Geo-electrical investigation for subsurface electrical system earthing at the school of management technology of the federal university of technology, Akure, Nigeria

Abstract

Electrical tomographic imaging and depth sounding techniques were employed in the investigation of the subsoil around the School of Management Technology of the Federal University of Technology, Akure, Nigeria for the purpose of Electrical Earthing. Wenner Dipole-dipole electrical resistivity imaging was conducted along seven traverses in the area with electrode inter spacing ‘a’ of 2m, with the probing level ‘n’ varied from 1 to 5. Twelve Vertical Electrical Soundings were conducted at selected locations based on the results of electrical imaging. The geoelectric sections obtained from inverted sounding data revealed three subsurface geologic layers, which comprise the topsoil, weathered bedrock and the fresh basement rock. The topsoil is composed mainly of clay or sandy clay/ clayey sand or laterite with resistivity values that range from 41 to 739 Ohm-m and thickness ranging from 0.5 to 5.3m. The weathered bedrock resistivity values ranges from 12 to 363 Ohm-m with thickness between 1.0m and 17.9m. The underlying fractured/fresh basement rock resistivity varies from 213 to 865 ohm-m. However, the underlying migmatite-gneiss basement rock is relatively shallow. The inverted resistivity sections from the Dipole–dipole and computed ground resistance distribution revealed typical 3- layer earth models revealing majorly five suitable localities with relatively low resistance (< 15 ohm ) with probable depth for the insertion of Earthing materials lying between 1.5m and 4m. In addition, areas characterized by resistance values, between 15 ohm and 25 ohm, can be improved upon by adding industrial salts.

Keywords: Earthing, Ground resistance, Tomographic Imaging, Wenner Dipole-dipole, Vertical Electrical Sounding