ABSTRACT
Preliminary results of a study of a residual clay profile developed in a temperate climate are presented. The study focuses on the mineralogy of the soil profile and its relationship to the expansive potential of the clay soils it contains. The soil mineralogy is quantitatively and semi-quantitatively assessed on the basis of two sets of xray diffraction results, which indicate a consistent dominance of randomly interstratified illite and smectite minerals throughout the profile. The soil mineralogy is compared with the expansive potential of the clay soils with respect to depth, assessed in terms of a measured shrink swell index, which is found to decrease consistently with depth. This reduction in expansive potential in a soil profile of consistent mineralogy is attributed to a consistent change in the fabric of the soil with increasing depth, which is due to an associated gradual decrease in the degree of weathering. The high proportion of smectite clay minerals in these soils explains why significant expansive soil movements are observed in an area where the influence of climate and the depth of clay soil only extend to the relatively shallow depth of 1.7m.
