Research Upon Dynamic Response And Modulus Backcalculating Of Cross-anisotropy Pavement Based On FWD Load

The pavement was treated as isotropic according to China's current pavement structure design and analysis.However,the pavement materials presented significant anisotropic characteristic,due to the structure composition and compaction method.Transversely isotropic is a special anisotropy,which can properly characterize the mechanical behavior of anisotropic materials.Lots of achievements have been made in the research of transversely isotropic asphalt pavement so far.There are many researches focus on the mechanical response and modulus back calculation of the pavement.However,insufficient researches focused on the mechanical response and modulus back calculation under FWD load,considering the transverse isotropic properties of the material.It is really necessary to analyze the mechanical response and modulus back calculation of the isotropic asphalt pavement under the FWD load.The transversely isotropic characteristics of pavement materials was considered.The dynamic response of pavement was analyzed and the database was established.The pavement structure modulus was back calculated based on three-layer BP neural network.The main findings were displayed as follows:(1)The finite element method was adopted to establish the three-dimensional finite element model.The dynamic response of the transversely isotropic asphalt pavement under FWD loads was analyzed,which included pavement surface deflection,the stress and strain of the surface layer bottom,the stress and strain of the base layer bottom,the compressive strain of the foundation top,and the influence of the different structure layer parameters on the bending basin.The results indicated that the transverse isotropic characteristics had significant influence on road surface deflection and dynamic response.When the transverse isotropic property is stronger,the influence on the road surface deflection,the vertical stress at load center,the stress and strain at the surface layer and the bottom of the base layer,and the compressive strain on the top of the soil foundation was stronger.When ? < 1,the current design standard is somewhat dangerous.(2)The transversely isotropic property of the surface layer was considered,a total of 780 sets of bending basin data of different structural layer thickness and modulus under FWD load were calculated by finite element software.The databasewas established.The pavement structure modulus was back calculated based on three-layer BP neural network.The pavement modulus and the surface layer transversely isotropic coefficient was back calculated.The judgment coefficients and errors of the back calculation results were calculated and analyzed.The results indicated that the inverse model established in this paper can be used to back calculate the horizontal modulus,the vertical modulus and the transverse isotropic coefficient of the transversely isotropic pavement.The error of the back calculation results is within a reasonable range.The neural network model was reliable and practical.