Abstract:To investigate the influence of cyclic liquid nitrogen cold-shock on coal pore-fracture evolution,specimens un-derwent cold-shock treatments at varying cycles(5,10,15,20).Large-scale nuclear magnetic resonance(NMR)analysis provided T2 spectra and imaging of treated samples.Multifractal theory was applied to quantify heterogeneous evolution in T2 distributions and NMR image intensity with increasing cycles.Spearman correlation analysis established relationships between cycle number and multifractal parameter variations,revealing structural heterogeneity progression.Results indic-ate cyclic liquid nitrogen exposure induces nonlinear,saturation-characteristic alterations to coal pore-fracture networks.During initial cycles(5-10),porosity increased sharply from 1.76％to 2.05％.Subsequent cycles(10-20)promoted cumu-lative damage propagation wherein micropores coalesced into macroscale fractures,reducing porosity increment to 2.05％-2.13％.NMR imaging reveals the characteristics of non-uniform distribution of pores and fissures in coal.Under the action of cyclic cold shock,the new pores and fissures mainly expand along the original pores,and the pore develop-ment area is more prone to connectivity damage,forming a local banded high permeability channel,which enhances the pore connectivity of coal samples.The non-uniform evolution characteristics of pores and fissures in coal under the action of cyclic cold shock are revealed by the combination of T2 spectrum and multi-fractal results of nuclear magnetic reson-ance imaging.With the increase of the number of cycles,the homogeneity of pore size distribution in coal increases but the homogeneity of pore space distribution decreases.The T2 spectrum multifractal mainly focuses on the quantitative characterization of the pore size and number in the sample,and the nuclear magnetic resonance imaging multifractal fo-cuses on the non-uniform quantitative characterization of the pore space.The fitting relationship between the change of multifractal parameters and the number of cycles is constructed,and the nonlinear saturation characteristics of the damage effect of cyclic cold shock on the pore and fracture of coal body are intuitively revealed.This integrated multifractal ap-proach reveals dynamic heterogeneity in coal pore-fracture systems,providing data-driven support for optimizing field parameters in liquid nitrogen fracturing operations.

Abstract:In the high-intensity mining process of shallow buried coal seams in the Shendong and North Shaanxi mining areas,the collapse-type water inrush and sand gushing has become a typical geological hazard that threatens the preven-tion and control of roof water damage in mining engineering.Thoroughly studying the water and sand seepage character-istics of fractured rock masses is of great significance for revealing their disaster mechanisms and corresponding disaster prevention and control.In view of this,using the self-developed water-sand seepage test system of broken rock mass,based on the fractal dimension calculation method of cumulative mass of rock fragments proposed by Xie Heping,the broken sandstone samples with different particle size ratios were prepared according to the Talbot continuous gradation formula.The water-sand seepage test with variable porosity and particle size ratio was designed.The variation of per-meability of water and water-sand mixture in broken sandstone with porosity and particle size ratio was analyzed.The per-meability expression considering porosity ratio and fractal dimension was established,and the influence of the viscosity of water-sand mixture on permeability calculation results was quantified.The variation law of sand inrush mass of broken sandstone with porosity and particle size ratio is revealed,and the critical sand inrush criterion driven by permeability and fractal dimension is constructed.Taking the 22402 working face of Halagou Coal Mine as an engineering example,the ac-curacy of the criterion is verified.The results indicate that:① The water-sand seepage process in crushed sandstone can be divided into three stages:initial fluctuation,relative stability,and decay.Permeability increases with porosity and Talbot's power index,while water seepage exhibits higher permeability than water-sand seepage.② The outflow mass of sand in-creases with porosity and Talbot's power index,showing a near-linear relationship with permeability.③ In existing re-search,many scholars have used simplified methods that use water viscosity as a substitute for water-sand mixture viscos-ity may introduce a maximum error of 18.3％in the calculations of this study,which could amplify to over 800％when up-scaled to field conditions of water inrush and sand gushing disasters.④ The introduction of fractal dimension can reduce the fitting error of fractured sandstone permeability by about 56.43％.The critical sand collapse curve proposed based on the variation law of permeability and fractal dimension on sand collapse quality has been applied well in the 22402 work-ing face of Halagou Coal Mine.

Abstract:Revealing the occurrence mechanism of coal-rock mechanics response in the stope is theoretical basis for the prevention and control of coal-rock disasters.By adopting a combination of field measurements,simulation experiments,and theoretical analysis,the occurrence mechanism of step changes in the static mechanical response of coal-rock in the stope was systematically studied through the construction of static mechanical models at two steady states before and after structural transient.The results show that the mechanical response of coal-rock in the stope is closely related to the transi-ent characteristics of overburden spatial structure.During the first weighting,the structural transient of overlying strata ex-hibits symmetry,leading to a symmetrical mechanical response.During periodic weighting,the structural transient region is mainly concentrated on working face side,resulting in a mechanical response that is also concentrated in coal-rock masses on the working face side.The transient change in the load transfer path of the overlying strata,induced by structur-al transient change,causes different instantaneous loading and unloading conditions for coal-rock in various areas of the stope.It leads to significant differences in the mechanical responses of coal-rock in these areas.Among them,the instant-aneous fracture of lower hard rock layer forms instantaneous unloading on the lower surface of upper hard rock layer,causing it to sink instantly.Meanwhile,the instantaneous unloading of internal forces along fracture surface in lower hard rock layer,coupled with the transient loading induced by transferring support load from structural transient region towards goaf,causes the instantaneous rebound in some areas near goaf side of lower hard rock layer.The instantaneous subsid-ence of some areas in the deep surrounding rock.Affected by this,the bearing capacity of the upper surface on the lower hard rock layer increases instantaneously.It leads the peak support pressure suddenly increases,and its position trans-itions towards the goaf side.Meanwhile,affected by the fracture unloading and subsidence-rebound of the lower hard rock strata,the bearing capacity on the coal body decreases instantaneously.The peak value of abutment pressure on coal body decreases sharply,and its position transitions to the depth of coal body.With the increase of transfer load in structural tran-sient region,the rebound amount of lower hard rock decreases,while the bearing capacity of the coal body increases.With the increase of action range of transfer load,the rebound amount of lower hard rock increases.The step change of coal-rock load decreases,while the range of step change increases.

Abstract:Grouting sealing quality is recognized as a critical factor ensuring gas drainage efficiency.Influenced by min-ing stress disturbance and slurry dehydration shrinkage,sealing materials tend to crack and form secondary fractures,lead-ing to gas leakage in drainage boreholes.To address this issue,a self-healing grouting sealing concept is proposed where sealing materials spontaneously react with environmental moisture and CO2 through self-healing agents to generate CaCO3 precipitation for crack closure when gas leakage occurs.However,the self-healing agent interferes with the hydration reac-tion of sealing materials and negatively impacts mechanical properties.Building on existing research,the content of self-healing agent is adjusted to balance self-healing capacity and mechanical performance.Results indicate that reduced self-healing agent content decreases crack-repairing capability.Specimen S1 achieves a maximum repairable crack width of 0.88 mm after 4 days of curing,while S2 and S3 specimens require 5 days to repair maximum crack widths of 0.73 mm and 0.71 mm,respectively.Meanwhile,mechanical properties improve significantly,with compressive strength increasing from 3.23 MPa(S1)to 4.31 MPa(S2)and 8.85 MPa(S3).To investigate self-healing agents' effects on pore-sealing ma-terials,microstructural and mineralogical analyses revealed that reduced agent dosage enhanced hydration product forma-tion and densification,forming a continuous network,while XRD indicated a mineralogical shift toward diminished un-hydrated clinker(3CaO·SiO2,2CaO·SiO2)peaks and intensified hydration product(C-S-H gel,Ca(OH)2)peaks.By optimizing the self-healing agent content,it is found that a 12％dosage achieves balanced self-repair capability and signi-ficantly improved mechanical performance.These findings hold substantial significance for regulating the self-healing properties and mechanical performance of sealing materials.

Abstract:Critical metals,as vital strategic resources,play an irreplaceable role in emerging energy and high-tech indus-tries.With China's rapid economic and technological development,research on the enrichment mechanisms of coal-hos-ted critical metals has become a crucial direction for alleviating resource shortages.This study focuses on the No.3 Coal Seam in Yunhe Mine,Jining Coalfield,Shandong Province,aiming to reveal enrichment patterns and controlling factors of critical metals.A total of 12 coal,roof,and floor samples were systematically collected from the study area using strati-fied channel sampling methodology.Analytical techniques including X-ray fluorescence spectrometry(XRF)and induct-ively coupled plasma mass spectrometry(ICP-MS)were employed to determine major and trace element contents.Integ-rated approaches encompassing elemental analysis,rare earth element and yttrium(REY)geochemical characteristics,and provenance tracing were applied to investigate enrichment mechanisms.Results indicate:In the No.3 Coal Seam of Yunhe Mine,Li exhibits an average content of 26.7 μg/g with a concentration coefficient of 2.23,while Th averages 6.72 μg/g with a concentration coefficient of 2.04.Both elements reach mild enrichment levels,indicating potential eco-nomic significance.Provenance analysis through w(Al2O3)/w(TiO2)ratios demonstrates dominant felsic rock sources in the study area.Concurrently,comparative assessment of rare earth element(REE)fractionation patterns integrated with re-gional geological context reveals that the critical metals in coal were likely derived from Neoarchean granites of the Yin-shan Old Land and Neoproterozoic granites within the Qinling Orogenic Belt.Furthermore,analysis of depositional envir-onments and groundwater-seawater interactions confirms that elevated Li and Th contents in samples YH3-6 and YH3-7 resulted from a geochemical barrier formed by interactions between acidic groundwater and infiltrating seawater under re-ducing peat depositional conditions.In conclusion,systematic geochemical analysis elucidates enrichment mechanisms of critical metals in Yunhe Mine's coal sequence,providing valuable insights for the exploration and enrichment assessment of coal-hosted critical metals in Shandong

Abstract:Coal gasification slag is a typical coal-based solid waste,and the separation of residual unburned carbon and ash components in coal gasification slag is an important guarantee for its resourceful and high-value utilization.Flotation is an effective way to separate unburned carbon and tailing from coal gasification slag,but facing the problem of high cost and consumption of collector.Crude oil wastewater contains substances such as long-chain alkanes,cyclic hydrocarbons,aromatic compounds,phenols,ketones,acids,and esters,which are similar to the components of commonly used collect-ors for coal gasification slag,has the potential to be applied to the flotation separation of coal gasification slag.In this pa-per,the physical and chemical properties of coal gasification slag and the material composition of crude oil were studied,and simulated crude oil wastewater was employed as a collector to investigate the flotation behavior on coal gasification slag.Results show that,the main substances in coal gasification slag are mullite,fused silica-aluminate,metal oxide and amorphous carbon.The relative content of unburned carbon in coal gasification slag is 25.37％,in addition to methyl and methylene,the surface of coal gasification slag also contains abundant oxygen-containing functional groups such as C—O/C＝O/O—C＝O,which makes coal gasification slag hydrophilic.Crude oil contains a large amount of structurally complex polycyclic alkanes,long-chain alkanes,and some polar substances.Polycyclic alkanes and aromatic hydrocar-bons have a stronger ability to capture unburned carbon than general n-alkanes,and the presence of polar components is also conducive to the flotation separation of coal gasification slag.Therefore,crude oil has a strong collection ability;The flotation results show that,with the stirring rate of 1 800 r/min,slurry concentration of 60 g/L,crude oil wastewater con-centration of 40 mg/L,and frother concentration of 30 mg/L,the recovery of unburned carbon reaches 84.62％,and the loss-on ignition of 76.82％;the tailings with loss-on ignition of 4.31％,which achieves the national level of the standard of loss-on ignition(＜5％);Meanwhile,the oil removal rate of simulated crude oil wastewater is 41.50％,and the chemical oxygen demand is reduced from 219.70 mg/L to 82.77 mg/L,which meets the secondary discharge standard in the nation-al petrochemical industry.The results of FTIR analysis showed that the—CH3 and—OH stretching vibration peaks indic-ated by the coal gasification slag were shifted after interacting with the simulated crude oil wastewater,and it could be judged that the crude oil molecules had hydrophobic interactions and hydrogen bonding interactions with the surface of the coal gasification slag,respectively.Zeta potential results shows that the electronegativity of the coal gasification slag sur-face is enhanced after the action of simulated crude oil wastewater.Combined with the XPS results,it further indicates that hydrogen bonding bridging occurs between the polar oxygenated compounds in the crude oil and the oxygenated function-al groups on the coal surface,forming a large three-dimensional spatial structure of the charge body,which makes the sur-face potential of the coal gasification slag more negative.This paper realizes the recovery of carbon products and the treat-ment of simulated crude oil wastewater through the co-disposal of coal gasification slag and crude oil wastewater,which has strong industrial application value.

Abstract:The utilization of high-speed jet technology to fracture coal bodies and construct gas flow channels within coal seams is a crucial method for enhancing coalbed methane recovery efficiency.The supercritical carbon dioxide(SC-CO2)jet enhances coal-seam permeability through its inherent dissolution and extraction capabilities,while the self-excited pulsed SC-CO2 jet exhibits markedly low critical fracturing pressure and high coal-breaking efficiency,demonstrating sub-stantial potential for strengthening coalbed methane recovery.However,the current performance evaluation methods for self-excited oscillating jet nozzles lack direct quantitative indicators,making it difficult to determine the optimal nozzle structural parameters and severely limiting their further promotion.The content is:In this paper,based on the evolution process of vortical structures inside the nozzle,a calculation method for the energy conversion efficiency of self-excited oscillation nozzles is proposed.Particle Image Velocimetry(PIV)experimental systems combined with Large Eddy Simu-lation(LES)are employed to capture the evolution process of vortical structures inside the nozzle,and to analyze the char-acteristics of fluid energy conversion and distribution inside the nozzle.Analysis of the flow-field images acquired at 1.75-1.79 s after the onset of jetting reveals that the nozzle's vortex structures are concentrated in the oscillation chamber.The self-excited oscillation pulses of the SC-CO2 jet moving along the shear layer within the oscillation chamber initially travel upstream upon contact with the collision wall.Over time,during this upstream movement,they gradually merge with the jet along the axis.Strong vortex structures are observed at both the downstream nozzle entrance and the upstream nozzle exit.The total energy input at the nozzle inlet of the SC-CO2 jet is converted into vortex kinetic energy within the oscillation chamber and the total energy of the self-excited oscillating pulsed SC-CO2 jet formed at the nozzle outlet.When the chamber diameter ratio is 3.5,the efficiency of jet energy conversion reaches its peak at 80.80％.The eddy kin-etic energy within the oscillating chamber induces the generation of self-excited oscillation pulsed SC-CO2 jets.However,when the proportion of eddy kinetic energy is significant,it can lead to energy dissipation.Furthermore,the eddy kinetic energy at the nozzle exit is utilized to regulate the jet's concentration.The smaller the dispersion of eddy kinetic energy at the nozzle exit,the more concentrated the jet becomes.The ranking of the maximum peak stress generated by self-excited pulsed SC-CO2 jets at different nozzle exits is as follows L3.5＞L1.5＞L25＞L2.0＞L3.0.

Abstract:Coal seam mining under thin bedrock with thick unconsolidated layers can lead to hydraulic connections between the working face and the overlying unconsolidated aquifer,potentially inducing water inrush and sand outburst disasters that severely threaten mine safety.Therefore,accurately characterizing the development of overburden failure is crucial.Using the 16041 working face in the Jiaozuo mining area of Henan Province as a case study,we combined numer-ical mining dynamics simulation,physical modeling with electrical similarity,and field monitoring to investigate the elec-trical response characteristics and dynamic monitoring techniques for overburden failure in thin-bedrock working faces.Both the numerical and physical modeling results clearly revealed the development patterns and typical electrical response characteristics of the caved zone and water-conducting fracture zone.During field monitoring,we utilized underground three-dimensional parallel electrical methods to determine the spatial distribution of bedrock thickness,which guided the layout of monitoring boreholes.We then applied a remote parallel electrical monitoring system to synchronously acquire both active and passive geo-electrical parameters.To overcome poor borehole formation and insufficient monitoring height near the bedrock interface,we developed a resistivity variation based dynamic imaging technique integrated with advanced detection.This method extended the effective monitoring height to 75 m,overcame the physical blind zone of the boreholes,and enabled cross-validation through full-space inversion.Field monitoring showed that the caving zone be-came compacted and stabilized during the mid-mining stage,with a measured height of approximately 18.5 m,terminat-ing within the sandy mudstone above the No.21 coal seam roof.The water-conducting fracture zone continued to propag-ate upward during the late mining stage,reaching a maximum height of 46 m,penetrating the entire thin bedrock layer and extending to the base of the Quaternary clay layer,potentially forming a direct water inrush pathway.The electrical re-sponse analysis indicates a distinct staged evolution during overburden failure:pre-mining damage caused an overall in-crease in apparent resistivity;the strong disturbance zone,corresponding to the caving zone,showed the largest resistivity variation and mid-term stability;the weak disturbance zone,corresponding to the water-conducting fracture zone,exhib-ited smaller resistivity variations but a clearly defined range and late-stage stabilization.These results are consistent with the staged overburden evolution characterized by mid-term compaction of the caving zone and late-stage upward expan-sion of the fracture zone.We developed an integrated monitoring approach combining pre-mining static detection,using three-dimensional electrical methods to determine bedrock thickness,with mid-mining dynamic monitoring,employing advanced borehole probing to extend beyond blind zones.This approach addresses the challenges of overburden failure monitoring in thin-bedrock working faces.Field application demonstrated that the method can accurately reveal the devel-opmental height and spatial morphology of the caving zone and the water-conducting fracture zone,and support the as-sessment of potential water inrush risks,providing key technical guidance for water hazard prevention and safe mining in coal mines under similar hydrogeological conditions in East China.

Abstract:Low methane extraction efficiency and prolonged treatment duration in deep,low-permeability coal seams con-stitute bottlenecks constraining safe and efficient coal mining.Liquid CO2 phase-change fracturing,as a water-free permea-bility enhancement measure,simultaneously avoids the water-lock effect in coal seams and displaces methane within coal,thereby intensifying extraction efficacy.To elucidate the mechanism by which liquid CO2 phase-change fracturing en-hances coal permeability,coal samples from Shenmu Ningtiaota and Pingmei No.10 Mine were studied.Through Hopkinson bar dynamic impact tests,high-pressure CO2 fracturing tests,and triaxial compression-seepage tests,the fracture behavior and permeability characteristics of coal at different stages were investigated.Results indicate:As impact velocity in-creases,peak strain rate and dynamic peak strength of coal samples exhibit an upward trend.The failure mode of Shenmu coal shifts from splitting to crushing,with stress-strain curves lacking a secondary compression phase.Pingmei coal primarily exhibits splitting failure accompanied by pronounced strain hardening.A significant linear relationship exists between the vertical principal stress and the coal's initiation pressure.For every 1 MPa increase in vertical principal stress,the initiation pressure increases by approximately 0.6 MPa.For the Shenmu coal sample with highly developed fractures,the fracturing effect primarily manifests as fracture connection and expansion.In contrast,for the structurally dense Ping-mei coal sample,the effect mainly involves the formation of new fractures.Inclined fractures significantly degrade the mechanical strength of coal,substantially reducing the stress required for failure.Under confining pressure,peak stress in coal samples with inclined fractures decreased by approximately 50％compared to pristine coal,while permeability in-creased to 12.7-14.9 times that of pristine coal.The research reveals the three-stage synergistic permeability enhancement mechanism of"dynamic crushing-static expansion-geostress extrusion"of liquid CO2 fracturing,which can provide theor-etical reference for the popularization and application of liquid CO2 fracturing permeability enhancement technology.

Abstract:Anchor bolt support is a commonly used surrounding rock control technology in deep underground engineering.To control the large deformation of surrounding rock under complex conditions,high prestress needs to be applied to the anchor bolts.Meanwhile,affected by mining disturbances,strong impacts,etc.,the anchor bolts are in a working state of dynamic-static coupling.Therefore,studying the impact resistance performance and safety reserve of anchor bolts under different working load conditions is crucial for the support design of deep underground engineering.Based on this,the multi-functional dynamic-static coupling test system is self-developed.The dynamic-static coupling mechanical perform-ance tests on Common Bolts(CB)and High-strength Bolts(HB)are conducted under initial forces of 0-200 kN.The dy-namic-static coupling mechanical properties and impact resistance mechanism of anchor bolts are clarified.The test res-ults show that:In terms of impact energy,under dynamic-static coupling conditions,the impact energy resisted by differ-ent anchor bolts exhibits the same attenuation law with the increase of initial force.In terms of energy absorption,the total energy absorbed by anchor bolts does not change significantly with initial force variations.Meanwhile,the single energy absorption of anchor bolts increases with the increase of initial force,resulting in a significant decrease in impact energy and a reduction in safety margin.Under initial forces of 0-200 kN,the maximum impact energy attenuation rates of CB and HB are 58.8％and 50.0％,respectively;the average total energy absorbed by CB and HB is 13.0×104 J and 14.4× 104 J,respectively.The energy absorption coefficient demonstrates a"phased growth"characteristic of slow increase followed by rapid increase as the strength utilization rate increases.By comprehensive analysis,the impact-resistant and energy-ab-sorbing mechanism of anchor bolts is clarified under dynamic-static coupling conditions.On this basis,the strength-en-ergy dynamic-static coupling design concept for anchor bolts is proposed,and the bilinear prestress design model of an-chor bolts under dynamic-static coupling conditions is established,which can provide new ideas for the safety control of dynamic disasters in deep underground engineering.

Abstract:In order to deeply understand the complex fracture propagation mechanisms and control mechanism in the inter-face of coal-rock under tension,Brazilian tests were performed on coal-rock specimens in various approximation angle with respect to the loading direction to study the fracture propagation patterns on the temporal and spatial evolution and then to explore the fracture cross-interface propagation mechanisms and control mechanism under tension,assist by Digit-al Image Correlation(DIC),Acoustic Emission(AE)and high-speed camera.For Brazilian condition,it is shown that ten-sion fractures initiation in coal,then propagates nearly alone the loading direction to coal-rock interface,and non-planar distortion occurs near the interface,producing a complex fracture pattern with fracture branching,deflection and penetra-tion.When the fracture cross the interface,the fracture usually turn to the loading direction due to the local stress,produ-cing arc-shaped fracture path.When the fracture propagate alone the coal-rock interface,the fracture propagate mainly in the lower strength side of the coal-rock combination,producing simple fracture pattern.The fracture primarily turns to in-terface and propagate alone the interface for a length,then towards to the principal stress,producing complex fracture path,when it propagates to the interface at an acute angle.Meanwhile,when the fracture is perpendicular to the interface,it will penetrate the interface,producing simple fracture pattern.Brazilian tests of coal-rock combined specimens show that:The main fracture behavior is tension fracture,even the fracture occurs deflection or inflection which does not change the main behavior,obtained by the finally fracture geometry,the propagation path,the surface displacement field acquire by DIC data and the RA value by AE.The research results provide important theoretical guidance for deeply understand-ing of the cross-interface propagation behavior and control mechanism of tensile fractures at the coal-rock interface.

Abstract:The application of hydraulic technology can markedly enhance the efficiency of coalbed methane extraction.Nevertheless,when it comes to enhancing permeability in deep,soft coal seams,existing hydraulic techniques often en-counter challenges such as water locking,hole collapse,and drill bit sticking.Anhydrous technology offers a robust solu-tion to these issues by eliminating the adverse effects of water on soft coal seams at the source.Due to its unique physical properties,CO2 has developed anhydrous technologies such as CO2 jet impact rock breaking and phase change induced fracturing blasting.CO2 flash boiling jet,a novel jet technology,demonstrates potential in achieving optimal matching between impact force and working area in coal seam drilling applications,attributed to its features of phase change impact,extensive working area,and balanced force distribution.The expansion and collapse characteristics of multi-hole liquid CO2 flash boiling jet are pivotal in determining its impact effectiveness.However,the traditional jet characterization meth-od is inadequate for capturing the intricate flow field structure of multi-hole flash boiling jets.By using a unified fitting method and characteristic parameters,it is possible to accurately compare the flow field characteristics of different jets,clarify the impact mechanism of each jet parameter on the flow field,and provide an effective characterization method for precise control of jet parameters to improve drilling capacity.A characterization method based on boundary fitting is de-veloped to analyze the flow field morphology of multi-hole liquid CO2 flash boiling jets through visualization experi-ments.The jet flow field images were collected,and image processing techniques were used to extract boundary point in-formation.A nonlinear fitting function was employed to fit the boundary points,revealing the limitations of the boundary fitting method.Two new methods for fitting the boundary points based on fixed extreme points were proposed,with the method based on tangent curve extreme points demonstrating superior fitting performance.The near and far field regions of the jet were separately optimized for fitting,resulting in region-specific boundary fitting functions.For the near field re-gion,a correction factor n was introduced to optimize the fitting method,compensating for nozzles with small deflection angles.In the far field region,the number of boundary points required for the jet fitting was reduced to decrease data pro-cessing costs.The role of different characteristic parameters in the jet morphology was analyzed.The characteristic para-meter b in the far-field fitting function represents the radial deviation of the jet,while the characteristic parameter k in the near-field fitting function quantifies the expansion level of the flash boiling jet.Furthermore,the ratio of the near-field to far-field k-value—collapse ratio γ was proposed to characterize the collapse level of the flash boiling jet.

Abstract:China boasts extensive distribution of soft,low-permeability coal seams,where prolonged gas control cycles severely constrain mining alternation and coal production capacity release.Hydraulic measures for pressure relief and per-meability enhancement often lead to issues such as borehole blowout,collapse,and blockage,failing to efficiently resolve gas control challenges.Pneumatic permeability enhancement technology represents a feasible approach to addressing gas control difficulties in soft coal seams.However,due to factors such as cost,efficiency,and technical applicability,current pneumatic technologies have not been widely adopted.To address this,an air jet slotting pressure relief and permeability enhancement technology is proposed.To achieve efficient slotting with this technology,this study first established a calcu-lation model for the nozzle's maximum allowable length and outer diameter.For drilling tools with a diameter of 73 mm,key parameters were determined:a maximum nozzle length of 20 mm and an outer diameter of 13 mm.Based on this,an air jet slotter was designed,and the nozzle installation space was optimized to maximize the nozzle length within the lim-ited space of the drilling tool.Secondly,nozzle structures with different expansion ratios(n=0.5,1.0,1.3,and 1.4)were designed.The influence of different expansion ratios on the airflow field structure and impact pressure of the air jet was compared and analyzed through numerical simulation to determine the optimal nozzle expansion ratio and design prin-ciples.Experimental studies were conducted on the distribution characteristics of impact pressure versus target distance for nozzles with different expansion ratios,and the variation characteristics of the air jet borehole enlargement radius over time were analyzed.Integrating the above research findings,a complete air jet slotting system was developed,and field tri-als were ultimately conducted at Xinyi Coal Mine.The results indicate that the expansion ratio significantly influences the velocity and pressure fields of the air jet.When the expansion ratio is 1.0,the alternating development of the jet expansion and compression waves is the most gradual,heat exchange with the environment is minimized,the constant velocity core length is the longest,and the resulting jet achieves the maximum target distance and impact pressure.As the target dis-tance increases,the impact stress of nozzles with different expansion ratios generally shows a decreasing trend.However,when the jet is under-expanded or over-expanded,the impact pressure exhibits an alternating pattern of increase and de-crease with increasing target distance.In contrast,when the expansion ratio is 1.0,this alternating characteristic is not ob-vious,and the impact pressure consistently remains greater than that under under-expanded or over-expanded states.Un-der a compressed air pressure of 0.6 MPa,for a soft coal seam with a firmness coefficient(f)of 0.3,the slotting radius ex-ceeded 0.5 m.Field trials further confirmed that the air jet slotting radius can reach over 0.56 m.Compared to hydraulic slotting technology,the gas extraction flow rate increased by 2 times,and the time required to achieve extraction stand-ards was reduced by one-third.This effectively resolved the issue of mining imbalance and established a new model for gas control in soft coal seams.

Abstract:With the continuous promotion of intelligent construction in coal mines in China,the development of mine aux-iliary transportation vehicles towards unmanned driving has become an inevitable trend.As the core unit of unmanned vehicles,the positioning system cannot meet the full process,high-precision,and low time delay positioning requirements of coal mine auxiliary transportation vehicles from the ground fabric field,inclined shaft roadway,underground roadway,to mining face with a single positioning method and traditional positioning algorithms.Firstly,based on the operating con-ditions of coal mine auxiliary transportation vehicles and the tunnel environment,a seamless positioning system for under-ground and above mines based on GNSS/UWB fusion IMU was designed,and a model switching delay(DMS)was pro-posed as the performance evaluation index for the seamless positioning system;Secondly,to address the issue of non line of sight(NLOS)errors in UWB positioning,a UWB/IMU tight combination downhole positioning algorithm was de-signed,and Error State Kalman Filter(ESKF)was used to filter and optimize it.Simulation results showed that the ESKF optimization algorithm had an average positioning error of 0.19 m,with an accuracy improvement of 56%compared to single UWB positioning;Once again,the influencing factors of interactive multiple models were analyzed.In response to the problem of large model probability matrix errors affecting seamless positioning accuracy,a mine seamless positioning algorithm based on ESKF and fuzzy adaptive improved interactive multiple models(FAIMM-ESKF)was designed.Simu-lation results showed that the positioning accuracy of the FAIMM-ESKF algorithm was improved by 29%compared to be-fore improvement;Finally,a simulated inclined shaft tunnel was constructed in the laboratory,and a seamless positioning system positioning and evaluation experiment was conducted using an unmanned test vehicle.The results showed that the average error of the seamless positioning system in the interaction area between the well and the underground was 0.131 m,and the maximum error was 0.452 m,which was reduced by 17.6%and 14.8%compared to traditional al-gorithms,respectively;Throughout the entire experimental process,the maximum error of the FAIMM-ESKF algorithm was 0.498 m,the average error was 0.25 m,and the average model switching delay was 35 ms,which can meet the posi-tioning accuracy and delay requirements of unmanned driving in the entire process of coal mine auxiliary transportation vehicles.The research results can provide theoretical reference for promoting the establishment of a seamless connection,precise and efficient positioning system and positioning algorithm for coal mines,and have important theoretical signific-ance and practical value for accelerating the normalization of unmanned driving of auxiliary transportation vehicles in coal mines and accelerating the intelligent construction of coal mines.

Abstract:In order to promote low-carbon development in the field of green mines and improve utilization efficiency of solid waste,a new type of high strength green cement based composite grouting material was obtained by employing silic-ate cement and fly ash as cementitious materials and using glass fiber powder(GFP)tailings for toughening.The effects of GFP dosage on the working properties,hydration products,setting time and mechanical strength of the composite grout were investigated through slurry property tests,mechanical strength tests,X-ray diffraction(XRD),fourier transform in-frared spectroscopy(FTIR),scanning electron microscopy(SEM)and thermodynamic modeling.The mechanical bearing performance of the new grouting material cemented gravel was evaluated by the coal gangue aggregate grouting consolid-ation simulation test,revealing the grouting reinforcement mechanism of GFP modified fly ash-cement composite slurry on coal gangue.The results showed that addition of GFP helped to shorten initial setting time of fly ash-cement composite slurry,while the fluidity,water separation rate,and compressive strength of the stone body increased first and then de-creased with the increase of dosage.When the content of GFP was 1%,the working performance of fly ash-cement com-posite slurry was the best.The initial setting time was shortened by 5.9%,and the compressive strength of 3 d and 28 d was increased by 12.6%and 37.8%.Microscopic characterizations confirmed that suitable GFP helped to improve the pozzolanic effect,promoting the consumption of Ca(OH)2 to produce a large amount of hydrated calcium silicate products.The unhydrated GFP could exert a filling effect for improving the compactness of the matrix.The grouting reinforcement test showed that 1.0%GFP modified fly ash-cement grouting material effectively inhibited the growth of micro-cracks and pore structure of coal gangue cement during the load process,improving the multifractal characteristics.Its peak stress was increased by 12.1%,showing an enhanced mechanical bearing characteristic.The reinforcement mechanism could be at-tributed to the good synergistic coupling effect between cement,fly ash,and GFP.It would provide ideas for developing low-cost and high-performance green grouting materials in the deep coal mine engineering field.

Abstract:In view of the complex environment,low light,dust and other interference factors in the auxiliary transporta-tion roadway in the coal mine,and the reflected light interference in the detection of workers,the mining unmanned vehicles using vehicle-mounted cameras have low detection accuracy and poor real-time detection of workers in the road-way.In addition,existing target detectors based on deep learning have the problems of large number of parameters and high computational complexity of the model.A detection model of mine unmanned vehicle assisted transportation road-way workers based on YOLOv8,namely GCDB-YOLOv8,was proposed.Firstly,lightweight modules Ghost Convolu-tion(GhostConv and GhostC2f)are introduced into the feature extraction network to achieve lightweight network design and reduce the number of model parameters and computational complexity.Secondly,the C2F-EMA module is designed and used to replace the C2f model of the neck,so as to enhance the attention of key areas in low light and complex back-ground,so that the model can make efficient use of the feature information of the staff.At the same time,the DicPSA module is designed and used to replace the spatial pyramid pooling module(SPPF)in the backbone network to enhance the ability of the model to capture,extract and utilize key feature information.Finally,the weighted bidirectional feature pyramid(BiFPN)mechanism is designed and improved,and the original FPN+PAN structure is replaced by BIFPN to re-duce the problem of feature information loss,achieve the full fusion and utilization of deep feature map target semantic in-formation and shallow feature map target location information,and improve the detection accuracy.On the Underground Transportation Roadway Workers Detection Dataset,the experimental results show that compared with YOLOv8n,the de-tection accuracy of GCDB-YOLOv8 model reaches 80.64%,which is improved by 6.06%.The detection speed reaches 112 f/s,which is faster than the baseline model and meets the requirement of real-time detection.The number of model parameters is 2.70 M,and the computational complexity is 7.50 GFLOPs,which is 0.31 M and 0.70 GFLOPs less than the baseline model,respectively.Compared with Faster R-CNN,SSD,YOLOv3-tiny,YOLOv5s,YOLOv7-tiny,YOLOv8s,YOLOv9s,IAT-YOLO,RT-DETR,MLFE-YOLOX,CDD-YOLO,YOLO_GD detection models,GCDB-YOLOv8 is su-perior to other comparison models in terms of detection accuracy,detection speed,number of parameters,and computa-tional complexity.On the Miner Action Detection Dataset,the mAP@0.5 and the mAP@0.5～0.95 of GCDB-YOLOv8 reach 87.69%and 64.77%,respectively,which are 3.43%and 2.26%higher than that of the baseline model YOLOv8n.GCDB-YOLOv8 model improves the detection accuracy of underground transportation roadway workers while taking in-to account the lightweight and real-time performance of the model,which is easy to deploy on mining unmanned vehicles.The model can meet the detection requirements of mining unmanned vehicles for workers in the roadway and reduce safety hazards.In addition,the accurate real-time detection of the workers in the underground transportation roadway by GCDB-YOLOv8 can provide security for the subsequent autonomous obstacle avoidance,path planning,decision control and other tasks of the mining unmanned vehicle,and promote the application of unmanned driving technology in the field of intelligent coal mines.

Abstract:Aiming at the technical problems of poor sealing performance,rapid decay of gas concentration volume in bore-holes and high economic costs of sealing in traditional sealing technology,a new sealing technology of"adaptive bore-hole deformation,flexible pressure holding,dynamic sealing and reuse"is proposed.A new type of"fetal sac type"re-usable sealing device for gas drainage is developed,and the basic structure design and sealing technology principle of"fetal sac type"sealing device are expounded.The core component of the sealing device(sealed fetal sac)is systematic-ally studied by means of numerical simulation,laboratory experiments and theoretical analysis.The results demonstrate that the fetal sacs with wall thickness of 1 mm and 2 mm can expand rapidly under lower grouting pressure,meeting bore-hole sealing requirements.The average contact pressure between the sealed fetal sac and the hole wall increases gradually with the increase of the applied force.Compared with the sealed fetal sac with a wall thickness of 1 mm,the sealed fetal sac with a wall thickness of 2 mm has a more stable overall sealing performance with the increase of the pressure.The res-ults of the sealing experiment demonstrate that the ultimate bearing capacity of the fetal sac is positively correlated with the wall thickness of the fetal sac.When the grouting pressure is greater than 0.32 MPa,the sealing device can effectively seal the borehole.Combined with the results of numerical simulation,hole sealing experiment and mechanical analysis of grouting hole sealing,the optimal combination solution of the structural design parameters of the fetal sac is that the length is 1 000 mm,the wall thickness is 2 mm.The field engineering practice show that compared with the traditional"two plugging and one injection"pressure sealing process,in the same extraction period,the average gas extraction concentra-tion volume of the new sealing process is 126.6%higher than that of the traditional sealing process,and the average ex-traction purity is increased by 120%.After the first extraction,the recycling rate of the fetal sac is 84%,and the recycling rate of the fetal sac is 65%after the third extraction,and the extraction concentration volume is increased by more than 30%.These results confirm that the new sealing technology not only enhances extraction efficiencyand prolongs the high concentration volume extraction time,but also achieves the effect of repeated utilization of the sealing device,provideing a new technical path for mine gas extraction methods.

Abstract:Autonomous mining trucks often operate autonomously in low-light environments,where accurate and reliable detection performance is critical to ensuring operational safety.However,the open-pit mining environment is highly com-plex,frequently involving large-scale occlusion and multi-scale feature interaction between the trucks and other objects such as personnel,which poses significant challenges for detection under low-light conditions.To address these issues,LECODNet is proposed,an occluded object detection network tailored for autonomous mining trucks in low-light environ-ments.Firstly,a Multi-Receptive Field Edge Perception Module is designed to extract edge features rich in local detail and global semantic spatial information,enhancing object boundary representation.Secondly,an Edge-Guided Feature En-hancement Module is introduced,using the extracted edge features as structural priors to guide the model's focus on ob-ject regions.Thirdly,a Channel-Aware Mapping Attention mechanism is further embedded to enhance the expressive power of the object features.Finally,a Bidirectional Spatial C2f module is incorporated into the neck,capturing spatial contextual information in both horizontal and vertical directions to improve the model's ability to perceive spatial structur-al cues.Extensive experimental results on the self-constructed LAOMD dataset for low-light occluded object detection demonstrate that LECODNet achieves mAP@0.5 of 83.5%and mAP@0.5∶0.95 of 71.2%,surpassing the baseline YOLOv8 by 3.3%and 2.3%,respectively.Compared to the state-of-the-art low-light occlusion detection model FeatEn-hancer,LECODNet shows improvements of 1.9%and 1.5%in mAP@0.5 and mAP@0.5∶0.95,respectively.These res-ults indicate that the proposed method effectively enhances object region perception and feature representation while im-proving spatial structural modeling,significantly boosting detection performance under low-light occluded conditions.

Abstract:Frequent occurrence of mine earthquakes poses a serious threat to coal mine safety production.According to the investigation,it is easy to cause gas disasters after the mine earthquake,showing the characteristics of"earthquake first and disaster later",which provides the possibility of early warning of gas disasters under the action of mine earthquake.However,the seepage law of gas disasters induced by mine earthquake is not clear.Considering the stress environment of coal body and the occurrence principle of gas disaster,based on the analysis of mine earthquake waveform characteristics,a self-designed dynamic triaxial loading seepage test system was adopted,and cyclic stress ratio(CSR)was introduced to simulate the characteristics of mine earthquake.At the same time,the dynamic load frequency and gas adsorption pressure were considered.The dynamic and static combined loading scheme was designed,and the mechanical,microscopic pore and seepage characteristics of gas-bearing coal samples under dynamic load were studied.The results show that the resid-ual strain of coal samples increases rapidly with the increase of vibration times at the beginning of dynamic load loading stage,and then gradually tends to be gentle.The permeability of coal samples increases exponentially with the increase of dynamic load frequency and CSR,while it changes in a negative exponential function with the initial adsorption gas pres-sure,and CSR has the most significant effect on the mechanics and permeability of coal samples.The peak strength and elastic modulus of gas-bearing coal samples after damage are negatively correlated with dynamic load frequency,CSR and gas adsorption pressure.When CSR is 0.75,peak strength and elastic modulus degradation rate reach the maximum,which are 15.3%and 68.2%respectively,and the damage variable is 0.68.Using CT scanning and three-dimensional reconstruc-tion technology,the quantitative characterization of pore volume changes before and after loading of coal samples was ob-tained.The total pore volume increased to 7 times of the initial state under different CSR loading.The influence character-istics of dynamic load on the porosity of coal samples were analyzed,and the effects of mine vibration stress on the devel-opment of pore cracks,seepage characteristics and damage deformation of coal were explained.The research can provide support for the mechanism revelation and disaster warning of deep coal-rock gas dynamic disasters under the action of mine earthquake.

Abstract:Autonomous driving in open-pit mines can reduce the number of operating personnel,lower production costs and safety risks,and has become an important direction for the intelligent development of open-pit mines.However,due to the relatively conservative driving speed of mining trucks planned by current autonomous driving algorithms,there is still a certain gap in its transportation efficiency compared with manned driving.To maximize the planned speed as much as possible on the premise of not violating vehicle-road physical constraints and ensuring driving safety,a motion planning method for fixed transportation routes in open-pit mines based on integral chain dynamics and Gröbner basis is proposed.First,a refined speed constraint curve for the entire section of the fixed transportation route is established according to the kinematic characteristics of mining trucks and road conditions in open-pit mines,with comprehensive consideration of conditions such as speed limit rules,road curvature,ground adhesion,and vehicle front-wheel angle.Subsequently,the in-tegral chain dynamics theory is used to characterize the autonomous driving motion planning problem in open-pit mines as a problem of solving a system of multivariate polynomial equations regarding the action time of force change rate.The Gröbner basis theory is applied to convert the system of multivariate polynomial equations into a parameterized regular polynomial system,and finally the motion planning problem is equivalent to the problem of solving a triangularized poly-nomial system.In practical deployment,only the start and end condition parameters need to be input to achieve fast iterat-ive solution,thus obtaining a motion planning scheme that meets driving safety requirements and has smooth acceleration.This method is used for motion planning of multiple sections of a real transportation route in an open-pit mine in Inner Mongolia under different initial and terminal conditions,and feasible solutions are quickly obtained in all cases.Finally,motion planning is conducted for a 3.61 km-long continuous curved round-trip route.Compared with the current actual op-eration records of manned mining trucks in the mine,the average operation time is reduced by 10.7%,and the calculation time for a 20 m planning task is within 100 ms,which indicates that this method can effectively improve the operation effi-ciency of vehicles in open-pit mines.