地铁“先隧后站”车站基坑施工力学效应分析

为了解“先隧后站”法先期隧道施工产生的土体扰动对后期地铁车站基坑开挖的影响规律,以厦门地铁2号线高林站工程为依托,根据工程经验考虑4种地层损失率η,通过数值模拟先盾构隧道后明挖法扩建地铁车站基坑开挖过程,研究基坑开挖破除隧道前后基坑变形及围护墙内力变化规律。计算结果表明:地表沉降和墙体侧移及内力分布规律基本不变,但极值存在一定变化;对于地表沉降极值η为0.5%、1%和2%时的比无隧道时(η=0)分别增大15.8%、12.6%和10.7%;对于围护墙侧移,η从0.5%增至2%,极值增幅约4.1%;先期盾构隧道施工力学效应不利于后期基坑开挖。为克服这种不利效应,现场提出了一套基坑土方开挖及管片拆除的施工方案,实践表明采取的方案可靠,基坑安全稳定。

Analysis on the Mechanical Effect of Foundation Pit Construction of Subway Station "Tunnel Before Station"

In order to understand the influence of soil disturbance caused by the "tunnel before station" method on the later excavation of subway station foundation pit, based on the Gaolin station project of Xiamen Metro Line 2, four kinds of ground loss rate η were considered according to the engineering experience, and the excavation process of subway station foundation pit by shield tunneling first and then open excewation method was studied by numerical simulation. The deformation of foundation pit and internal force change of the retaining wall before and after excavation of tunnel were studied. The results show that: the surface settlement, wall lateral displacement and internal force distribution are basically unchanged, but the extreme value has some changes; for the extreme value of surface settlement, when η is 0.5%, 1% and 2%, it increases by 15.8%, 12.6% and 10.7% respectively compared with that without tunnel (η= 0); for the lateral displacement of retaining wall, η increases from 0.5% to 2%, and the extreme value increases by 4.1%; the mechanical effect of early shield tunnel construction is not conducive to the later foundation excavation Pit excavation. In order to overcome this adverse effect, a set of construction schemes for earth excavation and segment removal of the foundation pit is put forward. Practice shows that the scheme is reliable and the foundation pit is safe and stable.