Mechanical Characteristics and Dynamic Seepage Evolution Laws of Inclined Single Fracture Rock Mass Under Three-Dimensional Stress

To investigate the influence of fractures on the mechanical and seepage characteristics of rock masses, the fracture network within the rock mass is simplified as a single fracture. Under three-dimensional stress conditions, stress-seepage tests are conducted on inclined single-fracture sandstone rock samples at different confining pressures and water pressures. Three-dimensional surface scanners are used to scan and analyze the morphology of the fractures after the tests, studying the relationship between morphology and mechanical and seepage characteristics. The research results demonstrate that: Confining pressure significantly enhances the peak effective stress and effective crack damage threshold, while water pressure has the opposite effect. Confining pressure also has a positive impact on the elastic modulus and Poisson's ratio, the elastic modulus and Poisson's ratio nonlinearly increased with increasing confining pressure, which can be described by log function. With increasing pore pressure, the elastic modulus exhibited a slight initial increase, followed by a significant decrease after reaching 6 MPa. The Poisson's ratio exhibited a noticeable decrease with increasing pore pressure. A revised permeability calculation formula for a rough single fracture was proposed by introducing the fractal dimension, under three-dimensional stress conditions, permeability is a dynamic evolutionary process that can be divided into two modes. In Mode 1, the evolution of permeability can be divided into three stages: a stage of permeability decrease (stage I), a stage of initial increase followed by decrease (stage II), and a stage of rapid increase (stage III). In Mode 2, due to the absence of new flow channels, only stages I and II are observed. The negative correlation between the fractal dimension of fracture surface morphology and permeability confirms the validity of the permeability calculation formula.