Seattle's Big Dig: Bertha starts to cut 2-mile tunnel beneath city

SEATTLE -- 'Bertha', the world's largest tunneling machine, began its 2-mile dig beneath Seattle Tuesday.

Courtesy: WSDOT

The tunnel will replace the aging, elevated Alaskan Way Viaduct (State Route 99) that drivers use to travel north-south along Seattle's waterfront.

Bertha is starting in the city's Sodo district, on the south end, but will travel north and emerge in 14 months near the intersection of Sixth Avenue North and Harrison Street.

Tuesday afternoon, Bertha’s 5-story-tall cutterhead broke through the north wall of her 80-foot-deep launch pit.

Crews working with the Washington State Department of Transportation will push forward slowly at first, digging about 6 feet per day. By the time the machine is beneath downtown, she will dig up to 35 feet per day.

As Bertha was started, workers above the launch pit waited for smoke to appear -- the sign that Bertha was actually doing its job.

“It’s always important to start something. If you can't start something, you'll never finish it,” said Chris Dixon, Seattle Tunnel Partners project manager. “So it's really nice to be under way with the tunneling.”

“This is a brand new piece of machinery; the crew is getting used to how it operates,” said Matt Preedy, a deputy administrator with the Washington State Department of Transportation.

Next week, Bertha will start moving dirt that has been mixed with concrete. Contractors say it’s basically a 1,500-foot safe zone for them.

“It’s a good opportunity for the tunneling crews to go through their learning curve, figure out the machine in a dynamic environment,” Dixon said.

The real test will be later this year, when the tunneling actually takes place downtown. Engineers say they don’t expect any problems then -- the vibration and noise should be minimal. But downtown business owners aren’t so sure.

“It’s great until something they didn't expect to happen happens,” said Ty Myers of the Fenix Tattoo & Piercing shop.

Myers’ shop isn’t directly above the tunneling route. But he said his business is going to be negatively affected by all the construction associated with this project over the next couple years.

“They’re going to shut down the waterfront, which is a huge tourist attraction, and all the businesses feed off that. So everyone from here to Broadway is going to get shortchanged.”

WSDOT said it will be worth it.

The tunnel is scheduled to open to drivers in late 2015. For more information about the SR 99 Tunnel Project, visit www.alaskanwayviaduct.org.