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The situation of coal as the stabilizer guarantee the energy safety in China cannot be changed in the short term, and it will continue to face the problems of coal resource protection and the low utilization rate of coal-based solid waste. Through innovative mining methods, improving the recovery rate of coal resources and the large-scale disposal of coal-based solid waste, a new path is being paved for the green and sustainable development of the coal industry. Based on the in-depth research on the development status of coal mining technology, a new roadway excavation method of “excavation-backfill-retention” is proposed. This paper systematically discusses the scientific problems and key technologies of the “excavation-backfill-retention” construction method from three aspects: rapid excavation, continuous and efficient backfilling and safe construction of large-section roadways. The research results show that ① aiming at the engineering problems such as the fast excavation of large section roadway and the stability control of surrounding rock of heading face, three scientific problems are summarized: the matching mechanism between coal and rock characteristics and cutting parameters of roadway boring machine, the spatial transfer mechanism of overburden load and the deformation mechanism of surrounding rock, the interaction relationship between anchor/cable roof and support mechanism. The technology system has been built, which is based on the real-time sensing of the geological environment in the excavation area, the intelligent cooperative operation of the multi-process of falling, loading and transporting coal, the aging control of surrounding rock of the drilling anchor support together with excavation, the anti-leakage and ventilation optimization of the large section roadway. ② The scientific problems of continuous and efficient backfilling are summarized from the two aspects of timely construction of large section roadway bearing system and its bearing performance regulation, including the co-bearing mechanism of background coal anchor/cable, the hydration consolidation mechanism of multi-component solid waste base backfill materials, and the space-time evolution law of physical and mechanical characteristics of backfill are clarified. A continuous and efficient backfill key technology system with the core of safe and efficient backfill space construction, backfill material performance control and backfill material flow-consolidation perception has been established. The breakthrough of relevant theories and technologies can provide a theoretical basis for raw material selection and ratio design of backfill materials, additive development/selection and working performance control, excavation rate and backfill step optimization design, consolidation monitoring of backfill body, etc. ③ Based on the key problems of roadway safety and surrounding rock easy to break, sheet and damage in the whole life cycle, the paper elaborates three scientific problems: the spatial and temporal distribution characteristics of stress field of roadway surrounding rock, the evolution mechanism of roadway deformation and damage, the engineering quality monitoring and stability regulation theory of roadway surrounding rock. The key technology system is formed with the intelligent stability warning of the rock surrounding the roadway and the deformation control of the rock surrounding the roadway as the core. It is of great significance to conduct the scientific research and technical demonstration of the “excavation-backfill-retention” construction method in coal mines, and to realize the synergy of large-scale solid waste disposal, efficient coal pillar section recovery and rapid roadway excavation, which can promote the green and low-carbon transformation and development of the coal industry.

In order to systematically understand the various types of water hazards and standardize the management of water prevention and control work in coal mines, the National Mine Safety Administration in June 2022 extended the “three zones” management methodology for old goaf water prevention and control to more types of water hazards, such as roof water, floor water, and structural water. However, in the process of dividing the “three zones” of water prevention and control in coal mines, it is revealed that the water damage causing factors and water damage management situation are not closely linked with the division standard, and that technically different divisions are not made for different coal seams and mining areas, and there are inconsistencies in the scope of the division area, and the standardization and timeliness of the division results. Accordingly, combined with the purpose of water hazard prevention and control “three zones” division, compared the similarities and differences between the new and old “three zones” division work, this paper clarifies the degree of hydrogeological conditions survey, water hazard analysis, water hazard management as elements of the division principles, and determines the technical path of the division of the “three zones”. Combining the characteristics of five common types of water hazards in coal mines, the paper puts forward the division method of different types of water hazards, that is: surface water hazard should be divided according to the distribution and development characteristics of surface water bodies in the mining area and the degree of influence of atmospheric precipitation, landslides and other geological disasters in mining. The roof water hazard should be divided according to whether there is a strong water-rich aquifer, a medium water-rich but hydrostatic reservoir-rich aquifer, a loose aquifer. The floor water hazard should be divided according to the relationship between the thickness of the floor water barrier and the depth of the floor mine pressure damage zone in the coal seam pressure mining area, as well as the size of the floor water inrush coefficient. The old goaf water hazard should be divided according to the distribution range and amount of water in the mine and the surrounding mines. The structural water hazards should be divided according to the water-richness, water content, and water source conduction of geological structures and bad geological bodies such as faults, trap columns and caves in the mining area. The key points and difficulties of the division work include the clear division of time and space scope, the comprehensive analysis of division standards, the clear management responsibilities for the “three zones”, and the dynamic transformation of division results. On this basis, typical coal mines with various types of water hazards and complex hydrogeological conditions are selected as case studies. Following the principle of division, according to the division standard, the mineable zone, the slow mining zone and no-mining zone are divided by the method of separating coal seams and mining areas, and detailed explanations are given. The significance of carrying out the division of the “three zones” for water hazard prevention and control is clarified, which can enhance the comprehensive detection level, strengthen the prediction ability, and identify the direction of water hazard management in order to guide and standardize the division of the “three zones” for water prevention and control in the coal mines of China.

Early detection and distinguish of mine fires can avoid or reduce casualties, property damage, and secondary accidents. There are no natural light sources such as sunlight, moonlight, starlight, and lightning underground, and the main factor affecting the recognition of mine fire images is the mine light source. Circularity can eliminate interference from circular light sources, but it is difficult to exclude interference from non-circular light sources. Rectangularity can eliminate interference from rectangular light sources, but it is difficult to exclude interference from non-rectangular light sources. In engineering practice, due to the different shooting angles of the camera, the image of the mine light source may deform and cannot present an ideal regular shape. It is difficult to eliminate the interference of the mine light source using circularity and rectangularity algorithms. It has been revealed that the area of the external connection graphic area of the flame image is significantly larger than the actual area of the image, and the external connection graphic area of the actual light source image of the mine, such as circular lamps, rectangular lamps, and square lamps, is approximately equal to the actual area of the light source image. In this study, a mine fire recognition and anti-interference method is proposed based on the internal concavity of image, the ratio of the target image area to the external connection graphic area of the image (i.e. internal concavity of image) is calculated, and the flames and mine light sources are distinguished based on the small concavity value in the flame image and the large concavity value in the mine light source image. The internal concavity method proposed in this paper is not affected by the distance from the camera to the detection target and the size of the image, the installation position and angle of the camera to capture the detection target, and the shape of the mine light source. It has strong adaptability and high recognition accuracy. The experiment shows that the internal concave recognition method calculates the maximum average difference between the mine interference light source and the flame image, with the smallest fluctuation and the best discrimination. It is also least affected by the camera’s shooting angle and distance, and has the strongest anti-interference ability, with an accuracy of 91.6%. The rectangular recognition method calculates the average difference between the mine interference light source and the flame image, with small fluctuations and good discrimination. It is less affected by the camera’s shooting angle and distance, and has average anti-interference ability, with an accuracy rate of 72.5%. The roundness recognition method calculates the minimum average difference between the mine interference light source and the flame image, with the highest fluctuation and the worst discrimination. It is less affected by the camera shooting distance and more affected by the camera shooting angle, and has the worst anti-interference ability, with an accuracy of 12.0%. Therefore, the internal concave recognition method proposed in this paper is superior to rectangular and circular degrees, with the best discrimination, minimal influence from camera shooting angle and distance, and the strongest anti-interference ability.

In order to further improve the intelligent control level of fully mechanized mining equipment in coal mines and achieve the normalized operation of intelligent mining face, this paper proposes the related concepts and system architecture of intelligent mining face driving control based on digital twin. The digital twin system of intelligent mining face is composed of physical equipment, virtual twin and virtual and real interaction model. The virtual model mapped with physical equipment is established by digital method to achieve the purpose of virtual and real interaction, intelligent decision, accurate control and dynamic evolution in fully mechanized mining equipment during operation. The paper expounds the normal operation requirements of intelligent mining face and related control difficulties of shearer, hydraulic support and scraper conveyor, and proposes the single-machine digital twin driving control architecture of smart mining face, including mechanism model, control model, twin data model and digital twin model synchronization and evolution. The method of digital twin virtual-real interaction is described, the Cyber-Physical System is used to guarantee the information interaction ability, and the knowledge model is used to solve the data congestion problem, which provides a real-time virtual-real interaction for the digital twin control system of intelligent mining face. A three-machine cooperative control method driven by the digital twin of intelligent mining face is proposed, including three-machine correlation, intelligent coal mining control, intelligent support control and intelligent transportation control. Finally, taking the practical application of digital twin in mines as an example, the intelligent control of digital twin is verified by establishing the relevant model and designing the relevant experiment scheme. By carrying out theoretical research on digital twin intelligent control architecture and mode, the paper aims to solve the current problems of low environmental perception, poor equipment prediction accuracy and high manual intervention intensity in fully mechanized mining face, realize an adaptive control and human-computer interaction of equipment under complex environmental conditions, and provide a reference for the intelligent construction of coal mines.

Surface mining is an important way of mining mineral resources. The state and local governments have put forward higher requirements for surface mining in China. Therefore, it is particularly urgent to take surface mining as a science to carry out systematic research, reveal the laws of mining process and phenomenon occurred, and make scientific explanations. First of all, the major technical achievements in the field of surface mining of solid mineral resources in China in the past 40 years were summarized from three aspects: the basic theory of surface mining, the development of key complete sets of equipment and blasting engineering technology. Then, the modern scientific metrology and information metrology technologies were used to conduct a multivariate dynamic analysis of 7128 papers and reports in the past 40 years, and a multi-dimensional quantitative description of the development and evolution process of the main research topics, including the time dimension, was carried out by the cluster analysis. It is found that the evolution of research topics is the result of the coupling effect of many factors, such as technological development, mining status, policy environment, etc. Based on the sorting of the existing major scientific and technological achievements and the objective literature measurement results, it is pointed out that the goal of the future surface mining science is to form a systematic and comprehensive safe, green, efficient and intelligent surface mining technology system, and the realization path is given, that is, to form a hot research topic of surface mining technology system and major equipment, and to strengthen the deep cross integration between the existing hot research and surface mining technology system and major equipment. It also provides some useful suggestions on how to jointly tackle major scientific and technological problems with the advantageous resources of various themes inside and outside the industry to achieve a substantial collaborative innovation among multiple themes. Finally, from the perspective of energy and ecology, the paper looks forward to the development direction of major basic theories and technologies of the future surface mining science from seven aspects: mining area planning theory, intelligent mining design principle, intelligent cluster scheduling theory, safe and efficient mining technology of coal mining in spontaneous combustion prone extra thick coal seams, high slope stability control technology, efficient belt conveyor transportation technology under complex working conditions, and intelligent surface mine system engineering. The development direction of the future surface mining equipment is prospected from five aspects: high efficiency mobile crushing equipment, modular semi-fixed crushing equipment, continuous mining process system equipment, large inclination transportation equipment and large dump machine. It is expected that the study can be used as a reference for scientists and engineers in the surface mining field.

Intelligent recognition technology for underground safety violations in coal mines has become the primary means of safety management and information acquisition. However, the accuracy of intelligent recognition is reduced by factors such as low illumination, point light sources, and high dust in the underground spatial environment. To overcome those problems, this paper proposes a multi-weight fusion image enhancement method, which achieves the fusion enhancement of image brightness and illumination balance. The monitoring image brightness is increased by using the Gamma algorithm. Based on the brightness enhancement, the HSV spatial transformation is carried out to keep the hue component and saturation component unchanged, the illumination component is extracted by using a multi-scale Gaussian function, and then the regions where the illumination component is too strong and too weak are adjusted by using an improved two-dimensional gamma function to achieve an illumination equalization. Combining the three weights of Laplacian contrast, luminance, and saturation and fusing the luminance-enhanced and illuminance-balanced images by Gaussian and Laplacian pyramids, the intelligent surveillance image enhancement is achieved. Through the experimental verification of the intelligent recognition of helmets in mine monitoring, the image enhancement method proposed in this paper and the MSR, MSRCP, MSRCR, and AMSRCR algorithms are evaluated in terms of image evaluation indexes such as standard deviation, peak signal-to-noise ratio, and information entropy, and the peak signal-to-noise ratio is improved by 32.44% on average compared with other algorithms, the standard deviation is improved by 115.38% on average compared with the original image, and the average improvement in standard deviation is 115.38% compared with the original image and 47.30% compared with other algorithms, and the accuracy of helmet recognition reaches 86.7%, an average improvement of 47.52% compared with other algorithms. The results show that the algorithm in this paper can effectively improve the contrast and clarity of mine images, reduce the halo phenomenon, and significantly improve the accuracy of target recognition in intelligent mine monitoring. It can lay a solid foundation for the intelligent identification of safety violations in underground coal mines.

Pulverized fuel ash (PFA) is a by-product from coal-fired power plants. The generation of PFA is huge and increases yearly. A large amount of untreated PFA is harmful to the environment, and it is also a waste of resources. Recycling PFA as construction materials would improve resource utilization efficiency, reduce environmental risks, conform to the demand for high-efficient and low-carbon utilization of solid waste and help to achieve the national strategy goals of carbon peak and carbon neutrality. The utilization efficiency of PFA as construction materials could be improved by optimizing production processes and developing new technologies, which would promote its large-scale and high-value utilization. In this paper, the general situation and physical and chemical properties of PFA are summarized. Various value-added utilization technologies of PFA as construction materials, including raw materials for cement production, supplementary cementitious materials, bricks and blocks, artificial aggregates, glass-ceramic materials, fire-resistant insulation materials, and new intelligent construction materials are comprehensively reviewed. This paper also introduces the research status of the utilization of PFA in construction materials, analyzes the applicability of different technologies, summarizes the latest technologies for preparing the PFA-based green construction materials and challenges faced in future research, provides detailed introductions to the mechanism of PFA application, and proposes thoughts on the problems existing in the utilization of PFA as construction materials. Finally, the further perspectives of the development of the PFA-derived low-carbon construction materials are highlighted. The study suggests that the “traditional large-scale consumption of PFA” and “high-value utilization of PFA” should be researched in parallel, and theoretical research and engineering practice should support each other, which would provide some scientific references for the sustainable management of PFA.

With the extension of coal mining in China, fault water inrush has become one of major disasters threatening the safety of coal mine production. Based on the research results related to the mining-induced fault water inrush, this paper proposes a conceptual model of water inrush caused by the erosion synergy of mining-induced rock mass damage rupture and fractured rock mass (fault), derives the permeability evolution equation of the two media, and systematically constructs the cooperative disaster causing mechanism model between mining failure and particle erosion inside faults. The numerical simulation is conducted to study the deformation and failure of rock mass, the particle transport in faults and the evolution characteristics of seepage channel, and systematically explain the temporal and spatial evolution mechanism of seepage catastrophe caused by mining-induced fault inrush. The results show that: ① With the continuous advancement of working face, the damage field of mine floor rock mass is connected with the fault erosion fracture, forming a seepage path of aquifer-fault-mining fracture-working face, and with the increase of erosion time, it finally develops into several dominant water diversion channels, resulting in a sharp increase in water inflow at the working face and a lagging water inrush. ② With the increase of seepage time, the water inflow and fracture opening degree inside faults all show three stages: slow change, sudden increase and stable, and the erosion particle concentration shows a trend of first increasing and then decreasing. ③ Under the geological conditions of the mining area studied in this paper, in order to prevent the occurrence of fault water inrush, the methods such as advanced grouting or leaving water prevention coal pillars can be adopted, and the advance grouting time should be before the bottom plate fracture zone connects faults, if grouting is not applied, the width of the reasonable water prevention coal pillar should not be less than 20 m.

Coal-rock interface recognition technology is one of the key technologies for intelligent mining in coal mines. Based on high-frequency radar wave detection technology, high-precision detection of coal-rock interfaces can be achieved with mining, but there are still safety risks for equipment caused by rib spalling and roof caving in ultra-high mining heights (≥6 m) in mines, as well as spatial restrictions on equipment passing through during sudden changes in mining height (mining height ≤2 m). Based on previous work, this paper proposes a rapid dynamic detection system and method for coal-rock interfaces in mines using nodal GPR. The main contents include: ① Explaining the principle of the nodal GPR observation system in mines, designing a coal-rock interface recognition observation system plan and radar antenna sensor installation method based on the actual environment of the mine working face; ② Studying and proposing a nodal acquisition control system and information interaction transmission design plan to achieve dynamic data acquisition, control, and storage; ③ Studying and proposing enhanced processing methods for sensor detection data and coal-rock interface recognition algorithms based on nodal acquisition methods and radar reflection echo characteristics of coal-rock interfaces, which can effectively achieve intelligent recognition and tracking of coal-rock interfaces, as well as calculation of coal seam thickness and spatial coordinates. To verify the feasibility of this method, multiple geological radar antenna sensors with a center frequency of 1.5 GHz were used for physical model verification experiments, and a comparative analysis of nodal data acquisition and continuous data acquisition results was conducted. The experimental results show that both nodal and continuous acquisition methods can effectively identify coal-rock interfaces. Compared with continuous acquisition methods, the nodal detection method proposed in this paper can achieve rapid and dynamic repetitive data acquisition, with a single acquisition time controlled within 10 seconds, an average error of 1.07 cm for coal seam thickness detection results, a maximum error of 1.47 cm, and an average error percentage of 7.64%. This method provides technical support for dynamic high-precision detection of coal-rock interfaces in intelligent mining in mines.

With the continuous increase of coal mining depth, the occurrence and prevention of deep rockburst in China have become normalized. In order to improve the effectiveness of deep rockburst prevention and control technology, starting from the technical difficulties of deep rockburst prevention and control in on-site engineering, combined with practical data statistics of disaster prevention and control engineering, this study demonstrates that the deep rockburst in China is due to its high geological stress and large range of human mining disturbance. The stress recovery of surrounding rock is fast after rock stress unloading during the disaster prevention and control process. The low effectiveness of rockburst prevention and control can be attributed to the new requirements of “three highs and one low” prevention and control technology in deep mining compared to that in shallow mining, including high-strength large-sized drilling to relieve pressure, in order to solve the collapse prone problem of thick and hard coal seams; small spacing high-density drilling to solve the problem of disconnected pressure relief range in drilling; multiple rounds of repeated high-frequency construction to solve the problem of rapid stress recovery after unloading pressure in deep coal seams; and the mining face is advancing at a low speed to solve the problem of high mining disturbance intensity. In response to the new requirements of “three highs and one low” prevention and control mode for deep rockburst, in order to further improve the safety and reliability of rockburst prevention and control, and based on the limitations of optimizing development and mining deployment for conventional source rockburst prevention and control, this paper proposes the technology of actively regulating the structure and load of overlying rock layers in the deep rockburst prevention and control areas, and presents some further scientific problems that need to be solved. Against the background of several typical rockburst accidents in recent years with the problem of “missed targets” in the prevention and control plans, a local targeted prevention and control technology for deep rockburst mining space has been developed, and the scientific challenges that need to be solved in the future have been pointed out. Against the background of the difficulty in evaluating safety issues after the implementation of coal mine rockburst prevention and control measures, a deep rockburst prevention and control unloading standard evaluation technology is proposed, and the scientific difficulties that need to be solved in the future are pointed out. The coal industry vigorously promotes intelligent mining, but the disaster control still relies on manual labor and personnel to operate in a high-risk environment. This paper also explores the emerging research direction and scientific challenges of intelligent mining and intelligent prevention and control of deep rockburst. Finally, it is objectively pointed out that the prevention and control of rockburst is not purely a theoretical and technical issue, and the human understanding of technical issues is also one of the important reasons for rockburst accidents. Combining with the on-site engineering practice, this paper discusses the concept and mechanism of rockburst, whether rockburst can be predicted, whether rockburst can be prevented and controlled, and how to deal with rockburst mines and other industry focused technical issues. It is pointed out that the problem of rockburst engineering is a struggle between humans and nature, which requires practitioners to objectively understand, objectively accept, and conduct in-depth research. The current achievement is of significance.

In order to improve the production of coalbed methane vertical wells in the central and northern Zhengzhuang block, southern Qinshui Basin, Shanxi, China, this paper analyzes the reasons for the poor stimulation effect of medium-deep coalbed methane vertical wells, based on the ground stress test data and fracturing monitoring data of these evaluation wells in the study area, proposes targeted stimulation techniques, designs and carries out field comparative pilot studies and analyzes their results. The results show that there are three main reasons for the low production of these vertical wells in the study area. Firstly, the vertical fracture is dominant, resulting in the shorter length of hydraulic fractures. With the increase of burial depth, the length and width of fractures decreases at the same fracturing scale. Secondly, with the increase of burial depth, the embedment depth of proppants into coal rock increases and the closure of hydraulic fractures speeds up. As a result, the stable production time is short, and the main form of gas production curve is “single peak” type. Thirdly, after the initial fracturing, the coal body structure is much more broken, and new fractures are easy to enter the initial fractures, which increases the difficulty of creating new fractures, resulting in poor stimulation effect. In view of the above reasons, the paper proposes an innovative technology of pre-plug, large-scale and remote-support re-fracturing. Pre-plug means that relatively low displacement, sand ratio and scale are first used to fill initial fractures, and then large-scale re-fracturing is carried out to create new fractures. Large-scale fracturing refers to the fracturing with large displacement, large fluid volume and high sand ratio. In order to improve the stimulation effect of middle-deep reservoirs, the fracturing fluid volume is increased from 600−800 m3 to more than 1 300−2 000 m3, the displacement is increased from 6−8 m3/min to more than 10−14 m3/min, and a low viscosity fracturing fluid system combined with low density proppants is used to increase the sand ratio from 7%−8% to more than 10%−15%. Remote-support is a combination of self-suspended proppants and large displacement to increase proppants migration distance and increase the proportion of the propped fractures. The average daily production of a single well reached 1 380 m3, which was 1 190 m3 higher than that before, and nearly 1 000 m3 higher than the stable gas production of adjacent wells, realizing the production breakthrough of vertical wells in the low-production area of the middle-deep reservoir in the north of Zhengzhuang block. Results of the comparative pilot studies showed that the average net construction pressure increased by 3.3 MPa after pre-plug, compared with the initial fracturing, which means that new fractures were formed and resulted in the production increase by 1 000 m3 compared with that of the wells without the Pre-plug. The pilot results show that, in general, the larger the technical parameters of pre-plug, large-scale and remote-support re-fracturing, the better the production performance.

Coal has made important contributions to the industrialization process of human society, and has played a key supporting role in ensuring China’s energy security and stable economic development. Since the mid-19th century, the coal-based fuel of coal, kerosene, gas and coal electricity has gradually entered the era of large-scale use. However, the traditional use of coal produces high carbon emissions, which has become a major problem in energy transition. Facing the development of ecological civilization society, the clean and efficient use of coal is imminent, and the innovation of modern coal-based energy technology is imperative. This paper proposes the definition and connotation of modern coal-based energy technology system, which is defined as the production of low-carbon energy products such as coal-based gas, coal-based oil, coal-based hydrogen and coal-based electricity, and the in-situ absorption of carbon dioxide in mining areas to form a clean and low-carbon energy production system with carbon neutrality. Its technical connotation includes coal-based gas, coal-based oil, coal-based hydrogen, coal-based electricity and dynamic carbon neutrality in mining areas, with a total of 5 technical modules, 19 technical units and 61 key technologies. The modern coal-based energy technology system will play an important role of “one main body, three supports and one breakthrough” in the future new energy system. Coal-based electricity provides the main body of electricity system stability. Coal-based oil supports the China’s oil safety. Coal-based gas supports the China’s gas safety. Coal-based hydrogen plays a supporting role in the development of hydrogen energy in China. The major breakthrough is the dynamic carbon neutral technology of coal-based energy. The paper supposes that when the ratio of non-fossil energy and low-carbon coal-based energy is maintained in the range of 2.5−3.0, coal-based energy, oil and gas and wind, water, nuclear energy can be reasonably integrated to form a new quality energy system with strong complementarity, high reliability and low carbon emissions. Based on the major breakthrough and practical application of modern coal-based energy technology, it is predicted that China’s low-carbon coal-based energy production will reach 1.02 billion −1.46 billion tons of standard coal equivalent (tce) in 2060, equivalent to 18%−24% of the national energy demand, and carbon dioxide emissions will be controlled below 500 million tons. Compared with the current energy transformation planning path based on “de coal” planning, the share of coal in our energy system can increase from 10% to more than 20%, and carbon dioxide emissions will reduce by 50%. At that time, the modern coal-based energy system has great technological innovation significance for China’s energy security and carbon dioxide emission reduction, and helps China to become a country with independent energy supply.

During the coal mining process, the change in the floor stress state of coal seam will produce deformation and failure. The seam floor failure in different coal mining processes has a certain law. At present, the water disaster monitoring of coal seam floors based on the DC resistivity method mainly focuses on the resistivity response characteristics of floor deformation and damage. To investigate the temporal changes in the electrical properties of the coal seam floor during mining, this study employs the inter-hole DC perspective observation system and the time-lapse resistivity reflection coefficient method. Through numerical simulation and field tests, the study uncovers the temporal variation law of the resistivity of coal seam floor induced by mining activities. First, this paper compares the results of individual inversion and time-lapse resistivity change rates for a typical geoelectric model to validate the reliability of the inter-hole DC perspective time-lapse method. Next, considering the mining-induced damage to the coal seam floor, this paper analyzes the electrical response patterns and charac-teristics of the rise of confined water and the damage zone in the floor during the mining process. It also discusses the feasibility of using a time-lapse resistivity reflection coefficient to assess the depth of coal seam floor damage, offering a theoretical basis for field construction. Finally, , the on-site monitoring tests reveal the electrical change characteristics of coal seam floor during the coal mining process. The time-lapse resistivity reflection coefficient R is utilized to determine the damage depth of the rock layer of the working face floor, which is found to be 15 m. The study results demonstrate that the time-lapse characteristics of the resistivity of coal seam floor mining damage obtained by the inter-hole DC perspective method can mitigate the influence of formation factors and random noise in the monitoring data to a certain extent. Additionally, the time-lapse resistivity reflection coefficient can be utilized to determine the depth of coal seam floor failure. This method transforms the detection target from the single study of geological anomalies to the full life cycle dynamic monitoring of the floor damage of the working face in the process of coal mining and then realizes the detailed depiction of structural damage to the working surface floor.

Based on the green development trend and requirements of China’s coal industry, this paper analyzed the factors that coal mines consider in choosing filling mining methods and the constraints that affect the promotion of filling mining technology. According to the geographical distribution characteristics of different mining areas and the differences in filling demands, four types of priority principles of “protecting the ecological environment, protecting surface buildings, addressing coal gangue and solid waste, and improving economic efficiency” for coal mine filling mining were defined. The ecological mining goal of “building the whole process holographic intelligent ecological mine by adopting filling mining as a regulation tool to protect the ecological environment in coal mines” was put forward. Based on the finite deformation mechanical model of the roof in filling mining, the factors affecting the subsidence of target rocks in filling mining were expounded, and the supporting strength calculation and overburden deformation control equations under three filling engineering modes such as ecological environment protection, ground building protection and gangue treatment were established. In addition, the paper introduced the development status and direction of universal filling technology in coal mines in China, including solid filling of raw gangue waste, modified solid filling, gangue concrete filling, integrated mining-filling-charging, large amount of gangue filling, filling method in thin coal seam, filling method for regional protection, filling method in continuous mining roadway and other filling technologies that meet various needs of coal mines. The material preparation and transportation of different filling technologies, the characteristics of filling process and the adaptive filling equipment were described in detail. In order to realize the intelligent filling of coal mines, a comprehensive data perception system was established, which realized the intelligent process from unit to whole filling working face through spatial planning and filling effect judgment. The sensor network and artificial intelligence algorithm were combined to monitor and control the solid filling process of coal mine in real time, and improve the filling quality and filling efficiency. Coal mine filling mining will play a more important role in the long-term planning of China’s green mine construction. Strengthening the scientific and technological research of the whole process of coal mine production based on active filling, the construction of universal filling technology and process system, the development of new solid filling materials, and the research of intelligent filling mining, will help the filling mining technologies in China’s coal mines have a very broad prospect.

The MILD combustion is a combustion mode that occurs in a moderate or extremely low oxygen environment, combining the advantages of high combustion heat utilization and very low NOx emissions, and is considered by the international combustion field to be one of the cleaner combustion technologies with great potential for application. Since the relevant research began around 1990, the technology for achieving a MILD combustion of gas fuels has been relatively mature, while the research on the MILD combustion mechanism and implementation conditions of solid fuels such as coal powder and biomass is still relatively lacking. Based on the high momentum oxidizer jet, internal recirculation is achieved, eliminating the need for external high-temperature preheating to establish MILD combustion, greatly expanding the application range of MILD combustion. This paper provides an overview of the basic characteristics of MILD powder fuel combustion from the aspects of particle dispersion, heating, ignition, combustion, and pollutants. Due to the uneven dispersion and reaction of particles, the MILD combustion process of carbon-based solid fuels such as coal powder is more complex than that of gas fuels. High speed jet MILD combustion not only increases ignition delay but also expands ignition and reaction zones, requiring systematic research on the characteristics and mechanisms of each combustion stage. This paper introduces the research achievements in the theoretical design and equipment development of solid fuel MILD combustion. It is recommended to improve the existing coal-fired boiler burner, adjust the process parameters to match the MILD combustion mode, increase the residence time of coke particles to improve combustion efficiency, improve combustion stability, and suppress various pollutant emissions, including fine particulate matter, through high-precision numerical simulation. Based on the overall approach of interconnected energy systems, the coupling research between MILD combustion and various new combustion technologies should be promoted, especially strengthening the research on the co-combustion characteristics of coal powder, biomass and hydrogen, ammonia and other combustible gases, and assisting in energy transformation. Exploring the characteristics of turbulent two-phase flow, turbulent interphase heat transfer, and turbulent chemical coupling in the powder MILD combustion is crucial for deepening the understanding of powder MILD combustion. It involves multivariate analysis and high-precision simulation, which will be the focus and difficulty of future research.

The safe, green, efficient and low-carbon coal mining is the common goal of surface coal mines around the world. The development intensity and ecological carrying capacity of surface coal mine resources in China show the reverse development characteristics, and the vulnerable ecological environment areas in northwest China have become the main surface coal production areas, which makes surface coal mining and ecological environment protection become important scientific problems, ecological problems and development problems to be solved urgently. On the basis of the development situation, natural conditions and main influencing factors of surface coal mines, the connotation characteristics and overall structure of realizing the safe-green-efficiency-low-carbon mining of surface coal mines were explained. Aiming at the characteristics of the whole life cycle of pre-mining, mid-mining and post-mining of surface coal mines, in terms of four levels: safe mining technology, green mining technology, efficient mining technology and low-carbon mining technology, this paper puts forward eight key technologies including the time-limited slope control technology, the intelligent early warning decision-making technology, the new mode of transportation link, the ecological construction of mining area, the coordinated mining of adjacent mines, the intelligent mining design, the application of electric mining trucks and the ecological damage reduction at mining sources. The key work and direction of safe-green-high efficiency-low carbon cooperative mining in surface coal mines are clarified. In terms of the measures of safety-green-efficiency-low carbon co-development, regarding strengthening a top-level design, accelerating the distributed implementation, enhancing key researches, promoting personnel training, and improving standards and regulations, the paper proposes the target tasks to be accomplished in different stages in 2025, 2030 and 2035. In the new era, surface coal mines should firmly follow the development path of safe-green-high efficiency-low carbon, and realizes the high-quality development goal of surface coal mines.

Coal mining machine is the core equipment of completely automated working face, and the research and development of intelligent coal mining robot is crucial for achieving the intellectualization of fully mechanized working face. This paper comprehensively analyzes the current research status of sensing detection, position and attitude control, speed control, cutting trajectory planning, and tracking control in the coal mining machine roboticization process, and proposes five key technologies that must be solved in the development of intelligent shearer robots, including sensing and detection, pose control, velocity control, cutting trajectory planning and tracking control. Aiming at the problem of intelligent perception, this paper proposes the construction thought of a coal mining robot intelligent perception system, as well as the architecture of a coal mining robot intelligent per-ception system. The architecture of the intelligent perception system for coal mining robots is outlined, enabling a comprehensive sensing of running state, posture, environment, and so on, thereby ensuring the safe and reliable operation of intelligent coal mining robots. In terms of the position and attitude control problem of intelligent coal mining robots, the intelligent PID position and attitude control thought is proposed, along with an improved genetic algorithm-based PID pose control method, enabling precise pose control for the coal mining robot. As to the problem of velocity control, the thought of cutting load measurement based on the fusion of “force-electricity” heterogeneous data is proposed. Additionally, a neural network-based algorithm for cutting load measurement is presented, achieving an accurate load measurement. Furthermore, a traction and cutting speed adaptive control approach is proposed, including an artificial intelligence-based decision-making method for traction and cutting speed and a sliding mode control method for traction and cutting speed with disturbance rejection. This approach enables a precise and adaptive speed control for the coal mining robot. Regarding the problem of cutting trajectory planning and tracking control, the precise cutting trajectory planning thought is proposed, incorporating geological data and historical cutting data into a cutting trajectory planning model. The precise cutting trajectory tracking control thought is proposed, and an intelligent interpolation algorithm-based cutting trajectory tracking control method is given, achieving a high-precision trajectory planning and accurate tracking control for the coal mining robot. Considering the “position-attitude-velocity” collaborative control problem, the intelligent optimization idea of "position-attitude-velocity" collaborative control parameters is proposed, which utilizes an improved particle swarm optimization method based on multi-system constraints to optimize the coordinated control parameters, resulting in intelligent and efficient operation of the coal mining robot. The in-depth investigation of these five key technologies for intelligent coal mining robot provides some valuable insights for accelerating the development of high-performance, efficient, and reliable intelligent coal mining robot.

In view of the intelligentization of coal mine roadway excavation, this paper discusses the current development status of four major categories of intelligent fast excavation equipment, including continuous mining machine, excavation and anchor machine, full-section excavation system, and anchor excavation machine, analyzes the applicability of the four major categories of intelligent fast excavation equipment with the geological conditions, proposes some key technological issues for the realization of intelligent coal mine excavation which need to be resolved, and also explores the information transmission and intelligent analysis technology, intelligent perception technology, precise positioning and navigation technology, autonomous stereotyped directional cutting technology, remote and autonomous cutting control technology of road-header and multi-level and multi-process intelligent cooperative control technology, as they are the basis for the realization of intelligent roadway excavation. Based on the key technological issues needed to be solved in the mine roadway excavation under the complex geological conditions, the paper puts forward the design method of systematic analysis, modular design and optimal combination of functions, according to the functional requirements of the excavation operation and the requirements of the excavation process. A multi-level digital twin architecture of virtual control and virtual-reality combination is studied based on the multi-dimensional information reproduction of heading equipment, environment, and geological structure to realize the remote control of road-heading machine. A control method that integrates single-machine intelligence, system synergism, and synergism of underground intelligent control and surface remote monitoring is proposed. A new type of flexible advance support technology without repetitive crushing, multi-stage telescopic cutting technology of cutting section, and multi-rig parallel operation technology of intelligent anchoring unit have been developed, and a new type of combined unit for rapid roadway heading operation with a parallel operation of excavating, supporting, anchoring, transporting, and exploring processes has been also developed, and a flexible parallel operation technology of excavation robot, advance support robot, anchoring robot, and auxiliary transportation robot group has been proposed. A data-driven multi-machine, multi-process collaborative control behavior planning and decision-making method is proposed. In addition, it is proposed to construct a complete coal mine underground cross-system full-temporal-spatial information digital sensing system, build a data sensing intelligent monitoring platform with multi-parameter, multi-scale and full-temporal-spatial characteristics, that integrates the production state of underground site, spatial information of roadway, state of heading equipment, and risk information, etc., and realize a real-time communication between virtual system and actual tunneling system, so as to realize the intelligent and less-manned heading through data-driven planning and analysis.

The safety in the coal-producing mines in China is continuously improving, but coal and gas outburst accidents still occur. The prediction of coal and gas outbursts allows the scientific application of outburst prevention measures, which can ensure the safe coal mining to a certain extent. Machine learning is an interdisciplinary field involving probability theory, statistics, and computer science, which can explore the nonlinear relationship between outburst accidents and its associated indicators. The application of machine learning in coal and gas outburst prediction has received relatively widespread attention, and with the rapid progress of artificial intelligence and computer technology, it will play a greater role in the field of outburst prediction. Therefore, this paper provides a comprehensive review of the research on machine learning in coal and gas outburst prediction, analyzes the difficulties in outburst prediction and prospects its development direction. Firstly, the paper provides a brief overview of the research status on the hypothesis, occurrence mechanism, and prediction index selection of coal and gas outbursts. Then, it summarizes the research progress in the field of outburst prediction, including the application of support vector machines, neural networks, extreme learning machines, and ensemble learning algorithms. In addition, it also points out the existing problems in the current research, such as imbalanced samples, missing data indicators, and small sample sizes. Finally, the paper gives an outlook on the developments of coal and gas outburst prediction based on machine learning, including improving algorithm performance, optimizing feature engineering, and increasing sample size. With the continuous improvement of computer performance, more powerful models may be proposed, which can further improve the prediction accuracy of outburst accidents.

The fragile ecological environment in the western coal mining areas of China, compounded by intensive mining activities, has led to water and soil erosion, soil degradation, and damaged root systems. With a low plant water use efficiency, the ecological restoration becomes challenging, making the improvement of water use efficiency a key aspect in the ecological restoration or reconstruction of western mining areas. Soil water is a critical factor limiting the ecological restoration of arid and semi-arid coal mining areas, as it connects atmospheric water, surface water, groundwater, and vegetation growth, serving as an important carrier for water circulation and nutrient transport. Efficient and rational utilization of soil water is crucial to the success of ecological restoration. Therefore, investigating plant root water utilization strategies plays a significant role in the ecological restoration of western coal mining areas. This paper analyzes the main research methods of plant water use at home and abroad, compares the advantages and disadvantages of different methods, and reviews the corresponding research progress. In the damaged ecological environments of arid and semi-arid coal mining areas, the application of plant-microbe combined microbial remediation technology can improve plant water use efficiency and enhance plant water use strategies. At the same time, the microbial inoculation reduces the proportion of water absorption by plants from shallow soil layers, effectively increasing the absorption and utilization of water from deep soil layers by plants, thereby enhancing plant water use efficiency. This enables the inoculated plants to exhibit a higher ecological adaptability in the arid and semi-arid coal mining areas. This paper analyzes the current research progress and existing problems of plant water use in the western coal mining areas, discusses the improvement of water use strategies through microbial remediation in mining areas, and proposes the impact of different plant combinations on water use strategies and their research focuses in the ecological restoration of western arid coal mining areas. This lays a solid foundation for achieving green, sustainable, and high-quality development in the arid and semi-arid coal mining areas, and has important ecological application value.

The central and western coal resources have the highest degree of enrichment and superior development conditions in China. With the improvement of mining efficiency, the disturbance of high-intensity and large-mining-height mining mode to groundwater system also increases. In particular, the groundwater in the aquifer outside the disturbance range of the water-conducting fracture zone gradually participates in the mine water inflow process during the coal mining. Such mode leads to a series of problems such as large deviation of mine water inflow prediction, inaccurate evaluation of water inflow risk and unclear water hazard prevention measures, which brings great hidden risks to the current mine water hazard prevention and control. In this paper, a derivative mode of dynamic water inrush is summarized. With the coal mining, the evolution of groundwater system caused by overburden failure will induce new disaster sources, resulting in different forms of water inrush. Its connotation is to change the basis of defining the derivative dynamic water inrush model from the traditional static analysis before mining to the dynamic evaluation considering the change in the whole mining cycle. The derived dynamic water inrush model of the mine can be preliminarily divided into three categories, namely, “skylight leakage type”, “bed separation disaster type” and “channel permeability increase type”. This paper mainly discusses the derivative dynamic water inrush mode of “skylight leakage type”. Taking the Shanxi Yushen mining area, a shallow buried coal seam mining area with high strength and large mining height, as an example, the disaster-pregnant conditions of “skylight supply type” derivative disasters are discussed in depth. Through supplementary analysis of water-richness and hydraulic connection strength of indirect water-filled aquifer, the comprehensive evaluation of water inrush risk in roof aquifer is achieved, and the evaluation method system of disaster derivative model is put forward. Through the transformation of mining mode, the active prevention and control system is constructed. A passive prevention and control system is constructed by multi-objective advance drainage before mining and local grouting after mining. By further refining the mine water inrush disaster model, optimizing the evaluation system and establishing comprehensive prevention and control technology, it provides a scientific basis for the protection of groundwater resources and safe low-carbon mining in ecologically fragile areas.

While giving full play to the role of coal energy security supply, it is an important proposition related to national energy security and overall development to realize green and safe mining and clean and low-carbon utilization of coal resources. This paper analyzes the influence of changes in the international development environment on the China’s utilization of oil and gas resources in the international market, and studies the rigid demand for energy supply in China. Based on the current situation of energy development and utilization with coal as the main energy source in China and following the fundamental requirements of building a harmonious modernization between man and nature, this paper puts forward the green and low-carbon development direction and path of coal industry in the process of realizing the goal of “dual carbon”. ① China’s external dependence on oil and gas resources exceeds 70% and 40% respectively, and its strategic reserves are insufficient. Under the background of profound changes in the international situation, the uncertainty of using oil and gas resources in the international market increases, and the external risks of national energy security have increased. ② Building a modern country will inevitably lead to the rigid growth of energy demand. At present, it is difficult for new energy sources to replace fossil energy safely and effectively, and the main energy position of fossil energy will be difficult to change in the short term. ③ Comparing with the “dual carbon” goal, the proportion of coal consumption before the peak shows a continuous downward trend, and the total consumption will usher in an inflection point. After the peak, the main energy position of coal will be weakened, but the role of strategic mineral resources and coal-based raw materials will be further highlighted. ④ Driven by the goal of “dual carbon”, the basic national conditions with coal as the main energy source determine that coal will continue to undertake the important mission of energy security supply and further play the role of strategic mineral resource as raw material. However, the high carbon resource attribute of coal determines that the development and utilization of coal will face the dual pressures of ensuring supply and reducing carbon emissions. Therefore, in order to serve the high-quality economic and social development, which requires security and green and low-carbon energy supply, it must be based on the current characteristics of energy production and supply with coal as the main energy source and new energy as the supplement at this stage, and take the new progress of ecological civilization construction as the fundamental principle. The research on the key technologies should be enhanced such as the technologies of coal mining and ecological carbon sink, CO2 geological storage in deep coal seams and coal mined-out areas, and collaborative development and utilization of new energy in coal mining areas, which will support the high-quality development of the China's coal industry with technological innovation under the goal of “dual carbon”.

With an increasing mining depth and intensity in Chinese coal mines, unprecedented frequency and intensity of mining tremors are attracting extensive attention from the government and society. Under the initiatives from the government and the intensive investigations, significant progress has been made in the research and engineering practice, which greatly enhances the understanding and hazard control of the mining tremors. This paper reviewed the state-of-the-art occurrence mechanism, damage characteristics and control of the mining tremors in Chinese coal mines and demonstrated their main challenges. The conclusions are as follows: due to the complicated occurrence conditions of mining tremors, various definitions and classifications of mining tremors have been proposed from different aspects. This paper has summarized these definitions and classifications and defines mining tremors from special and general aspects, respectively, which classify mining tremors in terms of phenomena and occurrence mechanisms. Because mining tremors are widespread in all mining countries in the world, targeted mining tremor hazards prevention and control are urgently needed. Although the research started late in China, the hazard control of mining tremors and the emergency dealing capacity have been significantly enhanced in recent years due to the implementation of the regulations and rules from the government for mining tremors prevention and control. It has been summarized that from the macro view, the triggering of mining tremors is mainly induced by the coal pillar failure, roof breakage and movement and fault slip, and from the micro view, the triggering of mining tremors mainly includes tension rupture, implosion rupture and shear rupture. The mining-tremor-induced hazards have been surveyed in terms of source parameters, seismic wave attenuation and seismic wave disturbances, and the methods for evaluating surface and underground damage triggered by mining tremors have been also concluded. To achieve hazard source control and precise prevention, the current situation of mining tremors treatment in Chinese coal mines has been outlined. At present, Chinese coal mines, it is still far away to achieve accurate hazard source identification and full hazard control. Therefore, to support the national strategy of deep resources development and energy security, future studies should focus on investigating the hazard-forming mechanism, damage effect and prevention and control technologies of mining tremors.

The accurate determination of coal temperature in the hidden spaces such as goaf has always been a worldwide problem that needs to be solved urgently. The study of acoustic temperature measurement technology is of great practical significance for a fast and accurate detection of loose coal temperature, and the scientific and accurate construction of the mapping relationship between sound velocity and coal temperature is the key to acoustic coal temperature measurement. In this paper, considering the influence of the characteristic parameters of spontaneous combustion process of loose coal on sound wave propagation, a mapping model of sound velocity and coal temperature in the quasi-porous media of loose coal was established. An acoustic temperature measurement experimental system for loose coal was designed and built. By conducting the acoustic temperature measurement tests for the loose coal with various particle sizes (0.6～1.5, 1～3, 3～5 cm), the effect of gas composition and concentration on sound propagation during the low-temperature oxidation stage (30～50 ℃) of coal samples with different particle sizes was studied, and the equivalent path conversion factor λ was determined. Based on the relationship between the measured sound velocity and the equivalent path conversion factor, the medium correction coefficient φ of the gas component was proposed and determined, and the feasibility of the sound-temperature mapping relationship model was verified. The results show that the acoustic wave propagation path of loose coal is affected by the characteristic parameters of coal particle size, temperature and the change of gas component medium, etc. A mapping model of sound velocity and coal temperature was established. At normal temperature, the propagation path of sound waves in the quasi-porous medium of loose coal is mainly affected by the pores between the coal particles. The equivalent path conversion factor λ of sound waves is 1.426 1, 1.371 1 and 1.315 2, respectively, when the coal particle size is 0.6～1.5, 1～3, 3～5 cm, which is negatively correlated with the particle size. The influence of coal temperature on acoustic wave propagation is manifested by the change of gas component medium in the process of spontaneous combustion of coal, which verifies the feasibility of the mapping relationship between sound velocity and coal temperature. The error rate between the inversion model and the experimental coal temperature is 0～6.46%, and the average coal temperature error is 2.52 ℃, which can reflect the coal body temperature well.

The site selection optimization of coal mine safety emergency reserve center is an important foundation for promoting the construction of coal mine safety emergency response system. In order to improve the accuracy and reasonableness of coal mine safety emergency reserve center site selection, it is proposed to establish a machine learning combination model for coal mine safety emergency reserve center site selection, integrating multi-source spatial data by using demographic, transportation, economic and natural factors to improve the accuracy and scientificity of coal mine safety emergency reserve center site selection. The accuracy and scientificity of coal mine safety emergency reserve center site selection are improved. Firstly, the ArcGIS is used to process multi-source spatial data through tasks such as fishing net division, spatial linking and projection respectively, and the SMOTEENN algorithm is utilized to avoid the negative impact of data imbalance, so as to construct the dataset applicable to the analysis of machine learning model. Secondly, by comparing and analyzing different machine learning algorithms, different feature selection methods and different parameter optimization methods, it is concluded that the XGBoost machine learning algorithm, the Boruta algorithm and genetic algorithm have better performance than other machine learning algorithms, feature selection methods and parameter optimization methods in the site selection analysis of coal mine safety and emergency reserve center. Therefore, based on the advantages of each algorithm, this paper obtains a combined machine learning model for coal mine safety emergency reserve center site selection. Finally, the SHAP analysis is introduced to analyze the influence degree and direction of different features to quantitatively assess the contribution of input data in decision-making and enhance the interpretability of the model. The results show that the combined model of coal mine safety emergency reserve center siting has an excellent performance, with 0.976, 0.966, 0.989, 0.977, 0.996 in accuracy, precision, recall, F1 value and AUC, respectively, which can provide a powerful support for siting decision-making, and the model interpretable analysis can also provide a scientific reference for coal mine safety emergency reserve center siting.

Hydraulic fracturing is a widely used technique for increasing the permeability of coal seams. Its impact on the production capacity of coalbed methane(CBM) wells is significant. This paper makes detailed observations on the exposed coal seams and fracture distribution of 5 CBM wells in Tunlan block of Xishan coalfield, and studies the distribution characteristics of coal structure, microfractures, quartz sand and coal fine by using stereoscopic microscope, scanning electron microscope, and micro CT. The fracturing effect and influencing factors of CBM wells are analysed by combining regional geostress and hydraulic fracturing construction parameters. The research results indicate that the macroscopic fractures morphology produced by hydraulic fracturing are complex and diverse, including horizontal, vertical, X and T-shaped fractures. The degree of coal body fragmentation increases with distance from the CBM well. The coal body closer to the CBM well is mainly composed of fragmented and granular coal, while the coal body further away is mainly composed of undeformed coal with primary fractures. The quartz sands are mainly deposited in horizontal fractures, with only a small amount in T-shaped fractures. Quartz sand rubs, collides, and embeds strongly with the coal fracture surface. The fracturing fluid is then superimposed to fracture the coal body, resulting in a large amount of coal fines. This causes the coal fines to wrap around the quartz sand and block the fractures. The coal fines within the macroscopic fracture are primarily a result of the fracturing of the coal body, the flushing of the coal body by fracturing fluid, and the friction between the quartz sand and the fracture surface during hydraulic fracturing. Coal fine generation in micro-fractures during coal body fracturing. Coal fines and quartz sand accumulate in the fractures, creating enormous resistance to the carrying fluid and preventing the quartz sand from migrating to the far end of the CBM well. The magnitude and direction of the geostress, as well as the strength of the coal seam roof and floor, are important factors that influence the opening and direction of the hydraulic fracturing fractures. The low viscosity of the carrying fluid cannot suspend quartz sand, and the accumulation of quartz sand and coal fine can block the fractures, easy to cause quartz sand and coal fine to aggregate and block fractures.

The fracture (pore) development of coal specimen under axial stress loading and hydraulic permeability affects directly the mechanical indexes and the permeability characteristics. In this paper, using theoretical analysis and mechanical test methods, the relationships between permeability and fractal dimension, ringing count response under coal specimen fracture (pore) were analyzed, and the acoustic emission fractal-permeability model of coal specimens under hydraulic-loading coupling were established. The permeability experiments of coal specimens with hydraulic-loading coupling in different confining pressures (2−5 MPa，Δpw/p'c=0.75) were carried out, and the mechanical behavior, permeability characteristics and acoustic emission rules of coal specimens in different confining pressures (water pressure) were analyzed, and the relationship between the failure morphology of coal samples under different confining pressures and the acoustic emission positioning was discussed. The strength enhancement characteristics and the relationships between failure pattern and acoustic emission location of coal specimens under confining pressures were discussed. The rationality of the fractal-permeability model of coal specimens under hydraulic-loading coupling was verified. The results showed that the fracture (pore) change of coal specimen was consistent with acoustic emission ringing, the fracture (pore) development was closely related to the fractal dimension and the permeability, and the acoustic emission fractal and permeability could be characterized by the volume strain in the permeability experiments. The acoustic emission fractal-permeability model of coal specimen under hydraulic-loading coupling could be analyzed by a two-stage mathematical model. The permeability of the coal specimen showed the process of short-term decrease, long-term slow increase, rapid increase and slight decline, and the ringing count showed the wave-like development of rapid increase - decrease - increase - decrease during the total stress-strain process of coal specimen, the minimum permeability lagged behind the critical point of volume strain compression and expansion, and the minimum permeability varied from 0.124×10−17 m2 to 1.250×10−17 m2. With the increase of confining pressure (2−5 MPa), the peak deviating stress, peak axial strain and peak volume strain of coal specimen all showed an increasing trend, the linear characteristics were significant, the lag of peak permeability behind peak strength showed a decreasing trend, the reduction reached 93.34%, and the loudest ringing count (corresponding to the peak strength) showed an increasing trend. The effective cohesion and the effective internal friction angle of the coal specimen increased to 6.511 6 MPa and 36.56º under hydraulic coupling, respectively. With confining pressure (2−5 MPa) increase, the acoustic emission information of coal specimen changed from single inclined plane to irregular inclined plane, the angle of the main fracture plane from small angle to high angle, and the instability mode from single block shear to multi-block compression, and the specimen fracture could be expressed by acoustic emission positioning ringing count. Three experiment curves of acoustic emission fractal-volume strain, permeability and volume strain, and fractal and permeability of the coal specimens were consistent with the theoretical curves, the correlation during compression stage with confining pressure 2−5 MPa was 0.882−0.999, 0.950−0.998 and 0.849−0.997, respectively. The correlation during the expansion stage was 0.937−0.996, 0.891−0.998 and 0.873−0.966, respectively.

The detailed seepage process and rainfall infiltration temporal variation cannot be observed visually due to the complexity and non-visibility of the internal structure of landslide body, thus making it difficult to identify the specific process of rainfall in the whole process of landslide catastrophic evolution, which leads to the incomplete understanding of the formation mechanism of rainfall-induced landslide. Therefore, the new technological methods for directly observing and monitoring the infiltration and seepage process of rainfall-induced landslide is of great significance for deep understanding the formation mechanism of landslide induced by raining. Transparent soil test technology enables non-invasive, continuous, non-destructive and visual measurement or monitoring inside soil or rock mass bodies. In this paper, the current status of the development of transparent soil testing technology and its application in different fields especially in the application of slope engineering and practice in the visual simulation of seepage processes are summarized from the aspects of transparent soil material properties, geotechnical engineering properties, experimental equipment and image processing analysis technology, and the feasibility of applying it to the visual observation of seepage in landslide is discussed. On this basis, the transparent soil material is screened and the preparation method is optimized. The transparent soil is used to replace the traditional geotechnical model material to establish a landslide transparent soil physical model suitable for seepage process observation. The physical simulation test of landslide seepage under rainfall conditions is carried out to obtain information on the whole process of rainfall infiltration-induced landslide disaster, and to determine the process and characteristics of the seepage process of the groundwater. The model test is an effective application of transparent soil test technology in the field of landslide seepage visual observation, expanding a new way of landslide disaster visual simulation, and further determining the complex impact of groundwater seepage on landslide. It is conducive to reveal the evolution law of rainfall-induced landslide, explore the sliding mechanism of landslide, and provide a scientific and technological support for rainfall landslide disaster prevention and disaster planning.

Coal energy has made a significant contribution to the development of human industrialization, but coal energy is faced with the major problem of high carbon emissions. Modern coal-based energy is a new path to crack the contradiction between coal energy and carbon. It can realize independent and controllable energy based on China’s resource endowment, enhance the autonomy of China’s oil and gas, support the clean transformation of electricity and the development of the renewable energy industry, and is an important innovative direction for guaranteeing energy security and realizing the dual-carbon goal. Based on the concept and technical system of modern coal-based energy, this paper systematically introduces the connotation and product lineage of modern coal-based energy. By analyzing and discussing the five core technology modules, 19 technical units and 61 key technologies of modern coal-based energy, including the new technologies such as coal-based gas, coal-based oil, coal-based hydrogen, coal-based electricity production, and dynamic carbon neutrality in mining area, ten revolutionary technologies for the development of low carbonization coal-based energy are proposed: ① Intelligent underground coal gasification technology based on self-moving plasma gasification machine which has the functions of automatic combustion, propulsion, sealing, monitoring and controlling; ② The coupling of underground coal gasification and indirect liquefaction can form a low-cost, low-emission, short-process coal-to-oil route (UCG-ICL); ③ In situ retorting chemical mining technology of oil-rich coal using solar heating or hot dry rock heating;④ In the deep coal underground gasification hydrogen production path (UCG-H2) based on in-situ carbon capture, utilization and storage (CCUS), recycled CO2 is used as a gasification agent to improve the production of effective components of coal gas, and captured CO2 is stored in the underground gasification cavity to form a zero-emission UCG-H2 technical route. ⑤ nanometer hydrogen-rich coal water slurry hydrogen-mixed power generation technology to achieve low-carbon coal-based power production at low temperature and low pressure, and significantly reduce carbon dioxide emissions of coal power; ⑥ The Low carbon power generation system concept of underground coal gasification coupled with IGCC (UCG+IGCC) reduces the coal-to-gas process of IGCC and significantly reduces CO2 emissions. ⑦ Pulverized coal deflagration linear drive power generation technology structure, the theoretical work energy is more than 15 times of coal combustion; ⑧ Based on the CO2 hydrogenation synthesis “green methanol” route of modern coal-based energy recycling, methanol is synthesized from coal-based “blue hydrogen” produced by low-carbon UCG and captured CO2; ⑨ The CO2 in situ storage technology system generated by modern coal-based energy can help achieve zero-carbon coal-based energy production; ⑩ Dynamic carbon neutral coal-based energy system architecture in mining area, coupling intelligent supply protection, green development, clean transformation, low-carbon utilization and clean emission in a closed-loop system in mining area to achieve dynamic carbon neutrality in mining area.

Sequestration of CO2 in the unmineable coal seams is not only one of the most ideal options for reducing greenhouse gas effects, but also the only way for the coal industry to reduce CO2 emissions and achieve low carbonization sustainable development. However, the key unresolved issues regarding the CO2 geo-sequestration in coal seams is: “how long does CO2 injected into a coal seam remain in the seam?”. In this regard, on the basis of clarifying the hysteresis law of CO2 desorption in coals, this paper reveals the mechanism of supercritical CO2 desorption hysteresis, establishes a quantitative model for the geological storage of CO2, and explores the use of desorption hysteresis to achieve a long-term safe storage of CO2 in coal seams. The study results shows that the degree of desorption hysteresis of supercritical CO2 in coal is greater than that of subcritical CO2, and a stable hysteresis characteristic similar to a “parallel line” in the supercritical phase is formed between the adsorption and desorption isotherm. The fundamental reason for the desorption hysteresis is that the micro and nano sized pores in coal form curved surfaces due to their hydrophilicity, which generate strong capillary pressure following the Laplace’s equation, absorb liquid water, truncate and fix the supercritical CO2 fluid, and ultimately form CO2 residual trapping. For example, the cylindrical inorganic pores with a diameter of 40–10 nm in coal can generate a capillary pressure of 7.30–29.12 MPa, which is sufficient to block supercritical CO2. Taking the desorption isotherm of Jiulishan coal as an example, using the quantitative model for the geological storage of CO2 established in this study, it has been estimated that the total trapping capacity of the No.21 coal seam at depths of 900–1 500 m is stable at 35–37 m3/t. Among them, the adsorption trapping capacity accounts for about 80%, residual trapping capacity accounts for about 15%, and structural trapping capacity only accounts for 5%. Desorption hysteresis suggests that some measures should be taken to increase the proportion of CO2 residual trapping in coal seams as much as possible, the reason is that the residual CO2 sealed by capillary blockage is safer and has no risk of leakage compared to the free and adsorbed CO2 sealed by surrounding rock. The physical parameters such as ash content, moisture content, pore size, and morphology of coal seams are the main factors affecting the residual trapping efficiency.

Coal gangue, a by-product of coal mining, is accumulating rapidly and As a by-product of coal mining, the amount of coal gangue is increasing in stock, which poses a serious threat to the environment. Due to the high content of SiO2 and Al2O3 mass fraction, the use of gangue to prepare molecular sieves to capture CO2 in order to realize the efficient resource utilization of coal gangue is a promising technology. In this paper, zeolite molecular sieves are prepared by hydrothermal crystallization method with coal gangue as raw material, and the effects of KOH addition and coal semi-coke doping on the structure and properties of molecular sieves are investigated; static adsorption test of CO2 is carried out to study the CO2 capture characteristics of coal gangue-based zeolite molecular sieves and amine-modified molecular sieves. The results show that when the mass ratio of KOH to coal gangue is 2∶1, the specific surface area of the molecular sieve is 100.17 m2/g. When the doping amount of coal semi-coke is 40%, the molecular sieve has a specific surface area of 249.86 m2/g, and the total pore volume is 0.249 cm3/g. Under the optimal preparation conditions, the CO2 adsorption capacity of the molecular sieve is 1.16 mmol/g. Amine loading modification could effectively enhance the CO2 capture capacity of the molecular sieves, but excessive polyethyleneimine will accumulate in the molecular sieve pores and block the pore channels, resulting in the weakening of the physical adsorption capacity of the molecular sieves.

Coal is the main energy source in China. It plays a crucial role in promoting economic and social development, and is the guarantee of China's energy security. This paper establishes a prediction model for the number of deaths in coal mine accidents under the influence of multiple factors through data analysis and modeling. Also, it predicts the safety production situation under the optimization of coal production capacity. Based on the statistical data of coal mine production capacity and the coal mine accident fatalities in China since 1949, the relationship between production capacity and accidents is analyzed. The regional characteristics of coal mine safety production situation is studied and a Long Short-Term Memory Network (LSTM) model is developed for predicting the number of deaths in coal mine accidents. And based on this model, the number of deaths in coal mine accidents under the influence of regional production capacity optimization policies was predicted. The research results show that ① based on China's coal production, accident fatalities, and million-ton mortality rate over the years, the development of the China's coal industry can be divided into five stages: initial establishment stage, exploration stage, recovery and rectification stage, institutional mechanism reform stage, and safe and efficient development stage. The national coal mine safety situation varies greatly in different periods due to the changes in safety policies and coal mine production capacity; ② There are significant differences in the production capacity and safety level of coal mines in different provinces of China. Through the chi square test analysis of contingency tables, the number and level of accidents in coal mine safety production are significantly correlated with the accident area. Therefore, the adjustment of coal mine production capacity in different regions is also a key factor affecting the safety situation of coal mines in China; ③ Establishing a time series prediction LSTM model that includes factors such as coal mining technology, degree of mechanization, and coal production in different regions can accurately predict the number of deaths in coal mine accidents. The correlation coefficient R2 between the true and predicted values is 0.99, the root mean square error of the predicted data is 40.49; ④ According to the prediction results, while the total coal production remains unchanged, increasing production capacity in the northwest region and reducing production capacity in the northeast or southwest regions will further improve the safety production situation of coal mines; ⑤ The prediction results indicate that the number of coal mine fatalities will decrease more significantly after the production capacity shifts from southwest to northwest, but the degree of reduction in accident fatalities will decrease with the increase of time. Although the coal mining conditions in the northwest region are relatively good, it is still necessary to pay attention to the safety mining risks under the rapid development of coal production capacity. The research results can provide a reference for scientifically formulating coal industry policies.

The surrounding rock of tunnel in cold region would produce serious damage and performance degradation under the action of freeze-thaw and dynamic loads. Therefore, it is of great significance to study the deterioration characteristics of rock under the coupling effect of freeze-thaw and dynamic loads. In this paper, the MTS815 loading system was used to carry out the triaxial multi-stage cyclic loading and unloading tests on the carbonaceous phyllite samples under 0, 30, 60 different freeze-thaw cycles. The effects of freeze-thaw and cyclic loading on the rock mechanical parameters and deformation were studied. Based on energy calculation, the energy evolution law of rocks with different freeze-thaw cycles under dynamic load was analyzed. Finally, the failure modes of rocks under static load and freeze-dynamic coupling were compared and analyzed from macro and micro perspectives, and the corresponding failure modes were revealed. The results are as follows: ① Compared with the compressive strength of static load, the strength of rock under the combined action of freeze-thaw and cyclic load is significantly reduced, and it shows obvious plasticity. Meanwhile the more freeze-thaw cycles, the more significant the phenomenon; ② With the increase of freeze-thaw cycles, the elastic modulus will gradually decrease and the Poisson's ratio will gradually increase; ③ During the cyclic process, the axial and hoop irreversible strains increase gradually, and the strain increments of both are the largest in the initial cycle of each level of stress and then decrease gradually, while the irreversible volume strain increases first and then decreases, that is, the volume is mainly compacted first and then gradually transformed into expansion; ④ The rock is mainly composed of elastic energy, and the proportion of dissipated energy decreases rapidly in the first cycle and increases stepwise in the subsequent cycle and then tends to be stable; ⑤ From the perspective of macro and micro analysis, the failure mechanism of monotonic loading and cyclic loading is different, but both are the shear failure of inclined section, but the degree of cyclic loading and unloading is greater.

Lake sediment, as a solid waste, can be disposed harmlessly through combustion. The ash melting temperature is an important factor affecting boiler coking and restricting its safe and stable operation. Determining the ash melting temperature after mixing lake sediment with coal is of great significance for achieving the resource utilization of lake sediment. This paper takes the Yunnan Xiaolongtan lignite and the Dianchi Lake sediment as the research objects. The Dianchi Lake sediment is a high moisture solid waste with high nitrogen content and rich heavy metal elements. The Yunnan Dianchi Lake sediment has a large residual stock, mainly generated by a large amount of sediment entering the Dianchi Lake with river water and rainwater. It is the main source of pollution in the Dianchi Lake. However, the Xiaolongtan lignite has problems such as high production, poor coal quality, and high transportation costs, which seriously affect its utilization rate, if the local conditions can be adapted and the problems of high production, difficult treatment, and insufficient efficiency of local sediment can be solved through mixed combustion, in addition to achieving an efficient utilization of lignite, it can also alleviate the local disposal pressure. However, there is currently little research on the blending of lignite with sediment. Through experiments on the ash melting characteristics, the deformation, softening, hemisphere, and flow temperature of ash at a 5%−15% mixing ratio were determined, and the variation law of ash melting point was derived. The mineral composition, oxide, and elemental composition were obtained through XRD, XRF, and SEM-EDS detection and analysis. The crystal structure and mineral composition in the ash were confirmed, and a ternary phase diagram was constructed for thermochemical calculations. The results show that when 5% sediment is mixed, the melting temperature of the ash decreases sharply, and then the downward trend tends to be gentle. The acid-base ratio and silicon aluminum ratio are positively correlated with the downward trend. The oxides of Fe+2, Fe+3, and Ca+2 play a main role in reducing the melting point of the ash, and these oxides are prone to react with refractory minerals to form fluxing minerals such as anorthite and calcium iron pyroxene. During the low temperature stage, Ca oxides mainly promote melting, while during the high temperature stage, Fe oxides act.

The mine anchor cable, which is mainly made of multiple steel strands, has the advantages of bendability, strong breaking resistance, and low cost. It is widely used in the stability control of coal roadway surrounding rock, especially the roadway roof. The twist is one of the important parameters for making anchor cable, which is often ignored in coal mines because of the lack of understanding when selecting anchor cable. In order to explore whether the lay distance parameter has an influence on the tensile mechanical properties and anchoring effect of anchor cable, this paper combines theoretical analysis with laboratory tests to preliminarily clarify the influence of the lay distance parameter on the geometric deformation characteristics of anchor cable during tensile and clarify its influence mechanism on the anchorage force of anchor cable. Based on the experimental data of anchor cable tension and anchorage drawing, a numerical simulation model was constructed, compared with underground test results, and the relationship between the twist distance and the ultimate load and the maximum anchorage force was obtained, and the optimal twist distance which could give full play to the tensile mechanical properties and anchorage effect of cable was obtained. The results show that when the anchor cable is stretched, the twist distance has a negative correlation with elongation and a positive correlation with tensile limit load in a certain range. There is a certain geometric matching relationship between cable and anchorage agent interface. When the twist is reduced to 13 times its nominal diameter, the maximum anchorage force increases with the decrease of the twist. Considering the ultimate tensile load and maximum anchorage force of anchor cable, it is found that the best twist range which can give full play to the tensile mechanical properties and anchorage effect of anchor cable is 13−14 times the nominal diameter. The research results increase the understanding of the influence of anchor cable twist on its tensile mechanical properties, clarify the understanding of its anchorage mechanism, and provide a reference and theoretical support for the production of anchor cables and the selection of anchor cables in coal mines.

As a technical measure to enhance the support effect of bolts (cable bolts) on weak surrounding rock roadway in coal mine, the borehole reaming has played an important role in improving the quality and safety of active support for weak surrounding rock of coal mine roadway. However, the reaming construction also significantly increases the size of the boreholes at the reaming location. This leads to problems such as the curing and filling effect of the resin in the borehole area reamed is not ideal when the construction is carried out in accordance with the conventional resin anchoring construction method of the bolt, which is obviously not conducive to the full play of the anchoring performance of the borehole reaming. In order to clarify the anchoring problem and its influence in the reaming area of the borehole and find an effective solution to ensure the anchoring performance of the bolts (cable bolts) under the reaming condition of the borehole, a systematic study was carried out by combining numerical simulation and laboratory experiments. The results show that the bending (curving) of the resin cartridges into the reaming area during construction process, which makes it impossible for the cable bolt to effectively mix and break resin cartridges, and the increase of the volume of the borehole at the reaming position makes the resin unable to fill effectively, they are the main reasons for the anchoring problems in the reaming area. The simulation results of cable bolt pull-out show that the anchoring defects in the reaming area have a great impact on the anchoring performance of the cable bolt and the failure mode of the anchoring system. In order to improve the anchoring effect of the reaming area, this paper proposes a method to guarantee the anchoring effect of the reaming area at the borehole bottom, and the effectiveness of the method is verified by experiments. The experimental results show that this method can effectively ensure the anchoring effect of the reaming area at the bottom of the borehole in weak surrounding rock, and enhance anchoring performance of the cable bolt. This study effectively solves the anchoring problem in the reaming area of the borehole, which is helpful to give full play to the high strength support ability of the cable bolt under the condition of weak surrounding rock in the coal mine, and provides a technical way to ensure the support effect of the cable bolt in weak surrounding rock.

The sublevel caving method has been widely used in the mines for mining medium-thick and steeply inclined orebodies, but the problem of ore loss and dilution still exists during the mining process and has yet to be fundamentally solved. In order to realize the green mining with the coordination of resources and environment, an insert drawing technology is proposed to address this issue with the medium-thick and steeply inclined orebody as the research object based on the structural principles of the insert within the silo. The influencing factors mainly considered in this paper are the orebody dip angle, thickness, and sublevel height. Eighteen experiments of the insert drawing with the conventional cut-off grade drawing with respect to these three factors were designed to investigated the impacts of these three factors on ore loss and dilution. The experimental results indicate that the ore recovery rate of the insert drawing technology is higher than that of the conventional cut-off grade drawing in mining ore bodies of different thicknesses and dip angles. In conditions of the same mixing rate of the waste rock, the ore recovery rate of the insert drawing technology is 69.09% to 82.9%, which is higher than that of the conventional cut-off grade drawing by 12.66% to 30.88%. Furthermore, the ore recovery ratio increases with the increasing the orebody dip angle when it is between 60° and 85°. On the other hand, the ore recovery rate of the insert drawing technology is higher than that of the conventional cut-off grade drawing in mining ore bodies when the orebody thickness ranges from 6 m to 10 m. Additionally, when it is between 10 m and 14 m, the ore recovery ratio increases with the increasing the sublevel height. Meanwhile, the mechanism of the insert drawing technology is studied. By setting up the insert structure and changing the opening and closing sequence of the clapboard in the quarry, the ore-rock flow path is changed, the ore flow range and flow rate is increased, and the ore-rock contact is controlled, thus ore loss and depletion is reduced. Research demonstrations that the insert drawing technology is superior to the conventional cut-off grade drawing, enrich and improve the issue of ore loss and dilution in an expict manner. This technology provides valuable technical support for mining medium-thick, steeply inclined orebodies.

Accelerating the exploration and development of deep ( > 1 000 m)coalbed methane (CBM) resources is an important way for the large-scale development of CBM and an important development direction in recent years. Guizhou Province is rich in CBM resources, with a large proportion of deep CBM resources. However, up to now, the geological research and exploration of deep CBM resources have not been carried out. Based on the geological background of CBM in Guizhou, this paper analyzes the geological characteristics and resource potential of deep CBM in Guizhou Province using a large number of CBM well test data. The research results show that the deep CBM resources in Guizhou are mainly distributed in many syncline units of the Liupanshui, North Guizhou and Zhina coalfields. Sedimentary differentiation and structural zoning lead to regional differences in the geological conditions of deep CBM reservoirs. The Liupanshui coalfield is characterized by “obvious overpressure, low temperature and high stress”, the Zhina coalfield is characterized by “overpressure, high temperature and low stress”, and the northern Guizhou coalfield is characterized by “overpressure, high temperature and high stress”. The permeability of deep CBM reservoir is low, and the permeability of 1 000 m deep will be generally lower than 0.1×10−15 m2. The CBM content of the coal reservoir is relatively high. The average CBM content of the middle-rank coal reservoir represented by the Liupanshui coalfield is 10.03 m3/t, and the average CBM content of the high-rank coal reservoir represented by the Zhina and Qianbei coalfields is 14.51 m3/t, and the deep supersaturation phenomenon is more obvious at 400 m. Based on the prediction model of free gas and adsorbed gas, considering the change of coal rack, it is predicted that the overall gas content in the deep part will further increase, and the supersaturation phenomenon will be more obvious, and the proportion of free gas will increase. At about 2000 m, the proportion of free gas will generally reach 10%−25%, and the proportion of free gas in medium-rank coal is higher than that in high-rank coal. On this basis, the geological resources of CBM in the key synclines of Guizhou Province with a depth of more than 2000 m are calculated. Based on the calculation results, the geological resources of CBM in Guizhou Province is 3.85 trillion m3, of which the geological resources of CBM in the depth of 1000 m reach 1.90 trillion m3, and the deep CBM resources in the Liupanshui and northern Guizhou coalfields account for a large proportion. Considering the scale and abundance of resources comprehensively, the development sequence is proposed. The Panguan-Tucheng-Zhaozihe-Jiupu'an syncline and the Gemudi syncline are the preferred development units. The above synclines are large gas fields with high abundance.

To solve the problem of long melting time of pore ice in coal seams frozen by liquid CO2, a technology of cold and hot cycling impact on coal seam for penetration enhancement was proposed using liquid CO2 high-temperature steam. This paper used the CT scanning testing technology to analyze the three-dimensional pore structure parameters and degradation mechanism of anthracite under cold and hot cycling impact. The research results indicated that: ① the three-dimensional pores of the coal under the cold and hot cycle impact of liquid CO2 high-temperature steam continued to extend, gradually forming through cracks. The number, surface area, volume, and maximum slice porosity of the three-dimensional pores were all related to the index of cold and hot cycle impact times; ② According to the Hodott pore classification method and the equivalent diameter calculation formula, it was found that in the early stage of cold and hot cycling impact, the proportion of seepage pore volume increased, and the three-dimensional pore degradation manifested as crack penetration. In the later stage of cold and hot cycling impact, the proportion of adsorption pore volume increased, and the three-dimensional pore degradation manifested as the generation of large number of new pores inside the coal. Further analysis shows that: ① the Fractal dimension of seepage pore radius of coal body impacted by liquid CO2 high temperature steam cold and hot cycle increased, the fractal characteristics of pores increased, the surface roughness increased, and the thermal storage performance decreased; ② The lg r in the pore radius classification model increased with the increase of the number of cold and hot cyclic impacts, indicating a significant expansion of pore size degradation; ③ Based on the characteristics of pore mechanical damage in coal under cold and hot cycling impact, a three-dimensional pore damage model of coal under liquid CO2 high-temperature steam cold and hot cycling impact was summarized; ④ The projection method was used to obtain the slice damage rate and define the three-dimensional pore damage amount of coal under the cold and hot cycle impact of liquid CO2 high-temperature water vapor. When subjected to 12 cycles of cold and hot impact, the three-dimensional pore damage was 48.55.

The topic of zonal fracture in deep surrounding rock roadway under high ground stress is a challenging and widely researched area in geotechnical engineering, with significant implications for the safety of deep engineering project. When the material yield damage occurs, there is a certain dissipation of energy, and as the dissipation proceeds, the material structure also produces some corresponding changes to form a new organizational structure, the process is similar to the self-organization process on the concordance, at this time the traditional elastic-plastic mechanics is not very useful, need to use the physical theory. Deep tunnel surrounding rock under high ground stress, when its deformation exceeds the elastic limit, will also has a similar dissipation structure phenomenon. The surrounding rock structure needs to go through a self-organization process to form a new dissipative structure, and this process is similar to the phenomenon of progressive phase change in physics. This paper explores the deformation and failure process of the surrounding rock in deep roadway, which is characterized as a gradual phase transition from solid to fluid. The study analyzes various zonal fracturing phenomena in field scale, laboratory scale, and simulation tests, and develops a phase transition theoretical model to approximate the nonlinear higher order control equation using Poincare-analytic parametric regression method. The sensitivity of each parameter in the approximate solution is also analyzed. Finally, the study validates the theoretical model by comparing the calculated results with the on-site measured data of zonal fracturing in a 700 m deep horizontal roadway in a metal mine.

As an important component of intelligent mine construction, the underground intelligent separation of coal and gangue can effectively improve the green utilization of mine resources. At present, the visible light image recognition technology for the identification of coal-gangue mixture in dark and humid underground environment remains to be improved. Based on the thermal infrared imaging technology and improved YOLOv5 algorithm model, this paper proposed a thermal image identification method for the coal-gangue mixed situation under dark and wet conditions. The neck part of the YOLOv5 model was changed to Bidirectional Feature Pyramid Network (BiFPN) structure, and the identification efficiency of coal-gangue was improved through multi-level feature fusion. The CIOU function was used as the loss function to improve the accuracy of coal-gangue detection. An experimental platform for the thermal image acquisition of coal-gangue mixture was constructed to simulate the low illumination and high humidity environment in underground confined space. The contrast enhancement and edge enhancement preprocessing of the thermal image collected by the infrared camera were performed by CLAHE and LAPLACE operators. The results of thermal image identification of coal gangue mixture were systematically analyzed from different data sets, different improved modules and different algorithm models, and the influence of humidity change on the accuracy of coal-gangue identification under dark and wet conditions was explored. The results show that the average accuracy of the preprocessed image is 1.7% higher than that of the original image, and the F-Measure value is increased by 6.9%. The average accuracy mean and F-Measure of the improved YOLOv5 model reaches 80.2% and 84.6%, which are higher than 74.6% and 79.7% of the classical model, which can effectively improve the detection accuracy of coal gangue thermal image. The relative humidity of the environment is positively correlated with the recognition accuracy, and negatively correlated after the humidity reaches a certain threshold. It is proposed that the thermal image can accurately identify the coal-gangue mixture in the dark and humid closed environment, which provides a scientific basis for the accurate identification of the coal-gangue mixed situation under the dark and wet conditions.

The reservoir of deep hot dry rock (HDR) geothermal energy is not intact rock mass, which includes a large number of fractures induced by geological tectonic movement. The tectonic fractures are subsequently filled by hydrothermal fluid. This kind of reservoir is so-called fracture-filled reservoir. To guide deep hot dry rock geothermal mining, this paper used a 600 ℃ high-temperature and high-pressure rock mass triaxial testing machine independently developed by the Taiyuan University of Technology to study the thermal and mechanical characteristics under high temperature (500 ℃) and high pressure (20 MPa confining pressure) of four types of granite from the Luya Mountain, Shanxi, China, including parent rock (type I granite), hydrothermal fluid backfill (type II granite), cementation interface between the backfill and the parent rock laterally positioned through the specimen (type III granite), and cementation interface between the backfill and the parent rock longitudinally positioned through the specimen (type IV granite). The research shows that the thermal expansion coefficient of four types of granite can be divided into three stages with the increase of temperature: the slow fluctuation stage at low temperature, the rapid increase stage at low and medium temperature, and the rapid decrease stage at medium and high temperature. The elastic modulus of four types of granite increases slowly and then decreases rapidly with the increase of temperature. The dissolution pore structure and the presence of minerals with low bonding strength lead to the lowest elastic modulus of hydrothermal fluid backfill. In addition, the critical temperature of the closure of pre-existing fractures in the fracture-filled granite is about 200 ℃. The critical temperature for the backfill near the cementation interface to restore the weak-plane structure characteristics is about 250 ℃. Finally, the failure modes of four types of granite under high temperature and high pressure are obtained. The coarse grain boundary of the parent rock, the dissolution pores of the hydrothermal fluid backfill and the cementation interface in the fracture-filled granite are very likely to form a large-scale efficient water channel during the reservoir construction by hydraulic fracturing, which provides a new idea for the theory and technology of reservoir construction for HDR geothermal exploitation.

To investigate the evolution of coal permeability during the process of gas pressure change, four different forms of permeability models were derived based on the correlation between mesoscale parameters of coal representative elementary volume (REV) and strain-related characteristics. The reliability of the models was verified using experimental data, and the variation law of strain caused by effective stress and adsorption strain was analyzed and compared with classical permeability models (P-M model, S-D model, Connell model). The sensitivity of model parameters was discussed, the relationship between REV mesoscale parameters and fracture porosity and permeability was clarified, and the influence mechanism of adsorption strain coefficient was analyzed. Furthermore, the extreme values of permeability of major coal mines in China were studied. Results show that for the four permeability models derived in this paper, the REV volume strain satisfies a linear relationship with its fracture volume strain, and the correlation coefficient is the initial fracture porosity. The bulk modulus and adsorption strain coefficient control the influence of effective stress and adsorption strain on permeability, respectively. Under three different experimental conditions of constant confining pressure, constant pore pressure, and constant differential pressure, the four permeability models have shown a better matching effect on the experimental data compared with the classical permeability models. However, compared with single-parameter fitting, the parameter error in the double-parameter fitting (bulk modulus and adsorption strain coefficient) is larger. From the sensitivity analysis of parameters, it is observed that when the parameters change within 10%, the predicted permeability deviates significantly from the true value. Therefore, for the double or multiple-parameter fitting of permeability models, the parameter fitting errors could lead to serious distortion of the predicted permeability results. Taking the experimental data of coal samples from the Qinshui Basin as an example, the mesoscopic scale parameters a0 and b0 of REV were calculated to range from 1.73 to 46.31 μm and from 0.06 to 0.49 μm, respectively. Under constant confining pressure and constant differential pressure conditions, the adsorption strain coefficient was related to differential pressure, gas types, and initial fracture porosity. Furthermore, the extreme values of CO2 gas and CH4 gas in major coal mines in China are within the ranges of 0.94−5.33 MPa and 1.06−6.94 MPa, respectively.

Energy security and the “dual carbon” goals are impacting the global energy industry and supply chains, presenting some urgent needs for the secure, efficient, and green low-carbon transformation of energy and power systems in China. To ensure energy security, the coal-fired power plant will remain an important support for electricity supply security and the integration of renewable energy for a considerable period into the future in China. To achieve carbon neutrality, the energy system is gradually shifting from primarily relying on fossil fuels to primarily relying on renewable energy. However, the intermittency, randomness, and volatility of renewable energy make power system regulation more challenging, highlighting the issues of system balance and security. In this context, the zero-carbon fuels such as ammonia play an indispensable role in dealing with the intermittency of renewable energy. They can serve as carriers for long-term and large-scale energy storage to facilitate the large-scale integration of renewable energy and can also be flexibly used directly in power equipment such as boilers to replace fossil fuels. However, due to the differences in physical and chemical properties between zero-carbon fuels and fossil fuels, some challenges arise in the widespread utilization of ammonia fuel, such as poor flame stability and the generation of nitrogen oxides during combustion. Therefore, based on the feasibility, economy and necessity of ammoniac-coal co-combustion, this paper comprehensively reviews the chemical reaction kinetics, combustion characteristics (ignition, steady combustion) and pollutants characteristics (NOx, fly ash particles and soot) of ammoniac-coal co-combustion, and discusses the scaling laws of burner based on the dimensionless number. The efficient and stable combustion control strategy of existing industrial grade ammonia-coal burners is discussed in detail. The C—N fuel separation, air staged and their joint control technology can effectively reduce NOx emissions. In the future, artificial intelligence, big data and digital twin and other information technologies are integrated. It is expected to provide a scientific support and path reference for the research and development of the next generation of new green power generation system oriented to the dual carbon strategy from the source.

Boundary identification of field sources is an indispensable task for interpreting field data. Initially, people used the distribution characteristics of data to obtain boundary information of field sources, making it difficult to identify weak anomalies amidst strong background anomalies. To address this issue, automatic control filters based on a certain window size were employed to identify the distribution of field sources. However, this method's results heavily relied on the window size and were not well applicable to complex anomalies. In recent years, features reflecting the boundary information of field sources have mainly been derived from the derivatives of scalar field data. Then, the correspondence between imaging results and boundaries is utilized to identify the horizontal boundaries of field sources. Specifically, extreme values of magnetic anomaly horizontal derivatives and zero values of vertical derivatives correspond to geological body boundaries. Existing boundary identification methods mainly utilize a balanced boundary identification filter composed of the ratio of first-order horizontal and vertical derivatives to delineate the positions of geological bodies, but the method has lower resolution and generality. Therefore, this paper proposes combining boundary detection filters based on ratios of derivatives of different orders with multiscale unsupervised deep learning. This approach utilizes different orders of derivative ratios to obtain higher-resolution edge imaging results. Additionally, a combination of Deep Image Prior (DIP) and Generative Adversarial Network-None Local (GAN-NL) networks for multiscale unsupervised deep learning is established to determine the horizontal position of sources based on extreme values of edge imaging results. The multiscale DIP network is used to identify the source position, and a self-attention mechanism neural network is added to the DIP network to enhance its learning ability, which can remove noise without requiring a large amount of data label.

In the context of “zero discharge” of mine water and the reverse distribution of coal and water resources in the western mining areas, the direct discharge of high-salinity mine water without proper treatment not only causes immeasurable damage to the local ecological environment, but also leads to serious water resource waste, ultimately constraining the green development of coal industry and the development of ecological civilization. The traditional zero discharge technology for high-salinity wastewater mainly relies on evaporation and crystallization to transform inorganic salts from a solution state to a crystalline state for recovery. From an economic perspective, this technology faces issues such as high investment, high operating costs, and low added value of inorganic salts. Based on this, this paper takes the mine water from a western mine as the raw water, aiming to achieve the resource utilization and desalination of mine water through the membrane integration technology, and focuses on exploring the influence of different operating conditions (operating voltage, feed solution concentration, temperature, acidity and alkalinity, current density, etc.) on the desalination performance of electrodialysis and the acid-base performance of bipolar membrane electrodialysis. Then, based on the experimental data and an economic evaluation model, the economic feasibility is explored, aiming to explore the membrane integration technology suitable for the treatment of high-salinity mine water in the western mining areas, and provide some new research ideas for the development of green resource utilization processes for high-salinity mine water. Through the exploration of the electrodialysis-bipolar membrane electrodialysis experimental process, it is found that the feed solution concentration of the bipolar membrane system should not exceed 80 g/L, the appropriate operating voltage is 18 V, the suitable feed solution temperature is 25 ℃, the feed solution pH should be kept neutral, and constant voltage operation is more suitable. In addition, it is confirmed that the membrane integration system centered on bipolar membrane electrodialysis can achieve the green resource utilization of high-salinity mine water. Taking the total salt content of the electrodialysis system feed solution as an example (20 g/L), the overall net profit is ￥18604299 per year, and it has a significant carbon dioxide emission reduction effect when coupled with a photovoltaic power supply system, with a carbon dioxide emission reduction of over 3162 tons per year, demonstrating good economic and social benefits.

Large-scale open-pit coal mining will cause ecological problems such as land excavation and occupation, groundwater drainage, soil erosion, vegetation destruction, air pollution, and regional landscape damage. The selection of existing open-pit coal mine ecological restoration technologies is relatively limited, and there is a lack of systematic research on ecological total factors. In this paper, the concept of “damage reduction mining and systematic restoration” was proposed, and the connotation and technical approach of ecological mining of open-pit coal mine were expounded. The key scientific issues and basic theoretical framework of ecological mining of open-pit coal were proposed. Then the whole life cycle ecological impairment mining technology and the coordination system restoration technology of ecological elements (water, soil, vegetation, landscape) of “pre-harvest ecological design-mining during mining loss-postharvest ecological restoration”were developed. At last, the theory and technical system of open-pit coal mine ecological mining was established, and a generalizable and replicable open-pit mine ecological mining mode was formed. The results show that in the semi-arid area, the ecological restoration technology has significant effects. The area of land excavation and occupation loss is reduced by 60003 m2 every year, the ecological restoration period of the dump site is advanced by more than one year, and the vegetation coverage rate increases by 41.78% compared with the background value in the semi-arid area of the Shengli open-pit mine demonstration area. A surface reservoir with a water storage capacity of 400 000 cubic meters has been built, and the seasonal and graded utilization of mine water has been realized. In the extremely cold area of Baorixiler, the area occupied by land excavation is reduced by 106 672 m2 per year, the number of new species has increased from 14 to 21, the soil moisture content has increased by 10%, the annual soil erosion rate has decreased by 59.6%, and the vegetation coverage rate has increased by 37.96% compared with the background value in the demonstration area of the Baorixiler open-pit mine. An open-pit coal mine underground reservoir with a water storage capacity of 1.22 million square meters has been built, realizing the “winter storage and summer use” of mine water.

China is the world’s largest CO2 emitter and coal consumer, and its coal dominated energy structure is difficult to be changed in the short term. In the context of carbon peaking and carbon neutrality, the capture and storage or conversion of carbon dioxide into renewable fuels and chemicals can reduce dependence on fossil fuels and at the same time reduce CO2 emissions, providing key technical support for the green transition of coal-fired power plants and energy chemicals. Electrocatalysis and microbial conversion are important ways to produce renewable fuels and chemicals from carbon dioxide. The reaction rate of electrocatalytic reduction of CO2 is high, but the products are mostly limited to C1 and C2 products. Microbial CO2 fixation has the advantages of high selectivity and variety of products. However, the low electron transfer and energy supply lead to a long reaction period in the microbial CO2 fixation. Integration of electrocatalysis and microbial conversion can play their advantages to efficiently produce the value-added multi-carbon products. In this paper, firstly, the reaction principles, typical products of electrocatalysis and microbial CO2 fixation under a single technical route were introduced respectively. The catalyst and reactor of electrocatalytic CO2 reduction were discussed, and the microbial species and biological metabolic pathways of microbial fixation of CO2 were summarized. Secondly, two methods of the integration of electrocatalysis and microbial conversion was reviewed, and the system structure, working principle, electrode materials and value-added products were analyzed. Finally, the technology readiness level of different coupling methods was compared, and the future prospects were highlighted from four aspects: the catalysts for electrocatalytic CO2 reduction, the engineered microbial strains, the design and integration of coupling systems and the linkage between academic research and industry.

Coal fine intrusion into hydraulic propped fractures of coal seam easily leads to the blockage of the fracture, resulting in the decrease of the conductivity and the reduction of coal reservoir permeability, which seriously affects the stable discharge and production of coalbed methane well. In this paper, the permeability dynamic evolution models of coal fine intrusion into propped fractures were established before the shutdown and after the restart of coalbed methane well, and the experiments of coal fine intrusion into propped fracture under continuous and intermittent flow conditions were carried out by using the coal-rock conductivity test system, which verified the correctness of the models and studied the influence of coalbed methane well stoppage and drainage velocity on the permeability spatial and temporal evolution laws. The results indicate that with the increase of coal fine migration time, the permeability of propped fracture decreases slowly after a sudden drop, and along the direction of coal fine migration, the spatial pore loss rate of propped fracture decreases gradually, resulting in the permeability of fracture decreases along the direction of coal fine migration. With the continuous coal fine intrusion into propped fracture, the propped fracture pore loss rate after the shut-in and restart of coalbed methane wells is larger than that before the shutdown, and the permeability cannot be restored to the level before the shutdown. The slower the flow rate of drainage, the slower the permeability attenuation rate of coal fine intrusion into propped fracture, and the higher the permeability. During the coal fine invasion into proppant fracture at the low drainage flow rate, the fracture permeability is more sensitive to the flow rate change, and the less damage to the propped fracture permeability caused by the well shutdown. In the process of coal fine intrusion, the larger the deposition coefficient of coal fine is, the smaller the proximal fracture permeability and the larger the distal fracture permeability. The larger the diffusion coefficient is, the smaller the distal fracture permeability of the propped fracture is. The permeability of the proximal fracture is very little affected by the diffusion coefficient, and the damage to the proximal fracture permeability is more serious. In the process of coal fine intrusion, the proximal fracture permeability declines faster, while the distal fracture permeability declines slowly. The deposition coefficient changes have a significant influence on the proximal fracture permeability, while the diffusion coefficient changes have a more significant influence on the distal fracture permeability.

Chemical inhibition is one of the important measures for the prevention and control of coal spontaneous combustion. This paper proposed a quasi-ionic liquid inhibition method based on deep eutectic solvents (DES). First, seven kinds of room temperature deep eutectic solvents were prepared and screened using a heating method. The changes in the functional groups and thermodynamic characteristics of different DES-treated coal samples were analyzed. On this basis, the density functional theory was utilized to analyze the differences in the modification of coal's physicochemical properties by the hydrogen bond strength in the DES, and the inhibition mechanism of deep eutectic solvents and their optimal hydrogen bond strength were deduced. The results showed that after the DES treatment, the hydrogen bond network in coal was disrupted and rearranged. The relative abundance of aliphatic and aromatic hydrocarbons increased by 10%−37%, the content of aliphatic side chains decreased by 9.38%−20.65%, the relative abundance of oxygen-containing functional groups (C=O and C—O) decreased by 22.88%−56.94%, and free low-molecular compound and minerals were leached out. After the DES treatment, the mass loss during the evaporation and desorption stage of coal and the oxygen uptake during the oxygen absorption stage decreased. The heat release during the low temperature oxidation stage and the thermal decomposition stage was reduced by 8.94%−77.51% and 5.40%−26.20%, respectively. The stronger the electronegativity of the hydrogen bond acceptor site in the HBA, the greater the hydrogen bond strength formed between HBA and HBD. The hydrogen bond strength in the DES was positively correlated with the degree of destruction of the hydrogen bond network in coal, and was locally correlated with the oxygen uptake during the oxygen absorption stage, the heat release during low temperature oxidation, and the mineral removal rate. The DES weakened the low-temperature oxidation reactivity of coal by dissolving its active components, and increased the bond dissociation enthalpy of coal by promoting the rearrangement of hydrogen bonds into more thermally stable [OH]4 and OH—N hydrogen bonds. However, the excessive strong hydrogen bond strength would inhibit the removal and dissolution of active side chains. Therefore, the hydrogen bond strength of deep eutectic solvents used to inhibit coal spontaneous combustion should be controlled between 69.45 kJ/mol and 160.00 kJ/mol.