Geophysical and Geotechnical Investigation of Road Pavement Failure in Part of Ibadan Metropolis Southwestern Nigeria

Abstract

Road pavement failure observed along a section of Apete-Akufo Major Road in Ibadan metropolis southwestern Nigeria, necessitates the need to ascertain whether the failure results from poor construction practices or poor engineering properties of subgrade materials. Geophysical and geotechnical survey results were compared to investigate the cause of the road pavement failure. Vertical Electrical Sounding (VES) with geotechnical study which include; grain size analysis, Atterberg limits and California Bearing Ratio (CBR) tests, were carried out on disturbed subgrade samples obtained between 0 – 1 m depth from VES Stations 1, 2 and 5, corresponding to unstable, stable and highly unstable sections of the road respectively. The quality of the subgrade was evaluated based on Atterberg limits, layer resistivity and CBR values. Eight (8) VES stations established 100m apart along the road section delineated 5 lithology; topsoil, clayey sand/lateritic clay, weathered bedrock and fresh bedrock with resistivity range of 68-238Ωm, 72-236Ωm, 224-859Ωm and 6720-15351Ωm respectively. Low overburden resistivity characterized failed sections. Sample from VES Station 5 has very low wet or dry bearing capacity responsible for observable failure of the road section. Sample from VES Station 1 presents high dry bearing capacity (70%) but low wet bearing capacity (11%), suggesting poor drainage may be responsible for pavement failure at the section. Sample from VES Stations 2 presents similar wet and dry bearing capacity resulting in stable road pavement. The study indicates poor construction practices, lack of proper drainage and poor engineering properties of subgrade materials as the causes of road pavement failure along the observed section of Apete-Akufo Major Road.