Previous work on the compressive and shear strength and failure characteristics of models of jointed rock is here extended to include measurements of volume change during deformation. A preliminary series of triaxial compression tests was carried out on idealized models of jointed rock prepared from gypsum plaster. Four rectangular prismatic speciman types were tested in triplicate at confining pressures of 50 psi and 250 psi. Axial loads were applied using a closed-loop electro-hydraulic testing system. This permitted control of fracture propgation and investigation of the progressive post-peak break-down of specimens. Volume change was measured by Crouch's met hod which depends on the fact that the volume of a fluid-filled pressure vessel must be adjusted to compensate for lateral expansion of the specimen if the fluid is to be kept at constant pressure. The result of one of the three tests carried out on each specimen and confining pressure is presented and discussed. The present tests and previous uniaxial compression tests on unjacketed specimens show five mechanisms of deformation are operative: brittle slip on joint planes, rotation of individual blocks, collapse of columns of blocks, and post-peak sliding on macroshear surfaces. It is concluded that a wide range of volumetric strain responses are possible in jointed media. Specimens containing multiple inclined joints are weaker, more dilatant and more sensitive to changes in confining pressure than injointed specimens or specimens with joints parallel to the principal stress directions.

Media Info

Subject/Index Terms

Filing Info

  • Accession Number: 00134657
  • Record Type: Publication
  • Report/Paper Numbers: ASCE #11962
  • Files: TRIS
  • Created Date: Jun 23 1976 12:00AM