Stability analysis of unsaturated soil slope under transient seepage flow state

The effects of hydraulic characteristics play an important role in many landslide hazards; accordingly the variation of matric suction and seepage are considerable factors to evaluate the stability of unsaturated soil slopes. This paper investigates the difference between finite element method with shear strength reduction technique (SSRFEM) and limit equilibrium method (LEM) which are applied to evaluate the stability of unsaturated riverbank in steady and transient seepage flow state. The results show that the effective shear strength equations for saturated soils which are introduced by Bishop and Fredlund are the same in essence. Besides, it is shown that the SSRFEM is more applicable to evaluating global stability of slopes than LEM from the slope stability analysis results in transient seepage flow state. Moreover, the factor of matric suction can be replaced by the relative degree of saturation when the degree of saturation is comparatively high; therefore the approach which is adopted by Bishop can evaluate unsaturated soil slope stability more conveniently, especially in rainfall or water level variation situation.