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Advanced Underground Coal Mining and Ground Control Technology
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Advanced Underground Coal Mining and Ground Control Technology

A special issue of Applied Sciences (ISSN 2076-3417). This special issue belongs to the section "Earth Sciences".

Deadline for manuscript submissions: 20 August 2024 | Viewed by 15840

Special Issue Editors

Dr. Changliang Han

E-Mail Website
Guest Editor
School of Mines, China University of Mining and Technology, Xuzhou 221116, China
Interests: intelligent control of roadway surrounding rock; rock mass mechanics and ground control
Dr. Xiaoqing Wang

E-Mail Website
Guest Editor
Coal Mining Branch, Coal Research Institute, Beijing 100013, China
Interests: control of roadway surrounding rock; rock mass mechanics

Special Issue Information

Dear Colleagues,

Human society has long maintained a high level of demand for coal resources. In recent years, underground coal mining technology has evolved rapidly around issues of safety, health, and efficiency. Equal emphasis has been placed on the development and innovative research of traditional technologies such as roadway support and rock control, as well as the development and application of new technologies such as intelligent mining and big data. However, the development and application of new technologies are always affected by unfavorable factors such as variable geological conditions. The relevant theoretical and technical research is still being improved and refined.

This Special Issue aims to publish academic papers related to Advanced Underground Coal Mining and Ground Control Technology. The centralized publication of these results will facilitate the collision, learning and inspiration of ideas, as well as the dissemination of successful technologies and cases, and will also facilitate the identification of shortcomings and the search for new research points.

The topics of interest include, but are not limited to, the following:

  • Ground control for roadways or stopes
  • Intelligent mining or driving theory and technology
  • New coal mining and roadway driving methods
  • Intelligent perception, analysis, and decision for underground mining
  • Large section chamber support theory and technology
  • Efficient and fast driving technology
  • Forewarning and prevention for dynamic disaster of coal and rock
  • Rock mass mechanics

Dr. Changliang Han
Dr. Xiaoqing Wang
Guest Editors

Manuscript Submission Information

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Applied Sciences is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2400 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • underground coal mining
  • ground control
  • roadway support
  • intelligent driving
  • intelligent mining
  • roadway driving
  • dynamic disaster
  • fast driving
  • rock mass mechanics

Published Papers (18 papers)

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Research

21 pages, 8831 KiB  
Article
Exploring the Distribution Characteristics of High Static Load in the Island Working Face of Extra-Thick Coal Seams with Hard Roof: Addressing the Challenge of Rock Burst Risk
by Xianglin Dai, Rui Gao, Weichen Gao, Dou Bai and Xiao Huang
Appl. Sci. 2024, 14(5), 1961; https://doi.org/10.3390/app14051961 - 28 Feb 2024
Viewed by 587
Abstract
A high static load state significantly increases the risk of rock burst occurrences on the island working face, posing a significant threat to the safety of coal mine production. This paper focused on the engineering background of the 8204-2 working face at Tashan [...] Read more.
A high static load state significantly increases the risk of rock burst occurrences on the island working face, posing a significant threat to the safety of coal mine production. This paper focused on the engineering background of the 8204-2 working face at Tashan Coal Mine. Field research indicated that there were noticeable differences in the frequency of coal bursts in different regions and working face ranges, with the mine pressure being complex and severe. Through theory analysis, the stress concentration degree of the island working face was mainly affected by the buried depth, working face length, gob length, coal seam thickness, and coal pillar width. The stress distribution and plastic zone changes of the island working face, influenced by different factors, were studied by numerical simulation. The entity coal stress equation of the island working face was fitted and the mechanism of rock burst in the island working face was revealed. The research findings presented in this paper provide important theoretical support and technical guidance for the safe and efficient mining of island working faces. Full article
(This article belongs to the Special Issue Advanced Underground Coal Mining and Ground Control Technology)
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24 pages, 9760 KiB  
Article
Research on the Failure Mechanism of Surrounding Rock in a Dynamic Pressure Roadway and Active and Passive Coordinated Support Technology
by Renliang Shan, Yonghui Wei, Chunhe Wang, Zhaolong Li, Yongzhen Li, Dong Liu and Xinpeng Zhao
Appl. Sci. 2024, 14(5), 1858; https://doi.org/10.3390/app14051858 - 23 Feb 2024
Viewed by 409
Abstract
To study the phenomenon of large deformation and the failure of roadways under dynamic pressure, this paper takes the 10607 gas drainage roadway as the research object and presents the results of a theoretical derivation of equations for the boundary of the plastic [...] Read more.
To study the phenomenon of large deformation and the failure of roadways under dynamic pressure, this paper takes the 10607 gas drainage roadway as the research object and presents the results of a theoretical derivation of equations for the boundary of the plastic zone of a dynamic pressure roadway with and without supporting force. The impacts of the mining influence coefficient and supporting force on the plastic zone boundary were explored for various lateral pressure coefficients. As the supporting force was increased, it was observed that there was a slight reduction in the radius of the plastic zone of the dynamic pressure roadway, while its scope and shape barely changed. Based on the failure mechanism of the dynamic pressure roadway, active and passive support technology was proposed, and the support effect was analyzed using FLAC3D 5.0 numerical simulation software for the case of the 10607 gas drainage roadway. Full article
(This article belongs to the Special Issue Advanced Underground Coal Mining and Ground Control Technology)
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20 pages, 13445 KiB  
Article
Shear Mechanical Properties of Bolt-Grout Interface under Different Bolt Surface Profiles
by Zhaoyun Zhang, Jiankang Liu, Hengjie Luan, Yahua Wang, Yujing Jiang, Qingzhai Shi, Changsheng Wang and Sunhao Zhang
Appl. Sci. 2024, 14(5), 1770; https://doi.org/10.3390/app14051770 - 21 Feb 2024
Viewed by 587
Abstract
The shear behavior of the Bolt-Grout interface has a significant effect on the stability of a bolting system. In this paper, a series of shear tests were conducted on Bolt-Grout interfaces, and the effects of rib spacing, rib angles, and normal stress on [...] Read more.
The shear behavior of the Bolt-Grout interface has a significant effect on the stability of a bolting system. In this paper, a series of shear tests were conducted on Bolt-Grout interfaces, and the effects of rib spacing, rib angles, and normal stress on the shear characteristics and failure modes of the Bolt-Grout interface were investigated. The results showed that the shear strength varied nonlinearly with an increase in rib spacing and angle, and also that it increased linearly with an increase in normal stress. With smaller rib spacings, the effect of rib spacing on peak shear strength was more apparent. The failure modes of the interface can be categorized as shear-slip failure, shear-break failure, and composite failure. The proportion of shear-slip failure and shear-break failure mainly depends on the rib spacing, rib face angle and normal stress. Full article
(This article belongs to the Special Issue Advanced Underground Coal Mining and Ground Control Technology)
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17 pages, 9897 KiB  
Article
Research on Coal and Rock Recognition in Coal Mining Based on Artificial Neural Network Models
by Yiping Sui, Lei Zhang, Zhipeng Sun, Weixun Yi and Meng Wang
Appl. Sci. 2024, 14(2), 864; https://doi.org/10.3390/app14020864 - 19 Jan 2024
Viewed by 690
Abstract
In the process of coal mining, one of the main reasons for the high labor intensity of workers and the frequent occurrence of casualties is the low level of intelligence of coal mining equipment. As the core equipment in the process of coal [...] Read more.
In the process of coal mining, one of the main reasons for the high labor intensity of workers and the frequent occurrence of casualties is the low level of intelligence of coal mining equipment. As the core equipment in the process of coal mining, the intelligence level of shearers directly affects the safety production and mining efficiency of coal mines. Coal and rock recognition technology is the core technology used to realize the intelligentization of shearers, which is an urgent technical problem to be solved in the field of coal mining. In this paper, coal seam images, rock stratum images, and coal–rock mixed-layer images of a coal mining area are taken as the research object, and key technologies such as the construction of a sample image library, classification and recognition, and semantic segmentation are studied by using the relevant theoretical knowledge of artificial neural network models. Firstly, the BP neural network is used to classify and identify coal seam images, rock stratum images, and coal–rock mixed-layer images, so as to distinguish which of the current mining targets of a shearer is the coal seam, rock stratum, or coal–rock mixed layer. Because different mining objectives will lead to different working modes of a shearer, it is necessary to maintain normal power to cut coal when encountering a coal seam, to stop working when encountering rock stratum, and to cut coal along the boundary between a coal seam and rock stratum when encountering a coal–rock mixed stratum. Secondly, the DeepLabv3+ model is used to perform semantic segmentation experiments on the coal–rock mixed-layer images. The purpose is to find out the distribution of coal and rocks in the coal–rock mixed layer in the coal mining area, so as to provide technical support for the automatic adjustment height of the shearer. Finally, the research in this paper achieved a 97.16% recognition rate in the classification and recognition experiment of the coal seam images, rock stratum images, and coal–rock mixed-layer images and a 91.2% accuracy in the semantic segmentation experiment of the coal–rock mixed-layer images. The research results of the two experiments provide key technical support for improving the intelligence level of shearers. Full article
(This article belongs to the Special Issue Advanced Underground Coal Mining and Ground Control Technology)
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17 pages, 8237 KiB  
Article
Simulation Study and Engineering Application of Weakening Mine Pressure Behavior in Stope through Ground Fracturing Thick and Hard Rock Strata
by Zhu Li, Chengen Qi, Rui Gao, Bin Yu, Yiran Zhu, Hong Zhang and Jingyu Zhang
Appl. Sci. 2024, 14(1), 415; https://doi.org/10.3390/app14010415 - 2 Jan 2024
Viewed by 617
Abstract
Fracturing hard roofs by ground hydraulic action is an important control technology for the strong mine pressure in the stope. In this paper, a new simulation method, “separate + interface,” is proposed, and two physical simulation experiments are conducted; the phenomenon of increased [...] Read more.
Fracturing hard roofs by ground hydraulic action is an important control technology for the strong mine pressure in the stope. In this paper, a new simulation method, “separate + interface,” is proposed, and two physical simulation experiments are conducted; the phenomenon of increased goaf pressure and decreased front abutment pressure is discovered after fracturing in the key strata, and then the influence of different fractured crack shapes on the front abutment pressure and the goaf stress is revealed. The results are as follows: Firstly, the separation under the high-level hard strata blocks the transmission of overburden load to the goaf, leading to the high-stress concentration of the coal seam, which is the main reason for the large deformation of roadways and the breakage of a single hydraulic prop in the roadway. Secondly, the weakening effect of mine pressure differs when hard rock strata are fractured artificially with different types of cracks. The peak value of abutment pressure is reduced from 24.91 to 20.60 MPa, 17.80 MPa, and 16.13 MPa with the vertical crack spacing of 20 m, 15 m, and 10 m, respectively, and the related goaf pressure is increased from 2.61 to 3.54 MPa, 3.91 MPa, and 4.34 MPa, respectively. The peak value of abutment pressure decreased from 24.79 to 22.08 MPa, 19.88 MPa, and 17.73 MPa. The related goaf pressure increased from 2.61 to 3.39 MPa, 3.81 MPa, and 4.43 MPa, respectively, with the key strata also fractured into two horizontal layers, three horizontal layers, and four horizontal layers with horizontal fractures. Thirdly, after the hard roof is fractured above the No. 8202 working face, the first breaking step distance of the main roof decreased from 112.6 to 90.32 cm, while the first breaking step distances of KS2 and KS3 decreased from 106.3 and 135.8 cm to 93.5 cm and 104.8 cm, respectively, and the goaf pressure also increased. Compared to the adjacent unfractured No. 8203 working face, the mine pressure intensity of the No. 8202 working face is significantly reduced. The research results can provide useful guidance for the treatment of strong mine pressure. Full article
(This article belongs to the Special Issue Advanced Underground Coal Mining and Ground Control Technology)
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28 pages, 7154 KiB  
Article
Uneven Stiffness Coal Seam: A New Structural Factor Prone to Coal Burst Based on Stiffness Theory
by Tiewu Tang, Zhigang Deng, Weiguang Ren, Shankun Zhao, Yin Wang, Yang Zhao and Wenxin Li
Appl. Sci. 2024, 14(1), 24; https://doi.org/10.3390/app14010024 - 19 Dec 2023
Viewed by 661
Abstract
The development of stiffness theory is constrained by its contradiction with engineering experience. Several easily overlooked details of stiffness theory were clarified, and a qualitative evaluation formula for the risk of coal burst was provided. Then a novel structure factor called uneven stiffness [...] Read more.
The development of stiffness theory is constrained by its contradiction with engineering experience. Several easily overlooked details of stiffness theory were clarified, and a qualitative evaluation formula for the risk of coal burst was provided. Then a novel structure factor called uneven stiffness coal seam structure (USCS), which consists of high stiffness zone (HSZ), low stiffness zone (LSZ), and contiguous roof and floor, was proposed. Many areas prone to coal bursts, such as thinning zones, bifurcating areas, magmatic intrusion areas, and remnant pillar affected areas of coal seam, are the HSZs of USCSs. Comparative analysis of the uneven stiffness coal seam under different roof conditions and examination of the simplified trisection model of the USCS were conducted. Then 6 groups of 14 simplified 2D models using COMSOL5.2 was constructed based on controlled variable method to simulate different responses of the USCS with varying parameters under same working conditions. The results demonstrate the following: (1) coal bursts occur only when both the failure criterion and the stiffness criterion are simultaneously satisfied, the risk of coal burst (rCB) is the product of the risk of failure (rF) and the risk of instability (rI). (2) The pressure concentration function of USCS facilitates stress concentration from LSZ to HSZ, thus raising the rF in HSZ. The stiffness reduction function of USCS reduces the local mine stiffness (LMS) of the HSZ, allowing the system to meet the stiffness criterion even with a hard roof, thereby raising the rI in HSZ and reconciling the contrast between stiffness theory and engineering experience. Failures within HSZ of the USCS enables the roof strata to release bending deformation energy without roof breakage. (3) The normal stress of HSZ is positively correlates with the value of ERHRKHSL/KLSH; The LMS of the HSZ is positively correlated with the value of ERKL/KHHRSLSH. The USCS boasts significant advantages in integrating and harmonizing various existing theories and explaining multiple specific types of coal bursts. By applying relevant USCS findings, new explanations can be provided for engineering phenomena such as the time-delayed coal bursts, the inefficient pressure relief in ultra thick coal seams, and the “microseism deficiency” observed prior to certain coal bursts. Full article
(This article belongs to the Special Issue Advanced Underground Coal Mining and Ground Control Technology)
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17 pages, 3801 KiB  
Article
The Active Roof Supporting Technique of a Double-Layer Flexible and Thick Anchorage for Deep Withdrawal Roadway under Strong Mining Disturbance
by Changliang Han, Yuxin Yuan, Guoli Ding, Wenjie Li, Haoxing Yang and Gang Han
Appl. Sci. 2023, 13(23), 12656; https://doi.org/10.3390/app132312656 - 24 Nov 2023
Viewed by 593
Abstract
Due to the strong disturbance of a mining face, the surrounding rock of the withdrawal roadway is susceptible to deformation and failure, which restricts the safe and efficient evacuation of mining equipment. To resolve this longstanding technical problem in mine production, an engineering [...] Read more.
Due to the strong disturbance of a mining face, the surrounding rock of the withdrawal roadway is susceptible to deformation and failure, which restricts the safe and efficient evacuation of mining equipment. To resolve this longstanding technical problem in mine production, an engineering investigation, numerical simulation, theoretical analysis, and other research methodologies were conducted in this study. Furthermore, the influence mechanism of mining-induced stress on the withdrawal roadway was revealed, the anti-disturbance principles of thick-layer anchorage of roadway roofs were elucidated, and a novel double-layer flexible support technique was proposed. The front abutment pressure, stress superposition, damage accumulation of the surrounding rock, and the fluctuation of mining-induced stress are the primary factors contributing to the significant deformation of the surrounding rock in a withdrawal roadway. However, the fluctuation of mining-induced stress has usually been ignored in previous studies, and it may be the most crucial cause of the significant deformation and instability of the surrounding rock. The thickness of the anchored rock beam is the most vital factor affecting the maximum subsidence and maximum tensile stress of the roof, and increasing the thickness of the anchored rock beam can significantly improve the stability and anti-disturbance performance of the roof. In the proposed double-layer flexible supporting technique, flexible steel strands serve as the carrier, which overcomes the constraint of the roadway height on the length of roof support components. The first layer of flexible support is used to construct a thick fundamental anchorage layer, while the second layer is employed to construct a thicker reinforced anchorage layer, facilitating the effective resistance of the roof against strong mining disturbances. The effectiveness of this technique was further validated through the application of an engineering practice. The research results have reference value for solving the difficult problem of mining roadway support. Full article
(This article belongs to the Special Issue Advanced Underground Coal Mining and Ground Control Technology)
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14 pages, 3077 KiB  
Article
A Dynamic Numerical Simulation on the Grouting Timing in Retained Rib of Pillarless Mining
by Xianyang Yu, Jinhao Xie, Yanju Wu, Qiuhong Wu, Zizheng Zhang and Hai Wu
Appl. Sci. 2023, 13(16), 9479; https://doi.org/10.3390/app13169479 - 21 Aug 2023
Viewed by 663
Abstract
A dynamic numerical method is established to simulate the stability of the surrounding rocks of the retained roadway in FLAC3D, along with a double-yield constitutive model to simulate the re-compaction process of gangue and a strain-softening constitutive model to simulate the strain-softening characteristic [...] Read more.
A dynamic numerical method is established to simulate the stability of the surrounding rocks of the retained roadway in FLAC3D, along with a double-yield constitutive model to simulate the re-compaction process of gangue and a strain-softening constitutive model to simulate the strain-softening characteristic of the coal and the grouted fragmented coal after yielding. The simulation reveals that the grouting slurry diffusion range, the mining affecting the stage behind the working face and the retained coal rib deformation are closely interrelated. Under severe mining-induced stress, the integrity of the surrounding rock is more likely to be destroyed, accompanied by a large number of cracks developing and gradually expanding in the surrounding rocks. The roadway deformation increases in a rapid manner. Meanwhile, the grouting diffusing range increases gradually. The simulation conducted in this study indicates that the optimum support effect can be achieved by grouting in the section before and after the working face affected by the high mining-induced stress. A timely grouting can be used to construct an enhanced surrounding rock-bolting-grouting support system and maintain the stability of the retained roadway. Full article
(This article belongs to the Special Issue Advanced Underground Coal Mining and Ground Control Technology)
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18 pages, 8413 KiB  
Article
Nonuniform Deformation Instability Mechanism of Gob-Side Entry Retained in Inclined Coal Seam and Stability Control
by Xubo Qiang, Ji Li, Chaosen Chen, Jihui Dong, Yingjian Zheng and Zhong Chen
Appl. Sci. 2023, 13(15), 8727; https://doi.org/10.3390/app13158727 - 28 Jul 2023
Viewed by 627
Abstract
In this study, the nonuniform deformation and failure of the goaf retaining roadway in an inclined coal seam due to repeated mining have been investigated by field verification, theoretical analysis and numerical simulation. As a case study, 3131 headentry of a coal mine [...] Read more.
In this study, the nonuniform deformation and failure of the goaf retaining roadway in an inclined coal seam due to repeated mining have been investigated by field verification, theoretical analysis and numerical simulation. As a case study, 3131 headentry of a coal mine in Sichuan province was considered. The deformation characteristics of the surrounding rock along the gob of inclined coal seam and the distribution characteristics and evolution of the plastic zone and stress field direction of gob-side entry retaining (GER) in 3131 coal faces during the service period were also studied. Based on the mechanical model of the plastic zone of surrounding rock, the stress field direction effect of nonuniform expansion of the plastic zone is explained, and the nonuniform deformation damage mechanism of the inclined coal seam along the empty tunnel is revealed. The results show that the plastic zone of the side always expands along the coal seam towards the side affected by mining during the whole service period of GER in the inclined coal seam, and the plastic zone of the roof and floor expands to the deep surrounding rock; and the expansion degree of the soft coal (rock) seam position of the roadway is the highest. At the same time, the direction of the surrounding rock stress field will be deflected during the service period of GER, and the plastic zone expands unevenly under the action of the coal seam dip angle and stress direction. The nonuniform expansion degree of the plastic zone is the largest when the angle between the maximum principal stress and the coal (rock) layer is 45° (±5°). A collaborative support method with “supporting and reducing span” as the core in GER is also proposed in this work. Field tests were also carried out. During the retaining period, the displacement of the roof and floor was reduced from 250 mm to 125 mm. Full article
(This article belongs to the Special Issue Advanced Underground Coal Mining and Ground Control Technology)
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16 pages, 4813 KiB  
Article
Deformation Characteristics and Destabilization Mechanisms of the Surrounding Rock of Near-Vertical Coal–Rock Interbedded Roadway
by Yanqiang Yao, Hongzhi Wang, Honglin Liu and Guodong Li
Appl. Sci. 2023, 13(14), 8397; https://doi.org/10.3390/app13148397 - 20 Jul 2023
Viewed by 686
Abstract
Aiming at the problem of serious deformation and difficult support in the surrounding rock of the near-vertical coal–rock-interbedded roadway, this paper studies the stress distribution characteristics of the roadway surrounding the rock based on the engineering geological conditions of the Wudong coal mine, [...] Read more.
Aiming at the problem of serious deformation and difficult support in the surrounding rock of the near-vertical coal–rock-interbedded roadway, this paper studies the stress distribution characteristics of the roadway surrounding the rock based on the engineering geological conditions of the Wudong coal mine, in particular with the +400 level B8 centralized transportation roadway. Meanwhile, both the deformation and destabilization characteristics of the roadway surrounding the rock is studied. The distribution of the plastic zone is numerically studied via the FLAC3D program. The research results showed that: the averaged maximum horizontal principal stress is 24.3 MPa, which is about 3.08 times of the vertical principal stress. The deformation and damage of the near-vertical coal–rock-interbedded roadway is asymmetrical, and the stress distribution of the roadway surrounding the rock shows obvious discontinuous characteristics. Moreover, the plastic zone of the roadway surrounding the rock is featured with the shear damage. It also suggests that the force of gravity along the coal–rock layer direction increases when the normal load at the level of the near-vertical coal–rock layer is relatively small. The overhanging area of the roof and the unconfined range of the floor increased, which was attributed to the shear slip damage, whereas the flexural deformation is produced under the effect of tectonic stress, which results in the instable mechanism of “the ribs heave, roof subsidence and floor heave” for near-vertical coal–rock-interbedded roadway. Full article
(This article belongs to the Special Issue Advanced Underground Coal Mining and Ground Control Technology)
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13 pages, 3890 KiB  
Article
Structural Stability and Surrounding Rock Integrity Analysis for Goaf-Side Entry with Small Coal Pillars in Longwall Mining
by Yiming Zhao and Zhi Xiang
Appl. Sci. 2023, 13(12), 6877; https://doi.org/10.3390/app13126877 - 6 Jun 2023
Viewed by 638
Abstract
Goaf-side entry with small coal pillars (GESCPs) has an intrinsic advantage of improving the coal recovery ratio by implementing drifts with a small pillar size next to previous goafs. This technology is increasingly gaining popularity in the longwall mining of underground coal mines [...] Read more.
Goaf-side entry with small coal pillars (GESCPs) has an intrinsic advantage of improving the coal recovery ratio by implementing drifts with a small pillar size next to previous goafs. This technology is increasingly gaining popularity in the longwall mining of underground coal mines in China. This study focuses on understanding the critical condition of the main roof failure above the solid coal side of the goaf-side entry and investigating the key parameters that affect the structural stability of the surrounding rocks for GESCP. Mechanical models of the main roof and multi-layer cracking structures of the side wall of GESCP were established and the limiting equilibrium equation for the structural stability of the surrounding rock was proposed. The characteristics affecting the main parameters of the structural stability of the surrounding rock were analyzed. The research findings suggest that the integrity of the coal side walls plays a major role in maintaining the structural stability of the surrounding rock for GESCP under the given cross-sectional dimensions. Other factors, including the uniform load of overburden, the width of the coal pillar, the length of the roof hanging along the goaf side, and the fracture length in the main roof of the entry side wall, are less important. The key to achieving structural stability of the surrounding rocks for GESCP is to enhance the strength of the supporting coal side walls and, especially, to ensure the integrity of the small coal pillars. These conclusions were verified by engineering practice at the 1252(1) haulage gateway in a Coal Mine in China. Full article
(This article belongs to the Special Issue Advanced Underground Coal Mining and Ground Control Technology)
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14 pages, 4081 KiB  
Article
Effects of Abrupt Cross-Section Area Change on theMultiparameter Propagation Characteristics of Premixed Methane–Air Explosion in Pipes
by Jinwei Qiu, Bingyou Jiang, Mingyun Tang, Liang Zhou and Yingdi Yang
Appl. Sci. 2023, 13(11), 6372; https://doi.org/10.3390/app13116372 - 23 May 2023
Cited by 1 | Viewed by 971
Abstract
This paper explores the effects of an abrupt cross-section area change of gas pipes on the propagation law of explosion. For this, an explosion pipe experimental system was established, and a numerical research was conducted. By experimental and numerical simulation, the evolution of [...] Read more.
This paper explores the effects of an abrupt cross-section area change of gas pipes on the propagation law of explosion. For this, an explosion pipe experimental system was established, and a numerical research was conducted. By experimental and numerical simulation, the evolution of the overpressure, temperature, vorticity, and kinetic energy of shock waves of gas explosion in abrupt pipelines was investigated. This allowed us to obtain expressions for the attenuation coefficient, increase coefficient, and reflection coefficient of gas explosion overpressure. The study indicates that an abrupt increase of the pipeline cross-section area leads to a decrease of shock wave overpressure and vice versa. For a given change of cross-section area, the attenuation coefficient gradually increases as the initial peak overpressure rises, whereas the increase coefficient and reflection coefficient both present a decreasing trend. An abrupt change in the pipe structure can inhibit the propagation of gas explosion flames. The explosive gas is affected by the turbulence effect after passing through the middle large-diameter pipe, and the vorticity curve exhibits a clear peak. In addition, the large eddy motion caused by strong confinement increases the kinetic energy of the gas in pipes. The above research outcomes contribute to further enriching the basic theory of gas explosion for the study of gas explosion propagation in mining laneway. Full article
(This article belongs to the Special Issue Advanced Underground Coal Mining and Ground Control Technology)
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14 pages, 4750 KiB  
Article
Detection of Coal Bust Risk in a Kilometer Depth Workface with Hard–Thick Roof Based on Active–Passive Seismic CT
by Hu He, Junming Zhao, Ruyi Cheng, Zhengbing Men and Zonglong Mu
Appl. Sci. 2023, 13(10), 6173; https://doi.org/10.3390/app13106173 - 18 May 2023
Cited by 1 | Viewed by 958
Abstract
Practice and theory research proved the “square effect” during longwall mining with hard–thick strata lying on the coal seam, which could cause severe underground pressure and even dynamic disasters, such as coal burst; therefore, it became a key area and stage that need [...] Read more.
Practice and theory research proved the “square effect” during longwall mining with hard–thick strata lying on the coal seam, which could cause severe underground pressure and even dynamic disasters, such as coal burst; therefore, it became a key area and stage that need special attention. The combined active–passive seismic computed tomography (CT) was introduced to detect the abutment stress concentration in the coal seam. The results of active–passive CT inversion show that the “square effect” appears as early as the workface ahead of the theoretical position of 50 m with a 100 m significant influencing zone, which provides a strong guarantee for accurate risk evaluation of coal burst. Precursor information before the “square effect” can be identified based on the everyday total energy of mining tremors, which had period peaks in this case. The everyday average energy of mining tremors indicates that the seismic type during the “square effect” stage belonged to a foreshock–mainshock pattern. The combination of the seismic events and CT can improve the accuracy of coal burst danger distinguishing notably. The research can provide worthwhile guidance for the monitoring and prevention of coal burst hazards in similar conditions. Full article
(This article belongs to the Special Issue Advanced Underground Coal Mining and Ground Control Technology)
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20 pages, 8298 KiB  
Article
A Study of the Deformation Law of the Surrounding Rock of a Laminated Roadway Based on FLAC3D Secondary Development
by Tuo Wang, Jucai Chang and Hongda Wang
Appl. Sci. 2023, 13(10), 6077; https://doi.org/10.3390/app13106077 - 15 May 2023
Cited by 4 | Viewed by 1076
Abstract
To investigate and analyze the influence of different stress environments on the deformation and destabilization of the rocks surrounding laminated roadways under high stress, this study conducted numerical simulations of coal–rock combination under different circumferential pressures and of the surrounding rocks of highly [...] Read more.
To investigate and analyze the influence of different stress environments on the deformation and destabilization of the rocks surrounding laminated roadways under high stress, this study conducted numerical simulations of coal–rock combination under different circumferential pressures and of the surrounding rocks of highly stressed laminated roadways under different lateral pressure coefficients. In addition, a new custom constitutive structure model was constructed based on the Mohr–Coulomb criterion and realized in FLAC3D software by combining field working conditions. The model was then developed in FLAC3D software for a second time. The results show that the calculated results of the model in this study are in good agreement with the experimental results and the errors are small, while the calculated results of the Mohr–Coulomb model differ from the experimental values under two types of surrounding rock pressure. The deformation of the Mohr–Coulomb model is significantly smaller than that of the customized model, which verifies the reasonableness and superiority of the self-built model in combination with the field conditions. This provides theoretical and practical bases for the design and optimization of stratigraphic roadway support in underground coal mines. Full article
(This article belongs to the Special Issue Advanced Underground Coal Mining and Ground Control Technology)
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19 pages, 8848 KiB  
Article
Experimental Study of the Mechanical Properties of a Flexible Grid Filling Body
by Xiaosheng Liu, Weijun Wang, Hai Wu, Jiaren Chen, Xuan Zhang and Liming Zhang
Appl. Sci. 2023, 13(10), 5858; https://doi.org/10.3390/app13105858 - 9 May 2023
Viewed by 1002
Abstract
The fill mining method has become more widely used due to its advantages of a high resource recovery rate, reliability and safety, and reduced surface tailings storage. However, the mechanical properties of the cemented fillings in fill mining are similar to those of [...] Read more.
The fill mining method has become more widely used due to its advantages of a high resource recovery rate, reliability and safety, and reduced surface tailings storage. However, the mechanical properties of the cemented fillings in fill mining are similar to those of ultra-low strength plain concrete, and there are problems such as high brittleness, low bending and tensile strength, and sudden failure. Using a flexible grid as reinforcement material, uniaxial compression, tensile, and shear tests of a flexible grid filling body were carried out, and the results were compared with the mechanical properties of the filling body without the flexible grid. We drew the following main conclusions: the uniaxial compressive strength of the flexible grid filling body gradually increased with the decrease in the grid spacing (the increase in the grid density); the grid dimension had little effect on the uniaxial compressive strength of the flexible grid filling body. The uniaxial tensile strength and shear strength of the flexible grid filling body increased with the increase in the grid dimension; and they first increased and then decreased with the increase in the grid spacing, and there was an optimal grid spacing. From the perspective of the macroscopic failure mode, the flexible grid filling body specimen after the uniaxial compression test had a conjugate shear failure, forming a “dumbbell shape” with two large ends and a small middle. After the uniaxial tensile test, the macroscopic failure mode of the specimen was tensile failure. After the shear test, the macroscopic failure mode of the specimen was shear slip failure. It is proposed that the tensile strength, shear strength, cohesion, and internal friction angle strengthening coefficients of the flexible grid filling body with different dimensions and spacing are higher than the elastic modulus strengthening coefficients. The experimental results can provide a certain reference and guidance for mine filling. Full article
(This article belongs to the Special Issue Advanced Underground Coal Mining and Ground Control Technology)
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17 pages, 6958 KiB  
Article
Weighting Failure Mechanisms of Pre-Driven Recovery Rooms and Evaluation of Hydraulic Fracturing Applications: A Case Study
by Guanjun Li, Xiangyu Wang, Jianbiao Bai, Yongqiang Zhang, Feiteng Zhang and Menglong Li
Appl. Sci. 2023, 13(8), 5116; https://doi.org/10.3390/app13085116 - 20 Apr 2023
Viewed by 887
Abstract
Roof weighting failures of pre-driven recovery rooms may cause huge economic losses and even casualties. The excessive dynamic load from the sliding of the broken main roof rock block causes the recovery room roof and inner supports to lose their support capacity during [...] Read more.
Roof weighting failures of pre-driven recovery rooms may cause huge economic losses and even casualties. The excessive dynamic load from the sliding of the broken main roof rock block causes the recovery room roof and inner supports to lose their support capacity during the last weighting. Discrete element software UDEC was used to investigate the surrounding rock deformation of the pre-driven recovery room with the main roof break at different positions. The results show that when the recovery room’s length from the main roof rock layer’s fracture region is short, the immediate roof is subjected to high deviatoric stress and the occurrence of horizontal stress concentration due to the deflection of the fractured rocks, and eventually the roof supports fail owing to the development of macroscopic shear crack zones. In this research, the hydraulic fracturing technique was applied to pretreat the main roof (fine-grained sandstone) of the 31108 panel at Huoluowan Coal Mine. Field observations suggest that the strength and duration of the periodic weighting after hydraulic fracturing treatment are both significantly reduced, effectively maintaining the bearing layer performance of the roof of the recovery room and coal pillar walls. The proposed fracturing design offers an effective method of ground control to the coal mines facing roof weighting failures of recovery rooms. Full article
(This article belongs to the Special Issue Advanced Underground Coal Mining and Ground Control Technology)
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16 pages, 9762 KiB  
Article
Determination of Hazardous Zone of Coal Spontaneous Combustion in Ultra-Long Working Face Based on the Gob Porosity Evolution and Flow Field Distribution
by Shuliang Xie, Gang Wang, Enmao Wang, Qiming Huang and Mingze Xia
Appl. Sci. 2023, 13(7), 4574; https://doi.org/10.3390/app13074574 - 4 Apr 2023
Viewed by 1124
Abstract
Coal fire remains one of the main hazards of underground work. Spontaneous coal fires cause serious casualties and property losses. At present, most of the studies on coal spontaneous combustion have been conducted on working faces shorter than 200 m. However, the ultra-long [...] Read more.
Coal fire remains one of the main hazards of underground work. Spontaneous coal fires cause serious casualties and property losses. At present, most of the studies on coal spontaneous combustion have been conducted on working faces shorter than 200 m. However, the ultra-long working face gob of shallow buried coal seam is much larger, the distribution of its flow field is more complex, and, thus, risk of spontaneous combustion in the gob is higher. Exploring the evolution law of the gob flow field of ultra-long working face to quickly determine the range of the coal spontaneous combustion hazardous zone is of great significance to the safe production of similar mines. In this study, the gas flow field distribution in the gob of an ultra-long working face was measured by buried pipeline method and oxygen concentration was used as the index. It is found that the oxygen concentration decreases with the advance of the working face. Based on the flow field distribution, the oxidation zone of the gob was determined. Meanwhile, a three-dimensional (3D) numerical model of the working face was established, and the overlying stratum collapse and porosity evolution in the gob were simulated using the particle flow software, PFC3D discrete element software, for the porosity distribution law of the gob. The obtained porosity data were then imported into FLUENT using the custom function UDF to construct a 3D grid model. The flow field distribution in the gob was then numerically simulated for the seepage and migration law of the wind flow in the gob. The results reveal an arch-shaped wind flow field distribution with a swirl shape on the intake airway side. In the strike direction, the wind flow gradually becomes weaker with the advance of the working face. In the dip direction, the wind flow seepage range on the return airway side is obviously higher than that on the intake airway side. In the vertical direction, the wind flow range in the upper gob is larger than that in the middle and lower gob. The spontaneous combustion and oxidation zone of the gob is determined to be at 140.4–313.3 m on the intake airway side, 201.2–351.6 m in the middle of the gob, and 153.2–328.1 m on the return airway side. Finally, the residual coal distribution was superimposed onto the oxygen concentration distribution to obtain the spontaneous residual coal combustion hazardous zone in the gob. Full article
(This article belongs to the Special Issue Advanced Underground Coal Mining and Ground Control Technology)
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14 pages, 5557 KiB  
Article
Damage Mechanism of Prefabricated Fracture-Grouted Rock Specimens under the Action of Dry and Wet Cycles
by Benniu Wu, Qinjie Liu, Qiang Fu, Qinggan Yang and Qiang Chen
Appl. Sci. 2023, 13(6), 3631; https://doi.org/10.3390/app13063631 - 12 Mar 2023
Cited by 3 | Viewed by 1126
Abstract
In order to study the damage mechanism of fissure-grouted rocks in abandoned mine pumped storage, uniaxial compression tests were conducted using fissure-grouted rock specimens after dry and wet cycles. Additionally, acoustic emission sensors were used to track the damage of the rock specimens. [...] Read more.
In order to study the damage mechanism of fissure-grouted rocks in abandoned mine pumped storage, uniaxial compression tests were conducted using fissure-grouted rock specimens after dry and wet cycles. Additionally, acoustic emission sensors were used to track the damage of the rock specimens. The results demonstrate a negative correlation between peak strength and elastic modulus and a linear decrease in wave velocity and the mechanical characteristics of the fracture-grouted rock specimens with increasing dry and wet cycles. As the number of dry and wet cycles increased, the deterioration of the fracture-grouted specimens significantly decreased, and the internal microstructural adjustment of the specimens gradually leveled off. A rock constitutive model considering deterioration due to the dry–wet cycle is introduced, and the stress–strain curves under different dry and wet cycles are fitted. The model, which also accurately shows the mechanism of damage to prefabricated fissure-grouted rock specimens after dry and wet cycles, better characterizes the damage development law of prefabricated fissure-grouted rock specimens under the influence of dry and wet cycles. Full article
(This article belongs to the Special Issue Advanced Underground Coal Mining and Ground Control Technology)
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