Geophysical, Geotechnical, and Geochemical Characterization of Subgrade Materials Along Six Road Corridors in Ondo and Edo States, Southern Nigeria

Abstract

This dataset presents geophysical, geotechnical, and geochemical data collected to evaluate subgrade material integrity along approximately 180 km of road corridors across Ondo and Edo States, southern Nigeria, spanning six corridors: Ondo-Ore, Ore-Irele, Auchi-Okpella, Auchi-Igarra, Igarra-Ibillo, and Ibillo-Okene. At each of 95 stations, I conducted a Vertical Electrical Sounding (VES) using a Schlumberger electrode array (ABEM Terrameter SAS 1000, maximum current electrode separation 20 m) and collected a soil sample at 1.5 m depth for laboratory testing. The dataset includes station coordinates; the digitized field apparent-resistivity curve for 92 of the 95 stations; the fitted three-layer geoelectric model (layer resistivity and thickness) for all 95 stations; the resulting VES curve type (A, H, K, or Q) and resistivity at 1.5 m depth, independently re-derived and verified from the original inversion software output for every station; measured California Bearing Ratio (CBR, %) and the corresponding Subgrade Strength Classification band (Road Note 31, Transport Research Laboratory 1993); and, for 50 samples along four of the six corridors, geochemical properties including effective cation exchange capacity, electrical conductivity, Expansive Soil Index, and clay content. The data support ongoing research on using near-surface geophysical methods, in combination with geotechnical and geochemical soil properties, to predict subgrade strength for flexible pavement design.