Electrical resistivity measurements in delineating near-surface lithologic units in Federal College of Education, Asaba, Delta State, Nigeria: Implications for building foundation failure

Abstract

An electrical resistivity investigation was carried out in parts of the College of Education (Technical) Asaba to delineate the subsurface lithologic units with special emphasis on the competence and suitability for engineering foundations. A total of ten (10) vertical electrical sounding and two (2) horizontal profiling stations were covered within the study area using the Schlumberger and dipole-dipole configurations. The acquired data was analyzed using WinResist and RES2DINV Software; the subsurface within the study area is composed of mostly 3 geoelectric layers: topsoil, clay/sandy clay/clayey sand and sand. The second and third layers have relatively low resistivity ranging between 29 – 94 Ωm and consist of incompetent clayey material underlying about 60 % of the investigated study area. The interpreted field results showed a significant clay overburden that is over 5 m thick. A fourth layer of sand with resistivity values ranging between 451 – 1258 Ωm was encountered at depths between 4.9 – 11.5 m; the thickness of this layer with reference from the borehole log is greater than 20 m. It is therefore recommended that the incompetent clayey material be avoided or excavated before constructing any structure.