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Numerical Analysis of the Behavior of Unsaturated Soil Slope Subjected to Wetting-Drying Cycles

Author: GaoYuKun
Tutor: ChenRui
School: Harbin Institute of Technology
Course: Civil Engineering
Keywords: wetting-drying cycles unsaturated soil slope parametric study safety factor
CLC: TU43
Type: Master's thesis
Year: 2011
Downloads: 49
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Abstract

Slopes are the most common engineering form, and most parts of the soils are unsaturated. Slopes subjected to long-term wetting-drying cycles are prone to landslide which would bring huge life and property loss to people. To study the mechanism of seasonal climate changes to unsaturated soil slope, minimize the possibility of landslide, and reduce the life and property loss to people, a thorough research and analysis was made on unsaturated soil slope subjected to wetting-drying cycles.Firstly, numerical simulations of wetting-drying cycles had been done on the Cambridge centrifuge tests with finite element software ABAQUS. The constitutive model of Mohr-Coulomb was used for the soil. By comparison of the centrifuge tests and simulation results, it is found that the change of pore-water pressure and the track of point are fit very well. That is to say, it is realized to simulate the unsaturated soil slope subjected to wetting-drying cycles. Simultaneously, detailed analyses of the displacement of slope, the change of pore-water pressure, stress and plastic deformation had been performed. The mechanism for landslides is revealed. The plastic deformation generates firstly in the toe of the slope under the effect of wetting-drying cycles. The plastic zone develops towards to slope with the increasing of numbers of wetting-drying cycles and the plastic zone is link-together and finally the slope collapses. Then it is realize to use the method of shear strength reduction in the application of wetting-drying cycles and calculate the safety factors of the slope after every process of wetting and drying. From the view of single wetting or single drying, it is found that the safety factor of slope is reduced with the increasing of wetting-drying cycles.Secondly, the changing regularities of the displacement, plastic deformation, pore-water pressure were found by changing the height and angle of the slope. By contrasts of the safety factors of slope after every process of wetting and drying, it is decreasing with the increasing of the height and angle of the slope and the wetting-drying cycles.Then, the magnitudes of wetting-drying cycles are changed. The changing regularities of displacement of slope and pore-water pressure and the safety factors of slope are discussed. The safety factor decreases during the process of wetting. But it may decrease or increase during the process of drying if the magnitude increases. It depends on the comprehensive results of this process of drying and the former process of wetting.Then, it studies the effect on the slope subjected wetting-drying cycles due to the change of some parameters. Such as SWCC, permeability coefficient, cohesion, friction angle, dilation angle and so on. It can get the changing regularities by the contrasts of the variation of deformation and pore-water pressure and so on. Through the comparative analysis of the variation of parameters, it is found that the soil water characteristic curve has an important and obvious effect on the unsaturated soil slope subjected to wetting-drying cycles. SWCC has a direct impact on the amplitude of variation of pore-water pressure during the wetting-drying cycles. Permeability coefficient has a great influence on the pore-water pressure and deformation of slope. The bigger the permeability coefficient, the smaller the changing amplitude of pore-water pressure, the smaller the deformation. Cohesion and friction angle of soil have an important effect on the deformation of the slope especially plastic deformation. Dilation angle has small influence on deformation of the slope, but the soil can generate bigger plastic deformation if the dilation angle increases.

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