Evaluating degraded ballast and track geometry variability along a Canadian freight railroad through ballast maintenance records and ground-penetrating radar

• Author / Creator

  Scanlan, Kirk M

• The majority of track comprising Canada’s large railway network is constructed on ballasted foundations. As such, the accumulation of fines within the void space between the ballast aggregate, referred to as ballast degradation, is considered to be a significant factor contributing to the development of long-term track geometry variability (roughness). The relationship is so prevalent that current maintenance practices designed to control the accumulation of fines within ballast are considered equivalent to the management of long-term track roughness. This spatial relationship between degraded ballast and increased long-term geometrical track roughness is based on laboratory test results and limited field evidence. A rigorous, subdivision-scale investigation into the effectiveness of current ballast degradation maintenance practices as well as the degree in which degraded ballast influences track geometry has yet to be performed. As part of this research, the influence of ballast degradation on long-term trends in track geometry is investigated by analyzing historical ballast undercutting (renewal) records. As undercutting alters only the fines content within the ballast, while the remaining track components (subgrade, ties, rails, and fasteners) are not affected, any change in long-term track roughness can be associated with the improved ballast conditions. The importance of improved ballast degradation levels on long-term trends in track geometry is also contrasted between segments of track founded on different subgrade materials. This research also investigates the spatial association between degraded ballast and prolonged or increasing track roughness using 400 megahertz (MHz) ground-penetrating radar (GPR) measurements of a 335 km-long section of Canadian heavy-haul railway. GPR is one of the only methods capable of generating ballast degradation levels across extended (100’s of kilometer long) sections of track in a non-destructive and efficient manner. The methodologies employed to infer ballast degradation from the GPR datasets are based on those gathered during a thorough literature review of current standard railway engineering practices. The results of this research demonstrate that the management of ballast fines is a significant factor related to the management of long-term track geometry for sections of track constructed on mineral-based subgrades. However, for track constructed on relatively softer, organic subgrades, long-term reductions in track roughness after ballast renewal are not as prevalent. This result suggests that, from a subdivision-scale track geometry management perspective, the accumulation of fines within the ballast void space, while important, is not the only factor to consider when preparing ballast maintenance campaigns in response to observed track geometry variability. The spatial association results derived from field measurements demonstrate no widespread, subdivision-scale correlation between track roughness and GPR-based ballast degradation estimates. Significant spatial correlations only exist when the datasets are compared at local scales (100’s of meters). Numerical modelling of 400 MHz GPR measurements demonstrate that the attributes used to infer ballast degradation are ambiguous in the presence of variable track foundations (including variable ballast thicknesses, saturations, conductivities and subballast materials) and investigating spatial correlations in the field datasets at a local-scale attempts to limit that ambiguity. However, GPR attribute ambiguity continues to be problematic even at the local-scale as significant spatial correlations are rare. Improved correlation results may be achievable considering ballast degradation levels inferred from a joint interpretation of multiple GPR datasets utilizing multiple operating frequencies.

• Subjects / Keywords

  • Ballast degradation
  • Ground-penetrating radar
  • Track geometry
  • Railway engineering

• Graduation date

  Spring 2018

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3PR7N874

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.