STRENGTH OF DISCONTINUOUS ROCKS IN DIRECT SHEAR

IF ONE ASSUMES THAT PRIMARY FAILURE OCCURS "IN THE ENFORCED DIRECTION" IN A DIRECT SHEAR TEST, THE MOHR ENVELOPES CORRESPONDING TO SUCH TESTS WILL NOT AGREE WITH THE ENVELOPES FOUND FROM CONFINED PRESSURE TESTS (THE SO-CALLED "TRIAXIAL" TEST). THE AUTHOR RECONCILES THE TWO TESTS BY NOTING THAT INITIAL FAILURE CAN OCCUR LOCALLY IF THE PEAK TENSILE STRESS REACHES THE TENSILE STRENGTH, OR IF THE EFFECTIVE SHEAR REACHES ITS ALLOWABLE LIMIT ON A PLANE OTHER THAN THAT OF "ENFORCED SHEAR." ALTHOUGH NOT EXPLICITLY STATED, THE AUTHOR'S HYPOTHESIS IS IDENTICAL WITH THE REVIEWER'S "MODIFICATION BY TENSION CUTOFFS" OF THE COULOMB-MOHR HYPOTHESIS (AMR 15 (1962), REV. 1293). THE FAILURE HYPOTHESIS IS CONFIRMED BY A NUMBER OF DIRECT SHEAR TESTS USING KAOLIN AND PLASTER OF PARIS. THE TESTS ALSO SHOW THAT, AFTER INITIAL FAILURE ACCORDING TO THE MODIFIED COULOMB-MOHR HYPOTHESIS, FURTHER SHEAR CAN BE CARRIED DUE TO THE INTERGRANULAR FRICTION OF THE CRUSHED MATERIAL, PROVIDED THAT THE APPLIED NORMAL PRESSURE IS SUFFICIENTLY GREAT. THIS RESULT AGREES WITH OROWAN'S INTERPRETATION (MEMOIR 79, BY VON KARMAN (1911) AND BOEKER (1915). AFTER ESTABLISHING HIS BASIC PREMISE, THE AUTHOR APPLIES IT SUCCESSFULLY TO THE CONSIDERATION OF JOINTED (PARTIALLY FAILED) ROCK SPECIMENS. /AMR/

  • Availability:
  • Supplemental Notes:
    • Vol 19, No 2, PP 218-233
  • Authors:
    • LAJTAI, E Z
  • Publication Date: 1969-6

Media Info

  • Serial:
    • GEOTECHNIQUE
    • Volume: 19
    • Issue Number: 2
    • Publisher: Thomas Telford Limited
    • ISSN: 0016-8505

Subject/Index Terms

Filing Info

  • Accession Number: 00235651
  • Record Type: Publication
  • Source Agency: Applied Mechanics Review
  • Files: TRIS
  • Created Date: May 19 1970 12:00AM