Abstract: On the basis of the theory of two-phase (water and air) flow, the law of water-air movement caused by rainfall infiltration in slope was revealed by means of finite element method. Daping landslide in Three Gorges Reservoir was taken as a case study. The simulation results show that the slope surface can be divided into the inflow area and the outflow area according to the inflow and outflow of water and air. Usually the upper part of slope is inflow area, and the lower part is outflow area. The total infiltration rate of water and air in slope is relatively stable, slightly affected by rainfall characteristics, slope surface runoff and temperature changes. In the inflow area, when rainfall intensity is greater than infiltration rate, water in slope will run off, otherwise water or air will completely infiltrate. The saturation pressure of slope surface could transmit to groundwater surface through pore air, which increases the groundwater pressure head, unfavorable for slope stability.

Key words: water-air two-phase flow, rainfall infiltration, finite element method, unsaturated seepage, slope in Three Gorges Reservoir