Technical analysis and prevention of the accident of the topping of the working face

In the production of coal mines, in case the gap is greater than the working face mining height strike fault, the fault can be bounded, the face is divided into upper and lower two-stage, the intermediate digging trough for recovery. For the inclined working face where the fault drop is larger than the mining height, the cut hole should be excavated and moved to the new working face for recovery. However, no matter which kind of fault, the drop is less than the height of the coal seam, generally 1/3~1/2 of the height of the coal seam, and should be taken by the method of pushing hard.

Since the fault destroys the integrity of the roof of the working face, it will inevitably cause the change and redistribution of the pressure of the roof, which makes the maintenance of the roof of the working face difficult, and even causes a roof accident. Therefore, in the management of production technology, corresponding measures should be taken to prevent the occurrence of roofing accidents on the mining face due to changes in roof pressure.

1 Technical analysis of the roof accident caused by faults in the mining face According to the analysis of the roof accident in the mining face of Xima Coal Mine, the proportion of roof collapse due to fault level is more than 40%, and most roof accidents occur in the working face and fault. Oblique or near the fault intersection parallel to the fault. Due to different coal mining heights and drop differences, the impact on coal mining varies. Practice has proved that the inclined fault and the oblique fault have a great influence on the pressure of the top surface of the working face, and the flat pushing hard time is very prone to roof accident. In the mining face, there is a roof accident in the fault. The main reasons for the technical analysis are as follows.

(1) The fault destroys the integrity of the roof, causing damage to the pseudo-top, direct roof and old roof of the coal seam, which makes it difficult to form a whole roof, which is difficult to maintain, and the old roof loses balance. Due to the influence of mining, the pressure on the working surface increases. In particular, the old roof is affected by the fault, and the pressure does not directly act on the coal wall and the goaf filling, and it slides along the fault plane and loses the "hinged" state. At this time, the roof pressure per unit area must be significantly increased in the fault zone. If the pressure is increased according to the normal support strength, the pressure exceeds a certain value, which will inevitably cause a roof accident due to insufficient support strength.

(2) Theoretical analysis. Normal face caving roof pitch and is a fixed value depending on the coal seam roof slate. The pressure calculation formula given by the old top to the bracket is:

Q1=1/2H1L1R

In the formula, H1—the thickness of the direct top and the old top; L1—the breaking distance of the old top; R—the density of the rock.

The above formula indicates that the distance of L1 exceeds a certain value, and the pressure exerted by the old top on the bracket Q1 is increased, and it is necessary to adopt forced topping or strengthening support measures. The forced topping is mainly to open the shots and make the roof fall. The support measures are mainly to take the stone belt, the raft and the top line to lift the shed to enhance the stability of the bracket and prevent the roof from separating. When the old top is pressed, the bracket effectively supports the top plate.

In the case of a faulty mining face, if the rock bulk density RI is constant and the periodic pressure distance L1 is the same, the thickness of the rock above the coal seam is increased due to the fault damage, that is, H1 increases. It must result in an increase in the pressure Q1 acting on the stent. Therefore, when there is a fault, the pressure exerted by the old top on the stent is stronger than the normal pressure, which is proved by field practice. In terms of mine pressure theory, the old top pressure is not entirely borne by the working face, and its numerical value is difficult to quantify, calculate and analyze. The introduction of the formula only indicates the pressure of the old top when the working surface is pushed hard over the fault. Significantly increased, the most impact on the working surface, causing the working face to recover from the top is also the most likely.

(3) Technical reasons. In the preparation of the technical measures for pushing the hard surface through the fault, the strict measures for strengthening the support and recycling of the faults have been formulated, and it is also an important technical means to ensure that the working face does not cause roof collapse in the technical management.

(4) Reasons for production management. When the fault is usually crossed, the roof is broken, the undulations are uneven, and the coal seams vary greatly, which brings difficulties to production management. In the case of heavy production tasks, the quality of the project is often neglected, and the roof conditions of the working face are deteriorated. On the other hand, faults occur in various working faces, and they do not fall into the top when they are in fault. Therefore, people are numb in their minds. Sometimes they simply observe the cracks in the roof and faults, neglecting the strengthening of support and management, and thus causing a roof accident. . This is mainly due to the lack of understanding of important factors such as the fault-cutting roof, the failure of the roof and the pressure on the roof.

2 The main technical measures for preventing the roof from hitting the hard surface through the fault are to prevent the working face from falling over the fault. First, we should choose a reasonable roof management method and support form to determine the reasonable support density and choose a reasonable pillar model to make the roof. The amount of sinking is small, so that all the brackets on the working surface should be in a stable working state and have good stability.

(1) When conditions permit, avoid mining when the coal wall between the working face and the fault are parallel. The angle between the working face and the fault is greater than 20° to reduce the area of ​​the working surface exposed to the fault for maintenance.

(2) Maintenance of raft or stone belt. The method of rafting or stone belt maintenance is to hit one every 5~10 m along the length of the fault exposed on the working surface, and follow the movement. Until the fault plane is outside the cut line. The purpose is to stabilize the pillars, strengthen the support strength of the working face, and prevent the top plate from pushing the working face off the floor.

(3) Erection of mast support. The method of erecting the mast support is to maintain along the top row of the ramming column. You can hit a column with a column, or you can continue to play without gaps. If the pressure on the roof is relatively large and the fault damage is serious, the raft and the stone belt can be used together. Specific requirements may be specified in the operating procedures, as appropriate.

(4) Adjust the top control distance and the top step distance. When the working face is pushed hard over the fault, the fault section is appropriately increased to control the top distance, and the top step distance is reasonably determined, so that the pillars of the fault in the empty disc are recovered once, which is also advantageous for safe production. However, before recycling, the coal wall side of the fault shall not be less than the minimum control top distance, that is, the minimum control top distance specified in the operating procedures. The pillars to be recovered on the side of the fault empty road shall not be less than two rows of pillars for the last recovery. However, it must not exceed three rows. From the field experience, it is best to keep 2 to 3 rows in one recovery.

(5) Advance fault support position. In the event of a fault, in order not to affect the normal mining and mining of the working face, the vicinity of the fault should be advanced, that is, the excavation should be carried out in advance near the fault, and the general working face can support the alley. The form of support is shown in Figure 1. When dealing with faults, it is necessary to play with shallow eyes, less charge, and zero-zero.

(6) Other measures. Through the fault to strengthen the roof support, to prevent roof accidents, to prevent roofing or local rockfall, it is very important to maintain the stability of the working face support. According to the conditions of coal seam occurrence, the situation of geological structure,

In the actual production work, the following measures are also taken: 1 encrypting the pillars under the fault and increasing the supporting force; 2 lifting the shed or using the long column cap to maintain the fault breaking belt to prevent the roof from leaking and destroying the integrity of the roof.

In short, the hard push through the fault, not only limited to the above measures in the mining process, there are still many special requirements and specific practices, this report will not be discussed.

3 Conclusion

Pushing hard through fault recovery is one of the ways to improve the recovery rate, reduce the tunneling rate, and ensure the mining and connection.

In order to prevent the mining face from passing through the fault, the specific measures for preventing the roof are proposed for the conditions of the coal seam. Practice has proved that these measures are effective in field applications. Prevent the occurrence of roofing due to faults. In the case of different conditions, according to the specific circumstances, according to the actual situation of the site, there are selected applications. The safety technical measures are prepared to ensure the smooth progress of the mining face across the fault and achieve safe production.

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