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January 10, 2018

In one year, get ready to drive underground through Seattle

Flickr photo from WSDOT [enlarge]

The northbound roadway inside the new waterfront tunnel in Seattle is now 6,000 feet long and two-thirds complete, according to a progress report released this week by the Washington State Department of Transportation.

The northbound roadway sits below the completed southbound roadway (pictured). Its deck is being built with 1,152 precast concrete slabs that are 32 feet wide and 8 feet long. Each tips the scales at 22 tons.

A gantry crane is installing the slabs atop corbels that run down both sides of the tunnel. Slabs are post-tensioned together and bolted to the corbels.

Concrete Technology Corp. in Tacoma built the slabs for the northbound roadway.

The southbound roadway was built with cast-in-place concrete. Only about 1 percent of that portion's lower west wall is left to build, along with about 20 percent of the upper west and east walls.

Crews with the Seattle Tunnel Partners team are installing the tunnel's 16 electrical rooms, which are on the west side of the upper roadway. They also are busy installing mechanical, electrical, fire protection, lighting systems, traffic cameras and electronic message signs.

At the ends of the tunnel, the south launch pit is 98 percent finished and the north disassembly pit, where the tunnel boring machine Bertha was removed, is 80 percent finished.

A Twitter post by WSDOT says STP is running two crews at the north portal in 10-hour shifts per day, with just Sundays off.

The tunnel is expected to open in early 2019. After that, WSDOT will begin demolishing the aging Alaskan Way Viaduct that the tunnel replaces.