Application of Shock Mats in Rail Track Foundation Subjected to Dynamic Loads

© 2016 The Authors. Published by Elsevier B.V. Rail track substructure (ballast, subballast and subgrade) is the most essential component of the railway system in view of track stability. The ballast is the largest component of the track substructure and it is the key load-bearing stratum packed with rock aggregates underneath and around the sleepers, thereby providing structural support against dynamic stresses caused by moving trains. However under large dynamic stresses exerted by heavy haul and high speed trains, the degradation of track substructure including ballast becomes significant. This in turn affects the track stability and creates frequent maintenance, thus increasing the life cycle cost of the rail network. Therefore, mitigating degradation of the ballast layer is vital in view of track longevity. In recent years, the use of resilient soft pads (shock mats) above the ballast (i.e. Under Sleeper Pad, USP) and below the ballast (i.e. Under Ballast Mat, UBM) has become a common practice. Many countries, including Australia have adopted the use of resilient pads in the rail track foundation. Currently, the studies on resilient mats are mostly limited to the reduction of vibration and noise. There is a lack of proper assessment of the geotechnical behavior of ballast when used along with shock mats. This paper provides an assessment of the triaxial behavior of the track substructure with and without shock mats under dynamic loading condition. A numerical model was developed based on the modified stress-dilatancy approach to capture the stress-strain and volume change behavior of ballast during impact loading. Model predictions are compared with laboratory results. It was found that the shock mats provide significant advantages in terms of reduced particle breakage and enhanced track stability

Recycled materials in railroad substructure: an energy perspective

Given that the current ballasted tracks in Australia may not be able to support faster and significantly heavier freight trains as planned for the future, the imminent need for innovative and sustainable ballasted tracks for transport infrastructure is crucial. Over the past two decades, a number of studies have been conducted by the researchers of Transport Research Centre (TRC) at the University of Technology Sydney (UTS) to investigate the ability of recycled rubber mats, as well as waste tyre cells and granulated rubber to improve the stability of track substructure including ballast and subballast layers. This paper reviews four applications of these novel methods, including using recycled rubber products such as CWRC mixtures (i.e., mixtures of coal wash (CW) and rubber crumbs (RC)) and SEAL mixtures (i.e., mixtures of steel furnace slag, CW and RC) to replace subballast/capping materials, tyre cells reinforcements for subballast/capping layer and under ballast mats; and investigates the energy dissipation capacity for each application based on small-scale cyclic triaxial tests and large-scale track model tests. It has been found that the inclusion of these rubber products increases the energy dissipation effect of the track, hence reducing the ballast degradation efficiently and increasing the track stability. Moreover, a rheological model is also proposed to investigate the effect of different rubber inclusions on their efficiency to reduce the transient motion of rail track under dynamic loading. The outcomes elucidated in this paper will lead to a better understanding of the performance of ballast tracks upgraded with resilient rubber products, while promoting environmentally sustainable and more affordable ballasted tracks for greater passenger comfort and increased safety

松本歯科大学学会会則

© Springer Nature Singapore Pte Ltd 2020. Railway industries are facing greater technical and economic challenges to increase the train speeds and hauling capacity of the trains to cope up with the growing population and increasing traffic problems. However, increasing dynamic stresses from the passage of faster and heavy haul trains progressively degrades the ballast layer and other track substructure layers which inevitably leads to excessive settlement and track instability. Nowadays, heavier concrete sleepers used in most of the ballasted tracks are subjected to even greater stresses and faster deterioration. Under Sleeper Pads (USPs) are resilient pads installed at the bottom face of concrete sleepers to increase the degree of vertical elasticity in the track structure and also with the intention of enhancing sleeper–ballast interaction to minimize dynamic stresses and subsequent track deterioration. In this study, cyclic loads from fast and heavy haul trains have been simulated using a large-scale Process Simulation Prismoidal Triaxial Apparatus (PSPTA) to investigate the performance of ballast improved by the USPs. The laboratory results indicate that the inclusion of USP at the harder interface of concrete sleeper-ballast significantly curtails the stresses transmitted and minimizes the amount of plastic deformation and degradation of ballast

Combined Discrete-Continuum Analysis for Ballasted Rail Tracks

A study on the load-deformation behaviour of railway ballast aggregates subjected to cyclic loadings using a combined discrete-continuum modelling approach is presented. Discrete ballast particles are simulated in the DEM and the continuum-based subgrade is simulated by the FDM. Interface elements are generated to transmit contact forces and displacements between the two domains (i.e. discrete and continuum) whereby the DEM exchanges contact forces to the FDM, and then the FDM transfers the displacement back to the DEM. Distributions of contact forces, coordination number, stress contours on the subgrade and corresponding number of broken bonds (representing ballast breakage) are analysed

Large expert-curated database for benchmarking document similarity detection in biomedical literature search

Document recommendation systems for locating relevant literature have mostly relied on methods developed a decade ago. This is largely due to the lack of a large offline gold-standard benchmark of relevant documents that cover a variety of research fields such that newly developed literature search techniques can be compared, improved and translated into practice. To overcome this bottleneck, we have established the RElevant LIterature SearcH consortium consisting of more than 1500 scientists from 84 countries, who have collectively annotated the relevance of over 180 000 PubMed-listed articles with regard to their respective seed (input) article/s. The majority of annotations were contributed by highly experienced, original authors of the seed articles. The collected data cover 76% of all unique PubMed Medical Subject Headings descriptors. No systematic biases were observed across different experience levels, research fields or time spent on annotations. More importantly, annotations of the same document pairs contributed by different scientists were highly concordant. We further show that the three representative baseline methods used to generate recommended articles for evaluation (Okapi Best Matching 25, Term Frequency–Inverse Document Frequency and PubMed Related Articles) had similar overall performances. Additionally, we found that these methods each tend to produce distinct collections of recommended articles, suggesting that a hybrid method may be required to completely capture all relevant articles. The established database server located at https://relishdb.ict.griffith.edu.au is freely available for the downloading of annotation data and the blind testing of new methods. We expect that this benchmark will be useful for stimulating the development of new powerful techniques for title and title/abstract-based search engines for relevant articles in biomedical research

Use of rubber mats to improve the deformation and degradation behavior of rail ballast under cyclic loading

The deterioration of a rail track due to large dynamic wheel loads is inevitable over the years and leads to frequent, high-cost maintenance. This problem is more critical in isolated rail track locations such as bridges and tunnels, where the substructure is much stiffer than the surface track assembly. One measure used to minimize track deterioration is geosynthetic inclusions such as rubber mats under the layer of ballast. In this study, cyclic loads from fast and heavy-haul trains were simulated on stiffer track foundation conditions using a large-scale process simulation triaxial (prismoidal) apparatus (PSPTA) to investigate the performance of ballast improved by rubber mats locally manufactured from recycled tires. The laboratory results indicate that the energy-absorbing (damping) characteristics of rubber mats reduce the amount of deformation and degradation of ballast under stiffer track conditions. The study shows that rubber mats distribute the stress applied from moving trains more uniformly by increasing the effective contact area, which then reduces the dynamic amplification of applied vertical stress and leads to much less ballast degradation

Stabilisation of Stiffer Rail Track Substructure Using Artificial Inclusion

© 2020, Indian Geotechnical Society. The railway transport system in many countries plays a significant role in the passage of bulk freight and passengers. However, increased train speeds and higher freight loads (large dynamic wheel loads) accelerate the deterioration of rail track substructure. This problem is more critical in isolated rail track locations where the track substructure is much stiffer than the regular surface track assembly such as track at the bridges and tunnels. Ballast is a key track foundation material placed underneath the sleepers which provides structural support against high cyclic and impact stresses caused by moving trains. Inclusion of rubber mats called under ballast mats (UBMs) placed between the ballast and stiffer base layer is one of the measures to minimise the ballast deterioration. In this study, cyclic loads representing fast and heavy haul trains were simulated on stiffer track foundation condition using a large-scale process simulation prismoidal triaxial apparatus to investigate the mitigation of strain, stress and degradation characteristics of ballast stabilised with UBM. These UBMs were locally manufactured from recycled tyre wastes. The results show that ballast on a stiff foundation substructure stabilised with UBM experienced significantly less vertical and lateral deformation, ballast interface and inter-particle stresses and degradation. This study also confirmed that the recycled tyre UBMs used in this study had adequate damping to absorb the energy transmitted to the moving train to the track, thus preventing excessive plastic deformation and degradation of the ballast layer

Influence of under sleeper pads on ballast behavior under cyclic loading: Experimental and numerical studies

Railway industries are placing greater emphasis on implementing fast and heavy haul corridors for bulk freight and commuter transport in order to deliver more efficient and cost-effective services. However, increasing dynamic stresses from the passage of trains progressively degrades and fouls the primary load-bearing ballast layer, which inevitably leads to excessive settlement and instability, damage to track elements, and more frequent maintenance. Ballasted tracks are subjected to even greater stresses and faster deterioration in sections where a reduced ballast thickness is used (e.g., bridge decks) or at locations where heavier concrete sleepers are used instead of lightweight timber sleepers. The inclusion of under sleeper pads (USPs) at the base of a concrete sleeper is one measure used to minimize dynamic stresses and subsequent track deterioration. In this study, cyclic loads from fast and heavy haul trains were simulated using a large-scale process simulation prismoidal triaxial apparatus (PSPTA) to investigate the performance of ballast improved by USPs. The laboratory results indicate that the inclusion of an elastic element at the harder interface of the concrete sleeper-ballast reduces the stresses transmitted to the ballast and the underlying layers and minimizes the amount of deformation and degradation of the ballast. A three-dimensional finite-element model was used to predict the behavior of ballast, and the influence of USPs on the stress-strain responses of ballast generally agree with the experimental findings

Application of Elastic Inclusions to Improve the Performance of Ballasted Track

© 2020 American Society of Civil Engineers. Ballast is the most common foundation material of railways and as such is subjected to deformation and degradation from the large cyclic and impact loads generated by heavy, fast moving trains. These inevitable effects hamper the safety and efficiency of tracks and increase the track maintenance frequency. One of several promising approaches to mitigate these problems is stabilizing ballasted track with rubber mats (under sleeper pads -USP and under ballast mats -UBM), to absorb energy and reduce particle breakage, track stability, longevity, and safety. This paper analyses the current knowledge of using rubber elements in ballasted track acquired through large scale laboratory testing carried out at the University of Wollongong (UOW). This investigation reveals that indicate that the damping characteristics of rubber mats reduce the deformation and degradation of ballast. The results shows that USPs are better at reducing vertical permanent deformation while UBMs are better at reducing lateral deformation