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20 pages, 11224 KiB

Open AccessArticle

Analysis of Rock Breaking Parameters and Simulation of Mechanical Characteristics of Multi-Nozzle Jet Impact

by Yanbao Liu, Lipeng He, Linchao Dai, Kai Shen and Quanbin Ba

Sustainability 2023, 15(16), 12414; https://doi.org/10.3390/su151612414 - 15 Aug 2023

Viewed by 864

Abstract

With the continuous development of high-pressure water jet technology, research on the optimization of structural parameters for multi-nozzle configurations, the perforation effect of jet rotational impact rock breaking, and the impact force during rock breaking has received increasing attention. Through the development of [...] Read more.

With the continuous development of high-pressure water jet technology, research on the optimization of structural parameters for multi-nozzle configurations, the perforation effect of jet rotational impact rock breaking, and the impact force during rock breaking has received increasing attention. Through the development of a self-designed high-pressure water jet rotational drilling test device, rock breaking experiments were conducted on sandstone of different strengths using jet streams with different inclination angles, various combinations of nozzles, different target distances, and different rotational speeds. The parameters and structure of the multi-nozzle jet drill bit were optimized, and the impact of water jet-rock breaking effects was studied. The rationality of different inclination-angle jet streams in rock breaking was verified using the ALE-FEM coupling method. The changes in the force on the target body and the fragmentation mode during rock breaking with different inclination-angle jet streams were analyzed. The results showed that under the condition of adjustable inclination angles, a smaller inclination angle resulted in greater depth and a smaller diameter of rock breaking, while a larger inclination angle resulted in greater width and a smaller depth of rock breaking. The optimal combination of multi-nozzle jet streams was determined to be 20°, 30°, and 60°, which achieved a balance between rock breaking and borehole expansion performance. The efficiency of multi-nozzle jet rotational rock breaking decreased with increasing target distance, with the optimal range being 2 to 4 mm. The rotational speed of the multi-nozzle jet stream had a significant impact on rock-breaking efficiency. Under the same target distance conditions, as the drilling speed increased, the volume of rock breaking initially increased and then decreased, and the rate of volume attenuation increased with increasing target distance. The forms of rock breaking in multi-nozzle jet streams were not identical. Jet streams with smaller inclination angles mainly caused tensile failure through axial impact, while those with larger inclination angles primarily caused shear failure through radial impact. This study provides valuable guidance for optimizing the structural parameters of multi-nozzle jet drill bits and researching rotational rock breaking. Full article

(This article belongs to the Special Issue Sustainable Mining and Emergency Prevention and Control)

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18 pages, 862 KiB

Open AccessArticle

Energy Saving and Emission Reduction Potential Evaluation of a Coal Mine Based on Fuzzy Hierarchical Analysis

by Fenfang Xu, Ruili Hu, Minbo Zhang, Weizhong Zhang, Qinrong Kang and Mengzhen Du

Sustainability 2023, 15(15), 11754; https://doi.org/10.3390/su151511754 - 30 Jul 2023

Viewed by 736

Abstract

Due to the non-renewability of coal resources and the effect of excessive resource loss on the economic development of enterprises forming a constraint, breakthroughs in high energy consumption to achieve energy saving and emission reduction in coal mines represent an important way to [...] Read more.

Due to the non-renewability of coal resources and the effect of excessive resource loss on the economic development of enterprises forming a constraint, breakthroughs in high energy consumption to achieve energy saving and emission reduction in coal mines represent an important way to promote the development of coal enterprises. This paper takes the energy-saving work of the Wuyang coal mine, which is very representative of China’s Shanxi Province, as an example, and uses hierarchical analysis to establish an assessment system for energy conservation and emission reduction in coal mines. We adopted on-site research, expert scoring, and project guidance to divide the factors affecting energy conservation and emission reduction in the Wuyang coal mine into 24 categories, and we then used fuzzy mathematical calculations to assess potential, which is of better practicability. The study shows that the grade of energy saving and emission reduction in the Wuyang coal mine is of a medium level, and the potential of energy saving and emission reduction is large. The main influencing factors are improving the recovery rate of refined coal, renovating pressurized filters, eliminating high-energy-consuming equipment, optimizing the parking process, replacing the flotation machine, and ensuring the intelligent management of power metering. According to the relevant factors derived from the energy-saving and emission reduction work at the Wuyang coal mine for implementing the relevant measures, we provide a reference for the work of energy saving and emission reduction in mines in order to promote the sustainable development of the coal mining industry. Full article

(This article belongs to the Special Issue Sustainable Mining and Emergency Prevention and Control)

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16 pages, 3083 KiB

Open AccessArticle

Experimental Study on Strength and Liquefaction Characteristics of Sand under Dynamic Loading

by Yongbo Cai, Yanlu Zhang, Qingjie Qi, Ye Cheng, Yongbo Shi and Zuo Sun

Sustainability 2023, 15(13), 10306; https://doi.org/10.3390/su151310306 - 29 Jun 2023

Viewed by 802

Abstract

To investigate the influence of moisture content, density, and loading frequency on the dynamic strength and liquefaction characteristics of sandy soil, a series of vibration triaxial tests were designed and conducted. The tests were divided into incremental loading tests and cyclic loading failure [...] Read more.

To investigate the influence of moisture content, density, and loading frequency on the dynamic strength and liquefaction characteristics of sandy soil, a series of vibration triaxial tests were designed and conducted. The tests were divided into incremental loading tests and cyclic loading failure tests. The results of the incremental loading tests indicated that the shear modulus decreases with increasing moisture content and density, while it increases with increasing loading frequency. The damping ratio of unsaturated samples showed no significant correlation with moisture content, whereas samples with a density above 50% exhibited an increasing trend in damping ratio with increasing density. The damping characteristics of the sandy soil were found to be related to the loading frequency, exhibiting the characteristics of viscous damping. The results of the cyclic loading tests revealed that the dynamic failure mode of the sand soil is the ultimate equilibrium failure mode. Increasing moisture content and decreasing density make the samples more susceptible to failure. During the process of cyclic loading leading to dynamic failure, the shear modulus of unsaturated samples remains constant, while the shear modulus of saturated samples gradually decreases. The damping ratio of saturated soil is significantly higher than that of unsaturated soil. During the process of cyclic loading leading to dynamic failure, the damping ratio of saturated soil shows no apparent correlation with loading frequency, but it decreases with increasing density. Full article

(This article belongs to the Special Issue Sustainable Mining and Emergency Prevention and Control)

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19 pages, 475 KiB

Open AccessArticle

Coal Mine Fire Emergency Rescue Capability Assessment and Emergency Disposal Research

by Kejiang Lei, Dandan Qiu, Shilong Zhang, Zichao Wang and Yan Jin

Sustainability 2023, 15(11), 8501; https://doi.org/10.3390/su15118501 - 24 May 2023

Cited by 3 | Viewed by 1449

Abstract

Nowadays, underground coal mine accidents occur frequently, causing huge casualties and economic losses, most of which are gas explosion accidents caused by fires. In order to improve the emergency rescue capability of coal mine fires and reduce the losses caused by coal mine [...] Read more.

Nowadays, underground coal mine accidents occur frequently, causing huge casualties and economic losses, most of which are gas explosion accidents caused by fires. In order to improve the emergency rescue capability of coal mine fires and reduce the losses caused by coal mine fires, this article is dedicated to the assessment of coal mine fire rescue capability. Taking the fire emergency rescue system of Lugou mine as an example, based on the introduction of gray system theory and gray evaluation method, an evaluation model was established to assess the risk of the fire emergency rescue index system of Lugou mine. Four primary and 19 secondary indicators were delineated, and a hierarchical structure model of the fire emergency rescue capability of the Lugou mine was established by combining expert opinions, and the weights of indicators at all levels were calculated by using hierarchical analysis. We then used the gray system evaluation method and expert scoring to judge the safety level of various indicator factors in the index system. The evaluation results show that the risk level of the emergency rescue system of the Lugou mine fire is higher than the fourth level. The main risk indicator factors are firefighting equipment, decision-making command, emergency education and training, and fire accident alarm. In response to this evaluation result, corresponding control measures were formulated in four aspects: rescue organization guarantee, personnel guarantee, material guarantee, and information guarantee, which optimally improved the emergency rescue capability of the Lugou mine fire and reduced the loss caused by fire. Full article

(This article belongs to the Special Issue Sustainable Mining and Emergency Prevention and Control)

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19 pages, 6633 KiB

Open AccessArticle

Simulation Study on the Characteristics of Gas Extraction from Coal Seams Based on the Superposition Effect and Hole Placement Method

by Jin Yan, Minbo Zhang, Weizhong Zhang and Qinrong Kang

Sustainability 2023, 15(10), 8409; https://doi.org/10.3390/su15108409 - 22 May 2023

Cited by 2 | Viewed by 967

Abstract

In order to obtain a reasonable extraction drilling method for coal seam working faces and to carry out targeted as well as cost-effective hole placement optimization, a gas–solid coupled model based on the coal rock deformation field and the matrix–fissure dual seepage–diffusion field [...] Read more.

In order to obtain a reasonable extraction drilling method for coal seam working faces and to carry out targeted as well as cost-effective hole placement optimization, a gas–solid coupled model based on the coal rock deformation field and the matrix–fissure dual seepage–diffusion field was established and numerically solved via the use of COMSOL Multiphysics finite element software to optimize the gas transport parameters of the Dongpang coal mine based on the study of the coal seam gas transport law. This study shows the following: With an increase in the extraction time, the gas content of the coal seam was reduced to a minimum. It shows that, with an increase in the extraction time, the gas pressure and seepage velocity keep decreasing the stable value, the main stress around the borehole redistributes, and the coal permeability keeps decreasing with an increase in the decay coefficient. The extraction radius of the boreholes increases exponentially with the extraction time, and the reasonable extraction hole size is 94 mm; the use of multiple boreholes for pre-drawing gas via the use of the interval between the effective extraction radius and the influence radius results in a blind extraction zone caused by the superposition effect between the boreholes, and the residual gas value of the coal seam increases with an increase in the borehole spacing. The use of an equilateral triangular hole layout can avoid the extraction blind zone, and the pre-sumping effect is good after field application, which ensures the safe production of coal mines as well as the reasonable use of resources. Full article

(This article belongs to the Special Issue Sustainable Mining and Emergency Prevention and Control)

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14 pages, 3340 KiB

Open AccessArticle

Numerical Simulation of Effective Extraction Radius of Pre-Drainage Borehole Based on Coal Damage Model

by Dangyu Zhang, Minbo Zhang, Shilong Zhang, Zichao Wang, Yan Jin and Rentao Liu

Sustainability 2023, 15(5), 4446; https://doi.org/10.3390/su15054446 - 02 Mar 2023

Cited by 2 | Viewed by 1031

Abstract

Borehole pre-drainage is an important technical means to control a coal mine gas disaster. In order to determine the optimal pre-drainage parameters of Dashucun mine, a coal damage permeability evolution model was established based on coal damage deformation, considering gas adsorption and desorption [...] Read more.

Borehole pre-drainage is an important technical means to control a coal mine gas disaster. In order to determine the optimal pre-drainage parameters of Dashucun mine, a coal damage permeability evolution model was established based on coal damage deformation, considering gas adsorption and desorption and the Klinkenberg effect, and a damage fluid-structure coupling model of coal seam containing gas was established by combining the coal seam deformation equation and the mass conservation equation. COMSOL software was used to simulate the influence of factors such as the initial permeability of coal seam, negative pumping pressure, aperture and pumping time on the effective pumping radius of pre-drainage borehole. The results show that the effect of negative pressure on the effective extraction radius can be ignored. The effect of borehole aperture, initial permeability of coal seam and extraction time on effective extraction radius is great, which conforms to the power function relationship, and the coefficient correlation value is high. The optimal extraction parameters of Dashucun mine are determined as borehole diameter 113 mm, coal seam permeability 1 × 10⁻¹⁷ m², negative extraction pressure 30 kPa and extraction time 180 d. The research results can provide theoretical reference for the pre-drainage of gas in Dashucun mine. Full article

(This article belongs to the Special Issue Sustainable Mining and Emergency Prevention and Control)

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23 pages, 8297 KiB

Open AccessArticle

Asymmetric Damage Mechanisms and Prevention Technology in Large-Section Gob-Side Entry Retaining

by Hongzhi Yang, Dongpan Wang, Wenjun Ju, Weiming Yuan and Chao Su

Sustainability 2023, 15(1), 739; https://doi.org/10.3390/su15010739 - 31 Dec 2022

Cited by 4 | Viewed by 1046

Abstract

Based on the deformation and damage characteristics of the surrounding rock in a large-section gob-side entry retaining and combined with field observations and an analysis of the dominant factors, an overall deformation control plan is formulated. The plan mainly includes a structure of [...] Read more.

Based on the deformation and damage characteristics of the surrounding rock in a large-section gob-side entry retaining and combined with field observations and an analysis of the dominant factors, an overall deformation control plan is formulated. The plan mainly includes a structure of high strength, high stiffness and high ductility for roadside support; the reinforcement of the roadway-in support; and the setup entry hydraulic fracturing pressure release mechanism and advanced long, horizontal borehole “fracturing-jet” pressure relief technology. Industrial field tests were completed taking Tangan coal mine as the engineering background. The research shows that the large-section gob-side entry retaining has the typical “asymmetric” overall deformation and damage characteristics, including top coal sinking along the inner side of the roadside support, the whole roadside support structure skewing, and even splitting damage; floor heaving; and the coal-side bolt support structure basically losing support ability and bulging out from the coal side. The dominant factors of deformation damage are disintegration of the floor mudstone by water and deflection deformation under horizontal stress, splitting damage in the concrete roadside support under asymmetric load, damage and expansion due to the insufficient strength of the coal side support, strong dynamic pressure on the roof, and the mutual influence of support and pressure relief. The industrial test shows that the deformation control scheme optimizes the stress environment of the gob-side entry retaining space, the deformation control effect is remarkable, and the roadside fully meets the reuse requirements. Full article

(This article belongs to the Special Issue Sustainable Mining and Emergency Prevention and Control)

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15 pages, 2876 KiB

Open AccessArticle

Allocation of Resources for Emergency Response to Coal-to-Oil Hazardous Chemical Accidents under Railway Transportation Mode

by Kaigong Zhao, Xiaolei Zhang, Hui Wang, Yongling Gai and Haiyan Wang

Sustainability 2022, 14(24), 16777; https://doi.org/10.3390/su142416777 - 14 Dec 2022

Cited by 4 | Viewed by 1222

Abstract

Railways of the National Energy Group using their own trains have become an important mode of transportation for coal-to-oil hazardous chemicals. Under the circumstances of the shortage of emergency resources and the coupling of multiple disasters, how to establish an effective and reasonable [...] Read more.

Railways of the National Energy Group using their own trains have become an important mode of transportation for coal-to-oil hazardous chemicals. Under the circumstances of the shortage of emergency resources and the coupling of multiple disasters, how to establish an effective and reasonable emergency resource allocation scheme for the railway transportation of dangerous chemicals from a disaster site is of great significance to the national task of ensuring safety for the transportation of energy. This paper focuses on the allocation of emergency rescue resources for railway transportation accidents involving coal-to-oil hazardous chemicals, considering the scenarios of the leakage of coal-to-oil, railway line damage, etc. According to the number of trapped people at the initial moment, the disaster situation and accident type, affected areas, etc., a multi-objective optimization model with the shortest response time of the emergency team and the lowest cost of transporting emergency materials along the railway transportation channel of coal-to-oil hazardous chemicals is constructed, based on the calculation method using the initial weight and the emergency weight assigned by the emergency rescue team. Furthermore, in order to avoid the problem of the weight of the local accident points being too small to participate in a rescue, a bee colony algorithm model based on pre-allocation was designed and compared with two traditional algorithms, allowing the realization of the search and selection of allocation methods. The analysis of the examples shows that the proposed method is efficient and fast, and the research results are practical and feasible, which can provide a scientific basis for the rapid decision of emergency rescue resource allocation in multi-disaster scenarios for large energy groups, and provide a reference for the allocation of public security emergency resources in the national emergency response. Full article

(This article belongs to the Special Issue Sustainable Mining and Emergency Prevention and Control)

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14 pages, 2942 KiB

Open AccessArticle

Vulnerability Assessment of Mine Flooding Disaster Induced by Rainstorm Based on Tri-AHP

by Zuo Sun, Qingjie Qi and Yingjie Liu

Sustainability 2022, 14(24), 16731; https://doi.org/10.3390/su142416731 - 13 Dec 2022

Viewed by 1136

Abstract

As a disaster-bearing body, the coal mine is vulnerable to the impact threat of rainstorm disasters, which easily induce flooding accidents. In view of this, this study is designed to propose the vulnerability assessment method of rainstorm-induced coal mine flooding disasters. On account [...] Read more.

As a disaster-bearing body, the coal mine is vulnerable to the impact threat of rainstorm disasters, which easily induce flooding accidents. In view of this, this study is designed to propose the vulnerability assessment method of rainstorm-induced coal mine flooding disasters. On account of the scientific theory of disaster risk, the evaluation model and index system of coal mine flooding disaster induced by rainstorm covering exposure, fortification level, and resilience are constructed, while the vulnerability assessment method based on Tri-AHP method is proposed. Study results demonstrate that population exerts the greatest impact on exposure, wellhead elevation matters the most for fortification level, and the emergency plan has a dominant influence on resilience. Therefore, for coal mines, it is suggested to strengthen the special rainstorm emergency plan drill, improve the fortification level, and solidify the emergency duty during the rainy season. In this study, the rainstorm disaster vulnerability assessment method of coal mine is innovatively put forward, which is conducive to sustainable energy and environmental development. Full article

(This article belongs to the Special Issue Sustainable Mining and Emergency Prevention and Control)

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18 pages, 8804 KiB

Open AccessArticle

Analysis of the Failure Characteristics and Main Controlling Factors of Surrounding Rocks Using the Standard Specimen with a Pre-Existing Hole

by Zheng Wu, Jun Li, Wen-Long Zhang and Chen Li

Sustainability 2022, 14(21), 14379; https://doi.org/10.3390/su142114379 - 03 Nov 2022

Viewed by 973

Abstract

To analyze the relationship between the butterfly-shaped plastic zone and stress in the rock with a single hole, we investigated the influence law of four factors, namely, the shape of the hole, the loaded confining pressure value, the bidirectional stress ratio, and the [...] Read more.

To analyze the relationship between the butterfly-shaped plastic zone and stress in the rock with a single hole, we investigated the influence law of four factors, namely, the shape of the hole, the loaded confining pressure value, the bidirectional stress ratio, and the hole location on the volume of the butterfly-shaped plastic zone of the standard specimen with a single hole based on the orthogonal test and numerical simulation. The results show that: (I) The bidirectional stress ratio has a significant effect on the size of the plastic zone of the rock with a single hole, while the shape of the hole has no effect. (II) The basic value of confining pressure can weaken the sensitivity of the bidirectional stress ratio required to generate the butterfly-shaped plastic zone, that is, when the confining pressure value increases, the bidirectional stress ratio required to generate the butterfly-shaped plastic zone decreases, but there is always a certain value for the infinite expansion of the plastic zone. (III) The plastic zone of the rock with a single hole has a butterfly-shaped invariance, which means that the failure form of the surrounding rock around the hole will eventually evolve into a butterfly-shaped plastic zone under the state of a non-uniform stress field that reaches a certain bidirectional stress ratio. The research results of this paper have guiding significance for the stability control of the surrounding rock in underground engineering under the non-uniform stress field environment. Full article

(This article belongs to the Special Issue Sustainable Mining and Emergency Prevention and Control)

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13 pages, 2086 KiB

Open AccessArticle

Characterization of Tensile Crack Propagation and Energy Evolution during the Failure of Coal–Rock Samples Containing Holes

by Chen Jing and Lei Zhang

Sustainability 2022, 14(21), 14279; https://doi.org/10.3390/su142114279 - 01 Nov 2022

Cited by 4 | Viewed by 1191

Abstract

The instability and fracturing of gas drainage boreholes are one of the main causes of low drainage efficiency. Based on the rock mass energy principle and the Barenblatt model, the energy evolution of the coal–rock mass around the hole, the conversion characteristics of [...] Read more.

The instability and fracturing of gas drainage boreholes are one of the main causes of low drainage efficiency. Based on the rock mass energy principle and the Barenblatt model, the energy evolution of the coal–rock mass around the hole, the conversion characteristics of the dissipated energy U^d, and the propagation pattern of the initial tensile cracks were investigated. The results show that based on the conversion process of the dissipated energy, the failure process of samples containing holes can be divided into an initial dissipation stage, a decelerated dissipation stage, a stable dissipation stage, and an accelerated dissipation stage. The dissipated energy is always greater than the elastic energy during the first half of loading, and it is mainly used for the continuous development and propagation of initial tensile cracks. Then, remote cracks and cracks to the left and right of the hole boundary are generated to inhibit the propagation of the tensile cracks. Later, when the energy storage limit is reached, the elastic strain energy around the hole is released, and the macroscopic failure cracks propagate and coalesce, which causes the stress environment to change and the tensile cracks to reopen and finally propagate. The tensile cracks in the upper and lower ends of the holes undergo an opening–closing–reopening process, and the presence of cohesion c(x) hinders the propagation of the tensile cracks that are formed by the generation and migration of fracture initiation zone, friction zone, and intact zone. The dissipated energy released was related to the different stages of the tensile crack propagation, which could be used for the structure monitoring and flaw predicting of the gas drainage borehole. Full article

(This article belongs to the Special Issue Sustainable Mining and Emergency Prevention and Control)

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12 pages, 4964 KiB

Open AccessArticle

Study on Mine Pressure Behavior Law of Mining Roadway Passing Concentrated Coal Pillar and Goaf

by Xiaolong Li, Shengjie Wei and Jun Wang

Sustainability 2022, 14(20), 13175; https://doi.org/10.3390/su142013175 - 14 Oct 2022

Cited by 2 | Viewed by 782

Abstract

Based on the special spatial position of 1–2 coal and 2–2 coal, this paper adopts a new way of modeling by fish and overcomes the difficulty of modeling, simulates the influence of the coal pillar on the 22,206 return airway after mining 1–2 [...] Read more.

Based on the special spatial position of 1–2 coal and 2–2 coal, this paper adopts a new way of modeling by fish and overcomes the difficulty of modeling, simulates the influence of the coal pillar on the 22,206 return airway after mining 1–2 coal seam by Flac3D, studies the 22,206 return airway under the influence of primary and secondary mining, and puts forward the support scheme of the 22,206 return airway. The following conclusions are obtained: (1) After mining 1–2 coal, the stress of the 22,206–return airway under the residual coal pillar of 1–2 coal increased. The maximum stress position is below the middle coal pillar of 1–2 coal, and its maximum vertical stress (σv_max) and maximum horizontal stress (σh_max) are 6.24 MPa and 4.09 MPa, respectively. (2) The rule of 22,206 return airway’s pressure appearance is that the stress and plastic zone becomes larger when near the coal pillar, becomes smaller when far from the coal pillar, the maximum failure radius of roof and floor is only 1.3 m, and 0.6 m, the maximum failure radius of roadway side is 0.6 m and 1.5 m after the second mining. (3) According to the proposed support scheme, field experiments found that the maximum displacement is less than 120 mm, which can effectively guarantee the stability of the roadway. Full article

(This article belongs to the Special Issue Sustainable Mining and Emergency Prevention and Control)

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20 pages, 5377 KiB

Open AccessArticle

Quantitative Evaluation of Complex Degree of Geological Structure in Yangquan Mining Area

by Yang Pu and Zhihua Yang

Sustainability 2022, 14(19), 12028; https://doi.org/10.3390/su141912028 - 23 Sep 2022

Viewed by 1124

Abstract

The study and analysis of tectonic activities on regional structures is of great significance to mine prospecting and production safety in mine work. We take the No. 3 coal seam in the Yangquan mining area as the object of study. The methods of [...] Read more.

The study and analysis of tectonic activities on regional structures is of great significance to mine prospecting and production safety in mine work. We take the No. 3 coal seam in the Yangquan mining area as the object of study. The methods of fractal dimension, structural curvature and trend surface analysis are applied to quantitatively evaluate and predict the mine structure. The folded meso-plane analysis is also carried out. The results show that the trend surface reflects that the monoclinic structure is high in the NE direction and low in the SW direction. The dip angle is small, and the overall structure is characterized by an NNE−NE trend. The curvature value of the coal seam in the mining area is generally small. The northwest structure is relatively simple. The eastern fracture is more developed. The southern structure is relatively simple. A large nearly EW direction Taohe syncline is developed in the middle and south. Several large fractures in the NE direction are developed in the southwest. The capacity dimension of fractures in the mine field is mostly between 0.6 and 1.6. It indicates that the complexity of the fracture structure in the mine field has obvious heterogeneity. The neutral surface of the mine is in the third section of Taiyuan formation, and the No. 3 coal seam is above it. The research results have reference significance for the evaluation and prediction of safe mining and gas outburst danger zones in mining areas. Full article

(This article belongs to the Special Issue Sustainable Mining and Emergency Prevention and Control)

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14 pages, 21013 KiB

Open AccessArticle

Prediction of Gas Emissions in the Working Face Based on the Desorption Effects of Granular Coal: A Case Study

by Cheng Cheng, Xiao-Yu Cheng, Han Gao, Wen-Ping Yue and Chao Liu

Sustainability 2022, 14(18), 11353; https://doi.org/10.3390/su141811353 - 09 Sep 2022

Cited by 1 | Viewed by 1154

Abstract

The aim of the study in this paper is to establish a prediction model of gas emission in the working face. The gas desorption variation characteristics of coal with different particle sizes were assessed using physical tests and based on the coal body [...] Read more.

The aim of the study in this paper is to establish a prediction model of gas emission in the working face. The gas desorption variation characteristics of coal with different particle sizes were assessed using physical tests and based on the coal body of No. 2 coal seam in Wangjialing Coal Mine, Shanxi, China, to reveal the influence law of coal particle size on coal gas desorption. The gas desorption characteristics in the working face, the law of gas emission of coal cutting, coal caving, coal wall, and remnant coal in the goaf of the production process were then analyzed after establishing a gas emission prediction model based on the particle size of the coal. The accuracy of the gas emission prediction model was finally validated through actual measurement of the coal particle size distribution and gas emission in the test working face. The results of the current study show that the coal particle size is negatively correlated with the gas desorption capacity within a certain range. The initial desorption intensity of the coal gas decreased with an increase in the coal particle size. However, the initial gas desorption intensity and attenuation coefficient of gas emission were constant after a certain level of increase in the coal particle size. It was found that the average error between the gas emission prediction model and the actual gas emission data in the mining process was 5.29% based on the desorption characteristics of granular coal. Therefore, the established gas emission prediction model can characterize the law of gas emission in the actual production process more effectively. Furthermore, it provides reliable support for the prediction and control of gas emissions from the goaf under the condition of fully mechanized mining with top coal caving. Full article

(This article belongs to the Special Issue Sustainable Mining and Emergency Prevention and Control)

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11 pages, 1967 KiB

Open AccessArticle

Research on Mechanical Properties and Energy Evolution Law of Coal–Rock Assemblage with Different Gas Pressures

by Linchao Dai, Zhigang Zhang, Haitao Sun and Huali Gao

Sustainability 2022, 14(16), 9904; https://doi.org/10.3390/su14169904 - 10 Aug 2022

Cited by 3 | Viewed by 1165

Abstract

In order to study the mechanical failure characteristics and energy evolution law of gas-bearing coal–rock composites under different gas pressures, a uniaxial mechanical loading experiment was carried out on an upper-rock lower coal binary coal–rock assembly under different gas pressures. The changes in [...] Read more.

In order to study the mechanical failure characteristics and energy evolution law of gas-bearing coal–rock composites under different gas pressures, a uniaxial mechanical loading experiment was carried out on an upper-rock lower coal binary coal–rock assembly under different gas pressures. The changes in parameters such as compressive strength and elastic energy of the coal–rock combination were analyzed, and the energy transfer in the failure process of the gas-bearing coal–rock assemblage was studied. The results showed that the compressive strength of the combined body decreased linearly with the increase in gas pressure, and the decreasing rate of compressive strength was 6.4%, 16.3%, and 21.4%. The elastic modulus of the combined body decreased with the increase in gas pressure in a power function relationship. The energy accumulated before the peak of the rock part of the composite body and the elastic energy released after the peak, the energy accumulated before the peak of the composite body, and the energy dissipated after the peak of the coal body part all decreased with the increase in gas pressure. The variation range of the indicators K₁ and K₂, which reflect the influence degree of the partially accumulated elastic energy of the rock on the failure of the assemblage, were 5.85~6.68% and 7.34~9.46%, respectively. Full article

(This article belongs to the Special Issue Sustainable Mining and Emergency Prevention and Control)

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13 pages, 6572 KiB

Open AccessArticle

Dynamic Response Characteristics and Damage Evolution of Multi-Layer Combined Coal and Rock Mass under Impact Loading

by Feng Li, Runchuan Sun, Yue Zhang, Guanghao Wang and Guangyou Xiang

Sustainability 2022, 14(15), 9175; https://doi.org/10.3390/su14159175 - 26 Jul 2022

Cited by 3 | Viewed by 1421

Abstract

The areas involved in coal and gas outbursts are composed of multi-layer coal and rock mass, in which external dynamic disturbance propagates in the form of stress waves; therefore, reflection, transmission and diffraction occur at the interfaces, resulting in dynamic effects such as [...] Read more.

The areas involved in coal and gas outbursts are composed of multi-layer coal and rock mass, in which external dynamic disturbance propagates in the form of stress waves; therefore, reflection, transmission and diffraction occur at the interfaces, resulting in dynamic effects such as reflected tension, convergence and superposition of stress and strain, and sudden changes of reflected and transmitted stress, which are the key factors leading to the outburst. Based on the Split Hopkinson Pressure Bar system, the dynamic time–history changes of stress, strain and strain rate of five-layer combined coal and rock mass were studied under impact loading. The results show that the time–history curves of stress and strain could be divided into five stages and that of strain rate three stages; the dynamic curves of the five stress–strain stages were significantly different between high-velocity and low-velocity impact. It was hypothesized that under high-speed impact loading, the mechanical anisotropy of combined coal and rock mass at the linear elastic stage tends to be isotropic. Based on ANSYS LS-DYNA, the damage evolution and failure process of five-layer combined coal and rock mass were simulated and analyzed under impact loading. It is concluded that the initial positions of damage of each layer were located at the circle center and its vicinity; radial cracks were mainly formed under low-speed impact loading, and circumferential cracks were mainly formed under high-speed impact loading. In the propagation and action of loading and unloading waves, the “weak layer” was damaged first by tensile stress and formed a free surface, and the subsequent loading waves were reflected on the free surface to form unloading waves and tensile stress, resulting in damage and spalling in multi-layer coal and rock mass. Full article

(This article belongs to the Special Issue Sustainable Mining and Emergency Prevention and Control)

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Other

Jump to: Research

21 pages, 14239 KiB

Open AccessViewpoint

Mechanism and Control of Asymmetric Floor Heave in Deep Roadway Disturbed by Roof Fracture

by Wensheng Wei, Guojun Zhang, Chunyuan Li, Wenshuai Zhang and Yupeng Shen

Sustainability 2023, 15(8), 6357; https://doi.org/10.3390/su15086357 - 07 Apr 2023

Cited by 1 | Viewed by 793

Abstract

In view of the serious problem of bottom-drum damage in deep mining along empty roadways, the asymmetric bottom-drum damage characteristics and control mechanisms of deep mining along an empty roadway were studied using the trackway of the 11060 working face in Zhao Gu [...] Read more.

In view of the serious problem of bottom-drum damage in deep mining along empty roadways, the asymmetric bottom-drum damage characteristics and control mechanisms of deep mining along an empty roadway were studied using the trackway of the 11060 working face in Zhao Gu II mine as the research background. Based on the slip-line theory, support-pressure distribution law, and Griffith’s damage-criterion theory, the mechanism of asymmetric bottom drums and the maximum fracture-development depth of the bottom plate in a deep roadway under top-plate fracture perturbation were analyzed. The 3DEC discrete-element software was used to simulate and analyze the characteristics and evolution of the asymmetric bottom bulge of the roadway under dynamic-load disturbance, and the asymmetric control scheme of “slurry anchor reinforcement + top cutting and pressure relief” was proposed. The results show that, under the influence of static load of deep high-abutment pressure and the dynamic-load impact of the instability of the masonry-beam structure under periodic pressure of the adjacent working face, the deep-mining goaf roadway was prone to producing asymmetric floor heave. The floor-heave degree and maximum fracture-development range of the roadway in the affected area under the influence of dynamic load > those in goaf roadway > those in the roadway in the stable area affected by tunneling. The distribution of stress, displacement, and maximum floor heave was skewed to the side of the coal pillar in the goaf, showing an inverted right oblique V shape. The asymmetric floor heave of a roadway can be effectively controlled by grouting anchor-cable reinforcement (increasing the anti-damage limit) and roof-cutting pressure relief (cutting off the dynamic-load source). The research results can provide an important reference for the control of roadway floors under similar geological conditions. Full article

(This article belongs to the Special Issue Sustainable Mining and Emergency Prevention and Control)

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Open AccessEssay

Evaluation of the Gas Drainage Effect in Deep Loose Coal Seams Based on the Cloud Model

by Dandan Qiu, Yanling Wu and Li Li

Sustainability 2022, 14(19), 12418; https://doi.org/10.3390/su141912418 - 29 Sep 2022

Cited by 3 | Viewed by 941

Abstract

The gas drainage effect is one of the important elements in the study of gas drainage in coal mines. It is critical to establish an effective evaluation model of the gas drainage effect for coal mines because the result of gas drainage is [...] Read more.

The gas drainage effect is one of the important elements in the study of gas drainage in coal mines. It is critical to establish an effective evaluation model of the gas drainage effect for coal mines because the result of gas drainage is directly related to the safety of the coal mines. Through the research related to the safety evaluation in the existing coal mining process, we discovered that there are few studies on the evaluation of the impact of deep and soft gas drainage, and the evaluation methods are not sufficiently effective to resolve the complex problems arising in the process of gas drainage. This paper took “three soft” coal seams in the Lugou Coal Mine as the research object and constructed the evaluation index system on the basis of thoroughly analyzing the factors of coal seam drainage. We then employed a combination weighting method to attain the optimal weight by organically integrating the Analysis Hierarchical Process subjective weighting method and the Criteria Importance Through Interaction Correlation objective weighting method and utilized the cloud model to compute the numerical characteristic value of the evaluation index. In the end, this method obtained an evaluation result of the gas drainage effect evaluation. The evaluation result grade is good. Additional analysis was performed according to the evaluation factors, and corresponding improvement measures were proposed. This is of great importance in promoting safe production and improving the efficiency of gas drainage. Full article

(This article belongs to the Special Issue Sustainable Mining and Emergency Prevention and Control)

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