New equipment brought in to fix cracked pontoons on new 520 bridge

by: Graham Johnson Updated:

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SEATTLE —

Work to fix cracked pontoons on the new 520 floating bridge took a step forward Friday.

A giant metal box called a "coffer cell" is now just north of the bridge. It's essentially a floating drydock that will be used to fix cracks on the ends of bridge pontoons.

Cracks in the pontoons have delayed the opening of the new bridge from 2014 to 2016 and have run up the costs.

Fixing the four pontoons built first will cost $49 million.

Two were repaired in drydocks, but two more were already in Lake Washington, and had been joined with smaller pontoons, which made them too wide to fit through the Ballard Locks.

"We needed to figure out a way to do the repairs out here and you have to do them in the dry so that's why we have a coffer cell," said Dave Becher, WSDOT's floating bridge project director.

Beginning next month, crews will move the coffer cell up to the end of a pontoon, lower it, attach floats and pump out the water, creating a dry spot to make repairs.

Crews will then install high-strength cables to squeeze the concrete together and fix the cracks.