Influence of the geological structure on the displacements measured ahead of the Šentvid tunnel face in small diameter exploratory tunnel; [Einfluss der geologie auf die in einem erkundungsstollen vor der ortsbrust des sentvid-tunnels gemessenen verschiebungen]

The Šentvid tunnel had first been designed as twin tube doublelane tunnel. Later on, the design included the third traffic lanes and connecting ramp tunnels. The underground junctions required the construction of large caverns. A small diameter exploration gallery was excavated in order to find the optimum locations for both caverns in foliated Perm-Carboniferous soft rock conditions and to provide geotechnical model and material parameters for the design. The exploration gallery furthermore enabled displacement measurements ahead of the excavation face of the main tunnel during its construction. This paper presents some details of the exploration gallery and the results obtained from it, showing the results of displacement measurements ahead of the tunnel face and comparisons of the observed displacements ahead of the tunnel face with geological conditions. The tunnel construction won international attention due to its complexity and as an example of best practice in the construction of very large excavations in diverse geotechnical conditions. During the decision making process, an international panel of recognized experts from consulting companies and universities was involved. Later on, the panel regularly monitored the progress of tunnelling works and contributed to the decisions during critical steps of the project. The decision to involve international experts with different experiences and approaches permitted the client to keep the construction risks within acceptable limits. © 2013 Ernst & Sohn Verlag für Architektur und technische Wissenschaften GmbH & Co. KG, Berlin.