Introduction:
Tailing dams are responsible for collecting tailings from mining operations. Tailing dams are built to conserve water for use in mining and protecting the environment. These structures are often constructed using the tailing. This issue, along with factors such as the relatively long construction period and inadequate design and supervision, has resulted in a high number of tailings dam failures. Tailing dam accidents have occurred frequently in recent years. The current rate of failure of large tailings dams is about 2 to 5 cases a year. In the recent failure tailing dam on 2022, Nov. 7, the tailings escaped through an approx. 150 m wide breach of the eastern wall of the impoundment, which caused the release of 12.8 million m3 of water and tailings (World Information Service on Energy 2022. Tailings Dam Safety. https://www.wise-uranium.org/mdaf.html). Some tailings dams have a water pond near the dam crest and the water and tailings liquefy or not contribute to the tailing dam breach. Other tailings dams have no water pond or the pond is far from dam's crest. Water has no or less contribution to the tailings dam failure and the runout of tailings liquefy or not is significant. (Small et al. (2017)).
Methodology:
This research explores a local failure dam near the tailings dam abutment with a water pond in the large-scale experimental setup that consists of a tailings pond by 505 cm(length), 310 cm (width) and 64 cm (height). The uniformity and curvature coefficient of tailings are 2.21 and 1.44 and the tailings are not liquefaction. The longitudinal slope of bed is 2%. A gate with a width of 20 cm as a local dam breach is applied near the left abutment of the dam. An ultrasonic equipment measured the time series of water surface elevation. The experimental tests were carried out at different water surface elevations and repeated three times to ensure the validity of the results. The bed topography is measured by the Kinect before and after the dam breach. These bed elevations were performed to calculate the volume of the eroded tailings by using Civil3D 2019 software. Moreover, some videos are provided to recognize the flow pattern and bed erosion.
Results and Discussion
In all experiments, after the local failure of the tailing dam, a pit is created inside the tailings dam pond near the breach. At the beginning of the experiment, the scour pit created has no effect on the water surface elevation. After that, the pit effect is recognized on it. Then, there is water at the end of the pond just near the dam body. At the end, there is a small water height inside the pit and a hydraulic jump occurs in the scour hole. The grooves are created on the bed and the eroded sediments do not have any ability to move towards the dam breach downstream.
The bed erosion pattern and sediment transfer rate were surveyed in water level variations of the tailings dam reservoir during a local failure near the abutment.
The largest scour height has occurred near the local failure. Due to the complex nature of the sediment, the topography bed images of the same experiments are different in detail.
Conclusion
Water and sediment are quickly released from the local tailing dam breach and a scour hole forms in the bed near the local failure. In all experiments, the ratio of the volume of eroded sediment near the local failure to the water volume of the dam pond is about one percent. The variation of the water surface elevation with time is about 0.45. It was observed that the length of the scour hole in the dam body direction is more than the direction perpendicular to the dam body. The ratio of the length to the width of the scour hole is 3 to 3.3, approximately.