Other Reports

HAL Substructure Investigation Using Rapid, Non-Destructive Techniques

  • 01
  • Jan
  • 2001
AUTHOR: Steven Chrismer, Joseph LoPresti
OFFICE: RPD
SUBJECT: Rail and Infrastructure Integrity
KEYWORDS: Cone Penetrometer, Heavy Axle Load, Subgrade
ABSTRACT: As part of a program to determine the nature of track substructure problems and to recommend the best remedial action, the Association of American Railroads has developed an on-track vehicle which houses a rapid, non-destructive subgrade test apparatus known as a cone penetrometer. Although still in the planning stage, another rapid, non-destructive diagnostic tool being developed is a moving vehicle which continuously measures track deflections under load. The cone penetrometer test (CPT) vehicle has been used to investigate the cause of excessive maintenance requirements on three member railroads. The data obtained is being used to determine the strength of the subgrade, the adequacy of the granular layer thickness over it, and the extent of weak soil deposits under and along the track. CPT data can be used as a guide to select the most appropriate maintenance remedy. This is one of the tools that can be used to asses the potential benefits of adding more ballast, modifying the soil in place, removing and replacing the subgrade with better material, or adding hot-mix asphalt over the weaker layer. Deflection data can determine whether the problem resides in the ballast/subballast (granular layer) or in the subgrade. The running deflection measurements can first be used over long track distances to identify whether the problems are granular or subgrade related. Then, for locations with apparent subgrade problems, the CPT can be called in for a more detailed assessment. The deflection and CPT data are also used to decide when and whether more intrusive techniques (such as cross-trenching) are needed to further identify the problem.
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