Improved performance of rail track substructure using synthetic inclusions: experimental and numerical investigations

Ballasted rail tracks offer the most important means of transporting bulk freight and passengers in terms of the sheer tonnage of traffic. Ballast is a prominent component of conventional rail infrastructure because it controls the stability and performance of track. Repetitive train loads degrade ballast grains due to breakage and the progressive accumulation of external fines or mud-pumping from the softer subgrade. They decrease the shear strength and drainage capacity of track embankments, while adversely affecting its safety and efficiency as speed restrictions are imposed and track maintenance becomes more frequent. Although synthetic inclusions such as geogrids and rubber mats placed between the ballast and subballast definitely improve track performance, further study is needed before incorporating them into existing design routines catering for future high speed trains and heavier haul trains. This paper presents the very latest knowledge of rail track geomechanics, including several important concepts and topics related to laboratory testing and discrete element modelling approaches to study the load and deformation of ballast improved by rubber mats and synthetic geogrids. This paper focuses on studies carried out at the University of Wollongong on track infrastructure, and includes examples whereby innovation progresses from theory to practice. Discrete element modelling is also used to carry out a micromechanical analysis of the ballast and geogrid interface to provide further insight into ballast subjected to shearing.