为解决黄土地区紧邻地铁盾构隧道施工难度大、支护体系设计复杂、隧道变形控制难等问题，以西安市某与地铁隧道小净距上跨的地道基坑工程为背景，采用考虑土体小应变硬化特性的有限元方法，分析传统分区分块开挖法、“隔离桩+土体加固”法和超前管幕法对地铁隧道变形的控制效果。基于排桩隔离、管幕压制的地铁隧道变形控制思路，提出“管幕+隔离桩”的地铁隧道变形控制新方法，并对新方法施工期和工后期的地铁隧道变形进行监测分析。结果表明： 1）新方法将管幕和隔离桩连接，使土体回弹荷载由管幕和桩体自重力、桩土摩擦力共同承担，能够有效限制管幕位移，极大程度地减小隧道上浮； 2）相较于传统分区分块开挖法、“隔离桩+土体加固”法和超前管幕法，新方法将地铁隧道最大上浮量分别减少了68%、57%、72%，控制管幕整体上浮效果显著； 3）由地铁隧道变形监测数据可知，新方法提出的管幕与隔离桩连接节点设计方法可行，能够约束管幕两端与跨中的位移； 4）采用新方法后，隧道实测拱顶最大上浮量为0.8 mm，最大沉降量为1.4 mm，满足隧道的变形控制要求。
Projects near metro shield
tunnels in loess areas encounter various challenges, including high
construction difficulty, complex support system design, and difficulty in
controlling tunnel deformation. A case study is conducted to examine a
foundation pit situated directly above a metro tunnel in Xi′an, China, and evaluate the effectiveness of different methods for
controlling tunnel deformation, including the traditional segmented and block
excavation method, the "isolation pile + soil reinforcement" method,
and the advance pipe curtain method. The analysis employs a finite element
method that considers the small strain hardening property of the soil. Based on
the concepts of pile isolation and pipe curtain restraint, a novel "pipe
curtain + isolation pile" method is proposed for controlling metro tunnel
deformation. The deformation of the metro tunnel during both construction and
post-construction periods is monitored and analyzed.
The results reveal the following: (1) The proposed method effectively manages
pipe curtain displacement by linking the pipe curtain with the isolation pile,
significantly reducing tunnel uplift by distributing the rebound load of the
soil between the weight of the pipe curtain and the pilesoil friction. (2) Numerical simulations demonstrate that the
maximum uplift of the metro tunnel using the proposed method is 68%, 57%, and
72% lower than the traditional segmented and block excavation, "isolation
pile + soil reinforcement", and advance pipe curtain methods,
respectively, thus highlighting the notable uplift control effect of the pipe
curtain. (3) Monitoring results reveal that the connection node design of the
pipe curtain and isolation pile, based on the proposed method, is effective in
constraining displacement at both ends and the mid-span
of the pipe curtain. (4) The measured maximum uplift of the tunnel crown and
the maximum settlement of the tunnel are 0.8 and 1.4 mm, respectively, both
complying with relevant deformation control standards.
