Finite Element Method (FEM) - Rock Mechanics Based on an Anisotropic Jointed Rock Model - page 264

Slopes
Figure 10.37 shows the representation of the displacements due to excavation in a
rock cut slope with an inclination of 60°, calculated in a two-dimensional FE analysis
(Wittke 1990). The stress-strain behavior of the rock mass is assumed to be isotropic
and elastic. The displacements resulting from unloading caused by the excavated rock
are clearly visible (Fig. 10.37).
Figure 10.37 Displacements of a rock slope resulting from excavation, elastic solution
(Wittke 1990)
The representation of normal and shear stresses calculated along horizontal and
vertical sections in Fig. 10.38 allows us to understand the load distribution within
the slope (Wittke 1990). Considerable shear stresses only appear near the surface of
the slope. At the same time the normal stresses are small in these areas.
If the rock mass is assumed to have two vertical joint sets J1 and J2 and a horizon-
tal set B of bedding-parallel discontinuities with reduced shear and tensile strength,
failure occurs near the surface of the slope as shown in Fig. 10.39, which shows the
principal normal stresses and plastic zone that are calculated after carrying out an
iterative viscoplastic analysis (Wittke 1990). The areas of shear failure on the bed-
ding-parallel discontinuities and areas of tensile failure on the joints J1 are visualized
by means of arrows.