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Bertha is now boring into Belltown as it breaks into yet another zone under Seattle. This comes after some of the fastest progress the machine has made.

If it seems like it hasn’t been that long since Bertha went from one zone to the next, it hasn’t. After spending nine days at a maintenance stop, Bertha began mining into zone 7 on Oct. 31. One month later, the boring machine has exited that zone and has moved into zone 8 (out of 10 total zones).

Where Bertha hit its deepest point

That’s relatively fast compared to the previous segments that the boring machine has moved through, though Laura Newborn with WSDOT notes that crews previously went through lengthy maintenance stops which slowed their pace.

“The 1,011 feet of progress made in November was the most tunnel Bertha鈥檚 crews built in a month,” Newborn said. “There were no longer maintenance stops required in November outside of the regular maintenance performed on the machine during the weekends.”

Also, previous stretches, such as zone 2 and 3, were shorter in length. It took Bertha a bit longer to get through those, however, as maintenance stops were planned during those segments. For example, while it took around a month to travel through zone 2 — a relatively short segment — it took well over a month to move through the next leg of the trip despite being roughly the same distance. That’s because crews had to stop for maintenance in zone 4 that almost took a month.

The progress overall is looking good for the tunnel project, which started back up in late 2015 after stalling for two years. Since exiting the access pit in January 2016 — Bertha has gone from zone 1 to zone 8 in nearly 11 months. There are roughly 3,174 feet to go until the machine will exit the tunnel. Once finished, Bertha will have bored 9,270 feet.

Where’s Bertha?

At this point, the boring machine has moved forward 6,096 feet under Seattle and crews have constructed 929 concrete rings to form the tunnel.

Zone 8 — out of 10 zones — stretches from Lenora Street to just past Bell Street. It crosses diagonally between 2nd Avenue and 4th Avenue. that this is a region that has seen quite a bit of human intervention. And that has affected the soils in the area. The area above Bertha is part of the famous Denny regrade where massive amounts of dirt was moved.

This is also where Bertha began moving up to the surface after hitting its deepest point in its journey. The machine will also have to pass under the Battery Street Tunnel before exiting zone 8.