GEOPHYSICAL AND GEOTECHNICAL INVESTIGATION OF SOME FAILED SECTIONS ALONG THE AKURE-ALADE-OWENA ROAD, SOUTHWESTERN NIGERIA

Abstract

Electrical resistivity measurement and geotechnical tests were undertaken along Akure-Alade Owena road, Southwestern Nigeria with a view to determining the possible causes of the pavement failure along the studied road. Four traverses were established in the study area, the dipole-dipole measurement was taken at 5 m electrode interval and a total of twenty three (23) vertical electrical sounding (VES) were obtained along the traverses. The geotechnical tests were carried out on 15 soil samples obtained at depths not exceeding 1 m. In the four studied locations, the geoelectric section revealed that the locations were underlain by four geoelectric layers namely; the topsoil, subsoil, weathered/fractured layer, and fresh basement rock. The major part of the topsoil was characterized by relatively low resistivity values (<100 Ωm) suggestive of weak zones that are capable of causing failure of the road. It was observed that the uppermost layer (0-6 m) exhibits very low resistivity values (<24 Ωm) along traverse 3, these suggests the presence of plastic clay as observed in the study area which can lead to reduction in the bearing capacity of the soil. The 2D resistivity model depicts the presence of linear features / fractures and shallow water table that could be inimical to the road pavement. The Susceptibility classification showed that the road could be rated as poorly to moderately susceptible to failure with location 3 being the most susceptible to failure. The geotechnical results revealed that most of the investigated soil samples are clayey in nature and have properties below Federal Ministry of Works specification. Finally, it was established from the results that the geophysical results correlates with the geotechnical results showing the clayey nature of the soil samples and thus are weak engineering materials