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Green Mining of Coal Mine in China
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Green Mining of Coal Mine in China

A special issue of Minerals (ISSN 2075-163X). This special issue belongs to the section "Mineral Processing and Extractive Metallurgy".

Deadline for manuscript submissions: closed (18 November 2022) | Viewed by 37514

Special Issue Editors

Prof. Dr. Dongsheng Zhang

E-Mail Website
Guest Editor
School of Mines, China University of Mining and Technology, Xuzhou 221008, China
Interests: underground mining; green mining; mine planning
Special Issues, Collections and Topics in MDPI journals
Prof. Dr. Gangwei Fan

E-Mail Website
Guest Editor
School of Mines, China University of Mining and Technology, Xuzhou 221116, China
Interests: green mining; rock mechanics; mine water
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Green mining, a fundamental technology of coal mines, aims to address ecological and environmental issues due to coal resource recovery. Mining-induced ground movement damages topsoil, construction, and localized ecosystems; continuous fracturing triggers water loss or even water inrush; gas released from coals leads to pollution or even disaster; solid wastes piled on ground surface bring about soil erosion; mine dusts deteriorate the underground working environment and air quality on the ground surface. More than 20 years of studies on green mining in China have witnessed theoretical and technological progress in water-protective mining, co-extraction of coal and gas, surface subsidence mitigation, mine waste reducing and recycling, mine dust control, etc. In this context, this Special Issue welcomes review articles, research articles, and technical notes that cover all the above areas, including experimental studies, model and algorithm innovations, analytical and numerical analyses, case studies, etc.

Prof. Dr. Dongsheng Zhang
Prof. Dr. Gangwei Fan
Guest Editors

Manuscript Submission Information

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Keywords

  • Water-protective mining
  • Co-extraction of coal and gas
  • Surface subsidence mitigation
  • Mine waste reducing and recycling
  • Mine dust control
  • Mine ecology
  • Underground backfilling

Published Papers (25 papers)

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Research

19 pages, 8558 KiB  
Article
Research on Roof Load Transfer by Passing Coal Pillar of Working Face in Shallow Buried Closely Multiple-Seam
by Yanpeng He, Qingxiang Huang, Yehao Wei and Junwu Du
Minerals 2023, 13(1), 118; https://0-doi-org.brum.beds.ac.uk/10.3390/min13010118 - 12 Jan 2023
Cited by 4 | Viewed by 1092
Abstract
The dynamic load effect of supports is mainly caused by the movement of the roof structure and the load transfer of overburden. In view of the practice issue that the phenomenon of strong ground pressure is easy to happen, when the working face [...] Read more.
The dynamic load effect of supports is mainly caused by the movement of the roof structure and the load transfer of overburden. In view of the practice issue that the phenomenon of strong ground pressure is easy to happen, when the working face of the lower coal seam passes the inclined coal pillar in shallow buried closely multiple-seam, it will lead to supprot damaged. This paper takes the mining of over-inclined coal pillars in the 22410 working face of the Bulianta Coal Mine as the background, based on the research method combining the field measurement, physical simulation experiment, and numerical calculation, the evolution law of the front abutment pressure (FAP) and roof weighting in mining under the inclined coal pillar is analyzed, and the mechanism of the stress transfer of the inclined coal pillar and the dynamic load of the support is revealed. The research shows that the concentrated stress of the coal pillar is jointly borne by the front coal wall of the working face and the interburden structure above the support. The vertical stress transmitted from the coal pillar to the floor acts on the key blocks of the interburden of the lower coal seam, which causes strong pressure and dynamic load effect, such as roof structure cut-off. The periodic breaking of the key stratum of the interburden leads to the development height and range of the cracks increasing stepwise. The partition characteristics of the mutual transformation of the interburden stress, the FAP, and the working resistance (WR) by passing the coal pillar stage are revealed, which is divided into three stages and four regions. With the working face passing through the inclined coal pillar, the influence area of the concentrated stress of the coal pillar is reduced, and the peak stress of the coal pillar is gradually transferred to the outside of the coal pillar. When the working face is 5 m away from the coal pillar, the peak of FAP and WR reaches the maximum values, the roof is cutting along the peak stress line, and the working face has a strong weighting phenomenon. The research results are consistent with the field measurement results, providing a reference for the mining of working faces under similar conditions. Full article
(This article belongs to the Special Issue Green Mining of Coal Mine in China)
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13 pages, 3812 KiB  
Article
Mining Stability Criterion of Weakly Cemented Aquiclude and Its Application
by Chuangju Chen, Shizhong Zhang, Gangwei Fan, Dongsheng Zhang, Liang Chen, Huining Ni, Xuesen Han, Yujian Chai and Yuxiang Lv
Minerals 2023, 13(1), 83; https://0-doi-org.brum.beds.ac.uk/10.3390/min13010083 - 05 Jan 2023
Cited by 10 | Viewed by 988
Abstract
The effective discrimination of aquiclude mining stability is one of the important indexes for the feasibility judgement of water-conserved mining. Based on the mining-induced deformation characteristics of weakly cemented aquiclude and the water level change of weakly cemented aquifer in northwest China, a [...] Read more.
The effective discrimination of aquiclude mining stability is one of the important indexes for the feasibility judgement of water-conserved mining. Based on the mining-induced deformation characteristics of weakly cemented aquiclude and the water level change of weakly cemented aquifer in northwest China, a mechanical model of mining stability of weakly cemented aquiclude is established, and the mining instability criterion of weakly cemented aquiclude and its influencing factors are analyzed. The results show that the weakly cemented aquiclude has strong plastic deformation ability and mainly undergoes bending deformation during coal mining. Considering the mining-induced bending deformation of weakly cemented aquiclude and the groundwater pressure variation of the weakly cemented aquifer, the expressions of the deflection, stress components, and strain components of weakly cemented aquiclude are derived. Furthermore, the stress instability and strain instability criteria of the weakly cemented aquiclude are proposed. The influences of aquiclude thickness, elastic modulus, Poisson’s ratio, groundwater level, coalface length, and longwall panel length on the mining stability of weakly cemented aquiclude are analyzed. The research results are applied to the feasibility judgment of water-conserved mining in Xinjiang Ehuobulake Coal Mine, and the validity of the mining stability criterion of weakly cemented aquiclude is verified. Full article
(This article belongs to the Special Issue Green Mining of Coal Mine in China)
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13 pages, 2908 KiB  
Article
Experimental Investigation of the Size Effect of Rock under Impact Load
by Jun Zhou, Guangming Zhao, Xiangrui Meng, Chonyan Liu, Longpei Ma, Wensong Xu and Xiang Cheng
Minerals 2023, 13(1), 43; https://0-doi-org.brum.beds.ac.uk/10.3390/min13010043 - 27 Dec 2022
Cited by 3 | Viewed by 1587
Abstract
When measuring the compressive strength of rock, size and strain rate are the two main influencing factors. To study the rock strength size effect, rock specimens with length-to-diameter ratios of 0.5, 0.6, 0.7, 0.8, 0.9 and 1 were subjected to static loading tests [...] Read more.
When measuring the compressive strength of rock, size and strain rate are the two main influencing factors. To study the rock strength size effect, rock specimens with length-to-diameter ratios of 0.5, 0.6, 0.7, 0.8, 0.9 and 1 were subjected to static loading tests using the RMT rock mechanics test system and dynamic loading with the split Hopkinson pressure bar, respectively. Based on the Weibull size-effect formula, the experimental results were compared with the improved formula obtained. The results show that rock strength is influenced by size and strain rate. Both the dynamic increase factor and rock strength are proportional to strain rate. The different failure modes of rock with size variation and strain rate variation are described according to the failure process of the specimens. The same length-to-diameter ratio specimens produced more fragments with a strain rate increase. Under the same strain rate of impact, the larger the rock specimen, the finer the broken fragments. Considering the factor of strain rate in the Weibull size-effect formula, the calculated result is accurate. The improved size-effect formula could be used to better elaborate the potential mechanisms of dynamic rock strength. In the unified theoretical formula containing static and dynamic loads, the relationship of rock strength, size and strain rate is well described. Full article
(This article belongs to the Special Issue Green Mining of Coal Mine in China)
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22 pages, 13304 KiB  
Article
Mechanism and Application of Hydraulic Fracturing in the High-Level Thick and Hard Gangue Layer to Improve Top Coal Caving in Fully Mechanized Caving Mining of an Ultra-Thick Coal Seam
by Hongye Luo, Shun Liang, Qiangling Yao, Yisong Hao, Xuehua Li, Furong Wang, Xiaoyu Chen and Miao Yang
Minerals 2022, 12(12), 1605; https://0-doi-org.brum.beds.ac.uk/10.3390/min12121605 - 14 Dec 2022
Cited by 3 | Viewed by 1240
Abstract
The thick and hard gangue layer has long been one of the key obstacles affecting the coal recovery rate in the fully mechanized top-coal caving mining of ultra-thick coal seams, and it is also one key factor restricting the development of the technology [...] Read more.
The thick and hard gangue layer has long been one of the key obstacles affecting the coal recovery rate in the fully mechanized top-coal caving mining of ultra-thick coal seams, and it is also one key factor restricting the development of the technology used for such work. In this study, to improve the poor top coal cavability and low recovery rate in fully mechanized caving mining of ultra-thick coal seams containing thick and hard gangue layers, the fully mechanized caving mining of longwall working face 42,108 of the Qinggangping Coal Mine is the engineering setting. Then, through a combination of theoretical analysis, numerical simulation, and field practice, a mechanical model of the cantilever beam with uniform load for fracture of the gangue layer is developed. Next, the mechanical action mechanism and influence of the gangue layer and thickness on the fracture of the cantilever beam are analyzed, and a method of pre-fracturing and weakening high-level thick and hard gangue layers using hydraulic fracturing technology is proposed. Finally, using RFPA2D-flow numerical simulation, the key technical parameters of hydraulic fracturing in the working face are designed and applied to field practice. The results show the following: After the high-level thick and hard gangue layer is treated by hydraulic fracturing technology, the amount of fractured gangue behind the support increases, while that of big coal blocks decreases significantly, and the overall fragmentation of top coal is at a reasonable level. In addition, after taking hydraulic fracturing technical measures during the mining period of the working face, the average recovery rate of the working face is 86.6%. This is an increase of 6.5% over the previous area without hydraulic fracturing. Full article
(This article belongs to the Special Issue Green Mining of Coal Mine in China)
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22 pages, 9135 KiB  
Article
Instability Mechanism and Control Method of Surrounding Rock of Water-Rich Roadway Roof
by Furong Wang, Chengle Wu, Qiangling Yao, Xuehua Li, Shengyan Chen, Yinghu Li, Haitao Li and Guiwei Zhu
Minerals 2022, 12(12), 1587; https://0-doi-org.brum.beds.ac.uk/10.3390/min12121587 - 10 Dec 2022
Cited by 4 | Viewed by 1148
Abstract
Surrounding rock properties and occurrence stability of a coal seam roof are prerequisites for ensuring the safe and efficient operation of mines. In this study, the mechanisms and control of weakened water-rich roadway roof slabs were investigated regarding the engineering background of water-rich [...] Read more.
Surrounding rock properties and occurrence stability of a coal seam roof are prerequisites for ensuring the safe and efficient operation of mines. In this study, the mechanisms and control of weakened water-rich roadway roof slabs were investigated regarding the engineering background of water-rich roadway roof slab destabilization in a coal mine in the western Qingyang mining area. The spatial and temporal evolution law of rock deformation and damage of such roadways during excavation were determined through field measurements. First, we tested the strength of the roof slab surrounding rock in water-rich roadways with different water contents and concluded that the primary and excavation-disturbing fissures of the coal-sedimentary rock body are the external conditions for the occurrence of water–rock interaction in water-rich coal seam roadways. Moreover, the rock mechanical damage phenomenon exhibited by clay minerals in contact with water is the key factor leading to the destabilization of the water-rich roof slab’s surrounding rock. Second, a technical approach for controlling the stability of the surrounding rock by adjusting the form of the roadway section and optimizing the support parameters was proposed, and the distribution law of the surrounding rock stress field and displacement field of each section was revealed via numerical calculation. It is considered that adjustment of the stress and displacement control of the surrounding rock of the roadway is more favorable for the straight wall circular arch section. Based on the results of the sensitive orthogonal numerical simulation test, the technical parameters and scheme of the roadway support optimization were proposed. Finally, the research results were applied in the field, and the deformations of the top and bottom slab and the two ribs of the roadway after optimizing the section and support parameters were calculated as 61% and 34% lower, respectively, than those before optimization, indicating that the proposed approach can effectively control the deformation of the water-rich roadway’s surrounding rock and achieve more economic and effective stability control of this type of roadway. The research results provide new ideas and methods for controlling the surrounding rock of water-rich soft rock roadways in the western mining areas of China, which has broad application value and prospects. Full article
(This article belongs to the Special Issue Green Mining of Coal Mine in China)
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24 pages, 8996 KiB  
Article
Deformation and Failure Characteristics of Bimaterial Samples Consisting of Sandstone and Cemented Coal Gangue–Fly Ash Backfill under Uniaxial Loading
by Zongxu Li, Dawei Yin, Ning Jiang, Feng Wang, Yisong Ding and Faxin Li
Minerals 2022, 12(12), 1546; https://0-doi-org.brum.beds.ac.uk/10.3390/min12121546 - 30 Nov 2022
Cited by 2 | Viewed by 1541
Abstract
Based on the acoustic emission (AE) system and the digital scattered-spot deformation monitoring system, uniaxial compression tests were conducted on composite samples consisting of sandstone and cemented coal gangue–fly ash backfill (CGFB) to investigate their deformation and failure characteristics. The results showed that [...] Read more.
Based on the acoustic emission (AE) system and the digital scattered-spot deformation monitoring system, uniaxial compression tests were conducted on composite samples consisting of sandstone and cemented coal gangue–fly ash backfill (CGFB) to investigate their deformation and failure characteristics. The results showed that the average uniaxial compressive strength of the composite samples was 83.09% higher than that of the pure CGFB samples and 92.28% lower than that of the pure sandstone samples. In the composite samples, damage occurred in the CGFB part, and they showed obvious plastic damage characteristics. On both sides of the intersection, the sandstone and the CGFB deformed synergistically in the absence of a macroscopic failure. After a macroscopic failure, the interface effect promoted sandstone deformation and restrained CGFB deformation, transforming the sandstone and the CGFB on both sides of the intersection into a nonsynergistically deformed state. The interface effect had the most obvious influence on the horizontal deformation of the sandstone and CGFB monitoring points near the intersection. The failure of the CGFB samples induced sandstone springback deformation with a springback capacity of 0.0089 mm in the vertical direction and 0.0055 mm in the horizontal direction, which led to the further rupture and failure of the CGFB. Full article
(This article belongs to the Special Issue Green Mining of Coal Mine in China)
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14 pages, 10566 KiB  
Article
Seepage Characteristics and Influencing Factors of Weakly Consolidated Rocks in Triaxial Compression Test under Mining-Induced Stress Path
by Zhiwen Chen, Honglin Liu, Chengyu Zhu, Shuqi Ma, Yinjian Hang and Wenjie Luo
Minerals 2022, 12(12), 1536; https://0-doi-org.brum.beds.ac.uk/10.3390/min12121536 - 29 Nov 2022
Cited by 2 | Viewed by 1212
Abstract
The rock of weakly consolidated coal measure strata has the characteristics of low mechanical strength and strong water sensitivity. Under the stress and seepage disturbance caused by coal seam mining, the surrounding rock structure is prone to instability, which leads to mine safety [...] Read more.
The rock of weakly consolidated coal measure strata has the characteristics of low mechanical strength and strong water sensitivity. Under the stress and seepage disturbance caused by coal seam mining, the surrounding rock structure is prone to instability, which leads to mine safety accidents and water resources loss. In order to master the mechanical response and permeability evolution law of weakly consolidated rock under the disturbance of coal seam mining, the specimens of Jurassic mudstone, sandy mudstone, and sandstone in the Ili mining area of China were collected, and a triaxial compression seepage test was carried out. A comprehensive analysis was carried out on the mineral composition and microstructure characteristics of the rock. The results show the following: (1) Compared to the constant confining pressure condition, mining-induced stress promotes the fracture development rate of weakly consolidated rocks. The ratios of strain at the yield point of mudstone, sandy mudstone, and sandstone under mining-induced stress and constant confining pressure are 0.33, 0.43, and 0.79, respectively, and the ratios of strain at the failure point were 0.48, 0.52, and 0.72, respectively. (2) Under the condition of mining-induced stress, the permeability change range and the permeability recovery rate of the three types of rocks were different, which decreased in the order of mudstone, sandy mudstone, and sandstone. (3) In the process of the triaxial compression test, there was a strong hysteresis in the permeability change of the mudstone, and the permeability and hysteresis of the three types of rocks decreased with the increase in the clay mineral content. (4) Combined with the analysis of the rock mineral composition and microstructure characteristics, it is believed that the clay minerals in the rock after water mud and swelling are the main reasons for the hysteresis of the permeability change of weakly consolidated rock, and the content of clay minerals is the main factor affecting the permeability characteristics of the weakly consolidated rock. Full article
(This article belongs to the Special Issue Green Mining of Coal Mine in China)
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18 pages, 12221 KiB  
Article
Study on Explicit–Implicit Simulation and In-Situ Measurement of Floor Failure Law in Extra-Thick Coal Seams
by Guoqiang Guo, Zhimin Wang, Shaobo Qu, Hao Li, Yang Zhou, Hanjiang Lyu and Yuan He
Minerals 2022, 12(12), 1511; https://0-doi-org.brum.beds.ac.uk/10.3390/min12121511 - 26 Nov 2022
Cited by 2 | Viewed by 962
Abstract
A reliable numerical simulation method and large-scale in-situ test method for super-thick coal seams are very important to determine the failure range of mining floors, which is often the basis to protect Ordovician limestone water, an important drinking water source for people in [...] Read more.
A reliable numerical simulation method and large-scale in-situ test method for super-thick coal seams are very important to determine the failure range of mining floors, which is often the basis to protect Ordovician limestone water, an important drinking water source for people in North China. This paper takes Yushupo Coal Mine as an example; the explicit–implicit coupling simulation method and the corresponding double scalar elastic–plastic constitutive model were established to predict the failure depth of the floor numerically, and verified by the full section borehole stress–strain in-situ testing method. The results show that the explicit–implicit coupling numerical program and the double scalar elastoplastic constitutive model are suitable for predicting the floor failure depth under the condition of extra-thick coal seams. In this condition, the overburden moves violently, resulting in a loading–unloading–reloading process with large stress variation amplitude in the mining floor, which leads to serious rock failure compared with that of medium-thick coal seam conditions. In Yushupo 5105 working face, the floor failure starts to develop from 9.3–24.2 m ahead of the coal wall of working face, and the failure depth no longer increases after 35 m behind the coal wall, with the maximum failure depth of 28 m; the envelope line of the floor failure depth presents an inverted saddle distribution. The above research results lay a foundation for further protecting the Ordovician limestone water, and realizing green coal mining. Full article
(This article belongs to the Special Issue Green Mining of Coal Mine in China)
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13 pages, 13852 KiB  
Article
Study on Mechanical Characteristics of Rock Surrounding the Roadway under Different Section Shapes
by Tao Li, Zheng Li and Fei Liu
Minerals 2022, 12(12), 1504; https://0-doi-org.brum.beds.ac.uk/10.3390/min12121504 - 25 Nov 2022
Cited by 2 | Viewed by 1163
Abstract
In order to understand the instability characteristics of surrounding rock during deep roadway excavation, the influence of different section shapes on the stability of surrounding rock was systematically analyzed. Four sections of roadway with circular, rectangular, semicircular arch and three-center arch were studied. [...] Read more.
In order to understand the instability characteristics of surrounding rock during deep roadway excavation, the influence of different section shapes on the stability of surrounding rock was systematically analyzed. Four sections of roadway with circular, rectangular, semicircular arch and three-center arch were studied. Simulation revealed that the maximum principal stress concentration and pressure relief degree of the three-center arch roadway is the highest, the minimum principal stress relief degree of the rectangular roadway is highest, the roof subsidence of the semicircular arch roadway is the lowest, the roof subsidence and left and right side displacement of the rectangular roadway are the highest, the surrounding rock failure areas of the circular roadway are evenly distributed, the surrounding rock failure areas of the other shape roadways are arch-distributed and the surrounding rock failure of the two sides of the rectangular roadway is the deepest. The mining stress environment coefficient is defined according to the stress state of the rock surrounding the roadway, and the range in which the coefficient is greater than 0.2 is defined as the destructive danger area. We found that the stability of the rock surrounding a circular roadway is greater than that of a semicircular arch roadway, a three-center arch roadway and a rectangular roadway. Full article
(This article belongs to the Special Issue Green Mining of Coal Mine in China)
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13 pages, 4989 KiB  
Article
Physical Simulation on Weakly Cemented Aquiclude Stability due to Underground Coal Mining
by Shizhong Zhang, Gangwei Fan, Dongsheng Zhang, Tao Luo, Xue Guo, Siqin Dun and Hua Chen
Minerals 2022, 12(12), 1494; https://0-doi-org.brum.beds.ac.uk/10.3390/min12121494 - 23 Nov 2022
Cited by 3 | Viewed by 1037
Abstract
In northwest China, underground mining is frequently conducted in weakly cemented rock environments, including the aquiclude that protects the aquifer from dewatering. In this context, understanding the aquiclude responses to longwall mining is significant for assessing the reliability of water-conserved mining in the [...] Read more.
In northwest China, underground mining is frequently conducted in weakly cemented rock environments, including the aquiclude that protects the aquifer from dewatering. In this context, understanding the aquiclude responses to longwall mining is significant for assessing the reliability of water-conserved mining in the weakly cemented rock environment. Taking the Jurassic and Paleogene coal measure geology in Yili Mine in Xinjiang Province, China, as a case study, the paper conducted a laboratorial three-dimensional simulation by configuring a longwall operation and induced groundwater migration. The study analysed the aquiclude depressurisation and revealed the aquiclude stability in response to longwall mining. The results indicated that the aquiclude had a significant plastic strain and self-healing ability in the ground depressurisation condition. The aquiclude experienced tension and then compression, and, accordingly, fracture initiation, propagation, and convergence, during which the aquiclude had significant bending deformation. On the aquiclude horizon, tensile fracturing dominated above the set-up and longwall stop positions. The self-healing behaviour was correlated to the high content of clay minerals and disintegration proneness. The simulation results had a good agreement with field measurements, suggesting that the aquiclude had a satisfactory water-resisting ability and that the simulation results were practically reliable. Full article
(This article belongs to the Special Issue Green Mining of Coal Mine in China)
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19 pages, 10656 KiB  
Article
Movement Laws of the Overlying Strata at the Working Face Ends and Their Effects on the Surface Deformation
by Jingmin Xu, Ping Juan and Weibing Zhu
Minerals 2022, 12(12), 1485; https://0-doi-org.brum.beds.ac.uk/10.3390/min12121485 - 23 Nov 2022
Cited by 1 | Viewed by 971
Abstract
Underground coal mining causes stress relief and strata/ground movement, threatening the safety of the surface structures. Investigating the movement laws of the strata above the working face ends is important because it determines the deformation level of the surface subsidence trough at the [...] Read more.
Underground coal mining causes stress relief and strata/ground movement, threatening the safety of the surface structures. Investigating the movement laws of the strata above the working face ends is important because it determines the deformation level of the surface subsidence trough at the boundary, which is also the zone with the largest deformation degree. This paper presents a study on the movement laws of the overlying strata at the working face ends, and assesses their effects on the surface deformation using field monitoring as well as physical and numerical modelling. The results show that the surface deformation at the subsidence trough boundary is closely related to the movement and rotation of the broken blocks of the primary key stratum (PKS), which control the development of the bed separation and the degree of the surface deformation at the corresponding locations. The numerical modelling results suggest that, the larger the mining height, the greater the rotation angle of the broken blocks and the more severe the surface deformation above the ends of the working face. The results also highlight the role of the thickness of the topsoil. The implications of the results and the limitations of the research are also briefly discussed. Full article
(This article belongs to the Special Issue Green Mining of Coal Mine in China)
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16 pages, 3067 KiB  
Article
Investigation of the Distribution of Heavy Metals in the Soil of the Dahuangshan Mining Area of the Southern Junggar Coalfield, Xinjiang, China
by Qiang Zeng, Li Shen, Tong Feng and Ruirui Hao
Minerals 2022, 12(10), 1332; https://0-doi-org.brum.beds.ac.uk/10.3390/min12101332 - 20 Oct 2022
Cited by 1 | Viewed by 1303
Abstract
Coal mining activities have a series of impacts on the local eco-environment, such as air pollution due to the release of toxic gases, contamination of soil with heavy metals, disturbance and contamination of surface and subsurface water, and damage to land resources with [...] Read more.
Coal mining activities have a series of impacts on the local eco-environment, such as air pollution due to the release of toxic gases, contamination of soil with heavy metals, disturbance and contamination of surface and subsurface water, and damage to land resources with surface subsidence and accumulation of solid waste materials. This study investigated the distribution of heavy metals in mining sites by analyzing the heavy metal content in soil samples from different sites in the Dahuangshan mining area of the southern Junggar coalfield (Xinjiang, China). The results show that area C has the highest Cu content; and area B has the highest Mn content, the highest Zn content, the highest As content, and the highest Cd content, which indicate that area B underwent potential multiple heavy metal contamination. It also shows that the Cd is the major heavy metal for all three areas. The different eco-environmental indices, including the Nemerow comprehensive pollution index, the geo-accumulation index, and the potential ecological risk index, all show the same results, i.e., that Cd is the major potential contaminant in all three types of soil. Full article
(This article belongs to the Special Issue Green Mining of Coal Mine in China)
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20 pages, 8453 KiB  
Article
Surrounding Rock Stability in Unsupported Roof Area and Rapid Heading Technique for Deep Arch Coal Roadways under Goaf
by Yewu Bi, Mingxing Wang, Chao Wu and Yucheng Huang
Minerals 2022, 12(10), 1329; https://0-doi-org.brum.beds.ac.uk/10.3390/min12101329 - 20 Oct 2022
Cited by 2 | Viewed by 1237
Abstract
In order to achieve rapid heading of deep arch coal roadways under goaf, the maximum unsupported roof distance (URD), surrounding rock stability of unsupported roof area and influencing factors, and rapid heading equipment and processes for these roadways are investigated in the context [...] Read more.
In order to achieve rapid heading of deep arch coal roadways under goaf, the maximum unsupported roof distance (URD), surrounding rock stability of unsupported roof area and influencing factors, and rapid heading equipment and processes for these roadways are investigated in the context of the working face geology and mining conditions of Coal #9 of a certain coal mine, through theoretical analysis, numerical simulation, equipment modification, and construction process optimization. The following work is carried out: (1) Based on the thin shell theory, a mechanical model of a top cover cylindrical shell for roadways with an arch section is built. The formula for calculating the maximum URD of arch roadways is developed. The influences of roadway width, tensile strength, buried depth, and arch height on the maximum URD are analyzed. The theoretical maximum URD is worked out to be 2.4 m. (2) Numerical simulation reveals that when the URD is around 2 m, the arch roadway is free of tensile failure and the surrounding rock is well stable; when the URD is greater than 4 m, tensile failure occurs on the roadway sides, and the surrounding rock becomes less stable. Therefore, the maximum URD for numerical computation is set to 2–3 m. No additional failure occurs on the arch roof with the increase in URD, suggesting that an arch roof has the best stability. Properly increasing URD can help U-steel to gain support strength more quickly. In the shallow part of a roadway surrounding rock under goaf, failures are primarily determined by vertical stresses, whereas in the deep part, failures are determined by horizontal stresses. (3) A combined onboard standing platform + onboard beam lift device and a new onboard temporary support device for long excavation are developed as a solution to the low shed and temporary support efficiency and safety of roadways with a URD of 2.4 m and used on-site in conjunction with the optimized construction process. The result shows an average footage of over 550 m per month with a peak footage of 846.4 m and 16 supports totaling 14.1 m per shift. Additionally, the forming quality of a shed roadway is good enough to accommodate normal mining of the working face, consequently the rapid heading of the roadway. Full article
(This article belongs to the Special Issue Green Mining of Coal Mine in China)
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16 pages, 3161 KiB  
Article
Pressure Relief and Bolt Grouting Reinforcement and Width Optimization of Narrow Coal Pillar for Goaf-Side Entry Driving in Deep Thick Coal Seam: A Case Study
by Liangshan Li, Deyu Qian, Xingguo Yang and Hexi Jiao
Minerals 2022, 12(10), 1292; https://0-doi-org.brum.beds.ac.uk/10.3390/min12101292 - 14 Oct 2022
Cited by 4 | Viewed by 1159
Abstract
Goaf-side roadway driving with narrow coal pillars could obviously improve coal resource recovery rates compared with traditional large, wide pillars, and this is pivotal to the sustainable development of underground mines. However, it is very difficult to control the stability of goaf-side roadway [...] Read more.
Goaf-side roadway driving with narrow coal pillars could obviously improve coal resource recovery rates compared with traditional large, wide pillars, and this is pivotal to the sustainable development of underground mines. However, it is very difficult to control the stability of goaf-side roadway driving, especially in deep, thick coal seams with large and high working faces. In order to control the stability of goaf-side entry driving in working face 210106 of the deep and thick coal seam in Xinji No. 2 Coal Mine in Anhui Province of China, we carried out field investigations, theoretical calculations, numerical simulations, and an engineering practice to identify the main factors influencing the deformation of the surrounding rock in order to optimize the width of the narrow coal pillar and to propose countermeasures for goaf-side entry driving. Our results show that the main factors influencing deformation of the rock surrounding the roadways at working face 210106 in Xinji No. 2 Coal Mine include high ground stress, large mining height, thick sandstone in the roof, and the residual abutment pressure of the adjacent goaf. The results obtained from theoretical calculations, the numerical simulations, and the engineering practice indicate that a 5 m-wide coal pillar is relatively appropriate and feasible. The countermeasures of pressure relief by blasting roof cutting and bolt grouting reinforcement were carried out to control the stability for goaf-side entry driving. Field measurements indicated that deformations of goaf-side entry driving in deep, thick coal seams could be efficiently controlled. The maximum deformations of sidewall-to-sidewall and roof-to-floor were 100 mm and 350 mm, respectively. Full article
(This article belongs to the Special Issue Green Mining of Coal Mine in China)
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30 pages, 17514 KiB  
Article
Mechanical Properties and Failure Mechanism of the Weakly Cemented Overburden in Deep Mining
by Guojian Zhang, Guangli Guo, Wei Wei, Jun Wang, Huaizhan Li and Qiu Du
Minerals 2022, 12(10), 1276; https://0-doi-org.brum.beds.ac.uk/10.3390/min12101276 - 10 Oct 2022
Cited by 1 | Viewed by 1152
Abstract
With increases in the mining depth and area in the Ordos coal field, the failure law of the super thick sandstone in the Zhidan group leads to frequent disasters, such as rock bursts and mine earthquakes, which have become a significant issue, restricting [...] Read more.
With increases in the mining depth and area in the Ordos coal field, the failure law of the super thick sandstone in the Zhidan group leads to frequent disasters, such as rock bursts and mine earthquakes, which have become a significant issue, restricting large-scale continuous mining. To adequately understand the movement mechanism of the super-thick and weakly cemented overburden, and to promote the large-scale mining of the coal resources under it, this study analyzes the physical and mechanical properties, along with the microstructural characteristics, of the weakly cemented overburden of the Yingpanhao Coal Mine through mechanics tests, scanning electron microscope tests (SEM) and hydrolysis experiments. A two-dimensional discrete element model of the survey region is then built to explore the temporal and spatial evolution laws of the overburden failure. The results show that, even though poorly cemented strata such as the Cretaceous Zhidan group sandstone and the Zhiluo group sandstone are weak in lithology, their unique mineral composition and microstructural characteristics give them a greater rigidity when their thickness reaches a certain value. The surface subsidence exhibits a sudden increase, and the dynamic disaster range of the overlying strata is wide when deep multi-face mining was carried out under the super-thick and weakly cemented overburden. The temporal and spatial evolution laws of the strata subsidence and influence boundary are closely related to their depth, and their relationships evolve into the Boltzmann function and Boltzmann–parabolic function, respectively. The failure mode of the super-thick and weakly cemented overburden is ‘beam–arch shell–half arch shell’, and the failure boundary exhibits arch fractures. Full article
(This article belongs to the Special Issue Green Mining of Coal Mine in China)
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17 pages, 6872 KiB  
Article
Hyperbolic Secant Subsidence Prediction Model under Thick Loose Layer Mining Area
by Jinman Zhang, Yueguan Yan, Huayang Dai, Liangji Xu, Jiewei Li and Ruirui Xu
Minerals 2022, 12(8), 1023; https://0-doi-org.brum.beds.ac.uk/10.3390/min12081023 - 14 Aug 2022
Cited by 4 | Viewed by 1605
Abstract
In China, as a major resource, coal has made great contributions to national energy security and social development. The mining of coal resources can cause surface subsidence damage, and in particular, the mining of coal resources in thick loose layer mines is the [...] Read more.
In China, as a major resource, coal has made great contributions to national energy security and social development. The mining of coal resources can cause surface subsidence damage, and in particular, the mining of coal resources in thick loose layer mines is the most serious. How to accurately predict the surface subsidence caused by coal mining in thick loose layer mines has become an urgent problem to be solved. To solve this problem, numerical simulations based on the measured data were used to reveal that the thickness of the loose layer is the intrinsic mechanism that affects the value of the surface subsidence and the large range of subsidence. On this basis, the hyperbolic secant function is used as the influence function of unit mining to derive the expected model of subsidence under thick loose layer conditions: the hyperbolic secant subsidence prediction model. Compared with the probability integral method, the hyperbolic secant subsidence prediction model’s prediction accuracy RMSE value is improved by 38%. The hyperbolic secant subsidence prediction model can realize accurate estimation of the subsidence value in the thick loose layer mine area. This greatly enriches the mining subsidence prediction theory and provides a scientific basis for the assessment of surface damage and ecological environment restoration after coal seam mining under a thick loose seam mining area. Full article
(This article belongs to the Special Issue Green Mining of Coal Mine in China)
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17 pages, 6459 KiB  
Article
Study on a High-Efficiency Mining Technology System for Gas Outburst in Coal Seams—Example of an H Coal Mine
by Chuming Pang, Yongkui Shi, Xin Wang, Benzheng Li and Hengjie Luan
Minerals 2022, 12(7), 795; https://0-doi-org.brum.beds.ac.uk/10.3390/min12070795 - 22 Jun 2022
Cited by 2 | Viewed by 1347
Abstract
Coal will continue to play an important role in China’s economic development and social development in the coming decades. However, due to the complex distribution conditions of coal resources, the mining of coal resources is subject to various restrictions. Coal and gas outburst [...] Read more.
Coal will continue to play an important role in China’s economic development and social development in the coming decades. However, due to the complex distribution conditions of coal resources, the mining of coal resources is subject to various restrictions. Coal and gas outburst is an important issue in coal mining, and the threat to the mining of coal resources caused by high gas outburst activity has been receiving more attention. In order to solve the problems related to safe and efficient mining under coal seams with gas outburst, such as mining difficulties, large amounts of work, resource waste, no guaranteed gas treatment time, and low economic efficiency, it is necessary to innovate mining technology and methods for managing gas outburst in coal seams to improve the efficiency of coal mines and to solve the above problems. This study proposes a green mining technical method system known as the “L-H method”, which is applicable to the safe and efficient mining of coal seams with gas outburst based on combined theoretical analysis and numerical simulation. The following research results are achieved: (1) The “L-H method” is proposed, and a mining area model of coal seams with gas outburst is established. The specific details of the method and the implementation process are introduced. (2) Examples of H coal mine applications are presented, and the effects of the implementation of the “L-H method” are analyzed and summarized through mine pressure observations from roadways, and it is concluded that the implementation of top-cutting and pressure-relief technology has a good control effect on the roadway-surrounding rock and that gas extraction reaches the national standard of less than 8 m3/t for protrusion prevention; this ensures safety and also achieves efficient mining. This study will provide a good reference for the implementation of green mining methods to similar coal and gas outburst mines. Full article
(This article belongs to the Special Issue Green Mining of Coal Mine in China)
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16 pages, 3680 KiB  
Article
Knothe Time Function Optimization Model and Its Parameter Calculation Method and Precision Analysis
by Qingfeng Hu, Ximin Cui, Wenkai Liu, Ruimin Feng, Tangjing Ma and Debao Yuan
Minerals 2022, 12(6), 745; https://0-doi-org.brum.beds.ac.uk/10.3390/min12060745 - 11 Jun 2022
Cited by 3 | Viewed by 1409
Abstract
Considering the shortcomings of the currently used time functions for dynamically predicting surface mining subsidence and calculating its parameters, a novel time function is proposed on the basis of an in-depth analysis on the movement characteristics of mining surface points in a fully [...] Read more.
Considering the shortcomings of the currently used time functions for dynamically predicting surface mining subsidence and calculating its parameters, a novel time function is proposed on the basis of an in-depth analysis on the movement characteristics of mining surface points in a fully mined area and the measured mining subsidence data in the field during the course of the mining process. The proposed function can be used to effectively characterize the surface subsidence, the subsidence velocity, and the acceleration of the mining area. All the parameters involved in the function have their physical meaning, and their influence on the function was also analyzed in this study. A parameter calculation method is proposed for the new time function based on the normalization method and least square principle. Taking the measured dynamic subsidence data of 22,618 working faces in a coal mine as an example, the reliability of the new time function model was verified by comparing the measured data with the predicted results. The results show that the average relative root-mean-square error was 5.2%, and the prediction accuracy was improved compared with the Knothe time function, double-parameter Knothe time function, and piecewise optimized Knothe time function. Full article
(This article belongs to the Special Issue Green Mining of Coal Mine in China)
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13 pages, 3726 KiB  
Article
Paste Backfill Corrosion Mechanisms in Chloride and Sulfate Environments
by Guangzheng Xu, Kegong Fan, Kun Wang and Jianguo Ning
Minerals 2022, 12(5), 551; https://0-doi-org.brum.beds.ac.uk/10.3390/min12050551 - 28 Apr 2022
Cited by 3 | Viewed by 1485
Abstract
To study paste backfill corrosion mechanisms in chloride and sulfate environments, we studied the effect of chloride and sulfate on the strength of paste backfill after 7, 14, 28, and 40 days. The chloride solutions and sulfate solutions in concentrations are 0 g/L, [...] Read more.
To study paste backfill corrosion mechanisms in chloride and sulfate environments, we studied the effect of chloride and sulfate on the strength of paste backfill after 7, 14, 28, and 40 days. The chloride solutions and sulfate solutions in concentrations are 0 g/L, 0.5 g/L, 1.5 g/L, 4.5 g/L, or 15 g/L. The obtained specimens were analyzed by performing uniaxial compressive strength tests, X-ray diffraction (XRD), and scanning electron microscopy (SEM). The results show that chloride and sulfate significantly increased the uniaxial compressive strength of the specimen at a very fast speed in the early stage of the test, and the original structure of the specimen was destroyed and its uniaxial compressive strength decreased with the gradual corrosion. The reason for this characteristic is because the chloride reacts with the paste backfill to form calcium chloroamine hydrate (Ca4Al2O6Cl2·10H2O), and the sulfate reacts with the paste backfill to form dihydrate gypsum (CaSO4·2H2O), mirabilite, and ettringite. In the early stage, these substances can fill the pores to improve the compressive strength, and then expand to damage the structure of the backfill and reduce its compressive strength. In addition, sulfate can enhance the decomposition of C-S-H, which results in a faster destruction of specimens than in chloride environments. Full article
(This article belongs to the Special Issue Green Mining of Coal Mine in China)
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22 pages, 7917 KiB  
Article
Numerical Simulation of Crack Initiation and Propagation Evolution Law of Hydraulic Fracturing Holes in Coal Seams Considering Permeability Anisotropy and Damage
by Liang Chen, Gangwei Fan, Dongsheng Zhang, Zhanglei Fan, Xufeng Wang, Wei Zhang and Nan Yao
Minerals 2022, 12(4), 494; https://0-doi-org.brum.beds.ac.uk/10.3390/min12040494 - 18 Apr 2022
Cited by 3 | Viewed by 1883
Abstract
Hydraulic fracturing has been widely used in practical engineering as an essential means to prevent coal seam gas outburst, increase coal seam permeability and improve gas drainage efficiency. Accurate prediction of fracture propagation law is an important basis for optimizing fracturing parameters to [...] Read more.
Hydraulic fracturing has been widely used in practical engineering as an essential means to prevent coal seam gas outburst, increase coal seam permeability and improve gas drainage efficiency. Accurate prediction of fracture propagation law is an important basis for optimizing fracturing parameters to achieve high-efficiency gas drainage in coal seams. In this paper, a new seepage–stress–damage coupling model considering permeability anisotropy is first established and then used to study the evolution laws of crack initiation pressure (σci), fracture pressure (σcd), AE behavior and pore water pressure with the lateral pressure coefficient (ξ) and permeability anisotropy coefficient (λ) in the process of hydraulic fracturing. Finally, the influence of initial pore water pressure on σci is discussed, and an efficient gas drainage method is proposed. Research results indicate that: the in situ stress still plays a leading role in the approach of crack propagation whether the permeability is isotropic or anisotropic; the non-uniform pressure condition is favorable for the crack growth compared with uniform pressure under the isotropic permeability condition; when the direction of maximum permeability is consistent with the direction of maximum principal stress (ξ = 0.5, λ < 0), the coal seams are easily fractured; AE behavior of fracturing holes can be divided into three stages: initiation stage, fracture smooth expansion stage and the breakdown stage for any λ or ξ; and the more complex the crack distribution, the more the area of the gas pressure release zone (GPRZ) increases, which is very beneficial to achieve high-efficiency gas drainage. This study can provide a basis for optimizing fracturing parameters and technology in improving the efficiency of coal seam gas drainage using the hydraulic fracturing method. Full article
(This article belongs to the Special Issue Green Mining of Coal Mine in China)
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16 pages, 9121 KiB  
Article
Rock Mass and Pore Fluid Response in Deep Mining: A Field Monitoring Study at Inclined Longwalls
by Qingdong Qu, Hua Guo, Liang Yuan, Baotang Shen, Guofeng Yu and Johnny Qin
Minerals 2022, 12(4), 463; https://0-doi-org.brum.beds.ac.uk/10.3390/min12040463 - 10 Apr 2022
Cited by 6 | Viewed by 1492
Abstract
The dynamics of stress, deformation and pore pressure in the surrounding strata of underground mines are of fundamental importance to groundwater and gas emission management. Compared to numerous studies on the overlying strata, there are significantly fewer investigations concerning the underlying strata, particularly [...] Read more.
The dynamics of stress, deformation and pore pressure in the surrounding strata of underground mines are of fundamental importance to groundwater and gas emission management. Compared to numerous studies on the overlying strata, there are significantly fewer investigations concerning the underlying strata, particularly involving large-scale field monitoring. This paper presents a comprehensive field monitoring study conducted at two longwall panels with a depth of around 800 m and an inclination angle of 21°. The monitoring program focused on the floor strata within 50 m below the mining operation, but also covered the roof strata close to the longwall roadway. The purpose was to characterise the favourable zone for gas extraction from the floor coal seams. A combination of stressmeters, extensometers and piezometers were deployed and installed underground. The monitored results demonstrated that the stress change exhibited a three-stage variation—increase, decrease and recovery—during which the strata deformed and the pore pressure changed correspondingly. Strata expansion in the floor occurred primarily in the region 0–35 m behind the longwall face and vertically to at least 42 m below. Some predictive methods of the depth of the failure zone used in shallow mines were analysed to determine if they were still applicable for mining at a depth of around 800 m. Full article
(This article belongs to the Special Issue Green Mining of Coal Mine in China)
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18 pages, 48974 KiB  
Article
Fracture Evolution between Blasting Roof Cutting Holes in a Mining Stress Environment
by Min Tu, Gaoming Zhao, Xiangyang Zhang, Qingwei Bu and Jiaxin Dang
Minerals 2022, 12(4), 418; https://0-doi-org.brum.beds.ac.uk/10.3390/min12040418 - 29 Mar 2022
Cited by 11 | Viewed by 1659
Abstract
The problem of strong ground pressure caused by thick and hard roofs in coal mine stopes has become more prominent. Blasting roof cutting and pressure relief are effective technical ways to solve this engineering problem. The key to achieving roof cutting and pressure [...] Read more.
The problem of strong ground pressure caused by thick and hard roofs in coal mine stopes has become more prominent. Blasting roof cutting and pressure relief are effective technical ways to solve this engineering problem. The key to achieving roof cutting and pressure relief is the evolution and penetration of cracks between blasting roof cutting holes in a mining stress environment. To solve this problem, research on the evolution of cracks between blasting roof cutting holes in a mining stress environment is being conducted. Along with specific engineering examples, the mechanical effect of blasting dynamic load in the surrounding rock medium between holes in a mining stress environment is analyzed using the research methods of field investigation, blasting simulation, and mechanical analysis. The fracture evolution law between blasting roof cutting holes under the conditions of different hole diameters and spacings, confining pressure environments, and rock mass strengths is analyzed using the univariate comparative analysis method. The research shows that the superposition effect of blasting dynamic load between adjacent blastholes in the transmission process leads to the “X” type penetration evolution of surrounding rock fracture area and fracture area between blastholes. Among them, the blasting effect of a hole diameter of 70 mm and a hole spacing of 0.8 m is best. When designing the blasting roof cutting scheme, we should pay attention to the key factors such as hole diameter and hole spacing. The hole spacing is particularly critical to the effect of roof cutting and crack formation, whereas the confining pressure and rock mass strength have little impact on the expansion and development of blasting cracks, which can be listed as secondary factors for comprehensive analysis in design. According to the transmission law of blasting dynamic load between holes, the critical criterion of blasting top clearance penetration under mining stress environment is deduced. Four important factors affecting blasting top cutting effect are simulated and studied for optimizing the design of roof cutting scheme. Practical engineering application results show that the blasting roof cutting scheme achieves a good seam- forming effect and creates good initial conditions for thick and hard roof cutting. It can serve as a reference for the decision making of blasting top caving technology under similar engineering conditions. Full article
(This article belongs to the Special Issue Green Mining of Coal Mine in China)
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13 pages, 6438 KiB  
Article
Study on Fracture and Seepage Evolution Law of Stope Covered by Thin Bedrock under Mining Influence
by Zhaolin Li, Lianguo Wang, Ke Ding, Bo Ren, Shuai Wang, Chongyang Jiang and Zhiyuan Pan
Minerals 2022, 12(3), 375; https://0-doi-org.brum.beds.ac.uk/10.3390/min12030375 - 18 Mar 2022
Cited by 4 | Viewed by 1824
Abstract
Aiming to better understand the fracture evolution characteristics of thin bedrock affected by mining, a program was developed to establish a numerical calculation model for the fracture evolution of the overlying rock in the stope under the coupled seepage-stress condition. The fracturing law [...] Read more.
Aiming to better understand the fracture evolution characteristics of thin bedrock affected by mining, a program was developed to establish a numerical calculation model for the fracture evolution of the overlying rock in the stope under the coupled seepage-stress condition. The fracturing law of mining overburden during the advancing process of the coal seam working face has been deeply studied. The dynamic change process of the development height of the overburden fissure zone is analyzed. The results show that with the advance of the working surface, shear and tension compound rupture occurs in the overlying rock layer bottom-up. The rupture penetrates into the sand-water layer and forms a stable rupture zone, which terminates at the bottom of the clay layer in the vertical direction and no longer develops upward. The equivalent stress concentration area is obviously separated at the bottom of the clay layer. Additionally, there is no obvious damage to the clay layer, indicating that the integrity of the clay layer has been protected. This pattern is consistent with the field monitoring results. Under the dual action of mining stress and pore water pressure, the bedrock aquifer ruptured in a wide range, and gradually caused water to flow to the goaf. The low pore pressure zone runs through the entire bedrock layer and ends at the bottom of the clay layer; also, the effective velocity of pore fluid shows a consistent pattern. The on-site water inflow monitoring results found that the main source of water inflow was the sandstone aquifer in the bedrock section, and the shallow groundwater and surface water did not enter the working face in large quantities with coal mining. This shows that the clay layer has a good water barrier effect, effectively blocking the inflow of shallow groundwater or surface water into the working face. It also shows that the “soft–hard” roof layer combination feature greatly buffers the impact of mining on the water isolation layer and has a good water separation effect. Full article
(This article belongs to the Special Issue Green Mining of Coal Mine in China)
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17 pages, 5191 KiB  
Article
Deformation and Failure Mechanism of Weakly Cemented Mudstone under Tri-Axial Compression: From Laboratory Tests to Numerical Simulation
by Haijun Yu, Honglin Liu, Yinjian Hang, Jinhu Liu and Shuqi Ma
Minerals 2022, 12(2), 153; https://0-doi-org.brum.beds.ac.uk/10.3390/min12020153 - 26 Jan 2022
Cited by 6 | Viewed by 2428
Abstract
The success of the water-preserved mining technology is closely related to the stability of the aquiclude and the aquifer, in particular, which is made of weakly cemented rock mas. This paper starts with the tri-axial compression tests on the mudstone specimens obtained from [...] Read more.
The success of the water-preserved mining technology is closely related to the stability of the aquiclude and the aquifer, in particular, which is made of weakly cemented rock mas. This paper starts with the tri-axial compression tests on the mudstone specimens obtained from the Ili mining area, followed by the systematic numerical simulation via the Particle Flow Code (PFC) program, aiming at obtaining an in-depth understanding of the response of weakly cemented mudstone under tri-axial compression loading state. The main outcomes obtained from this research indicated that: (1) the behavior of weakly cemented mudstone is closely sensitive to the confining pressure. As the confining pressure increases, both the peak strength and plastic deformation capacity of weakly cemented mudstone will be enhanced; (2) the main feature of weakly cemented mudstone after tests is its centrosymmetric “Z” shape, mainly attributed to the progressive separation of the particle element of mudstone; (3) the behavior of weakly cemented mudstone either in terms of the axial stress-axial strain or the failure mode is sensitive to the confining pressure. If the applied confining pressure is lower than 5 MPa, the micro-cracks are in the form of the single shear band, whereas the tested specimens will tend from brittle shear to plastic shear associated with the “X” shear when the confining pressure is higher than 5 MPa; and (4) The failure of weakly cemented mudstone is mainly attributed to the continuous expansion and penetration of internal microcracks under compression. The brittle failure mode of weakly cemented mudstone tends to ductile failure with the increase of confining pressure. The main contribution of this research is believed to be beneficial in deepening the understanding of the mechanics of weakly cemented mudstone under tri-axial compression and providing the meaningful reference to the practical application of water-preserved mining in the Ili mining area. Full article
(This article belongs to the Special Issue Green Mining of Coal Mine in China)
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16 pages, 15658 KiB  
Article
Research on the Rapid Strengthening Mechanism of Microwave Field-Controlled Gypsum-Cemented Analog Materials
by Senlin Nan, Wentao Li, Weiming Guan, Huabin Liu, Hongchao Zhao, Yingyuan Wen and Junhui Yao
Minerals 2021, 11(12), 1348; https://0-doi-org.brum.beds.ac.uk/10.3390/min11121348 - 30 Nov 2021
Cited by 1 | Viewed by 1370
Abstract
Various geotechnical experiments have used gypsum-cemented analog geotechnical materials. However, this material needs a long curing time, and the target strength is not easy to control. Therefore, this research adopted microwave heating as the curing method for this kind of material. Objectively, the [...] Read more.
Various geotechnical experiments have used gypsum-cemented analog geotechnical materials. However, this material needs a long curing time, and the target strength is not easy to control. Therefore, this research adopted microwave heating as the curing method for this kind of material. Objectively, the authors investigated the variations in the material strength versus heating power and heating time. On this basis, we clarified the influence mechanism of microwaves on the strength of analog materials by analyzing material temperature, moisture content, and microstructure, which eventually led to an experimental control method for rapid strengthening of microwave field-controlled gypsum-cemented analog materials. Consequently, we drew the following conclusions. The stable strength of the material under high-power microwave curing was much lower than that under natural curing, while the material strength under low-power microwave curing was the closest to the material under natural curing. Full article
(This article belongs to the Special Issue Green Mining of Coal Mine in China)
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