Lionel Buck
18 November 2021

Tailings storage facilities, or tailings dams, are dams built to hold waste from mining operations. As discussed in our previous post, tailings dams are not risk-free. There are major concerns about the safety and legacy of tailings dams following the devastating failure of a tailings dam in Brazil and the recent tailings dam failure in South Africa. It has become crucial to prevent these failings and improve the overall safety of tailings dams. In other words, the focus should be on more sustainable waste management systems.

In this post, we’ll be discussing factors that influence dam integrity, dam failure modes, and the technology that could prevent tailings dam failures.

Factors that influence dam integrity

Site Conditions

Certain site conditions need to be considered to ensure tailings dam integrity. Seismicity, geology, climatology, and hydrology are characteristics critical to the operation of a dam. It is imperative not to underestimate these characteristics and to consider them as part of the tailings process.

Specifically, it is important to keep the following in mind:

• Tailings materials are not natural soils and they may behave differently, which could affect the performance of the dam
• Proper operating procedures need to be in place to maintain water levels
• Drainage systems need to be in place
• Some chemicals in the tailings may react differently to water, air, or the foundation soil and affect the dam.

Quality control

The materials used to construct a tailings dam are crucial to its integrity. In order to ensure that a dam is safe for use, quality control of dam construction and construction materials needs to be in place. The duration of tailings dam construction can be long, which is why it’s essential to properly document the dam history and design. If that history is lost, quality control becomes almost impossible and the risk of failure increases drastically.  

Ongoing dam operating discipline

The following should be in place for tailings dams to remain in a safe condition:

• Effective water level management
• Effective monitoring systems, which includes remote monitoring
• Tailings characteristics and deposition must be in accordance with design specifications
• Consider operating changes, such as ore, context, and climate.

Possible mechanisms for tailings dam failures

Usually, there is no one cause alone that contributes to tailings dam failure. A variety of factors can play a role, which is why it’s important to understand what can cause failures. The following are common reasons for failures:

• Overtopping – when the water volumes exceed the capacity of the dam
• Structural failure – materials used in dam construction fail
• Foundation failure – the foundation of the dam fails due to movement or construction
• Surface erosion – the embankment or settlement cracks
• Internal erosion – also known as a piping erosion
• Design deficiencies – when choices are made that are not in line with the design criteria

Preventing tailings dam failures with technology

By using digital technology, mines can now monitor their tailings and gain access to relevant data that generates actionable insights. Monitor the following data to make informed decisions regarding tailings safety.

Climate

To prevent tailings dam failures, capture temperature, evaporation, and rainfall data regularly. Since climate has a significant effect on the condition and operation of a tailings dam, it is imperative to gather climate data. Tailings dam specialists can then evaluate the data to make decisions and monitor the dam.

Deposition Data

Deposition is the rate at which slurry is deposited into the tailings dam. It is important to track deposition data on a monthly basis to ensure that the rate of deposition is within the design specification.

Slurry Density

Slurry density is the ratio of the weight of water and additives to the volume of slurry. Similarly, the slurry density is continually monitored by onsite personnel to ensure that it stays within the required range. Deviations in the density have a significant effect on the overall load. It is therefore critical that it remains within the design specification.

Piezometers and Drain Flows

Piezometers and drain flow readings give an indication of the movement and level of control over the pore water (pressure) within the dam, and more specifically the embankment. Although measuring the flow from individual drains alone has limited value as a diagnostic tool when paired with piezometer readings, areas of the embankment can be identified in which there are potentially ineffective (or partially ineffective) drainage conditions. Additionally, it takes Piezometric and drain flow readings monthly.

New Generation Technologies to monitor tailings dams

Ground Penetrating Radar

Ground Penetrating Radar is capable of monitoring and detecting movement within an embankment in real-time and triggering an alarm. It works by sending a radar pulse through the ground and measuring the time it takes to rebound, building an internal map of the ground. The method has proven most effective when used on solid structures like cliff faces or concrete retaining walls.

Terrestrial LiDAR

LiDAR uses a laser scanner to measure minute movements in the dam wall, building up a topographical model. This model can be used to compare previous data or can be programmed to scan continuously, triggering an alarm if movement is detected. However, LiDAR is a relatively new technology in the industry and instances of its deployment are few.

LiDAR is best suited to closed sites where the dam structure is final. Due to limitations of data, power and the cost of LiDAR units, utilising it today would require very specific conditions for it to be successful.

Seismic sensors

Seismic sensors can detect activity caused by earthquakes, which could potentially result in a dam failure. They also detect blasting operations and heavy plant movements. Additionally, sensors using accelerometers and magnetometers detect minute movements in the dam walls, which can trigger alarms.

InSAR

InSAR is a high power radar that can produce a digital terrain map of the topography surrounding a dam from a satellite in orbit. This method is highly accurate and can detect sub centimetre movements in the dam walls. Over time it is possible to get an idea of movement trends and to see any potential buckling or swelling.

Total Station Automation

Total station automation surveys are something that many companies do. Usually, this form of monitoring is used in open pits to monitor slopes looking for movement in walls. The system works by having multiple survey points at known locations on a wall or dam and having one, or more, total stations set up in huts or other protected areas survey the points at the fixed interval; every 30 minutes, for example. The system then uploads this data for surveyors to compare to old scans. This system has a similar outcome to LiDAR or InSAR, in that it allows the user to see movement, but offers little in the way of insight into its causes.

Real-time instrument monitoring

Remote, real-time instrument monitoring describes the connection of sensors such as piezometers, weather stations, ultra-sonic height sensors and phreatic board sensors so that they produce data at very close intervals. This approach gives the fullest view of conditions on the dam site and is helpful to understand the conditions at a site over time. Real-time monitoring also uses alarms to indicate a change in conditions. By adding robust connectivity options such as satellites, this approach works at any site in the world, with all the data aggregated on a centralised system for site engineers, control centres, auditors and regulators to use to help improve tailings management.

Digital Technology at Integrove

At Integrove we are currently developing a view that provides data-driven insights to improve maintained protocols to manage safety and risks through digital alerting. Remote monitoring eliminates the need for ground teams to go into inaccessible and dangerous areas.

Furthermore, by aggregating multiple streams of data, from climate data, deposition data, slurry density, and drain flows, our view can help protect lives, the environment and infrastructure. Data-driven insights can also ensure mines meet regulatory compliance and take preventative action rather than reactive.

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