Effect of particle breakage on cyclic densification of ballast: A DEM approach

Thakur, Pramod Kumar; Vinod, Jayan S.; Indraratna, Buddhima

doi:10.1088/1757-899x/10/1/012229

Cited by 18 publications

(16 citation statements)

References 12 publications

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“…A linear contact model, following previous studies, was used for the numerical simulations (e.g. Thakur et al 2010;Indraratna et al 2010b;McDowel et al 2006). …”

Section: Discrete Element Modellingmentioning

confidence: 99%

Modelling geogrid-reinforced railway ballast using the discrete element method

Ngo

Indraratna

Rujikiatkamjorn

2016

Transportation Geotechnics

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Rail ballast is an unbounded granular material that spreads laterally when subjected to train loading. Railroads can be reinforced by geogrids to reduce lateral movement and to optimize track performance. This paper presents a study of the behaviour of geogrid-reinforced ballast subjected to monotonic and cyclic loading using a large-scale direct shear box and a novel Track Process Simulation Apparatus (TPSA). The shear stressstrain response of fresh and fouled ballast reinforced by geogrid was investigated using large-scale direct shear tests subjected to normal stresses from 15 kPa to 75 kPa, where the levels of fouling varied from 20% to 95% Void Contamination Index (VCI). Cyclic tests for fresh and fouled ballast were conducted using the TPSA to realistically simulate real track conditions. The experimental results showed that a geogrid provides extra internal confinement and interlocks the aggreagtes in its apertures, hence reduces ballast deformation. The discrete element method (DEM) was used to model geogrid-reinforced fresh and fouled ballast subjected to monotonic and cyclic loading. Irregularly-shaped particles and geogird were simulated by clumping spherical balls together, while the coal fines were simulated by adding 1.5mm diameter spheres into the pore spaces of ballast. The predicted stress-displacement responses obtained from the DEM were in good agreement with those measured in the laboratory, where the peak shear stress of fouled ballast decreased and the dilation of fouled ballast increased with an increasing level of fouling. The contact force distributions and the orientations of normal and shear force were analyzed to provide more insight into the behaviour of ballast subjected to shearing. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. ABSTRACTRail ballast is an unbounded granular material that spreads laterally when subjected to train loading. Railroads can be reinforced by geogrids to reduce lateral movement and to optimize track performance. This paper presents a study of the behaviour of geogrid-reinforced ballast subjected to monotonic and cyclic loading using a large-scale direct shear box and a novel Track Process Simulation Apparatus (TPSA). The shear stress-strain response of fresh and fouled ballast reinforced by geogrid was investigated using large-scale direct shear tests subjected to normal stresses from 15 kPa to 75 kPa, where the levels of fouling varied from 20% to 95% Void Contamination Index (VCI). Cyclic tests for fresh and fouled ballast were conducted using the TPSA to realistically simulate real track conditions. The experimental results showed th...

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“…A linear contact model, following previous studies, was used for the numerical simulations (e.g. Thakur et al 2010;Indraratna et al 2010b;McDowel et al 2006). …”

Section: Discrete Element Modellingmentioning

confidence: 99%

Modelling geogrid-reinforced railway ballast using the discrete element method

Ngo

Indraratna

Rujikiatkamjorn

2016

Transportation Geotechnics

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“…The discrete element method (DEM) based on discrete particle mechanics introduced by Cundall and Strack (1979) has progressed rapidly over the years and can now model the more insightful micro-mechanical behaviour of granular materials that cannot be examined experimentally (e.g. Sitharam and Vinod 2005;Lobo-Guerrero and Vallejo 2006;Lu and McDowell 2006;Hossain et al 2007;Sitharam and Vinod 2008;Sitharam and Vinod 2009;Huang et al 2009b;Thakur et al 2010;Indraratna et al 2010a;Wang and Gutierrez 2010;O'Sullivan et al 2008;O'Sullivan and Cui 2009;O'Sullivan 2011), among others. The use of DEM to predict the stress-strain response of fouled ballast has been very limited in literature.…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2014

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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.

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“…The fouling material is produced mainly from the particle crushing of large-size angular ballast particles. The subgrade soil intrusions or outside contaminations such as coal dust from coal trains also produce fouling materials (Selig and Waters, 1994;Thakur et al, 2010;Huang and Tutumluer, 2011). Selig and Waters (1994) reported that the main source of fouling materials in North American railway tracks is the ballast itself, due to the particle crushing (see Fig.…”

Section: Introductionmentioning

confidence: 99%

Deformation behaviour of gap-graded fouled ballast evaluated by a 3D discrete element method

2015

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The ballast fouling has been identified as a challenging issue in ballasted railway tracks due to huge maintenance costs. In this research, the deformation characteristics of gap-graded fouled ballast were studied from laboratory experiments and a Discrete Element Method (DEM). The fouled ballasts were prepared with different values of a fouling index, FI p . After the packing behaviour of fouled ballasts was studied by density tests, the stress-strain behaviour of them was studied from triaxial compression tests under both dense and loose states. It was found that the void ratio decreases with FI p up to 50%, then it increases with FI p . The results also indicate that the strain-hardening behaviour of ballast is weakened when fouled by FI p ≥ 30%. The DEM simulation by clump particles produce a similar stress-strain behaviour as the laboratory specimens than their spherical counterparts. The results also reveal that the dilation behaviour of ballast is deteriorated significantly when fouled by FI p > 50%. The peak frictional angle indicates that the strength properties of ballast are deteriorated significantly when fouled by FI p ≥ 30%. Therefore, we recommend that fouled ballast should be treated by a maintenance application when ballast is fouled by FI p > 30%.

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Effect of particle breakage on cyclic densification of ballast: A DEM approach

Cited by 18 publications

References 12 publications

Modelling geogrid-reinforced railway ballast using the discrete element method

Modelling geogrid-reinforced railway ballast using the discrete element method

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

Deformation behaviour of gap-graded fouled ballast evaluated by a 3D discrete element method

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