Aggregation in swelling clay soils

Abstract

Dry sieving, wet sieving, and aggregate bulk density measurements were used to study the mechanisms of dry aggregate formation in three swelling clay soils. These experiments showed that, for a given soil, a single probability function can be used for all dry aggregate fractions to predict their water stability and the distribution of water stable aggregates in their unstable portions. This result is explained in terms of the mode of formation of dry aggregates. Coarse aggregation in these soils was attributed to the binding action of dispersed clay. Soil disruption experiments showed that, above a certain moisture content, soil samples were susceptible to disruption by mechanical action. This moisture content is linearly related to the specific surface area of the soil, and agrees closely with the soil liquid limit. Aggregate disruption in the coarsely aggregated soil sample is explained in terms of soil mineralogy and electrolyte concentration. The effect of rate of reflocculation of disrupted clay on soil aggregation is considered.