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Laboratory Study of Varved Clay from Steep Rock Lake, Ontario Eden, W. J.

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NATIONAL RESEARCH COUNCIL CANADA

D I V I S I O N OF BUILDING RESEARCH

A LABORATORY STUDY OF VARVED CLAY FROM S T E E P ROCK LAKE, ONTARIO

by W . J. E d e n

(Assistant Heaearch O f f i c e r , D . B . R . , N . R . C . )

Ottawa

(3)

A

LABORATORY STUDY

OF

VARVED CLAY FROM STEEP ROCK LAKE, ONTARIO

by

W.

J. Eden

Throughout Canada, but especially in the northern areas, deposits of fine-grained glacial soils are found. These soils have frequently been the cause of a good deal of trouble to the construction and mining industries. When found in a saturated condition these

soils often have the ability to liquefy whenever they are disturbed. The Division of Building Research of the National Research Council has undertaken a study of such northern soils. When high-grade iron ore was discovered beneath the waters of Steep Rock Lake and mining operations led to the dewatering of the Lake and subsequent dredging of the Lake bottom deposits, a good opportunity for study arose.

The deposits of soil in Steep Rock Lake were for the most part varved clays, one of the more treacherous of the glacial soils. With the co-operation of Steep Rock Iron Mines Company Limited, the Division of Building Research undertook a detailed study of the Steep Rock varved clays with emphasis on the engineering standpoint.

At the outset of the study, varved clays were treated

by the usual practice of soil mechanics, as a uniform soil. Testing was conducted irrespective of the laminations which make up the

varved clay. The results of this study have been previously presented by Legget and Bartley (1). It was soon recognized that the separate laminations which make up a varve had remarkably different physical properties. Part of the detailed study was therefore directed toward finding the properties of the individual laminae and the variations in properties within the laminae.

(4)

T h i s p a p e r d e a l s w i t h some r e s u l t s of t h i s d e t a i l e d s t u d y . Although n o t t h e o b j e c t i v e of t h e s t u d y , a good d e a l of i n f o r m a t i o n h a s been assembled which may be v a l u a b l e t o g e o l o g i s t s , T h i s p a p e r p r e s e n t s t h e g e o l o g i c a l a s p e c t s of t h i s s t u d y . The test r e s u l t s a r e d i s c u s s e d i n t h e l i g h t of c u r r e n t t h e o r i e s concerning t h e f o r m a t i a n of varved c l a y s .

LABORATORY W QRK

To c a r r y out t h i s l a b o r a t o r y i n v e s t i g a t i o n , b l o c k samples sf

z

s i z e which could be c o n v e n i e n t l y handled were c o l l e c t e d by t h e a u t h o r a t S t e e p Rock Lake, s e a l e d bn p a r a f f i n o r petrowax, packed i n damp sawdust, and shipped t o O t t a w a f o r t e s t i n g . Samples were t a k e n from f r e s h exposures i n o r d e r t o p r e s e r v e t h e n a t u r a l w a t e r c o n t e n t of t h e varved c l a y s . The samples were chosen from w i d e l y s e p a r a t e d l o c a t i o n s , and w i t h t h e o b j e c t of r e p r e s e n t i n g t y p i c a l specimens of t h e varved c l a y which o c c u r s i n t h e Lake b o t t ~ m . Once

In t h e l a b o r a t o r y t h e samples were s p l i t i n t o f r a c t i o n s of l i g h t (summer) and d a r k ( w i n t e r ) l a y e r s f o r t h e v a r i o u s p h y s i c a l t e s t s .

( a ) N a t u r a l Water Content

The n a t u r a l w a t e r c o n t e n t i s determined by comparing t h e wet and oven d r y w e i g h t s of t h e m a t e r i a l . Qven d r y i n g was c a r r i e d

out a t a t e m p e r a t u r e of 1 0 5 ~ ~ . S i n c e t h e s e s o i l s were s a t u r a t e d , t h e m o u n t of w a t e r p r e s e n t r e p r e s e n t s t h e volume of v o i d s of t h e c l a y . The void r a t i o was determined s e p a r a t e l y , by c a r e f u l l y %rimming a sample, t h e n weighing and measuring. I n a l l c a s e s i t was found t h a t t h e varved c l a y s were a t l e a s t 99 p e r c e n t s a t u r a t e d . S i n c e t h e w a t e r c o n t e n t al3o r e p r e s e n t s t h e void r a t i o of t h e c l a y s , It 1s a measure of t h e s t r u c t u r e of t h e s o i l . Water c o n t e n t t e s t s

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were conducted with the objective of determining the variations in structure between the dark and light layers, and also the variations within any one layer.

The results of the water content determinations revealed a remarkable difference betweez t 5 e dark and light layers which aake up

a

varve. Figure 1, which illustrates the variation found

in one ample, is typical of the moisture content variations found fc all the

teat

w c ~ k . T h e wa'er content of the dark layers ranged from 60 to 100 per cent, and of the light layers from 20 to

40

per cent. This range in water content corresponds to a range from

1 - 6 9

to 2.83 in void ratio for the dark layers, and from

0.56

to

1-11

far

the light layers. Thus the dark layera have a void ratio approximately 2 1/2 to

3

times that of the light layers, The

specific gravity of the soil particles was 2.80 and 2.76 for the dark and light materials respectively.

(b) Plasticity

The plasticity in clays is due to the molecular forces acting between small particles. These forces vary acc~rding to the structure of the clay particless i,e., the type of clay mineral present, the aize and aurface development of the particles, and

according to the concentration and type of electrolyte in the water.

A ka~linite clay and a montmorillonite clay having the aame grain size would have entirely different plasticity characteristics, In a ayatem of pure kaolinite clay and pure water, Hauser and Le Beau

( 2 ) attribute plasticity to molecular attraction forces between uncharged particles (van der Waala forces). Recent inveatfgations show that plasticity is greatly influenced by the cation complex of the clay. Ahlberg

(3)

found that the a m e clay treated with hydrogen,

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sodium, and o t h e r c a t i o n s underwent g r e a t changes in p l a s t i c i t y depending on t h e c a t i o n .

The p l a s t i c i t y of t h e varved c l a y s from S t e e p Rock was i n v e s t i g a t e d by means of t h e A t t e r b e r g l i m i t s t e s t s . T h i s method h a s been s t a n d a r d i n s o i l mechanics p r a c t i c e ; a d e t a i l e d procedure f c r t h e t e s t may be found i n A.S .T.M. "Procedures f o r T e s t i n g S o i l s "

( 4 )

o r i n many of t h e r e f e r e n c e books on S o i l Mechanics. The A t t e r b e r g limits a r e made up of t h e l i q u i d l i m i t and p l a s t i c l i m i t . The l i q u i d i i m i t i s d e f i n e d a s t h e water c o n t e n t r e q u i r e d t o r e n d e r t h e s o i l j u s t f l u i d as d i s t i n c t from p l a s t i c . The p l a s t i c l i m i t i~ d e f i n e d as t h e water c o n t e n t r e q u i r e d t o r e n d e r t h e s o i l p l a s t i c a s d i s t i n c t from f r i a b l e o r crumbly. The d i f f e r e n c e i n w a t e r c o n t e n t s between t h e

l i q u i d and p l a s t i c l i m i t s i s t h e range i n which t h e s o i l i s p l a s t i c , and h a s been d e f i n e d as t h e p l a s t i c i t y index. Highly p l a s t i c s o i l s have a high numerical v a l u e f o r t h e p l a s t i c i t y index and c o n v e r s e l y n o n - p l a s t i c s o i l s have a v a l u e of z e r o f o r t h e p l a s t i c i t y index.

It should be noted t h a t t h e procedure followed f o r

d e t e r m i n a t i o n of t h e l i q u i d l i m i t v a r i e d s l i g h t l y from t h e s t a n d a r d procedure l i s t e d i n

( 4 )

whereas i t i s u s u a l t o conduct t h e l i q u i d

l i m i t on s o i l which h a s been a i r d r i e d , t h e v a l u s s of l i q u i d l i m i t l i s t e d were determined on s o i l i n i t s n a t u r a l s t a t e . It was found t h a t l i q u i d

l i m i t d e t e r m i n a t i o n s conducted on S t e e p Rock varved c l a y a i n t h e i r n a t u r a l s t a t e y i e l d e d g e n e r a l l y h i g h e r r e s u l t s t h a n d e t e r m i n a t i o n s

conducted on a i r - d r i e d samples.

The A t t e r b e r g t e s t s r e v e a l e d a g r e a t d i f f e r e n c e i n p l a s t i c i t y between t h e d a r k and l i g h t l a y e r s . The change i n p l a s t i c i t y i s of t h e same o r d e r a s t h a t f o r n a t u r a l w a t e r c o n t e n t and void r a t i o . F i n u r e 2

(7)

fraction (after Skemptcn

( 5 ) ) ,

Figure

3

shows the difference between light and dark layers when plotted on the Casagrande chart of plastici- ty index vs. liquid limit (6).

In

Figure 4 the variations in plastici- ty within one varve are shown, This figure shows results which are typical of the variations found in other samples in which the layers aye uf more equal thickness. Figure 4 demonstrates a very rapid change

in plasticity from dark to light material, as was the case with water content and grain size. Figures 2 and 3 contain results of tests from all portions of the varves, and indicate no transitional zone of any appreciable thickness between the dark and light layers,

( c ) Grain Size

The investigation of grain size was directed toward determf- ning the difference between the dark and light layers and whether any gradation in grain size existed within the varves, The techniques used for grain-size determinations were hydrometer analysis, pipette analyeis, and measurement of individual grains under the microscope. The procedures used have been thoroughly investigated by various authorities.

In

the hydrometer analysis, the procedure followed was developed by Arthur Casagrande (11) and is described by Lambe (121, In the pipette analysis, the procedure outlined by Krumbein (13) was

followed. Microscopic grain-size analysis was conducted by the

technique given by Krumbein (13), The three techniques for grain-size analysis were found necessary because of the difficulty in obtaining a sufficient amount of soil to make any one test standard. Comparative tests were conducted on the same sample by both the hydrometer and

pipette methods; the results were f,ound to compare closely, It is difficult to conduct a comparison between the hy&rometer or pipette methods with the microscopic method because, with the latter, the

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g r a i n - s i z e frequency i s based on number r a t h e r t h a n by weight as w i t h t h e o t h e r methods. The hydrometer and p i p e t t e a n a l y s e s were conducted on samples which had been d i s p e r s e d w i t h a s m a l l amount 0%

The r e s u l t s of mechanical a n a l y s i s f o r g r a i n s i z e a r e u s u a l l y p r e s e n t e d g r a p h i c a l l y by means of a g r a i n - s i z e d i s t r i b u t i o n

Pseqaencg curve c r a g r a i n - s i z e d i s t r i b u t i o n a c c w u l a t i o n c u r v e . Because of t h e barge number of tests conducted, i t i s d i f f i c u l t t o compare a l l t h e c u r v e s o n one diagram. The v a l u e s p r e s e n t e d i n F i g u r e s 4 and

5

weye obtained by s t a t i s t i c a l methods ~f d e s c r i b i n g such curves. The s t a t i s t i c a l methods a r e d e s c r i b e d by Ksumbein

(131,

O t t o ( 1 4 ) and

Irman ( 1 5 ) . The geometric mean d i a m e t e r i s t h e s i z e which c s r r e a p o n d s t o t h e g r a i n - s i z e diameter a s s o c i a t e d w f t h t h e most abundant g r a i n s i n a n a s m e t r i c a l d i s t r i b u t i o n . Using t h e geometric mean and t h e s t a n d a r d d e v i a t i o n i t f s p o s s i b l e t o d e s c r i b e most of t h e g r a i n - s i z e d i s t r i b u t i o n curve by: two numbers, By c o n v e r t i n g t h e g r a i n s i z e In

m i l l i m e t r e s t o t h e

9

s c a l e ( t h e g s a i n s i z e i n

9

u n i t s e q u a l l i n g t h e n e g a t i v e log2 g r a i n s i z e i n m i l l i m e t r e s ) and p l o t t i n g t h e g r a i n - s i z e d i s t r i b u t i o n curve on p r o b a b i l i t y paper, it i s p o s s i b l e t o d e r i v e t h e geometric mean d i a m e t e r and s t a n d a r d d e v i a t i o n by

a

simple g r a p h i c a l c o n s t r u c t i o n ( I m a n ( 1 5 ) )

.

The g r a i n - s i z e t e s t s were conducted t o determine t h e d i f f e r e n c e i n g s a i n s i z e between t h e d a r k and l i g h t l a y e r s and t o determine whether t h e S t e e p Rock varved c l a y s were d i a t a c t i c " .

% F r a s e r ( 1 8 ) d e i i n e s d i a t a c t f c s t r u c t u r e of a varve a s one i n which t h e m a t e r i a l s of t h e varve a r e s o r t e d a c c o r d i n g t o s i z e and s p e c i f i c

g r a v i t y of p a r t i c l e s , t h e c o a r s e s t a t t h e bottom and t h e f i n e s t a t t h e t o p .

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Symminct s t r x e t u r e r e f e r s t o c l a y d e p o s i t e d under c o n t r o l

cf a n e l e c t r o l y t e , i n which case p a r t i c l e s l a r g e and small go down

t ~ g e t h e r and form an u n s o r t e d mass due t o f l o c c u l a t i o n of t h e g r a i r L s . F S g u ~ e 2 shows a significant d i f f e r e n c e i n g r a i n s i z e . The d a r k

lagers c o n t a i n from

65

t o

95

p e r c e n t c l a y - s i z e d p a r t i c l e s whereas

t l . ~ ~ ~ l.!gnt, laye:cda co2t,air,, only f r o m 18 t o

35

p e r c e n t c l a y - s i z e d

p~tr'vl:?,es. F i g u r e

4

shsws a s i g n i f i c a n t d i f f e r e n c e w i t h i n a vakvz, The r e s u l t s of t e s t s conducted on s u b l z y e r s f a i l e d t o show a s i g r : f f i c a c t g r a d a t i o n i n g r a i c sZze w i t h i n one v a r v e . F i g u r e 4

Lnd%zates t h e r e s u l t s a h t a f n e d from varved c l a y w i t h abnormally t h i c k da2k l a y e r s ( b e l i e v e d t o be what Antevs ( 1 7 ) t e r n s a d r a i n a g e v a k v ~ ! . Although t h i s v a r v e i s a d m i t t e d l y n o t t y p i c a l , i t was chosen b e c a m e a l a r g e number of t e s t s were made on i t ; t e s t s conducted on samples w i t h v a r v e s of normal t h i c k n e s s a l s o f a i l e d t o i n d i c a t e any g r a d s t i o n wit.hin a varve. F i g u r e

6

P n d f c a t e s t h e r e s u l t s o b t a i n e d by t h e

microscopic examination of a l i g h t (summer) l a y e r which was d i v i d e d i n t o s i x e q u a l f r a c t i o n s throughout i t s p r o f i l e . No g r a d a t i o n w a s i n d i ~ a t e d by t h e r e s u l t s i n F i g u r e

6 ,

Admittedly t h e number of v a r v e s t e s t e d i n t h i s manner a r e comparatively few i n r e l a t i o n t o t h e t o t a l number of v a r v e s which e x i s t a t S t e e p Rock. The samples were, however, chosen t.0 be t y p i c a l

of t h e v a r i o u s t y p e s of v a r v e s which were uncovered. I n a l l t h e t e s t s conducted on t h e S t e e p Rock vakved c l a y , no g r a d a t i o n of p a r t i c l e s i z e w z t h i n a varve was i n d i c a t e d which i s somewhat p u z z l i n g c o n s i d e r i n g t h e work of Antevs

(17)

on t h e S t e e p Rock c l a y s , I n d i s c u s s i n g t h e f c - m a t i o n of t h e S t e e p Rock varved c l a y s , Antevs s t a t e s t h a t t h e

laminations were d i a t a c t i c , n o t s ~ m i n e t and l f t t l e f l o c c u l a t i c n t o ~ k p l a c e .

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To compare t h i s r e s u l t w i t h v a r v e s from o t h e r l o c a t i o n s , samples were o b t a i n e d from Amos, Quebec ( t h r o u g h t h e c o u r t e s y of D r , A . MacLaren of t h e G e o l o g i c a l Survey of ~ a n a d a ) arid from t h e Don V a l l e y a t Toronto. The Amos samples appeared v e r y similar t o t h e S t e e p Rock samples and l a c k e d any p a r t i c l e - s i z e g r a d a t i o n . The Toronto sample d i d a p p e a r t o have a p a r t i c l e - s i z e d i s t r i b u t i o n ; t h e r e s u l t s p r e s e n t e d i n F i g u r e

5

s u p p o r t t h i s view. T h i s i s , i n t h e a u t h o r ' s o p i n i o n , a d i a t a c t i c v a r v e , w h i l e t h e S t e e p Rock v a r v e s a r e n o t , It

can

be s e e n from F i g u r e

8

of a sample from Toronto t h a t t h e l i g h t m a t e r i a l grades g r a d u a l l y i n t o t h e d a r k w i t h no c l e a r boundary l i n e . I n F i g u r e s 9

and 1 0 , showing v a r v e s from S t e e p Rock, e a c h s i d e . o f t h e l i g h t l a y e s h a s a d e f i n i t e boundary. T h i s i s n o t t h e c a s e w i t h t h e Toronto v a r v e (which i s i n v e r t e d i n t h e p h o t o g r a p h ) .

( d ) Thixotropy

Thixotropy i s d e f i n e d a s a r e v e r s i b l e g e l - s o l - g e l t r a n s f o r m a t i o n i n c e r t a i n m a t e r i a l s brought about by a mechanical d i s t u r b a n c e f o l l o w e d by a p e r i o d of r e s t . The word means "change by t o u c h " and hence, s i n c e s o i l p a r t i c l e s a r e s o l i d m a t e r i a l s , t h i x o t r o p y a p p l i e d t o s o i b a i n v o l v e s s o i l s t r u c t u r e . According t o Green and Weltmann ( 7 ) t h i x o t s o p y cannot e x i s t w i t h o u t f l o c c u l a t i o n b u t t h e converse

i s

n o t n e c e s s a r i l y t r u e .

The term t h i x o t r o p y , a s used i n t h i s p a p e r , i n c l u d e s t h e s t a t e of " f a l s e body" as d e f i n e d by Psyce-Jones

(8)

as t h e two t e r n s are s o c l o s e l y a l l i e d , and t h i x o t r o p y h a s been used by many w r i t e r s t o c o v e r b o t h t r u e t h i x o t r o p y and f a l s e body.

T e s t s t o d e t e r m i n e t h e d e g r e e of t h i x o t r o p y of s o i l s a r e d i f f i - c u l t t o r e l a t e t o f i e l d c o n d i t i o n s . The l a b o r a t o r y i n v e s t i g a t i o n was d i r e c t e d toward merely p r o v i n g t h e e x i s t e n c e of a t h i x o t s o p i c s t a t e . The procedure f o l l o w e d was a c c o r d i n g t o Ackermann ( 9 ) and y i e l d s a r e s a l t e x p r e s s e d i n t e r m s of w a t e r c o n t e n t c a l l e d t h e " s t i f f e n i n g l i m i t " .

(11)

- Y

-

',LLLS metnod i s as f o l l o w s . H Y I I ~ L - L ~ arnoult of s o i l i s mixed 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 . S u f f i c i e n t w a t e r i s added i n s m a l l

i n c r e m e n t s and t h o r o u g h l y mixed until t h e p o i n t i s reached when the s o i l p a s t e w i l l begin t o flow when t h e t e s t t u b e i s i n v e r t e d a f t e r a

one-minute r e s t . The w a t e r c o n t e n t c o r r e s p o n d i n g t o t h i s c o n d i t f o n X s termed t h e s t i f f e n i n g l i m i t .

Again, a s t r i k i n g d i f f e r e n c e between t h e l i g h t and d a r k l a y e r s i s r e v e a l e d i n t h e i r s t i f f e n i n g l i m i t s . Table 1 g i v e s v a l u e s obta.%ned f o r sample 2-123 and may be compared w i t h F i g u r e

4,

Other t e s t r e s u l t s showed t h e same d i f f e r e n c e between d a r k and l i g h t l a y e r s . A few samples of t h e S t e e p Rock varved c l a y were t e s t e d by Boswell ( 1 0 ) u s i n g a s l i g h t l y d i f f e r e n t t e s t . He r e p o r t s v a l u e s of

65

f o r t h e l i g h t l a y e r s and 120 f o r t h e d a r k l a y e r s . A l l t h e t h i x o t r o p i c t e s t s show t h a t b o t h t h e l i g h t and d a r k l a y e r s of t h e varvad c l a y a r e t h i x o t r o p i c , and hence must be i n a f l o c c u l a t e d c o n d i t i o n .

( e ) Mineral A n a l y s i s

The m i n e r a l components of t h e varved c l a y s were determined q u a l i t a t i v e l y by t h e t e c h n i q u e s of d i f f e r e n t i a l t h e r m a l a n a l y s i s and X-ray d i f f r a c t i o n . T h i s work w a s done by t h e C r y s t a l Chemistry S e c t i o n

of t h e Department of Mines and T e c h n i c a l Surveys, Ottawa, and r e v e a l e d t h e f o l l o w i n g components f o r t h e l i g h t l a y e r s : quarDz, c a r b o n a t e s , f e l d s p a r , c l a y ( s m a l l amount), o r g a n i c m a t t e r ( t r a c e ) ; d a r k l a y e r s :

q u a r t z , f e l d s p a r , c l a y , p r o b a b l y m o n t m o r i l l o n i t e , more t h a n l i g h t l a y e r s , o r g a n i c m a t t e r

-

s m a l l amount, s l i g h t l y more t h a n l i g h t l a y e r s .

The above a n a l y s i s i s borne o u t by t h e " A c t i v i t y C h a r t " ( F i g u r e 2 ) . Both t h e l i g h t and d a r k l a y e r s p l o t as " i n a c t i v e c l a y s " , w i t h t h e d a r k m a t e r i a l d i s p l a y i n g more a c t i v i t y t h a n t h e l i g h t , T h i s can be a t t r i b u t e d t o t h e r e l a t i v e l y g r e a t e r q u a n t i t y of c l a y i n t h e d a r k l a y e r s . Normally m o n t m o r i l l o n i t e c l a y i s c o n s i d e r e d t o be a n

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TABLE

I

Water Content R e l a t i o n s h i p s f o r Sample 2-123

( i n

$

oven-dry weight)

Natural

P l a s t i -

Sample

Type

of

Water

Liquid

P l a s t i c

c i t y

No.

M a t e r i a l

Content

L i m i t L i m i t 4 Inden

Light

(summer)

25.1

Light (summer)

23.6

Dark ( w i n t e r )

69.5

Dark ( w i n t e r )

77.8

Dark ( w i n t e r )

84.6

Dark ( w i n t e r )

89.3

Dark

( w i n t e r )

90.2

Dark ( w i n t e r )

91.2

2-123-9

Dark

( w i n t e r )

92.8

93.7

30.2

63

.

5

2-1.23-10

Dark ( w i n t e r )

93

-8

95.2

33.4

61.8

2-123-11 Dark ( w i n t e r )

92.5

91

.9

34.0

57.9

2-123-12

ark

( w i n t e r )

79.3

64.0

2 3 0 9

4 0 , l

2-123-13

Light (summer)

27.9

26

.9

21

.?

5.2

2-123-14 Light (summer)

23.5

25.5

2 0 . 1

5 0 4

ST iff

et?-Eng

2 L l m l t

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" a c t i v e c l a y " , but i t p l o t s as a n " i n a c t i v e c l a y " because of t h e masking e f f e c t of t h e q u a r t z and f e l d s p a r mixed w i t h t h e c l a y .

The m i n e r a l a n a l y a i s r e v e a l s two i m p o r t a n t d i f f e r e n c e s i n t h e m i n e r a l c h a r a c t e r i s t i c s of t h e d a r k and l i g h t l a y e r s . One i s t h e

r e l a t i v e amounts of t r u e c l a y m i n e r a l s , and t h e second i s t h e f a c t t h a t t h e l i g h t l a y e r s c o n t a i n c a r b o n a t e s but t h a t t h e d a r k l a y e r s do n o t ,

(f) S h e a r S t r e n g t h

A few t e s t s were conducted t o determine t h e e f f e c t t h a t t h e varved s t r u c t u r e had on s h e a r s t r e n g t h . The t e c h n i q u e s used were t h e ~mcorafined compression t e s t and t h e d i r e c t s h e a r t e s t , Procedures f o r both t h e s e t e s t s a r e w e l l e s t a b l i s h e d and a r e d e s c r i b e d i n d e t a i l by Lambe ( 1 2 ) ,

F o r t h e unconfined compression t e s t , c y l i n d e r s of u n d i s t u r b e d s ~ i l were trimmed, w i t h due r e g a r d t o t h e o r 1 e n ; a t i o n of t h e v a r v e s s t o a d i a m e t e r of 1 112 i n c h e s and l e n g t h of

3

i n c h e s . T h i s c y l i n d e r was s u b j e c t e d t o a x i a l compression, w i t h t h e s t r e s s a t f a i l u r e b e i n g termed t h e unconfined compression s t r e n g t h . The Mohr t h e a r y of

sv.pture 5125~6 + h a t t h e s h e a r s t r e n g t h l a e q u a l t o one-half the

unconfined compression s t r e n g t h f o r moat c l a y s . The test rcaealts f o r two eamples a r e p r e s e n t e d i n F i g u r e

7,

by showing t h e v a r i a t i o n i n unconfined compression s t r e n g t h w i t h o r i e n t a t i o n of t h e v a r v e s . The d i f f e r z n c e between t h e two c u r v e s can be e x p l a i n e d by t h e r e l a t i v e amourits sf d a r k and l i g h t m a t e r i a l I n t h e samplea, The d a r k l a y e r s were approximately t w i c e t h e t n i e k r ~ e s s of t h e l i g h t l a y e r s i n

(14)

When 8 = 3 0 ° , f a i l u r e t o o k p l a c e e n t i r e l y i n t h e l i g h t l a y e r s as i n d i c a t e d i n F i g u r e 9 , Thus t h e v a l u e of unconfined c ~ m p r e s s i o n s t r e n g t h a t 3 0 O r e p r e s e n t s n e a r l y t w i c e t h e s h e a s s t r e n g t h of t h e l i g h t l a y e r s . The d a r k l a y e r s r e s i s t e d d e f o r m a t i o n t o a g r e a t e r e x t e c t t h a n t h e l i g h t l a y e z a . Because of t h i s d i f f e r e n c e

Ln

stiffness, t h e d e p a r t u r e c f t h e c u r v e s F c r t h e two samples a t 8 = 0 O i s a c t u a l l y t h e s t r e n g t h of t h e l i g h t m a t e r i a l , and because t h e e f f e c t i v e a r e s r e s i s t i n g l o a d i s l e a s t h a n I n d i c a t e d by F i g u r e

7,

t h e s t ~ e n g t h j.3 s l i g h t l y lower a t 8 =

3e0.

S t r e n g t h d e t e r m i n a t i o n s on s e p a r a t e s a m p l e s sf d a r k awd l i g h t material were conducted i n the d i r e e t s h e a r box. While t h i s

method of s t r e n g t h d e t e r m i n a t i o n i s not c ~ n s i d e r e d r e l i a b l e f o r cskaeaive m i l s , i t i s c o n s i d e r e d t h a t t h e r e l a t i v e s t r e n g t h s of t h e dark and

l i g h t m a t e r i a l a r e i n d i c a t e d , With t h e d i r e c t s h e a r t e s t , it was found t h a t t h e d a r k l a y e r s had a s h e a r s t ~ e n g t h of a p p s o x i m t e l y

6

p . s , $ . and

t h e l i g h t l a y e r s of a p p r ~ x ~ a t e l y

3

p . s , i . These r e s u l t s compare m a s o n a b l y w e l l w i t h s h e a r a t r e n g t h d e r i v e d from t h e m c s n f f n s d compression t e s t s .

It must be p o i n t e d o u t , t h a t o n l y two samples were t e s t f e d f o r s t r e n g t h , and t h e above r e s u l t s must be r e g a r d e d as p r e l i m i n a r y , The r e s u l t s do i n d i c a t e , however, t h a t t h e v a s v e s have a n i n f l u e n c e

on s h e a r s t r e n g t h , and t h a t t h e 19ght and d a r k l a y s r s have sadPcaLLy d i f f e r e n t s t r e s s - s t r a i n c h a r a c t e r f s t f c s . The d a r k l a y e r s , i n s p i t e

QF t h e i r l o o s e s t r u c t u r e and h i g h p l a s t i c i t y and w a t e r c o n t e n t , a p p e a r t o be much s t i f f e r and have g r e a t e r s t r e n g t h t h a n t h e l i g h t l a y e r s .

( g ) S e n s i t i v i t y

S e n s i t i v i t y Is t h e Cerm a p p l l e d t o d e s c r i b e t h e l o s s of s t r e n g t h i n a c l a y when i t 1 6 changed from t h e m d l a t i m b e d t o t h e

(15)

remoulded s t a t e . R e s u l t s from t h e unconfined compression t e s t have been used a s a c r i t e r i o n f o r s e n s i t i v i t y . The d e g r e e of s e n s i t i v i t y i s d e f i n e d as t h e r a t i o of u n d i s t u r b e d s t r e n g t h t o t h e remoulded s t r e n g t h , a t t h e same watep c o n t e n t .

The l i g h t m a t e r i a l , when remoulded a t n a t u r a l w a t e r c o n t e n t , d i d n o t have s u f f i c i e n t s t r e n g t h f o r a c y l i n d e r

3

i n c h e s l o n g and

1 1/2 i n c h e s i n d i a m e t e r t o s t a n d by i t s e l f . The d a r k l a y e r s had a n unconfined compression remoulded s t r e n g t h of a p p r o x i m a t e l y 1 p , s . i . o r o n e - t w e l f t h of t h a t f o r t h e same m a t e r i a l i n t h e u n d i s t u r b e d s t a t e .

Thus b o t h t h e d a r k and l i g h t l a y e r s of t h e varved c l a y can be c l a s s i f i e d as e x t r a - s e n s i t i v e s o i l s ( a f t e r Skempton ( 1 6 ) ) .

DISCUSSION OF TEST RESULTS WITH REGARD TO THEORIES ON VAWING

Before d i s c u s s i n g t h e t e s t r e s u l t s , i t i s n e c e s s a r y t o review some of t h e t h e o r i e s on t h e f o r m a t i o n of varved c l a y s . The word "va.rvedn i n f e r s a d i s t i n c t l y banded d e p o s i t . Thus a v a r v e i s u s u a l l y d e f i n e d i n g e o l o g i c a l l i t e r a t u r e as m a t e r i a l which c a n be d e f i n i t e l y i d e n t i f i e d t o have been d e p o s i t e d i n one y e a r , and i s q u i t e d i s t i n c t from p r e c e d i n g o r s u c c e e d i n g y e a r s . Baron Gerard d e Geer, a Swediph g e o l o g i s t , F i r s t recognized t h e s i g n i f i c a n c e of t h e s e l a m i n a t i o n s and s u g g e s t e d t h e a n n u a l t h e o r y of d e p o s i t i o n . Each varve c o n s i s t s of a c o u p l e t , a

l i g h t - c o l o u r e d r e l a t i v e l y c o a r s e summer l a y e r , and a d a r k e r - c o l o u r e d f i n e - g r a i n e d w i n t e r f r a c t i o n . Varved c l a y s a r e u s u a l l y a s s o c i a t e d w i t h g l a c i a l l a k e s , and were formed d u r i n g a tlme of r e t r e a t of a

g l a c i e r . De Geer b e l i e v e d t h a t d u r i n g t h e summer when l a r g e volumes of melt w a t e r charged w i t h g l a c i a l d e b r i s r e a c h e d a l a k e o r s e t t l i n g b a s i n , t h e r e l a t i v e l y l a r g e p a r t i c l e s would s e t t l e o u t . In t h e w i n t e r , when t h e l a k e was covered w i t h i c e , and no f u r t h e r f r e s h m a t e r i a l was s u p p l i e d , t h e f i n e - g r a i n e d m a t e r i a l c a r r i e d i n s u s p e n s i o n was g i v e n s u f f i c i e n t time t o p r e c i p i t a t e . Thus a varved c o u p l e t was formed e a c h

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y e a r .

Antevs ( 1 7 ) h a s conducted d e t a i l e d s t u d y of t h e vasved c l a y s a t S t e e p Rock and h a s w r i t t e n a n account of t h e t y p e s of v a r v e s found and d i s c u s s e d t h e i r mode of f o r m a t i o n . He d i s c o v e r e d e i g h t s e p a r a t e s e r i e s of varved c l a y s c o r r e s p o n d i n g t o e i g h t d i f f e r e n t c o n d i t i o n s of environment. A s p r e v i o u ~ l y mentioned, Anteva b e l f e v e s t h e S t e e p Rock v a r v e s t o be d i a t a c t i c and l i s t s seven c o n d i t i o n s which a f f e c t e d t h e d e p o s i t i o n of t h e S t e e p Rock c l a y s . These seven c o n d i t i o n s a r e a s f o l l o w s : ( 1 ) r e s t r i c t i o n of a p p r e c i a b l e mud s u p p l y t o t h e a m e r months; ( 2 ) f l u c t u a t i o n of mud i n f l u x and of t h e c u r r e n t s ;

( 3 )

d i f Przren-

t i a l r a t e of s e t t l i n g of unequal g r a i n s and p a r t i c l e s ;

( 4 )

low tempera- t u r e and accompanying h i g h v f a c o s % t y and d e n s i t y of t h e l a k e waters;

( 5 ) s e m i s t r a t i f i c a t i o n o r Isothermy of t h e l a k e w a t e r and o s c i l l a t i o n s between t h e s e s t a t e s ;

( 6 )

h e i g h t of f a l l of t h e p a r t i c l e s ; and,

( 7 )

v a r i a t i o n s i n t h e c o n c e n t r a t i o n s of t h e e l e c t r o l y t e s . Antevs h a s covered t h e f o r m a t i o n of t h e S t e e p Rock c l a y s completely, and t h e

r e s u l t s p r e s e n t e d i n t h i s paper can o n l y supplement p a r t i c u l a r a s p e c t s i n Antevsl t h e o r y . Only on t h e p o i n t t h a t t h e S t e e p Rock v a r v e s a r e d i a t a c t i c , does t h e a u t h o r d i s a g r e e w i t h Antevs. T h i s i s on t h e p o i n t t h a t d i a t a c t i c i n f e r s a g r a d a t i o n i n p a r t i c l e s i z e w i t h i n t h e v a r v e , Before developing t h e argument f u r t h e r o i t i s n e c e s s a r y t o examine t h e c o n d i t i o n n e c e s s a r y f o r t h e f o r m a t i o n of d i a t a c t i c v a r v e s as l a i d

down by F r a s e r ( 1 8 ) .

Using a s p e c i a l l y c o n s t r u c t e d t a n k i n which t h e t e m p e r a t u r e of t h e w a t e r could be c l o s e l y c o n t r o l l e d , F r a s e r conducted experiments on t h e f o r m a t i o n of varved c l a y s , e s p e c i a l l y d i a t a c t i c v a r v e s . From his experiments, F r a s e r concluded t h a t t h e f o l l o w i n g conditions were n e c e s s a r y f o r t h e f o r m a t i o n of varved c l a y s :

(17)

( a ) The l a k e was one of q u i e t w a t e r s and had a p r a c t i c a l absence of e r o s i o n ;

( b ) The supply of m a t e r i a l was n o t f l o c c u l a t e d ;

( c ) The l a k e waters contained a very low c o n c e n t r a t i o n of e l e c t r o l y t e s .

F r a s e r f s experiments l e d him t o conclude t h a t d i a t a c t i c varves were formed s u b j e c t t o t h e r e s t r i c t i o n s t h a t follow:

( i ) During t h e m e l t i n g Beason t h e r e would be a continuous supply

of m a t e r i a l , u n f l o c c u l a t e d and of a s s o r t e d s i z e s . The c o a r s e r matePfal would s e t t l e r e l a t i v e l y r a p i d l y . Because of t h e cold w a t e r , t h e f i n e m a t e r i a l would s e t t l e very slowly. The s e t t l i n g v e l o c i t y would be a d i r e c t f u n c t i o n of t h e temperature of t h e w a t e r and p a r t i c l e s i z e . Because of t h e d i f f e r e n c e i n s e t t l i n g v e l o c i t i e s between c o a r s e and f i n e m a t e r i a l , t h e sediment would have a d e f i n i t e g r a d i n g p w i t h c o a r s e r m a t e r i a l a t t h e bottom of t h e varve and becoming p r o g r e s s i v e l y f i n e r as t h e varve was b u i l t up;

( i i ) A t t h e c l o s e of t h e m e l t i n g season, t h e supply of Ereah m a t e r i a l would dwindle t o p r a c t i c a l l y zero. Thus n e a r l y a l l of t h e c o a r s e r m a t e r i a l would be d e p o s i t e d d u r i n g t h e summer, and t h e d i v i s i o n between t h e l i g h t and d a r k m a t e r i a l would correspond approximately t o t h e c l o s e of t h e melting season;

( i i i ) During t h e w i n t e r season, w i t h no f r e s h supply of m a t e r i a l t h e f i n e m a t e r i a l would be p a r t i a l l y a i d e d by f l o c c u l a t i o n . T h i s

f l o c c u l a t i o n would r e s u l t from an i n c r e a s e d s a l i n i t y because of t h e i n c r e a s e i n t h e c o n c e n t r a t i o n of e l e c t r o l y t e s s u p p l i e d over t h e m e l t i n g season. F r a s e r t s experiments showed t h a t f l o c c u l a t i o n would be r e t a r d e d by t h e cold w a t e r . In any c a s e t h e s a l i n i t y c o u l d n o t i n c r e a s e t o a p o i n t g r e a t e r t h a n o n e - f i f t i e t h of normal s e a w a t e r t o permit varving. Erases

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thought that t h i s small degree of s a l i n i t y would not a f f e c t t h e c o a r s e r p a r t i c l e s s u f f i c i e n t l y t o cause f l o c c u l a t i o n , because t h e l a r g e r t h e p a r t i c l e , t h e more i n d i f f e r e n t i t i s t o f l o c c u l a t i o n ;

( i v ) The p e r i o d i c supply of m a t e r i a l t h u s o u t l i n e d would continue on an annual cycle.

Considering t h e l a b o r a t o r y t e s t s described i n t h i s paper, t h e r e s u l t s of t h e g r a i n - s i z e t e s t s revealed no g r a d a t i o n of p a r t i c l e s i z e w i t h i n t h e laminae. This suggests t h a t t h e Steep Rock varves a r e not

d i a t a c t i c . The water content t e s t s show t h e c l a y s t o have a very loose s t r u c t u r e , and because both t h e l i g h t and dark m a t e r i a l e x h i b i t t h i x s - t r o p y , it ia thought t h a t both t h e l i g h t and d a r k m a t e r i a l were f l o c c u - l a t e d . Legget and B a r t l e y ( 1 ) i n d e s c r i b i n g t h e h y d r a u l i c dredging c a r r i e d out a t p a r t of t h e mining o p e r a t i o n s , p o i n t out t h a t t h e s a i l s , when redeposited i n t h e l a k e waters, remain i n p a r t i c l e assemblages, w i t h a mean diameter of about 0.01 m i l l i m e t r e s . This i n d i c a t e s t h a t t h e

s o i l p a r t i c l e s have s t r o n g f o r c e s a c t i n g between them t o cause t h i s f l o c c u l a t i o n . The mineral a n a l y s i s revealed t h a t t h e l i g h t l a y e r s contained carbonates, although t h e dark l a y e r s were void of carbonates, This p o i n t i s worth noting i n t h e l i g h t of Burwash ( 1 9 ) and Asrheniua

120)

Burwash ( 1 9 ) suggests t h a t t h e change i n t h e c a p a c i t y of t h e l a k e waters f o r holding d i s s o l v e d carbon dioxide and hence i t s c a p a c i t y f o r d i s s o l v i n g calcium carbonate may be r e s p ~ n s i b l e f o r t h e d e p o s i t i o n of varved c l a y s . In t h e w i n t e r , with a r e l a t i v e l y l a r g e c o n c e n t r a t i o n of carbonic a c i d , t h e lake waters a r e w e l l equipped t o maintain

calcium carbonate i n s o l u t i o n . In t h e s p r i n g , a s t h e l a k e waters become warm, t h e carbonic a c i d i s given up, l e a d i n g t o p r e c i p i t a t i o n of t h e

(19)

c a r b o n a t e s . T h i s , Burwash b e l i e v e s , l e a d s t o t h e f o r q a t i o n of c a l c i t e c o n c r e t i o n s i n t h e l i g h t o r summer l a y e r s . A s r e p o r t e d by Legget and B a r t l e y ( l ) , c o n c r e t i o n s a t S t e e p Rock a r e found only i n t h e Light

l a y e r s of t h e varves.

Arrhenius ( 2 8 ) i n a t t e m p t i n g t o e x p l a i n t h e causes f o r t h e g r e a t d i f f e r e n c e i n c o l o u r between t h e d a r k and l i g h t l a y e r s , found t h a t t h e d a r k o r w i n t e r m a t e r i a l showed d i s s o l u t i o n by carbonic a c i d on a f a r g r e a t e r s c a l e t h a n t h e summer m a t e r i a l , Arrhenius r e p o r t e d on varved marls which occur i n Sweden, but i n t h e opinion 'of t h e a u t h o r t h i s f a c t

s u p p o r t s Burwash's t h e o r y .

The d i f f e r e n c e i n p l a s t i c i t y between t h e d a r k and l i g h t m a t e r i a l may be due t o t h r e e c a u s e s , F i r s t , t h e d a r k l a y e r s c o n t a i n

more c l a y m i n e r a l s , which would i n c r e a s e p l a s t i c i t y , Secondly9 t h e l i g h t m a t e r i a l i s s l i g h t l y c o a r s e r , t h u s has l e s s s u r f a c e a r e a , which would

reduce i t s p l a s t i c i t y . A t h i r d cause could be a d i f f e r e n t c a t i o n complex i n t h e c l a y s , brought about by changes i n t h e d e p o s i t i o n a l e n ~ i r o ~ m e a ~ t ; . Test r e s u l t s b e a r out t h e f i r s t twc p o i n t s but t h e r e i s no proof

for

t h e Third.

In

conclusion, t h e t e s t r e s u l t s p r e s e n t e d i n t h i s paper

i n d i c a t e t h a t both t h e d a r k and l i g h t l a y e r s of t h e varved c l a y a t S t e e p Rock were a f f e c t e d by f l o c c u l a t i o n i n t h e i r d e p o s i t i o n , G r a i n - s i z e

r e s u l t s show t h a t t h e y cannot be termed d i a t a c t i c a s d e f i n e d by F r s a e r ( 1 8 ) . Regarding t h e i r mode of formation, t h e r e s u l t s lend support ti,

the t h e o r y put forward by Bumash, ACKNOWLEDGEMENTS

The a u t h o r wishes t o acknowledge t h e a s s i s t a n c e and f r i e n d l y co-operation extended t o him by t h e s t a f f of S t e e p Rock Ikon Mines

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Manager, and K . McRorie, Chief Engineer. S p e c i a l acknowledgement i s a l s o due S. Forman, of t h e Department of Mines and Technical Surveys

(Canada), who c a r r i e d out t h e mineral a n a l y s i s and t o D r . A . MacLasen of t h e Geological Survey of Canada who supplied samples of v a ~ v e d c l a y from Amos, Quebec. The a u t h o r a l s o wishes t o express h i s a p p r e c i a t i o n f o s t h e h e l p w i t h v a r i o u s a s p e c t s of t h e work given him by h i s colleagues i n t h e Division of Building Research, e s p e c i a l l y t h e D i r e c t o r , M r . R , F. Legget, w i t h whose approval t h i s paper i s now published as a c o n t r i b u t i o n from t h e Division of Building Research of t h e National Research Council of Canada.

BIBLIOGRAPHY

1. Legget, R . F. and M . W. B a r t l e y , An Engineering Study of G l a c i a l Deposits a t Steep Rock Lake, Ontario. 3conomic l e o l o g ~ r ~ Vole 48, p. 513-540, November 1953.

2 . Hauser, E . A . and D. S. Le Beau. Colloid Cheml3try of Clay Minerals and Clay Films. ' c l l o i d Chemistry ( ~ d i t e d by Jerome ~ i e . ~ a n d e r ) , Val.

6 ,

p.191-213, R.inhold 2 ~ b . L 1 . ~ h i n g Corp.

,

Neb Ycrk,

1946,

3. Ahlberg, H. A Contribution t o t h e Methods of Measuring t h e P l a s t i c i t y of Clays. Transactions of Chalmers U n i v e r s i t y of Technology

No. 119. Gothenburg, Sweden. 1951.

4. American S o c i e t y f o r T e s t i n g M a t e r i a l s , Procedures f o r T e s t i n g S o i l s . 1950. 418p.

5 . Skempton, A.W. The C o l l o i d a l ' A c t i v i t y 1 of Clays. Proc. 3rd I n t . Conf. on S o i l Mechanics and Foundation Engineeringp

V O ~ . 1, p.57-61, Switzerland, 1953.

6 Casagrande, Arthur, C l a s s i f i c a t i o n and I d e n t i f i c a t i o n of S o i l s . Proceedings, American S o c i e t y of C i v i l Engineers, Vol. 739 p.783-810. 1947.

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7 . Green, H. and Ruth

N.

Weltmann. Thixotropy. 3ollbid >heastry (Edfted by Jerome Alexander), Vol. 6, p.328-346, Reinhold Publishing Corg

.

,

New York, 1946.

8, Pryce-Jones,

.

J. The ?low ~f juspensions

-

Thixotropy and Dilatancy , Psoc

.

of Univer~ity of Durham Phil. Soc

.

,

Vol. 10, Dart

6 ,

p.427-467. March

1948.

11

9.

Ackernlann, E

.

k i x e t s ~ ? ! _ e a7.d Fliesseigenschaft e n ?einkoa*niger ~bldan (~hixotropy and Flow Properties

of Fins

Grained Solls)

.

Geologische Rurdschau, Vol. 36, 1948. Technical Translation No.

1509 National Research Council, Ottawa, Canada. April, 1950, 10. Boswell, P.G.H. The Trend of R2search on the Rheotropy of

Geological Materials, Science Progress No. 136, p .608-622. October 1951

11. Casagrande, Arthur." The Hydrometer Method for MechanicaJ Analysis of Soils and Other Granular Materials. Zambridge, Mass.

JUe, 1931. 51po

12. Lambe, T. W. Soil Testing for Engineers. John Wiley & Sons, Inc

.

1951.

13. Krmbein, W,C. and F.G. Pettijoh. Manual of Sedimentary Petography. D, Appleton Century Company, Inc

.

,

New York, 1938.

549~.

14. Otto, G.H.

A

Modified Logarithmic Probability Graph for the

Interpretation of Mechanical Analyses of Sediments. Journal of Sedimentary Petrology, Vol

.

9, No. 2, p -62-76. August, 1939, 15, Inman, D.L. Measures for Describing the Size Distribution of

Sediments. Journal of Sedimentary Petrology, Vol, 22, No. 3, p. 125-145. September, 1952,

16. Skempton, A.W, and R.D. Northey. The Sensitivity of Clays, Gc?otechnique, Vol. 3, No, 1, p.30-51, March, 1952.

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17. Antevs,

E.

G l a c i a l Clays I n S t e e p Rock Lake, Ontario, Canada. d

. b

B u l l . Geol. Soc, of America, Vol. 62, p.1223-1262, October, 1951,

18.

F r a s e r , H.J. An Experimental Study of Varve Deposition. Royal S o c i e t y of Canada Proceedings and Transactions, Vol. 23,

19. Burwash, E.M. The Deposition and A l t e r a t i o n of Varved Clays, Transactions, Royal Canadian I n s t i t u t e , Vol. 22, p-3-6, Toronto, Canada. 1938,

h his

paper i s p r i n t e d a s an appendix i n Legget ( 1 ) ) .

20. Arrhenius, G. Den G l a c i a l a Lerans Varvighet (The Varvity of t h e G l a c i a l Clay), Sveriges Geologiste Undersakning, S e s . C , No. 486, Stockholm, 1947. 74p.

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*

L N A T U R A L W A T E R C O N T E N T

-

Oi0 D R Y W T . 0 2 0 4 0 6 0 8 0 100 T O P

mi

... ... ... ... ... D A R K H T W N

-

V) J J 3 LL W 0

-

3 I- 11 W J a U V) /

a

FIG. 1 V A R I A T I O N IN N A T U R A L W A T E R C O N T E N T W I T H I N T H E V A R V E S ( S A M P L E - 2-65) p . o ~ * h 1 . / 5 4 D . 8 . n . REfOqT 9

-

24

(24)
(25)
(26)
(27)

G R A I N S I Z E

-

4

U N I T S 7 8 9 10 I I F I G U R E 5 \ \ M E D I A N V A R I A T I O N I N G R A I N S I Z E I N A G E O M E T R I C M E A N \ \ \ D I A M E T E R

.

D I A M E T E R - \ 0 \ \ \

i

h

D l A T A C T l C V A R V E

(28)
(29)
(30)

C U M U L A T I V E G R A I N - S I Z E D i S T R I B U T 1 0 N C U R V E S L E G E N D L O W E R T H I R D - U P P E R H A L F L O W E R T H I R D

-

L O W E R H A L F

---

F I G U R E 6 C

-

L O W E R T H I R D R E S U L T S O F M I C R O S C O P I C G R A I N - S I Z E A N A L Y S I S O F L I G H T L A Y E R O F V A R V E D C L A Y ( S A M P L E 2 - 1 2 4 )

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2 8 F I G . 7

1

2 6 '--

-.

V A R I A T I O N O F U N C O N F I N E D C O M P R E S S I O N I I

-

\ \

\.

S T R E N G T H W I T H O R I E N T A T I O N O F V A R V E S - I I 2 4 \ I L E G E N D - \

-

I

-

-B Z A N C L F -B E T W E E N V A R V E D P L A N E S 6 A X I S O F S T R E S S . S O L I D L I N E S - A V E R A C E V A L U E S P 0 z 0

-

-

C - - - - 0 U P S A M P L E 2 - 6 8 W z 6 - -- 3

I

i

4 -- 2 0 I o0 10' 20' 30- 4 0 - 8 50' 60 ' 7 0' 8 0- 9 0 ' 9

(32)

V A R V E USED

IN TESTS-'

F I G U R E 8

(33)

F i g .

9

-

Specimen on t h e l e f t

--

8 = 30'

-

f a i l e d a l o n g t h e l i g h t l a y e r .

-

Spscimen on t h e r i g h t

--

8 = 60°

-

f a i l e d t h r o u g h b o t h d a r k and l i g h t l a y e r s . ( s c a l e i n i n c h e s )

(34)

Fig. 1 0

-

Typical sample of v a r v e d

clay From S t e e p Rock Lake.

Figure

Fig.  1 0   -  Typical  sample  of  v a r v e d   clay  From  S t e e p   Rock  Lake.

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