At this time we only have fragmentary data from the media. Thus we will focus on “peripheral” but very important concepts that seem to get lost in the aftermath of each new tragedy.
These concepts emerged in the paper entitled A systemic look at tailings dams failure process, presented at Tailings and Mine Waste 2016, Keystone, Colorado, USA, October 2-5, 2016 as follows:
After each failure the mining community sees codes evolve and imposes tougher criteria and dam specifications. Meanwhile FMEA remains the common practice risk assessment methodology. FMEA lacks the finesse needed to predict the progress “toward zero failures” goal stated by experts in the aftermath of recent tragedies.
The effects of today’s risk mitigation programs will only slowly become visible. That is because the world-portfolio will contain mitigated and unmitigated (legacy) dams. During that time the public will perceive at best a status-quo.
It will be very difficult to evaluate progress, as factors such as climate change, seismicity and increase in population will further complicate the situation. Thus public outcry and hostility toward the mining industry, fueled by the diffusion of Information and Communication Technology will likely increase.
Dams’ codes and criteria evolution
It seems there was a risk assessment performed following rules and prescription. We touch on this later on.
However, we have read from the media that a third party inspection occurred and that, like in many other historic tailings dams failures, the dam was not showing trouble behavior in very recent time.
In summary:
How many more failures will we have to endure before we acknowledge that inspections and classic monitoring are not as efficient as commonly believed in preventing failures? We are not suggesting to avoid them, but to consider their now obvious limitations.
Also, codes and criteria evolution, tighter specifications and common practice risk assessments do not solve the problem on existing dams. And that is particularly true if failures have their root causes in “original sins” in design or construction that occurred decades before the failure day.
Slow change of state of the world-wide portfolio of tailings dams
Authorities have reportedly accused the dam owner of “not having learned anything from the prior failure.” As per last night, five arrests occurred. We are not in the position to discuss legal issues or procedures implemented by the owner due to lack of data. However, we have read the owner stating full compliance to laws and prescriptions when assessing the dam.
What if the laws and prescriptions and requirements missed some important points? For example, the spillway of the dam was reportedly a penstock with tunnel under the dam. If the prescriptions and requirements focused on the stability of the dam and forgot to mention other important elements of the dam system, would the regulator be liable of omission? A similar debate engaged in the aftermath of the Oroville debacle. We are of the opinion that excessive prescriptions may hinder safety and risk mitigation by misleading owners and operators into a “box checking” exercise. Risk assessment require thinking to the limits, not trying to box complex reality into 3×3 or 5×5 bins.
Finally, leaving legal aspect aside at this time, no one can expect a drastic change of a large portfolio of dams. That is even if significant measures were taken in 2014/2015. That is because, again, the failure root cause hides in old decisions, when the state of the art was different.
In summary:
As we stated in 2016, the effects of any risk mitigation program will become visible over long time spans. That’s because any portfolio will contain mitigated and unmitigated (legacy) dams.
During that time the public, regulators and legal authorities will perceive at best a status-quo. With obvious nefarious consequences to the owners and operators.
Evaluating progress in dams’ portfolio risk mitigation
Factors such as climate change, seismicity and increase in population will further complicate the situation. And that will occur in any portfolio, likely in any country around the world.
This consideration applies to any dam, from small to major structures. We cannot forget that Stava, one of the more deadly catastrophes reportedly had only a 300,000m3 volume.
As per the larger structures, the industry better investigates, designs, builds and manages/monitors modern ones better than any older ones. Based on our experience, we see their probability of failure decrease towards the range of hydraulic structures of the same caliber.
Of course dam break of larger structures may lead to way larger consequences than breaks of smaller structures. However, the interplay of probability and consequences does not necessarily means the risks are larger (or smaller).
The same reasoning holds with the dam height or the runout distance, with the same conclusions.
In summary:
Mining industry should avoid simplistic statements equating bigger dams to bigger risks.
As structures become larger, their probability of failure should go down towards the values commonly accepted for major hydro-dams. That reduction necessitates acting on all aspects of dam s’ life:
investigation,
design,
construction,
monitoring and finally
inspections and management, as all contribute to the chance of failure.
Population increase, land use shifts, environmental constraints increase consequences of failures and therefore increase risks. This is extremely important to note as tailings dams have a long life span during service and post-service.
Closing remarks
If we are not capable of communicating these points, do not show pertinent actions and care, public outcry and hostility toward the mining industry, fueled by the diffusion of Information and Communication Technology will likely increase. As a result Social License to Operate (SLO) and Corporate Social Responsibility (CSR) will be souvenirs from the past.
• Key issues & reforms for the Dam Sites:
1. Emergency Spillway System Construct somewhere behind the upstream area which must be first priority to meet such kind of happened, easily escaping from high flood situations.
2. The Diversion Tunnels as per design criteria round shape with RCC Complete before the heavy Rains & flood periods to bear the impacts of Static and other relevant forces of underground and Main Structure areas avoiding from Sliding’s, Cracks, Sink Holes & settlement factors.
3. The Project sites need to be add in provision of specific Cofferdams to controlling the water reservoir potential of upstream areas and not going towards the Dam sides, over Toping, especially protecting from the Leakages.
4. The Storage Capability in the Reservoir as per depend upon the Geological Site Condition of Soil and Rock Strata (Earth Works Status of 5 years , Earthquakes, Hydrology, previous disasters in 10 year results) also the Fracture and Weak Zones need to must be address)
5. Reviews must be considering as per Site Conditions in design criteria consulting during the Construction of Project Site execution stage wise pattern accordingly.>???
• Key issues & reforms for the Dam Sites:
1. Emergency Spillway System Construct somewhere behind the upstream area which must be first priority to meet such kind of happened, easily escaping from high flood situations.
2. The Diversion Tunnels as per design criteria round shape with RCC Complete before the heavy Rains & flood periods to bear the impacts of Static and other relevant forces of underground and Main Structure areas avoiding from Sliding’s, Cracks, Sink Holes & settlement factors.
3. The Project sites need to be add in provision of specific Cofferdams to controlling the water reservoir potential of upstream areas and not going towards the Dam sides, over Toping, especially protecting from the Leakages.
4. The Storage Capability in the Reservoir as per depend upon the Geological Site Condition of Soil and Rock Strata (Earth Works Status of 5 years , Earthquakes, Hydrology, previous disasters in 10 year results) also the Fracture and Weak Zones need to must be address)
5. Reviews must be considering as per Site Conditions in design criteria consulting during the Construction of Project Site execution stage wise pattern accordingly.>???