Tamping Process Research Articles

Field assessment of different tamping operations for newly constructed or renovated railway tracks

ABSTRACT The tamping process is crucial for correcting geometric irregularities on railway tracks, especially on newly constructed or renovated tracks that are more susceptible to accumulating defects. Recent studies have demonstrated that multiple insertions of tamping tines lead to greater ballast compaction and improved lateral resistance of the track. However, further evaluation is necessary to assess their impact on other important track parameters. This study evaluated single and multiple insertions to determine which would promote more effective maintenance for newly built or renovated track conditions, focusing on geometry correction, track structural behaviour, and potential ballast degradation. These tamping methods were tested in a heavy haul line, showing that multiple insertions improved geometric quality, increased lateral resistance, and enhanced vertical track stiffness without causing significant ballast degradation. Therefore, using multiple insertions is recommended for newly built or renovated tracks to enhance geometric quality and structural behaviour, providing a more effective maintenance solution.

A Methodology Linking Tamping Processes and Railway Track Behaviour

Today’s railway transport is built upon high-performance infrastructure. Cost-effective yet sustainable infrastructure presumes tracks with a precise and durable geometry. At ballasted tracks, the geometry is created and restored through tamping machines, which position the track panel and compact the ballast beneath the sleepers. It is commonly agreed that the ballast compaction plays an important role in the long-term stability of the track. Yet, there is no method available which allows a direct correlation between the compactness of the ballast and the stability of the track geometry. Available studies either model track behaviour without considering the bedding, or analyse ballast compactness locally while disregarding its influence on the track geometry. This paper presents a new methodology which establishes a relation between these two topics—ballast compaction during tamping and subsequent track behaviour. A state-of-the-art tamping machine has been equipped with an experimental measurement setup, constantly recording relevant data during every tamping process. These data can be used to derive an indication for the achieved compaction under every sleeper. Utilising the tamping machine’s internal measuring system for track geometry documentation, every tamping process (every sleeper) is assigned to the precise position along the track. The data set is merged and synchronised with regular track geometry measurements of the infrastructure manager. The result is a comprehensive data set which allows precise analyses between tamping machine measurements and track behaviour. This data set provides the foundation for future research, aiming towards a better understanding of the tamping process and its influence on the quality and durability of the established track geometry.

Discrete element analysis of the effect of manual tamping operation on the mechanical properties of ballast bed

At present, the theoretical analysis of manual tamping of ballast track has not been systematically carried out. The daily maintenance and repair is mainly based on experience. This paper uses the DEM-MBD co-simulation method to establish the ballast bed-sleeper-tamping machine model, simulates the manual tamping process under specific working conditions, and analyzes the influence of manual tamping on the movement trend, the compactness and the contact state of ballast. The results show that: a) The effect of filling the instantaneous “gap” at the bottom of the sleeper is mainly realized in the stage of inserting, b) The stage of withdrawing from the ballast bed will not cause secondary disturbance to the ballast bed area at the bottom of the sleeper, c) The compactness of the ballast bed in the shallow area at the bottom of the sleeper is improved after tamping, d) The bearing capacity of the ballast bed is guaranteed, e) The difference of contact state between ballast is significantly reduced after tamping and finally, f) The load transmission path inside the ballast bed can be improved after tamping.

Studying the Relation of the Residual Stresses in the Ballast Layer to the Elastic Wave Propagation

During track construction or ballast bed maintenance, ballast layer compaction quality plays an essential role in the following track irregularity accumulation, its lifecycle, and maintenance costs. The ballast compaction process is characterized by its compaction and the accumulation of the stressed state. The elastic wave propagation methods are an effective way for the identification of the ballast bed compaction properties. The paper presents the theoretical and experimental studies of the ballast consolidation under the vibration loading of the sleeper. The practical laboratory study is given by the 1:2.5 scaled physical model of one sleeper and the corresponding ballast layer box. The measurements of ballast pressure and deformations under the vibration loading in the ballast layer and the photogrammetric recording of the ballast flow are carried out. The measurements demonstrate the accumulation of the residual stresses under the ballast layer. Furthermore, the measurements of elastic wave time of flight (ToF) using the shakers under the sleeper and acceleration sensors under the ballast show the substantial increase of the ToF velocities after the tamping process. Moreover, the distribution of the velocities along the sleeper is spatially inhomogeneous. The numeric simulation using the discrete element method (DEM) of the tamping and the testing processes proves the inhomogeneous wave propagation effect. The modeling shows that the main reason for the wave propagation inhomogeneity is the accumulated residual stress distribution and the minor one – the compaction density. Additionally, a method for identifying wave velocity spatial distribution is developed by wave tracing the inhomogeneous medium. The procedures allow ballast identification in the zones outside the shakers.

In-situ ballast condition assessment by tamping machine integrated measurement system

The condition of the ballast bed is one of the most important parameters to be determined in order to assure a safe and economical operation of railway systems. Better knowledge of ballast condition provides an advantage in defining the optimum time for ballast bed cleaning or renewal. State of the art ballast condition quantification methods all require in-situ ballast sampling followed by laboratory tests, reducing track availability and making additional track closure necessary, thus making the determination of ballast condition a time-consuming and challenging task. The tamping process is the core maintenance activity in ballasted track and it is crucial for the economical service life of the track and essential in restoring the track geometry for safe train operations. During the tamping process, the tamping tines interact with the ballast matrix, transferring the displacement caused by the dynamic excitation to the ballast, compacting it under the sleeper. This interaction is observed and measured in-situ within the framework of a research project presented in this paper. Lateral forces and compaction energy, together with the loading and unloading response of the ballast matrix during compaction are used to determine the ballast condition. Serving as a confirmation of the ballast condition definitions made based on the in-situ measurements, a semi-analytical model of the tamping unit-ballast matrix interaction has been developed. The mechanical model is used to simulate different ballast conditions in order to optimize the ballast life cycle and improve the understanding of ballast behaviour under cyclic loading.

Modeling Cotton Module Builder and Loader to Enhance Biomass Testing

HighlightsPhysical models of module builder and module loader were developed to enhance biomass testing with reduced mass and volume of biomass.Models used dimensional analysis, Pi Terms, and engineering factors and emphasis on reduced module upsetting and disturbance.Some engineering terms such as tamping face pressure and velocity, and particle size were not scaled to reduce biological-material distortions.Switchgrass bulk density at 8% wet basis for prototype and model were 115 and 80 kg m-3, respectively.Abstract. The objective was to design and implement separate models of a first-generation cotton module builder and a module loader that facilitated tamping quasi-confined biomass and the minimal disturbances of modules during emptying from the builder and during loader operations including unloading. The 122-cm long model, compared to 978-cm long prototype, reduced the mass of module contents required for testing from 6188 to 44 kg, or by a factor of 141:1. The tamping process was emphasized with constant tamper pressure of 76.6 kPa applied to module contents for prototype and model. Consistent properties such as SG characteristic length were also held constant among module sizes to reduce the complications of introducing un-anticipated biological-material distortions. Similarities in design aspects beyond dimensional analysis were emphasized to reduce inadvertent module upset and disturbance. Hydraulics ensured uniform tamping and lifting. An efficient module box for the model resembled the prototype-scale commercial unit with z-shaped ribs and upward-tapered module sides. Seed cotton [8% moisture wet basis (w.b.)] bulk densities for prototype and model were 166 and 107 kg m-3, respectively. Bulk densities for switchgrass (8% w.b.) prototype and model were 115 and 81 kg m-3, respectively. Reduced bulk density of models was attributed to essentially no external confinement stresses being applied to modules at rest resulting in only self-imposed confinement stresses due to module content over-burden. However, unconfined modules may have a role in handling biomass for reduced distances. Also related to minimizing module upsetting, module loading emphasized the counter-motions of advancing the loader versus the conveyor motion in the opposite direction, all driven with an electric motor. Module stability during loading was attributed to a self-imposed normal stress of module weight acting downward onto a horizontal plane of the module. The fixed loading angle of 15° and material bulk properties were held constant between prototype and model. Dependent variable for the module loader was normal stress for module stability. Normal stresses resulting from seed cotton at 8% moisture content (wet basis) were 4.754 and 0.637 kPa, respectively. Normal stresses for chopped SG at 8% moisture content (wet basis) were 3.302 and 0.484 kPa, respectively. Biomass modules would not be as stable as cotton modules based on normal stress, and due to lack of intermeshing cotton fibers. Results of loading and unloading a dozen SG model modules resulted in one module failure due to upset, and that was attributed to a 2-layer fill versus 3-layer fill for that one module. Keywords:

Evaluating the applicability of multi-sensor equipped tamping machines for ballast condition monitoring

Ballast is a key component of most railway tracks and fulfils crucial tasks. The strong forces induced by train operation, however, wear the stones, and in combination with external pollution the condition of the bedding gradually deteriorates. Track alignment issues arise as a consequence and these are usually corrected by use of tamping machines. The importance of a functioning ballast bed implicates the necessity for sophisticated condition monitoring. A novel approach for addressing this need is presented here. The tamping unit of a high-performance tamping machine has been equipped with multiple sensors, which measure various parameters during every tamping process. A set of recorded data is analysed and compared with the prevailing ballast condition, which is evaluated using proven methods. The results verify that the measurements correlate with the condition of the bedding, thus confirming the assumption that sensor equipped tamping units allow conclusions regarding the condition of track ballast.

Experimental Study on Acoustic Emission of Confined Compression of Crushed Gangue under Different Loading Rates: Disposal of Gangue Solid Waste

The crushed gangue materials which are filled into the goaf in solid-backfilling coal mining become the main body of bearing the overburden after the tamping process. Its resistance to deformation is the key to control overburden movement and surface subsidence. Particle breakage affects the resistance to deformation of filling materials. In this paper, a confined compression test of crushed gangue under different loading rates was designed, and the acoustic emission (AE) signal was monitored in the process of confined compression. The test results showed that with the increase of loading rate, the anti-deformation ability of crushed gangue showed a dynamic change process of increasing, decreasing, and then increasing again. With the increase of loading rate, the breakage degree of the samples decreased, the proportion of large-sized gangue increased, the growth period of AE counts showed an obvious hysteresis phenomenon, and the AE activity level of the gangue increased gradually. The research results can not only provide a more in-depth and comprehensive understanding of the mechanical properties of crushed gangue filling materials but also provide a reference for the engineering application of solid-filling coal mining.

Study on quick consolidation method of strong drainage combined with compaction

In this paper, a quick consolidation technique for silt and silty clay foundation with strong drainage combined with compaction is developed through field test. The whole construction period is only 70 days. A strong drainage system is put forward. The whole reinforcement process only needs two inserts and pulls. During the tamping process, the strong drainage system works continuously and saves much time. After consolidation, the bearing capacity of the foundation meets the requirements, and the soil properties are greatly enhanced. The influence depth of consolidation is at least 10 m.

Surface Subsidence Control during Deep Backfill Coal Mining: A Case Study

Deep resource exploitation is imperative, but it is facing with more complicated mining environment and more dangerous mining disturbances to induce the potential catastrophe process. Solid backfill technology, which can control the strata movement and prevent potential hazards, has been used as the primary method in deep mining for surface subsidence control and ecosystem protection. In this study, taking backfill mining area no. 930 in the Tangkou coal mine as background, the probability integral model was adopted to predict the surface subsidence at different mining depths and filling ratios. The filling ratio was designed for deep mining based on the regression analysis of the predicted surface subsidence results. The study shows that the backfilling ratio at the Tangkou deep coal mining area should be controlled at a level greater than 82.5%, and the mining damage to the surface under this condition was analyzed. Furthermore, control strategies for deep backfill mining are proposed in which the backfill density can be enhanced by optimizing the tamping machine, material composition, and tamping process. Finally, the measurement of the backfill mass and surface subsidence showed that the actual filling ratio was controlled at 82.57%, which ensures adequate protection of the surface buildings during the mining process.

Development of condition‐based tamping process in railway engineering

AbstractBallast, rails and sleepers form a quasi‐elastic track system. When the deformations exceed the elastic limit of the system and the track is no longer lying in its correct position, precautions have to be taken. During a technical track examination several parameters are measured. Should the operational tolerance values of these parameters be exceeded, track maintenance needs to be conducted. Track maintenance includes levelling, lifting, lining and tamping of the track, which is performed by a tamping machine, where the tamping tines penetrate the ballast and compact it beneath the sleeper. For the purpose of this research project, a tamping machine was equipped with a number of strategically positioned sensors in order to perform the in‐situ measurements required to describe the interaction of the tamping tines with the ballast and its compaction beneath the sleeper. With a special emphasis on the energy transferred into the ballast and alteration of ballast stiffness during compaction, conclusions concerning efficiency of the tamping process in different ballast conditions are made and presented.

Stone blowing as a remedial measure to mitigate differential movement problems at railroad bridge approaches

Railroad track transitions such as bridge approaches often experience recurrent track geometry problems due to differential settlement between the bridge and the adjacent track. The resulting “bump at the end of the bridge” leads to significant passenger discomfort and causes rapid deterioration of the track as well as vehicular components. In general, railroad managers address recurrent track geometry defects through track resurfacing methods, such as tamping that involve raising the track through mechanically induced vibration and rearrangement of particles within the ballast layer. Although widely used for track resurfacing, the tamping process tends to destabilize the ballast layer, and the track may rapidly return to its former deteriorated state based on the traffic flow. The method of “stone blowing,” on the other hand, which was developed as an alternative to tamping, relies on the principle of injecting fresh ballast particles into gaps underneath ties and raising the track level rather than disturbing the packing condition of the existing ballast. In a recently completed research study in the United States, stone blowing was successfully implemented as a remedial measure to mitigate the problem of differential movement at a problematic bridge approach along Amtrak’s Northeast Corridor. Advanced geotechnical instrumentation was used to monitor transient deformations within individual track substructure layers before and after stone blowing. Moreover, tie support conditions and track geometry data were also analyzed to quantify the effectiveness of stone blowing on the improvement of track performance.

Evaluation of ballast compactness during the tamping process by using an image-based 3D discrete element method

We investigated the dynamic behavior of a railway ballast layer during tamping operation by 3D Discrete Element simulations. The ballast layer was prepared with ballast grains that had a realistic shape and was measured by a laser scanner and modeled by clumped spheres using the dynamic optimization technique. Three types of sleeper models that were embedded in the ballast layer were prepared, and a series of tamping operations (lifting of the sleeper, insertion of vibrating tines and packing, pulling out of tines, and settling of the sleeper) were simulated in a realistic manner. The compaction underneath the sleeper mainly occurred during the insertion of tines and the packing process, while the tine insertion zone was eventually loosened after the tines were pulled out. The final porosity differs with different sleeper models and packing process periods. On the other hand, the coordination number (the number of inter-granular contacts per grain) drastically decreased during the insertion of the vibrating tines and the packing process; then, it recovered to the original value after the tines were pulled out. This change is important to identify the extent of ballast grain agitation due to the processes. The contact force network is sensitive to the applied loading and the place where the tines are inserted, and the resulting force network localization at the final state can be understood by the Coulomb’s earth pressure theory. The degree of heterogeneity may be the key to the long-term stability of the ballast layer under repeated train wheel loading.

An underwater stress-testing technique for the heavy-hammer tamping of a rubble-mound foundation

Rubble-mound foundations are commonly used in port-channel engineering and protection embankment. Heavy tamping is usually used to attain the required total compactness and bear capacity of such foundations. Monitoring and controlling the tamping-impact stresses is difficult because of the noncontinuous nature of the medium, particularly under the high impulse conditions (e.g. large-scale stresses and rapid attenuation) of the tamping process. In this research, a new instrument for measuring tamping stress incorporating a wide stress range and high sampling frequency was designed for use underwater and under dry conditions. Effects of different monitoring device radii were investigated by analyzing the tamping stresses obtained with different heavy-hammer falling distances. Results indicated that the monitoring device with a larger radius provided more stable test outcomes. We further verified the feasibility of the proposed monitoring device for monitoring heavy-hammer tamping stress. Testing data demonstrated that the dynamic-load monitoring instrument can achieve tamping stress values under heavy-hammer tamping under dry and wet conditions. The instrument also followed the same rule in accordance with compactness and settlement, thereby proving that the technique can be used to determine the foundation-bearing capacity.

Augmented utilisation of possession time: Analysis for track geometry maintenance

The demand for increased capacity on existing railway networks is a challenge for many Europe-based infrastructure managers; addressing this challenge requires augmented utilisation of track possession time. It is considered that large-scale maintenance tasks such as geometry maintenance can be improved; thus, reducing the on-track maintenance time and allowing more traffic. In this study, an analysis of track geometry maintenance was performed with the objective of reducing the required possession time. The procedure and models for planning and optimizing track geometry maintenance are presented. A statistical model that uses a simulation approach was used to determine the condition of the track geometry, and a schedule optimization problem was formulated to support intervention decisions and optimize the track possession time. The results of the case study show that optimizing the maintenance shift length and cycle length are opportunities to reduce the extent of track possession required for the maintenance of the track geometry. In addition, continuous improvement of the tamping process through lean analysis promises about a 45% reduction in the required possession time for a tamping cycle.

Numerical Study Porosity of Railway Ballast during Tamping Process

Tamping operation is an important part of railway maintenance work. The porosity of railway ballast is an important maintenance quality evaluation index during tamping process. In this paper, based on the discrete characteristics of railway ballast, the discrete element analysis model of railway ballast is created using the discrete element method, numerical simulations are performed to study the evolution of porosity of railway ballast under sleeper during tamping process. This paper focuses on the influence of vibration frequency of tamping tines during tamping process; an optimal vibration frequency is obtained from the simulation and compared with the actual vibration frequency recommended by China Railway Large Maintenance Machinery Co., Ltd. Kunming, it is found that the two vibration frequency is consistent. This result verifies that the discrete element method is an effective method to study the evolution of porosity of railway ballast during tamping process.

Discrete Element Method Simulation of Railway Ballast Compactness During Tamping Process

Railway ballast tamping operation is employed in order to restore the geometry of railway track distorted by train traffics. In this paper, based on analysis of tamping principle, the discrete element analysis model of railway ballast is created using the discrete element method, numerical simulations are performed to study the change of railway ballast compactness during tamping process. This paper presents the motion trend of stone ballasts as the change trend of railway ballast compactness in qualitative analysis, and the distance between stone ballast and sleeper as the change index of railway ballast compactness in quantitative analysis. By comparing simulation data of different vibration frequencies, an optimal vibration frequency is obtained. The simulation results accord with the actual industrial tamping operation, which verifies that the discrete element method is an effective method to evaluate the change of railway ballast compactness during tamping process.

The Research on the DEM Simulation of the Railway Ballast Tamping Process

Ballast degradation and unrecoverable deformation are emerged on the railway ballast track under the loads of high-speed and heavy loading locomotive. With the change of tamping frequency, a better understanding of the physics of compactness degree is important for long-time stability of ballast. This paper presented a numerical investigation of the bulk materials dynamics and the transient impaction of a system of irregular polyhedral particles confined with a rectangular box with a retaining wall subjected to cyclic tamping loading. Sphere packing method was being used in this study to simulate typical full-sized ballast particles. This paper aimed to establish firm-soft coupling particle-flow tamping operation simulation numerical model based on contact dynamics theory. This study checked the validity of the model while different tamping working conditions and out-loads was being implemented. The study shows that discrete element method (DEM) is an efficient method to reveal the rearrangement rule of railway ballast after the process of tamping operation.

Discrete Element Method Simulation of Mesomechanics of Railway Ballast during Tamping Process

Railway ballast tamping operations is employed in order to restore the geometry of railway track distorted by train traffics. The selection of tamping parameter is usually dependent on field trials and practical experience, for lack of theoretical basis. This paper creates discrete element analysis model of railway ballast using the discrete element method, the numerical simulations are carried out to study the mesomechanics of railway ballast during tamping process. We focus on the change of railway ballast compactness and stone ballast interaction force during tamping process. The present study can be helpful for the analysis of the internal mechanism of ballast compaction during tamping process.

Experimental and Numerical Study of Railway Ballast Compactness during Tamping Process

Railway ballast tamping operations is employed in order to restore the geometry of railway track distorted by train traffics. The main goal is to compact the stone ballast under the sleepers supporting the railway squeezing and vibrations. The ballast compactness is the most direct index for evaluating the effect of tamping operation. This paper presents an experimental method used to detect the railway ballast compactness before and after tamping operation based on water-filling method, and creates a discrete element analysis model of railway ballast which analyzes the change of ballast compactness before and after tamping operation based on discrete element method. The simulation results are very similar with experimental results, which verify that the discrete element method is an effective method to evaluate the change of railway ballast compactness during tamping process.