Failure mechanism and integrated coordinative bearing design for rock-lining structure of hydraulic tunnel

Hydraulic tunnels are critical for the safe operation of hydropower stations. In this study, the surrounding rock and supporting structures are treated as an integrated rock-lining structure. Based on 40 typical cases, the failure modes and key parameters of the rock-lining structure, such as lining thickness and the ratio of lining thickness to tunnel diameter, are analyzed. Numerical simulations are then conducted to investigate the effects of tunnel depth, lateral pressure coefficient, thickness ratio, and stiffness ratio on rock-lining stability. Following the simulations, the failure mechanisms of the rock-lining structure are analyzed. Results show that increasing tunnel depth leads to a transition from symmetrical to asymmetrical failure, while a higher lateral pressure coefficient expands the tensile failure zone. Increasing the thickness ratio reduces displacements and plastic zones, which stabilize when the ratio exceeds 0.08. A stiffness ratio of 1.0 ensures more uniform stress and deformation distribution. The study identifies the mismatch between external stress and the internal rock-lining structure as the root cause of failure. Based on this understanding, a coordinative bearing design strategy and control measure considering strength, stiffness, and thickness coordination is proposed and successfully applied to a diversion tunnel of Pubugou Hydropower Station, where long-term monitoring confirms its effectiveness. The findings provide a practical approach for long-term deformation control and safety assurance in hydraulic tunnels.