Tunneling Industry Magazine Picks 3.5-Mile Northgate Link Tunnel Project as 2018’s “Tunnel Achievement” of the Year

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On time, on budget, twin-tube tunnel awarded for conquering unique construction challenges

Please view our award-winning work in this Sound Transit video of Northgate Link tunnel excavation. https://vimeo.com/288632644

Citing Sound Transit’s impressive work building the 3.5-mile tunnel from the University of Washington to Roosevelt, Tunnel Business Magazine, in partnership with the 11th annual Breakthroughs in Tunneling conference, awarded Sound Transit the 2018 “Tunnel Achievement Award for Project Excellence.”

The winning project is part of Sound Transit’s $1.9 billion, 4.3-mile regional light rail Northgate Link extension, scheduled to open in 2021. Northgate Link is one piece of Sound Transit’s regional commitment to complete 94 new miles of voter-mandated light rail, the biggest rail service expansion in the country.

Facing challenging ground and water conditions, along with urban construction constraints, Sound Transit and Northgate Link tunneling contractor JCM (a joint venture of Jay-Dee Contractors, Coluccio, and Michels) clocked more than 2 million staff hours successfully completing two parallel tunnels on budget and on time. Using two tunnel boring machines, weighing 600 tons each, JCM excavated more than 500,000 cubic yards of soil, yet kept community impacts to a minimum.

The award recognized that building the twin tunnels, one for northbound trains and one for southbound, presented several unique challenges. First, there was disruptive groundwater along the tunnel alignment where the design called for 23 cross-passages connecting the tunnels to maintain passenger safety. In order to dig those mini, 20-foot passages, Sound Transit opted for ground-freezing technology to control the groundwater. This innovative approach was more efficient, safer, and less disruptive than traditional dewatering.

Second, the project required construction below the UW campus, where the contract called for strict time and vibration limits to minimize impacts on University facilities. The team extracted, refurbished, and relaunched the tunnel boring machine with time to spare under the allowed 304-day construction window. The contractor also used Rubber-Tired Vehicles (RTVs) to transport equipment and materials during construction, instead of a traditional rail system, minimizing disruptive vibrations.

Third, there was a half-mile stretch of extremely hard ground between the University District station and the Roosevelt station. Attentive maintenance kept the project on schedule.

Sound Transit tunnel construction manager Brad Cowles accepted TBM’s 2018 “Tunnel Achievement Award for Project Excellence” at the annual Breakthroughs in Tunneling conference in Denver this year on September 11. Sound Transit is the seventh recipient of this prestigious industry award.

Sound Transit is simultaneously working to extend light rail north, south, east and west, opening new stations every few years to form a 116-mile regional system by 2041. Starting in 2021 the Northgate project will provide reliable, congestion-free travel to Seattle’s University District, Roosevelt and Northgate neighborhoods. Northgate Link will be followed in 2023 by the opening of service to Mercer Island, Bellevue and Redmond’s Overlake community. Additional extensions to Shoreline, Mountlake Terrace, Lynnwood, Kent/Des Moines, Federal Way and downtown Redmond are planned in 2024. Further light rail extensions are scheduled to reach West Seattle, Fife and Tacoma in 2030; Ballard in 2035; Paine Field and Everett in 2036; and South Kirkland and Issaquah in 2041.

The agency is also working on further investments including but not limited to expansions of Sounder South service and bus rapid transit service in 2024 along the north, east and south sides of Lake Washington. More information is available at https://systemexpansion.soundtransit.org