黄土地区基坑近接施工变形控制标准数值模拟研究

为得到湿陷性黄土地区基坑近接既有地铁结构的位移规律和控制标准,基于西安地铁5号线车站基坑临近区间隧道和车站施工,采用数值模拟手段,分析不同净距状态下新建基坑开挖引起的地表位移、新建基坑结构位移及既有结构位移,研究新建基坑开挖对既有车站、既有隧道的影响。结果表明:地表沉降值仅在新建基坑与既有结构之间的范围受水平净距影响较大,新建基坑围护结构位移仅在与既有结构邻近的一端受净距影响较大;既有结构向着新建基坑方向发生整体水平移动,且随着净距减小,水平位移增加;应尽量避免净距小于12 m的情况,当净距为18 m时,应控制新建基坑与既有结构邻近侧围护结构的水平位移最大值在15 mm以内。

Displacement Analysis and Control Standards of Foundation Pit Construction in Loess Area

In order to obtain the displacement law and control standard of the foundation pit adjacent to existing metro structures in collapsible loess area,the surface displacement resulted from the excavation of new foundation pit,the structural displacement of new foundation pit and the displacement of existing structure subjected to different net distances are analyzed by means of numerical simulation based on the construction of the tunnel and station adjacent to the foundation pit of Xi’an Metro Line 5 station.The influence of new foundation pit excavation on existing stations and tunnels is studied.The results show that the surface settlement value is only affected by the net horizontal distance between the newly built foundation pit and the existing structure,and the displacement of the retaining structure of the newly built foundation pit is greatly affected by the net horizontal distance only at the end adjacent to the existing structure;the existing structure moves horizontally in the direction of the newly built foundation pit,and the horizontal displacement value increases with the decrease of the net distance.The distance less than 12 m should be avoided as far as possible.When the distance is 18 m,the maximum horizontal displacement between the newly built foundation pit and the side retaining structure adjacent to the existing structure should be controlled within 15 mm.