Light Rail
6:14 pm
Fri March 4, 2011

Sound Transit's giant tunnel machine nearly finished

The giant digging machines that will bore twin tunnels from Husky Stadium to Seattle’s Capitol Hill are being assembled at the Port of Tacoma. They're called Tunnel Boring Machines, and they vaguely resemble Apollo-era rockets, lying on their sides. 

And with their current paint-jobs, sporting Sound Transit's green and blue colors, they might be Lego toys, inflated to a surreal scale.

The side-by-side tunnels will eventually carry Link Light Rail from downtown Seattle to the north.

The tunneling machines were custom built in Germany, by Herrenknecht.  Sound Transit's Joe Gildner, the engineer in charge of the project, says the face includes discs, blades, and scrapers specifically designed for the soils deep under Seattle.

"We have hard clay, dense sands, and we will hit some pockets of groundwater," along with boulders, says Gildner. All that debris was left behind by ancient glaciers.

The boring machines are being assembled at Tacoma's Jesse Engineering. In April, they’ll be trucked to Seattle and lowered into a 120-foot deep pit.  Digging starts in June.

They're nicknamed "Togo" and "Balto" in honor of two lead Husky sled-dogs that raced to bring vaccines to remote Alaska. That set the stage for the annual Iditarod race.

The machines will be underground for over a year, tunneling two miles to Capitol Hill. Simultaneously, a third machine, built by Hitachi Zosen in Japan and assembled in Seattle, will dig from the Capitol Hill station to downtown. 

The cost for all this tunneling is about $460 million, out of $1.9 billion for the entire downtown-to-university project.

The tunnels will also use nearly 40,000 slabs of concrete, manufactured near Tacoma.  They’ll be trucked to the tunneling site at Husky Stadium.