Survey of Fractured Glacial Till Geotechnical Characteristics: Hydraulic Conductivity, Consolidation, and Shear Strength
Creators:Allred, Barry J.
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Citation:The Ohio Journal of Science. v100, n3-4 (June-September, 2000), 63-72
A literature survey was conducted and fracture influences on engineering behavior of glacial till are summarized, specifically with regard to saturated hydraulic conductivity, consolidation potential, and shear strength. Saturated hydraulic conductivity is increased by fractures, in some cases by two or more orders of magnitude. This in turn results in larger values for the coefficient of consolidation, cv, governing the rate of consolidation. A larger cv corresponds to faster settlement. Modest increases in total settlement occur only if fractures are open. Fractures also have the overall effect of reducing shear strength. Upon removal of surface material by excavation or erosion, stress release and water infiltration lead to further decreases in shear strength. This strength loss process, called softening, is due mostly to a decrease in effective cohesion and usually takes years to complete. Once failure occurs, there is another substantial drop in shear strength to a residual value. This residual strength is a result of realignment of particles along the failure plane during shear, which decreases the effective angle of internal friction. The fracture impact magnitude on glacial till saturated hydraulic conductivity, consolidation potential, and shear strength is determined largely by aperture and spacing characteristics. As the number and/or size of fractures increase, changes in these geotechnical properties become more pronounced.
Author Institution: USDA-ARS Soil Drainage Research Unit
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