A method and system for identifying a key layer causing disasters due to abnormal gas emission during initial mining of a working face

Abstract

The application discloses a kind of working face initial mining period gas abnormal emission disaster-causing key layer discrimination method and system, comprising the following steps: basic parameter input;Overburden key layer structure identification;Key layer breakage advancing distance and gas-guiding fracture zone development height calculation;Adjacent layer pressure-relief gas emission, emission increment and high extraction roadway extraction rate calculation;High extraction roadway extraction lag necessary condition discrimination;Disaster-causing identification index calculation;Disaster-causing key layer and main control key layer determination and risk classification;Result output and prevention suggestion.The application divides the overburden key layer related to gas overrun during initial mining period into two types of main control key layer and disaster-causing key layer and identifies them respectively, and then outputs disaster-causing key layer horizon, breakage advancing distance, risk classification and prevention suggestion, to provide quantitative basis for gas precision prevention during initial mining period.

Description

Technical Field

[0001] This invention relates to a method and system for identifying key strata prone to gas outbursts during the initial mining stage of a working face, belonging to the field of coal mine gas disaster prevention and control technology. Background Technology

[0002] In multi-coal-seam mining conditions, initial disturbance at the working face triggers large-scale depressurization of the overlying strata. Adsorbed gas from adjacent coal seams and gas-bearing strata rapidly desorbs and becomes free, continuously migrating and converging along the mining-induced fracture network towards the goaf and the working face. Underground high-efficiency drainage roadways are crucial for intercepting depressurized gas from adjacent strata. However, efficient drainage channels in these roadways cannot be formed immediately upon the start of mining. Their gas interception capacity is constrained by multiple factors, including the timing of the fracture of the thick, hard overlying strata, the vertical development height of the gas-conducting fracture zone, and the degree of spatial connectivity between the fracture network and the high-efficiency drainage roadway. In the early stages of mining, before the gas-conducting fracture development height reaches the strata where the high-efficiency drainage roadway is located, large-scale depressurized gas from adjacent strata has already desorbed and surged out. Since the high-efficiency drainage roadway and the gas-rich area have not formed a continuous flow channel, the interception and drainage effect is severely delayed. A large amount of depressurized gas bypasses the drainage roadway and flows towards the working face and return airway, easily causing abnormal fluctuations in gas concentration or even exceeding limits during the initial mining stage. A key contributing factor to gas disasters during the initial mining phase is the significant spatiotemporal misalignment between processes such as gas release from adjacent layers, evolution of gas-conducting fractures, and efficient extraction in high-efficiency extraction roadways.

[0003] Existing research largely focuses on single dimensions such as optimizing stratigraphic parameters in high-efficiency drainage roadways, static prediction of gas emission from working faces, and post-exposure evaluation of drainage treatment effects. It fails to couple the periodic fracturing of key overburden strata, the evolution of fracture connectivity, the lag effect of high-efficiency drainage roadways, and abnormal gas emission behavior into a cohesive analysis. Consequently, it cannot quantitatively identify the main disaster-causing strata in the overburden that drive excessive gas emissions during initial mining. Therefore, the industry urgently needs a method to quantitatively identify key gas-causing strata in the overburden, providing quantitative support for advanced prediction of gas emission and proactive disaster prevention during the initial mining stage. Summary of the Invention

[0004] To address the problems existing in the prior art, this invention provides a method and system for identifying key strata causing abnormal gas outbursts during the initial mining stage of a working face. Using the columnar structure of coal-bearing strata, rock physical and mechanical parameters, gas occurrence parameters of adjacent strata, and high-speed drainage roadway layout and ventilation parameters as inputs, the system couples four processes within a unified spatiotemporal framework: failure of the overburden key strata, development of gas-conducting fracture zones, gas release from adjacent strata under pressure relief, and high-speed drainage roadway response. The system classifies the overburden key strata related to gas exceedances during the initial mining stage into two categories: controlling key strata and disaster-causing key strata, and identifies them separately. It then outputs the location of the disaster-causing key strata, the distance of failure advancement, the hazard classification, and prevention and control recommendations, providing quantitative basis for precise gas prevention and control during the initial mining stage.

[0005] To achieve the above objectives, the present invention employs a method for identifying critical strata prone to disaster due to abnormal gas outbursts during the initial mining stage of a working face, comprising the following steps:

[0006] S1, Basic Parameter Input

[0007] Input the columnar structure of the coal-bearing strata, the physical and mechanical parameters of each rock layer, the gas occurrence parameters of the overlying adjacent gas-bearing coal and rock strata, the high-level drainage roadway layout parameters, and the working face mining ventilation parameters;

[0008] S2, Identification of Key Overburden Layer Structure

[0009] Based on the key layer identification method, key layers in the overburden are identified from bottom to top, and their strata, thickness and the range of loads they control are determined. These are denoted as the j-th key layer, j = 1, 2, ..., n.

[0010] S3. Calculation of critical layer failure propulsion distance and gas-conducting fracture zone development height.

[0011] The key strata are equated to beams with fixed supports at both ends, and their initial fracture limit span is calculated. Combined with the underlying delamination space conditions and the rock fracture angle, the advance distance L of the working face at the initial fracture of each key stratum is calculated. Simultaneously, the step-like development height H of the gas-conducting fracture zone with the fracture of each key stratum is calculated. j (L), determine the critical lag distance L corresponding to the first breakthrough of the gas-conducting fracture zone into the high-extraction roadway. H Among them, the critical distance of extraction lag L H The gas-conducting fracture zone first reaches or exceeds the high-extraction roadway layer H. g The minimum critical layer initial breach propulsion distance corresponding to the time;

[0012] S4. Calculation of gas emission rate, emission increment, and high-level drainage roadway extraction rate in adjacent layers after pressure relief.

[0013] Based on the source prediction method and introducing the gas emission rate function β of the adjacent layer under the control of the key layer. i (L), calculate the dynamic change in adjacent layer depressurization gas emission Q with advancing distance. adj (L), from which the increase in gas outburst from adjacent layers before and after the failure of each key layer is obtained, ΔQ. adj Simultaneously, based on the evolutionary characteristics of "initial weak response - accelerated growth after fracture development - stable saturation after breakthrough", the gas extraction rate η(L) of the high-pressure extraction roadway is calculated as a function of the advancing distance.

[0014] S5. Determination of Necessary Conditions for Delayed Extraction in High-Pressure Drainage Lanes

[0015] For each critical layer, simultaneously verify the spatial connectivity condition L. j <L H Sampling response condition η(L) j )<η c Key layers that meet both conditions are included in the disaster causation index calculation; key layers that do not meet the conditions are excluded. j =LH The key layer is marked as the main control key layer; where η(L) j η represents the extraction rate of depressurized gas from the high-efficiency extraction roadway when the j-th key layer fails; c The critical extraction rate for a high-efficiency extraction roadway to enter the effective extraction stage is set at 0.5-0.6.

[0016] S6. Calculation of Disaster Identification Indicators

[0017] Calculate the amount of depressurized gas Q entering the working face. Wadj (L) Remaining ventilation capacity for depressurizing gas from adjacent layers (Q) A (L), and then calculate the working face gas over-limit risk coefficient R(L) and the disaster contribution coefficient G of the key layer. j With high-speed extraction roadway delayed disaster index I j ;

[0018] S7. Determination and Hazard Classification of Disaster-Causing Critical Layers and Main Controlling Critical Layers

[0019] For critical layers that break within the danger window, according to the judgment criteria, when their disaster contribution coefficient G j When G is ≥1, it is determined to be a critical layer for sudden disasters. j <1. Risk coefficient of exceeding the limit R(L) j When G ≥ 1, it is determined to be a cumulative disaster-causing critical layer. Both types are collectively referred to as disaster-causing critical layers, where G j The largest of these is the key layer responsible for the main disaster.

[0020] The key stratum that is the first to be connected to the high-efficiency extraction roadway after the gas-conducting fracture zone in the critical overburden stratum is the main controlling stratum, and the distance of its fracture advance is the critical distance of extraction lag L. H For those samples that meet the criteria of delayed extraction but not resulting in disaster, but with a delayed disaster index I... j Those ranking higher among similar critical layers are included in the continuous early warning list;

[0021] S8. Results Output and Prevention Recommendations

[0022] Output the layers of the main control critical layer, the disaster-causing critical layer, and the continuous early warning layer, the breakthrough advance distance and the corresponding identification indicators, verify whether the failure to exceed the limit after the main control critical layer breaks, and provide prevention and control suggestions for strengthening gas extraction, adjusting ventilation parameters and controlling the advance speed during the initial mining period.

[0023] As an improvement, in step S1, the physical and mechanical parameters of each rock layer include lithology and thickness h. i Elastic modulus E i Ultimate tensile strength R t With bulk density γ i ;

[0024] Gas occurrence parameters of the overlying adjacent gas-bearing coal and rock strata include coal thickness (m). i Original gas content X i Residual gas content X ci ;

[0025] The layout parameters of the high-level extraction roadway include the distance H of the high-level extraction roadway from the top of the coal seam. g ;

[0026] Ventilation parameters for working face mining include working face air volume Q T The permissible methane concentration limit for return air C lim The gas emission rate of this coal seam is Q1, and the daily output of the working face is A. d The thickness of the coal seam being mined is M, and the rock strata fracture angles β1 and β2 at both ends of the working face are β1 and β2.

[0027] As an improvement, in step S2, the key layer identification method is the key layer stiffness identification criterion, which determines the hard rock layer that controls the deformation and fracture of the overlying rock layer as the key layer from bottom to top, and determines the load borne by each key layer according to the range of soft rock layers it controls.

[0028] As an improvement, in step S3, the formula for calculating the ultimate span of the critical layer during initial failure is as follows:

[0029] ;

[0030] In the formula, h i R represents the thickness of the i-th rock layer, in meters. t q represents the ultimate tensile strength, in MPa; i For the rock strata to bear the load, kN, q i Determined based on critical layer theory;

[0031] The underlying delamination space condition refers to the effective free space formed below the key layer that meets its bending subsidence and fracture deformation requirements, including:

[0032] The underlying rock mass supporting the key layer is equivalent to a Winkler elastic foundation. When the exposed span of the i-th key layer reaches its ultimate failure distance, its maximum bending settlement y i Calculate using the following formula:

[0033] ;

[0034] In the formula, I i Let m be the moment of inertia per unit width of the i-th key layer cross section. 4 E i Let l be the elastic modulus of the i-th critical layer, in MPa; hi The span of the first failure limit of the i-th critical layer is half of the span of the first failure, in meters; α is a dimensionless correction coefficient determined by the boundary conditions of the elastic foundation beam; w is the characteristic coefficient of the elastic foundation beam, in meters.-1 Considering the compressive compaction of the underlying fractured rock strata and the tendency of its fragmentation coefficient to approach the residual fragmentation coefficient, the effective free space height below the i-th hard rock layer should deduct the space occupied by the residual fragmentation of the underlying fractured rock strata, and is determined by the following formula:

[0035] ;

[0036] In the formula, k si denoted as the residual breccia coefficient, and M as the thickness of the mined coal seam, in meters.

[0037] As an improvement, in step S3, the formula for calculating the initial fracture working face advance distance L of the key layer is:

[0038] ;

[0039] In the formula, L is the working face advance distance, m; β1 and β2 are the rock strata fracture angles at both ends of the working face, °; h i R t q i E i I i l hi α, ω, M and k si The meaning is the same as above; when the advance distance condition and the underlying effective free space condition are satisfied at the same time, it is determined that the i-th key layer has the initial fracture condition;

[0040] The formula for the step-like development height of the gas-conducting fracture zone is: In the formula, H j The height of the j-th key layer from the top of the coal seam. This represents all soft rock layers controlled by the j-th key layer.

[0041] As an improvement, in step S4, the gas emission rate Q from the adjacent layer is... adj The formula for (L) is:

[0042] ;

[0043] In the formula, A d M represents the daily output of the working face, in tons per day (t / d); M represents the thickness of the coal seam being mined, in meters (m). i Let X be the thickness of the i-th adjacent coal seam, in meters; i X ci These represent the original gas content and the residual gas content of the i-th adjacent layer, respectively; β i (L) represents the gas emission rate of the adjacent layer;

[0044] The adjacent layer gas emission rate βi(L) is dynamically corrected as the working face advances:

[0045] When the working face advances to the critical layer fracturing step distance of the j-th layer, the gas emission rate of the adjacent layer is taken as 1; for the upper adjacent layer that has not yet been penetrated by the gas-conducting fracture, the formula for its adjacent layer gas emission rate is:

[0046] ;

[0047] In the formula, h i L is the vertical distance from the i-th adjacent layer to the roof of the mined coal seam; j H represents the breakthrough propulsion distance of the j-th critical layer; j (L) is the highest interface height of the gas-conducting fracture after the fracturing of the j-th key layer, which can be taken as the upper boundary of the soft rock layer controlled by the j-th key layer; f(⋅) is the function determined by the relationship between the distance between adjacent layers and the gas emission rate in the source prediction method;

[0048] The increase in gas outburst from the adjacent layer ΔQ adj The formula is:

[0049] ;

[0050] In the formula, ΔQ adj m represents the incremental gas outburst from adjacent layers due to the failure of the j-th critical layer. 3 / min; Q adj (L j ) represents the gas release from adjacent layers after the failure of the j-th critical layer, m. 3 / min; Q adj (L j- ) represents the amount of gas released from adjacent layers before the failure of the j-th critical layer, m. 3 / min;

[0051] The semi-empirical relationship between the gas extraction rate η(L) of the high-pressure drainage roadway and the working face advance distance is as follows:

[0052] ;

[0053] ;

[0054] In the formula, L is the working face advancing distance, in meters; L H The critical advance distance (m) for effective connection between the gas-guided fracture zone and the high-efficiency extraction roadway; η max The maximum depressurized gas extraction rate that can be achieved after the high-pressure extraction roadway is connected is 0.80, which is taken as both engineering applicability and model conservatism; η0 is the extraction rate of the weakly connected high-pressure extraction roadway in the initial mining stage, which is taken as 0.03 to 0.08; a and b are the extraction rate growth morphology parameters, which control the degree of lag in the growth of the extraction rate before connection and the speed at which it tends to saturate after connection, respectively, and are taken as a=3 and b=2.

[0055] As an improvement, in step S6, the amount of depressurized gas Q entering the adjacent layer of the working face is... Wadj (L) and the remaining ventilation capacity Q for depressurizing gas in adjacent layers. A (L) Calculate according to the following formulas:

[0056] ;

[0057] ;

[0058] In the formula, Q T For the working face air volume, m 3 / min; C lim The permissible methane concentration limit; Q1 is the gas emission rate of this coal seam, in m³. 3 / min, in the initial sampling stage, a representative value can be taken as an approximation of a constant;

[0059] The formula for the risk coefficient R(L) of excessive gas at the working face is:

[0060] ;

[0061] When R(L) < 1, the remaining ventilation capacity of the working face can meet the dilution requirements of the depressurized gas from the adjacent layer entering the working face, and the risk of exceeding the limit is low; when R(L) ≥ 1, the amount of depressurized gas entering the working face has reached or exceeded the remaining ventilation capacity, and there is a risk of abnormal gas outburst or exceeding the limit at the working face.

[0062] The portion of the newly added depressurized gas induced by the failure of the j-th key layer that enters the working face and the disaster contribution coefficient G of the key layer. j Calculate them according to the following formulas:

[0063] ;

[0064]

[0065] The disaster-causing contribution coefficient G of the key layer j The incremental ΔQ from the fracture adj The proportion of samples not extracted at the time of fracture is determined together with the proportion of samples not extracted, where the proportion of samples not extracted is 1-η(L). j ); when G j When the value is ≥1, the amount of new gas inflow induced by its failure has reached or exceeded the remaining ventilation capacity, and it can be identified as a critical layer for sudden disaster.

[0066] When L j <L H At that time, the high-speed extraction roadway delayed disaster index I j Calculate using the following formula: .

[0067] As an improvement, in step S7, the criteria for determining the critical layer include:

[0068] 1) Criteria for determining the critical layer of sudden disasters

[0069] For breakage occurring within the gas over-limit danger window, meeting L j <L H The j-th critical layer is classified as a sudden-type disaster-causing critical layer when it simultaneously meets the following three sets of conditions:

[0070] ;

[0071] in, For the conditions of spatial connection, Both of these conditions constitute the necessary condition for extraction lag, and are used as extraction response conditions. This provides sufficient conditions for a sudden disaster.

[0072] 2) Criteria for determining the critical layer of cumulative disasters

[0073] Within the danger window, the necessary conditions for extraction lag are met, and G j <1 but the risk coefficient R(L) exceeds the limit j Critical layers with a value of ≥1 are classified as cumulative disaster-causing critical layers.

[0074] 3) Key Disaster-Causing Layer Screening Rules

[0075] Sudden-onset disaster-causing critical layers and cumulative disaster-causing critical layers are collectively referred to as disaster-causing critical layers. Both types of critical layers are sources of disaster caused by excessive gas levels at the working face within the danger window.

[0076] Disaster contribution coefficient G j The numerical value is used as the basis for ranking the contribution to disaster, G j The critical layer with the largest value is defined as the primary critical layer.

[0077] As an improvement, in step S8, the termination condition after the main control critical layer breaks satisfies the following formula:

[0078] (1-η max )Q adj (L)<Q A ;

[0079] In the formula: η max Q represents the maximum depressurization gas extraction rate after the high-pressure extraction tunnel is connected. adj (L) represents the gas emission rate from the adjacent layer at the working face advance distance L, Q A This is to dilute the remaining airflow at the working face.

[0080] In a second aspect, the present invention also provides a critical layer identification system for abnormal gas outbursts during the initial mining stage of a working face, characterized in that it is used to execute the critical layer identification method for abnormal gas outbursts during the initial mining stage of a working face as described in any of the above claims; the identification system is built on the Electron cross-platform desktop application framework, and the front-end interactive interface is developed using HTML5, CSS3, and JavaScript, and the overall system adopts a three-layer isolation architecture of main process, security bridging layer, and rendering layer;

[0081] The discrimination system includes:

[0082] The parameter input module is used to input all basic parameters related to coal-bearing strata, rock mechanics, gas occurrence, high-level drainage roadway layout, and ventilation mining, and supports the visual input of strata columnar structures.

[0083] The calculation and solution kernel module programmatically implements all the calculation formulas and identification logics recorded above, and sequentially completes the identification of key overburden layers, the solution of key layer fracture advance distance and gas-conducting fracture zone development height, the calculation of gas emission from adjacent layers and high-speed extraction roadway extraction rate, the solution of multi-dimensional disaster-causing indicators, the stratification determination of key overburden layers, and the verification of gas over-limit termination conditions.

[0084] The results output module is used to display the key strata, initial fracture advance distance, and all identification indicators in tabular form; it adaptively and in real time draws the overburden columnar structure diagram, gas-conducting fracture development diagram, and curves showing the variation of the over-limit risk coefficient R(L) and the high-extraction roadway extraction rate η(L) with the working face advance distance using the HTML5 Canvas component; it categorizes and displays the main control key strata, sudden disaster-causing key strata, cumulative disaster-causing key strata, and continuous early warning strata, and simultaneously outputs graded gas prevention and control technology recommendations;

[0085] The file and report management module is used to store calculation case data in JSON structured .gks format files. It supports saving, reading, and reproducing calculation cases, and can export standardized calculation reports.

[0086] The discrimination system can be packaged using electron-builder to generate a Windows single-file executable program that does not require installation and supports offline independent operation.

[0087] Compared with the prior art, the beneficial effects of the present invention are:

[0088] 1. This invention constructs an integrated coupled discrimination system for overburden migration, gas release, and extraction, breaking through the limitations of single-dimensional analysis in existing technologies. It incorporates processes such as the fracturing and evolution of key overburden layers, the vertical development of gas-conducting fracture zones, the desorption and migration of gas from overlying adjacent layers, and the dynamic extraction response in high-efficiency extraction roadways into a unified spatiotemporal analysis framework. By distinguishing between two types of overburden control layers—the main control key layer and the disaster-causing key layer—and establishing layered quantitative identification rules, it fundamentally reveals the intrinsic mechanism of gas exceeding limits caused by the spatiotemporal misalignment of gas release, fracture development, and extraction capacity during the initial mining stage of multi-coal seam working faces. This fills the technical gap in existing technologies that cannot identify gas-causing overburden layers in a layered manner.

[0089] 2. This invention adopts an incremental approach to quantitative disaster assessment, using the newly added gas emission from a single-layer key fracture as the core evaluation factor. It comprehensively couples multiple influencing factors such as gas source intensity, working face ventilation dilution margin, high-level drainage lag level, and risk duration to establish an over-limit risk coefficient R and a disaster contribution coefficient G. j Lagging Disaster Index I j Three-dimensional quantitative evaluation indicators; can accurately divide the key layers of sudden disasters and the key layers of cumulative disasters, and simultaneously screen the continuous early warning layer with long-term gas accumulation risk, solving the shortcomings of traditional single-factor risk assessment methods that are one-sided and unable to distinguish the form of disaster outbreak, and realizing the stratification and classification of gas disasters in initial mining for accurate judgment.

[0090] 3. This invention utilizes the extraction hysteresis critical distance L H Quantitatively delineate the gas exceedance danger window in the initial mining, identify the main control key layer as the control rock layer for shortening the exceedance window period, and set the gas exceedance termination check condition after the main control layer is broken. This can predict the gas control effect after the main control layer is weakened and treated in advance, and provide a quantitative basis for the overburden pre-fracture and pressure relief treatment.

[0091] 4. The entire discrimination logic of this invention can be programmatically encapsulated into a visual offline prediction system. Only basic parameters such as strata, gas, and ventilation need to be input, and the system can automatically output the key stratum position, critical failure advance distance, disaster risk level, and supporting graded treatment plan. It can be widely used in engineering scenarios such as optimizing the layout parameters of high-speed extraction roadways, controlling the initial mining advance rate of working faces, comparing and selecting gas-enhanced extraction schemes, and demonstrating mine gas prevention and control schemes. This enables advanced prediction and proactive prevention and control of gas disasters during the initial mining period of working faces, effectively ensuring safe production in underground coal mining operations. Attached Figure Description

[0092] Figure 1 This is a flowchart of the method for identifying key layers causing abnormal gas outbursts during the initial mining stage of the working face according to the present invention.

[0093] Figure 2This is a schematic diagram of the abnormal gas outburst mechanism during the initial mining stage of the working face; where a, b, and c are schematic diagrams of gas migration after pressure relief following the failure of KS1, KS2, and KS3, respectively.

[0094] Figure 3 Diagram showing the module composition of the critical layer identification system for identifying abnormal gas outbursts during the initial mining stage of the working face;

[0095] Figure 4 This is a diagram showing the overburden structure characteristics of the 8516 working face according to an embodiment of the present invention.

[0096] Figure 5 This is a diagram showing the results of determining the critical layer causing the disaster at the 8516 working face according to an embodiment of the present invention.

[0097] Figure 6 This is a graph showing the variation of the over-limit risk coefficient R(L) and the high-speed extraction rate η(L) with the advance distance in an embodiment of the present invention. Detailed Implementation

[0098] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the embodiments and specific features in the embodiments are detailed descriptions of the technical solution of the present application, rather than limitations thereof. In the absence of conflict, the embodiments and technical features in the embodiments can be combined with each other.

[0099] Example 1

[0100] In this invention, the key control layer refers to the layer whose initial fracture causes the gas-conducting fracture zone to develop for the first time and penetrate to the high-efficiency extraction roadway layer, thus transforming the high-efficiency extraction roadway from restricted extraction to efficient extraction. The working face advancement distance corresponding to its fracture is the critical extraction lag distance L. H The danger window for excessive gas levels during the initial mining phase (advance distance 0-L) was defined. H The critical layer for disaster prevention refers to the layer that breaks down within the danger window (L). j <L H The key layer that causes gas exceedance in the working face due to the failure of the high-extraction roadway is located below the main control key layer.

[0101] Specifically, in combination Figure 1 As shown, the present invention provides a method for identifying key strata prone to disaster due to abnormal gas outbursts during the initial mining stage of a working face, comprising the following steps:

[0102] S1. Basic Parameter Input

[0103] Input the columnar structure of coal-bearing strata, including the lithology and thickness h of each stratum. i Elastic modulus E i Ultimate tensile strength R tWith bulk density γ i Physical and mechanical parameters; coal thickness (m) of the adjacent gas-bearing coal seam. i Original gas content X i Residual gas content X ci Gas occurrence parameters; and the distance H of the high-level extraction roadway from the coal seam roof. g Working face air volume Q T The permissible methane concentration limit for return air C lim The gas emission rate of this coal seam is Q1, and the daily output of the working face is A. d Mining and ventilation parameters such as coal seam thickness M and rock strata fracture angles β1 and β2 at both ends of the working face;

[0104] S2. Identification of Key Overburden Layer Structures

[0105] Based on the key layer identification method, key layers in the overburden are identified from bottom to top, and their strata, thicknesses and the range of loads they control are determined. These are denoted as the j-th key layer (j = 1, 2, ..., n).

[0106] S3. Calculation of the initial fracture propulsion distance and the development height of the gas-conducting fracture zone in each key layer.

[0107] The key strata are equivalent to beams with fixed ends, and their initial fracture limit span is calculated (Equation (1)). Combined with the underlying delamination space conditions (Equations (2) and (3)) and the rock fracture angle, the initial fracture advance distance L of each key strata is determined (Equation (4)). Then, the step development height H of the gas-conducting fracture zone with the fracture of each key strata is calculated. j (L) (Equation (5)) determines the critical lag distance L of the extraction lag corresponding to the first breakthrough of the gas-conducting fracture zone in the high-extraction roadway. H ;

[0108] S4. Calculation of gas emission rate, emission increment, and extraction rate in high-pressure drainage roadways for adjacent layers.

[0109] Based on the source prediction method and introducing the gas emission rate function β of the adjacent layer under the control of the key layer. i (L), calculate the dynamic change in adjacent layer depressurization gas emission Q with advancing distance. adj (L) (Equations (6) and (7)), thereby obtaining the increase in gas outburst from adjacent layers before and after the failure of each key layer, ΔQ. adj (Equation (8)); At the same time, according to the evolution characteristics of "initial weak response - accelerated growth after fracture development - stable saturation after breakthrough", the gas extraction rate η(L) of the high-pressure extraction roadway with the change of advance distance is calculated (Equation (9) and Equation (10)).

[0110] S5. Determination of the necessary conditions for lag in high-pressure extraction roadways

[0111] Determine whether the necessary condition for high-speed extraction lag is met when the j-th key layer breaks, i.e., the spatial connection condition L. j <L H With the sampling response condition η(L) j )<η c (Equation (11)); those that do not meet the requirements are excluded (the high-efficiency extraction roadway has already entered the efficient extraction stage when it breaks, and is not a key disaster-causing layer with a delayed initial mining period), and those that meet the requirements are included in the subsequent identification; among which L j =L H The key layer is identified separately as the primary control layer;

[0112] S6. Calculation of Disaster Identification Indicators

[0113] For the key layer passing through step S5, calculate the amount of depressurized gas Q entering the working face. Wadj (L) (Equation (12)) and the remaining ventilation capacity Q of the working face for depressurizing gas in adjacent layers. A (L) (Equation (13)), and then calculate the working face gas over-limit risk coefficient R(L) (Equation (14)) and the disaster contribution coefficient G of the key layer. j (Equations (15) and (16)) and the delayed disaster index I of high-speed extraction roadway j (Equation (17), Equation (18));

[0114] S7. Determination of Disaster-Causing Critical Layers and Main Controlling Critical Layers and Hazard Classification

[0115] For breakage within the danger window (L) j <L H The key layer of the disaster, according to the judgment criterion (Equation (19)), when its disaster contribution coefficient G j When G is ≥1, it is determined to be a critical layer for sudden disasters. j <1 but the risk coefficient R(L) exceeds the limit j When )≥1, it is determined to be a cumulative disaster-causing critical layer. Both types are collectively referred to as disaster-causing critical layers, where G j The largest of these is the main disaster-causing key stratum; the key stratum that is the first to connect the gas-conducting fracture zone to the high-efficiency extraction roadway after the failure of the overburden key stratum is the main controlling key stratum (under normal conditions, the closest key stratum under the high-efficiency extraction roadway), and its failure and advancement distance is the critical distance L of the extraction lag. H For those that meet the criteria of delayed extraction but do not cause disaster (G) j <1 and R(L) j <1) while the lagging disaster index I j Those ranking higher among similar critical layers are included in the continuous early warning list;

[0116] S8. Results Output and Prevention Recommendations

[0117] Output the layer position, failure advancement distance, and corresponding identification indicators of the main control critical layer, the disaster-causing critical layer (including the main disaster-causing critical layer), and the continuous early warning layer. Verify whether the failure to exceed the limit terminates after the main control critical layer fails (i.e., (1-η)). max )Q adj (L)<Q A (Whether it is valid), and based on this, provide prevention and control suggestions such as strengthening gas extraction during the initial mining period, adjusting ventilation parameters, and controlling the advance speed.

[0118] Preferably, in step S2, the key layer identification is based on the key layer stiffness discrimination criterion, and the hard rock layer that controls the deformation and fracture of the overlying rock layer is determined as the key layer from bottom to top, and the load borne by each key layer is determined according to the range of soft rock layers it controls.

[0119] Preferably, in step S3, the key layer is approximated as a beam with fixed supports at both ends. Under the equivalent uniformly distributed load q of the overlying strata, as the working face advances, the exposed span of the key layer increases and the tensile stress at the beam ends concentrates. When the maximum tensile stress reaches the tensile strength of the strata, the key layer undergoes initial fracture. The ultimate span of its initial fracture is calculated using the following formula:

[0120] (1);

[0121] In the formula, h i R represents the thickness of the i-th rock layer, in meters. t q represents the ultimate tensile strength, in MPa; i The load on the rock strata is kN, determined according to the critical layer theory.

[0122] Preferably, in step S3, the underlying rock mass supporting the key layer is equivalent to a Winkler elastic foundation. When the exposed span of the i-th key layer reaches its ultimate failure distance, its maximum bending settlement y i Calculate using the following formula:

[0123] (2);

[0124] In the formula, I i Let m be the moment of inertia per unit width of the i-th key layer cross section. 4 E i Let l be the elastic modulus of the i-th critical layer, in MPa; hi The span of the first failure limit of the i-th critical layer is half of the span of the first failure, in meters; α is a dimensionless correction coefficient determined by the boundary conditions of the elastic foundation beam; w is the characteristic coefficient of the elastic foundation beam, in meters. -1 ;

[0125] in, , , The elastic foundation coefficient, E0 is the elastic modulus of the underlying equivalent foundation, MPa; d0 is the equivalent cushion layer thickness, m.

[0126] Considering the compressive compaction of the underlying fractured rock strata and the tendency of its fragmentation coefficient to approach the residual fragmentation coefficient, the effective free space height below the i-th hard rock layer should deduct the space occupied by the residual fragmentation of the underlying fractured rock strata, and is determined by the following formula:

[0127] (3);

[0128] In the formula, k si Let M be the residual breccia coefficient, and M be the thickness of the mined coal seam (m). Only when the effective free space formed below the key stratum meets its bending subsidence and fracture deformation requirements can the key stratum possess the spatial conditions for further fracture.

[0129] Preferably, in step S3, considering the upward transmission of mining-induced fractures along the rock strata fracture angle, the working face advance distance corresponding to the failure of the key stratum is not entirely equal to its own ultimate span. Based on the geometric relationship between the ultimate span of the key stratum, the height of the key stratum from the coal seam roof, and the rock strata fracture angle, the calculation formula for the working face advance distance L of the initial failure of the key stratum is as follows:

[0130] (4);

[0131] In the formula, L is the working face advance distance, m; β1 and β2 are the rock strata fracture angles at both ends of the working face, °; h i R t q i E i I i l hi α, ω, M and k si The meaning is the same as described above.

[0132] Preferably, in step S3, when the j-th key layer meets the failure condition and undergoes a through-break, the control of the original key layer on the development of overlying fractures is broken, and the gas-conducting fracture rises upward with the bottom of the adjacent key layer above it as the new development boundary. The development height of the gas-conducting fracture zone is calculated by the following formula:

[0133] (5);

[0134] In the formula, H j The height of the j-th key layer from the top of the coal seam. This represents all soft rock layers controlled by the j-th key layer.

[0135] Preferably, in step S4, based on the idea of ​​source-based prediction and introducing a key layer failure control function, the gas emission rate of the adjacent layer under pressure relief, considering the control effect of key layer failure, is calculated by the following formula:

[0136] (6);

[0137] In the formula, A d M represents the daily output of the working face, in tons per day (t / d); M represents the thickness of the coal seam being mined, in meters (m). i Let X be the thickness of the i-th adjacent coal seam, in meters; i X ci These represent the original gas content and the residual gas content of the i-th adjacent layer, respectively; β i (L) represents the gas emission rate of the adjacent layer.

[0138] Preferably, in step S4, the adjacent layer gas emission rate β i (L) Dynamic correction with working face advance distance: When the working face advances to the step distance of the j-th key layer failure, the adjacent layers within the control range of the key layer are fully depressurized and the gas-conducting fractures develop to the upper boundary of the soft rock layer controlled by it, and the gas emission rate of the corresponding adjacent layer is taken as 1; for the upper adjacent layers that have not yet been penetrated by the gas-conducting fractures, their gas emission rate is determined according to the relationship of "interlayer spacing - gas emission rate" in the source prediction method, but the interlayer spacing is no longer taken as the original distance from the mined coal seam to the adjacent layer, but as the vertical distance between the adjacent layer and the highest development interface of the current gas-conducting fracture, that is, the static interlayer spacing is transformed into a dynamic effective interlayer spacing that changes with the advance distance, calculated according to the following formula:

[0139] (7);

[0140] In the formula, h i L is the vertical distance from the i-th adjacent layer to the roof of the mined coal seam; j H represents the breakthrough propulsion distance of the j-th critical layer; j (L) represents the highest interface height of the gas-conducting fracture after the fracturing of the j-th key layer, which can be taken as the upper boundary of the soft rock layer controlled by the j-th key layer; f(⋅) is a function determined by the relationship between the distance between adjacent layers and the gas emission rate in the source prediction method.

[0141] Preferably, in step S4, the increment ΔQ of the gas outburst from adjacent layers before and after the failure of the j-th key layer is... adj The mobilization capacity of the fracture to relieve pressure on adjacent layers of gas is reflected by the following formula:

[0142] (8);

[0143] In the formula, ΔQ adj m represents the incremental gas outburst from adjacent layers due to the failure of the j-th critical layer. 3 / min; Q adj (L j ) represents the gas release from adjacent layers after the failure of the j-th critical layer, m. 3 / min; Qadj (L j- ) represents the amount of gas released from adjacent layers before the failure of the j-th critical layer, m. 3 / min.

[0144] Preferably, in step S4, based on the evolutionary characteristics of "initial weak response - accelerated growth after fracture development - stable saturation after breakthrough", a semi-empirical relationship is established between the gas extraction rate of the high-pressure drainage roadway and the working face advance distance:

[0145] (9);

[0146] (10);

[0147] In the formula, L is the working face advancing distance, in meters; L H The critical advance distance (m) for effective connection between the gas-guided fracture zone and the high-efficiency extraction roadway; η max The maximum depressurized gas extraction rate that can be achieved after the high-pressure extraction roadway is connected is 0.80, which is taken as both engineering applicability and model conservatism; η0 is the extraction rate of the weakly connected high-pressure extraction roadway in the initial mining stage, which is taken as 0.03 to 0.08; a and b are the extraction rate growth morphology parameters, which control the degree of lag in the growth of the extraction rate before connection and the speed at which it tends to saturate after connection, respectively, and are taken as a=3 and b=2.

[0148] Preferably, in step S5, the necessary condition for the high-speed extraction roadway extraction lag can be described from two perspectives: spatial connectivity and extraction response. The spatial connectivity condition is L... j <L H The sampling response conditions are:

[0149] (11);

[0150] In the formula, η(L) j η represents the extraction rate of depressurized gas from the high-efficiency extraction roadway when the j-th key layer fails; c The critical extraction rate for a high-efficiency extraction roadway to enter the effective extraction stage is taken as 0.5–0.6. From η(L) H )=η max As can be seen from ηc, the propulsion range defined by equation (11) is strictly smaller than that defined by L. j <L H When defining the danger windows, the intersection of the two is taken when both are listed; for the critical disaster-causing layer, the spatial connectivity condition is taken as L. j <L H L j =L H The critical layer that controls the main control is the one whose failure indicates the end of the danger window and is not counted as a critical layer that causes disaster.

[0151] Preferably, in step S6, the amount of depressurized gas Q from the adjacent layer entering the working face after the high-pressure extraction effect is considered. Wadj (L) and the remaining ventilation capacity Q for depressurizing gas in adjacent layers. A (L) Calculate according to the following formulas:

[0152] (12);

[0153] (13);

[0154] In the formula, Q T For the working face air volume, m 3 / min; C lim The permissible methane concentration limit; Q1 is the gas emission rate of this coal seam, in m³. 3 / min, the representative value in the initial sampling stage can be approximated as a constant.

[0155] Furthermore, the risk coefficient for excessive gas levels at the working face is defined as follows:

[0156] (14);

[0157] When R(L) < 1, the remaining ventilation capacity of the working face can meet the dilution requirements of the depressurized gas from the adjacent layer entering the working face, and the risk of exceeding the limit is relatively low; when R(L) ≥ 1, the amount of depressurized gas entering the working face has reached or exceeded the remaining ventilation capacity, and there is a risk of abnormal gas outburst or exceeding the limit at the working face.

[0158] Preferably, in step S6, the portion of the newly added depressurized gas induced by the failure of the j-th key layer that enters the working face and its proportion to the remaining ventilation capacity (i.e., the disaster contribution coefficient G of the key layer) is considered. j ), calculate them respectively according to the following formula:

[0159] (15);

[0160] (16);

[0161] Key layer disaster contribution coefficient G j The incremental ΔQ from the fracture adj The proportion of unextracted material at the time of breakage (1-η(L)) j The extraction rate η increases rapidly with the advancing distance. Although the incremental gas outflow may not be the largest in the key layer with an earlier failure time, the extraction rate of the high-efficiency extraction roadway is the lowest when it fails, and almost all of the newly added depressurized gas flows into the working face. Therefore, G j It often reaches its maximum value at the earliest critical layer where the structure breaks. When G j When the value is ≥1, the amount of new gas inflow induced by its failure has reached or exceeded the remaining ventilation capacity, and it can be identified as a critical layer for sudden disaster.

[0162] Preferably, in step S6, in order to characterize the continuous influx load of depressurized gas in each key layer within the danger window, in addition to the instantaneous disaster contribution, a high-extraction roadway delayed disaster index I is defined. j ;

[0163] When L j <L H Calculate using the following formula:

[0164] (17);

[0165] Substituting equation (17) into the equation, we get I j With G j Relationship:

[0166] (18);

[0167] That is I j The disaster contribution coefficient G j After lag persistence factor (L H -L j ) / L H The weighted result shows that the factor is between 0 and 1, therefore I always holds. j ≤G j The earlier the critical layer breaks (L j The smaller the value and the farther away from the critical layer of the main control (the greater the hysteresis persistence factor), the higher the I value. j Relative to G j The less the decay; when L j ≥L H When, take I j =0. I j It is not used as a criterion for determining whether a disaster has reached the standard, but is used to sort the identified disaster-prone critical layers according to the continuous inflow of load, and to identify critical layers that have not yet exceeded the limit but have a large continuous inflow of load and have a tendency to accumulate risk.

[0168] Preferably, in step S7, the criterion for determining the critical disaster layer is: for breaches occurring within the danger window (L... j <L H The j-th critical layer of a disaster is determined to be a sudden-type disaster-causing critical layer when it satisfies the following formula:

[0169] (19);

[0170] in, For the conditions of spatial connection, Both of these conditions constitute the necessary condition for extraction lag, and are used as extraction response conditions. The first two equations are two expressions of the necessary condition for sudden disasters: spatial connectivity and extraction response. The third equation is a sufficient condition for sudden disasters.

[0171] Apart from the sudden type, G j <1 but R(L) j Those with a value ≥1 are classified as cumulative disaster-causing critical layers; both types are collectively referred to as disaster-causing critical layers, both constituting the cause of exceeding limits on the working face within the danger window, among which G j The largest is the primary disaster-causing critical layer. Since R(L) is a cumulative state quantity including the base outflow, it is not suitable as a measure of a single layer's disaster contribution. Therefore, the primary disaster-causing critical layer is determined by G. j Instead of R(L) sorting.

[0172] Preferably, in step S7, the determination of the main control key layer is based on its stratum and fracture connectivity conditions rather than the amount of gas released by its own fracture: the key layer in the overburden key layer that first connects the gas-conducting fracture zone after fracture to the high-efficiency extraction roadway is taken as the main control key layer, and its fracture advancement distance is the critical distance L of extraction lag. H Because the gas-conducting fracture had already connected to the high-efficiency extraction roadway when the main control layer broke, and the extraction rate had risen to η. max Most of the depressurized gas released during its rupture is extracted, therefore its G j R(L) is often not high. It is the terminator of the over-limit process rather than the strongest source. It is the core stratum for controlling the termination of the danger window and preventing gas over-limit during the initial mining period.

[0173] Preferably, in step S7, before the main control key layer breaks, the main control key layer can be weakened in advance (such as deep hole pre-fracturing blasting, hydraulic fracturing) to reduce its breaking step distance and promote its early connection to the high-extraction roadway, thereby shortening the danger window; for the advancing section corresponding to the main disaster-causing key layer that breaks within the danger window, the advancing speed should be appropriately reduced and the gas concentration monitoring of the upper corner and return air side should be strengthened; for the continuous early warning layer, the extraction effect and dynamic monitoring of return air gas concentration should be strengthened when the working face advances to the corresponding section.

[0174] Preferably, in step S8, the failure of the main control critical layer only causes a step decrease in the risk of exceeding the limit, and does not necessarily cause the working face to escape the state of exceeding the limit; the condition for termination of exceeding the limit is (1-η max )Q adj (L)<Q A ;

[0175] In the formula: η max Q represents the maximum depressurization gas extraction rate after the high-pressure extraction tunnel is connected. adj (L) represents the gas emission rate from the adjacent layer at the working face advance distance L, Q A The remaining ventilation and dilution capacity of the working face; that is, the depressurized gas that has not been extracted after the high-efficiency extraction roadway enters the high-efficiency extraction stage is lower than the remaining ventilation and dilution capacity of the working face; when the gas resources of the adjacent layer are large or the remaining ventilation and dilution capacity of the working face is insufficient, even if the main control key layer has been broken, as the upper key layer continues to break, Q adjIf (L) increases further, the working face may still exceed the limit again. At this time, it is necessary to supplement the coal seam with pre-drainage, increase the working face ventilation, or add high-level drainage boreholes.

[0176] Example 2

[0177] A system for identifying critical strata prone to gas outbursts during the initial mining phase of a working face, such as... Figure 3 As shown, the system is capable of running the method for identifying key layers causing gas outbursts during the initial mining stage of the working face as described in Example 1;

[0178] The discrimination system is built on the Electron cross-platform desktop application framework. The front-end interactive interface is developed using HTML5, CSS3, and JavaScript. The program is divided into a three-layer isolated running architecture consisting of the main process, the security bridging layer, and the rendering layer.

[0179] The discrimination system includes:

[0180] The parameter input module is used to completely input coal-bearing strata information, rock mechanics parameters, gas occurrence parameters, high-level drainage roadway layout parameters, and working face ventilation and mining parameters. It also supports the visual input operation of coal-bearing strata columnar structure.

[0181] The calculation and solution kernel module programmatically implements all the calculation formulas and layer identification logic recorded above, and automatically completes the following steps in sequence: identification of key overburden layers, calculation of the initial fracture advance distance of key layers and development height of gas-conducting fracture zones, calculation of gas emission from adjacent layers and dynamic extraction rate of high-speed extraction roadways, solution of multi-dimensional gas disaster indicators, classification and determination of key overburden layer types, and verification of gas over-limit termination conditions.

[0182] The results output module is used to visually display the location of each key layer, the initial fracture advance distance, and all quantitative identification indicators in tabular form; relying on the HTML5 Canvas component to adapt the window size, it renders in real time the overburden columnar structure diagram, the overburden gas-conducting fracture development diagram, the over-limit risk coefficient R(L), and the high-extraction roadway extraction rate η(L) as a function of the working face advance distance; it displays the main control key layer, the sudden disaster-causing key layer, the cumulative disaster-causing key layer, and the continuous early warning layer in columns, and simultaneously outputs the graded gas control technology recommendation text;

[0183] The file and report management module is used to store calculation case data in JSON structured .gks format files. It supports saving, reading, and reproducing calculation cases, and can export standardized calculation reports.

[0184] The discrimination system can be packaged using the electron-builder tool to generate a single-file executable program for Windows systems that does not require installation. It does not rely on external networks or third-party packages and supports independent offline operation in mines.

[0185] Application examples

[0186] The outburst-prone working face of the 8516 coal seam in a certain mine was selected as an engineering example. The method for identifying the key layer causing the disaster due to abnormal gas outburst during the initial mining stage of the working face, as described in this invention, was used to carry out on-site identification and verification. The entire identification process was demonstrated in combination with measured strata, gas, and ventilation parameters, and the calculation and judgment results were shown in the accompanying drawings.

[0187] Specifically, in combination Figure 1 , Figure 2 As shown, the present invention provides a method for identifying critical strata prone to disaster due to abnormal gas outbursts during the initial mining stage of a working face, comprising the following steps:

[0188] S1. Basic Parameter Input

[0189] Collect measured columnar structure data of coal-bearing strata at the 8516 working face, and input the lithology and thickness h of each stratum. i Elastic modulus E i Ultimate tensile strength R t γ-rock strata i Physical and mechanical parameters; synchronously input the thickness (m) of the overlying adjacent gas-bearing coal seam. i Original gas content X i Residual gas content X ci Gas occurrence parameters, as well as high-efficiency extraction roadway layout and ventilation parameters;

[0190] The high-pressure gas extraction roadway is located at a stratum 53.71 m above the coal seam roof; the maximum depressurization gas extraction rate η that can be achieved after the high-pressure gas extraction roadway is completed is... max Take 0.80, the initial weakly connected extraction rate η0 is taken as 0.03~0.08, the extraction rate morphological parameters a=3, b=2, and the critical extraction rate η c Take a value of 0.5 to 0.6;

[0191] S2. Identification of Key Overburden Layer Structures

[0192] Using the key layer stiffness discrimination criterion of this invention, the hard rock strata of the overburden of the 8516 working face were identified layer by layer from bottom to top. A total of three key overburden layers were identified, numbered KS1, KS2, and KS3 from bottom to top. The occurrence location, thickness, lithology, and stratigraphic combination structure of each key layer are detailed in the appendix. Figure 4 KS3 is composed of sandy mudstone with a thickness of 13.25 m.

[0193] S3. Calculation of fracture propulsion distance and gas-guided fracture zone development height

[0194] According to equations (1) to (5) in Example 1, the initial fracture advancement distance and the development height of the gas-conducting fracture zone after fracture were calculated for each key layer: the fracture advancement distance of KS1 was 35.77 m, and the top boundary of the gas-conducting fracture zone developed to 21.43 m after fracture; the fracture advancement distance of KS2 was 83.06 m, and the top boundary of the fracture zone developed to 34.25 m; both were lower than the high-extraction roadway layer of 53.71 m, indicating that although the two fractures could promote the migration of depressurized gas from the underlying adjacent layer to the goaf and working face, an effective extraction channel to the high-extraction roadway had not yet been formed. The fracture advancement distance of KS3 was 110.15 m, and the top boundary of the fracture zone rose to 71.68 m after fracture, crossing the high-extraction roadway layer of 53.71 m for the first time and achieving penetration. Therefore, the critical extraction lag distance L corresponding to the first penetration of the gas-conducting fracture zone into the high-extraction roadway is... H =110.15 m, the initial mining period from 0 to 110.15 m is the dangerous window of gas exceeding the limit before the high-extraction roadway is connected.

[0195] S4. Calculation of Outflow Increment and Extraction Rate

[0196] The gas outburst and increment of adjacent layers before and after the failure of each key layer were calculated according to formulas (6), (7), and (8). The gas extraction rate of the high-pressure extraction roadway at each failure point was calculated according to formulas (9) and (10). When KS1 failed, the high-pressure extraction roadway had not yet penetrated the underlying gas-conducting fracture zone, and the extraction rate η was only 0.1. The failure added 4.646 m³ of gas. 3 / min; when KS2 fractures, the extraction rate η increases to 0.555, and the gas emission from adjacent layers increases to 18.666 m³. 3 / min; when KS3 breaks, the extraction rate η rises to η max =0.80.

[0197] S5. Determination of the Necessary Condition for Sampling Lag

[0198] Layer-by-layer discrimination L j <L H Both KS1 (35.77 m) and KS2 (83.06 m) are less than L. H =110.15 m, satisfying the extraction lag condition; KS3 breaking and advancing distance equal to L H This is identified as the main control key layer.

[0199] S6. Calculation of Disaster Identification Indicators

[0200] Calculate the amount of depressurized gas entering the working face, the remaining ventilation capacity, the risk coefficient R of exceeding the limit, the disaster contribution coefficient Gj, and the delayed disaster index I for each key layer according to formulas (12) to (18). j Qadj Substituting (L) and η(L) into equation (14), we obtain the variation of the over-limit risk coefficient R(L) with the advance distance, as follows: Figure 6 As shown. When KS1 breaks, approximately 90.0% of the newly added 4.646 m³ / min depressurization gas enters the working face. j =0.430; R jumps from 1.06 to a peak of 1.438. When KS2 breaks, the extraction rate has reached 0.555, R = 0.855, G j =0.144. The extraction rate η reached 0.80 when KS3 broke, G j =0.086, R=0.471.

[0201] S7. Determination of Disaster-Causing Critical Layer and Main Control Critical Layer

[0202] The judgment result is as follows Figure 5 As shown. The fracture distance of KS1 is 35.77 m, which is less than L. H Moreover, it broke earliest and had the lowest extraction rate, although the sudden-type indicator G... j =0.430 did not meet the criteria for sudden disaster, but after the fracture, the accumulated depressurized gas from the adjacent layer entered the working face, causing R to reach 1.438, exceeding the remaining ventilation capacity. Therefore, it was determined to be a critical layer for cumulative disaster; because its G j Among the three key layers, it is the largest and the main contributing layer to the disaster caused by the peak leakage during the initial mining period. After the KS3 (sandy mudstone, 13.25 m thick) fractured, the gas-conducting fracture zone first penetrated the high-efficiency extraction roadway, making it the main controlling layer for the transition from "delayed extraction" to "effective extraction." Its main controlling effect is reflected in its stratigraphic position and penetration effect rather than its contribution to outflow; therefore, G... j =0.086 and R=0.471 are both relatively low values ​​among the three layers. KS2's failure distance of 83.06m is still within the danger window, but R=0.855 and G j =0.144, which does not meet the disaster criterion, and its failure will further increase the total amount of gas released from the adjacent layer. Therefore, it is classified as a continuous warning layer.

[0203] S8. Results Output and Prevention Recommendations

[0204] After KS1 fractured, R reached a peak of 1.438, which was the most severe gas exceedance point during the initial mining phase. Subsequently, as the working face continued to advance and the high-efficiency drainage rate η(L) in the high-efficiency drainage roadway continued to increase, R gradually decreased and fell below 1 at L≈69.1 m. After KS3 fractured, η reached 0.80. According to the termination condition for exceeding the limit, (1-η max Qadj = 4.57 m³ / min < Q A=9.71 m³ / min, the working face has the capacity to absorb the depressurized gas from the adjacent layer, and the exceeding process terminates accordingly. Therefore, in this case, the "danger window" and the "actual exceeding range" should be distinguished: 0 to 110.15 m is the danger window of the extraction lag before the high-pressure extraction roadway is connected, while the actual exceeding range is about 0 to 69.1 m.

[0205] The corresponding prevention and control recommendations are as follows: For the key control layer KS3 (fault distance 110.15 m), deep hole pre-fracturing blasting or hydraulic fracturing can be implemented to reduce its fault step distance and promote its early connection to the high-extraction roadway, thereby shortening the danger window and the over-limit zone; for the fault location of the main disaster-contributing layer KS1 (advance approximately 35.77 m), which is the peak point of the over-limit risk, the advance speed should be appropriately reduced when advancing to the 30-40 m section, and the gas concentration monitoring of the upper corner and return air side should be strengthened; in the over-limit zone of 0-69 m, it is advisable to temporarily increase the air volume; for the continuous early warning layer KS2 (fault distance 83.06 m), dynamic monitoring of outflow should be maintained.

[0206] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for identifying key strata prone to gas outbursts during the initial mining stage of a working face, characterized in that, Includes the following steps: S1, Basic Parameter Input Input the columnar structure of the coal-bearing strata, the physical and mechanical parameters of each rock layer, the gas occurrence parameters of the overlying adjacent gas-bearing coal and rock strata, the high-level drainage roadway layout parameters, and the working face mining ventilation parameters; S2, Identification of Key Overburden Layer Structure Based on the key layer identification method, key layers in the overburden are identified from bottom to top, and their strata, thickness and the range of loads they control are determined. These are denoted as the j-th key layer, j = 1, 2, ..., n. S3. Calculation of critical layer failure propulsion distance and gas-conducting fracture zone development height. The key strata are equated to beams with fixed supports at both ends, and their initial fracture limit span is calculated. Combined with the underlying delamination space conditions and the rock fracture angle, the advance distance L of the working face at the initial fracture of each key stratum is calculated. Simultaneously, the step-like development height H of the gas-conducting fracture zone with the fracture of each key stratum is calculated. j (L), determine the critical lag distance L corresponding to the first breakthrough of the gas-conducting fracture zone into the high-extraction roadway. H Among them, the critical distance of extraction lag L H The gas-conducting fracture zone first reaches or exceeds the high-extraction roadway layer H. g The minimum critical layer initial breach propulsion distance corresponding to the time; S4. Calculation of gas emission rate, emission increment, and high-level drainage roadway extraction rate in adjacent layers after pressure relief. Based on the source prediction method and introducing the gas emission rate function β of the adjacent layer under the control of the key layer. i (L), calculate the dynamic change in adjacent layer depressurization gas emission Q with advancing distance. adj (L), from which the increase in gas outburst from adjacent layers before and after the failure of each key layer is obtained, ΔQ. adj Simultaneously, based on the evolutionary characteristics of "initial weak response - accelerated growth after fracture development - stable saturation after breakthrough", the gas extraction rate η(L) of the high-pressure extraction roadway is calculated as a function of the advancing distance. S5. Determination of Necessary Conditions for Delayed Extraction in High-Pressure Drainage Lanes For each critical layer, simultaneously verify the spatial connectivity condition L. j <L H Sampling response condition η(L) j )<η c Key layers that meet both conditions are included in the disaster causation index calculation; key layers that do not meet the conditions are excluded. j =L H The key layer is marked as the main control key layer; where η(L) j η represents the extraction rate of depressurized gas from the high-efficiency extraction roadway when the j-th key layer fails; c The critical extraction rate for a high-efficiency extraction roadway to enter the effective extraction stage is set at 0.5-0.

6. S6. Calculation of Disaster Identification Indicators Calculate the amount of depressurized gas Q entering the working face. Wadj (L) Remaining ventilation capacity for depressurizing gas from adjacent layers (Q) A (L), and then calculate the working face gas over-limit risk coefficient R(L) and the disaster contribution coefficient G of the key layer. j With high-speed extraction roadway delayed disaster index I j ; S7. Determination and Hazard Classification of Disaster-Causing Critical Layers and Main Controlling Critical Layers For critical layers that break within the danger window, according to the judgment criteria, when their disaster contribution coefficient G j When G is ≥1, it is determined to be a critical layer for sudden disasters. j <1. Risk coefficient of exceeding the limit R(L) j When G ≥ 1, it is determined to be a cumulative disaster-causing critical layer. Both types are collectively referred to as disaster-causing critical layers, where G j The largest of these is the key layer responsible for the main disaster. The key stratum that is the first to be connected to the high-efficiency extraction roadway after the gas-conducting fracture zone in the critical overburden stratum is the main controlling stratum, and the distance of its fracture advance is the critical distance of extraction lag L. H For those samples that meet the criteria of delayed extraction but not resulting in disaster, but with a delayed disaster index I... j Those ranking higher among similar critical layers are included in the continuous early warning list; S8. Results Output and Prevention Recommendations Output the layers of the main control critical layer, the disaster-causing critical layer, and the continuous early warning layer, the breakthrough advance distance and the corresponding identification indicators, verify whether the failure to exceed the limit after the main control critical layer breaks, and provide prevention and control suggestions for strengthening gas extraction, adjusting ventilation parameters and controlling the advance speed during the initial mining period.

2. The method for identifying key strata causing abnormal gas outbursts during the initial mining stage of a working face, as described in claim 1, is characterized in that... In step S1, the physical and mechanical parameters of each rock layer include lithology and thickness h. i Elastic modulus E i Ultimate tensile strength R t With bulk density γ i ; Gas occurrence parameters of the overlying adjacent gas-bearing coal and rock strata include coal thickness (m). i Original gas content X i Residual gas content X ci ; The layout parameters of the high-level extraction roadway include the distance H of the high-level extraction roadway from the top of the coal seam. g ; Ventilation parameters for working face mining include working face air volume Q T The permissible methane concentration limit for return air (C) lim The gas emission rate of this coal seam is Q1, and the daily output of the working face is A. d The thickness of the coal seam being mined is M, and the rock strata fracture angles β1 and β2 at both ends of the working face are β1 and β2.

3. The method for identifying key strata causing abnormal gas outbursts during the initial mining stage of a working face, as described in claim 1, is characterized in that... In step S2, the key layer identification method is the key layer stiffness identification criterion, which determines the hard rock layer that controls the deformation and fracture of the overlying rock layer from bottom to top as the key layer, and determines the load borne by each key layer according to the range of soft rock layers it controls.

4. The method for identifying key strata causing abnormal gas outbursts during the initial mining stage of a working face, as described in claim 1, is characterized in that... In step S3, the formula for calculating the ultimate span of the critical layer during its initial failure is as follows: ； In the formula, h i R represents the thickness of the i-th rock layer, in meters. t q represents the ultimate tensile strength, in MPa; i For the rock strata to bear the load, kN, q i Determined based on critical layer theory; The underlying delamination space condition refers to the effective free space formed below the key layer that meets its bending subsidence and fracture deformation requirements, including: The underlying rock mass supporting the key layer is equivalent to a Winkler elastic foundation. When the exposed span of the i-th key layer reaches its ultimate failure distance, its maximum bending settlement y i Calculate using the following formula: ； In the formula, I i Let m be the moment of inertia per unit width of the i-th key layer cross section. 4 ; E i Let l be the elastic modulus of the i-th critical layer, in MPa; hi The span of the first failure limit of the i-th critical layer is half of the span of the first failure, in meters; α is a dimensionless correction coefficient determined by the boundary conditions of the elastic foundation beam; w is the characteristic coefficient of the elastic foundation beam, in meters. -1 Considering the compressive compaction of the underlying fractured rock strata and the tendency of its fragmentation coefficient to approach the residual fragmentation coefficient, the effective free space height below the i-th hard rock layer should deduct the space occupied by the residual fragmentation of the underlying fractured rock strata, and is determined by the following formula: ； In the formula, k si denoted as the residual breccia coefficient, and M as the thickness of the mined coal seam, in meters.

5. The method for identifying key strata causing abnormal gas outbursts during the initial mining stage of a working face, as described in claim 4, is characterized in that... In step S3, the formula for calculating the initial fracture advance distance L of the key layer working face is: ； In the formula, L is the working face advance distance, m; β1 and β2 are the rock strata fracture angles at both ends of the working face, °; h i R t q i E i I i l hi α, ω, M and k si The meaning is consistent with claim 4; when the advance distance condition and the underlying effective free space condition are satisfied at the same time, it is determined that the i-th key layer has the initial fracture condition; The formula for the step-like development height of the gas-conducting fracture zone is: In the formula, H j The height of the j-th key layer from the top of the coal seam. This represents all soft rock layers controlled by the j-th key layer.

6. The method for identifying key strata causing abnormal gas outbursts during the initial mining stage of a working face, as described in claim 1, is characterized in that... In step S4, the gas emission rate Q from the adjacent layer is... adj The formula for (L) is: ； In the formula, A d M represents the daily output of the working face, in tons per day (t / d); M represents the thickness of the coal seam being mined, in meters (m). i Let X be the thickness of the i-th adjacent coal seam, in meters; i X ci These represent the original gas content and the residual gas content of the i-th adjacent layer, respectively; β i (L) represents the gas emission rate of the adjacent layer; The adjacent layer gas emission rate βi(L) is dynamically corrected as the working face advances: When the working face advances to the critical layer fracturing step distance of the j-th layer, the gas emission rate of the adjacent layer is taken as 1; for the upper adjacent layer that has not yet been penetrated by the gas-conducting fracture, the formula for its adjacent layer gas emission rate is: ； In the formula, h i L is the vertical distance from the i-th adjacent layer to the roof of the mined coal seam; j H represents the breakthrough propulsion distance of the j-th critical layer; j (L) is the highest interface height of the gas-conducting fracture after the fracturing of the j-th key layer, which can be taken as the upper boundary of the soft rock layer controlled by the j-th key layer; f(⋅) is the function determined by the relationship between the distance between adjacent layers and the gas emission rate in the source prediction method; The increase in gas outburst from the adjacent layer ΔQ adj The formula is: ； In the formula, ΔQ adj m represents the incremental gas outburst from adjacent layers due to the failure of the j-th critical layer. 3 / min; Q adj (L j ) represents the gas release from adjacent layers after the failure of the j-th critical layer, m. 3 / min; Q adj (L j- ) represents the amount of gas released from adjacent layers before the failure of the j-th critical layer, m. 3 / min; The semi-empirical relationship between the gas extraction rate η(L) of the high-pressure drainage roadway and the working face advance distance is as follows: ； ； In the formula, L is the working face advancing distance, in meters; L H The critical advance distance (m) is the distance required for effective connection between the gas-guided fracture zone and the high-efficiency extraction tunnel. η max The maximum depressurized gas extraction rate that can be achieved after the high-pressure extraction roadway is connected is 0.80, which is taken as both engineering applicability and model conservatism; η0 is the extraction rate of the weakly connected high-pressure extraction roadway in the initial mining stage, which is taken as 0.03 to 0.08; a and b are the extraction rate growth morphology parameters, which control the degree of lag in the growth of the extraction rate before connection and the speed at which it tends to saturate after connection, respectively, and are taken as a=3 and b=2.

7. The method for identifying key strata causing abnormal gas outbursts during the initial mining stage of a working face, as described in claim 1, is characterized in that... In step S6, the amount of depressurized gas Q entering the adjacent layer of the working face is... Wadj (L) and the remaining ventilation capacity Q for depressurizing gas in adjacent layers. A (L) Calculate according to the following formulas: ； ； In the formula, Q T For the working face air volume, m 3 / min; C lim The permissible methane concentration limit; Q1 is the gas emission rate of this coal seam, in m³. 3 / min, in the initial sampling stage, a representative value can be taken as an approximation of a constant; The formula for the risk coefficient R(L) of excessive gas at the working face is: ； When R(L) < 1, the remaining ventilation capacity of the working face can meet the dilution requirements of the depressurized gas from the adjacent layer entering the working face, and the risk of exceeding the limit is low; when R(L) ≥ 1, the amount of depressurized gas entering the working face has reached or exceeded the remaining ventilation capacity, and there is a risk of abnormal gas outburst or exceeding the limit at the working face. The portion of the newly added depressurized gas induced by the failure of the j-th key layer that enters the working face and the disaster contribution coefficient G of the key layer. j Calculate them according to the following formulas: ； ； The disaster-causing contribution coefficient G of the key layer j The incremental ΔQ from the fracture adj The proportion of samples not extracted at the time of fracture is determined together with the proportion of samples not extracted, where the proportion of samples not extracted is 1-η(L). j ); when G j When the value is ≥1, the amount of new gas inflow induced by its failure has reached or exceeded the remaining ventilation capacity, and it can be identified as a critical layer for sudden disaster. When L j <L H At that time, the high-speed extraction roadway delayed disaster index I j Calculate using the following formula: .

8. The method for identifying key strata causing abnormal gas outbursts during the initial mining stage of a working face, as described in claim 1, is characterized in that... In step S7, the criteria for determining the critical layer include: 1) Criteria for determining the critical layer of sudden disasters For breakage occurring within the gas over-limit danger window, meeting L j <L H The j-th critical layer is classified as a sudden-type disaster-causing critical layer when it simultaneously meets the following three sets of conditions: ； in, For the conditions of spatial connection, Both of these conditions constitute the necessary condition for extraction lag, and are used as extraction response conditions. This provides sufficient conditions for a sudden disaster. 2) Criteria for determining the critical layer of cumulative disasters Within the danger window, the necessary conditions for extraction lag are met, and G j <1 but the risk coefficient R(L) exceeds the limit j Critical layers with a value of ≥1 are classified as cumulative disaster-causing critical layers. 3) Key Disaster-Causing Layer Screening Rules Sudden-onset disaster-causing critical layers and cumulative disaster-causing critical layers are collectively referred to as disaster-causing critical layers. Both types of critical layers are sources of disaster caused by excessive gas levels at the working face within the danger window. Disaster contribution coefficient G j The numerical value is used as the basis for ranking the contribution to disaster, G j The critical layer with the largest value is defined as the primary critical layer.

9. The method for identifying key strata causing abnormal gas outbursts during the initial mining stage of a working face, as described in claim 1, is characterized in that... In step S8, the termination condition after the main control critical layer breaks is satisfied by the following formula: (1-η max )Q adj (L)<Q A ; In the formula: η max Q represents the maximum depressurization gas extraction rate after the high-pressure extraction tunnel is connected. adj (L) represents the gas emission rate from the adjacent layer at the working face advance distance L, Q A This is to dilute the remaining airflow at the working face.

10. A system for identifying critical strata prone to gas outbursts during the initial mining stage of a working face, characterized in that, The method for identifying critical layers of abnormal gas outbursts during the initial mining stage of a working face, as described in any one of claims 1 to 9, is used to execute the method for identifying critical layers of abnormal gas outbursts during the initial mining stage of a working face. The identification system is built on the Electron cross-platform desktop application framework, and the front-end interactive interface is developed using HTML5, CSS3, and JavaScript. The overall system adopts a three-layer isolated architecture consisting of the main process, the security bridging layer, and the rendering layer. The discrimination system includes: The parameter input module is used to input all basic parameters related to coal-bearing strata, rock mechanics, gas occurrence, high-level drainage roadway layout, and ventilation mining, and supports the visual input of strata columnar structures. The calculation and solution kernel module programmatically implements all the calculation formulas and identification logics recorded in claims 1 to 9, and sequentially completes the identification of key overburden layers, the solution of key layer fracture advance distance and gas-conducting fracture zone development height, the calculation of gas outburst volume of adjacent layers and high-speed extraction roadway extraction rate, the solution of multi-dimensional disaster-causing indicators, the stratification determination of key overburden layers, and the verification of gas over-limit termination conditions. The results output module is used to display the key strata, initial fracture advance distance, and all identification indicators in tabular form; it adaptively and in real time draws the overburden columnar structure diagram, gas-conducting fracture development diagram, and curves showing the variation of the over-limit risk coefficient R(L) and the high-extraction roadway extraction rate η(L) with the working face advance distance using the HTML5 Canvas component; it categorizes and displays the main control key strata, sudden disaster-causing key strata, cumulative disaster-causing key strata, and continuous early warning strata, and simultaneously outputs graded gas prevention and control technology recommendations; The file and report management module is used to store calculation case data in JSON structured .gks format files. It supports saving, reading, and reproducing calculation cases, and can export standardized calculation reports. The discrimination system can be packaged using electron-builder to generate a Windows single-file executable program that does not require installation and supports offline independent operation.

Images