Method for determining advanced controllable roof cutting parameters of thick and hard roof of coal mine stope face

Abstract

The invention provides a method for determining advanced controllable roof cutting parameters of a thick and hard roof of a coal mine stope face, which comprises the steps of engineering general situation field investigation and survey, in-situ geomechanical test, goaf roof thickness / thin plate theoretical analysis, coal pillar or filling body vertical load theoretical analysis, numerical simulation calculation and engineering test verification. Analyzing the mechanical behavior of the working face roof based on a plate theory, verifying the correctness of a theoretical model through measured data, and changing boundary conditions to predict the mechanical behavior of the roof after roof cutting; the method comprises the following steps: analyzing the vertical load of a coal pillar or a roadside support body after roof cutting and the influence rule of roof cutting height and angle on the roadside support body through a mechanical model, and preliminarily obtaining better roof cutting parameters; by establishing a numerical model of different topping parameter combinations, different performance parameters are used for comparing and evaluating different topping parameters, so that the optimal topping parameter is determined; according to the method, advanced controllable roof cutting of the hard roof of the coal seam is achieved, and the mine pressure treatment effect in mining is predicted.

Description

Technical Field

[0001] The present invention belongs to the technical field of rock stratum control in underground coal mining, and in particular relates to a method for determining parameters of advanced controllable top cutting of thick hard roof in a coal mine working face. Background Art

[0002] During underground coal mining, the overlying strata gradually sink and deform due to disturbances from mining. This causes the rock load to concentrate on the coal and rock mass surrounding the working face and goaf, generating abutment pressures within the coal and rock mass that are several times greater than the original rock stress. Currently, technical solutions for managing abutment pressure primarily consider coal seam depth, mining techniques, roof lithology, and roof management measures. These measures typically include improving hydraulic support performance, modifying support configurations, strengthening monitoring and early warning systems, and roof pressure relief through roof cutting. Among these, advanced roof cutting is the most effective method, primarily employing small-diameter blasting or hydraulic fracturing. Blasting or hydraulic fracturing is used to create a through-crack at a specific angle and depth in the roofs of two mining roadways within the coal seam. This fracture severs the physical connection between the roadway roof and the working face roof, thereby disrupting the load transfer path and reducing the abutment pressure on the coal and rock mass surrounding the working face or goaf. It can be applied to various working conditions such as mining tunnels with coal pillars protecting the tunnel or gob-side tunnels without coal pillars.

[0003] For specific working faces, the current design of top cutting and pressure relief parameters has the following technical problems: 1. The design basis for the topping parameters, centered around topping angle and topping height, was insufficient. The topping height was determined based on design experience and calculations based on rock expansion theory, while the topping angle was calculated primarily based on the "SR" stability criterion for masonry beams. This was insufficiently adapted to site conditions, resulting in parameter settings unable to adapt to complex and changing site requirements.

[0004] 2. The top cutting and pressure relief scheme does not match the geological conditions. It does not take into account the differences in the rock properties and physical and mechanical parameters of the coal seam roofs in different coal mines. Instead, it adopts relatively consistent top cutting parameters, which has extremely poor pertinence and adaptability to specific projects. This limits the effect of top cutting and pressure relief, and is not conducive to the predictable control of the top cutting adjustment effect.

[0005] 3. The mechanical response characteristics of roof load, deformation, etc. during the mining process of the working face using advanced roof cutting and pressure relief are unclear, and the roof cutting and pressure relief effects under various roof conditions cannot be predicted. It can only be verified through on-site engineering experiments. If the roof cutting parameters and plans are unreasonable, the on-site test will fail, wasting a lot of manpower, material resources and financial resources. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a method for determining the parameters of advance controllable top cutting of thick hard roof of coal mine mining face in response to the above-mentioned problems, which is used to design the advance top cutting parameters of mining tunnels and predict the fracture size of coal seam roof after top cutting, thereby improving the support of mining tunnels and the rock layer control of mining face roof.

[0007] The embodiment of the present application is implemented as follows: The present application provides a method for determining parameters of advanced controllable top cutting of thick hard roof in a coal mine working face, which is characterized by comprising the following steps: Step a, on-site investigation of project overview: Go deep into the underground coal mining frontline to conduct comprehensive research on geological mining conditions and working face layout parameters to provide basic data for subsequent analysis; Step b, in-situ geomechanical testing: Through panoramic structural observation of coal rock mass through drilling, the distribution and development characteristics of coal rock mass structure in the mining working face and mining roadway are understood; through strength penetration testing of coal rock mass, the strength and deformation laws of coal rock mass are obtained; through hydraulic fracturing, the magnitude and distribution characteristics of ground stress are tested; Step c, theoretical analysis of goaf roof thickness / thinness: A mechanical model with multiple boundary conditions based on on-site conditions was established. Through plate theory calculations, the distribution of roof deflection and bending moment, as well as their changing patterns, were obtained as the mining distance increased and the exposed area continued to increase. Step d, theoretical analysis of vertical loads on coal pillars or filling bodies: A mechanical model of vertical load transfer between the roof, coal pillar, or backfill, and floor of a mining roadway based on the rock separation method was established. The quantitative relationship between the roof cutting height, the roof cutting angle, and the load on the coal pillar or other roadway support structures was analyzed. The variation pattern of the vertical load on the coal pillar or backfill support structure with the change of the roof cutting height and the roof cutting angle was revealed, and the range of the roof cutting parameters was preliminarily calculated. Step e, numerical simulation calculation: Establish a two-dimensional or three-dimensional discrete element numerical simulation model. By carrying out numerical model calculations under different top cutting heights and angles, comprehensively analyze the deformation of the tunnel surrounding rock, the stress evolution law of the solid coal wall, and the stress evolution law of the coal pillar or roadside filling support, and obtain the top cutting parameter combination according to the evaluation and analysis standards; Step f, engineering test verification: The above-mentioned advanced top cutting parameter combination is applied to the advanced top cutting project of the mining roadway in the underground working face of the coal mine. The mine pressure data is monitored on site, and the above-mentioned top cutting parameters are fine-tuned after feedback.

[0008] In some alternative embodiments, the geological mining conditions in step a include coal seam depth, thickness, roof and floor lithology and coal seam inclination, geological structure conditions; and the working face arrangement parameters are working face inclination length and advancing length.

[0009] In some alternative embodiments, step c further comprises: determining the distribution characteristics of the tensile stress in the roof according to the relationship between the bending moment and the tensile stress, selecting a rock mass breakage criterion, comparing the tensile stress of the roof with the tensile strength thereof, calculating the breakage step distance of the roof, further predicting the deflection and bending moment distribution characteristics of the roof after the roof cutting measure is adopted, and accurately revealing the evolution law of the roof stability.

[0010] In some alternative embodiments, the evaluation and analysis criteria in step e are that the vertical load of the coal pillar or the roadside support body is minimum, the peak value of the solid coal bank support pressure is minimum, and the displacement amount and stress peak value of the surrounding rock of the roadway are both minimum.

[0011] In some alternative embodiments, the multiple boundary conditions in step c include: Four edges fixed support corresponding to no roof cutting condition goaf roof not yet collapsed working condition; three edges fixed support and one edge free corresponding to no roof cutting condition goaf roof initial collapse working condition; three edges fixed support and one edge simply supported corresponding to roof cutting condition goaf roof not yet collapsed working condition; two edges fixed support, one edge simply supported and one edge free corresponding to roof cutting condition goaf roof initial collapse working condition.

[0012] In some alternative embodiments, the calculation process in step d is as follows: Step d1, the basic roof load sources mainly include two aspects, one is the load transmission, and the other is the self-weight of the key block:

[0013] In the formula, K G —interlayer load transmission coefficient; H f —overburden height; γ f —overburden bulk density; L—length of the basic roof key block B1; H j —height of the basic roof key block B1; γ j —rock bulk density of the basic roof key block B1; After the basic roof breaks, the rock blocks B2 between the basic roof key block B1, the working face and the goaf which have not reached a stable state and the rock blocks C which have broken and sunk stably in the goaf form a masonry beam structure, at this time, the rock blocks B1, B2 and C have a mechanical relationship of friction and horizontal thrust, the load transmitted by the overburden and the self-weight are appropriately reduced in the structure balance process, and the key block B1 acting force on the direct roof can be obtained by introducing the masonry beam calculation formula:

[0014] In the formula: i - the block degree of the key block B1; θ1 - the rotation angle of the key block B1, - the internal friction angle of the basic roof rock; Step d2, the direct roof acts on the underlying structure, after cutting the roof, a short cantilever structure is formed on the side of the goaf, the bending moment generated by the gravity of the inner rock mass is ignored, and the gravity is directly considered as the direct roof load, so that:

[0015] In the formula: P Z - the direct roof load; H Z - the direct roof height; γ z - the direct roof rock bulk density; b - the effective support area of the support body; L P - the length of the blast hole, a - the cutting roof angle; H q - the cutting roof height; The hinged structure formed after cutting the direct roof can be regarded as a short masonry beam, and the force of the direct roof on the underlying coal pillar is calculated by the following formula:

[0016] In the formula: θ - the rotation angle of the short masonry beam.

[0017] The beneficial effects of the present application are: 1. The coal mining working face thick and hard roof advance controllable cutting parameter determination method provided by the present application is based on the engineering profile field conditions and in-situ geomechanical test data, a theoretical analysis model of the coal pillar or filling body vertical load under the cutting condition is established, the two parameters of the optimal cutting angle and height are theoretically calculated, the best cutting parameter combination is obtained combined with the numerical simulation analysis result, and the reliability of the cutting parameter is verified through the field engineering experiment. The parameters obtained by the above method are highly targeted, and provide sufficient basis for the advance cutting parameter design of the mining roadway; 2. Based on the engineering profile field conditions and in-situ geomechanical test data, a thick / thin plate theoretical analysis model of the goaf roof is established, the deflection and bending moment distribution of the goaf roof under the conditions of the goaf roof not yet collapsed under the condition of not cutting the roof, the goaf roof primary collapse under the condition of not cutting the roof, the goaf roof not yet collapsed under the condition of cutting the roof, and the goaf roof primary collapse under the condition of cutting the roof are predicted, the roof primary pressure step distance and the periodic pressure step distance are predicted, and the effectiveness and reliability of the prediction method are verified through the field measured data, so that the advance cutting pressure regulation effect is predicted and controlled; 3. After applying the advance controllable cutting technology, the stress distribution of the roadway surrounding rock is effectively improved, the deformation and damage of the surrounding rock are reduced, the overall support effect of the roadway surrounding rock is optimized, and the safety of the coal mine underground mining working face is greatly improved. BRIEF DESCRIPTION OF DRAWINGS

[0018] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed to be used in the embodiments will be briefly introduced as follows. It should be understood that the following drawings only show some of the embodiments of the present application, and therefore should not be regarded as a limitation on the scope. For those of ordinary skill in the art, other related drawings can also be obtained without creative labor on the basis of these drawings.

[0019] Figure 1 Flow chart in the embodiments of the present application; Figure 2a Working face layout schematic diagram in the embodiments of the present application; Figure 2b Working face drilling comprehensive column chart in the embodiments of the present application; Figure 3a Drilling panoramic observation result chart in the embodiments of the present application; Figure 3b Coal rock mass penetration method strength test result chart in the embodiments of the present application; Figure 3c Ground stress test result chart in the embodiments of the present application; Figure 4a 、 Figure 4b 、 Figure 4c 、 Figure 4d Four boundary condition thin plate theory mechanics model chart in the embodiments of the present application; Figure 5a 、 Figure 5b 、 Figure 5c 、 Figure 5d 、 Figure 5e Deflection distribution chart of roof at different advancing distances in the embodiments of the present application; Figure 6a 、 Figure 6b Four edge fixed thin plate bending moment M x , M y distribution chart in the embodiments of the present application; Figure 7a Coal pillar load mechanics model chart in the embodiments of the present application; Figure 7b Cutting height influence law chart in the embodiments of the present application; Figure 7c Cutting angle influence law chart in the embodiments of the present application; Figure 8 Numerical simulation calculation model chart in the embodiments of the present application; Figure 9a 、 Figure 9b Overburden strata collapse shape chart under two schemes in the embodiments of the present application; Figure 9c 、 Figure 9dThe displacement diagrams of the coal pillar (filling body), solid coal rib, and roadway roof and floor surrounding rock under the two schemes in the embodiment of this application; Figure 9e-9f Graphs of vertical stress of coal pillars (filling bodies) under two schemes in the embodiments of this application; Figure 9h-9g The vertical stress diagram of the solid coal seam under the two schemes in the embodiment of this application; Figure 10 This is a graph of measured data of the top plate pressure in an embodiment of the present application. DETAILED DESCRIPTION

[0020] To make the objectives, technical solutions, and advantages of the embodiments of the present application more clear, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Generally, the components of the embodiments of the present application described and shown in the drawings herein can be arranged and designed in various different configurations.

[0021] Therefore, the following detailed description of the embodiments of the present application provided in the accompanying drawings is not intended to limit the scope of the present application for protection, but merely represents selected embodiments of the present application. All other embodiments obtained by persons of ordinary skill in the art based on the embodiments in the present application without creative work are within the scope of protection of the present application.

[0022] It should be understood that the size of the serial numbers of the steps in the embodiment does not mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiment of the present application.

[0023] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, it does not need to be further defined or explained in subsequent drawings.

[0024] The features and performance of the present application are further described in detail below with reference to the embodiments.

[0025] like Figure 1 As shown, the present application provides a method for determining parameters of advanced controllable top cutting of thick hard roof in coal mine mining working face, which mainly includes specific steps such as on-site investigation of engineering overview, in-situ geomechanical testing, theoretical analysis of thickness / thinness of roof in goaf, theoretical analysis of vertical load of coal pillar or filling body, numerical simulation calculation, and engineering test verification.

[0026] The engineering profile field investigation, in-depth coal mine underground mining front line, comprehensive investigation of coal seam depth, thickness, roof and floor lithology and coal seam inclination, geological structure conditions and other geological mining conditions, and working face tendency length, length of advance and other working face layout parameters, provide basic data for subsequent analysis.

[0027] The in-situ geomechanics test, including specific methods such as coal rock mass drilling panoramic structure observation, in-hole rock mass strength in-situ test, and hydraulic fracturing ground stress test. Through coal rock mass drilling panoramic structure observation, the distribution and development characteristics of the coal rock mass structure surface of the mining face recovery roadway are mastered. The strength of the coal rock mass is tested by the strength sounding method, and the size and deformation law of the coal rock mass strength are obtained, of which the most critical parameter is the tensile strength of the coal rock mass. The size and distribution characteristics of the ground stress are tested by the hydraulic fracturing method. The above methods provide basic data for subsequent theoretical analysis.

[0028] The goaf roof thick / thin plate theoretical analysis is based on the technical characteristics, roof lithology and thickness of a certain working face of a specific coal mine, combined with the applicable conditions of the thick / thin plate theory, the specific recovery working face suspended roof is regarded as a regular rectangle, a mechanical model with multiple boundary conditions based on field conditions is established, and the distribution of the roof deflection and bending moment and their variation law are obtained by plate theory calculation under the condition that the roof deflection area continuously increases with the increase of the mining distance. According to the relationship between the bending moment and the tensile stress, the distribution characteristics of the tensile stress in the roof are determined, the appropriate rock mass breaking criterion is selected, the relationship between the roof tensile stress and its tensile strength is compared, the roof breaking step distance is calculated, and the distribution characteristics of the roof deflection and bending moment after the top cutting measure is further predicted, accurately revealing the roof stability evolution law.

[0029] The coal pillar or filling body vertical load theoretical analysis establishes a roof-pillar (or filling body)-floor vertical load transfer mechanical model based on the rock mass separation method, analyzes the quantitative relationship between the top cutting height, top cutting angle and the coal pillar or other roadway support body load, reveals the variation law of the coal pillar or filling support body vertical load with the change of the top cutting height and angle. The optimal top cutting parameter range is preliminarily calculated.

[0030] The numerical simulation calculation is based on the results obtained by field investigation, geomechanics test, theoretical model calculation, etc. A two-dimensional or three-dimensional discrete element numerical simulation model is established, the numerical model calculation under different top cutting heights and angles is carried out, and the roadway surrounding rock deformation, solid coal side stress evolution law, and coal pillar or roadway filling support body stress evolution law are comprehensively analyzed. Taking the minimum vertical load of the coal pillar or roadway support body, the minimum peak value of the solid coal side support pressure, and the minimum displacement and stress peak value of the roadway surrounding rock as the evaluation and analysis standards, the best top cutting parameter combination is obtained.

[0031] The field engineering experiment verified that the above-mentioned advanced top cutting parameter combination was applied to the advanced top cutting project of the mining roadway in the underground working face of the coal mine, and the mine pressure data was monitored on site to provide feedback and fine-tune the above-mentioned top cutting parameters.

[0032] Example 1 This embodiment provides a method for determining parameters of advanced controllable top cutting, taking a coal mine in northern Shaanxi as an example: 1. On-site investigation of project overview: A detailed on-site investigation was conducted on the working face of a thick coal seam with a hard roof in the mine. The geological mining information such as coal seam depth, thickness, roof and floor lithology, coal seam inclination, geological structural conditions, as well as working face layout parameters such as working face dip length and advance length were collected to obtain the working face layout diagram (see Figure 2a ) and the comprehensive histogram of drilling holes on the working face (see Figure 2b ).

[0033] 2. In-situ geomechanical testing: When the working face is not mined yet, select appropriate measuring points to carry out in-situ geomechanical testing, including observation of the roof surrounding rock and the side coal structure (see Figure 3a ), tunnel roof surrounding rock and coal wall strength test (see Figure 3b ) and geostress testing (see Figure 3c The physical and mechanical parameters of the coal and rock mass and the distribution of the ground stress field are obtained through methods such as core drilling and in-situ observation.

[0034] 3. Theoretical analysis of goaf roof thickness / thinness: According to the results of geomechanical tests and the applicable conditions of thick / thin plates, it was determined that the subsidence deformation of the goaf roof of the mine was consistent with the applicable conditions of thin plate theoretical analysis. Therefore, a thin plate theoretical analysis model of the hard basic roof of the working face was established. According to the changes in the support conditions of the goaf roof during the mining process of the working face, a thin plate theoretical mechanical model under various boundary conditions was established, including two working conditions: cutting the roof and not cutting the roof. Generally, it is: four-side fixed support (see Figure 4a ), three sides fixed and one side free (see Figure 4b ), three sides are fixed and one side is simply supported (see Figure 4c ), two sides are fixed, one side is simply supported, and the other side is free (see Figure 4d), which correspond to the working conditions of the goaf roof not yet collapsed under the condition of no top cutting, the working conditions of the goaf roof initially collapsed under the condition of no top cutting, the working conditions of the goaf roof not collapsed under the condition of top cutting, and the working conditions of the goaf roof initially collapsed under the condition of top cutting, as shown in Figure 4. Considering factors such as the thickness, strength, and boundary conditions of the roof, the deflection and bending moment distribution of the roof are calculated using the principle of minimum potential energy. According to the maximum tensile stress fracture theory, the initial pressure step and the periodic pressure step are predicted. The changes in the mechanical behavior of the roof after the advance top cutting of the working face mining tunnel are analyzed, including the deflection, bending moment distribution, and fracture step, to reveal the influence of top cutting on the stability of the roof. Taking the four-sided fixed boundary condition as an example, the deflection calculation process is as follows: Boundary conditions:

[0035]

[0036] Where: a, b are the side lengths of the thin plate; According to the Ritz method, the deflection surface equation of the four-side clamped elastic thin plate is:

[0037] Where: A mn —Undetermined coefficients; m, n—deformation order.

[0038] According to the principle of minimum potential energy, the potential energy of the four-side clamped thin plate system consists of elastic potential energy and external force potential energy:

[0039] Elastic potential energy represents the energy stored in a thin plate under bending:

[0040] After substituting the deflection function, the second-order partial derivatives of x and y are calculated:

[0041] Substituting the second-order derivative into U yields:

[0042] External potential energy is derived from uniformly distributed load cause:

[0043] Substituting into the deflection function:

[0044] make: get:

[0045] Solve to get the unknown coefficient Amn :

[0046] A mn Substituting the deflection equation back into the original equation, the deflection equation of the thin plate with four edges clamped can be obtained:

[0047] According to the above formula, the deflection distribution of the top plate at different advancing distances is calculated as shown in Figure 5a-5e .

[0048] According to the internal force bending moment calculation formula of elastic mechanics:

[0049] Substituting the second-order derivative of the deflection equation with respect to x and y into the bending moment equation, the following equation is obtained:

[0050] According to the above formula, the bending moment diagrams of the thin plate with four edges clamped in the x and y directions are made, as shown in Figure 6a , Figure 6b .

[0051] Using the above derivation process, the conditions of three edges clamped boundary-one edge free boundary, three edges clamped boundary-one edge simply supported boundary, two edges clamped boundary-one edge simply supported boundary-one edge free boundary can be solved in turn, that is, the deflection and bending moment distribution of the goaf roof under the conditions of initial caving of the goaf roof under the condition of not cutting the top, the goaf roof not yet caving under the condition of cutting the top, and the initial caving of the goaf roof under the condition of cutting the top, and then the initial weighting step distance and periodic weighting step distance of the goaf roof after using the advanced cutting top measure are predicted.

[0052] 4. Theoretical model analysis of vertical load of coal pillar or filling body: According to the results of geological exploration, based on the rock block separation method and the "long-short" masonry beam theory, a vertical load transfer mechanical model of coal pillar or roadside support body is established (see Figure 7a ), which reveals the vertical load transfer process of roof-coal pillar (or roadside filling body)-floor, analyzes the quantitative relationship between cutting height, cutting angle and vertical load of coal pillar or roadside support body, and obtains the optimal cutting parameters. The analysis process is as follows: (1) Basic roof load: the basic roof load mainly comes from two aspects, one is the transfer load, and the other is the self-weight of key block:

[0053] In the formula: K G —load transfer coefficient between rock strata; H f —overburden height; γ f —overburden bulk density; L—length of basic roof key block B1; Hj —Height of basic top key block B1; γ j —Body weight of basic top key block B1 rock.

[0054] After the basic roof breaks, the key block B1 of the basic roof, the rock block B2 between the working face and the goaf that has not reached a stable state, and the rock block C that has broken and sunk and stabilized in the goaf form a masonry beam structure. At this time, there is a mechanical relationship of friction and horizontal thrust between the rock blocks B1, B2, and C. The load transmitted by the overlying rock strata and its own weight are appropriately reduced during the structural balance process. By introducing the masonry beam calculation formula, the force exerted by the key block B1 on the direct roof can be obtained:

[0055] Where: i—block size of key block B1; θ1—rotation angle of key block B1, —Internal friction angle of basic top rock; Step d2: Directly top the structure and apply force to it. After the top is cut, a short-arm beam structure is formed on the goaf side. Ignore the bending moment caused by the weight of the rock within the hanging distance and directly consider its weight as the direct top load. The result is:

[0056] Where: P Z —Direct top load; H Z —direct top height; γ z —Body weight of the immediate top rock layer; b—Effective supporting area of ​​the support body; L P —blasthole length, a—cutting angle; H q —top cutting height; The hinged structure formed after the direct roof is cut off can be regarded as a short masonry beam. The force exerted by the direct roof on the coal pillar below is calculated by the following formula:

[0057] Where: θ—rotation angle of short masonry beam.

[0058] According to the mechanical parameters of the coal rock mass in the working face of the mine, the bulk density of the overlying rock layer is 25kN / m 3 The basic top rock density is 26.5kN / m 3 , direct top density 26kN / m 3 , the coal seam bulk density is 14kN / m 3 Rock expansion coefficient Take 1.4, the working face recovery rate is 0.95, and the coal body expansion coefficient Take 1.4. During the mining process of the working face, the average periodic pressure step distance is 32m, the overlying rock strata on the working face roof are sandy mudstone, fine-grained sandstone, mudstone, etc., the rock internal friction angle is 25°, and the load transfer coefficient between rock layers is Take 0.63, the key block B1 rotation angle θ is 5°, and the direct top rotation angle is the same as the basic top rotation angle. Based on the above conditions, the influence of the two factors of top cutting height and top cutting angle on the vertical load of coal pillar or filling body are analyzed respectively. The results are as follows Figure 7b 、 Figure 7c It is preliminarily determined that the optimal cutting parameters for this embodiment are a cutting height of 15m and a cutting angle of 75°.

[0059] 5. Numerical simulation analysis: Based on the basic information of the field investigation and the results of in-situ geomechanical tests, a two-dimensional block discrete element numerical model was established, such as Figure 8 As shown. Calculate the stress distribution and evolution law of the solid coal ridge of the working face, the stress evolution law of the coal pillar or roadside filling body, and the displacement evolution law of the roadway surrounding rock under the above-mentioned different cutting parameters. The specific steps are as follows: Using the two-dimensional block discrete element numerical simulation software - UDEC, a numerical analysis model with a length of 200m and a height of 124m was established. A boundary stress of 10.15MPa was applied to the upper surface of the model, which was equivalent to the uniformly distributed load generated by the deadweight of the overlying rock strata. The left and right boundaries of the model are support boundary conditions, and the bottom boundary is a zero displacement boundary condition. The blocks in the model adopt the Moore-Coulomb constitutive model, and the contact surface adopts the Coulomb slip model. The two variables of the top cutting angle and the top cutting height are controlled separately, and a certain top cutting angle and top cutting height joint surface are set in advance in the numerical simulation model. Under different top cutting heights and top cutting angles, the collapse of the goaf roof and its overlying rock strata and the stability of the tunnel surrounding rock are analyzed, and the numerical simulation experiments are carried out according to the following scheme: (1) The top cutting height is set at 15m. The collapse morphology of the overlying rock strata in the goaf and the displacement and stress evolution of the surrounding rock in the tunnel are analyzed under five conditions: top cutting angles of 90°, 80°, 75°, 70°, and 60°.

[0060] (2) The cutting angle is set to 75°, and the collapse morphology of the overlying rock strata in the goaf and the evolution law of the stress and displacement of the tunnel surrounding rock are analyzed under five conditions of cutting heights of 11m, 13m, 15m, 17m and 19m.

[0061] Numerical simulation solution calculation process: model establishment → stress balance → 11211 transport tunnel excavation → top cutting → 11211 working face excavation → 11209 transport tunnel excavation → calculation balance → output results.

[0062] Partial calculation results under two schemes: The collapse shape of the overlying rock strata in the goaf is as follows: Figure 9a 、 9b As shown in the figure, the displacement of coal pillar (filling body), solid coal wall and surrounding rock of roadway roof and floor (see Figure 9c 、 Figure 9d ), as well as the vertical stress of the coal pillar (filling body) and the solid coal rib (see Figure 9e-9h ) are both minimal, representing the optimal topping parameter assessment indicator. This means both the tunnel surrounding rock deformation and the surrounding rock vertical stress are at their minimums. Analysis of the numerical simulation monitoring data and stress cloud maps ultimately determined the optimal topping parameters for this embodiment to be a topping height of 15m and a topping angle of 75°, consistent with the theoretical analysis results.

[0063] 6. On-site engineering experimental verification: Based on the theoretical analysis and numerical simulation results, an on-site top cutting implementation plan was formulated, including top cutting parameters (top cutting height 15m, top cutting angle 75°), drilling arrangement, charging method, etc. Figure 10 As shown in the figure, advanced blasting and roof cutting measures are implemented in the working face mining tunnels. Directional blasting technology is used, and drilling, charging, and detonation are carried out according to the designed parameters to achieve controlled roof cutting. During the roof cutting process, the deformation of the tunnel surrounding rock is monitored in real time, and the roof cutting parameters are adjusted based on the monitoring data to ensure the desired roof cutting effect.

[0064] Field monitoring data shows that the use of the advanced controllable roof cutting method of the present invention reduces the relative movement of the tunnel walls and roof and floor by 40% and 34%, respectively, effectively improving the control of the tunnel surrounding rock. Furthermore, the periodic pressure step distance calculated by the theoretical model analysis of the coal seam roof thin plate is consistent with the measured data of the field project, both being 20-25 meters. This verifies the effectiveness and reliability of the present invention.

Claims

1. A method for determining parameters of advanced controllable top cutting of thick hard roof in coal mine working face, characterized in that: The steps include: Step a, on-site investigation of project overview: Go deep into the underground coal mining frontline to conduct comprehensive research on geological mining conditions and working face layout parameters to provide basic data for subsequent analysis; Step b, in-situ geomechanical testing: Through panoramic structural observation of coal rock mass through drilling, the distribution and development characteristics of coal rock mass structure in the mining working face and mining roadway are understood; through strength penetration testing of coal rock mass, the strength and deformation laws of coal rock mass are obtained; through hydraulic fracturing, the magnitude and distribution characteristics of ground stress are tested; Step c, theoretical analysis of goaf roof thickness / thinness: A mechanical model with multiple boundary conditions based on on-site conditions was established. Through plate theory calculations, the distribution of roof deflection and bending moment, as well as their changing patterns, were obtained as the mining distance increased and the exposed area continued to increase. Step d, theoretical analysis of vertical loads on coal pillars or filling bodies: A mechanical model of vertical load transfer between the roof, coal pillar, or backfill, and floor of a mining roadway based on the rock separation method was established. The quantitative relationship between the roof cutting height, the roof cutting angle, and the load on the coal pillar or other roadway support structures was analyzed. The variation pattern of the vertical load on the coal pillar or backfill support structure with the change of the roof cutting height and the roof cutting angle was revealed, and the range of the roof cutting parameters was preliminarily calculated. Step e, numerical simulation calculation: Establish a two-dimensional or three-dimensional discrete element numerical simulation model. By carrying out numerical model calculations under different top cutting heights and angles, comprehensively analyze the deformation of the tunnel surrounding rock, the stress evolution law of the solid coal wall, and the stress evolution law of the coal pillar or roadside filling support, and obtain the top cutting parameter combination according to the evaluation and analysis standards; Step f, engineering test verification: The above-mentioned advanced top cutting parameter combination is applied to the advanced top cutting project of the mining roadway in the underground working face of the coal mine. The mine pressure data is monitored on site, and the above-mentioned top cutting parameters are fine-tuned after feedback.

2. A method for determining parameters of advanced controllable top cutting of thick hard roof in coal mine working face according to claim 1, characterized in that: The geological mining conditions described in step a include coal seam burial depth, thickness, roof and floor lithology and coal seam inclination, and geological structural conditions; the working face layout parameters are working face dip length and advance length.

3. A method for determining parameters of advanced controllable top cutting of thick hard roof in coal mine working face according to claim 1 or 2, characterized in that: Step c also includes: determining the distribution characteristics of tensile stress in the roof based on the relationship between bending moment and tensile stress, selecting the rock fracture criterion, comparing the relationship between the tensile stress of the roof and its tensile strength, calculating the roof fracture step, and further predicting the deflection and bending moment distribution characteristics of the roof after taking the top cutting measure, accurately revealing the evolution law of the roof stability.

4. A method for determining parameters of advanced controllable top cutting of thick hard roof in coal mine working face according to claim 3, characterized in that: The evaluation and analysis criteria described in step e are: minimum vertical load of coal pillars or roadside support bodies, minimum peak value of support pressure of solid coal ribs, and minimum displacement and peak value of roadway surrounding rock.

5. A method for determining parameters of advanced controllable top cutting of thick hard roof in coal mine working face according to claim 3 or 4, characterized in that: The various boundary conditions described in step c include: Four-side fixed support corresponds to the working condition where the roof of the goaf has not collapsed under the condition of no roof cutting; three-side fixed support and one side free corresponds to the working condition where the roof of the goaf has collapsed for the first time under the condition of no roof cutting; three-side fixed support and one side simply supported corresponds to the working condition where the roof of the goaf has not collapsed under the condition of cutting the roof; two-side fixed support, one side simply supported and one side free corresponds to the working condition where the roof of the goaf has collapsed for the first time under the condition of cutting the roof.

6. A method for determining parameters of advanced controllable top cutting of thick hard roof in coal mine working face according to claim 5, characterized in that: The calculation process described in step d is as follows: In step d1, the basic top load comes from two main sources: the transfer load and the deadweight of the key block. Where: K G —Load transfer coefficient between rock layers; H f —height of overlying rock layer; f —density of overlying rock; L—length of basic top key block B1; H j —Height of basic top key block B1; γ j —Body weight of rock of basic top key block B1; After the basic roof breaks, the key block B1 of the basic roof, the rock block B2 between the working face and the goaf that has not reached a stable state, and the rock block C that has broken and sunk and stabilized in the goaf form a masonry beam structure. At this time, there is a mechanical relationship of friction and horizontal thrust between the rock blocks B1, B2, and C. The load transmitted by the overlying rock strata and its own weight are appropriately reduced during the structural balance process. By introducing the masonry beam calculation formula, the force exerted by the key block B1 on the direct roof can be obtained: Where: i—block size of key block B1; θ1—rotation angle of key block B1, —Internal friction angle of basic top rock; Step d2: Directly top the structure and apply force to it. After the top is cut, a short-arm beam structure is formed on the goaf side. Ignore the bending moment caused by the weight of the rock within the hanging distance and directly consider its weight as the direct top load. The result is: Where: P Z —Direct top load; H Z —direct top height; γ z —Body weight of the immediate top rock layer; b—Effective supporting area of ​​the support body; L P —blasthole length, a—cutting angle; H q —top cutting height; The hinged structure formed after the direct roof is cut off can be regarded as a short masonry beam. The force exerted by the direct roof on the coal pillar below is calculated by the following formula: Where: θ—rotation angle of short masonry beam.

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