United States Department of Transportation
i
Properties of fouled railroad ballast (phase 1).
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2012-10-01
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[PDF-3.21 MB]
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Edition:Final report.
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Abstract:Ballasted tracks are the most common tracks used in the railroad industry and are designed to provide a stable, safe, and efficient rail
foundation. A ballasted track consists of superstructure (ties, fasteners, and rails) and substructure (ballast, sub-ballast, and subgrade
layers). The main functions of ballast are to support the superstructure by distributing the loads from the moving train, and to provide
lateral resistance to tie movement and drainage. However, ballast deterioration and fouling are major issues in the railroad industry, and
can be caused by repeated loadings, which lead to crushing ballast that is in contact with ties. Upward migration of subgrade particles
into the ballast layer can increase fouling in the ballast and decrease drainage through the ballast layer. There is a need for methods to
easily and inexpensively identify areas that have fouled ballast. The objective of this preliminary study was to evaluate the potential for
estimating the level of fouling in a ballast layer by soil resistivity and permeability tests to be followed by a second study. A test box was
designed and fabricated at the lab at the University of Kansas to perform the constant head permeability test and soil resistivity tests.
Constant head tests were conducted to determine the coefficient of permeability of fouled ballast for different fouling percentages. Soil
resistivity tests were also conducted using the Wenner method (4 point method) to determine the resistivity of ballast for different
percentages of fouling. The tests showed a relationship between the percentage of fouling and ballast resistivity. The resistance of the
ballast layer decreased as the percentage of fouling increased due to the presence of water. Fouled material retained water and filled the
voids between the ballast particles, and therefore decreased resistivity in the ballast layer. The permeability (hydraulic conductivity) also
decreased as the percentage of fouling increased due to the presence of fine particles between the ballast particles; therefore,
permeability and resistivity were also correlated
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