Recent advances in railroad infrastructure and track performance - Australian experience

As trains become longer, heavier and quicker, ballast shows signs of distress and degradation, leading to deterioration of the track geometry. Appropriate stabilisation techniques using artificial inclusions such as polymeric geosynthetics and energy-absorbing shock mats are needed to improve track stability and longevity. Large-scale laboratory tests at University of Wollongong revealed that the geogrids with an optimum aperture governed the effectiveness of the reinforcement mechanism. The use of shock mats was influenced by their placement position and the type of subgrade (e.g. estuarine soil, rock etc.). In these studies, different types of geosynthetics and shock mats were placed beneath the ballast embankment constructed on varying subgrade conditions. Traffic induced stresses, ballast breakage, transient and permanent deformations of the substructure were routinely monitored using precise instrumentation schemes. The findings from the Bulli Study verified that the discarded aggregates could be reused in track construction, if reinforced with geogrids with appropriate apertures. The results of the Singleton Study also showed that geogrids could significantly reduce track deformation especially when subgrade was soft. In contrast, shock mats were more effective in reducing ballast degradation when placed above a concrete deck (i.e. rail bridges).