New Numerical Modelling of the Mechanical Long-term Behaviour of the GMR gallery in ANDRA's Underground Research Laboratory

Abstract : This paper deals with a new macroscopic numerical modelling of the mechanical long-term behaviour of ANDRA's underground research laboratory. The study focuses on the GMR gallery, oriented along the minor horizontal principal stress and located at the main level 490m deep. The simulations are made using the finite element method (FEM). Convergence measurements in this gallery exhibit an important dissymmetry between the vertical and horizontal directions, as well as a significant time effect in the vertical trend. In attempts to both understand the phenomena that lie beneath such dissymmetry and reproduce the experimental data, a modification to Lemaître's creep law has been proposed. The new viscoplastic law takes into account the following aspects: rock transverse isotropy, creep behaviour and rock expansion. The excavation history of the GMR gallery has also been considered in the numerical modelling. The numerical results are very satisfactory for the GMR drift. However, the mechanisms of anisotropic shear and expansion on which the new law is based do not lead to an accurate reproduction of the data measured in the galleries oriented in the perpendicular direction. Therefore, a thorough insight into the mechanical behaviour of the rock mass and into the proposed new law is needed before the latter can be applied to the Callovo-Oxofordian layer.