Geosynthetic Material Properties for Use in 2-D Finite Element Pavement Response Models

Abstract

Modern finite element response models for flexible pavement analysis and design are traditionally two-dimensional axisymmetric models. The inclusion of a geosynthetic reinforcement layer in such a model is generally accomplished by the insertion of a horizontal layer of membrane elements. These elements are particularly well-suited for describing geosynthetics in that they carry loads in tension while having zero bending stiffness. The use of a 2-D axisymmetric response model requires that the reinforcement be described by an isotropic material model. Geosynthetics commonly have direction dependent properties, the most notable being an elastic modulus that differs between the machine and cross-machine directions of the material, which are described best by an orthotropic constitutive model. This paper presents an approach that allows a geosynthetic’s orthotropic linear elastic properties to be converted to equivalent isotropic linear elastic properties for use in 2-D finite element response models. This is accomplished through a work-energy equivalency equation developed from a general stress application to a geosynthetic material modeled by an orthotropic and an isotropic linear elastic sheet. Parameters contained within the equation are calibrated by the comparison of pavement response of a completely 3-D finite element model containing a geosynthetic having an orthotropic material model to a 2-D finite element model having an isotropic material model for the geosynthetic. The study results in a simple equation to convert orthotropic properties to equivalent isotropic properties.