3025
Moisture-Suction Relationships for Geosynthetic Clay Liners
Courbes de rétention des membranes géotextiles chargées en argile
Hanson J.L., Risken J.L.
California Polytechnic State University, San Luis Obispo, U.S.A.
Yeşiller N.
Global Waste Research Institute, San Luis Obispo, U.S.A
ABSTRACT: A laboratory investigation was conducted to determine the moisture-suction relationships for Geosynthetic Clay Liners
(GCLs) under as-received conditions (moisture contents in the range of 14-27%) and subsequent to wet-dry cycles (20 cycles at 50%
moisture content). The moisture-suction relationships were developed using combined pressure plate, filter paper, and relative
humidity methods over a wide range of suction. Tests were conducted on three types of common GCLs (two conventional and one
multi-component) that contained granular bentonite and bonded with needlepunching. The responses of conventional and multi-
component GCLs and as-received and wet-dry cycled GCLs were different. For the multi-component GCL, the air entry suction was
lower for drying and higher for wetting than for the conventional GCLs. Residual suction for the multi-component GCL was higher
than that for the other GCLs. The extent of hysteresis decreased and the differences between drying and wetting curves reduced for
the wet-dry cycled specimens. Macro- and microstructural variations determined in grain size distribution and SEM analyses indicated
increasing void sizes and nonuniformity in fabric due to wet-dry cycling supporting the observations of moisture-suction variations.
RÉSUMÉ : Une étude en laboratoire a été menée pour déterminer les courbes de rétention des membranes géotextiles chargées en
argile dans les conditions de teneur en eau du commerce (de l'ordre de 14-27%) et suite à des cycles de mouillage-séchage (20 cycles
à 50% d’humidité). Les courbes de rétention ont été mesurées en utilisant une plaque de pression et du papier filtre, et des méthodes
de contrôle en humidité relative sur une large gamme de succion. Les tests ont été effectués sur trois types de membranes (deux
conventionnelles et une multi-composants) qui contenaient de la bentonite granulaire et assemblés par aiguilletage. Les réponses des
géomembranes conventionnelles et multi-composants étaient différentes selon les conditions d’essai. Pour la membrane multi-
composants, la succion d’entrée d’air était inférieure après séchage et supérieure après mouillage à celle des membranes
conventionnelles. La succion résiduelle pour la membrane multi-composants était également supérieure à celle des membranes
conventionnelles. L’amplitude de l'hystérésis a diminué, de même que les différences entre les courbes de mouillage et séchage se
sont réduites pour les échantillons ayant subi des cycles de mouillage-séchage. Les variations de la macro- et microstructure, en
termes de distribution de la taille des grains et des analyses au MEB, ont montré une augmentation de la taille des vides et une non-
uniformité de la structure induites par les cycles de mouillage-séchage. Ces résultats confirment les observations des courbes de
rétention.
KEYWORDS: Geosynthetic Clay Liner, GCL, suction, moisture-suction curve, fabric, shrinkage, unsaturated.
1
INTRODUCTION
Geosynthetic clay liners (GCLs) are increasingly used to replace
compacted clay liners in containment systems due to various
perceived advantages of the GCLs including low thickness, low
hydraulic conductivity, ease of installation, self-healing
capability, and resistance to environmental conditions (e.g.,
cyclic freeze-thaw or wetting-drying). Even though GCL use
has become commonplace in containment systems, concerns
remain regarding the long-term field performance (NRC 2007).
Significant variations in the field moisture content of GCLs
(e.g., Meer and Benson 2007, Scalia and Benson 2011) have
been reported. Moisture transfer between GCLs and soils also
has been reported (e.g., Olsen 2011). In general, GCLs remain
unsaturated in service based on reported moisture contents.
Limited information is available on moisture-suction
relationships and water retention characteristics of GCLs, which
control mechanical, hydraulic, and thermal properties of the
GCLs as well as directly influence moisture transfer between
GCLs and soils. Data for conventional GCLs indicated that the
structure of GCLs affected moisture retention characteristics
(Beddoe et al. 2011). Data are not available for multi-
component GCLs or GCLs that have undergone wet-dry
cycling.
This investigation was conducted to determine the influence
of GCL type and wet-dry cycling on moisture-suction
relationships. The investigation was supplemented by
microscopy analysis of the bentonite component of the GCLs.
2
EXPERIMENTAL TEST PROGRAM
The test program included investigation of three types of GCLs
(Table 1) representative of typical materials used in practice in
the U.S. All of the GCLs were bonded by needlepunching and
contained granular bentonite:
WN2: conventional medium weight GCL with a
lightweight slit-film woven geotextile and heavyweight
nonwoven geotextile
NN1: conventional heavyweight GCL with two
heavyweight nonwoven geotextiles
WNT: multi-component medium weight GCL with a
lightweight slit-film woven geotextile and heavyweight
nonwoven geotextile/textured geofilm (0.5 mm HDPE)
The GCL specimens were tested at as-received conditions
and subsequent to 20 wet-dry cycles. The cycles consisted of
wetting the specimens to 50% moisture content for 8 hours and
then oven drying the specimens at 60
C for 12 hours for a total
cycle duration of 24 hours. A common moisture content range
of 45-62% was reported for GCLs exhumed from composite
barriers in landfill covers (Scalia and Benson 2011). The 50%
moisture content was selected as this moisture content is
