Method for determining threshold value of water inrush coefficient of coal floor of strip mine based on numerical simulation

Abstract

The invention provides a numerical simulation-based strip mine coal floor water inrush coefficient threshold determination method, and relates to the technical field of strip mine floor water inrush prevention and control. The method comprises the following steps: acquiring hydrogeology and engineering geology data, constructing a three-dimensional numerical model, setting parameters and boundary conditions, and performing numerical simulation calculation under different confined water pressure conditions; based on simulation results, fitting function expressions of the maximum shear stress and the confined water pressure and the minimum principal stress and the confined water pressure of the exposed area of the coal floor are constructed respectively; shearing failure and tension failure criteria are put forward, water pressure at the critical water inrush moment is recognized, and finally a coal seam floor water inrush coefficient threshold value is obtained according to a water inrush coefficient calculation formula. The method integrates the elastic thin plate theory, the hydraulic fracture theory and the Moire-Coulomb criterion, has the advantages of being convenient and rapid to operate, high in adaptability and suitable for water inrush risk assessment under the complex geological condition, and can provide theoretical support for accurate evaluation and prevention and control of the water inrush risk of the open pit coal mine.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of open-pit coal floor water inrush prevention, and particularly relates to a method for determining an open-pit coal floor water inrush coefficient threshold value based on numerical simulation. BACKGROUND

[0002] Water disaster is one of the main reasons affecting and threatening the safety and efficient production of coal mines. When open-pit mining reaches the coal floor, if a confined aquifer is present at a certain distance below the coal floor, the confined water under the coal floor may break through the barrier of the coal floor rock layer during the mining process and rush into the open-pit mining area with a large water pressure and water flow, causing a dramatic increase in water volume in the pit, and further causing a serious threat to the safety production of the mine. At present, the identification means for open-pit coal floor water inrush still mostly follows the experience of underground mines, and it is difficult to fully reflect its unique damage characteristics. Unlike underground mines, open-pit coal mines have large mining depth, intense mining and large exposed area of the slope, and the water inrush risk is more spatially uneven and sudden. The water inrush coefficient evaluation method is a commonly used method for water inrush disaster risk evaluation, and the determination of the water inrush coefficient threshold value is the key to the accurate evaluation of the open-pit coal floor water inrush risk, and it is urgent to build a water inrush coefficient threshold value identification method suitable for open-pit mines.

[0003] In recent years, domestic and foreign scholars have done a lot of research on water inrush disaster prevention and control, and have made many research results. In the middle of the 20th century, W. F. Weiss, a Hungarian scholar, proposed the "relative aquifuge theory", which first took the thickness of the aquifuge and the water pressure as the main control parameters, laying the foundation for quantitative analysis; Elsworth established a seepage-stress coupling model based on the cubic law in 1992, and developed a numerical system using the finite element method, which promoted the research of water inrush mechanism into the stage of numerical simulation; Wang Jun-guang et al. established the critical P-M equation, revealing the precursor characteristics of water inrush; Yin Xi-wen et al. based on the "zero position damage" theory, constructed the top and bottom plate cooperative mining damage model, and revealed the water inrush mechanism of thick aquifuge under the condition of hard roof; Li Leng et al. proposed that the floor water inrush is mainly the whole shear and sharp splitting failure, and based on the mechanical model, the critical water pressure expression of the aquifuge is derived, and the safety thickness threshold is clear; In the aspect of numerical simulation, Zhang Gang-yang et al. carried out multi-field coupling simulation, and revealed the damage and seepage evolution law of the aquifuge; Dong Shu-ning constructed the mining disturbance intensity index, combined with numerical simulation and test, revealed the regulation and control effect of macroscopic and microscopic stress evolution on water inrush mechanism; Wang De-xun used FLAC3D to analyze the damage and activation law under different fault dip angles and advance distances; Jing Li-jun used FLAC3D to analyze the stress distribution and floor subsidence of working face, and found that low dip angle and large difference fault is more prone to water inrush; Gao Xiao-wu compared the damage and seepage characteristics of brittle and ductile floor under stress disturbance and coupling conditions by RFPA simulation, and pointed out that mining disturbance is an important inducement of water inrush. Yang Peng used RFPA numerical simulation software to analyze the evolution characteristics of stress field and seepage field of working face under the condition of containing fault. In summary, the current main methods to determine the threshold of water inrush coefficient are empirical method, theoretical analysis method, statistical analysis method and field monitoring test method. However, the existing methods are difficult to be directly applied to the working conditions of open-pit mine. The theoretical analysis method is too simplified for the mining conditions of open-pit mine, and cannot truly reflect the real geological conditions. In addition, the statistical analysis lacks representativeness due to the few cases of water inrush in open-pit mine. Although the field monitoring can reflect the real risk, it is limited by the equipment conditions, and has small monitoring range, low precision, long-term observation, large implementation difficulty and low efficiency. SUMMARY

[0004] In view of the shortcomings of the prior art, the present application provides a method for determining the threshold of coal floor water inrush coefficient in open-pit mine based on numerical simulation. According to the actual geological conditions of the mine, an accurate numerical model is established to simulate the water inrush failure process under different water pressure conditions. The numerical simulation results are analyzed, the elastic thin plate theory, the hydraulic fracturing theory and the Mohr-Coulomb criterion are combined, the water inrush criterion is proposed, the water pressure value at the critical water inrush time is identified, and the threshold of water inrush coefficient is determined based on the water inrush coefficient method, thereby providing theoretical and technical support for solving the problems of precise evaluation and prevention and control technology of water inrush in open-pit mine.

[0005] A method for determining the threshold of coal floor water inrush coefficient in open-pit mine based on numerical simulation, comprising the following steps:

[0006] Step 1: Collect the hydrogeological and engineering geological data of the studied mine area, obtain the confined water pressure and the thickness of the aquiclude in the mine area;

[0007] Step 2: Construct the numerical model of the open-pit mine and set the boundary conditions and mechanical parameters;

[0008] Step 3: Set different confined water pressure conditions, perform numerical simulation calculation, obtain the stress field distribution law under different confined water pressure conditions, and identify the minimum principal stress and the maximum shear stress of the coal floor aquiclude exposed area under each condition;

[0009] Step 4: Nonlinearly fit the minimum principal stress of the coal floor aquiclude exposed area, the confined water pressure, and the maximum shear stress and the confined water pressure respectively, and construct the fitting functions respectively;

[0010] The fitting function expression of the maximum shear stress and the confined water pressure is:

[0011] (1)

[0012] The fitting function expression of the minimum principal stress and the confined water pressure is:

[0013] (2)

[0014] In the formula, is the maximum shear stress of the coal floor aquiclude exposed area, is the minimum principal stress of the coal floor aquiclude exposed area, and P is the confined water pressure, represents the fitting function of the maximum shear stress changing with the confined water pressure under the condition that other conditions remain unchanged; represents the fitting function of the minimum principal stress changing with the confined water pressure under the condition that other conditions remain unchanged;

[0015] Step 5: Construct the shear failure criterion and tensile failure criterion of the coal floor.

[0016] When the thickness of the coal floor rock layer is less than 1 / 10 of its horizontal extension size, the internal layer structure is developed, and no fracture is seen in the transverse direction, it is regarded as an elastic thin plate subjected to transverse uniform load and simply supported at the boundary.

[0017] According to the Mohr-Coulomb criterion, when the maximum shear stress acting on the coal floor aquiclude exposed area exceeds the shear strength of the floor aquiclude, the floor aquiclude will fail in shear, and the shear failure criterion expression is:

[0018] (3)

[0019] In the formula, is the maximum shear stress of the coal floor aquifer exposed area, is the shear strength of the floor aquifer;

[0020] According to the tensile failure criterion of hydraulic fracturing, when the sum of the minimum principal stress of the coal floor aquifer exposed area and the tensile strength is less than the water pressure, the floor aquifer will be tensile failure, and the tensile failure criterion expression is:

[0021] (4)

[0022] In the formula, is the confined water pressure, is the tensile strength of the aquifer, is the minimum principal stress of the coal floor aquifer exposed area;

[0023] Step 6: Based on the shear failure criterion and the tensile failure criterion, the critical confined water pressure when the coal floor thickness is M is obtained;

[0024] Substitute the shear failure criterion into the maximum shear stress fitting function, and combine the shear strength of the aquifer , solve the corresponding confined water pressure P that meets the condition, as the critical value of water inrush caused by shear failure;

[0025] Substitute the tensile failure criterion into the minimum principal stress fitting function, and combine the tensile strength of the aquifer , solve the corresponding confined water pressure P that meets the condition, as the critical value of water inrush caused by tensile failure;

[0026] Step 7: Substitute the two groups of critical confined water pressure obtained into the water inrush coefficient calculation formula, and the smaller water inrush coefficient obtained is the water inrush coefficient threshold of the mine.

[0027] The water inrush coefficient calculation formula is:

[0028] (5)

[0029] In the formula, T is the water inrush coefficient, is the confined water pressure, and M is the aquifer thickness.

[0030] The beneficial effects produced by the above technical scheme are:

[0031] This invention provides a method for determining the threshold of water inrush coefficient in open-pit coal seams based on numerical simulation. By integrating elastic thin-plate theory, hydraulic fracturing principle, and Mohr-Coulomb strength criterion, this invention proposes a criterion applicable to water inrush in open-pit coal seams, achieving for the first time a complete path from stress response simulation to quantitative identification of critical water inrush conditions. Based on numerical simulation results under different confined water pressure conditions, this method constructs fitting functions for the relationship between maximum shear stress and confined water pressure, and minimum principal stress and confined water pressure. Based on shear and tensile failure criteria, it identifies the critical confined water pressure at which water inrush occurs, and determines the water inrush coefficient threshold using the water inrush coefficient method. This method significantly improves the scientific rigor and applicability of the water inrush criterion. Compared to traditional empirical methods, this invention has advantages such as clear theoretical basis, quantifiable parameters, and wide applicability, providing technical support for the assessment and precise prevention of water inrush hazards in open-pit coal mines, and possessing good engineering practical value and promising prospects for promotion. Attached Figure Description

[0032] Figure 1 This is a technical roadmap for a method of determining the threshold of water inrush coefficient in open-pit coal mine floor based on numerical simulation, according to the present invention.

[0033] Figure 2 This is a schematic diagram of a three-dimensional numerical simulation model in an embodiment of the present invention;

[0034] Figure 3 This is a maximum shear stress cloud diagram under different pressurized water pressure conditions in the embodiments of the present invention;

[0035] Where (a) - confined water pressure 0.07MPa, (b) - confined water pressure 0.08MPa, (c) - confined water pressure 0.09MPa, (d) - confined water pressure 0.10MPa, (e) - confined water pressure 0.11MPa;

[0036] Figure 4 This is a minimum principal stress cloud diagram under different pressurized water pressure conditions in the embodiments of the present invention;

[0037] Where (a) - confined water pressure 0.07MPa, (b) - confined water pressure 0.08MPa, (c) - confined water pressure 0.09MPa, (d) - confined water pressure 0.10MPa, (e) - confined water pressure 0.11MPa;

[0038] Figure 5 This is a fitting curve of the maximum shear stress under different pressurized water pressure conditions in the embodiments of the present invention;

[0039] Figure 6 This is a minimum principal stress fitting curve diagram under different pressurized water pressure conditions in the embodiments of the present invention. Detailed Implementation

[0040] The specific embodiments of the present application are described in further detail below in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present application but are not intended to limit the scope of the present application.

[0041] A numerical simulation-based coal floor water inrush coefficient threshold determination method for open-pit mines, the technical route is as shown in Figure 1 The steps are as follows:

[0042] Step 1: Collect the hydrogeological and engineering geological data of the studied mine area, and obtain the confined water pressure and the thickness of the aquiclude in the mine area;

[0043] Take a certain open-pit mine as an example. There are three aquifers in the area, all of which are pore aquifers. The Quaternary dune aquifer is a phreatic aquifer, the Neogene upper Neogene bottom sandstone aquifer of the coal seam roof and floor, and the Paleogene Paleocene-Eocene bottom sandstone aquifer are all confined aquifers, and there is no hydraulic connection between the aquifers. The hydrogeological model of the mine area is as shown in Figure 2 The block contains three coal groups, of which the main mining coal seam is C coal seam with a thickness of 10m-23m and an average thickness of 17m. There is a mudstone aquiclude between the C coal seam floor and the lower confined aquifer with a thickness of about 2-4m. At present, it has been mined to the C2 coal seam. Due to the exposure of the aquiclude and the influence of mining disturbance and confined water pressure, water inrush phenomenon is prone to occur. The current confined water pressure in the study area is 0.08MPa, and the thickness of the coal floor aquiclude is 2m. The physical and mechanical indexes of each layer of rock-soil in this simulation are shown in Table 1 below;

[0044] Table 1 Recommended values of physical and mechanical parameters of rock-soil

[0045] Rock formation cohesion c (KPa) friction angle φ (°) Bulk density of rock mass γ (kN / m 3 )]]> permeability coefficient K (m / s) Tensile strength K P (MPa) Quaternary system 9 33.38 17.54 2.5 x 10 -5 ]] 0.018 clayey siltstone 99.5 24.38 20.29 6.6 x 10 -7 ]] 0.05 phreatic aquifer 43.25 27.75 18.5 7.48 x 10 -5 ]] 0.001 confined aquifer 5 35 19 1.4 x 10 -4 ]]> 0.005 mudstone 105.5 22.5 17.98 3.1 x 10 -7 ]]> 0.014 coal 157.25 31.75 11.84 3.3 x 10 -6 ]] 0.015 waste 6.93 35 19 5.1 x 10 -6 ]]> 0.006

[0046] Step 2: Build an open-pit numerical model and set boundary conditions and mechanical parameters;

[0047] In this embodiment, the three numerical models are built by Rhino software. The boundary conditions and initial parameters of the numerical model are as follows: the lateral boundary and the bottom boundary of the model are set to horizontal and vertical displacement constraints, the top boundary is a free boundary, and the ground stress is applied, and the self-weight of each rock layer in the model is initialized; the roof of the confined aquifer is set as a control water head boundary, and the bottom bedrock is set as a permeable boundary to reflect the seepage characteristics of the aquifer, wherein the initial saturation of the confined aquifer is set to 1, and the initial saturation of the overburden rock layer is set to 0. In the initial operation stage, first, the mechanical field calculation is carried out, and the initial equilibrium state of fluid-solid coupling is established. On the basis of calculation convergence, the mechanical-seepage coupling iterative calculation is carried out, and the whole system reaches the steady state balance. The numerical simulation model in this embodiment is as shown in Figure 2 ​

[0048] Step 3: Set up different pressurized water pressure conditions and perform numerical simulation calculations to obtain the minimum principal stress and maximum shear stress in the exposed area of ​​the coal floor water-resistant layer under each working condition, thereby obtaining the stress field distribution law under different pressurized water pressure conditions.

[0049] Based on field survey data and monitoring data, this embodiment only considers the gravitational field caused by its own weight during calculation. It simulates a fluid-structure interaction state and explores the stress distribution variation law of the coal seam floor under different confined water pressure conditions. The different confined water pressure conditions are set as follows:

[0050] The thickness of the waterproof layer at the bottom of the coal seam is 2m, and the pressure of the pressurized water is 0.07MPa, 0.08MPa, 0.09MPa, 0.10MPa, and 0.11MPa, respectively.

[0051] In this embodiment, the minimum principal stress and maximum shear stress contour maps obtained by simulating different pressurized water pressure conditions are shown below. Figure 3 , Figure 4 As shown, Figure 3 as well as Figure 4 Figures (a)-(e) represent confined water pressures of 0.07 MPa, 0.08 MPa, 0.09 MPa, 0.10 MPa, and 0.11 MPa, respectively. According to the minimum principal stress contour maps, the minimum principal stress values ​​in the exposed area of ​​the slab change more significantly with increasing confined water pressure, and the area of ​​significant change gradually expands. The stress distribution contour lines are basically parallel to the slope surface. According to the maximum shear stress contour maps, there is a positive correlation between confined water pressure and the maximum shear stress of the slab. The higher the water pressure, the stronger the disturbance to the stress field of the slab, and the greater the possibility of shear failure of the rock strata. At low water pressure, the stress is concentrated in localized areas of the exposed slab, while at high water pressure, the high-value shear stress area extends to a wider area of ​​the slab, reflecting the expanded range of water pressure inducing shear failure in the rock strata.

[0052] Step 4: Perform nonlinear curve fitting on the minimum principal stress and maximum shear stress of the exposed area of ​​the coal floor water-resistant layer under various working conditions obtained from the simulation, and obtain the fitting functions of minimum principal stress and confined water pressure and maximum shear stress and confined water pressure respectively.

[0053] The fitting function expression for the maximum shear stress and the confined water pressure is as follows:

[0054] (1)

[0055] The fitting function expression for the minimum principal stress and the confined water pressure is as follows:

[0056] (2)

[0057] In the formula, is the maximum shear stress of the coal floor in the coal floor aquifer exposed area, unit: MPa; is the minimum principal stress of the coal floor in the coal floor aquifer exposed area, unit: MPa; P is the confined water pressure, unit: MPa; is the fitting function of the relationship curve between the maximum shear stress and the confined water pressure under the condition that the thickness of the aquifer and the length of the coal floor exposed area remain unchanged; is the fitting function of the relationship curve between the minimum principal stress of the coal floor in the coal floor aquifer exposed area and the confined water pressure under the condition that the thickness of the aquifer and the length of the coal floor exposed area remain unchanged;

[0058] The fitting function expression of the maximum shear stress of the coal floor in the coal floor aquifer exposed area and the aquifer pressure in the embodiment is: ;

[0059] The fitting function expression of the minimum principal stress of the coal floor in the coal floor aquifer exposed area and the aquifer pressure is: ;

[0060] Step 5: Construct the shear failure criterion and tensile failure criterion of the coal floor: when the thickness of the coal floor rock is less than 1 / 10 of the horizontal extension size, the internal layer structure is developed, and no fracture is found in the transverse direction, it is regarded as an elastic thin plate under the action of transverse uniform load and simply supported at the boundary.

[0061] According to the generalized Hooke's law of elastic mechanics, for the thin plate in the plane stress state, there is:

[0062]

[0063]

[0064]

[0065] In the formula: is the elastic modulus of the thin plate, unit: MPa; , are the normal stresses in x and y directions, unit: MPa; is the Poisson's ratio, is the shear stress, unit: MPa; w is the deflection, unit: m.

[0066] Since the floor is simply supported at the boundary, there is , , n is the normal of the boundary.

[0067] The expression of the deflection of the rectangular thin plate (a x b) under the action of uniform load is:

[0068]

[0069] In the formula: is the deflection, unit: m; is the uniform load, unit: N / m; and is the discrete frequency parameter of Fourier series expansion; a is the length of the thin plate, unit: m; b is the width of the thin plate, unit: m; D is the bending stiffness of the thin plate, unit: .

[0070] Therefore, the deflection is obtained by taking the second derivative:

[0071]

[0072] The above formula is brought into the shear stress expression, and the shear stress function is obtained:

[0073]

[0074] To further determine the distribution characteristics of the shear stress in the coal floor aquifer and the position of the extreme value, it is found that the shear stress is modulated by the sine and cosine functions in the Fourier series term. The partial derivatives of the shear stress function with respect to x and y are obtained:

[0075]

[0076]

[0077] Let the above two partial derivatives be zero at the same time, i.e.:

[0078]

[0079]

[0080] The stationary point position of the shear stress can be solved by the above formula. Considering the periodicity of the function and the geometric symmetry of the plate, it is easy to know that the extreme value of the shear stress often appears in the following areas: the geometric center of the plate (x=a / 2, y=b / 2), the midpoint of the plate boundary (x=a / 2, y=0 or x=0, y=b / 2), the corner point of the plate (x=0, y=0), etc.

[0081] According to the Mohr-Coulomb criterion, when the maximum shear stress acting on the exposed area of the coal floor aquifer exceeds the shear strength of the coal floor aquifer, the coal floor aquifer will fail in shear. Therefore, the shear failure criterion expression is:

[0082] (3)

[0083] In the formula, is the maximum shear stress of the exposed area of the coal floor aquifer, unit: MPa; The shear strength of the floor water-resisting layer, unit: MPa;

[0084] According to the thin plate formula in the plane stress state, the principal stress can be determined by solving the eigenvalue equation of the stress state. For the plane stress state, the eigenvalue equation is:

[0085]

[0086] In the formula, σx, σy and τxy are stress components, units: MPa; is the principal stress, unit: MPa;

[0087] Substitute the stress component expression into the eigenvalue equation to obtain:

[0088]

[0089] Therefore, the principal stress can be obtained as:

[0090]

[0091] Take the second-order derivative of x and y in the deflection expression, respectively, to obtain:

[0092]

[0093]

[0094] The minimum principal stress is obtained by taking the negative solution, and the minimum principal stress is:

[0095]

[0096] Considering the periodicity of the function and the geometric symmetry of the plate, it is easy to know that the minimum principal stress often occurs in the following regions: the geometric center of the plate (x=a / 2, y=b / 2), the midpoint of the plate boundary (x=a / 2, y=0 or x=0, y=b / 2), and other stress concentration regions.

[0097] According to the hydraulic splitting tensile failure criterion, when the sum of the minimum principal stress of the coal floor water-resisting layer exposed area and the tensile strength is less than the water pressure, the floor water-resisting layer will be tensile failure, and the tensile failure criterion expression is:

[0098] (4)

[0099] In the formula, is the confined water pressure, unit: MPa; is the tensile strength of the water-resisting layer, unit: MPa; is the minimum principal stress of the coal floor water-resisting layer exposed area of the coal floor, unit: MPa;

[0100] Step 6: Based on the shear failure criterion and the tensile failure criterion, the critical confined water pressure of the coal seam floor thickness M is obtained.

[0101] Based on shear failure criterion When the shear strength of the aquiclude is , solve the corresponding water pressure P that meets the condition as the water inrush critical value of shear failure; in this embodiment, the shear strength of the mudstone is 0.23 MPa, so when the maximum shear stress MPa, the floor occurs shear failure. Through analysis Figure 5 , it can be known that, under the condition that the thickness of the aquiclude is 2 m, when the water pressure is greater than 0.085 MPa, the maximum shear stress MPa, the floor aquiclude occurs shear failure, and water inrush may occur;

[0102] Based on tensile failure criterion When the tensile strength of the aquiclude is , solve the corresponding water pressure P that meets the condition as the water inrush critical value of tensile failure; in this embodiment, the tensile strength of the mudstone is 0.014 MPa, so when the minimum principal stress MPa, the floor occurs tensile failure. Through analysis Figure 6 , it can be known that, under the condition that the thickness of the aquiclude is 2 m, when the water pressure is greater than 0.09 MPa, the minimum shear stress MPa, the floor aquiclude occurs tensile failure, and water inrush may occur;

[0103] Step 7: substitute the two groups of critical water pressure values obtained into the water inrush coefficient calculation formula to calculate the smaller water inrush coefficient as the water inrush coefficient threshold of the mine.

[0104] The water inrush coefficient calculation formula is:

[0105] (5)

[0106] In the formula, T is the water inrush coefficient, the unit is MPa / m; P is the water pressure, the unit is MPa; and M is the thickness of the aquiclude, the unit is m.

[0107] In this embodiment, the water inrush coefficient threshold of the mine is calculated to be 0.0425 MPa / m.

[0108] The present application utilizes numerical simulation software, such as FLAC 3D ​, COMSOL, etc. to simulate the water inrush process under different mining conditions of the open-pit mine. The flow of underground water, rock deformation and damage under different geological conditions are simulated, and the threshold of the water inrush coefficient is determined by analyzing the simulation results. For example, the seepage conditions under different water pressures and thicknesses of the water-resisting layer are simulated, the water pressure value corresponding to the critical water inrush state is found out, and thus the threshold of the water inrush coefficient is determined. The method significantly improves the scientificity and applicability of the water inrush risk evaluation. Compared with the traditional empirical method, the present application has the advantages of clear theoretical basis, quantifiable parameters, wide application range, etc. The threshold of the water inrush coefficient under complex conditions can be determined through simulation, which can provide technical support for the water inrush risk evaluation and precise prevention and control of the open-pit coal mine, and has good engineering practical value and popularization prospect.

[0109] The above description is merely the preferred embodiments of the present disclosure and the explanation of the applied technical principles. Those skilled in the art should understand that the inventive scope involved in the embodiments of the present disclosure is not limited to the technical solutions formed by the specific combinations of the above technical features, and should also cover other technical solutions formed by any combinations of the above technical features or equivalent features without departing from the above inventive concept. For example, the technical solutions formed by mutually replacing the above features and the technical features disclosed in the embodiments of the present disclosure (but not limited to) having similar functions.

Claims

1. A numerical simulation-based coal floor water inrush coefficient threshold determination method for an open-pit mine, characterized in that, The method comprises the following steps: Step 1: collect hydrogeological and engineering geological data of the mine area under study, and obtain the confined water pressure and the thickness of the aquiclude in the mine area; Step 2: build a numerical model of the open-pit mine, and set boundary conditions and mechanical parameters; Step 3: set different confined water pressure conditions, perform numerical simulation calculation, obtain the stress field distribution law under different confined water pressure conditions, and identify the minimum principal stress and the maximum shear stress of the coal floor aquiclude exposed area under each condition; Step 4: respectively perform nonlinear fitting on the minimum principal stress of the coal floor aquiclude exposed area, the confined water pressure and the maximum shear stress of the coal floor aquiclude exposed area, and the confined water pressure, and respectively build fitting functions; Step 5: build a shear failure criterion and a tensile failure criterion for the coal floor; When the thickness of the coal floor rock stratum is less than 1 / 10 of the horizontal extension size, the internal layer structure is developed, and no fracture is found in the transverse direction, the coal floor is regarded as an elastic thin plate subjected to a transverse uniform load and simply supported at the boundary; Step 6: based on the shear failure criterion and the tensile failure criterion, the critical confined water pressure when the coal floor thickness is M and water inrush occurs is obtained; Step 7: substitute the two groups of critical water pressure values into the water inrush coefficient calculation formula, and the smaller water inrush coefficient obtained is the water inrush coefficient threshold of the mine.

2. The method for determining the water inrush coefficient threshold of the coal floor in the open-pit mine based on the numerical simulation according to claim 1, characterized in that, The fitting function expression of the maximum shear stress and the confined water pressure in step 4 is: （1） The fitting function expression of the minimum principal stress and the confined water pressure is: （2） In the formula, is the maximum shear stress of the coal floor, the coal floor, the coal floor, the aquifer exposed area, is the minimum principal stress of the coal floor, the coal floor, the coal floor, the aquifer exposed area, and P is the confined water pressure, represents the fitting function of the maximum shear stress changing with the confined water pressure under the condition that other conditions remain unchanged; represents the fitting function of the minimum principal stress changing with the confined water pressure under the condition that other conditions remain unchanged.

3. The method for determining the water inrush coefficient threshold of the coal floor in the open-pit mine based on the numerical simulation according to claim 1, characterized in that, The shear failure criterion and the tensile failure criterion in step 5 are specifically: According to the Mohr-Coulomb criterion, when the maximum shear stress acting on the coal floor aquiclude exposed area exceeds the shear strength of the coal floor aquiclude, the coal floor aquiclude will be sheared and damaged, and the shear failure criterion expression is: （3） In the formula, is the maximum shear stress of the coal floor, the coal floor, the coal floor, the water-resisting layer, the exposed area of the water-resisting layer, is the shear strength of the floor water-resisting layer; According to the hydraulic fracturing tensile failure criterion, when the sum of the minimum principal stress and the tensile strength is less than the water pressure, the coal floor aquiclude will be tensilely damaged, and the tensile failure criterion expression is: （4） wherein, Pw is the water pressure, Pm is the tensile strength of the aquiclude, Pm is the tensile strength of the aquiclude, 4. The method for determining the water inrush coefficient threshold of the coal floor in the open-pit mine based on the numerical simulation according to claim 1, characterized in that, The step 6 is specifically: substituting the shear failure criterion into the maximum shear stress fitting function, combining the water-resisting layer shear strength , solving the corresponding water pressure P satisfying the condition as the water inrush critical value of shear failure. The tensile failure criterion Substitute into the minimum principal stress fitting function, combined with the water-resisting layer tensile strength , solve the corresponding water pressure P that meets the conditions, as the water inrush critical value of tensile failure.

5. The method for determining the water inrush coefficient threshold of the coal floor in the open-pit mine based on the numerical simulation according to claim 1, characterized in that, Step 7 is specifically: The water inrush coefficient calculation formula is: （5） In the formula, T is the water inrush coefficient, is the confined water pressure, and M is the water-resisting layer thickness.

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