Study On Fatigue Performances And Design Method Of Flexible Base Asphalt Pavement

In recent years, there are much severe early distresses in asphalt pavements of high grade road in China. Structrual defect of semi-rigid pavament is likely to be one of the reasons. Flexible base asphalt pavements are used widely in many countries due to their good performance,but few in China. To study an approach to prolong the service lives of asphalt pavements, the fatigue performance characteristics of flexible base asphalt pavement are analysed and a pavement design method was brought forward in this dissertation.Firstly, Based on the analysis of fatigue damage develop process, the failure criterion in fatigue of asphalt mixtures was defined as the number of load cycles at which the damage begins to increase rapidly. And then fatigue damage model of asphalt mixtures based on damage theory was developed. Statistical examination indicates that the new fatigue damage model appeared to unify between two modes of loading, constant atress or constant strain.Secondly, the performances of different structure asphalt mixtures was analyzed. For the optimizing target as fatigue performance, rut-resistance property and compositive performance respectively, the asphalt mixture were optimized combining BP nerve net with Genetic Algorithms. The fatigue cracking of asphalt layers should be controlled using flexural-tensile strain in the bottom of asphalt layers. The factors which have great influence on fatigue life of asphalt mixtures and their influence rules were analyzed, thereby a fatigue model include those parameters was presented. Then, the shift factors of fatigue life of pavements in the field were achieved according to the survey results of asphalt pavements in China and the fatigue criterion for design was presented. In succession, factors effect the modulus of compression of asphalt mixtures were analyzed and a formula to estimate the modulus of compression of asphalt mixtures according to air void contents was presented. On the other hand, considering the nonlinear characteristic of unbound granular materials, modulus determination formulae and nomogram of granular base was developed. Axle load conversion methods based on fatigue equivalent were studied. And the calculation method of fatigue critical temperature of pavement was achieved on base of the analysis of fatigue damage of asphalt pavement in different temperature. Therefore the design process of flexible base asphalt pavements and a demonstration was given.Lastly, through the construction of MAPING test road in QINGHAI province, the reasonable construction method and economical characteristic of asphalt treated base were studied. And then economic characteristic of different structure asphalt pavements was analyzed. At last the performance of test road was predicted by the method which been presented before.