Influence of loading mode and water content on the mechanical properties and deterioration mechanisms of various lithologies: insights from acoustic emission characterization

Catastrophic failures in deep rock engineering are closely associated with the hydromechanical deterioration of rock masses, yet the lithology-dependent mechanisms of water-induced softening remain insufficiently understood. This study comparatively investigated the mechanical degrada-tion, acoustic emission characteristics, and microstructural mechanisms of granite and slate under different water-content conditions. The results reveal a pronounced lithological contrast in water sensitivity. Under saturated conditions, slate underwent severe degradation, with marked reduc-tions in tensile strength, compressive strength, and elastic modulus, whereas granite showed only moderate weakening. Acoustic emission analysis further indicated distinct damage evolution and failure processes between the two lithologies. Kernel smoothing analysis showed a more concen-trated and stage-dependent damage evolution in granite, while slate exhibited a right-skewed fre-quency distribution, suggesting a more abrupt and unstable fracture process associated with high-frequency microcracking. Microstructural observations indicate that slate deterioration is mainly governed by clay-mineral hydration, swelling, and interlayer weakening, whereas granite weak-ening is primarily related to pore-water effects, stress corrosion, and microcrack propagation. These findings clarify lithology-dependent water-softening pathways and provide a mechanistic basis for understanding seepage-driven instability in deep rock engineering.