A Rainwater Redistribution Model to Evaluate Two-Layered Slope Stability after a Rainfall Event

Rainfall infiltration usually leads to shallow landslides due to the reduction of matric suction within soil. However, experience has shown that not all of those landslides occur in the period of precipitation: Some landslides occur hours or even days after rainfall events. This phenomenon has not been widely investigated and addressed in the literature. This paper establishes a general rainwater redistribution model for fine-over-coarse and coarse-over-fine soil stratification profiles based on the one-dimensional Moore's infiltration model and the continuity of soil-water potential at the interface of the two-layered soil. A comparison of the results of the redistribution model with those of the numerical analyses shows that with the use of properly estimated input parameters, the proposed model is quite reasonable. Along with the validated rainwater redistribution model and the infinite slope model, the factors of safety are calculated for two hypothetical landslide cases. The results reveal that both factors of safety decrease slightly in the redistribution process and eventually reach stable values when the accumulative infiltration increases to a certain value. This finding may explain why shallow landslides occur after the rainfall event. Although simple, the analytical model can serve as a useful tool to assess the stability of shallow landslides that occur after a rainfall event.