INTEGRATION OF GEOELECTRIC SOUNDING AND STATIC CONE PENETRATION IN FOUNDATION STUDIES OVER SELECTED LOCATIONS IN ONDO STATE, NIGERIA.

Abstract

Geoelectric soundings are combined with static Cone Penetration Tests (CPT) in this study for the purpose of evolving a comprehensive site evaluation methodology for foundation designs. Five locations were selected for study within Ondo state. Cumulatively, forty-five (45) Schlumberger Vertical Electrical Sounding (VES) and sixty-four (64) CPT points were occupied. The geoelectric sounding curve types obtained from these locations are A, AA, H, KH, K and Q. The apparent resistivity values obtained vary between 66 and 4044 Ω-m. The cone penetration resistance values obtained vary between 2 and 170 kg/cm2. The cone penetrometer resistances were plotted against depth and blocked into litho-units. The quantitative interpretation of the sounding curves and CPT values showed that the area is generally underlain by subsurface lithological sequence consisting of the topsoil, weathered bedrock and the resistive basement. Empirical equations were generated for each location by plotting the results of cone tip resistance against the formation resistivity using logarithm-linear graphs. The empirical equations were used to generate CPT values from resistivity measurements at each VES station. The resistivity derived CPT values obtained from the logarithm-linear regression for each locality is compared with the field CPT values and correlation values ranging from 0.283 at Ifon to 0.643 at Oka-Akoko were obtained. Thus the combined results of integrated geophysical and geotechnical site studies have enhanced the understanding of predictable performance of soils and rocks when subjected to structural loadings