Coal mining working face separation layer mud-carrying sand water inrush position forecasting method

Abstract

The invention discloses a coal mining working face separation layer mud-carrying sand water inrush position forecasting method. The method comprises the following steps that the primary fracture position and the periodic fracture position of a lower water-resisting layer serve as the separation layer water inrush position of a mining working face; calculating the shearing force of the water flow to particles of the material source layer based on the flow velocity of the separation layer water reaching the material source layer, and judging whether the separation layer water inrush position carries silt or not, so as to determine the working face separation layer silt-carrying water inrush position; and calculating a risk index of the working face carrying mud-sand water inrush, and dividing the risk grade of the working face separation layer carrying mud-sand water inrush position based on the risk index of the working face carrying mud-sand water inrush to obtain a risk grade division result. According to the method, accurate forecasting of the separation layer mud-carrying sand water inrush disaster of the coal mining working face is achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of mine water disaster prevention and control, and particularly relates to a method for predicting the position and risk level of water inrush with mud and sand from separated strata in a coal mining face. Background Technique

[0002] During the coal mining process, the water inrush disaster with mud and sand from separated strata has become a new type of sand bursting disaster, with high suddenness, periodicity and instantaneousness. The occurrence of such disasters usually occurs during the excavation process of the working face. The originally stable rock strata suddenly rupture or separate, resulting in the rapid influx of groundwater and sediment, forming a water inrush disaster. Different from traditional sand bursting disasters, the water inrush disaster with mud and sand from separated strata usually comes from deep thick coal seams or soft rock strata, and is not necessarily directly related to the hydrogeological characteristics of the surface loose layer.

[0003] Currently, existing research mainly focuses on the treatment of water inrush and sand bursting disasters from the surface loose layer. However, there is still a large technical gap in accurately predicting the position of water inrush with mud and sand from separated strata during the working face mining period, especially during the excavation process. This problem arises from the complexity of the fracture of the high-level rock strata and the interaction between water and rock during the working face mining process, which makes it difficult to accurately grasp the temporal and spatial distribution of the water inrush disaster with mud and sand from separated strata, thus affecting the accuracy and efficiency of existing prevention and control technologies.

[0004] Due to the strong randomness and unpredictability of the occurrence of water inrush with mud and sand from separated strata, in the safety management and disaster prevention and control of actual mining areas, how to accurately predict the time, position, mud and sand carrying situation and risk level of water inrush from separated strata during the working face mining period has become a key problem in mine water disaster prevention and control. The application of existing monitoring technologies and prediction models is relatively limited in this regard, and they fail to effectively combine the dynamic changes during the excavation process and the actual situation of the fracture of the separated strata zone, resulting in insufficient accuracy and timeliness of the prediction, thus affecting the safe production of the mine. Summary of the Invention

[0005] In view of the above analysis, the embodiments of the present invention aim to provide a method for predicting the position and risk level of water inrush with mud and sand from separated strata in a coal mining face, so as to solve the problem in the prior art that it is difficult to predict the position and risk level of water inrush from separated strata during the coal mining face mining period.

[0006] The object of the present invention is achieved as follows:

[0007] A method for predicting the position of water inrush with mud and sand from separated strata in a coal mining face includes the following steps:

[0008] S1. Based on the mining-induced overlying strata engineering geological model, identify the potential water inrush separated strata zone and identify the strata position of the water inrush material source with mud and sand;

[0009] S2. Determine the initial fracture position and periodic fracture position of the lower aquifuge based on the identified potential water inrush separation zone, and use the initial fracture position and periodic fracture position of the lower aquifuge as the water inrush separation positions in the mining and excavation face;

[0010] S3. Calculate the flow velocity of the separated water reaching the source layer at the fracture position during the advancement of the working face, and calculate the shear force of the water flow on the particles of the source layer based on the flow velocity of the separated water reaching the source layer; By comparing the shear force of the water flow on the particles of the source layer with the shear strength of the source layer against water erosion, determine whether the water inrush separation position carries sediment, so as to determine the water inrush separation position with sediment in the working face;

[0011] S4. Calculate the risk index of water inrush with sediment in the working face, and classify the risk level of the water inrush separation position with sediment in the working face based on the risk index of water inrush with sediment in the working face to obtain the risk level classification result.

[0012] Furthermore, in step S2, establish an initial fracture model and a periodic fracture model;

[0013] For the initial fracture model, the distance of the initial fracture position of the lower aquifuge from the cutting eye is l, and the calculation formula is:

[0014]

[0015] For the periodic fracture model, the periodic fracture position of the lower aquifuge is located at the position of l + nL1 from the cutting eye, where n = 1, 2, 3......; L1 is the periodic fracture distance of the lower aquifuge, and the calculation formula is:

[0016]

[0017] In the above formula, P is the concentrated supporting force of the lower aquifuge by the underlying rock formation, N; q is the self-weight of the rock formation, kg; b is the width of the simply supported beam at both ends, m; h is the thickness of the lower aquifuge, m; σ c is the flexural strength of the rock formation, MPa; H is the distance from the neutral plane of the lower aquifuge to the coal seam roof, m; β is the fracture angle of the rock formation, generally taking 0.7° - 0.85°.

[0018] Furthermore, in step S3, calculate the flow velocity v of the separated water reaching the source layer according to the following formula:

[0019]

[0020] In the above formula, v is the flow velocity of the separated water reaching the source layer, m / s; g is the acceleration of gravity, m / s 2; h0 is the height of the water level in the separated layer, m; z0 and z are the heights of the separated layer position and the source layer position respectively, m; f is the friction coefficient; L is the flow path length of the water flow along the fracture, m; D is the equivalent hydraulic diameter of the fracture, m.

[0021] Furthermore, in step S3, the shear force τ of the water flow on the particles of the source layer is calculated according to the following formula:

[0022] τ = ρ w ·v 2 ·C d ;

[0023] In the above formula, τ is the shear force of the water flow on the particles of the source layer, N; ρ w is the density of water, kg / m 3 ; v is the flow velocity of the water in the separated layer when it reaches the source layer, m / s; C d is the shear force coefficient.

[0024] Furthermore, in step S3, the following principle is used to determine whether the position of the separated layer water inrush carries sediment:

[0025] When τ > τ s , then separated layer water inrush occurs and the water inrush carries sediment;

[0026] When τ ≤ τ s , then only separated layer water inrush occurs and no sediment will be carried.

[0027] In the above formula, τ is the shear force of the water flow acting on the particles of the source layer, N; τ s is the shear strength of the source layer against water erosion, MPa, which is obtained through experimental testing.

[0028] Furthermore, in step S4, the risk index R of the working face water inrush with sediment is jointly determined by the separated layer water volume factor W and the sediment carrying factor S. The risk index R of the working face water inrush with sediment is calculated according to the following formula:

[0029] R = αW βS ;

[0030] Among them, W is the separated layer water volume factor; S is the sediment carrying factor; α, β are normalized weight coefficients, taking α = 0.5 and β = 0.5.

[0031] Furthermore, the separated layer water volume factor W is calculated according to the following formula:

[0032]

[0033] Among them, k h is the water pressure response coefficient; P w is the water pressure at the bottom of the aquifer, MPa; M is the mining height of the working face, m; K pis the average swelling coefficient within the range of the water-conducting fissure zone in the coal seam; Hk is the distance from the water-accumulating separated strata to the roof of the coal seam, in m.

[0034] Further, the sediment-carrying factor S is calculated according to the following formula:

[0035]

[0036] where τ is the shear force of the water flow on the particles of the material source layer, in MPa; τ s is the shear strength of the material layer against water flow erosion, in MPa; h s is the thickness of the material source layer, in m; D is the disintegration coefficient, indicating the degree of easy disintegration of the material source layer, with 0 ≤ D ≤ 1.

[0037] Further, the calculation formula for the risk index R of water inrush with sediment in the working face is:

[0038]

[0039] In the above formula, k h is the water pressure response coefficient; P w is the water pressure at the bottom of the aquifer, in MPa; M is the mining height of the working face, in m; K p is the average swelling coefficient within the range of the water-conducting fissure zone in the coal seam; H k is the distance from the water-accumulating separated strata to the roof of the coal seam, in m; τ is the shear force of the water flow on the particles of the material source layer, in MPa; τ s is the shear strength of the material layer against water flow erosion, in MPa; h s is the thickness of the material source layer, in m; D is the disintegration coefficient, indicating the degree of easy disintegration of the material source layer, with 0 ≤ D ≤ 1.

[0040] Further, when R < R1, the risk level of the position of water inrush with sediment in the separated strata of the working face is low risk;

[0041] When R1 ≤ R < R2, the risk level of the position of water inrush with sediment in the separated strata of the working face is medium risk;

[0042] When R ≥ R2, the risk level of the position of water inrush with sediment in the separated strata of the working face is high risk;

[0043] where R1 is the risk level threshold from low risk to medium risk, and R2 is the risk level threshold from medium risk to high risk.

[0044] Compared with the prior art, the method for predicting the position of water inrush with sediment carried by separated strata in a coal mining face provided by the present invention comprehensively evaluates by combining the geological characteristics of the mining area, the mining progress, and the hydrodynamic behavior of water flow, and can accurately predict the position and risk level of water inrush with sediment carried by separated strata during the mining process of the coal mining face. Specifically, by calculating the fracture position of the water inrush separated strata zone, the position where the water inrush occurs can be accurately predicted, providing more accurate prediction information for water disaster prevention and control in the mining area; moreover, by comprehensively analyzing the underground water flow velocity and the water-rock interaction, and combining the critical initiation criterion, it is judged whether the water inrush from the separated strata carries sediment, and at the same time, a risk index of water inrush with sediment carried is proposed from the perspectives of water volume and sand source recharge degree, thus effectively improving the prediction accuracy of the position and risk level of water inrush with sediment carried by separated strata, which has a positive significance for the prevention and control of water inrush disasters.

[0045] In the present invention, the above technical solutions can also be combined with each other to achieve more preferred combined solutions. Other features and advantages of the present invention will be described in the subsequent description, and some advantages can be made obvious from the description, or understood by implementing the present invention. The objectives and other advantages of the present invention can be achieved and obtained through the content specifically pointed out in the description and the drawings. Brief Description of the Drawings

[0046] In order to more clearly illustrate the technical solutions in the embodiments of this specification or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings described below are only some embodiments recorded in the embodiments of this specification, and those of ordinary skill in the art can also obtain other drawings based on these drawings.

[0047] Figure 1 It is a schematic diagram for analyzing the force condition of the lower confining layer provided by an embodiment of the present invention;

[0048] Figure 2 It is a schematic diagram of the mechanical model of the lower confining layer provided by an embodiment of the present invention;

[0049] Figure 3 It is an operation flow chart of the method for predicting the position of water inrush with sediment carried by separated strata in a coal mining face provided by an embodiment of the present invention. Detailed Embodiments

[0050] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the following will clearly and completely describe the technical solutions in the embodiments of this application with reference to the drawings in the embodiments of this application. Obviously, the described embodiments are some, but not all, of the embodiments of this application. All other embodiments obtained by those of ordinary skill in the art without creative efforts based on the embodiments in this application belong to the scope of protection of this application.

[0051] For ease of understanding the embodiments of the present application, the following will further explain and illustrate with specific embodiments in conjunction with the accompanying drawings. The embodiments do not limit the embodiments of the present application. In the drawings, for clarity and / or descriptive purposes, the dimensions and relative dimensions of components may be exaggerated. When exemplary embodiments can be implemented differently, the specific process sequences may be performed in a different order than described. For example, two consecutively described processes may be performed substantially simultaneously or in an order opposite to the described order. In addition, the same reference numerals represent the same components.

[0052] The terms used herein are for the purpose of describing specific embodiments and are not intended to be restrictive. As used herein, unless the context clearly indicates otherwise, the singular forms "a", "an", and "the" are also intended to include the plural forms. In addition, when the terms "comprising" and / or "including" and their variants are used in this specification, it is stated that there are the stated features, wholes, steps, operations, components, assemblies, and / or groups thereof, but it does not exclude the presence or addition of one or more other features, wholes, steps, operations, components, assemblies, and / or groups thereof. It should also be noted that, as used herein, the terms "substantially", "about", and other similar terms are used as approximate terms rather than degree terms, so they are used to explain the inherent deviations of measured values, calculated values, and / or provided values that those of ordinary skill in the art will recognize.

[0053] Embodiment 1

[0054] A specific embodiment of the present invention, as Figures 1 to 3 shown, discloses a method for predicting the position of water inrush with mud and sand carried by separation in a coal mining face, including steps S1 to S4, specifically as follows:

[0055] S1. Based on the engineering geological model of overlying strata affected by mining, identify potential water-inrush separation zones and identify the strata positions of mud-and-sand-carrying water-inrush sources.

[0056] In this step, by collecting geological exploration data of the mining area / working face (including borehole data, hydrogeological data, etc.) and combining relevant information of the mined coal seam (such as coal seam thickness, burial depth, working face width, etc.), an engineering geological model of overlying strata affected by mining is constructed. Based on the constructed engineering geological model of overlying strata affected by mining, the "water-inrush separation zones" that may cause water inrush are identified. This step is the basis for subsequent prediction of the water-inrush position and provides key geological models and computational mechanics parameters for the subsequent steps.

[0057] S11. Collect geological data of the mining area / working face and construct an engineering geological model of overlying strata affected by mining.

[0058] This step aims to construct an engineering geological model that can reflect the characteristics of overlying strata structure during mining by collecting geological exploration data of the mining area / working face, including borehole data, hydrogeological data, etc., and combining relevant information of the mined coal seam (such as coal seam thickness, burial depth, working face width, etc.). The model needs to clarify information such as the sequence, thickness, lithology, structure, and burial depth of the strata above the coal seam, divide different engineering geological rock groups, and then identify key horizons such as coal seams, main aquifers, and aquicludes.

[0059] S12. Identify potential water-inrush separated strata zones based on the constructed engineering geological model of overlying strata during mining.

[0060] This step is based on the constructed engineering geological model of overlying strata during mining to identify the composite horizons that may cause separated strata water inrush, namely the "water-inrush separated strata zone", which needs to meet the following two basic conditions:

[0061] Condition 1: Specific strata combination structure: The water-inrush separated strata zone needs to have a combination structure of an upper hard stratum and a lower aquiclude. During the mining process, due to the mechanical property differences between the upper hard stratum and the lower aquiclude, uneven settlement will occur between the two. At the same time, the lower aquiclude needs to maintain integrity during the bending deformation process and no developed and connected fissures, so as to form a temporarily closed separated strata space between the upper hard stratum and the lower aquiclude, providing the necessary space conditions for separated strata water accumulation.

[0062] Condition 2: Spatial position of adjacent aquifers: The closed separated strata space needs to be located near the aquifer. Usually, the upper hard stratum is the aquifer. During the development of separated strata, the groundwater stored in the aquifer will continuously gather into the closed separated strata space to form a separated strata water accumulation body, which becomes the direct water source of separated strata water inrush.

[0063] In summary, the "water-inrush separated strata zone" in this embodiment refers to a composite horizon composed of a lower aquiclude, water-accumulated separated strata, and an upper hard stratum, as Figure 1 shown. Among them, the lower aquiclude is usually low-permeability strata such as mudstone, muddy sandstone, siltstone, and shale; the upper hard stratum is generally water-filled aquifers such as fine sandstone, medium sandstone, coarse sandstone, and conglomerate.

[0064] S13. Test and statistically analyze the basic physical and mechanical parameters.

[0065] On the basis of identifying the "water inrush separated strata zone" horizon, samples are collected from the relevant horizons, the collected samples are tested to obtain test data, and at the same time, by collecting existing geological materials in the mining area, a part of the required data can also be statistically obtained, so as to comprehensively obtain various data parameters required in the subsequent steps. Optionally, the basic physical and mechanical parameters that need to be tested and statistically analyzed mainly include: rock formation specific weight, thickness of the underlying water-resisting layer, distance from the neutral plane of the underlying water-resisting layer to the coal seam roof, rock formation fracture angle, working face width, distance between the aquifer and the coal seam, fracture friction coefficient, shear force coefficient, initial water level height of the aquifer, etc.

[0066] S14. Identify the source horizon of the mud-carrying water inrush

[0067] The disaster of high-level separated strata with mud-carrying water inrush refers to the situation where when there are "source materials" such as paleo-weathered crust rock formations, argillaceous rock formations, and weakly cemented sandstone rock formations in the surrounding rock strata of the water inrush channel, the separated strata water will carry a large amount of mud, sand, and stones into the working face. When this kind of disaster occurs, it may cause the supports to be crushed and the working face to be blocked, and in severe cases, it will pose a major hidden danger to the safety of mine production. In order to effectively identify the horizons that may contain "source materials", this step needs to test and evaluate the disintegration properties of the rock formations through the following methods, so as to determine the source horizons.

[0068] The disintegration coefficient refers to the ability of a rock formation to break and disintegrate under the action of external forces (such as mining pressure, groundwater flow, etc.). Rock formations with a high disintegration coefficient often have poor mechanical properties and are prone to disintegrate and generate mud and sand flows under the action of water flow. Therefore, first, the disintegration coefficient of the rock formation is determined through laboratory rock mechanics tests. The calculation formula for the disintegration coefficient D is as follows:

[0069]

[0070] Where, R c is the mass of the rock sample after disintegration, kg; R0 is the initial mass of the rock sample, kg.

[0071] According to the experimental results, rock formations with a disintegration coefficient greater than 0.4 can be regarded as having strong disintegration properties and belonging to possible "source horizons".

[0072] S2. Based on the identified potential water inrush separated strata zone, preliminarily determine the location of separated strata water inrush in the mining and excavation working face. Specifically, based on the identified potential water inrush separated strata zone, determine the initial fracture position and periodic fracture position of the underlying water-resisting layer, and take the initial fracture position and periodic fracture position of the underlying water-resisting layer as the location of separated strata water inrush in the mining and excavation working face.

[0073] This step is based on the potential water inrush separated strata zone identified in S1 ( Figure 1) Construct a mechanical model of the lower aquifuge in the water-inrush separation zone, establish mechanical criteria for the initial fracture and periodic fracture of the lower aquifuge, and further calculate the position of the initial fracture and the position of periodic fracture of the lower aquifuge. The position of the initial fracture and the position of periodic fracture of the lower aquifuge are used as the positions where separation water-inrush occurs. Predicting the position where separation water-inrush occurs is the result of further mechanical analysis based on the geological model identified in the previous step, and it is also the key basis for subsequent determination of whether muddy water-inrush occurs.

[0074] S21. Establish the initial fracture model and the periodic fracture model

[0075] To analyze the separation fracture behavior of the lower aquifuge in the mining face, the following two mechanical models are established:

[0076] 1.1. Initial fracture model, adopting the fixed-end beam model: that is, adopting a beam model with fixed supports at both ends and a concentrated force acting in the middle, and analyzing the initial fracture behavior of the rock stratum under the action of uniform load and concentrated support load.

[0077] 1.2. Periodic fracture model, adopting the cantilever beam model: that is, adopting a cantilever beam model with one end fixed and supported and the other end free, and analyzing the periodic fracture behavior of the rock stratum under the action of periodic load.

[0078] S22. Force analysis and boundary conditions

[0079] 2.1. Initial fracture: Fixed-end beam model

[0080] For the initial fracture, assume that the lower aquifuge is a beam with fixed supports at both ends (which can be simply referred to as a "fixed-end beam"), as Figure 2 shown. It is subjected to a uniform load q and a concentrated support force P from the underlying rock stratum. The concentrated support force acts at the middle position of the beam, that is, the abscissa x = L / 2, where L is the length of the beam, which is also the exposed length of the lower aquifuge, in m.

[0081] Both ends of the beam are fixed supports, that is, w(0) = and w(L) = 0, where w(x) is the deflection of the beam.

[0082] 2.2. Periodic fracture: Cantilever beam model

[0083] For the periodic fracture, assume that the lower aquifuge is a cantilever beam, which is subjected to a uniform load q and a concentrated support force P from the underlying rock stratum, and the support force acts at the free end of the beam (x = L).

[0084] One end is fixed, that is, w(0) = 0; the other end is free, that is, M(L) = 0, where M(x) is the bending moment of the beam.

[0085] S23. Mechanical derivation and criteria

[0086] 3.1, Initial fracture: Fixed-end beam model at both ends

[0087] For the fixed-end beam model at both ends, that is, both ends of the beam are fixed support structures, which are subjected to uniformly distributed load and concentrated support force. The maximum bending moment M of the fixed-end beam at both ends max Occurs at the middle position of the beam, that is, at x = L / 2, and its value is:

[0088]

[0089] In the formula, M max Is the maximum bending moment of the fixed-end beam at both ends, N·m; q is the load on the rock stratum, KN / m; q = γh, γ is the self-weight of the rock stratum, KN / m 3 ; h is the thickness of the lower aquifuge, m; L is the initial fracture distance of the lower aquifuge. In the fixed-end beam model at both ends, L is the exposed length of the lower aquifuge, m; P is the concentrated support force on the lower aquifuge from the underlying rock stratum, KN, P = λγh, λ is the support coefficient, 0 < λ < 1.

[0090] Calculate the maximum working face advance distance l when the lower aquifuge fractures for the first time according to the following formula:

[0091] l = L + 2Hcotβ (3)

[0092] l is the maximum working face advance distance when the lower aquifuge fractures for the first time, m; H is the distance between the neutral plane of the lower aquifuge and the coal seam roof, m; β is the fracture angle of the rock stratum, generally taken as 0.7° - 0.85°.

[0093] The maximum bending stress σ of the fixed-end beam at both ends max Is:

[0094]

[0095] In the formula, σ max Is the maximum bending stress of the fixed-end beam at both ends, N; b is the width of the fixed-end beam at both ends, approximately taken as the inclined length of the working face, m.

[0096] Since the rock stratum failure occurs when the maximum bending stress σ max Reaches or exceeds the flexural strength σ of the rock stratum c , Therefore, the calculation formula for the initial fracture distance L of the lower aquifuge is obtained as:

[0097]

[0098] Combining formula (3) and formula (5), the calculation formula for the maximum working face advance distance l when the lower aquifuge fractures for the first time is obtained as:

[0099]

[0100] In the above formula, P is the concentrated supporting force of the lower aquifuge by the underlying rock stratum, in N; q is the self-weight of the rock stratum, in kg; b is the width of the beam with both ends fixed, in m; h is the thickness of the lower aquifuge, in m; σ c is the flexural strength of the rock stratum, in MPa; H is the distance from the neutral plane of the lower aquifuge to the coal seam roof, in m; β is the fracture angle of the rock stratum, generally taken as 0.7° - 0.85°.

[0101] The maximum advancing distance l of the working face at the initial fracture of the lower aquifuge is obtained by calculating with the above formula, that is, the distance from the initial fracture position of the lower aquifuge of the working face to the cutting eye is l.

[0102] 3.2. Periodic fracture: Cantilever beam model

[0103] For the cantilever beam model, the distributions of the bending moment and the bending stress have been given in the previous derivation. The maximum bending moment of the cantilever beam appears at the free end x = L1, and its value is:

[0104]

[0105] In the formula, L1 is the periodic fracture distance of the cantilever beam.

[0106] The maximum bending stress σ max of the cantilever beam is:

[0107]

[0108] For periodic fracture, the criterion for the fracture of the cantilever beam under periodic load is:

[0109] σ max = σ c (8)

[0110] Based on formulas (6) - (8), the calculation formula for the periodic fracture distance L1 of the lower aquifuge is obtained as:

[0111]

[0112] In the above formula, P is the concentrated supporting force of the lower aquifuge by the underlying rock stratum, in N; q is the self-weight of the rock stratum, in kg; b is the width of the beam with both ends fixed, in m; h is the thickness of the lower aquifuge, in m; σ c is the flexural strength of the rock stratum, in MPa.

[0113] Therefore, under the cantilever beam model, the periodic fracture position of the lower aquifuge of the working face is at the position of l + nL1 from the cutting eye, where n = 1, 2, 3......

[0114] S24. Criterion results and prediction of possible water inrush positions

[0115] When the working face advances to the initial fracture position or the periodic fracture position of the lower aquifuge, the lower aquifuge fractures, and water inrush occurs at the fracture position, thereby realizing the prediction of the possible water inrush position.

[0116] S3. Calculate the flow velocity of the separated layer water reaching the source layer at the fracture position during the advancement of the working face, and calculate the shear force of the water flow on the particles of the source layer based on the flow velocity of the separated layer water reaching the source layer; by comparing the shear force of the water flow on the particles of the source layer and the shear strength of the source layer against water erosion, determine whether the separated layer water inrush position determined in S2 carries sediment, so as to determine the separated layer water inrush position with sediment carried by the working face.

[0117] In this step, by calculating the flow velocity of the separated layer water reaching the source layer at the fracture position determined in S2; through the comparison between the shear force of the actual water flow scouring on the particles of the source layer and the shear strength of the source layer against water erosion, it can be further determined whether the water flow will carry sediment, so as to predict the possibility of water inrush with sediment carried at different separated layer water inrush positions.

[0118] Since water inrush will occur at the fracture position, the fracture position is the separated layer water inrush position. Separation layers are formed in the overlying strata, and accumulated water converges to form separated layer accumulated water with a volume of V. After the lower aquifuge fractures, the separated layer accumulated water drains downward along the water-conducting fissures, passes through the source layer position of the roof, erodes the rock layer at a speed of v, resulting in particle loss, and the water flow mixed with sediment particles enters the working face, forming a water inrush and sand bursting disaster. When analyzing the flow velocity of the water flow from the high-level separated layer to the source layer position of the Yan'an Formation, factors such as the hydrogeological conditions of the aquifer, the initial hydrodynamic pressure caused by the deformed and fractured rock strata, the energy loss of the water flow passing through the fissures, and the conversion of potential energy into kinetic energy need to be considered.

[0119] S31. Obtain the flow velocity v when the separated layer accumulated water reaches the source layer according to the following steps:

[0120] The total initial pressure P0 of the separated layer accumulated water is:

[0121] P0 = pgh0 (10)

[0122] where ρ is the density of water, kg / m 3 ; g is the acceleration due to gravity, m / s 2 ; h0 is the water level height of the separated layer accumulated water, m; assuming that the separated layer is full of water and connected to the aquifer, then h0 can be regarded as the water level height of the aquifer.

[0123] Assume that after the separated layer fractures, the accumulated water flows downward along the fissures, and the initial pressure is converted into kinetic energy and the energy to overcome the flow resistance. Assume that the kinetic energy of the water at the initial position is zero, and there is only pressure and potential energy. The total energy of the water flow includes the initial pressure (hydrostatic pressure and additional hydrodynamic pressure), potential energy, and energy loss during flow. The Bernoulli equation is modified as:

[0124]

[0125] z0 and z are the heights of the separated layer position and the provenance layer position, respectively, in m; v is the flow velocity reaching the provenance layer, in m / s; P f is the resistance loss pressure of the fissure flow, in N.

[0126] Substitute the total initial pressure of the separated layer water accumulation into the formula:

[0127]

[0128] The flow in the fissure can be regarded as laminar flow or turbulent flow along the fissure pipeline. According to the Darcy-Weisbach formula, the resistance loss pressure P of the fissure flow f is expressed as:

[0129]

[0130] f is the friction coefficient, which is related to the roughness of the fissure wall; L is the flow path length of the water along the fissure, which can be equivalent to the distance between the separated layer water accumulation and the provenance layer, in m; D is the equivalent hydraulic diameter of the fissure, in m.

[0131] Based on formulas (11) to (13), the following formula is obtained:

[0132]

[0133] Then the flow velocity v when the separated layer water accumulation reaches the provenance layer is

[0134]

[0135] In the above formula, v is the flow velocity of the separated layer water accumulation reaching the provenance layer, in m / s; g is the acceleration due to gravity, in m / s 2 ; h0 is the water level height of the separated layer water accumulation, in m; z0 and z are the heights of the separated layer position and the provenance layer position, respectively, in m; f is the friction coefficient; L is the flow path length of the water along the fissure, in m; D is the equivalent hydraulic diameter of the fissure, in m.

[0136] S32. Calculate the shear force τ of the water flow on the particles of the provenance layer according to the following formula:

[0137] τ = ρ w ·v 2 ·C d (16)

[0138] In the above formula, τ is the shear force of the water flow on the particles of the provenance layer, that is, the frictional force of the water flow on the rock layer particles, in MPa; ρ w is the density of water, usually taken as 1000 kg / m 3 ; v is the flow velocity when the separated layer water accumulation reaches the provenance layer, in m / s; C dis the shear force coefficient, which is related to factors such as the morphology of particles and the roughness of the rock formation. For example, on the surface of sandstone or sand layers, the C d value is between 0.01 and 0.1; on the surface of mudstone or clay layers, the C d value is relatively small, usually between 0.005 and 0.05. The specific C d value can be obtained through experimental tests.

[0139] S33. Based on the shear force τ of the water flow on the particles of the provenance layer and the shear strength τ s of the provenance layer against water flow erosion, judge whether the position of the separated layer water inrush obtained in S2 carries sediment according to the following principle:

[0140] When τ > τ s , then separated layer water inrush occurs, and the water inrush carries sediment; under this condition, it means that the water flow has sufficient erosion ability to carry sediment particles into the working face, resulting in separated layer water inrush with sediment.

[0141] When τ ≤ τ s , then only separated layer water inrush occurs and no sediment will be carried.

[0142] In the above formula, τ is the shear force of the water flow acting on the particles of the provenance layer, MPa; τ s is the shear strength of the provenance layer against water flow erosion, MPa, which is obtained through experimental tests.

[0143] S4. After determining the position of the separated layer water inrush with sediment in the working face, calculate the risk index of the separated layer water inrush with sediment in the working face, and classify the risk level of the separated layer water inrush with sediment position in the working face based on the risk index of the separated layer water inrush with sediment in the working face to obtain the risk level classification result.

[0144] In the previous steps, the position of the separated layer water inrush with sediment in the working face is identified. This step further evaluates the risk level of each water inrush position. The risk level comprehensively considers two key factors: the separated layer water volume (water inrush scale) and the sediment volume that the provenance layer can provide.

[0145] The risk index R of the separated layer water inrush with sediment in the working face is jointly determined by the separated layer water volume factor W and the sediment carrying factor S. Calculate the risk index R of the separated layer water inrush with sediment in the working face according to the following formula:

[0146] R = αW βS (17)

[0147] where, W is the separated layer water volume factor, reflecting the influence of the water inrush scale; S is the sediment carrying factor, reflecting the influence of the water flow erosion ability and the sediment supply volume; α, β are normalization weight coefficients, which can be adjusted according to the specific mine geological conditions, and α = 0.5, β = 0.5 can be taken.

[0148] The calculation processes of the separated seam water volume factor W, the sediment carrying factor S, and the risk index R are as follows:

[0149] (1) Calculate the separated seam water volume factor W

[0150] The separated seam water volume factor W is jointly determined by the size of the separated seam space and the recharge capacity of the aquifer. The calculation formula is as follows:

[0151]

[0152] Among them, k h is the water pressure response coefficient, which depends on the permeability of the aquifer. For a weakly water-rich aquifer, k h takes a value of 0.2 - 0.5; for a moderately water-rich aquifer, k h takes a value of 0.5 - 0.7; for a strongly water-rich aquifer, kh takes a value of 0.7 - 1.0; P w is the water pressure at the bottom plate of the aquifer, MPa; M is the mining height of the working face, m; K p is the average swelling coefficient in the range of the water-conducting fissure zone of the coal seam; H k is the distance from the water-accumulable separated seam to the roof of the coal seam, m.

[0153] (2) Calculate the sediment carrying factor S

[0154] The sediment carrying factor S is determined by the shear force of the water flow on the source layer and the amount of sediment that the source layer can supply. The calculation formula is as follows:

[0155]

[0156] Among them, τ is the shear force of the water flow on the particles of the source layer, MPa; τ s is the shear strength of the source layer against water flow erosion, MPa; h s is the thickness of the source layer, m; D is the disintegration coefficient, indicating the degree of easy disintegration of the source layer, 0 ≤ D ≤ 1.

[0157] (3) Substitute the calculation formulas of the separated seam water volume factor W and the sediment carrying factor S into formula (17), and the calculation formula for the risk index R of mud and sand carrying water inrush at the working face is obtained as follows:

[0158]

[0159] Substitute the relevant parameters of the working face into formula (20), calculate the risk index R at all the breaking positions of the lower confining layers (at a distance l from the cutting eye, i.e., the water inrush position, and at l + nL1, n = 1, 2, 3......), and then, according to the magnitude of the index, divide the risk levels of mud and sand carrying water inrush at different positions. Optionally, the results of the risk level division include low risk, medium risk, and high risk, as follows:

[0160] Low risk (R < R1): The amount of water in the separated layer is small, the recharge rate is low, and the water flow shear force is not sufficient to erode the source layer. The water inrush mainly shows local seepage, with clear water quality and no sediment carried. It has little impact on the working face, and only local roof fissure seepage may occur, posing no obvious threat to the mining safety. It is recommended to closely monitor the water volume change, evaluate the range of separated layer water accumulation by combining borehole observations, ensure that the water inrush volume is maintained within a controllable range, and prevent it from evolving into a more serious water inrush event.

[0161] Medium risk (R1 ≤ R < R2): The amount of water in the separated layer is moderate, the recharge rate is relatively fast, and the water flow shear force is close to the shear strength of the source layer against water erosion. Water inrush events carrying a small amount of sediment may occur, manifested as turbid water quality and local surrounding rock erosion, which may induce local caving or expansion of roof separation, affecting normal coal mining. It is recommended to strengthen hydrogeological monitoring, focus on observing the water volume and water quality changes at the water inrush points, take grouting reinforcement measures to improve the anti-erosion ability of the source layer, and appropriately adjust the mining method, such as optimizing the working face advancing speed or adjusting the mining sequence, to reduce the risk of water and sand inrush.

[0162] High risk (R ≥ R2): The amount of water in the separated layer is large, the recharge rate is high, and the water flow shear force far exceeds the shear strength of the source layer against water erosion, resulting in a large amount of sediment being washed away, forming a serious sandburst water inrush disaster. The water inrush point may be accompanied by a large-scale collapse of the roof, the goaf is filled with sediment, and even the stability of the roadway is affected, seriously threatening the safe production of the mine. It is recommended to implement dewatering and pressure reduction measures in advance to reduce the water head pressure, cooperate with grouting plugging to enhance the compactness of the separated layer space, conduct mechanical analysis of the surrounding rock in high-risk areas, adjust the mining layout if necessary, avoid direct coal mining in high-risk areas, and set up an emergency drainage system to ensure rapid drainage and reduce the impact of disasters in case of emergencies.

[0163] Among them, R1 is the risk level threshold from low risk to medium risk, and R2 is the risk level threshold from medium risk to high risk; it should be noted that R1 and R2 can be specifically determined according to the historical water inrush data of the mine. Optionally, the value range of R1 is 0.001 - 0.01, and the value range of R2 is 0.01 - 0.1, which can be appropriately adjusted according to the mine historical data and current production data.

[0164] Compared with the prior art, the method for predicting the position of separated layer mud-carrying water inrush in a coal mining working face provided in this embodiment comprehensively considers the position of separated layer fracture during the advancement of the working face, the water flow velocity and its erosion ability, as well as the shear strength and particle loss characteristics of the source layer. By comprehensively analyzing the interaction between water flow and rock strata, the specific occurrence position of separated layer mud-carrying water inrush is finally determined, and it is evaluated whether the sediment will enter the working face with the water flow, realizing the accurate prediction of the position of separated layer mud-carrying water inrush in the working face.

[0165] The specific embodiments described above further elaborate on the purpose, technical solutions, and beneficial effects of the present application. It should be understood that the above description is only the specific embodiments of the present application and is not used to limit the protection scope of the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application shall be included within the protection scope of the present application.

Claims

1. A prediction method for the position of water inrush with mud and sand carried by strata separation in a coal mining face, characterized in that, Including the steps: S1. Based on the mining-induced overburden engineering geological model, identify the potential water-inrush separation zone and the source layer of water-inrush with mud and sand; S2. Based on the identified potential water-inrush separation zone, determine the initial fracture position and periodic fracture position of the lower aquifuge, and take the initial fracture position and periodic fracture position of the lower aquifuge as the water-inrush position of the separation zone in the mining face; S3. Calculate the flow velocity of the separated water reaching the source layer at the fracture position during the advancement of the working face, and calculate the shear force of the water flow on the particles of the source layer based on the flow velocity of the separated water reaching the source layer; by comparing the shear force of the water flow on the particles of the source layer and the shear strength of the source layer against water erosion, determine whether the water-inrush position of the separation zone carries mud and sand, so as to determine the water-inrush position of the separation zone with mud and sand in the working face; S4. Calculate the risk index of water-inrush with mud and sand in the working face, and divide the risk level of the water-inrush position of the separation zone with mud and sand in the working face based on the risk index of water-inrush with mud and sand in the working face to obtain the risk level division result.

2. The method for predicting the water inrush position with mud and sand carried by separation in a coal mining face according to claim 1, characterized in that, In step S2, establish the initial fracture model and the periodic fracture model; For the initial fracture model, the distance of the initial fracture position of the lower aquifuge from the cutting eye is l, and the calculation formula is: For the periodic fracture model, the periodic fracture position of the lower aquifuge is located at the position of l + nL1 from the cutting eye, where n = 1, 2, 3......; L1 is the periodic fracture distance of the lower aquifuge, and the calculation formula is: In the above formula, P is the concentrated supporting force of the underlying water-resisting layer by the underlying rock formation, N; q is the self-weight of the rock formation, kg; b is the width of the beam fixed at both ends, m; h is the thickness of the underlying water-resisting layer, m; σ c is the flexural strength of the rock formation, MPa; H is the distance from the neutral plane of the underlying water-resisting layer to the roof of the coal seam, m; β is the fracture angle of the rock formation, generally taken as 0.7° to 0.85°.

3. The method for predicting the water inrush position with mud and sand carried by separation in a coal mining face according to claim 1, characterized in that, In step S3, calculate the flow velocity v of the separated water reaching the source layer according to the following formula: In the above formula, v is the flow velocity of the separated seam water reaching the material source layer, in m / s; g is the acceleration due to gravity, in m / s 2 ; h0 is the water level height of the separated seam water, in m; z0 and z are the heights of the separated seam position and the material source layer position respectively, in m; f is the friction coefficient; L is the flow path length of the water along the fracture, in m; D is the equivalent hydraulic diameter of the fracture, in m.

4. The prediction method for the water inrush position with mud and sand carried by bedding separation in a coal mining face according to claim 3, characterized in that, In step S3, calculate the shear force τ of the water flow on the particles of the source layer according to the following formula: τ = ρ w ·v 2 ·C d ; In the above formula, τ is the shear force of water flow on the particles of the provenance layer, N; ρ w is the density of water, kg / m 3 ; v is the flow velocity when the accumulated water in the separated layer reaches the provenance layer, m / s; C d is the shear force coefficient.

5. The method for predicting the position of water inrush with mud and sand carried by strata separation in a coal mining face according to claim 4, characterized in that, In step S3, judge whether the water-inrush position of the separation zone carries mud and sand according to the following principle: When τ > τ s floor heave water inrush will occur, and sediment will be carried in the water inrush; When τ ≤ τ s , only floor heave water inrush occurs and no sediment is carried; In the above formula, τ is the shear force exerted by the water flow on the particles in the provenance layer, in N; τ s is the shear strength of the provenance layer against water erosion, in MPa, which is obtained through experimental tests.

6. The prediction method for the water inrush position with mud and sand carried by separation in a coal mining face according to claim 1, characterized in that, In step S4, the risk index R of water-inrush with mud and sand in the working face is jointly determined by the separated water volume factor W and the mud and sand carrying factor S, and calculate the risk index R of water-inrush with mud and sand in the working face according to the following formula: R = αW βS ; Where, W is the separated water volume factor; S is the mud and sand carrying factor; α, β are the normalization weight coefficients, and take α = 0.5, β = 0.

5.

7. The prediction method for the water inrush position with mud and sand carried by separated strata in the coal mining face according to claim 6, characterized in that Calculate the separated water volume factor W according to the following formula: where k h is the water pressure response coefficient; P w is the water pressure at the bottom of the aquifer, MPa; M is the mining height of the working face, m; K p is the average swelling coefficient in the range of the water-conducting fractured zone of the coal seam; H k is the distance from the water-accumulating separated strata to the roof of the coal seam, m.

8. The method for predicting the position of water inrush with mud and sand carried by separation in a coal mining face according to claim 7, characterized in that, Calculate the mud and sand carrying factor S according to the following formula: where τ is the shear force of water flow on the particles of the provenance layer, in MPa; τ s is the shear strength of the material layer against water erosion, in MPa; h s is the thickness of the provenance layer, in m; D is the disintegration coefficient, representing the degree of easy disintegration of the provenance layer, where 0 ≤ D ≤ 1.

9. The method for predicting the water inrush position with mud and sand carried by separation in coal mining working face according to claim 8, characterized in that The calculation formula of the risk index R of water-inrush with mud and sand in the working face is: In the above formula, k h is the water pressure response coefficient; P w is the water pressure at the bottom plate of the aquifer, MPa; M is the mining height of the working face, m; K p is the average swelling coefficient in the range of the water-conducting fissure zone of the coal seam; H k is the distance from the water-accumulating separated layer to the roof of the coal seam, m; τ is the shear force of the water flow on the particles of the material source layer, MPa; τ s is the shear strength of the material layer against water flow erosion, MPa; h s is the thickness of the material source layer, m; D is the disintegration coefficient, indicating the degree of easy disintegration of the material source layer, 0 ≤ D ≤ 1.

10. The prediction method for the water inrush position with mud and sand carried by separation in the coal mining face according to claim 1, characterized in that, When R < R1, the risk level of the water-inrush position of the separation zone with mud and sand in the working face is low risk; When R1 ≤ R < R2, the risk level of the water-inrush position of the separation zone with mud and sand in the working face is medium risk; When R ≥ R2, the risk level of the water-inrush position of the separation zone with mud and sand in the working face is high risk; Where, R1 is the risk level threshold from low risk to medium risk, and R2 is the risk level threshold from medium risk to high risk.

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