The Enormous Mission to Rescue the World's Largest Tunnelling Machine

By Robert Sorokanich on at

Big Bertha was all set to dig a nearly two-mile tunnel in Seattle, but just 1,000 feet (304m) into her journey she hit a mysterious object that halted her progress. Now, crews are beginning the process of rescuing her, in what could be the world's largest recovery mission.

The New York Times has an in-depth account of exactly what needs to happen to get Bertha digging again, and it's a massive undertaking. Crews will dig a vertical shaft down adjacent to where Bertha came to rest, then swing an enormous crane down to remove the 2,000-tonne nose—the actual digging apparatus which came grinding to a halt after hitting a buried steel pipe in January.

The detached nose will be hoisted up and laid on the ground for repair by the Japanese company that built Bertha. The repairs will fix damage from debris and grit that contaminated Bertha's precision bearings, and technicians will add about 200 tonnes of reinforcing steel. Here's an animation detailing the process, courtesy Washington State's DOT:

Crews compare re-fitting the repaired and modified nose onto Bertha's body, sitting 120 feet underground, to removing the engine from your family car and replacing it with a modified, hot-rodded powerplant.

"An engine mounts in there a certain way, it weighs a certain amount, everything connects in a certain way—now you're going to put it back in the car and it's a little different", Matt Preedy, the deputy programme administrator for the construction project, told The New York Times. "So obviously they're doing a lot of planning and engineering work to ensure that it will fit back in there."

If all goes according to plan, the newly-repaired Bertha will go back to work in March of 2015—nearly a year and a half after she came to a halt. The rescue alone could cost north of £74 million, added to the £1.84 billion cost of the overall project. Check out NYT's full article for much more information on the rescue, the construction project, and the controversy surrounding Bertha's malfunction. [NYTimes]