Numerical simulation based end coal caving area surrounding rock stability control method and device

Abstract

The application discloses a kind of based on numerical simulation's end coal releasing area surrounding rock stability control method and device, belong to surrounding rock control technical field, including S1, the bearing structure of end coal releasing area roadway surrounding rock is analyzed;S2, using PFC software establishes end coal releasing numerical simulation model;S3, based on the simulation result of S2 end coal releasing numerical simulation model is analyzed, including active support space-time analysis, end coal releasing area coal gangue flow form analysis and roadway surrounding rock bearing structure bearing capacity evolution analysis;A kind of based on numerical simulation's end coal releasing area surrounding rock stability control method and device provided by the application, coal rock flow law in the process of end coal rock falling, end surrounding rock stability and reasonable end coal releasing range are researched, not only improve the safety and efficiency of coal mining, also reduce cost, promote technological innovation.

Description

Technical Field

[0001] This invention relates to the field of surrounding rock control technology, and in particular to a method and apparatus for controlling the stability of surrounding rock in a coal discharge zone at the end based on numerical simulation. Background Technology

[0002] Fully mechanized longwall mining is a revolutionary technology for mining thick coal seams, solving problems such as stress concentration caused by coal pillars left from upper layers, easy ignition in lower goaf areas, difficulty in roadway support, relatively large gas emission in the first layer, low output, and high cost during layered mining of thick coal seams. Compared with high-extraction mining technology, fully mechanized longwall mining has advantages such as lower investment, lower cost, lower energy consumption, lower emissions, and adaptability to large variations in coal seam thickness. However, how to improve the top coal recovery rate of fully mechanized longwall mining faces has become one of the urgent problems to be solved in the further development of fully mechanized longwall mining technology.

[0003] To reduce top coal loss and improve top coal recovery, many scholars have conducted research on top coal crushing mechanisms and release patterns, optimization of coal release processes, and innovation in coal release methods, achieving significant results. However, existing research mainly focuses on the central part of the working face, while the end areas, due to space constraints and considerations for roadway stability, generally receive little or no coal release, thus receiving relatively little attention. Nevertheless, related studies indicate that the unreleased top coal above the transition frame and end frame accounts for 35%-45% of the total coal loss in the fully mechanized longwall face, consistently hindering the improvement of top coal recovery. Furthermore, research on the coal and rock flow patterns during the release process at the end, the stability of the surrounding rock at the end, and the reasonable range for coal release at the end is limited, thus necessitating further investigation. Summary of the Invention

[0004] The purpose of this invention is to provide a method and apparatus for controlling the stability of surrounding rock in the coal discharge area at the end based on numerical simulation, so as to solve the problems existing in the above-mentioned background art.

[0005] To achieve the above objectives, this invention provides a method for controlling the stability of surrounding rock in a coal discharge zone based on numerical simulation, comprising the following steps:

[0006] S1. Analyze the bearing structure of the surrounding rock in the coal discharge area at the end of the roadway;

[0007] S2. A numerical simulation model of coal discharge at the end is established using PFC software;

[0008] S3. The simulation results of the end coal discharge numerical simulation model based on S2 are analyzed, including the spatiotemporal analysis of active support, the coal and gangue flow morphology analysis of the end coal discharge area, and the evolution analysis of the bearing capacity of the roadway surrounding rock bearing structure.

[0009] Preferably, step S1 specifically includes:

[0010] Before coal release, the broken coal and rock mass in the end area of ​​the fully mechanized longwall face is tightly interlocked due to a lack of space for movement. As the coal is released, the tightly interlocked coal and rock mass around the roadway gradually loosens as the top coal is released. When the loosening reaches a certain point, the load-bearing structure formed by the tightly interlocked coal and rock mass around the roadway becomes unstable, increasing the difficulty of passive support within the roadway. If the passive support capacity within the roadway is insufficient, the roadway is at risk of instability, leading to serious safety accidents. Therefore, ensuring the stability of the surrounding rock at the end is essential. During end coal release, the coal and rock mass in the end area of ​​the working face has already broken into loose blocks. Based on Protodyakonov's equilibrium theory, due to the redistribution of stress in the surrounding rock, a parabolic pressure arch will form above the roadway, which is a equilibrium arch; and the angle between the arch and the horizontal direction is... In terms of direction, two sliding surfaces will be formed; the area formed by the balancing arch and the sliding surfaces is the area where the surrounding rock will be damaged.

[0011] The height of a naturally balanced arch is expressed as:

[0012]

[0013] Where, σ v γ is the vertical pressure at the top of the tunnel; h is the unit weight of the surrounding rock; B is the height of the balancing arch; b is the half-span of the balancing arch; and h0 is the tunnel height. Calculate the friction angle for the surrounding rock; f is the Protodyakonov rock firmness coefficient, as follows:

[0014]

[0015] Among them, R c c is the uniaxial saturated compressive strength of the surrounding rock; c is the cohesion of the surrounding rock.

[0016] Before the loose coal and rock mass within the natural equilibrium arch is released, the rock mass around the ends of the anchor bolts or anchor cables remains tightly interlocked, and the active support function does not fail. Furthermore, under the reinforcement effect of the pre-tightening force of the anchor bolts or anchor cables, the fractured coal and rock mass within the equilibrium arch will form a stable bearing structure within the direct range of the anchor bolt support, which is the bearing arch. The essence of the formation of the bearing arch is the active support effect generated by the pre-tightening force applied by the anchor bolts, which, together with the passive support, expands the support range and thus improves the stability of the interlocking force chain structure between fractured rock masses.

[0017] Based on the Mohr-Coulomb criterion, the frictional shear force in fractured rock mass is expressed as:

[0018]

[0019] Where, σ n This represents the normal stress between rock masses.

[0020] The load-bearing arch has a load-bearing function due to the interlocking force F formed by the crushed stones squeezing against each other. i Sufficient to balance the weight G of the crushed stone, the calculation formula is:

[0021] F i =F l μ (4)

[0022] Among them, F l denoted as , where is the lateral constraint force on the arch rubble; μ is the equivalent friction coefficient between the arch rubble.

[0023] The bearing arch will only fail and the roadway will lose its load-bearing capacity when the crushed stone at the arch foot becomes loose and the interlocking force between the stones is insufficient to support its own weight. Therefore, the safety of the roadway is ensured by stabilizing the bearing arch during end coal discharge. The bearing arch is formed within the direct action range of the anchor bolt support, which is:

[0024] h p =αβL (5)

[0025] Among them, h p α is the bearing arch height; α is the bearing arch height correction coefficient, and 0 < α < 1; β is the safety factor, 1 ≤ β ≤ 1 / α; L is the length of the direct action range of the anchor bolt.

[0026] Preferably, in S2, when coal is released at the end, the distance between the upper and lower ends of the working face is large, and the two will not affect each other. Models are established separately for the upper and lower end areas of the working face. The roadway support adopts a combination of active and passive support. Considering that the actual generation of anchor bolts or anchor cables in the two-dimensional simulation will produce limited small boundaries, the geometry module is used to apply pre-tightening force for equivalent replacement according to the actual spacing between anchor bolts. The anchor bolts or anchor cables in the roadway are numbered as the middle anchor cable mc, the right part of the roadway is numbered clockwise from the middle anchor cable as r1 to r7, and the left half of the roadway is numbered counterclockwise from the middle anchor cable as l1 to l7. The passive support uses the Fish language to generate wall units to simulate the frame.

[0027] Preferably, the initial state of the model in S2 includes six parts: coal seam 82, interbedded gangue layer, coal seam 81, immediate roof, basic roof, and overburden. The overburden density is calculated using the Fish language according to the following formula:

[0028]

[0029] Where P is the load of the overlying rock layer; g is the gravitational acceleration; and h is the height of the rectangular region of the overlying rock in the two-dimensional model.

[0030] Preferably, the spatiotemporal analysis of active support in S3 analyzes the spatiotemporal differences in the action of active support in the roadway. During coal release, using a basic time unit, the effective period of active support during coal release at the upper and lower ends of the working face at different dip angles is statistically analyzed, including:

[0031] Lower end: Although the timing of the failure of anchor bolts or anchor cables in the roadway during the initial coal release process varies at the lower end of working faces with different dip angles, the active support of anchor bolts or anchor cables in the middle and right parts of the roadway is basically ineffective after coal release. Before coal release, the passive support in the middle and right parts of the roadway is strengthened to ensure that the bearing arch around the roadway can still maintain its bearing capacity after the active support fails.

[0032] Upper end: When coal is released to the transition frame position, the active support of the anchor bolts or anchor cables in the middle and left part of the roadway is basically ineffective. Before releasing coal at the upper end of the working face, the passive support in the roadway should be strengthened to ensure the stability of the bearing arch foot.

[0033] Preferably, the coal and gangue flow morphology analysis in the end-face coal discharge area of ​​S3 involves observing and evaluating the flow and migration characteristics of the coal and rock mass and the evolution law of the surrounding rock structure during the end-face coal discharge process, using a basic time unit. This includes:

[0034] Lower end: When coal is released at the same position on working faces with different dip angles, the failure rate of the bearing arch at the lower end of the working face is negatively correlated with the dip angle of the working face;

[0035] Upper end: Coal release in the middle of the working face has a leading effect on the loosening of the upper end bearing arch, and the distance of the leading effect is positively correlated with the dip angle of the working face.

[0036] Preferably, the evolution analysis of the bearing capacity of the surrounding rock bearing structure in the S3 roadway should analyze the force chain field during the coal discharge process to represent the dynamic change process of the bearing capacity of the bearing arch. The force chain is the main form of load transfer in discontinuous and granular media. Based on the strength, the force chains are divided into three levels: strong force chain, medium-strong force chain, and weak force chain, according to the force chain classification method:

[0037]

[0038] Where F is the interparticle contact force; This represents the average contact force.

[0039] The fracture-regeneration process of the combined force chain structure formed by three types of force chains continues throughout the entire coal discharge process, including strong chain connectivity, strong chain fracture, and strong chain reconstruction. The Fish language is used in the model to filter and distinguish force chains of different strengths, and the changes in the force chain field during the end coal discharge process are analyzed, including:

[0040] Lower end: The bearing capacity of the lower end bearing arch of the working face is positively correlated with the dip angle of the working face;

[0041] Upper end: The bearing capacity of the upper end bearing arch on the working face is negatively correlated with the dip angle of the working face.

[0042] A device for controlling the stability of surrounding rock in a coal-discharging area based on numerical simulation is provided for the coal discharge needs of the coal-discharging area. The device includes a coal-discharging support, a shield beam, a window at the top of the shield beam, and hydraulic cylinders on both sides of the shield beam. A flexible metal mesh is installed in the window. The hydraulic cylinders control the extension and retraction of the flexible metal mesh to achieve precise control of the coal discharge opening and complete the coal discharge operation. The control system of the hydraulic cylinders is integrated into the intelligent electro-hydraulic control module of the entire device, realizing intelligent fully mechanized coal discharge from the coal-discharging support and improving the efficiency and accuracy of mining operations. A coal-crushing knife is installed at one end of the flexible metal mesh, and a coal-crushing knife groove adapted to the knife is provided on the shield beam. A mesh-winding device is installed below the shield beam, with a mesh-winding guide plate on one side of the device. The coal discharge opening is located on the side of the flexible metal mesh closest to the coal-crushing knife.

[0043] Therefore, the present invention adopts the above-mentioned method and device for controlling the stability of the surrounding rock in the end coal release area based on numerical simulation, and studies the coal and rock flow law, the stability of the surrounding rock at the end, and the reasonable range of end coal release during the release process. This not only improves the safety and efficiency of coal mining, but also reduces costs and promotes technological innovation.

[0044] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0045] Figure 1 This is a flowchart of the method for controlling the surrounding rock stability of the coal discharge zone based on numerical simulation according to the present invention.

[0046] Figure 2 This is a schematic diagram of a Protodyakonov equilibrium arch according to an embodiment of the present invention;

[0047] Figure 3 This is a schematic diagram of the load-bearing arch according to an embodiment of the present invention;

[0048] Figure 4 This is a schematic diagram of an equivalent anchor bolt according to an embodiment of the present invention;

[0049] Figure 5 This is a schematic diagram of the real-time monitoring process according to an embodiment of the present invention;

[0050] Figure 6 This is a statistical diagram illustrating the spatiotemporal effects of active end support in an embodiment of the present invention.

[0051] Figure 7This is a statistical diagram illustrating the spatiotemporal effects of active end support in an embodiment of the present invention.

[0052] Figure 8 This is a schematic diagram of the displacement field of coal discharge at different inclination angles according to an embodiment of the present invention;

[0053] Figure 9 This is a schematic diagram of the displacement field of the upper end coal discharge at different inclination angles according to an embodiment of the present invention;

[0054] Figure 10 This is a schematic diagram of the coal discharge force chain field at different inclination angles according to an embodiment of the present invention;

[0055] Figure 11 This is a schematic diagram illustrating the zoning of the danger levels of coal discharge at the end of an embodiment of the present invention;

[0056] Figure 12 This is a schematic diagram of the coal discharge chain at different inclination angles in an embodiment of the present invention;

[0057] Figure 13 This is a schematic diagram of the internal segmentation of frame No. 106 in Embodiment 1 of the present invention;

[0058] Figure 14 This is a schematic diagram of the maximum coal release progress at different inclination angles in an embodiment of the present invention;

[0059] Figure 15 This is an overall schematic diagram of the end coal discharge support according to an embodiment of the present invention;

[0060] Figure 16 This is a schematic diagram of the internal structure of the coal feeding support at the end of an embodiment of the present invention. Figure 1 ;

[0061] Figure 17 This is a schematic diagram of the internal structure of the coal feeding support at the end of an embodiment of the present invention. Figure 2 ;

[0062] Reference numerals in the attached diagram: 1. Shield beam; 2. Flexible metal mesh; 3. Coal crusher; 4. Hydraulic cylinder; 5. Coal crusher groove; 6. Mesh rolling device; 7. Mesh rolling guide plate; 8. Coal discharge port. Detailed Implementation

[0063] The following detailed description of embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0064] In this embodiment, taking a coal mine of a mining group as an example, the 825 fully mechanized longwall face mines the 82 and 81 coal seams. The 82 coal seam has an average thickness of 2.50m, and the 81 coal seam has an average thickness of 2.84m. There is an interbedded gangue layer with an average thickness of 1.94m between the 82 and 81 coal seams. The average dip angle of the coal seams is 10°, which is a gently dipping coal seam. The working face is buried at a depth of 262-380m. The working face has a strike length of 681m and a dip width of 160m. A total of 6 transition frames with a center-to-center distance of 1.5m and 102 intermediate frames with a center-to-center distance of 1.5m are arranged. The mining-to-loosening ratio is 1:1.91, and the coal is released from bottom to top. The working face roadway has a straight-walled semi-circular arch cross-section, with a roadway width of 5m and a distance of 3.75m from the arch crown to the roadway floor. It employs a combination of anchor bolts, anchor cables, and support structures. The anchor bolts are 2400mm long, the anchor cables are 6300mm long, and the spacing between the anchor bolts (cables) is 700×700mm. The immediate roof of the 825 fully mechanized longwall face is mudstone with an average thickness of 1.84m; the underlying roof is siltstone with an average thickness of 7.00m.

[0065] like Figure 1 As shown, the method for controlling the stability of the surrounding rock in the coal discharge area based on numerical simulation includes the following steps:

[0066] S1. Analysis of the bearing capacity structure of the surrounding rock in the coal discharge area roadway.

[0067] Before coal release begins, the broken coal and rock mass at the end of the longwall face remains tightly interlocked due to a lack of space for movement. However, as coal release progresses, the initially tightly interlocked coal and rock mass around the roadway gradually loosens as the top coal is released. When this loosening reaches a certain point, the load-bearing structure formed by the tightly interlocked coal and rock mass around the roadway becomes unstable, increasing the difficulty of passive support within the roadway. If the passive support capacity within the roadway is insufficient, the roadway is at risk of instability, leading to serious safety accidents. Therefore, ensuring the stability of the surrounding rock at the end is essential. During end coal release, the coal and rock mass in the end area of ​​the working face has already broken into loose blocks, which can be approximated as loose strata. Based on Protodyakonov's equilibrium arch theory, due to the redistribution of stress in the surrounding rock, a parabolic pressure arch, i.e., an equilibrium arch, will form above the roadway; and the angle between the arch and the horizontal direction is... In the direction, two sliding surfaces will be formed; the area formed by the balancing arch and the sliding surface is essentially the area where the surrounding rock may fail, such as... Figure 2 As shown.

[0068] The suspension function of the anchor cables is to anchor the easily collapsible rock mass within the natural equilibrium arch to the deep rock. The height of the natural equilibrium arch is expressed as:

[0069]

[0070] Where, σ v γ is the vertical pressure at the top of the tunnel, MPa; γ is the unit weight of the surrounding rock, kN / m³.3 h is the height of the balancing arch, m; B is the half-span of the balancing arch, m; b is the half-span of the tunnel, m; h0 is the height of the tunnel, m; The friction angle for the surrounding rock is calculated in °; f is the Protodyakonov rock firmness coefficient, as follows:

[0071]

[0072] Among them, R c c is the uniaxial saturated compressive strength of the surrounding rock, MPa; c is the cohesion of the surrounding rock, MPa.

[0073] From equations (1) and (2), the height of the natural equilibrium arch, h, is 8.08 m. This means that the entire anchor bolt (cable) is inside the natural equilibrium arch, and the coal and rock mass within it is released, rendering the anchor cable suspension ineffective. However, before the loose coal and rock mass inside the natural equilibrium arch is released, the rock mass around the end of the anchor bolt (cable) remains tightly interlocked, and the active support function does not fail. Furthermore, under the reinforcement effect of the anchor bolt (cable) pre-tightening force, the fractured coal and rock mass inside the equilibrium arch will form a stable bearing structure within the direct range of the anchor bolt support, namely, a bearing arch. The essence of the bearing arch formation is the active support effect generated by the pre-tightening force applied by the anchor bolt, which, combined with passive support, expands the support range, thereby improving the stability of the interlocking force chain structure between fractured rock masses.

[0074] Based on the Mohr-Coulomb criterion, the frictional shear force in fractured rock mass is expressed as:

[0075]

[0076] Where, σ n denoted as the normal stress between rock masses, in MPa.

[0077] The load-bearing arch has a load-bearing function due to the interlocking force F formed by the crushed stones squeezing against each other. i Sufficient to balance the weight G of the crushed stone, such as Figure 3 As shown, the calculation formula is:

[0078] F i =F l μ (4)

[0079] Among them, F l denoted as N, representing the lateral constraint force on the arch rubble; μ is the equivalent friction coefficient between the arch rubble.

[0080] As top coal is continuously released, the coal and rock mass at the ends of the anchor bolts (cables) will first loosen, causing the active support function of the anchor bolts (cables) to fail. However, under the dual effects of passive support in the roadway and compaction of the fractured coal and rock mass above, the crushed stone at the foot of the bearing arch remains tightly interlocked and has load-bearing capacity. Only when the crushed stone at the foot of the bearing arch loosens and the interlocking force between the crushed stones is unable to withstand its own weight will the bearing arch fail, and the roadway will lose its load-bearing capacity. Therefore, to ensure the safety of the roadway during end coal release, the stability of the bearing arch must be ensured first.

[0081] The bearing arch formation range is within the direct action range of the anchor bolt support, and is as follows:

[0082] h p =αβL (5)

[0083] Among them, h p Let L be the height of the bearing arch, in meters; α be the correction coefficient for the bearing arch height, where 0 < α < 1, and the value is 2 / 3; β be the safety factor, where 1 ≤ β ≤ 1 / α, and the value is 1.1; L be the length of the direct action range of the anchor bolt, in meters. The anchoring zone in the roadway is often small, usually 1.8 to 2.2 meters, and in some cases up to 2.5 meters. After removing the length of the resin cartridge segment, take L = 1.9 meters. Substituting into equation (5), we can obtain h. p =1.40m.

[0084] S2. Establish a numerical simulation model for coal discharge at the end.

[0085] S21, Model Building Process

[0086] Numerical models were established using PFC software for coal release experiments at the ends of gently inclined working faces with different dip angles. Since the top coal and immediate roof in the end area were already broken into loose blocks during the release stage, they were set as ideal loose media with zero cohesion, initial velocity, and displacement. During end coal release, the distance between the upper and lower ends of the working face is relatively large, and they will not affect each other. Therefore, separate models can be established for the upper and lower end areas. The following two basic principles should be followed when considering end coal release: ① Coal is released first from the intermediate frame of the working face, and after the top coal in the upper space of the intermediate frame is completely released, coal is released from the middle of the working face towards both ends; ② Windows are closed upon encountering gangue. Three transition frames and seven intermediate frames are arranged at the lower end of the model, numbered 1 to 10; three transition frames and seventeen intermediate frames are arranged at the upper end, numbered 89 to 108. Among them, frames No. 1 and No. 3 are transition frames at the lower end of the working face, and frames No. 106 and No. 108 are transition frames at the upper end of the working face.

[0087] The roadway support employs a combination of active and passive support. Considering that the actual generation of anchor bolts (cables) in the two-dimensional simulation would create confined small boundaries that obstruct the flow of top coal, a pre-tightening force of 100 kN is applied using the geometry module to provide an equivalent replacement based on the actual anchor bolt spacing. The anchor bolts (cables) in the roadway are numbered as follows: the middle anchor bolt (mc), the right half of the roadway starting from the middle anchor bolt and numbered clockwise from r1 to r7, and the left half starting from the middle anchor bolt and numbered counterclockwise from l1 to l7. The passive support uses Fish language to generate wall elements to simulate the support structure, such as... Figure 4 As shown. The entire coal discharge process is monitored in real time. When rock mass at the end of the anchor bolt (cable) fails, the active support function fails, and the process is as follows: Figure 5 As shown.

[0088] The initial state of the model includes six parts: coal seam 82, interbedded rock layer, coal seam 81, immediate roof, basic roof, and overburden. The thickness of the interbedded rock layer and coal seam 81 is 4.78m, the thickness of the immediate roof is 1.84m, and the thickness of the basic roof is 7m. To correct the difference in particle size between the simulated round particles and the actual irregular roof coal blocks and to simplify the number of round particles, the particle size was selected with reference to the coal and rock diameter in the field (see Table 1). The basic physical parameters of the particles were set according to the physical parameters of the coal and rock mass of the working face, and the motion behavior of the particles under the selected microscopic parameters was verified by the natural angle of repose calibration experiment to be consistent with the macroscopic conditions (see Table 2). Among them, the density of the overburden was converted according to formula (6) in Fish language to ensure that the equivalent load applied to the overburden layer remained unchanged during the experiment. The equivalent load was determined according to the key layer theory and was taken as 367.72KPa.

[0089]

[0090] Where P is the load of the overlying rock strata, kPa; g is the gravitational acceleration, m / s². 2 h represents the height (m) of the rectangular region of the overlying rock in the two-dimensional model.

[0091] Table 1 Particle Radius

[0092] Rock strata name Coal pillar / m End area / m Middle of working face / m Overlying rock 0.25～0.40 0.25～0.40 0.25～0.40 Basic top 0.25～0.40 0.25～0.40 0.25～0.40 Just top 0.30～0.35 0.25～0.30 0.15～0.20 81 coal seam 0.20～0.25 0.15～0.20 0.10～0.15 Interlayer of gangue 0.16～0.20 0.14～0.18 0.12～0.16 82 coal seam 0.20～0.25 0.15～0.20 0.10～0.15

[0093] Table 2 Physical and mechanical parameters of simulated coal and rock masses

[0094] Rock strata name <![CDATA[Density / (kg·m -3 )]]> <![CDATA[Normal stiffness / (GN·m -1 )]]> <![CDATA[Shear stiffness / (GN·m -1 )]]> coefficient of friction Overlying strata ρ 0.4 0.4 0.4 Basic top 2550 0.4 0.4 0.4 Just top 2030 0.3 0.3 0.3 81 coal seam 1500 0.2 0.2 0.1 Interlayer of gangue 2030 0.3 0.3 0.3 82 coal seam 1500 0.2 0.2 0.1

[0095] S22, Experimental Scheme

[0096] Based on the two basic principles of end-to-end coal release, the end-to-end coal release experiment was designed as follows: for working faces with dip angles of 8°, 17° and 25°, coal was released first in the middle, and then at the upper and lower ends.

[0097] S3. Simulation Results Analysis

[0098] 1. Spatiotemporal Analysis of Active Support

[0099] To analyze the spatiotemporal differences in active support in roadways, during coal release, a 5×10 4 The time step is defined as one basic time unit. The effective period of active support during coal release at the upper and lower ends of the working face at different inclination angles is statistically analyzed. The average number of coal release steps for the No. 4 intermediate frame is 1×10. 6 At this point, during the initial coal feeding process from the start to the end of the No. 4 intermediate frame, the active support function in the roadway began to gradually fail.

[0100] (1) Lower end

[0101] Statistics on the spatiotemporal effects of active support at the lower end are as follows: Figure 6 As shown, the failure times of the active support functions of r2 anchor cables and r3 anchor bolts in the lower end roadway of the working face are generally similar, both failing at the beginning of coal discharge, with an operating step count of approximately 1×10. 5 Time step. After the failure of anchor cable R2 and anchor bolt R3, the middle anchor cable MC begins to fail, and the time required for MC to fail increases with the increase of the working face dip angle. In addition, the larger the working face dip angle, the greater the horizontal component force on the lower end, causing the failure of anchor bolt R1 in the lower end roadway of the 8° dip working face.

[0102] Therefore, although the timing of anchor bolt (cable) failure varies at the lower end of working faces with different dip angles during the initial coal discharge process, the active support function of the anchor bolts (cables) in the middle and right half of the roadway is essentially ineffective after coal discharge. To ensure that the bearing arch around the roadway can maintain its bearing capacity after the active support fails, the passive support in the middle and right half of the roadway should be strengthened before coal discharge. This ensures that the advanced supports in the roadway are strictly connected to the roof and have sufficient strength, and ensures the tight interlocking of coal and rock at the arch foot of the bearing arch, preventing roadway instability caused by the failure of the bearing arch.

[0103] (2) Upper end

[0104] Statistics on the spatiotemporal effects of active support at the working face end are as follows: Figure 7As shown, the spatiotemporal characteristics of the failure of the active support function of anchor cables MC and L3 in the middle of the upper face roadway are not significantly affected by the face dip angle; both failed after coal was released from the middle of the face to frame 101. The spatiotemporal characteristics of the failure of the active support function of anchor cables L1 and L2 are most significantly affected by the face dip angle. Among them, the failure time of anchor cable L2 is earlier than that of anchor cable L1, and the larger the face dip angle, the farther the distance of the impact of coal release from the middle of the face on anchor cable L2 is. In the 8° dip face roadway, anchor cable L1 did not fail; in the 17° dip face roadway, anchor cable L1 failed after coal release from the middle of the face to frame 103; and in the 25° dip face roadway, anchor cable L1 failed after coal release from the middle of the face to frame 105. This indicates that as the face dip angle increases, the impact distance of coal release from the middle of the face on anchor cable L1 in the roadway decreases, and the affected range of anchor cable L1 is negatively correlated with the face dip angle. Similarly, the affected range of l2 anchor cables is positively correlated with the magnitude of the working face inclination angle.

[0105] Therefore, as coal is released from the middle of the working face, the active support of the anchor bolts (cables) in the middle and left half of the upper end roadway will gradually fail before the coal is released to the transition frame position. The distance at which the anchor bolts (cables) are affected and the order of their failure are both related to the dip angle of the working face. When the coal is released to the transition frame position, the active support of the anchor bolts (cables) in the middle and left half of the roadway is basically ineffective. Similar to the situation at the lower end, to ensure the safety and stability of the roadway, it is necessary to strengthen the passive support in the roadway before releasing coal at the upper end of the working face to ensure the stability of the bearing arch foot. It is worth noting that the upper end of the working face begins to be continuously affected by the coal release from the middle of the working face when it is 10 to 13 support center distances ahead of the upper end area during the coal release in the middle of the working face. Therefore, when the coal release operation is carried out in the vicinity of the upper end of the working face and subsequently, the passive support in the middle and left half of the roadway should be strengthened in advance to ensure the stability of the bearing arch.

[0106] 2. Analysis of coal and gangue flow patterns in the end coal discharge area

[0107] Due to the influence of the coal seam dip angle, the flow patterns of coal and gangue layers at the upper and lower ends of the working face differ. Therefore, the coal feeding process at the upper and lower ends is analyzed separately. When feeding coal at the ends, a 1×10⁻⁶ kJ / kg coal feed rate is used. 4 The time step is a basic time unit used to observe and evaluate the flow and migration characteristics of coal and rock mass and the evolution law of roadway surrounding rock structure during the coal discharge process at the end.

[0108] (1) Lower end

[0109] Coal was discharged from the lower end of working faces with different dip angles, and the displacement field results were obtained as follows: Figure 8As shown. During the coal release process at the lower end of the working face, the No. 3 support was generally safe, and the safety increased with the increase of the working face dip angle. During the No. 2 support coal release, rock spillage was highly likely, which could easily lead to misjudgment of the support window closing and result in top coal loss. After the No. 1 support coal release was completed, the supporting arch loosened, posing a risk of roadway instability. It is noteworthy that in the 8° dip working face, the edge of the supporting arch showed slight loosening after the No. 3 support coal release, which was significantly different from the state of the supporting arch after the No. 3 support coal release in the other two dip working faces. Based on the timeline analysis of the No. 3 support coal release process in the 8° dip working face, the coal and rock mass within the supporting arch range of the No. 3 support at the lower end of the 8° dip working face had already shifted after the coal release of the middle support in the working face. During the coal release process, the area within the supporting arch that had experienced displacement did not continue to develop, and its shape remained consistent, allowing the supporting arch to remain stable. For safety reasons, the roadway support can be strengthened before coal release to prevent the supporting arch from becoming unstable.

[0110] Therefore, when coal is released at the same location on working faces with different dip angles, the smaller the dip angle, the closer the displaced coal and rock mass is to the edge of the bearing arch. In other words, the failure rate of the bearing arch at the lower end of the working face is negatively correlated with the dip angle. Furthermore, after coal release from frame 1, compared to the 8° and 17° dip faces, the 25° dip face exhibited a sudden, tree-branch-shaped intrusive displacement within the bearing arch area, penetrating the bearing arch and causing loosening of the coal and rock mass in the left-central position. It is speculated that this is because the lower end of the working face with a larger dip angle is more compact, resulting in tighter interlocking of the coal and rock mass after fracturing, making it easier to form a local bearing structure. After the coal is released above the release port, a free surface is created on the side of the originally compacted coal and rock mass. The interaction force between the coal and rock mass causes it to move towards the free surface, resulting in displacement and damage to the local bearing structure. This causes the coal and rock mass, which was originally stable under the action of the local bearing structure, to move, ultimately triggering a sudden displacement of the coal and rock mass within the bearing arch area. Therefore, when releasing coal at the lower end of a working face with a large dip angle, it is also necessary to appropriately strengthen the support within the roadway.

[0111] (2) Upper end

[0112] Coal was discharged from the end face of the working face at different dip angles, and the displacement field results are as follows: Figure 9As shown, after coal release at the middle section of the working face at different dip angles, the supporting arches all exhibited varying degrees of loosening. In terms of the range of loosening and the displacement of the coal and rock mass within the arch, the 25° dip face > the 17° dip face > the 8° dip face. According to the coal release process at the middle support, as the coal release at the middle support gradually approaches the end area on the working face at different dip angles, a tree-like displacement occurs prematurely in the space between the upper left half of the supporting arch and the coal release opening. Unlike the sudden intrusive displacement at the lower end, the tree-like displacement at the upper end does not penetrate the supporting arch. As coal release progresses, the coal release funnel continues to develop, and the coal and rock mass between the supporting arch and the coal release opening gradually shifts and moves towards the tree-like shape until it eventually penetrates. Comparing the time points when the tree-like displacement occurs in working faces with different dip angles, the 25° dip face is the earliest, followed by the 17° face, and the 8° face is the latest. Comparing the penetration speed of the coal and rock mass between the bearing arch and the coal outlet after displacement, the 8° face is the fastest, followed by the upper end of the 17° face, and the upper end of the 25° face is the slowest.

[0113] Therefore, coal release in the middle of the working face has a leading effect on the loosening of the upper end bearing arch, with a leading effect distance of 6 to 11 support center distances. As the working face dip angle increases, the leading effect distance also increases, meaning the leading effect distance is positively correlated with the working face dip angle. This is because the larger the working face dip angle, the stronger the movement trend of the coal and rock mass at the upper end of the working face. Furthermore, as coal release progresses, the continuous development of the coal release funnel above the release opening leads to a continuous expansion of the range of coal and rock mass displaced between the bearing arch and the release opening. However, due to the different lateral constraints of the working face floor, the penetration speed of the coal and rock mass varies, with the fastest penetration speed at an 8° dip angle and the slowest at a 25° dip angle. Compared to the lower end of the working face, the bearing arch at the upper end of working faces with different dip angles has already loosened to varying degrees before coal release from the transition frame, indicating that the upper end roadway already faces the risk of instability after coal release from the middle support of the working face. Therefore, before coal release near the upper end of the working face, it is crucial to strengthen the roadway support. In addition, since the end face of the working face may experience "pre-penetration displacement" during the coal discharge process, it is necessary to be careful to prevent the sudden cavitation of the end face of the working face when performing coal discharge operations.

[0114] 3. Evolution analysis of bearing capacity of surrounding rock structure in roadway

[0115] While the above analysis addresses the displacement field during coal release from the working face, it only reflects the dynamic loosening process of the bearing arch and is insufficient to represent the dynamic changes in the bearing capacity of the bearing arch. Therefore, it is necessary to analyze the force chain field during coal release. Force chains are the primary form of load transfer in discontinuous and granular media, and also serve as a bridge connecting the macroscopic mechanical behavior and microscopic action mechanisms of granular media. Using existing force chain classification methods, force chains are divided into three levels based on strength: strong force chains, medium-strength force chains, and weak force chains.

[0116]

[0117] Where F is the interparticle contact force, N; Let N be the average contact force.

[0118] The fracture-regeneration of the combined force chain structure formed by three types of strength force chains continues throughout the entire coal discharge process. Generally, this manifests as the coal body becoming unstable after the fracture of the primary supporting force chain, followed by the regeneration of the strong force chain during the process of self-stabilization. Secondary and weak force chains fill the framework of the strong force chain to assist in bearing the load. The specific process is as follows: ① Strong force chains remain connected, resulting in good interlocking between the coal and rock masses, effectively forming a channel for the transmission of contact forces between them. The bearing arch has good load-bearing capacity, ensuring the continuous stability of the roadway. ② Strong force chains fracture, causing the interlocking between the coal and rock masses to loosen. The channel for the transmission of contact forces between the coal and rock masses gradually disappears, the bearing arch weakens, and the roadway faces the risk of instability. ③ Strong force chains reconstruct, as the interlocking between the coal and rock masses ceases, the channel for the transmission of contact forces completely disappears, the bearing arch loses its load-bearing capacity, the roadway becomes unstable, and the coal and rock masses re-contact under gravity, tending towards self-stabilization and reconstructing the strong force chain. In the numerical model, Fish language is used to screen and distinguish different strength force chains, analyzing the changes in the force chain field during the end-of-line coal discharge process.

[0119] (1) Lower end

[0120] The changes in the force chain field during coal discharge at the lower end of the working face were studied, and the results are as follows: Figure 10 As shown. After coal release from frame 3, the strong chains in the load-bearing arch combined force chain structure of the three inclined working faces were all in a state of strong chain connectivity. During coal release from frame 2, the support window closed prematurely due to rock spillage. Although the overall combined force chain structure remained basically unchanged, after coal release, the strong chains in the load-bearing arch combined force chain structure of the three inclined working faces were all in a state of strong chain breakage. After coal release from frame 1, the strong chains in the load-bearing arch combined force chain structure of the three inclined working faces were all in a state of strong chain reconstruction. Among them, after coal release from frame 3, the degree of good connectivity of the strong chains in the load-bearing arch combined force chain structure was as follows: 25° inclined working face, 17° inclined working face, and 8° inclined working face.

[0121] Therefore, during the coal release process at the lower end of the working face, after the coal release from frame 3 is completed, the coal and rock mass within the bearing arch are tightly interlocked, the bearing capacity of the bearing arch is good, and the roadway stability is good; after the coal release from frame 2 is completed, the interlocking of the coal and rock mass within the bearing arch becomes loose, the bearing capacity of the bearing arch weakens, and the roadway faces the risk of instability; after the coal release from frame 1 is completed, the bearing arch structure becomes unstable, loses its bearing capacity, and the roadway becomes unstable. It is worth noting that the bearing capacity of the bearing arch is closely related to the tightness of the interlocking of the coal and rock mass within the arch, and the degree of interlocking of the coal and rock mass at the lower end is affected by the working face dip angle. The larger the working face dip angle, the tighter the interlocking of the coal and rock mass, the stronger the bearing capacity of the bearing arch, and the higher the roadway safety. In other words, the bearing capacity of the bearing arch at the lower end of the working face is positively correlated with the working face dip angle. Simultaneously, combined with the displacement field analysis results above, the coal release hazard levels at the lower end of the working face from frame 3 to frame 1 can be divided into zones: ① Frame 3, safe coal release zone; ② Frame 2, risky coal release zone; ③ Frame 1, dangerous coal release zone. Figure 11 ).

[0122] (2) Upper end

[0123] The changes in the force chain field during coal release at the end of working faces with different dip angles were studied. However, after coal release at frame 106, the combined force chain structure of the bearing arch at the end of working faces with different dip angles was already in a state of strong chain fracture. To clarify the dynamic change process of the bearing capacity of the bearing arch during coal release at frame 106, the combined force chain state of the bearing arch at different time points was statistically analyzed. The total coal release at frame 106 of the 8° dip face was 1.4 × 10⁻⁶ tons. 5 At the time step, the total coal release from frame 106 of the 17° inclined working face was 2.1 × 10 5 At this time, the coal release from frame 106 of the 25° inclined working face totaled 2.4 × 10⁶ tons. 5 Time step. The state of the load-bearing arch combination force chain corresponding to the specific time node is as follows: Figure 12 As shown. The 8° inclined working face was operating at 1×10 coal release points on frame 107. 4 After the time step, the load-bearing arch combined force chain structure is in a state of strong chain fracture; the 17° inclined working face has reached 1.9×10 during coal release operation at frame 106. 5 At a certain time step, when the coal feeding progress is at 95%, the supporting arch combined force chain structure is in a state of strong chain fracture; the 25° inclined working face is operating at 1.5×10 on frame 106. 5 After the time step, when the coal feeding progress reaches 65%, the supporting arch composite force chain structure is in a state of strong chain fracture. Based on the order in which the strong chain fracture occurs in the supporting arch composite force chain structure, the sequence is: 25° dip angle working face, 17° dip angle working face, and 8° dip angle working face. Simultaneously, regarding the severity of the strong chain fracture when the supporting arch composite force chain structure is in a strong chain fracture state, the order from strongest to weakest is: 25° dip angle working face, 17° dip angle working face, and 8° dip angle working face.

[0124] Therefore, during coal release at the upper end of the working face, the dynamic change process of the supporting arch combined force chain structure is similar to that at the lower end of the working face, both undergoing three stages: strong chain connection, strong chain fracture, and strong chain reconstruction. The difference lies in the timing and spatial location of the strong chain fracture state reached by the supporting arch combined force chain structure at the upper end of the working face earlier than at the lower end. During coal release at frame 106, the combined force chain structure reaches the strong chain fracture state, meaning that the complete release of top coal above frame 106 will significantly weaken the bearing capacity of the supporting arch, posing a risk of roadway instability. Furthermore, the larger the working face dip angle, the earlier the combined force chain structure reaches the strong chain fracture state, and the more severe the fracture. This is contrary to the reason why the bearing capacity of the supporting arch at the lower end of the working face increases with the increase of the working face dip angle; the tightness of the interlocking between the coal and rock mass at the upper end of the working face decreases with the increase of the working face dip angle, and the bearing capacity of the supporting arch also weakens with the increase of the working face dip angle. In other words, the bearing capacity of the supporting arch at the upper end of the working face is negatively correlated with the working face dip angle. Based on the displacement field analysis results above, to ensure safety, coal release at the end of the working face should only be carried out on frame 106 and should not be completely released. The coal release section within the frame can be divided into a safe coal release section and a high-risk coal release section according to the degree of danger. Figure 13 As shown.

[0125] (3) Determining the safe coal release height inside the frame

[0126] To determine the specific height of the safe coal release section, the ultimate coal release progress of frame 106 at dip angles of 8°, 12°, 17°, 21°, and 25° was statistically analyzed, and the ultimate coal release progress equation was fitted, as follows: Figure 14 As shown, the variation of the maximum coal release progress of frame 106 with the dip angle is consistent with an exponential function. Therefore, when the dip angle of the working face increases to a certain extent, the maximum coal release progress of frame 106 will decrease exponentially. That is, when the dip angle of the working face is too large, the top coal at the end should not be released to ensure operational safety.

[0127] Based on this, the height of the safe coal release section during the coal release process of frame 106 can be deduced:

[0128] h s =[0.97901-0.0158exp(0.13103α)]h d (8)

[0129] Among them, h s The height of the safe coal discharge section, in meters (m); h d α is the coal discharge height, in meters; α is the working face inclination angle, in degrees.

[0130] like Figure 15-17 As shown, an apparatus for controlling the stability of surrounding rock in a coal discharge area based on numerical simulation includes a coal discharge support at the end.

[0131] Based on the simulation results above, taking the 825 face of a certain coal mine as an example, the calculated data shows that the maximum coal release progress of the No. 106 frame at the upper end of the 825 face is 92%, the height of the safe coal release section is 4.40m, and after deducting the thickness of the upper interlayer of gangue, the remaining height of the top coal that can be released is 2.46m. Comparing the top coal recovery volume of the 825 face with and without coal release at the face end, the recovery volume of top coal in the face end area is 1.8% higher than that of coal release only in the middle of the face. Furthermore, when performing segmented coal release within the frame at the upper end of the face, to accurately define the height of the safe coal release section and control the timing of coal release completion, a top coal displacement tracker can be installed at the interface between the safe coal release section and the risk coal release section above the No. 106 frame. By tracking the top coal displacement trajectory in real time, segmented coal release within the frame at the upper end of the face can be achieved quickly, accurately, safely, and efficiently.

[0132] Currently, coal feeding at the end of the mine faces the challenge of having numerous mechanical devices in the end area, but the existing coal feeding supports lack sufficient space for feeding coal on the working face and below the end area. Therefore, considering the time and cost of equipment development, the existing hydraulic supports can be directly modified to meet the needs of coal feeding at the end. Specific solution: ① A window is installed on the shield beam 1, with hydraulic cylinders 4 on each side. The window portion uses a high-strength flexible metal mesh 2 instead of the traditional structure; ② The extension and retraction of the metal mesh is controlled by the extension and retraction of the hydraulic cylinders 4, achieving precise control of the coal feeding port 8 and completing the end coal feeding operation; ③ The control system of the hydraulic cylinders 4 is integrated into an intelligent electro-hydraulic control module, realizing intelligent integrated feeding of the end hydraulic supports and improving the efficiency and accuracy of mining operations. The window on the shield beam 1 is expected to be 1200mm wide × 1500mm high. The two hydraulic cylinders 4 work together to push the high-strength flexible metal mesh 2, controlling the opening and closing of the coal feeding port 8. In addition, a mesh winding device 6 is installed below the shield beam 1, and a coal breaking knife 3 is used at the end of the metal mesh to break up coal blocks. The protective beam 1 is equipped with a coal breaking knife groove 5 that is compatible with the coal breaking knife 3. A mesh rolling device 6 is installed below the protective beam 1. A mesh rolling guide plate 7 is installed on one side of the mesh rolling device 6, and a coal discharge port 8 is installed on the side of the flexible metal mesh 2 near the coal breaking knife 3.

[0133] Based on the verification analysis of the above embodiments, the following conclusions are drawn:

[0134] (1) Before coal is released from the end area, the active support of the upper and lower end roadways on the working face is basically ineffective under the influence of coal release in the middle of the working face, and the timing and spatial location of the failure are different. The active support of the upper end roadway is affected by the advance of coal release in the middle of the working face, with an advance influence distance of 10 to 13 support center distances, and the advance influence distance is positively correlated with the working dip angle.

[0135] (2) During the coal release process in the end area, the lower end bearing arch does not loosen after the coal release in the middle of the working face. As the coal release from the transition frame gradually loosens, and when the working face dip angle is large, a sudden intrusion displacement occurs, damaging the bearing arch. The upper end bearing arch loosens ahead of time due to the coal release in the middle. The range of the advance influence is 6 to 11 support center distances. The coal and rock mass within the range of the advance influence gradually loosens and becomes connected. During the coal release process, it is necessary to fully consider the flow characteristics of the coal and rock mass and take appropriate protective measures.

[0136] (3) The coal feeding scheme at the working face ends is divided into three sections: the lower end is divided into an overall zone, and the upper end is divided into sections within the frame. During the coal feeding process, the lower end is divided into a safe coal feeding zone, a risk coal feeding zone, and a dangerous coal feeding zone. During the coal feeding process, the top coal above the transition frame at the upper end is divided into a safe coal feeding section and a risk coal feeding section. The height of the safe coal feeding section decreases exponentially with the increase of the working face dip angle.

[0137] (4) By modifying the existing hydraulic support, not only can costs be saved, but precise coal release control can also be achieved in conjunction with the top coal tracking device. The successful release of top coal at the end has increased the top coal recovery rate by 1.8%.

[0138] Therefore, the present invention adopts the above-mentioned method and device for controlling the stability of the surrounding rock in the end coal release area based on numerical simulation, and studies the coal and rock flow law, the stability of the surrounding rock at the end, and the reasonable range of end coal release during the release process. This not only improves the safety and efficiency of coal mining, but also reduces costs and promotes technological innovation.

[0139] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for controlling the stability of surrounding rock in a coal discharge zone at the end based on numerical simulation, characterized in that, Includes the following steps: S1. Analyze the bearing structure of the surrounding rock in the coal discharge area at the end of the roadway; S2. A numerical simulation model of coal discharge at the end is established using PFC software; S3. The simulation results of the end coal discharge numerical simulation model based on S2 are analyzed, including the spatiotemporal analysis of active support, the coal and gangue flow morphology analysis of the end coal discharge area, and the evolution analysis of the bearing capacity of the roadway surrounding rock bearing structure. Step S1 is as follows: Before coal release, the coal and rock mass in the end area of ​​the fully mechanized longwall face is tightly interlocked. As the coal is released, the previously tightly interlocked coal and rock mass around the roadway gradually loosens with the release of top coal. At the end of the face, the coal and rock mass has broken into loose blocks. According to Protodyakonov's equilibrium theory, due to the redistribution of surrounding rock stress, a parabolic pressure arch will form above the roadway, which is a equilibrium arch; and the angle between the arch and the horizontal direction is... In terms of direction, two sliding surfaces will be formed; the area formed by the balancing arch and the sliding surfaces is the area where the surrounding rock will be damaged. The height of a naturally balanced arch is expressed as: （1） in, This refers to the vertical pressure at the top of the tunnel; The unit weight of the surrounding rock; To balance the height of the arch; To balance the half span of the arch; This is half the span of the tunnel; The height of the tunnel; Calculate the friction angle for the surrounding rock; The Protodyakonov rock firmness coefficient is as follows: （2） in, The uniaxial saturated compressive strength of the surrounding rock; The cohesion of the surrounding rock; Before the loose coal and rock mass inside the natural balance arch is released, the rock mass around the end of the anchor bolt or anchor cable is still tightly interlocked with each other, and the active support will not fail. Moreover, under the reinforcement of the anchor bolt or anchor cable pre-tightening force, the broken coal and rock mass inside the balance arch will form a stable bearing structure within the direct range of the anchor bolt support, which is the bearing arch. Based on the Mohr-Coulomb criterion, the frictional shear force in fractured rock mass is expressed as: （3） in, This refers to the normal stress between rock masses; The load-bearing arch has a load-bearing function due to the interlocking force formed by the crushed stones pressing against each other. Sufficient to balance the weight G of the crushed stone, the calculation formula is: （4） in, The lateral constraint force on the rubble of the arch; The equivalent friction factor between the rubble in the arch; Therefore, the safety of the roadway is ensured by the stability of the bearing arch during end coal discharge. The bearing arch is formed within the direct action range of the anchor bolt support, which is: （5） in, The height of the supporting arch; This is a correction factor for the bearing arch height, and 0 < <1; For the safety factor, 1≤ ≤ ; This refers to the length of the direct effective range of the anchor bolt.

2. The method for controlling the stability of surrounding rock in the coal discharge area based on numerical simulation according to claim 1, characterized in that, In S2, when coal is released at the end, the distance between the upper and lower ends of the working face is large, and they will not affect each other. Separate models are established for the upper and lower end areas of the working face. The roadway support adopts a combination of active and passive support. Considering that the actual generation of anchor bolts or cables in the two-dimensional simulation will produce limited small boundaries, a pre-tightening force is applied using the geometry module to achieve an equivalent replacement based on the actual anchor bolt spacing. The anchor bolts or cables in the roadway are numbered as the middle anchor bolt (mc), and the right side of the roadway is numbered clockwise starting from the middle anchor bolt. The left half of the tunnel is numbered counterclockwise from the middle anchor cable. Passive support uses Fish language to generate wall units to simulate the scaffolding.

3. The method for controlling the stability of surrounding rock in the coal discharge area based on numerical simulation according to claim 1, characterized in that, The initial state of the model in S2 includes six parts: coal seam 82, interbedded gangue layer, coal seam 81, immediate roof, basic roof, and overburden. The overburden density is calculated using Fish language according to the following formula: （6） in, The load is the overlying rock strata. It is the acceleration due to gravity; This represents the height within the rectangular region of the overlying rock in the two-dimensional model.

4. The method for controlling the stability of surrounding rock in the coal discharge area based on numerical simulation according to claim 1, characterized in that, The spatiotemporal analysis of active support in S3 analyzes the spatiotemporal differences in the effect of active support in roadways. During coal release, using a basic time unit, the effective period of active support at the upper and lower ends of the working face at different dip angles is statistically analyzed, including: Lower end: Although the timing of the failure of anchor bolts or anchor cables in the roadway during the initial coal release process varies at the lower end of working faces with different dip angles, the active support of anchor bolts or anchor cables in the middle and right parts of the roadway is basically ineffective after coal release. Before coal release, the passive support in the middle and right parts of the roadway is strengthened to ensure that the bearing arch around the roadway can still maintain its bearing capacity after the active support fails. Upper end: When coal is released to the transition frame position, the active support of the anchor bolts or anchor cables in the middle and left part of the roadway is basically ineffective. Before releasing coal at the upper end of the working face, the passive support in the roadway should be strengthened to ensure the stability of the bearing arch foot.

5. The method for controlling the stability of surrounding rock in the coal discharge area based on numerical simulation according to claim 1, characterized in that, The analysis of coal and gangue flow morphology in the S3 end-face coal discharge area involves observing and evaluating the flow and migration characteristics of coal and rock mass and the evolution of the surrounding rock structure during end-face coal discharge, using a basic time unit. This includes: Lower end: When coal is released at the same position on working faces with different dip angles, the failure rate of the bearing arch at the lower end of the working face is negatively correlated with the dip angle of the working face; Upper end: Coal release in the middle of the working face has a leading effect on the loosening of the upper end bearing arch, and the distance of the leading effect is positively correlated with the dip angle of the working face.

6. The method for controlling the stability of surrounding rock in the coal discharge area based on numerical simulation according to claim 1, characterized in that, The evolution analysis of the bearing capacity of the surrounding rock bearing structure in the S3 roadway needs to analyze the force chain field during the coal discharge process to represent the dynamic change process of the bearing capacity of the bearing arch. Force chains are the main form of load transfer in discontinuous and granular media. Based on strength, force chains are divided into three levels: strong force chains, medium-strength force chains, and weak force chains, according to the force chain classification method: （7） in, This refers to the contact force between particles; This represents the average contact force. The fracture-regeneration process of the combined force chain structure formed by three types of force chains continues throughout the entire coal discharge process, including strong chain connectivity, strong chain fracture, and strong chain reconstruction. The Fish language is used in the model to filter and distinguish force chains of different strengths, and the changes in the force chain field during the end coal discharge process are analyzed, including: Lower end: The bearing capacity of the lower end bearing arch of the working face is positively correlated with the dip angle of the working face; Upper end: The bearing capacity of the upper end bearing arch on the working face is negatively correlated with the dip angle of the working face.

7. An apparatus for controlling the stability of surrounding rock in the coal discharge zone based on numerical simulation as described in any one of claims 1-6, characterized in that: The system is designed to meet the coal discharge requirements of the end-point coal discharge area. It includes an end-point coal discharge support, which consists of a shield beam. The top of the shield beam has a window, and hydraulic cylinders are installed on both sides of the shield beam. The window is fitted with a flexible metal mesh, and the extension and retraction of the flexible metal mesh are controlled by the hydraulic cylinders. One end of the flexible metal mesh is fitted with a coal breaking knife, and the shield beam has a coal breaking knife groove adapted to the coal breaking knife. A mesh winding device is installed below the shield beam, and a mesh winding guide plate is installed on one side of the mesh winding device. A coal discharge port is located on the side of the flexible metal mesh closest to the coal breaking knife.

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