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Investigation of particle degradation of railway ballast materials due to static and dynamic loadings

Investigation of particle degradation of railway ballast materials due to static and dynamic loadings
Investigation of particle degradation of railway ballast materials
due to static and dynamic loadings
Juhász Erika1 Dr. habil. Fischer Szabolcs2
1Széchenyi István University,
Department of Transport Infrastructure and Water Resources
telephone: 96/503 451
2Széchenyi István University,
Department of Transport Infrastructure and Water Resources
telephone: 96/503 451
Abstract: Nowadays the railway infrastructure has become significantly important regarding to the environmental
friendly and economic transportation. Ballasted railway tracks have to be improved to be able to
construct and maintain railway tracks economically and efficiently. In railway superstructure the
railway ballast plays a critical role as the main load distributor and energy damping element, as well as
it has the largest quantity in a railway superstructure. The degradation of ballast particles, i.e. the
resistance of mechanical impacts is a main issue. A simplified laboratory test method was developed for
determination of particle breakage of railway ballast materials. It contains a HDPE tube with closing
element, and geotextile covering in the inner side. The HDPE tube is important to be able to apply
computer tomography method during test procedure. Approximately 20-25 particle are filled into the
tube and uniaxial static and dynamic loading are applied to the samples with several loading steps and
loading cycles. Crumbling of grains can be determined by computer tomography and weight
measurements. As results it can be defined how the rock type, the particle size distribution, the particle
shape, etc. influence the mechanical degradation of the tested railway ballast samples.
Keywords: ballasted railway tracks, railway ballast, particle degradation, breakage, uniaxial compression test,
static and dynamic tests, computer tomography
The most commonly used type of superstructure on railway tracks is crushed stone. This is true not only
for our country but also for the whole world and this fact is confirmed by literary sources.
Observing this structure, it can be visible that the largest dimensional element of the superstructure is the
crushed stone itself, which usually consists of depth magmatic rock particles (mainly andesite or basalt).
The crushed stone aggregation layer in the track plays an important role in supporting the track in a solid
but at the same time flexible manner, as well as carrying the load towards the substructure. Structural
stability is also important, as drainage of rainwater and simplification of track geometry, too.
Except for their intended purpose, particles and aggregates need to have certain properties: toughness,
abrasion resistance, shape, structure, roughness, weather resistance, economy, etc., except for
completeness requirements, all of which are decisive for the ‘performance’ of embedded rocks.
Of course, it is also important which fraction of the rock material enters the superstructure itself. This
particle size distribution determines the drainage capacity and compactability of the rock mass, e.g. it
would be much easier to control the set of one-dimensional particles, but achieving the right compactness
would be a problem.
In the field of road construction layers with different fine grain contents are applied, while in Hungary
and almost everywhere in the world railway track structures have traditionally applied relatively large
granular bedding materials (31.5/50 and 31.5/63 mm; previously 20/65 mm). In contrast, in the hard-
surfaced track structure, a continuous (mainly fractured) granular base layer is deposited under the
reinforced concrete track, usually in terms of both load-bearing capacity and frost protection as well as
capillary interruption layers at high groundwater levels. The latter layers are also applied under the
bedding superstructure.
Investigation of particle degradation of railway ballast materials due to static and dynamic loadings
1. Presentation of research problem
According to the railway construction practice, on slopes with crushed stone structures, a hammer bearing
compaction method (e.g. Plasser & Theuer, Matisa machines) is used, but due to the technology, a larger
crushed stone bedding structure is required. One of the drawbacks of the technology is that the hammers
break the stone particles considerably during compaction, thus shortening the cycle time of the required
ballast tamping (together with the service life and maintenance costs). In addition to the compacted layers
are loosen underneath the concrete sleepers, which does not achieve perfect railway track geometry.
Technology as a solution currently in use, is recognized and appropriate in most countries of the world, so
during the authors’ research they focus on optimizing it as an innovation. Especially they investigate the
development of methods for measuring and reducing the aging processes of ballast particles by
fragmentation and degradation.
Degradation in the authors’ research means (as an unofficial definition) the cracking, obsolescence,
partial or total failure of railway crushed aggregate particles. Particles can be suffering matter and
abrasion. They usually occur simultaneously, in some cases reinforcing each other and at other times
In terms of the operating conditions of the railways, fragmentation is the greater of the two processes. In
this case, smaller or larger pieces are detached from the particles mainly from their edges, corners and
the ballast particle may fall apart into several pieces. The wear is due to the surface friction of the
particles and typically has smaller volumetric effect. The product of the wear is stone powder.
During the research the authors investigate the triggering effects of the degradation of the particles. In
ballasted tracks, the aggregate exposed to static and dynamic effects, of which the most significant are as
net weight load, forces of vehicles, environmental impacts and last but not least maintenance machinery
The degradation of the granules is influenced by several factors, e.g. rock physical properties of the
aggregation (material, mechanical resistance); the magnitude of the load (axle load, speed); material and
geometry of the rails, fastening systems, track system; the surface of the ballast particles; thickness of the
ballast bedding layer, etc.
In Hungary, the suitability of railway rock material is determined by the examination required by the
same product standard (MSZ EN 13450:2003):
Micro-Deval wear according to MSZ EN 1097-1:2012, as well as
Los Angeles fragmentation test in accordance with MSZ EN 1097-2:2012.
The examinations are well suited to determine the wear and tear resistance properties of a given
aggregate, which is essential to ensure the consistency of the manufactured product. However, the forces
and stresses caused by the operational conditions in the plant are not accurately simulated in the tests. In
connection with this, laboratory studies have been developed that can later serve as a basis for estimating
the real aggregation effects and stress ratios, and their uniqueness takes a new approach to the research
2. International literature research
The authors did a wide range of literature research in the topic. Notable material is available on this topic,
especially in laboratory and field studies, and also DEM and FEM modelling. The authors have collected
a number of relevant findings that have been applied in our research in the appropriate areas.
Parameters introduced by acknowledged foreign researchers, such as Among other parameters, LARB,
MDERB, FV, BBI [1], M, and λ [2] values were used to predict the prognosticated ballast tamping cycle
times for the prior “shear loading tests”. The authors also found valuable resources for granular shape
examinations. [3]
At present, the authors have found only a limited number of articles and publications on CT scans, which
show that so far there has been little research on the subject. In our opinion, combining CT scans with
other methods found in the literature research can be very useful.
Investigation of particle degradation of railway ballast materials due to static and dynamic loadings
3. Presentation of laboratory tests
The current test was preceded by several other laboratory measurements. The examinations needed to be
rethought and improved.
Single-particle fracture tests (shown in Figure 1-2.) did not yield accurate results because the shape,
surface, size and rock mechanical properties of the broken particles were significantly different from each
other. For these reasons, I decided to investigate the ballast aggregates counter to only one particle.
Figure 1-2. Single particle failure testing with ZD-40 crushing machine
In addition, the types of test for larger aggregates included many factors that significantly influenced the
results, so the results were not close to those predicted („shear box test”). [4, 5, 6, 7, 8, 9, 10, 11, 12, 13,
14, 15, 16, 17, 18]
After that it was necessary to develop a method and technique that can be used to examine a manageable
and traceable amount of aggregate.
For the current testing method, an approximately 140 mm outside diameter, 10 mm wall thickness HDPE
water pipe was applied, which is 300-400 mm high, with a pipe closure made for it.
A 1200 g/m2 high-strength geotextile piece (Viacon GEO TC 1200) was placed inside the tube due to the
reduction of friction between the inner surface of the HDPE tube and the crushed stone particles, and the
steel loading plate and the particles also. The loading plate is 120 mm diameter, 3289 grams, and
approximately 40 mm thick steel disc and the uniaxial (vertical) static load were applied to the
aggregation through this. The tube was filled with railway ballast particles approximately the height of
140-160 mm limited by the CT X-ray equipment measuring, because the height of the sample to be
screened optimally equal to the width (in the case, the inside diameter of the tube was a guideline). The
amount of material entering the HDPE tube is about 13-15, sometimes 20-25 pieces. The aggregates were
tested to uniaxial compression loading which combined with CT examination. The arrangements are
illustrated in Figure 3-4.
Figure 3-4. Uniaxial static load (left) in HDPE tube and CT (X-ray) equipment (right)
Investigation of particle degradation of railway ballast materials due to static and dynamic loadings
The developed measuring model cannot be paralleled to the real demands, nor can the standard tests
mentioned in the previous chapter, but presumably a good direction in our research.
With this method, even degradation of more particles can be observed simultaneously with high-precision
digital 3-D image capture and can be processed as particle or aggregate, as needed, to determine the exact
position of the particle and their contact with the wall or with other particles. For the time being, the
research is in its initial phase, but based on the results so far, it is encouraging to continue. The shape
model is shown in Figure 5. below, based on the initial measurements (for a three-step load, the four shots
are from left to right at a static pressure of 0, 300, 600 and 900 kPa).
Figure 5. Recordings made by CT equipment (in case of three-step loading)
The above image was not taken in this semester, currently the CT device is undergone maintenance,
anticipated to March 2020, so priorate to that the authors can only load the samples statically with the
ZD-40 crusher machine (which is a good basis for developing the exact method).
The colleagues helped us of the Material Testing Laboratory (dr. István Kozma and Imre Fekete) of the
Department of Material Science and Technology of the Faculty of Vehicle Engineering of the Széchenyi
István University, where a 450 kV tube of Yxilon Modular CT X-ray equipment was utilized. The is
device shown in Figure 4. The device is not suitable for static and dynamic load, but can be used
effectively to create high-precision 3-D digital surface and volume models in addition to these tests. The
surface models consist triangles, and the size of the triangles depends on the accuracy of the image. The
resulting models can be evaluated in the software provided with the device or the software of GOM
Inspect (presented in Figure 5.).
The models can be used to predict the degree of fragmentation during stepwise loading and to estimate
the magnitude (or proportion) of stresses within the set.
In the recent laboratory measurements, 183 pieces of crushed ballast particle were weighed individually,
according to a standard method. In the selection of the granules, the authors tried to select the granules of
all shapes and sizes (by visual inspection) so that they would have different shape and size particles, but
according to our experience, the result of particles’ distribution from the mine of Szob was mainly based
on one type of grain.
Before placing the washed and dried stones in the HDPE tube, the authors measured them with a digital
Mitutoyo calliper the two orthogonal axes by tenth of millimetre accuracy. One axis represented the
longest extent of the particle (h), the other one the smallest (s), the third value the mesh size (v).
Interestingly, one of the sources found in the literature research used a similar method, However, the
limits FI (flaky index) and the EI (elongated index) calculated from the axial values are used: if FI < 0.6,
the particle is flaky, if EI > 1.8, the particle is elongated, and if not elongated and not flaky, it is cubic:
surprising, but the limit values on my aggregate particles were exaggerated. [19]
Figure 7-9. clearly show the classification possibilities of the 2.5.1-3. points of already withdrawn
standard MSZ 18288/3-78, which taken together, could only interpreted in a “mixed” way to classify the
aggregate. Figure 6. illustrates that, despite of the variety of classification possibilities, most of the
particles are cubic and elongated at the same time, and only a small portion can be classified as obviously
elongated, cubic or flaky. In terms of numbers, only 7.1% of the selected particles were cubic and 19.7%
were flaky. This is due to the peculiarity of railway ballast.
Investigation of particle degradation of railway ballast materials due to static and dynamic loadings
Figure 6. Classification of weighed particles according to axis ratios in accordance with MSZ 18288/3-
78 standard
Figure 7-9. Classification possibilities according to MSZ 18288/3-78 based on axle ratios
Investigation of particle degradation of railway ballast materials due to static and dynamic loadings
To elaborate the refinement of the measurement method, three different aggregates of samples were
created, of which four measurements were made with uniaxial compressive load (most of the rock
composition is composed of cubic and elongated particles):
1130-1490 grams of rock with 50-69% flaky and flaky-like cubic/elongated content,
1245-1630 grams of rock with 12-30% clearly cubic and cubic-like cubic/elongated content,
1274-1685 grams of rock with only cubic and elongated particles.
The measurements were carried out by a ZD-40 crusher machine on the total of 12 samples (aggregates).
The authors performed uniaxial static compression load on the formed aggregate formations in the stress
range of 0 ... 1800 kPa with a statically increased load value.
4. Experimental results of the investigations
On the basis of the fracture tests in can be stated that the most broken/degradated particles were the flaky
elements, and the least broken particles were the cubic ones. This can be explained by the fact that
tensions wake up most along sharp edges and thin “protrusions”, while cubic particles are somewhat
exaggerated but more like spherical shapes.
The results are shown in Table 1.
Table 1. The propensity to degradation depending on particle shapes
Fragmentation average (%
by weight relative to the
original mass)
Average aggregate mass
1311.6 g
Average fragmentation
90.3 g
For each of the 12 samples, the grain size distribution curves were drawn for the pre- and post-load
condition, which is shown Diagram 1. The grain size distribution curves also confirmed the degradation
values shown in Table 1, which show that the flaky aggregate samples are more fragmented that the cubic
aggregate samples. The elongated ones (and partly cubic) are between the two curves.
Diagram 1. Grain Size Distribution diagrams for different aggregate samples
Investigation of particle degradation of railway ballast materials due to static and dynamic loadings
In this article the authors described the latest laboratory tests carries out on the research topic and results,
findings. The aim of the authors’ research is to determine the exact time course of the degradation of
railway ballast particle materials with the help of the performed investigations with CT (X-ray)
equipment, and with this new method one of the authors (Erika Juhász) propose the application conditions
and limits in her dissertation.
The publishing of this paper was supported by EFOP 3.6.1-16-2016-00017 project.
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... Part of our research to date has examined ballast (crushed stone) fragmentation using various visual imaging devices 3D scanner, in which the ballast bed itself was loaded mainly into closed vessels or boxes of various sizes (e.g., shear box or closed-ended, capped HDPE tube). In the authors' previous publications, they have already measured deformations and changes with the GOM system, focusing on the fragmentation of smaller aggregates (Juhász & Fischer, 2019a;Juhász & Fischer, 2020). However, load tests (static and dynamic) in closed boxes do not resemble real ballast bed conditions, so a new experiment methodology has been developed and applied. ...
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This paper summarizes the results of laboratory tests in which the authors investigated the effects of extremely high vertical load to a railway track segment. The segment consisted of a cut concrete sleeper (contact area: 290×390 mm) with a pair of direct-elastic rail fasteners; the sleeper pieces had a standard, full height; the structure had a typical 350 mm depth railway ballast, underneath approx. 200 mm sandy gravel supplementary layer. The whole assembly was built in a 2.00×2.20 m area wooden rack. The deformations due to the approx. 150 kN static concentrated vertical force were measured and recorded by Digital Image Correlation Method (DICM), ensuring the GOM ATOS technology. The 150 kN peak load meant 1326 kPa vertical stress at the sleeper-ballast interface. The 3D geometry was scanned before the loading and after the collapse. In this way, the comparison was able to be executed. The maximum vertical deformation was 115 mm. The DICM technique is a relatively new methodology in civil engineering; however, it has been applied for more than ten years in mechanical engineering. Therefore, the authors investigated the applicability of DICM in this field. As a result, the pre and the post-states were determined in 3D. The displacement of the ballast particles was able to be defined with the possibility of drawing the displacement trajectories of given points. The DICM can be a valuable methodology in railway engineering, e.g., laboratory tests and field test applications.
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This paper is the continuation of the previous article published in Sínek Világa journal 2019/1 issue, the title of this article is „Breakage tests of railway ballast stone material with using of laboratory dynamic pulsating” [1]. The goal of the authors was to demonstrate more detailed the degradation process (breakage and wear) of the railway ballast particles, also its generation reasons, as well as those parameters that mainly influence these processes. The authors systematized present the related areas’ (crushed) stone standards with given examples, in those Los Angeles abrasion and Micro-Deval wear tests are required. The authors introduce and show prescriptions and solutions with long experiences, it can be worth thinking about that’s occurrent modification. Connecting to that, for interesting examples the authors introduce prescriptions of some countries related to degradation limits of railway ballast crushed stones. Referred to the author’s previous publications, they delineate the more modern possibilities of measurement methodologies of ballast particle degradation in laboratory, which consider much better the service loads and acts, they show the applications of illustrated own methods, their limits, development opportunities and the expected results.
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Purpose. The most railway lines in the world have so called traditional ballasted superstructure. The authors think that it is important to learn about the process of ballast degradation. There are only two types of standardized laboratory test methods in the EU to assess railway ballast particle degradation and describe the rock physic characteristics, but are not suitable for modelling the railway stress-strain circumstances of ballast materials, and they particles. In this paper the authors represent some conclusions from their research that the authors experienced during their individual fatigue laboratory test and from new additional tests. With these kind of testing methods, the deterioration process of railway ballast particles can be assessed more realistic and precisely. Methodology and new directions. There are two types of laboratory tests which are presented in this article. The first one was performed by using a shear box with a special layer structure that is loaded by dynamic, pulsating force; while the second one was executed by using a 140 mm diameter HDPE tube with its original closing element that is loaded by ZD-40 machine. Findings and problems. There is a development after the R&D work made and published in 2014, in 2017 and 2018 years the ballast particle deterioration process is given according to more intermediate fatigue cycles with individual measurements that show more precise «picture» about the full particle degradation, i.e. breakage process. The authors give more accurate correlation functions between the calculated parameters and load cycles during fatigue. However, there are many factors in the test that need to be improved in the future. Therefore, the authors have discovered other additional tests. Originality. The most important goal of the authors that supplement the currently used regulation with new measurement methods. Practical value The authors’ developed and new methods may serve as a basis for a future instruction or regulation. The publishing of this paper was supported by EFOP 3.6.1-16-2016-00017 project.
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This paper contains some conclusions from the author’s research that the authors experienced during their individual fatigue laboratory tests. The most railway lines in the world have so called traditional superstructure (ballasted tracks). In the past few years there were a lot of railway rehabilitation project in Hungary, as well as abroad. The authors think that it is important to learn about the process of ballast degradation, because ballast material is the largest weight in the track. The authors’ research’s main goal is to be able to simulate the stress-strain effect of ballast particles in real and objective way in laboratory conditions as well as in discrete element modelling. The authors have developed an individual laboratory test, but due its the enormous time requirement, they are trying other laboratory test as supplement. The use of the available laboratory test tools has recently started as a new direction for the research topic. The authors worked out two types of test methods: one of that has wide range of literature, but for the other one there is no relevant source. The first method is based on 3-D scanning and image analysis, which can be used for examine one particle’s degradation and its surface change. For the second method a CT (computer tomograph or X-ray) device was used with a small aggregation. Hopefully, adequate new results can be achieved with developing the new methods in the research topic.
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This paper demonstrates the results in the research topic of the railway ballast particles’ breakage test with unique laboratory test. The most railway lines in the world have so called traditional superstructure (ballasted tracks). In the past few years there were a lot of railway rehabilitation projects in Hungary, as well as abroad. Nowadays cannot be expected that there is enough quantity of railway ballast in adequate quality, because of the modifications and restrictions in the related regulations in Hungary since 2010. In Hungary there are only a few quarries which are able to ensure adequate railway ballast material for construction and maintenance projects for speed values between 120 and 160 km/h. This may cause supply and quality risk in production of railway ballast. The authors’ research’s main goal is to be able to simulate the stress-strain effect of ballast particles in real and objective way in laboratory conditions as well as in discrete element modelling.
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Link: This paper summarizes the authors’ up-to-date results in the research topic of railway ballast particles’ breakage test with individual laboratory test. In the past few years there were a lot of railway rehabilitation and maintenance project in Hungary, as well as abroad. The largest part of world’s railways has traditional superstructure, i.e. they are so called ballasted tracks. The railway ballast is the highest mass in the railways’ superstructure. Nowadays, it is a naturally fact that there is enough quantity of railway ballast in adequate quality. However, due to the modifications and restrictions in the related regulations since 2010, there are only few quarries in Hungary, which are able to ensure adequate railway ballast material for railway construction and maintenance projects for speed values between 120 and 160 km/h. Quarrying industry is stricken by aggravated environmental, heritage and conservation regulations year by year, it limits the accessibility of mineral wealth in significant manner. This fact with quality requirements means supply and quality risk in production of railway ballast in medium term. The main goal of authors’ research is to be able to simulate the stress-strain effect of ballast particles in real and objective manner in laboratory circumstances, as well as in discrete element method modeling. This paper introduces the exact assembly of executed laboratory test and newest test results. The authors summarize the up-to-date international literature review, using that they give short outlook to the planned research with research directions in near future.
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A new laboratory test procedure was developed to be able to evaluate railway ballast particle degradation using dynamic fatigue test. There is a product standard (MSZ EN 13450:2003) that contains requirements for mechanic parameters of railway ballast, e.g. Los Angeles as well as Micro- Deval abrasion, according to MSZ EN 1097-2:2010 and MSZ EN 1097-2:2012 standards, respectively. These laboratory tests give the abrasion parameters of railway ballast (as well as other type of rocks, e.g. concrete, asphalt pavement, etc.) in the consideration of a rotating steel cylinder (railway ballast material has to be put into it) using steel balls, water or without them. In real circumstances this type of stress can never occur in railway tracks. The mentioned new laboratory test procedure is able to simulate more precisely the real stress and degradation of ballast particles. The calculation of degradation is in accordance with the methods written in international literature. The required time interval of ballast cleaning can be determined, too. The authors summarize the results of international researches, scientific papers and books related to laboratory degradation tests of railway ballast, as well as real field tests in tracks. Relevant parameters, statements are described, after it has been competed, own laboratory test programme and assembly are introduced and detailed. This paper contains the results of a laboratory test series related to specific railway ballast breakage evaluation method using laboratory measurement solution. Five types of andesite railway ballast sample were tested by dynamic pulsating force with three million load cycles that simulates approximately 4-year-loading in reality (e.g. MÁV No. 1. railway line). The authors detail their future research programme that will be performed in 2018, this research is supported by the ÚNKP-17-4 New National Excellence Program of Ministry of Human Capacities.
Ballast track is the most widely used track for the railway transport, and ballast bed plays a significant role to provide resistances during train operation. Generally, the ballast bed consists of crushed stones. To achieve the mitigation of ballast degradation, the first priority is to describe the degradation development and to study its effect factors. The influence of ballast morphology (particle size and shape) on ballast degradation is examined here using the Los Angeles Abrasion (LAA) test in combination with 3-D image analysis. LAA tests are used to obtain the deteriorated ballast. Then, based on the 3-D images, the changes of ballast particles after the tests were analysed. To quantify the ballast degradation (abrasion and breakage), the Abrasion Depth based on the analysis of 3-D images were proposed, while ballast breakage was estimated using the broken particles ratio. The results have shown that ballast degradation is directly related to the ballast morphology. The proposed image-based procedure can effectively be applied to assess ballast degradation. The results can be used for ballast material standardization, modelling of ballast degradation process and maintenance cycle prediction.