Application Of 2-D and 3-D Electrical Resistivity Tomography of Subsurface Weak Zones for Urban Infrastructure Stability Assessment: A Case Study of Anwai in Asaba, South-South Nigeria

Abstract

In the developing world, the need for comprehensive subsurface characterisation prior to infrastructure development has grown. The primary cause of the instability of the foundation, differential settlement, road failure and structural collapse is still ignorance of the subsoil. This study employed integrated two-dimensional (2-D) and three-dimensional (3-D) Electrical Resistivity Tomography (ERT) to identify subsurface weak zones and evaluate their implications for urban infrastructure stability in Asaba, Delta State, Nigeria. Electrical Resistivity data was collected along nine parallel traverses of 100 m using a PASI Earth Resistivity Meter using Wenner–Schlumberger array. The data were processed and inverted to generate 2-D resistivity sections, which were integrated into quasi-3-D depth slices, fence diagrams, and volumetric resistivity models for improved subsurface visualization. The inverted models revealed highly variable lithology, moisture content, and weathering conditions, with resistivity values ranging from approximately 20 Ωm to over 5000 Ωm. Low resistivity anomalies were interpreted as zones of weathered sediments, saturated clay lenses, and possibly groundwater accumulation along Traverses 3, 5, and 6 extending through the core area of the profiles from 1.7 m down to 11 m. These weak zones' continuity was verified by the 3-D volume diagram and iso-resistivity models, which showed how they were spatially connected over several traverses. Moderate-to-high resistivity values, suggestive of relatively competent sandy formations appropriate for foundation support, were the main characteristic of Traverses 1, 7, 8, and 9. The integrated 2-D and 3-D ERT approach effectively identified areas at risk of differential settlement, foundation instability and zones of geotechnical competence The results demonstrate that electrical resistivity imaging is a reliable, cost-effective, and non-invasive tool for urban geotechnical investigations and sustainable infrastructure planning in rapidly urbanising sedimentary environments.