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Landslides cause significant damage worldwide and therefore epitomize the most important problems in geotechnical engineering. Hence, perceiving the mechanics involved in the deformation process of landslides is necessary for risk assessment. In addition to the resistance offered by basal shear surfaces, internal shearing also influences the stability and kinematics of compound landslides. For compound landslides, internal shearing is essential to develop feasible sliding mechanisms. The internal distortion is caused by the formation of shear bands that develop within the sliding mass. The strain localization is generally attributed to slope changes along the basal sliding surface (or topography) that constrain the strain field of the landslide. The development of these internal shear bands also controls the energy dissipation, and its distribution determines the final degradation of the material. This work focuses on the study of internal failure mechanisms that develop in compound landslides. A theoretical model of a compound landslide is numerically analyzed using the Material Point Method (MPM), a state-of-the-art numerical technique appropriate to model large deformation problems. The internal failure pattern is identified for different basal sliding geometries. Based on that, a generalized method is proposed to estimate the internal failure mechanism of bi-planar compound geometries. The material degradation and energy dissipation are evaluated in terms of the accumulated deviatoric strain and the reaction forces exerted by the landslide on a vertical wall. Moreover, preliminary studies are conducted to analyze the use of barriers as a mitigation strategy to counter landslide damage, and their efficiencies are investigated. / Master of Science / Landslides consist of movement of rock and debris down a slope. They cause substantial damage each year and therefore represent an important class of problems in geotechnical engineering. Understanding the deformation process and internal shearing pattern occurring in landslides is an important aspect for assessing the risk that a landslide poses. The internal shear is caused due to the formation of shear bands that develop within the mass flowing down the slope and originate at the points of slope change on an incline. These shear bands also affect the amount of energy dissipated and the degradation of flow material. In this work, the internal failure mechanism in landslides is analyzed and effects on landslide kinematics are studied. Material Point Method (MPM) is used to simulate slope instabilities which is an advanced numerical technique appropriate for modeling large deformation problems such as landslides. Several theoretical models of compound landslides are presented considering variation in geometry (roundedness), friction, and slope angle. A generalized failure mechanism of a landslide is proposed based on its geometry and physical parameters. Finally, accumulated strains and reaction forces impacted by moving mass on a wall are calculated for different landslide geometries, and subsequently correlated to energy dissipation material degradation. These results also serve as a precursor to studying the role of barriers in mitigating landslide damage.

On September 14, 1981 a major slide was discovered in the upstream slope of San Luis Darn, located about 100 miles southeast of San Francisco, California. The slide occurred at the end of a period of rapid drawdown of the reservoir. Although this was the longest and fastest drawdown in the life of the dam, 180 feet in 120 days, there had been seven previous cycles of drawdown, some nearly as severe as the one that preceded the slide. Field measurements showed the slide was caused by the clayey slopewash material left in the foundation of the dam during construction. Although the slopewash was dry and extremely strong when the embankment was built, it apparently was weakened considerably when submerged beneath the reservoir and its strength was further degraded by cyclic loading effects as the reservoir level was raised and lowered during the 14 years preceding the slide. The objective of this research was to gain a better understanding of the mechanisms of strength loss in the slopewash that resulted in the 1981 slide at San Luis Dam. This was accomplished using laboratory tests on undisturbed samples of slopewash, analyses of seepage through the embankment and foundation, finite element analyses of stresses in the dam during construction and operation of the reservoir, and conventional equilibrium slope stability analyses. The laboratory tests showed that the shear strength of the slopewash decreases very quickly when the desiccated material is wetted. Wetting causes immediate reduction in shear strength to the fully softened value, and there is no lasting effect of consolidation by drying. After wetting the highly desiccated slopewash has the same strength as in the remolded, normally consolidated condition. Tests that simulated cyclic changes in normal stress and shear stress like those during drawdown and refilling of the reservoir showed that further strength loss results from cyclic loading of the slopewash. Cyclic loading at stress levels below the fully softened peak strength result in continual shear displacement, and eventually, when the cumulative horizontal displacement reaches approximately ten inches, the shear strength is reduced to its residual value. / Ph. D.

A field experiment was conducted at near Lake Coleridge in the Southern Alps of New Zealand, focusing on the kinematic response of bedrock-dominated mountain edifices to seismic shaking. The role of topographic amplification of seismic waves causing degradation and possible failure of rock masses was examined. To study site effects of topography on seismic ground motion in a field situation, a small, elongated, and bedrock-dominated mountain ridge (Little Red Hill) was chosen and equipped with a seismic array. In total seven EARSS instruments (Mark L-4-3D seismometers) were installed on the crest, the flank and the base of the 210 m high, 500 m wide, and 800 m long mountain edifice from February to July 2006. Seismic records of local and regional earthquakes, as well as seismic signals generated by an explosive source nearby, were recorded and are used to provide information on the modes of vibration as well as amplification and deamplification effects on different parts of the edifice. The ground motion records were analyzed using three different methods:comparisons of peak ground accelerations (PGA), power spectral density analysis (PSD), and standard spectral ratio analysis (SSR). Time and frequency domain analyses show that site amplification is concentrated along the elongated crest of the edifice where amplifications of up to 1100 % were measured relative to the motion at the flat base. Theoretical calculations and frequency analyses of field data indicate a maximum response along the ridge crest of Little Red Hill for frequencies of about 5 Hz, which correlate to wavelengths approximately equal to the half-width or height of the edifice (~240 m). The consequence of amplification effects on the stability and degradation of rock masses can be seen: areas showing high amplification effects overlap with the spatial distribution of seismogenic block fields at Little Red Hill. Additionally, a laboratory-scale (1:1,000) physical model was constructed to investigate the effect of topographic amplification of ground motion across a mountain edifice by simulating the situation of the Little Red Hill field experiment in a smallscale laboratory environment. The laboratory results show the maximum response of the model correlates to the fundamental mode of vibration of Little Red Hill at approximately 2.2 Hz. It is concluded that topography, geometry and distance to the seismic source, play a key role causing amplification effects of seismic ground motion and degradation of rock mass across bedrock-dominated mountain edifices.

京都大学 / 新制・課程博士 / 博士(工学) / 甲第24815号 / 工博第5158号 / 新制||工||1985(附属図書館) / 京都大学大学院工学研究科社会基盤工学専攻 / (主査)教授 渦岡 良介, 准教授 岩井 裕正, 准教授 上田 恭平, 教授 森 信人 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

by Wong, Tak-yee Tammy. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1995. / Includes bibliographical references (leaves 170-178). / ABSTRACT --- p.i-iii / ACKNOWLEDGEMENTS --- p.iv-v / TABLE OF CONTENTS --- p.vi-x / LIST OF FIGURES --- p.xi-xii - / LIST OF PLATES --- p.xiii-ix / LIST OF TABLES --- p.x-xii / Chapter CHAPTER I: --- INTRODUCTION --- p.1 / Chapter 1.1 --- Introduction --- p.1 / Chapter 1.2 --- Research Questions --- p.5 / Chapter 1.3 --- Study Significance --- p.7 / Chapter 1.4 --- Organization of the Thesis --- p.8 / Chapter CHAPTER II: --- LITERATURE REVIEW --- p.10 / Chapter 2.1 --- Introduction --- p.10 / Chapter 2.2 --- Nature of Landslides --- p.10 / Chapter 2.2.1 --- Landslide Classification --- p.10 / Chapter 2.2.2 --- Morphometry of Landslides --- p.12 / Chapter 2.2.3 --- Factors Affecting Landslide Occurrence --- p.16 / Chapter 2.2.3.1 --- Gradient --- p.19 / Chapter 2.2.3.2 --- Slope Shape --- p.21 / Chapter 2.2.3.3 --- Aspect --- p.22 / Chapter 2.2.3.4 --- Vegetation --- p.24 / Chapter 2.2.3.5 --- Drainage --- p.26 / Chapter 2.2.3.6 --- Precipitation/Seismicity --- p.26 / Chapter 2.2.3.7 --- Lithology and Geological Influences --- p.28 / Chapter 2.2.3.8 --- Regolith --- p.29 / Chapter 2.2.3.8.1 --- Hydrological Properties of Soils --- p.29 / Chapter 2.2.3.8.2 --- Engineering Properties of Soils --- p.30 / Chapter 2.3 --- Data Sources for Landslide Studies --- p.31 / Chapter 2.3.1 --- Aerial Photo Interpretation (API) --- p.32 / Chapter 2.3.2 --- Remote Sensing --- p.34 / Chapter 2.3.3 --- Field Survey --- p.35 / Chapter 2.3.4 --- Subsurface Investigation --- p.36 / Chapter 2.4 --- Landslide Studies in Hong Kong --- p.36 / Chapter 2.5 --- Applications of GIS on Landslide Studies --- p.38 / Chapter 2.5.1 --- Major Data in GIS for Landslide Studies --- p.39 / Chapter 2.5.1.1 --- Triangulated Irregular Network (TIN) as a Representation of Surface --- p.39 / Chapter 2.5.2 --- Applications --- p.42 / Chapter 2.5.2.1 --- Inventory --- p.43 / Chapter 2.5.2.2 --- Landslide Hazard Assessment --- p.43 / Chapter 2.5.2.2.1 --- Statistical Modeling --- p.46 / Chapter 2.5.2.2.2 --- Physical Processes or Three- Dimensional Modeling --- p.50 / Chapter 2.6 --- Suggestions for Future Research Directions --- p.51 / Chapter CHAPTER III: --- STUDY AREA --- p.54 / Chapter 3.1 --- Location and Choice of Study Area --- p.54 / Chapter 3.2 --- Climatic Aspects --- p.56 / Chapter 3.3 --- Geological Aspects --- p.62 / Chapter 3.3.1 --- General Information of GASP V --- p.62 / Chapter 3.3.2 --- Rock Types Specific to the Two Sites Chosen --- p.63 / Chapter 3.3.2.1 --- Volcanic Units - Repulse Bay Formation --- p.65 / Chapter 3.3.2.2 --- Sedimentary Units - Port Island Formation (PI) --- p.65 / Chapter 3.4 --- Geomorphological Aspects --- p.66 / Chapter 3.4.1 --- General Information of GASP V --- p.66 / Chapter 3.5 --- Erosion and Stability --- p.67 / Chapter 3.6 --- Vegetation --- p.67 / Chapter 3.7 --- Summary --- p.70 / Chapter CHAPTER IV: --- DATABASE CONSTRUCTION AND MANIPULATION --- p.71 / Chapter 4.1 --- Data Collection --- p.73 / Chapter 4.1.1 --- Aerial Photo Interpretation (API) --- p.73 / Chapter 4.1.1.1 --- Landslip Inventory --- p.75 / Chapter 4.1.2 --- Field Techniques --- p.78 / Chapter 4.1.2.1 --- Slope Failure/Deposit Field Survey sheet --- p.78 / Chapter 4.1.2.2 --- Collection of Landslide Data --- p.79 / Chapter 4.1.3 --- Collection of Existing Data --- p.80 / Chapter 4.1.3.1 --- 1:5000 Topographic Maps --- p.80 / Chapter 4.1.3.2 --- Terrain Classification --- p.81 / Chapter 4.1.3.3 --- WWF Vegetation Database --- p.85 / Chapter 4.2 --- Data Input and Conversion --- p.86 / Chapter 4.2.1 --- Digitizing of Data --- p.87 / Chapter 4.2.1.1 --- Landslip Capture in Stereocord --- p.87 / Chapter 4.2.1.2 --- Data Conversion --- p.94 / Chapter 4.2.1.2.1 --- Topographic Maps - Scanning and Vectorization --- p.94 / Chapter 4.3 --- Data Editing --- p.94 / Chapter 4.3.1 --- Line Cleaning for Landslide Coverage --- p.96 / Chapter 4.3.2 --- Line Cleaning and Height Tagging for Topographic Map --- p.96 / Chapter 4.3.3 --- Editing on Terrain Classification Map --- p.97 / Chapter 4.4 --- Database Construction --- p.97 / Chapter 4.4.1 --- Data Base Design --- p.97 / Chapter 4.4.1.1 --- Graphical Data Base --- p.98 / Chapter 4.4.1.2 --- Attribute Data Base --- p.99 / Chapter 4.4.2 --- Creation of a Triangulated Irregular Network (TIN) --- p.104 / Chapter 4.5 --- Data Preparation and Pre-analysis Manipulation --- p.105 / Chapter 4.5.1 --- Extraction of Terrain Variables from TIN --- p.105 / Chapter 4.5.1.1 --- TIN'S Derived Variable - Elevation --- p.105 / Chapter 4.5.1.2 --- TIN'S Derived Variable - Gradient --- p.107 / Chapter 4.5.1.3 --- TIN'S Derived Variable - Orientation --- p.109 / Chapter 4.5.1.4 --- TIN's Derived Variable - Dimensions (surface distance) of Landslides --- p.109 / Chapter 4.5.1.5 --- Micro-DEM and Profile --- p.109 / Chapter 4.5.1.6 --- Weighting Method Adopted in Calculating the Gradient and Orientation of Primary Depletion Scar --- p.110 / Chapter 4.5.2 --- Data Preprocessing --- p.110 / Chapter 4.6 --- Summary --- p.114 / Chapter CHAPTER V: --- STATISTICAL ANALYSIS OF LANDSLIDE DISTRIBUTION --- p.115 / Chapter 5.1 --- Sampling --- p.116 / Chapter 5.1.1 --- Sampling Frame --- p.116 / Chapter 5.1.1.1 --- Simple Random Point Sampling --- p.117 / Chapter 5.1.1.2 --- Stratified Random Point Sampling --- p.117 / Chapter 5.2 --- Comparison of the Two Study Areas --- p.119 / Chapter 5.3 --- Statistical Analyses of Landslip Variables --- p.123 / Chapter 5.3.1 --- Gradient (TIN) and Elevation --- p.124 / Chapter 5.3.2 --- "Aspect, Geological Materials, Gradient, Terrain Component, Erosion & Instability, and Vegetation" --- p.126 / Chapter 5.3.2.1 --- Aspect --- p.127 / Chapter 5.3.2.2 --- Geological Materials --- p.130 / Chapter 5.3.2.3 --- Gradient --- p.132 / Chapter 5.3.2.4 --- Terrain Component --- p.137 / Chapter 5.3.2.5 --- Erosion and Instability --- p.140 / Chapter 5.3.2.6 --- WWF Vegetation --- p.140 / Chapter 5.3.3 --- Result of the Partial Model --- p.145 / Chapter 5.4 --- Logistic Regression Model --- p.147 / Chapter 5.4.1 --- Landslide Probability Mapping --- p.154 / Chapter 5.4.2 --- Testing the Model Output --- p.157 / Chapter 5.5 --- Summary --- p.161 / Chapter CHAPTER VI: --- CONCLUSIONS --- p.162 / Chapter 6.1 --- Summary of Findings --- p.162 / Chapter 6.2 --- Limitations of the Study --- p.163 / Chapter 6.3 --- Recommendations for Further Studies --- p.166 / BIBLOGRAPHY --- p.167 / APPENDICES / "APPENDIX I Draft 3.3 slope failure/deposit field survey sheet (King, 1994a)" / "APPENDIX II Landslide/deposit field description sheet (King, 1994b)" / "APPENDIX III Hourly rainfall (mm) record at N05 in September 26-27，1993 (Source: Special Projects Division, Geotechnical Engineering Office, Civil Engineering Department)" / "APPENDIX IV Hourly rainfall (mm) record at R23 in September 1993 (Source: Hydrometeorology Section, Royal Observatory, Hong Kong,1993)" / "APPENDIX V Hourly rainfall (mm) record at R31 in September 1993 (Source: Hydrometeorology Section, Royal Observatory, Hong Kong,1993)"