Abstract:In complex disaster-prone mine environments,the utilization of underground imaging enables a clear grasp of under-ground conditions and enhances rescue efficiency.This study,taking two-dimensional underground image processing technology as the object,introduces and analyzes several 2D image processing techniques and their research status specifically adapted for com-plex mine environments,and points out the existing problems in the field of mine rescue in China.Under the complex conditions of mining environments,existing image enhancement algorithms(e.g.Retinex,CLAHE)exhibit limitations including vignetting effect,color distortion,noise sensitivity,and insufficient dynamic adaptation capabilities;existing denoising techniques(such as spatial do-main filtering,wavelet transform,and deep learning-based methods)demonstrate insufficient performance in suppressing mixed noise,exhibiting limitations including detail loss and low computational efficiency;the practical application of algorithms faces bot-tlenecks in data and models,including the lack of real-world datasets,high computational resource demands of deep learning models,and insufficient multi-task joint optimization frameworks.The future development of image processing in mine environments should focus on the following aspects.Developing enhancement algorithms adaptive to underground scenarios by integrating deep reinforce-ment learning with physical models to optimize multi-scale illumination separation and edge detail enhancement;constructing a mul-timodal noise suppression framework that combines self-supervised learning(such as Noise2Void:Learning Denoising from Single Noisy Images)with wavelet-neural network hybrid architectures to improve denoising efficiency and accuracy;promoting collaborat-ive optimization of data-algorithm-hardware systems through multi-task learning technology to achieve end-to-end scene adaptation and distributed real-time processing.Through systematic analysis and forward-looking discussion of existing 2D image processing technologies in underground operations,this study aims to provide theoretical foundations and technical guidance for intelligent mine monitoring systems,ultimately driving innovation in visual surveillance technology and enhancing safety standards in mining pro-duction.

Abstract:To address the technical challenges of sparse monitoring points in the protective range and significant errors in determin-ing protection boundaries during close-distance upper protective seam mining,this study takes the 21311 working face of Xiangshan Mine as the engineering background.By integrating FLAC3D numerical simulation with field multi-borehole joint measurements,a systematic analysis was conducted on the spatiotemporal evolution of the stress field,plastic zone,expansion deformation,and per-meability of the protected seam during upper protective seam mining.The effectiveness of gas control measures was also evaluated to achieve precise delineation of the pressure-relief range and optimization of the monitoring method.The results indicate that the floor stress field evolution exhibits a three-stage characteristic:"local pressure relief-symmetrical expansion-steady-state balance".The maximum vertical stress reduction in the pressure-relief zone reached 95%of the original rock stress.The plastic zone expanded in a"trapezoidal"pattern,with a maximum failure depth stabilized at 30 m,ensuring the protected seam entered a fully fractured and pressure-relieved state.The expansion deformation rate and permeability showed a"saddle-shaped"symmetrical distribution,with the permeability in the core pressure-relief zone increasing to 172.5 times its original value,providing favorable channels for ef-ficient gas drainage to optimize the field monitoring approach,20 boreholes were strategically arranged along the strike(Group A at the open-off cut side and Group D at the final line side)and dip(Group B at the auxiliary intake airway side and Group C at the main intake airway side)for intensive monitoring.Based on the critical expansion deformation rate index,the pressure-relief angles were accurately determined as 61° at the open-off cut side,58° at the final line side,79° at the auxiliary intake airway side,and 81° at the main intake airway side,significantly improving the accuracy of boundary identification.In combination with directional long bore-holes in the floor for intercepting and extracting downward pressure-relief gas,the maximum gas extraction rate reached 55.31%.The residual gas content in the protected seam was reduced to 2.29-3.90 m3/t,the permeability coefficient increased by 8-12 times,and the borehole gas flow decay coefficient decreased by approximately 40%-50%.

Abstract:In order to simulate the low-temperature oxidation process of coal samples immersed in mine water and explore the effect of immersion time on the low-temperature oxidation characteristics of undried coal,through the self-developed gas-bath coal low-temperature oxidation experimental system,programmed temperature experiments were conducted on 12 groups of undried coal samples with different immersion durations in Anze Mining Area.The gas production and apparent activation energy changes of coal at different stages of low-temperature oxidation were analyzed,and the microscopic mechanism was discussed based on the experi-mental results.The results show that different temperature stages and immersion durations have varying effects on the low-temperat-ure oxidation ability of coal.Before 75℃,moisture has an inhibitory effect on coal oxygen reaction and the longer the immersion time,the more significant the inhibitory effect,specifically,the volume fraction of exported oxygen and the apparent activation en-ergy during the slow oxidation(SⅠ)stage gradually increase with increasing immersion time,while the standard oxygen consump-tion rate and standard carbon monoxide generation rate gradually decrease with increasing immersion time;after 75℃,moisture pro-motes the coal oxygen reaction,and the longer the immersion time,the more obvious the promoting effect,specifically,the export oxygen volume fraction and apparent activation energy of the accelerated oxidation(SⅡ)stage gradually decrease with increasing immersion time,while the standard oxygen consumption rate and standard carbon monoxide generation rate gradually increase with increasing immersion time.According to the inference,this is related to a series of complex physical and chemical changes that oc-cur inside the coal sample after water immersion,before 75℃,the moisture in the coal absorbs heat and evaporates,hindering the diffusion of oxygen and inhibiting the coal oxygen reaction;after 75℃,a large amount of water evaporates from the coal,and under the erosion of water,the physical structure of the coal body changes,while also exposing more chemical groups.Some chemical re-actions release heat,jointly promoting coal oxygen reactions.

Abstract:Mining stress disturbance causes dynamic evolution of the pore and fracture structures of disturbed coal under complex loading conditions,leading to nonlinear changes in permeability,which significantly affects gas drainage efficiency.To address this issue,relying on triaxial test equipment,taking coal samples from the 150804 working face of Liuzhuang Coal Mine as the research object,and using an automatic coal core permeability measuring instrument,this study investigates the evolution characteristics and failure behaviors of coal permeability under different axial pressure,confining pressure,and gas pressure conditions,and analyzes the variation laws of permeability.The results show that within the range of axial pressure of 3 to 9 MPa,confining pressure of 1 to 3 MPa,and gas pressure of 0.2 to 1.0 MPa,the axial pressure and confining pressure are generally negatively correlated with the per-meability of the coal body.High gas pressure will cause the coal body fractures to close,resulting in a decrease in permeability.However,under high stress combinations,the variation range of permeability tends to decrease.The confining pressure compresses the pore structure of the coal body,and the permeability continuously decreases with the increase of confining pressure.When the axial pressure is 3 MPa and the confining pressure increases from 1 MPa to 3 MPa,the permeability decreases by 0.52×10-17 m2.The influence of axial pressure on permeability shows a trend of first increasing and then decreasing.In the initial stage(axial pressure of 3 to 5 MPa),due to coal body compaction,the permeability decreases.After exceeding the yield limit(axial pressure of 5 to 9 MPa),the internal fractures and cavities increase,and the permeability increases.

Abstract:In the process of coal seam mining,how to achieve large-scale disposal of coal gangue has always been an important prob-lem to be solved in the green and efficient development of the coal industry.As the main space for gangue grouting and filling,the evolution process of mining voids in the caving zone is closely related to the movement of overburden rock.By analyzing the move-ment law of overlying strata in the caving zone,it is found that the fillable space of the caving zone is one of the fundamental ways to solve the above problems.Taking the 122109 ultra-large height working face of Caojiatan Coal Mine as the research object,a meth-od combining similarity simulation experiment and theoretical analysis was adopted to study the morphological characteristics of the caving zone,the subsidence law of the overlying strata,and the fillable space of the caving zone.The evolution law of the overlying strata moving from bottom to top gradually was revealed.Based on this,the images were processed using the ImageJ software,and the fractal dimension of the fracture network diagram was calculated.This quantitatively characterized the development degree and complexity of the fractures.The results show that under the working face mining conditions,the development of overlying rock frac-tures in the caving zone can be divided into stages such as the stage of fracture development,the stage of accelerated fracture devel-opment,the stage of compaction,and the stage of overall stable fracture;the proportion of void area in the caving zone is 28.6%,and the void space on the side of the transportation roadway of the"O-shape ring",the bed separation zone between the caving zone and the fractured zone,and the void space on the side of the return air roadway of the"O-shape ring"and the void space within the cav-ing zone account for 14.6%,14.0%,15.1%,and 56.3%respectively.Based on the void calculation model of the loose rocks in the caving zone,the void ratio of loose rocks in the caving zone is 29.13%,the available filling space of the caving zone is 5 366 000 m3,the available filling volume of the coal gangue on one side of the caving zone is 2 065 000 t,and the filling rate is 9.4%.

Abstract:The fully mechanized mining face is among the most critical areas for dust pollution within a mine,in large mining height faces,the elevated coal fall height during the mining process facilitates the dispersion of particulate matter from the coal cutting ma-chinery into the pedestrian walkway,thereby posing a significant health risk to miners.To elucidate the dust control mechanism of coal buffle in large mining faces during the shearing process,a three-dimensional numerical model was constructed using 15211 working face of Zhangjiamao Coal Mine in northern Shaanxi as a case study.Computational Fluid Dynamics-Discrete Phase Model(CFD-DPM)numerical simulation techniques were utilized to analyze the airflow characteristics,turbulence distribution,dust trans-port trajectories,distribution range,and particle size distribution under varying coal baffle heights.The findings reveal that an incre-ment in the coal baffle height intensifies its air flow partitioning effect,resulting in a reduction of airflow streamlines in the pedestri-an walkway,a progressive decrease in wind velocity,and a precipitous increase in wind velocity near the drum,exceeding 2.5 m/s.When the height of the coal buffle reaches 1.6 meters,a 30-meter-long high wind speed area is formed in front of the coal shearer.The combination of enhanced airflow effect and physical barrier effectively changes the migration path and distribution pattern of dust,significantly suppresses the lateral diffusion of dust,and shortens the exposure time and migration distance of dust.The dust pollution area on the inner side of the sidewalk has been significantly reduced,with the dust mass concentration dropping to 50 mg/m3.Most of the dust is effectively confined to the outer side of the sidewalk,and the interception effect on dust with a particle size greater than 40 μm is particularly obvious.By comparing the dust concentration distribution when the coal buffle was 0.8 m and 1.6 m,the dust concentration at the breathing zone of the sidewalk decreased significantly,with a dust reduction rate of 50.2%.The numerical simulation results were compared with the on-site measured data,and the average error was 6.9%,further verifying the ac-curacy and reliability of the simulation.

Abstract:In order to solve the problem of serious dust pollution in the dust producing area of the core operation of coal mine,the latest research progress of coal mine dust control technology is comprehensively discussed,and the key issues in practical applica-tion of spray dust removal technology and ventilation dust removal technology are deeply discussed.In view of the current research status of new spray and ventilation technologies,the dust removal capabilities of different technologies are systematically described.Based on literature research methods,domestic and foreign literatures are divided into experimental research and numerical simula-tion for analysis.It is pointed out that ventilation and dust removal technologies have deficiencies such as imperfect airflow and dust migration laws,inaccurate air volume control,and poor capacity of auxiliary ventilation devices.The limitations of the gas-dust-fog three-phase coupling model,such as large calculation amount,poor simulation effect of spray environment,backward dynamic mon-itoring and control ability are revealed.In addition,although chemical dust suppression and water injection dust reduction can effect-ively inhibit dust diffusion,it is limited by the technical bottlenecks of poor compatibility of chemical reagents and low permeability efficiency of coal seam,resulting in unstable dust suppression effect.Therefore,in the future,advanced simulation technology should be developed to realize real-time monitoring and accurate control of air flow and dust,and a more accurate gas-dust-fog three-phase coupling model with less calculation should be developed to quantitatively analyze the dust removal efficiency of spray,and more accurately simulate the influence of complex air flow field disturbance on spray diffusion.Strengthen the research and development of environment-friendly dust suppressants to realize the coordination of efficient dust suppression and ecological safety,the collabor-ative application of water injection and chemical dust suppression technology is promoted to improve the dust control efficiency of coal mine.Through the combination of theoretical innovation and engineering practice,the intelligent development of dust control technology is promoted,the underground working environment is improved,and the health of workers is guaranteed,which provides theoretical support and research means for the development of coal mine dust control technology.

Abstract:To address the challenges of non-uniform grout diffusion and the difficulty in forming a continuous water cutoff curtain in water-rich muddy silt layers of open-pit coal mines,a novel method combining high-pressure pulsed gas pre-splitting for soil layer with pressure grouting was proposed and implemented in a pilot project of Chaoyang Open-pit Coal Mine in Heilongjiang Province.A discrete element method(DEM)model based on fluid-solid coupling theory was developed to investigate,from a mesoscopic per-spective,the influence of pulsed gas parameters(pressure and frequency)on soil fracture propagation.By integrating the geological characteristics of the stratam,the optimal pulsed gas parameters were determined.Field grouting tests were conducted using a self-developed pulsed gas pre-splitting grouting control system,and the grouting effectiveness was systematically evaluated through field monitoring data,core sampling tests,and water pressure tests.The results demonstrate that high-pressure pulsed gas significantly en-hances fracture density in muddy silt layers,with the fracture growth process categorized into three distinct stages:rapid growth(Stage I),slow growth(Stage Ⅱ),and stabilization(Stage Ⅲ).The effective fracture propagation range exhibits a positive correla-tion with gas pressure,while showing an initial increase followed by a decrease with the increasing of gas frequency.The optimal gas parameters were identified as a pressure of 2 MPa and a frequency of 2.5 Hz.The pulsed gas pre-splitting grouting technology effect-ively reduces grouting pressure,increasing grout volume by 24%in loose sand layers and 92%in silty sand layers,with a maximum diffusion radius of 2 meters in open-pit mine strata.This method significantly improves the injectability of low-permeability silty sand layers and achieves exceptional anti-seepage and water cutoff performance.

Abstract:To investigate the permeability enhancement mechanism of coal and the law of gas migration under the action of hydraul-ic punching and cavity-making,based on the characteristics of multi-flow regime coexistence and multi-physical field coupling in coal seams,the influence mechanism of cavity-making parameters on the evolution of coal permeability and the response of gas drainage was systematically revealed.Based on the idea of multi-flow regime transition,a fully coupled multi-physical field model integrating gas seepage theory with stress field and adsorption deformation field was constructed.The gas flow regimes in coal seams were distinguished,and the characteristics of gas flow transition from laminar flow to turbulent flow were revealed.Based on the spherical particle assumption,the permeability expression of the broken zone after cavity-making was derived.Combined with the effective stress principle and adsorption-induced deformation theory,a dynamic evolution model of permeability in the elastic zone was established.By coupling the gas flow field and coal-rock stress field,a unified description of the multi-flow regime transition process and the interaction of stress-seepage-adsorption was realized.Taking Well SX006-1 in Qinshui Basin as an engineering ex-ample,the model was verified by using field-measured gas pressure data.The calculation results of the model were in good agree-ment with the field pressure monitoring data,which could accurately reflect the spatiotemporal evolution characteristics of pressure during gas drainage under the condition of hydraulic punching and cavity-making.The results show that hydraulic punching and cav-ity-making significantly changes the local stress distribution of coal seams,forming a columnar plastic broken zone centered on cav-ity-making,which strengthens the unloading and structural fragmentation effects,and induces a wider range of micro-fracture expan-sion and pore connectivity,thus improving the overall permeability of coal.With the increase of cavity-making aperture,an annular permeability enhancement zone is gradually formed inside the coal seam,the influence range continues to expand,the permeability is significantly enhanced,and the gas migration capacity and drainage efficiency are improved synchronously.The gas flow in the broken zone shows the characteristics of flow regime transition from laminar flow to turbulent flow,and neglecting the turbulent ef-fect will lead to obvious deviations in flow velocity and pressure distribution.Hydraulic punching and cavity-making realizes coal permeability enhancement through the synergistic effect of stress unloading,structural fragmentation and pore connectivity,and the permeability enhancement effect is significantly affected by the cavity-making aperture.The increase of aperture can strengthen the unloading permeability enhancement and gas pressure drop effect,but the permeability improvement presents a nonlinear character-istic.When the aperture exceeds a certain range,the permeability enhancement benefit tends to be saturated,and an excessively large aperture may cause problems such as reduced slag discharge efficiency and increased construction risks.

Abstract:The Linxing Block on the eastern margin of Ordos Basin contains abundant coalbed methane resources.However,drilling operations in this area face challenges such as low efficiency and high technical difficulty due to factors including deep burial depth and strong formation heterogeneity.Existing mechanical specific energy models have limitations in accurately calculating weight on drilling pressure,rotational speed,and torque under complex downhole conditions,resulting in energy waste.Therefore,in view of the geological characteristics of deep coal seams in the Linxing Block,combined with the effect of hydraulic energy on rock frag-mentation and bottom hole purification,and considering the influence of screw drill tools on rotational speed and torque,a mechanic-al specific energy model considering jet and screw drill tools is proposed.Verified by the model,compared with the Teale model,the Pessier model and the MENG Yingfeng model,the mechanical specific energy value calculated by the proposed model has a better correlation with the compressive strength of the rock and is closer to the real mechanical specific energy value.Taking the well sec-tion of Well LX-55-7D in Linxing Block from 2 368 m to 2 776 m as an example,based on Pearson's correlation law,a correlation analysis was conducted on the drilling parameters.The parameters that have a strong positive correlation with mechanical specific energy were obtained in sequence as rotational speed,drilling pressure,displacement,vertical pressure,drill bit pressure drop,rock compressive strength,and large hook load.The parameters with strong negative correlation are mechanical drilling rate and torque.It is determined that the main influencing factors of mechanical specific energy are drilling pressure,rotational speed and displacement.A cross test was designed through the response surface method,and the drilling parameters were optimized.The optimal parameters suitable for coal and rock drilling in this well section were obtained as a drilling pressure of 50 MPa,a rotational speed of 55 r/min,and a displacement of 35 L/s.The optimized drilling parameters were applied to the drilling site design of Well LX-58-6D.The res-ults showed that the optimized combination of drilling parameters increased the mechanical energy conversion efficiency by 50.5%and the drilling rate by 19.1%.This method can reduce the energy dissipation caused by the interlayering of coal and rock,providing technical support for efficient drilling in deep coal seams.

Abstract:To enhance the operational safety and intelligent control level of underground trackless auxiliary transport rubber-tyred vehicles in coal mines,a motion simulation and human-computer interaction system integrating new-generation information techno-logy with the concept of digital twin is proposed to solve the limitations of traditional monitoring and simulation modeling methods in intuitively representing operational status and constructing high-fidelity models.The system takes a trackless rubber-tyred vehicle with multi-sensor redundancy as the research object,and the system architecture and functional modules are designed using MAT-LAB/Simulink,and the CAN bus is used for standardized conversion and high-speed transmission of multi-source sensor data.Real-time data interaction between the digital twin model and the physical entity is achieved through the I/O interface of the vehicle con-trol unit(VCU),forming a virtual-physical fusion environment that enables continuous monitoring of key safety parameters such as torque,speed,and brake pressure.A predictive simulation method based on physical modeling and real-time data is introduced to ac-curately simulate the dynamic response of vehicle under various working conditions,supporting VCU program optimization and con-trol algorithm parameter tuning.Taking a low-speed four-wheel steering scenario in an underground coal mine as an example,the di-gital twin-based simulation platform reproduces real turning conditions.Combined with the dynamic characteristics of vehicle,mul-tiple simulation experiments are conducted to optimize the proportional-integral-derivative(PID)control parameters.The optimized control strategy significantly improves yaw rate and reduces turning radius.The simulation results closely match the measured data,with a maximum relative error of 1.34%and an average error of 0.85%,verifying the accuracy and reliability of the model.The over-all time delay of the control system is controlled within 30 ms,fully demonstrating the real-time performance of the system.

Abstract:In order to solve the coal dust pollution problem in the process of coal mine production,transportation and storage and re-duce the incidence of pneumoconiosis among coal workers,based on the concept of natural polymer modification,a gel film-form-ing component was synthesized through graft copolymerization of N-hydroxymethyl acrylamide(NAM)chains onto a composite substrate of xanthan gum(XG)and hydroxypropyl methylcellulose(HPMC)under the action of initiators and cross-linking agents,this modified component was subsequently compounded with the surfactant sodium dodecyl sulfonate(SDDS)and the humectant polyvinylpyrrolidone(PVP)to fabricate a crust-type coal dust suppressant featuring a gel network structure.The grafting process and dust suppression mechanism were investigated using Fourier transform infrared spectroscopy(FTIR),X-ray photoelectron spectro-scopy(XPS)elemental analysis,and scanning electron microscopy(SEM).The performance advantages were validated through vis-cosity tests,swelling capacity tests,and dust suppression performance tests.The results demonstrated that the gel network structure within the dust suppressant significantly enhanced the cohesive properties and swelling capacity of the material.This improvement effectively bonded coal particles and formed a dense consolidated layer on the coal dust surface,thereby enhancing the dust suppres-sion efficiency;in the water retention test,the dust suppressant-treated coal sample exhibited a water retention rate exceeding 50%after evaporation at 45℃for 5 h;in the consolidation layer weather resistance test,the dust suppressant-treated coal samples exhib-ited a 79.5%enhancement in wind erosion resistance efficiency compared to traditionally water-sprayed samples under a wind speed of 15 m/s,while the consolidated layer morphology remained intact.In the wind erosion resistance test,the dust suppressant-treated coal samples subjected to 7 freeze-thaw cycles between-20℃and 50℃exhibited only a 12%reduction in consolidated layer hard-ness,with no visible cracks observed in the consolidated layer.The study shows that the developed gel-based dust suppressant signi-ficantly suppressed coal dust dispersion,thereby offering a novel approach for environmental protection in mining areas and occupa-tional health safeguarding for coal miners.

Abstract:During service,pressure equipment is frequently subjected to complex loading conditions such as start-stop fluctuations,assembly misalignments,and bending-torsion coupling,which can readily induce mixed-mode Ⅰ/Ⅲ cracks.Variations in crack-tip configurations significantly affect the equivalent fracture toughness and consequently alter the outcomes of failure assessments.To address this issue,an integrated framework of"configuration identification-equivalent threshold-FAD assessment"is developed based on a three-dimensional energy model.Five representative crack-tip configurations including tri-branching,side-branching,symmetric branching,kinking and extension are characterized,and a unified scaling approach is employed to normalize the equival-ent fracture toughness.Furthermore,a robust statistical method incorporating the median and MAD-based dispersion,combined with a nearest-neighbor decision rule,is applied to establish an engineering pathway that extracts representative values from scattered ex-perimental data,thereby transforming uncertain inputs into reliable assessment parameters.The method is applied to eight welded de-fects in three thick-walled pressure vessels,where-20℃charpy impact tests and fracture mechanics calculations are used to obtain the corresponding equivalent fracture toughness values,which are then embedded into FAD curves for evaluation.The results indic-ate that under the conventional assessment approach,all defect evaluation points fall within the safe region,whereas the coordinates of the points obtained using the present method shift upward overall,with some approaching the failure curve,suggesting potential risks.Compared with traditional approaches,the proposed procedure provides more conservative assessment results and demon-strates higher sensitivity and safety margins for crack-like defects.It offers a traceable technical basis for the integrity evaluation of process pressure equipment under complex loading conditions.

Abstract:Mining-induced stress concentration is one of the main reasons for the deformation and instability of coal and rock in stope.It is of great significance to master the evolution law of mining-induced stress of coal and rock in stope for preventing and controlling the dynamic disaster of coal and rock.In this paper,the macroscopic deformation and failure characteristics of overlying strata under repeated mining are analyzed by combining physical simulation with numerical simulation.The evolution path and dir-ection deflection characteristics of principal stress transfer in interbedded rock layer are studied,and the evolution mechanism of mining-induced stress in working face under repeated mining is revealed.The results show that during the mining process of the lower coal seam,the deformation and failure range of the interbedded rock layer increases first and then gradually stabilizes.A large number of micro-cracks appear in the interbedded rock layer below the upper coal floor,and the cracks are not connected with the upper coal floor.There is no secondary deformation and failure of the overlying rock.Under the action of repeated mining,the stress release range and principal stress deflection degree of the interbedded rock layer are increasing.Affected by the pressure relief of the upper coal floor and the deformation and failure range of the overlying rock,the stress concentration degree of the coal and rock in front of the working face is different.Affected by the pressure relief of the lower coal roof-pressurization of the upper coal floor-re-petitive pressure relief-pressurization of the lower coal roof-pressurization of the two coal seams,the deflection of the first principal stress angle of the interbedded strata is regional.In this process,under the action of overburden load transfer and upper coal floor stress release range,the peak value of coal abutment pressure in the front of the working face shows an evolutionary trend of first stable,then slowly increasing to rapidly increasing.When the ratio of working face advancing distance to working face length is greater than 1.2,the growth rate of mining stress peak value of working face increases rapidly,and the working face is prone to de-formation and instability.

Abstract:Underground coal fire is a kind of global major disaster,which can maintain long-term self-sustained smoldering under the thermal buoyancy driven by the high-temperature flue gas generated within the fire.This self-sustaining characteristic is the fun-damental reason for the persistent,disastrous,and highly challenging nature of underground coal fire control.However,understand-ing the mechanism behind this self-sustaining behavior remains an unresolved scientific challenge.This study aims to explore the principle of self-sustaining characteristics of underground coal fires from the perspective of energy analysis.A small-scale experi-mental device is set up to carry out physical similarity experiments of underground coal fires driven by thermal buoyancy.Porous foams with different thicknesses are used to construct different thermal buoyancy driven airflow conditions.Combined with numeric-al simulations,the study examines variations in flus gas temperature,thermal buoyancy,and the resulting airflow under different smoldering conditions.Furthermore,the relationship between oxygen supply energy consumption driven by thermal buoyancy and the energy of smoke exhaust is analyzed.The results show that with the increase of foam thickness,the flus gas temperature gradully decreases,thermal buoyancy and the wind speed caused by it decrease,the smoldering intensity of underground coal fire decreases,and the energy consumption driven by thermal buoyancy decreases,but the ratio of thermal buoyancy to the exhaust energy of flus gas changes little.The ratio of oxygen supply energy to flue gas emission energy of thermal buoyancy drive increases with increas-ing crack depth,but the overall ratio is very small,and the change of crack depth varies within the range of 10-5-10-3.Research shows that compared with flue gas discharge energy,only a very small proportion(as low as one in a hundred-thousand)can be used to realize the self-sustaining spread of underground coal fires driven by thermal buoyancy,which is one of the fundamental reasons why underground coal fires are extremely difficult to control.

Abstract:To improve the drainage efficiency of outburst and low-permeability coal seam gas,this study takes the liquid CO2 displa-cing coal seam CH4 technology as the core,and explores the influence of CO2 injection pressure parameters and borehole spacing on gas drainage effect through the combination of numerical simulation and field test.Based on the geological conditions of the out-burst coal seam in Jixian Coal Mine,a fluid-solid coupling model was established,and the dynamic evolution laws of coal seam gas pressure under different pressure injection pressures(2-7 MPa)and borehole spacings(5 m,8 m,12 m)of liquid CO2 were analyzed.Based on this,the optimal process parameters of the field test were optimized and determined.The results show that the influence of liquid CO2 injection pressure on the effective drainage radius shows obvious stage characteristics,and the effective drainage radius is significantly expanded with the increase of pressure:when the injection pressure is 2-3 MPa,the effective extraction radius is 5.0-8.0 m;when the pressure increases to 4-5 MPa,the radius increases to 8-13 m,when it is further increased to 6-7 MPa,the radius can reach 13-20 m.The pressure change in the process of gas drainage can be divided into three stages:in 0-100 d,the CH4 pressure drop rate under 6-7 MPa injection pressure is higher than the average value of 0.004 5,and the displacement effect is better than that un-der low pressure conditions;in 100-200 d,5-7 MPa pressure still maintains a high pressure drop rate;after 200 days,the pressure drop rate was significantly slowed down due to the large amount of CH4 drainage in the early stage.The study results show that the optimal injection pressure is 5-7 MPa.The drainage effect of 5 m spacing is better than that of 8 m and 12 m.It is suggested that the 5 m spacing should be preferred in the project.In the field application,after injecting 8.2 m3 liquid CO2 into a single hole,the volume fraction of gas drainage increased to 3.57 times of the original,the extraction purity reached 6.96 times of the original,and the active period of drainage lasted for more than 85 days.

Abstract:In order to investigate the moisture infiltration process of pre-oxidized coal,the wetting exothermic properties and the in-fluence on oxidation and heat accumulation capacity of the coal body,the moisture infiltration process of pre-oxidized coal,the pore permeability properties,the wetting heat,and the evolution law of the functional groups have been analyzed by the low-field coal-rock nuclear magnetic resonance apparatus,the C600 high-precision microcalorimeter,and the Fourier infrared spectroscopy.The experimental results show that the water signal content of coal samples show a stable linear increase during water immersion,but the increase trend of pre-oxidized coal is much larger than that of the original coal,after 60 min water immersion,the relative water con-tent of adsorption pores of the original coal and the coals treated with pre-oxidation temperatures of 40,60,80,and 100℃reach 94.8%,95.7%,97.7%,99.6%,and 99.8%,respectively,under the same water immersion time,the relative water content of the ad-sorption pores of the pre-oxidized coal increases more,and the adsorption performance is stronger.The overall proportion of medi-um and large pores in the pre-oxidized coal decrease,the development of micropores leads to an increase in the proportion of trans-ition pores,the porosity increases from 15.9%to 32.3%,and the permeability enlarges by about 50 times,which enhances the oxy-gen adsorption and seepage capacity.The aromaticity and the degree of aromatic core condensation of the coal body under pre-oxida-tion show an increasing trend,and the hydrocarbon potential shows a decreasing trend.The proportion of hydrophilic groups such as hydroxyl group and carbonyl group in coal body increase,and the proportion of hydrophobic groups such as aromatic hydrocarbons decreases,which leads to the enhancement of the coal water affinity,and the two-phase wetting heat of coal and water increases from 6.3 J/g to 25.7 J/g,and the difference of exothermic intensity before and after the wetting heat is obvious,and the exothermic intens-ity is enhanced obviously by the heat accumulation after wetting,and the loose and porous nature of the coal body is further embod-ied and oxidation and heat accumulation capacity of the coal body is enhanced.Under the joint influence of pre-oxidation and wet-ting,the risk of coal spontaneous combustion increases,and the higher the pre-oxidation temperature is,the greater the risk is.

Abstract:In order to determine the range of the stress concentration area in the bottom roadway under the influence of the upper coal pillar and to reveal the pressure-bearing behavior and failure characteristics of the surrounding rock,taking the close distance coal seams 15#and 16#in Lingxin Mine as the research objects,the"principal stress difference"was introduced instead of the tradi-tional"vertical stress"as the evaluation index for the pressure-bearing characteristics of the coal and rock mass.This research was carried out using methods such as the"half-plane body theory"and FLAC3D numerical simulation.The results show that the differ-ence curves of the principal stresses at different burial depths of the 15#coal seam bottom plate have a unique envelope line,based on the"mutation point"of the principal stress difference curve of the 16#coal seam roof,it is inferred that the range of this stress con-centration area is approximately 45 meters;after the 15#coal was mined,the distribution of the principal stress difference in the shal-low surrounding rock of the 35 m boundary coal pillar floor showed a"double-peak"pattern,as the burial depth increased,the prin-cipal stress difference began to change from a"double-peak"pattern to a"single-peak"pattern;based on the distribution of the main stress difference of the surrounding rock in the roadway under different widths of the coal pillar,combined with the particular-ity of the roadway section,the analysis indicated that although an elastic core zone of a certain width can be formed under the 20-meter coal pillar support condition,the roof rock still shows significant asymmetric stress and failure characteristics.

Abstract:In order to study the effect of low molecular compounds in coal on the spontaneous combustion of coal,this study utilizes the technique of organic solvent extraction of low molecular compounds in coal to analyze the effect of low molecular compounds on the spontaneous combustion of coal.The results show that the extraction method does not affect the trend of the extraction rate of the three solvents,which were DMF>THF>JC.The extraction rate of ultrasonic assisted extraction was greater than that of Soxhlet ex-traction.The ultrasonic-assisted extraction rates of JC,THF,and DMF were respectively 33.77%,112.15%,and 87.85%higher than those of the Soxhlet extraction.The effect of ultrasonic extraction on functional groups was greater than that of Soxhlet extraction.The functional group area increased by 22.74%,25.05%,and 15.26%after JC,DMF,and THF Soxhlet extraction,and increased by 28.85%,33.71%,and 21.31%after ultrasonic extraction.After the extraction of raw coal by methanol,the content of functional groups in the remaining coal changed with a small magnitude;after the extraction of THF,the content of-OH decreased,and the percentage of other oxygen-containing functional groups increased;after the extraction of DMF,the content of aliphatic hydrocar-bons in the coal samples decreased dramatically,the content of-OH and-COOH decreased slightly,and the content of C=O and C-O content increased substantially.The complexity of the pores increased after extraction of low molecular chemosynthesis.The maximum pore volume of JC,THF,and DMF reached 0.053 cm3/g,0.060 cm3/g,and 0.040 cm3/g after Soxhlet extraction,and the percentage of mesopores was expanded from 75%before to 83%,77.5%,and 83.3%,and the percentage of macropores was de-creased from 25%of the original coal to 17.0%,22.5%,and 16.7%.After ultrasonic extraction,the total pore volume increased by 0.129 cm3/g,0.120 cm3/g,0.120 cm3/g,compared with the Soxhlet extraction.The energy generated by ultrasound enables the solvent to better penetrate into the coal molecules,resulting in better ultrasonic extraction than Soxhlet extraction.The oxygen con-sumption capacity of the extracted coal was positively correlated with the magnitude of the extraction rate.For the same solvent,the oxygen consumption of ultrasonically treated coal samples was higher than that of Soxhlet-extracted coal samples because the in-crease in pore size and specific surface gave more active sites for the residual coal to facilitate oxidation reactions.The increasing trend of CO gas volume fraction and oxygen consumption capacity of the extracted coal were DMF>THF>JC,which indicated that the small molecular structure of coal had an inhibitory effect on the spontaneous combustion of coal.

Abstract:In order to achieve a novel disaster early warning mode of"autonomous modeling+integrated early warning+root cause tracing",and improve the knowledge engineering infrastructure for integrated intelligent disaster warning,this study developed an ontology model for integrated knowledge graphs of disaster based on the"human-machine-environment"system engineering the-ory.The model was constructed through a top-down approach across four dimensions:temporal,spatial,managerial,and process mechanisms.It encompasses eight core concepts in this field of personnel,equipment,environment,region,process,document,in-dex,and disaster,along with three categories of data attributes(basic information,spatial information,and temporal information).Three types of relationships were established:spatial positioning,numerical correlations,and process mechanism linkages.A hybrid data storage architecture integrating relational,spatial,temporal,and graph databases was built.Data extraction for entities,attrib-utes,and relationships was achieved through a combination of rule-driven workflow engines and manual data supplementation,form-ing mine-specific disaster-integrated knowledge graphs.By adopting graph database relationship reasoning methods,coupled with anomaly identification criteria for graph objects,root cause analysis of mine disasters was realized.The results show that a"top-down"knowledge graph construction scheme that involves expert modeling and regularized data extraction is suitable in the early stage in the field of integrated analysis of mine disasters;the framework of"eight core concepts,three data attributes,and three rela-tionship types"significantly enriches disaster knowledge systems;the hybrid methodology of rule-driven engines and manual sup-plementation effectively addresses the needs of mines at varying intelligentization stages;knowledge graph relationship reasoning in-tegrated with object attribute anomaly detection provides a robust technical solution for accident causation analysis.