Three-dimensional stability analysis of slope in unsaturated soils considering strength nonlinearity under water drawdown

In slope stability analyses, the soil has been frequently considered dry or saturated, whereas the soil is in fact unsaturated in many cases. Owing to the existence of matric suction, the strength properties of unsaturated soils are greatly different from dry or saturated soil, and thereby leading to diverse stability conditions of the slope. Based on the kinematical approach of limit analysis, in this study, a three-dimensional (3D) stability analysis was conducted for slopes in unsaturated soils. The effects of matric suction distribution patterns, the nonlinearity of the strength under soil-water characteristic curves and the water drawdown were investigated to explore the shear strength and stability of a slope in unsaturated soil. It was found that, when the matric suction is uniformly distributed, the stability factors of the slope increase linearly along with the matric suction. In addition, when the matric suction increases linearly with the depth, the enhancing effect of the matric suction on the slope stability intensifies as the variation magnitude of the matric suction increases, especially for a gentle slope with a narrower width. For nonlinear patterns, different soil-water characteristic curve (SWCC) models will lead to diverse shear strengths and stability conditions of the slope. The water drawdown has significant effects on the functions of the matric suction as well as slope stability.