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Mine Hazards Identification, Prevention and Control
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Mine Hazards Identification, Prevention and Control

A topical collection in Sustainability (ISSN 2071-1050). This collection belongs to the section "Hazards and Sustainability".

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A printed edition of this Special Issue is available here.

Editors

Dr. Xiangguo Kong

E-Mail Website
Collection Editor
College of Safety Science and Engineering, Xi’an University of Science and Technology, Xi’an, China
Interests: mine hazards prevention and control; rock mechanics; applied geophysics
Dr. Dexing Li

E-Mail Website
Collection Editor
School of Safety Engineering, China University of Mining and Technology, Xuzhou 221116, China
Interests: mining safety; tunnels and underground engineering; rock mechanics; rock burst; applied geophysics
Dr. Xiaoran Wang

E-Mail Website
Collection Editor
State Key Laboratory of Coal Resources and Safe Mining, China University of Mining and Technology, Xuzhou 221116, China
Interests: rock fracture mechanics; AE/MS location and source inversion; discrete element simulation for moment tensor; rockburst disaster monitoring and early-warning

Topical Collection Information

Dear Colleagues,

In the process of human social development, the consumption of fossil energy, especially coal, has promoted economic prosperity, cultural exchanges and social progress. With shallow coal resources exhausted, the coal mining engineering has entered into deep area.  Coal geology environment of deep area is obviously different from that of shallow. With mining depth increasing, all the stress of buried rock stratum and surrounding rock, and gas pressure of coal seam increase gradually. In addition, the geological structures such as complex fault, big fold and thick-hard roof will increase risk of coal mining. Once the dynamic disaster occurs, it will induce miner casualties and property losses. So It is urgent to identify mine hazards such as coal and gas outbursts, rock bursts, gas explosions and coal fires, and research the formation mechanism, occurrence and development process of them. What’s more important, the prevention and control methods should be proposed to reduce mine disasters. Only in this way can we promote the safe, green and efficient development of coal mining. This Topical Collection, titled “Mine Hazards Identification, Prevention and Control”, aims to provide an opportunity to researchers around the globe to conduct a broader scientific and technological discussion on such advances to improve the prevention and control level of the disasters encountered during underground coal mining. The discussion topics include, but are not limited to, the basic experiments, modeling, numerical simulation, and field tests of aforementioned disasters. Original research and review articles are welcome.

Dr. Xiangguo Kong
Dr. Dexing Li
Dr. Xiaoran Wang
Collection Editors

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Keywords

  • mine hazards
  • coal/rock disasters
  • coal and gas outburst
  • monitoring and early warning
  • prevention and control
  • identification method
  • gas explosions, coal fires, composite dynamic disasters

Published Papers (27 papers)

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2023

Jump to: 2022

18 pages, 17055 KiB  
Article
Characteristics of Pressure Stimulated Current and Damage Evolution of Granite under Progressive Uniaxial Loading
by Dexing Li, Enyuan Wang, Jianhua Yue, Manman Li, Li Li, Dongming Wang and Wei Liang
Sustainability 2023, 15(19), 14526; https://doi.org/10.3390/su151914526 - 06 Oct 2023
Cited by 5 | Viewed by 755
Abstract
The application of load on rock materials stimulates a weak current known as Pressure Stimulated Current (PSC). This study focuses on investigating the damage evolution of granite rocks through the analysis of PSC responses. Uniaxial loading experiments were conducted on granite samples, and [...] Read more.
The application of load on rock materials stimulates a weak current known as Pressure Stimulated Current (PSC). This study focuses on investigating the damage evolution of granite rocks through the analysis of PSC responses. Uniaxial loading experiments were conducted on granite samples, and the accompanying PSC was measured in real-time. The relationship between PSC characteristics and mechanical behaviors of granite was examined to explore precursory information related to granite failure. The damage evolution of granite was assessed using a damage variable defined as the cumulative charge (time integral of PSC). The results clearly demonstrate a close correlation between the variation of PSC and the mechanical behaviors of rock. Specifically, during the compaction and elastic deformation stages, PSC exhibits a slow and linear increase. However, once deformation enters the plastic stage, PSC demonstrates an accelerated upward trend. Additionally, it was observed that a stress drop coincides with an abnormal increase in PSC, which is followed by a rapid decay. The fluctuation observed after the abnormal increase in PSC during the accelerated growth phase can serve as a precursor of rock failure. Furthermore, the cumulative charge quantity effectively correlates with the damage process of granite samples. The stress–strain curve obtained from a theoretical constitutive model, established based on the damage variable represented by normalized cumulative charge, aligns reasonably well with the experimental results, affirming that the defined damage variable accurately reflects the damage evolution process of rocks. It is hypothesized that PSCs are carried by electrons within the rocks, which are stimulated by electron diffusion during deformation and experience a sharp increase upon rock fracturing. The research findings hold theoretical significance for predicting rockburst incidents using the PSC method. Full article
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17 pages, 5632 KiB  
Article
Precursor Signal Identification and Acoustic Emission Characteristics of Coal Fracture Process Subjected to Uniaxial Loading
by Xiangguo Kong, Mengzhao Zhan, Yuchu Cai, Pengfei Ji, Di He, Tianshuo Zhao, Jie Hu and Xi Lin
Sustainability 2023, 15(15), 11581; https://doi.org/10.3390/su151511581 - 26 Jul 2023
Cited by 8 | Viewed by 995
Abstract
In deep underground mine engineering, the critical warning signals before the sudden failure of coal are crucial to predict coal or rock dynamic catastrophes and to help the coal industry grow sustainably. Therefore, with the objective of accurately identifying the precursor signals of [...] Read more.
In deep underground mine engineering, the critical warning signals before the sudden failure of coal are crucial to predict coal or rock dynamic catastrophes and to help the coal industry grow sustainably. Therefore, with the objective of accurately identifying the precursor signals of coal fracture, a uniaxial compression test was adopted. Tests were performed on multiple sets of raw coal samples, and acoustic emission (AE) technology was used to capture the deformation and destruction courses of the coal samples. Furthermore, the signal intensity of AE energy was discussed. Based on the critical slowing down theory, the AE energy sequence was processed. The results indicate that there are significant discrepancies in the strength of coal affected by initial pore fissures. During the whole loading process, the AE energy signals showed obvious stage characteristics, and there was a high risk of rapid coal energy storage during the unstable rupture development (URD) stage, which predicted the imminent destruction of the coal. The variance mutation point that was not affected by the lag step selection was easier to identify than that of the autocorrelation coefficient, and the precursor points were all in the URD stage, which is more accurate than using the AE cumulative energy curve slope. Full article
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19 pages, 5294 KiB  
Article
Joint Characterization and Fractal Laws of Pore Structure in Low-Rank Coal
by Yuxuan Zhou, Shugang Li, Yang Bai, Hang Long, Yuchu Cai and Jingfei Zhang
Sustainability 2023, 15(12), 9599; https://doi.org/10.3390/su15129599 - 15 Jun 2023
Cited by 4 | Viewed by 901
Abstract
The pore structure of low-rank coal reservoirs was highly complex. It was the basis for predicting the gas occurrence and outburst disasters. Different scale pores have different effects on adsorption–desorption, diffusion, and seepage in coalbed methane. To study the pore structure distribution characteristics, [...] Read more.
The pore structure of low-rank coal reservoirs was highly complex. It was the basis for predicting the gas occurrence and outburst disasters. Different scale pores have different effects on adsorption–desorption, diffusion, and seepage in coalbed methane. To study the pore structure distribution characteristics, which are in different scales of low-rank coal with different metamorphism grade, the pore structure parameters of low-rank coal were obtained by using the mercury injection, N2 adsorption, and CO2 adsorption. These three methods were used to test the pore volume and specific surface area of low-rank coal in their test ranges. Then, the fractal dimension method was used to calculate the fractal characteristics of the pore structure of full aperture section to quantify the complexity of the pore structure. The experimental results showed that the pore volume and specific surface area of low-rank coal were mainly controlled by microporous. The pore fractal characteristics were obvious. With the influence of coalification process, as the degree of coal metamorphism increases, fluctuations in the comprehensive fractal dimension, specific surface area, and pore volume of the pore size range occur within the range of Rmax = 0.50% to 0.65%. Full article
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15 pages, 3565 KiB  
Article
Study on the Effect of External Air Supply and Temperature Control on Coal Spontaneous Combustion Characteristics
by Changkui Lei, Xueqiang Shi, Lijuan Jiang, Cunbao Deng, Jun Nian and Yabin Gao
Sustainability 2023, 15(10), 8286; https://doi.org/10.3390/su15108286 - 19 May 2023
Cited by 1 | Viewed by 834
Abstract
Coal spontaneous combustion in underground mine goaf has a great impact on coal mining. The temperature-programmed experiment is a commonly used and effective method for studying the characteristics of coal spontaneous combustion. Aiming at the problem that the numerical simulation of coal spontaneous [...] Read more.
Coal spontaneous combustion in underground mine goaf has a great impact on coal mining. The temperature-programmed experiment is a commonly used and effective method for studying the characteristics of coal spontaneous combustion. Aiming at the problem that the numerical simulation of coal spontaneous combustion characteristics under the condition of external air supply and temperature control in a temperature-programmed experiment is insufficient, a multi-physical field coupling numerical model of coal spontaneous combustion in the temperature-programmed experiment is established. The variation characteristics of coal temperature, oxygen, and oxidation products under external air supply and temperature control were studied. The results show that the numerical simulation results are consistent with the experimental results. With the increase in temperature, the volume fractions of oxygen and carbon dioxide decrease and increase, respectively. As the air supply volume increases, the oxygen volume fraction at the outlet increases, and the peak value of the oxygen volume fraction change rate exhibits a “hysteresis” feature, and the time corresponding to the peak value increases. Moreover, the temperature change rate increases. With the increase in the heating rate, the peak value of the oxygen volume fraction change rate increases and shows an “early appearance” characteristic, at the same time, the maximum coal temperature displays a linear increase trend. Full article
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24 pages, 9758 KiB  
Article
Study on the Pseudo-Slope Length Effect of Buried Pipe Extraction in Fully Mechanized Caving Area on Gas Migration Law in Goaf
by Pengxiang Zhao, Xingbao An, Shugang Li, Xinpeng Kang, Yitong Huang, Junsheng Yang and Shikui Jin
Sustainability 2023, 15(8), 6628; https://doi.org/10.3390/su15086628 - 13 Apr 2023
Cited by 4 | Viewed by 1149
Abstract
To study the law of gas transportation in mining areas, Fluent numerical simulation software was applied to examine the influence of different pseudo-slope lengths (PSL) on gas concentration in a U-ventilated working area under no-extraction conditions. Based on this, numerical simulation experiments were [...] Read more.
To study the law of gas transportation in mining areas, Fluent numerical simulation software was applied to examine the influence of different pseudo-slope lengths (PSL) on gas concentration in a U-ventilated working area under no-extraction conditions. Based on this, numerical simulation experiments were conducted on the buried pipe extraction arrangement parameters. The simulation found that when there was no extraction, the PSL had an impact on the airflow in the extraction area, which caused the airflow in the extraction area to be disordered, causing gas to accumulate locally at the working area. When the buried pipe depths (BPDs) and PSLs of the working area worked together, the gas concentration of the working area was lower when the inlet air influence zone and the extraction influence zone were through; otherwise, gas concentration accumulation occurred at the working area. The research results showed that when the PSL was at 25 m and BPD was at 20 m, the gas concentration at the working area was not abnormal, and the gas concentration in the upper corner was lower. By adjusting the PSL and BPD of the test working area, the maximum gas concentration in the upper corner was reduced to 0.46% and the maximum gas concentration in the return air outlet was reduced to 0.41%. The experimental and practical results provide important reference values for coal and gas co-mining. Full article
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11 pages, 8680 KiB  
Article
Creep Characteristic Test and Creep Model of Frozen Soil
by Yawu Shao, Yonglu Suo, Jiang Xiao, Yuan Bai and Tao Yang
Sustainability 2023, 15(5), 3984; https://doi.org/10.3390/su15053984 - 22 Feb 2023
Cited by 4 | Viewed by 1223
Abstract
In order to research the creep deformation characteristics of frozen soil and the effect of various influencing factors on creep, indoor uniaxial creep tests were carried out on frozen soil specimens at temperatures of −5, −4, −3 and −2 °C under loads of [...] Read more.
In order to research the creep deformation characteristics of frozen soil and the effect of various influencing factors on creep, indoor uniaxial creep tests were carried out on frozen soil specimens at temperatures of −5, −4, −3 and −2 °C under loads of 0.25, 0.5, and 0.75 σt, respectively. The creep deformation characteristics of frozen soil under different temperatures and load conditions are analyzed under unconfined conditions. The results show that under the uniaxial creep test conditions, when the load is low, there is no accelerated creep stage in the creep curve, which belongs to the decaying type creep; when the load is 0.75 σt, the creep curve enters the stage of accelerated creep, and the creep turns non-attenuated; temperature is the most important external factor affecting permafrost soil creep, and the proportion of ice is the key internal factor for affecting permafrost soil creep, the temperature is negatively correlated with the proportion of ice and the sensitivity of creep rate to temperature and load increases with the decrease of the proportion of ice; the damage variable D is introduced to modify the creep constitutive equation of the frozen soil, the creep process of frozen soil is well described by the modified creep constitutive equation for frozen soil. Full article
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14 pages, 10699 KiB  
Article
An Engineering Case History of the Prevention and Remediation of Sinkholes Induced by Limestone Quarrying
by Zhen Tang, Lei Song, Dianqi Jin, Ligen Chen, Gan Qin, Yongjun Wang and Lei Guo
Sustainability 2023, 15(3), 2808; https://doi.org/10.3390/su15032808 - 03 Feb 2023
Cited by 1 | Viewed by 1318
Abstract
This paper introduces an engineering case history of the prevention and remediation of sinkholes induced by limestone quarrying in Longmen county, Huizhou city, China, through karst groundwater-air pressure monitoring, the design and construction of a grouting curtain, and grouting effect detection. Based on [...] Read more.
This paper introduces an engineering case history of the prevention and remediation of sinkholes induced by limestone quarrying in Longmen county, Huizhou city, China, through karst groundwater-air pressure monitoring, the design and construction of a grouting curtain, and grouting effect detection. Based on hydrogeological surveys, the location of the main karst development zones and faults can be accurately delineated by combining geophysical exploration with drilling, providing a basis for curtain setting. According to the interpretation results of geophysical exploration, the monitoring boreholes of groundwater-air pressure were set up, which provided support for mine construction, optimization of prevention and remediation of the sinkhole scheme, and reduction of sinkhole risk. In order to prevent the further expansion of sinkhole hazards, grouting curtain technology was used for engineering treatment of the water inflow points of the quarry. After construction of the grouting curtain was completed, comprehensive detection methods were used to evaluate the grouting effect of the curtain. The results showed that the inflow rate reduced from 3500 to approximately 500 m3/day, the water plugging effect was significant, and the occurrence of sinkhole hazards was effectively reduced. The monitoring boreholes can capture the changes of groundwater-air pressure within karst conduit systems, and the purpose of monitoring and warning of sinkholes can be achieved by setting an appropriate warning threshold. Full article
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20 pages, 11046 KiB  
Article
Research on Deformation and Failure Law of the Gob-Side Roadway in Close Extra-Thick Coal Seams
by Shengquan He, Le Gao, Bin Zhao, Xueqiu He, Zhenlei Li, Dazhao Song, Tuo Chen, Yanran Ma and Feng Shen
Sustainability 2023, 15(3), 2710; https://doi.org/10.3390/su15032710 - 02 Feb 2023
Cited by 1 | Viewed by 1258
Abstract
To reveal the deformation and failure law of the gob-side roadway (GSR) and the main influencing factors in close extra-thick coal seams, the research methods of field monitoring, theoretical analysis, and numerical simulation are adopted in this paper. Field monitoring data shows that [...] Read more.
To reveal the deformation and failure law of the gob-side roadway (GSR) and the main influencing factors in close extra-thick coal seams, the research methods of field monitoring, theoretical analysis, and numerical simulation are adopted in this paper. Field monitoring data shows that microseismic events occur and accumulate frequently in the surrounding rock and some overlying key layers of the GSR. Large deformation is experienced in the middle part of roadway near the solid coal side, the middle and upper parts of the roadway near the coal pillar side, and the roadway floor. The overlying strata of the GSR are fractured to form a composite structure as “low-level cantilever beam and high-level masonry beam”. The coal pillar is squeezed and effected by the composite beam structure and the rotation moment M, causing serious bulge in middle and upper part of the coal pillar side. The stability of the solid coal side of the roadway is affected by the stress transferred from gangue contact point. Numerical simulation shows that the immediate roof and key layer breakage are induced by the mining of the 30,501 working face. Shear and tension failures happen in the GSR due to overburden subsidence and rotary extrusion. The stress and displacement at the middle and upper of the roadway on the coal pillar side are larger than the other area. Compared with the solid coal side, the coal on the coal pillar side is obviously more fractured, with a lower bearing capacity. The peak stress in the coal pillar shows up 2 m away from the roadway, which is close to the length of bolt support. The mining-induced stress and the stress transferred from gangue contact point are the direct reasons for solid coal bulge beside the roadway. The peak stress on the solid coal side is located 7 m away from the roadway, at the gangue contact point where overburden fractures. The overburden strata loads and the transferred stress near the gangue contact point are transferred from the sides to the roadway floor. Their coupling effect with the in situ horizontal stress acts as the force source for the plastic floor heave. Full article
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15 pages, 5482 KiB  
Article
Response Characteristics of Weak Current Stimulated from Coal under an Impact Load and Its Generation Mechanism
by Dexing Li, Enyuan Wang, Dianqi Jin, Dongming Wang and Wei Liang
Sustainability 2023, 15(3), 2605; https://doi.org/10.3390/su15032605 - 01 Feb 2023
Cited by 1 | Viewed by 1040
Abstract
Understanding the response law and mechanism of weak currents stimulated from coal under an impact load is significant for the prediction of coal bumps in deep coal mines. In this paper, the system for the weak current measurement of coal under an impact [...] Read more.
Understanding the response law and mechanism of weak currents stimulated from coal under an impact load is significant for the prediction of coal bumps in deep coal mines. In this paper, the system for the weak current measurement of coal under an impact load is established and the response characteristics of weak currents induced by the deformation of coal under an impact load are investigated. Physical models are established to describe the process of charge transfer and explain the generation mechanism of those currents. The results show that a transient current is stimulated from the coal sample when an impact load is applied, and then, the current decays slowly, tending to be a stable value that is slightly greater than the background current. The weak current flows from the loaded volume to the unloaded volume of the coal and increases with the impact velocity in a negative exponential form. Analysis of weak currents using non-extensive entropy shows that the attenuation of the weak current obeys non-extensive statistical mechanics and the non-extensive parameter q is greater than 2. The carriers are mainly electrons, of which the distribution obeys the tip effect that electrons tend to enrich towards the tip of a crack. The generation mechanism of those weak currents induced by coal deformation is the instantaneous movement of electrons under a density difference caused by the tip effect. Research results can provide a new perspective to understand the electric phenomena of coal under an impact load as well as a new method for coal bump prediction. Full article
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15 pages, 5892 KiB  
Article
Fracture Evolution of Overburden Strata and Determination of Gas Drainage Area Induced by Mining Disturbance
by Yuchu Cai, Shugang Li, Xiangguo Kong, Xu Wang, Pengfei Ji, Songrui Yang, Xi Lin, Di He and Yuxuan Zhou
Sustainability 2023, 15(3), 2152; https://doi.org/10.3390/su15032152 - 23 Jan 2023
Cited by 1 | Viewed by 1128
Abstract
Overburden strata fracture evolution is critical to dynamic disaster prevention and gas-relief drainage, so it is important to accurately determine the evolution relationships with mining disturbance. In this paper, experiments and numerical simulation were adopted jointly to characterize the time-varying fracture area of [...] Read more.
Overburden strata fracture evolution is critical to dynamic disaster prevention and gas-relief drainage, so it is important to accurately determine the evolution relationships with mining disturbance. In this paper, experiments and numerical simulation were adopted jointly to characterize the time-varying fracture area of overlying strata. The experimental results showed that the roof strata gradually broke and collapsed with coal mining, which indicated the fractures of overburden strata developed in an upward direction. The fracture development causes were explained by numerical simulation, which showed that stress increase exceeded the strength of coal and rock strata, and fractures were formed and expanded. Both experiments and numerical simulation results showed the two sides and the top of fracture areas provided channels and spaces for gas migration and reservoir, respectively. In addition, the breaking angle of overburden strata and the height of fracture areas were analyzed quantitatively. Through microseismic monitoring at the mining site, the fracture scales and ranges of overburden strata were verified by the energy and frequency of microseismic events, which were consistent with the support of maximum resistance. The position of drainage boreholes was considered based on the results of overburden strata fracture evolution. Our study is aimed at promoting coal mining in safety and improving gas drainage with a sustainable approach. Full article
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13 pages, 4589 KiB  
Article
Simulation Research on Energy Evolution and Supply Law of Rock–Coal System under the Influence of Stiffness
by Yanchun Yin, Xingxue Tang, Qinwei Ma, Zhenan Li and Wei Zhang
Sustainability 2023, 15(2), 1335; https://doi.org/10.3390/su15021335 - 10 Jan 2023
Viewed by 872
Abstract
The energy supply effect caused by the stiffness difference between roofs and sidewalls is an important factor that induces strain coal bursts. In order to quantitatively reveal the energy supply mechanism of strain coal bursts, this paper first establishes a coal burst energy [...] Read more.
The energy supply effect caused by the stiffness difference between roofs and sidewalls is an important factor that induces strain coal bursts. In order to quantitatively reveal the energy supply mechanism of strain coal bursts, this paper first establishes a coal burst energy model of the rock–coal system and proposes the calculation formula of coal burst kinetic energy considering supply energy and the stiffness ratio of rock to coal. Then the whole energy evolution law of the rock–coal system with different stiffness ratios is researched by using the numerical simulation method, and the whole process is divided into three stages. With the decrease in the stiffness ratio, the elastic strain energy of the coal changes little, while its kinetic energy is negatively correlated with the stiffness ratio in a power function. Meanwhile, the elastic strain energy and kinetic energy of the rock have power function relations with the stiffness ratio, too. When the rock–coal system is fractured, the kinetic energy of the coal comes from the release of elastic strain energy from the coal and the energy supplied from the rock. The energy supply rate is between 22% and 35% when the stiffness ratio changes from 3.0 to 0.5, and they show a linear relationship, while the supplied energy has a negative power function relationship with the stiffness ratio. Full article
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22 pages, 4027 KiB  
Article
Study on the Characteristics of Coal Ultrasonic Response during Loading and Its Influence Mechanism
by Gang Xu, Tingting Ma, Chaofeng Wang, Hongwei Jin and Yunlong Wang
Sustainability 2023, 15(2), 1093; https://doi.org/10.3390/su15021093 - 06 Jan 2023
Cited by 1 | Viewed by 1015
Abstract
The prediction and prevention· of mine disasters are crucial to identifying the stress and strain state of coal using ultrasonic response characteristics. In this study, ultrasonic testing experiments of primary structure coal samples under uniaxial loading were conducted using a low-frequency rock physics [...] Read more.
The prediction and prevention· of mine disasters are crucial to identifying the stress and strain state of coal using ultrasonic response characteristics. In this study, ultrasonic testing experiments of primary structure coal samples under uniaxial loading were conducted using a low-frequency rock physics measuring device. Based on the experimental results, the study focused on analyzing the relationship of the stress–strain state of coal samples with the ultrasonic velocity and quality factor of coal samples during stress loading, and exploring the influence mechanism of ultrasonic propagation in coal during stress loading. The results demonstrated that the stress-loading process of coal samples falls into the elastic deformation stage and the plastic deformation stage. In the elastic deformation stage, the ultrasonic velocity and the quality factor of the coal sample increased with the increase in the coal axial strain. In the plastic deformation stage, the ultrasonic velocity and quality factor of coal samples decreased as the axial strain of coal samples increased. Coal porosity was the fundamental factor affecting the coal wave velocity variation and the coal quality factor variation. In the elastic deformation stage, increased coal axial stress was accompanied by decreased coal porosity, contributing to the increase in coal wave velocity and coal quality factor. In the plastic deformation stage, the increase in the coal axial strain increased coal porosity and thus curtailed the wave velocity and quality factor of coal. Significant differences were observed in ultrasonic response characteristics of coal under various stress and strain states. The research results can lay a theoretical foundation for the safe and efficient development of coal resources and the prevention and control of mine disasters. Full article
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Graphical abstract

2022

Jump to: 2023

18 pages, 4988 KiB  
Article
Application and Optimization of the Parameters of the High-Level Boreholes in Lateral High Drainage Roadway
by Haiqing Shuang, Weitao Meng, Yulong Zhai, Peng Xiao, Yu Shi and Yu Tian
Sustainability 2022, 14(24), 16908; https://doi.org/10.3390/su142416908 - 16 Dec 2022
Cited by 1 | Viewed by 1071
Abstract
The key parameters of high-level boreholes in high drainage roadways affect the gas treatment effect of the working face directly. Therefore, the layout parameters of high-level boreholes in the lateral high drainage roadway (LHDR) are determined and optimized as necessary. Based on the [...] Read more.
The key parameters of high-level boreholes in high drainage roadways affect the gas treatment effect of the working face directly. Therefore, the layout parameters of high-level boreholes in the lateral high drainage roadway (LHDR) are determined and optimized as necessary. Based on the LHDR layout on the 2-603 working face of the Liyazhuang coal mine, the key technological requirements on high-level borehole parameters were analyzed and the distribution characteristics of the gas volume fraction in the coal roof were studied. The gas migration law in the mined-out areas was obtained and the layout locations of high-level boreholes were determined finally. The research demonstrates that the high-level boreholes lag the 2-603 working face distance and the position of the final borehole (the position of the final borehole in this paper refers to the distance between the final borehole and the roof) influence the stability of boreholes and the gas extraction effect. The distribution of the gas volume fraction from the intake airway to the return airway can be divided into the stable stage, slow growth stage, and fast growth stage. Influenced by the flow field in the mined-out areas, the mean volume fraction of the borehole-extracted gas has no obvious relationship with the gas volume fraction at the upper corner. According to the final optimization, the high-level borehole is determined as having a 15 m lag behind the working face and the position of the final borehole is 44 m away from the coal seam roof. These have been applied successfully in engineering practice. Full article
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17 pages, 6869 KiB  
Article
Numerical Simulation Study on Mechanical Characteristics and Width Optimization of Narrow Coal Pillar in Gob-Side Coal Seam Tunnel
by Pengxiang Zhao, Wenjin Zhang, Shugang Li, Zechen Chang, Yajie Lu, Congying Cao, Yu Shi, Yongyong Jia, Fang Lou, Zongyong Wei and Jun Liu
Sustainability 2022, 14(23), 16014; https://doi.org/10.3390/su142316014 - 30 Nov 2022
Cited by 1 | Viewed by 959
Abstract
To investigate the influence of coal pillar width on the stress variation of narrow coal pillar (NCP) in the gob-side tunnel in an inclined thick coal seam, theoretical analysis, numerical modeling, and field monitoring are performed to determine the optimal width of the [...] Read more.
To investigate the influence of coal pillar width on the stress variation of narrow coal pillar (NCP) in the gob-side tunnel in an inclined thick coal seam, theoretical analysis, numerical modeling, and field monitoring are performed to determine the optimal width of the narrow coal pillars in inclined coal seams. The mechanical characteristics of the NCP for varying widths were investigated. Furthermore, vertical and horizontal stress were calculated for various widths of the NCP. The results revealed that with the rise in the width, the vertical stress initially increased dramatically and then stabilized, whereas the mean horizontal stress increased gradually. The mathematical relation between stress and NCP widths was represented by two fitting equations. The evolution process of the plastic zone in the NCP under various widths and the damage form of various widths were obtained; that is, when the width was small, the position of the roadway near the shoulder corner of NCP was inclined to the top of NCP. The field monitoring data revealed that the optimum NCP width was 4 m. This NCP width could stabilize the roadway and improve the loss prevention of the NCP at the gob-side tunnel of similar mines. Full article
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16 pages, 2929 KiB  
Article
Experimental Study on the Effect of Gas Adsorption and Desorption on Ultrasonic Velocity and Elastic Mechanical Parameters of Coal
by Gang Xu, Jiawei Liu, Yunlong Wang, Hongwei Jin and Chaofeng Wang
Sustainability 2022, 14(22), 15055; https://doi.org/10.3390/su142215055 - 14 Nov 2022
Viewed by 1036
Abstract
The rapid and accurate identification of the physical characteristics of coal by means of ultrasonic detection is of great significance to ensure safe mining of coal and efficient development of coal seam methane. In this paper, the ultrasonic velocity testing experiments of coal [...] Read more.
The rapid and accurate identification of the physical characteristics of coal by means of ultrasonic detection is of great significance to ensure safe mining of coal and efficient development of coal seam methane. In this paper, the ultrasonic velocity testing experiments of coal during gas adsorption and desorption were carried out, utilizing a low frequency petrophysical measurement device with primary and fractured coal as the research objects. The variations in the elastic mechanical parameters and ultrasonic velocity of coal samples were analyzed to elucidate the influence mechanism that gas adsorption and desorption have on them. During gas adsorption and desorption, the longitudinal wave velocity of the primary structure coal varies from 1990 m/s to 2200 m/s, and the transverse wave velocity varies from 1075 m/s to 1160 m/s, while the longitudinal wave velocity of the fractured structure coal varies from 1540 m/s to 1950 m/s, and the transverse wave velocity varies from 800 m/s to 1000 m/s. The elastic modulus and wave velocities, in both directions of the primary structural coal, were higher than those of the fractured structural coal. In comparison to the fractured structural coal, the main structural coal had a lower Poisson’s ratio. In addition, the spread of the elastic mechanical parameters and wave velocities, in both the longitudinal and transverse directions, was more pronounced in the fracture−structured coal than in the primary−structured coal. During gas adsorption and desorption, the speed of the coal’s longitudinal waves increased, and then decreased, due to the combined effect of gas adsorption expansion and pore gas pressure compression matrix effect. For this experiment, the maximum longitudinal wave velocity of the coal occurred at a gas pressure of 1.5 MPa. Primary structural coal has a longitudinal wave speed of 2103 m/s, whereas fragmented structural coal has a speed of 1925 m/s. The variation in the shear wave velocity of the coal is controlled only by the gas adsorption expansion effects. The shear wave velocity increases during gas adsorption and decreases during gas desorption. With the change of gas pressure, the longitudinal wave velocity can increase by 23.34%, and the shear wave velocity can increase by 17.97%. Coal undergoes changes to both its Poisson’s ratio and elastic modulus as a result of gas adsorption and desorption; these modifications are analogous to the velocity of longitudinal and shear waves, respectively. Full article
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17 pages, 7455 KiB  
Article
Response and Application of Full-Space Numerical Simulation Based on Finite Element Method for Transient Electromagnetic Advanced Detection of Mine Water
by Changfang Guo, Tingjiang Tan, Liuzhu Ma, Shuai Chang, Yiding Chen and Ke Zhao
Sustainability 2022, 14(22), 15024; https://doi.org/10.3390/su142215024 - 14 Nov 2022
Cited by 2 | Viewed by 1041
Abstract
The issue of water hazards has led to the restriction of safe and efficient coal mine production in China. The transient electromagnetic method (TEM) is one of the most effective means of detecting the hidden dangers of water hazards in coal mines. However, [...] Read more.
The issue of water hazards has led to the restriction of safe and efficient coal mine production in China. The transient electromagnetic method (TEM) is one of the most effective means of detecting the hidden dangers of water hazards in coal mines. However, the current understanding of the whole-space transient electromagnetic response of mine water is only on the general law due to the late start of the forward research. Therefore, this paper established multiple sets of simulation models in the whole area in order to study the rules and factors of transient electromagnetic responses. Subsequently, these laws are used to explain the detection data of TEM in the field. According to the simulation results, the electric properties, distance, and size had the greatest influence on the transient electromagnetic response of regular anomalous geological bodies, while the electromagnetic field projection area also had an impact on irregular ones. Furthermore, field application demonstrated that the response law and TEM’s affecting factors are acceptable for directing the detection of transient electromagnetic in coal mines. This research can advance the TEM’s data processing and interpretation technology and offer a theoretical basis for detailed investigation. Full article
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12 pages, 8483 KiB  
Article
Particle Flow Analysis on Mechanical Characteristics of Rock with Two Pre-Existing Fissures
by Zhenzi Yu, Ang Li, Bo Zhang, Hongyue Li, Qian Mu, Yonggen Zhou and Shuai Gao
Sustainability 2022, 14(22), 14862; https://doi.org/10.3390/su142214862 - 10 Nov 2022
Viewed by 960
Abstract
Many research results show that under any stress state the rock mass is most likely to crack, swell, bifurcate, and infiltrate from the fissure tip, resulting in rock engineering instability and failure. In order to study the influence of double fissure angles on [...] Read more.
Many research results show that under any stress state the rock mass is most likely to crack, swell, bifurcate, and infiltrate from the fissure tip, resulting in rock engineering instability and failure. In order to study the influence of double fissure angles on rock mechanical characteristics, five rock numerical models with different fissure angles were established by numerical simulation software. Uniaxial compression tests were carried out, and the variation characteristics of rock stress, strain, failure, microcrack, and acoustic emission (AE) were recorded. The test results show that: With increases in the fissure angles, the elastic modulus of rock increased, while the peak strength decreased first and then increased. The number of microcracks in rock was greater at 15° and 75° than at other angles. The microcracks in rock were mainly tensile cracks, and relatively few were shear cracks. The angles of microcracks were mostly concentrated between 0 and 180°, most of which were between 60 and 110°. The failure of rock was relatively light when the fissure angle was15° or 75°, but it produced more and smaller fragments, and the failure was the most serious when the fissure angle was 30°. The angles of the fissures affected the maximum number of AE events, the strain values for the initial AE event, and the maximal AE event. This research can provide some reference for disasters caused by rocks with pre-existing fissures. Full article
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16 pages, 7241 KiB  
Article
Characteristics of Mining-Induced Slope Movement and Ground Behavior under Gully Landforms
by Shaojie Ma and Yueming Kang
Sustainability 2022, 14(21), 13941; https://doi.org/10.3390/su142113941 - 26 Oct 2022
Cited by 2 | Viewed by 997
Abstract
Exploring the phenomenon of surface cracks and the abnormal phenomenon of ground behavior during coal mining under gully landforms, laboratory physical similarity simulation models were established to study the movement characteristics and ground behavior laws of working faces of different mining methods under [...] Read more.
Exploring the phenomenon of surface cracks and the abnormal phenomenon of ground behavior during coal mining under gully landforms, laboratory physical similarity simulation models were established to study the movement characteristics and ground behavior laws of working faces of different mining methods under gully landforms. The results indicate that in cases when a roadway is situated below the top of the slope, the corresponding deformation of the surrounding rock of the roadway is aggravated by the mining stress. Furthermore, when a roadway is located below the base of the gully, it is less affected by mining; thus, it could remain relatively stable. The ground behavior laws of working faces in gully geomorphology areas are associated with the position of the working face and the direction of working: when mining towards the gully, the ground behavior appeared relatively gentle and the surface slipped towards the gully; when mining away from the gully, the ground behavior appeared intense, the pressure was sudden and short, and with the increase in overburden thickness, the interval distance periodically decreased. When a working face passes through a gully, dumping of the hydraulic support should be prevented in the section of mining towards the gully; in sections of mining away from gully, the support strength should be strengthened to prevent the support and other equipment from being crushed. In actual mining, mining towards a gully should be adopted as much as possible in the stoping of the working face. In this way, the ground behavior is gentle, the interval distance periodical weight is longer, and the advance abutment pressure is small. Full article
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17 pages, 5868 KiB  
Article
Patterns of Influence of Parallel Rock Fractures on the Mechanical Properties of the Rock–Coal Combined Body
by Yakang Li, Jiangwei Liu and Qian Yu
Sustainability 2022, 14(20), 13555; https://doi.org/10.3390/su142013555 - 20 Oct 2022
Cited by 3 | Viewed by 1133
Abstract
Hydraulic fracturing of a roof can attenuate the strong mineral pressure and stress transfer by creating a series of parallel artificial fractures in it, and different forms of hydraulic parallel fractures have different effects on the attenuation effect of the coal rock system. [...] Read more.
Hydraulic fracturing of a roof can attenuate the strong mineral pressure and stress transfer by creating a series of parallel artificial fractures in it, and different forms of hydraulic parallel fractures have different effects on the attenuation effect of the coal rock system. In this regard, this study investigated the influence law of different forms of parallel pre-cracks on the mechanical properties of a rock–coal combined body through PFC2D numerical simulation, and the following conclusions were obtained. Parallel pre-cracks significantly affected the mechanical properties of the rock–coal combined body. The stress–strain curve of the coal–rock assemblage containing Parallel pre-cracks changes significantly following reductions in peak strength, peak strain, elastic modulus, and crack initiation stress. The closer the angle θ between the single set of parallel pre-cracks and the horizontal is to 30°, the longer the length, L, and the lower the peak strength of the specimen, the peak strain, the modulus of elasticity, and the crack initiation stress. Macroscopic damage patterns are given for a rock–coal combined body containing single sets of parallel pre-cracks of different parameters, with coal sample damage, coal–rock sample damage and rock sample damage; a rock–coal combined body containing parallel pre-cracks is divided into three modes of fracture initiation when pressurized. These are the cracking of the coal sample, the simultaneous cracking of the parallel pre-crack tips in coal and rock samples, and the cracking of the parallel pre-crack tips in rock samples. Full article
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16 pages, 6496 KiB  
Article
Safety and Protection Measures of Underground Non-Coal Mines with Mining Depth over 800 m: A Case Study in Shandong, China
by Li Cheng, Qinzheng Wu, Haotian Li, Kexu Chen, Chunlong Wang, Xingquan Liu, Xuelong Li and Jingjing Meng
Sustainability 2022, 14(20), 13345; https://doi.org/10.3390/su142013345 - 17 Oct 2022
Cited by 1 | Viewed by 1197
Abstract
With the increase in mining depth, the risk of ground pressure disasters in yellow gold mines is becoming more and more serious. This paper carries out a borehole test for the pressure behavior in a non-coal mining area with a mining depth of [...] Read more.
With the increase in mining depth, the risk of ground pressure disasters in yellow gold mines is becoming more and more serious. This paper carries out a borehole test for the pressure behavior in a non-coal mining area with a mining depth of more than 800 m in the Jiaodong area. The test results show that under a depth of 1050 m, the increase in the vertical principal stress is the same as the increase in the minimum horizontal principal stress, which is about 3 MPa per 100 m. When the depth increases to 1350 m, the vertical principal stress increases by about 3% per 100 m, and the self-weight stress and the maximum horizontal principal stress maintain a steady growth rate of about 3 MPa per 100 m. In addition, based on the test results, the operation of the ground pressure monitoring system in each mine is investigated. The investigation results show that in some of the roadway and stope mines with depths of more than 800 m, varying degrees of rock mass instability have occurred, and a few mines have had sporadic slight rockbursts, accounting for about 5%. There was a stress concentration area in the lower part of the goaf formed in the early stage of mining, and slight rockburst phenomena such as rock mass ejection have occurred; meanwhile, the area stability for normal production and construction was good, and there was no obvious ground pressure. This paper compares the researched mines horizontally as well as to international high-level mines and puts forward some suggestions, including: carrying out ground pressure investigations and improving the level of intelligence, which would provide countermeasures to balance the safety risks of deep mining, reducing all kinds of safety production accidents and providing a solid basis for risk prevention and supervision. Full article
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12 pages, 5703 KiB  
Article
Acoustic Emission Waveform Characteristics of Red Sandstone Failure under Uniaxial Compression after Thermal Damage
by Herui Zhang and Weihong Guo
Sustainability 2022, 14(20), 13285; https://doi.org/10.3390/su142013285 - 16 Oct 2022
Cited by 1 | Viewed by 1002
Abstract
During the exploitation of deep resources, rocks are often in a high-temperature, high-pressure environment. It is of great significance to study the acoustic emission (AE) characteristics of thermal damaged rock under load to improve the accuracy of monitoring in practical engineering. In this [...] Read more.
During the exploitation of deep resources, rocks are often in a high-temperature, high-pressure environment. It is of great significance to study the acoustic emission (AE) characteristics of thermal damaged rock under load to improve the accuracy of monitoring in practical engineering. In this paper, sandstone was heated at different temperatures, before a uniaxial compression test was performed and the AE in the process was monitored. The results show that the strength and AE energy of sandstone decrease gradually with an increase in heating temperature. Through frequency domain analysis of the AE waveform at the time of failure, it was found that the frequency and intensity of AE also showed a downward trend with an increase in temperature. In addition, multifractal theory is introduced to deconstruct the waveform data. The multifractal characteristics of the waveforms decrease with an increase in temperature. It provides new parameters for waveform analysis, which can be combined with frequency analysis as parameters to more accurately identify rock failure in engineering practice. The attenuation of AE of thermally damaged sandstone may be related to an increase in porosity and a decrease in elastic energy release. Full article
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18 pages, 3134 KiB  
Article
A Novel Method for Gas Disaster Prevention during the Construction Period in Coal Penetration Tunnels—A Stepwise Prediction of Gas Concentration Based on the LSTM Method
by Penghui Li, Ke Li, Fang Wang, Zonglong Zhang, Shuang Cai and Liang Cheng
Sustainability 2022, 14(20), 12998; https://doi.org/10.3390/su142012998 - 11 Oct 2022
Cited by 4 | Viewed by 1125
Abstract
Aiming at the tunnel gas disaster can produce major safety problems such as combustion, explosion, and coal and gas outbursts. Firstly, a time series consisting of the tunnel gas concentration was used as the entry point for the article, and the gas prediction [...] Read more.
Aiming at the tunnel gas disaster can produce major safety problems such as combustion, explosion, and coal and gas outbursts. Firstly, a time series consisting of the tunnel gas concentration was used as the entry point for the article, and the gas prediction models based on multiple intelligent computational methods were established for comparison to determine the optimal network prediction model. Then, this study proposed a stepwise prediction method which is based on the optimal network prediction model for gas disaster prevention during the construction period of tunnels at the excavation workface. The length of the input step, output step, and interval step were considered by the method to investigate the effect on the predictive performance of the model. The model was extrapolated by the rolling prediction method, and the adaptive grid search method was used to determine the optimal parameter combination of stepwise prediction. Finally, a stepwise prediction of short-term gas concentration trends was achieved for each construction process at the excavation workface. As a result, the best LSTM network prediction model was preferred with an R2 value of 0.94 for the fit and MAE and RMSE values of 3.2% and 4.3%. Results based on stepwise predictions showed that single-step prediction is more accurate than multi-step predictions when a reasonable input step size was determined. Moreover, with the length of both the interval step and the output step, the model prediction accuracy showed a decreasing trend. Generally speaking, the single-step continuous and interval prediction of the gas concentration at the excavation workface can be realized by the gas stepwise prediction method, and the gas concentration value can be obtained at any time in the prediction. It can also realize the transformation from single-step point prediction to multi-step trend prediction, and obtain the accurate prediction of gas concentration change trends in the stepwise prediction range (t+1~t+5). Therefore, the important security guarantee can be provided by stepwise prediction for subsequent gas disaster safety prevention and efficient tunnel production. Full article
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21 pages, 4447 KiB  
Article
The Effects of True Triaxial Loading and Unloading Rates on the Damage Mechanical Properties of Sandstone
by Man Wang, Weihang Du, Yingwei Wang, Xinjian Li, Liming Qiu, Beichen Yu, Zehua Niu and Dongming Zhang
Sustainability 2022, 14(19), 11899; https://doi.org/10.3390/su141911899 - 21 Sep 2022
Viewed by 1188
Abstract
Coal is the main energy source in China. In the process of coal resource mining, the surrounding rock of roadways is often in the complex stress environment of “three heights and one disturbance”. At the same time, rocks in the stratum are often [...] Read more.
Coal is the main energy source in China. In the process of coal resource mining, the surrounding rock of roadways is often in the complex stress environment of “three heights and one disturbance”. At the same time, rocks in the stratum are often in a three-way unequal pressure state under the action of geological structure, and conventional rock mechanics tests cannot study the mechanical properties of rocks under actual stress conditions; thus, this is based on the self-developed true triaxial multifunctional fluid–structure coupling test system to study the damage mechanical Properties of Sandstone. The results are shown as follows: With an increase in loading rate, the peak damage Dcr of sandstone decreases, but the initial damage Da increases in the elastic stage, and the brittleness of sandstone weakens. With the increase in the unloading rate, Dcr increases, but Da decreases in the elastic stage, and the sandstone brittleness increases first, then decreases. In addition, the peak maximum principal strain ε1maxfirst decreases rapidly and then slowly; the peak minimum principal strain ε3max increases first, then decreases slowly, and increases slowly; the peak intermediate principal strain ε2max decreases slowly; and the peak volume strain εvmax increases rapidly first and then slowly with increases in the loading rate. With an increase in the unloading rate, ε1max increases rapidly first, then decreases slowly, then increases rapidly and finally increases slowly; ε3max first decreases slowly, then increases slowly, and finally decreases slowly; and ε2max increases slowly then decreases slowly. εvmax decreases rapidly first and then increases slowly with increasing loading rate. Full article
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11 pages, 3079 KiB  
Article
Experimental Study on Strength Weakening of Gypsum Rock with Effect of Long-Term Overlying Strata Pressure
by Shuli Wang, Zhihe Liu, Kaizhi Zhang, Guangli Zhu and Huaichang Zheng
Sustainability 2022, 14(18), 11442; https://doi.org/10.3390/su141811442 - 13 Sep 2022
Viewed by 1031
Abstract
A long time lag is the main characteristic of gypsum mined gob collapse disasters. With the coring of a gypsum rock specimen from the supporting pillars in gob, which formed over several years, the strength weakening effect of the gypsum rock with long-term [...] Read more.
A long time lag is the main characteristic of gypsum mined gob collapse disasters. With the coring of a gypsum rock specimen from the supporting pillars in gob, which formed over several years, the strength weakening effect of the gypsum rock with long-term overlying strata pressure is revealed by experimentation. The results show that: uniaxial compression stress–strain curves represent major differences in different lateral depths of the same supporting pillar. With the increase in lateral depth, peak strength increases and the corresponding strain decreases, which becomes more obvious as the age increases. As a function of time, peak strength decreases and the corresponding strain increases in the shallow part of the pillar as the age increases. Peak strength fluctuates in the middle part and increases in the deep part; the corresponding strain fluctuates in the middle and deep parts, but demonstrates the opposite changing law. Finally, the reason for the above law was comprehensively and thoroughly researched and demonstrated. The maximum strength weakening rate of gypsum rock in the shallow part of a supporting pillar of 0.5 m depth was 21.06% in the year 1996. The slow strength weakening effect of gypsum rock with long-term overlying strata pressure is the essential reason why gypsum mined gob collapses occur in subsequent years or even decades. Full article
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23 pages, 10890 KiB  
Article
Research on Deformation and Failure Control Technology of a Gob-Side Roadway in Close Extra-Thick Coal Seams
by Bin Zhao, Shengquan He, Xueqiu He, Le Gao, Zhenlei Li, Dazhao Song and Feng Shen
Sustainability 2022, 14(18), 11246; https://doi.org/10.3390/su141811246 - 08 Sep 2022
Cited by 3 | Viewed by 1086
Abstract
Close extra-thick coal seams are subject to the broken overburden of mined coal seams, and the deformation and damage of the roadways is serious, which affects the safe operation of the mine. To reduce the deformation and damage of the roadways, this paper [...] Read more.
Close extra-thick coal seams are subject to the broken overburden of mined coal seams, and the deformation and damage of the roadways is serious, which affects the safe operation of the mine. To reduce the deformation and damage of the roadways, this paper studied the deformation and damage law of the gob-side roadway in close extra-thick coal seams through numerical simulation and field monitoring, compared and analyzed the deformation and damage characteristics of the roadway under different reinforcement support methods, determined the optimal reinforcement support method, and carried out field verification. The obtained results indicated that the deformation and damage of the gob-side roadway showed asymmetric characteristics. The large deformation of the coal body in the deep part of the roadway wall is an important reason for the continuous occurrence of roadway wall heave in the coal pillar. Under the action of unbalanced support pressure, the floor is subject to the coupling effect of horizontal extrusion pressure and vertical stress that cause extrusion mobility floor heave. The horizontal and vertical displacement of the coal pillar side of the roadway under different support methods is much larger than that of the solid coal side. Increasing the anchor cable length and fan-shaped arrangement can improve the support effect. Grouting at the coal pillar side can significantly improve the bearing capacity and stability of the coal pillar. The effect of floor grouting is much better than the anchor cable in controlling the floor heave. The integrated reinforcement method of anchor cable + coal pillar side grouting + floor grouting has the best effect with the least horizontal and vertical deformation. The research results are of great significance for ensuring the stability of similarly endowed roadways. Full article
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16 pages, 4825 KiB  
Article
Research on Gob-Side Entry Retaining Mining of Fully Mechanized Working Face in Steeply Inclined Coal Seam: A Case in Xinqiang Coal Mine
by Xuming Zhou, Haotian Li, Xuelong Li, Jianwei Wang, Jingjing Meng, Mingze Li and Chengwei Mei
Sustainability 2022, 14(16), 10330; https://doi.org/10.3390/su141610330 - 19 Aug 2022
Cited by 1 | Viewed by 1227
Abstract
As a kind of non-coal pillar roadway support technique, gob-side entry retaining is of great significance to improve the production efficiency of a fully mechanized working face. However, the construction of the roadway is often subject to the surrounding rock conditions, the application [...] Read more.
As a kind of non-coal pillar roadway support technique, gob-side entry retaining is of great significance to improve the production efficiency of a fully mechanized working face. However, the construction of the roadway is often subject to the surrounding rock conditions, the application is mainly concentrated in the nearly horizontal and gently inclined coal seam conditions, and the application in the steeply inclined coal seam conditions is relatively less. This paper is based on the gob-side entry retaining roadway construction of the 58# upper right 3# working face in the fifth district of Xinqiang Coal Mine, and describes the investigation in which we measured the advanced abutment stress, mining stress, and roof stress and analyzed the moving rule of roof. On this basis, in this work, we determined the filling parameters and process and investigated the filling effect from the perspective of the deformation of the filling body and the surrounding rock. The results show that the influence range of the advanced abutment stress in the working face is about 20~25 m, the stress in the upper part is intense, and stress in the middle and lower parts are relaxed. The setting load, the cycle-end resistance, and the time-weighted mean resistance at the upper end of working face along the direction of length are the largest, followed by the middle part, and the lower end is the minimum. When exploiting the steep inclined coal seam, the upper part of the working face is more active than the lower part, and the damaging range of overlaying strata is mainly in the upper part of the goaf. With this research, we established the filling mining process in steeply inclined coal seams and determined the relevant parameters. The gangue cement mortar filling can ensure the deformation of the filling body, the surrounding rock of the roadway is small in the process of roadway retention, and the stress of the filling body is also small, which ensure the successful retention of the roadway. This study verifies the possibility of repair-less exploitation and provides a reference for the popularization and application of the gob-side entry retaining technique in steep inclined coal seam. Full article
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17 pages, 5201 KiB  
Article
Spatiotemporal Evolution Characteristics of Apparent Resistivity and Its Response Correlation with Acoustic Emission of Coal under Multi-Step Loading
by Xinyu Wang, Guoqing Zhu, Deqiang Cheng, Bin Miao, Fanbao Chen and He Tian
Sustainability 2022, 14(16), 10061; https://doi.org/10.3390/su141610061 - 14 Aug 2022
Viewed by 1073
Abstract
To understand the early warning signs of damage during the coal mass deformation process, an integrated monitoring procedure was designed that combines the apparent resistivity (AR) and acoustic emission (AE) of coal damage under multi-step loading. The spatiotemporal response characteristics of AR and [...] Read more.
To understand the early warning signs of damage during the coal mass deformation process, an integrated monitoring procedure was designed that combines the apparent resistivity (AR) and acoustic emission (AE) of coal damage under multi-step loading. The spatiotemporal response characteristics of AR and the time-varying evolution of AE were studied and the varying correlation between the two was discussed. Additionally, the macro–microscopic mechanics of the AR response during the coal deformation process was explored. The results show that the AR and AE signals corresponded well with the applied load during the coal deformation process. In the early loading stage, variations in AR and AE signals were not apparent. As the applied load increased, the high-resistance area of AR increased and the AE signals became active. The local variation characteristics of AR could be used to indirectly invert the internal structure of the coal samples. The electrical variation in the loaded coal was mainly controlled by the conductive surface of cracks. The acoustic and resistivity methods can strongly complement the spatial and temporal dimensions of early warning systems for disasters. The AE technique can continuously monitor a test area for abnormal occurrences in the engineering site, and AR tomography images that are obtained can be used to locate inversions in the source coal in order to take pre-emptive action before disaster occurs. This research can provide new ideas for monitoring and early warning systems for coal and rock dynamic disasters. Full article
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