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Alaskan Way Viaduct
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How Seattle plans to demolish the Alaskan Way Viaduct

What happens to the Alaskan Way Viaduct once the new SR 99 tunnel opens in 2019? After Jan. 11, the process of dismantling the viaduct begins.

RELATED: Seattle getting closer to Alaskan Way Viaduct closure

WSDOT laid out the process in a recent video on its website Tuesday, taking the public through step-by-step on what the demolition and dismantling process will look like.

In all, the demolition will take around six months, starting at the Columbia Street on-ramp, and extending north of Pike Street. From there, the demolition will extend out from Columbia north and southward.

Kiewet Infrastructure West will be overseeing the demolition, cordoning off two to three blocks at a time, and spending roughly 30 days on each section. The viaduct will be dismantled level-by-level from top to bottom.

Viaduct

The real difficulty of the project comes with how close the viaduct is from buildings and other elements of the city.

“What makes this unique is the close proximity of the buildings, [and] the massive grid of utilities that we’re going to be protecting,” said Dan Hemenway, Kiewet’s project manager overseeing demolition.

Girders close to those buildings will be removed via crane, and in some cases, barriers will added to protect them from rock, debris, and dust. Additionally, sensors will be implemented to ensure that noise and vibration are “kept within limit.”

WSDOT expects the the waterfront, Pike Place Market, Pioneer Square, and access to the ferry terminal to all be open and available during the demolition.

“Our goal is to have as little impact as possible,” Hemenway said.

The SR 99 tunnel will officially open in early 2019. Before that happens, there will be a three-week closure of SR 99 through downtown Seattle to realign the highway. Both the viaduct and the tunnel will be closed during this period. Additional ramp closures could mean up to six weeks of traffic disruption.

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