15
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
1
8
th
Terzaghi Oration
Protecting society from landslides – the role of the geotechnical engineer
8
e
allocution Terzaghi
La gestion de l’aléa glissements de terrain et le rôle de l’ingénieur géotechnicien
Lacasse S.
Norwegian Geotechnical Institute (NGI), Norway
ABSTRACT: Protecting society from landslides and reducing exposure and risk to population and property are areas where the geo-
technical profession can practice both the art and the science of engineering legated by Karl Terzaghi. The paper presents several case
studies of slope failure and examples of landslide risk management. Since factor of safety remains the practice’s main indicator to en-
sure slope safety, the significance of factor of safety is discussed. The geotechnical engineer’s role is not only to act as technologist
providing judgment on factors of safety. The role has evolved to providing input in the evaluation of hazard, vulnerability and risk as-
sociated with landslides. The geotechnical profession should be increasingly perceived as reducing risk and protecting people.
RÉSUMÉ : La réduction de l’aléa dû aux glissements de terrains est devenue l’une des sphères où l’ingénieur géotechnicien peut pra-
tiquer l’art et la science que nous a légués Karl Terzaghi. L’article présente plusieurs études de cas de glissements et des exemples de
gestion du risque au glissement. Puisque le facteur de sécurité demeure l’indicateur principal de la stabilité des pentes, l’article discute
les implications du facteur de sécurité. Le rôle de l’ingénieur géotechnicien n’est plus simplement d’offrir un jugement sur le facteur
de sécurité, mais aussi de générer les paramètres et l’analyse pour l’évaluation des aléas, de la vulnérabilité et des risques associés aux
glissements de terrain. Notre profession devrait de plus en plus être perçue comme réduisant le risque et protégeant la société.
KEYWORDS: landslide, slope stability, strain-softening, factor of safety, case studies, hazard, risk
1 INTRODUCTION
The ISSMGE hosted seven Terzaghi Orations. Table 1 lists the
topics covered earlier. The topics reflect an evolution and a
cross-section of our professional practice. The 1
st
Terzaghi Ora-
tion was on the progress over 30 years in the prediction of cliff
side instability. The 2
nd
described the design of the giant off-
shore structures marking the start of the suction anchor concept
now widely used around the world. The 3
rd
Oration looked into
prediction and performance for embankments on soft clay and
pile foundations. The Terzaghi Oration then gave us remarkable
case studies, (1) the shattering Kobe earthquake in Japan and (2)
how the movements of the Pisa tower can be curbed to preserve
the tower for future generations. The importance of the interac-
tion of soil and water for the Netherlands came with the 6
th
Ora-
tion. The 7
th
Terzaghi Oration marked the emergence of slender
high-rise buildings and introduced us to their challenging foun-
dations subjected to large vertical, lateral and moment loads.
Table 1. Terzaghi Orations 1985-2009.
Year
Author
Title
1985
T.W. Lambe
Amuay landslides.
1989
K. Høeg
Foundation engineering for the
Gullfaks C offshore gravity structure.
1994
V. De Mello
Revisiting our origins.
1997
K. Ishihara
Geotechnical aspects of the 1995
Kobe earthquake.
2001
M. Jamiolkowski
Leaning tower of Pisa: End of an
Odyssey.
2005
F. Barends
Associating with advancing insight.
2009
H.G. Poulos
Tall buildings and deep foundations –
Middle East challenges.
Over the past decade, the geotechnical profession has moved in
a direction of increased awareness of both its role and contribu-
tion to a safer society, and the need for targeted communication
has emerged more strongly than earlier.
Protecting society from landslide hazard and mitigating the
exposure and risk to population and property is one of the issues
where we can practice both the art and science legated to us by
Karl Terzaghi. Landslide issues and how to protect population
has become a key to recruiting concerned young talents to the
geo-profession. This is the reason why the topic of landslides, in
terms of protecting society, was selected for the 2013 Terzaghi
Oration.
The mandate of the Terzaghi Oration is to cover case histo-
ries derived from professional activities, and if possible to illus-
trate the dynamic interaction among consulting work, teaching,
research and publication. The case studies selected for this Ter-
zaghi Oration attempt to exemplify Karl Terzaghi's intellectual
approach to engineering and geology. Landslides and the pro-
tection of society from its hazards are a well-suited topic to
meet this mandate, as landslides require a good understanding
of the geology and soil behaviour, and have ample room for im-
provement.
The paper presents case studies of landslides and examples
of landslide risk management. Since factor of safety remains the
main indicator to ensure the safety of populations in practice,
the significance of factor of safety is discussed. The role of the
geotechnical engineer in protecting people is focused on as part
of the conclusions.
2 LANDSLIDE HAZARDS
Landslides represent a major threat to human life, constructed
facilities, infrastructure and natural environment in many re-
gions of the world. During the decade 2000-2009, natural disas-
ters caused nearly one million fatalities, affecting nearly 2.5 bil-
lion people across the globe.
In 2010 alone, 295,000 fatalities due to natural disasters
were recorded by Munich RE (2011) and the overall economic
losses were more than double those of 2009, for approximately
the same number of natural catastrophes. Table 2 presents the
2010 natural catastrophe data published by Munich RE NatCat-
