ABSTRACT
Compressible linings can be the solution for deep underground tunnels with differed mechanical behaviour. That is the case for the geomechanical response to excavation prevailing in the mid-level of the Callovo-Oxfordian (COx) claystone formation where Cigéo (the French Deep Geological Repository) will be implemented. In order to optimize the lining thickness, Andra studies different compressible solutions. An ongoing qualification process was set out, starting from the qualification at the product properties level until reaching the implementation phase in an experimental tunnel. The article presents the ongoing program, where qualification is twofold: scientific and technological. The solution concept has to prove that elasto-plastic behaviour remains uncompromised in a lining at full scale at while answering technological requirements at the different conception stages. A higher level of robustness was proposed by Andra and its partner University Gustave Eiffel (France), using a surface “accelerator” ring loading test system. This unique experimental device allows different loading simulations of long-term Cigéo interface behaviour, on different compressible full rings solutions (6m diameter). These loading tests confirm the long-term compressible behaviour of the rings and provide data to consolidate specific behavioural law modelling. The positive outcomes of this technical process will provide “elements of proof” of the robustness of the compressible lining designs forecast for Cigéo.
