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Title: Soil freeze-thaw effects on bank erodibility and stability
Authors: Gatto, Lawrence W.
Keywords: Bank erosion
Ground ice
Soil instability
Publisher: Cold Regions Research and Engineering Laboratory (U.S.)
Engineer Research and Development Center (U.S.)
Series/Report no.: Special report (Cold Regions Research and Engineering Laboratory (U.S.)) ; 95-24.
Description: Special Report
Abstract: When air temperature is below ground temperature, a thermal gradient is established in the soil that causes the soil to lose heat to the atmosphere. When the soil has lost sufficient heat for soil water to freeze, the newly formed ice changes soil structure by disaggregating, separating, and reorienting soil particles. The suction set up within the freezing soil draws water to the freezing zone through the film of unfrozen water surrounding soil particles, supplying additional water for freezing, so the volume of ice increases. When appropriate thermal and water supply conditions are in place, disseminated ice lenses can form in the soil. As the ice lenses grow, the soil surface is heaved in the direction of heat flow from the soil. Soil particles can be displaced down a bank face when surface ice in heaved soil melts. The amount of ice in a frozen soil by the end of winter can be higher than its water content when unfrozen. Thus, upon thawing, the previously frozen soil temporarily has an excess of soil water and a disrupted soil structure, which significantly reduces internal friction and cohesion and reduces the soil’s shear strength. In this weakened state, thawed bank soils are usually more easily eroded by raindrop impacts, overland flows, river and lake ice forces, currents and waves, and are highly susceptible to mass failures. In some instances newly thawed soils are weaker than at any other time of the year. Some studies show that processes related to bank soil freezing and thawing cause more bank recession annually than other processes in areas where seasonal frost forms. However, with time, the strength of the thawed soil returns as excess water drains from the soil, and soil particle packing and interlocking increase. Thus, frost-induced reductions in soil strength and soil particle displacements must be included in bank migration and bank erosion models to be applied in regions with seasonal soil frost.
Rights: Approved for public release; distribution is unlimited.
Appears in Collections:Special Report

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