围护墙后开挖对基坑变形影响的数值分析

以西江引水盾构一标盾构吊出井和阀门井深基坑工程为分析对象,考虑土体的小应变刚度特性,建立三维有限元分析模型,探讨围护墙后开挖对基坑的变形影响。通过计算结果和实测数据的对比分析,表明部分围护墙后开挖卸载,造成支撑两端产生不平衡力,使开挖一侧的墙体回弹而减小水平位移,而对侧墙体水平位移继续增大,墙后土体沉降也随之增大。墙后的局部开挖卸载还能引起支撑两端墙体最大位移向相反方向移动,产生错动趋势。而开挖卸载的同时在墙后适当增加支撑可调整墙体的位移增量,有助于减少对基坑的扰动。所获得的结论对于既有基坑墙后开挖工程的设计和施工具有重要的参考价值。

Numerical Analysis on Deformation of Foundation Pit by Excavation behind Retaining Walls

Based on a case of deep excavation of shield arrival shaft and valve well in the shield project of Xijiang River Diversion Works,a three-dimensional finite element model to analyze this typical problem is proposed. The small-strain stiffness of soil is considered to investigate the deformation characteristics of foundation pit by excavation behind the retaining wall. Analysis and measured data show that unbalanced force was generated on both ends of the strut as excavation was carried out behind a part of the retaining walls, and the displacement of the retaining wall was decreased on the excavation side, while on the opposite side the displacement increased. The settlement of the soil increased on the opposite side. Numerical results also show that the local excavation can cause the maximum displacement of retaining walls on both sides moving to the opposite direction, resulting in a dislocation trend. Installing strut while excavating can adjust the displacement of the retaining wall which helps to reduce the disturbance to the pit. The conclusions can serve as some instructions for the designs and constructions of similar projects.