Near-distance coal seam gob-side entry retaining stress control method

Abstract

The invention relates to the technical field of coal mines, in particular to a short-distance coal seam gob-side entry retaining stress control method which comprises the steps that roadways are dug at the preset position of a lower coal seam, the roadways comprise the first roadway and the second roadway, a first working face is formed between the first roadway and the second roadway, and a second working face is formed between the second roadway and the first working face; the second roadway is located below a goaf of the upper coal seam, top cutting is conducted on an overlying stratum above the side, close to the first working face, of the second roadway to form a top cutting line on the overlying stratum, and the top cutting line extends in the direction from bottom to top and is obliquely arranged in the direction of the first working face; according to the close-distance coal seam gob-side entry retaining stress control method, roadway deformation can be reduced, and the stability of the roadway is improved.

Description

Technical Field

[0001] The invention relates to the technical field of coal mines, and in particular to a method for controlling stress of gob-side lane retaining in a close-range coal seam. 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 the related technology, the tunnel is mostly supported by anchor rods and cables. However, under the action of strong mining stress, the tunnel is prone to deformation and its stability is reduced. Summary of the invention

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

[0005] The stress control method for leaving a lane along the goaf in a close-range coal seam according to an embodiment of the present invention 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; top cutting is performed on 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 extends in a direction from bottom to top and is arranged obliquely toward the direction of the first working face, wherein the overburden layer comprises a rock beam.

[0006] The stress control method for gob-side lane retention in a close-range coal seam according to the 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 top cutting lines, and the multiple top cutting lines are arranged at intervals in the length direction of the second tunnel, and / or the top cutting drill hole is a hydraulic fracturing top cutting hole.

[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 one 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-cutting 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 are arranged at intervals in the length direction of the second tunnel, and each anchor rod assembly includes 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 are arranged at intervals in the length direction of the second tunnel, each group of anchor cables includes a plurality of 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. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

[0018] Figure 3 It 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 viewing angle of the top cutting line of the embodiment of the present invention.

[0021] Figure 6 It is a schematic diagram of support for the second tunnel of an embodiment of the present invention.

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

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

[0024] Fig. 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, tunnel 11, first tunnel 111, second tunnel 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] 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] The stress control method for gob-side roadway retention in a close-range coal seam according to an embodiment of the present invention comprises excavating a roadway 11 at a preset position of a lower coal seam 1, wherein the roadway 11 comprises a first roadway 111 and a second roadway 112, a first working face 12 is formed between the first roadway 111 and the second roadway 112, and the second roadway 112 is located below the gob 21 of the upper coal seam 2. The overburden stratum 3 above the side of the second roadway 112 adjacent to the first working face 12 is top-cut to form a top-cutting line 4 on the overburden stratum 3, the top-cutting line 4 extends in a direction from bottom to top and is arranged obliquely toward the direction of the first working face 12, wherein the overburden stratum 3 comprises 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 depressurized. When mining the lower coal seam 1, since the top plate of the lower coal seam 1 is thin and has no key layer, the working face of the lower coal seam 1 is mined as it 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 lower coal seam 1 is mined to form a stable bearing structure and generate 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 of a close-range coal seam in an embodiment of the present invention starts from the root cause of the surrounding rock of the tunnel 11 of the close-range lower coal seam 1 being subjected to strong mining stress, 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 ​​may be used to determine that the interlayer distance between the lower coal seam 1 and the upper coal seam 2 is thick.

[0037] Optionally, a 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 overlying layer 3 of the lower coal seam 1 includes multiple rock layers, and the intermediate interlayers have different lithologies and have a strong, hard and stable distribution of 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 distance between the upper coal seam 2 and the lower coal seam 1 is about 20m, the average thickness of the upper coal seam 2 is 1.8m, the average thickness of the lower coal seam 1 is 2.1m, and the burial depth is 500-700m. All of them adopt comprehensive mechanized mining and natural caving method to manage the roof. Among them, the three working faces of the upper coal seam 2 have been mined, and the section coal pillars between the working faces are 30m and 50m respectively. From the upper coal seam 2 downward, there are mudstone 32, medium-grained sandstone, mudstone 32, thin coal seam, mudstone 32, fine-grained sandstone 33 and mudstone 32, with layer thicknesses of 3.84, 7.42, 2.4, 1.4, 1.57, 1, 1.61, and depths of 485.58, 493, 495.4, 496.8, 498.37, 499.37, 500.98. 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 collapses 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 tunnel 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 taken 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 stratified 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, the first tunnel 111 and the second tunnel 112 are excavated at the set position of the lower coal seam 1. The first tunnel 111 and the second tunnel 112 are arranged at intervals in the left-right direction. The first working face 12 is between the first tunnel 111 and the second tunnel 112, and the right side of the second tunnel 112 is the second working face 13. The first working face 12 is a tunnel-retaining working face along the goaf, and the second working face is a tunnel-retaining reuse working face. When excavating the second tunnel 112, the second tunnel 112 is staggered to the left and inward below the goaf 21 of the upper coal seam 2 to avoid the second tunnel 112 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 strata with large thickness, high strength and strong stability that will control the movement of the overburden strata of the upper and lower coal seams 1 during the mining process are weakened and cut off. By controlling the breaking position of the key rock strata, 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 strata is changed, so as to control the source of 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 the present embodiment, the overburden layer 3 of the first working face 12 of the lower coal seam 1 is pre-cut to prevent the overburden layer 3 from forming 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 destroyed and deflected and slid 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 cutting line 4 on the overburden layer 3, including: determining the length of the top cutting line 4 according to 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 cutting line 4; drilling the overburden layer 3 through a top cutting drill hole to form the top cutting 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 top cutting line 4 and the up-down direction in this embodiment is shown, that is, the top cutting line 4 is arranged to be inclined to the left, or the top cutting line 4 is arranged to be inclined to the right. Since the overburden layer 3 above the first working face 12 is top cut in the second tunnel 112 on the right side of the first working face 12, the top cutting 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-to-back direction. That is to say, the top cutting line 4 is arranged to be inclined forward, or the top cutting line 4 is arranged to be inclined 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 top cutting pressure relief while reducing the difficulty of drilling.

[0050] In some embodiments, Figure 4 As shown, the angle A between the top cutting line 4 and the up-down direction is 0-30°. By limiting the angle between the top cutting line 4 and the up-down direction, it is prevented that the top cutting line 4 tilts too much to the left, which affects the top cutting effect, and it is prevented that the top cutting line 4 tilts too little to the left, which increases 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, Figure 5 As shown, the included angle B between the top cutting line 4 and the length direction of the second lane 112 is 45°-55°. By limiting the included angle between the top cutting line 4 and the front-back direction, it is prevented that the top cutting line 4 tilts forward or backward at too large an angle, resulting in an increase in the drilling depth, and at the same time, it is prevented that the top cutting line 4 tilts forward or backward at too small an angle, resulting in insufficient operating space for the drilling equipment, increasing the difficulty of drilling.

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

[0054] In some embodiments, there are multiple top cutting lines 4, and multiple top cutting lines 4 are arranged at intervals in the length direction of the second roadway 112. By evenly arranging multiple top cutting lines 4 in the front-back direction, multiple positions of the rock beam 31 can be cut off at the same time, so that the first working face 12 cannot form a stable rock beam 31 structure after mining, and the movement mode of the key rock formation 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 roadway, weaken the mining pressure intensity of the remaining roadway, and improve the stability of the roadway 11.

[0055] In some embodiments, the top-cutting drill hole is a hydraulic fracturing top-cutting.

[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 top cutting line 4 to the goaf 21 of the lower coal seam 1, thereby achieving an improvement in the stress of the overburden 3 above the first working face 12. Through hydraulic fracturing, the top cutting efficiency can be effectively improved.

[0057] Since the overburden 3 above the lower coal seam 1 is mudstone 32, medium-grained sandstone, mudstone 32, thin coal seam, mudstone 32, fine-grained sandstone 33 and mudstone 32 from top to bottom, and the layer thicknesses are 3.84, 7.42, 2.4, 1.4, 1.57, 1, 1.61, when the lower coal seam 1 is mined, the composite coal rock layer of mudstone 32, thin coal seam, mudstone 32, fine-grained sandstone 33 and mudstone 32, which is about 8 meters, located below the medium-grained sandstone will not form a stable bearing structure as the total thickness of the first working face 12 is mined and exposed, and the medium-grained sandstone layer of about 8 meters thick is the key bearing layer for controlling the movement of the rock layer, that is, the top cutting target layer. During hydraulic fracturing, only the rock layer where the medium-grained sandstone is located needs to be hydraulically fractured.

[0058] For example, if the hole depth is 28m, the angle between the top cutting line 4 and the vertical direction is 20°, and the angle between the top cutting line 4 and the front-back direction is 45°, it is necessary to hydraulically fracture the range of boreholes 15-25, and adopt the interval reverse sequence method, fracture once every 2m, and fracture 5 times in total. The interval between two adjacent top cutting lines 4 in the front-back direction is 8-10m. Fracturing layer: overburden layer 38-16m range.

[0059] Of course, in other embodiments, the top cutting drilling may also be performed in other ways to arrange the top cutting line 4 .

[0060] In some embodiments, the horizontal distance C between the side wall of the second tunnel 112 away from the first working surface 12 and the support column 22 of the upper coal seam 2 adjacent to the goaf 21 is 10-50m. By limiting the horizontal distance between the right side of the second tunnel 112 and the left side of the support column 22 located on the right side of the upper coal seam 2, the stress of the support column 22 on the second tunnel 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 that the second tunnel 112 is located directly below the goaf 21 .

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

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

[0064] In some embodiments, after 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-cutting line 4 on the overburden layer 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, 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 empty space.

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

[0067] In some embodiments, the filling wall 5 on one 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 cut, the first working face 12 is mined to form a first goaf 14, and the filling wall 5 is advanced closely following the first working face 12, that is, the first working face 12 is advanced forward for a certain distance and the wall 5 is filled in the advanced part. The advancement distance is set according to the actual construction situation, which can be 2m or 20m. By filling the wall 5 in time after the first working face 12 is advanced, 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 top-cut to form a top-cutting line 4 on the overburden layer 3 , the control method further includes: supporting the second tunnel 112 .

[0069] Specifically, 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, the second tunnel 112 is supported, including: 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, Figure 6-Figure 7 As shown, high-strength anchor rods 61 are used to support the top wall of the second tunnel 112, and multiple anchor rod assemblies 6 are arranged at intervals in the front-to-back direction. Each anchor rod assembly 6 includes multiple anchor rods 61 arranged on the top plate of the second tunnel 112 and multiple anchor rods 61 arranged on the two walls, wherein the multiple anchor rods 61 arranged on the top plate are evenly spaced in the left-right direction, and the multiple anchor rods 61 arranged on the two walls are spaced in the up-down direction. Due to the limited length of the anchor rods 61, high-strength anchor cables 7 are used to support the top plate of the second tunnel 112, multiple groups of anchor cables 7 are spaced in the front-to-back direction, and each group of anchor cables 7 includes multiple anchor cables 7 spaced in the left-to-right direction, so as to enhance the support effect of the second tunnel 112.

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

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

[0074] Optionally, the number of anchor cables in each group 7 can be set to 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 6 anchor rods 61 on the top plate, 3 anchor rods 61 on each side, the size of the anchor rods 61 on the top plate is Φ22×2400mm, the size of the anchor rods 61 on the two sides is Φ20×2200mm, and the spacing between the top sides is 900mm×1000mm. The size of the anchor cable 7 is 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 Fig. 9 As shown, after the top plate of the first working face 12 is cut, the top plates are numbered 1#, 2# and 21# in sequence from the working face stop position along the length direction of the second tunnel 112, and 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 stratum by cutting 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 the surrounding rock stress of the goaf-retained tunnel in the close-range coal seam containing the key layer is controlled in the thick layer spacing, the mining stress of the goaf-retained tunnel in the close-range coal seam is weakened by cutting the top and unloading the pressure. By cutting the top of the thick key rock layer in the overburden 3 on the lower coal seam 1, the control of the top plate structure of the tunnel is changed, which plays a role in reducing the surrounding rock stress of the tunnel, ensuring the stability of the surrounding rock of the tunnel, and ensuring that the tunnel can be used for the second time.

[0080] In the description of the present invention, it is to 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”, etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element 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] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0082] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral one; it can be a mechanical connection, an electrical connection, or communication with each other; it can be a direct connection, or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0083] In the present invention, unless otherwise clearly specified and 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. Moreover, a first feature being "above", "above" or "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 higher in level than the second feature. A first feature being "below", "below" or "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 lower in level than the second feature.

[0084] In the present invention, the terms "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" etc. 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 representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the described specific features, structures, materials or characteristics may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0085] It is to be understood that the above embodiments are exemplary and are not to 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 method for controlling stress of gob-side entry in close-range coal seams, characterized in that: include: Digging a tunnel at a preset position in the lower coal seam, wherein the tunnel includes 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; The overburden layer above the side of the second tunnel adjacent to the first working face is top-cut to form a top-cutting line on the overburden layer, the top-cutting line extends from bottom to top and is inclined toward the first working face, wherein the overburden layer includes rock beams.

2. The stress control method for gob-side entry retention in a close-range coal seam according to claim 1 is characterized in that: 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, comprising: Determine the length of the top cutting line according to 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 cutting line; The top cutting line is formed by drilling a top cutting drill hole into the overburden layer, and the drill hole penetrates the rock beam.

3. The stress control method for gob-side entry retention in a close-range coal seam according to claim 2 is characterized in that: The inclination angle of the top cut line includes an angle between the top cut line and the up-down direction and an angle between the top cut line and the length direction of the second lane.

4. The stress control method for gob-side entry retention in a close-range coal seam according to claim 3 is characterized in that: The angle A between the tangent line and the up-down 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°.

5. The stress control method for gob-side entry retention in close-range coal seams according to claim 2 is characterized in that: 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.

6. The stress control method for gob-side entry retention 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.

7. The stress control method for gob-side entry retention in a close-range coal seam according to claim 1 is characterized in that: 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: A wall is filled on one side of the second tunnel adjacent to the first working surface.

8. The stress control method for gob-side entry retention in a close-range coal seam according to claim 7 is characterized in that: The filling wall on one side of the second tunnel adjacent to the first working face is located after the mining of the first working face.

9. The stress control method for gob-side entry retention in a close-range coal seam according to claim 7, characterized in that: Before cutting the overburden layer above the side of the second tunnel adjacent to the first working face to form a cutting line on the overburden layer, the control method further includes: The second tunnel is supported.

10. The stress control method for gob-side entry retention in close-range coal seams according to claim 9, characterized in that: Supporting the second roadway includes: Arrange a plurality of anchor rod assemblies on the inner wall surface of the second lane, the plurality of anchor rod assemblies are arranged at intervals in the length direction of the second lane, and each anchor rod assembly includes a plurality of anchor rods arranged at intervals in the circumferential direction of the second lane; A plurality of groups of anchor cables are arranged on the top wall surface of the second tunnel, and the plurality of groups of anchor cables are arranged at intervals in the length direction of the second tunnel. Each group of anchor cables includes a plurality of 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.

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