Abstract: Firstly, the definition of damage for rock was improved according to some insufficiency or disadvantages of the definition of damage in geometric damage theory. On basis of it, rock material under stress was abstracted into two parts for failed and un-failed material; and then a new damage model had been created according to differences of two parts under force. Secondly, a statistical damage evolution equation was established by making use of statistical damage theory; and furthermore a statistical damage constitutive model of rock under a specific confining pressure has been set up. Thirdly, the model has been modified rationally by discussing the empirical relation between parameters of the model and confining pressure of rock; and then a statistical damage constitutive model applying to the condition of different confining pressures has been founded. At last, with studying physical signification of the parameters of the model, a way to find critical physical and mechanical parameters reflecting conversion between hardening and softening mutually is initially developed. It could also reflect characteristic about conversion between hardening and softening mutually; and its rationality has been shown compared with its test.

Key words: rock, damage, constitutive model, hardening, softening, statistical