Two Decades of Advancement in Process Simulation Testing of Ballast Strength, Deformation, and Degradation

Abstract

This paper describes salient features of a set of large-scale ballast testing equipment developed at the University of Wollongong, Australia, and how the test results and research outcomes have contributed to transforming tracks in the Australian heavy haul and commuter networks, particularly with regards to the strength, deformation, and degradation of ballast. Ideally, ballast assemblies should be tested in prototype scale under actual loading conditions. This is because a reduction in particle sizes for testing in smaller equipment can reduce the internal angle of friction (shearing resistance) of the granular assembly in a macro sense, and the angularity of the particles in a micro sense, and hence the volumetric changes during the shearing process. In response to the worldwide lack of proper test facilities for ballast, the University of Wollongong has, since the early 1990s, designed and built a number of large-scale process simulation triaxial testing rigs. They are all custom made to minimize any boundary effects and also to evaluate the deformation and degradation of ballast, particularly the size, shape, and origin of aggregates used as ballast in Australian tracks. This triaxial process simulation equipment was originally used to characterize the behavior of coarse aggregate used for state railway standards for monotonic loading, but since then it has been fitted with dynamic actuators to simulate actual track conditions involving the true cyclic loading nature while also capturing the wheel-rail dynamics that correspond to high-speed commuter rail and fast heavy-haul operations. These tests invariably demonstrated completely different stress-strain and volumetric characteristics of ballast compared to conventional static or monotonic testing of the same test specimens. AbstractThis paper describes salient features of a set of large-scale ballast testing equipment developed at University of

Tutorial on the fragmentation of the railway ballast particles and calibration methods in discrete element modelling

“…Railroads ensure the biggest network for quick and secure, public and freight transportation on rails over the world [1].…”

“…The most important roles of ballast materials are to distribute and reduce forces affecting sleepers, provide horizontal resistance, and ensure quick dewatering. Ballast for high loads and stability must be angular, well graded, and dense (i.e., well compacted), but this structure hinders drainage [1].…”

Advancements in Geo-Inclusions for Ballasted Track: Constitutive Modelling and Numerical Analysis

“…to enhance rail ballast performance and reduce its degradation [6][7][8][9][10][11][12]. Field trials by Indraratna et al [13] showed that rubber mats could significantly minimise ballast deformations, apart from reducing particle breakage. Previous laboratory studies using large-scale test facilities indicated that plastic under sleeper pads placed beneath sleepers could minimise ballast breakage by mitigating the transmission of impact loading effects [14].…”

Application of geoinclusions for sustainable rail infrastructure under increased axle loads and higher speeds

“…placed at the interfaces between rails and sleepers); (ii) under sleeper pads (i.e. placed at the sleeper/ballast interfaces); (iii) rubber mats installed beneath the ballast (shock mats); and (iv) ballast mixed with rubber crumbs or shreds [17,41,60]. The inclusion of rubber shock mats decreases the hard interface between the ballast aggregates and other track components, such as the sleepers or underlying formations, and allows the particles bedding into softer pads, thus enhancing the area of contact of the aggregates and minimising the inter-particle contact forces [42,47,51].…”

“…The inclusion of rubber shock mats decreases the hard interface between the ballast aggregates and other track components, such as the sleepers or underlying formations, and allows the particles bedding into softer pads, thus enhancing the area of contact of the aggregates and minimising the inter-particle contact forces [42,47,51]. Moreover, indirect methods to reduce the degradation of ballast by using rubber products in the sub-ballast layer have also been proposed in recent times, such as replacing the traditional sub-ballast with an energy-absorbing layer composed of waste materials, including coal wash, steel furnace slag and rubber crumbs [28,55], and using a capping layer confined with recycled rubber tyre cells [17]. In this paper, some of these methods involving the use of recycled rubber products in rail tracks will be presented and discussed.…”