From theory to practice in track geomechanics – Australian perspective for synthetic inclusions

• Artificial inclusions decreased strains in ballast, thus improving track stability.
• Numerical models could capture stress–strain-degradation with reasonable accuracy.
• Use of geocomposite proved to be a feasible and effective in recycled ballast.

The adoption of heavier axle loads and high speed rails have posed serious geotechnical issues with ballasted railway tracks. These issues include poor drainage of soft coastal soils, ballast degradation under cyclic and impact loads, differential settlement of track and misalignment due to lateral movements, and inadequate bearing capacity of some compacted ballast. The mechanisms of ballast degradation and deformation, the need for effective track confinement, understanding of interface behaviour, determining dynamic bearing capacity and use of energy absorbing shock mats and synthetic grids require further insight to improve the existing design guidelines for future high speed commuter and heavier freight trains. In this paper, the current state-of-the-art knowledge of rail track geomechanics is discussed, with particular emphasis on the effects of geosynthetic applications on ballast degradation, and track performance. The stress–strain response and volumetric changes of ballast stabilised with geosynthetics observed in the laboratory experiments were captured through discrete element and finite element models. Installing shock mats and geosynthetics in the track substructure led to the attenuation of high cyclic and impact forces, thereby mitigating ballast degradation. Comprehensive field studies on instrumented tracks at Bulli (near Wollongong) and Singleton (near Newcastle) supported by Sydney Trains and ARTC, were carried out to measure the in situ stresses and deformation of ballast embankments. The paper focuses primarily on research conducted at University of Wollongong for enhanced track performance, highlighting some examples of innovation from theory to practice.