中文摘要：

超高层建筑的桩基础通常会打入到深度较大的承压含水砂土层中；在承压含水层的上方通常会进行超深基坑的开挖构建超高层建筑的地下室。为了保持超深基坑的基底稳定，需要在承压含水层中进行降水施工。由于深基坑存在大量的桩基础，基桩的存在会影响降水时地下水的渗流路径，继而影响土体的渗透性状。应用室内试验研究基桩对含水层渗流阻挡作用的机制。试验采用PVC管模拟基桩，将颗粒较均匀的砂土作为试验土体，通过室内渗流试验来研究基桩对地下水渗流的影响。试验结果表明，基桩对于地下水渗流有明显的阻挡效应：基桩的数量以及布置形式会对渗透效应产生较大的影响。考虑砂土体积置换率的有效介质理论可以用来分析矩形布置的基桩对渗透系数的影响，但对梅花形布置的基桩应用有效介质理论计算所得的渗透系数会有将近20％的偏差；其原因是梅花形布置的基桩，会使渗流路径增加。基于对渗流路径的分析，提出了考虑有梅花形布置的基桩存在时等效渗透系数计算的修正方法。

英文摘要：

The pile foundation of super-highrise buildings is generally installed into the deep sandy strata of confined aquifer. Deepexcavation is generally conducted for the basement over the aquifer. In order to keep the stability of pit bottom, dewatering isrequired to conduct in the confined aquifer. Since there are a large number of piles in the dewatering pit in aquifer, the existing pileswill affect the path of groundwater seepage. In order to reveal the mechanism of blocking effect of piles on groundwater seepage,laboratory tests are conducted. Polyvinylchloride （PVC） pipes and sand are employed to simulate pile and test soil, respectively. Testresults show that piles show an obvious blocking effect on groundwater seepage; meanwhile the quantity and the layout form of pileswill affect the blocking effect of piles. The effective media theory can be used to calculate the coefficient of permeability byconsidering the piles with rectangular layout. However, there is a difference of 20% with the quincunx layout, owing to theprolonged flow path. The formula to calculate the modified equivalent hydraulic conductivity is established based on the analysis ofthe flow path.