Civil Engineering Reference
In-Depth Information
Stress concentrations occur at the downstream side of the vault and the upstream side
of the invert. Extensive zones of rock mass adjacent to the cavern walls are unloaded
in the horizontal direction. The shear strength on the discontinuities in these areas is
exceeded. The displacements due to excavation that are calculated in this analysis are
represented in Fig. 22.11. Relatively high horizontal displacements at the cavern walls
take place that reach far into the rock mass on both sides of the cavern.
Figure 22.11
Displacements due to excavation of cavern, Δ
σ
H
= 8.5 MPa (Wittke & Soria 1983)
The steeply dipping master joints, which strike parallel to the cavern axis, form large
three-dimensional rock wedges with the cavern wall. The stability of these was investi-
gated according to limit equilibrium analysis (Section 11.3).
22.6
Monitoring Program
Before excavation of the cavern an extensive program was established for monitoring
the stability during and after construction (Fig. 22.12).
Prior to excavation, multiple-point rod extensometers (Section 17.4.1) were installed
with their heads in the exploration adits and the drainage tunnel for displacement
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