Enhancing Ground Water Flow through a Contiguous Pile Wall

A contiguous pile wall (CPW) constructed to retain soil typically has 100mm gaps between the piles. Should the excavation on one side of the CPW be below the water table, an open area of 10-20% offers very little resistance to groundwater flowing through the gaps. Finite element analysis demonstrates that around 96% of the groundwater flow would still pass through a 10% open area. Therefore, the exit velocity of the groundwater into the excavation can increase by a factor of 5-10 depending on pile diameter. The increased exit velocity through the gaps in the piles raises the likelihood of ground loss. To reduce ground loss, lateral drains can be driven between the contiguous piles to enhance the groundwater flow from distance behind the wall. These lateral drains reduce pore pressure behind the soil face and have the added benefit of filtering the groundwater. The resulting clear silt free water is easier to manage/discharge. This paper presents examples of system installations, supported by numerical analysis to demonstrate enhanced groundwater flow and reduced pore-water pressure behind the CPW.