A micromechanics-based damage constitutive model of porous rocks

A three-phase damage micromechanical model for rocks is developed through a combined consideration of micromechanical and thermodynamic theories. The rock is considered as a three-phase composite system, namely the rock skeleton without porosity, the initial pores, and the new cracks. The interaction among the three phases is considered. The kinetic equation of crack damage evolution is established in terms of the thermodynamic driving force derived from the reduction of Gibbs free energy of rocks. An equation that balances the thermodynamic driving force with the corresponding resistive force is obtained to calculate the damage volume fraction of crack under given stress. The stress-strain response of rocks is investigated under confining pressure or with different pore volume fraction. The theoretical results are found to be in good agreement with experimental data.