Impact of longitudinal cracks on the structural deformation and safety characteristics of tunnel lining

To investigate the influence of longitudinal crack development on the mechanics and deformation characteristics of the secondary lining structure, a load-structure calculation model was established based on tunnel crack investigation. Stress deformation analysis was conducted for the cracked lining structure. The results indicate that cracking in the lining leads to a decrease in stress (absolute bending moment) in the supporting structure (excluding invert). Moreover, an increase in crack depth causes two changes in bending moment within the structure, resulting in instantaneous local stress loss. However, an increase in lining thickness mitigates this stress loss to some extent. Severe structural deformations occur near cracks at both arch and spinner locations, significantly compromising structural safety. When crack depth accounts for approximately 70% of the lining thickness (around 40% for arch cracks), the safety factor of the lining structure decreases to zero and overall safety linearly declines with an increasing number of cracks. It is evident that when cracking reaches a certain extent, overall safety falls below design specification limits, therefore timely verification and control measures should be implemented for cracks above the arch line to effectively manage their associated deformations. Cracks below this line are prone to crushing damage; hence reinforcement support should be promptly applied to withstand downward pressure from above-the-arch footlining structures. It has theoretical guidance significance for the treatment of lining diseases in operating tunnels.