Progressing 3.5 to 5 feet a day on average, crews working on the East Link light rail tunnel have completed 700 of the 2,000 feet of tunnel that will eventually connect the future East Main and Downtown Bellevue stations under 110th Ave.
Due to the short tunnel length, approximately one-third of a mile, the tunnel is being constructed using the Sequential Excavation Method (SEM) rather than using a tunnel boring machine. As the soil is removed in small sections, pressurized concrete, known as shotcrete, is sprayed onto the tunnel’s sides. Steel lattice girders are added to give additional support as the shotcrete is drying. A waterproof layer will then be added, followed by a thicker layer of shotcrete.
A video by Sound Transit shows the tunnel excavation process in detail.
Crews have worked twenty-four hours a day, six days a week since construction began in late February. Work is expected to continue through the end of 2018.
Workers examine the soil before steel lattice girders are placed.
A piece of shotcrete.
A dump truck removes soil from the south portal of the tunnel. The tunnel’s depth will vary from 12 to 60 feet below the surface.
Chad Frederick, construction manager for Sound Transit.
The tunnel is 27 feet, 10 inches tall and 34 feet wide. A wall will eventually separate the two tracks.
The SEM method can minimize impacts on neighboring homes and businesses.