Near surface resistivity investigation of regolith of Middle Benue Trough: implications on road pavement along Lafia-Shendam Axis, North Central Nigeria

Abstract

ABSTRACT Electrical characteristics and subsurface structures associated with the regolith of Middle Benue Trough have been investigated. Vertical electrical sounding (VES) and constant separation traversing (CST) techniques were employed for data acquisition along Lafia-Shendam Road, Lafia, North Central Nigeria. Forty (40) Schlumberger sounding stations and four (4) Wenner resistivity profiles were occupied along opposite sides of the road to delineate and decipher the subsurface geological structures. Second-order Dar Zarrouk parameters (longitudinal and transverse resistivities, mean resistivity and coefficient of anisotropy) computed from VES parameters were also used to evaluate the pseudo-anisotropy characteristics of the regolith cover. Geoelectric sequences delineated within the study area include thin topsoil, alluvium deposit, weathered layer (laterite and saprolite) and fresh basement. The regolith is hosted by a weathered sedimentary rock at an average depth which varies from 10.2 to 37.3 m. The regolith structure is not complex and has a greater proportion of conductive laterite. The saprolite associated with the host sedimentary rock, masked in the VES technique, is revealed as a very thin zone with moderate resistivity in the CST 2-D structures. The predominance of laterite in the regolith is also corroborated by the range of values of the coefficient of anisotropy and mean resistivity.