Stress-Strain Behavior of Jointed Rock - Rock Mechanics Based on an Anisotropic Jointed Rock Model - page 61

Figure 3.12 Different modes of shear failure of a regular sawtoothed discontinuity and
corresponding bilinear and discontinuous failure criteria

τ res * of uneven or rough persistent discontinuities, a
distinction must also be made between shear failure due to sliding and that caused
by shearing off the asperities. At low normal stress

As regards the residual strength

σ ns , no reduction of strength
during shearing takes place and the residual friction angle

σ n <

φ D * may be considered to

φ D * can

be equal to φ D . At high normal stress σ n ≥ σ ns , the residual friction angle

φ IR' * of the sheared off rock material
(Fig. 3.12, lower). As a result, the residual shear strength of an uneven or rough discon-
tinuity can be described by a discontinuous failure criterion (Wittke 1990):

be assumed equal to the residual friction angle