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Geologic Hazards

Mega Earthquake Could Strike Closer to Seattle

Preliminary results from a study related to the subduction of the Juan De Fuca Plate beneath the North American Plate off the coast of Washington and British Columbia indicate that the potential mega-thrust earthquake could […]

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Project Related

Voids Open as a Result of Tunneling Under Seattle’s Beacon Hill

image 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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Project Related

Rising Costs and Delays in Seattle Area Wastewater Plant and Tunnels

In keeping with our theme of rising costs on tunnel projects, the Brightwater sewage-treatment plant and treated waste pipeline project in King County Washington (Seattle area) is now up to at least $1.84 billion according to the lead consultant on the project. The treated waste pipeline is 13 to 14-miles long and at depths of 40 to 440-ft! It is being constructed nearly entirely by TBM. One source of delay was due to a tunneling subcontractor  not being able to get parts (ball bearings?) because they were all being requisitioned by the US War Department for use in military equipment in Iraq and Afghanistan. Click through for information sources and links. 

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Project Related

Seattle Light-Rail Tunnel Likely to Break Ground This Year

Thanks to approximately $100 million from President Bush’s proposed 2009 budget, the $1.8 billion project creating a light-rail line from downtown Seattle to the University of Washington is likely to break ground some time this year. The project will involve twin bored tunnels on the order of 3 miles in length. It is scheduled to open for use in 2016.

There is another notable tunnel project associated with the Seattle Light Rail, known as the Beacon Hill tunnel which I have blogged about before.

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