Geophysical investigation of road failure in the Chad basin, a case study of Damaturu metropolitan roads, Nigeria

Abstract

Road failure is a significant factor contributing to the increased costs of transportation as well as road accidents in the research area. It has negatively impacted the prices of goods and services throughout the Chad Basin. To tackle the causes of road failure, this study analyzed road failure in Damaturu, employing both Electrical Resistivity Tomography (ERT) and Vertical Electrical Sounding (VES)
techniques. The road subgrades were characterized as low resistivity materials with resistivity varying from 5 to 40 Ωm. The subgrades were identified as clay formations in the study area based on their resistivity properties. The ERT findings and the VES findings correlated effectively in pinpointing the unsuitable materials beneath the road pavements. The clay soil appeared in the ERT outcomes across all three profiles in deep blue hues indicative of low resistivity. In some regions of the study area, the clay formation was found directly beneath the road pavement, while in other areas, it was interrupted by sand. In profiles 1 and 3, the clay formation serves as the subgrade, whereas in profile 2, it lays beneath the sandy-clay formation. The responses of the clay materials to moisture variations result in swelling and shrinking characteristics of the clay, which leads to the roads deformation and ultimate failure. It is therefore recommended that sections of roads with incompetent subgrades be removed and replaced with more solid and competent materials that possess the essential stability and load-bearing strength. Furthermore, road construction should include comprehensive geophysical surveys to identify areas with less competent subgrades and ensure they receive proper attention. The results of this
investigation also indicated that the closeness of clay formation to the Earth's surface in the study area is a key factor in the frequent and recurring road failures. Consequently, geophysical exploration during road construction in the Chad Basin should be prioritized to guarantee that the roads built in the study area are resilient and lasting.