Experimental investigation and micromechanical analysis of damage and permeability variation in brittle rocks

Induced anisotropic damage and related permeability variation in brittle rocks are investigated. Triaxial compression tests with permeability measurement are first performed. It is found that the permeability can significantly increase with the growth and coalescence of microcracks. The permeability change can be related to the density and opening of microcracks. Based on various experimental evidences, a micromechanics-based damage model is proposed for the description of anisotropic damage. This model takes into account unilateral effects and frictional sliding in closed microcracks. The normal opening of microcracks generated by the frictional sliding due to the roughness of crack surface is also considered. The overall permeability of cracked medium is estimated by the volumetric averaging of the local permeability in microcracks, which is described by an extended cubic law. Comparisons between numerical predictions and experimental data are presented for different mechanical and hydromechanical tests.