GEOTECHNICAL AND GEOCHEMICAL PROPERTIES OF LATERITIC SOIL ON MIGMATITE ALONG OGBOMOSHO - ILORIN HIGHWAY SOUTH-WESTERN NIGERIA

Abstract

ABSTRACT The geotechnical and geochemical properties of lateritic soil developed on migmatite along Ogbomosho – Ilorin road, south-western Nigeria was studied. Soil samples were collected from seven (7) different laterite profiles along the road cuts and analyzed in the laboratory so as to determine the geotechnical, geochemical and petro-graphical characteristics of each horizon within the profile and their suitability as construction and/or foundation material. The geotechnical tests conducted according to the British standard procedures (1377) include: index test and performance test. Field geological mapping shows that the parent rock from which the in – situ lateritic soil was derived is a migmatite with an average soil profile depth of 4.2m. The principal mineral compositions of the migmatite are quartz (40%), biotite (25%), feldspar (21%), hornblende (6%), and muscovite (5%). The moisture content obtained range between 3.1 and 14.2%,Specific gravity value range between 2.50 and 2.74, bulk density and dry density range between 1.44 and 1.77g/cm3 and 1.31 and1.62g/cm3 with an average value of 1.56 and 1.44g/cm3 respectively which indicate that the soil was produced through in - situ weathering of granitic rocks rich in felsic mineral. The results of the Atterberg consistency limit range between 3.3 and 14% (PL), 40 and 58% (LL), 17.7 and 35% (PI) with an average value of 47.2%, 49% and 8.1% respectively. Similarly plots on the plasticity chart shows that the soil falls above A- line corresponding to CL zone which is classified as inorganic clay of moderate plasticity based on Unified Soil Classification System (USCS). The grain size above 0.075 mm revealed fine to coarse grained sand.The OMC and MDD have an average value of 13.08% and 1.76kg/m3 and the CBR value for soaked and unsoaked ranging between 17 and 66% and 42 – 74% with an average of 57.58% and 34.8% which indicate that the soil can be used for sub - base and subgrade in pavement construction of roads. The value obtained from angle friction (ϕ) and cohesion (C) range between 22 and 32° and 10 and 30KN/m2 with an average value of 27.04 and 21.5KN/m2 which indicate that the soils can be used as material in the construction of fill road embankment. The x-ray fluorescence analysis shows that the major oxides include SiO2, Fe2O3, Al2O3, K2O, Na2O, TiO2, and MgO while SiO2, Fe2O3 and Al2O3 constitute 70–80% of the oxides. The research reveals that with the exception of Horizon A and C of the profile the geotechnical and geochemical characteristics of the lateritic soil derived from migmatite conform to Nigerian Federal Ministry of Works guidelines on road construction materials and compare favourably with the results of other authors. Sectional failures might have resulted from inappropriate material handling and/or equipment inadequacies.