Application of Ground Penetrating Radar for Subsurface Utility Mapping in Urban Construction Sites in Lagos

Background: Accidental damage to buried utilities during urban construction in Lagos, South West Nigeria, causes costly disruptions to water, electricity, and telecommunications services. Ground penetrating radar provides a non-destructive subsurface mapping capability. Aim: This study applied ground penetrating radar for subsurface utility detection and mapping at urban construction sites in Lagos. Methods: A GSSI SIR-4000 GPR system with 400 MHz and 900 MHz antenna frequencies was used to survey 8 construction sites in Lagos Island and Mainland. Hyperbolic reflections in radargrams were interpreted to identify buried utilities. Results were verified against available utility records and physical excavation at selected locations. Results: GPR correctly identified 87% of buried utilities verified by excavation. Pipe depths ranged from 0.3 to 2.8 metres. Detection accuracy was highest for metallic pipes (94%) and lowest for plastic conduits (74%). The 900 MHz antenna provided better resolution for shallow targets. Conclusion: GPR is an effective tool for pre-construction utility mapping in Lagos urban environments. The study recommends mandatory GPR surveys before major excavations and development of a digital utility cadastre for Lagos State to improve GPR correlation accuracy. Keywords: ground penetrating radar, subsurface mapping, utilities, Lagos, urban construction.