Granular Matter (2006) 8: 195–204 DOI 10.1007/s10035-006-0006-2 ORIGINAL PAPER Sebastian Lobo-Guerrero · Luis E. Vallejo Discrete element method analysis of railtrack ballast degradation during cyclic loading Received: 19 May 2005 / Published online: 8 March 2006 © Springer-Verlag 2006 Abstract Ballast materials forming part of railway struc- tures 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 induc- ing permanent deformations on the railways. Maintenance and rehabilitation costs of railtracks due to problems re- lated with ballast performance are substantial, and millions of dollars are annually spent around the world in these activi- ties. 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, crush- ing 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 consider- ing 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 evolu- tion of crushing. Keywords Railtrack ballast · Particle crushing · Cyclic loading · Discrete element method (DEM) S. Lobo-Guerrero · L.E. Vallejo (B ) Department of Civil and Environmental Engineering, University of Pittsburgh, 949 Benedum Hall, Pittsburgh PA 15261, USA E-mail: vallejo@civ.pitt.edu E-mail: sel2@pitt.edu Tel.: +1-412-6249884, Fax: +1-412-6240135, 1 Introduction Ballast materials forming part of railway structures are sub- jected to cyclic loads. As a result of these loads, ballast den- sification, aggregate degradation, and lateral spread of the ballast material underneath the ties takes place inducing per- manent deformations on the railways [22]. As reported by Indraratna et al. [8], 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 crush- able 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 (DEM) 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, crush- ing was allowed only in one simulation. The simulated track sections were subjected to a cyclic load, and the values of per- manent deformation as a function of number of cycles were recorded. Moreover, snap shots of the track sections are pre- sented allowing a visualization of the evolution of crushing. 2 Selection of railtrack ballast Rail track ballast should be crushed rock, nickel slag or crushed gravel composed by strong and durable particles having sizes typically between 0.25 in (6.4 mm) and 2.5 in (64 mm). In order to select a specific track ballast, economic factors such as production, transportation, placement, and maintenance costs need to be considered [12]. Moreover, the material properties need to be evaluated and compared with standards. Typical specifications for track ballast include ranges of acceptable values of bulk specific gravity, grada- tion, percentage of fractured particles, resistance to weath- ering (Magnesium soundness, absorption), and resistance to degradation (Los Angeles abrasion, mill abrasion) [5].