Ground Freezing For Groundwater Cutoff at the Seattle Seawall Replacement Project-Paper

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Ground freezing was used as a groundwater cutoff during Seattle’s seawall replacement, a major project replacing the deteriorated 1930s seawall with a seismically resistant structure. Construction involved excavations about 16 feet deep in highly permeable, debris-filled soils with tidally influenced, often contaminated groundwater. Conventional dewatering in the first two construction sections proved difficult: seepage exceeded several hundred gallons per minute, while pumping, storing, and treating contaminated water was costly.<br /><br />For later sections, contractors installed a frozen-soil barrier along the landside of the excavation. More than 1,400 steel freeze pipes, generally spaced 2.5 feet apart and extending to about 35 feet deep, circulated chilled calcium-chloride brine. The resulting wall was typically 3 feet or more thick. Angled and additional pipes were used around more than 130 buried utility crossings to maintain a continuous barrier without damaging services. Temperature sensors and remote monitoring tracked freezing and system performance.<br /><br />The barrier effectively stopped landside groundwater seepage, reducing inflow to negligible levels and largely eliminating the need to pump and treat contaminated groundwater. It also avoided the settlement risks that conventional dewatering could have caused beneath nearby buildings, utilities, and the Alaskan Way Viaduct. The project demonstrated that ground freezing can provide a flexible and effective groundwater cutoff in complex urban conditions, including areas with dense buried utilities.

Keywords

ground freezing

groundwater cutoff

Seattle seawall replacement

dewatering

contaminated groundwater

freeze pipes

calcium-chloride brine

seawall excavation

urban utilities

seepage control