The deterioration of a rail track due to large dynamic wheel loads is inevitable over the years and leads to frequent, high-cost maintenance. This problem is more critical in isolated rail track locations such as bridges and tunnels, where the substructure is much stiffer than the surface track assembly. One measure used to minimize track deterioration is geosynthetic inclusions such as rubber mats under the layer of ballast. In this study, cyclic loads from fast and heavy-haul trains were simulated on stiffer track foundation conditions using a largescale process simulation triaxial (prismoidal) apparatus (PSPTA) to investigate the performance of ballast improved by rubber mats locally manufactured from recycled tires. The laboratory results indicate that the energy-absorbing (damping) characteristics of rubber mats reduce the amount of deformation and degradation of ballast under stiffer track conditions. The study shows that rubber mats distribute the stress applied from moving trains more uniformly by increasing the effective contact area, which then reduces the dynamic amplification of applied vertical stress and leads to much less ballast degradation.