Discrete Element Analysis of Railway Ballast under Cycling Loading

Abstract

Railway ballast is a highly heterogonous material consisting of a multitude of stone sizes with varying physical characteristics. It is a critical layer of railroad track structures providing drainage, strength, stability and load distribution. Ballast degrades under cyclic train loads and needs to be maintained to prevent rail misalignment, settlement and buckling, which may necessitate lower train speeds to prevent derailments. This paper utilizes the Discrete Element Method (DEM) code PFC2D to model the behaviour of railroad ballast under cyclic loading. It introduces two innovative approaches to capture stone angularity by fitting circular shapes into each stone shape. One of these methods involves a MATLAB® routine and the other an AutoCAD® routine. Inter-particle contact laws in these agglomerations of circular elements reflect the strength of the stones. The advantage of these two techniques over the conventional clumping technique is that they allow modelling stone breakage which is a leading cause of ballast degradation. Previous studies have implemented techniques to simulate the behaviour of a circular particle idealized as a single aggregate under cyclic loads. Three different techniques are presented in this study to better understand the natural behaviour of ballast under loading. In this paper, particle angularity is being introduced by using another method. This numerical study demonstrated the effect of aggregates particle shape on the overall performance of railroad ballast as measured by permanent deformation and degradation of the ballast.