Method and system for monitoring surface subsidence pit of coal mine working face

Abstract

The present application relates to coal mining technology field, especially to a kind of coal mine working face surface mining subsidence pit monitoring method and system, coal mine working face surface mining subsidence pit monitoring method includes: target hard difficult collapse rock stratum is reformed, to reduce the strength, integrity and integrity of target hard difficult collapse rock stratum;The roof strata of working face initial mining stage are carried out surrounding rock structure detection, determine the damage range, strength and joint fissure distribution of target hard difficult collapse rock stratum of working face initial mining stage roof;The roof strata of working face initial mining stage are carried out pre-splitting, damage the integrity and strength of target hard difficult collapse rock stratum;The position of working face mining predicted subsidence pit is grouted and filled;Monitoring working face initial mining stage mining working face roof strata microseismic event, surface real-time displacement and surface subsidence during working face mining process.Effectively control roadway under the influence of double thick coal seam and hard roof working face mining surface subsidence pit management problem.

Description

Technical Field

[0001] This invention relates to the field of coal mining technology, and in particular to a method and system for monitoring surface subsidence pits in coal mine working faces. Background Technology

[0002] When the coal seam thickness reaches 20-30m, and the roof is composed of hard and intact sandstone and sandy mudstone, and the thickness reaches 80-100m, the working face has a large mining thickness. After mining, the surface is strongly disturbed and fractured. During the initial mining of extra-thick coal seams, giant subsidence pits are formed on the surface, posing a great danger. The main problems include:

[0003] (1) Mining of extra-thick coal seams causes great disturbance. The impact range of mining of extra-thick coal seams is much larger than that of working faces with general coal seam thickness. The distribution characteristics of the overlying "three zones" are significantly different from those of general working faces. The impact range of advance support pressure and lateral support pressure is large, and the mine pressure in the roadway is strong.

[0004] (2) The initial collapse step distance of the roof is large. The initial collapse step distance of some working faces reaches 70m, resulting in a large area of ​​suspended roof. When the roof collapses suddenly at one time, it is easy to form a hurricane and strong impact. When the initial pressure comes, the shrinkage of the support column increases sharply in a short period of time or even gets crushed, which can easily damage the support and other equipment of the working face. Moreover, the periodic pressure is unstable, which seriously affects the safe production of the mine.

[0005] (3) During the longwall mining process, the roof collapsed and the working face was directly connected to the ground surface. The abnormal ground surface subsidence caused the ventilation system of the working face to be disordered and the gas in the goaf to emerge abnormally, which seriously threatened safe production.

[0006] In response to the above problems, traditional single methods such as hydraulic fracturing and blasting have very limited effectiveness and cannot solve the serious problems caused by the mining face. Summary of the Invention

[0007] This invention provides a method and system for monitoring surface subsidence pits in coal mine working faces, addressing one of the shortcomings of existing technologies. It effectively controls the management of surface subsidence pits in working faces under the dual influence of thick coal seams and hard roofs, thus solving serious problems caused by working face mining.

[0008] This invention provides a method for monitoring surface subsidence pits in coal mine working faces, comprising:

[0009] S1, modify the target hard and difficult-to-collapse rock layer to reduce the strength, integrity and wholeness of the target hard and difficult-to-collapse rock layer, making the target hard and difficult-to-collapse rock layer easier to collapse;

[0010] S2, to conduct surrounding rock structure detection on the roof strata during the initial mining stage of the working face, and to determine the damage range, intensity and joint and fracture distribution of the target hard and difficult-to-collapse rock strata in the roof during the initial mining stage of the working face.

[0011] S3, based on the detection results of S2, pre-fracture the roof rock layer in the initial mining stage of the working face to destroy the integrity and strength of the target hard and difficult-to-collapse rock layer, so that the target hard and difficult-to-collapse rock layer collapses in an orderly and step-by-step manner after the initial mining of the working face.

[0012] S4, Grouting and filling of the expected subsidence pit location during the mining face;

[0013] S5 monitors microseismic events in the roof strata of the working face during the initial mining stage, real-time surface displacement, and surface subsidence during the mining process.

[0014] According to the present invention, a method for monitoring surface subsidence pits in a coal mine working face is provided, wherein the monitoring of microseismic events in the roof strata of the working face during the initial mining stage includes:

[0015] Obtain the actual frequency of microseismic events that generate actual energy during the first set unit time of the working face mining, based on the displacement of the overlying strata above the roof.

[0016] If the actual frequency of a microseismic event with actual energy greater than the first set energy is greater than the first set frequency, or if the actual frequency of a microseismic event with actual energy greater than or equal to the second set energy and less than or equal to the third set energy is greater than the second set frequency, it proves that the overlying rock activity above the working face is relatively intense and is expected to affect the surface in a short period of time, causing large-scale displacement of the surface.

[0017] According to the present invention, a method for monitoring surface subsidence pits in a coal mine working face includes monitoring real-time surface displacement as follows:

[0018] The actual displacement velocity of each measuring point is obtained during the second set unit time of the working face mining, wherein the measuring point is a monitoring point set at the center and around the location of the expected surface subsidence pit on the upper part of the ground surface corresponding to the mining working face.

[0019] If the number of measuring points whose actual displacement velocity is greater than the set displacement velocity is greater than or equal to the set number, it proves that a large-scale displacement has occurred on the ground surface.

[0020] According to the present invention, a method for monitoring surface subsidence pits in a coal mine working face is provided, wherein monitoring the surface subsidence during the working face mining process includes:

[0021] Obtain the actual width and length of surface fissures that appear during production at the underground mining face;

[0022] If the actual width is greater than the set width and the actual length is greater than the set length, it proves that manual intervention is needed to adjust the fracturing and grouting scheme.

[0023] According to the monitoring method for surface subsidence pits in coal mine working faces provided by the present invention, in step S1, the target hard and difficult-to-collapse rock strata are modified by high-pressure water injection crack grid modification and high-pressure blasting gas crack modification.

[0024] According to the method for monitoring surface subsidence pits in coal mine working faces provided by the present invention, in step S3, the roof strata of the working face are pre-fractured through deep regional fracturing boreholes and shallow hydraulic fracturing boreholes.

[0025] According to the monitoring method for surface subsidence pits in coal mine working faces provided by the present invention, in step S4, grouting and backfilling of underground space is carried out using deep regional fracturing boreholes and shallow hydraulic fracturing boreholes.

[0026] This invention also provides a monitoring system for surface subsidence pits in coal mine working faces, which executes the monitoring method for surface subsidence pits in coal mine working faces as described above, including:

[0027] The first monitoring device is used to monitor microseismic events in the roof strata of the longwall face during the initial mining stage.

[0028] The second monitoring device is used to monitor the real-time displacement of the ground surface. The second monitoring device includes multiple monitoring stations, which are arranged in a radial array of at least three concentric rings. The monitoring stations in adjacent rings are staggered, and the center of the array is 100m away from the mining face.

[0029] The third monitoring device is used to monitor surface subsidence during the mining process at the working face.

[0030] According to the present invention, a monitoring system for surface subsidence pits in a coal mine working face is provided. The first monitoring device includes a plurality of micro-vibration sensors, which are installed in two roadways of the working face.

[0031] The monitoring system for surface subsidence pits in a coal mine working face provided by the present invention also includes a detection device suitable for detecting the surrounding rock structure of the roof strata in the initial mining stage of the working face. The detection device includes an ultrasonic detector, an intensity meter, and a viewing device.

[0032] The method for monitoring surface subsidence pits in coal mine working faces provided by this invention first identifies the target hard and difficult-to-collapse rock strata that cause the surface subsidence pits. The target hard and difficult-to-collapse rock strata are then modified to reduce their strength, integrity, and overall structure, making them more prone to collapse. Next, a comprehensive surrounding rock structure survey is conducted on the roof strata during the initial mining phase to determine the damage range, strength, and joint and fracture distribution of the target hard and difficult-to-collapse rock strata in the roof during the initial mining stage. Finally, based on the survey results, a large-scale pre-fracture is performed on the roof strata of the working face during the initial mining stage to further damage the target hard and difficult-to-collapse rock strata. The integrity and strength of the hard, difficult-to-collapse rock strata ensure that the target hard, difficult-to-collapse rock strata can collapse in an orderly and gradual manner after the initial mining of the working face, preventing the hazards caused by the concentrated and sudden collapse of the target rock strata. Then, a grouting backfilling process is adopted, and a grouting backfilling pumping system is connected to the grouting backfilling pumping system to pre-fill the locations of the expected subsidence pits during the mining of the working face, reducing the space loss caused by the mining of the thick coal seam. Finally, micro-seismic events of the roof strata of the mining face are monitored during the initial mining period, and the real-time displacement of the surface is monitored. The surface subsidence during the mining process is monitored in real time, and the control effect of the target hard, difficult-to-collapse rock strata is comprehensively judged to prevent the occurrence of subsidence pits.

[0033] This invention proposes a method for managing surface subsidence pits during mining operations in thick coal seams with hard roofs. The method involves extensive pre-fracture and disruption of the target rock strata above the working face, further damaging their integrity to allow the hard, difficult-to-collapse strata to collapse in stages. This facilitates timely grouting and backfilling of the underground space created by the mining of the thick coal seam, ensuring the backfilling of the mining area above the working face and preventing the formation of large, dangerous subsidence pits later on. Finally, a comprehensive monitoring method is used to evaluate the effectiveness of subsidence pit deformation control under the combined influence of the thick coal seam and hard roof. Compared to traditional methods such as hydraulic fracturing and blasting, this invention demonstrates significantly improved effectiveness, effectively controlling surface subsidence pits during working face mining operations under the dual influence of thick coal seams and hard roofs, and solving serious problems caused by working face mining.

[0034] In addition to the technical problems solved by the present invention, the technical features of the technical solutions constituted by the present invention, and the advantages brought about by the technical features of these technical solutions as described above, other technical features of the present invention and the advantages brought about by these technical features will be further explained in conjunction with the accompanying drawings, or will be learned through the practice of the present invention. Attached Figure Description

[0035] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0036] Figure 1 This is a schematic diagram of the structure of the second monitoring device of the monitoring system for surface mining subsidence pits in coal mine working faces provided by the present invention;

[0037] Figure label:

[0038] 100. Monitoring station; 200. Return airway; 300. Intake airway. Detailed Implementation

[0039] The embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and should not be construed as limiting the scope of the invention.

[0040] In the description of the embodiments of the present invention, it should be noted that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of the present invention. In addition, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0041] In the description of the embodiments of the present invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "connected" and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in the embodiments of the present invention based on the specific circumstances.

[0042] In embodiments of the present invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "on top of," and "over" the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0043] Furthermore, in the description of the embodiments of the present invention, unless otherwise stated, "multiple", "multiple roots", and "multiple groups" mean two or more, and "several", "several roots", and "several groups" mean one or more.

[0044] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0045] The method for monitoring surface subsidence pits in coal mine working faces provided in this embodiment of the invention includes:

[0046] S1, modify the target hard and difficult-to-collapse rock layer to reduce the strength, integrity and wholeness of the target hard and difficult-to-collapse rock layer, making the target hard and difficult-to-collapse rock layer easier to collapse;

[0047] S2, to conduct surrounding rock structure detection on the roof strata during the initial mining stage of the working face, and to determine the damage range, intensity and joint and fracture distribution of the target hard and difficult-to-collapse rock strata in the roof during the initial mining stage of the working face.

[0048] S3, based on the detection results of S2, pre-fracture the roof rock layer in the initial mining stage of the working face to destroy the integrity and strength of the target hard and difficult-to-collapse rock layer, so that the target hard and difficult-to-collapse rock layer collapses in an orderly and step-by-step manner after the initial mining of the working face.

[0049] S4, Grouting and filling of the expected subsidence pit location during the mining face;

[0050] S5 monitors microseismic events in the roof strata of the working face during the initial mining stage, real-time surface displacement, and surface subsidence during the mining process.

[0051] The method for monitoring surface subsidence pits in coal mine working faces according to this invention first identifies the target hard and difficult-to-collapse rock strata that cause the surface subsidence pits. The target hard and difficult-to-collapse rock strata are then modified to reduce their strength, integrity, and overall structure, making them more prone to collapse. Next, a comprehensive surrounding rock structure survey is conducted on the roof strata during the initial mining phase to determine the damage range, strength, and joint and fracture distribution of the target hard and difficult-to-collapse rock strata in the roof during the initial mining stage. Finally, based on the survey results, a large-scale pre-fracture is performed on the roof strata of the working face during the initial mining stage to further damage the target hard and difficult-to-collapse rock strata. The integrity and strength of the hard, difficult-to-collapse rock strata ensure that the target hard, difficult-to-collapse rock strata can collapse in an orderly and gradual manner after the initial mining of the working face, preventing the hazards caused by the concentrated and sudden collapse of the target rock strata. Then, a grouting backfilling process is adopted, and a grouting backfilling pumping system is connected to the grouting backfilling pumping system to pre-fill the locations of the expected subsidence pits during the mining of the working face, reducing the space loss caused by the mining of the thick coal seam. Finally, micro-seismic events of the roof strata of the mining face are monitored during the initial mining period, and the real-time displacement of the surface is monitored. The surface subsidence during the mining process is monitored in real time, and the control effect of the target hard, difficult-to-collapse rock strata is comprehensively judged to prevent the occurrence of subsidence pits.

[0052] This invention proposes a method for managing surface subsidence pits during mining operations in thick coal seams with hard roofs. The method involves extensive pre-fracture and destruction of the target rock strata above the working face, further disrupting their integrity to allow the hard, difficult-to-collapse strata to collapse in stages. This facilitates timely grouting and backfilling of the underground space created by the mining of the thick coal seam, ensuring the backfilling of the mining space above the working face and preventing the formation of large, dangerous subsidence pits later. Finally, a comprehensive monitoring method is used to comprehensively evaluate the deformation control effect of the subsidence pit under the combined influence of the thick coal seam and hard roof. Compared to traditional methods such as hydraulic fracturing and blasting, this invention demonstrates significantly improved effectiveness, effectively controlling the problem of surface subsidence pit management during mining operations under the dual influence of thick coal seams and hard roofs, and solving serious problems caused by mining operations. According to one embodiment of this invention, monitoring microseismic events in the roof strata of the mining face during the initial mining stage includes:

[0053] Obtain the actual frequency of microseismic events that generate actual energy during the first set unit time of the working face mining, based on the displacement of the overlying strata above the roof.

[0054] If the actual frequency of a microseismic event with actual energy greater than the first set energy is greater than the first set frequency, or if the actual frequency of a microseismic event with actual energy greater than or equal to the second set energy and less than or equal to the third set energy is greater than the second set frequency, it proves that the overlying rock activity above the working face is relatively intense and is expected to affect the surface in a short period of time, causing large-scale displacement of the surface.

[0055] In this embodiment, monitoring of microseismic events in the roof strata of the working face during the initial mining stage is considered primary monitoring. Eight microseismic sensors are deployed in the two roadways of the underground working face. The energy magnitude, frequency, and location of microseismic events caused by the displacement of the overlying strata above the working face are monitored throughout the entire process after the coal face begins mining. An intelligent monitoring and judgment algorithm is established to comprehensively judge the energy, frequency, and location of microseismic events. Within the first set unit time of working face mining, microseismic events with actual energy exceeding the first set energy are considered large microseismic energy events, while those with actual energy greater than or equal to the second set energy and less than or equal to the third set energy are considered small microseismic energy events. When a large microseismic energy event exceeding the first set frequency or a small microseismic energy event exceeding the second set frequency is detected, it is considered that the activity of the upper strata of the working face is relatively intense and is expected to affect the surface in a short period of time, causing large-area displacement of the surface.

[0056] In one embodiment, the first set unit time can generally be selected as 24 hours, the first set frequency can be 5 times, the first set energy is 104 J, the second set frequency can be 50 times, the second set energy can be 102 J, and the third set energy can be 103 J. According to an embodiment of the present invention, monitoring real-time surface displacement includes:

[0057] The actual displacement velocity of each measuring point is obtained during the second set unit time of the working face mining. The measuring points are the monitoring points set at the center and around the location of the expected surface subsidence pit on the upper part of the ground surface corresponding to the mining working face.

[0058] If the number of measuring points whose actual displacement velocity is greater than the set displacement velocity is greater than or equal to the set number, it proves that a large-scale displacement has occurred on the ground surface.

[0059] In this embodiment, the monitoring of real-time surface displacement is a secondary monitoring method. Surface displacement monitoring stations 100 are deployed at the center and perimeter of the predicted location of a surface subsidence pit, corresponding to the upper surface of the underground mining face. The center of each monitoring station 100 is generally located 100m from the mining face, and three concentric rings with radii of 20m, 40m, and 60m are arranged around it, for a total of 13 monitoring stations 100 for surface displacement monitoring. By establishing data from the displacement monitoring stations 100 at different measuring points for different events, the surface movement is determined, providing data support for subsequent subsidence pit remediation.

[0060] If, within the second set unit time of the working face mining, more than the set number of monitoring stations simultaneously detect actual displacement velocities exceeding the set displacement velocity, it is determined that a large-scale displacement has occurred on the ground surface. Generally, the working face needs to reduce the mining speed and increase the flow rate and pressure of the filling grout to slow down the speed and amount of surface displacement.

[0061] In one embodiment, the second set unit time can generally be selected as 24 hours, the number of set units is 3, and the set displacement speed is 3mm.

[0062] According to one embodiment of the present invention, monitoring surface subsidence during the mining process includes:

[0063] Obtain the actual width and length of surface fissures that appear during production at the underground mining face;

[0064] If the actual width is greater than the set width and the actual length is greater than the set length, it proves that manual intervention is needed to adjust the fracturing and grouting scheme.

[0065] In this embodiment, monitoring of surface subsidence during the mining process is implemented as a level 3 monitoring system. During the underground mining operation, drones are deployed twice daily to monitor the development of surface fissures, conduct comparative analysis, and monitor the timing and width of fissure formation. When fissures with a width exceeding a set limit or a length exceeding a set limit appear on the surface, timely manual intervention is required to adjust the fracturing and grouting strategies to resolve the subsidence pit.

[0066] In one embodiment, the width can be set to 2cm and the length can be set to 10m.

[0067] According to an embodiment of the present invention, in step S1, the target hard and difficult-to-collapse rock strata are modified by high-pressure water injection fracture mesh modification and high-pressure blasting gas fracture modification.

[0068] In this embodiment, step S1 specifically involves: firstly, by detection, identifying the target hard and difficult-to-collapse rock layer that causes the surface subsidence pit; then, modifying the target hard and difficult-to-collapse rock layer with high-pressure water injection crack grid and high-pressure blasting gas fissures to reduce the strength, integrity, and overall strength of the target hard and difficult-to-collapse rock layer, making it easier for the target hard and difficult-to-collapse rock layer to collapse.

[0069] According to an embodiment of the present invention, in step S3, the roof strata of the working face are pre-fractured through deep region fracturing boreholes and shallow hydraulic fracturing boreholes.

[0070] In this embodiment, step S2 specifically involves using an ultrasonic detector, a strength meter, and a viewing instrument to conduct comprehensive surrounding rock structure detection of the roof strata during the initial stage of the working face, determining the damage range, strength, and joint and fracture distribution of the target hard and difficult-to-collapse rock strata in the roof during the initial mining stage. Step S3 specifically involves designing the technical parameters for regional fracturing boreholes, hydraulic fracturing boreholes, and blasting boreholes based on the detection results, thereby performing large-scale pre-fracture of the roof strata of the working face during the initial mining stage, destroying the integrity and strength of the target hard and difficult-to-collapse rock strata, so that the target hard and difficult-to-collapse rock strata can collapse in an orderly and gradual manner after the initial mining of the working face, preventing the hazards caused by the concentrated and sudden collapse of the target rock strata.

[0071] This invention combines deep-area fracturing drilling with shallow hydraulic fracturing to pre-fracturize and destroy the target rock strata on the upper part of the working face. At the same time, it uses high-pressure gas blasting to further destroy the integrity of the target rock strata, so that the hard and difficult-to-collapse target rock strata can collapse in a timely manner.

[0072] According to one embodiment of the present invention, in step S4, grouting backfill is performed on the downhole space using deep fracturing boreholes and shallow hydraulic fracturing boreholes.

[0073] like Figure 1 As shown, in this embodiment, step S4 specifically includes: employing a grouting backfilling process, utilizing regional fracturing boreholes and some hydraulic fracturing boreholes, connecting a grouting backfilling pumping system, and pre-filling the locations of anticipated subsidence pits during working face mining to reduce space loss caused by mining thick coal seams. By utilizing hydraulic fracturing boreholes to promptly grout backfill the underground space caused by mining thick coal seams, the space above the working face can be backfilled and replenished, preventing the formation of large and dangerous subsidence pits later. This embodiment also provides a monitoring system for surface mining subsidence pits in coal mine working faces, implementing the monitoring method for surface mining subsidence pits in coal mine working faces as described in the above embodiment, including:

[0074] The first monitoring device is used to monitor microseismic events in the roof strata of the longwall face during the initial mining stage.

[0075] The second monitoring device is used to monitor the real-time displacement of the ground surface. The second monitoring device includes multiple monitoring stations 100, which are arranged in a radial array of at least three rings. The monitoring stations 100 in adjacent rings are staggered, and the center of the array is 100m away from the mining face.

[0076] The third monitoring device is used to monitor surface subsidence during the mining process at the working face.

[0077] The monitoring system for surface subsidence pits in coal mine working faces according to this invention includes: a first monitoring device (impact energy monitoring device installed in the intake airway 300 and return airway 200 of the working face) to monitor micro-vibration events in the roof strata during the initial mining phase; a second monitoring device (surface movement monitoring device deployed on the surface) to monitor real-time surface displacement; and a third monitoring device (periodic drone patrols) to monitor surface subsidence during the working face mining process. The system comprehensively assesses the control effect on the target hard and difficult-to-collapse strata, thus preventing the occurrence of subsidence pits. This invention proposes a method for managing surface subsidence pits in working faces with thick coal seams and hard roofs. By employing a comprehensive monitoring method, it comprehensively evaluates the deformation control effect of subsidence pits under the influence of thick coal seams and hard roofs, effectively controlling the difficult problem of surface subsidence pit management in working faces under the dual influence of thick coal seams and hard roofs.

[0078] According to one embodiment of the present invention, the first monitoring device includes a plurality of micro-vibration sensors, which are disposed in two grooves of the working face.

[0079] According to one embodiment of the present invention, the monitoring system for surface mining subsidence pits in coal mine working faces further includes a detection device suitable for detecting the surrounding rock structure of the roof strata in the initial mining stage of the working face. The detection device includes an ultrasonic detector, an intensity meter, and a viewing device.

[0080] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for monitoring surface subsidence pits in coal mine working faces, characterized in that: include: S1, modify the target hard and difficult-to-collapse rock layer to reduce the strength, integrity and wholeness of the target hard and difficult-to-collapse rock layer, making the target hard and difficult-to-collapse rock layer easier to collapse; S2, to conduct surrounding rock structure detection on the roof strata during the initial mining stage of the working face, and to determine the damage range, intensity and joint and fracture distribution of the target hard and difficult-to-collapse rock strata in the roof during the initial mining stage of the working face. S3, based on the detection results of S2, pre-fracture the roof rock layer in the initial mining stage of the working face to destroy the integrity and strength of the target hard and difficult-to-collapse rock layer, so that the target hard and difficult-to-collapse rock layer collapses in an orderly and step-by-step manner after the initial mining of the working face. S4, Grouting and filling of the expected subsidence pit location during the mining face; S5 monitors microseismic events in the roof strata of the working face during the initial mining stage, real-time surface displacement, and surface subsidence during the mining process. In step S1, the target hard and difficult-to-collapse rock strata are modified by high-pressure water injection fracture mesh modification and high-pressure blasting gas fracture modification. In step S3, the roof strata of the working face are pre-fractured through deep fracturing boreholes and shallow hydraulic fracturing boreholes. In step S4, deep fracturing boreholes and shallow hydraulic fracturing boreholes are used to grout and backfill the downhole space.

2. The monitoring method for surface subsidence pits in coal mine working faces according to claim 1, characterized in that: The microseismic events in the roof strata of the longwall face during the initial mining stage of the monitoring face include: Obtain the actual frequency of microseismic events that generate actual energy during the first set unit time of the working face mining, based on the displacement of the overlying strata above the roof. If the actual frequency of a microseismic event with actual energy greater than the first set energy is greater than the first set frequency, or if the actual frequency of a microseismic event with actual energy greater than or equal to the second set energy and less than or equal to the third set energy is greater than the second set frequency, it proves that the overlying rock activity above the working face is relatively intense and is expected to affect the surface in a short period of time, causing large-scale displacement of the surface.

3. The monitoring method for surface subsidence pits in coal mine working faces according to claim 2, characterized in that: Monitoring real-time surface displacement includes: The actual displacement velocity of each measuring point is obtained during the second set unit time of the working face mining, wherein the measuring point is a monitoring point set at the center and around the location of the expected surface subsidence pit on the upper part of the ground surface corresponding to the mining working face. If the number of measuring points whose actual displacement velocity is greater than the set displacement velocity is greater than or equal to the set number, it proves that a large-scale displacement has occurred on the ground surface.

4. The monitoring method for surface subsidence pits in coal mine working faces according to claim 1, characterized in that: Monitoring surface subsidence during the mining process includes: Obtain the actual width and length of surface fissures that appear during production at the underground mining face; If the actual width is greater than the set width and the actual length is greater than the set length, it proves that manual intervention is needed to adjust the fracturing and grouting scheme.

5. A monitoring system for surface subsidence pits in coal mine working faces, characterized in that: The method for monitoring surface subsidence pits in coal mine working faces according to any one of claims 1 to 4 includes: The first monitoring device is used to monitor microseismic events in the roof strata of the longwall face during the initial mining stage. The second monitoring device is used to monitor the real-time displacement of the ground surface. The second monitoring device includes multiple monitoring stations, which are arranged in a radial array of at least three concentric rings. The monitoring stations in adjacent rings are staggered, and the center of the array is 100m away from the mining face. The third monitoring device is used to monitor surface subsidence during the mining process at the working face.

6. The monitoring system for surface subsidence pits in coal mine working faces according to claim 5, characterized in that: The first monitoring device includes multiple micro-vibration sensors, which are installed in two chute sections of the working face.

7. The monitoring system for surface subsidence pits in coal mine working faces according to claim 5, characterized in that: It also includes a detection device suitable for detecting the surrounding rock structure of the roof strata in the initial mining stage of the working face. The detection device includes an ultrasonic detector, an intensity meter, and a viewing device.

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