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Engineers to Begin Surveying 300 Buildings as Precaution to Viaduct Tunnel Boring

July 30, 2009 by  
Filed under Downtown (MLS Area 701), Featured

Washington State Department of Transportation (WSDOT) has already begun pre-construction work for the underground viaduct this month, and will now be doing surveys on an approximate 300 buildings to avoid any adverse affects during construction. During this time, above-ground conditions will also be noted for assisting the contractor to design the tunnel-boring machine.

The surveys will be used to determine how much settlement or horizontal movement could occur during the construction of the tunnel, then used to recommend assessments to prevent damage. Apparently WSDOT will be drafting reports over the next several weeks, but final proposals are not scheduled to be issued until next March. Engineers will be meeting with building managers to get information about the building, then taking visual surveys, notes, and taking photos. Therefore, there will more than likely be no disturbances.

There’s still a couple years before the boring machine begins to drill. WSDOT doesn’t expect boring to start until 2012 where they will start near the stadiums, then exit north of the Battery Street Tunnel by 2013. Here’s an animated video of what the new viaduct will be like as if you were driving north, then there’s a flyover of Alaskan Way coming back South:

We imagine that the biggest concern is if the tunnel boring machine will cause any damage to buildings. The best response WSDOT has at this time is that they will be “taking precautions to mitigate [the] potential impacts.” There are also concerns about settlement. However, Seattle has already had successful ground excavations and there’s some familiarity with the soil.

The ground conditions along the proposed tunnel route include soft soils at the tunnel’s southern entrance, then hard and dense glacier-deposited soils for the remainder of the alignment and at the north entrance. Numerous tunnel projects in Seattle, such as the BNSF rail tunnel and Metro’s transit tunnel, have successfully excavated ground conditions similar to those anticipated for the SR 99 bored tunnel.

WSDOT has also provided an interactive Google Map that shows the location and schedule for each geotechnical drilling.

View Alaskan Way Viaduct and Seawall Replacement Program in a larger map