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.

With the fast progress of infrastructure projects, super-large cross-section projects are constantly emerging, and, therefore, engineering challenges and problems are increasing. Taking the triple-arch tunnel project in the turn-back line section of Santunbei Station in Urumqi Metro Line 1# as a case study, this research applied numerical simulation software Midas GTS/NX 2022 for the analysis of tunnel force and deformation in triple-arch cross-sections under different support forms of partition wall. Following the optimization of the support design of the mixed partition wall to a single straight wall, the following analytical results were obtained: surface settlement was decreased by 21.15% at the original cross-section; maximum values of principal stress and displacement of partition wall were decreased by 6.73 and 10.64%, respectively; and corresponding values for initial support structure were decreased by 21.47% and 54.74%, respectively. Meanwhile, combined with comparative analysis of engineering measurement and numerical simulation results, surface settlement and vault deformation were found to be similar to the optimized simulation results, which not only verified the reliability of simulation results but also ensured the safe and smooth construction of the project, greatly improving construction efficiency and saving construction time and cost.