Performance of Ballast Influenced by Deformation and Degradation: Laboratory Testing and Numerical Modeling

Abstract

This paper presents a study on the deformation and degradation responses of railway ballast using largescale laboratory testing and computational modeling approaches. A series of large-scale triaxial tests were carried out to investigate the ballast breakage responses under cyclic train loading subjected to varying frequencies, f=10-40 Hz. The role of recycled rubber energy-absorbing mats (REAMs) on reducing ballast breakage was also examined. Laboratory test results show that the ballast experiences significant degradation (breakage) and deformation, while the inclusion of REAMs can reduce the ballast breakage up to about 35%. Numerical modeling using the coupled discrete-continuum approach [coupled discreteelement method-finite-difference method (DEM-FDM)] is introduced to provide insightful understanding on the deformation and breaking of ballast under cyclic loading. Discrete ballast grains were simulated by bonding of many circular elements together at appropriate sizes and locations. Selected cylinders located at corners, surfaces, and sharp edges of the simulated particles were connected by parallel bonds; and when those bonds were broken, they were considered to represent ballast breakage. The subgrade and rubber mat were simulated as a continuum media using FDM. The predicted axial strain εa and volumetric strain εv obtained from the coupled DEM-FDM model are in good agreement with those measured in the laboratory. The model was then used to explore micromechanical aspects of ballast aggregates including the evolution of particle breakage, contact force distributions, and orientation of contacts during cyclic loading. These findings are imperative for a more insightful understanding of the breakage behavior of ballast from the perspective of microstructure characteristics of discrete particle assemblies. Introduction

Advancements in Geo-Inclusions for Ballasted Track: Constitutive Modelling and Numerical Analysis

“…Numerical modelling via the coupled DEM-FEM approach enables an insightful investigation of the mechanical response of ballast and how rubber mats reduce ballast breakage under cyclic loading, as also observed from laboratory tests using a large-scale cyclic triaxial equipment (Figure 7a) [74]. Ballast particles are modelled by bonding many disks with predetermined sizes together (Figure 7b), and ballast breakage is assumed to occur when those bonds are broken.…”

“…Data Availability Statement: The data presented in this study are openly available in reference number [38,74].…”

A Critical Review of Sensors for the Continuous Monitoring of Smart and Sustainable Railway Infrastructures

“…Regarding the ballast layer, its degradation can be associated with the abrasion between the corners of the aggregates or its crushing due to traffic overloads, along with ballast fouling, due to any fine particles that considerably affect water drainage, negatively influencing rail track stiffness regularity [19]. Aggregate degradation could be caused by climatic factors and freeze-thaw cycles [20], but mainly from the breaking of aggregates due to the passing traffic [21]. The variation in stiffness along the railway track induces a dynamic load between wheel-rail contact and sleeper-ballast, further increasing the fatigue problems in the rest of components [22], while also varying the bearing capacity of the track.…”

A Critical Review on the Performance of Pile-Supported Rail Embankments under Cyclic Loading: Numerical Modeling Approach

“…The economic analyses of Wheat and Smith [4] based on UK rail systems found that more than one-third of the overall capital cost on all ballasted rail networks corresponds to the track substructure. As a consequence of severe ballast deterioration, the Australian rail sector invests a massive amount on regular track rehabilitation (e.g., over AUD 12 million per annum in the state of New South Wales alone), and substantial land development before track construction, where poor and deteriorated base soils (subgrade) provide significant challenges [5]. For this reason, numerous research studies have been conducted to address the challenges of increasing demand for higher performance track substructure, and thereby to effectively manage the growing need for high-speed commuter lines as well as higher axle heavy haul railways [6,7].…”