Journal of Emerging Trends in Engineering and Applied Sciences: Research Areas

Article Title: Geophysical Investigation at a Proposed Residential Estate in Ibadan of Nigeria: Hydrological and Geotechnical Implication
by J.O. Amigun, S.T. Owolabi and K.A.N. Adiat

Abstract:
In this study, geophysical method of electrical resistivity measurements using the vertical electrical sounding (VES) technique was utilized for the acquisition of geotechnical and hydrological subsurface information at a proposed estate in order to assist its foundation design and groundwater resource development. Thirty vertical electrical sounding (VES) stations with maximum AB/2 spacing of 65m was adopted for the proposed study covering an area of about 2km2. Typical sounding curves from the site include the H, KH, QH and A type; predominantly with H type constituting 60% of the survey points. A maximum of four geoelectric subsurface layers were identified, comprising the topsoil (clayey sand and laterite), weathered layer, partly weathered / fractured basement and fresh basement. The regions on the overburden map delineated as thick overburden (i.e. greater than 15m) and basement depression zones (i.e. areas at lower elevation) on the bed rock relief map are classified as high groundwater potential zones in the area and favored for optimal groundwater abstraction. The relatively high apparent resistivity range of the topsoil (740 - 1208 Ohm-m) and weathered layer (48 - 579 Ohm-m) respectively indicate that the underlain rock units are competent and therefore can withstand heavy structures. A few significant low resistivity anomalies on the pseudo-sections depicted as fractures / or shear zones were delineated as they might cause stability problem for overlying structures. The degree of soil corrosivity evaluated from the topsoil resistivity data shows resistivity (> 500 nm) in most part of this layer thus implies the soils may host metallic materials without serious danger of corrosion.

Keywords: electrical resistivity, foundation design, groundwater potential, pseudo-sections and soil corrosivity

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