How rock samples can be representative of in situ condition: A case study of Callovo-Oxfordian claystones

Conil, Nathalie; Talandier, Jean; Djizanne, Hippolyte; Vaissière, Rémi de La; Righini-Waz, C.; Auvray, Christophe; Morlot, Christophe; Armand, Gilles

doi:10.1016/j.jrmge.2018.02.004

Cited by 44 publications

(23 citation statements)

References 13 publications

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“…1 (triangles), together with data collected from other studies (dots) available in the literature on the same material. Combining these data with those presented by Conil et al (2018), it appears that the in-situ water content of COx ranges between 2 and 9 % and the void ratio between 0.15 to 0.25 and the material is considered saturated (Gs=2.7).…”

Section: Tested Materialssupporting

confidence: 56%

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Self-sealing capacity of argillite samples

et al. 2019

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Many countries are currently facing the issue of finding a proper solution to store radioactive wastes coming from nuclear energy production plants. The possibility to store them in underground tunnels is largely considered and investigated. In France, Andra (Agence Nationale pour la gestion des Déchets Radioactifs) selected the Callovo-Oxfordian rock clay (COx) situated in the Meuse/Haute Marne site (France) between 400 and 600 m depth as possible host rock deposit. The excavation of the storage tunnels is expected to create a fractured zone around galleries. However, the factures will be then gradually re-saturated by the underground water coming from the surrounding rock mass and the fractures are expected to self-seal in contact with water, thanks to the swelling potential of COx. The capacity of self-sealing of COx, i.e. closing of fractures after water contact and possibly restoring of hydraulic permeability, is thus of primary interest for the safety of the storage system with respect to water, gas and solutes transport. In the work presented in this paper, the self-sealing behaviour of the COx argillite was investigated through x-ray tomography. The tested samples show significantly different responses depending on the zone where they have been collected on site. The results of mineralogical analyses (x-ray diffraction) are used to understand the observed phenomena.

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Section: Tested Materialssupporting

confidence: 56%

“…being richer in carbonates and the U.T. being a transition between the two others (Conil et al, 2018). In this study, samples coming from the U.A.…”

Section: Tested Materialsmentioning

confidence: 98%

Self-sealing capacity of argillite samples

et al. 2019

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“…220 km ESE of Paris), the French National Radioactive Waste Management Agency (ANDRA) operates a URF to explore the feasibility of Callovo-Oxfordian Clay to host radioactive waste (Armand et al, 2013). There, the roughly 160 Ma old claystone is encountered in a depth between ~ 417 -547 m (Gaucher et al, 2004): Its mineralogical composition (26 -42 % phyllosilicates; 27 -42 % carbonates; 24 -30 % tectosilicates -mostly quartz) is comparable to the one of Boom Clay (see Table 1; Gaucher et al, 2004;Conil et al, 2018). Opposed to Boom Clay, Callovo-Oxfordian Clay is heavily cemented by secondary (i.e.…”

Section: Boom Clay and Callovo-oxfordian Clay: Two Endmembers For Thmentioning

confidence: 99%

Grain-scale deformation mechanisms and evolution of porosity in experimentally deformed Boom Clay

Schuck¹,

Desbois²,

Urai³

2019

Preprint

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Boom Clay is a soft, slightly overconsolidated, uncemented claystone considered as potential host material for a radioactive waste repository in Belgium. We studied the evolution of microfabrics in samples which were shortened to 20% bulk strain in consolidated-undrained (CU) triaxial experiments at effective confining pressures of 0.375, 0.750 and 1.5 MPa, respectively.Results show a geomechanical behavior in agreement with previous studies, with total strain partly localized in shear zones and partly diffuse outside the shear zones. The diffuse strain is accommodated by pore compaction without any discernible microstructural changes compared to the starting material. In the shear zones, pore collapse reduces SEM-visible porosity and further deformation mechanisms within the shear zones are particulate flow (grain boundary sliding), particle rotation and the formation of microcracks. There is no evidence for comminution of quartz and feldspar grains. Strain localization on macro- and mesoscale is governed by viscosity contrasts between harder clasts (e.g. quartz and feldspar) embedded in a soft, porous, phyllosilicate-rich matrix.Our microstructures are comparable to those observed in Boom Clay deformed naturally and in the Excavation Damaged Zone of the Underground Research Facility. This suggests that our results are representative of Boom Clay’s geomechanical behavior at the microscale.

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“…For sample preparation, a fresh claystone core was used (EST57917, h = 300 mm, d = 120 mm) extracted from a depth of 490 m. The samples have been cut to a cylindrical shape (h = d = 20 mm) using a wire saw in neighbouring locations within the core. The average water content ( m water m dry ) has been measured after drying at 105 • C for at least 24 h equal to 6.54 %, a value a bit lower than what has been reported by Conil et al (2018). This paper presents the analysis of the first sample of a series, the vertical axis of which is parallel to the bedding plane of the claystone.…”

Section: Sample Preparationmentioning

confidence: 84%

“…This additional term allows the exploration of the influence of the change of degree of saturation during swelling. Taking φ 0 as 17.5 % from Conil et al (2018), S can be evaluated, and lines for ±3 % are shown in Figure 8.…”

Section: Measurement Of Local Greyscale Variationsmentioning

confidence: 99%

Dynamics of Water Absorption in Callovo-Oxfordian Claystone Revealed With Multimodal X-Ray and Neutron Tomography

et al. 2020

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The Callovo-Oxfordian claystone is a material with notoriously complex hydro-mechanical behaviour. Combined neutron and x-ray tomography modalities are used for the first time to characterise the dynamics of water absorption in this material by comparing material deformation as well as water arrival. Exploiting recent work on multimodal registration, neutron, and x-ray datasets are registered pairwise into a common coordinate system, meaning that a vector-valued field (i.e., neutron and x-ray reconstructed values) is available for each timestep, essentially making this a 5D dataset. The ability to cross-plot each field into a joint histogram (an inherent input into the registration) allows an improved identification of mineral phases in this complex material. Material deformation obtained from the application of Digital Volume Correlation on the x-ray timeseries data is locally compared to changes in water content available from the neutrons, opening the way toward a quantitative description of the hydro-mechanics of this process.

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How rock samples can be representative of in situ condition: A case study of Callovo-Oxfordian claystones

Cited by 44 publications

References 13 publications

Self-sealing capacity of argillite samples

Self-sealing capacity of argillite samples

Grain-scale deformation mechanisms and evolution of porosity in experimentally deformed Boom Clay

Dynamics of Water Absorption in Callovo-Oxfordian Claystone Revealed With Multimodal X-Ray and Neutron Tomography

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