Utilization of 100% recycled asphalt pavement (RAP) material in the base layer of road construction can provide a cost-effective and sustainable solution. However, excessive permanent deformation of RAP reduces its applicability for such projects. In this study, the effectiveness of geocell reinforced RAP base (GRRB) layers for the flexible pavement sections constructed over the expansive subgrade is investigated. Furthermore, the mechanism involved in the improvement of material stiffness because of the development of additional confining stress in the reinforced base layer is also presented in this paper. During the initial monitoring period, the average vertical compressive stresses over the pavement subgrade for the reinforced sections were observed to be significantly lower in comparison with the corresponding unreinforced sections. The preliminary results indicate that GRRB layers can significantly improve the performance of the pavement by controlling the subgrade deformation.