Sound Transit has announced that work on its East Link light-rail tunnel is nearly complete, and crews are set to break through to the site of the future Bellevue Downtown Station in mid-July.
Crews are on track to complete the tunnel within 15 months, putting the project five months ahead of the forecast included in the project’s baseline construction schedule, Sound Transit said.
Tunnel construction is being performed through a process referred to as the Sequential Excavation Method (SEM), which uses conventional equipment including an excavator and cutting equipment to remove soil in small sections or bites.
This method provides several advantages for the Bellevue project as opposed to the use of a tunnel-boring machine or digging a large cut-and-cover trench, Sound Transit said. The benefits include minimizing disruption to traffic, reduced noise and dust impacts to neighboring residents and businesses, and the reduction of utility service disruptions.
The method also implements sophisticated continuous monitoring, enabling crews to react to changing ground conditions as they occur and boosting safety and efficiency, the agency said.
Following removal of soil, crews spray shotcrete on the sides of the tunnel, as well as its ceiling and floor. They also install arc-shaped lattice girders to provide additional structural support for the tunnel.
The transit agency released video footage, below, of the final excavation work in progress showing the excavation of a segment of the tunnel using the SEM method.
Sound Transit notes crews have been working on the tunnel since February 2017.
Excavation work began at the south portal site at 112th Ave. NE and Main, and when complete, will be span about one-third of a mile long, running between the future East Main and Downtown Bellevue stations under 110th Ave. NE, turning east near NE 6th St.