1 Reasons for local roofing accidents and preventive measures
Local roofing accidents occur during the advancement of the mining face. Such accidents occur under the conditions of broken roof (such as shale , coal roof, regenerative roof, etc.). According to the mining process of the mining face and the causes of the accident, such accidents can be further divided into: local roofing accidents occurring during coal mining and local roofing accidents occurring during the column returning process.
1.1 Analysis of the cause of the accident
The local roofing accident occurred during the coal mining process. The main reason is that the broken roof was not supported in time during the coal mining process. The large area of â€‹â€‹the roof was exposed and the roof was suspended for too long, resulting in direct deformation of the roof. Destruction, or, although the broken roof was timely supported, due to the poor quality of the pillar support, the direct roof was partially collapsed. The main cause of roof collapse occurred during the returning process. The main reason is that the operation mode of the return column is unreasonable. First, the pressure column is returned, causing the surrounding broken roof to fall, causing the large piece of stone to push down the pillar, so that the adjacent broken roof loses support. Caused.
1.2 preventive measures
(1) On the basis of understanding the nature of the roof, carefully predict and forecast the situation of the broken roof. In the process of coal mining, it is necessary to strengthen the awareness of safety precautions, carefully observe the deformation of the roof, and find out the problems in a timely manner without leaving any troubles.
(2) Reasonably select the direction of advancement of the working face and the mining process. In order to prevent the top plate from being exposed, the amount of sinking is increased, and the crushing is intensified, which causes the roof to fall, and the working face should be pushed as far as possible. In the mining process, if the blasting is adopted, the small-scale small coal should be adopted to open the window to prevent the large area of â€‹â€‹the roof from being exposed. If it is the machine, the single-drum shearer should be selected to minimize the space without the column. Width, reducing the exposed area of â€‹â€‹the top plate.
(3) Take reasonable support methods. In the process of pushing the mining face, the practical experience proves that under the condition of the broken roof, when supporting, the bare roof must first be supported. Therefore, the roof exposed after coal mining should be timely supported. In the supporting method, the vertical girders should be hung as far as possible, and the reasonable supporting density should be ensured to be compatible with the crack spacing.
(4) Strengthen the quality of the support of the pillars. When the quality of the pillars is poor, the stress on the roof is uneven due to uneven stress on the roof, which destroys the integrity of the roof. When the pillar is supported, the initial support force of the pillar is insufficient, causing the roof to have excessive separation or premature fracture at the initial stage of exposure, which destroys the integrity of the roof itself and causes local roofing. Therefore, when supporting the pillars, the pillars cannot be supported on the floating research, and it is necessary to find the brackets for the real top and the solid bottom to ensure the overall working characteristics of the bracket. In addition, it is necessary to increase the initial support force of the pillar as much as possible. At present, it is generally considered that the initial support force is 50% of the working resistance.
(5) Take the correct method of returning to the column. Taking the correct method of returning to the column is an important part of preventing the roof from falling. In the process of mining, the operating rules of the working face must be strictly implemented, and the correct column return method should be adopted to ensure uniform support of the pillars, prevent the pressure of the roof plate from concentrating to the local pillars, and make the pillars load unevenly, resulting in partial roof fracture to the column working zone. It is difficult.
2 Causes and control measures of the topping accident caused by direct top movement
2.1 Conditions of the accident
(1) Coal seam conditions. Most roof accidents occur when a coal seam thickness exceeds 1.5 m, a coal seam with a dip angle greater than 20 o, or a coal seam below the layer. In this case, the roof of the coal seam has sufficient space for movement, and the roof plate will generate a large sliding force in the oblique direction under the action of its own weight. At this time, under the traction of the sliding force, the top plate is prone to cracks and the crushing is intensified.
(2) Technical conditions for mining. Before the old top is pressed, due to the small amount of roof sinking at this stage, the pressure on the bracket is small, and the direct top is easy to separate from the layer, resulting in a decrease in the stability of the bracket and easy to be pushed down, or due to the caving of the goaf. Pushing down the pillar; causing local roof failure in the working face during coal mining and roofing, causing the roof to lose its support to the lower rock layer and the upper rock layer to make it; the working surface support is unreasonable, and the pillar initial support is low. The auxiliary structure has a large amount of compression, the bottom of the pillar is drilled, causing the top plate to be separated from the layer, and due to improper support, the direction of the strut reaction force is wrong, and the stability is low, which causes the support of the working face to prevent the roof from sliding down.
2.2 Control measures
(1) It is necessary to strengthen the daily roof management work of the mining face to prevent the occurrence of local roofing accidents on the mining face.
(2) Do a good job in predicting and forecasting the roof condition. First, it is necessary to strengthen the prediction of the possibility of the roof falling, and predict whether there is a falling coal seam condition in the coal roof; whether the roof is cut in the oblique direction and lose the upper portion; whether there is room for the roof to slide down. Secondly, according to the phenomenon that the coal wall slab, the roof sinking amount and the pillar load have obvious changes, the location and time at which the roof can slide down are judged, and the control and management are carried out in time.
(3) Carry out the correct support control design. The sliding force of the top plate in the oblique direction can generally be estimated by the following formula:
Where M is the direct top thickness of the slip, m;
Lâ€”recovery work surface control top distance, m;
Lâ€”the range in which the top plate may slide down in the oblique direction, m;
Xâ€”the coal seam inclination angle, o;
Râ€”direct top weight, t/mâŠƒ;
According to the estimated sliding force of the above formula, determine the number of inclined sheds to increase the ability to resist the roof sliding, improve the initial support of the pillars, ensure sufficient support resistance, and prevent direct separation from the layer; Cut the top line, set up a column or row of columns, and control the roof to sink. Practice has proved that, in a case where conditions permit, the use of hydraulic prop struts plus or metal rubbing inclined roof Roof control, the effect is significant.
(4) Pay attention to the effect of bracket support. The support of the mining face support must be adapted to the situation of the mine pressure. When supporting, the pillar must have a certain angle of the mountain.
In short, comprehensive preventive measures should be taken for the roof accident of the mining face. At the same time, according to the specific geological conditions of the coal seam, especially the roof conditions of the coal seam, reasonable and effective technical measures should be selected to prevent the roof accident from happening. Achieve good technical and economic results.
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