软土地层双线盾构隧道近距离上穿既有隧道引起的变形特征有限元分析

Finite Element Analysis of Deformation Characteristics of Existing Tunnels Induced by Close-Proximity Overcrossing of Double-Line Shield Tunnels in Soft Soil

摘要: 软土地层中双线盾构隧道近距离上穿既有隧道施工不可避免地引起土体扰动，易导致既有隧道结构产生变形，对既有结构安全构成潜在风险。为揭示该类工程中既有隧道的变形特征及其演化规律，依托某双线盾构隧道近距离上穿既有隧道工程，使用ABAQUS有限元软件建立盾构隧道近距离上穿施工的三维有限元模型，分析双线盾构上穿过程中既有隧道的变形响应特征，并研究加固措施对既有隧道变形的影响机理。研究结果表明，盾构上穿施工过程中，既有隧道以竖向隆起变形为主，伴随轻微扭转，影响范围约为3.5 D (D为隧道直径)，且隆起变形具有明显的滞后效应；双线施工中，后行线开挖对既有隧道产生明显的二次扰动作用，使隆起峰值及影响范围进一步增大，并导致最大隆起位置发生一定偏移；在新建隧道重叠区段内采用MJS工法桩加固措施，可有效抑制既有隧道的最终上浮变形。研究成果可为软土地层中盾构隧道近距离上穿既有隧道的设计与施工控制提供参考。

Abstract: The close-proximity overcrossing construction of double-line shield tunnels in soft soil inevitably induces soil disturbance, which may lead to deformation of existing tunnel structures and pose potential risks to structural safety. To investigate the deformation characteristics and their evolution of existing tunnels under such conditions, a case study of a double-line shield tunnel overcrossing an existing tunnel at close proximity was conducted. A three-dimensional finite element model of the shield tunneling process was established using ABAQUS to analyze the deformation response of the existing tunnel during the overcrossing process, and to investigate the influence mechanism of reinforcement measures on tunnel deformation. The results indicate that during the overcrossing construction, the existing tunnel predominantly undergoes vertical uplift deformation accompanied by slight torsion, with an influence range of approximately 3.5 D (D denotes the tunnel diameter). The uplift deformation exhibits a pronounced lag effect. In double-line construction, excavation of the trailing tunnel induces a significant secondary disturbance to the existing tunnel, resulting in an increase in the uplift magnitude and influence range, as well as a shift in the location of maximum uplift. The application of MJS method piles in the overlapping zone of the new tunnel effectively suppresses the final uplift deformation of the existing tunnel. The findings of this study can provide valuable references for the design and construction control of close-proximity overcrossing shield tunnel projects in soft soil conditions.