Ballast Degradation Characterized through Triaxial Testing

Transportation Technology Center, Inc. (TTCI) has supported the development of a large-scale triaxial test device for testing ballast size aggregate materials at the University of Illinois at Urbana-Champaign (UIUC). This new test equipment uses monotonic compression and repeated load testing to characterize shear strength, resilient modulus, and permanent deformation behavior of railroad ballast materials. The investigation was performed as part of the heavy-axle-load (HAL) Track Substructure research initiative co-sponsored by the Association of American Railroads (AAR) and the Federal Railroad Administration (FRA). Preliminary test results from the triaxial test device indicated that ballast characteristics could be captured adequately at different levels of degradation. To simulate ballast degradation due to breakage and abrasion, Los Angeles (LA) abrasion tests were used to generate degraded limestone ballast samples. The laboratory sieve analysis and triaxial tests produced the following results: (1) Ballast degradation can cause significant changes in ballast grain size distributions as well as particle shape properties: LA Abrasion Tests produced particles that exhibited considerable breakdown; (2) In permanent deformation testing, the heavily degraded ballast specimen with a Selig’s Fouling Index (FI) of 40 had the highest permanent deformation compared to the other specimens of new clean ballast and degraded ballast (coarse aggregate fraction) specimen. The specimen with coarse aggregate fraction (particles larger than 3/8 inch) from the degraded ballast yielded higher permanent deformation than the new clean ballast specimen; and (3) Ballast degradation did not lead to a significant strength loss in the monotonic shear strength tests. On the contrary, under dry sample conditions, the degraded ballast specimens with or without materials finer than 3/8 inch yielded higher strength than the new clean ballast specimen. The triaxial test setup should provide a better understanding of the factors that affect ballast life-cycle and field performance.

Language

  • English

Media Info

  • Media Type: Digital/other
  • Features: Figures; Photos;
  • Pagination: 4p
  • Serial:
    • Research Results
    • Issue Number: RR 16-21
    • Publisher: Federal Railroad Administration
  • Publication flags:

    Open Access (libre)

Subject/Index Terms

Filing Info

  • Accession Number: 01602592
  • Record Type: Publication
  • Files: TRIS, ATRI, USDOT
  • Created Date: Jun 21 2016 2:56PM