Abstract:Temperature field is required to be known when designing the insulation layer length of tunnels in cold region at present. To overcome the lack of measured temperature data inside the tunnel, this paper presents an approach for insulation layer length on the basis of temperature field analytical solution which is derived from inlet and outlet weather conditions and terrain conditions. Due to the equal of temperature amplitude that is subjected to the meteorological parameters, the critical length is obtained. When the distance from tunnel entrance is less than critical length, inlet meteorological parameters are adopted to calculate surrounding rock and lining temperature filed in tunnel inlet section. Otherwise outlet meteorological parameters are used. Moreover, the length of insulation layer is determined by the position where 0℃ is occurred on the interface of primary lining and surrounding rock. With the help of insulation layer, the convection heat transfer between air and surrounding rock has changed. Since energy flowing into the surrounding rock in the two cases is equal, the correction coefficient of insulation layer length is confirmed. Combined with the actual project, the length of insulation layer is calculated by the proposed approach. In addition, the influence of the critical parameters (temperature gradient, wind speed) on temperature field is analyzed. The research results show that the needed length of insulation layer decreases as the geothermal gradient increases, and the narrows can be up to 50%, while it increases rapidly as wind speeds up.
