Earthflows at the Beattie Mine: a case record

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Earthflows at the Beattie Mine: a case record Eden, W. J.

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NATIONAL

RESEARCH COUNCIL

CANADA

D I V I S I O N OF BUILDING

RESEARCH

EARTHFLOWS AT THE BEATTIE MIhrE

-

A CASE RECORD by W. 3 . Eden

I n t e r n a l

R e p o r t

No.

221

of

t h e

Division o f

Building

R e s e a r c h OTTAWA

May

1961

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PREFACE

The c o n s t r u c t i v e s t u d y of f a i l u r e s i s a n e s s e n t i a l p a r t of r e s e a r c h work. Such i n v e s t i g a t i o n s a r e of s p e c i a l v a l u e i n t h e f i e l d of s o i l mechanics s i n c e t h e r e i s s t i l l s o much -to be done i n t h e c o r r e l a t i o n of l a b o r a t o r y t e s t s of s o i l samples and t h e performance of s o i l s i n s i t u .

T h i s r e p o r t i s a p r o g r e s s s t a t e m e n t of s u c h a s t u d y t o which t h e w r i t e r had l o n g looked f o r w a r d . He was con- s u l t e d a b o u t t h i s f a i l u r e b y M r . F. E. Lathe e v e n b e f o r e t h e D i v i s i o n of B u i l d i n g Research was formed and had k e p t i n mind t h e v a l u e t o be d e r i v e d from a s t u d y of t h e u n u s u a l s l i d e s a t t h e B e a t t i e Mine. A c c o r d i n g l y , it was a p l e a s u r e t o a r r a n g e f o r t h e a u t h o r of t h i s r e p o r t , who i s a r e s e a r c h o f f i c e r i n t h e S o i l Mechanics S e c t i o n of DBR, t o v i s i t t h e B e a t t i e Mine w i t h a n a s s o c i a t e f o r a p r e l i m i n a r y s t u d y i n t h e f i e l d of t h e e a r t h f a i l u r e s . T h i s r e p o r t r e p r e s e n t s a summary of i n f o r m a t i o n t h e n o b t a i n e d and a l l t h e s u b s e q u e n t l a b o r a t o r y i n v e s t i g a t i o n s . The a s s i s t a n c e of t h e mine a u t h o r i t i e s i n t h i s s t u d y was g r e a t l y a p p r e c i a t e d and i n p a r t i c u l a r t h e i n t e r e s t of M r . W.

R.

_{S a l t e r , P r e s i d e n t , B e a t t i e Duquesne} Mines Limited. A s soon a s s t a f f a r e a v a i l a b l e , f u r t h e r s t u d i e s w i l l be c a r r i e d o u t a s s u g g e s t e d i n t h e body of t h e r e p o r t . A complete p a p e r on t h e p r o j e c t

w i l l

t h e n be p r e p a r e d and p u b l i s h e d i f t h e n e c e s s a r y a u t h o r i t y f o r t h i s c a n be g r a n t e d , t h e i n t e n t i o n of b o t h t h i s r e p o r t and a n y s u b s e q u e n t p a p e r b e i n g t o make a v a i l a b l e t o t h e e n g i n e e r i n g p r o f e s s i o n s i g n i f i c a n t i n f o r m a t i o n which w i l l a s s i s t w i t h f u r t h e r e a r t h works of t h e t y p e involved.. Ottawa May 1 9 6 1 D i r e c t o r . R. F. L e g g e t ,

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EARTHFLOWS

AT THE

BEATTIE M I N E

-

A CASE RECORD by

W.

J . Eden

I n J u n e 1943, a n e a r t h f l o w i n v o l v i n g 1 , 0 0 0 , 0 0 0 c u b i c y a r d s o c c u r r e d a t t h e B e a t t i e Mine, Duparquet, P. &.

,

f i l l i n g t h e open p i t and underground w o r k i n g s a t t h e mine. A t t e m p t s were made t o r e h a b i l i t a t e t h e mine, b u t t h e s e were f r u s t r a t e d by o t h e r l a r g e e a r t h f l o w s i n 1945 and 1946. m e s e n o t e s o u t l i n e t h e sequence of e v e n t s l e a d i n g u p t o t h e e a r t h f l o w s , d e s c r i b e t h e e a r t h f l o w s , a n d g i v e t h e r e s u l t s o f a two-day f i e l d s t u d y u n d e r t a k e n i n May 1960.

H i s t o r y of t h e Mine

The B e a t t i e Mine began p r o d u c t i o n i n 1933, t h e g o l d - b e a r i n g o r e b e i n g won from a l a r g e r e l a t i v e l y low-grade o r e body. The o r e body l a y a l o n g t h e n o r t h flanlc of

a

r o c k r i d g e o r i e n t e d i n a n e a s t - w e s t d i r e c t i o n . A t t h e w e s t e n d , t h e o r e body came t o s u r f a c e a n d plunged u n d e r o v e r b u r d e n t o w a r d s t h e e a s t . Ore w a s mined by

a

c o m b i n a t i o n of " g l o r y h o l e " and underground s t o p i n g methods. T u t t l e ( 1 9 3 9 ) g i v e s a d e t a i l e d d e s c r i p t i o n of t h e workings. The " g l o r y h o l e " was a n open p i t w i t h v e r y s t e e p s i d e s a n d s l o p i n g ends. The h a n g i n g w a l l

of

p i t was s u p p o r t e d by t h e f o o t w a l l by means of f o u r p i l l a r s l e f t a c r o s s t h e p i t a t f r e q u e n t i n t e r v a l s . The ends of t h e p i t s l o p e d a t a b o u t 40 d e g r e e s . Ore was mined from t h e e n d s of t h e p i t a n d r o l l e d down t h e s l o p e s i n t o t h e underground system. By 1943, t h e " g l o r y h o l e " w a s a b o u t

1 , 0 0 0 f t i n l e n g t h , a b o u t 40 f t wide

a t

t h e e a s t end a n d o v e r 200 f t pride a t t h e w e s t end. The d e e p e s t p o i n t of t h e p i t w a s a b o u t 300 f t below t h e s u r f a c e .

The p r o d u c t i o n a t t h e mine w a s s c h e d u l e d s o t h a t t h e g l o r y h o l e o r p i t w a s worked d u r i n g t h e summer months; t h e

more e x p e n s i v e underground development and mining were c o n d u c t e d d u r i n g t h e w i n t e r .

A s p r o d u c t i o n proceeded, t h e p i t w a s g r a d u a l l y

l e n g t h e n e d , r e q u i r i n g t h e s t r i p p i n g of g r e a t e r a n d g r e a t e r d e p t h s of overburden from t h e e a s t end a n d n o r t h s i d e of t h e p i t . I n

i t s

e a r l y s t a g e s , t h e s t r i p p i n g was a c c o m p l i s h e d by h o r s e a n d s c r a p p e r s . A s t h e amounts of s t r i p p i n g grew l a r g e r a tower d r a g l i n e system and mechanical equipment were used.

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I n a l l c a s e s , t h e s t r i p p e d m a t e r i a l w a s d e p o s i t e d n e a r t h e t o p of s l o p e s c u t i n t h e o v e r b u r d e n . The s l o g e s were c u t t o a s l o p e of

4 : l

w i t h a berm b o r d e r i n g t h e o r e body. The maximum d e p t h of overburden was a b o u t 1 0 0 f t , c o n s i s t i n g of

8 5

f t of c l a y u n d e r l a i n by 1 5 f t of sand. F i g u r e 1 i s a photograph showing t h e s l o p e s i n 1943. The o v e r b u r d e n con- s i s t e d of v a r v e d c l a y o v e r l y i n g a few f e e t of sand o v e r t h e bedrock. The varved c l a y was d e p o s i t e d i n l a t e g l a c i a l t i m e s i n Lake Barlow-Ojibway ( A n t e v s 1 9 2 5 ) and was f o u n d t o be n e a r l y n o r m a l l y c o n s o l i d a t e d . The mine was l o c a t e d a b o u t one m i l e n o r t h of Lake Duparquet and t h e r i m of t h e p i t on t h e w e s t end was a b o u t 60 f t below t h e l a k e l e v e l . S e i s m i c s u r v e y s showed t h e r e was no l e d g e of b e d r o c k between t h e r i m of t h e p i t and t h e s h o r e s of t h e l a k e . The t a i l i n g s d i s p o s a l s i t e was l o c a t e d

i n

swampy l a n d n e a r t h e s o u t h w e s t c o r n e r of t h e p i t . I t was n o t e d t h a t c o n s i d e r a b l e seepage i s s u e d from t h e sand u n d e r l y i n g t h e c l a y , p a r t i c u l a r l y a t t h e w e s t end of t h e p i t , c l o s e s t t o t h e l a k e s h o r e , and t h e t a i l i n g s d i s p o s a l a r e a .

By t h e n a t u r e of t h e s t r i p p i n g o p e r a t i o n s , a s l o p e f a i l u r e c o u l d be e x p e c t e d . The magnitude of t h e e v e n t u a l f a i l u r e , however, i s somewhat s u r p r i s i n g i n view of t h e v a r v e d c l a y s b e i n g f r e s h w a t e r d e p o s i t s . ! h e f i r s t s l i d e r e c o r d e d i n t h e a v a i l a b l e r e c o r d s w a s on 19 J u n e 1937. I t o c c u r r e d a t t h e n o r t h e a s t c o r n e r of t h e g l o r y h o l e , had t h e c h a r a c t e r i s t i c shape of a n e a r t h f l o w , a n d i n v o l v e d

a

few t h o u s a n d y a r d s o f m a t e r i a l .

The second s l i d e r e c o r d e d , i n 1942, was a b o u t midway a l o n g t h e n o r t h s i d e o f t h e g l o r y h o l e . Again, t h i s s l i d e d i d n o t s e r i o u s l y a f f e c t o p e r a t i o n s i n t h e mine. I n J u n e , 1943, a tremendous e a r t h f l o w o c c u r r e d which i n v o l v e d a m i l l i o n c u b i c y a r d s o f c l a y . This s l i d e c o m p l e t e l y f i l l e d t h e g l o r y h o l e a n d p e n e t r a t e d t h e underground w o r k i n g s . Some c l a y r a n n e a r l y h a l f a m i l e a l o n g t h e s i x t h l e v e l d r i f t t o w a r d s t h e Donchester Mine which

was

c o n n e c t e d t o t h e B e a t t i e Mine underground. !The _{main p i l l a r s u p p o r t i n g t h e h a n g i n g}

w a l l o f t h e p i t c o l l a p s e d , a l l o w i n g t h e h a n g i n g w a l l

a t

t h e e a s t end of t h e p i t t o f a l l i n t o t h e p i t . According t o i n f o r m a t i o n r e c e i v e d from M r . P.E. P a t t o n i n c o r r e s p o n d e n c e , t h e main p i l l a r c o l l a p s e d d u r i n g t h e n i g h t of 15-16 J u n e , 1943, p r i o r t o t h e s o i l movement. The e x t e n t of t h i s l a n d s l i d e i s shown i n F i g u r e 2 , a l o n g w i t h t h e s m a l l e r f a i l u r e s r e c o r d e d i n 1937 and 1942. F i g u r e 3 i s a photograph t a k e n from t h e w e s t end of t h e g l o r y h o l e on 1 6 J u n e , 1943, showing p a r t of

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t h e e a r t h f l o w .

While t h e n e i g h b o u r i n g D o n c h e s t e r mine remained i n o p e r a t i o n , s t e p s were t a k e n

t o

r e h a b i l i t a t e t h e B e a t t i e Mine, I n t h e underground w o r k i n g s , t h e c l a y was s l u i c e d by h i g h p r e s s u r e w a t e r j e t s and t h e r e s u l t i n g s l u r r y was pumped t o t h e s u r f a c e . Small hydr.?ulic d r e d g e s were s e t u p i n t h e g l o r y h o l e a n d i n t h e s l i d e c r a t e r t o remove t h e c l a y from t h e

p i t a r e a . By June 1946, a b o u t 1& m i l l i o n c u b i c y a r d s of c l a y h a d been removed from t h e p i t a r e a a n d t h e underground

w o r k i n g s . I t was e s t i m a t e d t h a t a f u r t h e r one m i l l i o n c u b i c y a r d s h a d

t o

be removed b e f o r e a n y p r o d u c t i o n c o u l d s t a r t i n t h e mine.

I n 1 9 4 5 , a few s m a l l s l i d e s o c c u r r e d i n t h e c r a t e r , undoing some o f t h e work o f t h e d r e d g e s . !I!he s l i d e s c o n t i n u e d i n 1946, t h e l a r g e s t one o c c u r r i n g on 25 J u n e , i n v o l v i n g a b o u t 250,000 c u b i c y a r d s . F i g u r e 4 i s a panorama view from t h e w e s t end of t h e mine t a k e n i n J u l y 1946. S l i d e s c o n t i n u e d t h r o u g h o u t t h e summer, t h e l a s t o n e s r e c o r d e d b e i n g on 1 3 a n d 2 8 September. A s F i g u r e 2 shows, Vnese s l i d e s o c c u r r e d towards t h e w e s t end o f t h e p i t . I n t h e f a l l of 1 9 4 6 ,

g o l d market p r i c e s were f a l l i n g , and s o f a r a s i s known, a l l s e r i o u s e f f o r t s

t o

r e h a b i l i t a t e t h e mine c e a s e d , e x c e p t f o r t h e s i n k i n g of

a

s h a l l o w s h a f t t o r e a c h a l o d e o f r i c h o r e a t t h e w e s t end of t h e p i t . F i e l d I n v e s t i g a t i o n I n May 1960,

a

t h r e e - d a y v i s i t w a s p a i d t o t h e B e a t t i e p r o p e r t y t o o b t a i n more i n f o r m a t i o n on t h e s o i l p r o p e r t i e s . F i g u r e

5

_{shows t h e s i t e c o n d i t i o n s i n}_1960. _{!Phe l a k e shown}

o c c u p i e s t h e c r a t e r formed by t h e e a r t h f l o w s . The f o o t w a l l of t h e g l o r y h o l e a p p e a r s a t t h e r i g h t of t h e p i c t u r e . The r o c k p o i n t j u t t i n g o u t a t t h e l a k e w a t e r i s t h e t o p of t h e f o r m e r h a n g i n g w a l l o f t h e p i t . !I!he photograph l o o k s i n t h e n o r t h e a s t d i r e c t i o n . !I!he s i t e chosen f o r s a m p l i n g w a s a l o n g t h e n o r t h s h o r e of t h e c r a t e r s l i g h t l y l e f t of c e n t r e of t h e photograph.

It was found t h a t t h e walls of t h e c r a t e r were formed of v a n e d c l a y . A r e t r o g r e s s i v e t y p e o f f a i l u r e w a s i n d i c a t e d by t h e slump b l o c k s which c o u l d be o b s e r v e d a r o u n d t h e c r a t e r . During t h e sampling work, l a y e r s o f sand o r s i l t were e n c o u n t e r e d i n t h e v a n e d c l a y . With t h e hand equipment, it was n o t p o s s i b l e

t o

p e n e t r a t e t h e sandy l a y e r s , s o t h a t t h e p r o f i l e of samples o b t a i n e d were t a k e n i n t h r e e b o r i n g s s p a c e d dovm t h e f a c e of t h e c r a t e r . From t h e t h r e e b o r i n g s , a p r o f i l e o f s a m p l e s r e p r e s e n t i n g 30 f t of v a r v e d c l a y

was

o b t a i n e d . The s a m p l e r

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u s e d w a s t h e N G I p i s t o n s a m p l e r (Bjerrum 1 9 5 4 ) .

It;

i s b e l i e v e d t h a t t h e bottom of t h e f a i l u r e s u r f a c e w a s 10 o r 1 5 f t below t h e bottom sample, s o t h a t t h e r e s u l t s o b t a i n e d c a n n o t be a p p l i e d t o a s t a b i l i t y a n a l y s i s . It i s hoped, however, t h a t a g e n e r a l i m p r e s s i o n of g e o t e c h n i c a l p r o p e r t i e s of t h e v a r v e d c l a y of t h e s i t e may be g a i n e d . E l e v a t i o n s of t h e b o r i n g s were t a k e n i n r e l a t i o n t o t h e c o l l a r of development s h a f t l o c a t e d

a t

t h e w e s t end of t h e g l o r y h o l e . From t h e mine r e c o r d s ,

it

i s i n f e r r e d t h a t t h e e l e v a t i o n of t h e c l a y p l a i n w a s a b o u t 930. Thus t h e l e v e l of t h e w a t e r i n t h e c r a t e r i n May 1960 w a s a b o u t e l e v a t i o n 900. No p r e c i s e bench mark c o u l d be found i n t h e mine r e c o r d s t o s e r v e a s a datum f o r t h e f i e l d i n v e s t i g a t i o n .

L a b o r a t o r y Work

The n i n e t u b e samples were t e s t e d t o determine t h e u n d r a i n e d s t r e n g t h , t h e p r e c o n s o l i d a t i o n p r e s s u r e , a n d

c l a s s i f i c a t i o n p r o p e r t i e s . Whenever

i t

w a s p o s s i b l e , c l a s s i f i c a t i o n a n d s e n s i t i v i t y t e s t s were performed on

s e p a r a t e d samples of dark and l i g h t l a y e r s of t h e v a r v e d c l a y , !&e r e s u l t s of t e s t s a r e p r e s e n t e d i n F i g u r e 6; l i n e A-A i s t h e e f f e c t i v e overburden p r e s s u r e , t a k i n g t h e s u r f a c e of t h e c l a y t o be a b o u t e l e v a t i o n 930 w i t h t h e w a t e r t a b l e c l o s e t o t h e s u r f a c e . The r e s u l t s of t h e c o n s o l i d a t i o n t e s t s i n d i c a t e t h a t t h e c l a y i s s l i g h t l y o v e r c o n s o l i d a t e d a n d i n d i c a t e s t h a t a d r y i n g c r u s t h a s developed

a t

t h e s u r f a c e . The u n d r a i n e d s t r e n g t h d e t e r m i n a t i o n s made i n d i c a t e t h a t t h e u n d r a i n e d s h e a r s t r e n g t h was a b o u t 500 p s f , i n c r e a s i n g s l i g h t l y w i t h d e p t h . C l a s s i f i c a t i o n t e s t r e s u l t s a r e p r e s e n t e d i n t h e form of s o l i d l i n e s f o r t e s t s conducted on mixed l i g h t and dark l a y e r s of t h e c l a y and by broken l i n e s f o r t h e s e t e s t s conducted on samples made u p of s e p a r a t e d d a r k a n d l i g h t l a y e r s . It w i l l be n o t e d t h a t d i f f e r e n c e i n p r o p e r t i e s between t h e d a r k a n d l i g h t l a y e r s w a s g r e a t .

S e n s i t i v i t y w a s determined f o r t h e mixed samples by means of a l a b o r a t o r y vane a p p a r a t u s and a r e p l o t t e d on F i g u r e 6. An a t t e m p t w a s made t o d e t e r m i n e t h e s e n s i t i v i t y of t h e i n d i v i d u a l l a y e r s o f dark a n d l i g h t m a t e r i a l by means of

a

f a l l cone d e v i c e . These r e s u l t s a r e t a b l e d i n F i g u r e 6 a n d i n d i c a t e t h a t the l i g h t l a y e r s were g e n e r a l l y more s e n s i t i v e t h a n t h e d a r k l a y e r s , !be o v e r - a l l s e n s i t i v i t y a p p e a r s t o be above 1 5 which i s u n u s u a l f o r f r e s h w a t e r c l a y s i n view of t h e f i n d i n g s of Skempton a n d Northey ( 1 9 5 2 ) a n d B jerrum a n d

(8)

Rosenqvist ( 1 9 5 6 ) .

To i n d i c a t e t h e v a r i a t i o n i n p r o p e r t i e s between

t h e

d a r k

and l i g h t l a y e r s , Figure

7 p r e s e n t s t h e p r o f i l e of

sample No. 99-5 a l o n g w i t h t h e v a r i a t i o n i n n a t u r a l w a t e r

c o n t e n t ,

me

v a r i a t i o n

ia

_{w a t e r c o n t e n t between}

_{t h e}

_dark

and

l i g h t

l a y e r s

i s

similar t o

that

found f o r t h e varved c l a y s

a t

S t e e p Rock (Eden 1 9 5 5 ) .

F i g u r e

8 i s

a Casagrande c l a s s i f i c a t i o n c h a r t showing

t h e A t t e r b e r g d e t e r m i n a t i o n s on t h e s e p a r a t e laminae of t h e

varved c l a y from t h e B e a t t i e Mine, a l o n g w i t h r e s u l t s from

o t h e r s i t e s ( M i l l i g a n 1 9 6 0 ) .

I t

can be s e e n t h a t t h e B e a t t i e

Mine c l a y

i s

comparable t o varved c l a y s from o t 5 e r s i t e s i n

Northern Ontario.

Undrained s t r e n g t h d e t e r m i n a t i o n s were made by t h r e e

methods:

t h e l a b o r a t o r y vane, t h e unconfined compression

t e s t and t h e u n c o n s o l i d a t e d , undrained t r i a x i a l t e s t

w i t h

l a t e r a l p r e s s u r e approximately e q u a l t o t h e e f f e c t i v e over-

burden s t r e s s . !he r e s n l t s of t h e t h r e e t e s t methods a r e

p r e s e n t e d and i n g e n e r a l a p p e a r t o have g i v e n comparable

r e s u l t s .

If

t h e l a b o r a t o r y vane t e s t s a p p e a r t o be s l i g h t l y

lower,

i t

is

because t h e vane d e t e r m i n a t i o n s were made on

t h e

f i r s t

specimen e x t r a c t e d from each t u b e and hence t h e

t e s t s were conducted on specimens which may have s u f f e r e d

more d i s t u r b a n c e t h a n t h e remaining samples.

I n t h e unconfined compression t e s t s on specimens

w i t h t h e v a r v i n g n e a r l y h o r i z o n t a l , f a i l u r e occurred by

s p r e a d i n g

i n

t h e l i g h t l a y e r s and v e r t i c a l c r a c k s i n t h e

more b r i t t l e dark l a y e r s ,

s i m i l a r

t o t h a t r e p o r t e d f o r t h e

S t e e p Rock c l a y s (Eden 1 9 5 5 ) .

Conclusions

1. %is

i n v e s t i g a t i o n h a s shown

t h a t

t h e v a n e d c l a y

a t

t h e B e a t t i e MLne

i s

n e a r l y normally c o n s o l i d a t e d and very

s e n s i t i v e .

A

sliallow d r y i n g c r u s t a p p e a r s t o have developed

a t t h e s u r f a c e .

I n t h e

30

f t

of c l a y i n v e s t i g a t e d , t h e

undrained s h e a r s t r e n g t h

w a s found t o be a b o u t 500 p s f ,

showing a v e r y s l i g h t i n c r e a s e i n s t r e n g t h w i t h depth.

m e r e w a s c o n s i d e r a b l e d i f f e r e n c e i n p r o p e r t i e s

between t h e l i g h t and dark l a y e r s of t h e c l a y comparable t o

t h a t

found f o r o t h e r s i t e s i n varved c l a y .

The l i g h t l a y e r s

appear t o be s l i g h t l y more s e n s i t i v e t h a n t h e dark l a y e r s .

(9)

t h e method o f s t r i p p i n g , and n o t t o s e e p a g e p r e s s u r e s i n t h e u n d e r l y i n g s a n d a l t h o u g h t h e s e e p a g e p r e s s u r e s may have c o n t r i b u t e d somewliat t o o v e r - a l l i n s t a b i l i t y . By t h e p r o c e s s o f g r a d u a l l y deepening t h e e x c a v a t i o n a n d p i l i n g t h e s p o i l on t o p o f t h e s l o p e , a f a i l u r e

was

i n e v i t a b l e w h e t h e r o r n o t t h e r e w a s h i g h w a t e r p r e s s u r e i n t h e sand. The i m p o r t a n t f e a t u r e o f t h e f a i l u r e

w a s

t h e l i q u e f a c t i o n t h a t o c c u r r e d i n d i s t u r b e d m a t e r i a l , i n d i c a t i n g t h a t v a r v e d c l a y s a r e prone t o t h e f l o w t y p e of l a n d s l i d e .

3.

_{Because o f t h e l a c k o f p r e c i s e i n f o r m a t i o n on t h e} dimensions o f t h e s l o p e a n d t h e l a c k o f d e e p e r s a m p l e s , o n l y

a

v e r y c r u d e s t a b i l i t y a n a l y s i s was a t t e m p t e d . By T a y l o r ' s method ( 1 9 3 7 ) a s h e a r s t r e n g t h of a b o u t 700 p s f i s r e q u i r e d f o r 8 0 f t s l o p e c u t a t 4 . 1 i n c l a y . The B e a t t i e Mine f a i l u r e i n f a c t i s a f u l l - s c a l e s h e a r s t r e n g t h t e s t on v a r v e d c l a y , a n d t h e w r i t e r would s u g g e s t t h a t f u r t h e r work i s t o be commended. A s a f i r s t s t e p , w i t h t h e c o - o p e r a t i o n of

B e a t t i e Duquesne Mines L i m i t e d , t h e p r e s e n t owners, a t h o r o u g h s e a r c h s h o u l d be made o f tine mine r e c o r d s a t Duparquet t o

o b t a i n more p r e c i s e i n f o r m a t i o n on t h e d i m e n s i o n s of t h e s l o p e s . S e c o n d l y , r e s p o n s i b l e o f f i c i a l s of t h e mine a t t h e t i m e o f t h e f a i l u r e s h o u l d be i n t e r v i e w e d i n a n e f f o r t t o o b t a i n a c l e a r e r p i c t u r e o f t h e sequence o f e v e n t s . T h i r d l y , s a m p l e s s h o u l d be o b t a i n e d t h r o u g h o u t t h e c l a y p r o f i l e . T h i s

w i l l

mean equipment c a p a b l e o f d r i v i n g a c a s e d b o r i n g t o

a

d e p t h of 100 f t o r more. From t h e w r i t e r 1 s e x p e r i e n c e , t h e p r e s e n c e o f sandy s i l t seems t o make a n u n c a s e d h o l e w i t h l i g h t hand equipment i m p r a c t i c a b l e .

Acknowledgments

The w r i t e r would l i k e t o acknowledge t h e a s s i s t a n c e g i v e n by A.O. Guibord a n d K. Timmins o f t h e S o i l Mechanics S e c t i o n , D i v i s i o n of B u i l d i n g R e s e a r c h , i n t h e f i e l d work a n d J . B . B o r d e l e a u a n d D. PhcbIillan who conducted most of t h e t e s t i n g . I&. G i l h u l y o f B e a t t i e Duquesne Mines L i m i t e d , Duparquet, was most h e l p f u l a t t h e s i t e i n g i v i n g a c c e s s

t o

t h e p r o p e r t y a n d l o o k i n g o u t t h e n i n e r e c o r d s .

Much of t h e i n f o r m a t i o n on t h e sequence o;P e v e n t s d u r i n g t h e l a n d s l i d e s were o b t a i n e d from t h e f i l e s of t h e l a t e D r . F.E. L a t h e , of t h e T e c h n i c a l I n f o r m a t i o n S e r v i c e , Department o f R e c o n s t r u c t i m a n d Supply (non p a r t o f t h e N a t i o n a l Research C o u n c i l ) . S p e c i a l acknowledgment i s due t o M r . _{F.E. P a t t o n , o f K i t c h e n e r , O n t a r i o , who} _{w a s} _{c h i e f}

e n g i n e e r , l a t e r manager, a t t h e B e a t t i e Mine i n 1934 t o 1957. H e k i n d l y s u p p l i e d p h o t o g r a p h s a n d o t h e r i n f o r m a t i o n on

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R e f e r e n c e s

1. Antevs, E. ( 1 9 2 5 ) . The R e t r e a t o f t h e L a s t I c e - S h e e t i n E a s t e r n Canada. Memoir No. 146, G e o l o g i c a l Survey of Canada, O t t a w a .

2. Bjerrum,

L.

( 1 9 5 4 ) . G e o t e c h n i c a l P r o p e r t i e s of Norwegian Marine Clays. G o t e c h n i q u e , Vol.

4 ,

lio. 2 ,

p . 49-69.

3 Bjerrum,

I,,

a n d R o s e n q v i s t , I. T h . _{( 1 9 5 6 ) .} _Some Experiments n i t h A r t i f i c i a l l y Sedimented Clay. Ggotechnique, Vol. 6 , No. 3, p. 124-136.

4. Eden, W . J . ( 1 9 5 5 ) . A L a b o r a t o r y Study of Varved Clay from S t e e p Rock Lake, O n t a r i o . American J o u r n a l of S c i e n c e , Vol. 253, p. 659-74.

.

M l l i g a n , V. ( 1 9 6 1 ) . D i s c u s s i o n t o a Preliminary Study of t h e G e o t e c h n i c a l P r o p e r t i e s of Varved C l a y s

as Reported i n Canadian E h g i n e e r i n g Case Records. J . B . Netcalf and

D.L.

Townsend. P r o c e e d i n g s , 1 4 t h Canadian S o i l Mechanics Conference, N a t i o n a l

Research C o u n c i l , A s s o c i a t e Committee on S o i l and Snow Mechanics, O t t a w a . ( I n P r e s s . )

6. Skempton, A.W. a n d Northey, R. D. ( 1 9 5 2 ) . !The S e n s i t i v i t y of Clays. Geotechnique, Vol. 3 , No. 1, p. 30-53.

7.

T a y l o r , D.W. ( 1 9 3 7 ) . S t a b i l i t y of E a r t h S l o p e s .

Journal,

Boston S o c i e t y o f C i v i l E n g i n e e r s , Vol. 24, No. 3 , p. 197-246.

8. T u t t l e , J. ( 1 9 3 9 ) . The S p i r a l S l o p i n g System a s Applied a t t h e B e a t t i e Mine. Can.

I n s t .

Mining and M e t a l l u r g y , T r a n s a c t i o n s , Vol. 42, p. 95-122.

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F i g u r e 1:

Clay

s l o p e s

a t

n o r t h w e s t s i d e o f B e a t t i e Mine

-

J u n e

1 5 , 1943.

(12)

(13)

Figure

3:

View from

west end of

p i t a f t e r l a n d s l i d e of June 1 6 ,

1943.

(14)

F i g u r e

4:

Panoramic v i e w t a k e n from w e s t end o f p i t showing e a r t h f l o w s i n 1945.

(15)

Figure

5:

Panoramic

v i e w

from

west

end of

p i t showing present

s i t e c o n d i t i o n s

-

May

1960.

(16)

(17)

WATER CONTENT, O/o DRY WT.

a

FIGURE 7

VARIATION IN WATER CONTENT FOR SAMPLE 9 9 - 5 VARVED CLAY- B E A T T I E MINE

I

-

P L _{DARK L A Y E R S}

-

_{P L} _I I L - L I G H T L A Y E R S AVG. W.C. AVG. W.C. L I G H T D A R K L A Y E R S

y

I

-

L A Y E R S

-

1 -

-

- -

-

- -

-

I

- 0 10 2 0 3 0 4 0 5 0 6 0 7 0 8 0

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0 ₁₀ ₂₀ ₃₀ _{4 0} 5 0 6 0 70 ₈₀ ₉₀ ₁₀₀

LIQUID LIMIT

F I G U R E 8

C A S A G R A N D E C L A S S I F I C A T I O N C H A R T FOR V A R V E D C L A Y ( A F T E R M l L L l G A N )