31
Terzaghi Oration
/ Allocution Terzaghi
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
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Rectify substandard Government man-made slopes.
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Maintain all Government man-made slopes.
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Ensure that owners take responsibility for slope safety.
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Promote public awareness and response in slope safety
through public education, publicity, information services
and public warnings.
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Enhance the appearance and aesthetics of slopes
Hong Kong has a history of tragic landslides. Since 1947, more
than 470 people died, mostly as a result of failures associated
with man-made cut slopes, fill slopes and retaining walls. To-
day, the risk to the community has been greatly reduced by con-
certed Government action. On average, about 300 incidents af-
fecting man-made slopes, walls and natural hillsides are
reported to the Government each year.
To reduce landslide risk, GEO assures the operation of a 24-
hour year-round emergency service by geotechnical engineers
to protect the public, investigates all serious landslides, and with
this experience continuously improves its knowledge and stan-
dards. GEO also audits the design and supervision of construc-
tion of all new slopes to ensure that they meet the required
safety standards, upgrades “substandard” slopes based on a pri-
ority matrix and takes steps to ensure that private owners take
responsibility for their own slopes through safety screening.
Natural terrain studies and risk mitigation actions are carried
our continuously.
In addition, GEO undertakes extensive public education on
personal safety precautions in order that the community can be
better informed on how to protect themselves during periods of
intense rainfall when landslides are likely to occur. There is also
a program to assess squatter villages for clearance of squatter
huts and to provide guidance to the residents on landslide risk
and self-protection. Complementary to enhancing the stability
of slopes, GEO also gives priority to beautifying the slopes, ei-
ther by making them look as natural as possible or blending
them with the surroundings. Technical guidelines have been is-
sued on good practice in landscape treatment and bioengineer-
ing for slope work.
11.4
Preparedness
NVE organized in 2010 an exercise in landslide preparedness,
and the Norwegian Directorate for Civil Protection and Emer-
gency Planning (DSB) in 2013. The first exercise simulated a
quick clay landslide of national dimension with fatalities. The
second assembled a group of experts to establish the premises
for the national risk that could be posed by quick clay slides.
Worst case scenario, estimates of hazard and vulnerability and
valuation of the consequences were discussed by the different
stakeholders involved. The results will become available in June
2013.
The NVE simulation in 2010 was made as realistic as possi-
ble with the participants not knowing beforehand what to expect
and having one party simulate fatalities. The participants were
briefed of the exercise ahead of time, but they did not know the
details of what was to happen. A majority of stakeholders were
invited, including authorities, police, private actors and media,
in addition to the technical instances required in such emer-
gency situation. The exercise aimed at improving the parties’
ability to respond under pressure in a complex context, and
making decisions under critical conditions. The emergency rou-
tines, information channels and response tools in each of the
participating organizations were tested. The exercise also tested
who took responsibility for the decisions made, and whether the
parties had the same understanding of the respective responsi-
bility and roles.
An evaluation report was prepared with, among others, les-
sons learned: the respective roles and responsibility should be
more clearly defined and communicated to all parties; not eve-
ryone received the required information in time and internal in-
formation within each of the organizations was insufficient;
control of the information given to the media was problematic
(it was not possible to check the wording with the journalists);
making notes and looking at maps in a high pressure context
proved very difficult; how could the private actors doing emer-
gency work/repair ensure that they had a contract (and would be
paid for their work); the authorities should create an emergency
group, and invite wide participation; a logistical and communi-
cation tool should be developed for crisis situations and made
available to all stakeholders; the need for frequent preparedness
exercise, as the people change in each of the organisations in-
volved; and some of the routines in the governmental hand-
books needed to be updated.
11.5
Recent developments
11.5.1
Mapping tool for quick clays
Geophysical methods, especially Electric Resistivity Tomogra-
phy, have emerged as reliable tools for quick clay mapping, as
witnessed at several quick clay sites in Norway (Pfaffhuber et al
2012). When combined with borehole data and electric resistiv-
ity cone penetrometer data, the methods are also cost-effective.
Geochemical analysis also demonstrated that changes in resis-
tivity are directly related to changes in clay salt content, and re-
lated to clay sensitivity. The usefulness of geophysical investi-
gations offshore for the determination of the soil characteristics
and correlation of layers has already been demonstrated in off-
shore work in deep waters.
11.5.2
Mitigation
The United Nations’ International Decade for Natural Disaster
Reduction (1990-2000) to reduce loss of life, property damage
and social and economic disruption caused by natural disasters,
was the start of international concerted actions.
Mitigation and prevention of the risk posed by landslides,
however, did not attract widespread and effective public support
in the past. The situation has changed dramatically during the
past decade, and it is now generally accepted that a proactive
approach to risk management is required to significantly reduce
the loss of lives and material damage associated with natural
hazards. The wide media attention on major natural disasters
during the last decade has clearly changed people's mind in
terms of acknowledging risk management as an alternative to
emergency management. A milestone in recognition of the need
for natural disaster risk reduction was the approval of the
"Hyogo Framework for Action 2005-2015: Building the Resil-
ience of Nations and Communities to Disasters" (ISDR 2005).
This document, approved by 164 UN countries during the
World Conference on Disaster Reduction in Kobe in January
2005, defines international working modes, responsibilities
In the 20
th
century, the economic losses from natural hazards
were greatly underestimated, the awareness of hazards and risk
was insufficient, and the mitigation and regulation to avoid
damage and loss was inadequate. Since 2005, the awareness of
the need for mitigation of natural hazards has greatly increased.
On the other hand, since the 80's, hazard and risk assessment of
the geo-component of a system has gained increased attention.
The offshore, hydropower, nuclear and mining industry were
the pioneers in applying the tools of statistics, probability and
risk assessment. Gradually, environmental concerns and natural
hazards started implementing hazard and vulnerability assess-
ment. Nowadays the notion of hazard and risk is a natural ques-
tion in most geotechnical engineering aspects and even project
management.
12 THE SIGNIFICANCE OF SAFETY FACTOR
The factor of safety against instability is a measure of how far a
slope may be from failure. Factors of safety are applied to com-
pensate for uncertainties in the load, resistance and parameters
