3D anisotropic modelling of deep drifts at the Meuse/Haute-Marne URL
Résumé
The Callovo-Oxfordian (COx) claystone is considered as a potential geological host formation for high-level and intermediate-level long-lived radioactive wastes in France. In 2000, the French National Radio-active Waste Management Agency (Andra) began to build an Underground Research Laboratory (URL) at Meuse/Haute-Marne in order to demonstrate the feasibility of a geological repository in the COx formation. The excavation of galleries at the main level (490 m depth) of the URL, essentially following two directions of in-situ minor (σh) and major (σH) horizontal stresses, shows a significant anisotropy of the excavation induced fractured zones (Armand et al 2014). Different factors contribute probably to this anisotropic re-sponse of the COx to the excavation operation, such as inherent anisotropy of the stiffness and strength, anisotropic initial stresses, excavation induced anisotropic pore pressure repartition, excavation induced instability of quasi-brittle rock, etc. The benchmark “Transverse action” consists in developing numerical models to characterize the COx be-havior and using them for modeling the COx response due to the excavation. In the framework of this benchmark, different models, such as anisotropic elasto-visco-plastic models incorporating with non-local or second gradient modeling, anisotropic elastic-damage model, discrete modeling, have been proposed to successful reproduce the excavation induced fractured zones and the convergence measurement for both drifts drilled following σh and σH (Seyedi et al 2017). However, those models are limited in 2D modeling, which cannot show some 3D effect on the claystone response, for instance: the delay of convergence at different sections, the pore pressure distribution at the drift front, etc. This study focuses on developing a nonlinear model including both the elastic anisotropy and the induced anisotropic plasticity. The basic assumption is that the failure of an anisotropic material is due to either fracturing of weakness planes (ubiquitous joints) and the failure of the rock matrix. The ubiquitous joints are introduced based on the orientation of the induced fractures to reproduce the induced anisotropy. Thus, the rock is composed of a matrix and of potential weakness planes as observed from the biaxial tests under plane strain conditions. The proposed model is implemented in FLAC3D (Itasca 2017). Comparisons with in-situ observations on two drifts within the URL, namely GCS and GED drilled following two directions of σH and σh, were made. Analysis is focused on the excavation induced the fractured zones and the gallery convergence.
Domaines
Sciences de la Terre
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