Engineers: Crews making good progress on new Bellevue light rail tunnel

Photo: KOMO News

BELLEVUE, Wash. -- The opening of Sound Transit’s East Link light rail extension is still years away, but crews say they're making good progress on tunnel excavation work underneath downtown Bellevue.

The tunnel will run between two future light rail stations at East Main and another near Bellevue City Hall. Construction inside the tunnel has advanced more than 700 feet, crews told reporters during a tour on Tuesday afternoon.

"We’ve just excavated and supported the top heading 4 foot, 3 inches," said Jake Coibion, tunnel manager for Atkinson Construction.

As crews dig, engineers pointed out the pressurized concrete called “shotcrete” that’s sprayed on the tunnel’s perimeter.

"This is pieces of fiber. This is fiber-reinforced. You can see even though it’s cracked, it still holds together. The purpose of the fibers is to hold it together. It makes it much stronger," said resident engineer Ted DePooter.

A truck soon brings in a load of lattice girders made from steel reinforced bars to make sure the tunnel stays secure.

"This over-consolidated glacial till here in Bellevue is not very wet," Coibion said. "Very, very consolidated and dense. So, it stands up pretty well. So, it allows us to go a pretty quick pace."

So far, crews have excavated about one-third of the 2,000-foot tunnel since work began in January.

"Because of the fact that this tunnel is fairly short, it’s not worth the expense to set up a tunnel boring machine and bore it with that. So we’re going through with this method," said DePooter. "Perfectly suited to go between buildings in downtown Bellevue."

The tunnel is part of Sound Transit’s project to extend light rail service from downtown Seattle to the Overlake area of Redmond.

Once the work is done, trains will travel over Lake Washington on the Interstate 90 floating bridge and stop at 10 new stations on the Eastside, including one near Bellevue City Hall.

At 3 to 4 feet each day, crews are expected to break through that end of the tunnel by the end of next year or early 2019, they said.

"Once you start, you can’t stop it until it’s completely supported," Coibion said. "So, when we start a week, we continue for 24 hours a day and then we stop on Saturday nights."

The entire East Link line is set to open in 2023. The following year, it’ll extend further east to new stations in southeast Redmond and downtown Redmond.

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