Abstract:Firstly,according to the limitations and deficiencies of the rock damage model based on the Lemaitre¢s hypothesis of strain equivalence,the concept of ratio of voids was applied to describe the volume change of voids or rock mass during the process of deformation of fissured rock mass on the basis of further discussion on the damage mechanism of deformation for fissured rock mass and considering the effect of volume change of fissured rock mass under loading. And a damage model for fissured rock mass was established by analyzing the force upon fissured rock mass on microscopic scale. Secondly,a strain softening damage constitutive model for fissured rock mass was brought forward by thoroughly investigating the relationship between the effective stress and macroscopic nominal stress and introducing the statistical damage theory. Meanwhile,a method to determine the model parameters was developed. This model can fully reflect the property of strain softening of deformation for fissured rock mass;especially it can be used to well simulate the initial phase of compression of voids in the process of fissured rock mass deformation. There is no need for unconventional rock mechanics test to determine the model parameters,moreover,the physical meanings of the model parameters are explicit. Thus,this model is more convenient for use. Finally,the rationality and feasibility of the model are identified by comparative analyses between the existing research results and measured date.