ABSTRACT
During operation, ballast deteriorates due to the breakage of angular corners and sharp edges, infiltration of fines from the surface and mud pumping from the subgrade under train loading. Fouling materials have traditionally been considered as unfavourable to track structure. The sources, quantifications and adverse effects of fouling are discussed. Fouling is caused by a number of mechanisms associated with traffic loads and various maintenance cycles, such as tamping, ballast-cleaning and reconstruction processes. The initial placement density of the ballast in the actual rail track is often ascertained as standard practice in most countries. Most Australian standards for ballast recommend the range of in situ densities of ballast. The thickness of ballast layer in most rail tracks varies between 300 and 500 mm, so 500 mm thick ballast layer was used to determine the permeability of fouled ballast.
