A simulation device and method for weakening the top coal of steep seam top coal caving

Abstract

The application discloses a device and method for simulating top coal magnetic weakening in steep coal seam top coal caving, and belongs to the technical field of physical similar simulation tests of mining engineering. The device comprises a fixed model cavity, a containing space in which coal body similar materials are laid, a coal caving opening in communication with the lower part of the coal body similar materials, a loading system for loading, and a gradient magnetic-weakening slip zone embedded in the coal body similar materials. The slip zone comprises a first flexible base strip and a second flexible base strip which are oppositely arranged and can slide relative to each other. The first flexible base strip and the second flexible base strip are respectively fixed with magnetic bodies to generate magnetic attraction holding force. When the shear threshold is not reached, the shear limiting piece is connected to limit the slip, and when the threshold is reached, the shear limiting piece is failed to make the slip occur. The device can truly reproduce the progressive instability process of the weak surface from stable holding to shear slip, and provides a test means for revealing the control mechanism of the weak surface on the top coal caving starting, migration path and caving range.

Description

Technical Field

[0001] This invention relates to the field of physical similarity simulation test technology in mining engineering, and in particular to a magnetic shear weakening simulation device and method for top coal caving mining in steeply inclined coal seams. Background Technology

[0002] In horizontal segmented fully mechanized top coal caving of steeply dipping coal seams, the top coal is significantly affected by the gravity dip component. During caving, the coal body is prone to local loosening, shear displacement, and lateral slippage, making its caving behavior more complex than that of gently dipping coal seams. Natural joints, bedding, fracture zones, and weakened regions formed by artificial pre-splitting within the top coal significantly control the location and migration path of top coal instability, potentially leading to difficulties in top coal initiation, uneven caving, and residual coal retention. Therefore, elucidating the influence mechanism of weak surfaces on the top coal caving effect is crucial for optimizing the top coal caving process.

[0003] Current research methods mainly include field observation, theoretical analysis, numerical simulation, and physical similarity simulation. Field observation is constrained by underground conditions and cannot fully track the loosening and slippage process inside the top coal; theoretical analysis simplifies the coal structure too much and cannot fully reflect the slippage characteristics controlled by discontinuous media and weak surfaces under steeply inclined conditions; numerical simulation results depend on constitutive parameters and need to be verified by physical experiments. Physical similarity simulation, due to its process visibility, controllable boundaries, and adjustable parameters, has become an important means of studying coal extraction laws.

[0004] Existing physical similarity simulation devices can mostly realize functions such as tilt angle setting, material laying, coal discharge port control, and coal discharge volume statistics, but there are still obvious shortcomings: First, some devices rely on the overall tilt model box to form a steep tilt condition, which makes it difficult to reflect the spatial relationship of the coexistence of fixed cavity, steep tilt, and horizontal coal discharge port; Second, most of them use loose granular materials, which makes it difficult to reflect the gradual destruction process of top coal from initial integrity to weak cementation failure; Third, there is a lack of weakening structures set inside the coal body with adjustable unlocking thresholds and low-resistance sliding interfaces, which cannot effectively simulate the guiding effect of weak surfaces on sliding paths and deflection discharge.

[0005] Therefore, there is an urgent need for a simulation device that can construct an equivalent weak surface with adjustable location, strength and spatial distribution inside the coal body, and reproduce its gradual process from stable maintenance to local unlocking to shear slip under coal discharge disturbance, so as to provide experimental support for the study of weak surface control mechanism and optimization of pre-splitting weakening scheme. Summary of the Invention

[0006] The purpose of this invention is to provide a magnetic shear weakening simulation device and method for top coal caving mining in steeply inclined coal seams. This addresses the problem that existing physical similarity simulation devices struggle to construct weak surfaces within similar top coal materials, where the location, equivalent shear strength, and spatial distribution are adjustable. Furthermore, they fail to reproduce the gradual instability process of these weak surfaces under coal caving disturbances, from stable holding, partial unlocking, shear displacement, to slip release. By setting the magnetic holding force, shear limit threshold, and its spatial gradient, this device can simulate the initiation of top coal release, slip path, release range, and residual coal distribution under different weak surface development degrees and spatial distributions. This reveals the controlling effect of weak surfaces within the top coal on the release effect and provides experimental basis for optimizing coal caving methods and designing artificial pre-splitting weakening schemes.

[0007] To achieve the above-mentioned technical objectives, the present invention provides the following technical solution: In a first aspect, the present invention provides a simulation device for magnetic shear weakening of top coal seam top coal caving mining in steeply inclined coal seams, comprising a fixed model cavity, a coal-like material laid inside the fixed model cavity, a coal discharge port located below and communicating with the coal-like material, a loading system for applying a load to the coal-like material, and a gradient magnetic-shear weakening slip band embedded inside the coal-like material; the gradient magnetic-shear weakening slip band includes a first flexible base band, a second flexible base band, a first magnetic attractor, a second magnetic attractor, and a shear limiting plate; the first flexible base band and the second flexible base band are arranged opposite to each other, and The two can slide relative to each other; the first magnetic chuck is fixed on the first flexible baseband, and the second magnetic chuck is fixed on the second flexible baseband, and a magnetic attraction force is generated between the first magnetic chuck and the second magnetic chuck; the shear limiting piece is connected between the first flexible baseband and the second flexible baseband, and is used to limit the relative sliding of the first flexible baseband and the second flexible baseband when the shearing action applied to the coal-like material does not reach a preset threshold, and fails when the shearing action reaches the preset threshold, so that the first flexible baseband and the second flexible baseband can slide relative to each other.

[0008] Optionally, the magnetic attraction strength, arrangement density, or arrangement spacing of the first magnetic attractor and the second magnetic attractor vary in a gradient along the coal seam dip direction, the working face length direction, or the area corresponding to the coal discharge port, so that different positions of the gradient magnetic-shear weakening slip zone have different degrees of weakening and local unlocking thresholds.

[0009] Optionally, the shear strength of the shear limiting plate varies in a gradient along the dip direction of the coal seam, the length direction of the working face, or the area corresponding to the coal discharge port, so that different locations of the gradient magnetic-shear weakened slip zone have different local unlocking thresholds.

[0010] Optionally, the gradient magnetic-shear weakening slip band further includes a low-friction slip film layer disposed between the first flexible base band and the second flexible base band.

[0011] Optionally, the low-friction slip film layer is one of polytetrafluoroethylene film, polyethylene film, silicone oil coated film, graphite lubricating film, or low-friction composite film.

[0012] Optionally, the gradient magnetic-shear weakening slip zone further includes an upper anchoring rough layer and a lower anchoring rough layer. The upper anchoring rough layer is disposed on the side of the first flexible base zone away from the second flexible base zone, and the lower anchoring rough layer is disposed on the side of the second flexible base zone away from the first flexible base zone. The coal-like material is embedded in the upper anchoring rough layer and the lower anchoring rough layer.

[0013] Optionally, the upper anchoring rough layer and the lower anchoring rough layer are one or more combinations of rough protrusions, barbs, embedding holes, mesh clamping layers, particle embedding grooves, or surface rough particle layers.

[0014] Optionally, the shearing limiting piece is one or more of the following: a shearable limiting piece, a thin-plate limiting piece, a slotted limiting piece, a bendable limiting piece, or a detachable limiting piece. The shear strength of the shearing limiting piece can be adjusted by the material thickness, the slotting form, the necking width, the connection depth, the number of limiting pieces, or the spacing between the limiting pieces.

[0015] Optionally, the coal-like material is a continuously graded, weakly cemented granular material, which is formed by mixing granular particles of different particle size distributions, a weak cementing agent, and a weighted component in a preset similarity ratio.

[0016] Optionally, a transparent observation plate is provided on at least one side of the fixed model cavity, a coal collection trough is provided below the coal discharge port, and a weighing sensor is provided in the coal collection trough.

[0017] Optionally, there are multiple coal discharge ports, arranged sequentially along the length of the working face, and each coal discharge port is equipped with an independent gate assembly.

[0018] Optionally, the independent gate assembly includes a gate plate, a drive component, and an opening limit component. The gate plate can be opened and closed using a rotary, flip-type, lifting, or pull-out structure.

[0019] Optionally, the loading system includes a loading beam, multiple loading elements spaced laterally along the model cavity, and a rigid loading plate disposed below the loading elements, wherein the multiple loading elements can independently adjust the loading force.

[0020] In a second aspect, the present invention provides a method for simulating the weakening of top coal magnetic shear in steeply inclined coal seam top coal caving mining, based on the aforementioned simulation device for top coal magnetic shear weakening in steeply inclined coal seam top coal caving mining, the method comprising the following steps: Mount the fixed model cavity onto the base; According to the preset coal seam dip angle, coal-like materials are laid in layers into the fixed model cavity, and when laid to the designed embedment position, the gradient magnetic-shear weakening slip zone is embedded in the coal-like material. The loading system is activated to apply a preset overburden load to similar materials of the coal body through the overlying strata. Control the opening of the coal discharge port so that materials similar to coal can be discharged through the coal discharge port; After coal discharge is completed, observe the loosening range, shear displacement path and slip direction of similar materials inside the coal body, check the failure state of the shear limit plate and the relative misalignment of the first magnetic suction body and the second magnetic suction body, and determine the unlocking range of the gradient magnetic-shear weakening slip zone in combination with the distribution of the discharged coal body.

[0021] Compared with the prior art, the present invention discloses at least the following beneficial effects: This invention, by setting up a fixed model cavity and laying coal-like materials inside it at a preset inclination angle, can realistically reflect the spatial relationship between steeply inclined coal seams and the coexistence of horizontal coal outlets without tilting the entire model cavity, thus avoiding the boundary effects and gravity direction distortion problems caused by traditional integrally tilted models. The gradient magnetic-shear weakening slip zone embedded inside the coal-like material utilizes the relative slip capability of the first and second flexible base zones, along with a shear limiting plate bridging them, to maintain interface stability when the coal discharge disturbance does not reach a preset threshold, thereby simulating the complete coal body stage. When the shear force reaches the threshold, the shear limiting plate fails, allowing relative slippage between the two base zones. Combined with the magnetic attraction force between the first and second magnetic attractors, this not only prevents premature interface instability but also provides a certain residual holding effect after slippage, thus completely reproducing the gradual instability process of the weak surface from stable holding through local unlocking to shear slippage. Therefore, this device can effectively simulate the control effect of weak joint surfaces, fracture zones or pre-weakening areas inside steeply inclined coal seams on the start-up release, sliding path and release range of top coal from the mechanical response level, providing a reliable test platform for coal release process optimization and pre-fracture weakening scheme design. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments 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.

[0023] Figure 1 This is a schematic diagram of the structure of the magnetic shear weakening simulation device for top coal caving mining of steeply inclined coal seams according to the present invention. Figure 2 This is a schematic diagram of a local AA cross-section enlarged before unlocking of the gradient magnetic-shear weakened slip zone of the present invention; Figure 3 This is a magnified view of a local AA cross-section structure after the gradient magnetic-shear weakened slip zone is unlocked according to the present invention; Reference numerals: 1. Overlying strata; 2. Coal-like material; 3. Reserved coal discharge window; 4. Coal collection trough; 5. Coal discharge port; 6. Gradient magnetic-shear weakened slip zone; 7. Loading system; 8. Base; 9. Upper anchoring rough layer; 10. First flexible base zone; 11. Low-friction slip film layer; 12. First magnetic accelerator; 13. Second magnetic accelerator; 14. Shear limiting plate; 15. Lower anchoring rough layer; 16. Second flexible base zone. Detailed Implementation

[0024] 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.

[0025] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0026] Example 1 Reference Figure 1 As shown, Embodiment 1 of the present invention provides a magnetic shear weakening simulation device for top coal mining in steeply inclined coal seams, including a base 8, a fixed model cavity, an overlying stratum 1, a coal-like material 2, a reserved coal discharge window 3, a coal discharge port 5, a coal collection trough 4, a loading system 7, and a gradient magnetic-shear weakening slip zone 6.

[0027] In this embodiment, the fixed model cavity is mounted on the base 8 and remains vertically fixed. Coal-like material 2 is placed inside the fixed model cavity, laid according to a preset coal seam dip angle, resulting in a steeply inclined arrangement of the coal-like material 2 within the cavity. The base 8, the reserved coal discharge window 3, the coal discharge port 5, and the coal collection trough 4 are all horizontally arranged. The steeply inclined coal seam simulation is achieved by setting an inclined laying template, a dip limit boundary, or a dip angle positioning groove inside the fixed model cavity, ensuring the coal-like material 2 is arranged according to the preset coal seam dip angle. A transparent observation plate is provided on at least one side of the fixed model cavity to observe local loosening, weak cementation failure, shear displacement, slippage, and discharge processes within the coal-like material 2.

[0028] Furthermore, the coal-like material 2 is a continuous graded weakly cemented granular material similar to the top coal of the coal seam. It is formed by mixing granular particles of different particle size grades, weak cementing agents, and heavy components in a preset similar ratio, and has an initial weak cementing quantity. This material can maintain a certain integrity during the initial laying and loading stages, and after the coal discharge port 5 is opened, particle rearrangement, local loosening, weak cementing failure, shear displacement, and flow release can occur.

[0029] Furthermore, the overlying rock layer 1 is positioned above the coal-like material 2. The loading system 7 is positioned on the upper part of the fixed model cavity and is used to apply loads to the coal-like material 2 through the overlying rock layer 1.

[0030] Furthermore, reserved coal discharge windows 3 are located at the same horizontal elevation below the coal-like material 2 and are arranged sequentially along the length of the working face. Coal discharge ports 5 are located at the reserved coal discharge windows 3 and are directly connected to the coal-like material 2. Coal collection troughs 4 are located below the coal discharge ports 5 and are used to receive the coal-like material 2 directly discharged from the coal discharge ports 5.

[0031] Furthermore, a gradient magnetic-shear weakened slip zone 6 is pre-embedded within the coal-like material 2 to construct a weak surface within the top coal seam with a preset equivalent shear strength and critical unlocking threshold. The gradient magnetic-shear weakened slip zone 6 is arranged along the dip direction of the coal seam to simulate the slip path of coal seams with different weak surface distributions. This weakened slip zone is not a direct coal discharge channel, but rather serves to mechanically simulate joint weak surfaces, fracture zones, bedding weak surfaces, locally fractured zones, or pre-weakened slip regions within the same coal seam.

[0032] Example 2 Reference Figure 2 and Figure 3As shown, Embodiment 2 of the present invention provides another simulation device for magnetic shear weakening of top coal in steeply inclined coal seam top coal caving mining. Based on Embodiment 1, the gradient magnetic-shear weakening slip zone 6 further includes an upper anchoring rough layer 9, a first flexible base zone 10, a first magnetic absorbing body 12, a low-friction slip film layer 11, a second magnetic absorbing body 13, a shear limiting plate 14, a lower anchoring rough layer 15, and a second flexible base zone 16.

[0033] Furthermore, the first flexible substrate 10 and the second flexible substrate 16 are disposed opposite each other on both sides of the weakened slip interface, and the low-friction slip film layer 11 is disposed between the first flexible substrate 10 and the second flexible substrate 16. The first flexible substrate 10 and the second flexible substrate 16 can be made of polyester fiber reinforced rubber tape or thin nylon reinforced tape, and have sufficient tensile strength and flexibility.

[0034] Furthermore, the first magnetic accumulator 12 is fixed to the first flexible baseband 10, and the second magnetic accumulator 13 is fixed to the second flexible baseband 16. The first magnetic accumulator 12 and the second magnetic accumulator 13 are arranged with opposite poles to form a cross-interface magnetic attraction and retention force between the first flexible baseband 10 and the second flexible baseband 16. The magnetic attraction and retention structure does not directly adsorb the coal-like material 2, but simulates the initial retention effect of the weakened interface through the attraction between the first magnetic accumulator 12 and the second magnetic accumulator 13. Both the first magnetic accumulator 12 and the second magnetic accumulator 13 are neodymium iron boron permanent magnets. The first magnetic accumulator 12 and the second magnetic accumulator 13 are respectively embedded in the mounting grooves of the first flexible baseband 10 and the second flexible baseband 16, and are fixed by thin film encapsulation, adhesive layer encapsulation, or pressing.

[0035] Furthermore, the upper anchoring rough layer 9 is disposed on the side of the first flexible base 10 opposite to the low-friction slip film layer 11, and the lower anchoring rough layer 15 is disposed on the side of the second flexible base 16 opposite to the low-friction slip film layer 11. The upper anchoring rough layer 9 and the lower anchoring rough layer 15 can be one or more combinations of rough protrusions, barbs, embedding holes, mesh clamping layers, particle embedding grooves, or surface rough particle layers. When the coal-like material 2 is laid, it is embedded in the upper anchoring rough layer 9 and the lower anchoring rough layer 15, and forms a mechanically embedded connection with the first flexible base 10 and the second flexible base 16 under the action of compaction and weak bonding. Thus, the shearing force generated by the coal-like material 2 under coal discharge disturbance can be transmitted through the upper anchoring rough layer 9 and the lower anchoring rough layer 15 to the first flexible base 10, the second flexible base 16, the first magnetic chuck 12, the second magnetic chuck 13, and the shear limiting piece 14.

[0036] Furthermore, the shear limiting piece 14 spans between the first flexible baseband 10 and the second flexible baseband 16, used to limit the relative slippage of the first flexible baseband 10 and the second flexible baseband 16 before the shearing action of the coal body reaches a preset threshold. The shear limiting piece 14 is a replaceable limiting component, and can be one or more combinations of shearable limiting pieces, thin-plate limiting pieces, slotted limiting pieces, bendable limiting pieces, or disengaged limiting pieces. The shear strength of the shear limiting piece 14 can be adjusted by the material thickness, slotting form, necking width, connection depth, number of limiting pieces, or spacing of the limiting pieces. When the shearing action of the coal body reaches the preset threshold, the shear limiting piece 14 bends, shears, disengages, or fails, allowing the first flexible baseband 10 and the second flexible baseband 16 to slip relative to each other along the low-friction slip film layer 11.

[0037] Furthermore, the low-friction slip film layer 11 is one of polytetrafluoroethylene film, polyethylene film, silicone oil coated film, graphite lubricating film or low-friction composite film, used to reduce the relative slip resistance between the first flexible baseband 10 and the second flexible baseband 16 after the shear limit piece 14 fails.

[0038] Example 3 Embodiment 3 of the present invention provides another simulation device for magnetic shear weakening of top coal in steeply inclined coal seam top coal caving mining. Based on the above embodiments, the magnetic attraction strength, arrangement density, and arrangement spacing of the first magnetic attractor 12 and the second magnetic attractor 13, or the shear strength of the shear limiting plate 14, vary gradient along the coal seam dip direction, the working face length direction, or the corresponding area of ​​the coal vent. This results in different degrees of weakening and local unlocking thresholds at different locations of the gradient magnetic-shear weakening slip zone 6. Specifically, the gradient magnetic-shear weakening slip zone 6 can be divided into multiple gradient zones along the coal seam dip direction, with different magnetic spacing and shear limiting plate necking widths set in each gradient zone, thereby forming differentiated unlocking thresholds.

[0039] When the coal discharge port 5 is opened, the coal-like material 2 near the coal discharge port 5 is directly discharged downwards and enters the coal collection trough 4, forming a local unloading zone in the coal body above the coal discharge port 5. Under the combined action of overburden load, gravity component of coal seam dip angle, and coal discharge disturbance, the shearing action of the coal body is transmitted to the first flexible baseband 10 and the second flexible baseband 16 through the upper anchoring rough layer 9 and the lower anchoring rough layer 15. When the shearing action reaches the preset threshold of the shear limiting plate 14, the shear limiting plate 14 bends, shears, disengages, or fails. The first flexible baseband 10 and the second flexible baseband 16 slip relative to each other along the low-friction slip film layer 11, causing the coal-like material 2 to experience local loosening, weak cementation failure, shear displacement, tendency slippage, and biased discharge.

[0040] Example 4 Embodiment 4 of the present invention provides another simulation device for magnetic shear weakening of top coal in steeply inclined coal seam top coal caving mining. Based on the above embodiments, a pre-reserved coal discharge window 3 is further provided through a horizontal bearing plate or gate plate. Each coal discharge port 5 is equipped with an independent gate assembly. The independent gate assembly includes a gate plate, a driving component, and an opening limit component. The gate plate can be opened and closed using a rotary, flip-type, lifting, or pull-out structure. When the independent gate assembly is closed, the coal discharge port 5 is in a closed state, and the coal-like material 2 remains stable. When the independent gate assembly is open, the coal discharge port 5 forms an open coal discharge boundary, and the coal-like material 2 is directly discharged downwards from the coal discharge port 5 and enters the coal collection trough 4.

[0041] Furthermore, the loading system 7 includes a loading beam, multiple loading components spaced laterally along the model cavity, and a rigid loading plate positioned below the loading components. The multiple loading components can independently adjust the loading force, thereby achieving differentiated control of the load on different areas.

[0042] Furthermore, the coal collection trough 4 is located below the reserved coal discharge window 3, and a weighing sensor is installed inside the coal collection trough 4 to record the weight of the coal discharged at different stages in real time.

[0043] Example 5 Embodiment 5 of this invention provides a specific simulation test scheme. In this scheme, the specific dimensions, material parameters, and loading parameters are only for illustrating the specific implementation of this invention and are not intended to limit the scope of protection of this invention. Specifically, as follows: A magnetic shear weakening simulation device for top coal caving mining in steeply inclined coal seams includes a base 8, a fixed model cavity, an overlying stratum 1, a coal-like material 2, a reserved coal discharge window 3, a coal discharge port 5, a coal collection trough 4, a loading system 7, and a gradient magnetic-shear weakening slip zone 6.

[0044] In this embodiment, the fixed model cavity adopts a combination structure of a steel frame and a transparent plexiglass observation panel. The effective internal dimensions of the model cavity are: length 3000mm, width 200mm, and height 2000mm. A 15mm thick transparent plexiglass panel is installed on the front side of the model cavity, a steel back plate or transparent observation panel is installed on the rear side, and limiting steel plates are installed on the left and right sides. The model cavity as a whole remains vertically fixed, and the coal seam dip angle is not formed by tilting the model cavity as a whole.

[0045] The simulated dip angle α of the coal seam was set to 65°. Dip angle positioning lines and tilt limit plates were set on both sides inside the model cavity to ensure that the coal-like material 2 was laid at a dip angle of 65°.

[0046] The coal-like material 2 is a continuously graded, weakly cemented granular similar material. The particle size distribution is as follows: 20% of particles with a diameter of 0.25~0.50 mm, 30% of particles with a diameter of 0.50~1.00 mm, 30% of particles with a diameter of 1.00~2.00 mm, and 20% of particles with a diameter of 2.00~5.00 mm. The weak cementing agent consists of gypsum powder and a small amount of water-soluble cementing agent, with the cementing agent accounting for 3%~6% of the total mass of the coal-like material, preferably 4.5%. The bulk density of the coal-like material is 1.20~1.35 g / cm³. 3 The preferred value is 1.28 g / cm³. 3 According to small-scale direct shear tests, the internal friction angle of similar coal materials is 28°~35°, preferably 32°, and the initial weakly cemented shear strength is 1.5~3.0 kPa, preferably 2.2 kPa.

[0047] Ten reserved coal discharge windows 3 are set at the same horizontal elevation at the lower part of the coal-like material 2, and each reserved coal discharge window 3 corresponds to a coal discharge port 5. The gate thickness is 3mm, the maximum opening angle is 90°, and the commonly used test opening angles are 30°, 45°, 60° or 90°. Each coal discharge port 5 is equipped with an independent gate assembly, which can independently control the opening, closing and opening degree.

[0048] Both the first flexible base strip 10 and the second flexible base strip 16 are made of polyester fiber reinforced rubber strips. Each flexible base strip has a width of 40 mm, a thickness of 1.0 mm, a length of 2000 mm, and a tensile strength of not less than 20 MPa. The upper anchoring rough layer 9 and the lower anchoring rough layer 15 adopt a combination structure of a rough particle coating layer and a grid-embedded hole structure, with a grid hole diameter of 2-4 mm and a hole spacing of 5 mm.

[0049] Both the first magnetic chuck 12 and the second magnetic chuck 13 use neodymium iron boron permanent magnets, with a magnet grade of N35. The size of a single magnet is 10mm × 6mm × 3mm, and the normal magnetic attraction force of a single pair of magnets is 0.8~1.5N. The magnetic chucks are respectively embedded in the flexible baseband mounting slots and fixed by thin-film encapsulation.

[0050] The shear limiting plate 14 is made of polypropylene sheet with a thickness of 0.20 mm, a total width of 8 mm, a necking width of 2 mm, 3 mm, or 4 mm, an effective length of 12 mm, an installation spacing of 80 mm, and a rated shear strength of 0.4~1.2 N per piece. The shear limiting plate 14 forms a controllable failure point through its necking structure. The low-friction slip film layer 11 is made of polytetrafluoroethylene film with a thickness of 0.05~0.10 mm, a static friction coefficient of 0.08~0.12, and a dynamic friction coefficient of 0.05~0.10.

[0051] The gradient magnetic-shear weakened slip zone 6 is divided into three gradient zones along the dip direction of the coal seam. Zone I, closer to the coal outlet, has a magnet spacing of 80 mm, a shear limit plate necking width of 2 mm, and a designed unlocking threshold of 1.0~1.5 N. Zone II, located in the middle region, has a magnet spacing of 60 mm, a shear limit plate necking width of 3 mm, and a designed unlocking threshold of 1.8~2.5 N. Zone III, farther from the coal outlet, has a magnet spacing of 40 mm, a shear limit plate necking width of 4 mm, and a designed unlocking threshold of 2.8~3.6 N.

[0052] The loading system 7 applies load to the coal-like material 2 through the overlying rock strata 1. In this embodiment, a staged loading method is used, with an initial preload of 0.5 kPa, a staged loading interval of 0.5 kPa, a maximum loading pressure of 5.0 kPa, and a holding time of 5 minutes for each stage. During the coal release test, a constant load holding method is used, with a preferred loading pressure of 3.0 kPa.

[0053] During the experiment, the fixed model cavity was first installed on the base 8, and the coal discharge port 5, coal collection trough 4, and loading system 7 were checked for normal operation. Then, coal-like material 2 was laid according to a simulated coal seam dip angle of 65°. When the coal-like material 2 was laid to the designed weakening position, the gradient magnetic-shear weakening slip band 6 was embedded inside the coal-like material 2 along the coal seam dip direction. During embedding, the upper anchoring rough layer 9 and the lower anchoring rough layer 15 were positioned so that they faced the adjacent coal-like material 2, ensuring that the coal-like material 2 could be embedded within the anchoring rough layer.

[0054] After continuing to lay the coal-like material 2 to the designed height, install the overlying stratum 1 and the loading system 7. Start the loading system 7 and gradually load it up to 3.0 kPa in stages of 0.5 kPa, maintaining the load for 5 minutes to allow the coal-like material 2 to reach a stable loading state.

[0055] Then, the designated coal discharge port 5 is opened. In this embodiment, the first coal discharge port 5 is opened first at an angle of 60°, and coal is discharged continuously for 30 seconds. After closing the first coal discharge port 5, the second coal discharge port 5 is opened after an interval of 60 seconds, and coal is discharged sequentially through all 10 coal discharge ports.

[0056] After the test, observe the local loosening range, shear slip path, directional slip direction, and deflection state within the coal-similar material 2. Check whether the shear limiting plate 14 has bent, broken, or disengaged, and observe whether the first magnetic chuck 12 and the second magnetic chuck 13 have undergone relative misalignment. Based on the distribution of the released coal in the coal collection trough 4, determine the coal release differences in the corresponding areas of different coal release ports and the unlocking range of the gradient magnetic-shear weakened slip zone 6.

[0057] Example 6 Embodiment 6 of the present invention also provides a method for simulating the weakening of top coal magnetic shear in steeply inclined coal seam top coal caving mining. Based on the simulation device for top coal magnetic shear weakening in steeply inclined coal seam top coal caving mining described in the above embodiments, the method includes the following steps: S1. Install the fixed model cavity on the base 8, and keep the fixed model cavity, the reserved coal discharge window 3, the coal discharge port 5 and the coal collection trough 4 in a stable state.

[0058] S2. Set up a reserved coal discharge window 3 at the same horizontal elevation position below the similar material 2 of the coal body, and arrange the reserved coal discharge window 3 along the length of the working face.

[0059] S3. Based on the simulated dip angle of the coal seam, the location of the coal outlet, the direction of coal slippage, and the experimental simulation target, determine the design weakening position of the gradient magnetic-shear weakening slip zone 6.

[0060] S4. Lay coal-like material 2 in layers into the fixed model cavity according to the preset coal seam dip angle until the designed embedment position of the gradient magnetic-shear weakened slip zone 6 is reached.

[0061] S5. Place the gradient magnetic-shear weakening slip band 6 at the designed position, so that the upper anchoring rough layer 9 and the lower anchoring rough layer 15 face the coal similar material 2 on both sides of the weak surface, and fix the position and inclination angle of the gradient magnetic-shear weakening slip band 6.

[0062] S6. Continue to lay and compact the coal-like material 2 in layers until the model design height is reached, so that the gradient magnetic-shear weakened slip zone 6 is completely embedded in the coal-like material 2.

[0063] S7. Start the loading system 7 and apply a preset overburden load to the coal-like material 2 through the overlying rock layer 1.

[0064] In one specific embodiment, the loading system 7 adopts a staged loading method, with an initial preload of 0.5 kPa, a staged loading interval of 0.5 kPa, a maximum loading pressure of 5.0 kPa, and a holding time of 5 min for each stage. During the coal discharge test, a constant load holding method is used, with a preferred loading pressure of 3.0 kPa.

[0065] S8. According to the test settings, control the independent opening, closing and adjustment of the opening degree of different coal discharge ports 5 so that the coal-like material 2 is directly discharged downward through the coal discharge port 5 and enters the coal collection trough 4.

[0066] S9. The process of single-level segmented top coal caving in a steeply inclined coal seam is simulated by sequentially opening and closing the coal discharge port 5, adjusting the opening degree, and controlling the coal discharge time.

[0067] In one specific embodiment, the first coal discharge port 5 is opened first at an angle of 60° and coal is discharged continuously for 30 seconds; after the first coal discharge port 5 is closed, the second coal discharge port 5 is opened after an interval of 60 seconds, and coal is discharged sequentially through the eight coal discharge ports.

[0068] S10. After coal discharge is completed, observe the local loosening range, shear displacement path, directional slip direction, and deviated discharge state inside the similar material 2 of the coal body; check whether the shear limiting plate 14 is bent, sheared, or disengaged; observe whether the first magnetic suction body 12 and the second magnetic suction body 13 are relatively misaligned; based on the distribution of the discharged coal body in the coal collection trough 4, determine the coal discharge differences in the corresponding areas of different coal discharge ports and the unlocking range of the gradient magnetic-shear weakened slip zone 6, and combine the location and discharge amount of the discharged coal body to analyze the weakened slip path inside the coal body, the deviated law of the discharged body, the coal discharge differences in different coal discharge ports, and the local unlocking mechanism of the gradient magnetic-shear weakened slip zone during the single-level segmented top coal discharge of steeply inclined coal seams.

[0069] In the description of this invention, it should be understood that the terms "longitudinal", "lateral", "up", "down", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this invention, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention.

[0070] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A simulation device for magnetic shear weakening of top coal in steeply inclined coal seam top coal caving mining, characterized in that, It includes a fixed model cavity, a coal-like material (2) laid inside the fixed model cavity, a coal discharge port (5) located below and connected to the coal-like material (2), a loading system (7) for applying loads to the coal-like material (2), and a gradient magnetic-shear weakening slip zone (6) embedded in the coal-like material (2). The gradient magnetic-shear weakening slip band (6) includes a first flexible base band (10), a second flexible base band (16), a first magnetic accumulator (12), a second magnetic accumulator (13), and a shear limiting piece (14). The first flexible baseband (10) and the second flexible baseband (16) are slidably disposed relative to each other; the first magnetic accumulator (12) is fixed on the first flexible baseband (10), and the second magnetic accumulator (13) is fixed on the second flexible baseband (16), and a magnetic holding force is generated between the first magnetic accumulator (12) and the second magnetic accumulator (13); The shear limiting piece (14) is connected between the first flexible baseband (10) and the second flexible baseband (16) to restrict the relative slippage between the first flexible baseband (10) and the second flexible baseband (16) when the shearing action applied to the coal-like material (2) does not reach a preset threshold, and to fail when the shearing action reaches the preset threshold, so that the first flexible baseband (10) and the second flexible baseband (16) can slip relative to each other.

2. The magnetic shear weakening simulation device for top coal caving mining of steeply inclined coal seams according to claim 1, characterized in that, The magnetic attraction strength, arrangement density or arrangement spacing of the first magnetic attractor (12) and the second magnetic attractor (13) vary in gradient along the coal seam dip direction, working face length direction or coal outlet (5) corresponding area, so that the gradient magnetic-shear weakening slip zone (6) has different weakening degree and local unlocking threshold at different positions.

3. The magnetic shear weakening simulation device for top coal caving mining of steeply inclined coal seams according to claim 1 or 2, characterized in that, The shear strength of the shear limiting plate (14) varies in gradient along the dip direction of the coal seam, the length direction of the working face, or the area corresponding to the coal outlet (5), so that the gradient magnetic-shear weakening slip zone (6) has different local unlocking thresholds at different locations.

4. The magnetic shear weakening simulation device for top coal caving mining of steeply inclined coal seams according to claim 1, characterized in that, The gradient magnetic-shear weakening slip band (6) further includes a low-friction slip film layer (11), which is disposed between the first flexible base band (10) and the second flexible base band (16).

5. The magnetic shear weakening simulation device for top coal caving mining of steeply inclined coal seams according to claim 4, characterized in that, The low-friction slip film layer (11) is one of polytetrafluoroethylene film, polyethylene film, silicone oil coating film, graphite lubricating film or low-friction composite film.

6. The magnetic shear weakening simulation device for top coal caving mining of steeply inclined coal seams according to claim 1 or 4, characterized in that, The gradient magnetic-shear weakening slip zone (6) further includes an upper anchoring rough layer (9) and a lower anchoring rough layer (15). The upper anchoring rough layer (9) is disposed on the side of the first flexible base zone (10) away from the second flexible base zone (16), and the lower anchoring rough layer (15) is disposed on the side of the second flexible base zone (16) away from the first flexible base zone (10). The coal-like material (2) is embedded in the upper anchoring rough layer (9) and the lower anchoring rough layer (15).

7. The magnetic shear weakening simulation device for top coal caving mining of steeply inclined coal seams according to claim 6, characterized in that, The upper anchoring rough layer (9) and the lower anchoring rough layer (15) are one or more combinations of rough protrusions, barbs, embedding holes, mesh clamping layers, particle embedding grooves or surface rough particle layers.

8. The magnetic shear weakening simulation device for top coal caving mining of steeply inclined coal seams according to claim 1, characterized in that, The shearing limiting piece (14) is one or more of the following: a shearable limiting piece, a thin-plate limiting piece, a slotted limiting piece, a bendable limiting piece, or a detachable limiting piece. The shear strength of the shearing limiting piece (14) can be adjusted by the material thickness, the slotting form, the necking width, the connection depth, the number of limiting pieces, or the spacing between the limiting pieces.

9. The magnetic shear weakening simulation device for top coal caving mining of steeply inclined coal seams according to claim 1, characterized in that, The coal-like material (2) is a continuously graded weakly cemented granular similar material, which is formed by mixing granular particles of different particle size grades, weak cementing agents and compounding components in a preset similar ratio.

10. A method for simulating the weakening of top coal magnetic shear in steeply inclined coal seam top coal caving mining, based on the simulation device for simulating the weakening of top coal magnetic shear in steeply inclined coal seam top coal caving mining as described in any one of claims 1 to 9, characterized in that, Includes the following steps: The fixed model cavity is installed on the base (8); According to the preset coal seam dip angle, coal-like material (2) is laid in layers in the fixed model cavity, and when it is laid to the designed embedment position, the gradient magnetic-shear weakening slip zone (6) is embedded in the coal-like material (2); The loading system (7) is started, and a preset overburden load is applied to the coal-like material (2) through the overlying rock layer (1); Control the opening of the coal discharge port (5) so that the coal-like material (2) is discharged through the coal discharge port (5); After coal discharge is completed, observe the loosening range, shear displacement path and sliding direction inside the coal similar material (2), check the failure state of the shear limit plate (14) and the relative misalignment of the first magnetic suction body (12) and the second magnetic suction body (13), and determine the unlocking range of the gradient magnetic-shear weakening slip zone (6) in combination with the distribution of the discharged coal body.

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