The Alaskan Way Viaduct, an elevated highway system along the Seattle waterway, is scheduled for demolition beginning in February 2019.
The viaduct, which was constructed in the 1950s, was damaged in the 2001 Nisqually Earthquake. Although it was strengthened to make safe for daily traffic, it is vulnerable to seismic activity in the future, according to the Washington State Department of Transportation (WSDOT).
The demolition, which is expected to take an estimated six months to complete, will make way for the opening of the State Route (SR) 99 tunnel downtown. According to the WSDOT, the opening of the new SR 99 will “set the stage for the biggest transformation of Seattle’s central waterfront in a generation.”
Kiewit Infrastructure West, with home offices in Omaha, Nebraska, will oversee the demolition. The company is tasked with safely removing the concrete structure with minimal disturbance to the public or nearby infrastructure.
WSDOT lays out five main phases of the project:
- Shifting Alaskan Way to the west of the viaduct. (This phase was completed in October.)
- Removing the Alaskan Way Viaduct from South Dearborn Street to the Battery Street Tunnel.
- Removing the Columbia and Seneca street ramps.
- Building a new, temporary pedestrian bridge across Alaskan Way to Colman Dock.
- Restoring the area where the viaduct once stood and then turning the space over to the city of Seattle's Waterfront Seattle Program.
On site, Kiewit will first fence off the immediate area and begin prep work and staging, then use impact hammers to remove the roadway deck. After this, hydraulic crushers will be used to remove the supporting girders and columns that hold up the deck. In some areas of the viaduct, crews will saw cut sections to be removed by crane. When the upper levels are removed, crews will start dismantling the lower decks using the same processes. Finally, crews will remove the viaduct’s foundations and then clean up the site after all demo work is complete.
Kiewit Project Manager Dan Hemenway talks about the planned demolition in the video below, courtesy of WSDOT: