Viaduct retrofit wins backing in state report

A new report for the state Department of Transportation acknowledges that the existing Alaskan Way Viaduct might be retrofitted to withstand an earthquake, but it would require extensive strengthening of the underground foundations.

The new report, by T.Y. Lin International, appears to validate some of the claims of retired structural engineer Victor Gray, who has long suggested the viaduct be repaired and not replaced. The report hasn't been publicly released, but a copy was obtained by The Seattle Times.

"This validates what we're saying," said Gray, who lives in Port Townsend. "They say if we do additional things the [retrofit] is all right."

In August, T.Y. Lin issued a retrofit report that found Gray's proposal had some merit but was incomplete and didn't deal with damage an earthquake might do to the foundation.

The state asked Lin to again look at the plan and what could make a retrofit work, and that was included in the new report issued Nov. 13. The state is now calculating what a retrofit might cost, although Gray said it could be done for $800 million. The state says it would cost $2.8 billion to build another elevated viaduct.

Still, it has long dismissed the notion of a viaduct retrofit, rather than replacement.

"The most egregious remaining vulnerability of the viaduct is of the foundations," according to the report. The engineers said extensive foundation retrofit would be required by adding additional pilings at each footing, 12 at some and 14 at others.

The engineers also said the foundations of the viaduct would require a retrofit, by adding stability and enlarging the footings.

They further said another concern, not addressed by Gray, is the "poor anchorage" between the lower (southbound) road deck and the vertical columns.

Also, the curved "knee joints" that tie the upper (northbound) deck to the columns need replacement — and some were damaged the 2001 Nisqually Earthquake, the report said.

Other recommendations, which Gray agrees with:

• Fiber wrap all the columns, both on the upper and lower levels.

• Infuse jet grouting to firm up the soil underneath the structure.

• Strengthen the lower floor beam.

The governor is expected to choose a viaduct-replacement option by the end of the year, choosing between rebuilding the aerial structure or replacing it with a tunnel.

Susan Gilmore: 206-464-2054 or sgilmore@seattletimes.com