The discrete element method (DEM) has been confirmed as an effective numerical method for modelling railway ballast, and successfully used to analyse a wide range of ballast-related applications (e.g. geomaterials). However, there still exists some aspects under development. Among them, the model calibration can be the most significant one (morphology, degradation and contact model). Because reliable and accurate results can be obtained only when the parameters are carefully selected. Therefore, diverse DEM applications and developments in railway ballast are critically reviewed. Furthermore, the model calibration methods are discussed. This is able to help future researchers improve the existing calibration methods, further, build more accurate, standardised and validated DEM models for ballast-related studies. Additionally, this paper can assist researchers to choose an appropriate model for specific applications.

Calibration for discrete element modelling of railway ballast: A review

On railway track structures, dynamic impact loads with very high magnitude but short duration are often caused by wheel or rail abnormalities such as flat wheels and dipped rails. The possibility of the large impact loading to cause an extreme failure to an in situ concrete sleeper could be very low about once or twice in the design life cycle. However, to the current knowledge, the behaviour of the in situ prestressed concrete sleepers under the ultimate impact loading has not yet been comprehended, resulting in the design deficiency. A high-capacity drop-weight impact testing machine was thus constructed at the University of Wollongong, in order to evaluate impulsive resistance of in situ prestressed concrete sleepers under impact loads. This paper describes the detail of the high-capacity impact testing machine, as well as the instrumentation, the calibration, and the analysis of failure mode, crack propagation, flexural toughness, and energy absorption mechanisms with respect to railway prestressed concrete sleepers. The impact tests were carried out using the prestressed concrete sleepers manufactured in Australia. An in situ track test bed was simulated in laboratory and calibrated against the frequency response functions obtained from the experimental modal analysis. The experiments using the high-capacity impact testing machine to investigate the impact energy transfer mechanism of the prestressed concrete sleepers are highlighted.

Experiments into impact behaviour of railway prestressed concrete sleepers

Due to the fact that ballastless tracks in high-speed railways are not only subjected to repeated train–track dynamic interaction loads, but also suffer from complex environmental loads, the fundamental understanding of mechanical performance of ballastless tracks under sophisticated service conditions is an increasingly demanding and challenging issue in high-speed railway networks. This work aims to reveal the effect of train–track interaction and environment loads on the mechanical characteristic variation of ballastless tracks in high-speed railways, particularly focusing on the typical interface damage evolution between track layers. To this end, a finite element model of a double-block ballastless track involving the cohesive zone model for the track interface is first established to analyze the mechanical properties of the track interface under the loading–unloading processes of the negative temperature gradient load (TGL) followed by the same cycle of the positive TGL. Subsequently, the effect of wheel–rail longitudinal interactions on the nonlinear dynamic characteristics of the track interface is investigated by using a vehicle-slab track vertical-longitudinal coupled dynamics model. Finally, the influence of dynamic water pressure induced by vehicle dynamic load on the mechanical characteristics and damage evolution of the track interface is elucidated using a fluid–solid coupling method. Results show that the loading history of the positive and negative TGLs has a great impact on the nonlinear development and distribution of the track interface stress and damage; the interface damage could be induced by the wheel–rail longitudinal vibrations at a high vehicle running speed owing to the dynamic amplification effect caused by short wave irregularities; the vehicle dynamic load could produce considerable water pressure that presents nonlinear spatial–temporal characteristics at the track interface, which would lead to the interface failure under a certain condition due to the coupled dynamic effect of vehicle load and water pressure.

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Mechanical characteristic variation of ballastless track in high-speed railway: effect of train–track interaction and environment loads

Influence of a tamping operation on the vibrational characteristics and resistance-evolution law of a ballast bed

The contribution of ballast layer components to the lateral resistance of ladder sleeper track

The heat flux density of solar radiation, received by each surface of a double-block ballastless track bed slab, is closely related to its alignment and geographical latitude. In this work, a tempe...

https://journals.sagepub.com/doi/pdf/10.1177/1687814018812325

Influence of track line environment on the temperature field of a double-block ballastless track slab:

Experimental study on the vibration reduction characteristics of the ballasted track with rubber composite sleepers

In this study, in situ experiments were conducted to study the changing characteristics of the lateral and longitudinal resistance of a ballast bed, and a three-dimensional model for the ballast be...

https://journals.sagepub.com/doi/pdf/10.1177/1687814018781461

Ballast bed resistance characteristics based on discrete-element modeling:

A novel algorithm for longitudinal track-bridge interactions considering loading history and using a verified mechanical model of fasteners

Heavy-haul railway has been developed rapidly in many countries in the world due to its great social and economic benefits. One of the key technologies for heavy-haul railway is the reduction of vibration on the track structures and its surrounding due to impact load induced by the train in service. The vibration behaviors of two kinds of low-vibration track (LVT) systems for heavy-haul railway are investigated in this paper. Firstly, two indoor full-scale low-vibration track models (new LVT and traditional LVT), which include rail, fastener, bearing block, rubber boot, track slab, and foundation base, were constructed according to design drawings. Secondly, the vibration responses of the different track components under the impact excitation of a dropping wheelset were measured. Thirdly, the time-domain characteristics of each track component of the two LVTs were compared by the acquired vibration time-history curves. Finally, the frequency-domain distribution was analyzed, and the vibration reduction performance was evaluated by the comprehensive time-frequency analysis results. The results show the new LVT has lower vibration acceleration, shorter duration of vibration period, lower vibration frequency of track components, and most importantly an obvious vibration reduction effect on the ground. The research results are useful to further optimize the design of LVT to reduce the vibration under train impact load.

/pdf/experimental-investigation-on-the-vibration-reduction-2coij7tfa2.pdf

Zhiping Zeng

Papers

Influence of track line environment on the temperature field of a double-block ballastless track slab:

Experimental study on the vibration reduction characteristics of the ballasted track with rubber composite sleepers

Ballast bed resistance characteristics based on discrete-element modeling:

A novel algorithm for longitudinal track-bridge interactions considering loading history and using a verified mechanical model of fasteners

Experimental Investigation on the Vibration Reduction Characteristics of an Optimized Heavy-Haul Railway Low-Vibration Track