季节性寒区隧道围岩融化分析的一种解析计算方法

Analytical method for thawing analysis of surrounding rock in seasonal cold region tunnels

融化与冻胀是影响寒区隧道围岩稳定的重要因素,为分析季节性寒区隧道融化时围岩应力分布规律,建立了一种理论分析模型。该模型是在围岩先发生冻胀的基础上进行的,考虑了冻结围岩融化时体积的缩小和融化围岩在荷载作用下的压缩过程,即当冻结围岩融化时体积缩小,融化范围外侧的围岩将向隧道方向移动,并对融化围岩进行压缩变形,当达到平衡后又有一部分冻结围岩进入融化圈范围内,使得该部分冻结围岩再次融化,外侧围岩再次移动,融化围岩再次压缩,最后再次达到平衡,如此往复,直至整个系统稳定为止。为简化分析,认为所有过程均是一次完成,且冻结围岩融化时体积的缩小量近似等于围岩冻结时体积的膨胀量;而融化围岩的压缩过程是将融化围岩和衬砌看作一复合支护结构并进行受力压缩的过程。通过算例分析可知:冻结围岩融化后,衬砌中的最大主应力有所减小,融化范围内的围岩应力减小明显,而未融化范围内(冻结状态)围岩由于几何尺寸的变化使得环向应力有所增加;同时进一步分析了冻胀线应变、地应力以及融化半径对融化过程的影响规律。该融化分析模型较好的吻合现场的实际情况,对寒区隧道围岩融化研究具有一定的参考意义,能较好地指导寒区隧道设计。

Thaw and frozen heave are both the important factors for the stability of surrounding rock in cold region tunnels. A theoretical model is estublished to study the stress distribution when the surrounding rocks melt in seasonal cold region tunnels. The model is based on the condition that frost heave occurs firstly in the surrounding rocks, and the deflation in volume and the compression progress of thawing surrounding rocks under load when the frozen surrounding rocks melt are considered. When the frozen surrounding rocks melt and the volume reduces, the surrounding rocks outside the thawing range move to the tunnel, the thawing surrounding rocks are compressed and deformation occurs. After the balance is reached, other frozen surrounding rocks also enter the thawing range. They will also melt and the surrounding rocks outside them also move to the tunnel. The melting surrounding rocks are compressed again and the new balance is reached at last. The phenomenon is repeated, until the entire system is stable. In order to simplify the analysis, it is assumed that all progress is completed one time and the deflation in volume when the frozen surrounding rocks melt is approximately equal to the frost heave. The lining and thawing surrounding rocks are regarded as a composite retaining structure. Its deformation is regarded as the compression process of thawing surrounding rocks. The results of the example show that when the frozen surrounding rocks thaw, the maximum principal stress in lining will reduce and the stress in thawing range will also decrease distinctly. The stress in the surrounding rocks without thaw increases due to the change of geometrical sizes. In addition, the influence law of the linear strain of frost heave, geostress and thawing radius is analyzed. The proposed model can well reflect the actual situation in the field. It may provide a certain reference for the thawing study of surrounding rocks in cold region tunnels and well guide the design of cold region tunnels.