EURAD state-of-the-art report: thermo-hydro-mechanical behaviour at high temperature of host clay formations

EURAD s a e-o - he-a epo :
he mo-hyd o-mechanical
beha iou a high empe a u e o
hos clay o ma ions
Ma ía Vic o ia Villa
1
*, Pie e Bésuelle
2
, F édé ic Collin
3
,
Robe Cuss
4
, Ch is ophe de Lesquen
5
*, A naud Dizie
6
*,
Ginge El Tabbal
7
, An onio Gens
8
, Ca oline G aham
4
,
D agan G gic
9
*, Jon Ha ing on
4
, Ch is ophe Imbe
10
,
Oli ie Leupin
11
, Sé e ine Le asseu
12
, As a Na kūnienė
13
,
E ic Simo
14
and Alexand u-Bogdan Ta omi
14
1
Cen o de In es igaciones Ene gé icas, Medioambien ales y Tecnológicas (CIEMAT), Mad id, Spain,
2
Uni e si é G enoble Alpes (UGA) & CNRS, G enoble, F ance,
3
Uni e si é de Liège (ULiège), Liege,
Belgium,
4
B i ish Geological Su ey (BGS), No ingham, Uni ed Kingdom,
5
Agence Na ionale pou la
Ges ion des Déche s Radioac i s (ANDRA), Châ enay-Malab y, F ance,
6
Eu opean Unde g ound
Resea ch In as uc u e o Disposal o nuclea was e in a Clay En i onmen (EURIDICE), Mol, Belgium,
7
Elec ici é de F ance (EDF), Pa is, F ance,
8
Uni e si a Poli ècnica de Ca alunya (UPC), Ba celona, Spain,
9
Uni e si é de Lo aine (ULo aine), Nancy, F ance,
10
Commisa ia à l’Ene gie A omique (CEA), Pa is,
F ance,
11
Na ionale Genossenscha ü die Lage ung adioak i e Ab älle (NAGRA), We ingen,
Swi ze land,
12
Belgian agency o adioac i e was e and en iched fissile ma e ials (ONDRAF/NIRAS),
B ussels, Belgium,
13
Li huanian Ene gy Ins i u e (LEI), Kaunas, Li huania,
14
Bundesgesellscha ü
Endlage ung (BGE), Peine, Ge many
Mos sa e y cases o adioac i e was e disposal concep s conside a empe a u e
limi o 90°C in he clay hos ock. Being able o ole a e highe empe a u e
would ha e significan ad an ages. Fo his eason, pa o he EURAD-HITEC
p ojec aimed a de e mining he influence o empe a u e abo e 90°C on clay
hos ock p ope ies, ying o es ablish he possible ex en o ele a ed
empe a u e damage in he nea and a field o clay hos ock o ma ions and
he consequences o any such damage. Th ee clay o ma ions conside ed o hos
adioac i e was e eposi o ies in Eu ope we e he ocus o he s udies: he Boom
Clay, he Callo o-Ox o dian clays one and he Opalinus Clay. A summa y o he
backg ound knowledge abou he he mo-hyd o-mechanical beha iou o hese
clay hos ocks is fi s p esen ed. Then, he expe imen al and modelling ac i i ies
ca ied ou in he amewo k o he EURAD-HITEC p ojec conce ning hese
ma e ials ha e been syn hesised. The labo a o y es s analysed he impac o
empe a u e on he sho - and long- e m beha iou o he clay hos ock and he
sel -sealing p ocesses. Hyd o-mechanical couplings be ween peak po e wa e
p essu e, empe a u e, pe meabili y and confining s ess we e iden ified. The
esul s confi med ha he clays one keeps i s good mechanical and e en ion
p ope ies e en when hea ed up o 100°C. P o ided ha he clay con en o he
samples is high enough, sel -sealing was an e ficien mechanism wha e e he
expe imen al condi ions, al hough empe a u e may ha e a delaying e ec . Po o-
elas ic models we e used o model gene ic cases o a high-le el was e eposi o y,
and consis en esul s we e ob ained by he di e en codes and eams, which
shows he obus ness o he modelling app oach used o design he eposi o ies.
Two hea ing es s, pe o med in he HADES (Belgium) and MHM (F ance)
unde g ound esea ch labo a o ies, we e selec ed as benchma ks o he
OPEN ACCESS
EDITED BY
Be nd G ambow,
UMR6457 Labo a oi e de Physique
Suba omique e des Technologies Associées
(SUBATECH), F ance
REVIEWED BY
Sayande Cha e jee,
Te aPowe LLC, Uni ed S a es
Ola Koldi z,
Helmhol z Cen e o En i onmen al Resea ch,
Ge many
*CORRESPONDENCE
Ma ía Vic o ia Villa ,
[email p o ec ed]
Ch is ophe de Lesquen,
ch is ophe.delesquen@and a.
A naud Dizie ,
[email p o ec ed]
D agan G gic,
d agan.g gic@uni -lo aine.
RECEIVED 22 May 2024
ACCEPTED 20 Feb ua y 2025
PUBLISHED 28 Ma ch 2025
CITATION
Villa MV, Bésuelle P, Collin F, Cuss R,
de Lesquen C, Dizie A, El Tabbal G, Gens A,
G aham C, G gic D, Ha ing on J, Imbe C,
Leupin O, Le asseu S, Na kūnienėA, Simo E
and Ta omi A-B (2025) EURAD s a e-o - he-a
epo : he mo-hyd o-mechanical beha iou a
high empe a u e o hos clay o ma ions.
F on . Nucl. Eng. 4:1436490.
doi: 10.3389/ nuen.2025.1436490
COPYRIGHT
© 2025 Villa , Bésuelle, Collin, Cuss, de
Lesquen, Dizie , El Tabbal, Gens, G aham, G gic,
Ha ing on, Imbe , Leupin, Le asseu ,
Na kūnienė, Simo and Ta omi . This is an open-
access a icle dis ibu ed unde he e ms o he
C ea i e Commons A ibu ion License (CC BY).
The use, dis ibu ion o ep oduc ion in o he
o ums is pe mi ed, p o ided he o iginal
au ho (s) and he copy igh owne (s) a e
c edi ed and ha he o iginal publica ion in his
jou nal is ci ed, in acco dance wi h accep ed
academic p ac ice. No use, dis ibu ion o
ep oduc ion is pe mi ed which does no
comply wi h hese e ms.
F on ie s in Nuclea Enginee ing on ie sin.o g01
TYPE Re iew
PUBLISHED 28 Ma ch 2025
DOI 10.3389/ nuen.2025.1436490
modelling ac i i ies. The e olu ions o empe a u e and po e p essu e we e well
modelled in he a field wi h a po o-elas ic app oach, bu mo e ad anced models
a e needed o ake in o accoun he p ocesses occu ing a ound he unnels (e.g.,
modifica ion o hyd aulic p ope ies wi hin he EDZ, c eep). The modelling o
labo a o y expe imen s showed he impo ance o a good unde s anding o he
es s se up and o he bounda y condi ions.
KEYWORDS
clays one, adioac i e was e, he mo-hyd aulic beha iou , c eep, hyd aulic conduc i i y,
empe a u e, nume ical modelling, aniso opy
1 In oduc ion
The wo k package “Influence o Tempe a u e on Clay-based
Ma e ial Beha iou ”(WP7) o he EURAD P ojec aimed o
de elop and documen imp o ed he mo-hyd o-mechanical (THM)
unde s anding o clay-based ma e ials (hos ocks and bu e s) exposed
a high empe a u es o ha ing expe ienced high empe a u e ansien s
o ex ended du a ions. The WP’s aison d’ê e was o e alua e whe he
o no ele a ed empe a u e limi s (up o 150°C o heclaybu e and
~90°C o he hos ock) a e easible o a a ie y o geological disposal
concep s o high hea gene a ing was es (high-le el was e, HLW). Fo
he disposal o HLW i is impo an o unde s and he consequences o
he hea p oduced on he p ope ies and long- e m pe o mance o he
na u al and enginee ed clay ba ie s. Being able o ole a e highe
empe a u e, whils s ill ensu ing an app op ia e pe o mance, would
ha e significan ad an ages (e.g., sho e abo e-g ound cooling imes,
mo e e ficien packaging, ewe disposal con aine s, ewe anspo
ope a ions, smalle acili y oo p in s, e c.). Consequen ly, HITEC is a
s ep owa d op imiza ion o he a chi ec u e o he deep geological
disposal, since he ange o empe a u es es ed had no been conside ed
sys ema ically in p e ious esea ch.
HITEC s udied he possible ex en o ele a ed empe a u e
damage in he nea and a field o clay hos ock o ma ions
(e.g., om o e -p essu isa ion) and indica ed he likely
consequences o any such damage. D illing unde g ound galle ies
o bo eholes leads o s ess edis ibu ion a ound he hole and some
damage in he nea field. F ac u es a e likely o o m a ound he
eposi o y as i is cons uc ed. The s ess ha was suppo ed by he
ma e ial emo ed du ing cons uc ion mus be aken up by he
emaining ock, leading o s ess concen a ions. Depending on he
s eng h o he hos - ock, his s ess concen a ion is likely o esul
in ac u ing and he o ma ion o an exca a ion damaged zone
(EDZ). The EDZ has di e en mechanical, hyd aulic and he mal
p ope ies o he sound hos ock, and he he mal impac on i can
also be di e en . This is why an impo an pa o he expe imen al
ac i i ies in HITEC was de o ed o he empe a u e influence on
sel -sealing.
The WP also looked a ben oni e bu e s and de e mined he
empe a u e influence on bu e p ope ies, ying o es ablish i he
bu e sa e y unc ions a e unaccep ably impai ed. These ac i i ies
a e desc ibed in a companion pape , whe e he common ea u es o
geological was e disposal concep s o he pa icipan o ganisa ions
a e also summa ised, o a be e con ex ualisa ion o he
esea ch pe o med.
P e ious ela ed esea ch ac i i ies we e pe o med in he
TIMODAZ p ojec , ha analysed he e olu ion o he EDZ
du ing he he mal ansien in he con ex o a geological
eposi o y o hea -emi ing was e in plas ic and indu a ed clay
hos ocks (Yu e al., 2010). The p ojec ocused on he possible
addi ional damage c ea ed by he he mal load. The knowledge
ga he ed du ing he p ojec indica ed ha an inc ease in
empe a u e due o he p esence o hea -emi ing was es will
induce s ong and aniso opic he mo-hyd o-mechanical
(THM) coupled esponses wi hin he clay. The he mal
expansion o po e wa e and he he mal-induced dec ease o
clay s eng h may pose a isk o addi ional mechanical damage.
Howe e , no e idence was ound h oughou he TIMODAZ
expe imen al p og amme showing empe a u e-induced
addi ional opening o ac u es o a significan pe meabili y
inc ease o he EDZ. The p ojec also concluded ha , wi h he
cu en knowledge, he capaci y o he eposi o y hos ock o
pe o m i s in ended ole as a ba ie and o main ain he long-
e m sa e y unc ions o he sys em will s ill be p ese ed, in spi e o
he combined e ec o he ine i able EDZ and he he mal ou pu
om he was e (Yu e al., 2010). I was concluded ha he
p ope ies o he clay hos ock ha gua an ee he e ec i eness
o he sa e y unc ions o he eposi o y sys em would be
main ained a e he hea ing-cooling cycle, bu his has o be
confi med wi h he echniques de eloped in he las decade and
he esul s o new la ge-scale in si u es s also o he a field.
In he ollowing sec ions syn heses o he s a e o knowledge on
he THM beha iou a di e en empe a u es o clay o ma ions
conside ed as po en ial hos ocks in di e en coun ies (namely,
Boom Clay, Callo o-Ox o dian clays one and Opalinus clay) a e
p esen ed, along wi h he p og ess made du ing HITEC. The
cha ac e is ics o he clay hos ocks analysed du ing he p ojec
a e desc ibed and hei he mal, hyd aulic and mechanical
p ope ies a e summa ised. Expe imen al p ocedu es, p ocesses,
pa ame e s and models a ailable o low o high empe a u e as
well as hose de eloped du ing he p ojec o he a ious hos ocks
a e summa ised. A significan e o has been de o ed o he
de elopmen o s a e-o - he-a equipmen . La ge-scale in si u
expe imen s ca ied ou in Unde g ound Resea ch Labo a o ies
(URL) and modelled du ing he p ojec a e b iefly desc ibed.
2 P ope ies o clay hos ocks and
empe a u e impac on hem
The ollowing subsec ions aim a summa ising he ele an
p ope ies o he h ee clays one o ma ions p oposed o hos
adioac i e was e and analysed du ing HITEC:
F on ie s in Nuclea Enginee ing on ie sin.o g02
Villa e al. 10.3389/ nuen.2025.1436490
−The Boom Clay Fo ma ion. A ma ine deposi om he
Oligocene (Rupelian s age), be ween 33.9 and 28.4 Ma. The
o ma ion is composed o hy hmically al e na ing clay- ich
and sil - ich ma e ials esul ing in a g ey- one banding. The
Boom Clay is a poo ly indu a ed clay wi h a well-de eloped
pa icle alignmen acco ding o he bedding plane and high
po osi y (Vandenbe ghe e al., 2014).
−The Callo o-Ox o dian (Cox) clays one. Deposi ed 160 Ma
ago (Middle-Uppe Ju assic) o e a pe iod o app oxima ely
5 Ma, in an open and calm ma ine en i onmen . I consis s o
h ee majo geological uni s, he ele an one being he
a gillaceous uni (UA) a he base, he mos homogeneous
and he iches in a gillaceous mine als (mo e han 40% on
a e age) o he h ee (e.g., Rebou s e al., 2005).
−Opalinus Clay (OPA). I occu s ex ensi ely in no he n
Swi ze land and neighbou ing coun ies. I is a mode a ely
o e -consolida ed clays one o igina ed om shallow
ma ine sedimen a ion in he Middle Ju assic pe iod
(Aleanian), ~173 Ma ago, wi h a complex bu ial and
compac ion his o y. I shows a low a iabili y in acies
and li hology, wi h a clay mine al con en >40 w % (e.g.,
NAGRA, 2014).
Hence, all o hem we e deposi ed in a ma ine en i onmen .
As a consequence o hei geologic his o ies (bu ial, subsidence,
upli , e osion) and pa icula mine alogy and g ain size, he
esul ing po osi y and mechanical cha ac e is ics a e
conside ably di e en . Thus, he Boom Clay, which is he
younges and subjec ed o less bu ial, has a po osi y o 35%–
40%, consequen ly wi h highe hyd aulic conduc i i y and lowe
he mal conduc i i y han he o he clays. I can be conside ed as
a poo ly indu a ed clay (o e consolida ion a io, OCR = 2.4 a he
le el o he URL) (Ho seman e al., 1987;Be nie e al., 2007a;Li
e al., 2023). In con as , he Cox clays one has a po osi y o 14%–
20% and he Opalinus clay o 10%–16%, ha ing been subjec ed o
la ge ex en o diagenesis and ec onic ac i i y (in he case o
Opalinus). The wo a e much s i e han he Boom Clay, hey can
be conside ed as mode a ely o e -consolida ed clays ones and
a eb i lema e ialsa lowconfining p essu e and mo e duc ile a
high confining p essu e.
Supplemen a y Tables summa ise he mine alogical and
po e wa e composi ion, hyd aulic, he mal and mechanical
p ope ies o he h ee clays suppo ed by app op ia e
e e ences. The ollowing sec ions summa ise aspec s o he
geology o he o ma ions, gene al pa ame e s and, in
di e en subsec ions, he hyd o-mechanical and THM
p ope ies de i ed om labo a o y es s and he impac o
empe a u e on some o hem. In pa icula , he ollowing
empe a u e-dependen ma e ial p ope ies a e conside ed o
be impo an (Li e al., 2023): hyd aulic conduc i i y, he mal
conduc i i y, s i ness and s eng h, c eep a es and he he mal
sensibili y on aniso opy. In o ma ion on he mechanical,
hyd aulic and he mal p ope ies o he EDZ is also gi en
below, because hese p ope ies may be di e en o hose o
he sound hos ock. Mos o he in o ma ion ga he ed comes
om esea ch p ojec s (including hesis) financed by o wi h
pa icipa ion o he was e managemen o ganisa ions o
se e al coun ies.
2.1 Boom Clay
The Boom Clay Fo ma ion (Te ia y clay o ma ion) is one o
he po en ial clay o ma ions s udied in ela ion wi h he easibili y
o a geological disposal o adioac i e was e in Belgium. The Boom
Clay dips gen ly owa ds he no heas , is loca ed in he no h pa o
Belgium and co e s a su ace o almos 5,000 km
2
(Supplemen a y
Figu e 1). The hickness o he o ma ion inc eases om a ew
decame es a ou c op o mo e han 150 m in he deepe pa o he
basin. A he le el o he URL in Mol (Belgium), he Boom Clay has a
hickness o abou 100 m and is loca ed a dep hs be ween 185 and
287 m, he unde g ound labo a o y is a a dep h o 223 m (Me ens
e al., 2004). The o al e ical s ess and po e wa e p essu e a he
le el o he URL in Mol a e espec i ely 4.5 MPa and 2.2 MPa. The
K
0
alue anges om 0.7 o 0.8 (Be nie e al., 2007a;ONDRAF/
NIRAS, 2013).
The g anulome y o he clay is composed o mo e han 60% o
e y fine pa icles (clay size) o he mo e clayey beds while he e a e
40% o clay pa icles o he mo e sil y beds. The majo i y o he
po es ha e a adius in he o de o 0.01 µm wi h a unimodal
dis ibu ion (Lima, 2011). Based on he di e ences in
g anulome y and mine alogical con en , he Boom Clay
Fo ma ion is subdi ided in h ee membe s: he Belsele-Waas
Membe , he Te hagen Membe and he Pu e Membe
(Vandenbe ghe e al., 2014).
The e ical and ho izon al hyd aulic conduc i i y alues a e
di e en wi h a a io (k
H
/k
V
)o ~2(Supplemen a y Table 3). The
di e en alues o he hyd aulic conduc i i y a e ela ed wi h he
g anulome y, o ins ance, he alues in he Belsele-Waas membe
a e highe han hose o he o he membe s o he o ma ion because
o i s highe sand con en .
A c i ical e iew o he labo a o y and in si u measu emen s can
be ound in Yu e al. (2013).
2.1.1 Hyd o-mechanical beha iou
Since he ope a ional s a o HADES URL ea ly in he 80s, many
labo a o y es s and in si u es ing ha e been pe o med o
unde s and he Boom Clay THM beha iou , among which
iaxial and oedome e es s. T iaxial es s pe mi o de e mine
de ia o ic beha iou and hen he s eng h pa ame e s, while
oedome e es s a e mo e ocused on he olume change
beha iou . Clay samples ha e been s udied in condi ions as close
as possible o hei na u al s a e a ound he HADES URL. As e-
sa u a ing Boom Clay samples a low confining p essu e induces an
impo an swelling ha a ec s he mic os uc u e and hus modifies
clay p ope ies (Coll, 2005;Sul an, 1997), Le (2011) sugges ed
sa u a ing Boom Clay a a confining p essu e close o he in si u
s a e o s ess o minimise his swelling and dis u bance o he clay.
The Boom Clay beha iou is cha ac e ised by a non-linea
s ess–s ain esponse. Labo a o y es s showed a end o
s i ness a ia ion wi h s ain le el: i s angen s i ness a 0.01%
de o ma ion may be one o de o magni ude la ge han ha a 1%
de o ma ion (Be nie e al., 2007a).
The elas ic p ope ies which go e n he clay beha iou in he
e e sible domain o de o ma ion ha e been de e mined wi h
iaxial es s. Acco ding o Be nie e al. (2007a) he iso opic
elas ic modulus o he Boom Clay is abou 300 MPa. This alue
was deduced by back-analysis o he in-si u measu emen s du ing
F on ie s in Nuclea Enginee ing on ie sin.o g03
Villa e al. 10.3389/ nuen.2025.1436490
he exca a ion o he Tes -d i ob ained by Mai e al. (1992) and
gi es sa is ac o y esul s o model mos o he iaxial es s on Boom
Clay (Cha lie e al., 2010). The alue o he Poisson’s a io anges
om 0.125 (Be nie e al., 2007b) o 0.15 (Ho seman e al., 1987). In
iso opic condi ion, a alue o 0.125 is commonly admi ed.
The uniaxial comp essi e s eng h (UCS) o he Boom Clay is
no well documen ed. Acco ding o Coll (2005), who de e mined he
UCS on Boom Clay samples om a dep h o 223 m, i should be
a ound 2.5 MPa. Be nie e al. (2007a) epo ed a alue o 2 MPa.
T iaxial es s o de e mine he shea s eng h pa ame e s o he
Boom Clay ha e been pe o med o se e al decades s a ing om
De Bee e al. (1977). These esul s we e mos ly ob ained h ough
und ained es s because o he e y low pe meabili y o he clay. The
moni o ing o he po e wa e p essu e pe mi s o calcula e he mean
e ec i e s ess and o in e p e he es s in e ms o e ec i e
pa ame e s. Fo example, esul s o und ained es s pe o med a
e y low confining p essu e (high OCR) showed ha he de ia o ic
beha iou p esen s a peak be o e a dec ease (s ain so ening) ill a
esidual s eng h (Supplemen a y Figu e 2). The e y low
comp essibili y o he clay-wa e mix u e implies ha he
olume ic de o ma ion o he sample can be assumed
heo e ically as null. The ep esen a i e s ess pa h o such kind
o es s is almos a s aigh line (Lima, 2011).
The alues o he d ained cohesion and he d ained ic ion
angle o he Boom Clay can be deduced om all he p e ious s udies.
Acco ding o Be nie e al. (2007a), who in e p e ed he es s o Baldi
e al. (1987),Baldi e al. (1991) and Mai e al. (1992) wi h a Moh -
Coulomb c i e ion, he d ained cohesion is equal o 300 kPa and he
ic ion angle o 18°.Figu e 1 p esen s he compa ison be ween he
D ucke -P age c i e ion wi h he chosen shea s eng h pa ame e s
and he peak s eng h alues om he iaxial es s on Boom Clay.
Wi h his se o pa ame e s a ela i ely good ag eemen can be ound
o high alues o he confining p essu e, while o e y low alues,
mo e disc epancies can be seen (ONDRAF/NIRAS, 2013;Dizie
e al., 2018).
Conce ning he olume change beha iou , Awa keh (2023)
summa ised he esul s o oedome e es s pe o med on Boom
Clay samples om Ho seman e al. (1987) o Nguyen e al. (2013)
and ga e a ange o a ia ion o he swelling index (C
s
) be ween
0.05 and 0.15, o he plas ic slope (C
c
) be ween 0.25 and 0.40, and o
he p econsolida ion p essu e be ween 5 and 6 MPa. The pa ame e s
p esen a la ge a ia ion ha can be explained by he na u al
a iabili y o he clay and by he e olu ion o he es p o ocols,
which a e cons an ly e ol ing om he ea ly es s.
Wi h a iew on he long- e m olume change beha iou , Deng
e al. (2012) pe o med oedome e es s wi h he pu pose o s udying
he seconda y consolida ion beha iou o Boom Clay samples aken
om wo di e en loca ions. They ound ha he seconda y
consolida ion coe ficien (C
α
) was posi i e du ing he loading
pa hs and nega i e du ing unloading, wi h an a e age alue o
abou 0.024, which ag ees wi h he gene al classifica ion c i e ion
o clay soils o Te zaghi e al. (1996), whe e a ange om 0.02 o
0.05 is gi en o shales and mud ocks. Simila esul s we e ob ained
by Awa keh (2023).
A se o labo a o y es s was pe o med unde di e en
condi ions o in es iga e he elas o- isco-plas ic beha iou o
Boom Clay unde long- e m de ia o ic condi ions (c eep).
T iaxial c eep es s pe o med by Coll e al. (2006) and Chen
e al. (2017) a ambien empe a u e e idenced he c eep
beha iou : he s eady s ain a e inc eased wi h he de ia o ic
s ess le el as obse ed o mos o he clay ma e ials. Simila
esul s we e ob ained mo e ecen ly wi h he wo k o Awa keh
(2023). I was shown ha he c eep s ain unde a de ia o ic loading
s a s a a ce ain alue o de ia o ic s ess, which means ha he e is
a h eshold unde which no c eep can be obse ed.
The coupling be ween mechanical and hyd aulic p ope ies was
s udied by Ho seman e al. (1987) and Coll (2005), who pe o med
se ies o hyd aulic es s on Boom Clay samples a di e en confining
p essu es and de e mined a end in he e olu ion o he hyd aulic
p ope ies wi h he mean e ec i e s ess. As expec ed, an inc ease o
he applied load induced a dec ease o he hyd aulic conduc i i y.
Coll (2005) also s udied he e ec o he de ia o ic s ess on
hyd aulic conduc i i y. E en i a discon inui y was ini ia ed in
he sample, no clea modifica ion o he hyd aulic conduc i i y
was obse ed. Indeed, e en i he pe meabili y was modified locally
a ound he c acks, his was no measu able a he scale o he sample.
A e shea ing, he c acks we e cha ac e ised by a e y hin size
which made di ficul he desc ip ion o he po osi y along he
localised shea band. Few yea s la e , Mon a ed (2011) pe o med
pe meabili y es s be o e and a e shea ing and obse ed again ha
he shea band had no significan e ec on he pe meabili y o he
sample, al hough–consis en ly wi h he esul s o Coll (2005)– e y
small a ia ions o he pe meabili y could be no iced. The
in e p e a ions gi en o hese esul s di e ed in bo h s udies
hough. Coll (2005) assumed ha he shea band had a e y local
and insignifican e ec on he global pe meabili y o he sample,
while Mon a ed (2011) made he hypo hesis ha he absence o
pe meabili y a ia ion was he esul o he sel -sealing beha iou
o he clay.
The labo a o y es p og amme summa ised abo e mainly
in es iga ed he THM beha iou o he Boom Clay as iso opic,
so a he aniso opic beha iou o Boom Clay has no been much
s udied. Baldi e al. (1987) compa ed he calcula ed and measu ed
olume ic s ain du ing a iaxial es . La e , Labiouse e al. (2014)
and F ançois e al. (2014) pe o med hollow cylinde es s and
p esen ed hei in e p e a ions wi h aniso opic nume ical models.
FIGURE 1
D ucke -P age c i e ion wi h he chosen se o shea s eng h
pa ame e s o Boom Clay plo ed wi h he peak s eng h alues
(Dizie e al., 2018).
F on ie s in Nuclea Enginee ing on ie sin.o g04
Villa e al. 10.3389/ nuen.2025.1436490
Di e en phases o loading and unloading we e applied o he
samples. Be o e and a e unloading, he sample was submi ed o
mic ocompu e ized omog aphy (µCT) and pa icle acking o
de e mine he displacemen o some specific poin s. The hole
clea ly con e ged a e unloading, bu he con e gence was no
homogenous and a ied wi h he di ec ion o he bedding plane,
which esul ed in aniso opic beha iou and a final eye-shape o he
hole (Labiouse e al., 2014). The adial displacemen s in hollow
cylinde es s acco ding o di e en di ec ions was analysed by
F ançois e al. (2014), who ound ha hey we e no uni o m,
highligh ing he aniso opic esponse o he clay. The highe
displacemen was pa allel o he bedding plane, while he lowes
one was pe pendicula o he bedding. These esul s we e confi med
mo e ecen ly by Pégui on (2021). Also he back-analysis o he
obse ed po e-wa e p essu e a ia ions in he a field o he
HADES URL galle ies du ing exca a ions and a ound he in-si u
hea e es s ATLAS and PRACLAY (see Sec ion 3.1) suppo he idea
ha he THM beha iou o he Boom Clay is aniso opic (Cha lie
e al., 2010;Van Ma cke e al., 2013). These las analyses e eal
no ably ha pe u ba ions in he a field–whe e de o ma ions a e
small–can be much be e ep esen ed by models when using
di e en Young’s moduli along he e ical and ho izon al
di ec ions, wi h alues gene ally la ge han hose summa ised in
Supplemen a y Figu e 5.
2.1.2 Hyd o-mechanical beha iou o he
ac u ed/damaged clays one
Du ing he SELFRAC p ojec , es s we e pe o med o s udy he
sel -sealing capaci y o he Boom Clay, using di e en po e wa e
chemis ies o sa u a e he samples a e he ini ia ion o a ac u e
(Be nie e al., 2007b). The Boom Clay showed e y good capaci y o
sel -sealing (Supplemen a y Figu e 3). Van Gee e al. (2008)
pe o med pe meame e es s on a ac u ed Boom Clay sample
and moni o ed he e olu ion o he hyd aulic conduc i i y wi h ime
o highligh he sealing p ocess (Supplemen a y Figu e 4). The
hyd aulic conduc i i y dec eased wi h ime, indica ing he sealing
p ocess om a hyd aulic poin o iew. Chen e al. (2014) showed
ha he e is no posi i e o nega i e impac o he empe a u e on he
sealing p ope ies o Boom Clay by exposing samples (damaged and
in ac ) o a hea ing cycle om 20°C o80
°C unde cons an olume
condi ions in a pe meame e cell.
2.2 Callo o-Ox o dian clays one
The Callo o-Ox o dian (Cox) clays one consis s o h ee majo
geological uni s, among which he a gillaceous uni (UA) a he base
is he hickes ( om 100 o 120 m in he zone o in e es ). I is
subdi ided in o h ee subuni s (UA1, UA2 and UA3) wi h small and
p og essi e a ia ions. Subuni UA2 co esponds o he s a ig aphic
le el whe e he clay con en is highe and whe e he Meuse/Hau e-
Ma ne (MHM) URL expe imen s a e ca ied ou . The o ma ion
dips gen ly (a e age 1°) owa ds he no hwes , he bedding plane
can he e o e be conside ed ho izon al. The main le el o he URL is
loca ed a a dep h o 490 m.
The a e age po osi y in he UA is 18%. The ne wo k o po es
mainly comp ises meso- and mic opo es wi h a p edominan po e
size o app oxima ely 10–30 nm, and an ex emely low connec i i y
o po es la ge han 40 nm. The ex u e is finely di ided and is an
assembly o ec osilica e and ca bona e g ains, connec ed by a fine
ma ix o med o clay mine als and calci e mic oc ys als. Bo h he
ec osilica e and he ca bona e g ains show a p e e en ial o ien a ion
o hei long axis pa allel o he sedimen a ion plane (Rebou s e al.,
2005;Robine e al., 2012).
The wa e pe meabili y is e y low and anges om 10
−21
m
2
o
10
−19
m
2
, wi h a ela i ely low aniso opy (2–3 a io). The s ess
egime in he a ea is aniso opic, wi h he majo p incipal s ess
being ho izon al and he a io be ween he maximum and minimum
ho izon al s esses being a ~1.3. Fo he calcula ions, a he URL
le el, he majo ho izon al s ess σ
H
is se a 16.1 MPa, σ
=
12.7 MPa, σ
h
= 12.4 MPa, and he po e p essu e is 4.7 MPa. A
geo he mal g adien o 0.025 °C/m is es ima ed in he a ea, wi h a
empe a u e o 22°C a 490 m (Gunzbu ge and Co ne , 2007;
Wile eau e al., 2007).
2.2.1 Hyd o-mechanical beha iou
The Cox clays one has a linea non- e e sible (pseudo-elas ic)
beha iou a low le els o de ia o s ess (below 40%–50% o ailu e)
and a non-linea beha iou beyond a le el, wi h significan
i e e sible s ains and sligh ly lowe moduli. B i le ailu e is
obse ed a low confining p essu es and a mo e duc ile
beha iou is seen a high confining p essu e (o e 21 MPa in he
UA). Beyond a ce ain le el o cumula i e o al s ain, some esidual
s eng h is shown.
The wa e sa u a ion has a significan e ec on he mechanical
beha iou o he Cox clays one. I was shown ha limi ed
desa u a ion o he Callo o-Ox o dian leads o an inc ease in he
elas ic mechanical p ope ies and in he s eng h o he ma e ial,
despi e some mic oc acking o he sample due o desa u a ion
(Wang e al., 2013;Agboli e al., 2024).
Unde ensile loading, he Cox clays one shows a b i le
beha iou . The measu ed ensile s eng h shows non-negligible
dispe sion, inc easing wi h he ca bona e con en and wi h a
mean alue in he UA o 1.4 MPa.
T iaxial es s pe o med on samples wi h a ious o ien a ions
wi h ega d o he bedding showed aniso opy, he E
//
/E
⊥
a io
a ying be ween 1.05 and 1.4. Simila numbe s we e ob ained
when calcula ing dynamic moduli om he comp essi e and
shea wa e eloci ies measu ed in bo h di ec ions in
pa allelepipedic samples. The a e age alues and s anda d
de ia ions o he pe pendicula and pa allel moduli om
UCS es s (calcula ed using he angen me hod) in he UA
uni we e 5.7 ± 2.5 GPa and 11.0 ± 4.6 GPa, espec i ely. The
a e age alues show a a io o almos 2, howe e hese alues a e
no di ec ly compa able because many mo e samples we e es ed
in he pe pendicula di ec ion (259 s. 52). In addi ion, he
s anda d de ia ion o he es s pe o med on samples pa allel
o he bedding (≈4 GPa) is ela ed no only o he mine alogical
a ia ions, bu also o he damage due o he di ficul y o cu some
plugs pa allel o he lamina ion.
The Poisson’s a io (ν) calcula ed om all he esul s a ailable a
oom empe a u e is on a e age 0.3 o all li hological le els.
The unconfined comp essi e s eng h in he di e en uni s o
he Cox o ma ion anges om 18 o 34 MPa. Fo he mos
a gillaceous pa o he UA (UA2 = IMA subuni ), he alues a e
23.3 ± 5.1 MPa.
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The expe imen al esul s o uniaxial comp ession es s we e
in e p e ed wi h he Hoek and B own (1980) ailu e c i e ion, and
he alues in Supplemen a y Figu e 2 we e ound. Fo he Cox
clays one, he pa ame e σ
c
(uniaxial comp essi e s eng h o he
in ac ock) is di e en om he UCS and is conside ed as a fi ing
pa ame e , no a ock p ope y. In o de o manage he unce ain ies
due o a ious e ec s (scale, ime e ec on he long- e m s eng h,
sample p ese a ion, e c.) wo c i e ia we e defined: 1) an a e age
c i e ion ha goes h ough he cloud o es esul s o e a ange o
confining p essu e 0<σ
3
<25 MPa, and 2) a low c i e ion ha goes
h ough he lowe limi o es esul s o e he same ange o
confining p essu es. F om hese pa ame e s he equi alen Moh -
Coulomb pa ame e s shown in Supplemen a y Figu e 7
we e de i ed.
Because o he a iabili y o hei mic os uc u e and o hei
mine alogy, he Cox clays one has an aniso opic beha iou ha
esul s in:
−an aniso opy be ween 1 and 2 on he elas ic moduli depending
on he me hods used o de e mina ion (dynamic and quasi-
s a ic modulus)
−comp essi e s eng hs measu ed on samples pe pendicula o
he s a ifica ion a e simila o o sligh ly lowe han hose
measu ed on samples pa allel o he s a ifica ion. A dec ease in
s eng h was obse ed o es specimens a 45°bu he na u al
a iabili y o samples can gi e an opposi e esul . Figu e 2
shows he e ec o he o ien a ion o bedding on he peak
s eng h in ecen samples om well-p ese ed co es wi h high
wa e sa u a ions.
An in es iga ion pe o med by Zhang e al. (2015) wi h co es
d illed a di e en inclina ions wi h espec o bedding, confi med
ha he s eng h depends bo h on he loading pa h and on he
di ec ion o loading compa ed o he bedding plane. Fo a gi en
loading o ien a ion, he peak s eng hs de eloped du ing TCD
( iaxial comp ession by axial de o ma ion a cons an adial
s ess) and TCS ( iaxial comp ession by axial loading a cons an
adial s ess) we e highe han hose eached du ing TES ( iaxial
ex ension by inc easing adial s ess a a cons an axial s ess) and
TEM ( iaxial ex ension by keeping he mean s ess cons an while
simul aneously inc easing he adial s ess and dec easing he axial
s ess) and he lowes s eng h was achie ed in iaxial ex ension
wi h cons an mean s ess. Fo all loading pa hs, he maximum
s eng hs we e eached wi h an axial s ess pa allel and
pe pendicula o bedding, and he lowes s eng h was ob ained
a 45°in comp ession and 30°in ex ension.
The e y low pe meabili y and po osi y o he Cox clays one
make i di ficul o di ec ly measu e he po e p essu e wi hin a
plug and o quan i y i s coupling wi h he mechanical beha iou .
Howe e , he hyd o-mechanical coupling was e ealed in si u
h ough changes in po e p essu e le els a ound he s uc u es
a e exca a ion and h ough he mal expe imen s. I is cu en ly
desc ibed h ough he concep o e ec i e s ess using Bio ’s
heo y. The mos ecen expe imen s o define Bio ’scoe ficien
(B aun, 2019;Belmokh a e al., 2017;Yuan e al., 2017) educed
he unce ain y on i s alue and ga e highe alues han
p e iously, be ween 0.8 and 1 (Supplemen a y Figu e 5). A
alue o 0.85 may be e ained o he Cox clays one. Howe e ,
i should be no ed ha hese esul s s ongly depend on he
sa u a ion and he mechanical s a e o he samples. The co e
p ocessing, he sample p epa a ion and he ( e)sa u a ion o he
samples may c ea e some damages p io o es ing, which may
pa ially explain he dispe sion o expe imen al alues.
Fu he mo e, all he es s show ha he Bio ’scoe ficien
seems o dec ease wi h he confining p essu e, while he
d ained bulk modulus inc eases. This could be explained by
he closu e o mic o ac u es induced when cu ing he co e
and/o p epa ing he samples. In addi ion, he e y small po e
size o he Cox clays one, he p esence o bo h clay-bound and
ee wa e , and he possible induced desa u a ion when acqui ing
o p epa ing he samples hinde he cha ac e isa ion o he po o-
elas ic pa ame e s and he applica ion o a simple
beha iou model.
C eep es s we e pe o med on dedica ed igs, wi h con olled
empe a u e o pe iods o ime o up o 3 yea s o cha ac e ise he
long- e m mechanical beha iou o he ock (Zhang e al., 2012).
These es s aced impo an challenges ela ed o he ini ial s a e o
he samples, he du a ion o he expe imen s, he con ol o
empe a u e and humidi y and he p ecision o he
measu emen s. The measu ed changes we e indeed e y low,
some imes o he same o de o magni ude as he accu acy o he
senso s. Howe e , some gene al ends we e obse ed:
−In mos cases, he c eeping a e diminished wi h ime,
al hough in some cases i appea ed o each an asymp o e.
The e olu ion o he c eeping a e was e y slow and because
o he p ecision o he measu emen s, i is di ficul o say
whe he a s eady s a e was eached o no .
−The c eeping a e appea ed o inc ease wi h he
de ia o ic s ess.
−The a e age s ess seemed o ha e e y li le influence on he
delayed de o ma ions.
−The calci e con en had a di ec e ec on he ins an aneous
beha iou bu no clea end was obse ed on he delayed
FIGURE 2
Peak s eng h o Cox clays one as a unc ion o he o ien a ion
o bedding.
F on ie s in Nuclea Enginee ing on ie sin.o g06
Villa e al. 10.3389/ nuen.2025.1436490
mechanical beha iou ; howe e , when checking he esul s pe
s udy, a sligh dec ease o he c eeping a e wi h he ca bona e
con en may be seen.
2.2.2 Hyd o-mechanical beha iou o he
ac u ed/damaged clays one
The EDZ can be spli in a connec ed ac u ed zone (ZFC), whe e
bo h ensile ac u es and shea ac u es coexis , and a disc e e
ac u ed zone (ZFD), whe e only he ends o some shea ac u es
a e ound. Fo HLW cells d illed in he di ec ion o he maximum
ho izon al s ess, he EDZ de elops mainly on he igh and le sides o
he bo ehole. I s maximum ex en is app oxima ely one diame e wide
on each side (0.8 adius o he ZFC and 2 adii o he ZFD), and he e
is no “scale e ec ”be ween la ge galle ies o hin bo eholes. The
hyd aulic conduc i i y in he ZFC is significan and ela ed o open
ac u es. Because o his, he po e p essu e d ops apidly o
a mosphe ic p essu e in he nea field (ZFC), bu an inc ease in
po e p essu e is obse ed u he away om he hole wi h some delay.
The appa en s i ness o he ZFC has been e alua ed in he CDZ
expe imen (de la Vaissiè e e al., 2015): i appea s o inc ease
apidly, eaching al eady 3 GPa 1 m away om he bo ehole wall.
Se e al obse a ions in he UA showed ha he EDZ has a
hyd aulic sel -healing capaci y due o he p esence o swelling clay
mine als such as smec i e. Bo h labo a o y and in-si u expe imen s
showed ha he hyd aulic conduc i i y o he ZFC educes apidly
when exposed o wa e and p og essi ely eaches ha o he in ac
clays one. De La Vaissiè e e al. (2015) showed he pa ial es o a ion
o he Cox clays one pe meabili y du ing in si u esa u a ion
expe imen s. O e a 1-yea esa u a ion pe iod, he hyd aulic
conduc i i y measu ed in he bo eholes dec eased by up o ou
o de s o magni ude, app oaching, bu no eaching, he alue o he
heal hy clays one. This esul illus a es he abili y o he clays one o
sel -seal. Howe e , wa e injec ion does no imp o e he s i ness o
he EDZ, ha emains a mechanically weak zone.
A s udy on Cox clays one looked a i s flow p ope ies (Cuss e al.,
2017) and desc ibed he s ess dependency ac u e flow by a powe -law
o cubic ela ionship, which is likely o be dependen on he ac u e
oughness, hickness o gouge ma e ial, sa u a ion s a e, pe meabili y o
he hos ma e ial, and clay mine alogy (i.e., swelling po en ial). The
s ess-dependency o flow was also seen o be dependen on o ien a ion
wi h espec o bedding, in ela ion o he aniso opic swelling
cha ac e is ics o Cox. F ac u es pe pendicula o bedding
accommoda ed g ea e comp ession and esul ed in a lowe
ansmissi i y.
2.3 Opalinus Clay
The Opalinus Clay is sligh ly il ed and he su ace o he o ma ion
lies be ween 0 o beyond 1,000 m below g ound su ace. A Mon Te i,
he Opalinus Clay eaches a maximum dep h o abou 1,000 m and he
p esen bu ial dep h is abou 200–300 m.
On a egional scale, he mine alogical composi ion o he
Opalinus Clay exhibi s mode a e la e al a iabili y and a sligh
inc ease in clay con en wi h dep h. A he Mon Te i URL a
clay- ich and a sandy acies can be iden ified. The a iabili y o he
acies is expec ed o be low and he same s uc u es can be ound in
sou he n Ge many as well (Jahn e al., 2016).
The aniso opy due o bedding is la gely a esul o mic oscopic
he e ogenei y. Po osi y depends on clay con en and bu ial dep h.
The po e space o he ock is o med by a ne wo k o mic o/meso
and mac opo es, bu he majo i y o po es can be classified as
mesopo es (1–25 nm) (NAGRA, 2002a).
Field in es iga ions sugges a hyd aulic conduc i i y o he
Opalinus Clay in he o de o 10
−13
o 10
−14
m/s. No significan
a ia ions in hyd aulic conduc i i y a e seen among he di e en
acies. A e e ence alue o 5·10
−13
m/s has been epo ed o he
Opalinus Clay a Mon Te i (Bossa and Thu y, 2008). The wa e /
ai pe meabili y expe imen s on he Opalinus Clay (NAGRA, 2002a;
Ma schall e al., 2005;Polle e al., 2007;C oisé e al., 2006;Rome o
and Gomez, 2013) show clea e idence o he dependency o wa e
pe meabili y on oid a io and hus on cons i u i e s ess. A ma ked
dependency o gas dissipa ion was obse ed on he di ec ion o gas
flow wi h espec o bedding o ien a ion.
A compila ion o wa e e en ion cu es (WRC) o Opalinus
Clay samples om Mon Te i, de e mined by GRS, UPC and EPFL
is depic ed in Supplemen a y Figu e 6. Cha ac e is ic ea u es o he
Opalinus Clay a e he high capilla y p essu es in he o de o 10 MPa
e en a high wa e sa u a ion >90% and he ma ked hys e esis
be ween we ing and d ying pa hs. In o ma ion abou he WRC
o deep Opalinus co e samples (880 m dep h) can be ound in Fe a i
e al. (2013) and Rome o and Gomez (2013).
2.3.1 Hyd o-mechanical beha iou
Geo echnical cha ac e is ics o he Opalinus Clay ha e been
de e mined as pa o comp ehensi e labo a o y p og ammes,
e ealing mode a e s i ness (Young’s modulus in he ange
5–15 GPa), mode a e s eng h (UCS alues o he in ac ock
ma ix be ween 10 and 35 MPa), dis inc swelling p essu es
(0.5–2 MPa) and OCR o be ween 1.5 and 2.5 (NAGRA, 2002b).
Pa ame e s o he Opalinus Clay as defined o he FE Expe imen
in Alcolea and Ma chall. (2019) a e shown in Supplemen a y Figu e 8.
2.3.2 Hyd o-mechanical beha iou o he
ac u ed/damaged clays one
Expe imen s a BGS looked a ac u e ansmissi i y in Opalinus
Clay along an idealised ac u e (Cuss e al., 2009;Cuss e al., 2011). A
ollow-on s udy in es iga ed hyd aulic flow along a ealis ic ac u e
(Cuss e al., 2012). This wo k showed ha hyd a ion alone educed
ac u e ansmissi i y by one o de o magni ude, while shea
displacemen educed i by a second o de o magni ude. Con inued
shea hen esul edininc easedflow, e en ually inc easing by fi e
o de s o magni ude, h ee o de s o magni ude g ea e han he s a ing
ansmissi i y. The injec ion o fluo escein showed ha only a ound
25% o he ac u e su ace was conduc i e.
The alues o he scoping calcula ions o he FE expe imen s
used in Senge (2015) o he EDZ o he Opalinus clay a e gi en in
Supplemen a y Figu e 10.
3 Rele an la ge-scale es s
Se e al hea ing es s ha e been pe o med in unde g ound
esea ch labo a o ies exca a ed in clay hos ocks. The aim o
hese es s is usually o de e mine he mal p ope ies o he hos
ock and help iden i y i s hyd aulic, mechanical and he mal
F on ie s in Nuclea Enginee ing on ie sin.o g07
Villa e al. 10.3389/ nuen.2025.1436490
esponses o a he mal load hanks o he ins umen a ion
inside o a ound he es . In he HADES acili y exca a ed in
Boom Clay, he small-scale ATLAS hea e es was se up in
1992 wi h a e y simple geome y (De B uyn and Laba , 2002),
and has unde gone se e al phases, p o iding in o ma ion on he
empe a u e and po e wa e p essu e e olu ion o e he yea s,
pa icula ly in he a field (Chen e al., 2011;Chen e al., 2023).
A he MHM URL, se e al in-si u hea ing es s on he Cox
clays one ha e been pe o med since 2006, among which he
TER, TED, TFW, ALC 1604 and CRQ. A he Mon Te i URL,
he hea ing es s HE-E and FE, exca a ed in Opalinus Clay
(desc ibed in he companion pape ), a e cu en ly unning. A
summa y o he main cha ac e is ics o hese es s is gi en
in Table 1.
The ollowing sec ions desc ibe in some de ail he es s
selec ed as modelling benchma ks in HITEC: he PRACLAY
in Boom Clay and he ALC 1605 in Cox clays one.
3.1 La ge-scale in si u PRACLAY hea e es
The PRACLAY galle y was exca a ed in 2007 a he HADES
URL and has a leng h o 45 m. The hea ed pa o he galle y is 34 m
TABLE 1 Summa y o ele an la ge-scale es s cha ac e is ics (BH: bo ehole).
Tes Du a ion Cha ac e is ics Hea e
empe a u e
/Powe
Dimensions Re e ences
Boom clay (HADES, Belgium)
ATLAS (I-IV) 1992–2008, in
4 phases
Small-scale hea e es , simple geome y. One
hea e BH and 5 obse a ion BHs wi h T, po e
wa e p essu e and s ess measu ed
900–1800 W 8 × 0.19 m (BH) De B uyn and Laba (2002)
Chen e al. (2011),Chen e al.
(2023a),Chen e al. (2023b)
Li e al. (2023)
PRACLAY
Hea e es
2014–2025 La ge-scale hea e es wi h a hea ed galle y
filled wi h sand and closed by plug (hyd aulic
cu -o ). Ne wo k o ins umen ed bo eholes
a ound (po e wa e p essu e, T, o al s ess
measu ed)
80°C (a he Boom Clay/
lining in e ace)
40 × 2.5 m (galle y) Van Gee e al. (2007);Van Ma cke
e al. (2013);Dizie e al. (2021);
Chen e al. (2023a,b);Li e al. (2023)
Cox (Bu e URL, F ance)
TER 2006–2009 Cyclic hea ing. T,Pand s ain measu ed in
close BHs. Lab es s on co e samples
300–900 W 3-m BH Wile eau e al. (2007);Ga i e e al.
(2014)
TED 2010–2012 3 hea e s. Focus on EDZ. T,Pand s ain
measu ed in close BHs. Lab es s on co e
samples
90°C/600 W pe hea e 16-m BHs wi h 4-m
hea e s
A mand e al. (2017);Conil e al.
(2020)
TFW 2011
(2 monh s)
Rapid hea ing. Tand Pmeasu ed 120°C–80°C/500 W 3-m BH A mand e al. (2017)
ALC1604 2013–2019 Full-scale HLW cell 90°C/220 W/m 25-m BH wi h 15-m
hea ed sec ion
Tou chi e al. (2021);Bumbiele e al.
(2021)
CRQ 2019, 2020 Rapid hea ing o each he mal
hyd o ac u ing. 10 hea ing BH, 2 hea ing
phases
80°C–95°C/
1750–2220 W
10 × 20 m BH wi h
10-m hea e s
Plúa e al. (2023);Plúa e al. (2024)
ALC1605 2020-now Full-scale HLW cell, annulus be ween casing
and clay o ma ion filled wi h MREA cemen
85°C/220 W/m 25-m BH wi h 15-m
hea ed sec ion
Bumbiele e al. (2024)
CRQ2 2023 Rapid hea ing o each he mal
hyd o ac u ing. 10 hea ing BH
89°C/1750–2220 W 10 × 20 m BH wi h
10-m hea e s
Opalinus (Mon Te i URL, Swi ze land)
HE-D 2003–2005 2 hea e s, 2 hea ing phases. T, po e wa e P,
gas mig a ion, de o ma ion measu ed in
24 B H
100°C/650–1950 W 14 × 0.3 m (BH) Wile eau (2005);
Zhang e al. (2007);
Wile eau and Ro h uchs (2007)
FE 2014-now Bu e be ween hea e and hos ock 60°C–80°C Real scale, galle y NAGRA (2019)
FIGURE 3
O e iew o he PRACLAY In-Si u Expe imen , including he
componen o hea e es . The PRACLAY galle y has an inne adius o
0.95 m and he hickness o he lining is 30 cm (©EURIDICE).
F on ie s in Nuclea Enginee ing on ie sin.o g08
Villa e al. 10.3389/ nuen.2025.1436490
long and is sepa a ed om non-hea ed pa by a hyd aulic seal. The
hea ed sec ion o he galle y was backfilled wi h sand, sa u a ed and
p essu ised wi h wa e a e he ins alla ion o he seal in 2010. The
main ole o he seal is o hyd aulically cu o he hea ed pa om
he non-hea ed pa (Figu e 3). Ben oni e clay, which has a high
swelling po en ial unde hyd a ion, was chosen o achie e his goal.
In his way, he in e ace be ween he Boom Clay and he ben oni e
is sealed and pe meabili y in he con ac zone su ounding he seal is
educed. The high p essu e inside he PRACLAY galle y is hus
main ained.
The hea ing sys em consis s o a p ima y hea e , a ached o he
galle y lining, and a seconda y hea e , which is placed in a cen al
ube ha es s on a suppo s uc u e. A con ol sys em egula ing
he hea ing powe as a unc ion o measu ed and a ge empe a u es
is also pa o he hea ing sys em. Du ing he s a -up phase, he
powe was inc eased in a con olled manne o limi he he mal
g adien o e he galle y lining.
The hea ed pa o he PRACLAY galle y is di ided in o
h ee zones:
- Zone 1: on -end zone, 2.26 m long, close o he
PRACLAY seal,
- Zone 2: middle zone, 28.48 m long, in he middle o he
expe imen al pa o he galle y,
- Zone 3: a -end zone, 3.29 m long, a he end o he galle y.
The powe inpu can be con olled independen ly in each o he
h ee zones. In his way, he end e ec s can be minimised and a
empe a u e field ha is as uni o m as possible can be c ea ed along
he hea ed sec ion.
The sand ha fills he galle y was pu in place by blowing i in a
d y s a e in o he galle y be o e Sep embe 2011. Subsequen ly, a
o al olume o abou 43 m
3
o ap wa e was injec ed in o his pa o
he galle y be ween Janua y and May 2012. Sa u a ion o he
backfilled galle y was hen na u ally comple ed wi h he wa e
flowing om he hos Boom Clay in o he galle y. The po e
wa e p essu e in he galle y g adually inc eased and a e
~2.5 yea s i eached 1 MPa, and he backfilled PRACLAY
galle y was es ima ed o be ully sa u a ed. Du ing he hea ing
phase o he expe imen , he p essu e in he backfilled galle y
e ol es na u ally wi hou any human in e en ion (adding o
sub ac ing an amoun o wa e ).
The PRACLAY In-Si u Expe imen was in ensi ely
ins umen ed wi h abou 1,100 senso s (piezome e s,
he mocouples, fla -jacks, s ain gauges, e c.). Ins umen ed
bo eholes we e d illed om bo h he Connec ing galle y (CG)
and he PRACLAY galle y (PG).
The hea e was swi ched on he 3 No embe 2014 wi h a
cons an powe o 250 W/m o he h ee zones o he p ima y
hea ing sys em. Two mon hs la e , he powe was inc eased om
250 W/m o 350 W/m. Finally, he powe was again inc eased o
450 W/m and main ained un il he empe a u e a he ex ados o
he conc e e lining eached 80°C, 8 mon hs a e he s a o hea ing.
This empe a u e was kep cons an by g adually educing he powe
in he h ee zones. A e 4 yea s o hea ing, he zone in which
empe a u e was a ec ed by he es ex ended up o abou 15–20 m
and con inued o g ow smoo hly and slowly. The e olu ion o he
empe a u e was seen o be sligh ly di e en be ween he ho izon al
and he e ical di ec ions, pu ing in e idence he aniso opy o he
he mal conduc i i y. The po e wa e p essu es in he expe imen al
se up and in he clay also e ol ed smoo hly, egula ly and wi hou
any sudden o o he wise unexpec ed changes. The po e wa e
p essu e eached a alue o 2.8 MPa in he backfilled pa o he
hea ed galle y and a maximum alue o 3 MPa in he Boom Clay. In
he a field, changes o po e wa e p essu e we e seen up o a
dis ance o 22 m om he axis o he hea ed galle y, while he
empe a u e had no inc eased a his loca ion ye . A he end o
2023 he empe a u e a he in e ace be ween he Boom Clay and
he ex ados o he conc e e lining was s ill main ained a 80°C.
Mo e de ails abou he la ge-scale in si u PRACLAY Hea e es
can be ound in Van Ma cke e al. (2013) and Dizie e al. (2021).
3.2 ALC 1605 HLW cell es
The ALC1605 ull-scale hea ing expe imen akes place in he
MHM URL in no h-eas e n F ance. The 25-m long cell was d illed
in he di ec ion o he maximum ho izon al s ess om he GAN
d i in No embe 2018. The cha ac e is ics o he cell co espond
o he 2015 e e ence design o he Cigéo HLW cell, excep o he
leng h, which will be ei he 80 m o 150 m long. Compa ed o he
p e ious ull-scale hea ing expe imen (ALC1604, Bumbiele e al.,
2021), he 30″casing is now cen alised and he annulus be ween
he casing and he o ma ion is filled wi h an alkaline cemen g ou
called MREA (Ma é iau de emplissage de l’Ex ados des Al éoles).
The MREA is injec ed in he annulus o educe he co osion a e
o he casing by: (i) neu alising he acidic d ainage p oduced by
py i e oxida ion, (ii) educing he amoun o oxygen coming om
he d i .
The de ailed objec i es o he expe imen a e o:
- S udy he impac o a he mal load on he TM beha iou o he
casing when he annulus is filled wi h an MREA cemen .
- S udy he impac o a he mal load on he THM beha iou o
he Cox clays one in he nea field (bu beyond he EDZ) and
in he a field (beyond a ew cell diame e s) wi h a filled
annulus. The empe a u e and p essu e e olu ion a e
moni o ed a ound he cell and a di e en o se s om he
d i . A compa ison wi h he measu emen s made du ing he
ALC1604 expe imen will help iden i y a po en ial impac o
he filling ma e ial on he kine ics and he ampli ude o he
he mal p essu ing in he nea field, and possibly he a field.
The casing comp ises hi een in e locked elemen s, each
measu ing 2 m in leng h. Each casing elemen is equipped wi h
empe a u e senso s on hei inne su ace, and fi e o hem include
con e gence measu emen s o moni o casing o alisa ion.
Addi ionally, wo casing elemen s a e equipped wi h ex e nal
fib e op ics o s ain and empe a u e measu emen s on he
ou e su ace. In he o ma ion, eigh bo eholes we e d illed
a ound he cell o po e p essu e, empe a u e, and pe meabili y
measu emen s (Figu e 4):
-3 bo eholes, di e ging om he cell in a e ical plane wi h
5 measu ing chambe s and a leas h ee o hem in he
hea ed zone;
F on ie s in Nuclea Enginee ing on ie sin.o g09
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BGS pe o med a se ies o no el expe imen s using a highly
ins umen ed bespoke di ec shea appa a us, he Hea ed Shea Rig
(Supplemen a y Figu e 11, desc ibed in, e.g;, Cuss e al. (2011)),
using hea ing ca idges and band hea e s a ached o he ig o
inc ease empe a u e up o 90°C. The samples, p epa ed by machine
la hing, we e 60 ± 0.01 mm in diame e and 53 ± 1 mm in heigh .
The in ac samples we e ini ially shea ed, hen hyd aulic flow was
imposed in o he ac u e, and finally ac i e shea ing ook place
unde cons an hyd aulic flow. The esul s epo ed in G gic e al.
(2023b) showed ha empe a u e has a conside able e ec on he
shea p ope ies o Opalinus Clay and Cox.
All es s wi h Opalinus Clay showed elas ic-b i le beha iou , wi h
peakshea s essinc easingby0.47MPape 10
°C empe a u e. Residual
s eng h also inc eased wi h empe a u e a a a e o 0.09 MPa pe 10°C.
Shea modulus showed conside able sp ead in he da a, bu also showed
an inc ease wi h empe a u e. Repea shea in Opalinus Clay also showed
a clea inc ease in peak s eng h o 0.175 MPa pe 10°C and esidual
s eng h o 0.178 MPa pe 10°C. A small inc ease in shea modulus was
seen bu wi h conside able sp ead in he da a. The e o e, in in ac and e-
shea ed Opalinus Clay, s eng h and compliance inc ease wi h
empe a u e. The inc ease was g ea e in in ac OPA.
Conside able a ia ion was seen in he flow a e in o he ac u e
ha could no be desc ibed by ac u e su ace cha ac e is ics.
The e o e, wo di e en sel -sealing po en ial (SSP) coe ficien s we e
defined: a) as a esul o hyd aulic flow along he ac u e (SSP
H2O
); b) as
a esul o ac i e shea along he ac u e while hyd aulic flow con inued
(SSP
τ
). The SSP coe ficien desc ibes he p opo ional change in flow as
opposed o he absolu e change in flow a e. Sel -sealing po en ial was
seen o change wi h empe a u e in Opalinus Clay. A clea ela ionship
wasseenwi hSSP
H2O
, wi h a educ ion in sel -sealing capaci y wi h
inc easing empe a u e (Figu e 12). A a empe a u e o 90°C, he sel -
sealing po en ial was negligible. A di e ence was seen be ween SSP
H2O
o ac u es ha we e o med a ambien empe a u e and hose
o med a empe a u e, al hough his may simply be explained by
na u al a ia ion be ween samples. This esul sugges s ha SSP
H2O
is
be e in ac u es ha ha e o med a empe a u e. This may be ela ed
o di e ences in ac u e opology. Conside able sp ead o esul s was
seen o sel -sealing po en ial because o ac i e shea (SSP
τ
). Howe e , a
educ ioninSSP
τ
was seen wi h inc easing empe a u e. In conclusion,
o Opalinus Clay, he e ec i eness o sel -sealing p ocesses educed a
ele a ed empe a u es.
All ac u e su aces we e lase scanned ollowing he ini ial and e-
shea s ages o he expe imen . Li le a ia ion was seen in oughness
cha ac e is ics o he ini ial shea samples, wi h a educ ion in
oughness seen du ing e-shea . Li le a ia ion was seen in ac u e
opology o shea ac u es c ea ed a di e en empe a u es in
ini ially in ac samples. The p esence o wa e du ing he e-shea
phase esul ed in he educ ion in ac u e oughness. As sel -sealing
po en ial (SSP
H2O
) is a unc ion o empe a u e and ac u e oughness
al e s wi h empe a u e, i is likely ha ac u e oughness played a ole
in he e ec i eness o ac u es o sel -seal.
In he es s pe o med wi h Callo o-Ox o dian clays one by BGS he
s ess-s ain esponse showed a simila o m o e he ull ange o
empe a u es, al hough as empe a u e inc eased he esponse was
mo e b i le. Peak s eng h was seen o inc ease by 0.13 MPa pe
10°C, wi h esidual s ess inc easing by 0.01 MPa pe 10°C. Shea
modulus educed wi h empe a u e, al hough his esul may be
influenced by a low modulus seen a he highes empe a u e.
Callo o-Ox o dian clays one he e o e inc eases in s eng h wi h
empe a u e bu has a educing s i ness. Sel -sealing p ocesses in
Callo o-Ox o dian clays one we e seen o g ea ly change o e he
ange o empe a u es in es iga ed. A ambien empe a u es, SSP
H2O
o Coxwas132and educed ojus 7a 90
°C. The e o e, a nea wo-o de
o magni ude educ ion was seen in he e ec i eness o sel -sealing
because o wa e flow. A educ ion was also seen in he e ec i eness o
sel -sealing becauseo ac i eshea (SSP
τ
), al hough he educ ion was no
as ma ked as o wa e and he da a showed conside able sp ead. The
p elimina y da a o Callo o-Ox o dian clays one sugges ha he
a ou able sel -sealing p ope ies o he ock educe wi h empe a u e
and become almos negligible a 90°C, ha is in con adic ion wi h wha
ULo aine and UGA ound (Figu e 9).
5 Modelling ools and app oaches
5.1 Boom Clay
The hyd o-mechanical beha iou o Boom Clay is ep oduced wi h
models such as he D ucke -P age c i e ion (D ucke and P age , 1952)
o he Cam-Clay model. Many o he cons i u i e mechanical laws ha e
been de eloped o simula e he clay in a ious he mo-hyd o-mechanical
condi ions. Fo example, he de elopmen o he mo-plas ic s ains by
he inc ease o empe a u e was aken in o accoun in models such as
ACMEG-T (F ançois, 2008) and in o he he mo-mechanical cap models
(Cui e al., 2000;Dizie , 2011). Dizie (2011) de eloped a he mo-
mechanical model consis ing in an ex ension o he cap model o
he mo-plas ici y. The model combines di e en plas ic mechanisms,
i.e., modified Cam-clay, ic ion angle c i e ion and a ac ion c i e ion. In
addi ion o hese h ee yield su aces, a he mo-plas ic mechanism is
added based on he wo k done by Sul an (1997) and Cui e al. (2000).The
he mo-plas ic model is based on he model de eloped by Hueckel and
Bo se o (1990) in which wo plas ic mechanisms we e added o
ep esen he he mo-mechanical beha iou o soils. These
mechanisms make possible o ep oduce he olume change induced
by empe a u e and he dec ease o he p econsolida ion p essu e wi h
he inc ease o empe a u e. Figu e 13 ep esen s hese mechanisms in he
(p’,T) plane. The he mal yield limi (TY) ep oduces he gene a ion o
olume ic he mal s ain depending on he s ess s a e o OCR o he
clay. This cu e is close o he p’axis because he soil is assumed o be
FIGURE 12
Influence o empe a u e on sel -sealing po en ial o Opalinus
Clay as a esul o hyd a ion (BGS esul s in G gic e al., 2023b).
F on ie s in Nuclea Enginee ing on ie sin.o g16
Villa e al. 10.3389/ nuen.2025.1436490

ini ially i gin o any empe a u e e ec s. The loading yield limi (LY)
ep esen s he dec ease o he p econsolida ion p essu e wi h
empe a u e.
Conside ing c oss-aniso opic models wi h aniso opic
p ope ies o he clay helps o ha e a be e unde s anding o
he Boom Clay beha iou . The fi s in eg a ion o his elas o-
plas ic aniso opy was done du ing he TIMODAZ p ojec
(Cha lie e al., 2010). E en i he simple app oach p oposed
a ha ime al eady p o ided e y p omising esul s, aniso opic
models o Boom Clay s ill need u he in es iga ions o
comple ely desc ibe i s elas o-plas ic esponse.
Some o he modelling exe cises ca ied ou using es s
pe o med wi h Boom Clay ( om iaxial es s o la ge-scale in-
si u es s) and hei main conclusions a e summa ised below. Some
o hese exe cises we e pa icula ly use ul o ob aining pa ame e s.
−Wi hin he amewo k o he EC p ojec TIMODAZ, a
backanalysis o se e al iaxial es s was pe o med (Dizie ,
2011; TIMODAZ, 2010) o de e mine a se o mechanical
pa ame e s. The modelling esul s pu in e idence ha
de ia o ic beha iou is well ep esen ed when conside ing
ha dening o so ening, bu he olume ic beha iou is
mo e di ficul o cap u e. The main conclusion o hese
modelling ac i i ies is ha a classical elas o-plas ic model
may be used o simula e quali a i ely he de ia o ic
beha iou o he clay unde d ained and und ained
condi ions. The smoo h ansi ion be ween he elas ic and
plas ic pa may be cap u ed hanks o well adap ed
ha dening pa ame e alues. In ha way, he elas ic domain
is educed and he plas ic s ains a e gene a ed ea lie .
−A D ucke -P age model, which akes in o accoun he
aniso opic na u e o Boom Clay, was used o model a
hollow cylinde es pe o med a EPFL du ing he
TIMODAZ p ojec (F ançois e al., 2014). The aniso opy
o he clay was conside ed by using a ans e se elas ici y and
by an e ec i e cohesion a ying acco ding o he angle
be ween he s a ifica ion plane and he di ec ion o he
p incipal s ess. This app oach was implemen ed wi hin he
LAGAMINE fini e elemen so wa e (Collin, 2003). The
compa ison be ween obse a ions and nume ical esul s in
he h ee di ec ions confi med he impo ance o he c oss-
aniso opy p ope ies o he Boom Clay.
−The la ge scale PRACLAY Hea e es (sec ion 3.1) was
modelled conside ing a D ucke -P age model wi h a c oss-
aniso opic elas ici y and a ha dening beha iou o he
e ec i e ic ion angle (Dizie e al., 2016;2017). In his
model, he empe a u e induces he mal elas ic s ains only
and he he mo-plas ici y was no conside ed. Dis inc e ical
and ho izon al o al s esses we e imposed and a coe ficien o
ea h p essu e a es (K
0
) o 0.7 (based on Be nie e al., 2002;
Be nie e al., 2007a;Dehandschu e e al., 2004;Co ne ,
2009). The e ec i e s esses we e defined acco ding o he
Te zaghi’s p inciple, he hea ans e using Fou ie ’s law o
conduc ion and he flow o wa e using he classic Da cy’s law.
The he mo-hyd aulic p ope ies selec ed we e based on
Be nie e al. (2007a),Bas iaens e al. (2006),Chen e al.
(2011),Ga i e e al. (2014),Ho seman e al. (1987),Chen
(2012),Chen e al. (2014). The mechanical p ope ies o he
exca a ion-damaged zone dec eased due o he exca a ion and
emained he same o he hea ing phase as hei po en ial
es o a ion equi es a longe ime (sel -healing). Al hough he
modelling esul s we e in a good ag eemen wi h he
obse a ions, he ollowing limi a ions we e iden ified:
1. Blind p edic ions o Dizie (2011) showed ha a his scale he
e ec o he mo-plas ici y should be e y limi ed in compa ison
wi h he mo-elas ic models. The empe a u e a ound
PRACLAY hea e es s should induce only e e sible
de o ma ions. This conclusion needs o be econside ed wi h
he cu en knowledge o he PRACLAY Hea e es , which
s a ed in 2014.
2. In he modelling o he PRACLAY Hea e es , he influence o
he EDZ is limi ed o an ab up a ia ion o pa ame e s wi h
ime. This desc ip ion o he EDZ equi es u he
in es iga ions o imp o e he modelling o hyd o-
mechanical dis u bances induced by he exca a ion (Chen
e al., 2021;Chen e al., 2023 G.).
3. The iscous cha ac e is ics o Boom Clay we e no aken in o
accoun while i is known ha i exhibi s a isco-elas o-plas ic
beha iou . This e ec needs o be in eg a ed in he cons i u i e
models o simula e he long- e m beha iou o he Boom Clay.
5.2 Callo o-Ox o dian clays one
In o de o alida e he heological models a he scale o a HLW
cell and, and i possible, o imp o e he de e mina ion o he
pa ame e s used, ANDRA se up om 2003 an in si u
expe imen al p og amme o p og essi ely:
FIGURE 13
The mal yield limi (TY) and loading yield limi (LY) in he (p’,T) plane (Dizie , 2011;Cha lie e al., 2010).
F on ie s in Nuclea Enginee ing on ie sin.o g17
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−Confi m he he mal design pa ame e s o he disposal
−P o ide a be e quan ifica ion o he THM p ocesses a ound
he HLW cells
−Pe o m some expe imen s o alida e he concep s o he
HLW cells
The in-si u es s in he MHM URL made i possible, h ough
in e se analysis, o es ima e ce ain THM pa ame e s on a me ic
scale and o compa e hem wi h he measu emen s on samples
(Ga i e e al., 2014). Fo example, he in e se analysis o he he mal
pa ame e s ( he mal conduc i i y, hea capaci y) confi med he low
a iabili y be ween he alues ob ained in he labo a o y
expe imen s and hose measu ed in he field.
The small-scale he mal es s (TER, TED) demons a ed ha he
nume ical simula ions conduc ed wi h a linea he mo-po o-elas ic
model could accu a ely ep oduce he empe a u e and he po e
p essu e a ia ions, while also aking in o conside a ion he he mal,
mechanical and hyd aulic aniso opy. F om hese es s, he
sensi i i y analyses showed ha he majo pa ame e s we e he
s i ness o he Cox clays one, he pe meabili y, and, o a lesse
ex en , he he mal conduc i i y and he Bio coe ficien .
The fi s esul s om he ull-scale HLW disposal cell
demons a ion es wi h he 2009 concep in he MHM URL
(ALC1604) showed ha he small-scale app oach ha was used,
wi hou conside ing he change in he mal pa ame e s in he EDZ,
enables a easonable p edic ion o he empe a u e ange. Fo he
changes in he “ a -field”po e p essu e (se e al me es away om
he hea ing cell), he influence o he modifica ionson henea -
field hyd o-mechanical p ope ies caused by he cell exca a ion,
emain low. Howe e , in he nea field, he pu ely linea po o-
elas ic app oach is no good enough o co ec ly ep oduce he
change in po e p essu e o he de o ma ions. A mo e comple e
modelling app oach is he e o e equi ed o be e ep esen he
physical p ocesses in he ac u ed zone caused by cell exca a ion
( a ia ions in pe meabili y, mechanical beha iou o
ac u ed zone, e c.).
The analysis o he empe a u e, p essu e and s ess a ia ions
a ound he HLW cells as a unc ion o he he mal load and o he
in e -cell spacing was done in e nally using wo well-known
nume ical simula ion p og ams: Code-As e and Code_B igh .
UPC also pe o med he modelling on Code_B igh o he
ALC1604 hea ing expe imen (Tou chi e al., 2021).
In addi ion, some benchma king exe cises we e ca ied ou ,
o example:
−Cons i u i e model o he EDZ. A benchma k exe cise was
o ganised in 2012 o model he induced ac u e ne wo ks
a ound a d i (Seyedi e al., 2017;Guayacan, 2016). Se e al
cons i u i e models we e de eloped, di ided in o ou main
amilies: mos we e based on isco-elas o-plas ici y, bu
damage-mechanics, igid body sp ing and compu a ional
homogenised models we e also es ed. I was shown ha
accoun ing o ma e ial aniso opy and s ain localisa ion
ea men echniques could imp o e he esul s when elas o-
isco-plas ic models a e used.
−THM modelling o he TED in-si u hea ing es . A benchma k
exe cise was o ganised as pa o he DECOVALEX
2019 in e na ional p og am wi h he pu pose o upscale he
THM modelling om small-size expe imen s (some cubic
me es) o eal-scale cell expe imen s ( ens o cubic me es)
and finally o he scale o he was e eposi o y (cubic kilome es).
I was based on he TED small-scale hea ing expe imen (Conil
e al., 2020) and ocused on he THM beha iou o he
undis u bed clays one in he a field (Seyedi e al., 2021). I
was concluded ha a good p edic ion o he e olu ion o
empe a u e and po e p essu e can be achie ed i aniso opic
po o-elas ic beha iou is conside ed.
5.3 Opalinus Clay
The modelling o se e al la ge-scale hea ing expe imen s
pe o med a he Mon Te i URL, such as he HE-E (Gaus
e al., 2014) modelled by Ga i e e al. (2017a) and he HE-D
(Bossa e al., 2017), modelled by, e.g., Gens e al. (2007) and
Ga i e e al. (2017b), acili a ed he hie a chical classifica ion o
c oss-coupling be ween di e en THM p ocesses in OPA:
−The s onges coupling was ound om he mal o hyd aulic and
mechanical beha iou . Po e wa e p essu e gene a ion is mainly
con olled by empe a u e inc ease, wi h he mal expansion
being he p ima y con ibu o o s ains and displacemen s.
−Significan bu mode a e e ec s esul om he coupling o
hyd aulic o mechanical beha io . Dissipa ion o po e
p essu es induces addi ional displacemen s and s ains,
albei smalle han he mally-induced de o ma ions due o
clay s i ness.
−Mechanical damage could heo e ically impac hyd aulic
esul s, causing highe pe meabili y, bu he damaged
zone’s size seems limi ed, wi h minimal impac .
−No no iceable coupling was obse ed om hyd aulic o
he mal beha io . Hea anspo is p edominan ly by
conduc ion, and ma e ial sa u a ion emains cons an
du ing hea ing.
−Coupling om mechanical o he mal beha io is negligible.
Sub le po osi y a ia ions in he clay hos ock do no a ec
he mal conduc i i y, and mechanical ene gy dissipa ion is
insignifican in he non-iso he mal case o he HE-D
expe imen .
In he con ex o he FE expe imen , a ious modelling exe cises
(e.g., Ewing and Senge , 2012;Senge , 2015;Ga i e, e al., 2014;
NAGRA, 2019) es ima e key pa ame e s, including empe a u e
e olu ion, deg ee o sa u a ion, po e wa e p essu e, and s ain in
he Opalinus Clay. Scoping calcula ions using he THM code_B igh
(Oli ella e al., 1994;1996), as epo ed in NAGRA (2019), yielded
key conclusions:
−Peak empe a u es a he hea e su ace ange om app oxima ely
100°C–195°C, depending on bu e p ope ies.
−The maximum simula ed empe a u e a he in e ace be ween
bu e and ock in he di ec ion o he bedding planes emains
a 85°C, i espec i e o bu e p ope ies.
−Desa u a ion o he Opalinus Clay is limi ed.
−The combined e ec o po e wa e flux and di e en ial he mal
expansion esul s in a maximum po e wa e p essu e inc ease
F on ie s in Nuclea Enginee ing on ie sin.o g18
Villa e al. 10.3389/ nuen.2025.1436490
o a ound 3 MPa a a dis ance be ween 7 and 15 m om he
unnel axis.
5.4 Modelling wo k done du ing HITEC
Nume ical models aking in o accoun mul i-physical couplings
in geome ic configu a ions ha may be complex (se e al ma e ials,
e c.) equi e sophis ica ed beha iou laws o which he e is no
always a simple way (e.g., analy ical solu ions) o alida e he
implemen a ion. Benchma ks a e hen one o he ways o
compa e he di e en app oaches wi h he in e na ional s a e o
he a , o alida e he esul s and o unde s and he di e ences
be ween he models and hei sensi i i ies. As men ioned be o e,
se e al benchma k ini ia i es ha e p e iously been ca ied ou ,
especially h ough he DECOVALEX (DE elopmen o COupled
models and hei VALida ion agains Expe imen s) p ojec . This
in e na ional esea ch and model compa ison collabo a ion was
ini ia ed in 1992 o ad ancing he unde s anding and modelling
o THMC and chemical p ocesses in geological sys ems. O e he
las h ee phases o his p ojec , he ollowing in si u expe imen s
in ol ing clays ones and high empe a u e ha e been modelled: he
HE (D2015 Task B1) and FE expe imen s (D2023 Task C) in he
Mon Te i URL and he TED, ALC1604 (D2019 Task E) and CRQ
(D2023 Task A) expe imen s in he MHM URL. These benchma k
exe cises allowed o imp o e he in e p e a ion o he in si u es s
and led o scien ific publica ions (some o which lis ed in he
p e ious sec ions) ha alida e he modelling app oaches and
ha can now be implemen ed o model and dimension di e en
componen s o he s o age acili y and suppo he sa e y assessmen .
The modelling o gene ic cases o a high-le el was e eposi o y
was unde aken du ing HITEC o compa e he ou pu o he
di e en codes and he beha iou o h ee clay hos ocks (bo h
in he nea field and in he a field). The modelling o some o he
labo a o y expe imen s desc ibed in Sec ion 4.2 was also ca ied ou ,
and he las s ep o he benchma k consis ed in modelling wo ull-
scale in-si u hea ing expe imen s (desc ibed in Sec ion 3). All his
wo k is desc ibed in de ail in de Lesquen e al. (2024).
A compa a i e 2D modelling exe cise o he nea and a field
was ca ied ou o h ee clay ocks conside ed o hos adioac i e
was e eposi o ies in Eu ope: he Boom Clay, he Callo o-Ox o dian
clays one and he Opalinus Clay. The nea -field gene ic case
conside ed he p oblem o a single deposi ion d i du ing
exca a ion, wai ing and hea ing phases. Th ee subcases we e
conside ed: 1) iso opic elas ic condi ions, 2) aniso opic s ess
condi ions wi h c oss-aniso opic elas ici y and he mo-elas ici y
and 3) aniso opic s ess condi ions wi h elas o-plas ici y/damage.
The goal o hese subcases was o compa e he nume ical codes on
fixed exe cises (subcases 1 and 2) by p esc ibing he same bounda y
condi ions and mechanical cons i u i e laws and p ope ies, and o
compa e di e en app oaches o ep oduce he beha iou o he hos
ock and he de elopmen o he EDZ (subcase 3). Bo h unsuppo ed
and suppo ed unnels we e conside ed. The a -field exe cise
conside ed he e ec o hea ing u he away om he disposal
unnels and o e a much longe ime pe iod (1,000 yea s).
A b ie desc ip ion o he app oaches o he a ious modelling
eams and he main de elopmen s achie ed du ing he p ojec is
gi en below:
−ANDRA an he elas ic cases on COMSOL Mul iphysics and
Code_As e . In he amewo k o an ongoing scien ific
collabo a ion, Ine is de eloped a egula ized aniso opic
elas oplas ic and damage model including bo h non-linea
sho - and long- e m esponses (Souley e al., 2024). This
model was implemen ed in COMSOL Mul iphysics and
applied o subcase 3. The a -field model was also un on
COMSOL Mul iphysics.
−BGE wo ked wi h he nume ical code FLACD3D and he open-
sou ce code OpenGeoSys. Wi hin he la e , a ma e ial model
o clays one, which inco po a es i s mechanical, he mal, and
hyd aulic beha iou , was de eloped and implemen ed (Mánica,
2018). The model alls wi hin he amewo ks o he elas o-
iscoplas ici y heo y and he plas ici y-c eep pa i ion
app oach (Chaboche, 2008), and i inco po a es ea u es
ele an o he desc ip ion o indu a ed clays beha iou : a
non-linea yield c i e ion, s eng h and s i ness aniso opy, a
non-associa ed flow ule, a e-dependency, s ain ha dening/
so ening, non-local egula isa ion, c eep de o ma ions, and
pe meabili y inc ease wi h damage. Conce ning he he mal
enhancemen o he model, wo main phenomena we e
conside ed o implemen a ion (Tou chi e al., 2023): he
con inuous a ia ion o mechanical p ope ies (e.g., shea
s eng h) wi h empe a u e, and he empe a u e-induced
e e sible expansi e s ains ollowed by, a some h eshold
empe a u e alues, i e e sible con ac i e s ains.
−EDF used hei in-house so wa e Code_As e and he LKR
model based on Laigle (2004),Kleine (2007) and Raude (2015).
−EURIDICE/SCK•CEN used he fini e elemen code COMSOL
Mul iphysics.
−LEI wo ked on he de elopmen o a cons i u i e model using
he COMSOL Mul iphysics. The mo-po oelas ici y was
conside ed o he modelling o nea field e ec s in he
iso opic and aniso opic s ess condi ions. Fo modelling o
he EDZ elas oplas ici y was conside ed.
−The cons i u i e model o ULiege o he nea field in he
second subcase conside ed aniso opic elas ici y, pe meabili y,
he mal conduc i i y, s ess and Bio coe ficien . They also
de eloped a new THM second g adien model able o
ep oduce he s ain localisa ion p ocesses occu ing wi hin
he EDZ (Song e al., 2023). The model o simula e he a field
conside ed he aniso opy o he elas ici y, he pe meabili y,
he he mal conduc i i y, he s esses and he Bio coe ficien
wi h wo he mal loads (Rawa , 2023).
−UPC de eloped a ully coupled THM cons i u i e model o
clay ocks o sa u a ed and unsa u a ed s a es. The
cons i u i e model is o mula ed wi hin he amewo k o
elas ic- iscoplas ici y, which conside s non-linea i y and
so ening a e peak s eng h, aniso opy o s i ness and
s eng h, as well as pe meabili y a ia ion due o damage. In
addi ion, mechanical p ope ies we e coupled wi h he mal
his o y (Song e al., 2024). The model was implemen ed in he
fini e elemen me hod so wa e CODE_BRIGHT.
A e fixing se e al disc epancies on he inpu pa ame e s o he
nea -field gene ic cases, all eams ob ained ma ching esul s o he
iso opic elas ic s ep. Some a ia ions we e howe e obse ed on he
p essu e and s ess calcula ions in he aniso opic cases. Di e ences
F on ie s in Nuclea Enginee ing on ie sin.o g19
Villa e al. 10.3389/ nuen.2025.1436490
in he THM o mula ions and assump ions made in he di e en
codes may be he main eason o hese dispa i ies. The p ecise
loca ion o he in eg a ion poin depending on he mesh and on he
a e aging me hod may also explain some disc epancies, especially a
o nea he con ou o he unnel whe e he g adien s a e he la ges .
The analysis o LEI showed ha he wa e d ainage condi ion on he
unnel bounda y had no e ec on he he mal s a e a ound he
unnel, bu i had a significan impac on he hyd o-mechanical
esponse (Na kūnienėe al., 2022). The hea ing applied o he low-
pe meabili y clays one/poo ly indu a ed clay esul s in po e p essu e
build-up because o he di e ence in he he mal expansion
coe ficien s o wa e and o he solid ma ix. As expec ed, he
esul ing o e p essu e is ela i ely low in he so e Boom Clay,
bu he exe cise showed ha he same hea load p oduced a e y
di e en p essu e and s ess esponses in he Callo o-Ox o dian
clays one and Opalinus Clay ha ha e simila p ope ies. All hese
elas ic models p edic some ensile e ec i e ho izon al s ess a he
bo ehole wall o he h ee clay hos ocks. In eali y, he exca a ion
induces some ac u ing in his a ea, and mo e ad anced models a e
needed o accoun o he p esence o he damaged zone. The las
s ep o he nea -field benchma k (modelling o he EDZ) ga e an
oppo uni y o imp o e he exis ing models and s udy he impac o
hea ing on he ex ension o he EDZ (Song, 2023). The esul s o
ULiege showed ha he gap dis ance be ween he d i wall and he
line plays a significan ole on he e olu ion o he s ain localisa ion
p ocess. ANDRA’s Comsol model was imp o ed implemen ing a
egula ised aniso opic elas oplas ic and damage model including
bo h non-linea sho and long- e m esponse. The influence o
damage and ac u ing on he anspo and iscous p ope ies was
also conside ed (Souley e al., 2024). This model was u he
de eloped o be able o ake in o accoun he dec ease o s eng h
wi h empe a u e ha was obse ed in labo a o y expe imen s
(sec ion 4.2.1). Di e en app oaches we e used bu simila esul s
we e ob ained, ma ching he EDZ geome y obse ed in si u. Some
a ia ions appea on he size o he damaged zone, bu he high
plas ic s ains a e always localised in he e y nea field and all he
models p edic ha hea ing o 10 yea s a cons an powe does no
esul s in any EDZ expansion.
In he a -field benchma king exe cise, all eams conside ed an
aniso opic po o-elas ic beha iou –which is known o p o ide a
good p edic ion o he e olu ion o bo h empe a u e and po e
p essu e (Seyedi e al., 2021)–and go ma ching esul s o he
p essu e and s ess e olu ion a mid-dis ance be ween wo pa allel
high-le el was e cells. This ou come wi h six modelling eams and
ou di e en codes imp o es he confidence in hese compu a ions
and he modelling app oach used o dimension eposi o ies. A
sensi i i y s udy pe o med by LaMcube on behal o ANDRA
wi h a phase-field model showed ha when aking in o accoun
he p esence o he EDZ, he ex ension o damage emains limi ed o
he nea field (Shao e al., 2024) and i has no impac on he po e
p essu e e olu ion in he a field.
The iaxial comp ession es s pe o med a di e en
empe a u es by ULo aine on hea ed Cox samples (sec ion 4.2.1)
we e modelled by fi e eams. The BGE model de eloped by Mánica
(2018) and implemen ed in he OpenGeoSys open-sou ce code was
applied success ully o his case. A non-local o mula ion was also
employed by UPC in he simula ion o hese es s o allow a p ope
simula ion o localisa ion phenomena. The cons i u i e model was
elas o-plas ic and included so ening and aniso opy o s i ness and
s eng h and he mal e ec s. Realis ic d ainage bounda y condi ions
we e adop ed. The amily o yield su aces we e based on a hype bolic
app oxima ion o he Moh -Coulomb en elope. A pa ame ic s udy
was pe o med o check he influence o he a e o empe a u e ise
and o he es ing pe iod. The ag eemen wi h expe imen al esul s
was sa is ac o y (Song e al., 2024). This exe cise showed ha a good
unde s anding o he bounda y condi ions is essen ial o a co ec
in e p e a ion o he expe imen s and use o hei esul s. The
modelling o he hea ing phase unde und ained condi ions
e ealed he gene a ion o o e p essu es when as hea ing a es
we e applied, ha may induce some damage in he samples. I
may explain he s eng h educ ion obse ed in he es s conduc ed
a low confining p essu es, implying ha he hea ing phase was no
conduc ed unde ully d ained condi ions. Pos mo em analysis o
samples hea ed in he ALC1604 and CRQ in si u hea ing expe imen s
ac ually showed no changes in he mechanical p ope ies. Some o he
models we e ne e heless de eloped o ake in o accoun he obse ed
s eng h educ ion wi h empe a u e (Souley e al., 2024) and i s
impac on he nea -field and a -field calcula ions will be e alua ed.
Fi e eams modelled he ALC1605 in-si u hea ing expe imen
(Sec ion 3.2) in 2D (LEI and ULg) and in 3D (And a, BGE and EDF).
A e he ini ial p edic i e modelling s ep, using he Callo o-
Ox o dian pa ame e s p o ided in he fi s benchma king
exe cises, la ge di e ences we e obse ed be ween he modelling
and he measu emen s. Mos eams unde es ima ed he aniso opic
impac o he cell exca a ion on he po e p essu e. On he o he hand,
plane s ain condi ions do no allow longi udinal fluid flow and hea
flux; as a esul , he empe a u e and po e p essu e e olu ion on
hea ing was o e es ima ed when 2D models we e used. In he
in e p e a i e modelling s ep, he eams had access o he his o ical
da a and could adap hei models o ma ch he esul s and imp o e
he unde s anding o he beha iou o he Callo o-Ox o dian
clays one. To his aim he models we e modified by educing he
alue o he applied hea flow, modi ying he Cox ma e ial p ope ies,
conside ing he hea loss, o in oducing an EDZ. Howe e , none o
his esul ed in a significan imp o emen o he ma ch be ween
p edic ions and measu emen s. Mo e ad anced models a e needed o
ake in o accoun he p ocesses occu ing a ound he unnels (e.g.,
modifica ion o hyd aulic p ope ies wi hin he EDZ, c eep).
Fou eams modelled he la ge-scale in si u PRACLAY Hea e
es (Sec ion 3.1): BGE, ULiège, UPC and EURIDICE/SCK CEN.
The benchma k exe cise s a ed by an academic case, using an elas ic
model wi h pa ame e s app op ia e o Boom Clay, and hen
inc eased in complexi y. The esul s o he fi s s ep showed a
good ag eemen be ween he in ol ed eams when modelling he
expe imen wi h elas ic and elas o-plas ic cons i u i e laws. In all
cases, he aniso opy o he clay was aken in o accoun , wi h
aniso opic in insic pe meabili y and he mal conduc i i y, and
he elas ic beha iou was modelled wi h c oss-elas ici y. Fo he
second phase, ULiège used an iso opic s ain ha dening D ucke -
P age elas oplas ic model. An EDZ wi h a highe pe meabili y was
in oduced and he pa ame e s o he sound laye we e op imised in
o de o ge a good ag eemen wi h he in-si u measu emen s. They also
in oduced a s ain-dependen iso opic e olu ion o he hyd aulic
pe meabili y enso and he shea s ain ep oducing he s i ness
deg ada ion cu e. To model he PRACLAY expe imen UPC used
he ad anced Hype bolic Moh -Coulomb model wi h ha dening-
F on ie s in Nuclea Enginee ing on ie sin.o g20
Villa e al. 10.3389/ nuen.2025.1436490
so ening and nonlocal o mula ion, wi h he ai gap app oach o
ep esen he con ac be ween he hos clay and he conc e e lining. A
sa is ac o y ag eemen wi h field obse a ions was achie ed by bo h
eams, and he analyses showed ha po e p essu es depend s ongly on
s i nesspa ame e sand ha he malp essu iza ionisla ge when he
d ained bulk modulus inc eases. This modelling wo k also showed ha
in insic pe meabili y plays a significan ole in he liquid dissipa ion and,
he e o e, changing he in insic pe meabili y can significan ly modi y he
po e p essu e e olu ion.
An o e all conclusion o hese modelling exe cises is ha e y
consis en esul s can be ob ained wi h di e en codes using a po o-
elas ic app oach when he pa ame e s and bounda y condi ions a e
co ec ly se . As his ype o model is known o p edic co ec ly he
empe a u e and p essu e e olu ions in he a field, his benchma k
inc eases he confidence and shows he obus ness o he modelling
app oach used o design he eposi o ies. Mo e ad anced models a e
howe e needed o accoun o he p ocesses occu ing a ound he
unnels (e.g., modifica ion and s ain dependency o hyd aulic and
mechanical p ope ies wi hin he EDZ, c eep). The modelling o
labo a o y expe imen s showed he impo ance o a good
unde s anding o he es se ups and o he bounda y condi ions
and helped explain some o he esul s.
6 Summa y and conclusions
This pape summa ised he knowledge abou he he mo-hyd o-
mechanical beha iou o h ee clay ocks wi h po en ial o hos
adioac i e was e eposi o ies in Eu ope: he Boom Clay, he
Callo o-Ox o dian clays one and he Opalinus Clay. Expe imen al
and modelling ac i i ies ca ied ou in he amewo k o he EURAD-
HITEC p ojec conce ning hese ma e ials ha e also been syn hesised.
The ocus has been placed on he impac o ele a ed empe a u e on
hese p ope ies.
Wo king a high empe a u e wi h clays ones poses expe imen al
challenges, and in his sense expe imen al imp o emen s we e achie ed
du ing he HITEC p ojec . Di e en es ing cells ( iaxial, oedome ic and
shea ing) and moni o ing ools (X- ay and neu on omog aphy) we e
used by he di e en pa ne s and adap ed o wo k a high empe a u e,
al hough mos es s we e pe o med below 90°C. The use o iaxial cells
wi h hea ing colla s, hough no uncommon, has been pa icula ly
de eloped du ing he p ojec and es s a empe a u es as high as
150°C we e pe o med by ULo aine, al hough wi h conside able
e apo a ion o he samples. Adding hea ing o he di ec shea ig o
BGS was pa icula ly complica ed. X- ay CT and neu on omog aphic
images we e used o ollow he e olu ion o c acks, bu a need o imp o e
he quali y o images and he es ing p o ocols ( ec ea e in si u s ess
condi ions and measu e he hyd aulic conduc i i y o he in e ace du ing
sel -sealing) was iden ified.
The impac o he es ing p o ocols on he esul s ob ained is always a
conce n. Fo example, i canno be uled ou ha he mal loading a es
applied, much highe han hose o be expec ed in a eposi o y, could
damage he samples and consequen ly hei subsequen beha iou .
Fu he mo e, he pa icula s ess condi ions du ing he es s may
a ec he esul s. Thus, he o ma ion o mic oc acks in Cox
clays one induced by he he mal expansion o he po e wa e unde
uniaxial condi ions–leading o a significan dec ease in he peak s eng h
wi h empe a u e–may be educed by applica ion o confining p essu e
du ing hea ing. In ac , he modelling o he iaxial es s e ealed he
gene a ion o o e p essu es when as hea ing a es we e applied unde
und ained condi ions. This o e p essu e could induce some damage in
he samples ha may explain he s eng h educ ion obse ed in he
iaxial es s conduc ed a low confining p essu es, which in u n would
imply ha he hea ing phase o hese es s was no conduc ed unde ully
d ained condi ions. Also in ela ion o he s ess condi ions, while K
0
expe imen s allow he measu emen o o ma ion o e p essu es, hey
impose a sligh ly a ificial bounda y condi ion unde which he sealing o
indu a ed ma e ials such as OPA and Cox may be mo e di ficul . This
geome y may also limi some ailu e mechanisms.
Impo an hyd o-mechanical couplings be ween peak po e
wa e p essu e, empe a u e, pe meabili y and confining s ess
we e iden ified. Tempe a u e was seen o ha e a clea e ec on
he ac u e shea p ope ies o bo h Cox and Opalinus clays ones
(inc ease in peak s eng h, esidual s eng h and shea modulus).
The iaxial comp ession es s showed ha empe a u e may ha e a
nega i e impac on he sho - e m s eng h o ailu e o he Cox
clays one. Bu i his THM damage we e induced, i would
p obably be limi ed o he e y nea field o he EDZ, whe e he
confining p essu e is he lowes . A 100°Cand150
°C, he peak
s eng h and he s i ness o he Cox clays one inc eased,
i espec i eo hesampleo ien a ion,because hepo ewa e
e apo a ed and he samples go desa u a ed. The he mal
p essu isa ion es s on Opalinus Clay and Callo o-Ox o dian
clays one samples did no show any s ong impac o hea ing
on he clay pe meabili y.
Many pa ame e s could influence he e ficiency o he sel -sealing
p ocess: he calcium ca bona e con en , he sample o ien a ion wi h
espec o bedding, he opening o he ini ial a ificial c ack, and he
empe a u e. The es s pe o med confi med he sel -sealing capaci y
o he Cox clays one, e en when hea ed a 90°C. P o ided ha he clay
con en o he samples was high enough, sel -sealing was an e ficien
mechanism wha e e he expe imen al condi ions. Tempe a u e may
ha e a sligh delaying e ec on he sel -sealing p ocess hough.
Howe e , he e ec i eness o sel -sealing p ocesses as a esul o
hyd a ion and shea was seen o educe significan ly a ele a ed
empe a u es. Indeed, ac u e oughness, which likely plays a ole
in his p ocess, is educed by he p esence o wa e du ing he e-shea
phase and by empe a u e.
The esul s o he labo a o y expe imen s confi med ha he
clays one keeps i s good mechanical and sel -sealing p ope ies, e en
when hea ed a high empe a u e (up o 100°C). None heless,
conside ing he hea ou pu o he was e and he he mally
induced po e wa e p essu es, a eposi o y should be loca ed a a
dep h below which he mally induced po e wa e p essu es could
emain lowe han he in-si u s ess. O e all, confidence was gained in
he posi i e impac o he sel -sealing p ocess on he es o a ion o he
ini ial sealing p ope ies o he clay hos ock, especially because he
du a ion o he labo a o y expe imen s was much sho e han he
eposi o y ime scale.
The modelling ac i i ies unde aken du ing HITEC in ended o
compa e he ou pu o he di e en codes used by he pa icipan s
and he beha iou o he h ee clay hos ocks. The benchma ks
comp ised he modelling o nea -field and a -field gene ic cases o a
high-le el was e eposi o y, wo la ge-scale in si u hea ing
expe imen s and iaxial labo a o y es s pe o med in he
amewo k o he p ojec .
F on ie s in Nuclea Enginee ing on ie sin.o g21
Villa e al. 10.3389/ nuen.2025.1436490

The nea -field gene ic case showed he po e p essu e build-up
esul ing om hehea ingapplied o heclayhos ock,and,as
expec ed, a ela i ely lowe o e p essu e in he so e Boom Clay han
in he Opalinus clay and he Cox clays one. All he models p edic ed ha
he high plas ic s ains (associa ed o he EDZ de elopmen ) a e always
localised in he e y nea field. Hea ing o 10 yea s a cons an powe
would no esul in any EDZ expansion. In he a -field model, six
modelling eams using ou di e en codes go ma ching esul s o he
p essu e and s ess e olu ion a mid-dis ance be ween wo pa allel high-
le el was e cells, which imp o es confidence in he modelling app oach
used o dimension eposi o ies.
The modelling o labo a o y expe imen s showed he
impo ance o a good unde s anding o he es se ups and o he
bounda y condi ions and helped explain some o he esul s.
Modelling o he hea ing phase unde und ained condi ions
e ealed he gene a ion o o e p essu es when as hea ing a es
we e applied, inducing some damage in he samples. This may
explain he s eng h educ ion obse ed in he es s conduc ed a low
confining p essu es, implying ha he hea ing phase was no
conduc ed unde ully d ained condi ions.
When modelling he ALC1605 in si u hea ing expe imen in 2D
and 3D, he eams success ully managed o ep oduce he aniso opic
esponse o he clay hos ocks o exca a ion and hea ing, bu mos
eams unde es ima ed he po e p essu e esponse induced by he cell
exca a ion. The use o 2D models does no allow longi udinal fluid
flow and hea flux; hence, hey also o e es ima e he empe a u e and
po e p essu e e olu ion on hea ing. The e olu ions o empe a u e
and po e p essu e we e well modelled in he a field wi h an
aniso opic po o-elas ic app oach, bu mo e ad anced models a e
needed o accoun o he p ocesses occu ing a ound he unnels (e.g.,
modifica ion o hyd aulic and mechanical p ope ies wi hin he EDZ,
c eep). Be e esul s we e ob ained when modelling he la ge-scale in
si u expe imen PRACLAY Hea e es , because a s ain-dependen
iso opic e olu ion o he hyd aulic pe meabili y enso and he shea
s ain ep oducing he s i ness deg ada ion cu e. The pa ame e s
ha played a significan ole o ma ch he in si u measu emen s we e
he s i ness o he sound clay ock and o he damaged clay, and he
pe meabili ies in bo h zones.
An o e all conclusion o hese modelling exe cises is ha e y
consis en esul s can be ob ained wi h di e en codes using a po o-
elas ic app oach when he pa ame e s and bounda y condi ions a e
co ec ly se . As his ype o model is known o p edic co ec ly he
empe a u e and p essu e e olu ions in he a field, his benchma k
inc eases he confidence and shows he obus ness o he modelling
app oach used o design he eposi o ies. Mo e ad anced models a e
howe e needed o accoun o he p ocesses occu ing a ound unnels
(e.g., modifica ion and s ain dependency o hyd aulic and mechanical
p ope ies wi hin he EDZ, c eep). Finally, his p ojec ga e an
oppo uni y o imp o e some o he codes and o alida e some
ecen de elopmen s.
Au ho con ibu ions
MV: Concep ualiza ion, W i ing–o iginal d a , W i ing– e iew
and edi ing. PB: Da a cu a ion, In es iga ion, So wa e,
W i ing–o iginal d a . FC: Da a cu a ion, In es iga ion, So wa e,
W i ing–o iginal d a . RC: Da a cu a ion, In es iga ion,
W i ing–o iginal d a . CL: In es iga ion, So wa e,
W i ing–o iginal d a , W i ing– e iew and edi ing,
Concep ualiza ion. AD: Da a cu a ion, In es iga ion,
W i ing–o iginal d a , W i ing– e iew and edi ing,
Concep ualiza ion. GE: In es iga ion, So wa e, W i ing–o iginal
d a . AG: In es iga ion, So wa e, W i ing–o iginal d a . CG:
Da a cu a ion, In es iga ion, W i ing–o iginal d a . DG: Da a
cu a ion, In es iga ion, W i ing–o iginal d a , W i ing– e iew
and edi ing, Concep ualiza ion. JH: Da a cu a ion, In es iga ion,
W i ing–o iginal d a . CI: Da a cu a ion, In es iga ion,
W i ing–o iginal d a . OL: Supe ision, W i ing–o iginal d a ,
Concep ualiza ion. SL: W i ing–o iginal d a . AN: In es iga ion,
W i ing–o iginal d a , So wa e. ES: In es iga ion, So wa e,
W i ing–o iginal d a . A-BT: W i ing–o iginal d a .
Funding
The au ho (s) decla e ha financial suppo was ecei ed o he
esea ch, au ho ship, and/o publica ion o his a icle. Eu opean
Union’s Ho izon 2020 Resea ch and Inno a ion P og amme unde
g an ag eemen No. 847593.
Acknowledgmen s
Conflic o in e es
The au ho s decla e ha he esea ch was conduc ed in he
absence o any comme cial o financial ela ionships ha could be
cons ued as a po en ial conflic o in e es .
Publishe ’s no e
All claims exp essed in his a icle a e solely hose o he au ho s
and do no necessa ily ep esen hose o hei a filia ed
o ganiza ions, o hose o he publishe , he edi o s and he
e iewe s. Any p oduc ha may be e alua ed in his a icle, o
claim ha may be made by i s manu ac u e , is no gua an eed o
endo sed by he publishe .
Supplemen a y ma e ial
The Supplemen a y Ma e ial o his a icle can be ound online
a : h ps://www. on ie sin.o g/a icles/10.3389/ nuen.2025.1436490/
ull#supplemen a y-ma e ial
F on ie s in Nuclea Enginee ing on ie sin.o g22
Villa e al. 10.3389/ nuen.2025.1436490
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