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May 27, 2016
State Route 520 pontoon construction
General contractor: Kiewit-General Joint Venture
Owner/developer: Washington State Department of Transportation
Primary designer: KPFF Consulting Engineers
Kiewit-General Joint Venture’s state Route 520 pontoon design-build project relied on innovation and team collaboration to overcome challenges and complete a difficult, fast-track project ahead of schedule.
The project involved two distinct elements: designing and constructing a 55-acre pontoon-casting facility, and constructing 33 concrete bridge pontoons designed by the Washington State Department of Transportation to support the new SR 520 floating bridge across Lake Washington. The pontoons weigh up to 11,000 tons and are up to 360 feet long, 75 feet wide and 28 feet tall.
The pontoon-casting facility, constructed at a former log yard in Grays Harbor County, included a concrete batch plant, on-site water treatment and a 4-acre pontoon-casting basin. At the completion of each cycle, the pontoons were launched out of the casting basin and towed to temporary moorage, inspected, and towed to Lake Washington for installation.