Finishing excavation five months earlier than expected allowed Atkinson Construction, even during delays brought on by the pandemic, to complete construction of a 1,985-ft-long tunnel in downtown Bellevue for Sound Transit on time.
With substantial completion of the civil construction portion of the tunnel connecting the East Main and Bellevue Downtown stations, work will now shift to a team of Stacy and Witbeck/Atkinson to finish installing track inside the tunnel.
The project is part of the $3.7-billion, 14-mile, 10-station East Link extension, planned for a 2023 opening, that extends light rail from downtown Seattle to downtown Bellevue. The track will go across the Interstate 90 floating bridge and connect to key alignments, such as the tunnel, in Bellevue.
The tunnel runs under 100th Avenue Northeast and turns east near Northeast Sixth Street to emerge at the Bellevue Downtown Station. “This tunnel represents Sound Transit’s commitment to a local plan that prioritized the best transit connection through downtown Bellevue,” said Claudia Balducci, Sound Transit board member and King County council chair, in a statement.
Planning started a decade ago on the tunnel, while excavation began in 2017. “Atkinson was our prime contractor and they did a really good job on delivering that work,” says Mike Bell, Sound Transit senior executive project director.
The 1,985-ft-long tunnel was short enough that a tunnel-boring machine wasn’t needed. Using the sequential excavation method, Atkinson crews relied on conventional equipment, such as track-mounted excavators and cutting equipment, to remove 72,000 cu yd of soil in small sections and then support excavated areas with spray-applied concrete. Next steps included applying waterproofing materials, construction of a center wall and final concrete lining.
The finished tunnel is 27 ft, 10 in. high and is 34 ft in width, split into two sides with a concrete dividing wall.
Sound Transit is busy extending light rail throughout the Puget Sound. The Northgate Link is scheduled to open in 2021 and the Tacoma Link Hilltop Extension in 2022. East Link is planned for 2023 and an additional 3.4 miles east to new stations in Southeast Redmond and downtown Redmond should open in 2024. Links to Lynwood and Federal Way are also scheduled for 2024 openings.
“These historic investments will finally give us the true mass transit network the Puget Sound region has sought for more than half a century,” says Peter Rogoff, Sound Transit CEO, in a statement. “They will more than double our current reach and simultaneously help fuel our region’s economic recovery.”