流固耦合作用下基坑开挖及降水对下卧既有地铁隧道的影响研究

为研究基坑开挖及降水对下卧既有地铁隧道变形的影响,基于比奥固结理论,结合修正摩尔库伦本构关系,建立考虑流固耦合的三维有限元分析模型,探讨基坑降水深度、降水速度、土体渗流特性、基坑开挖工艺等对下卧既有地铁隧道及其围护结构的影响,并与现场监测结果进行对比验证。研究结果表明:基坑降水深度对隧道结构变形有着较大影响,适宜的降水深度有利于抑制地铁隧道的隆起;在分块开挖效应下,隧道最终呈"M"形曲线隆起,竖向位移最大处位于隧道中部的两侧位置;土体渗流存在空间差异性;基坑降水速度会对隧道围护结构的内力产生重要影响,随着降水速度的增大,围护结构的内力会继续增长;隧道衬砌结构变形呈"水平向压缩、竖向拉伸"的竖椭圆状发展,隧道靠近基坑两侧的腰部变形较大;考虑基坑降水的流固耦合分析结果更接近现场实测结果。

Effect of Foundation Pit Excavation and Dewatering on Existing Subway Tunnels Subject to Fluid-Solid Coupling of Soils

In order to research the influence of foundation pit excavation and dewatering on the deformation of underground existing subway tunnel, this paper, based on the Biot’s consolidation theory and modified Mol-Coulomb constitutive relation, establishes three-dimensional finite element analysis model for the existing subway tunnel under the condition of the foundation pit excavation and dewatering, and discusses the effects of the depth of foundation pit dewatering, dewatering rate, studies the seepage characteristics of the excavation technology of geotechnical foundation pit for existing subway tunnel and the palisade structure, and compares them with the measured results. The results show that the dewatering depth of foundation pit has great influence on the deformation of tunnel;under the effect of block excavation, the tunnel finally shows "M" curve uplift, and the maximum deformation of subway tunnel is located on both sides of the middle part of the tunnel;the velocity of foundation pit dewatering has an important influence on the internal force of tunnel envelope;the deformation of lining structure shows a vertical elliptic development of "horizontal compression and vertical stretching";the results of fluid-solid coupling analysis considering foundation pit and dewatering are closer to the measured results.