THE UNIQUENESS OF THE MOHR-COULOMB CONCEPT IN SHEAR FAILURE WITH DISCUSSION

The Mohr-Coulomb concept has been widely used in soil mechanics to define the state of failure in shear. The concept is a combination of two failure criteria. The one relates failure to the extreme critical values of the principal stresses and defines the failure criterion by the envelope of a series of critical stress combinations; the other defines failure as the maximum ratio of the shear stress to the normal stress on the failure or slip plane(s). This concept proves to be valid for granular systems within a certain range of densities. The uniqueness of its applicability in these cases results from the unique physical property of the material, the internal friction of the aggregate. The concept proves to be invalidated in the case of the cohesive soil groups by additional properties of particle systems. The nature of particle bonds is discussed in connection with the recoverable, time-indpendent strains and the permanent, time-dependent strains in the range of flow. The flow properties are established by the strain rate of the material. Both the range of recoverable strains and the range of flow strains are demonstrated by results of "tricell" tests on saturated, remolded clays in the undrained condition. From a discussion of these results there follows a failure criterion related to the elastic behavior of the system. Neither the Mohr-Coulomb concept, nor the condition of plasticity (Von Mises-maximum elastic distortion energy) applies to the shear failure of clays in an undrained condition. Discussion: I.K. Lee emphasizes the significance of the permanent strains below the yield value resulting from the air content of the specimen. He attributes this to the lack of sensitivity of the apparatus. He also contends that the yeild value and the flow limit were obtained by an arbitrary selection of points on a stress- strain curve. Lee's criticisms on these points and others are counter by Geuze. Adel S. Saada discussion contains four distinct parts: (1) Coulomb failure conditions in a stress space; (2) references to investigations of the effect of the intermediate principal stress on the ratio of the extreme values of the principal stresses at failure. Saada discusses these results and arrives at the conclusion that comparison of these results with author's seems difficult. (3) Dr. Saada questions Geuze sources of information concerning the straightness of Mohr circle envelopes. (4) Saada then explores the applicability of Coulomb's law. Ronald F. Scott prefers the yeild surface in the principal stress space as a basis for a failure concept of a granular medium.

  • Corporate Authors:

    American Society for Testing and Materials

    100 Barr Harbor Drive, P.O. Box C700
    West Conshohocken, PA  United States  19428-2957
  • Authors:
    • Gauze, E C
  • Discussers:
    • LEE, I K
  • Publication Date: 1963-9

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Filing Info

  • Accession Number: 00095093
  • Record Type: Publication
  • Files: TRIS
  • Created Date: May 7 1975 12:00AM