Nayoma Tennakoon
University of Wollongong
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Featured researches published by Nayoma Tennakoon.
Geotechnical Testing Journal | 2012
Nayoma Tennakoon; Buddhima Indraratna; Cholachat Rujikiatkamjorn; Sanjay Nimbalkar; Tim Neville
The ballast layer is designed to be free draining, but when the voids of the granular medium are wholly or partially filled because of the intrusion of fine particles, the ballast is considered to be “fouled.” To ensure acceptable track performance, it is necessary to maintain good drainage within the ballast layer. This paper critically examines the current methods commonly used for evaluating the degree of ballast fouling and, because of their limitations, a new parameter, “void contaminant index” is introduced. A series of large-scale constant head hydraulic conductivity tests were conducted with different levels of fouling to establish the relationship between the void contamination index and the associated hydraulic conductivity. Subsequently, a numerical analysis was executed to simulate more realistic two-dimensional flow under actual track geometry capturing the drainage capacity of ballast in relation to the void contamination index. In the context of observed test data, the drainage condition of the track could be classified into different categories together with a classification chart capturing the degree of fouling. The contents of this paper have already been considered in track maintenance schemes in the states of Queensland and New South Wales.
GeoFlorida 2010 | 2010
Buddhima Indraratna; Sanjay Nimbalkar; Nayoma Tennakoon
Ballasted Rail tracks are widely used throughout the world due to its resiliency to the repeated wheel loads, low construction cost and ease of maintenance. However, the ballast layer needs periodic maintenance due to its deformation and degradation associated with particle breakage and fouling. A proper understanding of the contamination due to various types of fines and its implications on track drainage is a pre-requisite for effective implementation of track maintenance operations. A new parameter Void Contaminant Index (VCI) can accurately assess the contamination as it includes the effect of void ratio, specific gravity and gradation of ballast and fouling material. A series of constant head hydraulic conductivity tests using a specially designed large-scale permeability apparatus were performed on fresh ballast mixed with different proportions of fines to study the relationship between the percentage of fouling and drainage characteristics. A field trial is conducted on an instrumented track at Bulli, NSW Australia, to study the benefits of a geocomposite layer installed at the ballastcapping interface, and to evaluate the performance of recycled ballast in comparison to traditionally uniform fresh ballast. It is found that recycled ballast can be effectively reused if reinforced with a geocomposite. The geocomposite can effectively reduce vertical and lateral deformations of the ballast with obvious implications on improved track stability thereby reducing maintenance costs.
international colloquium on grammatical inference | 2012
Nayoma Tennakoon; Buddhima Indraratna; Sanjay Nimbalkar; Cholachat Rujikiatkamjorn
Railways offer an efficient and economic transport mode in many countries including Australia, China and USA. Conventionally, rail tracks are positioned on ballast due to several potential benefits, including economy (availability and abundance), rapid drainage and high load bearing capacity. However, the ballast becomes contaminated due to intrusion of pumped subgrade material (e.g. clay and silt). This is one of the primary reasons for rapid track deterioration. In severe circumstances, fouled ballast needs to be cleaned or replaced to maintain the desired track resiliency, load bearing capacity and the track alignment, all of which influence the level of safety. In Australia, massive amount of funds have been invested in track maintenance. By employing an effective maintenance program, both cost and the ballast quarrying can be reduced with significant favourable environmental implications and improved productivity. In order to identify the risk associated with fouling, it is important to accurately assess the amount of fouling. In this paper, the current methods commonly used for evaluating the degree of ballast fouling were critically examined and a new parameter, Void Contaminant Index (VCI) was proposed to capture the role of different fouling materials in terms of volume based air-voids reduction. A series of isotropically consolidated drained triaxial tests using a large scale cylindrical triaxial apparatus were conducted on both clean and fouled ballast with varying VCI to establish the relationship between the extent of fouling and the associated strength-deformation properties. Based on the laboratory findings, an empirical relationship between the peak deviator stress and VCI is proposed to assist the practitioners for preliminary track assessment and in the mitigation of the risk associated with ballast fouling. A non-linear shear strength envelope for clay fouled ballast is presented in a non-dimensional form, based on the proposed empirical equations.
18th Southeast Asian Geotechnical Conference (18SEAGC) & Inaugural AGSSEA Conference (1AGSSEA) | 2013
Buddhima Indraratna; Nayoma Tennakoon; Sanjay Nimbalkar; Cholachat Rujikiatkamjorn
Ballast is most commonly used as a structural component of rail track due to its high load bearing capacity, resiliency and rapid drainage. However, ballast along coal freight corridors often becomes fouled due to spilling of coal from moving wagons, in addition to further track deterioration attributed to particle breakage and pumping of soft subgrade. Highly fouled ballast needs to be cleaned or replaced to maintain the desired track resiliency, load bearing capacity and the track alignment. In order to identify the risk associated with fouling, it is important to accurately assess the amount of fouling. In this paper, the use of Void Contaminant Index (VCI) compared to other mass-based indices is critically examined. A series of isotropically consolidated drained triaxial tests using a large scale cylindrical triaxial apparatus have been conducted on both clean and fouled ballast with varying VCI to assess the stress-strain and degradation characteristics. In accordance, a non-linear shear strength envelope for clean and fouled ballast is presented in a non-dimensional form. The maximum permissible train speed under different level of fouling is also proposed. Introduction When ballast is fouled due to intrusion of fines from external sources, significant changes in the pore structure of the ballast occur resulting in reduced particle interlock and diminished void ratio. Numerous studies on granular materials through discrete element methods (Huang and Tutumluer 2011, Lim and McDowell 2005, Lu and McDowell 2006) and specific examination of the behaviour of clean ballast using discrete and continuum mechanics approaches (Indraratna et al. 2011) have been employed in the past. However, detrimental aspects of fouling on rail ballast have still not been assessed in detail. In this study, consolidated drained tests were conducted using a large-scale cylindrical triaxial apparatus to study the stress-deformation characteristics of
Geotechnique | 2013
Buddhima Indraratna; Nayoma Tennakoon; Sanjay Nimbalkar; Cholachat Rujikiatkamjorn
Computers and Geotechnics | 2015
Nayoma Tennakoon; Buddhima Indraratna; Sanjay Nimbalkar; Scott W. Sloan
Geotechnique | 2014
Nayoma Tennakoon; Buddhima Indraratna
Archive | 2014
Nayoma Tennakoon; Buddhima Indraratna; Cholachat Rujikiatkamjorn
Archive | 2012
Nayoma Tennakoon; Buddhima Indraratna; Cholachat Rujikiatkamjorn; Sanjay Nimbalkar
Archive | 2015
Nayoma Tennakoon; Buddhima Indraratna; Sanjay Nimbalkar