Viaduct still on the move; 2 inches shy of repair work

By Susan Gilmore
Seattle Times staff reporter

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The Alaskan Way Viaduct continues to move and is now only 2 inches away from potentially expensive repairs.

After the February 2001 Nisqually earthquake damaged the viaduct, the state Department of Transportation established semiannual inspections of the bridge to see if there was movement of structure, which is more than 50 years old.

Linda Mullen, spokeswoman for the DOT, said the most troublesome section of the viaduct has settled 4 inches since the earthquake, moving in a north-south direction. This section, less than a block long, is near the Colman Dock ferry terminal.

Engineers were asked if there was a threshold when the state would have to do something about the movement, and engineers last week came back with a level of 6 inches for north-south movement, or about 2 inches beyond the amount the viaduct has already settled.

"An inch may not seem much in distance," said Maureen Sullivan, urban-project director for the DOT. But she said there was no way to tell how much time it would take for that much movement to occur. She said more will be known after the second annual viaduct testing next month.

Mullen said the state is now preparing construction documents so that if more movement is discovered next month, the state will be ready to do remedial work.

That could mean bracing and strengthening the footings of the viaduct; moving heavy vehicles, such as trucks, to a particular lane; or, in the worst case, keeping them off the viaduct altogether. If the viaduct needs to be strengthened, that could eliminate some parking under the bridge while the work is being done.

	ELLEN M. BANNER / THE SEATTLE TIMES The state says it will know more about the movement of the viaduct after another test next month.

Mullen said the state would expedite its bid process and could start work within a month after the latest numbers come out. She said it would take two to three months to do the work if it's needed.

If the new numbers show an inch more of movement, the state will change to quarterly inspections, Mullen said.

The state inspection in September showed the viaduct had moved another couple of inches, Mullen said.

"We wanted to wait until we knew what kind of threshold we have," she said, adding that she doesn't know how much repairs might cost.

She said even if the bridge exceeds the 6-inch threshold, it doesn't mean the viaduct would be dangerous to drive on, just that repairs would be needed to keep it from getting worse. The viaduct will be closed the weekend of March 20-21 for testing.

Built in 1953, the viaduct carries 110,000 cars a day.

Sullivan doesn't know why the area around Colman Dock seems to be experiencing the most movement, but it is where a section of the Alaskan Way seawall has settled, and the soils may be more liquid in that area.

Officials also don't know how much of the viaduct movement can be blamed on the earthquake.

"The earthquake accelerated the problem," Sullivan said, "but (the viaduct) is also aging and near the end of its useful life."

Consultants are finishing an environmental-impact statement on five options for replacing the viaduct. The statement will be released March 31.

The options, which vary in cost from $2.5 billion to $4.1 billion, include rebuilding the viaduct in the same location with wider lanes; building a new six-lane aerial structure; digging a tunnel, the most expensive option; building a bypass tunnel that would include a four-lane tunnel on the central waterfront; and building a six- to eight-lane surface street on Alaskan Way, which would cause the most traffic congestion.

Consultants are also looking at a do-nothing option.

The state expects to pick a preferred option sometime this summer, though no money has been allocated yet for viaduct replacement.

"The viaduct is the No. 1 transportation issue in this state. It moved during the Nisqually earthquake, and it's moved three times since," said Seattle Mayor Greg Nickels. "This drives home the point that we need state and federal assistance to replace it sooner rather than later. Time is running out."

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

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