s. mahdevari

In longwall mining, after extracting each slice from the coal seam and advancing the face, a severe stress concentration is formed in the vicinity of the roof and coalface due to the stress disturbance and also the caving of the immediate roof, which resulted in roof displacement, cracks propagation, and roof failure. Due to the caving of the immediate roof and the displacement of the overburden layers by face advancement, there is a possibility of propagating the fractures and instability of the roof in the coalface. The roof failure in a longwall face will bring adverse consequences such as the stoppage of mining operations, damage to equipment, injuries, and fatalities. In this research, the critical events that are effective on the roof failure in the E3 panel at the Tabas coal mine were identified, and the risk of roof failure was evaluated using the fuzzy event tree analysis approach through filling out the questionnaire by the mining experts and faculties. In this way, ten scenarios were examined to analyze the risk of roof failure by checking the roof failure or non-failure, and then the probability of critical events was calculated. Based on the results, the probabilities of roof failure in the fourth, tenth, and seventh scenarios are respectively 5.68, 4.21, and 1.70 percent, and the risk values in these three scenarios are respectively 28.42, 21.05, and 8.51. Therefore, the most critical scenario in this research is the fourth one, in which the preventive measures should be taken through the timely control of critical events to reduce or prevent the risk of roof failure.

The first step for carrying out mining operations in surface mines is to build a network of communication routes to access different parts of the mine, and also transport ore and waste. For the successful design of ramps in open pit mines, it is necessary to evaluate and analyze the related safety risk based on the geological conditions, geomechanical characteristics, type of machinery, and the mine design. In this research, the ramp safety risk was investigated to determine the accident-prone zones.  In this regard, the information obtained from the exploration boreholes of the Chadormalu iron ore mine was used for modeling. At first, the economic block model of the mine and the ramp were modeled in different scenarios. After selecting the optimal ramp, the total length of the ramp was zoned at 100-meter distances to assess the safety risk in 42 zones, and to identify accident-prone zones by calculating the total risk index. Thus, by drawing a bow-tie diagram, the five initial events including wall instability, car crash, stone throwing, slippery, and accident were identified as the main events leading to incidents; then the probability and consequences severity of each initial event were determined. According to the results, the car crash and wall instability events have the most negative impact on the ramp safety. Also, the highest and the lowest values of the total risk index were 110 (in zones 37 and 42) and 5 (in zones 4, 5, and 9), respectively.