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Author(s):	Radon i , N.; Schubert, W.; Moritz, B.
Title:	Ductile support design / Zur Auslegung duktiler Ausbauten
Abstract:	Tunnelling in weak ground under high overburden normally results in very high displacements and if a stiff support concept is applied, this requires a very high load-bearing capacity. This has again and again proved to be both an uneconomical and an unsafe concept, leading to extremely high lining thickness and brittle failure behaviour. In order to avoid such problems, ductile support systems have been developed, which allow controlled deformation of the ground and plastic dissipation of excessive stresses accumulated in the lining. For the efficient design of such systems, the aspects of spatial and time-dependent development of displacement, time-dependent properties of shotcrete, and the load-displacement behaviour of the ductile elements have to be harmonized. The requirements posed on a ductile support system are presented, together with simple principles for the determination of ground behaviour boundaries when the application of a ductile support becomes imperative. Recent developments of ductile elements for use with shotcrete linings are described, and their general performance and efficiency are reviewed. A method for calculation of shotcrete stresses using absolute displacement monitoring data is presented, allowing the identification of both inefficient (lining stresses too low and strongly variable in the cross-section) or unsafe (lining stresses almost exceeding the strength) concepts and optimisation during construction. Bei Tunnelvortrieben in Gebirge geringer Qualität und hoher Überlagerung treten in der Regel große Verformungen auf. Bei steifem Ausbaukonzept ist zum Erzielen eines Gleichgewichts eine sehr hohe Ausbaukapazität erforderlich. Die Erfahrung hat gezeigt, dass steife Ausbauten sehr unwirtschaftlich sind, und dass ein Versagen der Schale oft trotzdem nicht verhindert werden kann, was zu Sicherheitsproblemen führt. Zur Lösung des Problems wurden schon vor geraumer Zeit duktile Ausbausysteme entwickelt, die einen kontrollierten Lastaufbau in der Auskleidung erlauben. Zur Auslegung eines solchen duktilen Ausbaus müssen die räumliche und zeitliche Entwicklung der Verschiebungen sowie die zeitabhängigen Eigenschaften des Spritzbetons und die Charakteristik der duktilen Elemente berücksichtigt werden. Eine Methode zur Ermittlung der Spannungen im Spritzbeton aus den Verschiebungsmessungen wird vorgestellt. Dies erlaubt eine einfache Abschätzung der Effizienz verschiedener Systeme sowie eine Optimierung der Auslegung duktiler Ausbauelemente.
Source:	Geomechanics and Tunnelling 2 (2009), No. 5
Page/s:	561-577
Language of Publication:	English/German

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