Crews will close the State Route 99 Alaskan Way Viaduct for two of the next three weekends to inspect the structure and reinforce a two-block section located above the path of the future SR 99 tunnel.

Both directions of SR 99 between the Battery Street Tunnel and the West Seattle Bridge will close from 6 a.m. Saturday, March 24, to 5 a.m. Monday, March 26. Crews will use the closure to inspect the viaduct and ensure it remains safe for drivers. WSDOT will release preliminary inspection results on Tuesday, April 10.

In addition to structural inspections and routine maintenance, crews building the SR 99 tunnel will begin reinforcing the viaduct between South Washington and Columbia streets in Pioneer Square. An additional full-weekend closure in April will be necessary to complete their work, which must occur before the world’s largest diameter tunnel boring machine passes beneath the structure in late 2013.

Viaduct closure details:

Both directions of SR 99 between the Battery Street Tunnel and the West Seattle Bridge will close from 6 a.m. Saturday, March 24, through 5 a.m. Monday, March 26.

Both directions of SR 99 between the Battery Street Tunnel and the West Seattle Bridge will close from 11 p.m. Friday, April 6, through 5 a.m. Monday, April 9.

Drivers should expect increased congestion in and near downtown Seattle during these closures and plan accordingly. WSDOT recommends leaving early, carpooling or taking transit. Drivers can check traffic conditions before they leave at http://www.wsdot.wa.gov/traffic. Up-to-the-minute traffic information is also available via the voice-activated driver information line, 511.

Reinforcing the viaduct
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The reinforcement work that starts this weekend and continues in April is a multi-step process. First, crews will sandblast a half-century of dirt and grime from damaged areas along a two-block section of the structure. Next, they will smooth corners of the bridge supports to prepare for the final step – wrapping the viaduct’s concrete in a protective reinforcing fiber.

“It’s like wrapping an injured ankle,” said Matt Preedy, WSDOT Alaskan Way Viaduct Replacement Program deputy administrator. “Reinforcing this section allows us to keep the viaduct safely open to traffic while we build the tunnel, but ultimately this is a short-term fix because the underlying structure remains at risk to earthquakes.”

The tunnel will be about 80 feet underground when it passes beneath the viaduct. In addition to the reinforcing fiber wrap, tunnel crews are building underground walls beneath the viaduct’s foundations to further protect it during tunneling.

The SR 99 tunnel boring machine is designed specifically for the soil and groundwater conditions along the tunnel alignment. Although tunneling crews do not anticipate significant levels of ground settlement, they are monitoring structures above and near the tunnel route as a precaution.

For more information on the Alaskan Way Viaduct Replacement program, visit http://www.alaskanwayviaduct.org/.