The vast majority of 2016 Bertha news has fallen into the positive category, a welcome respite for the $3.1 billion project to replace Seattle’s aging Alaskan Way Viaduct with a 1.7-mile-long bored tunnel. And with good news in 2016 comes high expectations for 2017.
Bertha has now bored over 1 mile of its length, completing 70 percent of its run from the stadium district south of downtown to its north portal near the Space Needle. With so much dirt churned by the world’s largest tunnel-boring machine, plenty of non-tunneling work continues also for owner Washington State Dept. of Transportation, including building the north and south portals and creating the double-deck highway inside the tunnel. In all, replacing the viaduct includes 32 separate but related projects and 21 of those are now complete with everything else, including the largest project—the tunneling—on path.
As Bertha continues north toward a June 2017 finish it has reached land beneath Belltown, allowing crews to install the tunnel’s 1,000 ring. In all, crews will place 1,426 rings over the course of the project. “We’re in a really good rhythm,” says ring-builder Cody Heck. “I think my first ring that I built here was about an hour and a half. Now it’s down to about 40 minutes.”
Construction of the highway behind Bertha occurs in 54-ft sections. Crews build each section in stages with multiple sections of the highway under construction at any given time. Building the highway in sections allows concrete the time it needs to strengthen before additional components get added. It also allows workers to spread out and complete the portion they’re working on more quickly than if they were all confined to one area at a time.
According to a report released on Dec. 9, wall foundations now extend past Pike Street, the tunnel walls reach Union Street and the southbound roadway deck nearly stretches to Spring Street.
As Bertha keeps mining, work continues on completing the operations buildings at each portal, buildings that will provide—with bright yellow ventilation stacks—one of the only above-ground markers of the tunnel.
Those stacks, while prominent visually, also provide the ability to remove 1.4 million cubic feet of air per minute from the tunnel, if necessary. Along with ventilation, the operations buildings will include operating systems for safety, lighting and communication.
As both buildings near completion with the installation of the stacks, main ventilation fans and all exterior glass, a portion of the north building won’t get finalized until after the tunneling machine is removed from the ground.
Both buildings were designed as open structures instead of simple concrete blocks and the ventilation rooms of both operations buildings will stay lit throughout the night, acting, as WSDOT says, “as luminous bookends to the bored tunnel.”
Those bookends will have a reason to light up if 2017 continues forward in the same vein as 2016 finishes.
Follow Tim Newcomb on Twitter at @tdnewcomb.