Drivers crossing State Route 520 may have noticed more heavy-duty construction equipment on Lake Washington than usual today, as a 660-ton “coffer cell” arrived in the SR 520 floating bridge construction zone.

The large steel structure stands 35 feet tall and measures 45 feet wide by 144 feet long. It will be used by Washington State Department of Transportation contractor crews to create a dry work environment in which repairs will be completed on the final two Cycle 1 SR 520 bridge pontoons.

When attached to the ends of pontoons U and V, the coffer cell will serve as a portable drydock.

Once in place, crews will pump water out of the coffer cell so they have a dry work environment to complete epoxy injections, crystalline waterproofing, transverse post-tensioning and application of carbon-fiber wrap. An overview of coffer cell operations is available online (pdf 290 kb).

“Using the coffer cell allows us to complete this work on Lake Washington and keeps the project moving forward,” said Dave Becher, floating bridge project director.

The coffer cell will remain on Lake Washington for about four months.

More information about the SR 520 Bridge Replacement and HOV Program is available at www.wsdot.wa.gov/projects/sr520bridge.