CONTACT: LINDSAY NEWLAND BOWKER compiler@worldminetailingsfailures.org
DATE: October 25, 2021 ( Revised October 26 to Reflect CIMNE/author comments)
The CIMNE report is not related to the decision to start over on the case against Vale’s former President Fabi Schwarzman and 15 others indicted under criminal charges in connection with the Brumadinho failure. That decision , which did, though, respond to a suit brought by Schwarzman, was not on any merits under Brazilian law. The Federal Prosector ruled only that it was not properly filed in Minas Gerais state court and needs to be refiled in federal court. Though not specifcally clarified, presumably all evidence and testimony material to Brazilian law would be preserved and brought into the case in Federal court.
The CIMNE report, co-authored by two of the world’s leading experts in liquefaction, Antonio Gens and Marcos Arroyo, both of UPC, adds to, rather than contradicts or alters the prior two expert panel reports on the cause of the January 25, 2019 failure of Dam 1, Brumadinho.
The work illustrates the use of a more informative and sensitive stability assessment, finite element, that may have, saved lives if used at Brumadiho, as TUV SUD had suggested in their 2017 report to Vale. The frail status of the Brumadinho dam was well understood going back to before the 2016 decision to stop depositions and focus on dewatering in an effort to get the dam in shape for safe execution of a planned re mining that Vale and Minas Gerais were counting on for a 20 year extension of local jobs.
Plaxis 2D, a finite element modeling tool was used by Gens and Arroyo to show that a drill operation all thought was safe actually triggered the failure. Applying the model to all known about the tailings stack and its history exactly replicated the failure and its sequences. In its 2017 report to Vale TUV SUD using the more prevalent limit equilibrium model also got a very low factor of safety for the modeling condition”unknown trigger”.
While the authors did not assert that that model could have been applied to rule out that drilling operation, they do say, and other experts in liquefaction agree, that a liquefaction susceptible stack should be evaluated by finite element analysis which better models flow dynamics and would have given a much lower factor of safety result than the undrained limit equilibrium more commonly still used.
The authors emphasize in their conclusion how risky it can be to attempt de risking , as had been ongoing at Brumadinho for three years prior to failure, without very complete and accurate data on the whole stack especially when conditions have reached the point they were at Brumadinho. Had a finite element analysis been undertaken much earlier the condition of the stack would have been better understood and perhaps different decisions made both in evaluating the feasibilty of the planned re-mining operation and about the ongoing use of the canteen and adminsitration building where most deaths occurred.
Their modeling work reaffirmed the December 12, 2019 expert panel finding that the failure emanated from the crest with a force that caused the break in the containmnet wall. ( Previously some had opinded that a lower portion of the TSF had failed triggering the flow failure.)
“It seemed likely from the first descriptions and images of the Córrego do Feijão Dam I failure that the cause was static liquefaction, a transformation of the nature of the tailings resulting from over saturation that makes them perform more like water than soil, causing a greater force that propels released tailings much farther than the same volume of compacted tailings would travel in a foundation failure. Initially some experts viewing the video of the actual event opined that, while a liquefaction event clearly occurred, it was not clear whether it followed from or caused the failure. The lower part of the dam had been previously identified as key to overall stability and also a place of vulnerability. The expert panel report released December 12, 2019 confirms that static liquefaction occurred at the crest and was the cause of failure of the outer shell. Static liquefaction was under active consideration by Vale and its engineers in 2017 and 2018 .
“Fundão, Stava, Merriespruitt, Los Frailes, Sullivan Mine and Pinto Valley are a few well-known examples of static liquefaction failures in history. At Merriespruitt, as at Fundao and Brumadinho stability analysis per prevailing methods found the dams safe. That prevailing practice is not, however, best practice/best knowledge is a subject of growing interest and concern that has evolved over at least two decades. It has forced a re-evaluation of what was taught in mining schools and has been best knowledge for a large part of the worldwide community of dedicated mining engineers. It is not now a major focus of education and apprenticeship as the world’s future engineers set to work. A great deal of knowledge has been advanced by Roberto Rodríguez Pacheco, by revered engineers such as our colleague Andrew Fourie , by the venerable Mike Davies and Todd Martin, and by Norbert Morgenstern among many others.
Their insights and urgings have not found their way into government regulations on stability and are not shaping main practice or even main stream discussion. It is just not part of the thought and decision making that has shaped the world’s existing portfolio of some 29,000-35,000 TSFs (Tailings Storage Facilities) and those that are planned to receive the world’s mineral production this decade.”
Lindsay Newland Bowker https://worldminetailingsfailures.org/corrego-do-feijao-tailings-failure-1-25-2019/
The CIMNE report is narrowly focused on the “proximate cause” of failure and in no way supercedes, replaces or contradicts the broader more comprehensive failure cause consideration of the prior two reports. It is in these two earlier reports that we are instructed on how and why failure conditions form and grow unnoticed and not fully understood until is too late for “loss prevention” or intervention to de risk as it was at Brumadinho. .
FINITE ELEMENT MODELLING CONFIRMS DRILLING OPERATION AS FAIlURE TRIGGER
The image below illustrates the location of a drilling operation which CIMNE cites as a likely trigger. WMTF’s website banner on the failure does not show this drilling operation but a longer video with higher resolution, possibly from a different camera, does clearly show the drilling operation.
According to the CIMNE report which cites the account of surviving contractors the holes being drilled were the deepest ever penetrating the stack.
LONG STANDING FRAGILITY OF STACK KNOWN
As Roberto Rodriguez’ pioneering work has established, TSF’s with poor hydrulaics, both active and inactive, have recurring saturation events over the life of the facility . The saturation, causing an exteme suceptibility to failure is quick to form and slow to subside but only in some cases does the susceptibility to flow side failure materialize.
All experts charged with cause of failure analysis and many others acknowledge that no trigger ( as trigger is generally understood) was needed to cause the failure at Brumadinho. All, back to even the Pirete thesis acknowledge that there certainly were many peculiarities and variations in the tailings stack and that it had a suceptibility to liquefaction. None question the extreme fragility of the stack not just in the months prior to failure but before the cessation of depositions.
Tractebel was fired (by Washington Pirete) for refusing to certify the TSF as stable. Vale commissioned TUV SUD to verify compliance with new Federal Law. TUV SUD was very clear in its assessment of the extreme fragility of the TSF and in their correct assertion that only undrained conditions was appropriate for stability assessment per limit qulibirum the most widely used sysem for stability assessment prior to the emergence of “Finite Element”on which Plaxis 2d is based.
Pimenta De Avila prior to TUV SUD and Tractebel questioned the required Vale geotechnical procedure which was premised on the Pirete thesis which according to Scott Olson misused his methodology(olson 2001) in concluding that the dam was strong enough to stand aganst a liquefaction flow failure event.
WMTF will note these exceptions to the report in our failure narrative unless anyone reading this in possession of recognized expertise advises that we have erred in our assessment of the CINME.
To briefly review the documentary evidence and background preceding release of CINME report, we offer the following.
Brazilian Law requires that the computation of factor of safety be based on the methodology appropriate to actual conditions. The methodology insisted on by Vale and imposed on all its consulting engineers was, according to the in house Vale review not appropriate. The methodology selected for stability assessment should be specific to the issue at hand and actual conditions, especially drained or undrained.
The dewatering needed to safely allow re-mining was progressing far more slowly than anticipated. There was no known drainage system in the original few raises and the inhouse expert panel reprt noted that an initial error in location of the toe of the dam had blocked a creek which had previously directed groundwater flow further impairing effective hydarulics of the structure. The slower than expected rate of dewatering was noted by both consulting and in-house project members .The record is clear that there was concern that the schedule for the planned re-mining of the tailings would be compromised possibly jeopardizing viability of the remining project.
Vale, TUV SUD and Minas Gerais were counting on 20 more years of jobs in re-mining the tailings which had a never explained extraordinary level of iron. (I am recalling 47%-55%). They couldn’t begin because the dam was not stable enough to withstand the vibration of the heavy construction involved in removal of the deposited contents.
Under Brazilian Law a version of absolute liability applies. It is not a negligence or tort based legal system. There is no defense. That Board members and senior executives chose not to monitor stability does not alter their culpability under Brazilian Law at failure.
Brazilian Law requires that the computation of factor of safety be based on the methodology appropriate to actual conditions. The methodology insisted on by Vale and imposed on all its consulting engineers for statutorily required reports to government was, according to the in house Vale Expert panel review, not appropriate. The methodology selected for stability assessment should be specific to the issue at hand. The Vale in-house report notes that methods appropriate for assessment of a planned raise are not the same as those appropriate for overall stability assessment of the entire structure. Further the methodology for factor of safety must reflect actual conditions, especially whether the stack is in a drained or undrained state. As TUV SUD pointed out in their 2017 reort for Vale the law does not specifically set a factor of safety standard for TSF with a liquefaction susceptibility.
The dewatering was progessing much more slowly than expected perhaps because, as noted in the inhouse Board expert panel report, it was discovered that the toe of the dam was buil which impeded he natural flow thriug of groundwater. The rate of dewatering was noted as way below plans and expectations from the time depositions ceased to failure. The record is clear about concern that the schedule for the planned remining of the tailings would be compromised possibly jeopardizing project viability.
Vale, TUV SUD and Minas Gerais were counting on lots of jobs continuing in re mining the tailings which had a never explained extraordinary level of iron. (I am recalling 47%-55%). They couldn’t begin because the dam was not stable enough to withstand the vibration of the heavy construction involved due to the high water level and state of saturation.
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Under Brazilian Law a version of absolute liability applies. It is not a negligence or tort based legal system. There is no defense. That Board members and senior executives chose not to monitor stability does not alter their culpability under Brazilian Law at failure.
Vale’s Board and Senior Officers deferred completely to its geotechnical staff and neither asked for nor received any reports from the geotechnical team on the warnings of De Avila, Tractebel and Tuv Sud. By the same token, though, I don’t recall that VOGBR, De Avila, or Tractebel wrote to Vale’s Board or senior executives with their concerns.
For all that was wrong with initial vetting of the stack and its management under Vale, Vale was and is “middle of the pack” on how these ultra large older cross valley, side hill upstream tailings dams are managed. Hence my sense of urgency about identifying at risk facilities and placing their assessment under truly expert independent teams as buildings are under the independent authority of buildings inspectors.
Having a separate Prosecutors Office as Brazil has doesn’t quite accomplish the safety corrections that a buildings department does!
lindsaynewlandbowker 