33
Terzaghi Oration
/ Allocution Terzaghi
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
required
γ
M
. The improvements are to be made through topog-
raphical modifications. As an example (lower diagram), for an
initial
γ
M
of 1.2, an improvement from
γ
M
= 1.2 to
γ
M
= 1.26 and
1.29 is required by NVE (2011) for the two levels of improve-
ment specified. Standing slopes with a material factor
γ
M
of 1.0
require an improvement up to
γ
M
= 1.10 and 1.15 for the two
levels of “improvement” specified by NVE.
The reason for allowing a material coefficient less than 1.4 is
that the fact that the slope is standing today is a confirmation
that the slope has a material coefficient of at least 1.0. Any im-
provement therefore represents a real gain to the present safety
of the slope. The NVE requirement needs to be satisfied for all
potential slip surfaces.
For sensitive clays, the peak undrained shear strength is re-
duced in limit equilibrium analyses to account for strain-
softening at large shear strains. A reduction of 10 to 15% in the
peak shear strength in triaxial compression, triaxial extension
and direct simple shear may be adequate, as discussed under the
Vestfossen case study. However a reduction factor should
probably be developed for different categories of clays and slip
surfaces..
1.0
1.1
1.2
1.3
1.4
1.5
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Initial material coefficient, ,
M
Minimum improvement in FS required through topographical modifications (%)
Substantial improvementrequired
Improvementrequired
1
1.1
1.2
1.3
1.4
1.5
1
1.1
1.2
1.3
1.4
1.5
Required
M
after improgvement
Initial material coefficient,
M
Substantial improvement required
Improvementrequired
Figure 40. Required increase in material coefficient (top diagram, NVE
2011) and resulting required material coefficient (lower diagram) for an
existing (standing) slope.
13 CONCLUSIONS
The geotechnical engineer’s role is not only to act as technolo-
gist providing judgment on factors of safety. The role has
evolved to providing input in the evaluation of hazard, vulner-
ability and risk associated with landslides. The geotechnical
profession should be increasingly perceived as reducing risk and
protecting people.
The geotechnical engineer should be aware that it is more
correct and safer to ensure that slopes have the same probability
of failure rather than the same factor of safety.
Mitchell and Kavazanjian (2007) presented “Geo-engineer-
ing Engineering for the 21
st
Century”. On request from the Na-
tional Science Foundation in the USA, an expert committee sug-
gested a vision for how geo-engineering could continue to
address societal needs in the 21
st
century, and identified emerg-
ing technologies that could contribute to this vision. Mitigation
of natural hazards was one of the areas identified. Emerging
technologies included:
An improved ability to “see into the earth” and interpret
geophysical surveys.
Improved sensing and monitoring, more reliable instrumen-
tation, enhanced data acquisition, processing and storage,
and appropriate information systems.
Improved ability to characterize the spatial variability of
soil properties and the uncertainty in the assessments made.
In addition, inter- and cross-disciplinary problem-solving is es-
sential for advancing in the practice of geo-engineering. More
emphasis must be placed on inter-disciplinary collaboration, in
research, consulting and education.
The expertise of geotechnical engineers is essential for meet-
ing the challenge of protecting society, worldwide. Safety and
life quality depends on our profession. We must however avoid
being unaware of the impact of the work we do as engineers. To
paraphrase Siegel (2010): civil engineers built the countries we
live in. Civil engineers make a difference in the world: “When
we flip a switch, the lights come on. When we turn on the tap,
we trust that the water is clean and potable. When we drive
home from work, we trust the roads will not collapse”. Over the
last 100 years, life expectancy has doubled. The main factor has
not been advances in medicine, but advances in clean water
technology and sanitation. Civil engineers are solving the
world’s problems every day.
In closing this 8
th
Terzaghi Oration, I return to Professor
Ralph B. Peck, who early in his career, already defined the civil
engineer’s role in a most adequate manner. The key to success
and happiness, in his view, was “[...] a love of civil engineering,
which, at its core, seeks to do 'good works' for humanity”. In
view of today’s needs and our profession’s evolution, Ralph
could not have been more right.
14 ACKNOWLEDGMENTS
The author wishes to thank President Jean-Louis Briaud for selecting
her to be the 2013 Terzaghi Orator. The author is also thankful to NGI
for the opportunities it gave her throughout her career. The author is in-
debted to many colleagues who provided data and information for the
case studies, especially Dr Hans-Peter Jostad, Håkon Heyerdahl, Bjørn
Kalsnes Dr Maarten Vanneste, Arnstein Aarset, Dr Farrokh Nadim, Odd
Gregersen, Dr Andi A Pfaffhuber,Tim Gregory and Dr Kaare Höeg, all
from NGI. The assistance and prompt reply to my questions from Pro-
fessor Steinar Nordal, from NTNU, Dr Denis Demers and his colleagues
at Ministère des Transport du Québec and Dr Chris Bunce from Cana-
dian Pacific are also greatly appreciated.
15 REFERENCES
Aas G. 1979. Skredfare og arealplanlegging. Vurdering av faregrad og
sikringstiltak. Ullensvang Hotell, Lofthus i Hardanger. Norske
sivilingeniørers forening. Oslo: NIF, 1979. 1. b.
Berre T., Lunne T., Andersen, K.H., Strandvik, S.O., Sjursen 2007. Po-
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of soft marine Norwegian clays.
Canadian Geotechnical Journal
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698-716.
Bondevik S., Løvholt F., Harbitz C., Mangerud,J., Dawson A and
Svendsen J.I. 2005. The Storegga Slide tsunami-comparing field ob-
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Marine and Petroleum Geol-
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