This dissertation documents the results of an extensive research study that was conducted to characterize the behavior of geogrid reinforced base course materials. The research was conducted through an experimental testing and numerical modeling programs. The experimental testing program included performing different laboratory tests to evaluate the effect of various factors on the performance geogrid reinforced base course materials. Finite element models were also developed to investigate the benefits of placing geogrids within the base course layer in a flexible pavement structure.

The results of the experimental testing demonstrated that the inclusion of the geogrid reinforcement layer(s) improved the compressive strength and stiffness of base course materials under static loading. This improvement was more pronounced at higher strain levels. Furthermore, the results showed that the geogrid significantly reduced the base course material permanent deformation under cyclic loading, but it did not show appreciable effect on their resilient deformation. The results also showed that for stress levels less than the plastic shakedown stress limit, the geogrid had a minimum contribution to the permanent deformation resistance during primary post-compaction stage; however, it significantly increased this resistance during the secondary stage. The results also showed that the change in the moisture content of the base material altered its state of stress; this significantly affected the geogrid improvement.

The finite modeling program showed that the geogrid reinforcement reduced the lateral, vertical, and shear strains within the base course and subgrade layers. Furthermore, the geogrid had appreciable reduction in permanent deformation for pavement sections built on top of weak subgrade soils with medium to thin base layer thickness; with the thin base layer thickness showing greater values of improvement. However, negligible to modest reinforcement effect on permanent deformation was obtained for sections having a fine subgrade or thick base layer thickness. The geogrid reinforcement had modest to high values of improvement in fatigue life of pavement structure.

Finally, regression models that can be readily used in the design of geogrid reinforced pavements were developed. In addition, an approach for the implementation of the shakedown concept in the design of unreinforced and geogrid reinforced pavement sections was recommended.