Ground-Penetrating Radar Investigation of Subsurface Anomalies Along Deteriorating Road Corridors in Ibadan, South West Nigeria

Urban road infrastructure in Ibadan, Oyo State, has experienced accelerated deterioration attributed to both heavy traffic loading and undetected subsurface voids, pipes, and weak zones that undermine pavement integrity. This study employs ground-penetrating radar to investigate subsurface anomalies along four selected road corridors in metropolitan Ibadan. A 250 MHz antenna was used to acquire continuous profiles along the centre and wheel-track positions of each road. Data were processed using REFLEXW software, incorporating gain adjustment, background removal, and migration to produce accurate depth-converted radargrams. Identified anomalies were classified according to their GPR signature characteristics, differentiating voids, utility conduits, saturated zones, and delamination layers within the pavement structure. Findings reveal the presence of multiple subsurface voids at depths of 0.3 to 1.8 metres beneath pavement surfaces, predominantly at road segments exhibiting surface cracking and pothole clusters. Utility conduit crossings are also mapped, providing updated as-built information for municipal infrastructure management. The results demonstrate the capacity of GPR to deliver rapid, non-destructive subsurface imaging that can pre-empt pavement failure events and inform targeted maintenance interventions. This study contributes field-based GPR benchmarking data for urban road management in Ibadan and offers a methodology transferable to other Nigerian cities experiencing similar infrastructure challenges. Keywords: ground-penetrating radar, road subsurface, pavement, Ibadan, utility mapping