Macro–Meso Failure Behaviors of Weak Interlayer Contained Hollow Cylindrical Granite Exposed to Alternative Fatigue–Creep–Unloading Conditions

Abstract

This study investigates the damage evolution and instability characteristics of hollow cylindrical granite with weak interlayers at 5°, 15°, 25°, and 35° inclinations under fatigue–creep–unloading conditions. Macro-mechanical tests, combined with real-time acoustic emission (AE) monitoring and post-test computed tomography (CT) scanning, were conducted to examine the effects of interlayer inclination on the stress–strain responses, AE patterns, damage evolution, and failure modes. Results show that volumetric deformation increases with inclination, reaching a minimum at 5° and a maximum at 35°. Specimens with lower inclinations produce more high-frequency, low-amplitude AE signals, but low-frequency, high-amplitude signals dominate at higher inclinations. A tensile-shear crack classification method based on the Kneedle algorithm was developed, revealing a higher proportion of shear fractures as the inclination increases. CT scans indicated that interlayer inclination affects mesoscopic failure mechanisms, with increasing inclination leading to smaller crack areas, lengths, and fractal dimensions. This suggests that the weak interlayer causes plastic flow and shear fracture formation.