Traffic Payout

Giant blue cranes and drill rigs at the SR 99 tunnel boring machine launch pit site.

By guest blogger Chad Schuster

They stand in clusters, a half-dozen or so of them, 170-foot towers of steel in a large field of dirt to the west of Seattle’s stadiums. From the sky they look like giant robots chatting it up, or preparing for battle, maybe. Whatever they’re doing, you can tell it’s big. Really big.

"They’re a little bit like trailblazers," said Matt Preedy, WSDOT’s deputy administrator for the Alaskan Way Viaduct Replacement Program, of the giant blue cranes and drill rigs at work on the SR 99 Tunnel Project. "Their job is to prepare a path for the tunnel boring machine."

This being a tunnel, that path ultimately leads underground. But before the boring begins, crews must first build a launch pit – the task currently being undertaken by the cranes and drill rigs – where the machine will begin tunneling next year. Significant work also must occur in the ground alongside the tunnel route, which is why the tunneling operation, mammoth machines included, is set to begin a slow march north toward the ferry terminal before stopping just south of Yesler Way.

To make room, crews today rerouted six blocks of waterfront traffic from Alaskan Way to a newly improved road beneath the Alaskan Way Viaduct. For visitors to the waterfront, that means big changes to traffic, parking and ferry access starting today and lasting through at least early 2014. For fans of extreme engineering, it means the show is about to begin.

"These cranes and drill rigs are amazing, but they’re really just the machines behind the machine," Preedy said.

The machine is the project’s 57.5 foot diameter tunnel boring machine, the world’s largest. Currently being manufactured in Japan, the machine is scheduled to arrive next spring and begin its northward journey by the middle of 2013. Its departure point? You guessed it – the dirt field currently occupied by the blue machines.

Right now the machines are drilling concrete piles 100 feet into the ground to form the walls of the launch pit. Excavation of the pit will begin this summer. Crews are also busy relocating utilities and reinforcing a two-block section of the viaduct near Yesler Way, above the path of the future tunnel.

If all of that sounds complicated, you’re right.

"Tunneling is complicated business," Preedy said. "Coordination is key because crews have to deal with so many moving parts. We have a lot of exciting work to do before we turn the keys on the tunnel boring machine."

Fortunately you don’t have to be an engineer to enjoy the spectacle.

"This is a once-in-a-lifetime project," Preedy said. "People really should come down and see it for themselves."

Note: Visitors to the waterfront can learn more about the SR 99 Tunnel Project and the nearby Pioneer Square neighborhood by visiting Milepost 31, WSDOT’s information center at 211 First Ave. S.