Considerations for nonlinear analyses of pavement foundation geomaterials in the finite element modeling of flexible pavements

Flexible pavements are commonly used for low to high volume roads subjected to many wheel load applications and also for airfields subjected to rather heavy aircraft gear/wheel loads. As the demand for applied wheel loads and number of load applications increase, it becomes very important to properly characterize the behavior of unbound aggregate layers and subgrade soils as the pavement foundation geomaterials. Laboratory studies have shown that resilient responses for these geomaterials follow nonlinear, stress-dependent behavior under repeated loading. Therefore, a finite element (FE) type layered elastic analysis is needed to employ nonlinear resilient material models to predict accurate pavement responses for mechanistic based pavement design. In this study, modulus models well proven over the years to adequately describe the nonlinear pavement geomaterial behavior were programmed in a user material subroutine (UMAT) to perform axisymmetric and three-dimensional (3D) analyses using the general-purpose ABAQUS FE program. The results indicated that modulus characterizations of the nonlinear, stress-dependent base and subgrade layers were essentially needed to reliably predict accurate pavement responses both in axisymmetric and 3D analyses. Copyright ASCE 2007.