西安地铁隧道穿越地裂缝带的计算模型探讨

通过对西安地铁隧道穿越地裂缝带的大型物理模型试验成果的分析,提出在地裂缝活动时,穿越地裂缝带的地铁隧道有以下两个方面的变化特征:一是作用于隧道的荷载发生改变;二是在隧道底部产生脱空现象。这种脱空现象无论在整体式隧道还是盾构隧道中都会出现。造成隧道在界面上与土体脱空的原因是隧道和周围地层的变形不协调。脱空区域的大小对地铁隧道的变形与内力计算会产生明显影响。在对隧道变形特征分析的基础上,总结得出了西安地铁穿越地裂缝带隧道变形的4种计算模型:对于整体式长隧道,可以采用一端固定而另一端简支,或一端固定而另一端定向支承的计算模型;对于整体式短隧道,可以采用外伸梁模型;对于盾构隧道,可以采用一端固定而另一端定向支承的计算模型。最后,对脱空条件下隧道数值分析的建模问题进行了讨论。算例分析表明:在数值计算中,对于隧道与土体接触面的界面处理非常关键,否则将造成计算结果的重大误差。

Discussion on the Computing Model for Xi'an Metro Tunnel Passing Through the Ground Fissure Zone

According to the analysis of the large physical model test on Xi'an Metro tunnel passing through the ground fissure zone, two deformation characteristics in the metro tunnel were found when ground fissures were active. Firstly, the change happened when the tunnel was in load; secondly, the gap appeared at the bottom of the tunnel. The gap appeared in monolithic and shield tunnels. The reason was that the deformations of the surrounding strata and tunnel were incongruous. The size of the gap had significant effect on metro tunnel deformation and internal force calculation. On the basis of the analysis of the tunnel deformation characteristics, four deformation calculating models of the tunnel passing through the ground fissure zone were summarized. For the long monolithic tunnel, to fix one end and simply support the other was a calculating model, another model was to fix one end and directly support the other; for the short monolithic tunnel, the simplified overhanging beam could be used; for the shield tunnel, to fix one end and directly support the other was the calculating model. Finally, the tunnel numerical models under the condition of the gap were discussed. The calculating examples showed that it was very crucial to process interface between the tunnel and the soil in the numerical calculation; otherwise, the calculation would cause the major error.