Demolition of the Alaskan Way Viaduct in Seattle is wrapping up along Seattle’s central waterfront as contractors turn their attention toward the project’s loose ends.
Crews from Kiewit of Omaha, Nebraska, and subcontractor Ferma Corp., based in Newark, California, have been splitting into groups to tackle demolition simultaneously in different sections of the viaduct, which is an elevated highway system along the Seattle waterway being demolished to make way for a tunnel downtown.
Crews started in the middle portion of the viaduct in March and worked their way outward. Currently, one crew is demolishing the southern-most remaining section of the viaduct and working its way north, while another crew is starting at the northern-most end and moving south.
The Washington State Department of Transportation (WSDOT) recently released a behind-the-scenes video of the demolition, where Kelly Arnold, Ferma Corp.’s national projects division manager who is overseeing the demolition, described the work that’s gone into the project so far.
“I’ve been in the demolition business for 32 years, and this is one of the toughest jobs I’ve ever done,” Arnold says in the video. “A lot of it is the close proximity of the buildings, the close proximity to the live traffic, the close proximity of pedestrians, and it just makes it very difficult.”
Crews have retained a similar demolition strategy throughout the extent of the project. First, they “punch out” the roadway between girders with impact hammers, Arnold says, which they call “swabbing the deck.” The hammers are wrapped with rubber to keep dust down and prevent rock from flying.
Because of the viaduct’s proximity to buildings and other structures, crews keep large curtains hung up to block dust and debris.
Then, crews remove the upper girders by either breaking through them or lifting them with a crane if they’re too close to other structures.
“We used the biggest machine we have to take down the upper girders,” Arnold says. “It’s got 1,600 tons of squeezing power and munches through girders pretty easily.”
Once girders are removed, crews use hydraulic crushers to remove the columns that hold up the deck. Then, they demolish the lower deck in a similar process and, finally, remove the footers.
“We look for failure. We create failures in structure. We have to know exactly how to create that failure safely,” Arnold says.
Once demolition on sections are complete, crews remove the viaduct’s foundation and then clean up the site and restore the ground to its previous condition. However, crews are often left working on top of the material before cleanup can commence to get the job done in a timely manner.
“There’s so much material [that] you can’t haul it all fast enough, so you’ve got to get it flattened out and leveled out to where you can work on it, and then your cleanup crew will come behind,” Arnold says.
The viaduct is mainly constructed from rebar, which the contractors bundle for recycling, and concrete, which is crushed, loaded and hauled to a recycling facility. Arnold estimates that the crew will be able to recycle 99 percent of the material through recycling facilities and by reusing the concrete back in the tunnel.
Arnold says space constrictions have been the most difficult part of the job.
“We’re in such tight quarters that these operators have really got to play attention. These radios are the key to our survival out there. Everyone is spotting and watching each other,” Arnold says. “These operators some of best in the business. I’m really proud of these guys.”
The demolition 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.”
The viaduct was constructed in the 1950s and damaged in the 2001 Nisqually Earthquake. Demolition is expected to wrap up by the end of the summer.
“[We’re] making history here,” Arnold says. “[We’re] changing skylines forever.”
Check out the behind-the-scenes look here, courtesy of WDOT: