Study of the initiation and propagation of excavation damaged zones around openings in argillaceous rock |
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| Authors: | Alain Millard Jobst Maßmann Amel Rejeb Shin Uehara |
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| Institution: | 1.Commissariat à l’Energie Atomique, CEN Saclay,Gif sur Yvette,France;2.Institute of Fluid Mechanics and Computer Applications in Civil Engineering,Leibniz Universit?t Hannover,Hannover,Germany;3.Institut de Radioprotection et de S?reté Nucléaire,Fontenay-aux-Roses,France;4.Department of Urban and Environmental Engineering,Kyoto University,Nishikyo-Ku,Japan |
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| Abstract: | The study of the creation and evolution of the excavation disturbed zone (EDZ) in argillaceous rocks is a major issue for
the safety of nuclear wastes underground repositories. In this context, the argillaceous Tournemire site has provided a unique
opportunity to study the evolution of the EDZ with time thanks to the existence of three openings of different ages. A thorough
characterization of the EDZ has been conducted by different means such as visual observation, analysis of samples extracted
from drilled boreholes, EDZ permeability measurements, etc. On the basis of these measurements, a conceptual model of the
EDZ initiation and propagation at the Tournemire site has been proposed. In order to validate this model, numerical simulations
of increasing complexity have been carried out. In a first attempt, the response of the rock mass to the excavation phase,
followed by seasonal cyclic variations of temperature and relative humidity inside the opening, has been simulated by means
of a purely mechanical analysis, using a simple elastic material model. The EDZ has been estimated by post-processing the
calculated stress states, using a Mohr–Coulomb failure criterion. The results obtained show that no EDZ could be predicted
unless adopting a low cohesion value for the rock mass. Moreover, the deferred nature of the EDZ formation in Tournemire could
not be reproduced. These limitations have then been suppressed by using a coupled viscoplastic-damaging mechanical model,
the parameters of which have been identified from different laboratory experiments. With this model, a time evolution of the
EDZ could be predicted, but the EDZ pattern could not match the one observed in situ. Finally, in view of the importance of
the hydraulic couplings, unsaturated hydro-mechanical calculations have been carried out to investigate the effect of the
numerous seasonal variations cycles and the resulting shrinkage. |
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| Keywords: | Excavation Argillite Damage Numerical simulation Hydro-mechanical coupling |
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