Stability analysis of unsaturated–saturated soil slopes under rainfall infiltration using the rigorous limit equilibrium method

The failure of soil slopes is usually triggered by rainfall infiltration. Under the rainfall infiltrating, soils transform from unsaturated state to saturated state, the matric suction gradually disappears, pore water pressure increases, and the safety factor of soil slopes decreases. In this paper, a novel rigorous limit equilibrium method is proposed to investigate the stability of unsaturated–saturated soil slopes under rainfall infiltration. The force equilibrium conditions along three coordinate axes and the overall moment equilibrium conditions around three coordinate axes are all strictly satisfied, which are more coincident with the real force state of the slopes. In addition, the seepage fields of soil slopes are investigated by using SEEP/W software. Then, the seepage fields are introduced to the rigorous limit equilibrium method. The effects of rainfall intensity, rainfall patterns and rainfall duration on the stability of the unsaturated–saturated soil slopes are investigated using the proposed method. For the unsaturated soils, in which there exists the matric suction, and the matric suction can improve the stability of soil slopes. The safety factors of soil slops under the different rainfall intensity and rainfall patterns are investigated. Moreover, the stability of Fanlingqian slope under rainfall infiltration is analyzed to verify the correctness and precision of the proposed method.