Tunnel boring machine ‘Bertha' begins digging

by: John Knicely Updated:

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SEATTLE - On Tuesday at 4pm Bertha, the world’s largest boring machine, started drilling a 2-mile tunnel under downtown Seattle.

The tunnel will replace Seattle's crumbling Alaskan Way Viaduct, which suffered damage in the 2001 Nisqually earthquake and is more than 50 years old.

Project leaders will be monitoring its movements and the movements of buildings above ground using 3,000 monitoring points.

Once crews are up to speed with the process, the 58-foot-wide tunneling machine will drill about 40 to 50 feet per day in two 10-hour segments; the schedule allows four hours for maintenance. 

It will stop every six and a half feet so crews can solidify its position in the earth it just dug through.

“Once you get to that six and a half feet, the machine will stop,” said WSDOT engineer Matt Preedy.  “The crew will take a couple hours to erect that concrete liner ring.  Once stopped, it can push off that erected ring.”

There’s a lot of anticipation as to how the drilling will impact people and buildings above ground.  If you’re near where Bertha is drilling, you’ll likely feel it.

“Obviously I’m anxious that it all works well. I’m trustful that it will, “said Pioneer Square Resident David Mosely.  Mosely is excited to have the drilling underway, “I’m thrilled the tunnel project is starting. It’s going to be good for Pioneer Square.”

“People are sensitive to vibration of any kind, so where you might sense vibration or a little noise, it's not anywhere close to any threshold that would cause any damage,” said Preedy.

That’s where the “Cyclops” devices come in.  Thirty-six of the automated survey machines are set up on downtown rooftops like the Alexis Hotel.  The machines shoot lasers at one another to track Bertha’s movements and detect any building shifting.

Pioneer Square Resident Gabe Ustanik’s reaction, “As long as it improves the city I’m okay with it.”

“The whole purpose of this multimillion-dollar monitoring downtown is so we can know in real time if the tunneling is having any effect,” said Preedy.

General Manager of the Alexis Hotel, Jenne Neptune, says some people at first thought it was a video camera tracking their movements because the Cyclops spins and moves.  But the Cyclops does not have a video component.

The devices are part of 1,200 measuring points and 3,000 monitoring points above ground and underground.  The data is constantly streaming live and project leaders will review the data every morning.

Crews will build the highway inside the tunnel as Bertha progresses underground along the waterfront.  The new Highway 99 tunnel is scheduled to open in late 2015.