sr 520 pontoon

Latest update

Date: Friday, December 14, 2012

Contact: Suanne Pelley, SR 520 Communications, 206-770-3578, 206-437-5717 (cell)

Quality assurance update: One column to be replaced at contractor direction

SEATTLE – Upcoming work on piers and columns for the new State Route 520 bridge will involve excavation in the lakebed inside a protective steel curtain known as a cofferdam. Crews are also removing and replacing one of 10 concrete columns atop a pontoon where the concrete pour failed to meet quality specifications.

These developments are part of the progress under way on eastside piers and columns that will support the floating and fixed structures. When complete, the eastern portion of the new SR 520 bridge roadway will be a seamless transition from the floating bridge to fixed bridges off the shore and on land in Medina.

Earlier this fall, crews used heavy machinery to drive massive, interlocking steel sheets into the lakebed, creating a curtain to cordon off a 170-foot-long by 50-foot-wide by 40-foot-deep area in Lake Washington. Next week, crews will pump approximately 2.5 million gallons of water, or nearly four Olympic-sized swimming pools worth, out of this area to create a work area that would otherwise be under water. Pumping will take several days. This work is being completed by floating bridge contractor Kiewit/General/Manson, A Joint Venture (KGM).

Once the cofferdam is drained, crews will excavate into the lakebed and start construction on the new bridge pier. This is the last of three piers that will connect the land-based SR 520 highway on the eastside to the new floating bridge currently under construction.

The new roadway deck will be installed atop bridge piers before sloping down onto columns already under construction on the new pontoons. In October, crews began construction on 10 58-foot-tall concrete columns on top of Pontoon W, one of two cross pontoons that will be installed on the east and west ends of the new floating bridge. This column work requires careful coordination to install reinforcing steel the height of the column, properly align iron forms, and guide concrete into the columns.

As part of its quality assurance process, KGM inspectors discovered that one of these concrete columns had too little buffer between the outer layer of concrete and reinforcing steel inside. This reinforcing steel helps provide resistance to earthquakes and provides strength to support the highway.

KGM project managers determined the column should be removed and replaced in order to meet the project quality requirements. The column will be removed, as early as today, so the replacement work can begin. The removed column will be dismantled and the concrete and steel rebar will be recycled.

“KGM’s decision to replace this column at their expense is the appropriate action. KGM is implementing the quality assurance program that is a key component of our contract,” said Julie Meredith, SR 520 program director.

Construction on the $367 million SR 520 Pontoon Construction Project broke ground in February 2011 in Aberdeen. Construction on the $586.6 million SR 520 Floating Bridge and Landings Project began in spring 2012. The floating bridge contract requires the new, six-lane SR 520 floating bridge to open to traffic by July 2015, but includes incentives for an earlier opening in December 2014. WSDOT is in negotiations with its contractors for pontoon issues encountered in spring 2012 and has not made an official determination on any potential schedule effects. WSDOT and KGM will continue to evaluate schedule opportunities throughout the construction duration.

The latest jobs report counted 832 jobs directly connected to the pontoon and floating bridge project sites in Aberdeen, Tacoma, Kenmore and Bellevue and on Lake Washington.

More project information is available online: