Twenty-five years of track geotechnology research

In the early 1980's the railroad industry increased funding to the AAR track research program to finds ways to mitigate the expected damage from the eventual introduction of heavy axle load (125-ton) freight cars. This research has provided valuable insights into the behavior of the geotechnical components of track (ballast, subballast, and subgrade) allowing certain long-held but erroneous assumptions about these components to be put to rest, such as the canard that fouling "muddy" material in the ballast resulted from subgrade material pumping upward. Analysis showed that typically the fouling material originated predominately from within the ballast layer itself due to ballast particle wear. With such improved understanding of substructure behavior the railroad industry was able to reduce costs by choosing more appropriate track maintenance and remediation methods. As understanding of track geotechnology has continued to advance, track substructure design and maintenance planning has become less empirical, less trial and error. The paper describes how, with today's more scientific approach, it is now possible to better address such track substructure problems as unstable "track transitions", soft subgrade, determining when ballast must be replaced, and more durable track geometry correction methods.