Ballast Pressure Research Articles

Effect of support conditions on the performance of B70 sleeper overlying reinforced ballast and sub-ballast layer: Experimental and analytical investigation

It is well known that the moment distribution on the sleepers is very sensitive to deformations of the ballast caused by cyclic axle load over time and other environmental factors. To limit the non-uniform deformations of the ballast, reinforcement of the ballast or sub-ballast with geosynthetics can be a cost-effective solution. In this study, B70 prestressed concrete sleepers were tested under static loading conditions in a special test box developed to simulate the in-situ condition of a railroad track in the laboratory. The main test parameters were the degree of settlement of the ballast and the type of geosynthetics used. Four different settlement levels and two reinforcement types (sub ballast with geonet and ballast with geocells) were considered. The deflections and surface strain maps of the concrete sleepers were measured using the two-dimensional digital image correlation (2D-DIC) method. Following the experimental part, an analytical study was also carried out to investigate the ballast pressure distribution and consequently the moment distribution on the concrete sleeper. Based on the vertical deflection shape of the sleeper, a new algorithm was developed to derive the ballast pressure distribution under the sleeper by back calculation. The experimental results showed that using geocells to reinforce the ballast layer increased the stiffness of the ballast against the vertical deflection of the sleeper. From the analytical results, the magnitude of the negative bending moment increased significantly with increasing settlement level.

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.

Mechanism of Sleeper–Ballast Dynamic Impact and Residual Settlements Accumulation in Zones with Unsupported Sleepers

Unsupported sleepers or void zones in ballasted tracks are one of the most recent and frequent track failures. The void failures have the property of intensive development that, without timely maintenance measures, can cause the appearance of cost-expensive local instabilities such as subgrade damages. The reason for the intensive void development lies in the mechanics of the sleeper and ballast bed interaction. The particularity of the interaction is a dynamic impact that occurs due to void closure. Additionally, void zones cause inhomogeneous ballast pressure distribution between the void zone and fully supported neighbour zones. The present paper is devoted to studying the mechanism of the sleeper–ballast dynamic impact in the void zone. The results of experimental in situ measurements of rail deflections showed the significant impact accelerations in the zone even for lightweight slow vehicles. A simple three-beam numerical model of track and rolling stock interaction has shown dynamic interaction similar to the experimental measurements. Moreover, the model shows that the sleeper accelerations are more than 3 times higher than the corresponding wheel accelerations and the impact point appears before the wheel enters the impact point. The analysis of ballast loadings shows the specific impact behaviour in combination with the quasistatic part that is different for void and neighbour zones, which are characterised by high ballast pre-stressed conditions. The analysis of void size influence demonstrates that the maximal impact loadings and maximal wheel and sleeper accelerations appear at a certain void depth, after which the values decrease. The ballast quasistatic loading analysis indicates an increase of more than 2 times in the ballast loading in neighbour zones for long voids and almost full quasistatic unloading for short-length voids. However, the used imitation model cannot explain the nature of the dynamic impact. The mechanism of the void impact is clearly explained by the analytic solution using a simple clamped beam. A simplified analytical expression of the void impact velocity shows that it is linearly related to the wheel speed and loading. The comparison to the numerically simulated impact velocities shows a good agreement and the existence of the void depth with the maximal impact. An estimation of the long-term influences for the cases of normal sleeper loading, high ballast pre-stress and quasistatic loading in the neighbour zones and high impact inside the void is performed.

MODEL OF PNEUMOMETRIC DENSITY METER FOR MEASURING THE DENSITY OF DRILLING SOLUTIONS OF OIL AND GAS WELLS

The development of automatic pneumometric densitometers is promising not only for drilling fluids. They can be used in the food, chemical, refining, oil depots and storage facilities. Based on them, you can build systems for quantitative accounting of liquid products in units of mass. Possessing high accuracy, pneumometric densitometers are simple and reliable, convenient in operation and, most importantly, are completed with the elements serially issued by the industry.
 The article presents a block diagram of a differential pneumometric densitometer with ballast pressure compensator in the minus pneumoline and shows the calculation which shows that the main source of error is the pressure loss in the pneumolines, zero drift of the differential pressure gauge, cancellation of real values ​​of static coefficients from differential. It is pointed out that in order to find the value of pressure and flow at each point of the pneumoline, even for simple models, it is necessary to make complex calculations. An analytical solution can only be obtained for individual cases that are of no practical value.
 Therefore, for the analysis of a pneumoline of a densitometer it is most rational to use a method of electrohydraulic analogy (EGDA) and to pass from a pneumatic line with the distributed parameters to similar electric with rarefied parameters. We obtained a model of a pneumometric densitometer in the form of an electrical circuit, which requires further research, electrical engineering methods, to clarify the coefficients and parameters of the model and check its adequacy.

Quantification of the Effect of Train Type on Concrete Sleeper Ballast Pressure Using a Support Condition Back-Calculator

Monitoring ballast support condition and improving current sub-structure and ballast maintenance strategies is critical to ensuring safe and efficient railroad operations. Researchers at the University of Illinois at Urbana-Champaign (Illinois) have developed a ballast support condition back-calculator, a non-destructive instrumentation method and corresponding analysis tool that quantifies ballast pressure distributions under concrete sleepers without interrupting revenue service train operations. This laboratory-validated non-intrusive method uses concrete sleeper bending moment profile and rail seat loads as inputs to back-calculate the reaction distribution using a Simulated Annealing optimization algorithm that incorporates Pareto Distribution as the random variable generator. In order to further understand in-service ballast support conditions, concrete surface strain gauges were installed on concrete sleepers at a revenue service field site to measure strains that could subsequently be converted into bending moments. This site is on a shared use rail corridor with traffic ranging from high speed passenger to heavy axle load (HAL) freight trains. Rail-mounted strain gauges were used to measure strains that were used to calculate the vertical wheel-rail loads to approximate rail seat loads. This paper quantifies the ballast pressure distributions beneath concrete sleepers under different types of rolling stock and evaluates how ballast support condition changes as a function of accumulated tonnage. A wide range of loads were observed at the field site, ranging from 4 to 35 kips (18–156 kN). Corresponding ballast pressures ranged from 14 to 175 psi (97–1,207 kPa), with sleeper-ballast contact area corresponding to 60% of the bottom of the sleeper area. The accumulation of 12.24 million gross tons (MGT) (12.44 million tons) did not generate a quantifiable change in ballast pressure values nor did it generate a change in the ballast support condition. The research results presented in this paper demonstrate the potential of the back-calculator to provide a stand-alone non-invasive method to quantify ballast support conditions, sleeper health, and sleeper bearing stress. Back calculator data will aid the rail industry in optimizing tamping cycles, enhancing safety, and developing more representative concrete sleeper flexural designs based on actual support conditions.

Experimental and numerical investigation of the performance of self-sensing concrete sleepers

Prestressed concrete sleepers with built-in fibre optic–based sensing systems have recently been developed to capture performance data within railway networks and to provide critical decision-support information to route managers and operators. To better understand how self-sensing sleepers can be fully utilized within the rail network, a study of their comprehensive performance under controlled conditions must be undertaken. This article presents the results of the full-scale laboratory testing of a self-sensing sleeper supported on ballast. A primary focus of this study was to investigate whether a self-sensing sleeper could also be used to estimate rail seat load, detect cracking, and identify differential ballast settlement. The ultimate capacity and resilience of the embedded fiber Bragg grating sensing system was tested by applying load up until concrete cracking followed by several cyclic load cycles. Through inference of the load versus strain response, the ability of the self-sensing sleeper to detect damage (concrete cracking and loss of ballast support) was evaluated. The experimental results revealed the effectiveness and robustness of the embedded sensing system to continue to provide reliable dynamic strain measurements well beyond the ultimate loading capacity of the prestressed sleeper. Cracking of the top surface of the sleeper was effectively detected by the fiber Bragg grating strain sensors at the mid-span section. After cracking, subsequent load cycles were carried out. During this period, the bottom fiber Bragg grating measurements captured the effects of differential ballast settlement under the rail seats. A three-dimensional nonlinear finite element model was developed to simulate the experimental test setup and to investigate the relation between fiber Bragg grating sensor measurements and rail track response. The combined experimental and numerical results suggest that a self-sensing sleeper may be deployed on an operational railway to provide reliable and long-term measurements of rail axle load and ballast pressure.

Railroad infrastructure 4.0: Development and application of an automatic ballast support condition assessment system

Abstract Industry 4.0, or the fourth industrial revolution, is the current trend of automation and data exchange in manufacturing technologies. Even though Industry 4.0 emerged as a manufacturing initiative, the idea of bridging digital and physical systems can be expanded beyond the manufacturing industry. “Railroad Infrastructure 4.0” is thus proposed in this study to revolutionize the maintenance operations of the railroad industry. In North America, most primary freight and passenger rail corridors are constructed using ballasted track. One of the primary maintenance activities is to ensure the ballast is performing adequately. Being able to monitor the ballast condition and conduct tamping operations (e.g. maintenance activities) at optimal intervals can increase the safety and efficiency of railroad operations. Previously, techniques such as ground penetrating radar (GPR) and Matrix Based Tactile Surface Sensors (MBTSS) have been used to assess the condition of ballast, but these investigative tools lack the capability of automatically and continuously monitoring the track system. Researchers at the University of Illinois at Urbana-Champaign and the University of South Carolina have developed a non-intrusive method as a key component of Railroad Infrastructure 4.0 to continuously quantify ballast pressure distribution (i.e. ballast condition) under the sleeper (also known as a “crosstie”). This method innovatively uses the bending moment profile across the concrete sleeper, and the approximated rail seat loads as inputs, to back-calculate the ballast support condition through the use of an optimization algorithm. The ballast support condition assessment system that was developed has been validated for accuracy from extensive laboratory experimentation. The laboratory validated system was deployed in the field on a Class I heavy axle load (HAL) freight railroad in the United States to continuously monitor the ballast pressure distribution beneath concrete sleepers in real-time under revenue service operating conditions. The evaluation of ballast pressure distributions between adjacent sleepers as well as tonnage accumulated are also included. To better quantify the variation of ballast pressure beneath the sleepers, the Ballast Pressure Index (BPI) is also proposed. The information presented in this paper demonstrates the concept and potential of Railroad Infrastructure 4.0 as a future framework for railroad maintenance planning and management.

Trade study of advanced ballast control systems for an extraterrestrial submarine

Saturn's largest moon, Titan, has seas of cryogenic liquid methane and ethane as well as dynamic geology and a cycle of methane evaporation and rain. NASA is evaluating concepts for an extraterrestrial submarine to explore these seas from surface to bottom to shoreline, representing an unprecedented design challenge. The Titan submarine ballast system that controls the vertical ascent and descent must operate autonomously for a minimum of 365 dives in cryogenic seas below 95 K and handle liquid density variations up to 30%. Further complicating the concept is the high solubility of nitrogen gas in the seas, which leads to potential phase change and boiling issues during ballast pressure control. This paper presents a trade study of 7 advanced concepts for an autonomous submarine ballast system for Titan; 4 were down-selected as viable concepts. For each concept, analytical system description and sizing, autonomous concept of operation, parts list, and pros and cons are given. Systems are traded using mass, power, and complexity in control as metrics.

Railway track inspection and maintenance priorities due to dynamic coupling effects of dipped rails and differential track settlements

Abstract Each year, there can be three to six millions of service train axles running over an open plain track. In fact, these trains could impose a variety of dynamic loading conditions depending on the wheel and rail maintenance levels. Inevitably, the risk of high-intensity dynamic loading conditions by wheel-rail interactions due to wheel or rail irregularity cannot be disregarded. Imperfection of rail tracks could lead directly to the exceedance of permissible stress of a track component and later amplify rapid track deterioration rates causing cracking in sleepers and failure of track substructure. Practical railway track irregularities can be typically classified into short wave length (high frequency) and long wave length (low frequency) defects, of which previous researchers had studied each in isolation. This paper is the first to study the influence on railway track inspection and maintenance priorities caused by the coupling of wave lengths between dipped rail joint and differential track settlements. To study the dynamic coupling effects, P1 and P2 forces are evaluated at the track irregularity together with rail/sleeper contact force, ballast pressure and bending moments of sleepers using dynamic multi-body simulation approach. It is found that some patterns of coupling irregularity could cause a significant reduction in dynamic impact factors whilst some are associated with an increase in the wheel/rail impact force. The insight has then been integrated to establish track performance indicators that are paramount for prioritising track inspection and maintenance.

Application of Granular Material Pressure Cells to Measure Railroad Track Tie/Ballast Interfacial Pressures

This paper describes the development of a method to measure railroad track tie/ballast interfacial pressures using pressure cells specially designed for granular materials. Repeat measurements were taken during a several-month period on a Norfolk Southern Corporation high-tonnage mainline. The research employed new wood crossties routed so pressure cells could be recessed within the ties. Thus, the active surfaces of the pressure cells were flush with the tie bottoms. Cabling was run through a recess to the tie end. This greatly reduced the likelihood of damage to the instrumentation during track surfacing and lining activity. The ties were installed such that multiple cells were directly under consecutive rail seats of one rail. Several ties also had cells either at the center or the rail seat of the opposite rail. The researchers expended considerable effort to provide consistent ballast conditions for the instrumented ties and adjacent, undisturbed (transition) ties. Norfolk Southern crews surfaced and tamped through and on either side of the test section. This, plus consolidation through normal accruing train traffic, resulted in consistent measurements through the section. The paper presents ballast pressure magnitudes and distributions and discusses results, including the effects of variable ballast support, wheel loadings, and impact loadings. Typical vertical ballast pressure measurements directly under the rail seat, with compacted ballast and minimal impact forces ranged from 20 to 30 psi (140 to 210 kPa) under the heaviest common revenue wheel loadings.

Field studies on sleeper deflection and ballast pressure in heavy haul track

Deflection of sleepers (vertical displacement) and ballast pressure (vertical stress) under traffic loads are two important performance indicators for determination of rail track quality. Excessive values of these parameters can adversely affect the track structural stability, accelerate the track deterioration and consequently affect the safety of running trains. This paper reports field tests on two heavy haul tracks in Australia with normal operating condition and similar traffic loads. In the first test site, the ballast pressure and sleeper deflection were measured. In the second site, only the sleeper deflections were recorded; however, in this site, the capping layer interface was modified using inserts of various design of geogrids. Analysis of results obtained from these field measurements provide valuable insights into the sleeper deflection and ballast pressure magnitudes and patterns under real life traffic in heavy haul tracks as well as the effects of geogrids on reducing the sleeper deflections.

Railroad Tie Spacing Related to Wheel-Load Distribution and Ballast Pressure

AbstractCurrently, there is no formula for tie and direct fixation fastener (DFF) spacing. Because the rail does not bend between the tie/DFF, it is not possible to calculate spacing by the bending stress formula. Usually, rail-stress analysis confirms a trial spacing. Such analysis may support a longer spacing that might not address issues related to load distribution, pressure on formation, torsional rigidity, noise, and vibration. Thus, tie spacing is formulated from the perspective of wheel-load distribution and load dispersion by ballast, considering the fact that ties under the Benkel beam support the vertical load. The DFF/tie spacing is related to the characteristic length of the track, and this study shows that the desired DFF/tie spacing should be less than the characteristic length. Codes and practical examples validate spacing formulated for DFFs, concrete ties, and wood ties.

Assessing the effects of track input on the response of insulated rail joints using field experiments

Manufacturers of insulated rail joints (IRJs) have to follow the quality assurance regime stipulated in the national design standards; unfortunately, IRJs still exhibit a very low and highly variable service life. It is widely believed that the service life of IRJs is affected by the track input under the passage of loaded wheels; however, there is a paucity of literature with regard to the actual mechanical behaviour of IRJs in the track. An extensive field test was, therefore, conducted on an in-service heavy haul corridor in Australia with the specific aim of understanding the effect of the track input on the response of the IRJs. Data on the wheel–rail force, rail/joint-bar strain, sleeper acceleration and ballast pressure signatures in the time domain were determined from the experiment. This data was subsequently systematically analysed to compare the relative structural merits of two IRJs resting on different sleeper spaces and a reference continuous rail subjected to similar real-life coal traffic loading.

Analysis of a typical railway turnout sleeper system using grillage beam analogy

A simplified grillage beam analogy was performed to investigate the behaviour of railway turnout sleeper system with a low value of elastic modulus on different support moduli. This study aimed at determining an optimum modulus of elasticity for an emerging technology for railway turnout application - fibre composites sleeper. The finite element simulation suggests that the changes in modulus of elasticity of sleeper, E sleeper and the sleeper support modulus, U s have a significant influence on the behaviour of turnout sleepers. The increase in U s from 10 to 40 MPa resulted in a 15% reduction in the bending moment while the increase in E sleeper from 1 GPa to 10 GPa has resulted in almost 75% increase in the bending moment. The shear forces in turnout sleepers is not sensitive to both the changes of the E sleeper and U s while the sleeper with low E sleeper tend to undergo greater settlement into the ballast. An E sleeper of 4 GPa was found optimal for an alternative fibre composite turnout sleeper provided that the U s is at least 20 MPa from the consideration of sleeper ballast pressure and maximum vertical deflection. It was established that the turnout sleeper has a maximum bending moment of 19 kN-m and a shear force of 158 kN under service conditions.

What influences rigid inflatable boat motions?

This paper presents results of full-scale and model-scale rigid inflatable boat (RIB) experiments identifying the influences of speed, ballast, wave height, encounter frequency, and tube pressure on the motion responses of Royal National Lifeboat Institution (RNLI) Atlantic RIBs. A discussion of the results and the influences on the motions is made with a description of the typical motion responses, measures to describe the motion, the function of a RIB tube, and the effect of the motions on the occupants.

Dynamic studies of railtrack sleepers in a track structure system

This paper discusses the dynamic response of a typical prestressed concrete railtrack sleeper due to wheel–track interaction dynamics, involving wheel and rail imperfections, under various parametric conditions. The interaction dynamics of the vehicle and track is first carried out in the time domain using MSC/NASTRAN. Using the resulting load time histories on an isolated sleeper, a detailed finite element model of the sleeper is used to analyze its dynamic behaviour. The dynamic amplification factors for deflection, ballast pressure and bending moments have been evaluated at the critical section (rail-seat and centre) for various exciting frequencies under different vehicle–track parametric conditions. The results provide a basis for improved and rational design of the sleeper.