For tunnelling in poor and heterogeneous ground a reliable on-site short-term prediction is required to allow a safe and economical construction. With the use of absolute displacement monitoring data and advanced software for evaluation of the data in combination with a routine update of the geological model a considerable increase in the reliability of the short-term prediction could be achieved. The paper deals with theoretical considerations, numerical studies and case histories from alpine tunnels in heterogeneous rock.
Tunnelbau in schlechtem und heterogenem Gebirge erfordert auf der Baustelle eine verlaessliche Kurzzeitprognose, um ein sicheres und wirtschaftliches Bauwerk gewaehrleisten zu können. Die Verwendung von absoluten Verschiebungsmessdaten und deren Auswertung mit Hilfe von hoch entwickelten Softwareprogrammen in Kombination mit einer laufenden Aktualisierung des Gebirgsmodells ermöglicht eine erhebliche Erhöhung der Verlasslichkeit von Kurzzeitprognosen. Dieser Beitrag beschaftigt sich mit theoretischen Ansatzen, numerischen Modellen und Fallstudien von Tunnelvortrieben in heterogenem Gebirge.
La construction de tunnels dans la montagne heterogène de faible resistance exige un pronostic fiable à court terme sur le chantier, afin de pouvoir garantir un ouvrage sûr et economique. L'utilisation des donnees de mesure de decalage absolues et de leur evaluation à l'aide de logiciels sophistiques en combinaison avec une mise à jour courante du modèle de la montagne permet une augmentation considerable de la fiabilite des pronostics à court terme. Cette contribution presente des approches theoriques, des modèles numeriques et de cas pratiques de progressions de tunnels dans des montagnes heterogènes.
During tunnel excavation a systematic monitoring is important for the determination of support type and quantity, as well as for controlling the tunnel stability. Geodetic methods of absolute displacement monitoring allow determining the spatial displacement vector of each measured point (Rabensteiner 1996). These methods to a large extent have replaced relative displacement measurements in many countries. The increase in information has led to additional possibilities in data evaluation. The plotting of displacement histories, deflection curves, trend lines or displacement vectors in a plane perpendicular to the tunnel axis have become common practice (Vavrovsky & Ayayadin 1998, Vavrovsky 1998, Schubert & Vavrovsky 1994, Heim & Rabensteiner 1995, Vavrovsky & Schubert 1995, Schubert et al 2002).
The evaluation of data gained from the excavation of tunnels constructed in Austria showed, that the ratio between radial and longitudinal displacement varied in a wide range. Matching the observed phenomena with the geological documentation, it was found that deviations of the ratio appeared when zones of different deformability were approached with the excavation (Schubert 1993). To verify the hypothesis, numerical 3-D simulations have been performed. The results showed that changing rock mass conditions ahead of the tunnel face clearly influence the displacement vector orientation (Schubert & Budil 1995, Steindorfer & Schubert 1997, Steindorfer 1998). To quantify the influence of weak zones on stresses and displacements, further research has been conducted (Grossauer 2001).
For safe and economical tunnelling through heterogeneous rock mass conditions a continuous adaptation of the support and excavation concept is required.
