The Influence of Geological Factors on the Engineering Properties of some Western Nigerian Residual Lateritic Soils as Highway Construction Material.
The fundamental influence of geology on some geotechnical properties of lateritic soils as highway -construction material within a restricted macroclimatic area of Akure and llesha in the deciduous rain forest belt of South Western Nigeria was investigated. Lateritic soils derived from four major petrological units, namely t'.aarse, P~yrphyrit.ie Granite, Coarse to medium Charnockite, Coarse to medium massive amphibolite, and medium Grained Talc Schist were concentrated upon the different ways in which Geochemistry, Clay Mineralogy, Degree of weathering and Laterization influenced the engineering properties of the sails were examined. The results have conclusively proved that geology is the main factor controlling the geotechnical properties of residual lateritic soils within the restricted climatic environment. A new parameter, termed the water absorption coefficient of lateritic soils was evolved. It is the angular relationship between the 48-hour soaked CBR value of a soil and average percent value of the soils' CBR at Optimum Moisture Content of Modified AASHO acompaction. The mean values of the coefficient in the four soils studied showed discernible relationship to the respective parent rocks. Recommendations for further research include an investigation of the relationship between the shear strength parameters of compacted genetic lateritic soils especially in the triaxial test: and the relationship between the water absorption coefficient and the geophysical resistivity values of similarly compacted genetic lateritic soils. Such subsequent research may eventually provide convenient quantitative engineering parameters which would relate the variations of moisture content, dry density, geophysical resistivity and the triaxial shear strength values in genetic lateritic soils in general.