Response of Asphalt Pavement Structure Layer and Particle Movement Velocity Based on Particle Flow Theory

An asphalt mixture is a heterogeneous material composed of coarse/fine aggregate, asphalt, and admixtures. The damage of asphalt mixtures under vehicle load is closely related to the movement law of various materials. In order to study the mechanical response of each structural layer of asphalt pavement and the movement velocity of particles in the upper layer under vehicle load, the vehicle–road coupling model was established in this paper using commercially available software. The dynamic force of the tire is obtained in the model. Then, in the discrete-element software, a three-dimensional discrete-element model of asphalt pavement with random distribution of coarse aggregate is constructed according to the material gradation and porosity. Finally, the dynamic force of the tire is loaded into the discrete metamodel by means of moving load. The dynamic response of each structure layer and the moving speed of particles of the asphalt pavement can be solved under the action of vehicle load. The results show that the vertical displacement response of each pavement structure layer is solved by the discrete-element method, and the trend is similar by comparing its vertical displacement curve with the curve obtained by the finite-element method. The difference between the two is 8.9%, which indicates that it is feasible to use the discrete-element method to establish the pavement model in this paper. The following data are obtained by the discrete-element method: as the depth of the pavement structure layer increases, the vertical displacement continues to decrease, and the vertical displacement above the base layer accounts for 75% of the total displacement. The pavement bears both compressive stress and tensile stress in the horizontal and vertical directions. The largest transverse and longitudinal compressive stresses appear in the upper layer, but the largest transverse and longitudinal tensile stresses appear in the middle layer. When the vehicle load crosses the measuring point, the shear stress changes in both ${\tau }_{xz}$ and ${\tau }_{xy}$ directions, but does not change in the ${\tau }_{yz}$ direction. At the beginning and end of the vehicle, the lateral, longitudinal, and vertical velocities of the upper-layer particles change dramatically. In the process of stable vehicle running, the velocity value of particles in each structural layer is small. The transverse and vertical velocity curves of particles are arranged in an antisymmetric way, whereas the longitudinal velocity curves of particles are symmetric. To sum up, under the action of vehicle load, the movement of particles in each structural layer of asphalt pavement has certain rules. The movement behavior of particles will damage the asphalt pavement to a certain extent.