ABSTRACT
In this Chapter, the authors describe the laboratory investigation of ballast response under monotonic, cyclic and impact loadings, using state-of-the-art large-scale cylindrical, prismoidal triaxial and drop-weight impact equipment. The entire testing equipment and experimental procedure have been developed at the University of Wollongong. In order to study the strength, deformation and degradation characteristics of both fresh and recycled ballast, a series ofmonotonic triaxial tests was conducted in the laboratory using the large cylindrical triaxial apparatus. The crushing strengths of fresh and recycled ballast grains were then studied in a separate series of single particle crushing tests. In order to investigate the deformation and degradation behaviour of fresh and recycled ballast under cyclic loading, a small section of trackwas simulated in the prismoidal triaxial chamber. Representative field lateral stresses were applied to the ballast specimens and a cyclic vertical load equivalent to a typical 25 tonne/axle train load was applied to the specimens. To enhance the engineering performance of recycled ballast in track, an attempt was made to stabilise recycled ballast in the laboratory model using various types of geosynthetics. In order to investigate progressive degradation of fresh ballast subjected to impact loading, a series of impact tests was conducted using the high-capacity drop-weight impact machine. The performance of shock mats in the attenuation of dynamic impact loads and subsequent mitigation of ballast degradation was studied. The details of these new items of equipment, test materials, specimen preparation and test procedures are described in the following Sections.
