Floating bridge taking shape in log yard

ABERDEEN, Wash. – Construction crews at the Highway 520 pontoon project in Aberdeen closed off the mouth of the massive casting basin Thursday morning, using a 300-ton crane to lower two 50-ton sections of gate into place and setting the stage for crews to finish a channel running from the basin to the harbor.

Where an empty Weyerhaeuser log yard once stood, hundreds of workers now toil amid towering concrete walls and metal reinforcements. Dozens poured concrete panels or set rebar Thursday while others constructed wooden forms or ran excavators.

Spokesman Joe Irwin with the state Department of Transportation looked out over the bustling construction site shortly after the huge, white sections of gate had been lowered into place.

“It looks a little different (now),” he said with a laugh. “They’ve been pretty busy.”

Crews broke ground earlier this year at the waterfront site to build a large graving dock for constructing the concrete pontoons needed to support the Highway 520 floating bridge in Seattle. Transportation officials plan to have dozens of pontoons, some measuring 360 feet long, finished by 2014 when the floating bridge is rebuilt.

Irwin said the local effort continues to ramp up, with new workers added each week as the basin project gets closer to completion. He said the project now employs nearly 300 people at the site.

“We’re still building up,” he said.

Many workers focused Thursday on installing the first two of three sections of gate to close off the mouth of the basin, which is about three stories deep. Each gate section measures 110 feet long and 10 feet high. The third section was scheduled to arrive today.

While crews will construct the pontoons in the dry basin, the gate and a system of pumps will allow them to flood the basin when the pontoons are finished and float them out into the harbor.

As the water level equalizes between the harbor and the basin, each gate can be pulled out until the harbor runs into the basin. Irwin said crews will have to time the flooding and draining with appropriate tide cycles.

“The tide plays a huge role,” he said, adding, “The whole process takes several hours to complete. … Seeing is believing. It’s impressive.”

When the basin is flooded, crews will use tugboats to tow approximately 32 pontoons up to Seattle as needed for the bridge project.

An excavation barge floated nearby as it dug away at the shoreline. Irwin said approximately 80,000 cubic yards of dirt will be removed to create the channel from the Harbor to the mouth of the casting basin.

Irwin said crews have already removed 280,000 cubic yards of dirt to create the casting basin.

“That’s just an astounding amount of material,” he said.