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EFFECT OF SLOPE ANGLE AND SOIL PROPERTIES ON

DEFORMATION AND STABILITY OF CUT SLOPES

SUNTHAR A/L ARUMOGAM

UNIVERSITI TEKNOLOGI MALAYSIA

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DECLARATION OF THESIS / UNDERGRADUATE PROJECT PAPER AND COPYRIGHT

Author’s full name : SUNTHAR A/L ARUMOGAM______________

Date of birth : 02 NOVEMBER 1986___

Title : EFFECT OF SLOPE ANGLE AND SOIL PROPERTIES ON

DEFORMATION AND STABILITY OF CUT SLOPES____

Academic Session : 2010/2011

I declare that this thesis is classified as :

I acknowledged that Universiti Teknologi Malaysia reserves the right as follows:

1. The thesis is the property of Universiti Teknologi Malaysia.

2. The Library of Universiti Teknologi Malaysia has the right to make copies for the purpose

of research only.

3. The Library has the right to make copies of the thesis for academic exchange.

Certified by :

___________________________ ______________________________ SIGNATURE SIGNATURE OF SUPERVISOR

861102 – 23 – 6079_____ ASSOC. PROF. DR. NURLY GOFAR (NEW IC NO. /PASSPORT NO.) NAME OF SUPERVISOR

Date : 12 MAY 2011 Date : 12 MAY 2011

NOTES : * If the thesis is CONFIDENTAL or RESTRICTED, please attach with the letter from

the organization with period and reasons for confidentiality or restriction.

UNIVERSITI TEKNOLOGI MALAYSIA

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CONFIDENTIAL (Contains confidential information under the Official Secret Act 1972)*

RESTRICTED (Contains restricted information as specified by the organization where research was done)*

OPEN ACCESS I agree that my thesis to be published as online open access (full text)

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“I hereby declare that I have read this thesis and in my opinion,

this thesis is sufficient in terms of scope and quality for the

award of the degree of Master of Engineering (Civil – Geotechnics)”

Signature : ________________________________

Name : ASSOC. PROF. DR. NURLY GOFAR

Date : 12 MAY 2011

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EFFECT OF SLOPE ANGLE AND SOIL PROPERTIES ON

DEFORMATION AND STABILITY OF CUT SLOPES

SUNTHAR A/L ARUMOGAM

A project report submitted in partial fulfillment of the

requirements for the award of the degree of

Master of Engineering (Civil - Geotechnics)

Faculty of Civil Engineering

Universiti Teknologi Malaysia

MAY 2011

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I declare that this thesis entitled “Effect of Slope Angle and Soil Properties on

Deformation and Stability of Cut Slopes” is the result of my own research except as

cited in the references. The thesis has not been accepted for any degree and is not

concurrently in candidature of any other degree.

Signature : __________________________

Name : SUNTHAR A/L ARUMOGAM

Date : 12 MAY 2011

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To My Beloved Mother and Father …

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ACKNOWLEDGEMENT

This report has been completed with the help and cooperation of many

individuals who played a vital role in providing intellectual, material and moral

supports. It is my pleasure to take this opportunity to thank all the people

contributing to it.

In particular, I would like to express my deep and sincere gratitude to my

supervisor, Assoc. Prof. Dr. Nurly Gofar for her generous advice, guidance and

encouragement. Thanks for supervising and guiding me through a year to finish this

project. Thanks a lot for being such a good and dedicated supervisor.

Apart from that, sincere appreciation is conveyed to my parents, sisters and

my loved one for their unconditional support and love that motivated me to

accomplish this project.

Last but not least, I would like to thank all my friends for their support and

encouragement during a year of study. The campus life is a lot more interesting with

all of them.

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ABSTRACT

The rapid development of an area has led to the cutting of natural slopes to

form man made slopes which will induce deformation and reduction in the stability

of the slope itself. The first part of the project focuses on the parametric study on the

influence of soil parameters and slope angle on the deformation and stability of a

slope. A total of 48 analyses were carried out on six types of soil with four slope

configurations. The analysis was carried out in two parts, which are,

deformation and stability analysis using finite element method and Strength

Reduction Technique (SRT) as well as stability analysis using Limit Equilibrium

Method (LEM). The outcome of this study is presented in the form of charts for

preliminary design of excavated slopes. The application of the charts is

demonstrated through a case study of a cut slope. The chart predicts that the slope

will have deformation of 15 mm and the factor of safety of 1.12 while finite element

analysis shows that the deformation of the case cut slope is 8.93mm. Meanwhile, the

factor of safety by SRT and LEM are 1.29 and 1.33 respectively. Hence, the slope is

in satisfactory condition. The results obtained from the charts show some differences

due to the assumptions and limitation used in the parametric study. However, the

differences are in the safe side, thus, in the absence of more sophisticated tools, the

chart can be used as preliminary estimation of slope deformation and stability.

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ABSTRAK

Pembangunan yang pesat di sesuatu kawasan telah menyebabkan

pemotongan cerun semulajadi untuk membentuk cerun potongan yang akan

membawa kepada deformasi and pengurangan kestabilan sesuatu cerun itu.

Bahagian pertama dalam projek ini tertumpu kepada kajian parametrik pada

pengaruh parameter tanah dan sudut cerun terhadap deformasi dan kestabilan cerun.

Sejumlah 48 analisis dilakukan pada enam jenis tanah dengan empat konfigurasi

cerun. Analisis dilakukan dalam dua bahagian, iaitu, deformasi dan analisis

kestabilan menggunakan kaedah FE dan SRT serta analisis kestabilan menggunakan

kaedah keseimbangan batas. Keputusan kajian tersebut dibentangkan dalam bentuk

grafik untuk reka bentuk awal cerun potongan. Aplikasi grafik ditunjukkan melalui

kajian kes cerun potongan. Graf meramalkan bahawa cerun potongan tersebut akan

mempunyai deformasi sebanyak 15mm dan faktor keselamatan 1.12 sedangkan

analisis finite element menunjukkan bahawa deformasi cerun potongan adalah

sebanyak 8.93mm. Sementara itu, faktor keselamatan oleh SRT dan LEM adalah

1.29 dan 1.33 masing-masing. Oleh itu, cerun berada dalam keadaan stabil.

Keputusan yang diperolehi daripada graf menunjukkan sedikit perbezaan kerana

andaian dan keterbatasan yang digunakan dalam kajian parametrik. Namun,

perbezaan berada di belah yang selamat, dengan demikian, dengan ketiadan alat-alat

yang canggih, graf tersebut boleh digunakan sebagai anggaran awal deformasi dan

kestabilan cerun.

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TABLE OF CONTENTS

CHAPTER TITLE PAGE

TITLE PAGE i

DECLARATION ii

DEDICATION iii

ACKNOWLEDGEMENT iv

ABSTRACT v

ABSTRAK vi

TABLE OF CONTENTS vii

LIST OF TABLES x

LIST OF FIGURES xi

LIST OF SYMBOLS xii

LIST OF APPENDICES xiii

1 INTRODUCTION 1

1.1 Background 1

1.2 Problem Statement 3

1.3 Objectives of Study 3

1.4 Scope of Study 3

1.5 Importance of Study 4

2 LITERATURE REVIEW 5

2.1 Introduction 5

2.2 Principles of Stability 6

2.2.1 Rotational Slips 7

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2.2.2 Effective Stress 7

2.2.3 Effect of Pore Pressure 8

2.2.4 Factor of Safety 8

2.2.5 Residual Strength 9

2.3 Modes of Slope Movement 10

2.4 Methods of Slope Stability Analyses 11

2.4.1 Limit Equilibrium Method (LEM) 13

2.4.2 Finite Element Method 16

2.4.3 Strength Reduction Technique 18

2.5 Summary of Literature Review 19

3 METHODOLOGY 21

3.1 Introduction 21

3.2 Parametric Study on Effect of Slope Angle on

Slope Deformation and Slope Stability 23

3.3 Deformation and Stability Analysis for

Case Cut Slope 24

3.4 Analysis Tool 27

3.4.1 Deformation Analysis 27

3.4.2 Stability Analysis 27

3.5 Data Analysis 28

4 RESULTS AND DISCUSSIONS 29

4.1 Introduction 29

4.2 Slope Deformation Simulation Modeling for

Various Slope Angle 30

4.2.1 Deformation Analysis for Cohesive Soil 31

4.2.2 Deformation Analysis for Cohesionless Soil 35

4.3 Slope Stability Simulation Modeling for Various

Slope Angle 39

4.3.1 Stability Analysis for Cohesive Soil 40

4.3.2 Stability Analysis for Cohesionless Soil 44

4.4 Slope Deformation and Stability Analysis for

Case Cut Slope 48

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4.4.1 Slope Deformation Analysis for

Case Cut Slope 48

4.4.2 Slope Stability Analysis for

Case Cut Slope 51

4.5 Discussions 53

5 CONCLUSIONS AND RECOMMENDATIONS 55

5.1 Introduction 55

5.2 Conclusion 55

5.3 Recommendation for Future Study 56

REFERENCES 58

Appendices A – C 61 - 105

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LIST OF TABLES

TABLE NO. TITLE PAGE

2.1 Factor of Safety used for design 14

2.2 Limit Equilibrium Method analysis in practice 16

3.1 Soil parameters for cohesive soil and cohesionless soil 23

3.2 Slope dimensions and angle 23

3.3 Slope material properties 25

4.1 Soil parameters for cohesive soil and cohesionless soil 30

4.2 Slope configurations and respective angle 30

4.3 Deformation for various slope configurations for

cohesive soil 33

4.4 Deformation for various slope configurations for

cohesionless soil 37

4.5 Soil parameters for cohesive soil and cohesionless soil 40

4.6 Factor of safety for various slope configurations for

cohesive soil 42

4.7 Factor of safety for various slope configurations for

cohesionless soil 46

4.8 Case cut slope material properties 48

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LIST OF FIGURES

FIGURE NO. TITLE PAGE

3.1 Overview of the activities for the study 22

3.2 Simulations Modeling for Various Degree of Slope Angle 24

3.3 Finite Element mesh of the case slope for

deformation analysis 26

3.4 Sketch of the case slope for stability analysis in Slope/W 26

4.1 (a) - (c) Deformation analysis for slope configuration of 1V:1H(45°) 32

4.2 Deformation versus slope configuration for cohesive soil 33

4.3 Deformation versus soil stiffness for cohesive soil 34

4.4 (a) - (c) Deformation analysis for slope configuration of 1V:1H(45°) 36

4.5 Deformation versus slope configuration for cohesionless soil 38

4.6 Deformation versus soil stiffness for cohesionless soil 39

4.7 (a) - (d) Stability analyses for medium clay for various slope angle 41

4.8 Factor of safety versus slope configuration for cohesive soil 42

4.9 Factor of safety versus cohesion 43

4.10 (a) - (d) Stability analyses for medium sand for various slope angles 45

4.11 Factor of safety versus slope configuration for

cohesionless soil 46

4.12 Factor of safety versus soil friction angle 47

4.13 (a) - (c) Deformation analysis for case cut slope 49

4.14 Relationship between soil stiffness and deformation

for case cut slope 50

4.15 (a) - (b) Stability analysis for case cut slope 51

4.16 Relationship between factor of safety and friction angle

for case cut slope 52

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LIST OF SYMBOLS

с - cohesion

c’ - effective cohesion

E - Young’s Modulus

F - failure function

FS - factor of safety

s - available shear strength

TD - total displacement

β - slope angle

γdry - dry unit weight

γwet - wet unit weight

ε - strain

ν - Poisson’s ratio

σ - stress

σn - normal stress

τ - equilibrium shear stress

τf - shear strength at failure

ø - angle of internal friction

ø’ - effective angle of internal friction

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LIST OF APPENDICES

APPENDIX TITLE PAGE

A Deformation Analysis (FEM) 61

B Stability Analysis (LEM) 84

C Data for Case Study 89

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CHAPTER 1

INTRODUCTION

1.1 Background

Many countries have experienced natural disasters such as landslide, slope

failures and soils collapse due to the lack of planning in dealing with sloping

ground. Demand for engineered cut and fill slopes on construction projects has only

increased the need to understand analytical methods, investigative tools, and

stabilization methods to solve slope stability problems since man-made slope has

disrupted the delicate balance of natural soil slopes. Existing natural soil slopes

have been cut to form man-made slope in the name of rapid infrastructure

development in the past fifty years has caused an imbalance in natural formations.

Disturbance to soil particles due to construction has led to soil instability and

deformation of slope faces. The movement or instability of natural slopes or man-

made slopes has become a common civil engineering problem for many construction

works and sometimes has major socio-economic impacts on the society (Lee, 2003).

Man-made slopes exist all over the world. In mountainous areas natural

slopes are adapted for construction of roads and other infrastructure. In deltaic

regions man-made slopes are created by construction of embankments and dykes.

The qualities posed by nature often are not well studied during the pre-investment

phase in a project in which stability problems may threaten the safety and economy

of exploitation of the product during its engineering lifetime. Design of man-made

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slopes should be based on evaluation of the natural physical, hydrological and rock

and soil mechanical conditions. (Rupke, et al, 2006)

Stability of slopes is controlled by several factors including stratigraphy,

groundwater levels, seepage gradients, weathering profiles, inaccurate measurement,

shear strength of the soil or rock mass, geometry, modes of failures and methods of

analysis. Hence, the stability of slopes depends on the internal factors such as soil

strength and groundwater level as well as external factors such as external loads

which induce destabilizing forces on the slope. Lee (2003) has stated that soil mass

located beneath a sloping ground surface has a tendency to move downward under

the influence of gravity. If the shearing resistance of soil is adequate, the slope is

stable. Otherwise, slope tends to move and this cause instability conditions.

The study and analysis of slopes is essential for understanding their

performance and, in particular, their stability, reliability and deformations. Thus

geotechnical engineers often seek to calculate values of quantitative indicators of

performance such as the factor of safety (safety factor), lateral deformation, and

probability of failure and reliability index.

Limit equilibrium method are commonly adopted for the stability analyses of

slope. This approach gives factor of safety as indication of the stability of the slope

while adopting of probability concept results in the probability of failure and

reliability index. Soil deformation may be simulated using numerical modeling

which has made significant strides in the past fifty years. By using numerical

modeling, engineers are now able to simulate detailed aspects of the construction

process for a variety of problems including embankment loading, deep excavation,

tunnels, and other static or dynamic soil-structure interaction boundary value

problems.

Finite element or the finite difference methods are numerical techniques

available to solve equilibrium equations governing the boundary value problem.

PLAXIS, FLAC and SIGMA/W are numerical modeling tools commonly use in

simulating the soil behaviour and deformation.

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1.2 Problem Statement

The rapid development of an area has led to the cutting of natural slopes to

form man made slopes which will induce deformation and reduction in the stability

of the slope itself. In general, the factor of safety calculated based on limit

equilibrium method for idealized slope geometry. In reality, the excavation activities

to form a cut slope can induce deformation of the slope face. Therefore, it is very

important to predict the amount and direction of soil displacement due to the

deformation and calculate the slope stability based on the actual geometry. In this

project, the deformation and stability analysis of a slope cut according to area

development were conducted by taking into account the factor of safety obtained by

Simplified Bishop method in limit equilibrium analysis. Therefore, the trends of the

deformations and factor of safety are studied for changes in degree of slope angles

for different types of soil.

1.3 Objectives of Study

The objectives of this study are:

a) to determine the effect of slope angle on the deformation and slope stability

by parametric study

b) to develop charts that correlates the slope angle, soil properties and factor of

safety as well as maximum deformations for preliminary assessment of slope

stability

c) to validate the application of the charts by using case study of cut slope

1.4 Scope of Study

The study is focused on deformation and stability analysis of cut slopes of

various slope angle mainly for two types of soil which is cohesive soil and

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cohesionless soil. For cohesive soil, it is grouped into three types which is soft clay,

medium clay and stiff clay and meanwhile, cohesionless soil also grouped into three

types which is loose sand, medium sand and dense sand. The study is also focused

on the Finite Element and Limit Equilibrium Method analysis of a man-made cut

slope for the road widening construction project at Damansara Perdana, Petaling

Jaya. Both analyses are made using Strength Reduction Technique and Simplified

Bishop Method since the analysis is considered for a long term analysis.

1.5 Importance of Study

The importance of the study is the evaluation of the effects of various degree

of slope angle on slope deformation and stability for different types of soil; and long

term stability and deformation analysis of a man-made cut slope. Furthermore, it is

important to understand the role of deformation of cutting slope in predicting the

failure. A practicing geotechnical engineer may save time, quality and cost in

dealing with slope problem if the deformation of the slope face can be predicted and

adopted for analysis during the design stage.