The pressure of the mining site is the general pressure of the pressure exerted by the original rock on the roof, the pillar and the surrounding rock and the pressure of the surrounding rock acting on the bracket due to displacement or landslide [1], which is a complex problem faced by the underground mining of the deposit. In order to ensure the continuous and safe recovery of underground mines, effective measures must be taken to reduce or avoid ground pressure hazards, or actively use ground pressure for mining [2-4]. Iron ore launched the original design using sub stope mining method, but when the first mining project in the middle of Preparatory construction, found the stability of the ore body and host rock and geological data near some differences, resulting in excavation roadway destroyed repeatedly, even With the combination of spray anchor net support or steel frame support, the deformation and damage of surrounding rock is still going on, especially the roof is most obvious. Without effective treatment, the mining roadway will not be able to be constructed, and the danger of permanent loss of a large amount of resources [5] . The main factor affecting the stability of the mining roadway is the ground pressure, and the stability of the ore rock is not good, so the mine should not be mined by the open field method. To this end, it was decided to take appropriate pressure relief measures and replace the original mining method with a sub-column sublevel caving method along the vein layout for pressure relief mining. The premise of the application of this method is to understand the variation law of rock mass stress field caused by underground mining, and adjust the structure of the stope according to this, and arrange the construction process reasonably, so as to achieve the purpose of pressure relief mining. Shangma Iron Mine is a sloping medium-thick ore body, and it is difficult to carry out pressure relief mining for this type of ore body [6]. In this study, the 2D-σ program is used to analyze the variation of the rock mass stress field under different excavation modes of the mine and the rock mass under the stope structure, which provides a reference for the mine safety and continuous mining.
1 numerical simulation analysis
1.1 Model construction and rock mechanics parameters
The numerical simulation analysis of the ore body has a dip angle of 48° and a horizontal thickness of 8 m. According to the need, the model size is 5 times of the excavation range [7], the model has: 1 model 1, two paths along the vein, see Figure 1 (a); 2 model 2, a path along the vein, Excavation to the ore body boundary, see Figure 1 (b); 3 Model 3, an approach along the vein, appropriate excavation of the upper disc rock, the excavation height is the same as the model 2, the span is larger than the model 2, see Figure 1 ( c); 4 Model 4, arrange an approach along the vein, properly excavate the upper disc rock, span the same model 3, excavation space, 5 m higher than model 3, see Figure 1 (d). The mechanical parameters of the Shangma iron ore rock mass are shown in Table 1.
1.2 Numerical simulation results
1.2.1 Arranging two ways along the vein
In the case of two paths along the vein, the stress distribution analysis of the lower section before and after mining shows that after the mining, a stress reduction zone appears below the excavation space, and the area is roughly the vertical projection of the upper section of the goaf in the lower section. In the range, the maximum stress reduction is located at the center of the projection, the lower segment 1 is approximately near the projection center, the access 2 is not in the projection area, the vertical stress at the access 1 is reduced by 36%, and the approach 2 is excavated. The vertical and vertical vertical stresses did not change substantially. It can be seen that after the picking structure of the two paths along the vein is recovered in the upper section, one of the approaches in the lower section of the empty section can achieve pressure relief, and the other approach cannot achieve pressure relief. In addition, the amount of mining engineering for arranging two approaches along the vein is larger than that for arranging along the vein. It can be seen that the ore body condition of Shangma Iron Mine is not suitable for the two approaches along the vein for recovery.
1.2.2 Arranging an approach along the vein
1.2.2.1 Excavation height is the same span
The variation of vertical stress at different levels below the excavation space is shown in Table 2 and Figure 2. It can be seen from Table 2 and Figure 2 that no matter whether or not the ore body rock is excavated, a certain range of vertical stress reduction area appears below the excavation space. The horizontal range of the area is about the vertical of the excavated space below it. In the projection area, the stress is reduced to the greatest extent at the center of the projection range. In the stress reduction zone, the closer to the floor of the empty zone, the greater the degree of stress reduction; the farther away from the floor of the empty zone, the degree of stress reduction becomes smaller, and finally approaches the original stress. However, in the same position of the stress reduction zone below the empty zone, the degree of stress reduction of the two excavation methods is different, and the vertical stress corresponding to the method of excavating the upper rock is more reduced. It can be seen that the span of the empty zone affects the degree of vertical stress reduction in the stress reduction zone below the excavation space. At the same position, the degree of vertical stress decreases with the increase of the excavation span.
1.2.2.2 The same height of the excavation space is the same
See Table 3 and Figure 3 for the horizontal stress reduction at the 5, 10, 15, 20, 25, 30 m level below the excavation space after the constant height of the span is increased. It can be seen from Table 3 and Figure 3 that no matter whether the height of the excavation space changes or not, a certain range of vertical stress reduction areas appear below the excavation space. In this area, the closer to the floor of the empty area, the greater the degree of stress reduction The farther away from the floor of the empty area, the degree of stress reduction gradually becomes smaller, and finally gradually approaches the original stress. However, in the same position of the stress reduction zone below the empty zone, there is a difference in the degree of stress reduction between the two excavation methods, and the hourly stress reduction of the empty zone height is greater. It can be seen that the height of the empty zone affects the degree of vertical stress reduction in the stress reduction zone below the excavation space. At the same position, the degree of horizontal stress decreases with the increase of the excavation height.
2 Factors affecting pressure relief mining and determination of route location
2.1 Factors affecting pressure relief mining
(1) Pressure relief angle. The angle between the upper section of the upper section of the upper section and the horizontal line of the lower section adjacent to the side of the ore body is the pressure relief angle. The pressure relief angle is not a fixed value, and is related to factors such as the level of the horizontal level of the recovery and the location of the approach. From the perspective of the entire stope layout, the reasonable range of pressure relief angle ranges from 2° to 90°.
(2) Edge hole angle. The hole angle of the upper disc becomes larger. Under the premise that the length of the blasthole is constant, the height of the empty area will become larger, the span of the empty area will be reduced, and the pressure relief effect will be reduced; if the length of the blasthole is constant, the decrease will be made. The hole angle on the upper plate will increase the span of the empty zone, and the height of the empty zone will become smaller, which is beneficial to improve the pressure relief effect. However, the hole angle on the upper plate should not be smaller than the upper plate.
Release the corner, otherwise it will cause ore loss.
(3) Section height. Under normal circumstances, the height of the section is mainly determined by the rock drilling capacity of the rock drill and the occurrence condition of the ore body. The section height of the medium-deep hole blasting is preferably 10~12m. After the upper section is mined, the closer to the bottom of the empty area, the greater the vertical stress reduction rate, the better the pressure relief effect; when the section height increases and other conditions remain unchanged, the height of the empty area will increase. The pressure relief effect below the large and empty areas will be reduced. The analysis shows that under the premise of not considering the amount of engineering, it is more conducive to pressure relief when the height of the section is within a certain range, which is more conducive to reducing ore depletion.
2.2 Route location determination
The projection area of ​​the excavation space is in the stress reduction zone in the lower section, and the arrangement of the approach in this area will remove part of the pressure, enhance the stability of the approach, and facilitate the safe recovery. Determining the location of the route requires a comprehensive consideration of pressure relief and economic benefits. According to the model 3, several inspection points are arranged in the lower section of the mining section (pressure relief section), wherein the 1# and 7# points are located at the left and right boundaries of the section of the mining section of the mining section, 2 The #, 3#, 4#, 5#, and 6# points are located at the 3, 5, 7, 8.5, and 10 m lower plates of the ore body (Fig. 4). It can be seen from the vertical stress variation of each point (Fig. 5) that the vertical stress reduction rate at the point 4# is the largest, 21.18%, which is located at the center of the upper segmental excavation space in the vertical projection range of the lower segment. If the route is arranged at other points except the 3# point, the optimal requirements of technical and economic indicators such as pressure relief and depletion rate cannot be met at the same time; if the approach is placed at point 3#, the stress is at this time. The reduction rate is 20%, which is close to the maximum value. Not only the pressure relief effect is good, but also the amount of rock excavation is relatively small. At this time, the hole angles of the upper and lower plates are 55° and 70°, respectively, and the ore can be smoothly released. It can be seen that the 3# point is optimal, and the approach can be arranged 5m away from the lower part of the ore body.
3 Safety measures for pressure relief mining
(1) Optimize the construction process. Measures such as the arrangement of the encrypted blastholes, the reduction of the charge, and the differential blasting of the sections are carried out to minimize the disturbance of the surrounding to the disturbance.
(2) Strengthen support. The joint support of spray anchor net is adopted, and some sections are supported by U-shaped steel frame, and the second reinforcement is carried out according to the situation.
(3) Rapid construction. Use multiple rigs to work at the same time. After blasting, use high-power pressure-mixing fan to quickly ventilate, use high-efficiency mechanical equipment to quickly mine, and send personnel to carry out continuous operation for 24 hours.
(4) Strengthen technology, safety, and organization construction management to ensure safety and ensure rapid and safe construction as planned. After the implementation of the above measures, the first mining section was completed after the loss of a small part of the ore, and the second section was also mined. After comparison, it was found that the second section of the road was arranged 5m away from the lower part of the ore body, the roadway The degree of stability has been significantly improved. Only U-shaped steel frame supports have been used in part. Most of them use only single or combined support of spray anchor nets to ensure the safety and stability of the mining roadway. The stress concentration at the lower section of the road after pressure relief is significantly reduced, indicating that pressure relief mining is a practical technical measure.
4 Conclusion
(1) The layout of the approach determines whether the pressure relief mining can be achieved. The numerical analysis shows that under the conditions of the Shangma iron ore body, after optimizing the structural parameters, an approach can be arranged along the vein to achieve pressure relief mining.
(2) Different excavation methods determine the different stress transfer laws in the unloading zone below the empty zone. The excavation method of increasing the span of the empty zone and reducing the height of the empty zone can produce a larger stress reduction zone below the empty zone. Conducive to the implementation of pressure relief mining.
(3) Under the conditions of the Shangma iron ore mine, when the approach is arranged 5m away from the lower part of the ore body, the loss depletion rate is low, and the vertical stress at the adjacent lower section approach is reduced by 20%. Help to ensure safe production.
references
[1] Liu Jianpo, Chen Bin, Yang Yujiang. Stress migration law of inclined medium and thick ore body under pressure relief mining [J]. Journal of Northeastern University: Natural Science Edition, 2010, 31(9): 1349-1352.
[2] Zhou Wei. Using ground pressure energy mining [J]. Jiangxi non-ferrous metals, 1994 (2): 1-5.
[3] Zhou Zonghong, Ren Fengyu, Wang Wenzhao, et al. Study on efficient mining scheme of inclined and broken ore body in Heshan Iron Mine [J]. China Mining, 2006, 15 (3): 47-50.
[4] Zhou Zonghong, Ren Fengyu, Yuan Guoqiang, et al. Application of induced caving technology in empty area processing [J]. Metal Mine, 2005 (12): 73-74.
[5] He Rongxing, Ren Fengyu. Research and application of pressure relief mining in Beibeihe Iron Mine [J]. Metal Mine, 2012 (2): 9-11.
[6] Wang Wenjie. Analysis of applicable conditions for pressure relief mining of medium-thick ore body caving method [J]. Metal Mine, 2011 (6): 9-12.
Article source: Modern Mining, 2011.5
Author: Ma Qibiao; Yantai Gold Mine Engineering Vocational College Copyright:
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