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Time-lapse video shows launch of first Tacoma-built 520 bridge pontoons

Post by John Gillie / The News Tribune on July 24, 2012 at 4:42 pm |
July 25, 2012 3:10 pm

A new video from the Washington State Department of Transportation shows the launch of the first of what will ultimately be 44 pontoons built in a graving dock at Tacoma’s Concrete Technology Corp. for the new SR 520 bridge over Lake Washington.

The first six pontoons were built in the dock leased from Concrete Tech along the Port of Tacoma’s Blair Waterway. The dock was flooded Sunday and the dock’s gate between it and the Blair was removed Sunday night.

As the tide rose Monday, tugs moved in a custom-built, T-shaped pontoon between the first two pontoons. The T-shaped pontoon was secured to the two bridge pontoons, providing enough additional buoyancy to lift them off the bottom of the dock.

The tug then towed them out into the waterway and moved them to a dock down the Blair for more outfitting. The same process was due to be repeated Tuesday and Wednesday nights.

The pontoons will be towed to Seattle where they will pass through the Ballard Locks and into Lake Washington. There they will be mated two larger pontoons built in Aberdeen.

The pontoons will be fitted with a roadway structure that will carry six lanes of traffic and a bicycle lane across the lake between Medina and the University of Washington vicinity.

Once all six pontoons that have been built over the last six months are floated out of the dock, the dock gate will again be put in position, the dock will be pumped out and construction of another eight pontoons will begin.

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