ORE2_Tailings Potential Failure Causality Analysis

ORE2_Tailings Potential Failure Causality Analysis

Dec 11th, 2019

ORE2_Tailings Potential Failure Causality Analysis is one of the features of Riskope’s tailings dam specific application.

ORE2_Tailings Potential Failure Causality Analysis

Indeed ORE2_Tailings looks at the causes of dam failure rather then the reasons why dams fail (the “failure modes”). That is because the root cause of a dam failure is typically the result of a combination of deviances. Recent forensic studies on major catastrophic failures have eloquently demonstrated that.

Normalization of deviance

Catastrophic failures, like most major accidents are indeed always generated by an unfortunate mix of multiple causes. Normalization of deviance (from original intent, design, scope, etc.) on one or more aspects of the dam life end-up generating the conditions for failure.

ORE2_Tailings looks at detected or suspected deficiencies in the following areas:

  • Sampling and testing including in situ and lab tests.
  • Design including 3 categories, namely:
    • initial understanding of geological and geotechnical conditions,
    • robusteness of the cross section,
    • projects soundness, including documentation and:
      • stability
      • seepage
      • liquefaction and
      • settlements.
  • Construction including:
    • quality of supervision,
    • possible E&O,
    • divergence from plans.
  • Operations and maintenance including:
    • monitoring,
    • inspections,
    • reviews and finally
    • repairs.

Accounting for uncertainties

For each area the analysts express a judgment encoded in a number.

Two sets of opinions (A,B) are always analyzed and their average (AVE) evaluation used. If the A,B opinions are too different it is better for the analysts to stop and think until a sort of consensus is reached. This may require additional studies.

A,B however will always exist and are necessary. That is because of the uncertainties on many aspects of the structure life from inception to the date of evaluation. It is not recommended for a single analyst to perform the evaluations as these obviously include a part of perception and judgment.

The graphs below describe the causalities (%) globally (left) and then in more details (right) for a specific real-life dam. As ORE2_Tailings mimics the results of major forensic investigations performed in the aftermath of recent catastrophic failures, none of the areas will ever show-up with nil causality. Indeed, that would sum-up to an excessive dose of deterministic judgment which does not fit with forensic experience.

ORE2_Tailings Potential Failure Causality Analysis

ORE2_Tailings Potential Failure Causality Analysis

In the considered case we see that construction, operations and maintenance sum up to only one fifth of the causality, whereas design, sampling and testing represent about 80% of the causality. This is due, in the considered case and among other, to:

  • excessive audacity of some of the assumptions (peak resistance in undrained conditions, for example),
  • poor consideration for static liquefaction and finally
  • defects of the water management systems (no diversion ditch, near-miss overtopping, etc.).

ORE2_Tailings Potential Failure Causality Analysis closing remarks

ORE2_Tailings Potential Failure Causality Analysis is one of the features of Riskope’s tailings dam specific application.

When tackling large portfolios it is interesting to study how the causality analysis varies from region to region, operation, construction time.

Portfolio owners can then prepare guidelines to better the knowledge base and mitigate risks, after evaluating the probabilities of failure and the consequences for each structure.

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Category: Consequences, Hazard, ORE2_Tailings, Probabilities, Risk analysis, Risk management, Uncategorized

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