The pile foundation of super-highrise buildings is generally installed into the deep sandy strata of confined aquifer. Deep excavation is generally conducted for the basement over the aquifer. In order to keep the stability of pit bottom

dewatering is required to conduct in the confined aquifer. Since there are a large number of piles in the dewatering pit in aquifer

the existing piles will 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. Test results show that piles show an obvious blocking effect on groundwater seepage; meanwhile the quantity and the layout form of piles will affect the blocking effect of piles. The effective media theory can be used to calculate the coefficient of permeability by considering the piles with rectangular layout. However

there is a difference of 20% with the quincunx layout

owing to the prolonged flow path. The formula to calculate the modified equivalent hydraulic conductivity is established based on the analysis of the flow path.