兰州地铁地温分布特性及其演化规律

以兰州地铁所在地区为研究对象,实测地铁隧道开挖前的地温(简称为初始地温),根据实测数据,提出地铁初始地温预测模型公式。采用非稳态传热的数值模型,分析运营条件下地铁隧道围岩温度的演化规律。结果表明:兰州地铁初始地温随环境气温和埋深的变化而变化;年变温层位于自地表至埋深12m处;年恒温层位于埋深12m及其以下,温度为15℃左右;年变温层中,1年内初始地温变化规律与环境气温变化规律相似,近似呈正弦曲线状分布,但存在相位滞后的现象;1年中初始地温的振幅随埋深的增大呈指数下降趋势。在隧道内空气与围岩之间热交换中,兰州地铁隧道围岩的温度及其梯度、热透厚度(未达到极限时)均与隧道内环境温度、热交换时间成正相关关系,但与距隧道内壁的距离成负相关关系。

Distribution Characteristics and Evolution Law of Ground Temperature in Lanzhou Subway

Taking Lanzhou subway as the research object,the ground temperature before the excavation of the subway tunnel was measured(referred to as the initial ground temperature).According to the measured data,the prediction model formula of the initial ground temperature of the subway was put forward.The numerical model of unsteady heat transfer was used to analyze the evolution law of surrounding rock temperature of the subway tunnel under operation conditions.Results show that the initial ground temperature of Lanzhou subway changes with the variation of the ambient temperature and burial depth;the annual variable temperature layer is located from the surface to the burial depth of 12 m;the annual constant temperature layer is located at the burial depth of 12 mand below,and the temperature is about 15℃;in the annual variable temperature layer,the variation of initial ground temperature within one year is similar to that of the ambient air temperature,which is approximately sinusoidal distribution,but there is the phase lag phenomenon;the amplitude of initial ground temperature decreases exponentially with the increase of the burial depth in one year;in the heat exchange between the air and the surrounding rock in the tunnel,the temperature and gradient of the surrounding rock in Lanzhou subway tunnel and the heat penetration thickness(when the limit is not reached)are all positively related to the temperature and the time of heat exchange in the tunnel,but negatively related to the distance from the inner wall of the tunnel.