Dec. 13 project update: Crews install the tunnel's 1,000th ring

Posted on Dec 13 2016 1:18 PM
Today was just an ordinary Tuesday morning 170 feet beneath Belltown, where crews building the SR 99 tunnel continue their subterranean push toward the north portal.
Build a concrete tunnel ring, dig forward. Build another ring, dig forward. It’s a task the ring-building crews working on Bertha, the SR 99 tunneling machine, will perform 1,426 times over the course of the project. As you might expect, they become more efficient with each ring they build.
“We’re in a really good rhythm,” said ring-builder Cody Heck, in our newest video, posted below. “I think my first ring that I built here was about an hour and a half. Now it’s down to about 40 minutes.”
Over time, of course, the rings add up. Which brings us back to Tuesday morning, when crews installed the tunnel’s 1,000th ring. With Bertha’s cutterhead approaching the ground beneath Third Avenue and Blanchard Street, tunnel boring is now 70 percent complete.
What will crews do now that they’ve reached 1,000 rings? Build more rings, of course. Heck explains the process below.
Highway construction progress
Ring-building is only one component of SR 99 tunnel construction. A separate crew is hard at work behind the tunneling machine, building the double-deck highway that will carry traffic when the tunnel opens.
Construction of the highway occurs in 54-foot sections. Crews build each section in stages. The time-lapse video below shows the process in 60 seconds. 

As you can see in the video, multiple sections of the highway are under construction at any given time. The graphic below shows the different stages.

SR 99 tunnel highway construction steps

Building the highway in this fashion allows concrete the time it needs to strengthen before additional components of the highway are added at a given section. It also allows workers to spread out and complete the portion they’re working on more quickly than would be possible if all crews were focused on the same area at the same time. 
As shown in this Dec. 9 report, wall foundations now extend past Pike Street. The tunnel’s walls now reach to Union Street. The southbound roadway deck has been completed to approximately Spring Street. Moving forward, we’ll be posting these reports every Friday on the Follow Bertha page.
It's been nearly one year since the SR 99 tunneling machine resumed mining following the tunneling delay. We're highlighting a different aspect of the program each day this week to illustrate the progress we've made to date. Yesterday’s post highlighted work at the tunnel’s future south portal.


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