大跨地铁风道导洞开挖的地表沉降分布规律研究

北京地铁8号线大红门桥站-和义站区间附属风道为跨度16.2 m的单跨结构,采用暗挖洞桩法(PBA工法)施工。为有效控制导洞开挖引起的地表沉降,必须合理安排导洞施工顺序。基于三维数值模拟方法对不同的导洞开挖方案地表沉降分布规律进行研究,并与地表沉降监测结果进行比较分析。结果表明:不同的导洞开挖顺序的地表沉降发展路径差别显著,但最终的沉降值基本一致;随着导洞的开挖,地表沉降槽宽度增加并不明显,但是由于导洞开挖的群洞效应,地表沉降速度发展较快。因此在后续的拱部开挖支护中,必须通过调整支护措施和开挖方案来严格控制地层沉降。

Distribution of Ground Subsidence Caused by Large-Span Subway Duct Excavation

The subway duct of Dahongmenqiao-Heyi interval tunnel of Beijing metro line 8 is a singlespan tunnel with 16. 2 m span. The subway duct is constructed with PBA method( Pile-Beam-Arcconstruction method). The construction sequence of pilot tunnels should be reasonably determined toensure that the ground subsidence is effectively controlled. The distribution of ground subsidence causedby different excavation methods for the pilot tunnel is studied with numerical simulation. The calculationresults are compared with the monitoring results, which show that the pilot tunnel excavation sequencehas significant impact on the development of the surface subsidence, but the final surface subsidenceshows no obvious difference. With the excavation of pilot tunnels, there is no significant increase in thewidth of subsidence zone, but the ground subsidence velocity increases rapidly due to the group effectgenerated by the excavation of the pilot tunnels. It is concluded that support measures and excavationscheme should be adjusted to control ground subsidence in the following progresses of arch excavation andsupport.