Numerical analysis of effect of large-scale unloading on underlying shield tunnels
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摘要: 杭州铁路东站西广场项目基坑是杭州地区第一个在已建地铁盾构隧道顶部进行大面积开挖卸荷的工程。以西广场项目基坑工程为背景,建立三维数值分析模型,对基坑施工全过程进行动态模拟,研究了分层分块开挖、底板加筋垫层、土体加固等施工措施控制隧道隆起的有效性,并将计算结果与实测结果进行对比分析,得出以下结论：顶部大面积卸荷引起隧道的变形以隆起为主,合理的设计施工能够将隧道变形控制在要求范围；分层分块开挖的同时尽快浇筑底板垫层可取得较好效果；加固土体在地基位移场中起屏障作用,可有效降低隧道隆起。Abstract: The foundation pit of West Square of Hangzhou East Railway Station is the first project that large-scale unloading is conducted on the top of shield subway tunnels. A 3D FEM model is used to simulate the whole excavation course of the foundation pit, and the effect of various adopted construction measures on underlying shield subway tunnel is studied. The construction measures include step excavation, reinforced cushion and reinforcement of soils surrounding the tunnel. Some conclusions are drawn through the comparison between the calculated and the monitoring results: (1) the heave occupieds a dominant position in the tunnel deformation caused by top excavation, and proper design and construction can lead to an desired tunnel deformation; (2) better results will be got by combining excavation by layers and by blocks with building reinforced cushion simultaneously; (3) the reinforcement around tunnels acts as a protective screen of tunnels in ground displacement field, so the tunnel heave decreases substantially .
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Keywords:
- unloading /
- shield tunnel /
- heave /
- numerical simulation /
- reinforcement
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