The effect of the particle-size-distribution on mechanical behaviour of ballast has been studied by several researchers in the past. The review of these past studies indicated that more uniform gradation than actually used by the railway industry would decrease permanent deformation and degradation of railroad ballast. In this study, the prismoidal cyclic triaxial apparatus designed and built at the University of Wollongong was used. The lateral displacement of railroad ballast in the field is not restricted in the absence of sufficient lateral stress (confining pressure); hence the prismoidal triaxial chamber with unrestrained sides provides an ideal facility for physical modeling of the deformations of ballast. Two different particle size distributions of ballast were tested under cyclic vertical maximum stress of about 450 kPa. One of them was according to PSD recommended by Indraratna et al. (2004) as an improvement to Australian Standard AS 2758.7 (1996) and the other one was prepared in accordance with Brazilian standard NBR 5564. The results showed that gradation had major influence on the permanent deformation and breakage of railroad ballast. Also, it is presented a compression test modelling on railway ballast using the discrete element method. Typical railways ballast properties, such as specific weight, particle-size-distribution, void ratio, layers thickness were used. The virtual test comprises monotonic vertical loading through a piece with similar dimensions to sleeper on particles that simulates ballast inside a 600 x 800 x 800 mm box. Stresses and velocities developed in particles are observed, which are difficult sighting characteristics in real conventional tests.