The Study On The Mechanism And Numerical Analysis Of Rainfall-induced Soil Slope Failure

Rainfall-induced landslide often caused catastrophic disasters. For this reason, the mitigation of landslide hazards is one of the major strategies for sustainable development in many countries. The landslide mechanism and slope safety evaluation are key issues in the study of geotechnical engineering. The available research results indicate that most slope failures are caused by the infiltration of rainwater into the slope. However, it is very difficult to evaluate the effect of rainwater infiltration quantitatively. Hence, it is important for research and mitigation practice to set up an uncomplicated and practical safety evaluation method to assess the occurrence of landslide during rainfall period.Based on the landslide hazard analysis, the study of unsaturated soil shear strength behavior and model tests of landslides, this dissertation discussed the pseudo-coupled flow-deformation method for analysis of saturated-unsaturated soil slopes in detail. Moreover, some experiences and useful results of rainfall-induced landslide mitigation were introduced. The main research work and creative results are summarized as follows.1. The shear strength behavior of unsaturated soils was investigated by coupling the pressure plate test and direct shear test. The results show that the unsaturated shear strength behavior can be illustrated by soil-water characteristic curves (SWCC). This relationship is helpful to build up a physical model to explain the influence of matric suction on shear strength behavior of unsaturated soils and explain the phenomenon along different state path.2. The pseudo-coupled flow-deformation numerical analysis method was used to simulate the landslide model tests, and the results show that this method can predict the landslide types, failure magnitude, slip surface and probable run-out distance of landslide rather well. Hence, the combined use of seepage finite element method and shear strength reduction FEM is expected to be a practical method for landslide mitigation. 3. According to the results of landslide model tests and the corresponding numerical analyses, the main drying and wetting curves of SWCC are the most significant simplified hysteresis model for the water content versus soil suction relationship for unsaturated soil slope seepage numerical analysis. Because the main drying and wetting curves represent the two boundaries of soil state path, it is appropriate for using these two boundary curves to build up rainfall warning criteria of landslide hazards.4. The results of landslide model tests and numerical analyses show that the seepage numerical analysis can quantify well the amount of infiltration occurring in a slope during heavy rainfall period. However, the infiltration effect is underestimated in the lightly rainfall condition. Therefore, it should be careful to predict landslide under lightly rainfall condition by using this method.