By Ron Bygness
The term wick drain is a misnomer because these clever devices do not actually wick away water. Wick drains, perhaps more accurately called strip or prefabricated vertical drains (PVDs), accelerate preconstruction soil consolidation.
The drains are composed of a plastic strip with drainage channels, wrapped in a nonwoven geotextile filter fabric (see photo in the box above). The geotextile filter prevents soil particles from entering the channels and clogging the drain.
The installation of the drains—often, but not always, vertically—into soft soils is performed using vibratory hammers or static methods, and the wick drain layout is typically a triangular or square pattern.
Once installed, the PVD field looks like a series of wicks.The time required for consolidation depends on the permeability of the soft strata, sand layers in the strata, the weight of the surcharge, and the spacing of the wicks.
The drains shorten the pore water drainage path, thereby permitting the soil consolidation to occur, typically in weeks instead of years.