Mesoscopic Analysis Of Triaxial Torsional Shear Characteristics Of Coarse-grained Asphalt Mixture Based On Discrete Element Method

Existing research shows that most of the early damage of asphalt pavement is directly related to the lack of shear strength of asphalt pavement.With the development of China transportation industry,pavement diseases appear more and more frequently.At present,the research on the shear resistance of asphalt mixture mostly stays at the laboratory macroscopic test level,and the failure characteristics of the material are not analyzed at the meso level.This paper analyzes the shear characteristics of asphalt mixture at the meso level using the discrete element method.The main work done are as follows:(1)Two methods are used to generate the numerical model of asphalt mixture.One is to use the ball distribute command to generate the numerical model of the specified gradation by writing the FISH function.The second is to use the external software Unity3D to generate particles of the specified gradation,and then export the position and radius information of the particles,and then read the particle information into PFC3D by writing the FISH function to generate the mixture specimen model.After the particle model is generated,the model is compacted by the particle expansion method.Finally,the gradation generated by the above two methods was compared with the theoretical gradation,and the coordination number,porosity and unbalanced force of the model were monitored,which showed the feasibility of these two methods.(2)Based on PFC3D,the uniaxial compression test of asphalt mixture is simulated.The parallel bonding contact model is selected to simulate the bonding effect of the asphalt mortar in the specimen.Analyze the influence of the contact meso-parameters in the model,effective modulus,bond strength,and friction coefficient on the compressive modulus and failure strength of the specimen.Based on the results of the uniaxial compression test,the meso-parameters of the mixture model at 20 ℃ are calibrated.The meso-mechanical characteristics such as the change of model particle displacement,the development of cracks and the change of contact force during uniaxial compression are analyzed.(3)Based on PFC3D,the triaxial shear test of asphalt mixture is simulated.Based on the existing triaxial compression test results,the meso-parameters of the mixture model at 60℃are calibrated.The stress-strain curves of the specimen under different confining pressures of138 k Pa,276 k Pa,and 414 k Pa are obtained.The meso-mechanical characteristics such as the change of model particle displacement,the development of cracks and the change of contact force during triaxial compression are analyzed.(4)Based on the establishment method of the initial model,a numerical model of coarse-grained SMA-13 asphalt mixture with a particle size greater than 4.75 mm is generated.A new method,the "top wall rotation method",was used to simulate the torsion shear numerical test on the SMA-13 asphalt mixture specimen.Based on the rotary shear tester developed by the research group,the mechanical parameters of SMA-13 asphalt mixture at20°C were measured.Comparing the results of the torsion shear test simulation with the results of the laboratory test,it proves the rationality of using the "top wall rotation method" to simulate the application of the torque in PFC3D.The effects of the mesoscopic parameters of the contact in the model,effective modulus,bond strength,friction coefficient,and stiffness ratio on the shear modulus and failure strength of the specimen are analyzed.The meso-mechanical characteristics such as the change of model particle displacement,the development of cracks and the change of contact force during the torsional shearing process are analyzed.