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Mechanics, Damage Properties and Impacts of Coal Mining
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Mechanics, Damage Properties and Impacts of Coal Mining

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

Deadline for manuscript submissions: closed (20 May 2024) | Viewed by 24213

Special Issue Editor

Prof. Dr. Hai Pu

E-Mail Website
Guest Editor
State Key Laboratory for Geomechanics and Deep Underground Engineering, China University of Mining and Technology, Xuzhou 221116, China
Interests: seepage mechanics; rock dynamics; coal mining
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

With the gradual depletion of the earth's shallow coal resources, deep coal mining has become the norm. The scale and disturbed area of coal mining projects at depth are far greater than those at shallow depths, subjecting the coal and rock masses to more intense deformation and loading. Due to the influence of mining disturbances, the internal structure of the surrounding rock and the in-situ stress field are out of balance, resulting in the coupling of multi-physical fields such as stress field, temperature field, seepage field, chemical field, and microorganisms. When the mining depth exceeds 800 meters, coal mining projects are extremely vulnerable to coal and gas outbursts, rockburst, significant deformation of roadway surrounding rock, mine water hazards, and coal mine thermal damage. The investigation of the spatial and temporal dynamic evolution of multi-physical and chemical fields in the coal mining process is of great significance to ensure the safe mining of coal resources in the deep underground. Potential topics include but are not limited to the following:

  • In-situ mechanical behavior of deep rock masses
  • Analysis and control of long-term stability of deep surrounding rock masses
  • Multi-field and multi-phase seepage theory under the influence of mining disturbing
  • Deep rock deformation monitoring and safety monitoring
  • Deep mining dynamic hazard prevention and control
  • Theory of coordinated exploitation of co-associated resources

Prof. Dr. Hai Pu
Guest Editor

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Keywords

  • deep mining
  • rock mechanics
  • multi-field and multi-phase coupling
  • damage mechanics
  • dynamic disaster

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Published Papers (17 papers)

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17 pages, 4798 KiB  
Article
Research on the Outburst–Rockburst Coupling Disaster Law Based on True Triaxial Unloading Tests
by Lei Shan, Fukun Xiao, Gang Liu and Kai Xie
Appl. Sci. 2024, 14(11), 4675; https://doi.org/10.3390/app14114675 - 29 May 2024
Viewed by 605
Abstract
The coal and gas outburst and rockburst coupling disaster is becoming increasingly serious due to deep mining. To clarify the mechanism inducing the outburst–rockburst coupling disaster, a true triaxial single-sided unloading mechanical test was conducted with the aid of a true triaxial solid–thermal–gas [...] Read more.
The coal and gas outburst and rockburst coupling disaster is becoming increasingly serious due to deep mining. To clarify the mechanism inducing the outburst–rockburst coupling disaster, a true triaxial single-sided unloading mechanical test was conducted with the aid of a true triaxial solid–thermal–gas coupling test device, an industrial computed tomography (CT) system, and an acoustic emission system. Through this test, the mechanical characteristics, meso crushing characteristics, and acoustic characteristics in the disaster formation process were obtained. Additionally, the outburst–rockburst coupling instability disaster law was verified by numerical simulation. The results demonstrated that the stress unloading degree of the coal body was negatively correlated with the initial gas pressure in the outburst–rockburst coupling disaster. The time domain parameter count and energy of acoustic emission exhibited a “bimodal” distribution pattern in the instability stage. The rockburst would occur when the peak value was in a “low-count and high-energy” state, while coal and gas outburst would occur when the peak value was in a “high-count and low-energy” state. The meso slice revealed that gas degradation promoted the development of microcracks in the coal body, and the penetration of cracks resulted in the main cracks of structural instability during rockburst. The coal and gas outburst was mainly attributed to the “cross” shear failure pattern of the coal body. These research findings may lay a foundation for the effective prevention and control of outburst–rockburst coupling disasters. Full article
(This article belongs to the Special Issue Mechanics, Damage Properties and Impacts of Coal Mining)
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18 pages, 4486 KiB  
Article
Study on the Vertical Stability of Drilling Wellbore under Optimized Constraints
by Ruixue Pan, Jimin Liu, Hua Cheng and Haixu Fan
Appl. Sci. 2024, 14(6), 2317; https://doi.org/10.3390/app14062317 - 9 Mar 2024
Cited by 1 | Viewed by 1069
Abstract
With the development of coal resource extraction and wellbore construction proceeding towards deeper depths, the stability of drilling wellbore structures has become increasingly severe, even posing a barrier to the use of drilling method technology in deep wellbore construction. To address this issue, [...] Read more.
With the development of coal resource extraction and wellbore construction proceeding towards deeper depths, the stability of drilling wellbore structures has become increasingly severe, even posing a barrier to the use of drilling method technology in deep wellbore construction. To address this issue, this study raised an optimized constraints method involving pre-throwing cement slurry to the bottom before wellbore decent, altering bottom constraints. Firstly, the critical depth and instability criterion of this optimized method was derived by catastrophe theory. Subsequently, the role of single-factor and multi-factor sensitivity analyses on critical depth was discussed. The engineering effects of optimized constraint methods were contrasted and examined in several drilling projects. Finally, the characteristic values of real engineering were computed using numerical techniques and ABAQUS2020 software, and the efficacy of optimization approaches was examined and validated. The results revealed that the critical depth increased by 41.39 ± 5%. The influence factors described in order of the degree were the counterweight water height, the elastic modulus, the thickness of the wellbore, and the self-weight of the wellbore, sequentially. The conclusion on structural stability between the numerical calculation solution and theoretical calculation solution was completely the same. The optimized constraints method can effectively improve the stability of the wellbore structure. Full article
(This article belongs to the Special Issue Mechanics, Damage Properties and Impacts of Coal Mining)
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16 pages, 7148 KiB  
Article
Experimental Study on Dynamic and Static Combined Dynamics of Temperature–Water-Coupled Sandstone and Energy Consumption Analysis
by Qi Ping, Jing Hu, Yijie Xu, Shiwei Wu, Xiangyang Li and Shijia Sun
Appl. Sci. 2024, 14(5), 1783; https://doi.org/10.3390/app14051783 - 22 Feb 2024
Viewed by 715
Abstract
In order to study the dynamic properties of temperature–water-coupled sandstone under axial pressure, impact compression tests were carried out on sandstone samples after temperature–water coupling under eight types of axial pressure (0.5~4.0 MPa) loading as well as no axial pressure loading by using [...] Read more.
In order to study the dynamic properties of temperature–water-coupled sandstone under axial pressure, impact compression tests were carried out on sandstone samples after temperature–water coupling under eight types of axial pressure (0.5~4.0 MPa) loading as well as no axial pressure loading by using the split-Hopkinson pressure bar (SHPB) test set. The results showed that the mass, volume, and density of the sandstone specimens increased by 0.57%, 0.37%, and 0.20%, respectively, after temperature–water coupling. With increasing axial pressure, the dynamic compressive strength of temperature–water-coupled sandstone samples decreased as a linear function, the dynamic strain increased as a quadratic function, the dynamic modulus of elasticity decreased as a quadratic function, and the average strain rate increased as an exponential function, indicating a strong strain rate effect. From the energy point of view, as the axial pressure increases, the absorption energy of the sample increases, the reflection energy gradually decreases, the crushing degree of the sample increases, and the size of the broken pieces decreases; the average particle size of the sandstone sample pieces decreases quadratically with the increase in the absorption energy and linearly with the increase in the axial pressure. Full article
(This article belongs to the Special Issue Mechanics, Damage Properties and Impacts of Coal Mining)
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21 pages, 8735 KiB  
Article
Dynamic Response and Energy Characterisation of High-Strength Sandstone under Progressive Cyclic Loading Based on Sustainable Mining
by Zhuolin Shi, Chengle Wu, Xuehua Li, Yingnan Xu, Kai Li and Jialong Sun
Appl. Sci. 2024, 14(3), 1101; https://doi.org/10.3390/app14031101 - 28 Jan 2024
Viewed by 878
Abstract
In the research on sustainable mining and environmental preservation, understanding the dynamic behaviour of rock formations in deep, high-stress mining environments is essential. In order to acquire the laws of rock dynamic disaster generation from mining in deep, high-stress environments, this research adopts [...] Read more.
In the research on sustainable mining and environmental preservation, understanding the dynamic behaviour of rock formations in deep, high-stress mining environments is essential. In order to acquire the laws of rock dynamic disaster generation from mining in deep, high-stress environments, this research adopts a multistage and multi-cycle triaxial cyclic loading test to obtain the stress–strain curves and macroscopic deformation characteristics of hard sandstone under different surrounding pressures. The results show that the cumulative damage displacement of hard sandstone under cyclic loading at a certain stress level for the first 3–4 cycles is half of the total damage displacement at that cycle stage, and its peak volumetric strain will increase with the increase. The elastic energy density ratio and dissipation energy density ratio of hard sandstone under cyclic loading show a sinusoidal fluctuation trend, and the fluctuation gradually decreases with the increase in the number of cycles and the increase in the cyclic stress level. Under the cyclic loading of different surrounding pressures, the hard sandstone shows brittle damage characteristics, where the damage form is mainly shear damage with a small amount of tensile damage in low surrounding pressure and the damage form is mainly shear damage, tensile damage, and local compression damage in high surrounding pressure. The study reveals the deformation and damage law, energy evolution, and dissipation characteristics of high-strength hard sandstone. It is essential for the development of mining strategies that minimize the impact on the environment, reduce the dynamic hazards generated by mining, and maximize the efficiency of resource extraction Full article
(This article belongs to the Special Issue Mechanics, Damage Properties and Impacts of Coal Mining)
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15 pages, 3815 KiB  
Article
Experimental Study on the Physical and Mechanical Properties of Cemented Gangue Backfill under Acid Mine Water Erosion
by Dejun Liu, Hai Pu, Hongyang Ni and Guohui Zhang
Appl. Sci. 2024, 14(1), 107; https://doi.org/10.3390/app14010107 - 21 Dec 2023
Cited by 1 | Viewed by 1072
Abstract
Ensuring the structural safety of cemented gangue backfill (CGB) is crucial for safe mining operations. However, the complex mine water environment makes it susceptible to erosion by chemical ions, which have a significant time dependency. In this study, we evaluated the appearance, mass [...] Read more.
Ensuring the structural safety of cemented gangue backfill (CGB) is crucial for safe mining operations. However, the complex mine water environment makes it susceptible to erosion by chemical ions, which have a significant time dependency. In this study, we evaluated the appearance, mass change, and unconfined compressive strength (UCS) of CGB during different chemical erosion times. We also determined the effect of chemical ion erosion time on the stress threshold for crack initiation and development in the specimens using acoustic emission (AE). Additionally, we examined the chemical erosion mechanism of CGB by scanning electron microscopy (SEM). Our results showed that as the erosion time increased, the CGB exhibited a decrease in brittleness and an increase in plasticity. During the first 60 days of CGB, the internal micropores and microfractures of the CGB were filled due to the hydration reaction and SO42− intrusion, resulting in increases in the UCS and the mass of the CGB. However, as the erosion time continued, H+ and SO42− intruded into the interior of the CGB, causing the erosion products of the CGB to expand in volume, leading to a decrease in the strength of the CGB. Our analysis of the stress thresholds for microcrack development and macrocracks initiation in the CGB showed an increase followed by a decline with time. After 60 days of immersion, the stress threshold for microcrack initiation and macrocrack extension increased by 20% and 6%, respectively. However, as the immersion time increased to 150 days, the stress threshold for microcrack initiation and macrocrack extension decreased by 56% and 16%, respectively. Therefore, the design of CGB safety needs to consider the long-term effects of chemical attacks on CGB. Full article
(This article belongs to the Special Issue Mechanics, Damage Properties and Impacts of Coal Mining)
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18 pages, 2397 KiB  
Article
A Case Study of the Radon Hazard at the Boundary of a Coal Minefield
by Timofey Leshukov, Konstantin Legoshchin and Aleksey Larionov
Appl. Sci. 2023, 13(24), 13188; https://doi.org/10.3390/app132413188 - 12 Dec 2023
Viewed by 1373
Abstract
The main purpose of this study is to assess the radon hazard in areas near the boundary of a coal mine. Our assessment included an analysis of the soil’s radon volume activity (VAR) and radon flux density (RFD), as well as their spatial [...] Read more.
The main purpose of this study is to assess the radon hazard in areas near the boundary of a coal mine. Our assessment included an analysis of the soil’s radon volume activity (VAR) and radon flux density (RFD), as well as their spatial characteristics and correlations with other factors. The soil VAR varies in the range from 3477.7 to 17,520 Bq/m3 (mean value 9786.9 ± 474.9 Bq/m3), and RFD from 10 to 160 mBq·m−2·s−1 with a mean value of 59.76 ± 2.45 mBq·m−2·s−1. The RFD parameter is spatially clustered (p ≤ 0.01). No significant differences between RFD and soil VAR were found, both inside and outside the minefield areas (p ≥ 0.05). However, we suggest considering the entire studied space of the minefield boundaries and surroundings to be radon-hazardous. This contributes to the understanding of the radon hazard of coal mines for ground structures both in the mine area and in its surroundings. Full article
(This article belongs to the Special Issue Mechanics, Damage Properties and Impacts of Coal Mining)
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18 pages, 39302 KiB  
Article
Analysis and Design of Protection Device for Anchor Cable Pull-Out in High-Stress Roadways
by Fuxin Guo, Min Tu and Jiaxin Dang
Appl. Sci. 2023, 13(21), 12023; https://doi.org/10.3390/app132112023 - 3 Nov 2023
Cited by 1 | Viewed by 1151
Abstract
In regions with high-stress roadway stress, anchor cables frequently experience damage, leading to risky pull-outs and ejections. This study aimed to determine the dynamics of such incidents, refine protective devices, and validate their efficacy in enhancing safety. Drawing from an ejection accident in [...] Read more.
In regions with high-stress roadway stress, anchor cables frequently experience damage, leading to risky pull-outs and ejections. This study aimed to determine the dynamics of such incidents, refine protective devices, and validate their efficacy in enhancing safety. Drawing from an ejection accident in the 1632 (3) roadway of Pan San Mine, a combination of laboratory experiments, theoretical analysis, simulations, and field applications was utilized. The kinetic energy and speed of cable ejections were determined from single-axis tension test data. Based on these insights, a spring-based protection device was conceptualized. Subsequent experiments and simulations evaluated the energy absorption and deformation characteristics of these devices with different diameters. The results included the following: A cable, during ejection, moved at 48 m/s. Spring protective devices of 4 mm can absorb more energy than the 5 mm, but the anti-ejection effect is poor respectively. Increasing the device diameter improved its performance, especially in controlling spring deformation rate and preventing cable lock-ups. This devised protection mechanism showed promising results when implemented in the 1511 (1) roadway of Zhangji Mine. Full article
(This article belongs to the Special Issue Mechanics, Damage Properties and Impacts of Coal Mining)
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18 pages, 5949 KiB  
Article
Infiltration Grouting Mechanism of Bingham Fluids in Porous Media with Different Particle Size Distributions
by Baojie Xu, Hualei Zhang, Jiadi Yin and Yonglin Xue
Appl. Sci. 2023, 13(21), 11986; https://doi.org/10.3390/app132111986 - 2 Nov 2023
Cited by 2 | Viewed by 1078
Abstract
Although permeation grouting technology has been widely used in engineering practice, there has not been sufficient research on how the distribution of pore sizes in porous media affects the diffusion of grout. In this study, based on the fractal theory of porous media [...] Read more.
Although permeation grouting technology has been widely used in engineering practice, there has not been sufficient research on how the distribution of pore sizes in porous media affects the diffusion of grout. In this study, based on the fractal theory of porous media and the Bingham fluid rheological equation, a Bingham fluid permeation grouting mechanism considering the distribution of pore sizes in porous media is proposed. The mechanism is validated through laboratory experiments and numerical simulations using COMSOL 6.0. During the experiments, parallel electrical resistance imaging is employed to monitor the diffusion range of the grout. Furthermore, the effects of grouting pressure, porosity, and water–cement ratio on the diffusion radius of the grout are analyzed. The results show that the Bingham fluid grout diffuses in a semi-spherical shape in the gravel. Additionally, parallel electrical resistance imaging can analyze the diffusion range of the grout in the gravel. The diffusion radius of the Bingham fluid grout in the gravel is smaller than the diffusion radius obtained by considering the particle size distribution theory, with an average difference of 31.8%. Compared to the diffusion radius obtained without considering the particle size distribution theory, the diffusion radius obtained by considering the distribution of pore sizes is closer to the experimental results. The numerically simulated program, which was developed for this study, can effectively simulate the diffusion law of the Bingham fluid in the gravel. So far, the Bingham fluid seepage grouting model considering the different particle size distribution of porous media has been built. The findings of this study can provide theoretical support and technical reference for practical grouting projects. Full article
(This article belongs to the Special Issue Mechanics, Damage Properties and Impacts of Coal Mining)
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16 pages, 26394 KiB  
Article
Dynamic Mechanical Characteristics of Horseshoe Tunnel Subjected to Blasting and Confining Pressure
by Chenglong He, Yingkang Yao, Yaqing Liu, Xiang Mao and Qihui Chen
Appl. Sci. 2023, 13(15), 8911; https://doi.org/10.3390/app13158911 - 2 Aug 2023
Viewed by 1073
Abstract
The blast loading direction and in-situ stress field have an effect on the destruction process in the surrounding rock around the tunnel. Five blasting directions are considered in the experiment and simulation. The static stress distribution by confining pressure and the superposition stress [...] Read more.
The blast loading direction and in-situ stress field have an effect on the destruction process in the surrounding rock around the tunnel. Five blasting directions are considered in the experiment and simulation. The static stress distribution by confining pressure and the superposition stress waves process are discussed by simulation in LS-DYNA. Results indicated that the hoop stress accelerates the radial cracks growing, and the damage around the hole is not influenced by the blasting direction. The stress wave superposition and failure process along the tunnel are affected by the blasting direction. The distribution of static prestress is symmetrical under the uniform confining pressure (k = 1) and decelerates the crack extension by confining pressure. Under the non-uniform confining pressure loading (k ≠ 1), the tensile prestress is formed with a k increase and accelerates the horizontal crack propagation after blast loading. The concentrated stress is serious in the partial region along the tunnel, especially in the vault position under the static-dynamic coupling loading. Notably, the horizontal destruction area between the hole and the tunnel further expands when k increases. Full article
(This article belongs to the Special Issue Mechanics, Damage Properties and Impacts of Coal Mining)
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20 pages, 27904 KiB  
Article
Study on Fracture Behavior of Directly Covered Thick Hard Roof Based on Bearing Capacity of Supports
by Jiawen Li, Baojie Fu, Hualei Zhang, Qingchong Zhao and Qingwei Bu
Appl. Sci. 2023, 13(4), 2546; https://doi.org/10.3390/app13042546 - 16 Feb 2023
Cited by 7 | Viewed by 1314
Abstract
Mine pressure at the working face is severe due to it being directly covered by a thick hard roof. To further investigate the technology of controlling the mine pressure of a thick hard roof, the upper working face of 13,121 in Gubei mine [...] Read more.
Mine pressure at the working face is severe due to it being directly covered by a thick hard roof. To further investigate the technology of controlling the mine pressure of a thick hard roof, the upper working face of 13,121 in Gubei mine of Huainan mining area was used as the engineering background, and similar simulation experiments, mechanical analysis, numerical simulation, and engineering applications were used to obtain the structure of a pre-cracked cut roof cut falling body, as well as establishing the mechanical model of hydraulic brace support resistance and direct covering. The results of the numerical simulation combined with the 20 m step pre-cracked top cutting showed that the cantilever length of the roof plate in the mining area was shortened by 25.61%, the stress concentration was reduced by 31.74%, and the stress level of the hydraulic brace was reduced by 26.59–28.38%, destroying the integrity of the thick hard rock body. According to the field monitoring data analysis, the working face’s initial pressure step and periodic pressure step were reduced, and the average dynamic load coefficients of the initial pressure and periodic pressure were 1.43 and 1.33, respectively, with a small dispersion of the dynamic load coefficient of the bracket. The pressure at the working face is regulated, and the chosen support equipment, in conjunction with the roof cutting scheme, can meet the thick hard roof’s support needs. Full article
(This article belongs to the Special Issue Mechanics, Damage Properties and Impacts of Coal Mining)
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18 pages, 5466 KiB  
Article
Mechanical Characteristics of Pre-Peak Unloading Damage and Mechanisms of Reloading Failure in Red Sandstone
by Yongjian Zhu, Peng Li, Ping Wang, Chengcheng Mei, Heng Ren and Xizhi Wang
Appl. Sci. 2022, 12(24), 13046; https://doi.org/10.3390/app122413046 - 19 Dec 2022
Cited by 4 | Viewed by 2011
Abstract
The mining of deep coal resources occurs in a high-stress geological environment as well as an engineering environment of rock excavation and unloading. Research on the re-bearing capacity characteristics and damage mechanism of rock masses damaged by peak front unloading is critical in [...] Read more.
The mining of deep coal resources occurs in a high-stress geological environment as well as an engineering environment of rock excavation and unloading. Research on the re-bearing capacity characteristics and damage mechanism of rock masses damaged by peak front unloading is critical in revealing the destabilization and rupture law of deep rock bodies. The triaxial pre-peak unloading point was controlled to prepare damaged sandstone specimens, and the RMT-150C rock mechanics test loading system and the AEwin USB-type acoustic emission monitor were used to perform uniaxial reloading tests on the pre-peak unloading-damaged sandstone and to monitor the acoustic emission signals during the rupture process. Among them, the peak front unloading point was set to 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, and 90% of the peak strength at 10 MPa of the surrounding pressure for a total of 11 working conditions. The test results show that: (1) The degree of unloading before the peak controls the uniaxial reload deformation characteristics of sandstone. The higher the unloading point, the faster the deformation of the rock sample, even directly into the crack instability extension stage, and the sandstone deformation characteristics transform from plastic—elastic to elastic—viscous. (2) The cumulative energy characteristics of the 40% to 60% sandstone at the unloading point are comparable to those of the complete sandstone and are separated into smooth, steady growth, and secondary smooth phases. The acoustic emission energy characteristics of the 65% and 70% sandstone at the unloading point are mostly focused on during the crack expansion stage. The sandstone’s acoustic emission energy characteristics exhibit a “double peak” occurrence at 75% of the unloading point. The cumulative energy characteristics of the 80% to 90% sandstone at the unloading point reveal a “stepped” rise. (3) Sandstone’s pre-peak unloading rupture morphology influences the reload damage characteristics: 40% to 70% of the specimens at the unloading point exhibit “Y”-type double-slope shear damage features. The predominant cause of specimen damage in 75% of the specimens at the unloading point is secondary primary cracks based on the pre-peak tensile rupture pattern. The damage path of 80% to 90% of the specimens at the point of unloading occurs in shear damage along the pre-peak unloading rupture pattern. (4) A closed crack mechanics analysis model under uniaxial reload was established, and the basic solution of pseudo-force for fine microcracks subjected to far-field stress, the stress intensity factor at the crack tip, and the crack fracture angle were theoretically derived. Furthermore, the relationship between the fracture angle θ of rock compression-shear cracks, the crack angle β, and the friction coefficient f at the crack surface was clarified. Full article
(This article belongs to the Special Issue Mechanics, Damage Properties and Impacts of Coal Mining)
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10 pages, 3183 KiB  
Article
Overburden Breaking Law and Safe Mining Technology in Thin Bedrock Stope with Thick Alluvium
by Lei Li, Shengxia Zhang, Yonglin Xue and Hualei Zhang
Appl. Sci. 2022, 12(24), 12833; https://doi.org/10.3390/app122412833 - 14 Dec 2022
Cited by 1 | Viewed by 1497
Abstract
For the thick alluvium and thin bedrock coal seam mining in East China, it is easy to produce water by pressing the frame. Taking the engineering geological conditions of the thin bedrock coal seam 1611 (3) working face in the Zhangji Coal Mine [...] Read more.
For the thick alluvium and thin bedrock coal seam mining in East China, it is easy to produce water by pressing the frame. Taking the engineering geological conditions of the thin bedrock coal seam 1611 (3) working face in the Zhangji Coal Mine of Huainan Mining Group as the research background, the breaking law of the thin bedrock coal seam working face with thick alluvium was studied by using a similar material physical simulation experiment and theoretical analysis. It is revealed that under the load transfer of the loose aquifer, the roof fracture of the stope with thick alluvium and thin bedrock is characterized by large and small periodic ground pressure, and the combination failure of the high key stratum and the low key stratum with large cycles is prone to support crushing accidents. Based on this, the safety mining technical measures of reducing the fracture distance of the high key stratum by forced roof caving are proposed, and the reasonable blasting parameters are calculated. After field application, no support crushing accident on the working face was recorded, and the mining was safe, which provides a technical reference for the mining of the working face under similar conditions. Full article
(This article belongs to the Special Issue Mechanics, Damage Properties and Impacts of Coal Mining)
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18 pages, 3428 KiB  
Article
Mechanical Analysis of Frozen Wall with Trapezoidal Temperature Field Distribution Based on Unified Strength Theory
by Yangyong Wu, Hao Shi, Wei Long and Xin Shi
Appl. Sci. 2022, 12(23), 11879; https://doi.org/10.3390/app122311879 - 22 Nov 2022
Viewed by 1078
Abstract
In order to study the elastic–plastic stress field distribution of a double-row-pipe frozen wall, the temperature field of the double-row-pipe frozen wall is equivalent to a trapezoidal distribution, and the frozen wall is regarded as an elastic–plastic thick-walled cylinder with functionally gradient material [...] Read more.
In order to study the elastic–plastic stress field distribution of a double-row-pipe frozen wall, the temperature field of the double-row-pipe frozen wall is equivalent to a trapezoidal distribution, and the frozen wall is regarded as an elastic–plastic thick-walled cylinder with functionally gradient material (FGM) characteristics in the radial direction. Considering that the elastic modulus and cohesion of the frozen wall material change linearly with the radius, the elastic–plastic analysis of the frozen wall is carried out based on unified strength theory. The analytical solutions of the elastic–plastic stress field distribution, the elastic ultimate bearing capacity, the plastic ultimate bearing capacity, and the relative radius of the plastic zone of the frozen wall are derived. The analytical solution is calculated based on the engineering case and compared with the numerical solution obtained based on COMSOL. At the same time, the influence of strength theory parameters on the mechanical properties of heterogeneous and homogeneous frozen walls is analyzed. The results show that the analytical solution and the numerical solution are in good agreement, and their accuracy is mutually verified. The external load on the frozen wall of the selected layer is greater than its elastic ultimate bearing capacity and less than its plastic ultimate bearing capacity, which indicates that the frozen wall is in a safe state of stress. The radial stress increases with the increase in the strength theoretical parameter b and the relative radius r, the tangential stress increases with the increase in the strength theoretical parameter b, and first increases and then decreases with the increase in the relative radius r. The larger the strength theoretical parameter b, the smaller the relative radius of the plastic zone of the frozen wall. The strength theoretical parameter b increases from 0 to 1, the elastic ultimate bearing capacity and plastic ultimate bearing capacity of the heterogeneous frozen wall increase by 33.3% and 40.8%, respectively, and the elastic ultimate bearing capacity and plastic ultimate bearing capacity of the homogeneous frozen wall increase by 33.3% and 41.0%, respectively. Therefore, considering the influence of intermediate principal stress, the potential of materials can be fully exerted and the ultimate bearing capacity of frozen walls can be improved. This study can provide theoretical reference for the design and construction of frozen wall. Full article
(This article belongs to the Special Issue Mechanics, Damage Properties and Impacts of Coal Mining)
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17 pages, 6354 KiB  
Article
Study of the Evolution of Water-Conducting Fracture Zones in Overlying Rock of a Fully Mechanized Caving Face in Gently Inclined Extra-Thick Coal Seams
by Yang Zhou and Xueyi Yu
Appl. Sci. 2022, 12(18), 9057; https://doi.org/10.3390/app12189057 - 9 Sep 2022
Cited by 12 | Viewed by 1910
Abstract
To study the caving of thick hard overburdens and evolution of water-conducting fracture zones in fully mechanized top-coal caving faces of gently inclined extra-thick coal seams, we comprehensively analyzed the 8103 working face of the Beixinyao Coal Mine. We investigated to the caving [...] Read more.
To study the caving of thick hard overburdens and evolution of water-conducting fracture zones in fully mechanized top-coal caving faces of gently inclined extra-thick coal seams, we comprehensively analyzed the 8103 working face of the Beixinyao Coal Mine. We investigated to the caving characteristics of thick hard overburden in fully mechanized top-coal caving faces, fracture information of the internal structure of overburden, and development heights of the “two zones” of overburden after coal mining. Our research methods included those of similarity simulation experiments, such as the use of microseismic monitoring systems, numerical simulations, theoretical analysis, and engineering practice. The results showed that the overlying strata generally experienced stages of roof caving, crack formation, delamination, crack development, and surface subsidence. Due to the influence of overlying strata movement and mining, the separation layer experienced an evolution process called “emergence-development-closure”, where the height of the overlying strata caving envelope increases with the advancing of the working face. When full mining was achieved, the overlying strata caving height was stable, and the height development range of the water-conducting fracture zone was 100–120 m, which is consistent with the height of the overlying strata caving envelope. Most microseismic events occurred near the water-conducting fracture zone, and the water-conducting fracture zone was formed in an area with concentrated energy density. In our numerical simulation, the concentrated distribution area of the fracture field was characterized by a “bridge arch”. The fracture development model in the middle of the goaf was higher than at both ends of the working face, and roof strata deformation was obvious. When the energy value of microseismic event reaches 108.708 J, cracks are produced, and these cracks gradually penetrate to form water-conducting fracture zones. Engineering practice showed that the height range of the water-conducting fracture zone was 98–123 m, and caving of the thick hard overburden and evolution of the water-conducting fracture zone in a fully mechanized top-coal caving face provide a scientific basis for water prevention and control. Full article
(This article belongs to the Special Issue Mechanics, Damage Properties and Impacts of Coal Mining)
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20 pages, 4295 KiB  
Article
Temperature Field and Stability Analysis of the Frozen Wall Based on the Actual Position of Freezing Holes
by Wei Long, Chuanxin Rong, Hao Shi, Shiqing Huang, Zhi Wang, Yin Duan and Haochen Ma
Appl. Sci. 2022, 12(18), 8943; https://doi.org/10.3390/app12188943 - 6 Sep 2022
Cited by 5 | Viewed by 1641
Abstract
Taking the Qingdong Mine as the research object, combined with field measurement data, numerical simulation and theoretical analysis are used to examine the temperature field and stability of the frozen wall in the mine, respectively. The results show that during the active freezing [...] Read more.
Taking the Qingdong Mine as the research object, combined with field measurement data, numerical simulation and theoretical analysis are used to examine the temperature field and stability of the frozen wall in the mine, respectively. The results show that during the active freezing period, under the same freezing time, the average temperature of the effective frozen wall of the fine sand layer is 0.2–1.0 and 0.5–2.5 °C lower than that of the sandy clay layer and clay layer, respectively. The effective frozen wall thickness of the fine sand layer is 0.04–0.17 and 0.17–0.33 m larger than that of the sandy clay layer and clay layer, respectively. The soil cooling between the two circles of freezing holes is the fastest. Due to the deflection of the freezing holes, the interface temperature field is asymmetrical. For deep clay with a depth of 200–250 m, it is most economical and reasonable for the brine temperature in the active freezing period to be −25 and −30 °C. At the designed brine temperature for cooling, during the excavation of the control layer of the topsoil layer (−216 m sandy clay), the side-wall temperature, average temperature, and thickness of the frozen wall meet the design requirements. The ultimate bearing capacity of the frozen wall is 3.20 MPa. When the well is empty for 30 h after excavation, the maximum radial displacement is 26.85 mm, so the frozen wall strength and stability are in a safe state. Overall, the findings of this study can serve as a useful reference for similar freezing projects. Full article
(This article belongs to the Special Issue Mechanics, Damage Properties and Impacts of Coal Mining)
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18 pages, 4653 KiB  
Article
Research on Mechanical Properties and Damage Constitutive Model of Water-Bearing Coal
by Feng Ju, Dong Wang, Zhongwei Wang, Meng Xiao, Zequan He, Pai Ning, Tengfei Wang, Cheng Zhou, Yazhen Zhang, Li Li and Chaosen Yan
Appl. Sci. 2022, 12(17), 8811; https://doi.org/10.3390/app12178811 - 1 Sep 2022
Cited by 3 | Viewed by 1794
Abstract
Many water-related problems are confronted in coal mining, and the mechanical properties of coal inevitably deteriorate due to water–rock interactions. Therefore, it is necessary to study the macroscopic mechanical properties and damage constitutive model of water-bearing coal for safe mining. The uniaxial compression [...] Read more.
Many water-related problems are confronted in coal mining, and the mechanical properties of coal inevitably deteriorate due to water–rock interactions. Therefore, it is necessary to study the macroscopic mechanical properties and damage constitutive model of water-bearing coal for safe mining. The uniaxial compression tests of raw coal samples with five moisture contents under four loading rates were carried out. Based on the test, the Drucker–Prager criterion is introduced to describe the failure law of micro-elements; assuming that the strength of micro-elements obeys a two-parameter Weibull distribution, a three-stage damage constitutive model is established. The model, existing model, and test curves were compared, and four indicators were introduced to evaluate the fitting effect. The results demonstrate that the stress–strain curve has a near horizontal step before the elastic stage, and its length is positively correlated with the moisture content ω. With the increase in ω, the peak strain increases linearly, and the compressive strength and Young’s modulus first increase and then decrease. The loading rate does not change the type of the fitting function between the mechanical parameters and ω. The three-stage model is more universal and can better fit the full stress–strain curve of water-bearing coal under uniaxial compression. Full article
(This article belongs to the Special Issue Mechanics, Damage Properties and Impacts of Coal Mining)
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22 pages, 12349 KiB  
Article
Numerical Study on the Pressure Relief Characteristics of a Large-Diameter Borehole
by Feng Cui, Suilin Zhang, Jianqiang Chen and Chong Jia
Appl. Sci. 2022, 12(16), 7967; https://doi.org/10.3390/app12167967 - 9 Aug 2022
Cited by 8 | Viewed by 1986
Abstract
Large-diameter drilling is an effective method for preventing rock burst disasters in coal mines. In this paper, the roadway stability of the W1123 fully mechanized caving work face of the Kuangou coal mine, located in northwest China, is investigated. A set of numerical [...] Read more.
Large-diameter drilling is an effective method for preventing rock burst disasters in coal mines. In this paper, the roadway stability of the W1123 fully mechanized caving work face of the Kuangou coal mine, located in northwest China, is investigated. A set of numerical modelling techniques were carried out to study the characteristics of stress, displacement, strain energy and the plastic zone of the roadway side rock with different parameters, including the large-diameter drilling hole diameter, depth and spacing. The results showed that: (1) after drilling, the peak values of the stress and strain energy are reduced and transferred to a deeper location, and the control effect presents a positive correlation with the diameter of the drilling hole; (2) when Lh < LP, there are no pressure relief and energy release effects, which may induce impact, whereas when LP < Lh ≤ 2.5LP, with the increase of the hole depth, the effects of pressure relief and energy release are enhanced, and further extension is not conducive to the long-term stability of the roadway; and (3) when the hole spacing decreases, the plastic zone and the broken zone between the holes are gradually penetrated, and the stress pattern transforms from a double peak to a saddle shape and then to single peak. Reducing the hole diameter reduces the efficiency of the plastic zone, failure zone and the stress form transformation between the boreholes, and weakens the pressure relief effect. Therefore, the main factor affecting the pressure relief effect is the hole diameter, and the secondary factor is the hole spacing. The engineering practice employed here showcases how a larger-diameter hole is an effective way of enhancing the effect of pressure relief and controlling the occurrence of rock burst. These research results are of great significance for guiding engineering practice. Full article
(This article belongs to the Special Issue Mechanics, Damage Properties and Impacts of Coal Mining)
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