A Vacuum wellpoint system is a complete dewatering system that consists of a wellpoint pump, a vacuum header, and a number of wellpoint connected to the vacuum header. The wellpoint pump is used to apply a vacuum to a series of wellpoint via a vacuum header. The wellpoint is a two to three-inch diameter self-contained vacuum well composed of casing, screen drawdown tube and check valve installed into a predrilled hole or jetted into the ground, usually no deeper than 25 to 30 feet. The vacuum header pipe provides groundwater removal by suction left of a series of wellpoints or dewatering Wells. Finally, dewatering wells are assisted by vacuum in order to improve their ability to remove entrained water, particularly for soils with fine grains.
Vacuum wellpoints are well suited for a wide range of soil permeability’s (fine to coarse grained soils). They are generally 15 to 25 feet deep and constrained by the limits of the vacuum to pull water out of the ground. They typically have a 3-foot length of slotted well screen at the bottom and are most often spaced from 2 to 10 feet on center, depending on the soils type.
The common HDPE header pipe, once installed, creates a vacuum that draws water from a series of individual wellpoints. This water is then transported through the riser and swing joint hose assemblies to the pump and ultimately to the discharge point. To prevent well screen clogging and reduce entrance loss, filter sands are used to fill the drilled holes around the PVC wellpoints. These sands also facilitate vertical drainage through silt and clay layers.
Vacuum wellpoints are an ideal choice for dewatering when excavations conclude impermeable soils, where groundwater movement is limited. In cases where the excavation depth exceeds the limits of vacuum lift (typically 15 to 20 feet), wellpoints can be strategically installed through the shoring walls, often with a battering technique, to maximize the efficiency of the vacuum system. These installations resemble tie-back installations through shoring walls. In such scenarios, the common HDPE header pipe and vacuum pumps can be suspended on the shoring wall’s surface, optimizing the excavation area.
Vacuum wellpoints can be integrated into any shoring system and are typically installed using the same equipment, which helps in cost reduction.