3053
Soil-geosynthetic interface strength on smooth and texturized geomembranes under
different test conditions
Résistance au cisaillement des interfaces entre sols et membranes géo-synthétiques lisses ou
rugueuses sous différentes conditions
Monteiro C.B., Araújo G.L.S., Palmeira E.M., Cordão Neto M.P.
Department of Civil and Environmental Engineering, FT, University of Brasilia,70910-900, Brasilia, DF, Brazil
ABSTRACT: Potential ground contamination from landfills justifies the use of sub-systems such as soil and geosynthetic layers as
barriers at the landfill bottom and slopes. In configurations of barrier systems, geomembranes have often been used. For this type of
application, the mechanisms of interaction between soil and geomembrane must be properly understood and failures along soil-
geomembrane interfaces in slopes have been observed. This paper presents experimental results of shear strength mobilization along
soil-geomembrane interfaces for different types of geomembranes and degrees of saturation of the underlying soils. Direct shear and
ramp tests were used in this study. The results showed a little or no increase on values of interface friction angles with increasing
degree of saturation of the soil. The highest values for interface shear strength were obtained for the texturized HDPE geomembrane.
RÉSUMÉ: Le potentiel de contamination des décharges sanitaires justifie l´utilisation de techniques d’imperméabilisation sur les
fonds et les talus latéraux, tels que des couches de sols et des membranes géo-synthétiques. Pour ces systèmes d’imperméabilisation,
on a souvent eut recours à des géo-membranes comme matériau imperméabilisant de protection. Pour ce type d’application, les
mécanismes d´interaction entre le sol et la géo-membrane sont encore peu connus, la rupture le long de ces interfaces a été observée
sur des talus par des phénomènes de glissement du sol sous la géo-membrane. Cet article présente des résultats expérimentaux de
mobilisation de la résistance au cisaillement pour des interfaces sol/géo-membrane, pour différents types de géo-membranes et
différents degrés de saturation des sols. Ces résultats montrent une augmentation légère voire nulle des valeurs d’angle de frottement
des interfaces avec l´augmentation du degré de saturation des sols. Les valeurs de résistance au cisaillement les plus élevées ont été
obtenues pour des géo-membranes en polyéthylène haute densité (PEHD) présentant une texture.
KEYWORDS: Interface strengh, geosynthetics, landfill, geomembranes.
1 INTRODUCTION
Geomembranes are often used as landfills barriers aiming at
avoiding contamination of underneath soils or ground water.
Some projects using these systems have a soil layer above the
synthetic materials. Sometimes this soil layer is executed with
sand for leachate drainage. Interaction between soil-
geomembrane in landfills slopes still need a better
understanding. Improper evaluation of soil-geosynthetic
interation parameters for this kind of construction has yielded to
slope failures along that interface (Dwyer
et al.
2002, Gross
et
al.
2002, Palmeira 2009, for instance).
Shear strength interfaces studies of different kinds of
materials can be found in the literature (Fleming
et al.
2006 and
Khoury
et al.
2011, for instance). An increasing number of
studies on soil-geosynthetic interface strength has been
observed due to the risk of failures along these interfaces.
Failures due to soil sliding on a geomembrane in slopes
under low stress levels can be more accurately modelled using
ramp tests (inclined plane tests). Conventional direct shear tests
sometimes is a adopted for this type of study, but some studies
have demonstrated that for low values of normal stresses
(typical in barrier systems of landfills), this kind of test may
overestimate interface shear strength interface parameters
(Girard et al. 1990, Giroud et al. 1990 and Gourc et al. 1996, for
instance).
Some aspects related to soil-geosynthetic interface strength
still need to be properly understood. With this regard, it might
could be expected that soil moisture content may influence the
interface strength parameters. Soil moisture content can increase
due to saturation by leachate or due to infiltration of rain water.
This paper presents and discusses results from ramp and
conventional direct shear tests on differents kinds of soil-
geomembrane interfaces with varying soil degree of saturation.
1.1
Parameters and interface shear strength
Nowadays there are some studies about interface shear strength
parameters using ramp tests, with several of them having
addressed the use of GCL´s as lining materials. Briançon
et al.
(2002) verified that for six types of interfaces between
geosynthetics and geocomposites, the effect of increasing GLC
bentonite moisture content can reduce friction angles between
20 and 40%. Viana (2007) evaluated interface shear strength
between soil and GCLs and found reductions of up to 43.5% on
the interface friction angle.
Mello (2001) highlights the importance of studies on the
influence of unsaturated soil conditions on displacements
stabilization and mobilized loads in the geosynthetic layer with
time. According to the author even after 120 hours using the
same inclination, it was not observed reduction of the adhesion
component or system failure. Besides, during this time the
displacements of the sample and the transferred loads to the
geosynthetic remained the same value.
Interface parameters between soils and geosynthetics
are usually evaluated using Mohr-Coulomb failure criteria
(Lima Júnior 2000, Mello 2001, Aguiar 2003 and Viana 2007 -
see Eq. 1):
τ = α + σ.tanδ
(1
)
Where:
α = Adesion;
σ = Normal stress;
δ = Interface friction angle.
