Micro-mechanical investigation of railway ballast behavior under cyclic loading in a box test using DEM: effects of elastic layers and ballast types

Nishant Kumar,Klaus Six,Bettina Suhr,Peter Dietmaier,Christof Marte,Stefan Marschnig

doi:10.1007/s10035-019-0956-9

Nishant Kumar, Klaus Six + Show 4 more

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https://doi.org/10.1007/s10035-019-0956-9

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Abstract

Ballasted tracks are the commonly used railway track systems with constant demands for reducing maintenance cost and improved performance.Elastic layers are increasingly used for improving ballasted tracks. In order to better understand the effects of elastic layers, physical understanding at the ballast particle level is crucial. Here, discrete element method (DEM) is used to investigate the effects of elastic layers – under sleeper pad (text {USP}) at the sleeper/ballast interface and under ballast mat (text {UBM}) at the ballast/bottom interface – on micro-mechanical behavior of railway ballast. In the DEM model, the Conical Damage Model (CDM) is used for contact modelling. This model was calibrated in Suhr et al. (Granul Matter 20(4):70, 2018) for the simulation of two different types of ballast. The CDM model accounts for particle edge breakage, which is an important phenomenon especially at the early stage of a tamping cycle, and thus essential, when investigating the impact of elastic layers in the ballast bed. DEM results confirm that during cyclic loading, text {USP} reduces the edge breakage at the sleeper/ballast interface. On the other hand, text {UBM} shows higher particle movement throughout the ballast bed. Both the edge breakage and particle movement in the ballast bed are found to influence the sleeper settlement. Micro-mechanical investigations show that the force chain in deeper regions of the ballast bed is less affected by text {USP} for the two types of ballast. Conversely, dense lateral forces near to the box bottom were seen with text {UBM}. The findings are in good (qualitative) agreement with the experimental observations. Thus, DEM simulations can aid to better understand the micro-macro phenomena for railway ballast. This can help to improve the track components and track design based on simulation models taking into account the physical behavior of ballast.Graphical

Highlights

Classical railway tracks consist of a framework of rails and sleepers, which are supported on a compacted bed of ballast and sub-ballast that is laid on subgrade
discrete element method (DEM) simulations are conducted to investigate the effects of elastic layers on two different types of ballast: Kieselkalk and Calcite
The two physical mechanisms are simulated in the present work, and calibrated parameters of Conical Damage Model (CDM) model accounting for the edge breakage, are used from Suhr et al [1] for the two types of ballast: Kieselkalk and Calcite

Summary

Introduction

Classical railway tracks consist of a framework of rails and sleepers, which are supported on a compacted bed of ballast and sub-ballast that is laid on subgrade. Few stones below the sleeper are responsible for the distribution of heavy loads to ballast bed that causes ballast deterioration, namely, edge breakage, wear and particle breakage [2, 5, 7, 10,11,12,13]. Due to the fresh nature of the ballast bed, the settlement is dominated by ballast rearrangement (compaction as well as side-wise spreading) and breakage of the sharp edges of the stones [5, 7]. Near to the end of phase III, a state with ‘hanging sleeper’ may develop in the worst case In this situation, the sleeper generates large impact forces, leading to significant ballast breakage and ballast rearrangement. Unavoidable differential settlement along the track at the end of phase III necessitates the tamping cycle to restore the track geometry [15]

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