For keeping an open-pit mine operational while a giant sliding mass exists and is flowing on the benches and minerals like debris, at this time, it is necessary to unload the sliding mass (debris). For achieving this, monitoring of sliding mass should be done along with unloading so that displacement and velocity values do not exceed a certain limit and do not cause a serious incident. One of the suitable software which is able to model this sliding mass and unload it, is PFC (Particle Flow Code) which is based on Discrete Element Method. This paper will describe how PFC was used to model a sliding mass in an open-pit mine and unloading it in seven stages has been done. During the unloading of sliding mass, maximum velocity and displacement among the particles have been obtained. Also, in this article the Angooran mine, which is the largest metal mine in Iran and also one of the most economical lead and zinc mines in the world, has been studied. Sliding mass volume that occurred in the Angooran mine was about 12 ×106 m3, i.e. 25×106tons. The sliding mass moved about 100 m horizontally and 45 m vertically.


Slope stability is one of the most important issues in the construction and mining activities and any mistake in analysis can lead to irreparable damage. Utilizing the subsurface geological model, and results which are obtained from the field investigation and lab testing can help for analyzing slope stability by using suitable modeling methods. Slope movements might be minor and be limited to falling a small boulder or might be huge and catastrophic. In many cases, advancing failure or the slope rupture can be prevented while in other cases, improvement methods cannot be remedial. One of the example of this huge slide is the Angooran mine, one of the most economical lead and zinc open-pit mines in the world. Angooran mine is located in the northwest of Iran and has experienced a large scale slope failure in northern wall. Sliding mass volume that occurred in the Angooran mine was about 12 ×106 m3, i.e. 25×106 tons (Fig. 1). Generally, the slope movements can affect engineering structures and human activities. Slope movements are different in many ways such as hugeness, speed of incidence, and predictability. Heavy or prolonged rainfall, melting snow, earthquakes, blasting in mining can be causes of slope instability. Creep, tensile cracks, and water leakage locations are surficial signs of instability. The Fig. 2 shows a sample of tensile cracks in the Angooran mine.

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