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July 24, 2006

Keeping tunnel site dry would be challenge for viaduct team

  • Planners working on the tunnel option have budgeted $30 million to $40 million for dewatering.
    • By JOHN C. RYAN
    Journal Staff Reporter

    Photo by Sam Bennett
    Downtown Seattle’s steep slopes put groundwater beneath the viaduct under greater pressure than is found in flatter areas.
    Dealing with groundwater would be one of the main difficulties of building a tunnel to replace the Alaskan Way Viaduct.

    Crews digging a tunnel up to 85 feet below the Seattle waterfront would hit two aquifers that drain the steep hills of downtown: one shallow and connected to the tides, and one deep and pressurized. Loose soils, like the fill beneath most of the waterfront, and groundwater can easily add up to slope failures and slides.


     
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