Bellevue Light Rail Tunnel: Sound Transit Wants To Avoid Disruptions

BELLEVUE, WA – If Sound Transit kept it a secret, you might not know that crews are busy digging a tunnel underneath downtown Bellevue right now.

Well, that might be an exaggeration - but Sound Transit is using a tunneling method meant to minimize disruptions.

Construction of the light rail tunnel underneath downtown Bellevue from East Main Street to Northeast 6th Street near City Hall kicked off last Friday, and crews will dig the tunnel using the “sequential excavation” method.

The tunnel will be dug in small bites using heavy equipment. After removing soil, the tunnel walls will be sprayed with pressurized concrete – “shotcrete” – and then girders will be added to support the structure. This method is less disruptive and messy than “cut and cover," which involves digging a trench and then covering it after construction. Crews won't have to dig up roads or move utilities, and truck traffic will be lower because less soil overall is being removed.

“This method was chosen to avoid major disruptions,” Sound Transit spokesperson Rachelle Cunningham said.

But it may take a little longer. The 2,000-foot-long Bellevue tunnel will move at a pace of 3 or 4 feet per day. By comparison, Bertha, the Seattle tunnel boring machine, moved at a pace of about 30 feet per day in February.

And although the tunnel construction will be less disruptive, you likely will notice it. The ground may vibrate during construction, Cunningham said, and there may be a few traffic detours.

The East Link rail line will extend service from Mt. Baker in Seattle to Mercer Island, through downtown Bellevue, and up to Redmond. The $3.7 billion East Link line is expected to be complete by 2023.

You can see a diagram of how the tunnel will be built here.

Image via Sound Transit