analysis of slope stability and proposed...
TRANSCRIPT
ANALYSIS OF SLOPE STABILITY AND PROPOSED REMEDIAL WORK FOR
FAILURE SLOPE AT KUALA LUMPUR
YONG CHIN YUNG
A project report submitted in partial fulfilment of the
requirement for the award of degree of
Master of Engineering (Civil-Geotechnics)
Faculty of Civil Engineering
Universiti Teknologi Malaysia
AUGUST 2014
iv
ACKNOWLEDGEMENT
I would like to express my sincere appreciation to my project supervisor
Dr. Nor Zurairahetty for her fully support, guidance and encouragement. Without her
continued patience on guiding and criticizing, I may not able to complete my
research appropriately.
My sincere appreciation also extends to Mr. Chen Tian Hee who is an
experiences senior geotechnical engineer. Mr. Chen is a senior engineer who
provided clearly explanation and assistance at various occasions to my project. His
opinion and hints are very useful indeed.
Last but not least, I wish to dedicate my grateful to my beloved family
members and my friends for their cares, loves, generous encouragement and support
to complete my Master Project.
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ABSTRACT
The objective of this study is to determine the cause of failure and evaluate
the slope stability in order to propose remedial measure for stabilization. The
investigate slope discussed in this paper is located at Persiaran Endah and within 10
kilometers from Kuala Lumpur. This slope is around 23 to 28 meter height and
approximate 550 to 66
0. The pertinent engineering properties were analyzed from
field test borings which were drilled up to 22 meters depth, seismic refraction survey,
inclinometer data, back analysis result, and engineer judgment. Back analysis was
carried out to estimate the mobilized shear strength of the problematic layer.
SLOPE/W program of Universiti Teknologi Malaysia was used for analysis. Based
on the result of the field investigation and numerical analysis the lowest factor of
safety (FOS) that evaluated from the existing slope in critical section was found to be
0.741. Therefore, soil nailing was recommended to reinforce the slope, which has an
acceptable FOS of 1.525 under static condition. Hence, the installation of soil
nailing, grid beam, and drainage were selected for remediation to ensure the long
term stability of the failure slope.
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ABSTRAK
Objektif kajian ini adalah untuk menganalisis punca kegagalan cerun serta
mencadangkan langkah pemulihan penstabilan cerun. Cerun yang dikaji dalam
projek ini adalah terletak di Persiaran Endah dan kira-kira jarak 10 kilometer dari
Kuala Lumpur. Cerun kajian ini adalah 23 hingga 28 meter tinggi dan anggaran
kecerunannya adalah 550 hingga 66
0. Sifat-sifat kejuruteraan yang berkaitan
dianalisis daripada borings yang telah digerudi sehingga kedalaman 22 meter, sismic
refraction survey, data inclinometer, back analysis, dan wajaran daripada jurutera.
Back analysis dijalankan untuk menganggarkan kekuatan ricih kerahan bagi lapisan
yang bermasalah. SLOPE/W program Universiti Teknologi Malaysia telah
digunakan dalam analisis tersebut. Berdasarkan keputusan penyiasatan sekitar dan
analisis berangka, faktor keselamatan terendah (FOS) yang dinilai pada kritikal cerun
seksyen adalah 0.741. Oleh itu, soil nailing telah dipasang untuk mengukuhkan cerun
denagn factor keselamatan 1.525 yang kukuh dalam keadaan statik. Kesimpulanya,
pemasangan soil nailing, grid beam, dan saliran pengailiran telah dicadangkan untuk
pemulihan supaya dapat memastikan kestabilan jangka panjang bagi cerun kegagalan
tersebut.
vii
TABLE OF CONTENTS
CHAPTER TITLE PAGE
DECLARATION ii
DEDICATION iii
ACKNOWLEDGEMENTS iv
ABSTRACT v
ABSTRAK vi
TABLE OF CONTENTS vii
LIST OF TABLES xi
LIST OF FIGURES xii
LIST OF ABBREVIATIONS xiv
LIST OF SYMBOLS xv
LIST OF APPENDICES xvi
1 INTRODUCTION
1.1 Background 1
1.2 Problem Statement 3
1.3 Aim and Objectives of Study 4
1.4 Scope of Research 4
viii
2 LITERATURE REVIEW
2.1 Introduction 6
2.2 Basic Requirement of Slope Stability Analysis 9
2.2.1 Geologic Conditions 9
2.2.2 Site Topography 10
2.2.3 Material Properties 10
2.2.4 Shear Strength 11
2.2.4.1 Drained Shear Strength 12
2.2.4.2 Drained Residual Shear Strength 12
2.2.5 Groundwater Conditions 13
2.3 Slope Stability Analysis 14
2.3.1 Factors Affecting Slope Stability 14
2.3.2 Limit Equilibrium Method 15
2.3.3 Method of Slices 16
2.3.3.1 Ordinary Method of Slices 17
2.3.3.2 Bishop’s Simplified Method 17
2.3.3.3. Janbu’s Method 18
2.4 Critical Slip Surface 19
2.5 Factor of Safety 19
2.6 Back Analysis 20
2.6.1 Application of Back Analysis in Analysis 21
2.6.2 Limitation of Back Analysis 22
2.7 SLOPE/W 22
2.8 Previous Study 23
2.9 Summary 25
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3 METHODOLOGY
3.1 Introduction 26
3.2 Field Observation 28
3.3 Data Collection 29
3.3.1 Surface Investigation 29
3.3.2 Subsurface Investigation 30
3.3.3 Laboratory Test 31
3.3.4 Rainfall Intensity Data 32
3.4 Experimental Methods 33
3.4.1 Standard Compaction Test 33
3.4.2 Triaxial Test (CIU) 35
3.5 Mohr Coulomb Analyses 37
3.6 SLOPE/W Software 40
3.6.1 Limit Equilibrium Methods 41
3.6.2 Defining the Problems 42
3.6.3 Slip Surface for Circular Failure Model 44
3.6.4 Verification and Computation 45
3.7 Conclusion 46
4 DATA AND ANALYSIS
4.1 Introduction 47
4.2 Back Analysis 47
4.3 Field Investigation 50
4.4 Soil Investigation Result 52
4.4.1 Geological Background 53
4.4.2 Borehole Result 54
4.4.3 Seismic Refraction Survey 54
4.5 Laboratory Testing and Interpretation 56
4.5.1 Soil Classification 56
x
4.5.2 Adopted Soil parameters 57
4.6 Slope Stability Analysis 58
4.7 Remedial Measure Recommendation 61
4.8 Summary 65
5 CONCLUSIONS AND RECOMMENDATIONS
5.1 Introduction 66
5.2 Conclusions 66
5.3 Recommendations 68
REFERENCES 69
APPENDICES 72
xi
LIST OF TABLES
TABLE NO. TITLE PAGE
2.1 Summary of static equilibrium conditions in
different limit equilibrium methods of slices
17
3.1 Summary of the site information 29
3.2 Summary of site investigation at study area 30
3.3 Summary of laboratory tests 31
3.4 Results from the Mohr’s circle analysis 38
3.5 Basic soil properties for slope stability analysis 40
4.1 Properties range in sensitivity study 48
4.2 The value of the parameter and the computed
factor of safety
50
4.3 Characteristics of soil, hard material and rock 55
4.4 Main regional soil strength parameters 58
4.5 Adopted soil parameters in the analysis 58
4.6 Summary of FOS for different slip surface
options
60
4.7 Summary of FOS for different LEM method 60
4.8 Summary of remedial work 62
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LIST OF FIGURES
FIGURE NO. TITLE PAGE
1.1 Site Location (Google Map) 5
2.1 Falls 8
2.2 Topple 8
2.3 Slide 8
2.4 Spread 8
2.5 Flow 8
2.6 Depiction of forces acting on a typical slice 16
2.7 c’ and ’ from back analysis of an intact and
failed slope
21
3.1 Plan of slope failure that under study 26
3.2 Flow chart of the research methodology 27
3.3 Slope failure at the section GG’ 28
3.4 Rainfall intensity near to study area 32
3.5 Triaxial apparatus 36
3.6 Graphical representation of Coulomb shear
strength equation
37
3.7 Mohr-Coulomb failure envelope 37
3.8 Undrained shear envelope 38
3.9a Mohr’s circle for sample UD/1 39
3.9b Mohr’s circle for sample UD/1 39
3.10 Slope stability analysis processes using Slope/W 41
3.11 Slip surface option 42
3.12 Entry and Exit point range 43
xiii
3.13 Assigned pore water pressure to the geometry 43
3.14 Key in material properties 44
3.15 Assigned material properties to the geometry 44
3.16 Verifying the input data 45
3.17 Solve dialog box 45
3.18 FOS of the slope 46
4.1 Actual slope that modelled in SLOPE/W 48
4.2 Sensitivity analysis 49
4.3 Slope failure happened in year 2008 & 2012 51
4.4 Explanatory diagram of water infiltration
induced slope failure
51
4.5 Wet soil indicate high content of water 52
4.6 Simplified geological map 53
4.7 Soil classification base on British Soil
Classification System
56
4.8 Plasticity chart 57
4.9 Slope stability analysis for section GG’ 60
4.10 Slope stability analysis for section HH’ 61
4.11 Typical dimensions of soil nailing application
based on slope angle
62
4.12 Remedial analysis for soil nailing 63
4.13 Remedial analysis for hybrid anchor 63
4.14 Example of finishing soil nailing with shotcreted 64
xiv
LIST OF ABBREVIATIONS
FS = Factor of Safety
FOS = Factor of Safety
F = Factor of Safety
ZR = Right Inter-slice Force
hR = Height of the ZR
CIU = Isotropic Consolidation Undrained Test
JKR = Jabatan Kerja Raya
BH = Borehole
INC = Inclinometer
SG = Specific Gravity
MC = Moisture Content
JPS = Jabatan Pengaliran & Saliran
UD = Undisturbed Sample
SPT = Standard Penetration Test
LEM = Limit Equilibrium Method
xv
LIST OF SYMBOL
cu = Unconfined Shear Strength
c’ = Drained Shear Strength
δ = Inter-slice Force Inclination Angle
c = Cohesion
υ = Angle of Internal Friction
’
=
=
Effective Friction Angle
Friction Angle
σ3 = Cell Pressure
σ3’ = Effective Consolidation Pressure
ub = Pore Water Pressure
ui = Steady Pore Pressure
δVc = Total Change in Volume
τ = Shear Strength
σ´n = Normal Stress
xvi
LIST OF APPENDICES
APPENDIX TITLE PAGE
A Overall Site Layout 73
B Mohr-Coulomb Analyses BH/4 74
C Inclinometer Result 76
D Piezometer Result 77
E Rainfall Intensity Data 78
F Simplified Borehole Profile 79
G Depth versus SPT-N Chart 80
H Line 2 Seismic Tomogram 81
I Slope Stability Analysis 82
CHAPTER 1
INTRODUCTION
1.1 Background
The developments in soil and rock mechanics play an important role in the
evolution of slope stability analyses in geotechnical engineering. The increasing
demand for the engineered cut and fill slopes in construction projects has enhanced
the needs for deepened understanding on the analytical methods, investigation tools
and stabilization methods in order to solve slope stability problems. (Abramson et
al., 2002)
In Malaysia, landslide records from the year 1966 to 2003 showed that 42%
of landslides occurred in hilly terrain areas and more than 90% occurred in
developed area such as in the infrastructural area, residential area and commercial
area. In order to carried out more investigation works for landslides in 2004, Public
Works Department Malaysia has establish a new branch called Slope Engineering
Branch that involved in mitigation, research and development, risk management,
safety and planning on slope and etc. (Slope Engineering Branch, 2010)
Slope Engineering Branch Malaysia state that the investigations carried out
thus far revealed that causes of landslides are due to physical, geological and human
elements. Based on landslide forensic statistical data for large scale failure from year
2004 to 2007, it was found that about 57% of landslides were due to human factor,
whereas 29% were attributed to physical factor and 14% was caused by various geo-
2
logical factors. It has also discovered that most of the landslides occurred at
manmade slopes.
With the incresed developments that have encroached into the hilly areas over
the pass two decades, Malaysia experience frequent landslides with a number of
major slope failure which cause damage and incovenience to the pulic. Among the
most notorious landslides was the colloapse of a slope with rubble wall, bringing
down Tower 1 Apartment of Highland Towers and killing 48 people on 11th
December 1993. The towers were built in 1978 at Taman Hillview, Hulu Klang
Selangor. (Gue & Cheah , 2007)
This landslide tragedy should be a good lessons for the relevant parties in
Malaysia so that improvement and more effective precaution measures can be taken
by them to avoid the destruction of lives and properties. Landslides not only bring
detrimental effects to the environment, but to the people and the economy as well.
Therefore, a reliable slope stability analysis should be carried out so that similar
incidents can be avoided in future.
To deal with these slope stability issues various approaches have been
adopted and developed over the years. The approaches now have been more of
computational rather than the manual. Various software are available to analyze the
slopes that are liable to failure by the calculating the factor of safety. Among the
famous approach are finite elements and limit equilibrium methods.
However, when using limiting equilibrium methods to analyze slopes, several
numerical inconsistencies and computational difficulties may occur in locating the
critical slip surface (depending on the geology) and hence establishing a factor of
safety. Despite these inherent limitations, due to its simplicity limiting equilibrium
continues to be the most commonly used approach (N. A. Hammouri et al. 2008).
Program SLOPE/W is formulated in terms of moment and force equilibrium factor of
safety equations. Limit equilibrium methods that used in this program include
Morgenstern-Price, General limit equilibrium, Spencer, Bishop, Ordinary, Janbu etc.
3
Hence, SLOPE/W is a main program that being chose to conduct the slope stability
analysis in various cases.
1.2 Problem Statement
Slope stability analysis is a vital analysis especially in a construction project
nearby the slope area. This analysis is performed to assess the safe design of human-
made or natural slopes and the equilibrium conditions. Improper slope analysis
design might cause slope failure which has been acknowledge as one of the most
frequent disaster that can lead to great loss of properties and life. Thus, the initial
soil investigation has to be done properly in order to achieve the actual soil condition
for the certain place where we want to start construction.
However, the stability of sloped land areas, landslide, is a main concern
where movements of existing or planned slopes would have an effect on the safety of
people and property or the usability and value of the area. Although, a lot of slope
analysis had carried out, but the possible of slope failure is still high. The quoted
phenomena take place due to either an incorrect approach to the assessment of their
stability, or mistakes made at the stage of geotechnical investigations, erroneous
assumptions made in the phase of carrying out calculation, or an improper location of
machines on the slope surcharge. One of the causes of the incorrect assessment of
slope stability may be inaccurate determination of the geological structure of the
slope in question. (Das, 2011)
Based on the Jabatan Pengairan dan Saliran Malaysia (JPS), Kuala Lumpur
was experienced a high intensity rainfall on March 2012. Consequently, three slope
failures were reported to occur along Jalan Persiaran Endah. These slope failures are
categorized as critical level because it is located beside the main road to a tourist spot
and just occur beside the residence areas. When slope failure occurs, the debris
encroaches on the road and may also cause damage to lives and properties from time
to time. Hence, the public safety is threatened directly and the immediately
4
remediation should be commenced. Therefore, this study is intended to carry out a
slope stability analysis on failure slope and in the same time, propose some remedial
measures based on the field investigation and stability analysis of the slope .
1.3 Aim and Objectives of Study
The aim of this study is to investigate the stability of the slopes by
determining the factor of safety and to proposed safe slopes at Jalan Pesiaran Endah,
Seputeh, Kuala Lumpur. Therefore, the objectives of this project are:
i. To identify the main cause of slope failure along Persiaran Endah,
Kuala Lumpur.
ii. To ascertain the design parameters and stability of the failure slopes
based on the SLOPE/W 2007 programme.
iii. To determine the appropriate remedial method on slope failure in term
of factor of safety.
1.4 Scope of Research
The investigation is limited to the colapsed section (hereafter will be referred
to as the investigated slope). SLOPE/W programme (by GEO-SLOPE) is use to
analyze the probability of failure of a slope. The minimum factor of safety will be
computed by using the critical parameters from the soil investigation reports data and
back analysis results. The data consists of soil investigation report which is gathered
from one related consultant company’s project. The case study is located at Persiaran
Endah Seputeh 50460, Wilayah Persekutuan Kuala Lumpur. This site can be
accessed via Jalan Robson and it is within 10 km from Kuala Lumpur City Centre.
The study area consists of three slopes failure namely Site 1, 2 and 3 and all are
different in geometry. However, in this study, the detail study on slope stability
analysis is only performed on failure slope at site 2 (section GG’ and HH’). This is
5
because site 2 is more critical in term of geometry if compare to another two sites.
The location of case study is shown in Figure 1.1.
Figure 1.1: Site Location (Google Map)
Failure Area
COORDINATE :
N = 3° 07’ 30.57’’
E = 101° 41’ 14.51’’
Investigated slope: Site 2
Site 3
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