Ballast Size Research Articles

An analytical model for particle-geogrid aperture interaction

The shear strength of geogrid-reinforced ballast is often dependent on the aperture size of geogrids and the nominal size of ballast. This paper presents a theoretical analysis based on probabilistic mechanics of how aperture size affects the interaction between particles and geogrid. Unlike past literature, in this study, the properties of the particle size distribution is analysed using a Weibull distribution. The probability of grain interlock is proposed to describe the interactive mechanisms between particles and geogrids based on the relative particle size, which is defined as the ratio of particle size to aperture size. The mathematical model is calibrated by a set of large-scale direct shear tests with almost single-size (highly uniform) ballast aggregates, and then validated by independent set of data taken from both literature and current study. The study concludes that more uniform particle size distribution increases the probability of grain interlock at the optimum aperture size but decreases it at non-optimum aperture sizes.

Ballast Flow Characteristics of Discharging Pipeline in Shield Slurry System

We adopted two-way coupling of discrete and finite elements to examine the non-spherical ballast flow characteristics in a slurry pipe system during a shield project. In the study, we considered the slurry rheological property and the flake shape of the ballast. A ballast size between 17 and 32 mm under different slurry flow rates and ballast volumetric concentration conditions was investigated for determining the law through which the mass flow rate, detained mass percentage, and ballast distribution state are influenced. The results indicate that increasing slurry flow rate and the ballast volumetric concentration increase the mass flow rate; the influence of the latter is stronger. Increases in both in the slurry flow rate and the ballast volumetric concentration can reduce the detained mass percentage in the slurry discharging pipeline, whereas increasing the ballast size has the opposite effect. The increase in both the slurry flow rate and the ballast size changes the ballast motion state. Experiments verified the numerical lifting model of the ballast in the vertical pipeline. The measurements of the actual pipeline wall thickness verified that the simulation results regarding the ballast distribution were accurate.

Investigation of the gradation effect on ballast mechanical behaviors by means of discrete element modeling - part 2

The ballast gradation has a strong influence on the mechanical behaviour of ballast aggregates. Discrete Element Method (DEM) based simulations are performed to investigate the gradation effect of ballast aggregates on their settlement, ballast position rearrangement, breakage rate and void ratio. In the second part of this article, DEM based simulations are performed to investigate the gradation effect of ballast aggregates on their settlement, ballast position rearrangement, breakage rate and void ratio (Part 2). The results indicate that the settlement and the ballast position rearrangement increase with the decrease of the averaged ballast size of a ballast aggregate, whereas the void ratio decreases. Besides, the breakage and the ballast position rearrangement occur mainly with the dynamic loading rather than the static loading. Based on the simulation result, appropriately enlarged ballast stones will benefit not only the stability, but also the hydraulic conductivity of ballast aggregates. The gained result can be used for the optimization of ballast aggregate regarding to its gradation, so that its service cycle can be prolonged.

Substituting polyacrylamide with an activated starch polymer during ballasted flocculation

Synthetic polymers, mostly polyacrylamides (PAMs), are frequently used in the water industry to improve the performance of clarification. However, synthetic polymers may increase headloss in granular media filters, biodegrade slowly, and are potentially toxic. Alternatively, bio-sourced starch-based polymers may eliminate the drawbacks of synthetic flocculants. Similarly to poly(acrylamide‐co‐acrylic acid), carboxymethylated starch is expected to adsorb on metal hydroxides via hydrogen bonding on carboxyl groups. However, it is already known that starch, like many other polysaccharide flocculants, is required in higher dosages for its performance to be comparable to PAM. This study identified the conditions favorable to the use of an activated starch polymer as an alternative to PAM during ballasted flocculation: mixing intensity and time, coagulation pH, ballast size and chemical composition, and polymer charge density. Ultimately, under optimal conditions, only 0.66 mg of activated starch/L was required to reach the settled water turbidity objective of 1 NTU.

The study of the interlock of ballast in triaxial geogrids

Rail transport is the most efficient way of transport from an energetic and environmental point of view. The integration of geosynthetics in the rehabilitation solutions has grown substantially in the last decade, such as the application of different geogrids for reinforcement and/or stabilization of ballast layer. It appears to be consensual that the effectiveness of the geogrid depends on the degree of interlock between the geogrid and the granular material. The main purpose of this study is to analyse the relation between the geogrid aperture size and the ballast size that maximizes the interlock. The influence of the geogrid location in the ballast layer and the ballast grading are also addressed. The results suggested that, in order to obtain a higher interlock percentage, a selected ballast layer, with a reduced maximum dimension, should be used in contact with the geogrid and the geogrid should be placed in the ballast layer, above the interface ballast/substructure. The results suggested that the relation between the geogrid aperture size and the maximum dimension of the aggregate should be around 1.22 in order to improve the interlock.

A spectral analysis of ground-penetrating radar data for the assessment of the railway ballast geometric properties

This paper presents a methodology for the assessment of railway ballast using ground-penetrating radar (GPR – 2 GHz horn antenna). The primary approach in this endeavour was the finite-difference time-domain (FDTD) simulations of ballast (a multi-stage process in terms of ballast size). To this effect, a combination of random sequential adsorption (RSA) and FDTD algorithms were applied. The results of the numerical simulation then were used to compare with the experimental investigations results using a container (methacrylate material) of the 1.5 × 1.5 × 0.5 m dimensions. Finally, the modelling of the frequency spectrum peak and the equivalent diameter of the ballast aggregates was developed.

Shear Resistance of Rubber-ballast Composites in Simulated Water and Acid Soaked Conditions

Ballast is one of the main structures for the railway tracks. It can resist the lateral movement under dynamic loading transferred by the passing trains with repeatedly. Under some circumstances, ballast can suffer degradation or breakdown due to the repeated loading and maintenance. Ballast is easily exposed to the weather because it is laid on the track. Acid rain affects the performance of the railway track near the industrial and urban area. As a result, it starts to foul and the small chips from ballast filled the void, as well as reduce the shear strength of ballast particles. This situation can contribute into the increasing of maintenance frequency and costing. This paper examines the potential of rubber inclusions in increasing the shear resistance of rubber-ballast composites in simulated water and acid soaked conditions with several configuration. This lab-based exploratory work is only static load simulation in conventional shear box setup measuring 60 mm × 60 mm. The aggregates size is 10 times smaller than actual size of ballast. In order to identify the shear resistance deterioration of rubber-aggregates mixture under poor drainage conditions by soaked a batch of aggregates in water and acid solution for 2 weeks to simulate accelerated weathering effects. The shear resistance did not rise dramatically with the rubber reinforcement. This susceptible shear strain plots indicate ductile behaviour on the aggregates-rubber composites. This is evident by the linear rise of shear stress with strain up to approximately 10% for the control samples (CS) until it reaches a constant value. Note that all the specimens including CS are in a loose state during the testing because there were no tamping been applied on the samples. Overall the circular patch (CP) specimen was the most favourable than the other configurations. Both mechanisms contributed to the reduced overall subsistence, accompanied by an increase in the shear resistance. The inclusion of rubber elements apparently prevented the dilation of the granular material when approaching the shear failure and the reducing the settlement.

The use of a four-stage sequential leaching procedure and the corresponding one-phase extractions for risk assessment of potential harmful substances in waste rock utilized in railway ballast

The purpose of environmental legislation in the EU is prevention, minimization, and utilization of waste, respectively. When utilization is not possible, the purpose becomes the safe landfill disposal of waste, or disposal by other ecologically beneficial methods. In addition, material efficiency is an essential topic nowadays to promote the sustainable use of natural resources, waste materials, and industrial by-products, in agreement with the principle of sustainable development and LCA. To promote these goals, a four-stage sequential leaching procedure and determination of total concentrations was used in this research to determine the distribution of Cu, Pb, Zn, and V samples taken from waste rock material, originating from a Finnish zinc mine, and used as railway ballast in Northern Finland. The leaching procedure consists of the following five sequential fractions: (i) an acidic water-soluble fraction (H2O, pH = 4), (ii) an exchangeable fraction (CH3COOH), (iii) an easily reduced fraction (NH2OH-HCl), and (iv) oxidizable fraction (H2O2 + CH3COONH4). The results show that conditions and the size of ballast have a significant effect on the solubility of all heavy metals, and therefore on their mobility, bioavailability, and environmental risk. In addition, the total concentration of every element is much larger than its solubility in each four fractions (i)–(iv) or the sum of these concentrations – this sum can be called by the potential bioavailability – because the highest concentration is in the residual fraction. The leachability results determined here for waste rocks utilized as railway ballast show in good agreement with all earlier investigations determined for other waste or industrial by-products. Sequential leaching studies provide valuable information about the effect of conditions on the leachability/solubility, mobility, and bioavailability for risk assessment of harmful heavy metals. This information is necessary if we want to know the real environmental risk of metals in different conditions, possible in natural conditions now and in the future, i.e. not only in terms of the conditions pertaining to permission applications.

Characterizing Ballast Degradation through Los Angeles Abrasion Test and Image Analysis

Ballast fouling, often associated with deteriorating railroad track performance, refers to the condition in which the ballast layer changes its composition and develops a much finer grain size distribution. Fouling is commonly caused by degradation or breakage of ballast aggregates under traffic loading, although other fine materials including but not limited to coal dust, fine-grained subgrade soils, and sand can also contaminate a clean and uniformly graded ballast layer. An experimental approach is described to characterize stages of railroad ballast degradation studied through Los Angeles abrasion testing in the laboratory. An aggregate image analysis approach is used to investigate ballast particle abrasion and breakage trends at every stage through detailed quantifications of individual ballast particle size and shape properties. The experimental study indicated that the fouling index (FI) commonly used by practitioners was indeed a good indicator of fouling conditions, especially when all voids created by larger particles were filled by fine materials as FI values approached 40. Image analysis results of ballast particles larger than 9.5 mm (3/8 in.) scanned after a number of turns of the Los Angeles abrasion drum showed good correlations between percentage changes in aggregate shape properties, that is, imaging-based fatness and elongation, angularity and surface texture indexes, and the FI. The establishment of such relationships between in-service track fouling levels and ballast size and shape properties with similar field imaging techniques would help to understand field degradation trends better and as a result improve ballast serviceability and life-cycle performance.

Ballast Flying DEM Microscopic Analysis and Counteracting Measures

Ballast flying problems obsess the high speed railway developments, causing damages to the train and deteriorations to the rail. In the paper, DEM is used to conduct ballast flying mechanism microscopic study, results show ballast flying increases with train dynamic force, and decreases with ballast size and friction coefficient, ballast flying counteracting measures are presented, such as ballast bed parameter and ballast glue. In the end, future possible microscopic ballast flying model method is presented by DEM coupled with CFD.

Estimation of stormwater flow through railway ballast

Seepage flow through railway ballast is estimated, with the aim of reducing design flows in conventional stormwater drainage components. Flow-head equations are derived for ballast on flat and superelevated railway formations. A simple but effective experimental determination of frictional parameters of the ballast material is described, with guidelines on selecting appropriate model scale and range of test conditions. Some test results are discussed, and a method of allowing for different ballast size and porosity is proposed. Justification is given for allowing for ballast flow in drainage design, discussing circumstances in which the additional flow capacity was and was not allowed.