In spite of recent advances in track geotechnology, the understanding of the mechanisms of ballast degradation is vital for improved design to withstand high speed cyclic loading. The research conducted at Centre for Geomechanics and Railway Engineering (CGRE) at University of Wollongong (UOW) has shown that ballast degradation is influenced by various factors including the amplitude, frequency, number of load cycles, particle size distribution, confining pressure, angularity and fracture strength of individual grains. A series of cyclic drained triaxial tests were conducted using a largescale cylindrical apparatus designed and built at UOW for frequencies ranging from 10-40 Hz. A low range of confining pressures to resemble ‘in-situ’ track conditions was applied. The results showed that permanent deformation and degradation of ballast increased with the frequency. Variation of the
resilient modulus with respect to the degree of degradation is also discussed. Two-dimensional discrete element method (DEM) and finite element method (FEM) simulations were also carried out to capture the behaviour of ballast and the numerical results were compared with the laboratory and field data. These results quantifying the geotechnical behaviour of ballast on the micro and macro scale are described in the paper. Practical implications of these findings are discussed through field monitoring of full-scale instrumented track sections at Bulli in New South Wales.