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May 31, 2013 at 1:49 PM

Tunnel machine Bertha’s big green disk descends in Sodo

Highway 99 tunnel workers, politicians and supporters gathered this morning to venerate the world-record cutting head while a huge crane lowered it into the south portal at Sodo.

The green, 57 1/2-foot disk had been resting on its side near the sports stadiums, a Sodo landmark in its own right, since a shipload of tunnel machine parts arrived from Japan in early April.

The $2 billion tunnel is part of a $3.1 billion replacement for the old Alaskan Way Viaduct, which sank a few inches after being damaged by the 2001 Nisqually earthquake. House Transportation Committee Chairwoman Judy Clibborn, D-Mercer Island, gave a cheerful tint to the project’s long gestation, which devoured tens of millions of dollars for preliminary engineering and public outreach.

“If you take two or three years to make a decision, or maybe five or six, the technology advances to a point where you could do this with a single bore,” she said, at similar cost to another viaduct.

99tunnel_backside

Photo by Steve Ringman, The Seattle Times

This photo shows the disk from its backside. The red device in the foreground is the segment erector, which will use vacuum suction to lift about 14,400 arc-shaped concrete pieces, which will form the tunnel tube to South Lake Union. The circular opening in the center is where a conveyor screw will push excavated dirt toward the rear of the 326-foot long machine.

The cutter head alone is 838 tons — of which 9 tons of steel will be scraped off by abrasive soil over the course of a 14-month dig, said state Transportation Secretary Lynn Peterson.

Nicknamed “Bertha” after former Seattle Mayor Bertha Knight Landes, the drill is expected to set out in mid- to late July.   One of the trickiest phases happens early, when Bertha will dive beneath the old Viaduct, which has been fortified with carbon wrap and steel rods to lower the odds of vibration damage.

The tunnel is scheduled to open to traffic at the start of 2016, for a yet undetermined toll rate. Resentment persists among environmental advocates who argue that a costly highway megaproject conflicts with the state’s official goal to reduce greenhouse gases. Peterson in particular was chosen by Gov. Jay Inslee because of her support for cleaner transportation, but defended the project today.

“It is a way to have redundancy within our overall transportation system,” Peterson said. “It parallels I-5, it allows us to have more person capacity. I would just say, if one or more of our roads fail or are congested, we need redundancy in our road system so buses, people and cars can find alternative routes.”

Comments | More in Traffic & Transit | Topics: Highway 99 tunnel, WSDOT Secretary Lynn Peterson

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