TRIAXIAL COMPRESSION TESTS ON AN

UNDISTURBED SENSITIVE CLAY

by

TERENCE JOHN HIRST

B o A o S c p University of British Columbia9 1962

A THESIS SUBMITTED IN PARTIAL FULFILMENT OF

THE REQUIREMENTS FOR THE DEGREE OF

Master of Applied Science

in the Department

of

C i v i l Engineering

We accept this thesis as conforming to the required standard

THE UNIVERSITY OF BRITISH COLUMBIA

MAYe 1966

In p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f

t h e r e q u i r e m e n t s f o r an advanced degree a t t h e U n i v e r s i t y o f

B r i t i s h C o l u m b i a , I a g r e e t h a t t h e L i b r a r y s h a l l make i t f r e e l y

a v a i l a b l e f o r r e f e r e n c e and s t u d y . I f u r t h e r a g r e e t h a t p e r ­

m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y

p u r p o s e s may be g r a n t e d by t h e Head o f my Department o r by

h i s r e p r e s e n t a t i v e s * I t i s u n d e r s t o o d t h a t c o p y i n g o r p u b l i ­

c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l not be a l l o w e d

w i t h o u t my w r i t t e n p e r m i s s i o n .

TERENCE JOHN HIRST

Department o f C I V I L ENSINEERING

The U n i v e r s i t y o f B r i t i s h Columbia Vancouver 8, Canada

Date MAY 1966

ABSTRACT

An experimental investigation into the st r e s s - s t r a i n behavior

of an undisturbed sensitive clay i s presented 0 The st r e s s - s t r a i n

characteristics of both drained and undrained t r i a x i a l tests are

considered., The drained and undrained shear strengths are compared

for both the maximum p r i n c i p a l stress difference and the maximum

eff e c t i v e p r i n c i p a l stress r a t i o f a i l u r e c r i t e r i a . An attempt i s

made to correlate the drained and undrained shear strength through

the use of energy equations which account for volume change. The

magnitude of pore pressures that develop during drained tests i s

estimated„ and a br i e f discussion of the effect of rate of s t r a i n

on the behavior of the clay i s also included.

The s o i l tested was a sensitive laminated s i l t y - c l a y of

marine o r i g i n . The experimental work consisted of standard s t r a i n -

controlled t r i a x i a l compression tests performed on saturated, nor­

mally consolidated, 2,8 i n s , by 1,4 i n s , diameter samples. The

s t r a i n rate i n both the drained and undrained tests was 0,5 percent

per hour,, except for one drained test sheared at 2,5 percent per

hour. A l l consolidation and drained shear was conducted under a

back pressure of 10 lbs,/sq, i n . Drainage was permitted from both

ends of the sample 8 but no f i l t e r paper side drains were used. Pore

pressures were measured at the base of the sample using a Bishop

and Henkel n u l l - i n d i c a t o r . The samples were sheared u n t i l approxi­

mately 30 percent a x i a l s t r a i n had been developed or u n t i l f a i l u r e

had occurred, A discussion of the testing procedures i s included.

The results of the investigation indicated that the s e n s i t i v i t y

of the c l a y i s of primary importance i n determining the behavior

of s o i l under l o a d , A r e l a t i o n s h i p between v o i d r a t i o and

s t r e n g t h that i s independent of s t r e s s path does not e x i s t i n

undistrubed s e n s i t i v e c l a y s , nor does there appear to be a common

d r a i n e d and undrained s t r e n g t h envelope at the maximum p r i n c i p a l

s t r e s s d i f f e r e n c e f a i l u r e c r i t e r i o n . A p p l i c a t i o n of the Bishop

and Rowe energy c o r r e c t i o n s to the d r a i n e d s t r e n g t h obtained at

the maximum e f f e c t i v e p r i n c i p a l s t r e s s r a t i o d i d not y i e l d the

same e f f e c t i v e s t r e n g t h envelope as that determined from undrained

t e s t s at the same f a i l u r e c r i t e r i o n , but the value of M (the s lope

of the q W~P* curve) i n the Roscoe, S c h o f i e l d , and T h u r a i r a j a h

energy equation was approximately c o n s t a n t 0 The uncorrected

e f f e c t i v e angle of s h e a r i n g r e s i s t a n c e , 0% was found to be a

f u n c t i o n of f a i l u r e c r i t e r i o n and drainage c o n d i t i o n . The s t r a i n

at which f a i l u r e occurred i n d r a i n e d t e s t s , although decreasing

with i n c r e a s e i n c o n s o l i d a t i o n s t r e s s , was l a r g e , i n d i c a t i n g that

the g e n e r a l l y accepted f a i l u r e c r i t e r i a of maximum p r i n c i p a l s t r e s s

d i f f e r e n c e and maximum e f f e c t i v e p r i n c i p a l s t r e s s r a t i o are not

s a t i s f a c t o r y f o r s e n s i t i v e c l a y . Although c a l c u l a t i o n s showed

that pore pressures were developed at low s t r a i n s i n drained

t e s t s , i n c r e a s i n g the r a t e of s t r a i n from 0,5 percent per hour

to 2,5 percent per hour d i d not n o t i c e a b l y a f f e c t the s t r e n g t h

or s t r e s s - s t r a i n behavior of the 2,8 ins„ by i 0 4 i n s 0 diameter sampl

iv

CHAPTER 1

1.1

1.2

CHAPTER 2

2,1

2,2

2,3

2,4

2,5

2,6

2,7

2,8

2,9

2,10

CHAPTER 3

3,1

3,2

3,3

3,4

3,5

TABLE OF CONTENTS

INTRODUCTION*) o o o o o o o o o o o o o o o o o o-o. o o o o o o o o o o o o o o

Pllirp08£ 0 0 0 0 O O O O O O O O O O O O O O ' O O O O O O O O O O O O O O O O O O O O O

S C O p & O O O O O O O O O O O O O O O O O O O H O O O O e O O O D D f i O O O O O O O O O

DESCRIPTION OF SOIL TESTED AND

TESTING P R O C E D U R E S , 0 0 0 0 0 0 0 , 0 0 0 0 0 0 0 0 0 0 0 . 0 0 , 0 0 0

Description of soil 0 0„ 0 0

Sampling and sto r i n g , , 0 .

Preliminary t e s t s 0 0 0 , 0 0 0 0 , 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

Preliminary c o n s i d e r a t i o n s , , 0 0 0 0 0 0 , 0 , 0 0 0 0 0 0 0 0

Description and preparation of equipment,0.0.

Test preparation, sample trimming and placing.

Application of chamber pressure, sample

saturation and i n i t i a l c o n s o l i d a t i o n 0 0 0 0 0 0 0 0 0 0

Drained shear t e s t s o 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

Undrained shear t e s t S o 0 o~s 6 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

Back-drainage, dismantling and cleaning,„ 00.0,

I 0 0 O O O O 0 O O O 0 0 O O O O 0 0 O O O

I O O O O O O O O O O O O Q O O O O O O O O O

O O O O O O O O O O O O O DISCUSSION OF TESTING PROCEDURES,,

IntTOdUCtion 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

Sampling$ waxing 9 and s t o r i n g 0 o o o o o o o o o o o o o o o o

Sample p r e p a i r e t i o n o o o o o o o o o o o o o o o o o o o o o o o o o o o o

Water content and volume measurementse 0 o 0 0 o o o 0

TeSt equipment o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o

PAGE

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4

4

8

8

11

12

16

18

19

19

21

22

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V

PAGE

CHAPTER 4 DISCUSSION OF TEST RESULTS, a„»o•>„o»oo«o»ooo,o 31

4 o l I n t r o d u c t i o n , O O O O O O 0 O O O O C O O O O O O , O O O O O O O O O O O O 0 31

4,2 Sensitivity and'Structure, Oooooo,oooooooo,ooo 33

4 0 3 Residual pore pressures developed during

drained shear t e s t s , 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 , 0 0 0 0 0 0 0 0 34

4 0 4 Energy c o r r e c t i o n s 0 o 0 0 0 0 0 0 0 0 0 0 o 0 0 0 0 0 0 0 0 0 0 0 0 0 0 42

4 0 5 Stress—strain r e l a t i o n s h i p s 0 0 0 0 , 0 0 0 0 0 0 0 0 0 0 0 0 0 53

4 0 6 Shear s t r e n g t h o 0 0 0 0 0 0 0 0 0 0 0 0 0 » 0 0 0 0 0 0 0 o 0 0 0 0 0 0 0 0 61

4 0 7 S u n u n a r y , 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 76

CHAPTER 5 C O N C L U S I O N S 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 , 0 0 0 0 0 0 0 0 0 77

CHAPTER 6 SUGGESTIONS FOR FURTHER R E S E A R C H , „ 0 0 0 0 0 0 . 0 « 0 0 79

NOMENCLATURES 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 b o o o o o o o o o o o o o o o o o o o o o o o 82

LIST OF R E F E R E N C E S 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 b 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 84

A P P E N D I X 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 9 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 87

LIST OF TABLES

P h y s i c a l p r o p e r t i e s of Haney clay„ „ 0 0 0 «<, «

Chemical p r o p e r t i e s of Haney c l a y , , o o o o o »

Water contents of s i d e trimmings compared

to the water content of the whole sample.

Summary of t e s t r e s u l t s o o i o t t i o i o o i i o i H

v i i

LIST OF FIGURES

FIGURE P A G E

1 „ Grain size distribution of Haney clay, „ 0 a »,,,,,o , o 0 , « , . 6

2 , Typical standard consolidation curve for Haney clay,,.. 7

3o Sampling the c l a y , o o o o o o o o o o o o o . o o o o o o o o o o o o o o o o o o , , , , , 1C

4 , T r i a x i a l c e l l and chamber pressure s y s t e m , , , , , 1 3

5 , Drainage and pore pressure.measuring system,,,,,,,,,,,, 14

6a T r i a x i a l . e q u i p m e n t ! 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

7 0 Trimming tools and prepared s a m p l e 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 17

8 0 Sample in place on t r i a x i a l b a s e 0 0 0 0 0 0 © 0 o 0 0 0 0 0 0 © 0 0 0 o 0 o 0 17

9o Sample during shear e o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o 20

1 0 , Relationship between coefficient of consolidation

and mean effective stresso 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 38

110 Relationship between computed pore pressure and axial

strain in a drained t e s t o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o ^0

1 2 , Showing the effect of computed pore pressure on the

effective principal stress ratio in a drained test,,,,, 4 1

1 3 , Relationship, between water content and mean effective

stress for t r i a x i a l consolidation,and unloading (back-

drainage) , 0 0 0 0 0 0 0 0 0 0 0 , 0 0 0 0 0 . 0 0 0 0 0 0 0 0 0 , 0 0 0 0 0 0 0 , 0 0 0 0 0 0 0 , 47

1 4 , Application of the Rowe energy correction to test S - 1 7 , , 4 9

1 5 , Application of the Roscoej Schofield and Thurairajah

energy correction to drained and undrained test data,,,, 5 1

1 6 , Stress-strain curves for test S - 1 7 o , o o , o o o o o o , o o o o , , o , , , 54

1 7 , Stress—strain curves for test S — 1 6 0 0 o , , o , , o o o o o o o , o , o o , , 55

1 8 , Stress-strain curves for test S - 1 5 , , 0 o o o o o o o o , o o o o o , , , , . 5 6

v i i i

PAGE

19o Load-deformation curves f o r rubber and Haney clay 0 ooo*oo 58

20e S t r e s s — s t r a i n curves f o r t e s t S—lOooo'ooo'ooooooooooooooo 59

2 1 0 S t r e s s — s t r a i n c u r v e s . f o r t e s t C—U—10 a oo o o o o o o <> o o o oo o oo o 62

22o S t r e s s — s t r a i n curves f o r t e s t C—U—5 0ooooooooooooooooooo 63

23o S t r e s s - s t r a i n curves, f o r t e s t C - U » 7 0 o o o o o o o o o o o o o o o o o o o 64

24o R e l a t i o n s h i p b e t w e e n . n a t u r a l - s e n s i t i v i t y and degree

of m o b i l i z a t i o n of <j>' at ( c i ' - 0 3 s )

maXo , 0 0 0 0 0 0 0 0 0 0 0 0 0 65

2 5 0 Uncorrected maximum p r i n c i p a l s t r e s s d i f f e r e n c e

f a i l u r e , e n v e l o p e s 6 0 0 0 0 0 0 0 0 b o 0 0 < r o 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 a 0 0 0 0 0 67

26 o Uncorrected maximum e f f e c t i v e p r i n c i p a l s t r e s s r a t i o

f a i l u r e envelopes00ooooooo-ooooooooooooooooboooooooooooo' 67

270 C o r r e c t e d maximum e f f e c t i v e p r i n c i p a l s t r e s s r a t i o

f a i l u r e e n v e l o p e s 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 67

28o R e l a t i o n s h i p between water content and a x i a l s t r a i n i n

a d r a i n e d t e s t o 0 0 o o o 0 0 0 0 o ' o « n 0 0 0 0 0 0 o o 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 69

290 R e l a t i o n s h i p between pore p r e s s u r e and a x i a l s t r a i n i n an

undrained . t e s t 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 70

3 0 „ T y p i c a l water c o n t e n t - s t r e s s r e l a t i o n s h i p s f o r s a t u r a t e d ,

n o r m a l l y c o n s o l i d a t e d remolded and i n s e n s i t i v e c l a y s o o o 71

3 1 0 R e l a t i o n s h i p between water content and s t r e s s a f t e r

normal c o n s o l i d a t i o n and at ( o i " - 03 ') max0 and ( c i ' / o ^ ' )

maxo f a i l u r e •.criteria© 0 0 0 0 0 0 0 0 6 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 72

32o V a r i a t i o n of the m o b i l i z e d . e f f e c t i v e angle of shearing

r e s i s t a n c e w i t h a x i a l ' s t r a i n 0 o o o o o o o o o o o o o o o o o o o o o o o o o o , 74

ACKNOWLEDGMENT

This thesis is a contribution to the research program at

the University of British Columbia on the strength and deforma­

tion characteristics of cohesive s o i l s 0 The program, which is

financed by the National Research Council of Canada under grants

Noo 1498 and No„ 1507, i s directed by Dr 0 W0D0 Liam Finn, Professor

and Head, Department of C i v i l Engineering,-and Professor N 0D„

Nathano

The author i s grateful to Professor Nathan and Dr 0 Finn for

their guidance and constructive criticism during the development

and preparation of this thesis a

The undrained test results were obtained by Mr0 Peter Byrne

with whom the task of developing satisfactory testing procedures

was shared„

Dr 0 EoHo Gardner, Department of Soil Science, kindly supplied

data on the chemical properties of the clay.

The technical assistance supplied by the staff:of the C i v i l

Engineering Department Workshop i s gratefully acknowledged„

1

CHAPTER 1

INTRODUCTION

l o l Purpose

Triaxial compression tests are a useful method of investigating the

stress-strain behavior of s o i l , and in particular, of determining the shear

strength of s o i l under drained and undrained conditions„ The stress-strain

characteristics of cohesive soils have been the subject of exhaustive re­

search in recent years 0 The need for a thorough understanding of these

aspects of s o i l behavior i s increasing daily as the number of building sites '

containing acceptable cohesionless. foundation material rapidly diminishes,

and the size of e a r t h - f i l l dams steadily increases 0 Two approaches have

been used to study the response of s o i l to applied stresses and strains.

The f i r s t approach, toward which most attention has been directed, examines

the macroscopic behavior of s o i l in laboratory and f i e l d tests 0 This has

led to the development of strength c r i t e r i a which satisfy the practicing

engineer in his search for solutions to everyday problems, but has not re­

vealed the fundamental properties governing soil., behavior 0 The second and

more recent approach inquires into the nature of the physical and chemical

bonds existing between individual s o i l particles and their environment, and

has the ultimate goal of relating these properties to the macroscopic be­

havior of the s o i l mass.

Primarily as a result of the macroscopic approach to s o i l behavior,

many empirical relationships have been proposed between s o i l strength and

such variables as void ratio and effective stresso "Of particular interest

to this investigation i s the concept of a common effective stress failure

envelope determined from drained and undrained t r i a x i a l compression tests

on saturated cohesive s o i l s 0 Many workers have confirmed the vali d i t y of

2

this concept for remolded clays (Hvorslev,1960)*0 In addition, attempts to

explain the common envelope in terms of the fundamental'physico-chemical

properties of remolded clays have met with limited success (Scott,1962) 0

Undisturbed clays, which possess characteristics significantly different

from remolded clays, have not received as much attention as the latter, and

published results of tests show conflicting data concerning the existence

of a common envelope (Henkel,1960)0

It was the purpose of this.thesis to investigate, experimentally, the

drained and undrained stress-strain behavior of a normally consolidated un-2

disturbed saturated clay of extra-sensitivity (Skempton and Northey,1952) ,

to report on the testing procedures used i n the investigation, and to examine

the concept of a common failure envelope (independent of stress path) for

sensitive clays 0

102 Scope

The experimental phase of this project was conducted in conjunction

with Mr0 PoMo Byrne, fellow graduate studento Consolidated drained and un­

drained t r i a x i a l compression tests were performed at constant strain rate

on undisturbed saturated samples of extra~sensitive elay 0 A l l samples were

normally consolidated prior to shearingo The series of drained tests were

performed by the author and the undrained tests, in which pore pressures

were measured, were performed by Mr0 Byrne0 With the exception of the drain­

age conditions and confining pressures, a l l features of both series of tests

were identical„ A description of testing procedures i s contained in Chapter

2 0

Io A l i s t of references, arranged alphabetically, may be found at the end of this thesis 0

2 0 For a definition of sensitivity, the reader i s referred to section 402 of this thesiso

3

Many preliminary tests were performed before a satisfactory testing

procedure was developed and a discussion of some of the problems encountered

has been included in Chapter 3.

The f i n a l test series consisted of six drained and six undrained tests

(two at each of six confining pressures). A discussion of the shape of the

stress-strain curves obtained i s included in Chapter 4, along with compari­

sons of the drained and undrained strength envelopes determined for failure

c r i t e r i a of maximum principal stress.difference (maximum deviator stress)

and maximum effective principal stress ratio. The use of energy corrections

to account for volume change i s discussed, and an estimate of the pore

pressures developed in drained tests Is presented 0 The effect of rate of

strain on the behavior of the clay i s briefly mentioned,

A summary of the conclusions reached in this investigation i s presented

in Chapter 5, and suggestions for further research may be found in Chapter 6.

The nomenclature used throughout this thesis conforms to that adopted

by the American Society of C i v i l Engineers (1962).

A l l symbols are defined as they occur and for convenience, a table

of nomenclature, assembled alphabetically, i s included at the end of this

thesis.

4

CHAPTER 2

DESCRIPTION OF SOIL TESTED AND TESTING PROCEDURES

2ol D e s c r i p t i o n of s o i l

The c l a y deposit from which the b l o c k samples were taken i s l o c a t e d at

Haney, B r i t i s h Columbia, which i s about t h i r t y m i l e s east of Vancouver on

the n o r t h bank of the F r a s e r R i v e r , The deposit i s the present s i t e of a

b r i c k p l a n t which uses the c l a y i n the manufacture of b r i c k and t i l e 0 The

s o i l i s known l o c a l l y as Haney c l a y and t h i s name w i l l be adopted i n t h i s

thesis, ,

D e p o s i t i o n of the m a t e r i a l apparently occurred d u r i n g or s h o r t l y a f t e r

the l a s t major g l a c i a t i o n of south-western B r i t i s h Columbia at a time when

the sea was h i g h e r ( r e l a t i v e to the land) than i t i s at present (Armstrong,

1957)o Thus the d e p o s i t was formed i n a marine or b r a c k i s h environment„

Subsequent u p l i f t of the land has permitted l e a c h i n g of the s o i l to o c c u r ,

l e a v i n g i t with a s e n s i t i v e s t r u c t u r e . The c l a y p r e s e n t l y comprises a s u r ­

face deposit covered only by a t h i n l a y e r of Weather s o i l , , a n d i s only l i g h t ­

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

Haney c l a y c o n t a i n s approximately h o r i z o n t a l l a m i n a t i o n s of medium to

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

i s a dark b l u e - g r e y c o l o r when wet, the c o l o r of neat cement when d r y , and

has l i t t l e o r g a n i c odor. Evidence of i t s d e p o s i t i o n s ! environment i s o f f e r e d

by the e x i s t e n c e of s m a l l marine s h e l l s which may be found i n the c l a y .

Results of standard l a b o r a t o r y i d e n t i f i c a t i o n t e s t s performed on

samples of Haney c l a y may be found i n Table I and F i g u r e s 1 and 2.

5

TABLE I

PHYSICAL PROPERTIES OF HANEY CLAY

s

S p C C i l f l r C gravity o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o b o o o o o o o o o o 2 o 8 0

Liquid X i l C l i t o o o o o o o o o o o o o o o o o o o o o o o o o o o o b o o o o o o o o o o o o o o o o o o o o o 44/>

Plastic l i l t t i t o O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O o o o o o o o o o o o o 2 6 ^

Plasticity illdeX o o o o o o o o o o o o o o o o b o o o o o o o o o o o o o o o o o o o o o o o o o o o o o 18/o*

Natural Water COntent o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o b o o ' a o o o o o o 42 /o 4" l> o

Percent finer than 2 m i c r o n s 0 0 o o o o o 0 0 o o o o 0 o o o o o o o o o o o o o o o o o o o o 4 6 %

A c t i v i t y o O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O o O o 3 9

Undisturbed unconfined compressive s t r e n g t h o 0 o o o o o o o o o ° o o o o o 1 0 o 8 l b s 0 / s q 0 i n 0

Remolded unconfined compressive s t r e n g t h o o 0 o o o o o 0 o o o o o o o o o o 0 0 0 0 9 lbs 0/sq 0 i n 0

Sensitivityo 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 o l 2

Maximum past p r e s s u r e 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 3 8 lbso/sqo ino

M. I. T. GRAIN SIZE CLASSIFICATION

FINE SAND

COARSE SILT

MEDIUM SILT

FINE SILT

COARSE CLAY

MED KlAYj

O.IO 0.05 0.02 0.01 0.005 0.002 0.001 0.0005

GRAIN DIAMETER (MMS)

FIGURE I. GRAIN SIZE DISTRIBUTION OF HANEY CLAY

7

FIGURE 2. T Y P I C A L STANDARD CONSOLIDATION C U R V E FOR H A N E Y C L A Y .

8

A small dry sample of the s o i l was subjected to x-ray diffraction analysis

to determine the mineral composition of the clay. Results of this test may

' be found in Table II,

The following testing procedures are the fi n a l procedures adopted0

Other procedures were tried and abandoned for various reasons, some of

which are discussed in Chapter 3,

202 Sampling and storing

A l l samples were obtained by hand excavation from the clay deposit at

Haney (Figure 3)<> After removing a l l the disturbed surface material from a

12 square foot area, 9 i n 0 by 9 i n 0 by 9 i n 0 block samples were excavated

using a fine wire saw0 The blocks were immediately coated with a layer of

Mobile #2300 wax and transported to the laboratory. In the laboratory, the

blocks were given further coatings of wax to ensure that there would be no

change of water content during storage. The waxed blocks were stored in a

moist room u n t i l used,

2,3 Preliminary tests

As previously mentioned, standard identification tests were performed

on the clay prior to conducting the main series of experiments. These tests

included the determination of natural water content, specific gravity,

Atterberg limits, grain size, unconfined compression strength, sensitivity,

maximum past pressure and coefficient of consolidation (Table 1, Figures 1

and 2)o A l l of these tests were performed in accordance with the procedures

suggested by Lambe (1958).

TABLE II

CHEMICAL PROPERTIES OF HANEY CLAY

GRAIN SIZE . MINERAL AMOUNT PRESENT

Quartz Large

S i l t fraction Feldspar Large

(greater than Chlorite Moderate - small

2 microns) Mica Moderate - small

Amphibole Small

Chlorite Large

Clay fraction Feldspar Moderate = small

(less than Mica/chlorite Moderate - small

2 microns) Quartz Small

Mica Small

Amphibole Small <= questionable

Figure 3: Sampling the c l a y .

11

2,4 Preliminary Considerations

The clay was brought to f a i l u r e by the application of a constant rate

of a x i a l strain,, The choice of a suitable rate of deformation was based on

the c r i t e r i a that minimal pore pressures should be present over most of a

drained stress path, and that adequate pore pressure equalization should be

present over most of an undrained stress path 0 Because the use of side drains

generally hastens the dissipation or equalization of pore pressures, t r i a l

t r i a x i a l consolidation tests were performed using Whatman8s No, 54 f i l t e r

paper side drains (Bishop and Henkel,1962), Other t r i a x i a l consolidation

tests were performed without the aid of side drains and although the use of

f i l t e r papers did hasten the rate of consolidation, the increase was not

significant,, In view of t h i s and because side drains are d i f f i c u l t to place

around the sample, i t was decided not to use f i l t e r papers, but to permit

drainage from the top and bottom of the sample only 0 Calculations based on

the method of obtaining rates of deformation suggested by Bishop and Henkel

(1962) indicated that, under the above drainage conditions, a rate of s t r a i n

of 0,25 percent per hour was satisfactory i f f a i l u r e occurred at 15 percent

a x i a l s t r a i n i n the drained tes t s . I t was subsequently determined that

drained f a i l u r e would occur at approximately 30 percent a x i a l s t r a i n and thus

a rate of s t r a i n of 0,50 percent per hour was believed adequate.

The choice of satisfactory e f f e c t i v e confining pressures was governed

by the following requirements;

1, A l l samples were to- be normally consolidated and therefore e f f e c t i v e confining pressures must ex­ceed the maximum past pressure (38 lbso/sq, in,)

2 0 The maximum allowable pressure i n the t r i a x i a l equipment i s 100 lbs,/sq, i n , , and

3, Because the test data obtained i n t h i s investigation was also to be used i n a separate study of drained and undrained e f f e c t i v e stress paths, the paths were to cross at convenient, well-spaced i n t e r v a l s .

The effective confining pressures for the drained tests were 40 l b s , / s q 0 i n 0 ,

55 lbs,/sq,in,, and 70 lbs,/sq,in, and for the undrained tests 60 lbs,/sq,

i n , , 75 lbs,/sq,in,, and 88,5 lbs,/sq,in 0

2.5 Description and preparation of equipment

A Clockhouse Engineering T010 t r i a x i a l c e l l capable of receiving 208

in, by 1„4 i n , diameter samples was used for a l l tests 0 Although drainage

was permitted from both the top and the bottom of the sample, pore pressures

were measured at the base of the sample only, using a Bishop and Henkel null

indicator. Volume changes were measured i n a 10 cubic centimeter capacity

burette, graduated to 0 01 cubic centimeters. To ensure complete saturation

of the sample, a back-pressure of 10 Ibso/sqoin, was applied to the drainage

line by means of a mercury column and balancing tank. A l l drainage leads

and pore pressure lines were constructed of small diameter copper tubing

except for the connection to the drainage burette which was of saran tubing.

Valves used in the system were Hoke non-displacement valves (incorporating

teflon seals) and Hoke stem valves. Schematic diagrams of the equipment are

shown in Figures 4 and 5, and a photograph of the equipment, taken during a

preliminary undrained test, i s shown in Figure 6,

Axial loads were measured by a proving ring and both the chamber

pressure and pore pressures were measured by bourdon gauges0 The proving

ring was calibrated against a Baldwin-Hamilton Universal Testing Machine and

both bourdon gauges were calibrated against a dead weight tester prior to

use.

De-airing was accomplished by passing large quantities of warm, de-

aired, d i s t i l l e d water through a l l the lines. The lines were then subjected

to positive and negative pressures in excess of those anticipated during any

test, A f u l l y reversible rise in the level of the mercury in the null tube

DIAL GAUGE

MACHINED SLEEVE

A TO PROVING * RING

LOADING CAP

SAMPLE

SATURATION SPIRAL

MEMBRANES

O l ®

TO PORE PRESSURE r AND DRAINAGE

SYSTEM

VALVES

X HOKE STEM (DISPL.)

(J) KLINGER ABIO (NON-DISPL.)

( £ ) HOKE BALL (NON-DISPL.)

POROUS STONE

TRIAXIAL CELL CLOCKHOUSE TYPE T.IO

POROUS STONE

0-RINGS

REGULATORS

/ \

STRAIN CONTROLLED AX.AL DRIVE j W H £ £ V

| IN. O.D. IMPERIAL POLYETHYLENE TUBING I—

DE-AIRED WATER

IN. O.D. COPPER

PRESSURE SUPPLY

_ VACUUM I SUPPLY

CONTROL PANEL

STEEL BALANCING TANK

CHAMBER PRESSURE GAUGE

(0-100 LBS./SQ.IN.)

NOT TO SCALE

FIGURE 4. TRIAXIAL CELL AND CHAMBER PRESSURE SYSTEM

DISTILLED DE-AIRED WATER SUPPLY

CONNECTIONS TO TRIAXIAL CELL-'

(7) LOWER STONE

(?) UPPER STONE •0

8 IN. O.D.

COPPER

3 IN.O.D.

COPPER

BISHOP AND HENKEL NULL INDICATOR

PRESSURE CONTROL CYLINDER

10 CU. CMS. BURETTE (ADJUSTABLE HEIGHT)

-7 IN. O.D. IMPERIAL 4

POLYETHYLENE TUBING

VALVES

X HOKE STEM (DISPL.)

KLINGER ABIO (NON-DISPL.)

(S) HOKE BALL (NON-DISPL.)

JL

0 PORE PRESSURE GAUGE (0-100 LBS /SQ. IN.)

^ - | N . o.D. SARAN 1 6 TUBING

BALANCI TANK

NG

4

4 FT. MERCURY MANOMETER TO MEASURE NEGATIVE PORE PRESSURE

\ OVERFLOW

4 FT. MERCURY " MANOMETER TO SUPPLY 10 LBS /SQ. IN. BACK PRESSURE

NOT TO SCALE

FIGURE 5 DRAINAGE AND PORE PRESSURE MEASURING SYSTEM

Figure 6 : Triaxial equipment.

16

of about 1/2 inch per 100 lbs,./.sq.in,, was achieved thus indicating the

pore-pressure equipment was satisfactorily de-aired, No change in level of

the water in the drainage burette was observed when the pressure in the

drainage lines was increased to 25 lbs,/sq.in. No measurable evaporation

occurred in the drainage burette 0

206 Test preparation sample trimming and placing

Before commencing each test, a l l drainage lines were flushed with

de-aired d i s t i l l e d water0 Two porous stones were placed in boiling water

for half-an-hour to ensure complete saturation. The stones were then allow­

ed to coolo The circumferences of the base pedestal and the loading cap

were coated with silicone grease before placing a rolled membrane (Sheik

natural rubber, 0,003 in, wall thickness) around each of them. Four rubber

0-rings were slipped onto ring expanders and placed around the saturation

spiral in preparation for binding the membranes to the pedestal and the

loading cap.

The samples were prepared in a humid atmosphere to reduce sample mois­

ture losses, and were trimmed with a fine wire saw to approximately 1.4 in,

diameter by 2,8 in, length, using a procedure similar to that recommended by

Bishop and Henkel (1962), The prepared sample and trimming tools are shown

in Figure 7, Four large (approximately 40 gm, wet weight) side samples were

removed from evenly spaced locations around the sample and the water content

of each was determined. These were averaged to obtain the i n i t i a l average

water content of the sample. Water content determinations of the end trimm­

ings were also made but not used because the laminated nature of the s o i l

rendered then unrepresentative. Due to the sensitive nature of the material,

extreme care was taken to keep handling of the sample to a minimum. The

whole sample was weighed prior to placing i t in the t r i a x i a l c e l l .

Figure 8: Sample i n p l a c e on t r i a x i a l base.

.The procedure adopted for placing the sample i n the c e l l was as

follows; A previously soaked porous stone was ca r e f u l l y s l i d into a convex

water meniscus covering the base pedestal, and the sample was car e f u l l y

placed on the stone. The top porous stone was then s l i d onto a convex water

meniscus covering the inverted loading cap and the whole upper assembly

(cap and stone) was righted and s l i d onto the top of the sample 0 A small:

quantity of water was permitted to flood both porous stones and the lower

membrane was then r o l l e d up around the sample. This membrane was coated

with s i l i c o n e grease and the second membrane r o l l e d down over the f i r s t .

Two 0=>rings were placed around both the top loading cap and base pedestal.

Figure 8 shows the sample, stones, loading cap, membranes, and 2 of the 4

0-rings i n place ? The v e r t i c a l alignment of the sample, stones, and load­

ing cap was checked o p t i c a l l y with an engineer's t r a n s i t . The chamber was

then placed on the t r i a x i a l base and the loading ram was brought into con­

tact with the loading cap and aligned with the sample and the base of the

proving ri n g . Again, the t r a n s i t aided i n t h i s alignment,

2 , 7 Application of chamber pressure, sample saturation and i n i t i a l consolidation

De-aired water was permitted to enter the t r i a x i a l chamber under 15

lbs,/sq.in, gauge pressure during which time no drainage was allowed to or

from the sample. The sample was checked for complete saturation by r a i s i n g

the chamber pressure to the desired value i n increments of 10 lbs,/sq,in.

The change i n pore pressure corresponding to each of these increments was

recorded and thus values of the pore pressure parameter B (Skempton, 1954)

were determined. The increments of pressure were applied at four minute

intervals and B values of l o 0 (indicating complete saturation) were obtained.

After the desired chamber pressure was applied, the sample was allowed to consolidate for exactly 24 hours at which time a l l excess pore pressures

had e f f e c t i v e l y d i s s i p a t e d (time f o r 90 percent c o n s o l i d a t i o n to occur,

tgg, never exceeded 200 minutes). During c o n s o l i d a t i o n , care was taken to

maintain v e r t i c a l alignment by ensuring the bottom of the l o a d i n g ram r e ­

mained i n contact w i t h the l o a d i n g cap as the sample decreased i n volume.

This was accomplished by r a i s i n g the l o a d i n g p l a t f o r m u n t i l a s m a l l d e f l e c ­

t i o n r e g i s t e r e d on the proving r i n g d i a l gauge i n d i c a t i n g that the ram was

bearing on the l o a d i n g cap,

2.8 Drained shear t e s t s

Upon completion of the 24 hour c o n s o l i d a t i o n p e r i o d , the sample was

sheared by a p p l i c a t i o n of a constant a x i a l s t r a i n r a t e of 0,014 i n s , per

hours (0,5 percent per hour). Shearing was continued u n t i l s h o r t l y a f t e r

the peak s t r e n g t h was reached which u s u a l l y occurred at about 30 percent

s t r a i n . Thus the shearing process, was continued f o r about 65 hours, A

photograph taken during a p r e l i m i n a r y shear t e s t i s shown i n Figure 9,

Elapsed time, volume change, a x i a l l o a d , a x i a l deformation and temperature

were recorded throughout the t e s t and a complete:set o f . t y p i c a l t e s t data

( f o r t e s t S-17) may be found i n the Appendix,

2.9 Undrained shear t e s t s

In the undrained shear t e s t s , pore pressures were measured w i t h a

Bishop and Henkel n u l l i n d i c a t o r . Minor m o d i f i c a t i o n s were made to the

t e s t i n g equipment a f t e r the drained t e s t s e r i e s was completed to ensure a

more s a t i s f a c t o r y supply of d e - a i r e d chamber water. The i n s t a l l a t i o n of an

a i r c o n d i t i o n e r permitted b e t t e r temperature c o n t r o l d u r i ng the undrained

t e s t s than was maintained during the drained t e s t s . Complete inform a t i o n

on the undrained t e s t r e s u l t s ( i n c l u d i n g t y p i c a l t e s t data) may be found i n

Byrne (1966),

Figure 9: Sample during shear.

21

2.10 Back-drainageo dismantling, and cleaning

Before removing the.sample from the chamber, the chamber pressure was

lowered to approximately 2 l b s o / s q . i n , , above the back pressure, and the

loading ram was raised off the loading capo Water was then permitted to

drain back into the sample from the drainage burette u n t i l any negative pore

pressures had dissipated (Henkel and Sowa, 1963) 0 The quantity of water

entering the sample was measured so that the change i n water content deter­

mined from i n i t i a l and f i n a l weights could be checked against volume chan­

ges measured i n the burette. After back-draining was complete, the chamber

was dismantled and the sample removed, weighed and measured0 The sample

was then dried to determine i t s f i n a l water content 0

After each te s t , a l l drainage l i n e s were again flushed with de-aired,

d i s t i l l e d water,, The loading cap and base pedestal were thoroughly washed

i n commercial detergent to remove a l l d i r t and grease thus reducing the

p o s s i b i l i t y of trapping a i r i n the equipment i n the following t e s t 0

CHAPTER 3

DISCUSSION OF TESTING PROCEDURES

3 d Introduction

As the experimental work proceeded, i t became obvious that there was

no such thing as a routine test, and much time was spent before satisfactory

test procedures were determined, A discussion of some of the test proce­

dures f i n a l l y adopted i s included in this chapter. Certain procedures which

were found undesirable are discussed, and further improvements are suggested,

3.2 Sampling, waxing and storing

Field sampling took place on a very warm day. The surface of the Haney

clay dried v i s i b l y during sampling and therefore exposed layers of clay were

removed just prior to waxing. Subsequent tests (Section 2,7).indicated that

the sampled clay was effectively 100 percent saturated and thus the above

precaution was believed adequate.

The blocks were covered with a 1/4 inch to 1/2 inch wax layer for stor­

age. As the samples were stored for a longer period of time than originally

anticipated (9 months instead of 3 months), i t is f e l t that a thicker layer

of wax would have been desirable. Periodically the blocks were checked for

signs of moisture loss or gain. The extent to which water had leaked into

the blocks was measured by the color change that the clay underwent during

this process. Two of the blocks were rewaxed when i t was discovered that a

small quantity of water had leaked into them0 Prior to rewaxing, the clay

which was contaminated was trimmed from the blocks and discarded,

3.3 Sample preparation

The sample was trimmed on a perspex lathe and miter box (Figure 7),

Although the resulting sample was adequate, small imperfections in the per­spex (such as warping) made i t very d i f f i c u l t to obtain a sample with

parallel ends exactly at right angles to i t s sides•<,. This resulted in

alignment d i f f i c u l t i e s when placing the sample in the t r i a x i a l c e l l , A

brass trimming lathe and miter box: would probably eliminate this problem.

Due to the highly variable nature of the clay in the vertical direc­

tion, every care was taken to ensure that each t r i a x i a l sample came from

the same vertical elevation. Because the laminations were not of regular

thickness and only approximately horizontal (insitu), i t was necessary to

trim the sample so that the laminations became horizontal when placed in

the t r i a x i a l c e l l . Thus i t was hoped to avoid the possibility of the sam­

ple undergoing irregular consolidation and therefore buckling prematurely

when sheared. In spite of these precautions, three preliminary samples did

buckle but i t i s not known whether buckling was due to the irregular nature

of the material or faulty alignment of the equipment. The horizontal varia­

tion of water content within the clay made i t necessary to attempt to con­

duct the f i n a l series of tests on samples taken from a single block. How­

ever, only five or six samples could be trimmed from each block and therefore

more than one block was used. Fortunately, no significant variation between

the blocks used was observed,

3,4 Water content and volume measurements

As mentioned i n Section 3,3, the water content of the clay varied both

vertically and horizontally. Variations i n water content of up to 8 percent

in 3 vertical inches and of up to 2 percent in 3 horizontal inches were

measured. It was feared that, because of this variation, the side trimmings

would not yield representative average water contents. Therefore four tests

were performed in which the average water content of four side trimmings

was compared with the water content of the whole sample. These specimens

were prepared in exactly.the same way as those used in the fi n a l test ser-

ies but were neither consolidated nor sheared. Although the individual side

trimmings showed up to 1,0 percent deviation from their average, the average

i t s e l f did not deviate more than 0,2 percent from the.measured water content

of the. whole sample (see Table III), It was therefore concluded that the

side sample method of obtaining the i n i t i a l water content of the specimen

was satisfactory. Trimmings taken from the top and bottom of the specimen

were not representative of the whole sample because they contained a pre-

dominance of one lamination.

The i n i t i a l volume of the specimen was determined by measuring i t s

length in four places and i t s circumference at the top, middle, and bottom.

These measurements invariably resulted i n the calculated i n i t i a l saturation

value exceeding 100 percent. Because tests on various samples of Haney clay

had indicated that the specific gravity of the s o i l was constant (»2,80)

although the clay was highly laminated (Section 2 03), and because the water

content of the sample was believed to be accurately known (see above para­

graph) , i t was assumed that the error in the calculated degree of saturation

stemmed from an error in measuring the volume. Therefore a new volume was

calculated assuming 100 percent saturation. Since circumference measurements

were the most d i f f i c u l t to make, i t was assumed that a measuring error occur­

red there, and thus the cross-sectional area of the sample was corrected to

conform to the calculated volume. The measured i n i t i a l length was assumed

correct, and the corrections to the area were always small (the calculated

volume never differed from the measured volume by more than 1 percent),

3,5 Test equipment

Compressed air from a house line was delivered to the equipment at

128 lbs,/sq, i n . I n i t i a l l y , the air was passed through one regulator to

supply the desired chamber pressure. However, regulation was poor and a

25

T A B L E I I I /

/ W A T E R C O N T E N T S O F S I D E T R I M M I N G S C O M P A R E D T O T H E

WATER C O N T E N T O F T H E WHOLE S A M P L E

W A T E R C O N T E N T (%)

T E S T T R I M M I N G S WHOLE

N O , S I D E S A V E R A G E S A M P L E

1 3 7 o 5 3 7 0 1 3 7 0 4 3 7 0 5 3 7 0 4 3 7 0 4

2 3 7 0 6 3 6 0 4 3 6 0 3 3 8 0 1 3 7 0 1 3 7 „ 2

3 3 7 o 9 3 7 o O 3 7 o 0 3 6 0 8 3 7 c 2 3 7 c 3

4 3 7 o 2 3 6 0 7 3 7 0 2 3 6 0 6 3 6 0 9 3 7 0 1

second regulator was Installed in series with the f i r s t 0 No further regula­

tion problems were encountered,, The back pressure of 10 lb8 0/sq,in, was

supplied by a column of mercury connected to a 1200 cubic inch capacity

balancing tank* The tank was required to prevent pressure fluctuation dur­

ing drainageo A l l measured pressures were corrected to a standard elevation

(the center of the sample). Chamber pressures and pore pressures were

measured by 0=100 lbs 0/sqoin 0 bourdon gauges which were calibrated against

a dead weight tester prior to use 0 It was observed that the bourdon tubes

crept irregularly under pressure and from time to time, further calibration

was necessary. It is suggested that el e c t r i c a l pressure transducers may

prove more reliable for these measurements.

The t r i a x i a l c e l l contained a machined stainless steel loading ram

which was lubricated at the start of each test. By measuring the force

required to move the ram at a constant rate against a chamber pressure, i t

was observed that the f r i c t i o n did not vary as different sections of the ram

came in contact with the collar. Prior to each shear test, the ram was run

for about an hour at the test deformation rate and against-the test chamber

pressure to determine the "zero" proving ring reading,

A double ring proving ring was used to measure axial loads and i t was

calibrated against a Baldwin-Hamilton Universal Testing Machine, The only

problem encountered with the proving ring occurred when the inner ring began

to deflect. The point at which this took place was not well defined and

had to be calculated for each test by plotting ring deflection against time.

The deflection at which an abrupt change in slope occurred represented the

reading at which the new calibration curve became applicable. The use of a

strain.gauge embedded in the loading ram appears to'be a promising alterna­

tive method of measuring axial loads. If the strain gauge is placed inside

27

the t r i a x i a l c e l l , the loads measured are true sample loads and are not

affected by ram f r i c t i o n at the c e l l head.

I n i t i a l l y , glycerin was used as a chamber f l u i d (Lame,1958)0 However,

leakage out of the sample was observed at a l l chamber pressures. It waB

subsequently discovered that previous investigators (Poulos, 196A) had re­

ported this problem and recommended that de-aired water be used as the cham­

ber fluido With de-aired water in the chamber, no further leakage though

the membranes or bindings was observed, Pressure was:applied to the chamber

water at an air-water interface located in a balancing tank at the end of a

four foot length of 3/8 in„ outside diameter polyethylene tubing leading

from the chamber0 This arrangement prevented dissolved air permeating the

water in the t r i a x i a l chamber (Poulos, 1964),

The drainage system included six valves 0 Originally three Klinger

AB10 non-displacement valves were installed but were found to leak e r r a t i ­

cally. They were replaced by three stainless steel Hoke non-displacement

valves which incorporate teflon seals, and no further problems were encount­

ered. The other three valves were brass Hoke stem valves which performed

very satisfactorily. An admittedly undesirable air-water interface was per­

mitted in the drainage burette. However, no evaporation losses were measur­

ed during a one week test period and although the meniscus was occasionally

misshapen, i t rarely presented any reading d i f f i c u l t i e s .

It has been mentioned that the use of f i l t e r paper side drains was

abandoned because they offered few advantages (Section 2,4). The reason

that they did not substantially increase the rate of drainage is believed to

stem from the extra-sensitive nature of the clay. It is thought that trimm­

ing disturbed (smeared) the structure of the clay at the edge of the sample,

thus creating an effectively impermeable barrier to drainage to the sides.

The sample was protected by two membranes with a layer of silicone

grease between them0 I n i t i a l l y only one membrane was used but i t was found

to be too permeableo Both the loading cap and- base pedestal were greased

around their circumferences to reduce leakage past the 0-rings, Two rubber

0-rings were placed around the loading cap and two were placed around the

base pedestalo The unstressed dimensions of the 0-rings were 1,46 ins 0 out­

side diameter by 0,125 ins 0 thick 0 The O-rings were moved into position on

1,6 ins, outside diameter brass ring stretchers, and in placing the 0-rings,

care was taken to avoid "s p i r a l l i n g " (Poulos, 1964), Leakage through the

membranes and past the bindings i s believed to be reduced to a tolerable

level in tests lasting up to 100 hours i f the above procedures are adopted,,

It i s suggested by Bishop and Henkel (1962) that a correction should be

applied to the measured principal stress difference to allow for membrane

restrainto Based on their assumptions that the sample deforms as a right

cylinder, with the sample and membrane acting as a unit, the correction was

found to be 0,5 lbs,/sq,in, at 30 percent axial strain. It was observed that

the membrane buckled during the drained tests and therefore-developed hoop

tension. Calculations (Henkel and Gilbert, 1952) indicated that the hoop

tension correction (to be applied to the radial stress) was about 0,3 lbs,/

sq,in. at 30 percent axial strain,, Because of the small magnitude of these

corrections, and because of the limited validity of the assumptions on which

the calculations were based, i t was decided to ignore the membrane correc­

tions.

Alignment of the sample, stones and loading cap was accomplished with

the aid of a transit. Alignment was maintained during the consolidation

phase by ensuring that the loading ram remained in contact with the loading

cap. If good alignment was not achieved, the samples buckled, particularly

29

since the loading cap was completely free to rotate and did not resist

buckling, A sample was considered to be buckled i f the loading cap rotated

through 2 degrees. Usually i t was observed that i f rotation exceeded 2

degrees (as i t did i n three preliminary tests), the system became unstable

and rotation continued un t i l the test was stopped. Although a fixed load­

ing head is recommended for undisturbed so i l s (Bishop and Henkel, 1962), i t

is believed that a free head i s superior because i t does not induce unmeas­

ured stresses in the sample when the tendency to buckle is present. It was

observed that i f care is taken when aligning the equipment, freely rotating

loading heads can be successfully used on highly laminated undisturbed s o i l s .

The air temperature in the laboratory was manually controlled to be­

tween 23°C and 26°C during the drained tests. The installation of an air

conditioner permitted air temperature control of 24°C + 0,2°C during the

undrained tests. The temperature of the sample did not vary to the same

extent as that of the air due to the insulating effect of the surrounding

chamber f l u i d . However, a l l ancillary equipment was not so insulated and

was thus subjected to similar temperature variations to the surrounding, a i r .

Although the strain controlled t r i a x i a l machine delivered a constant

rate of deformation to the t r i a x i a l c e l l , the deflection of the proving ring

imparted a rate of strain to the sample which gradually increased during a

test. Since this occurred in a l l tests, i t can be removed as a variable

when comparing results within this investigation.

The porous stones used in these experiments did not permit any lateral

movement of the ends of the sample. This was evidenced by the bulbous shape

of a l l failed samples. The end restraint, which creates a "dead zone" in

either end of the sample, is a possible source of error in the t r i a x i a l test

since i t introduces stresses which cannot be measured. At low strains,

30

these stresses may not be great, but at the large strains developed in this

series of tests, they may indeed have been significant, The stresses have

been computed on the basis of a corrected cross-sectional area calculated on

the assumption that the sample deformed as a right, cylinder. At 34 percent

axial strain, the cross-sectional area of the center of the sample was about

40 percent greater than that at the ends, and thus the physical significance

of the stresses calculated at high strains is questionable. However they are

s t i l l valid for comparison purposes.

CHAPTER 4

DISCUSSION OF TEST RESULTS

4 o l Introduction

Experimental data obtained during drained t r i a x i a l shear tests were

recorded as shown in the Appendix which contains data from test S-17, Ex­

perimental data obtained during undrained t r i a x i a l shear tests may be found

in Byrne (1966), Both drained and undrained test data were analyzed on the

University of British Columbia IBM 7 0 4 0 computer and a summary of some of

the results of this analysis may be found in Table IV, [The data presented

in Table IV has not been corrected for residual pore pressures developed

during drained tests nor have the stresses been corrected for an "energy

balance"]. These corrections w i l l be considered separately (Sections 4 , 3

and 4 , 4 ) ,

Wherever possible, two tests were performed at each confining pressure.

This procedure offered a check on the r e l i a b i l i t y of the test data and also

indicated the magnitude of the natural v a r i a b i l i t y of the clay. Less than

two percent variation in measured properties was obtained for specimens

taken from the same block samples as long as the precautions mentioned in

Section 3 , 3 were observed. However, as reported in Section 3 , 3 , specimens

taken from different block samples often exhibited larger variations than

that just quoted, particularly in. i n i t i a l water.content. Although the re­

sults reported herein were obtained from specimens taken from block samples

having very similar properties, i t should be emphasized that the natural

variability of the clay must be considered when comparing test results.

The results are discussed under the headings: residual pore pressures

developed during drained shear tests, energy corrections, stress-strain re­

lationships, and shear strength. The drained and undrained shear strength

32

TABLE IV

SUMMARY OF TEST RESULTS

Test No,

c l b s , / 8 f l o l n t

maxo

.u>% e%

max. w l e%

Undrained shear late, of Jih&aJL • 0^5% oc J: hour C—U—l 60,0 36,1 2,4 35,4 2,43 24,6 36,1 17,6 25,7 3,04 30,3

C-U-2 60,0 36,3 2,1 34,5 2,27 22,8 36,3 17,1 25,4 3,08 30,6

C-U-3 75,0 34,1 2,6 40,6 2,35 23,8 buckli id

C-U-4 88,5 33,5 4,1 45,9 2,50 25,4 33,5 18,6 38,3 3,06 30,5

C-U-5 75,0 33 0 y 3,6 39,4 2,46 24,9 33,7 15,0 33,0 3,06 30,5

C-U-7 88,5 33,1 4,0 47,2 2,54 25,8 33,1 14,8 41,7 3,07 30,5

AVGE, 3,1 2,42 24,5 16,6 3,06 30,5

s-12

S-13

S-14

S-15

S-16

S-17

AVGEt

40,0

55,0

70,0

70,0

'55,0

40o0

27,9

26,9

26,0

25,8

26,9

28,2

30,5

29,2

28,7

29,0

30,6

31,5

30,0

70,6

98,3

123,0

125,8

98,8

72,0

2,76

2,79

2,76

2,80

2,80

2,80

2,78

28,0

28,1

28,0

28,2

28,2

28,2

tat*, nf ahttflr - O.S2 par hmir

28,1

Drained shear Rate of shear » 2,5% S-10 40,0 j 26,6 I 31,9j70,6 |2,76 ^8,0 SSL hour

33

i s considered both from the maximum p r i n c i p a l stress difference f a i l u r e

c r i t e r i o n and the maximum ef f e c t i v e p r i n c i p a l stress r a t i o f a i l u r e c r i t e r i o n .

Before discussing these topics, a few comments on s e n s i t i v i t y and

structures are presented,

4,2 S e n s i t i v i t y and Structure

The s e n s i t i v i t y of clays has been defined i n numerous ways (Lambe,

1958), The most common d e f i n i t i o n which was o r i g i n a l l y proposed by Terzaghi

(1944), and which has been adopted i n t h i s thesis i s 2

S e n s i t i v i t y • S • undisturbed peak strength , o o o o , o o o , , ( l ) remolded peak strength

Skempton and Northey (1952) and Rosenqvist (1952) indicated that s e n s i t i v i t y

i s primarily a result of leaching (reduction of the s a l t concentration i n

the pore f l u i d ) , although thixotropy i s believed to be responsible for some

low to medium s e n s i t i v i t y , Haney clay, which has a s e n s i t i v i t y of 12, i s

classed as an extra-sensitive clay (Skempton and Northey, 1952),

Investigations into the microcharacteristics of clays have shown that

the structure which a clay develops during deposition i s : largely dependent

on the concentration of e l e c t r o l y t e i n the pore f l u i d (Lame, 1958a), I f

the pore f l u i d i s s a l i n e , a cardhouse (flocculated or edge-to-face) struc­

ture i s l i k e l y to develop which becomes unstable under applied shear stress­

es i f the s a l i n i t y of the pore f l u i d decreases. This change i n structure

leaves the s o i l with reduced strength thus giving r i s e to the phenomenon of

s e n s i t i v i t y .

The exact manner i n which the chemical properties of the clay minerals

and the surrounding pore f l u i d affect the structure of the clay i s not

known, and although some st r u c t u r a l phenomena are understood, l i t t l e quan­

t i t a t i v e knowledge of the influence that structure has on the s t r e s s - s t r a i n

behavior of a clay i s available 0 It i s known, however9 that the remolding

of the clay structure which occurs during shear, tends to create a more

parallel (dispersed) arrangement of the platey-like clay particles, This

rearrangement of the structure, along with any changes in void ratio which

may occur, affects the magnitude of the forces existing between the individ­

ual particles which in turn i s reflected in the stress-strain behavior of

the clay, Scott (1962) has suggested that a clay with an i n i t i a l l y floccu­

lated structure, regardless of whether subjected to drained or undrained

shear, exhibits ah unstable stress-strain curve with a more or less marked

peak. The peak represents the maximum shearing stress required to break

the interparticle contacts and to slide particles over each other, When

the contacts have been disrupted, failure continues at a lower level of

shearing stress compatible.with the: more dispersed structure now present.

On the other hand, a clay with an. i n i t i a l l y dispersed structure exhibits

a resistance to shear which gradually increases with deformation u n t i l a

constant shearing resistance i s reached. This type of curve i s stable and

is usually not as s t i f f as.the stress-strain curve exhibited by a floccu­

lated clay. Detailed discussions of the; physico-chemical properties of

clays and of the role of structure in stress-strain behavior may be found

in Grim (1953), Lambe (1958a, 1958b), Seed, Mitchell and Chan (I960),

Leonards (1962), and Scott (1962),

4y.3 Residual pore pressure developed during drained shear tests

The principle of effective stress developed by Terzaghi (1923) states

that the strength and deformation characteristics of any s o i l are a function

of the effective stresses acting in that so i l , , The effective stress (o'),

acting on a plane, i s defined as the total stress (o) acting on the plane

minus the pore pressure (u) 0

35

That i s ;

(2)

Thus, in a laboratory test, i f any meanful relationship i s to be proposed

between strength and applied stress, or deformation and applied stress, the

magnitude of the pore pressure developed during the test must be known0

Using the method suggested by Bishop and Henkel (1962), i t is possible

to compute a deformation rate for drained tests such that the pore pressures

developed during shearing are effectively (theoretically 95 percent) d i s s i ­

pated prior to any desired axial strain,, If the strength of the s o i l being

tested i s the only information required, then the governing deformation

usually chosen i s the failure strain. If a complete stress path is wanted,

as was the case in this investigation (see Byrne, 1966), the strain at which

most of the pore pressure must be dissipated i s determined by the f i r s t

significant reading that i s required. Even at very slow rates of strain,

measurable pore pressures are believed to exist in the early stages of a

drained test and, although this fact i s widely recognized, few researchers

have attempted to estimate the magnitude of the developed pore pressures

and the affect that they may have on the subsequent behavior of the s o i l 0

By assuming that the load i s applied in discrete increments during a

strain controlled test, i t i s possible to estimate the pore pressures pre­

sent at any time using the one-dimensional consolidation theory developed

by Terzaghi (1925), In this theory, the relationship between excess pore

pressure and time i s given by the equations

2 c 6 u 6u

6t o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o (3)

where c m coefficient of consolidation • v

k » permeability

e * void ratio

a v " coefficient of compressibility

Y u • unit of weight of water

g • distance from the surface of the clay layer

u «• pore pressure at time t

Solution of Equation (3) for the case of drainage from both ends of a

t r i a x i a l sample yields the approximate non-dimensionalized expressions;

» tr 2

m ^ U p (U ^ 60/£) ooooooooooooooooooooaoooooo (4)

T y » -0o9332 l o g 1 Q (1-U) -0o08519 (U » 60%) , H . . , „ . „ . . ( 5 )

where T - time factor v

d • one-half the length of the sample

U « average degree of consolidation ™ 1 - ~

u^ » i n i t i a l excess pore pressure

Thus the theory requires knowledge of the i n i t i a l excess pore pressure and

the coefficient of consolidation applicable to each1 load incrementu

Skempton (1954) has derived the following relationship between applied

stress and pore pressure i n the t r i a x i a l tests

Au » B (A03 +._A_ (Acj - AC3)) 0 0 0 0 0 0 0 0 0 0 0 0 0 ( 6 )

where Au » change in pore pressure

A03»change in the total minor principal stress

ha 1 •* change in the total major principal stress

B «••pore pressure coefficient reflecting the degree of saturation present in the sample

A » pore pressure coefficient reflecting the dilatancy of the sample

37

In the present investigation, the clay was saturated and therefore B - 100

(see Appendix)o Also the chamber pressure (03) was held constant and thus

Equation (6) simplifies to 3

All n A AO j 0 6 6 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 ( 7 )

It has been assumed that the value of A during drained tests, although not

necessarily constant, i s not less than 1/3 nor greater than 1, It should

perhaps be noted that in a sensitive material, the upper limit A-l i s open

to question since A i s known to exceed 1 i n undrained tests 0

It i s a relatively simple task to determine the value of c v during con­

solidation (prior to shearing), and also after failure either during unload­

ing or further consolidation of the sample, but none of these determinations

yield a value of c^ that i s directly applicable during the actual shearing

process. Figure 10 contains values of c^ (calculated b y the square root of

time f i t t i n g method developed by Taylor (1948)) plotted against mean effective

stress (p 5 • "" *j 11 ) for the oedometer, and for t r i a x i a l consolidation before

shearing and t r i a x i a l unloading after shearing. One value of c^ determined

from t r i a x i a l consolidation of a sample which had been subjected to undrained

shear, i s also shown. Guided by these values, upper and lower bounds for c^

were chosen and are indicated by the boundaries of the cross-hatched area on

Figure 10, For simplification of the computations i t was assumed that, over

the stress range of the tests (40 lbs,/sq, in, < mean effective stress, p°,

< 115 I b S o/sq, in), c v varied linearly with the logarithm of mean effective

stress. The upper bound was chosen to coincide both with the value of c^

obtained from t r i a x i a l consolidation at p 1 » 40 lbs,/sq, in, and with the value

of c y obtained from oedometer tests at p 5 • 115 lbs,/sq, i n . The lower bound

was drawn parallel to the upper bound such that, over the stress range investi­

gated, the lower bound was never less than the smallest value of c^ determined

from t r i a x i a l unloading after drained shear.

ALL VALUES PLOTTED AT MEAN OF LOAD INCREMENT

C v OBTAINED DURING FURTHER CONSOLIDATION AFTER UNDRAINED SHEAR

PROBABLE RANGE

OF C v DURING SHEAR

TRIAXIAL UNLOADING AFTER DRAINED SHEAR

10 20 30 40 50 60 70 80 90 100

MEAN EFFECTIVE STRESS (LBS. / SQ. IN.)

FIGURE 10. RELATIONSHIP BETWEEN COEFFICIENT OF CONSOLIDATION AND MEAN EFFECTIVE STRESS

39

From Figure 10, the upper bound of iss

2 c y m f l X - ( 0 „ 0 2 0 0 - O o 0 0 7 5 log 1 0p°> ins, / m i n 0 o 0 o , o 0 o o o 0 o o o o o o o o 0 ( 8 )

and the lower bound iss

2 C v min, " ^ O o 0 1 6 7 " 0 » Q 0 7 5 l o8io p 9^ i n S o / f f l i f t ' » « » « » » « » » « » « » » o o . c ( 9 )

With an estimate of the upper and lower bounds of A and c^ obtained

above, the pore pressures present at any time during a drained test can be

estimatedo Figure 11 shows the values of pore pressures calculated from a

typical drained test (test S - 1 7 ) , for various combinations of the bounding

values of A and c^o It can be seen that the lower bound pore pressures

(calculated using the upper bound value of r and A • 1 / 3 ) represent less

than 10 percent of the effective confining pressure, but that the upper bound

pore pressures (calculated using the lower bound value of and A « 1 ) are

in excess of 30 percent of the effective confining pressure. In the latter

case, although these pore pressures are mainly dissipated within 5 percent

axial strain, they do not completely dissipate u n t i l failure occurs at 30

percent axial strain. Figure 12 i s a graph of effective principal stress

ratio versus axial strain for test S - 1 7 and shows what effect the above pore

pressures have on the effective principal stress ratio. For the lower bound

pore pressures, the increase in effective principal stress ratio over that

obtained assuming no pore pressures, is only slight, and is not noticeable

beyond 3 percent axial strain. In the case of the upper bound pore pressures,

not* only is the effective principal stress ratio increased at a l l strains

except close to failure, but also the shape of the effective principal

stress ratio - axial strain curve i s substantially changed, exhibiting

a small peak at 1 , 5 percent axial strain. Thus the development of pore

14

AXIAL STRAIN (%)

FIGURE II. RELATIONSHIP BETWEEN COMPUTED PORE PRESSURE AND AXIAL STRAIN IN A DRAINED TEST.

41

FIGURE 12. SHOWING THE EFFECT OF COMPUTED PORE PRESSURE ON THE EFFECTIVE PRINCIPAL STRESS RATIO IN A DRAINED TEST.

42

pressures can lead to quite different values of effective principal stress

ratio than those obtained assuming no pore pressures„ What effect these

adjustments have on s o i l behavior i s not known, but there is no reason to

assume that the subsequent deformation characteristics of the s o i l do not

reflect any changes in effective principal stress ratio that may occur 0

No further use of these computed pore pressures has been made in this

thesis because of the uncertain nature of the assumptions upon which the

calculations are based 0 However, i t i s believed that before f u l l y meaning­

fu l comparisons of "drained" and "undrained" tests can be attempted, some

allowance for residual pore pressures developed in drained tests must be

made <,

4 o 4 Energy corrections

Before discussing the application of energy corrections to the present

data, a brief review of some of the publications dealing with this topic i s

presentedo Following this, energy corrections proposed by Bishop ( 1 9 5 4 ) ,

Rowe ( 1 9 6 2 ) , and Roscoe, Schofield, and Thurairajah ( 1 9 6 3 ) w i l l be applied

to the data obtained i n this investigation,,

Taylor ( 1 9 4 8 ) proposed that the observed discrepancy between the stress-

strain curves of loose and dense sand could be explained by considering the

work required to change the volume of the sand during shear, and he develop­

ed an expression to account for this boundary energy in the direct shear

test. Bishop and Eldin ( 1 9 5 3 ) developed a boundary energy correction to be

applied to the measured principal stress difference in drained t r i a x i a l

tests on sands„ Bishop ( 1 9 5 4 ) presented a theoretical development of this

energy correction (here-after referred to as the Bishop correction) in which

i t was shown that the correction was valid only at failure (when the major

effective principal where e\ m

4 3

axial strain), Hvorslev (1953) suggested that for clays, a significant

quantity of energy may be stored or released during drained and undrained

shear tests as a result,of induced shearing strains. Thus any attempt to

establish an energy equation for clays must recognize this internal energy.

It might be noted that during the shear of sands,, i t i s believed that very

l i t t l e energy i s released or stored internally and thus a correct energy

balance can be obtained by considering the external energy only,

Roscoe, Schofield and Wroth (1958) published experimental evidence

indicating that, for remolded- clays, good agreement between drained and un­

drained t r i a x i a l tests, could be obtained i f Bishop's energy correction was

applied to the principal stress difference (a{9 - 03") measured at a l l

stages in a drained t r i a x i a l test,- Poorooshasb and Roscoe (1961) indicated

that boundary energy corrections do not account for changes in internally

stored energy and subsequent development of this concept for an idealized

isotropic "wet" clay led to.an energy equation which included terms account­

ing for both boundary energy and internally stored energy (Roscoe, Schofield,

and Thurairajah, 1963), This equation was believed valid for a l l points

along stress paths in both drained and undrained t r i a x i a l tests,

Roscoe, Schofield and Thurairajah (1963), working with an idealized

isotropic "wet" clay, presented an energy equation which included terms

accounting for both boundary energy and internally stored energy, which was

valid for a l l points along a stress path, and which was to be applied to

both drained and undrained test data,

Rowe (1962), working with granular media, established an energy

correction to be applied to the.effective confining pressure at a l l stages

in the t r i a x i a l test and- showed that his correction was similar to the

Bishop correction (Rowe, Barden and-Lee, 1964), Rowe, Oates and Skermer

(1963), i n a paper dealing with overconsolidated clays, proposed that the

correction derived for granular media could be applied to clays i f volume

changes due to changes in mean effective stress were not included in any

computations involving volumetric strain, Rowe, Barden and Lee (1964)

offered a review of the energy corrections presented up to that data and

concluded that, on theoretical grounds, the Bishop energy balance (Bishop,

1954) i s correct, but the Roscoe energy balance (Roscoe, Schofield and

Thurairajah, 1963) does not correctly represent the behavior of dilating

materialso

The theoretical development of each of the above energy balances re­

quires the assumption of idealized materials and hence the resulting equa­

tions may be expected to only approximately reflect the behavior of real

s o i l s . There i s however, limited experimental evidence to support a l l of

the corrections proposed (Roscoe, Schofield, and Wroth, 1958, Roscoe,

Schofield, and Thurairajah, 1963, Rowe, Gates and Skermer, 1963, and other).

In the hope of shedding more light on the range of valid i t y of any or a l l

of these corrections, some of the test data obtained in the present research

program has been analysed using three of the proposed energy balances.

Bishop energy correction

The energy correction proposed by Bishop (1954) is given by:

<«l' " ° 3 ° ) C O J r r e c t e d " ( O l ' - ° y > O D 8 e r v e d - °3* ^ 0 0 0 , 0 , . o . o o o . ,,(10)

Coi0 - 0 3 ' ) » principal stress difference (deviator stress)

v • increase in volume per unit volume (volumetric strain) • - ( e j + £2 + £3)

°l'f> °V B major and minor effective principal stress respectively

e l o c 2 » , e 3 " principal strains (compression positive)

As has been mentioned previously, this correction, to be applied to drained

tests, i s valid only at failure (Bishop, 1964), In the above form, the

correction cannot be used directly to determine a corrected effective angle

of shearing resistance, 0 However, Bishop (1964) has shown that, by re­

solving the stress system into an ambient stress, 03", and a principal stress

difference, (oj° - 03°), an expression for <J>' corrected can be obtained into

which Equation (10) may be substituted:

Si„ «, for - <*V) „ frl.',„r, ?\) corrected , Y corrected ( o V +03") (ci - 03") corrected + 2o 3

9 0 0 o o o ( l l )

Application of Equations (10) and (11) to the failure condition in the

drained tests yielded an average corrected 4>9 of 29,1°, which is in only

f a i r agreement with the average <j>* of 30 05° measured at the maximum effec­

tive principal stress ratio, (Circs') max0 in the undrained tests e The

strains at which the maximum effective principal stress ratio occurred in

the drained and undrained tests were widely different 0 In the drained test

( o i ^ J 3 9 ) max, occurred at about 30 percent axial strain whereas in the un­

drained test ( a - a 35 ) max„ occurred at about 17 percent axial strain. Be­

cause the two $"s are based on stress calculations which assume that the

sample deforms as a right cylinder choughout the test whereas in fact the

sample bulges, perhaps the above lack of agreement can be expected. The

Bishop correction i s valid at failure only, and therefore no attempt has

been made to investigate the application of the correction to other points

along the stress path,

Rowe energy correction

Rowe (1962) proposed that, in a drained test

0

0*3 , 8 3 C7 3 ° - ,(1.4* ) 0 0 o 0 fl 0 0 0 o 0 0 o 0 0 o 0 o 0 o 0 0 c o 0 fl 0 o 0 (12) ^ corrected 3 observed VEJ

dV where -~r • rate of volumetric strain

ci * axial strain rate

at a l l stages in the test and that, for clays,

o , 8 2 * f 2 C £ * f . r . l i . i n , . . . i m fan (L*> 4- — ± ^ 4- r i,, 1 fan f £ S 4- «£•

r *

' 3 - ' V G i *3* (1 + S t )

^ • tan (45 + ~ ) 4- "^T~ t a n (45 + ) 0 o 0 o o o o , o o o (13)

where < • interparticle shearing parameter

C£ • interparticle cohesion parameter

Working with clays Rowe, Oates and Skermer (1963), found i t necessary to

modify the dllatancy term to account for the elastic component of volume

change which they assumed was due to changes in mean effective stress.

However, no method of determining the elastic component of volume change

was presented. Experimental evidence showed good agreement with the theory

when the clays were reloaded as long as the axial strain did not exceed 0,5

percent, but only f a i r agreement was abserved during the i n i t i a l loading

cycle. The authors concluded that the interparticle cohesion term, c f B was

zero for normally consolidated clays.

In the present test series, the elastic volume change was determined

from the elastic rebound curve of Haney clay (Figure 13) and was computed

as follows: AeeW C\A\ . -,e S " o o o o o o o o o o o o o , o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o \ L ^ ) AV • — » — — G Y s to

where AV • elastic volume change

Ae e » change in void ratio attributed to elastic volume change • «K°log^Q(p'/pn°)

Wg " weight of solids

G ** specific gravity of s o i l grains 8

FIGURE 13. RELATIONSHIP BETWEEN WATER CONTENT AND MEAN EFFECTIVE STRESS FOR TRIAXIAL CONSOLIDATION AND UNLOADING (BACK-DRAINAGE)

4 8

K' • coefficient of expansion* slope of the void ratio versus logarithm of mean effective stress during isotropic unloading • 0,11 for Haney clay

p ° • i n i t i a l mean effective stress

Thus the rate of volumetric strain used in Equation (12) to compute a

correction to 03' becomes:

The Rowe energy correction, modified for the assumed elastic volume

change was determined for test S-17 and the results are shown graphically

in Figure 14, It can be seen that the data indicates a value of c f » 23,3

lbs,/sq, i n , , and <f>£ • 12 02° for an effective confining pressure of 40 lbs,/

sq, i n . No attempt to reload the samples was made. At failure, application

of the Rowe energy correction to the drained data yielded an average correct­

ed <}>' » 31,5° which, like the Bishop correction, is in only f a i r agreement

with the of 30,5° measured at the maximum effective principal stress

ratio ( o V / o V ) max, in the undrained tests,

Roscoe, Schofield and Thurairajah energy correction

The energy equation proposed by Roscoe, Schofield and Thurairajah

(1963) i s based on the following assumptions:

o

1, The energy recoverable from a unit bulk volume of clay at voids ratio, e, under mean effective stress, p°, i s :

U SB Kp* O O O 0 0 O O O O 0 O O O O 0 O 0 0 0 0 0 O O O O O 0 0 O O O O O O 0 O 0 0 (15)

e 1+e

the increase in recoverable energy when the mean effective stress increases by 6p° i s :

5U O O 0 0 0 0 O O 0 0 0 O 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 O O O 0 0 O 0 O (16)

e 1+e

FIGURE 14. APPLICATION OF THE ROWE ENERGY CORRECTION TO TEST S - 17

2o The rate at which energy is dissipated during shear distortion of unit volume of s o i l when under mean effective stress, p°, iss

^ m Mp o o o o o o o o o b o o o o o o o o o o o o o o o o o o o o o o o ( 1 7 )

where K » a constant " s l o p e of the void ratio versus natural logarithm of mean effective stress » 0,048 for Haney clay

U"e = recoverable energy

W «• dissipated energy

de » 2 / 3 ( 6 e1 - 663) » distortion increment

M • a constant

Thus the energy equation may be written:

^v dp 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 CIS) Mw v n * 6e 1+e 6e

In equation ( 1 8 ) , the corrected principal stress difference, q w, is assumed

equal to a constant, M, times ste mean effective stress, and is seen to

consist of three termst the observed principal stress difference, q, the dv

boundary energy correction, p' ~ , and the elastic energy correction, K 60'

1+e" ° T h e c o r r e c t * o n * 8 applicable to both drained and undrained normal­

ly consolidated t r i a x i a l tests at a l l points along their stress paths 0

Applying the correction to the data of this investigation yields

the results shown in Figure 150 It may be seen that, except for the i n i t i a l

stages of the tests, the corrected data does approximate a straight line,

the slope of which is M «• l 0 2 7 o Using this value of M, a determination of

the corrected can be made as follows:

On the line q w • Mp °, 3

• . ' CORRECTED DATA

•O—o—o— UNCORRECTED DRAINED DATA

X * X UNCORRECTED UNDRAINED DATA

0 20 40 60 80 100 120 140 p' ( LBS./ SQ. IN.)

F I G U R E 15. A P P L I C A T I O N O F T H E R O S C O E , S C H O F I E L D A N D T H U R A I R A J A H E N E R G Y C O R R E C T I O N T O D R A I N E D A N D U N D R A I N E D T E S T D A T A .

Therefore a 1 / 0 3 ' - 1 - -(a^/a^) +

Therefore 0 2 / 0 3 ' - ~ ~ » | ™ » 3„20

This value of the effective principal stress ratio yields a corrected <J>°

of 3106° which i s in good agreement with the corrected <{>' of 31,5° deter­

mined from the Rowe energy correction 0

There is considerable scatter in the-plotted result of data corrected

by the Roscoe et a l 0 and Rowe energy corrections (Figures 14 and 15), par­

ticularly at low axial strains. Some of the low strain scatter may be

attributed to the measured axial strain which i n i t i a l l y may include seat­

ing of the porous stones, sample, loading cap and ram. Pore pressures

developed during the early stages of a drained test w i l l modify the value

of the mean effective stress and no allowance for this has been made. The

end restraint offered by the porous stones-prevents volume change occurring

uniformly throughout the sample and thus calculated volumetric strains

based on the total volume of the sample w i l l be too small (Rowe, 1963)„

The coarseness of the volume change readings (estimated to 0o01 cu, cms0),

taken at very small time intervals, w i l l also be reflected in any rate of

volume change that i s computed, It may be noted that the assumption that

the elastic energy component i s a function of p" only i s open to question,

particularly in sensitive clays where large structural changes are believed

to occur under deviatoric stresses.

It i s concluded that the Roscoe, Schofield and Thurairajah energy

correction does permit correlation of drained and undrained behavior

throughout the shearing process although considerable experimental scatter

i s observed in the early stages of the tests 0 The Bishop and Rowe energy

corrections bring the drained and undrained test data into only f a i r agree-

53

merit at failure (defined as the maximum effective principal stress r a t i o ) 0

Only limited use of the above energy corrections has been made in

subsequent sections of this thesis because none of them can be conclusively

shown to be applicable to Haney clay 0 Until further information as to the

role of energy corrections in t r i a x i a l tests i s available, i t i s f e l t that

no benefit can be derived from the application of energy corrections to the

stress-strain curves,, In an attempt to compare the drained and undrained

strengths j, however, a l l three energy corrections have been considered be­

cause i f indeed the strength developed in t r i a x i a l tests i s independent of

test type, then a correct energy balance should indicate t h i s 0

4 o 5 Stress-strain relationships

Drained shear tests

The relationships between principal stress difference and axial strain,

and between effective principal stress:ratio and axial strain are shown in

Figures 16g 1 7 , and 18„ The results of a l l drained tests have been includ­

ed in these diagrams0 The maximum principal stress difference and maximum

effective principal stress ratio, occur together at approximately 30 percent

axial strains Similar, high strains to failure in drained shear tests on

sensitive clays have been reported by Crawford ( 1 9 6 1 ) „

A feature of the drained stress-strain curves i s the abrupt change in

slope that occurs at about 2 percent axial strain in those samples consoli­

dated to an a l l round effective stress of 4 0 lbs<,/sq„ i n 0 This change in

slope may also be seen in samples consolidated to higher effective stresses

but i t is not so marked in these cases 0 The overall appearance of the

stress-strain curves may be crudely likened to that of steel which exhibits

zones of elastic, plastic, and strain-hardening deformations 0 However the

"plastic deformation" zone i s only v i s i b l e at an effective confining pres-

1 54

FIGURE 16. STRESS-STRAIN CURVES FOR T E S T S-17

AXIAL STRAIN (%)

FIGURE 17. STRESS-STRAIN CURVES FOR TEST S-16

56

FIGURE 18. STRESS-STRAIN CURVE FOR TEST S-15

sure of 40 lbso/sq 0 i n 0 Similar drained stress-strain curves for sensitive

clays have been reported by Crawford (1959)„

At f i r s t i t was believed that the change in slope was not a character-

i s t i c of the clay 9 but a fault, of the testing equipment,. To investigate

this, a sample of hard.rubber was prepared whose low stress-strain proper­

ties were approximately similar to those of the clay 0 The rubber sample

was placed in a Baldwin-Hamilton Universal Testing Machine and i t s load-

deformation curve obtained 0 The same sample was then placed in the t r i a x i a l

apparatus and subjected to a chamber pressure of 50 lbs 0/sq 0 in„ The sam­

ple was strained at the same rate as that applied to the clay (0 o5 percent

per hour) and the resulting load-deformation curve was recorded,, Figure 19

shows the load-deformation curve of the rubber sample compared to that of

a drained test on Haney clay at a chamber pressure of 50 lbs„/sqc i n 0 No

change in slope of the rubber load-deformation curve occurred and i t was

therefore concluded that the testing: equipment was not at f a u l t 0

Because the rate of testing was-slow (0„5 percent per hour) B i t was

thought that the deformation behavior-of the clay may have been influenced

by creep and that the sharp change in slope of the stress-strain curve cor­

responded to an upper yield stress at which the creep rate increased

(Murayama and Shibata 0 1961)0 However, testing at a rate of strain of 2,5

percent per hour (5 times the previous rate) did not substantially modify

the curve (see Figure 20) and thus creep does not appear to be directly

responsible for the observed behavior„

As has been pointed out, the change in slope.is only marked at the

low effective confining pressure (40 lbs 0/sq o i n 0 ) 0 This is very close to

the maximum past pressure (38 lbs 0/sq 0 in,) determined from oedometer tests„

Thus there exists the possibility that the sharp change in slope

70

0.00 0.02 0.04 0.06 0.08 0.10 0.12

DEFLECTION (INCHES)

FIGURE 19. LOAD-DEFORMATION CURVES FOR RUBBER AND HANEY CLAY.

59

af the stress-strain curve Is a reflection of the past history of the clay.

Another possible explanation for the break in slope is associated with the

pore pressures developed during the i n i t i a l stages of the tests (Section

4,3), These pore pressures cause temporary increases in the effective prin­

cipal stress ratio and thus may influence the deformation characteristics

of the clay* If this were the case, samples which developed higher pore

pressures (those tested at higher confining pressures and at higher rates

of strain) would be expected to develop more pronounced changes in stress-

strain slope but this did not occur. It is possible that the change in

slope i s a result of structural changes occurring within the sample and i s

thus related to the sensitivity of the clay 0 During consolidation, some of

the sensitivity may be destroyed and hence at higher consolidation stresses

the change in slope would not be as noticeable. This can be seen in Figures

17 and 18,

Investigations into the creep of clays (Murayama and Shibata, 1961)

have shown that significant rates of strain occur under small constant

principal stress differences. It is reasonable to assume, therefore, that

although creep was not responsible for the change in slope referred to

above, the overall deformation.characteristics of the s o i l were affected by

the creep strain occurring during the 60 hours of testing. However, test

S-10 (Figure 20), tested at an applied axial strain rate of 2,5 percent per

hour, did not f a l l at a lower axial strain thus indicating the influence of

creep was small.

Some clays are known to exhibit increases in strength attributed to

thixotropy. Because a sensitive clay undergoes substantial remolding dur-

ing shearing, i t i s believed that some thixotroplc strength increase is

l i k e l y to occur. No attempt was made to determine the fchixotropic proper-

ties or creep behavior of Haney clay,

Undrained shear tests

The most notable feature of the drained shear tests i f the different

strains at which the maximum principal stress difference and maximum effec­

tive principal stress ratio occur 0 Figures- 21, 22, and 23 show the rela­

tionship between principal stress.difference and axial strain and between

effective princiapl stress ratio and axial strain during undrained tests.

It may be seen that the maximum principal stress difference occurs at

approximately 3 percent axial strain, whereas the maximum.effective p r i n c i ­

pal stress ratio occurs at approximately 17 percent axial strain, neither

of which compare with the drained failure strain of 30 percent 0 Kenney

(1959) presented experimental evidence indicating that the degree of mobil­

ization of <f>s at (ox" ~ a 3°) maxois related to the sensitivity of the s o i l 0

This relationship i s shown in Figure 24 where the degree of mobilization of

4>° i s expressed as *^g^""^f""^^*,"~ "'^ ^ m a*° Haney clay, with a sensitivity tan 24 5°

of 12 has a degree of mobilization of $8 » 1 •',0 -o. • 0,77, and this value is seen to l i e f a i r l y close to the line proposed by Kenney,

It should be noted that i f creep and thixotropic effects are present

during drained shear tests, they are also l i k e l y to influence the undrained

deformation characteristics of the clay. As mentioned earlier, no study of

these phenomena was undertaken.

4.6 Shear strength

As implied earlier in this report, the shear strength of a s o i l i s

usually defined by the failure c r i t e r i a of maximum principal stress d i f f e r ­

ence, ( a j 8 = C3')max,, or maximum effective principal stress ratio,

(°l ' / ° 3 8 ) i n a x < ' Occasionally, the shear strength is quoted as the strength

developed at some particular strain. A l l three c r i t e r i a will be discussed

0 6-10 15 2 0 25

0.0 3 0

AXIAL STRAIN (%)

FIGURE 21. STRESS-STRAIN CURVES FOR TEST C-U-l

6 4

0 *- 0.0 10 15 20 25 30

AXIAL STRAIN (%)

FIGURE 23. STRESS-STRAIN CURVES FOR TEST C-U-7

FIGURE 24. RELATIONSHIP BETWEEN NATURAL SENSITIVITY AND DEGREE OF MOBILIZATION OF d j ' AT (<"•,'- 0-3 ) m f l X . (After T.C. KENNEY, 1959)

in the following paragraphs, with particular attention being directed to­

ward a comparison of drained and undrained strength.

The results are shown in the form of plots of 1/2(ai' - 0 3 ' ) versus

1/2(oj' + o 39) at failure. Thus i f a is the angle of slope of the best

Btraight line drawn through such points, i t can be shown that sin <t>" •

tan a where <J>" is the effective angle of shearing resistance. The un­

corrected drained and undrained envelopes for the-(oj' - o^^max, failure

criterion are shown in Figure 25, and for the (o\0/c3')maxo failure c r i t e r ­

ion i n Figure 26, Figure 27 shows the uncorrected undrained envelope,

(oi ' / o3')max,, and the drained envelope, (ay'/o3')max0 corrected for volume

change using the energy corrections presented in Section 4,4,

As reported in Section 4,4 only f a i r agreement is obtained between

drained and undrained strength at (01'/o^'lmax, i f the Bishop or Rowe

energy corrections are applied to the drained data. This may be seen in

Figure 27 in which the undrained <f> " i s 30,5° and the corrected drained 4>'s

are 29,1° (Bishop) and 31,5° (Rowe), The <J>" obtained using the Roscoe,

Schofield and Thurairajah energy correction is seen to l i e slightly above

these, having a value of 31,6°,

Henkel (1960), working with remolded clays, reported good agreement

between uncorrected drained and undrained strengths at (cy' - 0 3°)max. but

pointed out that the same correlation would not be expected in undisturbed

sensitive clays due to the important effect of structure. Reference to

Figure 25 shows that the undrained <J>° •» 24,5° and that the uncorrected

drained » 28,1° thus no agreement does exist for Haney clay at ( c i ' - 0 3 ' )

max,

Roscoe, Schofield and Wroth (1958) proposed a c r i t i c a l void ratio (CVR)

for remolded clays which represented an ultimate state for the clay 0 In

this state, continuous yield would occur at constant void r a t i o 0 The CVR

(LBS. / SQ. IN.)

FIGURE 27. CORRECTED MAXIMUM EFFECTIVE PRINCIPAL STRESS RATIO FAILURE ENVELOPES.

line was believed to be independent. of stress path. Figure 28 shows that

during a drained test, the volume decreases continuously and Figure 29 shows

that during an undrained. test the-pore pressure increases continuously, even

after f a i l u r e 0 Thus a c r i t i c a l state for Haney clay was not reached during

this test series. However, the flattening slopes of Figures 28 and 29 i n ­

dicate that a c r i t i c a l state may exist at strains greater than those applied

in this investigationo

It has been widely reported (Taylor, 1948, Roscoe, Schofield and

Wroth, 1958, Henkel, 1960, Hvorslev, 1960) that, for remolded and some

insensitive undisturbed saturated, normally consolidated clays, there is

a relationship between the strength.and the water content of a specimen

(at the maximum principal.stress difference) that i s independent of stress

path. This relationship i s shown in Figure 30, Figure 31 i s a plot of

water content versus various stresses for the cases of isotropic consolida­

tion, drained failure and undrained failure; again both failure c r i t e r i a

are included. It may be seen that the normal consolidation curve for the

drained (Hirst) and undrained (Byrne) test series, although approximately

parallel, do not coincide Although this attests to the variable nature of

Haney clay, i t is believed that the variation i s not large enough to i n v a l i ­

date comparisons of drained and undrained strengths. The test results do

not permit a direct comparison of the strengths (at the maximum principal

stress difference) for any given water content because the water contents

of the drained and undrained tests do not overlap. However i t can be seen

that, because the graph of strength (represented by (o^ * - 0"36)max, or 0 3 '

at failure) for the undrained tests does not l i e on a projection of the

graph of strength for the drained tests, the strength at any water content

i s not independent of stress path. If, for i l l u s t r a t i o n purposes, extra-

69

0 5 10 15 20 25 30

AXIAL STRAIN (%)

FIGURE 28. RELATIONSHIP BETWEEN WATER CONTENT AND AXIAL STRAIN IN A DRAINED TEST.

70 6 0

o Q.

15 •>

10 * 1 1 1 1 1 L -0 5 10 15 20 25 30

AXIAL STRAIN (%)

FIGURE 29. RELATIONSHIP BETWEEN PORE PRESSURE AND AXIAL STRAIN IN AN UNDRAINED TEST.

VARIOUS STRESSES (LOGARITHMIC SCALE )

FIGURE 30. TYPICAL WATER CONTENT - STRESS RELATIONSHIP FOR SATURATED, NORMALLY CONSOLIDATED REMOLDED AND INSENSITIVE CLAYS.

72

FIGURE 31. RELATIONSHIP BETWEEN WATER CONTENT AND STRESS AFTER NORMAL CONSOLIDATION AND AT (cr, - oV ) m a x

AND (o-; /a-') FAILURE CRITERIA. o n . 1 ° max.

73

p o l a t i o n of the data i s accepted (shown dotted i n Figure 31), i t may be seen

that at a water content of 30 percent, the maximum p r i n c i p a l s t r e s s d i f f e r ­

ence i s 63 l b s , / s q , i n , i n the undrained t e s t s and i s 51 l b s , / s q , i n , i n

the drained t e s t s . For the maximum e f f e c t i v e p r i n c i p a l s t r e s s r a t i o n f a i l ­

ure c r i t e r i o n , a s i m i l a r l a c k of agreement i s apparent. For example, at a

water content of 30 percent, 0 3 ' « 32 l b s , / s q , i n , i n the undrained t e s t s

and 28 l b s , / s q , i n , i n the drained t e s t s . I t has a l s o been reported ( T a y l o r ,

1948, Roscoe, S c h o f i e l d and Wroth, 1958, Henkel, 1960, Hvorslev, 1960) that

the change i n water content during drained shear t e s t s on normally c o n s o l i ­

dated samples i s independent of the i n i t i a l water content, that i s , the

l i n e r e p r e s e n t i n g f a i l u r e , (oV - o3')max,, i s p a r a l l e l t o the normal con­

s o l i d a t i o n curve (Figure.30), Reference t o Figure 31 shows that none of

the curves are p a r a l l e l to the normal c o n s o l i d a t i o n curve and thus the

change i n water content during drained shear i s not independent of i t s

i n i t i a l v a l u e . I t may t h e r e f o r e be concluded that the st r e n g t h - v o i d r a t i o

r e l a t i o n s h i p s developed f o r remolded c l a y s are not a p p l i c a b l e to undisturbed

e x t r a - s e n s i t i v e c l a y s . T h i s c o n c l u s i o n i s not new but was i m p l i e d by Taylor

(1948), Henkel (1960), and Hvorslev (1960),

Figure 32 shows the v a r i a t i o n of a x i a l s t r a i n w i t h uncorrected drained

and undrained s t r e n g t h . I t can be seen t h a t the st r e n g t h (which i s i n

terms of <(>') i s very n o t i c e a b l y a f u n c t i o n of both f a i l u r e c r i t e r i o n

(whether i t be ( o V - 03°) ( f l i V o V ) , or s t r a i n ) and type of t e s t , Ttl£LX 0 TI1£IX o

The v a r i a t i o n of st r e n g t h w i t h f a i l u r e c r i t e r i a may a l s o be seen i n Figures

25 and 26, At the maximum p r i n c i p a l s t r e s s d i f f e r e n c e , the uncorrected

drained s t r e n g t h (<J>' • 28,1°) i s gr e a t e r than the undrained s t r e n g t h

($' - 24 05°) whereas at the maximum e f f e c t i v e p r i n c i p a l s t r e s s r a t i o , the

uncorrected drained s t r e n g t h ($' • 28,1°) i s l e s s than the undrained

FIGURE 32. VARIATION OF THE MOBILIZED EFFECTIVE ANGLE OF SHEARING RESISTANCE WITH AXIAL STRAIN.

strength • 30,5°), Thus from a practical point of view, the choice

of a factor of safety in any problem concerned with sensitive clay becomes

d i f f i c u l t because both type of failure (drained or undrained) and failure

criterion must be considered,, Also, the strains required to develop the

(oV - 03 ') and ( o 1 ' / / 0 3 ° ) „ failure c r i t e r i a can be quite large and

therefore a definition of failure i n sensitive clays must recognize not only

the strength, but also the strain required to develop that strength, and the

drainage conditions presents

In Section 4,5 i t was stated that thixotropic strength gain probably

influenced the stress-strain characteristics of the clay tested. It was

also pointed out that the confining pressure to which the sample was i n i t i a l ­

ly consolidated caused structural adjustments to occur within the clay and

thus perhaps reduced i t s sensitivity. Evidence to support this can be found

in Figures 16, 17, and 18 where i t can be seen that the axial strain to

failure decreased slightly at the higher consolidation pressures. This de­

crease infers that the structure is less sensitive because, in general, soils

with low sensitivities f a i l at lower axial strains than those with high sen­

s i t i v i t i e s (Bishop and Henkel,. 1962),

The strength of the sample in test S-10 (Table IV) was very similar to

those samples tested at the slower rate of strain which indicated that, with­

in the limits investigated, the rate of strain does not significantly i n ­

fluence the measured strength.

No attempt was made to investigate the effect of sample disturbance on

the measured properties of the clay. Every precaution was taken to ensure

that minimum disturbance occurred and i t i s believed that the strengths

quoted above are representative of the undisturbed material.

76

4,7 Summary

I t i s appreciated that the number of tests conducted i n t h i s i n v e s t i ­

gation was smallo However0 the consistency of the results obtained i s an

encouraging indication of t h e i r v a l i d i t y . The o v e r a l l behavior of the clay

tested i s sim i l a r to that reported by Crawford (1959, 1961) who has conduct­

ed extensive t r i a x i a l shear tests on sensitive clays. The s i g n i f i c a n t

difference i n the s t r e s s - s t r a i n characteristics of drained and undrained

t r i a x i a l compression tests on ah extra-sensitive clay i s perhaps the most

important feature observed i n t h i s investigation, and points to the i n f l u ­

ence that structure has on the s o i l behavior. The fact that the strength

of an extra-sensitive clay i s very dependent on the f a i l u r e c r i t e r i a used

to define the strength, and on the drainage conditions present, must not be

overlooked i n any extrapolation of laboratory data to f i e l d conditions.

i

77

CHAPTER 5

CONCLUSIONS

The purpose of the present study has been to investigate the stress-

strain behavior of an undisturbed extra-sensitive clay during t r i a x i a l coin-

pressiono The following conclusions are based on the results of a limited

number of tests on one clay, and hence extrapolation of some of these con­

clusions should be avoided u n t i l further data on clays of other s e n s i t i v i ­

ties i s availableo

10 The sensitivity of a clay, which i s a measure of the sta b i l i t y

of i t s i n i t i a l structure, i s of primary importance in determining i t s stress-

strain behavioro

2 0 A relationship between void ratio and strength, which i s inde­

pendent of stress path, visualized by Taylor ( 1 9 4 8 ) , Hvorslev ( 1 9 6 0 ) and

others for remolded and insensitive undisturbed normally consolidated,

saturated clays, does not exist for an undisturbed extra-sensitive clay D

3o A failure envelope (failure being defined at the maximum pr i n c i ­

pal stress difference), independent of stress path, which was suggested by

Henkel ( 1 9 6 0 ) for remolded clays does not exist for an undisturbed extra-

sensitive clay„

4 0 A c r i t i c a l void ratio (Roscoe, Schofield and'Wroth, 1 9 5 8 ) at which

a s o i l yields continuously at constant, volume during drained shear was not

reached during this test series, although the available evidence indicates

that i t may exist at strains greater than those investigated.

5o The strength of an extra-sensitive clay at the maximum effective

principal stress ratio i s not independent of test type i f the Bishop ( 1 9 5 4 )

or Rowe ( 1 9 6 2 ) energy corrections are applied to the drained test data.

For Haney clay, Bishop <j>° corrected » 2 9 . 1 ° , Rowe <J>5 corrected » 3 1 0 5 ° ,

undrained $*^m 30,5°,,

6 0 The Roscoe, Schofield and Thurairajah (1963) energy equation,

when applied to the drained and undrained test data, does yield an approxi­

mately constant value for the slope of the q w versus p" curve, M » 1,27,

The corrected angle of shearing resistance, determined-from M($' - 31 06°)

is approximately the same as that obtained from the drained data corrected

by the Rowe (1962) energy correction • 31,5°),

7 0 The uncorrected effective angle of mobilized shearing resistance,

does not only vary widely with axial strain, but i s also a function of the

drainage conditions during shear, and of the criterion of failure that i s

usedo

8, Because of the large strains involved, and because of the i n ­

fluence of drainage conditions, the generally accepted failure c r i t e r i a of

maximum principal stress difference-and maximum effective principal stress

ratio are not satisfactory for an extra-sensitive clay,

9a In drained shear tests on an extra-sensitive clay, the strain at

which failure occurs appears to decrease with an increase in the consolida­

tion stress,

100 Calculations indicated that significant pore pressures may

develop at low strains in drained tests,

l l o For the clay tested, rates of strain between 0 05 percent and

2,5 percent per hour do not significantly affect the strength or stress-

strain behavior of 2,8 ins, by 1,4 ins, diameter t r i a x i a l samples.

CHAPTER 6

SUGGESTIONS FOR FURTHER RESEARCH

Since the number of t r i a x i a l tests-performed in this investigation

was small, i t i s suggested that further tests of a similar nature be per­

formed on other sensitive clays to establish i f the conclusions drawn from

this test series are applicable to a l l sensitive clays.

Following i s a l i s t of areas of investigation that have been

suggested by the present research program. Also included are recommenda­

tions for improved testing equipment,

1, Tests on larger samples of clay w i l l reduce the effects of

sample disturbance and also permit a more representative sample of clay

to be tested. This i s particularly necessary when investigating highly

laminated material such as Haney clay. Because sensitive clay does not

f a i l u n t i l high axial strains have developed, the use of frictionless end

platens (Rowe and Barden, 1964) w i l l significantly increase the uniformity

of stresses within the sample and improve the validity of stress calculations

which rely on the assumption that the s o i l deforms as a right cylinder

(Olson, 1962),

2, In remolded saturated clays, the existence of a relationship

between strength and water content at failure that i s independent of stress

path i s widely recognised (Roscoe, Schofield and Wroth, 1958, Hvorslev,

1960, Scott, 1962), It has been shown that such a relationship i s not pre­

sent in an undisturbed extra-sensitive clay, but no investigation of the

remolded properties of this clay has been undertaken. It i s therefore

suggested that the remolded properties of Haney clay be determined,

3, Although their existence i s accepted (Hvorslev, 1960), the development of pore pressures during drained tests has received l i t t l e

attentiono Before pore pressures can be accurately calculated, determina­

tions of the values of A and c^ during drained shear must be made. Alterna­

tively, the pore pressure may be measured through a probe inserted at the

mid-height of the sample, and a distribution of pore pressure within the

sample assumed. If drainage i s permitted through the base,only, the pore

pressure may be measured at the top stone.

El e c t r i c a l pressure transducers of low compliance are believed to

be the most satisfactory method presently available of measuring pore

pressures,

4, It has been suggested that the effective confining pressure i n ­

fluences the strain at which failure occurs i n drained tests, A possible

explanation for this i s that consolidation tends to destroy the sensitivity

of the material by causing structural re-arrangements within the sample.

Further investigation of this effect in both drained and undrained tests is

necessary before any definite conclusions may be drawn,

5, The sharp change in the slope of the stress-strain curve of an

extra-sensitive clay during drained shear has been reported by Crawford

(1959) and in the thesis. Possible explanations for this irregularity i n ­

clude the influence of past history, residual pore pressures, structure,

and creep. Perhaps further investigation of the stress-strain behavior of

extra-sensitive clay might indicate which of the above factors, i f any,

are responsible for the observed phenomenon,

6, It is generally accepted that the strength of clay and the shape

of i t s stress-strain curve i s affected by the rate of strain applied to the

sample (Whitman, I960), However, the.limited test' data reported herein

indicates that, within the range investigated, strain rate has l i t t l e effect

on the resulting behavior of an extra-sensitive clay. This suggests that an

investigation of the effects of a large range of strain rates on the behavior

of extra-sensitive clay is desirable. Such an investigation could report

on the effect of strain rate on thixotropic strength gain, creep, develop­

ment of pore pressures during drained tests, and equalization of pore pres­

sures during undrained tests,

7, An attempt to determine the type of structure which exists in a

clay at a l l points along its stress-path would undoubtably furnish a better

understanding of the contribution that structure makes to the behavior of

the clay, A series of identical tests could be stopped at various points

along the stress paths, and the structure determined at each.point by x-ray

diffraction technique or electron microscope.

NOMENCLATURE

Pore pressure coefficient reflecting the dilatancy of

the sample

Coefficient of compressibility

Pore pressure coefficient reflecting the degree of

saturation present in the sample

slope of water content versus logarithm of mean

effective stress during isotropic unloading

interparticle cohesion parameter

coefficient of consolidation

one-half sample height

void ratio

specific gravity of s o i l solids

permeability

slope of void ratio versus natural logarithm of mean

effective stress during isotropic unloading

slope of void ratio versus logarithm to the base 10 of

mean effective stress during isotropic unloading

A constant

mean effective stress » q1 *

i n i t i a l mean effective stress

observed principal stress difference • (aj' - 03')

corrected principal stress difference

sensitivity

time

time to 90 percent consolidation

time factor

average degree of consolidation

Ufi - recoverable energy

u - pore pressure

u i - i n i t i a l pore pressure

v - volumetric strain

W - dissipated energy

Wg - weight of solids

at - water content

8 - depth from surface of clay layer

a » slope of l / 2 ( c i ' - o 3') versus l/2( o i ' + 0 3 ' ) failure envelope e

Ae - change in void ratio attributed to elastic volume change

Au - change in pore pressure

Ao^(i»la3) - change in major or minor total principal stress respectively

AV - elastic volume change

- unit weight of water

6e - 2/3(6ei - 663) » distortion increment

e^(i»l,3) - major or minor strain respectively

li - rate of axial strain

41' - effective angle of shearing resistance

interparticle shearing parameter

a - total stress

a' - effective stress

o^(i"lt3) - major or minor total principal stress respectively

o^'(i"l e3) - major or minor effective principal stress respectively al'/aS* ~ effective principal stress ratio

(°1 - O j ) - principal stress difference (deviator stress)" ( 0 1 ' - 0 3 ' )

o c' - effective confining stress » 0 3 9

dV - rate of total volumetric strain V •e

dV - rate of elastic volumetric strain

84

LIST OF REFERENCES

AMERICAN SOCIETY OF CIVIL ENGINEERS , 1962, "Nomenclature for s o i l mechanics," Proc, Am, Soc, Civ, Eng., SMF Div,, Vol, 88, No, SM3, pp, 185-188,

ARMSTRONG, J,E,, 1957, " S u r f i c i a l Geology of New Westminster map-area, B r i t i s h Columbia," Geological Survey of Canada Paper 57-5, 25 pp,

BISHOP, A,W0, and A,K,G, ELDIN, 1953, "The effect of stress history on the r e l a t i o n between <J> and porosity of sand," Proc, 3rd, Int, Conf, S o i l Mech,, Vol, 1, pp, 100-105,

BISHOP, A , W o , 1954, Correspondence on a paper by A,D,M, Penman, Geotechnique, Vol, 4, pp, 43-45,

BISHOP, A o W , , and D,J, HENKEL, 19620 "The Measurement of S o i l Proper­t i e s i n the T r i a x i a l Tests," Edward Arnold Ltd,, 200 pp,

BISHOP, A , W o , 1964, Correspondence on paper by P,W„ Rowe, L, Barden, and I,K, Lee, Geotechnique, Vol, 14, pp, 370-371,

BYRNE, P,M,, 1966, "Effective stress paths i n a sensitive clay," M,A,Sc, thesis, University of B r i t i s h Columbia, Vancouver, Canada, (Typewritten),

CRAWFORD, C B o , 1959, "The influence of rate of s t r a i n on e f f e c t i v e stresses i n sensitive clay," ASTM Spec, Tech, Publ, No, 254, pp, 36-48,

CRAWFORD, C.B,, 1961, "The influence of s t r a i n on shearing resistance of sensitive clay," ASTM P r o c , Vol, 61, pp, 1250-1265.

GRIM, R,E,, 1953, "Clay Mineralogy," McGraw-Hill Book Company, Inc, 380 pp,

HENKEL, D,J,, and G,D, GILBERT, 1952, "The effect of the rubber membrane on the measured t r i a x i a l compression strength of clay," Geotechnique, Vol, 3, pp, 20-29,

HENKEL, D.J,, 1960, "The shear strength of saturated remoulded clays," Proc, Am. Soc, Civ, Eng,, Research Conference on Shear Strength of Cohes­ive S o i l s , pp, 533-554,

HENKEL, D,J., and V,A. SOWA, 1963, "The Influence of stress history on stress paths i n undrained t r i a x i a l tests on clay," ASTM Spec. Tech, Publ, No. 361, pp, 280-291,

HVORSLEV, M„J„, 1953, Discussion on s o i l properties, Proc, 3rd, Int, Conf, S o i l Mech,, Vol, 3, pp, 122-124,

HVORSLEV, M,J,, 1960, "Physical components of the shear strength of saturated clays," Proc, Am, Soc, Civ, Eng,, Research-Conference on Shear Strength of Cohesive S o i l s , pp, 169-273,

85

KENNEY, T.C, 1 9 5 9 o D i s c u s s i o n on paper by C.B, Crawford. ASTM Spec. Tech, P u b l , No, 254, pp, 49-58,

LAMBE, T , W , , 1958, " S o i l T e s t i n g f o r Engineers," John Wiley and Sons, Inc., 150 pp,

LAMBE, T.W,, 1958a. "The s t r u c t u r e of compacted c l a y , " Proc, Am, Soc, Ci v , Eng,, SMF Div , , V o l . 84, No, SM2, Paper 1654, 34 pp,

LAMBE, T,W,, 1958b, "The engineering behavior of compacted c l a y , " Proc. Am, Soc. C i v , Eng,, SMF Div , , V o l , 84, No, SM2, Paper 1655, 35 pp,

LEONARDS, G,A,, 1962, Chapter 2 of "Foundation Engineering," McGraw-Hill Book Company, Inc. 1100 pp,

MURAYAMA, S,, and T, SHIBATA, 1961. " R h e o l o g i c a l p r o p e r t i e s of c l a y s , " Proc, 5th, I n t , Conf, S o i l Mech,, V o l , 1, pp, 269-273.

OLSON, R.E,, 1962, Correspondence on a paper by J.E,B, Jennings and J,B, Burland, Geotechnique, V o l , 12, pp, 355-358,

POOROOSHASB, H.B,, and K.H, ROSCOE, 1961, "The c o r r e l a t i o n of the r e ­s u l t s of shear t e s t s w i t h v a r y i n g degrees of d i l a t i o n , " Proc. 5th I n t . Conf, S o i l Mech,, V o l , 1, pp, 297-304,

POULOS, S . J o , 1964, "Report on c o n t r o l of leakage i n the t r i a x i a l t e s t , " Harvard S o i l Mechanics S e r i e s No, 71, Cambridge, Mass., 230 pp,

ROSENQVIST, I , TH,, 1952, "Considerations on the s e n s i t i v i t y of Norwegian q u i c k - c l a y s , " Geotechnique, V o l , 3, pp, 195-200,

ROSCOE, K.H,, A,N, SCHOFIELD, and C P , WROTH, 1958. "On the y i e l d i n g of s o i l s , " Geotechnique, V o l , 8, pp, 22-53,

ROSCOE, K„H,, A,N, SCHOFIELD, and A. THURAIRAJAH, 1963, " Y i e l d i n g of c l a y s i n s t a t e s wetter than c r i t i c a l , " Geotechnique, V o l , 13, pp, 211-240,

ROWE, P , W o , 1962, "The s t r e s s - d i l a t a n c y r e l a t i o n f o r s t a t i c e q u i l i b r i u m of an assembly of p a r t i c l e s i n c o n t a c t , " Proc. Roy, Soc. A, V o l , 269, pp, 500-527,

ROWE, P o W , , D,B, OATES and N.A. SKERMER, 1963. "The s t r e s s - d i l a n t a n c y performance of two c l a y s , " ASTM Spec, Tech, P u b l , No, 361, pp, 134-143,

ROWE, P.Wo, 1963, D i s c u s s i o n on paper by R,C, H i r s c h f e l d and S,J, Poulos, ASTM Spec, Tech, P u b l , No, 361, pp, 340.

ROWE, P.W„, and L, BARDEN, 1964, "Importance of f r e e ends i n t r i a x i a l t e s t i n g , " P r o c , Am, S o c C i v , Eng., SMF Div , , V o l , 90, No, SMI, pp. 1-27,

ROWE 9 P,W,, L, BARDEN, and I.K. LEE, 1964, "Energy components during the t r i a x i a l c e l l and d i r e c t shear t e s t s , " Geotechnique, V o l . 14, pp. 247-261,

86

SCOTT, R,F„, 1962 0 " P r i n c i p l e s of S o i l MechaniCBo" Addison-Wesley P u b l i s h i n g Company, I n c , 500 pp 0

SEED, H.B,, J.K. MITCHELL, and C.K. CHAN, 1960. "The stre n g t h of compacted cohesive s o i l s . " Proc. Am. Soc. C i v . Eng 0, Research Conference on Shear Strength of Cohesive S o i l s , pp. 877-964.

SKEMPTON, A.W., and R.D. NORTHEY, 1952, "The s e n s i t i v i t y of c l a y s . " Geotechnique, V o l . 3, pp. 30-53.

SKEMPTON, A.W., 1954. "The pore pressure c o e f f i c i e n t s A and B." Geotechnique, V o l . 4, pp. 143-147,

SKEMPTON, A.W., and L, BJERRUM, 1957. "A c o n t r i b u t i o n t o the s e t t l e ­ment a n a l y s i s of foundations on c l a y , 1 ' Geotechnique, V o l . 7, pp, 168-178, TAxL0R, D,W„, 1948, "Fundamentals of S o i l Mechanics," John Wiley and Sons, Inc., 700 pp,

TERZAGHI, K,, 1923, "Die Berechnung der D u r c h l ' a s s i g k e i t s z i f f e r des Tones aus dem V e r l a u f der, hydrodynamishen Spannungserscheinungen," S i t z b e r , Akad, Wissen, Wien Math-Natur K l , Abt, H a , V o l , 132, pp. 105-124.

TERZAGHI, K,, 1925, "Erdbaumechanik auf bodenphysik-alischer Grundlage," L e i p z i g s D e u t i c k e , pp, 140,

TERZAGHI, K,, 1944, "Ends and means i n s o i l mechanics," Engineering J o u r n a l (Canada),, V o l , 27, pp, 608,

WHITMAN, R,V,, 1960. "Some c o n s i d e r a t i o n s and data regarding the shear s t r e n g t h of c l a y . " Proc. Am, Soc, C i v , Eng,, Research Conference on Shear Strength of Cohesive S o i l s , pp, 581-614,

87

APPENDIX

88 TRIAXIAL COMPRESSION TEST Sheet 1 of 2

SOIL SAMPLE: Haney Cla\ SPECIFIC GRAVITY J 2 080 TEST TYPES Drained

BEFORE TESTS WATER CONTENTS

TEST NOoS 17 DATES June 12 t 1965 TESTED BYs T 0 J 0Ho

Specimen L o c a t i o n Side Side Side Side Top Bottom

Container No 0 H ~ l H-2 H-3 H-4 H-5 H-6 Wt0 Container & Wet S o i l i n emn

57o80 58088 71o32 61096 42070 47o70

Wto Container & Dry S o i l i n gm0

46063 47o22 56019 49D27 35o60 38071

Wto Water i n gm0 U o l 7 Uo66 15013 12069 7ol0 8099 Wto Container In sma

18o99 18061 19o21 18030 18o70 18057 WtoDry S o i l i n gm 27o64 j 28061 36o98 30o97 16o90 20o14 Water Content |4004 | 4008 40o9 41o0 4200 4406

CircumoCMn DiamoCMc Area CM2

Top llo30 3o60 A ." 10 018 Center Ho27 3o59 A - 10 o12 c Bottom Uo24 3 058 A ^ 10 o07

Average Water Content, to » 40 08% 7ol0 + 7„10 + 7ol0 + 7nl0

2A Length

Wto Wet Sample and Container Wto Container I n i t i a l Wto Wet Sample, W

AFTER TESTS WATER CONTENTS

135o70 GM0

.3 o 36_ GM0

132o34 GMo

- 7ol0 CM0

Area <• t + c + 10ol2 CMo'

Specimen L o c a t i o n Whole

Container No 0 H-2

WtoContainer & Wet S o i l i n gm0 199o18 WtoContainer & Dry S o i l i n em„ 169„69 Wto Water i n gm0 29„49 Wto Container

i n gm0

76o01 Wt.Dry S o i l i n gm0 93o68 Water Content 31 o 5%

Volume drained d u r i n g Volume drained d u r i n g Volume back d r a i n e d T o t a l Volume Change •

c o n s o l i d a t i o n shear

AV

=> 2o75"CM0: - 9 031 CM0:

• 8085 CM,"

V, AV » 63o07 CM, | e. V 0o879

89

Sheet 2 of 2

TRIAXIAL COMPRESSION TEST

(CONTINUED)

MEASURED DIMENSIONS Clrcum0CMo DiamoCMc Area CM

Top 11.55 "5,68 A_- 10,64 Center 13o58 4032 A - 14,66 Bottom llo65 3,71 Af» 10,81

T i U 4.90 + 4.90 + 4.90 + 4,90 4.90 CM. Length * 1 1 ' r • r M i 1 n •ir^- •

Area » t + 12.69 CM,

V f - 62,18 CM

Remarks 8 Test #11-16 out ofi one block of clay

Teat #17 taken from new block.

Alignment f a i r .

D i s t i l l e d Water Supply Tank sprung leak under vacuum.

Traced to valve stem and fixed

TRIAXIAL COMPRESSION TEST

APPLICATION OF CHAMBER PRESSURE

NO DRAINAGE

Chamber Pressure • 5 0 » 0 P 0S 0 I o Test No„ s 17

Back Pressure « 1 0 0 0 P 0 S 0 I 0 Tested bys T 0 J o H 0

D/\TE T I M E HRS.

T E M R

° c CHAMBER PR. GuflGE

P.S.I.

P R E S S . Co«R. P.S.I.

Ct4flM8EA PRESSuRt

P.S.I.

PORE PR.

P.S.I.

PKESS. CoAR. P.S.I.

Pofte

P.S.I.

S KEMPT*

B June 12 /65 l i s 25 24 o0 15o0 • .2 0 2 1 2 0 8 1 4 0 9 - 4 0 2 10o7

9o8 9 0 9 l o O l

118 29 2 5 o 0 -2 04 2 2 0 6 2 4 0 8 - 4 0 2 2 0 o 6

9 0 9 9o9 loOO

l i s 35 3 5 0 0 - 2 0 5 3 2 0 5 3 4 0 8 - 4 0 3 30 05

1 0 0 0 10o0 loOO

118 40 4 5 0 0 - 2 0 5 4 2 0 5 4 4 0 8 - 4 o 3 4 0 o 5

7o5 7<,5 l o 0 0

lls45 2 4 o l 5 2 „ 5 - 2 0 5 5 0 0 0 5 2 0 4 »4 0 4 4 8 o 0

Remarks: Regulation good0

T R I A X I A L C O N S O L I D A T I O N

C H A M B E R P R E S S U R E G A U G E » 5 2 , 5 P , S , I , T E S T N 0 0 17

G A U G E C O R R E C T I O N » -1.1 P 0 S „ I 0 T E S T E D B Y 8 T 0 J , H ,

E L E V A T I O N C O R R E C T I O N » -104 P o S , ! , A V G E 0 I N I T I A L W A T E R C O N T E N T

C H A M B E R P R E S S U R E - 5 0 o 0 P 0 S 0 I o W E I G H T D R Y S O I L , W g - 93099 G M S

B A C K P R E S S U R E » 1 0 o Q P 0 S 0 I 0 W E I G H T W A T E R 8 W » 3 8 0 3 5 G M S

D A T E T I M E H R S - M W

E L A P S E D T I M £

M M . / E L A P S E D

V T I M E B U R E T T E

C M . 3

VERTiCfl L D I A L INS.

T E M P . °C

June 12g 1965 1 1 S 5 5 OsOO O o O O IOOOO 1,0000 24 i l

0?04 0,25 9„90 0sl5 0»50 9 o 8 4

0s34 0075 9078 1§00 1,00 9„70 ls34 1025 9 o 6 0

2tl5 1050 9,52 3s04 1075 9648 4s00 2o00 9o40 6sl5 2,50 9022 9 5 0 0 3o00 9,10 12 s 15 3050 8093 16 s 00 4o00 8o80 20 s 15 4050 80 66 2 5 s 00 5 o 0 0 8,51 30 s 15 5 o 5 0 8,41 36 8 00 6,00 8 o 3 2

42sl5 6,50 8,25 49s00 7,00 8 0 1 9 56 s 15 7 c 5 0 8 , 1 1 0,9680 24,2 61s 00 8000

June 13, 1965 10s08 7,29 0,9652 23,0 11* 55 r - 7,25 0„9645 24,0

A V - 2o.75 CM,3

After consolidation, weight of water » Ww - A V » 3 5 , 6 0 G M S ,

Water Content « 3 7 , 9 %

Remarks

92

TRIAXIAL COMPRESSION TEST , , „ ' Sheet 1 of 3

TEST" TYPE 8 Drained TEST N 0 o j 17

TEST RATES 0 o 0 1 4 Ins,/Hr, TESTED BYs T 0J 0H 0

PROVING RING N O , s 3 2 8 2 BACK PRESSURE - 1 0 7 1 FT,Hg, - 1 0 , 0 P.S d o

CALIBRATION FACTOR » 0 . 3 1 6 5 LBS0/DIV0 CHAMBER PRESSURE GAUGE - 52 , .5 P . S o I o

LOADS > 1 5 6 LBS, - 0 o 7 6 7 8 LBS0/DIV0 GAUGE CORRECTION * - 1 . 1 P o S . I o

INITIAL READING PROVING RING - 2 9 . 6 DIV. ELEVATION CORRECTION - - 1 , 4 P 0 S a I o

CONSOLIDATED AREA » 1 , 5 2 9 IN, 2 CHAMBER PRESSURE - . 5 0 , 0 P ' o S . I .

CONSOLIDATED LENGTH » 2 o 7 6 0 IN, CONSOLIDATED WATER CONTENT - 3 7 . 9 %

D A T E T I M E

HRSo

V E R T o D I A L

I N C H E S PROVo D I A L

0 , 0 0 0 1 I N S , B U R E T T E

• C M , 3

T E M P

° C

June 1 3 , 1 9 6 5 H o 92 0 o 9 6 4 5 2 9 , 6 1 0 , 0 0 2 4 , 0

1 2 0 1 5 O o 9 6 3 1 4 9 , 5 9 , 9 8 2 4 , 0

1 2 0 5 2 0 o 9 6 0 2 7 4 , 0 9 , 9 5 2 4 , 2

1 2 o 7 5 0 o 9 5 8 2 8 7 , 0 9 , 9 1 2 4 , 3

1 3 0 0 0 O o 9 5 5 9 1 0 0 , 7 9 , 8 8 2 4 , 5

1 3 o 3 3 0 o 9 5 2 1 1 1 6 o 2 9 , 8 0 2 4 , 8

1 3 o 6 7 0 o 9 4 8 2 1 3 0 , 0 9 , 7 2 2 4 , 8

1 4 o 0 0 0 o 9 4 4 1 1 4 3 o l 9 , 6 5 2 5 , 0

1 4 o 5 0 0 , 9 3 7 8 1 5 8 o 5 9 , 5 1 2 4 , 8

1 5 o 0 0 O.o 9306 1 6 8 , 4 9 , 3 9 2 4 . 8

1 5 0 5 0 0 0 9 2 3 2 1 7 4 , 3 9 , 2 2 2 4 , 6

1 6 0 3 3 0 , 9 1 1 5 1 7 8 , 8 8 , 9 7 2 4 . 6

1 7 0 5 0 0 , 8 9 5 2 1 8 2 , 4 8 , 6 2 24 o l

1 9 0 5 0 0 , 8 6 6 1 1 9 1 0 0 8 , 0 2 2 4 . 1

Remarks 8

T E S T E D B Y ? T o J o H , T E S T NOoS 17

D A T E

T I M E

HRSo

V E R T o D I A L

I N C H E S

PROVo D I A L

O o O O O l I N S o

B U R E T T E T E M P

° C

June 1 3 , 1 9 6 5 2 1 , 4 2 0 0 8 3 7 5 1 9 8 o 6 7 o 5 0 2 4 o 8

2 2 0 5 0 0 o 8 2 0 6 2 0 4 o l 7 o 2 0 2 4 o 8

2 3 0 5 2 0 o 8 0 5 2 2 0 9 o 6 6 0 9 2 2 5 o 0

June 1 4 e 1 9 6 5 2 4 0 7 5 0 o 7 8 7 8 2 1 4 0 4 6 0 6 0 2 4 o 7

2 6 0 0 0 0 0 7 7 0 5 2 2 0 o 2 6 0 3 0 2 5 o 0

3 2 0 5 0 0 0 6 7 4 7 2 6 4 o 2 4 0 9 4 2 4 0 5

3 4 0 0 0 0 0 6 5 3 3 2 7 2 0 1 4 0 6 8 2 4 „ 8

3 5 o 5 0 0 o 6 3 2 4 2 8 3 o 9 4 0 4 1 2 4 o l

3 8 0 0 5 0 o 5 9 5 0 3 0 1 o l 4 o 0 0 2 5 o l

3 9 „ 5 0 0 0 5 7 2 2 3 1 0 o 3 3 0 7 8 2 5 o 0

4 1 o 0 5 0 o 5 5 0 0 3 1 9 o l 3 o 5 5 2 4 0 7

4 2 0 1 3 0 o 5 3 5 1 3 2 4 o 3 3 o 4 0 2 4 0 8

4 3 o 4 5 0 , 5 1 7 0 3 3 4 o 0 3 o 2 2 2 4 o 9

4 5 , 0 3 0 0 4 9 3 8 3 4 4 0 7 3 o 0 1 2 4 , 6

4 6 o 0 0 0 0 4 7 9 4 3 5 1 o 0 2 0 9 1 2 4 0 7

4 7 o 0 O 0 o 4 6 3 8 3 5 7 0 9 2 0 8 0 2 4 , 6

June 1 5 , 1 9 6 5 4 8 o 0 0 0 , 4 4 7 9 3 6 3 0 3 2 o 6 9 2 4 o 0

5 6 0 4 3 0 0 3 2 4 3 4 0 8 o 3 1 , 8 8 25 o 3

5 8 o 0 7 0 , 3 0 1 8 4 1 4 o 7 l o 7 4 . 2 4 o 3

5 9 0 7 3 0 = 2 7 9 7 4 2 3 0 9 1 0 6 2 . . . . . 2 4 , 2

Remarks s

94

T R I A X I A L C O M P R E S S I O N T E S T

( C O N T I N U E D )

T E S T E D BY8 T o J o H 0

D A T E T I M E

HRSo

V E R T , D I A L

I N C H E S

PROVo D I A L

O o O O O l I N S o

B U R E T T E

C M o J

T E M P .

° C 0

June 1 5 , 1 9 6 5 6 1 o 9 5 0 , 2 4 6 0 4 3 3 0 2 l o 4 8 2 5 o 0

6 3 o 3 5 0 o 2 2 3 7 4 3 9 o 9 1 0 3 9 2 5 o 0

6 4 o 4 0 0 0 2 0 7 1 4 4 4 o 2 l o 3 0 2 4 o 9

6 5 o 0 5 0 o l 9 7 6 4 4 6 0 3 1 0 2 7 2 5 0 0

6 6 o 5 0 0 o l 7 8 2 4 4 9 0 9 1 0 1 8 ^ 2 5 o 0

6 8 0 1 8 0 o 1 5 5 0 4 5 7 0 1 l o l O 2 4 0 9

6 8 o 8 5 0 0 1 4 4 2 4 6 0 oO I 0 O 6 2 4 o 6

6 9 0 8 7 0 0 1 2 8 5 4 6 3 o 3 l o O O 2 4 o 8

7 0 o 9 7 0 o l l l 7 4 6 7 0 2 0 o 9 7 2 4 0 8

June 1 6 , 1 9 6 5 7 2 o 0 7 0 0 0 9 4 0 4 7 0 o 8 0 o 9 1 2 4 0 8

7 3 o 0 3 0 o 0 7 9 2 4 7 3 o l 0 0 8 8 2 4 o 8

7 3 o 7 5 0 o 0 6 9 1 4 7 3 o 8 0 , 8 4 2 5 o 0

7 3 o 7 5 O 0 I O 8 O 4 7 3 0 8 0 „ 8 4 2 5 0 0

7 5 „ 3 3 0 o 0 8 7 0 4 7 7 o 0 0 o 7 9 2 4 0 6

7 7 o O O 0 0 0 6 2 7 4 8 4 0 7 0 o 7 2 2 4 o 0

7 8 0 8 1 0 0 0 3 3 9 4 9 1 o 7 0 0 6 9 2 3 o 8

A V - 9 0 3 1 O M „ 3

Sheet 3 of 3

TEST N O 0 8 17

Remarks! Sample did not buckle 0

No failure plane visibleo

95

TRIAXIAL BACK-DRAINAGE

CHAMBER PRESSURE'GAUGE

GAUGE CORRECTION

ELEVATION CORRECTION

CHAMBER PRESSURE

BACK PRESSURE

TEST NO, 2 17

TESTED BY % T.J.H.

AFTER SHEAR WATER CONTENT = 28„0%

WEIGHT DRY SOIL, W

WEIGHT WATER, W W

• 9 3 , 9 9 GMS

2 6 c 2 9 GMS

D A T E TIME

H R S . - MIH. ELAPSED

T I M E MIN.

/ELAPSED V T I M E

BURETTE CM.3

VERTlCAt-D lAL 1 NS.

TEMR ° C

June 16, 1965 06;51 OsOO OoOO 0,69 0,0339 23„8 0204 0025 0sl5 0,50 0*34 0,75 1800 1,00 1834 1,25 2*15 1,50 3804 1,75 0,95 \

4200 2,00 1,00 \ 6*15 2,50 1,10 9*00 3,00 1,20 12*15 3,50 1,30 16800 4,00 1,40 20*15 4,50 1,50 25*00 5,00 1,59 30*15 5,50 1,69 36*00 6,00 1,78 42 §15 6,50 « ,

49 s 00 7.00 1.95 56 §15 7,50 2.02 64 §00 8.00 2,11 81*00 9,00 2,30

121§00 11.00 2,60 144*00 12,00 2,75 169„00 13,00 2,90 211,00 14,52 3,10 245 2 00 15,65 3„25

14*50 3,90 0,1579 25„8

A V - 3,21 CM,3

AFTER BACK-DRAINAGE, WEIGHT OF WATER - W + AV - 29,50 GMS,

WATER CONTENT - 31,4% Remarks 2