Abstract
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.
Highlights
Soils, the starting geological material of rocks are mostly heterogeneous by nature, this been due to the varying proportions in which their components combined both physically, chemically and biologically
The use of the drilling technique, for groundwater investigation and mapping would have been suitable for mapping seepages except for its limitations in the areas of time consumption, data coverage and expense preempting the need to adapt other proficient techniques to compensate for these limitations
Geoelectric sections, isopach maps and isoresistivity maps Due to the objectives and aims of this research, data obtained from Vertical Electrical Sounding (VES) were carefully planned and cited to produce a 2D Geo-section that mirrors the events of the underlying subsurface/subsoil
Summary
The starting geological material of rocks are mostly heterogeneous by nature, this been due to the varying proportions in which their components combined both physically, chemically and biologically. Ground Penetrating Radar technique (GPR) like its counterpart electrical resistivity (ER) has been used by several authors like [20] to carry out investigations of the shallow subsurface like the conductivity mapping of saline water; in bedrock profiling, fracture mapping, and in sedimentology [5, 18]; in lossless homogeneous and lossy heterogeneous environments [29].
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