Integrated Geophysical Survey for Road Pavement Failure Investigation Along the Nsukka-Onitsha Highway

Repeated pavement distress along the Nsukka-Onitsha highway has been attributed to diverse subsurface conditions, yet systematic geophysical characterization of the road corridor has not been undertaken. This study conducts an integrated geophysical survey combining ground penetrating radar (GPR) and electrical resistivity tomography (ERT) to investigate the subsurface conditions contributing to road pavement failure along the Nsukka-Onitsha highway. GPR data were collected continuously along both shoulders of the road using a 200 MHz antenna mounted on a survey wheel, providing continuous profiling along 45 km of the corridor. ERT measurements were conducted at fifteen selected locations where surface distress features were observed, using the Wenner array with 5 m electrode spacing. GPR radargrams reveal near-surface reflectors diagnostic of subbase deterioration, subsurface voids, buried drainage channels, and moisture infiltration zones. The ERT profiles image low resistivity bodies beneath the roadway at depths of 1 m to 6 m, interpreted as zones of saturated sub-grade material and clay swelling units. Correlation of GPR void anomalies with ERT moisture anomalies identifies fourteen critical zones of active pavement undermining along the corridor. The most severe pavement deterioration corresponds to sections underlain by montmorillonite-rich expansive clay that exhibits volumetric change in response to seasonal moisture variation. These findings provide actionable data for targeted rehabilitation and preventive maintenance along the highway. The study demonstrates the effectiveness of multi-method geophysical surveying in road condition assessment.

Keywords: ground penetrating radar, ERT, pavement failure, subgrade, highway investigation