基坑开挖对临近隧道的变形影响分析

Analysis of the Deformation Influence on Adjacent Tunnels Caused by Pit Excavation

随着城市交通运输量的急剧增大,地下地铁隧道工程越来越多,临近地铁隧道的基坑工程也越来越普遍,为研究基坑开挖对临近隧道变形的影响,以具体临近已建隧道的基坑支护工程为案例,阐述工程采用的主要施工方案、支撑体系以及挡土与止水措施,并运用MIDAS/GTS有限元软件模拟基坑的支护方案进行基坑开挖工况模拟,分析其对隧道位移及应力的影响,并进行基坑正常支护和基坑坍塌两种情况下隧道的变形分析。结果表明,对于周边土体主要是砾质黏土的基坑采用“地连墙+三道内环撑”支护能有效控制变形;临近隧道的变形不仅与土层开挖有关,还与基坑支护强度有关;利用数值模拟分析软件能更好地分析基坑对周围建筑的影响与进行相应的安全性评估。结论可为此类临近已建隧道的基坑支护工程的方案设计提供参考经验。

With the rapid increase in urban traffic volume,there are more and more underground subway tunnel projects,and foundation pit projects near subway tunnels are becoming more and more common.In order to study the influence of foundation pit excavation on the deformation of adjacent tunnels,the main construction scheme,support system,soil retaining and water stopping measures adopted in the foundation pit supporting project of a tunnel which has been built nearby are expounded.MIDAS/GTS finite element software to simulate the foundation pit support plan to simulate the excavation condition of the foundation pit is used;its influence on the tunnel displacement and stress is analyzed;and moreover deformation analysis of the tunnel in the case of the normal support and foundation pit collapse is carried out.The results show that,for the foundation pit whose surrounding soil is mainly gravelly clay,the use of“ground wall+three inner ring bracing”support can effectively control the deformation;the deformation of adjacent tunnel is not only related to the excavation of soil layer,but also related to the supporting strength of foundation pit;numerical simulation software can be used to better analyze the influence of foundation pit on surrounding buildings and the corresponding safety assessment is carried out.The conclusion can provide reference experience for the design of the foundation pit supporting engineering near the existing tunnel.