Jayan S Vinod

Field assessment of the performance of a ballasted rail track with and without geosynthetics

Understanding the complex mechanisms of stress transfer and strain accumulation in layers of track substructure under repeated wheel loading is essential to predict the desirable track maintenance cycle as well as the design of the new track. Various finite element and analytical techniques have been developed in the past to understand the behavior of composite track layers subjected to repeated wheel loads. The mechanical behavior of ballast is influenced by several factors, including the track confining pressure, type of aggregates, and the number of loading cycles. A field trial was conducted on an instrumented track at Bulli, New South Wales, Australia, with the specific aims of studying the benefits of a geocomposite installed at the ballast-capping interface, and to evaluate the performance of moderately graded recycled ballast in comparison to traditionally very uniform fresh ballast. It was found that recycled ballast can be effectively reused if reinforced with a geocomposite. It was also found t...

Experimental and numerical study of railway ballast behavior under cyclic loading

This paper presents the results of the influence of frequency on the permanent deformation and degradation behavior of ballast during cyclic loading. The behavior of ballast under numerous cycles was investigated through a series of large-scale cyclic triaxial tests. The tests were conducted at frequencies ranging from 10–40 Hz, which is equivalent to a train traveling from 73 km/h to 291 km/h over standard gauge tracks in Australia. The results showed that permanent deformation and degradation of ballast increased with the frequency of loading and number of cycles. Much of breakage occurs during the initial cycle; however, there exists a frequency zone of 20 Hz⩽f⩽30 Hz where cyclic densification takes place without much additional breakage. An empirical relationship among axial strain, frequency and number of cycles has been proposed based on the experimental data. In addition, discrete-element method (DEM) simulations were carried out using PFC2D on an assembly of irregular shaped particles. A novel app...

Behavior of fresh and fouled railway ballast subjected to direct shear testing: discrete element simulation

AbstractThis paper presents the three-dimensional discrete element method (DEM) that was used to study the shear behavior of fresh and coal fouled ballast in direct shear testing. The volumetric changes and stress-strain behavior of fresh and fouled ballast were simulated and compared with the experimental results. Clump logic in particle flow code in three dimensions (PFC3D) incorporated in a subroutine was used to simulate irregular-shaped particles in which groups of 10–20 spherical balls were clumped together in appropriate sizes to simulate ballast particles. Fouled ballast with a various void contaminant index (VCI) ranging from 20 to 70% VCI was modeled by injecting a specified number of miniature spherical particles into the voids of fresh ballast. The DEM simulation captures the behavior of fresh and fouled ballast as observed in the laboratory, showing that the peak shear stress of the ballast assembly decreases and the dilation of fouled ballast increases with an increasing VCI. Furthermore, th...

Shear and Compressibility Behavior of Sand–Tire Crumb Mixtures

AbstractScrap tire disposal has been a critical environmental problem in many urban cities due to the huge increase in the number of vehicles. Significant research efforts have been devoted in recent years to explore the use of scrap tires in civil engineering application, as reuse or recycling of scrap tires is the preferred option from a waste management perspective. This paper investigates shear and compressibility behavior of sand–tire crumb (S-TC) mixtures for their application in civil engineering projects. Unlike other studies where tire chips or tire shreds were used, shear strength of the S-TC mixtures has been found to decrease with the increase in the amount of tire crumbs in the mixtures. Significant increase in axial strain corresponding to peak deviator stress has been observed. This can be related to the ductility capacity of the mixtures, as confirmed by brittleness tests. It has also been observed that a larger proportion of plastic strain develops after the first cycle of unloading, and ...

Estimating the Rate of Erosion of a Silty Sand Treated with Lignosulfonate

AbstractThis paper describes a theoretical model to capture the rate of erosion of a silty sand based on the principle of conservation of energy. Erosion is considered to begin when the interparticle bonds between grains are broken by hydrodynamic stresses exerted on the soil particles. These detached particles are then suspended and transported by the flow of eroding fluid. It is further assumed that once the particles are fully suspended and have reached the flow velocity, resettlement does not take place. Stabilization of soil particles because of lignosulfonate (LS) treatment is represented by the increased strain energy required to break the interparticle bonds. The equation proposed in this study is based on the shear stress-strain characteristics, mean flow velocity, mean particle diameter, and the packing arrangement of particles. The result of the proposed study is presented in the form of erosion rate versus the hydraulic shear stress. The model is validated with a series of laboratory erosion t...

On the shear behavior of ballast-geosynthetic interfaces

Large-scale direct shear tests were performed to explore the behavior of rail ballast-geogrid interfaces and establish the role of geogrid aperture size on the interface shear strength. Fresh latite ballast with an average particle size (D50) of 35 mm, and seven geogrids with equivalent aperture sizes ranging from 20.8 to 88 mm were used for this current study. The laboratory experimental results confirm that the interface shear strength is influenced by the geogrid aperture size. The interface efficiency factor (α), defined as the ratio of the shear strength of the interface to the internal shear strength of the ballast varies from 0.8 to 1.16, and the ballast-geosynthetic interface friction angles vary from 52 to 67°. Moreover, a criterion to determine the minimum and maximum aperture sizes required to generate the beneficial effects of the geogrid has been identified in this study.

Semiempirical Cyclic Densification Model for Ballast Incorporating Particle Breakage

A number of constitutive models exist to model behavior of granular material under cyclic loading. Most of these models are useful to model soil behavior where the number of cycles is very small. Therefore, a semiempirical model is proposed to simulate the cyclic densification and degradation of coarse granular material under a railway environment where the number of loading cycles is very large. A kinematically expanding elastic surface is introduced to separate elastic and elastoplastic deformation of the material with the number of cycles. The reversible response is represented by the pressure-dependent elastoplastic rule. Empirical model parameters are introduced to consider the effect of stress history, stress ratio, number of cycles, and breakage. Model parameters are evaluated based on cyclic triaxial test results. Predicted results are compared with the laboratory data in order to demonstrate the model validity. The proposed model captures the realistic deformation and degradation of ballast at various frequencies and confining pressures for a large number of cycles.

Effect of particle breakage on cyclic densification of ballast: A DEM approach

In this paper, an attempt has been made to investigate the effect of particle breakage on densification behaviour of ballast under cyclic loading using Discrete Element Method (DEM). Numerical simulations using PFC2D have been carried out on an assembly of angular particles with and without incorporation of particle breakage. Two-dimensional projection of angular ballast particles were simulated using clusters of bonded circular particles. Degradation of the bonds within a cluster was considered to represent particle breakage. Clump logic was used to make the cluster of particles unbreakable. DEM simulation results highlight that the particle breakage has a profound influence on the cyclic densification behaviour of ballast. The deformation behaviour exhibited by the assembly with breakage is in good agreement with the laboratory experiments. In addition, the evolution of particle displacement vectors clearly explains the breakage mechanism and associated deformations during cyclic loading.

Liquefaction Potential and Dynamic Properties of Sand-Tyre Chip (STCh) Mixtures

This paper presented the results of the investigations on the liquefaction potential and the dynamic properties of sand-tyre chip (STCh) mixtures. A series of strain controlled consolidated undrained cyclic triaxial tests were carried out on specimens of sand mixed with varying proportions of tyre chips (TCh). The specimens of STCh mixture were prepared at a constant initial relative density and tested at an effective confining pressure of 69 kPa. The results show that TCh significantly reduces the liquefaction potential of sand with the addition of gravimetric proportion of TCh between 20 and 40 % to sand. The maximum shear modulus (Gmax) of the STCh mixture was determined by bender element tests for different gravimetric proportions of TCh and effective confining pressures. The initial shear modulus has been found to be influenced by the proportion of TCh and confining pressure. The shear modulus degradation and damping ratio curves were developed for dynamic analysis of sand-scrap tyre mixtures. The increase of scrap tyre in sand-scrap tyre mixtures reduced the shear modulus degradation and increased the damping ratio.

Internal erosional behaviour of lignosulfonate treated dispersive clay

Internal erosional behaviour of lignosulfonate treated dispersive clay has been studied using the Process Simulation Apparatus for Internol Crack Erosion (PSAICE) designed and built at UOw. Effectiveness of Iignosulfonate treated dispersive clay on the erosion resistance has been investigated and its advantage over traditional admixtures is presented. Test results show that the hydraulic shear stress increases with increase in the amount of lignosulfonate. In addition, the micro-chemical analysis has been carried out using FTIR. Based on the Fourier Transform Infrared (FTIR) Spectroscopy results a stabilization mechanism has been proposed for lignosulfonate treated dispersive soil.