Roof control of fully mechanized top coal caving face

1 Application of integrated mining technology in 3# coal seam

The 3# coal seam is the main coal seam of the Wulan Mine, accounting for 42% of the total reserves. From November 1992 to March 1993, the mine carried out industrial tests on fully mechanized top coal caving in the 33# coal seam. The technical appraisal committee composed of experts identified that the project technology has reached the domestic leading level, can effectively guide production, and promote its application in coal seams with similar conditions in China. After the successful test, the mining method of the 3# coal seam mainly adopts the fully mechanized top coal caving process. As of July 2002, the progress has reached 3,200m.

The arrangement of the fully mechanized caving face: the two wind lanes of the working face are arranged along the coal seam direction, and along the bottom plate, the trapezoidal bracket support made of mining 11# I-beam is used. A top plate is arranged along the top plate, which is offset from the working lane. The working face is cut along the bottom plate, and the inclined length is about 150m. The working face is 2.4m high (the normal support height of the bracket).

2 Analysis of the reasons for the topping of the fully mechanized caving face

The top plate of the fully mechanized caving face is actually the top coal overlaid on the support. According to the classification of the top plate, it should be a broken roof. The 3# coal seam has a Platt hardness coefficient of 0.6 to 1.2. Due to the influence and influence of various factors, the top of the work surface has repeatedly occurred in the front of the work surface frame, which seriously affects normal production and safety, and directly affects the advantages and benefits of the fully mechanized caving technology.

(1) The influence of coal rock properties. The root cause of the roof crushing of the coal mining face is that the roof is an unstable coal rock formation. The roof of the fully mechanized caving face is the coal seam, and the nature of the top coal on the support is one of the important factors leading to the fracture of the top coal. The No. 3 coal seam of Wulan Minefield is different in different mining areas, so that the control measures of the top surface of the working face are different. The 5321 working face, the 5331 working face, the 5332 working face, the 5333 working face and the 5334 working face of the northern and central mining areas, due to the relatively stable production of the coal seam, the joint cracks are not developed, and the hardness is higher than that of the mining area in the south wing. Analysis of the coal wall and roof control during the mining process, because the coal seam itself causes the leakage of the gang to cover only about 10%, and it is in the face of very obvious geological structures (such as faults, folds, etc.) Make the top plate difficult to control. The 5335 working face, 5326 working face and 5327 working face of the South Wing mining area, the accident of the roof leakage occurred during the mining process, nearly 90% of the analysis was due to the coal seam encounter geological structure (wrinkled soft coal area, small fault The group caused the cracks, the joints were very developed, the bedding was disordered, the bottom plate was abnormally bulged, and the mudstone pseudo-bottom appeared. In different fully mechanized caving face, the properties of coal seams have shown an important influence on roof control. From the perspective of roof control, we hope that the top coal covered by the support is complete and stable, but the top coal process itself requires that the top coal must reach a certain degree of fracture when it reaches the coal discharge. Therefore, the soft coal seam has better release. The top coal process is adopted, but it is unfavorable for the roof control.

(2) The role of mine pressure. The top coal in the fully mechanized top coal caving face is under the pressure of the mine, the supporting pressure of the coal wall in front of the working face and the self-gravity of the coal. The cracks occur and the separation layer gradually breaks down and falls behind the cutting line of the support. If the crushing has reached a certain level due to its own nature and external effects, there is a possibility that the front panel will fall. Analysis of the mining situation of 3# coal seam, the cycle pressure is not obvious, the working resistance of the bracket is generally small, the pressure point of the roof is moved forward, and it is unevenly distributed on the top beam of the bracket. After the top coal is moved forward of the bracket, Suspended ceilings rarely occur. The top coal in the front of the rack often cuts along the coal wall, but the coal body is not particularly broken, indicating that it has not been greatly squeezed. Therefore, the characteristics of the top coal caving process make the mine pressure on the 3# coal seam working face not obvious, and the occurrence of a large range of chip tops rarely occurs, so the impact of mine pressure on the roof control of the top coal caving face is not large. However, it should be clear that if there are other factors working together, the mine pressure will aggravate the deterioration of the stope and increase the difficulty of roof control.

(3) Personnel operations and labor organization factors. The top coal operation is different from the normal fully mechanized mining face in terms of operational and process organization requirements. The requirements for the operation of the roof control are to support in time, and to prevent the roof from falling, as much as possible, including the attention and handling of the front frame, the top leakage between the frames, and the chip. The top of the front beam of the fully mechanized caving support is often the broken top coal. The movement of the frame requires less drop of the support and the pressure is applied to the top. In the process arrangement, it is stipulated that the transfer drum should not exceed 3 rollers after the shearer. The technicians and construction personnel analyzed and summarized a large number of chip-topping accidents, and formulated corresponding measures for the 3# coal seam fully mechanized caving face moving process. Due to the nature of the coal seam and the pressure of the mine, the coal wall is crushed and broken before the support frame, and the depth of the gang is 0.4-0.6m. If the temporary support of the picking guard is used, the contact area between the guard plate and the coal wall is small, sometimes it is linear contact, the coal wall is not effectively supported, and the front roof is not improved. At the same time, due to man-made roof failure caused by operational errors, such as excessive down frame, improper bracket, inverted frame, bite frame, coal not discharged according to the coal mining process, etc., will also cause deterioration of the roof condition.

3 Fully mechanized caving work face to help the roof to deal with and prevent

After the fully mechanized caving face is used to help the roof, due to the broken top coal above the bracket, a large amount of broken top coal flows into the recovery space (in the conveyor, in front of the rack, in the space between the racks), the operation is interrupted, and the conveyor stops running. If you start the adventure conveyor continues to operate, it is possible to cause spalling and failing to expand, stone slate roof caving, conveyor being "crushed" and even affect the ventilation system face, sometimes lucky enough to have a large piece of coal gangue temporarily plugs No leaks, but the hidden dangers of the film help still exist, and the formation of "holes" above the bracket, posing a threat to the operation. Therefore, the comprehensive top-level work face should be based on prevention. Once the film has fallen, it must be managed to control its spread and then take appropriate measures.

3.1 film to help the roof to deal with

After the fully mechanized caving face is used to help the roof fall, the “crash wedge method” can be used to pass the fracture zone. This method is suitable for the case where there is a large block in the broken coal rock mass, and the one-sidedness is not too deep, and the hole is blocked by the wedge. Then strengthen the support to control the roof.

The “top net method” summed up by the construction personnel and technicians on the spot, when used alone or in combination with other methods, produces better results. After the roof fall loose depth of the shelf space filled with coal, spalling and failing is unknown, and when the top coal is crushed, the smaller the particles, the first attached to the front beam with a metal mesh, metal and wooden beams or steel beams with a single When the top of the body is facing the coal, when the resistance is large, the top of the coal in front of the truss beam can be used first; when the metal mesh is not long enough, the net can be added again; after seeing the coal gang, the single support is supported under the top beam. . In some deeper parts, the wedge is struck above the steel beam. After controlling the coal to prevent leakage, start the conveyor to transport the top coal. The top steel beam is strengthened from top to bottom and the coal gang is maintained. This method plays a very good role when the 3# coal seam passes through the soft coal area of ​​the geological structure belt.

There is also a situation in which there is an empty roof after the top of the film is raised. If the one-sided emphasis is on the top, it may delay the timing, but the top plate control is unfavorable. The empty top is not the top plate has been stabilized, but the temporary and relative. According to the actual situation at the scene, it is necessary to deal with it immediately, and it is not possible to delay the time. Otherwise, it will cause a bigger piece to fall. The roofing net can be used, and the frame can be lifted to the shed to close the empty roof area and support the coal wall. Of course, this is a very dangerous situation. It is necessary to use experienced workers to observe the roof and coal walls and clean up the safety passages. The lifting shed must have a certain supporting strength to prevent the top coal from slamming backwards and impacting the shed.

3.2 Prevention

From the previous analysis, it can be seen that the roof control of the fully mechanized caving face has its own characteristics. After the top plate is out of control, the impact is very great. Even if measures are taken, it will cause manpower, material waste, and even safety accidents. Therefore, prevention is even more important.

First of all, for the geological prediction of coal seams using fully mechanized caving technology, it is necessary to take preventive measures from the mining design to avoid hidden dangers for recovery. The layout of the working face and the selection of equipment must be considered to overcome the crushing of the coal body, which is conducive to the control of the roof. Generally, it is not suitable to arrange the bottom mining. The bracket should be fully closed to the top coal in front of the frame. Secondly, after mining, in the case of broken coal bodies and soft coal areas, it is necessary to formulate scientific and reasonable measures from personnel operations and implement them to reduce man-made gangs. The ideal method should be to solidify the coal, such as chemical injections. The water injection method was tested on site, that is, the water injection hole was arranged along the strike of the coal wall of the working face, and water injection was performed by dynamic pressure or static pressure. Our analysis believes that after water injection, the stress distribution in the coal has changed, which has increased the coal body adhesion to some extent, and may also change other physical properties, but how does water injection play a role in preventing the roof from falling? Further observation and research. In addition, the "early advance" method can also be used. Manually hand rubbing or wind smashing in the coal wall girders, erecting the shed, and maintaining the front of the rack and the coal gang to prevent the roof from falling when the coal is moved.

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