软土深基坑内超前疏干降水对地下墙受力变形的影响

Influence of Advanced Dredging Precipitation on Deformation of Underground Wall in Soft Soil Deep Foundation Pit

以上海北横通道某超深基坑工程为例,采用数值模拟与现场实测相结合,对比分析基坑内超前疏干降水与分步降水对超深基坑地下连续墙受力变形特性的影响。结果表明:软土深基坑内一次性超前疏干降水产生大幅降水卸荷作用,使地下连续墙净荷载产生复杂变化并伴随较大的先期变形,导致基坑变形增大为分步降水的1.3倍;此外,地下连续墙最大变形的位置受超前降水深度的控制,而非位于常规的开挖面位置。建议在超深基坑的施工中,应充分考虑基坑内超前疏干降水卸荷产生的不利影响,尽量采用基坑内分步按需疏干降水方案。

Taking a ultra-deep foundation pit project in the North Cross Passage of Shanghai as an example,a combination of numerical simulation and on-site measurement is used to compare&analyze the influence of advanced dewatering and step-by-step dewatering in the foundation pit on the stress&deformation characteristics of the underground continuous wall in the super deep foundation pit.The results show that the one-time advanced dewatering in soft soil deep foundation pits produces a significant precipitation and unloading effect,causing complex changes in the net load of the underground continuous wall and accompanied by significant initial deformation,resulting in an increase in the deformation of the foundation pit to 1.3 times that of step-by-step dewatering.In addition,the maximum deformation position of the underground continuous wall is controlled by the advanced precipitation depth,rather than being located at the conventional excavation surface position.It is recommended that in the construction of ultra-deep foundation pits,full consideration should be given to the adverse effects of advanced dewatering and unloading within the foundation pit,and a step-by-step dewatering and unloading plan should be adopted as much as possible.