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Crews Strengthen the Viaduct to Prepare for Tunnel Machine

FROM THE DJC

March 22, 2012

By Journal Staff

Seattle Alaskan Way Viaduct under construction-1952

Crews are getting ready to wrap a section of the Alaskan Way Viaduct’s support columns in carbon-fiber to bolster the against earthquakes and a tunnel boring machine that will pass below.

The work will require closing the viaduct this weekend and the weekend of April 7-8.

“It’s like wrapping an injured ankle,” said Matt Preedy, WSDOT Alaskan Way Viaduct Replacement Program deputy administrator, in a statement. “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.”

Reinforcing the viaduct is a multi-step process. It starts with sandblasting a half-century of grime from damaged areas along a two-block section between South Washington and Columbia streets in Pioneer Square.

Before the wrap goes on, crews will fill cracks in the concrete and round out corners where the concrete is spalling. Exposed rebar will be cleaned and fresh concrete will be placed in the spalled areas. Most of the work this weekend is cleaning.

Wrapping the columns will happen during the second weekend closure. A WSDOT spokesman said if wrapping takes longer it could mean partial viaduct closures in the future.

A few other sections of the viaduct already have been wrapped. The latest work will wrap the upper horizontal arches of several column pairs that join in an inverted U-shape to support the road deck.

WSDOT is also installing micro piles to stabilize the ground the columns rest on. That work started last month and is expected to be finished in June.

Seattle Tunnel Partners, the joint venture building the replacement tunnel, is in charge of the wrap and micro-pile operations. Its tunnel boring machine is expected to travel 80 feet below the reinforced section of viaduct late next year. WSDOT and the Seattle Department of Transportation are squeezing in some other work while the viaduct is out of service: WSDOT will inspect it for cracks, settlement and shifting; SDOT will re-strip the road deck.

The WSDOT spokesman said the viaduct was last inspected in October, when engineers found mild settlement near Columbia Street. Preliminary results from this weekend’s inspections are expected April 10.

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