地铁车站洞桩法施工扩挖并行下穿既有建筑物的施工影响

PBA Construction Technology for Metro Station Expanding Excavation Undercrossing Parallel Existing Structure

[目的]受地面既有建(构)筑物影响,有的地铁车站两端盾构接收区车站主体围护桩无法施作,须采用洞桩法施工。对此需研究地铁车站洞桩法施工扩挖并行下穿既有建筑物的施工影响。[方法]以成都地铁18号线新建倪家桥站下穿既有建筑物工程为研究对象,建立有限元模型,根据实际施工方案,对地面和既有建(构)筑物沉降特征进行分析,并采用现场监测数据进行验证。[结果及结论]采用超前大管棚、临时立柱支撑体系、7导洞分部开挖以及人工挖孔灌注桩等洞桩法施工技术,能够在有效控制地面和既有建筑物沉降的前提下,成功实现车站主体围护桩的施作;对地面沉降和既有建筑物沉降影响最大的施工步骤是导洞(1)、(3)、(5)、(7)的开挖;既有建筑物在导洞(1)、(2)处沉降明显,最大沉降值为9.62 mm,是模拟结果沉降值的1.5倍,现场监测结果与模拟结果均满足安全控制要求。

[Objective]Affected by the occupation of existing buildings(structures)on the ground,the main retaining piles in shield receiving areas at both ends of some metro stations cannot be built.Therefore,it is necessary to study the pile-beam-arch(PBA)construction technology for expanding excavation of metro station undercrossing the parallel existing buildings or structures.[Method]With the project of Nijiaqiao Station on New Line 18 in Chengdu Metro undercrossing the existing structures as the research object,a finite element model is established to analyze the subsidence characteristics of the land and the existing structures according to the actual construction plan,and the results are verified by on-site monitoring data.[Result&Conclusion]PBA construction technologies including advanced large pipe shed,temporary column support system,staggering excavation of 7guiding holes and manual excavation cast-in-place pile are used,successfully implementing the station main retaining pile construction under the premise of effectively controlling the subsidence of land and the existing buildings.The construction steps that have the greatest impact on the above-mentioned subsidence are the excavation of guiding holes 1,3,5,7.The subsidence of existing structures is obvious at guiding holes 1 and 2 with the maximum value of 9.62 mm,1.5 times the simulated value.Both the on-site monitoring results and the simulated results meet the safety control requirements.