Subsurface Lithological Characterization of Custech Internal Road Using Integrated Geophysical and Geotechnical Methods

Abstract

The durability and performance of road pavements are strongly influenced by the competence and engineering characteristics of the underlying subsurface materials. Inadequate knowledge of subsurface lithology, weak foundation materials, and spatial variations in weathered or fractured zones can contribute to pavement instability and premature failure. Therefore, integrating geophysical and geotechnical investigations provides a more reliable basis for assessing subsurface conditions before road construction. This study presents an integrated geophysical and geotechnical investigation carried out along the proposed internal road of Confluence University of Science and Technology (CUSTECH), Osara, Kogi State, Nigeria. The study aimed to evaluate the subsurface materials to support competent road-pavement structures using an integrated geophysical and geotechnical approach. The investigation combined Vertical Electrical Sounding (VES), 2D Electrical Resistivity Tomography (ERT), and dynamic Cone Penetration Tests (dCPT). The VES and ERT results were quantitatively and qualitatively analysed using WinResist and DiprofwWin software, detecting four (4) distinct geoelectric layers. The topsoil resistivity values vary between 86.1 Ωm and 286.4 Ωm from the surface to a depth of 1.3 m, followed by the weathered basement, with resistivity values varying from 191.5 Ωm to 330.1 Ωm and basal depths ranging from 3.5 m to 5.2 m. This is underlain by competent basement with resistivity values of 1654.9 Ωm and 861.1 Ωm on VES 1 and 2, respectively, while VES 3 has fractured basement with a resistivity of 175.3 Ωm at this layer and competent basement (1106.5 Ωm) underneath. The ERT models showed that the layers identified by the VES are horizontally continuous, with average basement depths of 4.5 m, 4.7 m, and 10.0 m at the beginning, midpoint, and end of the road, respectively. The CPT results showed maximum cone resistances of 95 kg/cm² at 0.75 m, 130 kg/cm² at 1.25 m, and 85 kg/cm² at 2.00 m at the beginning, midpoint, and end of the road, respectively. The study concludes that the proposed road alignment is generally underlain by competent basement materials suitable for road pavement at differing depths and advises that the near-surface weak section be enhanced by adequate grouting. This research underscores the importance of an integrated study for subsurface lithological evaluation for road-pavement construction.