Demolition has begun on the Alaskan Way Viaduct, an elevated highway system along the Seattle waterway being demolished to make way for a tunnel downtown.
Kiewit, the Omaha, Nebraska-based demolition contractor for the project, has begun removing the first section of the double-deck structure. Until now, crews have used hydraulic crushers and impact hammers to work on and remove sections of the viaduct’s edges and tucked-away sections. Starting the week of March 11, they began removing sections from the middle.
Kiewit and its subcontractor Ferma Corp., based in Newark, California, have a multi-step schedule for taking down the viaduct that involves crews working at several locations at once. They began in mid-February at three locations: the Columbia Street on-ramp; the western half of the viaduct near Pike Street; and the very north end of the viaduct around the intersection of Western Avenue and Bell Street.
So far, Kiewit has removed 450 feet of the Columbia ramp, about 360 feet of the viaduct near Pike street, and about 650 feet of bridge at the viaduct’s north end.
In all, roughly 22 million pounds of concrete and steel has been hammered and munched off the structure, according to the Washington State Department of Transportation (WSDOT). Kiewit trucks the rubble down to Terminal 25, where the rebar is removed and the concrete broken into small pieces for eventual use as fill in the Battery Street Tunnel. A small amount of the concrete is being used as rubble pads in work areas.
The hydraulic crusher first got to work on Pike Street and slowly moved down to Columbia Street. Crews will use that machine to begin demolishing the viaduct between Columbia Street and Yesler Way. First removing the top deck and then the lower deck, crews will work their way north along the waterfront.
During demolition, Kiewit first fences off the immediate area and begins prep work and staging, then uses impact hammers to remove the roadway deck. After this, hydraulic crushers remove the supporting girders and columns that hold up the deck.
In some areas of the viaduct, crews saw cut sections to be removed by crane. When the upper levels are removed, will start dismantling the lower decks using the same processes.
Once demolition on sections are complete, crews remove the viaduct’s foundations and then clean up the site and restore the ground to its previous condition.
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 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, which WSDOT says will “set the stage for the biggest transformation of Seattle’s central waterfront in a generation.”
Watch the demolition of the Columbia ramp below, courtesy of WSDOT: