Effect of the combination of geogrid and rubber granules on the performance of ballast under impact loads

Impact loads can exacerbate the deterioration and deformation of railway ballast, leading to changes in the mechanical properties of the track bed. Geogrid and rubber granules (RG) have been widely used in research to enhance the performance of ballast, however, the effects and mechanisms of these two materials working together are not yet clear. Therefore, in this study, a series of drop hammer impact tests were carried out on ballast aggregates with geogrids and RG. The tests were set up with different geogrid placement locations and RG contents on rigid and flexible subgrades. During the tests, the deformation, impact force and impact time of specimens were measured and recorded, the ballast specimens were sieved after the tests to investigate the breakage of the ballast, and the mechanical properties of the ballast specimens were analyzed after the impact using stiffness and damping ratio. It was found that the deformation and breakage of ballast specimens were significantly reduced by the combination of geogrid and RG, which was better than the geogrid or RG alone, and that the RG improved the damping ratio of ballast, while the geogrid reduced the reduction of stiffness of ballast caused by the addition of RG. Comparing and analyzing the results of each group of tests, the study confirmed that RG with 10% by volume and geogrid placed at 100 mm from the subgrade were the best combination to enhance the ballast performance. Graphical Abstract