Alaskan viaduct shifts a bit, but not enough to merit fix

SEATTLE – The Alaskan Way Viaduct has settled a smidge over the past six months, part of a 4¼-inch slump in the highway since the 2001 Nisqually earthquake prompted periodic surveys by the state Department of Transportation.

The state agency has set 6 inches as the threshold for action on the elevated highway that runs along Seattle’s waterfront.

The measurement had hovered around 4 inches for the past couple of surveys, conducted every six months, state bridge engineer Jerry Weigel said Friday.

In fact, the quarter-inch movement detected in two columns near Piers 93 and 94 during last weekend’s check is within the margin of error for surveying, Weigel said. But it was backed by the widening of a crack – from the width of one pencil lead to the width of four, or about a millimeter – just north of Colman Dock.

Still, the shift was too slight – “extremely minor” – to trigger repairs, he said.

“If it reaches 6 inches, we’ll stop it” by strengthening the viaduct footings, Weigel said.

That would cost $2 million to $2.5 million and take a few months, agency spokeswoman Linda Mullen said. But the road would not be closed. “The work we’d be doing would be on the ground and underground,” Mullen said. It might affect parking areas and under-viaduct businesses.

“It’s not a threat to public safety now, or we wouldn’t have it open,” she said.