Comparison of ORE2_Tailings estimated dam failure probabilities

Comparison of ORE2_Tailings estimated dam failure probabilities

Sep 2nd, 2020

The comparison of ORE2_Tailings estimated dam failure probabilities is an important element of Riskope continued commitment to test the validity of the approach.

Tailings dam interdependent failures and consequences quantifications

Quantitative risk assessment in tailings

One can perform a Quantitative Risk Assessments (QRA) using various methods. Indeed, for tailings dam risks, they all consist in evaluating the:

  • probability of failure of the dam generated by various pertinent hazards,
  • potential consequences of a dam system collapse (failure) and finally
  • the risk.

The technical and mathematical tools for performing QRAs are of public and widespread knowledge. Lack of specific instruction or experience in this field may result in oversimplification of the process. Oftentimes analysts end-up using bits and pieces of “methods” and  they end-up creating a patchwork of partial processes. Finally, fuzziness beyond the inevitable uncertainties emerges. As such, these attempts to generate QRA have a very low reproducibility rate. As a matter of fact, two analysts will oftentimes come out with significantly different results.

More recently, the new Global Industry Standard for Tailings Management asks mining companies and operators to develop QRAs for their dams. In addition the Standard formulates the need to update them regularly. However, at this time the Standard does not indicate how one should perform such a QRA.

We created ORE2_Tailings™ anticipating the requirements of the Standard. The methodology shines when tackling portfolios of dams. We deliver a short description after we describe a case history.

Indeed, we decided to test the reproducibility of ORE2_Tailings results and a formal QRA approach performed by very reputable company specializing in QRA. Comparing ORE2_Tailings™ results in such a way also allowed to prove once again the validity of ORE2_Tailings. This post relates such a comparison.

Case history for comparison

In this case history we deployed ORE2_Tailings™ on a small portfolio of tailings systems. The portfolio includes four dams: TSF A,B,C, and finally D. A reputable independent international engineering company then analyzed the same portfolio using formal quantitative approaches. Failure trees (FTA) constituted the core of that formal approach.

Riskope used various engineering reports, and other documentation available at time of their deployment. These included of course engineering stability analyses developed for a series of conditions, i.e. Model Case I ,J ,K , L and finally M. Thus, the ORE2_Tailings™ deployment was a “completely remote” one, with no interaction with the owner or the engineers of record (EoR) of the tailings systems. However, the engineering company, acting later, had the opportunity to discuss with the owners EoR and thus gained more knowledge on the systems.

ORE2_Tailings™ description

Riskope developed the ORE2_Tailings™  proprietary methodology  to streamline and facilitate the risk assessment of portfolios of tailings dams. Indeed, ORE2_Tailings will allow painless compliance with the Global industry standard once the knowledge base of each dam is acquired. As a matter of fact, ORE2_Tailings™ allows for:

Riskope has provided a summary description of ORE2_Tailings™  earlier, including in books and conferences, courses and finally presentations.

ORE2_Tailings also includes a simplified consequences analysis (see bottom of the table below) together with a knowledge base evaluation/causality analysis.

ORE2_Tailings benchmarks both the probability of failure pf and the consequences, i.e. multidimensional losses with respect to the world-wide portfolio. That is to ensure as good as possible anchoring to reality.

Comparison of ORE2_Tailings estimated dam failure probabilities

The table below displays  ORE2_Tailings™ preliminary deployment results. Indeed, these are pf , consequences and finally risk yielded by the methodology before additional information was obtained through any workshop.

Table: ORE2_Tailings™ estimates of the annual probability of failure with PMF=1/10,000 and “as is” assumptions.

ORE2_Tailings™ estimates of the annual probability of failure

  • Dams C is approaching upper world-wide benchmark (Oboni, Oboni, 2013)
  • Dam B is nearest to lower world-wide benchmark in this portfolio and finally,
  • the highest risks are generated by dam D.

The comparison of the probabilities of failure, consequences and finally risks between ORE2_Tailings™ results and the formal approach shows very good agreement, as shown in the graphs below. Indeed, they are all well within one order of magnitude. That is true even for a case (TSF C) where, later on, workshops brought some new information for one dam. As a matter of fact that case was the one displaying the wider difference, but again, well within one order of magnitude. In addition and more importantly, the conclusions, i.e. the risk relative values lead to the same prioritization with the two methods.

The graph below shows the results of the comparison in terms of probability of failure and bench-marking. Blue indicates ORE2_Tailings whereas red indicates the formal traditional approach. Finally the horizontal lines correspond to the bench-marking thresholds.

Comparison of ORE2_Tailings™ estimated dam failure probabilitiesThe following two graphs show the:

  • consequences comparison and finally
  • risk comparison between the ORE2_Tailings results and the formal approach.

Keep in mind that the formal approach was carried out after new information was acquired, whereas the ORE2_Tailings™ approach was a priori, without any additional information. The effect of new information is particularly visible for TSF C.

Comparison of ORE2_Tailings™ estimated dam failure probabilities

Comparison of ORE2_Tailings™ estimated dam failure probabilities

Effects of additional investigations following ORE2_Tailings™ approach

This analysis was also conducted before the workshops on the dams using ORE2_Tailings™ “knowledge base” evaluator. The question Riskope answers is: “What happens to a dam if the level of knowledge goes from “no knowledge” to a hypothetical future “enhanced knowledge?”.

We have described this approach in a prior post.

This approach opens the door to further investigations cost-benefit analyses, based on quantitative risk analyses. Thus, it can lead to:

  • better mitigative roadmaps, especially when a dam portfolio is analyzed and finally
  • a new understanding of terms such a ALARP, when paired with mitigative effects.


ORE2_Tailings unique innovation in the QRA of tailings dams of any kind, including:

  • earthen-dams,
  • rockfill dams of all types,
  • active or inactive and finally
  • closed,

lies in:

  • quickly arriving to a result with ~3 days of work per dam once the necessary files are made available.
  • streamlining of the QRA process while bringing all the necessary operations in a self-contained approach defined in clear steps,
  • using a well-defined set of Key Performance Indicators (KPI) that engineers can define using a standardized manual after minimal skill acquisition,
  • having a standardized auditable approach to QRA,
  • featuring a built-in reality check using world-wide benchmarks (lessons learned),
  • allowing to generate a standardized summary report on risks, including a rating on the health and knowledge of the dam. In addition get a potential failure causality report either for one dam or for an entire portfolio of dams, and finally,
  • strongly increasing the reproducibility of results while fostering healthy dialogue between key stakeholders.

Contact Riskope for a swift deployment.

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Category: Consequences, Mitigations, Optimum Risk Estimates, Probabilities, Risk analysis, Risk management

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