ABSTRACT One of the major reasons of railway ballast deterioration is grain breakage due to train traffic and maintenance activities. Breakage modifies the particle size distribution and the shape of the grains which modifies the bulk-level strength. The existence of non-compact grains increases the internal friction angle of the assembly [1], however non-compact grains tend to break more easily [2]. Therefore, finding the optimal size and shape content requires the complex understanding of breakage mechanisms. A discrete element model consisting of breakable polyhedral elements was used in this study. The two common techniques to model grain breakage are (i) to make up grain from smaller elements and define breakable bonds between them, e.g. [3] or (ii) to replace the broken elements with smaller ones when a suitably defined breakage criterion is fulfilled, e.g. [4]. The drawback of the latter one is that failure criteria and modes have to be preliminarily and artificially defined, but it is computationally much more advantageous, hence method (ii) was chosen. Convex polyhedral elements allow a simple shearing mode by defining splitting plane(s), which overcomes the problems, like element overlap, void creation and the need for element density/size adjustment. Shear box tests were modelled with and without grain breakage to study its influence. Multiple breakage models were tested, and the numerical results were compared with experimental results. The results showed that breakage have qualitative and quantitative effect on the bulk behaviour of the assembly. It was also concluded that implementing breakage in the model can help to eliminate unrealistically strong force chains and make the force distribution more even. REFERENCES [1] Y. Liu, R. Gao and J. Chen, “Exploring the influence of sphericity on the mechanical behaviors of ballast particles subjected to direct shear”, Granul. Matter, 21 (4), 94 (2019). [2] T. Zhang, C. Zhang, J. Zou, B. Wang, F. Song and W. Yang, “DEM exploration of the effect of particle shape on particle breakage in granular assemblies”, Comput. Geotech., 122, 103542 (2020) [3] D. O. Potyondy and P. A. Cundall, “A bonded-particle model for rock”, Int. J. Rock Mech. Min., 41 (8), 1329–1364 (2004) [4] J. Eliáš, “Simulation of railway ballast using crushable polyhedral particles”, Powder Technol., 264, 458–465, (2014)