Tunneling Completed on Northgate Link

Tunneling for the Northgate Link project for Sound Transit in Seattle was completed on Sept. 1 as the TBM mining the southbound tunnel arrived at the University of Washington Station. The arrival of the TBM marked the completion of 6 tunnel drives and more than 7 miles of tunnel.

The $1.9 billion Northgate Link project will add another 4.3 miles of twin-track railway from the University of Washington Station to a new elevated station at NE 103rd Street. Northgate Link includes 3.6 miles of twin-tube tunnel and two underground stations. A $440 million contract was awarded to JCM (Jay Dee/Coluccio/Michels JV), the same joint venture that completed the U230 project, part of the University Link program.

JCM used the Hitachi Zosen TBM from U230 and a Robbins EPB, which was recently used on a project in Singapore, to complete the bores.

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Since work began in 2014, the two tunnel boring machines weighing 600 tons each excavated more than 500,000 cubic yards of soil and installed 7,352 concrete tunnel liner rings. The excavation is complete three months ahead of schedule.

JCM continues work digging 23 cross passages between tunnels that will serve as emergency evacuation routes and will contain controls for electrical and mechanical systems. Work on this contract will be complete in 2018. Future work within the tunnels includes installation of track beds, rails and communications systems. Construction of the three stations for Northgate Link begins soon, with work on the Northgate Station starting this fall. Construction of underground stations in the Roosevelt and U District neighborhoods begins next year.

Northgate Link is schedule to open for service in 2021. For a video of the breakthrough, click here.