Method for evaluating impact risk of multi-face adjacent goaf working face of rock burst-free coal seam

Abstract

The invention discloses a non-impact ground pressure coal seam multi-face adjacent goaf working face impact risk evaluation method. The method comprises the following steps of 1, obtaining mine data; 2, judging that the rock burst attribute of the mined coal seam is a rock burst-free coal seam; 3, judging that the to-be-evaluated region belongs to a multi-surface adjacent goaf; 4, evaluating the impact risk of the multi-face adjacent goaf working face of the non-impact ground pressure coal seam; according to the method for judging the multi-face adjacent gob-side working face of the rock burst-free coal seam, after it is judged that the target area conforms to the multi-face adjacent gob-side working face of the rock burst-free coal seam, the impact danger is evaluated from the macroscopic perspective through a comprehensive index method, a possibility index method and the like, and the risk of the rock burst-free coal seam is judged. And then, a multi-factor stress superposition impact risk evaluation method and numerical simulation are adopted to evaluate the impact risk under special geology and mining conditions, and guidance is provided for impact risk evaluation of the multi-face adjacent goaf working face of the rock burst-free coal seam.

Description

Technical Field

[0001] The invention belongs to the technical field of coal mining safety, and in particular provides a method for evaluating the impact hazard of multi-faceted adjacent working faces in a coal seam without impact ground pressure. Background Art

[0002] In the case of mines without rock burst or without the conditions for starting the rock burst tendency assessment of coal seams (roof and floor strata), no forward-looking work was carried out in the early stages of production from the perspective of optimizing mining design, such as mining deployment, mining sequence, and coal pillar retention. Consequently, isolated coal pillars or even areas surrounded by goafs on three or four sides were inevitably formed. In my country, there are many mines without rock burst and coal seams without rock burst that still need to mine isolated coal pillars now or in the future. Article 37 of the "Detailed Rules for Preventing and Controlling Rock Burst" clearly stipulates that "when mining or recovering coal pillars in areas surrounded by goafs on three or four sides of coal seams without rock burst, an impact hazard assessment must be conducted, special anti-rock burst measures must be formulated, and expert review must be organized before mining can take place."

[0003] Common methods for assessing rockburst hazard include comprehensive index, multi-factor coupling, geodynamic zoning, probability index, and numerical simulation. Currently, Chinese scholars' research on rockburst hazard assessment for multi-faceted adjacent working faces mostly uses rockburst hazard assessment methods for rockburst coal seams, which can lead to inaccurate evaluation results. The engineering and technical challenges of determining which working faces in non-rockburst coal seams require rockburst hazard assessment and whether the results can ensure safe mining remain largely empirical, lacking effective theoretical support.

[0004] Therefore, it is necessary to propose an effective method for assessing the impact hazard of multi-faceted adjacent working faces in coal seams without impact ground pressure. Summary of the Invention

[0005] In order to solve the above problems, the present invention provides a method for assessing the impact hazard of multi-sided adjacent working faces in a coal seam without impact ground pressure.

[0006] To achieve the above object, the present invention adopts a technical solution: a method for assessing the impact hazard of multi-faceted adjacent working faces in a coal seam without impact ground pressure, comprising the following steps:

[0007] Step 1: Obtain mine information;

[0008] Step 2: determining the rock burst attribute of the mined coal seam to be a rock burst-free coal seam;

[0009] Step 3: determine whether the area to be evaluated belongs to the multi-faceted adjacent goaf area;

[0010] Step 4: Conduct a preliminary assessment of the rock burst hazard of the multi-faceted working faces of the coal seams without rock burst for the area to be assessed that has both rock burst hazard and multi-faceted adjacent goafs, and conduct a review based on the preliminary assessment results.

[0011] Step five: Take special prevention and control measures according to the level of danger.

[0012] Furthermore, in step one, the mine data includes coal rock mechanical properties, mining depth, overburden structure, geological structure, mining technical conditions, impact tendency, mining stress field, and coal rock structure.

[0013] Furthermore, in step 2, the rock burst attribute of the mined coal seam is determined to be a rock burst-free coal seam based on the absence of any of the following circumstances:

[0014] a. Rock burst has occurred during coal seam mining;

[0015] b. Impact hazard assessment shows that the device has impact hazard;

[0016] c. The coal seam impact tendency assessment should be conducted but the impact hazard assessment has not been conducted or the assessment shows that there is no impact rock pressure hazard;

[0017] d. The coal seam is buried more than 400m deep;

[0018] e. There is a hard rock layer above the coal seam.

[0019] Furthermore, in step 3, the determination of the multiple adjacent goafs is that there are multiple adjacent goafs in the plane of the area to be mined and the width of the coal pillar between the area to be mined and the adjacent goafs is smaller than the width of the plastic zone on the side of the goaf;

[0020] The calculation formula for the width of the plastic zone on the goaf side is:

[0021]

[0022] in:

[0023] x0 is the width of the plastic zone on the goaf side, in m;

[0024] m is the thickness of the coal seam, in m;

[0025] λ is the lateral pressure coefficient;

[0026] ρ is the average density of the overlying rock layer, unit is t / m 3 ;

[0027] H is the depth of coal seam, in m;

[0028] α is the coal seam inclination;

[0029] K is the lateral support stress concentration factor;

[0030] τ is the cohesion of coal body;

[0031] is the internal friction angle of the coal body;

[0032] N is the supporting capacity of the coal wall, unit is MPa.

[0033] Furthermore, in step four, the preliminary evaluation of the rock burst hazard of the multi-sided adjacent working faces of the coal seam without rock burst is carried out using the comprehensive index method and the rock burst occurrence possibility index diagnosis method, and the preliminary evaluation results are no rock burst hazard, weak rock burst hazard, moderate rock burst hazard and strong rock burst hazard.

[0034] Furthermore, in step 4, the evaluation review includes the following contents:

[0035] If the preliminary assessment result shows that there is no ground pressure impact hazard, the safety level can be directly determined as no impact hazard;

[0036] If the preliminary assessment result indicates a weak rock burst hazard, the rock burst hazard assessment method using multiple factors and the numerical simulation method will be used to assess the rock burst hazard, and the latter result will be used as the final result to determine the safety level as no rock burst hazard or a "weak" level.

[0037] If the preliminary evaluation result is a moderate rock burst hazard or a strong rock burst hazard, the multi-factor coupling analysis method is used to analyze the influencing factors of rock burst in the area, superimpose the influence of geological and mining factors on the rock burst hazard, and finely divide the rock burst hazard level of the evaluation area. The safety level is determined by superimposing and coupling the multi-factor rock burst hazard levels to obtain "weak", "medium" and "strong" levels.

[0038] Furthermore, the multi-factor coupling analysis method sequentially performs the following steps:

[0039] a. Analyze the factors affecting rock burst hazards in various areas;

[0040] b. Determine the rock burst hazard level as one of no rock burst hazard, weak rock burst hazard, moderate rock burst hazard, and strong rock burst hazard based on the impact of each single factor on rock burst;

[0041] c. The final hazard level of the area is obtained by superimposing and coupling the hazard levels of multiple factors;

[0042] d. Once the hazard levels of all areas are determined, the hazard levels of the evaluation areas will be carefully delineated on the mining project plan using different legends and colors.

[0043] Furthermore, the factors affecting rock burst risk include the following:

[0044] Fault areas with a drop greater than 3m and less than 10m; folds with drastic changes in coal seam inclination; parts of coal seam erosion and merging or thickness changes; areas with changes in roof and floor lithology; areas below coal pillars left over from mining of the upper protective layer; areas with a drop greater than 10m for faults or fault groups; working faces advancing into goafs; areas with irregular working faces or multiple working faces where the openings and stop lines are not aligned; tunnel intersection areas; coal pillars along goafs; working face advance support pressure areas; near the initial pressure position of the old roof; "square" areas in the goaf of the working face; areas with retained bottom coal; and areas disturbed by mining.

[0045] Furthermore, the principle of superposition and coupling of the multiple factors of rock burst hazard level is:

[0046] 1. Areas assessed as having no impact risk by the comprehensive index method do not need to be divided into different zones or grades;

[0047] 2. When multiple "strong" levels are superimposed or when "strong" level is superimposed with other levels, it will be classified as "strong" level;

[0048] 3. When one "medium" level is combined with one or more "weak" levels, it will be classified as a "medium" level;

[0049] 4. When two or more "medium" levels are superimposed, it will be classified as a "strong" level;

[0050] 5. When two or more "weak" levels are superimposed, they will be classified as "weak" or "medium" levels.

[0051] The beneficial effects of using the present invention are:

[0052] The present invention proposes a method for determining multi-sided adjacent empty working faces in coal seams without impact ground pressure. After determining that the target area meets the requirements for multi-sided adjacent empty working faces in coal seams without impact ground pressure, the comprehensive index method and possibility index method are used to evaluate the impact hazard from a macro perspective. Then, a multi-factor stress superposition impact hazard evaluation method and numerical simulation are used to evaluate the impact hazard under special geological and mining conditions, thereby realizing segmented rating and comprehensive judgment of the area to be mined, and achieving refined calibration of the safety level. In addition, the evaluation results can be combined with the prevention and control measures to dynamically optimize the prevention and control plan, which helps to carry out prevention and control work more meticulously and effectively and increase safety in subsequent work.

[0053] The present invention complies with the requirements of Article 37 of the "Detailed Rules for Preventing and Controlling Impact Ground Pressure", clarifies the method for determining multiple adjacent empty working faces in coal seams without impact ground pressure, avoids the expansion of evaluation objects, and the impact hazard evaluation method of macro-evaluation, multi-factor stress superposition and numerical simulation makes the evaluation results tend to be quantitative, and the evaluation results are consistent with the actual situation. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 This is a flow chart for the impact hazard assessment of multiple adjacent working faces in impact rock pressure coal seams according to the present invention.

[0055] Figure 2 This is a schematic diagram of the three-sided goaf area of ​​the present invention.

[0056] Figure 3 This is a schematic diagram of the four-sided goaf area of ​​the present invention. DETAILED DESCRIPTION

[0057] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0058] Example 1

[0059] Reference Figure 1 A method for assessing the impact hazard of multiple adjacent working faces in a coal seam without impact ground pressure comprises the following steps:

[0060] Step 1: Obtain mine information;

[0061] Among them, mine data include coal rock mechanical properties, mining depth, overburden structure, geological structure, mining technical conditions, impact tendency, mining stress field, coal rock structure, etc.

[0062] Step 2: determining the rock burst attribute of the mined coal seam to be a rock burst-free coal seam;

[0063] Mined coal seams are divided into rock burst coal seams, rock burst-free coal seams with potential rock burst risks, and rock burst-free coal seams;

[0064] Rock burst coal seams refer to coal seams that have experienced rock burst within the mine field, or coal seams that have been assessed to have rock burst hazards. There are two types of non-rock burst coal seams with potential rock burst risks: one is a coal seam that should undergo rock burst tendency assessment (roof and floor rock formations) but has not undergone rock burst hazard assessment or has been assessed as having no rock burst hazard; the other is a coal seam with a burial depth exceeding 400m, or a coal seam with hard rock formations above it. Coal seams without rock burst are coal seams other than rock burst coal seams and non-rock burst coal seams with potential rock burst risks.

[0065] The presence of hard rock strata above the coal seam means that there is a hard rock stratum with a single layer thickness exceeding 10m and a uniaxial compressive strength greater than 60MPa within 100m above the coal seam.

[0066] The judgment basis for determining that the rock burst attribute of the mined coal seam is a rock burst-free coal seam is that none of the following situations exist:

[0067] a. Rock burst has occurred during coal seam mining;

[0068] b. Impact hazard assessment shows that the device has impact hazard;

[0069] c. The coal seam (roof and floor rock strata) impact tendency assessment should be conducted but the impact hazard assessment has not been conducted or the assessment shows that there is no impact rock pressure hazard;

[0070] d. The coal seam is buried more than 400m deep;

[0071] e. There is a hard rock layer above the coal seam.

[0072] Step 3: determine whether the area to be evaluated belongs to the multi-faceted adjacent goaf area;

[0073] like Figure 2 and Figure 3 As shown, the multi-sided adjacent goaf areas include three-sided goaf areas and four-sided goaf areas;

[0074] The judgment of multiple adjacent goafs is that there are multiple adjacent goafs in the plane of the area to be mined and the width of the coal pillar between the area to be mined and the adjacent goaf is less than the width of the plastic zone on the side of the goaf.

[0075] The calculation formula for the width of the plastic zone on the goaf side is:

[0076]

[0077] in:

[0078] x0 is the width of the plastic zone on the goaf side, in m;

[0079] m is the thickness of the coal seam, in m;

[0080] λ is the lateral pressure coefficient;

[0081] ρ is the average density of the overlying rock layer, unit is t / m 3 ;

[0082] H is the depth of coal seam, in m;

[0083] α is the coal seam inclination;

[0084] K is the lateral support stress concentration factor;

[0085] τ is the cohesion of coal body;

[0086] is the internal friction angle of the coal body;

[0087] N is the supporting capacity of the coal wall, unit is MPa.

[0088] Step 4: Conduct a preliminary assessment of the rock burst hazard of the multi-faceted working faces of the coal seams without rock burst for the area to be assessed that has both rock burst hazard and multi-faceted adjacent goafs, and conduct a review based on the preliminary assessment results.

[0089] The preliminary evaluation of the rock burst hazard of multiple adjacent working faces in coal seams without rock burst was carried out using the comprehensive index method and the rock burst occurrence possibility index diagnosis method. The preliminary evaluation results were no rock burst hazard, weak rock burst hazard, moderate rock burst hazard and strong rock burst hazard.

[0090] Evaluation review, including the following:

[0091] If the preliminary assessment result shows that there is no ground pressure impact hazard, the safety level can be directly determined as no impact hazard;

[0092] If the preliminary assessment result indicates a weak rock burst hazard, the rock burst hazard assessment method using multiple factors and the numerical simulation method will be used to assess the rock burst hazard, and the latter result will be used as the final result to determine the safety level as no rock burst hazard or a "weak" level.

[0093] If the preliminary evaluation result is a moderate rock burst hazard or a strong rock burst hazard, the multi-factor coupling analysis method is used to analyze the influencing factors of rock burst in the area, superimpose the influence of geological and mining factors on the rock burst hazard, and finely divide the rock burst hazard level of the evaluation area. The safety level is determined by superimposing and coupling the multi-factor rock burst hazard levels to obtain "weak", "medium" and "strong" levels.

[0094] The multi-factor coupling analysis method performs the following steps in sequence:

[0095] a. Analyze the factors affecting rock burst hazards in various areas;

[0096] b. Determine the rock burst hazard level as one of no rock burst hazard, weak rock burst hazard, moderate rock burst hazard, and strong rock burst hazard based on the impact of each single factor on rock burst;

[0097] c. The final hazard level of the area is obtained by superimposing and coupling the hazard levels of multiple factors;

[0098] d. Once the hazard levels of all areas are determined, the hazard levels of the evaluation areas will be carefully delineated on the mining project plan using different legends and colors.

[0099] Factors that affect rock burst risk include the following:

[0100] Fault areas with a drop greater than 3m and less than 10m; folds with drastic changes in coal seam inclination; parts of coal seam erosion and merging or thickness changes; areas with changes in roof and floor lithology; areas below the coal pillars left over from mining of the upper protective layer; areas with a drop greater than 10m for faults or fault groups; working faces advancing towards the goaf; areas with irregular working faces such as "knife handle" shapes or where the opening holes and stop lines of multiple working faces are not aligned when approaching the goaf; areas near the intersection of tunnels; coal pillar areas along the goaf; areas affected by the advance support pressure of the working face; near the initial pressure position of the old roof; "square" areas in the goaf of the working face; areas with retained bottom coal; areas disturbed by mining.

[0101] The principle of superposition and coupling of multiple factors of rock burst hazard level is:

[0102] 1. Areas assessed as having no impact risk by the comprehensive index method do not need to be divided into different zones or grades;

[0103] 2. When multiple "strong" levels are superimposed or when "strong" level is superimposed with other levels, it will be classified as "strong" level;

[0104] 3. When one "medium" level is combined with one or more "weak" levels, it will be classified as a "medium" level;

[0105] 4. When two or more "medium" levels are superimposed, it will be classified as a "strong" level;

[0106] 5. When two or more "weak" levels are superimposed, they will be classified as "weak" or "medium" levels.

[0107] Once the final hazard levels of different areas are determined, they will be marked on the mining work plan using different legends and colors.

[0108] The factors affecting rock burst risk include: the influence of faults with a drop greater than 3m and less than 10m, folds with drastic changes in coal seam dip (greater than 15°), coal seam erosion and merging or thickness changes, areas with roof and floor lithology changes, below the coal pillars left over from mining the upper protective layer, near faults or fault groups with a drop greater than 10m, working faces advancing toward the goaf when approaching the goaf, irregular working faces such as "knife handle" shapes, or areas where the opening and stop lines of multiple working faces are not aligned, near the intersection of roadways, coal pillar areas along the goaf, areas affected by the advanced support pressure of the working face, near the initial pressure position of the old roof, "square" areas in the goaf of the working face, areas affected by the retained bottom coal, and areas disturbed by mining. The prediction and judgment contents of the multi-factor superposition analysis method are detailed in Table 1.

[0109] Table 1: Prediction and discrimination table of multi-factor superposition analysis method

[0110]

[0111]

[0112] Step 5: Take special prevention and control measures according to the risk level;

[0113] If the assessment shows no rock burst hazard, mining operations will continue as normal; if the assessment shows rock burst hazard, the rock burst hazard level of the working face will be carefully classified, and special rock burst prevention measures will be formulated and implemented;

[0114] Example 2

[0115] The impact hazard assessment of multiple adjacent working faces in the coal seam without impact pressure in the 210 working face includes the following steps:

[0116] Step 1: Obtain mine information;

[0117] The No. 2 coal seam mined at the 210 working face has a stable thickness averaging 5.2 meters, a dip angle of 3° to 5°, and a depth of 101.8 to 205 meters. The roof is primarily composed of thick siltstone or sandy mudstone with an ultimate compressive strength of 22.8 to 46.8 MPa. The mining method is strike-based longwall fully mechanized top-coal caving, with full caving for roof management. The length of each working face is 185 meters. There are no faults within the working face, and the coal seam exhibits gentle undulations along strike and dip, demonstrating the development of wide and gentle folds.

[0118] Step 2: determining the rock burst attribute of the mined coal seam to be a rock burst-free coal seam;

[0119] The coal seams within the mine field have never experienced rock burst, and the surrounding mines are all non-rock burst mines; the maximum burial depth of the working face is 205m, and the compressive strength of the rock layer above the coal seam is less than 60MPa. This coal seam is a non-rock burst coal seam.

[0120] Step 3: Determine whether the area to be evaluated belongs to the multi-faceted adjacent goaf area;

[0121] There are no mineable coal seams above the 210 working face, and all coal seams below it have not been mined. The northern part is the goaf of the 208 working face, the western part is the goaf of the 211 working face, and the eastern part is the goaf of the 209 working face. The south side is the track tunnel, and the southern end is the mine boundary. The coal seam thickness m is 5.2m; the lateral pressure coefficient λ is 1.15; the average density ρ of the overlying strata is 2.5t / m 3; The coal seam burial depth H is 205m; the coal seam inclination α is 4.5°; the lateral support stress concentration coefficient K is 1.5; the cohesion τ of the coal body is 9.5MPa; the internal friction angle φ of the coal body is 25°, and the supporting capacity of the coal wall is 13.8MPa; substituting the above data into the calculation formula of the width of the plastic zone on the side of the goaf, it is concluded that the width of the area where the lateral support stress of the goaf is significantly affected is 25m; a 20m coal pillar is left between the 210 working face and the 211 goaf and the 209 goaf, and the width of the coal pillar with the 208 goaf is 50m, but there is an abandoned roadway in the middle of the coal pillar, which satisfies that the 210 working face to be mined has three adjacent goafs; therefore, the 210 working face is judged to be a multi-faceted adjacent goaf working face.

[0122] Step 4: Conduct a multi-faceted adjacent goaf working face impact hazard assessment on the No. 2 coal seam in the 210 working face, which has both the attributes of a non-burst coal seam and multiple adjacent goafs;

[0123] The results of the impact hazard evaluation during mining of the 210 working face based on the comprehensive index method are as follows: the influence weights of geological factors and mining technical factors are 0.238 and 0.292 respectively, and the comprehensive impact hazard index of the 210 working face is 0.292; the evaluation results of the rock burst possibility index diagnosis method are as follows: the membership degree of stress to the "rock burst" event UIc=0.27, the membership degree of impact tendency to the "rock burst" event UWet=1, and the rock burst possibility index U of the 210 working face is 0.635; that is, the rock burst tendency conditions for rock burst are met, but the stress conditions for rock burst are not met; the multi-factor stress superposition impact hazard evaluation adopts the incremental principle and the structural priority principle to superimpose the self-weight stress on the rock burst. The total stress of the coal body is obtained by adding residual mining stress, tectonic stress, mining stress and other stress increments; the maximum stress of the 210 working face during mining is 15.01MPa, the uniaxial compressive strength of No. 2 coal is 13.8MPa, the stress ratio is 1.09, and there is no impact hazard; the stress evolution simulation analysis during mining shows that the vertical stress in the original stress area of ​​the coal seam is 5.0MPa; when the working face is mined to the first square (185m) and the second square (370m), the maximum support pressure in the surrounding rock of the two inclined shafts is about 12.0MPa and 14.0MPa, and the peak value of the advanced support pressure in front of the working face is 18.0MPa and 19.2MPa, the Ic in the out-of-district area is 1.01, and the Ic in the advanced stress area in front of the working face is 1.39, both less than 1.5.

[0124] Step 5: Take special prevention and control measures according to the risk level;

[0125] The 210 working face is a multi-faceted adjacent working face of a coal seam without rock burst. When the comprehensive index method and possibility index method are used to carry out rock burst hazard assessment, the main influencing factors are the elastic energy index of coal, uniaxial compressive strength, goaf on three sides of the working face and the coal pillar width of 20m. The conclusion is that it has a weak rock burst hazard, that is, it has the rock burst tendency conditions for rock burst, but does not have the stress conditions for rock burst. It can be seen that the evaluation results of a coal seam without rock burst may be inaccurate when it is evaluated as a rock burst coal seam. When multi-factor stress superposition rock burst hazard assessment and numerical simulation analysis are used to analyze the stress evolution during mining, the stress ratios are 1.09 and 1.39, respectively, both less than 1.5. It can be determined that the stress concentration area and the drift area of ​​the 210 working face have no rock burst hazard during mining and are operating normally.

[0126] Example 3

[0127] The impact hazard assessment of multiple adjacent working faces in the coal seam without impact pressure in the 001 working face includes the following steps:

[0128] Step 1: Obtain mine information;

[0129] B4 coal is buried at a depth of 320 to 359 meters in the 001 working face. The hard old roof of the working face is less than 20 meters away from the coal seam. The characteristic parameter value of the roof thickness Lst is 81.42. The compressive strength of the coal is 2.8 to 3.8 MPa. The inclined length of the working face is 74 meters. A coal pillar of 10 meters is left. No bottom coal is left during the mining process.

[0130] Step 2: determining the rock burst attribute of the mined coal seam to be a rock burst-free coal seam;

[0131] The coal seams within the mine field have never experienced rock burst, and the surrounding mines are all non-rock burst mines; the maximum burial depth of the working face is 205m, and the compressive strength of the rock layer above the coal seam is less than 60MPa. This coal seam is a non-rock burst coal seam.

[0132] Step 3: Determine whether the area to be evaluated belongs to the multi-faceted adjacent goaf area;

[0133] The 001 working face mines the middle coal pillar between the 211 working face and the 212 working face. The west is the 211 face goaf, the south is the 213 face goaf, the east is the 212 face goaf (a 46m to 69m coal pillar is left between the 001 working face air lane and the 212 working face goaf), and the north is the 002 face. Therefore, the 001 working face is determined to be a multi-faceted adjacent goaf working face.

[0134] Step 4: Conduct a rock burst hazard assessment on the multi-faceted adjacent goaf working face of the 001 working face B4 coal seam, which has both rock burst-free coal seams and multi-faceted adjacent goaf attributes;

[0135] The result of the impact hazard evaluation during the mining period of the 001 working face based on the comprehensive index method is that the influence weights of geological factors and mining technical factors are 0.417 and 0.476 respectively, and the comprehensive impact hazard index of the 001 working face is 0.476, which is evaluated to have a weak impact hazard; then the multi-factor coupling analysis method is used to analyze the factors affecting the rock burst in the area, superimpose the influence of geological and mining factors on the rock burst hazard, and finely divide the rock burst hazard level of the evaluation area; specifically: the detailed execution steps are: factors affecting the rock burst hazard in each section; according to the influence of each single factor on the rock burst, the rock burst hazard level is determined as one of no impact hazard, weak impact hazard, medium impact hazard and strong impact hazard; the hazard levels of multiple factors are superimposed and coupled to obtain the final hazard level of the area; when the final hazard level of all areas is determined, the hazard level of the evaluation area is finely delineated on the mining engineering plan with different legends and colors;

[0136] Step 5: Take special prevention and control measures according to the risk level;

[0137] The 001 working face is a multi-faceted adjacent working face of a coal seam without impact ground pressure. The multi-factor coupling analysis method is used to accurately divide the dangerous areas into 5, including 2 medium impact danger areas (for example, marked as yellow areas), 2 strong danger areas (for example, marked as magenta areas), and the other areas are all weak impact danger areas; special prevention and control measures are formulated: for areas with strong or medium danger levels, pre-unloading is used to eliminate the danger in advance and strengthen anti-impact management before the working face is mined; for areas with general or weak danger levels, targeted prevention and control measures are taken according to the monitoring results during the working face mining process.

[0138] The above content is only a preferred embodiment of the present invention. For ordinary technicians in this field, according to the concept of the present invention, many changes can be made in the specific implementation method and application scope. As long as these changes do not deviate from the concept of the present invention, they all fall within the scope of protection of the present invention.

Claims

1. A method for assessing the impact hazard of multiple adjacent working faces in a coal seam without impact pressure, characterized by: The following steps are involved: Step 1: Obtain mine information; Step 2: determining the rock burst attribute of the mined coal seam to be a rock burst-free coal seam; Step 3: determine whether the area to be evaluated belongs to the multi-faceted adjacent goaf area; Step 4: Conduct a preliminary assessment of the rock burst hazard of the multi-faceted working faces of the coal seams without rock burst for the area to be assessed that has both rock burst hazard and multi-faceted adjacent goafs, and conduct a review based on the preliminary assessment results. Step five: Take special prevention and control measures according to the level of danger.

2. A method for assessing the impact hazard of multiple adjacent working faces in a coal seam without impact pressure according to claim 1, characterized in that: In step 1, the mine data includes coal rock mechanical properties, mining depth, overburden structure, geological structure, mining technical conditions, impact tendency, mining stress field, and coal rock structure.

3. The method for assessing the impact hazard of multiple adjacent working faces in a coal seam without impact pressure according to claim 1, characterized in that: In step 2, the rock burst attribute of the mined coal seam is determined to be a rock burst-free coal seam based on the absence of any of the following circumstances: a. Rock burst has occurred during coal seam mining; b. Impact hazard assessment shows that the device has impact hazard; c. The coal seam impact tendency assessment should be conducted but the impact hazard assessment has not been conducted or the assessment shows that there is no impact rock pressure hazard; d. The coal seam is buried more than 400m deep; e. There is a hard rock layer above the coal seam.

4. The method for assessing the impact hazard of multiple adjacent working faces in a coal seam without impact pressure according to claim 1, characterized in that: In step 3, the determination of the multiple adjacent goafs is that there are multiple adjacent goafs in the plane of the area to be mined and the width of the coal pillar between the area to be mined and the adjacent goafs is less than the width of the plastic zone on the side of the goaf. The calculation formula for the width of the plastic zone on the goaf side is: in: x0 is the width of the plastic zone on the goaf side, in m; m is the thickness of the coal seam, in m; λ is the lateral pressure coefficient; ρ is the average density of the overlying rock layer, unit is t / m 3 ; H is the depth of coal seam, in m; α is the coal seam inclination; K is the lateral support stress concentration factor; τ is the cohesion of coal body; is the internal friction angle of the coal body; N is the supporting capacity of the coal wall, unit is MPa.

5. The method for assessing the impact hazard of multiple adjacent working faces in a coal seam without impact pressure according to claim 1, characterized in that: In step four, the preliminary evaluation of the rock burst hazard of the multi-sided adjacent working faces of the coal seam without rock burst is carried out using the comprehensive index method and the rock burst occurrence possibility index diagnosis method. The preliminary evaluation results are no rock burst hazard, weak rock burst hazard, moderate rock burst hazard and strong rock burst hazard.

6. The method for assessing the impact hazard of multiple adjacent working faces in a coal seam without impact pressure according to claim 5, characterized in that: In step 4, the evaluation review includes the following: If the preliminary assessment result shows that there is no ground pressure impact hazard, the safety level can be directly determined as no impact hazard; If the preliminary assessment result indicates a weak rock burst hazard, a multi-factor stress superposition rock burst hazard assessment method and a numerical simulation method are used to conduct rock burst hazard assessments. The latter result is used as the final result to determine the safety level as no rock burst hazard or "weak" level. If the preliminary assessment result indicates a moderate or strong rock burst hazard, a multi-factor coupling analysis method is used to analyze the factors affecting the rock burst in the area, superimposing the effects of geological and mining factors on the rock burst hazard. The rock burst hazard level of the assessment area is then finely divided, and the safety level is determined by superimposing and coupling the multi-factor rock burst hazard levels to obtain "weak", "medium" and "strong" levels.

7. A method for assessing the impact hazard of multiple adjacent working faces in a coal seam without impact pressure according to claim 6, characterized in that: The multi-factor coupling analysis method sequentially performs the following steps: a. Analyze the factors affecting rock burst hazards in various areas; b. Determine the rock burst hazard level as one of no rock burst hazard, weak rock burst hazard, moderate rock burst hazard, and strong rock burst hazard based on the impact of each single factor on rock burst; c. The final hazard level of the area is obtained by superimposing and coupling the hazard levels of multiple factors; d. Once the hazard levels of all areas are determined, the hazard levels of the evaluation areas will be carefully delineated on the mining project plan using different legends and colors.

8. The method for assessing the impact hazard of multiple adjacent working faces in a coal seam without impact pressure according to claim 7, characterized in that: The factors that affect rock burst danger include the following: Fault areas with a drop greater than 3m and less than 10m; folds with drastic changes in coal seam dip; parts of coal seam erosion and merging or thickness changes; areas with lithologic changes in the roof and floor plates; areas below the coal pillars left behind from mining the upper protective layer; areas with a drop greater than 10m for faults or fault groups; working faces advancing into the goaf; areas with irregular working faces or multiple working faces where the opening holes and stop lines are not aligned; roadway intersection areas; coal pillars along the goaf; areas of advanced support pressure on the working face; near the initial pressure position of the old roof; "square" areas in the goaf of the working face; areas with retained bottom coal; and areas disturbed by mining.

9. The method for assessing the impact hazard of multiple adjacent working faces in a coal seam without impact pressure according to claim 6, characterized in that: The principle of superposition and coupling of multiple factors of rock burst hazard levels is:

1. Areas assessed as having no impact risk by the comprehensive index method do not need to be divided into different zones or grades; 2. When multiple "Strong" levels are superimposed or when "Strong" level is superimposed with other levels, it will be classified as "Strong" level; 3. When one "medium" level is combined with one or more "weak" levels, it will be classified as "medium" level; 4. When two or more "medium" levels are combined, it will be classified as a "strong" level; 5. When two or more "weak" levels are superimposed, they will be classified as "weak" or "medium" level.

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