Evaluation of lateritic soil using 2-d electrical resistivity methods at Alapoti, Southwestern Nigeria
A 2-D resistivity survey was carried out in Alapoti, Ogun State, a sedimentary terrain of South-western Nigeria. This area lies between longitude 0060 34′0″N and 0060 40′0″N and latitude 00302′0″E and 00306′0″E. The wenner alpha electrode configuration was engaged through out in this study. Ten profiles were covered; five in the north-south direction, and the other five in the west-east direction. To obtain a good 2-D picture of the subsurface, the coverage of the measurements must be 2-D as well. The distance between adjacent traverse is 25 metres. The data from each 2-D survey line was inverted independently with RES2DINV to give 2-D cross-sections with averages of 4.8 iteration and RMS error of 8.15%. A contoured pseudosection conveys a qualitative two- dimensional resistivity variation with depth within the subsurface. The inversed model resistivity sections created models for the subsurface resistivity using an iterative smoothness constrained least square inversion and are interpreted to generate the subsurface geologic characteristics. Results from 2-D inversed resistivity section showed that the second layer with resistivity value of about 200m to 600m and thickness of about 4.0m is composed of lateritic clay. The third layer is made up of moderate laterite having a thickness of about 3.0m and apparent resistivity ranging from 600m to 1,000 m, while the fourth layer of apparent resistivity value 1,000m to 1,500m is laterite but rich in sand and it is located at a deep of about 12.0m.
Keywords: Laterite, Inverse model resistivity, 2-D, Iteration, Wenner array.