In the recent past the use of geosynthetic-reinforcement to stabilise the rail tracks has been on the rise. The performance of such reinforced track is governed by the shear behavior of the ballastgeosynthetic interface. In view of this, large-scale direct shear tests were performed to explore the shear behaviour of rail ballast-geogrid interfaces. Fresh Latite ballast with an average particle size (D50) of 35 mm, and geogrids with different aperture sizes and shapes were used for this purpose. The laboratory experimental results indicate that the shear strength of ballast can be improved significantly when reinforced with geosynthetics, but the degree of effectiveness depends on the aperture to particle size ratios. It is expected that this study will assist rail engineers in selecting suitable geosynthetics for stabilising a given ballast gradation, to reduce track maintenance costs.