温度对隧道初期支护安全性的影响

在已建立的隧道支护结构可靠性评价的位移方法中,将测量得到的支护变形都视为是由于荷载引起的.但是,除荷载产生的变形外,初期支护的变形还与隧道所处的温度场有关.本文在前期研究基础上,探讨了喷混凝土的温度变形对隧道安全性的影响.首先,按平壁法从理论上研究了隧道围岩的热传递规律,根据理论分析结果和现场实测数据确定了隧道围岩日、月、年温度变化的影响深度.然后,提出了支护温度的计算公式,给出了围岩和喷混凝土的热力学参数.随即推导了支护温度变形的计算公式,列出了支护结构截面失效的功能函数.最后,进行工程实例分析.结果表明,当日间温度差或日内温度差超过5℃时,工程中应考虑温度的影响.本研究提高了施工期隧道喷混凝土支护安全性评价位移方法的计算精度.

Influence of Temperature on the Safety of Primary Lining of Tunnels

In the displacement-based method previously proposed, all the measured deformation of primary lining of a tunnel was thought to be totally caused by loads. However, in addition to the loads, the deformation is also related to the temperature field where the tunnel is located in. On the basis of the past study, this paper approaches the influence of thermal deformation of shotcrete on the stability of tunnels. At first, adopting one-dimensional thermal conduction model, the heat conduction within the surrounding rock is studied, and the depths that heat travels in surrounding rock in one day, one month or one year are determined according to the results by theoretical analysis and in-situ instrumentation. Then, the formulae to compute the temperature of shotcrete lining are put forward, and the thermal parameters of surrounding rock and shotcrete are worked out. After that, the formulas to calculate the thermal deformation of primary lining are derived and a performance function for the failure of a cross section is given. At last, three case studies are done. The results show that the influence of temperature should be taken into account when the change of the temperature within one day or between two consecutive days is larger than 5℃. This paper improves the accuracy of the displacement-based method for assessment of the safety of shotcrete lining of a tunnel under construction.