Mucked up no more: Seattle Tunnel project gears up to haul away all its dirt

The giant boring machine digging the Seattle Tunnel, known as “Bertha,” will be able to dig 900 feet in the next four weeks. It’s only accomplished two-thirds of that distance in four months.

The reason for the increased production: the labor dispute involving a small number of longshoreman has been resolved.

But how can a few jobs make such a big difference in digging speed?

When you’re digging a tunnel this big, you end up with a lot of dirt to get rid of.

A giant conveyor belt was constructed to take the dirt right out of the hole and dump it on a waiting barge alongside Terminal 46, but those barge operations weren’t allowed to begin because of the labor dispute. The longshoreman’s union handles all maritime-related work at the Port.

They weren’t happy, so no barges. The project was simply dumping the dirt in a pit on the pier.

Workers have been trying to keep up with all the dirt by removing it by truck, but it takes 30 dump trucks to remove the dirt created every time the drill moves just 6 1/2 feet. That’s enough dirt to cover a football field with three inches of dirt.

And every day, the drill moves between 26-and-32 1/2 feet.

It’s been less than efficient using trucks project director Chris Dixon said.

“When we try to do any more tunnel production in a day, we become what we call muck-bound,” he said. “The muck pit fills up so we can’t deposit any more muck in there, which means the machine can’t go forward so we have to stop tunneling until we truck that material away.”

But now that the longshoreman’s union has been given a few jobs on this project, it has agreed to let the barge operations start up. The union workers will be in charge of tying the barges to the dock.

And with barges able to handle bigger loads, digging can speed up significantly. “One barge can haul what 150 trucks can haul,” Dixon said.

Adding barges will nearly triple the amount of dirt they can remove in a day so Big Bertha can keep moving without having to shut down.

“We can haul four to five rings away with trucks every day, but with barges we can haul eight to ten away,” Dixon said. “By adding barges to the mix, we automatically triple the amount of muck that we can haul away in a day.” That’s because the project is still going to be using trucks.

Eventually, three barges will be used in the operation so there will always be one at Terminal 46 to handle the dirt.

When it’s all said and done, the tunnel will remove enough dirt to cover 175 football fields in three feet of dirt.

So where’s the dirt going?

Some of it is going to a dump. The majority of it will end up in an abandoned quarry in Port Ludlow. That dirt will be used to fill it up in a reclamation project.