Abstract: Introducing the fluid-mechanical interaction model based on continuous porous media theory and mixture theory, applying FISH language to program, the initial seepage field setting function, the saturated-unsaturated seepage analysis module, the special stress-correction module and shear strength correction module are established. Saturated-unsaturated seepage analysis is conducted with FLAC3D. The effective stress and shear strength of soil zone in the semi-saturated region is modified based on the saturated-unsaturated seepage field and the principle of fluid-mechanical coupling for completely saturated element and extended to unsaturated soil element in FLAC3D. Based on these analysis modules from secondary development, the water drainage experiment from a sand column conducted by Liakopoulos is numerically simulated to verify the correctness of the model and program. The effect of rainfall infiltration on the seepage field, displacement field and stability evolution of soil slope reveals the mechanism of rainfall-induced failure of slope.

Key words: fluid-mechanical interaction model, initial seepage field, saturated-unsaturated analysis, stress correction