When conventional end platens are used in the triaxial test, frictional forces are developed at the sample ends and specimen deformation adjacent to the platens is restrained resulting in non-uniform loading and deformation of the test specimen. The note describes the use of lubricated platens so that lateral restraint is not developed. The compression of the free-ends, called the bedding error, is due to the initial lack of fit between the sample surface and the lubricated platen and penetration of the grease and disc layer by particles of the specimen. Details are given of the method and apparatus used to determine bedding error which is independent of sample height and must be expressed as a deformation and not as a strain. It is shown that during loading, bedding error can account for up to 80 per cent of the observed axial deformation when lubricated platens are used in constant effective stress ratio tests. The error occurring in initial loading is considerably larger than that during unloading and reloading. After several load cycles, bedding deformation is totally recoverable. The magnitude of the bedding error is shown to be directly proportional to the logarithm of the major principal effective stress over a wide range. Its magnitude increases non-linearly with particle size and increases with sample porosity. (TRRL)


  • English

Media Info

  • Features: Figures; References;
  • Pagination: p. 302-309
  • Serial:
    • Volume: 30
    • Issue Number: 3
    • Publisher: Thomas Telford Limited
    • ISSN: 0016-8505

Subject/Index Terms

Filing Info

  • Accession Number: 00334088
  • Record Type: Publication
  • Source Agency: Transport and Road Research Laboratory (TRRL)
  • Files: ITRD, TRIS
  • Created Date: Sep 16 1981 12:00AM