Finite element modeling of ballasted rail track capturing effects of geosynthetic inclusions

© 2019 Jiang and Nimbalkar. This paper presents a two dimensional finite element (FE) approach to investigating beneficial aspects of geogrids in the railway track. The influences of different factors including the subgrade strength, the geogrid stiffness, the placement depth of geogrid, the effective width of geogrid, the strength of ballast-geogrid interface and the combination of double geogrid layers were investigated under the monotonic loading. The results indicated the role of geogrid reinforcement is more pronounced over the weak compressible subgrade. A stiffer geogrid reduces ballast settlement and produces a more uniform stress distribution along a track. The placement location of a geogrid is suggested at the ballast-sub-ballast interface to achieve better reinforcement results. Although the width of a geogrid layer should be sufficient to cover an entire loaded area, excessive width does not guarantee additional benefits. Higher interface strength between a ballast and a geogrid is beneficial for effective reinforcement. Increasing the number of geogrid layers is an effective way to reinforce the ballast over weak subgrades. The results of the limited cyclic FE simulations revealed the consistency of the reinforcement effect of the geogrids under monotonic and cyclic loads

Effect of water drawdown and dynamic loads on piled raft: Two-dimensional finite element approach

© 2019 by the authors. The piled raft foundations are widely used in infrastructure built on soft soil to reduce the settlement and enhance the bearing capacity. However, these foundations pose a potential risk of failure, if dynamic traffic loading and ground conditions are not adequately accounted in the construction phase. The ground conditions are complex because of frequent groundwater fluctuations. The drawdown of the water table profoundly influences the settlement and load sharing capacity of piled raft foundation. Further, the dynamic loading can also pose a potential risk to these foundations. In this paper, the two-dimensional finite element method (FEM) is employed to analyze the impact of water drawdown and dynamic loading on the stability of piled raft. The seismic response of piled raft is also discussed. The stresses and deformations occurring in and around the raft structure are evaluated. The results demonstrate that water drawdown has a significant effect on the stability and seismic response of piled raft. Various foundation improvement methods are assessed, such as the use of geotextile and increasing thickness of the pile cap, which AIDS of limiting the settlement

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

Evaluation of additional confinement for three-dimensional geoinclusions under general stress state

Three-dimensional cellular geoinclusions (e.g., geocells, scrap tires) offer all-around confinement to the granular infill materials, thus improving their strength and stiffness. The accurate evaluation of extra confinement offered by these geoinclusions is essential for predicting their performance in the field. The existing models to evaluate the additional confinement are based on either a plane-strain or axisymmetric stress state. However, these geoinclusions are more likely to be subjected to the three-dimensional stresses in actual practice. This note proposes a semi-empirical model to evaluate the additional confinement provided by cellular geoinclusions under the three-dimensional stress state. The proposed model is successfully validated against the experimental data. A parametric study is conducted to investigate the influence of input parameters on additional confinement. Results reveal that the simplification of the three-dimensional stress state into axisymmetric or plane-strain condition has resulted in inaccurate and unreliable results. The extra confinement offered by the geoinclusion shows substantial variation along the intermediate and minor principal stress directions depending on the intermediate principal stress, infill soil, and geoinclusion properties. The magnitude of additional confinement increases with an increase in the geoinclusion modulus. The findings are crucial for accurate assessment of the in situ performance of three-dimensional cellular geoinclusions.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Performance of ballasted track under impact loading and applications of recycled rubber inclusion

© 2018 Chinese Academy of Sciences. All rights reserved. In this paper a review of the sources of impact loads and their effect on the performance of ballasted track is presented. The typical characteristics and implications of impact loading on track deterioration, particularly ballast degradation, are discussed. None of the procedures so far developed to design rail track incorporate the impact that dynamic loading has on the breakage of ballast and therefore it can be said to be incomplete. An intensive study on the impact of induced ballast breakage is needed in order to understand this phenomenon and then use the knowledge gained to further advance the design methodology. A stiff track structure can create severe dynamic loading under operating conditions which causes large scale component failure and increases maintenance requirements. Installing resilient mats such as rubber pads (ballast mat, soffit pad) in rail tracks can attenuate the dynamic force and improve overall performance. The efficacy of ballast mats to reduce structural noise and ground vibration has been studied extensively, but a few recent studies has reported how ballast mats and soffit pads reduce ballast degradation, thus obviating the necessity of a comprehensive study in this direction

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 faffects 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 (f60 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

Particle breakage of granular materials during sample preparation

© 2019 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences Particle breakage is commonly observed in granular materials when subjected to external loads. It was found that particle breakage would occur during both sample preparation and loading stages. However, main attention was usually paid to the particle breakage behaviour of samples during loading stage. This study attempts to explore the breakage behaviour of granular materials during sample preparation. Triaxial samples of rockfill aggregates are prepared by layered compaction method to achieve different relative densities. Extents of particle breakage based on the gradings before and after test are presented and analysed. It is found that particle breakage during sample preparation cannot be ignored. Gradings after test are observed to shift away from the initial grading. Aggregates with larger size that appear to break are more than the smaller-sized ones. Irrespective of the initial gradings, an increase in the extent of particle breakage with the increasing relative density is observed during sample preparation

Three-dimensional characterisation of particle size and shape for ballast

© 2014, Thomas Telford Services Ltd. All rights reserved. The size and shape of particles influence how effectively coarse angular aggregates of ballast interact. The aim of this study was to improve the characterisation of ballast particles using a threedimensional (3D) imaging method. Various size and shape indices, such as elongation ratio, sphericity and roundness, were determined from the scanned 3D images. A modified index called ‘ellipsoidness’ was proposed to capture adequately the shape of the 3D particles. Variation of these indices with particle size was studied. Comparison of the 3D true sphericity and the corresponding two-dimensional sphericity indicated that the latter would underestimate sphericity. A modified approach for transforming particle size distribution to constriction size distribution is proposed by capturing the size and shape effects of particles

Contact Pressure Distribution on Subgrade Soil Underlying Geocell Reinforced Foundation Beds

© Copyright © 2019 Dash, Saikia and Nimbalkar. High contact stresses generated in the foundation soil, owing to increased load, causes distress, instability, and large settlements. Present days, geocell reinforcement is being widely used for the performance improvement of foundation beds. Pressure distribution on subgrade soil in geocell reinforced foundation beds is studied through model tests and numerical analysis. The test data indicates that with provision of geocell reinforcement the contact pressure on the subgrade soil reduces significantly. Consequently, the subgrade soil tends to remain intact until large loadings on the foundation leading to significant performance improvement. Through numerical analysis it is observed that the geocells in the region under the footing were subjected to compression and beyond were in tension. This indicates that the geocell reinforcement right under the footing directly sustains the footing loading through mobilization of its compressive stiffness and bending rigidity. Whereas, the end portions of the geocell reinforcement, contribute to the performance improvement in a secondary manner through mobilization of anchorage derived from soil passive resistance and friction

Ethnoveterinary practices (EVP) for control of ectoparasite in livestock

The inclusion of traditional plant-based ectoparasite control methods in primary healthcare of livestock is increasingly becoming an important intervention for improving livestock productivity in resource challenged tribal areas. The study was conducted at Peint and Jawhar blocks of Nashik and Palghar districts of Maharashtra. The effectiveness of Ethno veterinary practices (EVP) for control of ectoparasite was assessed through social acceptance and field study. The formulations were prioritized considering its effectiveness, accessibility, easy to treat and fast post recovery. The formulations were co-related with modern literatures to gauge its scientific reference.The prevalence of tick infestation on different body part examined of cows, buffaloes was suggested that udder had maximum presence of ticks on buffaloes and cows. The EVP has significant effect in reduction of tick population in Buffaloes, Bulls and Cows was recorded. The study reveals that, the efficacy of herbal medicine to reduce the tick’s incidence on buffalo is 63%, bull 60% and cow 61% were recorded