Abstract: Based on the basic theory of unsaturated soil mechanics， a solid-liquid-gas three-phase coupling control equation for two-dimensional unsaturated soil slopes was established by considering the compressibility of porous media. The numerical simulation results of the established coupling control equations based on the PDE platform of COMSOL multiphysics software was compared with the experimental results of the classical Liakopoulos sand column. The established three-phase coupling control equation was verified， and the influences of different factors on the seepage field and displacement field were discussed. The simulation results showed that the permeability can slightly retard the rainfall seepage process and delay the deformation of unsaturated soil slope. The air intake coefficient has a slight impact on the settling process of unsaturated soil slope.

Key words: unsaturated soil, solid-liquid-gas three-phase coupling, permeability, air intake coefficient, rainfall