Numerical Analysis of Representative Inverted Pavement Incorporating Cross-Anisotropic Material Properties for Unbound Granular Layers

Unbound aggregate base (UAB) layers in multilayer pavement systems exhibit an intrinsic anisotropy that is characterized by directionally dependent material properties. This anisotropic nature is evident prior to experiencing traffic loads and partly arises from the random compaction-induced arrangement of the particles. The level of anisotropy substantially impacts pavement performance. To emphasize the influence of anisotropy, a finite element (FE) model for an inverted pavement structure was developed, considering varying ratios of horizontal Modulus (E_x) to vertical Modulus (E_y) for the UAB layer. The numerical simulation was based on the layer configuration of a full-scale inverted pavement constructed in Bull Run Route 659 in Virginia, consisting of an asphalt-wearing course, an UAB layer at the bottom, and an underlying cement-treated layer placed on top of the subgrade (SG) soil. Falling Weight Deflectometer (FWD) data were used to back-calculate the moduli of the layers. To validate the model, computed stresses and strains were compared to field measurements obtained from instruments embedded at critical depths within the pavement structure during construction. Pavement responses were modeled by incrementally adjusting the E_x/E_y ratios in steps of 0.1, from 0.1 representing highly anisotropic medium to 1.0 which corresponds to an idealized isotropic behavior. The numerical simulations demonstrate that modeling the UAB layer as a cross-anisotropic medium with a level of anisotropy in the proximities of 0.3 yields superior agreement between the calculated responses and measured data from the field.