i

DETERMINATION OF FAILURE ZONE OF VANE SHEAR TEST USING

ARTIFICIAL TRANSPARENT SOIL

NOORSUBHA BINTI HUSSIN

A project report submitted in the partial fulfillment of the

requirements for the awards of the degree of

Master of Engineering (Civil-Geotechnic)

Faculty of Civil Engineering

Universiti Teknologi Malaysia

JANUARY 2015

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To my beloved family

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ACKNOWLEDGEMENT

In the name of Allah, Most Gracious and Most Merciful.

Alhamdulillah, praise be to Allah for his blessing and giving me strength to

complete this report. First and foremost, my deepest gratitude goes to Jabatan

Perkhidmatan Awam (JPA) and Jabatan Kerja Raya (JKR) for awarding me the

scholarship and the opportunity to continue my study in Universiti Teknologi

Malaysia (UTM).

I wish to express sincere appreciation to my supervisor, Dr. Ahmad Safuan A.

Rashid for his constant academic guidance, patience and support throughout this

project. Without his guidance, this project will not have been accomplished. I am

also very thankful to all the staffs in Geotechnical Laboratory, UTM for their

assistance and co-operation during this project.

My warmest appreciation also extends to all my friends for helping me

directly or indirectly in completing this project. Last but not least, my deepest

appreciation goes to my beloved family that give me undivided supports and

comforts during this challenging period. For every one of you, thank you very much.

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ABSTRACT

The vane shear test method is used extensively in a variety of geotechnical

exploration to determine the undrained shear strength fine grained clays and silts. A

small scale physical model was developed to study the failure mechanism during the

vane shear test. The soil was simulated using a mixture of amorphous silica and

mineral oil, which becomes transparent when the refractive indices the oil and the

silica are well matched. A special fabricated rowe cell equipped with vane shear

device was developed to determine the strength of the transparent soil. One

dimensional consolidation test was carried out to obtain the consolidation properties

of the transparent soil. The laboratory vane shear test used is similar to the field vane

shear test but is on smaller scale. The vane was mounted vertically at the centre of

the rowe cell based which the vertical section aligned with the vane centerline was

illuminated with laser light and sequence of digital image was recorded using a

digital camera. Particle image velocimetry (PIV) was used to analyze the failure

mechanism during vane shear test. The result obtained and the observation made in

this study suggested that the failure zone was close to the conventional assumption of

a uniform shear stress distribution at the vertical sides of the failure surface.

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ABSTRAK

Ujian ram ricih digunakan secara meluas dalam pelbagai penerokaan

geoteknikal untuk menentukan secara terperinci kekuatan ricih tak bersalir bagi tanah

liat lembut. Kajian ini menggunakan model fizikal berskala kecil direka untuk

mengkaji mekanisme kegagalan dalam ujian ram ricih. Tanah buatan yang digunakan

dalam kajian ini dihasilkan daripada campuran amorfus silika dan minyak mineral.

Hasil daripada campuran bahan ini, tanah buatan bersifat lutsinar terhasil kerana

minyak mineral dan amorfus silika tersebut mempunyai indeks biasan (refraktif)

yang sama. Kekuatan ricih tanah buatan lutsinar yang dihasilkan akan ditentukan

menggunakan sel Rowe yang direkabentuk khas dengan bilah ram di dalamnya.

Ujian pengukuhan 1-dimensi telah dijalankan untuk mendapatkan sifat-sifat

pengukuhan tanah buatan lutsinar. Prinsip ujian ram ricih yang dijalankan di makmal

adalah sama dengan ujian ram ricih yang dijalankan di tapak, tetapi ia dijalankan

pada skala yang lebih kecil. Ram dipasang secara menegak di tengah sampel dalam

sel Rowe dan bahagian tegak sejajar dengan garisan tengah bilah ram itu diterangi

dengan cahaya laser dan turutan imej digital telah direkodkan menggunakan kamera

digital. Kaedah particle image velocimetry (PIV) telah digunakan untuk menganalisis

mekanisme kegagalan semasa ujian ram ricih. Berdasarkan keputusan dan

pemerhatian yang diperolehi dalam kajian ini, bentuk zon kegagalan adalah

menyerupai dengan andaian konvensional di mana agihan tegasan ricih yang

seragam berlaku pada permukaan kegagalan .

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TABLE OF CONTENTS

CHAPTER TITLE PAGE

TITLE PAGE i

DECLARATION PAGE ii

DEDICATION PAGE iii

ACKNOWLEDGEMENT PAGE iv

ABSTRACT v

ABSTRAK vi

TABLE OF CONTENTS vii

LIST OF TABLES ix

LIST OF FIGURES x

LIST OF SYMBOLS AND ABBREVIATIONS xii

LIST OF APPENDICES xiv

1 INTRODUCTION 1

1.1 Background 1

1.2 Problem Statement 3

1.3 Objectives Study 4

1.4 Scope and limitation of study 5

1.5 Significant of Study 5

2 LITERATURE REVIEW 7

2.1 Introduction 7

2.2 Vane Shear Test 7

2.2.1 Assumptions on formula derivation 13

1

CHAPTER 1

INTRODUCTION

1.1 Background of the study

Early geotechnical engineers found difficulty in determining the shear

strength of very soft and sensitive clays by means of laboratory tests due to the

disturbance induced by poor-quality samplers. These difficulties lead to the

development of vane shear test (VST). Since the late 1940s, the VST method is used

extensively in a variety of geotechnical exploration to estimate the in situ undrained

shear strength, cu of a cohesive soil in saturated soft clays.

The test is routinely performed in conjunction with other field and laboratory

tests. The VST is different from other method because it directly measures a specific

soil property, the undrained shear strength, cu of clay.

As the name implies, the undrained shear strength, cu refers to a shear

condition where water is not permitted to enter or leave the cohesive soil during the

shearing process. Therefore, the water content remains constant during the process.

(Day, 2006).

2

Although the VST is a simple and effective test to determine the undrained

shear strength, cu for soft clays, the interpretation of the results from the test is not an

easy task. The results may be affected by several factors and this can underestimate

the actual undrained shear strength, cu of the soil.

In deducing the undrained shear strength, cu, from the VST, it is commonly

assumed that the rectangular blades of the vane shear the soil along a circumscribing

cylinder and the mobilized shear strength is uniform over the surface of rotation at

the maximum torque (De Alencar et al. 1988).

Works by Chandler (1988), gives a comprehensive summary and issues

related in measuring the insitu undrained shear strength cu, of clays using the field

vane. He reviews the current understanding of the use of the field vane test to

measure the insitu undrained strength, cu, of soft clays and the factors influenced the

measurement.

Discussion about these factors (vane insertion procedure, the rest period

before shear, rate of rotation , undrained condition and stress distribution) are also

presented by looking at the previous studies done by other researchers (e.g,

Torstensson,1977; Menzies and Merrifield, 1980; Wroth, 1984; Roy and Le Blanc,

1988).

In reviewing the influence of the shear stress distribution around the vane,

Chandler (1998), concluded that the distribution of shear stress around vane may be

assumed to be uniform on the vertical edges of the vane blades but are probably

highly non uniform on the top and bottom surfaces.

3

Incorrect assumption about the stress distribution around the vane can lead to

uncertainty in determining the undrained shear strength cu,.The displacement and

failure mechanism is not easy to observe in natural soil mass whether doing the field

or laboratory test.

Ni et al. (2010) states that development of transparent synthetic soils

(Iskander et al., 1994; Sadek et al., 2002) made it possible to see the movement

inside the body of soil in laboratory test. The transparent soil is created by mixing the

amorphous silica particles and pore fluid with a matched refractive index (RI). The

material produced is almost transparent and has geotechnical properties similar to the

clay soil.

White et al. (2003) developed techniques of using particle image velocimetry

(PIV) and photogrammetry to measure deformation in geotechnical models. These

techniques are widely used in geotechnical engineering research.

Thus, this study attempts to model the failure zone of VST using artificial

transparent soil and a closer look at the impact towards the formulation of the

undrained shear strength cu, was also considered.

1.2 Problem statement

The development of a synthetic material by Iskander et al (1994) and PIV

techniques developed by White et.al (2003) has made it possible to observe the

displacement and quantify the movement in a soil mass.

4

However, there has been relatively little research concerning the

displacement caused by VST using this artificial transparent soil. In VST, since the

cylinder has different strains along the edge and towards the centre at the failure, the

shear stress distribution may not be uniform as assumed and several types of shear

distribution may exists.

Thus, this study attempts to model the failure zone using artificial soil for

VST with the aim of having closer look at the failure mechanism and the impact

towards the formulation of the undrained shear strength, cu.

1.3 Objectives

The main objective of this study is to model the failure mechanism occurs

during VST in artificial transparent soil and its impact towards the formulation of the

undrained shear strength, cu,.

To meet this objective the following goals were developed using which the

success of the investigation may be measured:

1. To design small scale physical modelling experiments that maximise

the modeling capacity of transparent soils and allows observation of

the failure mechanism of VST

2. To assess the capability of transparent soils for the investigation of

geotechnical problems using small scale physical modelling by

conducting a thorough review of published literature.

5

3. To measure accurately the displacement and shear strain fields

generated during VST using particle image velocimetry (PIV) and

photogrammetry.

1.4 Scope and limitation of study

The methods of producing the transparent material and the optical

measurement system will follow the same procedure which has been developed by

previous researcher (Hird et al., 2010; Ni et al., 2010; Stanier, 2011). The soil sample

used in this study is artificially made with mixing amorphous silica with a blend of

two mineral oil.

The undrained shear strength, cu, obtained from this study is from the VST

only and the scope of study will combine the use of artificial transparent soil and PIV

in laboratory physical modeling.

1.5 Significance of study

This study attempt to model the failure mechanism occurs during vane shear

test in artificial transparent soil and its impact towards the formulation of the

undrained shear strength, cu,..

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The undrained shear strength cu, is calculated based on the assumption of an

uniform stress distribution developed around the vane during VST From the failure

zone, the actual shape of failure will be observed and the assumption of a uniform

distribution stress will be validated.

Different stress distribution will have a different impact in calculation of

undrained shear strength, cu,. Thus, this research will help geotechnical engineers in

determining the actual failure surface obtained during the laboratory VST

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2.2.2 Factors affecting vane shear test 14

2.2.3 Sensitivity 16

2.2.4 Consistency 18

2.2.5 Failure mechanism in vane shear test 19

2.3 Transparent artificial soil 23

2.4 Particle image velocimetry (PIV) 27

3 METHODOLOGY 29

3.1 Introduction 29

3.2 Artificial transparent soil preparation 31

3.3 Consolidation test 36

3.3.1 Principle of the test 37

3.3.2 Procedure 37

3.4 Testing of the sample 41

3.4.1 Procedure of VST 43

3.4.2 Digital camera and laser light 44

4 RESULT AND DISCUSSION 50

4.1 Consolidation test 50

4.2 Vane shear test and failure zone determination 57

5 CONCLUSION AND RECOMMENDATION 62

5.1 Conclusion 62

5.2 Recommendation 63

REFERENCES 64

APPENDIX A-F 67-74

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LIST OF TABLES

TABLE NO. TITLE PAGE

2.1 Factors that may affect the results of VST 16

3.1 Transparent soil mix proportion 34

3.2 Consolidation and unloading stages 39

3.3 Typical torsion spring for laboratory vane 41

3.4 Digital camera setting 46

4.1 Typical range of values of coefficient of

consolidation and compression index for inorganic

soils

53

4.2 Summary of the consolidation data for the

transparent artificial soil.

54

x

LIST OF FIGURES

FIGURE NO. TITLE PAGE

2.1 Vane shear test equipment 8

2.2 Resisting moment of shear force 9

2.3 Variations in shear strength mobilization 10

2.4 Uniform stress distribution around the vane 11

2.5 Vane insertion disturbance 20

2.6 Transparency of transparent soil 24

3.1 Theoretical framework in methodology of the study. 30

3.2 Paraffin Oil (P1000) and technical white oil

(Grade A)

31

3.3 Timiron and fumed amorphous silica 33

3.4 Slurry mixture after stirring 35

3.5 De-airing process of transparent artificial soil 36

3.6 Consolidation test apparatus 40

3.7 Laboratory vane shear apparatus 42

3.8 Angular scale on laboratory vane apparatus: (a) details;

(b) example readings after a test

42

3.9 Digital camera and laser light apparatus 45

3.10 Testing equipment setting for digital camera and laser

light

46

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3.11 Target marker as control point 48

4.1 Consolidation plot for 3.125 kPa to 12.5 kPa

increment expressed in terms of displacement.

51

4.2 Consolidation plot for 12.5 kPa to 100 kPa increment

expressed in terms of displacement.

52

4.3 Void ratio data derived from the consolidation process 55

4.4 Void ratio data derived from the previous research data 56

4.5 Typical values of coefficient of compressibility 57

4.6 100 pixel mesh on the vane shear blade. 59

4.7 Displacement vector 60

4.8 Vertical displacement contour 61

4.9 Horizontal displacement contour 61

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LIST OF SYMBOLS AND ABBREVIATIONS

ASTM - American Society for Testing and Material

BS - British Standard

cu - Undrained shear strength

Cv - Coefficient of consolidation

Cc - Compression index

Cs - Swelling index

D - Diameter

e - Void ratio

H - Height

k - Hydraulic coductivity

M - Moment

Ms - Resisting moment of the shear force along the side

surface of the soil cylinder

Me - Resisting moment of the shear force at each end of the

soil cylinder

Mv - Coefficient of compressibility

PIV - Particle image velocimetry

PTV - Particle tracking velocimetry

r - Radius

RI - Reflective index

T - Torque

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St - Sensitivity

VST - Vane shear test

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LIST OF APPENDICES

APPENDIX TITLE PAGE

A Fumed amorphous silica specifications 67

B Paraffin Oil (P1000) data sheet 68

C White Oil (Grade A) specification 69

D Spring calibration data 70

E Spring calibration chart 71

F Load-settlement data for consolidation 72

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