# Impacts of Material Orthotropy on Mechanical Behaviors of Asphal Pavements
## 1 Introduction
Recently, the orthotropy (i.e., different material properties in the transverse and longitudinal directions) of pavement materials was proposed and considered in the HMA layer to increase the prediction accuracy [33]. In recent decades, the finite element (FE) model has become a widely used simulation method in pavement engineering due to its universality and effectiveness [37; 38]. In particular, with the help of commercial software (e.g., SAP, NASTRAN, ANSYS, and ABQUES), the pavement mechanical behaviors [39; 40] (e.g., deformation, stress, and strain) at any position can be obtained easily. Therefore, the FE model has increasingly been implemented to evaluate the effect of material anisotropy on pavement mechanical behaviors [5]. It should be noted that the model inputs (material parameters), such as the elastic modulus and Poisson's ratio, can considerably impact the evaluation results. However, these inputs in most literature are based on assumptions, which may not reflect the actual pavement performance. Therefore, it is critical to determine the inputs of the FE model via the experimental data to evaluate the pavement mechanical behaviors. To fill these gaps, the effect of material orthotropy of each layer on the mechanical behaviors was investigated, and a new and efficient method for determining material parameters was developed. Specifically, this paper aims to address two questions: What are the parameter relationships of the orthotropic body considering the consistency of the parameters and What are the impacts of material orthotropy on the mechanical behaviors of asphalt pavement? The main contributions of the present work are as follows:  
1. We developed a new and efficient 3D FE model of the anisotropic pavement material considering the consistency of the parameters (e.g., the elastic modulus, shear modulus, and Poisson's ratio), which derives the relationship among anisotropic parameters. 2. Based on the degree of anisotropy and considering the parameter consistency, the anisotropic model's independent parameters were reduced from nine to five, which is convenient for determining the input parameters. 3. We designed nine different combinations of material characteristics considering the contributions of each layer of material characteristics to the pavement mechanical properties. Using the FE model, the differences in the pavement mechanical behaviors resulting from the material isotropy, transverse isotropy, and orthotropy were compared and discussed. Furthermore, the need for treating pavement materials as orthotropic is addressed. The remainder of this paper is organized as follows: Section 2 describes the methodology, including the experimental design, mathematical method, measurement of the anisotropy parameters, design of combinations, and finite element model. Section 3 presents the verification of the proposed model. Section 4 presents the analysis results, including the impact of anisotropy on surface deflection, impact of anisotropy on tensile stress, and impact of anisotropy on compressive strain. Section 5 presents the discussion of the results, and finally Section 6 presents the conclusions.