Degradation Of Railway Ballast Research Articles

Machine learning approach to railway ballast degradation prognosis considering crumb rubber modification and parent rock strength

Parent rock strength and crumb rubber modification are two critical mechanical parameters that significantly decide the ballast layer degradation subjected to train dynamic loading. Using machine learning to predict ballast degradation considering these two parameters is helpful for deciding ballasted track maintenance cycle. In the current study, the ballast degradation process data (variables: parent rock types, loading types, ballast gradations and compositions of crumb rubber-ballast mixture) were used to train machine learning models. The drop-weight impact loading tests were performed to simulate different train dynamic loadings.Two well-established machine learning models, i.e., random forest (RF) and support vector regression (SVR) were trained and verified, to more effectively assess the importance of these variables. The results from the validated machine learning models confirm that the parent rock type is the most influential parameter, followed by the loading type (applied stress level), to control and predict the degradation of the ballast-CR mixture.The experimental assessment reveals that although the incorporation of CR suppresses degradation across all characterized rock types, the improvement in performance of the ballast-CR specimen against degradation is more noticeable for high-strength parent rock subjected to a considerable stress level. Meanwhile, this positive influence is also observed for ballast of weaker strength when the applied stress level is low.

Degraded Ballast Stiffness Characterization Using Bender Element Field Sensor and PANDA® Penetrometer

The progressive degradation of railway ballast over time increases the degree of ballast fouling and poses significant drainability concerns leading to frequent maintenance activities. To avoid such issues, an effective and continuous characterization of the physical properties of the ballast layer is deemed necessary. This paper introduces the combined use of a bender element (BE) piezoelectric field sensor and a PANDA® dynamic cone penetrometer for periodic evaluations of ballast condition over the traffic use. To simulate various levels of ballast degradation, box tests were conducted using a dolomitic ballast material compacted in a laboratory-sized testbed with fouling indices ranging from zero to 39%. BE sensor pairs were embedded in the ballast layer to calculate the small strain modulus behavior of the ballast assessed through shear wave velocity measurements under different confinement conditions. Strength profiles of the ballast at different fouling levels were also measured using the PANDA® penetrometer. Experimental findings from both test methods indicate the existence of a dense state of ballast linked to a certain fouling index that maximized stiffness and strength characteristics of the tested ballast in dry condition. Accordingly, the potential use of BE field sensors embedded within in-service ballasted track coupled with periodic penetration testing can be a viable approach to evaluate ballast layer degradation. Various void packing conditions associated with ballast fouling levels can be linked to important ballast layer modulus and strength behavior. Further, such smart sensing of ballasted track behavior can provide long-term performance monitoring solutions for ballast cleaning and maintenance scheduling.

Comparative Evaluation of Railway Ballast Degradation

Ballast bed is one of the most important components of ballasted railway track system. Over a period of service, it undergoes axial deformation due to the accumulation of train cyclic loading. However, there has not been a universally accepted method of evaluating ballast degradation, hence, this study focused on comparing two most common methods namely; Marsal breakage ratio and fouling index (FI). The degraded ballast material was prepared using Los Angeles abrasion (LAA) method at an interval of 250 turns of the LAA test drum, from the fresh ballast to degraded ballast at 2000 turns of the LAA test drum. Series of sieve analysis were conducted and the changes in ballast gradations were evaluated. A strong correlation was observed between the results obtained using the two approaches with a coefficient of determination of 99.24%. Based on the results obtained from the ballast degradation analysis both Marsal’s breakage ratio and the fouling index can be used for the evaluation of ballast degradation. However, Marsal’s breakage index is recommended due to its ability to give the breakdown of the particle size variations. Keywords: Ballast degradation; fouling; Los Angeles Abrasion; gradations; breakage ratio

PERFORMANCE EVALUATION OF RAILWAY BALLAST DEGRADATION USING THE MORPHOLOGICAL PROPERTIES

Ballast degradation through attrition and breakage during operations affects the structural performance of the railway track system. In an attempt to study railway ballast degradation changes due to train cyclic loading at micro-scale. This study quantified and compared the changes that occur on ballast particles due to ballast degradation using LAA test and image analysis techniques. TB/T 2328.14-2008 gradation use by china railways was adopted. Series of LAA tests were conducted to accelerate the ballast particle breakage and abrasion, in a sequence of 250 turns of the LAA test drum, after which the changes in gradation and morphological properties were quantified. The morphological properties were quantified using imaging techniques (Aggregate Image measurement system (AIMS)). At the end of the study, the overall results showed that ballast degradation has a strong correlation with the ballast particle's morphological properties. The relationships and the indices of morphological changes can be used for numerical modeling and simulations using discrete element method (DEM) to study the performance of ballast at different degradation levels.

The Technology of Multilayer Mechanical Stabilization of the Railway Ballast by Flat Polymer Geogrids

The problem of railway ballast degradation during service life is receiving considerable attention. The primary reason of aggregate particles cracking and abrasion is the maintenance operation of machine ballast tamping. Reduction of tamping operations frequency helps to maintain the quality of crushed stone and therefore, reduce the deformation of ballast. This may be achieved by increasing aggregate stiffness by mechanical stabilisation with flat rigid polymer geogrid. Laboratory modeling of cyclic loaded ballast shows that one layer of geogrid at the bottom of ballast reduces the settlement by 34 % while multilayer stabilisation by 3 geogrids reduces it by 67 % and possibly allows avoiding tapping during service life. As an alternative maintenance option, the authors propose bedding with pneumatic stone blowing or shallow tapping to the depth of 70 mm.

Quantification of Railway Ballast Degradation by Abrasion Testing and Computer-Aided Morphology Analysis

AbstractBallast degradation (particle breakage and abrasion) induced by repeated train loads may lead to insufficient track stiffness and excessive track settlement. For safe operation and effectiv...

Degradation of railway ballast under impact loading considering the morphological properties of aggregate

Degradation of railway ballast aggregate is ensued from breakage of single particle as well as from abrasion of angular corners. The present study evaluates the change in morphological characteristics as well as particle size distribution of ballast aggregate degraded under applied impact loads to further illuminate the degradation mechanism of particles. The utilized drop-weight impact loading apparatus implemented on prepared ballast specimens is modified to take into account the real stress levels applied over ballast course. The morphological features of aggregate including angularity and surface roughness are quantified by establishment of extended image processing method. Generally, the obtained results uphold the evident effect of parent rock type on degradation mechanism. Also, the percent reduction of indices related to angularity and surface roughness are in line with increment of degradation level measured by fouling index (FI). Furthermore, the change in morphological indices is not significant in case of using particle size distribution with higher uniformity coefficient compared with more uniform gradation. Indeed, major effect of selection of broader sieve size range is exhibited on reduction of breakage of larger-sized aggregate. Meanwhile, provision of flexible subgrade instead of rigid type considerably diminishes the percentage of reduction of sharp corners and surface roughness which confirms evident effect of stiffness of underlying layer on level of abrasion of coarse particles.

Effect of deconstructed tire under sleeper pad on railway ballast degradation under cyclic loading

In this paper, the effect of different thicknesses of Deconstructed Tires Under Sleeper Pads (DT-USP) and different Unconfined Compressive Strength (UCS) values of mother rocks of ballast aggregates were studied in the degradation of railway ballast. For this purpose, in the first step, both static and dynamic bedding modulus of DT-USP's were extracted in the laboratory according to DIN standard requirements. In continuation, the physical and mechanical properties of the three different ballast types taken from Shahriar, Anjilavand, and Kouhin quarries in Iran were obtained via a series of standard lab tests. The UCS of core specimens taken from the mother rocks of the mentioned queries were ranked as low (159 MPa), medium (216 MPA), and high (285 MPa) respectively. Finally, 36 ballast box test experiments with and without the presence of DT-USPs in three thicknesses of 7, 11, and 13 mm were carried out and their results were compared up to 200,000 loading cycles to investigate the cyclic behavior of ballast samples. Experiment results were elicited in the form of settlement, Hardin breakage index (Br), ballast stiffness, and ballast Damping Ratio (DR). The results demonstrate for ballast of Shahriar quarry by increasing of the DT-USP's thickness from 7 to 13 mm, settlement, Br, and stiffness have decreased by 38.4%, 6.9%, and 80.5% respectively and DR has increased by 199.2% while these reported percentages, i.e. settlement, Br, and Stiffness have decreased and DR has increased after strengthening the ballast mother rock in the cases of Anjilavand and Kouhin quarries. On the other side, based on the achieved results for all three categories of ballast strengths, the DT-USP with 11 mm thickness has shown the most suitable performance.

Prognosis of railway ballast degradation for turnouts using track-side accelerations

Maintenance of railway turnouts is a major cost driver for any infrastructure manager, which performs it based on preventive or periodic policies to guarantee minimum downtime of the infrastructure. Ballast maintenance activities, such as tamping, are scheduled by thresholding indicators derived from track geometry data in agreement with European standards. Current industrial practice adopts the same procedures for the evaluation of track geometry degradation in open track and turnouts. This lack of specificity may determine unnecessary maintenance actions with detrimental effects to the turnout dynamical performance. By employing track-side measurements of track acceleration, a probabilistic method for turnout’s ballast quality monitoring was derived by Barkhordari et al. The paper further develops such monitoring system by establishing a mapping between its output and the standard indicator of track geometry quality used by infrastructure managers to schedule ballast maintenance. This results in a predictor of track geometry quality with variable prediction horizon that is functional to the railway infrastructure manager for the predictive planning of ballast maintenance.

Field assessment of railway ballast degradation and mitigation using geotextile

Rail tracks continue to deform due to degradation of ballast under the application of heavy train traffic. The resulting track deformations often lead to drainage impairment as well as loss of resiliency. For track replenishment, deep screening of ballast is usually adopted by Indian Railway (IR) either after 10 years or passage of 500 MGT traffic, whichever is earlier. To study the effectiveness of geotextile on track stability and assess possible reductions in maintenance costs, a layer of woven geotextile was installed at the ballast-subgrade interface in Bhusawal-Akola central railway section of IR which is the present study area. The results show that the amount of degradation and fouling are different in UP and DN tracks due to inherent variation in traffic characteristics. This study also shows that the placement of geotextile in the track has led to prolonged maintenance cycle with favorable implications on cost and track shutdown periods. The findings of the present case study results will be useful for IR to reduce the ballast procurement and reuse of discarded material during deep screening in future.

Degradation of railway ballast under compressive loads considering particles rearrangement

ABSTRACTThe performance of the railway track structure is highly affected by degradation of the ballast aggregate in which breakage and abrasion of coarse angular particles result in production of fine grains. Maintenance activities including ballast cleaning and tamping operation can intensify ballast degradation during service life. In addition, initial gradation of ballast aggregate can influence the level of ballast degradation. The main purpose of the present study is to simulate the effect of rearrangement of aggregate during maintenance activities on the degradation of ballast by evaluating the influence of initial gradation of aggregate and rock type. For this purpose, a series of lab-scale compression tests with multiple-step loading are conducted during which ballast particles are taken out from the mould after each step and remoulded before the next step. According to the obtained results, multiple-step loading compression test results in more degradation as well as more axial strain of aggregate samples. In addition, gradation comprised of broad range of ballast particles leads to less degradation of ballast under applied loads. Furthermore, less degradation of ballast particles subjected to compressive loads results in lower axial strains in the specimens.

A hypo-plastic approach for evaluating railway ballast degradation

Repetitive or cyclic rail loading deteriorates the engineering properties of the railway ballast by particle crushing and rearrangement. Most of the classical elasto-plastic models are unable to predict such ballast degradation despite successfully predicting the overall load–deformation behavior during cyclic densification. In this context, the present study delivers a novel hypo-plastic modeling approach coupled with breakage mechanics theory to bridge the gap of the conventional models. The hypo-plastic approach enables to predict the nonlinear load–deformation response of ballast-type granular materials for both monotonic and cyclic loading conditions, while circumventing the requirement of notional yield condition to predict the inelastic behavior. Breakage mechanics theory, on the other hand, establishes the links between particle comminution and the macroscopic deformation. The novelty of the proposed approach is threefold. Firstly, unlike the conventional hypo-plastic approaches, the development of the proposed model is within the continuum thermodynamics framework. Secondly, the model requires less number of physically identifiable parameters as compared to that of earlier models employed for assessing the particle breakage under cyclic loading. Third and finally, the numerical implementation of the model as a user-defined material is simple for solving boundary value problems. Under the compressive deformation regime, the model prediction of the ballast degradation along with the cyclic densification response agrees reasonably well with the experimental results found in the literature.

Effect of particle size distribution and subgrade condition on degradation of railway ballast under impact loads

Ballasted rail tracks are generally exposed to impact loads generated from abnormal wheel-rail interface as well as sudden variations in support rigidity. These induced impact loads can lead to railway ballast degradation by attrition of the angular edges of the aggregate and breakage of single particle into finer fragments. In the present study, the degradation of ballast particles under impact loads is investigated by considering various fouling and breakage indices. For this purpose, impact test is conducted on ballast aggregates obtained from different quarries (rock types of basalt, marl, dolomite and trachyte) by varying the gradation of ballast aggregates, impact energy and subgrade type. According to the obtained results, the degradation of ballast specimens under impact loading is less for more broadly-graded ballast. In addition, providing a flexible subgrade as support condition leads to reduction in ballast degradation resulted from diminishing impact energy. Furthermore, the axial strain of ballast specimens reduces with decrease in degradation of aggregates under repeated impact loads.

Evaluating the impact of ballast undercutting on the roughness of track geometry over different subgrade conditions

The progressive degradation of railway ballast is often cited as a primary factor that contributes to the development of track roughness, while ballast renewal (undercutting) attempts to manage its long-term development. Soft subgrades have been shown to strongly influence track geometry and are a contributing factor that has not been considered during conventional track maintenance. This study evaluated the impact of undercutting on long-term trends in track geometry roughness, and what impact softer subgrades had on the effectiveness of undercutting. A combined 6.90 km of Class II–IV heavy-haul track in Western Canada (undercut in 2010 and 2011) formed the basis for this analysis. Annual traffic on these sections typically totals 50 million gross tonnes. Long-term trends in the track crosslevel, alignment, and surface roughness after ballast renewal were derived from 50 track geometry surveys carried out over a five-year period (2010–2015). The results showed that undercutting significantly reduced track roughness over sand, silt, clay, or till subgrades; however, it was often ineffective when used over soft organic subgrades. Thus, while ballast degradation is the primary cause of track roughness in segments constructed on mineral subgrades, it is not a mechanism that results in track geometry roughness over soft organic soils.

Bitumen stabilized ballast: A potential solution for railway track-bed

Railway ballast degradation under dynamic loads progressively leads to loss of mechanical performance and geometry of the track, so that maintenance interventions are frequently needed. In order to systematically avoid this issue, recently solutions have been proposed to reinforce track-bed by using polyurethane and/or resins as well as asphalt layers among others. Nonetheless, their main limitations are related to the high initial cost and low productivity.To cope with these limitations, in this study, bitumen stabilized ballast (BSB) is proposed as a new solution for ballast stabilization. This method aims at improving durability and reducing settlement by modifying both stiffness and the ability of energy dissipation of the layer. The paper introduces the potential of this technology as material to be used in railway track-beds by presenting the results of a laboratory-based investigation using the Precision Unbound Material Analyser (PUMA). Different variables such as ballast grading, bitumen emulsion dosage, compaction method and stress levels are considered. Results showed a significant decrease in permanent deformation and deformation rate associated with modified stiffness and energy dissipation properties of BSB, which suggest the potential for improving long-term performance and sustainability of ballasted track.

Quantifying Degradation of Railway Ballast Using Numerical Simulations of Micro-deval Test and In-situ Conditions

Throughout the life of the track, ballast grains wear as a result of both the trains passing over the track and the maintenance operations (tamping). The morphology of the grains is changed: they lose angularity and fine particles are produced, causing a gradual loss of track performance. Eventually ballast renewal becomes necessary. In order to predict the evolution of this degradation, a multi-scale study is proposed. A comparison between discrete element method (DEM) simulations of Micro-Deval attrition test and of the passage of trains over a sleeper is performed in order to both detect the different loading and wearing mechanisms involved and quantify the amount of friction work produced, which is directly related to friction wear. The same numerical approach is also used with the simulations of the track to detect families of contacts in order to determine characteristic loading paths at the micro-scale. Loads and displacements of both systems are then compared in order to discuss the relevance of the Micro-Deval test.

Effect of cyclic loading frequency on the permanent deformation and degradation of railway ballast

A series of large-scale cyclic triaxial tests were conducted on latite basalt aggregates (ballast) to investigate how the frequency f affects the permanent deformation and degradation of railway ballast. During testing the frequency was varied from 5 Hz to 60 Hz to simulate a range of train speeds from about 40 km/h to 400 km/h. Three categories of permanent deformation mechanisms were observed in response to the applied cyclic loads, namely, the inception of plastic shakedown (f ≤ 20 Hz), then plastic shakedown and ratcheting (30 Hz ≤ f ≤ 50 Hz), followed by plastic collapse at higher frequencies (f ≥ 60 Hz). The permanent strain of ballast and particle breakage increased with the frequency and number of load cycles. A cyclic strain ratio was introduced to capture the effect of frequency on the permanent axial and volumetric strains, respectively. An empirical equation was formulated to represent this relationship for latite basalt, and a critical train speed was identified. A good correlation was obtained between particle breakage and volumetric strain under cyclic loading.

An Inspection of Railway Ballast Quality Using Ground Penetrating Radar in Finland

The maintenance of heavy haul railway lines causes considerable cost and in many cases difficulties to rail traffic. Railway infrastructure management in Finland is important because in many locations the same railway lines are used by both freight and passenger trains. Along with the mixed traffic, the cold climate presents challenges in keeping the track in good condition. There is a great demand for economical and non-destructive methods that provide continuous condition information of track structure. In recent years, the ground penetrating radar (GPR) technology for structure inspection has improved to faster systems and better data quality. This article presents the main results from a research programme that was aimed to identify different GPR-based railway ballast degradation classes and to develop a preventative maintenance planning system. An extensive reference sampling and laboratory analysis has been performed to aid in developing the GPR-based classification method for qualifying the ballast fouling. Classification is made by a fouling index, which is calculated from the frequency contents of the GPR signal. This quality classification can be utilized in the planning of undercutting programmes.