Slope modelling applied for slope movement at kalibawang irrigation channel, KM 15 9 yogyakarta, indonesia

SLOPE MODELLING APPLIED FOR SLOPE MOVEMENT AT KALIBAWANG IRRIGATION CHANNEL, KM15.9 YOGYAKARTA, INDONESIA Dissertation Submitted to Gadjah Mada University to obtain the Degree of Doct

SLOPE MODELLING APPLIED FOR SLOPE MOVEMENT AT

KALIBAWANG IRRIGATION CHANNEL, KM15.9

SLOPE MODELLING APPLIED FOR SLOPE MOVEMENT AT

KALIBAWANG IRRIGATION CHANNEL, KM15.9

YOGYAKARTA, INDONESIA

Dissertation Submitted to Gadjah Mada University to obtain the Degree

of Doctor in Geological Engineering at Gadjah Mada University

Defended against the objections of the Dissertation

Examination committee, The Graduate School Gadjah Mada University on

STATEMENTS

Hereby, I declare that there is no result or duplication in this dissertation that has been proposed to obtain an academic degree from university There is no result or idea that has been reported or published by other authors except those cited in this dissertation and written in the reference

Yogyakarta, July, 2007

Nguyen Dinh Tu

Acknowledgments

First of all, I would like to deeply thank my Mom, a virtuous Mom who has managed to bring her son up all the way to his PhD She has devoted all her life to her children Mom, you and Papa have instilled the love of learning in me

by telling me the disadvantages that an illiterate has to face up to in his life Since Papa died, you have alone brought all your children up, alone managed to overcome the hardships Mom, you are my idol and I love you so much This thesis is for you

Second, my gratitude and appreciation is specified to my Promotor, Prof Kabul Basah Suryolelono, Department of Civil Engineering and Environmental, Faculty of Engineering, Gadjah Mada University, for his enthusiasm, fortitude, and precious guidance in detail during my research at UGM Thanks to Co- Promotor, Prof Kenji Aoki, Department of Urban and Environmental Engineering, Faculty of Engineering, Kyoto University, Kyoto, Japan who strongly encouraged me to finish my research I consider you as a father who has given an affection and perseverance for his son

I would like to give a special thanks to Assoc Prof Dr Heru Hendrayana, Co- Promotor, Department of Geological Engineering, Faculty of Engineering, UGM; and Dr Hary Christady Hardiyatmo, Co- Promotor, Department of Civil Engineering and Environmental, Faculty of Engineering, UGM; Assoc Prof Dr Subagyo Pramumijoyo, Department of Geological Engineering, Faculty of Engineering, UGM, for their lots of invaluable guidance not only in this research but suggestions on other social things during my staying in Yogyakarta

A special-big thanks goes to Assoc Prof Dr Dwikorita Karnawati, Co- Promotor, Head of Department of Geological Engineering, Faculty of Engineering, Gadjah Mada University, for her encouragement and her infinite guidance throughout this research work I deeply appreciate for her care in everything throughout this research

I would like to show my deep appreciation to all my lecturers at UGM, for their attention to give valuable discussion on related subjects I would like to give

a special thanks to Assoc Prof Dr Yoshitada Mito, Department of Urban and Environmental Engineering, Faculty of Engineering, Kyoto University, Kyoto, Japan for his intensive guidance and priceless suggestion during my research Thanks to Mr Chang Chuan Sheng, doctor student, Mr Susumu Kurokawa, master student, and all students of Department of Urban and Environmental Engineering, Faculty of Engineering, Kyoto University, for their intensive guidance and expert help during my staying in Kyoto

I have to say special thanks to Assoc Prof Dr Nguyen Viet Ky and Assoc Prof Dr Le Phuoc Hao, Dr Phan Thi San Ha, Dr Nguyen Manh Thuy,

Dr Dau Van Ngo, Ms Hoang Thi Hong Hanh, Geology and Petroleum Faculty,

Ho Chi Minh City University of Technology, Vietnam for their intensive leading and kind help to study at Gadjah Mada University and Kyoto University

A deep thanks goes to Mr Dany and Mr.Sito, my very good collaborators, for their useful help during monitoring time Thanks to Ms.Angeline Abrenica, AUN-SEED/Net master student, Department of Geological Engineering, UGM, for her kind helps to during writing this thesis Thanks for her checking and

correcting on my writing Thanks are also due to Dissertation Examination Committee for their comments and suggestions

I would like to show my sincere thanks to all my teachers since my younger age up to now for their guidance to upgrade my knowledge to the right way Other special thanks go to all AUN/SEED-Net scholar friends regardless of their background, nationality, religion and political belief

I gratefully acknowledge to JICA and AUN/SEED-Net for providing me financial support for attending International Conferences and throughout my study

of Doctoral Degree Thanks to Gadjah Mada University and Geological Engineering Department as well as Kyoto University and Department of Urban and Environmental Engineering, for their cooperation as host institution Meanwhile, thanks also go to Ho Chi Minh City University of Technology and Geotechnics Department, where I studied Bachelor and Master degree as well as where I have been working from 2001 to now

Last but not least, I would like to deeply thank my family, my brother Mr Nguyen Xuan Thuy and all my closed friends, who strongly encouraged me to overcome the hardships during this research I am indebted to all of you

ABSTRACT

Kalibawang Irrigation Channel has been found to be threatened by landslide risk in every rainy season Among many types of slope movement ever found, slope creeping is the most devastating hazard to the infrastructures and the private properties In the case of slope at Km 15.9 which is located in Mejing village of Kulon Progo Regency, Yogyakarta Special Province, the continuously slow slope movement is suspected to induce additional stress on the bridge and the channel bridge downhill to deform in every rainy season To help solve that problem, this research is conducted, under the AUN/SEED-Net program supported by JICA, to understand the mechanism of creeping as well as to choose the most appropriative modeling applied for slope movement prediction with special consideration given to the local climate and geology

Field investigation, laboratory testing, and field performance monitoring are utilized to investigate the site characteristics and to monitor the spatial and temporal slope behaviors Numerical analysis, consisting of modeling of slope hydrological process and slope stability analysis, (the Distinct Element Methods

of Particle Flow Code 2D, the limit equilibrium methods of GeoSlope/W) are used to enhance or add to the engineering judgment on that process

Results show that the movement of colluvial slope is very complex It has been found that some movements have occurred not only at the contact between the colluvial deposit and the base of mudstone, but also at the zone above ground water table The movements at the contact between colluvial deposit and mudstone may have been induced by pore-water pressure in response to the fluctuations in ground water level (increasing or losing pore-water pressure) or perhaps caused by the capillary rise or suction loss in response to the wetting of soil by rain infiltration Meanwhile, creeping occurred dominantly at the contact between the mudstone layer and tuffaceous medium sandstone as well as tuffaceous fine sandstone, although the tuffaceous fine sandstone had a high SPT value It has been observed that the slope movement depends on both rainfall and the stage of rainfall Moreover, all of the recorded movements are noticed to be not only relatively parallel to the slope dip direction but also followed different trends It has also been noted that the groundwater table achieved its maximum level with the same value as the accumulated 5 rain days (275-285mm) and 7 rain days (300-310mm) Hence, these values can be used to infer the time when the GWT level is at its maximum and the movement will be most intense

Meanwhile, the results of PFC model are in close agreement with the monitoring results Therefore, it can be said that the PFC model is the appropriate model which could be applied for slope movement of this area as well as of other areas with the same condition

Keywords: slope movement, creeping zone, colluvial deposits, strain-gauges,

stress, rainfall, PFC model

TABLE OF CONTENTS

Page

ACKNOWLEDGEMENTS .i

ABSTRACT .iv

TABLE OF CONTENTS v

LIST OF TABLES .viii

LIST OF FIGURES x

ACRONYMS AND SYMBOLS .xvii

CHAPTER 1 INTRODUCTION 1

1.1 Formulation of the Problem 1

1.2 Authenticity of the Research 3

1.3 Objectives of the Research 7

1.4 Expected Benefits of the Research 7

1.5 Scope of Research Work 8

CHAPTER 2 LITERATURE REVIEWS 10

2.1 Definition and Classification of Landslides 10

2.2 Landslide in Colluvial Soil 15

2.2.1 Definition of creep 15

2.2.2 Definition of colluvium 17

2.2.3 Slope instability in colluvium 17

2.2.4 Description and mechanics of colluvial landslide processes 19

2.2.5 Characteristics of colluvium affecting slope stability 23

2.2.6 Effect of geomorphic factors 26

2.2.7 Hydrological effect 27

2.2.8 Effect of Fire 29

2.3 Movement of water 31

2.3.1 Saturation runoff 31

2.3.2 Infiltration 32

2.3.3 Water flow in saturated zone 37

2.4 Water affect soil properties 40

2.5 Hydrological landslide-triggering thresholds 48

2.5.1 Direct correlation between Rainfall and Landslide 50

2.5.2 Statistical rainfall-triggering thresholds 51

2.5.3 Ground water level trigger shallow mass movement 54

2.5.4 Identification of hydrological triggering mechanisms 57

2.5.5 Deterministic rainfall triggering thresholds Shallow soil slips 59

2.5.6 Landslides at the soil-bedrock contact 63

2.6 Analysis and Modeling of Slope Hydrology 66

2.7 The Theory of Limit Equilibrium in GeoSlope/W Model 72

2.8 The Contact Constitutive Model in Particle Flow Code 80

2.9 Hypotheses 91

CHAPTER 3 METHOD OF RESEARCH 92

3.1 Desk Study and Literature Review 92

3.2 Research Instruments 93

3.2.1 Field Apparatus 93

3.2.2 Laboratory Work 93

3.3 Research Procedure 94

3.3.1 Initial site investigation 94

3.3.2 Field Instrumentation and Field Performance Monitoring 94

3.3.3 Monitoring Program 96

3.3.3.1 Installation of Piezometers 97

3.3.3.2 Installation of extensometers 99

3.3.3.3 Installation of strain gauges 101

3.4 Simulation modelling and Slope stability analysis 104

CHAPTER 4 RESULT AND DISCUSSION 106

4.1 Characteristic of Study Area 106

4.1.1 General settings 106

4.1.2 Stratigraphy and Lithology of Study area 107

4.1.3 Creeping condition 109

4.1.4 Geotechnical properties of soil 110

4.1.5 Soil properties and Slope stratigraphic 113

4.1.6 Slope hydrology 119

4.1.6.1 Characteristic of rainfall from 1985 to 2004 119

4.1.6.2 Permeability 123

4.2 Slope Monitoring Analysis Result 124

4.2.1 Slope hydrological monitoring 125

4.2.2 Extensometer monitoring 136

4.2.3 Strain-gauges monitoring 141

4.3 GeoSlope/W Model 158

4.3.1 The basic input parameters 158

4.3.2 Simulation and discussion 159

4.4 PFC Model 166

4.4.1 The basic input parameters 166

4.4.2 PFC2D Model result 167

4.4.2.1 Setting the model 167

4.4.2.2 Simulation and discussion 170

CHAPTER 5 CONCLUSION AND RECOMMENDATION 176

5.1 Conclusion 176

5.2 Recommendation 180

REFERENCES 182

LIST OF TABLES

Table 2.1 Type of material movement (Varnes, 1978) 11 Table 2.2 Factors that control the mass movement (Karnawati, 1996) 14 Table 2.3 Shear strength parameters obtained by a simple linear-regression for

the dataset of each specimen group (Matsushi, 2006) 42 Table 2.4 Characteristics of a slope selected for a study of the relation between

antecedent soil moisture, rainfall amount, rainfall intensity, and slope failure (in Thomas, 1998) 63 Table 2.5 Methods of stability analysis for soil slopes 71 Table 3.1 Summary of installed equipment; plural of equipment is still equipment 96 Table 3.2 Length, installation date and coordinate of Extensometers 101 Table 3.3 Depth of boreholes, amount & depth of gauges for each borehole 102 Table 4.1 Summary of laboratory test results (Departemen Pemukiman dan

Prasarana, 2002) 112 Table 4.2 Summary of laboratory test results (Civil Engineering Dept, UGM,

2005) 112 Table 4.3 Geoelectrical analysis following Schlumberger method (Civil

Engineering Dept, UGM, 2005) 115 Table 4.4 The result of Standard Penetration Test blows/30cm 116 Table 4.5 Summary of laboratory test results (Civil Engineering Dept, UGM,

2005) 118 Table 4.6 Maximum and average of maximum value of rain intensity in 20 years 119 Table 4.7 Maximum value and average value of rain days/month in 20 years

(1985-2004) 120 Table 4.8 Maximum and average value of total rainfall/month in 20 years (1985-

2004) 121 Table 4.9 Total rainfall and total rainy day in recent 20 years (1985-2004) 122 Table 4.10 Total rainfall and total rainy day in recent 21 years (1985-2005) 127

Table 4.11 Maximum and minimum fluctuation of ground water table at all

boreholes (elevation) 131

Table 4.12 Ground water table characteristics of 7 boreholes 132

Table 4.13 The maximum daily GWT fluctuations of 7 boreholes and accumulate rain 134

Table 4.14 The vibration amplitude of extensometers 140

Table 4.15 Number of movement days of SG-1 145

Table 4.16 Number of movement days of SG-2 147

Table 4.17 Number of movement days of SG-3 149

Table 4.18 Number of movement days of SG-4 153

Table 4.19 Number of movement days of SG-5 154

Table 4.20 Summary of all depth dominant creeping 157

Table 4.21 Summary of the properties of each layers set for the GeoSlope/W model 159

Table 4.22 The average values of each layer set for the first case 160

Table 4.23 The special values of each layer set for the second case 162

Table 4.24 The assumed values of each layer set for the third case 164

Table 4.25 The FoS with respect to the assumed values on the third case 164

Table 4.26 The soil properties of each layer at the time failure 165

Table 4.27 The micro-parameters used in PFC model 167

Table 4.28 The parameters used in fluid flow simulation 169

Table 4.29 The average unbalanced and maximum unbalanced force in first 10.000 steps in case without water flow ( force unit: kN) 170

Table 4.30 The average unbalanced and maximum unbalanced force in first 10.000 steps in case with water flow ( force unit: kN) 172

LIST OF FIGURES

Figure 1.1 Location of the study area 3

Figure 2.1 Diagram of mass movement type (Varnes, 1978) 12

Figure 2.2 Pressure distribution above and below a free water surface (Domenico and Schwarts, 1971, in Fredlund and Rahardjo, 1993) 34

Figure 2.3 Flow line in Darcy’ Law 38

Figure 2.4 The cross-section area and its elements 39

Figure 2.5 Simplified phase diagrams for soil (Davison, 2000) 41

Figure 2.6 Angle of shearing resistance (A) and soil cohesion (B) obtained by a simple linear-regression for the dataset of each specimen group (Matsushi, 2006) 42

Figure 2.7 Relation between ua and uw, using axis translation technique (Hilf, 1956 in Fredlund and Rahardjo, 1993) 46

Figure 2.8 Development of pore-air and pore-water pressure (Fredlund and Rahardjo, 1993) 46

Figure 2.9 Soil-water characteristic curve for some Dutch soils (Koorevaar et al 1983a) and Volume water content versus matric suction (Liakopoulos, 1965 b) (in Fredlund and Rahardjo, 1993) 47

Figure 2.10 Shear stress versus confining pressure relationship for various suctions for Madrid grey clay (Escario and Saez, 1986, in Fredlund and Rahardjo, 1993 ) 48

Figure 2.11 Results of direct shear tests on sands under low matric suctions (Donald, 1956, in Fredlund and Rahardjo, 1993) 48

Figure 2.12 Rainfall intensity/duration thresholds for shallow landslides developed by Caine (1980), Wieczorek (1987), and Cancelli and Nova (Pollini et al 1991) based on data from Moser and Hohensinn (1983) in Thomas, 1998 52

Figure 2.13 Plots of normalized accumulated rainfall versus normalized daily rainfall for landslide events (■) and non-landslide events (ο): a) for 2) days; b) for 5 days; c) for 15 days; d) for 25 days (Terlien, 1996) 54

Figure 2.14 Schematic representation of mechanisms initiating landslides

(Bogaard, 2001) 56

Figure 2.15 Mean vertical pressure head distribution as a function of depth for the dry and rainy season in relation to vertical changes in saturated hydraulic conductivity (Caris and Van Asch, 1996) 59

Figure 2.16 Critical combinations of rainfall intensity and duration as a function of slope angle (40 o and 43 o ) and antecedent soil moisture (wet and dry) calculated with HYSWASOR (Thornthwaite and Mather 1957) 62

Figure 2.17 Flow chart of quasi-three-dimensional transient hydrological model (Kirkby et al 1987) 66

Figure 2.18 Forces acting on a slice through a sliding mass with a circular slip surface (GeoSlope Manual, 2002) 73

Figure 2.19 Forces acting on a slice through a sliding mass with a composite slip surface (GeoSlope Manual, 2002) 74

Figure 2.20 Forces acting on a slice through a sliding mass defined by a fully specified slip surface (GeoSlope Manual, 2002) 76

Figure 2.21 Moment equilibrium factor of safety (GeoSlope Manual, 2002) 78

Figure 2.22 General solution procedure 81

Figure 2.23 Calculation cycle in PFC (picture source: manual of PFC, Itasca) 85

Figure 2.24 The notations for the ball-ball contact in (a) and ball wall contact in (b) (PFC 2D manual) 86

Figure 2.25 Flow condition through particles within the cell (PFC 2D manual ) 89

Figure 3.1 Location of the installed equipments and boreholes 95

Figure 3.2 Typical profile of stand-pipe piezometer 98

Figure 3.3 Twelve inches piezometer tip to be installed in the borehole 98

Figure 3.4 Manual measurement of water depth in a borehole with electric probe (Water Level Indicator) 99

Figure 3.5 Cracks are observed on top of the slope (a), on the school wall (b) 99

Figure 3.6 Extensometer 1(a), and its starting point (b) 100

Figure 3.7 Big cracks at Ex-1 (a), and how the movement affect the school

foundation (b) 100

Figure 3.8 Cores of soil and rock were recovered (a), P.V.C pipe and gauge (b) installing strain-gauge pipe (c), completing and measuring (d) 103

Figure 4.2 Cracks are observed on the school yard (a), on the school wall (b) 110

Figure 4.3 Cracks are observed on the top of the slope (a) and how the movement affect the school foundation (b) 110

Figure 4.4 Conventional core (a) and drilling core log (b) of study area (Civil Engineering Dept, UGM, 2005) 114

Figure 4.5 The result of Standard Penetration Test (N-value, blow/30cm) (Civil Engineering Dept, UGM, 2005) 116

Figure 4.6 Cross-section of the Kalibawang Channel around KM 15.9 117

Figure 4.7 Chart of maximum and average value of rain intensity in 20 years 119

Figure 4.8 Chart of maximum and average value rain days/month in 20 years 120

Figure 4.9 Chart of Maximum and average value of total rainfall/month in 20 years 121

Figure 4.10 Chart of Total rainfall and total rainy day in recent 20 years (1985-2004) 122

Figure 4.11 The result of permeability test in situ (unit: cm/s) 124

Figure 4.12 Chart of Total rainfall and total rainy day in recent 21 years (1985-2005) 127

Figure 4.13 Rainfall graph from January to December, 2005 127

Figure 4.14 Rainfall graph of monitoring time (Jan 2005 to Jun 2006) 129

Figure 4.15 GWT and Tuff layer, Basement at all boreholes, Jan 2005-Jun 2006 130

Figure 4.16 Maximum and minimum fluctuation of ground water table at all boreholes, Jan 2005-Jun 2006 131

Figure 4.17 The correlation between the accumulated rain and the GWT fluctuations 135

Figure 4.18 Fluctuation of pore-water pressure in monitoring time 136

Figure 4.19 Monitoring result of Extensometers and rainfall 138 Figure 4.20 Extensometer 4 (a), and land cultivation at research area (b) 139 Figure 4.21 New result from July 2006 to November 12, 2006 of 5

extensometers 140 Figure 4.22 Ground deformations observed in SG-1 in NS direction (the

movement is difficult to recognize at depth of 10.5m) 143 Figure 4.23 Ground deformations observed in SG-1 in EW direction (the

movement is easy to recognize at depth of 10.5m) 143 Figure 4.24 The real ground deformations observed in SG-1 by synthetic force

method (strain-value unit: 10 -3 strain) 143 Figure 4.25 The real ground deformations observed in SG-1 in response to

groundwater fluctuation, precipitation and lithology (strain-value

unit: 10 -3 strain) 144 Figure 4.26 The note for movement days of SG-1 and strain value at 10.5m in

response to rainfall, (strain-value unit: 10-6 strain) 145 Figure 4.27 The real ground deformations observed in SG-2 in response to

groundwater fluctuation, precipitation and lithology (strain-value

unit: 10 -3 strain) 146 Figure 4.28 The note for movement days of SG-2 and strain value at 11.5m,

13.5m and 15.5m in response to rainfall, (strain-value unit :10-6

strain) 147 Figure 4.29 The real ground deformations observed in SG-3 in response to

groundwater fluctuation, precipitation and lithology (strain-value

unit: 10 -3 strain) 148 Figure 4.30 The note for movement days of SG-3 and strain value at 6.5m and

9.5m in response to rainfall, (strain-value unit: 10 -6 strain) 149 Figure 4.31 The correlation between increasing of strain value at the depth of

6.5m and decreasing of GWT in the last month of rain season

(strain-value unit: 10 -6 strain) 150

Figure 4.32 The correlation between increasing of strain value at the depth of

9.5m and decreasing of GWT in the last month of rain season

(strain-value unit: 10 -6 strain) 151

Figure 4.33 The real ground deformations observed in SG-4 in response to groundwater fluctuation, precipitation and lithology (strain-value unit: 10-3 strain) 152

Figure 4.34 The note for movement days of SG-4 and strain value at 2.5m in response to rainfall, (strain-value unit: 10 -6 strain) 153

Figure 4.35 The real ground deformations observed in SG-5 in response to groundwater fluctuation, precipitation and lithology (strain-value unit: 10 -3 strain) 154

Figure 4.36 The note for movement days of SG-5 and strain value at 1.5m and 3.5m in response to rainfall, (strain-value unit: 10 -6 strain) 154

Figure 4.37 The strain-value of all creeping depth (strain-value unit: 10 -6 strain) 155

Figure 4.38 The average strain-value of all creeping depth (strain-value unit: 10-6 strain) 155

Figure 4.39 Direction and positions of all movement 156

Figure 4.40 Nine lithological layers set for the GeoSlope/W model 158

Figure 4.41 Ten levels of ground water table set for the GeoSlope/W model 159

Figure 4.42 The factor of safety of slope ( FoS =3.684) with respect to GWT at level 1 on the first case 160

Figure 4.43 Factor of safety of slope ( FoS =3.680) with respect to GWT at level 8 on the first case 160

Figure 4.44 Factor of safety of slope (FoS) with respect to 10 levels of GWT on the first case 161

Figure 4.45 Factor of safety of slope ( FoS =1.575) with respect to GWT at level 10 on the second case 162

Figure 4.46 Factor of safety of slope (FoS) with respect to 10 levels of GWT on the second case 162

Figure 4.47 The most unstable zone at the time failure (FoS =1) 165

Figure 4.48 The weakest part in unstable zone at the time failure (FoS=1) 165

Figure 4.49 Total 7.000 balls with distribution radius of 0.52-0.86m after reaching a steady state condition 168

Figure 4.50 The model consists 3.530 balls are set in 9 layers 168

Figure 4.51 The model is applied with 2300 fluid cells before fluid flow simulation 169

Figure 4.52 The average unbalanced force (a) and maximum unbalanced force (b) in first 10.000 steps in case without water flow 170

Figure 4.53 The motion (a) and contact force (b) at the beginning in case without water flow 171

Figure 4.54 The motion (a) and contact force (b) after 5.000 steps in case without water flow 171

Figure 4.55 The motion (a) and contact force (b) after 10.000 steps in case without water flow 171

Figure 4.56 The average unbalanced force (a) and maximum unbalanced force (b) in first 10.000 steps in case with water flow 173

Figure 4.57 Comparing average unbalanced force (a) and maximum unbalanced force (b) between two cases with and without water flow 173

Figure 4.58 The simulation after 5.000 steps ( in case with water flow) 174

Figure 4.59 The simulation after 10.000 steps (in case with water flow) 174

Figure 4.60 Comparing the PFC simulation result with monitoring result 175

ACRONYMS AND SYMBOLS

ACRONYMS

AEV Air-Entry Value

AMI Approximate Mobility Index

DPPW Departemen Pemukiman dan Prasarana Wilayah - Department of

Settlement and Infrastructures

DEM Distinct Element Method

FoS Factor of Safety

GIS Geographic Information System

GWT Ground Water Table

PWP Pore Water Pressure

IRE Indonesian Institute of Road Engineering

LEA Limit Equilibrium Analysis

LEM Limit Equilibrium Method

SCS Soil Conservation Service

SPT Standard Penetration Test

SWCC Soil-Water Characteristic Curve

Fmax maximum allowable shear contact force

μ friction coefficient (in Particle Flow Code)

λ Pore size distribution index

μ particle friction coefficient that applies when the contact bond has

c′ Effective cohesive strength of the soil (N/m 2 )

DF Rate of soil particle detachment by flow

Ec Young’s modulus at each particle-particle contact (N/m 2 )

f(t) Infiltration at time t (cm/hr)

F(t) The cumulative infiltration

f 0 Initial infiltration rate (cm/hr)

f c Constant infiltration rate (cm/hr)

F i contact force vector

f int force per unit volume, related to interaction between particles and fluid

(N/m 3 )

g gravitational acceleration ( m/s 2 )

Gs : Specific gravity

i / i wy Gradient / hydraulic head gradient

I a The initial abstraction

k / k w Hydraulic Conductivity/ Coefficient of permeability (m/s)

u a Pore-air pressure (Pa)

u w Pore-water pressure (Pa)

Va Volume of air (m 3 )

V s Volume of soil particle (m 3 )

v w Flow rate of water (m 3 /s)

V w Volume of water (m 3 )

z(1) Elevation head (m)

z(2) Depth of the failure (m)

γ Volumetric weight of the soil/rock (g/cm3)

ρ Total density (g/cm3)

ρ d Dry density (g/cm3)

σ normal stress (N/m2)

σ′n Effective normal stress (N/m 2 )

σc mean and std dev., normal strength ( N/m 2 )

σn Total normal stress ( N/m 2 )

τ viscous stress tensor

τ' Effective shear strength ( N/m 2 )

τc mean and std dev., shear strength (N/m 2 )

τf Shear stress at failure (N/m 2 )

φ Angle of internal friction (degree)

φ' Effective angle of internal friction (degree)

CHAPTER 1 INTRODUCTION

1.1 Formulation of the Problem

Landslide is one of the geological hazards that commonly occur in tropical areas especially in rainy season It is major process in mountainous regions Some of those are volcanically and tectonically very active and their related geological and climatological conditions are the induced parameters of slope instability Landslides cause many losses of lives and significant amount of property destructions They are occurring at an alarming rate so that systematic and effective management of landslide have to be developed urgently Currently, appropriate and simple technology for landslide prevention has to be developed

The rain-induced landslide is one of the most common landslides, which frequently occurs in this area as well as in South East Asia Region In Indonesia, the recent landslide disasters, occurring in Java and Sumatra Barat during the rainy season last November to December 2000, resulted in 522 people lost their lives, thousands of people lost their homes and 657 ha land destroyed Those total loss was estimated about 10 billion rupiahs (which is about hundred thousands US dollars, Karnawati, 2003) To avoid such substantial loss, landslide occurrence should be prevented and minimized

The research area, Kalibawang Irrigation channel, is located approximately 20 km west of Yogyakarta, South central Java Island, Indonesia The channel is located at the toe of Kulon Progo hilly mountains and has been disrupted by some landslides This area is also within tropical zone and in rainy season most of the landslides frequently occur along this channel area The

disruption of exploitability of the channel and the budget spent for that channel and neighboring structures restoration bring into high economic loss To tackle this disaster, a research was conducted by Departemen Pemukiman dan Prasarana Wilayah, 2002 on “Landslide Identification and Geological Engineering Investigation along Kalibawang Irrigation Channel.” As a result, landslide and land deformation were found to be occurring; they are still the most hazardous phenomena for that area

Slow mass movement, or creep (rates <1 m per year of lateral movement), occurs in between Channel Section KM 12.0 to KM 19.00 These slow movements, in most cases, cause a serious risk to the development rather than risk

to lives In the case of slope at KM 15.9, the continuous slow movement is suspected to induce additional stress on the bridge and the channel downhill to deform every rainy season These structural damages still exist although engineering works have been done in that site for several years This is due to the limited understanding of the triggering rainfall, slope stratigraphy, geological structures, slope hydrological and the mechanism of slope movement in that area

The writer is interested in those problems: slope hydrological analysis in response to the rain infiltration on tropical soil, slope hydrology controls on slope stability on tropical soil, slope hydrology effects soil creeping on tropical soil to establish slope modelling for predicting mechanism of slope failure in Kalibawang, Indonesia, and the other area have the same conditions as Vietnam

Figure 1.1 Location of the study area

1.2 Authenticity of the Research

It was apparent that studies and researches on landslides had been extensively conducted since more than 20 years ago According to Terzaghi (1958), the Indonesian soil has unusual properties due to the particles being cemented together in clusters or aggregates This cluster hypothesis has been commented on elsewhere (Wesley, 1973) These research papers are emphasized

Site for slope monitoring

Kalibawang Channel

Progo/Tinalah rivers

Aerialphoto of KALIBAWANG

Km 13

Km 12

100m

on the particular engineering properties but the correlation between their sole behaviour and landslide is still need to investigate in detail

According to Wesley, (1977) slope failures in Indonesia relates with these problems in homogeneous soils on steep volcanic residual-soil slopes Engineering properties of Indonesia soil shows low compressibility, especially when in their undisturbed state and have high shear strength, whether undisturbed

or compacted (Wesley, 1973) He pointed out that these soils appear to maintain the same water content all year round despite climatic changes There is no tendency for the soil to shrink or swell as loss or gain of water does not occur The water table in latosol and andosol areas is usually fairly deep He also stated that the andosols has the depth up to at least 50 m

Health and Sarosa, (1998) and Karnawati, (2001) reported that mechanism

of landslide in many slopes of colluvial or residual soils in Java is mainly induced

by infiltrated rainwater in the permeable soil (such as clay, sandy clay of clay) which are underlain by more impermeable soil or rocks (Andesitic breccias, Andesite, claystone, tuff, or marl)

sand-Karnawati (1996, 2000) suggested that the triggering rainfall characteristics are strongly controlled by the permeability of soil/rock covering the slope and the initial groundwater table

According to Karnawati et al (2003) loss of suction is one common

mechanism of landslides on steep slope with thick soil cover and deep water table

In dry season, many steep tropical slopes remain stable due to the suction held by surface tension at soil particles The rainwater infiltrated into the soil pores, and then the suction reduced This results in the relatively shallow landslides

Comparing both Karnawati and Wesley statements, if the volcanic soil has

an outstanding property of water retention capacity, the suction cannot be a governing factor in the lowering of safety factor in landslide So suction is one of the important governing mechanisms of landslides in volcanic soil is still need to identify Furthermore, it needs to classify whether the research area has the andosol soil dominant or not

According to Kesumadharma et al (2000) landslides in Cukuhbalak,

Lampung region are related to geological structure Most of the landslides were occurred at the segment of the fault, which is parallel with the lineament of the river Although it is one of the causative factors in landslide, detailed studies on this research area is needed to identify how much the fault-associated landslide is controlled

Landslide hazard at Warungkiara (Sochowo et al 2001), west Java,

landslides occurred at weathered volcanic breccia unit at the upper part and the stratification of sand and clay at lower part The irregular cracks due to fault zone

at the slope that may allow the infiltration of surface water and then followed by seepage and the increase of the pore water pressure The high rainfall intensity, steep slope and discontinuities such as cracks or fault and groundwater flow are determined as the primary factors that cause landslides at that area However, each factor related to landslide is not revealed in detail

Brotodihardjo et al (2001) aslo stated the hugest landslide in Windusakti

village, central Java caused by the precedential rainfall that collected the sliding material mixed with rainwater and floodwater of the river broke the natural dam

About modelling, Karnawati et al (2003) carried out numerical modeling

by using Combined Hydrology and Slope Stability Modeling (CHASM) to analyze

the role of vegetation type in controlling slope hydrodynamic condition and stability of volcanic tropical soils However, result of such research was not yet calibrated with the field data The influences of vegetation on slope infiltration

and stability have also been carrying out by Christady et al (in Karnawati, 2004)

at the Tertiary volcanic area, nevertheless the control of slope stratigraphy and geological structures are not considered yet Therefore, this current research is deliberately designed to mainly investigate the dominant parameters on landslide mechanism and triggering rainfall characteristics in the volcanic tropical area

The records of forty-eight movements (Dept or Settlements and Regional Infrastructures, 2002 in Veasna, 2005) have been assessed in Kulon Progo mountain area since about ten years ago It is still need to identify the real mechanism of landslide governing in this volcanic area

Under support of JICA, the AUN/SEED-Net students, at Gadjah Mada University, Yogyakarta, Indonesia, have been studying about geology of Indonesia At this research area, Kalibawang Irrigation channel, Nimol (2005) studied about application of geographic information system (GIS) for landslide susceptibility mapping from KM 6 to KM 19, Veasna (2005) studied about process of rain-induced landslides at KM 15.9, Su Su Kyi (2007) studied about slope stratigraphy, microzonation map, geological structures affect landslides, and this research for establishing a slope modelling applied for slope movement

1.3 Objectives of the Research

In response to such serious problems and consequences, this research is urgently required with the purpose to:

a the rainfall and rain infiltration effects groundwater table and pore water pressure,

b prediction on slope stability and factor of safety of slope base on the rainfall and fluctuation of ground water table,

c evaluation on mechanism of slope failure in study area,

d suitable slope model, related to geotechnical combined with hydrogeological characteristics of the slope at area study and on tropical soil

1.4 Expected Benefits of the Research

This research could provide about: slope hydrological analysis in response

to the rain infiltration on tropical soil, slope hydrology controls on slope stability

on tropical soil, slope hydrology effects landslide on tropical soil and to establish slope modelling for predicting mechanism of slope failure in Kalibawang, Indonesia, and the other area have the same conditions

Those outcomes were then developed to support the mitigation system to reduce landslide risk Afterwards, this mitigation system was transferred into simple and communicative-public language so that it can be easily understood and implemented by the community in the vulnerable landslide area

1.5 Scope of Research Work

Main scope of research work are understanding the slope stratigraphy, geological structures, engineering geological condition, rainfall intensity, slope hydrology and the mechanism of slope movement to build the slope hydrological modelling applied for slope movement of study area Base on this scope, field observation, field measurement, laboratory test, desk study have been performed They include:

ƒ preliminary field investigation of the study area, collecting the data related

to study area,

ƒ detailed investigation and drilling works, collecting the samples, laboratory testing to determine stratigraphy, geological structures, engineering geological condition of study area,

ƒ installing the equipments (piezometers, extensometers and pipe strain gauges) recording daily data (groundwater table, strain gauge, pore-water pressure, rainfall intensity),

ƒ slope hydrological analysis in response to the rain infiltration, slope hydrology controls on soil properties and slope stability

The resulted data from fieldwork and laboratory measurements are characterized and analyzed systematically to obtain reliable input parameters for the development of modelling

All research is presented in five chapter of dissertation They include:

ƒ Chapter 1 highlights the background problem about landslide disaster, the objectives, the originality of this research and outcomes of this dissertation

ƒ Chapter 2 reveals the literature reviews on the landslide phenomenon and some theoretical background concerning with this research The hypotheses are derived from those reviews and the real condition from the field

ƒ Chapter 3 deals with all the methods applied in this research This includes preliminary investigation, site investigation of the whole research area, detailed investigation and instrumentation of monitoring devices at target slope The data from fieldwork and laboratory are characterized and analyzed systematically to obtain reliable input parameters for the development of statistical and numerical simulation The GeoSlope/W and PFC2D model are used for understanding the mechanism of slope movement

ƒ Chapter 4 presents the result and discussion on the monitoring analysis and simulation result The mechanics of movement as well as affect slope hydrology (rainfall and fluctuation of ground water table) to slope movement are elucidated It states the comparison of the result from the numerical simulation of the Particle Flow Code 2D as well as the GeoSlope/W with the actual monitoring result

ƒ Chapter 5 summarizes the conclusion on the overall research and some recommendations on further research The summary of the research, the references, the appendix and curriculum vitae are followed at the end of this dissertation

CHAPTER 2 LITERATURE REVIEWS

2.1 Definition and Classification of Landslides

Landslide is the sliding movement of masses of loosened rock and soil down a hillside or slope Landslide hazard is defined as the probability for a landslide within a given area and within a given period of time (Varnes, 1984) In landslide hazard studies a spatial and temporal component should be present The spatial component must be aimed at the prediction of the location of future landslides while the temporal component must be focused on the prediction of landslide frequency

Varnes (1978) emphasized type of movement and type of material Movements are divided into five types: falls, flows, slides, spreads and topples Doe (1994) recognizes the existence of complex landslides where ground displacement is achieved by more than one type of mass movement and emphasizes that this should not be confused with landslide complex, which is an area of instability within which occur many different types of mass movement Cruden and Varnes (1996) suggest that landslide complexity can be indicated by combining the five basic types of movement and the three divisions of materials

If the type of movement changes with the progress of movement, then the material should be described at the beginning of each successive movement For example,

a rock fall that was followed by the flow of the displaced material can be described as a rock-fall debris-flow

Only an accurate diagnosis makes it possible to properly understand the

landslide mechanisms and then to propose effective remedial measures Terzaghi

(1950) divided landslide causes into external causes which result in an increase of

the shearing stress (e.g geometrical changes, unloading the slope toe, loading the

slope crest, shocks and vibrations, drawdown, changes in water regime) and

internal causes which result in a decrease of the shearing resistance (e.g

progressive failure, weathering, seepage erosion)

It does not matter if the ground is weak as such - failure will only occur as

a result if there is an effective causal process that acts as well Such causal

processes may be natural or anthropogenic, but effectively change the static

ground conditions sufficiently to cause the slope system to fail, i.e to adversely

change the stability state (Popescu, 1984)

Table 2.1 Type of material movement (Varnes, 1978)

Type of material

Type of movement

Falls Rockfall Debrisfall Earthfall

Rotational Few units

Block Glide Block Glide Block Glide Slides

Figure 2.1 Diagram of mass movement type (Varnes, 1978)

Earth block slide

Debris flow Sand or silt flow

Earth flow

Debris avalanche Sand run

fine-grained

Joint opened Original support removed

FALLS

source area Main track depositional area

rock fall

flow tongue of rock debris

mixed sediments undercut by river

gravel clean sand

clay-main scarp head

graben

slip surface

toe pressure ridge

failure along faults

dip slope control by bedding planes

scarp face control by joints

moderate

Leroueil and Tavenas (1981) defined the following four possible different stages of landslide activity:

1 pre-failure stage, when the soil mass is still continuous, this stage is mostly controlled by progressive failure and creep,

2 onset of failure characterized by the formation of a continuous shear surface through the entire soil or rock mass,

3 post-failure stage, which includes movement of the soil or rock mass, involved in the landslide, from just after failure until it essentially stops,

4 reactivation stage when the soil or rock mass slides along one or several pre-existing shear surfaces This reactivation can be occasional

or continuous with seasonal variations of the rate of movement

According to Varnes (1978), landslide hazard zonation is a technique of classifying an area into zones of relative degrees of potential hazards by ranking

of various causative factors operative in a given area, based on their influence in initiation of landslides According to literature surveys and field checking, Su Su Kyi (2007) made comment that the significant parameters causing slope instability problems in Kalibawang area are: slope aspect; slope morphometry; yearly and monthly rainfall condition; landuse / landcover; dip slope relation; rockmass strength; existence of spring; weathering; type of surface weak soil; road or channel; tectonic/lineament and relative relief

Karnawati (1996) have compiled of some research result about landslide in Indonesia and conclude that some factor having an effect on for example and presented at Table 2.2

Table 2.2 Factors that control the mass movement (Karnawati, 1996)

TYPE OF MASS MOVEMENT CONTROL

FACTOR Fall Slide Slump Flow, Creep, Lateral movement

1.Slope

condition

Generall more than 45º

Middle slope until steep slope (20º - 60º)

Middle slope (20º - 45º) Foot mountain (12º - 20º)

by crack or fracture

Generally form of rock block

1.Residual soil 2.Colovial 3.Weathering volcanic deposite

4 Debris rock

1.Residual soil 2.Colovial 3.Weathering volcanic deposite

4 Debris rock

Soil Clay (smectite) (montmorilonit dan vermicullite)

Representing contact area between cover material which in character release and get away the water with the layer lithology/soil pillowing which in character more compact and impermeable Representing area dissociating two different zona degree of weathering Frequently slip area in the form of clay layer of type smectite (montmorillonite), silt stone layer, chip and tuff

b Slip area No slip area

Form of slip area

is diametrical Form of slip area is concave Form of slip area generally diametrical

c Soil/rock

mass not

movement

The rock block which still

stabilize

Soil/bedrock having the character of more compact and more massifs, for example bedrock in the form of andesite breccia and andesite

flow, creep and lateral movement b.Geological

history With the active geology lay in the subduction zone, generally have association with the activity volcanic and hill morphology 4.Weather

and rainfall 1 High rainfall intensity (more than 70 mm/hour or 2500 mm/year 2 Rainfall intensity which less than 70 mm/hour but happened by continuing

during several hours, few days or week

Comparing with mass movements are occurring in study area, this phenomenon is considered as colluvial creep, and the important controlling factors are: geology structure, slope condition, creep-material and slope hydrology Those

factors will be discussed detail in Landslide in Colluvial Soil section

2.2 Landslide in Colluvial Soil

2.2.1 Definition of creep

Creep is the term used to describe the tendency of a material to move or to deform permanently to relieve stresses Material deformation occurs as a result of long term exposure to levels of stress that are below the yield or ultimate strength

of the material

Stages of creep

Initially, the strain rate slows with increasing strain This is known as primary creep The strain rate eventually reaches a minimum and becomes near-constant This is known as secondary or steady-state creep It is this regime that is most well understood The "creep strain rate" is typically the rate in this secondary stage The stress dependence of this rate depends on the creep mechanism In tertiary creep, the strain-rate exponentially increases with strain

Mass movement-Soil creep

Mass movement is the down slope movement of earth materials under the

influence of gravity The detachment and movement of earth materials occurs if the stress imposed is greater than the strength of the material to hold it in place

Shear strength is a measure if the resistance of earth materials to be moved The

interlocking of soil particles increases the ability of material to stay in place Plant

roots also help bind soil particles together Shear stress is primarily a function of

the force exerted by the weight of the material under the influence of gravity acting in the down slope direction The slope of the surface determines the amount

of stress that occurs on earth materials Water destabilizes hill slopes by creating pressure in the pore spaces of earth materials Water infiltrating into slope materials saturates the soil particles at depth by filling the pore spaces between The weight of water lying above creates water pressure that drives soil particles apart This lessens the friction between them and enables them to slip past one another Material is mobilized when the shear stress imposed on a surface exceeds the shear strength The movement, especially in the case of slides and slumps, is along a failure plane The failure plane may be a well-defined layer of clay or rock upon which sets the destabilized surface material Humans induce mass movement when subjecting a slope to a load that exceeds its ability to resist movement People building houses on scenic hill slopes often find their homes threatened by

a landslide Undercutting of hillsides during road construction commonly creates unstable slopes making them prone to failure

Soil creep is nearly imperceptible to the naked eye as it is the slowest of all

types of mass movement Soil creep generally occurs in the top few meters of the surface and is accomplished by expansion and contraction of the soil For instance, when water in the soil freezes the ice pushes soil particles outward perpendicular to the slope Upon warming, the ice melts and the soil is pulled down slope under the influence of gravity Over many freeze-thaw cycles soil moves slowly down slope In many cases one might not be able to tell that soil creep is occurring by just examining the surface However, trees growing on

surfaces undergoing creep will have curved trunks or roots that are curved Broken retaining walls and curved railroad tracks also indicate creep in action

2.2.2 Definition of colluvium

Bates and Jackson (1980) defined colluvium as follows: “A general term applied to many loose, heterogeneous, and incoherent mass of soil material and/or rock fragments deposited by rain wash, sheet wash, or slow continuous downslope creep, usually collecting at the base of gentle slopes or hillsides” Typically, colluvium is a poorly sorted mixture of angular rock fragments and fine-grained materials These deposits rarely are more than 8 to 10 m thick, and they usually are thinnest near the crest and thickest near the toe of each slope

Colluvium may be the most ubiquitous surficial deposit Costa and Baker (1981) reported estimates that colluvium covers more than 95 percent of the ground surface in humid temperate regions and from 85 to 90 percent of the ground surface in semiarid mountainous areas At the base of slopes, colluvium interfingers with alluvial deposits and may actually constitute the major portion of these deposits and may actually constitute the major portion of these deposits

2.2.3 Slope instability in colluvium

Given the ubiquitous nature of colluvium and its distribution within many hilly or mountainous areas, it should not be surprising that the instability of colluvial slopes has resulted in major economic losses and on some occasions the loss of human life (Costa and Baker, 1981)

The most common class of landslides in colluvium involves two distinct components of movement: an initial shallow rotational or translational slide

followed by flowage of the disturbed mass (Ellen and Fleming, 1987; Ellen, 1988) This failure mode results in a relatively small circular scar at the location

of the initial slide, a long narrow track leading directly down the hillside formed

by the flowage of the liquefied soil and debris, and a zone of deposition in the minor drainage channel at the base of the slope Numerous individual such slides provide large volumes of debris that clog stream channels Liquefaction of this material causes it to remobilize and produce large and rapidly moving debris flows that destroy lives and property downstream

Sidle et al (1985) identified five natural factors that have the greatest

influence on the stability of colluvial slopes:

1 soil properties, especially the hydrologic and mineralogical conditions that affect engineering soil behavior and strength properties of the colluvium,

2 geomorphology, including the geologic and tectonic setting, slope gradient, and shape,

3 hydrology, especially soil water recharge and effective evapotranspiration rates that reflect local climate and vegetation conditions,

4 vegetative cover, including the reinforcing effect of roof systems and the loss of such strength when roots deteriorate following timber harvesting or fire,

5 seismicity, especially the potential for liquefaction of marginally stable soils on steep slopes