ABSTRACT
Expansive clay soils realise significant changes in their volume in response to changes in moisture content. The magnitude of these changes depends on many variables including clay mineralogy, stress state and confinement, and the magnitude and range of the moisture content change. This paper examines the role played by the structure of a residual soil in affecting the realised volume change. Residual soils are those soils derived from the weathering of rocks in situ. A residual soil profile is considered in which a heavy clay soil has developed from a mudstone parent rock, resulting in a soil with a gradual textural change from desiccated clay near the surface, to extremely weathered rock at depth. The expansiveness of clay samples from these shallow and deep horizons is compared. It is shown that despite having similar clay mineralogies, the soils from deep and shallow levels exhibit significantly different volume change potentials, with the relict rock structure which is present in the deeper sample considered to inhibit volume change. This conclusion is verified by assessing the expansive potential of samples of the deeper soils which were physically broken down and reconstituted, enabling them to realise an increased volume change. The roles of repeated wetting and drying, and mechanical disintegration, in unlocking the expansive potential of a clay soil are considered.
