Abstract: Shallow deformation of ancient landslides induced by heavy rainfall is the most serious geological disaster in China's Three Gorges Reservoir Area (TGRA). It is important to explore the infiltration characteristics and its shallow deformation mechanism caused by heavy rainfall. In this study, the rainfall-induced landslide of the TGRA was selected as the research object, and the distributions of the soil permeability coefficients for rainfall-type landslide were summarized. Considering the effects of heavy rainfall, one-dimensional (1D) soil column infiltration test and two-dimensional (2D) landslide model test were conducted to study the infiltration characteristics of landslide soil and the corresponding shallow deformation mechanisms under different rainfall intensities. The results of the rainfall infiltration tests show that the speed of rainfall infiltration into soil depends on the magnitudes of rainfall intensity and soil permeability coefficient, i.e. when the rainfall intensity is less than or equal to the soil permeability coefficient, the infiltration capacity increases with rainfall intensity; when the rainfall intensity is greater than the soil permeability coefficient, the infiltration capacity decreases. The model test results show that the infiltration of heavy rainfall makes the surface soil transiently saturated and then the gas in the unsaturated zone below the surface is temporarily closed, which leads to the compression of gas by the surface pore water pressure. This means that the pore gas pressure increases with the infiltration of heavy rainfall. Overall, for the rainfall-induced landslides in TGRA, short-term torrential rain can create transient saturation zones and generate closing gas which is the main reason affecting the infiltration capacity of heavy rainfall. The water pressure transmitted by the closing gas causes the pore water pressure of the shallow soil to increase sharply, which is also the main reason for the shallow deformation and damage of many landslides.

Key words: Three Gorges Reservoir Area, model test, rainfall-induced landslides, infiltration characteristics, deformation mechanism