landslides;  progressive destruction;  safety factor;  Strain softening

Considering the rheological effect of soil, a mechanical model for the gradual failure of soil slope with strain softening properties is proposed by generalizing the unbalanced thrust method. This model adopts the Maxwell relaxation model to describe the change of shear strength of soil on the slip surface after local failure, and uses the time safety factor to describe the stable state of the slope, and does not have to assume that the gradual failure starts from the slope angle, so it is closer to the actual situation. Through numerical simulation, the diachronic evolution process of slope progressive failure is clearly revealed, and the law that the safety factor of slope gradually decreases with time is confirmed.