Geoelectrical and Geotechnical based-assessment of Subsurface Soil Electrical Earthening Property and Corrosive Vulnerability along Coker Village Road, Osogbo, Nigeria

Abstract

This study integratesa geophysical and geotechnical approach tothe subsurface soil along Coker Village Road located about 200 meters from the Osun State University, Main Campus gate in Osogbo, Southwestern Nigeria. This is with the aim of assessing the subsurface electricalearthening properties and the corosivity of the soils within the study area.Twelve vertical electrical sounding (VES) surveys,one 2D Wenner profiling were collected, with four located 100 m apart from another four, while three cone penetration test measurements were collected at the midpoint of each of the four VES points to determine the in-situ shear strength properties. The VES data were interpreted using partial curve matching and later iterated using the DCInversion software, while the 2D Wenner profiling data were interpreted using the DiprofWin software. The corrosivity of the subsurface soil was inferred from appropriateclassification ranges of resistivity values, while the cone penetrometer data were interpreted using the Microsoft Excel spreadsheet.The results of the investigation reveal that there exist four to five geoelectric layers that alternate between lateritic topsoil with a resistivity ranging from 424.7 Ωm to 819.9 Ωm, lateritic layer with a resistivity rangingfrom 290.5 Ωm to 512.3 Ωm, and sandy bedrock with resistivity ranging from 265.9 Ωm to 1205.5 Ωm. All the first three geoelectric layers occur to a depth of more than 5 meters, possess a high shear stress to support the hosting of the mast, do not possess reliable earthing properties due to the high resistivity oflateritic subsurface materials and are practically non-corrosive with resistivity values above 180 Ωm.  The result of 2D Wenner profiling showed that the topmost part of the study areais composed of high resistance materials, that extend from a minimum depth of 4-5 meters to a maximum depth of up to 12 meters.This study demonstrates the efficacy of integrating geophysical, geological, and geotechnical approaches in obtaining more information about the subsurface condition of the soil in the studied area as opposed to using only one technique. The study recommends that a conductive earth medium be created by using clay or salt (brine) chambers within the study area so as to make electrical conduction continuous.