浅埋地铁隧道在两侧密贴深基坑异步开挖影响下的变形分析

Analysis on influence of existing shallow tunnel due to asynchronous excavation of bilateral closely attached deep foundation pits

摘要

城市地下空间开发常在地铁线路两侧开挖基坑，两侧基坑一般采用同步对称开挖，但受外部环境影响很难实现完全同步，异步开挖对控制隧道变形不利，严重时将影响运营安全。然而近年来随着地下空间开发强度加大，基坑越来越贴近地铁既有线路，开挖深度也远超既有线深度，形成浅埋隧道高悬在两侧深基坑之间的情况，在这种工况下异步开挖对隧道变形更为不利，因此有必要研究其变形规律，为控制隧道变形提供依据。依托广州地铁十二号线赤岗站在既有八号线两侧密贴基坑的异步开挖，将既有地铁运营隧道变形监测数据与开挖工况、开挖速率、地层等相结合进行变形分析。结果显示：隧道开始向先行开挖基坑侧平移，最大平移量3.14 mm,发生在先行开挖侧基坑开挖至隧道底板高度时；随着另一侧基坑的开挖平移速率减缓，当另一侧基坑也开挖至隧道底板以下时，隧道转向后续开挖侧基坑平移，最大平移量6.12 mm,发生在基坑封底前；异步开挖在一定程度上抑制隧道沉降，但会导致隧道产生横向差异沉降，横向差异沉降在基坑封底前最大值3.38 mm,封底稳定后2.51 mm。结果表明：在异步开挖工况下隧道两侧平移量不等，平移方向在开挖过程中会发生改变，与基坑变形高度相关；异步开挖导致隧道向先行开挖基坑侧倾斜；隧道水平位移和差异沉降最大值出现在基坑封底前，基坑封底能有效控制隧道变形，两侧基坑封底后隧道变形趋于稳定。

Abstract

The urban underground development typically involves the excavation of foundation pits adjacent to subway lines. Conventionally, the excavation on both side of existing tunnel generally adopts synchronous symmetrical excavation, however it's difficult to execute synchronous symmetrical excavation in whole process due to the influence of external environment. Asynchronous excavation is detrimental to tunnel deformation control, in severe cases, it will affect operational safety. Furthermore, in order to get more space, the foundation pit is getting closer and closer to the existing tunnel and the depth of the pit exceeds the depth of existing tunnel is more and more, the shallow tunnel is formed suspended between the foundation pits on both sides, in this case asynchronous excavation is more detrimental to tunnel deformation. Therefore it is necessary to study the tunnel deformation rule to provide a basis for controlling tunnel deformation. Taking Guangzhou Subway Line 12 project Chigang station bilateral deep foundation pits which close contact with both side of operating subway tunnel of Line 8 as a study case, the deformation monitoring date was analyzed combined with different working conditions, excavation speed, geology etc. The result shows that: The tunnel began to shift to the foundation pit of excavation in advance, the maximum translation is 3.14 mm, which occurs when the excavation in advance reaches the bottom of the exist tunnel; With the excavation on another side of the tunnel, the translation speed slows down and the tunnel translation shift the moving direction to another side which foundation pit was subsequently excavated when excavation below the existing tunnel, the maximum translation is 6.12 mm, which occurs before the foundation pits is bottom closed. Asynchronous excavation can restrain tunnel settlement to some extent, but it can lead to transverse differential settlement, the transverse differential settlement is 3.38 mm before bottom closed, but after bottom closed and stabilized is 2.51 mm. The above implementation fully demonstrates that: in the case of asymmetrical excavation condition, the horizontal displacement on both sides of the tunnel is unequal and the displacement direction will be reversed during the excavation process, it is highly related to the deformation of foundation pit; Asynchronous excavation cause the tunnel to tilt towards the foundation pit of excavation in advance; The maximum deformation occurs before the foundation pit is closed, casting bottom slab of the foundation pit can effectively stabilize the deformation of the tunnel, deformation tends to be stable after the foundation pits on both side of the tunnel is bottom closed.

关键词

深基坑 / 异步开挖 / 变形分析 / 浅埋隧道 / 密贴

Key words

deep foundation pit / asynchronous excavation / deformation analysis / shallow tunnel / closely attached

Author summay

康大勇(1976—), 男, 高级工程师, 总工, 学士, 主要从事土木工程施工技术研究。E-mail: [e-mail]