The specified top size and grading (or grain size distribution) of railroad ballast affects its method of production and its performance in track. Both parameters affect any economic evaluation of ballast; as such it is essential to optimize both. The main source for ballast gradings in North America is the American Railway Engineering Association's (AREA) Manual for Railway Engineering (3). Railroad ballast gradings tend, not only in North America but also world wide, to be uniformly graded (i.e., single sized with the opening of the major percent passing sieve being 1.5-3 times the size of the percent retained on sieve). Herein a laboratory examination of ballast top size and grading are made in the triaxial apparatus. Particular attention will be paid to plastic strains, which cause rail twist, and strength, which affects lateral track stability. For the limited data obtained under laboratory triaxial conditions, broader graded ballast than presently used by most railroads have been shown to perform, in terms of minimizing plastic deformations, as well as or better than uniformly sized ballasts within the same size range. In terms of sample strengths with the same stress history broader graded ballasts performed better than single sized ballasts. These two properties are important in terms of minimizing rail or track twist and lateral track stability, respectively. As aggregate hardness and toughness qualities improve so does the importance of broader grading to minimize plastic deformations and increase compacted strengths. In a comparison of uniformly graded ballasts alone the results showed that smaller size ballast deform less, but have a lower final compacted strength, than larger size ballast provided that, in the former case, stress levels do not exceed a critical level. A grading that fits within the limits of presently used AREA ballast particles sizing and is broadly graded is shown as a recommended grading. /Author/

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Filing Info

  • Accession Number: 00196138
  • Record Type: Publication
  • Report/Paper Numbers: ASCE 14556 Proceeding
  • Files: TRIS
  • Created Date: Oct 17 1979 12:00AM