Nonlinear Pavement Foundation Modeling for Three-Dimensional Finite Element Analysis of Flexible Pavements

Pavement foundation geomaterials, i.e., fine-grained subgrade soils and unbound aggregates used in untreated base/subbase layers, exhibit nonlinear behavior under repeated wheel loads. This nonlinear behavior is commonly characterized by stress-dependent resilient modulus material models that need to be incorporated into finite element (FE) based mechanistic pavement analysis methods to predict more accurately the pavement resilient responses, such as stress, strain, and deformation. Many general-purpose FE programs have been used to predict such pavement responses under various traffic loading conditions while not considering accurately material characterizations of the unbound aggregate base/subbase and subgrade soil layers. This paper describes the recent pavement FE modeling research efforts at the University of Illinois focused on using both the specific purpose axisymmetric and general-purpose three-dimensional (3D) FE programs for flexible pavement analyses. To properly characterize the resilient behavior of pavement foundations, nonlinear stress dependent modulus models have been programmed in a User Material Subroutine (UMAT) in the commercial general-purpose finite element program ABAQUSTM. The axisymmetric pavement FE program GT-PAVE was used to verify the nonlinear material models in the ABAQUS UMAT subroutine. The results indicated that proper characterizations of the nonlinear, stress-dependent pavement foundation geomaterials significantly impacted accurate predictions of critical pavement responses and this consideration should be adequately implemented in the 3D FE analyses of flexible pavements.