APPLICATION OF ELECTRICAL RESISTIVITY TOMOGRAPHY IN ENGINEERING SITE CHARACTERIZATION: A CASE STUDY OF IGARRA, AKOKO EDO, SOUTHWESTERN NIGERIA

To better understand the subsurface geological composition (relief, fault, fracture, discontinuities, orientation of structures) of the surrounding environment that anticipates infrastructural development in the near future due to population explosion, an Electrical Resistivity Tomography (ERT) survey was conducted in Igarra, Akoko Edo area of Edo state, Nigeria. The depth to bedrock, possible geologic structures (faults, fractures, voids) were some of the properties investigated. To determine the orientation and continuity of the underlying geological features, 2D resistivity surveys were conducted along three parallel traverses (S-N orientation) with a total length of 205m and an inter-traverse spacing of 50m. The ERT results demonstrate that there are constant areas of low resistivity along the three traverses. Stations between 70 m – 90 m and 110 m – 150 m revealed low resistivity values, indicating possible geological structure. As seen in the resistivity pseudo-section, competent beds can be found at around 5 m and about 10 m in some stations (70 – 90 m and 110 – 150 m). It is generally accepted that geological features (fault, fracture) that pose a risk to geotechnical and engineering projects can be found in the regions with low resistivity. According to the research, pervasive underground geological structures are to blame for most road failures. Since electrical resistivity tomography is useful in describing an engineering site, further geophysical investigation for hydrogeological objectives should be undertaken on the identified faulted and fractured zones to establish its hydrologic importance and reserved for such.