Sound Transit finishes second Northgate Link light rail TBM drive

In Seattle, the second of two TBMs working on Sound Transit’s Northgate Link light rail extension reached the wall of the future Roosevelt light rail station on July 13, completing the first 1.5-mile segment of a 3.4-mile tunnel that will serve light rail trains from Northgate Mall to the University of Washington starting in 2021.

The 6.4m diameter refurbished Robbins EPBM completed the second of six tunnel drives being mined by JCM North Link LLC – a joint venture of Jay Dee, Coluccio, and Michels – having been 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.

The other TBM on the contract, a Hitachi Zosen machine nicknamed “Brenda” was previously used on Sound Transit’s University Link 230 contract, was launched from the Maple Leaf Portal last July. That machine 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 in 2021, light rail trains will enter and exit the tunnels at the Maple Leaf Portal.

Each tunnel boring machine weighs 600 tons and is more than 300 feet long with trailing gear. The cutter heads -the rotating faces of the machine that bore underground – are 21 ½ feet 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 $2.1 billion 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. The 4.3-mile extension from Northgate will provide 14-minute rides to downtown, seven-minute rides to Husky Stadium, and 47-minute rides to Sea-Tac Airport. Riders from Roosevelt Station will reach the airport in 44 minutes.

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