1607
Stability analysis of earth dams under static and earthquake loadings using
geosynthetics as a seepage barrier
Analyse de stabilité des barrages en terre sous des charges statiques et sous séisme à l'aide de
géosynthétiques comme une barrière d'infiltration
Srivastava A.
Department of Civil Engineering, Jaypee University of Engineering & Technology, Guna, MP, India
Sivakumar Babu G.L.
Department of Civil Engineering, Indian Institute of Science (IISc), Bangalore, India
ABSTRACT: In recent years, geosynthetics have played a major role in dam and reservoir rehabilitation projects and provided
promising solutions to the safety issues for earth dams experiencing seepage losses. In the present study, the structural stability of the
earth dam under static and earthquake loading conditions is investigated in which geosynthetics lining system is used as seepage
barrier and results are discussed in the light of the results obtained for the same earth dam section with no geosynthetics lining
systems. A typical example of homogeneous earth dam of height 10 m and top width 5 m with slope angle 1V:2H (U/S) and 1V:3H
(D/S) is considered. The geotechnical properties of the earth dam are chosen in such a way that it is stable under static condition
without any geosynthetics lining system. For the dynamic numerical analysis of earth sinusoidal motion of different frequency and
displacement amplitude (constant time duration) as well as acceleration–time history record of the Bhuj (India) earthquake as well as
five other major earthquakes recorded worldwide, i.e., EL Centro, North Ridge, Petrolia, TAFT, Loma Prieta, are used. The objective
of doing so is to perform the dynamic numerical analysis of the dam section for the range of amplitude, frequency content and time
duration of input motions. The results of the analysis clearly showed that geosynthetics lining system enhance the stability of the dam
sections under static as well as earthquake loading conditions apart from providing a better alternative to controlling seepage in earth
dams. Commercially available finite element code PLAXIS 2D has been utilized for the analysis.
RÉSUMÉ : Ces dernières années, les géosynthétiques ont joué un rôle majeur dans les projets de réhabilitation des barrages et des
réservoirs et fourni des solutions prometteuses pour les questions de sécurité des barrages en terre subissant des pertes par infiltration.
Dans la présente étude, la stabilité structurelle d’un barrage en terre sous chargement statique et sous séisme est étudiée lorsque des
systèmes de revêtement avec géosynthétiques sont utilisés comme barrière de l'infiltration. Les résultats sont discutés à la lumière de
ceux obtenus pour la même section barrage en terre avec des systèmes de revêtement sans aucun géosynthétique. Un exemple typique
de barrage en terre homogène de hauteur 10 m et largeur 5 m avec un angle de pente 1V:2 H (U/S) et 1V H (D/S) est considéré. Les
propriétés géotechniques du barrage en terre sont choisies de telle manière qu'il est stable dans des conditions statiques sans aucun
système de revêtement avec géosynthétiques, Pour l'analyse de la stabilité du barrage en terre sous séisme, les données du séisme de
Bhuj (Inde) ainsi que cinq autres grands tremblements de Terre enregistrées dans le monde entier, c'est-à-dire, EL Centro, la crête
nord, Petrolia, TAFT, Loma prieta, sont utilisés. L'objectif est donc d'effectuer l'analyse numérique dynamique de la section de
barrage pour la plage d'amplitude, de plage de fréquences et de durée correspondant aux données d'entrée. Les résultats de l'analyse
montrent clairement que les géosynthétiques qui tapissent le système accroissent la stabilité des sections de barrage sous chargement
statique ainsi que sous séisme en plus d’une meilleure alternative au contrôle des infiltrations dans les barrages en terre. Le Code
d'éléments finis disponibles sur le marché PLAXIS 2D a été utilisé pour l'analyse.
Keywords : seepage, earth dams, numerical, earthquake, geosynthetics, stability
1 INTRODUCTION
Geosynthetics have played a major role in solving various
complex civil engineering problems. Being a polymer product,
it is durable and provides good strength. Geosynthetics are
generally designed for a particular application. There are five
primary functions, such as, seperation, reinforcement, filtration,
drainage, containment. For detailed discussion on the topic one
may refer to Jewell (1996), Shukla and Yin (2006), and Koerner
(2012). Geosynthetics, with different functions, i.e., barrier (to
fluid), drainage, protection (geomebbrane), filtration,
reinforcement, erosion control have also been used in almost all
types of dams, both for new construction and rehabilitation
purpose. The first large earthdam using geosynthetic materials
was built in 1970 in France (Valcros dam) in which geotextiles
were used for filtration purpose. In case of embankment dams,
geomembrane was first used as waterproofing element in 1959
at 32.5 m high Contrada Sabetta rock-fill dam in Italy (Cazzuffi,
1987). Since then, a number of earth dams have been provided
with geomembrane as waterproofing (ICOLD 1991). Cazzuffi
(2000) provided an excellent literature review on geosynthetic
applications in all types of dams according to their performed
functions.
The first application of a geosynthetic as chimney drain was
at 11 m high Brugnens earth dam in France, constructed in
1973. The geosynthetic used in was a thick PET needle-punched
nonwoven geotextile (Giroud, 1992). Other French applications
of drainage geosynthetics have been reported in Navassaartian
et al. (1993). Since 1980s, a geocomposite shaft drain (including
a PP-polypropylene) nonwoven geotextile draining core
between two PP nonwoven geotextile filters has been used
instead of granular drains for the construction of a number of
homogeneous earthfill dams of height 10 m or so.
For rehabilitation purpose, where embankment dams exhibit
seepage through their downstream slope, Geocomposite drain
(GCD) can be placed on the entire downstream slope or only the
lower portion and covered with backfill. The technique has been
used at 13 m high Reeves Lake dam in USA in 1990 by placing
a GCD (including a PE-polyethylene geonet core between two
PP thermobonded nonwoven geotextile filters) on the
downstream slope (Wilson, 1992).
For protecting geomembrane from potential damage by
adjacent materials, typically the granular layer underneath and
