Stress control method for gob-side entry retention in close-range coal seams

Abstract

The present invention relates to the field of coal mine technology, and in particular to a method for controlling stress of a goaf-retained lane in a close-range coal seam. The method comprises: excavating a lane at a preset position in a lower coal seam, wherein the lane comprises a first lane and a second lane, a first working face is formed between the first lane and the second lane, and the second lane is located below the goaf of the upper coal seam, and the overburden layer above the side of the second lane adjacent to the first working face is top-cut to form a top-cutting line on the overburden layer, the top-cutting line extends in a direction from bottom to top and is arranged inclined toward the direction of the first working face, wherein the overburden layer comprises a rock beam. The method for controlling stress of a goaf-retained lane in a close-range coal seam according to an embodiment of the present invention can reduce lane deformation and improve lane stability.

Description

Technical Field

[0001] The present invention relates to the technical field of coal mines, and in particular to a stress control method for gob-side entry retaining in close-range coal seams. Background Art

[0002] During the mining process of close-range coal seams, the upper and lower coal seams have a great influence on each other. The surrounding rock of the lower coal seam tunnel of the close-range coal seam is subjected to not only the mining stress caused by the mining of the lower coal seam, but also the additional mining stress caused by the mining of the upper coal seam.

[0003] In related technologies, tunnels are mostly supported by anchor rods and cables. However, under the action of strong mining stress, tunnels are prone to deformation and their stability is reduced. Summary of the Invention

[0004] The present invention aims to solve at least one of the technical problems in the related art to a certain extent. To this end, an embodiment of the present invention provides a stress control method for gob-side entry in a close-range coal seam, which can reduce entry deformation and improve entry stability.

[0005] A stress control method for retaining a lane along a goaf in a close-range coal seam according to an embodiment of the present invention includes: excavating a lane at a preset position in a lower coal seam, wherein the lane includes a first lane and a second lane, a first working face is formed between the first lane and the second lane, and the second lane is located below the goaf of the upper coal seam; top-cutting the overburden layer above the side of the second lane adjacent to the first working face to form a top-cutting line on the overburden layer, the top-cutting line extending in a direction from bottom to top and arranged inclined toward the direction of the first working face, wherein the overburden layer includes a rock beam.

[0006] The stress control method for retaining a gob-side lane in a close-range coal seam according to an embodiment of the present invention can reduce lane deformation and improve lane stability.

[0007] In some embodiments, the overburden layer above the side of the second tunnel adjacent to the first working face is top-cut to form a top-cut line on the overburden layer, including: determining the length of the top-cut line based on the spacing distance between the top wall surface of the second tunnel and the upper end surface of the rock beam and the inclination angle of the top-cut line; drilling the overburden layer through a top-cut drill hole to form the top-cut line, and the drill hole penetrates the rock beam.

[0008] In some embodiments, the inclination angle of the top cutting line includes an angle between the top cutting line and the up-down direction and an angle between the top cutting line and the length direction of the second lane.

[0009] In some embodiments, an angle A between the top cutting line and the up-down direction is 0-30°; and / or an angle B between the top cutting line and the length direction of the second lane is 45°-55°.

[0010] In some embodiments, there are multiple topping lines, and the multiple topping lines are spaced apart in the length direction of the second tunnel, and / or the topping drill holes are hydraulic fracturing topping holes.

[0011] In some embodiments, a horizontal distance C between a side wall surface of the second tunnel facing away from the first working surface and a support column of the upper coal seam adjacent to the goaf is 10-50 m.

[0012] In some embodiments, after the overburden layer above the side of the second tunnel adjacent to the first working face is top-cut to form a top-cut line on the overburden layer, the control method further includes: filling a wall on the side of the second tunnel adjacent to the first working face.

[0013] In some embodiments, the backfill wall on the side of the second tunnel adjacent to the first working face is located after the first working face is mined.

[0014] In some embodiments, before the overburden layer above the side of the second tunnel adjacent to the first working face is top-cut to form a top-cut line on the overburden layer, the control method further includes: supporting the second tunnel.

[0015] In some embodiments, supporting the second tunnel includes: arranging a plurality of anchor rod assemblies on the inner wall surface of the second tunnel, the plurality of anchor rod assemblies being arranged at intervals in the length direction of the second tunnel, and each anchor rod assembly including a plurality of anchor rods arranged at intervals in the circumferential direction of the second tunnel; arranging a plurality of groups of anchor cables on the top wall surface of the second tunnel, the plurality of groups of anchor cables being arranged at intervals in the length direction of the second tunnel, each group of anchor cables including a plurality of anchor cables arranged at intervals in the width direction of the second tunnel, and at least one anchor rod assembly being provided between two adjacent groups of anchor cables. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 Schematic diagram of the overburden layer of the lower coal seam according to an embodiment of the present invention.

[0017] Figure 2 This is a state diagram of the overburden layer after the first working face is mined according to an embodiment of the present invention.

[0018] Figure 3 This is a state diagram of the overburden layer after the first working face is mined according to an embodiment of the present invention, and the overburden layer is in a top-cut state.

[0019] Figure 4Schematic diagram of a tangent line according to an embodiment of the present invention.

[0020] Figure 5 2 is a schematic diagram of another perspective of the tangent line of the embodiment of the present invention.

[0021] Figure 6 Schematic diagram of support for the second tunnel according to an embodiment of the present invention.

[0022] Figure 7 It is a schematic diagram from another perspective of the support of the second tunnel in an embodiment of the present invention.

[0023] Figure 8 It is a schematic diagram of the deformation of the second lane in the related art.

[0024] Figure 9 Schematic diagram of the deformation of the second lane in an embodiment of the present invention.

[0025] Reference numerals:

[0026] Lower coal seam 1, roadway 11, first roadway 111, second roadway 112,

[0027] The first working face 12, the second working face 13, the first goaf 14,

[0028] Upper coal seam 2, goaf 21, support column 22,

[0029] Overburden 3, rock beam 31, mudstone 32, fine-grained sandstone 33,

[0030] Top cutting line 4, wall 5, anchor rod assembly 6, anchor rod 61, anchor cable 7. DETAILED DESCRIPTION

[0031] The embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to be used to explain the present invention, but should not be understood as limiting the present invention.

[0032] A stress control method for gob-side entry retention in a close-range coal seam according to an embodiment of the present invention includes excavating a tunnel 11 at a preset position in a lower coal seam 1, wherein tunnel 11 includes a first tunnel 111 and a second tunnel 112, a first working face 12 is formed between the first tunnel 111 and the second tunnel 112, and the second tunnel 112 is located below a gob 21 of an upper coal seam 2. An overburden stratum 3 above a side of the second tunnel 112 adjacent to the first working face 12 is top-cut to form a top-cut line 4 on the overburden stratum 3. The top-cut line 4 extends from bottom to top and is arranged obliquely toward the first working face 12. The overburden stratum 3 includes a rock beam 31.

[0033] It should be noted that the upper coal seam 2 has been mined when the tunnel 11 is excavated at the preset position of the lower coal seam 1. That is, before the lower coal seam 1 is mined, the upper coal seam 2 needs to be mined first to form a goaf 21.

[0034] The inventors discovered that when the interlayer spacing between the lower coal seam 1 and the upper coal seam 2 is relatively thin, a low-stress environment is formed after the upper coal seam 2 is mined and the bottom plate is unloaded. When mining the lower coal seam 1, since the top plate of the lower coal seam 1 is thin and there is no key layer, the working face of the lower coal seam 1 is mined and cannot form a stable bearing structure. Although the tunnel 11 of the lower coal seam 1 will be affected by the mining of the lower coal seam 1 twice, the mining stress is small, the tunnel 11 is subjected to little force, and the tunnel 11 has high stability.

[0035] When the interlayer spacing between the lower coal seam 1 and the upper coal seam 2 is relatively thick, the thicker the interlayer spacing, the more likely it is to contain a key layer that is easy to form a stable bearing structure. In the initial stage of mining the lower coal seam 1, the tunnel 11 is also in a low stress state. However, as the working face advances, the working face mining collapses and forms a stable bearing structure. The mining stress is large, the deformation of the tunnel 11 is large, and the stability of the tunnel 11 is low. In other words, in a close-range coal seam with a thick interlayer spacing and a key layer, the mining roof of the lower coal seam 1 forms a stable bearing structure and generates strong mining stress. The tunnel 11 is deformed under the action of the strong mining stress, which is the fundamental reason for the large deformation and damage of the tunnel. Based on this, the stress control method for tunneling along the goaf in a close-range coal seam of an embodiment of the present invention starts from the root cause of the strong mining stress on the surrounding rock of the tunnel 11 in the close-range lower coal seam 1, and changes the structure of the overburden 3 after the mining of the lower coal seam 1 so that it cannot form a stable bearing structure, thereby reducing the mining stress, reducing the deformation of the surrounding rock of the tunnel 11, and improving the stability of the tunnel 11.

[0036] Optionally, when the interlayer distance between the lower coal seam 1 and the upper coal seam 2 is greater than 10 m, the interlayer distance between the lower coal seam 1 and the upper coal seam 2 is determined to be thick. Of course, in other embodiments, other values ​​can be used to determine that the interlayer distance between the lower coal seam 1 and the upper coal seam 2 is thick.

[0037] Optionally, the key layer refers to at least one relatively thick and hard rock layer between the upper and lower coal seams 1. Whether the lower coal seam 1 and the upper coal seam 2 contain a key layer can be determined based on the lithology distribution between the upper and lower coal seams 1. If the overburden 3 of the lower coal seam 1 includes multiple rock layers, and the intermediate interlayers have different lithologies and are distributed with high strength, hard and stable rock layers, such as sandstone layers, then it is determined that there is a key layer between the upper and lower coal seams 1.

[0038] Optionally, when the overburden stratum 3 collapses in layers after the lower coal seam 1 is mined and a rock beam 31 of a stable bearing structure is formed, the upper and lower coal seams 1 are determined to be close-range coal seams.

[0039] like Figure 1As shown, the inter-seam spacing between upper coal seam 2 and lower coal seam 1 is approximately 20 meters. The average thickness of upper coal seam 2 is 1.8 meters, while that of lower coal seam 1 is 2.1 meters. Buried at depths of 500 to 700 meters, both seams are mined using comprehensive mechanized mining, with natural caving used for roof management. All three working faces of upper coal seam 2 have been mined, with coal pillars of 30 meters and 50 meters remaining between the working faces, respectively. From upper coal seam 2 downward, the layers are mudstone 32, medium-grained sandstone, mudstone 32, thin coal seam, mudstone 32, fine-grained sandstone 33, and mudstone 32, with thicknesses of 3.84, 7.42, 2.4, 1.4, 1.57, 1, and 1.61, respectively, and depths of 485.58, 493, 495.4, 496.8, 498.37, 499.37, and 500.98, respectively. Among them, the interlayer spacing between the upper coal seam 2 and the lower coal seam 1 is about 20m, which is a thick interlayer spacing. The thickness of the medium-grained sandstone is 7.42m. The medium-grained sandstone is a hard rock layer. During the mining process of the lower coal seam 1, the overburden layer 3 of the lower coal seam 1 collapsed in layers. The medium-grained sandstone layer will form a rock beam 31 due to its thick and hard characteristics. It is determined that there is a key layer between the upper and lower coal seams 1, and it is a close-range coal seam.

[0040] like Figure 2 As shown, the upper coal seam 2 can adopt the method of leaving a lane along the goaf or the method of leaving a coal pillar. In this embodiment, the method of leaving a coal pillar in the upper coal seam 2 is used as an example for description. After the upper coal seam 2 is mined, the coal pillar generates concentrated stress and transmits and expands to the lower coal seam 1. Since the interlayer between the upper and lower coal layers is distributed with thick, high-strength and highly stable sandstone, due to the mining of the first working face 12 in the lower coal seam 1, the layered collapse of the overburden layer 3 will cause the coal pillar structure of the upper coal seam 2 to become unstable again, and superimpose and couple movement with the overburden layer 3 of the lower coal seam 1, forming a stronger mining stress.

[0041] After the upper coal seam 2 is mined, a first tunnel 111 and a second tunnel 112 are excavated at set positions in the lower coal seam 1. The first tunnel 111 and the second tunnel 112 are spaced apart in the left-right direction. The first working face 12 is located between the first tunnel 111 and the second tunnel 112, and the second working face 13 is located to the right of the second tunnel 112. The first working face 12 is a tunnel-retaining tunnel working face along the goaf, and the second working face is a tunnel-retaining reused tunnel working face. When excavating the second tunnel 112, the second tunnel 112 is offset to the left and inward below the goaf 21 of the upper coal seam 2 to avoid being located directly below the coal pillar of the upper coal seam 2, thereby reducing the stress of the coal pillar of the upper coal seam 2 on the second tunnel 112.

[0042] In this embodiment, the overburden 3 above the lower coal seam 1 is cut off and depressurized on the side of the second tunnel 112 adjacent to the first working face 12. Before the first working face 12 is mined, the key rock layer with large thickness, high strength and strong stability that will form the overburden movement of the upper and lower coal seams 1 during the mining process is weakened and cut off. By controlling the fracture position of the key rock layer, a stable rock beam 31 structure cannot be formed after the first working face 12 is mined, and the movement mode of the key rock layer is changed, so as to control the source of the strong mining stress of the first working face 12, reduce the mining stress gradient of the remaining tunnel, weaken the mining pressure intensity of the remaining tunnel, and improve the stability of the tunnel 11.

[0043] Furthermore, in this embodiment, the overburden layer 3 of the first working face 12 of the lower coal seam 1 is pre-cut, so that the overburden layer 3 cannot form a rock beam 31 structure. After the first working face 12 is mined, the goaf 21 naturally collapses, and the rock beam 31 structure of the upper working face is damaged and deflected and slipped down to the goaf 21, thereby avoiding the superimposed movement of the overburden structures of the upper and lower coal seams 1 to form a stronger mining stress, thereby improving the stability of the tunnel 11.

[0044] In some embodiments, the overburden layer 3 above the side of the second tunnel 112 adjacent to the first working face 12 is top-cut to form a top-cut line 4 on the overburden layer 3, including: determining the length of the top-cut line 4 based on the spacing distance between the top wall surface of the second tunnel 112 and the upper end surface of the rock beam 31 and the inclination angle of the top-cut line 4; drilling the overburden layer 3 through a top-cut drill hole to form the top-cut line 4, and the drill hole penetrates the rock beam 31.

[0045] like Figure 3 As shown, the top cutting line 4 extends from bottom to top and is arranged tilted to the left. The smaller the tilt angle of the top cutting line 4, the smaller the drilling depth. Conversely, the larger the tilt angle of the top cutting line 4, the greater the drilling depth. By adjusting the tilt angle of the top cutting line 4 and the distance between the top wall surface of the second tunnel 112 and the upper end surface of the rock beam 31, it is ensured that the drill hole penetrates the rock beam 31, so that the rock beam 31 cannot form a bearing structure when the first working face 12 is mined.

[0046] In some embodiments, the inclination angle of the top cutting line 4 includes the angle between the top cutting line 4 and the up-down direction and the angle between the top cutting line 4 and the length direction of the second lane 112 .

[0047] like Figure 4-Figure 5 As shown, Figure 4 The angle between the topping line 4 and the up-down direction in this embodiment is shown, that is, the topping line 4 is arranged to be inclined to the left, or the topping line 4 is arranged to be inclined to the right. Since the overburden 3 above the first working face 12 is to be toppled in the second tunnel 112 on the right side of the first working face 12, the topping line 4 extends from bottom to top and is arranged to be inclined to the left.

[0048] Figure 5 The angle between the top cutting line 4 and the length direction of the second tunnel 112 in this embodiment is shown. The length direction of the second tunnel 112 is consistent with the excavation direction of the first working face 12. For the convenience of description, the length direction of the second tunnel 112 is consistent with the front-back direction as an example. That is, the top cutting line 4 is arranged to be tilted forward, or the top cutting line 4 is arranged to be tilted backward.

[0049] In this embodiment, by limiting the inclination angle of the top cutting line 4, the top cutting of the drilling hole can radiate a larger range, ensuring the effect of the top cutting pressure relief while reducing the difficulty of drilling.

[0050] In some embodiments, as Figure 4 As shown, the angle A between the top cutting line 4 and the vertical direction is 0-30 degrees. By limiting the angle between the top cutting line 4 and the vertical direction, it is possible to prevent the top cutting line 4 from tilting too much to the left, which would affect the top cutting effect, and to prevent the top cutting line 4 from tilting too little to the left, which would increase the difficulty of drilling.

[0051] For example, the value of A is 5°, 10°, 15°, and 20°. In this embodiment, A is 20°.

[0052] In some embodiments, as Figure 5 As shown, the included angle B between the tangent line 4 and the longitudinal direction of the second tunnel 112 is 45°-55°. By limiting the included angle between the tangent line 4 and the front-to-back direction, it is possible to prevent the tangent line 4 from tilting too far forward or backward, which would increase the drilling depth. At the same time, it is possible to prevent the tangent line 4 from tilting too far forward or backward, which would result in insufficient operating space for the drilling equipment and increase the drilling difficulty.

[0053] Optionally, the value of B is 45°.

[0054] In some embodiments, there are multiple topping lines 4, which are spaced apart in the longitudinal direction of the second roadway 112. By evenly spacing the multiple topping lines 4 in the front-to-back direction, multiple locations of the rock beam 31 can be cut simultaneously, so that a stable rock beam 31 structure cannot be formed after the first working face 12 is mined, the movement mode of the key rock layer is changed, and the source of strong mining stress in the first working face 12 is controlled, the mining stress gradient of the remaining roadway is reduced, the mining pressure intensity of the remaining roadway is weakened, and the stability of the roadway 11 is improved.

[0055] In some embodiments, the top cut drill hole is a hydraulic fracture top cut.

[0056] Before the first working face 12 of the lower coal seam 1 is mined, hydraulic fracturing is used on the left side of the second tunnel 112 to advance cut off the rock layer that will form a rock beam 31 structure in the overburden 3 above the first working face 12, so that after the first working face 12 is mined, the overburden 3 above the first working face 12 will naturally collapse along the cutting line 4 to the goaf 21 of the lower coal seam 1, thereby improving the stress of the overburden 3 above the first working face 12. Through hydraulic fracturing, the cutting efficiency can be effectively improved.

[0057] Because the overburden 3 above the lower coal seam 1 consists, from top to bottom, of mudstone 32, medium-grained sandstone, mudstone 32, thin coal seam, mudstone 32, fine-grained sandstone 33, and mudstone 32, with thicknesses of 3.84, 7.42, 2.4, 1.4, 1.57, 1, and 1.61, respectively, during mining of the lower coal seam 1, the approximately 8-meter composite coal-rock layer of mudstone 32, thin coal seam, mudstone 32, fine-grained sandstone 33, and mudstone 32 beneath the medium-grained sandstone will lose its overall thickness as the first working face 12 is mined, failing to form a stable bearing structure. The approximately 8-meter-thick medium-grained sandstone layer, due to its thickness and hardness, is the key bearing layer controlling rock movement and is therefore the target layer for top cutting. During hydraulic fracturing, only the medium-grained sandstone layer needs to be hydraulically fractured.

[0058] For example, if the hole depth is 28m, the angle between the top cut line 4 and the vertical direction is 20°, and the angle between the top cut line 4 and the front-back direction is 45°, then hydraulic fracturing is required for the area between boreholes 15-25. A reverse interval fracturing method is used, with one fracturing cycle every 2m, for a total of five cycles. The distance between adjacent top cut lines 4 in the front-back direction is 8-10m. The fracturing horizon is the overburden stratum 38-16m.

[0059] Of course, in other embodiments, the top cutting line 4 may be arranged in other ways by the top cutting drilling.

[0060] In some embodiments, the horizontal distance C between the sidewall of the second roadway 112 facing away from the first working surface 12 and the support pillars 22 in the upper coal seam 2 adjacent to the goaf 21 is 10-50 m. By limiting the horizontal distance between the right side of the second roadway 112 and the left side of the support pillars 22 located on the right side of the upper coal seam 2, the stress exerted by the support pillars 22 on the second roadway 112 is effectively reduced.

[0061] It can be understood that the maximum horizontal distance between the second tunnel 112 and the support column 22 is when the second tunnel 112 is located directly below the goaf 21 .

[0062] Optionally, the support pillar 22 is a coal pillar.

[0063] For example, the value of C is 10m, 15m, 20m, 30m, 40m, and 50m.

[0064] In some embodiments, after the overburden 3 above the side of the second tunnel 112 adjacent to the first working face 12 is top-cut to form a top-cut line 4 on the overburden 3 , the control method further includes: filling a wall 5 on the side of the second tunnel 112 adjacent to the first working face 12 .

[0065] Specifically, if Figure 3 As shown, after the top of the first working surface 12 is cut, the wall 5 is filled at the left end of the second tunnel 112. By limiting the angle between the cutting line 4 and the up and down directions, space is reserved for the wall 5. The wall 5 provides support for the left side of the second tunnel 112, thereby realizing a tunnel left along the air.

[0066] For example, the filling wall 5 adopts flexible formwork high water filling retaining wall, and the flexible formwork size is 3m long, 2.5m wide and 3m high. The net width of the tunnel after filling is not less than 4.2m. The tunnel is lagged behind by 200m and strengthened with 3.6mπ-shaped beams and single pillars "one beam and three columns".

[0067] In some embodiments, the filling wall 5 on the side of the second tunnel 112 adjacent to the first working face 12 is located after the first working face 12 is mined. After the overburden stratum 3 above the first working face 12 is topped, the first working face 12 is mined to form a first goaf 14. The filling wall 5 is advanced closely following the first working face 12. In other words, the wall 5 is filled in the advanced portion of the first working face 12 after it advances a certain distance. The advancement distance is set based on actual construction conditions and can be 2 meters or 20 meters. By promptly filling the wall 5 after the first working face 12 advances, the stability of the second tunnel 112 is ensured.

[0068] In some embodiments, before the overburden layer 3 above the side of the second tunnel 112 adjacent to the first working face 12 is cut to form a cutting line 4 on the overburden layer 3 , the control method further includes: supporting the second tunnel 112 .

[0069] Specifically, if Figure 6-Figure 7 As shown, after the second tunnel 112 is excavated on the lower coal seam 1, the second tunnel 112 needs to be supported to ensure the stability and safety of the tunnel 11.

[0070] In some embodiments, supporting the second tunnel 112 includes: arranging a plurality of anchor rod assemblies 6 on the inner wall surface of the second tunnel 112, the plurality of anchor rod assemblies 6 are arranged at intervals in the length direction of the second tunnel 112, and each anchor rod assembly 6 includes a plurality of anchor rods 61 arranged at intervals in the circumferential direction of the second tunnel 112; arranging a plurality of groups of anchor cables 7 on the top wall surface of the second tunnel 112, the plurality of groups of anchor cables 7 are arranged at intervals in the length direction of the second tunnel 112, each group of anchor cables 7 includes a plurality of anchor cables 7 arranged at intervals in the width direction of the second tunnel 112, and at least one anchor rod assembly 6 is provided between two adjacent groups of anchor cables 7.

[0071] Specifically, if Figure 6-Figure 7 As shown, high-strength anchor rods 61 are used to support the top wall of the second tunnel 112. Multiple anchor rod assemblies 6 are spaced apart in the front-to-back direction. Each anchor rod assembly 6 includes multiple anchor rods 61 arranged on the roof of the second tunnel 112 and multiple anchor rods 61 arranged on the two walls. The multiple anchor rods 61 arranged on the roof are evenly spaced apart in the left-right direction, while the multiple anchor rods 61 arranged on the two walls are spaced apart in the top-to-bottom direction. Due to the limited length of the anchor rods 61, high-strength anchor cables 7 are used to support the top wall of the second tunnel 112. Multiple groups of anchor cables 7 are spaced apart in the front-to-back direction, and each group of anchor cables 7 includes multiple anchor cables 7 spaced apart in the left-to-right direction, thereby enhancing the support effect on the second tunnel 112.

[0072] Optionally, at least one anchor rod assembly 6 is provided between two adjacent anchor cables 7. It can be understood that one anchor rod assembly 6 is provided between two adjacent anchor cables 7, that is, the anchor rod assembly 6 and the anchor cable 7 group are arranged alternately in the front-to-back direction; or, two anchor rod assemblies 6 are provided between two adjacent anchor cables 7, that is, one group of anchor cables 7 is provided every two anchor rod assemblies 6.

[0073] Optionally, the multiple anchor cables 7 in the anchor cable group 7 and the multiple anchor rods 61 in the anchor rod assembly 6 are staggered in the left-right direction.

[0074] Optionally, the number of anchor cables in each group 7 can be the same or different.

[0075] For example, the number of anchor cables 7 in two adjacent groups of anchor cables 7 is set to three and four respectively.

[0076] Optionally, in order to facilitate the support of anchor rods 61 on the two adjacent sides of the top plate, the anchor rods 61 on the two adjacent sides can be arranged tilted, that is, the anchor rod 61 on the leftmost side of the top plate is tilted to the left, and the anchor rod 61 on the rightmost side of the top plate is tilted to the right.

[0077] For example, there are six anchor rods 61 on the top plate and three on each side. The dimensions of the anchor rods 61 on the top plate are Φ22×2400mm, and the dimensions of the anchor rods 61 on the two sides are Φ20×2200mm. The spacing between the top sides is 900mm×1000mm. The dimensions of the anchor cable 7 are Φ21.6×7300mm.

[0078] like Figure 8 As shown, the lane length refers to the size of the filling wall in the front-to-back direction. When the top plate of the first working surface 12 is not cut, the average displacement of the top and bottom plates of the second lane 112 is about 150 mm, and the average displacement of the two sides of the second lane 112 is about 830 mm.

[0079] like Figure 9 As shown, after the top plate of the first working face 12 is cut off, the top plates are numbered 1#, 2# and then 21# in sequence along the length direction of the second tunnel 112 starting from the position where the working face stops mining. The displacement of the top and bottom plates and the two sides of the second tunnel 112 is obviously effective. The maintenance and control of the surrounding rock of the goaf-retained tunnel is difficult. The goaf-retained tunnel is a special type of tunnel 11 where mining stress affects the dynamic pressure. The control of the rock layer by cutting off the top and unloading the pressure is also an effective method for controlling and reducing the mining stress of the goaf-retained tunnel. In this embodiment, when controlling the surrounding rock stress of the goaf-retained tunnel in the close-range coal seam containing the key layer with thick intervals, the mining stress of the goaf-retained tunnel in the close-range coal seam is weakened by cutting off the top and unloading the pressure. By cutting off the top of the thick key rock layer in the overburden 3 on the lower coal seam 1, the structure of the control top plate of the goaf is changed, which plays a role in reducing and alleviating the stress of the surrounding rock of the goaf, ensuring the stability of the surrounding rock of the goaf, and ensuring that the goaf can be used for a second time.

[0080] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like to indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0081] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. In the description of the present invention, "plurality" means at least two, such as two, three, etc., unless otherwise specifically defined.

[0082] In the present invention, unless otherwise specified or limited, the terms "installed," "connected," "connect," "fixed," etc. should be understood in a broad sense. For example, they can refer to fixed connection, detachable connection, or integration; mechanical connection, electrical connection, or communication; direct connection or indirect connection through an intermediate medium; internal communication between two elements or interaction between two elements, unless otherwise specified. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0083] In the present invention, unless otherwise expressly specified or limited, a first feature being "above" or "below" a second feature may mean that the first and second features are in direct contact, or that the first and second features are in indirect contact through an intermediate medium. Furthermore, a first feature being "above," "above," and "above" a second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is at a higher level than the second feature. A first feature being "below," "below," and "below" a second feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is at a lower level than the second feature.

[0084] In the present invention, the terms "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and the features of different embodiments or examples without contradiction.

[0085] It is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. A stress control method for gob-side entry in close-range coal seams, characterized in that: include: Excavating a tunnel at a preset position in the lower coal seam, wherein the tunnel comprises a first tunnel and a second tunnel, a first working face is formed between the first tunnel and the second tunnel, and the second tunnel is located below a goaf in the upper coal seam; Cutting the overburden layer above the side of the second roadway adjacent to the first working face to form a cutting line on the overburden layer, wherein the cutting line extends from bottom to top and is inclined toward the first working face, wherein the overburden layer includes a rock beam; The overburden layer above the side of the second roadway adjacent to the first working face is cut to form a cutting line on the overburden layer, comprising: determining the length of the top cutting line according to the distance between the top wall surface of the second roadway and the upper end surface of the rock beam and the inclination angle of the top cutting line; Drilling the overburden stratum through a top-cutting drill hole to form the top-cutting line, wherein the drill hole penetrates the rock beam; The inclination angle of the top cutting line includes the angle between the top cutting line and the up-down direction and the angle between the top cutting line and the length direction of the second lane; There are multiple tangent lines, and the multiple tangent lines are arranged at intervals in the length direction of the second lane, and / or, The top-cutting drill hole is a hydraulic fracturing top-cutting drill hole; After the overburden layer above the side of the second tunnel adjacent to the first working face is cut to form a cutting line on the overburden layer, the control method further includes: filling a wall on the side of the second tunnel adjacent to the first working face; The filling wall on one side of the second tunnel adjacent to the first working face is located after the first working face is mined; Before cutting the overburden layer above the side of the second roadway adjacent to the first working face to form a cutting line on the overburden layer, the control method further includes: supporting the second roadway; Supporting the second roadway includes: Arrange a plurality of anchor rod assemblies on the inner wall surface of the second roadway, the plurality of anchor rod assemblies are arranged at intervals in the longitudinal direction of the second roadway, and each anchor rod assembly includes a plurality of anchor rods arranged at intervals in the circumferential direction of the second roadway; Multiple groups of anchor cables are arranged on the top wall surface of the second tunnel, and the multiple groups of anchor cables are arranged at intervals in the length direction of the second tunnel. Each group of anchor cables includes multiple anchor cables arranged at intervals in the width direction of the second tunnel, and at least one anchor rod assembly is provided between two adjacent groups of anchor cables.

2. The stress control method for gob-side entry retaining in close-range coal seams according to claim 1 is characterized in that: The angle A between the tangent line and the vertical direction is 0-30°; and / or, An included angle B between the top cutting line and the length direction of the second lane is 45°-55°.

3. The stress control method for gob-side entry retaining in close-range coal seams according to claim 1 is characterized in that: A horizontal distance C between a side wall surface of the second tunnel facing away from the first working surface and a support column of the upper coal seam adjacent to the goaf is 10-50 m.

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