Stress-Strain Behavior of Jointed Rock - Rock Mechanics Based on an Anisotropic Jointed Rock Model - page 89

3.4.3 Combination of the Homogeneous Model with Discrete Models of
Individual Discontinuities
The homogeneous model allows us to consider sets of discontinuities in stability ana-
lyses with relatively little effort, taking into account the anisotropy of deformability
and strength caused by the discontinuities. The application of the homogeneous model
leads to reliable results if the dimensions of the engineering structure are large in com-
parison to the rock blocks that are bounded by the individual discontinuities; that is,
the mean spacing s of discontinuities must be small compared with the characteristic
dimension D of the tunnel, slope or dam. This condition can be considered as fulfilled
if the spacing of the discontinuities is smaller than 1/8 to 1/10 of the characteristic
dimension of the considered structure. Master joints and faults of large spacing must
therefore be modeled discretely (Fig. 3.28).
Figure 3.28 Spacing s of discontinuities in comparison with the characteristic dimension D of
engineering structures (Wittke 1990)
Discrete models of individual discontinuities can be coupled with the homogeneous
model by modeling large joints and faults discretely, while the influence of smaller joints
and discontinuities on strength and deformability is taken into account using the homo-
geneous model.
As an example, Fig. 3.29 shows a three-dimensional finite element mesh for a tun-
nel. This mesh was used to simulate the driving of a tunnel through a steeply dip-
ping fault zone with a thickness of 8 m, which intersects the tunnel axis at an angle