Seasonal Creep of Silty Clay Soil and the Formation of Small Gullies.
Final rept. Jun 75-May 77,
STANFORD UNIV CA LAB FOR RATIONAL GEOMECHANICS
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This report summarizes a two-year investigation of seasonal creep in a black silty clay soil that is common in the San Francisco Bay Area. Because of drought during the two years, the soil did not become entirely saturated and there apparently was no creep, so that field instrumentation provided no new data on creep rates. Nevertheless, much data was obtained on seasonal changes of the soil and on displacements produced by shrinking and swelling of the soil. The data indicate that directions and magnitudes of horizontal displacements of soil that occur between a wet and a dry season are controlled by the positions and attitudes of nearby shrinkage cracks. These displacements, averaged over a large area, are therefore random. During the wet seasons wetting of the soil occurred along an irregular front advancing from the ground surface. The wetting front advanced more rapidly in debris that had filled shrinkage cracks than in the soil in polygons surrounded by shrinkage cracks. Many of the features of seasonal creep of the silty clay soils can be understood in terms of a theoretical model that utilizes rate process theory. Three essential features of creep of this soil are that the creep displacement profile is convex upwards, that creep begins shortly after initial wetting of the soil, and that creep eventually stops without obvious changes in water content.
- Soil Mechanics