ستار مهدوری

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.

In this research, the optimal parameters have been investigated with the aim of increasing the efficiency and improving the quality of rock cutting using abrasive waterjet (AWJ) through the modeling of high-velocity two-phase flow (water and abrasive). In the current research, the rock cutting process by AWJ has been simulated using the finite element method-smoothed particle hydrodynamics in LS-DYNA software. For this purpose, the effect of parameters of jet velocity, dwell time, changes in volumetric concentration, and changes in diameter of abrasive particles on the cutting depth and cutting volume of Siltstone and Shale rock specimens have been investigated. Numerical modeling results show that with increasing velocity, the amount of rock cutting depth and cutting volume increases. As the dwell time increases, the energy used by the AWJ to cut the rock increases, which will lead to an increase in the depth and volume of the cut. By increasing the volumetric concentration of abrasive particles up to 3%, the depth and volume of the cut increased with a gentle slope, and after that no significant improvement was observed. Also, by increasing the diameter of the abrasive particles up to 1.25 mm for Siltstone and 1 mm for Shale, the depth and volume of the cut increases at first, and after that the depth and volume of the cut remains constant or decreases.

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.

In parts of constructing east-west section of line7 Tehran subway, the excavating machine (EPB-TBM) passes from the top of the Abouzar’s wastewater conveyance tunnel with clear distance of 2.25 m. The FLAC 3D has been used to model this problem and find the deformations and forces of ground and linings. The modeling results showed that after excavating subway tunnel, lining of Abouzar tunnel will move upward due to the increasing plastic zones and stress relaxation. This rate of displacement induced the internal force more than allowable designed amount in concrete lining of Abouzar tunnel. Generally, excavating a tunnel near another tunnel may lead to significant interaction effects, which mainly depends on tunnels position relative to each other (parallel or cross), the distance between two tunnels, tunnel dimensions, lining rigidity, stress and boring environment condition as well as the method of tunnel boring. The interaction between adjacent tunnels have been investigated by different researchers using methods such as analytical and empirical, field observation, physical modeling and numerical modeling. In the current project, the tunnel of Tehran metro line7 passes with a distance of 2.25 meters from the top of the Abouzar tunnel. Because of the three-dimensional nature of the interaction problem between underground spaces, numerical modeling is an appropriate tool for the analysis of these complicated problems. Therefore, FLAC3D software has been used in order to investigate the interaction analysis. The purpose of modeling is to study stability of support system of Abouzar tunnel during tunnel excavation of Tehran metro line7. In this paper, the finite difference method (FDM) is used for modeling and solving the problem. FLAC 3D program which uses FDM was selected in order to study the interaction between the two tunnels, in construction stage. For this purpose, at first Abouzar tunnel modeled and excavated, then impact of stepwise excavating of line7 Tehran subway on lining system of Abouzar tunnel is investigated numerically. History of Internal forces, bending moments and structural displacement of Abouzar’s tunnel lining have been provided and studied. Engineering recommendations have been proposed in different-leveled intersecting tunnels. The results of the modeling showed that after excavation of metro tunnel, the support system of Abouzar tunnel will be uplifted because of increasing plastic zone and stress relaxation. This displacement causes internal forces in Abouzar tunnel lining which are more than allowed values.