1 Project Overview
A vanadium- iron mine in Gansu has two resources, vanadium ore and iron ore. Due to market reasons, the mine currently only mines iron ore and vanadium mines are not mined. The vanadium iron ore is near east-west, and the vanadium ore body is located in the north of the iron ore body. The strike length is 4200m and the surface outcrop is obvious. The vanadium ore body is located on the upper plate of the iron ore body and is nearly parallel layered with the iron ore body. The horizontal distance from the lower plate of the vanadium ore to the upper part of the same middle iron ore is 60-190m. The upper vanadium mine is within the surface movement zone of the lower iron ore mining. Therefore, the feasibility of future mining of vanadium ore should be considered in the mining of the lower iron ore.
The main ore body of iron ore is a continuous and stable layered ore body. The ore body is distributed along the 7#～21# line and its western part, with a length of 3200m. The ore body is nearly east-west, tending to the north, and the inclination is 28°~66°. . The thickness of the ore body is 4.6~29.4m, the part is over 60m, and the average true thickness is 12.35m. The iron ore is currently mined by the segmented empty field method, with a height of 65 m in the middle section, 50 m in the direction of the nugget, 8 m in the column and 7 to 8 m in the top column. The average elevation of the surface is 2400m, and the middle section of 2280m has been mined, and a large number of continuous goafs are formed. The volume of the empty area is 2,879,100 m3; the middle section of 2215m is the main production middle section. Continue mining down, the volume of the goaf will be further increased, and more pillars need to be reserved for maintaining the stability of the stope, which seriously restricts the sustainable recovery of the iron ore body, increases the loss of ore, and cannot be used for future vanadium. Mining conditions provide conditions. To this end, it is necessary to study new mining schemes to improve the ore recovery rate and maintain the stability of the stope.
2 ore mining plan optimization
In view of the temporary non-mining of vanadium mines and the positional relationship between vanadium and iron ore bodies, the mining scheme of “casting iron and vanadium†was proposed. Different mining methods are adopted for the iron ore mine. The 7#~10E# line (eastern area) and the 13#~21# line (western area) are relatively thin, 10~20m, using the segmentation empty field and the paste micro-coal. Filling mining method; 10E#～13# line (middle area) ore body is thicker and larger, 15~30m, and adopts the step-by-step mining method of sub-cavity method.
2.1 Mining plan
The iron ore in the east and west areas is preferentially mined. After the mining is completed, the post-filling is carried out by means of paste micro-coagulation [1-3] to control the ground pressure. Keep a 20m wide security pillar along the direction of the ore body (as shown in Figure 1). This pillar acts as a recovery channel for vanadium ore. After the vanadium mine is recovered, it is decided whether to recycle 20m according to the actual situation. Security pillar.
The Central District is dominated by iron ore mining, and iron ore is preferentially mined. The iron ore mine adopts the method of step-by-step mining. Each mining block adopts the method of mining 30m ore in the 30m mining room. After the mining of the 30m mine, the 30m pillar is used as a channel to strengthen the upper vanadium ore. With the shortest time and the highest efficiency, more vanadium ore is produced as much as possible. After the recovery of the vanadium ore in the upper plate, the remaining 30m pillar of the iron ore is recycled in two steps. The first step is to cut 7.5m on both sides of the pillar, and the second step is to recover the remaining 15m pillar by the caving method. At the same time, the goaf is treated by caving surrounding rock [4].
2.2 Mining sequence
The mining plan of “casting iron and vanadium†requires adjustment of the original iron ore mining sequence. The east and west areas are changed from the top to the bottom, and the middle area is sub-step mining. It is the mining sequence from top to bottom. The mining sequence of the iron ore body from the middle section of 2215 to 2020m is shown in Fig. 2, and the mining effect is shown in Fig. 3.
3 pillar stability analysis
For the mining schemes of different sections of iron ore bodies, the theoretical analysis method is used to calculate the stability of the pillars in the eastern, western and central areas. The east and west blocks are 50m along the strike, of which 42m is the mine and 8m is the pillar; the middle block is 60m along the strike, of which 30m is the mine and 30m is the mine (2 steps). The middle section of the planned mining is three middle sections of 2020, 2085 and 2150m, and the middle section is 65m high.
3.1 Central area pillar stability
After mining in the middle section of the iron ore body pillar in the central area, the pillars with a length of L=15m, a width (the thickness of the ore body) b=15~30m and a height of H=195m are left. This pillar needs to be recovered after the three middle sections of the central area are recovered. Therefore, the stability of the pillar determines the safe production of the stope. The stability of the pillar is mainly determined by the strength of the pillar and the load on the pillar [5].
3.1.1 pillar strength
The strength of the pillar is greatly affected by the aspect ratio of the pillar. The strength of the pillar in this region can be determined by equation (1).
Where: σu———the actual strength of the pillar, MPa; σc———the uniaxial compressive strength of the rock, the compressive strength of the magnetite rock is 185.39 MPa, and the rock mass strength after the reduction is 55.6 MPa.
It can be seen from equation (1) that since the length of the pillar is unchanged at 15 m, the strength of the pillar changes with the width of the pillar, and the variation of the pillar strength and the pillar width is plotted as a curve (see Figure 4). Show).
It can be seen from Fig. 4 that the pillar strength is smaller and smaller as the pillar width (ie, the thickness of the ore body) increases as the pillar length is 15 m. When the pillar width is 15m, the pillar strength reaches a maximum of 70.4MPa; when the pillar width is 30m, the pillar strength is at least 48MPa. At the same time, the strength of the pillar is also affected by the height of the pillar. The higher the pillar height, the smaller the pillar strength.
3.1.2 pillar load
3.1.2.1 Bearing column bearing load area
The area under which the column is subjected to load should be discussed in two cases: one is the vertical alignment of the long axis of the column, and the other is the long axis along the column. Different arrangements, the load area is not the same. In the middle area, the iron ore body is mined, and the long axis of the pillar is arranged vertically. The bearing load area is shown in Fig. 5. The load area that the pillar is subjected to is shown by the broken line in Fig. 5, which can be calculated according to the formula (2).
B———The span of the mine, 45m. The calculated load area S of the pillar is calculated to be 900-1800 m2.
3.1.2.2 pillar load bearing
The supporting stress of the pillar can be calculated according to formula (3).
Where: σp———the compressive stress of the pillar, MPa; Ï—the average density of the overlying strata, 2.9×103 kg/m3; h—the thickness of the overlying strata, 245 m. It was calculated that σp was 26.1 MPa.
3.1.3 Stability calculation
As the cross-sectional dimension of the pillar increases, the strength of the pillar also increases, but at the same time the load on the pillar increases. Therefore, it is difficult to correctly evaluate the stability of the pillar by either of them. In order to better evaluate the stability of the pillar, the actual strength of the pillar is compared with the vertical stress of the pillar, so that the safety factor of the pillar is obtained. The formula is given by formula (4).
Where: k——— the safety factor of the pillar. The length l of the pillar is 15m, and the width b is 15, 20, 25, 30, 35, 40, 45, 50m. The safety factors are shown in Table 1.
It can be seen from Table 1 that when the width of the pillar reaches 50 m, that is, when the span of the mine reaches 50 m, the safety factor of the pillar is k=1.3. The "metal and nonmetal mine safety regulations" requirements, when the safety coefficient k> 1.1, the pillar can basically meet the stability. It can be seen that the mining of the iron ore body in the central area can maintain the stability of the pillar when the column is 15m long and 15~30m wide.
3.2 East and West District pillar stability
The eastern and western districts use the same mining scheme. Each time a middle section is mined, the paste is micro-cemented and then the next middle section is mined. Therefore, the calculation of the stability of the pillar is only calculated according to the height of the middle section. After the iron ore mining, the strips are 8m long from the top to the bottom of the ore body. The width of the ore is 10-20m and the height is 65m.
The calculation method of pillar stability refers to the calculation method of the central zone. The length l of the pillar is 8m, and when the width b of the pillar is 10-20m, it still satisfies l≤b≤0.3H. The strength of the pillar is calculated by formula (1), and the safety factor is calculated by formula (4).
Calculate the length of the pillar l is 8m, and the width b is 10, 12, 14, 16, 18, 20m, respectively. See Table 2 for the safety factors.
It can be seen from Table 2 that when the pillar width reaches 20m, that is, when the mine span reaches 20m, the safety factor of the pillar is at least 1.2, so the 8m pillar can be maintained stable.
4 recovery benefits
Compared with the original plan, the new iron ore mining plan will not retain horizontal pillars in the middle and west sections, and the horizontal pillars and pillars in the central area will be fully recovered, thus greatly increasing the ore recovery rate. The recovery rate of the eastern and western regions increased from 70% to 82%, an increase of 12%; the recovery rate of the central region increased from 70% to 91%, an increase of 21%.
From the overall middle section of the 7#～21# line 2020～2150m, the amount of iron ore in the east and west areas increased by 3.23 million tons, and the amount of iron ore in the middle area increased by 2.32 million tons, which increased the recovery of iron ore. The amount is 5.55 million tons. According to the calculation of 450 yuan / t, the economic benefits of mining iron ore can increase by 2.475 billion yuan.
5 Conclusion
(1) According to the mining status of vanadium ore and iron ore in a vanadium iron ore mine in Gansu, the vanadium mine is temporarily unexplored and is within the surface movement zone of the lower iron ore mining. The volume of the goaf has been formed in the middle section of the iron ore body above 2280 m. Up to 2,879,100 m3, the mining plan for “casting iron and vanadium†was proposed. The iron ore mine adopts different mining schemes in different sections. The east and west districts adopt the segmentation empty field and the paste micro-cement filling mining method, and the 20m pillars are retained along the strike every 200-300m as the vanadium ore mining passage; the central district adopts the segmental empty field. The step-by-step mining method of the method of turning to the caving method, each mining block adopts the method of mining 30m ore in a 30m mining room, and the 30m pillar as a recovery channel of vanadium ore.
(2) Through theoretical analysis of the stability of the pillars of different mining schemes in each sub-area, when the width of the pillar in the central area reaches 50m, that is, when the span of the mine reaches 50m, the safety factor of the pillar is 1.3; the east and west mines When the column width reaches 20m, that is, when the mine span reaches 20m, the safety factor of the pillar is at least 1.2. According to the thickness of the ore body, the thickness of the ore body is 4.6 to 29.4 m, and the pillar can reach the stability requirement.
(3) Compared with the original plan, the iron ore optimized mining plan has increased the recovery rate of the eastern and western regions by 12%; the recovery rate of the central area has increased by 21%, and the estimated economic benefits are 2.475 billion yuan.
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Article source: Mining Technology: 2016, 16 (5);
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