Hard roof control and tile period prevention measu

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High gas mine hard roof control and tile period prevention measures

Dongbao mine of Shuangyashan Mining Group Co., Ltd. is a high gas mine. The 41 layer roof on the left of the first mining area of the mine is hard, and the periodic pressure is obvious. It is quite difficult to manage the roof during the initial caving and periodic pressure of the mining face, accompanied by a large amount of gas emission from the goaf, which increases the difficulty of safety management of the mining face. In view of this situation, we carried out special research and found out a set of effective methods to ensure the safety production of the mining face

1 mining area overview

the first mining area of Dongbao mine is located in the east wing of the mine field, and is arranged up and down the mountain with the level of - 200m, up to the coal seam outcrop and down to the level of - 370m. The length of the East-West strike is 1200m, with a total of 36 and 41 main coal seams. The thickness of the coal seam is 1.7 ~ 1.9m, and the dip angle of the coal seam is 7 ° ~ 31 °, with an average of 20 °. The coal seam is developed stably, and the geological structure is moderately complex. The roof is gray fine sandstone, and the floor is gray medium sandstone

the gas content in the left of the first mining area is high, and the absolute gas emission is 4.8m3/min. The gas volume of the working face is related to the activities of the goaf. The 41 storey direct roof is class III stable roof, and the main roof is class III roof. The main roof has strong incoming pressure and serious periodic incoming pressure. During the initial pressure and periodic pressure of the main roof, a large amount of gas is emitted from the goaf. The maximum gas emission concentration at the initial roof caving is 10%, and the maximum gas emission concentration at the periodic pressure is 9%

2 gas emission mechanism and law during the initial pressure and periodic pressure

when the main roof strata have not yet broken, the whole mined area is supported by the surrounding coal pillars, and the roof subsidence is not large. With the work moving forward, the roof exposed area gradually increases, the roof pressure increases, the surrounding coal body is gradually compressed and fractured, and a large amount of gas is released from the coal body. Because the air flow flows along the arc of the working face, the air flow velocity on the side near the working face is large, and the air flow velocity gradually decreases when it reaches the four or five rows of pillars of the working face. When it reaches the goaf, the air flow velocity is very small. There is no wind or breeze in the goaf, which cannot dilute the gas. The upper and inner parts of the goaf become the warehouse for gas accumulation

the pressure of the main roof acts on the support through the direct roof, and the support force of the support controls the main roof through the direct roof. When the main roof is about to break and collapse, the main roof above the goaf bends and sinks, and the supporting pressure in the coal wall reaches the maximum. This strong supporting pressure causes the direct roof and coal wall to be sheared and destroyed. When the exposed area of the main roof reaches the limit, the main roof breaks and collapses. The collapsed direct roof and main roof occupy the existing space of gas in the goaf, and a large amount of gas is squeezed out of the goaf and enters the upper corner, resulting in a large amount of gas gushing out of the goaf during the initial pressure

as the working face continues to advance, the rock stress in the fracture zone after the primary fracture of the main roof forms periodic pressure according to the change law of "stability instability re stability". During periodic pressure, the collapsed rock blocks also occupy the existing space of gas, causing a large amount of gas to gush out periodically in the goaf

3 countermeasures for the first caving and periodic pressure

the first caving on the left side of the 41st floor - 270m in mining area I. after one month, the upper part of the working face is advanced by 71m and the lower part is advanced by 65m. The caving area is large, and the first caving is very difficult. The periodic weighting step distance of this face is 17 ~ 25m. During periodic weighting, local roof is cut off along the coal wall, which is very serious to the support of the working face. In response to this situation, we have taken the following measures

(1) reasonably design the stope support, so that the stope support has sufficient initial support force, working resistance and compressibility. The working face selects 4 ~ 5 rows of single hydraulic props to manage the control roof, and ensures that there are 5% spare props. During the initial caving and periodic pressure, a row of berms shall be set on the first row of soft top to strengthen support and prevent pushing. The upper and lower ends are supported by four pairs of eight long steel beams, moving forward alternately

(2) determine the caving form according to the actual situation of the mining face. The 41 floors - 270m left side of the first mining area is arranged in a pseudo inclined way. During the initial caving, the mining adjustment method is adopted, and the mining adjustment at the upper end is adopted, so that the top plate of the upper half comes down first, and the caving is carried out section by section in turn. The method of regulating mining is fan-shaped regulating mining, that is, the head of the chute in the working face does not move, and the tail of the chute is regulated. The feeding mode of 3 short and 1 long or 4 short and 1 long is adopted in the production adjustment. The coal wall should be straightened every time the working face advances a whole cycle, so as to prevent the coal wall of the working face from "belly" bending. While adjusting production, set up a signal plug to observe the roof pressure. The signal top is made of round wood with a diameter of 16cm. The food packaging film (including large and small packaging) produced with the new brand of iquid XP has excellent toughness and heat sealing performance. A 5cm deep gap is cut in the middle. After the working face is advanced by 6m, the signal top shall be set with a column spacing of 30m. It shall be set every 7 cycles, and the signal top shall not be withdrawn. Attention must be paid to the adjustment and mining. After the adjustment of the working face, the adjustment and mining shall be stopped immediately and the normal progress shall be resumed. The working face cannot be adjusted into a false one, so as to prevent the upper roof from collapsing onto the lower pillar, resulting in a push collapse roof fall accident. Results after the upper part of the working face was pushed 74m, the upper roof first fell 40m along the strike, and the roof pressure was effectively released, realizing the expected top caving effect

(3) strengthen on-site management to ensure the friction coefficient function engineering quality of measured data. The mine establishes a leading group for initial caving and periodic pressure, with the production mine head as the group leader, the chief engineer as the Deputy group leader, and the production section chief, coal mining engineer, coal mining area chief, deputy production area chief, coal mining area technician, coal mining section chief and deputy section chief as the main members. Be responsible for following the shift to check the quality of mining face engineering, and timely supervise and rectify quality problems; In case of liquid leakage and unloading, the monomer prop shall be timely organized to raise the well for maintenance and timely supplement the insufficient part; Observe the signs of incoming pressure on the signal roof and hard wall, put forward the prediction of initial incoming pressure and periodic incoming pressure, and formulate targeted safety technical measures according to the actual situation on site; In case of danger, organize operators to withdraw in time to ensure safe production during the initial roof caving and periodic pressure

(4) strengthen the management of column return and top caving to prevent column return injury accidents. During the initial caving and periodic pressure, it is very difficult to return the column. When returning the column to the top, we always insist on working in groups of two people to achieve joint protection. One person shall retreat and one person shall observe the top plate. It is strictly forbidden to operate alone. When retreating the column, the operator must stand above the slope of the removed column and retreat between the first and second rows of supports. The length of the retracted drainage hook rope shall not be less than 3m. The column retractor must stand at the place where the support is complete to avoid accidents such as rope collapse, notch impact ≥ 10kj/m2, column collapse, hook throwing, rope breaking, etc. When returning the pillar in sections, the principle of bottom-up must be adhered to to to prevent falling gangue from rolling down and hurting people. When retreating the last few pillars at the junction of sections and dealing with buried pillars, the body must be protected and supported, and the principle of hitting first and retreating later must be adhered to

4 prevention and control measures of gas in goaf during roof pressure

(1) strengthen the management of ventilation system to prevent air flow short circuit. The ventilation doors of the mining area parking lot are interlocked. When opening to traffic, one ventilation door is opened and the other ventilation door is closed to ensure the normal ventilation of the mining face when opening to traffic

(2) increase the fresh air volume of the working face to prevent gas accumulation. Increase the air volume of the working face to 410m3/min, and set a fan in the upper lane to blow the upper corner, increase the air volume to dilute and take away the gas in time

(3) strengthen gas monitoring in the mining area to prevent gas from exceeding the limit. The working face is equipped with full-time tile inspectors and shift guards, who follow the machine to check the gas situation at the notch and the upper corner. If the gas is found to exceed the limit once, 30 yuan will be awarded. The ventilation Department and the safety supervision department shall assign special personnel to spot check the working conditions of the tile inspectors to prevent the missing and false inspection of the tile inspectors. The shift foreman, the tile inspector and the cadres entering the well all carry portable gas detectors. A portable tile detector is hung in the upper corner. A gas power-off instrument is set in the return air duct. The operators are equipped with an alarm miner's lamp. If the gas exceeds the limit, the operators are organized to withdraw from the working face in time

(4) strengthen the management of electrical equipment with higher machine cost to prevent electrical appliances from exploding. The mechanical and electrical department shall set full-time explosion-proof officers to check the explosion-proof condition of mechanical and electrical equipment, and timely repair and replace the explosion-proof equipment if found. The mining area power supply realizes "three special and two locking", that is, dual power supply, special transformer, special power supply line, special switch, wind power and gas power interlocking

(5) strengthen shooting management to prevent shooting accidents. Water cannon mud, cannon mud and emulsion explosives must be used for blasting. Strictly implement the "three person firing system" and the "one gun three inspection system"

(6) strengthen the inspection of entering the well and prohibit carrying fireworks. Personnel entering the well must bring a self rescuer, and it is forbidden to enter the well without a self rescuer. All personnel entering the well shall be checked, and those who are found to be carrying fireworks will be fined 10000 yuan

after long-term exploration, Dongbao mine has found out the law of gas activity in the hard roof and goaf of the first mining area, and summarized a set of hard roof management and high gas control methods. At present, the part above the elevation of - 200m in the mining area has been mined. The 36 floors of the downhill part have been mined to the elevation of - 270m, and the 41 floors have been mined to the elevation of - 320m. No roof and gas accidents have occurred, ensuring safe production

(Lang Fengqi, Cai leilin, Xianyu, zhangqingping)

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