Urban paradox: Crews must be extra careful as they demolish Alaskan Way Viaduct
Demolition of Seattle's Alaskan Way Viaduct is underway. Crews began tearing down a former on-ramp near First Avenue and Columbia Street on Friday. Another piece near the market began coming down shortly thereafter.
Unlike the almost instantaneous implosion of the Kingdome just a few blocks away 19 years ago, the removal of the old double-decker freeway has to happen in relative slow motion.
Over the next six months, contractors will be working bit by bit, taking out individual frames of the 66-year-old structure in multiple locations at once. That approach is possible because the main line of the viaduct is built like a series of independent bridges.
It’s also necessary because demo crews will often be working in incredibly tight proximity to locations where people continue to live and work.
MANEUVERING IN TIGHT SPACES
In some places, buildings are as close as 5 or 10 feet from the old structure that has to be torn down. Phil Wallace, senior operations manager for Kiewit Infrastructure West, says they'll use saw cutters and cranes to carefully pull out small pieces and generally do everything necessary to minimize disruptions and ensure safety.
"Debris netting to keep any kind of fractures of the concrete from hitting the buildings. We’ll have a jersey barrier at the bottom with some fencing set up,” Wallace said. “Our priority is to make sure that none of the public gets into the demolition area and none of our material gets outside of our area into the public.”
CRUNCHING AND SPRAYING
Special equipment is pulverizing much of the concrete on site into 3-inch chunks, some of which will be used to fill the old Battery Street Tunnel. Dust from the activities is being controlled with water sprayers.
“One thing I can say about the dust is I’m glad we’re doing this in the winter months, so we’re going to have probably rain every day,” Wallace said. “There will also be a water filtration system that collects all that water and processes it. We’re going to try to reuse that water. It’ll be tested so it can go into the sewer system.”
Noise and vibration levels also will be continuously monitored and kept within permitted limits. The demolition contract also says the crews must move along quickly; no city block can remain closed for more than 30 consecutive days.
Despite a couple of days of snow delays, Kiewit says crews remain on schedule and the waterfront should be free of demolition noise around June 1.