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Development Law of Overlying Strata in Coal Mining Face in Working Face Advancing Direction
Release time:
2022-12-22
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Development Law of Overlying Strata in Coal Mining Face in Working Face Advancing Direction
1. Direct top first collapse
After the long-wall coal mining face starts from the cutting hole, the hanging dew span of the direct roof increases continuously, and the bending and sinking under the action of self-weight also increases continuously. Generally, after the span of the direct roof reaches 6~20m, the direct roof begins to collapse.
Falling. When the caving thickness of the direct roof reaches 1.5~2 times of the mining height (if it cannot be reached, the measure of manual forced caving can be adopted) and the caving length reaches more than half of the length of the coal mining face, it is called the first caving of the direct roof.
The span of the first collapse of the direct roof is called the initial collapse step as shown in Figure 3-6.
Fig. 3-6 Initial collapse of direct roof
The strength of the rock stratum of the direct roof itself is large and small, and there may be various cracks in the direct roof, so the difference in the size of the initial caving step is relatively large.
2. Basic top pressure for the first time
After the first collapse of the direct roof, the coal mining face continues to move forward. With each return to the top of the column, the direct roof above the goaf also collapses. The volume of the roof shall be increased after collapse and crushing, and the broken body
The ratio of the product to the original volume is called the rock's fragmentation coefficient. When the rock is just broken, the crushing expansion coefficient is generally 1.25~1.5. If the thickness of the direct top is equal to or greater than 2~4 times of the mining height, the direct top can fall behind.
Fill the goaf, as shown in Figure 3-7.
As the caved direct roof is compacted, the basic roof rock layer will sink, bend and fracture, but these activities will affect the working surface. Figure 3-7 The goaf will be filled after the caved direct roof is compacted.
The sound is very small, that is, the basic top pressure is not obvious on the working face.
If the goaf is not filled after the direct top collapse, the basic top is above the goaf in the state of double fixed fulcrum beams at the beginning, and the basic top rock beam presses the quality of itself and its overlying strata onto the coal pillars around the working face, then the working face will not be affected by the basic top pressure. As the working face continues to advance, the span of the basic top rock beam becomes larger and larger, and the basic top will gradually bend and sink. When the double fixed fulcrum beam reaches the limit span, it will break and sink, as shown in Figure 3-8a.
At this time, the sinking of the top plate of the working face is accelerated, the coal wall piece is serious, and the force of the pillar is increased. when the coal mining working face crosses the basic top fracture line, the phenomenon of step sinking of the top plate may even occur, as shown in fig. 3-8b. This is the first time that the basic roof has been pressed since the beginning of coal mining in the working face, which is called the first time that the basic roof has been pressed. The distance from the cutting hole to the initial pressing of the basic top is called the initial pressing step distance of the basic top, which is generally 20~35m. After that, the working face entered the positive
Regular coal mining period.
a-Basic roof fracture and subsidence;
B- Roof step sinking
Fig. 3-8 Initial Pressure of Basic Top
3. Basic top cycle to press
After the basic roof is pressed for the first time, as the working face continues to advance, the basic roof rock beam will periodically break and sink. In the working face, the roof sinking will accelerate periodically, the coal wall will be serious, the pillar force will increase, and even the roof will appear on the platform.
Phenomena such as step sinking are called basic top cycle pressure (Figure 3-9). The periodic fracture distance of the basic roof rock beam is called the pressing step distance of the old roof period, which is generally 1/2~1/4 of the initial pressing step distance of the basic roof.
a-basic roof fracture subsidence;
B- roof abutment theory sinking
Figure 3-9 Basic Top Cycle Pressure
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