EVALUATING THE IMPACT OF VEHICULAR CHARACTERISTICS ON THE DYNAMIC RESPONSE AND RUTTING OF FLEXIBLE PAVEMENT STRUCTURES A CASE STUDY OF AWASH TO METEHARA ROAD

Abstract

Nowadays, the cost for the reconstruction or maintenance of paved roads is increasing at alarming rate. Prior to carrying out maintenance works, by examining the pavements response and performance using effective tools and methods the Ethiopian road networks must be rated. This enables to minimize misallocation of the maintenance funds. Although a lot of investigations was carried out on pavement material failures and viable solutions in Ethiopia. However, the trunk road failures caused by truck-related factors were not studied yet. This was one of the reasons behind conducting this study along the Awash to Metehara road. Hence, the objective of the study was to evaluate the impact of vehicle characteristics on the pavement dynamic response and rutting. Using Asphalt core cutter samples were taken from the field to conducts asphalt laboratory tests and DCP tests were carried out at the field to determine sublayers thickness and CBR. The minimum, average and maximum truck speeds surveyed using the direct timing procedure along the Awash to Metehara road was 11km/h, 32km/h and 48km/h. The maximum axle load collected from both Awash and Modjo size and weight control stations was 16tones for the front axle and 21tones for rear axle. The measured rear tandem axle spacing of the truck was 1.40m. For the tridem axle truck the spacing between the rear axles was 1.32m for the first and 1.37m for the second axle. The impact of these study subjects was examined at three sections of the road using the 3D Move Analysis Software. In most cases, as the speed of the truck was increased from 11km/h to 48km/h, the longitudinal tensile strain at the bottom of the Ac layers also increased. The compressive strain at the top of the subgrade and the displacements does not fluctuate with these speed changes. During the wheel load increase from 26kN to 51kN the longitudinal tensile strain was also increased under tandem axle and decreased under tridem axle. The rest compressive strain and displacement responses was increased with the load increase. The tandem axle configuration produced lower longitudinal tensile strains than the tridem axle. Axle configurations had no significant effect on the compressive strain. Under legal loading conditions of the trucks, tandem axles induced around 65% more displacements than tridem axles. However, under overloaded conditions of the truck, the tandem axles produced around 69% lower displacements than the tridem axles. At all sections of the road, as speed of tridem axle truck increases from 11km/h to 48km/h, AC rutting decreases up to a maximum vii of 28.33%. However, the sublayers rutting either remains the same or increases up to a maximum of 10.38%. As the wheel load of tridem axle truck increases from 26kN to 51kN, AC rutting also increases up to a maximum of 20.25%. However, the sublayers rutting decreases up to a maximum of 46.05%. Under legal loading condition of the truck, the tandem axle caused a maximum of 193% and 673% lesser AC and sublayer rutting than the tridem axle, respectively. However, under overloaded condition, the tandem axle caused 18.54% and 50% more AC and sublayer rutting than the tridem axles. The impact of the tire load increase from 26kN to 51kN on the pavement response and rutting was found higher than speed changes and axle configurations. Therefore, the need of weight restrictions was more sensitive issue than the speed