Sound Transit wraps up Bellevue tunnel excavation

Sound Transit's contractors late last week completed excavation of a light-rail tunnel in Bellevue, Washington, that will connect two stations on the East Link extension.

Using the sequential excavation method (SEM) process, crews completed the tunnel excavation in 15 months, which was five months quicker than forecasted, Sound Transit officials said in a press release.

The method employs conventional equipment such as track-mounted excavators and cutting equipment to remove soil in small sections. The SEM process also supports excavated areas with spray-applied concrete.

Atkinson Construction — Sound Transit's contractor — used observational methods and numerical modeling to adapt its excavation to different ground conditions in different areas of the tunnel. That enabled crews to complete the work safely and efficiently, agency officials said.

Sound Transit began the excavation in February 2017.

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, via Interstate 90. The project includes building light-rail track on a floating portion of I-90 across Lake Washington.

Trains are expected to begin rolling on the East Link extension in 2023.