Rock parameters and support details for power caverns are compared with earlier recommendations for tunnel support using rock mass quality indices. New diagrams are proposed for cavern wall support. Estimates of economical cavern sizes and admissible rock stresses are discussed on the a.m. basis. Observed cavern deformations and recommended grids for monitoring installations are presented.


Les paramètres des roches ainsi que les dispositifs de soutènement de centrales souterraines preconises sont compares à des recommandations anterieures ayant trait au soutènement de tunnels et utilisant des indices sur la qualite des masses rocheuses. De nouveaux diagrammes afferents au soutènement des parois des cavernes sont proposes. Des estimations sur les dimensions economiques des cavernes ainsi que sur les tensions rocheuses sont analysees de manière analogue. Les deformations des cavernes observees et les espaces recommandes entre les instruments de mesure sont egalement mentionnes.


Felsparameter und Sicherungsvorschlage fuer Krafthauskavernen werden mit frueheren Empfehlungen fuer den Tunnelausbau verglichen, die Felsqualitatsindizes benutzen, Neue Diagramme werden fuer den Ausbau der Kavernenwande vorgeschlagen. Auf der gleichen Basis werden Schatzungen fuer wirtschaftliche Kavernenabmessungen und zulassige Gebirgsspannungen diskutiert. Beobachtete Kavernenverformungen und empfohlene Abstande von Meβeinrichtungen werden angegeben.


The design of powerhouse caverns requires extensive efforts for investigation, stability analysis and construction monitoring which will only be exceeded by design of underground waste storage caverns. The stepwise design process shows the requirement for strongly increasing reliability of parameter evaluations with growing chances of realization. The presented approach is expected to be useful at least for earlier design stages and to be confirmed in later design stages:

  • Intact rock parameters can be modified to rock mass parameters after careful evaluation of joint persistence and spacing in detailed mappings of investigation admits.

  • Rock mass classification can be used to decide on the economy of planned cavern size, on the possible construction under given in situ stresses and the admissible deformations of the cavern contour.

  • Previous examples of cavern support can be considered before numerical modelling of excavation and support.

The work described was conducted from a consultant's point of view. Some simplifications which may seem too crude for research purposes were inevitable. This approach was largely influenced by the report of BARTON et al. (2,1980) and the report of KAISER (9,1986) in which the construction risks for caverns were estimated by means of rock quality indices. The safety and economy of cavern construction can be significantly improved by appropriate modelling of the rock mass behaviour and investigating necessary support upgrading due to parameter changes well in advance of actual construction. Great importance has to be paid to trigger values of partial and total deformations of cavern excavation contours. This requires stepwise modelling of excavation and reliable monitoring of later representative rock deformations. Sometimes, inadequate investigations in earlier design phases have limited availability of rock mass parameters and prohibited stability analyses and the possible design input that can be gained from them. Necessary design decisions have then been postponed which has caused even more time consuming design changes and contract negotiations at a later date. A procedure is presented herein for using empirical support design rules based on simple modelling of rock mass behaviour and based on published and unpublished experience of the design and construction of existing power caverns. Evaluation and comparison of rock mass classification results are based on references 1 and 3. The classification was performed for 100 power caverns and the title for this paper was chosen accordingly.

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