Analysis Of Propagation Of Top-down Crack In Asphalt Pavement Using Three Dimensional Finite Element Method

Top-down crack in asphalt pavement is a kind of destruction generated at the surface of asphalt pavement. Due to the effect of repeated load, the top-down cracks will propagate downwards vertically, and influence the service of pavement greatly, even cause the failure of pavement structure. In this thesis, the stress intensity factors of top-down cracks caused by load are calculated using three dimensional finite element method, and the fatigue propagation rules and fatigue lives of top-down cracks are analyzed using Paris Law.During the previous analysis of asphalt pavement structure with cracks, the stress intensity factors were usually calculated approximatively using plane strain model for some limitation. However, the assumptive load of this model is not coincident to the practical load. In this thesis, the stress intensity factors of top-down cracks caused by loading are calculated using three dimensional finite element model and compared to the results of plane strain model. The stress intensity factors calculated using three dimensional finite element model are obviously less than the stress intensity factors calculated using plane strain model (the ratios are about 30% to 100%) and the distinctions increase with grew depth of cracks continuously. Therefore, the obvious distinctions of fatigue lives of top-down cracks calculated by Paris Law are also existed: the ratios of the fatigue lives of top-down cracks using plane strain model to the ones using three dimensional finite element model are about 34% to 94%. As the wheel load assumed in three dimensional model is more consistent to practical loading, the results are more accurate.Based on Paris Law, the effects of different parameters of fatigue model and pavement structure on the fatigue propagation rules and fatigue lives of top-down cracks are analyzed using appropriate numerical method, and some recommendations about pavement material selection and structure design are presented. The analyses of overloading and non-uniform distributed load show that the fatigue lives of asphalt pavement decrease rapidly for the increment of load and non-uniform distribution of load resulted from overload. Therefore, it should be attached great importance to the limitation of overload.