By By MIKE VOSS
Contributing Editor
The N.C. Department of Transportation and Flatiron/United have received a Federal Highway Administration Award for Environmental Excellence in Ecosystems, Habitat and Wildlife for the U.S. Highway 17 bypass in Beaufort County.
The project is a joint venture between Flatiron Constructors and United Contractors.
“Flatiron/United is grateful our Washington bypass project has been selected for a Federal Highway Administration Award for Environmental Excellence in Ecosystems, Habitat and Wildlife. We appreciated being recognized for all the efforts and unique bridge building engineering ingenuity that went into this project,” said Mark Mallett, project supervisor for Flatiron/United, in an e-mail to the Washington Daily News.
Mallett confirmed that an innovative method, called top-down construction, is being used to build the bridges that are part of the project.
“Yes. The top-down, launching-gantry construction process was developed specifically for this project to minimize the amount of onsite activity at ground level and minimize the overall ‘construction footprint’ required to build the bridge,” Mallett said. “The custom-built launching gantry was outfitted with a patented pile-driving system able to drive piles by cantilevering from the previous span of bridge. Our methods also minimized the amount of ‘in-water work’ for the portions of bridge crossing the Tar River.”
DOT awarded a $192 million design-build contract to a team led by Flatiron of Longmont, Colo., and United Contractors of Chester, S.C. to build the 6.8-mile, four-lane bypass around Washington. Under design-build contracts, teams of designers and contractors simultaneously conduct design and construction of a project to expedite its completion.
“Our top-down, pile-driving gantry system worked very well and has already completed installing all 128 spans of bridge components. All efforts are being made to complete the entire project ahead of the November 2010 contract completion date,” Mallett said.
Two 750-ton gantries were built to move the concrete bridge components. A gantry was built in each of the two materials yards on either side of the Tar River.
The large, yellow structures seen from U.S. 17 north of Chocowinity and from U.S. Highway 264 in western Washington are the yard gantries. Beneath each are two 585-foot trusses, parallel to the ground, that lowered each span of the bridge into place as construction progressed out over the river. Each crane had to be transported to the site in pieces and assembled in place.
The gantries lowered each 120-foot span of the bridge into place. What made them unique was their ability to drive piles to support the bridge as construction progressed. The spans were placed on 30-inch-square concrete pilings.
The patented gantries were developed by an international team made up of firms from the United States, Italy and Canada.
Construction on the $192 million project began in March 2007. The bypass, a 6.8-mile project stretching from Price Road near Chocowinity to Springs Road at Washington, is the first highway project in Beaufort County to be constructed using the design-build method. According to DOT, that method reduces a project’s completion time by contracting a single firm to simultaneously design and construct the project.
The Environmental Excellence awards is a biennial program developed by the FHWA to honor those partners, projects and processes that excel in meeting growing transportation needs while protecting and enhancing the environment.
For more information on the U.S. 17 Washington bypass project, including photos of the gantry system, visit http://www.ncdot.org/projects/us17bypass/.