Performance appraisal of ballasted rail track stabilised by geosynthetic reinforcement and shock mats
Rail tracks serve the principal mode of transportation for bulk freight and passengers in Australia. Ballast is an essential constituent governing the overall stability and performance of rail tracks. However, large repetitive loads from heavy haul and passenger trains often lead to excessive deformation and degradation of the ballast layer, which necessitate frequent and expensive track maintenance works. In Australia, the high cost of track maintenance is often associated with ballast degradation, fouling (e.g. coal and subgrade soil) and associated poor drainage, differential settlement of track, pumping of subgrade soils, and track misalignment due to excessive lateral movements. With increased train speeds, the track capacity is often found to be inadequate unless more resilient tracks are designed to withstand the substantially increased vibration and repeated loads. A field trial was conducted on a section of track in Bulli, New South Wales, and findings indicated that the moderately-graded recycled ballast when used with a geocomposite resulted in smaller deformations in both vertical and lateral directions in comparison to uniformly-graded fresh ballast. Installing resilient (shock) mats in the track substructure led to significant attenuation of high impact forces and thereby mitigated ballast degradation. In addition, a series of full-scale field experiment was undertaken on track sections near Singleton, New South Wales to investigate the effects of geosynthetics on the performance of the track built on subgrade soils with varying stiffness. The finding suggested that geogrids can decrease vertical strains of the ballast layer and a few selected types of geogrids can be used more effectively with soft subgrade soils. This state of the art & practice (SOAP) paper describes the results of two unique full-scale field trials, series of large-scale laboratory tests and numerical models to assess the improved performance of ballasted rail tracks using synthetic grids and shock mats.