Temperature distribution and calculation methods for freezing length and laying length of insulation layer of a tunnel in cold regions

Abstract

Over 50 % of tunnels in cold regions of China suffer from frost damage, significantly affecting their normal operation. Laying insulation layer is a primary measure for preventing frost damage of tunnels. However, due to improper laying length of insulation layer, many tunnels with insulation layer still suffer from frost damage. It is a challenge to accurately determine the tunnel freezing length and laying length of insulation layer. Focusing on the Yushuchuan tunnel on the Jilin-Tumen-Hunchun Passenger Dedicated Line as the research object, the temperature distribution, freezing length, and laying length of insulation layer of the tunnel under the action of natural wind are analyzed by field monitoring, numerical simulation and theoretical calculation. The results show that: (1) Ambient temperature primarily affects the temperature distribution of the tunnel at the entrance section. The freezing lengths at the tunnel entrance under the wind speeds of 1, 2, 4, 5.44 and 6 m/s are 303, 743, 1044, 1462 and 1581 m, respectively, while the freezing length at the exit section varies within the range of 21 to 37 m. The entrance section is the critical area for frost damage. (2) After laying the insulation layer, cold air can penetrate into the deeper position of the tunnel, and the laying length of insulation layer should be longer than the tunnel freezing length, with the values of 400, 990, 1370, 1900 and 2060 m, respectively under the wind speeds of 1, 2, 4, 5.44 and 6 m/s. (3) Considering the tunnel size, surrounding rock temperature, lining thickness and meteorological conditions at the tunnel site, the theoretical formulas for the tunnel freezing length and laying length of insulation layer are proposed and verified through a large amount of survey data on frost damage of tunnels in cold regions.