Abstract: In order to understand the failure mechanism of slope due to rainfall infiltration, a soil-water-air seepage-deformation coupling finite element program is developed based on finite element-finite difference scheme. In the program, the unsaturated elastoplastic constitutive model using Bishop effective stress and degree of saturation as state variables, proposed by Zhang et al[1], is used to describe the mechanical behaviors of soil from unsaturated state to saturated state due to rainfall infiltration. Meanwhile, Green-Naghdi stress rate tensor is used in the program so as to be able to consider the finite deformation in the process of failure. The program can not only simulate the seepage of water due to rainfall, the change of the degree of saturation, the migration of the air pressure, but also can describe the mechanical behaviors of the unsaturated soil such as the deformation of the ground, the change of pore water pressure, the formation of the shear band occurred in the slope failure on the whole in a unified way. In addition, a laboratory slope model test is simulated by the proposed soil-water-air seepage-deformation coupling FEM. By comparing with the test results, the availability of the proposed numerical method is verified.

Key words: soil-water-air coupling analysis, seepage-deformation coupling analysis, FEM, rainfall infiltration, slope failure