邻近运营隧道的大型基坑放坡开挖影响与实测兮析

Influence of Large-scale Foundation Pit Sloping Excavation on Adjacent Operating Metro Tunnel and Actual Measurement Analysis

[目的]基坑及隧道因建设过程的差异存在复杂的耦合作用,在基坑施工过程中会不可避免地对既有运营隧道产生扰动,引起隧道的位移,严重时将影响隧道运营安全。因此,有必要研究合理的基坑开挖方法和开挖步序,以减少基坑开挖过程中对既有邻近隧道的影响。[方法]依托某下沉式广场基坑,采用有限元数值模拟的方法针对邻近既有隧道的基坑的4种开挖工况进行研究,分析了不同开挖方法、开挖步序下的隧道内力分布规律、位移变化趋势及地层变形特征,比较了不同工况对施工期间隧道变形的影响,并结合基坑开挖期间的现场实际监测数据加以验证分析。[结果及结论]与拉槽放坡开挖相比,普通放坡开挖引起的隧道竖向变形较小;与整层开挖相比,接续开挖引起的隧道竖向变形较小;不同工序的隧道竖向变形最终结果较接近;与接续开挖相比,整层开挖引起的隧道水平变形比较大,这主要是由开挖步序多、基坑的时空效应明显所导致。根据现场实际监测数据,施工期间隧道竖向变形、水平变形,以及轨道竖向相对变形呈现先增大、后减小的趋势。

[Objective]There are complex coupling effects between foundation pit and tunnel due to different construction processes.The foundation pit construction will inevitably cause disturbance to the existing operation tunnel,leading to displacement of the tunnel and even affecting its operation safety in serious cases.Therefore,it is necessary to study proper foundation pit excavation methods and excavation steps to reduce the excavation influence on the existing adjacent tunnel.[Method]Based on a sunken plaza foundation pit,the finite element numerical simulation is used to study four excavation conditions of the foundation pit adjacent to the existing tunnel.The distribution pattern of the tunnel internal force and the tunnel displacement trend as well as the deformation characteristics of the stratum under different excavation methods and steps are analyzed,and the effects of different working conditions on the tunnel deformation during excavation are compared.The results are verified and analyzed in combination with the actual monitored on-site data during the foundation pit excavation.[Result&Conclusion]Compared with the trenching excavation,the ordinary slope excavation causes less vertical tunnel deformation.Compared with the layered excavation,the continuous excavation induces less vertical deformation.The final vertical deformations of the tunnel under different steps are close to each other.Compared with continuous excavation,the layered excavation causes larger tunnel horizontal deformation,mainly resulting from multiple excavation steps and notable spatial and temporal effect of the foundation pit.According to the actual monitored on-site data,the vertical and horizontal deformations of the tunnel and the relative vertical deformation of the track present a trend of first increasing and then decreasing during construction.