The large block rate of open pit mining is an important indicator to measure the effectiveness of the blasting. In 2011, the 3.8 million t/a open pit of Yuxi Dahongshan Mining Company experienced the problem of excessive blasting. For this reason, the A33~A34 line blasting of the 910-895m platform of the open pit was studied in depth. By collecting relevant mining and blasting parameters, and analyzing according to the actual production, relevant measures are formulated to solve the problem of high block rate.
1 geological overview
The mining blasting dolomite marble rocks, metamorphic sodium lava, tuff, diabase, gabbro green mud, gravel angle, low grade ore is iron ore lava. The joints of mineral rock in this area have a general development degree, f=8~10, which is moderately stable and stable ore with good explosiveness. However, due to the destruction of the civil mining area and the previous blasting in the area,
The cavity is hollow and the cracks are developed, and the step surface layer is 1~2m broken, which is not conducive to perforation and charge blasting, and the blastability is not good.
2 blasting
Blasting range: 910 ~ 895m steps, A33 ~ A34 section line, the actual elevation of the top board is 908 ~ 910m, the actual height of the bottom board is 895m. The number of designed blasting rows is 5 rows, the number of blasting holes is 48, the blasting quantity is 18240m3, the total hole depth is 808.5m, and the total charge is 8206kg.
The measured explosive zone length is 54.5m, width is 23.1m, step height is 14m, the actual amount of blasting is calculated to be 17625.3m3, which is different from the design blasting amount by 638.7m3, the total amount of blasting ore and the total amount of designed blasting. Basically consistent.
2.1 blasting parameter design
There are 5 rows of blastholes in this blasting. The blastholes are arranged in a triangle. The total number of blasting holes is 48, the aperture is 165mm, the single hole depth is 16.5m, the design total hole depth is 808.5m, and the clogging length is 7.4m. The second row is 7.2m. ~ The fifth row is 7.2, 7.6, 5.3m, the total length of the blockage is 320.7m, the length of the charge is about 487.8m, the utilization of the blasthole is about 60.3%, and the total charge of the design is about 8206kg. The unit consumption is 0.45m3. Among them: 1 the first row of 10 holes, the chassis resistance line W=5m, the hole distance a=4.5m, the blasthole density coefficient M=0.9; 2 the second row to the first four holes, the fourth row the first 6 holes The first five holes in the fifth row are b=4m, the hole spacing is a=5.5m, M=1.38; the remaining holes are b=5, the hole spacing is a=6, M=1.2.
According to the relevant formula calculation, the above parameters of the blasthole blocking length, chassis resistance line, row spacing, and hole spacing are reasonable design [1].
2.2 Actual measurement analysis of blasthole construction
After field measurement, the blasting parameters have undergone major changes, and the number of blasting rows is still 5 rows. Due to the influence of recoil crevices and goafs, the number of blastholes varies from 10, 12, 6, 10, respectively. 11 parts, local row spacing and hole spacing have certain deviations from the design, the mesh parameters are smaller than the design, the blastholes are basically triangular; the total number of blasting holes is 49 (including one waste hole), and the 30 holes are hollowed out. The impact of the area, 20 unqualified (hole depth and design in and out more than 2m, including 8 holes at the bottom affected by the old goaf), the number of qualified holes is 7, the blast hole pass rate is 14.5%; the hole diameter 165mm, The average hole depth is 13.8m, and the total construction hole depth is 676.1m, which is 132.4m lower than the design 808.5m. Since the bottom of most of the blasthole holes is a goaf, the depth of the blasthole charge is greatly shortened compared with the design. The installed explosive is 5040kg, and the designed charge is 8068kg. After conversion, the filling hole depth is about 305.5m, and the blasthole utilization rate About 45.2%. The explosive consumption is 0.29kg/m3, which is 0.16kg/m3 lower than the design [2-3].
(1) There are 10 holes in the first row, 4 holes are unqualified, and the design is more than 2m. There are empty areas at the bottom of 7 holes (including 2 holes are unqualified), and the number of qualified holes is 1 The hole pass rate is 10%; the hole depth is 9-17 m, the average hole depth is 14.4 m, which is 2.6 m less than the design 17 m; the chassis resistance line is about 4.7 m, which is 0.3 m less than the design 5 m; the hole pitch average a= 4.8m, 0.3m larger than design 4.5m; blasting hole density coefficient M=1.02, 0.12 larger than design 0.9; 1125kg installed explosive, 465kg less than design 1590kg. The reason is that the pores increase and the medicine is less. The reason is that the length of the blasthole charge is shortened due to the goaf at the bottom of the hole; the row spacing and charge amount are reduced compared with the design, and the explosive unit consumption is reduced.
(2) 12 holes in the second row, 3 holes are added in design, 6 holes are unqualified, and the design is more than 2m, and 6 holes have empty areas at the bottom (including two hole depths are unqualified), qualified holes The number is 2, the blast hole pass rate is 16.7%; the hole depth is 5.5~17m, the average hole depth is 12.2m, which is 4.7m less than the design 16.9m; the row spacing is 4.4m, which is more designed. 4.6m less 0.2m; average pitch of 5.6m, 0.2m less than design 5.8m; blasthole density coefficient M=1.27, larger than design 0.01; installed explosive 945kg, less than design 2123kg less 1178kg .
The reason for the analysis is that it is affected by the goaf and cracks at the bottom of the hole, and the length of the blasthole charge is shortened. Although the row spacing is increased compared with the design, the charge is larger than the design, and the single consumption of the explosive is generally reduced.
(3) The third row of 6 holes, compared with the design to reduce 3 holes, 1 unqualified hole. The hole depth is less than 2m in design hole depth, and there are goafs at the bottom of 5 holes. The number of qualified holes is 0, and the pass rate of the hole is 0. The hole depth is 16~17.3m, the average hole depth is 16.1m, which is 0.7m less than the design 16.8m; the row spacing is 5m, which is more than 4.5m for the design 4.5m; the hole spacing is a=6m, which is more designed. 5.8m more than 0.2m, the blasthole density coefficient M=1.20, which is smaller than the design 1.29 is 0.09. The installed explosives are 840kg, which is 119kg less than the designed 959kg. The reason is that due to the goaf and cracks at the bottom of the hole, the length of the blasthole charge is shortened, and the row spacing is increased compared with the design. However, the charge amount is larger than the design, and the explosive unit consumption is generally reduced.
(4) The 10 rows of the fourth row are in conformity with the design, 4 unqualified holes, the hole depth and design are more than 2m, and there are empty areas at the bottom of 7 holes (including two holes with unqualified holes). The number of qualified holes is One, the blast hole pass rate is 10%. The hole depth is 4.6~18m, the average hole depth is 14.1m, which is 3.6m less than the design 16.7m; the row spacing is 4.5m, which is more than 4.3m and 4.3m; the hole spacing is a=5. 7m, consistent with the design, the blasthole density coefficient M=1.26, which is 0.5 less than the design 1.31. The installed explosives are 1170kg, which is 506kg less than the designed 1676kg. The reason for the analysis is that it is affected by the goaf and cracks at the bottom of the hole, and the length of some blasthole charges is shortened. Although the row spacing is more designed, the charge is more reduced than the design, and the explosive unit consumption is generally reduced.
(5) 11 holes in the fifth row, 5 unqualified holes (more than 2m in hole design), 5 holes at the bottom of the hole (including two holes are unqualified), 3 holes are qualified, and the hole is The pass rate is 27%. The hole depth is 6～17.4m, the average hole depth is 13.5m, which is 3.3m less than the design 16.8m; the average row spacing is 4.55m, which is more than 4.5m than the design 4.5m; the average hole spacing is a=5.75m. Compared with the design of 5.45m and 0.3m, the blasting hole density coefficient is M=1.20, which is smaller than the design 1.27 and 0.07; the installed explosive is 960kg, which is 954kg less than the design of 1914kg. The reason for the analysis is that it is affected by the goaf and cracks at the bottom of the hole, and the length of some blasthole charges is shortened. Although the row spacing is more designed, the charge is larger than the design and the unit consumption of the explosive is generally reduced.
Overall, the blasting, blast hole spacing and hole spacing have basically met the design requirements, but the blasting area perforation and charge blasting are greatly affected by the gap formed by the goaf and blasting recoil damage, most of the medium and deep holes can not be worn. To the design position, the hole can not be arranged according to the design arrangement, the length of the charge can not reach the design length, the pass rate of the blasthole is low, the charge amount and the unit consumption of the explosive are less than the design amount, and the blasting effect is difficult to control.
2.3 Charge and detonation methods
The method of continuous charge and space charge is adopted, the hole depth reaches the design value and is not affected by the empty area, the old roadway and the crack, and the length of the blasthole charge section is spaced; the blasthole receiving area, the old roadway and the crack The effect of the blasthole charge segment is insufficient for continuous charging [4].
2.4 detonation method
The inter-row differential detonation method is adopted, and the connection of the blasthole is shown in Fig. 2.
3 blasting effect
The total amount of blasting ore is about 17625.3m3. The edge of the step before blasting is uneven, the resistance line of the chassis is 3~10m; the height of the step plane is about 3m, mainly due to excessive mining after the last blasting loosening. Due to the irregularity of the front row, the step plane is uneven, and affected by the empty area and the charge, the blasting energy is released unevenly, the blasting effect is poor, the bulk is large, the collapsed boundary is irregular, and the empty area The amount of collapse is large [5].
The steps before the blasting are shown in Figure 3. The effect after blasting is shown in Figure 4.
4 causes of blasting large blocks
(1) Perforation parameters and construction quality. According to the diameter of the blasthole, the height of the step and the nature of the rock, the blasthole is arranged. The blasthole and the row spacing are too large, and the ore rock cannot be fully broken and a large block is produced.
(2) Mineral rock properties. In the area where the fractured geological fractures are developed and there are many mezzanine rocks, the detonation gas leaks from the rock cracks, and the bulk rock is not effectively broken and forms a large block. The yellow brown is often seen in the large pile. The original surface (Fig. 4), rather than the fresh section produced after the blasting of the rock; the hard and soft rock interface is equivalent to the free surface, which unloads the stress wave, and changes the softness and hardness of the rock to cause collision and fracture. The effect is weakened, resulting in more large chunks.
(3) Explosive unit consumption. Unreasonable explosive unit consumption is also one of the reasons for the large block, especially in the case of low consumption of explosives, the bulk rate is significantly improved.
(4) The mutual influence of each process in the production process. During the production process, the perforation, charging, blasting, shovel loading and transportation processes need to be closely coordinated. If the ultra-deep is too much, the shovel is not timely or over-excavated, the top line of the slope and the bottom line of the slope will be irregular, resulting in large blocks. produce.
(5) Empty old lanes and empty areas. The existence of empty roadways and empty areas increases the difficulty of perforation operations, resulting in low quality of blastholes, serious problems of under-depth and ultra-deep problems, resulting in poor blasting effects; uncertainties in the range and shape of goafs and empty areas. It is difficult to determine the amount of explosives, which brings difficulties to design and construction [6].
5 countermeasures
(1) Determine reasonable blasting parameters. Combined with the nature of the ore and the actual situation on site, it is determined that the reasonable hole diameter, hole spacing, row spacing, charge amount, explosive unit consumption, packing method, charging method, and detonation method can effectively reduce the bulk rate.
(2) Strengthen the cooperation of various processes in the production process to create favorable conditions for the next production process. Pre-split blasting is carried out in the last row of holes to protect the integrity of the step slope of the next blasting area; the ultra-deep excess and over-excavation phenomena are strictly controlled, and the next step slope and the top ore are protected from damage.
(3) Try to use the interval filling method in the hole. In the way of continuous charging, the explosive energy is concentrated in the middle and lower part of the step, and the upper part of the step is less affected by the blasting. The interval charge can make the explosive energy evenly act on the rock mass, effectively improve the utilization rate of the explosive and reduce the large block.
(4) Use large hole spacing and small spacing to make holes. Increasing the hole distance can prevent the blasthole from being torn prematurely, prolong the action time of the blasting energy in the rock mass, and increase the crushing effect.
(5) Strengthen the exploration of old lanes and empty areas in goaf. The goaf area and the old mining roadway are the biggest factors affecting the quality of the perforation. It is technically difficult to overcome, but it can provide a reliable basis for the perforation blasting design and operation by finding out the shape and position of the old roadway and empty area. Reduce construction difficulty, improve work efficiency and blasting effect.
references
[1] Lin Deyu. Mine blasting engineering [M]. Beijing: Metallurgy Industry Press, 1993.
[2] Chinese Society of Mechanics Engineering Blasting Professional Committee. Blasting Engineering [M]. Beijing: Metallurgical Industry Press, 1992.
[3] Li Baoxiang. Open mining of metal deposits [M]. Beijing: Metallurgical Industry Press, 1992.
[4] Li Jinghuan. Discussion on the way of ore block optimization for deep hole blasting in open pit mine [J]. Metal Mine, 1992 (4): 15-21.
[5] Yu Feng. Technical measures to reduce blasting large blocks and roots [J]. Mining Express, 2000 (16): 18-21.
[6] Tax Chenghui. Causes and countermeasures for the production of large blocks and roots in open-pit blasting [J]. Mining Express, 2003 (3): 11-13.
Author: Michael Zong Hua, Lang Kai Fu; Dahongshan Yuxi Mining Limited;
Article source: "Modern Mining"; 2016.7;
Copyright: Â
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