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Dam Failure Vale Brazil Jan 25, 2019
6

Dam Failure Vale Brazil Jan 25, 2019

Dam Failure Vale Brazil Jan 25, 2019

(OP)
Breaking news, 11 dead hundreds missing after a release of a tailings dam.


https://www.mercurynews.com/2019/01/25/brazil-tail...

Slideshow pictures

https://www.reuters.com/article/us-brazil-vale-dis...


Videos of rescue

http://www.mining.com/tragic-deja-vu-vales-dam-bre...



Vale website
http://saladeimprensa.vale.com/en/Paginas/Articles...

Clarifications on the Dam I of the Mine Bean Stream

Vale is investigating the causes to ascertain why this happened
Vale is investigating the causes to ascertain why this happened. The following information is in regard to the structure and management of the project.

Dam I of Bean Creek Mine is used to dispose tailings from ore production and was located in Brumadinho, Minas Gerais. It was inactive (no tailings were being added), there was no pond and there was no other type of operational activity in progress. The decommissioning project was also under development.

The dam was built in 1976 by Ferteco Mineração (acquired by Vale on April 27, 2001), using the upstream method. The height of the dam was 86 meters and had a crest length of 720 meters. The waste disposal area was 249.5 thousand m2 and the volume disposed was 11.7 million cubic meters.

Dam I had 'Stability Condition Statements' issued by TUV SUD of Brazil, an international company specializing in Geotechnics. The 'Stability Condition Statements' were issued on 06/13/18 and 26/09/18, related to the Periodic Safety Review of Dams and Regular Dam Safety Inspection procedures, respectively, as determined by DNPM Decree 70.389 / 2017. The dam had the Safety Factor in accordance with world best practices and above the Brazilian Standard reference point. Both of these stability declarations attest to the physical and hydraulic safety of the dam.

The Dam went through biweekly field inspections, all of which reported to ANM (National Mining Agency) through the SIGBM (Integrated System for Safety Management of Mining Dams). The last inspection registered on the ANM system was executed on 12/21/18. In addition, it underwent inspections on 1/8/19 and 01/22/19, and was registered on Vale's own monitoring system. The registration of each inspection on the ANM, according to legislation, must be executed by the end of the following fortnightly period. All these inspections did not detect any change in the state of the structure.

The dam had 94 piezometers (an instrument for measuring the pressure of a liquid) and 41 Water Level Indicators to monitor its integrity. The information from the instruments was collected periodically and all their data analyzed by the geotechnitians responsible for the dam. Of the 94 piezometers, 46 were automated.

The dam had a PAEBM (Mining Dam Emergency Action Plan), as established by DNPM regulation 70.389 / 2017. The same was filed in Federal, State and Municipal Civil Defenses between June and September of 2018. The PAEBM was constructed based on a hypothetical breach study that defined the flooding area. In addition, the dam had a video monitoring system, siren alert system (all tested) and downstream population registration. The external emergency simulation was also carried out on 06/16/2018, under the coordination of Civil Defenses, with Vale's full support, and internal training with employees on 10/23/18.

In spite of all the points described above, we are still seeking answers to find out exactly what happened.

RE: Dam Failure Vale Brazil Jan 25, 2019

Interesting that this disaster, which is the second such event in the same area within the last three years, which will likely have a death toll in excess of 200, has not warranted a comment here. Lack of interest in foreign parts??? Lack of familiarity with mining???

Falling bridges and such are pretty trivial in comparison , both in terms of lives lost and associated financial costs

RE: Dam Failure Vale Brazil Jan 25, 2019

We never seem to get comments about failures in Brazil. The tailings dam failure before this one got some attention, but that was probably because BHP Billiton was a partner in that mine. Not sure if they are involved in this one. The other one which comes to mind is the overpass collapse just before the Olympics there. Reporting as to the cause seemed nonexistent or censored.

RE: Dam Failure Vale Brazil Jan 25, 2019

As an engineer who doesn't do anything in dam design, I'm not sure what I could even offer as far as comments go other than the general concern over lives lost.

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RE: Dam Failure Vale Brazil Jan 25, 2019

Best guess it was this dam that failed.



Google Maps Link

Perhaps an underwater landslide.

Photo: Link

RE: Dam Failure Vale Brazil Jan 25, 2019

I don't know that being in Brazil makes a difference so much. But lack of technical information on the failure and lack of expertise in anything related to the failure, limit what I can offer. If this was 5 miles from the house, I likely wouldn't have much to add to it.

RE: Dam Failure Vale Brazil Jan 25, 2019

Miningman,

I think was mainly just lack of information, pictures, videos of[img the collapse etc.

Now I'm sure you know more than us, but the key to me is in that description of the dam as a "upstream construction"

I had to go look that up but it seems to be based on using the deposited material in the dam as the basis of the foundation of the next stage. Now if all those sensors and readings and analysis was being done correctly, then this appears to be a sudden catastrophic failure probably starting from the bottom. From the photo above it looks to me like the initial section is the bottom 3-4 layers which have an enhanced V shape and then followed by straighter lines. As this website state, upstream design is the most common design to fail. I've not heard any mention of an alarm or warnings from the dam itself so this seems to be a very sudden collapse.

http://www.tailings.info/disposal/conventional.htm



Basically don't live or work downstream of a dam built using upstream methods. Much easier said than done, especially when it was built 40+ years ago.




Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Dam Failure Vale Brazil Jan 25, 2019

(OP)
Update death toll rises to 58 and hundreds missing.

Looking at the first link photo, I think it was the dam on the right in Epoxybot's image. As others and the press have mentioned this is oddly similar to the Fundoa failure. Looking at the dam this one also has a flat bench offsetting the dam (similar to Fundao) and has two outward bends (looses 3d beam strength). I wonder if they will find similar causes as with the fundao dam failure. The starter dam being built in 1976 it is unlikely they started out with good beaching practices to prevent slimes near the starter dam. Given the overall height is 86 m the structural shell would need to be thicker than a compacted perimeter road.


From the fundoa investigation an animation explaining the causes of failure.
http://fundaoinvestigation.com/demonstrative-anima...

The first stage of site investigation is desktop and it informs the engineer of the anticipated subsurface conditions. By precluding the site investigation the design engineer cannot accept any responsibility for providing a safe and economical design.

RE: Dam Failure Vale Brazil Jan 25, 2019

As someone who works on dams on a regular basis, not enough information to even begin to know what happened here.

When dams fail quickly it is typically due to large rainfall or seismic events. Additional loading has to come from somewhere. The statements in the first post make it sound like the dam was very well monitored and inspected on a very regular basis, much more so than most dams in the US.

As for the comments about "upstream construction"; many, if not most, tailings dams are constructed this way. There have been several problems and failures, but most perform just fine.

Will be interesting to see what the triggering event was for this failure.

Mike Lambert

RE: Dam Failure Vale Brazil Jan 25, 2019

I wouldn't be too critical of the upstream construction method. Altho dam construction is not my primary area of expertise , yes I do have some experience here. The attached article, altho specific to the 2015 failure, does I think give a usefull perspective especially to lay people. The entire process is to a large extent predicated on maximising the rate at which water can drain from the pond, at at the same time, preventing the really fine slime particles reaching the dam itself.

https://www.bbc.com/news/business-37218145


Its very instructive to watch as the deposition location is moved around the perimeter of the dam , allowing substantial sand beaches to build up above the water level. The slime is retained in the middle of the pond . Regular monitoring of the phreatic surface gives a good understanding of general hydraulic conditions.

I wouldn't place too much faith in the self serving references by Vale as to their monitoring practices etc. To consider two actual failures within 3 years , and already identification of a third structure that causes sufficient concern to warrant local evacuation, tells me theres been some very poor practices.

RE: Dam Failure Vale Brazil Jan 25, 2019

(OP)
Before and after shots


The first stage of site investigation is desktop and it informs the engineer of the anticipated subsurface conditions. By precluding the site investigation the design engineer cannot accept any responsibility for providing a safe and economical design.

RE: Dam Failure Vale Brazil Jan 25, 2019

I have no experience with anything dam related being a mechanical engineer. How do these dams handle drying, I had a look at the location on sentinel hub play ground and it appears the failed dam has had periods of drying between heavy rain events. For this area and type of dam I would have thought that would be common (as the dam is designed to dewater the tailings). Other than a sudden influx off water what are sudden failure modes off these types of dams?

Sentinel Hub Playgrond

RE: Dam Failure Vale Brazil Jan 25, 2019

The Mount Polley failure about 7 years ago was determined to be caused by a deep rotational failure in the sub surface geology that had not been identified in the initial site investigation.. Certainly excess water volumes / rain fall would be the most likely cause but any seismic event cal cause liquifaction and resultant increase in hydraulic head. Never heard of drying being an issue, generally too much moisture available. Piping caused by drainage channels being eroded can also be problematic

RE: Dam Failure Vale Brazil Jan 25, 2019

Video of the dam collapse: Link

RE: Dam Failure Vale Brazil Jan 25, 2019

Someone on linked in said that it was due to static liquefaction....not sure how they arrived at that conclusion.

RE: Dam Failure Vale Brazil Jan 25, 2019

Within the context of tailings dams, liquefaction is normally caused by a seismic event of some sort......earthquake, nearby blasting. etc. Certainly the photos todate suggest a massive failure, over period of less than a minute, rather than a progessive such as might be caused by localised failure. And yet , having said that , the Mount Polley failure was not liquefaction , and yet would have been effectively almost instantaneous. Instrumentation , if monitored 24/7. might have provided some warning but human inertia being what it is, the number of fatalities would be essentially unchanged.

RE: Dam Failure Vale Brazil Jan 25, 2019

2
(OP)
Video of failure from multiple vantage points.

https://www.youtube.com/watch?v=SeHEVJWPAao

Edit
The videos are difficult to watch and can cause shock, horror, and nightmares for geotechnical engineers. Other videos available online highlight people on the dam and at the base consumed in the failure.

RE: Dam Failure Vale Brazil Jan 25, 2019

Those videos are horrifying!

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RE: Dam Failure Vale Brazil Jan 25, 2019

Quote (miningman)

Instrumentation , if monitored 24/7. might have provided some warning but human inertia being what it is, the number of fatalities would be essentially unchanged

I don't have experience here other than calculating flow nets in university, but surely the monitoring records will tell a story that could have anticipated failure well in advance. The entire face collapses simultaneously. I don't see how the dam could have been in so precarious a condition without warning signs, short of a large seismic event. Again, I defer to the experts.

Perhaps the automated piezometers were only in the newer/higher levels, with manual readings required in the older/lower levels that were neglected.

RE: Dam Failure Vale Brazil Jan 25, 2019

My heart sank as I saw all the relatively small individuals running, or driving, from the oncoming water and debris.

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RE: Dam Failure Vale Brazil Jan 25, 2019

"The order from Brazil’s mining agency was a preventative measure, Vale said, after engineering company Walm refused to give the mine’s Sul Superior tailings dam a declaration of stability."

It looked a bit like Vale tried to throw TUV SUD under the bus for the Feijao failure (Edit: and there were also the arrests). I'm not surprised the geotechs don't want to sign off now.

RE: Dam Failure Vale Brazil Jan 25, 2019

Bet this was popular with the locals for something that was not an immediate emergency:

Warning sirens sounded and evacuations began at about 1am local time, TV Globo reported. “Attention, attention. This is an emergency … Abandon your homes immediately and follow the escape route,” the announcements said.

----------------------------------------

The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

RE: Dam Failure Vale Brazil Jan 25, 2019

8 staff of Vale (the mining company) arrested. Apparently they knew the dam was at risk.

The report also says that tailing mud is up to 15m deep!!

https://www.bbc.com/news/business-47252043

RE: Dam Failure Vale Brazil Jan 25, 2019

Interesting 1-hr press conference on the Vale link. I'm sure I couldn't keep my composure as well as they did. Aside from that it reads a bit like damage control.

Vale's message seems to be that they did everything they could and that all the proper monitoring and inspections and experts and reports and technologies were in place, and that there were no advance indicators of failure. If that is their position then it begs the question as to how they can simultaneously express confidence in the condition of the other similar dams. I'm not sure it helps their case that they double down on the impeccability of their procedures in the face of an actual failure.

I didn't see any reference to slime encroachment in the press conference but from GeoEnvGuys link regarding Fundao it seems like a possible mechanism, and one that someone would have known about well in advance, notwithstanding any monitoring reports. I think they do refer to a possible seismic event in the press conference but I didn't read/watch the whole thing closely.

RE: Dam Failure Vale Brazil Jan 25, 2019

Interesting that the dam looked like nothing more than a huge pile of dirt with plants growing on it and poof! it all goes in liquid motion.

Seems to me that if that whole thing is half water half solids, in sort of an uneasy truce, that eventually you can have a wetter area migrating to the lower areas which tend to be the face of the damn. If there's a bunch of water there 'somewhere' but you can't actually see it anywhere you will have a very hard time knowing where it is. Clearly, going there and drilling or using seismic mapping are out of the question so you end up blind to what exactly is going on.

From my ignorant position I predict the face reached a prestaged liquefaction state ready for the slightest trigger which the passing train provided that day.

Keith Cress
kcress - http://www.flaminsystems.com

RE: Dam Failure Vale Brazil Jan 25, 2019

2
(OP)
I managed to read through some of the liquefaction assessment completed for the site. From what I gather it was done by graduate students using data from a consultant in 2006, made into a masters thesis in 2010 and published in 2013.

They used the methods primarily proposed by Olson in 2001 and 2003. They used SPT and CPT data to determine which layers would be liquefiable. They also correlated a shear strength ratio with the data.

They then did 2d limit equilibrium analysis and reduced the shear strength of the liquefiable layers until they got a factor of safety of 1. They compared the shear strengths from the correlation to the stability results and got a factor of safety between 1.1 and 1.3.

My thoughts on this start with graduate students doing work, I hope actual engineers also did the job and Vale wasn't relying dam safety to students. Looking at the shear strengths determined they are on the upper end of what I would expect as peak or yield shear strength of loose tailings. Those shear strengths also represent the steady state condition so a factor of safety of 1.1 to 1.3 is low, if they would have used liquefied shear strengths, even the correlation by Olson in 2003 the factor of safety would be less than 1 which would be the post earthquake condition which anything above 1 is good. Also if you read Olson's work he provides a plus minus on his shear strength correlation. If you use the minus the factor of safety by the authors may be closer to 1.


Looking at the geometry in the stability analysis it's odd that dilative (strong) tailings are in the middle area which is traditionally slimes as it's full of uncompacted tailings settling in the pond. The failure surface is rounded where it should be a sliding block along the weak liquefiable layer.

Thinking about the state of the art in liquefaction most of the new methods were published between 2008 and 2014 by the Berkley university group. Newer research would only increase the amount of material inferred to be liquefiable. Provide new correlations for liquefied shear strength ratios in the 0.05 to 0.10 and peak or yield shear strength ratios between 0.2 and 0.25, which is close to what the authors determined.

Now that we have some hindsight, the failure geometry from the video shows a large failure surface from the top beach area starting upstream of the compacted perimeter area to a lower bench. This was not shown in the authors stability analysis. Instead the failure surfaces shown started on the middle of the slope through an inferred perimeter dam and out along the bottom of the slope in an offset bench area.

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