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General and project-specific tolerability of risk framework (Adapted from HSE 2001 by Munger et al 2009)
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... is also designed to resemble the decision process that people use in everyday life. Figure 1 is adapted from HSE (2001) by Munger et al (2009) to illustrate general and project-specific aspects of TOR on the left and right sides, respectively. The width of the triangle in Figure 1 represents the magnitude of risk for a type of hazard (e.g. ...
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... 1 is adapted from HSE (2001) by Munger et al (2009) to illustrate general and project-specific aspects of TOR on the left and right sides, respectively. The width of the triangle in Figure 1 represents the magnitude of risk for a type of hazard (e.g. dams) measured by individual risk and societal concerns. ...
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... measured by individual risk and societal concerns. Under the general TOR framework, risks are assigned to one of three categories of risk shown as regions on the left side of Figure 1: a) At the bottom is the "broadly acceptable" region in which risks compare with those that people live with everyday, and that they regard as insignificant and not worth worrying about (e.g., mobile phones). b) At the top is the "unacceptable" region in which risks are generally believed by indi- viduals and society to be not worth taking regardless of the benefits (e.g., locating resi- dential areas on toxic landfills); unless they can be reduced to fall in a lower region or "there are exceptional reasons for the activity or practice to be retained". ...
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... applying the general TOR on the left side of Figure 1 to the regulation and management of risks two types of limits have been used. A "tolerable risk limit" is defined between the un- acceptable and range of tolerability of risk regions. ...
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... the right side of Figure 1 the dashed line illustrates the level of residual risk for a specific dam below which the risk is tolerable. This level can fall anywhere within the general range of tolerability region provided that all conditions for a risk to be considered tolerable are met, as summarized in c) in Section 3.1, including a demonstration that the residual risk is as-low-as- reasonably-practicable (ALARP). ...
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... Grenzrisiko für individuelle und kollektive Risiken durch den Bruch von Talsperren (nach US Army Corps of Engineers, zitiert in[12]) Zahl der Todesfälle pro Ereignis Nach[1] gab es in Deutschland bisher keine gesellschaftliche Diskussion über Grenzrisiken. Die genannten Beispiele stammen daher insbesondere aus englischsprachigen Ländern.Die Nutzung des Sicherheitsniveaus des Eurocodes als Grenzrisiko ist für geotechnische Fragestellungen nicht praktikabel. ...
... Das "Common Law" in vielen englischsprachigen Ländern stützt sich vor allem auf Präzedenzfälle, während das auch in Deutschland verbreitete napoleonische "Civil law" auf der Interpretation von Gesetzen beruht[12]. Im Civil law reicht es aus, das Risiko unter dem Grenzrisiko zu halten. ...
In the Lusatian lignite mining area, a large number of opencast lignite mines were closed down and recultivated. In the loosely stored tips, which mainly consist of sandy soil, a considerable number of soil liquefaction events have occurred in the course of the groundwater rise since approx. 2006. These represent a hazard to persons and therefore led to the closure of the tipping areas. The aim of the work was to determine the risk of personal injury caused by soil liquefaction events on inner tips of the Lusatian brown coal mining area. The results provide an opportunity to plan actions to improve safety on the dump and thus achieve better social acceptance. The paper uses examples to illustrate how the degree of risk to people posed by different processes can be determined and represented. The simple physical and empirical correlations form the basis for determining the risk which takes into account the probability of occurrence and the extent of damage of a soil liquefaction event. The process of spontaneous soil liquefaction on tips is described. It is worked out that the effects of a soil liquefaction event depend essentially on the shape of the terrain surface and the position of the groundwater level relative to the terrain surface. For the terrain morphology, the significance number is used as a parameter in order to establish an empirical dependence of the effects of a soil liquefaction event together with the groundwater level. With these results, a hazard map is derived on the basis of a digital terrain model and a groundwater model. By spatial evaluation of the hazard map and an assumed number of persons based on the planned use of the tips, the collective risk of personal injury is calculated. The calculation also includes the probability of soil liquefaction events occurring, which was determined on the basis of evaluations of digital terrain models in the period from 2006 to 2018. The calculated risk from soil liquefaction is compared with everyday risks. Based on this, a limiting risk is proposed. The results are interpreted and a recommendation is given on how to deal with the identified risk.
... According to the ICOLD bulletin 2005, cited in Westberg (2009), there are several limitations to the use of risk assessment in dam engineering, such as the difficulty to estimate the probability of failure with a certain reliability, estimate the dam failure's consequences, the fact that there is not a widely recognised and accepted methodology to evaluate risk and finally, the fact that there is not a good acceptance of the concept of tolerable risk by society. Tolerable risk is defined as being a risk with whom society is ready to live with in exchange of certain benefits as compensation (Bowles, 2012;SPANCOLD, 2013). This definition meets the previously described balance between equity and efficiency. ...
The use of fully probabilistic approaches to account for uncertainties within dam engineering is a recently emerging field on which studies have been mostly done concerning the safety evaluation of dams under service. This thesis arises within this framework as a contribution on moving the process of risk analysis of dams beyond empirical knowledge, applying probabilistic tools on the numerical modelling of a roller compacted concrete (RCC) dam during its construction phase.The work developed here aims to propose a methodology so as to account for risks related to cracking during construction which may compromise the dam’s functional and structural behaviour.In order to do so, emphasis is given to uncertainties related to the material itself (i.e.strength, water-to-cement ratio, among others) as well as to ambient conditions during the construction phase of RCC dams. A thermo-chemo-mechanical model is used to describe theRCC behaviour. Concerning the probabilistic model, two aspects are studied : how the uncertainties related to the input variables are propagated through the model, and what is the influence of their dispersion on the dispersion of the output, assessed by performing a global sensitivity analysis by means of the RBD-FAST method. Also, spatial variability of some input parameters is accounted for through bi-dimensional random fields. Furthermore, a coupling between reliability methods and finite element methods is performed in order to evaluate the cracking potential of each casted RCC layer during construction by means of a cracking density concept. As an important outcome of this applied research,probability curves for cracking density within each casted layer as functions of both age and boundary conditions are predicted, which is believed to be an original contribution of this thesis. The proposed methodology may therefore be seen as a contribution to help engineers understand how uncertainties will affect the dam behaviour during construction and rely on it inthe future to improve and support the design phase of the dam project.
... An "objective limit" or "broadly acceptable risk level" is sometimes defined between the range of tolerability and broadly acceptable regions. The writer has argued that the tolerable risk limit has applicability in common law countries, whereas the objective limit has applicability in countries with a civil code legal system, unless legal provisions are made to support the use of an objective limit in common law countries (Bowles 2010). ...
A key principle in achieving tolerable risk is " reducing risks as low as reasonably practicable " (ALARP). The following factors are commonly taken into account in making a judgment on whether risks are ALARP: the level of risk in relation to the tolerable risk limits; the disproportion between the cost (money, time, trouble and effort) of implementing the risk-reduction measures and the subsequent risk reduction achieved; the cost-effectiveness of the risk-reduction measures; compliance with good established practice; and societal concerns as revealed by consultation with the community and other stakeholders. Thus, the ALARP evaluation and demonstration is both qualitative and quantitative in nature. Consideration of the cost effectiveness of achieving life-safety risk reduction relative to life-safety benefit achieved is a quantitative aspect; but it introduces the consideration of cost only to justify further risk reduction below tolerable risk limit(s), and not to justify achieving the limits in the first place. Following a background overview of the definition tolerable risk, the tolerability of risk framework and examples of tolerable risk guidelines, the paper discusses various considerations in evaluating and demonstrating ALARP for a dam. Reference is made to experience from ALARP evaluations conducted for actual dams.
While reservoir dams have created significant social and economic benefits, dam failure caused by various reasons bring about great threats to the downstream areas. Many countries determine management investment according to the risk level of reservoir dams and the “as low as reasonably practicable” (ALARP) principle. However, life cannot be directly quantified in currency, and the traditional “cost-benefit” method cannot be effectively applied to reservoir dam management decisions. Hence, the life quality index (LQI) was introduced and improved to solve this problem based on the targeted analysis of the parameters of the life quality index, considering the fact that the per capita GDP changes over time. Without monetary quantification of life, an annual economic investment was determined to effectively control the risk level of the reservoir dam in a certain period of time in the future to ensure people’s life safety and quality of life. The improved LQI method was applied to a small-scale reservoir in China. The results showed that (a) the annual investment in dam risk management calculated by the improved LQI method was 20.07% higher than that of the traditional LQI method; (b) the annual investment in dam management changed 24 times due to changes in warning time and public risk awareness; and (c) dam management investment should be used not only to ensure the safety of the structure but also to improve early warning capacity and public risk awareness. This study focuses on how to reasonably determine the management investment of reservoir dams when the dam risk is in the ALARP region, which can effectively promote the application of dam risk standards.
The paper explains the background of currently used risk evaluation criteria and guidelines in the field of dam safety assessment.
