Abstract: In the aim of investigating the influence of rainfall infiltration on slope stability at shallow surface, the permeability coefficient and pore water pressure of slip surface of shallow layer in rainy period and non-rainy period were analyzed based on unsaturated seepage theory. The rule of slope stability variation in shallow layer was also researched. Results showed that in rainy period pore water pressure at slope toe increased to saturation, and at slope top increased until approaching saturation. After rainfall stopped, the decline margin of pore water pressure at slope top was larger than that at slope toe. In the early stage of rainfall, the stability of slip surfaces decreased continuously, and in the later stage of rainfall the safety factor of slip surface at slope top tended to convergence; whereas the safety factor at slope toe kept decreasing.After rainfall stopped, the safety factors of slip surfaces in shallow layer all increased; while the safety factor of deep layer fluctuated.

Key words: rainfall infiltration, slope stability, unsaturated seepage, unsaturated soil, safety factor