Deepwell groundwater control systems are employed to lower groundwater levels to provide stable working conditions in excavations. As can be seen from the Roberts diagram, deepwell systems are effective in a range of soil conditions from gravel to fine sands.
A deepwell consists of a bored well with a multi-stage electric submersible borehole pump. In unstable granular soils wells are fitted with a liner and screen to provide borehole support and allow ingress of groundwater. Filter packs and grout seals may be required around the well liner. In order to achieve the required drawdown it is usually necessary to install an array of several interacting wells. The pumps are powered from a central control cabin and discharge water is normally collected in a ring main.
Because the pump is installed at depth in the well there is no physical limit on drawdown other than the aquifer response and the performance characteristics of the pump in use. In fine soils, individual well performance may be enhanced by the application of a vacuum. Well yields can also be improved by specialist development techniques such as airlift in granular soils and acid development in chalk.
The technique is particularly suited to deeper excavations or where artesian groundwater pressures threaten base stability. The system is reliable in long term operation and the relatively widely spaced wells cause a minimum of access restrictions.
More information on deepwell systems: