Investigation into the Large Deformation Mechanism and Control Technology of Variable Cross-Section Tunnel in Layered Mudstone Stratum

Buildings (structures) with various structural forms are becoming increasingly prevalent and are encountering more challenging engineering issues. Field investigations, laboratory tests, and numerical simulations were used to study the disaster-causing mechanism and the control technology for a variable cross-section tunnel passing through layered, expansive mudstone stratum. The deformation and stress characteristics of the surrounding rock and supporting structure were examined by both numerical simulation and field monitoring. The results indicated that the stress was more complex at different section positions; the rock and supporting structure underwent substantially more deformation and stress in the broadened sections. The mean values of the surrounding rock's horizontal convergence and vault settlement in the broadened section were 15.71% and 16.36% higher than those in the general section, respectively, and the value of lining stress was 35.51% higher. Additionally, the simulation results under the improved construction measures matched the measured results. The maximum deformation and stress of the surrounding rock were reduced by 16.95% and 40.04%, respectively, under the improved scheme, while the lining stress was reduced by 45.38%. The stress state of the secondary lining was significantly improved; in particular, the tensile stress in the lining structure under the original construction scheme was converted into a compressive state under the new measures, fully utilizing the bearing effect. Finally, the rationality and effectiveness of the adopted reinforcement measures were evaluated, and the experiences and lessons learned were summarized to provide insights for preventing similar incidents from reoccurring.