Research On Modulus Field Distribution And Dynamic Response Of Asphalt Pavements

As a typical viscoelastic material,the dynamic modulus of the asphalt mixture is closely related to temperature and load duration.In order to objectively reflect the distribution of the dynamic modulus of the asphalt layer along the depth of the pavement,its modulus should be regarded as a "field",that is,a "modulus field".This thesis analyzed the influence of the external environment and driving speed on the distribution characteristics of the modulus field of the asphalt pavement.Based on the calculation result of the modulus field,the influence of the modulus field on the dynamic response of the asphalt pavement was studied and a method for checking the fatigue life of pavement structure considering the influence of annual change of modulus field was proposed.Firstly,the surface layer of typical semi-rigid asphalt pavement was subdivided into 0.1cm thick sublayers,and the hourly modulus field of the pavement was obtained through iterative calculation based on the Odemark method.The data analysis results show that in the time domain,the modulus field of the asphalt pavement changes significantly with time.At the reference speed(70km/h),the ratio of the annual maximum value to minimum value of the dynamic modulus at each depth of the pavement reaches 20.1 to 34.9.In the spatial domain,the dynamic modulus at different depths of the same structural layer also differs greatly.At the reference speed,the ratio of the maximum values to the minimum values of the dynamic modulus in the AC-13,AC-20,and AC-25 structural layers reachs 1～1.18,1～1.20,1～1.74 respectively.The dynamic modulus at the reference speed,the depth of the calculation point,and the temperature satisfy a good correlation.With the nonlinear surface fitting method,a model for calculating the dynamic modulus at the reference speed was established based on more than 2.2 million sets of representative data.Vehicle speed is an important factor affecting the distribution of the modulus field of the asphalt pavement.At various depths of the pavement,the ratio of the dynamic modulus at speed of 120km/h to the modulus at speed of 10km/h reaches1.12～2.28.The speed correction factor was defined as the ratio of the dynamic modulus at different vehicle speeds to the dynamic modulus at the reference speed,and with the nonlinear surface fitting method,the correlation between speed correction factor,vehicle speed and the dynamic modulus at reference speed was established based on more than 1.89 million sets of representative data.Secondly,in order to analyze the impact of the changes of external environment and vehicle speed on the dynamic response of the pavement,the asphalt surface layer was subdivided into 1cm thick sublayers in the 3D dynamic finite element model of the pavement structure,and the material parameters of each sublayer were determined based on the calculation results of the modulus field.The dynamic response of the asphalt pavement under different modulus field was calculated based on the dynamic implicit solution algorithm.The results show that the dynamic response of the asphalt pavement varies greatly in different seasons of the year and at different times on the same date,and the vehicle speed has a significant impact on the dynamic response.During the design of the asphalt pavement,the impact of external environment and vehicle speed on the pavement structure check results should be reasonably considered.Finally,taking one year as the analytical period and 456 working conditions were set during the analytical period.The condition under 20°C and 10 Hz was set as the standard working conditions.Based on the Miner linear fatigue damage model,the fatigue damage of the pavement structure under various working conditions was calculated and the fatigue life correction factor was defined as the ratio of the annual fatigue damage of the reference pavement structure to the annual fatigue damage of the pavement structure considering the effect of annual changes of the modulus field.The fatigue life correction factor at various vehicle speeds were calculated based on the results of the dynamic response under each working condition and the "fatigue life correction factor-vehicle speed" relationship of the upper base layer,the lower base layer,and the asphalt surface layer were fitted with the power function,the shah function,and the rational function respectively.