A method for identifying water inrush from coal seam floor

Abstract

The present invention discloses a method for identifying water inrush from a coal seam floor. A simplified stress model of a coal seam floor is established based on a semi-infinite theory. Based on the simplified stress model, the total stress component of the coal seam floor is obtained according to the coal seam depth, rock formation parameters, advance support pressure, original rock stress, floor gravity and confined water pressure, which is beneficial to improving the reliability of identifying water inrush channels from the coal seam floor. In addition, by using numerical simulation to verify the identification results, and determining the water inrush danger zone of the water inrush channel based on the verification results combined with microseismic monitoring, the advantages of the three methods of identifying water inrush channels based on rock formation parameters, numerical simulation and microseismic monitoring can be effectively integrated, thereby improving the identification accuracy of water inrush danger zones and providing a reliable basis for the prevention and control of water inrush disasters from coal seam floors.

Description

Technical Field

[0001] The invention relates to the field of exploration technology, and in particular to a method for identifying water inrush from a coal seam floor. Background Art

[0002] The key to achieving safe pressure mining is to recognize the destruction characteristics of the floor aquiclude under the combined effects of mine pressure and water pressure, and accurately identify the evolution of the floor water inrush channel during mining. At present, the research methods for the floor destruction characteristics are mainly divided into three categories: theoretical analysis, numerical simulation, and on-site monitoring. Theoretical analysis mainly uses the elastic mechanics thin plate theory to derive the destruction of the key layer of the floor, but most of them consider the water pressure as a uniformly distributed load with a certain length, and the reliability of this assumption remains to be discussed. In numerical simulation, the finite element method is used, which makes it difficult to simulate the initiation, expansion and penetration evolution of cracks in the floor water channel, and it is impossible to fully reflect the progressive destruction process of the surrounding rock. Conventional monitoring methods such as on-site mine pressure and floor destruction cannot overcome the limitations of time and space to conduct real-time monitoring and early warning in three-dimensional space, and it is even more difficult to perceive the internal micro-fractures and their evolution laws of the coal rock mass before the formation of the water inrush channel. In addition, the deformation and failure process of the floor aquiclude is affected by the heterogeneity of coal and rock, the redistribution of ground stress caused by excavation, and fluid-solid coupling. It is difficult to comprehensively evaluate the failure characteristics and evolution laws of the floor by using one or two methods. Summary of the invention

[0003] The technical problem to be solved by the present invention is: how to provide a method for identifying water inrush from coal seam floors that integrates advantages, so as to improve the accuracy of identifying water inrush danger zones and provide a reliable basis for preventing and controlling water inrush disasters from coal seam floors.

[0004] In order to solve the above technical problems, the present invention provides a method for identifying water inrush from coal seam floor, which comprises:

[0005] Obtain the coal seam depth and the rock parameters of the coal seam floor;

[0006] Based on the semi-infinite theory, a simplified force model of the coal seam floor is established, wherein the upper part of the coal seam floor is subject to the advance support pressure and the original rock stress, the coal seam floor is subject to its own floor gravity, and the lower part of the coal seam floor is subject to the pressure of the pressurized water;

[0007] Based on the simplified force model, the total stress component of the coal seam floor is obtained according to the coal seam depth, the rock formation parameters, the advance support pressure, the original rock stress, the floor gravity and the confined water pressure;

[0008] Identifying the water inrush channel of the coal seam floor based on the total stress component and the failure criterion of the floor;

[0009] Numerical simulation is used to verify the identification results, and based on the verification results combined with microseismic monitoring, the water inrush hazard area of ​​the water inrush channel is determined.

[0010] Optionally, obtaining the rock parameters of the coal seam floor includes: obtaining the pressure step distance, elastic zone length, plastic zone length, floor thickness, rock density and stress coefficient of the coal seam floor.

[0011] Optional,

[0012] Based on the simplified force model, according to the coal seam depth, the rock formation parameters, the advance support pressure, the original rock stress, the floor gravity and the confined water pressure, the total stress component of the floor of the coal seam is obtained, including:

[0013] Based on the simplified force model under the influence of the advance support pressure, the first stress component caused by the advance support pressure on the coal seam floor is calculated according to the coal seam depth, the pressure step distance of the coal seam floor, the elastic zone length, the plastic zone length, the floor thickness, the rock mass density and the stress coefficient;

[0014] Based on the simplified stress model under the influence of the original rock stress, according to the coal seam depth and the rock mass density, calculate the second stress component caused by the original rock stress on the coal seam floor;

[0015] Based on the simplified force model under the influence of the confined water pressure, calculating the third stress component caused by the confined water pressure on the coal seam floor;

[0016] Based on the simplified force model under the influence of the floor gravity, according to the Lame constant, the coal seam depth and the rock mass density, calculate the fourth stress component caused by the floor gravity on the coal seam floor;

[0017] Based on the first stress component, the second stress component, the third stress component and the fourth stress component, the total stress component of the floor of the coal seam is obtained.

[0018] Optionally, based on the simplified force model under the influence of the advance support pressure, according to the coal seam depth, the pressure step distance of the coal seam floor, the elastic zone length, the plastic zone length, the floor thickness, the rock mass density and the stress coefficient, the first stress component caused by the advance support pressure on the coal seam floor is calculated, including:

[0019] Simplifying the advance support pressures in the plastic zone and the elastic zone into triangular loads respectively;

[0020] According to the coal seam depth, the pressure step distance of the coal seam floor, the elastic zone length, the plastic zone length, the floor thickness, the rock mass density and the stress coefficient, respectively calculate the stress components caused by the triangular load in the plastic zone and the triangular load in the elastic zone on the coal seam floor;

[0021] The first stress component caused by the advance support pressure on the coal seam floor is calculated based on the stress components caused by the triangular load in the plastic zone and the triangular load in the elastic zone on the coal seam floor.

[0022] Optionally, based on the simplified stress model under the influence of the original rock stress, according to the coal seam depth and the rock mass density, calculating the second stress component caused by the original rock stress on the coal seam floor includes:

[0023] Simplifying the original rock stress in the empty area into a uniformly distributed rectangular load;

[0024] The second stress component caused by the original rock stress on the coal seam floor is calculated according to the coal seam depth and the rock mass density.

[0025] Optionally, based on the simplified force model under the influence of the confined water pressure, calculating the third stress component caused by the confined water pressure on the coal seam floor includes:

[0026] Simplifying the confined water pressure into a semi-infinite uniformly distributed load and obtaining the confined water pressure value;

[0027] Establishing a volume strain equation based on the rock mass displacement and establishing an equilibrium equation of the rock mass displacement;

[0028] Based on the volume strain equation and the equilibrium equation of the rock mass displacement, the third stress component caused by the uniformly distributed load on the coal seam floor is calculated.

[0029] Optionally, obtaining the total stress component of the floor of the coal seam based on the first stress component, the second stress component, the third stress component and the fourth stress component includes:

[0030] According to the stress superposition principle of elasticity theory, based on the first stress component, the second stress component, the third stress component and the fourth stress component, the total stress component of the coal seam floor is obtained.

[0031] Optionally, identifying the water inrush channel of the coal seam floor based on the total stress component of the floor and the failure criterion includes:

[0032] The water inrush channel of the coal seam floor is identified based on the total stress component of the floor and the Coulomb modified failure criterion.

[0033] Optionally, the method for identifying water inrush from coal seam floors further includes:

[0034] Numerical simulation of stress wave propagation process and output of acoustic emission graph and stress contour map; and,

[0035] A microseismic monitoring device is arranged in the tunnel based on the verification result, so as to collect microseismic signals by using the microseismic monitoring device.

[0036] Optionally, the method of verifying the identification result by numerical simulation and determining the water inrush hazard zone of the water inrush channel based on the verification result in combination with microseismic monitoring includes:

[0037] Verifying the identification result according to the acoustic emission graph and the stress cloud graph;

[0038] When the verification is consistent, the water inrush hazard zone of the water inrush channel is determined based on the microseismic signal.

[0039] Compared with the prior art, one or more embodiments of the above scheme may have the following advantages or beneficial effects:

[0040] The coal seam floor water inrush identification method of the present invention is applied, and a simplified stress model of the coal seam floor is established based on the semi-infinite theory. Based on the simplified stress model, the total stress component of the coal seam floor is obtained according to the coal seam depth, rock formation parameters, advance support pressure, original rock stress, floor gravity and confined water pressure, which is conducive to improving the reliability of identifying the coal seam floor water inrush channel. In addition, by using numerical simulation to verify the identification results, and determining the water inrush danger zone of the water inrush channel based on the verification results combined with microseismic monitoring, the advantages of the three methods of identifying the water inrush channel based on rock formation parameters, numerical simulation and microseismic monitoring can be effectively integrated, the identification accuracy of the water inrush danger zone can be improved, and a reliable basis can be provided for the prevention and control of water inrush disasters in the coal seam floor. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] The scope of the present disclosure may be better understood by reading the following detailed description of exemplary embodiments in conjunction with the accompanying drawings. The drawings included are:

[0042] Figure 1 A schematic flow chart of a method for identifying water inrush from a coal seam floor provided by an embodiment of the present invention is shown;

[0043] Figure 2 The schematic diagram of the structure of the coal mine working area is shown;

[0044] Figure 3 A schematic diagram of a two-dimensional coordinate system established at the interface between the coal seam floor and the coal seam provided by an embodiment of the present invention is shown;

[0045] Figure 4The schematic diagram of the force model of the coal seam floor under the advanced support pressure is shown;

[0046] Figure 5 A schematic diagram of a force model of a coal seam floor under the influence of pressurized water pressure provided by an embodiment of the present invention is shown;

[0047] Figure 6 A schematic diagram of a coal mine rock formation provided by an embodiment of the present invention is shown;

[0048] FIG7(1) shows a schematic diagram of acoustic emission of a coal seam floor provided by an embodiment of the present invention; FIG7(2) shows a partial enlarged diagram of a shear failure zone located to the left of a tensile failure zone in the schematic diagram of acoustic emission of a coal seam floor; FIG7(3) shows a partial enlarged diagram of a shear failure zone located to the right of a tensile failure zone in the schematic diagram of acoustic emission of a coal seam floor;

[0049] Figure 8 A microseismic monitoring system for real-time monitoring of microfracture information on the coal seam floor is shown;

[0050] FIG9(1) shows a contour map of vertical stress during initial pressure provided by a specific embodiment of the present invention; FIG9(2) shows a contour map of horizontal stress during initial pressure provided by a specific embodiment of the present invention; FIG9(3) shows a contour map of shear stress during initial pressure provided by a specific embodiment of the present invention;

[0051] Fig.10 A bottom plate damage diagram provided by a specific embodiment of the present invention is shown;

[0052] FIG11(1) is a schematic diagram showing the stress state corresponding to the working surface provided by the specific embodiment of the present invention when it is 10 m away from the cut; FIG11(2) is a schematic diagram showing the stress state corresponding to the working surface provided by the specific embodiment of the present invention when it is 20 m away from the cut; FIG11(3) is a schematic diagram showing the stress state corresponding to the working surface provided by the specific embodiment of the present invention when it is 30 m away from the cut; FIG11(4) is a schematic diagram showing the stress state corresponding to the working surface provided by the specific embodiment of the present invention when it is 40 m away from the cut;

[0053] Fig.12 A schematic diagram of the structure of a coal mine provided with a microseismic monitoring device provided in a specific embodiment of the present invention is shown;

[0054] Fig.13 A schematic diagram of microseismic event density provided by a specific embodiment of the present invention is shown;

[0055] Fig.14 A schematic diagram showing the relationship between the event elevation and the Es / Ep ratio of a microseismic event provided by a specific embodiment of the present invention is shown;

[0056] Fig.15A schematic diagram of a method for identifying water inrush from a coal seam floor that combines advantages provided by an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0057] In order to make the objectives, technical solutions and advantages of the present invention clearer, the implementation method of the present invention will be described in detail below in conjunction with the accompanying drawings and embodiments, so that the implementation process of how the present invention applies technical means to solve technical problems and achieve technical effects can be fully understood and implemented accordingly.

[0058] The research methods for the failure characteristics of the floor are mainly divided into three categories: theoretical analysis, numerical simulation, and field monitoring. Theoretical analysis mainly uses the elastic mechanics thin plate theory to deduce the failure of the key layer of the floor, but most of them consider the water pressure as a uniformly distributed load with a certain length, and the reliability of this assumption is still questionable. In numerical simulation, the finite element method is used, which is difficult to simulate the initiation, expansion and penetration evolution of cracks in the floor water channel, and it is impossible to fully reflect the progressive failure process of the surrounding rock. Conventional monitoring methods such as on-site mining pressure and floor failure cannot overcome the limitations of time and space to conduct three-dimensional real-time monitoring and early warning, and it is even more difficult to perceive the internal micro-fractures and their evolution laws of the coal rock mass before the formation of the water inrush channel. In addition, the deformation and failure process of the floor aquiclude is affected by the heterogeneity of coal and rock mass, the redistribution of ground stress caused by excavation, and fluid-solid coupling. It is difficult to comprehensively evaluate the failure characteristics and evolution laws of the floor using one or two methods.

[0059] In view of this, the present invention provides a method for identifying water inrush from coal seam floor, and establishes a simplified stress model of coal seam floor based on semi-infinite theory. Based on the simplified stress model, the total stress component of the coal seam floor is obtained according to the coal seam depth, rock formation parameters, advance support pressure, original rock stress, floor gravity and confined water pressure, which is conducive to improving the reliability of identifying water inrush channels from coal seam floor. In addition, by using numerical simulation to verify the identification results, and determining the water inrush danger zone of the water inrush channel based on the verification results combined with microseismic monitoring, the advantages of the three methods of identifying water inrush channels based on rock formation parameters, numerical simulation and microseismic monitoring can be effectively integrated, the identification accuracy of water inrush danger zones can be improved, and a reliable basis can be provided for the prevention and control of water inrush disasters from coal seam floor.

[0060] Embodiment 1

[0061] See also Figure 1 As shown, Figure 1 A schematic flow chart of a method for identifying water inrush from a coal seam floor provided by an embodiment of the present invention is shown, which includes:

[0062] Step S101: Obtaining the coal seam depth and the rock parameters of the coal seam floor;

[0063] Step S102: Based on the semi-infinite theory, a simplified force model of the coal seam floor is established, wherein the upper part of the coal seam floor is subject to the advance support pressure and the original rock stress, the coal seam floor is subject to its own floor gravity, and the lower part of the coal seam floor is subject to the pressure of the pressurized water;

[0064] Step S103: Based on the simplified stress model, the total stress component of the coal seam floor is obtained according to the coal seam depth, rock formation parameters, advance support pressure, original rock stress, floor gravity and confined water pressure;

[0065] Step S104: identifying the water inrush channel of the coal seam floor based on the total stress component of the floor and the failure criterion;

[0066] Step S105: using numerical simulation to verify the identification results, and determining the water inrush danger zone of the water inrush channel based on the verification results and microseismic monitoring.

[0067] See also Figure 2 As stated, Figure 2 A structural schematic diagram of the coal mine working area is shown. The black area in the figure represents the coal seam. The upper part of the coal seam may be the coal seam roof. The coal seam floor is between the coal seam and the pressurized water layer. The coal seam floor can be divided into a water-conducting destruction zone, a protective layer zone and a pressurized water lifting zone.

[0068] Among them, the coal seam depth can be the distance between the coal seam and the upper surface of the coal seam roof, represented by h. Obtaining the rock parameters of the coal seam floor can include: obtaining the pressure step distance, elastic zone length, plastic zone length, floor thickness, rock density and stress coefficient of the coal seam floor. The pressure step distance can be represented by 2l, the elastic zone length can be represented by a, the plastic zone can be represented by b, the floor thickness can be represented by H, the rock density can be represented by γ, and the stress coefficient can be represented by n.

[0069] In the embodiment of the present invention, the constitutive model of the coal seam floor can be set to satisfy linear elasticity. After simplifying the force of the coal seam floor based on the semi-infinite theory, the stress component of any point M in the coal seam floor parallel to the plane of the coal seam floor when subjected to normal distributed force on the boundary can be obtained from the elastic theory:

[0070]

[0071] For details, please refer to Figure 3 As shown, Figure 3 FIG. 2 shows a schematic diagram of a two-dimensional coordinate system established at the interface between the coal seam floor and the coal seam provided by an embodiment of the present invention, wherein the pressure on the upper part of the coal seam floor can be simplified to a load q, and the load q is a function of the load micro-segment ξ, σ x is the stress component at point M in the x direction, σ y is the stress component at point M in the y direction, τ xyis the plane shear stress at point M.

[0072] Step S103 may specifically be:

[0073] Step S1031: Based on the simplified force model under the influence of advance support pressure, calculate the first stress component caused by the advance support pressure on the coal seam floor according to the coal seam depth, the pressure step distance of the coal seam floor, the elastic zone length, the plastic zone length, the floor thickness, the rock density and the stress coefficient.

[0074] Step S1032: Based on the simplified stress model under the influence of the original rock stress, according to the coal seam depth and rock density, calculate the second stress component caused by the original rock stress on the coal seam floor.

[0075] Step S1033: Based on the simplified stress model under the influence of the confined water pressure, calculate the third stress component caused by the confined water pressure on the coal seam floor.

[0076] Step S1034: Based on the simplified force model under the influence of floor gravity, according to the Lame constant, coal seam depth and rock density, calculate the fourth stress component caused by floor gravity on the coal seam floor.

[0077] Step S1035: Based on the first stress component, the second stress component, the third stress component and the fourth stress component, the total stress component of the coal seam floor is obtained.

[0078] Among them, see Figure 4 As shown, Figure 4 A schematic diagram of the force model of the coal seam floor under advance support pressure is shown, with the midpoint of the initial pressure step as the origin, the x-axis parallel to the coal seam floor and horizontally to the right along the junction of the coal seam and the coal seam floor as the x-axis, and the z-axis perpendicular to the floor downward as the z-axis to establish a coordinate system.

[0079] Step S1031 may specifically include:

[0080] The advance support pressures in the plastic zone and the elastic zone are simplified into triangular loads respectively;

[0081] According to the coal seam depth, the pressure step distance of the coal seam floor, the length of the elastic zone, the length of the plastic zone, the thickness of the floor, the bulk density of the rock mass and the stress coefficient, the stress components caused by the triangular load in the plastic zone and the triangular load in the elastic zone on the coal seam floor are calculated respectively;

[0082] According to the stress components caused by the triangular load in the plastic zone and the triangular load in the elastic zone on the coal seam floor, the first stress component caused by the advance support pressure on the coal seam floor is calculated.

[0083] As an example, see Figure 4As shown in Figure 1, the advance support pressure in the plastic zone on both sides of the working area can be simplified to triangular loads q1 and q3, and the advance support pressure in the elastic zone on both sides of the working area can be simplified to triangular loads q2 and q4, respectively. The maximum value of the triangular load can be nγh, and θ is the angle between the line connecting any point M under the bottom plate and the load edge and the Z-axis direction. Therefore, the first stress component caused by the advance support pressure on the coal seam bottom plate can be the sum of the stress components caused by the triangular loads q1, q2, q3 and q4 on the coal seam bottom plate.

[0084] Specifically, the stress component caused by the triangular load q1 on the coal seam floor can be:

[0085]

[0086] Among them, z is the coordinate of point M in the Z-axis direction, σ z1 is the stress component of the triangular load q1 in the z direction at point M, σ x1 is the stress component of the triangular load q1 in the x direction at point M, τ xz1 is the plane shear stress of the triangular load q1 at point M,

[0087] The stress component caused by the triangular load q2 on the coal seam floor can be expressed by formula (2-2):

[0088]

[0089] σ z2 is the stress component of the triangular load q2 in the z direction at point M, σ x2 is the stress component of the triangular load q2 in the x direction at point M, τ xz2 is the plane shear stress of the triangular load q2 at point M,

[0090] The stress component caused by the triangular load q3 on the coal seam floor can be expressed by formula (2-3):

[0091]

[0092] σ z3 is the stress component of the triangular load q3 in the z direction at point M, σ x3 is the stress component of the triangular load q3 in the x direction at point M, τ xz3 is the plane shear stress of the triangular load q3 at point M,

[0093] The stress component caused by the triangular load q4 on the coal seam floor can be expressed by formula (2-4):

[0094]

[0095] σ z4 is the stress component of the triangular load q4 in the z direction at point M, σ x4 is the stress component of the triangular load q4 in the x direction at point M, τ xz4 is the plane shear stress of the triangular load q4 at point M,

[0096] Step S1032 may specifically include:

[0097] The original rock stress in the empty area is simplified into a uniformly distributed rectangular load;

[0098] According to the coal seam depth and rock mass density, the second stress component caused by the floor gravity on the coal seam floor is calculated.

[0099] As an example, the uniformly distributed rectangular load q5 with the original rock stress of the empty area being γh can be used. Therefore, the second stress component caused by the original rock stress on the coal seam floor can be:

[0100]

[0101] Among them, σ z5 is the stress component in the z direction of the uniformly distributed rectangular load q5 at point M, σ x5 is the stress component in the x direction of the uniformly distributed rectangular load q5 at point M, τ xz5 is the plane shear stress of the uniformly distributed rectangular load q5 at point M,

[0102] Step S1033 may specifically be:

[0103] Simplify the confined water pressure into a semi-infinite uniformly distributed load and obtain the confined water pressure value;

[0104] Establish the volume strain equation and the equilibrium equation of rock mass displacement according to the rock mass displacement;

[0105] Based on the volume strain equation and the equilibrium equation of rock mass displacement, the third stress component caused by the uniformly distributed load on the coal seam floor is calculated.

[0106] As an example, see Figure 5 As shown, Figure 5A schematic diagram of the force model of the coal seam floor under the influence of the pressurized water pressure provided by an embodiment of the present invention is shown. The pressurized water pressure can be simplified to an infinitely wide uniformly distributed load, that is, a uniformly distributed load that extends infinitely in the xy plane, and the size of the uniformly distributed load is p. When analyzing the stress component of the coal seam floor caused by the pressurized water pressure alone, since the pressurized water only affects the pressurized water lifting zone of the coal seam floor, and the bottom drum amount generated by the coal seam floor of the working face during the initial pressure is small relative to the thickness of the coal seam floor, the coal-rock junction can be regarded as a fixed boundary. Therefore, the third stress component caused by the uniformly distributed load on the coal seam floor can be calculated by the following method:

[0107] From the symmetry, the rock mass displacement is: x =0,u y =0,u z =w(z) (4-1)

[0108] Among them, u i (i=x, y, z) represents the displacement component of the rock mass in the i direction, and w is a function of the independent variable z.

[0109] The volume strain equation is established based on the rock mass displacement:

[0110]

[0111] Establish the equilibrium equation of rock mass displacement:

[0112]

[0113] Where G is the shear modulus, λ is the Lame constant, and f i is the body force in the i direction, which is zero in the above formula. After simplification, we can get w=Bz+A(4-4), where A and B are arbitrary constants. Based on formula (4-2) and formula (4-4), the third stress component caused by the uniformly distributed load on the coal seam floor can be calculated, which can be expressed by formula (4-5):

[0114]

[0115] According to the boundary condition [σ zls ] z＝H =-p, and in the above formula σ z is a constant, we can get σ zls =-p, then solve for B and substitute it into equation (4-5) to obtain A can be represented by [w] z＝0 = 0. Taking pressure as positive, the stress component of the coal seam floor caused by pressurized water is obtained: σ zls =p, τ zxls =0.

[0116] Step S1034 may be specifically to calculate the fourth stress component caused by the floor gravity on the coal seam floor according to the Lame constant, the coal seam depth and the rock mass bulk density, wherein the stress component σ of the floor gravity in the z direction is z6 is γ(h+z), the stress component of the bottom plate gravity in the x direction is σ x6 is λγ(h+z).

[0117] Step S1035 may specifically calculate the total stress component according to the following expression (5):

[0118]

[0119] Step S104 can be specifically to identify the water inrush channel of the coal seam floor based on the total stress component of the floor and the Coulomb modified failure criterion. Specifically, there is tensile stress at the coal seam floor, and the Coulomb modified failure criterion with tensile truncation is introduced to reflect the characteristics of rock failure under tensile stress and shear stress. The Coulomb modified failure criterion can be expressed as formula (6):

[0120]

[0121] Among them, σ1 is the maximum principal stress, σ3 is the minimum principal stress, and σ t is the uniaxial tensile strength, c is the bonding strength, is the internal friction angle. σ1 is the maximum principal stress and σ3 is the minimum principal stress, which can be obtained based on the total stress components calculated by formula (5) through the following expressions:

[0122]

[0123]

[0124] In addition, the weighted average method can be used to obtain the average friction angle of the coal seam floor and cohesion c, and use MATLAB to give the σ3 contour map that does not satisfy the above formula, which is the floor failure map. According to formula (6), the stress distribution law and maximum stress of the coal seam floor can be determined. At the same time, based on the stress contour map, the failure depth and failure nature of the coal seam floor can be determined, thereby identifying the water inrush channel of the coal seam floor.

[0125] Step S104 may specifically include:

[0126] Verify the identification results based on the acoustic emission diagram and stress cloud diagram;

[0127] When the verification is consistent, the water inrush hazard area of ​​the water inrush channel is determined based on the microseismic signals.

[0128] It should be noted that before using numerical simulation to verify the identification results and determining the water inrush hazard area of ​​the water inrush channel based on the verification results combined with microseismic monitoring, it can also include: numerical simulation of the stress wave propagation process, and output of acoustic emission diagrams and stress cloud diagrams; and, based on the verification results, setting up a microseismic monitoring device in the tunnel to collect microseismic signals using the microseismic monitoring device.

[0129] See also Figure 6 As shown, Figure 6 A schematic diagram of the coal mine rock layer provided by an embodiment of the present invention is shown. In the embodiment of the present invention, adjacent rock layers with similar physical properties can be merged to establish a two-dimensional numerical analysis generalized model of coal mine working face excavation to simplify it into a plane strain problem. At the same time, boundary conditions are set and corresponding water heads are applied to the Ordovician limestone layer to simulate the water pressure of the confined water layer, and distributed excavation is used to simulate the advancement of the working face.

[0130] By analyzing the shear stress and unit failure of the coal seam near the dynamic excavation process, the tensile failure area of ​​the bottom plate is delineated. Figure 7(1) to Figure 7(3) As shown, Figure 7 (1) shows the acoustic emission schematic diagram of the coal seam floor, and Figure 7 (2) shows a partial enlarged diagram of the shear failure zone on the left side of the tensile failure zone in the acoustic emission schematic diagram of the coal seam floor; Figure 7 (3) shows a partial enlarged diagram of the shear failure zone on the right side of the tensile failure zone in the acoustic emission schematic diagram of the coal seam floor; the acoustic emission diagram output by numerical simulation is used to analyze the floor failure depth and failure law, and it can also vividly reflect the distribution of the tensile shear failure zone of the coal rock mass, so that the relevant parameters of the identified coal seam floor water inrush channel can be verified based on the coal seam floor failure depth obtained by numerical simulation. In addition, the stress change trend can also be analyzed based on the stress cloud map.

[0131] When the verification is consistent, the identified water inrush channel in the coal seam floor can be regarded as the key area, and a microseismic monitoring device can be set up in the key area. The microseismic monitoring device can be used to collect microseismic signals to further improve the identification accuracy and accurately determine the water inrush danger zone.

[0132] As an example, see Figure 8 As shown, Figure 8 The present invention shows a microseismic monitoring system for real-time monitoring of microfracture information of coal seam floors. Specifically, sensors are arranged on the tunnel floor to receive microseismic signals released by microfractures of coal and rock masses, which are then transmitted to the Paladin signal collector via cables. The electrical signals are then converted into digital signals via optical fiber transmission and stored in the Hyperion data processing system for on-site personnel to perform data analysis and locate microseismic events. Data transmission and interaction can be implemented through the Internet.

[0133] By monitoring the micro - fracture events of coal and rock masses within the key areas and processing the micro - seismic waveforms, the spatio - temporal distribution characteristics of micro - fractures in the coal seam floor can be macroscopically presented. In addition, by combining the micro - seismic event matrix level, micro - seismic event density, etc., the floor failure depth and failure characteristics reflected by micro - seismic events can be obtained.

[0134] As another example, the distribution of the energy ratio (Es / Ep) released by the P - wave and S - wave of micro - seismic events can also be statistically analyzed. When Es / Ep > 10, the micro - seismic events are induced by faults or shear failures; when Es / Ep < 3, the seismic events are induced by non - shear - type failures; when 3 < Es / Ep < 10, the micro - seismic events are induced by composite failures. Thus, the rock mass failure mode can be identified based on micro - seismic signals.

[0135] In the embodiment of the present invention, the floor failure depth obtained by using the micro - seismic monitoring device can be further verified with the result obtained by numerical simulation to improve the accuracy of identification.

[0136] In addition, the floor failure depth and failure nature obtained by the three methods of identifying water - inrush channels based on rock - layer parameters, numerical simulation, and micro - seismic monitoring can be mutually verified, and the credibility of the results can be verified by combining on - site water - inflow data. Thus, the water - inrush dangerous area prone to forming water - inrush channels can be accurately delineated to effectively provide a reinforcement plan for the coal seam floor.

[0137] The above is a method for identifying water - inrush in the coal seam floor provided by the embodiment of the present invention. Based on the semi - infinite theory, a simplified mechanical model of the coal seam floor is established. Based on this simplified mechanical model, according to the coal seam depth, rock - layer parameters, advanced support pressure, virgin rock stress, floor gravity, and confined water pressure, the total stress components of the coal seam floor are obtained, which is beneficial to improving the reliability of identifying the water - inrush channel in the coal seam floor. In addition, by using numerical simulation to verify the identification results and determining the water - inrush dangerous area of the water - inrush channel based on the verification results in combination with micro - seismic monitoring, the advantages of the three methods of identifying water - inrush channels based on rock - layer parameters, numerical simulation, and micro - seismic monitoring can be effectively integrated, improving the identification accuracy of the water - inrush dangerous area and providing a reliable basis for the prevention and control of coal seam floor water - inrush disasters. Specific embodiments

[0139] According to Equation (5), the theoretical calculation of the total stress distribution of the coal seam floor under confined water mining is carried out. From the geological exploration report and relevant data of Dongjiahe Coal Mine, the coal seam depth is 355m, the initial weighting interval is 40m, the length of the elastic zone is 15m, the length of the plastic zone is 5m, the floor thickness is 30m, the average unit weight of the overlying rock and soil mass is 24.5kN / m3, and n is taken as 1.5. According to the on - site engineering geological conditions, the stress contour map of the coal seam floor is obtained through the mathematical calculation software matlab. For details, please refer to Figure 9(1) to Figure 9(3)As described above, Figure 9 (1) shows a contour map of vertical stress during initial pressure provided by a specific embodiment of the present invention; Figure 9 (2) shows a contour map of horizontal stress during initial pressure provided by a specific embodiment of the present invention; and Figure 9 (3) shows a contour map of shear stress during initial pressure provided by a specific embodiment of the present invention.

[0140] There is tensile stress in the coal seam floor. By introducing the Coulomb modified failure criterion with tensile truncation, the characteristics of tensile stress failure and shear stress failure of the coal seam floor can be reflected. Fig.10 As shown, Fig.10 The bottom plate damage diagram provided by the specific embodiment of the present invention is shown. According to the obtained bottom plate damage diagram, it can be seen that the damage form is an "inverted saddle shape", and the damage depth of the coal seam bottom plate below the advance support pressure is the largest, reaching 11.0m. The coal seam bottom plate within 1.7m below the goaf is tensile damage, which causes the bottom bulging phenomenon of the coal seam bottom plate. Shear damage occurs 1.7m to 3m below the goaf, and shear damage circles are formed on both sides of 5m to 11m below the coal seam bottom plate. The bottom plate damage depth increases, making it easy for pressurized water to rise from the shear damage circle to the end of the bottom plate, and then a water inrush accident occurs.

[0141] Combined with numerical simulation and microseismic monitoring, the evolution process of the progressive destruction of the floor coal rock mass until the formation of the water inrush channel and its stress distribution characteristics are reproduced: the RFPA numerical analysis software is used to establish a two-dimensional numerical analysis generalization model of coal mine working face excavation. The model is 200m long and 100m high. The model is divided into 400*200=80000 units. One unit represents a small square with an actual size of 0.5m on a side. For details, please refer to the above embodiment 1. Figure 6 As shown. The boundary conditions are: the horizontal displacement on both sides is 0, vertical displacement can occur, the bottom plate is fixed, and the upper boundary is free. The load condition is to apply a vertical uniformly distributed load of 6.6Mpa on the upper boundary to simulate the deadweight of the overlying rock strata. It is simplified into a plane strain problem. In order to eliminate the influence of the boundary effect, continuous step-by-step excavation is carried out 80m to the left from the right boundary. The coal seam thickness is 4m, and the full height is mined at one time. The first step is the calculation process of the deadweight stress of the overlying rock strata. From the second step onwards, each step is excavated 10m, and a total of 4 steps are excavated. A 150m head is applied to the Ordovician limestone layer to simulate a confined water layer with a water pressure of 1.5Mpa.

[0142] Furthermore, the shear stress and unit damage of the unit near the coal seam during dynamic excavation are analyzed. For details, see Figures 11(1) to 11(4)As shown, FIG11(1) shows a schematic diagram of the stress state corresponding to the working face provided by the specific embodiment of the present invention when it is 10m away from the cut; FIG11(2) shows a schematic diagram of the stress state corresponding to the working face provided by the specific embodiment of the present invention when it is 20m away from the cut; FIG11(3) shows a schematic diagram of the stress state corresponding to the working face provided by the specific embodiment of the present invention when it is 30m away from the cut; FIG11(4) shows a schematic diagram of the stress state corresponding to the working face provided by the specific embodiment of the present invention when it is 40m away from the cut. As the working face advances (when the advance distance is 0-30m), obvious stress concentration appears around the four corners and short sides of the goaf, and only a small number of cracks with shallow damage depth appear in the coal seam floor. When the working face advances to 40m, separation occurs between the basic roof and the direct roof and the fracture occurs at the limit span, and the initial pressure is formed. Through cracks appear under the floor and extend downward, and the advance support effect appears.

[0143] The acoustic emission diagram provided by numerical simulation is then used to analyze the floor failure depth and failure law. The acoustic emission diagram can vividly reflect the distribution of tensile and shear failure zones in the coal and rock mass and determine the floor failure depth.

[0144] On the other hand, a microseismic monitoring system is built for real-time monitoring of micro-fracture information on the coal seam floor. Sensors are arranged on the tunnel floor to receive microseismic signals released by micro-fractures of the coal and rock masses. The signals are transmitted to the Paladin signal collector via cables, and then converted into digital signals via optical fiber transmission. The digital signals are stored in the Hyperion data processing system for on-site personnel to perform data analysis and event location. Data transmission and interaction can be achieved through the Internet.

[0145] Taking the typical working face progress of Dongjiahe Coal Mine as an example, the floor microseismic events from December 23, 2014 to May 19, 2015, with a distance of 600m to 1000m from the point front, are selected for analysis. Fig.12 As shown, Fig.12 The schematic diagram of the structure of a coal mine provided with a microseismic monitoring device provided by a specific embodiment of the present invention is shown. According to statistics, during this period, the microseismic system detected a total of 29 microseismic events on the floor, of which there were 12 microseismic events within a range of 600 to 1000 meters from the point, all of which were distributed above the confined aquifer. It was preliminarily determined that no floor water inrush event occurred as of May 19, 2015.

[0146] See also Fig.13 As shown, Fig.13It shows the schematic diagram of the microseismic event density provided by the specific embodiment of the present invention. By combining the microseismic event density and the matrix level for analysis, the microseismic events are relatively dense at about 726 m in front of the point, indicating the aggregation of microfractures in the rock mass in this area and the tendency to form through cracks. The moment magnitude of the microseismic event with the lowest elevation in this area is relatively large, and it can be identified that through cracks have been formed in this area. In addition, based on the positioning information of the microseismic event provided by the ESG software, the elevation of this microseismic event is +221 m, and the floor elevation here is +234 m. Taking the difference between the elevation of this microseismic event and the floor as the maximum failure depth of the floor, the failure depth is obtained as 13 m.

[0147] Furthermore, the distribution of the energy ratio (Es / Ep) released by the P-wave and S-wave of the microseismic event can be statistically analyzed. When Es / Ep≥10, the microseismic event is induced by a fault or shear failure; when Es / Ep≤3, the seismic event is induced by a non-shear type failure; when 3<Es / Ep<10, the microseismic event is induced by a composite failure. Based on this, the Es / Ep ratios of the floor microseismic events at a front distance of 600 m to 1000 m are sorted out, as can be seen Fig.14 shown in Fig.14 It shows the schematic diagram of the relationship between the event elevation of the microseismic event provided by the specific embodiment of the present invention and the Es / Ep ratio. In the elevation range of +230 m to +250 m, Es / Ep≤3 for most microseismic events. The floor elevation of the coal seam in this range is approximately in the range of +235 m. It can be identified that most of the microseismic events 5 m below the coal seam are induced by tensile failure. In the range of +205 m to +220 m, Es / Ep≥10 for the microseismic events. It can be identified that the microseismic events below 15 m below the coal seam are induced by shear failure, and its identification result can verify the method of identifying the water inrush channel based on rock stratum parameters and the method identified based on numerical simulation.

[0148] By comprehensively using the advantages of multiple methods to identify the nature and depth of floor damage, the preliminary work that needs to be carried out includes: mastering the typical characteristics of the mining area, such as engineering geological structures (faults, joints, lithology), physical and mechanical parameters of rock formations, surveying hydrogeological conditions, and arranging microseismic sensors. Secondly, combining the advantages of different methods, the floor damage depth and damage characteristics are analyzed. By simplifying the model, the total stress of the floor during the initial pressure during the excavation process is solved, and the sensitivity of the load is analyzed. The Coulomb modified failure criterion with tensile truncation is introduced to obtain the damage depth and damage nature of the floor, which is conducive to improving the reliability of identification. By combining the numerical simulation method, the stress change trend can be grasped through the stress cloud map during the simulation of continuous excavation, and the identified coal seam floor water inrush channel can be verified by combining the acoustic emission map. At the same time, the identification results of the numerical simulation can also be used as a tool to test the accuracy of microseismic event positioning. Based on the microseismic waveforms obtained by the microseismic monitoring device, the temporal and spatial distribution laws of microseismic activities can be explored, and the distribution laws of microseismic events can also be used to discover undisclosed geological structures as a supplement to theoretical analysis and numerical simulation. In addition, the maximum damage depth of the bottom plate can be obtained through microseismic information positioning, so that the identified bottom plate damage depth and damage nature results can be mutually verified by combining the three methods. Further combined with the on-site water inflow data, the identification accuracy can be improved, and it is conducive to timely warning of bottom plate water inrush disasters and providing prevention and control plans. For details, please refer to Fig.15 As shown, Fig.15 A schematic diagram of a method for identifying water inrush from a coal seam floor that combines advantages provided by an embodiment of the present invention is shown.

[0149] Although the embodiments disclosed in the present invention are as above, the contents described are only embodiments adopted for facilitating the understanding of the present invention and are not intended to limit the present invention. Any technician in the technical field to which the present invention belongs can make any modifications and changes in the form and details of the implementation without departing from the spirit and scope disclosed in the present invention, but the protection scope of the present invention shall still be subject to the scope defined in the attached claims.

Claims

1. A method for identifying water inrush from coal seam floors, characterized in that: include: Obtain the coal seam depth and the rock parameters of the coal seam floor; Based on the semi-infinite theory, a simplified force model of the coal seam floor is established, wherein the upper part of the coal seam floor is subject to the advance support pressure and the original rock stress, the coal seam floor is subject to its own floor gravity, and the lower part of the coal seam floor is subject to the pressure of the pressurized water; Based on the simplified force model, the total stress component of the coal seam floor is obtained according to the coal seam depth, the rock formation parameters, the advance support pressure, the original rock stress, the floor gravity and the confined water pressure; Identifying the water inrush channel of the coal seam floor based on the total stress component and the failure criterion of the floor; The identification results are verified by numerical simulation, and the water inrush hazard area of ​​the water inrush channel is determined based on the verification results and combined with microseismic monitoring; Wherein, based on the simplified force model, according to the coal seam depth, the rock formation parameters, the advance support pressure, the original rock stress, the floor gravity and the confined water pressure, the total stress component of the floor of the coal seam is obtained, including: Based on the simplified force model under the influence of the advance support pressure, the first stress component caused by the advance support pressure on the coal seam floor is calculated according to the coal seam depth, the pressure step distance of the coal seam floor, the elastic zone length, the plastic zone length, the floor thickness, the rock mass density and the stress coefficient; Based on the simplified stress model under the influence of the original rock stress, according to the coal seam depth and the rock mass density, calculate the second stress component caused by the original rock stress on the coal seam floor; Based on the simplified force model under the influence of the confined water pressure, calculating the third stress component caused by the confined water pressure on the coal seam floor; Based on the simplified force model under the influence of the floor gravity, according to the Lame constant, the coal seam depth and the rock mass density, calculate the fourth stress component caused by the floor gravity on the coal seam floor; Based on the first stress component, the second stress component, the third stress component and the fourth stress component, the total stress component of the coal seam floor is obtained.

2. The method according to claim 1, characterized in that Obtaining the rock parameters of the coal seam floor includes: obtaining the pressure step distance, elastic zone length, plastic zone length, floor thickness, rock mass density and stress coefficient of the coal seam floor.

3. The method according to claim 1, characterized in that Based on the simplified force model under the influence of the advance support pressure, according to the coal seam depth, the pressure step distance of the coal seam floor, the elastic zone length, the plastic zone length, the floor thickness, the rock mass density and the stress coefficient, the first stress component caused by the advance support pressure on the coal seam floor is calculated, including: Simplifying the advance support pressures in the plastic zone and the elastic zone into triangular loads respectively; According to the coal seam depth, the pressure step distance of the coal seam floor, the elastic zone length, the plastic zone length, the floor thickness, the rock mass density and the stress coefficient, respectively calculate the stress components caused by the triangular load in the plastic zone and the triangular load in the elastic zone on the coal seam floor; The first stress component caused by the advance support pressure on the coal seam floor is calculated based on the stress components caused by the triangular load in the plastic zone and the triangular load in the elastic zone on the coal seam floor.

4. The method according to claim 1, characterized in that: Based on the simplified stress model under the influence of the original rock stress, according to the coal seam depth and the rock mass density, the second stress component caused by the original rock stress on the coal seam floor is calculated, including: Simplifying the original rock stress in the empty area into a uniformly distributed rectangular load; The second stress component caused by the original rock stress on the coal seam floor is calculated according to the coal seam depth and the rock mass density.

5. The method according to claim 1, characterized in that Calculating the third stress component caused by the confined water pressure on the coal seam floor based on the simplified force model under the influence of the confined water pressure includes: Simplifying the confined water pressure into a semi-infinite uniformly distributed load and obtaining the confined water pressure value; Establishing a volume strain equation based on the rock mass displacement and establishing an equilibrium equation of the rock mass displacement; Based on the volume strain equation and the equilibrium equation of the rock mass displacement, the third stress component caused by the uniformly distributed load on the coal seam floor is calculated.

6. The method according to claim 1, characterized in that Obtaining the total stress component of the floor of the coal seam based on the first stress component, the second stress component, the third stress component and the fourth stress component, comprises: According to the stress superposition principle of elasticity theory, based on the first stress component, the second stress component, the third stress component and the fourth stress component, the total stress component of the coal seam floor is obtained.

7. The method according to claim 1, characterized in that Based on the total stress component and failure criterion of the floor, the water inrush channel of the coal seam floor is identified, including: The water inrush channel of the coal seam floor is identified based on the total stress component of the floor and the Coulomb modified failure criterion.

8. The method according to claim 1, characterized in that The method further comprises: Numerical simulation of stress wave propagation process and output of acoustic emission graph and stress contour map; and, A microseismic monitoring device is arranged in the tunnel based on the verification result, so as to collect microseismic signals by using the microseismic monitoring device.

9. The method according to claim 8, characterized in that The method of verifying the identification result by numerical simulation and determining the water inrush danger zone of the water inrush channel based on the verification result and microseismic monitoring includes: Verifying the identification result according to the acoustic emission graph and the stress cloud graph; When the verification is consistent, the water inrush hazard zone of the water inrush channel is determined based on the microseismic signal.

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