Viaduct Replacement
12:09 pm
Fri July 19, 2013

Bertha To Get Send-Off Before Burrowing Below Seattle

Credit Flickr Photo/WSDOT

Very soon, a massive piece of machinery will start to burrow two miles out from Seattle. It’s building the tunnel that will replace the Alaskan way viaduct.

Tomorrow, WSDOT is hosting a big sendoff for the biggest tunneling machine in the world, affectionately named Bertha. The public is invited to check it out Saturday between 11:30 a.m. and 3:00 p.m., provided closed-toed shoes are worn.

The question of how to replace the Alaskan way viaduct has spawned decades of controversy. The fixture of Seattle’s landscape has been around since the 1950s and it’s damaged. The debate over a tunnel or no tunnel to replace it was fierce. Governors, City Council members, mayors both old and new sparred over it; but there’s no denying the tunnel now.

It’s happening, and it’ll cost $2 billion.

At the entrance to this loud construction site, I met Matt Preedy, the head of the entire tunnel project for the state. Bertha is a metal monstrosity, but the way it works is more akin to a humble member of the natural order. “I’d say that if I had to compare Bertha to an insect, the way it operates is kind of like an inchworm. It pushes forward into the ground 6.5 feet at a time,” said Preedy.

If it were an insect, it would make for a great horror film. The front that cuts through the soil is five stories high. Altogether, the machine and attached trailing gear are nearly as long as a football field at 326 feet, about 35 feet shorter than the space between the uprights at CenturyLink Field.

Matt Preedy, the head of the tunnel project, surveys the site where Bertha will start digging. Behind him is the viaduct, which will be replaced by the project, and CenturyLink Field, which is just a little longer than the massive machine.
Credit KUOW Photo/Sara Lerner

We walked up to a viewing platform to stand on the edge of the viaduct. Luckily a fence and low concrete barriers were between me and the cars whizzing by.

Preedy explained how Bertha will do its job. “You know how you shave the cheese off with the little teeth on the cheese grater? When that cutter head rotates around, it acts just like that. It shaves the ground off. The pieces of ground go in through the holes in the cutter head just like a cheese grater."

Conveyor belts bring the dirt out. They’ll start at just 6.5 feet long, but will grow as Bertha moves farther into the ground. By the end, they’ll be more than two miles long.

Bertha also features a lunchroom for the crew of 25 or so, bathrooms, and a decompression chamber.

In about 14 months, we’ll see Bertha again — at the other end, near Seattle Center.

However, Preedy said in the meantime there’s a chance people walking around downtown Seattle might actually feel the tunneling machine. “History has shown that from some other tunnels that have been bored through downtown recently that if you’re standing on the ground near where the machine is, even if it is 200 feet down, you might feel a little bit of ground vibration as it goes by.”

Eventually, the familiar sound of rumbling traffic on the viaduct will be a part of Seattle’s history.