Research on Calculation Methods for Frost-Resistance Fortification Length of Cold-region Tunnels

Currently, the determination of frost resistance fortification length for tunnels in cold regions relies primarily on empirical analogy methods and lacks relevant theoretical calculation approaches. On the basis of steady-state heat conduction and the thermal resistance theory of multilayer flat walls, a theoretical calculation model for the critical frost resistance temperature of tunnels in cold regions is established. This study investigated the variation patterns of frost resistance and fortification length under the influences of factors such as the external wind speed, ambient temperature, lining thickness, and surrounding rock temperature. The Yushuchuan Tunnel was selected as a case study to validate the proposed model. The research results indicate that the external wind speed, external air temperature, surrounding rock temperature, and lining thickness are key factors influencing the frost resistance of a tunnel. Among these factors, the frost resistance fortification length is positively correlated with the external wind speed but negatively correlated with the external air temperature, surrounding rock temperature, and lining thickness. Under conditions without an insulation layer, the critical frost resistance temperature to prevent freezing at the secondary lining‐primary lining interface is -2.2°C, whereas the critical temperature to prevent freezing at the surrounding rock‐lining interface is -4.75°C. With an insulation layer, the critical frost resistance temperature to prevent freezing at the secondary lining‐primary lining interface becomes -9.56°C, and the critical temperature at the surrounding rock‐lining interface is -22.5°C. These findings can provide valuable references for the frost resistance insulation design of tunnels in cold regions.