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Idea of fixing viaduct seen as having merit but problems as well
Seattle Times staff reporter
A proposal by retired structural engineer Victor Gray to retrofit the Alaskan Way Viaduct has some merit but is incomplete and doesn't deal with damage an earthquake might cause to the viaduct's foundation.
These are the findings in a 165-page report by T.Y. Lin International, scheduled to be released today.
The state said it isn't ready to entirely dismiss Gray's idea, which was crafted as an alternative to the state's options of replacing the viaduct either with another aerial structure or with a tunnel. The state plans to study Gray's idea further and work out cost estimates.
Gray says his retrofit plan would cost about $800 million, far less than the $2.4 billion to $4 billion replacing the viaduct would cost.
"The viaduct has some apparent seismic deficiencies," said David Goodyear, engineer with T.Y. Lin, who helped prepare the report. "What Gray's proposal does is improve the conditions on the upper portion but aggravates the foundation."
Goodyear said T.Y. Lin in a computer analysis used Gray's idea of bracing the viaduct with steel beams, adding dampers and mixing cement grouting with soil and then subjecting it to the kind of force that could occur in an earthquake. The upper part of the viaduct, which would be braced under Gray's plan, would be stabilized, but the bracing isn't enough to deal with problems the retrofit would create to the foundation, the engineers said.
According to their report, the stabilizing itself could cause more damage in an earthquake because the viaduct wouldn't sway with the movement of the earth and could uproot the foundations.
"While ground improvement could lessen the risk of an abrupt collapse of the structure, the foundation failures would either render the viaduct unusable for an extended period of time, or require total replacement," said the T.Y. Lin report, which cost the state $180,000.
Gray disagreed and said his proposal to mix the soil with cement grout would strengthen it and protect it in an earthquake. He said even the viaduct's supplemental environmental-impact statement released recently talked about strengthening the soil with cement grout.
"I think we're in good shape," Gray said of the T.Y. Lin study. "Whatever shortcomings they say we have, we can answer them quite easily."
The DOT asked T.Y. Lin to look at three retrofit proposals: Gray's original one, another one he modified and a third plan put forth by engineer Kit Miyamoto, from California, who was asked by Gray to look at his plan.
Gray said there are 62 structural units comprising the 2.2-mile viaduct and only two are damaged, an assessment that DOT agrees with. But the DOT said Gray's plan doesn't go far enough to keep the viaduct safe in an earthquake.
Goodyear said the fact that the viaduct was damaged in the 2001 Nisqually earthquake shows it has a substandard structure.
"We characterize this as an incomplete retrofit," said Ron Paananen, viaduct project manager with the DOT. "It misses some major things, and it doesn't stand on its own." He said the state will try to address what it sees as deficiencies in Gray's plan and try to come up with good cost estimates.
"We want to make sure we fully air this out," Paananen said. "We looked at the retrofit and came up dry, but we want to make sure we give it a complete look." He doesn't know when that might be completed.
Replacing the viaduct with another aerial structure is estimated to cost at least $2.4 billion. Paananen said the bridge, itself, would only cost $1 billion, not much higher than Gray's $800 million retrofit plan. The rest of the cost goes into utility relocation, replacing the Alaskan Way seawall and rerouting traffic during construction.
If the cost of a retrofit is more than half the cost of a new bridge, the new bridge should be built, Goodyear said.
Jugesh Kapur, the DOT's bridge engineer, said the state has never ruled out retrofit as an option and has 70 retrofit schemes.
"If this buys us another 20 to 30 years and then it would cost $8 billion to replace the viaduct, it would still be on crutches for the next 20 years," he said. "There are some safety issues looming over our heads."
The state will turn the T.Y. Lin report over to a team of engineers with the American Society of Civil Engineers, who in 2002 looked at an earlier Gray plan. It found then that a retrofit didn't make financial sense because so much of the viaduct needs replacing.
"From the foundation up to the columns to the beams to the decking, everything was in very poor condition," said Ted Bell, who chaired the civil-engineering group.
Paananen said Gray will be invited to work with the engineering group to help evaluate the T.Y. Lin report. Gray said he'd be happy to join the team.
Susan Gilmore: 206-464-2054
Copyright © 2006 The Seattle Times Company