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基坑施工将打破周围地层已平衡的应力场,引起应力释放,对既有下卧地铁隧道产生不利的影响。针对既有研究的不足,提出考虑隧道剪切效应的基坑开挖对下卧隧道影响的解析解。既有隧道简化为搁置于Winkler地基上的Timoshenko梁。通过两阶段分析法,考虑基坑卸荷作用下已建隧道的响应。首先基于Timoshenko梁理论,建立考虑隧道剪切效应的隧道纵向变形微分方程,然后将由Mindlin弹性解计算得到附加荷载施加于既有隧道上,最后通过有限差分法得到在附加荷载作用下隧道的纵向变形解答。收集3个已发表工程实例的实测数据,并与本文方法及Euler-Bernoulli梁法的计算结果进行对比分析,发现实测结果与2种方法得计算结果有较好的一致性。然而,在内力分析上,相对比于本文方法,Euler-Bernoulli梁法明显高估基坑卸荷引起的隧道弯矩与剪力。由于本文方法可有效模拟既有隧道剪切效应,因而可进一步给出1在卸荷作用下隧道管片间错台量。研究成果可为合理预测邻近基坑施工对既有隧道的影响提供一定的理论支持。
Construction of the foundation pit will break the balanced stress field in the surrounding strata and cause stress release, adversely affecting the existing sub-metro tunnel. Aiming at the deficiency of the existing research, an analytical solution to the influence of excavation on the tunnel under the influence of tunneling shear effect is proposed. The existing tunnel is reduced to a Timoshenko beam resting on a Winkler foundation. Through the two-stage analysis method, the response of the built tunnel under unloading of foundation pit is considered. Firstly, based on Timoshenko beam theory, the tunnel longitudinal deformation differential equation considering the tunneling effect is established, and then the additional load calculated by the Mindlin elastic solution is applied to the existing tunnel. Finally, the longitudinal deformation of the tunnel under additional load is obtained by finite difference method answer. The measured data of three published engineering examples are collected and compared with the results of the present method and the Euler-Bernoulli beam method. It is found that the measured results are in good agreement with the calculated results of the two methods. However, in the internal force analysis, the Euler-Bernoulli beam method obviously overestimates the tunnel bending moment and shear force caused by unloading of the foundation pit compared with the method in this paper. Because the method in this paper can effectively simulate the existing tunnel shear effect, we can further give a breakdown of the tunnel segment between unloading and tunneling. The research results can provide some theoretical support for the reasonable prediction of the influence of adjacent excavation on existing tunnels.