Systematic experimental investigation of strain-induced changes in the anisotropy of fractured rock percolation and permeability

Abstract:

Progress toward understanding fractured rock permeability has been limited by the difficulty of systematic experimental investigation of three-dimensional crack networks that allow for testing different conceptual models. Consistent with the predictions of percolation theory for random crack networks, using ice as a model for rock, new systematic experiments reveal that when subject to uniaxial loading at a constant strain rate, the onset of percolation occurs in all directions nearly simultaneously despite the strongly anisotropic crack network geometry. However, the permeability of the networks is strongly anisotropic. As we have observed previously, crack density remains nearly constant after onset of percolation even while permeability increases, indicating that after the onset of percolation the increase in permeability is primarily due to the opening of existing cracks, including near crack intersections. These experiments allow us to determine if the recorded changes in anisotropic strain can be related to the measured changes in anisotropic permeability. Understanding the relationship between anisotropic strain and permeability during rock deformation is critical for conceptual models for groundwater flow and transport and understanding the hydromechanics of crustal rocks.