Discrete element method analysis of railtrack ballast degradation during cyclic loading

Ballast materials forming part of railway structures are subjected to cyclic loads. As a result of these loads, ballast densification, aggregate degradation, and lateral spread of the ballast material underneath the ties takes place inducing permanent deformations on the railways. Maintenance and rehabilitation costs of railtracks due to problems related with ballast performance are substantial, and millions of dollars are annually spent around the world in these activities. Understanding the crushable behavior of railtrack ballast could lead to the design of better railways that will reduce these costs. This paper presents the results of two discrete element method simulations intended to study the effect of crushing on the behavior of a simulated track ballast material forming part of a simulated track section. Even though the two simulations consider the same idealized material, crushing was allowed only in one simulation. The simulated track sections were subjected to a cyclic load, and the values of permanent deformation as a function of number of cycles were recorded. The obtained results showed that the induced permanent deformation strongly increased when considering particle crushing even though only a few particles were broken. Moreover, it was found that crushing concentrated underneath the simulated sleepers. Snap shots of the track sections are presented allowing a visualization of the evolution of crushing.