Assessment of near surface corrosivity and competence within Alex Ekwueme Federal University and Environs, Southeastern Nigeria using electrical resistivity method

Abstract

The corrosivity and competence of sub-soils within and around Alex Ekwueme Federal University Ndufu Alike Ikwo (AEFUNAI) has been evaluated using the electrical resistivity method. The main objective was to provide guide for construction of foundations and laying of utility pipes in order to forestall future failure of structures, contamination of potable water, and observed rusting and rotting of overhead tanks in the area. Twenty six (26) vertical electrical soundings (VES) were carried out using the schlumberger configuration with ABEM SAS 1000 terrameter. A maximum half current electrode spacing (AB/2) of 200m was used in the acquisition of earth resistivity data. IPI2win^TM software was used for processing and modelling of data. Second layer isoresistivity map was used to categorize the study area into four zones (α,β, γ and Ø) indicating varying degrees of subsoil corrosivity and competence. The study revealed that within zone Ø of layer 2, a predominantly moist clay lithology with resistivities from VES points ranging from 14.03 to 29.29Ωm and having a mean thickness of 9.29m is highly corrosive. Zones β, γ, and α have resistivities ranging from 54.4 – 63.97Ωm, 128 – 163.9Ωm and 201.8 – 3789.6Ωm and mean thicknesses of 2.36m, 2.20m and 2.17m respectively. In terms of corrosivity, zones β, γ, and α are respectively moderately corrosive, mildly corrosive and essentially non-corrosive. Layer two sub-soils in VES points 7, 18 and 22 (predominantly in zone α) revealed resistivities indicating that they are both essentially non-corrosive and highly competent. The findings from this study will help to mitigate corrosion of buried metal structures bearing overhead tanks. The potability of water borne by buried metal pipes and structure credibility will also be improved.