Geophysical Investigation for Pre-Engineering Construction Works in Part of Ilorin, Northcentral Nigeria

A geophysical investigation involving geoelectric depths sounding has been conducted as pre-foundation study in part of Ilorin, Nigeria. The area is underlain by the Precambrian basement complex rocks. 15 sounding stations were established along five traverses. The Vertical Electrical Sounding (VES) (three-five) conducted along each of the traverses was subjected to computer iteration using IP2Win software. Three -five subsurface geologic layers were delineated in the study area. These include the topsoil with resistivity and thickness values ranging from 103 Ωm-210 Ωm and 0 m-1 m; lateritic (117 Ωm-590 Ωm and 1 m-4.7 m); sandy clay (137 – 859 Ωm and 2.9 m – 4.3 m); weathered (60.5 Ωm to 2539 Ωm and 3,2 m-10 m) and fresh basement (2253-∞ and 7.1 m-∞) respectively. The resistivity pseudosection shows continuous high resistivity zone on the surface. Resistivity of this layer from depth 0-5 m varies from 300-800 Ωm along traverse 1 and 2. Hence, this layer is rated competent as it has the ability to support engineering structure. However, along traverse 1, very low resistive layer occurs between VES 5 and 15 with resistivity values ranging from 30 Ωm-70 Ωm. This layer was rated incompetent based on the competence rating. This study revealed the importance of geophysical survey as a pre-construction engineering survey at any civil engineering site since it can reliably evaluate the competence of the subsurface geomaterials.

[1] Oluwafemi, O. and Ogunribido, T. H. T. “Integrated geophysical and geotechnical assessment of the permanent site of Adekunle Ajasin University, Akungba Akoko, Southwestern” Nig. Advan. Appl. Scien. Res., vol. 5, no. 2, pp.199-209, 2014.
[2] Oyedele, K. F. and Okoh, C. “Subsoil Investigation using Integrated Methods at Lagos”, Nigeria. J. Geol. Min. Res., vol. 3, no. 7, pp. 169-179, 2011.
[3] Augie, A. I. Saleh, M. Aku, M. O. and Bunawa, A. A. (2019): Assessment of the Integrity of Goronyo Dam Sokoto North Western Nigeria Using Geoelectrotomographic Technique, Bayero Journal of Physics and Mathematical Sciences, Vol. 10(1), Pp. 231 –243.
[4] Augie, A.I. Saleh, M. and Gado. A.A. “Geophysical Investigation of Abnormal Seepages in Goronyo Dam Sokoto, North Western Nigeria Using Self-Potential Method”, World Academy of Science, Engineering and Technology, Int. J. Geotech., Geol. Eng., vol. 14, no. 3, pp. 103 – 107, 2020.
[5] Rahaman, M. A. “Review of the basement geology of southwestern Nigeria in Geology of Nigeria” Elizabethan Publishing Company, Nigeria Pp. 44 – 58, 1976.
[6] Olabode, A.D. and. Ajibade, L.T. “Environment Induced Conflict and Sustainable Development-A Case of Fulani-Farmers Conflict in Oke-Ero LGA, Kwara State”, Nig. J. Sust. Dev. Afr, vol. 12, no. 5, pp. 159-173, 2010.
[7] Olasehinde, P.I., “Characteristics of rain, groundwater and surface water in the area of Ilorin, Kwara State, Nigeria” Geol. Palaont Teil, vol. 3, no. 4, pp.149-158, 1999.
[8] Aisabokhae, J and Ologe O “Geo-electric Characterization of Subsurface Lithology for Engineering Applications: A Case Study of Gwandu Formation, Birnin Kebbi, Nigeria” Amer. J. Ear. Scien. Eng. vol. 2, no. 2, 2019, pp. 8-14.
[9] Bayowa, O.G. and Olayiwola, N.S. “Electrical Resistivity Investigation for Topsoil Thickness, Competence and Corrosivity Evaluation: A Case Study from Ladoke Akintola University of Technology, Ogbomoso, Nigeria”, 2nd International Conference on Geological and Civil Engineering, vo 80, no. 11, pp. 52-56, 2015.
[10] Idornigie, A.I. and Olorunfemi, M.O “Electrical Resistivity Determination of Subsurface Layers, Subsoil Competence and Soil Corrosivity at an Engineering Site Location in Akungba –Akoko, Southwestern Nigeria”, Ife J. of Scien., vol.8, pp. 22-32, 2006.