Evaluation of Performance of Pavement Founded on Reinforced Earth Sections along Outer Ring Road, Nairobi

Abstract

There are no existing local design manuals and construction guidelines for reinforced earth structures in Kenya. The objective of this study was to evaluate the performance of the pavement found on reinforced earth sections along Outer Ring Road. The structural evaluation was determined from deflection measurements using Falling Weight Deflectometer (FWD), while the functional evaluation was by visual condition survey, roughness, and rut depth measurements. Classified traffic counts and axle load surveys were undertaken. It was established that the design traffic would be exceeded in year 10 after opening the road. The surface condition survey indicated that the pavement surface for the entire road was generally in good condition. The roughness rating for the entire road was rated "Good", while ten sections of reinforced earth embankment were rated "Fair". The characteristic rut depths on the reinforced earth sections were higher than the lane characteristic rut depth for the entire road. Three sections of the reinforced earth showed low severity, while the rest had no rutting. The PCI for the pavement on reinforced earth sections were lower than pavement on other sections of the road due to a higher International Roughness Index (IRI). The FWD deflections were higher on reinforced earth sections. It was found that the mean pavement moduli for surfacing and base, crack relief and subbase layers at reinforced earth sections were lower than for the pavement in other sections hence requiring thicker overlays. The overall residual life of the road was 17 years, while for the reinforced earth sections was 15 years. Based on the findings, monitoring of the traffic and performance of pavement on the reinforced earth embankments is vital for interventions to prevent premature pavement failure. There is a necessity to develop a design manual and construction guidelines for reinforced earth structures based on the local conditions in Kenya.