فن آوری استخراج ناحیه ای و تجزیه و تحلیل های شبیه سازی عددی در معدن زغال سنگ روباز

In order to enhance coal recovery ratio of open pit coal mines, a new extraction method called zonal mining system for residual coal around the end-walls is presented. The mining system can improve economic benefits by exploiting haulage and ventilation roadways from the exposed position of coal seams by utilizing the existing transportation systems. Moreover, the main mining parameters have also been discussed. The outcome shows that the load on coal seam roof is about 0.307 MPa and the drop step of the coal seam roof about 20.3 m when the thickness of cover and average volume weight are about 120 m and 0.023 MN/m3 respectively. With the increase of mining height and width, the coal recovery ratio can be improved. However, when recovery ratio is more than 0.85, the average stress on the coal pillar will increase tempestuously, so the recovery ratio should also be controlled to make the coal seam roof safe. Based on the numerical simulation results, it is concluded that the ratio of coal pillar width to height should be more than 1.0 to make sure the coal pillars are steady, and there are only minor displacements on the end-walls.

Because of slope angle, mining boundary, changes of coal seam thickness, and so on, a large number of coal will be left under the end-walls in the open pit coal mines [1], [2] and [3]. In traditional mining systems, the coal under the end-walls will be buried by the inner dumping site. The coal resources are normally discarded and wasted in vain. So how to recycle the residual coal under the end-walls with safe and efficient methods is a valuable and challenging research. To recover coal remnants around the end-walls, underground mining system is normally adopted by excavating some adits into end-walls [4], [5] and [6]. Due to long wall underground mining system, the fully caving method is used to manage the coal roof, and it will cause a greater ground subsidence [7] and [8]. Hence, zonal mining is usually adopted in some regions where only minor ground placement is permissible [9] and [10]. In zonal mining system, the coal field is divided into some regular strips, one strip is mined and the next strip is reserved. The reserved strips can support the load of the overburdened strata, as a result only minor and uniform movements happen on the ground [11], [12], [13], [14] and [15]. Thus, some unrecoverable reserves can be extracted on the premise of the controllable ground subsidence. Practice has proved that zonal mining is an effective method to control the overlying strata and ground subsidence, and is usually used for extracting coal seams under buildings and railway lines [16], [17], [18], [19], [20] and [21]. According to the past investigations about zonal mining technology, we try to recover the residual coal under end-walls of open pit mines. Thus, the key issue of this research is to ensure the extraction system and mining parameters.

5. Conclusions Based on the results mentioned in the discussion, the following conclusions were obtained: (1) The extraction of residual coal from the end-walls with zonal mining technology, a method which can utilize existing mining technology and transportation systems for open pit mines, the cost of transportation can be reduced. Moreover, since the coal around end-walls is exposed and there is no extra stripping engineering quantity, then the economic benefit of the open pit mine may be improved. (2) The main mining parameters of residual coal extraction system have already been presented in this paper. By analytical calculation, the load on coal seam roof is about 0.307 MPa and the drop step of the coal seam roof is about 20 m when the thickness of cover and average volume weight are about 120 m and 0.023 MN/m3 respectively. (3) With the increase of mining height and width, the coal recovery ratio can be improved. However, when recovery ratio is more than 0.85, the average stress on the coal pillar will increase tempestuously, so the recovery ratio should also be controlled to make the coal seam roof safe. (4) From the numerical simulation results, it is concluded that the ratio of the coal pillar width to height should be more than 1.0 to make sure the coal pillars are steady, and there are only minor displacements on the end-walls.