Finite Element Method (FEM) - Rock Mechanics Based on an Anisotropic Jointed Rock Model - page 274

Figure 10.49 Advancing vault excavation with temporary invert, geometry, overburden
and parameters (Wittke 2000b)

In case 1 shear parameters of c B = 0, φ B = 20°, c J = 0 and φ J = 35° are assumed. In case

2 φ J are reduced to 10° and 20°, respectively, accounting for unfavorable ground

conditions (Fig. 10.49). The assumed tensile strength normal to the discontinuities in
both cases is zero.
Figure 10.50 shows the normal and shear stresses along a horizontal section above
the roof and a vertical section adjacent to the sidewalls of the tunnel computed for
case 1. Accordingly, an arch is formed around the vault so that the greatest part of
the overburden is transferred by the rock mass. This arching effect can be recog-

φ B and