Assessing the Strength of Individual Railway Ballast Aggregate by Setting up Bilateral Point Loading Condition

Assessment of the strength of parent rock is characterized as one of the most crucial step for selection of appropriate ballast material. In this regard, conducting the point load test (PLT) is a well-established procedure to determine the strength of rock core as well as fresh crushed aggregate. Meanwhile, the PLT is carried out under unconfined condition to axially apply conical concentrated load on the specimen, while the ballast layer comprises of assembly of aggregate in contact with each other. Therefore, providing lateral confinement in the PLT could be a more appropriate testing procedure to determine the strength of an individual particle. In the present study, a modified PLT was conducted on irregular-shaped ballast particles in which the bilateral point loading condition was provided on individual aggregates of different size ranges derived from various parent rock types. As expected, the results demonstrated that the confinement of single aggregate subjected to the conical loading led to the increment in the estimated strength. The failure patterns of individual ballast particles were substantially altered so that each particle was broken into higher number of fragments. The correlation between the results of PLT and the impact loading test further confirmed that the strength of the individual particles estimated based on the modified PLT could better correlate with the measured degradation levels of aggregate assembly subjected to impact loading.