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Data required for ORE2-Tailings risk assessment

Data required for ORE2-Tailings risk assessment

May 16th, 2018

Every group we present ORE2-Tailings to is curious about the Data required for ORE2-Tailings risk assessment.

Data required for ORE2-Tailings risk assessment

Author Xtremizta

In follow-up to a presentation, the client requested the following three information:

  1.  What are the 30 diagnostic points ORE2-Tailings uses to evaluate the annual probability of failure of a dam?
  2.  Is there a peer reviewed publication about the methodology?
  3.  What are the steps to define the risk tolerance of a corporation or an operation/project?

Data required for ORE2-Tailings risk assessment

This section summarily describes the data used in ORE2-Tailings to estimate the annual probability of failure of a dam.

The last section bears on the estimate of the Consequences of a failure.

Many of the elements in the list below may be space observable or measurable using extant monitoring and may have been the object of dams inspections. There are indeed many instances where the “dam owner” has to deliver data (if they have them).

ORE2-tailings is built in such a way that missing data do not block the analysis, but impact the uncertainties.

The 30 diagnostic “points” used in the assessment

Six points cover the physical aspects of the dam and its equipment (weirs, pipes, spiggots, pennstocks, etc.)

Five points cover the construction: type of materials, cross section, supervision, berms & erosion, divergence from plans, etc.

Further five points are used to characterize the geotechnical investigations and testing, whereas points 19-22 cover the analyses and documentation of the project.

Points 23-29 allow to characterize the impact of:

  • stability analyses (of various types, ESA, USA, pseudostatic, etc.),
  • instability symptoms,
  • settlements (actual and analyses),
  • liquefaction and finally,
  • internal erosion

on the probability of failure.

The last point does the same from a operation and monitoring, maintenance & repairs point of view.

Consequences

From a consequence standpoint, if the owner does not have yet dam breach analyses and did not evaluate the “cost” of failure, ORE2-Tailings will necessitate a consequence analysis step.

Topography precise enough to allow detailed calculations will be necessary. Indeed, the presence of man made fills, ditches, even only a couple meters high/deep, a few meters wide brings significant influence on the flooding behaviour.

Of course, satellite mapping may be an option if Lidar data are not available.

If water bodies are present their bathymetry is important as well.

Extant peer reviewed publication

In 2016 we wrote a paper explaining the methodology in the Canadian Dam Association bulletin. Interested readers can easily download the paper following the link below.

The exact reference is:

Oboni, F., Oboni, C., Screening Level Risk Assessment for a Portfolio of Tailings Dams, Fall issue of Canadian Dam Association (CDA, ACB) Bulletin, Vol. 28 No. 4 Fall 2017.

We remind our readers that at publications and presentations all our papers on tailings risk assessment can be freely downloaded.

Risk Tolerance Definition

Older approach

There was a time when we used to derive risk tolerance thresholds point by point through a rather lenghtly Q/A session with key stakeholders.

Below are some examples of risk tolerance based on monetary losses. Of course, other metrics are possible.

On the horizontal axis we represent the losses (in M$, in this case), and on the vertical axis the annual probability of incurring those losses.

  • We developed the light brown envelope  over twenty years ago for a group of European and international companies.

  • The orange envelope dates back over two decades as well. We developed it for a large North American mining operation. The domain “width” illustrates the uncertainty and the presence of risk prone (with risk “appetite”) and risk averse factions.

  • Finally, a very large Latin American mining group developed  the dotted line linking the two black crosses over thirty years ago by .

Obviously one should actualize the losses to gain a perception of the risk tolerance of those groups today, due to inflation and other financial issues.

Of course, each company, operation has to develop a specific curve.

Data required for ORE2-Tailings risk assessment

Today’s approach

Based on our experience we have developed a mathematical model for the risk tolerance.

So, we have condensed the data necessary to apply that proprietary model in four questions we ask the stakeholders to answer, preferably with ranges to include their uncertainty.

Contact us is you want a ORE2-Tailings risk assessment presentation based on a real life case.

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Category: Consequences, Mitigations, Optimum Risk Estimates, Risk analysis, Risk management, Tolerance/Acceptability

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