An evaluation method for the effect of pre-cracking and pressure relief of coal mine roof

Abstract

The present invention provides a method for evaluating the effect of pre-splitting and pressure-relieving roof pressure in a coal mine, the method comprising: constructing a pre-splitting hole in the first lane of a coal mining face; constructing displacement observation holes inclined toward the first lane along the non-pre-splitting area and the pre-splitting area of ​​the roof in the second lane of the coal mining face; installing a displacement measuring device in the displacement observation hole of each roof layer for measuring the downward displacement of each roof layer; pre-splitting the roof through the pre-splitting hole; during coal mining, the working face passes through the non-pre-splitting area and the pre-splitting area; measuring the displacement data of each roof layer in the non-pre-splitting area and the pre-splitting area using the displacement measuring device; and comparing the displacement data of the same roof layer in the pre-splitting area and the non-pre-splitting area to evaluate the effect of pre-splitting roof pressure. The method for evaluating the effect of pre-splitting and pressure-relieving roof pressure in a coal mine provided by the present invention is low in cost, highly operable, and effective, and can quantitatively evaluate the effect of pre-splitting roof pressure.

Description

Technical Field

[0001] The present invention relates to the technical field of safe mining of coal mines, and in particular to a method for evaluating the effect of pre-cracking and pressure relief of a coal mine roof. Background Art

[0002] The thick and hard roof of a coal mine is difficult to collapse during the mining process of the working face, and it is easy to form a large area of ​​hanging roof, causing large deformation of the tunnel. Especially when a large area of ​​the roof suddenly breaks, it can instantly produce strong vibrations and release a large amount of energy, which may cause large-scale roof collapse in the working face or tunnel, or even impact ground pressure accidents, seriously affecting the life safety of underground workers.

[0003] At present, the treatment measures for the hard and thick roof of coal mines are mainly to pre-crack the hard and thick roof above the coal seam by using roof deep hole blasting or hydraulic fracturing technology before or during working face mining, so as to reduce the integrity and strength of the roof so that it can collapse in time during working face mining, eliminating the hidden dangers of roof disaster accidents caused by large areas of roof hanging without collapsing.

[0004] Due to the lack of effective means to evaluate the effect of roof pre-cracking and pressure relief, many mines have taken roof pre-cracking measures, but are unable to determine whether the requirements for eliminating roof disaster hazards have been met, and are unable to optimize or strengthen the pre-cracking plan in a timely manner, which still easily leads to frequent roof disaster accidents.

[0005] Therefore, there is an urgent need for an evaluation method for the pre-cracking and pressure-relieving effect of coal mine roof to achieve quantitative evaluation of the pre-cracking effect of roof, which solves the current problem that the pre-cracking effect of roof cannot be quantitatively evaluated. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a method for evaluating the pre-splitting and pressure-relieving effect of coal mine roof with low cost, strong operability and good effect, so as to realize quantitative evaluation of the pre-splitting effect of the roof and solve the problem that the pre-splitting effect of the roof cannot be quantitatively evaluated at present.

[0007] To solve the above technical problems, the present invention provides a method for evaluating the effect of pre-cracking and pressure relief of coal mine roof, comprising the following steps:

[0008] Construct roof pre-crack holes in the roof pre-crack area in the first tunnel of the coal mining face;

[0009] In the second roadway of the coal mining face, displacement observation holes inclined toward the first roadway are constructed along the non-pre-cracked area and the pre-cracked area of ​​the roof;

[0010] A displacement measuring device for measuring the downward displacement of each roof plate is installed in the displacement observation hole of each roof plate;

[0011] Pre-crack the roof through the roof pre-crack holes;

[0012] To recover coal resources, the working face passes through the non-pre-cracked roof area and the pre-cracked roof area;

[0013] The displacement data of each layer of roof in the non-pre-cracked area and the pre-cracked area of ​​the roof are measured respectively by a displacement measuring device;

[0014] The displacement data of the roof at the same layer in the roof pre-cracking area and the non-pre-cracking area were compared to evaluate the roof pre-cracking effect.

[0015] Furthermore, there are a plurality of roof pre-crack holes, which are sequentially and spaced apart in the roof pre-crack zone along the direction of the first tunnel.

[0016] Furthermore, the roof pre-crack hole extends from the top of the first tunnel toward the inside of the roof in a direction perpendicular to the roof, and the roof pre-crack hole includes a sealing section and a fracturing section.

[0017] Furthermore, a plurality of displacement observation holes are respectively provided in the roof non-pre-cracked area and the roof pre-cracked area, and the displacement observation holes are sequentially spaced in the roof non-pre-cracked area and the roof pre-cracked area along the direction of the second tunnel.

[0018] Furthermore, the vertical distance between the displacement observation hole and the coal seam is not less than the vertical distance between the roof pre-splitting hole and the coal seam.

[0019] Furthermore, the roof pre-crack holes are roof blasting holes or hydraulic fracturing holes, and cracks are generated in the roof above the coal seam by explosive blasting or high-pressure water fracturing through the roof pre-crack holes.

[0020] Furthermore, the displacement measuring device includes an in-hole device that can be fixed on the inner wall of the displacement observation hole and an out-hole device connected to the in-hole device through a wire rope. The out-hole device is provided with a counting device for recording and storing the change value of the wire rope length.

[0021] Furthermore, the distance between the opening of the displacement observation hole and the side of the second laneway, the length of the displacement observation hole, and the azimuth angle of the displacement observation hole inclined toward the first laneway are all the same.

[0022] Furthermore, the method for evaluating the roof pre-cracking effect is:

[0023] The downward displacement of the roof in the non-pre-cracked area and the pre-cracked area at the same distance from the working face is set as L0 and L1 respectively. The distance from the working face when the roof in the non-pre-cracked area and the pre-cracked area begins to have obvious displacement is set as T0 and T1 respectively. The pre-crack effect is quantitatively evaluated according to the following formula:

[0024] △T=T1-T0

[0025] △L=L1-L0

[0026] The larger the △T and / or △L value is, the better the roof pre-cracking effect is.

[0027] The present invention provides a method for evaluating the effect of coal mine roof pre-splitting and pressure relief. By using a displacement measuring device, the downward displacement of each layer of roof in both the non-pre-splitting and pre-splitting areas is measured. The downward displacement of the roof in the pre-splitting and non-pre-splitting areas is then compared. This allows for a quantitative evaluation of the roof pre-splitting effect, partially resolving the current difficulty in quantitatively evaluating the effect of roof pre-splitting. Furthermore, the method provides a new means for evaluating the effect of roof pre-splitting under deep, high-pressure conditions, providing a novel approach for evaluating the effects of roof pre-splitting under conditions of high pressure, and is of great significance to the development and advancement of technologies for preventing and controlling high-pressure and rock burst disasters in coal mines. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 A process flow chart of a method for evaluating the effect of pre-cracking and pressure-relieving of a coal mine roof provided by an embodiment of the present invention;

[0029] Figure 2 A schematic top view of the arrangement of roof pre-splitting holes and displacement observation holes in a method for evaluating the effect of coal mine roof pre-splitting and pressure relief provided by an embodiment of the present invention;

[0030] Figure 3 A schematic side cross-sectional view of the arrangement of roof pre-splitting holes and displacement observation holes in a method for evaluating the effect of coal mine roof pre-splitting and pressure relief provided by an embodiment of the present invention;

[0031] Figure 4 A schematic diagram of the arrangement of a displacement test device in a method for evaluating the effect of pre-cracking and pressure relief of a coal mine roof provided by an embodiment of the present invention;

[0032] Figure 5 A schematic top view of a working face after the working face has successively advanced through unfractured and fractured areas in a method for evaluating the effect of pre-cracking and pressure-relieving of a coal mine roof provided by an embodiment of the present invention;

[0033] Figure 6 A schematic diagram of roof displacement changes in a pre-cracked zone and a non-pre-cracked zone in a method for evaluating the pre-cracked and pressure-relieving effect of a coal mine roof provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0034] See also Figure 1 The embodiment of the present invention provides a method for evaluating the effect of pre-cracking and pressure relief of a coal mine roof, comprising the following steps:

[0035] Step 1) Design roof pre-crack holes and roof displacement observation holes in the coal mining face tunnel. Specifically, the process includes: designing a plurality of roof pre-crack holes 3 in the roof pre-crack zone of the first tunnel 1, which are sequentially spaced along the direction of the first tunnel 1 and arranged in the roof pre-crack zone, wherein the roof pre-crack holes 3 extend from the top of the first tunnel 1 into the interior of the roof in a direction perpendicular to the roof. Designing a plurality of displacement observation holes 4 inclined toward the first tunnel 1 in the second tunnel 2 of the coal mining face, along the non-pre-crack zone and the pre-crack zone of the roof, respectively. The plurality of displacement observation holes 4 in the roof pre-crack zone are sequentially spaced along the direction of the second tunnel 2 within the roof pre-crack zone, and the plurality of displacement observation holes 4 in the non-pre-crack zone of the roof are sequentially spaced along the direction of the second tunnel 2 within the non-pre-crack zone of the roof. Furthermore, the vertical distance between the displacement observation holes 4 and the coal seam is not less than the vertical distance between the roof pre-crack holes 3 and the coal seam. At the same time, the distance between the opening of each displacement observation hole 4 and the sidewall of the second lane 2, the hole length of each displacement observation hole 4, and the azimuth angle of each displacement observation hole 4 inclined toward the first lane 1 are all the same.

[0036] Step 2) See Figure 2 and Figure 3 , a number of roof pre-crack holes 3 are constructed in the roof pre-crack area in the first tunnel 1 of the coal mining face. Each roof pre-crack hole 3 is arranged in sequence and at intervals in the roof pre-crack area along the direction of the first tunnel 1. Moreover, each roof pre-crack hole 3 extends from the top of the first tunnel 1 to the inside of the roof in a direction perpendicular to the roof. As a specific embodiment of the present invention, the roof pre-crack hole 3 is a roof blasting hole or a hydraulic fracturing hole. By using the roof pre-crack hole 3, explosive blasting or high-pressure water fracturing can be used to generate cracks in the roof above the coal seam, thereby achieving pre-crack of the roof. During or after coal seam mining, the roof near the mined coal seam is prone to displacement such as sinking and fracture.

[0037] Step 3) Several displacement observation holes 4 inclined toward the first roadway are constructed in the second roadway 2 of the coal mining face along the non-pre-cracked area of ​​the roof and the pre-cracked area of ​​the roof. Each displacement observation hole 4 in the pre-cracked area of ​​the roof is arranged in sequence along the direction of the second roadway 2 in the pre-cracked area of ​​the roof, and each displacement observation hole 4 in the non-pre-cracked area of ​​the roof is arranged in sequence along the direction of the second roadway 2 in the non-pre-cracked area of ​​the roof. In order to meet the previous design requirements for the displacement observation holes 4, the vertical distance between the displacement observation hole 4 and the coal seam is not less than the vertical distance between the pre-cracked hole 3 of the roof and the coal seam. At the same time, the distance between the orifice of each displacement observation hole 4 and the side of the second roadway 2, the length of each displacement observation hole 4, and the azimuth angle of each displacement observation hole 4 inclined toward the first roadway 1 are all the same.

[0038] Step 4) A displacement measuring device 5 for measuring the displacement of each roof layer is arranged in the displacement observation hole of each roof layer. Figure 4The displacement measuring device 5 includes an in-hole device 51 fixed to the inner wall of the displacement observation hole 4 and an out-hole device 53 located outside the displacement observation hole 4. Each in-hole device 51 is connected to the out-hole device 53 via an independent wire rope. Furthermore, the out-hole device 53 is equipped with a counting device that records and stores the length change of each wire rope 52. Because the roof above the coal seam is layered, an in-hole device 51 is placed in the displacement observation hole 4 of each layer of roof in both the pre-cracked and pre-cracked roof zones. When the roof of a particular layer moves downward, the in-hole device 51 fixed to the roof of that layer moves along with it. The in-hole device 51 pulls the wire rope 52, causing the length of the wire rope 52 to change. The change in the length of the wire rope 52 is recorded and stored by the counting device on the out-hole device 53. The change in the length of the wire rope 52 represents the displacement value of the roof at that layer.

[0039] As a specific embodiment of the present invention, the in-hole device 51 fixed in the displacement observation hole 4 adopts a claw anchor, which is provided with barbs. When the claw anchor is arranged in the displacement observation hole 4 of the top plate, it can prevent it from sliding down. When the top plate moves, it will drive the claw anchor to move together. Each claw anchor is connected to the out-hole device 53 by an independent wire rope 52. When the claw anchor moves with the top plate, the wire rope 52 connected to the claw anchor will be pulled. Each wire rope 52 is wrapped around the out-hole device 53 with a certain amount of excess. When the wire rope 52 is pulled, the wire rope in the displacement observation hole 4 will become longer. The amount of length increase is the amount of displacement of the top plate. The counting device installed in the out-hole device 53 to record the length change of the wire rope 52 will measure the length change of the wire rope 52 and record and store the length change value.

[0040] Step 5) Pre-crack the roof through the roof pre-crack holes 3. The roof pre-crack holes 3 can be roof blasting holes or hydraulic fracturing holes, and can respectively use explosive blasting or high-pressure water fracturing to generate cracks in the roof above the coal seam. As a specific embodiment of the present invention, the roof pre-crack is performed by explosive blasting, wherein each roof pre-crack hole 3 includes a sealing section 31 and a blasting pre-crack section 32. When pre-crack the roof, explosives are first loaded into the blasting pre-crack section 32, and then the roof pre-crack hole 3 is sealed through the sealing section 31. Then, the explosives are detonated, and cracks are generated in the roof near the roof pre-crack hole 3 by explosive blasting. By constructing a plurality of roof pre-crack holes 3 to pre-crack the roof, the roof within a certain range can be pre-cracked, thereby reducing the integrity and overall strength of the roof.

[0041] Step 6) The working face mines coal resources, and the working face passes through the roof non-pre-cracked area and the roof pre-cracked area. Figure 5, as the working face advances, the coal in the non-precracked roof area and the precracked roof area is gradually mined out. Due to the extraction of the coal, the roof above the coal seam will fracture or move. At this time, the value of the change in the length of a certain steel wire rope measured by the displacement observation hole 4 in the second roadway 2 is the displacement value of the roof where the connecting claw of the steel wire rope is anchored.

[0042] Step 7) Collect the displacement values of each layer of the roof in the non-precracked roof area and the precracked roof area measured by the displacement measuring device respectively. See Figure 6 , draw the displacement change curves of the roofs at the same layer in the non-precracked area and the precracked area according to the collected displacement values of each layer of the roof in the non-precracked roof area and the precracked roof area, so as to obtain the displacement change law of the roof during the advancement of the working face.

[0043] Step 8) Compare the displacement data of the roofs in the precracked roof area and the non-precracked roof area at the same layer respectively to evaluate the roof pre-cracking effect. The specific evaluation method is as follows:

[0044] Take the displacement amounts of the roofs at the same distance from the working face in the non-precracked roof area and the precracked roof area of the roof (that is, the roofs in the non-precracked roof area and the precracked roof area of the roof at the same layer) as L0 and L1 respectively. If L0 < L1, it means that the roof in the precracked area of the roof at the same layer moves more fully and the roof is easier to break. Similarly, the distances from the working face when the roofs in the non-precracked roof area and the precracked roof area of the roof start to have obvious displacements are set as T0 and T1 respectively. If T0 < T1, it means that the roof in the precracked roof area of the roof has a displacement ahead of the coal wall of the coal mining face farther, and the roof in the precracked roof area of the roof is more broken. Therefore, the pre-cracking effect of the roof in the pre-cracked area can be quantitatively evaluated according to the following formula:

[0045] △T = T1 - T0

[0046] △L = L1 - L0

[0047] When the value of △T or / and △L is larger, it means that the pre-cracking effect of the roof above the coal seam after pre-cracking is better.

[0048] Finally, it should be noted that the above specific implementation manners are only used to illustrate the technical solutions of the present invention rather than to limit them. Although the present invention has been described in detail with reference to the examples, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present invention, and they should all be covered within the scope of the claims of the present invention.

Claims

1. A method for evaluating the effect of pre-cracking and pressure relief of coal mine roof, characterized in that: The steps include: Construct roof pre-crack holes in the roof pre-crack area in the first tunnel of the coal mining face; In the second roadway of the coal mining face, displacement observation holes inclined toward the first roadway are constructed along the non-pre-cracked area and the pre-cracked area of ​​the roof; A displacement measuring device for measuring the downward displacement of each roof plate is installed in the displacement observation hole of each roof plate; Pre-crack the roof through the roof pre-crack holes; To recover coal resources, the working face passes through the non-pre-cracked roof area and the pre-cracked roof area; The displacement data of each layer of roof in the non-pre-cracked area and the pre-cracked area of ​​the roof are measured respectively by a displacement measuring device; Compare the displacement data of the same layer of roof in the pre-cracked area and the non-pre-cracked area to evaluate the effect of roof pre-cracked. The method for evaluating the roof pre-cracking effect is: The downward displacement of the roof in the non-pre-cracked area and the pre-cracked area at the same distance from the working face is set as L0 and L1 respectively. The distance from the working face when the roof in the non-pre-cracked area and the pre-cracked area begins to have obvious displacement is set as T0 and T1 respectively. The pre-crack effect is quantitatively evaluated according to the following formula: △T=T1-T0 △L=L1-L0 The larger the △T and / or △L value is, the better the roof pre-cracking effect is.

2. The method for evaluating the effect of pre-cracking and pressure relief of coal mine roof according to claim 1, characterized in that: There are a plurality of roof pre-crack holes, which are sequentially and spaced apart in the roof pre-crack zone along the direction of the first tunnel.

3. The method for evaluating the effect of pre-cracking and pressure-relieving of coal mine roof according to claim 2, characterized in that: The roof pre-crack hole extends from the top of the first tunnel toward the inside of the roof along a direction perpendicular to the roof, and the roof pre-crack hole includes a sealing section and a fracturing section.

4. The method for evaluating the effect of pre-cracking and pressure relief of coal mine roof according to claim 1, characterized in that: A plurality of displacement observation holes are respectively arranged in the roof non-pre-cracked area and the roof pre-cracked area, and the displacement observation holes are sequentially spaced along the direction of the second roadway in the roof non-pre-cracked area and the roof pre-cracked area.

5. The method for evaluating the effect of pre-cracking and pressure-relieving of coal mine roof according to claim 4, characterized in that: The vertical distance between the displacement observation hole and the coal seam is not less than the vertical distance between the roof pre-crack hole and the coal seam.

6. The method for evaluating the effect of pre-cracking and pressure-relieving of coal mine roof according to claim 5, characterized in that: The roof pre-crack holes are roof blasting holes or hydraulic fracturing holes, through which cracks are generated in the roof above the coal seam by explosive blasting or high-pressure water fracturing.

7. The method for evaluating the effect of pre-cracking and pressure-relieving of coal mine roof according to claim 1, characterized in that: The displacement measuring device includes an in-hole device that can be fixed on the inner wall of the displacement observation hole and an out-hole device connected to the in-hole device through a wire rope. The out-hole device is provided with a counting device for recording and storing changes in the length of the wire rope.

8. The method for evaluating the effect of pre-cracking and pressure-relieving of coal mine roof according to claim 1, characterized in that: The distance between the opening of the displacement observation hole and the side of the second laneway, the hole length of the displacement observation hole, and the azimuth angle of the displacement observation hole inclined toward the first laneway are all the same.

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