Coupled elastoplastic damage model for gas-saturated coal

Under triaxial compressive conditions, with an increase of loading, the propagation and sliding of microcracks in rocklike materials become increasingly intense and lead to a serial of consequences, such as nonlinear stress-strain relationships, deterioration of elastic modulus, anisotropic deformation, volumetric dilatancy and irreversible plastic strain, etc.. These phenomena may be described by continuum damage mechanics and plastic theory. Firstly, in order to take into account the effect of gas adsorption, the swell stress of gas adsorption is introduced into the effective stress principle of porous media; and the effective stress formulation for gas-saturated coal is derived. Anisotropic damage with plasticity yield criterion and damage criterion are introduced to be able to adequately describe the plastic and damage behavior of gas-saturated coal. Damage evolution law and the coupling between plastic deformation and damage are represented using the framework of irreversible thermodynamics. On the basis of the experimental results, a general coupled elastoplastic damage constitutive model is developed for the mechanical responses of gas-saturated coal under various loading conditions by adopting a non-associated plastic flow rule. The comparison between experimental dada and their simulation equivalents is performed for gas-saturated coal under various stress states. It is obvious that the proposed model is able to effectively depict the main features of mechanical behavior observed in gas-saturated coal. At the same time, the proposed model is also suitable for constitutive description of other rocklike materials.