滨海软土地层浅埋超大直径盾构隧道开挖面破坏机理及加固范围研究

为了确定软土地层中隧道加固的合理范围,保证盾构隧道在软土地层施工的安全性,以珠海横琴杧洲隧道工程为背景,开展了软土地层浅埋超大直径盾构隧道开挖面破坏机理及合理加固范围的研究。基于三维有限元分析,研究了加固范围对开挖面主、被动破坏形式及地表变形的影响。结果表明:随着加固土层厚度t的增加,地层受开挖扰动的区域逐渐缩小,地层显著位移区域由地表收缩至开挖面前方土体,破坏形式由整体破坏转为局部破坏,t=0.20D(D为隧道直径)相比t=0时地表沉降(隆起量)减少70%～80%,地表最大变形点沿纵向的位置基本一致,均在开挖面前方约0.5D处; 随着t的增加,开挖面支护压力可调节范围增加,t=0.20D时相比t=0时可调节范围增加了32.5%,这使得实际施工过程更有利于维持开挖面的稳定性; 结合经济及加固效果两方面考虑,实际工程进行地层加固时取加固土层厚度t=0.20D为较合理的方案。

Study on Failure Mechanism of Excavation Face and Reinforcement Range of Shallow-buried Super Large Diameter Shield Tunnel in Coastal Soft Soil Stratum

In order to determine the reasonable range of ground reinforcement and ensure safe construction of shield tunnel in the soft soil stratum, based on Hengqin Mangzhou tunnel project in Zhuhai, the excavation failure mechanism and reasonable reinforcement range for the shallow-buried super large diameter shield tunnel in the soft soil stratum were investigated. The influence of reinforcement range on the active and passive failure forms of the excavation surface and the deformation at the ground surface were studied using the three-dimensional finite element analysis. The results show that as the reinforcement range t increases, the range disturbed by the excavation gradually shrinks, the significant displacement area of the stratum shrinks from the surface to the soil in front of the excavation face, and the failure evolves from the overall-damage mode to the local-damage mode. Compared with that in the case of t=0, the settlement and heaving at the ground surface in the case of t=0.20D(D is tunnel diameter)is reduced by 70%-80%, and the position of the maximum deformation point along the longitudinal direction is basically the same, which is about 0.5D in front of the excavation face. With the increase of t, the adjustable range of excavation face support pressure increases. Compared with t=0,when t=0.20D, the adjustable range is increased by 32.5%, which is conducive to maintaining the stability of the excavation surface during construction. Considering the economy and reinforcement effect, it is reasonable to take the reinforcement thickness of about 0.20D for stratum reinforcement in practical engineering.