Seattle’s public transit agency Sound Transit in the US has announced that civil construction of the East Link Bellevue tunnel is now substantially complete.

The tunnel structure is now complete while the installation of track and systems will continue.

Atkinson Construction completed the excavation and construction works a few months early, which helped the project to remain on schedule despite Covid-19-related delays.

Once complete, the Bellevue tunnel will connect the East Main and Bellevue Downtown stations as part of the East Link extension.

Sound Transit board member and King County Council Chair Claudia Balducci said: “Ten years from planning, through excavation to substantial completion, this tunnel represents Sound Transit’s commitment to a local plan that prioritised the best transit connection through downtown Bellevue.”

The excavation works commenced in 2017 using a process known as the sequential excavation method (SEM).

The workers used conventional equipment to remove soil in small sections and supported excavated areas with spray-applied concrete. Subsequently, waterproofing works and the construction of the centre wall and final concrete lining was carried out.

The 14-mile-long East Link will comprise ten stations stretching from downtown Seattle to downtown Bellevue and the Overlake area of Redmond via the I-90.

The project is slated to commence operations from 2023.

Sound Transit CEO Peter Rogoff said: “East Link’s opening in 2023 will be preceded in 2021 by Northgate Link and in 2022 by the Tacoma Link Hilltop Extension. One year later, in 2024, we will extend Link to downtown Redmond, Lynnwood and Federal Way.

“These historic investments will finally give us the true mass transit network the Puget Sound region has sought for more than a half-century. They will more than double our current reach and simultaneously help fuel our region’s economic recovery.”