Geophysical Investigation of Road Pavement Failures in Osun State

This study applies near-surface geophysical methods to investigate the subsurface causes of recurring road pavement failures along a major highway section in Osun State, South West Nigeria. Recurrent pothole formation and pavement deformation along the Osogbo-Ikirun road section have created safety hazards and economic losses, yet conventional geotechnical investigations have not identified the underlying causes. Near-surface geophysical methods can detect subsurface voids, saturated zones, and weak layers non-invasively, providing complementary information to standard geotechnical borings. This study deploys GPR with 400-megahertz and 200-megahertz antennae, seismic refraction with 24 geophones at 3-metre spacing, and Wenner resistivity profiling along the most heavily damaged road sections, totalling 1.8 kilometres of survey coverage. GPR data are processed for migration, DC removal, and dewow in ReflexW. Refraction data provide shallow P-wave velocity information, and resistivity profiles identify low-resistivity anomalies indicating saturated or weak subgrade zones. Findings reveal low-resistivity anomalies of 5 to 18 ohm-metres in the subgrade beneath the worst-damaged sections, associated with water accumulation from blocked drainage culverts identified on satellite imagery. GPR images show hyperbolae at 0.5 to 1.2 metres depth interpreted as buried metal drainage pipes, two of which show surrounding halos interpreted as void development from pipe corrosion leaks. Refraction velocities below 300 metres per second confirm soft, water-logged subgrade in these locations. The study attributes pavement failure to drainage malfunction and recommends targeted subgrade drainage improvement and pipe replacement before resurfacing.

Keywords: GPR, road pavement failure, near-surface geophysics, drainage investigation, Osun State.