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Posts Tagged ‘tailings failure’

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I was always healthy until I visited the doctor for a checkup.  Then they found all sorts of things wrong with me:  internal components not working; high levels of this and that and consequential concerns; indications of too much drink and smoking; blood pressure where it should not be;  weight too high; and so on.  Although I did loose some fifteen lbs on my recent trip to Peru and Chile. Maybe not enough alcohol,  lots of walking, and all that terrible Peruvian food.  How can you like raw fish in vinegar; black potatoes in squid ink; or slimy muscles in red pepper?  I cannot and probably ate too little.

No matter.  We get old and things go wrong.   I suppose it is all a matter of what will get me first.  As long as it is not an angry reader of this blog.  But the doctor laughed and told me to keep going for there are many years yet to write this stuff, she said.  When did the doctor become a lady younger than my daughters?  It is just not fare.

So instead I spent the day writing reports on tailings dam I have recently observed.  I am amazed at the low standard of stability analyses I have seen.  Fourteen analyses and not one of them is correct!  Here is a list of the most common mistakes.  At least I have set those so-called reputable consultants working again.

  • Failure to include foundation soils in the stability analyses.  Apparently they did no foundation drilling, so did not include foundation layers.  Subsequent drilling has shown there are liquefiable layers in the foundation.
  • Failure to include the phreatic line in the cross section.  Apparently they had not yet installed piezometers so had no water table.  Subsequent work has shown that there is a high phreatic line in the cross section.
  • Use of circular arc failure surfaces in cohesionless materials.  We all know that planar failure surface develop in such materials.
  • Failure to use planar failure surface to calculate stability analyses involving sliding along a weak foundation layer.  They used circular arcs which simply cut through strong and weak foundation layers.
  • Use of the pseudostatic coefficient for seismic stability analyses in high earthquake regions.  They should be doing deformation analyses in order to estimate deformation.
  • Failure to account for buildup of excess pore pressures as the tailings rises.  Too complex to do I suppose.
  • Incorrect use of strengths of materials:  UU for slow failure and CU for fast failure.

No wonder these things fail.  Not only are the stability analyses done by amateurs, the phreatic surfaces they calculate using standard programs are just simply wrong.  But that is another blog topic.

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A little bit more on the failure of that tailings facility in Brazil from some-one on the ground:

The accident was in a very small mine close to Belo. It was an old tailings dam that was not  supposed to be in operation anymore. But they decide to pile dried tailings on top of it. I don’t have technical details about the failure but I guess it is very similar to a previous one I took you to see. At the moment of the failure, equipment was working at the same point. That’s the reason for the deaths. It is going to take some time for us to get the conclusions about the real cause of the accident. But, as soon as I get some more information I will let you know.

Thanks to this fellow for letting us know.

Here is another comment from someone in Brazil:

The Minas Gerais dam failure is worst because of dead people (3), which means that there is environmental process and also criminal. The problem I see from the two failures is that we still don´t know the causes. In Canada the cause seems to be overtopping or seepage thru the embankment (high pore pressures or piping); in Brazil it seems to have occurred static liquefaction, and the triggering cause possibly excavation of the outer slopes. But we haven´t seen any word about the causes. It is just my guess. In Canada the pictures we saw doesn´t show a good appearance of the dykes. It resembles coarse and loose material, not prepared to have any contact with water. In Brazil it was an old tailings dam, upstream construction, that was being used as a platform for the operation of settling ponds (we call it here “baias”), where the coarse settles and are removed by shovels and transported to piles, and the fines have the same destiny, but need more time to drain and do dry.

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Today we have read all we can find on the failure of the Mt Polley tailings facility.  It is all distressing.  And mostly misleading.  Here are a few clear thoughts on the topic. (more…)

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Risk resilience is a term that I heard for the first time today.  The people who used the term assure me that it is not new, just not recognized in mining for its power. There was a conference last year in South Africa on risk resilience in mining.  There is a successful consultant on the topic in Australia. (more…)

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There is no such thing as a typical mining investor.  That much was brought home to me today.  (more…)

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Mike Davies is the pre-eminent tailings engineer of present times.  He and his team in Vancouver can solve any tailings challenge your mine may face.  He and his team at AMEC are the best of the best.  They have not paid me to say this; I write, as always, on the basis of personal opinion & conviction. (more…)

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This morning a pleasant-voiced lady from CBC TV called me and asked my opinion about the recent failure of a tailings impoundment in Hungary and its impact on towns, villages, and the Marcal river.   I am not sure why she called me—maybe this blog and the opinions I express.  She asked simple, direct questions and we hung up.  A short while later, most breathlessly, she phoned again and asked if I would be prepared to be interviewed for a piece the CBC is running tonight on the topic.  I told her that I am old and ugly and thus not a good TV candidate.  She has the training, and she turned on the charm—who am I to resist the charms of a smart woman?  So I walked down a few blocks to the CBC and there they interviewed me.  (more…)

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