Effects of Parallel Gradation on Strength Properties of Ballast Materials

The railroad ballast is used to fill in irregular surface topology, distribute and transfer loads from a surface structure or system to the subgrade or subsoils as uniformly and widely as possible in order to provide stable and stiff long-term embankment support for railways. A typical ballast grain sizes range from 30 to 70 mm, which makes large-scale laboratory tests difficult to conduct. The parallel gradation technique is to preserve the particle shape, particle surface roughness, and particle mineralogy, and creates a parallel gradation of soil with a maximum particle size for the available apparatus. This paper presents the result of a series of monotonic direct shear tests for three ballast materials having parallel gradation curves, which are served as background study for the ongoing research on validating it under loading-unloading condition