Building New State Route 99 through Seattle - page 2 of 3 >>>
As of June 2016, half of the viaduct is already gone, demolished and replaced by crews at the south end of downtown, near Seattle’s stadiums. Completed on budget and one year ahead of schedule, this new section of SR 99 connects to the remaining viaduct along the waterfront to keep SR 99 traffic moving until the tunnel opens to traffic.
The massive tunneling machine specifically built for the project is nicknamed Bertha - after Seattle’s first female mayor, Bertha Knight Landes.
Bertha was manufactured by Hitachi Zosen Corp., a Japanese firm that has successfully built more than 1,300 tunneling machines, a number of them for large-diameter tunnel projects. Seattle Tunnel Partners, the contracting team building the tunnel, is responsible for ensuring that the TBM functions properly.
Seattle Tunnel Partners has now bored more than one-half mile of the SR 99 tunnel. Bertha, the SR 99 tunneling machine, had travelled a total of 2,724 feet and installed 411 concrete rings. Crews have tunnelled more than 1,100 feet since leaving the machine’s most recent planned maintenance stop. The completed bored tunnel will be 9,270 feet.
A mile-long stretch of new highway connects to the south entrance of the tunnel, near Seattle’s stadiums.
The top of the machine’s cutterhead is approximately 115 feet below Madison Street, east of Western Avenue. It is approaching the southern edge of Zone 4, which continues the tunnel’s path toward First Avenue.
Seattle Tunnel Partners (STP) has begun preparing for its next planned maintenance stop. The details of the stop are still being developed, but it will likely occur sometime in July. During the stop, crews will inspect the machine and perform cutterhead maintenance, a process that could take several weeks.