In order to ensure the safety of the tunnel approaching the fault and prevent water inrush disasters, and then take reasonable protective measures, a fault-tunnel-surrounding rock is established by using a three-dimensional (3D) discrete element numerical analysis method, which takes into account the fluid-structure coupling effect. Based on the method of control variables, the catastrophe information characteristics of displacement and water pressure of the surrounding rock of the tunnel face and the corresponding characteristics of changes before the occurrence of water inrush disasters were studied under different fault water pressures during the excavation of the tunnel approaching the water-rich fault. The results show that, during excavation at the same step, displacement and its magnitude in the surrounding rock escalate as fault water pressure increases. The maximum pressure of the water in the surrounding rock is also constantly increasing. As tunnel excavation progresses, at constant fault water pressure, longer excavation distances result in greater axial displacement of the surrounding rock mass and increased water pressure at corresponding positions within the surrounding rock, leading to higher magnitude increases. As excavation proceeds, the displacement and water pressure in the surrounding rock and the increase of its amplitude continue to increase. Pre-reinforcement grouting techniques and pipe umbrella support systems that are very effective protective measures can be determined by a comprehensive approach integrating advanced geological forecasting methods, real-time water pressure detection, and the analysis of stress-strain and seepage pressure field variations in the surrounding rock mass.

The thermo-hydrological (TH) coupling model constitutes the foundational framework for investigating the temperature distribution of surrounding rock in cold region tunnels. In this study, a fully coupled TH model is proposed that takes into account multiple physical phenomena during the freezing process of surrounding rock. Firstly, the model was established based on thermodynamics, seepage theory, and ice–water phase change theory, which accounted for unfrozen water, latent heat of phase change, ice impedance, and convective heat transfer. The model was successfully verified by comparing its results to field data. Next, the sensitivity of surrounding rock temperature to environmental, thermodynamic, seepage, and coupling parameters in the fully coupled TH model was systematically studied using a numerical analysis method. The results show that the annual temperature amplitude and thermal conductivity represent the main factors affecting the surrounding rock temperature at a radial depth of 0 m, while the initial temperature and porosity are the key factors at a radial depth of 5 m. Permeability has the least influence on the surrounding rock temperature, but the temperature field will experience sudden changes if its value exceeds its value exceeds 1 × 10⁻¹² m². Finally, using the proposed numerical model, the thickness of insulation layer was simulated, and the degree of influence of the parameters on the thickness of insulation layer was analyzed. This study reveals that the annual temperature amplitude has the greatest influence on the calculation of insulation layer thickness, with its normalized sensitivity factor being approximately 50%. These findings not only expand the methodology for exploring the laws of TH coupling but also provide a theoretical foundation for improving the parameter calibration efficiency and calculation accuracy of the fully coupled TH model, and they have significant reference value.

To mitigate freeze-thaw damage in tunnels located in high-altitude cold regions, insulation layers are implemented to prevent the freezing of surrounding rocks. Currently, the selection of laying methods lacks a solid scientific basis, with the merits and demerits of various techniques remaining insufficiently evaluated. This study seeks to establish a scientifically grounded equilibrium between the anti-freezing efficacy and the construction impact of tunnel insulation in cold regions through the optimization of insulation design via numerical calculations. First, the advantages and disadvantages of the four insulation layer laying methods were summarized. Then, a multilayer media heat transfer model that accounts for the latent heat of phase change was developed, grounded in solid heat transfer and porous media heat transfer theories, and corroborated by typical case studies. Finally, taking Duolong tunnel as a case study, the insulation effect of various laying methods at different positions of the tunnel was analyzed based on the finite element method. The results show that the unfavorable position of the four laying methods is at the inverted arch of the tunnel, and the unfavorable time point occurs when the temperature rises from below 0℃ to above 0℃. Among the four laying methods, off-wall laying exhibits the superior insulation performance at tunnel vault, while sandwich laying has best insulation effect at the arch foot and inverted arch. The research results can provide reference and basis for the thermal insulation and anti-freezing design of tunnels in high-altitude cold regions.