Quantifying the relative strengths of railway ballasts

It is important to be able to distinguish easily between ballasts of poor quality and good quality in terms of strength. For a range of uniformly graded granular materials compacted to the same relative density, there will be two important factors influencing the strength of the aggregate: particle strength and voids ratio (which will be a function of particle shape). Large oedometer tests have been performed in addition to box tests and single particle crushing tests and a new parameter, called the relative strength index, is defined to incorporate the effects of both particle strength and voids ratio. It is found that the relative strength index correlates well with the amount of degradation of ballast in both the large oedometer tests and the box tests, and therefore shows promise as a suitable method for comparing ballast types without having to apply thousands of cycles of load on each ballast.