Working face impact risk evaluation method based on transient induced impact of coal rock structure

Abstract

The invention discloses a coal rock structure transient induced impact-based working face impact risk evaluation method, which comprises the following steps: acquiring geological data of a target working face, and determining a to-be-evaluated area of the working face; determining a stress state of the to-be-evaluated region before structure transient and a stress state of the to-be-evaluated region after structure transient; according to the stress state before the structure transients and the stress state after the structure transients, calculating the impact stress of the working surface under the transient excitation action of the overlying strata space structure; according to the stress state before the structure transients and the impact stress during the structure transients, establishing an impact risk evaluation index of the to-be-evaluated area of the working face; and according to the impact risk evaluation index, performing impact risk evaluation division on the to-be-evaluated area of the working face. The method can effectively improve the working face impact risk evaluation precision, provides guidance for mine rock burst prevention work, and ensures safe production of the working face.

Description

Technical Field

[0001] The present application relates to the technical field of coal mining, and in particular to a method for assessing the impact hazard of a working face based on transient induced impact of coal-rock structures. Background Art

[0002] With the increase in the depth of coal mining, coal-rock dynamic disasters represented by rock burst have become one of the main risks faced by deep mines. Rock burst has the characteristics of strong suddenness, great destructive power, and complex influencing factors, which makes rock burst accidents difficult to predict and seriously restricts the safe and efficient production of deep mines. The construction of a working face rock burst hazard assessment method is of great significance for the prediction and prevention of rock burst in deep mines.

[0003] The superposition of dynamic and static loads of surrounding rocks is the main factor inducing rock burst, and the overburden structure, as the carrier of large-scale transfer and transmission of overburden load in the mining field, has a controlling effect on the distribution, transmission and evolution of mining stress in the surrounding rock. In particular, when the overburden contains hard rock layers, its instantaneous fracture causes transient changes in the spatial structure of the overburden, which in turn leads to the occurrence of dynamic and static mechanical responses of coal and rock within the mining influence range, causing changes in dynamic and static loads in the mining field, resulting in an increase in the impact risk of the working face.

[0004] In the prior art, the "Mechanical Response of Coal Rock in Mines under Structural Transient Excitation" in the Journal of China Coal Society, Issue 12, 2023, proposed the academic concept of the occurrence of dynamic mechanical response of coal rock in mines induced by structural transients and the order change of static mechanical response, but did not further consider how to evaluate the impact hazard of the working face based on this concept. In addition, patent CN108960653A discloses a multi-scale impact hazard evaluation method based on the comprehensive index method. This method can more comprehensively reflect the impact hazard status of regions of different scales and improve the evaluation accuracy of impact hazard. However, for specific geological conditions, this method needs to consider many influencing factors, and the evaluation of the impact hazard of the working face is more difficult. Patent CN110298107B discloses an incremental superposition working face impact hazard evaluation method, which analyzes the main dynamic and static load control factors of the working face impact hazard from four aspects: static load source, dynamic load source, coal body properties, and stress transfer conditions, but does not consider the influence of the spatial structure of the overburden on the static and dynamic load distribution characteristics of the mine. Patent CN116993111A discloses a rock burst dynamic evaluation system that takes into account the difference in principal stress increments, but this method does not consider the influence of the spatial structure of the overburden rock on the mining stress of the surrounding rock. Summary of the invention

[0005] The embodiment of the present application provides a working face impact hazard assessment method based on transient induced impact of coal-rock structure, which can effectively improve the accuracy of working face impact hazard assessment, provide guidance for mine rock burst prevention and control work, and ensure safe production on the working face.

[0006] To achieve the above object, the technical solution of the embodiment of the present invention is as follows:

[0007] In a first aspect, the embodiment of the present invention provides a method for evaluating the impact hazard of a working face based on the transient induced impulse of coal-rock structure, including: obtaining geological data of a target working face and determining the area to be evaluated of the working face; the area to be evaluated of the working face is the high stress concentration area of the working face; according to on-site monitoring and a preset numerical calculation method, determining the stress state of the area to be evaluated of the working face before the transient of the coal-rock structure, that is, the first stress; according to the preset numerical calculation method and physical similarity simulation experiment, determining the stress state of the area to be evaluated of the working face after the coal-rock transient, that is, the second stress; calculating the impact stress of the working face under the excitation of the coal-rock structure transient according to the first stress and the second stress; establishing an impact hazard evaluation index for the area to be evaluated of the working face according to the first stress and the impact stress of the working face; and performing impact hazard evaluation and division on the area to be evaluated according to the impact hazard evaluation index.

[0008] In some possible implementation manners, the geological data of the target working face includes but is not limited to the thickness of coal and rock layers, lithology, bulk density, information on the breaking step distance of overlying strata, mechanical parameters of mine coal and rock, borehole columnar diagram, and working face operation regulations information.

[0009] In some possible implementation manners, according to on-site monitoring and a preset numerical calculation method, determining the first stress of the area to be evaluated before the transient of the overlying strata spatial structure specifically includes: measuring the third stress at the working face site before the coal-rock structure transient by the hollow inclusion stress relief method; wherein, the measuring points are arranged along the return airway of the target working face; based on the discrete element numerical software and the geological data of the target working face, constructing a numerical calculation model, optimizing and correcting the mechanical parameters of the mine coal and rock, and assigning the corrected mechanical parameters to the numerical calculation model to make the numerical calculation model in an equilibrium state; setting the excavation steps according to the working face operation regulations information to simulate the mining disturbance effect of the working face; monitoring the fourth stress of the working face before the coal-rock structure transient during the mining process by pre-arranging measuring lines in the numerical calculation model; and using a preset mathematical software to fit and correct the third stress and the fourth stress before the coal-rock structure transient to obtain the first stress before the coal-rock structure transient.

[0010] In some possible implementation manners, according to a preset numerical calculation method and a physical similarity simulation experiment, the second stress of the area to be evaluated at the working face after the transient change of the coal-rock structure is determined, including: preprocessing the numerical calculation model to realize the instantaneous fracture of the hard rock stratum, and monitoring the fifth stress of the working face after the transient change of the coal-rock structure in the numerical calculation model through a measuring line; laying a physical similarity experiment model according to the geological data of the target working face according to a preset geometric similarity ratio; simulating the compensation load by laying heavy objects on the top of the physical similarity experiment model, and laying stress sensors at the bottom of the model to monitor the stress of the working face during the mining process; wherein, the magnitude of the compensation load is determined by the thickness and unit weight of the coal and rock strata; carrying out mining of the working face in the physical similarity experiment model according to the working face operation regulation information, and using the stress sensors to monitor the sixth stress of the working face after the transient change of the coal-rock structure in the physical similarity experiment model; using a preset mathematical software to fit and correct the fifth stress and the sixth stress to obtain the second stress after the transient change of the coal-rock structure.

[0011] In some possible implementation manners, the impact stress of the working face under the action of the transient change of the coal-rock structure is expressed as:

[0012] P d (x,y) = 2[P2(x,y) - P1(x,y)],

[0013] wherein, P d (x,y) is the impact stress of the working face under the action of the transient change of the coal-rock structure, P2(x,y) is the second stress of the area to be evaluated at the working face after the transient change of the coal-rock structure, and P1(x,y) is the first stress of the area to be evaluated before the transient change of the overlying rock spatial structure.

[0014] In some possible implementation manners, according to the first stress before the transient change of the coal-rock structure and the impact stress of the working face, an impact hazard evaluation index for the area to be evaluated at the working face is established, including:

[0015] According to the first stress and the impact stress of the working face, determine the maximum stress instantaneously acting on the coal body during the transient change of the structure; the maximum stress is expressed as:

[0016] P(x,y) = P1(x,y) + P d (x,y),

[0017] According to the maximum stress, construct an impact hazard evaluation index for the area to be evaluated; the impact hazard evaluation index is expressed as:

[0018]

[0019] wherein, Q s is the impact hazard evaluation index, [σ cIt is the stress of coal mass impact failure and is determined through the geological data of the target working face.

[0020] In some possible implementation manners, according to the impact hazard evaluation index, the impact hazard evaluation and division of the area to be evaluated in the working face are carried out, including:

[0021] Based on the equal division principle, the impact hazard evaluation index is divided into four levels;

[0022] According to the calculation result of the impact hazard evaluation index, the impact hazard level division of the area to be evaluated in the working face is carried out.

[0023] One or more technical solutions provided in the embodiments of the present invention have at least the following technical effects or advantages:

[0024] From the perspective of the overlying strata spatial structure, the present invention proposes a method for evaluating the impact hazard of a working face based on the transient impact induction of coal and rock structures, reducing the influencing factors to be considered during the evaluation of the impact hazard of the working face, lowering the difficulty of impact hazard evaluation, having wide applicability for the impact hazard evaluation of mines with different engineering geological conditions, and ensuring the safe production of the working face; in addition, when calculating the stress of the area to be evaluated in the working face before and after the transient change of the coal and rock structure, various methods such as on-site monitoring, numerical calculation, and physical similarity simulation experiments are used to fit and correct the calculation results. The calculation process is simple, easy to operate, and the calculation results can more accurately reflect the stress distribution characteristics of the working face before and after the transient change of the coal and rock structure, significantly improving the accuracy of the impact hazard evaluation of the working face. Compared with the existing impact hazard evaluation methods, starting from the concept of the transient induction of dynamic and static mechanical responses in the stope by the transient change of the coal and rock structure, the present invention designs a method for evaluating the impact hazard of the working face by calculating the stress state of the working face before the transient change of the coal and rock structure and the impact stress of the working face under the excitation of the structural transient change, realizing the progress of the concept of rock burst prevention and control. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present invention, the drawings required to be used in the embodiments of the present invention will be briefly introduced below. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0026] Figure 1 It is a schematic flow chart of the embodiment of a method for evaluating the impact hazard of a working face based on the transient impact induction of coal and rock structures provided for the implementation of the present invention;

[0027] Figure 2 It is the working face excavation plan in the embodiment of the present invention;

[0028] Figure 3It is a numerical model diagram in the embodiment of the present invention;

[0029] Figure 4 It is a distribution curve diagram of mining stress and impact stress before and after the first weighting in the embodiment of the present invention;

[0030] Figure 5 It is a distribution curve diagram of mining stress and impact stress before and after the periodic weighting in the embodiment of the present invention;

[0031] Figure 6 It is a physical similarity simulation experiment diagram in the embodiment of the present invention;

[0032] Figure 7 It is a stress distribution diagram of the surrounding coal bodies in the stope during the coal mining process in the embodiment of the present invention;

[0033] Figure 8 It is a superposition schematic diagram of mining stress and impact stress before and after the transient change of the coal-rock structure in the embodiment of the present invention;

[0034] Figure 9 It is a force diagram of the coal body during the transient change of the coal-rock structure in the embodiment of the present invention;

[0035] Figure 10 It is a distribution curve diagram of the maximum stress instantaneously acting on the coal body under the excitation of the transient change of the coal-rock structure in the embodiment of the present invention;

[0036] Figure 11 It is an equivalent division diagram for evaluating the impact hazard in the embodiment of the present invention. Specific embodiments

[0037] Next, the technical solutions in the embodiments of the present application will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present application.

[0038] In the relevant descriptions of this embodiment, terms such as "including", "containing", "having", etc. are all open terms, generally preferably understood as including but not limited to; the term "at least one" is generally preferably understood as one or more, where "multiple" means two or more; the term "at least one (item)" or its similar expressions refer to any combination of these items, including any combination of single item (item) or plural items (items). For example, "at least one (item) of a, b or c", or "at least one (item) of a, b and c" can all represent: a, b, c, a - b (i.e., a and b), a - c, b - c, or a - b - c, where a, b, c can be single or multiple respectively; the symbol "A / B" is used to describe the selection relationship of associated objects, generally representing an "or" relationship before and after.

[0039] In the following description of this embodiment, the terms used in the embodiments of the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application. The singular forms "a" and "the" used in the embodiments of the present application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0040] Those skilled in the art should understand that in the following description of the embodiments of the present application, the sequence numbers do not mean the order of execution, and some or all steps can be executed in parallel or successively. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation to the implementation process of the embodiments of the present application.

[0041] Those skilled in the art should understand that the numerical ranges in the embodiments of the present application should be understood as specifically disclosing each intermediate value between the upper and lower limits of the range. The intermediate value within any stated value or stated range and each smaller range between any other stated value or intermediate value within the range are also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded from the range.

[0042] Unless otherwise specified, the technical / scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which this application belongs. Although this application only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein can also be used in the implementation or testing of this application. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0043] In order to illustrate the technical solution of the present invention, specific embodiments are used for illustration below.

[0044] An embodiment of the present invention provides a method for evaluating the impact hazard of a working face based on the transient characteristics of the overlying rock space structure, which can effectively improve the accuracy of the impact hazard evaluation of the working face, provide guidance for the prevention and control of mine rock bursts, and ensure the safe production of the working face.

[0045] Figure 1 It is a schematic flowchart of an embodiment of a method for evaluating the impact hazard of a working face based on the transient impulse of coal and rock structures provided for the implementation of the present invention. Refer to Figure 1 As shown, the above-mentioned method for evaluating the impact hazard of a working face based on the transient impulse of coal and rock structures may include:

[0046] S101, obtaining the geological data of the target working face and determining the area to be evaluated of the working face;

[0047] Among them, the area to be evaluated of the working face is the high-stress concentration area of the working face;

[0048] In some embodiments, the geological data of the target working face includes but is not limited to the thickness of coal and rock layers, lithology, bulk density, information on the breakage step distance of overlying rocks, mechanical parameters of mine coal and rock, borehole columnar diagrams, and working face operation regulations information;

[0049] Among them, the thickness of coal and rock layers records in detail the thickness of the coal seam and overlying rock layers of the target working face, which is the basis for evaluating the stability of the overlying rock space structure and calculating static load data. Lithology is used to understand the lithological characteristics of the coal seam and overlying rocks, including the hardness, strength, etc. of the rocks. Bulk density includes the bulk density of the coal seam and overlying rocks, which is used to calculate the original rock stress and the abutment pressure of the working face. The breakage step distance of overlying rocks is estimated according to geological data and mining experience, that is, the distance at which the overlying rocks break during mining. The mechanical parameters of mine coal and rock include the tensile strength, compressive strength, elastic modulus, etc. of the rocks. These data are of great significance for understanding the stress state of the rock mass, evaluating the mining stability, and designing a reasonable mining layout. The borehole columnar diagram is a chart obtained through geological drilling that intuitively shows the stratigraphic structure, which details the distribution and characteristics of all rock layers from the surface to the target coal seam, and is an important basis for geological analysis, resource assessment, and mining planning. The working face operation regulations information includes the mining process, safety operation procedures, disaster emergency plans, etc. for a specific working face, ensuring the efficient and safe progress of mining operations.

[0050] It can be understood that during the mining process of coal mines or other mineral resources, as the area where mining operations are directly carried out, the geological conditions and mining activities of the working face will have an important impact on the stability of the working face. When there is high stress concentration in the working face, it may cause changes in the mechanical properties of rocks or coal seams, thereby weakening their original strength. This stress state will directly act on the rocks or coal seams, possibly resulting in a decrease in their physical strength. Once the strength of the rocks or coal seams is weakened, the risks of surrounding rock disasters such as overlying rock fracture and fault slip will increase accordingly. Therefore, in the embodiments of the present invention, these high stress concentration areas can be determined as the areas to be evaluated in the working face.

[0051] S102. Determine the first stress of the area to be evaluated in the working face before the transient change of the coal-rock structure according to on-site monitoring and a preset numerical calculation method;

[0052] Wherein, the first stress is the stress state of the working face to be evaluated before the transient change of the coal-rock structure;

[0053] Specifically, the above step S102 may include:

[0054] S1021. Measure the third stress at the working face site before the transient change of the overlying rock spatial structure by the hollow inclusion stress relief method; wherein, the measuring points are arranged along the return airway of the target working face; wherein, the third stress is the stress state of the working face site to be evaluated before the transient change of the coal-rock structure;

[0055] Among them, the hollow inclusion stress relief method is a commonly used stress measurement method. It drills holes at the measuring point positions in the return airway of the target working face and installs hollow inclusion stress gauges, and then gradually relieves the rock stress around the inclusion, and uses the reading changes of the stress gauges to calculate the magnitude and direction of the stress in the rock. The selection of the measuring points can be based on in-depth analysis of the geological structure, mining activities and potential impact hazard areas of the working face to ensure that the measuring points can comprehensively reflect the stress state of the working face. Arranging the measuring points along the return airway of the target working face can ensure the representativeness and accuracy of the data. The measuring point spacing can be determined based on the actual situation of the working face, or the measuring point spacing can also be determined according to experience. For example, the measuring point spacing can be 15 m, or it can also be other commonly used measuring point spacing values. The selection of the measuring point spacing does not limit the protection scope of the embodiments of the present invention, and the embodiments of the present invention do not specifically limit this.

[0056] Through the above hollow inclusion stress relief method, on-site monitoring of the target working face can be directly carried out, and the on-site stress data of the target working face, that is, the above-mentioned third stress, can be directly measured.

[0057] S1022. Based on the discrete element numerical software and the geological data of the target working face, construct a numerical calculation model, optimize and correct the mechanical parameters of the mine coal and rock, and assign the corrected mechanical parameters to the numerical calculation model to make the numerical calculation model in an equilibrium state;

[0058] S1023. Set the excavation steps according to the working face operation regulations information to simulate the mining disturbance effect of the working face;

[0059] S1024. By pre-arranging measuring lines in the numerical calculation model, monitor the fourth stress of the working face before the transient change of the coal and rock structure during the mining process;

[0060] Wherein, the fourth stress is the stress state before the transient change of the coal and rock structure in the numerical model;

[0061] Wherein, the arrangement of the measuring lines can be based on the analysis of the geological structure and mining activities of the working face to ensure that the stress state change of the working face can be comprehensively reflected. Through the real-time monitoring function of the above discrete element numerical software, the stress data of each point on the measuring line during the mining process can be recorded in real time to obtain the above fourth stress.

[0062] S1025. Use the preset mathematical software to fit and correct the third stress and the fourth stress to obtain the first stress.

[0063] Wherein, the preset mathematical software can be any existing mathematical software such as MATLAB, Python, etc. Taking MATLAB as an example, use the least squares polynomial fitting in MATLAB to fit and correct the third stress measured on site and the fourth stress obtained by the above numerical calculation. Considering the on-site measured data and the numerical calculation results comprehensively to obtain a more accurate first stress value.

[0064] S103. According to the preset numerical calculation method and physical similarity simulation experiment, comprehensively determine the second stress of the area to be evaluated on the working face after the transient change of the coal and rock structure;

[0065] Wherein, the second stress is the stress state of the area to be evaluated on the working face after the transient change of the coal and rock structure;

[0066] Specifically, the above step S103 may include:

[0067] S1031. Preprocess the numerical calculation model to achieve the instantaneous fracture of the hard rock stratum, and monitor the fifth stress of the area to be evaluated on the working face after the transient change of the overlying rock space structure in the numerical calculation model through the measuring line;

[0068] Among them, the fifth stress is the stress state of the area to be evaluated in the working face after the transient change of the coal-rock structure in the numerical model. The numerical calculation model can be the numerical calculation model constructed in the above step S102, and the instantaneous fracture process of the hard rock stratum is simulated through this calculation model. Multiple measuring lines are set in the model as described above to monitor the change of the stress state of the working face after the transient change of the coal-rock structure. Through numerical calculation, the stress values of each point on the measuring line are obtained, so as to obtain the fifth stress of the area to be evaluated in the working face after the transient change of the coal-rock structure in the above numerical calculation model.

[0069] S1032. According to the geological data of the target working face, lay a physical similarity experiment model according to a preset geometric similarity ratio.

[0070] Among them, the geometric similarity ratio can be determined according to the size of the model, the mechanical properties of the material, and the experimental purpose in actual application. According to the geometric similarity ratio, lay a physical similarity experiment model using similarity materials including but not limited to sand, gypsum, white powder, fly ash, etc., and make the model accurately reflect the actual geological structure and mining conditions as much as possible.

[0071] S1033. Simulate the compensation load by laying heavy objects on the top of the physical similarity experiment model, and lay stress sensors at the bottom of the model to monitor the stress of the working face during the mining process.

[0072] Among them, the size of the compensation load is determined by the thickness and unit weight of the coal and rock strata; the heavy object can be any existing material, such as iron bricks, loading oil cylinders, etc.

[0073] S1034. According to the working face operation regulations information, carry out mining of the working face in the physical similarity experiment model, and use stress sensors to monitor the sixth stress of the working face after the transient change of the coal-rock structure in the physical similarity experiment model.

[0074] Among them, the sixth stress is the stress state of the area to be evaluated in the working face after the transient change of the coal-rock structure in the similarity simulation.

[0075] S1035. Use mathematical software to fit and correct the fifth stress and the sixth stress to obtain the second stress.

[0076] Among them, the second stress is the stress state of the area to be evaluated in the working face after the transient change of the coal-rock structure.

[0077] The process of fitting and correction can use the same mathematical software as in the above step S102. For example, use the least squares polynomial fitting in MATLAB to fit and correct the fifth stress of the working face after the transient change of the coal-rock structure monitored in the numerical calculation model and the sixth stress of the working face after the transient change of the coal-rock structure monitored in the physical similarity experiment model, so as to obtain the second stress of the area to be evaluated in the working face after the transient change of the coal-rock structure.

[0078] S104. Calculate the impact stress on the working face under the transient excitation of the coal-rock structure according to the first stress and the second stress;

[0079] Specifically, the instantaneous fracture of the hard rock stratum triggers the transient change of the overlying rock spatial structure, causing the uncollapsed rock stratum to unload and rebound to release strain energy, forming a dynamic load, and inducing the dynamic response of the coal and rock in the stope, that is, the sudden change of the load acting on the coal body, forming an impact stress. At the same time, before and after the roof weighting, due to the transient change of the overlying rock spatial structure, the step change of the static mechanical response within its influence range is caused.

[0080] Based on the concept of the static and dynamic method of material mechanics, combined with the above first stress and second stress, it is determined that the maximum impact stress acting on the coal body during the transient change of the overlying rock spatial structure is 2 times the stress step change amount. Therefore, the impact stress on the working face under the transient excitation of the above overlying rock spatial structure can be expressed by the following formula (1):

[0081] P d (x,y) = 2[P2(x,y) - P1(x,y)] (1)

[0082] Wherein, P d (x,y) is the impact stress on the working face under the transient excitation of the overlying rock spatial structure, P2(x,y) is the second stress in the impact risk area of the working face after the transient change of the overlying rock spatial structure, and P1(x,y) is the first stress in the impact risk area of the working face before the transient change of the overlying rock spatial structure.

[0083] S105. Establish an impact risk evaluation index for the impact risk area of the working face according to the first stress and the impact stress on the working face;

[0084] In some embodiments, the above step S105 may include:

[0085] S1051. Determine the maximum stress acting on the coal body instantaneously during the transient change process according to the first stress before the structural transient change and the impact stress on the working face during the structural transient change; the maximum stress P(x,y) can be expressed by the following formula (2):

[0086] P(x,y) = P1(x,y) + P d (x,y) (2)

[0087] S1052. Construct an impact risk evaluation index for the impact risk area according to the maximum stress; the impact risk evaluation index can be expressed by the following formula (3):

[0088]

[0089] Wherein, Q s is the impact risk evaluation index, [σ cis the stress of coal mass impact failure, [σ c can be determined by the geological data of the target working face.

[0090] S106. According to the impact risk evaluation index, the impact risk of the area to be evaluated on the working face is evaluated and divided.

[0091] It should be noted that according to the impact risk evaluation index Q s , as the stress step change amount of the area to be evaluated on the working face before and after the transient change of the coal-rock spatial structure increases, the maximum stress P(x,y) acting on the coal mass during the structural transient change increases accordingly, and the impact risk of the working face rises. When Q s is less than 1, the impact risk of the working face decreases. When Q s exceeds 1, the impact risk of the working face rises.

[0092] In some embodiments, the above step S106 may include:

[0093] S1061. Divide the impact risk evaluation index into four levels based on the equal division principle;

[0094] S1062. According to the calculation result of the impact risk evaluation index, conduct impact risk level division on the impact risk area.

[0095] Exemplarily, the impact risk level division of the impact risk area can be expressed by the following formula (4):

[0096]

[0097] In the embodiment of the present invention, from the perspective of the overlying rock spatial structure, a method for evaluating the impact risk of the working face is proposed, which reduces the influencing factors to be considered during the evaluation of the impact risk of the working face, reduces the difficulty of impact risk evaluation, has wide applicability for the impact risk evaluation of mines with different engineering geological conditions, and ensures the safe production of the working face; in addition, when calculating the stress state of the area to be evaluated on the working face before and after the transient change of the coal-rock structure, various methods such as on-site monitoring, numerical calculation, and physical similarity simulation experiments are used to fit and correct the calculation results. The calculation process is simple, easy to operate, and the calculation results can more accurately reflect the distribution characteristics of the stress state of the working face before and after the transient change of the coal-rock structure, significantly improving the accuracy of the impact risk evaluation of the working face. Compared with the existing impact risk evaluation methods, starting from the concept of the dynamic and static mechanical responses of the stope induced by the transient change of the coal-rock structure, the present invention designs a method for evaluating the impact risk of the working face by calculating the mining-induced stress of the working face before the transient change of the coal-rock structure and the impact stress of the working face under the excitation of the structural transient change, realizing the progress of the concept of preventing rock bursts in the working face.

[0098] The method of the present invention will be described below with a specific embodiment:

[0099] Aiming at the problem that the influencing factors of impact risk assessment in the prior art cannot fully correspond to the occurrence of rock bursts in the stope, the present invention provides a method for evaluating the impact risk of the working face under the transient excitation of the coal-rock structure. By calculating the stress in the impact risk area of the working face before and after the transient of the coal-rock structure, determining the maximum stress acting on the coal body instantaneously during the transient process of the structure, and constructing an evaluation index for the impact risk of the working face, the accuracy of the evaluation result of the impact risk of the working face during the mining process is improved.

[0100] Exemplarily, the present invention is described with the existing actual longwall fully-mechanized mining W1143 working face in a mine as the background. The main coal seam mined in the working face is the B4-1 coal seam, with a mining height of 3 m, a coal seam burial depth of 317 m, a strike length of 1495 m, a dip length of 162 m, and a coal seam dip angle of 10°-16°, with an average dip angle of 13°. At the initial stage of the mining of the W1143 working face, affected by the goaf of the adjacent working face W1141, it is in a high-stress concentration state. In the middle and later stages of the mining of the W1143 working face, affected by the superposition of the goaf of the overlying pre-B4-2 coal seam W114(2)3 and the goaf of the W1141, the stress concentration degree of the working face is further increased, and rock bursts are likely to occur. The mining plan of the working face can be seen Figure 2 as shown. Figure 2 It is a mining plan of the working face in the embodiment of the present invention. The specific evaluation process can be seen in the following steps:

[0101] S1. Collect the geological data of the W1143 working face on site, including data such as the thickness, lithology, bulk density, information on the breakage step distance of the overlying strata, the mechanical parameters of the mine coal and rock, the borehole columnar diagram, and the working face operation regulations information, etc., to determine the high-stress concentration area of the working face. Based on the on-site borehole coring, multiple groups of standard coal and rock specimens are made, and point load experiments, uniaxial compressive experiments, uniaxial tensile experiments, etc. are carried out based on the indoor rock mechanics testing machine to obtain the physical and mechanical properties of the coal and rock.

[0102] The specific implementation steps of the above step S1 include:

[0103] S11. Make standard specimens of the immediate roof, main roof, immediate floor, main floor, and coal seam based on the on-site borehole coring method. Among them, multiple groups of specimens can be made for each coal and rock layer, for example, 5 groups.

[0104] S12. Through the coal and rock specimens made in step S11, carry out point load experiments, uniaxial compressive experiments, uniaxial tensile experiments, and splitting experiments, with 5 groups for each experiment, measure the mechanical parameters such as the uniaxial compressive strength, uniaxial tensile strength, and shear strength of the coal and rock layers, and optimize and correct the obtained mechanical parameters based on the average principle to obtain the final mechanical parameters of the coal and rock.

[0105] Furthermore, to obtain better coal and rock mechanical parameters, the number of rock mechanics experiments can be adjusted according to the test results.

[0106] S13. Measure the in-situ third stress of the working face before the transient change of the coal and rock structure by the hollow inclusion stress relief method, denoted as P 11 (x, y), and determine the high stress concentration area of the working face. Among them, the measuring points are arranged along the return airway of the working face, and the positions of the measuring points can be adjusted according to actual requirements. In the embodiment of the present invention, the distance between the measuring points can be 15 m.

[0107] S14. Determine the area to be evaluated of the working face according to the in-situ stress monitoring data measured in step S13. For example, in the embodiment of the present invention, the area to be evaluated of the working face can be 50 m around the working face.

[0108] S2. Obtain the first stress of the impact hazard area of the working face before the transient change of the coal and rock structure through on-site monitoring and numerical calculation, denoted as P1(x, y). The specific implementation steps include:

[0109] S21. According to the collected mine geological data, establish a numerical model by discrete element numerical software. The model size is 500 m × 300 m × 180 m, as Figure 3 shown, Figure 3 which is a numerical model diagram in the embodiment of the present invention. Displacement boundary conditions are adopted for the front, rear, left, right, and lower surfaces of the numerical model, and stress boundary conditions are applied to the top. According to the dichotomy principle, the coal and rock mechanical parameters in step S12 are corrected and optimized, and the corrected mechanical parameters are added to the numerical model and balanced calculation is performed to generate an initial state stress model.

[0110] S22. According to the working face operation regulations obtained in step S1, perform simulated excavation calculation on the numerical model in step S21 to simulate the excavation effect of the working face.

[0111] S23. Write a survey line program according to the built-in fish language of the software, and arrange the survey line above the coal seam to extract the fourth stress of the working face before the transient change of the overlying rock spatial structure, denoted as P 12 (x, y).

[0112] S24. Import the P 11 (x, y) and P 12 (x, y) obtained in steps S13 and S23 into the matlab mathematical software, and based on the least squares polynomial fitting function in the software, perform fitting correction on P 11 (x, y) and P 12 (x, y) to obtain the stress P1(x, y) of the area to be evaluated of the working face before the transient change of the coal and rock structure.

[0113] In the embodiments of the present invention, the stress state at the stage before the first weighting and the periodic weighting of the working face can be selected as the stress state before the transient change of the coal-rock structure, and the final correction result can be as Figure 4 and Figure 5 shown by the curve before weighting. Among them, Figure 4 is the distribution curve of mining stress and impact stress before and after the first weighting in the embodiments of the present invention, Figure 5 is the distribution curve of mining stress and impact stress before and after the periodic weighting in the embodiments of the present invention.

[0114] S3. By means of numerical calculation and similarity simulation analysis methods, obtain the second stress of the area to be evaluated on the working face after the transient change of the coal-rock structure, denoted as P2(x,y). The specific implementation steps include:

[0115] S31. Based on fish language programming, search for the joint position with the maximum tensile stress of the hard rock formation in the stope during the advancement of the numerical model working face in step S21, and judge whether the tensile stress exceeds the ultimate strength value of the rock mass. If it exceeds this value, set parameters such as the tensile strength, cohesion, and internal friction angle of the joint at this position to 0 to achieve the instantaneous fracture of the hard rock formation. The preset maximum tensile stress value of the hard rock formation can be determined by querying the mine geological data in step S1.

[0116] S32. According to the survey line arranged in step S23, extract the fifth stress of the area to be evaluated on the working face after the transient change of the coal-rock structure, denoted as P 21 (x,y).

[0117] S33. Design the geometric similarity constant according to the mine geological conditions in step S1, and lay the physical similarity experimental model. In the embodiments of the present invention, the geometric similarity ratio can be 1:100. Similar materials can be selected as river sand, fly ash, gypsum, and white powder, etc. The size of the similar model rack can be 300cm×20cm×140cm. At the same time, lay sensors at the bottom of the model. The size of the sensor can be 20cm×3.5cm×4cm. Lay iron bricks at the top of the model to simulate the overlying rock load. The overlying rock load can be determined by the borehole columnar diagram and the thickness of the coal and rock layers in step S1. The assembled model is as Figure 6 shown, Figure 6 which is the physical similarity simulation experimental diagram in the embodiments of the present invention.

[0118] S34. Set the working face advancement step distance and roadway size according to the working face operation regulations and geometric similarity ratio in step S1, and simulate the working face excavation after the model is air-dried.

[0119] S35. Through the stress sensors laid in step S33, monitor the sixth stress of the working face after the transient change of the coal-rock structure, denoted as P 22 (x,y). And compare it with P in step S32 21(x, y) are jointly imported into the data processing software, and the function of least squares polynomial fitting in the software is used to process P 21 (x, y) and P 22 (x, y) are fitted and corrected to determine the working face stress P2(x, y) after the transient change of the coal and rock structure.

[0120] In the embodiment of the present invention, the stress distribution states after the first weighting and the periodic weighting can be selected as the stress distribution states after the transient change of the coal and rock structure, and the correction results can also refer to the above Figure 4 and Figure 5 as shown by the weighting distribution curve.

[0121] S4. Determine the impact stress P d (x, y) of the working face under the action of the transient change of the coal and rock structure, specifically including:

[0122] S41. Determine the stress evolution mechanism of the coal body in the stope under the excitation of the transient change of the coal and rock structure;

[0123] Specifically, during the coal mining process of the working face, the overlying rock load above the goaf transfers to the surrounding of the stope, resulting in the increase of the local mining-induced stress at different positions in the stope. As Figure 7 shown, Figure 7 is the stress distribution diagram of the coal body around the stope during the coal mining process in the embodiment of the present invention. The instantaneous fracture of the hard rock layer triggers the transient change of the overlying rock spatial structure. The uncollapsed rock layer unloads and rebounds to release strain energy, forming a dynamic load, and inducing the coal and rock in the stope to produce a dynamic response. The load acting on the coal body changes suddenly, forming an impact stress. After the roof weighting, the amount of overlying rock load transferred to the coal body around the stope decreases, and the working face stress evolves from P1(x, y) in step S24 to P2(x, y) in step S35. The evolution process is as Figure 8 shown, Figure 8 is the schematic diagram of the superposition of mining-induced stress and impact stress before and after the transient change of the overlying rock spatial structure in the embodiment of the present invention. The maximum stress acting on the coal body instantaneously is the superposition of the impact stress of the working face during the transient change of the coal and rock structure and the mining-induced stress before the transient change, as Figure 8 shown by P(x, y).

[0124] S42. Calculate the formula for the maximum impact stress of the coal body under the excitation of the structural transient change;

[0125] Specifically, the stress characteristics of the coal body during the structural transient change are as Figure 9 shown, Figure 9 is the stress diagram of the coal body during the transient change of the overlying rock spatial structure in the embodiment of the present invention. It is approximately considered that the initial velocity of the coal body before and after the structural transient change is 0, and the strain energy U of the coal body before the structural transient change is obtained ft , the kinetic energy W before and after the result transient change k and the deformation amount ΔL of the coal body under the action of the mining-induced stress P1(x, y) ftThe score can be expressed by the following formula (5):

[0126]

[0127] Wherein, L0 is the mining height of the coal seam, in m; E is the elastic modulus of the coal body, in kN / m 2 ; S0 is P d (x, y) acting on the unit area of the coal body, in m 2 . According to the principle of conservation of energy, the reduced kinetic energy W k and potential energy W p of the coal body during the impact process are equal to the increased strain energy U εd of the coal body, and can be expressed by the following formula (6):

[0128] W k + W p = U εd (6)

[0129] During the structural transient process, under the impact load P d (x, y) (the impact stress of the working face under the action of the transient excitation of the coal-rock structure), the maximum deformation ΔL of the coal body and the strain energy U stored at the maximum deformation ΔL of the coal body lt and the reduced potential energy W p can be expressed by the following formula (7):

[0130]

[0131] Wherein, L0 is the mining height of the coal seam, ΔP d (x, y) is the maximum impact load; ΔP(x, y) is the step-changing load before and after the transient of the coal-rock structure.

[0132] According to the strain energy U ft of the coal body before impact in the above formula (5), and the strain energy U lt stored at the maximum deformation ΔL of the coal body in the formula (7), the newly added strain energy U εd in the coal body can be obtained and can be expressed by the following formula (8):

[0133]

[0134] Substituting ΔL ft in the formula (5) and ΔL in the formula (7) into the formula (8), the following formula (9) can be obtained:

[0135]

[0136] According to the kinetic energy W k in the formula (5) and W pSubstituting the formula (9) into the formula (6), the maximum impact load P on the coal body can be obtained d (x, y) can be expressed by the following formula (10):

[0137]

[0138] S43, the calculation of the maximum stress on the upper coal body during instantaneous action, includes:[[]]

[0139] According to steps S24 and S35, determine the distribution characteristics of the mining stress on the working face before and after the structural transient, and calculate the impact stress during the structural transient. Specifically, substitute the corrected working face pressure data P2(x, y) and P1(x, y) into formula (10) to calculate and determine the maximum impact stress P on the coal body during the structural transient process d (x, y). In the embodiment of the present invention, the impact stresses during the first weighting and periodic weighting are calculated as Figure 4 and Figure 5 shown in the impact stress curve.

[0140] S5, establish an evaluation index for the impact hazard area of the working face. The specific steps include:[[]]

[0141] S51, substitute the stress P1(x, y) calculated in step S24 before the structural transient and the stress P d (x, y) calculated in step S43 before the structural transient into the following formula (11), and the maximum stress acting on the coal body instantaneously during the structural transient of the overlying strata space structure can be obtained. In the implementation of the present invention, the maximum stress acting on the working face coal body during the first weighting and periodic weighting is calculated, as Figure 10 shown,[[]] Figure 10 which is the distribution curve of the maximum stress acting on the coal body instantaneously under the excitation of the coal-rock structure transient in the embodiment of the present invention.

[0142] P(x, y) = P1(x, y) + P d (x, y) (11)

[0143] S52, according to the maximum pressure acting on the coal body instantaneously calculated in the above formula (11), obtain the evaluation index P s of the impact hazard of the working face, which can be expressed by the following formula (12):

[0144]

[0145] where, [σ c can be determined by the optimized uniaxial compressive strength R c of the coal body in step S12. The calculation method can be expressed by the following formula (13):

[0146] [σ c= 2Rc (13)

[0147] S53. According to the maximum impact stress acting on the coal body during the first weighting and periodic weighting calculated in step S52, substitute it into formula (12) to determine the impact risk index P of the working face s .

[0148] S54. Repeat step S53 to calculate the impact risk evaluation index P for the remaining advancing stages of the W1143 working face s , and divide the impact risk area of the W1143 working face in combination with the following formula (14). The division results are as Figure 11 shown Figure 11 Impact risk evaluation equivalent division diagram in the embodiment of the present invention

[0149]

[0150] The various embodiments in this specification are described in a progressive manner. For the same or similar parts between the various embodiments, reference can be made to each other. The key points of each embodiment are the differences from other embodiments

[0151] The above embodiments are only used to illustrate the technical solutions of the present application, rather than limiting the present application; although the present application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the present application

Claims

1. A method for evaluating the impact hazard of a working face based on the transient induced impulse of coal and rock structure, characterized in that, Including: Obtain geological data of the target working face and determine the area to be evaluated on the working face; the area to be evaluated is the high-stress concentration area of the working face; According to on-site monitoring and a preset numerical calculation method, determine the stress state of the area to be evaluated on the working face before the transient change of the coal-rock structure; define the stress state before the transient change of the coal-rock structure as the first stress before the transient change of the coal-rock structure; According to the preset numerical calculation method and physical similarity simulation experiment, determine the stress state of the area to be evaluated after the transient change of the coal-rock structure; Define the stress state after the transient change of the coal-rock structure as the second stress after the transient change of the coal-rock structure; Calculate the impact stress on the working face under the excitation of the transient change of the overlying rock space structure according to the first stress before the transient change of the coal-rock structure and the second stress after the transient change of the coal-rock structure; Establish an impact risk assessment index for the area to be evaluated on the working face according to the stress state before the transient change of the coal-rock structure and the impact stress on the working face; Conduct an impact risk assessment and classification for the area to be evaluated on the working face according to the impact risk assessment index; 2. The method according to claim 1, wherein The geological data of the target working face includes, but is not limited to, the thickness of coal and rock layers, lithology, bulk density, information on the breaking step distance of overlying rocks, mechanical parameters of mine coal and rock, borehole columnar diagrams, and working face operation regulations information; 3. The method according to claim 2, characterized in that, The step of determining the stress state of the area to be evaluated on the working face before the transient change of the coal-rock structure according to on-site monitoring and a preset numerical calculation method includes: Determine the stress state of the area to be evaluated on the working face before the transient change of the coal-rock structure by the hollow inclusion stress relief method, where the measuring points are arranged along the return airway of the target working face; define the stress state of the area to be evaluated on the working face before the transient change of the coal-rock structure as the third stress; Based on the discrete element numerical software and the geological data of the target working face, construct a numerical calculation model, optimize and correct the mechanical parameters of mine coal and rock, and assign the corrected mechanical parameters to the numerical calculation model to make the numerical calculation model in a balanced state; Set the excavation steps according to the working face operation regulations information and simulate the mining disturbance effect of the working face; By pre-arranging measuring lines in the numerical calculation model, monitor the stress state of the area to be evaluated during the transient change of the coal-rock structure during the mining process, and define the stress state of the area to be evaluated on the working face before the transient change in the numerical simulation as the fourth stress; Use a preset mathematical software to fit and correct the third stress and the fourth stress before the transient change of the coal-rock structure to obtain the first stress before the transient change of the coal-rock structure; 4. The method according to claim 3, characterized in that, The step of determining the stress state of the area to be evaluated after the transient change of the coal-rock structure according to the preset numerical calculation method and physical similarity simulation experiment includes: Perform preprocessing on the numerical calculation model to achieve the instantaneous fracture of hard rock layers, and monitor the stress state of the area to be evaluated after the transient change of the coal-rock structure in the numerical calculation model through the measuring lines; define the stress state of the area to be evaluated on the working face after the transient change in the numerical simulation as the fifth stress; Lay a physical similarity experimental model according to the preset geometric similarity ratio according to the geological data of the target working face; The compensation load is simulated by laying heavy objects on the top of the physical similarity experiment model, and stress sensors are laid at the bottom of the model to monitor the working face stress during the mining process; wherein, the magnitude of the compensation load is determined by the thickness and unit weight of the coal and rock strata; According to the working face operation regulation information, the working face is mined in the physical similarity experiment model, and the stress sensor is used to monitor the stress state of the to-be-evaluated area of the working face after the transient change of the coal and rock structure in the physical similarity experiment model; the stress state of the to-be-evaluated working face after the transient change of the coal and rock structure in the physical similarity simulation is defined as the sixth stress; The fifth stress and the sixth stress are fitted and corrected by using a preset mathematical software to obtain the second stress of the to-be-evaluated area of the working face after the transient change of the coal and rock structure.

5. The method according to claim 4, wherein The impact stress of the working face under the excitation of the transient change of the coal and rock structure is expressed as: P d (x,y) = 2[P2(x,y) - P1(x,y)], Among them, P d (x, y) is the impact stress of the working face in the area to be evaluated under the transient excitation of the coal-rock structure, P2(x, y) is the second stress of the area to be evaluated on the working face after the transient change of the coal-rock structure, and P1(x, y) is the first stress of the area to be evaluated before the transient change of the coal-rock structure.

6. The method according to claim 5, wherein Based on the first stress of the transient change of the coal and rock structure and the to-be-evaluated impact stress of the working face during the transient change of the coal and rock structure, the impact risk assessment index of the to-be-evaluated impact risk area of the working face is established, including: According to the first stress before the transient change of the coal and rock structure and the to-be-evaluated impact stress of the working face, the maximum stress acting on the coal body instantaneously during the transient change of the coal and rock structure is determined; the maximum stress is expressed as: P(x,y) = P1(x,y) + P d (x,y), According to the maximum stress, the impact risk assessment index of the to-be-evaluated area of the working face is constructed; the impact risk assessment index is expressed as: Among them, Q s is the impact risk evaluation index, and [σ c is the impact failure stress of the coal body, which is determined by the geological data of the target working face.

7. The method according to claim 6, characterized in that, According to the impact risk assessment index, the impact risk assessment and division of the to-be-evaluated area of the working face are carried out, including: The impact risk assessment index is divided into four grades based on the equal division principle; According to the calculation result of the impact risk assessment index, the impact risk grade of the to-be-evaluated area of the working face is divided.

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