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November 9, 2015
The tunnel boring machine named Brenda bored through the wall of Sound Transit's University District light rail station on Friday, completing the third segment of twin 3.5-mile tunnels that will carry trains between Northgate Mall and the University of Washington.
The $1.9 billion, 4.3-mile Northgate Link Extension is set to open in 2021. It will have six tunnel segments, an elevated section from about Northeast 92th Street to the mall, and four stations.
The tunneling contractor is JCM Northlink LLC, a joint venture of Jay Dee Contractors, Coluccio and Michels. Hoffman Construction is building the U District station.
Brenda launched in July 2014 from the Maple Leaf Portal near Northeast 92nd Street, where the line running north will transition to an elevated track connecting to the elevated station at Northgate. The other three stations will be below ground.
Crews will perform maintenance on Brenda at the U District site before the machine continues its journey south to the station by Husky Stadium, which is expected to open early next year with University Link.
A sister machine named Pamela was launched a year ago to dig a tunnel parallel to Brenda's. Sound Transit expects Pamela to reach the U District site early next year.
Each machine weighs 600 tons and is more than 300 feet long including the trailing gear. Cutterheads are 21.5 feet in diameter.
Tunneling is scheduled to be finished by the third quarter of 2016. Related work — tunnel finishes and cross passages that will connect the tunnels and provide emergency exits — should be wrapped up in early 2018.
By the time tunneling is finished, more than 500,000 cubic yards of soil will have been excavated and more than 7,200 concrete rings will line the tunnels.
A video of Brenda breaking into the U District station box can be viewed at https://vimeo.com/144926809.