Seepage investigations of heterogeneous soils beneath some buildings using geophysical approaches: example from southwestern Nigeria

Buildings along the flood plain of River Osun, southwest Nigeria, are usually thought of as been a safe haven for residence over the years. But in recent times with vast (increasing) population and growing urbanization, some of the buildings currently experience structural damages not related to constructional designs but rather ground conditions around building foundations. The ground conditions (seepages in this case) and how it influences properties of soils (water moisture, permeability etc.) to support the foundation of buildings. This paper attempts to map out seepages in heterogeneous soils around buildings in Erinle, southwest Nigeria where building cracks probably as a result of water seepages from subsurface through fissures and fractures where noticed. These cracks are a probable manifestation of a weakened foundation that could overtime result to a collapse, hence the need to investigate seepage prone zones. To achieve this, electrical resistivity (ER) and Electromagnetic Ground Penetrating Radar (EM-GPR) surveys were made along affected buildings to map out possible causes of deterioration. Geo-sections (analyzed ER data) shows high resistivity layer (topsoil) underlain by low resistivity layer (weathered basement) confirmed by planer reflections (topsoil) and fairly smooth to smooth reflections (weathered basement) in Radargrams (analyzed GPR data). An integration of the geo-section and radargram produced from ER and GPR data shows that buildings along traverses 1, 2, 3 and 5 is most prone to seepages especially as it exhibits very low anomalously resistivity values (< 25 Ωm) but this is not the case for buildings along traverses 4, 6, 7 and 8.