Abstract
Railway tracks are conventionally built on compacted ballast and structural fill layers placed above the natural (subgrade) foundation. However, during train operations, track deteriorations occur progressively due to ballast degradation. The associated track deformation is usually accompanied by a reduction in both load bearing capacity and drainage, apart from imposing frequent track maintenance. Suitable ground improvement techniques involving plastic inclusions (e.g., geogrids) and energy absorbing materials (e.g., rubber products) to enhance the stability and longevity of tracks have become increasingly popular. This paper presents the outcomes from innovative research and development measures into the use of plastic and rubber elements in rail tracks undertaken at the University of Wollongong, Australia, over the past twenty years. The results obtained from laboratory tests, mathematical modelling and numerical modelling reveal that track performance can be improved significantly by using geogrid and energy absorbing rubber products (e.g., rubber crumbs, waste tire-cell and rubber mats). Test results show that the addition of rubber materials can efficiently improve the energy absorption of the structural layer and also reduce ballast breakage. Furthermore, by incorporating the work input parameters, the energy absorbing property of the newly developed synthetic capping layer is captured by correct modelling of dilatancy. In addition, the laboratory behavior of tire cells and geogrids has been validated by numerical modelling (i.e., Finite Element Modelling-FEM, Discrete Element—DEM), and a coupled DEM-FEM modelling approach is also introduced to simulate ballast deformation.
Highlights
Railways are one of the most popular and important modes for transporting freight and passengers worldwide, of which Australia is one of the countries who has the longest heavy haul trains from3–5 km long with axle loads up to 40 tons [1]
P2 forces are related to the mechanical resistance of the ballast layer against the shock, leading to its significant deformation
The stress-strain behavior of the steel furnace slag (SFS)+coal wash (CW)+rubber crumbs (RC) matrix was examined using a number of static triaxial tests
Summary
Railways are one of the most popular and important modes for transporting freight and passengers worldwide, of which Australia is one of the countries who has the longest heavy haul trains from3–5 km long with axle loads up to 40 tons [1]. During train operations the track progressively deteriorates due to: (i) the lateral spreading and settlement of ballast or sub-ballast layers because of inadequate confinement [2,4]; (ii) ballast deteriorations caused by breakage of sharp edges and angular corners, the intrusion of fine particles, and mud-pumping from the layers of soft soil lying below, all of which seriously compromise its particle angularity, shear strength and hydraulic conductivity [2,5,6,7] Such track deterioration leads to costly and frequent maintenance, especially when the heavy haul tracks undergo heavier axle loads and higher speeds [8,9]; for example, in New South Wales, Australia alone the cost of track maintenance for ballast-related work is estimated to be around 14–15 million dollars per year [10]. One potential method of enhancing the substructure capacity to withstand the large cyclic and impact loads induced by fast-moving heavy-haul trains is to improve the performance of the ballast layer using plastic (e.g., geogrids) and rubber inclusions (e.g., rubber mat, tire cell, and rubber crumbs) [2,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30]
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