Subsoil Competence Characterization of the Akure Metropolis, Southwest Nigeria

Five hundred and thirteen Vertical Electrical Sounding data sets were acquired within the Akure9. Metropolis, processed and interpreted quantitatively. Akure Metropolis lies within Latitudes 07°10. 09' and 07° 19'N and Longitudes 05° 07' and 05° 17'E and covers an areal extent of about 340 km2. The soil map of the study area was extracted from existing soil map and subsequently digitized. Geologic lineaments were delineated from satellite imageries acquired for the study area. The VES interpretation results delineate four subsurface layers which include the topsoil, weathered Basement, partly weathered/fractured basement and the fresh basement. The layer resistivity values for the topsoil used in this study range from 13 – 7133 ohm-m with layer thicknesses of between 0.3 and 5.2 m. Three major soil associations were identified. These include Iwo, Ondo and Itagunmodi Associations. The satellite-imagery-delineated lineaments show predominantly NNW-SSE, ENE-WSW and NNE-SSW orientations with subsidiary NW-19. SE and W-E trends. The topsoil resistivity, lineament density and soil thematic maps were integrated in a GIS environment to generate the subsoil competence map which classifies the Akure Metropolis into low competence (3.5%), moderately competent (26.6%) and highly competent (69.9%) zones. The study concluded that most parts (96.5%) of the metropolis are underlain by moderately to highly competent subsoil.