寒区隧道保温层铺设长度的计算方法

An Approach for Determining Length of Insulation Layer in Cold Region Tunnels

目前寒区隧道保温层铺设长度的设计要求隧道洞内温度场已知,为克服设计时暂无洞内气温实测资料的问题,基于由隧道进、出口气象条件及隧道地形条件求解的温度场解析解,提出了一种保温层铺设长度的计算方法.首先根据由隧道进口气象参数得到的洞内空气年温度振幅与由出口气象参数得到的洞内空气年温度振幅相等这一条件,计算得到受进出口气象影响的临界长度lM.当距隧道进口的长度小于临界长度lM时,利用进口气象参数计算隧道进口段围岩及衬砌温度场;当距隧道进口的长度大于临界长度lM时,利用出口气象参数计算出口段围岩及衬砌温度场,然后由隧道温度场中初期支护与围岩交界面出现0℃的位置确定保温层铺设长度.在铺设保温层后,洞内空气与围岩的对流换热发生变化,根据未铺设保温层和铺设保温层两种情况下的流入控制体的能量相等的条件,推导了保温层铺设长度的修正系数,从而计算出保温层铺设的最终长度.结合实际工程,利用提出的方法计算出保温层铺设长度,分析了关键参数对铺设长度的影响,结果表明:铺设长度随着地温梯度的增加逐渐减小,铺设长度随洞内风速的增加迅速增大.

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 temperaturedata 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 O^C 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.