邻近基坑预降水影响下既有隧道受力变形分析

Force and Deformation of Shield Tunnel under the Influence of Pre-Dewatering in Adjacent Foundation Pit

为探讨基坑降水引起的既有隧道受力变形特性,依托实际工程建立三维数值模型,以隧道的最大竖向位移为评价指标,使用正交表筛选最优组合和主要影响因素,而后对主要影响因素进行单变量分析,研究隧道受力变形规律。研究表明:通过极差分析和方差分析发现,连续墙插入深度是影响坑外隧道最大竖向位移的主要因素,故邻近既有隧道的新建基坑工程有降水需求时,可先选取该因素进行隧道变形控制;随着连续墙插入深度的增加,隧道弯矩和变形均会随之减少,当连续墙插入深度到达透水性较差的土层后隧道变形显著减小,此时隧道变形能得到有效控制,而继续增加插入深度对于控制隧道变形意义不大;降水使坑外邻近隧道产生朝向坑内斜向下的“横鸭蛋”沉降变形,施工过程中应重点关注隧道拱顶和邻近基坑侧拱腰的变形情况。

To explore the stress and deformation characteristics of an existing tunnel caused by foundation pit dewatering,a three-dimensional numerical model was established based on an actual project.Taking the maximum vertical displacement of the tunnel as the evaluation index,an orthogonal table is used to screen the optimal combination and the main influencing factors.Then,the main influencing factors are analyzed via univariate analysis to study the stress and deformation law of the tunnel.The results of the range and variance analyses showed that the insertion depth of the diaphragm wall was the main factor affecting the maximum vertical displacement of the tunnel outside the pit.Therefore,when a new foundation pit project adjacent to an existing tunnel has a dewatering demand,this factor can be selected first to control tunnel deformation.As the insertion depth of the diaphragm wall increases,the bending moment and deformation of the tunnel decrease.After the insertion depth of the diaphragm wall reaches a soil layer with poor water permeability,the tunnel deformation decreases significantly.At this time,the deformation of the tunnel can be effectively controlled;however,controlling the deformation of the tunnel by increasing the insertion depth is of little significance.The dewatering causes the adjacent tunnel outside the pit to produce“horizontal duck egg”settlement deformation toward the pit,obliquely downward,and the deformation of the tunnel vault and the side arch waist of the adjacent foundation pit should be emphasized during the construction process.