ENGINEERING PROPERTIES OF A LATERITIC SOIL-PROFILE

The classification properties and composition of a lateritic soil, developed on Tertiary basalt in coastal south-east Queensland, Australia, have been investigated. X-ray diffraction analyses showed that the soil comprised kaolinite, quartz, gibbsite and haematite. Chemical analyses showed there was no amorphous material present in the soil. The results of electron scanning microscopy revealed that sesquioxides coat and bind the clayey constituents of the lateritic soil into porous micro-aggregations. Analyses of the grain size distribution and other physical properties indicated that the soil was not homogeneous within the laterite zone. Atterberg limit test results for the soil plotted anomalously below the Casagrande A-line. There were significant differences between the values of plasticity index determined for air-dried compared with oven-dried samples. High values for both the liquid and plastic limits were due to the water retention capacity of porous micro-aggregations in the soil. This was correlated with the degree of laterisation, which depends on the ambient climate, topography and vegetation of the area.