July 23, 2012

First set of SR 520 pontoons expected to float out today

Photo courtesy of WSDOT [enlarge]

The first six concrete pontoons for the new Highway 520 floating bridge on Lake Washington will be floated from their Tacoma graving yard this week.

Crews will tow pairs of pontoons out of Concrete Technology Corp.'s yard on high tides tonight, and Tuesday and Wednesday evenings. The basin where they are being built was expected to be flooded starting Sunday night for the operation.

Pontoons will go through watertight inspections nearby at the Port of Tacoma and be readied for the next round of construction.

The completed pontoons are the first of 77 of various sizes that are needed for the six-lane floating bridge. Of the total, 44 are being built in Tacoma and the rest in Aberdeen.

“Construction crews have worked for months to build these pontoons, and seeing them float out and towed to Lake Washington this summer will be a huge accomplishment,” said Julie Meredith, SR 520 program director for WSDOT, in a statement.

Crews in Tacoma worked for about six months to build the first six supplemental stability pontoons. These smaller pontoons will attach to the sides of larger new pontoons to provide additional floatation for the bridge. The 44 smaller pontoons each weigh 2,500 to 2,820 tons and measure 100 feet long, 50 to 60 feet wide and about 28 feet tall.

The next few construction cycles in Tacoma will build eight pontoons at a time. Work will continue for two years.

In Aberdeen, crews are completing the first six of 33 pontoons that will form the backbone of the floating bridge. Pontoons were repaired in June and July after cracks were discovered, and crews are preparing to float them into Grays Harbor and tow them to Lake Washington this summer.

A peer review panel is examining the cause of the cracking and preliminary recommendations are pending.

The Kiewit-General Joint Venture is building the Aberdeen pontoons under a $367.3 million contract. The joint venture of Kiewit/General/Manson is building the floating bridge, anchors and 44 supplemental pontoons under a $586.6 million contract.

Officials hope to open the new bridge in December 2014. It will be the world's longest floating bridge at 7,710 feet.