| At present,the static analysis theory is inconsistent with the actual situation,some back-calculation methods have narrow applicability,and the dynamic back-calculation takes a long time with back-calculation of dynamic modulus of pavement structure by deflection,which reduces the reliability and convenience of modulus back-calculation.Therefore,an axisymmetric model of dynamic response of pavement structure under impact load is established by means of spectral element method based on dynamic analysis theory.On this basis,a differential evolution algorithm for dynamic modulus back-calculation is constructed,and the application of the algorithm is verified by field tests.The main research contents and conclusions of this thesis are as follows:(1)Using Laplace,Hankel integral transform and Helmholtz displacement potential function,combined with the basic principle of spectral element method,a dynamic response model of isotropic pavement under impact load under axisymmetric condition was established,and two undetermined parameters in the process of integral inverse transformation were determined.The correctness and efficiency of the dynamic response model were verified by comparing with the finite element calculation results of two typical pavement structures.The influence degree of the modulus and thickness of each structure layer on the bending results was analyzed,in which the thickness variation had the greatest influence on the bending results.Based on the sensitivity analysis of bending,it is determined that the modulus of the surface layer has the greatest influence on the bending at the load center,the modulus of the subgrade has the greatest influence on the far bending,and the thickness of the structural layer has the greatest influence on the bending at about 0.3m away from the load position.(2)By introducing the Buchwald displacement potential function under axisymmetric conditions,a spectral element calculation model for the dynamic response of transverse isotropic pavement structure under impact load was established,and the correctness and effectiveness of the established dynamic response calculation was verified by comparison with literature and finite element results.At the same time,the influence of different transverse isotropic coefficients of each structural layer on the bending results is analyzed.The coefficient changes of surface layer,base and bottom layer only affect the peak of bending,while the change of subgrade coefficient will affect the peak and the recovery stage of bending curve,and the coefficient of each structural layer has a great influence on the bending when it is less than 1.0,and has a small influence on the bending when it is greater than 1.0.(3)According to the results of the sensitivity analysis,the sum of the relative error squares between the peak value of the bending at each measuring point and the bending curve at the center of the load in the middle of the development and recovery stages was taken as the objective function,and the differential evolution algorithm was established to invert the dynamic modulus of the road structure.By taking 50 parallel modulus backcalculation results as normal distribution,the robustness of the algorithm is analyzed.Under 95% confidence,the maximum relative error of the back-calculation modulus is1.57%,among which the subgrade modulus results have the best stability and the least error.At the same time,the influence of the parameters on the modulus back-calculation results is analyzed to determine the value of the initial parameters,and the algorithm is compared with Evercalc to verify the effectiveness of the algorithm.(4)Accelerated loading test was carried out on full scale test road,and dynamic modulus inverse calculation was carried out on FWD bending and subsidence data by differential evolution algorithm.Through comparing the changes of modulus of each structural layer before and after loading,it was found that the modulus of surface layer and base layer increased because the compaction degree did not meet the design requirements during pavement construction.The dynamic modulus results of three asphalt layers in the test road were compared by impact echo,and the correlation between the inverse dynamic modulus and impact echo dynamic modulus was established by power regression model.The correlation coefficient was 0.9092,which showed good correlation. |
