Shear characteristics and strength model in the slip zone soil of reservoir-induced landslides: Insights into the dislocation effects

The shear mechanical behaviour of slip zone soil is considerably significant for the stability analysis of reservoir-triggered landslides. In this study， the shear responses of slip zone soil obtained from the Muyubao landslide in the Three Gorges Reservoir area (China) and microscopic deterioration process were clarified using indoor direct shear tests and DEM simulations. The results indicate that the shear stress-displacement curves for the soil samples with and without dislocation distances exhibit different shapes， and the effect of dislocation distance on the shear strength is negative; however， this can be partially compensated for by the normal load. Increasing the dislocation distance can decrease the elastic modulus and shear strength， and the effects on cohesion are greater than those on the internal friction angle. Numerical results indicate that the relationship between dilatancy and dislocation is opposite to the correlation between shrinkage and dislocation and the dilatancy angle tends to decrease with increasing dislocation distance. The maximum contact force between the particles decreased with an increase in the dislocation distance， and the displacement field gradually evolved from irregular to hierarchical. Based on this， a strength deterioration evolution model was proposed for describing the dislocation weakening behaviour of the slip zone soil， which was also integrated with the residual thrust method for achieving a dynamic evaluation of the Muyubao landslide stability. The research results provide insights into the mechanical decay mechanism of the slip zone soil subjected to varying degrees of dislocation and theoretical guidance for studying slope stability assessment in a reservoir area.