The $2B tunnel project for the replacement of the Alaskan Way Viaduct crossed a major hurdle with the approval of a document that will allow the environmental studies for the project to continue. Mayor McGinn’s position is that more time was needed to evaluate the document and he was concerned that a tunnel option was a predetermined outcome of the study. He went even farther by alleging that WSDOT and the City Council conspired to ‘violate the city charter [regarding separation of powers] and state law’. Nevertheless, Councilman Conlin signed the document allowing WSDOT to continue their progress towards a construction contract in early 2011. [Source: Seattle Times Newspaper. Image: Seattle Times]
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Voids Open as a Result of Tunneling Under Seattle’s Beacon Hill
The Seattle Times (hat tip to ASCE SmartBrief) has reported that seven voids have been discovered above the Beacon Hill Tunnel with one opening up at the ground surface. The tunnel is being constructed by Sound Transit, the area’s transportation agency as part of a roughly $2.6 billion (yep, billion) light-rail project connecting downtown Seattle with the University of Washington and SEA-TAC airport. The voids were a result of running sand pockets in the otherwise stable clay units that were encountered by the tunnel boring machine or TBM. These voids migrated up like a chimney with one reaching the surface, almost 160-ft above the tunnel. This void was apparently 21-ft deep and opened up in a resident’s front yard and could have easily swallowed her up as she noticed it while gardening. The other voids were discovered at a depth of 20- to 65-ft below the ground surface. More after the break. (Illustration from Seattle Times)