The Alaskan Way Viaduct and a few blocks of Fairview Avenue North will close on alternate weekends.

Share story

The Alaskan Way Viaduct will close this weekend so workers can sandblast, patch, glue and wrap nine overhead beams.

The goal is to lower the risk that vibrations from a tunnel-boring machine loosen concrete pieces of the old viaduct, so they won’t rain down on drivers or pedestrians.

The giant 57.4-foot-diameter drill will launch in mid-2013 from Sodo and burrow diagonally under the viaduct foundations, then continue beneath Pioneer Square and downtown. A new four-lane tolled tunnel to South Lake Union is scheduled to open at the end of 2015, part of a $3.1 billion viaduct replacement.

This weekend’s viaduct closure will include routine inspections and lane striping. Four columns near the ferry terminal have sunk 5 ½ inches since the 2001 Nisqually earthquake, but were reinforced in 2008 by inserting thin steel rods into the soil alongside.

Similar rods are being driven into other columns to prepare for tunneling vibrations, said Travis Phelps, spokesman for the state Department of Transportation.

Repairs will be done on nine horizontal crossbeams that support the southbound and northbound decks. Weekend closures are needed to remove loose concrete, to sandblast any rust from exposed steel rebar, then to apply concrete patches.

The actual wrapping, with grayish carbon fiber, will be completed later, requiring only limited nighttime lane closures.

Meanwhile, two weekend closures are coming soon to Fairview Avenue North where it meets the two-way Mercer Street reconstruction site.

The viaduct and Fairview closures are on alternate weekends:

• 6 a.m. Saturday until 5 a.m. Monday, Highway 99 closes in both directions from the Battery Street Tunnel to the West Seattle Bridge.

• 7 p.m. Friday, March 30, until 5 a.m. Monday, April 2, Fairview closes from Republican to Mercer streets.

• 11 p.m. Friday, April 6, until 5 a.m. Monday, April 9, Highway 99 closes in both directions from Battery Street Tunnel to the West Seattle Bridge.

• 7 p.m. Friday, April 13, until 5 a.m. Monday, April 16, Fairview closes from Republican to Mercer streets.

Mike Lindblom: 206-515-5631 or mlindblom@seattletimes.com. On Twitter @mikelindblom.