Method for improving the recovery of top coal based on roof strata fracturing

Abstract

The present application belongs to the field of top coal caving mining method, and particularly relates to a method for improving top coal caving recovery rate based on roof strata fracturing. In the initial mining period, the present application creatively proposes to fracture the coal rock mass behind the cut, so that the gangue generated by the fractured coal rock can replace the broken top coal which needs to be left in the goaf in the traditional top coal caving mining, and on the basis of preserving the buffer to the roof, reducing the impact and protecting the function of the hydraulic support, the top coal in the initial mining period can be normally caved / recovered. In the final mining period, it is proposed to construct a filling retaining wall in the preparation roadway and reserve a caving chamber, the gangue generated by the fractured roof is used to replace the broken top coal which needs to be left in the goaf in the top coal caving mining, and the recovery of the top coal on the stop line side is realized. For the end side / two roadway sides, the present application proposes to construct a caving chamber in the coal pillar, the gangue generated by the fractured roof is used to replace the broken top coal which needs to be left in the goaf in the top coal caving mining, and the recovery of part of the end side / two roadway side top coal is realized.

Description

Technical Field

[0001] This invention belongs to the field of top coal caving mining methods, specifically relating to a method for improving the top coal caving recovery rate based on roof strata fracturing. Background Technology

[0002] Depending on the geological conditions such as coal seam thickness and dip angle, as well as the geological structure and surface structures, different mining techniques are employed. Currently, commonly used methods include: fully mechanized roof caving mining (generally referring to mining the entire thickness of the coal seam in a single operation), backfilling mining, and fully mechanized top-coal caving mining (used for mining thicker coal seams). The greater the thickness of the coal seam mined in a single operation, the greater the impact of roof collapse on the mining area, and the larger the required hydraulic supports. Due to technical limitations, the maximum maximum height that can be mined in a single operation is currently about 8 meters. However, due to equipment costs and coal seam conditions, even coal seams with a thickness of 6 meters are often mined using top-coal caving. Coal seams thicker than 8 meters are almost exclusively mined using top-coal caving.

[0003] The top-coal caving mining method divides the coal seam into two layers in height. A coal mining machine mines the lower layer, and then, based on the characteristics of fractured top coal caused by mine pressure, the top layer is released through a vent at the rear of the top-coal caving support (the coal mining machine is in front of the hydraulic support), thus enabling the mining of thick coal seams. However, in the initial mining stage of top-coal caving, near the cut-off side, only the coal mining machine cuts the lower layer without releasing the top coal. This uses the fractured top coal to buffer the fall of the broken roof, preventing the goaf from being too open and causing a large initial impact from the roof collapse, protecting the hydraulic support, and facilitating the subsequent orderly collapse of the roof. On the stop-mining line side, in the final mining stage of top-coal caving, near the exit roadway (retreat passage), only the coal mining machine cuts the lower layer without releasing the top coal. The fractured top coal provides support for the (fractured) roof, reducing the surrounding rock pressure at the exit roadway, ensuring the stability of the exit roadway and its surrounding rock, and safely retrieving the hydraulic support and other mining equipment. In addition, transitional hydraulic supports and / or end hydraulic supports will be set on both sides of the working face (both ends). At this position, only the coal mining machine will cut down the coal seam without releasing the top coal. The broken top coal will be used to support the (broken) roof, thereby reducing the surrounding rock pressure at both roadways and maintaining the stability of both roadways to ensure safe mining.

[0004] In other words, the top coal around the top coal caving face is not released and is allowed to collapse into the goaf, which inevitably leads to resource waste, especially when the release is relatively large. Therefore, how to increase the release rate of top coal around the top coal caving face, thereby increasing the coal recovery rate and reducing resource waste, under the premise of safe mining, has become an urgent problem for mining companies to solve. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention proposes a method for improving top coal caving recovery rate based on roof strata fracturing, comprising the following steps: S1: Construct fracturing boreholes in the coal and rock strata and roof at the same location as the top coal behind the cut; construct roof cutting boreholes in the roof directly above the cut, close to the back wall of the cut; mine the bottom coal; fracture the coal and rock strata and roof through the fracturing boreholes; release the broken top coal through hydraulic supports; mine the entire coal seam using the top coal caving process until mining is close to the stop line. S2: Pre-excavate the working roadway and drill fracturing boreholes into the suspended roof; when the working face is back-mined to a set distance from the stop line, only bottom coal is mined and top coal is not released; when the working face is back-mined to the working roadway, the hydraulic supports are withdrawn sequentially along the axis of the working roadway and the filling retaining wall is constructed, with a coal release chamber reserved inside the filling retaining wall; after the withdrawal is completed, the broken top coal is released from the coal release chamber. S3: Construct the ventilation roadway of the next working face adjacent to the machine roadway of the already mined working face, and drill fracturing holes into the suspended roof; construct a coal discharge chamber in the coal pillar along the axial direction, and discharge the broken top coal from the coal discharge chamber; S4: Refer to steps S1-S3 and sequentially return each working face within the mining area.

[0006] Preferably, in step S1, a drilling site is constructed in the machine tunnel, and a fracturing borehole is constructed from the drilling site.

[0007] Preferably, in step S1, the roof includes roof one and roof two. Roof one is the rock stratum above the coal seam that includes the basic roof, and roof two is the rock stratum within a certain thickness range above the basic roof. The fracturing borehole is constructed at least in roof one of the roof, and the cutting borehole is constructed only in roof one, forming a cut of a certain width.

[0008] Preferably, in step S1, a crack-causing borehole is also drilled into the top plate above the cut eye.

[0009] Preferably, in step S1, after the broken top coal is released, the gangue generated by the fractured roof and coal and rock strata enters the goaf to replace the released broken top coal.

[0010] Preferably, in step S2, fan-shaped fracturing boreholes are constructed at intervals between the first and second roof slabs along the axial direction of the mining roadway, with the inclination angle of the fracturing borehole closest to the stop line being consistent with the rock strata collapse angle.

[0011] Preferably, in step S2, only the bottom coal is mined without releasing the top coal. The broken top coal is used to support the suspended roof, thereby reducing the pressure on the surrounding rock at the exit roadway and ensuring the stability of the exit roadway and its surrounding rock.

[0012] Preferably, in step S2, a coal release chamber is reserved at set intervals within the filling retaining wall; a portion of the broken top coal left in the goaf is released in advance, and then the roof is fractured through fracturing boreholes; then as much broken top coal as possible is released.

[0013] Preferably, in step S3, the ventilation roadway of the next working face is constructed by excavating along the goaf, and a coal pillar with a width of 8-10m is left between the ventilation roadway and the machine roadway.

[0014] Preferably, in step S3, several rows of fan-shaped fracturing boreholes are drilled at intervals between the roof slab one and roof slab two on the side of the machine tunnel along the axial direction, and the inclination angle of the fracturing borehole closest to the ventilation tunnel is consistent with the rock stratum collapse angle.

[0015] Preferably, in step S3, a coal release chamber is constructed at set intervals within the coal pillar; a portion of the broken top coal left in the goaf is released in advance, and then the roof is fractured through fracturing boreholes; then as much broken top coal as possible is released.

[0016] Preferably, the method further includes step S5: referring to step S3, constructing a coal discharge roadway on the side of the ventilation roadway of the first mining face to recover the broken top coal left in the goaf on the side of the ventilation roadway of the first mining face; constructing a coal discharge roadway on the side of the machine roadway of the last mining face to recover the broken top coal left in the goaf on the side of the machine roadway of the last mining face.

[0017] Preferably, in step S5, a coal release roadway is constructed by excavating along the goaf, and the width of the coal pillar between the coal release roadway and the ventilation roadway of the first mining face, and between the coal release roadway and the machine roadway of the last mining face, is 4-6m.

[0018] Beneficial technical effects: 1. In the initial mining stage, this invention creatively proposes fracturing the coal and rock mass behind the cut-off, thereby allowing the use of gangue generated from the fracturing coal and rock strata to replace the broken top coal that needs to be left in the goaf during traditional top coal caving mining. While retaining the functions of buffering the roof, reducing impact, and protecting the hydraulic supports, it enables the top coal in the initial mining stage to be released / recovered normally. In addition, because the basic roof is cut, it can be broken like a cantilever beam, changing the initial pressure to periodic pressure. This facilitates the monitoring of the roof movement and the prediction of its breaking timing based on the monitoring results, changing the disadvantage of the difficulty in predicting the breaking timing of the traditional initial pressure, which requires leaving broken top coal in the goaf.

[0019] 2. In the final stage of mining, this invention, while ensuring safety through traditional top coal caving mining methods, creatively proposes to construct a backfill retaining wall and reserve a coal release chamber in the exit roadway, then release the broken top coal and fracture the roof. This allows the gangue generated from the fractured roof to replace the broken top coal left in the goaf during top coal caving mining, thus realizing the recovery of the top coal on the side of the stop mining line.

[0020] 3. For the end face / two roadway sides, this invention, while ensuring safety through traditional top coal caving mining methods, creatively proposes to use goaf excavation for the ventilation roadway of the next working face, and to use goaf excavation for the ventilation roadway side of the first working face and the machine roadway side of the last working face for dedicated coal release roadways; and to construct coal release chambers in the coal pillars, then release the broken top coal, and fracture the roof, so that the gangue generated by the fractured roof can be used to replace the broken top coal left in the goaf during top coal caving mining, thereby realizing the recovery of part of the top coal on the end face / two roadway sides. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the coal release area during top coal caving mining in the existing technology; Figure 2 This is a schematic cross-sectional view of the method for releasing top coal on the side of the cut in this invention; Figure 3 This is a schematic cross-section of the area where no coal is released on the side of the stop line during top coal caving mining in the existing technology. Figure 4 This is a schematic diagram of the construction cross-section of the fracturing borehole in the method for releasing top coal on the side of the stop mining line in this invention; Figure 5 This is a plan view of the coal release method on the side of the stop mining line in this invention. Figure 6 This is a schematic diagram of the cross-sectional view of the fracturing borehole construction in the method for releasing coal at the top and bottom ends of the present invention. Figure 7 This is a planar schematic diagram of the coal discharge method at the top and bottom ends of the present invention. In the diagram: 1-Ventilation roadway; 2-Stop mining line; 21-Containment roadway; 22-Coal pillar; 3-Machine roadway; 4-Cut-out; 5-Coal seam; 51-Bottom coal; 52-Roof coal; 53-Fracturing roof coal; 54-Backfilling retaining wall; 55-Coal discharge chamber; 61-Roof 1; 62-Roof 2; 63-Roof cutting borehole; 64-Fracturing borehole; 65-Gange; 7-Coal discharge roadway; 8-Drilling area; 9-Coal pillar. Detailed Implementation

[0022] The invention will now be further described with reference to the accompanying drawings.

[0023] This specific implementation method takes the No. 2 mining area of ​​Zhaoxian Coal Mine as an example. The No. 2 mining area of ​​Zhaoxian Coal Mine mines the Jurassic Yan'an Formation No. 3 coal seam, with a thickness of 8.4–20.78 m, an average thickness of 13 m, a dip angle of 3°–19°, an average dip angle of 8°, a burial depth of 336.0 m–516.0 m, and a mining elevation of +1055.7–+946.6 m. For example... Figure 1-3 , Figure 7As shown, the working face in the second mining area is 1497m long and 220m wide. All working faces use top coal caving mining technology. The machine mining height is 3.5m (bottom coal 51), and the caving height is 9.5m (top coal 52). Initial caving: No coal is caved in the first 20m of the working face. After the initial pressure from the old roof ends and the roof collapses, caving begins. Final caving: No coal is caved when the coal face is 30m from the stop line. To ensure unobstructed safety exits at the upper and lower ends, no coal is caved at the head (4 frames) and tail (5 frames). Based on a center-to-center distance of 1.8m for the end supports and / or transition supports, a width of 6.0m for machine roadway 3 and ventilation roadway 1, and a width of 9.0m for cut-off point 4, there will be a 13.2m wide section of top coal 52 that will not be mined on the machine roadway (head) side, a 15m wide section of top coal 52 that will not be mined on the ventilation roadway (tail) side, a 29m wide section of top coal 52 that will not be mined on the cut-off point side, and a 30m wide section of top coal 52 that will not be mined on the stop-mining line side. The overall mining rate of the top coal 52 area is only 83.7%. The bulk density of coal seam 3 is 1.4t / m³, and a single working face will result in a loss of approximately 712,000 tons of coal body. Based on a raw coal price of 550 yuan / t, the economic loss of a single working face is 390 million yuan.

[0024] To address the aforementioned problem of top coal resource waste, and in order to increase the top coal recovery rate and reduce resource waste by improving the release rate of top coal around the top coal caving face while ensuring safe mining, this invention proposes a method for improving the top coal caving recovery rate based on roof strata fracturing, such as... Figure 1-7 As shown, it includes the following steps: S1: As Figures 1-2 As shown, drilling site 8 is constructed in machine roadway 1. From drilling site 8, a fracturing borehole 64 is constructed in the roof 62 above the cut hole 4, and in the coal and rock strata at the same position as the top coal 52 outside the cut hole 4 (away from the working face advance direction), roof 61, and roof 62. A roof cutting borehole 63 is constructed in the roof 61 directly above the cut hole 4, close to the rear wall of the cut hole 4. The bottom coal seam 51 is mined using a coal mining machine. After a trial advance of 3-6 feet (2.4-4.8m) and stabilization, the roof 62 above the cut-out 4, the coal and rock strata in the same layer as the roof coal 52 outside the cut-out 4, the roof 61, and the roof 62 are fractured through the fracturing borehole 64. Then, the broken top coal 53 is released through the hydraulic support and the mining stops when gangue is encountered. After the broken top coal 53 is released, the fractured roof 61, roof 62, and the coal and rock strata in the same layer as the roof coal 52 are fractured, and the generated gangue will enter the goaf to replace the released broken top coal 53. The roof 61 is cut off through the cutting borehole 63, leaving a certain width of cut (to avoid obstructing the rotation and downward movement of the roof 61). Then, the entire coal seam 5 is mined using the top coal release process until the mining is close to the stop line 2.

[0025] In this invention, Roof 1 61 generally refers to the roof strata above coal seam 5 that have a significant impact on the mining pressure in the stope (for example, a break in the roof would cause a large impact), while Roof 2 refers to the roof strata above coal seam 5 that have a smaller impact on the mining pressure in the stope. For example, Roof 1 61 is the strata above coal seam 5 that includes the basic roof, and Roof 2 62 is the strata within a certain thickness range above the basic roof, such as the strata between the basic roof and the subcritical layer 2.

[0026] As a preferred embodiment of step S1, the fracturing borehole 64 can be a directional hydraulic fracturing borehole or a directional carbon dioxide fracturing borehole; wherein, the axial direction of the straight section of the directional borehole is consistent with the axial direction of the cut hole 4. The top-cutting borehole 63 adopts a vertical blasting borehole, and in order to ensure a sufficient cut width, the top-cutting borehole 63 can be constructed in two rows along the axial direction of the cut hole 4. Since the parameters of hydraulic fracturing boreholes and hydraulic fracturing construction, and blasting boreholes and blasting borehole construction are mature existing technologies, they will not be described in detail here.

[0027] During the initial mining phase, this invention creatively proposes fracturing the coal and rock mass behind the cut-off point. This allows the gangue generated from the fracturing coal and rock strata to replace the broken top coal 53 that needs to be left in the goaf during traditional top coal caving mining, enabling the top coal 52 to be released / recovered normally during the initial mining phase. Furthermore, since the gangue generated from the fracturing coal and rock strata replaces the broken top coal 53, it can still buffer the collapse and fall of the roof 61, preventing the initial impact of the roof 61 from being too large due to an overly open goaf, thus protecting the hydraulic supports. Furthermore, since the roof 61 has been cut, it can be broken as a cantilever beam (changing the initial pressure to periodic pressure). As the working face advances, the roof 61 will continuously move down into the goaf, which is conducive to monitoring the movement of the roof 61 and predicting its breaking time based on the monitoring results. This changes the disadvantage of the traditional method of making it difficult to predict the breaking time of the initial pressure, which requires leaving broken top coal 53 in the goaf. It is also more conducive to guiding the roof 61 to collapse in an orderly manner.

[0028] S2: As Figure 1 , Figure 3-5 As shown, a pre-excavated working roadway 21 (retreat passage) is located adjacent to the stop line 2. Several rows of fan-shaped fracturing boreholes 64 are constructed at intervals along the axial direction of the working roadway 21 towards the middle of the roof 61 and roof 62. The fan-shaped fracturing boreholes 64 are constructed within the suspended roof (uncollapsed and broken portion) of the roof 61 and roof 62 when the working face is retreated into the working roadway 21. The inclination angle of the fracturing borehole 64 closest to the stop line 2 is consistent with the rock collapse angle (62° in this embodiment). When the working face is retreated to a set distance from the stop line 2 (30m in this embodiment), only the bottom coal 51 is mined by the coal mining machine, without releasing the roof coal 52. The broken roof coal 53 is used to support the suspended roof 61 and roof 62, thereby reducing the surrounding rock pressure at the working roadway 21, ensuring the stability of the working roadway 21 and its surrounding rock, and safely retracting the hydraulic supports and other coal mining equipment.

[0029] When the working face is mined back to the receiving roadway 21, the hydraulic supports are sequentially withdrawn along the axial direction of the receiving roadway 21, and a backfilling retaining wall 54 is constructed at the withdrawal position of the hydraulic supports along the axial direction of the receiving roadway 21. A coal discharge chamber 55 is reserved at every set interval (10-15m in this embodiment) of the backfilling retaining wall 54; the construction position of the backfilling retaining wall 54 is adjacent to the withdrawal position of the hydraulic supports. After the coal mining equipment is withdrawn, a portion of the broken top coal 53 left in the goaf is pre-released from the coal discharge chamber 55 to provide free space for the subsequent fracturing of the suspended roof 61 and roof 62; then, the roof 61 and roof 62 are fracturing and roof cutting is performed through the fracturing borehole 64 (the fracturing borehole 64 closest to the stop line 2 plays the role of roof cutting); then, as much broken top coal 53 as possible is released.

[0030] As a preferred embodiment of step S2, the fracturing borehole 64 can be a hydraulic fracturing borehole, a carbon dioxide fracturing borehole, or a conventional blasting borehole.

[0031] During the final mining phase, this invention, while adhering to the traditional method of top coal caving mining to ensure safety, creatively proposes to construct a backfill retaining wall 54 in the exit roadway 21. The construction of the backfill retaining wall 54 is adjacent to the hydraulic support retraction position, ensuring the safety of the backfill retaining wall 54 construction and the stability of the exit roadway 21. A coal release chamber 55 is reserved in the backfill retaining wall 54, and then the broken top coal 53 is released, and the roof is fractured. Thus, the gangue generated by the fractured roof can be used to replace the broken top coal 53 left in the goaf during top coal caving mining, realizing the recovery of the top coal 52 on the side of the stop mining line.

[0032] S3: As Figures 6-7 As shown; the next working face is arranged immediately next to the working face mined in steps S1-S2. In the prior art, the next working face is generally arranged on the side of the machine roadway 3 of the already mined working face; specifically, in this embodiment, the ventilation roadway 1 of the next working face is constructed by excavating along the goaf in the machine roadway 3 immediately next to the already mined working face. A coal pillar 9 is left between the ventilation roadway 1 and the machine roadway 3. The width of the coal pillar 9 is 8-10m.

[0033] Along the axis of ventilation roadway 1, several rows of fan-shaped fracturing boreholes 64 are constructed at intervals between the roof 61 and roof 62 on the side of machine roadway 3. Among them, the fan-shaped fracturing boreholes 64 are constructed in the suspended roof of roof 61 and roof 62 on the side of machine roadway 3 (the part of roof 61 and roof 62 that has not collapsed and broken due to the lack of top coal 52 at the transition hydraulic support and / or end hydraulic support). The inclination angle of the fracturing borehole 64 closest to ventilation roadway 1 is consistent with the rock stratum collapse angle (62° in this embodiment). Along the axial direction of ventilation roadway 1, a coal release chamber 55 is constructed at intervals of a set distance (10-15m in this embodiment) in coal pillar 9. A portion of the broken top coal 53 left in the goaf is released from the coal release chamber 55 in advance to provide free space for the subsequent fracturing of the suspended roof 61 and roof 62. Then, the roof 61 and roof 62 are fracturing and roof cutting is performed through fracturing borehole 64 (the fracturing borehole 64 closest to ventilation roadway 1 plays the role of roof cutting). After that, as much broken top coal 53 as possible is released.

[0034] S4: Referring to steps S1-S3, sequentially mine each working face within the mining area. For all working faces within the mining area except the last one, the technical solution of this embodiment can achieve the release / recovery of the top coal 52 that was not released from the original cut-in side, the stop-mining line side, and the machine roadway side in the existing technology. For the last working face, at least the release / recovery of the top coal 52 that was not released from the original cut-in side and the stop-mining line side in the existing technology can be achieved.

[0035] S5: In order to further recover the broken top coal 53 in the mining area; if the first mining face ventilation roadway 1 side is designed as a long-term stable stratum, then refer to step S3, construct a coal discharge roadway 7 along the goaf on the first mining face ventilation roadway 1 side to recover the broken top coal left in the goaf on the first mining face ventilation roadway 1 side. The width of the coal pillar 9 between the coal discharge roadway 7 and the first mining face ventilation roadway 1 is designed to be 4-6m.

[0036] If the last working face machine roadway 3 is designed as a long-term stable stratum, then refer to step S3 and construct a coal discharge roadway 7 along the goaf on the side of the last working face machine roadway 3 to recover the broken top coal left in the goaf on the side of the last working face machine roadway 3. The width of the coal pillar 9 between the coal discharge roadway 7 and the last working face machine roadway 3 is designed to be 4-6m.

[0037] Specifically: Along the axial direction of the coal release roadway 7, several rows of fan-shaped fracturing boreholes 64 are constructed at intervals between the roof 61 and roof 62 on the side of the ventilation roadway 1 of the first mining face / machine roadway 3 of the last mining face; wherein, the fan-shaped fracturing boreholes 64 are constructed in the suspended roof of the roof 61 and roof 62 on the side of the ventilation roadway 1 of the first mining face / machine roadway 3 of the last mining face (the part of the roof 61 and roof 62 that has not collapsed and broken due to the lack of roof coal 52 at the transition hydraulic support and / or end hydraulic support), and the inclination angle of the fracturing borehole 64 closest to the coal release roadway 7 is consistent with the rock stratum collapse angle (62° in this embodiment). Along the axial direction of the coal discharge roadway 7, a coal discharge chamber 55 is constructed at intervals of a set distance (10-15m in this embodiment) in the coal pillar 9. A portion of the broken top coal 53 left in the goaf is pre-released from the coal discharge chamber 55 to provide free space for the subsequent fracturing of the suspended roof 61 and roof 62. Then, the roof 61 and roof 62 are fracturing and roof cutting is performed through the fracturing borehole 64 (the fracturing borehole closest to the coal discharge roadway 7 plays the role of roof cutting). After that, as much broken top coal 53 as possible is released.

[0038] For the end face / two roadway sides, this invention, while ensuring safety through traditional top coal caving mining, creatively proposes to use goaf excavation for the ventilation roadway of the next working face, and to use goaf excavation for the ventilation roadway side of the first working face and the machine roadway side of the last working face for dedicated coal release roadways; and to construct coal release chambers 55 in the coal pillar 9, then release the broken top coal 53, and fracturing the roof, so that the gangue generated by fracturing the roof can be used to replace the broken top coal 53 left in the goaf during top coal caving mining, thereby realizing the recovery of part of the top coal 52 on the end face / two roadway sides.

[0039] In this invention, top coal caving employs a multi-round, cyclical, and uniform sequential caving method. To ensure recovery rate, the multi-round sequential caving can be conducted in a "wave-like" pattern, meaning that after the first round of caving, a distance of 10 supports is maintained before the second round, and so on, until gangue is encountered and the gate is closed. If caving is incomplete, a third round of caving or partial supplementary caving can be performed until gangue is encountered. The sequential caving is as follows: starting from one end of the working face across the entire dip width, the hydraulic support caving ports are opened sequentially, consistent with the support shifting sequence. If large pieces of coal are encountered during caving, they are broken up using the support tail beam or crushed using insert plates. To ensure recovery rate, the caving port is closed when gangue is encountered, ending the caving operation for that frame.

[0040] Economic benefit analysis: On average, one working face can realize the release / recovery of 52 tons of top coal that has not been released from the original cut-off side, the stop-mining line side, and the machine roadway side in the existing technology; calculated at a recovery rate of 70%, a single working face is expected to recover about 300,000 tons of coal. Based on the raw coal price of 550 yuan / ton, a single working face can increase economic benefits by 165 million yuan.

[0041] While the present invention has been described above with reference to preferred embodiments, it is not intended to limit the invention. Those skilled in the art can make various modifications and refinements without departing from the spirit and scope of the invention. Therefore, the scope of protection of the present invention shall be determined by the claims.

Claims

1. A method for improving top coal caving recovery rate based on roof rock fracturing, characterized in that, Includes the following steps: S1: Construct fracturing boreholes in the coal and rock strata and roof at the same location as the top coal behind the cut; construct roof cutting boreholes in the roof directly above the cut, close to the back wall of the cut; mine the bottom coal; fracture the coal and rock strata and roof through the fracturing boreholes; release the broken top coal through hydraulic supports; mine the entire coal seam using the top coal caving process until mining is close to the stop line. S2: Pre-excavate the working roadway and drill fracturing boreholes into the suspended roof; when the working face is back-mined to a set distance from the stop line, only bottom coal is mined and top coal is not released; when the working face is back-mined to the working roadway, the hydraulic supports are withdrawn sequentially along the axis of the working roadway and the filling retaining wall is constructed, with a coal release chamber reserved inside the filling retaining wall; after the withdrawal is completed, the broken top coal is released from the coal release chamber. S3: Construct the ventilation roadway of the next working face adjacent to the machine roadway of the already mined working face, and drill fracturing holes into the suspended roof; construct a coal discharge chamber in the coal pillar along the axial direction, and discharge the broken top coal from the coal discharge chamber; S4: Refer to steps S1-S3 and sequentially return each working face within the mining area.

2. The method for improving the top coal caving recovery rate according to claim 1, characterized in that, In step S1, the roof includes roof one and roof two. Roof one is the rock stratum above the coal seam that includes the basic roof, and roof two is the rock stratum within a certain thickness range above the basic roof. The fracturing borehole is constructed at least in roof one of the roof. The cutting borehole is constructed only in roof one and forms a cut of a certain width.

3. The method for improving the top coal caving recovery rate according to claim 2, characterized in that, In step S1, a crack-causing drill hole is also drilled in the top plate above the cut eye; And / or, in step S1, after the broken top coal is released, the gangue generated by the fractured roof and coal and rock strata enters the goaf to replace the released broken top coal.

4. The method for improving the top coal caving recovery rate according to claim 2, characterized in that, In step S2, fan-shaped fracturing boreholes are constructed at intervals between the first and second roof sections along the axial direction of the working roadway. The inclination angle of the fracturing borehole closest to the stop line is consistent with the rock strata collapse angle.

5. The method for improving the top coal caving recovery rate according to claim 1 or 2, characterized in that, In step S2, only the bottom coal is mined without releasing the top coal. The broken top coal is used to support the suspended roof, thereby reducing the pressure on the surrounding rock at the exit roadway and ensuring the stability of the exit roadway and its surrounding rock.

6. The method for improving the top coal caving extraction rate according to claim 4, characterized in that, In step S2, a coal release chamber is reserved at set intervals within the filling retaining wall; a portion of the broken top coal left in the goaf is released in advance, and then the roof is fractured through fracturing boreholes; then, as much broken top coal as possible is released.

7. The method for improving the top coal caving extraction rate according to claim 2, characterized in that, In step S3, the ventilation roadway of the next working face is constructed by excavating along the goaf, and a coal pillar with a width of 8-10m is left between the ventilation roadway and the machine roadway. And / or, in step S3, several rows of fan-shaped fracturing boreholes are drilled at intervals between the roof slab one and roof slab two on the side of the machine tunnel along the axial direction, and the inclination angle of the fracturing borehole closest to the ventilation tunnel is consistent with the rock stratum collapse angle.

8. The method for improving the top coal caving extraction rate according to claim 1 or 2, characterized in that, In step S3, a coal release chamber is constructed at set intervals within the coal pillar; a portion of the broken top coal left in the goaf is released in advance, and then the roof is fractured through fracturing boreholes; then, as much broken top coal as possible is released.

9. The method for improving the top coal caving extraction rate according to claim 1 or 2, characterized in that, It also includes step S5: referring to step S3, constructing a coal discharge roadway on the side of the ventilation roadway of the first mining face to recover the broken top coal left in the goaf on the side of the ventilation roadway of the first mining face; constructing a coal discharge roadway on the side of the machine roadway of the last mining face to recover the broken top coal left in the goaf on the side of the machine roadway of the last mining face.

10. The method for improving the top coal caving recovery rate according to claim 9, characterized in that, In step S5, a coal release roadway is constructed by excavating along the goaf. The width of the coal pillar between the coal release roadway and the ventilation roadway of the first mining face, and between the coal release roadway and the machine roadway of the last mining face, is 4-6m.

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