3061
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
1
Factors affecting hydration of Geosynthetic Clay Liners in landfill applications
Facteurs influençant l’hydratation des géosynthétiques bentonitiques dans les applications
d'enfouissement
M.T. Rayhani & H. Sarabadani
Department of Civil and Environmental Engineering, Carleton University, Ottawa, Canada
ABSTRACT: The progression of hydration of Geosynthetic Clay liner (GCL) from underlying subsoil was studied for three GCL
products under simulated landfill conditions, before and after being covered by municipal solid waste. GCL hydration is shown to be
highly dependent on the GCL manufacturing techniques, the grain size distribution and initial moisture content of the subsoil. The
hydration behaviour of the GCL was also affected by the exposure conditions in the landfill. Prior to waste placement, the composite
liner may be exposed to daily and seasonal thermal cycles for a period of time (weeks to months). These cycles significantly
suppressed the hydration of the GCLs and kept the equilibrium moisture content of the GCLs far less than what expected under
isothermal conditions at room temperature (22
C). After waste placement, the GCL may experience elevated temperatures that occur
during waste decomposition in municipal solid waste landfills. Results indicated that as the temperature increased (from 22 to 55
C),
the final equilibrium moisture content decreased, from about 96% at room temperature to about 14% at 55
C. Moreover, the normal
stress of 2 to 5 kPa was shown to induce an adequately high rate of hydration and the maximum equilibrium moisture content.
RÉSUMÉ: La progression de l'hydratation de Géosynthétique Bentonique (GSB) du sol a été étudiée pour trois GSB produits dans des
conditions simulées d'enfouissement, avant et après avoir été recouverts par des déchets solides municipaux. Hydratation est
dépendante des techniques de fabrication GSB, la distribution de granulométrie et la teneur en humidité initiale du sol. Hydratation de
GSB a également été affectée par les conditions d'exposition d'enfouissement. Avant déposer des déchets, le revêtement composite
peut être exposé à des cycles journaliers et saisonniers thermiques pendant une période de temps (quelques semaines ou mois). Ces
cycles ont supprimé l'hydratation des GSBs de manière sévère et ont gardé la teneur en humidité d'équilibre des GSB beaucoup moins
ce que prévue dans des conditions isothermes à température ambiante (22
C). Après déposer des déchets, le GSB peut subir des
températures élevées qui se produisent lors de la décomposition des déchets dans les sites d'enfouissement des déchets solides
municipaux. Les résultats ont montré que lorsque la température a été augmentée (de 22 à 55
C) le contenu d'humidité d'équilibre
final a été diminué de manière sévère, de 96% à la température ambiante à environ 14% à 55
C. En outre, la pression normale de 2 à
5 kPa a été montrée de causer un taux suffisamment élevé d'hydratation et de la teneur maximale en humidité d'équilibre.
KEYWORDS: Geosynthetic Clay Liners (GCL), hydration, thermal gradient, normal stress
1 INTRODUCTION
Geosynthetic Clay Liners (GCLs)
are utilized as part of a
barrier system while covered by a geomembrane liner to prevent
the escape of contaminants form solid waste landfills (Rowe
2005, Benson et al. 2010, Gates and Bouazza 2010). The GCLs
typically consist of a core of bentonite encapsulated by
nonwoven or woven geotextiles. The hydraulic performance of
the GCL depends on the degree of hydration from the pore
water of the underlying soil prior to contact with leachate
(Rowe 2005). Previous studies have shown that the hydraulic
performance of the GCL is influenced by the GCL
manufacturing techniques as well as the grain size distribution,
and initial moisture content of the subsoil (e.g., Chevrier et al.
2012, Beddoe et al. 2010 and 2011, Rayhani et al. 2011).
Beddoe et al. (2011) showed that the GCL manufacturing
techniques affect the Water Retention Curve (WRC) of the
GCL, indicating that the hydration of the GCL depends on the
WRCs of both GCL and subsoil. Also, a reduction of
approximately 12.5 % in the final moisture content of a needle-
punched GCL with sand subsoil was observed as the initial
normal stress of 7 KPa was increased to 28.2 KPa (Chevrier et
al. 2012).
Composite liners in landfill applications might be left
exposed to daily thermal cycles induced by solar radiation for a
period of time prior to waste placement. Rowe et al. (2011)
reported that the daily thermal cycles significantly suppressed
the rate of hydration of GCLs placed on silty sand subsoil. Also,
constant thermal gradients applied to the GCLs placed over
subsoil have shown to induce loss of moisture and, hence,
desiccation and cracking of the GCLs. The temperature at the
base of bioreactor landfills and also the Municipal Solid Waste
(MSW) landfills where the Leachate Collection System (LCS)
has failed could increase up to 40-60ºC after placing the waste
(Azad et al. 2011). Furthermore, the temperature within the
aquifer is significantly lower which in turn causes temperature
gradients. This induces downward flux of vapor (diffusion)
from the GCL to the subsoil which causes the moisture loss of
GCLs and the desiccation cracking of the GCLs (Barclay and
Rayhani 2012, Azad et al. 2011, Southen and Rowe 2005). This
paper summarizes the results of an extensive testing program
which was initiated to evaluate the effect of field conditions
such as the elevated temperatures and normal stresses on the
GCL hydration from different underlying subsoils. Also, the
effect of the GCL manufacturing techniques and the initial
water content of the subsoil are investigated.
actors affecting hydration of eosynthetic lay Liners in landfill applications
Facteurs influençant l’hydratation des géosynthétiques bentonitiques dans les applications
d'enfouissement
Rayhani M.T., Sarabadani H.
Department of Civil and Environmental Engineering, Carleton University, Ottawa, Canada
