Non-Invasive Geophysical Investigation of Failure Along a Section of Ago-Iwoye Market Road, Ago-Iwoye, Southwestern Nigeria

Abstract

A detailed geophysical investigation was carried outto determine ifthe subsurface geology is responsible for the failures along this road section. This study aims to imageand identifycompetent, moderately competent,and incompetent zones of the subsurface soiland thus to findout ifgeology is responsiblefor the failure along this section of the road.Electrical Resistivity Imaging (ERI) using the Wenner array 2D Imaging, and Vertical Electrical Sounding (VES) using the Schlumberger array were adopted for this survey. The geoelectric section from the VES revealed the presence of 3 lithological layers; topsoil, weathered layer (clay, sandyclay, clayey sand),and basement,which is also true for the electrical resistivity images revealed by the 2D electrical resistivity imaging. The results showed that the shallow subsurface beneath the road section is mostly underlain with clay thatis geotechnically incompetent andnot suitable for construction. The causes of road failure are believed to be theresult of the incompetent clayey topsoiland theweathered layer seen inthe profiles, which expand whenabsorbing water and shrink when drying, thuscausing instability beneath the pavement due tothe low shear strength and high compressibility,and also due to fractured basement rocks at shallow depths.