Prefabricated Vertical Drains, also known as Wick Drains, are used to accelerate the consolidation of compressible soils.
The consolidation of compressible soils involves the removal of pore water from the soil. This is traditionally done by applying a surcharge of preload to the construction area to “squeeze” the water out. Unfortunately, compressible soils are also often low-permeability soils (peats, silts, clays) with long drainage paths, and as such the pore water is not easily squeezed out resulting in very slow rates of consolidation.
Therefore, to accelerate the dewatering process, it is necessary to install PVDs into the soil to provide a conduit for the pore water to flow easily.
PVDs consist of a specially designed synthetic core extruded into a unique configuration to transmit maximum water flow on both sides of the core. The core is fully wrapped in a durable non-woven geotextile filter that is ultrasonically welded at the edges to maintain effective filtration. The PVD is designed to allow free flow of water in all directions and to ensure the integrity of the drainage system when subjected to tensile, compressive and buckling forces as the compressible soil deforms and consolidates.
PVDs are installed into the ground using a hollow mandrel that houses and protects the PVD material. The mandrel is hydraulically driven into the compressible soil to the design depth so that the wick drain anchors in the incompressible materials underlying the compressible soils. The mandrel is then withdrawn leaving the PVD in place.
The pattern and depth of the PVDs are a function of the consolidation properties of the soil and the required time for consolidation to occur. Wick Drains are typically installed at 1.0m to 3.0m centres, with depths ranging from 5m to 45m.
Once the PVDs have been installed, a surcharge load is applied over the area to be consolidated. This surcharge layer, combined with the PVDs accelerates the consolidation of the compressible soils so that it occurs over a period of months as opposed to a period of years.
Manufactured for SoilWicks by CeTeau and supplied by Australian-based Global Synthetics our PVD material has been proven in a wide range of environments, depth and subsoil conditions.