Massive Concrete Pontoons To Support World's Longest Floating Bridge

A joint-venture team began reconstruction work this month of the longest floating bridge in the world, while two of its members also near completion on a key related facility to build massive pontoons.

Omaha-based Kiewit Corp., General Construction Co. of Federal Way, Wash., and Manson Construction, Seattle, began work on Sept. 2 on its $586.5-million contract to rebuild Washington’s state Route 520 floating bridge over Lake Washington—the longest in the world at 1.44 miles. The bid for a new, six-lane, 115-ft-wide floating bridge came in $163.5 million under WSDOT’s anticipated mark this summer, says Mike Cotten, the agency’s construction director.

Kiewit and General are already working—under a separate $367-million contract awarded in February 2010—to build a 55-acre pontoon casting facility in Aberdeen. The facility, slated for completion in December, will feature a concrete batch plant, on-site water treatment and a 4-acre casting basin, where the project’s 33 main pontoons will be built.

Crews have placed some 11,200 cu yd of concrete for the pontoon casting-basin floor, completed excavation of approximately 260,000 cu yd of material and driven most of the 874 piles needed for the basin’s foundation, crane beams and bulkhead wall, according to WSDOT.

Twenty-one concrete pontoons with airtight, ballast-filled cells will serve as the foundation for the bridge. They will each be 360 ft long, 75 ft wide and 28 ft deep. Rounding out the order, 10 supplemental flanker pontoons and two heavier “cross” pontoons support the transitional spans at either end of the bridge.

http://enr.construction.com/infrastructure/transportation/2011/0919-floatingbridgereplacementworkunderwaynearseattle.asp

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