Simulation Study Of Asphalt Pavement Cracking Based On Discrete Element Method

Asphalt pavement is a multi-layered structural system composed of different materials,the characteristics of each structural layer material directly affect performance of pavement structure.Pavement cracking is one of the main forms of damage to asphalt pavement,some of them are directly cracked by the surface layer,and some are cracked by the base layer and reflected to the surface layer to cause cracking.The structural layers of the pavement are typical multiphase composites,the particle shape and distribution of aggregates and the bonding state between aggregates have certain influence on the cracking of road surface.In this paper,through the discrete element method PFC2D,nonlinear models are used to define the contact between particles,numerical calculation is carried out at the mesoscopic level to simulate the formation and expansion of the internal crack of asphalt pavement under vehicle load and monitor the mechanical state of corresponding positions,analysis of the causes of cracks and research solutions.In this paper,the discrete element analysis model of pavement structure is established.Firstly,according to material characteristics of asphalt surface layer,graded gravel base layer and cement stabilized base layer,the author select suitable contact models for particles.Then,the mesoscopic parameters of contact models are calibrated by uniaxial compression test,splitting test and biaxial compression test that will provide contact model parameters for discrete element models.Finally,the author establish three sets of semi rigid base asphalt pavement models with the thickness of asphalt surface layer as a single variable,and six sets of graded gravel base semi-rigid subbase asphalt pavement models are established with the thickness of asphalt surface layer and graded gravel base layer as control variables.Each set of pavement models is 2m in length,simulating a section of the road longitudinally,a preset crack is set in the cement stabilized base layer to represent shrinkage crack,vehicle load is arranged in an off-load manner and measurement circles are set at the interface between surface layer and base layer to monitor and record relevant mechanical response.The formation and expansion of cracks in different pavement structures under vehicle load are compared and analyzed.In the semi-rigid base asphalt pavement model,the preset crack extends from the tip to the surface layer to form the reflective crack in the direction of inclined loading plate.As the thickness of surface layer increases,the development trend of reflective cracks slows down,the total number of mesoscopic cracks in the model decreases,the concentration of stress at the tip of the preset crack is weakened,and the peak values of horizontal stress,vertical stress and shear strain decreases.In the graded gravel base semi-rigid subbase asphalt pavement models with same thickness of asphalt surface layer,the number of reflective cracks is reduced and their distribution position is relatively discrete,the total amount of cracks inside structures is large,and it increases with the increase of the thickness of graded gravel base layer,the fatigue damage of asphalt surface layer is aggravated.At the same time,the thickness of base layer increases,the peak values of vertical stress at the interface between surface layer and base layer of preset crack directly above decreases,the attenuation amplitude increases,and the concentration of stress at the tip of the preset crack is weakenedBased on two test road structures,deflection test,load plate test and drilling core sampling were carried out.It was found that under the action of vehicle load,transverse reflection crack in the semi-rigid base asphalt pavement developed seriously.There is no reflection crack in graded gravel base semi-rigid subbase asphalt pavement,but there is longitudinal crack along the driving direction.