Investigation of Causes of Pavement Failure on Urban Roads in Ibadan, Oyo State

Urban road pavement failure in Ibadan, one of Nigeria's most densely populated cities, has become a critical infrastructure challenge with significant economic and social consequences. This study investigates the causes of pavement failure on selected urban roads within the Ibadan North and Ibadan South-West Local Government Areas of Oyo State, in the South West geopolitical zone. Fifteen road sections totalling 22 kilometres were surveyed using a standardised pavement condition index protocol, documenting distress types including potholing, alligator cracking, rutting, and edge failures. Subgrade soil samples were collected and tested for California bearing ratio, grain size distribution, and plasticity index. Pavement layer thicknesses were verified at selected cut sections against the original design specifications. Results indicate that subgrade failure was the primary cause of pavement distress in sixty percent of surveyed sections, attributed to the prevalence of high-plasticity soils and inadequate drainage design that allows subgrade saturation during the rainy season. Overloading by commercial vehicles exceeding the legal axle load limit of 8.2 tonnes per axle was identified through axle load surveys at two arterial road entry points, with non-compliance rates exceeding seventy percent. Inadequate pavement thickness in three sections was traced to contractor deviation from design specifications. The study recommends a comprehensive urban drainage master plan for Ibadan, strict enforcement of axle load regulations, and adoption of stabilised subgrade layers in future urban road reconstruction. Keywords: pavement failure, urban roads, Ibadan, subgrade, potholing.