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X-ray fluorescence spectroscopy analysis is a major method for quantitative analysis of metal elements in coal. The accuracy of background subtraction directly affects mineral metal sorting. As traditional background subtraction methods feature low background fit and large diffraction peak area errors, this study proposes an optimized method of complex wavelet transform with inverse derivative fitting for background subtraction. We obtained a simulated background spectral line through reversed peak searching and separated the overlapping peaks and valleys using Largrange's interpolation to push the simulated background close to the actual background. We then decompose and reconstruct the simulated background spectral line through complex wavelet transform to accomplish background subtraction of XRF analysis. We used the optimized method of complex wavelet with inverse derivative fitting for background subtraction of the simulated XRF spectrum and the real XRF spectrum, and compared with Continuous Wavelet and Dual-tree Complex Wavelet. The experimental results indicate that the optimized method outperforms the traditional methods in background subtraction accuracy, with less than 1 % of diffraction peak area error and less than 0.1 % of background area.

Studies on mining-induced overburden rock movement, damage and surface deformation cracks are essential to the safety production of coal mines and mining damage protection. Taking the 12203 working face of a mine of Zhengzhou Coal Group as an example, this study analyzed the evolution mechanism of overburden rock affected by mining via theoretical analysis, on-site measurement and numerical simulation. We investigated the functional relationship between back-mining distance and height of overburden development and between sufficiently destructive depth of overburden and back-mining distance. Moreover, we analyzed the distribution of the ground cracks in this geological conditions. Results show that: ① The overburden destruction of thin bedrock in thick loose layer encompasses 4 stages: the beginning, rapid increase, slow increase and stabilization; the overburden destruction height shows a Logistic relationship with back-mining distance, and a linear relationship with the thickness of the coal seam. The back-mining distance is equal to the depth of burial when the overburden is sufficiently destroyed in this geologic condition. ② In the evolution of overlying rock fracture, bedrock is more violently damaged than the loose layer. ③ The cracks in the ground are mainly tensile cracks interacting with step cracks. The cracks at the edge of the working face show an "elliptical-circular-elliptical" dynamic variation pattern along with the back mining of the working face; the development of cracks in the ground occurs at a certain distance in front of the working face. The distance of the dynamically overrunning cracks is 84.07m, and its angle is 73.15°.

The conventional pretreatment methods for mine water generally include coagulation, sedimentation (flotation), and filtration. However, large equipment footprint, long processing time and pollution from coagulants and flocculants have been limiting the further development of underground mine water treatment. In this light, we designed an underground mine water pretreatment device based on ultrasonic atomization for clarifying and pre-softening mine water so that the turbid mine water could be treated to meet the needs of underground production, firefighting, and dust reduction. We conducted indoor experiments on mine water clarification and pre-softening treatment using water and rock samples from the field mined-out area. The results show that: (1) This method can clarify black-gray turbid mine water with a large amount of solid impurities, effectively removing insoluble solid impurities in the water. (2) Ultrasonic atomization reduces the total hardness of the water by 72.24%. The milligram equivalent concentration of Ca2+ is reduced from 5.33 mg/L to 0.81 mg/L and the milligram equivalent concentration of Mg2+ drops from 5.23 mg/L to 2.13 mg/L, with little impact on pH. (3) The water from the mined-out area after ultrasonic atomization can meet the requirements of sprinkling in underground firefighting, spraying in dust reduction, the mining process of coal mining equipment, and the use of cooling water.

Deep geothermal resources in China are widely distributed, with large reserves, and have broad prospects for development and utilization. In order to investigate the seepage characteristics and evolution laws of deep high-temperature reservoirs under the condition of intermittent water injection geothermal exploitation. Using the combines method of laboratory testing and microscopic analysis, a seepage test was carried out on granite after alternating thermal and cold cycles at different temperatures, and the variation of permeability with temperature under different confining pressure were analyzed. Combining microscopic characteristics and CT scaning reconstruction results, the evolution of the microscopic pore and crack structure with temperature and cycle times was studied. The results indicated that: (1)The permeability of granite is related to temperature and cycle numbers. Under the two cooling methods, the permeability of granite gradually increases with the increase of temperature, and the permeability increases sharply when the temperature exceeds 500℃. In addition, the permeability increase under water-cooled conditions is significantly greater than that under natural cooling conditions, and the parameter changes after 10 water-cooled cycles are more significant. (2)The stress state has a significant influence on the permeability. Under the confining pressure, the internal pore and fracture structure of the specimen is closed. With the increase of confining pressure, the permeability of the granite decreases after the alternating hot and cold cycles at different temperatures, and gradually increases with the increase of osmotic pressure. (3)Under the action of high temperature cooling cycle, micro-pore cracks in granite gradually develop, temperature gradient stress causes non-uniform deformation among mineral particles, and degradation damage such as intergranular cracks, transgranular cracks and particle spalling occurs under the combined action of physical and chemical reactions such as dehydration and phase transformation. With the increase of cycle times, the number, size and connectivity of cracks further increase. The research results can provide theoretical support and technical reference for geothermal development and reservoir construction in deep dry hot rock.

The Crushed Coal Pressurized Slagging Gasification (British Gas-Lurgi, BGL) renders the use of gates obsolete and changes from dry slag discharge to liquid slag discharge, significantly improving the gasification performance. This study aims to reveal the essential structural characteristics of BGL coal gasification to further improve the performance of gasification equipment. We established the thermodynamic equilibrium model, coal gasification dynamics model and Euler multiphase flow model via numerical simulation, and validated these models. The simulation results show that 1) compared with Lurgi coal gasification, the gasification equilibrium temperature increases from 795 ℃ (Lurgi gasifier) to 1 029 ℃, and the decomposition rate of water vapor increases from 32.66 % to 93.12 %. The maximum bed temperature increases from 1 110 ℃ to 1 837 ℃, much higher than the coal ash flow temperature (1 210 ℃). This improves the gasification intensity and ensures liquid slag discharge. 2) BGL coal gasification reaction is mainly completed in the lower part of the furnace, with only a small amount of water vapor participating in the shift reaction. CH4 in the crude gas mainly comes from coal pyrolysis. 3) The fluctuation of bed surge in gasifier enhances heat and mass transfer. 4) Nozzle Jet impacts and squeezes coal char particles, forming an ellipsoidal combustion raceway extending to the central area. This becomes an important functional unit of BGL gasification, realizing primary gas distribution and providing heat for gasification layer and slag pool. 5) The liquid slag in the slag pool whirls up and down, which is beneficial to reduce carbon residue in slag and ensure smooth slag discharge.

This study investigates the influence of water accumulation in goaf on the stability of surrounding rock in a coal mine in Shanxi Province via field test, laboratory experiment and numerical simulation. Specifically, we established 3D geometric models of water bodies and goaf in water-bearing goaf based on 3D laser scanning and sonar. We then conducted permeability test on coal rock under different degrees of damage, and obtained permeability variation patterns. We then analyzed the stability of surrounding rock near water-cut goaf using numerical software by considering the dynamic changes of permeability. Results show that: ① pore water pressure exerts significant impact on the surrounding rock and overlying rock mass. ② The surrounding rock is prone to water seepage and percolation after the old goaf is flooded. ③ A large range of plastic zone with low stability is observed in the coal pillar between the goaf and roadway due to mining disturbance and water seepage. Therefore to ensure the safety of underground production, it is suggested to increase temporary underground drainage facilities for in-time water discharge to avoid flooding accidents.

In order to enhance the efficiency of tunnel support in coal mines, a study focused on the six-degree-of-freedom drill anchor robot manipulator arm and proposed an optimal trajectory planning method based on an improved grey wolf optimization algorithm. Firstly, the kinematic model of the manipulator arm was established using the D-H parameter method. Monte Carlo method was utilized for workspace analysis of the manipulator arm, and MATLAB software was employed for simulation verification; Secondly, joint-space trajectory of the manipulator arm was planned using piecewise polynomial interpolation; Finally, an improved grey wolf optimization algorithm was proposed and its performance tested for time optimization of the manipulator arm based on trajectory planning. The results show that the drill-anchoring robot manipulator meets the requirements for coal mine roadway anchoring operations; the 3-5-3 piecewise polynomial interpolation method provides smoother operation of the manipulator; and the time required for the manipulator to reach predefined trajectory points under constraint conditions is reduced by 30.40 % to 50.28 %, outperforming traditional trajectory planning methods.

Briquette production method is vital to improving its strength and permeability in physical simulation test of coal mine gas disasters. This study adopts the Horsfield dense packing theory to optimize the ratio of briquette materials and investigates the mechanical-seepage characteristics, molecular and pore structure of hot-pressed briquettes under different heating rates. Results show that as the heating rate increases, the proportion of C1s elements and the contents of alcohol, C—O/C—OH, aromatic hydrocarbons and C—C/C—H in functional groups in the molecular structure of hot-pressed briquettes show a fluctuating pattern of initial increase, subsequent decrease and final increase; the uniaxial compressive strength first increases and then decreases, while the initial permeability first decreases and then increases. The optimum heating rate is 5 ℃/min. This study offers references to improving the similarity between briquette and raw coal.

This study proposes a new algorithm to enhance the accuracy of measuring internal deformation, identify and quantify damage in rocks using digital volume correlation (DVC). This algorithm integrates the multimesh refinement technology into a mechanically regularized global DVC algorithm that incorporates nodal force equilibrium. The accuracy of different DVC algorithms was assessed through scanning experiments on particles with different sizes and digital virtual fracture models. The internal deformation and damage patterns of red sandstone were quantitatively analyzed using in-situ CT scanning during uniaxial compression experiments. The results indicate that the introduction of the mechanical regularization term reduced the measurement uncertainty of the global DVC method by 1-2 orders of magnitude. For the red sandstone specimens, the new algorithm was able to identify sub-voxel microcracks with an aperture of 0.15 voxels, while reducing the computational cost by 85.15%. The damage quantification analysis revealed that newborn cracks with a maximum aperture of 0.32 voxels occurred in the specimen when the axial stress reached 50.58% of its peak value, and these microcracks evolved into voxel-scale fractures when the stress increased to 84.27% of the peak value. The new algorithm not only improves the computational efficiency, but also demonstrates a strong capability in identifying sub-voxel scale newborn cracks, providing a novel method for quantifying internal deformation and damage in rocks.

The roof of the main coal seam in Tingnan Coal Mine of Binchang Mining Area is a typical thick sandstone aquifer structure, and the multi-dynamic disaster outburst problem of rock burst, water damage and gas. Based on the analysis of the field measured data, two typical disaster chains of' rock burst-water disaster and rock burst-gas disaster' in Tingnan Coal Mine were obtained. The disaster-causing mechanism of the disaster chain was studied through laboratory tests, and the principle of coordinated prevention and control of disasters was formulated. The coordinated prevention and control methods of roof disasters in extremely thick sandstone aquifers were designed, including two stages of pre-mining and mining, as well as the overall prevention and control of source chain breaking and systematic prevention and control of isolated chain breaking, and were applied in Tingnan Coal Mine. The results show that with the increase of impact amplitude, the ultimate bearing capacity of dynamic damaged coal and rock mass decreases, and the impact leads to the damage and weakening of roof, which communicates with the thick sandstone aquifer. The porosity of sandstone samples after strong impact is 8.23 %, which is 34.48 % higher than that without impact. The occurrence of rock burst increases the fracture of rock mass and provides a channel for gas escape. Through the cooperative prevention and control technology of roof disaster in extremely thick sandstone aquifer, the average resistance of the support is 35.03 MPa, and there is no obvious stress surge. The water inflow of the working face is stable at 250~280 m3/h, and the methane emission fluctuates at the level of 0.2 %. The research can provide basic theoretical support for the prevention and control of multi-dynamic disasters in coal mines in Binchang mining area, help to achieve efficient prevention of coal mine disaster risks, and promote the progress of multi-disaster collaborative prevention and control technology.

In order to reveal the characteristics of overlying rock migration and mining pressure manifestation in deep well long wall paste filling mining, the 1123 filling working face of Gucheng Coal Mine was taken as the research object, and geological radar, multi-point displacement meter, microseismic monitoring and other methods were used for research. The research results show that: (1) The range of influence of advanced mining in the working face is 33~37 m, and the range of influence of advanced mining on the coal pillar side of the intake roadway increases to 50 m. The range of influence of advanced mining in the fault affected area of the return airway shows an increasing trend; (2) The microseismic events in the filling working face exhibit distribution characteristics such as asymmetry, low energy, low vertical development height, concentrated bottom plate, and dispersed top plate, with a majority of small energy events; (3) The top plate of the filling working face is mainly deformed and sunk, without large-scale damage or major energy events, indicating that filling mining reduces the migration mode and strength of the overlying rock layers; (4) When the progress of filling the working face reached 165.6 meters, there was no significant subsidence on the surface, indicating that filling mining has a good inhibitory effect on surface subsidence.

Changes of wind barrier angles exert significant effect on the occurrence of low oxygen gas in the upper corner. Taking the 100510 working face of a mine in Shanxi Province as example, this study uses Ansys Fluent software to build a gas migration model of the working face to simulate the occurrence patterns of low oxygen gas in the upper corner under different wind barrier angles, and verifies the model through field measurement. Results show that setting wind barrier could increase wind speed in the upper corner, which offers a solution to the low oxygen problem in upper corner. The optimal treatment of low oxygen in the upper corner is realized with wind barrier angle set at 60° at the position 5m away from the return air channeling. This study provides implications for solutions to the low oxygen issue in the upper corner and thereby ensure safety production.

This study aims to investigate the crack propagation mechanism of directional hydraulic fracturing of coal mine roof and explore the relationship between fracture criteria. By drawing on fracture mechanics, we propose a hydraulic fracturing mechanical model of drilling and derive the calculation formulas of crack initiation angle and critical water pressure under different fracture criteria to analyze the impact of different variables on crack initiation angle and critical water pressure. Results show that: ① the increase of stress difference leads to a gradual increase of the crack initiation angle; ② the effect of prefab crack length and borehole radius on crack initiation angle is caused by two factors. The crack initiation angle increases with the decrease in the ratio of these two factors; ③ Poisson's ratio has limited effect on crack initiation angle; ④ under high stress difference and low prefab crack inclination angle, the critical water pressure decreases with the increase of stress difference and inclination angle, and vice versa; ⑤ the increase of borehole radius and prefabricated crack length would significantly reduce the critical water pressure. The two criteria yield different calculation results as ① prefab crack length and borehole radius would impact crack initiation angle; ② principal stress difference and prefab crack angle would impact critical water pressure. The theoretical calculation results and the experimental results show a good fit. The present study offers reference to the hydraulic fracturing site construction.

Coal mine solid waste is an industrial solid waste generated during coal mining, washing, and utilization. Despite a recent increase in its utilization rate in China, it still possesses substantial storage, which not only encroaches on land resources, but also causes serious environmental pollution. This paper reviews existing studies on the environmental impact of coal mine solid waste that were published in CNKI, Web of Science, and Google Scholar databases between 2014 and 2024. Results reveal that the environmental impact of coal mine solid waste mainly includes: ① the emitted gases such as polycyclic aromatic hydrocarbons and SO2 and the fine particulate matter generated during the storage process of coal mine solid waste could pollute the atmosphere; ② the heavy metals in coal mine solid waste would pollute the surrounding groundwater during the leaching process; ③ the heavy metals such as Cd, Cr, Hg in coal mine solid waste could migrate and be released to the surrounding soil through weathering and leaching, causing serious heavy metal pollution in soil. Given the current research progress in the comprehensive utilization and treatment of coal mine solid waste, this study proposes future research foci by drawing on the current regulations in mining safety, environmental protection and monitoring.

This study proposes a layout scheme for external staggered roadway and builds a mechanical model for unconventional coal pillars with staggered positions as a solution to the waste of resources caused by the large coal pillar size between the sections of 1301 fully mechanized top coal caving face and the difficulty in supporting the roadway in Xinjulong Coal Mine. We analyzed the stress environment and characteristics of the extreme equilibrium zone of unconventional coal pillars using the limit equilibrium theory. For the bottom roadway, the reasonable horizontal staggered distance in the lower section is set at 3.0 meters after considering its stress environment at different horizontal offset conditions and the distribution of elastic strain energy density of the section coal pillars. Meanwhile, we proposed a joint support scheme for adjacent roadways between sections. We simulated and verified the original support scheme and the joint support scheme in actual geological conditions during the mining stage of the continuous working face. Results show that the joint support scheme for adjacent roadways between sections outperforms the original support scheme. The peak stress of the joint support scheme reduced from 80 MPa to 64 MPa, with a reduction rate of 20 %, indicating that the it is more effective in controlling the surrounding rock of the roadway. Moreover, the unit reserved area of coal pillars in the section was 111.5 m2, which is a 34.4 % reduction from 170 m2 in the original support scheme. This study offers implications for reducing the reserved size of coal pillars in fewer sections and improving the coal recovery rate.

The CO2 flooding and sequestration technology displays significant effect in CO2 emission reduction and oil displacement, which could alleviate global warming, achieve China's dual carbon goals and sustainable development. This study reviews existing CO2-EOR projects with 100 000 tons and above, with a focus on domestic engineering cases. Specifically, we analyzed such major issues as technology matching, safety monitoring, economic constraints and legal policy preference in implementing CO2-EOR projects in China, and discussed its future prospects. The implementation of this technology shows a late start in China and still lags behind those in Europe and the USA due to a lack of large-scale commercialized projects. By drawing on foreign scholarly efforts, we need to optimize the whole process of CO2 flooding and storage through the introduction of artificial intelligence, upgrade CO2 leakage risk identification and control as well as CO2 dynamic monitoring to accelerate the commercialization and industrialization of large-scale CO2-EOR projects.

To extract and transport the residual heat from mine return air over long distances, and considering the high moisture content and large volume of return air, along with the heat transfer theory of heat pipe systems, this paper designs a gravity-type split heat pipe air supply system for mine return air heat recovery. This system can transfer the recovered low-temperature residual heat to the mine's fresh air platform for preheating, meeting the anti-freezing heat demand at the mine shaft entrance and successfully realizing the extraction of low-temperature heat sources for industrial application. Through continuous three-day testing of certain heat exchange modules, the results show that the system can raise the temperature of low-temperature fresh air by 12℃ to 16.5℃, achieving the goal of preventing freezing at the shaft entrance. These findings demonstrate practical industrial application value.

As the main bearing structure of the reservoir in the goaf of the mine, the damage instability mechanism under the influence of multi-field coupling of water immersion directly restricts the long-term safe and stable operation of the reservoir in the goaf. In this paper, nuclear magnetic resonance (NMR)was used to study the T2 spectrum, pore throat, porosity change and nuclear magnetic image evolution of coal samples under different times of cyclic immersion under'unilateral' immersion conditions. With the increase of cyclic immersion times, the number of pores, pore throat ratio and porosity of coal samples maintained an increasing trend, which increased by 67.18%, 3.48% and 3.49% respectively. The nuclear magnetic resonance imaging further obtained the permeability and pore change law of water molecules in different times of unilateral cyclic immersion of coal samples: the water molecules in unilateral cyclic immersion of coal samples gradually flow from the immersion side to the internal of coal samples, and finally expand to the whole coal samples, further resulting in an increase in porosity. With the increase of cyclic soaking times, the uniaxial compressive strength and residual strength of coal samples decreased gradually. The average peak strength of coal samples decreased from 15.74 MPa to 11.76 MPa, 9.65 MPa and 8.41 MPa, respectively. The average uniaxial compressive strength of coal samples decreased by 46.56% compared with that of initial coal samples. The average residual strength decreased from 5.55 MPa to 3.08, 2.44 and 0 MPa, respectively. Long-term cyclic immersion has a significant softening effect on coal samples. Based on the experimental results, the evolution law of internal pores and the morphological characteristics of uniaxial compression failure of coal samples under the increasing number of unilateral cyclic immersion were analyzed, and the mechanism of water immersion damage and failure of coal samples was revealed. The experimental results provide a scientific basis for the stability control of reservoir spatial structure in goaf.

This study investigates the fracture characteristics and damage mechanism of granite after treatment under different heating rates. The cracked straight-through Brazilian disc(CSTBD)specimen was used for high-temperature treatment with four heating rates under four sets of heating temperatures. The Brazilian splitting experiments were carried out using electro-hydraulic servo press after cooling down to room temperature, and the static fracture process was analyzed to investigate the effect of heating rate on the fracture mechanical properties of specimens. The results show that: (1) Granite treated at different high temperatures shifted from brittle to ductile damage. (2)The peak damage load of granite treated with different heating rates at the same temperature decreased with the increase of heating rate. At the same temperature, the increase of heating rate doesn't lead to obvious difference in the apparent color of granite, but with gradual increase of apparent cracks. (3)At different heating rates, the longitudinal wave velocity and elastic modulus at 200 ℃ and 400 ℃ show subtle changes, yet at 600 ℃ and above, the longitudinal wave velocity and elastic modulus decrease significantly with the increase of heating rate. (4) The fracture toughness of granite shows gradual decay with the increase of temperature. At the same temperature, type I fracture toughness of granite specimens decreases with the increase of heating rate. At 400 ℃, heating rate exerts maximum influence on the fracture toughness of granite.

The large quarry face with a strike length of 3 300 m in Sijiazhuang Mine features high gas reserve, large gas outflow and its upper corner is easy to exceed the limit.This study adopts the gas management technology of extracting the gas from the coal seam by drilling large-diameter downhole holes.We established a numerical model of fluid-solid coupling by considering the superposition effect of drill holes to analyze the evolution of gas pressure, effective extraction radius, and the effect of gas extraction when the diameter of drill holes is 113 mm and 400 mm respectively.The results show that ①after implementing pre-extraction technology in the large diameter drill hole, the effective extraction radius of the drill hole increased by 21.12 %; ②When introducing the coefficient k=pm/pc as a judgment index of the superposition effect, taking the effective extraction radius of a single 113 mm diameter drill hole as a reference, the effective radius of a 113 mm diameter drill hole is improved by 3.7 times compared with that of a single hole when using a common diameter drill hole for multi-hole extraction; ③The concentration of the gas extracted from the drill hole increased by 2 times, and the pure amount of extraction increased by 5 times, which provides technical and theoretical references for the gas management and safe production of the working face of large mining fields.

This study investigates the influence mechanism of particle size and gas pressure on the dynamic diffusion law of CO2 in coal.We used a self-developed high pressure adsorption and desorption experimental system for coal seam to analyze the dynamic adsorption-diffusion characteristics before the adsorption equilibrium of gas in coal based on the volumetric adsorption experiment, which was combined with the classical single hole diffusion model to calculate the CO2 diffusion coefficient at different times.The results show that the adsorption equilibrium time is positively correlated with the coal particle size, and decreases with the increase of adsorption equilibrium pressure.Larger coal particle size would result in more obvious decreasing trend.The effective diffusion coefficient is found to be more effective than the diffusion coefficient in explaining the relationship between particle size and equilibrium time.Smaller particle size would result in higher effective diffusion coefficient and shorter adsorption equilibrium time.The effective diffusion coefficient shows a power function with time.The initial effective diffusion coefficient (De0) and effective diffusion attenuation coefficient (β) both decrease with the increase of particle size.De0 first increases and then decreases with the increase of equilibrium pressure, and the β exhibits varying relationships with the increase of equilibrium pressure depending on different particle sizes of the coal.Smaller particle size would result in better connectivity between the pores of coal, leading to shorter diffusion paths of gas molecules and lower diffusion resistance, thus more facilitated to adsorption.Gas pressure poses a driving effect on CO2 adsorption and diffusion, but with the continuous adsorption of coal samples, the coal matrix expands and blocks the pores, leading to a narrowing of the diffusion channel and diminished driving effects.

To address the issue of severe mine pressure manifestations and difficult-to-control deformation in deep coal seam roadways, an orthogonal numerical simulation experiment was conducted based on the Kastner formula.This experiment examined five factors affecting the stability of roadway surrounding rock: height-to-width ratio, lateral pressure coefficient, depth, cross-sectional shape, and surrounding rock strength.Sensitivity of each factor to roadway deformation and damage was studied using variance analysis and intuitive analysis charts.The stress distribution patterns of elliptical and rectangular roadways under different lateral pressure coefficients and height-to-width ratios were analyzed using the plane elasticity complex variable function theory.Optimal designs for the height-to-width ratio and shape of elliptical and rectangular roadways were developed.The results showed that the main factors affecting the stability of surrounding rock are the strength of the surrounding rock and the lateral pressure coefficient, while depth, cross-sectional shape, and height-to-width ratio are secondary factors.Elliptical roadways exhibit the smallest difference in surrounding rock stress under isotropic stress ratios.Rectangular roadways have lower stress concentration when the width is 5 m and the height-to-width ratio is approximately 0.6.For areas with rapid stress increase in rectangular roadways, an optimized rounded rectangular roadway was designed considering bearing characteristics and cross-sectional utilization, and a calculation formula for the corner radius was established.The optimization performance of this design was verified through numerical simulation.

The Shendong mining area, located in Northwestern China, is characterized by a dry climate and scarce water resources. A large amount of mine water is used for ecological irrigation in this mining area. This study investigated the suitability of mine water for irrigation through on-site sampling and hydrochemical testing of mine water in the mining area. We analyzed the spatial distribution patterns of water quality parameters and hydrochemical types. This study also evaluated and predicted the suitability of long-term irrigation using sodium ion adsorption ratio(SAR), soluble sodium percentage (KNa), Kelly ratio (KR), permeability index (PI), residual sodium carbonate (RSC), magnesium adsorption ratio (KMg) single indicator methods, as well as USSL and Wilcox graphical methods. Taking into account the groundwater level, we discussed soil texture types, climatic conditions of the mining area and the applicability of the evaluative indicators. The results show that the main ions in the mine water of Shendong mining area are sorted by mass concentration. The cations are Na+, Ca2+, Mg2+ and K+, and the anions are HCO3-, SO42-, Cl-and NO3-. The mine water is weakly alkaline as a whole, and the concentrations of Cl-and NO3- vary significantly with space. There was a significant positive correlation among Na+, Cl-, SO42-, total dissolved solid (TDS), electric conductivity (γ), Ca2+ and Mg2+, and a negative correlation between F-and Ca2+, Mg2+. The hydrochemical type of mine water in the mining area is primarily the NaHCO3 type. The chemical composition of mine water is mainly affected by ion exchange and evaporation. Na+, Cl-, SO42-, Ca2+, Mg2+ and F-in the mine water were abnormally enriched and the TDS and γ values exceeded the standard. The salt accumulation effect is not obvious under the combined influence of groundwater and surface water waterlogging in the mining area, and the soil compaction is not prominent. The PI method and the USSL graphic method are not suitable for evaluating irrigation water quality in this area. The evaluation results based on Wilcox graphical method show that the mine water of Halagou, Shigetai and Daliuta mines are suitable as irrigation water. The mine water from Bulianta, Shangwan, Buerta, Wulanmulun, and Huojitu mines should not be used for long-term direct irrigation. This study has theoretical and practical significance for the rational development and utilization of mine water resources in mining areas.

Using steel slag for the preparation of mine backfill materials is vital to utilizing its resources. Therefore, this study reviewed the impact of different processing technologies and sources on the physical and chemical properties of steel slag, analyzed the application modes and hydration mechanisms of six kinds of steel slag backfill cementitious materials, and discussed the advantages, disadvantages, and development trends of steel slag in the field of mine backfill. This study indicates that: (1) Desulfurized gypsum could promote the hydration and dissolution of steel slag, while cement clinker, slag, and fly ash provide an alkaline environment for steel slag hydration, and silica fume offers a large amount of highly reactive silicon; (2) Steel slag could improve the workability of filling slurry and increase the late strength of backfill, extend the setting time of backfill material and reduce the early strength of backfill. (3) The addition of steel slag could enhance the plastic deformation characteristics of the backfill body, therefore offering references for the prevention and control of dynamic impact hazards in coal mines.

The open field subsequent filling method in segmented drilling stage is an efficient mining method for inclined medium thick ore bodies.However, blasting, filling and stope stability show complex relationships, causing surface subsidence, roof and floor collapse, and high mining loss rate.This study adopts engineering analogy and industrial experiments to optimize the process of the sublevel drilling and stage open-stoping with backfill of inclined medium thick ore bodies in the aspects of mining sequence, cutting method, and bottom structure layout, and propose a layout method without leaving pillars in the stope.This method directly connects the side walls of the filling body to the chamber after one-step of filling, and improves the strength of the filling body and the recovery rate of the ore block through extrusion blasting.As the key to this method lies in the implementation time, numerical simulation using ANSYS/LS-DYNA shows that medium-depth hole extrusion blasting is used to form cutting grooves, it should be carried out between 7~9 d after filling and curing of the filling body in the stope.Engineering practice has proved the feasibility of this method, which provides technical support for mining production.

This study explores the environmental changes in the disturbed area of coal mining and presents the driving factors of ecological self-restoration. Specifically, we measured the soil nutrient and soil enzyme indicators in the mining area and non-mining area from 2014 to 2017 and 2019, and evaluated the stoichiometric characteristics of soil carbon (C), nitrogen (N), and phosphorus (P). The experimental results show that the total phosphorus concentration gradually recovered with the increase of mining years, while organic matter, available potassium, and urease first increased and then decreased with the increase of mining years. There were significant differences in total phosphorus, C/N ratio, N/P ratio, and C/P ratio between the working face and the subsidence disturbance zone. Random forest analysis showed that soil sucrase, urease, available potassium, total nitrogen, total phosphorus, C/P ratio, C/N ratio, and water-soluble salts were the key factors influencing soil nutrient cycling in different time periods; while C/N ratio, N/P ratio, total phosphorus, alkaline phosphatase, and water-soluble salts were the key factors influencing soil nutrient cycling at different locations. Mining years of the working face has differing influence path on soil factors and soil enzymes. This study could provide theoretical proof for the artificial guided self-restoration plan in coal mining subsidence areas and for ecological restoration in western mining areas.

This study investigates the fracture evolution patterns of overlying strata under the mining conditions of close-distance coal seams.Taking the 9305 working face of Anshun Coal Mine as the research object, this study probed into the evolution of displacement field and strain field during the mining process of close-distance coal seams through physical similarity simulation test.The results show that ①with the continuous advancement of distance from the working face, the overburden strata first form separation cracks and longitudinal cracks, and then the middle part of the goaf is gradually compacted.②The displacement field is asymmetrically distributed in the advancing direction of the working face, The displacement of the overlying rock on the side of the working face is obviously smaller than that on the left side of the goaf, and the peak displacement is mainly concentrated in the middle of the goaf.③The maximum principal strain concentration position is asymmetrically transferred from the middle of the goaf to the open-off cut side and the working face side.The concentration degree of the open-off cut side is significantly higher than that of the working face side.This reveals that a potential correlation exists between the maximum principal strain concentration position and the gas enrichment area.

The construction of ultra-wide working face is helpful to promote the safe and efficient mining of coal resources. However, due to the limitation of roadway space and construction conditions, the detection depth of conventional mine geophysics is limited, and the geological information inside the ultra-wide working face and within a certain range of roof and floor cannot be accurately obtained. In order to improve the detection accuracy of the water rich area on the bottom plate of the ultrawide working face and provide a basis for the processing and interpretation of measured data, based on the summary and analysis of current mine geophysical detection technology, the three-dimensional(3D) DC resistivity method that can be applied to the detection of the ultrawide working face, combined with the occurrence characteristics of limestone water on the bottom plate of the working face 21106 in a coal mine in Yongcheng, Henan, was systematically studied using a combination of theoretical analysis, numerical simulation, and measured data to study the data characteristics and resolution ability of 3D observation and 2D observation modes. The research results show that: Compared with the traditional two-dimensional observation mode of the same side transmitter-receiver, the three-dimensional observation mode of the opposite side transmitter-receiver is more sensitive to the low resistance body on the floor of the mining face. The data obtained by the three-dimensional observation mode of the opposite side transmitter-receiver are calculated by the conventional apparent resistivity formula, the obtained apparent resistivity is sometimes opposite to the actual electrical property, so it is necessary to use the three-dimensional inversion method for data processing. Finally, the 3D model data observed during the 21106 work in a coal mine in Yongcheng, Henan Province was subjected to 3D inversion processing, and the reliability of the 3D inversion results was verified through underground drilling data. The research results provide a theoretical basis for the two-dimensional observation and three-dimensional observation data interpretation of the pole-pole device conditions.

The temperature prediction of geothermal reservoirs at different depths is to determine the key parameters such as thermal energy storage, heat output capacity, and the sustainable utilization period of geothermal reservoirs. Taking the geothermal wells in the Qiabuqia area of Gonghe Basin as an example, this study proposes a temperature prediction model for heat reservoirs under different constraints based on particle swarm optimization (PSO) and long short-term memory network (LSTM). The prediction effect of this model is verified by comparing with those of the BP model and LSTM model. The results show that the RMSE value, MAPE value and MAD value in the prediction results of the model are the smallest compared with those in BP and LSTM models, and the minimum RMSE value is only 1.192. The determination coefficient of the model is 0.929, showing a good prediction effect. This indicates that this model could realize the prediction of reservoir temperature in geothermal system, which provides references for the efficient and long-term development of geothermal system.

The extreme working conditions in coal mining, petrochemical industries, and other related fields have imposed higher demands on the wear resistance of materials used for critical components in mechanical equipment. This study prepared a hybrid-particles reinforced metal matrix composite (MMC)that combines large-size zirconia-toughened alumina particles (ZTAp)as load-bearing elements with small-size tungsten carbide particles (WCp)for reinforcement. Specifically, we probe into the composites' structure, focusing particularly on the effects of media, erosion angle, ZTAp size, and WCp content on their erosion-wear resistance and the underlying mechanisms. The results indicate that the addition of appropriate amounts of ZTAp and WCp significantly enhances the composites' erosion-wear resistance. Within a fixed volume fraction of ZTAp, larger particle sizes are associated with better erosion-wear resistance. The primary failure mechanisms observed are brittle spalling and fatigue fracture. Through second-phase reinforcement, solid solution strengthening, and precipitation strengthening, the WC particles enhance the hardness and wear resistance of the matrix, suppressing the interactive effects of corrosion and wear in acidic media. The primary failure mechanism during erosion is brittle fracture and spalling.

This study conducted bearing capacity test of high-steep rock slope foundation under different slope angles and slope distances to investigate the bearing capacity of high-steep rock slope foundation. We carried out numerical simulation to analyze the influencing factors of the bearing capacity of the high-steep rock slope foundation, combined with the deep waste pit project. The results show that: (1)The capacity coefficient η gradually decreases with the increase of the slope angle β, and increases nonlinearly with the increase of slope distance B. When the slope distance B exceeds a certain value, the bearing capacity coefficient η no longer increases and approximates 1.0. (2)Compared with slope angle β, geological strength index GSI exerts significant influence on the bearing capacity coefficient, and both of them increase nonlinear synchronously. (3)Anchor cable could improve the bearing capacity coefficient η. When four anchor cables are set, the bearing capacity coefficient η demonstrates more significant improvement. Yet, further increase in the number of anchor cables has little effect on the bearing capacity coefficient η.

Exploring land cover change is very important for the sustainable development of regional land resources. However, there are few studies on land cover change in the construction of Xinjiang electricity transmission energy channel. In this paper, the temporal variation characteristics of land cover in a 10 km buffer zone along Jiquan Line in Changji Hui Autonomous Prefecture were analyzed by using multi-scale geographically weighted regression model (MGWR) to explore the spatio-temporal changes and driving factors of land cover in this region during 2010-2022. The results showed that: ① Grassland, bare land and cultivated land were the main areas in the study area, and the proportion of grassland and bare land was more than 90%. During the construction of Xinjiang electricity transmission channel, the land cover changes were more drastic and complicated; ② There are differences in the driving factors in terms of time. In the preparation and formal construction stages of the channel construction, the distance to the base station and the distance to the power grid rank first and second respectively in importance. However, during the operation period after the construction is completed, the distance to the water source and the minimum temperature rank first and second respectively. ③ The spatial ranges of different factors are different. Annual minimum temperature and distance to water source mainly affect grassland, bare land and farmland. The research results can provide reference for the construction of similar projects in the future, and promote sustainable land use and ecological protection.

Coal is a porous material containing pore structures and mineral components, exhibiting pronounced anisotropy and size effects.In order to investigate the influence of coal anisotropy and size effects on its failure characteristics, this paper proposes a simulation method for characterizing and reconstructing three-dimensionally the internal pores and mineral components of coal samples based on CT scanning, nuclear magnetic resonance, and X-ray diffraction.Specifically, we obtained simulation parameters of three-dimensional reconstruction models of coal matrix and mineral components through inverse laboratory uniaxial compression experiments, while simulated and analyzed the strength damage characteristics of coal bodies with different aspect ratios.The simulation results show that: ① During the loading process, the plastic zone first gradually expands and connects outward around the pores and mineral components.In terms of spatial distribution, the plastic zone expands vertically from the loading end to the interior in the early stage, and in the later stage, it expands horizontally from the surroundings to the interior.After the model is damaged, a "double truncated cone structure" is formed in the non-plastic zone.② The increase of aspect ratio leads to an increase in the compressive strength(p) of coal samples, the strain(ζ) at yielding strength, and the elastic modulus(K), among which ζ and K increase linearly, while the margin of increase in p gradually decreases.③ The total energy and elastic energy of coal sample loading increase exponentially, while the dissipated energy increases linearly.The increase of aspect ratio leads to an increase both in the accumulated elastic energy in the coal body and in the released energy during failure, which easily induce dynamic impact-related disasters.This study provide references for the reasonable selection of coal pillar size in impact mine pressure area.

Aiming at the corrosion problem of steel bars in concrete in subtropical marine environment, the full immersion corrosion experiments of reinforced concrete specimens with different strength grades and rust inhibitor contents were carried out by simulating the subtropical marine environment.The macroscopic indexes such as chloride ion content were tested by electrochemical non-destructive testing, and the experimental results were verified by microscopic detection methods.The corrosion degradation patterns of reinforced concrete was analyzed.The results show that the improvement of concrete strength grade and the increase of rust inhibitor content can significantly improve the corrosion resistance of reinforced concrete.Among them, the corrosion resistance of C30 concrete is the worst.At 120 d, the corrosion current density is 0.118 μA/cm2, the polarization resistance is 220 kΩ cm2, the concrete resistance is 87.3 kΩ cm2, and the transfer resistance of the steel-concrete interface area is 77.3 kΩ cm2, reaching the passivation state.When the concrete strength grade is increased to C50, the corrosion current density is reduced by 58.47%, the polarization resistance is increased by 3.82 times, and the concrete resistance is increased by 44.56%;when the amount of rust inhibitors is 6 kg/m3, the corrosion current density is reduced by 47.45%, the polarization resistance is increased by 2.81 times, and the transfer resistance at the reinforcement-concrete interface is increased by 72.43%.

The shale in Doushantuo Formation is the main source rock of the Ediacaran in Sichuan Basin and the major hydrocarbon source layer of the ancient marine strata for natural gas exploration in recent years. Forty-six samples were collected from two outcrops(Baibaoxi and Shiping)in Chengkou county in northeastern Sichuan Basin.We analyzed the change of the sedimentary environment of the Member Ⅱ and Ⅳ of Doushantuo Formation in terms of their organic geochemical characteristics(total organic carbon, rock pyrolysis, kerogen carbon isotopes)and element geochemical characteristics(major elements, trace elements and rare earth elements).Results show that the shale of Doushantuo Formation in northeastern Sichuan Basin exhibit a high abundance of organic matter, with TOC content ranging from 0.19 % to 20.38 % (mean value is 4.76 %). The dominant type of organic matter is type Ⅰ kerogen, and it has reached over-maturity stage. High δEu anomalies and abnormally richness in V, Mn, Mo, Ba and U elements of the black shale revealed strong hydrothermal action during this period. The distribution pattern of rare earth elements and various redox indexes indicated that the redox fluctuates repeatedly under the conditions of anaerobic-anoxic-sulfidic environment during the depositional period of the Member Ⅱ. The water environment of Member Ⅳ changed from anoxic to anaerobic-sulfidic environment. In general, the water connectivity of the basin is strong, the depositional rate is relative high. The nutrients carried by upwelling from hydrothermal sources proliferate productivity, which promotes the formation of organic shale.

Sprayed fireproofing materials in underground coal mine roadways are limited due to their poor adhesion, easy-to-crack, easy-to-fall off and poor sealing effect. This study therefore develops a fireproofing spraying material with fly ash as aggregate, ordinary silicate cement, sulphur-aluminate cement and gypsum as base material, and re-dispersible latex powder(VAE)as additive. Specifically, we conducted the uniaxial compressive strength test and used coal rock multiphase multi-field triaxial dynamic seepage experimental system, and scanning electron microscopy to study the effects of dispersible latex powder on the adhesive, cementation, mechanical, and blocking properties of the spray material. The results show that adding dispersible latex powder could promote the formation of filamentary bonding bridges in the hydration product, and realize the riveting and bridging of the binder bridges with the hydration products to form a dense network structure. This improves the cracking resistance of the spray material and enhances the material's adhesion, sealing and cementing properties when combined with coal. Adding 1 % VAE spraying material can fully encapsulate the coal body, forming a dense coating on the surface of the coal body, effectively isolating the air from contact with the coal body, thus preventing spontaneous combustion of coal. The proposed materials are useful in preventing spontaneous combustion of coal at the top of the roadway.

This study conducted the CO2-PTF coal experiment to further reveal the fracturing transformation mechanism of CO2 phase transition fracturing(CO2-PTF)coal. According to the CT scanning and 3D fracture reconstruction, we analyzed the fracture structure parameters of coal before and after CO2-PTF, and clarified the evolution characteristics of the three-dimensional fracture structure of coal induced by CO2-PTF. The research results indicated that after CO2-PTF, the total number of fractures in the coal sample decreased, while the total volume and surface area of fractures increased. The CO2-PTF generated fracture expansion and transformation effects where the small-scale fractures were expanded and transformed into larger scale fractures under the CO2-PTF pressure. The number, volume, and surface area of fractures of less than 1 000 μm in length were significantly reduced, while the volume and surface area of fractures of longer than 1 000 μm in length were significantly increased. The expansion and connection between fractures caused a decrease in their quantity. CO2-PTF improves the connectivity of the three-dimensional fracture in coal and is conducive to gas migration and production. This study offers new insights into and evaluation method for the effect of CO2-PTF, and could provide references for the research on fracture evolution characteristics in other unconventional natural gas reservoirs and their modifications.

Natural fractures are important storage spaces and seepage channels in tight carbonate reservoirs. It is therefore of practical significance to quantitatively predicting their development and distribution patterns and revealing the dominant geological factors that control the development of gas reservoirs. This study looks at the fractures in the tight carbonate reservoir of Dengying Formation in Gaoshiti block of Leshan-Longnusi ancient uplift in the central Sichuan Basin. Based on the characterization of fracture parameters, we established a calculation model of stress field-energy-fracture parameters, and carried out quantitative prediction of fracture development and distribution patterns by combining multi-phase fracture superimposition algorithms. We then analyzed the influence of lithology, faults, and structural morphology on fracture development. The results show that: (1)The fractures in Dengying Formation of Gaoshiti block are mainly tension-shear fractures, high-angle fractures, and semi-filled fractures. The preferential fracture strike is NW-SE and near N-S directions. The fracture density is between 0 and 2 fractures per meter, and the high-value areas are mainly distributed in the fault zones and central regions; (2)There is a negative exponential power relationship between the length and density of natural fractures in the Gaoshiti block. Fracture development exhibits interlayer differences: The limestone reservoir has a high degree of fracture development, and mudstone has a blocking effect on fracture propagation; (3)Fracture development scale and occurrence are significantly affected by faults and folds: fracture around faults shows high density, large aperture and short length. Shear fractures are nearly parallel or at a low angle to strike-slip faults, and tensile fractures are at a high angle to the main strike-slip faults; folds mainly affect fracture aperture through structural curvature, with larger fracture apertures in high-degree deformation structural positions, and smaller values in the wings. The results could provide references for efficient exploration and profitable development of gas reservoirs in the study area and other regions with similar geological conditions.

Coal production enterprises at present are facing immediate urgency to reduce their high carbon emissions so as to meet the "dual carbon" targets. This study therefore analyzed their potential in carbon emission reduction from the perspective of their coal products, mining processes and emission types. Specifically, this study proposed pathways for 1)upgrading coal production equipments, including the application of advanced clean technologies, upgrading and retrofitting production equipments, and implementing energy efficiency management strategies; 2)technology updates for coal exploration, mining, beneficiation and monitoring; 3)upgrading new energy vehicles and intelligent platforms for logistics management, and improving energy-consuming equipments for personnel in mining areas, all targeting at the major factors causing high carbon emissions; 4)upgrading coal and gas co-capture technologies and carbon sequestration methods during coal mining and beneficiation processes, based on which specific suggestions are offered for coal production enterprises. A comprehensive pathway for carbon emission reduction is thus constructed for coal production enterprises to achieve carbon peak and carbon neutrality.

The high geothermal environments encountered in deep mineral mining induce thermal damage to rocks, which can trigger geotechnical disasters in deep engineering projects. Therefore, exploring the degradation characteristics of rock mechanical properties and the damage evolution laws after high-temperature exposure is of significant importance for rock engineering in deep high-geothermal environments. By subjecting granite to the temperature range from ambient to 1200 ℃ and conducting macro-microscopic studies using optical microscopy, the degradation characteristics of Young's modulus and compressive strength in granite samples post various high-temperature treatments were investigated. Additionally, an analysis was performed on the internal cracks and damage evolution in thermally damaged granite from a microscopic perspective. The experimental results demonstrate that high-temperature treatments significantly reduce the mechanical properties of granite. The granite's compressive strength and Young's modulus decrease with increasing treatment temperatures, and the extent of crack development increases with temperature. The mechanic cal properties of granite are highly correlated with the development of internal crack structures. There is a power function relationship between the crack density and compressive strength in granite after different temperature treatments, indicating that crack density can effectively reflect the extent of thermal damage in granite.

In light of the significant presence of liquefiable sandy silt layers in the foundation of the airfield area at the Beijing Daxing airport, this study employed a low-energy, small spacing, and low blow count dynamic compaction method to treat it.To assess the compaction effects and determin the parameters of the compaction process, two energy levels of 1 000 kN·m and 2 000 kN·m were selected, with each energy level tested at 4, 6, 8, 10, and 12 blow counts. Additionally, the effect of the surface frozen soil layer on compaction was investigated using 1 000 kN·m energy level with 4, 6, and 8 blow counts. The full depth standard penetration, surface wave and dry density tests were carried out in the dynamic compaction test area. The experimental results revealed that the sandy silt soil foundation exhibited increased compaction, propagation wave velocity, and enhanced liquefaction resistance after dynamic compaction. Optimal blow counts were determined as 10 and 8 for energy levels of 1 000 kN·m and 2 000 kN·m, the corresponding dynamic consolidation depth is 4.5m and 5.5m, and the eliminating liquefaction depth is 4.3m and 5.3m, respectively. Besides, the standard penetration test requires a minimum of 10 and 12 blows in the depth range of 4.5 m and 5.5 m for energy levels of 1 000 kN·m and 2 000 kN·m. At the optimal blow counts, the dry density of the surface layer of the original foundation should not be less than 1.45 g/cm3. The experimental results suggest that, for foundation treatment in the runway area, the dynamic compaction level of 2 000 kN·m is suitable, and 1 000 kN·m dynamic compaction level is used for foundation treatment in the apron and taxiway area.

The use of prestressing anchor active support technology in tunnel engineering is becoming morecommon.However, the support characteristics and mechanism of action have not been fully understood for shallow, large-span rocky tunnels.In order to investigate the bearing characteristics of the surrounding rock under the prestressed anchor support system, a concealed excavation station of Qingdao Metro Line 6 was used as the engineering background, and based on the similarity principle of formulating experimental materials for stratum and support structure modelling, the bearing characteristics of the anchors under the prestressed anchor and ordinary anchor support were investigated by hydraulic loading tests.The results indicate that: ① The interaction between prestressed anchors and the surrounding rock creates a load-bearing anchor solid that can effectively support most of the overlying loads.The application of prestressed anchors during the overburden loading process increased the warning load value of tunnel instability damage by 42.8% and the ultimate load value by 41.2%.② The overburden loading process involved the prestressing anchors going through the tight anchorage load holding stage and the de-anchorage unloading stage.Simultaneously, the lining underwent the strain accumulation stage, strain surge stage, and strain release stage during the overlay loading process.③ The prestressed anchor under active support has better force synergy with the rock body than an ordinary anchor, without the axial force mutation phenomenon.This allows the support performance of the anchor to be fully utilized.Additionally, the prestressed active support effectively inhibits the development of fissures and significantly improves the overall stability of the tunnel.

The evolution of fractures in mining overburden plays a pivotal role in interlayer gas migration. Therefore, a comprehensive study of crack development and distribution improve the efficiency of gas extraction. This study the west 2107 fully mechanized mining face in Weijia Mine of Gansu Province as the engineering background, Specifically, this study established numerical models of different mining heights by using the UDEC simulation software, and analyzed the relationship between the evolution of near-field fractures in the overburden of the working face and different mining based on fractal geometry theory. The optimal working face height for gas extraction was determined and validated through theoretical empirical formulas, field observations of overburden fractures, and gas extraction results. The results show that the total number of mining fractures increases with the increase of mining height, but the amplitude of increase is different at different stages, and the overburden fractures continue to develop in an "umbrella" shape around the overburden. The near-field fractures of the overburden rock at different mining heights have undergone three stages: generation, expansion and penetration, and compaction stability. Increasing mining height, smaller compaction zones. When the mining height is 4 m, the development density and range of roof fractures at 10 m and 40 m are significantly higher than those in other areas, which is consistent with the optimal position of the collaborative extraction roadway with high and low roadways.

As the core unit of backfill mining method, the strength of backfill is an important indicator to ensure safe mining. Na-based bentonite features a high methylene blue adsorption capacity and green compressive strength, making it a high-quality additive for preparing filling materials. However, there are few studies probing into the relationship between the dosage and the strength of the filling materials. This paper analyzes the changes in shear wave velocity, dominant frequency amplitude, amplitude attenuation coefficient, and waveform fractal dimension of filling materials with different Na-based bentonite dosages at different ages through ultrasonic testing technology and uniaxial compression tests. Combined with sensitivity analysis, we selected the most sensitive acoustic parameters to changes in compressive strength. Furthermore, this study establishes a strength prediction model for backfill with different Na-bentonite contents and combining significance testing and comparative analysis. The research findings can serve as a valuable reference for theoretical research and engineering applications related to predicting the uniaxial compressive strength of backfill materials.

Improving the positioning accuracy of underground personnel can not only strengthen mine safety monitoring, but also increase the speed of rescue, thus ensuring the life safety of underground personnel to the maximum extent.This paper proposes a positioning model based on IPSO-LSTM for position prediction of underground moving targets in response to the problem of existing ranging algorithms which are affected by the on-site environment, resulting in insufficient positioning accuracy.This article uses LSTM to build a fingerprint positioning model.It collects distance information through the UWB wireless module to build a distance-position fingerprint relationship database, which is used to train the PSO-LSTM model.Then we use the trained model to predict target trajectories.We compared four improvement strategies on PSO including random initialization of population position by chaotic mapping, nonlinear inertia weight reduction and fitness function optimization.Experiments show that the improved PSO optimization algorithm in this paper exhibit fast convergence speed and good robustness.In order to verify the positioning effect of IPSO-LSTM, we compared the IPSO-LSTM model with the Chan algorithm, PSO-LSTM model, LSTM neural network, SSA-LSTM model and GWO-LSTM.The average positioning error is used as the evaluation index.The results show that the average positioning error of the IPSO-LSTM positioning model proposed in this study is 30mm, which is 76% higher than the traditional Chan algorithm, 49% higher than the LSTM, and 24% higher than the PSO-LSTM model.In order to reduce large local errors, we used median filtering to process input information, further improving positioning accuracy.This study offers references for improving the accuracy and stability of the existing underground moving target positioning system.

This study aims to address existing problems of complex stress conditions and difficulties in retaining roadway so as to achieve long-term stability of roadway surrounding rock in gob-side entry in thin coal seam. Specifically, we investigated the 4301 working face of Liangshuijing Coal Mine in Huisen Coal Industry of Shaanxi Province through theoretical analysis, numerical simulation and engineering practice, with an aim to study the failure characteristics and control countermeasures of surrounding rock of gob-side entry retaining in shallow buried "triple hard" thin coal seam, and analyse the influence of structural parameters of roadside support on roadway stability. The results show that 1)maintaining the roadway through roadside filling body requires sufficient support strength and appropriate shrinkage to the roof and ensuring the overall stability of the roadway; 2)the mechanical behaviour of high water filling material under uniaxial compression can be divided into four stages: "uniform compaction, elastic deformation, dynamic instability and deterioration failure". The numerical simulation results show that in increasing the width of the filling body, the maximum stress first increases, then decreases and then increases, and a stable bearing stress core appears at 1.6 m. Theoretical calculation shows that the optimal height of roof cutting is 10.7 m, and it offers the roof cutting scheme and parameters of shaped blasting. Engineering practice shows that there is no large deformation and no obvious stress concentration in the 60 m range behind the working face. The surrounding rock exhibits good overall control effect and stable structure, and the effect of retaining roadway meets the design requirements.

To reduce the pollution of the roadway environment and the damage caused by the personnel and equipment by the dust escaping from the fully mechanized driving face, a chemical and environmentally friendly dust suppressant with strong wettability and strong adhesion was developed based on the engineering background of the west-wing track roadway of Jining Jinqiao coal mine, and inhalable dust as the research object, with surfactants as the key skeleton and inorganic salts and polymer adhesives as auxiliary materials.The results of field verification show that the chemical dust suppressant has a better ability to lithological particles and can effectively reduce the concentration of respirable dust in the roadway.

Multistage fracturing is a commonly-used method to improve gas production in tight hydrocarbon reservoirs. Stress shadowing effect among multi-fractures is crucial in effectively connecting the pre-existing natural fracture of reservoir and forming a complex fracture network that facilitates gas flow. Challenges remain in accurately characterizing the fracture structure and propogation patterns of naturally fractured reservoirs. In this study, we adopt an adaptive finite-discrete element method to simulate the multistage fracturing of a naturally fractured reservoir by improving the mesh auto-refinement and identification of multiple fracture propagation. The numerical model covers interactions among hydraulic fractures, pre-existing fractures, and microscale pores, while integrates the nonlinear Carter leak-off criterion to describe fluid leak-off and hydromechanical coupling effects during multistage fracturing. We introduce the proppant transport equation for idealised parallel plate flow in fractures, and Darcy's law is adopted to analyse the seepage flow in the fracture network and determine gas recovery. We then compare the fracture network and consequent fluid flow induced by the hydrofracturing of unfractured and naturally fractured models to assess the influence of pre-existing fractures on multistage fracturing behaviour and gas production. This study provides a new approach to determine and optimize fracturing cluster spacing in tight gas reservoirs.

Groundwater pollution induced by Underground Coal Gasification(UCG)seriously hinders its development.Permeable Reactive Barrier(PRB)remediation therefore stands out as a major research focus for in-situ groundwater remediation, where the characteristics of PRB material is crucial to their effective operation.This study thus examines the adsorption properties of sand, organic bentonite, and activated carbon on phenol, a characteristic organic pollutant associated with UCG.A self-constructed permeation experimental system is employed to study the adsorption and permeation characteristics of sand, organic bentonite, activated carbon, mixtures of sand and organic bentonite, as well as sand and activated carbon to investigate their comprehensive impact in purifying contaminated water.The results indicate that: ①Organic bentonite exhibits a rapid adsorption rate for phenol in solution, reaching adsorption equilibrium within 10 minutes, despite a relatively low adsorption capacity(1.98 mg/g). Activated carbon, on the other hand, demonstrates a slower adsorption rate yet a higher adsorption capacity(2.22 mg/g).②The adsorption of phenol by organic bentonite conforms to the Freundlich isotherm model, with parameters kF = 0.040 and n = 1.207.Activated carbon follows the Langmuir isotherm model, with parameters Smax = 2.44 mg/g and kL= 0.125 L/mg.③The permeability coefficients of sand and activated carbon are 1.006×10-3 m/s and 4.761×10-2 m/s, respectively.The mixture of sand with activated carbon or organic bentonite could effectively moderate the permeability of the mixed material.When the mass ratio of sand to organic bentonite increases from 1∶1 to 3∶1, the permeability coefficient of the mixed material increases from 2.624×10-6 to 3.468×10-5 m/s.Conversely, when the ratio of sand to activated carbon increases from 1∶1 to 3∶1, the permeability coefficient of the mixed material decreases from 1.379×10-3 to 1.301×10-4 m/s.

The feasibility of underground gasification of Yan 9 coal seam of the middle-lower Jurassic Yan ′an Formation in J148 area of Dongsheng gas field is systematically studied from the perspectives of geological structure, hydrogeology and coal gasification characteristics, and the prospects of carbon sequestration by using the pore layer, aquifer layer and tight gas layer in the deep coal gasification cavity are discussed.The results show that the coal seam of Yan 9 in this area is stable when the buried depth is 1 264~1 285 m and the dip angle is less than 1°.In the interior of the gasification target constituency, the structural faults are not developed, the joint cracks are not developed, there are occasional cracks but the section is fresh and closed, and the cavity of the coal seam after gasification has a good tightness, which has little influence on the construction and expansion of coal gasification furnace, and can meet the implementation of large-scale coal gasification projects.There is a continuous water barrier layer on the top and bottom of Yan 9 coal seam, which can prevent the influence of groundwater on the direct water filling of coal seam, and is conducive to the layout of underground gasifier.The thickness of the roof water-barrier layer is less than the height of the water-conducting fissure zone, there is a risk of indirect water filling through the roof aquifer, but the roof aquifer is a weak water-rich aquifer, and the risk of small water inflow is controllable.The thickness of the floor water barrier layer is greater than the safe thickness of the floor water barrier layer, which can effectively prevent the risk of direct water filling to the coal seam.In general, Yan 9 coal seam has moderate thickness, little waste, low ash, low sulfur, high calorific value non-stick coal, high coke reactivity, and has a good development prospect.In view of the large amount of CO2 emission from large-scale gasification mining of deep coal seam, the feasibility of CO2 safe geological storage by using coal seam burning and caving area, top and bottom aquifer and lower tight natural gas layer was discussed.The analysis shows that 60.8 % ~88.2 % of CO2 produced by coal seam gasification can be stored in the pore layer and the top and bottom aquifer in the gas-burning and air-burning zone of Yan 9 coal seam.Combined with the development of tight natural gas in the Upper Paleozoic of Dongsheng gas field, it is expected to achieve near-zero carbon emissions in the process of deep coal seam gasification mining by using CO2 generated by coal gasification for natural gas displacement and storage.