SEATTLE – The tall blue construction machines digging holes on the south end of the Alaskan Way Viaduct project are creating a launching pit for the tunnel-boring machine that will begin its descent below Seattle next year.
In Japan, meanwhile, the machine, which will measure 57 feet in diameter, is being built by Hitachi Zosen, a company that specializes in massive tunneling equipment.
The machine will be built and tested in Japan, then disassembled into about 40 pieces, placed on a barge and shipped to Seattle. When it's complete, it will be one of the largest tunnel-boring machines ever built.
“It’s a project itself just to build it, get it over here and reassemble it in this launch pit,” said David Sowers, the project's engineering manager.
If all goes as planned, that machine will arrive in Seattle early next year. Digging would begin in the summer of 2013.
But before then, a lot of work needs to be done on both sides of the Pacific Ocean.
The launching pit alone is a massive project. Crews are currently digging hundreds of long, slender columns that reach about 100 feet below the surface. The columns, which are filled with concrete, will form the pit’s walls. Once those walls are in place, crews will dig out the center, clearing a space for the tunnel-boring machine to begin its journey.
In all, the pit will be slightly larger than a football field.
But digging so deep into Seattle’s unknown underground is not easy. The Washington Department of Transportation brought in special equipment that can chew through glacial sediment and chunks of wood left behind by Seattle’s old sawmills.
“These machines just go right through it,” Sowers said. “They haven’t had any trouble with it.”
But they could have a little more trouble if they run into boulders, which is a possibility.
“It’ll slow the operation down a few hours, maybe a day or two,” Sowers said. “But we’ll get through them.”
The goal is to make sure the launching pit is ready to receive the tunnel-boring machine early next year.
If everything stays on schedule, the tunnel will be open to traffic in 2015, WSDOT says.