Integrated Assessment of Subsoil Corrosivity and Hydrogeological Characteristics Using Vertical Electrical Sounding (VES): A Case Study of Oron, Akwa Ibom State, Nigeria

Background: Understanding subsoil corrosivity is critical in foundation and infrastructure design, particularly for projects involving buried metallic structures such as pipelines, storage tanks, foundation reinforcements, and cathodic protection systems. Despite the extensive application of Vertical Electrical Sounding (VES) in groundwater exploration and foundation studies, there is a limited number of integrated studies that simultaneously evaluate subsoil corrosivity and hydrogeological characteristics for engineering design purposes, particularly in coastal and deltaic environments. Aim: To assess the subsoil corrosivity and hydrogeological characteristics of Oron, Akwa Ibom State, Nigeria, by delineating subsurface geoelectric layers, estimating apparent resistivity, and evaluating the corrosive potential of soils for engineering and infrastructure planning purposes. Study Design, Place and Duration of Study: A Field geophysical survey employing Vertical Electrical Sounding (VES) and Constant Separation Traversing (CST) techniques using the Schlumberger electrode configuration was conducted in Oron, Akwa Ibom State, Nigeria. Methodology: Four VES stations and two CST profiles were acquired using an ABEM SAS 300 Terameter. VES was used to delineate subsurface geoelectric layers and estimate apparent resistivity, while CST assessed lateral resistivity variations and subsurface heterogeneity across the site. Data interpretation involved qualitative assessment of apparent resistivity variations and quantitative modelling using partial curve matching and RESIST software. Soils were classified based on the British Standard BS-1377 corrosivity classification scheme. Results: Six geoelectric layers were identified, comprising topsoil, clay, silty clay/clayey silt, silty sand, clayey/silty sand, and coarse sand and gravel. Apparent resistivity values ranged from 6.5 to 214.0 Ωm, with the majority falling below 50 Ωm, indicating possible saline influence, fine-grained sediments, and poor aeration conditions associated with high corrosion potential. Based on BS-1377 classification, soils range from very corrosive to slightly corrosive, with the majority classified as corrosive, signifying a high risk to buried metallic structures. CST profiles revealed slight lateral heterogeneity in resistivity distribution, with variations between profile lines indicating non-uniform subsurface conditions. Conclusion: Subsurface materials in Oron exhibit significant corrosive tendencies. Cathodic protection, pipe coating, and other protective engineering measures are recommended for metallic installations in the area.