Optimizing tailings dam safety: integrating human factors and evolving hazards For instance it can be assumed that the buttress would be based on enhanced geological and
geotechnical understanding, selected materials, new stability analyses, deformations analyses and would be monitored under a well-designed inspections schedule and oversight by a competent EoR and independent review board. This exercise has been conducted in various real-life cases and, as shown in the next sections has led to the evaluation of the ALARP level in cooperation with the EoR and the owner.
7.2. Other possible scripts There are no limitations to the scripts that could be written to facilitate new users and quick scenario building for single dams, and even portfolios. It appears that a good approach could be to develop three identical scripts per scenario, offering a
good-bad-ugly set of alternatives to pick from. The user would then:
a) Decide is the dam belongs to the “good-bad-ugly” quality category to start with b) Insert the “as is” set of factors of safety delivered by the engineers for the dam. c) Run as many scripts as needed to test alternative mitigations on the dam, including alternatives that may provoke a “jump” of quality category.
7.3. ALARP analyses Several examples of ALARP (As Low as Reasonably Practicable) quantitative analyses have been published to date[21]
including a development[22] that looks at the evolution of ALARP over time.
Indeed, defining the ALARP should not be seen as a static process, as it has to encompass various time horizons along the life of a project/facility. Short term ALARP mitigation level may indeed be very different from the long term one due to different uncertainties, changing system conditions and external evolution, such as for example land use around the considered facility which will require adaptation. The term ALARP is present in various guidelines, such as the Canadian Dam Association (CDA), the Mining Association of Canada (MAC), and the Australian National Committee on Large Dams (ANCOLD), as well as in GISTM/ICMM. In some older literature ALARP was defined as a probability level linked to harm to people; then it was defined as the trade-off equilibrium between risk mitigation costs and risk reduction. This has unfortunately introduced confusion among users and even regulators, oftentimes stemming precisely from the evolution of the definition (see Figures 5, 6 for an example). Let’s note that ALARP should not be confused with tolerance thresholds. Indeed both the tolerability of the risk generated by a dam as well as its mitigation level reaching ALARP should be demonstrated.
In its most modern definition ALARP is reached when it is possible to demonstrate disproportion between mitigative cost and the risk-benefit gained. Being able to demonstrate ALARP status, is paramount to various stakeholders such as owners, Engineer of Record (EoR), insurers, lenders, regulators and finally the public.
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