Research

15 pages, 2847 KiB

Open AccessArticle

The Physical Behavior of Protected Coal Seams Based on Triaxial Unloading Conditions

by Zhiheng Chen, Junhua Xue, Lanlan Guo, Renhui Cheng, Quanlin Yang and Jian Xiao

Sustainability 2024, 16(2), 922; https://doi.org/10.3390/su16020922 - 22 Jan 2024

Viewed by 474

Protective seam mining is the most economical and effective measure for eliminating coal and gas herniation. To study the unloading effect of the mining of a protective seam on the protected layer, and to better grasp the effect of the protective layer on [...] Read more.

Protective seam mining is the most economical and effective measure for eliminating coal and gas herniation. To study the unloading effect of the mining of a protective seam on the protected layer, and to better grasp the effect of the protective layer on the abatement, conventional triaxial tests were conducted on coal samples with the unloading of the axial pressure and the peripheral pressure. The results showed that, under the unloading path, the bias stress–axial strain curve showed a sudden upward trend upon unloading, and the slope of the curve increased suddenly, which was more obvious after the peripheral pressure exceeded 10 MPa; stress unloading before the peak accelerated the yielding of the specimen. Under the unloading test path, the deformation modulus of the coal samples decreased with the decrease in the perimeter pressure, while the damage factor and Poisson’s ratio increased with the decrease in the perimeter pressure. Compared to the conventional triaxial test, under the unloading condition, the cohesion of the coal samples at peak stress decreased by 93.41% and the angle of internal friction increased by 37.41%, while the cohesion at the moment of residual strength decreased by 89.60% and the angle of internal friction increased by 37.44°. The brittleness index of the coal samples under unloading conditions with a peripheral pressure of 5 MPa, 10 MPa, 15 MPa, and 20 MPa increased by 178.83%, 159.18%, 87.93%, and 63.89%, respectively, compared to the conventional triaxial test. It can be seen that the greater the enclosing pressure, the smaller the difference in the brittleness index of the coal body. Full article

(This article belongs to the Special Issue Prevention and Control of Coal Mine Gas Disasters)

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18 pages, 11979 KiB

Open AccessArticle

A Method for Dividing Rockburst Risk Zones—A Case Study of the Hegang Mining Area in China

by Jiewen Pang, Xiaojie Yang, Shaoqiang Yang, Yongliang He, Jianlin Xie and Qiaoyun Han

Sustainability 2023, 15(20), 14808; https://doi.org/10.3390/su152014808 - 12 Oct 2023

Viewed by 523

Abstract

Rockbursts are serious mine disasters. Through the division of rockburst risk zones, risks can be predicted in advance and measures can be implemented to prevent disasters. In this paper, taking the Hegang mining area as an example, we propose a method for dividing [...] Read more.

Rockbursts are serious mine disasters. Through the division of rockburst risk zones, risks can be predicted in advance and measures can be implemented to prevent disasters. In this paper, taking the Hegang mining area as an example, we propose a method for dividing rockburst risk zones based on in-situ stress measurements. First, 24 survey points were established in the Hegang mining area to measure the in-situ stress. Second, based on the in-situ stress measurement data, eight representative prospecting lines were selected to establish a numerical model, and the distribution characteristics of the in-situ stress field at mining elevations of −330 m and −450 m in the Hegang mining area were obtained via the linear differential method. Afterward, division criteria for rockburst risk zones were proposed in accordance with the energy criterion and the minimum energy principle. Finally, the Hegang mining area was divided into rockburst risk zones in accordance with the in-situ microseismic monitoring data and simulation results for the in-situ stress field. Coal seam #3 was chosen as an example to illustrate rockburst risk-zone division in the Hegang mining area considering the division criterion proposed herein, and a rockburst risk zoning map of coal seam #3 in the Hegang mining area was finally obtained. The locations of the five rockbursts that have occurred in coal seam #3 of the Hegang mining area were marked on the risk zoning map and were found to have occurred in the threatened zone. Thus, it was shown that the proposed rockburst risk-zone division method is reasonable. Therefore, the results of this study could serve as a reference for the division of rockburst risk zones. Full article

(This article belongs to the Special Issue Prevention and Control of Coal Mine Gas Disasters)

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13 pages, 3376 KiB

Open AccessArticle

Research on Hole Collapse Monitoring Technology of Coal Seam Gas Extraction Boreholes

by Renhui Cheng, Chao Zhang, Fuhuai Fan, Chenye Duan and Zhiheng Chen

Sustainability 2023, 15(13), 10262; https://doi.org/10.3390/su151310262 - 28 Jun 2023

Viewed by 678

Abstract

It is difficult to monitor the collapse position of a gas extraction borehole in a coal seam. In order to solve this problem, a fiber-optic grating collapse monitoring technology was proposed. Five kinds of grating arrangements (0°, 45°, 90°, 135°, 180°) were examined [...] Read more.

It is difficult to monitor the collapse position of a gas extraction borehole in a coal seam. In order to solve this problem, a fiber-optic grating collapse monitoring technology was proposed. Five kinds of grating arrangements (0°, 45°, 90°, 135°, 180°) were examined to simulate the hole collapse. The relationship model between the center wavelength offset and the amount of collapsed coal and extraction flow was constructed to obtain the distribution curve of the hole collapse position and quality along the length of the hole, and flow decay rates of 80% and 50% were used as the critical values to classify the three levels of hole collapse. The results show that the hole collapse monitoring accuracy is the highest with the grating measurement points located below the substrate material arrangement. Finally, the effectiveness of fiber-optic grating monitoring technology was verified in the 2202 working face of the Changcun coal mine of the Lu’an Group, and the pure amount of gas extraction from the repaired borehole after monitoring was increased by 62.6% compared with that before the repair. Full article

(This article belongs to the Special Issue Prevention and Control of Coal Mine Gas Disasters)

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23 pages, 8434 KiB

Open AccessArticle

Fracture Evolution Characteristics and Deformation Laws of Overlying Strata during the Initial Period of Longwall Mining: Case Study

by Chuantian Li, Yongliang He, Xiaoyuan Sun and Yuping Fu

Sustainability 2023, 15(11), 8596; https://doi.org/10.3390/su15118596 - 25 May 2023

Cited by 1 | Viewed by 790

Abstract

Coal mining causes overlying rocks to collapse and be destroyed. Overburdened crevasses provide a channel for gas discharge, which is a serious safety hazard. To study the evolution characteristics and migration pattern of overburdened fissures during the initial mining period, the 24207 working [...] Read more.

Coal mining causes overlying rocks to collapse and be destroyed. Overburdened crevasses provide a channel for gas discharge, which is a serious safety hazard. To study the evolution characteristics and migration pattern of overburdened fissures during the initial mining period, the 24207 working face of the Shaquan mine was used as a research object. Through similar physical simulation tests, a mechanical model of the mining structure during the initial mining period was constructed to explore the factors influencing the movement pattern of the overburden strata during the initial mining period. The research results show that the evolution of mining-induced fractures in the overburdened strata in the initial mining period mainly experience the slow and rapid rising stages of the fracture dimension, while the stable mining period is in the stable development stage of the fracture dimension. The research results will help supplement and improve the theory of gas disaster prevention and comprehensive resource utilization in the initial mining stage under the mining conditions of high gas and low permeability coal seam group, achieve the goal of “coal and gas co-mining”, and ensure the safe and efficient production of mines. Full article

(This article belongs to the Special Issue Prevention and Control of Coal Mine Gas Disasters)

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14 pages, 6440 KiB

Open AccessArticle

Numerical Investigation on Potential Influencing Factors Affecting Drainage Effective Radius of Crossing Borehole

by Wu Xiao, Ke Li, Chuanjie Zhu, Ziwen Li, Baiquan Lin, Cong Ma and Mingkai Si

Sustainability 2023, 15(3), 2485; https://doi.org/10.3390/su15032485 - 30 Jan 2023

Viewed by 973

Abstract

Crossing borehole is an effective means to eliminate the outburst risk of coal and gas. The influence of borehole inclination angle, borehole diameter, and drainage time on the effective radius of gas drainage are studied by numerical simulation and engineering example verification. The [...] Read more.

Crossing borehole is an effective means to eliminate the outburst risk of coal and gas. The influence of borehole inclination angle, borehole diameter, and drainage time on the effective radius of gas drainage are studied by numerical simulation and engineering example verification. The study shows that the effective radius changes in a “U” shape with the increase in borehole inclination angle. When the angle α of the borehole and coal seam plane decreases, the effective radius increases. Furthermore, the coal mass around the borehole is broken by shear deformation, which is consistent with the results of the inner peephole. The effective radiuses are different in coal seam dip X and strike Y. When α is small, the effective radius in the X direction is generally wider. When α is large (α ≤ 90°), the effective radiuses in the X and Y directions are close. The effective radius is positively correlated with the borehole diameter and is more significantly influenced by increasing borehole diameter when α is small. The effective radius increases as a negative exponential function with time and eventually converges to a constant. The study has practical implications for the design of crossing borehole in the coal seam floor. Full article

(This article belongs to the Special Issue Prevention and Control of Coal Mine Gas Disasters)

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11 pages, 2968 KiB

Open AccessArticle

Investigation on the Gas Drainage Effectiveness from Coal Seams by Parallel Boreholes

by Chuantian Li, Yingfeng Sun, Shiyue Wu and Xiaoyuan Sun

Sustainability 2023, 15(2), 942; https://doi.org/10.3390/su15020942 - 04 Jan 2023

Cited by 1 | Viewed by 749

Abstract

Gas drainage is an important technology to prevent coal and gas outburst, and the drained gas is a kind of clean energy. The gas pressure can characterize gas drainage effectiveness. In this paper, we investigated the effectiveness of gas drainage by gas pressure. [...] Read more.

Gas drainage is an important technology to prevent coal and gas outburst, and the drained gas is a kind of clean energy. The gas pressure can characterize gas drainage effectiveness. In this paper, we investigated the effectiveness of gas drainage by gas pressure. Determined by the space shape of the gas flow field, the gas flow state surrounding the drainage boreholes is radial flow. According to the basic equations of radial flow, discrete equations were achieved by the implicit difference scheme, and then we obtained the gas pressure surrounding the drainage boreholes. Results showed that the midpoint between two holes presents the highest gas pressure, and gas pressure declined from the midpoint of two boreholes to both sides. The midpoint gas pressure of the two holes reflects gas drainage effectiveness in a certain degree. Gas pressure declined with segmented characteristics in the first period decline curve in the form of a cubic curve, and the second period decline curve in the form of a straight line. When the drainage pressure reaches a certain value, the decline rate of gas pressure had little relationship with the drainage negative pressure, mainly influenced by the permeability coefficient. To improve the drainage effectiveness, anti-reflection measures are feasible, instead of increasing the drainage negative pressure. Moreover, the conclusion was verified by field data. Full article

(This article belongs to the Special Issue Prevention and Control of Coal Mine Gas Disasters)

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16 pages, 4662 KiB

Open AccessArticle

Data Mining in Coal-Mine Gas Explosion Accidents Based on Evidence-Based Safety: A Case Study in China

by Jiaqi Hu, Rui Huang and Fangting Xu

Sustainability 2022, 14(24), 16346; https://doi.org/10.3390/su142416346 - 07 Dec 2022

Cited by 3 | Viewed by 1663

Abstract

From an informatics perspective, decision-making failures in accident prevention are due to insufficient necessary safety evidence. Analyzing accident data can help in obtaining safety evidence. Currently, such a practice mostly relies on experts’ judgement and experience, which are subjective and inefficient. Furthermore, due [...] Read more.

From an informatics perspective, decision-making failures in accident prevention are due to insufficient necessary safety evidence. Analyzing accident data can help in obtaining safety evidence. Currently, such a practice mostly relies on experts’ judgement and experience, which are subjective and inefficient. Furthermore, due to the inadequate safety-related theoretical support, the sustainable safety of a system can hardly be achieved purposefully. To automatically explore and obtain latent safety evidence in coal-mine data, and improve the reliability and sustainability of coal-mine safety management, a novel framework of combining data mining technology and evidence-based safety (EBS) theory is proposed, and was applied to a coal gas explosion accident. First, the term frequency-inverse document (TF-IDF) and TextRank algorithms were fused to extract keywords, and keyword evolution word cloud maps from the time dimension were drawn to obtain keyword safety evidence. Then, on the basis of the latent Dirichlet allocation (LDA) model, the best safety evidence, such as accident causation topics and causation factors, were mined, and safety decisions were given. The results show that accident data mining, based on evidence-based safety, can effectively and purposefully mine the best safety evidence, and guide safety decision making to optimize safety management models and achieve sustainable safety. Full article

(This article belongs to the Special Issue Prevention and Control of Coal Mine Gas Disasters)

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18 pages, 6484 KiB

Open AccessArticle

Study on Coal Seepage Characteristics and Secondary Enhanced Gas Extraction Technology under Dual Stress Disturbance

by Xiong Ding, Cheng Zhai, Jizhao Xu, Xu Yu and Yong Sun

Sustainability 2022, 14(22), 15118; https://doi.org/10.3390/su142215118 - 15 Nov 2022

Cited by 1 | Viewed by 1049

Abstract

During the mining of coal seams with outburst hazard, abnormal gas emissions in front of the coal mining working face (CMWF) may induce gas overrun. To address this technical problem, this study analyzed the permeability variation of coal in front of the CMWF [...] Read more.

During the mining of coal seams with outburst hazard, abnormal gas emissions in front of the coal mining working face (CMWF) may induce gas overrun. To address this technical problem, this study analyzed the permeability variation of coal in front of the CMWF at different stress paths through physical experiments, numerical simulation and on-site tests. The spatial-temporal evolution law of the unloading area of the working face under dual stress disturbance caused by hydraulic punching (HP) and coal seam mining was explored; next, a secondary enhanced extraction technology was proposed and applied in the Shoushan No. 1 Coal Mine, Henan Province, China. The results reveal the following: (1) the coal permeability decreases linearly with increasing confining pressure (CP) and axial pressure (AP) under Stress Paths 1 and 2 (that is, fixed AP and CP). (2) The coal permeability is negatively related to the distance from the stress peak point under Stress Paths 3 and 4 (that is, AP and CP are, respectively, the vertical stress and horizontal stress before the stress peak). (3) As the distance from the peak stress declines, the reduction amplitude of coal permeability in the test area first decreases, and then increases, under Stress Paths 5 and 6 (that is, the vertical stress as CP and the horizontal stress as AP). The plastic damage range of coal around the HP cavities expands due to the dual impact of HP and coal seam mining, which can realize both regional unloading and provide channels for gas extraction within 60 m in front of the CMWF. According to the gas extraction concentration of boreholes, the coal body in front of the CMWF is divided into three zones: efficient, effective and original extraction zones. The efficient extraction zone is within 20 m in front of the CMWF, with an average gas extraction concentration of over 30%. In the effective extraction zone, the gas extraction concentration falls with the increase in the distance from the CMWF. The original extraction zone is beyond 50–60 m, and the borehole gas concentration stabilizes below 10%. The number of extraction boreholes in the stress disturbance area of the middle-floor gas extraction roadway accounts for 5–10% of the total number of boreholes, but its maximum monthly extraction volume can reach 38.5% of the total volume. Full article

(This article belongs to the Special Issue Prevention and Control of Coal Mine Gas Disasters)

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15 pages, 6578 KiB

Open AccessArticle

Numerical Simulation Study of High-Pressure Air Injection to Promote Gas Drainage

by Wenjie Xu, Xigui Zheng, Cancan Liu, Peng Li, Boyang Li, Kundai Michael Shayanowako, Jiyu Wang, Xiaowei Guo and Guowei Lai

Sustainability 2022, 14(21), 13699; https://doi.org/10.3390/su142113699 - 22 Oct 2022

Viewed by 967

Abstract

Coal-accompanying gas is an essential resource, with numerous mining methods. The practice has proved that injecting high-pressure air into the coal seam can replace and flush the gas in the coal seam, effectively solving the problem of inadequate single gas drainage in soft [...] Read more.

Coal-accompanying gas is an essential resource, with numerous mining methods. The practice has proved that injecting high-pressure air into the coal seam can replace and flush the gas in the coal seam, effectively solving the problem of inadequate single gas drainage in soft and low permeability coal seams. This paper uses the finite element method to solve the model, simulate and study the gas drainage by high-pressure air injection in the bedding drilling, and establish a fluid-structure coupling model for gas drainage by high-pressure air injection. The competitive adsorption of N₂, O₂, and CH₄, diffusion and migration of CH₄ in coal matrix and fissure, matrix deformation caused by CH₄ adsorption, and desorption and control of coal deformation by applied stress are considered in the model. When the fixed extraction time is 600 days (d), the optimal spacing between the extraction hole and injection hole is 12.5 m. The safe extraction effect and minimum drilling amount can be ensured. It provides a basis for guiding gas drainage by injecting high-pressure air on-site. Full article

(This article belongs to the Special Issue Prevention and Control of Coal Mine Gas Disasters)

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