Behavior of Fresh and Fouled Railway Ballast Subjected to Direct Shear Testing: Discrete Element Simulation

Abstract

This paper presents the three-dimensional discrete element method (DEM) that was used to study the shear behaviour of fresh and coal fouled ballast in direct shear testing. The volumetric changes and stress-strain behaviour of fresh and fouled ballast were simulated and compared with the experimental results. 'Clump logic' in Particle Flow Code (PFC3D) incorporated in a MATLAB Code was used to simulate irregular shaped particles in which groups of ten to twenty spherical balls were clumped together in appropriate sizes to simulate ballast particles. Fouled ballast with various Void Contaminant Index (VCI), ranging from 20%VCI to 70%VCI, were modelled by injecting a specified number of miniature spherical particles into the voids of fresh ballast. The DEM simulation captures the behaviour of fresh and fouled ballast as observed in the laboratory showing that the peak shear stress of the ballast assembly decreases and the dilation of fouled ballast increases with an increasing of VCI. Furthermore, the DEM also provides insight to the distribution of contact force chains and particle displacement vectors, which cannot be determined experimentally. These micromechanical observations clearly justify the formation of a shear band and the evolution of volumetric changes during shearing. The reduced maximum contact force associated with increased particle contact area due to fouling explains the decreased breakage of fouled ballast. An acceptable agreement was found between the DEM model predictions and laboratory data.

Micromechanics-Based Investigation of Fouled Ballast Using Large-Scale Triaxial Tests and Discrete Element Modeling

“…Nevertheless, the current DEM analysis was limited to the linear contact model to reduce the computation time, and therefore the damping ratio was not required . The micromechanical parameters used in this study to model ballast were adopted from Indraratna et al (2014) since the same ballast material was tested (i.e. latite basalt, collected from the Bombo quarry near the city of Wollongong).…”

“…Huang and Tutumluer (2011) used DEM to simulate fouled ballast under direct shear test conditions and reported that fouling is a critical agent that could affect particle interaction and cause the track to become distressed. Indraratna et al (2014) used DEM to model direct shear tests for coal-fouled ballast and showed that coal fines would reduce the shear strength of fouled ballast. They observed that miniature particles (i.e.…”

Effect of Rolling Resistance in Dem Models With Spherical Bodies

“…First was published in [9] and the dimensions of a large scale shear box (Fig. 7) were a = 300 mm, b = 300 mm, and c = d = 100 mm.…”

Performance improvement of rail track substructure using artificial inclusions – Experimental and numerical studies

“…The discrete element method (DEM) that was introduced by Cundall and Strack [15] has been widely used to simulate granular materials [16][17][18][19], but the application of DEM to study the behaviour of fouled ballast and analyse its interface mechanism with the reinforcing geogrid is limited. Several multi-layer track models have been developed to analyse the inherent stresses and deformations in all the major components of track and subgrade, i.e., the rails, fasteners, sleepers, ballast, sub-ballast, and subgrade [20][21][22], but they all assume an elastic behaviour for the track layers, including the ballast.…”