September 13, 2018

Northgate Link tunnel wins national award

Photo from Sound Transit [enlarge]

Crews extracted and reused one of the boring machines to stay within the 304-day construction window.

One part of Sound Transit's Northgate Link that you can't see yet won an award this week from Tunneling Industry Magazine.

Northgate Link's twin tunnels won the 2018 Tunnel Achievement Award for Project Excellence.

The 3.5 miles of parallel tunnels will connect Husky Stadium and the Roosevelt district when the line opens in 2021. They are a major component of the $1.9 billion, 4.3-mile Northgate Link extension.

JCM Northlink — a joint venture of Jay Dee Contractors, Coluccio and Michels — logged more than 2 million worker hours to finish the tunnels on time and on budget. Two 600-ton boring machines dug the tunnels, and together excavated more than 500,000 cubic yards of soil.

JCM used ground-freezing technology to control groundwater while digging 23 cross-passages for emergency exits. This method was more efficient, safer and less disruptive than traditional dewatering.

Another challenge was digging under the University of Washington campus, which required strict limits on timing and vibrations to keep from disturbing ongoing research.

JCM extracted, refurbished and relaunched one of the boring machines to stay within the 304-day construction window. It also used rubber-tired vehicles to move equipment and materials, minimizing vibrations that would have come from using a rail system.

JCM also had to contend with a half-mile stretch of extremely hard ground between the University District and Roosevelt stations.

Brad Cowles was Sound Transit's tunnel construction manager.

A video of the tunnel excavation is at https://vimeo.com/288632644.