The nature of swelling in soils

Abstract

While existing swelling models adequately describe the swelling in extensively-swelling soils, their applicability to moderately-swelling soils has not been previously tested. The swelling of different layers of a transitional red-brown earth measured in situ using swelling gauges could not be described using existing swelling models. Values of �, defined as the ratio of change in bulk volume of the soil to change in gravimetric moisture content, were less than 0.33 over the whole of the measured moisture range in all layers of this soil, except the 0.25-0.55 m depth. This indicates that the extent of swelling was less than the normal, three-dimensional swelling described by existing models. Modifications to these existing models are proposed to describe the swelling in soils with moderate swelling characteristics. The compressibility factor (�), defined as the ratio of the change in void ratio to the change in moisture ratio, measures the same soil property as the values. Values of � determined in previous field studies and on soil cores of several clay soils are also less than the 0.33 specified for normal swelling, in keeping with the expectations of the modified swelling model. However, the need for further field testing of this model for moderately-swelling soils is emphasized. The limitations of existing methods for determining swelling characteristics of soils using core samples are discussed and several alternative procedures for in situ measurements are suggested.