Geoelectrical-Geotechnical Studies forNear Surface Characterization, CaseHistory: Lagos, SW Nigeria

Incessant building collapse and foundation failures in Nigeria have continued unabated in recent years, causing loss of lives and properties worth hundreds of thousands of US dollars. This research in Gioni estate Lakowe, Lekki-Epe, Lagos, Nigeria is concerned with an integrated characterization of near-subsurface geomaterials using geoelectrical resistivity tomography and geotechnical techniques as part of the preliminary investigations for foundations studies and other building construction projects. Four traverses of the geoelectrical resistivity measurements using Wenner array configuration were conducted, and cone penetrating data were equally obtained along the same traverse. A borehole data point was equally acquired for ground thruthing. Based on their geoelectrical properties, three lithologies including loose sand, compacted clayey sand and clay/peat units were delineated with apparent resistivity values ranging 50 – 260 Ωm, 20 – 72.2 Ωm and ≤ 27.5 Ωm respectively. Average Cone penetrometer (CPT) value was about 110 kg/cm2 with an average SPT ‘N’ value of 25, indicating that the soil material is of good geotechnical properties. Laboratory tests conducted on the representative soil specimen at 3.75 m depth revealed moisture content (MC) of 66% which can be attributed to the clay contents. The Liquid Limit (WL), Plastic Limit (WP) and Plasticity Index (PI) tests results gives 84%, 30% and 54% respectively. The choice of deep seated foundation such as pile foundation is considered a better alternative to shallow foundation for proposed buildings in the study area where higher loadings are anticipated to transmit the loads to a stable soil layer