Island working face impact risk evaluation method based on digital core

Abstract

The invention relates to the technical field of coal mine rock burst risk judgment, in particular to an island working face impact risk evaluation method based on a digital rock core, which adopts a method of combining small-diameter coring and large-diameter pressure relief drilling, and can obtain a solid coal core of a dangerous area of an island working face, and also can obtain a real coal core of a dangerous area of the island working face. The conditions of fracture distribution and collapse of the large-diameter pressure relief drill holes can be observed, the large-diameter pressure relief drill holes can be used for pressure relief and relief of the island working face, and harm caused by rock burst disasters is weakened. Impact risk evaluation is carried out on the island working face in mining based on the entropy weight method, and whether the current mining state is safe or not can be analyzed more visually. According to the method, the evaluation object is more specific, the evaluation index is more targeted, the evaluation factor is more scientific and reasonable, and the evaluation result can truly reflect the impact danger state of the evaluation area. The method is based on actual requirements of a coal mine, guides the coal mine to carry out rock burst prevention and control work, and has important practical significance for guaranteeing safe production of the coal mine.

Description

Technical Field

[0001] The invention relates to the technical field of coal mine rock burst hazard identification, in particular to an island working face rock burst hazard assessment method based on digital rock cores. Background Art

[0002] Coal is one of the main energy sources. With the increase of mining years, mines will enter the deep development stage. Due to the unreasonable mining design in the early stage, some rock burst mines adopt the mining method of skipping, resulting in the emergence of isolated working faces in a large number of mining areas at the end of mining, and the potential risk of underground dynamic disasters represented by rock burst is greatly increased. Rock burst in coal mines is a dynamic disaster phenomenon in which the accumulated elastic energy is released instantly when the coal rock mass is unstable and destroyed during the mining process. In order to reduce the impact of rock burst disasters on the normal mining operations of isolated working faces, the evaluation of rock burst hazards in isolated working faces is particularly important. The "Coal Mine Safety Regulations" (revised in 2016) stipulates that when mining coal seams with rock burst tendency, rock burst hazard assessment must be carried out; however, there is currently no unified "rock burst hazard assessment method" standard, and most of the existing evaluation indicators also ignore the role of changes in coal and rock physical properties in the potential rock burst disaster area in the evaluation. The reason is that it is difficult to obtain the physical properties and internal structure changes of rock burst coal and rock using traditional monitoring methods. With the maturity of mine full-core CT scanning technology, digital core technology, which comprehensively reflects the physical properties of coal and rock, has gradually been applied in engineering sites for prevention and control of rock burst disasters, becoming an important means of predicting rock burst disasters. Summary of the invention

[0003] In view of the deficiencies in the above-mentioned prior art, the present invention proposes a method for assessing rock burst risk of an isolated working face based on digital cores, which is used for assessing rock burst risk during mining of an isolated working face in a coal mine, and comprises the following steps:

[0004] S1: For longwall isolated working faces with potential rock burst danger, in the mining tunnels on both sides of the isolated working face, ahead of the coal mining area by a certain distance, several layer-by-layer core drilling holes are constructed from the side of the tunnel to the coal mining working face, and then a large-diameter spiral drill is used to concentrically expand the hole to form a pressure relief hole;

[0005] Preferably, the distance between the advanced coal mining area and the core drilling area is about 40-50m, the core drilling depth is 20-40m, the core drilling spacing is 2-5m when multiple core drilling holes are constructed, and the core drilling diameter is The diameter of the hole is

[0006] S2: Use laser endoscope technology to observe and record the cracks and deformation of the inner wall of the pressure relief borehole; count the length of the borehole, the total number of cracks on the inner surface of the borehole, and the crack opening of each crack; calculate the crack density, average crack opening and maximum crack opening of the inner wall of the borehole;

[0007] S3: After a certain period of time after the pressure relief borehole is formed, observe the collapse of the pressure relief borehole; measure the arbitrary radial cross-sectional area and arbitrary radial cross-sectional volume of the pressure relief borehole after collapse by laser endoscopy technology; obtain the ratio of the collapsed volume to the original volume of the pressure relief borehole; use the ratio of the maximum collapsed area of ​​the pressure relief borehole to the original cross-sectional area of ​​the pressure relief borehole to statistically describe the collapse variable of the pressure relief borehole;

[0008] S4: Perform CT scanning on the drilled core, reconstruct and analyze the core CT scanning data to obtain a detailed three-dimensional model of the drilled core; use the data statistics function in the avizo software to obtain the core fracture density, average fracture opening and maximum fracture opening;

[0009] S5: The mining conditions of the isolated working face are described by the mining depth, the distance between the basic top and the coal seam, the structural complexity of the area where the isolated working face is located, the impact tendency of the coal, and the coefficient of variation of the coal seam thickness;

[0010] S6: The fracture characteristics in the pressure relief borehole obtained in step S2, the collapse characteristics of the pressure relief borehole obtained in step S3, the core fracture characteristics of the coring borehole obtained in step S4, and the mining conditions of the isolated working face are used as impact hazard evaluation indicators. Each impact hazard evaluation indicator is divided into multiple value ranges and corresponding hazard index scores are set. The more dangerous the hazard index, the greater the score.

[0011] Determining the impact hazard index of isolated working face using entropy weight method

[0012]

[0013] Where, M is the impact hazard index of the isolated working face; M i is the risk index score corresponding to the i-th impact risk assessment index; M imax is the maximum risk index score corresponding to the i-th impact risk assessment index; n i The number of indicators for impact risk assessment;

[0014] S7: The impact hazard level is determined according to the impact hazard index, which is divided into five categories; when M<0.25, there is no impact hazard; when 0.25≤M<0.5, there is a weak impact hazard; when 0.5≤M<0.75, there is a medium impact hazard; when 0.75≤M<0.95, there is a strong impact hazard; when M≥0.95, it is an unsafe state; when 0.5≤M, an early warning warning needs to be issued.

[0015] Beneficial effects: Aiming at the problem of rock burst evaluation in isolated working faces, the present invention adopts a method combining small-diameter coring with large-diameter pressure relief drilling, which can not only obtain the solid coal core in the dangerous area of ​​the isolated working face, but also observe the distribution and collapse of the cracks in the large-diameter pressure relief drilling holes, and can also use the large-diameter pressure relief drilling holes to relieve the pressure of the isolated working face and reduce the harm caused by rock burst disasters. Based on the entropy weight method, the impact hazard evaluation of the isolated working face in mining can more intuitively analyze whether the current mining status is safe. In the present invention, the evaluation object is more specific, the evaluation indicators are more targeted, the evaluation factors are more scientific and reasonable, and the evaluation results can truly reflect the impact hazard status of the evaluation area. The present invention introduces advanced digital core technology, which can more accurately obtain the fracture structure in the core and better enable the early warning evaluation of the impact hazard of the isolated working face; the present invention is based on the actual needs of coal mines, guides coal mines to carry out rock burst prevention and control work, and has important practical significance for ensuring the safe production of coal mines. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a flow chart of the impact hazard assessment method for an isolated working face of the present invention;

[0017] Figure 2 It is a schematic diagram of the method for determining the distribution parameters of cracks in the pressure relief borehole;

[0018] Figure 3 Schematic diagram of the method for determining the collapse variables of the depressurized borehole. DETAILED DESCRIPTION

[0019] The technical solution of the present invention is described in more detail below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0020] The present invention is a method for evaluating rock burst risk of isolated working face based on digital core, which is used for evaluating rock burst risk during mining of isolated working face in coal mines. Figure 1 As shown, the following steps are included:

[0021] S1: For longwall isolated working faces with potential rock burst danger, in the mining tunnels on both sides of the isolated working face, ahead of the coal mining area for a certain distance, 1-3 layer-by-layer core drilling holes are constructed from the side of the tunnel to the coal mining working face, and then a large-diameter spiral drill is used to concentrically expand the hole to form a pressure relief hole; the ahead coal mining area for a certain distance is about 40-50m, the core drilling depth is 20-40m, and the core drilling spacing is 2-5m when constructing multiple core drilling holes. The core drilling diameter is The diameter of the hole is

[0022] The small-diameter coring and large-diameter hole expansion method of the present invention can not only obtain the core of the high-stress area of ​​the isolated island working face, but also release the pressure accumulated in the coal body of the isolated island working face through the large-diameter pressure relief drilling, thereby reducing the risk of rock burst.

[0023] S2: Figure 2 As shown in the figure, the laser endoscope technology is used to observe and record the cracks and deformation of the inner wall of the pressure relief borehole; the borehole length L, the total number of cracks on the inner surface of the borehole N, the crack opening C of each crack are counted i ; Calculate the crack density N on the inner wall of the borehole avg =N / L; average crack opening Maximum crack opening C m =Max{C i};

[0024] S3: Figure 3 As shown in the figure, 24 hours after the pressure relief borehole was formed, the collapse of the pressure relief borehole was observed; the arbitrary radial cross-sectional area S of the pressure relief borehole after collapse was measured by laser endoscopy technology. i And any radial cross-sectional volume V s The ratio of the collapsed volume to the original volume of the decompression borehole can be expressed by the formula The ratio of the maximum collapse area of ​​the pressure relief borehole to the original cross-sectional area of ​​the pressure relief borehole is obtained. To statistically describe the variables of decompression borehole collapse;

[0025] S4: For the drilled core, the whole core CT scanning method is used to scan the whole core of more than 1m at a time; the fine three-dimensional model of the drilled core is obtained by reconstructing and analyzing the core CT scanning data; the data statistics function in the avizo software is used to obtain the fracture density n, average fracture opening c and maximum fracture opening c of the core m ;

[0026] S5: Analyze the mining conditions of the isolated working face, using the mining depth h, the distance d between the key roof layer (basic roof) and the coal seam, the structural complexity f of the area where the isolated working face is located, the impact tendency of coal, and the coefficient of variation γ of the coal seam thickness as the description of the mining conditions of the isolated working face;

[0027] S6: The fracture characteristics in the pressure relief borehole obtained in step S2, the collapse characteristics of the pressure relief borehole obtained in step S3, the core fracture characteristics of the coring borehole obtained in step S4, and the mining conditions of the isolated working face are used as impact hazard evaluation indicators. Each impact hazard evaluation indicator is divided into multiple value ranges and a corresponding hazard index score is set. The more dangerous the hazard, the greater the hazard index score. The impact hazard evaluation indicators and the corresponding hazard index scores in this embodiment are shown in Table 1;

[0028] Table 1 Impact hazard evaluation indicators and corresponding hazard index scores

[0029]

[0030]

[0031] Determining the impact hazard index of isolated working face using entropy weight method

[0032]

[0033] Where, M is the impact hazard index of the isolated working face; M i is the risk index score corresponding to the i-th impact risk assessment index; M imax is the maximum risk index score corresponding to the i-th impact risk assessment index; n i The number of indicators for impact risk assessment;

[0034] The present invention adopts the entropy weight method to determine the impact hazard index of the isolated working face, which can standardize various impact hazard evaluation indicators, eliminate the influence of dimension and order of magnitude, and make the weight calculation more accurate.

[0035] S7: As shown in Table 2, the impact hazard level is determined according to the impact hazard index, which is divided into five categories; when M < 0.25, the impact hazard level belongs to Class A, which means no impact hazard; when 0.25 ≤ M < 0.5, the impact hazard level belongs to Class B, which means weak impact hazard; when 0.5 ≤ M < 0.75, the impact hazard level belongs to Class C, which means medium impact hazard; when 0.75 ≤ M < 0.95, the impact hazard level belongs to Class D, which means strong impact hazard; when M ≥ 0.95, the impact hazard level belongs to Class E, which means unsafe state; when 0.5 ≤ M, that is, when the impact hazard level is higher than Class C, an early warning warning needs to be issued; for different impact hazard levels, corresponding levels of response measures should be taken.

[0036] Table 2 Impact hazard levels and solution strategies

[0037]

[0038] Although the present invention has been described in detail above by general description and specific embodiments, it is obvious to those skilled in the art that some modifications or improvements can be made to the present invention. Therefore, these modifications or improvements made without departing from the spirit of the present invention all belong to the scope of protection claimed by the present invention.

Claims

1. A method for assessing rock burst risk of isolated working face based on digital core, which is used for assessing rock burst risk during mining of isolated working face in coal mines, and is characterized by: The following steps are involved: S1: For longwall isolated working faces with potential rock burst danger, in the mining tunnels on both sides of the isolated working face, ahead of the coal mining area by a certain distance, several layer-by-layer core drilling holes are constructed from the side of the tunnel to the coal mining working face, and then a large-diameter spiral drill is used to concentrically expand the hole to form a pressure relief hole; S2: Use laser endoscope technology to observe and record the cracks and deformation of the inner wall of the pressure relief borehole; count the length of the borehole, the total number of cracks on the inner surface of the borehole, and the crack opening of each crack; calculate the crack density, average crack opening and maximum crack opening of the inner wall of the borehole; S3: After a certain period of time after the pressure relief borehole is formed, observe the collapse of the pressure relief borehole; measure the arbitrary radial cross-sectional area and arbitrary radial cross-sectional volume of the pressure relief borehole after collapse by laser endoscopy technology; obtain the ratio of the collapsed volume to the original volume of the pressure relief borehole; use the ratio of the maximum collapsed area of ​​the pressure relief borehole to the original cross-sectional area of ​​the pressure relief borehole to statistically describe the collapse variable of the pressure relief borehole; S4: Perform CT scanning on the drilled core, reconstruct and analyze the core CT scanning data to obtain a detailed three-dimensional model of the drilled core; use the data statistics function in the avizo software to obtain the core fracture density, average fracture opening and maximum fracture opening; S5: The mining conditions of the isolated working face are described by the mining depth, the distance between the basic top and the coal seam, the structural complexity of the area where the isolated working face is located, the impact tendency of the coal, and the coefficient of variation of the coal seam thickness; S6: The fracture characteristics in the pressure relief borehole obtained in step S2, the collapse characteristics of the pressure relief borehole obtained in step S3, the core fracture characteristics of the coring borehole obtained in step S4, and the mining conditions of the isolated working face are used as impact hazard evaluation indicators. Each impact hazard evaluation indicator is divided into multiple value ranges and corresponding hazard index scores are set. The more dangerous the hazard index, the greater the score. Determining the impact hazard index of isolated working face using entropy weight method Where, M is the impact hazard index of the isolated working face; M i is the risk index score corresponding to the i-th impact risk assessment index; M imax is the maximum risk index score corresponding to the i-th impact risk assessment index; n i The number of indicators for impact risk assessment; S7: The impact hazard level is determined according to the impact hazard index, which is divided into five categories; when M<0.25, there is no impact hazard; when 0.25≤M<0.5, there is a weak impact hazard; when 0.5≤M<0.75, there is a medium impact hazard; when 0.75≤M<0.95, there is a strong impact hazard; when M≥0.95, it is an unsafe state; when 0.5≤M, an early warning warning needs to be issued.

2. The method for assessing the impact hazard of an isolated working face based on digital core according to claim 1 is characterized in that: The distance to the advanced coal mining area is about 40-50m, the core drilling depth is 20-40m, the core drilling spacing is 2-5m when constructing multiple core drilling holes, and the core drilling diameter is The diameter of the hole is

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