INVESTIGATION INTO THE SOURCE AND PROGRESSION OF RAILWAY TRACK BALLAST LAYER FOULING MATERIAL FOR THE CN JOLIETTE, QC SUBDIVISION
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Railway track ballast fouling is an ongoing issue without a clear understanding regarding either the cause for generation or the source of the fouling materials. This study was conducted to determine what physical processes are likely causing ballast fouling, where in the track sub-structure fouling material is concentrating, and what factors affect the severity of ballast fouling. A field investigation on a CN railway track was conducted in Joliette, QC during undercutting maintenance operations. Data for in-situ ballast, sub-ballast, and subgrade samples were gathered from a series of trenches excavated through the track embankment. The geotechnical and mineralogical characteristics of a selected set of ballast samples were gathered through a regime of laboratory testing. Grain size distribution data for the select samples was collected from sieve and hydrometer testing. Three sets of LA abrasion tests were conducted on both in-situ and freshly quarried ballast rock to determine the degradation characteristics of the various ballast types. The petrographic analysis of the sample types was conducted using bulk hand sample characterization, thin-section analysis, and X-Ray Diffraction Analysis. The petrographic, grain size, and LA abrasion combined analysis indicated that ballast fouling was primarily caused through degradation of the ballast. The fouling material within the ballast pores was sourced to the abraded pieces of ballast that had degraded over time through XRD and grain size distribution analysis. It was found with statistical confidence that ballast layers with harder, structureless rock types have less fouling material form within the ballast void spaces compared to ballast rock types that are soft on the Mohs hardness scale or have planes of weakness due to structural factors. Analysis of the grain size data also showed that ballast fouling was generally concentrated within the section of the ballast layer directly underlying the steel rail, within the topmost parts of the ballast layers. Overall it was recommended that the effects of chemical degradation on ballast rock types and the historical operational duration of ballast be incorporated into future ballast fouling studies.