Analysis of Rutting Development in Flexible Pavements with Geogrid-reinforced Base Layers Using 3D Finite Element Analysis

Geogrid can provide the base layers of flexible asphalt pavements with tensile strength, which may ultimately lead to improvements in rutting behavior. Significant experimental and finite element-based research has been conducted in the recent past to examine the benefits of geogrid reinforcement. The benefits are well established for relatively thin pavement sections, but inconclusive results have been reported for relatively thick pavement sections. The objective of this study was to develop a method of quantifying the rutting performance improvements associated with geogrid in a variety of relatively thick pavement sections. A three-dimensional finite element model was developed to simulate the response of relatively thick flexible pavement sections with geogrid-reinforced base layers. Data from extensively instrumented test sections was used to calibrate the model. The model was capable of accurately predicting strains in the asphalt, base, and subgrade layers, as well as in the geogrid reinforcement. Optimal soil layer moduli were determined to be close to average values obtained through FWD testing. Conventional accepted permanent deformation models were modified in this study to reflect the improvements in pavement response associated with geogrid reinforcement. The permanent deformation models were calibrated using strains from the FE model and measured permanent deformations in individual material layers from three test sections. The permanent deformation models were capable of reasonably predicting the response of pavement sections that include varying asphalt layer thickness and the presence of reinforcement. The permanent deformation models were limited to a base layer thickness of 300mm. A parametric study was conducted to examine the predicted benefits of geogrid reinforcement with varying asphalt modulus, base modulus, subgrade modulus, asphalt thickness, and location of geogrid within base layer. Unreinforced models were also examined for comparison. It was found that geogrid is relatively more effective in pavement sections with larger asphalt moduli, lower base moduli, lower subgrade moduli, and thinner asphalt layers. The optimal location of the geogrid was always predicted to be at the bottom of the base layer. General conclusions agree with the results from prior studies. Geogrid is predicted to offer significant benefits to pavement sections with asphalt thickness up to 200mm (8in) and base layer thickness of 300mm (12in). It is recommended that future work should investigate the use of nonlinear material models. Data from the remaining test sections in this study should be used to recalibrate the permanent deformation models in order to consider the effect of increased base layer thickness up to 600mm (24in). The effect of geogrid location within relatively thick base layers should be further investigated