基于盾构隧道冻结扩挖施工的数值模拟研究

Numerical research on construction sequence of cross and overlapping shield tunnel

为研究在盾构隧道基础上进行冻结扩挖施工的可行性,本文以郑州地铁3号线二七广场站暗挖段的盾构隧道扩挖工程为背景进行研究。该段工程埋深浅、断面大、地下水位极低,且位于富水粉细砂层,施工风险和难度极高。本文考虑冻结与不冻结降水等4种工况,采用PLAXIS软件建立车站盾构隧道扩挖模型,对盾构隧道扩挖施工过程进行数值模拟,并通过分析地表沉降、隧道周边变形及初支内力情况,预评价盾构隧道扩挖施工风险。研究结果表明:冻结扩挖施工条件下,地表沉降满足要求,其他工况下,不仅地表沉降量值远远高于工况,沉降影响范围也显著增大,表明长期降水对地表影响较大;长期降水对隧道初支位移影响很大;冻结扩挖施工条件下,轴力、剪力和弯矩均小于不冻结条件。根据研究结果,本文建议盾构隧道扩挖之前采用冻结法形成冻结帷幕,以将变形和受力控制在允许范围内。

In order to study the feasibility of freezing and expanding construction on the shield tunnel foundation,in this article,research is conducted relying on the shield tunnel expansion project of the Erqi Square Station of Zhengzhou Metro Line 3.The buried depth of the project is shallow,the cross-section is large,the groundwater level is extremely low,and it is located in a fine sand layer rich in water,and the construction risk and degree of difficulty are extremely high.Taking into account four working conditions,including freezing and non-freezing precipitation,the shield tunnel expansion model of the station is established using the PLAXIS software.The construction process of shield tunnel expansion is numerically simulated,and the construction risk of shield tunnel expansion is pre-evaluated by analyzing the surface settlement,surrounding deformation of the tunnel and the internal force of the initial support.The research results show that under the construction condition of freezing and expanding excavation,the maximum settlement occurs below the foundation of the office building which meets the requirements of the code.Under other working conditions,not only the surface settlement value is much higher than the working condition,but also the influence range of settlement is significantly increased,indicating that long-term precipitation has a greater impact on the surface.Under the construction condition of frozen excavation,the axial force,shear force and bending moment are all smaller than the non-freezing condition.According to the results,it is suggested to adopt the freezing method to form the freezing curtain before the shield tunneling to control the deformation and force within the allowable range.