In cold regions, heat-insulating layers play a crucial role in frost prevention in tunnels. This paper presents a numerical study on the anti-freezing behavior of a cold region tunnel (the Dege tunnel) with heat-insulating layers. A numerical model based on the temperature field coupling theory is firstly proposed and validated using field test data of the Dege tunnel. Subsequently, a comprehensive parametric study is carried out to investigate the influences of heat-insulating layers on the temperature characteristics of airflows inside the tunnel, the surrounding rock, and the tunnel lining. Furthermore, a numerical investigation based on the proposed numerical model is carried out to propose reasonable design parameters of heat-insulating layers for different velocities of mechanical ventilation, and different heat-insulating materials for cold region tunnels. The numerical results show that using the heat-insulating layer can effectively reduce the heat transfer between the surrounding rock and the airflow inside the tunnel. It is also found that the design parameters for the heat-insulating layer are greatly affected by the tunnel ventilation conditions and heat-insulating materials.

The tunnel boring machine (TBM) is a core equipment for mountain tunnel engineering, but it often faces problems such as surrounding rock deformation, collapse, and TBM entrapment when crossing fault fracture zones. Taking the TBM crossing of F1 fault in the Pilot Tunnel of Daliangshan No.1 Tunnel as the engineering case, this study adopted a combined method of laboratory tests, numerical simulation, and field monitoring to clarify the deformation characteristics of surrounding rock during TBM’s passage through the fault fracture zone, and proposed and verified effective reinforcement measures. The results show that the tunnel deformation in the F1 fault zone presents a "larger in the middle and smaller at both ends" pattern. When tunneling reached the fault core area, the maximum vertical vault settlement was 92 mm and the maximum ground settlement was 42 mm, with the vault settlement response occurring earlier than the sidewall springline deformation. Away from the fault zone, the stress release of surrounding rock stabilized, with a settlement increment of less than 5 mm. The comprehensive reinforcement system proposed for problems such as fractured surrounding rock in the fault zone and insufficient gripper shoe bearing capacity achieved remarkable effects. After reinforcement, the maximum vertical vault settlement and ground settlement of all monitored sections were reduced to approximately 17 mm and 7 mm, respectively, decreasing by 79.3% and 83.3% compared with those before reinforcement. This effectively mitigated construction risks and ensured continuous TBM advancement. The research findings can provide data support and technical reference for TBM construction in mountain tunnels under similar "weathered rock + fault fracture zone" conditions.