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  New yielding elements: layout, performance and aspects of lining design

  The expansion of the current European infrastructure demands the construction of several major and challenging tunnelling projects, such as Gotthard and Ceneri in Switzerland, LyonTurino in Italy/France and Koralm, Brenner and Semmering tunnels in Austria. Due to their length and alignment as “base tunnels”, they encounter various geological formations and tectonical faults under high overburden. This leads to a frequent combination of weak ground and high primary stresses, causing high displacement magnitudes. Loads unsustainable by a stiff support, support damage and costly re-profiling are a usual consequence. Over the past decades, various approaches for creation of ductile tunnel linings have been proposed and sometimes successfully applied. While most systems fulfilled their role of “deforming element”, the imperatives of costs and operational feasibility, as well as their general interaction with shotcrete and deforming ground are seldom discussed. This publication concentrates on a new yielding element type developed at the Institute for Rock Mechanics and Tunnelling, Graz University of Technology. It is based on the venerable Lining Stress Controllers. Their drawbacks such as relatively large amount of machined parts (load bearing pipe, inner and outer leading pipes) have been addressed and removed, while the already favourable load-displacement relationship has been considerably improved. The new element’s interaction with shotcrete lining and its overall influence on the system behaviour is discussed in detail.

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