A system and method for determining a lower coal critical mining height in multi-layer coal mining

Abstract

The present application belongs to the technical field of mining engineering safety, and discloses a system and method for determining the critical mining height of lower coal in multi-layer coal mining. The system comprises a shell and a simulation material layer, and the simulation material layer comprises upper coal and lower coal. The upper coal has a caving method mining goaf, and pressure sensors and vibration sensors. The lower coal has a filling method mining working face, which is filled with hard boards, and the side of the simulation material layer is covered with speckles. There are also scanning devices and data processing devices. The data processing device is used to obtain real-time speckle position, pressure and vibration data when the hard boards are extracted layer by layer, and to analyze the influence of lower coal filling mining on the overburden structure of upper coal caving method mining based on machine learning when the lower coal filling mining height increases from small to large, so as to obtain the critical mining height of lower coal. The system solves the problem of calculating the critical mining height of lower coal, can realize water prevention and control during coal mining, and is beneficial to safe, efficient and low-cost filling mining of lower coal. The above method also has the same advantages.

Description

Technical Field

[0001] This invention belongs to the field of mining engineering safety technology, and in particular relates to a system and method for determining the critical mining height of the lower coal seam in multi-layer coal mining. Background Technology

[0002] As coal mining depths gradually increase, especially in multi-layered coal mines, the mining scope and intensity of the upper coal seams continue to increase, making backfilling a necessary method for mining the lower coal seams. However, the overburden space structure after the upper coal seam is mined is in a temporarily stable state. During the mining of the lower coal seam, the entire overburden space structure will become unstable and reconstructed. Therefore, under conditions such as roof confined water, accurately determining the height of overburden fissure development becomes crucial to ensuring water control safety during the mining of the lower coal seam.

[0003] In existing technologies, the mechanism by which the effect of lower coal seam backfilling mining affects overburden structure migration and stress evolution is unclear. If the backfilling height of the goaf is too low, it will affect safety; if the backfilling height is too high, it will increase mining costs. Therefore, it is difficult to determine the optimal backfilling height scheme that balances water control and mining costs. Currently, to simulate the backfilling effect of different goafs, a method of excavating to a specific height is generally used. However, this method cannot achieve a refined and continuous simulation of the overburden migration characteristics and stress distribution under specific backfilling height conditions. The disadvantages of this method are that a single excavation is affected by the manual excavation method and the particle size of the similar materials, and it can generally only be excavated once. It is difficult to reproduce high-precision continuous excavation under specific backfilling effects, nor can it be excavated continuously at certain intervals. Moreover, each excavation is a one-time test, which cannot achieve a full-process simulation of the overburden structure migration law, cannot determine the trend of the influence of backfilling height on overburden structure migration, and cannot combine monitoring data to determine the critical value of backfilling height when the overburden structure type changes. Summary of the Invention

[0004] To address the aforementioned issues, this invention provides a system and method for determining the critical mining height of the lower coal seam in multi-layer coal mining. This system can simulate the entire range of the lower coal seam filling mining face from 100% filling to caving mining, accurately determining the critical equivalent mining height that influences the linkage between the lower coal seam filling mining face and the overlying coal overburden structure. This is the critical mining height of the lower coal seam when the fracture zone develops to the roof confined aquifer, thereby achieving the purpose of waterproofing and water control during the coal mining process. This is beneficial for the safe, efficient, and low-cost mining of the lower coal seam filling mining face.

[0005] The present invention provides a system for determining the critical mining height of the lower coal seam in multi-layer coal mining, comprising an outer shell and a simulated material layer arranged from bottom to top within the outer shell to simulate the actual coal seam and rock strata, wherein the simulated material layer includes the upper coal seam and the lower coal seam.

[0006] The upper coal seam has a goaf area mined by caving method. A first pressure sensor is installed in the first rock stratum below the upper coal seam, and a first vibration sensor is installed in the second rock stratum below the first rock stratum.

[0007] The lower coal seam has a backfilling mining face located below the goaf of the caving mining method. A second pressure sensor is installed in the third rock stratum below the lower coal seam, and a second vibration sensor is installed in the fourth rock stratum below the third rock stratum.

[0008] The filling method mining face is filled with a predetermined number of hard plates, and the total thickness of the hard plates is equal to the height of the lower coal seam. The predetermined sides of the hard plates and the simulated material layer are exposed from the open side of the shell.

[0009] The preset side surface of the simulated material layer is covered with speckles;

[0010] It also includes a scanning device facing the preset side, used to acquire images of the preset side in real time;

[0011] It also includes a data processing device electrically connected to the scanning device, the first pressure sensor, the first vibration sensor, the second pressure sensor, and the second vibration sensor;

[0012] The data processing device is used to acquire images of the real-time positions of speckle patterns on the preset side surface, the first pressure data of the first pressure sensor, the first vibration data of the first vibration sensor, the second pressure data of the second pressure sensor, and the second vibration data of the second vibration sensor during the process of the hard plate being extracted layer by layer. Based on machine learning, it performs stress and strain field analysis on the impact of the lower coal filling mining on the overburden structure of the upper coal caving method under the condition that the lower coal filling mining height is from small to large. It obtains the equivalent mining height of the aquifer by the secondary migration of the overburden structure of the upper coal induced by the development of the lower coal and the height of the water-conducting fracture zone, and finally obtains the critical mining height of the lower coal.

[0013] Preferably, in the above-mentioned system for determining the critical mining height of the lower coal seam in multi-layer coal mining, the top surface of the simulated material layer is covered with a pad, and a top beam is provided above the pad. The top beam and the pad are supported by multiple hydraulic cylinders, with the free end of the hydraulic cylinders facing the pad, for applying a static load. The static load is the self-weight of the strata above the top rock layer of the simulated material layer up to the surface, calculated according to the stress similarity ratio.

[0014] Preferably, in the above-mentioned system for determining the critical mining height of the lower coal seam in multi-layer coal mining, a third vibration sensor is also installed in the top rock stratum. The third vibration sensor is also electrically connected to the data processing device, and the data processing device is also used to obtain the critical mining height of the lower coal seam by combining the third vibration data obtained by the third vibration sensor.

[0015] Preferably, in the above-mentioned system for determining the critical mining height of the lower coal seam in multi-layer coal mining, the outer shell includes a bottom beam, a left side plate, a right side plate, and a top beam that are bolted together.

[0016] Preferably, in the above-mentioned system for determining the critical mining height of the lower coal seam in multi-layer coal mining, the first pressure sensor, the first vibration sensor, the second pressure sensor, and the second vibration sensor are electrically connected to the data processing device using a programmable static resistance strain gauge.

[0017] Preferably, in the above-mentioned system for determining the critical mining height of the lower coal seam in multi-layer coal mining, the hard plate is a PVC plate with mechanical properties consistent with the material simulating the lower coal seam.

[0018] Preferably, in the above-mentioned system for determining the critical mining height of the lower coal seam in multi-layer coal mining, the number of hard plates is 20 to 25.

[0019] Preferably, in the above-mentioned system for determining the critical mining height of the lower coal seam in multi-layer coal mining, the scanning device is a high-speed scanner with the camera optical axis arranged perpendicular to the preset side.

[0020] This invention provides a method for determining the critical mining height of the lower coal seam in multi-layer coal mining, utilizing the critical mining height determination system for the lower coal seam in multi-layer coal mining as described in any of the above claims, including:

[0021] Establish a system for determining the critical mining height of the lower coal seam in multi-layer coal mining;

[0022] The upper coal seam is mined using the caving method, with the mining height being equal to the thickness of the upper coal seam, to obtain the goaf mined by the caving method;

[0023] The rigid plates are pulled out sequentially from top to bottom until they are completely removed, while simultaneously acquiring images of the real-time location of the speckle, the first pressure data, the first vibration data, the second pressure data, and the second vibration data.

[0024] Based on machine learning, stress and strain field analyses were performed on the impact of lower coal filling mining on the overburden structure of upper coal caving mining under conditions of increasing lower coal filling mining height. The equivalent mining height of the aquifer was obtained by obtaining the secondary migration of the overburden structure of the upper coal induced by the development of the lower coal and the height of the water-conducting fracture zone. Finally, the critical mining height of the lower coal was obtained.

[0025] Preferably, in the above-mentioned method for determining the critical mining height of the lower coal seam in multi-layer coal mining, a third vibration sensor is also installed in the top rock layer of the simulated material layer. The third vibration sensor is also electrically connected to the data processing device, and the data processing device is also used to obtain the critical mining height of the lower coal seam by combining the third vibration data obtained by the third vibration sensor.

[0026] As described above, the system for determining the critical mining height of the lower coal seam in multi-layer coal mining provided by the present invention includes an outer shell and a simulated material layer arranged from bottom to top within the outer shell to simulate the actual coal seam and rock strata. The simulated material layer includes an upper coal seam and a lower coal seam. The upper coal seam has a caving-mined goaf. A first pressure sensor is installed in a first rock stratum below the upper coal seam, and a first vibration sensor is installed in a second rock stratum below the first rock stratum. The lower coal seam has a filling-mining face located below the caving-mined goaf, and a third rock stratum below the lower coal seam... A second pressure sensor is installed, and a second vibration sensor is installed in the fourth rock layer below the third rock layer. The backfilling mining face is filled with a predetermined number of hard plates, and the total thickness of the hard plates is equal to the height of the lower coal seam. The predetermined sides of the hard plates and the simulated material layer are exposed from the open side of the shell. The predetermined sides of the simulated material layer are covered with speckle patterns. A scanning device is also included facing the predetermined sides for real-time image acquisition of the predetermined sides. A data processing device is also included, electrically connected to the scanning device, the first pressure sensor, the first vibration sensor, the second pressure sensor, and the second vibration sensor. The data processing device is used to acquire images of the real-time positions of speckle patterns on the predetermined sides, the first pressure data of the first pressure sensor, the first vibration data of the first vibration sensor, the second pressure data of the second pressure sensor, and the second vibration data of the second vibration sensor during the process of the hard plates being extracted layer by layer. Based on machine learning, the device performs stress and strain field analysis on the impact of the lower coal seam backfilling mining on the overburden structure of the upper coal seam caving mining under the condition of increasing lower coal seam backfilling mining height, and obtains the lower coal seam backfilling mining face. The development of a coal seam induces secondary migration of the overlying coal strata—the height of the water-conducting fracture zone is used to obtain the equivalent mining height of the aquifer, ultimately determining the critical mining height of the lower coal seam. The beneficial effect of this invention is that it can simulate the entire range of the lower coal seam filling mining face from 100% filling to caving mining, accurately determining the critical equivalent mining height affecting the linkage between the lower coal seam filling mining face and the overlying coal strata structure, that is, the critical mining height of the lower coal seam when the fracture zone develops to the roof confined aquifer. This achieves the purpose of waterproofing and water control during the coal mining process, which is beneficial to the safe, efficient, and low-cost mining of the lower coal seam filling mining face. The method for determining the critical mining height of the lower coal seam in multi-layer coal mining provided by this invention has the same advantages as the aforementioned system for determining the critical mining height of the lower coal seam in multi-layer coal mining. Attached Figure Description

[0027] 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 embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0028] Figure 1 This is a schematic diagram of an embodiment of a system for determining the critical mining height of the lower coal seam in multi-layer coal mining provided by the present invention;

[0029] Figure 2 This is a schematic diagram of an embodiment of a method for determining the critical mining height of the lower coal seam in multi-layer coal mining provided by the present invention. Detailed Implementation

[0030] The core of this invention is to provide a system and method for determining the critical mining height of the lower coal seam in multi-layer coal mining. This system can simulate the entire range of the lower coal seam filling mining face from 100% filling to caving mining, and accurately determine the critical equivalent mining height that affects the linkage between the lower coal seam filling mining face and the overlying coal overburden structure. That is, the critical mining height of the lower coal seam when the fracture zone develops to the roof confined aquifer. This achieves the purpose of waterproofing and water control in the coal mining process, which is conducive to the safe, efficient and low-cost mining of the lower coal seam filling mining face.

[0031] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] An example implementation of the system for determining the critical mining height of the lower coal seam in multi-layer coal mining provided by this invention. Figure 1 As shown, Figure 1 This is a schematic diagram of an embodiment of a system for determining the critical mining height of the lower coal seam in multi-layer coal mining according to the present invention. The system may include an outer shell 1 and a simulated material layer 2 arranged from bottom to top within the outer shell 1 to simulate actual coal seams and rock strata. The outer shell 1 may include a bottom beam 11, a left side vertical plate 12, a right side vertical plate 13, and a top beam 14 bolted together. The front and back can be shielded using baffle channel steel to provide a sealed space for the simulated material layer 2. The simulated material layer 2 includes an upper coal seam 21 and a lower coal seam 22. It should be noted that the similarity material ratio can be determined experimentally, based on the actual mechanical parameters of siltstone, fine sandstone, medium sandstone, coarse sandstone, and coal seams, according to the stress similarity ratio C. σThe mechanical parameters of the similar material layer were calculated. Polymers made of river sand, lime and gypsum were used to conduct multiple batches of combined tests and mechanical tests. When the mechanical parameters of the similar material layer met the index requirements, it was the similar material ratio of the layer. Then, a similar simulation material layer was built. From bottom to top, the similar materials determined by the test were laid in layers, and mica powder was used to isolate the layers.

[0033] The upper coal seam 21 has a goaf 211 mined by caving method. A first pressure sensor 231 is installed in the first rock layer 23 below the upper coal seam 21, and a first vibration sensor 241 is installed in the second rock layer 24 below the first rock layer 23. In this way, the pressure changes in the upper coal seam 21 can be monitored and analyzed in real time by detecting the stress changes and vibrations in the first rock layer 23 caused by coal seam excavation.

[0034] The lower coal seam 22 has a backfilling mining face 221 located below the caving mining goaf 211. A second pressure sensor 251 is installed in the third rock stratum 25 below the lower coal seam 22, and a second vibration sensor 261 is installed in the fourth rock stratum 26 below the third rock stratum 25. In this way, the pressure changes in the lower coal seam 22 can be monitored and analyzed in real time by detecting the stress changes and vibrations in the third rock stratum 25 caused by coal seam excavation.

[0035] The backfilling mining face 221 is filled with a predetermined number of hard plates 222, and the total thickness of the hard plates 222 is equal to the height of the underlying coal seam 22. These hard plates 222 are used to simulate the unmined coal in the underlying coal seam. This plate-like structure can be easily extracted to continuously simulate different mining heights. The predetermined sides of the hard plates 222 and the simulated material layer 2 are exposed from the open side of the outer shell 1. This predetermined side is... Figure 1 This is the side that is being shown;

[0036] The simulated material layer 2 has speckle patterns all over its preset side surface. Figure 1 (Not shown, that is, many points distributed throughout the entire surface). These speckles can be used to characterize the strain occurring at each location, thereby providing strain data for subsequent analysis. The number and spacing of these speckles can be selected according to actual needs and are not limited here.

[0037] It also includes a scanning device 3 facing the preset side, which is used to acquire images of the preset side in real time. This allows the position of all speckles on the preset side to be acquired in real time, and strain data can be obtained based on the change of the position of each speckle relative to the initial position during the experiment. Combined with stress data and vibration data, the critical sampling height can be determined.

[0038] It also includes a data processing unit 4 electrically connected to the scanning device 3, the first pressure sensor 231, the first vibration sensor 241, the second pressure sensor 251, and the second vibration sensor 261 (to avoid excessive wiring, these connections are not detailed in the original text). Figure 1 (As shown), this data processing device 4 can be a computer with data processing software installed;

[0039] The data processing device 4 is used to acquire images of the real-time position of speckle on the preset side surface, the first pressure data of the first pressure sensor 231, the first vibration data of the first vibration sensor 241, the second pressure data of the second pressure sensor 251, and the second vibration data of the second vibration sensor 261 during the process of the hard plate 222 being extracted layer by layer. Based on machine learning, it performs stress and strain field analysis on the impact of the lower coal filling mining on the overburden structure of the upper coal caving method under the condition of the lower coal filling mining height increasing from small to large. It obtains the equivalent mining height of the aquifer by the secondary migration of the overburden structure of the upper coal induced by the development of the lower coal and the height of the water-conducting fracture zone. Finally, it obtains the critical mining height of the lower coal. Specifically, the critical mining height of the lower coal can be obtained by Bayesian catastrophe analysis, but is not limited to.

[0040] As described above, in the embodiment of the multi-layer coal mining critical mining height determination system for the lower coal seam provided by the present invention, the system includes an outer shell 1 and a simulation material layer 2 arranged from bottom to top within the outer shell 1 to simulate real coal seams and rock strata. The simulation material layer 2 includes an upper coal seam 21 and a lower coal seam 22. The upper coal seam 21 has a caving-mined goaf 211. A first pressure sensor 231 is installed in a first rock stratum 23 below the upper coal seam 21, and a first vibration sensor 241 is installed in a second rock stratum 24 below the first rock stratum 23. The lower coal seam 22 has a filling-type mining structure located below the caving-mined goaf 211. The mining face 221 is equipped with a second pressure sensor 251 in the third rock stratum 25 below the lower coal seam 22, and a second vibration sensor 261 in the fourth rock stratum 26 below the third rock stratum 25. The filling mining face 221 is filled with a predetermined number of hard plates 222, the total thickness of which is equal to the height of the lower coal seam 22. The predetermined sides of the hard plates 222 and the simulated material layer 2 are exposed from the open side of the outer shell 1. The predetermined sides of the simulated material layer 2 are covered with speckle patterns. The mining face 221 also includes a scanning device 3 facing the predetermined sides for real-time image acquisition. The mining face 221 also includes a second pressure sensor 251 installed in the third rock stratum 25 below the lower coal seam 22, and a second vibration sensor 261 installed in the fourth rock stratum 26 below the third rock stratum 25. A data processing device 4 electrically connected to force sensor 231, first vibration sensor 241, second pressure sensor 251, and second vibration sensor 261; the data processing device 4 is used to acquire images of the real-time positions of speckle patterns on a preset side surface, first pressure data from the first pressure sensor 231, first vibration data from the first vibration sensor 241, second pressure data from the second pressure sensor 251, and second vibration data from the second vibration sensor 261 during the process of the rigid plate 222 being extracted layer by layer; and based on machine learning, it performs lower coal filling mining on the upper coal caving method for overburden mining under conditions of increasing lower coal filling mining height. By analyzing the stress and strain fields of the structural influence, the secondary migration of the overburden structure induced by the development of the lower coal seam and the height of the water-conducting fracture zone are obtained, leading to the equivalent mining height of the aquifer. Ultimately, the critical mining height of the lower coal seam is obtained. This allows for the simulation of the entire range of the lower coal seam filling mining face from 100% filling to caving mining, accurately determining the critical equivalent mining height that affects the linkage between the lower coal seam filling mining face and the overburden structure of the upper coal seam. In other words, it is the critical mining height of the lower coal seam when the fracture zone develops to the confined aquifer in the roof. This achieves the purpose of waterproofing and water control in the coal mining process, which is conducive to the safe, efficient, and low-cost mining of the lower coal seam filling mining face.

[0041] In a specific embodiment of the above-mentioned system for determining the critical mining height of the lower coal seam in multi-layer coal mining, reference continues... Figure 1The top surface of the simulated material layer 2 is covered with a pad 5, and a top beam 14 is located above the pad 5. Multiple hydraulic cylinders 6 hold the top beam 14 and the pad 5 in place. The free ends of the hydraulic cylinders 6 face the pad 5 and are used to apply a static load. The static load is calculated by converting the self-weight of the strata above the top rock layer 27 of the simulated material layer 2 up to the surface according to the stress similarity ratio. It should be noted that this top rock layer 27 is the rock layer containing pressurized water above the upper coal seam. The pad 5 is laid directly on top of this top rock layer 27 in contact with it. A force F is applied using the hydraulic cylinders. The area of ​​the pad 5 is S, so the stress δ = F / S. Furthermore, the pad 5 is made of a hard material, capable of withstanding the static load applied by the hydraulic cylinders 6 and transmitting it evenly downwards.

[0042] In another specific embodiment of the above-mentioned system for determining the critical mining height of the lower coal seam in multi-layer coal mining, a third vibration sensor 271 is further installed within the top rock stratum 27, based on the aforementioned specific embodiment. The third vibration sensor 271 is also electrically connected to the data processing device 4. The data processing device 4 is used to combine the third vibration data obtained by the third vibration sensor 271 to obtain the critical mining height of the lower coal seam. This allows the vibration situation within the top rock stratum 27 to be taken into account, thereby making the determination of the critical mining height more accurate. Furthermore, the first pressure sensor 231, the first vibration sensor 241, the second pressure sensor 251, and the second vibration sensor 261 can preferably be electrically connected to the data processing device 4 using a programmable static resistance strain gauge. This programmable static resistance strain gauge has high precision and high stability, and a high degree of automation, making it more suitable for situations requiring multi-point synchronous measurement and long-term monitoring. Of course, other instruments can also be selected according to actual needs, and there are no restrictions here.

[0043] In another specific embodiment of the above-mentioned system for determining the critical mining height of the lower coal seam in multi-layer coal mining, the aforementioned rigid plate 222 can preferably be a PVC plate with mechanical properties consistent with the material of the simulated lower coal seam. This ensures mechanical consistency with the lower coal seam at the same height, which is more in line with reality. This is because the rigid plate 222 is used to simulate different filling mining effects of the lower coal seam in reality. Initially, these rigid plates 222 are used to fill the space. After the upper coal seam is excavated and the overburden settles, these rigid plates 222 are gradually removed in batches. This can simulate different filling mining processes in reality, realize continuous coal mining tests, monitor displacement, stress and vibration signals during mining, and use machine learning methods to study the overburden migration law and stress evolution characteristics under different mining heights of the lower coal seam. This makes it easier and more accurate to find the critical mining height, providing data support and technical guidance for ensuring water control and roof control in the lower coal seam.

[0044] In a preferred embodiment of the above-mentioned system for determining the critical mining height of the lower coal seam in multi-layer coal mining, the number of hard plates 222 can be 20 to 25. Specifically, taking 20 hard plates 222 as an example, the following explanation is provided: The lower coal seam is excavated in layers using the filling method. The excavation area is the filling method mining face. Excavation is carried out in cycles, with the single excavation height being the height of a single hard plate layer. When excavating the first layer, the single excavation height is the thickness h1 of a single hard plate layer, which is 1 / 20 of the lower coal seam thickness, i.e., the equivalent mining height is h1 = 1h0 / 20. At this time, the filling effect of the corresponding goaf is 95%. When excavating the second layer, the cumulative excavation height of 2 hard plates is 2, i.e., the cumulative equivalent mining height is h2 = 2h0 / 20. At this time, the filling effect of the corresponding goaf is 90%. The third layer is excavated…; the 20th layer is excavated, and the cumulative excavation height of 20 hard plates is 20, i.e., the cumulative equivalent mining height is h… 20 =20h0 / 20, at this time the filling effect of the goaf is 0%, which is completely consistent with the caving method mining face on both sides, h 20 =h0. Data from various stress sensors, vibration sensors, and surface speckle displacement were recorded during excavation.

[0045] In another preferred embodiment of the above-mentioned system for determining the critical mining height of the lower coal seam in multi-layer coal mining, the scanning device 3 can preferably be a high-speed scanner with the camera optical axis perpendicular to the preset side. Specifically, during the entire excavation test, the position of the high-speed scanner must not be moved, and the camera's focus must not be adjusted. The non-contact optical deformation measurement system uses the basic principles of digital image processing to acquire images through a digital camera, capturing the surface morphology features before and after deformation. The grid point image coordinates are obtained using digital image correlation calculations, and the image coordinates are reprojected onto the specimen coordinates through camera calibration parameters, thereby realizing the deformation measurement of the specimen. During the entire excavation test, the high-speed scanner must not be moved, and the camera's focus must not be adjusted. In subsequent analysis, the initial image before excavation is used as the reference image, and subsequent images are used as the images to be analyzed to ensure the accuracy of the strain data.

[0046] It should also be noted that, Figure 1 The design also showcases the fifth, sixth, and seventh rock layers 20, arranged sequentially from bottom to top between the upper coal layer 21 and the top rock layer 27, thus fully simulating the actual conditions of each underground layer.

[0047] An example implementation of the method for determining the critical mining height of the lower coal seam in multi-layer coal mining provided by this invention. Figure 2 As shown, Figure 2 This is a schematic diagram of an embodiment of a method for determining the critical mining height of the lower coal seam in multi-layer coal mining provided by the present invention. Utilizing the multi-layer coal mining critical mining height determination system as described above, it may include the following steps:

[0048] S1: Establish a system for determining the critical mining height of the lower coal seam in multi-layer coal mining;

[0049] Specifically, after the system is set up, the simulated material layer is dried and then sprayed with speckled paint. The front and back baffle channels are removed, and the system is placed in a cool and ventilated place. After 28 days of standing, the similar material reaches the required strength. Then, white paint is sprayed on the surface of the system and random speckled paint is drawn.

[0050] S2: The upper coal seam is mined using the caving method, and the mining height is equal to the thickness of the upper coal seam, resulting in the caving goaf.

[0051] Specifically, the caving method working face in the upper coal seam is excavated, with the excavation height equal to the thickness of the upper coal seam. The excavation method is from one end to the other. To prevent the model from collapsing due to excessively rapid excavation, the excavation step distance l1 in each experiment is based on the geometric similarity ratio C. l The excavation step distance l0 at the coal mine site is determined by l1 = l0 / C. l The excavation interval t1 for each test was based on the time similarity ratio C. t The interval t0 between excavations at the coal mine site is determined, i.e., t1 = t0 / C. t Data from the second pressure sensor 251, the second vibration sensor 261, and the surface speckle displacement were recorded during excavation.

[0052] S3: Pull out the rigid plates from top to bottom until they are all pulled out, and at the same time acquire images of the real-time position of the speckle, the first pressure data, the first vibration data, the second pressure data, and the second vibration data.

[0053] Taking 20 hard slabs as an example, the lower coal seam is excavated using the backfilling method in a layered manner. The excavation area is the backfilling method mining face, and excavation is carried out in cycles. The height of a single excavation is the height of a single hard slab. When excavating the first layer, the height of a single excavation is the thickness h1 of a single hard slab, which is 1 / 20 of the thickness of the lower coal seam. That is, the equivalent mining height is h1 = 1h0 / 20, and the corresponding goaf filling effect is 95%. When excavating the second layer, the cumulative excavation height of 2 hard slabs is reached, which is the cumulative equivalent mining height h2 = 2h0 / 20. At this time, the corresponding goaf filling effect is 90%. The third layer is excavated... until the 20th layer is excavated, with a cumulative excavation height of 20 hard slabs, which is the cumulative equivalent mining height h1. 20 =20h0 / 20, at this time the filling effect of the goaf is 0%, which is completely consistent with the caving method mining face on both sides, h 20 =h0. Data from various stress sensors, vibration sensors, and surface speckle displacement were recorded during excavation.

[0054] S4: Based on machine learning, stress and strain field analysis was conducted on the influence of lower coal filling mining on the overburden structure of upper coal caving mining under the condition of increasing lower coal filling mining height. The secondary migration of the overburden structure of upper coal induced by lower coal development - the height of the water-conducting fracture zone was obtained to obtain the equivalent mining height of the aquifer, and finally the critical mining height of lower coal was obtained.

[0055] It is evident that the above method can simulate the entire range of the lower coal filling mining face from 100% filling to caving mining, accurately determine the critical equivalent mining height that affects the linkage between the lower coal filling mining face and the overlying coal overburden structure, that is, the critical mining height of the lower coal when the fracture zone develops to the roof confined aquifer, thereby achieving the purpose of waterproofing and water control in the coal mining process, which is conducive to the safe, efficient and low-cost mining of the lower coal filling mining face.

[0056] In a specific embodiment of the above-mentioned method for determining the critical mining height of the lower coal seam in multi-layer coal mining, a third vibration sensor can also be installed in the top rock layer of the simulated material layer. The third vibration sensor is also electrically connected to a data processing device. The data processing device is also used to combine the third vibration data obtained by the third vibration sensor to obtain the critical mining height of the lower coal seam. In this way, the vibration situation in the top rock layer can be taken into account, thereby making the determination of the critical mining height more accurate.

[0057] It should also be noted that the meanings of different critical mining heights are shown in Table 1, which is a table of the meanings of critical mining heights.

[0058] Table 1. Meaning of Critical Mining Height

[0059]

[0060] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A system for determining the critical mining height of the lower coal seam in multi-layer coal mining, characterized in that, It includes an outer shell and a simulated material layer arranged from bottom to top within the outer shell to simulate real coal seams and rock strata, the simulated material layer including an upper coal seam and a lower coal seam; The upper coal seam has a goaf area mined by caving method. A first pressure sensor is installed in the first rock stratum below the upper coal seam, and a first vibration sensor is installed in the second rock stratum below the first rock stratum. The lower coal seam has a backfilling mining face located below the goaf of the caving mining method. A second pressure sensor is installed in the third rock stratum below the lower coal seam, and a second vibration sensor is installed in the fourth rock stratum below the third rock stratum. The filling method mining face is filled with a predetermined number of hard plates, and the total thickness of the hard plates is equal to the height of the lower coal layer. The predetermined sides of the hard plates and the simulated material layer are exposed from the open side of the shell. The preset side surface of the simulated material layer is covered with speckles; It also includes a scanning device facing the preset side, used to acquire images of the preset side in real time; It also includes a data processing device electrically connected to the scanning device, the first pressure sensor, the first vibration sensor, the second pressure sensor, and the second vibration sensor; The data processing device is used to acquire images of the real-time positions of speckle patterns on the preset side surface, the first pressure data of the first pressure sensor, the first vibration data of the first vibration sensor, the second pressure data of the second pressure sensor, and the second vibration data of the second vibration sensor during the process of the hard plate being extracted layer by layer. Based on machine learning, it performs stress and strain field analysis on the impact of the lower coal filling mining on the overburden structure of the upper coal caving method under the condition that the lower coal filling mining height is from small to large. It obtains the equivalent mining height of the aquifer by the secondary migration of the overburden structure of the upper coal induced by the development of the lower coal and the height of the water-conducting fracture zone, and finally obtains the critical mining height of the lower coal.

2. The system for determining the critical mining height of the lower coal seam in multi-layer coal mining according to claim 1, characterized in that, The top surface of the simulated material layer is covered with a pad, and a top beam is located above the pad. The top beam and the pad are held together by multiple hydraulic cylinders. The free ends of the hydraulic cylinders face the pad and are used to apply a static load. The static load is the self-weight of the strata above the top rock layer of the simulated material layer up to the ground surface, calculated according to the stress similarity ratio.

3. The system for determining the critical mining height of the lower coal seam in multi-layer coal mining according to claim 2, characterized in that, A third vibration sensor is also installed in the top rock layer. The third vibration sensor is also electrically connected to the data processing device. The data processing device is also used to obtain the critical mining height of the lower coal seam by combining the third vibration data obtained by the third vibration sensor.

4. The system for determining the critical mining height of the lower coal seam in multi-layer coal mining according to claim 3, characterized in that, The outer casing includes a bottom beam, a left side plate, a right side plate, and a top beam, all bolted together.

5. The system for determining the critical mining height of the lower coal seam in multi-layer coal mining according to claim 4, characterized in that, The first pressure sensor, the first vibration sensor, the second pressure sensor, and the second vibration sensor are electrically connected to the data processing device using a programmable static resistance strain gauge.

6. The system for determining the critical mining height of the lower coal seam in multi-layer coal mining according to claim 5, characterized in that, The rigid plate is a PVC plate with mechanical properties consistent with the material simulating the lower coal seam.

7. The system for determining the critical mining height of the lower coal seam in multi-layer coal mining according to claim 6, characterized in that, The number of rigid plates is 20 to 25.

8. The system for determining the critical mining height of the lower coal seam in multi-layer coal mining according to claim 7, characterized in that, The scanning device is a high-speed scanner with the camera optical axis arranged perpendicular to the preset side.

9. A method for determining the critical mining height of the lower coal seam in multi-layer coal mining, characterized in that, The system for determining the critical mining height of the lower coal seam in multi-layer coal mining as described in any one of claims 1-8 includes: Establish a system for determining the critical mining height of the lower coal seam in multi-layer coal mining; The upper coal seam is mined using the caving method, with the mining height being equal to the thickness of the upper coal seam, to obtain the goaf mined by the caving method; The rigid plates are pulled out sequentially from top to bottom until they are completely removed, while simultaneously acquiring images of the real-time location of the speckle, the first pressure data, the first vibration data, the second pressure data, and the second vibration data. Based on machine learning, stress and strain field analyses were performed on the impact of lower coal filling mining on the overburden structure of upper coal caving mining under conditions of increasing lower coal filling mining height. The equivalent mining height of the aquifer was obtained by obtaining the secondary migration of the overburden structure of the upper coal induced by the development of the lower coal and the height of the water-conducting fracture zone. Finally, the critical mining height of the lower coal was obtained.

10. The method for determining the critical mining height of the lower coal seam in multi-layer coal mining according to claim 9, characterized in that, A third vibration sensor is also installed in the top rock layer of the simulated material layer. The third vibration sensor is also electrically connected to the data processing device. The data processing device is also used to obtain the critical mining height of the lower coal seam by combining the third vibration data obtained by the third vibration sensor.

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