Consolidation of an Unsaturated Illitic Clay Soil

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Abstract
Soil stabilizes with time after disturbance as a function of thixotropy and soil water stress. This study was undertaken to delineate the effects of soil water suction history and thixotropy on soil stabilization and effective stress. Unconfined compressive strength, tensile strength, density, and effective stress as a function of water stress history and time were obtained for a Paulding clay soil (very fine, illitic, non acid, mesic Typic Haplaquepts). Compressive strength was five times greater at 64 kPa suction than at 4 kPa suction, and twice as great at 32 d than at 4 d. Density also increased with suction and time. Compressive strength at 2 kPa suction was 1.8 and 3.2 kPa for prestress suctions of 4 and 32 kPa, respectively; and was 4.4 and 8.9 kPa for prestress suction of 64 kPa after 4 and 32 d, respectively. Prestress and time had no effect on tensile strength apparently because no volume change was allowed. The data supported the hypothesis that strength in unsaturated soil was controlled by soil water stress history. Prestress due to drying induced bonding, which persisted after suction was released if volume change was not restricted. Effective stresses due to soil water suction were greater for strength than for volume change and were influenced by soil structure for the case of strength, but not for the case of volume change.

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