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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. Contents. Introduction The model of risk acceptance criterion

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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

contents
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
slide3

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.
slide4

Risk Acceptance Criteria

Collection of Information

Risk Management and Control

Tunnel and

Underground Projects

Introduction

Risk Decisions

WORLD

Risk System Boundary

The process of risk decision-making

slide5

The purpose of risk management

Introduction

Risk Management

  • Risk identification
  • 风险辨识
  • Risk Assessment
  • 风险估计
  • Risk Analysis
  • 风险分析
  • Risk Decision-making
  • 风险决策
  • Risk Control
  • 风险控制

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 classification of risk acceptance criteria

The risk acceptance criteria can be classified into fourelementary 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

Risk Matrix

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VROM:

  • TWA:

Public:

Workers:

The classification of risk acceptance criteria

(1)Individual Risk

  • Bohnenblust:
  • HSE:
slide15

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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(fatalities/year)

(fatalities/year)

The classification of risk acceptance criteria

(2)Social Risk

Some international standards limiting the FN-curve

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(US $/per year)

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.

slide20

Highly potential ER:

Lowly potential ER:

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?

slide22

Discussion and Conclusion

The model of risk occurrence mechanism of

tunnel and underground engineering

slide23

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

slide24

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.
thanks for your attention

Thanks for Your Attention !

to Shanghai and Tongji!

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