Experimental and numerical analysis into the coupled effect of rubber granules and geogrids on the mechanical behaviour of railway ballast under impact loading

Ballast degradation under high-energy impact loads, such as that caused by wheel–rail irregularities and stiffness variations in railway tracks, significantly compromises track stability and exacerbates maintenance and repair costs. This study investigates the coupled effect of rubber granules and geogrid reinforcement on enhancing ballast performance under impact loading. A series of large-scale impact tests was conducted using a custom-designed drop hammer apparatus. The results show that when rubber granules are used in combination with geogrids, the two exhibit a synergistic effect, mitigating the deformation of ballast, optimising load transmission and striking a balance between deformation control and structural stability. A coupled discrete-element–finite-difference method (coupled DEM–FDM) numerical model was developed and validated against experimental data to investigate the rubber–ballast interaction from a micromechanical perspective. The simulation results confirm that rubber granules decrease the coordination number and reduce interparticle contact forces, leading to a more homogeneous force distribution, and play a key role in energy dissipation, while geogrids restrict particle movement and mitigate structural deformation. These findings offer a novel reinforcement strategy for railway tracks, enhancing ballast longevity and track resilience under dynamic loading conditions.