Stress-Strain Behavior of Jointed Rock - Rock Mechanics Based on an Anisotropic Jointed Rock Model - page 79

where δ s,D is the shear displacement

on the discontinuities. G res is the equivalent shear modulus for a shear loading parallel
to the discontinuities. Thus, the deformability of the rock mass in general is anisotropic.

δ s,IR is the shear deformation of the intact rock and

Figure 3.24 Influence of discontinuities on the deformability of a rock mass separated by one
discontinuity set (Wittke 2003)

The equivalent elastic constants of a regularly jointed rock mass with isotropic intact
rock and three persistent, orthogonal discontinuity sets were derived by Duncan &
Goodman (1968) under the assumption that the discontinuities have negligible thick-
nesses. As a result, such a rock mass can be described by seven independent elastic
constants. In the special case that the rock mass is separated by only one set of discon-
tinuities the elastic behavior turns out to be transversely isotropic with only three inde-
pendent equivalent elastic constants. Gerrard (1982b) provides extended approaches
describing the elastic behavior of a rock mass consisting of isotropic intact rock having
one, two and three perpendicular sets of joints with not negligible thicknesses. Singh
(1973) derived a similar equivalent continuum model describing the anisotropic elastic
behavior of a rock mass containing orthogonal joint sets with staggered cross joints .
A model for the elastic behavior of a rock mass which is separated by one set of
non-persistent, open discontinuities according to the homogeneous model was devel-