Properties of stones for railway foundation
Railway Foundation Properties of Some South African Quarry Stones by Felix N. Okonta and S. G. Magagula Department of Civil Engineering Science, University of Johannesburg, in The Electronic Journal of Geotechnical Engineering, Volume 16  Bundle A, pp. 179-197.
From the paper:
"Railway ballasts are broken pieces of hard rock within the grain size range of 25mm - 60mm, over which the railway tracks are laid. Quarries in dolerite, greywake, shale, pebbles and granitic rock formations are some of the major sources of large stones that may be selected as railway ballast based on a range of properties. Flakiness index, Roundness, sphericity and shape factor, and Los Angeles Abrasion indices of samples of the five rock types were determined.
The image analysis method was done using computer software called Pixcavator. The pixcavator analyzes an image which is imported into the program and gives the identification, type, location, size in pixels, perimeter, roundness, gray, contrast and dimensions of the image in a form of an Excel spreadsheet. The program analyzes the image in two-dimension (2D), and it can analyze an image containing a set of particles or an image having one particle in it.
Two methods were used to determine the roundness of the ballasts. Firstly, an image containing the ten ballasts was analyzed with the pixcavator where the program could determine the roundness for all individual ballasts in the image. Secondly, an image containing only one ballast particle was used and this was done for all five samples of ballasts. "