Failure Mechanisms in Unsaturated Silty Sand Slopes Triggered by Rainfall - -

Failure mechanisms in unsaturated silty sand slopes triggered by rainfall

Imprint

Dedication

Foreword

Acknowledgments

Contents

List of Figures

List of Tables

Kurzfassung

Abstract

1 Introduction

1.1 Motivation

1.2 Objectives of the project

1.3 Methodology and layout of the thesis

2 Literature review

2.1 Unsaturated soil mechanics

2.2 Triggering mechanisms of landslides due to rainfall

2.3 Previous field tests

2.4 Centrifuge modelling

2.5 Concluding remarks

3 Ruedlingen experiment field

3.1 Test slope

3.2 Characterisation

3.3 Field instrumentation

4 Ruedlingen soil characterisation

4.1 Grain size distribution and Atterberg limits

4.2 Volumetric properties of the soil in saturated and unsaturated conditions

4.3 Shear properties of Ruedlingen soil

4.4 Hydraulic properties of Ruedlingen soil

4.5 Compaction test

5 Slope monitoring and landslide triggering experiments

5.1 Slope monitoring experiment (October 2008)

5.2 Slope monitoring under natural atmospheric conditions

5.3 Landslide triggering experiment

5.4 Comparison between the slope monitoring and landslide triggering experiments

6 Physical modelling in a geotechnical drum centrifuge

6.1 Scaling laws

6.2 The basic concept of the climate chamber

6.3 Rain simulator and the tool table

6.4 Bedrock

6.5 Instrumentation and monitoring

6.6 Centrifuge tests

6.7 Effect of bedrock shape on the stability of slopes

6.8 Drainage into the bedrock with buttress (test T10_1)

6.9 Discussion: the effects of bedrock shape and drainage on slope stability

6.10 Exfiltration from bedrock

6.11 Effect of vegetation on slope stabilisation

6.12 Static liquefaction

6.13 Summary

7 Analytical and numerical simulations

7.1 Analytical modelling (based on Askarinejad et al., 2012b)

7.2 Uncoupled 2D simulations of Ruedlingen experiments (based on Bischof, 2010 and Askarinejad et al., 2012b)

7.3 Coupled hydro-mechanical simulations of the behaviour of slope during rainfall

7.4 Conclusions of the hydro-mechanical simulations

8 Summary, conclusions and outlook

8.1 Summary and conclusions

8.2 Suggestions for future work

9 References

Appendix A: Pixel-based slope monitoring

Appendix B: Centrifuge model preparation

Appendix C: Discharge charts and location of the nozzles

Appendix D: Direct shear test on vegetated soil

Appendix E: Viscous pore fluid and its effects on Ruedlingen soil

Appendix F: Calibration charts for the field sensors

Appendix G: DPL Results for Ruedlingen test slope (Askarinejad & Kienzler, 2008)

Appendix H: Field measurements

Appendix I : Results of numerical simulations

Appendix J: Data from the geological borehole (Based on Brönnimann, 2011)