TGEP 53: Wick Drains for Ground Improvement in Geotechnical Engineering The Geotechnical Engineering Podcast

In this episode, we talk to Martin (Marty) Taube, P.E., P.G., about wick drains, what they are, how they work, and some of the challenges associated with installing wick drains.





Here Are Some of the Questions We Ask Martin:



What are wick drains and how do they work?

How are wick drains designed and who is typically responsible for the design?

How long have they been used in the US?

What types of soils are they installed in and what types of structures are they installed for?

When shouldn’t wick drains be installed?

What ground improvement techniques would you go to for soft clays if wick drains aren’t appropriate?

What are the biggest challenges with installing wick drains?

Are there any specific safety concerns when working with wick drains?

What advice would you like to give to engineers that are specifying wick drains?



Here Are Some of the Key Points Discussed About Wick Drains for Ground Improvement in Geotechnical Engineering:





When you place fill on some types of soils, they experience issues because there is pore pressure building up in the soil. These soils are slow-draining fine-grain soils such as clay. It is known as consolidation settlement which can take years or even decades to occur. Wick drains are installed to shorten the drainage pattern pathway, speed up the consolidation process, and increase the strength of the soil. Wick drains are thin prefabricated drains that consist of a plastic core with channels in them and are encased by a geotextile fabric that acts as a filter that prevents fine soil from migrating into the drain.

Wick drain designs can be made in many ways depending on the schedule and economics of the project. It is an iterative process while looking at the different factors. Wick drains are used to speed up the settlement while other ground improvement techniques are used to mitigate settlement. They are best designed by the project’s engineer as opposed to the installer because of the many variables that must be considered.

Wick drain has been used since the late 1970s with the development of geosynthetics and replaced sand drains by the mid-1980s.

Wick drains bring the water up to the surface of the soil, or below the consolidating layer. When the water comes up to the surface, you need a way of receiving the water like a drainage blanket made from sand or rock.

Pre-drilling is a common issue when installing wick drains. The drilling is more expensive than only installing the wick drains. It is required when you have a dense or stiff layer at the surface.

Wick drains are installed in fine grain slow draining soil like clays, silts, silty clays, sludges, and fine grain dredged materials. They are used in transportation projects, storage tank projects, large port projects, and general buildings and structures.

Wick drains are used for up to 3-story buildings but cannot be used in mid or high-rise buildings.

Wick drains are typically used in soft clays. If wick drains are not appropriate, Controlled Modulus Column (CMC) rigid inclusions can be used because stone columns or aggregate piers have issues with the lack of confinement in the soft clays.

When working with wick drains, you must look at how stiff the soils are and if the mandrel will be able to penetrate them. If the soils are too stiff, then other ways of assisting the mandrel must be considered. When installing the wick drain with the mandrel, there is a rebar anchor that must be secured before extracting the mandrel. If the soils are too soft, then the wick drain will not be securely anchored and will be pulled up with the mandrel. Rupturing artesian pressure layers can cause a high velocity of up flow which can cause the wick drain to not anchor securely.

When using very long masts to insert the wick d...