Application of Combined 2-Dimensional Imaging and Dipole-Dipole Technique in Depth to Bedrock Delineation within UNIOSUN Main Campus Car Park, Osogbo, Nigeria

Abstract

An integrated geophysical investigation consisting of two-dimensional Wenner resistivity imaging and dipole-dipole techniques was carried out within Osun State University Main Campus, Osogbo, Nigeria on a site temporarily used as public car park. The aim of the study was to image the subsurface conditions of the site and delineates the overburden - bedrock interface of the subsurface in the car park in readiness for the concrete flooring of the car pack and to compare the results from using two different equipment; PASI and integrated geophysical information system (IGIS) terrameters. Wenner data was interpreted using the MS Excel while the dipole-dipole data was interpreted using DiprofWin software. Interpretation of field data produces 2D Wenner imaging and dipole-dipole pseudo-sections. Dipole-dipole pseudo-section revealed that the subsurface layers of the site comprises of about 10 meters of weak and incompetent sandy layer having a resistivity of 296 Ωm with the layer underlain by a 4-meters thick low-resistance lateritic layer of resistivity value of 372.18 Ωm. The bedrock underlying the sequence is about 15 m deep, with resistivity value between 4169.09 Ωm, and 4670.132 Ωm. The 2-D imaging interpretations using the two pieces of equipment correlate at shallow depth but differ at greater depth. The results obtained from the Wenner interpretation of the two pieces of equipment do not correlate due to the very high exaggerated values obtained while using the IGIS instrument. The result concludes that the depth-to-bedrock interface is best defined using the PASI resistivity instrument compared to the IGIS resistivity meter.