Wick drains, also known as pre-fabricated vertical drains, are a cost-effective solution for accelerating the consolidation of fine-grained soils to expedite construction and limit long-term settlement.
Used in combination with pre-loading, or surcharging, wick drains evacuate pore water from soft, compressible soils to induce consolidation and settlement. This allows construction to begin in as little as one to three months as opposed to much longer wait times if wick drains are not used.
The reduction of water content of the saturated layers allows the soils to better accommodate superimposed loads and minimizes future settlement.
WHAT THEY ARE:
Consist of a band-shaped plastic core wrapped in a geotextile fabric—installed by static or vibratory methods into compressible saturated silts, clays, and sludges on a triangular or rectangular grid spacing. Where stiff or dense layers are present, it may be necessary to pre-auger or pre-drill to facilitate wick drain installation.
HOW THEY WORK:
Act as a preferred drainage path to alleviate pore water pressure created by a surcharge or preloading. A drainage layer is typically installed at the working surface elevation to receive the water emanating from the wick drains.
WHY USE THEM:
Accelerate the consolidation of fine-grained soils to expedite construction and limit long term settlement—typically used in combination with a preloading or surcharge program.
Wick drains are installed within a steel mandrel that is pushed into the ground to the required depth. An anchor plate is used to prevent soil from entering the mandrel and to secure the drain in place as the mandrel is extracted.
Advantages of Wick Drains Include:
- Virtually no spoil is created (unless pre-augering is required)
- Simple installation process
- Fast rate of installation
- An economical method for expediting consolidation settlement
- Layers gain strength as they consolidate
- Allows for more rapid fill placement for embankments and fills constructed on compressible soils
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