ABSTRACT
The degradation of ballast is one of the major substructure problems, which leads to increased track settlement, increased ballast fouling, and reduced drainage. Ballast gradation is a prime factor for the stability, safety, and drainage of tracks. Well-graded ballast generally attains a higher degree of compaction, hence a superior shear strength. It is expected that both the settlement and degradation of ballast can be significantly reduced by optimising the PSD. The various PSDs currently used by different rail authorities in Australia (e.g. Rail Infrastructure Corporation of NSW, Queensland Rail) are primarily based on the gradation specified by the Australian Standard for railway ballast. To evaluate the effects of PSD on the deformation and degradation behaviour of ballast, Indraratna et al. conducted cyclic triaxial tests on four different gradations of ballast. The cyclic test results of ballast varying the gradation indicate that even a modest change in the uniformity coefficient substantially affects the deformation and breakage behaviour of ballast.
