Sound Transit East Link Tunnel Construction is Underway in Downtown Bellevue

Feb. 26, 2017
Sound Transit briefed elected officials and media on East Link light rail tunnel construction that is now underway in downtown Bellevue.

Sound Transit briefed elected officials and media on East Link light rail tunnel construction that is now underway in 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. SEM removes soil in small sections or bites using an excavator and cutting equipment. As soon as soil is removed, pressurized concrete, called shotcrete, is sprayed on the tunnel's sides, ceiling and floor. Lattice girders provide additional structural support for the tunnel. Advantages of SEM include minimizing disruption to traffic, reduced noise and dust impacts to neighboring residents and businesses versus cut-and-cover tunnel construction, and elimination of utility service disruptions.

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) is 34 feet.
    • Each side is 16 feet, 3 inches wide, with a center dividing wall.
  • Tunnel is 30 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 permitting, 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. By the end of 2017, all segments of the East Link extension will be 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 in 2023 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 approximately 600,000 riders each weekday.

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Sept. 26, 2013