Light rail takes a leap forward in Bellevue

On Friday, Sound Transit finished a major milestone in bringing light rail to Bellevue: excavating a tunnel under the city's downtown. 

The arrival of rail on the east side will fundamentally change the map of the region, Sound Transit CEO Peter Rogoff said. Bellevue is known for its car-centered culture, so getting light rail here by 2023 required compromise—and risk on the part of some of Bellevue's political leaders.

"Eastlink," the name for Sound Transit's Eastside 10-station expansion, faced early resistance in Bellevue. Local leaders didn't want the surface track to disrupt their city, so they lobbied hard for an underground tunnel. The city got that tunnel and paid for it too, donating $100 million in land and more to Sound Transit. It covered about half the cost of the tunnel.

Most Seattle-area tunnel afficionados are familiar with tunnel boring machines, such as Seattle's infamous "Bertha." In comparison to Seattle's downtown, deep-bore tunneling project—plagued with delays and litigation—the method used to excavate the relatively short 2,000-foot tunnel under Bellevue's downtown seems quaint.

The method boils down to this: Dig a little bit, look at the walls, reinforce them if you need to, dig a little more. Austrians developed the method in the 1970's because of unpredictable soil conditions in the Alps. Solid rock, pockets of gravel—you never know what you'll hit. You just have to make it up as you go along.

In comparison to the Alps, digging through the glacial till underneath downtown Bellevue was a piece of cake, according to Austrian engineer Walter Klary. He was flown in from overseas to monitor the project.

Contractors lucked out with the dry spring, and digging concluded six months early. Sound Transit CEO Peter Rogoff said his only worry now is whether the extra California-built trains he ordered will be finished when the track is ready to open in five years.