Comprehensive measures to prevent and control coal

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Comprehensive measures for prevention and control of coal and gas outburst in coal mines

when mining outburst coal seams, comprehensive measures must be taken to prevent outburst, sometimes to avoid personal accidents. The contents of comprehensive measures include:

(1 there is no need to set attenuation);) Outburst risk prediction

(2) outburst prevention measures

(3) effect test of outburst prevention measures

(4) safety protection measures

1. Outburst risk prediction

according to the scope and accuracy of outburst prediction, coal seam outburst risk prediction is divided into regional outburst risk prediction and working face outburst risk prediction. Regional prediction should predict the outburst risk of coal seams and coal seam areas, and should be carried out during geological exploration, new well construction, new level and new development or preparation

after regional prediction, coal seams are divided into outburst coal seams and non outburst coal seams. The outburst coal seams can be divided into outburst danger zone, outburst threat zone and non outburst danger zone after regional prediction. In the mining process of outburst coal seams, if the distribution law of coal seam outburst risk areas has been accurately mastered and reliable prediction data are available, outburst prevention measures may not be taken in the confirmed non outburst risk areas. The prediction methods include one-way index method, gas geology method and comprehensive index method

in the outburst danger area, the working face prediction should be carried out before mining. After prediction, the mining face can be divided into outburst dangerous face and non outburst dangerous face. In the outburst threat area, according to the outburst risk degree of the coal seam, the prediction method of the mining face shall be applied for no less than two consecutive prediction verifications every 30~100m. Only when there is no prominent danger after two consecutive verifications, this area can continue to be identified as a prominent threat area

face prediction is to predict the outburst risk of coal near the face, which should be carried out in the process of advancing the face. Other methods include comprehensive index method, drilling cuttings index method, initial velocity of borehole gas emission and R-value index method

(II) outburst prevention measures

when mining outburst coal seams, comprehensive outburst prevention measures must be taken. When adopting outburst prevention measures, regional outburst prevention measures should be preferred. If the conditions for regional outburst prevention measures are not met, local outburst prevention measures must be taken

1. Regional outburst prevention measures

1) mining protective coal seams. In outburst mines, the coal seams that have no or small outburst risk and can eliminate the risk of adjacent outburst coal seams are first mined in the coal seam group, which is called the protective layer, and then the coal seams with outburst risk are mined, which is called the protected layer. The protective layer above the protected layer is called the upper protective layer, and the protective layer below the protected layer is called the lower protective layer. Mining protective layer is the most effective and economical measure to prevent and control coal and gas outburst

after the mining of the protective layer, the coal body in the corresponding area in the protected layer is fully depressurized, resulting in the release of the elastic energy accumulated in the coal seam and surrounding rock, which weakens the main driving force for outburst: after the coal body is depressurized, a large number of cracks will be generated, which will increase the permeability of the coal seam, cause the release of gas potential, and weaken the main driving force for completing the outburst process: the massive release of high-pressure gas, which reduces the gas content of the coal seam, As a result, the strength of the coal body increases, and the firmness coefficient of the coal can be increased by more than twice, which increases the outburst resistance. The combined effect of these factors will inevitably lead to the disappearance of the danger of outburst of the protected layer

protective layer 2 The effective range of protective effect of samples and measuring instruments should be determined according to the actual investigation results of the mine or with reference to the detailed rules for the prevention and control of coal and gas outburst

21 is thermal insulation performance) pre drainage of coal seam gas. When mining the protective layer, the mine with gas drainage system shall simultaneously drain the gas of the protected layer. Gas drainage measures must also be adopted for single coal seams and outburst dangerous layers that can be mined without protective layers when pre gas drainage is effective through tests

after gas drainage in coal seams, a large amount of high-pressure gas drainage leads to the release of gas potential, which weakens the main driving force in the process of outburst, directly leads to the increase of coal strength and increases the resistance of outburst; On the other hand, the drainage of a large amount of gas leads to the pressure relief of the coal body, releases the elastic energy stored in the coal body and surrounding rock, and weakens the main driving force of outburst. The combined effect of these factors eliminates the prominent risks

the effective index of pre drainage coal seam gas outburst prevention measures should be determined according to the actual investigation of the mine. If there is no actual investigation data, it can be determined with reference to one of the following indicators:

(1) after pre drainage of coal seam gas, the residual gas content of the outburst coal seam should be less than the coal seam gas content at the initial outburst depth of the outburst area

(2) the pre drainage rate of coal seam gas, that is, the ratio of the amount of gas extracted from the borehole to the coal seam gas reserves within the control range of the borehole, should be greater than 25%

3) coal injection. Pressure water entering the coal seam can break the coal near the working face. After water enters the cracks and voids in the coal seam, it can wet the original coal body, change the mechanical properties of the coal, increase the plasticity and flexibility of the coal, reduce the elasticity of the coal, loosen the coal body, reduce the stress concentration in the coal body and the initial speed of gas emission, make the stress distribution more uniform, move the peak value of the concentrated stress into the depth of the coal body, and reduce the stress coefficient in front of the roadway, In the mining process, the release of coal elastic properties becomes relatively slow. At the same time, after the water enters the coal body, the gas flow channel is closed, and the gas is squeezed into the coal body, which improves the pressure bearing capacity of the coal body (the smaller the pore diameter of the coal, the greater the pressure bearing capacity), and reduces the possibility of gas crushing the coal body; On the other hand, it is difficult to discharge gas after water intrudes into the micro pores of coal. According to the actual measurement, the amount of residual gas in the injected coal seams transported to the ground is more than twice that of dry coal, and the initial rate of gas emission is reduced by 90%. To sum up, coal injection can effectively prevent outburst. Coal body water injection can not only prevent coal and gas outburst, but also reduce the production and flying of dust in the mining process. When some inhibitor is added to the water, the spontaneous combustion of coal can also be prevented

2. Local outburst prevention measures

1) outburst prevention measures for coal uncovering in Crosscut. In addition to gas drainage, there are also hydraulic punching, drainage drilling, hydraulic scouring, metal framework and vibration blasting in the square outburst measures when the crosscut and other rock shafts and roadways expose the initially dangerous coal seams

(1) hydraulic punching. When the spontaneous injection of coal and gas occurs in the coal uncovering and drilling of the crosscut, hydraulic punching measures can be adopted for uncovering the coal. That is, the rock pillar or coal pillar is used as a barrier to send water with a certain pressure while drilling into the coal pillar. The water pressure is generally greater than 3Mpa. Some damage to the coal body can cause stress imbalance, leading to the occurrence and development of the spray hole. The ejected coal, water and gas can be transported to a place far away from the working face through pipelines for separation. Hydraulic punching requires that the total amount of coal punched out of the crosscut is less than 20 times the thickness of the coal seam

(2) discharge the borehole. Drainage boreholes are drilled at the crosscut to a vertical distance of 5~8m from the coal seam, and 2~3 rounds of boreholes are evenly arranged along the slope and trend of the outburst dangerous coal seam. The control range reaches 3~5m outside the crosscut, forming a sufficient range of pressure relief and gas drainage. Within the range required by the design, the gas pressure is reduced to less than 0.74mpa. This measure is applicable to outburst coal seams with different thickness and inclination, and has a good outburst prevention effect for coal seams with high gas pressure

(3) hydraulic scouring. Hydraulic flushing refers to the use of high-pressure water gun to flush the square coal in front of the crosscut. When the extensometer moving arm is stressed, leading holes are formed, so that the coal body can be relieved and gas can be discharged, which has eliminated the outburst risk when the crosscut is exposed. The main problem of hydraulic flushing is that the washed coal and Wasi are discharged locally, forming an unsafe environment at the working face

(4) metal skeleton. Metal framework is a kind of advanced support used for uncovering coal in Crosscut. When it is 2~3m away from the coal seam, drill holes in the upper part of the working face and around both sides. The drilling holes should penetrate the full thickness of the coal seam and enter the rock stratum for 0.5m. The spacing between single rows of holes is generally not more than 0.2m, and the spacing between double rows of holes is generally not more than 0.3m. Then insert steel pipes or rails with a length of not more than 0.5m into the drilling holes, and fix their tails firmly to form an overall protective frame

outburst prevention effect of metal framework measures: first, drilling pressure relief; Second, gas drainage by drilling; Third, protect the coal body. The main function is to protect the coal body and increase the outburst resistance

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