Sound Transit marks progress on East Link tunnel

Sound Transit is one-third finished with construction of its East Link light-rail tunnel under downtown Bellevue, Washington, the agency announced Tuesday.

Crews continue to excavate at the south portal site at 112th Avenue Northeast and Main Street in Bellevue. When completed, the 2,000-foot tunnel will connect the future East Main and Downtown Bellevue stations.

Because of the tunnel's short length, Sound Transit is building the tunnel using the "sequential excavation method" (SEM) instead of using a tunnel boring machine. SEM requires the removal of soil in small sections using an excavator and support equipment, agency officials said in a press release.

After the soil is removed, pressurized concrete is sprayed on the tunnel's perimeter, and lattice girders provide additional support for the tunnel. This method is expected to minimize disruption to motorists and pedestrians, reduce noise and dust impacts, and decrease utility service relocation.

Earlier this year, Sound Transit began building the light-rail tunnel in Bellevue.

The $3.7 billion East Link project will extend light-rail 14 miles from downtown Seattle to downtown Bellevue and the Overlake area of Redmond, Washington.