黄土地区地铁车站换乘改造施工力学行为研究

以西安地铁5号线新建南稍门站对既有地铁车站换乘改造工程为背景,运用有限元方法分析研究既有地铁车站换乘改造的空间施工力学行为,重点论证既有地铁车站侧墙开洞工法的合理性。研究结果表明:(1)新建换乘厅基坑开挖卸荷是引起邻近雨污水管及既有地铁车站上抬变形的主因,而侧墙开洞后板墙支承约束减弱是导致孔洞顶部发生下沉变形的关键工序;(2)侧墙开洞后洞顶由受压区转变为受拉区,且洞口周边竖向压力突增,而侧墙弯矩变化幅度较小,故侧墙开洞应遵循"化整为零,随挖随支"的原则,即加强圈梁应尽快封闭成环,以抵抗由于侧墙开洞所引发的周边结构复杂的内力形式;(3)随着侧墙开洞跨度的增加,既有线车站的变形和内力均显著增大,而横通道水平净距对既有线车站的变形和内力影响较小,因此破除既有线侧墙方案建议选取7.5 m净跨、0.5D水平净距的施工方案,可确保既有线的运营及施工安全。

Study on Mechanical Behavior of Transfer and Reconstruction of Metro Stations in Loess Area

Based on the transfer and transformation project of Nanshaomen Station of Xi'an Metro Line 5, the finite element method is used to analyze the spatial mechanical behavior of the existing metro stations, and the rationality of the construction method of side-wall-opening in existing metro stations is emphatically demonstrated. The research results show that:(1)The excavation and unloading of the foundation pit of the new transfer hall is the main cause of the uplift deformation of adjacent rain and sewage pipes and existing subway stations; the weakening of supporting restraint resulted from the opening of the side wall leads to the subsidence deformation of the top of the opening.(2)When the side wall opens, the top of the hole changes from compression to tension, and the vertical pressure around the hole increases suddenly, while the bending moment of the side wall changes slightly. Therefore, the opening of the side wall should be conducted in such a way that supporting is followed up immediately after each individual excavation. That is to say, the reinforcing ring beam should be closed as soon as possible to resist the complicated internal forces in the surrounding structure caused by the opening.(3)With the increase of the span of the side wall opening, the deformation and internal force of the existing railway station increase significantly, while the horizontal clearance of the cross passage has little effect on the deformation and internal force of the existing railway station. Therefore, it is recommended that the construction scheme of 7.5 m net span with 0.5D horizontal net spacing should be employed instead of the side wall of the existing line to ensure the operation of the existing line and construction safety.