Experimental and Numerical Investigation of the Shear Behavior of Geogrid-Reinforced Ballast Mixed with Tire Chips

This study presents the results of large-scale laboratory direct shear tests and discrete element method (DEM) simulations conducted on railway ballast mixed with varying proportions of tire chips (TCs) under both unreinforced and geogrid-reinforced conditions. The results of the Los Angeles abrasion test indicated that abrasion resistance of the GB-TC mix enhanced with the increase in TC content. The results of direct shear tests revealed that both friction angle (φ) and dilation angle (ψ) of the GB-TC mix decreased with increase in TC content in both the experiment and DEM simulations. However, with the inclusion of geogrid, the value of φ increased, whereas the value of ψ decreased compared to the unreinforced conditions. Further, it was found that with the increase in TC content, the amount of breakage decreases significantly. Furthermore, the inclusion of geogrids substantially reduces particle breakage in the GB-TC mix as compared to the unreinforced conditions. The peak φ is observed to be lower than that of unreinforced GB when the proportion of TC exceeds 3.3–3.8%, depending on the magnitude of the applied normal stress. Therefore, the optimal TC content to be mixed with geogrid-reinforced GB is suggested to be in the range of 3.3–3.8%.