Current projections put the project completion 35-months behind schedule because of problems with a portion of the TBM constructed tunnel. The County is suing for $74M in damages associated with the delays. This massive sewer project involves the construction of a 13- to 14-mile treated waste pipeline constructed by TBM at depths of 40 to 440-ft. You can also see previous GeoPrac coverage of this project and its cost overruns, also here and here. [Source: SeattlePI via ASCE SmartBrief. 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)
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