Variability in Some Geotechnical Properties of Two Residual Lateritic Soils from Southwestern Nigeria

Lateritic soils derived from granite and banded gneiss along Ondo Ore road in South Western Nigeria were assessed for their suitability or otherwise as landfill liners and highway sub-base/subgrade soils. The investigation was also meant for the determination of variability in the values of some geotechnical parameters. Representative rock samples were collected. Twelve disturbed and undisturbed soil samples were won from an area of 150m2 in each of the study area. Texture and mineralogy of the rocks were determined. Geotechnical tests were carried out on the soil samples by following standard procedures with some modifications to take care of peculiar characteristics of lateritic soils. Coefficient of variation was determined for each of the geotechnical parameters. Permeability coefficient was found to exhibit highest variability (91.25% in granite derived soil and 70.52% in the migmatite – gneiss derived soil). Parameters such as plasticity index, amounts of fine fraction and natural moisture content showed moderate variability, while maximum Dry Density, optimum moisture content and specific gravity of grains showed low variability. The soil were found suitable as landfill liners but unsuitable for sub-base and subgrade soils on the basis of permeability coefficient. The high degree of variability in the values of permeability coefficient calls for detailed sampling of lateritic soils either as foundation or construction materials.