1809
Ideas for improved geotechnical structures for natural disaster mitigation
Idées pour l'amélioration des ouvrages géotechniques pour l'atténuation des catastrophes
naturelles
Heerten G.
Naue GmbH & Co. KG, Germany
Vollmert L.
BBG Bauberatung Geokunststoffe GmbH & Co. KG, Germany
ABSTRACT: Floods, earthquakes, tsunamis, landslides or avalanches / rock fall are current threats to human beings around the world.
Geotechnical structures can be improved or developed with the use of geosynthetics to mitigate the impact of these kinds of natural
disasters and to minimize damage and causalities. With erosion-resistant dykes the impact of flooding can be significantly reduced
when the overtopping of a dyke cannot lead to a dyke failure with a big gap in the dyke with concentrated discharge. Embankment
dams reinforced with geosynthetics are much more resistant to earthquake loading than conventional concrete structures. Artificial
tsunami shelters as artificial hills are currently discussed to establish safe places near the coast. Finally new model studies are showing
that the behaviour of embankments against dynamic rock fall impact can be significantly improved by reinforcing the structure with
geogrids
RÉSUMÉ : Les inondations, tremblements de terre, tsunamis, glissements de terrain ou avalanches / chutes de pierres, sont des
menaces courantes pour les êtres humains partout dans le Monde. Les ouvrages géotechniques peuvent être améliorés ou développés
par l’utilisation de géosynthétiques pour atténuer l’impact de ces catastrophes naturelles et minimiser les dommages et causalités.
L’impact des inondations peut être considérablement réduit avec des digues résistantes à l’érosion, car en cas de débordement, un
déversement concentré n’entrainerait pas de rupture dans la digue. Les digues en remblai renforcé par géosynthétiques sont beaucoup
plus résistantes aux contraintes sismiques que les ouvrages conventionnels en béton. Les abris artificiels contre les tsunamis, tels que
des collines artificielles, sont actuellement considérés pour établir des lieux sûrs à proximité des côtes. Enfin, les études menées sur de
nouveaux modèles montrent que le comportement des remblais de protection contre les chutes de blocs à impact dynamique peuvent
être considérablement améliorés par le renforcement de la structure avec des géogrilles.
KEYWORDS: geosynthetics /geogrids, natural disasters mitigation, dykes/levees, embankments, tsunami shelter, rock fall protection.
1 INTRODUCTION
World´s population is growing further. Increasing numbers
of people are living in mega cities close to flood plains of
rivers and oceans endangered by floods or tsunamis, but also
in areas endangered by earthquakes or landslides. Natural
disasters have created and will create huge material damage
and a high number of causalities. But already after a short
time the experience is forgotten and the intention to spend
money for improving the safety fades away. But it is the
responsibility of governments and authorities to ensure that
appropriate strategies and measures for risk mitigation are in
place and applied. And it is our obligation as geotechnical
engineers to communicate improved design and construction
methods for geotechnical structures for natural disaster
mitigation. Ideas for safer dykes of higher erosion resistance,
for embankments with improved resistance to earthquake
loading and/or higher protection against impacts from
rockfall, avalanches or landslides and tsunami shelters are
presented.
2 EROSION-RESISTANT DYKES / LEVEES
In the aftermath of past disastrous flood events in Germany and
other European countries it became evident that levees are part
of the society's infrastructure and need careful control and
maintenance. Immediately after major flood events the
willingness to improve flood protection structures is great and
(tax) money is available. These programs to improve the flood
protection should consider the present technical improvements
e.g. for the construction of levees. The improvement of levee
cross-sections by using different geosynthetics has developed to
be state-of-the-art (Heerten 2010). The use of nonwoven filter
materials to form a filter-stable, erosion-resistant transition
between levee core and the air-side drain and ballast body or the
arrangement of geosynthetic clay liners (bentonite mats) as a
water-side surface seal have already been included as
established alternatives in current regulations and guidelines.
Beyond the three-zone levee the effects of geosynthetics
integrated into levees as safety measures have been investigated
and documented to have a high resistance capability during
overflow load conditions. Erosion processes on the inner
embankment and the risks of unexpected levee breaches can be
minimized with geosynthetic construction techniques;
geosynthetics can also be employed as support facilities for
emergency reinforcing measures. Internal erosion in the
embankments and sudden breaches to the surface of dykes can
be prevented with knowledge and implementation of
geosynthetics. Thus, these technologies provide not just
structural defences but more time for evaluating risk and
providing emergency response to populated areas that are
threatened by rising water levels.
Geosynthetic clay liners (GCL) as needle-punched bentonite
mats have gained widespread acceptance for levee improvement
projects in a lot of countries because these products create a
simple, effective, economical seal for a levee that
simultaneously provides erosion protection for the levee body
(Heerten and Horlacher 2002). Following the Elbe River floods
that took place in Germany between 2002 and the end of 2005,
about 150 levee reconstruction projects are known, being
carried out in this period, in which about 2.2 million m² of
needle-punched nonwovens, about 300 000 m² of geogrids and
about 700 000 m² of needle-punched geosynthetic clay liners
