Geoelectric and geochemical assessment of sub-soil corrosivity and competence for civil infrastructures at Utue-Ogume, Delta State, Nigeria

The corrosive nature of sub-soil, its susceptibility to aggressive attack on buried metallic pipes and concrete, and its competence to withstand overburden stress from civil engineering infrastructures at Utue-Ogume, an oil producing community in Delta State was assessed with geo-electric and geochemical methods. Nine Vertical Electrical Soundings (VES) were carried out with Mini-Res Resistivity Meter using the Schlumberger array. Soil samples were also collected with hand auger at varying depths of 0–1 m, 1–2 m and 2–3 m at each of the nine VES stations for geochemical analysis. The VES data was processed with IPI2WIN software and delineated six to eight geo-electric layers whose resistivity, thickness and depth ranged respectively from 53.04Ωm to 4535Ωm, 0.6 m to 79.2 m and 0.6 m to 134.8 m. The geochemical parameters (pH, Cl-, and SO42-) determined by ion chromatography and Tyurin methods were lower than the permissible standards, although the Cl- and SO42- concentration could be potentially high with time due to seasonal fluctuations which can trigger the corrosion dynamics of the soil. The subsurface soil layers were characterized as essentially non-corrosive, moderately corrosive and mildly corrosive to concrete and metallic pipes. The subsurface soils were also characterized as highly competent, competent and moderately competent confirming that it can withstand erecting of massive buildings or civil engineering infrastructures to depth of 2 m. Moderately and mildly corrosive sub-soil layers require treatment before burying crude oil and gas transmission pipes to prevent future corrosion.