This milestone completes the second 1.5-mile (2.4km) segment of a 3.4-mile (5.5km) tunnel that will serve light rail trains in Seattle, starting in 2021.
"Our second Northgate Link tunnel machine has reached the Roosevelt Station, halfway from the North Portal to the U District," said Sound Transit board chair and King County executive Dow Constantine. "This keeps Sound Transit right on schedule to get the digging done by mid-2016 and Northgate Link in operation by 2021."
This is the second of six tunnel drives being mined by Sound Transit tunnelling contractors as part of the Northgate Link light rail extension. The TBM that reached the Roosevelt site on Monday launched last November from the Maple Leaf Portal just east of Interstate 5 and south of Northgate Mall. When the machine finishes boring through the station wall at Roosevelt, it will be refurbished before continuing to the U District station site and later connecting with the completed University of Washington Station.
Another TBM launched from the Maple Leaf Portal in July 2014. That TBM reached the Roosevelt site in March and is expected to arrive at the U District site this fall.
Both tunnels are expected to be complete by mid-2016. Cross-passages and tunnel finishes are scheduled for completion in early 2018. When service starts light rail trains will enter and exit the tunnels at the Maple Leaf Portal.
Each TBM weighs 600 tons and is more than 300ft (91.5m) long with trailing gear. The cutter heads are 21.5ft (6.5m) in diameter. By the time tunneling is finished, a total of more than 500,000 cubic yards of soil will have been excavated and over 7,200 concrete rings used to line the tunnels.
When complete, the USD 2.1bn Northgate Link Extension will connect the University of Washington Station at Husky Stadium to underground stations in the U District and Roosevelt neighborhood, and to an elevated station at Northgate.
