Subsurface Competence Evaluation Using Electrical Resistivity Method At A Proposed Building Site Along Futa Staff Quarters, Oba Nla, Akure Southwestern Nigeria

A detailed geophysical investigation has been undertaken to evaluate the subsurface/subsoil competence of a proposed building site in Federal University of Technology, Akure. The study utilized electrical method involving the use of horizontal profiling, vertical electrical sounding and the combined vertical electrical sounding and horizontal profiling at the site of investigation. Four traverses were occupied in order to have a detailed understanding of the area. Twenty (20) Vertical Electrical Sounding (VES) locations were occupied using Schlumberger electrode configuration with AB/2 varying from 1 to 100 m. This was quantitatively interpreted using manual partial curve matching and computer iteration. The results were used to generate geoelectric sections and maps. Three to five subsurface geologic layers were delineated across the study area comprising; the topsoil, clay, weathered layer, laterite and fresh bedrock. The topsoil exhibits fairly high resistivity with resistivity ranging from 31 to 451 Ωm with thickness in excess of 1.5 m. Based on this, the upper layer can host the foundation of less heavy weight buildings using strip foundation. However, the top layer is underlain by the weathered layer which is predominantly composed of a sandy clay formation, with resistivity values ranging from 85 to 190 Ωm and thickness between 0.5 and 12 m. The last layer, with resistivity values ranging from 383 to 2491 Ωm, is considered to be the competent layer capable of supporting heavy engineering structures with deeper foundations.