A method for mining the protective layer of a coal seam based on high-pressure water jet grooving

Abstract

A method for mining the protective layer of a coal seam based on high-pressure water jet grooving includes the following steps: (i) installing a high-pressure water jet grooving device in the upper and lower roadways of the coal mining face; (ii) drilling high-pressure water jets at predetermined drilling positions in the middle of the backfill side in the upper and lower roadways of the coal mining face using the high-pressure water jet grooving device; (iii) after drilling, retracting the high-pressure water jet grooving device to make a grooving cut in the borehole; and (iv) performing high-pressure water jet grooving operation on the protective layer of the coal mining face using the high-pressure water jet grooving device. This invention features a simple process, overcomes geological conditions, is easy to implement, provides good pressure relief, and has high work efficiency. It integrates high-pressure water jet drilling and retracting grooving, enhancing the pressure relief effect, simplifying the traditional coal seam pressure relief work, and reducing pressure relief costs, thereby achieving significant improvement in coal seam pressure relief while also considering economic and social benefits.

Description

Technical Field

[0001] This invention relates to the field of coal mine rockburst prevention technology, specifically to a method for mining the protective layer of a coal seam based on high-pressure water jet grooving. Background Technology

[0002] Rockbursts have always been a major challenge affecting coal mining safety, posing a significant threat to safe production. Since the world's first rockburst occurred in a coal mine in 1738, the probability of rockbursts and the resulting losses have increased with the intensity and depth of mining. This has attracted great attention from engineering and technical personnel, who have conducted extensive research and adopted various methods to prevent and control rockbursts in order to reduce their occurrence and minimize losses.

[0003] Currently, the main methods for coal seam pressure relief include mining the release layer, deep-hole blasting, borehole pressure relief, and coal seam water injection. One of the main measures for "anti-surge" in coal mines is drilling holes in the coal seam to release coal seam pressure. It is also a common method for coal seam gas drainage and solving gas exceedances and pressure issues. However, the effectiveness of borehole "anti-surge" is affected by the borehole diameter and the pressure relief range. Currently, coal mines use drilling rigs for drilling, which presents significant problems in high-stress areas: firstly, it is difficult to drill long-distance, large-diameter holes; secondly, slag removal is difficult; and thirdly, "drill jamming" occurs, all of which cause many problems for mechanical drilling pressure relief. Secondly, mining the release layer is also an effective and fundamental measure for coal seam pressure relief. Mining the release layer refers to mining one coal seam (or layer) first, allowing adjacent coal seams to unload for a certain period of time. However, mining the release layer cannot achieve pressure relief for the coal seam itself and is limited by many factors such as geological conditions.

[0004] To address the aforementioned technical problems, this invention provides a method for mining the protective layer of a coal seam based on high-pressure water jet grooving. Summary of the Invention

[0005] The purpose of this invention is to provide a method for mining the protective layer of a coal seam based on high-pressure water jet grooving. This invention has a simple process, can overcome geological conditions, is easy to implement, has a good pressure relief effect, and high work efficiency. It integrates high-pressure water jet drilling and retreat grooving, which enhances the pressure relief effect, simplifies the traditional coal seam pressure relief work, and reduces the pressure relief cost. Thus, it achieves both significant improvement in coal seam pressure relief effect and economic and social benefits.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for mining the protective layer of a coal seam based on high-pressure water jet grooving specifically includes the following steps:

[0008] (i) Install a high-pressure water jet cutting device at the predetermined drilling position in the middle of the backflush in the upper and lower roadways of the coal mining face;

[0009] (ii) High-pressure water jet drilling is carried out at predetermined drilling positions in the middle of the backflush in the upper and lower roadways of the coal mining face using a high-pressure water jet grooving device.

[0010] (iii) After drilling is completed, the high-pressure water jet grooving device retracts and cuts a groove in the borehole;

[0011] (iv) High-pressure water jet grooving operation of protective layer is carried out in coal mining face using high-pressure water jet grooving device.

[0012] The high-pressure water jet grooving device includes a high-pressure water supply device, a water jet direction changer, a hose propulsion device, a nozzle support and guide device, and a high-pressure water jet nozzle. The high-pressure water supply device, hose propulsion device, nozzle support and guide device, and high-pressure water jet nozzle are arranged sequentially from front to back. The water outlet of the high-pressure water supply device is connected to the water inlet of the hose propulsion device. The water outlet of the hose propulsion device passes through the nozzle support and guide device and is connected to the water inlet of the high-pressure water jet nozzle. The spray end of the high-pressure water jet nozzle sprays high-pressure water jets backward and to the left and right sides. The water jet direction changer is connected to the high-pressure water jet nozzle via a signal connection.

[0013] The high-pressure water supply device includes a first frame platform, a water storage tank, and a high-pressure water pump. The water storage tank is located on the front side of the upper surface of the first frame platform. A pump base located behind the water storage tank is fixedly connected to the rear side of the upper surface of the first frame platform by several bolts. The high-pressure water pump is mounted on the pump base and located behind the water storage tank. The inlet end of the high-pressure water pump is connected to the outlet end of the water storage tank, and the outlet end of the high-pressure water pump is connected to the inlet end of the hose propulsion device.

[0014] The hose propulsion device includes a second frame platform and an electric hose reel. The second frame platform is located behind the first frame platform. The electric hose reel is installed on the front side of the upper surface of the second frame platform. The center line of the electric hose reel's drum is horizontally arranged in the front-rear direction. A first low-carbon high-pressure hose is wound on the drum of the electric hose reel. The water inlet end of the first low-carbon high-pressure hose is fixed to the center of the front end of the electric hose reel's drum and connected to a second low-carbon high-pressure hose through a rotating pipe joint. The other end of the second low-carbon high-pressure hose is connected to the outlet end of a high-pressure water pump. A first flexible waterproof cable is fixedly laid along the length of the outer surface of the first low-carbon high-pressure hose, and a second flexible waterproof cable is fixedly laid along the length of the outer surface of the second low-carbon high-pressure hose. The adjacent ends of the first flexible waterproof cable and the second flexible waterproof cable are connected by a signal slip ring. The other end of the first flexible waterproof cable is connected to the high-pressure water jet nozzle, and the other end of the second flexible waterproof cable is connected to the water jet direction changer. Two limiting pulleys are rotatably installed on the rear middle of the upper surface of the second frame platform, with the central axis of the limiting pulleys set vertically. The water outlet end of the first low-carbon high-pressure hose extends backward from the drum of the electric hose reel and extends horizontally backward through the gap between the two limiting pulleys. The first low-carbon high-pressure hose is in squeezing and rolling contact with the two limiting pulleys. A hose reel controller is set on the second frame platform to control the winding and unwinding actions and winding and unwinding speed of the electric hose reel.

[0015] The nozzle support and guide device includes a steel bracket, which is a vertically arranged isosceles triangular frame structure with the apex facing upwards. The steel bracket is located directly behind the second frame platform. The height of the steel bracket is the same as the height of the two limiting pulleys. A support and guide ring is provided on the top of the steel bracket. The center line of the support and guide ring is set horizontally in the front-back direction. The support and guide ring corresponds directly to the middle of the two limiting pulleys. The outlet end of the first low-carbon high-pressure hose passes between the two limiting pulleys and then passes horizontally backwards through the support and guide ring.

[0016] The high-pressure water jet nozzle includes a hollow cylindrical nozzle body, which is horizontally arranged along the front-to-back direction. The front side of the hollow cylindrical nozzle body is open, and its front end is fixedly connected to the outlet end of a first low-carbon high-pressure hose. A direct-jet nozzle orifice communicating with the internal cavity of the hollow cylindrical nozzle body is opened at the center of its rear end. A direct-jet nozzle with a solenoid valve is installed inside the direct-jet nozzle orifice. The outer circumference of the rear end of the hollow cylindrical nozzle body is left... Both right side walls are provided with slit jet nozzles that communicate with the inner cavity of the hollow cylindrical nozzle body. Each of the two slit jet nozzles is equipped with a slit jet nozzle with a solenoid valve. The other end of the first flexible waterproof cable extends and is embedded in the hollow cylindrical nozzle body and is connected to the straight jet nozzle and the slit jet nozzle respectively. The water jet direction change controller is set on the pump base and is connected to the straight jet nozzle and the slit jet nozzle respectively through the first flexible waterproof cable and the second flexible waterproof cable.

[0017] Step (1) is as follows: At the predetermined drilling position in the middle of the backflush in the upper and lower roadways of the coal mining face, connect and assemble the high-pressure water supply device, hose propulsion device, nozzle support and guide device and high-pressure water jet nozzle in sequence according to the design requirements to form a high-pressure water jet grooving device, so that the high-pressure water jet nozzle is 100mm away from the coal wall. After the connection is completed, check whether the entire high-pressure water jet grooving device is intact and whether the pipeline connection is firm.

[0018] Step (II) is as follows: Open the straight jet nozzle and close the two slotted jet nozzles through the water jet direction changer, thereby adjusting the water jet of the high-pressure water jet nozzle to a straight jet. Then, start the high-pressure water pump, which draws water from the water tank and pressurizes it to pump the high-pressure water into the hollow cylindrical nozzle body through the second low-carbon high-pressure hose and the first low-carbon high-pressure hose. The straight jet nozzle then sprays high-pressure water jet backward to drill holes in the coal wall. Then, start the electric hose reel and control the hose reel controller to unwind the hose. The electric hose reel releases the first low-carbon high-pressure hose at a certain speed, thereby controlling the drilling speed of the high-pressure water jet nozzle. The first low-carbon high-pressure hose passes through the gap between the two limiting pulleys and the support guide ring and pushes the hollow cylindrical nozzle body toward the coal seam to drill. The support guide ring makes the high-pressure water jet nozzle drill in a predetermined direction, and the drilling depth is 1 / 2 of the length of the coal mining face.

[0019] Step (III) is as follows: When the borehole reaches 1 / 2 of the length of the coal face, drilling is stopped, the drilling is completed, the high-pressure water pump and the electric hose reel are turned off, and when the pressure of the high-pressure water pump drops to zero, the two slotting jet nozzles are opened through the water jet direction changer, and the straight jet nozzle is closed. Then the water jet of the high-pressure water jet nozzle is adjusted from a straight jet to a slotting jet. Then the high-pressure water pump is started, the high-pressure water pump draws water from the water tank and pressurizes it, and pumps the high-pressure water through the second low-carbon high-pressure hose and the first low-carbon high-pressure hose into the hollow cylindrical nozzle body. Then the two slotting jet nozzles spray high-pressure water jets to hydraulically slot the coal seam on the left and right sides of the borehole wall. At the same time, the electric hose reel is started, and the hose reel controller is used to control the electric hose reel to start During the rewinding process, the electric hose reel retracts the first low-carbon high-pressure hose at a certain speed, thereby controlling the retraction speed of the high-pressure water jet nozzle. Through the support guide ring, the high-pressure water jet nozzle gradually retracts along the borehole. During the retraction process, the high-pressure water jets ejected from the two slit jet nozzles impact the coal seam surface inside the borehole. Coal dust is peeled off from the coal seam surface to form coal seam fissures, exposing a new coal seam surface. As the high-pressure water jets impact the coal seam, they enter the coal seam fissures, deepening them. Simultaneously, as the high-pressure water jet nozzle gradually retracts from the bottom of the borehole to the borehole opening, the high-pressure water jets ejected from the two slit jet nozzles create 1-meter-deep grooves on both sides of the entire borehole wall.

[0020] Step (four) is as follows: In the upper and lower roadways of the coal mining face, drill a hole every 1m along the roadway according to step (two), and then cut back the left and right sides of the drill hole wall according to step (three) to finally connect all the drill holes and slots in the two roadways to complete the mining of the protective layer of the coal seam.

[0021] This invention possesses outstanding substantive features and significant advancements compared to existing technologies. Specifically, the beneficial effects of this invention are as follows: During drilling, the water jet from the high-pressure water jet nozzle is adjusted to a straight jet, ensuring non-contact contact between the nozzle and the coal face. The drilling energy originates from the high-pressure, high-speed water flow, utilizing the impact force of the water and the fissures in the coal seam to generate erosion and form a borehole. Since the diameter of the borehole drilled by the high-pressure water jet is typically much larger than the diameter of the drilling nozzle, there is no possibility of the nozzle getting stuck. Furthermore, due to the large water flow rate, slag removal is easy. To better relieve pressure and prevent impact, after the high-pressure water jet completes drilling (penetrating the coal face), the water jet from the nozzle is adjusted from a straight jet to a slotted jet. The nozzle is then pulled back using an electric hose reel, allowing the slotted jet from the high-pressure water jet nozzle to effectively penetrate the coal seam borehole. Two deep and wide horizontal slits are cut on the left and right sides. As the high-pressure water jet nozzle gradually retreats from the bottom of the borehole to the borehole opening, the high-pressure water jets ejected from the two slit nozzles create 1-meter-deep grooves on both sides of the borehole wall. Then, in the upper and lower roadways of the coal mining face, a borehole is drilled every 1 meter along the roadway, and the retreating slit cutting process is repeated until all the boreholes and grooves in the two roadways are connected, completing the mining of the protective layer of the coal seam. This method provides better pressure relief. This invention introduces high-pressure water jet technology into the prevention and control of rockbursts, using it for coal seam pressure relief to solve problems that are difficult to address using mechanical equipment in some "anti-rockburst" measures. It can also achieve pressure relief of the coal seam and overcome the limitations of geological conditions and other factors. Therefore, the use of high-pressure water jet drilling and slit cutting pressure relief technology to prevent and control rockbursts is a viable approach. Compared to traditional mechanical methods, high-pressure water jet technology offers superior pressure relief and is easier to implement. It is a highly effective method for coal seam pressure relief. During the high-pressure water jet slit-cutting process, the slit-cutting jet moves backward along with the high-pressure water jet nozzle, flowing closely against the cut coal seam wall. Subjected to the frictional resistance of the solid wall, the slit-cutting jet forms a three-sided wall-attached jet within the slot, achieving a superior pressure relief effect. This invention features a simple process, overcomes geological conditions, is easy to implement, provides excellent pressure relief, and boasts high work efficiency. It integrates high-pressure water jet drilling and backward slit-cutting, enhancing the pressure relief effect, simplifying the traditional coal seam pressure relief process, and reducing costs. Thus, it significantly improves coal seam pressure relief while simultaneously achieving economic and social benefits. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the overall structure and connection of the high-pressure water jet grooving device of the present invention.

[0023] Figure 2 This is a schematic diagram of the high-pressure water jet nozzle of the present invention drilling into the coal seam.

[0024] Figure 3This is a schematic diagram of the high-pressure water jet nozzle of the present invention for mining the protective layer of the coal seam by retracting the cutting.

[0025] Figure 4 This is a cross-sectional schematic diagram of the high-pressure water jet nozzle of the present invention.

[0026] Figure 5 This is a schematic diagram of the protective layer of the coal seam that is ultimately mined according to the present invention. Detailed Implementation

[0027] The embodiments of the present invention are further described below with reference to the accompanying drawings.

[0028] like Figure 1-5 As shown, a method for mining the protective layer of a coal seam based on high-pressure water jet grooving is presented.

[0029] Specifically, the following steps are included:

[0030] (i) Install a high-pressure water jet cutting device at the predetermined drilling position in the middle of the backflush in the upper and lower roadways of the coal mining face;

[0031] (ii) High-pressure water jet drilling is carried out at predetermined drilling positions in the middle of the backflush in the upper and lower roadways of the coal mining face using a high-pressure water jet grooving device.

[0032] (iii) After drilling is completed, the high-pressure water jet grooving device retracts and cuts a groove in the borehole;

[0033] (iv) High-pressure water jet grooving operation of protective layer is carried out in coal mining face using high-pressure water jet grooving device.

[0034] The high-pressure water jet grooving device includes a high-pressure water supply device, a water jet direction changer 22, a hose propulsion device, a nozzle support and guide device, and a high-pressure water jet nozzle. The high-pressure water supply device, hose propulsion device, nozzle support and guide device, and high-pressure water jet nozzle are arranged sequentially from front to back. The water outlet of the high-pressure water supply device is connected to the water inlet of the hose propulsion device. The water outlet of the hose propulsion device passes through the nozzle support and guide device and is connected to the water inlet of the high-pressure water jet nozzle. The spray end of the high-pressure water jet nozzle sprays high-pressure water jets backward and to the left and right sides. The water jet direction changer 22 is signal-connected to the high-pressure water jet nozzle.

[0035] The high-pressure water supply device includes a first frame platform 1, a water storage tank 2, and a high-pressure water pump 3. The water storage tank 2 is located on the front side of the upper surface of the first frame platform 1. The rear side of the upper surface of the first frame platform 1 is fixedly connected to a pump base 4 located behind the water storage tank 2 by several bolts. The high-pressure water pump 3 is mounted on the pump base 4 and located behind the water storage tank 2. The inlet end of the high-pressure water pump 3 is connected to the outlet end of the water storage tank 2, and the outlet end of the high-pressure water pump 3 is connected to the inlet end of the hose propulsion device.

[0036] The hose propulsion device includes a second frame platform 5 and an electric hose reel 6. The second frame platform 5 is located behind the first frame platform 1. The electric hose reel 6 is installed on the front side of the upper surface of the second frame platform 5. The center line of the drum of the electric hose reel 6 is horizontally arranged in the front-back direction. A first low-carbon high-pressure hose 7 is wound on the drum of the electric hose reel 6. The water inlet end of the first low-carbon high-pressure hose 7 is fixed to the center of the front end of the drum of the electric hose reel 6 and connected to a second low-carbon high-pressure hose 8 through a rotating pipe joint (not shown). The other end of the second low-carbon high-pressure hose 8 is connected to the water outlet end of the high-pressure water pump 3. A first flexible waterproof cable 9 is fixedly laid along its length on the outer surface of the first low-carbon high-pressure hose 7, and a second flexible waterproof cable 10 is fixedly laid along its length on the outer surface of the second low-carbon high-pressure hose 8. The adjacent ends of the first flexible waterproof cable 9 and the second flexible waterproof cable 10 are connected by a signal slip ring (not shown). The other end of the first flexible waterproof cable 9 is connected to the high-pressure water jet nozzle, and the other end of the second flexible waterproof cable 10 is connected to the water jet direction change controller 22. Two limiting pulleys 11 with front and rear intervals are rotatably installed on the middle of the rear side of the upper surface of the second frame platform 5. The central axis of the limiting pulleys 11 is set vertically. The water outlet end of the first low-carbon high-pressure hose 7 extends backward from the drum of the electric hose reel 6 and extends horizontally backward through the gap between the two limiting pulleys 11. The first low-carbon high-pressure hose 7 is in squeezing and rolling contact with the two limiting pulleys 11. A hose reel controller 12 is provided on the second frame platform 5 to control the winding and unwinding action and winding and unwinding speed of the electric hose reel 6.

[0037] The nozzle support and guide device includes a steel bracket 13, which is a vertically arranged isosceles triangular frame structure with the apex facing upwards. The steel bracket 13 is located directly behind the second frame platform 5. The height of the steel bracket 13 is the same as the height of the two limiting pulleys 11. A support and guide ring 14 is provided on the top of the steel bracket 13. The center line of the support and guide ring 14 is horizontally arranged in the front-back direction. The support and guide ring 14 corresponds directly to the middle of the two limiting pulleys 11. The water outlet of the first low-carbon high-pressure hose 7 passes between the two limiting pulleys 11 and then horizontally backwards through the support and guide ring 14.

[0038] The high-pressure water jet nozzle includes a hollow cylindrical nozzle body 15, which is horizontally arranged along the front-to-back direction. The front side of the hollow cylindrical nozzle body 15 is open, and the front end of the hollow cylindrical nozzle body 15 is fixedly connected to the water outlet end of the first low-carbon high-pressure hose 7. A straight jet nozzle 16 communicating with the inner cavity of the hollow cylindrical nozzle body 15 is opened at the center of the rear end of the hollow cylindrical nozzle body 15. A straight jet nozzle (not shown in the figure) with a solenoid valve is installed in the straight jet nozzle 16. The outer circumference of the rear end of the hollow cylindrical nozzle body 15 is... The left and right side walls are provided with slit jet nozzles 17 that communicate with the inner cavity of the hollow cylindrical nozzle body 15. Each of the two slit jet nozzles 17 is equipped with a slit jet nozzle 18 with a solenoid valve. The other end of the first flexible waterproof cable 9 extends and is embedded in the hollow cylindrical nozzle body 15 and is connected to the straight jet nozzle and the slit jet nozzle 18 respectively. The water jet direction change controller 22 is set on the pump base 4 and is connected to the straight jet nozzle and the slit jet nozzle 18 respectively through the first flexible waterproof cable 9 and the second flexible waterproof cable 10.

[0039] Step (1) is as follows: At the predetermined drilling position in the middle of the backflush in the upper and lower roadways of the coal mining face, connect and assemble the high-pressure water supply device, hose propulsion device, nozzle support and guide device and high-pressure water jet nozzle in sequence according to the design requirements to form a high-pressure water jet grooving device, so that the high-pressure water jet nozzle is 100mm away from the coal wall. After the connection is completed, check whether the entire high-pressure water jet grooving device is intact and whether the pipeline connection is firm.

[0040] Step (II) is as follows: The direct jet nozzle is opened via the water jet direction changer 22, and the two slotted jet nozzles 18 are closed, thereby adjusting the water jet of the high-pressure water jet nozzle to a direct jet. Then, the high-pressure water pump 3 is started. The high-pressure water pump 3 draws water from the water storage tank 2 and pressurizes it, pumping the high-pressure water through the second low-carbon high-pressure hose 8 and the first low-carbon high-pressure hose 7 into the hollow cylindrical nozzle body 15. The direct jet nozzle then sprays high-pressure water jets backward to perforate the coal wall. Finally, the electric hose reel 6 is started. The electric hose reel 6 is unwound by the hose reel controller 12. The electric hose reel 6 releases the first low-carbon high-pressure hose 7 at a certain speed, thereby controlling the drilling speed of the high-pressure water jet nozzle. The first low-carbon high-pressure hose 7 passes through the gap between the two limiting pulleys 11 and the support guide ring 14 and pushes the hollow cylindrical nozzle body 15 toward the coal seam 19. The high-pressure water jet nozzle is drilled in a predetermined direction by the support guide ring 14. The depth of the borehole 20 is 1 / 2 of the length of the coal mining face.

[0041] Step (III) is as follows: When borehole 20 is drilled to 1 / 2 of the length of the coal face, drilling is stopped, the drilling is completed, the high-pressure water pump 3 and the electric hose reel 6 are turned off, and when the pressure of the high-pressure water pump 3 drops to zero, the two slit-jet nozzles 18 are opened through the water jet direction changer 22, and the straight jet nozzle is closed, thereby adjusting the water jet of the high-pressure water jet nozzle from a straight jet to a slit-jet. Then, the high-pressure water pump 3 is started, the high-pressure water pump 3 draws water from the water storage tank 2 and pressurizes it, pumping the high-pressure water through the second low-carbon high-pressure hose 8 and the first low-carbon high-pressure hose 7 into the hollow cylindrical nozzle body 15. Then, the two slit-jet nozzles 18 spray high-pressure water jets to hydraulically slit the coal seam 19 on the left and right sides of the borehole wall of borehole 20. At the same time, the electric hose reel 6 is started, and the hose reel controller 12 controls the opening of the electric hose reel 6. When the rewinding begins, the electric hose reel 6 retracts the first low-carbon high-pressure hose 7 at a certain speed, thereby controlling the retraction speed of the high-pressure water jet nozzle. Through the support guide ring 14, the high-pressure water jet nozzle gradually retracts along the borehole 20. During the retraction process, the high-pressure water jets ejected from the two slit jet nozzles 18 impact the surface of the coal seam 19 inside the borehole 20. Coal dust peels off from the surface of the coal seam 19, forming coal seam fissures and exposing a new coal seam surface. As the high-pressure water jet impacts the coal seam, it enters the coal seam fissures, deepening them. Simultaneously, as the high-pressure water jet nozzle gradually retracts from the bottom of the borehole 20 to the opening of the borehole 20, the high-pressure water jets ejected from the two slit jet nozzles 18 form 1m deep grooves 21 on both sides of the borehole wall.

[0042] Step (IV) specifically involves drilling a borehole 20 every 1m along the upper and lower roadways of the coal mining face, as per step (II). Then, following step (III), back-cut grooves are made on both sides of the borehole 20 walls, ultimately connecting all the boreholes 20 and grooves 21 in the two roadways to complete the mining of the protective layer of the coal seam. The protective layer in step (IV) refers to the coal seam mined from the cut-in roadway of the coal mining face along the two roadways to the entrance of the two roadways.

[0043] The water jet direction changer 22, electric hose reel 6, first low-carbon high-pressure hose 7, rotary pipe joint, second low-carbon high-pressure hose 8, first flexible waterproof cable 9, second flexible waterproof cable 10, signal slip ring, hose reel controller 12, straight jet nozzle and slit jet nozzle 18 are all existing conventional components that can be purchased on the market. The specific structure and working principle will not be described in detail. The control part in this invention uses conventional control technology and does not involve new computer programs.

[0044] The beneficial effects of this invention are as follows: During drilling, the water jet from the high-pressure water jet nozzle is adjusted to a straight jet, ensuring no contact between the nozzle and the coal face. The drilling energy originates from the high-pressure, high-speed water flow, utilizing the impact force of the water and the fissures in the coal seam to create erosion and form a borehole. Since the diameter of the borehole drilled by the high-pressure water jet is usually much larger than the diameter of the drilling nozzle, there is no possibility of the nozzle getting stuck. Furthermore, the large water flow rate facilitates slag removal. To better relieve pressure and prevent impact, after the high-pressure water jet completes drilling (penetrating the coal face), the water jet from the nozzle is adjusted from a straight jet to a slotting jet. The nozzle is then pulled back using an electric hose reel 6. The slotting jet from the high-pressure water jet nozzle can horizontally cut two deep and wide slots on both sides of the borehole in the coal seam. As the high-pressure water jet nozzle gradually retreats from the bottom of the borehole to the borehole opening, the high-pressure water jets ejected from the two slotted jet nozzles 18 create 1-meter-deep slots 21 on both sides of the borehole wall. Then, in the upper and lower roadways of the coal face, a borehole is drilled every 1 meter along the roadway, and the retreating slotting process is repeated until all the boreholes and slots in the two roadways are connected, completing the mining of the protective layer of the coal seam. This method provides better pressure relief. This invention introduces high-pressure water jet technology into the prevention and control of rockbursts, using it for coal seam pressure relief to solve problems that are difficult to address using mechanical equipment in certain "anti-rockburst" measures. It can also achieve pressure relief of the coal seam and overcome limitations imposed by geological conditions and other factors. Therefore, the use of high-pressure water jet drilling and slotting pressure relief technology to prevent and control rockbursts is a viable approach. Compared to traditional mechanical methods, high-pressure water jet technology offers better pressure relief and is easier to implement. It is a highly effective method for coal seam pressure relief. During the process of cutting grooves in the coal seam with high-pressure water jet, the cutting jet moves backward along with the high-pressure water jet nozzle. As a result, the cutting jet flows closely against the wall of the cut coal seam. Due to the frictional resistance of the solid wall, the cutting jet forms a three-sided wall-attached jet in the groove 21, which can achieve a better pressure relief effect.

[0045] The above embodiments are only used to illustrate and not limit the technical solutions of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the present invention without departing from the spirit and scope of the present invention. Any modifications or partial substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for mining the protective layer of a coal seam based on high-pressure water jet grooving, characterized in that: Specifically, the following steps are included: (i) Install a high-pressure water jet cutting device at the predetermined drilling position in the middle of the backflush in the upper and lower roadways of the coal mining face; (ii) High-pressure water jet drilling is carried out at predetermined drilling positions in the middle of the backflush in the upper and lower roadways of the coal mining face using a high-pressure water jet grooving device. (iii) After drilling is completed, the high-pressure water jet grooving device retracts and cuts a groove in the borehole; (iv) High-pressure water jet grooving operation of protective layer in coal mining face is carried out by high-pressure water jet grooving device; The high-pressure water jet grooving device includes a high-pressure water supply device, a water jet direction changer, a hose propulsion device, a nozzle support and guide device, and a high-pressure water jet nozzle; The high-pressure water supply device includes a first frame platform, a water storage tank, and a high-pressure water pump; The hose propulsion device includes a second frame platform and an electric hose reel. The center line of the electric hose reel's drum is set horizontally in the front-to-back direction. A first low-carbon high-pressure hose is wound on the drum of the electric hose reel. A hose reel controller is set on the second frame platform to control the winding and unwinding actions and winding and unwinding speed of the electric hose reel. The high-pressure water jet nozzle includes a hollow cylindrical nozzle body, which is horizontally arranged along the front-to-back direction. The front side of the hollow cylindrical nozzle body is open, and the front end of the hollow cylindrical nozzle body is fixedly connected to the water outlet end of the first low-carbon high-pressure hose. A straight jet nozzle hole communicating with the inner cavity of the hollow cylindrical nozzle body is opened at the center of the rear end of the hollow cylindrical nozzle body. A straight jet nozzle with a solenoid valve is installed in the straight jet nozzle hole. Slit jet nozzle holes communicating with the inner cavity of the hollow cylindrical nozzle body are opened on the left and right side walls of the outer circumference of the rear end of the hollow cylindrical nozzle body. Slit jet nozzle holes with solenoid valves are installed in both slit jet nozzle holes. Step (III) is as follows: When drilling reaches 1 / 2 of the length of the coal face, drilling is stopped, the drilling is completed, the high-pressure water pump and electric hose reel are turned off, and when the pressure of the high-pressure water pump drops to zero, the two slit-jet nozzles are opened through the water jet direction changer, and the straight-jet nozzle is closed. The water jet from the high-pressure water jet nozzle is then adjusted from a straight jet to a slit-jet. The high-pressure water pump is then started, drawing water from the storage tank and pressurizing it to pump the high-pressure water into the hollow cylindrical nozzle body. The two slit-jet nozzles then spray high-pressure water jets to hydraulically slit the coal seam on the left and right sides of the borehole wall. Simultaneously, the electric hose reel is started, and the hose reel controller is used to control the electric hose reel to begin winding. The hose reel retracts the first low-carbon high-pressure hose at a certain speed, thereby controlling the retraction speed of the high-pressure water jet nozzle. This causes the high-pressure water jet nozzle to gradually retract along the borehole. During the retraction process, the high-pressure water jets ejected from the two slit nozzles impact the coal seam surface inside the borehole. Coal dust is peeled off from the coal seam surface, forming coal seam fissures and exposing new coal seam surfaces. As the high-pressure water jets impact the coal seam, they enter the coal seam fissures, deepening them. Simultaneously, as the high-pressure water jet nozzle gradually retracts from the bottom of the borehole to the borehole opening, the high-pressure water jets ejected from the two slit nozzles create 1-meter-deep grooves on both sides of the entire borehole wall.

2. The method for mining the protective layer of a coal seam based on high-pressure water jet grooving according to claim 1, characterized in that: The high-pressure water supply device, the hose propulsion device, the nozzle support and guide device, and the high-pressure water jet nozzle are arranged in sequence from front to back. The water outlet of the high-pressure water supply device is connected to the water inlet of the hose propulsion device. The water outlet of the hose propulsion device passes through the nozzle support and guide device and is connected to the water inlet of the high-pressure water jet nozzle. The spray end of the high-pressure water jet nozzle sprays high-pressure water jets backward and to the left and right sides. The water jet direction change controller is connected to the high-pressure water jet nozzle signal.

3. The method for mining the protective layer of a coal seam based on high-pressure water jet grooving according to claim 2, characterized in that: The water storage tank is located on the front side of the upper surface of the first frame platform. The pump base located behind the water storage tank is fixedly connected to the rear side of the upper surface of the first frame platform by several bolts. The high-pressure water pump is installed on the pump base and located behind the water storage tank. The inlet end of the high-pressure water pump is connected to the outlet end of the water storage tank, and the outlet end of the high-pressure water pump is connected to the inlet end of the hose propulsion device.

4. The method for mining the protective layer of a coal seam based on high-pressure water jet grooving according to claim 3, characterized in that: The second frame platform is located behind the first frame platform. An electric hose reel is installed on the front side of the upper surface of the second frame platform. The inlet end of the first low-carbon high-pressure hose is fixed to the center of the front end of the electric hose reel's drum and connected to a second low-carbon high-pressure hose via a rotating pipe connector. The other end of the second low-carbon high-pressure hose is connected to the outlet end of the high-pressure water pump. A first flexible waterproof cable is fixedly laid along the length of the outer surface of the first low-carbon high-pressure hose, and a second flexible waterproof cable is fixedly laid along the length of the outer surface of the second low-carbon high-pressure hose. The adjacent ends of the flexible waterproof cable are connected by a signal slip ring. The other end of the first flexible waterproof cable is connected to the high-pressure water jet nozzle, and the other end of the second flexible waterproof cable is connected to the water jet direction changer. Two limiting pulleys are rotatably installed on the rear side of the upper surface of the second frame platform, with the central axis of the limiting pulleys set vertically. The water outlet end of the first low-carbon high-pressure hose extends backward from the drum of the electric hose reel and extends horizontally backward through the gap between the two limiting pulleys. The first low-carbon high-pressure hose is in squeezing and rolling contact with the two limiting pulleys.

5. The method for mining the protective layer of a coal seam based on high-pressure water jet grooving according to claim 4, characterized in that: The nozzle support and guide device includes a steel bracket, which is a vertically arranged isosceles triangular frame structure with the apex facing upwards. The steel bracket is located directly behind the second frame platform. The height of the steel bracket is the same as the height of the two limiting pulleys. A support and guide ring is provided on the top of the steel bracket. The center line of the support and guide ring is set horizontally in the front-back direction. The support and guide ring corresponds directly to the middle of the two limiting pulleys. The outlet end of the first low-carbon high-pressure hose passes between the two limiting pulleys and then passes horizontally backwards through the support and guide ring.

6. The method for mining the protective layer of a coal seam based on high-pressure water jet grooving according to claim 4, characterized in that: The other end of the first flexible waterproof cable extends and is embedded in the hollow cylindrical nozzle body and is communicatively connected to the straight jet nozzle and the slit jet nozzle respectively. The water jet direction change controller is set on the pump base and is signal connected to the straight jet nozzle and the slit jet nozzle respectively through the first flexible waterproof cable and the second flexible waterproof cable.

7. The method for mining the protective layer of a coal seam based on high-pressure water jet grooving according to claim 6, characterized in that: Step (1) is as follows: At the predetermined drilling position in the middle of the backflush in the upper and lower roadways of the coal mining face, connect and assemble the high-pressure water supply device, hose propulsion device, nozzle support and guide device and high-pressure water jet nozzle in sequence according to the design requirements to form a high-pressure water jet grooving device, so that the high-pressure water jet nozzle is 100mm away from the coal wall. After the connection is completed, check whether the entire high-pressure water jet grooving device is intact and whether the pipeline connection is firm.

8. The method for mining the protective layer of a coal seam based on high-pressure water jet grooving according to claim 7, characterized in that: Step (II) is as follows: Open the straight jet nozzle and close the two slotted jet nozzles through the water jet direction changer, thereby adjusting the water jet of the high-pressure water jet nozzle to a straight jet. Then, start the high-pressure water pump, which draws water from the water tank and pressurizes it to pump the high-pressure water into the hollow cylindrical nozzle body through the second low-carbon high-pressure hose and the first low-carbon high-pressure hose. The straight jet nozzle then sprays high-pressure water jet backward to drill holes in the coal wall. Then, start the electric hose reel and control the hose reel controller to unwind the hose. The electric hose reel releases the first low-carbon high-pressure hose at a certain speed, thereby controlling the drilling speed of the high-pressure water jet nozzle. The first low-carbon high-pressure hose passes through the gap between the two limiting pulleys and the support guide ring and pushes the hollow cylindrical nozzle body toward the coal seam to drill. The support guide ring makes the high-pressure water jet nozzle drill in a predetermined direction, and the drilling depth is 1 / 2 of the length of the coal mining face.

9. The method for mining the protective layer of a coal seam based on high-pressure water jet grooving according to claim 8, characterized in that: Step (four) is as follows: In the upper and lower roadways of the coal mining face, drill a hole every 1m along the roadway according to step (two), and then cut back the left and right sides of the drill hole wall according to step (three) to finally connect all the drill holes and slots in the two roadways to complete the mining of the protective layer of the coal seam.

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