Railways play an essential role in advancing urban and national development across the globe, offering efficient transportation for passengers and freight. The Australian railway system stands as one of the world's most extensive, encompassing over 33,000 route kilometers of rail lines that traverse the nation, catering to urban as well as rural regions. The rising demand for railway services has presented new challenges, as increased train frequency, heavier loads, and higher speeds have strained the existing infrastructure . Consequently, the cost of maintaining Australia's railway tracks has surged, primarily attributed to ballast and regular substructure maintenance. Presently, the majority of Australian rail tracks need to be maintained and upgraded regularly to meet the growing demand, emphasizing the urgent need for innovative and sustainable solutions to enhance ballasted tracks . These improvements are essential to accommodate faster, heavier, and longer trains, while ensuring passenger comfort and safety.
Geogrids, composed of synthetic materials such as polyester, primarily serve to reinforce rail track structures. These planar geogrids consist of parallel tensile ribs with opening apertures that secure and lock granular aggregates, effectively reducing the deformation of tracks. When integrated into ballasted tracks, geogrids offer confinement, preventing ballast from lateral movement, and subsequently diminishing track deformation. Past research has supported the efficacy of incorporating geogrids as an appropriate and cost-effective solution to mitigate ballast breakage, fouling, and track deterioration, underlining their importance in rail track applications, among others. Recently, experimental and DEM works on railways carried out by Naeini et al. and Oskooei et al. on recycled materials have demonstrated the application of recycled materials in tracks. Large-scale direct shear tests have been commonly adopted to study the effect of geogrids and recycled materials. The performance of geogrids in rail tracks is influenced by several factors, including aperture shape and size, material stiffness, interface conditions, and grid placement location. Subgrade conditions can also impact the reinforcement effects provided by geogrids. Among these factors, it is well accepted that the primary reason for the improved performance of the geogrid-stabilized ballast assembly is the geogrid–ballast interlocking.