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The Sedrun section in the middle of the Gotthard Base Tunnel was critical in terms of scheduling and without doubt the section with the most complicated logistics. The article gives an overview of the complex overall construction measures and describes in detail the geotechnical and logistical challenges that had to be overcome. Der Teilabschnitt Sedrun im Zentrum des Gotthard-Basistunnels war zeitlich kritisch und zweifelsohne der logistisch komplizierteste Bauabschnitt, die bautechnischen Anforderungen lagen auf Weltrekordniveau. Der Beitrag gibt eine Übersicht über die komplexe Gesamtbaumaßnahme und beschreibt die zu bewältigenden geotechnischen und baubetrieblichen Herausforderungen im Detail. [ABSTRACT FROM AUTHOR]

Squeezing intensity in tunnelling often varies over short distances, even where there is no change in the excavation method or lithology. Reliable predictions of the ground conditions ahead of the face are thus essential to avoid project setbacks. Such predictions would enable adjustments to be made during construction to the temporary support, to the excavation diameter and also to the final lining. The assessment of the behaviour of the core ahead of the face, as observed by means of extrusion measurements, provides some indications as to the mechanical characteristics of the ground. If the ground exhibits a moderate time-dependent behaviour and the effects of the support measures are taken into account, the prediction of convergence is feasible. If the ground behaviour is pronouncedly time-dependent, however, convergence predictions become very difficult, because core extrusion is governed by the short-term characteristics of the ground, which may be different from the long-term properties that govern final convergence. The case histories of the Gotthard Base Tunnel and of the Vasto tunnel show that there is a weak correlation between the axial extrusions and the convergences of the tunnel. By means of the case histories of the Tartaiguille tunnel and Raticosa tunnel, it is shown that to identify potentially weak zones on the basis of the extrusion measurements, careful processing of the monitoring data is essential: the analysis of the data has to take account of the effects of tunnel support and time, and has to eliminate errors caused by the monitoring process. [ABSTRACT FROM AUTHOR]