地铁换乘站坑中坑开挖变形特性

Deformation characteristics in pit-in-pit of metro interchange station

为了研究坑中坑开挖变形特性,分析了卸载条件下坑中坑基坑不同区域土体应力路径的变化规律,采用土体卸载的HS有限元模型,对某地铁换乘站坑中坑土体开挖进行数值模拟.结果表明:该坑中坑的内坑开挖对外墙侧移影响较小,每次开挖外墙侧移仅为2 mm左右;外坑、内坑开挖都导致内墙向坑内侧移,内坑开挖导致内地连墙侧移值增加超过11 mm;内坑开挖对外墙外侧土体位移影响较小;内坑外侧土体(即外坑坑底)的隆起量有随着开挖深度增大的趋势,外坑土体卸载导致外墙外侧地面水平位移较为明显,局部超过15 mm;内坑每次开挖引起外墙外侧土体侧移增量不超过1 mm.因此,有针对性地确定支护结构设计和施工方案,既能保证坑中坑基坑安全和环境影响的要求,又能节省造价.

To research the deformation properties in pit-in-pit,the variation regularity of the stress path in different regions in unloaded ＂pit in pit＂ was analyzed by using the hardening-soil finite element model based on unloading.The excavation deformation of the ＂pit in pit＂ in a metro interchange station was studied.The results show that the influence of unloading in the internal pit on lateral deformation is small and the displacement is about 2 mm for each unloading.The lateral deformation of the internal walls reduced with unloading in the internal and lateral pit induced by unloading.The displacement in the internal pit is more than 11 mm.The influence on the ground behind the lateral walls is very small with unloading in the internal and lateral pits.The uplift values of the ground behind internal pit（namely the site of bottom in lateral pit） may increase gradually with increasing of excavation depth.The vertical deformation induced by unloading in the lateral pit is distinct.The displacement in the internal pit may exceed 15 mm in some areas,and the deformation increment in each unloading is no more than 1 mm.Hence,selecting a rational scheme for design and construction according to special conditions is important,which can not only guarantee the pit safety and environment influencing,but also save the engineering cost.