Geotechnical Evaluation of Traffic-induced Load effects on Pavement Sub-Grade Bearing Capacity Along the Okene–Auchi Highway, Nigeria

This study investigates the effects of heavy traffic loading on subgrade bearing capacity using field and laboratory data obtained from Jattu Junction along the Okene–Auchi Highway, Nigeria. Manual traffic count data were converted into Equivalent Single Axle Loads (ESAL), resulting in an Index Daily Traffic (IDT) of 7,985 ESAL/day and a corresponding daily axle mass of 2,984.86 tonnes. Heavy vehicles, including trucks and trailers, account for over 95% of the total traffic loading, imposing substantial stresses on the pavement subgrade. Geotechnical laboratory tests revealed specific gravity values ranging from 2.46 to 2.49, liquid limits of 11–35%, plasticity indices of 5–12%, maximum dry density (MDD) values of 1.81–1.95 Mg/m³, optimum moisture content (OMC) of 10.2–11.8%, and soaked California Bearing Ratio (CBR) values between 5% and 45%. The results indicate that more than half of the sampled soils fail to satisfy the minimum soaked CBR requirement of 30% specified for subgrade design, demonstrating inadequate load-bearing capacity under prevailing traffic conditions. The study establishes a strong relationship between heavy traffic loading, moisture susceptibility, and reduced subgrade strength, all of which accelerate pavement deterioration through rutting, deformation, and premature failure. These findings highlight the importance of integrating traffic loading characteristics with geotechnical properties during pavement design and maintenance planning. To enhance pavement durability and long-term service performance, the study recommends appropriate subgrade stabilization techniques, strict enforcement of axle load regulations, and improved drainage systems to minimize moisture-induced weakening of the subgrade.