Testing continues on Seattle tunneling machine

A new round of testing began Tuesday for the Washington State Route 99 tunneling machine "Bertha" near Pier 48 as it installed a tunnel ring at the bottom of a 120-foot-deep access pit.

Seattle Tunnel Partners (STP), the contractor on the tunnel project, plans to dig a little farther in the access pit tunnel before stopping for the holidays. Digging resumes after Jan. 1 and continues toward a planned maintenance stop 450 feet farther north. During the entire process, work crews will install tunnel rings and continue testing Bertha.

At the maintenance stop south of Colman Dock, crews will perform final adjustments before digging beneath the viaduct. Tunneling under the viaduct requires the complete closure of SR 99 through the downtown for an estimated 14 days. The contractor estimates the closure will happen in March, but the actual date may vary, depending upon progress.

STP paused the project two years ago after Bertha overheated. Since then, the machine's main bearing and seal system have been replaced.

"Testing the machine in the conditions it will face during the rest of the tunnel drive is a critical part of our work to resume full-production mining," Chris Dixon, STP project manager, said. "The next several hundred feet of excavation will give us the information we need to make final adjustments before we tunnel beneath the viaduct and downtown."