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smooth and exhibit isolated slickensides (Section 2.6). A relatively large friction angle
of
φ
Sch
= 50° was estimated because of the undulating surfaces (Fig. 22.9).
The joints of D1 and D2 have mean orientations of
α
D1
= 110° and
β
D1
= 45°, and
α
D2
= 20° and
β
D2
= 90°. These discontinuities are somewhat less uneven and were con-
sequently assumed to have a slightly smaller friction angle of
φ
D1/D2
= 45° (Fig. 22.9).
The spacing of the discontinuities of all three sets is in the same order of 1 - 1.5 m. Both
cohesion c and tensile strength
σ
t
of the discontinuities were generally assumed to be
zero (Fig. 22.9).
The master joints because of their large extent need to be considered as individual ele-
ments (Section 2.7.3) and are not included in the model illustrated in Fig. 22.9.
22.5
Stability Analyses
The stability analyses for the cavern were carried out according to the FEM, using
two-dimensional computation sections. As an example, Fig. 22.10 shows the principal
normal stresses and zones of shear failure on discontinuities after excavation of the
cavern as a result of a stability analysis, in which a maximum horizontal tectonic stress
normal to the cavern axis of
Δσ
H
= 8.5 MPa was accounted for.
Figure 22.10
Principal normal stresses and plastic zones after excavation of cavern, Δ
σ
H
= 8.5 MPa
(Wittke & Soria 1983)
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