Civil Engineering Reference
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22.8
Support of the Cavern Walls
Further stability analyses accounting for the steeply dipping discontinuities of D3 and
D3', as well as high horizontal in-situ stresses normal to cavern axis, led to a consid-
erable amount of the required support to stabilize the cavern walls during the further
excavation of the cavern.
The support of the cavern walls consists of a combination of reinforced shotcrete, 5 m
long rock bolts and 15 - 20 m long tendons. The working loads for the rock bolts and the
tendons were 0.1 MN and 0.63 MN, respectively. The 25 cm thick shotcrete membrane
was reinforced by two layers of square wire mesh. Rock bolts and tendons form a grid
with a spacing of 1.5 m in horizontal and vertical directions. The average pre-stressing
load of the cavern walls thus amounts to 0.1 MPa (Fig. 16.23).
The excavation of the cavern was carried out stepwise in benches. Shotcrete, bolts and
tendons were installed step by step, parallel to the excavation of the benches. The shot-
crete and the bolts were placed immediately after part of the bench had been excavated,
whereas the installation of tendons followed with some delay. Figures 22.16 - 22.18
show photos of different stages of construction.
Figure 22.16
Excavation and support of benches (Soria & Wittke 1985)
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