Work began this week to install 3.5 million feet (662 miles) of wick drains at the port expansion site on the former Navy Base in Charleston, signaling that construction of the new, 280-acre container terminal is moving forward.
The wick drains, also known as prefabricated vertical (PV) drains, provide a channel for water to migrate vertically from sub-surface soils in order for the land to consolidate and the site to settle. This work is a necessary step before any construction may commence, and greatly reduces the destructive effects long-term settlement would have on above-ground pavement and structures.
The wick drains are pushed vertically deep into the silty clay soils. Once the wicks are in place a thick layer of soil (surcharge) is placed over the area to provide weight. The surcharge presses down on the wet soils, causing water to migrate vertically up the wick drains into the horizontal drainage layer above.
The area currently under way is the future location of Tidewater Road accessing the county marina. The area was initially prepared with placement of a layer of course sand that will provide horizontal drainage. Using heavy installation rigs, each wick drain, spaced five feet apart, is installed as much as 81 feet below the surface. Placement of the wicks and surcharge is expected to take two and a half months and the surcharge will remain on the area for another six to nine months. Then, the surcharge will be removed to the desired elevation and the road will be constructed in the prepared area.
This is one aspect of the more than $13.6 million Phase 1 – Upland Site Preparation contract the South Carolina State Ports Authority (SCSPA) awarded in December 2007 to Gulf Stream Construction Company of North Charleston. Also included under the contract is the construction of the storm water detention pond (currently under way) and construction of Tidewater Road. The entire first phase of the terminal is expected to cost approximately $550 million and will be funded by the SCSPA.
The new terminal, at build out, will boost total port capacity by about 50%. This additional port capacity is crucial to handle the more than 20 million square feet of distribution space being developed in and around the Charleston region over the next few years.