Investigation of the Top-Down Cracking Propagation Behavior of Flexible Asphalt Pavement Based on Numerical Modeling and Full-Scale Accelerated Pavement Tests

Top-down cracks (TDCs) and their associated secondary damage have emerged as critical factors limiting the long-term service performance of flexible asphalt pavements. The mechanisms underlying various types of TDCs, however, remain inconclusive. This study develops a three-dimensional finite-element (FE) viscoelastic road dynamic response model to investigate pavement responses at different locations under traffic loads. The initiation mechanisms of different TDC types are identified, and the propagation behavior of cracks in damaged pavements is examined using the extended finite-element method (XFEM) to simulate existing fractures. Comparative analyses between simulated and experimental results validate the accuracy of the developed FE model in predicting pavement behavior. The findings reveal that longitudinal wheel-path TDCs are primarily caused by shear stress, transverse TDC by longitudinal tensile stress, and longitudinal non-wheel-path TDCs by transverse tensile stress. The stress intensity factor (SIF) at the crack tip is used as the evaluation criterion. Overloading exhibits a uniform effect on the propagation of various TDC types, whereas low speed demonstrates differential effects. Furthermore, the impact of overloading on TDC propagation is significantly greater than that of low speed. Mitigation strategies indicate that a thicker asphalt layer and shallower cracks effectively reduce crack propagation, with the former being more impactful.