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In order to quantitatively calculate the critical depth and critical load of mines affected by rock burst, and to achieve effective prevention and control of rock burst in coal mines, this paper proposes a mechanical model for predicting the occurrence of rock burst in coal mine roadways based on catastrophe theory. Additionally, a theoretical calculation formula for initiating rock burst is derived. The first step was to establish a mechanical analysis model, which directly correlated with the in-situ stress, physical and mechanical characteristics of the coal-rock mass, and engineering structural parameters. Following this, a mechanical instability criterion was derived for the key load-bearing circle within the surrounding rock of the roadway. In the final step, the critical depth and load for rock burst initiation were verified for 25 distinct coal mines in China that were prone to rock burst hazards. The research results demonstrate that the discrepancy between the theoretically calculated critical depth and the actual measured statistical values was less than 35%. In addition, the difference between the theoretically determined critical depth and the value calculated by Pan Yishan was less than 32%. Notably, the ratio of the theoretically calculated critical load to the uniaxial compressive strength of the coal-rock mass ranged from 0.38 to 1.93. This aligns with empirical data on rock burst occurrences, as set out in the engineering classification standards for rock masses. These research outcomes substantiated the practical utility of the proposed theory, thereby laying a robust theoretical groundwork for the quantitative control of rock burst. [ABSTRACT FROM AUTHOR]

Intelligent computing is transforming safety inspection methods and response strategies in coal mines. Due to the significant safety hazards associated with mining excavation, this study proposes a multi-source data based predictive model for assessing gas risk and implementing countermeasures. By examining the patterns of gas dispersion at the longwall face, utilizing both temporal and spatial correlation, a predictive model is crafted that incorporates safety thresholds for gas concentrations, four-level early warning method and response strategy are devised by integrating weighted predictive confidence with these correlations. Initially tested using a public dataset from Poland, this method was later verified in coal mine in China. This paper discusses the validity and correlation of multi-source monitoring data in temporal and spatial correlation and proposes a risk warning mechanism based on it, which can be applied not only for safety warning but also for regulatory management. [ABSTRACT FROM AUTHOR]

With the deep extension of coal mining in China, fault water inrush has become one of the major disasters threatening the safety production of coal mine. Based on the control equations of steady state and non-Darcy seepage in fractured rock mass, the multi-parameter nonlinear dynamic seepage equations of fractured rock mass are established in this paper. Based on the nonlinear dynamics theory, the function of the state variable in the system is derived, and the influence of the gradual change of non-Darcy flow factors on the structural stability of seepage system is studied. The research achievements show that there are three branches in the equilibrium state of the seepage system. Specifically, the stability of the equilibrium state changes abruptly near the limit parameter. The seepage dynamic system of fractured rock mass has the delayed bifurcation, and the coal mine disaster such as fault water inrush occurs easily at the bifurcation point. The research results are of great significance to enrich the theory of fault water inrush in coal mine, and to reveal the disastrous mechanism of fault water inrush and guide its prevention and control technology in coal mine, which can provide the theoretical reference for predicting the water seepage stability in fractured rock mass. [ABSTRACT FROM AUTHOR]

Longwall top coal caving technology is one of the main methods of thick coal seam mining in China, and the classification evaluation of top coal cavability in longwall top coal caving working face is of great significance for improving coal recovery. However, the empirical or numerical simulation method currently used to evaluate the top coal cavability has high cost and low-efficiency problems. Therefore, in order to improve the evaluation efficiency and reduce evaluation the cost of top coal cavability, according to the characteristics of classification evaluation of top coal cavability, this paper improved and optimized the fuzzy neural network developed by Nauck and Kruse and establishes the fuzzy neural network prediction model for classification evaluation of top coal cavability. At the same time, in order to ensure that the optimized and improved fuzzy neural network has the ability of global approximation that a neural network should have, its global approximation is verified. Then use the data in the database of published papers from CNKI as sample data to train, verify and test the established fuzzy neural network model. After that, the tested model is applied to the classification evaluation of the top coal cavability in 61,107 longwall top coal caving working face in Liuwan Coal Mine. The final evaluation result is that the top coal cavability grade of the 61,107 longwall top coal caving working face in Liuwan Coal Mine is grade II, consistent with the engineering practice. [ABSTRACT FROM AUTHOR]

Underground coal mining leads to land subsidence, which, in turn, results in damage to buildings and infrastructure, disturbs the original ecological environment, and hinders the sustainable development of coal mining cities. A reasonable estimation of land subsidence, on the other hand, is the foundation for building protection, land reclamation, and ecological environment reconstruction. However, when we applied the existing land subsidence estimation theory to the deep mining areas of the Ordos coalfield in western China, there was a significant deviation between the estimations and the measurements. To explain such unusual case, we propose using the overburden's average GSI (Geological Strength Index) value instead of the compressive strength (UCS) of rock specimens for a better representation of the overburden's overall properties. By using on-site subsidence monitoring results and historical data, we provided evidence which supports that the overburden's average GSI value has a much greater impact on subsidence rates than the UCS. Subsequently, we investigated the relationship between three typical overburden's GSI values and the subsidence rates via a calibrated numerical model, revealing the variation patterns of maximum surface subsidence when the overburden's average GSI value is set at 30, 50, and 75, respectively. Finally, on the basis of the measured and simulated results, we discussed a non-conventional strip mining method for mining subsidence control in the deep mining areas of the Ordos coalfield in western China, and explained why it is possible and what are the significant advantages behind. The proposed methods, findings, and suggestions in this paper are therefore quite helpful for researchers and engineers who wish to estimate and control the mining-induced land subsidence, as well as for those who are particularly interested in the study of environment science related to land subsidence. [ABSTRACT FROM AUTHOR]

Coal mining has a significant impact on the movement of the overburden, leading to potential safety hazards in the working face. In this paper, a similarity simulation experiment was conducted to investigate the migration of overburden during the mining process of a specific working face in the Liuzhuang Coal Mine located in southern China. Sand and gravel were used to simulate the geological environment of each rock stratum. The deformation of the stratum was monitored using strain gauges, the fracture and displacement changes of the overburden stratum were recorded using cameras, and the characteristics of roof collapse was monitored using infrared thermal imager. The experimental model fully simulated the situation of the working face, and the actual working face size was obtained by enlarging the model by 100 times. The experiment found that during the initial stage of mining, there was no significant subsidence of the roof. In the course of the advancement of the working face, the primary roof intermittently fractured behind the working face, with subsequent propagation of upper cracks in an upward direction. The overburden rock layer above the goaf experienced continuous compaction, leading to the gradual closure of the separation layer. Simultaneously, new cracks constantly emerged in front of the working face, resulting in the progressive stabilization of the height of the crack zone. The stress measurements at each point exhibit a pattern of initial increased, followed by decrease, and ultimately stabilization. By considering the stress variation law of the overburden rock, the stress changes in key layers of the bedrock during mining could be categorized into four zones: the stress stable zone, stress increasing zone, stress reducing zone, and compaction stable zone. During the initial phase of coal seam mining, the presence of rock layers provided support, resulting in minimal subsidence of the overburden rock. However, as the mining operation progressed, the disturbance force and collapse of the overburden rock leaded to further downward subsidence. When the working face reached the stop line, the collapsed overburden rock gradually consolidates, resulting in a deceleration of energy release and the formation of a pressure relief zone. Consequently, the overburden rock above the working face underwent a slight additional subsidence, reaching its maximum level. A short cantilever rock beam structure was formed in the experiment. This study will provide valuable reference for future coal mining and serve as a vital theoretical basis for roof control in deep coal seam mining. [ABSTRACT FROM AUTHOR]

With the enhancement of environmental protection awareness of the international community and the continuous promotion of green and sustainable development of manufacturing industry, water lubrication instead of mineral oil has become the future development trend due to its green, pollution-free, clean, safe, and sustainable advantages especially in ships, marine, coal mining, and other fields. In recent years, with the rapid development of water lubrication research, significant progress has been made in related research knowledge domain and discipline. A systematic and extensive assessment of water lubrication research has become increasingly important. The objective of this research is to reveal the research status, research hotspots, and development trends in the field of water lubrication. Therefore, CiteSpace was used to conduct a systematic bibliometric and scientometrical analysis of 1,792 publications from Web of Science core collection database (1997–2021). The results show that China and USA are the most productive countries in the field of water lubrication and have made outstanding contributions. Through the analysis of hot key words and co-citation references, this paper reviews the research status of water lubrication in three aspects: (1) lubricating medium modification; (2) material preparation; (3) surface optimization. It has become a research hotspot to promote the superlubricity contact interface and the application of nanotechnology. The results of this study can make a significant contribution to the development of water lubrication by providing a comprehensive understanding of the research status and research hotspots in this field. Personal understanding and discussion of research hotspots and research status are expected to provide insights into future research trends. In addition, this study will provide valuable references and guidelines for researchers who are interested in this field. [ABSTRACT FROM AUTHOR]

The contradiction between the exploitation of coal resources and the protection of the ecological environment in western China is becoming increasingly prominent. Reasonable ecological environment evaluation is the premise for alleviating this contradiction. First, this paper evaluates the eco-environment of Ibei coalfield by combining the genetic projection pursuit model and geographic information system (GIS) and using remote sensing image data and other statistical data of this area. The powerful spatial analysis function of GIS and the advantages of the genetic projection pursuit model in weight calculation have been fully used to improve the reliability of the evaluation results. Furthermore, spatial autocorrelation is used to analyze the spatial characteristics of ecological environment quality in the mining area and plan the specific governance scope. The geographic detector is used to determine the driving factors of the eco-environment of the mining area. The results show that Ibei Coalfield presents a spatially heterogeneous eco-environment pattern. The high-intensity mining area (previously mined area of Ili No.4 Coal Mine) has the worst ecological environment quality, followed by the coal reserve area of Ili No.4 Coal Mine and the planned survey area of Ili No.5 Coal Mine. The eco-environment quality (EEQ) of the study area is affected by both human and natural factors. Mining intensity and surface subsidence are the main human factors affecting the ecological environment in the study area. The main natural factors affecting the ecological environment in the study area are annual average precipitation, elevation, annual average evaporation, NDVI and land use type. Meanwhile, the interaction effect of any two indicators is greater than that of a single indicator. It is also indicated that the eco-environment of the mining area is nonlinearly correlated to impact indicators. The spatial autocorrelation analysis shows three areas that should be treated strategically that are the management area, close attention area and protective area. Corresponding management measures are put forward for different regions. This paper can provide scientific references for mining area eco-environmental protection, which is significant for the sustainability of coal mine projects. [ABSTRACT FROM AUTHOR]

The underground mining roadways are composed of different strata in southern China mining areas. In the rock-coal composite roadways (RCCRs), surrounding rock comprises coal seam and other strata, such as sandstone, mudstone and siltstone. In this paper, a systematic laboratory experimental study was carried out in which uniaxial compressive strength test was used to investigate the reinforcement of fabricated rock-coal composite (RCC) specimens possessing different anchoring (bolting) setups: no bolt, one horizontal bolt in the coal, two horizontal bolts in the coal and one horizontal bolt in the coal together with an inclined bolt crossing the coal-rock interface. The results show that the failure of RCC specimens with no bolts initially occurs in the coal. Bolting improves the mechanical behaviour of the RCC specimens and the level of improvement is related to the number and orientation of the bolts. Using one horizontal bolt in the coal together with a 30° inclined bolt crossing the coal-rock interface results in the highest strength and the most effective reduction of differential deformation of the RCC specimens. Based on the experimental laboratory results, a field study was carried out to demonstrate further the effectiveness of the inclined bolting and anchoring crossing the coal-rock interface in the stress compression zone for restraining the uneven deformation of the RCCR. [ABSTRACT FROM AUTHOR]

This paper analyzed the current situation and development trends of energy consumption and carbon emissions, and the current situation and development trend of coal consumption in China. In the context of recently established carbon peak and carbon neutralization targets, this paper put forward the main problems associated with the green and low-carbon development and utilization of coal. Five key technological innovation directions in mining were proposed, including green coal development, intelligent and efficient mining, low-carbon utilization and conversion of coal, energy conservation and emission reduction, carbon capture, utilization and storage (CCUS). Focusing on the above technological innovation directions, it is suggested to carry out three basic theories, including the theory of green efficient intelligent mining, clean and low-carbon utilization and transformation of coal, and CCUS. Meanwhile, it is proposed to develop 12 key technologies, including green coal mining and ecological environment protection, efficient coal mining and intelligent mine construction, key technologies and equipment for efficient coal processing, underground coal gasification and mining, ultra-high parameter and ultra-supercritical power generation technology, intelligent and flexible coal-fired power generation technology, new power cycle coal-fired power generation technology, the development of coal-based special fuels, coal-based bulk and specialty chemicals, energy conservation and consumption reduction, large-scale and low-cost carbon capture, CO2 utilization and storage. Finally, necessary measures from the governmental perspective were also proposed. [ABSTRACT FROM AUTHOR]

Since the western region of China, which is typical of extraordinary resource endowments, has gradually emerged as the major mining zone in China, the mining of thick coal seams and roadways with coal-rock composite roof have become more and more common in this region. However, it is extremely difficult to realize safe and effective maintenance and control of such roadways due to the differences in natural endowments of coal-rock masses. With the roadway with coal-rock composite roof of Hulusu Coal Mine in western China as the engineering background, experiment research on large-scale similarity model was conducted through comprehensive measures such as the pneumatic loading system, the surrounding rock stress monitoring system, the roadway deformation monitoring system, the bolt load monitoring system, and the displacement field monitoring system in this paper. According to the results of the experiment, the control effects of the three support systems on the roadway with coal-rock composite roof were significantly different. When the single support of short anchor bolts was applied, the comparatively low initial anchor-hold failed to constrain the initial micro deformation of the roof. Consequently, wide-range fractures of the roof were triggered at a loading pressure of 0.8 MPa. In the meanwhile, the deep surrounding rocks witnessed a downward inflection point in stress, accompanied by the possibility of the collapse of the thin-layer anchorage zone at any time. As for the support combining both short anchor bolts and long anchor cables, though a reinforced effect on the bolt anchorage zone could be achieved with the help of the cables, the active reinforcement capacity of the bolt was limited. The bolt anchorage zone was the first to be damaged at a loading pressure of 0.9 MPa, which would subsequently affect the effective bearing capacity of the deep surrounding rocks. In the application of the single support of high-strength long anchor bolts, the long bolts with high pre-tightening force were able to lock multiple groups of coal-rock strata to form a thick-layer anchorage bearing structure capable of withstanding a load as high as 1.0 MPa. The crash and collapse of the coal wall eventually caused the subsidence of the roof. Based on the intense dynamic load experiment and the feedbacks of engineering application outcomes in the field, it was concluded that the high-pretension thick-layer (HPTL) anchoring technology can effectively constrain the deformation of roadways with coal-rock composite roof with favorable application outcomes. [ABSTRACT FROM AUTHOR]

Nearly half of coal mine disasters in China have been found to occur in clusters or to be accompanied by earthquakes nearby, in which all the disaster types are involved. Stress disturbances seem to exist among mining areas and to be responsible for the observed clustering. The earthquakes accompanied by coal mine disasters may be the vital geophysical evidence for tectonic stress disturbances around mining areas. This paper analyzes all the possible causative factors to demonstrate the authenticity and reliability of the observed phenomena. A quantitative study was performed on the degree of clustering, and space–time distribution curves are obtained. Under the threshold of 100 km, 47% of disasters are involved in cluster series and 372 coal mine disasters accompanied by earthquakes. The majority cluster series lasting for 1–2 days correspond well earthquakes nearby, which are speculated to be related to local stress disturbance. While the minority lasting longer than 4 days correspond well with fatal earthquakes, which are speculated to be related to regional stress disturbance. The cluster series possess multiple properties, such as the area, the distance, the related disasters, etc., and compared with the energy and the magnitude of earthquakes, good correspondences are acquired. It indicates that the cluster series of coal mine disasters and earthquakes are linked with fatal earthquakes and may serve as footprints of regional stress disturbance. Speculations relating to the geological model are made, and five disaster-causing models are examined. To earthquake research and disaster prevention, widely scientific significance is suggested. [ABSTRACT FROM AUTHOR]

Coal remote sensing technology was founded in the period of coal resources survey after the founding of People's Republic of China. Aerophoto Grammetry & Remote Sensing Bureau of China National Administration of Coal Geology was established, specializing in the application and promotion of coal remote sensing technology. With the rapid development of coal geological exploration in China, coal remote sensing technology has evolved from coal geology based survey to comprehensive survey that factors in resources, environment, ecology and so on. This paper summarizes the general situation, theories, development process, key research and future of remote sensing technology for coal mining in China. Spanning over 50 years, the history of China's coal remote sensing technology can be divided into five stages: aero-geological mapping, coal remote sensing theory experimental research, application research and promotion, architecture planning and productionisation, "3S" technology integration and application. This paper expounds the main technical progress, application fields, major projects and major achievements in various historical periods, and points out that the coal remote sensing has entered a unified development stage of "Aviation, Aerospace and Ground", with a focus on high-resolution remote sensing, hyperspectral remote sensing, radar remote sensing, "3S" technology integration and multi-means comprehensive exploration and evaluation. In the future, coal remote sensing technology will develop rapidly in data mass, technology integration, evaluation intelligence, integration application programming, system visualization, etc. Coal remote sensing technology has entered the industrial development from technology application. [ABSTRACT FROM AUTHOR]

The study of water-conducting fracture zone development height is key to the scientific prevention and control of water damage in mines. Based on the geological conditions of the Wenjiapo coal mine in Binchang, China, this paper investigates the development of water-conducting fracture zone in overlying bedrock during mining under large buried depth and huge thick aquifer by combining on-site well-location microseismic monitoring and laboratory similar material simulation. To overcome the limitation of the " limited outlook " of water-conducting fracture zone investigation, the spatial development characteristics of roof fissures in coal seam mining were determined by on-site " the underground - ground" combined microseismic monitoring and follow-up monitoring, and the development of overlying rock fracture under the large depth of burial was concluded. The fractures were mainly distributed in the upper part of the protective coal pillar on both sides of the working face, but less in the upper part of the working face, and primarily distributed in the protective coal pillar on the side of the working face and the adjacent mining area. To verify the accuracy of the conclusion, the overlying bedrock movement and deformation characteristics and the development process of the hydraulic fracture zone during coal seam mining were analyzed by simulating similar materials in the laboratory, using the monitored area as a prototype. The results show that the development height of the mining fracture zone obtained from microseismic monitoring is basically consistent with the simulation results of similar materials. The research finding have significant implications for the study of fracture distribution characteristics and the evolution law of mining overburden, and provide a foundation for scientific prevention and control of water damage on the roof. [ABSTRACT FROM AUTHOR]

This paper presents an experimental study to assess the behaviour of coal samples under tensile loadings to better understand the failure mechanisms and the interactions with the coal characteristics. A set of Brazilian splitting tests were carried out using disk specimens obtained from Tashan Coal Mine in China. The digital speckle correlation method and acoustic emission (AE) were used to capture the deformation localisation and AE characteristics of each specimen during the loading process. The precursor characteristics of AE and the failure mechanism are discussed. It was found that the entire loading process mainly consists of compaction, elastic and post-peak dropping stage without an obvious yielding stage. Two kinds of deformation localisation were observed: central symmetry and axis symmetry. The corresponding AE evolution patterns have different phases, including gradual rise, step rise, transient rise and steady rise. During the subcritical failure stage, AE counts demonstrate a "rapidly increasing + flatten" intermittent feature. The results provide a reference for a better understanding of the damage process of the brittle coal material and its application in ground control design. [ABSTRACT FROM AUTHOR]

Deep coal seam mining often leads to water resource loss due to bedrock water entering the workings of the mine and is discharged adjacent to the mining area. Using the geological conditions of the Maiduoshan coal mine, this paper applied a physical simulation experiment. The specified rock above the coal seam was hydraulically fractured in advance to form a postmining grouted fracture network, followed by grouting to construct a flexible isolation layer that blocked the infiltration of groundwater from the aquifer into the water-conducting fracture zone. Stress sensors, flow sensors and strata displacement monitoring technology were deployed inside the experimental material to study the spatial distribution characteristics and evolution law of the water-conducting fracture zone in the overlying rocks. Analysis of the water-conducting fracture zone development law, stress variation, overburden evolution characteristics, fracturing and grouting sequence of the flexible isolation layer and the effect of postmining grouting on the water barrier was conducted. These experiments verified the feasibility of fracture and grouting of the flexible isolation layer. These research results will provide practical guidance for the transition from the current safe and efficient mining methods to safe and green mining methods of deep coal mining in the western mining areas of China. [ABSTRACT FROM AUTHOR]

In order to explore the effective method for the comprehensive evaluation of ecological environment quality of environmental pollution governance in China's coal mining areas, based on the review of domestic and foreign research literature and the requirements and actual situation of environmental pollution control in China's coal mining areas, this paper selects four categories of 20 evaluation indicators, including land resource, water resource, air, and sustainable development status. According to the land, surface water, air quality standards, and China's sustainable development strategy issued by the Chinese government, and drawing on the latest research results at China and the world, taking the Yanzhou Mining in China as an example, the traditional niche model is introduced to reconstruct the spatial niche model for the case evaluation. It is found that the evaluation results of the spatial niche model lie between the evaluation results of the absolute niche model and the relative niche model. According to the evaluation results, during 2010–2018, the quality of land resources, water resources, and sustainable development in Yanzhou Mining has been upgraded from level IV to II, and the air quality has been upgraded from level IV to level III, which is still the focus of improving the ecological environment quality in Yanzhou Mining. The research findings are significant for guiding the Yanzhou Mining to improve the quality of the ecological environment and promote sustainable development. The conclusion of this paper has guiding significance for the improvement of ecological environment quality of other similar coal mining areas and provides empirical support for the government to formulate environmental pollution governance and ecological environment quality policy. [ABSTRACT FROM AUTHOR]

High-intensity coal mining activities in China's western mining area are damaging fragile ecological environments. The key to coordinating ecological protection and coal mining is to understand the law of overlying strata migration in high-intensity mining. However, it is difficult for conventional monitoring methods to efficiently monitor overburden movement in high-intensity mining areas in real time. In this paper, a space-sky-surface (3S) integrated system is proposed to conquer this challenge. This monitoring system consists of three parts: a space monitoring component (a combination of a global navigation satellite system (GNSS) and interferometric synthetic aperture radar (InSAR)), a sky observation component (an unmanned aerial vehicle (UAV) equipped with a measuring camera (MC)), and a surface exploration component (ground-penetrating radar (GPR) and high-density electricity method (HDEM)). This system was successfully applied to the 12,401 longwall face in the Shangwan coal mine (the maximum mining height is 8.8 m). The deformation cloud map of the entire mining area was obtained through InSAR monitoring technology accompanying the 3D laser scanning to improve the accuracy in the local region of 12,401 longwall face. The distribution characteristics and dynamic evolution of surface fractures were obtained using UAV and MC (visible light camera + infrared camera). Using the HDEM and GPR technologies, the fracture development was well detected. Based on the strata movement theory, combined with the monitoring results, a three-dimensional model of overburden rock fracture after 12,401 longwall face mining was constructed. Monitoring results and the fracture model provide a basis for controlling air leakage in the goaf and remediation of surface fracture. [ABSTRACT FROM AUTHOR]

When using a Terrestrial 3D laser scanning (TLS) to monitor the mining subsidence in a mining area, the conventional methods are to set up the public target manually, or to set up the ground control network in advance. However, these have the disadvantages of high labor intensity and low efficiency. In order to overcome the shortcomings of the conventional methods, this paper presents the subsidence monitoring method using TLS without a target in the mining area. Feature points are used to splice the multi-station point clouds in the same phase, and a few station coordinates are used to uniformly transform the multiphase data into a geodetic coordinate system. Afterwards, the surface digital elevation model (DEM) is established by using the point clouds after coordinate transformation, and the dynamic subsidence value and subsidence basin during the period of observation are obtained by DEM subtraction. Compared to traditional methods, this method simplifies the field measurement process, reduces the labor intensity, and transfers the main work to the internal industry. It is suitable for surface subsidence monitoring with a harsh external environment and complicated topographic conditions. Surface deformation values are important basic data for mining area subsidence parameters acquisition, mining area environmental assessment, land reclamation, and ecological restoration. As a consequence, it is of great value to popularize and apply in mining area for subsidence monitoring. [ABSTRACT FROM AUTHOR]

Mining extremely thick coal seams under layer of loose unconsolidated Cenozoic alluvium is common in north China. However, this may cause serious consequences including breaking down workface, submerging equipment, even serious flooding accident and casualties, because there is an alluvium aquifer composed of sand, clay, and gravels directly overlying above coal seams. Formulating preventive and control measures in advance is extremely important to a mine. In this paper, case study of water and sand inrush prevention is taken in Xiexin coal mine. A 15.5-m thick coal seam is threatened by unconsolidated Cenozoic alluvium water hazard during mining. By the research and exploitation of hydrological characteristics and strata lithology of unconsolidated Cenozoic alluvium, the lowermost layer in some areas is the layer of clay with good water resistance, and part of areas is permeable water-bearing sand mixed with gravel belonging to weak aquifer, which provide an advantageous condition to possibly set and optimally design sand-proof and caved-proof pillars. Considering its geological and hydrogeological characteristics, slice long-wall mining technology which extracts thick coal seams from top to bottom by dividing it into two slices is employed. Based on observations carried out in the field and physical model testing in the lab, strata failures induced by slice long-wall mining were investigated. The study indicated that the maximum height of the caved zone for upper slice was about 5.62 times of the upper slice mining height and the comprehensive height of the caved zone for two slices was about 4.71 times of the total mining height of two slices. The height of caved zone derived from physical model testing was consistent with the height obtained from field measurements. According to the hydrogeology of alluvium, overlying strata lithology, and mining conditions, the optimal design of sand-proof pillar at areas with weak water rich aquifer, and caved-proof pillar at areas with the lowermost layer of clay for workface 1702, workface 1704, and workface 1706 were given for safe production. The optimal design and technique measures, such as slice mining and reducing the thickness of extractions within the upper or lower slice, were successfully practiced. Overall, the conclusions are of engineering significance for coal mines suffering from water and sand inrush of unconsolidated Cenozoic alluvium. [ABSTRACT FROM AUTHOR]

Low-rank coal reservoirs of Badaowan Formation and Xishanyao Formation are mainly developed in Junggar Basin. This paper discussed their features and coalbed methane (CBM) exploration potential based on geological survey, coal samples testing and mathematical fitting analysis. The pores are mainly small-micro- and large pores, and the porosity is 3.25–27.4% with an average of 9–10.51%; and macro-cracks and micro-fissures are well developed leading to a great variation of the permeability. The shallow coal reservoirs are mostly undersaturated, and the gas saturation tends to increase toward the deep coalbed. The J2x has a stronger methane adsorption and storage capacity than that of J1b and better physical properties, making CMB recovery easier. The coalbed reservoirs in middle-east of southern margin, eastern part and hinterland of Junggar Basin reach methane-rich to extremely methane-rich coalbeds and have strong ability to adsorb and store CBM. Coal seam gas shows generally, and the measured gas-bearing property is good. Low-rank CBM accounts for the majority of CBM resources in the basin. According to Langmuir volume, the gas provinces are classified into four types of blocks, i.e., CBM-poor (< 8 m3/t), CBM-bearing (8–15 m3/t), relatively CBM-rich (15–20 m3/t) and CBM-rich (> 20 m3/t). The relatively CBM-rich blocks cover block of well Qing 1 to Qi 8, Changji–Urumqi–Fukang area and slope belt of northwest margin to basin hinterland; while the CBM-rich blocks include most of eastern Junggar Basin. Since 2005, a series of special exploration and research of CBM have been carried out successively, and significant progress has been made in exploration of deep and shallow combination, conventional (gas) and unconventional (gas) combination. Recently shallow CBM exploration has achieved gas extraction at Dahuangshan coal mine, industrial gas flow wells in western Baiyanghe, and breakthrough of deep CBM exploration in Baijiahai area has been made, which confirmed the great development potential of low-rank CBM. The southern margin and the east of Junggar Basin have become the new frontier of low-rank CBM exploration in China. [ABSTRACT FROM AUTHOR]

In China, the connection between coal utilization and environmental pollution has been increasingly evident due to the rapid growth in energy consumption. Clean coal technology (CCT) is one of the effective methods to address coal-associated pollution. However, CCT needs the practical and theoretical support of clean coal geology (CCG). In this paper, a new definition of CCG is proposed, based on the definitions of coal, coal geology, and CCT, combined with the development of national CCG. CCG is the discipline comprehensively researching the genesis, nature, distribution, cleaning potential, clean utilization and environmental effects of resources (coal, coal bed methane, and other coal-associated resources) that can be cleaned by CCT. The research content of CCG is discussed from different aspects, such as cleaning potential evaluation, geological guarantee for coal mining, ash yields and sulfur contents, trace elements, pollution caused by coal, and mine reclamation. The progress of CCG in China is also briefly divided into four stages and delineated. Finally, scientific problems in CCG are summarized and an outlook for CCG is given. [ABSTRACT FROM AUTHOR]

Square confined concrete arch is increasingly used in deep soft rock roadway support because of its advantages of high strength and construction convenience. However, the design of confined concrete arch in underground engineering still remains in experience-based method and lacks quantitative analysis. As a connecting component between arch sections, the connection joints have an important influence on the internal force distribution and failure mechanism of support arch. Therefore, a reasonable design of arch joints is the premise of rational support design. Taking Liangjia Coal Mine, a typical deep soft rock mine in China, as research background, this paper fully compared the most widely used joint types of confined concrete arch as analytical objects: flange joints and casing joints. The main failure modes of these two kinds of joints under bending moment are defined. Laboratory and numerical tests are carried out to study the mechanical characteristics of joints. Based on the M–θ curve, the influence law of different design parameters is analyzed, and the design principles of joints are proposed. The research results could provide a theoretical basis for the design and application of confined concrete arch in related projects. [ABSTRACT FROM AUTHOR]

Green infrastructure is a concept aimed at realizing a strategically planned network of valuable natural and semi-natural areas, designed and managed to deliver a wide range of ecosystem services and to protect biodiversity in rural and urban settings. In the general post-mining context of China and Germany, this paper suggests and outlines an approach that combines green infrastructure with specific concepts of post-mining landscapes. While Germany has a long tradition of post-mining restoration, concepts of green infrastructure are still poorly developed. China, on the other hand, has taken its first steps in the restoration of coal regions, and could profit from the new concepts while drawing on Germany’s experience. The potentials of relevant strategies are investigated here through two case studies from Germany and China. Although there are significant differences in the post-mining development strategies of these two countries, it is clear that the green infrastructure concept can contribute significantly to a growth in ecosystem services. Four advantages of the green infrastructure concept are seen: First, it enables a systematic and highly objective assessment of mining impacts on the ecosystem. Second, the concept assists in the implementation of urban sustainability goals. Third, it is rooted in the local characteristics of landscapes. And finally, the green infrastructure concept seems to be highly compatible with tools of landscape and regional planning. [ABSTRACT FROM AUTHOR]

In order to study the carbon emission of coal resources from mining to utilization and its influencing factors, the Life Cycle Assessment method was used to calculate the carbon emission of coal mining, transportation and consumption from 2001 to 2018, Then, Logarithmic Mean Divisia Index method is used to decompose the factors that affect the carbon emissions in each stage: (1) Mining stage: energy structure, energy intensity, per capita output, personnel scale; (2) Transportation stage: Diesel utilization efficiency, coal cargo turnover; (3) Consumption stage: economic scale, industrial structure, coal consumption intensity, respectively calculate the contribution value and contribution rate of each factor to carbon emission growth. The results show that the carbon emission in the whole life cycle of coal mainly comes from the stage of mining and consumption; Energy intensity, diesel utilization efficiency and coal consumption intensity have inhibitory effects on carbon emissions, and personnel scale and industrial structure have changed from promoting factors to restraining factors; Per capita output, coal cargo turnover and economic scale have a sustained role in promoting carbon emissions; The energy structure effect is unstable. Through in-depth analysis of the above carbon emission influencing factors, relevant conclusions and suggestions are put forward. [ABSTRACT FROM AUTHOR]

Coal is one of the most important fossil energy sources and is ensuring global energy security. Annual maximum NDVI (Normalized Difference Vegetation Index) data is an important indicator for the research in balancing coal mining and vegetation conservation. However, the existing annual maximum NDVI data displayed lower values with temporally inconsistent and a noticeable mosaic line. Here we propose an algorithm for automatically generating the annual maximum NDVI of China's coal bases in Google Earth Engine called: Auto-NDVIcb. The accuracy of the Auto-NDVIcb algorithm has been verified with an average RMSE of 0.087 for the 14 coal bases from 2013 to 2022. Based on the proposed Auto-NDVIcb algorithm, an annual maximum NDVI dataset for all 14 coal bases in China from 2013 to 2022 was publicly released. This dataset can be fast and automatically updated online. Hence, the public dataset will continuously serve to monitor the vegetation change induced by coal mining, exploring the mechanism of vegetation degradation, and providing scientific data for developing vegetation protection policies in coal mines. [ABSTRACT FROM AUTHOR]

Coal is one of the primary energy sources in China. Due to different mining processes, the environmental impact of each mining method varies. Traditional mining methods have relatively low costs but a substantial ecological impact. For example, backfilling mining is environmentally friendly but raises mining costs for surface settlement, coal gangue solid waste pollution, etc. Therefore, to meet the current sustainable development concept, based on the principles of coal mining, a novel economic benefit calculation modeling applied to coal mining is presented to analyze the economy's differential benefits under different mining methods and their impact on the environment. First, a model was established to investigate the economic benefits of coal mining. Secondly, the differential benefits under three mining methods, collapse mining, cemented backfill mining and material-improved cemented backfill mining were calculated for a mining site in China as an example. Finally, four crucial factors affecting coal mine efficiency were identified using hierarchical analysis, the intersection of the differential benefits of the three mining methods under the four essential factors was derived, and the degree of influence of the vital factors on the economic efficiency of coal mines was analyzed using the univariate method. The differential benefits of the material-improved cemented backfill mining method are more prominent than the other two mining methods, with an overall economic increase of about 8%. Coal reserves, the national coal tax reduction rate and the differential benefits of coal mines show a significant positive relationship. The model applies to all types of coal mines and can be used to select low-consumption, low-cost and high-yield mining methods according to the actual situation of coal mines and local policies, guiding the formulation of government policies and the selection of mining methods for coal mining enterprises, which is of great significance to the sustainable development of the environment and the rational exploitation of energy. [ABSTRACT FROM AUTHOR]

In coal mining roadway support design, the working resistance of the rock bolt is the key factor affecting its maximum support load. Effective improvement of the working resistance is of great significance to roadway support. Based on the rock bolt's tensile characteristics and the mining roadway surrounding rock deformation, a mechanical model for calculating the working resistance of the rock bolt was established and solved. Taking the mining roadway of the 17102 (3) working face at the Panji No. 3 Coal Mine of China as a research site, with a quadrilateral section roadway, the influence of pretension and anchorage length on the working resistance of high-strength and ordinary rock bolts in the middle and corner of the roadway is studied. The results show that when the bolt is in the elastic stage, increasing the pretension and anchorage length can effectively improve the working resistance. When the bolt is in the yield and strain-strengthening stages, increasing the pretension and anchorage length cannot effectively improve the working resistance. The influence of pretension and anchorage length on the ordinary and high-strength bolts is similar. The ordinary bolt's working resistance is approximately 25 kN less than that of the high-strength bolt. When pretension and anchorage length are considered separately, the best pretensions of the high-strength bolt in the middle of the roadway side and the roadway corner are 41.55 and 104.26 kN, respectively, and the best anchorage lengths are 1.54 and 2.12 m, respectively. The best anchorage length of the ordinary bolt is the same as that of the high-strength bolt, and the best pretension for the ordinary bolt in the middle of the roadway side and at the roadway corner is 33.51 and 85.12 kN, respectively. The research results can provide a theoretical basis for supporting the design of quadrilateral mining roadways. [ABSTRACT FROM AUTHOR]

As China's coal mines have transitioned to deep mining, the ground stress within the coal seams has progressively increased, resulting in reduced permeability and poor wetting ability of conventional wetting agents. Consequently, these agents have become inadequate in fulfilling the requirements for preventing washouts during deep mining operations. In response to the aforementioned challenges, a solution was proposed to address the issues by formulating a composite wetting agent. This composite wetting agent combines a conventional surfactant with a chelating agent called tetrasodium iminodisuccinate (IDS). By conducting a meticulous screening of surfactant monomer solutions, the ideal formulation for the composite wetting agent was determined by combining the monomer surfactant with IDS. Extensive testing, encompassing evaluations of the composite solution's apparent strain, contact angle measurements, and alterations in the oxygenated functional groups on the coal surface, led to the identification of the optimal composition. This composition consisted of IDS serving as the chelating agent and fatty alcohol polyoxyethylene ether (JFCS).Subsequent assessment of the physical and mechanical performance of the coal briquettes treated with the composite wetting agent revealed notable enhancements. These findings signify significant advancements in the field and hold promising implications. Following the application of the composite wetting agent, notable reductions were observed in the dry basis ash and dry basis full sulfur of coal. Additionally, the water content within the coal mass increased significantly, leading to a substantial enhancement in the wetting effect of the coal body. This enhanced wetting effect effectively mitigated the coal body's inclination towards impact, thereby offering technical support for optimizing water injection into coal seams and preventing as well as treating impact ground pressure. [ABSTRACT FROM AUTHOR]

This study investigates the correlation between previous coal mine safety policies and accidents in China. Data on coal mine accidents and government regulatory information from 2008 to 2021 are collected. The characteristics of coal mine accidents are analyzed, and safety policy indexes are identified. An ordinary least squares (OLS) regression model is established to quantitatively analyze the correlation between accidents and safety policy. The study finds that safety policies have some impact on accident occurrence in coal mines. Although there has been a decrease in accidents and deaths over time, higher mortality rates are observed during periods of increased production intensity and on weekends. Gas accidents are the most common, followed by roof and flood accidents. The study concludes that national safety policies with wider coverage and a stronger system are effective in preventing accidents, but caution should be exercised to avoid reduced vigilance with decreasing death rates. [ABSTRACT FROM AUTHOR]

Alluvial soil plays an important role in ground subsidence caused by coal mining and groundwater extraction. Coal mining areas covered with thick alluvial soil (CMATASs) are widely distributed in China, and ground subsidence in these areas exhibits unique features-for instance, the maximum subsidence is greater than the extracted coal seam thickness. Consequently, studies on the regularity and mechanism of mining subsidence in CMATASs have gained much attention. However, current research methods mainly involve numerical/physical simulation and theoretical analysis, while convincing verification using field data is lacking, leading to limited research results and weak practicability. This paper proposes a new approach for studying the spreading process of mining subsidence in rock mass and alluvial soil, as well as the response of alluvial soil to mining subsidence in these areas, through the use of field data. This approach includes the following steps and assumptions: First, the overlying rock mass and alluvial soil are regarded as a dual medium; subsidence data obtained in coal mining areas covered with thin (non-)alluvial soil (N-CMATASs) are taken as the bedrock surface subsidence in the CMATASs (the lower boundary condition of thick alluvial soil). Second, ground subsidence data obtained in CMATASs are taken as the upper boundary condition of the thick alluvial soil. And lastly, by considering the measured mining-induced overburden fracture datum and geo-mining conditions in CMATASs, we can study the spreading process of mining subsidence in rocks and soils and determine the underlying mechanism as well as the response of the soil to mining subsidence in CMATASs. A major feature of the proposed approach is that the overlying rock mass and alluvial soil can be separated and the measurement data can be obtained in different boundaries, thus compensating for the shortage of measured data in current study methods. This approach was successfully applied in the Huainan coal mining area in China, and can provide a basis for accurate calculation of ground subsidence in similar mining areas. [ABSTRACT FROM AUTHOR]

Introduction: The use of Top Coal Caving for exploiting the thick coal seam with shallow buried depth most likely has a strong negative impact on the stability. Case description: Anjialing No. 1 Underground Mine is located in Shuozhou City, Shanxi Province of China. The 4# Coal Seam of this coal mine is the thick coal seam with shallow buried depth, which has the thickness of 12 m and the depth of 180 m in average. This paper focuses on predicting the distribution of ground fissures and water-conducted fissures induced by the exploiting of the 4# Coal Seam. Discussion and evaluation: We first create a 3D computational model, and then use FLAC $$^{3D}$$ software to simulate the mining of coal seam. We then calculate the displacements and tensile strain of the ground surface and strata, and predict the distribution of the ground fissures and water-conducted fissures. Finally, we further analyze the possibility of the perviousness and air leakage of the coal mine on the basis of the predicted distribution of fissures. Conclusions: The prediction results indicate that: (1) the water-conducted fissures are strongly developed and go through the Neogene aquifuge in some region; thus, it may lead to potential perviousness of coal mine; (2) part of these water-conducted fissures connect with the ground fissures; and this behavior may cause the risk of air leakage. [ABSTRACT FROM AUTHOR]

In order to comprehend the dynamic disaster mechanism induced by overburden rock caving during the advancement of a coal mining face, a physical simulation model is constructed basing on the geological condition of the 21221 mining face at Qianqiu coal mine in Henan Province, China. This study established, a comprehensive monitoring system to investigate the interrelations and evolutionary characteristics among multiple mechanical parameters, including mining-induced stress, displacement, temperature, and acoustic emission events during overburden rock caving. It is suggested that, despite the uniformity of the overburden rock caving interval, the main characteristic of overburden rock lies in its uneven caving strength. The mining-induced stress exhibits a reasonable interrelation with the displacement, temperature, and acoustic emission events of the rock strata. With the advancement of the coal seam, the mining-induced stress undergoes four successive stages: gentle stability, gradual accumulation, high-level mutation, and a return to stability. The variations in other mechanical parameters does not synchronize with the significant changes in mining-induced stress. Before the collapse of overburden rock occurs, rock strata temperature increment decreases and the acoustic emission ringing counts surges with the increase of rock strata displacement and mining-induced stress. Therefore, the collaborative characteristics of mining-induced stress, displacement, temperature, and acoustic emission ringing counts can be identified as the precursor information or overburden rock caving. These results are in good consistent with on-site situation in the coal mine. [ABSTRACT FROM AUTHOR]

Background: The mining-induced stress in the surrounding rock after coal seam mining is the primary cause of damage and failure of the surrounding rock in the mining area. However, the magnitude and direction of the stress field induced by mining in the overburden strata during the excavation process of deep and adjacent coal seams are not yet clear, and it is difficult to determine how adjacent working faces interact with each other. Results: In this study, a large-scale numerical model was built using FLAC3D (Fast Lagrange Analysis Continua) to simulate the sequential mining process of three adjacent working faces (No.1, No.2, and No.3) in Liuzhuang Coal Mine located in southern China. The results showed that the maximum height of plastic zone development after mining in the No.1 working face was 41 m, and the maximum height of plastic zone development was 33.8 m away from the 13 coal seam. It did not affect the top and bottom of the No.3 working face. The development height of the plastic zone on the roof of the No.2 working face after mining was 52m, and the top and bottom plates of the No.3 working face remained intact. The plastic zone of the floor of the No.3 working face after mining was not communicated with the plastic zone of the roof of the No.1 and No.2 working faces. There was a complete rock layer between the two coal seams, and there was not the mutual influence of the mining activities. During the mining process of working faces No.1 and No.2, the range of dynamic pressure influence was extended up to 100m ahead of the working face. During the mining process of the No.3 working face, the range of dynamic pressure influence was 120 m ahead of the working face. The No.1 working face goaf and the mining of No.2 working face had not disturbance to the No.3 working face. Conclusions: After the mining of No.1 and No.2 working faces, the stress in the goaf significantly decreased, and the lateral support stress concentration area of No.1 and No.2 working faces had a relatively small impact on the 13 coal seam. Therefore, the No.1 goaf and mining of No.2 working faces had not disturbance to No.3 working face. [ABSTRACT FROM AUTHOR]

Under the carbon neutrality goal, coal enterprises must seek breakthroughs from abandoned mines, develop new resources in the new era, turn problems into countermeasures, and participate in the carbon emissions market, for contributing to the accomplishment of the national strategic goal of carbon neutrality. To this end, we investigated the relevant national policies and regulations to clarify the boundaries disclosed by the carbon information of enterprises, understood the development direction of carbon storage in abandoned mines, and clarified the transformation and development of carbon storage in abandoned mines. We made a few suggestions: (1) China should learn from its past experience and other countries to develop the energy industry with Chinese characteristics and reform the economic system. (2) Coal enterprises must actively respond to the national carbon information disclosure policy, clarify their own responsibilities and carbon emission boundaries. (3) It is necessary to proactively obtain advanced knowledge and plan carbon storage pathways for abandoned mines. (4) Development problems of coal enterprises should be deduced using cases. The 'dual carbon' goals should be achieved steadily step-by-step. (5) Three measures, i.e. improving the existing resource structure, coordinating the information of abandoned mines, and promoting the cultivation of scientific and technological talents. [ABSTRACT FROM AUTHOR]

Mine reclamation bonds are used in countries with mineral mining to ensure that reclamation of the mined area is completed. The United States, Canada, and Australia are countries with established mine reclamation bond programs, with the United States coal system having been in place since 1977. China implemented a bonding system in 1998 and by 2013 all 31 provinces had established a system. An effective bonding system must be conditioned on fair and enforceable nationwide reclamation standard, stimulate companies to conduct reclamation by forming economic incentives rather than penalties that become a liability, and allow for full public participation. Based on these principles, this paper compares seven important factors for a successful reclamation bonding system: laws and regulations, administrative authority, bond types, bond size, calculation method, bond release, and public participation. The results show variation in policies and procedures for bonding among countries. Using principles and policies primarily from the United States, China should establish a national reclamation bonding system with legislation that forms a national authority to oversee and enforce reclamation standards and bond requirements. In addition, China can expand bond financial types and strategies, set the size of reclamation bonds at the level of a third-party reclamation cost, and set unified standards for calculation. Phased bond release should be established with specific reclamation criteria for each phase of release. Finally, bonding regulations should clearly identify opportunities for full public participation in the process. [ABSTRACT FROM AUTHOR]

With the increase of mining depth, disaster degree of rock burst in fault-controlled area is becoming more and more serious. To analyze mechanism and control method of fault rock burst, No. 3316 mining face controlled by No. 3DF56 fault in Jining mine, China, is selected as case study. First, by analysis of general situation of the mining face, mechanical characteristics of coal rock, and micro-seismic events, it is determined that the coal seam has the possibility of rock burst in the process of the face mining towards the fault. Second, based on strength theory of rock, criterion of fault shear instability is obtained, and influence of cohesion and friction angle on the stability of fault is analyzed, and it is concluded that improving the cohesion of rock can control the fault slip. Third, by borehole detection recorder, it is determined that fracture areas of fault surrounding rock distribute in the range of 0–4 m from the surface of roadway surrounding rock and 0–5.0 m from the fault. Finally, control method of "precise grouting to couple shallow and deep boreholes" is introduced, and the grouting borehole scheme is optimized. Field test results show that the method can improve the compressive strength of coal rock and distribution laws of micro-seismic events, weaken the possibility of fault slip, effectively control the deformation of roadway surrounding rock and improve the control effect of rock burst. It can provide a reference for other coal mines with similar geological conditions. [ABSTRACT FROM AUTHOR]

China is a major coal-producing country that consumes large amounts of coal every year. Due to the existence of many small coal kilns using backward mining methods, numerous worked-out areas have been formed. The coal mines were abandoned with no mitigation, so air penetrates into the roadways and contacts the coal seams; as a result, the residual coal seams spontaneously ignite to form coal fires. These coal fires have burned millions of tons of valuable coal resources and caused serious environmental problems. To implement fire suppression more effectively, coal fire detection is a key technology. In this paper, thermal infrared remote sensing from unmanned aerial vehicle combined with a surface survey is used to identify the range of coal fires in the Huojitu coal mine in Shenmu city. The scopes and locations of the fire zones are preliminarily delineated, which provides an accurate basis for the development of fire suppression projects. [ABSTRACT FROM AUTHOR]

A water-bursting evaluation of the coal seam floor is critical to ensure safety of coal mine production. The vulnerability index method based on AHP is selected for this study's evaluation method. Water pressure, measured specific yield, equivalent thickness of effective aquiclude, brittle rock thickness under mining pressure damage zone, distribution of faults, distribution of collapse column, distribution of endpoints, and the intersection of fault are taken as the evaluation index based on the analysis of geological data in the study area. The authors assessed the threat posed by the two aquifers in the lower portion of the coal seam. Separate evaluations were conducted on the Benxi and Ordovician limestone aquifers. The results' veracity was confirmed by comparing the obtained results to the water bursting point and a few boreholes. The evaluation results provide recommendations for the safe operation of coal mines. [ABSTRACT FROM AUTHOR]

China is the largest producer and consumer of coal in the world. The extraction of coal is increasing intensively to meet the needs of the ever-increasing population and industries. However, coal mining has resulted in environmental changes, including deforestation, air, water, soil, and landform deterioration. This study investigates the impact of mining on the environment in Ruqigou coalfield by utilising in situ and remote sensing data. Field data collected include temperature, gas compositions, and water samples. Multi-temporal Landsat data of 1991, 2003, and 2019 were used in monitoring the impact of mining on different land covers, especially vegetation. A supervised classification was performed to assess the changes in land cover. In order to track the changes in vegetation, normalised difference vegetation index (NDVI) was employed. To study the changes in coal fire areas, thermal anomalies were extracted from the thermal infrared data using a dynamic thresholding technique. The results of in situ analyses show that water quality is unfit for domestic, industrial, and agricultural use. All the gas sampling sites emit noxious gases such as CO2, CO, NO2 and degrade the local air quality. The classified maps and vegetation indices show a significant decrease in vegetation. The thermal anomalies show an increase in fire areas over the years. Thus, it could be concluded that the conjunctive use of field-based measurements and remote sensing data can be a powerful tool for gaining a comprehensive understanding of the environmental impacts associated with large-scale mining. [ABSTRACT FROM AUTHOR]

Height identification of water-permeable fractured zone (WPFZ) is one of the decisive influence factors for mining safety, especially in some specific conditions, such as mining under aquifer. In order to demonstrate the formation process of the WPFZ, the scaling model experiment is carried out. Through the analysis of movement and breaking in overlying strata, the WPFZ height is significantly affected by mining range, movement characteristics of key strata and its follow-up strata. Based on the research findings, a new theoretical method, " overlying strata synchronous movement method " (OSSM) is established to predict the WPFZ height. Taking 3301 mining face of Zhujiamao Coal Mine in China as the engineering background, the WPFZ height is estimated by OSSM. Additionally, the field detection is carried out by the downhole segmented water injection method combined with borehole camera method. By comparing the results of different methods, the accuracy of OSSM is verified and the WPFZ height is determined finally. What´s more, various methods for determining WPFZ height are evaluated. [ABSTRACT FROM AUTHOR]

The coal-bearing Longtan Formation is widely distributed in South China. However, its gas concentration often exceeds the standard limit in tunnels, which compromises the safety of tunnel construction and operation. In this study, statistical analysis of gas-bearing tunnels in the Longtan Formation (GTLF) and coal bed methane (CBM) experiment of Longtan Formation as related to engineering information, gas content, and pressure are discussed with the regional distribution features and influencing factors of GTLF revealed. The hazards of Longtan Formation in each province to tunnels are evaluated by fuzzy synthetic evaluation approach. The findings strongly suggest that the distribution of GTLF is characterized by east–west zonation and controlled by coal-rich zones and sedimentary facies. The western region is more harmful than the eastern region because of weak tectonic movement and more developed karstification. The influencing factors mainly include coal seam conditions, sedimentary environments, tectonic evolution history, hydrogeology, geological structure, and CBM weathering zone. Longtan Formation in Guizhou and Chongqing is the most harmful to tunnels. [ABSTRACT FROM AUTHOR]

To provide an effective risk assessment of water inrush for coal mine safety production, a BP neural network prediction method for water inrush based on principal component analysis and deep confidence network optimization was proposed. Because deep belief network (DBN) is disadvantaged by a long training time when establishing a high-dimensional data classification model, the principal component analysis (PCA) method is used to reduce the dimensionality of many factors affecting the water inrush of the coal seam floor, thus reducing the number of variables of the research object, redundancy and the difficulty of feature extraction and shortening the training time of the model. Then, a DBN network was used to extract secondary features from the processed nonlinear data, and a more abstract high-level representation was formed by combining low-level features to find the expression of the nonlinear relationship between the characteristics of water in bursts. Finally, a prediction model was established to predict the water inrush in coal mines. The superiority of this method was verified by comparing the prediction of the actual working face with the actual situation in typical mining areas of North China. The prediction accuracy of coal mine water inrush obtained by this algorithm is 94%, while the prediction accuracy of traditional BP algorithm is 70%, and the prediction accuracy of SVM algorithm is 88%. [ABSTRACT FROM AUTHOR]

For non-directional drilling cores, selection of samples and the test methods for in situ stress measurements to evaluate the Kaiser effect (KE) were proposed, and the magnitude and direction of the principal stresses were derived from first principles. Based on this approach, the KE for 423 samples in the Burtai and Baode coal mines in the northern Ordos Basin (NOB), China, have been investigated. The results show that the maximum horizontal principal stress (σH), the minimum horizontal principal stress (σh) and the vertical stress (σv) varied with depth and location, and the values increase with increasing depth. Generally, the horizontal stresses play a leading role. For the main stress regimes in the NOB, σH > σh > σv (Burtai Mine, < 172 m; Baode Mine, < 170 m) and σH > σv > σh (Burtai Mine, 170–800 m; Baode Mine, 170–400 m), and the σv > σH > σh stress regimes are mainly distributed in moderately deep to deep coal mines. For rock masses with a depth of 350 m, k ((σH + σh)/2σv) tends to 1, indicating that a deep critical state will gradually emerge. The test results are compared with those for the overcoring (OC) method, the anelastic strain recovery (ASR) method and micro-hydraulic fracturing (HF). The relative errors for σH, σh and σv were 14.90%, 19.67%, 15.47% (Burtai Mine) and 10.74%, 22.76%, 19.97% (Baode Mine), respectively, and the errors are all within an acceptable range, thus verifying the reliability of the KE method. The dominant orientation for the σH (Burtai mine, NE-NNE; Baode Mine, NEE) is obtained via paleomagnetic technology, and the data are consistent with those (NE-NEE) of the earthquake focal mechanism solutions for the area. Based on the Byerlee–Anderson theory, a discussion is given on the levels of stress accumulation in the rock mass of the mines. For dry rocks or hydrostatic pressure rocks, the friction coefficients of the faults are low for both locations, and the values are less than the lower limit (0.6) of the strike-slip faults slip, indicating that the stress fractures at a low level around the study areas are lower than the friction limit stress. The stress accumulation levels in the Baode Mine are slightly larger than those in the Burtai Mine. [ABSTRACT FROM AUTHOR]

The roof usually collapses when exposed to the repeated underground mining; this will potentially lead to the instability of coal wall and even cause serious mining disasters. Based on this specific mining hazard, this work investigates the roof leak characteristics and corresponding control technology based on a coal mine in Guizhou province, China. The theoretical analysis, numerical simulation, and physical testing were carried out. By establishing a physical model, the roof structure and roof "pressure" law under repeated mining are studied, and the instable conditions of face-end roof are analyzed, so as to determine the influencing factors of face-end roof instability. By analyzing different roof structures, the working resistance of hydraulic support with stable face-end roof under repeated mining is determined. The leakage of face-end roof under different support working resistance, tip-to-face distance, and surrounding rock strength is simulated, and different methods are proposed to control face-end roof leaks. The results show that in the process of 17# coal seam mining, the roof collapse is serious, the roof pressure is frequent, and the broken roof instability would form the "granular arch" structure. Through the analysis of the roof structure, the tip-to-face distance, the strength of granular arch structure, and the working resistance of the hydraulic support affect the stability of the face-end roof. Using UDEC simulation software, it is obtained that the higher the strength of roof and surrounding rock, the smaller the tip-to-face distance, the more stable the face-end roof is. The prevention measures such as strengthening the broken face-end roof under repeated mining, improving the support strength of the working face hydraulic support and controlling the reasonable tip-to-face distance are put forward. Through field application, the face-end roof leaks have been effectively controlled, which has played a good reference for the prevention and control of face-end roof leaks under repeated mining. [ABSTRACT FROM AUTHOR]

Thin coal seams in mines usually lack gas data. Thus, preventing and controlling gas outbursts of thin coal seams are difficult. In this study, a coal structure index, which is used to express the damage degree of coal, was estimated by logging curve. In accordance with the contour line of the floor of the coal seam, structural curvature was calculated to express the complexity of the coal seam structure quantitatively. Subsequently, relationships among the burial depth, thickness, coal structure index, structural curvature were analyzed on the basis of the gas pressure of coal seam. The gas pressure values of the coal seams of Nos. 22, 24, and 27 in the study area were predicted by multiple linear regression (MLR) and were then verified and analyzed. The deviation rate of the MLR method was 6.5%–19.7%, with an average of 13.0%. The average deviation rate between the predicted value and the measured value was 11.6%, except for the measuring point of No. 2, which had a large deviation. Results show that the prediction accuracy of the aforementioned method is acceptable and has practical value in the prediction of gas pressure in thin coal seams without measured data. The results in the gas pressure prediction provide a basis for evaluating the risk of gas outbursts in thin coal seams. [ABSTRACT FROM AUTHOR]

This study investigated the development and formation of ground fissures at panel 12,401 of the Shangwan Colliery in the Shendong mining area, characterized by the current largest mining height and an aeolian sand surface in China. An integrated monitoring method was employed to examine the ground subsidence, distribution and development pattern of ground fissures, and the relationship between fissure width and depth, including an unmanned aerial vehicle, ground penetrating radar, and real-time kinematic and manual measurements. Then, the development and formation mechanisms of ground fissures were elucidated through theoretical analysis and physical simulation. The results indicate that ultra large mining height longwall panel extraction causes a greater ground subsidence and horizontal deformation than those of the conventions, resulting in more severe damage in the permanent margin area. The ratio of burial depth to mining height (H/M) decreases to less than 30 due to the ultra large mining height, and deep-burial panel displays the characteristics of shallow coal seam mining, such as "step subsidence". The sliding instability of the primary key stratum causes the simultaneous cutting-off of the aeolian sand layer to form step-like ground fissures. The cause of the tensile fissures is the horizontal surface deformation exceeding the deformation threshold of the aeolian sand layer, and the dynamic tensile fissures were self-restored in 2 weeks as the panel advanced. Step-like fissures connected the working face with the ground, but the depth of the tensile fissures was less than 5.0 m and increased linearly with the fissure width. [ABSTRACT FROM AUTHOR]

In this study, the life cycle assessment method was used to evaluate energy and material consumption and pollutant emission based on the 2013 ledger data of a coal chemistry factory in western China and the subprocesses used include coal gasification, conversion, purification, Fischer–Tropsch synthesis and liquid hydrocarbons separation. This method provides a comprehensive understanding of the potential environmental burden of coal-to-liquid (CTL) production and can be used to identify areas with significant potential for improving energy efficiency and reducing pollutant emissions. The results indicate that the main source of pollution in the CTL program is CTL processing step. Large amounts of water are consumed in the coal mining and CTL processing. The total amount of gaseous pollutants discharged to produce one ton of liquid hydrocarbon is 25.629 t, and 99.5% of this total consists of greenhouse gases. Over the entire life cycle of one ton of this liquid hydrocarbon, 31.955 tons of greenhouse gases (calculated as CO2) are emitted, and the weighted impact potential value is 3.149/PET2010. A series of relevant and consistent emission standards, laws and policies must be issued for the reasonable and orderly growth of the coal chemical industry. [ABSTRACT FROM AUTHOR]

The massive mechanized and irrational coal mining has generated many goafs (i.e., mined-out areas) in China. To manage these goafs effectively, grouting technique has been commonly used to fill the fractures in the overburden strata. However, little is known about the development and distribution of fractures in the overburden strata above the goaf. The lab-scale simulation of fracture development, as well as the grouting process, can provide valuable information for managing a real goaf by the grouting technique. Based on the mechanical properties of rocks and soils in the goaf of Kangjiagou coal mine in Shanxi Province, an experimental system was designed to simulate the development of fractures in the overburden strata above the goaf and study the diffusion behaviors of the grout slurry under different conditions (such as grout volume, grouting pressure, porosity, and water-solid ratio). The physical model test showed that more fractures were found in the fractured and caved zones, with fracture porosity ranging from 15.05 to 40.79%. The grouting experiment showed that, when the water-solid ratio was smaller than 1.15 and the grouting pressure was lower than 0.3 MPa, the changes in diffusion radius were stable during the grouting process. To maintain the stable changes in diffusion radius and reach a high filling ratio, the grouting pressure should be controlled in the range of 0.2–0.4 MPa at the porosity of 24.8% and 0.5 MPa at the porosity of 35.1%. The findings derived from this study are widely applicable under real engineering contexts. [ABSTRACT FROM AUTHOR]

Asymptotically correct simultaneous confidence bands (SCBs) are proposed in both multiplicative and additive form to compare variance functions of two samples in the nonparametric regression model based on deterministic designs. The multiplicative SCB is based on two-step estimation of ratio of the variance functions, which is as efficient, up to order n - 1 / 2 , as an infeasible estimator if the two mean functions are known a priori. The additive SCB, which is the log transform of the multiplicative SCB, is location and scale invariant in the sense that the width of SCB is free of the unknown mean and variance functions of both samples. Simulation experiments provide strong evidence that corroborates the asymptotic theory. The proposed SCBs are used to analyze several strata pressure data sets from the Bullianta Coal Mine in Erdos City, Inner Mongolia, China. [ABSTRACT FROM AUTHOR]