Fracture evolution mechanism of tunnel surrounding rock induced by 3D stress and structural combination

Excavation of deep-buried tunnels can result in the degradation of mechanical properties and damage fracture of the surrounding rock. By prefinancing true triaxial tests at different stress levels, the mechanical characteristics and the evolution of cohesion c and friction angle φ during the rock failure were analyzed. The research results indicate: as σ ₂ or σ ₃ increases, the peak strength of rocks rises gradually; the peak and residual strain gradually decrease as σ ₂ increases or σ ₃ decrease. During the rock fracture process, c and φ exhibit an initial rise followed by a decline. Furthermore, this study established a mechanical model reflecting rock behavior under true three-dimensional stress and developed its numerical implementation. The model's accuracy and reliability were validated by comparisons between experimental results and numerical simulation results. Using the proposed mechanical model, the influence of the arrangement between deep tunnel orientation and in-situ stress direction on the damage evolution mechanism of rock mass was further investigated. The failure degree and energy release in the rock mass during tunnel excavation first gradually decreases and then increases as the in-situ stress rotation angle increases. These research results can provide crucial theoretical foundations for the routing and excavation design of deep-buried tunnels.