GEOPHYSICAL INVESTIGATION FOR DESIGN AND CONSTRUCTION OF CIVIL ENGINEERING STRUCTURES IN SABON-GARI-MAU, YOLA, ADAMAWA STATE, NIGERIA

Abstract

Electrical resistivity method was carried out using Vertical Electrical Sounding (VES) at Sabon-Gari-MAU, Adamawa State, Nigeria; to evaluate the competence of the shallow subsurface for construction of civil engineering structures. VES data was generated using the schlumberger configuration. The half- currents electrode (AB/2) was used and the quantitative interpretation of the VES involved partial curve matching and 1-D computer iteration and the outcome was presented as geoelectric curves and geoelectric sections. Twelve VES points were sounded and seven geoelectric sequences were identified; the topsoil (sand, silt, silty sand and laterite) with resistivity (10Ωm-683Ωm) and thickness (0.3m-6.39m); the ferruginized sandstone with resistivity (15Ωm-2666 Ωm) and thicknesses (0.11m-4.91m); the indurated and resistive sandstone having resistivity (1241Ωm-17,781Ωm) and thickness (2.85m - 30m); the water-bearing sandstone with resistivity (57Ωm-188Ωm) and thickness (2.68Ωm-55.66Ωm); the wet sandstone with resistivity (10Ωm-119 Ωm) and thickness (0.367m - 54m); the dry sandstone with resistivity (209Ωm-389Ωm) and thickness (0.783m-15.37m); and the clay unit with resistivity (2.11Ωm-35 Ωm) and thickness of 0.06m. The VES results showed a significant overburden that is up to 6.39m. The VES curves revealed six geoelectric layer combinations of A, AH, HA, HK, KH and KHA types. The A, HA and HK curve types; each constituting 25% and the AH, KH and KHA curve types each constituting 8.33% of the total. The upper subsoils proved competent to support civil engineering structures having appreciable resistivity values. The VES indicate no major geologic structure or appreciable clay content in the upper subsoil. Hence the subsoils are competent for foundation and buried metallic engineering structures are not liable to corrosion.