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Final filling of Battery Street Tunnel now underway

A look at the partially filled Battery Street Tunnel. (Photo courtesy of WSDOT)

Since the new Seattle tunnel opened 18 months ago, you probably haven’t given a second thought to the old Battery Street Tunnel, but the state is close to finally filling it in.

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Contractors have been hard at work filling in the old tunnel since last December. Most of the fill came from pieces of the old Alaskan Way Viaduct.

“We crushed up the viaduct and put most of it inside the tunnel, the concrete portion not the metal, of course,” said the Washington Department of Transportation’s Laura Newborn.

There is only about seven feet of height left to fill in.

Once that viaduct concrete was compacted into place, contractors have been building a utility corridor on top.

“There are now some major electrical lines and major electrical vaults,” Newborn said. “The crews have protected all the existing utilities, like sewers inside the tunnel, and they are ready to do the final filling.”

Starting this week, the final filling will begin, this time filling from the top. Workers will cut holes in Battery Street where necessary to fill the gap with a very special, lightweight concrete.

“Think of it as a concrete meringue,” Newborn said. “It’s much, much lighter than standard concrete, and it’s very strong, much like those geoform supports that are used for road construction.”

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This lightweight concrete is also easily cut to make any future utility work easier.

There will be some intermittent road closures and other impacts in the area. Newborn said it’s going to take several months to fill the rest of the tunnel. The contractors are mixing the concrete on site, which will eliminate about 4,000 dump truck loads being driven in.

Check out more of Chris’ Chokepoints.

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