New yielding elements for tunnel linings: Design requirements, layout and influence on system behavior

摘要

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