Discrete element modeling of ballast reinforced with triangular aperture geogrid

Geogrids have been successfully used in railroad applications for ballast and sub-ballast stabilization purposes for many decades. When granular material is placed and compacted over the geogrid, aggregate particles interlock within the geogrid and are confined within the apertures. A triangular aperture geogrid was used to stabilize railroad ballast in this study. The performance of the stabilized ballast samples were evaluated in the laboratory using a large scale triaxial test device and strength testing of the geogrid-reinforced ballast samples. Both single and multiple layers of the triangular aperture geogrid were placed at different locations in test specimens to identify optimal application of geogrid for maximizing ballast strength properties. Interestingly, the highest strength was achieved when two triangular aperture geogrids were placed in mid-specimen lateral bulging zone. To further investigate the geogrid reinforcement mechanisms, an imaging based Discrete Element Modeling (DEM) approach was also adopted with the capability to create actual ballast aggregate particles as three-dimensional polyhedron elements having the same particle size distributions and imaging quantified average shapes and angularities. The DEM approach successfully predicted the measured strength properties of the geogrid-reinforced ballast specimens with the geogrids placed at different depths in the cylindrical test specimens.