Northgate Link Extension Light Rail Tunneling

As part of a joint venture, Michels Trenchless, Inc. constructed the 3.5-mile Northgate Link Extension, which connects three northern Seattle neighborhoods to downtown. The scope of work included the excavation and construction of new twin tunnels and three new light rail transit (LRT) stations to provide passenger rail transit in one of the region’s most congested traffic areas.
Two 18-foot, 10-inch diameter tunnels, each 3.5 miles long, were excavated simultaneously using Earth Pressure Balance Tunnel Boring Machine (EPTBM), supported by precast concrete segmental lining. Seven curves exist in the tunnels’ alignments with radii ranging 810-3,140 feet. Waterproofing, electrical, and mechanical systems were installed throughout the tunnels, and finish work of 23 cross passages connecting the two tunnels was completed.
The highly congested urban areas required close coordination with the local communities and various government agencies including the University of Washington (UW). Work along the corridor was planned to reduce construction impacts during routine and special events, including farmer’s markets, sporting events, performances, and UW commencement activities.