An Australian perspective on modernization of rail tracks using geosynthetics and shockmats

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Ground Improvement Case Histories: Compaction, Grouting and Geosynthetics, 2015, pp. 583 - 608
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Faster and cheaper rail transport(s) is an essential means of catering for the demand for travel and supply chains in the public and private sectors. Such a development in coastal areas would necessitate the use of ground improvement techniques to improve track performance and sustainability. While ballast stabilizes tracks so they can support heavy traffic loads and provide rapid drainage, ballast settlement, fouling, and excessive lateral displacement leads to differential settlement, loss of track geometry, and requires costly and regular maintenance. Optimizing the use of maintenance funds is a challenging task because comprehensive methods of predicting track longevity due to time-dependent and rapid deterioration of ballast simply do not exist. Track construction therefore requires appropriate ballast stabilization techniques using geosynthetics and shock mats, the effectiveness of which depends also on the type of subgrade. Comprehensive field trials were carried out on two rail lines at Bulli and Singleton, New South Wales, Australia. In these studies, several track sections were reinforced with various types of geosynthetics: three types of biaxial geogrids and a geocomposite (a combination of biaxial geogrid and nonwoven geotextile) and a layer of shock mat placed beneath the ballast embankment. Both fresh and recycled ballast were examined for varying subgrade conditions, and recoverable and irrecoverable deformations of the track substructure were routinely monitored. It was found that geogrids and geocomposites can decrease the vertical strains of the ballast layer, and thus reduce maintenance costs. It was also found that geogrids were more effective when the subgrade was soft, and shock mats also helped mitigate particle breakage when laid on a stiff base such as the deck of a concrete bridge. This chapter describes the comprehensive field instrumentation, construction procedures, and evaluation of these full-scale ballasted tracks stabilized with geosynthetics and shock mats.
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