Today we present a story about Limitations, disclaimers and risks.
The case related to limitations, disclaimers and risks.
This is a case history on limitations, disclaimers and risks. Below is the summary of the case.
Like all other consultants, we introduce in our reports verbiage clarifying our reports address specifically a project, a situation. Thus no one should generalize them to other operations, even if these may appear similar.
In particular, the verbiage aims at protecting the client from the temptation to “run away” with a piece of IP. That is because if poorly understood and then poorly generalized, that piece of IP may lead said client and the pubic to unwanted exposures.
Thus, it is with deep consternation that we heard a while ago a client explain to an international audience a generalization to an entire portfolio of mines of a specific report. Out of professional courtesy and care, we immediately warned the client of numerous omissions we immediately spotted. We urged them to be cautious while congratulating them for “their idea”.
Of course, we were at first angered because they did not reference the source of the IP. However, we then decided it was better they did not mention Riskope. Indeed, we do not want anything to do with such a flawed approach.
Risk is a job for specialists, not a hobby.
The numerous omissions we spotted show a fact many have recognized as we discuss at the end of this text.
Even well respected and experienced engineers cannot improvise and develop quantitative risk assessments. Indeed, there is a large volume of knowledge that has to be acquired before anyone can claim to be able to perform a sensible risk assessment on a tailings facility.
It is interesting to see that, for the time being, the brand new Global Industry Standard on Tailings Management explains the role and qualifications of key personnel (e.g. EoR, ITRB). However, and very unfortunately it forgets to explain who should perform a risk assessment and what a risk assessment should deliver. We will discuss this in more detail soon, although we know that Prof. N. Morgenstern is reportedly working on filling this gap.
For the time being we will note that the flawed approach developed by our client does indeed deliver results that could be accepted by the new code while being extremely misleading.
Example of risk assessment flaws we have seen over the years.
At Riskope we do not think ethical to evaluate probabilities below credibility (10-6) using a semi-empirical method like Silva Lambe Marr (2008). Thus, we impose a cap, even if the engineers declare very high Limit Equilibrium Method (LEM) derived Factors of Safety (FoS).
We also note that, for example, a number of Class 5+ nuclear accidents have occurred for reasons not included in very detailed analyses. Examples of these analyses are the Walsh report and French nuclear safety studies in the mid 70’s. Therefore the factual rate of Class 5+ nuclear accidents is several orders of magnitude higher than the fault tree/event tree derived theoretical values (Oboni, Oboni, 2013).
Incidentally, we also have concerns in accepting engineers evaluating Fos>2 for any geo-structure, because of LEM intrinsic limitations.
Silva Lamb Marr developed their approach for slopes, not necessarily for dams. Thus, it does not include liquefaction considerations, does not include potential hazards from tailings distribution lines, etc. As a result, its application to dams is very limited. We have used the methodology in some specific studies for clients, we have used in our book as an example. However we added a discussion of the effect of liquefaction on the overall probability.
We cannot imagine characterizing a dam by a single FoS. A dam can indeed succumb to many “diseases”.
A couple philosophical thoughts
Furthermore, at Riskope, we adhere to Peck’s ideas. We urge you to read Peck, R.B., 1980. ” Where has all the judgment gone?” The fifth Laurits Bjerrum memorial lecture. Canadian Geotechnical Journal, 17(4), pp.584-590. if you haven’t done it lately. Peck’s ideas we refer to are related to failure modes. They were confirmed by the most recent post mortem analyses of the Brazilian and Canadian accidents. They also cover oversights versus theoretical analyses etc. Please note that Peck was talking about hydro-dams. Today, well-designed hydro dams have likely gone one order of Probability of failure (PoF) magnitude down (10-5) with respect to the 10-4 Peck quotes as “historic” in 1980. Tailings dams are a different story, of course.
Talking about the oversight and excessive reliance on analyses, at Riskope we would not accept to consider a loading case as “completely not credible”. That’s in particular the case of known “defect” in a geological formation the engineers may want to discard as not credible. What about possible pressurizing a pre-sheared foundation zone, for example? Who knows, right? But there are good examples of this in the dam failure history.
Closing remarks on limitations, disclaimers and risks.
Of course, this is just the tip of the iceberg.
As Terry Eldrige (Golder, TMW2019 Key note lecture), risk is a job for specialists. and cannot be improvised. See in particular:
4:38-5:36 Success requires avoiding many separate causes of failure; failure mechanism and cause may not be the same; failure caused by complex factors.
25:22-26:10 Shortcomings of engineers performing risk assessments
We will be delighted to discuss these topics with you. Contact us.
Leave a Reply