Research on determination method of tunnel depth and shallow burial based on temperature field distribution in cold area

Abstract Due to the combined action of the low-temperature air inside and outside the tunnel, the temperature field distribution law of the shallow buried section of the tunnel in cold areas is significantly different from that of the deep buried section, which makes the problem of frost damage more prominent and the prevention and control of frost damage more difficult. Therefore, from the perspective of frost damage prevention, it is necessary to divide the depth and shallow burial of tunnels in cold areas based on the distribution of temperature fields. Based on the Chengde-Tacheng (G335) Yejishan Tunnel, this paper proposes a method for determining the depth and shallow burial of tunnels in cold areas through field tests of the temperature fields inside and outside the tunnels, combined with the numerical simulation of the tunnel temperature fields. The following conclusions are obtained: (1) When the buried depth of the tunnel is less than the sum of the thickness of the stratum and the thickness of the surrounding rock, the temperature in the tunnel overlaps with the surface air temperature, and it can be regarded as a shallow buried tunnel within the range of the longitudinal influence of the air outside the tunnel on the temperature of the surrounding rock along the longitudinal depth, and vice versa. (2) The distribution of the formation and the surrounding rock variable temperature zone is calculated by the control variable method and the inverse analysis method by using the Fluent fluid simulation software, and the distribution of the formation and the surrounding rock is mainly affected by the ratio of the thermal conductivity to the product of the specific heat capacity and density (i.e., the temperature conductivity) and the air annual temperature amplitude; (3) The terrain at the inlet end of Yeji Mountain is gentle, and the surface slope at the outlet end is large. According to the tunnel depth and shallow burial judgment method based on temperature field distribution proposed in this paper, the length of the shallow buried section at the entrance and exit is 375.6m and 25.05 m, respectively, and the length of the shallow buried section at the entrance and exit is shortened by 119.3m and 20.85m compared with the standard method of determining the depth and shallow burial of tunnel. If the shallow buried section of the cave entrance is reinforced with grouting to prevent frost damage, the scope of grouting reinforcement can be reduced, and the effect of low-carbon emission reduction is significant.