Implications of subgrade geoelectric characteristics on road pavement performance of Shagamu-Benin Expressway, southwestern Nigeria: A case study
vol 70, pp 91-100
The Ogbere, Arowoselu, Omotosho, Asejire and Okada localities of the Shagamu-Benin Expressway have been investigated using electrical resistivity method of geophysical prospecting. The aim was to delineate the subsurface conditions of the road pavement at the localities with a view to establish possible modes of failures. Sixty-five (65) Schlumberger Vertical Electrical Sounding (VES) points were occupied at five localities. The VES data were interpreted by partial curve-matching technique and computer-assisted 1D forward modelling. The geoelectric parameters (resistivity versus thicknesses) obtained from the VES interpretation were used to generate 2D geoelectric sections beneath the ground. 2D electrical resistivity imaging (ERI) was conducted at the same localities using dipole-dipole array. The 2D ERI data were inverted using the DIPRO software. The geoelectric sections and 2D resisitivity structures beneath Ogbere, Arowoselu, Omotosho, Asejire and Okada localities delineated lateritic clay/laterite and clayey weathered layer as the near-surface layers/subgrade materials. At the failed localities, the resistivities of the subgrade materials are generally below 400 ohm-m with thicknesses ranging from 0.8 to 7.6 m. The stable portions of the road segments are characterized by subgrade materials with relatively high resistivities> 600 ohm-m) in general. The low resistivity of subgrade materials and underlying layers is diagnostic of incompetent substrata which are suspected to have precipitated the pavement failure along the studied highway segments.