旁侧基坑开挖对超大直径盾构隧道变形影响分析

Analysis on Impact of Adjacent Foundation Pit Excavation on Deformation of Large-diameter Shield Tunnels

密集城市区近接基坑工程易引发超大直径(>15m)盾构隧道变形、结构开裂及渗漏水.当前超大直径盾构隧道建设处于起步阶段,基坑影响下隧道变形响应规律不明,合理的影响分区匮乏.本文采用有限元软件建立超大直径隧道旁侧基坑开挖的三维有限元模型,分析超大直径隧道的结构变形响应机制,并探讨隧道埋深、隧道-基坑间距、基坑开挖深度等因素影响规律.结果表明,基坑开挖引发地层朝向基坑的“鼓肚子”水平位移和“勺子”状竖向位移;与小直径隧道相比,超大直径盾构隧道表现出较小的纵向变形和较为显著的横向变形;隧道变形随隧道-旁侧基坑围护结构距离增大而减小、随埋深增大先增大后减小、随基坑开挖深度的增大而增大.通过基坑开挖深度归一化后,隧道最大变形与隧道-基坑间距可用指数函数高精度拟合.提出归一化后的影响分区图,为实际工程超大直径隧道结构保护提供重要的参考.

Adjacent foundation pit engineering in dense urban areas is easy to cause deformation,structural cracking,and water leakage of shield tunnels with super-large diameters(>15m).At present,the construction of super-large diameter shield tunnels is in the initial stage,the deformation response law of tunnels under the influence of foundation pits is unclear,and there is a lack of reasonable influence zoning.In this paper,a threedimensional finite element model of the excavation of the side foundation pit of the super-large diameter tunnel is established by using finite element software.The structural deformation response mechanism of the super-large diameter tunnel is analyzed,and the influence laws of factors such as tunnel buried depth,tunnel-foundation pit spacing,and foundation pit excavation depth are discussed.It is found that"bulge belly"horizontal displacement and"spoon"vertical displacement towards the foundation pit are caused by the excavation of the foundation pit.Compared with the small-diameter shield tunnel,the large-diameter shield tunnel presents a weaker longitudinal deformation and more significant transverse deformation.The tunnel deformation decreases with the increase of tunnel-retaining wall distance,increases first,then decreases with the burial depth,and increases with the excavation depth.After normalization by the excavation depth,the maximum tunnel deformation and distance can be fitted well by an exponential function.A normalized influenced zone was proposed,which provides an important reference for the protection of the large-diameter shield tunnels in engineering practice.