Effect of pavement roughness and vehicle dynamic loads on decrease of fatigue life of flexible pavements

Due to the fact that pavement surfaces are not ideally even, dynamic loads of vehicle axles deviate from static loads. Higher dynamic loads contribute to faster pavement distress. The distribution of dynamic loads is similar to normal distribution and can be described by static load and factors DI (dynamic impact) and DLC (dynamic load coefficient). With the deterioration of pavement condition its evenness decreases as well and the roughness index IRI increases. The maximum dynamic loads increase and their detrimental effect on pavement structure increases. The main objective of the paper is to assess how dynamic loads caused by pavement roughness affect pavement distress. In the article a new measure – the coefficient of pavement dynamic susceptibility DSC has been introduced. The coefficient DSC expresses the absolute increase in equivalent axle load factor caused by dynamic load effects. It was shown that with the increase in roughness from IRI = 1.0 mm/m (which is the value measured for new properly constructed pavements) to IRI = 2.0 mm/m, the coefficient DSC increases by up to 8%. Further deterioration of roughness to IRI = 4.0 mm/m causes increase of DSC by up to 32%. In consequence of increase of coefficient DSC the fatigue life of pavement structure decreases by 5.5% for IRI = 2mm/m and by 23% for IRI = 4 mm/m. It means that low initial roughness of pavement structure gained by high quality of road construction and proper maintenance of pavement during service will reduce pavement distress and increase its service life.