The structure was damaged by a 2001 earthquake, and for much of the 2000s, Seattle debated whether a new elevated structure should be erected or if it made more sense to send traffic through an underground tunnel instead. Officials concluded it would be more cost-effective to replace it than to repair it and voters approved the tunnel plan in 2011.
This summer, "Bertha," a 7,000-ton tunnel boring machine, is set to finally make that tunnel a reality when she starts clawing through dirt 80 feet beneath the earth's surface. With a diameter of 57.5 feet, it's the world's largest machine of its type. It was affectionately named after Bertha Knight Landes, the city's first female mayor.
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The machine was built in Japan and transported by ship to Seattle earlier this year. Today, crews are working to re-assemble Bertha inside the launch pit where she'll begin cutting her pathway in mid-July, says Matt Preedy, the state's deputy program administrator for the tunnel project.
To prepare for Bertha's arrivals, crews last summer began digging the launch pit, relocating utilities and reinforcing the hole they dug with protective walls to minimize the effects of the machine's reverberations on surrounding buildings downtown. Crews have also installed monitoring devices throughout downtown to gather data before and during the tunneling process to make sure the work doesn't damage existing buildings.
Once Bertha has drilled about 1,000 feet through the ground, crews will start constructing the underground roadway. That work and the tunneling can then occur simultaneously.
Fourteen months and two miles after Bertha finishes tunneling, she'll emerge from a retrieval pit where she'll be disassembled.
The goal is to have the tunneling and roadway complete by late 2015, at which point the remaining portion of the viaduct will be demolished. The $3.1 billion undertaking is being funded by a combination of state gas tax revenue, federal funds, tolls and a contribution from the Port of Seattle.
"It's a history-making job," says Preedy. "We're getting rid of an out-of-date facility, and we're building a brand new one that will serve the Seattle and Puget Sound area for decades to come."
