Failures of tailings dams are one of the most hazardous processes that may occur and can cause extensive damage to life, property, and health. The mining industry has experienced several significant dam failures in recent history: Merriespruit 1994 (South Africa), Omai 1994 (Guyana), Aznalcollar 1998 (Spain), Baia Mare 2000 (Rumania), Aitik 2000 (Sweden), Bento Rodrigues 2015 (Brazil) and recently in Mexico (2018). Historical records of tailings dam failure are of about 20 events per decade, showing a tendency to shift from developed countries to developing countries.
For decades, tailings dams have been monitored via manual monitoring systems. This typically involves selected spots along the barrage, where boreholes are drilled and periodically visited. Here, manual measurements are taken with a variety of instruments, mostly consisting of water level meters, piezometers, or inclinometers. However, this kind of measurement does not produce sufficient data to consistently measure the performance of the embankment dam if sporadic readings are collected manually. As such, some failures of dams can be attributed both to the combined effect of rapid dike construction and to poor maintenance and monitoring – usually through wired and/or manual means. Below are some reasons why a wireless monitoring system is a key tool for the safety management of the embankments.
1. Improves knowledge of the most critical potential failure mechanisms
It is important to identify the main cause of failings in order to plan better and to implement the correct measures to stop them.
Tailings dam failures can originate from overloads, anomalous behaviour of the material used to build the dam (normally tailings), or from problems with the drainage mechanisms, which result in an increase of pore water pressure, and therefore a loss of resistance.
They can also result from other things, like poor monitoring systems, for instance. With manual or wired in-situ readings, operators do not have sufficient amounts of data to gain a clearer picture of the main factors playing a role in failure mechanisms. This massively increases risks in and around tailings dams, as those supervising the area cannot predictively act in order to stop potential failures. The amount of data and regularity with which it is collected through wireless monitoring solutions provides a solid basis for a correct risk analysis, and for building risk-potential models. This is key for long-term risk-planning and for understanding critical failure mechanisms.
2. Detects situations that are likely to trigger a failure of the dam
Real-time data-gathering means that operators have continuous knowledge of the dam’s status. It also means that they can very quickly build “normative” models of how the dam should be behaving, meaning that any anomalies are flagged up as soon as they occur. This allows operators to detect situations that are likely to trigger a failure of the dam – such as water level exceeding a certain limit, or acceleration of horizontal displacements in depth – and to respond preemptively to these situations.
As such, wireless monitoring systems permit for the implementation of corrective measures as soon as possible, preferably before any kind of incident can take place.
This is key not only to reducing risk and saving human lives but also to a business’ profit margins. Post-incident remedial action and the downtime of the dam cost significantly more than predictive maintenance activities.
3. Serves as a tool for designing the dam’s growth
Accumulated data-sets gathered through wireless monitoring devices are key to the successful future planning of the dam’s growth. Rather than create a growth strategy based on historical memory and previous actions, with a wireless monitoring solution, operators can use solid data to implement models that show the future probable status of the dam and its environs, and allow them to plan more accurately for any possible future changes and incidents within the context of its growth.
As part of an Operational Intelligence solution, wireless monitoring data can also be used to create “digital twins” or parts of the dam, or the whole site, in order to virtually model future actions in a “videogame” version of the environment.
Either way, wireless monitoring means that the risk of future failures and incidents is significantly reduced, through using the most scientific methods possible to calculate future risk potential.
4. Provides a sound basis for the establishment and implementation of the proper response in case of a failure involving human hazards
Equipped with the ability to model future incidents and predictively respond, operators can establish set responses to particular incidents that regularly happen, and set up crisis contingency plans in the case of an emergency.
This is all enabled through the constant relay of precise data about the status of different parts of the tailings dam.
For example, wireless nodes transmitting data from water level meters and inclinometers installed on boreholes enable periodic controls. Piezometric sensors provide information regarding the pore water pressure, and the measurement of the ground displacement in depth is automated by an in-place inclinometer which allows operators to measure the horizontal displacement on depth. Waste management gauges, which measure the water level in the dam or settlement cells to monitor the settlement processes of the walls and surroundings, are also crucial here. Moreover, meteorological stations measure variables such as rainfall and wind speed and are critical in terms of allowing operators to consider and plan for new climatic scenarios – especially in the context of climate change and increasingly erratic weather patterns. Again, this allows for predictive and early-stage responses to any potential anomalies that arise, massively reducing the risk of incidents occurring.
5. Provides long-term monitoring with very little maintenance
A monitoring system that is both long-term and low-maintenance is absolutely critical for tailings dam environments.
Manual maintenance of sensors and data-loggers – and more – is in itself incredibly risky, meaning that maintenance of a monitoring solution must be minimal.
This requires durability so that equipment can survive in sometimes very harsh physical conditions; longevity of battery life, so that equipment does not need to be placed frequently; and long-distance transmittance, so that it can continuously relay data from difficult, hard to reach environments over long periods of time. Depending on the system used, the long-range communication between the gateway and the data loggers in most wireless monitoring systems allows for a distance of up to 9 miles or 15 km between the gateway and the data-loggers in an optimal situation. In the context of a mine, this means that, by placing the gateway in the mine’s central office, almost any point of the mine where a sensor is placed can be reached, meaning that no manual readings ever need to take place. Embedded, long-life batteries make remote data acquisition systems autonomous for up to 10 years, enhancing the maintenance cycles of the monitoring system. This massively reduces risks as equipment rarely fails, meaning continuous, accurate readings for years. In turn, this decreases potential downtime and means that there is no need to manually maintain the monitoring system.
Wireless monitoring is realistically the only way to properly monitor tailings dams to prevent and manage failures. Many mining and damming companies still rely on manual or wired in-situ readings as part of their core instrumentation and monitoring processes. This is problematic as tailings dam failures are incredibly dangerous – indeed they threaten lives – but manual monitoring systems do not give sufficient amounts of data to allow the situation on the ground to be monitored consistently or frequently enough to prevent this kind of incident from happening. Moreover, wired in-situ monitoring systems – using cables, for example – are vulnerable to physical damage over time. It is hard and expensive work to protect the cables, and they require a wired centralized acquisition system that relies on external power supply (solar kit or electricity).
Wireless monitoring systems eliminate all of these problems, providing a real-time, continuous flow of data enabled through reliable, long-distance, low-energy and low-maintenance technologies. The flexibility and longevity of this kind of system fit well with an embankment dam and its raises. Crucially, wireless data acquisition systems can transmit readings from in-ground sensors that measure the cause of any potential anomalies, not only the effect, as is often the case with other instrumentation and monitoring systems. Measuring the cause allows for the implementation of early, preventative actions if any anomalous performance of key variables is detected. Transmitting data from all these different sensors means that all site areas are covered and hazards are therefore reduced. This comprehensive monitoring system is thus indispensable to any tailings dam company, significantly reducing the risk of failure onsite through producing actionable insights that allow operators to make better, evidence-based decisions.
Article courtesy of Worldsensing