北京地铁大兴机场线矩形断面大跨度隧道上穿施工时对既有线结构变形的控制

Existing Line Structural Deformation Control during Beijing Metro Daxing Airport Express Rectangular Section Large-span Tunnel Over-crossing Construction

目的:新建地铁线路上穿既有线时,若穿越的地层浅薄,地质松散软弱,则需选择合适的施工方法来有效控制既有线的结构变形,以保证既有线的运营安全。方法:依托北京地铁大兴机场线磁各庄站—草桥站区间矩形断面大跨度隧道上穿既有地铁10号线草桥站—纪家庙站区间盾构隧道工程,研究施工期间对既有线变形的控制。对施工方案进行比选,运用FLAC3D软件模拟施工过程,预测既有线隧道及道床的结构变形,总结施工过程中的既有线结构变形规律,进而确定关键工序的变形控制措施。在实际施工时密切监测既有线结构变形指标,并对实际监测结果和预测结果进行对比分析。结果及结论:通过方案比选,确定了采用PBA法(洞桩逆作法)暗挖上穿施工。制定了管幕、分段分层开挖均衡卸荷、预应力锚索及底板下低压注浆等关键工序的变形控制措施。根据模拟预测结果,既有线隧道结构底部最大上浮值为0.41 mm,顶部最大上浮值为1.72 mm,符合累计最大变形2 mm的控制要求。根据实际监测结果,既有线隧道结构上浮1.32 mm、水平收敛1.00 mm,道床上浮1.20 mm,管片错台-0.04 mm,施工过程中的既有线结构变形零预警,说明既有线变形始终可控。

Objective:When a new metro line over-crosses existing lines and encounters shallow and stratigraphically loose and weak layers,it is essential to select appropriate construction methods to effectively control existing line structural deformation caused by the engineering,ensuring existing line operational safety.Method:Based on the project of Beijing Daxing Airport Express Cigezhuang Sta.-Caoqiao Sta.rectangular section where the large-span tunnel over-crosses Caoqiao Sta.-Jijiamiao Sta.interval on existing Metro Line 10,the control on existing line deformation during construction is studied.Through comparative selection of construction schemes,the FLAC3D software is used to simulate the construction process and predict the structural deformation of existing line tunnel and track bed.The deformation law of existing line structure throughout construction is summarized,and deformation control measures for key construction steps are determined.During actual construction,existing line structural deformation indicators are closely monitored,and a comparative analysis is performed between field-monitored and predicted results.Result&Conclusion:Through scheme comparative selection,PBA(pile-beam-arch)method is determined for underground excavation over-crossing construction.Deformation control measures are established for key construction steps,including the use of pipe canopies,segmented excavation with balanced unloading,prestressed anchorages,and low-pressure grouting beneath bottom plate.According to the simulation prediction results,the maximum uplift value at existing tunnel structure bottom is 0.41 mm,and the maximum uplift value at the top is 1.72 mm,meeting the control requirement of a cumulative maximum deformation of 2 mm.Based on the field-measured results,existing line tunnel structure uplift is 1.32 mm,horizontal convergence is 1.00 mm,track bed uplift is 1.20 mm,and segment staggered value is-0.04 mm.The absence of existing line structural deformation warnings during construction process indicates that the deformation is within control.