十字换乘车站基坑开挖影响分析及变形控制研究

Research on influence analysis and deformation control of cross transfer station affected by the foundation pit excavation

在十字换乘工程既有地铁车站两侧深基坑开挖过程中,土体的卸载会导致地铁轨道上浮变形,从而影响地铁正常运营。以北京地区实际工程为背景,基于现场监测数据、地层变形理论及FLAC3D方案对比数值模拟,分析了两侧基坑近距离施工对既有车站的影响规律及作用机理,得出控制措施及优化建议。研究表明:两侧基坑近距离开挖时,土体卸载产生的应力释放会导致邻近车站上浮;基坑施工引起的轨道上浮贯穿整个工程,其中基坑开挖与邻近段回筑阶段导致的上浮量各占约45%,影响范围为邻近基坑边中心两侧各约110m;通过增大抽水量、在既有结构上方堆载等措施,可减小、平衡应力释放,通过调整开挖步序可优化应力释放,从而控制既有结构的上浮量,有效降低基坑开挖对地铁车站的影响,其中优化施工步序可降低19.7%上浮变形。

During the excavation of deep foundation pits on both sides of an existing subway station in cross transfer construction,the soil unloading leads to the floating and deformation of the subway track,which affects the normal operation of the subway.On the basis of the site monitoring data,stratum deformation theory and numerical simulations comparison in FLAC3D,the influence law and action mechanism of the adjacent construction of foundation pit on the existing station are analyzed based on the practical projects in Beijing,also the control measures and optimization suggestions are obtained.The study shows that:excavation of foundation pits besides both side of the existing station is within a close distance so that the stress release caused by soil unloading results in adjacent station floating.The floating runs through the entire project including the excavation and station construction stage each accounting for 45%of the floating value.The influence range starts with the center point of the foundation pit side wall and extents to the direction of its two edges for about 110m each way.Following measures can be taken to effectively reduce the impact of foundation pit excavation on subway station.By increasing the amount of pumping water or surcharge load onto the existing structure can decrease or even balance the stress release.By adjusting construction sequences can lower the floating amount by 19.7%,and consequently optimize the stress release style.