Bridging the Gulf
Port's land area increased by 60 acres in Gulfport

By Angelle Bergeron

One man's geotechnical wonder is often mere child's play to another. So it is with the expansion of the Mississippi State Port Authority's port at Gulfport.

By the time W.C. Fore Trucking Inc. completes construction of the perimeter dyke and 60-acre extension to the southwest tip of the existing port, the Gulfport-based contractor will have moved 2.5 million yds. of sand. WCF is using 150 to 200 trucks per day, working 7 a.m. to 5 p.m. on weekdays and a half-day on Saturday to accomplish the feat in three years.

Although the $18.6 million contract is substantial for the local contractor, project manager R.F. "Bob" Gavin described the project as "a plain old dirt job; just a lot of it. It's nothing exotic like a 50-story building or a condo or casino. It's just moving around a bunch of dirt."

But from an engineering point of view, the soft, silty soil conditions and compressible clays that exist on the floor of the Gulf of Mexico presented an unprecedented obstacle.

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"Thompson (Engineering Inc.) did some high-tech engineering for this project to come up with the design to suit these conditions," said Peter Hopkins, project manager for URS Corp., the worldwide engineering firm that manages the project. When the Corps of Engineers granted the MSPA approval in 1998 for an expansion, designers assumed soil conditions would be similar to those found when WCF did a 29-acre expansion there in 1993.

"The previous expansion had one bad area that turned out to be fairly common for this new 60-acre area," Hopkins said. "When soil borings were taken and we realized what the conditions were, we looked at many alternative methods of construction." Engineers considered bulkheads, caissons, sunken barges, rock and even building a conventional wharf structure. The wharf was quickly ruled out because of the cost.

Thompson eventually decided to use alternating layers of geogrid fabric and sand, dotted throughout with wick drains to help soil compression.

Two layers of geogrid were placed before any fill was added. Next, the contractor added fill in 3-ft. lifts, allowing for time in between while engineers monitored the subsurface soils for sufficient consolidation levels.

"We've got three layers of geo grid and basically we would put down the fabric, a layer of sand, wick through, then more sand," Gavin said. "We used clean, coarse grain sand up to a plus-two elevation (with water level being zero), then a lesser grade once we got above the water."

The contractor began by constructing the north levee while hauling fill for the interior acres. The constant flow of trucks provides both accurate placement of fill and compaction, Gavin said. The port built a separate gate entrance to accommodate the steady stream of trucks, and WCF had to beef up its truck fleet.

"We had some difficulty having enough trucks on a day-to-day basis to haul all of the material and stay within the schedule," Gavin said.

To construct the levee, the contractor is using a barge that holds 320-ft.-wide rolls of geo grid and a mandrill fitted with a 4-in. feeder pipe to install the wick drain.

"We've calculated what the toe-to-toe is on the levee," Gavin said. "The levee is 10 ft. wide at the top and with the slope we've got as much as 300 ft. at the bottom." The barge gradually moves further into the Gulf, unrolling the fabric. As trucks and dozers follow with mountains of fill, workers on the barge join pieces of the fabric to make a continuous levee.

A mandrill moving back and forth across the width of the fabric strategically places the 55- to 65-ft. lengths of wick drain.

The fabric, a uniaxial grid supplied by Atlanta-based Mirafi Construction Materials, has been around for several years and is commonly used in a variety of applications, said Dusty McClure, southeast region manager.

"Uniaxial grid denotes the method of reinforcing, which is in one direction," and the engineers chose the product for this application, McClure said. The funny thing about geosynthetics is that, if all goes well, no one will ever see them, he added.

"It's good people don't see it because that means it's working."

The wick drain is basically a plastic cord wrapped with geotextile fabric, said Mike Obermeyer with supplier American Wick Drain Corporation. The plastic cord produces passage for water flow and the geotextile fabric provides a filter. Basically, it takes the water out of the soil, consolidates it and makes it stronger.

The use of wick drains has enormously accelerated compression and the construction schedule.

"We went in and evaluated putting in wick drains at different spacings to get it down to 65 to 70 days of settlement time before putting on additional materials," said Dwayne Smith, chief design engineer with Thompson. "Without drains, that process would take years."

Thompson is a familiar name in the oil and gas industry and the firm has successfully designed a number of structures in and along the edge of the Gulf. However, this project required some creative design and a great deal of analysis, Smith said.

"We've done several sites with soft soils, but this one was slightly different," he added. "We have not done a job like this where we were doing land creation in the Gulf. We did the 30-acre expansion at the same site in the late 80s, but the soils were twice as good as these."

To verify the design, Smith consulted with a professor at the Massachusetts Institute of Technology in Boston.

"He mentioned that this site was one of the three worst he has ever run across," Smith said.

In April 2003 W. C. Fore was awarded the contract for construction of a dyke around the perimeter of a 60-acre expansion. It filled to grade 20 acres of that area and relocated a channel that serves a small, commercial craft harbor in the path of the expansion.

"Part of our contract was 130,000 to 150,000 yds. that were mechanically dredged to create that new channel," Gavin said. "You can't get a big hydraulic company to come in and do that kind of job unless you've got at least a million yds."

The project is part of a strategic master plan originally laid out by the MSPA in 1998 and updated in 2003, which includes a five-, 10- and 20-year vision plan, said John Webb, deputy director of engineering.

"This is a portion of the five-year plan that will allow us to enhance our container capabilities," Webb added.

The port handles an equal amount of imports and exports, primarily bananas, Webb said.

Although the object of the expansion is to develop the port's container capacity, the current project will simply create a swatch of land that may be developed by future tenants, he said.

"More than likely, we will use this space to allow existing tenants to grow, or we will lease parcels to owners and allow them to develop," Webb said.

In November the MSPA received approval from the Corps of Engineers to increase the expansion to 84 acres as well as add a 125-by-750-ft., pile-supported pier. Construction of that pier and fill of the remaining 64 acres won't be open for bid until this current project is complete.

WCF expects to finish way ahead of the 1,200 calendar-day reference schedule.

"We will finish by the first part of 2006, maybe even the last quarter of 2005," Gavin said.

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For more information about the port, go to: http://www.mscoast.org/advantages/Transportation/ports.html