A method for predicting the timing of rockburst in extra-thick coal seams with hard roofs

Abstract

This invention discloses a method for predicting the timing of rockbursts in extra-thick coal seams with hard roofs, belonging to the field of coal mining technology. It is used to predict the timing of rockbursts in such seams. The method includes: identifying the key seismic stratum; sequentially calculating the deflection and rotation angle of the key seismic stratum; establishing governing equations and boundary equations; then calculating the stress, shear stress, maximum tensile stress, and maximum shear stress; finally determining the fracture distance of the key seismic stratum; inferring the timing of rockburst occurrence; and enabling early prediction and prevention, thereby controlling seismic disasters at their source.

Description

Technical Field

[0001] This invention relates to the field of coal mining technology, and more specifically to a method for predicting the timing of rockbursts in extra-thick rock seams with hard roofs. Background Technology

[0002] In recent years, as shallow coal resources have become increasingly depleted, most mining areas have gradually shifted to deep mining. Compared with shallow mining, deep mining involves more complex geological conditions and stress environments, leading to a sharp increase in the frequency and intensity of rockburst disasters. Major rockburst accidents occur frequently, seriously affecting the safe and efficient mining of coal resources.

[0003] In recent years, numerous scholars have conducted extensive research on predicting the timing of rockbursts, proposing various methods based on different mathematical and mechanical models. However, current geological rockburst hazard assessment methods only consider the physical and mechanical properties of coal and rock masses and the influence of the height and thickness of hard rock strata on the timing of rockbursts, without fully considering the impact of overlying structure type and the fracturing of (multiple) key strata on the timing of rockbursts. Therefore, there is an urgent need for a method that can accurately predict the timing of rockbursts in extra-thick rockburst coal seams with hard roofs. Summary of the Invention

[0004] In view of this, the present invention provides a method for predicting the timing of rockbursts in extra-thick rockburst coal seams with hard roofs. By identifying the key seismic strata, establishing their governing equations and boundary equations, and calculating parameters such as stress, the timing of rockbursts is predicted based on the fracture step distance and fracture criteria. This method effectively predicts the timing of rockbursts in extra-thick rockburst coal seams with hard roofs, providing a scientific basis for safe coal mine production and reducing the harm caused by rockbursts to personnel and equipment.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A method for predicting the timing of rockbursts in extra-thick coal seams with hard roofs includes:

[0007] Step 1: Determine the critical seismic layer: Define a formula for determining the critical seismic layer using a multi-parameter comprehensive evaluation model:

[0008]

[0009] Among them, E kc It is the key stratum identification index for mine earthquakes, w i It is the weight of the i-th parameter, X i It is the standardized value of the i-th parameter, and n is the total number of parameters in the index system. The parameters include: tensile strength, elastic modulus, Poisson's ratio and geological parameters.

[0010] The weight of the i-th parameter is calculated using the following formula:

[0011]

[0012] Among them, H i It is the information entropy of the i-th parameter. Where p ij is the proportion of the i-th parameter in the j-th sample, and k is a constant;

[0013] The key seismic layer determination index is compared with a preset threshold. If the key seismic layer determination index is greater than the preset threshold, it is determined to be a key seismic layer.

[0014] Step 2: Deflection of the key layer in the mine seismic event w Corner Define the governing equations and boundary equations, including:

[0015] The seismic critical layer is divided into two regions: a suspended region and an elastic region. The seismic critical layer is further divided into two mutually perpendicular x and y directions, and discrete points are marked, with a distance α between adjacent discrete points. Using the center point (i,j) as the base point, and deflection w and rotation angle as parameters, the seismic critical layer is further divided into these regions. The governing equations are defined as follows:

[0016] The initial failure occurs in the linear form of the governing equations within the overhang region, which is a system of equations with 9 nodes and 27 parameters:

[0017]

[0018] In the formula, D represents the flexural stiffness of the critical layer in the mine earthquake. C represents the shear stiffness of the critical layer in the mine earthquake. E is the elastic modulus of the rectangular plate, h is the thickness and Poisson's ratio, μ is the Poisson's ratio, and q is the external force load on the plate. w is the deflection function of the mid-surface of the key layer in the mine seismic event; Let xoz be the angle of the straight line perpendicular to the mid-surface before plate deformation within the xoz plane. The angle of the straight line perpendicular to the mid-surface before plate deformation in the yoz plane;

[0019] The linear form of the governing equations for the initial fracture within the elastic region is also a system of equations with 9 nodes and 27 parameters:

[0020]

[0021] In the formula, k e Elastic foundation stiffness of coal and rock mass;

[0022] Calculate the deflection and rotation angle based on the boundary linear equation:

[0023] The boundary linear equation of the suspended region at the initial fracture is:

[0024]

[0025] The boundary conditions for the mechanical model of the initial failure of the key layer in a mine earthquake are as follows:

[0026]

[0027] Step 3: Calculate the stress and shear stress of the key seismic layer;

[0028] Define the principal bending moment and shear force values ​​at node (i,j), and then obtain the linear equations of the stress components at node (i,j):

[0029]

[0030]

[0031] Step 4: Define the maximum tensile stress and maximum shear stress of the key seismic layer:

[0032] The linear equations for the principal stresses and maximum shear stresses of the key seismic layer are solved as follows:

[0033] The three principal stresses σ at node (i,j) 1(i,j) , σ 2(i,j) and σ 3(i,j) The calculation formula is:

[0034]

[0035] In the formula,

[0036] I 1(i,j) I 2(i,j) and I 3(i,j) Let be the first, second, and third stress invariants at node (i,j), respectively, and their calculation formulas are as follows:

[0037]

[0038] The formula for calculating the maximum shear stress at node (i,j) is as follows:

[0039] τ max(m,n) =max{|σ 1(i,j) -σ 2(i,j) |,|σ 2(i,j) -σ 3(i,j) |,|σ 3(i,j) -σ 1(i,j) |} / 2

[0040] Step 5: Determine the fracture distance of the key seismic strata to predict the timing of rockburst;

[0041] The critical stratum fracture step distance in mine seismic events is defined as follows:

[0042]

[0043] Where L is the fracture step distance, E is the elastic modulus of the critical layer, and σ t is the tensile strength of the key rock layer, and h is the thickness of the key layer.

[0044] The corresponding breaking criterion is σ. max =max{|σ1|,|σ2|,|σ3|}≥σ t or τ max ≥τ s In the formula σ t and τ s These represent the tensile strength and shear strength of the key layer in the mine earthquake, at which point rockburst will occur.

[0045] As can be seen from the above technical solution, compared with the prior art, this invention discloses a method for predicting the timing of rockbursts in extra-thick coal seams with hard roofs. First, by identifying the key seismic strata, deflection and rotation angle calculations are performed sequentially to establish governing equations and boundary equations. Then, stress, shear stress, maximum tensile stress, and maximum shear stress are calculated. Finally, the fracture distance of the key seismic strata is determined to infer the timing of rockbursts, thus controlling seismic disasters at the source, predicting in advance, and taking preventative measures to ensure the safe and efficient mining of coal resources. Furthermore, compared with current geological rockburst hazard assessment methods that only consider the physical and mechanical properties of coal and rock mass and the influence of the height and thickness of hard rock strata on the timing of rockbursts, this invention fully considers factors such as overburden structure type and the fracture movement of (multiple) key strata, making the prediction method more accurate and comprehensive. Attached Figure Description

[0046] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0047] Figure 1 This is a schematic diagram of the process provided by the present invention.

[0048] Figure 2 Number the nodes.

[0049] Figure 3(a) shows the initial fracture model of the key layer in the mine earthquake, and Figure 3(b) shows the I-I and II-II cross sections of the initial fracture of the key layer in the mine earthquake. Detailed Implementation

[0050] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0051] This invention discloses a method for predicting the timing of rockbursts in extra-thick coal seams with hard roofs. Taking a working face of a mine of a certain company as an example, the method calculates the accumulation law of elastic energy density during the initial fracture of the hard roof. The average thickness of the coal seam in this working face is M = 6.09m, and the width is L = 200m; the overlying sandstone layer has a thickness h = 90m and a tensile strength σ t =3.4MPa, elastic modulus E=4GPa, Poisson's ratio v=0.2, according to the key layer theory, the overburden load transferred to the hard roof is q=0.79MPa; the foundation stiffness of the coal and rock mass in the mining-affected area is k=1000MN / m. For example... Figure 1 As shown, the specific steps include:

[0052] Step 1: Identify the critical seismic strata. Using a multi-parameter comprehensive evaluation model, establish a comprehensive index system for determining the critical seismic strata, mainly including the following parameters: tensile strength σ. t =3.4MPa, elastic modulus E=4GPa, Poisson's ratio v=0.2, and other geological conditions. Based on the above indicators, the following formula for determining the key strata for mine seismic events is defined:

[0053]

[0054] Among them, E kc It is the key layer determination index for mine seismic events, where wi is the weight of the i-th parameter, and X is the key layer determination index for mine seismic events. i is the standardized value of the i-th parameter, and n is the total number of parameters in the indicator system.

[0055] The weights are determined using the following weight calculation formula:

[0056]

[0057] Among them, H i It is the information entropy of the i-th parameter. Where p ij is the proportion of the i-th parameter in the j-th sample, and k is a constant.

[0058] According to the calculated Ekc The value is compared with the set threshold of 0.7. If E kc If the value is greater than the threshold of 0.7, the layer is determined to be a key layer for mine seismic activity, thus determining that the hard top plate of the target layer is located at the overlying sandstone layer with a thickness of h = 63.8m.

[0059] Step 2: Deflection of the key layer in the mine seismic event w Corner Define the governing equations and boundary equations.

[0060] Assume that the rock strata supporting the rigid roof undergo elastic deformation under the compression of the rigid roof, while the rigid roof bears a uniformly distributed load. The key seismic strata are divided into regions, as shown in Figures 3(a) and 3(b), where the suspended roof region is region ABCD (Ω1 region, length and width 2b×a, b=100m, a=90m in the figure), and the elastic region is ABCD-A1B1C1D1 (Ω2 region). Figure 2 As shown, the key seismic layer is divided into two mutually perpendicular x and y directions, and discrete points are marked. The distance between adjacent discrete points is α = 1m. Taking the center point (i,j) as the base point, and the deflection w and rotation angle as the reference points, the seismic key layer is divided into two mutually perpendicular x and y directions. Define the governing equations as follows:

[0061] The initial failure occurs within the suspended region ABCD (Ω1 region), and the governing equations are in linear form. These equations consist of 9 nodes and 27 parameters:

[0062]

[0063] In the formula, , respectively, represent the bending stiffness and shear stiffness; E, h, and μ represent the elastic modulus, thickness, and Poisson's ratio of the rectangular plate, respectively; q represents the applied external load. w Let be the deflection function of the mid-surface; These are the rotation angles of the straight line perpendicular to the mid-plane before deformation in the xoz and yoz planes, respectively.

[0064] The linear form of the governing equations for the initial fracture of a medium-thick plate within the elastic region ABCD-A1B1C1D1 (Ω2 region) is also a system of equations with 9 nodes and 27 parameters:

[0065]

[0066] In the formula, k e Stiffness of elastic foundation of coal and rock mass.

[0067] The role of boundary linear equations is to reduce the number of parameters, make the linear equations unique, and thus define the deflection and rotation at the nodes.

[0068] At the initial fracture, the medium-thick plate satisfies the following equation on the cantilever boundary ABCD.

[0069]

[0070] The boundary conditions for the mechanical model of the initial failure of the key layer in a mine earthquake are as follows:

[0071]

[0072] Step 3: Define stress and shear stress.

[0073] Define the principal bending moment and shear force values ​​at node (i,j), and then obtain the linear equations of its stress components, which provides a basis for defining the linear equations of principal stress and maximum shear stress.

[0074]

[0075] Step 4: Define the maximum tensile stress and the maximum shear stress.

[0076] Shear or tensile failure may occur, therefore it is necessary to solve the linear equations for the principal stresses and the maximum shear stress, as follows:

[0077] The three principal stresses σ at node (i,j) 1(i,j) , σ 2(i,j) and σ 3(i,j) ,as follows:

[0078]

[0079] In the formula,

[0080] I 1(i,j) I 2(i,j) and I 3(i,j) Let be the first, second, and third stress invariants at node (i,j), respectively, and their calculation formulas are as follows:

[0081]

[0082] The formula for calculating the maximum shear stress at node (i,j) is as follows:

[0083] τ max(m,n) =max{|σ 1(i,j) -σ 2(i,j) |,|σ 2(i,j) -σ 3(i,j) |,|σ 3(i ,j)-σ 1(i,j) |} / 2

[0084] Step 5: Determine the fault distance of the key layer in the mine earthquake to infer the timing of the rockburst.

[0085] The critical stratum fracture step distance in mine seismic events is defined as follows:

[0086]

[0087] Where L is the fracture step distance, E is the elastic modulus of the critical layer, and σ t is the tensile strength of the key rock layer, and h is the thickness of the key layer.

[0088] The corresponding fracture criterion for medium-thick plates is σ. max =max{|σ1|,|σ2|,|σ3|}≥σ t or τ max ≥τ s In the formula σ t and τ s These represent the tensile strength and shear strength of the key layer in the mine earthquake, at which point rockburst will occur.

[0089] In this working face, the elastic modulus of the key layer is E = 4 GPa, and the tensile strength of the key layer is σ. t =3.4MPa, critical layer thickness h = 63.8m, substitute into the formula The calculated critical stratum fracture step distance is L = 750m. Based on the fracture criterion σ... max =max{|σ1|,|σ2|,|σ3|}≥σ t σ can be obtained max =4.5MPa>σ t =3.4MPa, at which point a rockburst will occur.

[0090] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to the method section.

[0091] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for predicting the timing of rockburst in extra-thick coal seams with hard roofs, characterized in that, include: Step 1: Determine the critical seismic layer: Define a formula for determining the critical seismic layer using a multi-parameter comprehensive evaluation model: in, It is an index for determining key layers in mine earthquakes. It is the weight of the i-th parameter, X i It is the standardized value of the i-th parameter, and n is the total number of parameters in the index system. The parameters include: tensile strength, elastic modulus, Poisson's ratio and geological layer parameters. The weight of the i-th parameter is calculated using the following formula: in, It is the information entropy of the i-th parameter. ,in is the proportion of the i-th parameter in the j-th sample, and k is a constant; The key seismic layer determination index is compared with a preset threshold. If the key seismic layer determination index is greater than the preset threshold, it is determined to be a key seismic layer. Step 2: Deflection of the key layer in the mine seismic event Corner , Define the governing equations and boundary equations, including: The seismic critical layer is divided into two regions: a suspended region and an elastic region. The seismic critical layer is further divided into two mutually perpendicular x and y directions, and discrete points are marked, with a distance α between adjacent discrete points. Using the center point (i,j) as the base point, and deflection as the reference point... Corner , The governing equations are defined as follows: The initial failure occurs in the linear form of the governing equations within the overhang region, which is a system of equations with 9 nodes and 27 parameters: In the formula, D represents the flexural stiffness of the critical layer in the mine earthquake. C represents the shear stiffness of the critical layer in the mine earthquake. E is the elastic modulus of the rectangular plate, and h is the thickness. q is Poisson's ratio; q is the external force load on the plate; is the deflection function of the mid-surface of the key layer in the mine seismic event; Let xoz be the angle of the straight line perpendicular to the mid-surface before plate deformation within the xoz plane. The angle of the straight line perpendicular to the mid-surface before plate deformation in the yoz plane; The linear form of the governing equations for the initial fracture within the elastic region is also a system of equations with 9 nodes and 27 parameters: In the formula, Elastic foundation stiffness of coal and rock mass; Calculate deflection and rotation angle based on the boundary linear equation: The boundary linear equation of the suspended region at the initial fracture is: The boundary conditions for the mechanical model of the initial failure of the key layer in a mine earthquake are as follows: Step 3: Calculate the stress and shear stress of the key seismic layer; Define the principal bending moment and shear force values ​​at node (i,j), and then obtain the linear equations of the stress components at node (i,j): Step 4: Define the maximum tensile stress and maximum shear stress of the key seismic layer: The linear equations for the principal stresses and maximum shear stresses of the key seismic layer are solved as follows: The three principal stresses at node (i, j) , and The calculation formula is: In the formula, , , ; , and Let be the first, second, and third stress invariants at node (i,j), respectively, and their calculation formulas are as follows: The formula for calculating the maximum shear stress at node (i, j) is as follows: Step 5: Determine the fracture distance of the key seismic strata to predict the timing of rockburst; The critical stratum fracture step distance in mine seismic events is defined as follows: Where L is the fracture step distance and E is the elastic modulus of the critical layer. is the tensile strength of the key rock layer, and h is the thickness of the key layer; The corresponding breaking criterion is or In the formula and These represent the tensile strength and shear strength of the key layer in the mine earthquake, at which point rockburst will occur.

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