A Boom, A Whoosh And Then: Bertha Breaks Free

The tunnel machine that’s been stuck underground for more than a year reached daylight Thursday.

Now Bertha is slowly inching into position for repair work to begin.

TRANSCRIPT

For the last couple days, you could feel the sidewalk at Jackson and Alaskan Way vibrate slightly as Bertha gnawed its way through 20 feet of concrete.

At around noon Thursday, Jerry Carter was sitting in his wheelchair out in front of the Compass homeless shelter across the street from Bertha.

Carter: “I was sitting here when it blew. I heard a loud boom underground, and then — whoosh, a big steam cloud came up. Sounded like a compression tank exploding, that’s what I was thinking.”

That steam Carter saw was concrete dust as Bertha’s cutter head busted through the concrete lining of the pit wall.

Engineers had been moving Bertha forward in short bursts at about one sixth of the drill’s usual speed.

Workers pumped chemicals into the ground up concrete so it could pass smoothly through Bertha’s digestive system, like toothpaste squeezing out of a toothpaste tube. Never once did the drill exceed its safe temperature range.

Now, construction workers will move the drill forward about six feet at a time, installing concrete tunnel linings at the conclusion of each forward thrust. A few more pushes like that and Bertha will be in position for a facelift.

A massive crane will lift the cutter head very slowly and lay it on the ground. Workers will then take it apart. They’ll replace a broken seal and a damaged bearing. They’ll add metal reinforcing to the hull. Nobody will say how long that’s going to take.

But Chris Dixon, of the Seattle Tunnel Partners, says the drilling should get easier as Bertha moves past the unpredictable fill material that pioneers dumped on Seattle’s waterfront and into the kind of glacial till that’s deeper underground.

Dixon: “One of the things that we’ve been dealing with coming up Alaskan Way here is we’ve been very shallow. The deeper we get, the better soils we get into, the better conditions for tunneling.”

He says Bertha should finish drilling by the end of 2016. A year after that, the tunnel should open for traffic.