Experimental investigation on damage and seepage characteristics of layered slate under cyclic loading and unloading of stress

Abstract

To investigate the damage deterioration and seepage evolution of bedded slate under cyclic axial loading–unloading, triaxial tests were conducted on specimens with bedding angles of 0°, 30°, 45°, 60° and 90° under 10 MPa confining pressure and 5 MPa pore pressure. The study systematically analyzed the influence of bedding structure on rock strength, deformation, damage accumulation, and permeability. Consequently, a damage constitutive model and a permeability evolution model were developed, incorporating bedding angle, cyclic fatigue, loading path, and effective stress. Results indicate that bedded slate exhibits pronounced nonlinear deformation, hysteresis, and stiffness degradation under cyclic loading, with responses strongly dependent on bedding angle. Peak strength follows a “U-shaped” distribution, where specimens near 45° show the greatest damage due to combined shear-tensile failure along bedding planes. Permeability initially decreases due to fracture compaction but subsequently increases as stress exceeds the historical maximum, facilitating fracture interconnection. This evolution shows distinct anisotropy; intermediate bedding angles promote more efficient seepage channel formation, leading to larger permeability increments. The proposed models accurately reproduce the experimental stress–strain and permeability behaviors across different angles. These findings provide a theoretical framework for stability analysis and seepage hazard mitigation in stratified rock masses subjected to cyclic disturbances and fluid flow.