Study On Mechanical Properties Of Asphalt Pavement Structure Based On Frequency Attenuation Of Stress Response In Depth Direction

Under the loading of vehicle on asphalt pavement,the influence range of vehicle load is affected along the depth direction of the pavement structure,which can lead to the change of stress response frequency at different depths.Asphalt mixture mechanical parameters can be influenced by the non-uniform distribution of frequencies along the depth direction,such as dynamic modulus and fatigue equation.At present,the frequency inside the asphalt pavement surface layer is regarded as a uniform distribution in Chinese specification,it is difficult to reflect the superimposed influence of the dynamic modulus and the strain fatigue equation on pavement mechanical properties at different frequencies.In this paper,finite element calculation was carried out for six commonly used forms of asphalt pavement structures in China to analyze the variation of stress response frequency with depth,and based on the decay characteristics of stress response frequency to analyze the mechanical response and fatigue damage of asphalt pavement structures.Firstly,a three-dimensional model of the pavement structure was established using ABAQUS finite element software.The asphalt layer was subdivided into 2-cm-thick sub-layers,and the load influence range and stress response frequency were identified by analyzing the vertical stress variation curve of each sub-layer along the longitudinal direction of the road.The modulus at the corresponding frequency was selected from the dynamic modulus master curve.The variation law of the stress response frequency along the depth of different pavement structures under different axle loads,vehicle speeds,asphalt layer thickness and asphalt mixture types was analyzed by iterative calculation,and compared with the measured data and theoretical methods in the relevant literature for verification.The results show that the method for determining the stress response frequency was consistent with the trend of the measured data,and was closer to the measured value than the classical Odemark method;under the action of the standard axle load and the reference speed 70km/h,the stress response frequency of the asphalt layer was in the range of 5～3 7Hz;The stress response frequency was affected by axle load,vehicle speed and asphalt layer thickness.Secondly,based on the results of the stress response frequency and dynamic modulus,the pavement structure calculation was carried out to obtain mechanical response of the key points;At the same time,the fatigue life of asphalt pavement structures was analyzed.In order to facilitate practical application,equivalent force response frequency values are recommended for the upper,middle and lower layers of each grade of highway based on fatigue analysis.The results show that the fatigue life calculated by the method in this paper was larger than the frequency determination method used in Chinese specification.Finally,the UMAT subroutine for fatigue damage analysis of asphalt pavement structures based on the frequency attenuation of stress response was written,the evolutionary process of pavement fatigue damage and the influencing factors were analyzed by ABAQUS.