Seepage characteristics of fractured sandstone under deep high-confined water and mining-induced stress

Under deep mining conditions, fractured rock masses are subjected to sustained high confining stress and elevated water pressure, resulting in complex seepage evolution. This study conducts triaxial seepage experiments on single-fractured sandstone to investigate the coupled effects of confining pressure, water pressure, fracture roughness (JRC), and fracture aperture under a unified stress–seepage framework representative of deep high-confined water environments. Results show that seepage flow increases linearly with water pressure but decreases nonlinearly with confining pressure, exhibiting a three-stage evolution involving elastic deformation, elasto-plastic transition, and compaction equilibrium, with a clear stabilization threshold. Elevated water pressure reduces the effective normal stress on fracture surfaces, thereby weakening fracture closure, particularly in rough fractures where asperity degradation contributes to permeability enhancement. Comparative analyses reveal that fracture roughness and aperture jointly control permeability magnitude, attenuation rate, and stabilization behavior. Quantitative relationships between stabilized permeability and key fracture parameters are established, providing a concise, parameter-based description of fracture seepage under high-stress conditions. The findings offer practical insights for predicting seepage evolution and mitigating floor water inrush risks in deep mining environments.