Research On Nonlinear Viscoelastic Mechanical Analysis Method Of Asphalt Pavement And Lane Load Effect

Mechanical empirical method is the most important design method of asphalt pavement structure,and the research of pavement mechanical system and analysis method is its core problem.In most countries and regions,the design of highway asphalt pavement is based on the layered elastic system mechanics under the double circular uniform vertical load.However,many research results show that the ground pressure of automobile tire is not in the form of circular uniform vertical load,and asphalt mixture shows viscoelastic or nonlinear viscoelastic properties under the action of ambient temperature,especially at high temperature.At the same time,the lane load effect of large traffic volume or traffic congestion should be considered in the structural analysis.In view of this,this paper study the mechanical response of layered elastic system under non axisymmetric load,nonlinear viscoelasticity of asphalt mixture and lane load effect.Based on the analysis of the research on tire grounding pressure at home and abroad,the elliptic paraboloid load is proposed as the asymmetric load form.Based on the theoretical solution of asymmetric load layered elastic system,the theoretical solution of asymmetric load layered elastic system is completed,and the corresponding calculation program(ASYLAYER)is compiled.The calculation program of elastic half space under asymmetric load and the division of structural layer is used to verify the accuracy of the calculation program of multi-layered system.The typical structure of asphalt pavement is selected and the influence of asymmetric load on the vertical displacement of asphalt pavement surface,top-down fatigue cracking and base fatigue performance is studied with comparison with circular uniform vertical load.In view of the low efficiency of the calculation of the mechanical response at the surface of the layered elastic system,the calculation efficiency of the mechanical response at each position of the surface under the asymmetric load is analyzed.Then,according to the integral kernel form of the theoretical solution of the asymmetric loaded layered elastic system,the solution is divided into two parts: the rational number(the first half,RP)and the oscillation function(the second half,RL).The attenuation of the solution with the independent variable oscillation is studied respectively.Then,the calculation theory of the mechanical response of the asymmetric load surface point is proposed by using the surface remainder theory.The accuracy of the calculation theory is verified by using the calculation program ASYLAYER,and the calculation efficiency of the surface point calculation theory is analyzed.Finally,it is proposed that the near surface area is defined within the depth range of 0.02 cm from the surface through the calculation results of the mechanical response of the near surface point,and the mechanical response of the near surface point is replaced by the mechanical response of the surface point.Aiming at the nonlinear viscoelastic problem of asphalt mixture,SMA-13,AC-20 and ATB-25 asphalt mixtures were selected,and the creep tests of asphalt mixtures under different loads were carried out.The creep models of three asphalt mixtures were established by Prony series and Power law.Based on the transformation relationship between the relaxation modulus in Laplace domain and the creep flexibility in viscoelastic theory,the calculation theory of the relaxation modulus in Laplace domain is put forward.Compared with the calculation results of the relaxation modulus by Gauss integral method,the calculation results of the relaxation modulus in Laplace numerical inversion method are analyzed.The nonlinear viscoelastic properties of asphalt mixture are studied by using Schapery,Findley and multiple integral constitutive models respectively.The applicability of the constitutive model is analyzed by using the fitting degree.Schapery model is proposed as the nonlinear viscoelastic constitutive model of asphalt mixture.Based on the theory of layered elastic system and multi circle load superposition calculation method,the influence of lane load range and its influence(single axle,double axle and triple axle)on asphalt pavement performance(pavement surface deflection,topdown fatigue cracking and permanent deformation)is studied.According to the characteristics of nonlinear viscoelasticity and driving load of asphalt mixture,a pavement mechanics analysis method considering driving load and nonlinear viscoelastic theory is proposed.According to the characteristics of nonlinear viscoelasticity and driving load of asphalt mixture,a pavement mechanics analysis method considering driving load and nonlinear viscoelastic theory is proposed.Based on the mechanical calculation program developed by this analysis method,the influence of single lane asymmetric load and multi Lane load on vertical deformation of asphalt pavement structure is analyzed,and the influence coefficient of asymmetric load and lane load on vertical deformation of pavement is determined.The above research completed the theoretical solution and program calculation of the mechanical response of the layered elastic system under asymmetric load,established the nonlinear viscoelastic constitutive model of asphalt mixture,analyzed the lane load effect of asphalt pavement structure,and provided the basis and reference for the structural design of highway asphalt pavement.