Subplasticity in Australian soils. III. Particle size properties of soil materials of varying plasticity

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Abstract
Soil materials from the Riverina, N.S.W., ranging from superplastic to highly subplastic on field criteria, were disaggregated by various mechanical and chemical methods. Of these methods, an ultrasonic probe proved to be the most successful in disaggregating subplastic soils. The behaviour of soils under this treatment was consistent with their field plasticity rating. Chemical treatments such as hydrochloric acid for carbonate enriched soils and sodium dithionite for the removal of iron oxide were unsuccessful in disaggregating subplastic soils. Detailed particle-size analyses showed that superplastic and normal plastic soils were readily disaggregated with gentle methods, and only minor changes occurred in their particle-size distributions with prolonged ultrasonic treatment. In particular, the fine clay fractions of these soils were readily released. Soils with subplastic properties showed an increasing stability of silt-size aggregates with increasing subplasticity and a corresponding difficulty in the release of fine clay. It was concluded that subplasticity in these soils is closely associated with the presence of a fine clay fraction, a high proportion of which is very strongly bonded into silt-size aggregates.