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SR 99 tunnel rings
Tunnel rings which make up the outer wall are transported inside the new SR 99 tunnel. (WSDOT Photo via Flickr)

It’s been a busy week deep beneath Seattle, as Bertha the tunneling machine keeps on trucking through Belltown. Two new videos from the Washington State Department of Transportation capture some of the amazing work that goes into digging a hole under a city and running a double-decker highway through it.

On Wednesday, Bertha passed 170 feet beneath the intersection of Third Avenue and Blanchard Street. In the eighth of 10 zones that make up the nearly 2-mile tunnel, the machine begins it’s eventual climb toward the surface.

Crews building the SR 99 tunnel installed the 1,000th ring out of 1,046 that will make up the tunnel’s outer wall. It’s a process that has gotten much speedier over time.

“We’re in a really good rhythm,” said ring-builder Cody Heck, who is featured in one new WSDOT video. “I think my first ring that I built here was about an hour and a half. Now it’s down to about 40 minutes.”

Check out Heck at work, including his use of a large remote box which will make your XBox controller seem a little wimpy.

As Bertha digs and rings are placed in her wake, further back behind the machine crews are building the new highway that will replace the Alaskan Way Viaduct. Construction of the highway occurs in 54-foot sections, and a time-lapse video captures all that goes into that phase of the operation.

A report from Dec. 9 shows how much progress Seattle Tunnel Partners has made in constructing the roadway. Wall foundations now extend past Pike Street, tunnel walls now reach to Union Street and the southbound roadway deck has been completed to approximately Spring Street.

SR 99 tunnel progress
(WSDOT Graphic)

Above ground, the operations buildings located near the north and south tunnel portals are nearing completion. The bright yellow ventilation stacks on the buildings are one noticeable part of the city’s massive construction project.

Those vent stacks will be capable of removing 1.4 million cubic feet of air per minute, if necessary, according to WSDOT. In addition to ventilation, the buildings will house operating systems, including safety, lighting and communications and provide space and access for the WSDOT maintenance vehicles.

SR 99 tunnel building
The north portal operations building. (WSDOT Photo)

Also this week, during its semi-annual update to the state legislature’s Joint Transportation Committee, project leaders presented a revised estimate for how much additional money will be needed to complete the SR 99 viaduct replacement.

The current legislatively approved budget for the program is $3.1 billion. In July, the estimated provisional need was $223 million over the remaining life of the program. On Thursday, that figure had dropped to $149 million. The reduction of $74 million was credited to simply having more information about the project schedule and cost estimates.

Read more about the funding here.

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