The use of geosynthetic above subgrade or within base course has demonstrated their success on reducing rut depth and prolonging pavement life. Experimental studies showed that geosynthetics can minimize the movement of particles in the base course. A new performance-based method was developed by the authors to modify an Asphalt Pavement Analyzer (APA) that measures the rut depth of the geosynthetic-reinforced base for a desired number of wheel passes to evaluate geosynthetic-soil interaction. In this study, numerical software-Particle Flow Code (PFC) 2D, which is based on discrete element modeling (DEM) of micromechanics, was used to simulate this performance-based test to investigate the geotextile-soil interaction. The analysis was focused on the effect of geotextile location and packing density of particles on the rut depth of geotextile-reinforced bases. A similar approach can be used to evaluate geogrid-soil interaction. The results and phenomena from the numerical analysis are discussed and compared with experimental data. The behavior of unreinforced and geotextile-reinforced bases is captured qualitatively by DEM for medium dense particle assembly as compared with the experimental data. It is observed that the geotextile helped distribute contact forces to a wider area.