A method for predicting a position of a separation and mud sand water inrush in a coal mining working face

Abstract

The application discloses a coal mining working face separation layer mud-carrying water inrush position prediction method, comprising the following steps: taking the initial breaking position and the periodic breaking position of the lower aquiclude as the separation layer water inrush position of the mining working face; calculating the shear force of the water flow on the material source layer particles based on the flow velocity of the separation layer water reaching the material source layer, judging whether the separation layer water inrush position carries mud, and thus determining the working face separation layer mud-carrying water inrush position; calculating the risk index of the working face mud-carrying water inrush, and dividing the risk grade of the working face separation layer mud-carrying water inrush position based on the risk index of the working face mud-carrying water inrush, to obtain the risk grade division result. The application realizes the accurate prediction of the coal mining working face separation layer mud-carrying water inrush disaster.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of mine water disaster prevention and control, and specifically relates to a method for predicting the position and risk level of water inrush caused by separation and mud sand in a coal mining working face. BACKGROUND

[0002] In the process of coal mining, water inrush disaster caused by separation and mud sand has become a new type of sand inrush disaster, which has high suddenness, periodicity and instantaneousness. This type of disaster usually occurs during the mining process of the working face, and the sudden rupture or separation of the originally stable rock layer leads to the rapid influx of underground water and mud sand, forming a water inrush disaster. Unlike traditional sand inrush disasters, water inrush disasters caused by separation and mud sand usually come from deep thick coal seams or soft rock layers, and are not necessarily directly related to the hydrogeological characteristics of the surface loose layer.

[0003] At present, existing researches mainly focus on the control of water inrush and sand inrush disasters from the surface loose layer. However, there is still a great technical gap in accurately predicting the position of water inrush caused by separation and mud sand during the mining of the working face, especially during the mining process. The occurrence of this problem is due to the complexity of the high-position rock layer breakage and water-rock interaction during the mining process of the working face, which makes it difficult to accurately grasp the spatio-temporal distribution of water inrush caused by separation and mud sand, thereby affecting the accuracy and efficiency of existing prevention and control technologies.

[0004] Due to the strong randomness and unpredictability of water inrush caused by separation and mud sand, in the actual safety management and disaster prevention and control of the mine, how to accurately predict the time, position, mud sand carrying condition and risk level of water inrush caused by separation during the mining of the working face has become a key problem in mine water disaster prevention and control. The existing monitoring technology and prediction model are limited in this respect, and they cannot effectively combine the dynamic changes in the mining process and the actual situation of separation and layer breakage, resulting in insufficient accuracy and timeliness of the prediction, thereby affecting the safety production of the mine. SUMMARY

[0005] In view of the above analysis, the embodiments of the present application aim to provide a method for predicting the position and risk level of water inrush caused by separation and mud sand in a coal mining working face, to solve the problem that the position and risk level of water inrush caused by separation during the mining of the working face are difficult to predict in the prior art.

[0006] The purpose of the present application is achieved as follows:

[0007] A method for predicting the position of water inrush caused by separation and mud sand in a coal mining working face, comprising the following steps:

[0008] S1, based on the mining overburden engineering geological model, identifying the potential water inrush separation zone and identifying the mud sand carrying water inrush source layer;

[0009] S2, determining the initial breaking position and periodic breaking position of the lower aquitard based on the identified potential water inrush separation zone, and taking the initial breaking position and periodic breaking position of the lower aquitard as the position of water inrush caused by separation at the mining working face;

[0010] S3, calculating the flow velocity of the separated water at the breaking position reaching the source layer during the advancing of the working face, and calculating 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 eroded by the water flow, it is determined whether the position of water inrush caused by separation carries silt, so as to determine the position of water inrush caused by separation and carrying silt at the working face;

[0011] S4, calculating the risk index of water inrush caused by separation and carrying silt at the working face, and dividing the risk level of the position of water inrush caused by separation and carrying silt at the working face based on the risk index of water inrush caused by separation and carrying silt at the working face, to obtain the risk level division result.

[0012] Further, in step S2, an initial breaking model and a periodic breaking model are established.

[0013] For the initial breaking model, the distance of the initial breaking position of the lower aquitard from the cut is l, and the calculation formula is:

[0014]

[0015] For the periodic breaking model, the periodic breaking position of the lower aquitard is located at a position l+nL1 away from the cut, where n=1, 2, 3,...; L1 is the periodic breaking distance of the lower aquitard, and the calculation formula is:

[0016]

[0017] In the above formula, P is the concentrated support force of the lower aquitard received from the underlying rock layer, N; q is the weight of the rock layer, kg; b is the width of the beam with both ends fixed, m; h is the thickness of the lower aquitard, m; σ c is the bending strength of the rock layer, MPa; H is the distance from the neutral surface of the lower aquitard to the coal seam roof, m; β is the breaking angle of the rock layer, generally 0.7°-0.85°.

[0018] Further, in step S3, the flow velocity v of the separated water reaching the source layer is calculated 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 2h0 is the height of the water level at the delamination, in meters; z0 and z are the heights of the delamination location and the source layer location, respectively, in meters; f is the friction coefficient; L is the length of the flow path along the fracture, in meters; D is the equivalent hydraulic diameter of the fracture, in meters.

[0021] Further, in step S3, the shear force τ exerted by the water flow on the source layer particles 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 source layer particles, N; ρ w The density of water is kg / m³. 3 v is the velocity of the delamination water reaching the source layer, in m / s; C d This is the shear force coefficient.

[0024] Furthermore, in step S3, the location of the delamination water inrush is determined to be carrying sediment according to the following principles:

[0025] When τ>τ s At this time, delamination and water inrush will occur, and the water inrush will carry silt and sand;

[0026] When τ≤τ s At this time, only delamination water inrush will occur, without carrying mud and sand.

[0027] In the above formula, τ is the shear force exerted by the water flow on the source layer particles, in N; τ s The shear strength of the source layer under water erosion, in MPa, was obtained through experimental testing.

[0028] Furthermore, in step S4, the risk index R of water inrush carrying mud and sand at the working face is jointly determined by the separation water volume factor W and the mud and sand carrying factor S, and is calculated according to the following formula:

[0029] R = αW βS ;

[0030] Where W is the delamination water factor; S is the sediment carrying factor; α and β are normalized weighting coefficients, with α = 0.5 and β = 0.5.

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

[0032]

[0033] Where, k h P is the water pressure response coefficient. w Water pressure at the bottom of the aquifer, MPa; M is the working face height, m; K pH is the average dilatancy coefficient of the water-conducting fractured zone of the coal seam; H k h is the distance from the water-carrying parting to the roof of the coal seam, m.

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

[0035]

[0036] wherein τ is the shear force of the water flow on the particles of the source rock, MPa; τ s h is the shear strength of the source rock under the erosion of the water flow, MPa; h s h is the thickness of the source rock, m; D is the disintegration coefficient, representing the disintegration degree of the source rock, 0≤D≤1.

[0037] Further, the calculation formula of the risk index R of the mud-carrying water inrush of the working face is as follows:

[0038]

[0039] In the above formula, k h is the water pressure response coefficient; P w is the water pressure of the aquifer floor, MPa; M is the mining height of the working face, m; K p H is the average dilatancy coefficient of the water-conducting fractured zone of the coal seam; H k h is the distance from the water-carrying parting to the roof of the coal seam, m; τ is the shear force of the water flow on the particles of the source rock, MPa; τ s h is the shear strength of the source rock under the erosion of the water flow, MPa; h s h is the thickness of the source rock, m; D is the disintegration coefficient, representing the disintegration degree of the source rock, 0≤D≤1.

[0040] Further, when R

[0041] When R1≤R

[0042] When R≥R2, the risk level of the position of the mud-carrying water inrush of the working face is high risk.

[0043] wherein 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 coal mining working face separation mud sand water inrush position prediction method provided by the present application can accurately predict the position and risk level of the separation mud sand water inrush in the coal mining working face during mining by comprehensively evaluating the mining area geological characteristics, mining progress and water flow dynamics behavior, and specifically by calculating the breaking position of the water inrush separation layer, the position of the water inrush can be accurately predicted, more accurate prediction information is provided for the prevention and control of water disasters in the mining area, and moreover, the underground water flow velocity and water rock interaction are comprehensively analyzed, the critical start criterion is combined to judge whether the separation water inrush carries mud sand, and the mud sand water inrush risk index is proposed from the aspects of water quantity and sand source supply degree, so that the prediction accuracy of the separation mud sand water inrush disaster position and risk level is effectively improved, and the water inrush disaster prevention has a positive significance.

[0045] In the present application, the above technical solutions can be combined with each other to realize more preferred combination solutions. Other features and advantages of the present application will be described in the subsequent specification, and some advantages will become apparent from the specification or will be understood by implementing the present application. The purposes and other advantages of the present application can be realized and obtained from the contents specifically pointed out in the specification and the drawings. BRIEF DESCRIPTION OF DRAWINGS

[0046] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments described in the present application, and other drawings can also be obtained by those skilled in the art based on these drawings.

[0047] Figure 1 The lower aquiclude stress condition analysis schematic diagram provided for the embodiments of the present application;

[0048] Figure 2 The lower aquiclude mechanical model schematic diagram provided for the embodiments of the present application;

[0049] Figure 3 The operation flowchart of the coal mining working face separation mud sand water inrush position prediction method provided for the embodiments of the present application. DETAILED DESCRIPTION

[0050] In order to make the purposes, technical solutions and advantages of the embodiments of the present application more clear, the technical solutions in the embodiments of the present application will be clearly and completely described below in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are only some embodiments of the present application, not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the protection scope of the present application.

[0051] For the purpose of clarity and acommodation of the embodiments of the present application, further explanation will be given below with specific embodiments in conjunction with the accompanying drawings. The embodiments do not limit the embodiments of the present application. In the drawings, the size and relative size of components can be exaggerated for clarity and / or descriptive purposes. When the exemplary embodiments can be implemented differently, a specific process sequence can be performed in an order different from that described. For example, two consecutively described processes can be performed substantially simultaneously or in an order opposite to that described. 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 limiting. As used herein, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. Furthermore, to the extent that the terms "including" and / or "containing" and variations thereof are used in either the detailed description or the claims, such terms are intended to be inclusive in a manner similar to the term "comprising" and / or "including" and / or "containing" as an open-ended transition. It is also noted that, as used herein, the terms "substantially," "approximately," and other similar terms are used as synonyms for "about," and are employed to account for inherent variations in measuring, calculating, and / or providing a value or quantity.

[0053] Embodiment 1

[0054] One specific embodiment of the present application, as shown in Figures 1 to 3 A method for predicting the position of a water inrush caused by separation and mud-carrying sand in a coal mining working face is disclosed, which comprises steps S1 to S4, and specifically as follows:

[0055] S1, based on the mining overburden engineering geology model, identify the potential water inrush separation zone and identify the mud-carrying sand water inrush source layer.

[0056] This step collects the geological exploration data of the mining area / working face (including drilling data, hydrogeological data, etc.), and combines the relevant information of the mining coal seam (such as coal seam thickness, buried depth, working face width, etc.) to construct a mining overburden engineering geology model. Based on the constructed mining overburden engineering geology model, the "water inrush separation zone" that may cause water inrush is identified. This step is the basis for subsequent water inrush position prediction and provides key geology model and calculation mechanics parameters for subsequent steps.

[0057] S11, collect the geological data of the mining area / working face, and construct a mining overburden engineering geology model.

[0058] This step aims to construct an engineering geology model that can reflect the structure characteristics of overburden strata affected by mining by collecting geological exploration data of the mining area / working face, including drilling data, hydrogeological data, etc., and combining with relevant information of the mining coal seam (such as coal seam thickness, buried depth, working face width, etc.). The model needs to clarify the sequence, thickness, lithology, structure and buried depth of the rock strata above the coal seam, and divide different engineering geology rock groups, and then identify the key horizons such as coal seam, main aquifer and aquiclude.

[0059] S12, identifying potential water inrush separation zone based on the constructed overburden strata engineering geology model.

[0060] This step identifies the composite horizon that may cause separation water inrush, i.e. "water inrush separation zone", based on the constructed overburden strata engineering geology model, which needs to meet the following two basic conditions:

[0061] Condition one: specific rock combination structure: the water inrush separation zone needs to have the combination structure of upper hard rock layer and lower aquiclude. In the mining process, due to the difference in mechanical properties between the upper hard rock layer and the lower aquiclude, uneven settlement of the two will occur. At the same time, the lower aquiclude needs to remain intact during bending deformation, without developing connected fissures, thereby forming a temporarily closed separation space between the upper hard rock layer and the lower aquiclude, providing necessary space conditions for separation water accumulation.

[0062] Condition two: spatial position adjacent to the aquifer: the closed separation space needs to be located near the aquifer, usually the upper hard rock layer is the aquifer. During the development of the separation layer, groundwater stored in the aquifer will continue to collect in the closed separation space, forming a separation water body, which becomes the direct water source for separation water inrush.

[0063] In summary, the "water inrush separation zone" in this embodiment refers to a composite horizon composed of lower aquiclude, separation water accumulation and upper hard rock layer, as shown in Figure 1 . Among them, the lower aquiclude is usually low-permeability rock strata such as mudstone, argillaceous sandstone, siltstone, shale, etc.; the upper hard rock layer is usually fine sandstone, medium sandstone, coarse sandstone, conglomerate, etc. water-filled aquifer.

[0064] S13, test and count basic physical and mechanical parameters.

[0065] On the basis of identifying the "water inrush separation layer zone", samples are collected at the relevant layer, and the collected samples are tested to obtain test data. At the same time, by collecting the existing geological materials of the mining area, part of the required data can also be 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 counted include: rock layer specific gravity, lower aquifuge thickness, distance between lower aquifuge neutral plane and coal seam roof, rock fracture angle, working face width, distance between aquifer and coal seam, fracture friction coefficient, shear force coefficient, initial aquifer water level height and other parameters.

[0066] S14, identifying the mud sand water inrush source layer

[0067] The high-position separation layer mud sand water inrush disaster refers to that when there are "sources" such as ancient weathering crust rock layer, argillaceous rock layer and weakly cemented sandstone layer in the surrounding rock layer of the water inrush channel, the separation layer water will carry a large amount of mud, sand and stone into the working face. This disaster may cause the support to collapse and the working face to be blocked when it occurs, and in severe cases, it may cause major hidden dangers to the safety of mine production. In order to effectively identify the layer where the "source" may exist, the disintegration property of the rock layer needs to be tested and evaluated in this step, so as to determine the source layer.

[0068] The disintegration coefficient refers to the ability of the rock layer to break and disintegrate when subjected to external forces (such as mining pressure, groundwater flow, etc.). The rock layer with high disintegration coefficient often has poor mechanical properties and is easy to disintegrate and produce mud sand flow under the action of water flow. Therefore, the disintegration coefficient of the rock layer is first determined through laboratory rock mechanics test. The calculation formula of the disintegration coefficient D is as follows:

[0069]

[0070] wherein, R c is the mass of the disintegrated rock sample, kg; R0 is the initial mass of the rock sample, kg.

[0071] According to the experimental results, the rock layer with a disintegration coefficient greater than 0.4 can be considered to have strong disintegration property and belong to the possible "source layer".

[0072] S2, based on the identified potential water inrush separation layer zone, the position of the separation layer water inrush in the mining working face is preliminarily determined. Specifically, based on the identified potential water inrush separation layer zone, the initial break position and the periodic break position of the lower aquifuge are determined, and the initial break position and the periodic break position of the lower aquifuge are taken as the position of the separation layer water inrush in the mining working face.

[0073] This step is based on the potential water inrush separation layer zone identified in S1 Figure 1), a mechanical model of the lower aquitard under the water inrush separation layer is constructed, mechanical criteria of the initial breakage and periodic breakage of the lower aquitard are established, and the initial breakage position and periodic breakage position of the lower aquitard are further calculated. The initial breakage position and periodic breakage position of the lower aquitard are taken as the positions where the water inrush occurs. The prediction of the water inrush position is based on the result of the further mechanical analysis of the geological model identified in the previous step, and is also the key basis for further determining whether the mud-carrying water inrush occurs.

[0074] S21, establishing an initial breakage model and a periodic breakage model

[0075] In order to analyze the breakage behavior of the lower aquitard under the water inrush separation layer, the following two mechanical models are established:

[0076] 1.1, the initial breakage model, a two-end fixed beam model is adopted: that is, a beam model with two ends fixed and a middle part subjected to a concentrated force is adopted, and the initial breakage behavior of the rock stratum under the action of the uniform load and the concentrated support load is analyzed.

[0077] 1.2, the periodic breakage model, a cantilever beam model is adopted: that is, a cantilever beam model with one end fixed and the other end free is adopted, and the periodic breakage behavior of the rock stratum under the action of the concentrated load is analyzed.

[0078] S22, stress analysis and boundary conditions

[0079] 2.1, initial breakage: two-end fixed beam model

[0080] For the initial breakage, the lower aquitard is assumed to be a beam with two ends fixed (which can be referred to as "two-end fixed beam"), as shown in FIG. 1. It is subjected to the uniform load q and the concentrated support force P from the underlying rock stratum. The concentrated support force acts on the middle position of the beam, that is, the horizontal coordinate x = L / 2, L being the length of the beam, that is, the exposure length of the lower aquitard, m. Figure 2

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

[0082] 2.2, periodic breakage: cantilever beam model

[0083] For the periodic breakage, the lower aquitard is assumed to be a cantilever beam subjected to the uniform load q and the concentrated support force P from the underlying rock stratum, and the support force acts on 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 breakage: two-end fixed beam model

[0087] For two-end fixed beam model, i.e. both ends of the beam are fixed support structure, under the action of uniform load and concentrated support force. The maximum bending moment M max occurs at the middle position of the beam, i.e. at x = L / 2, and its value is:

[0088]

[0089] In the formula, M max is the maximum bending moment of the two-end fixed beam, N.m; q is the load received by 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 aquifer, m; L is the initial breakage distance of the lower aquifer, which is the exposure length of the lower aquifer in the two-end fixed beam model, m; P is the concentrated support force received by the lower aquifer from underlying rock stratum, KN, P = λγh, λ is the support coefficient, 0 < λ < 1.

[0090] The maximum working face advancing distance l at the initial breakage of the lower aquifer is calculated according to the following formula:

[0091] l = L + 2Hcotβ (3) l is the maximum working face advancing distance at the initial breakage of the lower aquifer, m; H is the distance between the neutral plane of the lower aquifer and the coal seam roof, m; β is the rock breakage angle, generally taken as 0.7° ~ 0.85°.

[0092] The maximum bending stress σ max of the two-end fixed beam is:

[0093]

[0094] In the formula, σ max is the maximum bending stress of the two-end fixed beam, N; b is the width of the two-end fixed beam, approximately taken as the oblique length of the working face, m.

[0095] Since the rock failure occurs when the maximum bending stress σ max reaches or exceeds the bending strength σc of the rock stratum, the calculation formula of the initial breakage distance L of the lower aquifer is obtained as follows:

[0096]

[0097] Combining formula (3) and formula (5), the calculation formula of the maximum working face advancing distance l at the initial breakage of the lower aquifer is obtained as follows:

[0098]

[0099] P is the concentrated support force of the underlying rock stratum on the lower aquiclude, N; q is the weight of the rock stratum, kg; b is the width of the beam with both ends fixed, m; h is the thickness of the lower aquiclude, m; σ is the flexural strength of the rock stratum, MPa; H is the distance between the neutral plane of the lower aquiclude and the coal seam roof, m; β is the rock fracture angle, generally 0.7°-0.85°. c P is the concentrated support force of the underlying rock stratum on the lower aquiclude, N; q is the weight of the rock stratum, kg; b is the width of the beam with both ends fixed, m; h is the thickness of the lower aquiclude, m; σ is the flexural strength of the rock stratum, MPa; H is the distance between the neutral plane of the lower aquiclude and the coal seam roof, m; β is the rock fracture angle, generally 0.7°-0.85°.

[0100] The maximum working face advancing distance l of the lower aquiclude at the initial fracture is obtained by the above formula calculation, that is, the distance between the initial fracture position of the lower aquiclude of the working face and the cut is l.

[0101] 3.2, Periodic fracture: cantilever beam model

[0102] For the cantilever beam model, the distribution of bending moment and bending stress has 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:

[0103]

[0104] In the formula, L1 is the periodic fracture distance of the cantilever beam.

[0105] The maximum bending stress σ of the cantilever beam is: max

[0106]

[0107] For periodic fracture, the criterion for the fracture of cantilever beam under periodic load is:

[0108] σ max =σ c (8)

[0109] Based on formulas (6)-(8), the calculation formula of the periodic fracture distance L1 of the lower aquiclude is obtained as:

[0110]

[0111] In the formula, P is the concentrated support force of the underlying rock stratum on the lower aquiclude, N; q is the weight of the rock stratum, kg; b is the width of the beam with both ends fixed, m; h is the thickness of the lower aquiclude, m; σ is the flexural strength of the rock stratum, MPa. c

[0112] Therefore, under the cantilever beam model, the periodic fracture position of the lower aquiclude of the working face is located at a distance of l+nL1 from the cut, where n=1, 2, 3,...

[0113] S24, criterion result and prediction of possible water inrush position

[0114] ​​When the working face advances to the initial breaking position or the periodic breaking position of the lower aquiclude, the lower aquiclude breaks and water inrush occurs at the breaking position, thereby realizing the prediction of the position where water inrush may occur.

[0115] S3, calculate the flow velocity of the water in the breaking position during the working face advancing to the source rock layer, and calculate the shear force of the water flow on the source rock layer particles based on the flow velocity of the water in the breaking position to the source rock layer; compare the shear force of the water flow on the source rock layer particles with the shear strength of the source rock layer eroded by the water flow to determine whether the water inrush position determined in S2 carries silt, thereby determining the water inrush position of the working face carrying silt.

[0116] This step further determines whether the water flow carries silt by calculating the flow velocity of the water in the breaking position determined in S2 to the source rock layer, and comparing the shear force of the source rock layer particles eroded by the actual water flow with the shear strength of the source rock layer eroded by the water flow, thereby predicting the possibility of water inrush carrying silt at different water inrush positions.

[0117] Since water inrush occurs at the breaking position, the breaking position is the water inrush position. The overburden rock forms a separation layer, and water accumulates to form a separation layer water with a volume of V. When the lower aquiclude breaks, the separation layer water flows down along the water-conducting fracture, erodes the rock layer at the source rock layer position with a velocity v, causes the loss of particles, and the water flow carrying silt particles enters the working face, forming a water inrush and sand burst disaster. When analyzing the flow velocity of the water flow from the high separation layer to the source rock layer position, the hydrogeological conditions of the aquifer, the initial dynamic water pressure caused by the deformation and breaking of the rock layer, the energy loss of the water flow flowing through the fracture, and the conversion of potential energy into kinetic energy need to be considered.

[0118] S31, obtain the flow velocity v of the separation layer water to the source rock layer according to the following steps:

[0119] The total initial pressure P0 of the separation layer water is:

[0120] P0=pgh0 (10)

[0121] Wherein, ρ is the density of water, kg / m 3 ; g is the acceleration of gravity, m / s 2 ; h0 is the water level height of the separation layer, m; assuming that the separation layer is full of water and connected with the aquifer, h0 can be regarded as the water level height of the aquifer.

[0122] Assuming that after the separation layer breaks, the water flows down along the fracture, the initial pressure is converted into kinetic energy and energy to overcome the flow resistance. Assuming that the initial position has zero water kinetic energy, only pressure and potential energy. The total energy of the water flow includes the initial pressure (hydrostatic pressure and additional dynamic water pressure), potential energy and energy loss in the flow, and the Bernoulli equation is modified as:

[0123]

[0124] z0 and z are the height of the off-layer position and the source layer position, respectively, m; v is the flow velocity to the source layer, m / s; P f is the resistance loss pressure of fissure flow, N.

[0125] The total initial pressure of off-layer accumulated water is brought into the formula:

[0126]

[0127] The flow in the fissure can be considered as laminar flow or turbulent flow along the fissure pipeline. According to the Darcy-Weisbach formula, the resistance loss pressure P f of fissure flow is expressed as:

[0128]

[0129] f is the friction coefficient, which is related to the roughness of the fissure wall; L is the flow path length of water flow along the fissure, which can be equivalent to the distance from the off-layer accumulated water to the source layer, m; D is the equivalent hydraulic diameter of the fissure, m.

[0130] Based on the formulas (11) to (13), the following formula is obtained:

[0131]

[0132] The flow velocity v of off-layer accumulated water to the source layer is

[0133]

[0134] In the above formula, v is the flow velocity of off-layer accumulated water to the source layer, m / s; g is the acceleration of gravity, m / s 2 ; h0 is the water level height of off-layer accumulated water, m; z0 and z are the height of the off-layer position and the source layer position, respectively, m; f is the friction coefficient; L is the flow path length of water flow along the fissure, m; D is the equivalent hydraulic diameter of the fissure, m.

[0135] S32, calculate the shear force τ of water flow on the particles of the source layer according to the following formula:

[0136] τ = p w · v 2 · C d (16)

[0137] In the above formula, τ is the shear force of water flow on the particles of the source layer, that is, the friction force of water flow on the particles of the rock layer, MPa; p w is the density of water, usually 1000 kg / m 3 ; v is the flow velocity of off-layer accumulated water to the source layer, m / s; C dFor the shear force coefficient, it is related to the shape of the particles, the roughness of the rock stratum, etc., for example, the surface of sandstone or sand layer, C d the value is between 0.01 and 0.1; the surface of mudstone or clay layer, C d the value is relatively small, usually between 0.005 and 0.05. The specific C d value can be obtained by experimental test.

[0138] S33, based on the shear force τ of the water flow on the particles of the source layer and the shear strength τ of the source layer eroded by the water flow, judging whether the position of the separation layer water inrush obtained in S2 carries mud sand according to the following principles: s

[0139] When τ > τ s , the separation layer water inrush occurs, and mud sand is carried; under this condition, it indicates that the water flow has sufficient erosion capacity to carry mud sand particles into the working face, resulting in separation layer water inrush with mud sand.

[0140] When τ ≤ τ s , only separation layer water inrush occurs, without carrying mud sand.

[0141] In the above formula, τ is the shear force of the water flow acting on the particles of the source layer, MPa; τ s is the shear strength of the source layer eroded by the water flow, MPa, which is obtained by experimental test.

[0142] S4, after determining the position of the separation layer water inrush with mud sand in the working face, calculating the risk index of the working face water inrush with mud sand, and based on the risk index of the working face water inrush with mud sand, dividing the risk level of the working face water inrush with mud sand, to obtain the risk level division result.

[0143] In the foregoing steps, the position of the separation layer water inrush with mud sand in the working face is identified, and the risk level of each water inrush position is further evaluated. The risk level comprehensively considers two key factors of the separation layer water amount (water inrush scale) and the amount of mud sand that can be provided by the source layer.

[0144] The risk index R of the working face water inrush with mud sand is determined by the separation layer water amount factor W and the mud sand carrying factor S, and the risk index R of the working face water inrush with mud sand is calculated according to the following formula:

[0145] R = αW βS (17)

[0146] Wherein, W is the separation layer water amount factor, reflecting the influence of the water inrush scale; S is the mud sand carrying factor, reflecting the influence of the water flow erosion capacity and the amount of mud sand supply; α, β are normalization weight coefficients, which can be adjusted according to the specific mine geological conditions, and α = 0.5 and β = 0.5 can be taken.

[0147] ​The calculation process of the water amount factor W, the mud and sand carrying factor S and the risk index R is as follows:

[0148] (1) Calculation of the water amount factor W

[0149] The water amount factor W is determined by the water amount in the water separation space and the recharge capacity of the aquifer, and the calculation formula is as follows:

[0150]

[0151] Wherein, k h is the water pressure response coefficient, which depends on the permeability of the aquifer, for the weak water-rich aquifer, k h is 0.2-0.5, for the medium water-rich aquifer, k h is 0.5-0.7, and for the strong water-rich aquifer, k h is 0.7-1.0; P w is the water pressure of the aquifer bottom plate, MPa; M is the working face mining height, m; K p is the average broken expansion coefficient of the coal seam water flowing fractured zone range; H k is the distance from the water accumulation water separation space to the coal seam roof, m.

[0152] (2) Calculation of the mud and sand carrying factor S

[0153] The mud and sand carrying factor S is determined by the shear force of the water flow to the source layer and the amount of mud and sand supplied by the source layer, and the calculation formula is as follows:

[0154]

[0155] Wherein, τ is the shear force of the water flow to the source layer particles, MPa; τ s is the shear strength of the source layer eroded by the water flow, MPa; h s is the thickness of the source layer, m; D is the disintegration coefficient, which represents the disintegration degree of the source layer, 0≤D≤1.

[0156] (3) Substitute the calculation formula of the water amount factor W and the mud and sand carrying factor S into formula (17), and the calculation formula of the risk index R of the working face mud and sand water inrush is obtained as follows:

[0157]

[0158] Substitute the working face related parameters into formula (20), and the risk index R of all the lower water-resisting layer breakage positions (from the cut, i.e. the water inrush position, l, l+nL1, n=1, 2, 3...) is calculated. Then, according to the index size, the risk grades of the mud and sand water inrush at different positions are divided, and the risk grade division results include low risk, medium risk and high risk, and the specific results are as follows:

[0159] Low risk (R < R1): The amount of water in the separation layer is small, the recharge rate is low, and the shear force of the water flow is not enough to erode the source layer. Water inrush mainly shows local seepage, and the water quality is clear without carrying mud and sand. It has less impact on the working face, and only local roof fracture seepage may occur, which has no obvious threat to mining safety. It is recommended to closely monitor the water volume changes, evaluate the separation layer water accumulation range combined with borehole observation, and ensure that the water inrush volume is maintained within a controllable range to prevent it from evolving into a more serious water inrush event.

[0160] Medium risk (R1≤R < R2): The amount of water in the separation layer is moderate, the recharge rate is fast, and the shear force of the water flow is close to the shear strength of the source layer eroded by the water flow. It may cause water inrush events carrying a small amount of mud and sand, showing turbid water quality and local wall rock erosion, which may induce local caving or roof separation expansion, affecting normal mining. It is recommended to strengthen hydrogeological monitoring, focus on observing water volume and water quality changes at the water inrush point, take grouting reinforcement measures to improve the erosion resistance of the source layer, and appropriately adjust the mining method, such as optimizing the working face advance speed or adjusting the mining sequence, to reduce the risk of water and sand inrush.

[0161] High risk (R≥R2): The amount of water in the separation layer is large, the recharge rate is high, and the shear force of the water flow is far beyond the shear strength of the source layer eroded by the water flow, resulting in a large amount of mud and sand being eroded, forming a serious sand inrush disaster. The water inrush point may be accompanied by large-scale roof caving, the goaf may be filled with mud and sand, and even the stability of the roadway may be affected, seriously threatening mine safety production. It is recommended to implement water drainage and pressure reduction measures in advance to reduce the water head pressure, cooperate with grouting to enhance the compactness of the separation layer space, and conduct a mechanical analysis of the surrounding rock in high-risk areas. If necessary, adjust the mining layout to avoid direct mining in high-risk areas, and set up an emergency drainage system to ensure that water can be quickly drained and the impact of disasters can be reduced in the event of an emergency.

[0162] wherein R1 is a risk level threshold from low risk to medium risk, and R2 is a risk level threshold from medium risk to high risk; it should be noted that R1 and R2 can be determined according to historical water inrush data of the mine, and optionally, R1 has a value range of 0.001-0.01, and R2 has a value range of 0.01-0.1, which can be appropriately adjusted according to historical data or current production data of the mine.

[0163] Compared with the prior art, the coal mining working face separation layer mud and sand water inrush position prediction method provided in the embodiment comprehensively considers the position of the separation layer breakage in the working face advance process, the water flow velocity and its erosion capacity, and the shear strength and particle loss characteristics of the source layer. By comprehensively analyzing the interaction between the water flow and the rock stratum, the specific occurrence position of the separation layer mud and sand water inrush is finally determined, and whether the mud and sand will enter the working face with the water flow is evaluated, thereby realizing accurate prediction of the separation layer mud and sand water inrush position of the working face.

[0164] The above detailed description of the specific implementation is further detailed for the purpose of the application, technical solutions and beneficial effects, and it should be understood that the above description is only for the specific implementation of the application and is not used to limit the protection scope of the application, and any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the application shall be included in the protection scope of the application.

Claims

1. A method for predicting the position of a water inrush caused by separation and mud carrying of a coal mining face, characterized in that, The method comprises the steps of: S1, identifying a potential water inrush separation layer and identifying a mud-carrying sand water inrush source layer based on a mining overburden engineering geological model; S2, determining a primary break position and a periodic break position of a lower aquifer based on the identified potential water inrush separation layer, and taking the primary break position and the periodic break position of the lower aquifer as the water inrush position of the separation layer of the mining and excavation face; S3, calculating the flow velocity of the separation layer water at the break position to the source layer during the advance of the working face, and calculating the shear force of the water flow on the source layer particles based on the flow velocity of the separation layer water to the source layer; by comparing the shear force of the water flow on the source layer particles and the shear strength of the source layer eroded by the water flow, it is determined whether the water inrush position of the separation layer carries mud sand, so as to determine the water inrush position of the separation layer of the working face carrying mud sand; S4, calculating the risk index of the working face carrying mud sand water inrush, and dividing the risk level of the water inrush position of the separation layer of the working face carrying mud sand based on the risk index of the working face carrying mud sand water inrush, to obtain the risk level division result; In step S2, a primary break model and a periodic break model are established. For the primary break model, the distance of the primary break position of the lower aquifer from the cut is l, and the calculation formula is: For the periodic break model, the periodic break position of the lower aquifer is located at a distance of l+nL1 from the cut, where n=1, 2, 3, …; L1 is the periodic break distance of the lower aquifer, and the calculation formula is: In the formula, P is the concentrated support force of the underlying rock stratum on the lower aquiclude, N; q is the weight of the rock stratum, kg; b is the width of the beam with both ends fixed, m; h is the thickness of the lower aquiclude, m; σ c is the flexural strength of the rock stratum, MPa; H is the distance between the neutral plane of the lower aquiclude and the coal seam roof, m; β is the break angle of the rock stratum, generally taken as 0.7°-0.85°; In step S3, the flow velocity v of the separation layer water to the source layer is calculated according to the following formula: In the above formula, v is the flow rate of the bedded water to the source bed, m / s; g is the acceleration of gravity, m / s 2 ; h0 is the height of the bedded water level, m; z0 and z are the heights of the bedded position and the source bed position, respectively, m; f is the friction coefficient; L is the flow path length of the water along the fracture, m; and D is the equivalent hydraulic diameter of the fracture, m. In step S3, the shear force τ of the water flow on the source layer particles is calculated according to the following formula: τ = p w • v 2 • C d ; In the above formula, τ is the shear force of water flow on the particles of the source bed, N; p w is the density of water, kg / m 3 ; v is the flow velocity of the water in the detachment layer when it reaches the source bed, m / s; C d is the shear force coefficient; In step S3, the following principles are used to determine whether the water inrush position of the separation layer carries mud sand: When τ > τ s , then the separation layer water inrush occurs, and the water inrush carries the silt; When τ≤τ s , then only the water in the bed separation occurs, without carrying the mud sand; In the above formula, τ is the shear force of water flow acting on the particles of the source layer, N; τ s is the shear strength of the source layer eroded by water flow, MPa, obtained by experimental test.

2. The coal mining face separation and mud water inrush position forecasting method according to claim 1, characterized in that, In step S4, the risk index R of the working face carrying mud sand water inrush is determined by the separation layer water volume factor W and the mud sand carrying factor S, and the risk index R of the working face carrying mud sand water inrush is calculated according to the following formula: R = aW βS ; Wherein, W is the separation layer water volume factor; S is the mud sand carrying factor; α, β are normalization weight coefficients, and α=0.5, β=0.

5.

3. The coal mining face separation and mud water inrush position forecasting method according to claim 2, characterized in that, The separation layer water volume factor W is calculated according to the following formula: wherein k h is the water pressure response coefficient; P w is the water pressure of the aquifer floor, MPa; M is the working face mining height, m; K p is the average dilatancy coefficient of the coal seam water-conducting fractured zone range; H k is the distance from the water-accumulating separation layer to the coal seam roof, m.

4. The coal mining face separation and mud water inrush position prediction method according to claim 3, characterized in that, The mud sand carrying factor S is calculated according to the following formula: wherein τ is the shear stress of water flow on the particles of the source bed, MPa; τ s is the shear strength of the source bed against the erosion of water flow, MPa; h s is the thickness of the source bed, m; and D is the disintegration coefficient, which represents the degree of easy disintegration of the source bed, 0≤D≤1.

5. The coal mining face separation and mud water inrush position forecasting method according to claim 4, characterized in that, The calculation formula of the risk index R of the working face carrying mud sand water inrush is: In the formula, k h is the water pressure response coefficient; P w is the water pressure of the aquifer floor, MPa; M is the working face mining height, m; K p is the average broken expansion coefficient of the coal seam water flowing fractured zone range; H k is the distance from the water-carrying separation layer to the coal seam roof, m; τ is the shear force of the water flow to the source layer particles, MPa; τ s is the shear strength of the source layer position eroded by the water flow, MPa; h s is the source layer thickness, m; D is the disintegration coefficient, indicating the easy disintegration degree of the source layer, 0≤D≤1.

6. The coal mining face separation and mud water inrush position forecasting method according to claim 5, characterized in that, When R < R1, the risk level of the water inrush position of the separation layer of the working face carrying mud sand is low risk; When R1≤R < R2, the risk level of the water inrush position of the separation layer of the working face carrying mud sand is medium risk; When R ≥ R2, the risk level of the water inrush position of the separation layer of the working face carrying mud sand is high risk; Wherein, 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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