Subsurface investigation for road construction using electrical resistivity method along Oloko road, Apatapiti, Akure, Ondo State, Nigeria

Evaluation of the shallow geologic materials in terms of types, nature, and bedrock structure as possible causes of pavement failure was carried out along Oloko road Apatatpiti, Akure, Nigeria, using Schlumberger vertical electrical sounding and 2-D imaging dipole-dipole techniques. Three lithological layers, namely thin top soil, weathered layer and weathered basement, were revealed by the 2-D resistivity structure. Vertical electrical soundings were made at locations with a very low resistive medium typical of linear features such as fractures/faults at some distances on the 2-D resistivity structure. Four geologic layers, namely the top soil, clay/sandy clay, fractured basement, weathered/fresh basement, were identified by the geoelectric section. The geoelectric section and the 2-D resistivity structure revealed that the upper 0-6m, which constitutes the subgrade, has a low resistivity (36 Ωm to 108 Ωm) characterised to be clayey materials and suggestive of weak zones that might impair the stability of the road. A relatively shallow depth, ranging from 3.7 m to 4.29 m, was the depth to the water table of the four wells close to the road. Therefore, the possible causes of pavement failure are the thick and low resistive layer, the near-surface linear features suspected to be fractures/faults, and the water table's shallow depth.