Bertha, the deep boring machine stuck underneath Seattle, will slide on greased metal rails after crashing into a pit.
That’s the plan, anyway, to free the machine from its den, where it has lived for more than a year. Matt Preedy of the Washington Department of Transportation revealed that new nugget of information during an informal chat in Pioneer Square.
The presentation at Milepost 31, a transportation information center, was designed to give Seattle residents a chance to ask questions. Preedy, who has held many First Thursday Art Walk talks on his own time, has developed a regular following. These citizens talk like engineers, throwing around acronyms like TBM, which stands for Tunnel Boring Machine.
A man in the audience asked when the TBM would be back in service. Preedy said he didn’t have a timeline.
“The contractor has to get the machine mined through 20 feet of concrete,” he said. “They have an idea of what they need to do to repair it. But they’re not setting it in stone because they haven’t taken it apart yet."
The good news, Preedy said, is that construction crews have finished digging the vertical shaft to get down to Bertha.
The shaft goes a little deeper than Bertha’s current elevation. It has concrete walls. And if everything goes right, Bertha will grind through one of those walls and into daylight.
After breaking through, Bertha will slide onto lubricated rails. Engineers hope it doesn’t slide too fast – or it’ll crash into the other side of the pit. The hope is that the machine will stop in the middle, so a crane can slowly and carefully lift its cutter head to the surface for repairs.
Retired schoolteacher Terry Osborn drove from Edmonds, north of Seattle, to hear Preedy speak.
"I’m passionate about these subjects," Osborn said. "Because I’ve seen about 90 percent of the buildings in Seattle being built. I’m just a citizen who’s passionate about construction."
You can see why Preedy likes talking to this crowd. A.J. Kleinosowski is an aerospace engineer who lives in a residential tower downtown. If everything goes as planned, Bertha will tunnel directly beneath where she lives.
Kleinosowski is OK with that.
"Oh, God, I love living on top of this project," she said. "It is so cool. I brag to all my family and friends out of town that I live on the largest tunnel of its kind."
Preedy said it won't be long before Bertha can start drilling through the thick concrete wall (workers must finish pouring the concrete floor of the pit, first, then test its strength). He would like to see that plan succeed, because Bertha can chew up the concrete, "digest it," and push it out its back end.
But if Bertha is not able to break through the concrete, it will take much longer to get it out – because workers will have to chip away at the concrete from inside the pit. Then, they’ll have to scoop out the rubble one crane load at a time.