Contributing Factors to Fatalities in Mining: Key Insights from Five Case Studies on Slope Stability Monitoring

This white paper summarises the original paper titled: Lesson Learned from Five Case Studies and Reveal Contributing Factors to Fatalities in Mining Industries Insights from Slope Stability Monitoring

AUTHORS

Winda Putri Anggraeni*
Dwi Prio Utomo*
Rahardian Dwitya*
Rachmat Hamid Musa*

*GroundProbe Geotechnical Support Services, Balikpapan, Indonesia
Contact: winda.anggraeni@groundprobe.com

ABSTRACT

Slope failures pose significant risks in mining, potentially leading to catastrophic events that endanger both personnel and assets. Effective slope stability monitoring is critical for mitigating these risks. This study examines factors contributing to fatal slope failures through case studies from multiple mines across different regions. While advanced monitoring systems identified unstable areas, incidents still occurred due to vulnerabilities such as improper implementation of Trigger Action Response Plans (TARP), unqualified personnel analysing data, insufficient monitoring coverage, inadequate system knowledge, and failure to detect warning signs. These findings highlight the need for improvements in slope monitoring practices. The research provides insights and corrective actions to enhance monitoring effectiveness and strengthen mining safety.

INTRODUCTION

Slope stability in open-pit mining is essential for both economic and safety reasons, requiring well-designed, cost-effective excavated slopes to maintain stability. Over the past few decades, extensive research has advanced the understanding of slope failures, categorising contributing factors into internal and external influences. Internal factors include rock composition, geotechnical properties, and environmental conditions such as rainfall and weathering, while external factors are primarily related to human activity (Sha, 2016).

Despite significant advancements in monitoring technology, fatal slope failures continue to occur, exposing gaps in existing systems and protocols. While monitoring systems provide critical data, effective slope stability management also requires skilled human intervention. The combination of advanced technology and well-trained personnel is essential for improving risk mitigation strategies and ensuring safer mining operations. Addressing both technological and organisational challenges is crucial to enhancing overall mine safety and reducing the likelihood of future slope failures.

1.1. Risk of Slope Failure

Managing slope stability is critical in mining, as slope failures pose severe risks to both safety and productivity, leading to injuries, equipment damage, and operational disruptions. Numerous case studies and statistical analyses highlight the significant impact of slope failures on mining safety. A study found that over a ten-year period, slope failures accounted for approximately 30% of all mining-related fatalities (International Council on Mining and Metals [ICMM], 2016).

A major slope failure at the Grasberg Mine in Indonesia forced operations to halt (Down to Earth [DTE], 2021). In October 2003, a catastrophic failure on the southern wall killed eight people and injured five, displacing 2.3 million tons of rock and mud. A similar incident in 2000, triggered by heavy rainfall, caused a rock mass to slip into Lake Wanagon, West Papua (Graham, 2003).

In India, surface mine slope failures have led to substantial losses of life and property, with 23 catastrophic failures between 1901 and 2016 resulting in 143 fatalities. The Rajmahal disaster, a more recent event, tragically claimed 23 lives (Dash, 2019). These incidents underscore the significant and ongoing risks associated with slope instability in mining operations.

1.2 Importance of Slope Monitoring

Slope monitoring is crucial for risk management in mining and civil engineering projects. It plays a key role in identifying and mitigating potential instability that can lead to slope failures, rockfalls, or collapses, endangering lives and causing economic losses. The primary goal is to detect early signs of instability, enabling timely actions like evacuation, reinforcement, or redesign to prevent catastrophic events.

Slope failures have historically led to fatalities and significant financial losses, especially in mining, where workers are often near unstable slopes. Slope monitoring allows engineers to track slope deformation and movement, providing data that can predict potential failures. This is vital as slope failures can occur without visible signs (Turner & Schuster, 1996). Monitoring systems, including radar-based, optical, and sensor-driven technologies, provide critical data to assess changes in slope behaviour and ground conditions, helping to identify instability patterns. Methods used in slope monitoring range from visual inspections to advanced techniques like LiDAR, GPS, Slope Stability Radar (SSR), and fibre optic sensing, offering high-precision, real-time data.

1.3 Slope Movement Behaviour

Understanding typical deformation patterns is crucial when monitoring rock mass or construction deformation. These patterns help in early warning analysis, enabling the anticipation of potential failures. Depending on geological conditions, stress levels, and external factors, structures often show signs of movement before failure. A common pattern in rock mass behaviour includes stable, regressive, linear, and progressive movements, which may ultimately lead to failure (Dwitya et al, 2024). Failure occurs when the resisting force becomes smaller than the driving force.

Figure 1. Typical deformation patterns illustrate stable, regressive, linear, and progressive (Dwitya et al., 2024).

1.4 Massive Slope Failures in the Mining Industry

Slope failures are a common challenge in mining, with even minor incidents leading to significant losses. One of the most notable failures in history occurred at the Bingham Canyon Mine on April 10, 2013, near Salt Lake City, Utah. This event involved the movement of approximately 66.2 million cubic yards (144.4 million tons) of material, which slid more than 2,000 feet and travelled over 1.5 miles. The failure occurred in two phases, roughly 90 minutes apart, with each lasting about 90 seconds (Ross, 2017).

Remarkably, no injuries or fatalities were reported. Proactive measures taken by mine personnel—including continuous monitoring, the relocation of buildings and equipment, and the construction of a backup road—helped mitigate the impact. The company’s swift response and well-executed safety protocols allowed the event to be managed as a crisis rather than a disaster, ensuring a smooth return to operations. This incident highlights the critical role of leadership, strategic planning, and teamwork in effectively managing geotechnical hazards in mining.

MATERIALS AND METHOD

Geotechnical slope monitoring is essential in the mining industry, with each site employing its own instruments and strategies. Geotechnical engineers increasingly use advanced technologies to detect slope instability early in open-pit mines, managing risks more effectively. Despite identifying geotechnical risks, the possibility of multiple fatalities due to slope failures remains high.

This study examines lessons learned from five case studies across Asia, Africa, and North America (2016-2024), where slope failures were identified early but still resulted in fatalities. Data was gathered from incident reports, news, discussions with on-site engineers, monitoring data, geotechnical articles, and other sources. By analysing these events, the study aims to prevent recurrence and enhance mining safety.

Case Study 1: A coal mine in Asia, 2022

In 2022, a slope failure at a coal mine in Asia resulted in two fatalities and injuries to two others. The collapse also caused significant equipment losses, including one drilling unit and two excavators. The failure occurred within a high-risk fault zone previously identified by the on-site geotechnical team. Continuous monitoring with an SSR system detected slope movement in the area.

Engineers observed a long-term linear deformation trend, indicating constant slope movement. Heavy rainfall the day before the failure further exacerbated the instability. Radar data showed progressive deformation five hours before the incident. At 4:00 a.m., the night shift engineer reported these findings via a mobile app. Although no operations were underway due to rain, a drilling machine remained parked nearby. The day shift engineer relayed the warning during the morning toolbox meeting. However, four heavy equipment operators missed the meeting and were unaware of the potential risks.

Lacking critical information about the hazard, these operators were in the danger zone when the slope failed. No barricades had been installed to restrict access to the unstable area. At approximately 6:00 a.m., as the operators arrived on-site, the slope collapsed, sweeping away two operators and a drilling machine. Nearby excavators were also impacted, though their operators managed to escape with serious injuries.

Figure 2. Illustration of the slope failure at the top of the pit swept away and buried two operators, along with property damage. A coal mine in Asia, 2022.

Figure 3. Graph of the slope behaviour. A coal mine in Asia, 2022.

Case Study 2: A coal mine in Asia, 2020

In 2020, a slope failure at a coal mine in Asia resulted in one fatality and three injuries. The victim was buried beneath mud embankment material and heavy equipment. The embankment had been designed to prevent mud from reaching the coal loading area.

SSR monitoring detected slope movements on the low wall side, prompting engineers to track the data continuously for early warnings. Two days before the failure, progressive movement was identified in the embankment, but it was not flagged as high risk, as it did not meet the 10-pixel threshold for action. However, the monitoring team reported the findings to the on-site engineers.

The following day, the movement became linear before transitioning to regressive. On the day of the failure, progressive movement was detected again an hour before the incident. Per Trigger Action Response Plan (TARP) procedures, the night shift monitoring engineer alerted the site team via phone calls, app groups, and emails. Despite the warnings, no evacuation was carried out, and operations continued.

At 4:21 a.m., the slope collapsed, burying the operator inside a PC 400 cabin. Three other operators were away from the site at the time. A two-month search and recovery effort, led by the Emergency Rescue Team (ERT) and supported by advanced technologies such as Ground Penetrating Radar (GPR) and metal detectors, ultimately confirmed the tragic loss of the operator.

Figure 4. Illustration of the failure of the slope embankment caused mud flooding in the work area, burying the operator and the excavators. A coal mine in Asia, 2020.

Figure 5. Graph of the slope behaviour of the embankment. A coal mine in Asia, 2020.

Case Study 3: A cobalt and copper mine in Africa, 2016

In 2016, a geotechnical failure at a cobalt and copper mine in Africa resulted in seven fatalities. Three bodies were recovered two days later, while the remaining four workers were presumed dead. The incident also caused significant infrastructure damage within the pit.

The slope failure affected approximately 20 benches, with a total height of around 200 metres. The mine was equipped with multiple ground-based radars monitoring the pit, and radar data indicated a gradual deformation sequence in the three weeks leading up to the failure. A linear deformation trend was observed, with a steady average velocity of approximately 7 mm/day, which escalated to 400 mm/day in the three days preceding the collapse.

Despite this, the monitoring team’s report failed to highlight the significant and progressive deformation trend in the failure zone. Although notable movement was detected, no early warning was issued. The geotechnical team identified an increasing velocity of slope movement the day before the failure; however, the operations team did not evacuate all workers in time.

At approximately 6:00 a.m., a massive failure occurred, claiming the lives of seven workers. Despite the presence of advanced monitoring technology and geotechnical oversight, the lack of timely intervention led to a tragic outcome.

Figure 6. Illustration of the slope failure that resulted in multiple fatalities and property damage. A cobalt and copper mine in Africa, 2016.

Figure 7. Graph of the slope behaviour. A cobalt and copper mine in Africa, 2016.

Case Study 4: A copper mine in Asia, 2020

In 2020, a catastrophic slope failure struck a copper mine in Asia following a tropical storm. The incident resulted in four confirmed fatalities, while six workers remained missing, as reported during a meeting between the mining company and government officials the following day. Initial investigations revealed that no mining activity was taking place in the affected area at the time.

The failure occurred at approximately 4:15 p.m. when debris from the slope collapsed into the pit, located at 41 metres above sea level. The displaced material generated a powerful wave, resembling a tsunami, which surged to an elevation of 105 metres, reaching the southern section of the pit where workers were present.

Remarkable video footage captured the event, showing the slope slowly creeping downward for approximately two minutes before the wave reached the workers’ location 50 seconds later. Several workers were seen desperately running to escape. The wave was triggered by the collapsing material pushing water at the pit bottom, which then surged toward the work area.

Discussions with the engineering team later revealed that the potential for such a large-scale failure had been identified prior to the incident.

Figure 8. Illustration of the slope failure that occurred in the pit, with the failure material debris falling into the water at the base of the pit, causing a tsunami-like wave to reach the working area. A copper mine in Asia, 2020.

Case Study 5: A gold mine in North America, 2024

In 2024, a slope failure at a gold mine in North America injured mining personnel and significantly damaged heavy equipment. The mine had been using an SSR system to monitor slope movements in areas with high operational activity, and the SSR was strategically positioned to monitor the failure area effectively.

Radar data analysis required a connection between the radar and the geotechnical team’s computer, which was set up via a Wi-Fi network extending from the pit to the geotechnical office through a repeater. However, approximately 14 days before the failure, the geotechnical team relocated the repeater to the pit area, and a request was made to reinstall the repeater for continuous data transmission. Due to a communication failure, the repeater was not reinstalled, which left the radar data disconnected from the geotechnical team’s computer.

During the 14-day period without data transmission, the geotechnical team did not regularly check data availability, leading to the radar data being unreceived at the geotechnical office. In the critical zone under surveillance, an excavator was working alongside a dump truck. A slope failure on a 15-meter-high slope to the left of the truck resulted in debris hitting the operator’s cabin. Despite the radar’s data being available on the radar itself, it had not been transmitted to the geotechnical team’s computer.

After the failure, technicians repaired the communication network, restoring the data flow. Post-incident analysis revealed a clear sequence of movements detected by the SSR: a linear movement starting two days before the failure, followed by progressive movement for six hours prior to the slope failure at 6 a.m. on May 6, 2024. The radar data provided a distinct record of the slope’s behaviour leading up to the event.

Figure 9. Illustration of the slope failure that hit the dump truck, injuring the operator. A gold mine in North America, 2024.

Figure 10. Graph of the slope behaviour. Gold Mine in North America, 2024.

RESULTS AND DISCUSSION

3.1 Improper and Unimplemented TARP

The implementation of an effective Trigger Action and Response Plan (TARP) is essential for the safety of workers in the event of slope instability or failure. However, the success of a TARP is dependent on clear communication, a shared understanding of the risks, and the roles and responsibilities of personnel. When an alarm is triggered or movement is detected, the response should be swift and well-defined. Without input from the responsible persons and proper assignment of roles, TARPs risk being ineffective. Clear and straightforward communication is vital, and monitoring systems should be integrated with the TARP to provide real-time alerts. In the 2020 slope failure incident at a coal mine in Asia, the failure to properly implement TARP resulted in fatalities as the responsible person failed to inform workers of the hazard and ensure the exclusion area was clear. The lack of communication left the fleet and operators at risk, leading to tragic consequences.

Figure 11. Improper TARP Implementation.

3.2 Incompetent Engineer

Effective slope monitoring relies heavily on the competence of geotechnical engineers who must interpret slope movement data to assess whether stability is improving or deteriorating. Engineers must manage the exposure of personnel and equipment to risks associated with slope instability. In the 2016 Cobalt & Copper Mine incident in Africa (Case Study 3), the failure of engineers to accurately interpret slope movement led to fatalities. This highlights the critical role of competent geotechnical engineers in identifying and managing geotechnical hazards, particularly understanding typical slope behaviour before failure, to ensure operational safety.

3.3 Inadequate Communication Systems and Protocols

In complex mining operations, effective communication systems are essential to ensure that information regarding slope stability is relayed to all relevant personnel. Communication protocols should be well-established and reliable, especially during emergencies. The 2022 incident in Asia (Case Study 1) illustrates the risks posed by communication breakdowns. Operators were not informed of the slope risk, as they were not included in the communication line. This lack of communication contributed to fatalities during a slope failure when critical safety information failed to reach the operators in time. Thus, ensuring that all personnel understand and receive relevant safety information through reliable communication channels is crucial.

3.4 Ignoring Ground Controls

Ground control measures, such as barricade lines, safety cones, and stand-off signs, are essential for restricting access to hazardous areas and ensuring personnel remain safe from slope failure risks. Proper use of these controls can prevent incidents, as shown by the 2022 coal mine incident in Asia (Case Study 1). Despite early warning signs of progressive slope movement, the lack of an exclusion zone around the high-risk area led to the deaths of two workers and the injury of others. A failure to implement proper ground control measures left workers exposed to the risk, underlining the need for robust safety procedures.

3.5 Lack of Emergency/Evacuation Drills

As Case Study 1 and 2 illustrates, evacuation drills are a vital component of any mine’s emergency preparedness. These drills enable personnel to familiarise themselves with evacuation procedures, equipment, and safe routes. The lack of sufficient emergency drills can delay response times during an actual emergency. When an elevated TARP status requires evacuation, a coordinated and practised response is essential. Regular evacuation drills involving all relevant departments help identify weaknesses in the emergency response plan and ensure that actions can be taken quickly and effectively in the event of an emergency.

3.6 Inadequate Geotechnical Risk Assessment

Geotechnical risk assessment is fundamental to identifying potential slope hazards and determining their severity. Engineers must understand the physical characteristics and potential mechanisms of slope failure to evaluate the risks involved. In the case of the 2020 slope failure at the copper mine in Asia (Case Study 4), engineers identified the potential for a massive failure but failed to assess the full impact of the hazard, particularly regarding the creation of a tsunami-like wave caused by the debris in the pit. This failure to fully assess the risk, including the potential effects on nearby areas, contributed to the severity of the incident. Comprehensive risk assessments must consider all potential hazards, both on-site and off-site, to mitigate risks effectively.

3.7 Network Connection Issue

The health and performance of the monitoring system, including data transmission, are crucial for the timely detection and response to slope movement. Case study 5, the case of the 2024 slope failure at a North American gold mine, highlights the importance of a reliable communication network. Due to a 14-day disconnection in the Wi-Fi network, radar data was not transmitted to the geotechnical team’s office, preventing them from analysing the signs of instability leading up to the failure. This communication breakdown delayed the response, resulting in injuries and equipment damage. Regular monitoring of system health and promptly resolving technical issues is essential to ensuring data is available for decision-making and mitigating risks.

CONCLUSION

This study highlights several critical factors contributing to fatal slope failures in mining operations, even when advanced monitoring systems detect early signs of slope instability. Failures in the execution of TARP, combined with issues such as incompetent personnel, poor communication between responsible parties, inadequate ground controls, insufficient emergency drills, and a lack of comprehensive risk assessment, can all lead to devastating fatalities within the mining industry.

Although geotechnical engineers were able to detect early indicators of slope instability, these vulnerabilities continued to expose mining operations to significant risks, ultimately culminating in tragic outcomes. Addressing these systemic weaknesses is essential to reducing the likelihood of future fatalities.

To improve safety, mining operations must prioritize the effective implementation of TARP, enhance engineering training, strengthen communication protocols, and ensure that robust emergency response plans are in place. By addressing these critical areas, the risk of fatal slope failures can be significantly mitigated.

This study provides actionable insights for the mining industry, underscoring the importance of a holistic approach—one that integrates technology, human factors, and procedural improvements. Such an approach is vital for safeguarding lives and assets in high-risk mining environments.

REFERENCES

Dash, A. K. (2019). Analysis of accidents due to slope failure in Indian opencast coal mines. Current Science, 117(2), 304–308. https://doi.org/10.18520/cs/v117/i2/304-308

Down to Earth (DTE). (2021, July 19). Protests over fatal collapse at Freeport-Rio Tinto West Papua mine. Down to Earth. Available at https://www.downtoearth-indonesia.org/story/protests-over-fatal-collapse-freeportrio-tinto-west-papua-mine

Dwitya, R., Hendrianto Pratomo, A., Agung Cahyadi, T., Rianto Budi Nugroho, A., Prio Utomo, D., & Sulo, C. (2024). Slope stability monitoring of hydroelectric dam and upstream watershed areas utilizing satellite interferometric synthetic aperture radar (InSAR). IOP Conference Series: Earth and Environmental Science, 1339(1), 012037. https://doi.org/10.1088/1755-1315/1339/1/012037

Graham, R. (2003, July 25). Slippage causes deaths at Grasberg. The Northern Miner. Available at https://www.northernminer.com/news/slippage-causes-deaths-at-grasberg/1000143698

International Council on Mining and Metals (ICMM). (2016). The role of risk management in improving mining safety: A global review. ICMM.

Ross, B. (2017). Rise to the occasion: Lessons from the Bingham Canyon Manefay Slide. Society for Mining, Metallurgy, and Exploration.

Sha, L. (2016). Analysis of slope instability factors and protection. International Journal of Multidisciplinary Research and Development, 3, 181–182.

Turner, A. K., & Schuster, R. L. (1996). Landslides: Investigation and mitigation (Special Report 247). Transportation Research Board, The National Academies Press.

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