True triaxial mechanical behavior and damage mechanisms of water-saturated shale under blasting dynamic disturbance

Deep roadway excavation in water-rich shale formations faces coupled challenges of long-term water saturation and cyclic blasting dynamic disturbance, yet the true triaxial mechanical behavior and coupled damage mechanisms of water-saturated shale under such conditions remain unclear. This study converts field blasting loads into laboratory stress paths via on-site monitoring, Fourier transform processing, and Miner's rule derivation, and conducts true triaxial fluid-structure coupling tests on shale specimens with varying saturation durations and pore water pressures, integrated with acoustic emission (AE) monitoring, post-test computed tomography (CT) scanning, 3DEC numerical simulation, analytical modeling, and neural network verification. The results show that pore water pressure acts as a damage amplifier, accelerating strain accumulation and damage evolution, while water saturation preconditions the microstructure: it transforms failure modes from localized brittle fracture to distributed ductile shear damage, and suppresses the permeability threshold of natural specimens via clay swelling-induced fracture network modification. Notably, a maximum damage point is identified at 24 h of water saturation, where the synergistic degradation of saturation-induced weakening and disturbance-induced damage peaks across all pore water pressure conditions. The developed neural network model achieves high accuracy in predicting post-disturbance mechanical properties. This work provides critical theoretical support for stability control and support design of water-rich shale roadways during blasting excavation.