Railway Ballast Research Articles

Implementation of real contact behaviour in the DEM modelling of triaxial tests on railway ballast

In the Discrete Element modelling of soils, the micromechanical behaviour at contacts has often been considered to have a minor influence on the macromechanical response, leaving basic theoretical models (e.g., Hertz) to describe the contact response in the normal direction. A realistic description of the contact response may be crucial especially when investigating small strain ranges. Recent experimental inter-particle loading tests on gravel suggest that the classic contact models fail to reproduce certain mechanical features, especially when roughness is significant. Here, some of these experimental observations, including a softer response than the Hertz model under loading in the normal direction, and plasticity on unloading, are implemented in a DEM model for the simulation of small strain tests on railway ballast. The influence of these features on small strain stiffness is highlighted. A micromechanical analysis is carried out to show how each of the contact-level features introduced affects the macroscopic response. • Classic contact models do not work well for rough surfaces. • Accounting for lower normal stiffness due to contact with asperities and plasticity. • True contact behaviour implemented in numerical DEM simulations of ballast. • Contact behaviour can explain small strain stiffness degradation.

Modelling real particle shape in DEM: a comparison of two methods with application to railway ballast

Two different methods for the modelling of real particle shape in 3D DEM simulations are assessed in this paper. The first method uses overlapping spheres (clumps), while the second uses a block defined as a closed and convex polyhedron. The two methods are applied to the modelling of triaxial tests on a railway ballast. The macroscopic responses obtained with the two methods are compared, and it is observed that with clumps a higher shear strength, closer to the experimental response, can generally be achieved. A micromechanical analysis is also carried out to highlight how the modelled particle shape affects the mechanics, and consequently explain the difference in the macroscopic response. It is observed, in particular, that a key feature of real particle shape is concavity, that plays an important role in the mechanics of a granular assembly. Finally, the combined effect of particle shape and interparticle friction coefficient on the shear strength is assessed. This confirms that even for real (angular) shapes, peak strength increases with interparticle friction, while critical state strength first increases and then tends to saturate above a certain interparticle friction.

Closure to “Influence of Coal Fouling on the Shear Behavior of Elastan-Treated Railroad Ballast” by Dinesh Gundavaram and Syed Khaja Karimullah Hussaini

Closure to “Influence of Coal Fouling on the Shear Behavior of Elastan-Treated Railroad Ballast” by Dinesh Gundavaram and Syed Khaja Karimullah Hussaini

Discussion of “Influence of Coal Fouling on the Shear Behavior of Elastan-Treated Railroad Ballast” by Dinesh Gundavaram and Syed Khaja Karimullah Hussaini

Discussion of “Influence of Coal Fouling on the Shear Behavior of Elastan-Treated Railroad Ballast” by Dinesh Gundavaram and Syed Khaja Karimullah Hussaini

Fibre reinforcement of railway ballast to reduce track settlement

Most of the world's railways run on ballasted track. However, ballast accumulates differential settlement with trafficking, hence the correct track level must be restored periodically – typically by tamping, which is costly. To reduce the cost of maintenance, several interventions have been proposed with the objective of increasing the interval between tamps by reducing the rate of differential settlement. These include broader ballast gradings, geogrids and under-sleeper pads. A possible alternative is the addition of unbound random fibres to the ballast. Fibres formed from polymer materials, randomly mixed with sands and gravels, have been shown to increase their shear resistance owing to the additional effective confinement associated with the mobilisation of tension in the fibres. However, the effect of the fibres on the permanent strain accumulated under cyclic loading has not been extensively investigated. This paper presents the results of an experimental programme carried out to assess the performance of full-size ballast reinforced with different proportions of polyethylene strip fibres of different lengths and widths. It shows that the addition of a moderate amount (0·6–0·7% of the volume of solids) of narrow fibres has negligible influence on grain packing and can reduce ballast plastic settlement without affecting track resilient stiffness.

Experimental studies on shape and size effects on particle breakage of railway ballast

Particle breakage, which contributes to ballast bed deforms and degradation, highly affect the performance of the railway track. Experimental studies on particle breakage of ballast are difficult, not only due to the large size and high strength of the material, but also because of complex shape and size effects. In this study, these effects on the particle breakage of ballast are investigated, by a self-designed trapezoidal groove device for single particles and an impact loading device for uniform aggregate. The results show as follows. (1) Single ballast particle is broken as a brittle shear failure, with penetrating cracks and small particles. The more uniform the contact positions are, the less likely shear failure happens. (2) Under the impact energy of 26.8 kJ, the mass loss of flaky particles and elongated particles can exceed 40 %, mainly by fracture breakage; yet that of cube particles is less than 4 %, mainly by wear-out failure. (3) The particle breakage index Bg could be a reasonable index describing the breakage evolution. (4) There is a critical particle size where the ballast takes the highest energy per volume to break. (5) There are three stages in the volumetric change: void filling, skeleton failure, and final stabilization.

Analysis of railway ballast contamination in terms of its potential reuse

In light of the ever-increasing need for a circular economy in all sectors, the rail ballast reuse during the railway lines reconstruction can be an important element in the implementation of sustainability principle. However, this activity should be carried out in a responsible way based on environmental risk analysis due to the contaminated ballast may pose a hazard, especially to deterioration for the quality of soil and water. This paper presents new method for environmental risk assessment of the impact of rail ballast reused as a construction material. The proposed method was verified on a real site at five selected point on trans-European TEN-T transport network in south Poland. The obtained results confirm the possibility of direct reuse of ballast at 4 of the 5 analyzed points. The case study highlights the technical feasibility and desirability of using recycled ballast in the reconstruction of railway tracks. Moreover, papier presents a new tool to assess when such a process can be carried out safety for an environmental. Additionally based on the results of presented studies may establish an understanding on relevant processes and environmental risk of railway emissions to soil, drainage water and groundwater.

Design Method for Geogrid Stabilisation of Railway Ballast and Subballast

Railways are often built on soft soils. Railways present peculiar characteristics in terms of loads applied to subgrade: a single train may produce hundreds wheels loads in few seconds, that is a train produces rapid, repeated and cyclic loads; loads are first distributed from rails to sleepers, then from sleepers to ballast, and finally from ballast to subgrade; loads are always applied to the same area. The effect of such loads on soft soils generates absolute and differential settlements, which may quickly degrade the quality of the railway segment. Reinforcing geogrids may be used for stabilizing the railway base, in such a way as to decrease settlements and to increase the railway lifetime. The paper aims to present a design method for geogrid stabilisation of railway ballast and subballast, taking into account the wheel loads, the number of passages, the railway geometry, the subgrade characteristics and the geogrid properties. The proposed design method can be considered as an extension of design methods for geogrid stabilisation of road bases and it is based on the same engineering principles.

Analysis of the breakage parameters of railway ballast based on the discrete element method

Analysis of the breakage parameters of railway ballast based on the discrete element method

Why are Silica Dust Exposures and Silica-Related Health Effects Still a Global Concern?

Background and aim Epidemiology studies of workers exposed to silica dust demonstrate that crystalline SiO2 is a multipotential hazard. Research among construction workers, miners, ceramic and brick workers, countertops workers, and sandblasters where respirable silica dust levels has been measured has demonstrated excess risk for silicosis, cor pulmopale, silica-tuberculosis (SiTB), several chronic respiratory conditions, coal workers pneumoconiosis (CWP), several auto-immune diseases, and cancers of the lung and gastro-intestinal tract. Methods Despite knowledge of these links over the past decades, occupational and environmental health professionals have not been able to address three new silica-related health issues. They are silicosis and CWP among US coal miners, severe silicosis and auto-immune ailments among countertop workers; and ongoing risk for SiTB among Africa miners. The author examined the literature for other novel silica-related health risks. Results Current workers and their managers seem to not have sufficient awareness of the occupational hazards of silica dust. There are new silica dust concerns including fracking sand, railroad ballast, and dust control in countertop machining. There are new cancer links with silica, including women and nonsmokers with excess lung cancer; excess lung cancer among patients with CWP; children’s dust exposure in small-scale gold mining; and excess lung diseases and pulmonary cancer among railroad workers. There is need for research on improved silica sampling techniques and protective gear. Pathologists should explore whether silicosis leads to differences in cell characteristics that produce silica-linked lung cancers compared to ‘garden variety’ malignancies. Conclusion Despite promises that global silica problems were controlled, that seems to be countered by excesses of CWP and SiTB that still bedevil the occupational medicine and public health communities. We need more worker education, prevention or regulatory policy, and basic silica biology and pathology to effectively intervene. Keywords Silica health effects, future prevention efforts; improved sampling methods

Efficient DEM simulations of railway ballast using simple particle shapes

For complex shaped materials, computational efficiency and accuracy of DEM models are usually opposing requirements. In the literature, DEM models of railway ballast often use very complex and computationally demanding particle shapes in combination with very simple contact laws. In contrast, this study suggests efficient DEM models for railway ballast using simple particle shapes together with a contact law including more physical effects. In previous works of the authors, shape descriptors, calculated in a shape analysis of two types of ballast, were used to construct simple particle shapes (clumps of three spheres). Using such a shape in DEM simulations of compression and direct shear tests, accurate results were achieved only when the contact law included additional physical effects e.g. edge breakage. A parametrisation strategy was developed for this contact law comparing DEM simulations with the measurements. Now, all the constructed simple particle shapes are parametrised allowing to study their suitability and relating their shape descriptors to those of railway ballast. The most suitable particle shapes consist of non-overlapping spheres, thus have a high interlocking potential, and have lowest sphericity and highest convexity values. In a micromechanical analysis of the four best performing shapes, three shapes show similar behaviour on the bulk and the micro-scale, while one shape differs clearly on the micro-scale. This analysis shows, which shapes can be expected to produce similar results in DEM simulations of other tests/load cases. The presented approach is a step towards both efficient and accurate DEM modelling of railway ballast.Graphic abstract

Real-time evaluation of railroad ballast condition through change of contact stress using SmartRock

Ballast is a critical part of railroad track for load bearing and drainage as well as offering lateral confinement of the rail ties. It is important to understand the particulate behavior of ballast particles, and have a reliable method or device to assess ballast conditions. In this study, a ballast box test with the full set-up of rail track structure was performed to study the stress change pattern between ballast particles in different ballast conditions such as fouling and shoulder instable, etc. Two new SmartRocks with additional triaxle stress cells were utilized for automatically recording not only accelerations, angular rotations but the measurement of contact stress between SmartRock and ballast particles. The results show that the stress changes are really different in different ballast conditions and SmartRock is capable of automatically detecting ballast fouling and shoulder instability through the change of contact stress.

An assessment of the relationship between the petrographic, physical, and morphological properties of aggregates used for railway ballast

• Qualitative petrographic variables affect aggregate degradation resistance. • Mineralogy defines the physical and morphological behavior of aggregates. • Rocks with a higher concentration of felsic have undergone greater degradation. • Rocks with higher concentrations of mafic and biotite showed angularity gain. The performance of the ballasted permanent track is linked to the quality of the aggregates that make up the ballast layer. This layer is the only one that allows the regularization and leveling of the rail pavement. Evaluating the relationships between the properties of rocks and aggregates helps in predicting the behavior of rail ballast and in reducing wear and premature failures in the permanent way. The objective of this study is to evaluate the relationship between the petrographic, physical and morphological properties of the aggregates. The materials were selected from the literature with application of rocks for different areas. The petrographic properties of the rocks were filtered or identified through photomicrographs. The physical and/or morphological tests of the rocks were verified. Based on the database of 21 rocks, the results show the strong influence of grain shape, granulation, texture, contact between minerals and, mainly, mineralogy on the physical and morphological behavior of the aggregates. Rocks with higher mafic content provide greater resistance to aggregate degradation. Rocks with higher mafic and biotite contents contribute to increase the angularity value of aggregates after Micro-Deval (MD) wear tests. Medium/coarse grained rocks induce a higher value of unfilled intergrain microcracks between minerals and, consequently, higher porosity and water absorption and higher compression degradation. Furthermore, the results show that it is possible to predict the morphological behavior of aggregates after degradation from the morphological variables before their degradation.

Role of particle breakage on damping, resiliency and service life of geogrid-reinforced ballasted tracks

A series of cyclic loading tests were performed to establish the effect of particle breakage on the damping, resiliency and serviceability of railroad ballast. Five geogrids of triangular, square and rectangular apertures with different sizes were used to stabilize the ballast having the mean diameter (D50) of 42 mm. It was established that the particle breakage that occurs during cyclic loading helps in energy dissipation and also enhances the track resiliency. Further, the quantum of particle breakage is governed by the extent of lateral and vertical strains in ballast. Accordingly, empirical relationship has been established between breakage reduction index, BRI with the lateral and vertical spread reduction indices, LSRI and VSRI. The damping ratio (Dr) and resilient modulus (Mr) is shown to increase with the increase in particle breakage (Bg). Furthermore, the volumetric (εvol) and shear strains (εs) in ballast at the end of testing was found to be influenced by the particle breakage (Bg). Further, the track life enhancement factor (Lef), defined as the ratio of number of load cycles (N) required to attain a given extent of strains in ballast in case of geogrid-reinforced ballast (Grb) to that of unreinforced ballast (Urb), is found to vary from 500 to 1 for 0.3 and 0.5 % lateral strain and 12.50 to 1 for 2 and 3 % vertical strain. The Lef was found to be highest in case of geogrid G1. In addition, a unique relationship is established between Bg and Lef wherein it was found that as the particle breakage increases, the service life of track reduces.

Grain characterisation of fresh and used railway ballast

Ballasted railway track requires regular maintenance to reverse the effects of plastic deformation of the trackbed, which leads to a gradual loss of level. Maintenance is usually by tamping, an aggressive process, which damages ballast grains such that the interval between maintenance interventions steadily reduces with increasing number of tamps. After a certain number of tamps, the ballast is deemed life expired and renewed, with the recovered ballast usually being down-cycled to lower grade uses. The ability to re-use the recovered ballast in the trackbed would make a significant contribution to decarbonising and improving the sustainability of railway infrastructure. This requires detailed knowledge of how the grain characteristics affecting mechanical behaviour differ between fresh and used ballast—specifically grain shape. This paper compares the shape parameters of form, angularity and surface roughness of fresh and used ballast, and proposes a method to synthesize full-size and scaled used ballast for use in laboratory and model tests.

Kurtpınar (Ceyhan) Bazaltlarının Demiryolu Balastı Olarak Kullanımının Değerlendirilmesi

Bazaltlar, demiryolu balastları, binalar, tarihi yapılar ve anıtlar gibi birçok mühendislik projesinde doğrudan yapı malzemesi olarak kullanılmaktadır. Bu çalışmada; Ceyhan Kurtpınar bazaltlarının, fiziksel, mekanik ve kimyasal özellikleri belirlenerek demiryolu balastı olarak kullanım olanakları araştırılmıştır. Çalışma kapsamında; söz konusu bölgede incelemeler yapılmış ve yapılacak deneyler için kaya örnekleri alınmıştır. Kaya numunelerinin fiziksel (Los Angeles aşınma direnci tayini, Mikro-Deval aşınma direnci, su emme oranı, tane yoğunluğu ve MgSO4 dona dayanıklılık direnci), mekanik (tek eksenli basınç dayanımı, nokta yük dayanımı, Brezilya Yarma Deneyi) ve mineralojik özellikleri incelenmiştir. Ayrıca P dalga hızı ve sertlik analizleri de yapılmıştır. Deneysel çalışmalar Ceyhan Kurtpınar Bazaltlarının konvansiyonel hatlarda demiryolu balastı olarak kullanılabileceğini göstermiştir.

Railway ballast layer inspection with different GPR antennas and frequencies

Ground penetrating radar (GPR) is a popular technology for inspecting railway ballast layer, mainly on the ballast fouling level. However, different GPR antennas with different frequencies are suitable for different inspection emphasis and diverse railway lines (weather and sub-structure). In addition, the full-scale track model (with subgrade) for experimental tests was not seen in earlier studies. For further application of GPR in China, the GPR inspections (with 400 MHz, 900 MHz and 2 GHz antennas) were performed on a 30 m long full-scale track and three railway lines (different weather and sub-structure). Results show that ballast layer inspection should be performed mainly with the 2 GHz antenna and supplemented by the 400 MHz and 900 MHz antennas. The weather has great influence on the results of GPR inspection. This study is helpful for supplementing the guidance of ballast layer inspection with GPR.

Assessing the Strength of Individual Railway Ballast Aggregate by Setting up Bilateral Point Loading Condition

Assessing the Strength of Individual Railway Ballast Aggregate by Setting up Bilateral Point Loading Condition

Identification of railroad ballast fouling through statistical process control on ballast particle movement

Ballast fouling is an undesirable condition which adversely impacts track stability. As early detection of this condition is critical for the safety of train operations, various inspection technologies have been developed to provide information about state of the ballast and its substructure. Several studies have been conducted with the aim of providing a method for automatic and continuous monitoring of the track system. Ongoing efforts are focused on the development of techniques that enable real-time analysis of the ballast condition while remaining compatible with existing technologies. As an attempt toward that end, this study was designed to utilize statistical pattern recognition technique with data input from an innovative wireless sensor called RTS SmartRockTM (referred as SmartRock in this paper). This method was implemented in a field experiment on two sections of railroad track with homogenous traffic but different track conditions: one with clean ballast and the other with mud pumping. Four SmartRock sensors were installed at different locations on each section. With time-history data from the SmartRocks, an unsupervised statistical model was developed and evaluated for damage detection. The algorithm used was successful in distinguishing between data sets obtained from different ballast conditions. The results of the study show potential suitability of this method for timely detection of ballast fouling, thereby facilitating maintenance planning of rail tracks for a safer and more efficient transportation system.

Geogrid reinforcement of ballasted railway superstructure for stabilization of the railway track geometry – A case study

BackgroundThis article deals with a unique topic related to railway infrastructure, civil and geotechnical engineering, and modern materials. In the past 20–30 years, more and more synthetic materials have been applied in engineering and everyday life. Geogrid and geotextile products are adequate for substituting lacking abilities of the soils, and granular materials, mainly low tensile and shear strength, etc. This paper aims to introduce the result of the author's research dealing with investigating the behavior of geogrid-reinforced railway ballast based on a long-term field test in the busiest main railway line in Hungary. The duration of the test is more than eleven years. MethodsFive different types of geosynthetics were installed in the superstructure of the No. 1 main railway line (Kelenföld – Hegyeshalom state border) in Hungary in 2010. More than eleven years have elapsed since the installation. The experiences are formulated in this paper. Mathematical-statistical analysis was performed to compare the (sub)sections with each other and with the designated reference sections where no geogrids were applied. ResultsAs a result of the examination, the author summarized the main differences in the behavior of railway track geometry, and the geometrical deterioration rates, considering the different types of reinforcement products.