Geotechnical and Geochemical Properties of Lateritic Profile on Migmatite-Gneiss along Ogbomosho-Ilorin Highway, Southwestern Nigeria

Lateritic soils are very important in the construction industries and activities as construction material and foundation support for engineering structures in the tropical regions. This research tends to focus on the influence of position of horizon within the laterite soil profile and the resultant geotechnical and geochemical properties of soils developed over migmatite gneiss rock and also examine their suitability as construction and /or foundation material. A total of twenty three (23) soil samples and two rock samples were obtained from 8 different locations along Ogbomosho – Ilorin Highway, Southwestern Nigeria and considered under this study. The area is underlain by Basement Complex rock and migmatite gneiss is the most widely spread rock type. The laboratory test carried out includes specific gravity, grain size analysis, Atterberg limits (liquid limit, plastic limit, plasticity index and linear shrinkage), Standard proctor test, California Bearing Ratio (CBR), and Shear test. Geochemical analysis for major oxides and thin sectioning of rocks for petrological analysis was also carried out. The oxides are SiO2, Al2O3, Fe2O3, K2O, Na2O, TiO2, CaO and MnO while SiO2, Al2O3 and Fe2O3 constitute about 70-80 % of the soils chemical composition. Petrology reveal strongly foliated rock that composed of mafic mineral such as biotite, hornblende, and felsic mineral consisting of quartz and feldspar. Quartz, biotite and feldspar constitute about 77% of the minerals with quartz having 40% of the total mineral composition. The position of the horizon within the soil profile was found to have varying influence on the plasticity, moisture density relationship, CBR, and shear strength. This study showed that the influence of the parent rock on engineering properties and the position of the horizon within the lateritic profile determine the engineering properties and behaviour of residual soils. Keywords: Assessment, Laterite Soil, Migmatite-gneiss, Ogbomosho-Ilorin Highway, Southwestern Nigeri