E330 Downtown Tunnel


Sound Transit

Completion Date



H-J-H Final Design Partners, a JV


Bellevue, Washington

Delivery Method

General Contractor



Contract Value

$121 million
East Link Extension E330

The project is part of the 14-mile East Link light rail extension from downtown Seattle to Redmond. The project consisted of two cut and cover portal structures (250 LF and 200 LF), a 1,983-foot-long tunnel, a mid-tunnel access shaft, and connecting adit. The typical cross-section of the SEM tunnel was 38 feet wide by 31 feet high. The tunnel was constructed in soft ground (glacial till) with ground cover ranging from 20 to 55 feet. The tunnel was excavated in multiple headings (initially three, then six). A temporary side wall separated the lead and lagging headings.

The initial lining and pre-support elements included 10-inch-thick fiber-reinforced shotcrete lining, lattice girders/steel sets, welded wire fabric (WWF), self-drilling spiles, grouted pipe spiles, face bolts, and groundwater control. The overburden above the portal structure excavation was cleared and soil-nails and rock bolts with shotcrete and WWF were used as ground support for the portal structure excavations. The tunnel final lining included a waterproofing membrane, a 12-inch cast-in-place lining, a shotcrete final lining in the expanded area and a dividing center wall and elevated platform in the expanded area of the tunnel for future utilities. Pre-support work for the tunnel included roadway removal, excavation, and replacement of fill materials with controlled low-strength material (CLSM), sawcutting, temporary utility support, and surface restoration. LIDAR laser scanning system provided extremely accurate surface and cross-sectional scans, which were used to control the tunnel alignment and profile.  


2021 AGC Build Washington, Heavy/Industrial Project over $20 million