The characteristics of surface subsidence under the condition of repeated mining in weakly cemented strata are of great significance to the safe and efficient mining and ecological restoration of coal resources in weakly cemented mining areas in western China. Theoretical analysis, similar simulation, numerical simulation and field monitoring are used to study the migration law of overlying strata and surface subsidence model under repeated mining conditions in weakly cemented strata, and the model is applied in engineering. The bulking characteristics of weakly cemented rock and the influence mechanism of repeated mining overburden strata movement on surface subsidence are discussed through theoretical analysis. The ‘maximum surface subsidence model under the condition of repeated mining in weakly cemented strata’ is established. There is a linear relationship between the bulking coefficient of weakly cemented rock, the mining thickness of lower coal and the maximum surface subsidence of weakly cemented strata. Through similar simulation and numerical simulation, the characteristics of repeated mining overburden and surface subsidence in weakly cemented strata are analyzed. The research results show that the development law of the separation height of the initial mining and repeated mining of the weakly cemented strata is basically the same, and both show a step-like rise. The surface subsidence curve of repeated mining is asymmetrically distributed, and the maximum subsidence value is biased towards the side of open cut. The maximum development height of overlying strata, the maximum surface subsidence value and the surface subsidence coefficient after initial mining and repeated mining are given. The established maximum surface subsidence model is used to predict the maximum surface subsidence value on site. The predicted value of the maximum surface subsidence model is similar to the measured value on site during the mining process of the working face, which verifies the rationality of the ' maximum surface subsidence model under the condition of repeated mining of weakly cemented strata '. At the same time, the predicted value of the maximum surface subsidence after the mining of the working face can provide a reference for the actual work on site.

The surface subsidence in the thick loose layer and thin bedrock mining area in the east of China has the characteristics of large subsidence value, wide movement range and long settling time. Taking a coal mine in Southern Shandong Mining Area as an example,this paper discusses the variation rules of coal seam mining surface deformation parameters under different loose layer and bedrock thickness ratio conditions, on the basis of field measurements, using FLAC^3D, and establishes a surface deformation calculation model for coal seam mining under the conditions of different loose layer bedrock thickness ratios (0.25−5.00), studies the characteristics of surface deformation, analyzed the influence of ratio of loose layer thickness to bedrock thickness on the parameters of probability integral method, and quantitatively analyzed and discussed the conditions of thick loose layer and thin bedrock from the perspective of mining subsidence. Research shows: ①Under the same mining thickness conditions,when the ratio of loose layer thickness to bedrock thickness increases, the surface deformation amount obviously increases first and then decrease, when the ratio reaches a certain limit, the ground surface deformation tends to be stabilized; ②The subsidence coefficient, the horizontal movement coefficient and the tangent of the main influence angle all increase first and then decreases, and the inflection point is 1.75,1.25 and 1.25, respectively; ③The proportion of loose bed thickness in the average mining depth has great influence on the angle of draw and boundary angle. The boundary angle and the angle of draw gradually decrease with the increase of the ratio. Based on the above research, it is proposed that the ratio of 1.25−1.75 is the critical value for the condition of thick loose bedding and thin bedrock, which provides a theoretical basis and technical reference for the prediction of surface deformation and the prevention and control of mining subsidence disasters in typical thick loose layer thin bedrock mining areas in eastern China.

The existing rockburst risk assessment methods generally belong to static assessment method which normally depends on the geological and mining conditions that are revealed prior to mining. There is commonly a certain gap between the assessment results and the real situation. How to combine with the monitoring data in the mining process to get more realistic evaluation results is a problem that needs to be further solved. To this end, this work proposes a static-dynamic coupling rockburst risk assessment method taking into account the geological and mining conditions as well as the monitoring data, and the method has been being applied in typical panels in near-vertical coal seams. Firstly, a static evaluation method used before mining based on the improved comprehensive index method is proposed. The evaluation indicators contained in the comprehensive index method are linearly normalized to obtain the single indicator risk index. The AHP method is used to assign weights to each evaluation indicator, and the weighted summation of all indicator risk indexes is calculated to obtain the risk indexes determined by geological factors and mining technology factors, respectively. Then the weighted mean of the two risk indexes is used as the static evaluation risk index. Secondly, a dynamic evaluation method used during mining by utilizing the monitoring data is constructed. According to the characteristics of microseismic monitoring and borehole stress monitoring and their relationship with rockburst risk, the dynamic evaluation indicators are constructed based on the microseismic energy density and borehole stress variation. The evaluation indicators are linearly normalized to obtain two evaluation indexes. The weighted mean of the two indexes is used as the dynamic evaluation risk index. Finally, the two proposed methods are combined to get a static-dynamic coupling evaluation model. The coupling evaluation risk index is obtained by weighted average of the static evaluation risk index and the dynamic evaluation risk index, and then the risk grade and risk area are determined. The method is applied in +450B3+6 panel of Wudong Coal Mine. Results show that the static evaluation method demarcates 4 medium risk areas and 1 weak risk area before the mining of the panel, the dynamic evaluation method determines that the rock pillar side has high risk level in the mining process of the panel, and the static dynamic coupling evaluation re-evaluates the weak risk area of the static evaluation to the medium risk area. By investigating the monitoring data of support pressure, the numerical simulation results and the rockburst occurrence on site during the mining process of the panel, the evaluation results are verified, and it is found that the static and dynamic coupling evaluation results are more consistent with the actual situation. This work provides a new method and a new idea for the risk assessment of rock burst.

In order to scientifically evaluate the impact risk of steeply inclined extra-thick coal seam in folded area and provide theoretical guidance for the prevention and control of rock burst, a numerical model including folds is established in this paper based on the prevention and control of rock burst in south mining area of Wudong Coal Mine. With the help of multiple linear regression and CASRock engineering software, the back analysis of ground stress field of steeply-inclined extra-thick coal seam in folded area of Wudong Mine is carried out. Taking B1+2 coal seam as the research object, the stress data in coal seam, roof and floor are extracted, the stress-cover depth variation curve is plotted, the distribution characteristics of pre-mining stress field are explored, and the risk assessment index related to pre-mining stress is determined. According to the back analysis data of in-situ stress and previous research results, the evaluation indexes of burst risk are determined from the aspects of geological factors and mining conditions. The static weights of 7 geological factors and 5 mining conditions are obtained by Analytic Hierarchy Process. By substituting the static weight into the dynamic weight calculation formula and combining with the traditional comprehensive index method, the risk assessment of B1+2 panel at +500 m level in the south area of Wudong Mine is carried out. According to the rockburst risk classification table, the burst risk of this panel is medium, which is consistent with the conclusion of the geological report, and the rationality of the method was verified. This method is used to estimate the burst risk of coal seam with different depths. Control group is chosen, using the traditional comprehensive risk index method to evaluate the burst of the same area, the results show that the method to obtain the risk ratings were higher than the traditional methods, approach of this paper highlights the risk factors in the evaluation index, overcoming the other indicators evaluation error caused by the interference factors.

When the mining of the underlying working face of shallow and close seam passes under the overlying remnant coal pillar, it is easy to have an intensive mine pressure-induced dynamic disaster, resulting in personnel and equipment damage, which seriously threatens the safety of mine production. The characteristics induction, numerical simulation calculation, mechanical model analysis and other research methods are used to clarify the occurrence of the hazards of the overlying remnant coal pillars in the shallow and close seams, and reveal the disaster mechanism caused by intensive mining pressure. The research shows that the disaster mechanism of the intensive ground pressure caused by the overlying remnant coal pillar is that when the working face passes under the coal pillar, the coal pillar and the overlying bearing body are disturbed and suddenly lose stability, and the energy is transferred to the stope instantly, which is released in the form of kinetic energy, resulting in the intensive ground pressure-induced dynamic disaster. Based on the prevention and control idea of “collapsed rock support+weakening of key rock stratum+transfer of stress transmission path”, the prevention and control technology of weakening for front area using subsectional-hydraulic fracturing was proposed by modifying the coal pillar and bearing body migration space, weakening key rock stratum, uniformly distributing concentrated stress and transferring stress transmission path, and engineering tests are carried out at typical working faces. The engineering test results show that during the implementation of hydraulic fracturing, the peak value of pumping pressure reaches 23.4 MPa, the pressure changes generally in a “zigzag” shape, accompanied by a sudden drop of pressure for more than 60 times, and the artificial main fractures and micro fractures in the rock mass continue to develop alternately, effectively destroying the integrity of the rock mass; After treatment, the peak value and average value of periodic pressure decreased by 15.41% and 8.29% respectively, and the peak value and average dynamic load coefficient decreased by 17.39% and 11.88%, respectively. The maximum contraction of the shield cylinder was 50.00% and less than 0.4 m, and the maximum contraction of the gate road roof was 33.33%. The working face safely passed through the affected area of the overlying remnant coal pillar, and the advanced area weakening technology of subsectional- hydraulic fracturing can effectively prevent and control the intensive ground pressure disaster of the overlying remnant coal pillar in shallow and close seams.

Coal wall of large mining height face in steeply dipping coal seam has large free height, wide free movement space and poor self-stabilization balance, coal wall is not an isolated body in the face, it can form a load-bearing structure with the surrounding rock, supports and other mediators, and the mining behavior is closely linked. The dip angle effect can easily promote the dissimilation of the coal wall bearing environment, complicate its response behavior, increase the difficulty of coal wall and surrounding rock stability control, and restrict the safe and efficient production of the face. In order to solve the problem of coal wall stability control of large mining height face in steeply dipping coal seam, theoretical analysis and numerical calculation are comprehensively used for research. The stress in the plastic zone of large mining height face in steeply dipping coal seam increases exponentially, there is an asymmetric arch residual stress influence zone in the vicinity of the coal wall, the plastic zone breadth is dissimilated in different regions, and the  width from large to small is the upper, middle and lower part, and the distribution pattern is in the shape of stepped arch, coal in the plastic zone bears repeated pressure, and will be enhanced with the expansion of plastic zone. As the mining height increases, the residual abutment pressure near the coal wall decreases, the compressive strength, displacement value and disturbed range of the coal in front of the coal wall will increase. The stress and transport of the coal wall under the dip angle effect develop in a zonal manner, in which the stress distribution is lower> upper> middle, while for the displacement is middle> upper> lower. In addition, the working face inclination under the oblique angle will lead to the transformation of the coal wall instability mode, when the oblique angle is large, the dip angle of face is small, the compression component of abutment pressure is enhanced, and the external convex spalling mainly occurs. On the contrary, it’s the sliding instability under the coupling of mining stress and self weight. The comprehensive analysis shows that the coal wall mining behavior is regionally heterogeneous under the coupling effect of dip angle and mining height, and because the stress unloading and migration in the middle and upper part of the face are larger, therefore the two regions should be the key prevention and control areas for coal wall instability of large mining height face in steeply dipping panel.

The high-intensity mining of shallow-buried coal seams leads to the fracture of the bearing strata to form a combined bearing structure, which complicates the distribution of cracks in the overlying rock and causes serious damage to the surface. In order to study the relationship between the evolution law of the overburden fissures and the bearing structure of the bearing rock in the mining of the shallow coal seam group, and the working resistance value of the support to keep the bearing rock stable, the coal mining of Hanjiawan Coal Mine 2⁻² and 3⁻¹ in the Shenfu mining area in northern Shaanxi was studied. In the background, through field observation and similar simulation experiments, the evolution law of coal seam group mining cracks, the combined bearing structure of bearing rock layers and the relationship between the two were obtained. The mechanical model of combined bearing structure was established by theoretical calculation method, and the support work of the combined bearing rock layer to maintain stability was studied. resistance. The research shows that the evolution process of overlying fissures in coal seam mining can be divided into four stages: the upper coal seam mining rapid growth stage, the upper coal seam mining steady growth stage, the lower coal seam mining rapid growth stage, and the lower coal seam mining stable growth stage. This leads to different fissure evolution forms and subsidence characteristics on the surface. The surface of the “step rock beam” structure subsides in steps, and the surface of the “hinge rock beam” structure subsides continuously; The fractured structure of the bearing rock formation in the lower coal seam is obtained from the filling rate and mining height of the interlayer, and it is revealed that the fractured combined structure of the bearing rock formation in the shallow buried coal seam mining group is “step-hinged” structure, “hinged-hinged” structure, “hinged-hinged” structure. The combined form of the “step” structure and the “step-step” structure. Based on the fractured composite structure of the bearing rock, the mechanical model of the bearing rock bearing structure of the shallow buried coal seam group mining is established, and the calculation method of the working resistance of the bearing rock to maintain the stability of the support is obtained, and the field measurement results are verified.

In order to alleviate the shortage of underground aggregate sources and time cost of vibration and compaction during backfilling, a new type of high-porous low-cementitious waste backfilling material (HPLCM), which was composed of self-compacting slurry and loose packing waste with high porosity, was developed to achieve the purpose of low cementitious backfilling. Uniaxial compression tests were carried out on HPLCM in the laboratory, using orthogonal strength variables of cement slurry and waste aggregate, to study their failure strength characteristics and statistical laws. Considering the combined impact of solid waste and slurry strength, a generalized strength model of shear fracture was established based on the fracture statistical results. The coupled strength utilization ratio of solid waste aggregate and self-compacted slurry was defined, and the optimal ratio and cost of mix proportion of HPLCM were analyzed. The results indicate that the uniaxial compressive strength and failure mode of HPLCM are jointly controlled by the component strength of self-compacting cementitious slurry and solid waste aggregate. The strength of both components has a positive correlation with the strength of HPLCM, which is limited by the weaker component, and when one component grows stronger, the failure mode will be dominated by the other component. The uniaxial compressive test of HPLCM presents shear failure modes, including shear planes in single oblique and cross oblique patterns with an average angle of 55.4°. The density of loose packing aggregates can be reduced from 85% to 58% by using the proposed backfilling material, and the strength of cementitious slurry can be optimized within the optimal mixing range to maximize the utilization of filling material strength when the strength of in-situ solid waste aggregates is obtained. Thus, the compaction time of solid filling and the amount of single gangue can be reduced.

Water content is one of the critical factors affecting frost damage to rock masses in alpine regions. A dynamic disturbance load further complicates the issue. In this study, the effects of saturation and impact loading on the dynamic behavior of the frozen red sandstone were investigated using a low-temperature split Hopkinson pressure bar (LT-SHPB) experimental system. By combining low-field nuclear magnetic resonance (NMR) and scanning electron microscopy (SEM), the dynamic evolution of the microstructure of the frozen sandstone due to changes in saturation was investigated. The experimental results show that the increase in saturation reshapes the pore structure of the frozen sandstone and promotes the expansion of pores of different sizes during freezing, while the frozen samples at complete saturation are mainly developed with mesopore and macropore. The dynamic strength, elastic modulus and brittleness index of the frozen sandstone under impact loading, which are limited by the critical saturation S_rc, tend to increase and then decrease with saturation increase. In contrast, the ultimate deformation capacity of the frozen sandstone showed an opposite trend with saturation. With increasing impact loading, the dynamic strength, elastic modulus, and peak strain of the frozen sandstone gradually increase, showing an obvious strain-rate enhancement effect; while the brittleness index decreases by 8.1% at full saturation when the impact velocity increases from 4 m/s to 6 m/s, indicating that the dynamic damage mode develops from brittle to ductile. Moreover, the frozen samples changed from tensile damage to composite damage with increasing saturation and impact loading; the distribution of crushing masses remained closely related to their dynamic strength. Based on the experimental results, the mechanism of the effects of saturation variation on the dynamic mechanical behavior of frozen sandstone is discussed.

With the increase of the depth of the blast hole, the rock clamping effect at the bottom of the blast hole is enhanced, resulting in low rock breaking efficiency and blast hole utilization. The past continuous charging method can not solve the above problems. On this basis, this paper studies the rock roadway deep hole segmented charging cut blasting technology to improve the cut blasting efficiency. Using the smooth particle hydrodynamics-finite element method (SPH-FEM), a single-hole cut blasting model with different segmented charge structures was established, and the blasting speed of rock particles in the rock, the number of rock blasting and the characteristics of blasting cavity were analyzed in the blasting process under different models. The results show that different charge structures affect the damage range of the rock near the blast hole, and the damage area of the traditional continuous charge structure in the direction of the blast hole is larger than that of the segmented charge structure. In addition, the continuous charge structure makes the energy distribution of the explosive uneven because the explosive is concentrated at the bottom of the blast hole, resulting in poor blasting effect. The segmented charge structure can increase the number of rock fragments and optimize the blasting cavity, and the rock particles accelerate twice in the process of flying. The large or small proportion of the first segment charge obviously causes the unreasonable use of explosive energy and the poor effect of blasting cavity. Under the conditions of blast hole length, rock parameters and explosive performance set in the simulation, when the first stage charge ratio is 0.4, deep-hole rock tunnel excavation and blasting can make full use of explosive energy to achieve better cut blasting effect. The optimal subsection ratio obtained by numerical simulation was applied to the blasting construction of roadway excavation, and the delay initiation of two explosives in the cut hole was realized by using digital electronic detonator. The field test results show that the segmented charging can create good blasting effect and improve the utilization rate of blast holes in deep hole cut blasting.

It is easy to form a coupling effect between ground stress and gas, and cause the accident of coal and gas outburst dominated by ground stress during deep mining. In order to improve the accuracy of mine gas disaster prevention, it is urgent to deeply understand the influence of water intervention on the desorption characteristics of gas-containing coal under ground stress. A simulation test device was set up for the effect of water injection on the gas desorption characteristics of coal under overburden stress and water injection by applying overburden stress and injecting water at the same time to the experimental coal sample. Based on the experimental setup, the gas desorption data of coal samples from Guhanshan Mine (GHS) were tested at overburden stresses of 5 MPa, 10 MPa and 15 MPa, moisture content of 0%, 2%, 4% and 6%, and the same inflation amount. By analyzing the experimental data, the influence of overburden stress and water injection on the cumulative gas desorption amount, gas desorption rate, initial gas desorption rate influence coefficient and residual gas content of GHS coal samples was obtained. The result shown that the overburden stress effect increased the cumulative desorption amount and the initial gas desorption rate of the dried coal samples, which promoted gas desorption. With the intervention of water, the cumulative gas desorption amount and initial gas desorption rate of coal samples with large overburden stress became smaller, indicating that the moisture inhibited gas desorption, and the overburden stress effect transitioned from promoting to inhibiting gas desorption. Theoretical analysis shown that the piston effect of overburden promoted gas desorption of dried coal sample. As moisture intervention, it produced a strong capillary resistance in the pores and cracks of coal. With the increasing overburden stress, the coal sample was crushed and compacted, and the capillary resistance became larger as the pore fissures got smaller, resulting in a stronger inhibition of desorption. The experimental results have certain positive significance for an in-deep understanding of the mechanism of hydrodynamic measures to prevent coal and gas outburst.

Coal reservoirs with high gas content and low permeability seriously restrict the efficient production of coal and coalbed methane. It is necessary to fracture and enhance the permeability of coal reservoirs. Aerospace solid propellant deflagration can generate a large amount of high-energy gas to impact coal reservoirs, which can achieve the purpose of fracturing and enhancing permeability of coal reservoirs. To study the characteristics of aerospace solid propellant for fracturing coal, a solid propellant for fracturing and permeability enhancement of coal reservoir was firstly researched and developed based on the formula of civil aerospace solid propellant, was, and its performance, sensitivity, pressure and temperature resistance were tested. The aerospace solid propellant fracturing test was then carried out using simulated coal samples, and the borehole wall pressure and strain within the simulated coal samples were monitored during the test. Finally, the destruction characteristics of simulated coal samples were analyzed according to the test results. The results shown that the aerospace solid propellant had good performance, with the advantages of waterproof, pressure resistant, and no CO generation, which could be adapted to the underground environment of coal mine. During the test, the time curve of the borehole wall pressure shown the stages of rapid pressure rise, slow pressure rise, and nonlinear pressure drop, in which the rise time of the borehole wall pressure was about 18 ms. The peak pressure in the borehole was low and unevenly distributed. The peak pressure in the middle of the borehole was 118.1 MPa, and the peak pressure at the bottom of the borehole was 85.3 MPa. Stress wave generated in simulated coal sample during aerospace solid propellant fracturing was composed of compressive and tensile phases with low intensity, long duration and slow decay with distance. The aerospace solid propellant fracturing technology was dominated by the quasi-static action of high-energy gas, with high utilization of stress wave energy. The research results provide a reference for the application of aerospace solid propellant in the field of coalbed methane mining.

In order to grasp the influence of structural parameters of internal mixing air atomizing nozzles on the atomization characteristics and dust reduction efficiency, so as to obtain economical and reasonable nozzle structure parameters, the self-designed and developed spray dust reduction experimental platform and the orthogonal design method was used to carry out experiment on nozzle atomization characteristics and dust reduction efficiency under the combination of structural parameters. The experimental results shown that, with the diameter of the liquid cap injection hole increased, the nozzle water flow rate increased, while the air flow rate decreased continuously. Nozzle air flow increased with the number of liquid cap injection hole, whereas nozzle water flow was less affected by the number of liquid cap injection hole. When the diameter of the water injection hole gradually increased, the Sauter Mean Diameter (SMD) increased continuously. SMD with the increase of the number of air injection holes shown a change law of first decrease and then increase, and the minimum value was reached when the number of air injection holes was 4, where the atomization effect was the best. When the air cap outlet diameter was 2.0 mm and 2.5 mm, the nozzle droplet size was smaller. With the increase of the diameter of the water injection holes and the number of air injection holes of the liquid cap, the dust reduction efficiency of total dust and respirable dust both first increased and then decreased, and the best effect of the dust reduction was obtained in the diameter of water injection holes of 1.5 mm and the number of air injection holes of 4, respectively. With the diameter of the air cap outlet increased, the dust reduction efficiency of both total dust and respirable dust increased, but the increase of the dust reduction efficiency was smaller when the diameter of the air cap outlet was greater than 2.0 mm. Comprehensively considering the nozzle atomization characteristics and dust reduction efficiency, for the nozzle air cap, the outlet diameter should be 2.0 mm, for the nozzle liquid cap, it was reasonable to use a water injection hole diameter of 1.5 mm and the number of air injection holes to be 4, which can obtain the highest dust reduction efficiency. It is more reasonable to use the nozzles with the combination of above structure parameters for industrial applications, which can obtain smaller droplet size and higher dust reduction efficiency with lower air and water consumption.

Utilizing the adsorption characteristics of coal rock in the goaf to storage CO₂ not only reduces the cost of carbon capture and separation, but also prevents spontaneous combustion of coal left in goaf area. The effects of pore structure, mineral content and moisture content on the CO₂ adsorption characteristics of coal were investigated using adsorption experiments at ambient temperature and pressure, ASAP specific surface area and pore size analysis experiments. Then the quantitative relationship equations of factors affecting CO₂ adsorption in coal were fitted, and the importance weights of each influence was calculated by Random Forest algorithm. The results shown that, the pore size distribution of three coals from the mining area of Dananhu (DNH), Hegang (HG) and Tongxin (TX) were basically the same. The number of pores in the range of 0.5-0.7 nm and 0.8-0.9 nm was more, and that in the range of 0.7-0.8 nm was less. The number of micropores was the fundamental reason for the difference in CO₂ adsorption capacity of three coals. At ambient temperature and pressure, the saturated adsorption amount of CO₂ in coal increased with the increasing specific surface area, and decreased with the increasing mineral content and moisture content. The more the number of micropores of coal, the more significant the influence of mineral content and moisture content on the adsorption amount. After the coal reached the critical moisture content, the saturated CO₂ adsorption amount gradually tended to be stable because the water molecules hindered the flow channels of CO₂ molecules, resulting in the CO₂ molecules not being able to enter into the pores inside the coal. The specific surface area had the greatest influence on the adsorption amount, followed by the moisture content and pore volume, and the mineral content was the weakest. Specific surface area and moisture content had a combined importance weight of 75.1%, which was much higher than the other two factors. According to the fitting equation, the saturated adsorption amount of CO₂ in coal can be inferred by determining the specific surface area, mineral content and moisture content of coal, which provide a theoretical basis for CO₂ adsorption and storage by coal left in goaf area.

The gas reservoirs co-production in multi-pressure system is one of the important measures to improve the development efficiency of the superposed gas-bearing systems. However, the co-production effect is not ideal due to the special reservoir forming background. The mechanism of co-production and high-efficient development of the multi-pressure system has become an key scientific problem, which restricts the efficient exploration and development of superposed gas-bearing systems. This paper focuses on the gas reservoirs co-production in multi-pressure system, and divides the physical simulation types of co-production into two separate fields: coalbed methane and non coalbed methane. It clarifies the current research status of gas reservoirs co-production in multi-pressure system from the aspects of device functions and characteristics, understanding of co-production, and existing problems. Firstly, the large-scale physical simulation test device can effectively eliminate or weaken the problems of homogeneous single-type reservoir samples, single monitoring data means and single stress loading form caused by paralleling multiple core grippers to build the physical simulation model. The development direction of the physical simulation for co-production in multi-pressure system should be to achieve true three-dimensional heterogeneous complex in-situ stress state of large-scale heterogeneous multi-type reservoir samples. The characteristics of fluid pressure transmission between adjacent reservoirs, the inter-layer crossflow, the multi-phase natural gas symbiosis should be considered. On this basis, the sensitivity of co-production of multi-pressure system to reservoir physical properties was deeply summarized. The differences in inter-layer pressure difference, permeability, effective stress, water saturation and other factors may induce the fluid interference and reservoir gas production damage, and optimizing co-production style may be a way to reduce the fluid interference and reservoir gas production damage. In totally, the next research should focus on exploring the influence of the coupling effect of low porosity and low permeability, gas water two-phase flow, multiphase gas symbiosis and coexistence of multiple types of reservoirs on the dynamic evolution law of reservoir-wellbore flow field induced by co-production fluid interference, clarifying the reservoir damage and its mechanism of different phase fluid intrusions on the reservoir, and revealing the coupling flow characteristics of inter-layer crossflow and wellbore pipe flow considering the fluid interference effect.

The morphology of complex fracture network in hydraulic fracturing engineering in deep tight oil and gas reservoir is a crucial factor affecting oil and gas recovery, and it is necessary to accurately evaluate and optimize the fracture propagation behavior. Multistage fracturing of horizontal wells with multiple perforation clusters involves thermal diffusion, fluid flow and deformation of rock matrix between the reservoir and fluid in pores and fractures. Thermal diffusion effect and multi-physical field coupling are typical characteristics of fracturing in deep tight rock reservoirs. At the same time, the propagation of fracture network is related to the disturbance between adjacent fractures. The perforation clusters spacing and initiation sequence in fracturing process will lead to different degrees of unstable propagation of parallel fractures. It is of great significance to understand the influence mechanisms of internal and external factors for the effective evaluation of fracture networks, such as the coupling of multiple physical fields and fractures disturbance. The thermal-fluid-solid coupling effect in deep reservoir was considered comprehensively to investigate the stress shadow effect and the disturbance deflection behaviors of multiple fractures in three-dimensional (3D) propagation process of hydraulic fracture network. 3D engineering scale numerical model for multistage fracturing in horizontal wells was established. The influence of thermal diffusion effect on 3D fracture, and the propagation disturbance behaviors of 3D fracture network under different perforation cluster spaces and different fracturing scenarios (sequential, simultaneous and alternate fracturing) were analyzed in typical engineering conditions. The results shown that, the stress disturbance region caused by fracture propagation in deep tight oil and gas reservoirs had superposition and overlaying behaviors in multiple fractures, forming a stress shadow effect and spatial deflection of fractures. The decrease of space between multiple perforation clusters in horizontal wells would increase the stress shadow areas and aggravate the mutual interaction between fractures. Compared with the sequential fracturing of multiple perforation clusters, the simultaneous fracturing would increase the stress shadow areas, and the alternate fracturing may conversely reduce the stress shadow areas to alleviate 3D propagation disturbance of fracture network to form an effective scheme for optimizing the spatial morphology of fracturing fracture network. The heat transfers between the fracturing fluid and the rock matrix in deep tight rock reservoirs, and the fracture propagation area and volume under each fracturing scheme were significantly enhanced, indicating that the thermal effect promoted fracture propagation and became an important factor affecting the fracture propagation.

The roof of the Jurassic main coal seam in western China generally contained low level weak rich water layer, which led to the long-term watering of the roof of the coal roadway especially the roof anchor cable hole and the reduction of the roof surrounding rock strength and the roof support effect, and affected the safety of the coal roadway roof. In order to study the damage mechanism and control measures of the water sprayed roof, the No.414106 auxiliary transportation water spraying area of Yangjiacun Coal Mine of Shuangxin Mining in Inner Mongolia was taken as the research object. Through field investigation and roof drilling sampling, it could be seen that there were obvious water conducting cracks in the area 4m above the roof of the roadway in the synclinal area. The water flowing from the anchor cable hole was in a linear water spraying state. The roof surrounding rock had a large degree of deflection, and some anchor cable anchorage sections were separated from the surrounding rock. The mineral composition analysis and water physical test showed that the clay minerals in the roof sandy mudstone contain up to 73% kaolinite, and the softening coefficient is 0.162, which had obvious water softening characteristics. At the initial stage, the roof of the coal roadway in the water spraying area was mainly destroyed by hydrostatic pressure, and the water softening property reduced the mechanical properties of the fracture structural plane, which led to the expansion of the size of the surrounding rock fractures in shear under the action of hydrostatic pressure. In the later stage, the roof surrounding rock was mainly destroyed by hydrodynamic pressure, which was mainly manifested in the deformation and expansion of fracture structural plane, displacement of fracture fillings, piping, etc. The destruction speed of roof surrounding rock was gradually accelerated. The whole process of surrounding rock of water drenching roadway roof from ground pressure appearance deformation and crack softening expansion to piping corrosion failure was analyzed. According to the main forms of the surrounding rock failure of roof drilling (physical softening, seepage failure, suction corrosion expansion failure, scouring deformation failure), it was divided into four different stages. The criteria for determining the development stage of roof failure of roadway drenching water had been formed with the main forms of roof drilling surrounding rock failure, the flow state of the roof anchor cable hole, roof surrounding rock fracture development characteristics and water control reinforcement principles as the key indicators. Combined with the site conditions, the 414106 auxiliary transportation water spraying area was the Ⅲ stage of the development of spraying roof damage. The structural form of anchor cable sealing grouting (drainage) and the principle of “deep hole drainage + shallow water sealing + deep reinforcement + high pressures support” were proposed for the roof of the roadway in the spraying area. An integrated reinforcement scheme of anchoring, sealing and grouting, which combined the reinforcement of high pre-tightened long anchor cables and sealing and grouting on the roof of the roadway in the water-spraying area, had been formulated. According to the field industrial test and rock pressure monitoring, the effect of roof water control and surrounding rock reinforcement was achieved.

With abundant mineral resources, many types of mining industry and many mines, mining development in China has led to the decline of groundwater level around the mines, waste of water resources, water quality pollution, surface collapse, land degradation, reduction of vegetation cover, and different degrees of impact on groundwater resources and ecological environment. In order to solve the problems of water waste and ecological damage caused by the lateral recharge of water from the strong seepage loose layer to the mine pit, we proposed a vertical curtain water interception technology with flexible magnetic suction membrane to protect the groundwater resources and ecological environment of coal mines. We firstly studied the performance of the suction membrane material, developed the magnetic absorption suction membrane connection process, and carried out indoor tests of different suction membrane connection processes, then we conducted a 1 369 m strong seepage loose layer water interception curtain field test application in the test mine. The research results show that the impermeable membrane has low permeability coefficient, dense structure, high flexibility, resistance to deformation and durability, and is a good material for water cut, pollution control and seepage control, which can meet the requirements of vertical curtain for the strong seepage loose layer of the mine. The self-developed magnetic suction joint material and connection process solved the problems of shallow laying depth, joint leakage and complicated operation of existing connection processes such as overlapping lap, joint lock and joint box, etc. The construction depth of suction membrane curtain connected by magnetic suction joint is not limited by the connection conditions, and the water interception effect of magnetic suction joint connection process is better than that of overlapping lap and joint lock (joint box) connection process. Through the test of making, laying, connecting and backfilling the curtain into a wall with 2 kinds of flexible magnetic absorbent impermeable membranes, the gap at the joint of the impermeable membrane was reduced from 5-20 cm to 0, and the two adjacent impermeable membranes were closely connected as an organic whole, which reduced the water passage of the interception curtain at the joint. Through the mine-field site test, it was found that the water catchment pits below the curtain which had been filled with strong seepage loose layer water leakage for a long time, had dried up, and the water level of strong seepage loose layer outside the curtain had increased by 5.55-9.12 m, and the water level inside the curtain had decreased by 3.21-5.84 m, so the protection of strong seepage loose layer water resources had achieved good results.

In order to study the deformation localization failure characteristics of sandstone under the coupling action of seepage and stress, the triaxial compression tests of sandstone under different drainage conditions were carried out using the visualized triaxial servo control test system combined with three-dimensional digital image correlation (3D-DIC). The rock mechanics, seepage and deformation localization characteristics were analyzed, and the micro-morphology of fracture surface after sandstone failure was analyzed using electron microscope scanning. The results shown that the peak strength and elastic modulus of sandstone under drainage condition were higher than those under undrained condition, the peak strength, elastic modulus and Poisson’s ratio of sandstone increased with the increasing seepage water pressure, the time point of penetration crack and maximum permeability would be advanced. When the seepage water pressure was the same, the localized zone of deformation field cloud map of the sand surface was wider in the undrained condition than that in the drained condition, i.e., the macroscopic crack of rock was more obvious. Water flow under drained condition took away the mineral particles inside the rock and formed holes, the rupture surface of which was smoother than that under undrained condition, whereas flakes cuttings were obviously attached to the surface of the particles under undrained condition. The initiation point of radial deformation localization was consistently higher than that of axial deformation localization for all drainage conditions, with an average increase of 1.23%. The initiation stress levels of the radial and axial deformation localization increased with increasing seepage water pressure, i.e., the initiation time point was earlier. The radial and axial initiation stress level of sandstone under drainage condition were higher than those under undrained condition, with an average increase of 1.85% and 2.21% respectively. When the water pressure was the same, the initiation stress and stress level were more significantly affected by water pressure in the undrained condition than in the drained condition.

It has always been a common demand to stay away from the harsh environment with narrow space, numerous devices, complex operation process, and hidden hazards, and realize intelligent unmanned mining in the coal industry. To achieve this goal, it is very necessary for us to develop an effective theory of vision computing for underground coalmine applications. Its main task is to build effective models or frameworks for perceiving, describing, recognizing and understanding the environment of underground coalmine, and let intelligent equipment get 3D environment information in coalmine from images or videos. To effectively develop this theory and make it better for intelligent development of coalmine, this paper first analyzed the similarities and differences about computer vision and visual computing in coalmine, and proposed its composition architecture. And then, this paper introduced in detail the key technologies involved in visual computing in coalmine including visual perception and light field computing, feature extraction and feature description, semantic learning and vision understanding, 3D vision reconstruction, and sense computing integration and edge intelligence, which is followed by typical application cases of visual computing in coalmines. Finally, the development trend and prospect of underground visual computing in coalmine was given. In this section, this paper focused on concluding the key challenges and introducing two valuable applications including coalmine Augmented Reality/Mixed Reality and parallel intelligent mining. With the breakthrough of underground vision computing, it will play a more and more important role in the intelligent development of coal mines.

The safe and reliable operation of the hoisting system is very important for the production of the whole mine. Therefore, it is necessary to realize the single-point global visualization and virtual remote cooperative linkage control of the mining hoisting system, so as to solve the problem that the traditional multi-point video surveillance can only cover some key components and obtain incomplete information. To solving the problem, the digital twin framework of a mining hoisting system that with the function of monitoring, control and servicing is constructed by industrial sensing, artificial intelligence, rapid modeling, cloud storage and other technologies. Based on the framework, a multi-dimensional and multi-scale digital twin rapid modeling method is proposed. Firstly, a large scale geometric model of the mining hoisting system is built by 3D laser scanning technology, filtering, Poisson 3D reconstruction and other point cloud processing algorithms. Secondly, using industrial sensor network, PLC data reading and conversion technology, the behavior model of mining hoisting system under massive data is established. Lastly the fault knowledge model of the mining hoisting system is constructed using the database technology, domain expert knowledge and cases. The multi-dimensional and multi-scale digital twin rapid modeling experiment is carried out in a mine, and the results are as follows. The efficiency of the geometric modeling method has improved 93% compared with the traditional CAD modeling method and the modeling result has great similar to the real mining hoisting system. The behavior modeling method realizes the mapping of real entity behavior without adding new sensors and without shutting down, saves a lot of cost and has strong real-time performance. The driving Scripts are written based on Unity3D software to deeply integrate behavioral model, knowledge model and geometric model. Synchronization and deduction of behavioral model are carried out based on the component level model with high fidelity of the geometric model and it can realize the non-delay cooperative linkage between virtual and real systems. Meanwhile, relevant professional knowledge in the field is triggered by real-time behavioral data to assist decision making. The establishment process of the whole digital twin model takes into account the cost and effect, which will greatly improve the operation security and intelligence degree of the mining hoisting system.

Due to the complexity of the spatial environment and poor lighting conditions in underground coal mines, the images obtained by vision devices are prone to problems such as insufficient contrast and poor texture details, which seriously affect the reliability of the work of vision devices and limit further image-based intelligent applications. To improve the contrast of low-illumination images in underground mines while enhancing their texture details, a deep neural network-based low-illumination image enhancement model is proposed, which contains three sub-networks, namely, decomposition network, illumination adjustment network and reflection reconstruction network. The decomposition network decomposes the underground coal mine image into light and reflection components; the light adjustment network effectively reduces the parameters of the model using depth-separable convolutional structure and strengthens the feature extraction ability of the network; in addition, the MobileNet network structure is introduced to further lighten the light adjustment network while maintaining its feature extraction accuracy and effectively realizing the contrast adjustment of light components; the reflection reconstruction network introduces a residual network structure to improve the contrast adjustment of light components. Finally, the processed illumination and reflection components are fused based on Retinex theory to obtain enhanced images, which achieve contrast enhancement and detail enhancement of underground mine images, overcoming the problems of detail loss, blurred edges, and lack of contrast and clarity of the enhanced image that exist in existing enhancement algorithms. Numerical experiments show that the proposed model can effectively enhance the texture details of the image while improving the contrast of underground mine images, and has good stability and robustness, which can well meet the needs of low-light image enhancement in coal mines.

Mining contra-rotating fan are prone to rotational stall when it operates at low flow rates, which seriously affects the operational stability. The unsteady flow in the full flow passage of a FBCDZ-10-No20 contra-rotating fan at five axial spacings was numerically simulated by using the SST k-ω turbulence model. The effect of axial spacing on the stall process of contra-rotating fan was studied, and the mechanism of stall inception and development at different axial spacings was revealed. The results shown that the axial spacing had a significant influence on the initial position, type and development of stall inception. For the axial spacings of 70 mm and 100 mm, the stall inception first occurred at the tip of the front stage, and subsequently appeared at the tip of the rear stage due to the rotor-rotor interaction between the two stages. However, compared with the axial spacing of 70 mm, the rotor-rotor interaction at the axial spacing of 100 mm was relatively weak, making it take longer for a stall inception to occur in the rear stage. For all three axial spacings of 140 mm, 170 mm and 225 mm, the stall inception occurred first in the root of rear stage. The difference was that for the axial spacing of 140 mm, the leakage flow at the tip of the front stage cannot completely flow out of the channel with the main flow, and a localized tip blockage area was formed. However, for both spacings of 170 mm and 225 mm, there was almost no blockage area at the tip of the front stage, and eventually only mature stall vortices formed in the rear stage. With the increase of the axial spacing, the blockage area formed by both the leading edge overflow and the trailing edge reverse flow those originated from the leakage flow at the tip of the front stage gradually reduced. In contrast, the blockage area formed by the radial vortex on the suction surface near the root of the rear stage gradually increased. When the leakage flow at the tip of the front stage failed to form blockage area, the stall type changed from the “spike type” induced by the tip leakage flow at the front stage to the “localized surge type” induced by the radial vortex flow at the root of the rear stage.

Fully mechanized top coal caving technology has become the mainstream way of high yield and high efficiency mining in extra thick coal seams in China. The accurate control of the top-coal drawing mechanical parts is of significance to realize the automation and intellectualization of top-coal caving mining. Mastering the spatial motion law of the coal caving mechanism is the premise of accurate control. The immediate shape of the hydraulic support coal caving mechanism is jointly controlled by the support height, support attitude, extension length of the plug plate, and the relative position of the rear scraper, which has an important impact on the coal caving opening and the coal-passing height of the support. This study establishes a 3–D numerical model of four- legs top-coal caving hydraulic support (No. ZF15000/27.5/42) by using the finite element software ABAQUS. Hinge and translator connectors are used to simulate the rotation behavior and expansion-contraction behavior for hinge point and plug plate, respectively. Taking the support height (H), tail beam swing angle (α), and the plug plate extension length (l) as control variables, the spatial motion law of the hinge point between shield beam and tail beam and the end of the plug plate are modeled. The critical security equation for evaluating collision between top-coal drawing mechanical parts and rear scraper is obtained by using Levenberg-Marquardt fitting iteration method. A database for describe the calibration relationship, which contains the end coordination of plug plate, the dimension of the top-coal drawing opening, and H, α, and l, is established. The sensor type and installation position for sensing and controlling the attitude of the top-coal drawing mechanism are recommended, the approach for calculating the tail beam angle based on travel sensor is derived. Through field verification of top-coal drawing opening width, it is concluded that the relative error between measured value and calculated value meets the requirements for accurate control of top-coal drawing mechanism. The approach for controlling the top-coal drawing opening dimension is proposed, which has been successfully applied in the field.

In order to realize the mechanized construction of hard rock tunnel boring, and improve the construction efficiency of three-boom drilling jumbo when applied to hard rock tunnel boring, the research and analysis are conducted on the positioning accuracy of three-boom drilling jumbo borehole and the optimization of multi-boom cooperative borehole path. Firstly, the kinematic model of three-boom drilling jumbo is established based on the D-H method, and the effective working space of three-boom drilling jumbo is obtained by Monte Carlo method, and the RBF neural network algorithm is used to realize the accurate positioning of drill boom borehole. Secondly, an improved genetic algorithm is implemented to optimize the hole sequence of the three-boom drilling jumbo with the shortest moving distance of the end of the drill boom and the minimum sum of the joint variables during the movement of the drill boom as the optimization objectives, and it is compared with two existing hole sequence planning algorithms, namely, the ant colony optimization algorithm and the adaptive genetic algorithm. Finally, a numerical simulation is conducted to analyze the collision interference of multiple drill booms with two different drilling sequences and the divided working space. The numerical simulation results show that: ① The maximum drilling positioning error of the three drill booms is 2.94 mm, and the error is controlled within 3%. ② Compared with two existing hole sequence planning algorithms, the total distance traveled at the end of three drill boom are shortened by 5.39 m and 10.84 m, respectively, when the shortest distance traveled at the end of drill boom is taken as the optimization objective; the sum of each joint variable of three drill boom are reduced by 2.76 rad and 5.34 rad, respectively, when the minimum sum of joint variables is taken as the optimization objective. ③ The shortest distance between the middle drill boom and the left and right drill boom is 984.6 mm and 580.8 mm respectively, when the drilling operation is carried out in the drilling sequence with the shortest distance, there will be no collision and interference between the drill booms, but when the drilling operation is carried out with the smallest hole sequence scheme of joint variables, the shortest distance between the middle drill boom and the left drill boom is 193.5 mm, considering the structure size of the drill boom and safety, and collision may occur. In summary, the RBF neural network algorithm can achieve precise positioning of the borehole and improve the efficiency of hard rock tunneling when the borehole sequence is constructed based on the shortest distance as the optimization objective, which provides theoretical support for hard rock tunneling construction.

Water resources determine the vegetation structure and types in the ecological restoration process, and are the main limiting factor for achieving green production and ecological restoration in mining areas. To investigate the effects of inoculation of Arbuscular Mycorrhiza Fungi (AMF) on plant root water extraction, simulated soil water distribution and water isotope fractionation in a semi-arid coal mining area, this study conducted  the indoor stratified soil column simulation experiment with maize as the test plant. Three treatments were set up as pure soil column (CK1), soil column + maize (CK2), and soil column + inoculated maize (AMF), with three replicates for each treatment. Meanwhile, the height of capillary water rise in soil columns, soil water content, as well as hydrogen and oxygen isotopes of maize stem water and soil water were measured. The growth and development of maize, water transport patterns, and discrepancies in soil water isotope fractionation at different depths among different treatments were also analyzed in this article. Results showed that: (1) Inoculation could effectively promote the growth and development of maize, with plant height, aboveground biomass, underground biomass and total root length increased by 15.8%, 23.4%, 43.4% and 21.0%, respectively, compared to CK2 treatment. (2) AMF have also promoted the root system to absorb the retain water in the bottom clay layer, increased the capillary water elevation by 18.9%, and expanded the water absorption space of maize by approximately 50%, thereby  affecting the water distribution in the soil columns. (3) There were significant fractionation differences between the surface and deep soil water of soil column compared to the initial water. At the surface layer of 0 ~ 10 cm, the ¹⁸O and ²H enrichment coefficients of CK2 and AMF treatments were significantly lower than those of CK1 treatment, while at the deep layer of 60 ~ 70 cm, the ¹⁸O and ²H enrichment coefficients of AMF treatment were significantly higher than those of CK2 treatment, indicating that AMF could enhance the phenomenon of isotopic fractionation in deep subsoil water. In summary, inoculation can improve the absorption of deep soil water by maize in the reconstructed soil layer, prompt the root system to counter-release to the upper dry soil through the water lifting effect, improve the water redistribution capacity, and affect the soil water isotope fractionation at different depths. The results could provide scientific basis and technical support for addressing the shortage of water resources for land reclamation in semi-arid coal mining areas.

Taigemiao Mining Area is rich in coal resources, but water resources are scarce and the ecological environment is fragile, and the use of hydrogeochemical methods to carry out research on the chemical characteristics and evolution law of groundwater in the whole basin of mining areas can provide scientific support for green mining in mining areas. Piper three-line diagram was used to analyze the types of Cretaceous groundwater, Jurassic groundwater, river water and lake water, and the water chemical characteristics met the characteristics of lake water mixed by river water and evolving groundwater; through Gibbs diagram analysis, it is concluded that the Cretaceous and Jurassic groundwater in the cyclic evolution process It is controlled by rock and evaporation; the ion ratio endmember method further shows that the Cretaceous and Jurassic groundwater is dominated by silicate rock salt and rock salt, accompanied by ion exchange; finally, the mass balance simulation shows that the Cretaceous groundwater circulation During the evolution process, dolomite, gypsum, and rock salt minerals are dissolved, CO₂ is absorbed, and calcite is precipitated. With ion exchange, it can be mixed with different proportions of river water to form lake water, but Jurassic groundwater can only be mixed with a small amount of river water or not mixed with river water. The river water accounts for 83% of the water supply of Hongjiannao Lake. Jurassic groundwater cannot be the main source of water supply. The main sources of water in Hongjiannao Lake are Cretaceous groundwater and river water. Combined with the hydrogeological conditions of the mining area, the groundwater flow system of the mining area is divided into the Cretaceous groundwater flow system in the south, the Cretaceous groundwater flow system in the north and the Jurassic groundwater flow system in the deep. Coal mining directly affects the Jurassic groundwater flow system. On the premise of ensuring that the two Cretaceous groundwater flow systems are not damaged, when coal mining drainage only captures the outflow water from the Jurassic boundary or a small amount of Jurassic replenishment to Hongjiannao, coal mining will affect Hongjiannao and surrounding rivers. impact is minimized.

Fourier transform infrared spectroscopy (FTIR), as a non-destructive method, is widely used for the identification of compounds and the characterization of molecular structures. In order to characterize the changes in the chemical structure of charcoal under different combustion temperatures, and thus to provide a theoretical basis for the formation of fusinite in coal, plant samples (charcoal) from modern wildfires with different degrees of combustion were selected to quantify their chemical structures using FTIR. The results shown that the sample reflectance was positively proportional to the combustion temperature. The sample No. 1 with maximum combustion temperature had the highest degree of combustion, which was measured to reach 518 ℃. The aromatic structure was dominated by tri-substituted benzene rings in all samples except the highest combustion sample No. 1, but dehydrocondensation occurred with increasing combustion temperature, resulting in a reduction of tri-substituted content of benzene rings to 20.5%. The tetra-substituted content was elevated due to dehydroaromatization of the naphthenic structure, while the change in the penta-substituted content was related to the cyclization of aliphatic chain and the decarboxylation of benzene ring. With the increase of combustion temperature, the CC content gradually increased due to the formation of aromatic hydrocarbons or the shedding of molecular side chains after dehydrogenation of cycloalkanes, reached 32% in the sample No. 1. The content of C－O first decreased and then increased. In the sample No. 1, the content of alkyl ether and aryl ether was the lowest, and the content of phenolic hydroxyl group was the highest, which may be the generation of phenolic substances by thermal breakage of ether bond under high temperature combustion. The CO content increased and then decreased to as low as 5.6% in the sample No. 1, which was due to the poor stability of the bond. Due to the influence of combustion temperature, the content of fatty substances varied greatly, with an overall gradual increase in methylene content, a decrease in methyl group, and an increase in branching degree. There were five types of hydrogen bonds in the samples, with ether-oxygen hydrogen bonds predominating in samples affected by low temperature (>55%). Cyclic hydrogen bonds and hydroxyl-N hydrogen bonds appeared in sample No. 1, while the content of ether-oxygen hydrogen bonds decreased significantly to 13.2%, which was attributed to the reduction of oxygen-containing functional groups caused by the increasing temperature. Comparison of reflectance and FTIR characteristics of fusinite in coal revealed that the characteristics of fusinite (semifusinite) in coal were very similar to those of charcoal, which might be produced mainly by wildfires. These changes indicated the effect of combustion temperature on the chemical structure in charcoal, reflecting the process of organic molecular structure changed with temperature in charcoal, and providing a theoretical basis for the evolution of organic matter and the formation of fusinite in coal.

To explain the effect of maceral composition on the combustion characteristics of coal, a series of low-rank coals with different vitrinite/inertinite ratio were collected as the research object, and the combustion characteristics, heat change process and gas escape behavior of the samples under air atmosphere were investigated using thermoanalytical methods (TG-MS-DTA). The results show that the maceral content has little effect on the temperature of the maximum reaction rate. However, it has an effect on the value of the maximum reaction rate, and the maximum reaction rate of the inertinite-rich coal is larger. Meanwhile, higher minerals in coal allow the reaction to reach its maximum rate at a higher temperature. The combustion process shows two obvious stages. The first stage (before 400 ℃) is exothermic slowly, corresponding to the devolatilization process, and the second stage (after 400 ℃) is exothermic rapidly, corresponding to the fixed-carbon combustion process. The exothermic characteristics of coal combustion show a slow to fast exothermic transition. Coal with different vitrinite/inertinite ratio mainly release CO₂, CO, H₂O during the combustion process, however, the relative content of the released gas is different. In the devolatilization stage, there is less CO₂ and CO released, while more H₂O release. In the fixed-carbon combustion stage, a large amount of CO₂ is released, the amount of CO released is slightly lower, and H₂O is the lowest. Among them, the inertinite-rich coal releases relatively more CO₂ during the combustion process and burns more completely under the same conditions. In addition, the kinetic calculation of the coal combustion process is carried out with the Coats-Redfern method, and the trend of reaction activation energy increases as the vitrinite/inertinite ratio decreases. However, it does not affect the inertinite-rich coal in the fixed-carbon combustion stage. The ability to burn rapidly may be due to the cell lumen structure formed by a large number of fusinites, which enlarges the contact area between the surface of coal particles and O₂, and the combustion reaction is sufficient.

Coal gangue, as a mixture of carbon, silicon and aluminum, can be used for the preparation of composite materials. It shows a good prospect as the preparation of composite materials can avoid the difficulties of element separation and impurity interference. In this paper, activated carbon-mesoporous silica composite (AC-SiO₂) was prepared from coal gangue by alkali fusion, acid leaching and other processes. The effects of reaction conditions on the pore volume and specific surface area of coal gangue-based AC-SiO₂ were investigated; then the phase transformation during the preparation of coal gangue-based AC-SiO₂ was studied by means of X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The results showed that several experimental parameters of alkali fusion and acid leaching process were related to the pore volume and specific surface area of coal gangue-based AC-SiO₂, among which the KOH-impregnated concentration, roasting temperature and HCl-leached concentration were the most important factors. The kaolinite and quartz in coal gangue would be transformed into potassium nepheline and potassium silicate phases, and the solid carbon would be transformed into activated carbon, when the KOH-impregnated concentration was ≥ 10.7 mol/L and the roasting temperature was ≥ 700 °C; AC-SiO₂ was further formed by acid leaching process, when HCl-leached concentration ≥ 6.0 mol/L. At the optimized conditions, the conversion ratio of carbon and silicon in coal gangue is 90.28%, and the yield can reach 40.2%. The micropore and mesopore of AC-SiO₂ were formed by the accumulation of lamellae (the micropores and mesopores account for 1/2, specific surface area was about 835.1 m²/g, average pore diameter was about 2.97 nm and total pore volume was about 0.62 cm³/g) was prepared. The prepared AC-SiO₂ had obvious adsorption on the different molecular weight pollutants of methyl orange and Rhodamine B, and the adsorption capacity of methyl orange and Rhodamine B were exceed 99.01 mg/g and 99.87 mg/g, respectively.