Calhoun: The NPS Institutional Archive

Theses and Dissertations Thesis Collection

1977

Determination of undrained shear strength of marine

clays by combined vane and direct shear analysis.

Foster, James Edward

University of Washington

http://hdl.handle.net/10945/18076

MRUYIOIOXUBMRYMAimRfiAftMESCHtOl

DETERMINATION OF UNDRAIMED SHEAR

STRENGTH OF MARINE CLAYS BY COMBINED

VANE AND DIRECT SHEAR ANALYSIS

BY

JAMES EDWARD FOSTER

'I

A thesis submitted in partial fulfillment

of the requirements for the decree of

Master of Science in Civil Engineering

University of Washington

1977

Approved by(Chairman of Supervisory Committee)

Program Authorizedto Offer Degree

Date

Ad^?

own moot ummvNAVAL POSTGRADUATE SCHOOL

In presenting this thesis in partial fulfillment of

the requirements for a Master's degree at the Univer-

sity of Washington, I agree that the Library shall

make its copies freely available for inspection. I

further agree that extensive copying of this thesis

is allowable only for scholarly purposes. It is under-

stood

,

however, that any copyini? or pub lication of this

thesis fo:r commercial pur poses

,

or for financial gain,

shall not be allowed with out my wri tten permission

,

Signature

Date

TABLE OF CONTENTS

Page

LIST OF TABLES iv

LIST OF FIGURES v

LIST OF PLATES vii

ACKNOWLEDGEMENTS viii

CHAPTER

I INTRODUCTION 1

II DISCUSSION OF SHEAR STRENGTH 5

1. Methods of Collecting andAnalyzing Data 5

2. Effects of Loading History onShear Strength 7

3. Laboratory vs. In-Situ Resultsfor Shear Strength 8

4. Theories for Shear Strength 9

III DISCUSSION OF DIRECT AND VANE SHEARAPPARATUS AND TESTS 17

. 1. Direct Shear Test 17

2. Direct Shear Apparatus 22

3. Vane Shear Test 2h

h . Vane Shear Apparatus 29

IV SAMPLES AND TEST PROCEDURE 31

1. Samples 31

1.1 Pacific Ocean Sample - KK076 31

1.2 Gulf of Mexico Sample - GM 32

1.3 Atlantic Ocean Sample - ATL 32

2. Test Procedure 33

ii

CHAPTER

V

VI

Page

EXPERIMENTAL RESULTS AND ANALYSIS 36

1. Water Content vs. LogConsolidation Pressure 36

1.1 Sample - KK076 36

1.2 Sample - GM 37

1.3 Sample - ATL 37

1.4 Discussion of Water Content vs.Log Consolidation Pressure 37

2. Water Content vs. Log Shear Stress 38

3. "Combined" Shear Strength Analysis 38

CONCLUSIONS AND RECOMMENDATIONS 4 5

1. Conclusions 45

2. Recommendations 46

BIBLIOGRAPHY

TABLES

FIGURES

PLATES

47

49

54

107

iii

LIST OF TABLES

TABLE Page

1 Classification of sensitivity ^9

2 Geotechnical properties of a typical corefrom deeper portions of the Gulf of Mexico 50

3 Properties of near surface samples fromthe seafloor 51

4 Soil properties vs. depth - Sample KK076 52

5 Soil properties vs. depth - Sample ATL 53

iv

LIST OF FIGURES

FIGURE Page

1 Soil parameters vs. depth 54

2 Cone penetrometer 55

3 Cone penetration data compared to vaneshear data 56

4 In-situ vane shear strength vs.vane penetration 57

5 Void ratio vs . log of pressure 58

6 Generalized e-log P diagram 59

7 Shear strength - deformation diagram 60

8 Shear strength diagram 60

9 Shear strength hysteresis loop 61

10 Determination of the cohesion andfriction components, C and

<J>

' 62

11 Water content vs. log consolidation pressure 63

12 Illustration and definition of terms for"combined" vane and direct shear teststrength analysis Gh

13 Types of soil shear tests 65

1*1 Types of direct shear tests 65

15 Atterberg Limits of test samples 66

16 Water content vs. log consolidationpressure - Sample KK076 67

17 Water content vs. log consolidationpressure - Sample GM 68

18 Water content vs. log consolidationpressure - Sample ATL 69

19 Water content vs. log shear strength -

Sample KKO76 70

20 Water content vs. log shear strength -

Sample GM 71

21 Water content vs. log shear strength -

Sample ATL 7?v

FIGURE Page

22 Shear strength vs. normal stress andconsolidation pressure - Sample KK076 73

23 Shear strength vs. normal stress andconsolidation pressure - Sample GM 74

24 Shear strength vs. normal stress andconsolidation pressure - Sample ATL 75

25 "Combined" shear strength analysis -

shear stress vs. normal stress andconsolidation pressure - Sample KK076 76

26 "Combined" shear strength analysis -

shear stress vs. normal stress andconsolidation pressure - Sample GM 77

27 "Combined" shear strength analysis -

shear stress vs. normal stress andconsolidation pressure - Sample ATL 78

28 Illustration of "friction" componentof direct shear test 79

2Q Water content vs. ratio C /C, for a =0 80J v d n

30 Plasticity index vs. ratio C /C, for a =0 8lJ v d n

A-l Recording chart calibration for directshear test 82

A-2 Common area vs. displacement for directshear test ( R = 1.31 in.) 83

A-3 Common area vs. displacement for directshear test (R = 1.0 in.) 84

A-4 Recording chart calibration forvane shear test 85

A-5 - A-l4 Test Results - Sample KK076 86

A-15 - A-20 Test Results - Sample GM 96

A- 21 - A-25 Test Results - Sample ATL 102

vi

LIST OF PLATES

PLATE Page

1 Direct shear test apparatus 107

2 Direct shear load cell 108

3 Strain gage conditioner anddata strip recorder 109

4 Direct shear box, ring adapters,and pressure plates 110

5 Assembled modified direct shearbox and pressure plate 111

6 Checking horizontal displacementduring direct shear test 112

7 Monitoring consolidation indirect shear machine 113

8 Vane shear machine, strain gagevane torque pick-up replacement ll^J

9 Modified Wykham-Farrance vaneshear machine 115

10 Vane shear test in progresswith sample in direct shear box 116

vii

ACKNOWLEDGEMENTS

The author wishes to express his profound apprecia-

tion to Professor Mehmet A. Sherif, the Chairman of his

Supervisory Committee, for his dynamic and unselfish

guidance and encouragement. In addition, the author wishes

to thank the other members of his Committee, Professor

Richard H. Meese and Dr. Isao Ishibashi for their sug-

gestions and guidance. Thanks are also extended to Mr.

Bob Bea of the Shell Oil Company and Dr. Leland Kraft,

McClellan Engineers, Inc. for their assistance in ob-

taining the Gulf of Mexico sample and to Dr. Armand Silva

and Mr. Dave Calnan, University of Rhode Island for their

assistance in obtaining the Atlantic Ocean samples.

Gratitude is also extended to the U.S. Navy for having

funded my pursual of this Master of Science degree.

Finally, the author expresses his sincere gratitude

to his wife, Susan, daughter, Carrie and son, Travis for

their patience and help in the preparation of this thesis.

viii

CHAPTER I

INTRODUCTION

With the rapid increase in offshore exploration and con-

struction in the 1970 's, the need to determine quality geotech-

nical properties of marine sediments has greatly increased.

Since the initial stages of off-shore developments in shallow

Gulf of Mexico waters in the late 19^0' s, submarine soil testing

has been required in progressively deeper water. Testing is

presently being accomplished in water depths exceeding 1000 feet

(Bhushan, et. al. ref. 3) from dynamically positioned drillships

and samples have been taken from depth exceeding 3 miles (ref.

20). As the water depths increase, the structures being construc-

ted are designed to resist larger and larger vertical and lateral

loads, amplifying the requirement for quality geotechnical pro-

perty determination for the design of their foundations. There

are no standardized procedures for obtaining geotechnical pro-

perties and there is no agreement within the off-shore design/

construction community as to what tests (in-situ or laboratory)

are the best for determining geotechnical properties. Eide (ref.

5) in his comprehensive review of applications of soil mechanics

to off-shore structures in 197^, pointed out that most of the

available drilling and sampling techniques were rather crude and

result in significant disturbance of the sample, hence results

of tests on such samples show great scatter making the selection

of design parameters very difficult.

Presently, empirical formulas are being used almost exclu-

sively for designing seafloor foundations on marine clay.

2

McClellan (ref. 11) presented design procedures which are currently-

being utilized by McClellan Engineers, Inc. for ocean foundations.

These procedures which have been generally accepted by the pro-

fession involve equations of the follov/ing types:

Q = A(a +2C)A 1-1s m m s

where: Q = total friction capacity of a pile

X = frictional capacity coefficient

a = mean effective vertical pressure for depthof pile embedment

C = mean undrained shear strength for depth ofm pile embedment

A = surface area of embedded pile

Valent in ref. (7) presented the following equation for the

uplift resistance of an embedded plate (anchor) in cohesive soils:

Q = N C A (0.84 + 0.16 B/L) 1-2u cu

where: Q = total uplift capacity of a plate

N = uplift capacity factorcu l f J

C = undrained shear strength near the plate elevation

A = projected area of the plate

B = one-half the width of the plate

L = the length of the plate

Hermann in ref. (6) presented the following equation for

the bearing capacity of a footing on the ocean floor:

%lt Kl

Nc

C + K2 * N

yB + NqY D 1-3

where: q , . = the ultimate bearing capacity of the footing

K, ,K„ = shape coefficients

N ,N ,N = bearing capacity factorsc ' y Q

C = cohesive strength

Y = submerged soil density

B = width or diameter of footing

D = depth of footing base below mudline

The value of C, the undrained shear strength, is the key

value in each of the above equations. There is no agreement as

to the best method for determining C. in this paper, the author

will focus on one procedure for determining undrained shear

strength of marine clays by utilizing combined vane and direct

shear tests which will provide quality, economical data from re-

latively "undisturbed" samples. Furthermore, an attempt is made

to corroborate the equipment and test procedures used by Webb

(ref. 21) and to expand his data and theory for shear strength

envelope to determine application to a general case versus a

specific case. This investigation will study the relationship

between the direct shear test and the vane shear test as deter-

mined from a combined analysis of clay samples from the Pacific

Ocean, the Gulf of Mexico and the Atlantic Ocean.

The equipment used was: a) direct shear device modified to

receive a relatively "undisturbed" marine sample, to have a re-

fined vertical loading system, and to provide electronic print-

out of data, b) vane shear device modified to provide constant

and controlled strain and electronic printout of data.

Consolidated undrained (CU) tests were conducted on samples

that were consolidated under varying normal loads in the direct

shear machine. These direct shear tests were followed imme-

diately by vane shear tests on those same samples, performed

'I

while the samples remained In the direct shear box. The data was

plotted and analyzed and a general theory proposed that will des-

cribe the entire strength envelope of marine clays utilizing

only two samples. Acceptance of this theory will greatly reduce

the number of samples and testing required to determine the

strength envelope of a marine clay.

CHAPTER II

DISCUSSION OF SHEAR STRENGTH

II - 1 Methods of Collecting and Analyzing Data

For determining the shear strength of today's marine clay, the

vane shear and penetrometer tests are primarily utilized in-situ,

v:hile the vane shear and triaxial test are most often used in

the laboratory. For terrestial soils, the triaxial test is con-

sidered to provide the best results because it has better control

over stress, strain, pore pressure measurement and it does not

have a pre-determined failure plane. However, primarily due to

sampling methods, recovery and handling, the triaxial shear

strength test is not as reliable when dealing with marine soils.

In the marine environment we are forced to cope with materials

whose moisture contents are near or exceed the liquid limit

(figure 1). Historically, the direct shear test on a marine

clay has been thought to be unreliable because of unknown drain-

age conditions. However, the author feels that under controlled

conditions the direct shear test can provide reliable results.

The direct shear test utilized in conjunction with the vane

shear test will be investigated in this paper.

The cone penetration device is widely used to determine

shear strength of marine clays. There are several types of pene-

trometers, all of which basically involve transcribing the pene-

tration energy to values for shear strength. Figure 2 is repre-

sentative of a typical cone penetrometer. This method has the

distinct advantage of providing a continuous strength profile

with depth. The cone penetrometer is usually used in conjunction

6

with a vane shear device. The vane is essentially used to

"calibrate" the penetrometer profile. Such a system is used by

the Naval Civil Engineering Laboratory (NCEL) on the DOTIPOS

(Deep-Ocean Tests in Place and Observation System) retrievable

platform. Figure 3 represents correlations resulting from this

type of combined testing.

Soil "Sensitivity" is important when considering the shear

strength of marine clays. Sensitivity is defined as the "undis-

turbed" shear strength divided by the "remolded" shear strength

(figure 4). Table 1 indicates the range of values of sensiti-

vity. Some highly sensitive clays have little or no strength

after being disturbed. There appears to be a close relationship

between liquidity index and sensitivity (Buchan, et . al . , ref.

15); sensitive clays with high moisture content have liquidity

indices much greater than one. It has been shown that abrupt

changes in moisture content bring about abrupt changes in sensi-

tivity (Buchan, et.al., ref. 15)

•

In general, shear strength and bulk density increase with

depth below the mudline, while water content and void ratio de-

crease. Table 2 gives a good indication as to the typical mag-

nitudes of shear strength values that can be expected. Shear

strengths of marine clays range from values as low as 0.1 psi

to values exceeding 5-0 psi, at water contents ranging between

30$ and 300$ (Noorany, ref. 13). Calcareous oozes indicate an

undrained shear strength of 0.5 to 2.5 psi. These values are

surprisingly low for such deep burial (^00-500 feet below mudline)

and are probably the result of a high degree of disturbance

(Noorany, ref. 13). Attempts have been made to simulate in-situ

7

conditions by consolidating in a triaxial cell at effective over-

burden pressure. The results were values for strength in excess

of 10 times the undrained vane strength. The difference again

was attributed to disturbance and change in the stress system as

a result of sampling.

II - 2 Effects of Loading History on Shear Strength

Noorany (ref. 13) summarized the relationship between shear

strength and consolidation for marine sediments. There are areas

in the oceans where sediments accumulate at such a high rate

that there is not adequate time for consolidation; pore pressure

builds up, resulting in a soil that has very little strength for

great depths. These sediments are termed under-consolidated.

The area off the mouth of the Mississippi River is such a region,

having an estimated deposition of approximately 1,500,000 tons

of material daily. Shear strength values determined in 250 feet

of underconsolidated clay near the South Pass area of the Gulf

of Mexico showed little change in strength with depth and was

nearly equal to the determined cohesion of that clay (Noorany,

ref. 13). Terzaghi calculated that for an underconsolidated

marine soil, slopes of 10° could be subject to failure if that

sediment reached a depth of ^7 feet (ref. 12).

Normally consolidated clays exhibit ratios of unconsolidated

undrained shear strength, C , to effective over-burden pressure,

P', in the range of 0.1 to 0.4. This ratio for the Gulf of Mexicoo

prodeltaic clays averages 0.31- The value of shear strength pre-

viously mentioned for calcareous oozes were also representative

of normally consolidated marine clays.

8

Overconsolidated and "apparently" overconsolidated clays

exhibit higher shear strengths; clays of the South Timbalier

area of the Gulf of Mexico have C values of almost 10 psi.

Table 3 shows typical values for some overconsolidated clays.

It should be noted that the C /P ' ratio looses meaning near the

mudline as P' approaches zero. Overconsolidation is usually

associated with removal of overburden, however, massive erosion

of the continental shelf or the abyssal plain is unlikely.

Figure 5 showing e-log P curves for Gulf of Mexico sediments,

indicates consolidation behavior similar to that for overcon-

solidated clays. This behavior is attributed to the cementation

brought about by the chemical alteration of the volcanic or car-

bonate fraction of the sediment.

The terms "under", "over" and "normally" consolidated, al-

through appropriate for land and shallow water soil mechanics,

are not necessarily appropriate for deep water sdeiments (Rich-

ards, ref. 15)- It is known that any factor that imparts unusual

structural strength to a soil will result in an e-log P diagram

that appears to represent an overconsolidated condition. It

has been further shown that complete remolding of samples re-

duces the consolidation curves to near straight lines (figure 6)

II - 3 Laboratory Vs. In-Situ Results for Shear Strength

Since the initial attempts at marine soils investigations

it has been known that in-situ values differ from laboratory

values despite extreme care to simulate seafloor conditions. The

reasons for these deviations and ways to correct them are the

objects of tremendous research effort. Numerous papers on this

subject are presented each year at the Annual Offshore Technology

Conference in Texas. Some of the factors producing deviation in

laboratory vs. in-situ values were summarized by True (ref. 17)

and include the following:

1. Replacement of in-situ stress with uniform hydrostatic

effective stress.

2. Mechanical sampling disturbance; hydrostatic stresses

and soil structure are changed by disturbance from sampl-

ing, transporting, storage, trimming, and test sample

preparation. The result is decreased shear strength and

compressibility

.

3. Pore water expansion: sea water expands 0.5^/1000 m.

,

thus a sample from 3500 meters has a pore pressure ex-

pansion of approximately 2%. The result is a reduction

of effective stress, strength and compressibility.

4. Changes in pressure affect dissolved pore water gases.

5. Changes in temperature causes direct changes in stresses

and strength.

6. Changes in temperature and pressure can cause rapid de-

composition or growth of organic matter in the soil.

II - k Theories For Shear Strength

Shear strength as defined in terms of soil failure, has long

been the subject of discussion and disagreement. The develop-

ment of shear strength concepts began with Coulomb in 1776.

Since that time, complicated apparatus has been developed in

order to more fully define the elements of shear strength. For

this study, the direct shear test was combined with the vane shear

10

test to determine the strength envelope. Both of these tests

generate enforced failure planes between stationary and moving

equipment or sample sections. A well-defined peak in the shear

stress versus strain curve (figure 7) is usually considered to

be the shear strength of a soil. The shape of this curve is

very much dependent on loading type, shearing rate, and drainage

conditions (Hvorslev, ref. 1).

Coulomb's first expression of soil failure criteria was:

xf

= C + of

tan (ji 2-1

Where xf

is the shear stress at failure, C is cohesion, of

is

the normal stress applied at failure, and<f>

is the angle of in-

ternal friction. Coulomb considered C and cf> to be constant for

a given soil and that simple tests could be used for their deter-

mination. Subsequent investigations have shown these parameters

to vary widely depending on such factors as initial water content,

shearing rate and anisotropy (Wu, ref. 22).

Casagrande, as well as Terzaghi, concluded that normal stress,

f , should be replaced by effective normal stress, ol where:

ol = o„ - y 2-2

with the pore water pressure, y, equal to zero in fully drained

tests. Terzaghi expressed the soil failure criteria in terms of

effective stresses as opposed to total stresses. The Terzaghi

failure criteria appears as

tf

= C + o£ tan 4>

'

2-3

where C' and<J>

' are the effective cohesion and effective angle

11

of Internal friction. This function is illustrated as a part of

figure 8. The line OAC represents the shear strength line for

a normally consolidated clay with C = and 4> =<J>

'. Precon-

colidation of a clay has considerable effect on the representa-

tion of shear strength. The line BA is the shear strength curve

for a clay preconsolidated at a pressure of o' and exhibits an

angle of internal friction of <(>' . Preconsolidat ion to pressures

other than a' produce shear strength lines represented by the

dashed line parallel to BA . The significance of this is that C'

is proportional to the preconsolidation pressure a' in the fol-

lowing manner:

C = a' tan* 1 2-kp c

therefore equation 2-3 would appear as (Hvorslev, ref. 1)

t„ = 0' tan <j> ' + a ' tan <j>

' 2-5Af p

vc f r

For a normally consolidated clay, this formula can be modified

further such that

t„ = o' tan d> ' + a I tan <j>

' 2-5Bf f c i r

Hvorslev referred to this presentation as the Krey-Tiedman fail-

ure criteria. The general concept was proposed initially by

Krey and subsequently extended by Tiedman. It should be noted

that equations 2-4 and 2-5, as well as their representation in

figure 8, are based upon results of fully drained direct shear

tests on normally and overconsolidated clays. The first term

on the right side of equation 2-5B can be referred to as the

cohesion component and the second term as the friction component,

12

thus the anomally of having two angles of internal friction, t

'

and tj>' , for the same clay and no cohesion for a normally consoli-

dated clay is thereby eliminated (Hvorslev, ref. 1).

Terzaghi (Wu, ref. 22) determined that the stress or loading

history of a sample affects the determined shear strength. Hvor-

slev (ref. 1) summarized this effect which is represented in

figure 9- This figure indicates different values of a' and ol.

The unloading and reloading of a sample produces the hysteresis

loop shown in figure 9- It is evident that the idealized straight

lines represented in figure 8 are actually complex curves.

The dashed line, DE, in figure 9 represents a slight double

curvature noted by several researches (V/u, ref. 22) from tests

on undisturbed samples. D represents the strength of a sample

at pressure oj, that was preconsolidated at a'. If tests are^ d ^p

performed at values of normal pressure greater than o\, the

strength line will pass to the reloading curve of the hysteresis

loop

.

Hvorslev (ref. 1) conducted exhaustive studies using direct

shear tests on Vienna and Little Belt clays in order to better

define the effect of over-consolidation. Hvorslev summarized

his results in an equation very similar to the Krey-Tiedman

formula

T f= C

e+

CT ftan

*e2 " 6

where C' and 6* are the "true cohesion" and "true angle of in-e v e &

ternal friction". Hvorslev concluded that C is a function ofe

water content only while $ ' is constant for a given soil. In

order to separate the two strength components, it is necessary

13

to conduct tests on a series of samples having the same water

content at failure, but different effective stresses. This can

be accomplished by using the consolidation, unloading, and re-

loading technique illustrated in figure 10. It has also been

shown that the true cohesion at any water content Is proportional

to the equivalent consolidation pressure, o . In the triaxial

test, a is the consolidation pressure producing that water con-

tent in a normally consolidated sample (Bishop and Henkel, ref.

2). Only drained or consolidated-undrained tests with pore

pressure measurements can be used to evaluate the true cohesion.

Besides being difficult to determine, the parameters of the

Hvorslev failure criteria were formulated based upon drained

direct shear tests that considered only peak shear stress as

the failure strength. It is therefore questionable as to the

application of this criteria to other test results (Wu, ref. 22).

A change in void ratio or water content causes a change

in the shear strength of a clay, therefore a complete expression

of shear strength should include consolidation characteristics.

The semi-logarithmic plot of the consolidation diagram (u% vs.

Log P) of a normally consolidated clay is usually straight (Hvor-

slev, ref. 1). Figure 11 shows the consolidation diagram for a

sample consolidated normally, unloaded, and then reloaded.

As an alternative to the Hvorslev method of determining

shear strength, Webb (ref. 21) has proposed a simple theory for

determining the undrained shear strength envelope of marine

soils. He ran a series of "combined" vane and direct shear tests

on naturally occurring marine soils. A sample specimen was con-

solidated and sheared in the direct shear machine under a normal

ll\

stress equal to that consolidation pressure. The normal load

was immediately removed and a vane shear test was run. The data

derived from one direct shear test and the subsequent vane shear

test is referred to as one "combined" shear strength plot. Be-

cause the vane shear tests are conducted at zero normal stress,

their resulting shear strength can be thought of as being a

function of "preconsolidation" pressure.

When plotting shear stress versus normal stress (direct

shear) or consolidation pressure (vane shear), Webb found the

vane shear plot to be linear over all values of consolidation

pressure. The direct shear plot was higher and roughly parallel

to the vane shear plot for a < P (preconsolidation pressure)

and for o > P the slope of the plot increased and passedn c K ^

through the origin when extended back. This last portion of the

direct shear plot is usually interpreted as representing the

strength of normally consolidated samples. These observations

of his experimental results led Webb to suggest a "combined"

analysis of shear strength that utilizes direct and vane shear

tests on only two samples to determine the complete strength en-

velope. The terms, definitions and relationships of this theory

are depicted on fig. 12. The plot of direct shear strength vs.

normal stress was referred to as the "Total Failure Stress En-

velope". The plot of vane shear strength vs. consolidation pres-

sure was termed the "Cohesion Line," since the vane test measures

only sample cohesion. The angle of slope of the cohesion line

was designated as cf> , while the angle' of slope of the normally

consolidated portion of the total failure stress envelope was

referred to as * . The value of shear stress at a equal toH n n ^

15

zero was termed C -, . C was the value of vane shear stress at

consolidation pressure equal to zero. The difference in the

terms C, and C is referred to as AC. The value of o aboved v n

which the total failure stress envelope is linear is termed the

"apparent" precompression stress, P .

The factor that made this theory possible was the obser-

vation that the total failure stress envelope, as defined by

the direct shear test results, is rougnly parallel to the co-

hesion line for values of a less than P . As illustrated inn c

figure 12, the angle of slope of the total failure stress en-

velope is <j) for a less than P . Therefore, the entire total* c n c '

failure stress envelope can be drawn if C , , <j> , and<J>

are known.j-d ' c ' n

It follows that only two "combined" shear strength tests are

required to generate the total failure stress envelope; one test

at o and consolidation pressure equal to zero and the other atn f m

a and consolidation pressure greater than P . A preliminary

estimate of P is required to ensure that o for the second datac M n

point is greater than P . This method gives four data points;

two direct shear strengths and the two vane shear strengths, C,

and C . <j> is determined by connecting C with the vane shearv c v

strength at the higher consolidation pressure. A line is drawn

from the origin to the direct shear strength value at the higher

value of a . This enables the determination of<J>

. Finally, an n J '

line is drawn from C,

, at an angle of slope <}> , to intersect

the line drawn through the origin. The result is the total fail-

ure stress envelope that would have resulted from a series of

direct shear tests at progressively increasing values of normal

stress .

16

Mathematical descriptions of this theory are as follows:

a) For a <P t„ = C,+o tan <j> 2-7n c f d n c

b) For o >P t _ = C, + P tan $ + (o - P ) tan <j> 2-8n c f d c en c n

c) For o > P t- = C +o tan <\> +AC+(a -P )(tan <\> -tan $ )n c f v n en c n c

2-9

V/here t„ = the maximum shear stress at failure

The purpose of this investigation will be to validate this

theory. Test apparatus and procedures similar to those used by

V/ebb will be utilized. A general set of samples will be used

to determine general applicability of the theory.

17

CHAPTER III

DISCUSSION OF DIRECT AND VANE SHEAR APPARATUS AND TESTS

As outlined in the introduction, this study uses the direct

shear test in conjunction with the vane shear test in a combined

strength analysis of marine clays. Both tests have been subject

to criticism and praise. This chapter will outline the advan-

tages, disadvantages, apparatus, application, and the test pro-

cedure associated with both tests.

Ill - 1 Direct Shear Test

The direct shear test is one of the simplest soil strength

tests known as well as being the oldest; it was first used by

Coulomb in 1776 (Lambe and Whitman, ref. 10). The cylindrical

or triaxial shear test and the torsional shear test are the other

commonly used methods for soil shear strength determination. The

vane shear and cone penetrometer tests were previously discussed

and continue to have limited use.

The torsional shear test is more commonly used in Europe.

In this test, a cylindrical soil sample is twisted by applying

a twisting moment at the top and bottom (figure 13)- A lateral

stress can be applied to the sample if desired. During the dir-

ect shear and triaxial shear tests, the sample becomes badly de-

formed causing non-uniform stress and strain thus making the

measurement of the failure surface area difficult. The torsional

shear test has the advantage in that the cross-section remains

more nearly constant during shear (Lambe, ref. 9). This ad-

vantage is out-weighed by the fact that the shear displacements

vary with radius, promoting progressive failure of the soil

18

sample. The use of an annular sample somewhat reduces this pro-

blem. The torsional shear test has the definite disadvantage

of requiring considerable specimen handling for test preparation

The triaxial test involves the axial loading of a cylindri-

cal sample (figure 13) that is usually encased in a rubber mem-

brane. Uniform pressure is applied using a pressure cell con-

taining the sample and surrounding fluid.

The direct shear test requires the placing of a soil sample

in a container having fixed and movable sections. The test is

performed by displacing the sections of the container relative

to each other. During this displacement, the soil is sheared

along one or more internal surfaces. The only resistance to

that shearing is provided by the soil. There are several types

of direct shear tests and apparatus with their names being de-

rived primarily by the design of the soil container or the shape

of the shear surface. These include (figure 1*0 :

1. 2-piece single shear box

2. single or double ring shear apparatus

3. annular or "punching" shear apparatus.

The annular direct shear test provides a more nearly con-

stant shear area than does the box or ring shear test, and con-

sequently, more uniform strains (Lambe, ref. 9)- The test is

more complex to perform and the specimen is more difficult to

prepare than those of the box or ring shear type of test.

In the double ring shear apparatus, the shearing force is

applied to a central, movable ring (figure 1*4). Samplers have

been designed such that their liners arc composed of continuous

close fitting rings (Lambe, ref. 9). These rings fit directly

19

into the ring shear device. This eliminates the transfer of the

sample from the liner to the shear apparatus, as well as any

required sample trimming. This advantage is somewhat questionable

because the sampler is necessarily thick walled having a high

area ratio, A (Terzaghi and Peck, ref. 18). High area ratios

result in "disturbed" (A greater than 20£) samples, increasing

the danger of remolding and weakening the soil before testing.

Of the three direct shear tests discussed, the 2-plece

simple shear box is the most used in the United States. A basic

representation of the simple shear box appears in figure 1*J . The

soil to be tested fills the two sections of the box and is fitted

with a plate on top and bottom. The plates can be pervious or

impervious depending on the nature of the direct shear test

being conducted. Usually the lower section of the shear box is

fixed and the upper section is allowed to move. The reverse ar-

rangement is sometimes used although is is considered to give too

high values for shearing resistance because of restraint to sample

expansion (Tschebotariof f , ref. 19)- In either case, a normal

force, N, is applied to the upper plate distributing that force

over the soil surface. A lateral load, P-, is applied to the

movable section of the shear box. The direct shear test is fur-

ther designated by the manner in which loading is applied and

displacement measured. The test can be either a stress-controlled

direct shear test or a strain-controlled direct shear test.

In the case of the stress-controlled direct shear test, the

lateral force is applied in discrete increments, often by using

dead weights. Shear displacement is recorded as a function of

time until it ceases or until failure occurs. Failure is in-

20

dicated by a rapid increase in displacement. The stress-controlled

test is preferable in those situations requiring very low rates

of loading. The load can be kept constant for any given period

of time. It is more difficult to obtain a value for ultimate

strength due to the rapid shear displacement that occurs immedia-

tely following the exceeding of the maximum shear resistance of

the soil (Lambe, ref. 9)- This test is used for most soil

mechanics applications.

The strain-controlled direct shear test is used mostly for

research (Jumikis, ref. 8), but has some practical applications.

Normally, controlled and constant strain (shear displacement) is

applied to the movable box section by means of a gear assembly

that is either manual or motorized. The force is usually de-

termined by using a calibrated proving ring and is recorded as

a function of time or displacement. This type of direct shear

test has the advantage of providing a good measurement of both

peak and ultimate shear resistance (Lambe, ref. 9)- The stress-

controlled test requires the manual regulation of loading and

is thus more difficult to conduct.

Jumikis (ref. 8) summarized the disadvantages of the dir-

ect shear test as follows:

1. The shear area in a direct shear test is constantly

changing causing unequal distribution of shear and nor-

mal stresses over the potential sliding surfaces. This

makes the stress conditions across the sample very com-

plicated .

2. The water content of saturated samples of many types

changes rapidly as the result of changes in stress.

21

3. There is question as to the effect of the lateral re-

straint of the walls of the shear box. The stress con-

ditions produced thus do not correspond to conditions

in a foundation. The shear stress obtained by dividing

shear force by rupture area is only approximate.

k . The time required to remove the sample from the test

apparatus can effect the water content determination.

Also, the water content at the sample boundaries show

different values than the sample interior. (Hvorslev,

ref. 1).

5- The complete state of stress at any time prior to fail-

ure is unknown.

6. The majority of "undrained" tests using the direct shear

test are not completely undrained. There appears to be

no way to determine to what degree these tests approach

undrained conditions. Ultimate strength is more affected

by this unknown merely because of the longer time re-

quired to reach ultimate shearing resistance (Lambe, ref.

9).

'

The advantages of the direct shear test comprise a short but

important list, especially as it concerns marine clays.

1. The direct shear test offers a simplicity of operation

requiring less test time and sample handling.

2. The smaller height of sample used in the direct shear

test requires less drainage time. This facilitates

more rapid Q or S tests. The shear rate can be larger

than that used in the triaxial test.

3. The direct shear test requires much less sample than

22

does the trlaxial test.

The direct shear apparatus used in this study was a strain-

controlled single shear box type. The complete apparatus ap-

pears on Plate 1.

Ill - 2 Direct Shear Apparatus

The direct shear apparatus (Plate 1) was originally designed

and built by the Department of Civil Engineering of the Univ-

ersity of Washington and was modified slightly to conform to

the requirements of this study. This system is designed to per-

form strain-controlled direct shear tests.

Shear displacement is provided by a variable-speed motor

coupled directly to a multiple output shaft gear box. This

combination is manufactured by Karol Warner, Inc., and provides

for a wide range of rotational speeds by the proper selection

of output shaft and motor speed. The output shaft is coupled to

a gearbox mounted on the direct shear test stand. This gear ar-

rangement translates the rotational motion into the transverse

motion used to provide shear displacement in the shear box. The

various output shaft and motor speeds were calibrated against

shear displacement as a function of time. The strain (shear dis-

placement) rate can be accurately controlled from 0.001 in/min.

to 0.5 in/min. (Webb, ref. 21). The gearbox offers output ro-

tational rates that increase in steps of 10. The output shaft

designated as 1/10 rotates at 1/10 the rate of the variable

speed motor. Using a motor setting of 55 and the 1/10 output

shaft, a translational displacement rate of the shear box of

0.06 in/min. was observed.

23

The majority of commercially manufactured strain controlled

direct shear machines use calibrated proving rings to measure

the shearing force applied to the sample. The system used in

this study employs a BLH Electronics, Inc., Type U3G1 load cell

(Plate 2) between the second gear assembly and the shear box.

This load cell was calibrated using a proving ring and the

Gould strip recorder (Plate 3). The calibration refers only to

this particular load cell-strip recorder combination at the

strain gage conditioner and chart sensitivity settings speci-

fied. The calibration appearing in the appendix as figure A-l

was determined by Webb (ref. 21) and verified by the author.

The strip recorder provided for more accurate determination of

force vs. displacement. It has the added advantages of making

the recording of the test easier as well as providing an im-

mediate and permanent visual presentation of the test data.

The direct shear box is shown on Plates 4 and 5- The area

2of the shear box in its original configuration was 9 in . The

top portion of the box is fixed and the bottom is free to move.

There is a porous stone at the bottom of the lower section allow-

ing drainage. The shearing surface is 0.5 inches above this

stone. The samples used in this study have a round cross-section

Ring adapters (Plate ^) were designed to fit inside the square

shear box and accept the samples directly from their liner.

Plate 5 shows the ring adapters in place along with the vertical

pressure plate. Adapters were designed for liners with a 2.62 in

inside diameter as used to collect Pacific sample KK076 and a

2.00 in. inside diameter for the Gulf of Mexico and Atlantic

samples. The Gulf of Mexico samples were approximately 2.25 in.

2H

In diameter and were trimmed to 2.00 in. with a thin-walled

cutter. The atlantic samples v/ere 2.00 in. in diameter.

The air pressure operated vertical loader, apparent in

Plate 1, used for conventional applications of the direct shear

test, proved inappropriate for this study. This loader did not

allow for accurate control of small values of normal load. A

simple lever arm system was designed to replace the air loader

(Plates 1, 6 and 7). The arm has a lever ratio of 10 to 1. By

knowing the cross-sectional area of the ring adapters, the de-

sired normal load was easily applied by placing the proper weights

in the tray.

The area of sample resisting shear was reduced as a function

of displacement as the test progressed. This area is easily

determined when the shear box has a rectangular or square sec-

tion. This determination was more difficult for overlapping

circular sections as was the case in this study. This area is

plotted as a function of displacement in the appendix, figure A-2

for the 2.62 in. samples and figure A-3 for the 2.00 in. samples

and was based upon the following relationship:

-1 _X_

2R90° "~* L ^ ^2R

2ttcos

2R . . _i . xA = R { ^ - sin [2cos x (^)]} 3-1

where A is the coincidental or "common" area of two overlapping

circles of radius R, as a function of displacement, X.

Ill - 3 Vane Shear Tests

Granular soils that are free draining and contain signi-

ficant amounts of water, present little problem when determining

25

shear strength, either in the field or the laboratory. V/ith

marine clays, the foundation engineer is confronted v/ith the

problem of determining the strength of a saturated clay with

very low permeability that does not allow free drainage. The

pore pressures associated with shear stress application do not

readily dissipate in such materials. The time required for

dissipation of these pore pressures, with its accompanying in-

crease in shear resistance, is a function of the boundary con-

straints, dimensions, and consolidation characteristics of the

particular clay material.

When testing a saturated clay using the unconfined compres-

sion test or triaxial test with the minor and the intermediate

principal stresses equal to zero, the result is the <j>= con-

dition described by Terzaghi (ref. 18). The shear strength

under these conditions is described by the equation:

S = C = %q 3-2^Hu

Where S is the shear strength, C is the cohesion, and q is the

ultimate unconfined compressive strength. There are relatively

quick, uncomplicated strength tests available when the undrained

condition exists, whether in the field or the laboratory. The

test that fulfills these needs is the vane shear test. The vane

test is analogous to the Q test, if carried out rapidly enough.

The vane test, in its simplest form, consists of pushing a four

bladed vane, mounted on the end of a thin rod, into the soil

with as little disturbance as possible. The vane is rotated

and the torque required to turn the vane is recorded as a func-

tion of vane rotation. In more refined field vane shear tests

26

the vane is pushed into the soil inside a shield and is protruded

only at the time of the test (ref. 18). Elaborate laboratory

vane devices are available that can control boundary conditions

and stress-strain rates during testing.

Investigation has shown that the soil fails along a cylin-

drical surface circumscribed by the outer vane edges. Both the

top and bottom of the vanes are included as failure surfaces

in most vane shear tests. The relationship between angular ro-

tation and torque must be known along with applied torque and

vane dimensions in order to determine shear strength. The re-

lationship is expressed by the formula:

2 3

M = it t (2gS + \-) 3-3

where M = net applied torque, x = C = q /2 = shear strength,

D = vane diameter, and H = vane height.

If the top of the vanes are not into the soil enough to

contribute to the resistance, the formula appears as:

The test and formulas make the assumption that the failure is a

right circular cylinder with a diameter equal to the vane blade

diameter, D, in which the stress distribution at maximum torque

is everywhere equal on the surface of the cylinder.

Sensitivity can be determined using the vane shear test.

The vane is rotated several times after determining the "undis-

turbed" strength and then allowed to consolidate. The test is

then repeated thus measuring "remolded" strength from which the

27

sensitivity is determined. Values for sensitivity determined in

this manner differ from those determined if the sample is re-

molded by kneading (ref. 18).

Sibley and Yamane invented (1965) a small, convenient, hand-

held vane shear device known as the TORVANE. It has gained wide

acceptance and is widely used, both in the field and laboratory.

The vanes are pushed to their full height into the soil and tor-

que is applied by turning the upper knob until the soil fails.

The value of C is read directly from the scale on the top of the

TORVANE. Typically, the scale is calibrated so that one re-

volution of the pointer corresponds to C = 1 tsf. In spite of

several modifications, the TORVANE cannot be used accurately

on saturated clays with a q much greater than 1 tsf or on

materials that contain pebbles, sandy layers, or any other secon-

dary structure (ref. 1*0. A larger vane attachment is available

to obtain more accurate values for C less than 0.25 tsf. Also

available are miniature torque wrenches that can give torque

directly and with fair accuracy.

The TORVANE is the object of considerable criticism includ-

ing: 1) it only samples the surface of the unit, 2) there is

poor control over the rate of shear, and 3) it is not firmly

mounted, thus allowing for something other than a cylindrical

shear surface. The TORVANE should be used with some discretion

with these objections in mind. Its primary uses should be to

make preliminary estimates of shear strength, to compare mater-

ials, or to identify soils that require further testing.

More elaborate vane shear devices are available for the

laboratory. One manufactured by the Leonard Farrell and Co.,

Ltd. and another by Wykham-Farrance Engineering, Ltd. are the

28

most commonly used. The devices operate using the same princi-

pals and assumptions, but allow for more accurate determination

of torque and vane rotation than devices such as the TORVANE

.

Torque is applied through interchangeable, calibrated springs

with different spring constants; the proper spring being deter-

mined by the soil being tested. The Wykham-Farrance machine is

available with a motor driven vane. It is this machine that was

modified for this study. The modifications will be discussed

in detail in subsequent pages.

Neil Monney (ref. 7) has recently experimented with the

vane shear test. Monney listed several serious deficiencies

with the vane shear test that include:

1. the test is not applicable to granular soils

2. the failure surface is predetermined and oriented

3. the failure surface is not a perfect cylinder

4. the confining pressure is unknown in the laboratory test

5. the vane size is not standardized

6. the drainage conditions are not known

7. the rate of shear is not standardized

Monney concerned himself with item 7- He hypothesized that since

a saturated clay behaves as a visco-elastic material, it should

exhibit an increase in strength as the shear rate is increased.

The rate of shear used by most researchers and engineers ranges

from l°/min. to 90°/min. with 6°/min. being most common. In

Monney ' s study, Wykham-Farrance machine was modified in a manner

similar to that used during this study. Saturated clay was

tested for "undisturbed" and "remolded" values over ranges of

angular strain rate up to 720°/min. and the following was ob-

29

served

:

1. Vane shear strength varies significantly with ranges of

angular strain rate commonly used by engineers and

researchers

.

2. The shear rate should be standardized.

3- The standardized rate should be 90°/min.

These conclusions leave considerable room for discussion. It

is not apparent how different soils or vane sizes would have af-

fected the results. Values of strength determined at 90°/min.

strain rate may not be appropriate to evaluate every foundation

performance; different strain rates could be more appropriate

for different applications.

The ASTM is presently considering several vanes and test

procedures for standardization of the laboratory vane shear test

A field vane shear test using a larger vane is standardized as

ASTM £D-2 573.

Ill - H Vane Shear Apparatus

The basic vane shear apparatus used for this study was the

Wykham-Farrance, Ltd., instrument previously mentioned. This

machine was modified to transform this stress-controlled appara-

tus to a strain-controlled unit.

In its normal configuration, the above vane device has a

small one-speed motor that drives a small gear assembly at the

head of the instrument. This gear assembly is attached to the

vane through a calibrated spring. During the test a torque is

applied to the vane, the amount of which is determined by the

angular deflection of the spring which is read at the head of

30

the instrument. The test is completed when the torque reaches

the point where the soil fails as indicated by a sudden release

of spring deflection. Uniform rate of shear is not possible

using this arrangement.

The major modification to the Wykham-Farrance machine was

the replacement of the spring with a plate mounted with strain

gages in a configuration designed to measure torque on the vane

shaft. The strain gage replacement is shown on Plate 8. The

modified vane shear device is shown on Plate 9-

The variable-speed motor and multiple output shaft gear-box

described for use with the direct shear machine has also been

adapted for use on the vane shear machine. This apparatus was

calibrated enabling the accurate selection of sustained vane ro-

tation rates that range from 0.005°/min. to 100°/min.

The strain gage torque pick-up was also connected to the

Gould strip recorder in order to get a detailed record of the

test data. The torque pick-up was calibrated by alternately

applying known values of torque and recording the movement on

the strip chart. The calibration is expressed in terms of shear

stress as a function of chart sensitivity and vane configuration

in the Appendix as figure A— -4 as determined by Webb (ref. 21)

and verified by the author.

31

CHAPTER IV

SAMPLES AND TEST PROCEDURE

IV - 1 Samples

In order for this investigation of shear strength character-

istics of marine clays to be of a general nature, quality "undis-

turbed" samples were obtained from three areas with vastly dif-

ferent geographic location and sedimentation and loading history.

The three samples were from the Pacific Ocean, Gulf of Mexico and

the Atlantic Ocean. The samples from the Pacific Ocean were

supplied by the U.S. Naval Civil Engineering Laboratory, Port

Hueneme, California, and were collected by the Hawaii Institute

of Geophysics in late 1973- The samples from the Gulf of Mexico

were supplied by McClellan Engineers, Inc., Houston, Texas, and

were originally collected for the Shell Oil Co. The samples from

the Atlantic Ocean were supplied by the Ocean Engineering Depart-

ment, University of Rhode Island and were collected by a research

vessel from Worcester Polytechnical Institute.

IV - 1.1 Pacific Ocean Sample - KK076

This sample was from a ^0 foot core taken in water in excess

of 5000 meters in depth by a modified Ewing piston corer (ref.

20). Inside diameter of the polycarbonate core liner measured

an average of 2.62 inches. The sample was taken northeast of

the Hawaiian Islands at : Latitude 30° - 59 ' - 2*4" N

Longitude 1^9° - 50 ' - 6" W

KK076 was from an area of basaltic abyssal hills covered by a

thin layer of deep-sea, pelagic clay (reT . 20). The material

tested was from a depth in the core of ^ICWl-^28 inches. At this

32

depth the material was a dark brown clay classified by the Uni-

fied Soil Classification System as OH (fig. 15). Table 4 sum-

marizes the soil properties of KK076 as a function of depth of

core.

IV - 1.2 Gulf of Mexico Sample - GM

This sample was taken in 167 feet of water on May 28, 1976,

near Eugene Island in the Gulf of Mexico (exact location pro-

prietary). The sample was part of a 2k inch long core taken at

30 feet below the mudline with a 2.25 in. inside diameter thin

wall push tube. The material at this depth was a soft olive-

gray clay classified by the Unified Soil Classification System

as CH (fig. 15). The following properties were observed by

McClellan Engineers, Inc., at the 30 ft. level:

Vane Strength .15 tsf with water content = 5 6 . 7 55

Liquid Limit 97$

Plastic Limit 33$

Plasticity Index 6k%

IV - 1.3 Atlantic Ocean Sample - ATL

This sample was taken in ^935 meters of water near the

Bahama Outer Ridge in the Atlantic Ocean at:

Latitude 28° - 17 ' - 5^" N

Longitude 72° - 17' - 48" W

The sample specimens were part of a 136 foot, 2.0 inch diameter

core, and were from approximately 11 meters below the mudline.

The material at this depth was a soft-olive gray clay classified

by the Unified Soil Classification System as Oil (fig. 15). Table

5 lists the geotechnical properties of ATL as a function of depth

33

of core.

IV - 2 Test Procedure

The procedure used in this investigation consisted of sam-

ple preparation, consolidation, direct shear test and then im-

mediate removal of normal load and vane test. For each test, a

1.5 inch section of sample is cut and the remainder quickly re-

sealed and placed back under refrigeration. The direct shear ring

adapters (Plate 4) were designed to match the inside diameter of

samples KK076 and ATL, 2.62 inches to 2.00 inches respectively.

A cutter was designed to trim sample GM from approximately 2.25

inches to 2.00 inches. Filter paper is placed in J~he bottom on

the lower porous stone. The sample is pushed into the shear box

directly from the liner in the case of K076 and ATL, and from the

cutter in the case of GM . The outer portion of the shear box is

filled with water in order to keep the porous stone moist and

water is placed on the top of the sample to keep it from drying

out or sticking to the top plate. The pressure plate and lever

arm are attached and the desired normal stress is applied by add-

ing weights to the tray (Plate 6).

The sample is allowed to consolidate at the total normal

stress level overnight. A dial gage is placed (Plate 7) in order

to monitor consolidation. The shearing of the sample proceeded

after the consolidation had ceased, at a rate (i.e., 0.06 in/min)

to ensure "undrained" test conditions.

Immediately prior to shearing the sample, the locking pins

are removed from the direct shear box. The shear rate is adjusted

and the load cell voltage, chart speed, and chart sensitivity

3 'I

selected. The shear rate chosen for this study was 0.06 in/min.

as utilized by Webb (ref. 21). The test commences after placing

a dial gage to check the horizontal displacement of the shear

box (Plate 6). The test is stopped after 0.3 inches of shear has

taken place. The pins connecting the shaft from the load cell

to the shear box (Plate 2) are removed and the zero point on the

recording chart is checked for drift. The shear box is removed

from the direct shear apparatus, the water emptied, and the box

placed under the vane shear machine for the vane shear portion

of the test. The vane is lowered into the surface of the sample

.5 inch. At this depth, the vane does not pass through the dir-

ect shear surface. This is shown schematically as follows:

Direct She;Box

Vane

~~:^lJL

Porous Stone V

— Direct ShearRing Adapters

Samule

Direct ShearFailure Surface

-Filter paper

Before starting the vane shear test, the gear box output

shaft and motor settings are changed in order to facilitate vane

shear at the same rate as the direct shear. Per Webb (ref. 21),

these rates are 7°/min. for vane shear and 0.06 in/min. for dir-

ect shear. The strain gage conditioner voltage is changed as is

35

the chart sensitivity. The chart is zeroed on a line of the

chart and the test proceeds_ through a vane rotation of at least

30° (Plate 10). The vane is then raised out of the sample and

the zero point checked for drift.

The final item is to determine the water content of the

sample. The method used in this study is to take the water

content sample down through the direct shear failure surface

inclusive of the material sheared by the vane shear machine.

This sample is immediately weighed and placed in an oven for

drying and subsequent reweighing for water content determination

36

CHAPTER V

EXPERIMENTAL RESULTS AND ANALYSIS

The first portion of the experimental work involved the cali-

bration of the loading and recording devices (figures A-l and

A-4) of the direct and vane shear equipment and strip recorder

setup. The primary work of this investigation was to verify the

reliability and reproducibility of the test procedures described

in Chapter IV and to run the "combined" direct and vane shear

tests and analysis on a general set of samples in order to vali-

date the theory proposed by Webb (ref. 20), as discussed in Chap-

ter II. Figures A-5 through A-25 contain the data collected

from running the "combined" vane and direct shear tests on the

three samples. Sample shear strengths are represented by:

a) water content vs. log consolidation pressure

b) water content vs. log shear strength

c) shear strength vs. normal pressure and consolidation

pressure

.

These relationships are discussed in the following paragraphs.

V - 1 Water Content vs. Log Consolidation Pressure

Immediately following completion of the "combined" direct

and vane shear tests, the water content was determined on each

specimen as described in Chapter IV. These water content values

were plotted against the log of the pressure used to consolidate

each specimen prior to the direct shear test.

V - 1.1 Sample KK076

Water content as a function of laboratory consolidation pres-

37

sure for sample KK076 is depicted in figure 16. As anticipated

and as previously discussed, the consolidation curve for this

sample appears to be the reload portion of the curve of consoli-

dation, figure 11. The "apparent" precompression stress, P,

from this plot appears to be approximately 5-2 psi.

V - 1.2 Sample GM

Figure 17 indicates a plot of the water content of sample

GM as a function of laboratory consolidation pressure. Results

similar to those reported for sample KK076 were observed except

that the change in slope of the curve at the "apparent" P was

not as great as for sample KK076. The "apparent" ? from this

plot appears to be approximately 6.0 psi.

V - 1.3 Sample ATL

Figure 18 indicates a plot of the water content of sample

ATL as a function of laboratory consolidation. Results similar

to those reported for samples KK076 and GM were observed. The

"apparent" P^ from this plot appears to be approximately 7-2 psi

V - 1.4 Discussion of Water Content vs. Loc Consolidatio n

Pressure

The plot of water content vs. log consolidation pressure

for all three samples indicate two distinct straight line seg-

ments with a change to a steeper negative slope at the apparent

P for increasing consolidation pressure. This is the classical

indication of an over-consolidated soil.

V - 2 Water Content vs. Log Shear Strength

Figures 19, 20 and 21 summarize the results of this part of

38

the investigation. There are both similarities and variances

among the three plots. The water content was plotted against the

log shear strength for the results obtained by both the direct

shear test and the vane shear test. The water content vs. log

direct shear strength for sample KK076 was a straight line over

the whole range of normal stresses, while this plot for samples

GM and ATL indicates two straight lines with a change of slope

at (n% = 70.4, a = 5.5 psi and w% = 159-0 or = 6.7 psi, res-

pectively. The water content vs. log vane shear strength for all

samples was a straight line over the whole range of consolidation

pressures. These plots, although not corresponding precisely

with each other, did closely approximate the observations by

Webb (ref. 21). The "apparent" P determined from this part of

the investigation was 5.5 psi and 6.7 psi for samples GM and ATL

respectively, compared with 6.0 psi and 7.2 psi as determined by

the water content versus log consolidation pressure curves.

These values compare favorably and appear to present evidence

that the test apparatus, loading procedure, data collection sys-

tem and data presentation worked as designed.

V - 3 "Combined" Shear Strength Analysis

A "combined" test consists of a direct shear test conducted

at a normal stress equal to the consolidation pressure of a

sample followed immediately by removal of normal load and a vane

shear test. Because the vane shear tests are conducted at zero

normal stress, their resulting shear strength can be thought of

as being a function of "consolidation" pressure. The data de-

rived from one direct shear test and the subsequent vane shear

39

test is referred to as one "combined" shear strength test.

Conventional techniques for presentation of shear strength

data plot shear strength versus normal stress. The conventional

technique was modified in this presentation by the addition of

the vane shear data plotted on the same graph with shear strength

as a function of consolidation pressure. The direct shear strength

results were plotted versus normal stress. The results of the

"combined" shear strength tests on samples KK076, GM and ATL are

presented in figures 22, 23 and 2H . These figures plot shear

strength during direct shear and vane shear tests as a function

of applied normal stress, o and consolidation pressure. The

results of the strength tests shown in figures 22, 23 and 2h ex-

hibit several similarities. Above a certain value of o , then'

plot of the direct shear data appears linear and when extended

back, passes through the origin. The generally accepted inter-

pretation is that this linear portion of the curve represents

the strength of "normally" consolidated samples. Below this

value of normal stress, a change in slope of the curve is appa-

rent. These observations were evident for all three samples.

The "apparent" P determined by this part of the investi-

gation was 5-2 psi, 5-9 psi and 6.7 psi for samples KK076, GM

and ATL, respectively. A summary of "apparent" P values de-

termined by the three different test methods is as follows:

KK076 GM ATL1. Water content vs.

log consolidation pressure 5-2 psi 6.0 psi 7-2 psi

2. Water content vs.log shear strength 5.5 psi 6.7 psi

3. Shear strength vs.normal pressure 5-2 psi 5-9 psi 6.7 psi

40

The values of "apparent" P determined experimentally are in

relatively close agreement indicating consistency in the testing

and analysis methods.

The direct shear strengths measured always exceeded the vane

shear strength values at the consolidation pressures that cor-

responded to the normal stresses at which each direct shear test

was conducted. The plots of the vane shear strength vs. con-

solidation pressure were approximately linear in the three samples

although there was some scatter of data points. The vane shear

strength plots did not exhibit the change in slope characteristic

of the direct shear strength plots. The plots of direct shear

strength, in the regions at low values ol* a , seemed to be almost

parallel with the plot of the vane shear data although the slope

of the envelope was slightly greater for the direct shear values.

Similar observations by Webb (ref. 21) led him to propose

the "combined" analysis of shear strength as described in Chapter

II and as depicted on figure 12. Only two "combined" tests are

required to determine the complete failure envelope; one test

at o and consolidation pressure eaual to zero and the other atn l

o and consolidation pressure greater than P . The proceduren * & c y

outlined in Chapter II was used to analyze the results of the

direct shear and vane shear tests on samples KK076, GM and ATL

.

The analyses are summarized in figures 25, 26 and 27. The com-

plete failure envelope was drawn for each sample using only two

"combined" shear strength tests. The remainder of the test re-

sults were plotted on the same figure for comparison. There was

reasonably good correlation between the total shear strength en-

velope and the plotted data points. As previously mentioned,

4]

the results of this investigation seem to indicate that the dir-

ect shear line between o =0 and o = P is not exactly paralleln n c J ^

to the vane shear line in this area but is slightly steeper . Fig-

ures 22, 23 and 2k indicate the slope that best represents the

direct shear data points in the region o = to o = p for sam-^ n n c

pies KK076, GM and ATL. These figures indicate that the slope

in the portion of the direct shear envelope for a < p is higher^ ^ n c to

than(f>

obtained from the vane shear results by approximately

1.5°, 2.0°, 3.0°, respectively for samples KK076, GM and ATL.

This would seem reasonable since theoretically the vane shear

test only measures cohesion, therefore if the portion of the

direct shear line for a < P were parallel to the vane shearn c ^

line, it too, would only measure "cohesion". It is generally

accepted that since the direct shear test is run under a normal

stress that it measures both "cohesion" and "friction". Accord-

ingly, it would be expected that the slope of the direct shear

line for a < P would be greater than that of the vane shearn c °

test by the amount of the "frictional" component. Figure 28

illustrates this point. With the exception of<f> f , all the terms

of figure 28 are the same as those of Webb's theory of "combined"

analysis of shear strength as depicted on figure 12. <J> fis the

angle of the slope of the friction component of the total failure

envelope in the overconsolidated range of the plot for o < P

Therefore, from the results of this investigation, It is felt

that Webb's theory should be modified to reflect a "frictional"

component in the portion of the direct shear line for o < P .

Based on limited data, this "friction" component should be ap-

proximately 2° - 3° for $ as shown on figure 28.

l\2

Another point that merits discussion is the fact that the

cohesion value at o =0 obtained from the direct shear test,

C , , and the vane shear test, C , are considerably different for

each of the three samples. Theoretically, these values should

be equal so that AC is zero (refer to fig. 12). It was thought

that perhaps the water content or the plasticity index might show

some correlation between C and C, because of the idea that the

geometry of the failure planes seem to be a function of water

content. Figures 29 and 30 plot the ratio of C /C , versus water

content and plasticity Index at o = for the three specimens

used in this investigation. The data is scattered and no real

correlation can be drawn except that the ratio, C /C , , is in the^ ' v d'

range 0.66 to 0.76. Another thought was that the two tests

measure shear resistance along planes orthogonal to one another

and that due to the platy shape of the clay particles the shear

resistance along the horizontal plane might differ from that

along a vertical plane. Limited testing was accomplished with

the vane test in both the vertical and horizontal directions. It

was found that the shear resistance along the horizontal plane

was actually less than that along a vertical plane which would

cause the C /C, ratio to be further divergent and increase AC.v d to

The most likely explanation of the difference between C, and C

is in the failure mechanism of both tests and how it relates to

the current theory. Presently, the shear stress of the direct

shear test result is the shear force required to move the shear

boxes relative to one another divided by the cross-sectional

area of the sample. In the vane shear test the shear stress

is taken as the torque required to turn the vane divided by the

'13

first moment of the cylindrical area that the ends of the vanes

transcribe. In this investigation a one-inch diameter, one inch

deep vane was pushed one-half inch into the sample while running

the vane shear test. As the test was performed and the soil

failed, the vanes initially did not cut out a cylindrical sec-

tion, but tension cracks commenced propulgating away from the

ends of the vanes, and also from the ends of the vanes toward

the interior of the vane shaft. This apparently weakened the

sample so that with subsequent rotation of the vane the peak of

the shear stress versus strain curve (fig. 7), was consistently

lower by a constant amount than the direct shear line in the

region o < P .to n c

As discussed and illustrated in Chapter I, present state-

of-the-art criteria for designing marine foundations still con-

sists mainly of empirical formulas. One of the key components

of these formulas for bearing capacity, pile capacity or up-

lift capacity is the value of C, undrained shear strength. There

are many methods for determining the undrained shear strength of

a marine clay such as TORVANE, cone penetrometer, triaxial com-

pression, vane shear, direct shear or fall cone. However, each

of these tests has advantages and disadvantages, as described in

Chapter II, with no general agreement as to which is better. The

geotechnical engineer must use his own judgement, which may be

affected by availability of test equipment, magnitude of pro-

posed project, his own confidence in particular tests, etc. in

choosing the undrained shear strength tests that he will specify.

He will probably require that a combination of these methods be

used in arriving at realistic values of C. The author feels that

by using the "combined" vane and direct shear method discussed

in this paper, reliable data will be produced with considerable

sample conservation and reduced time for testing, which makes

the method attractive from an economical standpoint.

In summary, it is felt that the "combined" vane and direct

shear analysis will provide an economical, consistent and real-

istic procedure to the geotechnical engineer for determining

the undrained shear strength of marine clays. The method is

simple, direct and does not require complicated equipment. It

is highly reproducable and provides a permanent documentation of

test results. As in most laboratory analysis, it is mandatory

that rigorous adherance to strict, consistent laboratory pro-

cedures be observed in order for the data collected to be use-

able and representative.

'15

CHAPTER VI

CONCLUSIONS AMD RECOMMENDATIONS

VI - 1 Conclusions

The conclusions of this investigation are as follows:

1. With rigorous control and consistency of laboratory procedures,

using strain controlled testing and electronic data printout,

the tests and data resulting from the direct shear and vane

shear procedure described herein are both reliable and re-

producible from one researcher to the next.

2. With similar results on tests of clay samples from the Pacific

Ocean, Gulf o? Mexico, and the Atlantic Ocean, the "combined"

theory for "Total Failure Envelope" is a general theory that

can be used (with slight modification) for any and all marine

clays regardless of water content, deposition rate, geographic

location, water depth, etc.

3. When using the "combined" theory, the slope of the portion of

the direct shear failure envelope for a < P should be in-1 n c

creased by approximately 2° - 3° (4> f ) to more closely approxi-

mate the failure envelope in this region (see figure 28).

4. For each sample there is a constant difference between C-, and

C in the range o = to P . This difference appears to bev to n c

^a function of the differences between failure mechanisms for

the direct and vane shear tests and present theory used to

calculate shear stress in each case. The ratio of C /C,

varies from 0.66 to 0.76 indicating a consistent underestima-

tion of shear strength by the vane shear test.

5. Acceptance of the "combined" shear testing procedure will

he

significantly reduce the number and size of sample specimens

required and the number of laboratory tests required to de-

termine the geotechnical properties of marine clays.

6. The values of "C" and "<j>" obtained from this "combined"

analysis can be easily and readily used in the present empiri-

cal formulas being utilized to determine the strength of the

ocean floor for the design of foundations for ocean structures

VI - 2 Recommendations

1. A procedure could be arranged to measure pore pressure

during the direct and vane shear tests allowing analysis of shear

strength in terras of effective normal stresses rather than total

normal stresses.

2. By using larger diameter samples and a special pressure

plate it may be possible to run the vane shear test under a nor-

mal stress rather than removing the normal stress during the

vane test. This should give much better correlation between

the direct and vane shear test results.

3. Great potential lies in the area of standardizing the

vane shear test, i.e., diameter of vane, depth of vane, depth

vane is pushed into sample and rate of rotation of vane, etc.

H . A correlation between the "combined" shear strength analy-

sis presented herein and the results of triaxial tests would be

of great interest.

hi

BIBLIOGRAPHY

1. American Society for Testing and Materials, Research Confer -

ence on Shear Strength of Cohesive Soil , Col orado , i960

.

2. Bishop, A.W., Henkel, D.J., The Measurement of Soil Proper-ties in the Triaxial Test , London: Edward Arnold, Ltd., 1974.

3. Bhushan, K., "Resistance of Ocean Sediments to Sampler Pene-tration", Eighth Annual Offshore Technology Conference, PaperNumber. OTC 2624 , Texas, 1976.

4. Bouma, A.H., et . al.

, "Comparison of Geological and Engineer-ing Properties of Marine Sediments", Fourth Annual OffshoreTechnology Conference, Paper No., OTC~15l4 , Texas 1972.

5. Eide, 0., "Marine Soil Mechanics - Applications to North SeaOffshore Structures", Norwegian Geotechnical Institute , Pub-lication Number 103.

6. Herrman, H.G., et.al., Interim Design Guidelines for Sea-floor Footing Foundations , U.S. Navy Civil Engineering Labora-tory, Technical Report R799, October, 1973-

7- Inderbitzen, A.L., et.al., Deep Sea Sediments , New York:Plenum Press, 1974.

8. Jumikis, A.R., Soil Mechanics , New Jersey: D. Van Jostrand,Co., Inc., 1962.

9. Lambe, T.W., Soil Testing for Engineers , New York: Wiley andSons, Inc., 1951.

10. Lambe, T.W., Whitman, R.V., Soil Mechanics , New York: Wileyand Sons, Inc., 1969.

11. McClellan, B., "Design of Deep Penetration Piles for OceanStructures", Journal of the Geotechnical Engineering Division ,

Proceedings of the American Society of Civil Engineers , Volume100, Number GT7, July, 1974.

12. Monney, N.T., Submarine Slope Stability , M.S. Thesis, CivilEngineering Department, University of Washington, Seattle,1965.

13. Noorany, I., Gizienski, S.F., "Engineering Properties ofMarine Soils: A State of the Art Review", Journal of theSoil Mechanics and Foundation Division, Proceedings of theAmerican Society of Civil Engineers , Volume 96, Number 4-6,

1970.

48

Ik. Peck, R.B., Hanson, W.E., Thornburn, T.H., Foundation Engineer' '

ing , New York: Wiley and Sons, Inc., 19 7 z*

.

15- Richards, A.F., et.al., Marine Geotechnique , Illinois: Univ-ersity of Illinois Press^ 19 6 7 .

16. Scott, R.F., Principles of Soil Mechanics , Massachusetts:Addison - Wesley Publishing Co., Inc., 196 3 -

17. Sherif, M.A., et . al.

, Proceedings: The International Sympos-ium on the Engineering Properties of Sea Floor Soils andTheir Geophysical Identification, UNESCO, National ScienceFoundation, University of Washington, Seattle, 1971-

18. Terzaghi, K., Peck, R.W., Soil Mechanics in Engineering Prac -

tice , New York: Wiley and Sons , Inc.

, 1967

.

19. Tschebotariof f , G.P., Foundations, Retaining and EarthStructures , 2nd Ed., New York: McGraw - Hill Book Company,1973-

20. U.S. Naval Civil Engineering Laboratory, "Geotechnical Prop-erties of the Deep Sea Floor, Northeast Pacific", addendum toMarine Geology of a Region on the Northwest Pacific , Califor-nia, 197^.

21. Webb, M.S., Combined Vane and Direct Shear Strength Analysisof Naturally Occurring Marine Soils , M.S. Thesis, Civil Engi-neering Department, University of Washington, Seattle, 1976.

22. Wu, Ming-Jiun, Dynamic Properties of Overconsolidated SeattleClays , Ph.D. Dissertation, Civil Engineering Department,University of Washington, Seattle, 1972.

49

Description SensitivityPercentage of StrengthLost on Refolding

Insensitive

Slightly sensitive

Mediuc sensitive

Yery sensitive

Slightly quick

Hediun quick

Very quick

Less then 1

1-2*

k - 8

e - 16 •

16 - 32

Greater than 32

- 50

50 - 75

75 - 87.5

67.5 - 93.8

93.8 - 96.9

Creater than 96.9

Table 1 Classification of sensitivity(Aftcr Buchan, ct al , reference 15

P9. 72).

50

Shear Bulk Water .

Depth in Strength Void Density,(cy/cA l)

Content SpecificCore (en) ( PS F ) Ratio K dry v/t. 1 Gravitv

20 45 3.92 1.361 141 2.7740 57 3.58 1.375 132 2.72

. 60 53 3-21 1.407 118 2.71. 80 55 3.32 1.390 124 2.68100

. ^3 3.11 1.411 116 2.69120 77 3.29 1.392 123 2.68140 53 3.20 - 1.409 . 118 2.711*0 70 3.18 1.400 119 2.67l8o 75 3.03 1.418 113 2.68200 93 . 2.82 1.442 '. 105 2.69220 113 3.02 1.410 114 - 2.65240 .120 2.83 1.428 107 2.64260 143 2.98 1.434 109 2.72270 127 3.02 1.425 112 2;71310 130 2.76 3.456 • 102 2.71320 125

•

2.80 1.444 104 . 2.63340 133 2.85 1.462 103 2.77360 110 2.81 1.466 101 2.77

•375 135 2.77 I.458 102 2.734oo 143 2.73 1.466 100 2.73420 . 157 2.60 1.479 95 2.72kkO 157 2.54 1.483 •93 2.73480 175 2.57 1.500 92 ' 2.78500 180 2.55 1.495 93 2.76520 197 2.61 I.470 97 2.7054o 195 2.53 1.494 92 2.74560 230 2.47 1.495 91 2.72600 225 • 2.42 1.510 . 88 2.74620 220 2.30 1.526 84 2.7364o 240 • 2.36 I.526 85- 2.76660 217 . 2.31 1.523 85 .. 2.73680 253 2.38 1.525 86 2.77720 240 2.29 1.523 84 .2.7474o 267 2.26 1.534 82 2.74760 247 2.20 1.5 i(

. 81 2.73-800 273 2.31 1.523 85 2.7386o 277 2.38 I.506 88 2.71

Table 2 Geotechnical properties of a typical core from deeper portions ofthe Gulf of Mexico(After Bouma, reference H pg. 32).

51

A. * l«Estimated

LocationSamplenu rn be r

Depth,

In

feel

P <Irl

kllcjr2ms

p-er

tquare

centimeter

Pc <*

kilograms

per

square

centimeter

CjPo <=c

C„, In

square

centimeters

per second

(1) (2) (3) (4) (5) (6) (7) (8)

Mediterranean A-D! 3.1 0.C5 0.07 1.2 0.41 4 x 10-<

Mediterranean D-83 0.5 0.02 0.04 2.6 0.34 2 x 10-*

Mediterranean B-87 1.6 0.03 0.15 2 0.34 1.5 x 10"'

. Forth Atlantic C-15 2.1 0.045 0.15 1.5 0.36 1.5 x 10-'

Forth Atlantic C-I3 2.1 0.04 0.16 1 0.55 6 x l0-<Forth Atlantic COO 1.1 0.02 0.2 2 0.59 —West Atlantic D-lp 6 0.10 0.2 1 0.75 —Vest Atlantic F-6 5.1 0.10 0.15 0.4 0.63 1 x 10-'

„Wes! Atlantic F- 11 4.8 C.05 0.2 0.7 0.83 8 x 10~«

V.'cf.t Atlantic G-6 T..5 0.03 0.05 1.2 1.4 ex io—«

Easl Pacific I-KACA 0.5 0.CC5 0.09 — 0.77 —Easl Pacific J-29 — 0.005 0.08 .— " 0.9 * '*

Tcrm/^J » the effective overburden prcssjrc; f e« the estimated prcccnsotldatlcn pres-

rurt based en Casacrandc method; Ct,B the ur.dralncd shear strength, In Migrans per

f^uarc centimeter; C(« compression Index; and C r coefficient of consolidation.

Tabic 3 Properties of near surface samples from the sea floor (After Noorany,reference 13 pg. 1705).

>>P•H XO CD

•H T3 VP CCO IHctf

rHCH

o•H -PP -H

Cd -HrH ^P-.

T5•H -P

•H «H

>3•P

P•HCO

CO

0) PH CHO <D CO

6 tn acd p ^K co

CD bO-HC £ wcd <D a> <-,—pCO

eopOPJ->CQ D,Cm

I CD w

CO

OJ

op0\.

LP* C*-

t>- coCM CMrH rH

CM

OP

VO

LP

LP

VOrH

IP

oorH

LP

LP

CM

CMCO

OVOCM

t— VO VO O OP LP LP CO

3 rH VO LP C^v t~~ zp CM c- OA3 O o> c^ CO o\ CM O o O

rH rH rH rH rH

On VO CO CO OP LP CO O CO

CT\ co LP -=r LPLP CM CM rH COrH CM CM CM rH

OP

CM

LP O On LPLP VO CO OOCM CM CM CM

O^ CO

OP rH

ON. OP

CM

rH

CM

rH CO

CM

OP VO

CM CM

CM

OP

VOOP

OnOrH

CM0\

VOCO

LPVO

OPOP

LPVO

rHC7\ CO VO

rH

rH

COOn

rH

COOP

rH

OnOP

rH

oco

CM

OP

CM

OP

CM

CO LP

VO

oo

COrH

LP

CM

LP

LPCM

LP

CT\

CM

LP

ooOP

52

oCM

CD

U

UCD

-PCmctf

VO

o«

t I

£cd

CO

I

£1PP,CD

T3

CO

>

CO

CD

•HPFh

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53

q:iii

cr 5u~>

Z3O

a:

C£ u< a

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CO 1oo_j

!.i

0:o

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v-

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*

8*

UJ uj

f— °Si uj> a.

uj 5

°8

CO

, .0H- CMCL—

°--omo

u.

oSuUJ <tcc

grg

1 : i 'ssK

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irJ.VVl./V-l;.

' T..

!Tol

o .

-j

T [! ,

VV..'

u_

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i,

IiSZB ,'<!

1

i

w1n-

a.

5 1 1 •L 1

JC CO

H jor Eh

UJ <Dl ^ W

CLO

P-.

Sa. <

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< ro1

a:

En

2; WQ^: •

UJco>

h-CO[:!

UJ HO Eh

cr:

wp-l

cr;

P-,

Hc O

CO

>-

O_JOXH

COCJ m u

S'uoto

11J omo

oooOHi

<-> o

om6 O

fli

,

/vJ-W-»p^iLV»^1-tfr4i^j|> i

tLi

t

,

.%ii1ii

r!:

o »n o in o

wen<Eh

SI/J13W '31/00 30 dOl M013Q 30NV1S1Q

51

8

Od

(T)

UJ

X•

cc

UJo2:

*-UJ

h- 2 H

fc

5: .J O•

-j V CJ

f- h- or<n D

O10 UJ

<-J

< £CL -J CL £11 11 11

11

*-« .J .J *>»

a. .J CL •>

in j_o o 8

o

IT) i/j

O ex

s_rjCJ.cc/)

OJcO rj

O >•

in

CD

o

a

in

o s(*ui) djoq sq; jo doj. MO^ag M^^dq

in

en

aocrCJS-o<+-

OJ5~

oxzCO

CJ-l->

fXCJ

to>to

Q)4->

rdi~

ex

CI00

0)

en

55

Coblo

Connection to

Dontitomefor

\Yolerproofed

Stroin Gouges

Abrosion Shield

Free Flooding

Lood Cell

60* Com

Figure 2 Cone penetrometer

56

23

Z to

13

1W

L<it f?;» Unit Cent lea J

*ilfjje Vine Sr.tar Strength

Test location

D Site I

GSite 2

10 15 JO

CO

3—

D

0-

P D

O

D

-O—i

O

-Q-

-Q-

K

Figure 3 Cone penetration data compared to vane shear data

57

v

O6

Csj w(SBipUj) S183 313"U7 UOT3P^33USJ 3U?A

(E01JDU7) Gaoqoa uj uojijua^ouoj 3Uua

CO

en

ocCJ

o*+-

CDv.

CJ

^-

S--

CD

«+-

co+->

«3S~+-J

C)

CaQ.

GJC>

>

CDC

*->

c>

+->

CO

<u

58

1.2 r-

ri

2.C

!| P' r 0.0l32 TSF I!!;

-J_'Lc^r iiiiil

= 0.0315 TSF

mil

iiiii

-CORE 65-A-4; A5-P?jP = 0.0272 TSF

ji

!"A 2 4

o 05 5'f.'. 95*57*W

!A WATER DEPTH = 1443 FMS

o =28 -34 en.a =62-63 cm.

nr-m

—

0.001 0.01 0.1 uo

PRESSURE (TSF)

10.0 100.0

Fi re 5 Void ratio vs. log of pressure(After Bryant, et al, reference 15

pg. 61)

59

V-<

LABORATORYSEVERELYDISTURBED

LABORATORY REBOUND(ALSO TO O

LABORATORYSLIGHTLYDISTURBED

LOO PRESSURE

Figure 6 Generalized e-log P diagram(After Richards, reference 15.' pg. 104)

Peak shear stress t

60

Deformation or Strain

Figure 7 Shear strength - deformation diagr?m.

Figure 8 Shear strength diagram(After Hvdrslev, reference 1, pg. 175)

61

+->

CDcoi-<->

CO

OJJZto

Simple Overconsolidation(Rebound Curve) ^^

Normal Stress

Figure 9 Shear strength hysteresis loop(After Hvorslcv, reference 1 pg. 175)

62

Normal Stress, a I

Figure 10 Determination of the cohesion and friction components, C' and<>• (After Mvorslev, reference i pg. 203).

63

+->

cooJ-

4->

Virgin Curve

Rebound

Log Consolidation Pressure

Figure IX 'Water Content vs. log consolidation pressure(After Hvorslev,

reference 1, pg. 196).

$n

rj

wco

ai-

a.

eo•r—

-t->

ru

X>

oCOiZ

Ooe*5

CO

CJ

i-

CO

E

o

CO•«—

co>>r—<ac

enc<ul-4-*

CO

co

<x>

szCO

oas-

-o

CD

>

-aac•I—XIEoo

o

CO •

a ^

O CD

o•r- r.

4-> p-•<- CMC•r- CD<+- oCD d-O CU

i_

-a ,<l>

c «•-

°xT^ cu

i_—

+J $_to a)

r— l|_

i— cC

C\J

a/

co

A~->

Cylindrical Compression"Triaxial Shear"

Torsional Shear

65

Figure 13 Types of soil shear tests

V/AWWW- V//\. ,J'V/'<V>*'

Tv/o-piece Single Shear Box

i

Annular or "Punching" Shear Ring Shear

Figure 14 Types of direct shear tests.

66

to

CD

iHaSctf

CO

pw03

Eh

Cm

O

CO

-P•He•H

bOfn

CD

£>

CD

PP<

inr-\

CD

hO•H

o oo V£)

OJ rH

oooo

oo

{%) xspui A^TOT^sBid

67

V£>

o«^Q)

rHat;

cd

CO

11

0)

t*

3CO

CO

CD

£h

o.

cO•H-Pcdro•Hr 1

oCO

Coo

^ faO

•H oW Ha

CO

<D >Ph

3 -pw £CO (U

<D Pf i CIX o

oCo Ph

•H CD

-P 43

cd cd'C ^2•HHOWCO VDo H

Q'

J^

=5

hO•Hfo

(#)C

Mf ^U9^uoo ja^BM

68

75

20

- 10

70 65

Water Content, W, (%)

Figure 17 Water content vs. log consolidationpressure - Sample GM

69

160 155

Water Content, W, (%)

150

Figure 18 Water content vs. log consolidation pressureSample ATL

70

20

CO

Pw rH•4-3 3H CO

3 <u

CO Pi

(D

fn •PCO

4^> <D

CO -PCD

coP*CD

P

co

CD

ct

W

270 260 250 2^40 230

Water Content, W, {%)

220 210

Figure 19 Water content vs. log shear strength -

Sample KK076

71

co

pco rHp 3iH CO

3 CD

co UCD

£h PCO

P (D

CO pCD

P ^Ctf

Sh <D

Ctf x:CD CO

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Calibration determined for:

1. BLH Electronics, Inc. Load Cell, Type U3G1

2. Strain Gage Conditioner = 20 volts

3. Chart Sensitivity = 10 mv/division

Figure A-l. Recording chart calibration for djrect shear test.

83

0.2 0.3 0.4

Displacement, X, (in)

0.5

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Figure A-2. Common area vs. displacement for direct shear test.

84

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Figure A-3"1

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Common Area vs. displacement for directshear test (R = 1.0 in.)

.G

I-

4->

o

llote: Calibration applies for strain qocjc

conditioner voltaee of 6 volts.

o 2

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Voltage (mv)

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3

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r - Shear Stress (psi) M s Moment en Vane Shaft (in- lb)

II *• Vane Height (in) D = Vane Diameter (in)

figure A- 1; Recording chart calibration for vane shear test.

86

Date DO/S/76 Tested by: J. For, tor

Sample if:KK °7° Water depth: ?QOO+m Sample depth: + 36'

• 25 mm/rnin Chart speed 25 mm/mi

n

20 v Signal Conditioner G v

10 mv Sensitivity 20 mv

O.o psi Normal Stress, Consolidation Pressure q.O psi

1.57 psi rmax

1.16 psi

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1 mm = 1.5 lb. 1 mm = .11 psi

10

20

30

40

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Figure A- 5 Test Results - Sample KKO76

87

Dale: 10/6/76 Tested by: J. Poster

Sample //.'KK076 Water depth: ^'ooo+m Sample depth: ± 36'

• 25 rnm/min Chart speed 25 mm/mi

n

20 v Signal Conditioner 6 v

10 mv Sensitivity 20 mv

1.1(6 psi Normal Stress, Consolidation Pressure l.h/psi

3.82 P si rm.ax 1.^ P si

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Water Content [%): 255 .8

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10

20

30

40

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Figure A- 6 Test Results - Sample KKO76

88

Date: 10 /7/76 Tested by: j. For . tor

Sample H'yyOIG Water depth :c;ooCH- m Sample depth:-:- 3^1

25 mm/mi

n

Chart speed 25 mm/mi n

20 v Signal Conditioner 6 v

10 mv Sensitivity 20 mv

?.n P si Normal Stress, Consolidation Pressure 2 -JS1

1.97 P s "> Tmax 1.39 psi

c

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to

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10

20

30

40

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Figure A- 7 Test Results - Sample KKO76

89

Date: 10/8/76 Tested by: j. Footer

Sample ^KK076 ^'a ^ er depth: i^000+m^amP^ e depth: ± 3^1

25 mm/mi

n

Chart speed 25 mm/mi

n

20 v Signal Conditioner 6 v

10 mv Sensitivity 20 mv

I4..0 psi Normal Stress, Consolidation Pressure U. . psi

2.1;2 psi Tmax 1.95 Psi

4->

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1 mm = 1.5 lb. 1 mm = .11 psi

10

20

30

40

cr>

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Figure A- 8 Test Results - Sample KKO76

qn

Date: 10/9/76 Tested by:fl . Pofiter

Sample //:j<K076' Water depth: ^Q 00+:,,Sample depth: ± 5 ,

25 mm/mi

n

Chart speed 25 mrn/min

20 v Signal Conditioner G v

10 mv Sensitivity 20 mv

5.0 psi Normal Stress, Consolidation Pressure 5.0 psi

2.89 P si Tmax 2.20 P si

paECJu

to

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0.2

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1 mm = 1.5 lb. 1 mm = .11 psi

10

20

30

40

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Figure A- 9 Test Results - Sample KK0?6

91

Date: ] 0/11/76 Tested by: j, ^storSample 'I'v^otS

^'a ter depth :-;ooo+rn Sample depth: ± -^i

25 mm/mi

n

Chart speed 25 mm/mi

n

20 v Signal Conditioner 6 v

10 mv Sensitivity 20 mv

6.0 psi Normal Stress, Consolidation Pressure 6.0 psi

3.31 Psi Tnax 2.75 psi

cr

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40

Figure A- 10 Test Results - Sample KKO76

92

Dale: 10/12/76 Tested by: j, pos tor

Sample //: j<kq76 ^a ter depth: ^000+m Sample depth: t 36'

25 mm/mi

n

Chart speed 25 mm/mi

n

20 v Signal Conditioner 6 v

10 mv Sensitivity 20 mv

8.0 psi Normal Stress, Consolidation Pressure psi

h.la= psil

rmax 2.81 psi

o

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0.2

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Figure A- 11 Test Results - Sample KKO76

93

Date: 10/1V76 Tested by: Jg Vo , t ,, v

Sample i/:kK07o Water depth: £003+m Sample depth: t 36'

25 nim/min Chart speed 25 mm/mi

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20 v Signal Conditioner G v

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Datc: m/ii,/76 ^stcd by:fT _

,,_ tr;r

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• 25 mm/mi

n

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30 mv Sensitivity 20 mv

12.0 psi Normal Stress, Consolidation Pressure 12.0 psi

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Figure A- 13 Test Results - Sample KKO76

Q^

Date: 10/1 S/7 6 Tested by:>T m poster

Sample //: i<j'076' Water depth: £00C+rrjSample depth: + 36'

25 mm/mi

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Figure A- 3.I4. Test Results - Sample KKO76

96

Date: 10/18/76 Tested by: j, poster

Sample ii: ay{

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25 mm/mi

n

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20 v Signal Conditioner 6 v

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97

Date: 10/19/76 Tested by: j. Foster

Sample if: ( ^- Water depth: -,>.n\ Sample depth: .L -> q 1

25 mm/mi

n

Chart speed 25 mm/mi

n

20 v Signal Conditioner 6 v

10 mv Sensitivity 20 mv

3.0 psi Normal Stress, Consolidation Pressure 3.0 psi

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Figure A- 16 Test Results - Sample GM

98

Date: io/P. 1/7 J,Tested by: J. J•'0 ster

Sample //: r»i Wciter depth: 1.671 Sample depth: f • 3 '

25 mrn/min Chart speed 25 mm/ mi

n

20 v Signal Conditioner 6 v

3 mv Sensitivity 20 mv

h'S psi Normal Stress, Consolidation Pressure h.Spsi

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Figure A- 1? Test Results - Sample GM

99

Date: 10/22/76 Tested by: J. Fester

Sample H: r>M Water depth: 167' Sample depth: ± 30'

25 mm/mi

n

Chart speed 25 mm/mi

n

20 v Signal Conditioner 6 v

10 mv Sensitivity 20 mv

6.0 psi Normal Stress, Consolidation Pressure 6.0 psi

3.76 Psi Tmax 2Ji8 psi

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10

20

30

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Figure A- IB Test Results - Sample OM

100

Dale: 10/26/76 Tested by: J. Poster

Sample //: GM Water depth: 167 ' Sample depth: t 30'

• 25 mm/mi

n

Chart speed 25 mm/mi

n

20 v Signal Conditioner 6 v

10 mv Sensitivity 20 mv

9.0 Psi Normal Stress, Consolidation Pressure 9.0 psi

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Figure A- 19 Test Results - Sample GK

101

Dale: 10/20/76 Tested by: J. Foster

Sample if: OU Water depth: 16?' Sample depth:* 30'

• 25 mm/mi

n

Chart speed 25 mm/mi

n

20 v Signal Conditioner G v

10 rnv Sensitivity 20 mv

12.0 psi Normal Stress, Consolidation Pressure 12.0 psi

6.61; psi Tmax 3-30 psi

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Figure A- 20 Test Results - Sample OM

102

Dale: 11/15/76 Tested by: J. Poster

Sample if: ,\TL Water depth: ij.93 5n Sample depth: ± 11m

25 mm/mi

n

Chart speed 25 mm/mi

n

20 v Signal Conditioner 6 v

10 mv Sensitivity 20 mv

0.0 psi Normal Stress, Consolidation Pressure 0.0 psi

2.01 psi Tmax,

1.32 psi

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Figure A- 21 Test Results - Sample ATL

103

Date: 11/18/7 6 Tested by: J . Poster

Sample //: A7L Water depth :i;93£ rn Sample depth: ± lira

25 mm/rnin Chart speed 25 mm/mi

n

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Figure A- 22 Test Results - Sample aTL

] O'l

Date: ] 1/16/76 Tested by: J . Poster

Sample ii: ;,y r ,Water depth:

j, 93^ ro

Sample depth: t ] -) m

25 mm/mi

n

Chart speed 25 mm/mi

n

20 v Signal Conditioner 6 v

10 mv Sensitivity 20 mv

6.0 psi Norma 1 Stress, Consolidation Pressure 6.0 psi

01 psi Tmax 1.82 psi

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Direct Shear Vane Shear

Water Content {%): 159-7

1 mm = 1.5 lb. 1 mm - .11 psi

10

20

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30

• 40

Figure A- 23 Test Results - Sample ATL

10 5

Date: 11/19/76 Tested by: J. Foster

Sample if: t,-vj Water depth: i.cyj^ ™ Sample depth: ± 11 m

25 ram/mi n Chart speed 25 mm/mi

n

20 v Signal Conditioner 6 v

10 mv Sensitivity 20 mv

9.0 psi Normal Stress, Consolidation Pressure 9.0 psi

ll..26 psi T 2.53 P si

4->

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to

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to

0.1

0.2

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Direct Shear Vane Shear

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1 mm = 1.5 lb. 1 mm = .11 psi

40

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f3

Figure A- 2ij. Test Results - Sample ATL

106

Date: H/22/76 Tested by: J. Foster

Sample il: ATI Water depth: h.935 m Sample depth: ± 11 m.

25 mm/mi

n

Chart speed 25 mn/min

20 v Signal Conditioner G v

10 mv Sensitivity 20 mv

12.0psi Normal Stress, Consolidation Pressure 12. Ops i

5.52 psi_5lMZ_

2.86 psi

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Direct Shear Vane Shear

Water Content (%): 153-6

1 mm B 1.5.1b. 1 mm = .11 psi

10

20

30

40

en

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Figure A- 25 Test Results - Sample ATL

107

PLATE 1 DIRECT SHEAR TEST APPARATUS

108

mi

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PLATE 2 DIRECT SHEAR LOAD CELL

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110

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112

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PLATE 6 CHECKING HORIZONTAL DISPLACEMENTDURING DIRECT SHEAR TEST

113

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PLATE 7 MONITORING CONSOLIDATION IN DIRECTSHEAR MACHINE

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PLATE 8 VANE SHEAR MACHINE, STRAIN GAGE VANETORQUE PICK-UP REPLACEMENT

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PLATE 9 MODIFIED WYKHAM-FARRANCE VANE SHEAR MACHINE

116

PLATE 10 VANE SHEAR TEST IN PROGRESS WITH SAMPLEIN DIRECT SHEAR BOX

I

Thesis

IF654Foster

i

7

4 ?65

Determination ot

undrained shear

^

strength of marine

clays by combined

vane and direct shear

analysis.

ThesisF654 Foster

Determination ofundrained shearstrength of marineclays by combinedvane and direct shearanalysis.

171265

University „. WashingtonDeportment of Printing

Seottle. Washington 98195