Time and Spatial Dependence of the Fouling of Railroad Track Ballast

With the increased use of heavy axle load (HAL) trains, the improvement of railways is more important than ever. Because maintenance costs are so high, any way to reduce the amount of fouling that occurs—or to better predict when maintenance is necessary—and thus reduce the amount of maintenance required, would be financially beneficial. The problem however is that because there are so many variables that exist between railroads, it is difficult to control these variables in the field in a way that would allow experiments to be run that will further our knowledge of ballast fouling and degradation. In the early 1990's, samples were taken from a section of rail in the hopes of understanding the nature of how fouling occurs. The samples of the ballast were taken over the course of three years, and sieve analyses were run on these samples. Sampling was done with location as a major consideration, retrieving samples from specific locations in the ballast cross-section. Using the grain size distribution data, the fouling was quantified using the conventional Fouling Index (percent of particles, by mass, passing the 3/8" sieve). Single-factor analysis of variance tests were designed and run using these data to determine how certain variables related to the fouling of ballast. Parameters of interest were time after placement and location of sample. It was statistically determined that ballast fouling increased over time, and that the fouling was more prevalent in the lower depths of the ballast layer, as well as in the tamping zones.