Structural, Geotechnical, and Traffic-Induced Mechanisms of Early Flexible Pavement Failure: Empirical study of the Ugep–Idomi Highway Strip, Cross River State, Nigeria

Abstract

The early deterioration of flexible highway pavements is a significant infrastructure issue in tropical developing areas. This research examines the structural, geotechnical, and traffic-related factors that contribute to pavement damage along the Ugep–Idomi road corridor in the Yakurr Local Government Area of Cross River State, Nigeria. Field studies included measuring the structural profile of exposed layers, conducting a six-day manual traffic volume survey, and collecting soil samples at depths of 3.28 ft (1.0 m) and 3.94 ft (1.2 m). Laboratory tests assessed index properties, particle size distribution, Atterberg limits, Modified Proctor compaction, and soaked California Bearing Ratio (CBR) values

Physical measurements indicated in-situ layer thicknesses of 3.91 in (99.3 mm) for the surface course and 9.35 in (237.6 mm) for the sub-base course. Geotechnical analysis classified the subgrade material as low-plasticity silty clay (AASHTO A-4/A-6), with 59.4% passing the No. 200 sieve, a Liquid Limit of 25.5%, a Plastic Limit of 16.5%, and a Plasticity Index of 6.5%. The Modified Proctor compaction test resulted in a Maximum Dry Density (MDD) of 116.74 lb/ft³ (1.87 g/cm³) at an Optimum Moisture Content (OMC) of 12.5%, while the average soaked CBR was 8.3%. Traffic analysis showed an Average Daily Traffic (ADT) of 13,422 vehicles per day (northbound) and 13,128 vehicles per day (southbound), total 26,550 vehicles per day for the corridor. Structural assessment determined that a minimum sub-base thickness of 13.39 in (340.0 mm) is necessary based on current Equivalent Single Axle Load (ESAL) projections, indicating a structural deficiency of 4.04 in (102.6 mm), or a 30.2% shortfall. Key factors contributing to pavement distress included inadequate sub-base design, high moisture sensitivity of the subgrade, unmanaged capillary rise, heavy commercial traffic, and a complete lack of side drainage infrastructure. Recommendations for restoring the corridor's functionality include chemical stabilization, structural reconstruction using locally sourced high-strength aggregates, and the implementation of integrated drainage systems.