Settlement of Buildings in Workshops Area of Steep Rock Iron Mines

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Settlement of Buildings in Workshops Area of Steep Rock Iron Mines

Eden, W. J.

SETTLE?~ET?T

OF UUILDIJJGS

IZJ IdOlIKSIIOPS ARjZA 02'

STEEP ROCK

IHCN MINES

W .

J,. Eden

" P r e p a r e d f o r S t e e p Rock

Iron

Mines Limitedt'

R e p o r t

No.

52

of t h e

Civision of Buiiding R e s e a r c h

OTTAWA

December

1954

PREFACE The D i v i s i o n o f B u i l d i n g R e s e a r c h o f t h e N a t i o n a l R e s e a r c h C o u n c i l h a s b e e n p r i v i l e g e d t o m a i n t a i n c l o s e l i a i s o n w i t h t h e S t e e p Rock I r o n Mines L i m i t e d s i n c e t h e i n c e p t i o n o f t h e D i v i s i o n . The Company, f o r t h e i r p a r t , have p e r m i t t e d t h e D i v i s i o n t o u s e t h e g r e a t s o i l d e p o s i t s u n c o v e r e d i n t h e m i n i n g o p e r a t i o n s a s a l a r g e - s c a l e s o i l mechanics l a b o r a t o r y . D u r i n g one of t h e r e g u l a r v i s i t s of a member o f t h e

U.B,R.

s t a f f t o t h e Mine i n 1 9 5 4

(Mr..

W. J. Eden, o f t h e S o i l Mechanics S e c t i o n ) i n f o r m a t i o n was o b t a i n e d r e g a r d i n g s e r i o u s s e t t l e m e n t of some o f t h e s e r v i c e b u i l d i n g s o f t h e Mine. A s t u d y o f t h i s s e t t l e m e n t problem was, t h e r e f o r e , u n d e r t a k e n by t h e D i v i s i o n , s i n c e t h e t e s t s on t h e n e c e s s a r y s o i l s a m p l e s d e v e l o p e d most u s e f u l i n f o r m a t i o n r e g a r d i n g t h e s o i l p p o p e r t i e s o f t h e S t e e p Rock d e p o s i t s , T h i s r e p o r t s-arizes t h e i n v e s t i g a t i o n ,

It

i s n o t a c o m p l e t e t r e a t m e n t o f t h e f o u n d a t i o n problem which t h e Mine i s f a c i n g , b u t i t i s hoped t h a t i t w i l l

c o n t r i b u t e t o t h e s o l u t i o n o f t h i s problem.

Ottawa

December 2 7 , 1954

R o b e r t F. Legget D i r e c t o r

NQTZS OW SETY:'LET4li?JT OF BUILGINGS I N WORKST!QPS AHEA AT STESP ROC'( IHOLI

MIMES

by

W.

J o

Eden

The workshops a r e l o c a t e d i n a former s h a l l o w bay of' t h e Middle A r m of S t e e p Rock Lake. The b u i l d i n g s a r e founded on a r o c k f i l l p l a c e d over a c o n s i d e r a b l e d e p t h o f

r a r v e d c l a y . F i g u r e 1 i s a p l a n of t h e a r e a . The f i r s t r o c k f i l l was p l a c e d i n t h e p e r i o d from 1945 t o 1946, It extended e a s t w a r d s from t h e former s h o r e l i n e t o t h e l i n e i n d i c a t e d on t h e p l a n . I n 1945 a shop was b u i l t on t h e s i t e of t h e

p r e s e n t Unit R e p a i r Shop b u t i t was d e s t r o y e d by f i r e i n 1 9 4 6 ~ The p r e s e n t shops were c o n s t r u c t e d on t h e same s i t e i n t h e

s a n e y e a r . S t a r t i n g i n 1950, t h e r o c k f i l l was extended e a s t w a r d s t o t h e edge of t h e Highland Creek Gulley. T h i s f i l l averaged about

15

f e e t i n d e p t h . The E l e c t r i c a l Shops and Dry House were founded on t h e new p o r t i o n of r o c k f i l l ,

The f i r s t i n d i c a t i o n of t r o u b l e o c c u r r e d i n January, 1953. A c r a c k appeared i n t h e warehouse and t h e

s h o v e l r e p a i r shop, a l s o on t h e roadway between t h e two

s t r u c t u r e s . S i n c e J a n u a r y 1953, e l e v a t i o n s have been checked i n t h e v a r i o u s b u i l d i n g s . The l e v e l r e a d i n g s i n d i c a t e a

p r o g r e s s i v e movement. Contours o f t h e observed s e t t l e m e n t a r e a l s o p l o t t e d on F i g . 1 f o r t h e p e r i o d between J a n u a r y , 1953 and June, 1954. The measurements i n d i c a t e t h a t t h e aaximum s e t t l e m e n t i n t h e 18-month p e r i o d was

1.5

f e e t .

Two new shops a r e b e i n g planned a t p r e s e n t , one of which i s shown on F i g . 1. B o r i n g s have been p u t down on t h e proposed s i t e i n t h e l o c a t i o n s shown on Fig. 1. The

s o i l p r o f i l e s r e v e a l e d by t h e b o r i n g s a r e i n d i c a t e d on

F5gs. 2 and

3.

Four u n d i s t u r b e d t u b e samples were o b t a i n e d from b o r e h o l e

3 A

a t d e p t h s of 1 9 and 26 f e e t ,

33

and 39 f e e t , C o n s o l i d a t i o n t e s t s were conducted on t h e s e samples by t h e D i v i s i o n of B u i l d i n g Research, N a t i o n a l Research Council. The o b j e c t of t h i s r e p o r t i s t o p r e s e n t t h e 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 r e l a t i o n t o t h e f o u n d a t i o n d e s i g n of t h e proposed s t r u c t u r e .

2. C o n s o l i d a t i o n of S o i l s

Compressible s o i l s , when s a t u r a t e d , a r e made up of a s k e l e t o n of s o l i d p a r t i c l e s with t h e i n t e r s t i c e s f i l l e d w i t h w a t e r . Whenever a l o a d i s a p p l i e d t o such a s o i l , t h e

s k e l e t o n s making up t h e s o i l s t r u c t u r e b e g i n t o deform,

p r e s s u r e imrnediately s t a r t s a p r o c e s s o f d r a i n a g e , t h e r a t e d e p e n d i n s on t h e t h i c k n e s s of t h e s o i l l a y e r and t h e p e r m e a b i l i t y o f t h e s o i l . The p r o c e s s w i l l c o n t i n u e u n t i l t h e s o i l s t r u c t u r e h a s r e g a i n e d e q u i l i b r i u m and t h e p o r e p r e s s u r e h a s b e e n n e u t r a l i z e d . The c o n s o l i d a t i o n o f a c l a y l a g e r i s t h e r e f o r e a p r o c e s s r e q u i r i n g a c o n s i d e r a b l e t i m e t o c o m p l e t e . Every s o i l t h a t h a s b e e n d e p o s i t e d i n w a t e r w i l l have i t s o-m p e c u l i a r c o n s o l i d a t i o n c u r v e . S o i l j u s t f r e s h l y d e p o s i t e d w i l l h a v e a l o o s e s t r u c t l l r e s i n c e t h e r e h a s b e e n no p r e s s u r e above i t t o c a u s e c o n s o l i d a t i o n . A s s u c c e e d i n g l a y e r s o f s o i l a r e d e p o s i t e d , a n e f f e c t i v e p r e s s u r e e q u a l t o t h e buoyant w e i g h t o f t h e s u p e r i q p o s e d s o i l a c t s on t h e s o i l , T h i s e f f e c t i v e p r e s s u r e w i l l c a u s e t h e s o i l t o c o n s o l i d a t e t o a p o i n t termed t h e normal c o n s o l i d a t i o n . The v a r v e d c l a y s a t S t e e p Kock were n o r m a l l y c o n s o l i d a t e d up t o t h e p o i n t

where t h e l a k e was d r a i n e d and t h e r o c k f i l l w a s added. The w e i g h t o f t h e r o c k f i l l h a s c a u s e d f u r t h e r c o n s o l i d a t i o n . F i g u r e

lI.

i l l u s t r a t e s t h e v a r i a t i o n o f e f f e c t i v e p r e s s u r e s w i t h d e p t h . The c o n s o l i d a t i o n p r o p e r t i e s o f a s o i l c a n b e d e t e r m i n e d i n t h e l a b o r a t o r y . An u n d i s t u r b e d sample i s p l a c e d i n a t i g h t l y f i t t e d r i n g . P o r o u s p l a t e s a r e p l a c e d on t o p and bottom o f t h e sample. T h i s a r r a n g e m e n t i s p l a c e d i n a chamber f i l l e d w i t h w a t e r and it i s t h e n l o a d e d by i n c r e m e n t s . A f t e r e a c h i n c r e m e n t l o a d i s a p p l i e d , s u f f i c i e n t t i m e i s a l l o w e d f o r t h e sample t o c o n s o l i d a t e . A f t e r a s e r i e s o f i n c r e m e n t l o a d s h a s b e e n a p p l i e d , a p r e s s u r e - v o i d r a t i o d i a g r a m c a n b e o b t a i n e d . T h l s diazrarn i s v e r y c l o s e T O t h e o r i g i n a l c o n s o l i d a t i o n c u r v e o f t h e c l a y . The p r e - c o n s o l i d a t i o n l o a d i s due t o t h e e f f e c t i v e p r e s s u r e o f t h e superimposed c l a y and t h e p r e s s t l r e o f t h e r o c k f i l l , A s c a n b e s e e n from t h e s h a p e o f t h e p r e s s u r e - v o i d - r a t i o c u r v e , t h e s o i l c a n b e l o a d e d t o 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 w i t h o u t a p p r e c i a b l e s e t t l e m e n t . I f , however, t h i s p r e s s u r e i s e x c e e d e d , t h e c l a y w i l l b e g i n t o c o n s o l t d a t e r a p i d l y a l o n g t h e v i r g i n c o m p r e s s i o n c u r v e . C o n s o l i d a t i o n would p r o c e e d u n t i l a v o i d r a t i o c o r r e s p o n d i n g t o t h e new p r e s s r z e was r e a c h e d .

3.

L a b o r a t o r y T e s t s

Four t u b e samples were o b t a i n e d from b o r e h o l e

3 A

a t d e p t h s of

1 7

t o 1 9 f e e t , 25 t o 27 f e e t , 32 t o

34

f e e t , and

35

t o 40 f e e t . C o n s o l i d a t i o n t e s t s were c o n d u c t e d on e a c h sample. Unconfined c o m p r e s s i o n t e s t s were u s e d i n a d d i t i o n t o i n d i c a t e d i s t u r b a n c e i n t h e s o i l . The t e s t s r e s u l t s a r e t a b u l a t e d i n T a b l e I,

TABLE

I

SUMMARY

OF

TEST Rl3SULTS

!

f

: -, '

! ,

i

l a - r , i.nf ir!.e CI cc?rlprlc. 5 5 ic,?.-l ti^^>.;^.- d L I . . ' . . 1-

m o s t probable pre consolidation load

4; indicates

disturbed specimen.

Again c o n s i d e r i n g F i g .

4,

which i l l u s t r a t e s t h e

v a r i a t i o n o f e f f e c t i v e p r e s s u r e w i t h d e p t h , l i n e AB r e p r e s e n t s t h e e f f e c t i v e p r e s s u r e i n t h e c o m p r e s s i b l e l a y e r i m m e d i a t e l y a f t e r t h e l a k e had b e e n d r a i n e d . I f , a t t h i s s t a g e , a sample was o b t a i n e d and t e s t e d , t k 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 would}

l i e on l i n e AB a t a p r e s s u r e c o r r e s p o n d i n g t o p o i n t

x,

s i n c e t h e v a r v e d c l a y i s n o r m a l l y l o a d e d . When t h e r o c k f i l l was a p p l i e d , w i t h zhe g r o u n d w a t e r l e v e l a t t h e s u r f a c e o f t h e : : l a g , t h 2 e f f e c t i v e p r e s s u r e p l u s t h e p o r e w a t e r p r e s s u r e would b e r e p r e s e n t e d by l i n e OCD. C o n s i d e r i n g d e p t h a g a i n , t h e e f f e c t i v e p r e s s u r e would a g a i n b e W X, and t h e p o r e p r e s s u r e would b e X Y. Owing t o t h e p o r e p r e s s u r e , d r a i n a g e would b e g i n and t h e e f f e c t i v e p r e s s l x r e would i n c r e a s e . The p r o c e s s would c o n t i n u e u n t i l t h e e f f e c t i v e press:n-e h a s

r e a c k s d p o i n t "Y" o n l i n e CD. I f c o n s o l i d a t i o n was due s o l e l y t o t h e w e i g h t o f t h e r o c k f i l l , t h e p r e c o n s o l i d a t i o n l o a d s f o u n d by t e s t i n g a r e c o n s i s t e n t l y h i g h e r t h a n t h e v a l u e s r e - p r e s e n t e d by l i n e CU. Some a d d i t i o n a l f a c t o r s must h a v e

c a u s e d f ~ ~ r t b e r c o n s o l i d a t i o n . The most l i k e l y c a u s e tsoulci b e a 1-owering o f t h e g r o u n d w a t e r t a b l e

i n

t h e c l a y l a y c r . When t h e g r o u n d w a t e r t a b l e i s l o w e r e d , t h e p r e s s u r e e x e r t e d by t h e c l a y above t h e g r o u n d w a t e r l e v e l c h a n g e s f r o m t h a t e x e r t e d by szbmerged w e i g h t t o t h a t e x e r t e d by f u l l wet w e i g h t . L i n e

CCEG r e p r e s e n t s t h e c o n d i t i o n when t h e g r o u n d w a t e r t a b l e was

l o w e r e d t o a d e p t h c o r r e s p o n d i n g t o E, The e f f e c t i v e p r e s s u r e diar;rarn w i l l u l t i m a t e l y b e OCEG. The t e s t s r e v e a l t h a t

c c ? s o l i d a t i o n h a s n o t g e t b e e n c o m p l e t e d f o r t h i s s e c o n d c o n d i t i o n . The s t a g e o f c o n s o l i d a t i o n a t p r e s e n t i s r e -

presented by l i n e 0CE:F. Thus c l a y a t d e p t h W, o r i g i n a l l y was c o n s o l i d a t e d t o p o i n t X; t h e r o c k f i l l c a u s e d i t t o b e con- s o l i d a t e d t o Y, and t h e assumed l o w e r i r ~ g o f g r o u n d w a t e r w i l l ca>-se i t e v e n t u a l l y t o c o n s o l i d a t e t o p o i n t Z. P r e p r e s e n t s t h e d e g r e e o f c o n s o l i d a t i o n i n i t s p r e s e n t s z a t e . The change i n e f f e c t i v e p r e s s u r e f r o m P t o Z w i l l c a u s e f u r t h e r s e t t l e m e n t . It i s d i f f i c u l t t o e s t i m a t e how much t h i s s e t t l e m e n t w i l l b e , b e c a u s e o f t h e wide v a r i a t i o n i n p r o p e r t i e s o f t h e v a r v e d c l a y . Based on t h e r e s u l t s o f sample 2-129-3, t h e s e t t l e m e n t y,et t o o c c u r u n d e r p r e s e n t c o n d i t i o n s w i l l b e 0.076 f e e t c r 9/10 o f a n i n c h , which would n o t b e e x c s s s i v e , I n a u n i f o r m c l a y , i t i s p o s s i b l e t o d e r i v e a n e s t i m a t e of t h e t i m e which i s r e q u i r e d f o r a c l a y l a y e r t o c o n s o l i d a t e u n d e r a n i n c r e a s e i n l o a d , Because o f t h e v a r i a b i l i t y o f t h e v a r v e d c l a y , p a r t i c u l a . r l y of t h e d r a l n a g e f a c e s p r o v i d e d by t h e l i g h t l a y e r s , any e s t i m a t e i n t h i s c a s e i s a p t t o b e m i s l e a d i n g ,

.

E f f e c t of Proposed S t r u c t u r e

I f t h e proposed shops a r e p l a c e d on t o p of t h e p r e s e n t rock f i l l , t h e a d d i t i o n a l weight w i l l cause t h e c l a y t o

c o n s o l i d a t e f u r t h e r . The a d d i t i o n a l s e t t l e m e n t s w i l l be d i f f e r e n t i a l i n n a t u r e becallse of t h e v a r i a t i o n

ir,

t h i c k n e s s of t h e c l a y l a g e r .

T h i s a d d i t i o n a l s e t t l e m e n t can be p r e v e n t e d by f l o a t i n g t h e f o u n d a t i o n , i . e . , e x c a v a t i n g a weight of' r o c k f i l l

equival-ent t o t h e weight o f t h e s t r u c t u r e

and

p l a c i n ~ ; t h e f o u n d a t i o n i n t h e e x c a v a t i o n . I n t h i s c a s e , t h e weight of t h e s u p e r s t r u c t u r e w i l l be v e r y l i p > h t i n c o m ~ n r i s o n t o t h e weight of t h e f o o t i n g , t h u s i t may almost he n e g l e c t e d . As

a n example, suppose t h e r e q u i r e d t h i c k n e s s of t h e f o u n d a t i o n s l a b was

3

f e e t . Assuming c o n c r e t e t o have a u n i t weight o f 150 l b . p e r cu. f t , , and t h e r o c k f i l l 120 lb. p e r c u e f t . , f o r a 3 - f o o t s l a b , t o f l o a t t h e s l a b f o u n d a t i o n , t h e d e p t h of e x c a v a t i o n would be

&

1 0

_{x 3 = 3.75}

f t . ~f t h i s

was

c a r r i e d o u t , t h e r e should be no s e t t l e m e n t caused by t h e weight of t h e b u i l d i n g .

As p r e v i o u s l y o u t l i n e d , t h e s e t t l e m e n t s due t o c a u s e s c t h e r t h a n t h e b u i l d i n g have n o t y e t been completed. Some d i f f e r e n t i a l mcvement, which c a l c u l a t i o n s skiow t o be i n t h e ol.der ot' 1 i n c h , w i l l occur. Thus p r o v i s i o n should be made f o r r e l e v e l l i n e any c r i t i c a l machinery zuch a s c r a n e s from time t o time a s r e q u i r e d .

It i s hoped t h i s r e p o r t w i l l d e m o n s t r a t e a r a t i o n a l d e s i g n f o r f o u n d a t i o n s founded on a h i g h l y c o m p r e s s i b l e s o i l . The b a s i s of such a d e s i g n i s t e s t s conr-lucted on u n d i s t u r b e d samples of t h e s o i l and t h e t h e o r y of c o n s o l i d n t i o n of s o i l s .

T h i s s h o r t r e p o r t p r e s e n t s t e s t r e s u l t s conducted on samples t a k e n from under a proposed E u c l i d R e p a i r Shop. A

b r l e f d i s c u s s i o n i s p r e s e n t e d o u t l i n i n g t h e w r i t e r ' s r e a s o n i n g behind

( a )

s e t t l e m e n t s which have o c c u r r e d i n t h e r r e a . ( b ) t h e recomrriendation f o r

a

f l o a t i n g s l a b f o u n d a t i o n f o r .the p ~ ~ o p o s e d s t r u c t u r e .