A method for evaluating safety of rock burst mine

Abstract

The present application relates to the technical field of coal mine safety, and relates to a rock burst mine safety evaluation method, which is used for evaluating the reliability and safety level of rock burst prevention and treatment, and specifically comprises: roadway stress safety evaluation, roadway energy safety evaluation and comprehensive evaluation of the rock burst mine, and safety level is given to provide reliable basis for coal mine safety production, supervision, inspection, resumption of work and production, capacity determination, mining speed change and the like; roadway stress safety coefficient index is obtained, the smaller the stress safety coefficient is, the lower the roadway safety degree is, and the greater the probability of rock burst is; the greater the stress safety coefficient is, the less likely the roadway is to have rock burst; roadway energy safety coefficient index is obtained, the greater the energy safety coefficient is, the higher the roadway safety degree is; the smaller the energy safety coefficient is, the lower the safety degree is; the roadway stress safety coefficient and the energy safety coefficient are comprehensively considered to divide the safety level of the rock burst mine.

Description

Technical Field

[0001] This invention relates to the field of coal mine rockburst technology, and more specifically, to a method for evaluating the safety of mines prone to rockburst. Background Technology

[0002] Rockburst is one of the most serious dynamic disasters in coal mines, and there are currently 146 rockburst mines nationwide. Article 9 of the "Detailed Rules for the Prevention and Control of Rockburst in Coal Mines" issued by the State Administration of Mine Safety stipulates: "A coal seam that has experienced rockburst within the mining area, or a coal seam (or its roof and floor strata) that has been identified as having a tendency to rockburst and is evaluated as having a rockburst hazard, is a rockburst coal seam, and a mine with a rockburst coal seam is a rockburst mine."

[0003] Currently, the primary concern regarding rockburst-prone mines is the risk of rockbursts. This is characterized through rockburst hazard assessment, which includes evaluating the mine shaft, coal seam, levels, mining areas, working faces, main roadways, and chambers. The assessment provides a rockburst hazard level and a classification of hazardous areas, and the results serve as the basis for rockburst prevention design and mine rockburst management. However, some rockburst-prone mines, despite implementing rockburst prevention measures, have still experienced rockbursts. The root cause is a problem with the reliability of the rockburst prevention design. The lack of a comprehensive assessment of the reliability of the rockburst prevention design and the mine's rockburst prevention capacity is a crucial step, making it difficult to guarantee the mine's rockburst safety.

[0004] In some geotechnical engineering projects, safety assessments are typically conducted on load-bearing structures, and safety factors are used to evaluate the degree of safety, such as the safety factor for pit heave resistance, slope stability, dam body safety, and tunnel surrounding rock stability. However, currently, no concept or evaluation method for safety has been proposed for the evaluation and treatment of rockburst mines. The surrounding rock and its support system of mine roadways and working faces are the main load-bearing structures in mine roadway engineering, and it is absolutely necessary to conduct safety assessments. Summary of the Invention

[0005] The present invention provides a method for evaluating the safety of mines prone to rock bursts, which can overcome some or all of the defects of the prior art.

[0006] According to the present invention, a method for evaluating the safety of mines prone to rockbursts is used to assess the reliability and safety level of rockburst prevention and control. The safety evaluation method specifically includes the following steps:

[0007] S1. Conduct a roadway stress safety assessment for mines prone to rock bursts;

[0008] S2. Conduct an energy safety assessment of roadways in mines prone to rock bursts;

[0009] S3. Conduct a comprehensive evaluation of roadways in mines prone to rock bursts and assign a safety level to provide a reliable basis for coal mine safety production, supervision, inspection, resumption of work and production, capacity verification, and changes in mining speed.

[0010] The purpose of conducting a roadway stress safety evaluation is to obtain the roadway stress safety factor index. The roadway stress safety factor is the ratio of the critical stress value for roadway rockburst to the actual stress of the surrounding rock. The smaller the stress safety factor, the lower the roadway safety level and the greater the probability of rockburst. Conversely, the larger the stress safety factor, the less likely the roadway is to experience rockburst.

[0011] The purpose of conducting an energy safety assessment of roadways is to obtain an energy safety factor index. The energy safety factor is the ratio of the energy absorbed by the support system plus the energy absorbed by the softened rock zone to the energy released by the mine. The larger the energy safety factor, the greater the energy absorbed by the support and the surrounding rock, and the higher the safety level of the roadway. The smaller the energy safety factor, the smaller the energy absorbed by the support and the surrounding rock, and the lower the safety level.

[0012] Taking into account both the roadway stress safety factor and the energy safety factor, the safety level of mines subjected to rockburst is classified.

[0013] Preferably, the mine safety is evaluated based on the obtained roadway stress safety factor and energy safety factor, and the mine rockburst safety is divided into three levels: A, B, and C, corresponding to safe, basically safe, and unsafe, respectively. For a level A safe mine, the mine has rockburst prevention capability, the stress safety factor is greater than 1.5 and the energy safety factor is greater than 1.0, and it can be mined normally. For a level B basically safe mine, the mine has rockburst prevention capability, the stress safety factor is greater than 1.0 and the energy safety factor is greater than 1.5, and it can be mined normally. For a level C unsafe mine, the mine does not have rockburst prevention capability or the safety factor is neither level A nor level B, and mining activities should be suspended.

[0014] Preferably, for mine rockbursts with a safety level of C, the rockburst prevention design needs to be optimized to improve the mine's rockburst prevention capability. Normal mining can only proceed after the safety assessment is re-evaluated and the mine reaches a safe or basic safety level.

[0015] Preferably, after implementing anti-rockburst measures, the safety evaluation result of mining faces with a risk assessment of medium or strong rockburst should reach level A; after implementing anti-rockburst measures, the safety evaluation result of mining faces with a risk assessment of weak rockburst should be no lower than level B.

[0016] Preferably, the method for obtaining the roadway stress safety factor includes:

[0017] A1. Calculate the tunnel support stress P S ;

[0018]

[0019] In the formula, F s The sum of the support resistance of all support equipment within a unit distance L, in N;

[0020] L C Let m be the perimeter of the tunnel.

[0021] F mg The sum of the support resistance of the anchor bolts within a unit distance L, in N;

[0022] F ms N represents the sum of the support resistance of the anchor cables within a unit distance L.

[0023] F U The sum of the support resistance of the U-shaped steel within a unit distance L, in N;

[0024] F zj The support resistance of the support structure within a unit distance L, expressed in N;

[0025] The unit distance L is usually 1m.

[0026] A2. Determine the critical surrounding rock stress P for a mine rockburst. cr However, the occurrence of rockbursts is complex due to the combined influence of geological conditions, mining technology, tunnel geometry, and stress environment. The critical surrounding rock stress P cr There will be some deviations, so a correction factor η is added for the critical surrounding rock stress P. cr The critical surrounding rock stress P is corrected. cr It can be obtained from equation (2);

[0027]

[0028] In the formula:

[0029] σ c The uniaxial compressive strength of the surrounding rock mass;

[0030] K is the impact tendency index (approximately equal to the impact energy index);

[0031] p s Tunnel support stress;

[0032] A3. Obtain the actual stress P of the surrounding rock in the roadway. The actual stress P of the surrounding rock can be obtained through two methods: actual monitoring or theoretical estimation. The theoretical estimation formula for the actual stress P is as follows:

[0033] P=K f P z(3)

[0034] In the formula:

[0035] P z The stress is due to its own weight.

[0036] K f K is the stress concentration factor of the surrounding rock. fi Let n be the stress concentration factor of each influencing factor, and n be the number of influencing factors. Then:

[0037]

[0038] A4. The roadway stress safety factor can be obtained through formula (4).

[0039]

[0040] Preferably, the correction factor η is related to the uniaxial compressive strength σ of the surrounding rock of the roadway. c The corresponding relationship is shown in equation (5), which can be obtained by fitting the ratio of the measured data of the mine to the theoretical value.

[0041]

[0042] Preferably, the method for obtaining the energy safety factor of the roadway includes:

[0043] B1. Energy released by rock burst (W) o ;

[0044] B2. Energy absorbed by the plastic zone of the surrounding rock, the energy absorption capacity (W) of the surrounding rock per unit distance from the roadway. c It can be obtained through equation (6);

[0045]

[0046] In the formula, ρ is the depth of the softened zone of the surrounding rock in the tunnel, in meters;

[0047] L is the tunnel length (calculated per unit length), in meters (m).

[0048] B3. Energy absorbed by roadway support, the overall absorption capacity of the roadway support system per unit distance (W) s It can be obtained through equation (7);

[0049]

[0050] In the formula, U mg J represents the sum of energy absorbed by all anchor bolts within a unit distance along the roadway.

[0051] U ms J represents the sum of energy absorbed by all anchor cables within a unit distance along the roadway.

[0052] U uz J represents the sum of energy absorbed by all U-shaped steel supports within a unit distance along the roadway.

[0053] U zj J represents the sum of energy absorbed by all supports within a unit distance along the roadway.

[0054] B4. The energy safety factor of the roadway can be obtained through equation (8), which represents the energy W absorbed by the support system. s In addition to the energy absorbed by the softened zone of the surrounding rock (W) c The energy W released by the rock burst o The ratio is defined as the energy security factor S. en :

[0055]

[0056] Preferred, U mg U ms U uz U zj The specific value needs to be determined through testing of the overall structure or the main energy-absorbing components. The most reasonable testing method is to conduct the test under the supported condition or under simulated support condition.

[0057] Preferably, the energy W released by the rock burst o The estimation method varies depending on the type of rockburst, specifically divided into the energy released by coal seam type rockbursts (W). mt Energy released by roof-type rock bursts (W) db Energy released by fault-type rock bursts (W) dc ;

[0058] To determine the energy released during a coal-bearing rockburst, only the energy (W) released per unit length of surrounding rock in a roadway under critical conditions is required. mt It can be obtained through equation (9);

[0059]

[0060] In the formula, μ is Poisson's ratio.

[0061] The energy released by a roof-type rockburst, specifically the energy released when the roof reaches a critical fracture state and suddenly becomes unstable, is W. db It can be obtained from equation (10);

[0062]

[0063] In the formula, L cr The span of the goaf;

[0064] p represents the load and self-weight of the overlying strata on the top plate, in MPa;

[0065] b = b0 - 2d cotγ, where b0 is the working face length (m); γ is the overburden fracture angle (rad); and d is the distance from the roof to the coal seam (m).

[0066] h1 is the thickness of the top plate, in meters;

[0067] E r The elastic modulus of the roof rock is given in MPa.

[0068] k is the coal seam stiffness coefficient, kN / m;

[0069]

[0070] The energy released by fault-type rock bursts, and the energy released when the surrounding rock of the fault zone reaches the critical state of slippage and suddenly becomes unstable (W). dc It can be obtained from equation (11);

[0071]

[0072] In the formula, z is the effective length of the strike of the slip fault, in meters (m).

[0073] h2 is the fault elevation drop, in meters (m).

[0074] G is the shear modulus of the rock in the fault zone, in MPa;

[0075] S1 and S2 are the far-field shear displacements before and after fault slip, respectively, in meters;

[0076] u1 and u2 are the shear displacements before and after the fault slip, respectively, in meters;

[0077] 2X represents the width of the surrounding rock of the fault, in meters (m).

[0078] Compared with the prior art, the present invention has at least the following beneficial effects:

[0079] 1. A method for evaluating roadway safety is proposed, which comprehensively assesses the reliability of anti-scour design and the mine's anti-scour capability, providing a reliable basis for coal mine safety production, supervision, inspection, resumption of work and production, capacity verification, and changes in mining speed;

[0080] 2. Taking into account both the roadway stress safety factor and the energy safety factor, the safety level of the rockburst-prone mine is classified, so that the reliability of the rockburst prevention design and the mine safety level can be rationally understood. Attached Figure Description

[0081] Figure 1 This is the basic procedure for using the present invention to conduct roadway safety assessment;

[0082] Figure 2These are the support parameters for the auxiliary transport roadway of the M working face in this embodiment of the invention. Detailed Implementation

[0083] To further understand the content of this invention, a detailed description of the invention will be provided in conjunction with the accompanying drawings and embodiments. It should be understood that the embodiments are merely illustrative and not limiting of the invention.

[0084] Example 1

[0085] like Figure 1 As shown, a safety evaluation method for mines prone to rockbursts is used to evaluate the reliability and safety level of rockburst prevention and control. The safety evaluation method specifically includes the following steps:

[0086] S1. Conduct a roadway stress safety assessment for mines prone to rock bursts;

[0087] S2. Conduct an energy safety assessment of roadways in mines prone to rock bursts;

[0088] S3. Conduct a comprehensive evaluation of roadways in mines prone to rock bursts and assign a safety level to provide a reliable basis for coal mine safety production, supervision, inspection, resumption of work and production, capacity verification, and changes in mining speed.

[0089] The purpose of conducting a roadway stress safety evaluation is to obtain the roadway stress safety factor index. The roadway stress safety factor is the ratio of the critical stress value for roadway rockburst to the actual stress of the surrounding rock. The smaller the stress safety factor, the lower the roadway safety level and the greater the probability of rockburst. Conversely, the larger the stress safety factor, the less likely the roadway is to experience rockburst.

[0090] The purpose of conducting an energy safety assessment of roadways is to obtain an energy safety factor index. The energy safety factor is the ratio of the energy absorbed by the support system plus the energy absorbed by the softened rock zone to the energy released by the mine. A higher energy safety factor means greater energy absorption by both the support and the surrounding rock, resulting in a higher level of roadway safety. Conversely, a lower energy safety factor means less energy absorption by both the support and the surrounding rock, resulting in a lower level of safety. When the energy safety factor is less than 1, the sum of the energy absorbed by the support and the surrounding rock is less than the released energy, leaving surplus energy. This surplus energy will be converted into kinetic energy, causing damage to the surrounding rock and support structures. If personnel are working in the roadway, this will inevitably lead to casualties.

[0091] Taking into account both the roadway stress safety factor and the energy safety factor, the safety level of mines subjected to rockburst is classified.

[0092] The mine safety assessment is based on the obtained roadway stress safety factor and energy safety factor, classifying the mine's rockburst safety into three levels: A, B, and C, corresponding to safe, basically safe, and unsafe, respectively. For level A safe mines, the mine has rockburst prevention capabilities, with a stress safety factor greater than 1.5 and an energy safety factor greater than 1.0, and can operate normally. For level B basically safe mines, the mine has rockburst prevention capabilities, with a stress safety factor greater than 1.0 and an energy safety factor greater than 1.5, and can operate normally. For level C unsafe mines, the mine does not have rockburst prevention capabilities or its safety factor is neither level A nor level B, and mining activities should be suspended.

[0093] For mines with rockbursts classified as safety level C, the rockburst prevention design needs to be optimized to improve the mine's rockburst prevention capabilities. Normal mining can only resume after the safety assessment is re-evaluated and the mine reaches a safe or basic safety level.

[0094] Specifically, for mining faces with a risk assessment of medium or strong rockburst hazard, the safety assessment result should reach level A after anti-rockburst measures are taken; for mining faces with a risk assessment of weak rockburst hazard, the safety assessment result should be no lower than level B after anti-rockburst measures are taken.

[0095] The methods for obtaining the roadway stress safety factor include:

[0096] A1. Calculate the tunnel support stress P S ;

[0097]

[0098] In the formula, F s The sum of the support resistance of all support equipment within a unit distance L, in N;

[0099] L C Let m be the perimeter of the tunnel.

[0100] F mg The sum of the support resistance of the anchor bolts within a unit distance L, in N;

[0101] F ms N represents the sum of the support resistance of the anchor cables within a unit distance L.

[0102] F U The sum of the support resistance of the U-shaped steel within a unit distance L, in N;

[0103] F zj The support resistance of the support structure within a unit distance L, expressed in N;

[0104] The unit distance L is usually 1m.

[0105] A2. Determine the critical surrounding rock stress P for a mine rockburst.cr However, the occurrence of rockbursts is complex due to the combined influence of geological conditions, mining technology, tunnel geometry, and stress environment. The critical surrounding rock stress P cr There will be some deviations, so a correction factor η is added for the critical surrounding rock stress P. cr The critical surrounding rock stress P is corrected. cr It can be obtained from equation (2);

[0106]

[0107] In the formula:

[0108] σ c The uniaxial compressive strength of the surrounding rock mass;

[0109] K is the impact tendency index (approximately equal to the impact energy index);

[0110] p s Tunnel support stress;

[0111] A3. Obtain the actual stress P of the surrounding rock in the roadway. The actual stress P of the surrounding rock can be obtained through two methods: actual monitoring or theoretical estimation. The theoretical estimation formula for the actual stress P is as follows:

[0112] P=K f P z (3)

[0113] In the formula:

[0114] P z The stress is due to its own weight.

[0115] K f K is the stress concentration factor of the surrounding rock. fi Let n be the stress concentration factor of each influencing factor, and n be the number of influencing factors. Then:

[0116]

[0117] A4. The roadway stress safety factor can be obtained through formula (4).

[0118]

[0119] Among them, the correction factor η is related to the uniaxial compressive strength σ of the surrounding rock of the roadway. c The corresponding relationship is shown in equation (5), which can be obtained by fitting the ratio of the measured data of the mine to the theoretical value.

[0120]

[0121] The methods for obtaining the energy safety factor of the roadway include:

[0122] B1. Energy released by rock burst (W) o ;

[0123] B2. Energy absorbed by the plastic zone of the surrounding rock, the energy absorption capacity (W) of the surrounding rock per unit distance from the roadway. c It can be obtained through equation (6);

[0124]

[0125] In the formula, ρ is the depth of the softened zone of the surrounding rock in the tunnel, in meters;

[0126] L is the tunnel length (calculated per unit length), in meters (m).

[0127] B3. Energy absorbed by roadway support, the overall absorption capacity of the roadway support system per unit distance (W) s It can be obtained through equation (7);

[0128]

[0129] In the formula, U mg J represents the sum of energy absorbed by all anchor bolts within a unit distance along the roadway.

[0130] U ms J represents the sum of energy absorbed by all anchor cables within a unit distance along the roadway.

[0131] U uz J represents the sum of energy absorbed by all U-shaped steel supports within a unit distance along the roadway.

[0132] U zj J represents the sum of energy absorbed by all supports within a unit distance along the roadway.

[0133] B4. The energy safety factor of the roadway can be obtained through equation (8), which represents the energy W absorbed by the support system. s In addition to the energy absorbed by the softened zone of the surrounding rock (W) c The energy W released by the rock burst o The ratio is defined as the energy security factor S. en :

[0134]

[0135] Among them, U mg U ms U uz U zj The specific value needs to be determined through testing of the overall structure or the main energy-absorbing components. The most reasonable testing method is to conduct the test under the supported condition or under simulated support condition.

[0136] Among them, the energy released by the rock burst is Wo The estimation method varies depending on the type of rockburst, specifically divided into the energy released by coal seam type rockbursts (W). mt Energy released by roof-type rock bursts (W) db Energy released by fault-type rock bursts (W) dc ;

[0137] To determine the energy released during a coal-bearing rockburst, only the energy (W) released per unit length of surrounding rock in a roadway under critical conditions is required. mt It can be obtained through equation (9);

[0138]

[0139] In the formula, μ is Poisson's ratio.

[0140] The energy released by a roof-type rockburst, specifically the energy released when the roof reaches a critical fracture state and suddenly becomes unstable, is W. db It can be obtained from equation (10);

[0141]

[0142] In the formula, L cr The span of the goaf;

[0143] p represents the load and self-weight of the overlying strata on the top plate, in MPa;

[0144] b = b0 - 2d cotγ, where b0 is the working face length (m); γ is the overburden fracture angle (rad); and d is the distance from the roof to the coal seam (m).

[0145] h1 is the thickness of the top plate, in meters;

[0146] E r The elastic modulus of the roof rock is given in MPa.

[0147] k is the coal seam stiffness coefficient, kN / m;

[0148]

[0149] The energy released by fault-type rock bursts, and the energy released when the surrounding rock of the fault zone reaches the critical state of slippage and suddenly becomes unstable (W). dc It can be obtained from equation (11);

[0150]

[0151] In the formula, z is the effective length of the strike of the slip fault, in meters (m).

[0152] h2 is the fault elevation drop, in meters (m).

[0153] G is the shear modulus of the rock in the fault zone, in MPa;

[0154] S1 and S2 are the far-field shear displacements before and after fault slip, respectively, in meters;

[0155] u1 and u2 are the shear displacements before and after the fault slip, respectively, in meters;

[0156] 2X represents the width of the surrounding rock of the fault, in meters (m).

[0157] The following is an application example of this invention:

[0158] 1. Basic data of the mine

[0159] The M working face of a certain mine has a strike length of 2680m and a working face length of 290m. The average thickness of the coal seam is 6.5m, and the average burial depth is 700m, making it a near-horizontal coal seam. The immediate roof is mainly composed of soft to semi-hard sandy mudstone and fine sandstone, with a thickness of approximately 9.1m. The basic roof is composed of medium-grained sandstone, with a thickness of approximately 21.1m. The floor is sandy mudstone. The working face has poor structural development, with a maximum fault displacement of 3.4m.

[0160] The auxiliary transport roadway of the M working face is affected by the initial pressure, single-sided, double-sided, roadway intersections, and lateral support pressure from the goaf of the adjacent N working face. Therefore, the roadway safety evaluation is carried out on the auxiliary transport roadway under this complex working condition.

[0161] The auxiliary transport roadway has a rectangular cross-section, 3.8m high and 5.2m wide, and is supported by a combination of anchor, mesh, and cable. The support parameters are as follows: Figure 2 As shown; uniaxial compressive strength σ of coal c The stress is 29.56 MPa, and the impact energy index K is 3.11. The effects of measures such as roof breaking and borehole decompression on the actual stress of the coal seam are ignored.

[0162] Analysis shows that the auxiliary transport roadway is located in the goaf of the N working face within a range of 65–1186m from the cut-off point; the range of 33–53m will be affected by the initial pressure; the ranges of 238–338m and 613–713m will be affected by single and double square cuts; and there are intersecting roadways in the ranges of 1723–1763m and 2660–2680m.

[0163] 2. Calculation of roadway stress safety factor

[0164] According to mine data, the depth of the mine's dynamic manifestation is approximately 700m. From equation (5), the correction coefficient η is 1.66. From equation (1), the support stress P is obtained. s The critical stress P is 0.28 MPa. Substituting this into equation (2) yields the critical stress P. cr =33.67 MPa.

[0165] A single-axis coordinate system is established with the intersection of the auxiliary transport roadway and the cut-off point of the M working face as the origin and the roadway axis as the x-axis.

[0166] ①Self-weight stress

[0167] The working face coal seam is a near-horizontal coal seam with a surface elevation difference of no more than 30m. The auxiliary haulage roadway is buried at a depth of 700m, and the overburden density is 25kN / m³. 3 Then the stress P along the roadway due to its own weight is respectively z =17.50 MPa (0≤x≤2680).

[0168] ② First visit

[0169] Empirical values ​​show that the stress concentration factor K under the influence of the initial pressure is... f1 If the value is 1.5, then the stress distribution in the range of 33–53 m is as follows:

[0170] P ch =26.25 MPa (33≤x≤53)

[0171] ③ The working face is square.

[0172] Empirical values ​​show that the stress concentration factor K under the influence of the square working face... f2 If the value is 1.7, then the stress distribution in the ranges of 238–338 m and 613–713 m is as follows:

[0173] P ji =29.75Mpa(238≤x≤338, 613≤x≤713)

[0174] ④ Lane intersection

[0175] Empirical values ​​show that the stress concentration factor K under the influence of roadway intersections is... f3 If the value is 1.2, then the stress distribution in the ranges of 1723–1763 m and 2660–2680 m is as follows:

[0176] P ha =21.00Mpa(1723≤x≤1763; 2660≤x≤2680)

[0177] ⑤ Lateral support pressure in the goaf

[0178] Empirical values ​​show that the stress concentration factor K under the influence of lateral support pressure in the goaf is... f4 If the value is 1.4, then the stress distribution within the mining range of 65–1186m is:

[0179] P zh =24.50 MPa (65≤x≤1186)

[0180] Substituting the calculation results from ① to ⑤ into equation (3) yields the distribution of the actual stress P in the surrounding rock of the roadway. Further, the actual stress P and the critical stress P... crSubstituting into equation (4), the stress safety factor f of the auxiliary transport roadway of working face M was obtained. s Distribution.

[0181] 3. Calculation of energy safety factor for roadways

[0182] Based on the geological structure and overburden conditions of the M working face, it is known that the working face is susceptible to both roof-type and coal-body-type rockbursts.

[0183] The radius of the circumcircle of the rectangular tunnel is taken as the equivalent radius a, which is 3.2m; the Poisson's ratio μ of the surrounding rock is 0.28, and the elastic modulus E is 2.11Gpa.

[0184] Based on the roadway damage caused by coal-type rockbursts that have occurred in the mine, the energy W released by the coal-type rockburst is estimated by substituting it into equation (9). mt It is 7.59E+06J.

[0185] Elastic modulus E of the roof rock r Given a pressure of 7 GPa and a load of 1.1 MPa, the energy released by the roof-type rockburst is calculated in W. db It is 9.35E+06J.

[0186] Based on the materials used for the roadway support, each anchor bolt absorbs 30kJ of energy, each anchor cable absorbs 70kJ of energy, and each support frame absorbs 990kJ of energy. Substituting this into equation (7), we obtain W. s =1547kJ / m.

[0187] The energy absorbed by the plastic zone of the surrounding rock is calculated according to equation (6) as W. c =6.73E+06J.

[0188] The energy safety factor of the auxiliary transport roadway under the condition of coal seam rockburst is:

[0189]

[0190] The energy safety factor of the auxiliary transport roadway under the condition of roof rockburst is:

[0191]

[0192] The calculation results show that if a coal seam-type rockburst occurs in the roadway, the roadway energy safety factor is 1.09, indicating a low probability of damage to the auxiliary transport roadway. If a roof-type rockburst occurs, the roadway energy safety factor is only 0.88, indicating a high probability of damage to the auxiliary transport roadway.

[0193] The safety of the auxiliary transport roadway is evaluated by combining the comprehensive stress safety factor and energy safety factor. Based on the classification of mine rockburst safety levels, the safety level of the working face under coal seam rockburst conditions can be obtained. It is evident that most areas of the auxiliary transport roadway are classified as unsafe, level C. Similarly, under roof rockburst conditions, since the roadway energy safety factor is less than 1, the entire working face is classified as unsafe, level C.

[0194] The present invention and its embodiments have been described above illustratively. This description is not restrictive, and the figures shown are only one embodiment of the present invention; the actual structure is not limited thereto. Therefore, if those skilled in the art are inspired by this description and design similar structures and embodiments without departing from the spirit of the present invention, such designs should fall within the protection scope of the present invention.

Claims

1. A method for safety evaluation of mines prone to rock bursts, characterized in that: Used to evaluate the reliability and safety level of rockburst prevention; the safety evaluation method specifically includes the following steps: S1. Conduct a roadway stress safety assessment for mines prone to rock bursts; S2. Conduct an energy safety assessment of roadways in mines prone to rock bursts; S3. Conduct a comprehensive evaluation of roadways in mines prone to rock bursts and provide a safety level to provide a reliable basis for coal mine safety production, supervision, inspection, resumption of work and production, capacity verification, and changes in mining speed. The purpose of conducting a roadway stress safety evaluation is to obtain the roadway stress safety factor index. The roadway stress safety factor is the ratio of the critical stress value for a roadway to experience rockburst to the actual stress of the surrounding rock. The smaller the stress safety factor, the lower the roadway safety level and the greater the probability of rockburst. Conversely, the larger the stress safety factor, the less likely the roadway is to experience rockburst. The purpose of conducting a roadway energy safety assessment is to obtain the roadway energy safety factor index. The energy safety factor is the ratio of the energy absorbed by the support system plus the energy absorbed by the softened rock zone to the energy released by the mine. The larger the energy safety factor, the greater the energy absorbed by the support and the surrounding rock, and the higher the safety level of the roadway. The smaller the energy safety factor, the smaller the energy absorbed by the support and the surrounding rock, and the lower the safety level. Taking into account both the roadway stress safety factor and the energy safety factor, the safety level of mines subjected to rockburst is classified. The methods for obtaining the roadway stress safety factor include: A1, calculate the roadway support stress P S ; In the formula, F s The sum of the support resistance of all support equipment within a unit distance L, in N; L C The perimeter of the tunnel is in meters (m). F mg The sum of the support resistance of the anchor bolts within a unit distance L, in N; F ms N represents the sum of the support resistance of the anchor cables within a unit distance L. F U The sum of the support resistance of the U-shaped steel within a unit distance L, in N; F zj The support resistance of the support structure within a unit distance L, expressed in N; The unit distance L is 1m; A2. Determine the critical surrounding rock stress P for a mine rockburst. cr However, the occurrence of rockbursts is complex due to the combined influence of geological conditions, mining technology, tunnel geometry, and stress environment. The critical surrounding rock stress P cr There will be some deviations, so a correction factor η is added for the critical surrounding rock stress P. cr The critical surrounding rock stress P is corrected. cr It can be obtained from equation (2); In the formula: σ c The uniaxial compressive strength of the surrounding rock mass; K represents the shock tendency index; p s Tunnel support stress; A3. Obtain the actual stress P of the surrounding rock in the roadway. The actual stress P of the surrounding rock can be obtained through two methods: actual monitoring or theoretical estimation. The theoretical estimation formula for the actual stress P is as follows: In the formula: P z The stress is due to its own weight. K f K is the stress concentration factor of the surrounding rock. fi Let n be the stress concentration factor of each influencing factor, and n be the number of influencing factors. Then: A4. The roadway stress safety factor can be obtained through equation (4): The methods for obtaining the energy safety factor of the roadway include: B1. Energy released by rock burst (W) o ; B2. Energy absorbed by the plastic zone of the surrounding rock, the energy absorption capacity (W) of the surrounding rock per unit distance from the roadway. c It can be obtained through equation (6); In the formula, ρ is the depth of the softened zone of the surrounding rock in the tunnel, in meters; L is the length of the tunnel, expressed in units of distance, in meters; E is the elastic modulus of the surrounding rock; K represents the shock tendency index; σ c The uniaxial compressive strength of the surrounding rock mass; B3. Energy absorbed by roadway support, the overall absorption capacity of the roadway support system per unit distance (W) s It can be obtained through equation (7); In the formula, U mg J represents the sum of energy absorbed by all anchor bolts within a unit distance along the roadway. U ms J represents the sum of energy absorbed by all anchor cables within a unit distance along the roadway. U uz J represents the sum of energy absorbed by all U-shaped steel supports within a unit distance along the roadway. U zj J represents the sum of energy absorbed by all supports within a unit distance along the roadway. B4. The energy safety factor of the roadway can be obtained through equation (8), which represents the energy W absorbed by the support system. s In addition to the energy absorbed by the softened zone of the surrounding rock (W) c The energy W released by the rock burst o The ratio is defined as the energy security factor S. en : （8）。 2. The method for safety evaluation of mines prone to rock bursts according to claim 1, characterized in that: Based on the obtained roadway stress safety factor and energy safety factor, the mine safety is evaluated, and the mine rockburst safety is divided into three levels: A, B, and C, corresponding to safe, basically safe, and unsafe, respectively. For level A safe mines, the mine has rockburst prevention capabilities, with a stress safety factor greater than 1.5 and an energy safety factor greater than 1.0, and can be mined normally. For level B basically safe mines, the mine has rockburst prevention capabilities, with a stress safety factor greater than 1.0 and an energy safety factor greater than 1.5, and can be mined normally. For level C unsafe mines, the mine does not have rockburst prevention capabilities or its safety factor is neither level A nor level B, and mining activities should be suspended.

3. The method for safety evaluation of mines prone to rock bursts according to claim 2, characterized in that: For mine rockbursts with a safety level of C, the rockburst prevention design needs to be optimized to improve the mine's rockburst prevention capabilities. Normal mining can only resume after the safety assessment is re-conducted and the mine reaches a safe or basic safety level.

4. The method for safety evaluation of mines prone to rock bursts according to claim 2, characterized in that: After implementing anti-rockburst measures, the safety evaluation result of a mining face with a risk assessment of medium or strong rockburst should reach level A; after implementing anti-rockburst measures, the safety evaluation result of a mining face with a risk assessment of weak rockburst should be no lower than level B.

5. The method for safety evaluation of mines prone to rock bursts according to claim 1, characterized in that: Correction factor η and uniaxial compressive strength σ of roadway surrounding rock c The corresponding relationship is shown in equation (5), which can be obtained by fitting the ratio of the measured data of the mine to the theoretical value; （5）。 6. The method for safety evaluation of mines prone to rock bursts according to claim 1, characterized in that: U mg U ms U uz U zj The specific value needs to be determined through testing of the overall structure or the main energy-absorbing components. The most reasonable testing method is to conduct the test under the supported condition or under simulated supported condition.

7. The method for safety evaluation of rockburst mines according to claim 1, characterized in that: Energy released by rock burst W o The estimation method varies depending on the type of rockburst, specifically divided into the energy released by coal seam type rockbursts (W). mt Energy released by roof-type rock bursts (W) db Energy released by fault-type rock bursts (W) dc ; To determine the energy released during a coal-bearing rockburst, only the energy (W) released per unit length of surrounding rock in a roadway under critical conditions is required. mt It can be obtained through equation (9); In the formula, μ is Poisson's ratio; 'a' is the radius of the tunnel; E is the elastic modulus of the surrounding rock; K represents the shock tendency index; The energy released by a roof-type rockburst, specifically the energy released when the roof reaches a critical fracture state and suddenly becomes unstable (W), represents the energy released during the rockburst. db It can be obtained from equation (10); In the formula, L cr The span of the goaf; p represents the load and self-weight of the overlying strata on the top plate, in MPa; b0 is the working face length, m; γ is the overburden fracture angle, rad; d is the distance from the roof to the coal seam, m; h1 is the thickness of the top plate, in meters; E r The elastic modulus of the roof rock is given in MPa. k is the coal seam stiffness coefficient, kN / m; ， ； The energy released by fault-type rock bursts, and the energy released when the surrounding rock of the fault zone reaches the critical state of slippage and suddenly becomes unstable (W). dc It can be obtained from equation (11); In the formula, z is the effective length of the strike of the slip fault, in meters (m). h2 is the fault elevation drop, in meters (m). G is the shear modulus of the rock in the fault zone, in MPa; S1 and S2 are the far-field shear displacements before and after fault slip, respectively, in meters; u1 and u2 are the shear displacements before and after the fault slip, respectively, in meters; X represents the width of the surrounding rock of the fault, in meters (m).

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