Analysis on the laying method and thermal insulation effect of tunnel insulation layer in high-altitude cold regions

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.