0 Preface
Blasting operations are an important process in mining processes. A large number of roadway excavation projects, ore mining, and geotechnical stripping are all required to be completed by blasting methods. To blast, it is necessary to use blasting equipment , such as explosives, detonators, detonating tubes, etc., and these blasting materials are generally flammable and explosive dangerous goods, in the event of an accident, it will threaten the health and safety of employees, and may cause Serious economic losses. Therefore, it is very important to do a good job in blast safety.
1 Explosive detonation theory
Detonators are commonly used in blasting projects to detonate the pack. The explosive energy of the detonator is much smaller than the explosive energy of the packet. The role of the detonator is only to provoke a local explosive explosion adjacent to it and then spread quickly. Whether the entire package can be completely exploded is the key to making full use of the explosive energy, ensuring the quality of the explosion and the safety of production. Once the explosive is detonated, an explosive reaction occurs at the detonation point to generate a large amount of high-temperature, high-pressure, and high-speed airflow, and the shock wave is excited in the explosive. The shock wave strongly compresses the adjacent explosive layer to cause the explosive reaction, which generates a large amount of gas and a large amount of heat. The part of the heat released by the reaction is enough to compensate the energy loss when the shock wave propagates, and the shock wave can maintain the natural wave velocity and the wavefront pressure to continue forward. spread. This is followed by a chemical reaction of the explosive and propagation at the same speed.
2 Analysis of blasting effect
2.1 Analysis of blasting vibration effect
The seismic wave generated by the blast will form a shock wave, which will propagate the huge blasting energy to the surrounding. When the seismic wave is transmitted to the building and its velocity or acceleration value exceeds the seismic design standard of the building, it will cause deformation and cracking of the building. And even destroyed. The explosive energy tends to cause the looseness or destruction of the slope rock mass with the blasting seismic wave propagating and releasing in the slope rock mass. Therefore, it is also one of the factors that cause the displacement of the slope rock mass.
The degree of influence of blasting vibration on the slope rock mass is generally evaluated by the magnitude of the blasting vibration velocity. The formula for calculating the blasting vibration velocity is as follows:
V-blasting vibration velocity, cm/s; Q-maximum dose, kg; R-explosion heart distance, m; k, a1 regression coefficient.
Determine the vibration speed according to the formula to prevent exceeding the allowable safe vibration speed. In order to reduce the impact of blasting seismic waves on buildings around the blast zone, the following measures can be taken: 1) Strictly limit the charge of the largest segment. When the total dose is the same, the more segments, the smaller the blasting vibration intensity. 2) Reasonably select the interval time and blasting parameters to reduce the use of blasting clamps. 3) Select low explosive speed explosives and uncoupled charges. 4) Pre-cracking technology is adopted, and the pre-crack has a significant earthquake-reducing effect. 5) Excavation of the earthquake-proof trench in the protected object and the source of the explosion is an effective isolation measure. The single-row or multi-row dense holes can have a shock reduction rate of 20% to 50%.
2.2 Analysis of blasting shock wave effect
Explosives can cause various degrees of damage or damage to surrounding buildings, people, etc. when they explode in the air. In the near zone, it is affected by the detonation product and the air shock wave; in the far zone, it is only affected by the shock wave.
The minimum safe distance that shock waves do not cause damage is:
Where: R is the minimum safe distance, m; Q is the explosive amount, kg; K is a coefficient.
Calculate the minimum safety distance according to the formula to ensure that the distance between the person and the explosion center is greater than the minimum safety distance. The following measures can be taken during blasting to reduce the damage of air shock waves: 1) Ensure reasonable packing length, packing quality and reverse blasting. 2) Reasonably determine the blasting parameters, and reasonably select the differential detonation scheme and the time difference. 3) When performing large-scale blasting, in order to reduce the intensity of the air shock wave, various materials are used to stack the wave blocking wall or the baffle in the roadway through which it flows.
3 blast damage
The blasting hazard is mainly a fly ash hazard. Part of the energy of the explosive explosion is used to break up the medium (rock, etc.), and the other part is in the form of gas expansion, which strongly injects the atmosphere and pushes the rock in front of the rock to produce flying stones. In blasting, flying stones are produced where resistance lines or packing lengths are too small. Due to the inaccurate positioning and improper inclination of the drill pipe during drilling, the actual parameters are larger or smaller than the calculated parameters. If the resistance line is low, flying stones will be produced. If the blastholes are not detonated in the intended order or the blasthole charge is too large, flying stones will also be produced. Flying stones can cause damage to mining equipment such as machinery and cables.
In engineering blasting, the following measures can be taken to control individual flying stones: 1) When designing the position of explosives, avoid soft interlayers, cracks or concrete joints, etc., so as to avoid flying stones from these aspects. 2) Carefully check the minimum resistance line of each drug pack before charging, and it is strictly forbidden to overfill explosives. 3) Ensure the filling quality of the blasthole and take cover measures if necessary. 4) Low explosive explosives, non-coupling charge, extrusion blasting and millisecond differential detonation.
4 Conclusion
Blasting operations must strictly abide by the "Blasting Safety Regulations" (GB6722), "Big Blasting Safety Regulations" (GBl3349), "Explosives Management Regulations", etc., in accordance with the actual situation of the mining area to develop a corresponding management system, while actively researching new blasting technology Use reasonable blasting parameters to reduce and reduce the damage of blasting to production and personnel, and ensure the safe production and operation of the mine. In order to prevent accidents during underground blasting operations, the following measures should be taken:
1) When blasting, warnings must be set on the road leading to the subsidence area and the rolling stone area, and the goal should be set up to prevent personnel from entering the project. 2) When the empty top distance of the working surface exceeds the value specified in the design, no blasting is allowed. The power detonate main blasting, wire zone, the suspension cable must not be electrically conductive contact with the object tubes and the like metals, nor close to cables, wires, signal line; 3) through the tunnel by blasting method, have accurate barium 0 quantity map, each shift should be filled in the progress on the map, geological surveyers must give notice in advance when the two working faces are 15m apart. Thereafter, it is only allowed to excavate from a work front, and should be guarded at a safe place where both sides lead to the working face. The personnel on both sides of the work face are all evacuated to a safe place before they are allowed to start. After the roadway is connected, the excavation faces on both sides shall coordinate the time of firing; 4) When one of the two parallel roadways with a spacing of less than 20 m needs to be blasted, the personnel of the adjacent working face must be evacuated to a safe place. It is forbidden to blast within the area within 30 m of the explosives warehouse; 5) When the boring of the heading roadway is blasted, it is necessary to keep the working surface and the fresh air flow path clear. After blasting, the working surface must be ventilated, sprinkled, treated with pumice , cleaned by the well and treated with the blind cannon before the rock grab operation; 6) When the tunnel boring adopts the deep hole segmental charge blasting, it must pass before the charge Send a warning to the safe place at the bottom of the entrance and exit of the aisle to confirm that there is no one at the bottom, and to detonate; 7) When the underground deep hole or the chamber is blasted, all personnel must be evacuated before the detonation; 8) to the secondary blasting site For each entrance, a warning sign must be set. Only when the blasting danger zone is confirmed, the explosives are to be detonated. 9) Unused explosives, detonators, fuses, and detonators are carried by the personnel who support the blasting equipment. Go to the underground explosives warehouse (distribution station), the detonator warehouse to handle the procedures for returning the warehouse, and keep records, it is strictly forbidden to hide and transfer to others.
references
[1] Tao Yulin. Rock drilling and blasting [M]. Beijing: Metallurgical Industry Press, 1986.
[2] Lin Deyu. Mine blasting engineering [M]. Beijing: Metallurgical Industry Press, 1993
[3] Li Wenquan. Blasting principle and application [M]. Dalian: Dalian Publishing House, 1997.
[4] Zhang Shouzhong. The basic principle of explosion [M]. Beijing: National Defense Press, 1988.
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