Method and system for predicting dynamic load coefficient of working face of shallow coal seam

Abstract

The invention discloses a shallow coal seam working face dynamic load coefficient prediction method and system, and the method comprises the following steps: collecting the geological data of the same coal seam working face, the geological data including the working face length, the bed rock thickness, the unconsolidated bed thickness, the coal thickness, the key layer lithology and the key layer thickness; processing the geological data, including median processing of interval measurement data of bed rock thickness and unconsolidated formation thickness, and lithologic characterization valuing of tensile strength of a key layer; working face geological data and actually measured dynamic load coefficients of the same coal seam are used as a fitting set; establishing a dynamic load coefficient prediction model DP; substituting a fitting set consisting of the geological data of the working face of the same coal seam and the actually measured dynamic load coefficient into the dynamic load coefficient prediction model DP to determine an optimal parameter eta of the model; and inputting geological data collected by a new working face into the dynamic load coefficient prediction model DP, and predicting the dynamic load coefficient.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of coal mine roof dynamic disaster prevention and control, and particularly relates to a shallow coal seam working face dynamic load coefficient prediction method and system. BACKGROUND

[0002] In the field of fully mechanized mining in shallow coal seams, the selection of hydraulic supports is directly related to the roof control effect and mine pressure behavior characteristics. At present, the support selection method based on the average value of the dynamic load coefficient of the same coal seam is generally used in the industry. This method assumes that the coal seam geological conditions are uniformly distributed, and the average value of the dynamic load coefficient is obtained by statistical historical data as the design basis. However, with the extension of the mining range in the mining area to complex geological areas, the spatial variability of key parameters such as coal seam bedrock thickness and burial depth has significantly increased. Actual engineering shows that when there is significant geological heterogeneity in the working face, the traditional average dynamic load coefficient method ignores the influence of the gradient change of the bedrock thickness on the stability of the overburden structure, resulting in that the "one-size-fits-all" selected support cannot adapt to the mine pressure behavior characteristics of different sections, making it difficult to accurately guide the support selection of the working face, and easily causing the problem of mismatch between the initial support force and the roof pressure. Therefore, it is urgent to build a shallow coal seam working face dynamic load coefficient prediction method and system to solve the above problems. SUMMARY

[0003] The present application proposes a shallow coal seam working face dynamic load coefficient prediction method and system to solve the above problems and meet the needs. The technical features adopted can achieve the above technical purposes and bring other technical effects.

[0004] One purpose of the present application is to propose a shallow coal seam working face dynamic load coefficient prediction method, which includes the following steps:

[0005] S10: Collecting geological data of the same coal seam working face, including: working face length, bedrock thickness, loose layer thickness, coal thickness, key layer lithology and key layer thickness;

[0006] S20: Processing the geological data, including: median processing of the interval measurement data of the bedrock thickness and the loose layer thickness, lithology characteristic valuation of the key layer tensile strength, directly selecting the standard tensile strength value of the corresponding lithology when the key layer is single lithology, and using the average method to calculate the comprehensive tensile strength when there is a composite rock layer;

[0007] S30: Taking the geological data of the same coal seam working face and the measured dynamic load coefficient as a fitting set;

[0008] S40: Establishing a dynamic load coefficient prediction model DP;

[0009] S50: Substituting the fitting set composed of the geological data of the same coal seam working face and the measured dynamic load coefficient into the dynamic load coefficient prediction model DP to determine the optimal parameters η of the model;

[0010] S60: input the geological data collected in the new working face into the dynamic load coefficient prediction model DP, and predict the dynamic load coefficient.

[0011] In addition, the shallow seam working face dynamic load coefficient prediction method and system according to the present application can also have the following technical features:

[0012] In one example of the present application, in the step S40, establishing the dynamic load coefficient prediction model DP includes the following steps:

[0013] S41: the static load of the working face is mainly the stress field of the overburden rock self weight, and the self weight stress of the overburden rock above the working face is calculated as the static load, and the specific formula is as follows:

[0014] σ static = γ rock H rock + γ soil H soil

[0015] Wherein, σ static is the static load received by the working face; H rock is the thickness of the bedrock; H soil is the thickness of the loose layer; γ rock is the average unit weight of the bedrock; γ soil is the average unit weight of the loose layer;

[0016] S42: for the characteristics of the shallow seam working face, the rock mass formed after the overburden bedrock breaks is simplified as a rigid body, which rotates around the midpoint O of the block under the restriction of horizontal stress, and the friction between the rock masses and the plastic deformation are ignored; according to the geometric relationship, the maximum rotation range of the overburden bedrock after breaking is the distance of the roof caving and filling the goaf, so the tangent value of the rotation angle θ is the ratio of the height H m of the mining seam to the horizontal projection length L b of the broken block;

[0017] S43: the periodic pressure step distance of the working face is regarded as the horizontal projection length L b of the broken block, and based on the simply supported beam model, the expression of the horizontal projection length L b of the broken block is obtained as follows:

[0018]

[0019] In the formula, h is the thickness of the rock layer; σ t is the tensile strength of the rock layer;

[0020] S44: the dynamic load is regarded as the instantaneous impact force generated by the roof rotation, and the expression of the impact force approximately estimated according to the change of momentum is as follows:

[0021]

[0022] In the formula, g is the acceleration of gravity; Δt is the rotation time of the broken block;

[0023] S45: the stress area is calculated according to the entire working face length L and the support roof control distance L c The dynamic stress increment is calculated as follows:

[0024]

[0025] The formula of the DP dynamic load coefficient prediction model is finally obtained as follows:

[0026]

[0027] In the formula, η is the release coefficient; σ t is the tensile strength of the key layer; Δt is the rotation time of the broken block; L is the working face length; L c is the hydraulic support roof control distance.

[0028] In one example of the present application, in the step S42, the rotation angle θ is calculated by considering the roof crushing effect, and the actual broken rock block maximum rotation distance is greater than the actual mining seam height H, and the calculation formula of the rotation angle θ is as follows:

[0029]

[0030] In the formula, H m is the mining seam height; k is the rock crushing coefficient; L b is the horizontal projection length of the broken block.

[0031] In one example of the present application, in the step S43, the rotation block edge line speed v is also calculated, considering that L b >>H m , based on the small angle approximation, the rotation angle is approximately The rotation block edge line speed v is:

[0032]

[0033] In the formula, α represents the angular acceleration; τ represents the generated torque; I represents the moment of inertia; m represents the mass of the broken block; ω is the rotation linear speed of the broken block; v is the rotation linear speed of the broken block.

[0034] In one example of the present application, after the step S60, the dynamic load coefficient predicted by the dynamic load coefficient prediction model DP is verified, and the verification specifically includes the following steps:

[0035] The prediction result of the DP prediction model is compared with the result of the dynamic load coefficient according to the average of the dynamic load coefficients of other working faces in the same coal seam, to verify the accuracy and general applicability of the dynamic load coefficient prediction model DP under different working faces.

[0036] In one example of the application, in the process of determining the model parameter η by using the LM algorithm for nonlinear least squares optimization method, the parameter update direction is determined by modifying the normal equation, and the expression of the normal equation is:

[0037] (J T J+μI)Δθ=-J T r

[0038] In the formula, is the Jacobian matrix; r=[r1,r2,r3...r m ] T is the residual vector; μ is a damping factor, which is adjusted adaptively, and is reduced to 1 / 10 of the original value if the iteration is effective, and is expanded to 10 times of the original value if the iteration is ineffective; I is the unit matrix.

[0039] Another object of the application is to provide a dynamic load coefficient prediction system for a shallow coal seam working face, comprising:

[0040] The data acquisition module is configured to acquire geological data of the working face in the same coal seam, and the geological data includes: working face length, bedrock thickness, loose layer thickness, coal thickness, key layer lithology and key layer thickness.

[0041] The data processing module is configured to process the geological data, including: median processing the interval measurement data of the bedrock thickness and the loose layer thickness, and lithology characteristic value of the key layer tensile strength, directly selecting the standard tensile strength value corresponding to the lithology when the key layer is single lithology, and calculating the comprehensive tensile strength by using the average method when there is a composite rock layer.

[0042] The data fitting module is configured to use the geological data of the working face in the same coal seam and the measured dynamic load coefficient as a fitting set.

[0043] The model establishment module is configured to establish a dynamic load coefficient prediction model DP.

[0044] The optimal parameter determination module is configured to determine the optimal parameter η of the model by substituting the fitting set composed of the geological data of the working face in the same coal seam and the measured dynamic load coefficient into the dynamic load coefficient prediction model DP.

[0045] The dynamic load coefficient prediction module is configured to input the geological data collected from a new working face into the dynamic load coefficient prediction model DP, and predict the dynamic load coefficient.

[0046] In one example of the present application, the model establishing module comprises:

[0047] The static load calculating unit is configured to calculate the self-weight stress of the overburden strata above the working face as the static load by mainly considering the self-weight stress field of the overburden strata, and the specific formula is as follows:

[0048] σ static = γ rock H rock + γ soil H soil

[0049] Wherein, σ static is the static load received by the working face; H rock is the thickness of the bedrock; H soil is the thickness of the loose layer; γ rock is the average unit weight of the bedrock; γ soil is the average unit weight of the loose layer;

[0050] The rotation angle calculating unit is configured to simplify the rock mass formed after the overburden bedrock breaks as a rigid body, which rotates around the midpoint O of the rock mass under the restriction of the horizontal stress, ignoring the friction between the rock masses and the plastic deformation effect, according to the characteristics of the working face of the shallow buried coal seam; according to the geometric relationship, the rotation range of the overburden bedrock after breaking is the distance of the roof caving and filling the goaf, so the tangent value of the rotation angle θ is the ratio of the height H m of the mining coal seam to the horizontal projection length L b of the broken rock mass;

[0051] The horizontal projection length unit is configured to take the periodic pressure step distance of the working face as the horizontal projection length L b of the broken rock mass, and based on the simply supported beam model, the expression of the horizontal projection length L b of the broken rock mass is as follows:

[0052]

[0053] In the formula, h is the thickness of the rock stratum; σ t is the tensile strength of the rock stratum;

[0054] The instantaneous impact force unit is configured to take the dynamic load as the instantaneous impact force generated by the roof rotation, and the expression of the impact force approximately estimated by the change of momentum is as follows:

[0055]

[0056] In the formula, g is the acceleration of gravity; Δt is the rotation time of the broken rock mass;

[0057] The prediction model unit is configured to calculate the dynamic load of the working face based on the stress area according to the length L of the entire working face and the support roof control distance L cThe dynamic stress increment is then calculated as:

[0058]

[0059] The formula of the DP dynamic load coefficient prediction model is finally obtained as:

[0060]

[0061] In the formula, η is the release coefficient; σ t is the tensile strength of the key layer; Δt is the rotation time of the broken block; L is the length of the working face; L c is the hydraulic support roof control distance.

[0062] In an example of the present application, the rotation angle θ is calculated considering the roof crushing effect, and the maximum rotation distance of the actual broken rock mass is greater than the actual mining seam height H, so the crushing coefficient k is introduced to obtain the rock mass rotation angle θ, and the formula of the rotation angle θ is as follows:

[0063]

[0064] In the formula, H m is the mining seam height; k is the rock crushing coefficient; L b is the horizontal projection length of the broken block.

[0065] In an example of the present application, in the step S43, the rotation block edge line speed v is also calculated, considering that L b >>H m , based on the small angle approximation, the rotation angle is approximately The rotation block edge line speed v is:

[0066]

[0067] In the formula, α represents angular acceleration; τ represents the generated torque; I represents the moment of inertia; m represents the mass of the broken block; ω is the rotation linear speed of the broken block; and v is the rotation linear speed of the broken block.

[0068] Compared with the prior art, the present application has the following beneficial effects:

[0069] The present application creatively discards the above inherent strategy, fully considers the spatial heterogeneity characteristics of different working face geological parameters, accurately analyzes the difference evolution law of each working face pressure dynamic load, and further constructs a fine prediction model integrating the spatial variation characteristics of geological parameters, so that the accuracy of the prediction result is significantly improved.

[0070] Based on the above improvement, the technical scheme of the present application can provide a reliable basis for working face support selection, effectively solve the problem of mismatch between support initial support force and roof pressure caused by uneven spatial distribution of geological parameters, thereby greatly improving the safety and effectiveness of working face support, and having significant technical progress and practical application value.

[0071] The most preferred embodiments of implementing the present application will be described in more detail below with reference to the accompanying drawings, so as to make the features and advantages of the present application easy to understand. BRIEF DESCRIPTION OF DRAWINGS

[0072] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings of the embodiments of the present application will be briefly introduced below. Among them, the drawings are only used to show some embodiments of the present application, and not to limit all embodiments of the present application to this.

[0073] Figure 1 Flow chart of the shallow coal seam working face dynamic load coefficient prediction method according to the embodiment of the present application;

[0074] Figure 2 Mining field overburden rock fracture structure mechanics model according to the embodiment of the present application;

[0075] Figure 3 Key layer impact simplified dynamic load model according to the embodiment of the present application;

[0076] Figure 4 η value mean square error curve according to the embodiment of the present application. DETAILED DESCRIPTION

[0077] In order to make the purpose, technical scheme and advantages of the technical scheme of the present application more clear, the technical scheme of the embodiments of the present application will be described clearly and completely below with reference to the drawings of the specific embodiments of the present application. The same reference signs in the drawings represent the same parts. It should be noted that the described embodiments are part of the embodiments of the present application, not all embodiments. Based on the described embodiments of the present application, all other embodiments obtained by those skilled in the art without creative labor belong to the scope of protection of the present application.

[0078] Unless otherwise defined, technical terms or scientific terms used herein shall have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terms "first", "second", and similar terms, used herein do not necessarily have any sequence or order, unless otherwise defined, but are used for the purpose of nomenclature. Similarly, the terms "one", "another", and similar terms, do not necessarily refer to the same article, unless otherwise defined, but are used for the purpose of nomenclature. The terms "including", "containing", and similar terms, are meant to encompass the elements listed thereafter, and equivalents thereof, without precluding other elements. The terms "connected", "coupled", and similar terms, are meant to encompass a physical or mechanical connection, electrical or magnetic connection, whether direct or indirect, without implying a direct mechanical or electrical connection. The terms "upper", "lower", "left", "right", and similar terms, are used to describe relative positions for the purpose of illustration only and are not meant to limit the scope of the application.

[0079] In the prior art, an estimation strategy based on the average value of the dynamic load coefficient of adjacent working faces is usually adopted. However, this strategy does not fully consider the spatial heterogeneity of different working face geological parameters, resulting in a deviation in the prediction result and making it difficult to accurately guide the working face support selection, which is prone to cause the problem of mismatch between the initial support force of the support and the roof pressure.

[0080] According to the shallow seam working face dynamic load coefficient prediction method of the first aspect of the present application, as shown in the accompanying drawings, the method comprises the following steps: Figure 1

[0081] S10: Collecting geological data of the same seam working face, the geological data comprising: working face length, bedrock thickness, loose layer thickness, coal thickness, key layer lithology, and key layer thickness;

[0082] S20: Processing the geological data, comprising: performing median processing on the interval measurement data of the bedrock thickness and the loose layer thickness, and performing lithology characteristicization on the key layer tensile strength, when the key layer is single lithology, directly selecting the standard tensile strength value corresponding to the lithology, and when there is a composite rock layer, calculating the comprehensive tensile strength by using the average method;

[0083] S30: Taking the geological data of the same seam working face and the measured dynamic load coefficient as a fitting set;

[0084] S40: Establishing a dynamic load coefficient prediction model DP;

[0085] S50: Substituting the fitting set composed of the geological data of the same seam working face and the measured dynamic load coefficient into the dynamic load coefficient prediction model DP to determine the optimal model parameter η; for example, using the LM algorithm to determine the model parameter η by using the nonlinear least squares optimization method.

[0086] ​S60: input the geological data collected by the new working face into the dynamic load coefficient prediction model DP, and predict the dynamic load coefficient; specifically, according to the working face operation procedure, the fixed parameters of the dynamic load coefficient prediction model DP formula are determined, and the related geological parameters of the working face are brought into the formula of the DP prediction model to obtain the dynamic load coefficient.

[0087] The prediction method creatively discards the above inherent strategy, fully considers the spatial heterogeneity characteristics of different working face geological parameters, accurately analyzes the difference evolution law of the working face pressure dynamic load, and then builds a refined prediction model integrating the spatial variation characteristics of the geological parameters, so that the accuracy of the prediction result is significantly improved.

[0088] Based on the above improvement, the technical scheme of the prediction method can provide a reliable basis for working face support selection, effectively solve the problem of mismatch between support initial support force and roof pressure caused by uneven spatial distribution of geological parameters, thereby greatly improve the safety and effectiveness of working face support, and have significant technical progress and practical application value.

[0089] In one example of the present application, in the step S40, establishing the dynamic load coefficient prediction model DP includes the following steps:

[0090] S41: the static load of the working face is mainly the stress field of the overburden rock, and the self-weight stress of the overburden rock above the working face is calculated as the static load, and the specific formula is as follows:

[0091] σ static =γ rock H rock +γ soil H soil

[0092] Wherein, σ static is the static load of the working face, Mpa; H rock is the thickness of the bedrock, m; H soil is the thickness of the loose layer, m; γ rock is the average unit weight of the bedrock, kN / m 3 ; γ soil is the average unit weight of the loose layer, kN / m 3 ;

[0093] S42: for the characteristics of the shallow coal seam working face, the rock block formed after the overlying bedrock breaks is simplified as a rigid body, which rotates around the midpoint O of the block under the restriction of horizontal stress, as shown in Figure 2 Ignore the friction between the rock blocks and the plastic deformation effect; according to the geometric relationship, the maximum rotation range of the overlying bedrock after breaking is the distance of the roof caving and filling the goaf, so the tangent value of the rotation angle θ is the ratio of the mining coal seam height H m to the horizontal projection length L b of the broken block.

[0094] S43: The working face cycle step distance is regarded as the horizontal projection length L of the broken block b Based on the simply supported beam model, the expression of the horizontal projection length L of the broken block is obtained as follows: b

[0095]

[0096] In the formula, h is the thickness of the rock stratum, m; σ t is the tensile strength of the rock stratum, MPa;

[0097] S44: The dynamic load is regarded as the instantaneous impact force generated by the roof rotation, and the impact force is approximately estimated according to the expression of the change in momentum as follows:

[0098]

[0099] Substituting , we obtain:

[0100]

[0101] In the formula, g is the acceleration of gravity, m / s 2 ; Δt is the rotation time of the broken block, s;

[0102] According to the local impact theory, the force size of the broken energy transmission of the key layer to the roof is proportional to the distance between them, as shown in the following formula: Figure 3 Therefore, the action force F0 of the direct wave emitted from the key layer to the working face roof is:

[0103] F0 = ηF

[0104] In the formula, η is the release coefficient, which is a correction to the action force transmission strength, which is usually caused by the buffering or amplification effect of the rock stratum to the dynamic load.

[0105] S45: The stress area is calculated according to the entire working face length L and the support roof control distance L c Therefore, the dynamic stress increment is:

[0106]

[0107] Finally, the formula of the DP dynamic load coefficient prediction model is obtained as follows:

[0108]

[0109] In the formula, σ t is the tensile strength of the key layer; Δt is the rotation time of the broken block; L is the working face length; L c is the roof control distance of the hydraulic support.

[0110] ​In one example of the present application, in the step S42, the rotation angle θ is calculated considering the roof crushing effect, and the maximum rotation distance of the actual broken rock mass is greater than the actual mining seam height H, so the crushing coefficient k is introduced to obtain the rock mass rotation angle θ, and the formula of the rotation angle θ is as follows:

[0111]

[0112] In the formula, H m is the mining seam height, m; k is the rock crushing coefficient; L b is the horizontal projection length of the broken mass.

[0113] In one example of the present application, in the step S43, the rotation mass edge line speed v is also calculated, considering that L b >>H m , based on the small angle approximation, the rotation angle is approximately The rotation mass edge line speed v is:

[0114]

[0115] In the formula, α represents the angular acceleration, rad / s 2 ; τ represents the generated torque, N / m; I represents the moment of inertia, kg / m 2 ; m represents the mass of the broken mass, m; ω is the rotation line speed of the broken mass, rad / s; v is the rotation line speed of the broken mass, m / s.

[0116] In one example of the present application, after the step S60, the dynamic load coefficient predicted by the dynamic load coefficient prediction model DP is verified, specifically including the following steps:

[0117] The LM algorithm is used to determine the model parameters η by the nonlinear least squares optimization method;

[0118] According to the working face operation procedure, the fixed parameters of the dynamic load coefficient prediction model DP formula are determined, and the related geological parameters of the working face are brought into the formula of the DP prediction model to obtain the dynamic load coefficient;

[0119] The prediction result of the DP prediction model is compared with the average value of the other same seam working face to verify the accuracy and general ability of the dynamic load coefficient prediction model DP under different working faces.

[0120] For example, the relative error between the actual dynamic load coefficient D real of the working face, the average value estimated dynamic load coefficient D mean , and the DP model predicted dynamic load coefficient D pre is calculated and compared.

[0121] In one example of the present application, in the process of determining the model parameter η by using the LM algorithm for the nonlinear least squares optimization method, the parameter update direction is determined by modifying the normal equation, and the expression of the normal equation is:

[0122] (J T J+μI)Δθ=-J T r

[0123] In the formula, is the Jacobian matrix; r=[r1,r2,r3...r m ] T is the residual vector; μ is a damping factor, which is adjusted adaptively, and is reduced to 1 / 10 of the original value if the iteration is effective, and is expanded to 10 times of the original value if the iteration is ineffective; I is the unit matrix.

[0124] According to the shallow coal seam working face dynamic load coefficient prediction system of the second aspect of the present application, comprising:

[0125] The data acquisition module is configured to acquire geological data of the same coal seam working face, and the geological data includes: working face length, bedrock thickness, loose layer thickness, coal thickness, key layer lithology and key layer thickness;

[0126] The data processing module is configured to process the geological data, including: median processing of the interval measurement data of the bedrock thickness and the loose layer thickness, and lithology characteristic value of the key layer tensile strength, when the key layer is single lithology, directly selecting the standard tensile strength value corresponding to the lithology; when there is a composite rock layer, the average method is used to calculate the comprehensive tensile strength;

[0127] The data fitting module is configured to use the geological data of the same coal seam working face and the measured dynamic load coefficient as the fitting set;

[0128] The model establishment module is configured to establish a dynamic load coefficient prediction model DP;

[0129] The optimal parameter determination module is configured to input the fitting set composed of the geological data of the same coal seam working face and the measured dynamic load coefficient into the dynamic load coefficient prediction model DP to determine the optimal model parameter η;

[0130] The dynamic load coefficient prediction module is configured to input the geological data collected from the new working face into the dynamic load coefficient prediction model DP, and predict the dynamic load coefficient.

[0131] The prediction system creatively discards the above-mentioned inherent strategy, fully considers the spatial heterogeneity characteristics of different working face geological parameters, accurately analyzes the difference evolution law of each working face pressure dynamic load, and then constructs a refined prediction model integrating the spatial variation characteristics of geological parameters, so that the accuracy of the prediction result is significantly improved.

[0132] Based on the above improvement, the technical scheme of the prediction system can provide a reliable basis for working face support selection, effectively solve the problem of mismatch between support initial support force and roof pressure caused by uneven spatial distribution of geological parameters, thereby greatly improve the safety and effectiveness of working face support, and have significant technical progress and practical application value.

[0133] In an example of the present application, the model establishing module comprises:

[0134] The static load calculating unit is configured to consider the overburden rock self-weight stress field as the main factor for considering the working face static load, and calculate the self-weight stress of the overburden rock layer of the working face as the static load, and the specific formula is as follows:

[0135] σ static = γ rock H rock + γ soil H soil

[0136] Wherein, σ static is the static load of the working face, Mpa; H rock is the thickness of the bedrock, m; H soil is the thickness of the loose layer, m; γ rock is the average unit weight of the bedrock, kN / m 3 ; γ soil is the average unit weight of the loose layer, kN / m 3 ;

[0137] The rotation angle calculating unit is configured to simplify the rock mass formed after the overburden bedrock breaks as a rigid body, which rotates around the midpoint O of the block under the restriction of horizontal stress, as shown in Figure 2 Ignore the friction between the rock masses and the plastic deformation effect; according to the geometric relationship, the maximum rotation range of the overburden bedrock after breaking is the distance of the roof collapse filling the goaf, so the tangent value of the rotation angle θ is the ratio of the height of the mining coal seam H m to the horizontal projection length L b of the broken block; but due to the roof crushing effect, the maximum rotation distance of the broken rock mass is greater than the actual mining coal seam height H, so the crushing coefficient k is introduced to obtain the rotation angle θ of the rock mass. The specific formula is as follows

[0138]

[0139] Wherein, H m is the height of the mining coal seam, m; k is the rock crushing coefficient; L b is the horizontal projection length of the broken block.

[0140] Horizontal projection length unit, configured to take the working face cycle step distance as the broken block horizontal projection length L b Based on the simply supported beam model, the expression of the broken block horizontal projection length L b is obtained as follows:

[0141]

[0142] In the formula, h is the thickness of the rock stratum, m; σ t is the tensile strength of the rock stratum, MPa;

[0143] Because L b >>H m , based on the small angle approximation, the rotation angle is approximately The edge line speed v of the rotating block is:

[0144]

[0145] In the formula, α represents the angular acceleration, rad / s 2 ; τ represents the generated torque, N / m; I represents the moment of inertia, kg / m 2 ; m represents the mass of the broken block, m; ω is the linear speed of the broken block, rad / s; v is the linear speed of the broken block, m / s;

[0146] Instantaneous impact force unit, configured to take the dynamic load as the instantaneous impact force generated by the roof rotation, and the impact force is approximately estimated according to the expression of the change in momentum as follows:

[0147]

[0148] Substituting , we have:

[0149]

[0150] In the formula, g is the acceleration of gravity, m / s 2 ; Δt is the rotation time of the broken block, s;

[0151] Wherein, according to the local impact theory, the broken energy of the key layer is transmitted to the roof, and the force size is proportional to the distance between them, as shown in Figure 3 . Then the direct wave action force F0 of the working face roof from the key layer is:

[0152] F0=ηF

[0153] In the formula, η is the release coefficient, which is a correction to the action force transmission intensity, which is usually caused by the buffering or amplification effect of the rock stratum to the dynamic load.

[0154] A prediction model unit is configured to be used for calculating the dynamic stress increment based on the stress area per entire working face length L and support roof control distance L c The dynamic stress increment is calculated as follows:

[0155]

[0156] The formula of the DP dynamic load coefficient prediction model is finally obtained as follows:

[0157]

[0158] In the formula, σ t represents the tensile strength of the key layer; Δt represents the rotation time of the broken block; L represents the working face length; L c represents the hydraulic support roof control distance.

[0159] In an example of the present application, the rotation angle θ is calculated by considering the roof crushing effect, and the maximum rotation distance of the actual broken rock mass is greater than the actual mining seam height H, so the crushing coefficient k is introduced to obtain the rock mass rotation angle θ, and the formula of the rotation angle θ is as follows:

[0160]

[0161] In the formula, H m represents the mining seam height, m; k represents the rock crushing coefficient; L b represents the horizontal projection length of the broken block.

[0162] In an example of the present application, in the step S43, the rotation block edge line speed v is also calculated, considering that L b >>H m Based on the small angle approximation, the rotation angle is approximately The rotation block edge line speed v is:

[0163]

[0164]

[0165] In the formula, α represents the angular acceleration, rad / s 2 ; τ represents the generated torque, N / m; I represents the moment of inertia, kg / m 2 ; m represents the mass of the broken block, m; ω represents the rotation linear speed of the broken block, rad / s; v represents the rotation linear speed of the broken block, m / s.

[0166] Particular cases

[0167] In order to verify the effectiveness of the method of the present application, the relevant geological data of Halagou Coal Mine of Shendong Mining Area are used for parameter fitting and dynamic load coefficient verification. The fitting set selects the measured data of the same coal seam in the working face. Five working face data are collected as the fitting set, and the dynamic load coefficients of two working faces with different geological conditions are verified.

[0168] Since the thickness of bedrock and loose layer in the collected data is a range value, the median value is used to determine (such as H rock = 53.5m corresponding to the interval 44-63m); the tensile strength σ t According to the lithology selection, the average value is selected for the composite rock layer (5.2MPa for fine-grained sand, 2.6MPa for medium-grained sandstone, and 4.8MPa for sandy mudstone); the time Δt is 0.03s; and the rock crushing coefficient k is 1.3.

[0169] Table 1 related parameters of working face in fitting set

[0170]

[0171]

[0172] In order to determine the model parameter η, the LM algorithm is used for nonlinear least squares optimization. The initial parameter is set as η = 1, and the MSE curve obtained after iterative convergence is as shown in Figure 4 , which is a non-symmetrical concave structure as a whole, and the MSE value is the lowest when η = 2.5807, that is, the optimal parameter is η = 2.5807.

[0173] According to the operation rules of working face 22309, the roof control distance of working face support is Lc = 5.146m, the gravitational acceleration g is 9.8m / s2, the rock crushing coefficient k is 1.3, the broken rock block rotation time Δt is 0.03s, and η is the optimal parameter 2.5807. The fixed parameters are substituted into the dynamic load coefficient prediction model DP formula applicable to working face 22309:

[0174]

[0175] The other related geological data of the working face are shown in Table 2. Multiple sets of geological parameters shown in Table 2 are substituted into the DP prediction model, and the DP prediction results are compared with the average value of the other same coal seam working face to verify the accuracy and general ability of the dynamic load coefficient prediction model DP under different working faces.

[0176] Table 2 related geological data of working face 22309

[0177]

[0178] The average dynamic load coefficient of other coal seam working face is:

[0179]

[0180] The actual dynamic load coefficient D of the 22309 working face is obtained real The average value of the estimated dynamic load coefficient D mean The dynamic load coefficient prediction model DP is used to predict the dynamic load coefficient D pre The relative error is shown in Table 3:

[0181] Table 3: Prediction results and error analysis of the 22309 working face

[0182]

[0183] Through the prediction experiment, it is found that for the dynamic load coefficient difference between the 22309-1 working face (dynamic load coefficient 1.10) and the 22309-2 working face (dynamic load coefficient 1.21) in Halagou, the prediction error of the dynamic load coefficient prediction model DP is 91.05% and 98.05% respectively, which is 7.14% and 4.5% higher than the accuracy of the traditional average dynamic load coefficient method. Under the condition of dynamic load coefficient gradient change, the average fluctuation of the prediction error of the dynamic load coefficient prediction model DP is 7.36%, which is significantly lower than the 10.64% of the traditional method. The experiment proves that the model proposed in the present application performs more efficiently and accurately in the dynamic load coefficient prediction task, and the prediction accuracy meets the engineering demand of support selection, which can provide important reference for the stability control of non-homogeneous geological working face and support selection.

[0184] The above describes the exemplary embodiments of the shallow coal seam working face dynamic load coefficient prediction method and system proposed in the present application in detail with reference to the preferred embodiments, however, those skilled in the art can understand that various modifications and improvements can be made to the above specific embodiments without departing from the concept of the present application, and various technical features and structures proposed in the present application can be combined without exceeding the protection scope of the present application, and the protection scope of the present application is determined by the appended claims.

Claims

1. A method for predicting the dynamic load coefficient of a shallow coal seam working face, characterized in that: The steps include: S10: Collect geological data of the working face of the same coal seam, including: working face length, bedrock thickness, loose layer thickness, coal thickness, key layer lithology and key layer thickness; S20: Processing geological data, including: median processing of interval measurement data of bedrock thickness and loose layer thickness, lithologic characterization of key layer tensile strength, directly selecting the standard tensile strength value of the corresponding lithology when the key layer is of a single lithology; and using the average method to calculate the comprehensive tensile strength when there are composite rock layers. S30: The geological data of the working face of the same coal seam and the measured dynamic load coefficient are used as the fitting set; S40: establishing a dynamic load coefficient prediction model DP; S50: Substitute the fitting set consisting of geological data of the same coal seam working face and measured dynamic load coefficient into the dynamic load coefficient prediction model DP to determine the optimal parameter η of the model; S60: Input the geological data collected from the new working face into the dynamic load coefficient prediction model DP, and predict the dynamic load coefficient.

2. The method for predicting dynamic load coefficient of shallow coal seam working face according to claim 1, characterized in that: In step S40, establishing the dynamic load coefficient prediction model DP includes the following steps: S41: The static load of the working face is mainly based on the self-weight stress field of the overburden. The self-weight stress of the overburden on the working face is calculated as the static load. The specific formula is as follows: s static =c rock H rock +g soil H soil Among them, σ static is the static load on the working surface; H rock is the bedrock thickness; H soil is the thickness of the loose layer; γ rock is the average bulk density of bedrock; γ soil is the average bulk density of the loose layer; S42: In view of the characteristics of the shallow coal seam working face, the rock block formed after the overlying bedrock is broken is simplified as a rigid body. It is restricted by horizontal stress and rotates around the midpoint O of the block. The friction between the rock blocks and the influence of plastic deformation are ignored. According to the geometric relationship, the maximum rotation range after the overlying bedrock is broken is the distance of the roof collapse filling the goaf. Therefore, the tangent value of the rotation angle θ is the height of the mined coal seam H. m Horizontal projection length L of the broken block b The ratio of S43: The periodic pressure step of the working face is regarded as the horizontal projection length L of the broken block b Based on the simply supported beam model, the horizontal projection length L of the broken block is obtained b The expression is: Where h is the thickness of the rock layer; σ t is the tensile strength of the rock formation; S44: The dynamic load is regarded as the instantaneous impact force generated by the rotation of the top plate. The impact force can be estimated approximately based on the momentum change as follows: Where g is the acceleration of gravity; Δt is the rotation time of the broken block; and k is the rock expansion coefficient. S45: The load-bearing area is calculated based on the total working surface length L and the support top control distance L c Calculation, the dynamic stress increment is: The final formula of the DP dynamic load coefficient prediction model is: Where η is the release coefficient; σ t is the tensile strength of the key layer; Δt is the rotation time of the broken block; L is the length of the working surface; L c Control the top distance of the hydraulic support.

3. The method for predicting dynamic load coefficient of shallow coal seam working face according to claim 2, characterized in that: In step S42, the rotation angle θ is calculated taking into account the roof expansion effect. The actual maximum rotation distance of the broken rock block is greater than the actual mining coal seam height H. The calculation formula of the rotation angle θ is as follows: Where H m is the height of the mined coal seam; k is the rock expansion coefficient; L b is the horizontal projection length of the broken block.

4. The method for predicting dynamic load coefficient of shallow coal seam working face according to claim 2, characterized in that: In the step S43, it also includes calculating the linear velocity v of the edge of the rotating block, taking into account L b >>H m , based on the small angle approximation, the rotation angle is approximately The linear velocity v of the rotating block edge is: Where α represents the angular acceleration; τ represents the torque generated; I represents the moment of inertia; m represents the mass of the broken block; ω is the linear velocity of the broken block; and v is the linear velocity of the broken block.

5. The method for predicting dynamic load coefficient of shallow coal seam working face according to claim 1, characterized in that: After step S60, the method further includes: verifying the dynamic load coefficient predicted by the dynamic load coefficient prediction model DP, which specifically includes the following steps: The prediction results of the DP prediction model are compared with the results of taking the average value of the dynamic load coefficient as the dynamic load coefficient based on other working faces of the same coal seam to verify the accuracy and adaptability of the dynamic load coefficient prediction model DP under different working faces.

6. The method for predicting dynamic load coefficient of shallow coal seam working face according to claim 5, characterized in that: When the LM algorithm is used to perform nonlinear least squares optimization to determine the model parameter η, the parameter update direction is determined by modifying the normal equation. The expression of the modified normal equation is: Where, is the Jacobian matrix; r=[r1,r2,r3...r m ] T is the residual vector; μ is the damping factor, which uses an adaptive adjustment mechanism. If the iteration is effective, it is reduced to 1 / 10 of the original value, and if the iteration is invalid, it is expanded to 10 times the original value; I is the unit matrix.

7. A dynamic load coefficient prediction system for shallow coal seam working face, characterized in that: include: A data acquisition module is configured to collect geological data of a working face of the same coal seam, the geological data including: working face length, bedrock thickness, loose layer thickness, coal thickness, key layer lithology and key layer thickness; The data processing module is configured to process geological data, including: median processing of interval measurement data of bedrock thickness and loose layer thickness, lithologic characterization of key layer tensile strength, directly selecting the standard tensile strength value of the corresponding lithology when the key layer is of a single lithology; and using the average method to calculate the comprehensive tensile strength when there is a composite rock layer; a data fitting module configured to use geological data of a working face of the same coal seam and measured dynamic load coefficients as a fitting set; A model building module configured to build a dynamic load coefficient prediction model DP; The optimal parameter determination module is configured to substitute the fitting set consisting of geological data of the same coal seam working face and the measured dynamic load coefficient into the dynamic load coefficient prediction model DP to determine the optimal parameter η of the model; The dynamic load coefficient prediction module is configured to input the geological data collected from the new working face into the dynamic load coefficient prediction model DP and predict the dynamic load coefficient.

8. The dynamic load coefficient prediction system for shallow coal seam working face according to claim 7, characterized in that: The model building module includes: The static load calculation unit is configured to consider the static load of the working face. The deadweight stress field of the overburden is used as the main factor. The deadweight stress of the overburden on the working face is calculated as the static load. The specific formula is as follows: s static =c rock H rock +g soil H soil Among them, σ static is the static load on the working surface; H rock is the bedrock thickness; H soil is the thickness of the loose layer; γ rock is the average bulk density of bedrock; γ soil is the average bulk density of the loose layer; The rotation angle calculation unit is configured to simplify the rock block formed after the overburden bedrock is broken into a rigid body according to the characteristics of the shallow coal seam working face. It is restricted by horizontal stress and rotates around the midpoint O of the block. The friction and plastic deformation between the rock blocks are ignored. According to the geometric relationship, the maximum rotation range after the overburden bedrock is broken is the distance of the roof collapse filling the goaf. Therefore, the tangent value of the rotation angle θ is the mining coal seam height H. m Horizontal projection length L of the broken block b The ratio of The horizontal projection length unit is configured to treat the periodic pressure step of the working face as the horizontal projection length L of the broken block. b Based on the simply supported beam model, the horizontal projection length L of the broken block is obtained b The expression is: Where h is the thickness of the rock layer; σ t is the tensile strength of the rock formation; The instantaneous impact force unit is configured to regard the dynamic load as the instantaneous impact force generated by the rotation of the top plate. The impact force is approximately estimated by the momentum change as follows: Where g is the acceleration due to gravity and Δt is the rotation time of the broken block. The prediction model unit is configured to be used for calculating the total working surface length L and the support top control distance L based on the load area. c Calculation, the dynamic stress increment is: The final formula of the DP dynamic load coefficient prediction model is: Where σ t is the tensile strength of the key layer; Δt is the rotation time of the broken block; L is the length of the working surface; L c Control the top distance of the hydraulic support.

9. The dynamic load coefficient prediction system for shallow coal seam working face according to claim 7, characterized in that: The rotation angle θ is calculated taking into account the roof expansion effect. The actual maximum rotation distance of the broken rock block is greater than the actual mining coal seam height H. The calculation formula of the rotation angle θ is as follows: Where H m is the height of the mined coal seam; k is the rock expansion coefficient; L b is the horizontal projection length of the broken block.

10. The shallow coal seam working face dynamic load coefficient prediction system according to claim 7, characterized in that: In the step S43, it also includes calculating the linear velocity v of the edge of the rotating block, taking into account L b >>H m , based on the small angle approximation, the rotation angle is approximately The linear velocity v of the rotating block edge is: Where α represents the angular acceleration; τ represents the torque generated; I represents the moment of inertia; m represents the mass of the broken block; ω is the linear velocity of the broken block; and v is the linear velocity of the broken block.

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