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The zone of expansion, formed on a wetted surface of a potentially dispersive clay, is modeled as a dilute clay slurry. This allows existing data from rheological studies of clay slurries to aid the understanding of the failure mechanism of dispersive clays.
Dispersive erosion is visualized as requiring three conditions: a passageway filled with flowing water, a zone of expansion on the wetted surface of the soil forming the walls of the passageway, and sufficient shear stress applied by the flowing water in the passageway to exceed the shear strength of the zone of expansion. Shear strength limits for dispersive, intermediate, and nondispersive soils are determined from an analysis of the pinhole dispersion test. The relative effects on the shear strength of the zone of expansion due to varying clay mineral type, predominant cation, slurry clay concentration, and electrolyte concentration are examined. Explanations are offered for anomalies in current chemical-empirical criteria for defining dispersiveness.
clays, dispersions, geology, rheology, shear stress, slurries, soil chemistry, soil mechanics, soil structure, testing
Geotechnical engineer, Hoskins-Western-Sonderegger, Lincoln, Nebr.