Experimental study of the hydromechanical coupling in argillaceous rocks: the example of Boom clay

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Winifred Katrina Scott
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1 Experimental study of the hydromechanical coupling in argillaceous rocks: the example of Boom clay Financial support of the EU: SELFRAC scientific project DIGA network Cécile Coll (GeomaC, Liège) Jacques Desrues (L3S, Grenoble) Pierre Bésuelle (L3S, Grenoble) Cino Viggiani (L3S, Grenoble) Pascal Charrier (L3S, Grenoble) W(H)YDOC 05 (23-25 Nov. 2005) 1

2 Outline Framework HM coupling in argillaceous rocks Boom clay : main properties Experimental techniques Experimental results Conclusions & Perspectives W(H)YDOC 05 (23-25 Nov. 2005) 2

3 General framework Storage of nuclear waste in deep geological formations engineered barrier storage natural barrier Safety condition : to preserve environment of internal radioactivity W(H)YDOC 05 (23-25 Nov. 2005) 3

4 Natural barrier (clay, crystalline rock, salt) Properties : high dimensions (100 aine meters) homogeneous no seismic activity very low permeability Function : avoid fluid circulation (radionucleides) from the waste disposal to the natural medium Issue : excavation of underground structures EDZ (Excavated Disturbed Zone) state of stress changes fissuration temperature and moisture changes W(H)YDOC 05 (23-25 Nov. 2005) 4

5 Natural Barrier Performance? Characterisation of the EDZ C-T-H-M coupling processes H-M coupling Argillaceous formation: Boom Clay (Mol, Belgium) Permeability evolution with time due to damaging UE project SELFRAC (Self Healing of Fractures, ) W(H)YDOC 05 (23-25 Nov. 2005) 5

6 HM coupling in argillaceous rocks great complexity low to very low permeability (<10-12 m/s) saturation drainage/pore pressure homogenisation clay particles/fluid : strong interactions clay particles arrangement multiscale porosity (infra macro) consolidation swelling flows (kinetics, amplitude) W(H)YDOC 05 (23-25 Nov. 2005) 6

$clay fraction > 55% (Mol, Belgium) w n = 25% n = 39% (agregates)$ k n = 2-4.

healing/sealing not cimented q c = 2 MPa c < 300 kpa ϕ = 18-24

7 Boom clay (soil type) HADES Underground Research Lab. clay fraction > 55% (Mol, Belgium) w n = 25% n = 39% (agregates) k n = m 2 highly plastic Second shaft prone to swelling self healing/sealing not cimented q c = 2 MPa c < 300 kpa ϕ = Connecting gallery Test Drift First shaft URL Bastiaens W., Euridice report , 2003 (z = 223 m) W(H)YDOC 05 (23-25 Nov. 2005) 7

8 Experimental Objectives HM behaviour Isotropic / Deviatoric stress permeability Strain localisation - permeability experimental study on natural, intact & saturated specimens CD Triaxial tests (detection of strain localisation) Permeability measurement W(H)YDOC 05 (23-25 Nov. 2005) 8

9 Experimental techniques Experimental installation triaxial apparatus: HP cell + pressure generators local measurements of axial & radial displacements (LVDTs) system of temperature control Permeability measurement procedure W(H)YDOC 05 (23-25 Nov. 2005) 9

Experimental set up (1/4) Triaxial high pressure cell Schematic view Axial piston (q max = 270 MPa) Force gauge specimen + jacket + Confining cell HEAV porous = 60 MPa)

10 Experimental set up (1/4) Triaxial high pressure cell Schematic view Axial piston (q max = 270 MPa) Force gauge specimen + jacket + Confining cell HEAV porous = 60 MPa) ceramics (σ 3max Pore pressure line (bottom, U max =60 MPa) Pore pressure line (top, U max =60 MPa) U and V/V 0 controlled at both ends of the specimen W(H)YDOC 05 (23-25 Nov. 2005) 10

11 Experimental set up (2/4) Global view of the installation Temperature regulator (2 niveaux de régulation) Pressure Regulators p c, q, U t, U p 4 pressure generators (jacks, water or oil) Data acquisition and control W(H)YDOC 05 (23-25 Nov. 2005) 11

12 Experimental set up (3/4) Technical improvement : temperature control T = 25 C (+/ C) Negligible influence of T : pore pressure volume change W(H)YDOC 05 (23-25 Nov. 2005) 12

13 Experimental set up (4/4) On-specimen local axial/radial strain measurements 4 radial + 3 axial LVDTs (+/ mm) Detection of strain localisation Volumetric strain measurement W(H)YDOC 05 (23-25 Nov. 2005) 13

14 Permeability measurement: Motivation for an improved method Steady state method (direct method) U+ U/2 Q e + Q p = Q in measured Steady state U U- U/2 x Q s Saturated specimen (H, S) + Q p = Q out measured Q e = Q s H k = µ * Q (m 2 ) S U q volumetric strains (consolidation/swelling,dilatancy, creep, adsorption) leakages p. Triaxial compression test «Parasite» flows Influence on Q e and Q s W(H)YDOC 05 (23-25 Nov. 2005) 14

15 Volume (mm3) 3 ) U+ U/2 U- U/2 x Phase 1 : U pied < U tête p 0 = 2.3 MPa Q 1 y = -1,136x - 7,1442 R 2 = 0,9833 Q 1 in Q 1 out y = 3,3539x + 1,1652 R 2 = 0, Time Temps (hr) (hr) Déformation volumique Volumetric strain -0,04-0,035-0,03-0,025-0,02-0,015 p 0 = 2.3 MPa Charge effective isotrope appliquée: 2,3 MPa ,01 Temps (hr) in 3.40 mm 3 /hr Q entrant Q sortant Phase 2 Phase 1 Q 1 out 1.15 mm 3 /hr W(H)YDOC 05 (23-25 Nov. 2005) 15 Fin Q g = 0.5 mm 3 /hr x Time (hr) Q 2 out Q 2 in ε v lvdt ln(v/v 0 ) U- U/2 U U+ U/2

16 Improved steady state method Volume (mm3) Phase 1 Phase 1 : U pied < U tête Q 1 in 3.40 mm3 /hr (top) y = 3,3539x + 1,1652 R 2 = 0,9998 Q entrant Volume (mm3) Phase 2 Phase 2 : U pied > U tête Q 2 in 3.80 mm3 /hr (bottom) y = 3,8312x + 10,982 R 2 = 0,9978 Q entrant y = -1,136x - 7,1442 R 2 = 0,9833 Time Temps (hr) Q Q 1 sortant out 1.15 mm3 /hr y = -1,1409x + 2,032 R 2 = 0,9975 Time Temps (hr) Q sortant Q 2 out 1.15 mm3 /hr hydraulic gradient Q d =1/4*[ (Q 1 out-q 1 in)-(q 2 out-q 2 in)] others (consolidation, leakage, ) Q c = (Q 1 out+q 1 in)+(q 2 out+q 2 in) W(H)YDOC 05 (23-25 Nov. 2005) 16

17 Experimental study of HM behaviour of Boom Clay: Results Testing program Results volumetric behaviour under isotropic load behaviour under deviatoric load permeability evolution with p 0 and q W(H)YDOC 05 (23-25 Nov. 2005) 17

18 Testing program specimen: h=d=40 mm uniaxial compression test (σ 3 =0) triaxial compression (axisym.)» p 0 = p 0 -u = 0.4 ; 2; 2.3 ; 5 MPa» u = 2.2 MPa (synthetic fluid) triaxial extension (axisym.)» p 0 = 2 MPa» u = 2.2 MPa drained consolidated tests» v = 0.25 µm/min (6, min -1 )» v = 25 µm/min (1 test) permeability: axial direction ( strati.) d h W(H)YDOC 05 (23-25 Nov. 2005) 18

19 Déformation volumique lvdt Volumetric strain Isotropic consolidation Time (hr) Temps (hr) ,12 BC19 p' 0 = 0,4 MPa -0,1 BC08-0,08 BC11-0,06-0,04-0,02 0 Deformation volumique lvdt Volumetric starin Time (hr) Temps (hr) ,06-0,05-0,04-0,03 p' 0 = 2,3 MPa BC06 BC20b BC07-0,02-0,01 BC12 0 0,01 BC05 0,02 Deformation volumique lvdt Volumetric strain Time (hr) Temps (hr) ,015 p' 0 = 2 MPa BC17-0,01 BC18-0, ,005 Volumetric Déformation volumique strain -0,035-0,03-0,025-0,02-0,015-0,01-0,005 0,01 0 Time (hr) Temps (hr) p 0 = 3 MPa p 0 = 2 MPa p 0 = 1,5 MPa BC09 ε v fl ε v lvdt p 0 = 5 MPa ( consolidation (stress changes) swelling (physico-chemical processes) W(H)YDOC 05 (23-25 Nov. 2005) 19

20 Deviatoric stage (p 0 =0.4 MPa, v=0.25µm/min) 1 σ 1 -σ 3 (MPa) Déviateur (MPa) 0,9 0,8 0,7 0,6 0,5 0,4 0,3 0,2 0,1 0-0,03 BC11-0,4 tc = 280 hr BC08-0,4 t c = 500 hr 0 0,01 0,02 0,03 0,04 0,05 0,06 Axial strain Déformation axiale ε 1 externe BC19-0,4 t c = 770 hr (a) «destructuration» during the swelling phase Déformation Volumique fl Volumetric strain -0,02-0,01 0 0,01 0,02 BC11-0,4 0 0,01 0,02 0,03 0,04 0,05 0,06 BC19-0,4 BC08-0,4 (b) Essai BC11 Essai BC08 (BC19 : strain localisation detected but no discontinuity observed) 0,03 Déformation axiale externe ε 1 externe W(H)YDOC 05 (23-25 Nov. 2005) 20

σ 1 -σ 3 (MPa) Volumetric strain Deviator stress (MPa) 2.5 2 1.5 1 0.5 BC07 t iso = 275 hr ε = 3,75.10 4 hr BC12 t iso = 160 hr ε = 3,75.

005 Deviatoric stage (p 0 = 2.3 MPa) BC07 2.3 t c = 275 hr BC12 2.3 t c = 160 hr Axial strain BC07 t iso = 275 hr ε = 3,75.

3 t c = 380 hr Test (p 0 = 2.3 MPa) Test BC07 Test BC07 Displ. rate (um/min) Starin rate (min -1 ) BC07 0.25 6,25.10-6 BC20 0.25 BC12 25 6,25.

21 σ 1 -σ 3 (MPa) Volumetric strain Deviator stress (MPa) BC07 t iso = 275 hr ε = 3, hr BC12 t iso = 160 hr ε = 3, hr BC20 t iso = 360 hr ε = 3, hr Axial strain ε a Deviatoric stage (p 0 = 2.3 MPa) BC t c = 275 hr BC t c = 160 hr Axial strain BC07 t iso = 275 hr ε = 3, hr 1 BC12 t iso = 160 hr ε = 3, hr 1 BC20 t iso = 360 hr ε = 3, hr 1 BC t c = 160 hr BC t c = 380 hr BC t c = 380 hr Test (p 0 = 2.3 MPa) Test BC07 Test BC07 Displ. rate (um/min) Starin rate (min -1 ) BC , BC BC , , Test BC20 Failure Non localised localised localised 0.01 BC t c = 275 hr Axial strain Test BC12 Test BC12 W(H)YDOC 05 (23-25 Nov. 2005) 21

22 p 0 k relation Permeability (m 2 ) Perméabilité (m 2 ) 7,05E-19 6,05E-19 5,05E-19 4,05E-19 3,05E-19 2,05E-19 BC06 BC07 BC08 BC09 BC11 BC12 BC15 BC17 BC18 BC02 (pulse) k p 0 decrease of the macropores 1,05E-19 5E-21 0, Isotropic effective stress (MPa) Contrainte effective isotrope (MPa) 2,3 MPa 0.4 < p 0 < 32 MPa k m 2 6, < k < 1, m 2 W(H)YDOC 05 (23-25 Nov. 2005) 22

23 Relation e - k Indice des vides Void ratio 0,8 0,7 0,6 0,5 0,4 0,3 0,2 0,1 BC07 BC11 BC12 BC15 - charge BC18 BC20 BC15 - décharge BC18 BC17 k stress history several macroporosities? Indice des vides Void ratio 0 1E-21 1E-20 1E-19 1E-18 0,7 e 0 = 0,557 0,6 0,5 0,4 0,3 0,2 0,1 Permeability Perméabilité (m 2 ) Perform more tests at high p 0 Isotropic compression test 0-32 MPa p c 5 MPa 0 p' c Isotropic effective stress p (MPa) Contrainte effective isotrope p' (MPa) W(H)YDOC 05 (23-25 Nov. 2005) 23

24 q k relation Axial strain 0,8 0,7 BC11 (p' 0 = 0,4 MPa) 1E-18 9E-19 Deviatoric Déviateur stress q (MPa) 0,6 0,5 0,4 0,3 0,2 0,1 Strain localisation 8E-19 7E-19 6E-19 5E-19 4E-19 3E-19 2E-19 Permeability Permébilité k (m 2 ) ) Volumetric strain Permeability (m 2 ) 0 1E ,005 0,01 0,015 0,02 0,025 0,03 0,035 0,04 Axial strain Déformation axiale externe p 0 = 0.4 MPa p 0 = 5 MPa no significant evolution of the permeability contractancy k decreases W(H)YDOC 05 (23-25 Nov. 2005) 24

25 Conclusions A long experimental campaign : CD tests with permeability measurements k-measurement procedure developed Under isotropic loading swelling/consolidation coexisting physico-chemical swelling k decreases macroporosity reduction k influenced by stress history (more tests needed) W(H)YDOC 05 (23-25 Nov. 2005) 25

26 Conclusions HM behaviour influenced mean effective stress water content strain rate p 0 : ductile-contractant loss of strength Permeability not influenced by q and strain localisation? Global axial measurement / localised discontinuities? W(H)YDOC 05 (23-25 Nov. 2005) 26

27 Perspectives physico-chemical behaviour k evolution Studies at the microscale level Swelling influence of strain rate self-healing evidence Visco-élasto-plastic behaviour W(H)YDOC 05 (23-25 Nov. 2005) 27

28 Thank you for your attention! W(H)YDOC 05 (23-25 Nov. 2005) 28

Multi scale porosity elementary sheet stacks/particles aggregates (n>20%) laminar interlayer pores intra-aggregate pores inter-aggregate pores infra micro macro 2-5 µm fluid flows : interconnected

29 Multi scale porosity elementary sheet stacks/particles aggregates (n>20%) laminar interlayer pores intra-aggregate pores inter-aggregate pores infra micro macro 2-5 µm fluid flows : interconnected macropores i.e. inter-aggregate porosity (free water) consolidation/swelling concerns also smallest pores (microporosity) 10 µm adsorption: interlayer porosity + chemical reactions: infra macro porosity SEM images of undisturbed Boom Clay: section perpendicular to the bedding with interstitial pores (p) (Dehandschutter et al., 2004). W(H)YDOC 05 (23-25 Nov. 2005) 29

30 reduced section for drainage zone with less friction limit friction drainage at both ends specimen flow lines not // between each other non homogeneous gradient porous HEA discs d=16 mm k is underestimate total drainage Modelling : correction of k W(H)YDOC 05 (23-25 Nov. 2005) 30

31 Overview of CD tests on Boom clay -0,04 σ 1 -σ 3 (MPa) Déformation Volumique fl Volumetric strain -0,03-0,02 BC18-2 BC11-0,4-0,01-0,06-0,04-0,02 0 0,02 0,04 0,06 0,08 0,1 0 BC12-2,3 BC19-0,4 BC20-2,3 0,01 BC07-2,3 BC08-0,4 0,02 BC09-5 0,03 Déformation axiale externe ε 1 externe Axial strain Axial strain mean effective stress p 0 : ductile-contractant HM behaviour water content strain rate loss of strength W(H)YDOC 05 (23-25 Nov. 2005) 31

Collaborating partners: NAGRA (CH), L3S (FR), G3S (FR), KUL (B), EPFL (CH), SOLEXPERTS (CH)

SELFRAC Fractures and self-healing within the excavationdisturbed zone in clays Type of test: Clay characterisation Collaborating partners: NAGRA (CH), L3S (FR), G3S (FR), KUL (B), EPFL (CH), SOLEXPERTS