Abstract:During deep resource extraction,various disasters often exhibit characteristics of group occurrence and interrelation,with severe interactions and overlapping effects,making traditional prevention and control methods increasingly inadequate.Focusing on the core scientific issues of disaster prevention and control in deep mining stopes,this study systematically analyzes the manifesta-tions and distribution characteristics of multi-scale fractures in deep mine stopes.By introducing the Knudsen number to delineate different flow regimes,such as free molecular flow,slip flow,and continuous medium flow,it reveals the dominant influence of frac-ture scale on the transition from laminar to turbulent flow,frictional heating,and convective heat transfer efficiency.Combining Darcy and Forchheimer seepage models with convective heat transfer relations,a multi-level transmission chain of"fracture scale-permeability-flow velocity-heat flux density-temperature field"is constructed.The heat transfer enhancement coefficients under laminar and turbulent conditions are derived,elucidating the regulatory mechanism of fracture scale on flow regimes and heat-mass transfer from a mathematical modeling perspective.The research shows that during the coupling process of stress field,seepage field,fracture field,and temperature field in the incubation of deep mine disasters,the fracture field serves as the dominant primary field,while the others are secondary fields regulated by it.Based on this,a new perspective is proposed:"the fracture field is the funda-mental driver of disaster evolution,and scale effects are the dominant controlling parameter in disaster incubation".Taking the coupled disaster of gas and coal spontaneous combustion in typical deep mine scenarios as an example,a disaster prevention and control technical approach centered on actively regulating fracture scale is proposed.Through the application of liquid-phase sealing materials and inorganic grouting leakage-plugging materials,the area prone to spontaneous combustion defined by both seepage ve-locity and oxygen concentration is significantly reduced,seepage velocity within the region noticeably decreases,and air leakage around gas extraction boreholes is improved.Under optimal grouting conditions,the area of the composite hazardous zone is re-duced by 746 m2,and the flow field structure in the goaf is further optimized.Engineering practices demonstrate that liquid-phase sealing materials and inorganic grouting leakage-plugging filling materials can regulate the scale distribution of the fracture field,al-ter the mass and heat transfer characteristics of the flow field,and enable active intervention in and control of disaster evolution pathways.

Abstract:During the intelligent mining process in coal mines,the phenomenon of backwater from the drilling not only affects the safety and efficiency of the drilling operations,but also may cause equipment damage and personnel injuries.Therefore,accurately and efficiently identifying the phenomenon of backwater from the drilling openings is of great significance for ensuring the safety of the operations and improving the automation level of intelligent drilling machines.In view of the problems such as low accuracy,slow response and poor robustness in the current identification of backwater at borehole openings of underground coal mines,an in-telligent visual recognition method for backwater at drilling openings of the drilling rig based on the improved YOLOv5 is proposed,which effectively improves the accuracy and real-time performance of the identification.We has established a complete visual recog-nition system for backwater at drilling openings,including core components such as explosion-proof cameras,AI image processors,and drilling rig controllers.Through self-developed visual recognition devices,the system realizes the up-down adjustment and 360° rotation functions of the cameras,thereby obtaining video images from different angles.This avoids recognition failures caused by complex working conditions such as obstructions or backlighting,significantly improving the adaptability and recognition accuracy of the system.In terms of the model structure,several optimizations were made to the original network structure of YOLOv5.A TRANS(transformer)module was introduced in the backbone network to enhance the feature extraction capability of model;in the neck network,the GhostBottleneck structure was adopted to replace the traditional cross stage partial(CSP)module,which reduced the computational load and improved the lightweighting level of model;in addition,the activation function was replaced from sig-moid linear unit(SiLU)to the more efficient Hardswish,further enhancing the nonlinear expression ability and inference speed of the model.By using the self-collected and labeled dataset of waterback images from drilling openings,the model training and optimiza-tion were completed.To verify the effectiveness of the proposed method,the improved YOLOv5 model was compared with YOLOv3,YOLOv4,YOLOv5,YOLOv8n through experimental tests.The results show that the improved YOLOv5 has increased the recognition accuracy by 1.49%,1.06%,0.49%,and 0.18%respectively,and the average recognition time has been shortened to 7.4 ms.It demonstrates excellent recognition performance and real-time response capability.Currently,this system has been de-ployed and applied in 4 coal mines in Inner Mongolia-Shaanxi region.The on-site test results show that the accuracy rate of backwa-ter recognition at drilling openings is as high as 99.63%,which is significantly better than traditional methods.The system operates stably and reliably.

Abstract:Frequent"muffled blast"sounds accompany coal mining in some coal mines in central China,which characterize the sudden release of stored energy and pose a potential threat to the safe production of coal mines.To investigate the generation mech-anism of"muffled blast"sounds in the surrounding rock of coal seam roadways,taking the No.15 coal seam of Yangsheng Coal In-dustry as the engineering background,the sources of"muffled blast"sounds were located via micro-seismic monitoring.After on-site sampling,mechanical tests and acoustic emission monitoring were carried out on coal and rock masses,and a comprehensive analysis was conducted through numerical simulation with the real failure process analysis(RFPA)software combined with field measurements.The results show that the limestone roof stratum has high brittleness,low strength and well-developed fractures.Un-der the action of stress disturbance or periodic stress concentration in high-position strata,fracture propagation occurs in the sur-rounding rock of roadways,generating a large number of acoustic emission signals.The failure of roadway surrounding rock is dom-inated by shear failure,and the acoustic emission signals are mainly concentrated within the range of 15 m in the two ribs and 10 m in the roof of the roadway,with most accumulating near the rib-roof corners.During the deformation and failure process of the road-way,a large amount of elastic energy accumulates in the area where acoustic emission signals concentrate,and the release of this elastic energy gives rise to the"muffled blast"phenomenon.This verifies that the"muffled blast"phenomenon is mainly caused by the instantaneous release of energy during the deformation and failure of surrounding rock,and is not a precursor of rock burst.

Abstract:In order to investigate the competitive adsorption pattern of N2/CH4 gases in coal under thermal and displacement effects,the study is based on the macromolecular model of bituminous coal,the adsorption behaviors of methane molecules,water mo-lecules and fracturing fluid molecules under heated nitrogen injection are simulated by molecular dynamics and Monte Carlo meth-ods,to investigate the interaction energy between fracturing fluid and coal surface molecules,and the microscopic laws of different gas injection temperatures,water contents and pore diameters on the competitive adsorption of N2/CH4.The results show that:the in-teraction between fracturing fluid molecules and coal molecules is 18.469 kJ/mol,the van der Waals interaction force between the systems is 23.732 kJ/mol,the electrostatic interaction force is-598.125 kJ/mol,and the stability of the system between the fracturing fluid molecules and the coal molecules is poor,which provides conditions for the injection of heated nitrogen to increase the seepage of the de-blocking;in the process of heated nitrogen injection,along with the increase of temperature,the adsorption capacity of N2 relative to CH4 in the model is enhanced;the increase in water content leads to a significant decrease in the adsorption of both CH4 and N2,and the adsorption capacity of CH4 remains stronger than that of N2 in the model;pore size has a significant effect on N2 ad-sorption,the dominance of CH4 begins to decrease with the increase of pore size,and the effect of N2 replacement to drive out CH4 is obvious when the pore size is 4 nm.

Abstract:The protective coal pillars in the downhill sections of deep mines are long-term in a complex environment of"three highs and one disturbance"(high stress,high water pressure,high ground temperature and excavation disturbance),and their cumulative creep damage effect significantly affects their long-term stability.Traditional design methods based on static assumptions are diffi-cult to meet engineering requirements.Taking the north No.3 mining area of Yangcheng Coal Mine as the engineering background,aiming at the long-term stability problem of downhill protective coal pillars,a numerical analysis method based on the Burgers creep model is proposed.Five groups of comparative tests were conducted to calibrate the parameters of the Burgers model,revealing the calibration laws of each parameter of the Burgers model on the instantaneous creep deformation,initial creep rate,and stable strain,and verifying the consistency between the numerical simulation results of coal samples and the laboratory creep test results(the max-imum error<3.5%).based on the FLAC3D numerical simulation software to construct a geomechanical model,this study integrates theoretical calculation,static simulation and creep analysis to compare the widths of downhill protective coal pillars in the mining area when the time effect is not considered,including the"three unders"mining(mining under buildings,railways and water bod-ies)specification method(56.3 m),the limit equilibrium theory(53.7 m)and the Mohr-Coulomb elastoplastic model(58.8 m),fur-thermore,the Burgers model is introduced to analyze the creep characteristics of coal pillars.The simulation results show that within the 10-year service period of the protective coal pillar,creep of the coal pillar causes the in-situ stress boundary to migrate toward the roadway.The distance between the final mining line of the working face and the stress boundary increases from 58.8 m to 72.3 m,the horizontal displacement remains basically stable after 3 years,and accumulated displacement during the creep period is approx-imately 70 mm.Considering the influence of advance abutment pressure and the cumulative effect of creep damage comprehens-ively,the reasonable width of the downhill protective coal pillar in the north No.3 mining area is finally determined to be 75 m.

Abstract:Cavity-making technology in coal seams is one of the main technologies for controlling gas in loose,low-permeability,and difficult-to-drain coal seams.Due to the limitations of equipment and process technology,the on-site construction parameters of cavity-making are mostly determined based on equipment feasibility.To achieve uniform and refined gas drainage,the design para-meters of mechanical cavity-making need to comprehensively consider the drilling results of cavity-making boreholes and the evolu-tion law of the effective influence range.In order to clarify the influencing factors of borehole formation and the spatio-temporal evolution law of drainage characteristics of mechanical cavity-making in high-gas loose coal seams,and to provide a basis for the reasonable design of construction parameters,a study on the dynamic response law of drainage characteristics of cavity-making per-meability enhancement technology in high-gas loose coal seams was carried out through numerical calculation and on-site experi-ments.The results show that during the drainage process,the effective influence range of mechanical cavity-making boreholes in high-gas loose coal seams presents a geometrically non-uniform distribution in space.On the spatial plane where the section normal is parallel to the borehole axis,the evolution of the effective influence range of drainage boreholes presents a concentric circle distri-bution with the diameter gradually increasing from the inside to the outside.On the spatial plane where the section normal is perpen-dicular to the borehole axis,the evolution of the effective influence range of drainage boreholes presents a spindle-shaped distribu-tion.The effective influence range of drainage boreholes in three-dimensional space presents a frustum-shaped dynamic evolution.During the cavity-making operation,the coal pillars between cavities are mainly shear instability under cyclic loading,and the scope of the instability zone is mainly affected by the cavity diameter and the length of coal pillars between cavities.Based on the above results,a cavity-making parameter design model coupled with factors such as plastic zone change,cavity diameter,and coal pillar length between cavities was established,and on-site experiments were carried out based on the parameters designed by the model.The on-site experimental results show that the mechanical cavity-making technology has a significant promoting effect on gas con-trol in high-gas loose coal seams.Compared with conventional drainage methods,the overall gas drainage effect is improved by 4 to 6 times.

Abstract:In order to reveal the influence of bedding properties on the stability of coal mine roadway,the study established a 3D nu-merical model combined finite differential method(FDM)coupling discrete element method(DEM).In the model,the two sides of the roadway,the floor and the far-field surrounding rock are simulated by the continuous medium domain created by FLAC3D,while the layered roof rock mass of the roadway is created by the bonded particle model(BPM)in PFC3D,and the bedding planes are real-ized by adding parallel weak planes with specific stiffness and strength.In the study,the properties of the bedding were simulated by varying the strength of the weak plane to investigate the fracture characteristics of the layered roof under the action of excavation and unloading.The results showed that the fracture distribution in the intact roof was dome-shaped,while the fractures in the layered roof were distributed along the weak plane.The failure of the layered roof started from the layer adjacent to the goaf and expanded in-ward.The increase in bedding strength will change the stress field distribution within the roof,and to alter the development process of fractures in the roof.The coupling strategy of PFC3D/FLAC3D can effectively reproduce the fracture development process of the layered roof in coal mines under the action of roadway excavation and unloading.

Abstract:In order to clarify the deformation law of the coal body in the adsorption-desorption process and reveal its intrinsic domin-ant mechanism,a study on the strain characteristics of the coal body in the CH4 adsorption-desorption process was carried out.The isothermal CH4 adsorption-desorption experimental test of the coal body was carried out at room temperature on an independently constructed experimental platform.Using He as the reference gas,the transient and residual strains during CH4 adsorption-desorp-tion process were systematically analyzed in the pore pressure range of 1.0-5.0 MPa,and the deformation law of coal body during the interaction between coal and gas was studied in depth.The results show that coal has complex pore structure and strong adsorption capacity,CH4 adsorption causes swelling and deformation of the coal body,and desorption leads to contraction of the coal body,which triggers a series of coupled effects of stress change and seepage behavior.In the CH4 adsorption-desorption process,the pore pressure and coal body strain showed a positive correlation trend.With the increase of pore pressure,the volumetric strain induced by CH4 adsorption on the coal body increases significantly,and the residual strain after desorption also increases.Compared with He,the adsorption swelling strain produced by CH4 under the same pressure condition is 1.77-3.52 times,and the desorption residual strain is 2.02-3.36 times,indicating that CH4 adsorption-desorption has an obvious irreversible deformation characteristic on the coal body.The swelling deformation caused by CH4 adsorption is mainly dominated by the filling and swelling elastic deformation of the pore-crack structure,the adsorption swelling deformation of the coal matrix,and the pore damage deformation induced by the ad-sorption stress,while the residual deformation after desorption is mainly controlled by the micro-damage effect caused by the release of pore pressure,the reorganization behavior of the coal molecular structure during desorption,and the irreversible deformation of the pore structure,among other factors.

Abstract:To address the issues of high dust concentration at coal mine belt transfer points and the insufficient efficiency of existing dust suppression technologies,a closed-type spray-induced jet purification and dust removal technology is proposed.This techno-logy integrates a coal baffle plate,an arched enclosed hood,and a double-flared-mouth jet ejector to create an enclosed environment,thereby minimizing dust leakage.The ejector generates a negative pressure zone through high-pressure water spray,drawing dust-laden airflow into the ejector throat.The collision and coalescence of fog droplets with dust particles facilitate wetting and sediment-ation,while the secondary negative pressure expands the dust suppression range,forming a synergistic mechanism of"enclosed en-vironment+negative pressure induction+fog droplet capture".This approach surpasses the efficiency limitations of traditional spray dust suppression methods,enhancing dust capture efficiency.Initially,the effectiveness of the dust removal technology of the physical model of corresponding device was validated through numerical simulations based on the Standard k-ε turbulence model and the Taylor analogy breakup(TAB)model,revealing its notable dust removal capabilities.A positive correlation was observed between spray pressure and induced airflow volume,with higher spray pressures yielding better dust removal results.Building on this,a nozzle performance testing platform was developed to systematically investigate the induced airflow volume patterns of five nozzle types under varying pressures.The nozzle with the optimal induced jet efficiency was selected and paired with the closed-type spray-induced jet dust removal device for field application verification at a coal mine underground transfer point.The dust suppres-sion efficiency of three methods(enclosed device only,enclosed+conventional spray,and enclosed+induced spray)was compared by sampling and analyzing the dust concentration at the air outlet.The application results indicated that the closed-type spray-in-duced jet purification and dust removal device,operating at a pressure of 6 MPa,reduced the total dust mass concentration at the transfer point from 155.33 mg/m3 to 8.67 mg/m3,achieving a dust suppression efficiency of 94.42%,which significantly outper-formed other dust removal methods.The study shows that through multi-physical field coupling effects,this technology can markedly enhance dust capture efficiency,offering an innovative solution for dust management at coal mine transfer points and demonstrating substantial engineering application value.

Abstract:To enhance the impact resistance and energy absorption performance of hydraulic supports in mitigating coal mine rock burst,a hyperbolic shallow shell anti-impact energy-absorbing component was designed.Finite element numerical simulations were conducted to analyze the performance of a navel anti-impact energy-absorbing component under various parameters,including base arc chord height,lateral arc eccentricity,lateral arc chord height,stacking layers,as well as wall thickness and different materials.The finite element analysis results show that:increasing the base arc chord height(Lc)improved the load-bearing capacity of the component,with the average load-bearing force approaching the initial peak value,specifically,when the base arc chord height in-creased from 10 mm to 20 mm,the initial peak load-bearing capacity rose by 28%,and the average load-bearing capacity increased by 61;a larger lateral arc eccentricity(Lp)reduced the initial peak load-bearing capacity,while the average load-bearing capacity and total energy absorption peaked at an eccentricity of 5 mm,achieving values of 3 126 kN and 312.6 kJ,respectively;increasing the lateral arc chord height(Ld)decreased both the initial peak and average load-bearing capacities,with a notable acceleration in reduc-tion observed when the lateral arc chord height increased from 2 mm to 4 mm,resulting in an 11.9%decrease in initial peak capacity and a 12.5%reduction in average capacity;stacking additional layers stabilized the load-bearing capacity but widened its fluctuation range,with minimal variation in peak impact force Fmax;thicker walls enhanced load-bearing capacity without significantly affecting the fluctuation coefficient;material selection had a negligible impact on structural stability.When the chord height distance of the bottom surface of the hyperbolic shallow shell anti-impact energy absorption component is 20 mm,the side chord height distance is 2.5 mm,the eccentricity is 5 mm,the stacking layer number is 3,and the thickness is 8 mm,the initial peak bearing capacity of the hyperbolic shallow shell anti-impact energy absorption component reaches 3 390 kN,the average bearing capacity reaches 3 341 kN,the load fluctuation coefficient is 1.01,the total plastic deformation energy absorption of 100 mm is 334.1 kJ,the energy absorption per unit mass is 35.4 kJ/kg,which best meets the requirements of the energy absorption support,and it can be applied to various hy-draulic supports by adjusting the size,material and thickness.

Abstract:To address the dual challenges of upgrade efficiency and service reliability in wireless firmware updates for underground coal mine positioning systems,this study proposes a dual-mode redundant upgrade architecture based on coordinated transmission of ultra-wideband(UWB)and long range low-power wireless communication technology(LoRa).The architecture organically integ-rates centimeter-level high-precision positioning capability of UWB with wide-area communication coverage of LoRa,thereby estab-lishing a heterogeneous network system with spatial self-adaptation.In communication strategy design,a dynamic dual-mode co-ordination mechanism is developed.In sparsely distributed terminal areas,the system employs UWB technology for time-division multiplexing of positioning signals and firmware upgrade channels,which simultaneously meets precise positioning requirements and enables point-to-point firmware transmission;in terminal-dense areas,a dual-mode division-of-labor mechanism is enabled,while UWB continuously provides real-time positioning services,independent channels of LoRa are used for parallel broadcast-style firmware distribution,thereby significantly enhancing the efficiency of multi-terminal upgrades.To ensure secure operation in com-plex underground environments,a triple-layer protection system is implemented.First,a hierarchical key management system com-bining RSA asymmetric encryption and AES symmetric encryption establishes peer-to-peer encryption for firmware transmission,ef-fectively preventing data leakage and tampering.Second,an adaptive firmware acquisition mechanism based on spatial distribution characteristics enables terminals in sparse areas to actively initiate firmware requests while base stations proactively broadcast up-grade packages in dense areas,incorporating firmware breakpoint resume functionality to enhance transmission reliability.Third,a dual-partition firmware upgrade strategy performs CRC-32 cyclic redundancy checks and SHA-256 Hash verification at the Boot-loader layer,ensuring automatic rollback to stable backup partition versions upon upgrade failures.Experimental results demonstrate that the system maintains the maximum positioning error below 30 cm regardless of whether in the sparse area or the dense area of the terminals,achieving 100%firmware upgrade success rate.This fully validates the comprehensive advantages of the dual-mode redundant architecture in precision positioning,upgrade efficiency,and operational reliability.

Abstract:To study the stability and cumulative failure of Beskuduk Open-pit Mine slope under repeated blasting vibration,the 3DEC software is adopted to deeply investigate it.The slope numerical model is set up according to the slope structure characteristic.The measured blasting seismic wave of the mine is used as the vibration input of the model,and the variation laws of the slope hori-zontal displacement,stability coefficient and failure process with the number of blasting vibrations are simulated and analyzed.The field displacement monitoring results are adopted to validate this numerical model.The results show that the failure process of the slope under repeated blasting vibration can be divided into three stages:the initial failure stage,the crack development stage and the instability failure stage;with the increase of the number of blasting,the cumulative displacement of each bench continuously in-creases,and shows a slow-fast-slow variation law.The stability coefficient of the slope gradually decreases,and shows a slow-fast variation law.When the slope is subjected to 320 repeated blasting vibrations,the stability coefficient of the slope drops to 1,reach-ing the critical failure state.The influence law of the vibration acceleration amplitude and layer thickness on the dynamic response of the slope is studied with the parameter sensitivity analysis.It was found that with the increase of the number of vibrations,the cumu-lative displacement of each bench continuously increases.When the peak acceleration of the seismic wave is 0.1g,0.2g and 0.4g re-spectively,the number of vibrations required for the slope stability coefficient to drop from the initial 4.7 to 1 is 290,180 and 24 re-spectively.That is,the larger the vibration load amplitude,the smaller the number of vibrations required for slope instability failure.When the layer thickness is 3 m and 8 m respectively,the slope stability coefficient decreases from the initial 3.82 and 6.58 to 1 after 162 and 467 vibrations respectively,and the slope becomes unstable.That is,the larger the layer thickness is,the stronger the initial stability of the slope is,and the more vibrations are required for failure.

Abstract:Coal modification treatment is an important technical means to improve the methane desorption performance of coal and the permeability of coal seam,so as to improve the ability of coal seam gas extraction.Three kinds of quaternary ammonium surfact-ants were prepared into solution to modify long-flame coal,and the influence of quaternary ammonium surfactants on the key chem-ical structure of long-flame coal was studied.Based on Fourier transform infrared(FTIR)spectroscopy experiment,combined with peak-splitting fitting method to calculate relevant structural parameters,this study aims to clarify the variation characteristics of key functional groups in coal samples during methane adsorption and evaluate methane desorption capacity.The results show that the treatment of quaternary ammonium surfactants does not change the position of infrared absorption peak,but only affects the absorp-tion peak intensity and the relative content of functional groups.After the treatment of quaternary ammonium surfactants,the oxy-gen functional groups and condensation degree parameters of long flame coal are reduced.In particular,after benzalkonium bromide solution treatment with a mass fraction of 0.1%,the absorption peak area of aromatic structure decreased by 35.56%,maturity para-meter decreased by 96.8%,aliphatic chain length increased by 61.2%,and the aromatic ring condensation degree parameter de-creased by 58.56%.By analyzing the relationship between structural parameters and methane desorption capacity,it is found that 0.1%benzalkonium bromide solution has the most significant effect on the desorption capacity of long-flame coal.

Abstract:Coal mine accident prevention measures are of extremely crucial significance for safeguarding the lives of miners and en-suring the stable operation of coal mines.Assessing the efficacy of these measures is a core component in optimizing accident pre-vention strategies and enhancing prevention capabilities.However,current accident prevention measures lack systematic means for efficacy validation,making it difficult to precisely quantify their actual impact.This study focuses on this issue,conducting a com-prehensive analysis of accident prevention measures and developing a quantitative model for efficacy assessment from a resource perspective.The study thoroughly reviewed the research,practice,and evaluation status of coal mine accident prevention measures,categorizing them into six types:technical,managerial,regulatory and policy,economic incentive,social participation,and emer-gency response measures.The differences in resource utilization among these types were carefully analyzed.Based on this analysis,a quantitative model for assessing the effectiveness of coal mine accident prevention measures was developed,incorporating four in-dicators:types of resource allocation,allocation ratios,effectiveness duration,and utilization capabilities.Taking Pan'er Mine of Huainan Mining Group as a case study,the efficacy value of its accident prevention measures was calculated using a combination of expert ratings,questionnaires,and on-site data.A refined resource allocation plan was then proposed as the output of the model,di-viding resources into eight categories:human,technical,financial,material,physical,informational,managerial,and emergency re-sources.The efficacy of the optimized plan was re-evaluated.By comparing the results before and after optimization,suggestions for improving accident prevention measures were put forward.Additionally,the data validity of eight key indicators within the model was examined to verify the accuracy and rationality of the model results.The study results indicate that the efficacy value increased from 1.235 5 before optimization to 1.300 4 after optimization.The quantitative model can effectively assess the efficacy level of coal mine accident prevention measures and provide an optimization direction for resource allocation plans.

Abstract:To address the issue of dust dispersion in fully mechanized mining faces,a novel negative pressure-spraying dust suppres-sion device based on the principle of the Coanda effect was designed.This device not only effectively covers the dust generated by the shearer drum but also utilizes the suction effect generated by the device itself to collect the dispersed dust in the tunnel.Computa-tional fluid dynamics(CFD)was used to conduct numerical analysis of the airflow field and droplet characteristics in the shearer working face.An orthogonal experiment was performed to investigate the effects of nozzle aperture(A),spraying pressure(B),in-stallation angle(C),and negative pressure device pressure(D)on the atomization characteristics and suction effect of the device.The results indicate that the importance order of the factors influencing droplet size is B>D>C>A,and the importance order of the factors influencing suction velocity is D>C>B>A.As the spraying pressure increases,the droplet size distribution becomes in-creasingly concentrated,which promotes droplet refinement.For droplet mass concentration,a larger nozzle aperture helps form a higher mass concentration droplet field,while spraying pressure has a minimal effect on droplet mass concentration.The pressure of the negative pressure device significantly affects droplet velocity;as the negative pressure device pressure increases,the droplet velo-city increases,while changes in spraying pressure have little effect on droplet velocity.Comprehensive analysis revealed that the op-timal parameter combination for droplet size distribution,droplet velocity,and dust suppression performance is:nozzle aperture(A)of 2.4 mm,spraying pressure(B)of 8 MPa,installation angle(C)of 0°,and negative pressure device pressure(D)of 0.2 MPa.Un-der these conditions,the suction airflow can reach 360 m3/min,and the device achieves optimal dust suppression performance.A comparison of the effectiveness of dust suppression device before and after its application on the shearer shows that the device not only effectively encapsulates the dust source from the drum but also guides the airflow in the tunnel,reducing the diffusion of dust into the working area.

Abstract:To prevent water inrush accidents in the coal mining face caused by the development of the water-conducting fracture zone in the overlying strata to the aquifer,this study conducts an in-depth study on the height of the water-conducting fracture zone and the caving zone(hereinafter referred to as"two zones")under the condition of fully mechanized caving mining of the ex-tremely thick coal seam in 8514 working face of Chenjiagou Coal Mine.The overlying strata of 8514 working face are mainly com-posed of mudstone,sandy mudstone and siltstone,and the geological unit structure is relatively simple.The overlying strata have been significantly affected by mining activities due to the fully mechanized caving mining of the thick coal seam.Based on the integ-ration of multi-source data such as ground drilling measurements,theoretical calculations using empirical formulas,numerical simu-lations(3DEC and FLAC3D),and similar simulations,the development heights of the collapse zone and the water-conducting frac-ture zone are comprehensively analyzed.The research shows that:the water-conducting fracture zone height of the ZK-1 borehole is 151.71 m and the height of the collapse zone is 87.21 m;the theoretical calculation results using empirical formulas show that the height of the water-conducting fracture zone is 134.21 m and the height of the caving zone is 53.92 m;the numerical simulation ana-lysis results(using 3DEC and FLAC3D methods)show that the height of the water-conducting fracture is 122.6 m and the fracture-to-mining ratio is 10.66;the similar simulation analysis results show that the height of the water-conducting fracture zone is 135.7 m and the fracture-to-mining ratio is 11.8;from the perspective of safe production,the height of the water-conducting fracture zone is 151.71 m and the fracture-to-mining ratio is 12.24;the height of the collapse zone is 87.21 m and the caving-to-mining ratio is 7.03.

Abstract:The study on the dynamic mechanical characteristics of rocks under impact loading holds significant theoretical guiding significance for achieving controlled blasting during roof cutting blasting.Based on a split Hopkinson pressure bar(SHPB)test sys-tem,sandstone from the roof of Dingji Coal Mine in Huainan city was tested.By varying impact velocities to achieve different strain rates,the stress-strain relationship of sandstone under impact loading at different strain rates was obtained.The strength characterist-ics of sandstone specimens under different strain rates were analyzed and internal crack evolution and fractal dimension changes were investigated by CT scanning.The results indicate that stress-strain curves under varying strain rates comprise four stages,namely:the primary fracture compaction stage with concave sections,the approximately elastic linear deformation stage with differ-ent slopes,the yield stage with nonlinear increase of stress,and the softening failure stage with significant decrease of stress as de-formation increases.The dynamic peak stress,dynamic elastic modulus and strain rate show a significant positive correlation.The in-crease of strain rate can enhance the ultimate bearing capacity of the specimen.The dynamic strength growth coefficient of the speci-men increases with the increase of strain rate,but there exists a critical strain rate state.Under the action of impact dynamic loading,the cracks in sandstone specimens expand from the outside to the inside,tangential to radial,and interpenetrate each other,present-ing the characteristics of tensile splitting failure evolution.With the increase in the number of impacts,the specimen as a whole shows an increase in the number of cracks,an increase in the volume and area of cracks,and a slow to significant increase trend in the volume and area of cracks,while the fractal dimension shows a significant to slow increase trend.

Abstract:Coal spontaneous combustion is a major hidden danger in coal mine safety production,and the traditional coal spontan-eous combustion inhibition material has the problems of single principle,complex preparation process and high cost.In view of the existing problems,we use sodium carboxymethyl cellulose(CMC),citric acid and sodium secondary alkyl sulfonate(H95)as raw materials to prepare a new type of gel inhibitor material that can simultaneously play two roles of physical barrier and chemical in-hibition in the process of coal oxidation by reasonable ratio.The chemical structure of the new material before and after preparation was characterized by Fourier transform infrared spectroscopy.The inhibition performance of the new material was analyzed by test-ing its viscosity,wettability and water retention,and the inhibitory effect of the new material on coal oxidation was evaluated by tem-perature programmed experiments and thermogravimetric analysis experiments.The results showed that in the prepared new materi-als,CMC and citric acid produced chemical crosslinking and hydrogen bonding,which proved that the gel was successfully com-pounded with chemical inhibitors.When the mass fraction of CMC was 2%,the viscosity of the new material and pure CMC gel reached 1.12 Pa·s and 3.83 Pa·s,respectively.At this time,the solution state of the new material is most suitable for spraying;the maximum wetting heights of the new material,mass fraction 2%pure CMC gel and deionized water on pulverized coal were 12.5 mm,10.3 mm and 9.9 mm,respectively.The water loss rates of the three materials after vacuum drying for 10 h were 87.06%,82.71%and 97.61%,respectively.Compared with raw coal and citric acid treated coal,the cross point temperature of coal samples treated with new materials increased by 5.5 ℃and 2.1 ℃respectively.When the oxidation temperature reaches 180 ℃,the CO gas volume fraction,oxygen consumption rate and exothermic intensity are reduced by 50.57%,69.5%and 59.5%respectively com-pared with raw coal,and reduced by 33.1%,45.1%and 28.3%respectively compared with citric acid treated coal.The five oxidation characteristic temperature points of coal samples treated with new materials in thermogravimetric analysis experiment are signific-antly lower than those of raw coal and citric acid treated coal,and the spontaneous combustion tendency is weaker than that of the other two groups of coal samples.This study verifies the feasibility of new materials to inhibit coal spontaneous combustion,and puts forward the application of new materials to the underground atomization spraying process.

Abstract:To clarify the spontaneous combustion risk of residual coal under long-term water immersion and gas-containing airflow in underground mines and investigate the effects of dual water immersion and gas action on its spontaneous combustion characterist-ics,water-soaked coal samples were prepared by immersing partial coal samples in distilled water at a constant temperature of 30℃for 30 days.Programmed temperature rise experiments for coal spontaneous combustion,simultaneous thermal analysis,and in-frared spectroscopy were conducted to analyze the temperature-dependent variations in oxidation products,apparent activation en-ergy,and heat release intensity during the low-temperature oxidation process of air-dried raw coal and water-soaked coal under three gas volume fractions(0,1.5%,and 3%).Additionally,the evolution characteristics of functional groups after low-temperature oxida-tion.The results show that with the increase of gas volume fraction during low-temperature oxidation,the oxygen consumption rate,oxidation product generation rate,total heat release,and relative content of active functional groups of two coal samples gradually decrease,with more significant reductions observed in water-soaked coal compared to raw coal;the temperatures corresponding to the occurrence of C2H4,the achievement of thermal equilibrium,and the peak of heat flux all increase with the rise in gas volume fraction,Showing an obvious temperature hysteresis,and the increase in water-soaked coal is greater than that of raw coal;the activ-ation energy required for low-temperature oxidation increases progressively,with a larger increment in water-soaked coal.Under the same gas volume fraction,water-soaked coal demonstrates higher oxygen consumption rate,oxidation product generation rate,total heat release,and relative active functional group content than raw coal;the appearance of C2H4,thermal equilibrium,low-temperat-ure oxidation activation energy,and heat flux peak temperature are lower in water-soaked coal than in raw coal.Comprehensive ana-lysis reveals that water-soaked coal exhibits stronger spontaneous combustion tendency than raw coal,indicating that gas exerts a more stronger inhibitory effect on the oxidation of water-soaked lean coal at the same gas volume fraction.However,the promoting effect of water immersion on the spontaneous combustion of lean coal outweighs the inhibitory effect of gas on water-soaked coal.In environments with low gas volume fractions,water-soaked lean coal is more prone to oxidation and spontaneous combustion than raw coal.

Abstract:Pre-injection of inhibitor solution is the source prevention technology of coal spontaneous combustion,which can effect-ively solve the fire problem caused by oxidation of coal.In order to study the effect of the inhibitor solution on the pore and fracture structure of the coal body and its seepage law,based on CT scanning experiments and CT three-dimensional reconstruction techno-logy,we constructed a three-dimensional pore and fracture structure model of the coal body,elucidated the effect of the inhibitor solution on the microscopic pore and fracture structure of the coal body.Based on the real pore and fracture structure of the coal body,Comsol was used to simulate the seepage characteristics of the inhibitor solution in the microscopic pore and fracture of the coal body,and to study the influence of the pore and fracture structure of the coal body and different pressure injection conditions on the seepage effect of the inhibitor solution and its role in the law.The results show that the pore and fracture structure of the original coal is denser than that of the inhibited coal samples.In the range of pore size of 0-100 μm,the number of pore and fractures in treated coal samples of inhibitor solution was smaller than that of the original coal,and the fractal dimension and porosity of the coal samples were reduced by 0.63%and 19.30%,respectively.The degree of throat development of the original coal was more signific-ant than that of the inhibited coal samples,and the inhibitor solution hindered the development of the coal body throat to a certain ex-tent.After the original coal was treated with the inhibitor solution,the average coordination number decreased by 17.9%,and the connected pore area and connected volume percentage of the coal samples decreased by 32.4%and 4.7%,respectively.With the in-crease of seepage pressure,the average seepage velocity gradually increased,and the maximum seepage velocity appeared at the pore with larger pore diameter,specifically at the position of section 192 μm;within the range of 0-192 μm at the cross-section position,the pressure field changes were more gentle due to the existence of well-connected pore channels with larger pore diameter.From the above analysis,it can be concluded that inhibitor solution inhibits the development of the pore throat structure and connectivity of the coal body to a certain extent,and the change of the structure affects the seepage characteristics of the inhibitor solution inside the coal body,which in turn affects the coverage area of the inhibitor solution inside the coal body,reduces the contact area between the coal body and oxygen,and slows down the rate of coal-oxygen composite reaction to achieve the flame retardancy purpose.