Railways are expected to be the main mode of future transport in Australia, and its large network should provide the essential needs for the quick and safe mobility of both freight and commuters. In spite of recent advances in rail track geotechnology, the optimum choice of ballast for track design is still considered critical because aggregates progressively degrade under heavy cyclic loading. Ballast degradation is influenced by
various factors, including the amplitude and number of load cycles, particle gradation, confining pressure, and the angularity and fracture strength of individual grains. The relationship between the size of the geogrid aperture and the shear strength of the ballast-geogrid interface was obtained using large scale direct shear tests. The role of ‘Void Contaminant Index’ (VCI) to improve the assessment of fouling compared to other
mass based indices is discussed. A series of large scale hydraulic conductivity tests were conducted on fouled ballast with varying VCI to establish a relationship between the extent of fouling and associated hydraulic conductivity. The stress-strain behaviour of coal-fouled ballast with and without geogrid reinforcement was studied using a large scale direct shear apparatus. The outcomes of this research are now elucidated in view of industry practices.