The stability of underground structures is the most important and complicated concept in rock engineering. There is no explicit way to evaluate the stability of a structure in rock. For this reason implicit methods accounting for the stability through exploration and analysis of rock mass structure are discussed. This includes properties of the rock mass, support measures and excavation/construction technology, possible modes of structural behaviour and accumulating experience and engineering judgment. The significance of in situ measurements, rock mass and structure monitoring and back analysis is also emphasized.


La stabilite de constructions souterraines est Ie concept Ie plus important et complique en ingenierie de la roche. II n'ya pas de manière explicite pour evaluer la stabilite d'une construction dans la roche. Pour cette raison, ce rapport discute des methodes implicites qui tiennent en compte de la stabilite par l'exploration et l'analyse de la structure de la masse rocheuse. Ceci inclut les proprietes de la roche, les mesures de soutènement et la technologie de l'excavation/construction, l'operation des modes possibles de construction et l'experience accumulee et Ie jugement de l'ingenieur. La signification des mesures in situ, la surveillance de la masse rocheuse et de la construction et l'analyse inverse sont aussi soulingnees.


Die Stabilitat unterirdischer Felsbauten ist das wichtigste und schwierigste Konzept innerhalb des Felsbaus. Es gibt keine direkte Methode, urn die Stabilitat von unterirdischen Felsbauten zu bestimmen. Aus diesem Grund werden implizite Methoden diskutiert, welche Voruntersuchungen und Analysen des Felsbauwerkes umfassen. Diese beinhalten Felseigenschaften, Verstarkungsmaβnahmen, Ausschachtungs- und Baumethoden, unterschiedliche Betriebsverfahren, gesammelte Erfahrungen und technisches Verstandnis. Auf die Bedeutung von in situ Messungen, Zustandsueberwachung des Felsens und des Bauwerkes und Rueckrechnungen wird ebenfalls eingegangen.


The stability of underground structures is the most important and complicated concept in rock engineering. There is no explicit way to evaluate the stability of a structure in rock. Referring to the preamble above, it can be said that our knowledge of this matter is really limited. The structure may be considered stable at a given point in time, but fail to comply with a required mode of operation shortly afterwards due to the loss of stability. So, when we speak about the stability of an underground structure, we usually have in mind either prediction of stability for some period of time, or physical evidence of its existence at a given moment as a source for further predictions. In this respect, the best we can do is to refer to the concept of stability in terms of time and probability. Some uncertainty exists in the definition of the concept itself: stability may be understood as a local feature when failure of some structural elements does not lead to the cave-in of the structure as a whole; or as an overall attribute opposite to complete collapse. There are many natural openings in rock which have been stable for thousands of years, and manmade underground structures which have remained stable for centuries, i.e., for time periods which, in recent engineering practice, relate to caverns for underground radioactive waste disposal facilities. The last decades of monitored performances have provided us with many valuable experiences of the creation of underground structures in rock for mining and construction activities. Almost fifty papers were submitted and accepted for Theme 3 of this Symposium. One is actually related to soil mechanics and not rock mechanics, but otherwise adds to our understanding of the concept of stability. The authors of the papers included in the Proceedings of the Symposium will be referenced herein by the name(s) only. All other publications will be referenced in accordance with normally adopted procedure, including date.

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