Page 52 - ILLS Annual Report 2018

MATERIALS SCIENCE
Eleni Stavropoulou. Greek
University Grenoble Alpes, 3SR, France
‘My work focuses on the mechanical behaviour of interfaces of geomaterials, these being the weakest points in terms of mechanical resistance in geotechnical structures. The study of interfaces involves understanding not only the materials
composing them (rock, concrete, etc.), but also their eventual hydro-thermo-chemo mechanical interaction.’
Liquid water uptake in unconfined Callovo-Oxfordian clay rock studied with neutron and X-ray imaging
Neutron reflectometer and neutron-imaging instrument D50
The Callovo-Oxfordian clay rock (COx)
is studied in France for its use in the disposal of radioactive waste, because of its extremely low permeability. This host rock is governed by a hydromechanical coupling of high complexity. This experimental study explores the mechanisms of water uptake in small, unconfined, prismatic specimens of COx. Water uptake is monitored using both X-ray tomography (3SR Lab) and neutron radiography (ILL) for the first time, the combination of these imaging techniques allowing material deformation and water arrival respectively to be quantified.
AUTHORS
E. Stavropoulou (University Grenoble Alpes and Andra Agency, France) E. Andò (University Grenoble Alpes, France)
A. Tengattini (ILL and University Grenoble Alpes, France)
M. Briffaut, F. Dufour and D. Atkins (ILL)
G. Armand (Andra Agency, France) ARTICLE FROM
Acta Geotech. (2018)—doi: 10.1007/s11440-018-0639
REFERENCES
[1] C. Zhang and T. Rothfuchs, Appl. Clay Sci. 26 (2004) 325
[2] G. Armand, F. Bumbieler, N. Conil, R. de la Vaissière, J.-M. Bosgiraud
and M.N. Vu, J. Rock Mech. Geotech. Eng. 9 (2017) 415
[3] H.G. Montes, J. Duplay, L. Martinez, S. Escoffier and D. Rousset,
Appl. Clay Sci. 25 (2004) 187
[4] A. Tengattini, D. Atkins, B. Giroud, E. Andò, J. Beaucour and
G. Viggiani, ICTMS2017 (2017)
The management of radioactive waste is an important environmental issue. In eastern France, the French National Radioactive Waste Management Agency (Andra) is studying the behaviour of a deep geological repository in Callovo-Oxfordian clay rock (COx). The permeability of the Callovo-Oxfordian stratum is extremely low; it is, however, governed by complex thermo-hydro-mechanical behaviour, which is continuously under investigation in both laboratory and in-field experiments [1].
During the operation phase, tunnels are excavated and then ventilated until they are finally closed. In specific sections, swelling clay such as bentonite is positioned in between two concrete plugs in order to seal the tunnel
and apply pressure to the rock wall in sections where the concrete lining is removed [2]. The study of the mechanical behaviour of the concrete/COx interface in the laboratory requires representative and reproducible concrete/COx samples to be created under controlled conditions.
Figure 1
Selected in situ images acquired during imbibition for two clay rock samples. X-ray data are presented as a vertical slice in the middle of the specimen, whereas neutron radiographs are averaged together in 5-min intervals in order to match the X-ray tomography times.
ANNUAL REPORT 2018
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Neutron radiographies
high
wet matrix
dry matrix low
highinclusions
matrix
cracks low & air
Vertical slices through 5m X-ray tomography reconstructions
X-ray attenuation
Neutron attenuation
Normal