Geogrids have been used commonly in the past three decades to stabilize and to improve the service life of pavements. Various researchers have done large-scale model experiments, full-scale accelerated pavement testing, and numerical model simulations to evaluate the benefits of reinforcement in pavements. Most of the literature focuses on behavior of pavement layers by placing the geogrid either below the asphalt layer to improve the fatigue resistance or at the interface of granular base layer and subgrade soil to enhance the rutting resistance. Even though various numerical studies are performed to find the effect of geogrid on pavement layers, a proper parametric study using an advanced numerical model considering the nonlinear behavior of pavement layers and precise simulation of geogrid soil interface in order to propose the optimal location of geogrid in granular bases has not been conducted. The optimal location of geogrid depends upon various factors such as strength of subgrade, thickness of base layer, and stiffness of the reinforcement and various other factors. This paper focuses on developing a 3D numerical model of reinforced flexible pavement using explicit finite difference program- Fast Lagrangian Analysis of Continua (FLAC^3D).

FLAC3D is capable of modeling complex behavior of continuum models including non-linear material behavior, large displacements and strains. The convergence of the model is obtained by satisfying the maximum unbalanced force ratio obtained for the equilibrium of the model with focus also given towards reducing computational time. Modeling is done by activating large strain mode to update the coordinates at the end of each cycle. Traffic loading and pavement material properties for the analysis are chosen from the existing literature. Asphalt concrete layer is modelled using linear elastic material model, and granular base course and subgrade are modelled using the Mohr-Coulomb plasticity model. Linear elastic ‘geogrid’ element available in FLAC is used for modeling of biaxial geogrid in FLAC3D.

The study involves series of three-dimensional simulations including modeling of unreinforced and reinforced cases along with parametric studies for different geogrid stiffness, thickness, modulus and strength of pavement materials. The benefits of reinforcement is presented by the axial force and axial strain mobilized in the reinforcement. The improvement in reinforcing base layer was presented in terms of load-settlement curves and the reduced normal stresses transferred to the subgrade layer, and in the settlements at the surface. Thus, the optimal position of geogrid on the unbound pavement layers can be proposed. This research is especially relevant at places where competent aggregate material is not available and demands reinforcing the aggregate base layers to improve the performance of pavement system or to reduce the quantity of aggregate material needed for their construction.