Inspections on the Alaskan Way Viaduct on March 1 found new cracks forming near Seneca Street, and some existing cracks have lengthened, according to state highway engineers.
The Washington State Department of Transportation will be removing ivy to get a better view, then will close the elevated highway March 22 to conduct follow-up inspections.
After that, there would likely be three overnight closures to repair the cracks, said Dave McCormick, assistant regional administrator. That work will include injecting epoxy into the cracks, as well as fastening gauges to measure whether cracks continue to widen, senior engineers said.
Tom Baker, WSDOT bridge engineer, said the most likely cause for cracking is the 2001 Nisqually Earthquake, which he said weakened the underground foundations in ways that aren’t fully understood. Cracks have recently spread on vertical columns, as well as the horizontal girders that support the road deck, he said.
The widest crack is less than one-sixteenth of an inch, said Keith Metcalf, assistant state engineer for WSDOT. Inspectors marked several with chalk, including one noted “0.3 mm,” or just over 1/100 of an inch.
“It’s not related to the tunnel project, because the tunneling activity is a half-mile south,” Baker said. Near the ferry terminal and Yesler Way, the Viaduct sagged more than five inches since the earthquake, and settled slightly this winter, due to suspected groundwater loss related to tunneling. This spring a temporary 120-foot-deep pit must be dug to repair Bertha, the stranded tunnel drill for a four-lane replacement highway, to open in 2016. The pit excavation requires careful monitoring and protection of the Viaduct columns.
Baker said the cracks illustrate the importance of replacing the 61-year-old Viaduct. “The repair work and monitoring we’re doing should get us to the end of the project. That’s all we need,” he said.