THE OVERVIEW AND STUDY ON THE MODELING OF RISK ACCEPTANCE CRITERIA FOR TUNNEL AND UNDERGROUND ENGINE

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THE OVERVIEW AND STUDY ON THE MODELING OF RISK
ACCEPTANCE CRITERIA FOR TUNNEL AND UNDERGROUND
ENGINEERING

• Hu Qunfang
• Department of Geotechnical Engineering Tongji
  University
• 2005-8-27

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Contents

• Introduction
• The model of risk acceptance criterion
• The classification of risk acceptance criteria
• Individual Risk
• Social Risk
• Economic Risk
• Environmental Risk
• Discussion and Conclusion

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Introduction

• Some Uncertainties within the Tunnel and
  Underground Projects
• the inherent uncertainties and adverse unexpected
  conditions, including ground and groundwater and
  their variability, the complicated surrounding of
  construction site, etc.
• much engineering investment, long construction
  time and long service life.
• the complexity and immaturity of applied
  technology.
• the incompetence of decision-making, management
  and organization.
• human factors and /or human errors.

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Introduction
Risk Decisions
WORLD
Risk System Boundary
The process of risk decision-making
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Introduction

• Risk Management
• Risk identification
• ????
• Risk Assessment
• ????
• Risk Analysis
• ????
• Risk Decision-making
• ????
• Risk Control
• ????

The mode of risk management and control
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Introduction
Therefore, in order to decrease and
mitigate all these risks in tunneling and
underground projects, we should pay much
attention to the risk management and control
during the different stages of the entire
projects life from the theory to start of
operation. And some risk acceptance criteria for
decision-making should be established
qualitatively or quantitatively in advance.
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The model of risk acceptance criterion
The development and implementation of risk
acceptance criteria involves

• Perception of risk ensure that levels of system
  risk, such as safety, economy and environment, is
  acceptance (or tolerable).
• Formal decision analysis analytical techniques
  to balance or compare risks against benefit (e.g.
  risk cost-benefit analysis, life-cycle cost
  analysis) .
• Regulatory safety goals legislative and
  statutory framework for the development and
  enforcement of risk acceptance criteria.

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The model of risk acceptance criterion
Some countries and organizations have
established and adopted some risk acceptance
criterion, such as the U.S Nuclear Regulatory
Commission (NRC), U.K Health and Safety Executive
(HSE), Dutch Technical Advisory Committee on
Water Defenses (TWA) and other regulatory
authorities, etc. Mainly, there are two basic
principles for defining the risk level used for a
qualitative or quantitative risk analysis.

• As Low As Reasonably Possible (ALARP)
• As Low As Reasonably Achievable (ALARA)

The definition foe such terms as Low,
Reasonably, Possible and Attainable are
highly subjective and prone to being interpreted
in a conservative manner. Some expressions and
models have been made to define these criteria in
more tangible limit in terms of quantitative
risks.
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The model of risk acceptance criterion
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The classification of risk acceptance criteria
The risk acceptance criteria can be classified
into four elementary categories from the recent
overview of recent research around the world (Li
Dianqing et al, 2003, S. N. Jonkman et al, 2003)
.

• Individual Risk
• Social Risk
• Economical Risk
• Environmental Risk

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The classification of risk acceptance criteria
(1)Individual Risk
The individual risk (IR), as used by the Dutch
Ministry of Housing, Spatial Planning and
Environment (VROM), is defined as the probability
that an average unprotected person, permanently
present at a certain location, is killed due to
an accident resulting from a hazardous activity.
To limit the risks, there are many criteria
such as ALARA, Risk Matrix, AFR (Annual Fatality
Risk), AIR (Average Individual Risk) and AI
(Aggregated Indicator) etc.
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The classification of risk acceptance criteria
(1)Individual Risk
ALARP
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The classification of risk acceptance criteria
(1)Individual Risk
Risk Matrix
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The classification of risk acceptance criteria
(1)Individual Risk

• Bohnenblust

• HSE

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The classification of risk acceptance criteria
(1)Individual Risk
Besides the individual risk as
mentioned above, four other expressions are
described (T. Bedford et al, 2001).

• The Loss of Life Expectancy
• Social Risk The Delta Yearly Probability of Death
• The Activity Specific Hourly Mortality Rate
• A variant is the Death per Unit Activity

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The classification of risk acceptance criteria
(2)Social Risk
The societal risk is defined as the
relationship between frequency and the number of
people suffering from a specified level of harm
in a given population from the realization of
specified hazards (Institute of Chemical
Engineering, 1985) . To limit the social risks,
there are many criteria such as ALARP, Risk
Matrix, F-N curve, PLL (Potential Loss of Life),
FAR (Fatal Accident Rate), VIIH (Value of
Injuries and Ill Health), ICAF (Implied Cost of
Averting a Facility) and LQI (Life Quality Index)
etc.
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The classification of risk acceptance criteria
(2)Social Risk
The societal risk is often represented
graphically in an F-N curve which is first used
by Farmer F.R. (Farmer FR, 1967) and originally
introduced for the assessment of the risks in the
nuclear industry (H.W. Kendall et al, 1977) .
PLL(the potential loss of life)
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The classification of risk acceptance criteria
(2)Social Risk
Some international standards limiting the
FN-curve
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The classification of risk acceptance criteria
(3)Economic Risk
Besides the loss of life due to certain
activities, the economic risks play an important
role in risk analysis. A FD-curve displays the
probability of exceedance as a function of the
economic damage (S. N. Jonkman et al, 2003). The
FD-curve and the expected value of the economic
damage can be derived from the PDF of the
economic damage.
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The classification of risk acceptance criteria
(4)Environmental Risk
The competitive standing of the Norwegian
offshore sector (NORSOK) has proposed the
probability of exceedance of the time needed by
the ecosystem to recover from the damage as a
measure for environmental risk (NORSOK, 1998).
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Discussion and Conclusion

• The unitive model of risk occurrence mechanism in
  tunnel and underground engineering is showed as
  follow

How can we get the parameter values of C and
n?
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Discussion and Conclusion
The model of risk occurrence mechanism of tunnel
and underground engineering
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Discussion and Conclusion

• In order to establish the unitive model of risk
  acceptance criteria in detail, we should design a
  database, which is used for storing some risk
  events investigation and record data, and do some
  research work based on the existing risk
  acceptance criteria (Beacher GB et al,1987) all
  over the world.

Some Empirical Rates of Failure for Civil
Engineering
By Robert V. Whitman and Greg Baecher
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Discussion and Conclusion

• Human error is an important source of risk. How
  to assess the human errors and whether it can be
  accepted that depend on the context of risk
  acceptance. But it is a blank research area that
  needs us to pay attention.
• Risk analysis is a systematical science which is
  composed of many main subjects. There are many
  problems which need to be resolved in future.
  Fortunately, Our workgroup has a good beginning
  and promotes the further research by our
  teachers.

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Thanks for Your Attention !
to Shanghai and Tongji!