Geo-electrical investigation of soil as foundation material in Ajayi Crowther University, Oyo, Oyo State, South Western Nigeria

Abstract

Geo-electrical investigation of soils in Ajayi Crowther University (ACU), Oyo, Oyo State, Nigeria, was undertaken in order to determine the competence of the soils as foundation materials. A total of Ten (10) Vertical Electrical Sounding (VES), using Schlumberger configuration was carried out. The Schlumberger configuration was used for the data acquisition. The half-currents electrode (AB/2) was used and the quantitative interpretation of the VES involved partial curve matching and 1-D computer iteration. The field data acquired was presented as geo-electric curves and geo-electric section. The results revealed three to four distinct geo-electric sequences with resistivities ranging from 13.9 Ωm to 1340.8 Ωm and variation in topsoil thickness with the least as 0.7 m at vicinity of VES point 6 and 8 of Ajayi Crowther University (ACU) and highest as 23.2 m at VES point 2 of ACU. Base on result of the survey the most competent soil within which large engineering structures will be founded within the study area VES point 5, 6 and 8. The major subsurface layers are the topsoil (mainly clayey sand and sandy clay), lateritic layer and weathered formation. The VES Points 1,2,3,4 and 10 of the study area shows the lowest resistivity values that suggest high clay content or possible fracture which may have impact on the competence and integrity of the soil construction and building development. Therefore, for building development in the study area, the topsoil must be excavated to a reasonable depth at which the soil is adequately competent and choice of foundation material must take into account the characteristics of the clayed material.