From theory to practice in rail geotechnology

In recent times the increase in axle loads and train speeds have posed serious geotechnical issues with ballasted railway tracks, both in Australia and the world. The large deformations and degradation of ballast under cyclic and impact loads, and the low bearing capacity of compacted ballast and impaired drainage often exacerbate track maintenance. In recent times in Australia, geosynthetics have been trialed in ballasted tracks constructed on soft and saturated formations to help improve stability and longevity. Comprehensive field studies on instrumented tracks at Bulli (near Wollongong) and Singleton (near Newcastle) supported by RailCorp and ARTC, were carried out to measure the in-situ stresses and deformation of ballast embankments. The findings of the Bulli Study indicated that recycled ballast could be effectively reused in track construction if it was re-graded and reinforced with geocomposites. The results of the Singleton Study showed that geogrids with an optimum aperture size can significantly reduce deformations of ballast layer by proving improved interlock with the particles. It was also found that the strains accumulated in geogrids were influenced by deformation of the subgrade, whereas the induced transient strains were mainly affected by the stiffuess of the geogrids. A better understanding of such performance would allow for a safer and more effective design and analysis of ballasted rail tracks with geosynthetic reinforcement and resilient shock mats.