What are Wick Drains?

Wick Drains, also known as Prefabricated Vertical Drains or PV Drains, consist of a channelized plastic core wrapped in geotextile fabric. The fabric, which acts as a filter, maintains a very high permeability while retaining the finest of soil particles. Wick Drains greatly reduce the distance water travels to reach a free drainage path; greatly decreasing the time of settlement.

How are Wick Drains installed?

Wick Drains are installed by pushing a steel mandrel (approximately 5 inches by 2 inches in section) vertically into the ground. The Wick Drain material is protected inside of the mandrel and is affixed to an anchor plate or bar at the base of the mandrel. Once a firm layer or target depth is encountered, the mandrel is retracted and the wick drain, which is held in the ground by the anchor, stays in place. Once the bottom of the mandrel reaches the ground surface, the Wick Drain material is cut and the anchor for the next drain is attached. The mandrel is part of a mast assembly which is supported and powered by a hydraulic e xcavator or crane.

What types of projects are Wick Drains typically used on?

Wick Drains are widely used for warehouses, storage tanks, buildings, roadways, embankments, airport runways, industrial facilities, port and marine facilities, and MSE walls.

What soils are suitable for Wick Drain applications?

Soils suitable for Wick Drains include clays, silts, organic layers, peat, clayey and silty sands, dredge spoils, and wastes such as mine tailings and industrial sludges. Wick Drains can be used whenever consolidation settlement is an issue.

What is Consolidation Settlement?

Consolidation occurs as water is squeezed out of fine-grained soil layers. This type of settlement can take a very long time to occur - in some cases, decades. Fine-grained soils, especially clays have very low permeability so it takes a long time to squeeze the water out of these layers. In sands, the settlement occurs nearly immediately.

What is meant by a surcharge?

Surcharging refers to placing more load on the ground than the ground will see from the proposed construction. The load is typically in the form of a large pile of soil that covers the footprint of the construction.

Are surcharges always used when Wick Drains are used?

Not always. When Wick Drains are used to expedite consolidation for soft ground underlying fills and earthen features such as berms, dikes, levees, and embankments, the primary goal is typically to allow for the feature to be constructed and put into service as quickly as possible. In particular, Wick Drains serve to accelerate construction and reduce both the time and magnitude of post-construction settlement. They may also allow for construction of higher fills and steeper slopes because of the rapid strength increase in the treated soils.

Do Wick Drains reduce settlement?

Yes and no. Wick Drains do not reduce the amount of settlement that occurs from the proposed load, but rather, it speeds up the settlement. If pre-loads are used after the Wick Drains are installed (typically in the form of a soil pile), the settlement will occur while the preload is in place. Once the settlement has occurred, the preload is removed and structure/facility can be built. Since the ground has already experienced greater loads from the pre-load, minimal if any settlement will occur from the structure/facility.

Are there any other applications for Wick Drains?

In addition to expediting settlement for fills and preloads, wick drains have been used to reduce potential down drag on piles, to increase storage capacity for future landfills and waste containment sites, and for collection and extraction of floating product and contaminated groundwater.

Are Wick Drains very expensive?

Wick Drains are a low-cost and practical ground improvement technique. With installation costs under 50¢ per linear foot for larger projects, the cost for wick drains can be less than 25¢ per square foot of improved ground. In the U.S., the technology is now widely accepted and proven to provide expedient, low-cost treatment of soft, compressible soils.