A step-by-step cracking method for hard roof based on static blasting technology

Abstract

The present invention discloses a method for causing step-by-step fracturing of a hard roof based on static blasting technology. By adding early strength agents of different contents to static medicine rolls, the hydration expansion stress and thermal stress of the static medicine rolls are improved, and the hydration time is reduced. Modified static medicine rolls with different hydration times are sequentially loaded at different depths of annular grooves in a borehole, so that a time difference is formed when the modified static medicine rolls are hydrated, the weakening and fracturing effect is significantly improved, and the strength and stability of the rock mass around the borehole are greatly reduced. Since the modified static medicine rolls at the borehole mouth position are hydrated first, under the joint action of various forces, the roof rock at the borehole mouth position collapses first, and after the collapse is completed, a new free weak surface is formed. The second hydrated position continues to use the free weak surface and cracks generated by the first hydration fracturing to continue fracturing and collapsing. After repeated superposition effects are formed, a layered and step-by-step fracturing effect of the hard roof rock layer is finally achieved.

Description

Technical Field

[0001] The present invention relates to a step-by-step fracturing method for a hard roof based on static blasting technology, which is particularly suitable for weakening and fracturing a coal seam roof with hard and dense rock, high strength, strong self-bearing capacity and high integrity. Background Art

[0002] Cracking and collapsing the hard roof in the goaf is an effective measure to prevent dynamic impact disasters such as roof fall, underground hurricanes, mine tremors, and gas over-limit problems. At present, coal mines mainly use a variety of weakening methods such as high-pressure water injection, deep hole blasting, gas phase fracturing, mechanical roof cutting, and comprehensive weakening to crack the hard roof. However, the above weakening methods all have some shortcomings. The high-pressure water injection fracturing equipment has a complicated operating procedure and is large in size, making it inconvenient to operate in a narrow space. In addition, this technology consumes a large amount of water resources and is not suitable for arid areas. Deep hole blasting has a low safety factor and generates very large impact energy at the moment of explosion, which can easily cause dynamic disasters such as mine tremors and roof collapse. In addition, the sparks generated during the blasting process can easily induce gas explosion accidents in the goaf, posing a safety hazard. Gas phase fracturing and mechanical roof cutting equipment are large in size, making it difficult to operate in a narrow working face.

[0003] In recent years, static blasting technology, centered around static charge cartridges, has been widely used due to its advantages of being pollution-free, free of flying rocks, noiseless, vibration-free, easy to operate, and highly safe. However, this technology also suffers from issues such as long fracturing time and the susceptibility of coal dust spraying during the drilling process.

[0004] Therefore, how to provide a new fracturing method that can shorten the fracturing time, improve the efficiency of weakening the roof rock layer, increase the degree of rock fragmentation, and prevent the occurrence of blowouts during the fracturing process is one of the research directions of this industry. Summary of the Invention

[0005] In response to the problems existing in the above-mentioned prior art, the present invention provides a method for step-by-step fracturing of a hard roof based on static blasting technology. By layering and collapsing the hard roof rock layer multiple times and step by step, it can shorten the fracturing time, improve the efficiency of weakening the roof rock layer, increase the degree of rock layer fragmentation, and prevent the occurrence of blowouts during the fracturing process.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is: a method for gradually fracturing a hard roof based on static blasting technology, the specific steps are as follows:

[0007] A. Using a drilling rig, weakening and fracturing boreholes are drilled at the working face cut location and the tunnel end location, respectively, toward the hard roof in the direction of the coal mining working face and the direction of the goaf, so that the boreholes pass through the false roof and the direct roof to reach the old roof. The weakening and fracturing boreholes are arranged in a straight line; the depth of the weakening and fracturing boreholes is determined based on the relationship between the collapse height and the crushing expansion characteristics;

[0008] B. After completing the weakening and fracturing drilling, multiple predetermined positions are set at equal intervals at different depths along the axial direction of the weakening and fracturing drilling hole. A groove cutting drill bit is used to circumferentially cut the wall of the weakening and fracturing drilling hole at each predetermined position to form an annular groove. The grooves are numbered from the inside out as annular grooves a, b, c...n, and the hole is cleaned.

[0009] C. Select static rolls with the same number of annular grooves as those formed in step B, and each static roll has the same mass. Then, add a different mass of early strength agent to each static roll to form a modified static roll, so as to shorten the hydration time of the static roll. The mass of the early strength agent added to each modified static roll is arranged in an arithmetic progression, and the modified static rolls are classified and marked using labels of different colors.

[0010] D. First, select the modified static roll containing the least accelerator, completely immerse it in water, and fill it into the deepest annular groove a in the weakened cracking borehole and compact it. Then, select modified static rolls in the order of the amount of accelerator added in the modified static roll from small to large, and fill them into the corresponding annular grooves b, c, ... n from deep to shallow, until all the annular grooves in the borehole are filled. Finally, use a sealing device compatible with the annular groove structure to seal the borehole. This can fully utilize the hydration expansion stress and thermal stress of the modified static roll, improve the cracking efficiency, and effectively prevent the occurrence of blowout.

[0011] E. After the hole is sealed, the modified static medicine rolls filled in the annular cuts contain different early strength agents, which makes the hydration time of each modified static medicine roll different. As a result, the time for each modified static medicine roll to generate expansion stress and thermal stress during hydration is different, and the hydration time decreases from the inside to the outside of the borehole. The modified static medicine roll closest to the borehole mouth reaches the hydration time first, so that the annular cut where it is located is subjected to expansion stress and thermal stress generated by hydration, and under the combined action of gravity and ground pressure, the top rock at the borehole mouth position collapses first, and the collapse is complete. After that, a new free weak plane is formed. Then, the modified static drug coil closest to the borehole reaches the hydration time, causing the annular groove where it is located to generate expansion stress and thermal stress under hydration. Under the combined action of gravity and ground pressure, the rock at the current annular groove location continues to collapse, and a new free weak plane continues to form at this location. This cycle continues. By placing modified static drug coils with different hydration times at different depths, the hydration performance of each modified static drug coil forms a superposition effect, and ultimately the hard roof rock layer around the borehole is collapsed in layers multiple times.

[0012] F. According to the area of ​​the hard roof that needs to be cracked, multiple weakening and cracking drill holes are constructed at the same time, and steps B to E are repeated synchronously for each weakening and cracking drill hole, so as to simultaneously achieve the weakening and cracking effect of multiple weakening and cracking drill holes on the hard roof, and ultimately effectively improve the weakening and cracking efficiency of the hard roof.

[0013] Furthermore, the upper part of the annular groove is an arc-shaped inclined surface and the lower part is a flat surface. When the modified static medicine coil in the annular groove is hydrated to generate expansion stress and thermal stress, the arc-shaped inclined surface can change the pressure direction of the expansion stress and thermal stress after being subjected to force, thereby suppressing the axial stress output of the modified static medicine coil, achieving a self-sealing hole effect, and effectively preventing the occurrence of blowout holes.

[0014] Furthermore, the weakening and fracturing drill holes are single-row drill holes, which are inclined toward the advancing direction of the coal mining face and the goaf area respectively. The drilling inclination angle is 30° to 60°, the hole diameter is 36 to 50 mm, and the drilling spacing is 0.4 to 0.8 m; the diameter of the annular groove inside the weakening and fracturing drill hole is 80 mm, and the axial spacing is 30 mm.

[0015] Furthermore, the sealing device in step D includes a push rod, a disc plug, a control block and a positioning pin, a radially variable diameter through hole is provided inside the disc plug, and the radially variable diameter through hole consists of a front section, a middle section and a rear section, and the diameter of the middle section is larger than the diameters of the front section and the rear section, and the diameters of the front section and the rear section are the same; the control block is installed in the middle section of the through hole and can rotate in the middle section of the through hole; the control block is a rectangular body, which consists of an upper rectangular surface, a lower rectangular surface, two rectangular side surfaces and two square side surfaces, and the two rectangular side surfaces and the two square side surfaces are embedded with a first magnet; there are two positioning pins, and the two positioning pins are respectively installed in the front section and the rear section, and can move axially in the through hole; the two positioning pins are equipped with a second magnet near one end of the control block, and the polarity of the second magnet is opposite to that of the first magnet; there are multiple push rods, one end of which extends into the disc plug and is fixedly connected to the center of the lower rectangular surface of the control block by a thread, and the other end of the push rod It is coaxially connected with the rest of the push rods in sequence, and when the push rod rotates, it can drive the control block to rotate in the middle section of the through hole; when the hole is not sealed, the two rectangular side surfaces of the control block are perpendicular to the axis of the through hole, and at this time, the two positioning pins are magnetically connected to the two rectangular side surfaces by the first magnet and the second magnet respectively; so that the two positioning pins are completely in the disc plug, which is convenient for the sealing device to extend into the drilled hole; when the sealing device extends into the drilled hole to seal the hole, the rotating push rod drives the control block to rotate in the middle section of the through hole, so that the two rectangular side surfaces are separated from the two positioning pins, and the control block can push the two positioning pins to move in the front section and the rear section respectively during the rotation process, so that the two positioning pins extend from the disc plug away from one end of the control block until the two rectangular side surfaces are parallel to the axis of the through hole, and the two positioning pins reach the maximum extension distance. At this time, the two positioning pins are magnetically connected to the two square side surfaces by the first magnet and the second magnet respectively, thereby achieving a sealing effect on the drilled hole.

[0016] Furthermore, the polarity of the first magnet is an S pole, and the polarity of the second magnet is an N pole.

[0017] Furthermore, the time t1 required for the modified static medicine roll to be completely immersed in water is 2 to 2.5 minutes. The modified static medicine roll after being completely immersed in water must be filled into the annular groove of the drilled hole within 10 minutes. The hydration time t2 of each modified static medicine roll is within the range of 1 to 2 hours.

[0018] Furthermore, the process of determining the depth of the weakening and fracturing drill hole in step A is as follows: the depth of the weakening and fracturing drill hole is determined based on the relationship between the collapse height and the crushing and expansion characteristics, wherein the collapse height is the coal seam mining height, and the specific formula is:

[0019] H=M / (K P -1)

[0020] Where H is the depth of the weakened fractured borehole; M is the mining height of the coal seam; K P is the coefficient of expansion.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] 1. Compared with blasting cracking, the static blasting weakening technology adopted in the present invention generates expansion stress that is applied continuously rather than a high-energy impact in a short period of time. This method can effectively reduce the impact load on the working surface, has the advantages of being environmentally friendly, no flying rocks, no noise, no vibration, etc., and can effectively ensure safe production in mines.

[0023] 2. In the present invention, by adding different amounts of early strength agents to the static medicine roll, the hydration expansion stress and thermal stress of the static medicine roll are increased, the hydration time is reduced, and the hydration efficiency is improved. Moreover, based on the different depths of the annular groove in the borehole, modified static medicine rolls with different hydration times are sequentially loaded, so that a time difference is formed when the modified static medicine roll is hydrated, which can form a superposition effect in the subsequent fracturing, significantly improving the weakening fracturing effect, greatly reducing the strength and stability of the rock mass around the borehole, and generating cracks. Moreover, because the modified static medicine roll at the borehole mouth is hydrated first, under the combined action of the expansion stress and thermal stress generated by hydration, gravity, and ground pressure, the roof rock at the borehole mouth position is the first to collapse. After the collapse is completed, a new free weak surface is formed. The second hydrated position can utilize the free weak surface and cracks generated in the first hydration fracturing process to continue fracturing and collapsing. After the superposition effect is repeatedly formed, the layered and step-by-step fracturing effect of the hard roof rock layer is finally achieved.

[0024] 3. The present invention adopts a specific sealing device and a specially designed annular groove structure, which not only increases the charge of the fracture-inducing drill hole and gives full play to the hydration expansion stress and thermal stress of the modified static drug roll, but also when the modified static drug roll in the annular groove is hydrated to generate expansion stress and thermal stress, the arc inclined surface can change the pressure direction of the expansion stress and thermal stress after being subjected to force, thereby suppressing the axial stress output of the modified static drug roll, achieving a self-sealing effect, effectively preventing the occurrence of blowout phenomenon, and improving construction safety.

[0025] 4. The present invention determines the drilling depth of the weakened fracturing borehole based on the relationship between the collapse height and the crushing expansion characteristics, and adjusts the hydration time by adjusting the size of the annular groove, the spacing between adjacent annular grooves, and the content of the early strength agent added to the modified static medicine roll, thereby adjusting the time and position of multiple collapses of the hard roof in the goaf during fracturing, so that the collapse height gradually increases and the block size gradually decreases, and finally the controllable block size of the hard roof collapse is achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 A schematic diagram of the arrangement of weakened fracturing drilling holes according to the present invention;

[0027] Figure 2 Schematic diagram of charge and sealing of weakened fracture drilling in the present invention;

[0028] Figure 3 Schematic top view of the arrangement of weakened fracturing drill holes in the present invention;

[0029] Figure 4 This is a schematic structural diagram of the sealing device of the present invention when the holes are not sealed;

[0030] Figure 5 for Figure 4 Top view and partial enlarged view of the sealing device;

[0031] Figure 6 A top view and a partially enlarged view of the sealing device of the present invention when sealing a hole;

[0032] Figure 7 It is a construction flow chart of the step-by-step cracking method for a hard roof according to the present invention.

[0033] In the figure: 1-pseudo-top; 2-direct top; 3-old top; 4-annular groove; 5-annular groove a; 6-annular groove b; 7-annular groove c; 8-weakened fracture-inducing borehole; 9-sealing device; 10-modified static medicine roll; 11-coal mining face; 12-air intake tunnel; 13-return air tunnel; 14-hydraulic support; 15-goaf; 16-fracture-inducing fissure; 91-push rod; 92-disc plug; 93-locating pin; 94-control block; 95-radial reducing hole; 96-first magnet; 97-second magnet. DETAILED DESCRIPTION

[0034] The present invention will be further described below.

[0035] like Figure 7 As shown, the specific steps of the present invention are:

[0036] A. Use a drilling rig to construct a weakened fracture-causing drill hole 8 at the working face opening position and the tunnel end position, respectively, in the direction of the coal mining working face 11 and the direction of the goaf 15, such as Figure 1 As shown, it passes through the pseudo roof 1 and the direct roof 2 to reach the old roof 3, and the weakening and fracturing drill holes 8 are arranged in a straight line. The depth of the weakening and fracturing drill holes 8 is determined as follows: the depth of the weakening and fracturing drill holes 8 is determined based on the relationship between the collapse height and the crushing and expansion characteristics, where the collapse height is the coal seam mining height. The specific formula is:

[0037] H=M / (K P -1)

[0038] Where, H is the weakening fracture drilling depth, m; M is the coal seam mining height, 1.1~1.8m; K P is the coefficient of expansion, 1.3.

[0039] B. After completing the construction of the weakening and fracturing borehole 8, five predetermined positions are set at equal intervals at different depths along the axial direction of the weakening and fracturing borehole 8. A groove drill bit is used to circumferentially cut the wall of the weakening and fracturing borehole at each predetermined position to form an annular groove 4. The grooves are numbered from the inside to the outside as annular grooves a5, b6, c7, d and e, and the holes are cleaned. The weakening and fracturing boreholes 8 are single-row boreholes, inclined toward the advancing direction of the coal mining face 11 and the direction of the goaf 15, respectively, with a drilling inclination angle of 30° to 60°, a hole diameter of 36 to 50 mm, and a drilling spacing of 0.4 to 0.8 m. The annular grooves 4 inside the weakening and fracturing boreholes 8 have a diameter of 80 mm and an axial spacing of 30 mm.

[0040] C. Select five static medicine rolls having the same number of annular grooves 4 as formed in step B, and each of the static medicine rolls having the same mass. Then, add different masses of an accelerator to each static medicine roll, with the masses of the added accelerator being 0.4%, 0.8%, 1.2%, 1.6%, and 2% of the mass of the static medicine roll, respectively, to form modified static medicine rolls 10, thereby shortening the hydration time of the static medicine rolls. The hydration time t2 of each modified static medicine roll 10 is within the range of 1 to 2 hours. Different colored labels are used to classify and label the modified static medicine rolls.

[0041] D. First, select a modified static medicine roll 10 containing 0.4% early strength agent, immerse it completely in water for 2 to 2.5 minutes, and then fill it into the deepest annular groove a5 at the weakened cracking borehole 8 and compact it. The modified static medicine roll 10 that is completely immersed in water must be filled into the annular groove 4 of the borehole within 10 minutes. Then, according to the order of the amount of early strength agent added in the modified static medicine roll 10 from small to large, select the modified static medicine roll 10 in turn, and fill it into the annular grooves b, c, d and e from deep to shallow respectively, until all the annular grooves 4 of the borehole are filled. Figure 2 As shown, the drilled hole is finally sealed using a sealing device compatible with the structure of the annular groove 4. This can fully utilize the hydration expansion stress and thermal stress of the modified static medicine roll 10, improve the fracturing efficiency, and effectively prevent the occurrence of blowouts. The annular groove 4 has an upper arc slope and a lower flat surface. When the modified static medicine roll 10 in the annular groove 4 hydrates and generates expansion stress and thermal stress, the arc slope is subjected to force and can change the pressure direction of the expansion stress and thermal stress, thereby suppressing the axial stress output of the modified static medicine roll 10, achieving a self-sealing effect, and effectively preventing the occurrence of blowouts.

[0042] E. After the hole is sealed, since the modified static medicine rolls 10 filled in the annular grooves 4 contain different early strength agents, the hydration time of each modified static medicine roll 10 is different, and then the time for each modified static medicine roll 10 to generate expansion stress and thermal stress during hydration is different, and the hydration time decreases from the inside to the outside of the borehole; the modified static medicine roll 10 closest to the borehole mouth reaches the hydration time first, so that the annular groove 4 where it is located is subjected to expansion stress and thermal stress generated by hydration, and under the combined action of gravity and ground pressure, a crack 16 is first generated at the borehole mouth position, and after continuous pressure is applied, the top plate at this position is The rock collapses first, forming a new free weak plane after the collapse is completed. Then, the modified static drug roll 10 closest to the borehole reaches the hydration time, causing the annular groove 4 where it is located to generate expansion stress and thermal stress due to hydration. Under the combined action of gravity and ground pressure, the rock at the current annular groove location continues to collapse, and a new free weak plane continues to form at this location. This cycle continues. By placing modified static drug rolls 10 with different hydration times at different depths, the hydration performance of each modified static drug roll 10 forms a superposition effect, and ultimately the hard roof rock layer around the borehole is collapsed layer by layer multiple times.

[0043] The specific principle of the superposition effect is: since the difficulty of fracturing the pseudo top 1, direct top 2 and old top 3 increases successively, the present invention sets a fracturing method from outside to inside in sequence in the borehole, which just corresponds to the pseudo top 1, direct top 2 and old top 3 that the borehole passes through from shallow to deep; first, the borehole position at the pseudo top 1 (that is, the borehole mouth position) is fractured, and after its collapse, it will impact the direct top 2 to produce cracks, and then when the direct top 2 is fractured again, the free weak surfaces and cracks formed before can be utilized, making the direct top 2 easier to fracture and collapse. Similarly, after the direct top 2 collapses, the free weak surfaces and cracks formed before can be utilized when the old top 3 is fractured again, making the old top 3 easier to fracture and collapse. Except for the first and last time, each hydration fracturing can utilize the free weak surfaces and cracks formed before the previous fracturing, and provide new free weak surfaces and cracks for the next time. This superposition effect ultimately realizes the layered and multiple step-by-step collapse of the hard roof rock layer around the borehole.

[0044] F. According to the hard top plate area required for cracking, such as Figure 3 As shown, multiple weakening and fracturing boreholes 8 are constructed simultaneously, and steps B to E are repeated synchronously for each weakening and fracturing borehole 8, thereby simultaneously achieving the weakening and fracturing effect of multiple weakening and fracturing boreholes 8 on the hard roof, and ultimately effectively improving the weakening and fracturing efficiency of the hard roof.

[0045] As an improvement of the present invention, Figure 4As shown, the sealing device 9 in step D includes a push rod 91, a disc plug 92, a control block 94 and a positioning pin 93. A radial variable diameter through hole 95 is provided inside the disc plug 92. The radial variable diameter through hole 95 consists of a front section, a middle section and a rear section, and the diameter of the middle section is larger than the diameters of the front section and the rear section, and the diameters of the front section and the rear section are the same; the control block 94 is installed in the middle section of the through hole and can rotate in the middle section of the through hole; the control block 94 is a rectangular body, which consists of an upper rectangular surface, a lower rectangular surface, two rectangular side surfaces and two square side surfaces, and the two rectangular side surfaces and the two square side surfaces are embedded with a first magnet 96; There are two positioning pins 93, and the two positioning pins 93 are respectively installed in the front section and the rear section and can move axially in the through hole; the two positioning pins 93 are equipped with a second magnet 97 at one end close to the control block 94, and the polarity of the first magnet 96 is the S pole, and the polarity of the second magnet 97 is the N pole; There are multiple push rods 91, one end of which extends into the disc plug 92 and is fixedly connected to the center of the lower rectangular surface of the control block 94 by a thread, and the other end of the push rod 91 is coaxially connected to the remaining push rods 91 in turn. When the push rod 91 rotates, it can drive the control block 94 to rotate in the middle section of the through hole; Figure 5 As shown, when the hole is not sealed, the two rectangular side surfaces of the control block 94 are perpendicular to the axis of the through hole. At this time, since the polarities of the first magnet 96 and the second magnet 97 are opposite, based on the principle that opposite polarities will produce magnetic attraction, the two positioning pins 93 are magnetically connected to the two rectangular side surfaces through the first magnet 96 and the second magnet 97 respectively, so that the two positioning pins 93 are completely located in the disc plug 92, making it easy for the sealing device 9 to extend into the drilled hole; Figure 6 As shown, when the sealing device 9 is extended into the drill hole to seal the hole, the rotating push rod 91 drives the control block 94 to rotate in the middle section of the through hole, so that the two rectangular side surfaces are separated from the two positioning pins 93, and the control block 94 can push the two positioning pins 93 to move in the front section and the rear section respectively during the rotation process, so that the two positioning pins 93 extend from the disc plug 92 away from one end of the control block 94 until the two rectangular side surfaces are parallel to the axis of the through hole, and the two positioning pins 93 reach the maximum extension distance. At this time, the two positioning pins 93 are magnetically connected to the two square side surfaces through the first magnet 96 and the second magnet 97 respectively, so as to achieve a sealing effect on the drill hole; after hydration is completed, the push rod 91 is rotated again to drive the control block 94 to rotate, so that the two rectangular side surfaces of the control block 94 are perpendicular to the axis of the through hole. At this time, due to the action of magnetic attraction, the two positioning pins 93 will retract into the disc plug 92, so that the sealing device 9 can be taken out and retrieved from the drill hole.

[0046] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for causing step-by-step fracturing of a hard roof based on static blasting technology, characterized in that: The specific steps are: A. Use a drilling rig to construct weakening and fracturing boreholes at the working face cut location and the tunnel end location, respectively, toward the hard roof in the direction of the coal mining working face and the direction of the goaf. The boreholes are laid out in a straight line. The depth of the boreholes is determined based on the relationship between the collapse height and the crushing expansion characteristics. B. After completing the weakening and fracturing drilling, multiple predetermined positions are set at equal intervals at different depths along the axial direction of the weakening and fracturing drilling hole. A groove cutting drill bit is used to circumferentially cut the wall of the weakening and fracturing drilling hole at each predetermined position to form an annular groove. The grooves are numbered from the inside out as annular grooves a, b, c...n, and the hole is cleaned. C. Select static rolls with the same number of annular grooves as those formed in step B, and each static roll has the same mass. Then, add a different mass of early strength agent to each static roll to form a modified static roll, so as to shorten the hydration time of the static roll. The mass of the early strength agent added to each modified static roll is arranged in an arithmetic progression, and the modified static rolls are classified and marked using labels of different colors. D. First, select the modified static roll containing the least accelerator, immerse it completely in water, and fill it into the deepest annular groove a in the weakened and cracked borehole and compact it. Then, select the modified static rolls in the order of the amount of accelerator added in the modified static roll from small to large, and fill them into the corresponding annular grooves b, c...n from deep to shallow, until all the annular grooves in the borehole are filled. Finally, use a sealing device that is compatible with the annular groove structure to seal the borehole. E. After the hole is sealed, the modified static medicine rolls filled in the annular cuts contain different early strength agents, which makes the hydration time of each modified static medicine roll different. As a result, the time for each modified static medicine roll to generate expansion stress and thermal stress during hydration is different, and the hydration time decreases from the inside to the outside of the borehole. The modified static medicine roll closest to the borehole mouth reaches the hydration time first, so that the annular cut where it is located is subjected to expansion stress and thermal stress generated by hydration, and under the combined action of gravity and ground pressure, the top rock at the borehole mouth position collapses first, and the collapse is complete. After that, a new free weak plane is formed. Then, the modified static drug coil closest to the borehole reaches the hydration time, causing the annular groove where it is located to generate expansion stress and thermal stress under hydration. Under the combined action of gravity and ground pressure, the rock at the current annular groove location continues to collapse, and a new free weak plane continues to form at this location. This cycle continues. By placing modified static drug coils with different hydration times at different depths, the hydration performance of each modified static drug coil forms a superposition effect, and ultimately the hard roof rock layer around the borehole is collapsed in layers multiple times. F. According to the area of ​​the hard roof that needs to be cracked, multiple weakening and cracking drill holes are constructed at the same time, and steps B to E are repeated synchronously for each weakening and cracking drill hole, so as to simultaneously achieve the weakening and cracking effect of multiple weakening and cracking drill holes on the hard roof, and ultimately effectively improve the weakening and cracking efficiency of the hard roof.

2. The method for causing hard roof fracture step by step based on static blasting technology according to claim 1, characterized in that: The upper part of the annular groove is an arc-shaped inclined surface, and the lower part is a flat surface. When the modified static medicine coil in the annular groove is hydrated to generate expansion stress and thermal stress, the arc-shaped inclined surface can change the pressure direction of the expansion stress and thermal stress after being subjected to force, thereby suppressing the axial stress output of the modified static medicine coil, achieving a self-sealing hole effect, and effectively preventing the occurrence of blowhole phenomenon.

3. The method for causing hard roof to fracture step by step based on static blasting technology according to claim 1, characterized in that: The weakened fracture drill holes are single-row drill holes, inclined toward the advancing direction of the coal mining face and the goaf respectively, with a drill hole inclination angle of 30°~60°, a hole diameter of 36~50mm, and a drill hole spacing of 0.4~0.8m; the annular groove inside the weakened fracture drill hole has a diameter of 80mm and an axial spacing of 30mm.

4. The method for causing hard roof fracture step by step based on static blasting technology according to claim 1, characterized in that: The sealing device in step D includes a push rod, a disc plug, a control block and a positioning pin, a radially variable diameter through hole is provided inside the disc plug, and the radially variable diameter through hole consists of a front section, a middle section and a rear section, and the diameter of the middle section is larger than the diameters of the front section and the rear section, and the diameters of the front section and the rear section are the same; the control block is installed in the middle section of the through hole and can rotate in the middle section of the through hole; the control block is a rectangular body, which consists of an upper rectangular surface, a lower rectangular surface, two rectangular side surfaces and two square side surfaces, and the two rectangular side surfaces and the two square side surfaces are embedded with a first magnet; there are two positioning pins, and the two positioning pins are respectively installed in the front section and the rear section and can move axially in the through hole; the two positioning pins are equipped with a second magnet near one end of the control block, and the polarity of the second magnet is opposite to that of the first magnet; there are multiple push rods, one end of which extends into the disc plug and is fixedly connected to the center of the lower rectangular surface of the control block by a thread, and the push rod The other end of the rod is coaxially connected to the remaining push rods in sequence, and when the push rod rotates, it can drive the control block to rotate in the middle section of the through hole; when the hole is not sealed, the two rectangular side surfaces of the control block are perpendicular to the axis of the through hole, and at this time, the two positioning pins are magnetically connected to the two rectangular side surfaces through the first magnet and the second magnet respectively; so that the two positioning pins are completely in the disc plug; when the sealing device is extended into the drilled hole to seal the hole, the rotating push rod drives the control block to rotate in the middle section of the through hole, so that the two rectangular side surfaces are separated from the two positioning pins, and the control block can push the two positioning pins to move in the front section and the rear section respectively during the rotation process, so that the two positioning pins extend out of the disc plug away from one end of the control block until the two rectangular side surfaces are parallel to the axis of the through hole, and the two positioning pins reach the maximum extension distance. At this time, the two positioning pins are magnetically connected to the two square side surfaces through the first magnet and the second magnet respectively, thereby achieving a sealing effect on the drilled hole.

5. The method for causing hard roof to fracture step by step based on static blasting technology according to claim 4 is characterized in that: The polarity of the first magnet is an S pole, and the polarity of the second magnet is an N pole.

6. The method for causing step-by-step fracturing of a hard roof based on static blasting technology according to claim 1, characterized in that: The time t1 required for the modified static medicine roll to be completely immersed in water is 2 to 2.5 minutes. The modified static medicine roll after being completely immersed in water must be filled into the annular groove of the drilled hole within 10 minutes. The hydration time t2 of each modified static medicine roll is within the range of 1 to 2 hours.

7. The method for causing hard roof fracture step by step based on static blasting technology according to claim 1, characterized in that: The process for determining the depth of the weakening and fracturing drilling hole in step A is as follows: the depth of the weakening and fracturing drilling hole is determined based on the relationship between the collapse height and the crushing and expansion characteristics, wherein the collapse height is the coal seam mining height, and the specific formula is: ； Where H is the depth of the weakened fractured borehole; M is the mining height of the coal seam; K P is the coefficient of expansion.

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