01 August 2012
Construction of SR520 Bridge reached a major milestone this week, when the first six of the massive concrete pontoons were floated out of the casting basin in Aberdeen in the US state of Washington.
The pontoons will be used as the floating foundation for the new floating bridge across Lake Washington.
Crews filled the casting basin with water and towed the pontoons into Grays Harbor on the high tides on Monday night, 30 July, and yesterday morning.
The new SR 520 floating bridge requires 77 pontoons in all: 33 to be built in Aberdeen and 44 in Tacoma. So far, crews in Aberdeen have built three longitudinal pontoons, one cross pontoon and two smaller supplemental pontoons. The longitudinal pontoons are the largest, weighing 11,000t apiece and measuring 110m long, 23m wide and 8.8m tall – as wide as they can be and still fit through the locks.
In May, cracks developed in an isolated area of a longitudinal pontoon. Additional cracks developed in a different pontoon in June. Repairs made since then were reviewed and endorsed by a panel of construction experts.
The SR 520 pontoon construction project created a casting basin to build 33 pontoons for a replacement SR 520 floating bridge on Lake Washington. Under a US$367.3 million contract with Washington State Department of Transportation (WSDOT), Kiewit-General built the basin and is constructing pontoons. Construction began in spring 2011.
Kiewit-General-Manson Joint Venture has a US$586.6 million contract with WSDOT to build the floating bridge project – including 44 pontoons in Tacoma and assembly of the floating bridge on Lake Washington. Construction began spring 2012.
The replacement six-lane floating bridge is scheduled to open to traffic by July 2015, but could open as early as December 2014 under the contractor’s schedule.