I THINK MINING

A casual conversation in the parking garage involved this question: “What are the five tailings failures that set the course of history?”

I pondered this question on the drive home.  I decided it would take more time and insight than I have to answer.  So I perverted the question to the following: “What tailings failures had the most significant impact on my career?”

That is an easy one to answer, and here is the list and the reason for designating the failure significant.

The first failure may be termed The De Beers Kimberlite Dam Failure.  It happened thus:  I was young and arrogant and thought I knew it all.  I was asked to design a new kimberlite slimes dam for De Beers next to the Big hole in Kimberly.  For decades the mine had simply let the slime go from a single spigot and flow forever across the landscape.  Then they realized the slime was flowing forever.  So they pushed up an earthen dike to stop the flow.  By the time I was engaged, the dike was topped by the slimes and was threatened with overflow.  The mine wanted a new slimes dam built atop the beached material near the spigot. 

It was all so simple: build a conventional upstream dike on top of the old slimes.  They built the dike and for a few years this worked.  Until on day the pool of water came too close to the outer dike and it failed. 

I had told them not to do this, that is let the water of the pool get too close to the dike.  I knew enough to know that a phreatic line would develop and induce pore pressures that would fail the dike.  I was correct: when the pool got to close, the water pressure increased and the dike failed. 

No particular harm resulted, for the slimes just flowed a while over the old slime and then congealed before it got to the old perimeter dike.

From this lesson I learnt never to trust the promises of those who operate the slimes dam—your design has to be idiot proof.  And ever since my tailings facility designs have been idiot proof.

The second slimes dam failure that significantly impacted my career was the failure of the Bafokeng dam at the Impala Platinum Mine.  Much has been written about the causes of failure—most of it uniformed or just wrong.  Regardless, thirteen people were killed and the slimes flowed fifty miles to fill a water reservoir. 

I was a student and was assigned by Professor Jennings to do the leg work of going to the  site and measuring, photographing, and taking samples to get data to try to explain the failure. 

At first, I concluded that the failure was the old story: water too close to the outer perimeter embankment.  Then the professor concluded the cause of failure was piping through permeable sand layers between less permeable clay layers.  A good friend convinced me the cause of failure was the bulldozer sent to beef-up the small berm around the pool.  Either the bulldozer induced liquefaction of the sand or he cut too deep making an opening through which the water and subsequently all the slimes in the interior of the dam flowed.  On the basis of later failures of similar platinum tailings impoundments, I concluded that at thirty meters height these outer perimeter slopes just failed by sliding along the layer of ubiquitous clay that has a cohesion of about eight psi  or whatever the unit was we used in those days. 

The next failure that impacted my thinking on the failure of tailings storage facilities (to use the facile and puerile nomenclature of the present) was the failure of the Teton Dam in Idaho.  I had been brought up in South Africa to revere American dam engineers, but this time they got it wrong and shattered my reverence.  The water-retaining reservoir failed when the foundations of the embankment failed as a result of piping through the friable sandstones on which the earth structure was constructed.

A few years later, I found myself the designer of the Cannon Mine tailings dam and on site overseeing its construction.  The foundations were those self-same friable sandstones that had piped and failed at Teton.  I read everything I could find and with senior engineers far wiser than me (Syd Hillis in particular) we did everything we cold possibly do to eliminate a reoccurrence of the Teton failure mode.  This included placing thick filters over the foundations to preclude piping in the event of seepage.  Plus a deep, expensive grout curtain.

The Cannon Mine tailings impoundment is now reclaimed and safe.  Past failures guided us aright.

The final failure of a mine geowaste facility that has impacted my thinking is the hoary old favourite, namely the failure of the Bellavista heap leach pile.  You will no doubt have read my many writings on this.  But the story of its impact on my life is more interesting and has not hitherto been told.

I was in the midst of a nasty divorce.  A very old lady friend was also involved in a nasty divorce.  Our mutual liking and divorces were not connected.  But we got together often to bemoan our spiteful ex-spouses and their errant ways.  This nice lady mentioned one day that she did not like mining but did like Costa Rica, mainly because there was no mining  in Costa Rica. 

I noticed a report on the failure of a heap leach pad in Costa Rica.  So I blogged about it and bragged to the nice lady next time we shared a few bottles of wine and mutual recriminations of e-spouses.  She was irate but interested.  So I did a bit more searching and wrote a bit more on this self-same blog.  It made for interesting drinking discussions.

Then I chanced on the fact that the designer of the failed facility was a fellow we both new and whom neither of us liked.  The blogging and drunken discussions became more intense.  I attacked with fervour, both to show off and to vituperate a mutual dislike. 

Only later did I discover the extent of involvement in this failure.  Let me say no more, but even people I like and maybe respect had a hand in the failure. 

Now I know they were motivated by a desire to survive in a bad economy and an absence of reasonable corporate procedures to control quality.   All involved were, in my humble opinion, motivated by instincts of survival, pressure from impatient clients, and a silly reliance on fools employed by the mining company involved.  I had best stop at this point for the failure is still the subject of wide-ranging law suites, and I may get called on to tell a jury all I wrote and why.

The point of this personal reverie is to highlight mine geowaste facility failures that have impacted me and my career, from young designer to ancient blogger. 

I have concluded from all these failures that the only way is extreme conservatism, no reliance on the opinions of others—however reputable—and full site characterization and detailed analyses.  For even now I am involved in the design of a tailings facility in a part of the world where the design earthquake is 8.5.   That is big and could send everything down the valley and the experts say there is no problem and I think they are deluded. 

I have written that I believe those who focus on single causes of failure are deluded.  There is no single reason for failure of a mine geowaste facility.   All failures that I have known are the result of a string of minor incidents.  If but one of this string of incidents had been dealt with, no failure would have occurred.  This is pretty much standard accident theory these days, although it seems not to have entered the otherwise bright minds of those who write on the failure of mine geowaste facilities.  Pity them, and pity the profession for remaining so ignorant and failure oriented through failing to keep up with modern ideas and theories. 

So the failure of mine geowaste facilities will keep on happening.  It is inevitable.  The professionals are blind and behind times.  The operators are greedy and careless.  Nobody reads the guidelines.  The peer reviewers are old and sleepy.  The pressures to profit are intense. 

Now maybe, prompted by this posting we can reconsider and reconvene and change.

Perhaps you can do the following:  tell us of the failures that have affected your career and opine on my scurrilous opinions.  Thanks.