Journal of Geology & Geophysics
Open Access

Abstract

Application of Electrical Resistivity and Ground Penetrating Radar Techniques in Subsurface Imaging around Ajibode, Ibadan, Southwestern Nigeria

Adelekan AO, Oladunjoye MA and Igbasan AO

Integrated geophysical investigation involving Electrical Resistivity (ER) and Ground Penetrating Radar (GPR) techniques were carried out around a site underlined by Basement Complex rocks of southwestern Nigeria. The study was aimed at imaging the subsurface lithological units and delineating shallow geologic structures for the purpose of characterizing the area for construction suitability. A total of twenty five (25) Vertical Electrical Sounding (VES) data using Schlumberger array, ten (10) traverses of Electrical Resistivity Imaging (ERI) using Wenner array and Ground Penetrating Radar (GPR) surveys were carried out along the established traverse lines within the area. The VES data were quantitatively interpreted using partial curve matching technique and subsequently improve upon by inversion software using IPI2Win, to obtain the layer geoelectric parameters. The ERI data was inverted and interpreted using Res2Dinv and Res3Dinv inversion software’s respectively to generate 2D and 3D resistivity image of the subsurface. The GPR data was processed into radar section using RadExplorer software. Vertical electrical sounding results delineates typically three to four geologic layers which are the topsoil/lateritic hardpan, weathered basement (consisting clay and sandy clay) and fractured/fresh basement with layer resistivity value ranges of 10-2684 Ωm, 12-242 Ωm and 229-3213 Ωm respectively and thickness value ranges of 0.5-2.1 m and 4.0-14.1 m respectively. 2-D inverted resistivity results also delineated three major geologic layers which are the topsoil, weathered basement and fresh basement and correlates well with the results obtained from the VES results. Layers 1 to 3 of 3D inverted resistivity slice results show high degree of variation in resistivity distribution at shallow depth, consisting of highly resistive material towards the eastern part with low resistivity material concentrating at the south-western part. Results of the GPR survey also delineated three to four geologic layers which include the topsoil/lateritic hardpan, weathered basement and fractured/ fresh basement. The study area was categorized to have semi-competent to competent basement rock based on the resistivity value of the underlying material within the area. Bedrock depression delineated at some location could pose threat of differential settlement to construction works within the study area. Thus, it should be ensured that foundation is designed to sit comfortably on the competent bedrock or by employing suitable foundation work, such as piling to ensure foundation stability and prevent structural failure. Thus, electrical resistivity and ground penetrating radar techniques are versatile tools in site characterization.