Determination of flexible pavement thickness: A case study.

Traffic volumes have increased rapidly in recent years across all major highways of Iraq due to the ongoing increases in economic growth in the region. The ability of a pavement structure to perform its main function decreases as traffic load increases, especially where overloaded heavy vehicles pass along a road. The majority of the road pavement is designed with vehicle legal load limits in mind: however, these may not always be adhered to, as most transportation businesses seek to reduce transportation costs by avoiding repetition of vehicle routes. Excessive truck traffic can cause economic, environmental, and social harm, however, and in this paper, the Iraqi State Commissions of Roads and Bridges (SCRP) code, AASHTO, and the Asphalt Institute method are used to analyse the effects of overloaded vehicles on road pavement thickness as compared to standard conditions. For both standard conditions and overloading cases, the traffic load expressed by Equivalent Single Axle Load (ESAL) and truck factor were thus calculated, and the differences resulting from overloading thus identified. Traffic data from the Khalis–Odayam road were used in this paper to form a case study, allowing assessment of the impact of repetitive load conditions on the structural design, and any increase in layer thickness above the legal axle load limit that ensues. The results obtained from this work show that the total thickness of the paving layers as assessed using the AASHTO method was 805 mm and that by the Asphalt Institute method was 800 mm; these results were thus relatively close, despite the fact that the value of the ESAL was valued at 9.8*10^8 in the AASHTO method and 7.9*10*8 in the asphalt institute method, while the thickness values required by the two methods was greater than the current thickness of the road, indicating failures and distortions in the road after each successive road maintenance. According to these findings, overloaded vehicles on the road thus have a significant impact on pavement service life and necessitate to laying of thicker pavement. [ABSTRACT FROM AUTHOR]