Wellpoint systems are employed primarily to lower groundwater levels around foundations to provide stable working conditions. They are particularly effective where a relatively modest drawdown is required over a wide area.
As can be seen from the Roberts diagram, wellpoint systems are effective in a wide range of soils from gravel through to silty fine sand. In favourable ground a single stage of wellpoints can be used to lower groundwater levels by up to 6m. Rapid and cost-effective installation may be achieved by jetting using high-pressure water. Jetting promotes good hydraulic connection and allows the placement of a granular filter pack that may enhance performance in stratified fine soils. Wellpoint systems are particularly suited to control of groundwater levels for shallow foundations and trench works in water-bearing granular soils.
A wellpoint system consists of a closely spaced series of small-diameter shallow wells. The wellpoints are connected to a common headermain. One high efficiency vacuum dewatering pump can operate 50 or more wellpoints. For drawdowns in excess of 6 m further stages of wellpoints are required, installed at successively lower levels as excavation proceeds.
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