Roof caving coal mining based on roof strength and water hazard prevention method

Abstract

The present application belongs to the field of top coal caving and water disaster prevention, and particularly relates to a top coal caving and water disaster prevention method based on roof strength. The method comprises the following steps: for hard roof condition, dividing the coal seam into lower layer, middle layer and top layer; draining water in overburden rock; pre-splitting the top layer coal body; caving the lower layer, and caving the middle layer and top layer together; for soft roof condition, dividing the coal seam into lower layer, middle layer and top layer; constructing drainage borehole to drain water in overburden rock; caving the top layer by longwall caving method, and performing net laying operation during caving; caving the lower layer, and caving the middle layer. The top coal caving method of the present application considers the influence of roof strength on top coal caving rate, and gives the corresponding optimized process based on the strength of the roof. The top coal caving method of the present application can greatly improve the top coal caving rate, reduce the amount of gangue, and achieve water disaster prevention while ensuring the overall coal mining efficiency.

Description

Technical Field

[0001] This invention belongs to the field of top coal caving mining and water hazard prevention, specifically involving a method for top coal caving mining and water hazard prevention based on roof strength. Background Technology

[0002] When mining thick coal seams, the method of first mining the coal in the lower longwall working face and then releasing the top coal is called longwall top coal caving mining. The key equipment in top coal caving mining is the top coal caving hydraulic support. Compared with traditional hydraulic supports, it has a telescopic plate on the tail beam. The telescopic plate forms an opening at the tail beam to release the top coal, which is then transported out by a scraper conveyor under the tail beam.

[0003] For thick coal seams, the lower coal extraction method is generally the same as for ordinary medium-thick coal seams. After the lower coal is extracted, the upper top coal is broken behind the top coal caving hydraulic support due to mining activity, and can then be released from the caving hydraulic support's discharge port. However, after the lower part of the coal seam is extracted, not only the upper top coal but also the roof strata above it will fracture. This results in the top coal caving hydraulic support releasing not only top coal but also roof gangue. How to release as much top coal as possible and reduce the amount of roof gangue released has always been a research hotspot in this field, with the aim of increasing the overall coal seam extraction rate while reducing the overall workload.

[0004] In one section of our mine, the coal seam is approximately 8.0 meters thick and is mined using a top-coal caving method. For such a thick coal seam, a key technical challenge is how to increase the proportion of coal caving while reducing the amount of roof rock released, thereby improving the overall extraction rate of the thick coal seam. Furthermore, overburden water hazards can also affect the safe production of top-coal caving operations. Summary of the Invention

[0005] To address the problems of low top coal recovery rate, large amount of interbedded rock, and water hazards in thick coal seam top coal caving mining technology, this invention, based on the strength of the immediate roof, adopts different optimization schemes for different immediate roof strengths. This significantly improves the recovery rate of thick coal seams and achieves water hazard prevention while ensuring overall mining efficiency. Specifically, the top coal caving mining and water hazard prevention method based on roof strength proposed in this invention includes the following steps:

[0006] S1, determine the roof strength and coal seam strength. When the roof strength is significantly stronger than the coal seam strength, it is considered a hard roof condition; otherwise, it is a soft roof condition.

[0007] Preferably, in step S1, the top plate refers to the direct top.

[0008] Preferably, in step S1, a hard roof condition is defined as the roof is sandstone, and a soft roof condition is defined as the roof is mudstone.

[0009] S21, for hard roof conditions, the coal seam is divided into lower layer, middle layer and top layer; track roadway and transport roadway are arranged in the lower layer to form a top coal caving working face;

[0010] Drilling tunnels are constructed on the outer side of the top coal caving face.

[0011] Preferably, in step S21, the ratio of the thickness of the lower layer to the thickness of the middle layer plus the top layer is 1:2 to 1:1.

[0012] Preferably, in step S21, the ratio of the thickness of the middle layer to the thickness of the lower layer is 1:3 to 1:2.

[0013] Preferably, in step S21, the drilling tunnel is located outside the transport tunnel and is at the same elevation as the top layer.

[0014] S22 is a drainage borehole drilled from the drilling tunnel to the top overburden to drain water from the overburden and prevent water damage.

[0015] Pre-splitting boreholes are drilled from the top of the self-drilling roadway to the top layer of coal seam for pre-splitting.

[0016] S23 involves top coal caving and mining, mining the lower layers, and caving coal from the middle and top layers together.

[0017] S31. For soft roof conditions, the coal seam is divided into lower layer, middle layer and top layer, where the thickness of the middle layer is greater than the thickness of the floor fracture zone produced by mining the top layer.

[0018] Preferably, in step S31, the thickness of the top layer is 2-3m.

[0019] Preferably, in step S31, the middle layer includes the bottom fracture zone after the top layer is mined and the isolation layer.

[0020] Preferably, in step S31, the ratio of the thickness of the isolation layer to the thickness of the lower layer is 1:3 to 1:2.

[0021] Preferably, in step S31, the ratio of the thickness of the lower layer to the thickness of the middle layer is 1:2 to 1:1.

[0022] S32, arrange the top-level track roadway and the top-level transport roadway to form the top-level return roadway;

[0023] S33 is a drainage borehole drilled from the top layer track tunnel or top layer transport tunnel to the top overburden to drain water from the overburden and prevent water damage.

[0024] S34 uses the longwall caving method to mine the top layer. During mining, a mesh laying operation is carried out so that the soft roof collapses onto the metal mesh after the top layer is mined.

[0025] Preferably, in step S34, the metal mesh separates the collapsed roof caused by the top layer mining from the middle layer, and the mesh laying operation is carried out on the top beam of the hydraulic support for longwall mining or under the base of the hydraulic support for longwall mining.

[0026] S35 involves top coal caving and back mining, back mining of the lower layers, and coal caving of the middle layers.

[0027] The beneficial technical effects of this invention are as follows: The top coal caving mining process of this invention considers the influence of roof strength on the top coal release rate, and provides corresponding optimized processes based on the strength of the roof. Using the top coal caving mining method of this invention, the top coal release rate can be greatly improved while ensuring overall coal mining efficiency, reducing the amount of interbedded rock, and achieving water hazard prevention. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of a top-coal caving mining scheme under hard roof conditions;

[0029] Figure 2 This is a schematic diagram of a top-coal caving mining scheme under soft roof conditions;

[0030] In the diagram, coal seam 1; hard roof 2; lower layer 3; middle layer 4; top layer 5; track roadway 6; transport roadway 7; borehole construction roadway 8; in-seam borehole 9; soft roof 10; top layer track roadway 11; top layer transport roadway 12; floor fracture zone 13; isolation layer 14. Detailed Implementation

[0031] In one section of our mine, a coal seam reaches a thickness of approximately 8.0 meters and is mined using a top-coal caving technique. The immediate roof of this coal seam is mainly composed of mudstone and sandstone, while the floor is primarily sandy mudstone. For a coal seam approximately 8.0 meters thick, a key technical challenge is how to increase the proportion of coal caving while reducing the amount of gangue released from the roof, thereby improving the overall extraction rate of the thick coal seam. Furthermore, overburden water hazards can also affect the safe production of top-coal caving operations.

[0032] To address the aforementioned problems, this invention, considering the strength of the immediate roof, adopts different optimization schemes for different immediate roof strengths. This significantly improves the recovery rate of thick coal seams and achieves water hazard prevention while ensuring overall coal mining efficiency. For details, please refer to... Figures 1-2 The method for top-coal caving mining and water hazard prevention based on roof strength proposed in this invention includes the following steps:

[0033] S1. Determine the strength of the roof and the coal seam. The roof refers to the immediate roof. If the compressive strength of the immediate roof is three times or more than the compressive strength of the coal seam, or the tensile strength of the immediate roof is twice or more than the tensile strength of the coal seam, it is considered a hard roof condition, such as when the immediate roof is fine or medium-grained sandstone in this embodiment; otherwise, it is considered a soft roof condition, such as when the immediate roof is mudstone or sandy mudstone in this embodiment.

[0034] When the strength of the immediate roof is significantly greater than that of the coal seam, after mining the lower part of the coal seam, the upper roof coal is easier to break and has a smaller particle size than the immediate roof. Furthermore, the broken upper roof coal is located below the broken immediate roof, and the broken roof coal is easier to release from the coal outlet, with a larger release ratio.

[0035] When the strength of the immediate roof is not much different from that of the coal seam, after mining the lower part of the coal seam, both the upper roof and the immediate roof are easily broken and the broken particle size is not much different. Although the broken upper roof is located below the broken immediate roof, the broken immediate roof is easily mixed with the broken roof coal and discharged from the coal outlet because the broken particle size is not much different. This results in a small proportion of the discharged roof coal and a large amount of gangue (gangue here refers to the broken immediate roof).

[0036] S21, for hard cap conditions, such as Figure 1 As shown, above the coal seam 1 is a hard roof 2. If the immediate roof in this embodiment is fine or medium-grained sandstone, the coal seam 1 is divided into three layers, including the lower layer 3, the middle layer 4, and the top layer 5, with thicknesses of 3m, 1m, and 4m, respectively. A track roadway 6 and a transport roadway 7 are arranged in the lower layer 3 to form a top coal caving working face. The height range of the track roadway 6 and the transport roadway 7 is 3-4m.

[0037] On the outside of the top coal caving face, specifically on the outside of the transport roadway 7, a borehole construction roadway 8 is constructed at the same horizontal elevation as the top layer 5. The horizontal distance between the borehole construction roadway 8 and the lower layer transport roadway 7 is about 15m, so as to reduce the mutual influence between the borehole construction roadway 8 and the transport roadway 7 and facilitate the support and maintenance of the borehole construction roadway 8 and the transport roadway 7.

[0038] S22, drilling holes are drilled from the drilling roadway 8 to the top overburden to drain water from the overburden and prevent water hazards (not shown in the figure); along the advancing direction of the top coal caving face, drilling holes 9 are drilled sequentially from the cut-out at fixed intervals of 2m in the drilling roadway 8 towards the top layer 5 to pre-crack the top layer coal body in the top coal caving face, making the top layer coal body easier to break and with smaller particle size during top coal caving mining, thus facilitating the release of the top layer coal body;

[0039] S23, with a fracturing process of more than 30m after the top layer, top coal caving is carried out in the longwall face. Specifically, the lower layer 3 is caved, and the middle layer 4 and the top layer 5 are caved. During caving, the middle layer 4 plays an isolation role to prevent the pre-cracked top layer coal from leaking out from the front of the top coal caving hydraulic support. After caving, the middle layer 4 is broken by the mining stress behind the top coal caving hydraulic support and is released from the caving port together with the broken coal of the top layer 4.

[0040] Because the middle layer 4 is close to the top beam of the hydraulic support for top coal caving, the movement of the support will cause cracking in the middle layer 4. In addition, after the hydraulic support for top coal caving is moved, the coal body in the middle layer 4 will break under its own weight and the pressure of the coal and rock mass above it, and the broken particles are small. The hard roof 2, due to its high hardness, will break, but the block size is large, making it difficult to flow downward into the coal discharge port and difficult to discharge from the coal discharge port.

[0041] S31, for soft-top conditions, such as Figure 2 As shown, the soft roof 10 is above the coal seam 1. If the direct roof of this embodiment is mudstone or sandy mudstone, the coal seam 1 is divided into three layers, including the lower layer 3, the middle layer 4, and the top layer 5, with thicknesses of 3m, 3m, and 2m, respectively. The upper 2m of the middle layer will be broken due to the mining of the top layer 5. The upper 2m of the middle layer 2 is located within the bottom fracture zone 13 after the top layer is mined. A 1m coal seam is left between the bottom fracture zone 13 and the lower layer 3 as an isolation layer 14. The 1m isolation layer 14 and the aforementioned bottom fracture zone 13 together form the middle layer 4.

[0042] S32, in the top layer 5, a top layer track lane 11 and a top layer transport lane 12 are arranged to form a top layer 5 return lane, and the lane height of the top layer track lane 11 and the top layer transport lane 12 is 2m-4m;

[0043] S33, drilling a drainage hole from the top layer track tunnel 11 or the top layer transport tunnel 12 to the top overburden to drain the water in the overburden and prevent water damage (not shown in the figure).

[0044] S34. The top layer 5 is mined using the longwall caving method (not top coal caving). During the mining, a mesh laying operation is carried out so that after the top layer 5 is mined, the soft roof 10 collapses onto the metal mesh. The metal mesh separates the collapsed roof caused by the mining of the top layer 5 from the middle layer 4. The mesh laying operation can be carried out on the top beam of the hydraulic support in longwall mining (laid on the bottom surface of the soft roof 10) or under the base of the hydraulic support in longwall mining (laid on the top surface of the middle layer).

[0045] S35, track roadway 6 and transport roadway 7 are arranged in the lower layer to form a top coal caving working face. The height range of track roadway 6 and transport roadway 7 is 3-4m. The lower layer 3 and the middle layer 4 are mined together using the top coal caving process. Specifically, the lower layer 3 is mined and the middle layer 4 is caving. During the mining, the 1m thick isolation layer 14 at the bottom of the middle layer 4 plays an isolation role to prevent the broken coal body in the bottom plate fracture zone 13 generated by the mining of the top layer 5 (i.e., the already broken coal body in the upper 2m of the middle layer) from leaking out from the front of the top coal caving hydraulic support. After mining, the coal body in the middle layer 4 is broken and released from the caving port behind the top coal caving hydraulic support due to the mining stress. Although the soft roof 10 is already broken and will be further broken, it will not enter the caving port due to the metal mesh isolation.

[0046] Because the 1m thick isolation layer at the bottom of the middle layer 4 is close to the top beam of the hydraulic support for top coal caving, the isolation layer will be cracked when the support is moved. In addition, after the hydraulic support for top coal caving is moved, the coal in the isolation layer 14 will be broken under its own weight and the pressure of the coal and rock mass above it. The broken particles are small and are discharged from the coal outlet together with the broken coal in the bottom plate broken zone 13 (the broken coal in the upper 2m of the middle layer 4).

[0047] Of course, the above description is only a preferred embodiment of the present invention. The present invention is not limited to the above-described embodiments. It should be noted that any equivalent substitutions or obvious modifications made by those skilled in the art under the guidance of this specification fall within the scope of this specification and should be protected by the present invention.

Claims

1. A method for top-coal caving mining and water hazard prevention based on roof strength, characterized in that, Includes the following steps: S1. Determine the strength of the roof and the coal seam. The roof refers to the immediate roof. If the compressive strength of the immediate roof is three times or more than the compressive strength of the coal seam, or the tensile strength of the immediate roof is twice or more than the tensile strength of the coal seam, it is considered a hard roof condition; otherwise, it is considered a soft roof condition. S21, for hard roof conditions, the coal seam is divided into lower layer, middle layer and top layer; track roadway and transport roadway are arranged in the lower layer to form a top coal caving working face; Drilling tunnels are constructed on the outer side of the top coal caving face. S22 is a drainage borehole drilled from the drilling tunnel to the top overburden to drain water from the overburden and prevent water damage. Pre-splitting boreholes are drilled from the top of the self-drilling roadway to the top layer of coal seam for pre-splitting. S23 involves top coal caving and mining, mining the lower layers, and caving coal from the middle and top layers together. S31. For soft roof conditions, the coal seam is divided into lower layer, middle layer, and top layer, where the thickness of the middle layer is greater than the thickness of the floor fracture zone produced by mining the top layer; the ratio of the thickness of the isolation layer to the thickness of the lower layer is 1:3 to 1:2; the ratio of the thickness of the lower layer to the thickness of the middle layer is 1:2 to 1:

1. S32, arrange the top-level track roadway and the top-level transport roadway to form the top-level return roadway; S33 is a drainage borehole drilled from the top layer track tunnel or top layer transport tunnel to the top overburden to drain water from the overburden and prevent water damage. S34 uses the longwall caving method to mine the top layer. During mining, a mesh laying operation is carried out so that the soft roof collapses onto the metal mesh after the top layer is mined. S35 involves top coal caving and back mining, back mining of the lower layers, and coal caving of the middle layers.

2. The method for top-coal caving mining and water hazard prevention according to claim 1, characterized in that, In step S1, a hard roof condition is defined as the roof is sandstone, and a soft roof condition is defined as the roof is mudstone.

3. The method for top-coal caving mining and water hazard prevention according to claim 1, characterized in that, In step S21, the ratio of the thickness of the lower layer to the thickness of the middle layer plus the top layer is 1:2 to 1:

1.

4. The method for top coal caving mining and water hazard prevention according to claim 3, characterized in that, In step S21, the ratio of the thickness of the middle layer to the thickness of the lower layer is 1:3 to 1:

2.

5. The method for top-coal caving mining and water hazard prevention according to claim 1, characterized in that, In step S21, the drilling tunnel is located outside the transport tunnel and is at the same elevation as the top layer.

6. The method for top-coal caving mining and water hazard prevention according to claim 1, characterized in that, In step S31, the thickness of the top layer is 2-3m.

7. The method for top coal caving mining and water hazard prevention according to claim 6, characterized in that, In step S31, the middle layer includes the bottom fracture zone after the top layer is mined and the isolation layer.

8. The method for top-coal caving mining and water hazard prevention according to claim 1, characterized in that, In step S34, the metal mesh separates the collapsed roof caused by the top layer mining from the middle layer. The mesh laying operation is carried out on the top beam of the hydraulic support in longwall mining or under the base of the hydraulic support in longwall mining.

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