Ma Hang large-scale iron ore skarn type magnetite, geological reserves of 450 million t, is one of the largest iron ore in East China. Originally used shallow hole retention method, the scale is 2 million t / a, with the improvement of the production system, it now reaches 3 million t / a, by 2018 design reached 5 million t / a. Obviously, the shallow hole retention method can not meet the production requirements, and it has been decided by technical experts to change from the original shallow hole retention method to the medium deep hole blasting method.
Medium-deep hole blasting ore is to arrange fan-shaped holes in the cutting roadway (along the vein or the way), and use the cutting patio as the free surface to carry out the blasting and falling mine. The cutting patio construction is a key part of the medium-deep hole blasting. The original manual rock blasting is used. There are two kinds of construction sequence: one is to cut the patio before the construction of the medium hole blasthole, and the construction after the construction of the cutting patio is completed. The hole in the mine, the rock drill and the operator entering the cutting well cause great difficulties, and the safety risk is high, which is generally not considered. Secondly, the medium hole blasthole is constructed first, then the construction cuts the patio, and the middle hole charges. When the personnel need to enter the cutting patio, some blastholes are not convenient for charging operations, resulting in serious safety hazards. The ordinary artificial construction method has stricter safety conditions when the geological conditions are poor or under the upper stratified empty area, and the production efficiency is low and the production cost is high. Changing the original cutting patio construction method is a problem that must be solved at the moment.
1 Project Overview
The main distribution strata in the mining area are the Carboniferous Forest Group (C1L), the Meridian Formation (C1L), and the Permian Qixia Formation (P1q). The woodland group is gray and white quartz glutenite, gray and dark gray medium-fine sandstone , which is brittle and dense. It is affected by tectonic action, and the fissure is relatively developed, containing fissure water but small amount of water. The Carboniferous Meridian Group (C1L) is the main layer of magnetite ore body. Qixia (P1Q) comprises Chuanshan, Huang limestone, is not separated, gray, white marble limestone. The surrounding rock of the courtyard is mainly sandstone, f=10～12, and the surrounding rock has good integrity.
The bottom of the magnetite is quartz sandstone, and the top plate is limestone. The rock hardness coefficient is f=10~14, the middle section is 100m high, the section height is 15m, and the ore body thickness is about 30m.

According to the thickness of the ore body, single-pulse, double-path vein mining or approach mining [1], the distance between the roads is 15m, 50m is a mine, and the mine is set in two mines, and the shovel is used to mine. The slippery section of the cutting and cutting section is 4000mm×3530mm (width×height), and the section of the cutting patio is 2m×3m. The original YGZ-45 type drilling rig was used for rock drilling and blasting construction, and the footage was about 1.8m.
2 cutting patio construction method
The T100 medium-deep hole rock drill is used to make parallel eyes in the cutting lane. The compensation hole is made of 90mm or 110mm drill. The boring hole, auxiliary eye and caving eye are made of 76mm drill bit. Once construction is in place, the large-aperture boring eye is used as blasting. The compensation space is divided into several times to form a cutting patio. The height of the cutting patio is generally controlled within 15m. The use of medium-deep hole blasting to form a cutting well requires high precision in the arrangement and construction of the blasthole, and must be strictly in accordance with the design and construction. The lower the cutting well height, the better the blasting effect.
3 deep hole blasting parameters in cutting well
3.1 blasthole parameters
Taking the 29# mine in the middle section of Machio Iron Mine 203 as an example, the mine is 14m high and the cutting well is 11.9m high. The V-shaped gutter is used to arrange the blasthole [2]. The parameters are as follows:
(1) The sulcus eye is divided into compensation holes (the holes are not charged), the main sulcus and the auxiliary sulcus. The compensation hole (1#) has a diameter of 110mm and a hole depth of 13.4m (considering the effective utilization of the blasthole is 90%), 90°; firstly, it is constructed with a 76mm drill bit, and then a 110mm drill bit is used to ream the hole, which is convenient for speeding up the construction and reducing the wear of the drill rod. . The main grooving eyes (2#~5#) are arranged along the circumference of the compensation hole at a spacing of 400 mm, arranged in a diamond shape, with a hole diameter of 76 mm and a hole depth of 7 m and 83°. The auxiliary gutter eyes (6#~13# holes) are arranged along the main gutter hole at a spacing of 700mm, arranged in a diamond shape with a hole diameter of 76mm and a hole depth of 13.2m and 87°.
(2) Four auxiliary eyes (14#~17# holes) are arranged at a spacing of 500mm near the contour of the cutting well, with a hole depth of 13.2m and a hole diameter of 76mm and 90°.
(3) Six caving eyes (18#~23#) are arranged on the contour line of the cutting well, the hole depth is 13.2m, and the hole diameter is 76mm, 90°.

The blasthole arrangement is shown in Figure 1.

The inclined hole is mainly considered to improve the use of the ore itself to improve the clamping of the hole in the blasthole. The burr hole is greatly improved in the blasting effect, but the construction requirements are high. The angle and depth of the grooving eye must be paid attention to during construction. Without perforation, the diameter of the blasthole can be adjusted according to the actual situation. The spacing of the blasthole is adjusted according to the rock coefficient f. The larger the f, the smaller the spacing.
3.2 Charge packing
Powdered ammonium nitrate rock explosives are used, and there are many fillings in the gutters. Generally, the orifices are filled with 600mm; the auxiliary eyes must be well controlled, and the general orifices are filled with 900mm; the cavities are generally filled with holes of 700mm, and the general line loading density is It is 6kg/m.

Taking the cutting patio of No. 29 mine in the middle section of Megeng Iron Mine 203 as an example, the main gutter is blocked by 600mm, the charging length is 6.4m, the line loading density is 6kg/m, the charging amount is 153.6kg; the auxiliary gutter is blocked by 600mm. The length of the charge is 12.8m, the density of the line charge is 6kg/m, the charge is 614.4kg, the auxiliary eye is blocked by 600mm, the charge length is 12.6m, the line charge density is 6kg/m, and the charge is 302.4. Kg; the collapsed eye is blocked by 600mm, the charge length is 12.6m, the line charge density is 6kg/m, and the charge is 453.6kg. The total charge of the blasthole is 1524kg.
3.3 detonation method
The slanting eye adopts one section of simultaneous detonation, the auxiliary eye adopts three sections simultaneously detonating, the caving eye adopts five sections simultaneously detonating, and the detonating tube is detonated in parallel, in order to ensure complete detonation, the detonating tube is detonated by using the same double detonator when the detonating tube exceeds 15 m. When the rock hardness coefficient f is large, secondary blasting can be used, and the lithology is poor when it is formed once. The blasting parameters are shown in Table 1.

4 blasting effect

After blasting, the cutting patio is rectangular, 3.0m×2.1m (length×width), depth 12.2m, blasting efficiency is 92%, blasting depth is greater than 11.9m, all meet the design requirements. The blasting shock wave has less damage to the roadway and does not collapse. The hole does not affect the blasting of the later mine.

The construction cost of the common law construction patio project is 5,000 yuan/m, and the construction cost of the 12.2m high cutting patio is 61,000 yuan. With medium-deep hole blasting construction, the drilling cost of T100 rock drill is 30 yuan/m, the drilling engineering volume is 280.6m, the drilling cost is 8418 yuan; the explosive is 18288 yuan, the detonator is 132 yuan, and the total cost is about 26838 yuan. It can be seen that the construction of the cutting patio by the medium-deep hole blasting method is reduced by 56% compared with the common method, and the economic benefit is remarkable.
5 Conclusion
Through the design of the blasthole parameters of the cutting well, the quality of the medium-hole rock drilling and the amount of charge are strictly controlled, the blasting network design is optimized, and the deep hole blasting in the cutting well has achieved good results, simplifying the construction process, improving the production efficiency and safety factor, and reducing The labor intensity and production cost have achieved cost reduction and efficiency. In the practical application, the medium-deep hole blasting is not only used to cut the patio, but also to construct a small section of high ventilation patio and slip mine.
references
[1] Xu Yongqi. Mining science [M]. Xuzhou: China University of Mining and Technology Press, 2003.
[2] Liu Niansu. Lane engineering [M]. Beijing: Metallurgy Industry Press, 2011
Article source: "Modern Mining", 2017.4
Author: Yangfa Fu, Zhao Shao Wei; Fujian Province Changlong Mining and Construction Co., Ltd:

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