浅埋暗挖地铁车站下穿既有线结构施工方法研究

以北京地铁5号线崇文门车站过既有线段为研究对象,对下穿既有线结构的新线地铁车站施工方法进行研究。采用三维有限差分软件FLAC3D,对柱洞法、中洞法和侧洞法3种大断面地铁车站施工方法的施工全过程进行三维仿真分析,研究地表沉降、既有线沉降、既有线变形缝两端结构差异沉降和塑性区分布。研究结果表明:3种工法下第1阶段开挖造成的地表沉降在总沉降中占主要部分,柱洞法施工造成的地表沉降和既有线结构沉降最小,中洞法次之,侧洞法最大;不同工法下相同位置处的变形缝两端结构的差异沉降趋势相同,洞室上方变形缝两端结构的差异沉降先增大后减小,远离洞室的变形缝两端结构的差异沉降始终增大;3种地铁开挖方法产生的塑性区基本位于洞室周围,但侧洞法的塑性区深入到既有线结构,影响既有线结构的安全运营。可见,柱洞法相对于其他2种工法具有一定优势,在地层沉降控制要求比较严格时,推荐首选柱洞法。

Study on the Shallow Tunnel Construction Methods for a New-Built Subway Station Passing through the Bottom of the Existing Subway

The background of this paper is Line 5 Beijing Metro Chongwenmen subway station which is a new-built subway station crossing through the bottom of the existing subway.It is based on direct search method and constructed using FLAC3D,a commercial finite difference program,to find the most appropriate construction method for large cross-section station by making whole process simulations of three different construction methods,namely pioneer heading-column construction method,mid-tunnel construction method and side-tunnel construction method The settlement of ground surface,the settlement of the existing subway,and the differential settlement between two adjacent settlement joints and the distribution of the plastic zone state are studied to get the most effective construction method.The study indicates that the settlement of ground surface during the first construction stage is dominated in the total ground surface settlement and different construction methods have different settlement value in ground surface.The tendencies of the differential settlement between two adjacent settlement joins are same with different construction methods.The settlement of the settlement joint above the tunnel firstly increases and then decreases while the settlement joints beside the tunnel increase all the time.Plastic zone induced by tunnel excavation mainly exists around the tunnel while it can go deep to the existing structure under some construction method which will influence the operation of the existing subway.Based on all the analysis and comparison above we get that pioneer heading-column construction method is the best construction method of all the three construction methods and can be recommended as the first choice under some difficult conditions.