穿越运营地铁车站的基坑开挖及对周边环境影响的安全分析

Safety Analysis on Excavation of Foundation Pit Crossing Subway Station in Operation and Influence on the Surrounding Environment

以上海轨道交通9号线宜山路站换乘通道下穿轻轨3号线车站的基坑工程为背景,建立三维数值分析模型,对基坑施工进行全过程动态模拟。分析结果表明,计算结果与工程监测数据基本吻合,下穿轻轨车站的基坑开挖可引起上部车站结构的不均匀沉降。为保护上部车站结构,采用了全方位旋喷加固(MJS)的施工新工艺,首次在相对于桩基如此近距离的范围内把MJS法应用在既有地铁车站正下方进行施工,指出了地基加固体对基坑开挖产生的位移传递具有阻断作用。结合规范要求,在对基坑施工进行全过程动态模拟条件下,通过预测地表和基坑自身变形特征及最大值来分析和评价整个基坑开挖过程中基坑自身结构的安全性;同时为了评价基坑开挖对周边环境的影响,还对上部车站结构进行承载能力极限状态验算和正常使用极限状态验算,得出在相应位移约束条件下的安全状态。对比分析表明,在紧贴基坑地下连续墙的土体中进行二次加固及结构逆筑施工,可有效控制上部车站结构变形。

Taking the foundation pit for the change from Yishan Road Station of Shanghai Metro Line 9 to the station of Under-cross Light Line 3 as the background, the 3D numerical model for analysis is established for the dynamic simulation of the whole course of the pit construction. The analysis result shows that the calculation result agrees with the monitoring data and the excavation of foundation pit for the station of under-cross light rail may cause uneven settlement of the upper structure of the station. In order to protect this upper structure, the new construction process, multi-jet spray （MJS） , is adopted firstly applying MJS process in the construction under the existing subway station within the scope so close to the pile foundation and indicating foundation stabilization body can block displacement transfer caused by excavation of foundation pit. Combining with the standard requirement, the safety of the own structure of foundation pit is analyzed and evaluated during the whole course of the excavation depending on the prediction of the own deformation feature and maximum value of the ground surface and foundation pit on the condition that this whole construction course is simulated dynamically; at the same time, in order to evaluate the influence of such excavation on the surrounding environment, the ultimate state of bearing capacity and that under normal operation are calculated for the upper structure of the station for the purpose of check so as to obtain the safe state subject to relevant displacement constraint. The eontrastive analysis shows that the secondary reinforcement and inverse construction on structure carried out in the soil mass of underground continuous wall adjacent to foundation pit can control the deformation of upper structure of station effectively.