DELINEATION OF CLAY FORMATION USING 1-D ELECTRICAL RESISTIVITY METHOD: A CASE STUDY AT A PROPOSED BUILDING SITE IN FUPRE CAMPUS

ABSTRACT The problem associated with the delineation of clay formation using the electrical resistivity method arises from the difficulty in accurately identifying and mapping clay layers in the subsurface, which are often geologically complex and lack distinct physical markers. These clay layers significantly impact groundwater flow, contaminant migration, and geotechnical stability, making their precise mapping crucial for environmental and engineering applications. The Schlumberger array method is a widely used configuration in electrical resistivity surveys to investigate subsurface conditions. It involves four electrodes: two current electrodes (C1 and C2) to inject electrical current into the ground, and two potential electrodes (P1 and P2) to measure the voltage difference. The current electrodes are placed far apart, while the potential electrodes remain closer to the center. The spacing between the current electrodes is increased progressively to explore deeper subsurface layers. The apparent resistivity is calculated from the measured voltage and injected current, and the resistivity data are plotted to create a sounding curve, which can be interpreted to reveal the subsurface structure. Six resistivity images were obtained from the resistivity surveys carried out in Federal university of petroleum resources Effurun (FUPRE) using the Schlumberger array to determine its clay formations, depth and thickness. The images fig 11-16 showed the presence of clay deposits occurring at 33m for traverse 1, 15.8m for traverse 2, 10.4m for traverse 3, 15.5m for traverse 4, 15.5m for traverse 5 and 5.1m for traverse 6. The resistivities of the clay deposit varied from about 160 to 9500 Ωm. It is therefore recommended that high resolution three-dimensional quantitative electrical resistivity imaging survey be conducted in the study area where clays are inferred and delineated, to further confirm the extent of depths and sizes with greater precision.