The Electrical Resistivity Imaging (ERI) method of geophysics has gained large-scale applications in civil engineering for pre-construction site assessment and post-construction investigative and remedial interventions. However, the cost of ERI equipment limits its applications in underdeveloped/developing countries and unfunded studies. This limitation is overcome in this study by applying an alternative and reliable technique of multiple imaging of subsurface for engineering applications using traditional 1D Earth Resistivity equipment and collocated electrodes array. This technique was used to investigate the principal cause of road pavement failure along University Teaching Hospital Road, Ilorin, Nigeria. Five profiles of 100 m were established at different parts of the road to acquire subsurface resistivity data. Resistivity models inverted from the data acquired by the improvised 2D surveys show low resistivity breakouts, weathered sections with high moisture content, weak zones, and elongated brittle structures in the top ten meters of the subsurface. The high resistivity layer corresponds to the stable portions of the pavement while the low resistivity breakouts in the shallow part of the resistivity models correspond to the failed pavements and potholes on the road. Elongated vertical structures were identified as weak zones that served as conduits for rainwater from the top and groundwater from subsurface accelerated weathering activities in the area. Water ingress due to lack of drainage, high moisture content in the top layers, and intense subsurface weathering were found as the cause of the road pavement failure. The study recommends some remedial interventions prior to reconstructing the road pavement.

Keywords: Road failure investigation, Geophysical survey, Electrical resistivity imaging, 2D augmented array, subsurface resistivity models

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