Abstract: To consider the impact of displacement factor on the progressive development of landslide, a modified Janbu slices method considering the relationship between shear stress and shear displacement of sliding face was presented to evaluate the stability of a landslide. The modified Janbu slices method is improved in the following two aspects: firstly, combined the constitutive shear stress-strain model and shear displacement model along the slide face to simulate the progressive failure process of landslide with deformation development; secondly, the overall safety factor was redefined using concept of partial safety factor with clearer physical meaning. The formula of the simplified method was derived and implemented by Matlab code. An example of simulation shows that the stability factor for slope with strain-softening behavior depends on the strength parameters, and also on the shear stress-shear displacement relationship of slip zone soil. It is unsafe for the limit equilibrium method to be applied to practical engineering, This method can also effectively simulate the development process from the beginning towards the entire sliding face failure of slope. The simulation realizes the quantitative correspondence relationship between displacement and safety factor, and can be used to predict the long-term stability of slope.

Key words: displacement, landslide, progressive property, strain-softening, safety factor