Abstract:Polycrystalline diamond compact(PDC)drill bits are increasingly used in coal mine drilling due to their efficient rock-breaking capabilities.To better understand how cutting parameters affect the forces on PDC cutters,a single-cutter cutting experiment was conducted.A corresponding cutting force calculation model was developed and validated through simulation.Building on global force balance principles,a MATLAB GUI based software was created to optimize cutter layout parameters.This software was applied to a five-wing flat-bottom drill bit,optimizing the circumferential angle(θ),back rake angle(α),and side rake angle(β)through multi-objective analysis.Experimental and simulation results revealed that cutting depth has the greatest influence on cutting force,followed by back rake angle and cutting speed.Using the optimization software,both lateral force and bending moment on the drill bit were significantly reduced.Specifically,the lateral thrust ratio(lateral force to drilling pressure)decreased to 1/1 000,and the bending-torsion ratio(bending moment to torque)decreased to 1/100.Abaqus simulations further confirmed the effectiveness of the optimization,with the average lateral force reduced by 1.81 kN and the average bending moment by 0.163 kN·m,alongside a noticeable reduction in data variability.These reductions in lateral force and bending moment are expected to enhance drilling efficiency.Additionally,the software's computational requirements remained stable despite changes in cutter layout parameters.Overall,this optimization software provides an effective tool for improving cutter layout design,thereby increasing the efficiency of drill bit development.

Abstract:In order to explore the influence of light environment on the recognition ability of safety mark,an eye movement experiment was designed to analyze the change rule of the recognition ability of the subjects under different light environment and mark color conditions.The experiment simulated 12 mixed light environments,9 color temperatures and safety mark color matching schemes.The eye movement data of the subjects were recorded,and the two-way and one-way ANOVA were used to explore the changes of recognition ability under different environments.The experimental results show that the change of illumination has a significant impact on the recognition ability of safety marks.The fixation times,fixation time and blink frequency in the range of 20 lx to 240 lx are significantly higher than those in the range of 240 lx to 900 lx.The change of color temperature has a certain impact on the recognition ability,and the color temperature range of about 3 500 K is easier for the subjects to accept.Different mixed light environments will change the difficulty of identifying safety marks.When the contrast between the color of safety marks and the ambient color temperature is low,the identification efficiency of the subjects decreases.Under conditions of sufficient illuminance,the influence of both color temperature and mark color on recognition ability is weakened.In actual workplaces,managers should give priority to improving unreasonable light conditions to enhance the overall recognition efficiency of safety marks.

Abstract:In view of the great influence of No.2 coal seam mining in Yangchangwan Mining Area on the overlying rock aquifer(from the bottom sandstone section of Zhiluo Formation to the roof sandstone aquifer group of No.2 coal seam and the quaternary phreatic aquifer group),in order to find out the hydrochemical characteristics of groundwater in the mining area and the source of mine water inrush,15 water samples were collected.The Piper three-line diagram,Gibbs diagram and ion ratio method were comprehensively used to analyze the conventional hydrochemical components of groundwater in Yangchangwan Mining Area,and the cluster analysis and fuzzy evaluation method were used to identify the source of mine mixed water.The results show that the TDS of each aquifer is generally high and increases with the increase of buried depth.The main cations are K+and Na+,and the anions are mainly Cl-and SO2-4.The Quaternary pore phreatic aquifer is Na-SO4 type,and the sandstone aquifer at the bottom of Zhiluo Formation and the mine mixed water quality type are Na-Cl type.The hydrochemical components of each aquifer are mainly affected by evaporation and concentration,and are basically not affected by atmospheric precipitation.In the Zhiluo Formation aquifer,K+and Na+mainly come from the dissolution of silicates.In the mine mixed water,K+and Na+originate from the dissolution of silicates and salt rocks.In the Quaternary aquifer,K+and Na+mainly come from the dissolution of salt rocks.The source of mine mixed water mainly originate from Zhiluo Formation aquifer,with an average proportion of 93.23%,and only a small part water originates from the Quaternary aquifer,with an average proportion of 6.77%.

Abstract:Faced with the problems of low permeability of coal reservoirs and low production of coalbed methane in China,the research on microwave heat injection technology for reservoir transformation has become an important topic to increase the production rate of coalbed methane.In this study,by combining experimental research with numerical simulation,we review the effects of single microwave radiation on coalbed gas production from the perspectives.We clarify how microwave heat injection influences the mechanical properties,microstructure,and physicochemical characteristics of coal seams.Furthermore,we summarize the factors affecting microwave heat injection by examining both coal petrophysical properties and microwave field parameters.Additionally,we analyze the advantages and disadvantages of combining microwave heating with other methods.The research results show that microwave heat injection significantly reduces the compressive strength of coal,while simultaneously increasing its porosity and permeability.This process alters the microstructure of coal and reduces its gas adsorption capacity.When combined with other coal seam permeability increased technologies,such as microwave-assisted acidification,microwave-assisted oxidation and microwave-liquid nitrogen freeze-thaw cycles,the efficiency of coalbed methane extraction can be further improved.

Abstract:In order to study the application of real-aperture radar in the monitoring and early warning of open-pit mine landslide disaster,based on the three-stage theory of creep deformation,a real-aperture radar early warning model was established.The prediction method of landslide time was analyzed,and the monitoring displacement data of radar was extracted.The linear fitting method of the pearly warning model with the inverse velocity method under different Time Windows(TW)was discussed,and the rule of the prediction of landslide time was carried out according to the deformation velocity data after the Onset of Acceleration(OOA)before the pre-slip.The results show that,based on the three-stage creep theory of slope deformation,with the passage of the new Start Point(SP),the predicted landslide time is closer to the real landslide time.With the decrease of the time window,the landslide prediction time is constantly approaching the real landslide time.A smaller time window should be selected in the monitoring and early warning to improve the sensitivity of data display and the accuracy of landslide prediction time.

Abstract:In order to investigate the influence of lateral pressure on the fracturing processes of fractured sandstone,the fracture mechanism of micro-cracks under different lateral pressures was studied by using acoustic emission(AE)monitoring technology and discrete element model.A discrete element meso-scale numerical model considering mineral composition was established to quantify the mechanical behavior of micro-crack fracture during loading,and the multi-fractal characteristics of AE signals of fractured sandstone under three kinds of lateral pressure were analyzed.The results show that the deformation and fracture process can be divided into microcrack closure stage,crack initiation stage,crack slow growth stage,crack uniform growth stage and crack accelerated growth stage.With the increase of the lateral pressure,the through failure mode of the sandstone specimens changes from macroscopic crack to local spalling failure,and the spalling range gradually increases.In addition,the level of initiation stress corresponding to tensile crack and shear crack increases gradually.The proportion of tensile crack is smaller than that of shear crack.With the increase of stress level,the average frequency width(Δα)shows a trend of first decreasing and then increasing.The average bandwidth difference(Δα0)and the spectrum measure subset(Δf)show an opposite evolutionary trend.When the stress level is less than 0.8σc,Δα0 is greater than zero,indicating that the small fracture scale signal occurs in sandstone specimens.When the stress level is greater than 0.8σc,Δα0 gradually changes from a positive value to a negative one,and the large fracture scale signal is dominant in sandstone specimens.

Abstract:In order to solve the high temperature damage occurs in the deep roadways of Jiaojia Gold Mine and understand the influence of different ventilation conditions on the temperature and velocity fields in deep roadways,based on obtaining the overall distribution of the ground temperature field in the middle sections of-580 m and-670 m,by using CFD numerical simulation,the distribution characteristics of the temperature field and velocity field in the two areas under natural ventilation conditions were calculated.For the-670 m middle section,by adding a forced ventilation system,the cooling effect of different ventilation conditions on the roadway was simulated.The results indicate that,the geothermal gradient in the study area ranges from 3.0℃/hm to 3.2℃/hm,categorizing it as a geothermal anomaly area.The original rock temperature in the middle section of-580 m has exceeded 30.4℃,and the temperature of the roadway is 29.3℃.Heat damage has begun to emerge.Under natural ventilation conditions,the average temperature at the-670 m middle section of the tunneling working face is 33.4℃,which is relatively high.After the addition of the forced ventilation system,the air supply volume and air supply temperature were altered.When the air supply temperature was decreased by 5.0℃,the average temperature of the working face dropped by 4.7℃,and the cooling degree reached 18.5%.When the air supply temperature was kept constant and only the air supply volume was changed,it had a negligible impact on the temperature and wind speed of the tunneling face.

Abstract:To carry out effective comprehensive prevention and control of rock burst,taking Tangkou Coal Mine as an example,theoretical analysis,numerical simulation and engineering practice were used to study the mechanism of roof-cutting and pressure relief of fully mechanized caving face in deep well.It is found that the thickness of the suspended roof of the key layer is an important factor affecting the release of key energy.Based on this,the non-through pre-split and roof-cutting technology is proposed to reveal the mechanical mechanism of the non-through pre-split and roof-cutting of the key layer in fully mechanized caving mining.By creating pre-split surfaces in the key layer,the length and stress concentration of the cantilever beam can be effectively reduced,thereby controlling the release of energy and reducing the risk of rock burst.The value of the spatial parameter of the non-through pre-split slit is mastered,which provides the theoretical basis for the implementation of the technology.A 3D numerical model of non-through pre-split roof cutting was established.The results show that the effect is most significant when the combined fan-shaped holes with roof cutting angles of 45°,60°and 75°are adopted and the pre-split roof-cutting spacing is 10.0 m.This technology can effectively reduce the probability of rockburst and promote the safety and high efficiency of pre-split and roof-cutting blasting.

Abstract:Based on land-use data from 2000,2010,and 2020,a comprehensive analysis of the spatiotemporal evolution characteristics and driving mechanisms of land-use in Taiyuan,a typical resource-based city,was conducted by integrating the land-use dynamic degree,the PLUS model,and the geographical detector.Furthermore,the land-use patterns under different development scenarios for 2030 were simulated.The results show that from 2000 to 2020,the construction land increased by 84.05%,while the cultivated land decreased by 12.7%,and the structure of ecological land tended to be optimized.The driving mechanisms for the expansion of different land types varied,with cultivated land primarily driven by distance to fourth-level roads,forest land by population density,grassland and construction land by elevation,and water areas by distance to lakes.Among individual factors,GDP showed the strongest explanatory power,and factor interactions demonstrated nonlinear enhancement effects.Multi-scenario simulations revealed clear differences in land-use change trends under natural development,ecological protection,economic development,and cultivated land protection scenarios,reflecting the impact of different policy orientations on land use allocation.This research provides a scientific basis for land resource optimization,ecological protection,and the coordinated socio-economic development of resource-based cities.

Abstract:In order to enhance the fire prevention property of the gel,using chitosan(CS),acrylamide(AM),and N,N'-methylene bisacrylamide(MBA)as the base materials,a physical-chemical cross-linked Al3+-CS/PAM-MBA double network gel was prepared.The chemical network formed by the covalent bond cross-linked of polyacrylamide(PAM)and MBA was used as the first network,and the second network was formed by the ionic bond cross-linked of chitosan molecules and Al3+.The optimal ratio of the gel was optimized by testing the gel formation time and viscosity of the gel.The fire prevention property of gel was studied by thermal stability analysis,temperature programmed experiment,infrared spectroscopy,thermal analysis and fire extinguishing experiment.The results show that Al3+-CS/PAM-MBA double network gel has good thermal stability and good effect of spontaneous combustion inhibition.It can effectively inhibit coal spontaneous combustion oxidation.This gel can inhibit the process of the coal-oxygen reaction by destroying the functional groups closely related to it,which makes the coal oxygen reaction more difficult to carry out,thus playing a role in inhibiting coal spontaneous combustion.The fire extinguishing test further indicated that the gel had a significant inhibitory effect on the spontaneous combustion of coal.After the addition of the gel,the temperature of the coal dropped rapidly,and no re-ignition phenomenon occurred.

Abstract:At present,the dust concentration sensors of the light scattering method in underground coal mines have problems such as easy clogging of the dust extraction pipeline,easy contamination of the detection window and difficult maintenance.In order to solve the problems,an open dust concentration detection structure based on light scattering method was proposed.An open dust concentration sensor based on the light scattering method was designed,which was composed of laser source,photodiode,filter cap and signal processing circuit,etc.In order to ensure the detection accuracy,the influence of ambient light and wind speed on the output results of the sensor was studied.A dynamic differential algorithm and wind speed compensation algorithm were designed to eliminate the influence of ambient light and wind speed.The initial value of the analog-to-digital conversion detected by the open dust concentration sensor using the light scattering method had a good positive correlation with the actual dust concentration.A mathematical model was established between the initial value of analog-to-digital conversion detected by an open dust concentration sensor using the light scattering method and the dust concentration,achieving accurate characterization of the dust concentration.Finally,it was experimentally proven that the open dust concentration sensor using light scattering method had high detection accuracy for dust concentration,with a detection error of less than 10%.

Abstract:To understand the flow field evolution in a composite goaf under layered mining of near-vertical coal seam conditions,this study investigates the impact of upper layer mining on the distribution of gas and temperature fields in the goaf of the lower layer working face.Researchers first established a three-dimensional numerical model of goaf under segmented mining conditions and used PFC particle flow simulation software to simulate the collapse of the overlying rock and the distribution of porosity in the goaf.Subsequently,the porosity distribution data were imported into CFD using UDF functions to perform numerical simulations of the flow field evolution in the composite goaf under non-nitrogen injection and low-temperature nitrogen injection conditions.The study predicted the distribution of spontaneous combustion"three zones",analyzed air leakage conditions,and examined the dynamic evolution of the flow field and temperature field under low-temperature nitrogen injection.Finally,the simulation results were validated against field measurements of CO concentration and temperature variations in different areas.The results show that areas with higher porosity were mainly concentrated at both ends of the original intake and return airways in the horizontal sectional goaf.High-oxygen concentration regions in the composite goaf were mainly located near the intake and return airways,with a general trend of decreasing oxygen concentration towards the deeper parts of the goaf.In the upper layer goaf,high-oxygen concentration regions were mainly located near the stop line and the upper part of the intake and return airways.After injecting low-temperature nitrogen,the width of the heat dissipation zone in the goaf decreased by 1.7 m to 6.4 m,and the width of the oxidation zone decreased by 9.6 m to 12.2 m.The closer to the nitrogen injection point,the greater the temperature reduction.Field observations show that the width of the oxidation zone in the current layer significantly decreased,the temperature at the return air corner dropped by 16.6℃,and the CO volume concentration gradually decreased from a maximum of 16.5 μL/L to 0 μL/L.In the upper layer return air corner,the temperature decreased from an average of 32.1℃to 20.1℃,and the CO volume concentration dropped from 14.0 μL/L to 0 μL/L.The error between the field test results and the simulation results was less than 5%,verifying the feasibility of the research method.

Abstract:Aiming at the problem of large deformation of the crushed stone slope support in the roadway formed by cutting roof under the condition of thick coal seams and hard roof,the collapse characteristics of the three stages of deformation and collapse impact of the crushed stone slope,crushed stone bearing,and compaction stability were analyzed through mechanical calculation and theoretical analysis,and the influencing factors were determined.Then,a combined control system for the crushed stone slope of"combined blasting+retractable U-beam+steel mesh+gangway rockbolt+unit bracket+hydraulic prop"was proposed.The optimization measures were simulated by 3DEC,and it was found that the stress and displacement of the crushed stone slope were reduced to different degrees.The joint control optimization scheme was applied in the field.The actual measurement shows that the lateral pressure of the optimized crushed stone slope is reduced by 18.6%.The peak pressure is reduced by 24.6%.The overhang distance after the rack is reduced by 42.1%.It effectively weakens the impact of rubble collapsing in the goaf,and the effect of pressure relief is obvious.

Abstract:In order to determine the optimum hole spacing for gas extraction borehole,a gas-solid coupling mathematical model considering the evolution of coal permeability,solid mechanics and gas diffusion-seepage was established based on the assumption of pore-fracture dual media.Taking the N2206 working face of Yuwu Coal Mine in Shanxi Province as the research object,the numerical simulation study of gas extraction in single borehole and multi-borehole was carried out,and it was found that the effective extraction radius and the extraction time changed as a power exponential function,and the average error between the numerical simulation results and the field test results was 4.69%.Based on the model validation,the influence of hole spacing on the superposition effect was analysed according to the principle of superposition effect in multi-well gas extraction,and a mathematical model of hole spacing in multi-well gas extraction was established based on effective extraction radius and the influence radius of a single well.It was found that the optimal hole spacing of N2206 working face was 9.2 m.Field testing has confirmed the accuracy of the formula correlating hole spacing with the effective extraction radius and influence radius of a single hole.

Abstract:In order to study the correlation between the fractal features of sandstone meso-structure and the macro-scopic damage and failure,four typical sandstones selected from E-zhuang Coal Mine of Xinwen coalfield were taken as the research objects.The gray-scale images were obtained by scanning electron microscopy,and the appropriate segmentation method was selected by the experimental goodness method,and the image was processed to obtain the parameter information such as the length,perimeter and area of the sandstone pores and fissures.The fractal dimension of crack in sandstone samples was obtained by slit island method and the damage variables were calculated to study the correlation between the fractal feature,damage variables and strength.The results show that the strength of sandstone is inversely proportional to the fractal dimension of its meso-structure.The higher the complexity of sandstone pore and fracture structure,the larger the fractal dimension and the smaller the uniaxial compressive strength.The fractal features of sandstone meso-structure can provide a basis for the evaluation and influence analysis of its strength characteristics.The damage variable of sandstone has a positive correlation with the fractal dimension,and the damage variable increases nonlinearly with the increase of the fractal dimension.The fractal dimension can better characterize the damage degree and fragmentation degree of sandstone,and also affect the damage characteristics of sandstone.

Abstract:Addressing the urgent demand for autonomous positioning and environmental modeling technology in the context of intelligent mine development,and targeting the performance degradation of traditional SLAM algorithms caused by the unique underground environment in coal mines,this study innovatively proposes a mine positioning and mapping algorithm that fuses laser reflection intensity information.The algorithm is constructed based on feature point method laser SLAM framework,but it comes up with a novel classification method,which gets the intensity edge points using the changing rate of point cloud intensity.With the classical edge feature points and surface feature points based on point cloud curvature remain,the algorithm enriches the categories and quantities of point cloud features.Meanwhile,the algorithm constructs an intensity image of each frame based on its intensity data of point cloud,and tracks the image features using image processing technology,obtains more matched points.Furthermore,a modification of scan-matching procedure is made to import the intensity edge features and intensity image features,and improve the accuracy of pose estimation in underground coal mines.Experimental validation demonstrates that this method exhibits excellent stability and environmental adaptability in typical coal mine tunnel environments.Its positioning accuracy meets the requirements for underground applications,offering an effective solution to the problem of point cloud feature degradation underground coal mine.

Abstract:Separation grouting is an important technology to achieve surface subsidence reduction and green mining,and the injection of slurry into the separation space will also affect the characteristic of mine pressure behavior in the working face.Taking the 2309 working face of Zhaozhuang No.2 well as the engineering background,the mine pressure behavior under different mining stages was compared and analyzed.The results show that:the average end resistance of the whole face is 2 661.7 kN and pressure step is 24.2 m in the normal mining stage,and the average end resistance of the whole face is 3 229.1 kN and pressure step is 16.5 m in the mining stage with separation grouting,compared with the normal mining,the end resistance of the support in the case of separation grouting is obviously increased,and the periodic pressure step is reduced;When the working face is drilled through grouting borehole,the working resistance of the support increases as a whole in the direction of the trend,and incline to gradually decrease from the middle to the two sides.Under the combined action of the grout support reaction force,self-weight and grouting pressure,the underlying rock layer is compacted and the force of the rock beam is increased,which leads to the increase of end resistance of the support and the decrease of the periodic pressure step,the morphology of separation space and the arrangement of the grouting borehole lead to a higher stress on the inclined middle support.The proposed inducements explain the special characteristic of mining pressure behavior in the separation grouting working face.

Abstract:To address the maintenance challenges of fractured surrounding rock in main roadways subjected to dynamic pressure from multi-layered thick-hard roofs,a mechanical model was developed to describe load transfer in multi-layered hard roof strata.The stress increment formula was derived to quantify the transmission of stress from medium and high-level key strata groups to the front coal pillars in the working face.The pressure relief mechanism of the regional fracturing technology was clarified.Numerical simulations confirmed that regional fracturing can rdhuce the energy accumulation of the roof.Taking the 3206 working face of Wangpo Coal Industry as an example,the echnical parameters for regional fracturing at the mining end line were determined and the field tests were carried out.The results show that regional fracturing reduces the exposed length of articulated blocks in key strata,and increases the dip fracture angle(β2),and shortens the horizontal fracture length(li)of key strata groups.These changes shift stress peaks toward the goaf area,effectively reducing compressive stress of the surrounding rock in the main roadway.The displacement of the surrounding rock in the 3206 working face kept within allowable limits and the maximum reduction in supporting stress is approximately 1 MPa.

Abstract:In order to expand an adaptive evaluation method for the fracability of coal seam hydraulic fracturing,six on-site case studies from mining working faces were used as samples and the main controlling factors affecting the fracability of coal seam hydraulic fracturing were determined in combination with experimental tests.Based on fuzzy comprehensive evaluation theory,a combination weight for each factor was determined using Analytic Hierarchy Process(AHP)and entropy weight methods.This led to the establishment of a model for evaluating coal seam fracability based on"indicator input-effect output-actual fracturing effect verification"thinking.The evaluation results show that under a confidence level satisfying"reasonably effective"criteria(α>0.5),the fracability of coal seams in Gaocheng Coal Mine's 25011 working face and 25031 working face shows medium to poor levels,while the working face in Songzao Coal Mine and Shihao Coal Mine exhibits medium levels,and Sijiazhuang Coal Mine's 15301 working face and 15118 working face demonstrate good levels.The evaluation results are basically consistent with actual hydraulic fracturing effects observed on site,thus validating both the rationality of selecting indices for evaluating coal seam fracability and the feasibility of employing fuzzy comprehensive evaluation methods.The research results show that most significant factor influencing coal seam fracability is found to be firmness coefficient.However,it should be noted that wetting properties and clay mineral content also have considerable impact.Conversely,depth had relatively minor influence within selected case samples.

Abstract:To investigate the deformation and failure mechanisms of deep coal seam floors,we compared and analyzed the stress-strain behavior,acoustic emission energy events,and strength variations of sandstone samples subjected to different initial confining pressures and varying loading and unloading rates.We also examined changes in damage factor,elastic modulus,and Poisson's ratio under these conditions.The results indicate that,at an unloading rate of 0.06 MPa/s,the onset of elastic modulus degradation under an initial confining pressure of 40 MPa occurs earlier than the change in Poisson's ratio,whereas the opposite trend is observed at an initial confining pressure of 25 MPa.When the confining pressure is unloaded at 0.04 MPa/s,regardless of whether the initial confining pressure is 25 MPa or 40 MPa,the sandstone undergoes rapid crack propagation as a result of significant internal energy accumulation.This process is accompanied by a sudden drop in stress and is classified as energy-driven damage.Under an initial confining pressure of 25 MPa and an unloading rate of 0.06 MPa/s,internal cracks in the sandstone fully develop,allowing accumulated energy to be released gradually,resulting in a more stable stress response.This behavior is defined as damage deterioration-driven failure.In contrast,at an initial confining pressure of 40 MPa and the same unloading rate,the sandstone first experiences a rapid stress drop due to the sudden release of internal energy.Subsequently,the failure mode shifts to crack propagation and deformation,influenced by confining pressure and axial compression,marking a transition from energy-driven damage to damage degradation-driven failure.