Seattle Tunnel Construction in High Gear

The SR 99 tunnel is moving a portion of the north-south state highway underground. A tunnel launch pit that is 400 feet long and 80 feet deep has been built.

Road construction in Seattle and Washington state is in high gear this month, with a major tunnel project under way in the city and contractors beginning work Aug. 6 to demolish a 77-year-old bridge and construct the replacement span.

Seattle Tunnel Partners is the design-build contractor for the SR 99 tunnel, a two-level project that is part of the Alaskan Way Viaduct Replacement Program. The existing SR 99 Alaskan Way Viaduct along the Seattle downtown waterfront is coming down, with the bored tunnel beneath downtown Seattle replacing it. Environmental and other approvals for the project were secured in 2011. A tunnel launch pit that is 400 feet long, 80 feet deep, and 80 feet wide has been built for the project.

When the tunnel is completed, it will open more than nine acres of public space along the waterfront. The viaduct is at risk of failing in earthquakes, according to the Washington State Department of Transportation.

WSDOT is building several new highway bridges this year, as well, including the $8.8 million US 101 Bone River Bridge demolition and replacement project starting Aug. 6. on Willapa Bay, with a new bridge that can withstand coastal flooding and a 1,000-year earthquake event set to open in 2014. Other bridges are being built on US 101 and SR 105 using funds from a 2005 gas tax package and pre-existing state funds, according to WSDOT.

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