Abstract: In order to explore properties of coaly shale compression deformation and its damage identification, by using the mechanical testing & a simulation system, the uniaxial and triaxial compression curves of coaly shale were obtained and their difference of damage softening properties was analyzed. Based on these, the mechanism of external work，energy dissipation，energy release were studied. Meanwhile, a damage formulation based on energy principle was deducted according to shale mechanics characteristic and rock strength and failure theory．① The resultant constitutive model based on energy principle can be used to simulate the damage of shale under uniaxial compression．② Under the condition of triaxial compression, the constitutive model of shale can be simulated by linear equation (or constitutive equation based on energy principle) when the axial stress is less (or more) than confining pressure. The comparison between the model and the experiment results shows that the mechanical parameters of model are simple and its physical parameters clear. It can also reflect deformation characteristics of softening under uniaxial compression and hardening under triaxial compression.

Key words: coaly shale, compression curve, energy principle, damage variable, response equation