软土地层浅埋盾构施工的精细化数值模拟

为研究盾构隧道浅埋施工过程中多种因素对地层的扰动影响,基于有限差分平台建立模拟盾构动态开挖的精细化数值模型,考虑刀盘摩擦力、开挖面支护力、盾尾注浆压力和盾壳摩擦力对周围土层的综合作用,并将盾尾注浆时压力消散和浆液凝固的对应关系分阶段、分区域赋值,实现了对施工过程的精细模拟。利用厦门地铁1.0D埋深盾构隧道工程现场监测结果对数值模型进行验证,计算并总结了浅埋开挖引起软土地层的扰动变形规律,进而研究了各施工因素对扰动效果的影响。结果表明：软土地层盾构施工过程中,以刀盘顶推作用为主的机械开挖使前方土体径向扩张,开挖空间上方土体隆起,两侧土体外移；盾尾注浆阶段,在开挖空间两侧各1.0D范围内形成沉降槽,且随注浆压力消散逐步加深,隧道侧面土体水平位移在注浆层凝固期间,出现近场回弹和远场扩张现象；刀盘驶过目标断面3.0D后地层变形趋于稳定。刀盘摩擦力和盾壳摩擦力的增大会进一步加剧地层扰动变形,而开挖面支护力及盾尾注浆压力增大时,地表沉降有所减缓,侧面水平位移显著增加。因此,施工参数的选取应考虑对隧道周边地层扰动程度的均衡。

Refined Numerical Simulation of Shallow Shield Construction in Soft Soil Stratum

To study the influence of various factors on the stratum disturbance during the shallow construction of the shield tunnel, an elaborate numerical model for simulating the shield dynamic excavation was established based on the finite difference platform. The model includes the combined effects of four factors on surrounding soil: cutter head friction, excavation supporting force, grouting pressure, and shield friction. In addition, the corresponding relationship between the pressure dissipation and slurry solidification during shield tail grouting is assigned in stages and regions to achieve an elaborate simulation of the construction process. The numerical model was verified by the field monitoring results of the shield tunnel project of 1.0D buried depth in Xiamen Metro. The disturbed deformation law of soft soil stratum caused by shallow excavation was calculated and summarized, and then the influence of construction factors on the disturbance effect was studied. The results show that during the shield construction in soft soil stratum, the mechanical excavation with the main action of cutter head pushing causes the soil in front to expand radially, resulting in uplift of the stratum above the excavation space and outward displacement of the soil on both sides. In the grouting process, a settlement groove is formed within 1.0D on both sides of the excavation space, which gradually deepens as the grouting pressure dissipates, and the soil lateral displacements on two sides of the tunnel occur near-field rebound and far-field expansion during the solidification of the grouting layer. After the cutter head exceeds target section 3.0D, the stratum deformation tends to be stable. The increase of the cutter head friction and shield friction will further aggravate the stratum disturbance deformation, and with the increase of the excavation supporting force and grouting pressure, the surface settlement has slowed down and the stratum lateral displacement has increased significantly. Therefore, the selection of construction parameter values should consider the equilibrium of stratum disturbance.