Inversion judgment method for roof stability of retreat channel in fully mechanized mining face

Abstract

The present invention discloses a method for inverting and distinguishing the stability of the roof of the retreat channel of a fully mechanized mining face, comprising the following steps: on-site monitoring of the retreat channel roof subsidence and coal pillar stress, and analysis of the geological structure and mine pressure observation data of the working face; establishing a surrounding rock stress model of the retreat channel under three different basic roof failure forms, and deriving the corresponding theoretical calculation formula for the retreat channel roof subsidence; substituting the on-site roof subsidence monitoring data into the theoretical calculation formula, inverting the basic roof break position, and combining the coal pillar stress monitoring data to realize the quantitative evaluation of whether the retreat channel roof is stable. The present invention takes into account the influence of different basic roof break positions on the retreat channel roof subsidence, and can use the monitoring data to invert and distinguish the roof failure form and stability of the retreat channel, provide guidance for the safe retreat of coal mining equipment in the fully mechanized mining face, and avoid accidents such as casualties and equipment damage caused by the instability of the retreat channel roof.

Description

Technical Field

[0001] The invention belongs to the technical field of underground engineering, and in particular relates to an inversion judgment method for the stability of a roof of a retreat channel of a fully mechanized mining face. Background Art

[0002] In recent years, with the continuous promotion and application of the withdrawal channel technology in my country's fully mechanized mining mines, the risk of large roof deformation has gradually become prominent. Since the withdrawal channel is the only channel for the withdrawal of coal mining equipment and hydraulic supports in the fully mechanized mining face, once a large roof deformation occurs, it will affect a series of subsequent schedules of the mine. The stability of its surrounding rock is the key to ensuring orderly and safe production in coal mines.

[0003] In the final mining stage of the comprehensive mining face, due to the influence of the periodic pressure of the working face, the roof deformation of the withdrawal channel is usually much greater than that of other mining tunnels. Among them, the roof structure state formed after the last periodic pressure and fracture of the basic roof is the main factor affecting the stability of the withdrawal channel roof. However, the existing technology of the research level of the stability of the withdrawal channel roof is still limited to the traditional field monitoring and qualitative evaluation level. A large amount of roof deformation and coal pillar stress monitoring data have not been effectively utilized. There is no quantitative theoretical analysis of the deep-level stability analysis of the withdrawal channel roof, and there is a lack of a method to distinguish the structural state of the withdrawal channel roof. The current roof stability analysis method combining monitoring data with theoretical inversion is not involved in the withdrawal channel technology. Summary of the invention

[0004] The purpose of the present invention is to provide a method for inverting and judging the stability of the roof of the withdrawal channel of a fully-mechanized mining face, which can use monitoring data to invert and judge the damage form and stability of the roof of the withdrawal channel, provide guidance for the safe withdrawal of coal mining equipment in the fully-mechanized mining face, and avoid casualties and equipment damage accidents caused by instability of the roof of the withdrawal channel.

[0005] The technical solution adopted by the present invention is a method for inverting and judging the stability of the roof of the retreat channel of the fully-mechanized mining face, which is specifically implemented according to the following steps:

[0006] Step 1: Monitor the deformation and stress of the surrounding rock of the withdrawal channel to obtain the roof subsidence and coal pillar stress concentration coefficient after the fully mechanized mining face and the withdrawal channel are connected;

[0007] Analyze the geological structure and mine pressure observation data of the working face to determine the coal seam occurrence parameters, surrounding rock mechanical parameters, mine pressure parameters and engineering parameters;

[0008] Step 2: Establish the surrounding rock stress model of the retreat channel under three different basic roof failure forms, and derive the corresponding theoretical calculation formula for the retreat channel roof subsidence;

[0009] Step 3: Substitute the on-site roof subsidence monitoring data into the theoretical calculation formula to invert the basic roof fracture position.

[0010] The present invention is also characterized in that:

[0011] In step 1, the surrounding rock deformation and stress of the withdrawal channel are monitored specifically as follows: the roof subsidence and coal pillar stress changes of the withdrawal channel at 3 to 5 monitoring stations are monitored to obtain the roof subsidence and coal pillar stress monitoring data, and the coal pillar stress concentration coefficient is calculated.

[0012] Step 1 The calculation method of the stress concentration factor of the coal pillar is:

[0013]

[0014] Among them, k b is the stress concentration coefficient of the coal pillar side of the retreat channel; σ0 is the monitored initial original rock stress; σ m It is the peak stress obtained by monitoring after the fully mechanized mining face and the withdrawal channel are connected.

[0015] The coal seam occurrence parameters, surrounding rock mechanical parameters, mine pressure parameters and engineering parameters in step 1 specifically include: elastic modulus E0 of the immediate top rock layer, elastic modulus E c , basic top rock internal friction angle The weight of the direct roof rock layer γ0, the weight of the basic roof rock layer γ1, the thickness of the direct roof h0, the key block formed after the basic roof breaks and the thickness of its overlying rock layer h1, the lateral pressure coefficient λ, the stress concentration coefficient k at the basic roof breaking position, the buried depth of the withdrawal channel H, and the periodic pressure step distance of the working face, i.e. the length of the key block l.

[0016] The theoretical calculation formula for the corresponding retracement channel top plate sinking amount derived in step 2 includes the following three cases:

[0017] 1) When the basic roof breaks behind the working face, the roof is simplified to a cantilever rock beam with one side fixed and subjected to a uniformly distributed load q1. q1 is expressed as:

[0018]

[0019] According to the cantilever beam deflection curve equation, the mid-span deflection of the withdrawal channel is obtained, that is, the amount of top plate subsidence u1 of the withdrawal channel when the basic top breaks behind the working surface:

[0020]

[0021] Where d1 is the fracture position when the basic roof breaks behind the working face, w1 is the width of the withdrawal channel, f1 is the support strength of the stacked hydraulic support in the withdrawal channel, and f2 is the support strength of the hydraulic support covering the working face;

[0022] 2) When the basic roof breaks above the retreat channel and the working face, the roof is simplified into a short cantilever rock beam with one side fixed and subjected to a uniformly distributed load q1, and a rotating sinking rock beam with a key block formed after the basic roof breaks and the overlying rock stratum load q2, where q2 = γ1h1; the roof sinking amount u of the short cantilever beam part is 2a for:

[0023]

[0024] Where d2 is the break position when the basic top breaks above the retracement channel;

[0025] The roof subsidence of the rotating sinking rock beam is solved by the energy conservation principle:

[0026] W1+W2=W3+W4+W5 (5)

[0027] Among them, W1 is the deformation energy released by the rotation and sinking of the key block and its overlying rock formation, W2 is the deformation energy released by the rotation and sinking of the direct top, W3 is the deformation energy released by the key block and its overlying rock formation absorbed by the direct top, W4 is the deformation work done by the stack-type hydraulic support supporting the top plate in the withdrawal channel, and W5 is the deformation work done by the hydraulic support supporting the top plate of the working face shielding type;

[0028] The deformation energies of each part are:

[0029]

[0030] Where α is the basic top rotation angle, M is the mining height, k c is the rock formation expansion coefficient, w2 is the top control distance of the working face shield support;

[0031] According to the principle of energy conservation, the roof subsidence u of the rotating sinking rock beam is solved 2b for:

[0032]

[0033] The subsidence of the short cantilever rock beam and the rotary sinking rock beam is superimposed to obtain the subsidence of the top plate of the withdrawal channel when the basic top breaks above the withdrawal channel:

[0034]

[0035] 3) When the basic roof breaks above the coal pillar, the roof is simplified to the key block formed after the basic roof breaks and the rotating sinking rock beam under the action of the overlying rock stratum load q2. The roof sinking amount can also be solved by the principle of energy conservation:

[0036]

[0037] in, The meaning is the same as W1, W2, W3, W4, and W5 above. the deformation energy released by the critical mass of the coal pillar and its overlying strata;

[0038] The deformation energies of each part are:

[0039]

[0040] Among them, d3 is the fracture position when the basic top breaks above the coal pillar.

[0041] According to the principle of energy conservation, the amount of roof subsidence u3 of the retreat channel when the basic roof breaks above the coal pillar is obtained as:

[0042]

[0043] The specific process of step 3 is as follows:

[0044] Step 3.1, the roof subsidence after the fully-mechanized mining face and the withdrawal channel are connected, the coal seam occurrence parameters, the surrounding rock mechanical parameters, the mine pressure parameters and the engineering parameters are substituted into the corresponding theoretical calculation formula of the roof subsidence of the withdrawal channel, and the theoretical values ​​of 2 to 3 basic roof breaking positions are obtained by inversion;

[0045] Step 3.2, according to the monitored coal pillar stress value and coal pillar stress concentration coefficient, remove 1 to 2 abnormal values ​​in the theoretical value of the basic roof breaking position obtained by inversion, and after removing the abnormal values, select and retain 1 theoretical value, which is the basic roof breaking position corresponding to the current roof subsidence;

[0046] Step 3.3: Inversion of basic roof failure forms and quantitative evaluation and determination of roof stability.

[0047] The specific process of step 3.2 is as follows:

[0048] When the stress concentration coefficient of the coal pillar is less than 2, it means that the stress increase of the coal pillar is very small, which means that the basic roof is broken behind the working face. That is, the basic roof breaking position after screening should satisfy d1≥w1+w2. At this time, it is necessary to eliminate the abnormal values ​​with inversion results of 0<d2<w1+w2 and d3≤0.

[0049] When the stress concentration coefficient of the coal pillar is 2-2.5, it means that the stress of the coal pillar has increased significantly, which means that the basic roof is broken above the withdrawal channel and the working face. That is, the basic roof breaking position after screening should satisfy 0<d2<w1+w2. At this time, it is necessary to eliminate the abnormal values ​​with inversion results of d1≥w1+w2 and d3≤0.

[0050] When the stress concentration coefficient of the coal pillar is greater than 2.5, it means that the stress of the coal pillar increases sharply, which means that the basic top breaks above the coal pillar. That is, the basic top breaking position after screening should satisfy d3≤0. At this time, it is necessary to eliminate the abnormal values ​​whose inversion results are d1≥w1+w2 and 0<d2<w1+w2.

[0051] The quantitative evaluation and discrimination process is as follows:

[0052] (1) The basic roof is broken behind the working face, and the overall structure of the roof is stable and easy to maintain;

[0053] (2) The basic roof is broken above the retreat channel and the working face, and part of the roof structure is prone to instability, with moderate maintenance difficulty;

[0054] (3) The basic roof is broken above the coal pillar, and the overall structure of the roof is very likely to become unstable, making maintenance difficult.

[0055] The beneficial effects of the present invention are:

[0056] (1) The present invention takes into account the influence of the basic roof breaking position on the stability of the withdrawal channel roof, analyzes the subsidence of the withdrawal channel roof under different basic roof damage forms, and finally establishes a theoretical analytical solution for the subsidence of the withdrawal channel roof that conforms to reality, thereby providing guidance for the safe withdrawal of coal mining equipment in the fully mechanized mining working face and avoiding casualties and equipment damage accidents caused by the instability of the withdrawal channel roof.

[0057] (2) The present invention utilizes the on-site monitoring data of the roof subsidence of the withdrawal channel to invert the basic roof fracture position, and combines the monitoring data of the coal pillar stress of the withdrawal channel to determine and evaluate the stability of the roof, thereby realizing the effective use of the monitoring data. The stability of the roof of the withdrawal channel can be determined and evaluated through the basic roof deformation and coal pillar stress monitoring. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Figure 1 It is a flow chart of the inversion determination method of the roof stability of the retreat channel of the fully mechanized mining working face of the present invention;

[0059] Figure 2 It is a schematic diagram of the mechanical model in which the basic top breaks behind the working surface;

[0060] Figure 3 It is a schematic diagram of the mechanical model of the basic top breaking above the retracement channel and the working surface;

[0061] Figure 4 Schematic diagram of the mechanical model of the basic roof breaking above the coal pillar. DETAILED DESCRIPTION

[0062] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0063] The present invention proposes a method for inversion determination of roof stability of a fully mechanized mining face retreat channel, which is specifically implemented according to the following steps:

[0064] Step 1: Monitor the deformation and stress of the surrounding rock of the withdrawal channel to obtain the roof subsidence and coal pillar stress concentration coefficient after the fully mechanized mining face and the withdrawal channel are connected;

[0065] Monitoring the surrounding rock deformation and stress of the withdrawal channel is specifically carried out as follows: monitoring the roof subsidence and coal pillar stress changes of the withdrawal channel at 3 to 5 monitoring stations, obtaining roof subsidence and coal pillar stress monitoring data, and calculating the coal pillar stress concentration coefficient.

[0066] The calculation method of the stress concentration factor of the coal pillar in step 1 is:

[0067]

[0068] Among them, k b is the stress concentration coefficient of the coal pillar side of the retreat channel; σ0 is the monitored initial original rock stress; σ m It is the peak stress obtained by monitoring after the fully mechanized mining face and the withdrawal channel are connected.

[0069] Analyze the geological structure and mine pressure observation data of the working face to determine the coal seam occurrence parameters, surrounding rock mechanical parameters, mine pressure parameters and engineering parameters including: elastic modulus E0 of the immediate top rock layer, elastic modulus E of the coal seam c , basic top rock internal friction angle The weight of the direct roof rock layer γ0, the weight of the basic roof rock layer γ1, the thickness of the direct roof h0, the key block formed after the basic roof breaks and the thickness of its overlying rock layer h1, the lateral pressure coefficient λ, the stress concentration coefficient k at the basic roof breaking position, the buried depth of the withdrawal channel H, and the periodic pressure step distance of the working face, i.e. the length of the key block l.

[0070] Step 2: Establish the surrounding rock stress model of the retreat channel under three different basic roof failure forms, and derive the corresponding theoretical calculation formula for the retreat channel roof subsidence; specifically:

[0071] 1) If Figure 2 As shown in the figure, when the basic roof breaks behind the working face, the roof is simplified to a cantilever rock beam with one side fixed and subjected to a uniformly distributed load q1(x). q1(x) is expressed as:

[0072]

[0073] According to the cantilever beam deflection curve equation, the mid-span deflection of the withdrawal channel is obtained, that is, the amount of top plate subsidence u1 of the withdrawal channel when the basic top breaks behind the working surface:

[0074]

[0075] Where d1 is the fracture position when the basic roof breaks behind the working face, w1 is the width of the withdrawal channel, f1 is the support strength of the stacked hydraulic support in the withdrawal channel, and f2 is the support strength of the hydraulic support covering the working face;

[0076] 2) If Figure 3 As shown in the figure, when the basic roof breaks above the retreat channel and the working face, the roof is simplified into a short cantilever rock beam with one side fixed and subjected to a uniformly distributed load q1, and a rotating sinking rock beam with a key block formed after the basic roof breaks and the overlying rock stratum load q2, where q2 = γ1h1; the roof sinking amount u of the short cantilever beam part is 2a for:

[0077]

[0078] Where d2 is the break position when the basic top breaks above the retracement channel;

[0079] The roof subsidence of the rotating sinking rock beam is solved by the energy conservation principle:

[0080] W1+W2=W3+W4+W5 (5)

[0081] Among them, W1 is the deformation energy released by the rotation and sinking of the key block and its overlying rock formation, W2 is the deformation energy released by the rotation and sinking of the direct top, W3 is the deformation energy released by the key block and its overlying rock formation absorbed by the direct top, W4 is the deformation work done by the stack-type hydraulic support supporting the top plate in the withdrawal channel, and W5 is the deformation work done by the hydraulic support supporting the top plate of the working face shielding type;

[0082] The deformation energies of each part are:

[0083]

[0084] Where α is the basic top rotation angle, M is the mining height, k c is the rock formation expansion coefficient, w2 is the top control distance of the working face shield support;

[0085] According to the principle of energy conservation, the roof subsidence u of the rotating sinking rock beam is solved 2b for:

[0086]

[0087] The subsidence of the short cantilever rock beam and the rotary sinking rock beam is superimposed to obtain the subsidence of the top plate of the withdrawal channel when the basic top breaks above the withdrawal channel:

[0088]

[0089] 3) If Figure 4As shown in the figure, when the basic roof breaks above the coal pillar, the roof is simplified to the key block formed after the basic roof breaks and the rotating sinking rock beam under the action of the overlying rock stratum load q2. The roof sinking amount can also be solved by the principle of energy conservation:

[0090]

[0091] in, The meaning is the same as W1, W2, W3, W4, and W5 above. the deformation energy released by the critical mass of the coal pillar and its overlying strata;

[0092] The deformation energies of each part are:

[0093]

[0094] Among them, d3 is the fracture position when the basic top breaks above the coal pillar.

[0095] According to the principle of energy conservation, the amount of roof subsidence u3 of the retreat channel when the basic roof breaks above the coal pillar is obtained as:

[0096]

[0097] Step 3: Substitute the on-site roof subsidence monitoring data into the theoretical calculation formula to invert the basic roof breaking position. The specific process is as follows:

[0098] Step 3.1, the roof subsidence after the fully-mechanized mining face and the withdrawal channel are connected, the coal seam occurrence parameters, the surrounding rock mechanical parameters, the mine pressure parameters and the engineering parameters are substituted into the corresponding theoretical calculation formula of the roof subsidence of the withdrawal channel, and the theoretical value of the basic roof breaking position is obtained by inversion;

[0099] Step 3.2, according to the monitored coal pillar stress value and coal pillar stress concentration coefficient, remove 1 to 2 abnormal values ​​in the theoretical value of the basic roof breaking position obtained by inversion, and after removing the abnormal values, select and retain 1 theoretical value, which is the basic roof breaking position corresponding to the current roof subsidence;

[0100] The specific process of step 3.2 is as follows:

[0101] When the stress concentration coefficient of the coal pillar is less than 2, it means that the stress increase of the coal pillar is very small, which means that the basic roof is broken behind the working face. That is, the basic roof breaking position after screening should satisfy d1≥w1+w2. At this time, it is necessary to eliminate the abnormal values ​​with inversion results of 0<d2<w1+w2 and d3≤0.

[0102] When the stress concentration coefficient of the coal pillar is 2-2.5, it means that the stress of the coal pillar has increased significantly, which means that the basic roof is broken above the withdrawal channel and the working face. That is, the basic roof breaking position after screening should satisfy 0<d2<w1+w2. At this time, it is necessary to eliminate the abnormal values ​​with inversion results of d1≥w1+w2 and d3≤0.

[0103] When the stress concentration coefficient of the coal pillar is greater than 2.5, it means that the stress of the coal pillar increases sharply, which means that the basic top breaks above the coal pillar. That is, the basic top breaking position after screening should satisfy d3≤0. At this time, it is necessary to eliminate the abnormal values ​​whose inversion results are d1≥w1+w2 and 0<d2<w1+w2.

[0104] Step 3.3, inversion of basic roof failure forms and quantitative evaluation and identification of roof stability;

[0105] The quantitative evaluation and discrimination in step 3.3 are:

[0106] (1) The basic roof is broken behind the working face, and the overall structure of the roof is stable and easy to maintain;

[0107] (2) The basic roof is broken above the retreat channel and the working face, and part of the roof structure is prone to instability, with moderate maintenance difficulty;

[0108] (3) The basic roof is broken above the coal pillar, and the overall structure of the roof is very likely to become unstable, making maintenance difficult.

[0109] Example

[0110] Hongliulin Coal Mine is located in the northern part of the Loess Plateau in northern Shaanxi, in the central part of Shenmu City, Shaanxi Province. -2 Coal seams 15205 and 15206 are mined using a comprehensive mechanized mining method, with equipment withdrawal using pre-excavation withdrawal channel technology. The average thickness of the coal seam is 7.23m, with a stable thickness and small variability. It is a medium-thick to extra-thick coal seam with a simple structure.

[0111] As shown in Table 1, the monitoring data of roof subsidence and coal pillar stress at three stations in the middle of the retreat channel of the 15205 and 15206 working faces are summarized as follows:

[0112] Table 1

[0113]

[0114]

[0115] The coal seam occurrence and surrounding rock mechanical parameters of the two working faces are shown in Table 2:

[0116] Table 2

[0117]

[0118] The mine pressure and engineering parameters of the two working faces are shown in Table 3:

[0119] Table 3

[0120]

[0121] Substitute the roof subsidence monitoring data in Table 1 and the parameters in Tables 2 and 3 into the theoretical calculation formulas of u1, u2, and u3, combine them with the stress monitoring data, remove the outliers, and invert to obtain the basic roof breaking position. The inversion and screening results of the basic roof breaking position are shown in Table 4.

[0122] Table 4

[0123]

[0124] From the monitoring data, inversion and screening of the basic roof fracture position, it can be seen that the basic roof of the 15205 working face withdrawal channel was damaged at 3.4m above the coal pillar. The overall structure of the roof is very prone to instability and is difficult to maintain, which is not conducive to the safe and rapid withdrawal of coal mining equipment. The basic roof of the 15206 working face withdrawal channel was damaged at 9.1m outside the withdrawal channel, and the damage position was close to the rear of the working face protective support. The overall structure of the roof is stable and easy to maintain, which can meet the needs of safe withdrawal of the working face.

[0125] At present, the commonly used method for estimating the basic roof breaking position in coal mines is mainly calculated by the periodic pressure step recorded by the mine pressure observation system. Table 5 shows the calculation process of determining the basic roof breaking position after the working face and the withdrawal channel are connected using the periodic pressure step in the mine pressure observation system of the 15205 and 15206 working faces, where the last pressure position is the basic roof breaking position after the working face and the withdrawal channel are connected. The calculation method is:

[0126] s n =s n-1 -l n (n=2,3,…,12)

[0127] Among them, s is the pressure position, that is, the working face mining distance when the basic top breaks, l is the periodic pressure step distance, that is, the key block length, and n is the number of periodic pressure times.

[0128] Table 5

[0129]

[0130] By comparing the calculation results of Table 4 and Table 5, it can be seen that the two methods calculated that the basic top of the withdrawal channel of the 15205 working face was destroyed at 3.4m and 2.2m above the coal pillar, respectively, and the calculation results differed by 1.2m; the basic top of the withdrawal channel of the 15206 working face was destroyed at 9.1m and 10m outside the withdrawal channel, and the calculation results differed by 0.9m. The calculation results of the two methods are basically consistent, indicating that the inversion calculation method of the present invention has good reliability.

[0131] Through the above-mentioned method, the present invention takes into account the influence of the basic roof fracture position on the stability of the withdrawal channel roof, analyzes the amount of subsidence of the withdrawal channel roof under different basic roof damage forms, and finally establishes a theoretical analytical solution for the amount of subsidence of the withdrawal channel roof that conforms to reality, providing guidance for the safe withdrawal of coal mining equipment in the comprehensive mining working face, and avoiding casualties and equipment damage accidents caused by the instability of the withdrawal channel roof. The present invention uses the field monitoring data of the withdrawal channel roof subsidence to invert the basic roof fracture position, and combines the withdrawal channel coal pillar stress monitoring data to determine and evaluate the roof stability, thereby realizing the effective use of monitoring data. The stability of the withdrawal channel roof can be determined and evaluated through basic roof deformation and coal pillar stress monitoring.

Claims

1. The inversion judgment method of the roof stability of the retreat channel of the fully mechanized mining face is characterized by: Follow the steps below to implement it: Step 1: Monitor the deformation and stress of the surrounding rock of the withdrawal channel to obtain the roof subsidence and coal pillar stress concentration coefficient after the fully mechanized mining face and the withdrawal channel are connected; Analyze the geological structure and mine pressure observation data of the working face to determine the coal seam occurrence parameters, surrounding rock mechanical parameters, mine pressure parameters and engineering parameters; Step 2: Establish the surrounding rock stress model of the retreat channel under three different basic roof failure forms, and derive the corresponding theoretical calculation formula for the retreat channel roof subsidence; Step 3: Substitute the on-site roof subsidence monitoring data into the theoretical calculation formula to invert the basic roof breaking position; The monitoring of surrounding rock deformation and stress of the withdrawal channel described in step 1 is specifically: monitoring the roof subsidence and coal pillar stress changes of the withdrawal channel at 3 to 5 monitoring stations to obtain monitoring data; The calculation method of the stress concentration factor of the coal pillar in step 1 is: （1） in, k b is the stress concentration factor of the coal pillar side of the withdrawal channel; σ 0 is the initial in-situ rock stress monitored; σ m It is the peak stress obtained by monitoring after the fully mechanized mining face and the withdrawal channel are connected; The coal seam occurrence parameters, surrounding rock mechanical parameters, mine pressure parameters and engineering parameters in step 1 specifically include: elastic modulus of the immediate top rock layer E 0. Coal seam elastic modulus E c , basic top rock internal friction angle φ 1. Weight of the immediate top rock layer γ 0. Basic top rock mass γ 1. Direct top thickness h 0. The key block formed after the basic top breaks and the thickness of its overlying rock layer h 1. Lateral pressure coefficient λ , stress concentration factor at the basic top breaking position k , Depth of retracement channel H , working surface periodic pressure step distance, i.e. key block length l ; The theoretical calculation formula for the corresponding retracement channel top plate sinking amount deduced in step 2 includes the following three cases: 1) When the basic roof breaks behind the working face, the roof is simplified to a cantilever rock beam with one side fixed and subjected to a uniformly distributed load q1. q 1 is represented by: （2） Among them, k is the stress concentration coefficient at the breaking position of the basic top, γ1 is the weight of the basic top rock layer, H is the burial depth of the withdrawal channel, h is the height of the withdrawal channel, λ is the lateral pressure coefficient, φ1 is the internal friction angle of the basic top rock layer, e is a constant, equal to 2.71828, which is the base of the natural logarithm, and x represents any point on the x-axis; According to the cantilever beam deflection curve equation, the mid-span deflection of the withdrawal channel is obtained, that is, the amount of subsidence of the withdrawal channel roof when the basic top breaks behind the working surface. u 1: （3） Among them, k is the stress concentration coefficient at the breaking position of the basic roof, γ1 is the weight of the basic roof rock layer, H is the burial depth of the withdrawal channel, h is the height of the withdrawal channel, λ is the lateral pressure coefficient, φ1 is the internal friction angle of the basic roof rock layer, E0 is the elastic modulus of the direct roof rock layer, h0 is the thickness of the direct roof, e is a constant, equal to 2.71828, which is the base of the natural logarithm, x represents any point on the x-axis, d 1 is the fracture position when the basic top breaks behind the working surface. w 1 is the retracement channel width, f 1 is the support strength of the stacked hydraulic support in the withdrawal channel, f 2 is the support strength of the working face shield hydraulic support; 2) When the basic roof breaks above the retreat channel and the working surface, the roof is simplified into a section with one side fixed and subjected to uniform load. q 1 short cantilever rock beam, as well as a key block formed after the basic top breaks and its overlying rock strata load q 2-action rotary sinking rock beam, q 2= γ 1 h 1. Top plate subsidence of the short cantilever beam u 2a for: （4） Among them, k is the stress concentration coefficient at the breaking position of the basic roof, γ1 is the weight of the basic roof rock layer, H is the burial depth of the withdrawal channel, h is the height of the withdrawal channel, λ is the lateral pressure coefficient, φ1 is the internal friction angle of the basic roof rock layer, E0 is the elastic modulus of the direct roof rock layer, h0 is the thickness of the direct roof, e is a constant, which is equal to 2.71828, which is the base of the natural logarithm, and x represents any point on the x-axis; in d 2 is the breaking position when the basic top breaks above the retracement channel; The roof subsidence of the rotating sinking rock beam is solved by the energy conservation principle: （5） in, W 1 is the deformation energy released by the rotation and sinking of the key block and its overlying rock strata, W 2 is the deformation energy released by direct top rotation and sinking, W 3 is the deformation energy released by the key block absorbed directly by the top and its overlying rock strata, W 4 is the work done by the top plate deformation supported by the stacked hydraulic support in the withdrawal channel. W 5 is the work done by the top plate deformation supported by the hydraulic support of the working face; The deformation energies of each part are: （6） Among them, γ1 is the weight of the basic top rock formation, γ0 is the weight of the immediate top rock formation, l is the periodic pressure step of the working face, that is, the length of the basic top key block, h1 is the thickness of the basic top key block and its overlying rock formation, E0 is the elastic modulus of the immediate top rock formation, h0 is the thickness of the immediate top, α is the basic top rotation angle, , M To collect height, k c is the rock formation expansion coefficient, w 2 is the top distance control of the working face shield support; According to the principle of energy conservation, the roof subsidence of the rotating sinking rock beam is solved u 2b for: （7） Among them, γ1 is the weight of the basic top rock formation, γ0 is the weight of the immediate top rock formation, l is the periodic pressure step of the working face, that is, the length of the basic top key block, h1 is the thickness of the basic top key block and its overlying rock formation, E0 is the elastic modulus of the immediate top rock formation, and h0 is the thickness of the immediate top; The subsidence of the short cantilever rock beam and the rotary sinking rock beam is superimposed to obtain the subsidence of the top plate of the withdrawal channel when the basic top breaks above the withdrawal channel: （8） Among them, k is the stress concentration coefficient at the breaking position of the basic roof, H is the burial depth of the withdrawal channel, λ is the lateral pressure coefficient, h is the height of the withdrawal channel, γ1 is the weight of the basic roof rock formation, l is the periodic pressure step distance of the working face, that is, the length of the basic roof key block, E0 is the elastic modulus of the direct roof rock formation, and h0 is the thickness of the direct roof; 3) When the basic roof breaks above the coal pillar, the roof is simplified to the key block formed after the basic roof breaks and the load of the overlying rock strata q 2. The roof sinking amount can also be solved by the energy conservation principle: （9） in, , , , , Meaning and above W 1. W 2. W 3. W 4. W 5 same, the deformation energy released by the critical mass of the coal pillar and its overlying strata; The deformation energies of each part are: （10） Among them, h is the height of the withdrawal channel, γ1 is the weight of the basic top rock formation, γ0 is the weight of the direct top rock formation, l is the periodic pressure step of the working face, that is, the length of the basic top key block, h1 is the thickness of the basic top key block and its overlying rock formation, E0 is the elastic modulus of the direct top rock formation, h0 is the thickness of the direct top, E c is the elastic modulus of the coal seam, d 3 is the fracture position when the basic top breaks above the coal pillar; According to the principle of energy conservation, the amount of roof subsidence in the retreat channel when the basic roof breaks above the coal pillar is obtained. u 3 is: （11）； Among them, γ1 is the weight of the basic top rock formation, γ0 is the weight of the immediate top rock formation, l is the periodic pressure step of the working face, that is, the length of the basic top key block, h1 is the thickness of the basic top key block and its overlying rock formation, E0 is the elastic modulus of the immediate top rock formation, h0 is the thickness of the immediate top, E c is the elastic modulus of the coal seam; The specific process of step 3 is as follows: Step 3.1, the roof subsidence after the fully-mechanized mining face and the withdrawal channel are connected, the coal seam occurrence parameters, the surrounding rock mechanical parameters, the mine pressure parameters and the engineering parameters are substituted into the corresponding theoretical calculation formula of the roof subsidence of the withdrawal channel, and the theoretical value of the basic roof breaking position is obtained by inversion; Step 3.2, according to the monitored coal pillar stress value and coal pillar stress concentration coefficient, remove 1-2 abnormal values ​​in the theoretical value of the basic roof breaking position obtained by inversion, and after removing the abnormal values, select and retain 1 theoretical value, which is the basic roof breaking position corresponding to the current roof subsidence; Step 3.3, inversion of basic roof failure forms and quantitative evaluation and identification of roof stability; The specific process of step 3.2 is as follows: When the stress concentration coefficient of the coal pillar is less than 2, it means that the stress increase of the coal pillar is very small, which means that the basic roof is broken behind the working face. That is, the breaking position of the basic roof after screening should meet d 1≥ w 1+ w 2. At this time, it is necessary to eliminate the inversion results of 0 < d 2< w 1+ w 2 and d 3≤0 outliers; When the stress concentration coefficient of the coal pillar is 2~2.5, it means that the stress of the coal pillar has increased significantly, which means that the basic roof is broken above the withdrawal channel and the working face. That is, the breaking position of the basic roof after screening should meet 0< d 2< w 1+ w 2. At this time, the inversion result needs to be eliminated. d 1≥ w 1+ w 2 and d 3≤0 outliers; When the stress concentration coefficient of the coal pillar is greater than 2.5, it means that the stress of the coal pillar increases sharply, which means that the basic top breaks above the coal pillar. That is, the breaking position of the basic top after screening should meet the requirements. d 3≤0, then the inversion result needs to be eliminated. d 1≥ w 1+ w 2 and 0< d 2< w 1+ w Outlier of 2; in, w 1 is the retracement channel width, w 2 is the top distance control of the working face shield support; The quantitative evaluation and discrimination process described in step 3.3 is as follows: (1) The basic roof is broken behind the working face, and the overall structure of the roof is stable and easy to maintain; (2) The basic roof is broken above the retreat channel and the working face, and part of the roof structure is prone to instability, with moderate maintenance difficulty; (3) The basic roof is broken above the coal pillar, and the overall structure of the roof is very likely to become unstable, making maintenance difficult.

Images