State says settling viaduct safe

The aging Alaskan Way Viaduct continues to settle, but it is still safe for motorists, says the state Department of Transportation.

Crews examined the viaduct last weekend to see if there had been movement in the 53-year-old structure since the 2001 Nisqually earthquake and found that an area they had been monitoring near Columbia Street and Yesler Way in Seattle has settled three-eighths of an inch in the past six months.

"The Alaskan Way viaduct remains safe for drivers," said state bridge engineer Jugesh Kapur.

The state will continue to inspect the viaduct every six months to see whether there is more movement. At the section near Columbia and Yesler, the DOT determined that if it should settle a total of 6 inches, or another inch and a half, repair work would be needed. The state has completed design work for the repair but is awaiting a decision on the future of the span.

Mayor Greg Nickels on Wednesday continued to press for a tunnel to replace it. Voters likely will decide this fall on whether it should be rebuilt as a tunnel or elevated structure.

"The viaduct's continued movement shows that we are an inch and a half away from the day of reckoning," Nickels said in a prepared statement. "Time and time again tunnels have proven to be safer in an earthquake than elevated structures."

The City Council is divided on whether it should be rebuilt, made into a tunnel or removed and simply not replaced.

Six months ago, when the viaduct was last inspected, engineers found that a large crack near Colman Dock had grown 3 millimeters.

But George Comstock, another bridge engineer, said that crack has been repaired and that no other cracking was spotted in the inspection.

"Right now it appears to be taking the settlement without showing signs of distress," he said of the viaduct.

DOT engineers aren't certain why the viaduct is settling but say it may be because of failing support columns. The columns are 90 feet long and were meant to go through soft soil to hard glacial till. Some of the columns may not be long enough to go all the way through the soft earth.

If the viaduct needs to be repaired, Comstock said, it could be as simple as putting up additional steel columns for shoring or as significant as putting extra columns around the existing footing to reinforce the foundation.

If repairs are made, there would not be major closures, Comstock said.