Discrete element simulation of railway ballast: modelling cell pressure effects in triaxial tests

Harkness, J.B.L.; Zervos, A.; Pen, Louis Le; Aingaran, Sinthuja; Powrie, W.

doi:10.1007/s10035-016-0660-y

Cited by 54 publications

(72 citation statements)

References 23 publications

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“…This turned out to be impossible (at least for the used simple clump shape), as in the Hertz-Mindlin model the Young’s modulus determines both the simulated stiffness in compression and the initial slope of the shear force leading to an unresolvable contradiction. Instead, a different contact law was applied, a modification of the conical damage model (CDM), first introduced in [7]. In the normal contact an elastic regime exists, which is modelled with Hertz law.…”

Section: Dem Modelling Of Railway Ballastmentioning

confidence: 99%

“…In tangential direction, the classical Mindlin law together with a constant coefficient of friction can be used. If needed, the coefficient of friction can be adapted for every single contact to be stress dependent, as introduced in [18] or [7]. A detailed description of the CDM model equations and the used algorithm is given in [19].…”

Section: Dem Modelling Of Railway Ballastmentioning

confidence: 99%

“…Here, in contact normal direction, the Hertz model is combined with the simplified Mindlin model together with Coulomb’s law in tangential direction. In [7], Harkness et al conducted simulations of monotone and cyclic triaxial tests on railway ballast using potential particles. They found that the Hertz-Mindlin model was not able to fulfil the “simultaneous requirements of an apparently low initial stiffness in monotonic loading at high confining pressures (through crushing of the asperity), while retaining high elastic stiffness for the case of cyclic loading, which is of crucial importance in modelling railway ballast” [7].…”

Section: Introductionmentioning

confidence: 99%

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Comparison of two different types of railway ballast in compression and direct shear tests: experimental results and DEM model validation

2018

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Railway ballast is an angular and coarse material, which demands careful DEM modelling and validation. Particle shape is often modelled in high accuracy, thus leading to computational expensive DEM models. Whether this effort will increase the DEM model’s overall prediction quality will also vitally depend on the used contact law and the validation process. In general, a DEM model validated using different types of principal experiments can be considered more trustworthy in simulating other load cases. Here, two types of railway ballast are compared and DEM model validation is conducted. Calcite and Kieselkalk are investigated under compression and direct shear test. All experimental data will be made openly accessible to promote further research on this topic. In the experiments, the behaviour of Calcite and Kieselkalk is surprisingly similar in the direct shear test, while clear differences can be seen in the stiffnesses in the compression test. In DEM modelling, simple particle shapes are combined with the Conical Damage Model contact law. For each type of ballast, one set of parameters is found, such that simulation and experimental results are in good accordance. A comparison with the simplified Hertz-Mindlin contact law shows several drawbacks of this model. First, the model cannot be calibrated to meet both compression and shear test results. Second, the similar behaviour in shear testing but differences in compression cannot be reproduced using the Hertz-Mindlin model. For these reasons, the CDM model is considered the better choice for the simulation of railway ballast, if simple particle shapes are used.

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Section: Dem Modelling Of Railway Ballastmentioning

confidence: 99%

Section: Dem Modelling Of Railway Ballastmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Comparison of two different types of railway ballast in compression and direct shear tests: experimental results and DEM model validation

2018

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“…Each research group independently devised a method for modelling the behaviour of scaled ballast with reference to the same laboratory data [27]. The work at Southampton, in a paper submitted for review [28] simultaneously with this one, proposed a new contact damage model as an alternative method for modelling the observed behaviour.…”

Section: Introductionmentioning

confidence: 99%

Discrete element modelling of scaled railway ballast under triaxial conditions

McDowell

2016

Granular Matter

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The aim of this study is to demonstrate the use of tetrahedral clumps to model scaled railway ballast using the discrete element method (DEM). In experimental triaxial tests, the peak friction angles for scaled ballast are less sensitive to the confining pressure when compared to fullsized ballast. This is presumed to be due to the size effect on particle strength, whereby smaller particles are statistically stronger and exhibit less abrasion. To investigate this in DEM, the ballast is modelled using clumps with breakable asperities to produce the correct volumetric deformation. The effects of the quantity and properties of these asperities are investigated, and it is shown that the strength affects the macroscopic shear strength at both high and low confining pressures, while the effects of the number of asperities diminishes with increasing confining pressure due to asperity breakage. It is also shown that changing the number of asperities only affects the peak friction angle but not the ultimate friction angle by comparing the angles of repose of samples with different numbers of asperities.

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“…The Discrete Element Method (DEM) introduced by Cundall and Strack [18] has been used to study the mechanical behaviour of granular materials [19][20][21][22][23][24]. Chen et al [25] used DEM to simulate a box test of ballast reinforced with geogrid under confined and unconfined conditions and they reported that geogrid reinforcement can reduce ballast settlement when it is placed at an optimum location; and thus reduced the associated maintenance costs.…”

Section: Introductionmentioning

confidence: 99%

A study of the geogrid–subballast interface via experimental evaluation and discrete element modelling

2017

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A study of the geogrid-subballast interface via experimental evaluation and A study of the geogrid-subballast interface via experimental evaluation and discrete element modelling discrete element modelling Abstract Abstract This paper presents a study of the interface of geogrid reinforced subballast through a series of largescale direct shear tests and discrete element modelling. Direct shear tests were carried out for subballast with and without geogrid inclusions under varying normal stresses of σ n = 6.7 to 45 kPa. Numerical modelling with three-dimensional discrete element method (DEM) was used to study the shear behaviour of the interface of subballast reinforced by geogrids. In this study, groups of 25-50 spherical balls are clumped together in appropriate sizes to simulate angular subballast grains, while the geogrid is modelled by bonding small spheres together to form the desired grid geometry and apertures. The calculated results of the shear stress ratio versus shear strain show a good agreement with the experimental data, indicating that the DEM model can capture the interface behaviour of subballast reinforced by geogrids. A micromechanical analysis has also been carried out to examine how the contact force distributions and fabric anisotropy evolve during shearing. This study shows that the shear strength of the interface is governed by the geogrid characteristics (i.e. their geometry and opening apertures). Of the three types of geogrid tested, triaxial geogrid (triangular apertures) exhibits higher interface shear strength than the biaxial geogrids; and this is believed due to multi-directional load distribution of the triaxial geogrid. ABSTRACTThis paper presents a study of the interface of geogrid reinforced subballast through a series of large-scale direct shear tests and discrete element modelling. Direct shear tests were carried out for subballast with and without geogrid inclusions under varying normal stresses of ߪ = 6.7 kPa to 45 kPa. Numerical modelling with three-dimensional discrete element method (DEM) was used to study the shear behaviour of the interface of subballast reinforced by geogrids.In this study, groups of 25-50 spherical balls are clumped together in appropriate sizes to simulate angular subballast grains, while the geogrid is modelled by bonding small spheres together to form the desired grid geometry and apertures. The calculated results of the shear stress ratio versus shear strain show a good agreement with the experimental data, indicating that the DEM model can capture the interface behaviour of subballast reinforced by geogrids. A micromechanical analysis has also been carried out to examine how the contact force distributions and fabric anisotropy evolve during shearing. This study shows that the shear strength of the interface is governed by the geogrid characteristics (i.e. their geometry and opening apertures). Of the three types of geogrid tested, triaxial geogrid (triangular apertures) exhibits higher interface shear strength than the biaxial geogrids; and thi...

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Discrete element simulation of railway ballast: modelling cell pressure effects in triaxial tests

Cited by 54 publications

References 23 publications

Comparison of two different types of railway ballast in compression and direct shear tests: experimental results and DEM model validation

Comparison of two different types of railway ballast in compression and direct shear tests: experimental results and DEM model validation

Discrete element modelling of scaled railway ballast under triaxial conditions

A study of the geogrid–subballast interface via experimental evaluation and discrete element modelling

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