A two-step homogenization-based permeability model for deformable fractured rocks with consideration of coupled damage and friction effects

The permeability variation induced by anisotropic damage of rock blocks and nonlinear deformation of fractures is modeled with a two-step homogenization technique for deformable fractured rocks containing arbitrarily-distributed penny-shaped microcracks in rock blocks separated by multiple sets of critically orientated fractures of much large scales. The proposed model accounts for the influences of the microstructural alteration of rock blocks and fractures at the laboratory scale and the development pattern of the fracture system as well as the rock-fracture interaction at the field scale on the permeability of a fractured rock under mechanical loading or excavation condition. The proposed model was first validated by laboratory data of compression tests with permeability measurements on the Beishan granite, coupled shear-flow tests with hydraulic conductivity measurements on a granite fracture and anisotropic strength tests on the Martinsburg slate, with good agreement between the model predictions and the laboratory measurements. Numerical simulations were finally performed to examine the excavation-induced permeability change in the surrounding granitic rock of the Stripa tunnel, demonstrating the importance in considering both the damage of rock blocks and the deformation of fractures for better understanding the excavation-induced permeability change in the surrounding rock near the excavation surface.