Damage Evolution and Energy Dissipation Mechanisms in Marble Subjected to Cyclic Stress-Path Disturbances

Deep rock masses often experience complex cyclic loading during excavation; however, their failure mechanisms under true-triaxial stress states remain inadequately understood. This study examines the anisotropic deformation, failure mechanisms, and damage evolution of marble through true-triaxial cyclic loading and unloading tests under different intermediate principal stress differences ( λ ). Results show that the plastic strain increment ratio is larger in the σ 3 -direction than in the σ 2 -direction, and volumetric dilation is predominantly governed by strain in the σ 3 -direction. The peak strength and crack damage stress conform to the linear Mogi strength criterion, while the peak dilation angle exhibits a V-shaped trend with increasing λ . The failure mode transitions from splitting tensile failure to tension-shear mixed failure as λ increases from 0 to 90 MPa, accompanied by a decrease in fracture angle from 83° to 63°. Energy dissipation follows a concave-up trend, with energy storage in the σ 1 - and σ 2 -directions increasing as λ rises. Acoustic emission (AE) activity intensifies near the peak stress during each cycle, and the AE b -value fluctuates before a sharp decline. Both the sharp drop in the AE b -value and the occurrence of the Felicity effect (at > 88% peak stress) are recognized as critical precursors to instability. Furthermore, both energy-based and strain-based damage variables exhibit a three-stage growth pattern and are well described by the Logistic growth model. A higher λ delays rapid damage accumulation and enhances rock stability. Accordingly, a comprehensive damage model integrating energy-based continuity and AE sensitivity is proposed for stability prediction in deep underground engineering.