针对超大型基坑降水设计中采用的部分悬挂、部分落底式止水帷幕,利用数值模拟对比分析了不同落底率Rc下深基坑降水的地下水控制效果及其对邻近地铁隧道的影响。研究结果表明:相同落底率Rc下,随着悬挂止水帷幕的插入比L/M的增大,降水对周边环境的影响逐渐降低,存在明显转折点,可根据承压水位降深变化曲线选择相对经济合理的插入比范围;止水帷幕中的悬挂帷幕部分插入比L/M对基坑单位面积抽水量q的影响较小,而落底率Rc对q的影响更为显著,且落底率Rc在0~80%范围内时,Rc与q具有较好的线性相关关系。通过计算结果与现场监测数据对比分析,落底式帷幕一侧的坑内外水头差要明显大于悬挂式帷幕一侧的坑内外水头差,故部分落底式止水帷幕也可有效阻隔环境敏感一侧的地下水渗流;根据不同落底率Rc下地铁隧道的变形计算结果,可以得到满足变形要求的最低落底率Rc。对类似基坑工程的降水及止水帷幕设计,可根据周边环境的敏感程度灵活使用部分落底式止水帷幕。
Abstract
Numerical simulation is employed to analyze the groundwater control effect of super-large deep foundation pit dewatering using partially suspended impervious curtains and partially closed impervious curtains. The influence of different rates of closed impervious curtain (Rc) on the dewatering process and its impact on adjacent subway tunnels are investigated. The findings reveal a gradual decrease in the influence of dewatering on the surroundings at a given Rc as the insertion ratio (L/M) of the suspended impervious curtain increases, with a distinct turning point. Therefore, an economical and reasonable insertion ratio can be determined based on the descending depth variations of the pressure water head. L/M exhibits minimal influence on the water pumping capacity (q) per unit area. In contrast, Rc significantly affects q, showing a good linear correlation when Rc ranges from 0% to 80%. A comparison between calculated results and field monitoring data indicates a notable difference in water head between the inside and outside of a foundation pit, favoring the closed impervious curtain side over the suspended impervious curtain side. Consequently, partially closed impervious curtains prove effective in controlling groundwater seepage in sensitive surrounding areas. Furthermore, deformation calculation results of subway tunnels under different values of Rc could help determine the minimum Rc required to meet deformation requirements. Therefore, partially closed impervious curtains can be employed flexibly in the impervious curtain design for large foundation pits depending on the sensitivity of the surroundings.
关键词
部分落底式止水帷幕 /
落底率 /
基坑降水 /
地下水渗流
Key words
partially-closed impervious curtain /
ratio of closed impervious curtain /
foundation pit dewatering /
seepage of groundwater
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基金
国家自然科学基金资助项目(11802215)
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