Influence Of Graded Gravel Base Material’s Anisotropy On Mechanical Properties Of Asphalt Pavement

At present,in the design of asphalt pavement at home and abroad,the base graded gravel is mostly regarded as isotropic linear elastic material,which is different from the anisotropic and nonlinear elastic mechanical properties of intermediate gravel in engineering.To solve this problem,in order to further improve the theory of structural design and calculation of asphalt pavement,the finite element method is used in this paper to establish asphalt pavement model by treating graded gravel as nonlinear anisotropic material.The influence of orthotropic anisotropy on mechanical properties and crack propagation of pavement model was analyzed by comparing the evaluation index data of asphalt pavement and crack propagation with or without considering orthotropic anisotropy of nonlinear elastic graded gravel material.The specific research contents are as follows:Firstly,based on the basic theory of material anisotropy and related research results at home and abroad,the compliance matrix of anisotropy constitutive relation is analyzed.On this basis,the nonlinear user material(UMAT)subroutine N37 AR in the finite element model was developed and the UMAT subroutine in the finite element model of orthotropic graded machete base material was written according to the characteristics of the flexibility matrix of orthotropic elastic orthotropic materials.Secondly,considering the viscoelasticity of asphalt mixture and orthogonal anisotropy of nonlinear graded macadam,the finite element model of anisotropy of asphalt pavement was established to analyze the influence of orthogonal anisotropy of graded macadam on mechanical properties of asphalt pavement.The results show that the wheel gap bending and the transverse principal stress at the base layer decrease with the increase of orthotropic anisotropy.The shear stress of base layer decreases with the increase of transverse anisotropy.When the material is transversely isotropic and the vertical anisotropy coefficient is 0.20,the shear stress at the bottom of the base layer reaches the maximum.When the vertical anisotropy coefficient is 0.10,the bottom shear stress of the base layer is the minimum.When the transverse anisotropy coefficient is 0.2 and the longitudinal anisotropy coefficient is 0.20,the shear stress at the bottom of the base layer reaches the maximum.When the longitudinal anisotropy coefficient is 0.10,the bottom shear stress of the base layer is the minimum.Thirdly,cracks were added to the lateral side of the vehicle load belt in the road model,and a crack asphalt pavement model was established to study the influence of orthogonal anisotropy of graded gravel on crack propagation.It is found that the J integral decreases with the vertical anisotropy of graded gravel increasing.When the longitudinal anisotropy coefficient is 0.2 and the transverse anisotropy coefficient is 0.05,the J-integral reaches the maximum.When the transverse anisotropy coefficient is 0.10,the J-integral is minimum.When the transverse anisotropy coefficient is 0.2 and the longitudinal anisotropy coefficient is 0.10,the J-integral reaches the maximum.When the longitudinal anisotropy coefficient is 0.20,the J-integral is minimum.Finally,the grey relational degree calculation scheme is designed to study the influence of orthogonal anisotropy of graded gravel on mechanical properties of asphalt pavement and crack propagation of base.The results show that the longitudinal anisotropy has the greatest influence on wheel gap bending and transverse principal stress at the bottom of the base layer,while the shear stress at the bottom of the base layer and j-integral have the greatest influence on vertical anisotropy.