Negative angle top caving along void self-boring method

Abstract

The present application belongs to the field of coal mine roadway construction, and particularly relates to a method for self-forming a roadway by top cutting at a negative angle. The method comprises the following steps: drilling a field in front of a working face and close to a right side of a mining roadway; drilling anchor holes and top cutting holes along a strike and staggered construction, and installing grouting anchor cables in the field; cutting the basic roof and the immediate roof at a negative angle through the top cutting holes at the back of the working face, constructing a roadway-side gangue retaining structure, grouting through the grouting anchor cables and anchoring the grouting anchor cables on the roadway-side gangue retaining structure; and monitoring the deformation of the steel mesh at the grouting anchor cable and adjusting through a nut. The present application can ensure that the construction position of the roadway-side gangue retaining structure does not affect the width of the self-supporting roadway and the integrity of the roof by constructing a field of a certain width in advance. The negative angle top cutting holes can cut a section that is deviated to the direction of the goaf, so that the gangue formed by the collapse of the immediate roof moves to the direction of the goaf and does not move to the mining roadway in large quantities, thereby ensuring the safety of the construction in the mining roadway.

Description

Technical Field

[0001] This invention belongs to the field of coal mine roadway construction, specifically involving a method for forming a roadway by cutting the roof at a negative angle along the goaf. Background Technology

[0002] Goaf retention is a pillarless roadway construction technique that maintains the existing mining roadway along the boundary of the goaf behind the current working face, so as to continue mining for the next working face. Goaf retention is an important technology in coal mine pillarless mining systems. Its advantages include reducing the amount of roadway excavation, alleviating the tension between mining and excavation, and increasing coal recovery rate.

[0003] Currently, the mainstream construction method for roadway retention along the goaf is to construct a roadway backfill wall using high-water or paste materials on the side of the roadway closest to the goaf. However, since high-water and paste materials require time to solidify, the roadway backfill wall can only support the roof of the roadway after the backfill material has solidified, which severely restricts the coal mining speed. Furthermore, the roadway backfill wall will reduce the width of the roadway cross-section and affect the production of the next working face.

[0004] To address this, existing technologies have proposed a method of roof-cutting self-forming roadway with gob-side roadway retention (roof-cutting self-forming roadway with gob-side roadway retention method). This involves drilling a positive-angle roof-cutting borehole along the gob boundary towards the gob in the roof of the mining roadway to cut off the roof and reduce the cantilever length, thereby reducing the stress on the gob-side roadway retention. Then, a simple roadway-side retaining structure is formed using single hydraulic props and steel mesh, thereby improving the construction efficiency of the gob-side roadway retention. However, the positive-angle roof-cutting method easily leads to collapsed rock entering the mining roadway, impacting the single hydraulic props, endangering worker safety, and making it difficult to handle these rocks entering the mining roadway. In addition, as the working face continues to advance, the continuous collapse of the overlying roof strata will further impact the collapsed rock in the gob, and the impacted rock is prone to squeezing the flexible steel mesh into the gob-side roadway retention, which may even cause damage to the steel mesh in severe cases. Therefore, how to improve the stability and safety of the roof-cutting self-forming roadway with gob-side roadway retention process has become an urgent problem to be solved. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention proposes a method for forming a self-contained alleyway by cutting the roof at a negative angle, comprising the following steps:

[0006] S1: At the front of the first working face, the drilling site is always ahead of the mining area near the right side of the return roadway; the first working face is located on the right side of the return roadway, and the left side of the return roadway is the next working face;

[0007] S2: On the right side of the drilling site, near the coal seam, staggered anchor cable boreholes and top-cutting boreholes are constructed along the strike; the anchor cable boreholes are constructed to the right to the direct top center, and the top-cutting boreholes are constructed to the left to the basic top center; grouting anchor cables are installed in the anchor cable boreholes;

[0008] S3: In the mining area, the coal seam is continuously mined forward. When the grouting anchor cable and the top-cutting borehole are exposed behind the mining area, the main roof and the immediate roof are cut at a negative angle through the top-cutting borehole. The collapsed gangue carries the grouting anchor cable into the goaf and presses the grouting anchor cable into the collapsed gangue. The roadway retaining structure is constructed by using steel mesh in conjunction with single hydraulic props. Grouting is carried out through the grouting section of the grouting anchor cable to form a grout body mixed with gangue. Then the grouting anchor cable is anchored to the steel mesh.

[0009] S4: Monitor the deformation of the reinforcing mesh at the grouting anchor cable. When the reinforcing mesh protrudes towards the mining roadway, tighten the nut to move the reinforcing mesh towards the goaf. When the reinforcing mesh moves towards the goaf due to the tension of the anchor cable, loosen the nut to move the reinforcing mesh towards the mining roadway.

[0010] S5: Repeat steps S1-S4 until the first working face is mined and the goaf retention work of the return roadway is completed.

[0011] Preferably, in step S1, hydraulic supports are arranged in the mining area; the drilling area is rectangular in plan view, and the right boundary of the drilling area is located in the gap between the first hydraulic support and the second hydraulic support starting from the mining roadway; individual hydraulic supports are intermittently installed on the left side of the drilling area along the strike.

[0012] Preferably, in step S2, the angle between the anchor cable borehole and the vertical direction is 55°-65°, and the angle between the top-cut borehole and the vertical direction is 5°-8°.

[0013] Preferably, in step S2, the length of the grouting anchor cable is greater than the drilling depth of the anchor cable, and the outer end of the grouting anchor cable is not anchored after installation; explosives are installed in the top-cutting borehole.

[0014] Preferably, in step S3, the coal seam is continuously mined forward in the mining area, and the individual hydraulic props located near the mining area in the drilling area are recovered.

[0015] Preferably, in step S3, the steel mesh is located between the single hydraulic support and the collapsed gangue, covering the entire height of the mining roadway; the gangue retaining structure is set at the original right boundary of the mining roadway and is located on the left side of the entire cut-off section of the basic roof above the mining roadway.

[0016] Preferably, in step S3, the grouting anchor cable consists of a grouting section, a conventional section, and a threaded section from the inside out. The center of the grouting anchor cable is a grouting pipe, and steel strands are wound around the outside. The grouting pipe is provided with a grout outlet hole in the grouting section. The threaded section is provided with a tray and a nut for anchoring the grouting anchor cable.

[0017] Preferably, in step S3, anchor bolts are installed at intervals along the direction of the gangue to reinforce the support.

[0018] The inventive points and beneficial technical effects of this invention are as follows: 1. This invention involves constructing a pre-mining drilling site, where top-cutting boreholes and anchor cable boreholes are drilled. Compared to drilling top-cutting boreholes and anchor cable boreholes in the goaf behind the mining area, this significantly improves construction efficiency and ensures safety. Furthermore, by designing the positions of the top-cutting boreholes and anchor cable boreholes, the exposed anchor cables can smoothly pass through the hydraulic supports.

[0019] 2. This invention allows the construction of a drilling site to shift the location of the roof-cutting borehole towards the goaf, thus facilitating the construction of negative-angle roof-cutting boreholes. However, when constructing negative-angle roof-cutting boreholes, it is difficult to install a roadway-side retaining structure at the borehole opening, as this could easily damage the roof. Therefore, when using negative-angle roof-cutting boreholes, the roadway-side retaining structure needs to be shifted towards the mining roadway. If negative-angle roof cutting is performed directly in the mining roadway without a drilling site, the final constructed roadway-side retaining structure will be located within the mining roadway, reducing the width of the goaf-side retaining roadway and hindering service to the next working face. In other words, this invention, by constructing a drilling site of a certain width in advance, ensures that the construction location of the roadway-side retaining structure does not affect the width of the goaf-side retaining roadway while also maintaining the integrity of the roof. Meanwhile, by using negative-angle roof-cutting boreholes, a cross-section biased towards the goaf can be cut, allowing the gangue from the collapse of the immediate roof to move towards the goaf instead of moving in large quantities into the recovery roadway, thus ensuring construction safety in the recovery roadway. Due to the large cumulative thickness of the immediate roof, the collapsed gangue, under the influence of its gravity and the forces of the overlying strata, will move towards the recovery roadway, occupying the exposed roof space outside the retaining wall structure beside the roadway. This space serves as a buffer for gangue movement, preventing it from encroaching on the width of the recovery roadway.

[0020] 3. This invention creatively proposes the pre-construction of grouting anchor cables within the immediate roof. This allows the anchor cables to be entirely encased within the gangue after the immediate roof collapses into it. Grouting is then performed to reinforce the inner end and anchor the outer end after the gangue has stabilized. This completes the anchor cable construction, improves support strength, and solves the problem of not being able to construct anchor cables within the gangue in the goaf. Gangue near the return roadway in the goaf tends to move towards the return roadway under the pressure of the overlying strata. However, because the anchor cables penetrate deep into the goaf far from the return roadway, the gangue in this area is continuously compressed under the force of the overlying strata, reducing its fragmentation. This reduces the tension in the grouting anchor cables, creating a pulling force towards the goaf. This effectively holds back the gangue moving towards the return roadway, improving the stability of the roadway-side retaining structure. Attached Figure Description

[0021] Figure 1 This is a schematic plan view of the negative angle top-cutting self-forming alleyway method of the present invention;

[0022] Figure 2This is a schematic diagram of the dip profile at the drilling site of the negative angle top-cutting self-forming tunnel method of the present invention;

[0023] Figure 3 This is a schematic diagram of the dip section behind the stope of the negative angle top-cutting and goaf-forming self-contained roadway method of the present invention.

[0024] Figure 4 This is a schematic diagram of the grouting anchor cable structure used in the negative angle top-cutting and free-form roadway method of the present invention;

[0025] In the diagram, 1-first working face; 11-coal seam; 12-drilling area; 13-gangue; 2-recovery roadway; 3-second working face; 4-single hydraulic prop; 5-mining area; 51-hydraulic support; 61-anchor cable borehole; 62-roof cutting borehole; 71-steel mesh; 72-anchor bolt; 81-direct roof; 82-basic roof; 9-grouting anchor cable; 91-threaded section; 92-pallet; 93-nut; 94-conventional section; 95-ring; 96-grouting section; 97-grouting body. Detailed Implementation

[0026] The invention will now be further described with reference to the accompanying drawings.

[0027] like Figures 1-4 As shown, in a certain coal mine, coal seam 11 dips at 1°-3°, with a designed mining height of 2.1m. The recovery roadway 2 is 2.5m high and 4.2m wide. Recovery roadway 2 is constructed along the floor of coal seam 11 and partially excavates the direct roof 81 to meet the height requirements of recovery roadway 2. The direct roof 81 consists of three layers with a cumulative thickness of 6.5m, mainly composed of mudstone with a compressive strength of approximately 20MPa. The basic roof 82 is 7.4m thick, composed of oil shale with a compressive strength of 37MPa. The recovery roadway 2 utilizes gob-side entry technology to continue serving the next working face. In response, this invention proposes a negative-angle roof cutting and gob-side entry method, suitable for working conditions where the thickness of the direct roof 81 is moderate, especially when the thickness is large. The specific steps include:

[0028] S1: As Figures 1-2As shown, in the front part of the mining area 5 of the first working face 1, near the right side of the retreat roadway 2, the advanced mining area 5 tunneling drilling site 12 is located. The mining area 5 is equipped with hydraulic supports 51, a coal mining machine, and a scraper conveyor, among other coal mining equipment, for mining the coal seam 11. The retreat roadway 2 is supported by a comprehensive anchoring method combining anchor bolts, anchor cables, and anchor mesh, with individual hydraulic props 4 spaced along the strike in the middle of the retreat roadway 2 for reinforcement. The first working face 1 is located on the right side of the retreat roadway 2, and the left side of the retreat roadway 2 is the second working face 3. The second working face 3 is a continuing working face, serving the second working face 3 after the retreat roadway 2 is left behind. In this application, the strike and the preceding / following direction are considered as... The direction is consistent, and the inclination is consistent with the left and right directions; the inclination width of the drilling site 12 is greater than the width of a single hydraulic support 51 but does not exceed the sum of the width of a single hydraulic support 51 and the inclination spacing of the hydraulic supports 51, that is, the right boundary of the drilling site 12 is located in the gap between the first hydraulic support 51 and the second hydraulic support 51 starting from the mining roadway 2; the length of the drilling site 12 along the strike is about 10m, that is, a drilling site 12 with a length of about 10m is always constructed ahead of the mining site 5; a small tunneling machine or drilling rig is used to excavate the drilling site 12; the drilling site 12 is rectangular in plan view; in order to maintain the stability of the drilling site 12, single hydraulic supports 4 are installed at intervals along the strike on the left side of the drilling site 12.

[0029] S2: As Figures 1-2 As shown, near the coal seam 11 on the right side of drilling site 12, anchor cable boreholes 61 and roof-cutting boreholes 62 are constructed alternately along the strike, with an interval of 1.5m between adjacent anchor cable boreholes 61 and roof-cutting boreholes 62 along the strike. The anchor cable boreholes 61 are constructed to the direct roof 81, extending towards the first working face 1 on the right, with a positive construction angle and an angle of 55°-65° with the vertical direction. In this invention, the drilling angle extending towards the first working face 1 on the right is positive, while the drilling angle extending towards the second working face 3 on the left is negative. The roof-cutting boreholes 62 are constructed to the basic roof 82, extending towards the second working face 3 on the left, with a negative construction angle and an angle of 5°-8° with the vertical direction. Grouting anchor cables 9 are installed in the anchor cable boreholes 61, with a length greater than the construction depth of the anchor cable boreholes 61, exceeding the length by about 2m. After installation, the outer ends of the grouting anchor cables 9 are not anchored. Explosives are installed in the roof-cutting boreholes 62.

[0030] S3: As Figures 1-3As shown, coal seam 11 is continuously mined forward in stope 5, and the single hydraulic prop 4 located near stope 5 in drilling site 12 is recovered. As stope 5 moves forward, grouting anchor cable 9 and roof-cutting borehole 62 for installing explosives are exposed behind stope 5. At this time, the basic roof 82 and immediate roof 81 are cut at a negative angle through roof-cutting borehole 62. The immediate roof 81 collapses into gangue 13 and supports the broken basic roof 82. Since the anchor cable borehole 61 in step S2 is located in the gap between the first hydraulic support 51 and the second hydraulic support 51, the part of the grouting anchor cable 9 that extends beyond the anchor cable borehole 61 can pass smoothly between the two hydraulic supports 51.

[0031] Furthermore, due to the negative angle used for roof cutting, the gangue 13 formed by the collapse of the immediate roof 81 will slide to the right along the cut section, away from the return roadway 2, thus preventing the gangue 13 from directly sliding into the return roadway 2; at the same time, the collapsed gangue 13 carries the grouting anchor cable 9 into the goaf, pressing the grouting anchor cable 9 into the collapsed gangue 13; since the cumulative thickness of the immediate roof 81 is moderate or large, the collapsed gangue 13 will move towards the return roadway 2 under its own sliding characteristics, occupying a certain width below the exposed roof. At this time, a gangue retaining structure is constructed beside the roadway using steel mesh 71 and single hydraulic props 4 to prevent the gangue 13 from continuing to move towards the return roadway 2 under the pressure of the overlying strata, while also preventing... The exposed roof is supported by a steel mesh 71 located between the individual hydraulic prop 4 and the collapsed gangue 13, covering the entire height of the mining roadway 2. The exposed length of the grouting anchor cable 9 is about 2m, which can accommodate the problem of it shrinking towards the goaf due to compression by the gangue 13. The roadway retaining structure, namely the steel mesh 71 and the individual hydraulic prop 4 that cooperate with it, is set at the original right boundary of the mining roadway 2, and is located outside the entire cut-off section of the basic roof 82 above the mining roadway 2. That is, a vertical line is drawn downward from the leftmost cut-off position of the basic roof 82 above the mining roadway 2, and this vertical line is located on the right side of the roadway retaining structure. This can ensure that the roadway retaining structure supports the roof and avoids damaging the roof.

[0032] like Figure 4As shown, the grouting anchor cable 9 consists of a grouting section 96, a conventional section 94, and a threaded section 91 from the inside out. The threaded section 91 is approximately 1.5m long, the grouting section 96 is approximately 3m long, and the conventional section 94 is approximately 5m long. The grouting anchor cable 9 has a grouting pipe at its center, with steel strands wound around it. The grouting pipe has a grout outlet at the grouting section 96. The conventional section 94 is a standard anchor cable section and does not require grouting functionality compared to the grouting section 96, nor does it require threads compared to the threaded section 91. 91 is provided with a tray 92 and a nut 93 for anchoring the grouting anchor cable 9; the outer periphery of the conventional section 94 and the grouting section 96 is fixed with rings 95 at intervals along the length direction of the grouting anchor cable 9, and the rings 95 have the function of increasing the sliding resistance in the crushed gangue 13; grouting is performed through the grouting section 96 of the grouting anchor cable 9 to form a grouting body 97 mixed with gangue 13, the grouting section 96 of the grouting anchor cable 9 is fixed in the crushed gangue 13, and then the grouting anchor cable 9 is anchored to the steel mesh 71 by the tray 92 and the nut 93.

[0033] Anchor bolts 72 are installed at intervals along the direction of the gangue 13 to reinforce the support. Since the anchor bolts 72 are rigid and short in length, they are easy to install.

[0034] S4: Monitor the deformation of the reinforcing mesh 71 at 9 of the grouting anchor cable. When the reinforcing mesh 71 protrudes towards the mining roadway 2, tighten the nut 93 to move the reinforcing mesh 71 towards the goaf. When the reinforcing mesh 71 moves towards the goaf under the tension of the anchor cable, loosen the nut 93 to move the reinforcing mesh 71 towards the mining roadway 2.

[0035] S5: Repeat steps S1-S4 until the first working face 1 is mined out and the goaf retention work of the return roadway 2 is completed for use in the second working face 3.

[0036] This invention is not limited to the preferred embodiments described above. Anyone can derive other methods in various forms under the guidance of this invention. Any technical solution that is the same as or similar to this application falls within the protection scope of this invention.

Claims

1. A method for forming a self-contained tunnel along the goaf with a negative angle roof cutting, characterized in that: Includes the following steps: S1: At the front of the first working face, the drilling site is always ahead of the mining area near the right side of the return roadway; the first working face is located on the right side of the return roadway, and the left side of the return roadway is the next working face; S2: On the right side of the drilling site, near the coal seam, staggered anchor cable boreholes and top-cutting boreholes are constructed along the strike; the anchor cable boreholes are constructed to the right to the direct top center, and the top-cutting boreholes are constructed to the left to the basic top center; grouting anchor cables are installed in the anchor cable boreholes; S3: In the mining area, the coal seam is continuously mined forward. When the grouting anchor cable and the top-cutting borehole are exposed behind the mining area, the main roof and the immediate roof are cut at a negative angle through the top-cutting borehole. The collapsed gangue carries the grouting anchor cable into the goaf and presses the grouting anchor cable into the collapsed gangue. The roadway retaining structure is constructed by using steel mesh in conjunction with single hydraulic props. Grouting is carried out through the grouting section of the grouting anchor cable to form a grout body mixed with gangue. Then the grouting anchor cable is anchored to the steel mesh. S4: Monitor the deformation of the reinforcing mesh at the grouting anchor cable. When the reinforcing mesh protrudes towards the mining roadway, tighten the nut to move the reinforcing mesh towards the goaf. When the reinforcing mesh moves towards the goaf due to the tension of the anchor cable, loosen the nut to move the reinforcing mesh towards the mining roadway. S5: Repeat steps S1-S4 until the first working face is mined and the goaf retention work of the return roadway is completed.

2. The method for forming a self-contained alleyway along the goaf with a negative angle cutting according to claim 1, characterized in that, In step S1, hydraulic supports are arranged in the mining area; the drilling site is rectangular in plan view, and the right boundary of the drilling site is located in the gap between the first hydraulic support and the second hydraulic support starting from the mining roadway; individual hydraulic props are set at intervals along the strike on the left side of the drilling site.

3. The method for forming a self-contained alleyway along the goaf with a negative angle cutting according to claim 1, characterized in that, In step S2, the angle between the anchor cable borehole and the vertical direction is 55°-65°, and the angle between the top-cut borehole and the vertical direction is 5°-8°.

4. The method for forming a self-contained alleyway along the goaf with a negative angle cutting according to claim 3, characterized in that, In step S2, the length of the grouting anchor cable is greater than the drilling depth of the anchor cable, and the outer end of the grouting anchor cable is not anchored after installation; explosives are installed in the top-cutting borehole.

5. The method for forming a self-contained alleyway along the goaf with a negative angle cutting according to claim 4, characterized in that, In step S3, the coal seam is continuously mined forward in the mining area, and the individual hydraulic props located near the mining area in the drilling area are recovered.

6. The method for forming a self-contained alleyway along the goaf with a negative angle cutting according to claim 4, characterized in that, In step S3, the steel mesh is located between the single hydraulic support and the collapsed gangue, covering the entire height of the mining roadway; the gangue retaining structure is set at the original right boundary of the mining roadway and is located on the left side of the entire cut-off section of the basic roof above the mining roadway.

7. The method for forming a self-contained alleyway along the goaf with a negative angle roof cutting according to any one of claims 4-6, characterized in that, In step S3, the grouting anchor cable consists of a grouting section, a conventional section, and a threaded section from the inside out. The center of the grouting anchor cable is a grouting pipe, and steel strands are wound around the outside. The grouting pipe is provided with a grout outlet hole in the grouting section. The threaded section is provided with a tray and a nut for anchoring the grouting anchor cable.

8. The method for forming a self-contained alleyway along the goaf with a negative angle cutting according to claim 7, characterized in that, In step S3, anchor bolts are installed at intervals along the direction of the gangue to reinforce the support.

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