By: Bill Wilson
Bertha will not be coming in contact with the Alaskan Way Viaduct during demolition.
That’s a good thing, because crews will have no more time to spare when they rip down the 1953 structure piece by piece. Bertha was the tunnel-boring machine used to create the new S.R. 99 tunnel, which will replace the viaduct, and caused almost complete chaos when it shut down for months in 2013. It took four years for the boring machine to break through on the north end of the job, which happened during the first week of April. What will be touching the old viaduct is a team of concrete breakers, as Kiewit Infrastructure West breaks the 1.7-mile elevated roadway one section at a time.
At press time a lot of the details of the design-build demolition contract were unknown. The contract was executed on July 10 and includes demolishing the viaduct, decommissioning and filling in the Battery Street Tunnel, which was built in 1954, and creating new surface streets at the north end of the project. Aurora Avenue, which takes motorists into the Battery Street Tunnel, will be raised and connected to cross streets. Three streets will open as through streets to get people from lower Queen Anne to South Lake Union. Harrison, Thomas and John streets will be constructed and should create a big impact in terms of traffic management.
“It is really great we are at the point where the viaduct demolition is in sight,” Laura Newborn, spokesperson for the Washington State Department of Transportation (WSDOT), told Roads & Bridges. “Mainly because at the end of the day this whole project, and all of the other projects associated with this whole program, was a safety program, because the viaduct is old and is not seismically safe. It will be a relief for a lot of people.”
But before the relief there may be some tension. Final ramps and roads still need to be connected to the tunnel, and WSDOT will have to close S.R. 99 for three weeks in order for crews to get the work done. Over 90,000 vehicles use the route daily.
“We are talking about it now,” said Newborn. “We are making sure people know. We are coordinating with a lot of transit agencies in the area as well as the city. It is a lot to ask, and we know that, but there really is no choice. It is the only way we can get the work done.”
In late July, the project’s prime contractor, Seattle Tunnel Partners, was in the middle of doing extensive testing on the systems inside the tunnel. The testing consisted of three layers. The first layer—pre-functional testing—involved making sure each individual piece of equipment worked. When Roads & Bridges checked in on the project, crews were in the middle of conducting functional testing to make sure all of the systems work. Fire safety, ventilation, lighting and communication systems were all being checked. Then in the final stage—integrating testing—the goal is to make sure all of the systems are communicating with one another.
Newborn said the fire safety system in the new S.R. 99 tunnel is one of the most complex in the world. If linear heat detectors in the tunnel pick up a high level of heat, cameras swing into action to pinpoint the location of the heat source. Video is sent to the tunnel operator and a countdown starts for the sprinkler system to activate. The tunnel operator can speed up the countdown, slow it down or cancel it.
