An Engineering Foundation Investigation using the Geoelectric Method. A Case Study: Southwestern Nigeria

Abstract

The geoelectric method – Schlumberger vertical electrical sounding (VES) technique – was utilised in the geophysical investigation of an engineering site in Ode- Aye Southwestern Nigeria. The aim of the study was to determine the existence of competent and incompetent geologic layers and the depth at which they occur. A total of twenty VES stations were used in this study. Three distinct geoelectric layers were observed- sand, loose sandstone and shale layers respectively. The sand and especially the loose sand /sandstone layers were inferred to be the competent beds in the area from their resistivity values and thickness. They were classified as the stable and suitable beds for engineering construction purposes although their foundations should not extend to great depths – beyond 20 m – due to the presence of an underlying impervious shale bed.