The second set of six pontoons destined to become part of the new Highway 520 floating bridge across Lake Washington took to the water Monday in Tacoma’s Blair Waterway.
The pontoons will be towed two at a time to Seattle, through the Lake Washington Ship Canal and into Lake Washington where they will be mated to larger roadway floating sections being built in Aberdeen.
The Tacoma-built floating concrete sections each measuring about 100 feet long and 50 to 60 feet wide will provide extra stability for the roadway pontoons.The new bridge will be six lanes wide, two lanes wider than the bridge it will replace. The new bridge will also be equipped with a wide bicycle and pedestrian pathway.
The completed bridge will be made up of 77 pontoons, 33 forming the roadway and 44 built in Tacoma to provide additional bouyancy. Those pontoons will be bolted to the main structure outboard of the roadway sections.
The 44 stabilizing pontoons are being built in a graving dock on the west side of Tacoma’s Blair Waterway just south of East 11th Street. That dock is owned by Tacoma’s Concrete Technology Corp.
The first set of six pontoons was completed last summer. The pontoons are built inside the dry dock. When they’re complete, the gate blocking the waterway from entering the dock is opened, and the pontoons rise off the floor of the dock. Those sections are then pulled from the dock two at a time into the waterway.
The Tacoma pontoon fabrication project is part of a $586.6 million contract with contractor Kiewit-General-Manson to build the bridge, anchors and supplemental pontoons. About 170 construction jobs are being created by the project in Tacoma, said the state Department of Transportation.
Each set of six pontoons take about six months to build. The next batch will float out this summer.
The bridge is scheduled to be open for traffic by July 2015. The contractors will receive incentive payments for an earlier opening.