Sound Transit wraps up Northgate extension tunnel mining

Sound Transit has completed tunnel mining on its Northgate extension.

Sound Transit

Sound Transit has announced that contractors have completed mining the final of six tunnel segments along the Northgate Link Extension twin tunnels.

The completed work is part of the $1.9 billion Northgate Link project and includes seven miles of tunneling. Representatives say cross passages and other work is ongoing inside the new tunnels.

“In just a few years, light-rail riders will be enjoying fast, frequent, congestion-free service to the U-District, Roosevelt and Northgate,” said Sound Transit Board Chair and King County Executive Dow Constantine. “By this time next month, we’ll have opened the Angle Lake station in SeaTac, our third new station in six months. These are just two examples of Sound Transit’s steady progress as we work to expand light rail throughout the Central Puget Sound region.”

The work involved in this contract is set for completion in 2018, and representatives say the next steps for work inside the tunnels includes the installation of communications systems, rails and track beds. The project is meant to extend light-rail service 4.3 miles north from the University of Washington to a station adjacent to the Northgate Mall.

The newly finished work is the final tunnel segment to be mined by JCM Northlink LLC, a joint venture of Jay Dee Contractors, Frank Coluccio Construction Company and Michels Corporation. Officials say JCM will continue to dig 23 cross passages between tunnels intended as emergency evacuation routes that are set to be equipped with controls for electrical and mechanical systems.

Crews are expected to break ground on the three Northgate Link extension’s stations “soon,” with work on the Northgate Station slated to take place this fall, officials say. The Roosevelt and U District neighborhoods are set to see the construction of underground stations beginning in 2017.

Trains will travel through the tunnels via the Maple Leaf Portal at First Avenue Northeast and Northeast 95^th when light-rail service on the Northgate Link extension begins—an expected start date sometime in 2021, representatives say.

Officials say two 600-ton tunnel boring machines have excavated more than 500,000 cubic yards of soil and installed 7,352 concrete tunnel liner rings in the roughly two years since the work began in 2014.