Assessment of Vulnerability of a Failed Section of the Iju-Itaogbolu/Ikere-Ekiti Road in Southwestern Nigeria

Abstract

An integrated study that included both geotechnical and geophysical analysis was conducted to assess the geological materials beneath certain sections of the Iju-Itaogbolu/Ikere road that have experienced failure in terms of their strength and stability as a road surface. The electrical resistivity imaging (ERI), induced potential (IP), and ground magnetic methods provide details about the nature of the geological materials that could undermine the stability of pavement materials along these sections. The 2D geo-electric model showed the presence of three layers beneath the pavement, including topsoil, weathered or fractured basement, and fresh basement. Failure in most of the road section is attributable to noticeable fractured layers and weak (relatively low resistivity) subgrade materials delineated at shallow depths in some areas of the road. The geotechnical results reveal that soil layers beneath the failed section are clayey and saturated, while those within the less vulnerable zone are composed of competent materials (meta-conglomerates) capable of bearing civil engineering structures and heavy loads. Clay soil generally has low bearing capacity to support the load induced by heavy-duty vehicles and is very sensitive to changes in temperature and moisture content. Vulnerable zone constitutes about 60% of the examined road segments, while the less vulnerable zone accounts for approximately 40%. This integrated approach shows good correlation between results of geophysical and geotechnical studies.