A Geophysical Approach to Site Characterization for Construction and Related Purposes; Case Study of ABUAD Teaching and Research Farm, Ado - Ekiti, Southwest Nigeria.

Abstract

Geophysical survey involving the VLF Electromagnetic and the Electrical resistivity methods using the Schlumbeger Electrode Configuration have been carried out at the  Afe  Babalola University Teaching and Research Farm, Ado Ekiti. The interpretation and modelling of the reconnaissance  VLF –EM data acquired along 17 West- East Traverses had earlier been used in an earlier study in the area to delimit the farm area into 29 VES stations from where detailed study using the  electrical  resistivity method were carried out. The results from the 2-D  interpretation of the VES data were used to prepare the geoelectric sections along five cross sections AA^I, BB^I, CC^I, DD^I and EE^I so as to reveal the subsurface lithologic successions vis-à-vis their geoelectric characteristics. The resistivity curve types obtained include the H-,KH-, HA-, KHA-, A-, K-, QH-, and the HKH-types in decreasing order of frequencies. The preponderance of  H-and its’ combination type- curves is indicative of the dominance of the weathered layer lithology, and as anticipated in the study area, being a basement complex environment. The general lithological sequence include the topsoil, lateritic clay, sandy clay, weathered basement and fresh basement.  From these, it was revealed that section  DD ^I has the thinnest sequence of  loose overburden materials spread over the  longest lateral distance and is considered most favourable and suitable for siting heavy engineering infrastructures,such as agricultural products processing plants and industries,  this is because the fresh basement is at the shallowest depth here, thus requiring the least excavatory work. This is followed in order of  merit by sections CC^I, BB^I, EE^I with the least being AA^I , in addition, siting of waste dump and incinerating plant will be best here because the least concrete  blinding will be required for the thinnest  weathered sequence for the prevention of  leachate infiltration in the  prevention of pollution to the  groundwater aquifer in the farm . In addition, further studies involving cone penetrometer  and or auger boring  tests is recommended to be carried out to confirm the detailed competence levels of the rocks along the specified section as necessarily required.

Keywords: VLF-Electromagnetic, Type-curves, Fresh Basement, Geoelectric characteristics, cross-section