Civil Engineering Reference
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22.7
Mapping and Monitoring Results during Excavation of Vault
The cavern's vault was excavated in three steps. In the first step, the exploration adits
were enlarged to a height and width of 6.5 m, thus forming the middle section of the
vault. In two further steps the vault was then excavated to its full width (Figs. 22.13 -
22.15). In parallel, the systematic support was installed as described above. In addition,
15 - 20 m long tendons were placed locally for the support of large rock wedges.
Figure 22.13
Support of vault (Soria & Wittke 1985)
During excavation, extensive geotechnical mapping was conducted. The statistical eval-
uation of the mapping (Section 13.9.2) confirmed that the discontinuities of sets Sch
and D1 appear most frequently and are clearly visible (Fig. 22.14). As expected, the
discontinuities of D2 and D4 appear less frequently. However, steeply dipping discon-
tinuities of sets D3 and D3', striking parallel to the cavern axis, were mapped more fre-
quently than expected (Fig. 16.21). These are relatively planar and quite often have thin
coatings of cohesive material. The orientations of D3 and D3' were realized as rather
unfavorable for the stability of the cavern.
Figure 22.15 shows average values of relative displacements due to excavation moni-
tored by means of convergence measurements in the middle section and the complete
vault, respectively. Thereby, the measured displacements were assigned equally to op-
posing pins. The monitored displacements, however, were too small to gain improved
information with regard to the rock mass modulus and the in-situ stress state.
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