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Caractérisation par la mesure de perméabilité au gaz de l'endommagement mécanique et hydrique dans l'EDZ des argilites du Callovo-Oxfordien

Abstract : On the feasibility evaluation of nuclear waste storage in deep formations, the essential issues are as follows: the stability of underground structures over the reversible period, the influence of cavity excavation on geomechanical properties of the wall rock and the variation of those properties during the different phases while storage realization. The work presented here covers the investigations on the variation of geomechanical proprieties of the approximately 500 m deep MHM in France (mudstone in the departments of Meuse/Haute-Marne), chosen as a potential medium for nuclear waste disposal by ANDRA. In order to measure the very low permeability of mudstone and to observe the dependency on saturation, a special test scheme on measurement of gas permeability has been developed. In the scheme, in situ referenced stresses have been chosen as the stresses acting on the solid matrix. The gas permeability has been determined with both analytical and numerical methods. To estimate the mechanical damage of storage induced by the excavation, laboratory tests on gas permeability have been conducted on samples recovered from different locations situated at different distances from the wall of the main access shaft of the MHM (from 0,1 m to 12,5 m). Results of gas permeability obtained under an isotropic stress of 11 MPa vary between 10-21 and 10-22 m² and do not show significant variations between damaged zones (near the wall) and intact zones (sample located 12 m from the wall). The observations in laboratory tests coincide with in situ damage characterizations. The variation of gas permeability under the cycle of loading and unloading is an order less than the initial value under the isotropic stress. Taking into account the precision of the testing system, this variation is not significant. The oviparous intact samples have been imposed different saturations by salt solutions (with a relative humidity from 25 % to 98 %) to form a cycle of de- and re-saturation. The water retention curve, the kinetic dehydration, the dehydration shrink and wetting crack in samples were measured and analyzed. The coefficient of hydraulic diffusion determined from the evolution of mass is about 5.10-10 m².s-1. The gas permeability (k) under the isotropic stress of 5 MPa increases from 10-21 to 10-18 m² when the imposed relative humidity decreases from 98 % to 25 %. A quasi-linear relation between log(k) and Saturation has been observed and mathematically formulated. The gas permeability as a function of deviator stress has also been studied and the results confirm that the effect of the deviator is not evident, even when the deviator excesses the damage threshold. These results coincide with Zhang's observations on the same rock of MHM. The deformation and the acoustics velocity of samples have been traced during the tests and the microstructure of mudstone has been studied with the method of mercury intrusion. The factors influencing the measure of gas permeability, such as the Klinkenberg effect, the variation of saturation during the tests, the dissolution of gas in water and the water transformation due to the gas pressure, especially the leak tightness of the testing system, have been discussed in the study.
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https://pastel.archives-ouvertes.fr/pastel-00004660
Contributor : Ecole Mines Paristech <>
Submitted on : Friday, January 30, 2009 - 8:00:00 AM
Last modification on : Thursday, April 9, 2020 - 5:08:15 PM
Document(s) archivé(s) le : Thursday, September 30, 2010 - 8:46:33 PM

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  • HAL Id : pastel-00004660, version 1

Citation

Diansen Yang. Caractérisation par la mesure de perméabilité au gaz de l'endommagement mécanique et hydrique dans l'EDZ des argilites du Callovo-Oxfordien. Sciences de l'ingénieur [physics]. École Nationale Supérieure des Mines de Paris, 2008. Français. ⟨pastel-00004660⟩

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