The impact of standard of care on dams survivability

The impact of standard of care on dams survivability

Nov 25th, 2020

Using ORE2_Tailings we can quantify the impact of standard of care on dams survivability.

In this blogpost we take three dams, namely Dam x, Dam y and Dam z. Their design was identical with initial factor of safety of 1.3. In addition, they had similar QA/QC, construction method, same systemic approach, efforts and uncertainties consideration.

The impact of standard of care on dams survivability

Various small mishaps hit the dams along their history. Some repairs occurred, under different contracts, different quality control and finally, at different times. It turns out Dam x and Dam y were in rather poor shape, whereas Dam z had an “easier life” at the time of our analysis.

ORE2_Tailings probabilities of failure of the three dams

Due to those differences, when we performed ORE2_Tailings assessment the dams came out with different probabilities of failure, despite the initial identical factor of safety.

Dam # FoS Annual probability of failure
Dam x 1.3 5.90E-03
Dam y 1.3 1.70E-03
Dam z 1.3 2.14E-04

The fact that identical factors of safety may lead to over one order of magnitude difference in terms of probability of failure is not a surprise. Indeed,  we showed that in our 2020 book Tailings Dam Management for the Twenty First Century.

As a result, the client was impressed by these differences and asked us what would be the effect of releasing the operations (inspections, audits, etc.) and monitoring standard of care on these dams.

Effect of releasing the standard of care on the three dams

Thus, we used the results above as base case and we built two scenarios: namely a reduction of 25% and then 50% of the standard of care for operations (inspections, audits, etc.) and monitoring.

The figure below displays the results.

The impact of standard of care on dams survivability

As it can be seen and as expected, the reduction of standard of care increases the probability of failure of each dam. As a matter of fact, the largest the release the higher the probability.

The impact of standard of care changes on dams survivability becomes evident. In addition, if the client wanted, we could even back-calculate the corresponding reduction of the factor of safety. Thus, it is possible to design a level of care that keeps a dam probability of failure within a certain range.

Standard of care reduction vs. benchmarking

It is then very interesting to see how the three dams behave with respect to last century world-wide performance benchmark which is part of ORE2_Tailings.

As the standard of care goes from as is to the 50% reduction:

  • The best of the dams, Dam z, remains in an area which is better than world dam portfolio performance.
  • With 25% reduction Dam y which was also in the “better than world wide” area, becomes an “average dam” with respect to the last century experience. In addition,
  • at 50% reduction of care, Dam y reaches the higher bound of the “average dams” range.
  • Dam x starts in the top half of the average worldwide range. As the standard of care release reaches 25-50% the dam pops up in the range of “worse than the world portfolio” area. Because of that shift, the position of the owner may become difficult to defend within the frame of the Global Industry Standard on Tailings Management (Global Industry Standard on Tailings Management – Global Tailings Review).

The impact of standard of care on dams survivability

 The impact of standard of care on dams survivability can be evaluated quantitatively. It is multifaceted because it increases the probability of failure and changes the benchmarking of any structure.

Of course, changing the probability of failure alters the risks generated by a dam.

Now you can really decide if it is worth not rebuilding that broken inclinometer or embarking in that new monitoring campaign.

This is an illustration of risk-informed decision at its best. As a result we get more transparency, more clarity and finally more awareness of the effects of our decisions.

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Category: Mitigations, Optimum Risk Estimates, ORE2_Tailings, Probabilities, Uncategorized

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