10th Asian Regional Conference of IAEG (2015)

Experimental investigation on soil-water retention properties of compacted GMZ01
bentonite with consideration of temperature and initial dry density
YE Wei-min(1),(2), ZHU Junyi(3), CHEN Bao(1), CHEN Yonggui(1), CUI Yunjun(1),(4)(1). Key Laboratory of Geotechnical and Underground Engineering of Ministry of Education,
Tongji University, Shanghai 200092，China
Email：ye_tju@tongji.edu.cn(2). United Research Center for Urban Environment and Sustainable Development, the Ministry of Education,
Shanghai 200092，China(3). Shanghai Harbor Engineering Design & Research Institute Co., Ltd(4). UR Navier, Ecole des Ponts ParisTech, France
Abstract
Soil-water retention curve (SWRC) of clay is mainly influenced by its initial dry
density and temperature. Soil-water retention tests were conducted on compacted GMZ01
Bentonite with consideration of initial dry density and temperature, corresponding SWRCs
were obtained. Results show that for high suctions, the water retention capacity of confinedcompacted GMZ01 bentonite decrease with increasing temperature. Whereas for low
suctions, the influencing rate of temperature on water content decreases as temperatures
increases. The influence of initial dry density on water retention property of GMZ01
bentonite is very little for high suctions, while significant for low suctions.
Key words: GMZ01 bentonite, soil-water retention curve, temperature, initial dry density,
suctionknowledge of the dependence of the water retention
curve on dry density is necessary (Simms and Yanful,2005). Using the vapor phase method, Sánchez(2004) obtained the SWRCs of confining
high-compacted bentonite with different initial dry
densities. It turned out that the initial dry density canstrongly influence the water holding capacity ofconfined high-compacted bentonite over the low
suction range.
For investigating temperature effects on the water
retention properties of compacted bentonite, various
experimental and theoretical explorations (Villar and
Lloret, 2004; Sánchez, 2004; Villar et al., 2010; Tangand Cui, 2005; Ye et al., 2009; Wan et al., 2015)
were conducted. Villar and Lloret (2004) conductedwater retention tests on FEBEX bentonite by meansof the vapor equilibrium technique. Results showedthat the higher the temperature, the lower the water
holding capacity of the highly compacted bentonite
for both under confined and unconfined conditions.
Gaomiaozi (GMZ) bentonite, collected from
Inner Mongolia Autonomous Region of China, hasbeen considered as a buffer/backfill material in the
Chinese HLW repository (Ye et al., 2010). Using theosmotic technique for low suction and the vapor

1 Introduction
During the operation of the repository, thebentonite will experiences a process from unsaturated
to saturated state by absorbing water from thesurrounding formations accompanied by bentonite
blocks expansion to the nearby voids. As a result, dry
density of the barrier will decrease from the
manufacturing density of the blocks (Villar, 2007).
At the same time, decay heat from the canister, which
will induce the variation of temperature in the barrier,is another factor influencing the water retention
capacity of bentonites (Villar and Lloret, 2004).
Contributions have been made for investigation
on influence of dry density on water retention
property of compacted bentonite. Based on an in-situ
hydration test performed at the Grimsel test site
(Switzerland), ENRESA (2000) reported that the
final overall dry density of the barrier was 1.6 g/cm3,
which was lower than its manufacturing density 1.7
g/cm3 of the FEBEX blocks. This observation
confirmed the dry density variation of the barrier
during the hydration of bentonite blocks. Therefore,
for an appropriate characterization of thehydro-mechanical behavior of deformable clays,1

10th Asian Regional Conference of IAEG (2015)

equilibrium technique for high suction control, Chenet al. (2006) measured the water retention property ofhighly compacted GMZ bentonite specimens withinitial dry density of 1.70g/cm3 under constantvolume and free-swelling conditions. Results showthat there was a closed relationship between water
retention property of bentonite and its microstructure.
With the SWRCs of confined/unconfined highly
compacted GMZ bentonite specimens (1.70g/cm3)
measured at temperatures 20℃, 40℃ and 60℃, Ye
et al. (2009) analyzed the effects of temperature andconstraint condition on the water retention capabilityof GMZ bentonite.
In this work, complementary suction-controlledwater retention tests were conducted on thecompacted GMZ01 bentonite specimens with initial
dry densities of 1.50g/cm3 and 1.90g/cm3 attemperatures 20°C, 40°C and 60°C. Soil water
retention curves were thereby obtained atcorresponding temperatures and dry densities.
Combined with the SWRCs of GMZ01 bentonite
specimen previously measured by Ye et al. (2009) at
temperatures 20°C, 40°C and 60°C, a modified
model for describing the water retention behavior ofcompacted GMZ01 bentonite was proposed andverified with consideration of temperature and initial
dry density effects.

technique (Delage et al., 1998) (for suctions lower
than 4 MPa) were used for suction control in a
combined way, in order to obtain SWRCs over alarge suction range. Detailed descriptions for these
two techniques can be found elsewhere (Ye et al.,2012; Blatz and Graham, 2000; Lloret et al., 2003).
Table 1 Basic physical and chemical propertiesof GMZ01 bentonite (Wen, 2005)
Property
Description
Specific gravity of soil
2.66
grain
pH
8.68-9.86
Liquid limit（%）
276
Plastic limit（%）
37
597
Total specific surfacearea（m2/g）
Cation exchange
77.3
capacity （mmol/100g）
Na+ （ 43.36 ） ,2+Main exchanged cation Ca （29.14）,（mmol/100g）
Mg2+ （12.33）,+
K （2.51）
Montmorillonite（75.4%）,
Quartz（11.7%）,
Main minerals
Feldspar（4.3%）,
Cristobalite（7.3%）

2 Materials and methodology
2.1 Materials
The material tested in the present work is
GMZ01 bentonite, which originates from GaoMiaoZi(GMZ) in the Inner Mongolia Autonomous Region,
300 km northwest from Beijing, China (Ye et al.,2009). As a light gray Na-bentonite powder, it isdominated by montmorillonite (75.4% in mass).
Basic physical and chemical properties of GMZ01
bentonite are presented in Table 1 (Wen, 2005). A
high cation exchange capacity and adsorption ability
can be identified (Ye et al., 2010; Ye et al., 2012).
2.2 Specimen preparation
The GMZ01 bentonite powder with an initialwater content of 10.7% was statically compacted totarget dry densities of 1.50g/cm3 and 1.90g/cm3
respectively. Compaction was displacementcontrolled at a speed of 0.1 mm/min. Cylindrical
specimens with dimensions of 10 mm in height and
50 mm in diameter were obtained.

Oven(temperature control ¡ 0À.1¡ãC)

Pump
SampleSalt

Fig. 1 Setup for the vapour equilibrium method withtemperature control (Ye et al., 2012)
For consideration of temperature influence, salt
solutions and their corresponding suctions at different
temperatures calibrated by Tang and Cui (2005) for
the vapor equilibrium technique were referred in thispaper (Table 2). However, according to thecalibration result reported by Tang et al. (2010), theinfluence of temperature on suction measured by theosmotic technique was insignificant. Therefore, forsuction controlled by the osmotic technique atdifferent temperatures did not consider any
temperature corrections in this work.

2.3 Methodology
For suction control at given temperatures, thesetups developed by Ye et al. (2012) for the vapor
equilibrium technique (Fig.1) and the osmotic
technique (Fig. 2) were employed in this study.
Generally, the vapor equilibrium technique (forsuctions higher than 4 MPa) and the osmotic2

10th Asian Regional Conference of IAEG (2015)

dry density 1.90g/cm3 following wetting path atdifferent temperatures are presented in Fig. 3. It canbe observed form the results in Fig.3 that, underconstant volume conditions, temperature influence oncompacted GMZ01 bentonite depends on suctionlevel. For high suctions (>4 MPa), water retention
capacity of the specimen decreases as temperature
increases. It may be attributed to that, under constantvolume conditions, the transfer of tightly boundintra-aggregate water to free inter-aggregate water
caused by temperature. This inter-aggregate water
will consequently occupy a greater pore volume andgive rise to higher degrees of saturation (Villar and
Lloret 2004).

Fig. 2 Setup for the osmotic technique withtemperature control (Ye et al., 2012)
Table 2 Salt solutions and their corresponding
suctions (MPa) (Tang and Cui, 2005)
Salt solution
20℃
40℃
60℃
LiCl2

309

319

340

MgCl2

150

162.4

187.7

K2CO3

113

122

144.8

Mg(NO3)2

82

103.1

139

NaNO2

57

NaNO3

39

49.5

61.6

NaCl

38

40.6

44.2

(NH4)2SO4

24.9

32.2

KCl

21

27.8

33.4

ZnSO4

12.6

KNO3

9

K2SO4

4.2

5.1

5.5

Fig. 3 Influence of temperature on water retention
properties (initial dry density 1.90g/cm3)
It can be observed form the results in Fig.4 that,for high suctions, the water retention curve of
GMZ01 bentonite specimens measured at different
temperatures are nearly linear and parallel to eachother, which indicates that they almost have the same
slope. This observation is consistent to that reported
by Ye et al. (2009) on confined compacted GMZ
bentonite specimen with an initial dry density of
1.70g/cm3.
It also can be calculated from the curves in Fig.4
that, for a given water content, the decreasing rate ofsuction with increasing temperature (∆log s / ∆T) is
approximately -2.5×10-3 (log MPa/℃). This data isapproximately to -2.9×10-3 (log MPa/℃), which wasreported by Tang and Cui (2005) on temperatureeffects on water retention curves of compacted MX80
bentonite.
For low suctions (<4MPa), temperature
influence on water retention capacity is insignificant,especially for suction lower than 0.1MPa, theinfluence of temperature is hardly observed. It may
be attributed to that, under constant volume
conditions, decreasing suction could not make morewater moving into large pores because most pores has
already been filled by water in the case of low
suctions (Villar and Lloret 2004).

2.4 Water Retention Tests
In this study, using the vapor equilibrium
technique for high suctions and the osmotic techniquefor low suctions, water retention tests on compacted
GMZ01 bentonite specimens with initial dry densitiesof 1.50g/cm3 and 1.90g/cm3 were performed attemperatures 200C, 400C and 600C, respectively. With
the previous results reported by Ye et al. (2009) on
GMZ01 bentonite specimen with dry density of
1.70g/cm3 at different temperatures, SWRCs of
GMZ01 bentonite with initial dry densities of
1.50g/cm3, 1.70g/cm3 and 1.90g/cm3 at temperatures
20℃, 40℃ and 60℃ were obtained.
3 Results and discussion
3.1 Influence of temperature on the water
retention properties
Measured water retention curves of confinedcompacted GMZ01 bentonite specimens with initial3

10th Asian Regional Conference of IAEG (2015)

the bentonite the greater the water content for a given
suction. This is the expected behavior, as the porosityof samples of low density, and consequently the porevolume available for water uptake, is greater.
The same results were observed at the different
temperatures of 40℃ and 60℃ respectively.
4 Conclusions
In this paper, the soil-water retention curves ofconfined compacted GMZ01 bentonite specimen withdifferent dry densities at different temperatures 20°C,
40°C and 60°C were determined from a series ofsuction-controlled tests. Influences of temperatureand dry density on the water retention capacity of thehighly compacted GMZ01 bentonite were analyzed.
The following conclusions can be reached.
For high suctions, the water retention capacityof compacted GMZ01 bentonite under confinedconditions decreases as temperature increases. For
low suctions, water content decreases with increasing
temperature. For suction lower than 0.1 MPa, thetemperature influence on the water retention capacityof compacted GMZ01 bentonite was insignificant.
For suctions higher than 10 MPa, dry density
influence on the water retention curve isinsignificant. Explanations to this observation could
be that the water must be predominantly in the
microstructure, and because the density changes
affect mainly the macrostructure, they are notreflected on the retention curve.
For suctions lower than 10MPa, the lower thedry density of the bentonite the greater the watercontent for a given suction. This is the expectedbehavior, as the porosity of samples of low density,and consequently the pore volume available for water
uptake, is greater.

Fig. 4 Influence of temperature on SWRCs of
GMZ01 bentonite at high suctions (1.90g/cm3)
3.2 Influence of dry density on water retention
capacities
Measured water retention curves of confinedcompacted GMZ01 bentonite specimens withdifferent dry densities following wetting path arepresented in Fig. 5 (20℃). It can be observed from hemeasured data in Fig. 5 that, under constant volume
conditions, influence of dry density on the water
retention capacity also can be analyzed at high andlow suctions separately.

Acknowledgements
The authors are grateful to China Atomic
Energy Authority (Project [2011]1051) and the
National Natural Science Foundation of China(Projects No. 41030748) for the financial supports.

Fig. 5 Influence of dry density on water
retention curves（20℃）
For suctions higher than 10MPa, dry density
influence on the water retention curve is insignificant.
Explanations to this observation could be that thewater must be predominantly in the microstructure,and because the density changes affect mainly themacrostructure, they are not reflected on the retention
curve (Villar, 2007). Similar results were obtained byother authors (Villar et al., 2002; AGUS, 2005;
DELAGE et al., 2006; IMBERT et al., 2005).
For lower suctions (<10 MPa), i.e. for highrelative humidity and when the specimen isapproaching saturation, the lower the dry density ofReferences
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