0 Preface

Lee F - Wu set iron ore rock drilling phase piecewise room mining method, the stage height of 100m, the height of the segment of 25m, a typical large stope underground structure [1]. In the staged rock drilling stage, the bottom mining structure of the ore mining method leaves a large amount of ore. According to incomplete statistics, the part of the ore body accounts for 8% to 10% of the total ore of the large structure. If not, the part of the ore body is not Mining will cause huge ore waste [2-4].
       According to the status quo of the mine, some of the stope has been filled, some of the stope has not been filled, and the presence or absence of the stop has a greater impact on the recovery of the bottom structure. When the stope is not filled, the bottom structure will be recovered under the goaf. The space in the goaf is high, and it is difficult for personnel equipment to enter the empty field, and the safety of mining is poor. After the stope is filled, the bottom structure is affected by the stability of the filling body. Since the bottom structure is mostly triangular, the upper filling body is in contact with the inclined surfaces on both sides of the bottom pillar, and the pressure on both sides of the bottom structure is large, and the blasting is filled. The damage of the body is large, and once the filling body collapses, it will cause a huge safety accident. Therefore, the bottom structure mining has always been a production problem of major mines [5]. Based on the actual situation of the mine and the experience of domestic mine recovery, this study proposes to use the bottomless column caving method and the room column method to recover the bottom structure.
       1 mining technical conditions
       Lee F - Wu set of roof rock ore mainly schist, gneiss, amphibolite, marble, cracks are not developed, the addition of chlorite and carbonate minerals is filled, good integrity, but by Li Yi cracked along the film and its stability was poor. The rock of the ore body is mainly dolomite marble, and the fractures and karst are not developed, and the rock integrity and stability are good. The structure of the deposit is relatively simple, and the engineering geological conditions of the deposit are moderately complex.
       Mine and rock Platts hardness coefficient: ore f = 12 ~ 16; rock (general) f = 6 ~ 7. The looseness coefficient of mine and rock is 1.5. The deposit is a concealed fissure-filled deposit. The ore body is located below the local erosion reference surface and the groundwater level, and the topography is not conducive to natural excretion. The hydrogeological conditions of the deposit are generally simple—medium [6-7].
       The segmental empty field and the post-filling method are arranged in the vertical ore body direction of the stope. The length is the thickness of the ore body, the width of the stope is 20m, the interval is recovered, and the pillars of the mine are arranged at intervals. The stope is divided into -400m, -375m, -350m, -325m4 levels, and the bottom structure is arranged at -400m level. The mining house adopts the Simba1354 hydraulic drilling rig to cut the vertical upward fan-shaped hole, the blast hole spacing is 1.7m, the hole bottom distance is 2.6~3m, the -375m, -350m, -325m3 horizontal hole The angle is 40°, and the side hole angle of the -400 m level is 55°. The cutting groove is pulled in the middle of the cutting lane, and the cutting groove is used as a free surface to blast one by one. The caving ore is transported by the scraper to the chute from the bottom structure of -400m.
       The bottom mined structure is 55° at the edge of the mine, and the bottom structure of a standard stop (100m×20m) accounts for about 9%. The average thickness of the thick ore is 60m, the bottom of a standard stop. The structure is about 38,000 tons of ore [8].
       2 mining plan
       Aiming at the technical conditions of Lilou-Wuji iron ore mining, the mining plan of the remote-controlled scraper without bottom column collapse method and the bottom structure plan of the shallow-hole room-column mining method are proposed, and the bottomless uncompleted caving method is adopted for the bottom of the unfilled stope. The shallow hole retaining method is used to recover the bottom of the filled stop.
       2.1 bottomless column caving method
       The use of the bottomless column caving method has high efficiency, good safety, low cost and mature technology. The ore approach is used for rock drilling, and the empty area is used as the free surface for blasting. The mining is led to the direction of the mining and crossing, and the remote control scraper is used for the mining. As shown in Figure 1, the mining road is used as a rock drilling roadway, and the mining roadway is a mining roadway.

        Rock drilling: In the mining road, the Simba1354 hydraulic rock drilling rig is equipped with Φ76mm drill bit to drill the fan-shaped blasthole, the row spacing is 1.7m, the hole bottom distance is 2.5~2.7m, the blast hole A distance of 1.5 m is left between the bottom and the top of the bottom structure, and the blastholes between the front and rear rows are staggered.
        In order to recover more ore, it is difficult to drill small angle holes and horizontal holes in the Simba 1354 hydraulic rock drilling rig. Therefore, the ore body rock in the lower part of the bottom structure is drilled with a small angle hole and a horizontal hole by a YG-40 rock drill .
Blasting: The BQF-100 type chargeer is used to charge the blasting device into the bottom of the hole, and the hole is blocked by the gun mud and the cork. The non-electrical differential detonator is used for differential blasting, and the stepping distance is 5.1m, that is, 3 rows per blasting. From the mining roadway to the mining and crossing the roadway, the backward blasting is resumed.
        Ventilation: Fresh air flows through the middle section along the vein transportation lane into the bottom structure. When ventilation is difficult, the local fan can be arranged to enhance the ventilation of the stope.

Mining in the stope: After the ore collapsed, it was shoveled to the mining area by a remote-controlled scraper, and then pulled from the motor car to the main chute at a level of -425m.

Roof management: Before entering the stope operation, you need to knock on the top and confirm the safety before you can work.
After the recovery is completed, the filling operation can be performed. Before filling, fill the retaining wall with concrete masonry at the stable part of the surrounding rock at the bottom of the mine, and install water filtering facilities on the partition wall. The bottom of the stope is filled with a 1:4 ratio of lime to sand. The middle of the stope is filled with a ratio of 1:8 to 1:10; the top of the stop is filled with a 1:4 ratio of lime to sand.
         2.2 room column method mining plan
         The bottom structure of the filled stop is recovered by shallow hole column method.
        The shallow hole room column method is simple in process, mature in technology, small in blasting scale, and has the use of protective filling body. The rock drilling and blasting is carried out by using the mining and crossing roadway. The mining project is not added, and the cutting trough is transported back to the vein along the vein. The mining cross-section is the free surface and the stratified mining is carried out from the bottom to the top. Ensure that the ore heap leaves 2~2.5m of working space from the roof of the stope, and the scraper is used for mining.
         As shown in Figure 2, the vertical ore body of the mine is oriented. The size of the mine is 8m wide, 10m long and 14m high. The vertical ore body is arranged at a spacing of 10m and a point column is arranged. The specification of the point column is 3m×3m.

         Rock drilling: In the mining and cross-section, the 7565-type gas-leg rock drill is equipped with Φ38mm drill bit for rock drilling, the row spacing is 0.5m, the hole bottom distance is 1.0-1.2m, and the blastholes are arranged in parallel.
         Blasting: 2# rock explosives are manually loaded, and the bottom of the non-electrical differential detonator is used to detonate. From the bottom of the mine crossing, the blasting is carried out from the bottom up.
         Ventilation: Fresh air flows through the middle section along the vein transportation lane to enter the mining cross-section to wash the working surface. When the ventilation is difficult, the local fan can be arranged to enhance the ventilation of the stope.
         Mining in the stope: After the ore collapses, a small amount of ore is released in the early stage, leaving the ore as the working platform for the next rock blasting. After the collapse of the mining site, the scraper is used to concentrate the ore, and the scraper is transported to the mining area. Then, at the -425m level, the motor car is pulled to the main chute.
         Roof management: Before entering the stope operation, it is necessary to carry out the top of the knockout and confirm the safety before the operation; when the exposed area of ​​the roof of the stope is too large, the anchor roof should be used according to the situation to protect the safety of personnel and equipment. Filling: The filling operation is basically the same as the bottomless column collapse method.
        3 program comparison
        According to the technical conditions of the bottom structure mining of Lilou-Wuji Iron Mine and the status quo of the project, the technical analysis of the remote-controlled scraper mining without bottom pillar caving mining method and shallow hole housing-column mining method is carried out. The advantages and disadvantages of the two schemes are shown in the table. The technical and economic indicators of 1, 2 schemes are shown in Table 2. Due to the special location of the bottom structure, the loss rate of the ore body back to the ore is relatively large. The bottomless column caving method has a large production capacity. Because of the relatively large depletion of medium-deep hole blasting, the rock drilling efficiency is relatively high. The shovel is used for mining, the mining capacity is relatively small, and the remote control is scraped. There is a visual blind zone when the machine is out of mine, and the relative ore loss rate is high. The shallow hole housing column method has a relatively small production capacity, but the mining capacity is large; due to the use of shallow holes, the depletion rate is low.

         4 Conclusion
         (1) According to the mining problem of the bottom structure of large structure stope, according to the filling situation of the stope, the mining plan of the bottomless column caving method and the shallow hole room column mining plan are proposed respectively.
         (2) The main processes of the bottomless structure of the bottomless column caving method and the shallow hole room column method are described in detail. The two schemes have advantages and disadvantages for the bottom structure of the mining, and the technical and economic indicators have their own advantages and disadvantages.
         (3) The bottom structure mining is a common problem in the mining industry. The safe and efficient mining method has always been pursued by the mine. This study provides two feasible solutions for this type of ore body mining, which can provide reference for similar mine ore mining. .
         (4) It is recommended to conduct on-site tests in the next step, accumulate empirical data, and promote the application in the whole mine.
         references:
         [1] Ren Haike, Gong Shangchao, Zhu Guotao. Discussion on the mining of the bottom pillar of the large stope in the high-stage post-filling mining [J]. Modern Mining, 2014, 30 (7): 50-53.
         [2] Chen Qingkun. Application of mining method in section rock drilling stage in Mengku iron ore [J]. Mining Technology, 2014(4): 002.
         [3] Hong Zengyou. Practice of blasting process of mining room in staged rock drilling stage [J]. Mining Research and Development, 2000, 20(5): 45-47.
         [4] Ren Congpo, Wang Juyong. Improvement of mining method of mining method in section rock drilling stage [J]. Mining Technology, 2009, 9(6): 88-89.
         [5] Li Meifu, Wang Xu. Recycling of the bottom structure of the mining method in the staged rock drilling stage [J]. Mining Technology, 2014 (4): 006.
         [6] Zhang Lixin. Discussion on mining method and filling process of Lilou Iron Mine [J]. Mining Research and Development, 2012(1): 002.
         [7] Zhu Guotao, Hao Hongxing, Wang Xiaofei. Research on safe mining of thick ore body in Lilou Iron Mine [J]. Modern Mining, 2013 (11): 1-4.
         [8] Lin Weixing, Zhan Jin, et al. Large-scale stope mining industry test and its key technology research [R]. Changsha: Changsha Mining Research Institute Co., Ltd., 2014.