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February 26, 2013 at 1:00 PM

Fixing 520 bridge pontoon cracks to cost tens of millions

The new floating bridge, shown from the west, is now estimated to be completed by September 2015. (Mike Siegel / The Seattle Times)

Millions of dollars must be spent to fix the pontoons being built for a new 520 bridge, transportation officials said Tuesday, after underwater inspections revealed that the pontoons’ worst cracks grew over the winter.

Transportation Secretary Paula Hammond also said Tuesday the state is unlikely to meet its December 2014 goal to open the floating section of the new six-lane bridge. “I’m hopeful the project will be done within 2015,” she said.

Hammond acknowledges the cost, yet to be precisely determined, will be in the tens of millions. She doesn’t know if it will reach $100 million, but says she’s confident it will be less than the $200 million still in the bridge contingency budget. Much depends on whether the state and contractors Kiewit-General-Manson can agree on ways to accelerate the job, through double shifts or overlapping tasks, she said.

The state released the new findings Tuesday from three pontoon investigative reports.

The most serious cracks begin in the end walls, and wrap around the upper and lower edges to continue along the top and bottoms. These are blamed on state design mistakes. During post tensioning, which involves cinching the pontoons tight using steel bands, the high forces caused cracking. An untreated underwater crack can let in water at rates of 1 cubic foot per hour, a technical report says.

The main remedy for pontoons already on Lake Washington, and more being built in Grays Harbor, is to use high-tension steel bands to compress the pontoons from side to side, at each end.

Hundreds of smaller cracks, blamed mainly on concrete-handling flaws by contractors, are relatively easy to seal with epoxies, and comparable to cracks on other floating bridges.

Hammond also said disciplinary action will be taken against state bridge division staff who signed off on the design without running models that might have foreseen the cracking. She says the state was moving fast to meet elected officials’ desire for quick completion, but that’s no excuse.

Hammond is leaving her post March. 8. Gov. Jay Inslee last week named Lynn Peterson, a highway engineer and adviser to Oregon Gov. John Kitzhaber, as her replacement.

Comments | More in Government | Topics: 520 bridge, Paula Hammon, pontoons


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