Hard roof extra-thick impact coal seam risk evaluation method

Abstract

The invention relates to the technical field of coal mining, in particular to a hard roof extra-thick impact coal seam risk evaluation method. Comprises: identifying a target layer; carrying out regional division on the hard roof; defining a linear equation for obtaining a stress component, and providing a basis for solving the linear equation of the main stress and the maximum shear stress; using a boundary linear equation to define the deflection and the corner at the node; defining a linear equation of the principal stress and the maximum shear stress when the medium-thickness plate is possibly subjected to shear or tensile failure; displaying an elastic energy density distribution rule on a plane; by comparing the elastic energy density of the hard roof under different rock stratum strengths, the danger of the hard roof extra-thick impact coal seam is quantitatively analyzed and evaluated. According to the method, the target layer is sequentially recognized, the model is constructed, the initial fracture energy accumulation and dispersion rule of the hard roof of the extra-thick coal seam in the coal mining process is obtained, finally, the initial fracture energy accumulation and dispersion rule is compared with the maximum approximate disaster energy for judgment, risk evaluation and early prediction are conducted for prevention and control, and mine earthquake disasters are controlled from the source.

Description

Technical Field

[0001] The present invention relates to the technical field of coal mining, and specifically provides a method for evaluating the risk of a very thick impact coal seam with a hard roof. Background Art

[0002] In recent years, as the shallow coal resources are on the verge of exhaustion, most mining areas have gradually entered deep mining. Compared with shallow mining, the geological conditions and stress environment in deep mining are more complex, the frequency and intensity of rock burst disasters have increased sharply, and serious and major rock burst accidents occur frequently, seriously affecting the safe and efficient exploitation of coal resources.

[0003] In recent years, in the aspect of rock burst risk assessment, many scholars have carried out a lot of explorations and proposed some rock burst risk assessment methods based on different mathematical and mechanical models. However, the current geological rock burst risk assessment methods only consider the influence of the physical and mechanical properties of coal and rock masses and the height and thickness of hard rock layers on the roof rock burst risk, and do not fully consider the influence of the overlying rock structure type, key layer fracture movement, etc. on the rock burst risk. Therefore, there is an urgent need for a risk assessment method that can accurately evaluate the risk of a very thick impact coal seam with a hard roof. Summary of the Invention

[0004] To solve at least one technical problem in the background art, the present invention provides a method for evaluating the risk of a very thick impact coal seam with a hard roof, which sequentially identifies the target layer, constructs a model, calculates the law of energy accumulation and dissipation during the initial fracture of the very thick coal seam hard roof during coal mine mining, and finally compares it with the maximum disaster-causing energy for judgment to conduct risk assessment, predict in advance for prevention and control, and achieve the control of mine tremor disasters from the source.

[0005] To achieve the above object, the present invention provides a method for evaluating the risk of a very thick impact coal seam with a hard roof, including the following steps:

[0006] Step S1: Identify the target layer;

[0007] Step S2: Divide the hard roof into regions, where the suspended roof region is region ABCD and the elastic region is ABCD - A 1 B 1 C 1 D 1 ;

[0008] Step S3: Divide the hard roof into two mutually perpendicular x and y directions, and mark discrete points, with the distance between adjacent discrete points being α; taking the center point (i, j) as the base point, in the x and y directions, expand the deflection w and rotation angle of the hard roof, and define the deflection w and rotation angle Relationship equation; substituting the above equations into the control equation, stress equation, boundary equation, and failure equation of the hard roof to obtain the corresponding system of linear algebraic equations; obtaining the deflection w and rotation angle of node (i, j). Furthermore, solve the corresponding stress.

[0009] Step S4: Define the principal moment and shear force values of node (i, j), and then obtain the linear equation of its stress components, providing a basis for solving the linear equations of principal stress and maximum shear stress.

[0010] Step S5: Use the boundary linear equation to reduce the number of parameters, making the system of linear equations have a unique solution, so as to solve the deflection and rotation angle at the node.

[0011] Step S6: Define the linear equations of principal stress and maximum shear stress when the medium-thick plate may undergo shear or tensile failure.

[0012] Step S7: Derive the elastic energy accumulated at node (i, j) during the initial fracture of the hard roof, and integrate the elastic density formula along the thickness direction of the hard roof, so as to show the distribution law of elastic energy density on the plane.

[0013] Step S8: According to the system of linear equations established above, it can be known that there are at most 9 nodes with unknown deflection and rotation angle in any system of linear equations. By establishing a 9-point system of linear equations for each node with unknown deflection and rotation angle, an algebraic system of equations is formed. By solving the system of equations, the deflection solutions of each node can be obtained; use the Sparse function in MATLAB software to construct a coefficient sparse matrix to form an algebraic system of equations, so as to obtain the deflection and rotation angle values of each unknown node; substitute the deflection and rotation angle values of the node into the formula to obtain the elastic energy density of the hard roof at node (i, j). Subsequently, input the coordinates of the node and the corresponding elastic energy density into the commercial software Surfer to display the elastic energy of the hard roof of the working face.

[0014] Step S9: By comparing the elastic energy density of the hard roof under different rock strengths, quantitatively analyze and evaluate the danger of the extremely thick impact coal seam of the hard roof.

[0015] Furthermore, in step S1, the method for identifying the target layer is as follows:

[0016] Arrange geological radar detection lines on the working face, scan the rock strata, and obtain the propagation characteristics of electromagnetic waves in the rock strata; identify the reflection wave characteristics of the rock strata, process the received signal using the finite-difference time-domain algorithm, generate detailed data on the coal seam thickness, construct a three-dimensional model of the working face to analyze the geological radar image, and combine the geological conditions and rock mechanics parameters to determine the position of the target layer.

[0017] Further, in step S3, the linear form of the control equation for the initial fracture in the suspended roof area ABCD is a system of equations with 9 nodes and 27 parameters:

[0018]

[0019] Among them, α is the distance between adjacent discrete points; w is the deflection of the hard roof; is the rotation angle of the hard roof; are the flexural rigidity and shear rigidity of the hard roof respectively; E, h, and μ are the elastic modulus, thickness, and Poisson's ratio of the hard roof respectively; q is the external force load on the hard roof;

[0020] The linear form of the control equation for the initial fracture of the medium-thick plate in the elastic region of area ABCD-A 1 B 1 C 1 D 1 is also a system of equations with 9 nodes and 27 parameters:

[0021]

[0022] Further, in step S4, the linear equations for the stress components σ x , σ y and σ z are as follows:

[0023]

[0024] Further, in step S5, when the hard roof is initially fractured, it satisfies the following equations on the suspended roof boundary ABCD:

[0025]

[0026] The boundary conditions of the mechanical model for the initial fracture of the hard roof are:

[0027]

[0028] Further, in step S7, the elastic density formula is integrated along the thickness direction of the hard roof, so as to show the distribution law of the elastic energy density on the plane. Its calculation formula is as follows:

[0029]

[0030] Further, in step S9, the maximum value of the elastic energy density under different rock strengths is regarded as the maximum energy density value released when the rock layer fractures under specific conditions, that is, the maximum disaster-causing energy density value; under specific conditions, the critical value of the rock layer fracture is related to the average thickness, width, elastic modulus, Poisson's ratio, tensile strength, etc. of the coal seam, which is called the critical energy density value. The formula is Given;

[0031] Wherein, E is the elastic modulus of the rock stratum, L is the width of the working face, M is the average thickness of the coal seam, v is the Poisson's ratio of the rock stratum, and σ t is the tensile strength of the rock stratum;

[0032] If the maximum disaster-causing energy density value is greater than or equal to the critical energy density value, it is considered that the rock stratum will break; if the maximum disaster-causing energy density value of the rock stratum is less than the critical energy density value, it is considered that the rock stratum will not break, so as to evaluate the danger of the hard roof and extra-thick impact coal seam.

[0033] The beneficial effects of the present invention are as follows:

[0034] The present invention provides a method for evaluating the danger of a hard roof and extra-thick impact coal seam, which is used for evaluating the danger of a hard roof and extra-thick impact coal seam. It sequentially identifies the target layer, constructs a model, obtains the law of energy accumulation and dissipation of the first break of the extra-thick coal seam hard roof during coal mine exploitation, and finally compares it with the maximum disaster-causing energy for judgment to conduct a danger evaluation, predict in advance for prevention and control, and achieve the control of mine tremor disasters from the source. Brief Description of the Drawings

[0035] Figure 1 is the schematic diagram of on-line detection of ground penetrating radar of the present invention;

[0036] Figure 2 is the mechanical model diagram of the first break of the hard roof of the present invention;

[0037] Figure 3 is the schematic diagram of node numbering;

[0038] Figure 4 is the schematic diagram of the energy accumulation law of the hard roof. Detailed Embodiments

[0039] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0040] It should be noted that the terms "first", "second", etc. in the description, claims and the above-mentioned drawings of this application are used to distinguish similar objects, and do not necessarily describe a specific order or sequence. It should be understood that the data used in this way can be interchanged under appropriate circumstances, so as to implement the embodiments of this application described herein. In addition, the terms "comprising" and "having" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device that includes a series of steps or units does not necessarily limit to those steps or units clearly listed, but may include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0041] In this application, the orientation or positional relationship indicated by the terms "upper", "lower", "left", "right", "front", "rear", "top", "bottom", "inner", "outer", "middle", "vertical", "horizontal", "lateral", "longitudinal", etc. is based on the orientation or positional relationship shown in the drawings. These terms are mainly used to better describe this application and its embodiments, and are not used to limit that the indicated device, element or component must have a specific orientation, or be constructed and operated in a specific orientation.

[0042] Moreover, in addition to being used to represent the orientation or positional relationship, some of the above terms may also be used to represent other meanings. For example, the term "upper" may also be used to represent a certain attachment relationship or connection relationship in some cases. For those of ordinary skill in the art, the specific meanings of these terms in this application can be understood according to specific circumstances.

[0043] In addition, the terms "installed", "set up", "provided with", "connected", "linked", "socketed" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral structure; it can be a mechanical connection or an electrical connection; it can be directly connected, or indirectly connected through an intermediate medium, or there is an internal connection between two devices, elements or components. For those of ordinary skill in the art, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0044] To achieve the above object, the present invention provides a method for evaluating the risk of a hard roof and extra-thick impact coal seam, including the following steps:

[0045] Step S1: Identify the target layer: Arrange a geological radar detection line on the working face, scan the rock formation, and obtain the propagation characteristics of electromagnetic waves in the rock formation; identify the reflection wave characteristics of the rock formation, perform finite-difference time-domain (FDTD) algorithm processing on the received signal, generate detailed data of the coal seam thickness, construct a three-dimensional model of the working face to analyze the geological radar image, and combine the geological conditions and rock mechanics parameters to determine the position of the target layer.

[0046] Step S2: Assume that the rock stratum supporting the hard roof undergoes elastic deformation under the extrusion of the hard roof, and at the same time, the hard roof bears a uniform load. The hard roof is divided into regions, where the cantilever roof region is region ABCD (Ω 1 region, with length and width 2b×a), and the elastic region is ABCD - A 1 B 1 C 1 D 1 (Ω 2 region).

[0047] Step S3: Divide the hard roof into two mutually perpendicular x and y directions, and mark discrete points. The distance between adjacent discrete points is α; taking the center point (i,j) as the base point, in the x and y directions, expand the deflection w and rotation angle of the hard roof, and define the relationship equations of the deflection w and rotation angle ; substitute the above equations into the control equation, stress equation, boundary equation, and failure equation of the hard roof to obtain the corresponding system of linear algebraic equations; obtain the deflection w and rotation angle of node (i,j), and then solve the corresponding stress;

[0048] The linear form of the control equation for the initial fracture in the cantilever roof region ABCD (Ω 1 region) is a system of equations with 9 nodes and 27 parameters:

[0049]

[0050] The linear form of the control equation for the initial fracture of the medium-thick plate in the elastic region of region ABCD - A 1 B 1 C 1 D 1 (Ω 2 region) is also a system of equations with 9 nodes and 27 parameters:

[0051]

[0052] Step S4: Define the principal moment and shear force values of node (i,j), and then obtain the linear equations of its stress components, providing a basis for solving the linear equations of the principal stress and maximum shear stress;

[0053] The linear equations of the stress components σ x , σ y and σ z of the medium-thick plate are as follows:

[0054]

[0055] Step S5: Use the boundary linear equation to reduce the number of parameters, so that the linear equations have a unique solution, enabling the deflection and rotation angle at the nodes to be solved;

[0056] When the hard roof initially breaks, it satisfies the following equation on the overhanging boundary ABCD:

[0057]

[0058] The boundary conditions of the mechanical model for the initial breakage of the hard roof are:

[0059]

[0060] Step S6: Define the linear equations for the principal stress and the maximum shear stress when the medium-thick plate may undergo shear or tensile failure;

[0061] Step S7: According to the energy calculation method, derive the elastic energy accumulated at the node (i,j) during the initial breakage of the hard roof, and integrate the elastic density formula along the thickness direction of the hard roof, so as to display the distribution law of the elastic energy density on the plane;

[0062] Integrate the elastic density formula along the thickness direction of the hard roof, so as to display the distribution law of the elastic energy density on the plane. Its calculation formula is as follows:

[0063]

[0064] Step S8: According to the established linear equations above, it can be known that there are at most 9 nodes with unknown deflection and rotation angle in any linear equation set. By establishing a 9-point linear equation set for each node with unknown deflection and rotation angle, an algebraic equation set is formed. By solving the equation set, the deflection solution of each node can be obtained; Use the Sparse function in MATLAB software to construct a coefficient as a sparse matrix to form an algebraic equation set, so as to obtain the deflection and rotation angle values of each unknown node; Substitute the deflection and rotation angle values of the nodes into the formula to obtain the elastic energy density at the node (i,j) of the hard roof. Subsequently, input the coordinates of the nodes and the corresponding elastic energy density into the commercial software Surfer to display the elastic energy of the hard roof of the working face;

[0065] Step S9: By comparing the elastic energy density of the hard roof under different rock stratum strengths, quantitatively analyze and evaluate the risk of the hard and extra-thick impact coal seam.

[0066] Regard the maximum value of the elastic energy density under different rock stratum strengths as the maximum energy density value released when the rock stratum breaks under specific conditions, that is, the maximum disaster-causing energy density value; Under specific conditions, the critical value of the rock stratum breakage is related to the average thickness, width, elastic modulus, Poisson's ratio, tensile strength, etc. of the coal seam, and is called the critical energy density value, which is given by the formula given;

[0067] Among them, E is the elastic modulus of the rock stratum, L is the width of the working face, M is the average thickness of the coal seam, v is the Poisson's ratio of the rock stratum, and σ t is the tensile strength of the rock stratum;

[0068] If the maximum disaster-causing energy density value is greater than or equal to the critical energy density value, it is considered that the rock stratum will break; if the maximum disaster-causing energy density value of the rock stratum is less than the critical energy density value, it is considered that the rock stratum will not break, so as to evaluate the danger of the extremely thick impact coal seam with hard roof.

[0069] The present invention sequentially identifies the target layer, constructs a model, calculates the law of energy accumulation and dissipation during the initial fracture of the extremely thick coal seam hard roof in the process of coal mine exploitation, and finally compares it with the maximum disaster-causing energy for judgment, conducts danger assessment, and predicts and prevents in advance to achieve the control of rock burst disasters from the source.

[0070] Embodiment

[0071] Taking the 8222 working face of Tashan Mine as an example, the law of elastic energy density accumulation during the initial fracture of the hard roof is calculated. The average thickness M of the coal seam in this working face is 6.09 m, the width L is 200 m; the thickness h of the overlying sandstone layer is 90 m, the initial fracture step distance is 750 m, the tensile strength σ t = 3.4 MPa, the elastic modulus E = 4 GPa, the Poisson's ratio v = 0.2. According to the key stratum theory, the overlying load q transferred to the hard roof is 0.79 MPa; the foundation stiffness k of the coal and rock mass in the mining load-bearing area is 1000 MN / m.

[0072] Step 1: Identify the target layer. As Figure 1 shown, arrange geological radar detection lines on the working face, scan the rock stratum, and obtain the propagation characteristics of electromagnetic waves in the rock stratum; identify the reflection wave characteristics of the rock stratum, process the received signal by the finite-difference time-domain algorithm (FDTD), generate detailed data of the coal seam thickness, construct a three-dimensional model of the working face to analyze the geological radar image, and combine the tensile strength of 3.4 MPa, the elastic modulus E = 4 GPa, and the Poisson's ratio v = 0.2 to determine that the target layer hard roof is located at 56.3 m above the overlying sandstone layer with a thickness of 90 m.

[0073] Step 2: Assume that the rock stratum supporting the roof undergoes elastic deformation under the extrusion of the hard roof, and at the same time the hard roof bears a uniform load. Divide the hard roof into regions, as Figure 2 shown, where Figure 2 (a) is the initial fracture model of the hard roof, where the cantilever roof area is the area ABCD (Ω 1 area, length and width 2b×a), and the elastic area is ABCD - A 1 B 1 C 1 D1 (Ω 2 region), while the overlying layer bears a uniform load, Figure 2 (b) shows the I-I and II-II profiles of the initial fracture of the hard roof;

[0074] Step 3: As Figure 3 shown, divide the hard roof into two mutually perpendicular x and y directions, and mark discrete points. The distance between adjacent discrete points is α = 1m; taking the center point (i, j) as the base point, in the x and y directions, for the hard roof's w, rotation angle perform Taylor expansion, and ignore higher-order small quantities, establish the relationship equation regarding the deflection w and rotation angle ; substitute the above equations into the control equation, stress equation, boundary equation, and failure equation of the hard roof to obtain the corresponding system of linear algebraic equations; solve for w and the rotation angle at node (i, j) and then solve for the corresponding stress.

[0075] The linear form of the control equation for the initial fracture in the suspended roof area ABCD within the (Ω 1 region) is a system of equations with 9 nodes and 27 parameters:

[0076]

[0077] Among them, α is the distance between adjacent discrete points; w is the deflection of the hard roof; is the rotation angle of the hard roof; are the flexural rigidity and shear rigidity of the hard roof respectively; E, h, and μ are the elastic modulus, thickness, and Poisson's ratio of the hard roof respectively; q is the external force load on the hard roof;

[0078] The linear form of the control equation within the elastic region of the initial fracture of the medium-thick plate in the area ABCD - A 1 B 1 C 1 D 1 (Ω 2 region) is also a system of equations with 9 nodes and 27 parameters:

[0079]

[0080] Step 4: Solve for the principal moment and shear force values at node (i, j), and then obtain the linear equations of its stress components, providing a basis for the solution of the principal stress and maximum shear stress linear equations.

[0081] Step 5: Use the boundary linear equation to reduce the number of parameters, making the system of linear equations have a unique solution, so as to be able to solve for the deflection and rotation angle at the node.

[0082] Step 6: Solve the difference equations of the principal stress and the maximum shear stress when the medium-thick plate may undergo shear or tensile failure.

[0083] Step 7: According to the calculation method of energy, deduce the elastic energy accumulated at the node (i,j) during the initial fracture of the hard roof, and integrate the elastic density formula along the thickness direction of the hard roof, so as to show the distribution law of elastic energy density on the plane.

[0084] Step 8: According to the established linear equations above, it can be known that there are at most 9 nodes with unknown deflections and rotations in any linear equation system. By establishing 9-point linear equations for each node with unknown deflections and rotations, an algebraic equation system is formed. By solving the equation system, the deflection solutions of each node can be obtained. Use the Sparse function in MATLAB software to construct a coefficient sparse matrix to form an algebraic equation system, so as to obtain the deflection and rotation values of each unknown node. Substitute the deflection and rotation values of the node into the formula to obtain the elastic energy density at the node (i,j) of the hard roof. Subsequently, input the coordinates of the node and the corresponding elastic energy density into the commercial software Surfer to display the elastic energy of the hard roof of the working face. As Figure 4 shown, the distribution law of the initial fracture elastic energy density of the sandstone layer is given when the rock layer strength is 3.4 MPa and the corresponding fracture step distance is 750 m.

[0085] Step 9: By calculating the elastic energy density of the hard roof under different rock layer strengths, the danger of the hard roof in the extra-thick impact coal seam can be quantitatively analyzed and evaluated.

[0086] Regard the maximum value of the elastic energy density under different rock layer strengths as the maximum energy density value released during the fracture of the rock layer under specific conditions, that is, the maximum disaster-causing energy density value. Under specific conditions, the critical value of the rock layer fracture is related to the average thickness, width, elastic modulus, Poisson's ratio, tensile strength, etc. of the coal seam, which is called the critical energy density value and is given by the formula where E is the elastic modulus of the rock layer, L is the width of the working face, M is the average thickness of the coal seam, v is the Poisson's ratio of the rock layer, and σ t is the tensile strength of the rock layer.

[0087] If the maximum disaster-causing energy density value is greater than or equal to the critical energy density value, it is considered that the rock layer will fracture; if the maximum disaster-causing energy density value of the rock layer is less than the critical energy density value, it is considered that the rock layer will not fracture, so as to evaluate the danger of the hard roof in the extra-thick impact coal seam.

[0088] As Figure 4 shown, the tensile strength of the hard roof is 3.4 MPa, its elastic energy accumulates a large amount near the two headings, and the maximum value of the elastic energy density is 0.90×10 5 J / m 2, that is, the maximum disaster-causing energy density value is 0.90×10 5 J / m 2 .

[0089] In the 8222 working face of Tashan Mine, the average thickness M of the coal seam in this working face is 6.09 m, the face width L of the working face is 200 m, the tensile strength σ t = 3.4 MPa, the elastic modulus E = 4 GPa, and the Poisson's ratio v = 0.2. Substituting into the formula Calculating, the critical energy density value can be obtained as 5.73×10 4 J / m 2 .

[0090] The maximum disaster-causing energy density value of 0.90×10 5 J / m 2 > the critical energy density value of 5.73×10 4 J / m 2 , and rock bursts will occur in the rock strata.

[0091] The above are only preferred embodiments of the present invention, and do not impose any limitation on the technical scope of the present invention. Therefore, any minor modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A method for evaluating the hazard of a hard roof and a very thick impact coal seam, characterized in that: The steps include: Step S1: identifying the target layer; Step S2: Divide the hard top plate into regions, wherein the suspended top region is region ABCD and the elastic region is region ABCD-A1B1C1D1; Step S3: Divide the hard top plate into two mutually perpendicular x and y directions, and mark the discrete points. The distance between adjacent discrete points is α; Taking the center point (i, j) as the base point, in the x and y directions, the disturbance w of the hard top plate, the rotation angle Expand and define the deflection w and rotation angle Relation equation; Substitute the above equation into the control equation, stress equation, boundary equation, and failure equation of the hard top plate to obtain the corresponding linear algebraic equation system; obtain the deflection w and rotation angle of the node (i, j) Then the corresponding stress is solved; Step S4: define the principal bending moment and shear force value of the node (i, j), and then obtain the linear equation of its stress component, which provides a basis for defining the solution of the linear equation of the principal stress and the maximum shear stress; Step S5: using the boundary linear equation to reduce the number of parameters so that the linear equation composition has a unique solution, thereby being able to solve the deflection and rotation angle at the node; Step S6: defining linear equations of principal stress and maximum shear stress when the medium and thick plate may fail in shear or tension; Step S7: deriving the elastic energy accumulated at the node (i, j) when the hard top plate is first broken, and integrating the elastic density formula along the thickness direction of the hard top plate, thereby showing the elastic energy density distribution law on the plane; Step S8: According to the linear equations established above, there are at most 9 nodes with unknown deflections and rotations in any linear equations. A 9-point linear equation system is established for each node with unknown deflection and rotation, and an algebraic equation system is constructed to obtain the deflection solution of each node. The Sparse function in MATLAB software is used to construct coefficients as a sparse matrix to form an algebraic equation system, and the deflection and rotation values ​​of each unknown node are obtained; the deflection and rotation values ​​of the node are substituted into the formula to obtain the elastic energy density of the hard roof at the node (i, j), and then the coordinates of the node and the corresponding elastic energy density are input into the commercial software Surfer to show the elastic energy of the hard roof of the working face; Step S9: By comparing the elastic energy density of the hard roof under different rock formation strengths, quantitative analysis and evaluation are performed on the danger of the hard roof and the extra-thick impact coal seam.

2. A method for evaluating the hazard of a hard roof and extra-thick impact coal seam as claimed in claim 1, characterized in that: In step S1, the method for identifying the target layer is as follows: A geological radar detection line is arranged on the working face to scan the rock strata and obtain the propagation characteristics of electromagnetic waves in the rock strata. The reflected wave characteristics of the rock strata are identified, and the received signals are processed using the time-domain finite difference algorithm to generate detailed data on the thickness of the coal seam. A three-dimensional model of the working face is constructed to analyze the geological radar images, and the location of the target layer is determined by combining the geological conditions and rock mechanics parameters.

3. A method for evaluating the hazard of a hard roof and extra-thick impact coal seam as claimed in claim 2, characterized in that: In step S3, the linear form of the control equation in the overhanging region ABCD is initially broken, which is a set of equations with 9 nodes and 27 parameters: Where α is the distance between adjacent discrete points; w is the disturbance of the hard top plate; The corners of the rigid top plate; are the bending stiffness and shear stiffness of the hard top plate respectively; E, h, μ are the elastic modulus, thickness and Poisson's ratio of the hard top plate respectively; q is the external force load on the hard top plate; The linear form of the governing equation for the initial fracture of a medium-thick plate in the elastic region of the region ABCD-A1B1C1D1 is also a set of equations with 9 nodes and 27 parameters:

4. A method for evaluating the hazard of a hard roof extra-thick impact coal seam as claimed in claim 1 or 3, characterized in that: In step S4, the stress component σ of the medium and thick plate x , σ y and σ z The linear equation is as follows:

5. A method for evaluating the hazard of a hard roof and extra-thick impact coal seam as claimed in claim 4, characterized in that: In step S5, at the initial break, the hard top plate satisfies the following equation on the hanging top boundary ABCD: The boundary conditions of the mechanical model of the first fracture of the hard roof are:

6. A method for evaluating the hazard of a hard roof and extra-thick impact coal seam as claimed in claim 5, characterized in that: In step S7, the elastic density formula is integrated along the thickness direction of the hard top plate to display the elastic energy density distribution law on the plane. The calculation formula is as follows:

7. A method for evaluating the hazard of a hard roof and extra-thick impact coal seam as claimed in claim 5, characterized in that: In step S9, the maximum value of elastic energy density under different rock formation strengths is regarded as the maximum energy density value released when the rock formation breaks under specific conditions, that is, the maximum disaster-causing energy density value; under specific conditions, the critical value of rock formation breaking is related to the average thickness, width, elastic modulus, Poisson's ratio, tensile strength, etc. of the coal seam, which is called the critical energy density value, which is given by the formula given; Among them, E is the elastic modulus of the rock formation, L is the width of the working face, M is the average thickness of the coal seam, v is the Poisson's ratio of the rock formation, σ t is the tensile strength of the rock formation; If the maximum disaster-causing energy density value is greater than or equal to the critical energy density value, it is considered that the rock formation will break; if the maximum disaster-causing energy density value of the rock formation is less than the critical energy density value, it is considered that the rock formation will not break, thereby evaluating the danger of the hard roof and extra-thick impact coal seam.

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