Performance of large deep tunnel complex considering strike-slip fault dislocation

The safe construction and operation of large-scale high-pressure hydraulic tunnel complexes crossing active faults represent a critical engineering challenge in the development of major hydropower bases in western China. Tunnel complexes are subjected to a complicated mechanical environment characterized by the group effect and faulting, which significantly exacerbates the risks of surrounding rock damage and structural instability. However, existing design methodologies for tunnel spacing fail to account for the influence of fault dislocation. In this study, the necessity of studying tunnel spacing under fault conditions was demonstrated through a comparative model test between single tunnel and twin-tunnel. Subsequently, numerical analyses were conducted to investigate the evolution mechanism of the mechanical response of the surrounding rock in tunnel complexes, and reasonable tunnel spacing under varying geological conditions was evaluated based on three distinct criteria. Both experimental and numerical results indicate that the middle rock pillar between adjacent tunnels is the critical load-bearing component for the overall stability of the tunnel complex, and its mechanical state is highly sensitive to both fault dislocation and tunnel spacing. Furthermore, the assessment of reasonable tunnel spacing suggests that larger tunnel spacing should be adopted in cases where the rock mass exhibits poor mechanical quality, the tunnels are deeply buried, or the fault dip angle is gentle. These results provide valuable references for the design and performance of deep tunnel complexes crossing active faults.