First, pressure relief blasting

Vibration blasting has vibration relief blasting, vibration falling coal blasting, vibration decompression and falling coal blasting, and roof blasting.

(1) Principle of vibration relief blasting

In the mining face and the upper and lower roads, the vibration blasting can release the elastic energy accumulated in the coal body to the maximum extent, and form a pressure relief zone near the working face and the roadway, so that the pressure rise zone is transferred to the deep part of the coal body.

(2) Vibration relief blasting

In the case of personnel evacuation, in addition to causing impact rock pressure, such blasting can transfer a high stress concentration zone to the deep part of the coal body to form a loose belt. The effect is to induce impact rock pressure, slow down the pressure rise zone in the deep coal body, and blasting triggers the release of some seismic energy.

(3) Vibration falling coal blasting

The purpose of vibration and coal blasting is to induce impact rock pressure in the case of evacuation, and to slow down or remove the bearing pressure zone within the deep coal or shearer depth range. This blasting requires full length blasting of the blasthole so that stress is released in the next depth range. In this case, the shearer only acts as a coal loader.

(4) Vibration decompression and falling coal blasting

This kind of blasting combines vibration, pressure relief blasting and vibration, and falling coal blasting. Vibration, pressure relief, and coal blasting are used both in front of the mining face and in tunneling. The parameters are determined according to specific conditions. However, after the blasting of the long pressure relief, the blasting holes in the same eye position should be avoided.

(5) Roof blasting

Roof blasting is to break the top plate, reduce its strength, release the energy accumulated by the pressure, and reduce the impact vibration on the coal seam and the support.

There are two ways to destroy the roof of explosives. One is short borehole blasting and the other is long borehole blasting.

Second, the drilling pressure relief

The use of coal body drilling can release the elastic energy accumulated in the coal body and eliminate the stress rise zone. The effect of the borehole on the stress state is detailed below, as shown in Figure 10-3.

Figure 10-3 Schematic diagram of the influence of coal body drilling on stress distribution

Acting on the layer of roof coal, the pressure on the front side of the working curve of coal available Gz FIG. Gk indicates the ultimate stress value at which the impact rock pressure occurs, that is, the impact rock pressure will occur when the stress of the coal seam reaches this value. Starting from the coal wall, the stress on the coal seam reaches the maximum value Gzmax , and this value is close to the ultimate stress value, indicating that the impact rock pressure is very dangerous. In this case, a bore with a diameter d = 2r and a length l is used, and the length of the middle of the bore is compressed by a , resulting in a pressure drop of the drilled coal body to Gsc . The higher the stress Gz , the greater the extent to which the borehole is moved by the squeeze.

In the bearing pressure region, the large-diameter drill bit is used to drill, reducing the stress value, while the localized range of the borehole has a small stress concentration G'z . When the stress G'z exceeds the strength of the borehole wall, over time During the transition, the weathering and fracturing of the coal body between the boreholes results in pressure relief within a range of diameter D around each borehole.

Therefore, when the drilling is arranged, the spacing S is at least equal to D. Thus, within a certain range, the stress is lowered. The distance from the highest point of stress G"zmax from the coal wall is moved to b" . It should be noted that the pressure relief belt formed by the borehole loosens the coal body, does not collect elastic energy and forms permanent yield deformation.

Third, the orientation crack

Directional hydraulic crack method

The directional hydraulic crack method is to artificially create a crack in the rock formation. In a relatively short period of time, high pressure water is used to rupture the rock mass along the prefabricated crack. Under the action of high pressure water, the fracture radius of the rock mass can reach 15~25m, and some even larger.

There are two kinds of directional hydraulic methods. One is that the pre-crack is circumferential and the other is that the pre-crack is axial. Studies have shown that in the case of forming a circumferential pre-crack, in order to achieve a better effect, the diameter of the circumferential pre-crack should be at least twice the diameter of the borehole, and the end of the crack should be sharp. The pressure of the high pressure pump should be above 30 MPa, and the flow rate should be above 60 l / min. The axial cracking rule is to make a pre-crack along the axial direction of the borehole, thereby breaking the rock mass along the crack.

2. Directional blasting crack method

The principle of the directional blasting crack method is the same as that of the directional hydraulic cracking method. The only difference is that the high pressure water is replaced by an explosive. The pre-cracks also have circumferential and axial divisions.

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