Permeability Evolution and Damage Characterization of Sandstone under Various Confining Pressures and Seepage Pressure Gradients

Abstract

Abstract In the realm of deep hydraulic engineering, diversion caverns often confront significant challenges due to high in-situ stress and high seepage pressure gradient. These conditions result in intricate mechanical behavior and permeability characteristics within the surrounding rock. In light of this, the present study aims to investigate the relationship between damage evolution and permeability characteristics of sandstone prior to failure under hydromechanical coupling conditions through a series of hydromechanical coupling tests. The results of these tests demonstrate that the strength and deformation resistance of sandstone exhibit variations corresponding to changes in the seepage pressure gradient. Moreover, an increase in seepage pressure gradient leads to a shift in the failure patterns of sandstone from low-inclination shear failure to steep-angle shear failure. Throughout the failure process of sandstone, the permeability curve initially decreases, followed by a rapid increase before ultimately stabilizing. Notably, the peak value of the permeability curve lags behind that of the stress-strain curve. Furthermore, when the seepage pressure gradient initially rises and then drops, the permeability of sandstone undergoes an irreversible change in the opposite direction, failing to return to its initial value. Based on these observations, a statistical damage model is proposed for rocks, accounting for hydromechanical coupling. Remarkably, the theoretical values derived from this model align well with experimental results. This model, grounded in the laws governing permeability evolution and damage properties of sandstone prior to failure, offers valuable guidance for monitoring and controlling rock stability in diversion caverns subjected to hydromechanical coupling actions.