Method for determining anti-impact safety level of goaf remaining coal pillar

Abstract

The invention relates to a goaf remaining coal pillar anti-impact safety level determination method, which comprises the steps of calculating a damage variable D, triaxial strength R and a maximum principal stress sigma 1 value of a remaining coal pillar based on petrology physical parameters and crustal stress parameters of the remaining coal pillar, and determining the anti-impact safety level of the remaining coal pillar based on the damage variable D, the triaxial strength R and the maximum principal stress sigma 1 value, calculating a static stability coefficient k1 of the left coal pillar; calculating a dynamic stability coefficient k2 of the remaining coal pillar based on the size and range Se of the elastic region of the remaining coal pillar and the average stress sigma e and yield stress sigma y values of the elastic region; and based on the static stability coefficient k1 and the dynamic stability coefficient k2 of the remaining coal pillar, determining a safety level result, and taking corresponding safety protection measures according to the safety level result. According to the method, the anti-impact safety level of the goaf remaining coal pillar in the rock burst coal seam mining process is evaluated.

Description

Technical Field

[0001] The invention belongs to the technical field of safe mining of coal mines, and in particular relates to a method for determining the anti-bumping safety level of coal pillars left in goaf areas. Background Art

[0002] Rock burst is a typical mining dynamic phenomenon, which is extremely harmful. This dynamic phenomenon instantly releases a large amount of elastic deformation energy accumulated in the coal and rock mass in a sharp and violent form, causing the coal and rock mass to be destroyed and produce strong vibrations. The power will throw the broken coal and rock into the mining space of the shaft and tunnel, making a strong sound, causing equipment damage, shaft and tunnel damage, and casualties. Due to the complex and changeable geological conditions of coal mines and changes in production and technical conditions, coal pillars are often left behind during coal seam mining. The sides and above of these coal pillars are goafs, which are called "coal pillars left behind in goafs". The coal pillars left behind in goafs are under the pressure of the overlying rock strata, and the stress is highly concentrated. The possibility of rock burst is very high. Therefore, Article 31 of the "Detailed Rules for Preventing and Controlling Rock Burst in Coal Mines" stipulates that rock burst coal seams should be mined strictly in sequence, and no isolated coal pillars should be left. No coal pillars should be left in the goaf. If there are special circumstances where coal pillars must be left in the goaf, safety demonstration should be carried out and reported to the technical person in charge of the enterprise for approval, and the location, size and impact range of the coal pillars should be marked on the mining project plan.

[0003] At present, the main method for determining the rock burst safety level of coal pillars left in goafs in the prior art is the engineering analogy method. This method is based on engineering experience, on-site mine pressure data monitoring and analysis, and qualitatively determines whether the coal pillar has rock burst danger and the rock burst danger level. However, this engineering analogy method does not take into account the differences between projects and the special conditions of the project, and many mines have only one or a few cases of coal pillars left in goafs, and the surrounding areas of the coal pillars are no longer monitored, and the on-site mine pressure data cannot be obtained. It can only refer to the impact hazard assessment method of the mining face or the excavation face, thus ignoring the particularity of coal pillars left in goafs, and the safety level conclusion drawn cannot effectively guide mine safety production. The particularity of coal pillars left in goafs refers to the different shapes or sizes of coal pillars left due to different working face layouts or mining conditions. According to engineering experience, it is impossible to completely summarize coal pillars of all shapes and sizes. At the same time, the deformation and failure mode of "legacy coal pillars" is also particular, that is, dynamic impact failure may occur, and overall instability, that is, creep (rheological) large deformation instability may occur.

[0004] In summary, there is no standard or theoretical formula for determining the safety level of coal pillars left in goafs in the prior art. The safety level is mainly qualitatively evaluated based on empirical analogy, and the reliability of the results is poor, which cannot meet the safety production requirements of mines. Therefore, it is of great significance to propose a scientific and reasonable method for determining the safety level of rock burst of coal pillars left in goafs for the safe and efficient mining of rock burst mines. Summary of the invention

[0005] In view of the above analysis, an embodiment of the present invention aims to provide a method for determining the anti-bumping safety level of coal pillars left in goafs, so as to solve the problem that the method of determining the anti-bumping safety level of coal pillars left in goafs based on empirical analogy in the prior art has poor reliability and cannot meet the problem of safe and efficient mining of impact rock pressure mines.

[0006] The object of the present invention is achieved in that:

[0007] A method for determining the anti-bumping safety level of coal pillars left in goaf areas, comprising:

[0008] The damage variable D, triaxial strength R, and maximum principal stress σ1 value of the remaining coal pillar are calculated based on the petrological physical parameters and ground stress parameters of the remaining coal pillar, and the static stability coefficient k1 of the remaining coal pillar is calculated based on the damage variable D, triaxial strength R, and maximum principal stress σ1 value;

[0009] Elastic zone size and range S based on the remaining coal pillar e , the average stress in the elastic region σ e , yield stress σ y Value, calculate the dynamic stability coefficient k2 of the remaining coal pillar;

[0010] Based on the static stability coefficient k1 and the dynamic stability coefficient k2 of the remaining coal pillar, the safety level result is determined, and corresponding safety protection measures are taken according to the safety level result.

[0011] Furthermore, the static stability coefficient k1 of the remaining coal pillar is calculated according to the following formula:

[0012]

[0013] Where:

[0014] R: triaxial strength of coal body, MPa;

[0015] D: damage variable of coal body, %;

[0016] σ1: Maximum principal stress in the remaining coal pillar area, MPa.

[0017] Furthermore, the stability of the remaining coal pillar was preliminarily evaluated for the first time based on the value of the static stability coefficient k1:

[0018] When k1≥1, the remaining coal pillar is in a stable state; when k1<1, the remaining coal pillar is in an unstable state.

[0019] Furthermore, the dynamic stability coefficient k2 of the remaining coal pillar is calculated according to the following formula:

[0020]

[0021] Where:

[0022] S: The total area of ​​the horizontal section in the middle of the remaining coal pillar, m 2 ;

[0023] S e : The area of ​​elastic zone in the horizontal section of the middle part of the remaining coal pillar, m 2 ;

[0024] σ e : Average stress in the elastic zone of the remaining coal pillar, MPa;

[0025] σ y : yield stress of the remaining coal pillar, MPa;

[0026] D: Damage variable of coal body, %.

[0027] Furthermore, the stability state of the remaining coal pillar is preliminarily evaluated for the second time according to the value of the dynamic stability coefficient k2 of the remaining coal pillar:

[0028] 0≤k2<0.25: the remaining coal pillar enters the plastic state;

[0029] 0.25≤k2<0.5: the remaining coal pillar is in a state of impact danger;

[0030] 0.5≤k2<0.75: the remaining coal pillar is in a metastable state;

[0031] 0.75≤k2<1: the remaining coal pillar is in an unstable state;

[0032] k2=1: The remaining coal pillar is in a stable state.

[0033] Furthermore, based on the stability of the remaining coal pillars obtained in the two preliminary assessments and the values ​​of the static stability coefficient k1 and the dynamic stability coefficient k2, the following safety level results are determined, and corresponding safety protection measures are taken according to different safety level results:

[0034] ① The remaining coal pillar is in a stable state as a whole and has no risk of dynamic impact damage. The safety level result is assessed as having no impact risk;

[0035] Safety protection measures under this safety level are: develop a monitoring plan for the area affected by the legacy coal pillar and increase monitoring of microseismic activity to identify potential changes earlier;

[0036] ② The remaining coal pillar is in a plastic state, and the whole coal pillar is in a state of large deformation and instability, and the safety level is assessed as high risk;

[0037] Safety protection measures under this safety level: immediately strengthen the surface support measures of the remaining coal pillars, install high-performance anchors and steel mesh and spray concrete to stabilize the remaining coal pillars;

[0038] ③ The remaining coal pillar is in an unstable state as a whole and is at risk of dynamic impact damage. The safety level result is assessed as having a strong impact risk.

[0039] Safety protection measures at this safety level: restrict access to high-risk areas; install hydraulic support systems with energy absorption and buffering functions; adopt a multi-stage pressure relief strategy to systematically reduce stress in the remaining coal pillars;

[0040] ④ The remaining coal pillar is in an unstable state as a whole and is at risk of dynamic impact damage. The safety level result is assessed as having a medium impact risk.

[0041] Safety protection measures under this safety level: add stress and microseismic monitoring points around the remaining coal pillars to achieve more accurate stress field mapping; adopt enhanced support systems and implement targeted pressure relief;

[0042] ⑤ The remaining coal pillar is in an unstable state as a whole and is at risk of dynamic impact damage. The safety level result is assessed as having a weak impact risk.

[0043] Safety protection measures under this safety level: strengthen the dynamic update of geomechanical models; implement light support measures in the area of ​​residual coal pillars; perform regular drilling decompression;

[0044] ⑥ The remaining coal pillar is in a stable state as a whole, but has the risk of dynamic impact damage, and the safety level result is assessed as having medium impact risk;

[0045] The safety protection measures at this safety level are the same as those at ④;

[0046] ⑦ The remaining coal pillar is in a stable state as a whole, but has the risk of dynamic impact damage, and the safety level result is assessed as having a weak impact risk;

[0047] The safety protection measures under this safety level are the same as ⑤;

[0048] ⑧ The remaining coal pillar is in a stable state as a whole, but has the risk of dynamic impact damage, and the safety level result is assessed as having no impact risk;

[0049] The safety protection measures at this safety level are the same as ①.

[0050] Furthermore, the triaxial strength R value of the remaining coal pillar is calculated according to the following formula:

[0051]

[0052] Where:

[0053] C: cohesion of coal body, MPa;

[0054] E: elastic modulus of coal body, MPa;

[0055] h: height of the remaining coal pillar, m;

[0056] B: Width of the remaining coal pillar, m;

[0057] K: lateral pressure coefficient of coal body (unitless);

[0058] ν: Poisson's ratio of coal body (unitless);

[0059] σ h : horizontal stress of coal body, MPa;

[0060] σ ν : vertical stress of coal body, MPa;

[0061] Internal friction angle of coal body, °.

[0062] Furthermore, the scheme for obtaining the maximum principal stress σ1 of the remaining coal pillar is:

[0063] The maximum principal stress σ1 of the remaining coal pillar is obtained directly by numerical simulation;

[0064] or,

[0065] The stress relief method is used to measure the ground stress in the working face area adjacent to the coal pillar left in the goaf to obtain the maximum principal stress σ1 of the coal body, thereby inferring the maximum principal stress σ1 of the coal pillar left behind;

[0066] or,

[0067] When the goafs on both sides of the remaining coal pillar are in a fully mined state, the maximum load P on the remaining coal pillar is calculated, and the maximum principal stress σ1=P / B of the remaining coal pillar is obtained, where B is the width of the remaining coal pillar, m.

[0068] Furthermore, when the goafs on both sides of the remaining coal pillars are in a fully mined state, the maximum principal stress σ1 of the remaining coal pillars is calculated according to the following formula:

[0069] or,

[0070] Where:

[0071] B is the width of the remaining coal pillar, m;

[0072] γ is the bulk density of the overlying rock layer of the coal seam, and the average value is taken during the calculation process, KN / m 3 ;

[0073] H is the burial depth of the remaining coal pillar, m;

[0074] L b The step length for the old top cycle, m;

[0075] α is the coal wall support influence angle, °.

[0076] Furthermore, the method for determining the anti-bumping safety level of the coal pillars left behind in the goaf also includes: obtaining the petrological and physical parameters of the remaining coal pillars based on the petrological and physical parameters of the coal body in the working face area adjacent to the coal pillars left behind in the goaf; and performing ground stress measurement in the working face area adjacent to the coal pillars left behind in the goaf to obtain the ground stress parameters of the remaining coal pillars.

[0077] Compared with the prior art, the method for determining the anti-bumping safety level of the coal pillar left in the goaf provided by the present invention, based on the theoretical calculation of the triaxial stress strength of the coal pillar left, obtains the vertical stress distribution in the coal pillar left through numerical simulation to obtain the static stability coefficient; at the same time, based on the mechanism of rock burst, the ratio of the area of ​​the elastic zone to the area of ​​the coal pillar left is determined to obtain the dynamic stability coefficient of the coal pillar left; based on the static stability coefficient and the dynamic stability coefficient of the coal pillar left, the impact hazard and hazard level of the coal pillar left are obtained; according to the determined impact hazard level, more scientific anti-bumping safety protection measures for the coal pillar left are given.

[0078] In the present invention, the above-mentioned technical solutions can also be combined with each other to achieve more preferred combination solutions. Other features and advantages of the present invention will be described in the subsequent description, and some advantages can become obvious from the description, or can be understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained through the contents particularly pointed out in the description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0079] In order to more clearly illustrate the embodiments of this specification or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the embodiments of this specification. For ordinary technicians in this field, other drawings can also be obtained based on these drawings.

[0080] Figure 1 This is a schematic diagram of the coal pillars left behind in a typical goaf;

[0081] Figure 2 A schematic diagram of the operation flow of the method for determining the anti-bumping safety level of coal pillars left in goaf areas provided by the present invention;

[0082] Figure 3 A schematic diagram of the maximum stress calculation model of the coal pillars left over from the uphill after full mining on both sides provided by the present invention;

[0083] Figure 4 This is a schematic diagram of the output of the numerical simulation elastic zone in the method provided by the present invention. DETAILED DESCRIPTION

[0084] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0085] To facilitate the understanding of the embodiments of the present application, the following will be further explained with reference to the accompanying drawings, and the embodiments do not constitute a limitation on the embodiments of the present application. In the accompanying drawings, the sizes and relative sizes of the components may be exaggerated for clarity and / or descriptive purposes. When the exemplary embodiments can be implemented differently, the specific process sequence may be performed in a different order than described. For example, two continuously described processes may be performed substantially simultaneously or in an order opposite to the described order. In addition, the same reference numerals represent the same components.

[0086] The terms used here are for the purpose of describing specific embodiments, and are not intended to be restrictive. As used here, unless the context clearly indicates otherwise, the singular forms "one (kind, person)" and "said (the)" are also intended to include plural forms. In addition, when the terms "comprise" and / or "include" and their variations are used in this specification, it is explained that there are stated features, integral bodies, steps, operations, parts, assemblies and / or their groups, but it is not excluded that there are or add one or more other features, integral bodies, steps, operations, parts, assemblies and / or their groups. It should also be noted that, as used here, the terms "substantially", "approximately" and other similar terms are used as approximate terms and not as degree terms, so that they are used to explain the inherent deviations of the measured values, calculated values ​​and / or the values ​​provided that will be recognized by those of ordinary skill in the art.

[0087] Example 1

[0088] A specific embodiment of the present invention discloses a method for determining the anti-bumping safety level of coal pillars left in goaf areas, which is particularly suitable for anti-bumping safety evaluation of coal pillars where both sides and above of the remaining coal pillars are goaf areas and the goaf areas are / will be in a fully mined state, such as Figure 1 shown.

[0089] A method for determining the safety level of coal pillars left in goaf areas, the operation process is as follows: Figure 2 As shown, the following steps are included:

[0090] Step S1: Based on the petrological and physical parameters of the coal body in the working face area adjacent to the leftover coal pillar in the goaf, the petrological and physical parameters of the leftover coal pillar are obtained; and the ground stress measurement is performed in the working face area adjacent to the leftover coal pillar in the goaf to obtain the ground stress parameters of the leftover coal pillar.

[0091] S11: Infer the petrological and physical parameters of the coal body of the legacy coal pillar from the petrological and physical parameters of the coal body adjacent to the legacy coal pillar.

[0092] Specifically, the coal body in the adjacent working face area of ​​the coal pillar left in the goaf was collected, and the physical and mechanical tests of the coal body were carried out according to the national standards GB / T23561.3-2009 and GB / T 23561.7-2009 to obtain the elastic modulus E, Poisson's ratio ν, lateral pressure coefficient K, cohesion C, internal friction angle of the coal body. Uniaxial compressive strength R C , uniaxial tensile strength R t During the test, acoustic emission technology was used to monitor the formation and expansion of internal cracks, and the damage variable D of the coal body was obtained through the number, energy and distribution of acoustic emission events.

[0093] S12: Conducting geostress measurement in the working face area adjacent to the remaining coal pillar in the goaf to obtain geostress parameters of the coal body, that is, obtaining geostress parameters of the remaining coal pillar.

[0094] Specifically, hydraulic fracturing method in-situ stress measurement is carried out in the adjacent working face area of ​​the coal pillar left in the goaf to obtain the minimum horizontal principal stress σ of the coal body. h and the vertical stress σ ν .

[0095] It should be noted that the petrological physical parameters and geostress parameters of the coal body obtained in this step can be considered to be equal to or approximately equal to the petrological physical parameters and geostress parameters of the legacy coal pillar. That is to say, in this embodiment, the relevant parameters of the legacy coal pillar involved in the calculation process, except for the parameters that can be directly obtained such as the width, height, and cross-sectional area of ​​the legacy coal pillar, the remaining parameters can directly use the coal body related parameters of the working face area adjacent to the legacy coal pillar in the goaf.

[0096] Step S2: Based on the petrological physical parameters and ground stress parameters of the remaining coal pillar obtained in step S1, calculate the damage variable D, triaxial strength R, and maximum principal stress σ1 value of the remaining coal pillar, and based on the damage variable D, triaxial strength R, and maximum principal stress σ1 value of the remaining coal pillar, calculate the static stability coefficient k1 of the remaining coal pillar.

[0097] S21: Obtain the maximum principal stress σ1 of the remaining coal pillar and the triaxial strength R of the remaining coal pillar.

[0098] The FLAC computer numerical simulation software was used to model the coal pillars left in the goaf based on the working face layout parameters, stratum characteristic parameters, rock mechanics parameters of each stratum, mining sequence of each working face and other parameters. The constitutive relationship of the coal and rock mass was the MC criterion, that is, the Mohr-Coulomb strength criterion, and the height h and width B of the remaining coal pillars were obtained.

[0099] The triaxial strength R of the remaining coal pillar is calculated using the following formula:

[0100]

[0101] Where:

[0102] C: cohesion of coal body, MPa;

[0103] E: elastic modulus of coal body, MPa;

[0104] h: height of the remaining coal pillar, m;

[0105] B: Width of the remaining coal pillar, m;

[0106] K: lateral pressure coefficient of coal body (unitless);

[0107] ν: Poisson's ratio of coal body (unitless);

[0108] σ h : horizontal stress of coal body, MPa;

[0109] σ ν : vertical stress of coal body, MPa;

[0110] Internal friction angle of coal body, °.

[0111] In this embodiment, when obtaining the maximum principal stress σ1 of the remaining coal pillar in step S21, the following three methods are included:

[0112] The first method: when executing step S21, the maximum principal stress σ1 of the remaining coal pillar is directly obtained by numerical simulation.

[0113] The second method is to measure the ground stress by stress relief method in the working face area adjacent to the coal pillar left in the goaf to obtain the maximum principal stress σ1 of the coal body, thereby inferring the maximum principal stress σ1 of the remaining coal pillar.

[0114] The third method: when the goafs on both sides of the remaining coal pillar are in a fully mined state, the maximum load P on the top of the remaining coal pillar is calculated to obtain the maximum principal stress σ1=P / B of the remaining coal pillar.

[0115] Specifically, the maximum principal stress σ1 of the remaining coal pillar is calculated according to the following steps:

[0116] The first step is to determine whether the goaf on both sides of the remaining coal pillar is in a fully mined state according to the following formula:

[0117] Lc≥L Z ;

[0118] Where: Lc is the size of the goaf, including the dip length and strike length, m; L Z is the breaking step distance of the main key layer, m.

[0119] Among them, according to the columnar diagram of the boreholes in the area of ​​the remaining coal pillar, the distribution of the key layers of the rock strata is judged (the key layer is judged by referring to the "Key Layer Theory of Rock Strata Control"), and the breaking step distance L of the main key layer is calculated according to the following formula: Z ;

[0120]

[0121] In the above formula:

[0122] h ks : thickness of the main key layer, m;

[0123] σ ks : tensile strength of the main key layer, MPa;

[0124] q: The load borne by the main key, MPa, is the self-weight stress of the overlying rock strata above the main key layer.

[0125] Step 2: After determining that the goaf on both sides of the remaining coal pillar is in a fully mined state, calculate the maximum load P above the remaining coal pillar, and then obtain σ1=P / B.

[0126] For full mining on both sides, such as the attached Figure 3 As shown, the maximum load P on the remaining coal pillar is calculated according to the following formula:

[0127] P=BγH+0.3γH 2 ;or,

[0128] Based on the calculation formula of the maximum load P above the remaining coal pillar, the calculation formula of the maximum principal stress σ1 of the remaining coal pillar is:

[0129] or,

[0130] In the above formula:

[0131] B is the width of the remaining coal pillar, m;

[0132] γ is the bulk density of the overlying rock layer of the coal seam, and the average value is taken during the calculation process, KN / m 3 ;

[0133] H is the burial depth of the remaining coal pillar, m;

[0134] L b The step length for the old top cycle, m;

[0135] α is the coal wall support influence angle, which is generally 60 to 80°.

[0136] Step S22: Based on the petrological physical parameters and ground stress parameters of the coal body obtained in step S1, the damage variable D, triaxial strength R, and maximum principal stress σ1 value of the remaining coal pillar are calculated, and based on the obtained damage variable D, triaxial strength R, and maximum principal stress σ1 value of the remaining coal pillar, the static stability coefficient k1 of the remaining coal pillar is calculated using the following formula:

[0137]

[0138] Where:

[0139] R: triaxial strength of coal body, MPa;

[0140] D: damage variable of coal body, %;

[0141] σ1: Maximum principal stress in the remaining coal pillar area, MPa.

[0142] Step S23: Preliminarily evaluate the stability of the remaining coal pillar for the first time according to the value of the static stability coefficient k1, specifically: when k1≥1, the remaining coal pillar is in a stable state; when k1<1, the remaining coal pillar is in an unstable state.

[0143] Step S3: Based on the elastic zone size and range S of the remaining coal pillar e , the average stress in the elastic region σ e , yield stress σ y value, calculate the dynamic stability coefficient k2 of the remaining coal pillar, and evaluate the status of the remaining coal pillar.

[0144] Step S31: Obtain the elastic zone size and range S of the remaining coal pillar e , the average stress in the elastic region σ e , yield stress σ y The steps are as follows:

[0145] Based on the numerical simulation results in step S2, the total horizontal section area S of the middle of the remaining coal pillar is taken to obtain the elastic zone size and range S in the remaining coal pillar. e and the average stress σ in the elastic region e , see Figure 4 ;

[0146] According to the coal test data in step S1, based on the Mohr-Coulomb yield criterion in rock mechanics theory, the cohesion C and internal friction angle of the remaining coal pillar are calculated. To calculate the yield stress σ of the remaining coal pillar y :

[0147]

[0148] Step S32: Based on the obtained S of the remaining coal pillar e , σ e , σ y , the dynamic stability coefficient k2 of the remaining coal pillar is calculated using the following formula:

[0149]

[0150] Where:

[0151] S: The total area of ​​the horizontal section in the middle of the remaining coal pillar, m 2 ;

[0152] S e : The area of ​​elastic zone in the horizontal section of the middle part of the remaining coal pillar, m 2 ;

[0153] σ e : Average stress in the elastic zone of the remaining coal pillar, MPa;

[0154] σ y : yield stress of the remaining coal pillar, MPa;

[0155] D: Damage variable of coal body, %.

[0156] Step S33: Preliminarily evaluate the stability of the remaining coal pillar for the second time according to the value of the dynamic stability coefficient k2 of the remaining coal pillar, specifically:

[0157] 0≤k2<0.25: the remaining coal pillar enters the plastic state;

[0158] 0.25≤k2<0.5: the remaining coal pillar is in a state of impact danger;

[0159] 0.5≤k2<0.75: the remaining coal pillar is in a metastable state;

[0160] 0.75≤k2<1: the remaining coal pillar is in an unstable state;

[0161] k2=1: The remaining coal pillar is in a stable state.

[0162] Step S4: Based on the stability state of the remaining coal pillars obtained through two preliminary assessments and the static stability coefficient k1 and the dynamic stability coefficient k2, the safety level result is determined using the following standards, and corresponding prevention and control pressure relief measures are taken according to the safety level result.

[0163] ① The remaining coal pillar is in a stable state as a whole and is not at risk of dynamic impact damage. Taking into account the static and dynamic stability factors, the safety level is assessed to be free of impact risk.

[0164] At this safety level, the remaining coal pillar is in a safe state. It will not be destroyed by dynamic impact and can maintain long-term stability. However, the following safety protection measures are still needed: a strict monitoring plan is needed for the area affected by the remaining coal pillar, and increased monitoring of microseismic activities is needed to identify potential changes earlier.

[0165] ② The remaining coal pillar is in a plastic state, and the whole coal pillar is deformed and unstable, and cannot remain stable. The safety level is assessed as high risk.

[0166] At this safety level, the following safety protection measures are adopted: the surface support measures of the remaining coal pillars need to be strengthened immediately, and high-performance anchors and steel meshes, as well as shotcrete and other measures need to be installed to stabilize the remaining coal pillars.

[0167] ③ The remaining coal pillar is in an unstable state as a whole and is at risk of dynamic impact damage. Based on the comprehensive static and dynamic stability factors, the safety level is assessed as having a strong impact risk.

[0168] At this safety level, the following safety protection measures are adopted: access to high-risk areas needs to be restricted; advanced hydraulic support systems with energy absorption and buffering functions are installed; and multi-stage pressure relief strategies, including hydraulic fracturing, drilling pressure relief and blasting pressure relief, are adopted to systematically reduce the stress in the remaining coal pillars.

[0169] ④ The remaining coal pillar is in an unstable state as a whole and has the risk of dynamic impact damage. Based on the comprehensive static and dynamic stability factors, the safety level result is assessed as having a medium impact risk.

[0170] At this safety level, the following safety protection measures are adopted: additional stress and microseismic monitoring points need to be added around the remaining coal pillars to achieve more accurate stress field mapping; enhanced support systems such as fiber reinforced plastic (FRP) anchors and high-power shotcrete are used; and targeted pressure relief is implemented, such as intensive drilling and water injection in the expected stress concentration areas.

[0171] ⑤ The remaining coal pillar is in an unstable state as a whole and has the risk of dynamic impact damage. Based on the comprehensive static and dynamic stability factors, the safety level result is assessed as having a weak impact risk.

[0172] At this safety level, the following safety protection measures are adopted: it is necessary to strengthen the dynamic update of the geomechanical model, especially when the mining activities change; implement light support measures in the area of ​​​​remaining coal pillars, such as installing resin anchors and light steel frames; perform regular drilling decompression, especially at critical moments before and after mining.

[0173] ⑥ The remaining coal pillar is in a stable state as a whole, but has the risk of dynamic impact damage. Considering the static and dynamic stability factors, the safety level result is assessed as having a medium impact risk.

[0174] At this safety level, the prevention, control and pressure relief measures are the same as ④.

[0175] ⑦ The remaining coal pillar is in a stable state as a whole, but has the risk of dynamic impact damage. Considering the static and dynamic stability factors, the safety level result is assessed as having a weak impact risk.

[0176] At this safety level, the prevention, control and pressure relief measures are the same as ⑤.

[0177] ⑧ The remaining coal pillar is in a stable state as a whole, but has the risk of dynamic impact damage. Considering the static and dynamic stability factors, the safety level result is assessed as having no impact risk.

[0178] At this safety level, the prevention and pressure relief measures are the same as ①.

[0179] Compared with the prior art, the method for determining the anti-bumping safety level of coal pillars left in goaf provided in this embodiment has the following beneficial effects:

[0180] 1. On the basis of theoretical calculation of triaxial stress strength of the remaining coal pillar, the vertical stress distribution in the remaining coal pillar is obtained through numerical simulation, and the static stability coefficient is obtained; at the same time, based on the mechanism of rock burst, the ratio of the elastic zone area to the remaining coal pillar area is determined to obtain the dynamic stability coefficient of the remaining coal pillar; based on the static stability coefficient and dynamic stability coefficient of the remaining coal pillar, the impact hazard and hazard level of the remaining coal pillar are obtained; according to the determined impact hazard level, more scientific anti-impact safety protection measures for the remaining coal pillar are given.

[0181] 2. The parameters used in the present invention include: uniaxial compressive strength of coal, uniaxial tensile strength or internal cohesion of coal, bulk density of coal and burial depth of remaining coal pillars, etc. These parameters are basic macroscopic mechanical parameters that are easy to obtain, the data are stable and reliable, and the proposed calculation formula is concise, the calculation process is simple and clear, and the operability is strong. It can not only ensure that the remaining coal pillars do not cause impact ground pressure, but also recover coal resources to the greatest extent, solving the contradiction between coal resource recovery and safety, and transforming the traditional empirical design method into quantitative calculation, which is scientific and reasonable.

[0182] 3. The present invention realizes specific analysis of specific areas, from qualitative empirical judgment to quantitative mechanical calculation. The calculation parameters are basic macroscopic mechanical parameters, which are very easy to obtain in the laboratory, and the values ​​are stable. The results are of universal significance. Compared with the engineering analogy method in the prior art, the theoretical basis of the present invention is more sufficient and targeted, the operability of engineers is stronger, the analysis and calculation process is clearer, the formula is simpler, the parameters are easier to obtain, the calculation and design results are more reliable and accurate, and the prevention and control of rock burst is more targeted. At the same time, the method of the present invention can also be extended to the evaluation and design of various types of legacy coal pillars.

[0183] The specific implementation methods described above further illustrate the purpose, technical solutions and beneficial effects of the present application in detail. It should be understood that the above description is only the specific implementation method of the present application and is not intended to limit the scope of protection of the present application. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present application should be included in the scope of protection of the present application.

Claims

1. A method for determining the safety level of coal pillars left in goaf, characterized in that: include: The damage variable D, triaxial strength R, and maximum principal stress σ1 value of the remaining coal pillar are calculated based on the petrological physical parameters and ground stress parameters of the remaining coal pillar, and the static stability coefficient k1 of the remaining coal pillar is calculated based on the damage variable D, triaxial strength R, and maximum principal stress σ1 value; Elastic zone size and range S based on the remaining coal pillar e , the average stress in the elastic region σ e , yield stress σ y Value, calculate the dynamic stability coefficient k2 of the remaining coal pillar; Based on the static stability coefficient k1 and the dynamic stability coefficient k2 of the remaining coal pillar, the safety level result is determined, and corresponding safety protection measures are taken according to the safety level result.

2. The method for determining the anti-bumping safety level of coal pillars left in goaf according to claim 1 is characterized in that: The static stability coefficient k1 of the remaining coal pillar is calculated according to the following formula: Where: R: triaxial strength of coal body, MPa; D: damage variable of coal body, %; σ1: Maximum principal stress in the remaining coal pillar area, MPa.

3. The method for determining the anti-bumping safety level of coal pillars left in goaf according to claim 2 is characterized in that: The stability of the remaining coal pillar was first preliminarily evaluated based on the value of the static stability coefficient k1: When k1≥1, the remaining coal pillar is in a stable state; when k1<1, the remaining coal pillar is in an unstable state.

4. The method for determining the anti-bumping safety level of coal pillars left in goaf according to claim 2 or 3, characterized in that: The dynamic stability coefficient k2 of the remaining coal pillar is calculated according to the following formula: Where: S: The total area of ​​the horizontal section in the middle of the remaining coal pillar, m 2 ; S e : The area of ​​elastic zone in the horizontal section of the middle part of the remaining coal pillar, m 2 ; σ e : Average stress in the elastic zone of the remaining coal pillar, MPa; σ y : yield stress of the remaining coal pillar, MPa; D: Damage variable of coal body, %.

5. The method for determining the anti-bumping safety level of coal pillars left in goaf according to claim 4 is characterized in that: The stability of the remaining coal pillar is preliminarily evaluated for the second time according to the value of the dynamic stability coefficient k2 of the remaining coal pillar: 0≤k2<0.25: the remaining coal pillar enters the plastic state; 0.25≤k2<0.5: the remaining coal pillar is in a state of impact danger; 0.5≤k2<0.75: the remaining coal pillar is in a metastable state; 0.75≤k2<1: the remaining coal pillar is in an unstable state; k2=1: The remaining coal pillar is in a stable state.

6. The method for determining the anti-bumping safety level of coal pillars left in goaf according to claim 5 is characterized in that: Based on the stability of the remaining coal pillars from the two preliminary assessments and the values ​​of the static stability coefficient k1 and the dynamic stability coefficient k2, the following safety level results are determined, and corresponding safety protection measures are taken according to different safety level results: ① The remaining coal pillar is in a stable state as a whole and has no risk of dynamic impact damage. The safety level result is assessed as having no impact risk; Safety protection measures under this safety level are: develop a monitoring plan for the area affected by the legacy coal pillar and increase monitoring of microseismic activity to identify potential changes earlier; ② The remaining coal pillar is in a plastic state, and the whole coal pillar is in a state of large deformation and instability, and the safety level is assessed as high risk; Safety protection measures under this safety level: immediately strengthen the surface support measures of the remaining coal pillars, install high-performance anchors and steel mesh, and spray concrete to stabilize the remaining coal pillars; ③ The remaining coal pillar is in an unstable state as a whole and is at risk of dynamic impact damage. The safety level result is assessed as having a strong impact risk. Safety measures at this safety level: restrict access to high-risk areas; install a hydraulic support system with energy absorption and buffering functions; A multi-stage decompression strategy is used to systematically reduce stress in the legacy coal pillar; ④ The remaining coal pillar is in an unstable state as a whole and is at risk of dynamic impact damage. The safety level is assessed as having a medium impact risk. Safety protection measures under this safety level: add stress and microseismic monitoring points around the remaining coal pillars to achieve more accurate stress field mapping; adopt enhanced support systems and implement targeted pressure relief; ⑤ The remaining coal pillar is in an unstable state as a whole and is at risk of dynamic impact damage. The safety level result is assessed as having a weak impact risk. Safety protection measures under this safety level: strengthen the dynamic update of geomechanical models; implement light support measures in the area of ​​residual coal pillars; perform regular drilling decompression; ⑥ The remaining coal pillar is in a stable state as a whole, but has the risk of dynamic impact damage, and the safety level result is assessed as having medium impact risk; The safety protection measures at this safety level are the same as those at ④; ⑦ The remaining coal pillar is in a stable state as a whole, but has the risk of dynamic impact damage, and the safety level result is assessed as having a weak impact risk; The safety protection measures under this safety level are the same as ⑤; ⑧ The remaining coal pillar is in a stable state as a whole, but has the risk of dynamic impact damage, and the safety level result is assessed as having no impact risk; The safety protection measures at this safety level are the same as ①.

7. The method for determining the anti-bumping safety level of coal pillars left in goaf according to claim 1 is characterized in that: The triaxial strength R value of the remaining coal pillar is calculated according to the following formula: Where: C: cohesion of coal body, MPa; E: elastic modulus of coal body, MPa; h: height of the remaining coal pillar, m; B: Width of the remaining coal pillar, m; K: lateral pressure coefficient of coal body; ν: Poisson's ratio of coal body; σ h : horizontal stress of coal body, MPa; σ ν : vertical stress of coal body, MPa; Internal friction angle of coal body, °.

8. The method for determining the anti-bumping safety level of coal pillars left in goaf according to claim 1 is characterized in that: The scheme for obtaining the maximum principal stress σ1 of the remaining coal pillar is: The maximum principal stress σ1 of the remaining coal pillar is obtained directly by numerical simulation; or, The stress relief method is used to measure the ground stress in the working face area adjacent to the coal pillar left in the goaf to obtain the maximum principal stress σ1 of the coal body, thereby inferring the maximum principal stress σ1 of the coal pillar left behind; or, When the goafs on both sides of the remaining coal pillar are in a fully mined state, the maximum load P on the remaining coal pillar is calculated, and the maximum principal stress σ1=P / B of the remaining coal pillar is obtained, where B is the width of the remaining coal pillar, m.

9. The method for determining the anti-bumping safety level of coal pillars left in goaf according to claim 8, characterized in that: When the goaf on both sides of the remaining coal pillar is in a fully mined state, the maximum principal stress σ1 of the remaining coal pillar is calculated according to the following formula: Where: B is the width of the remaining coal pillar, m; γ is the bulk density of the overlying rock layer of the coal seam, and the average value is taken during the calculation process, KN / m 3 ; H is the burial depth of the remaining coal pillar, m; L b The step length for the old top cycle, m; α is the coal wall support influence angle, °.

10. The method for determining the anti-bumping safety level of coal pillars left in goaf according to claim 1, characterized in that: Also includes: Based on the petrological and physical parameters of the coal body in the adjacent working face area of ​​the coal pillar left behind in the goaf, the petrological and physical parameters of the coal pillar left behind are obtained; The ground stress measurement is carried out in the working face area adjacent to the remaining coal pillar in the goaf to obtain the ground stress parameters of the remaining coal pillar.

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