盾构施工渗流场有限元模拟及其对临近土层的影响分析

Finite element simulation of seepage field and analysis of soil deformation around tunnel due to shield tunneling

根据渗流场和温度场控制方程及边界条件的相似性,将有限元软件ANSYS的温度场分析功能应用于盾构施工渗流场的研究,分析了盾构施工渗流场的特点,并利用ANSYS软件自带的APDL参数化语言开发渗流力计算模块.首先在渗流场内计算渗透力,然后将其作为应力边界条件施加于各节点进行应力和变形分析,以获取考虑渗流的隧道周边土体的应力和变形.研究结果表明,渗透力的存在是导致水下隧道开挖面失稳的重要因素,水向开挖面流动使得开挖面前方土体下沉,并使其具有向土压仓滑动的趋势.渗流引起的最大剪应力出现在开挖面前方拱顶和拱底处,最大剪应力值基本上与土仓内外水头差成正比;渗流的存在使得施工扰动的程度和范围加大,相比无地下水情况,掘进时必须增加掌子面推力来平衡渗透力,以控制地表变形,维持开挖面的稳定.

Based on the similarity of the governing equations and boundary conditions between the temperature field and seepage flow field,the numerical simulation of the seepage flow field in shield tunneling was carried out.The characteristics of seepage field around shield tunnel were analyzed by the FEM（finite element method） software ANSYS function of temperature field analysis,and a seepage program was developed using program redevelopment language APDL（ANSYS parametric design language）of ANSYS.The seepage force is calculated first in the flow field and then added to the stress field.Subsequently,the deformation and stress distribution around the tunnel can be achieved with the consideration of seepage flow.The calculation results show that the seepage force has a significant effect on the tunnel face stability when the groundwater table is above the tunnel crown.In this case,seepage causes the soil deformation with sliding to soil chamber in front of the working surface of the tunnel.Moreover,maximum shear stress caused by seepage is observed at arch crown and invert of the tunnel,and maximum shear stress is approximately proportional to the difference of hydraulic head inside and outside the chamber.Seepage enlarges the extent and range of construction disturbance.Compared with the case without ground water,the influence of seepage force should be taken into account in the analysis of the workface stability and ground surface deformation,and the seepage force can be balanced by increasing the supporting pressure in the chamber.