0 % p o r e p r e s s u r e i s s u m m a r i z e d i n F i g u r e 3. T h i s r e s i s t a n c e i s i n d e p e n d e n t o f o i o w i t h i n t h e s t u d i e d p r e s s u r e r a n g e . I t d e c r e a s e s w i t h i n c r e a s e i n v o i d r a t i o o r i n t h e number o f c y c l e s t o c a u s e l i q u e f a c t i o n . The r e s i s t a n c e o f t h e u n d i s t u r b e d s a m p l e s i s s i g n i f i c a n t l y h i g h e r t h a n t h a t o f t h e r e c o n s t i t u t e d o n e s . The r e s u l t s o f t h e t r i a x i a l t e s t s f o r s t u d y i n g t h e s t e a d y s t a t e c h a r a c t e r i s t i c s o n r e c o n s t i t u t e d s a m p l e s a r e shown i n F i g u r e 4. It a p p e a r s t h a t b o t h t h e l o a d c o n t r o l l e d and t h e s t r a i n r a t e c o n t r o l l e d t e s t s y i e l d t h e same s t e a d y s t a t e l i n e and t h e same s t e a d y s t a t e s t r e n g t h l i n e . T e s t s on u n d i s t u r b e d s a m p l e s w i t h i n t h e c a p a b i l i t y o f t h e t e s t c e l l s

(maximum c o n f i n i n g p r e s s u r e = 1 MPa) showed t h a t t h e s o i l i s d i l a t i v e and t h e r e s u l t s a r e , t h e r e f o r e , n o t shown h e r e . LIQUEFACTION POTENTIAL The l i q u e f a c t i o n p o t e n t i a l a t t h e s i t e c a n b e a s s e s s e d by c o m p a r i n g t h e n o r m a l i z e d i n d u c e d s e i s m i c s t r e s s ( r h / o i 0 ) w i t h t h e n o r m a l i z e d 1 i q u e f a c t i o n r e s i s t a n c e ( ~ ~ / o ; ~ ) o f t h e d e p o s i t . The s e i s m i c s t r e s s c a n be e s t i m a t e d by t h e m e t h o d o f Seed e t a l . ( 1 9 7 1 ) : w h e r e a m a x = maximum g r o u n d s u r f a c e a c c e l e r a t i o n g = g r a v i t a t i o n a l a c c e l e r a t i o n o v = t o t a l o v e r b u r d e n p r e s s u r e r d = a s t r e s s r e d u c t i o n f a c t o r = l - 0 . 0 1 5 z z = d e p t h i n m. As n o t e d e a r l i e r , t h e maximum b e d r o c k a c c e l e r a t i o n a t t h e s i t e i s e q u a l t o 0.049 f o r STRhIN RATECONTROLLRI E S T

0 LOAD COMDLLED TEST

t 10 100 I000

STEADY STATE SHEAR STRENGTH, kPa FIGURE 4

STEADY STATE CHARACTERISTICS

a r e t u r n p e r i o d o f 475 y r s . and a t a f r e q u e n c y o f 5 Hz. I t i s u n l i k e l y t h a t s i g n i f i c a n t a c c e l e r a t i o n amp1 i f i c a t i o n w i l l t a k e p l a c e a t t h i s f r e q u e n c y d u r i n g t h e wave t r a n s m i s s i o n t o t h e s u r f a c e . T h e r e f o r e , a m a x / g i s t a k e n e q u a l t o .04. The l i q u e f a c t i o n r e s i s t a n c e (rl/o;,) c a n b e e s t i m a t e d f r o m t h e p i e z o c o n e d a t a o r t h e c y c l i c s i m p l e s h e a r t e s t s . F o r t h e p i e z o c o n e d a t a , q i s f i r s t c o n v e r t e d t o N1 u s i n g : w h e r e CN i s a c o e f f i c i e n t t o a c c o u n t f o r t h e e f f e c t i v e o v e r b u r d e n p r e s s u r e ( S e e d e t a l . 1 9 8 3 ) ; N1 i s t h e m o d i f i e d p e n e t r a t i o n r e s i s t a n c e and K = q I N . K was d e t e r m i n e d e a r l i e r as e q u a l t o 8.25 and 5 f o r t h e s i l t a n d t h e f i n e s a n d o f t h i s s i t e , r e s p e c t i v e l y . The l i q u e f a c t i o n r e s i s t a n c e i s e v a l u a t e d u s i n g f u n c t i o n a l r e l a t i o n s h i p s s u g g e s t e d b y Seed e t a l . ( 1 9 8 3 ) : D i f f e r e n t f ~ n c t i o n s ~ a p p l y f o r s a n d a n d f o r s i l t . A t y p i c a l r / a p r o f i l e f o r a n e a r t h q u a k e m a g n i t u % e

!a)

o f 6.5 i s shown i n F i g u r e 5. The l i q u e f a c t i o n r e s i s t a n c e f r o m t h e c y c l i c s i m p l e s h e a r t e s t s on u n d i s t u r b e d s a m p l e s c o r r e s p o n d i n g t o M = 6.5 i s a l s o p l o t t e d o n F i g u r e 5. T h i s r e s i s t a n c e i s a b o u t h a l f o f t h a t f r o m t h e p i e z o c o n e t e s t s . The d i s c r e p a n c y h a s b e e n a t t r i b u 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 i n t h e s o i l s a m p l e s a n d t h e n o n p l a s t i c n a t u r e o f t h e s i l t ( Z h u a n d Law, 1 9 8 8 ) . I n t h i s s t u d y t h e d e s i g n l i q u e f a c t i o n r e s i s t a n c e o f t h e s i l t l a y e r was o b t a i n e d f r o m t h e p i e z o c o n e d a t a c o r r e c t e d b y r e d u c t i o n t o t h e v a l u e f r o m t h e c y c l i c s i m p l e s h e a r t e s t s . U n d o u b t e d l y , t h i s p r o d u c e s a c o n s e r v a t i v e e s t i m a t e o f rl/a;o as t h e l a b o r a t o r y v a l u e i n c l u d e s t h e e f f e c t s o f m e c h a n i c a l s o f t e n i n g d u e t o d i s t u r b a n c e .

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LIOUEFACTION RESISTANCE ( Ti1 a;,)

L~~ SlMRE ;HEAR

TEST C# UND'STURBED

MMFLES

FIGURE 5

LIQUEFACTION RESISTANCE PROFILE AT A137 FOR EARTHOUME MAGNITUDE

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6 5 F o r t h e f i n e s a n d l a y e r , zl/a;o f r o m p i e z o n c o n e d a t a d o e s n o t r e q u i r e c o r r e c t i o n b e c a u s e p l a s t i c i t y i s no l o n g e ; a f a c t o r . I n F i g u r e 6 a c o r r e c t e d zl/uv p r o f i l e f r o m p i e z o c o n e d a t a f o r t h e w e a k e s t ? o c a t i o n ( A J 3 4 A ) i s c o m p a r e d w i t h t h e s e i s m i c s t r e s s f o r t h a t w h i c h c o u l d be d e v e l o p e d f o r an e a r t h q u a k e o f M = 6.5. The c o m p a r i s o n shows t h a t t h e t o p 3 m o f f i n e s a n d may l i q u e f y u n d e r s u c h c o n d i t i o n s and, t h e r e f o r e , r e q u i r e s s t r e n g t h e n i n g . A s i m i l a r o b s e r v a t i o n was a l s o made f o r t h e t o p 2.5 m a t PC2 w h i l e f o r a l l o t h e r l o c a t i o n s l i q u e f a c t i o n i s u n l i k e l y .

STRESS RATIO, r 1 a;,

0 02 0.4 0 1 1 1 I I 1 I e x a m i n e d . Hence, a s t a b i l i t y a n a l y s i s b a s e d on l i m i t e q u i l i b r i u m was c a r r i e d o u t t o c a l c u l a t e t h e a v e r a g e d r i v i n g s h e a r s t r e s s ( z ) a l o n g t h e c r i t i c a l s l i p s u r f a c e . The c a l c u l a f e d ( z d ) i s p l o t t e d on F i g u r e 48. As t h i s p o i n t l i e s b e l o w t h e s t e a d y s t a t e s t r e n g t h l i n e , t h e d y k e i s u n l i k e l y t o f a i l i n t h e f o r m o f a f l o w s l i d e . SUMMARY AND CONCLUSIONS

The L i t t l e J a c k f i s h d y k e i s t o b e c o n s t r u c t e d o v e r a t h i c k l a y e r o f n o n p l a s t i c s i l t and f i n e sand. The 1 i q u e f a c t i o n p o t e n t i a l o f t h e s e g r a n u l a r s o i l s was s t u d i e d u s i n g i n s i t u and l a b o r a t o r y m e t h o d s . The s t u d y shows t h e f o l l o w i n g : 1. The r a t i o s o f t i p r e s i s t a n c e i n k g / c m 2 t o p e n e t r a t i o n r e s i s t a n c e i n b l o w s p e r f o o t a r e 4.25 a n d 5 f o r t h e s i l t and t h e f i n e s a n d , r e s p e c t i v e 1 y . 2. The l i q u e f a c t i o n r e s i s t a n c e o f t h e s i l t f r o m p i e z o c o n e t e s t s i s d o u b l e t h a t d e t e r m i n e d f r o m c y c l i c s i m p l e s h e a r t e s t s on u n d i s t u r b e d s a m p l e s . 3. The t o p l o o s e s a n d l a y e r a t t w o t e s t e d l o c a t i o n s was f o u n d t o b e l i q u e f i a b l e u n d e r t h e d e s i g n e a r t h q u a k e w h i l e f o r t h e o t h e r s t u d i e d l o c a t i o n s , b o t h t h e s a n d a n d s i l t l a y e r s a r e n o t l i k e l y t o l i q u e f y . 4. B a s e d on t h e s t e a d y s t a t e a p p r o a c h , t h e p r o p o s e d d y k e i s u n l i k e l y t o f a i l i n a f l o w s l i d e c o n d i t i o n . ACKNOWLEDGEMENTS The a u t h o r s a r e g r a t e f u l t o D r . C.F. Lee of O n t a r i o H y d r o f o r h i s i n t e r e s t a n d e n c o u r a g e m e n t t h r o u g h o u t t h i s s t u d y . The s e i s m i c c o n d i t i o n s a t t h e s i t e w e r e c a l c u l a t e d b y J.R. B o w l b y o f O n t a r i o H y d r o . The p i e z o c o n e t e s t s and s a m p l i n g w e r e p e r f o r m e d b y T. H o o g e v e e n a n d A. L a b e r g e . The s t u d y was p a r t l y f u n d e d b y G r a n t No. A 4 3 8 7 f r o m t h e N a t u r a l S c i e n c e s a n d E n g i n e e r i n g R e s e a r c h C o u n c i l o f Canada. T h i s G r a n t was a w a r d e d t o t h e f i r s t a u t h o r as an A d j u n c t P r o f e s s o r o f C a r l e t o n U n i v e r s i t y . L Q E L E

I

NON-LIQUEFIABLE REFERENCES FIGURE 6 LIQUEFACTION POTENTIAL A T A I M FOR M = 6 5 F i g u r e 4 shows t h e r e s u l t s o f a n o t h e r a p p r o a c h f o r a s s e s s i n g t h e l i q u e f a c t i o n p o t e n t i a l b a s e d on t h e m e t h o d o f P o u l o s e t a l . ( 1 9 8 5 ) . The a v e r a g e v o i d r a t i o and e f f e c t i v e h o r i z o n t a l s t r e s s o f t h e t o p 1 5 m o f s u b s o i l a f t e r c o n s t r u c t i o n o f t h e d y k e a r e r e p r e s e n t e d by a r a n g e on F i g u r e 4A. It a p p e a r s t h a t t h e s o i l l a y e r w i l l be c o n t r a c t i v e and t h e p o s s i b i l i t y o f a f l o w s l i d e f a i l u r e n e e d s t o b e C a s a g r a n d e , A. ( 1 9 7 6 ) . L i q u e f a c t i o n a n d c y c l i c d e f o r m a t i o n

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a c r i t i c a l r e v i e w . P r o c . 5 t h Pan. Am. CSMFE, B u n e o s A i r e s , A r g e n t i n a . Hasegawa, H.S., Basham, P.M. and B e r r y , M.J.

( 1 9 8 1 ) . A t t e n u a t i o n r e l a t i o n s f o r s t r o n g s e i s m i c g r o u n d m o t i o n i n Canada. B u l l e t i n o f S e i s m . Soc. o f Am., 7 1 ( 6 ) , 1 9 4 3 - 1 9 6 2 . P o u l o s , S.J., C a s t r o , G. and F r a n c e , J.W. ( 1 9 8 5 ) . L i q u e f a c t i o n e v a l u a t i o n p r o c e d u r e . J. G e o t . Engg. ASCE, 1 1 1 ( 6 ) , 772-792.

Seed, H.B. and I d r i s s , I.M. ( 1 9 7 1 ) . S i m p l i f i e d p r o c e d u r e f o r e v a l u a t i n g s o i l l i q u e f a c t i o n p o t e n t i a l . JSMFD, ASCE, 9 7 ( 9 ) , 1 2 4 9 - 1 2 7 3 . Seed, H.B. I d r i s s , I.M. and A r a n g o , I. ( 1 9 8 3 ) .

E v a 1 u a t i o n o f 1 i q u e f a c t i o n p o t e n t i a l u s i n g f i e l d p e r f o r m a n c e d a t a . JGEO, ASCE, 1 0 9 ( 3 ) , 4 5 8 - 4 8 2 .

Seed, H.B. and Lee, K.L. ( 1 9 6 6 ) . L i q u e f a c t i o n o f s a t u r a t e d s a n d d u r i n g c y c l i c l o a d i n g . JSM FD, ASCE. 9 2 ( 6 ) , 105-134.

Zhu, R. and Law, K.T. ( 1 9 8 8 ) . L i q u e f a c t i o n p o t e n t i a l o f s i l t . 9 t h W o r l d C o n f . E a r t h q u a k e Engg., T o k y o , J a p a n .