Application of hole bottom spacer charging technology in Heshangqiao Iron Mine

Heshangqiao iron ore mining company affiliated with Maanshan Iron & Steel Nanshan Group, located in Maanshan Jia Shan 5km southwest of the town, to the territory of the town, the total annual stripping 15 million t, as a depression open pit mine. At present, it has been mined to a level of -60m. The ore body is mainly magnetite. The Platts coefficient of the ore is 10-15, and the fissure is relatively developed. The surrounding rock is mainly diorite porphyrite with a Platts coefficient of 8-10, and the fissure is relatively developed. The shallow ore body and surrounding rock of the mine are relatively broken, while the deep ore body and surrounding rock are hard and the joint fissures are relatively developed. Both the deposit and the surrounding rock contain water, and the water-rich water is small-medium. The local fissure is rich in water, which often causes more water in the blasthole, especially in the rainy season. The underground water-rich area is not only difficult to perforate, but also has a great influence on construction organization, blasting quality and blasting cost. To this end, this study explored the mine blasting method.
1 Influence of blast hole water on blasting effect
(1) The rock powder in the blasthole is easy to form mud when it meets water, and it is prone to blockage of the blasthole. The blasthole is soaked in the accumulated water for a long time, which causes the rock to be loosely broken, easy to collapse, and the porosity is low, and the medicine roll is easily stuck in the blasthole.
(2) The density of water is equivalent to the density of emulsion explosives. Due to the buoyancy of water, it is difficult for the emulsion explosive to sink to the bottom, resulting in insufficient explosive force of the bottom explosive, poor fracture, and rooting.
(3) Under the immersion of water, the slag on the wall of the hole loosely falls or loose, and the falling of the slag is likely to cause blockage of the blasthole, and the pore diameter of the blasthole becomes small or deformed, causing the explosive roll to be stuck, in gravity and upper part. Under the impact of the falling of the medicine roll, a part of the medicine roll can slowly slide over the mud layer, and there is a water column with no explosive between the explosive at the bottom of the blasthole and the upper medicine column. If the interval length exceeds the explosive, the explosive itself is in the water medium. The distance will cause the bottom drug roll to be detonated, or the explosive force will be insufficient due to the reduced density of the wire charge [1].
In this regard, the usual measures are as follows: (1) increase the perforation depth of the blasthole in the water-rich area, check the blasthole hole by hole before charging to prevent the phenomenon of collapse, and find that special conditions should be treated in time; 2 for shallow water with less water The blasthole can take measures such as artificial drainage before blasting, high-pressure air duct blowing, manual use of small iron drums, submersible pump pumping, etc.; 3, the problem that the medicine roll is not easy to sink, and the medicine roll is easily caught in the blasthole, Open the plastic bag of explosives, cut the emulsified explosive with larger viscosity into the hole, and try to make the explosive sink into the bottom of the hole to ensure the continuous column. After the explosive is installed, the upper part is tamped with the bamboo raft. This kind of measures has large investment, complicated on-site operation, and has little effect on the blastholes with deeper groundwater system development or cracks in the pore walls, which cannot fundamentally eliminate the negative impact of water on the blasting effect.
2 hole bottom interval charge mechanism
In order to eliminate the influence of water on the blasting quality, and make full use of the positive effect of the water medium in the blasthole in the blasting, when the water content in the blasthole is shallow, the hole bottom spacing charging technique can be used. An air spacer is placed above the water surface at the bottom of the blasthole, and a drug pack is placed above the spacer so that there is a water column between the medicine package and the bottom of the hole, that is, the water content in the bottom of the hole is not charged, so that the explosive is separated from the water (Fig. 1).

Water has the characteristic of uniformly transmitting pressure in all directions. Under normal pressure, water cannot be compressed, but under high pressure, water can be compressed and form shock waves in water. At the same time, since the wave impedance of the water medium is much larger than that of air, the strain strength decays slowly, the impact on the rock and the loading process are relatively gentle, and the loading time is prolonged [2]. Based on the characteristics of water, it is determined that the water column and the charging wall are also subjected to dynamic loads in the initial stage of the explosion of the drug package. When the explosive gas expands and works, the energy accumulated in the water is accompanied by release, which enhances the crushing effect on the rock. Due to the prolonged time of the stress wave acting on the rock mass, the explosive impulse transmitted to the rock mass is increased, which expands the fracture range of the rock. In the deep hole step blasting of open pit mine, the overcoming of the chassis resistance line mainly depends on the shearing effect caused by the expansion of the explosive product. Because the water interval at the bottom of the hole prolongs the expansion of the explosive gas product, it is more advantageous to overcome the continuous charge. foundation. The bottom water interval makes the charging position relatively higher, so that the explosion energy of the explosive in the hole is more evenly distributed along the axial direction, which can reduce the generation of the large block rate. Tests have shown that the optimal hole bottom water separation height to ensure the rational utilization of the deep hole charge explosion energy is 1.2 ~ 1.8m [3].
According to the shock wave theory, after the upper and lower explosives of the water column in the blasthole detonate, the detonation wave front reaches the surface of the upper and lower water column, and is subjected to strong impact compression. It continues to propagate along the water column in the axial direction of the blasthole, and also compresses the rock wall around the radial direction of the water column. Due to the small compression deformation of the rock at the wall of the hole, a reflected shock wave is formed [4]. If the incident wavefront pressures are P1 and P2, respectively, the relationship between the two can be expressed as:

In the formula, P1 is the incident shock wave front pressure, Pa; P2 is the reflected shock wave front pressure, Pa; n is a constant, 3-8. It can be seen from the above formula that the intensity of the shock wave excited in the water column is 5-8 times of the intensity of the original incident explosive detonation shock wave, so the aqueous medium plays an "equivalent" drug column.
3 field test
Four holes bottom interval charge blasting tests were carried out on the -12m platform of the Heshangqiao Iron Mine. The blastholes in the test area generally have water below 2m. The down hole drilling machine is used to wear vertical holes, the hole diameter is 200mm, the hole distance is 8.5m, the row spacing is 5.5m, and the hole depth is determined according to the elevation at the position of the piercing, which is 14-15m. The strip type rock emulsified drug pack is manually charged, and the BJK type air spacer is selected at the bottom. According to the water content of the blasthole, the bottom is 1.5 to 2 m apart. Explosive parameters are shown in Table 1.

The blasting uses a non-electrical squib detonator to detonate, and the inside of the hole and the outer blasting of the hole are combined. Due to the complex environment around the explosion area, considering the safety of buildings such as residential buildings, the design uses Orica high-precision millisecond detonating detonator detonators to detonate the network sequentially. In the hole, the detonator is extended for 400ms in the high section, and the detonator is detonated by the 25ms delay between the same row of holes in the hole, and the detonator is detonated by 42ms between the row and the row. The test results are shown in Table 2.

The results of the blasting test show that the bottom spacer is charged by the air spacer, and the water hole treatment measures are taken to effectively eliminate the adverse effects of the water hole on the blasting construction, and eliminate the shortage of the roots due to the insufficient amount of charge in some areas. Phenomenon, compared with the 4.1% block rate of conventional blasting, the block rate is reduced by 31.7%, which greatly improves the utilization rate of explosives, reduces the cost of root and large processing, and creates convenient conditions for the shovel loading process. At the same time, it also avoids the inconvenience caused by excessive smashing of the floor rock due to excessive pressure in the initial stage of the detonation of the coupled charge to the next step. The reduction of unit consumption in the test area is 0.064kg/m3, the average charge is 30-40kg per hole, and the explosive reduction rate is about 16%, which produces good economic benefits.
4 Conclusion
According to the water content of the blasthole in the open pit, the adverse effects of the blasthole water on the blasting effect and the commonly used methods for treating the blasthole water were analyzed. Based on the theory of water-medium blasting, a blasting method using a spacer at the bottom of the hole is proposed. The field test of the Shangqiao iron ore shows that when the water depth in the blasthole is small, the bottom spacer charge with the air spacer can effectively suppress the water hole. The adverse effects brought by the blasting construction can improve the blasting effect, and the large block rate is reduced by 31.7%, which saves production costs and has significant economic benefits.
references
[1] Shao Mingjing. Medium-deep hole blasting blasthole water solution problem [J]. China Cement, 2004 (2): 74-75.
[2] Liu Weizhou, Yuan Yingjie, Zhang Xiliang, et al. Hydraulic booster blasting test [J]. Engineering Blasting, 2014, 20(2): 10-13.
[3] Guo Dejun. Application of deep hole hydraulic blasting technology in water-bearing rock mass [J]. Railway Construction Technology, 2001 (5): 1-3.
[4] Xiang Yuanzhi. Open-air deep hole water medium blasting [J]. Metal mines, 1993 (12): 13-17.
Author: Yuan Yingjie; Magang (Group) Holding Co., Ltd. Nanshan Mining Company;
Article source: "Modern Mining"; 2016.8;
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