In the standard triaxial shear test frictional resistraint at the loading platens results in nonuniform stresses in the test specimen. Because of this the pore pressure set up in the end zones of the specimen is different from that set up at mid-height. To obtain accurate measurements of the shear strength of a soil in terms of effective stresses, it is essential that the measured pore pressure be representative of conditions in the zone of shear failure. The simplest way of attaining this is by allowing the pore pressure to equalize throughout the specimen by transfer of moisture. This paper investigates the relation between the equalization of pore pressure and the duration of the test for drained and undrained triazial compression tests. The effect of the stress history of the soil on the magnitude of pore pressure differences in the triazial test is also studied. It is shown that the time of loading which will result in a given percentage of equalization of pore pressure can be calculated from a knowledge of the coefficient of consolidation of the soil, but that the error in measured effective stress at this time will depend on the stress history of the soil. Discussion: Discussion: L. Barden states that an alternative approach to minimize end restraint is by using lubricated end platens; they can be effective in two ways: (1) free ends reduce the tendency to barrel at large strains, and (2) elimination of the end- friction dead zones allows the use of shorter test specimens. C.B. Crawford questions whether it is prudent to use Dr. Bright and others approach in computing the required test duration from the boundary conditions of the test and the coefficient of consolidation. R.E. Olson mentions the effects of secondary consolidation on the pore pressure behavior of sensitive clays. He states that the primary consolidation theory for pore pressure equalization errs on the unsafe side. Dr. Rowe comments on step loading as a means of avoiding gradients of pore pressure during shear.

  • Corporate Authors:

    American Society for Testing and Materials

    100 Barr Harbor Drive, P.O. Box C700
    West Conshohocken, PA  United States  19428-2957
  • Authors:
    • BLIGHT, G E
  • Discussers:
    • Barden, L
  • Publication Date: 1963-9

Media Info

  • Features: Figures; References; Tables;
  • Pagination: p. 173-191
  • Serial:

Subject/Index Terms

Filing Info

  • Accession Number: 00095099
  • Record Type: Publication
  • Files: TRIS
  • Created Date: May 7 1975 12:00AM