ABSTRACT
From a geomechanical point of view, viscoplastic rock behavior is likely to create significant loads on the lining, which can considerably increase its size. Excessive rock deformations can also challenge the construction method, which affects project costs and planning. A concrete lining covered with a compressible layer is therefore of great interest for tunnel design in viscoplastic rock.
With this new lining concept, the compressible layer absorbs deformations to limit stresses in the outer concrete ring. It thus allows the use of TBMs in strongly time-dependent viscoplastic rock. In the present case, the effectiveness of this solution has been studied for two construction methods: TBM and conventional. Application of the double-layer solution has also been considered for tunnel intersections. This concept has been adapted to the basic design for the galleries in “Cigeo”, the deep geological repository for Intermediate Level (ILW) and High Level (HLW) radioactive waste in France.
