Etude des ouvrages de stockage souterrain de déchets de haute activité ULg – équipe de géomécanique SCK – CEN / ULg 02/09/10

2 ULg Geomechanics team R. Charlier, Pr. O, chairman SAC Praclay F. Collin, Chercheur Qualifié FNRS S. Levasseur et B. François, Chargés de Recherche FNRS A. Dizier (FRIA), P. Gérard, S. Delvoie, B. Cerfontaine, doctorants JP Radu, F. Pascon, ingénieurs de recherche Lab’s team 4 people.

3 Research themes Geomechanics Rupture Thermo-hydro-mechanical coupling Numerical modelling : LAGAMINE code Experimental investigations

4 Stockage géologique profond: différents concepts  2 options  Forages profonds creusés à partir de la surface  Enfouissement dans des mines

5 The PRACLAY in-situ experiment comprises three tests: the “Gallery&Crossing Test”, the “Seal Test” and the “Heater Test”

6 Underground nuclear waste disposals Rock behaviour around disposals Mechanical behaviour Fluid transfers Heating / cooling effect Numerical simulation Clayey rocks : URL Mol, Bure, Mont Terri

7 Fractures observed at Bure and HADES COX BC Slickenside

8 Fracture traces observed on the excavation walls COXBC

9 Fractures pattern observed along borehole cores in COX and BC COX BC

10 Typical herringbone pattern observed during excavation in COX and BC COXBC ~4 m

11 DZ as a preferential transport pathway DZ : damaged zone, i.e. zone strongly modified by the mechanical loading Mechanical loading : excavation, heating, gas generation Transport pathway : fluid (liquid and gas) flow as radionuclide advective transport

12 Geomechanics coupled to fluid flow : geomechanics know-how Fluid pressure direct influence on mechanical state of stress : Terzaghi / Bishop effective stress, net stress + suction But few effect of geomechanics on fluid flow, unless changes in permeability Damage, permeability and stress distribution studies in Excavation Damaged Zone needed

13 DZ as a preferential transport pathway Describe the Damaged Zone Damage as a rather general concept Transport pathway : considered based solely on fluid flow Basic question : what is the permeability evolution related to “damage”

14 Chip formation : experimental results (LML) and numerical modelling (ULg)

15 Essais sur cylindre creux – LMR EPFL – V. Labiouse

16 Essais sur cylindre creux – LMR EPFL – V. Labiouse

17 Comparison between experimental data and modelling (at the end of the second phase): Experimental data show anisotropy MODÈLE NUMÉRIQUE / EXPÉRIMENTAL Radial evolution of the radial displacement

18 Modélisation de la localisation des déformations – ¼ de cylindre creux avecet Déplacements Localisation des déformations de cisaillement Déplacement maximum = 3.2 mm 7 mm 42 mm

19 EDZ permeability distribution Horizontal drilling Vertical drilling Coupling : Mechanic – Permeability (Andra, G. Armand) Changes of permeability : 5 order of magnitude

20 EDZ permeability distribution Structural and hydrogeological characterisation of the excavation- disturbed zone in the Opalinus Clay (Mont Terri Project, Switzerland) Paul Bossart, Thomas Trick, Peter M. Meier, Juan-Carlos Mayor Applied Clay Science 26 (2004) 429– 448 Changes of permeability : 2 order of magnitude

21 Research structure 1.Damage zone observations 2.Damage zone simulations 3.Evidences of permeability evolution in DZ 4.Constitutive equations for permeability evolution 5.Anisotropy considerations 6.Numerical simulations of coupled HM problems with permeability evolution

22 Conclusions Permeability may be strongly modified in EDZ : in situ evidences. Some models relating permeability to strain or damage exist or are in development. Numerical modelling is complex but possible. Few simulations have been done.

23 Conclusions : Open questions Lab evaluation of permeability evolution with strain / damage remains difficult. Nevertheless progresses are ongoing. Strain and micro fissure localisation effect on permeability needs to be better understood. Strong need of model validation both on lab and in situ experiments.

24 Collaborations Euridice SCK CEN ONDRAF ANDRA NAGRA University : Barcelona, Lausanne, Paris, Grenoble, Lille, etc…

25 European projects CATSIUS CLAY (benchmarks : clay modelling) TIMODAZ (thermal effects and Excavated Damage Zone) FORGE (gas transfers)

26 Future cooperation with SCK-CEN FORGE project : numerical simulation of gas flow – Mol in situ test Gas flow in EDZ … Anisotropy and elastoplastic behaviour Mol geological history and fracture prediction Doctoral thesis ?