East Link downtown Bellevue tunnel excavation is one-third complete

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Tunnel construction has advanced more than 700 feet of the total 2,000-foot length, and turned north under 110th Ave. Northeast

Sound Transit today briefed media on East Link light rail tunnel construction that is now one-third complete under downtown Bellevue.

Crews are excavating at the south portal site at 112th Ave. Northeast and Main. When complete, the tunnel will be approximately one-third of a mile long, running between the future East Main and Downtown Bellevue stations under 110th Ave. Northeast, turning east near Northeast 6th Street. 

Because of the short tunnel length, and to minimize impact on neighboring homes and businesses, Sound Transit is constructing the tunnel using the Sequential Excavation Method (SEM) rather than using a tunnel boring machine or digging a large trench that is later covered (cut-and-cover tunnel construction). SEM removes soil in small sections or bites using an excavator and support equipment. As soon as soil is removed, pressurized concrete, called shotcrete, is sprayed on the tunnel’s perimeter. Lattice girders made from steel reinforcing bar provide additional structural support for the tunnel. Advantages of SEM include minimizing disruption to traffic and pedestrians, reduced noise and dust impacts to neighboring residents and businesses compared to cut-and-cover tunnel construction, and significant reduction of utility service relocation and associated disruptions. A video of the tunnel excavation process can be viewed at vimeo.com/229918007

Tunnel facts:

  • Tunnel is approximately 2,000 linear feet long, or approximately one-third of a mile.
  • Height of the tunnel is 27 feet, 10 inches.
  • Overall width (north and south-bound sides together) is 34 feet.
    • Each side is 16 feet, 3 inches wide, with a center dividing wall.
  • Tunnel is between 12 to 60 feet below the surface.
  • Excavation is expected to progress at approximately three to four feet per day.

The tunnel’s inclusion in East Link project was enabled by City of Bellevue in-kind contributions of $100 million, including property and permits, formalized in an MOU executed by the Sound Transit Board in April, 2015.

East Link will extend light rail 14 miles from downtown Seattle to downtown Bellevue and the Overlake area of Redmond via Interstate 90, with 10 stations. All segments of the East Link extension are currently under construction, and the entire line will be operational in 2023. The following year Sound Transit will open a 3.7-mile extension further east to new stations in Southeast Redmond and downtown Redmond under funding approved in November 2016.

The Northgate Link light rail extension that is currently under construction will reach Seattle’s University District, Roosevelt and Northgate areas in 2021. Additional Link extensions that are nearing construction will reach north to Lynnwood and south to Federal Way in 2024. Later extensions to form a 116-mile regional system will reach Everett, Tacoma, West Seattle, Ballard, South Kirkland and Issaquah. By 2040 Sound Transit projects Link trains will carry between 480,000 to 590,000 riders each weekday.

For more information on the East Link Extension see: www.soundtransit.org/Eastlink