SR 99 TBM Passes Halfway Mark

The SR 99 TBM Bertha passed a significant milestone in its journey underneath Seattle. When the machine tunneled past Pike Place Market on Friday, Sept. 30, it pushed beyond the halfway mark of a 9,270-ft tunnel that will lead to the removal of the Alaskan Way Viaduct.

The contractor, Seattle Tunnel Partners (STP), has now excavated more than 4,635 ft of the SR 99 tunnel. Much of that progress occurred during the past five months, with STP tunneling more than 3,000 ft since leaving a planned maintenance stop on April 29 to begin the push beneath the viaduct.

Bertha is now about 190 ft beneath First Avenue between Pike and Pine streets. According to STP, crews will continue mining for a short time and then stop to perform approximately one month of planned maintenance.

The finish line – a 90-ft deep receiving pit near Thomas Street, at the north end of downtown – is largely complete, along with many other aspects of the tunnel portals. Although future contractors will make final connections to the highway, several of the ramps and roadways into and out of the tunnel are already in place, along with tunnel operations buildings at each of the portals. New drone footage of Bertha’s finish line is now available.

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Other important work is ongoing, including construction of the double-deck highway within the tunnel.

While STP’s crews are making progress, they are also taking time for routine maintenance to help ensure the machine successfully completes the tunnel drive. Like previous maintenance stops, crews will use the upcoming stop to inspect machine components and replace cutterhead tools in hyperbaric conditions. STP expects this round of maintenance to last approximately one month, but it could take more or less time depending on the extent of work needed.

STP’s most recent schedule shows that tunneling will wrap up in summer 2017. Work to complete the tunnel’s interior structures, along with installing and testing systems should be finished by late 2018. Based on STP’s schedule, WSDOT estimates the tunnel would open to traffic in early 2019 when crews finish connecting the tunnel to the existing SR 99 roadways.