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Open-pit blasting produces large blocks and effective solutions for roots

From： Hunan ZEGA Date：2019-05-11 15:30:18 Hits：753 Belong to：Company News

According to the blasting theory and the on-site practice and investigation of large-scale open-pit mines in the past few years, the main parts of the large area appear: the empty surface and orifice part of the upper part of the step, the center part of the hole network parameter is large, the area around the unblocked waste hole, the base of the step where the chassis resistance line is too large and the blind gun part. The root base mainly appears at the root of the step with a large resistance line of the chassis, the bottom of the step in the middle part with large hole and network parameters, the bottom of the step rock mass and the blind gun part where the gun hole is ultra-deep and insufficient.

cause

(1) The ultra-depth of the same explosion area varies greatly. Due to the large depth of individual gun holes, the center of gravity of the medicine column is lowered, and the ore rock in the upper part of the step is prone to produce too many large blocks. If the ultra-depth is too small, the ore at the bottom of the step is reduced by the energy of explosives, and the site is often raised or even the root after the explosion.

(2) The hole mesh parameters are too large. In the middle part of the hole network parameter, due to the small effect of explosive damage, the large block here increases after explosion, and the root base appears seriously.

(3) The uniformity of the hole mesh parameters. Due to perforation and the geological conditions of the palm surface, the spacing between individual gun holes is too large, and large blocks appear after explosion, and the root base is produced in severe cases.

(4) The nose row gun hole chassis resistance line is large. Due to the influence of blasting thrust and rock inclination angle, the slope angle of the step is reduced, coupled with the limitation of the safe working distance of the drilling rig, the root base appears at the root of the step after blasting. The situation of Yihua open-pit mine is more common.

(5) The length of the gun hole is too large. The blocked part of the gun hole is too large, so that the upper part of the gun hole is reduced by the destructive effect of explosives, resulting in more large pieces.

(6) Unblocked waste holes. Because the penetrated gun hole seriously deviates from the design hole position and needs to be re-drilled, if the waste hole is not blocked as necessary, large blocks often appear around it after blasting, and flying stones are easy to produce at the moment of blasting, endangering safety. This is mainly due to the fact that unblocked waste holes play a guiding role in blasting and waste explosive energy.

(7) The degree of fracture and joint direction of rock mass. Due to the influence of the vibration of the upper step over-drilling, the blasting backlash of the front step and the adjacent blasting of open-pit mine, most of the blasting rock mass is a block structure, so the blasted rock mass is usually broken along the original fractures and joints, especially the rock mass in the upper part of the step is more obvious. When the blasting surface is diagonally or perpendicular to the rock formation, the impact of the fracture on the blasting block is more obvious.

(8) Blind cannons. Blind guns are an important factor in generating base and bulk, and affecting the quality of blasting.

1. Select reasonable blasting parameters

1. Chassis resistance line

The chassis resistance line, which refers to the horizontal distance from the bottom line of the step slope to the central axis of the first row of holes, is an important blasting parameter [2]. Too large a chassis resistance line can cause a larger root, and too small will cause an increased consumption of explosives. Under the premise of meeting the safety and charging conditions, it is selected according to experience, and the empirical formula can be referred to

(See Equation (1)): W=kd (1).

where W is the chassis resistance line, m; d is the diameter of the drilling hole, mm; k is the coefficient, generally take 20 ~ 30, the ore rock is explosive to take the large value, and the difficult to explode take the small value.

2. Hole spacing

and row spacing

The hole spacing and row spacing are generally calculated according to the aperture, that is: a=(20 ~ 30)d, b=(0.75 ~ 1)a.

Practice has proved that the use of regular triangular pores, even if B=0.866a, can significantly improve the crushing effect of ore. Especially when detonating hole by hole, the resistance lines in all directions are equal, and the blasting effect is basically uniform, which can improve the crushing effect.

3. Super deep

Ultra-deep refers to the depth of the deep hole below the elevation of the step chassis, and its effect is to reduce the height of the charge center in order to effectively overcome the resistance at the bottom of the step and avoid or reduce the root base. According to experience, the ultra-deep value is determined as follows: h=(5 ~ 10)d.

When selecting ultra-deep

, it should be noted that the ultra-deep value of the rear row hole is generally about 0.5m smaller than that of the front row. The chassis resistance line is small, take a small value; When the chassis resistance line is large, take the value of the larger one, and you can appropriately increase the super depth to overcome [3]. However, when the slope angle of the step is too small and the chassis resistance line is too large, it can not be too large to increase the ultra-deep, because the ultra-deep is too large not only wastes drilling and explosives, but also because the center of the explosive is too low, it will produce more large blocks in the upper part of the step, and destroy the integrity of the rock mass on the surface of the next step, affecting the perforation operation of the next cycle, and even causing collapse and forming waste holes.

4 Blockage length

A reasonable plugging length should prevent the explosive gas product from rushing out of the hole prematurely, so that the crushing is more complete. When using continuous columnar charge, the blockage length is generally 0.7 ~ 0.8 times the chassis resistance line leopard, depending on the nature of the ore and explosives. The blockage length of open-pit deep hole blasting is relatively large, and sometimes the blockage length of the gun hole can be appropriately reduced to achieve the purpose of reducing the upper block of the gun hole. After practice and observation, it is believed that the length of the blockage should not be less than 20 ~ 25 times of the aperture, otherwise it is easy to produce flying stones.

5 Explosive consumption

Relationship between explosive consumption and rock solidity coefficient.

Table 1 The data are based on porous granular ammonium oil explosives, and if other types of explosives are used, conversion is required to determine the actual unit explosive consumption. According to experience, under the premise of ensuring blasting safety, Q can be appropriately increased to improve blasting quality.

6 Charge per well

Under the condition of reasonable selection of other blasting parameters, the charge Q per well can be calculated according to equation (2): Q=qaHW (2).

where H is the step height, m.

According to experience, when multiple rows of holes are blasted, the q value of the rear row hole should be taken as 1.1 ~ 1.3 times the q value of the first row hole.

Second, the initiation method of using isochrone as diagonal diagonal line

The holes along the diagonal direction of the quadrilateral enclosed by the gun holes were basically detonated at the same time. Diagonal detonation is a model for the application of wide-bore blasting technology, which is to appropriately expand the aperture distance and reduce the resistance line. Diagonal detonation is the same as the principle of wide hole pitch technology, the number of gun holes is the same as the ordinary method, and the charge of each gun hole is the same, but the resistance line is reduced, and the hole distance A is increased in the same proportion, so that the stress reduction zone is located in the space outside the ore rock initiation layer, which is conducive to reducing the generation of large blocks.

3. Adopt a reasonable charge structure

When using vertical hole blasting, due to the large resistance of the bottom, it is necessary to use ultra-deep to lower the center of the package to near the level of the bottom of the slope, but this is easy to make the explosive distribution on the upper part of the step too little and produce a large block, and a reasonable charge structure must be adopted.

(1) Intermediate gas interval sectional charge. Intermediate interval sectional charge refers to the dividing of explosives in deep holes into 2 ~ 3 segments, separated by appropriate length of gas or artillery mud and other spacers. The use of segmented charge can avoid the explosive being too concentrated in the lower part of the deep hole, so that the ore rock in the middle and upper parts of the step can also be broken to varying degrees, reducing the large blocks formed by collapse.

(2) Mixed charge. High-density, high-power explosives are installed at the bottom of the deep hole, and ordinary ammonium nitrate explosives are loaded in the upper part to adapt to the law of large and small under the resistance of step ore, which not only avoids the bottom of the step, but also reduces the generation of large blocks in the upper part of the step. At present, when the resistance line of the perforated chassis of the open-pit mine head of Yihua is large, the bottom is mostly loaded with latex explosives, and the upper part is loaded with porous granular ammonium oil explosives, which has achieved certain good results.

Fourth, the use of ballast blasting

Ballast blasting [5] refers to the blasting in the case of a certain thickness of blasting on the working surface, the existence of ballast pile creates conditions for extrusion, not only controls the width of the blasting pile, avoids the scattering of ore, but also can extend the effective action time of blasting, improve the utilization and crushing effect of explosives, thereby reducing the generation of large blocks. At the same time, a certain thickness of the blast pile is left on the working surface, which can narrow the head row hole chassis resistance line and avoid or reduce the root. This method is more suitable when the inclination angle of the step slope is slow during ballasting.

5. Choose a reasonable interval between holes

Determining a reasonable explosion interval between holes is an important issue related to the blasting quality, and most of the actual blasting work at home and abroad is used △ t=kW

where △ t is the detonation interval between adjacent holes that have been detonated successively, ms; Rather, the coefficient is taken 2 ~ 5 after the open-air step is blasted.

Generally, the actual micro interval time used in mine blasting is 17 ~ 100ms, usually 25 ~ 65ms. Hard rock takes a smaller value, soft rock takes a larger value, and extrusion blasting can take a little longer, which will achieve better crushing quality.

6. Optimize drilling methods

1. Oblique hole blasting is adopted

From the point of view of the blasting effect of the deep hole of the step, the oblique hole is better than the vertical hole, because the resistance line along the full length of the deep hole is equal, so the ore rock is broken evenly, the large block, the root base is less, and it is easy to maintain the slope angle of the required step, and the slope

surface is flat after the explosion, which is conducive to the perforation blasting work of the next cycle, and because the distance between the drilling rig and the top line of the step slope is large, the operator and the drilling rig equipment are safer. At present, the highest comprehensive efficiency of drilling rig perforation and blasting is the tooth wheel drilling rig, and it is mainly limited to vertical downward perforation, although the DTH drilling rig can punch oblique holes, but the efficiency is not too high, nevertheless, sometimes oblique hole blasting can also be considered. When conditions permit, a combination of vertical gun holes and inclined gun holes is used at the front row large resistance line to overcome the front row large resistance line, while the rear row gun hole adopts vertical holes, which does not affect the overall efficiency of perforation and blasting, and can effectively improve the blasting quality.

2. Make the right holes

When the front row of hole chassis resistance line is

large, punching the hole is to punch the encrypted hole, the spacing between the holes in the same group is within 5 times the aperture, the distance between the holes of the adjacent group is appropriately increased, increased to close to the front chassis resistance line, and the same group of holes detonate at the same time, in essence, it is to increase the charge at the bottom of the step, which is conducive to overcoming the chassis resistance line with the step and reducing the root.

3. Pull the bottom hole before bursting

When the resistance line of the open-pit mine step chassis is too large and the step slope is ballasted, it is also an effective method to pull the bottom before bursting. Before the explosion of the bottom pulling is to use the DTH drilling rig to drill the oblique hole in advance at the root of the excessive resistance line of the ballast step chassis, and detonate at the same time as the normal mining blast hole to avoid the root after the explosion.

Sunward Intelligent Equipment Co., Ltd. belongs to Sunward Intelligent Equipment Group. Founded in 1999 by Professor He Qinghua of Central South University, Sunward Intelligent Equipment Group has developed into an international enterprise group with the listed company Sunward Intelligent Equipment Co., Ltd. (stock code: 002097) as the core, Changsha as the headquarters, engineering equipment as the main business, and a certain influence at home and abroad, ranking among the top 50 construction machinery enterprises in the world and the top 20 excavator enterprises in the world. The SWD series DTH drilling rig developed by the company is widely used in cement, metallurgy, coal mine, quarry and other mines and railway highway, water conservancy and hydropower, national defense construction and other engineering construction of blasting hole drilling, its hole diameter range is 90~250mm. As the most advanced DTH drilling rig in China, it has an efficient high-pressure DTH drilling system, which is convenient for high-precision and high-efficiency blast hole drilling. International procurement, computer optimization design, and the development and application of power matching and load adaptation systems have realized the global power matching of the power system from power to pump to load.

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