基坑开挖对临近地铁隧道影响的两阶段分析方法

Two-stage method for analyzing effects on adjacent metro tunnels due to foundation pit excavation

城市高层建筑施工中进行基坑开挖必然引起周围地层移动,从而造成临近地铁隧道纵向不均匀沉降,最终对地铁正常运营产生严重影响。针对目前该领域存在的三维有限元建模复杂及计算耗时的缺点,考虑基坑开挖引起的坑底和四周坑壁土体同时卸荷产生的影响,提出了基坑开挖对临近地铁隧道纵向变形影响的两阶段分析方法。首先计算基坑开挖作用在地铁隧道上的附加荷载,然后基于Winkler地基模型建立地铁隧道纵向变形影响的基本微分方程,根据Galerkin方法将该方程转换为一维有限元方程进行计算,同时研究了不同隧道埋深、距离基坑开挖现场远近、不同地基土质和不同隧道外径等因素对隧道纵向变形的影响。结合大型三维有限元数值模拟以及现场实测数据将计算结果进行了对比,得到较好的一致性。成果可为合理制定基坑开挖对临近地铁隧道的保护措施提供一定的理论依据。

Unloading of foundation pit excavation will no doubt induce the soil deformation and have result in uneven settlements of adjacent metro tunnels. The excessive settlements may induce the crack of tunnel segments and eventually may affect the safety use of metro trains. Two-stage method is presented for determining the longitudinal deformation of metro tunnels caused by adjacent foundation pit excavation. The soil unloading effects of the bottom plan and the surrounding walls induced by the foundation pit excavation can be considered by this method. Firstly the additional stress due to adjacent foundation pit excavation is calculated. Secondly the governing differential equation is built up based on Winkler model. Then the differential equation is deduced to the finite element equation by the Galerkin method; and vertical displacement and internal forces along longitudinal axis are obtained. Furthermore, the parametric analysis of existing tunnels is carried out; such as, the different depths, the distance from the excavation site, the different geologic conditions and the different outer diameter of the tunnel. Finally, the results from present approach are compared with that from 3D numerical simulation and measured data; good agreement is obtained. It may provide certain basis to draw up correctly protective measures of metro tunnels influenced by adjacent excavation.