Analytical Modelling And Thickness Design For Bearing Layer Of Asphalt Concrete Trackbed

The high speed,safety and comfort of high-speed railways impose stricter requirements on the stability,durability and smoothness of the under-rail foundation.The dense-grade asphalt mixture combines elasticity,water resistance and maintainability.It is a cushioning support and waterproof sealing material under the rail,and can be introduced asphalt mixture into the under-rail foundation layer,which can effectively improve the Stiffness coordination problem.In this paper,the asphalt concrete paved trackbed is studied,and its structural composition,material design,analytical model and numerical model verification,and structural quasi-static design method are discussed respectively.The major work and results are:(1)Proposing asphalt paved trackbed structure.Through the domestic and international research review,it can be known that the asphalt concrete material used for the under-rail foundation structure,has the advantages of good waterproofness,vibration and noise reduction,and easy maintenance.Based on this,this paper proposes the optimized structural scheme of the unit slab ballastless track supported by asphalt concrete(ie asphalt concrete paved trackbed),and designs the material of each structural layer.(2)Establishing theoretical models and numerical verification model.Combined with the structural characteristics of the asphalt concrete paved trackbed,based on the theory of elastic layered system,a multi-layer elastic ground plate model of asphalt concrete paved trackbed is established to calculate the structural mechanics index.Assuming that the track plate is a rigid plate,the four-layer elastic foundation simplified model under uniform load is established.After MATLAB programming,the stress and displacement can be solved at any point.In order to verify the reliability of the theoretical analytical model,static finite element models of five different asphalt layer thicknesses are established.Comparing the stress,strain and displacement values,it can be seen that the finite element results are smaller than the theoretical value,regardless of the vertical stress at the top of each structural layer or the lateral stress and longitudinal stress at the bottom of the asphalt layer.In terms of the vertical displacement at the subgrade,the maximum values of the two are close.In terms of strain,the theoretical value of the tensile strain at the bottom of the asphalt layer is close to twice the finite element value,while the compressive strain at the subgrade surface is relatively close.It shows that the results obtained by the theoretical simplified model are conservative and can be used for the structural design of the asphalt paved trackbed support layer after reasonable correction.(3)Establishing a quasi-static design method for the structure.Refering to the road pavement design method,the key design indexes are proposed for the asphalt concrete paved trackbed including the asphalt layer bottom tensile stress,the subgrade vertical stress and the subgrade vertical displacement.Based on the MATLAB programming results,quasi-static design method of the asphalt concrete paved trackbed is established.The example shows: the threshold of the design index can control the minimum design thickness of the asphalt layer;increasing the thickness of the asphalt layer is beneficial to improve the mechanical response of the underlying foundation structure,but in order to save costs,the asphalt layer should not be too thick,and should be reasonably adjusted according to the actual project.