The twin-track railway line of the existing 45m long Ittertunnel had a track spacing of 3.5 m. The masonry tunnel, which was constructed in 1874, was in a poor state and required rehabilitation. Faced with the need of having to provide typical track spacing and the need of having to rehabilitate the tunnel, the Austrian Federal Railways asked for a design for demolishing the tunnel with its 20moverburden and to replace it by a cut (rock slope). One of the most important boundary conditions for the project was the reduction of construction time during which the route had to be closed for rail traffic. Therefore, it was necessary to excavate most of the overburden while the railway line was operating. For this reason, numerical calculations were carried out to determine the maximum allowable depth of the open cut for which sufficient safety for railway operation could still be guaranteed. In the course of the construction works, the results of the calculations were continuously compared with measurements so that the extension of the open cut could be optimized.

1.1 Project overview

The railway line between Salzburg and Wörgl (Tyrol) is part of an important railway connection through Austria. Between Hopfgarten and Wörgl, both the existing Itterbridge crossing the river Brixentaler Ache and the 45mlong Ittertunnel with a track spacing of 3.5mhave to be removed due to operational and safety aspects. The objective of the rehabilitation of the route is a continuous upgrade providing a track spacing of 4m in order to increase the capacity of this significant route and to adapt it to the demands of modern railway traffic. Furthermore, the cut had to be prepared as much as possible to ensure that the works to be carried out during the closure could be completed.

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