An experimental investigation on the deformation and degradation behaviour of geogrid-reinforced ballast

Railroad ballast, owing to its unbounded granular nature, spreads laterally when subjected to large vertical axle loads, which influences the track stability. In this view, large-scale cyclic tests have been conducted on ballast to explore the role of geogrid in controlling the lateral deformation of ballast and hence improving the track performance. Fresh latite ballast having a mean particle size of 35 mm and geogrids with different aperture sizes was used for the investigations. Tests were conducted using a modified process simulation test (MPST) apparatus at a loading frequency of 20 Hz, with geogrid placed at the subballast-ballast interface and within the ballast. The laboratory experimental results indicate that the geogrid arrests the lateral spreading of ballast, reduces the extent of permanent vertical settlement and minimises the particle breakage under high-frequency cyclic loading. However, the improvement in track performance is directly influenced by the effectiveness of the ballast-geogrid interface. It is shown that the higher the shear strength at the ballast-geogrid interface, the lower is the deformation and degradation of ballast. In addition, the geogrid also reduces the extent of vertical stress in the subgrade soil. These test results highlight the role of geogrid in stabilising the ballast thus encouraging its use as track reinforcement in railway applications.