A surface and subsurface model for the simulation of rainfall infiltration in slopes

Rainfall infiltration is one of the major triggering factors leading to slope failures in geotechnical engineering. Numerical investigation on rainfall infiltration is often based on Richards' equation, which ignores the surface water effects and simplifies the boundary conditions. In reality, rainfall, infiltration, and surface runoff are interacted simultaneously. In this paper a new conjunctive one-dimensional surface flow and two-dimensional subsurface flow model for geotechnical slope is developed. The interaction between surface and subsurface flow is the interface infiltration rate, which is obtained by iterations. The results of comparisons between coupled and uncoupled models show that the surface water depth rises up as runoff increases and it tends to a dynamic balance state with a steady surface water depth. Interaction between surface and subsurface flow has remarkable effects on infiltration process. According to the results of coupled model, more rainwaters infiltrate into the slope. Therefore, pore water pressure changes faster and the wetting front moves deeper into the soil. Under initial drier condition, the capacity of infiltration is higher and more rainfall can be absorbed into slope, thus the differences of infiltration rate and pore water pressure between the coupled and uncoupled model are more significant.