Abstract：Local void ratio and average void ratio in shear band are investigated as residual shear strength is reached. For quasi-brittle materials that dilate，some experimental results show that maximum void ratio occurs in critical state of the shear band. Further discussion is made based on gradient-dependent plasticity with consideration of the effect of microstructures. Local maximum void ratio is different from average maximum void ratio. Local means are dependent on coordinates，while the average stands for the whole shear band. Influences of dilation angle，initial void ratio with shear localization initiated，residual shear strength，shear elastic modulus and shear softening modulus on the average maximum porosity and on the maximum porosity are analyzed. In the process of residual deformation，maximum void ratio is reached and remains constant. The presented contclusion lays a foundation for problem of instability involved in coupling of fluid and porous media.
