Omen and measurement of large area pressure of the top plate
1. omen
The harbinger of large-area pressure is mainly manifested by the increase of the frequency and sound of the sound of the roof fracture; the coal gang has obvious pressure and lumps; the bottom drum or the bottom plate near the coal pillar is cracked; the roadway pressure is more obvious. The strut load and the roof sinking speed in the working face are obviously increased; sometimes the crack in the roof of the goaf or the drenching is increased, and the hole drilled in the top plate originally flows clear water, and then becomes a white paste-like liquid, which It is a mixture of rock powder and water formed by friction between fractured rocks.
2. Measurement and forecast
The measurement principle of large-area pressure is the same as that of impact rock pressure. The microseismic instrument, geophone and ultrasonic formation stress meter can be used to measure the pulse signal when the rock layer breaks. According to the above-mentioned mechanism of large-area pressure on the top plate, the destruction process of thick and hard rock layers, sounds and other anomalies appear for dozens of days before the pressure is applied, and short signs appear in the days before and even after the pressure. . Therefore, according to the results of the instrument measurement and the combination of the characteristics of the previous pressures, it is possible to make a more accurate prediction of the large-area pressure to avoid disasters.
Prevention measures for large area pressure on the roof
The main danger of the large area of ​​the roof is the impact load and storm formed by the roof falling. The basic principle of preventing and weakening the damage is to change the physical and mechanical properties of the rock mass to reduce the ceiling and the area of ​​the roof, and to reduce the falling height of the roof to reduce the air discharge speed. The specific methods can be as follows.
1. Roof high pressure water injection
Roof water injection can soften the top plate, increase and expand the crack, and lubricate the weak surface. The main mechanism is that it can dissolve the water of roof rock and a portion of mineral cements; reduced interlayer adhesion; high-pressure water can form a water wedge to expand and increase the weak fractured rock surface. Therefore, the strength of the rock after water injection will be significantly reduced. The injection test sandstone Contiguous II cemented clay, rock compressive strength softening soaking 6 ~ 9d coefficient of 0.39 to 0.49, an average of 0.43. If immersed in 2~8% hydrochloric acid solution, the effect is better. The longer the immersion time, the lower the softening coefficient.
2. Forced topping
The blasting method artificially cuts the top plate and causes the top plate to fall to form a vermiculite cushion. Cutting the top plate can control the falling area, weaken the pressure of the top plate and the impact load generated when falling off; forming a cushion can alleviate the storm generated when falling. In order to form a mat, the height of the top can be calculated as the thickness of the mat. According to practical experience, the fullness of meteorite in the goaf can reach 2/3 of the sum of the emptying and the topping height, so as to avoid excessive impact load and prevent the formation of storm.
3. Storm prevention measures
In mines or areas where there is a large area of ​​pressure, precautions can be taken to avoid damage to production and safety. For prevention, it is generally used to block and vent.
Blocking, that is, using the isolation of the coal pillars and the installation of anti-storm enclosure, the separated mining area and the production area are isolated. Venting, that is, by specifically draining the air duct, the isolated area is connected to the ground to lead the formed storm out of the earth's surface.
It should be noted that these two measures must be adopted simultaneously. The isolation area should be divided according to the roof falling performance. The general goaf range can be controlled at 50,000 to 100,000 m:. The width of the isolated coal pillar is 15~20m. The communication channel should not be digging in the middle of the coal pillar. If there is a passage, it must be protected against storm. At the same time, there is a venting channel in the isolated area to effectively isolate.
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