The construction of a casting facility in Aberdeens harbor is a vital component of Seattles planned bridge replacement.

Photos courtesy of Washington DOT

Crews are nearing completion of the casting basin.

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.

The 33 concrete pontoons will make up the base of the bridge from Grays Harbor in southwest Washington to Lake Washington. Another 44 supplemental concrete pontoons and 58 anchors also will be built, along with a new maintenance facility and dock on the east shore of Lake Washington.

The joint-venture bid, submitted on June 8, beat out bids from Flatiron-Skanska-Traylor and Walsh Construction Co.- PCL Construction Services-Weeks Marine. “Kiewit has and continues to learn about building pontoons, and they have a history of building floating bridges,” notes Cotten. The contracting firm was involved in building the state Route 104 Hood Canal floating bridge, while General was involved in the original 1963 construction of the state Route 520 bridge as well as the recent upgrading of the Hood Canal bridge and Interstate 90 floating bridge. The joint venture will engage engineering firms KPFF, Seattle, and BergerABAM, Morristown, N.J.

The floating-bridge links Seattle to communities to the east. Completion of the new bridge is slated for December 2014. It is part of a larger plan to improve state Route 520 from Interstate 5 East to Medina. A joint venture of Granite Construction Co. and PCL has a $306-million contract to improve 8.8 miles of Route 520 east of the floating bridge.