Journal of Rock Mechanics and Geotechnical Engineering. 2013, 5 (3): ???–???
On the chemo-thermo-hydro-mechanical behavior of geological and
engineered barriers
YuJun Cui*, Anh Minh Tang
Laboratoire Navier/CERMES, Ecole des Ponts ParisTech, 6 et 8, avenue Blaise Pascal, 77455 Marne-la-Vallée cedex 2, France
Received 26 March 2013; received in revised form 10 April 2013; accepted 25 April 2013
Abstract: An overview of the recent findings about the chemo-hydro-mechanical behaviour of materials used for both geological and engineered barriers
in nuclear waste disposal is presented, through some examples about natural Boom Clay (BC) and compacted bentonite-based materials. For the natural
BC, it was found that compression index identified from both oedometer and isotropic compression tests is similar and the compressibility of BC from the
Mol site is higher than that of BC from the Essen site; the shear strength of Mol BC is also higher that the Essen BC, suggesting a significant effect of
carbonates content; the thermal volume change is strongly overconsolidation ratio (OCR) dependent – low OCR values promote thermal contraction while
high OCR values favour thermal dilation; the volume change behaviour is also strongly time dependent and this time dependent behaviour is governed by
the stress level and temperature; the effect of pore-water salinity on the volume change behaviour can be significant when the smectite content is relatively
high. For the bentonite-based materials, it was found that thermal contraction also occurs at low OCR values, but this is suction dependent – suction
promotes thermal dilation. Under constant volume conditions, wetting results in a decrease of hydraulic conductivity, followed by an increase. This is
found to be related to changes in macro-pores size – wetting induces a decrease of macro-pores size followed by an increase due to the aggregates
fissuring. The presence of technological voids can increase the hydraulic conductivity but does not influence the swelling pressure.
Key words: Boom Clay (BC); bentonite-based materials; mechanical behavior; hydraulic conductivity; pore-water salinity; technological voids
1. Introduction
from heat emission by the waste canisters, from water flow and

from field stress/materials swelling. This justifies the wide
In the high-level radioactive waste geological disposal,
multi-barrier concept with geological barrier and engineered
studies conducted on their CTHM behaviors in both laboratory
and field conditions.
barriers is usually considered. The geological barrier is the
In field, tests have been performed in different Underground
natural host formation as claystones (France and Switzerland),
Research Laboratories (URLs). For instance, the French agency
salts (Germany), granite (China and Sweden) and stiff clays
(Andra) has carried out various tests in the Bure URL to
(Belgium), etc. The main functions of geological barrier are its
investigate the involved Oxfordian claystone behavior during
low hydraulic conductivity and its capacity of self healing. The
excavation, heating, etc. The Swiss agency (Nagra) has done
engineered barrier is made up of compacted bentonite-based
the same in the Mont Terri URL. The Belgian agency
materials. It is usually used with granite geological barriers
(Ondraf/Euridice) has investigated the hydraulic behavior and
(China and Sweden) and constitutes a barrier before the
mechanical behavior of Boom Clay (BC) in the Mol URL. Note
geological one. Note that these materials are also used as filling
also
materials for other geological barriers. Main functions of the
Radioprotection et de la Sûreté Nucléaire) has been conducting
bentonite-based materials are its sealing capacity related to its
the infiltration tests aiming at identifying the key factors related
volume change behaviors, including its swelling properties and
to the long-term performance of bentonite-based sealing
its retention capacity mainly related to its hydraulic behavior.
systems when considering the initial technological void. The
that
the
French
institution
IRSN
(Institut
de
In the situation of nuclear waste disposal, the constitutive
thermal loading effect has been also investigated in different
materials of both barriers are subjected to complex coupled
URLs, for instance, in the Mol URL, a 10-year heating project
chemo-thermo-hydro-mechanical (CTHM) loadings stemming
– Praclay project is underway, aiming at investigating the effect
from interaction between clay minerals and pore-water
of heating on the hydro-mechanical of BC on one hand, and the
chemistry or other chemicals resulted from concrete alteration,
sealing capacity of the compacted bentonite ring on the other
hand.
Doi:
*Corresponding author. Tel: +33-164153550; E-mail: yujun.cui@enpc.fr
??
Y.J. Cui and A.M. Tang / J Rock Mech Geotech Eng. 2013, 5
In the laboratory, several studies on the hydro-mechanical
100 mm in diameter) were taken from the Essen site and one
behavior of geological formations have been conducted
core was taken from the Mol site at depth of 223 m. The
(Horseman et al., 1987; Baldi et al., 1988, 1991; Sultan, 1997;
geotechnical properties of these cores are shown in Table 1.
Sultan et al., 2000, 2002; Coll, 2005, Deng et al., 2011a, 2011b,
For the BC at Essen, two cores were taken from the Putte
2011c, 2012). A large number of studies have also been
member (Ess75 and Ess83) and three cores from the Terhagen
performed on the thermo-hydro-mechanical (THM) behavior of
member (Ess96, Ess104 and Ess112). The geotechnical
bentonite-based materials (Pusch, 1979; Dixon et al., 1985,
properties of these cores are similar: specific gravity, Gs =
1987, 1992, 1996, 1999; Yong et al., 1986; Delage et al., 1998,
2.64–2.68; liquid limit, wL = 62%–78%; plastic index, IP = 36 –
2006; Lee et al., 1999; Romero et al., 1999, 2011; Börgesson et
45. The void ratio (e0) ranges from 0.700 to 0.785. The
al., 2001; Cui et al., 2002, 2008, 2011; Marcial et al., 2002;
carbonate content of the core Ess104 (4.36%) is significantly
Marcial, 2003; Montes-H et al., 2003; Villar and Lloret, 2004,
higher than those of other cores (lower than 1%). Note that the
2008; Andra, 2005; Agus, 2005; Villar, 2005; Lloret and Villar,
carbonate content for Ess112 is also relatively high: 2.64%.
2007, Agus and Schanz, 2008; Agus et al., 2010; Gatabin et al.,
After Francois et al. (2009), the main parameters of the BC at
2008; Karland et al., 2008; Komine et al., 2009; Ye et al., 2009;
Mol, e.g. Gs, wL and IP are similar to those of the BC at Essen.
Komine, 2010; Komine and Watanabe, 2010; Tang and Cui,
The void ratio ranges from 0.49 to 0.67, significantly lower
2010a, 2010b; Wang et al., 2012).
than that of BC at Essen. These differences suggest that the BC
In this paper, some advances on the CTHM behaviors of
at Mol is denser and more carbonated.
materials used for geological and engineered barriers are
Table 2 depicts the mineralogical compositions of different
presented through some examples about natural BC from both
cores. It is observed that BC at Essen contains more active
Mol site and Essen site in Belgium and compacted bentonite-
minerals such as smectite, but the total amount of smectite and
based materials.
interstratified illite/smectite is similar.
The particle size distribution curves are shown in Fig. 1. The
2. Volume change behavior of Boom Clay
curves of Ess83 and Ess96 are close to that of Mol, showing a
clay content (< 2 µm) of 57%–60%. The curves of Ess75 and
In the Belgian program for nuclear waste disposal, BC has
Ess104 are slightly below the curves of Ess83, Ess96 and Mol,
been investigated for both Mol site (URL location) and Essen
showing a clay content of 43%–50%. The core Ess112 presents
site (about 50 km east from Mol). In order to compare its
significantly larger particles and a lower clay content (about
volume change behavior for both sites, five cores (1 m long and
40%).
Table 1. Geotechnical properties of the soil cores studied.
Core
Depth (m)
Member
Gs
wL (%)
IP (%)
e0
Carbonate content (%)
Ess75
218.91-219.91
Putte
2.65
78
45
0.785
0.91
Ess83
226.65-227.65
Putte
2.64
70
37
0.730
0.76
Ess96
239.62-240.62
Terhagen
2.68
69
36
0.715
0.24
Ess104
247.90-248.91
Terhagen
2.68
68
39
0.700
4.36
Ess112
255.92-256.93
Terhagen
2.67
62
37
0.755
2.64
Mol
223
Putte
2.67
59-83
0.49-0.67
5.9 – 8.3
Table 2. Mineralogical composition of clay fraction (< 2 µm).
Core
Mineral content (% )
Chlorite
Kaolinite
Illite
Smectite
Ill/Smecta
Ess75
5
35
20
10
30
Ess83
5
35
20
20
20
Ess96
5
35
20
10
30
Ess104
5
35
15
30
15
Ess112
5
35
10
50
10
Mol
5
35
20
10
30
100
t passing (% )
90
80
70
??
Y.J. Cui and A.M. Tang / J Rock Mech Geotech Eng. 2013, 5
The overconsolidation ratio (OCR) is known to have a major
Fig. 1. Particle size distribution curves.
effect on the volume change of soil heated under a constant load.
Both oedometer and isotropic compression tests were carried
At low OCR values, heating induces thermal contraction
out, allowing determination of the compression index Cc. The
(Paaswell, 1967; Plum and Esrig, 1969). On the contrary, at
obtained values of Cc are shown in Table 3. It appears clearly
high OCR values heating results in thermal dilation (Baldi et al.,
that both tests give similar results. Comparison between the two
1988; Towhata et al., 1993).
sites shows that BC at Mol is more compressible than BC at
This aspect was investigated for BC at various OCR values
(OCR = 1, 2, and 12) by carrying out heating tests in a triaxial
Essen.
cell from 22 °C to 100 °C or tests with temperature cycles
(22 °C-100 °C-22 °C). The results are shown in Fig. 3. The
Table 3. Compressibility parameters.
Core
Oedometer compression
Isotropic compression
Ess75
Ess83
Ess96
Ess104
Ess112
Mol
0.378
0.345
0.375
0.327
0.302
0.405
0.383
0.313
0.280
0.346
OCR =1 condition was achieved under confining stresses c of
1.2 and 3.85 MPa; the OCR = 2 condition was achieved under
c = 4 MPa and the OCR = 12 condition was achieved under c
= 4.2 MPa and 6 MPa, respectively.
The results of Fig. 3 confirm the four major trends of the
thermal volume change behavior of saturated clays:
3. Shear strength of Boom Clay
(1) The thermal contraction of a normally consolidated
samples is independent of the mean effective stress (see tests at
In Fig. 2, the results at failure of BC at Mol by various
OCR = 1 under 1.2 and 3.85 MPa, and OCR = 12 under 4.2 MPa
authors (Horseman et al., 1987; Sultan, 1997; Van Impe, 1993;
and 6 MPa). This trend was initially demonstrated by Demars
Baldi et al., 1991; Coll, 2005) and the results on BC at Essen are
and Charles (1982).
gathered in p-q plane (mean stress–deviator stress plane) for a
direct comparison. It appears clearly that the slope of intact BC
100
OCR = 12
at Mol in the range of p > 2 MPa and the slope of intact BC at
OCR = 2
Essen is very close (0.46 against 0.47), suggesting a similar
OCR = 1
80
(intersection) for Mol is significantly larger than that for Essen
T (C)
internal friction angle (12°–13°). However, the q0 value
60
(1.12 MPa against 0.39 MPa). This corresponds to a higher
effective cohesion for Mol as compared with that for Essen:
OCR =1   c  1.2 MPa
OCR =1   c  3.85 MPa
OCR =2   c  4 MPa
OCR =12   c  4.2 MPa
OCR =12   c  6 MPa
40
0.53 MPa against 0.19 MPa. This difference in cohesion is
likely due to the difference in carbonate contents: BC at Mol has
20
1
0
a higher carbonate content (see Table 1).
1
vT (%)
2
3
4
The reconstituted Essen BC has an effective cohesion c' =
0.01 MPa and an internal friction angle ' = 20°. These values
Fig. 3. Thermal volumetric changes of Boom Clay samples at different OCR
values.
are close to those of Essen core Ess112.
(2) The thermal contraction increases when OCR is decreased,
4
leading to pure contraction at OCR = 1, in accordance with the
Deviator stress q (MPa)
q=1.06p+0.08
results of Plum and Esrig (1969), Demars and Charles (1982)
3
q=0.46p+1.12
and Baldi et al. (1988).
(3) The slope of the volumetric strain in the cooling stage is
Mol intact
(literature)
Essen intact
Ess 112
Reconstituted
(Bouazza et al.,1996)
2
q=0.47p+0.39
1
independent of the applied mean effective stress.
(4) The temperature at which the transition between thermal
expansion and contraction occurs decreases with OCR (T =
80 °C at OCR = 12, T = 50 °C at OCR = 2), in accordance with
q=0.77p+0.33
Baldi et al. (1988) and Towhata et al. (1993).
0
0
2
4
Mean effective stress p (MPa)
6
Fig. 2. Summary of failure envelopes of all Boom Clay considered.
It is interesting to note that the slope of cooling is parallel to
the slope of heating dilation. As physically the cooling process
corresponds to a pure thermal contraction of the constituents of
4. Thermal volume changes
soil (solid and water), it can be considered as elastic. Thereby,
the thermal contraction corresponds to a plastic process. Based
Y.J. Cui and A.M. Tang / J Rock Mech Geotech Eng. 2013, 5: ??–
??
on this consideration, Cui et al. (2000) developed a constitutive
cores Ess83 and Ess96 (De Craen et al., 2006) and that of BC at
model allowing describing the thermo-mechanical behavior of
Mol (Cui et al., 2009). The results show that the pore-water at
saturated clays.
Essen has NaCl as main salt, while the pore-water taken from
5. Time dependent behavior of Boom Clay
Mol has NaHCO3 as main salt. Comparison between the values
for Ess83 and Ess96 shows that there is little difference
The time dependent behavior of saturated BC was
between the two cores. The total salinity of the pore-water at
investigated in a triaxial cell under different isotropic stresses
Essen site is 5.037–5.578 g/L, while that at Mol site is only
and at different temperatures (Cui et al., 2009). Fig. 4 presents
1.286 g/L. The results also show that the main cation at both
the variation of consolidation rate from tests 7, 11, 13, and 15
sites is Na+, with a concentration of 0.072–0.080 Mol/L at
as a function of temperature. A clear increase in consolidation
rate with increasing temperature is observed. Furthermore, the
relationship between the consolidation rate and time can be
described by an exponential function. Note that this observation
is made for a quite low stress range; experimental data for a
Test 7
Test 11
Test 13
Test 15
Expon. (Test 13)
Expon. (Test 15)
Expon. (Test 11)
14
dv/d(log10t)100
12
10
8
of salinity on the hydro-mechanical behavior of BC.
Oedometer tests were carried out for this purpose on cores
water in tests Ess83Odo3 and Ess96Odo04; distilled water in
y = 0.0216e0.0841x
R2= 0.8801
tests Ess83Odo4 and Ess96Odo05. The compression curves
y = 0.0075e0.0901x
R2= 0.9975
6
obtained
after
saturating
the
soil
samples
with
the
corresponding pore-water was used to determine different
parameters for each loading/unloading stage (see for instance
y = 0.0389e0.0645x
R2= 0.6473
4
difference in salinity shows the need of investigating the effect
Ess83 and Ess96 using two different pore-waters: synthetic
larger stress range are needed to confirm this point.
16
Essen and 0.014 Mol/L at Mol, i.e. 5–6 times lower. This
Fig. 6a for test Ess83Odo3) such as the compression index
2
( Cc* ), the swelling index ( Cs* ) and the oedometer modulus EOdo
0
20
30
40
50
60
70
80
90
T (°C)
Fig. 4. Consolidation rate versus temperature for different heating tests on
Boom Clay.
that is defined as:
EOdo  h i (d  v / d h )
(1)
where hi is the initial height of the soil sample; dh is the height
change induced by a vertical stress increment d  v .
Fig. 5 presents the variation of consolidation rate versus
Table 4. Pore-water salinity of Boom Clay.
temperature for all the tests performed. The significant scatter
observed is related to the influence of stress level, void ratio,
Salt
Ess83 (10–3 Mol/L)
thermal or mechanical loading rate, loading mode and loading
NaHCO3
7.16
7.16
13.93
Na2SO4
5.23
5.81
0.002
KCl
0.61
0.61
0.34
CaCl2.2H2O
0.52
0.57
MgCl2.6H2O
1.44
1.60
0.11
NaCl
54.7
61.6
0.17
interval, In spite of this, a clear trend showing an increase in
Ess96 (10–3 Mol/L) Mol (10–3 Mol/L)
consolidation rate with increasing temperature can be observed.
100
dv/d(log10t)100
10
1
0.1
Test 7
Test 12
Test 8
Test 13
Test 11
Test 15
Test 3
H3BO3
0.70
NaF
0.26
CaCO3
0.05
Na+
72.32
80.38
14.104
Total salinity (g/L)
5.037
5.578
1.286
0.01
10
20
30
40
50
T (°C)
60
70
80
90
Fig. 5. Consolidation rate versus temperature for all tests performed on
Boom Clay.
6. Effect of chemistry
In Fig. 6b, the void ratio change versus time is plotted for a
loading step. This consolidation curve allows determination of
the consolidation coefficient cv following the Casagrande’s
method. Using the expression k = cvwg/EOdo, the hydraulic
Table 4 shows the chemical composition of pore-water of
??
Y.J. Cui and A.M. Tang / J Rock Mech Geotech Eng. 2013, 5
conductivity k can be calculated with w as the density of water
experimental errors. As for Ess83, a linear k-e relationship was
and g as the gravitational acceleration.
also obtained for Ess96.
Moreover, the curve shown in Fig. 6b can be used to
determine the secondary deformation coefficient C that
corresponds to the slope of the line after the part of primary
deformation. This definition implies that C is positive for
loading stages as IIIII, and negative for unloading stages as
III and IIIIV.
8
(II)
0.85
(IV)
6
Permeability k (1012 m/s)
0.90
0.80
e (-)
0.75
0.70
 d e / dlog 10  v
Cc*  d e / d(log10 v )
0.65
Cs*
0.60
EOdo   v (1  e 0 ) / e
2
0
(III)
(a)
0.1
 v (MPa)
0.88
4
(I)
0.55
0.50
0.01
1
0.5
0.6
10
0.7
e (-)
0.8
0.9
Fig. 7. Hydraulic conductivity versus void ratio for Ess83.
0.87
8
0.86
0.85
6
Permeability k (1012 m/s)
e (-)
Ess83Odo3
Ess83Odo3 by CPV
Ess83Odo4
Ess83Odo4 by CPV
C  d e / d log10 t
0.84
0.83
t50
0.82
0
1
10
100
1000
Elapsed time (min)
10000
(b)
Ess96Odo4
Ess96Odo4 by CPV
Ess96Odo5
Ess96Odo5 by CPV
4
2
Fig. 6. Determination of parameters from the test Ess83Odo3.
0
0.5
Figs. 7 and 8 show the hydraulic conductivity k versus void
ratio e for the tests Ess83 and Ess96, respectively. For each
0.6
0.7
e (-)
0.8
0.9
Fig. 8. Hydraulic conductivity versus void ratio for Ess96.
core, the results obtained with different water (synthetic water
or distilled water) and by different methods (the direct method
Figs. 9 and 10 present oedometer modulus EOdo versus void
based on the water volume injected by the controller of
ratio e during both loading and unloading paths for Ess83 and
pressure/volume (CPV) and the indirect Casagrande’s method)
Ess96, respectively. For Ess83, it is observed that the points of
are gathered in a same figure for comparison. For Ess83, it can
test Ess83Odo4 with distilled water lies slightly below the
be observed that the measurements by the two methods gave
points of test Ess83Odo3 with synthetic water, suggesting a
similar results. On the other hand, the water chemistry did not
weakening effect of distilled water. However, for Ess96, a
affect the hydraulic conductivity since similar values were
good agreement is observed between the points of test
obtained with two different pore-water salinities. On the whole,
Ess96Odo5 with distilled water and the points of test
a linear k-e relationship is observed. For Ess96, a little
Ess96Odo4 with synthetic water.
difference can be identified between test Ess96Odo4 with
1000
synthetic water and test Ess96Odo5 with distilled water. In
addition, a relatively higher value was also obtained in
Ess83Odo3 III
Ess96Odo5 based on the CPV measurements. These differences
Ess83Odo3 IIIII
Ess83Odo3 IIIIV
Ess83Odo4 III
Ess83Odo4 IIIII
Ess83Odo4 IIIIV
EOdo (MPa)
are not significant and can be included in the range of
100
10
1
0.5
0.6
0.7
e (-)
0.8
0.9
Y.J. Cui and A.M. Tang / J Rock Mech Geotech Eng. 2013, 5: ??–
??
Fig. 12. Consolidation coefficient versus void ratio for Ess96.
Fig. 9. Oedometer modulus versus void ratio for Ess83.
1000
Changes in the secondary deformation coefficient C with
Ess96Odo4 III
Ess96Odo4 IIIII
Ess96Odo4 IIIIV
Ess96Odo5 III
Ess96Odo5 IIIII
Ess96Odo5 IIIIV
EOdo (MPa)
100
void ratio e is depicted in Figs. 13 and. 14 for Ess83 and Ess96,
respectively. For Ess83, the absolute values of C from test
Ess83Odo4 with distilled water are larger than those from test
Ess83Odo3 with synthetic water, especially for the unloading
paths (III and IIIIV). By contrast, for Ess96, this
phenomenon is not obvious and the curves corresponding to
10
two water chemistries almost overlap.
0.02
1
0.5
0.6
0.7
e (-)
0.8
Ess83Odo3 III
Ess83Odo3 IIIII
Ess83Odo3 IIIIV
Ess83Odo4 III
Ess83Odo4 IIIII
Ess83Odo4 IIIIV
0.9
0.01
C
Fig. 10. Oedometer modulus versus void ratio for Ess96.
The results of consolidation coefficient Cv are shown in Figs.
0
11 and 12 for Ess83 and Ess96, respectively. As for the
0.01
oedometer modulus EOdo, the values of Cv from test Ess83Odo4
with distilled water are slightly lower than that from test
Ess83Odo3 with synthetic water; by contrast, test Ess96Odo5
0.02
0.5
with distilled water gave quite consistent results when
compared to test Ess96Odo4 with synthetic water.
0.6
0.7
e (-)
0.8
0.9
Fig. 13. Secondary consolidation coefficient versus void ratio for Ess83.
12
Ess83Odo3 III
Ess83Odo3 IIIII
Ess83Odo3 IIIIV
Ess83Odo4 III
Ess83Odo4 IIIII
Ess83Odo4 IIIIV
Ess96Odo4 III
Ess96Odo4 IIIII
Ess96Odo4 IIIIV
Ess96Odo5 III
Ess96Odo5 IIIII
Ess96Odo5 IIIIV
0.01
C
Cv (108 m2/s)
8
0.02
0
4
0.01
0
0.5
0.6
0.7
e (-)
0.8
0.9
0.02
0.5
Fig. 11. Consolidation coefficient versus void ratio for Ess83.
0.6
0.7
e (-)
0.8
0.9
Fig. 14. Secondary consolidation coefficient versus void ratio for Ess83 and
Ess96.
8
Ess96Odo4 III
Ess96Odo4 IIIII
Ess96Odo4 IIIIV
Ess96Odo5 III
Ess96Odo5 IIIII
Ess96Odo5 IIIIV
Cv (108 m2/s)
6
Examination of the mineralogical composition of Ess83 and
Ess96 showed that the smectite content is likely the main factor
to be considered in investigating the pore-water chemistry
effects on the hydro-mechanical behavior of BC. As Ess83
4
contains more smectite (10% more, see Table 2), it appears
2
0
0.5
0.6
0.7
e (-)
0.8
0.9
??
Y.J. Cui and A.M. Tang / J Rock Mech Geotech Eng. 2013, 5
normal that the Ess83 shows more effects of pore-water
chemistry. But on the whole, these effects are quite limited.
T5 (s = 39 MPa)
7. Volume change behavior of bentonitebased materials
90
The volume change behavior of compacted MX80 bentonite
70
temperature to be controlled (Tang et al., 2007; Tang and Cui,
2010a). The results of thermal volume change under a pressure
Temperature (°C)
was investigated using an isotropic cell that enables suction and
80
Cooling
induced an expansion. Considering that this expansion is linear,
a coefficient of thermal expansion  = 2  10–4 °C–1 can be
deduced. On the contrary, the result from test T3 (s = 9 MPa)
shows that heating induced a contraction. In addition, the
Cooling
60
50
Heating
40
Heating
p = 0.1 MPa are presented in Fig. 15. The results from tests T1
(suction s = 110 MPa) and T2 (s = 39 MPa) show that heating
T4 (s = 110 MPa)
30
Dilation
Contraction
0.5
0.0
0.5
Volumetric strain (%)
20
1.0
1.0
1.5
Fig. 16. Volumetric strain during thermal loading under constant pressure at
5 MPa of tests T4 and T5.
subsequent cooling-reheating cycle undertaken shows a
reversible behavior. Note that significant data scatter was
Based on the compression curves in the e-ln p plane, the

observed in this test and it is thus difficult to quantify the
plastic compression coefficient (s) and elastic coefficient
volume change behavior during the cooling-reheating stage.
were determined. It was observed that these parameters are
independent of temperature but strongly dependent on suction
T2 (s = 39 MPa)
T1 (s = 110 MPa)
(see Fig. 17 for the tests at 25 °C). It appears that wetting
T3 (s = 9 MPa)
increases the two compressibility parameters.
80
1000

70
60
50
40
 (s)
Heating
Suction (MPa)
Temperature (°C)
Heating
Cooling
Heating
100
10
30
Contraction
Dilation
20
1.0
0.5
1
0.0
Volumetric strain (%)
0.5
1.0
Fig. 15. Volumetric strain during thermal loading under constant pressure at
0.1 MPa of tests T1, T2 and T3.
0
0.04
0.08
0.12
0.16
 and  (s)
Fig. 17. Compressibility parameters ( and  (s)) versus suction for the tests
at 25 °C.
The values of yield pressure (p0) determined versus
Fig. 16 presents the results obtained from the tests T4 (s =
110 MPa) and T5 (s = 39 MPa) at p = 5 MPa. It can be
temperature for different suctions are shown in Fig. 18. It can
be observed that p0 decreases upon heating and wetting.
observed that, at high suction, heating from T = 25 °C to 80 °C
90
induced an expansion and cooling from T = 80 °C to 25 °C
expansion  = 210–4 °C–1 can be estimated. At a suction of 39
MPa (test T5), as opposed to the case in test T2 (s = 39 MPa, p
= 0.1 MPa), heating from T = 25 °C to 80 °C resulted in a
thermal contraction and cooling from T = 80 °C to 25 °C also
70
Temperature (°C)
cycle is approximately reversible; a coefficient of thermal
60
50
40
30
resulted in a contraction. The volumetric strain and the
20
temperature during cooling from T = 55 °C to 25 °C can be
10
correlated with a linear function, defining a coefficient of
thermal expansion  = 210–4 °C–1 which is similar to that
deduced from tests T1, T2 and T4.
s = 110 MPa
s = 39 MPa
s = 9 MPa
80
induced a contraction. The volume change during this thermal
0
0.1
1
10
100
Yieldtemperature
pressure (MPa)
Fig. 18. Yield pressure (p0) versus
for different suctions.
Y.J. Cui and A.M. Tang / J Rock Mech Geotech Eng. 2013, 5: ??–
8. Hydraulic behavior
??
Upon wetting, the suction is decreasing and water
conductivity kunsat is in general increasing because water
The hydraulic conductivity of compacted bentonite Kunigel
retention force is reduced (Daniel, 1982; Benson and Gribb,
V1 at different initial water contents was determined by the
1997; Chiu and Shackelford, 1998). On the other hand, wetting
simultaneous profile method (Cui et al., 2008). The results are
under constant-volume conditions reduces the volume of the
presented in Fig. 19. It can be observed that unsaturated
macro-pores family (Cui et al., 2002), giving rise to a decrease
hydraulic conductivity ksat determined by Loiseau et al. (2002)
of kunsat. These two opposing mechanisms explain the results on
reduces with time. The decrease of ksat during the tests was
constant-volume conditions presented in Fig. 19: during wetting,
equally observed by Haug and Wong (1992) and Hoffmann et
k decreases initially because of the reduction of the volume of
al. (2007) on compacted expansive soils. Lloret and Villar
macro-pores. As the volume of macro-pores is dependent on the
(2007) mentioned that the permeability of compacted bentonite
initial water content (Delage et al., 1996), the decrease of k with
measured under water saturated conditions is much lower than
suction is different for different initial water contents. Thereby,
that measured by gas under unsaturated or dry conditions. This
test T03 shows a constant decrease whereas test T01 and T02
phenomenon can be explained by the decrease of the volume of
shows that k started to increase from s = 22 MPa.
macro-pores during wetting as observed by Cui et al. (2002).
mercury intrusion porosimetry (MIP) was conducted on the
1E-12
k initial
T01
compacted MX80/sand mixture wetted at different suctions.
T02
The pores larger than 2 μm are defined as macro-pores. Fig. 20
T03
k (m/s)
In order to verify the wetting effect on the macro-pores,
T04 (e = 0.34)
shows that the macroscopic void ratio (emacro) defined by the
Loiseau et al. (2002)
volume of macro-pores changes with decreasing suction. It can
be observed that the macro-pores quantity is progressively
1E-13
reduced with decreasing suction in zone I and then increased in
Zone II. The increase in zone II can be explained by the
k final
creation of the 2D (two-dimensional) pores due to aggregates
fissuring (Wang, 2012). These changes of emacro upon wetting
explain the decrease of hydraulic conductivity shown in Fig. 19.
1E-14
0
10
20
30
s (MPa)
40
50
60
0.30
0.28
From the analysis mentioned above, it can be concluded that
kini corresponds to the initial microstructure of the compacted
sand/bentonite mixture. Note that the plot of test T04 in Fig. 19
corresponds to the k-s curve of a soil sample having a
microstructure similar to the initial microstructure of a
Macroscopic void ratio
Fig. 19. Hydraulic conductivity versus suction.
0.26
0.24
0.22
compacted soil sample at e = 0.34. Moreover, the soils tested by
Loiseau et al. (2002) and in test T04 have similar initial state (e
0.20
0
20
40
60
= 0.34, wi = 8.0%±0.3%). It can be observed that the k-s curve
Suction (MPa)
determined from test T04 trends to reach kini when suction is
Fig. 20. Changes of macroscopic void ratio with suction.
80
decreased to zero. This confirms that the microstructure of the
soil tested in the two tests is similar.
9. Technological void effect
On the other hand, kfinal corresponds to the final
microstructure of the soil after wetting under constant-volume
As engineered barriers are often made up of compacted
conditions; the macro-pore family was almost eliminated.
bricks, when the bricks are placed around waste canisters or to
Interestingly, the k-s curves obtained from the three tests
form sealing buffers, the so-called technological voids either
performed at constant-volume conditions (T01, T02 and T03)
between the bricks themselves or between bricks, canisters and
trend to join kfinal when suction is decreased to zero, whatever
the host rock are unavoidable. As an example, 10 mm thick
the water content is.
gaps between bentonite blocks and canister and 25 mm thick
??
Y.J. Cui and A.M. Tang / J Rock Mech Geotech Eng. 2013, 5
gaps between the bentonite blocks and the host rock have been
considered in the basic design of Finland (Juvankoski, 2010).
These technological voids appeared to be equal to 6.6% of the
volume of the gallery in the FEBEX mock-up test (Martin et al.,
2006). Fractures that appear in the excavation damaged zone
within the host rock in the near field constitute additional voids.
In the French concept, the volume of the bentonite/rock gaps is
estimated at 9% of the volume of the gallery by the French
waste management agency (Andra, 2005). This value reaches
Fig. 21. Hydraulic conductivity versus dry density of mixture.
14% in the SEALEX in situ test carried out in the Tournemire
URL (Barnichon and Deleruyelle, 2009). This technological
void
can
significantly
influence
the
9.2. Effect of technological void on swelling pressure
hydro-mechanical
In order to analyze the effect of technological void on
behaviour of bentonite-based material and needs to be
swelling pressure, various constitutive parameters of the
investigated in depth.
compacted mixture are defined. It is supposed that in the
9.1 Effect of technological void on hydraulic conductivity
mixture the volume of bentonite (Vb) in the mixture is equal to
Compacted MX80/sand mixture was considered to study the
the difference between the total volume (V) and the volume of
effect of technological void on hydraulic conductivity. With a
sand (Vs). Vb is equal to the sum of the bentonite particle
ring diameter of 38 mm, the annular technological void selected
volume (Vbs) and the volume of void, namely intra-void volume
(14% of the total cell volume representing 17% of the initial
(Vi). The bentonite void ratio (eb) consists of two parts (Eq. (2)),
sample volume) corresponds to a sample diameter of 35.13 mm.
the intra-bentonite void ratio inside the soil (ebi) and the void
Four tests with the same technological void of 14% were
ratio corresponding to the technological void (etech). Eqs. (3)
conducted on samples with the same initial water content of
and (4) define these two voids, respectively.
11% and various initial dry densities obtained by changing the
e b  e bi  e tech
(2)
Vi
V bs
(3)
compaction pressure (between 65 MPa and 85 MPa, giving rise
to dry densities comprised between 1.93 Mg/m3 and 1.98
Mg/m3).
e bi 
The saturated hydraulic conductivity was determined after
saturation of the samples, by both the constant head test and the
e tech 
indirect Casagrande’s method. Fig. 21 compares the results
V tech
V bs
(4)
obtained with that obtained by Gatabin et al. (2008) by constant
where Vtech is the volume of technological voids. The value of
head test on homogeneous samples at similar densities. The
ebi can be deduced from the initial dry unit mass of the mixture
data obtained for the heterogeneous samples with both methods
(dm) using the following equations:
are in good agreement. On the whole, the hydraulic
conductivity decreases with density increase, following a slope
comparable to that obtained by Gatabin et al. (2008). An in-
e bi 
Gsb w
depth examination shows that the samples with initial
technological voids exhibit higher hydraulic conductivity than
that by Gatabin et al. (2008), with a difference of one order of
magnitude. This difference is suspected to be due to a
preferential water flow in the looser zone (initial technological
voids) around the samples.
db 
db
1
(B / 100) m Gss w
Gss w (1  w m / 100)  m (1  B / 100)
(5)
(6)
where  w is the water unit mass, Gsb is the specific gravity of
bentonite, db is the initial dry unit mass of bentonite in the
mixture, which was calculated using Eq. (6) (Dixon et al., 1985;
1E-10
Lee et al., 1999; Agus and Schanz, 2008; Wang et al., 2012),
1E-11
content (in dry mass) in the mixture, Gss is the specific gravity
Hydraulic conductivity (m/s)
 m is the unit mass of the mixture, B (%) is the bentonite
of sand, w
m
is the water content of the mixture. In this study
the decrease of water unit mass (  w ) during hydration (e.g.
1E-12
Skipper et al., 1991; Villar and Lloret, 2004) was not
1E-13
considered and the value was assumed to be constant (1.0
Mg/m3), B = 70%, Gss = 2.65.
1E-14
1E-15
1.4
1.6
1.8
Dry density of mixture (Mg/m3)
2
Y.J. Cui and A.M. Tang / J Rock Mech Geotech Eng. 2013, 5: ??–
??
The values of vertical stress measured at the end of the
is similar and the compressibility of BC from the Mol site is
hydration tests on samples with technological voids are
higher than that of BC from the Essen site; the shear strength of
presented in Fig. 22 with respect to the bentonite void ratio.
Mol BC is also higher than that of the Essen BC, suggesting a
The data of swelling pressure measured in homogeneous
significant effect of carbonates content; the thermal volume
samples under the same conditions of constant volume by other
change is strongly OCR dependent: low OCR values promote
authors are also plotted for comparison (MX80 70/30
thermal contraction while high OCR values favour thermal
bentonite/sand mixture from Karnland et al. (2008), and pure
dilation. The volume change behaviour is also strongly time
MX80 bentonite from Börgesson et al. (1996), Dixon et al.
dependent and this time dependent behaviour is governed by
(1996), Karnland et al. (2008), and Komine et al. (2009)).
the stress level and temperature. The effect of pore-water
salinity on the volume change behaviour can be significant
100
when the smectite content is relatively high. However, the pore-
Mixture 70/30 (Present work)
Mixture 70/30 (Karnland et al., 2008)
Pure bentonite (Karnland et al., 2008)
conductivity.
Pure bentonite (Dixon et al., 1996)
10
Vertical stress (MPa)
water chemistry does not seem to affect the hydraulic
For the bentonite-based materials, it was found that thermal
Pure bentonite (Komine et al., 2009)
Pure bentonite (Borgesson et al., 1996)
contraction occurs also at low OCR values, but this is suction
dependent – suction promotes thermal dilation. Under constant
1
volume conditions, wetting results in a decrease of hydraulic
conductivity followed by an increase. This is found to be
related to changes in macro-pores size – wetting induces a
0.1
decrease of macro-pores size followed by an increase due to the
aggregates fissuring.
The presence of technological voids can form a loose zone
with benonite gel after hydration. This zone corresponds to the
0.01
0
1
2
3
4
Bentonite void ratio (-)
preferential path for water flow, with a relatively higher
hydraulic conductivity.
Fig. 22. Relationship between vertical stress and bentonite (MX80) void
However, the swelling pressure
depends only on the global bentonite void ratio, regardless of
the technological void.
ratio.
References
All data remarkably agree, giving a unique relationship
Agus SS. An Experimental study on hydro-mechanical characteristics of compacted
between the vertical pressure and the bentonite void ratio,
regardless of the sample nature (homogeneous or not). The
correspondence with data from Karnland et al. (2008) (pure
bentonite and 70/30 bentonite sand mixture) at bentonite void
ratio close to 1 is particularly good. This confirms that the
stress at equilibrium is not affected by the heterogeneity of the
samples. The swelling pressure depends only on the global
bentonite void ratio (eb), regardless of the technological void
and the presence of sand.
bentonite-sand mixtures. PhD thesis. Weimar: University of Weimar, 2005.
Agus SS, Schanz T. A method for predicting swelling pressure of compacted bentonites.
Acta Geotechnica, 2008, 3 (2): 125–137.
Agus SS, Schanz T, Fredlund DG. Measurements of suction versus water content for
bentonite-sand mixtures. Canadian Geotechnical Journal, 2010, 47 (5): 583–594.
Andra. Référentiel des matériaux d’un stockage de déchets à haute activité et à vie
longue - Tome 4: Les matériaux à base d’argilites excavées et remaniées. Rapport
Andra N° CRPASCM040015B, 2005.
Baldi G, Hueckel T, Pellegrini R. Thermal volume changes of the mineral-water system
in low-porosity clay soils. Canadian Geotechnical Journal, 1988, 25 (4): 807–825.
Baldi G, Hueckel T, Peano A, Pellegrini R. Developments in modelling of thermo-
10. Conclusions
hydro-geomechanical behaviour of Boom Clay and clay-based buffer materials
(Vol. 2). Commission of the European Communities, Nuclear Science and
An overview of the recent findings about the CTHM
behaviour of materials used for both geological and engineered
barriers in nuclear waste disposal is presented, through some
examples about the natural BC and the compacted bentonitebased materials.
For the natural BC, it was found that compression index
identified from both oedometer and isotropic compression tests
Technology EUR 13365/2, 1991.
Barnichon JD, Deleruyelle F. Sealing experiments at the Tournemire URL. EUROSAFE,
2009.
Benson CH, Gribb MM. Measuring unsaturated hydraulic conductivity in the laboratory
and field. In: Unsaturated Soil Engineering Practice. New York: ASCE,
Geotechnical Special Publication, 1997: 113–168.
Börgesson L, Karnland O, Johannesson LE. Modelling of the physical behaviour of clay
barriers close to water saturation. Engineering Geology, 1996, 41 (1-4): 127–144.
??
Y.J. Cui and A.M. Tang / J Rock Mech Geotech Eng. 2013, 5
Börgesson L, Chijimatsu M, Fujita T, Nguyen TS, Rutqvist J, Jing L. Thermo-hydro-
Dixon DA, Cheung SCH, Gray MN, Davidson BC. The hydraulic conductivity of dense
mechanical characterisation of bentonite-based buffer material by laboratory tests
clay soils. In: Proc. 40th Canadian Geotechnical Conference. Regina,
and numerical back analyses. International Journal of Rock Mechanics and
Mining Sciences, 2001, 38 (1): 95–104.
Chiu TF, Shackelford CD. Unsaturated hydraulic conductivity of compacted sand-kaolin
mixtures. Journal of Geotechnical and Geoenvironmental Engineering, 1998, 124
(2): 160–170.
Coll C. Endommagement des roches argileuses et perméabilité induite au voisinage
d’ouvrage souterrains. Ph.D. Thesis. Grenoble: Université Joseph FourierGrenoble 1, 2005.
Cui YJ, Sultan N, Delage P. A thermomechanical model for clays. Canadian
Geotechnical Journal, 2000, 37 (3): 607–620.
Cui YJ, Loiseau C, Delage P. Microstructure changes of a confined swelling soil due to
Saskachewan, Canada, 1987: 389–396.
Dixon DA, Gray MN, Hnatiw D. Critical gradients and pressures in dense swelling
clays. Canadian Geotechnical Journal, 1992, 29 (6): 1113–1119.
Dixon DA, Gray MN, Graham J. Swelling and hydraulic properties of bentonites from
Japan, Canada and USA. In: Proceedings of the second International Congress on
Environmental Geotechnics. Osaka, Japan, 1996: 5–8.
Dixon DA, Graham J, Gray MN. Hydraulic conductivity of clays in confined tests under
low hydraulic gradients. Canadian Geotechnical Journal, 1999, 36 (5): 815–825.
Francois B, Laloui L, Laurent C. Thermo-hydro-mechanical simulation of ATLAS in
situ large scale test in Boom Clay. Computers and Geotechnics, 2009, 36 (4):
626–640.
suction controlled hydration. In: Jucá, JFT, de Campos TMP and Marinho FAM
Gatabin C, Touze G, Imbert C, Guillot W, Billaud P. ESDRED Project, Module 1-
ed. Unsaturated Soils. Proc. 3rd Int. Conf. on Unsaturated Soils (UNSAT 2002),
Selection and THM characterization of the buffer material. In: International
Recife, Brazil. Lisse: Swets & Zeitlinger, 2002: 593–598.
Conference Underground Disposal Unit Design & Emplacement Processes for a
Cui YJ, Tang AM, Loiseau C, Delage P. Determining the unsaturated hydraulic
Deep Geological Repository. Prague, 2008: 16–18.
conductivity of a compacted sand-bentonite mixture under constant-volume and
Haug MD, Wong LC. Impact of molding water content on hydraulic conductivity of
free-swell conditions. Physics and Chemistry of the Earth, Parts A/B/C, 2008, 33
compacted sand-bentonite. Canadian Geotechnical Journal, 1992, 29 (2): 253–
(Supp. 1): 462–471.
262.
Cui YJ, Le TT, Tang AM, Delage P, Li XL. Investigating the time dependent behaviour
of Boom Clay under thermo-mechanical loading. Geotechnique, 2009, 59 (4):
319–329.
Cui YJ, Tang AM, Qian LX, Ye WM, Chen B. Thermal-mechanical behavior of
compacted GMZ Bentonite. Soils and Foundations, 2011, 51 (6): 1065–1074.
Daniel DE. Measurement of hydraulic conductivity of unsaturated soils with
thermocouple psychrometers. Soil Science Society of America Journal, 1982, 20
(6): 1125–1129.
De Craen M, Wemaere I, Labat S, Van Geet M. Geochemical analyses of Boom Clay
pore water and underlying aquifers in the Essen-1 borehole. SCK•CEN external
report (REPORT SCK•CEN-ER-19), Belgium, 2006.
Delage P, Audiguier M, Cui YJ, Howat M. Microstructure of a compacted silty clay.
Canadian Geotechnical Journal, 1996, 33 (1): 150–158.
Delage P, Howat MD, Cui YJ. The relationship between suction and swelling properties
in a heavily compacted unsaturated clay. Engineering Geology, 1998, 50 (1-2):
31–48.
Delage P, Marcial D, Cui YJ, Ruiz X. Ageing effects in a compacted bentonite: a
microstructure approach. Geotechnique, 2006, 56 (5): 291–304.
Demars KR, Charles RD. Soil volume changes induced by temperature cycling.
Canadian Geotechnical Journal, 1982, 19 (2): 188–194.
Deng YF, Tang AM, Cui YJ, Li XL. A study on the hydraulic conductivity of Boom Clay.
Canadian Geotechnical Journal, 2011a, 48 (10): 1461–1470.
Deng YF, Tang AM, Cui YJ, Nguyen XP, Li XL, Wouters L. Laboratory Hydromechanical Characterisation of Boom Clay at Essen and Mol. Physics and
Chemistry of the Earth, 2011b, 36 (17-18): 1878–1890.
Deng YF, Cui YJ, Tang AM, Nuyen XP, Li XL, Van Geet M. Investigating the porewater chemistry effects on the volume change behaviour of Boom Clay. Physics
and Chemistry of the Earth, 2011c, 36 (17-18): 1905–1912.
Deng YF, Cui YJ, Tang AM, Li XL, Sillen X. An experimental study on the secondary
deformation of Boom Clay. Applied Clay Science, 2012, 59-60: 19–25.
Dixon DA, Gray MN, Thomas AW. A study of the compaction properties of potential
clay-sand buffer mixtures for use in nuclear fuel waste disposal. Engineering
Geology, 1985, 21 (3-4): 247–255.
Hoffmann C, Alonso EE, Romero E. Hydro-mechanical behaviour of bentonite pellet
mixtures. Physics and Chemistry of the Earth, 2007, 32(8-14): 832–849.
Horseman ST, Winter MG, Entwistle DC. Geotechnical characterization of Boom Clay
in relation to the disposal of radioactive waste. Commission of the European
Communities, 1987: 87.
Juvankoski M. Description of basic design for buffer (working report 2009-131).
Technical report, EURAJOKI, Finland, 2010.
Karnland O, Nilsson U, Weber H, Wersin P. Sealing ability of Wyoming bentonite
pellets foreseen as buffer material–laboratory results. Physics and Chemistry of
the Earth, Parts A/B/C, 2008, 33 (Supp. 1): 472–475.
Komine H, Yasuhara K, Murakami S. Swelling characteristics of bentonites in artificial
seawater. Canadian Geotechnical Journal, 2009, 46 (2): 177–189.
Komine H, Watanabe Y. The past, present and future of the geo-environment in Japan.
Soils and Foundations, 2010, 50 (6): 977–982.
Komine H. Predicting hydraulic conductivity of sand bentonite mixture backfill before
and after swelling deformation for underground disposal of radioactive wastes.
Engineering Geology, 2010, 114 (3-4): 123–134.
Lee JO, Cho WJ, Chun KS. Swelling pressures of a potential buffer material for highlevel waste repository. Journal of the Korean Nuclear Society, 1999, 31 (2): 139–
150.
Lloret A, Villar M. Advances on the knowledge of the thermo-hydro-mechanical
behaviour of heavily compacted FEBEX bentonite. Physics and Chemistry of the
Earth, 2007, 32 (8-14): 701–715.
Loiseau C, Cui YJ, Delage P. The gradient effect on the water flow through a compacted
swelling soil. In: Jucá, JFT, de Campos TMP and Marinho FAM ed. Unsaturated
Soils. Proc. 3rd Int. Conf. on Unsaturated Soils (UNSAT 2002), Recife, Brazil.
Lisse: Swets & Zeitlinger, 2002: 395–400.
Marcial D, Delage P, Cui YJ. On the high stress compression of bentonites. Canadian
Geotechnical Journal, 2002, 39 (4): 812–820.
Marcial D. Comportement hydromécanique et microstructural des matériaux de barrière
ouvragée, thèse ENPC, 2003.
Martin PL, Barcala JM, Huertas F. Large-scale and long-term coupled thermo-hydromechanic experiments with bentonite: the febex mock-up test. Journal of Iberian
Geology, 2006, 32 (2): 259–282.
Y.J. Cui and A.M. Tang / J Rock Mech Geotech Eng. 2013, 5: ??–
Montes-H G, Duplay J, Martinez L, Mendoza C. Swelling–shrinkage kinetics of MX80
bentonite. Applied Clay Science, 2003, 22 (6): 279–293.
Paaswell RE. Temperature effects on clay soil consolidation. Journal of Soil Mechanics
and Foundation Engineering, ASCE, 1967, 93 (SM3): 9–22.
Plum RL, Esrig MI. Some temperature effects on soil compressibility and pore water
pressure. In: Effects of Temperature and Heat on Engineering Behavior of Soils,
Special Report 103. Highway Research Board, 1969: 231–242.
Pusch R. Highly compacted sodium bentonite for isolating rock-deposited radioactive
waste products. Nuclear Technology, 1979, 45 (2): 153–157.
??
Tang AM, Cui YJ. Experimental study on the hydro-mechanical coupling behaviour of
highly compacted expansive clay. Journal of Rock Mechanics and Geotechnical
Engineering, 2010a, 2 (1): 39–43.
Tang AM, Cui YJ. Effects of mineralogy on thermo-hydro-mechanical parameters of
MX80 bentonite, Journal of Rock Mechanics and Geotechnical Engineering,
2010b, 2 (1): 91–96.
Towhata I, Kuntiwattanakul P, Seko I, Ohishi K. Volume change of clays induced by
heating as observed in consolidation tests. Soils and Foundations, 1993, 33 (4):
170–183.
Romero E, Gens A, Lloret A. Water permeability, water retention and microstructure of
Van Impe WF. Boom Clay for storage of nuclear waste (discussion session 2b). In:
unsaturated compacted Boom Clay. Engineering Geology, 1999, 54 (1-2): 117–
Athen Al AE ed. Geotechnical Engineering of Hard Soils-Soft Rocks. Rotterdam:
127.
A.A. Balkema, 1993: 1885–1895.
Romero E, Della Vecchia G, Jommi C. An insight into the water retention properties of
compacted clayey soils. Geotechnique, 2011, 61 (4): 313–328.
Skipper NT, Refson K, McConnell JDC. Computer simulation of interlayer water in 2:1
clays. Journal of Chemical Physics, 1991, 94 (11): 7434–7445.
Sultan N. Etude du comportement thermo-mécanique de l'argile de Boom: expériences
et modélisation. Ph.D. Thesis. Paris: Ecole Nationale des Ponts et Chaussées,
1997.
Villar MV, Lloret A. Influence of temperature on the hydro-mechanical behaviour of a
compacted bentonite. Applied Clay Science, 2004, 26 (1-4): 337–350.
Villar MV. MX-80 bentonite, thermo-hydro-mechanical characterisation performed at
CIEMAT in the context of the prototype project. CIEMAT Technical Report:
CIEMAT/DIAE/54540/2/04, 2005.
Villar MV, Lloret A. Influence of dry density and water content on the swelling of a
compacted bentonite. Applied Clay Science, 2008, 39 (1-2): 38–49.
Sultan N, Delage P, Cui YJ. Comportement thermomécanique de l’argile de Boom.
Comptes-Rendus de l’Académie des Sciences, Série II B-Mécanique, 2000, 328
(6): 457–463.
Wang Q. Hydro-mechanical behaviour of bentonite-based materials used for high-level
radioactive waste disposal. Ph.D. Thesis. Paris: Université Paris-Est, 2012.
Wang Q, Tang AM, Cui YJ, Delage P, Gatmiri B. Experimental study on the swelling
Sultan N, Delage P, Cui YJ. Temperature effects on the volume change behaviour of
Boom Clay. Engineering Geology, 2002, 64 (2-3): 135–145.
behaviour of bentonite/claystone mixture. Engineering Geology, 2012, 124: 59–
66.
Tang AM, Cui YJ, Barnel N. A new suction–temperature controlled isotropic cell used to
Ye WM, Cui YJ, Qian LX, Chen B. An experimental study of the water transfer thro ugh
study the thermo-mechanical behaviour of unsaturated expansive clays.
confined compacted gmz bentonite. Engineering Geology, 2009, 108 (3-4): 169–
Geotechnical Testing Journal, 2007, 30 (5): 341–348.
176.
Yong RN, Boonsinsuk P, Wong G. Formulation of backfill material for a nuclear fuel
waste disposal vault. Canadian Geotechnical Journal, 1986, 23 (2): 216–228.
Dr. Yu-Jun Cui is working as a professor at Ecole des Ponts ParisTech (ENPC), France. His research interests cover
unsaturated soil mechanics, laboratory testing, constitutive modelling, environmental geotechnics, railway geotechnics,
nuclear waste disposal, lime/cement stabilized soils, soil-vegetation-atmosphere interaction, compaction of agricultural soils,
etc.
Contact information: Laboratoire Navier/CERMES, Ecole des Ponts ParisTech, 6 et 8 avenue Blaise Pascal, Cité
Descartes, Champs-sur-Marne, 77455 Marne-la-Vallée cedex 2, France.
Tel: +33-(0)1 64153550
E-mail: yujun.cui@enpc.fr