In-situ performance assessment of ballasted railway track stabilised using geosynthetics and shock mats
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In Australia, ballasted railway tracks are one of major modes of transportation. The main objectives of Australian railways are to cater for the demands of the supply chain in the mining and agriculture sectors, as well as to provide quicker and cost effective commuter transport in urban areas. However several geotechnical problems in the populated coastal areas pose significant issues. Ballasted tracks are conventionally constructed on compacted granular embankments overlying the natural subsoil. The granular embankments comprises of ballast and capping layers which undergo substantial deformations and degradation under the heavy cyclic loading of passenger and freight trains. This in turn, may lead to a loss of track geometry, and require costly frequent maintenance. In order to rectify these issues, appropriate stabilization techniques for ballast and capping are necessary, the extent of which depends also on the type of subgrade. When appropriately designed and installed, synthetic inclusions such as geosynthetics and/or shock mats can provide a cost effective alternatives to traditional techniques of ground improvement. Comprehensive field trials were carried out on two railway networks in Bulli and Singleton in New South Wales, Australia. In these studies, several track sections were instrumented with precise sensors for real-time monitoring of stress-deformation response of granular embankments. Different types of geosynthetics were placed beneath the ballast embankment. Recoverable and irrecoverable components of vertical deformations of the track substructure were routinely monitored. The amount of ballast breakage was evaluated by collecting samples from the field and by performing sieve analysis in the laboratory. It was evident that geosynthetics in the form of geogrids can decrease the vertical strains of the ballast layer, resulting in reduced maintenance costs. This paper describes the comprehensive field instrumentation, site geology, construction procedures, and field performance evaluation of these full-scale geosynthetic- and shock mat- stabilized ballast embankments in Australia.