A method for determining the pressure relief range of overburden space in longwall face mining

Abstract

The present application relates to a kind of longwall face mining overburden space pressure-relief range determination method, with stress recovery distance of goaf as core input parameter, by "FLAC3D numerical simulation quantification+ similarity simulation verification correction+ three-dimensional parameter definition" technical thought, constructs overburden stress-displacement field simulation model, defines standardization pressure-relief parameter and critical condition, realizes the accurate quantification division of overburden space pressure-relief range, solves the core defects of traditional method.

Description

Technical Field

[0001] This invention relates to a method for determining the pressure relief range of the overburden space in longwall mining. Background Technology

[0002] Existing technologies for determining the stress relief range in the overburden space of longwall mining suffer from several key issues: low quantification of the stress relief range, lack of integration with the stress recovery characteristics of the goaf, and absence of verification methods. Consequently, they cannot provide precise data for the spatial layout of gas drainage boreholes. Specific shortcomings are as follows:

[0003] (1) The decompression range is vague and lacks quantitative standards: Traditional methods are mostly based on experience to vaguely divide the "decompression zone" and "non-decompression zone". The degree of decompression of the overlying rock is judged only by the "fracture zone height". The direction, dip and height of the decompression range are not quantified, making it difficult to reflect the decompression difference in different spatial locations, resulting in a large degree of blindness in the layout of gas drainage boreholes.

[0004] (2) Failure to combine the stress recovery characteristics of the goaf: Ignoring the core influence of the stress recovery distance of the goaf on the stress relief range of the overburden, and failing to combine the stress recovery law with the stress-displacement field of the overburden, resulting in unreasonable setting of the extraction borehole depth. If it is too deep, it will enter the re-compaction zone of the goaf (without stress relief effect), and if it is too shallow, it will not enter the effective stress relief zone (low extraction efficiency).

[0005] (3) Numerical simulation is disconnected from engineering reality: The existing numerical simulation model does not fit the stress boundary according to the actual stress recovery characteristics on site. The model parameters are mostly general values, which cannot restore the recovery process of stress in the goaf from 0 to the original rock stress. The simulation results deviate greatly from the actual engineering reality.

[0006] (4) The verification methods are limited and lack dual calibration: Most methods obtain the pressure relief range only through numerical simulation, without combining similar material simulation tests and field measurements for verification and correction. There is no error control mechanism, and the reliability of the theoretical division results is low. Summary of the Invention

[0007] In view of the shortcomings of the existing technology, the technical problem to be solved by the present invention is to provide a method for determining the stress relief range of the overburden space in longwall mining. Taking the stress recovery distance of the goaf as the core input parameter, the method constructs an overburden stress-displacement field simulation model through the technical approach of "FLAC3D numerical simulation quantification + similar simulation verification and correction + three-dimensional parameter definition", defines standardized stress relief parameters and critical conditions, and realizes the accurate quantitative division of the stress relief range of the overburden space, thus solving the core defects of the traditional method.

[0008] To solve the above-mentioned technical problems, the technical solution of the present invention is: a method for determining the pressure relief range of the overburden space in longwall mining, the method comprising the following steps:

[0009] S1: Determine the stress recovery distance in the goaf;

[0010] S2: Construct a FLAC3D numerical model;

[0011] S3: Simulated overburden stress-displacement field;

[0012] S4: Define the pressure relief parameters and critical conditions;

[0013] S5: Define the pressure relief range of the overburden space;

[0014] S6: Similarity simulation verification and correction;

[0015] S7: Output overburden space depressurization range.

[0016] Preferably, in step S1, the final stress recovery distance of the goaf in the longwall working face is accurately obtained through the steps of "basic parameter collection, independent calculation of multiple models, obtaining measured values ​​through similar material model tests, verification of field measured data, and weighted fusion of multiple results". This parameter is used as the core input for this method, and it is required that... The calculation error, verified by on-site measurements, is less than 10%. The specific operating method is as follows: First, obtain the coal seam mining height M, coal seam burial depth H, and uniaxial compressive strength of the roof rock mass through on-site geological exploration, laboratory tests, and similar simulation tests. , Collapsed rock mass fragmentation coefficient b, Overburden unit weight Working face width P0, internal friction angle of coal The complete set of basic parameters is obtained; then the stress recovery distance is calculated using the load conservation model, the lateral propagation model, and the surface subsidence fitting model, respectively. Subsequently, a 1:100 similarity ratio material model was constructed to obtain the measured value X of the stress recovery distance in the goaf. 实测 Then, based on the calculated values ​​from the three sets of models and X... 实测 The weighting coefficients are determined by the inverse ratio of the absolute error. Through weighted average method The fusion results are obtained; finally, a vibrating wire stress sensor is deployed at the coal mine site for field measurement and verification. If the error is greater than 10%, the basic parameters are recalibrated and the above calculation process is repeated until the error meets the requirements.

[0017] Preferably, in step S2, the stress recovery distance of the goaf is used. Based on this core principle, a FLAC3D numerical model for mining overburden in longwall face mining was constructed. The model dimensions, constitutive model, and rock mechanics parameters were determined. The stress recovery boundary of the goaf was fitted to ensure a high degree of matching between the model and actual geological and mining conditions. The specific steps are as follows:

[0018] (1) Model size determination: based on the stress recovery distance of the goaf. The dimensions of the three-dimensional model are determined by the coal seam burial depth H, ensuring that the model covers the stress recovery area of ​​the goaf and the overlying rock pressure relief area:

[0019] Along the direction of length: Sufficient stress recovery and boundary effect areas are reserved;

[0020] Length along dip: X = 300 (m), suitable for the dip width of conventional coal mine working faces;

[0021] Height: Z = H + 100 (m), covering the full thickness of the coal seam overburden, with a reserved area at the top boundary of the overburden;

[0022] (2) Constitutive model selection: The Hoek-Brown strength criterion is adopted, which is suitable for stress analysis of overburden with fractured rock mass and developed fissures, and fits the actual mechanical properties of overburden in goaf.

[0023] (3) Transformation of rock mass mechanical parameters: The macroscopic mechanical parameters of the rock mass are transformed into numerical simulation parameters, such as the elastic modulus E, by using the GSI rock mass geological strength index and the rock mass disturbance coefficient D. m The conversion formula for (MPa) is:

[0024]

[0025] in, The uniaxial compressive strength of the rock mass (MPa) is given by denoted as D, which is the rock mass disturbance coefficient. The standard values ​​are: D=0.8 for coal seams, D=0.3 for roof sandstone, and D=0.5 for floor mudstone.

[0026] (4) Stress fitting in the goaf: By applying vertical stress to the nodes of the top and bottom plates of the goaf, the vertical stress of the top and bottom plates of the goaf is simulated to change continuously as the working face advances, and the support also moves forward continuously as the working face advances; finally, the stress recovery distance of the goaf is calculated. Fitting the numerical model, the simulated stress in the goaf linearly recovers from 0 MPa behind the working face to... Original rock stress The process restores the actual stress evolution characteristics of the goaf;

[0027] Input: Stress recovery distance in the goaf Coal seam burial depth H, rock mass GSI index, and rock mass uniaxial compressive strength Rock mass disturbance coefficient D, original rock stress ;

[0028] Output: FLAC3D three-dimensional numerical model, including model dimensions, constitutive model, mechanical parameters, and stress fitting boundary.

[0029] Preferably, in step S3, based on the constructed FLAC3D numerical model, the actual advancement process of the longwall working face is simulated, and stress and displacement data at different spatial locations of the overburden are extracted to provide data support for the subsequent decompression range division. The specific steps are as follows:

[0030] (1) Working face advance simulation: According to the actual mining step distance at the coal mine site, simulate the gradual advance process of the working face, advance 2m each time, until the working face advance distance reaches the actual mining distance at the site, and record the overburden stress-displacement data after each advance;

[0031] (2) Monitoring point layout: Monitoring points are arranged along the strike, dip and height of the overburden in three dimensions, with a spacing of 5m×5m×5m, to achieve full-range monitoring in three-dimensional space;

[0032] (3) Data extraction: Extract the effective stress values ​​of each monitoring point. With absolute displacement value This forms a three-dimensional dataset of overburden stress-displacement field;

[0033] Inputs: FLAC3D numerical model, actual advance step and distance of the working face, and monitoring point layout parameters;

[0034] Output: Stress values ​​of the overburden along its strike, dip, and height. Displacement value Three-dimensional dataset.

[0035] Preferably, in step S4, to achieve a quantitative division of the overburden pressure relief range, two core pressure relief parameters, "pressure relief coefficient" and "pressure relief angle," are defined. Furthermore, based on the requirements for gas extraction and outburst prevention, the critical conditions for effective pressure relief are clarified. The parameter definitions and critical conditions are as follows:

[0036] (1) Stress relief coefficient k: reflects the degree of stress relief in the overburden, and is the percentage of the difference between the original rock stress and the actual stress in the overburden relative to the original rock stress. The calculation formula is as follows: ;

[0037] in, The original rock stress (MPa) The actual effective stress of the overlying strata (MPa) is given by k. The larger the k value, the higher the degree of stress relief.

[0038] (2) Pressure relief angle : Reflects the spatial morphology of the overburden pressure relief range, and is the arctangent value of the pressure relief height and the horizontal distance of pressure relief. The calculation formula is: ;

[0039] in, b1 is the pressure relief height (m), which is the vertical distance from the coal seam roof to a certain pressure relief position in the overburden; b2 is the pressure relief horizontal distance (m), which is the horizontal distance from the coal wall to a certain pressure relief position in the overburden.

[0040] (3) Critical conditions for effective pressure relief:

[0041] Critical stress relief coefficient: k0≥10%, at which point the overburden stress is significantly reduced, fractures are fully developed, and the risk of gas outburst in the protected layer is eliminated; when the gas content of the protected layer is >15m 3 At / t, the critical pressure relief coefficient is dynamically adjusted to k0≥15%;

[0042] Critical pressure relief angle: At this time, the spatial morphology of the overlying rock pressure relief range meets the spatial requirements for the arrangement of gas drainage boreholes;

[0043] Input: original rock stress Actual stress of overlying rock Decompression height , pressure relief horizontal distance b1, gas content of the protected layer;

[0044] Output: Pressure relief coefficient k and pressure relief angle at each monitoring point of the overburden. Effective pressure relief critical condition k0 for on-site adaptation .

[0045] Preferably, in step S5, based on the overburden stress-displacement field dataset and the calculation results of the pressure relief parameters, combined with the effective pressure relief critical conditions, the overburden spatial pressure relief range is quantitatively divided from three dimensions: along strike, along dip, and along height, and the pressure relief boundaries of each dimension are clarified. The specific division method is as follows:

[0046] (1) Division of stress relief range along strike: Based on the distribution characteristics of stress relief coefficient k, the overburden is divided into five regions along strike. The horizontal distance boundary of each region is determined with the working face position as the origin:

[0047] In the original rock stress zone: k < 5%, the overlying rock stress has not changed, and there is no pressure relief effect;

[0048] Compression zone: 5%≤k<10%, the overburden stress is slightly compressed, and the degree of pressure relief is low;

[0049] The expansion zone, also known as the pressure relief core zone, has a k≥k0, where the overburden stress is significantly reduced and the fractures are fully developed, making it the optimal area for gas extraction.

[0050] Stress recovery zone: 5%≤k<10%, overburden stress gradually recovers, and the degree of stress relief decreases;

[0051] Recompacted zone: k < 5%, the rock mass in the goaf is recompacted, the overlying stress is restored to the original rock stress, and there is no stress relief effect;

[0052] The effective pressure relief range along the direction was ultimately determined to be the horizontal distance boundary of the expansion zone;

[0053] (2) Division along the depressurization range: based on the depressurization angle Based on the distribution characteristics, starting from the coal pillar side and ending in the middle of the goaf, the variation law of the pressure relief angle is determined: the pressure relief angle changes from the coal pillar side... Gradually increasing to the middle of the goaf area Then gradually reduce the size to the side of the incision. The effective pressure relief range along the dip direction was ultimately determined to be the pressure relief angle. Horizontal distance from the boundary;

[0054] (3) Division along the height of the pressure relief range: based on the stress value of the overlying rock. Based on the distribution characteristics, the overburden pressure relief height H is determined upwards from the coal seam roof. 卸压 (m), that is, the stress recovery from the coal seam roof to the overburden is... The vertical distance of the location; the final effective pressure relief range along the height is determined to be from the coal seam roof to H. 卸压 The vertical height boundary;

[0055] (4) Integration of three-dimensional pressure relief range: The effective pressure relief boundaries along the strike, dip and height are integrated, and the boundaries of the overburden space pressure relief range are defined by three-dimensional coordinates, namely strike Y, dip X and height Z, to form the outline of the three-dimensional pressure relief area.

[0056] Input: Overburden stress-displacement field dataset, stress relief coefficient k, stress relief angle Critical conditions for effective pressure relief ( , );

[0057] Output: Effective stress relief boundaries of the overburden along strike, dip, and height; three-dimensional coordinates (Y, X, Z) of the stress relief range in the overburden space.

[0058] Preferably, in step S6, a similar material model for longwall mining is constructed to simulate the overburden pressure relief process. The overburden pressure relief range is measured and compared with the FLAC3D numerical simulation results. The boundary of the pressure relief range is corrected to ensure that the error is controlled within 8%. The specific steps are as follows:

[0059] (1) Construction of similar material model: Similar materials are configured according to geometric similarity ratio of 1:100, bulk density similarity ratio of 0.6 and time similarity ratio of 1:12 to restore the lithology and mechanical properties of coal seam, roof and floor and overburden, and replicate the on-site mining parameters and stress recovery characteristics of goaf;

[0060] (2) Monitoring methods deployment:

[0061] Displacement measuring points: arranged at intervals of 10cm×10cm to monitor the three-dimensional displacement changes of the overlying rock;

[0062] Strain gauges: arranged in 4 layers, 15 gauges per layer, to monitor stress and strain changes in the overburden;

[0063] Ground-penetrating radar: A ground-penetrating radar with a resolution of 0.1m was used to detect the development of overlying rock fissures and verify the consistency between the stress relief zone and the fissure connection zone;

[0064] (3) Test and data acquisition: Simulate the working face advance process, record the measured data of overburden pressure relief coefficient, pressure relief angle and pressure relief range, and obtain similar simulated measured pressure relief range;

[0065] (4) Result comparison and correction: Compare the measured pressure relief range of similar simulation with the FLAC3D numerical simulation results, calculate the error of each dimension boundary, and correct the pressure relief range of the overburden space obtained by numerical simulation to ensure that the error after correction is ≤8%;

[0066] Input: FLAC3D numerical simulation results of decompression range, similar material proportioning parameters, monitoring layout parameters, and similar simulation measured data;

[0067] Output: Corrected three-dimensional coordinates (Y, X, Z) of the overburden space decompression range.

[0068] Preferably, in step S7, the corrected overburden space pressure relief range is output in the form of "3D model + engineering drawings", which clarifies the specific values ​​of the pressure relief boundary in each dimension, the location and range of the pressure relief core area, and marks the distribution characteristics of the pressure relief coefficient and pressure relief angle, providing direct engineering guidance for the layout of gas drainage boreholes and the design of surrounding rock support in coal mines.

[0069] Input: Corrected three-dimensional coordinates of the overburden space decompression range and distribution characteristics of decompression parameters;

[0070] Output: 3D model of the overburden space depressurization range, engineering drawings, and marking of depressurization boundaries and depressurization core area.

[0071] Compared with the prior art, the present invention has the following beneficial effects:

[0072] This invention uses the stress recovery distance of the goaf as the core input parameter. Through a technical approach of "FLAC3D numerical simulation quantification + similar simulation verification and correction + three-dimensional parameter definition," it constructs a stress-displacement field simulation model for the overburden, defines standardized stress relief parameters and critical conditions, and achieves precise quantitative division of the overburden spatial stress relief range, thus overcoming the core shortcomings of traditional methods. Specific advantages and beneficial effects are as follows:

[0073] (1) High degree of quantification and accurate three-dimensional division: For the first time, standardized pressure relief coefficient and pressure relief angle parameters are defined, the critical conditions for effective pressure relief are clarified, the boundary of the overburden pressure relief range is quantified from three dimensions: strike, dip and height, and the pressure relief area is defined by three-dimensional coordinates, which completely solves the problem of fuzzy division by traditional methods.

[0074] (2) Core parameter correlation, in line with engineering reality: The stress recovery distance of the goaf is used as the core input and stress fitting basis of numerical simulation, restoring the linear recovery process of the stress in the goaf from 0 to the original rock stress, so that the numerical simulation model is highly matched with the actual stress evolution characteristics of the goaf, and the simulation results are more in line with engineering reality.

[0075] (3) Dual verification, controllable error: The pressure relief range is calibrated and corrected by using the dual verification method of "FLAC3D numerical simulation + similar material simulation test". At the same time, the development of overlying rock fissures is detected by ground radar to verify the consistency between the pressure relief area and the fissure penetration area, ensuring the reliability of the results.

[0076] (4) Parameters are adjustable and highly adaptable: The critical pressure relief coefficient can be dynamically adjusted according to the gas content of the protected layer. The rock mass mechanical parameters are accurately converted from the GSI index to the rock mass disturbance coefficient, which can be adapted to the mining conditions of high gas and low permeability coal seam groups with different gas contents and different lithologies.

[0077] (5) The project is highly practical and has direct guiding significance: the quantified overburden space pressure relief range can directly guide the design of parameters such as direction, inclination, height, diameter and spacing of gas drainage boreholes, accurately locate the pressure relief core area, significantly improve gas drainage efficiency, reduce the risk of gas outburst accidents, and provide scientific basis for strata control and surrounding rock support.

[0078] (6) Standardized methods are easy to promote in the industry: A standardized process has been established from core parameter input, numerical modeling, depressurization range division to verification and correction. Depressurization parameter definition, model construction and test methods have all formed a unified standard, which is convenient for coal mine on-site engineering technicians to operate and is suitable for promotion and application in the high-gas coal mine industry.

[0079] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments. Attached Figure Description

[0080] Figure 1 This is a technical roadmap for an embodiment of the present invention.

[0081] Figure 2 This is a schematic diagram of the protective layer mining according to an embodiment of the present invention.

[0082] Figure 3 This is a schematic diagram of the FLAC3D numerical model (numerical model) of an embodiment of the present invention.

[0083] Figure 4 This is a schematic diagram of the FLAC3D numerical model (stress distribution profile of the goaf) in an embodiment of the present invention.

[0084] Figure 5 This is a schematic diagram illustrating the effect of pressure relief along the strike of the overburden in an embodiment of the present invention.

[0085] Figure 6 This is a schematic diagram of the distribution of the overburden pressure relief coefficient along the dip direction in an embodiment of the present invention (working face advance 100m).

[0086] Figure 7 This is a schematic cloud map of the pressure relief area in the upward mining space of the coal seam group according to an embodiment of the present invention.

[0087] Figure 8 This is a diagram of a similar simulation experimental setup according to an embodiment of the present invention.

[0088] Figure 9 This diagram illustrates the testing instruments and data collection methods used in an embodiment of the present invention.

[0089] In the diagram: ①- Stress recovery distance input module for goaf, ②- FLAC3D numerical modeling module, ③- Overburden stress-displacement field simulation module, ④- Pressure relief coefficient and pressure relief angle calculation module, ⑤- Overburden three-dimensional pressure relief range division module, ⑥- Similar simulation verification module, ⑦- Overburden spatial pressure relief range output module. Figure 2 middle and γ is the pressure relief angle of the intermediate protective layer relative to the upper protected layer, and ε is the pressure relief angle of the intermediate protective layer relative to the lower protected layer. Figure 4 In this context, γ represents the unit weight of the overburden, H represents the burial depth, and λ represents the vertical stress concentration factor.

[0090] Figure 10 This is a technical roadmap for step S1 in an embodiment of the present invention.

[0091] Figure 11 This is a schematic diagram of the load conservation model calculation in step S1 of an embodiment of the present invention.

[0092] Figure 12 This is a schematic diagram of the lateral expansion model calculation in step S1 of an embodiment of the present invention.

[0093] Figure 13 This is a diagram showing the relationship between surface subsidence and stress recovery distance in step S1 of an embodiment of the present invention.

[0094] In the picture: The support angle in the goaf direction; A, B, and C represent different areas; H is the coal seam depth in the model; P0 is the working face width; L s To bear the concentrated load in the goaf; S x Sgx S represents the ground subsidence and goaf compression at a distance X from the mined coal face; gm S represents the compression of the fractured rock mass in the goaf of the stress recovery zone; s S represents the amount of bending and subsidence of the old roof. f Vertical dilatation of the fractured zone; S m H represents the ground settlement corresponding to the stress recovery location in the goaf; b H represents the thickness of the curved subsidence zone. f H represents the height of the fault zone. c h represents the height of the caving zone; h represents the coal seam mining height. This refers to the distance from the coal face to the stress recovery point in the goaf. Detailed Implementation

[0095] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0096] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0097] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0098] like Figures 1-13 As shown in the figure, this embodiment provides a method for determining the pressure relief range of the overburden space in longwall mining. The method includes the following steps:

[0099] S1: Determine the stress recovery distance in the goaf;

[0100] S2: Construct a FLAC3D numerical model;

[0101] S3: Simulated overburden stress-displacement field;

[0102] S4: Define the pressure relief parameters and critical conditions;

[0103] S5: Define the pressure relief range of the overburden space;

[0104] S6: Similarity simulation verification and correction;

[0105] S7: Output overburden space depressurization range;

[0106] To achieve precise quantification of the pressure relief range of the overburden space.

[0107] In embodiments of the present invention, such as Figures 10-13 As shown, the specific method for determining the stress recovery distance of the goaf in step S1 is as follows:

[0108] Step 1: Collection of basic parameters;

[0109] Step 2: Calculate the stress recovery distance based on the load conservation model ;

[0110] Step 3: Calculate the stress recovery distance based on the lateral propagation model ;

[0111] Step 4: Calculate the stress recovery distance based on the surface subsidence fitting model ;

[0112] Step 5: Obtain measured values ​​through similar material model experiments;

[0113] Step 6: Verification of on-site measured data;

[0114] Step 7: Weighted fusion of multiple results to determine the final stress recovery distance.

[0115] In step 1, geological and mechanical parameters of the coal seam in the longwall working face are comprehensively obtained through three methods: on-site geological exploration, laboratory testing, and similar simulation testing. This provides basic data for subsequent model calculations. The parameter acquisition methods and specific indicators are as follows:

[0116] (1): On-site geological exploration: using ground-penetrating radar to detect the thickness, depth, roof lithology distribution and dip angle of the coal seam, measuring the actual width of the working face, and determining the coal seam mining height. Coal seam burial depth Working surface width Coal seam dip angle ;

[0117] (2): Laboratory test: Uniaxial compression tests were conducted on the roof rock mass and coal body using an electro-hydraulic servo triaxial rock testing machine to determine the uniaxial compressive strength of the roof rock mass. , friction angle in coal body Cohesion at the interface between the coal seam and the roof and floor The bulk density of the overburden was determined by overburden sampling tests. The lateral pressure coefficient was determined by combining on-site measurements at the coal mine. interlayer friction coefficient ;

[0118] (3): Similarity simulation test: A similar material model of longwall mining was constructed using a 1:100 similarity ratio, and the collapse rock mass fragmentation coefficient b and the surface subsidence propagation angle were determined. The coefficient of rock mass fragmentation, b, ranges from 1.2 to 1.5, and the surface subsidence extension angle... The value ranges from 18° to 21°.

[0119] (4): Parameter calibration requirements: Uniaxial compressive strength of the roof rock mass The scale effect needs to be considered, and 15% of the strength of the laboratory rock sample should be taken; all parameters need to be tested in three or more parallel tests, and the average value should be taken as the final calculated value to ensure the accuracy of the parameters.

[0120] Inputs: Field geological survey data, laboratory rock sample test data, and raw data from similar simulation tests;

[0121] Output: Coal seam mining height Coal seam burial depth Uniaxial compressive strength of the roof rock mass Coefficient of fracture and swelling of collapsed rock mass Overburden density Working surface width , friction angle in coal body interlayer friction coefficient Cohesion at the interface between the coal seam and the roof and floor Lateral pressure coefficient Coal seam dip angle Surface subsidence extension angle Complete set of basic calculation parameters.

[0122] In step 2, based on the elastoplastic limit equilibrium theory and considering the load transfer law of the overlying rock mass in the mining area, the load transfer relationship between the plastic and elastic zones in front of the coal face is taken into account. The load conservation model formula is derived, and the stress recovery distance is calculated. The specific steps are as follows:

[0123] (1): Theoretical derivation: According to the principle of energy conservation, the increase in the support pressure in front of the coal wall is equal to the decrease in the load in the goaf. The total load in the load-increasing zone in front of the coal wall is Ls, the initial load is Lo, and the total load increment is Ls'. The rock mass in front of the coal wall is divided into a plastic zone and an elastic zone, and the range of the plastic zone is determined. , elastic zone range The roadway support constraint force is ;

[0124] (2): Model formula:

[0125]

[0126] In the formula, P is the dip angle of the coal seam. x The constraint force exerted by the roadway support on the coal face along the x-direction, in MPa; is the cohesion at the interface between the coal seam and the roof and floor, in MPa; The friction angle at the interface between the coal seam and the roof and floor; The internal friction angle of the coal; The density of the overlying rock strata is given in kN / m³. 3 ; The coefficient of interlayer friction; M is the coal seam burial depth, in meters; M is the coal seam thickness, in meters. Let be the distance, in meters, from any point within the stress-increased zone to the coal face. Stress concentration factor at the coal face;

[0127] (3): Numerical simulation calibration: The FLAC3D numerical simulation software was used to construct the pressure distribution model of the coal wall front support, and the boundary between the plastic zone and the elastic zone was calibrated to ensure that the boundary calculation error was less than 5%;

[0128] (4): Integral calculation: Combine the basic parameters and the calibrated plastic zone , elastic zone Substituting into the model formula, the stress recovery distance under the load conservation model is obtained through integration. ;

[0129] Input: The complete set of basic parameters obtained in step 1, and the roadway support constraint force. FLAC3D numerical simulation calibration of the plastic zone range , elastic zone range ;

[0130] Output: Stress recovery distance calculated by the load conservation model .

[0131] In step 3, considering the characteristics of surface subsidence expansion, the surface subsidence expansion angle is used. The core parameter is based on the coal seam burial depth. With working surface width The ratio relationship is used to derive the formula for the lateral propagation model under different working conditions, and to calculate the stress recovery distance. The specific steps are as follows:

[0132] (1): Working condition judgment: Calculate the ratio of coal seam burial depth to working face width Combined with the surface subsidence extension angle The tangent value is used to divide the calculation into two working conditions, among which... The value was determined by fitting measured data from similar mining areas, and ranged from 18° to 21°.

[0133] (2): Model formula:

[0134]

[0135] In the model, when the coal seam burial depth H is equal to the working face width... satisfy At that time, the goaf area bears the concentrated load as ,and ;when At that time, the additional load at the boundary of the goaf was ,and In the formula The strata are highly saturated.

[0136] (3): Formula calculation: Based on the working condition judgment results, substitute the basic parameters into the corresponding formula to calculate the stress recovery distance under the lateral propagation model. ;

[0137] Input: Coal seam burial depth obtained in step 1 Working surface width Surface subsidence extension angle ;

[0138] Output: Stress recovery distance calculated by the lateral spread model. .

[0139] In step 4, combining the stress-strain relationship of the goaf rock mass with the variation law of surface subsidence, the stress recovery distance is calculated by fitting the model formula with the measured surface subsidence data in the field, using the overburden unit weight, the collapse rock mass fragmentation coefficient, and the uniaxial compressive strength of the roof rock mass as core parameters. The specific steps are as follows:

[0140] (1): Model derivation: Based on the compaction characteristics of rock mass in the goaf, the surface subsidence is positively correlated with the stress recovery distance of the goaf. The surface subsidence fitting model formula is obtained by multiple linear fitting.

[0141] (2): Model formula:

[0142]

[0143] (3): Parameter substitution: Substitute the overburden unit weight obtained in step 1 Coal seam burial depth Coefficient of fracture and swelling of collapsed rock mass Uniaxial compressive strength of the roof rock mass Coal seam mining height Substituting into the formula, the stress recovery distance under the surface subsidence fitting model is calculated. ;

[0144] Input: Overburden unit weight obtained in step 1 Coal seam burial depth Coefficient of fracture and swelling of collapsed rock mass Uniaxial compressive strength of the roof rock mass Coal seam mining height ;

[0145] Output: Stress recovery distance calculated by the surface subsidence fitting model. .

[0146] In step 5, based on the actual geological conditions of the coal mine, a 1:100 similarity ratio longwall mining similar material model is constructed to simulate the process of working face advancement and goaf formation, and the measured value of the stress recovery distance of the goaf is obtained, providing a basis for subsequent weight determination and result verification. The specific steps are as follows:

[0147] (1): Model construction: Similar materials were configured according to a geometric similarity ratio of 1:100, a bulk density similarity ratio of 0.6, and a time similarity ratio of 1:12 to simulate the lithology and mechanical properties of the coal seam, roof and floor, and overburden, and to restore the actual mining parameters of the working face;

[0148] (2): Monitoring setup: Vibrating wire stress sensors are set up on the side of the model goaf with a spacing of 5cm to monitor the stress changes of the rock mass in the goaf in real time and determine the location where the stress recovers to the original rock stress.

[0149] (3): Experimental test: Simulate the gradual advancement process of the working face, record the rock stress data of the goaf at different advancement distances, and when the stress value stabilizes at the original rock stress When the distance is within the specified range, the horizontal distance between this location and the coal face is determined as the measured value of the stress recovery distance in the goaf. ;

[0150] Input: Actual coal mine geological conditions, working face mining parameters, similar material mix proportions, and stress monitoring data;

[0151] Output: Measured values ​​of stress recovery distance in the goaf of longwall mining. .

[0152] In step 6, stress sensors, displacement gauges and other equipment are set up on-site at the longwall working face of the coal mine to measure the stress distribution and displacement of the roof. The numerical model and similar simulation results are verified. If the error between the measured value and the simulation result is greater than 10%, the process returns to step 1 to recalibrate the basic parameters until the error is less than 10%, ensuring the engineering applicability of the results.

[0153] In step 7, the load conservation model is fused using the weighted average method. Lateral expansion model Surface subsidence fitting model The calculation results are used to determine the weighting coefficients based on the inverse ratio of the absolute value of the error between the calculated values ​​of the three models and the measured values ​​of the similar material model tests. This ensures that the model with the smaller error has a higher weight, ultimately yielding the accurate stress recovery distance of the goaf. The specific steps are as follows:

[0154] (1): Error calculation: Calculate the calculated values ​​and measured values ​​of the three sets of models. absolute error :

[0155]

[0156] (2): Determining the weighting coefficient: Let the weighting coefficient be... The weights are inversely proportional to the absolute error and satisfy the following condition: The calculation formula is:

[0157]

[0158] If the absolute error of a certain model is 0, its weight coefficient is taken as the average of the weights of the other models;

[0159] (3): Weighted fusion calculation: Substitute the weighting coefficients and the calculated values ​​of the three models into the weighted average formula to calculate the final stress recovery distance of the goaf. :

[0160]

[0161] enter: Calculated weight coefficients ;

[0162] Output: Final stress recovery distance in the goaf of the longwall working face .

[0163] The specific implementation process for determining the stress recovery distance in the goaf is as follows:

[0164] Changping Coal Mine 84306 Working Face

[0165] 1. Basic parameters

[0166] Parameters were obtained through on-site geological surveys, laboratory tests, and similar simulation experiments.

[0167] ,

[0168] ,

[0169] ,

[0170] Tunnel support constraint .

[0171] 2. Multi-model calculation

[0172] (1) Load conservation model: obtained from FLAC3D numerical simulation calibration Substituting into the formula, we get ;

[0173] (2) Lateral extension model: If condition 2 is satisfied, substituting into the formula yields... ;

[0174] (3) Surface subsidence fitting model: Substituting the parameters, we get .

[0175] 3. Similar material model test

[0176] Construct a 1:100 similarity model and obtain the results from actual measurements. .

[0177] 4. Weighted fusion of multiple results

[0178] (1) Error calculation: ;

[0179] (2) Weight determination: ;

[0180] (3) Fusion computing: .

[0181] 5. Field verification and engineering application

[0182] The stress recovery distance measured by the vibrating wire stress sensor deployed on site was 137m, which is consistent with... The error is only 0.7%; based on This can further determine the pressure relief area for protective layer mining, guide the layout of gas drainage boreholes, and improve the concentration and efficiency of gas drainage.

[0183] In this embodiment of the invention, the invention accurately obtains the final stress recovery distance of the goaf in a longwall working face through the aforementioned steps of "basic parameter collection, independent calculation of multiple models, obtaining measured values ​​through similar material model experiments, verification of on-site measured data, and weighted fusion of multiple results". This parameter is used as the core input for this method, and it is required that... The calculation error, verified by on-site measurements, is less than 10%. The specific operating method is as follows: First, obtain the coal seam mining height M, coal seam burial depth H, and uniaxial compressive strength of the roof rock mass through on-site geological exploration, laboratory tests, and similar simulation tests. , Collapsed rock mass fragmentation coefficient b, Overburden unit weight Working face width P0, internal friction angle of coal Obtain all basic parameters; then calculate the stress recovery distance using the load conservation model, lateral propagation model, and surface subsidence fitting model respectively. Subsequently, a 1:100 similarity ratio material model was constructed to obtain the measured value X of the stress recovery distance in the goaf. 实测 Then, based on the calculated values ​​from the three sets of models and X... 实测The weighting coefficients are determined by the inverse ratio of the absolute error. Through weighted average method The fusion results are obtained; finally, a vibrating wire stress sensor is deployed at the coal mine site for field measurement and verification. If the error is greater than 10%, the basic parameters are recalibrated and the above calculation process is repeated until the error meets the requirements.

[0184] Core input parameter data specifications: Input stress recovery distance of the goaf Complete parameter traceability information must be provided, including: a detailed list of basic parameters, the calculation process and results of the three sets of models, measured data from similar material model tests, the basis for calculating the weighting coefficients, and the layout and data records of on-site verification points, ensuring... Accuracy and traceability; The numerical units are uniformly set to meters (m), retaining either integer places or one decimal place to meet the accuracy requirements of subsequent numerical model dimensional calculations.

[0185] Parameter applicable range: input It needs to be adapted to the geological conditions of longwall mining, corresponding to mining scenarios of coal seam groups with mining height range of 1-5m, coal seam burial depth of 300-1000m, and roof lithology of medium-hard / soft rock, and be consistent with the applicable scope of this method to ensure the matching of subsequent numerical simulation with engineering reality.

[0186] Input: A complete set of basic parameter details for determining the stress recovery distance in the goaf, and the calculation process and results of the load conservation model / lateral propagation model / surface subsidence fitting model. Measured values ​​from similar material model tests Weighting coefficients The calculation basis, the layout map and measured data of the points verified by on-site measurement, and the initial results after weighted fusion. .

[0187] Output: Stress recovery distance of the goaf in a longwall working face with an error of <10% after on-site measurement and verification. (m), and the accompanying parameter traceability report (including all calculation, experimental, and measured data).

[0188] Subsequent technical steps are all based on the output of this stage. Expand, if Actual measurement verification error If the error occurs, the process must be repeated at this stage and the process cannot proceed to the subsequent numerical modeling steps to ensure the accuracy and reliability of the computational foundation of the entire method.

[0189] In this embodiment of the invention, in step S2, the stress recovery distance of the goaf is used. Based on this core principle, a FLAC3D numerical model for mining overburden in longwall face mining was constructed. The model dimensions, constitutive model, and rock mechanics parameters were determined. The stress recovery boundary of the goaf was fitted to ensure a high degree of matching between the model and actual geological and mining conditions. The specific steps are as follows:

[0190] (1) Model size determination: based on the stress recovery distance of the goaf. The dimensions of the three-dimensional model are determined by the coal seam burial depth H, ensuring that the model covers the stress recovery area of ​​the goaf and the overlying rock pressure relief area:

[0191] Along the direction of length: Sufficient stress recovery and boundary effect areas are reserved;

[0192] Length along dip: X = 300 (m), suitable for the dip width of conventional coal mine working faces;

[0193] Height: Z = H + 100 (m), covering the full thickness of the coal seam overburden, with a reserved area at the top boundary of the overburden;

[0194] (2) Constitutive model selection: The Hoek-Brown strength criterion is adopted, which is suitable for stress analysis of overburden with fractured rock mass and developed fissures, and fits the actual mechanical properties of overburden in goaf.

[0195] (3) Transformation of rock mass mechanical parameters: The macroscopic mechanical parameters of the rock mass are transformed into numerical simulation parameters, such as the elastic modulus E, by using the GSI rock mass geological strength index and the rock mass disturbance coefficient D. m The conversion formula for (MPa) is:

[0196]

[0197] in, The uniaxial compressive strength of the rock mass (MPa) is given by denoted as D, which is the rock mass disturbance coefficient. The standard values ​​are: D=0.8 for coal seams, D=0.3 for roof sandstone, and D=0.5 for floor mudstone.

[0198] (4) Stress fitting in the goaf: By applying vertical stress to the nodes of the top and bottom plates of the goaf, the vertical stress of the top and bottom plates of the goaf is simulated to change continuously as the working face advances, and the support also moves forward continuously as the working face advances; finally, the stress recovery distance of the goaf is calculated. Fitting the numerical model, the simulated stress in the goaf linearly recovers from 0 MPa behind the working face to... Original rock stress The process restores the actual stress evolution characteristics of the goaf;

[0199] Input: Stress recovery distance in the goaf Coal seam burial depth H, rock mass GSI index, and rock mass uniaxial compressive strength Rock mass disturbance coefficient D, original rock stress ;

[0200] Output: FLAC3D three-dimensional numerical model, including model dimensions, constitutive model, mechanical parameters, and stress fitting boundary.

[0201] In this embodiment of the invention, in step S3, based on the constructed FLAC3D numerical model, the actual advancing process of the longwall working face is simulated, and stress and displacement data at different spatial locations of the overburden are extracted to provide data support for the subsequent decompression range division. The specific steps are as follows:

[0202] (1) Working face advance simulation: According to the actual mining step distance at the coal mine site, simulate the gradual advance process of the working face, advance 2m each time, until the working face advance distance reaches the actual mining distance at the site, and record the overburden stress-displacement data after each advance;

[0203] (2) Monitoring point layout: Monitoring points are arranged along the strike, dip and height of the overburden in three dimensions, with a spacing of 5m×5m×5m, to achieve full-range monitoring in three-dimensional space;

[0204] (3) Data extraction: Extract the effective stress values ​​of each monitoring point. With absolute displacement value This forms a three-dimensional dataset of overburden stress-displacement field;

[0205] Inputs: FLAC3D numerical model, actual advance step and distance of the working face, and monitoring point layout parameters;

[0206] Output: Stress values ​​of the overburden along its strike, dip, and height. Displacement value Three-dimensional dataset.

[0207] In this embodiment of the invention, in step S4, to achieve a quantitative division of the overburden pressure relief range, two core pressure relief parameters, "pressure relief coefficient" and "pressure relief angle," are defined. Furthermore, based on the requirements for gas extraction and outburst prevention, the critical conditions for effective pressure relief are clarified. The parameter definitions and critical conditions are as follows:

[0208] (1) Stress relief coefficient k: reflects the degree of stress relief in the overburden, and is the percentage of the difference between the original rock stress and the actual stress in the overburden relative to the original rock stress. The calculation formula is as follows: ;

[0209] in, The original rock stress (MPa) The actual effective stress of the overlying strata (MPa) is given by k. The larger the k value, the higher the degree of stress relief.

[0210] (2) Pressure relief angle : Reflects the spatial morphology of the overburden pressure relief range, and is the arctangent value of the pressure relief height and the horizontal distance of pressure relief. The calculation formula is: ;

[0211] in, b1 is the pressure relief height (m), which is the vertical distance from the coal seam roof to a certain pressure relief position in the overburden; b2 is the pressure relief horizontal distance (m), which is the horizontal distance from the coal wall to a certain pressure relief position in the overburden.

[0212] (3) Critical conditions for effective pressure relief:

[0213] Critical stress relief coefficient: k0≥10%, at which point the overburden stress is significantly reduced, fractures are fully developed, and the risk of gas outburst in the protected layer is eliminated; when the gas content of the protected layer is >15m 3 At / t, the critical pressure relief coefficient is dynamically adjusted to k0≥15%;

[0214] Critical pressure relief angle: At this time, the spatial morphology of the overlying rock pressure relief range meets the spatial requirements for the arrangement of gas drainage boreholes;

[0215] Input: original rock stress Actual stress of overlying rock Decompression height , pressure relief horizontal distance b1, gas content of the protected layer;

[0216] Output: Pressure relief coefficient k and pressure relief angle at each monitoring point of the overburden. Effective pressure relief critical condition k0 for on-site adaptation .

[0217] In this embodiment of the invention, in step S5, based on the overburden stress-displacement field dataset and the calculation results of the pressure relief parameters, combined with the effective pressure relief critical conditions, the overburden spatial pressure relief range is quantitatively divided from three dimensions: along strike, along dip, and along height, and the pressure relief boundaries of each dimension are clarified. The specific division method is as follows:

[0218] (1) Division of stress relief range along strike: Based on the distribution characteristics of stress relief coefficient k, the overburden is divided into five regions along strike. The horizontal distance boundary of each region is determined with the working face position as the origin:

[0219] In the original rock stress zone: k < 5%, the overlying rock stress has not changed, and there is no pressure relief effect;

[0220] Compression zone: 5%≤k<10%, the overburden stress is slightly compressed, and the degree of pressure relief is low;

[0221] The expansion zone, also known as the pressure relief core zone, has a k≥k0, where the overburden stress is significantly reduced and the fractures are fully developed, making it the optimal area for gas extraction.

[0222] Stress recovery zone: 5%≤k<10%, overburden stress gradually recovers, and the degree of stress relief decreases;

[0223] Recompacted zone: k < 5%, the rock mass in the goaf is recompacted, the overlying stress is restored to the original rock stress, and there is no stress relief effect;

[0224] The effective pressure relief range along the direction was ultimately determined to be the horizontal distance boundary of the expansion zone;

[0225] (2) Division along the depressurization range: based on the depressurization angle Based on the distribution characteristics, starting from the coal pillar side and ending in the middle of the goaf, the variation law of the pressure relief angle is determined: the pressure relief angle changes from the coal pillar side... Gradually increasing to the middle of the goaf area Then gradually reduce the size to the side of the incision. The effective pressure relief range along the dip direction was ultimately determined to be the pressure relief angle. Horizontal distance from the boundary;

[0226] (3) Division along the height of the pressure relief range: based on the stress value of the overlying rock. Based on the distribution characteristics, the overburden pressure relief height H is determined upwards from the coal seam roof. 卸压 (m), that is, the stress recovery from the coal seam roof to the overburden is... The vertical distance of the location; the final effective pressure relief range along the height is determined to be from the coal seam roof to H. 卸压 The vertical height boundary;

[0227] (4) Integration of three-dimensional pressure relief range: The effective pressure relief boundaries along the strike, dip and height are integrated, and the boundaries of the overburden space pressure relief range are defined by three-dimensional coordinates, namely strike Y, dip X and height Z, to form the outline of the three-dimensional pressure relief area.

[0228] Input: Overburden stress-displacement field dataset, stress relief coefficient k, stress relief angle Critical conditions for effective pressure relief ( , );

[0229] Output: Effective stress relief boundaries of the overburden along strike, dip, and height; three-dimensional coordinates (Y, X, Z) of the stress relief range in the overburden space.

[0230] In this embodiment of the invention, in step S6, a similar material model for longwall mining is constructed to simulate the overburden decompression process. The overburden decompression range is measured and compared with the FLAC3D numerical simulation results. The decompression range boundary is then corrected to ensure that the error is controlled within 8%. The specific steps are as follows:

[0231] (1) Construction of similar material model: Similar materials are configured according to geometric similarity ratio of 1:100, bulk density similarity ratio of 0.6 and time similarity ratio of 1:12 to restore the lithology and mechanical properties of coal seam, roof and floor and overburden, and replicate the on-site mining parameters and stress recovery characteristics of goaf;

[0232] (2) Monitoring methods deployment:

[0233] Displacement measuring points: arranged at intervals of 10cm×10cm to monitor the three-dimensional displacement changes of the overlying rock;

[0234] Strain gauges: arranged in 4 layers, 15 gauges per layer, to monitor stress and strain changes in the overburden;

[0235] Ground-penetrating radar: A ground-penetrating radar with a resolution of 0.1m was used to detect the development of overlying rock fissures and verify the consistency between the stress relief zone and the fissure connection zone;

[0236] (3) Test and data acquisition: Simulate the working face advance process, record the measured data of overburden pressure relief coefficient, pressure relief angle and pressure relief range, and obtain similar simulated measured pressure relief range;

[0237] (4) Result comparison and correction: Compare the measured pressure relief range of similar simulation with the FLAC3D numerical simulation results, calculate the error of each dimension boundary, and correct the pressure relief range of the overburden space obtained by numerical simulation to ensure that the error after correction is ≤8%;

[0238] Input: FLAC3D numerical simulation results of decompression range, similar material proportioning parameters, monitoring layout parameters, and similar simulation measured data;

[0239] Output: Corrected three-dimensional coordinates (Y, X, Z) of the overburden space decompression range.

[0240] In this embodiment of the invention, in step S7, the modified overburden space pressure relief range is output in the form of "three-dimensional model + engineering drawings", which clarifies the specific values ​​of the pressure relief boundary in each dimension, the location and range of the pressure relief core area, and marks the distribution characteristics of the pressure relief coefficient and pressure relief angle, providing direct engineering guidance for the layout of gas drainage boreholes and the design of surrounding rock support in coal mines.

[0241] Input: Corrected three-dimensional coordinates of the overburden space decompression range and distribution characteristics of decompression parameters;

[0242] Output: 3D model of the overburden space depressurization area, engineering drawings, with depressurization boundaries and depressurization core area marked.

[0243] Specific implementation process:

[0244] Example 1: Changping Coal Mine 84306 working face (protected layer No. 8 coal seam, protected layer No. 3 coal seam)

[0245] 1. Core Input Parameters

[0246] Determining the stress recovery distance in the goaf Coal seam burial depth (H=530m), original rock stress The gas content of the protected layer is 12m. 3 / t, critical pressure relief coefficient (k0=10%), critical pressure relief angle .

[0247] 2. Construction of FLAC3D Numerical Model

[0248] (1) Model dimensions: Length along the strike Y = 2 × 136 + 200 = 472 m, length along the dip X = 300 m, height Z = 530 + 100 = 630 m;

[0249] (2) Rock mass parameter conversion: GSI of protected layer #3 is 75. D=0.8, substituting into the formula, we get ; 8# protective layer GSI=75, D=0.8, therefore E m =3020.50MPa; GSI of the roof sandstone =90, D=0.3, therefore E m =6566.53MPa;

[0250] (3) Stress fitting: The stress in the goaf is linearly restored from 0 MPa behind the working face to 13 MPa of the original rock stress at 136 m by writing code in FISH language.

[0251] 3. Simulation of stress-displacement field in overlying rock

[0252] The simulated working face advanced 2m at a time, and data was extracted when it reached 120m. The results show:

[0253] The overlying swell zone (k≥10%) is distributed along the strike from 10m in front of the working face to 80m behind it;

[0254] It is distributed along the dip from 40m to 150m in the middle of the goaf;

[0255] Distributed along the height from the top of the coal seam to a height of 37m (corresponding to the location of the No. 3 protected layer);

[0256] Calculation of pressure relief angle: coal wall side Cut the side of the eye Maximum pressure relief angle .

[0257] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for determining the stress relief range of the overburden space in longwall mining, characterized in that: The method includes the following steps: S1: Determine the stress recovery distance in the goaf; S2: Construct the FLAC3D numerical model; S3: Simulated overburden stress-displacement field; S4: Define the pressure relief parameters and critical conditions; S5: Define the pressure relief range of the overburden space; S6: Similarity simulation verification and correction; S7: Output overburden space depressurization range.

2. The method for determining the pressure relief range of the overburden space in longwall mining according to claim 1, characterized in that: In step S1, the final stress recovery distance of the goaf in the longwall working face is accurately obtained through the following steps: "basic parameter collection, independent calculation of multiple models, obtaining measured values ​​through similar material model tests, verification of field measured data, and weighted fusion of multiple results". This parameter is used as the core input for this method, and it is required that... The calculation error, verified by on-site measurements, is less than 10%. The specific operating method is as follows: First, obtain the coal seam mining height M, coal seam burial depth H, and uniaxial compressive strength of the roof rock mass through on-site geological exploration, laboratory tests, and similar simulation tests. , Collapsed rock mass fragmentation coefficient b, Overburden unit weight Working face width P0, internal friction angle of coal The complete set of basic parameters is obtained; then the stress recovery distance is calculated using the load conservation model, the lateral propagation model, and the surface subsidence fitting model, respectively. Subsequently, a 1:100 similarity ratio material model was constructed to obtain the measured value X of the stress recovery distance in the goaf. 实测 Then, based on the calculated values ​​from the three sets of models and X... 实测 The weighting coefficients are determined by the inverse ratio of the absolute error. Through weighted average method The fusion results are obtained; finally, a vibrating wire stress sensor is deployed at the coal mine site for field measurement and verification. If the error is greater than 10%, the basic parameters are recalibrated and the above calculation process is repeated until the error meets the requirements.

3. The method for determining the pressure relief range of the overburden space in longwall mining according to claim 1, characterized in that: In step S2, the stress recovery distance of the goaf is used as the reference. Based on this core principle, a FLAC3D numerical model for mining overburden in longwall face mining was constructed. The model dimensions, constitutive model, and rock mechanics parameters were determined. The stress recovery boundary of the goaf was fitted to ensure a high degree of matching between the model and actual geological and mining conditions. The specific steps are as follows: (1) Model size determination: based on the stress recovery distance of the goaf. The dimensions of the three-dimensional model are determined by the coal seam burial depth H, ensuring that the model covers the stress recovery area of ​​the goaf and the overlying rock pressure relief area: Along the direction of length: Sufficient stress recovery and boundary effect areas are reserved; Along the dip length: X = 300 (m), suitable for the dip width of conventional coal mine working faces; Height: Z = H + 100 (m), covering the full thickness of the coal seam overburden, with a reserved area at the top boundary of the overburden; (2) Constitutive model selection: The Hoek-Brown strength criterion is adopted, which is suitable for stress analysis of overburden with fractured rock mass and developed fissures, and fits the actual mechanical properties of overburden in goaf area; (3) Transformation of rock mass mechanical parameters: The macroscopic mechanical parameters of the rock mass are transformed into numerical simulation parameters, such as the elastic modulus E, by using the GSI rock mass geological strength index and the rock mass disturbance coefficient D. m The conversion formula for (MPa) is: in, The uniaxial compressive strength of the rock mass (MPa) is given by denoted as D, which is the rock mass disturbance coefficient. The standard values ​​are: D=0.8 for coal seams, D=0.3 for roof sandstone, and D=0.5 for floor mudstone. (4) Stress fitting in the goaf: By applying vertical stress to the nodes of the top and bottom plates of the goaf, the vertical stress of the top and bottom plates of the goaf is simulated to change continuously as the working face advances, and the support also moves forward continuously as the working face advances; finally, the stress recovery distance of the goaf is calculated. Fitting the numerical model, the simulated stress in the goaf linearly recovers from 0 MPa behind the working face to... Original rock stress The process restores the actual stress evolution characteristics of the goaf; Input: Stress recovery distance in the goaf Coal seam burial depth H, rock mass GSI index, and rock mass uniaxial compressive strength Rock mass disturbance coefficient D, original rock stress ; Output: FLAC3D three-dimensional numerical model, including model dimensions, constitutive model, mechanical parameters, and stress fitting boundary.

4. The method for determining the pressure relief range of the overburden space in longwall mining according to claim 1, characterized in that: In step S3, based on the constructed FLAC3D numerical model, the actual advancement process of the longwall working face is simulated, and stress and displacement data at different spatial locations of the overburden are extracted to provide data support for the subsequent decompression range division. The specific steps are as follows: (1) Working face advance simulation: According to the actual mining step distance at the coal mine site, simulate the gradual advance process of the working face, advance 2m each time, until the working face advance distance reaches the actual mining distance at the site, and record the overburden stress-displacement data after each advance; (2) Monitoring point layout: Monitoring points are arranged along the strike, dip and height of the overburden in three dimensions, with a spacing of 5m×5m×5m, to achieve full-range monitoring in three-dimensional space; (3) Data extraction: Extract the effective stress values ​​of each monitoring point. With absolute displacement value This forms a three-dimensional dataset of overburden stress-displacement field; Inputs: FLAC3D numerical model, actual advance step and distance of the working face, and monitoring point layout parameters; Output: Stress values ​​of the overburden along its strike, dip, and height. Displacement value Three-dimensional dataset.

5. The method for determining the pressure relief range of the overburden space in longwall mining according to claim 1, characterized in that: In step S4, to quantitatively define the overburden pressure relief range, two core pressure relief parameters, "pressure relief coefficient" and "pressure relief angle," are defined. Based on gas extraction and outburst prevention requirements, the critical conditions for effective pressure relief are clarified. The parameter definitions and critical conditions are as follows: (1) Stress relief coefficient k: reflects the degree of stress relief in the overburden, and is the percentage of the difference between the original rock stress and the actual stress in the overburden relative to the original rock stress. The calculation formula is as follows: ; in, The original rock stress (MPa) The actual effective stress of the overlying strata (MPa) is given by k. The larger the k value, the higher the degree of stress relief. (2) Pressure relief angle : Reflects the spatial morphology of the overburden pressure relief range, and is the arctangent value of the pressure relief height and the horizontal distance of pressure relief. The calculation formula is: ; in, b1 is the pressure relief height (m), which is the vertical distance from the coal seam roof to a certain pressure relief position in the overburden; b2 is the pressure relief horizontal distance (m), which is the horizontal distance from the coal wall to a certain pressure relief position in the overburden. (3) Critical conditions for effective pressure relief: Critical stress relief coefficient: k0≥10%, at which point the overburden stress is significantly reduced, fractures are fully developed, and the risk of gas outburst in the protected layer is eliminated; when the gas content of the protected layer is >15m 3 At / t, the critical pressure relief coefficient is dynamically adjusted to k0≥15%; Critical pressure relief angle: At this time, the spatial morphology of the overlying rock pressure relief range meets the spatial requirements for the arrangement of gas drainage boreholes; Input: original rock stress Actual stress of overlying rock Decompression height , pressure relief horizontal distance b1, gas content of the protected layer; Output: Pressure relief coefficient k and pressure relief angle at each monitoring point of the overburden. Effective pressure relief critical condition k0 for on-site adaptation .

6. The method for determining the pressure relief range of the overburden space in longwall mining according to claim 1, characterized in that: In step S5, based on the overburden stress-displacement field dataset and the calculation results of the pressure relief parameters, combined with the effective pressure relief critical conditions, the overburden spatial pressure relief range is quantitatively divided from three dimensions: along strike, along dip, and along height, and the pressure relief boundaries of each dimension are clarified. The specific division method is as follows: (1) Division of stress relief range along strike: Based on the distribution characteristics of stress relief coefficient k, the overburden is divided into five regions along strike. The horizontal distance boundary of each region is determined with the working face position as the origin: In the original rock stress zone: k < 5%, the overlying rock stress has not changed, and there is no pressure relief effect; Compression zone: 5%≤k<10%, the overburden stress is slightly compressed, and the degree of pressure relief is low; The expansion zone, also known as the pressure relief core zone, has a k≥k0, where the overburden stress is significantly reduced and the fractures are fully developed, making it the optimal area for gas extraction. Stress recovery zone: 5%≤k<10%, overburden stress gradually recovers, and the degree of stress relief decreases; Recompacted zone: k < 5%, the rock mass in the goaf is recompacted, the overlying stress is restored to the original rock stress, and there is no stress relief effect; The effective pressure relief range along the direction was ultimately determined to be the horizontal distance boundary of the expansion zone; (2) Division along the depressurization range: based on the depressurization angle Based on the distribution characteristics, starting from the coal pillar side and ending in the middle of the goaf, the variation law of the pressure relief angle is determined: the pressure relief angle changes from the coal pillar side... Gradually increasing to the middle of the goaf area Then gradually reduce the size to the side of the incision. The effective pressure relief range along the dip direction was ultimately determined to be the pressure relief angle. Horizontal distance from the boundary; (3) Division along the height of the pressure relief range: based on the stress value of the overlying rock. Based on the distribution characteristics, the overburden pressure relief height H is determined upwards from the coal seam roof. 卸压 (m), that is, the stress recovery from the coal seam roof to the overburden is... The vertical distance of the location; the final effective pressure relief range along the height is determined to be from the coal seam roof to H. 卸压 The vertical height boundary; (4) Integration of three-dimensional pressure relief range: The effective pressure relief boundaries along the strike, dip and height are integrated, and the boundaries of the overburden space pressure relief range are defined by three-dimensional coordinates, namely strike Y, dip X and height Z, to form the outline of the three-dimensional pressure relief area. Input: Overburden stress-displacement field dataset, stress relief coefficient k, stress relief angle Critical conditions for effective pressure relief ( , ); Output: Effective stress relief boundaries of the overburden along strike, dip, and height; three-dimensional coordinates (Y, X, Z) of the stress relief range in the overburden space.

7. The method for determining the pressure relief range of the overburden space in longwall mining according to claim 1, characterized in that: In step S6, a similar material model for longwall mining is constructed to simulate the overburden decompression process. The overburden decompression range is measured and compared with the FLAC3D numerical simulation results. The decompression range boundary is corrected to ensure that the error is controlled within 8%. The specific steps are as follows: (1) Construction of similar material model: Similar materials are configured according to geometric similarity ratio of 1:100, bulk density similarity ratio of 0.6 and time similarity ratio of 1:12 to restore the lithology and mechanical properties of coal seam, roof and floor and overburden, and replicate the on-site mining parameters and stress recovery characteristics of goaf; (2) Monitoring methods deployment: Displacement measuring points: arranged at intervals of 10cm×10cm to monitor the three-dimensional displacement changes of the overlying rock; Strain gauges: arranged in 4 layers, 15 gauges per layer, to monitor stress and strain changes in the overburden; Ground-penetrating radar: A ground-penetrating radar with a resolution of 0.1m was used to detect the development of overlying rock fissures and verify the consistency between the stress relief zone and the fissure connection zone; (3) Test and data acquisition: Simulate the working face advance process, record the measured data of overburden pressure relief coefficient, pressure relief angle and pressure relief range, and obtain similar simulated measured pressure relief range; (4) Result comparison and correction: Compare the measured pressure relief range of similar simulation with the FLAC3D numerical simulation results, calculate the error of each dimension boundary, and correct the pressure relief range of the overburden space obtained by numerical simulation to ensure that the error after correction is ≤8%; Input: FLAC3D numerical simulation results of decompression range, similar material proportioning parameters, monitoring layout parameters, and similar simulation measured data; Output: Corrected three-dimensional coordinates (Y, X, Z) of the overburden space decompression range.

8. The method for determining the pressure relief range of the overburden space in longwall mining according to claim 1, characterized in that: In step S7, the corrected overburden space depressurization range is output in the form of "3D model + engineering drawings", which clarifies the specific values ​​of the depressurization boundary in each dimension, the location and range of the depressurization core area, and marks the distribution characteristics of the depressurization coefficient and depressurization angle, providing direct engineering guidance for the layout of gas drainage boreholes and the design of surrounding rock support in coal mines. Input: Corrected three-dimensional coordinates of the overburden space decompression range and distribution characteristics of decompression parameters; Output: 3D model of the overburden space depressurization range, engineering drawings, and marking of depressurization boundaries and depressurization core area.

Images