Geotechnical News • December 2017
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GEOHAZARDS
Residual Risk
Residual refers to the risk that remains
following an event, assessment, or
mitigation. It reflects our uncertainty
about the stochastic nature of the
physical world, the potential for even
low probability events to occur at any
time, and our knowledge and iden-
tification of more likely events that
remain following an assessment or
mitigation.
In the L’Aquila case, the knowledge
of the day was that small earthquake
swarms were not statistically cor-
related with a major earthquake
(this assumption is being rigorously
re-examined globally as a result of the
outcome). The residual risk of a major
earthquake remained but was inad-
equately communicated.
Increasing risk and increasing
challenges of risk assessments
While credible arguments can be
made for a decreasingly risky world
(increased lifespans, wealth and gen-
eral human health, earthquake resistant
infrastructure, better land use zoning,
emergency management applications
and increased medical care), there are
objective measures whereby geotech-
nical risk has increased substantially.
With a global population at more than
7.5 billion and growing, humans have
disrupted natural systems and imposed
themselves on the landscape (Guthrie,
2015). Obvious examples include cli-
mate change and subsequent changes
to sea level, slope stability, distribu-
tion of permafrost, flooding and storm
intensity, as well as geotechnical risks
that result from a systematic intrusion
into, and occupation of, higher hazard
areas.
The assessment of geotechnical
risk cannot rely unquestioningly on
standards and practices developed
by those pioneers of the discipline.
We must continue to use our best
understanding and judgement in
a world where the rate of change,
and our role in it (as both drivers of
change and those effected by change)
is increasing, and our assessments
should in some manner, account for
that change. Errors in judgement are
assured (Nasmith, 1986), but hope-
fully through the careful and judicious
application of our knowledge, training
and experience, and clear communica-
tion to our clients, we do indeed serve
the public good.
Abdulahad et al. (2010) reviewed 41
legal cases involving geotechnical
practice in Canada between 1982 and
2006. While not strictly risk assess-
ments, risk is implicit in each exam-
ple. Of those cases, more than 50%
were based on different soil conditions
and recommendations than expected
from the geotechnical report. The
courts allowed the actions based on a
provision of reasonable evidence to
expect different soil conditions (about
40% of the time).
Nasmith (1986) stated similarly that
incorrectly located boreholes are
among the most common errors in
geotechnical engineering.
In addition, slope stability and land-
slide risk assessments are inherently
high-risk for the practitioner. They
rely on uncertain knowledge, chang-
ing ground conditions, and constantly
changing driving forces (such as the
weather, manipulation of the slopes,
and re-direction of water among other
things).
The questions remain: How do we, as
a discipline, increase our predictive
accuracy in an increasingly complex
world. How do we communicate
effectively to our clients both the
legitimacy and the uncertainty in our
work? How do we provide practical,
useful advice that decreases geotechni-
cal risk?
Answers in the code
Geotechnical scientists and engineers
conducting hazard and risk assess-
ments perform a valuable public
service. The Engineer’s and Geosci-
entist’s code of ethics is designed to
protect the public, but simultaneously
offers protection to the practitioner. In
this case, answers to the above ques-
tions are framed in the context of the
Association of Professional Engineers
and Geoscientists of British Columbia
(APEGBC). This has been renamed
to Engineers and Geoscientists British
Columbia (EGBC).Code of Ethics:
(Author’s note: other Codes have
similar clauses).
Code Bullet 2: Undertake and accept
responsibility for professional assign-
ments only when qualified by training
or experience
It is a human condition to overesti-
mate our knowledge or the accuracy
of our own judgement (Kahneman,
2011). We’re simply not very good at
knowing what we don’t know. An anti-
dote to this is, ironically, training and
experience. The more we learn, the
more we are exposed to the exceptions
to the rule, to the rare black swans, to
solutions arrived at through an entirely
different mechanism. We have a duty
therefore, to recognize when inde-
pendent or senior review is helpful
(almost always), to cross-pollinate
and discuss our ideas with peers and
colleagues, to mentor junior and inter-
mediate staff and to approach other
disciplines with humility and respect.
Another antidote to the training
and experience issue occurs when a
problem is approached by an engi-
neering geologist or geomorphologist
and a geotechnical engineer working
together. Each has a comprehensive
background that is not likely to be
fully realized by the other, but together
can dramatically improve the results of
an assessment. These advantages have
been made clear by others (Redlich,
Terzaghi, & Kemp, 1929; Fookes &
Vaughan, 1986; VanDine, Nasmith,
& Ripley, 1992; PRCI, 2009) but this
approach remains under-utilized.
Code Bullet 3: Provide an opinion on
a professional subject only when it is
founded upon adequate knowledge
and honest conviction
Similar to the previous bullet and
subject to the same solutions, this one
also speaks to a tension that frequently
arises between a client looking for a
conclusive answer from a specialist
