Under certain geological conditions, mining height is the most fundamental factor in forming the destructive influence of the cover layer. The higher the mining height, the more severe the damage to the cover. And it also directly affects the amount of sinking of the top surface of the working face.
For obtaining roof subsidence L S L at the control from the top, the linear patterns may be reduced to a certain distance from the rock face displacement curve.
The amount of roof sinking in the mining face is directly proportional to the height of the mining and the top distance.
Second, the impact of the speed of the work surface
1. The sinking of the top surface of the work surface is a process of time.
As time increases, the amount of roof sinking also increases.
Therefore, some people think that "accelerating the speed and shortening the time of each cycle of the working surface will inevitably reduce the amount of sinking of the roof, so that the pressure of the roof can be removed."
2. The foreign measurement data proves that after the acceleration speed is increased, the sinking speed of the roof is also increased.
3. According to the actual measurement, the roof sinking is more intense when falling coal and topping, and it is more moderate in normal times.
(1) When the coal is dropped, the control top distance of the mining face is increased, the stress balance in front of the coal wall is destroyed, and the supporting pressure has a process of moving deep into the coal wall; on the other hand, when the coal is dropped, With the advancement of the working face, the A rock block gradually became unstable.
(2) When the roof is lowered, removing the bracket on one side of the gob is equivalent to removing a part of the supporting force on the overburden and equivalent to moving the P forward a distance, that is, reducing value.
The influence range of the topping is 10~20m along the working surface, and the severe impact range is 5~10m.
4 Conclusion
(1) Speed ​​up the advancement of the working face is actually shortening the time interval between falling coal and topping and from topping to falling again. The result will inevitably reduce the amount of roof sinking caused by the usual time influence, but it must not Eliminate the majority of the effects of the two processes of falling coal and topping. Because the effects of falling coal and topping are completed in a short period of time (1~2 hours).
(2) It is impossible to speed up the advancing speed to the extent that the overburden is broken. The maximum shear force always occurs at the occlusion point near the coal wall. In this sense, it is unlikely that the mine pressure will be removed.
Third, the impact of mining depth
The greater the depth of mining, the greater the stress of the original rock.
The mining depth shows the obvious pressure on the mine roadway.
There are two different perspectives on the mining face.
One believes that although the depth has a great influence on the supporting pressure in front of the mining face, the mine pressure on the mining face may not be very serious. The other thinks that there is an impact.
Fourth, the impact of the inclination of the deposit
1. As the dip angle of the deposit increases, the amount of subsidence of the roof will gradually become smaller. The weight of the overburden will increase the tangential slip force along the plane due to the change of the dip angle, while the vertical force acting on the layer will be It has become smaller.
2. Due to the increase of the dip angle, the meteorite falling in the goaf may slide along the bottom plate, thus changing the movement law of the overlying strata.
3. When the longwall mining is inclined, the rock movement mode also changes.
5. Mine pressure appears in stratified mining
Artificial false top, broken rock.
1. The pressure of the old top is generally mild or not obvious, and the pressure step is small;
2. The bracket is loaded small;
The dynamic load of the first layer becomes a static load.
3. The amount of sinking of the top plate becomes larger.
Above the lower stratified working surface is the artificial false top and the bottom is the coal bottom. The stiffness of the "support-surrounding rock" system is smaller than that of the first layer.
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