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GLF Raises Wilmington Bypass Over Protected Wetlands

Tue December 23, 2003 - Southeast Edition
Gwenyth Laird Pernie



Travelers passing through Wilmington, NC, will soon have an alternative route –– the new U.S. 17 bypass.

Divided into four projects, construction of the new bypass will route traffic eastbound on I-40 and southbound on U.S. 17 around Wilmington, improving access to the State Port at Wilmington and Sunny Point Military Ocean Terminal.

“Current conditions make it necessary for traffic traveling south on U.S. 17 or east on I-40 to go through the center of Wilmington, leading to traffic delays and congestion,” explained O.T. Anderson, North Carolina Department of Transportation (NCDOT) resident engineer. “The new U.S. 17 construction will bypass Wilmington.”

The bypass between U.S. 421 and I-40 A, located on the north side of the city, is one of the four projects. It will be 2.7 mi. (4.3 km) of four-lane divided highway, including a bridge spanning the Northeast Cape Fear River and adjoining wetlands. This portion of the new bypass is particularly important because it will alleviate congestion in downtown Wilmington by separating through-traffic from local traffic and also providing another bridge over the river. This should play out to be especially important in the summertime when average daily traffic numbers along the route can be 15 percent above normal numbers.

The $85.5 million contract, which began in January 2001, was awarded to GLF Construction Corporation and was fully funded by the state of North Carolina.

Designers combined two different construction methods on the 1.4-mi. (2.3 km) bridge. First, the approach uses precast girders with cast-in-place concrete decks. Second, the main span incorporates two cast-in-place cantilevered box girder elements. The 479-ft. (146 m) main span will provide a vertical clearance of 82 ft. (25 m) over the western navigation channel of the river. Both bridge structures will be founded upon drilled shafts, ranging from 48 to 96 in. (122 to 244 cm) in diameter, installed to an average 75 ft. (23 m) depth of elevation. Clearwater, FL-based Trevi Icos South installed the shafts.

“The new bridge will be environmentally sensitive,” Anderson said. “The bridge design limited the number of foundations, or substructures, supporting the bridge, which will reduce the disruption to the natural flow of water in the river and wetlands.”

Sub Triangle Grading and Paving, Burlington, NC, was hired to bring in 1.2 million cu. yds. (881,000 cu m) of fill dirt. GLF was responsible for laying the asphalt.

Crews laid more than 15,000 tons (13,600 t) of service course asphalt, 14,300 tons (13,000 t) of intermediate asphalt and 33,000 tons (30,000 t) of roadway base on the project.

To minimize any negative impact to the environment, NCDOT mandated that all construction activities be staged from a temporary work platform raised over the wetlands.

“In the past, this type of work would have been done on a dirt fill,” said Michael Miles, project manager. “This was obviously not good for the environment.”

GLF constructed a 27.9 ft. (8.5 m) wide work platform, reducing the size of the temporary work platform by more than 50 percent using a railway and higher-capacity cranes.

“While use of the platforms is best for the environment, they have created a real challenge to the job site,” said Miles. “Everything has to be taken out on the trains, so scheduling is crucial to ensuring construction moves along as planned.”

Seven 220-ton (199 t) 9310 American cranes perform all the substructure and superstructure concrete work. GLF leased the cranes from M.D. Moody.

To lower equipment costs, GLF contracted DEAL, based in Italy, to develop a special girder placement truss, which enabled GLF to set girders from one side of the bridge only.

While completion of the U.S. 421 and I-40 A bypass is anticipated for December 2004, all four phases of the Wilmington Bypass won’t be finished until June 2006.