Abstract:Confining stress is one of the key factors affecting the anchoring performance of rockbolts.To investigate the effect of confining pressure on rockbolt anchoring performance and its influencing factors,the anchor pull-out tests under the conditions of the surrounding rock properties and stress environment were carried out using the self-developed rockbolt confining pressure pull-out test device.The influence of factors,such as confining pressure,rockbolt diameter,anchoring length and surrounding rock strength,on the anchoring performance of rockbolts was investigated.The results show that confining pressure is a critical factor influencing rockbolt anchoring performance.With increasing confining stress,the lateral constraint exerted by the surrounding rock on the anchoring interface strengthens,leading to an approximately linear increase in the ultimate anchoring force of the rockbolt at a rate of 4.28 kN/MPa.This manifests as a significant improvement in the overall bearing capacity of the rockbolt anchoring system.Under constant confining pressure,the rockbolt diameter and anchoring length exhibit a positive correlation with the ultimate anchoring force.The larger rockbolt diameters and longer anchoring lengths enhance the anchoring force more effectively,although this enhancement is limited by the material strength of the rockbolt and the bearing capacity of the surrounding rock.The anchoring performance of rockbolt is highly sensitive to the strength of the surrounding rock.Under the same confining stress,the anchoring force of rockbolt is positively correlated with the strength of the surrounding rock,and the stronger surrounding rock provids better anchoring conditions and greater system stability.Furthermore,recommendations to improve rockbolt anchoring performance in coal mine roadway support were proposed,which is valuable for the design and optimization of deep coal mine roadway support under complex geological conditions.

Abstract:River embankments often suffer from weak foundation conditions,making them susceptible to seepage,piping and slope failures during flood seasons.Regular,rapid and accurate inspections are essential for ensuring the safe operation of embankments.As an effective non-destructive geophysical technique,Ground Penetrating Radar(GPR)has been widely applied in potential hazard detection in embankments.However,raw GPR signals often contain considerable high-frequency noise and background interference,making it difficult to extract reliable features under complex field conditions.Traditional spectral analysis methods,such as the Fourier Transform,typically suffer from spectral smearing and unclear dominant frequency components,limiting their practical application.To address these limitations,a three-dimensional spectral energy ratio imaging method was proposed for potential embankment hazard detection based on combined wavelet-fourier transforms.In this approach,wavelet transform is first applied to analyze non-stationary and transient components of the radar signal,allowing for multiscale decomposition of its frequency characteristics.Subsequently,a short-time Fourier transform is used to calculate the temporal evolution of frequency-domain information and extract dominant frequency components and energy distribution across time windows.Based on this,a classification criterion of hazard types is developed using the spectral energy ratio,enabling the effective separation of loose zones and water-enriched zones within the embankment.This approach facilitates high-resolution,efficient and non-destructive identification of internal embankment anomalies.Finally,a field investigation was carried out on the triangular joint polder embankment in Yongxiu County,Jiujiang City,Jiangxi Province.The results demonstrate that the proposed method successfully detects and delineates loose and water-rich areas within the embankment,indicative for hazard assessment and routine inspection of earthen dams.

Abstract:It is of significant importance to investigate the energy evolution characteristics and progressive damage behavior of gas-bearing coal-rock combinations under both conventional and graded cyclic loading conditions for the prevention and control of deep coal-rock-gas composite dynamic disasters.By laboratory testing and theoretical analysis,a series of coupled acoustic emission(AE)-seepage-damage triaxial tests were conducted under various confining pressures and stress paths.The mechanical response,progressive damage behavior,and energy evolution patterns of loaded gas-bearing coal-rock combinations were systematically analyzed.By combining macro-meso failure characteristics,the influence mechanisms of confining pressure and stress loading on the failure behavior of gas-bearing coal-rock combinations were revealed.The results show that the peak strength,elastic modulus and residual strength of the composite specimens increase linearly with confining pressure.Under the same confining pressure,the elastic modulus under graded cyclic loading is lower by 0.13-1.76 GPa,and the peak strength is lower by 8.91%-20.81%than those under the conventional triaxial loading.Increasing confining pressure significantly suppresses crack development,while graded cyclic loading exhibits the lower crack initiation stress and damage stress ratios,making specimens more prone to cracking at lower stress levels.Acoustic emission(AE)signals exhibit stage-wise variations corresponding to characteristic stresses during progressive damage.Peak acoustic emission counts increase with higher confining pressure.Elevated confining pressure restricts internal crack propagation and coalescence.Under graded cyclic loading,the Kaiser effect zone of acoustic emission counts extends,while the Felicity effect zone shortens.The total energy,elastic energy and dissipated energy under graded cyclic loading are all higher than those under conventional triaxial loading.Energy dissipation is more pronounced in intervals with the larger stress amplitudes.SEM observations reveal more complex and rougher failure surfaces under graded cyclic loading,with more evident cracks and pores,and fractal dimension values larger by 0.057-0.280 than that under conventional triaxial loading.High confining pressure induces greater damage effects than compressive restrictions,exacerbating interfacial failure in coal-rock combinations,with shear failure being the dominant failure mode.These findings provide a theoretical basis for preventing and controlling coal and gas composite dynamic disasters in high-stress and high-gas-pressure zones in deep coal mining.

Abstract:ully-mechanized top-coal caving with large-cutting-height(LC-HTCC)is a key technology for the safe and efficient mining of ultra-thick coal seams.However,the exceptionally large mining space intensifies the inherent contradiction between wall stability and the cavability of hard top coal.This conflict becomes particularly acute when both the coal seam and the immediate roof are highly competent,significantly limiting the potential for achieving super-high production rates.Taking Panel 111 of the Jinjitan coal mine as a case study,theoretical analysis,laboratory testing,numerical simulation and in-situ monitoring were performed to investigate the coupled failure mechanism of the high rib and hard top coal under these challenging geological conditions.A structural model of the support-surrounding rock system is established,and analytical expressions for support resistance and rib pressure under massive hard-roof impact are derived,demonstrating that support stiffness governs load transfer within the roof.By applying the principle of minimum potential energy,the ultimate bearing capacities of the high rib and hard top coal are determined,and the conditions for coupled instability,cooperative stability and asynchronous response are clarified.Stability and cavability indices are defined and found to change with the cutting-to-caving ratio according to a negative exponential law,quantitatively characterizing the negative feedback between rib stability and top-coal cavability.A synergistic control strategy was developed,incorporating massive hard-roof fracturing,high-strength/high-stiffness support,optimization of the cutting-to-caving ratio,and face layout redesign.Field implementation resulted in a 60％reduction in rib damage and a top-coal recovery rate of 83％,enabling the safe and efficient extraction of an ultra-thick coal seam using the LC-HTCC method.

Abstract:Fluid injection-induced seismicity has garnered global attention,causing a key technical challenge to the safe extraction of clean energy resources,such as shale gas.Taking a representative shale gas development area in the southern Sichuan Basin as the background,this study investigated the evolution and fluctuation of seismicity parameters during fluid injection,and examined the spatiotemporal dynamics of the seismic front and back-front behavior.The underlying fluid-driven patterns of earthquake swarms in the region were explored.The results show a clear spatiotemporal correlation between fluid injection and moderate-to-strong earthquakes(ML≥3.5),with the injection process significantly enhancing the intensity and complexity of seismicity.We confirm the ubiquity of the seismic back-front phenomenon,characterized by a progressively expanding central zone devoid of seismicity.The seismic front and back-front are found to be controlled by aseismic slip,while the swarms between them are governed by a combination of mechanisms:alternating dominance of slow diffusion driven by fluid pressure and rapid migration driven by aseismic slip.These findings helps the understanding of the physical origins of fluid-induced seismicity in shale gas regions,as well as for assessing and mitigating associated seismic hazards.

Abstract:To study the damage and deterioration characteristics of coal-rock combinations with the same fractures under cyclic loading,experiment and numerical simulation were conducted to investigate the effects of coal-rock ratio and cyclic loading amplitude on the damage evolution and macro-micro failure mechanisms of rock-coal-rock combinations.The results show that the coal fracture network dominates the strength and failure of the combination.During the cyclic loading and unloading process,the stress-strain curve shows a hysteresis effect,which is small and dense at the initial stage and large and sparse at the later stage.The displacement changes sinusoidally with time,and the overall displacement increases in the first few cycles before instability.When the force on the particles is greater than the particle bonding strength,cracks first initiate at the tip of the coal fractures,and then the force concentration point shifts to the surrounding particles,causing the cracks to develop in a band-like manner.Multiple sets of crack bands and fracture zones coalesce through crack bands,causing the specimen to lose its load-bearing capacity.As the proportion of coal in the combination increases,the strength of the combination decreases,the displacement increases,the b value of acoustic emission decreases,and the number of cycles before instability decreases.As the cyclic loading amplitude increases,the displacement of the combination increases,the b value of acoustic emission decreases,the degree of deterioration of the combination deepens,and it is more likely to cause instability of the combination specimen.

Abstract:To obtain the variation patterns of hydraulic fracture propagation trajectories caused by abrupt lithological changes of formation interfaces,the propagation behavior of hydraulic fractures in coal measure strata under different combined lithological modes was investigated through true triaxial hydraulic fracturing experiments and inversion of direct current resistivity method.The influence mechanisms of in-situ stress,lithological strength difference,and formation interface strength on the propagation trajectories of hydraulic fractures were analyzed.The results show that the morphology of hydraulic fractures in coal measure strata exhibits significant asymmetric characteristics,and the following seven modes are identified:single,cross,"T"-shaped,"+"-shaped,"I"-shaped,"干"-shaped,and complex fractures.The hydraulic fracturing pressure curve can be divided into four stages:rapid increase to fracture initiation pressure,sudden pressure drops,stable fluctuation,and pressure decrease after pump shutdown.When hydraulic fracture propogation encounters natural fractures or formation interfaces,the pressure curve shows obvious fluctuations,and the sudden pressure drop value is negatively correlated with the complexity of the hydraulic fracture.The influence of in-situ stress on hydraulic fractures is related to the direction of the maximum principal stress and the vertical stress difference coefficient.When the maximum principal stress is vertical,the larger the vertical stress difference coefficient,the easier it is for the hydraulic fracture to penetrate the interface and continue to propagate vertically.The lithological strength difference influences the propagation trajectory of hydraulic fractures as well.When a hydraulic fracture initiates and propagates from soft rock to a formation interface,its propagation trajectory mostly stops and extends along the formation interface;whereas when a hydraulic fracture initiates in hard rock,the larger the lithological strength difference ΔS,the easier it is for the fracture to penetrate the formation interface and to continue to propagate vertically.Otherwise,it tends to extend along the formation interface.

Abstract:With the continuous increase in mining depth,the risks associated with roof instability have become more prominent,where the diagnosis,monitoring,early warning and prevention of roof-related hazards are critically important.A theoretical framework has been established for the fully-automated recognition of multiple seismic sources induced by mining activities.A novel source localization method,applicable to multi-level and multi-stope environments,has been proposed,which eliminates the requirement for pre-measured wave velocities.Additionally,a rapid wave velocity imaging technique has been developed,which transforms seismic noise into usable signals through velocity field inversion.A series of proprietary technologies have been developed,including intelligent acoustic emission sensors,data acquisition instruments,and a real-time data processing system.These components have been integrated into a comprehensive technical solution for intelligent acoustic perception and microseismic monitoring,incorporating collaborative sensing,information processing,and intelligent early warning.Furthermore,a multi-index joint early warning methodology for rock mass instability in roof strata has been proposed,along with a partitioned support and prevention strategy based on rock mass damage and dynamic responses of surrounding rock.These technologies have been successfully applied in over 20 domestic mining enterprises,providing early warnings of roof collapses and other hazards on multiple occasions,and enabling timely and safe evacuation of personnel and equipment.The research outcomes have significantly enhanced the overall effectiveness of roof stability monitoring and disaster prevention.

Abstract:In time series prediction of microseismicity in coal mines,data-driven deep learning model can effectively extract key features and rules of microseismic data,and achieve accurate prediction.However,due to the constant change of working conditions with the advance of working face,the causes of microseismic events are complex and disordered.It is difficult for a single prediction model to learn local time series features to maintain a stable and accurate prediction,and it is impossible to predict the initial stage of mining.To improve the stability,completeness and accuracy of time series prediction of microseismicity in coal mine,the time series characteristics of microseismicity of different working faces and different mining stages of the same working face were analyzed by using massive microseismic data.Based on adaptive-dickey-fuller(ADF)stationarity and volatility tests,the significant influence of event causes on microseismic timing characteristics was identified,and multiple microseismic timing data sets were constructed under different event causes.Using blending integration learning algorithm and combining one-dimensional convolutional neural network(1D-CNN)and bidi-rectional short-and long-term memory network(BiLSTM),a timing prediction model of coal mine microseismicity based on adaptive ensemble learning was proposed.Based on the microseismic data of 7302 working face in Zhaolou Coal Mine,the daily maximum energy,average energy and frequency of microseismic are predicted by the integrated model,and the daily maximum energy is analyzed in detail.The results show that on the premise of ensuring the integrity of prediction,the proposed integrated model can better adapt to the actual situation of complex,variable and disordered distribution of event causes.The error between the prediction and field monitoring values is small,and the goodness of fit calculation results of each parameter is above 0.8.The research provides a new idea for the time series prediction of microseismicity in coal mines.

Abstract:To investigate the load-induced fracture instability of cavernous fractured sandstone under varying hole diameters and fracture dips,uniaxial compression tests were performed on red sandstone samples from the Linyi mountainous area.Based on the minimum energy theory and the hard body hypothesis,the stress-strain curves,energy evolution laws,and AE characteristics of different specimens were analyzed.The results show that fracture propagation and coalescence lead to the instability and failure of sandstone,and the mechanical properties of the sandstone differ with varying hole diameters and fracture dip angles.The stress of sandstone first decreases and then increases with the fracture dip angle.An increase in hole diameter reduces the stress,but the magnitude of reduction is small.The strain exhibits an"M"-shaped variation pattern with the fracture dip angle.The strain energy of sandstone during loading shows a pattern of slow increase,rapid increase,and post-peak stability.With the increase of fracture size,the strain energy first decreases and then increases.The AE energy during sandstone loading increases intermittently,and a"quiet period"phenomenon is observed before reaching the peak stress.The AE energy is greatest after failure.The relationship between AE energy and strain energy follows a power function.A hypothesis for the disturbance-induced instability failure of fractured rock masses was proposed:after the fracture of the hard body,disturbance leads to the instability failure of sandstone in a self-organized critical state.This was validated through AE localization and the actual fracture propagation patterns.The research findings hold significant theoretical and practical value for stability monitoring,early warning,and disaster prevention and control in fissured sandstone.

Abstract:The water-cement ratio is a key factor affecting the performance of cement-based grouting materials.The hydration characteristics of multi-component cementitious systems at different water-cement ratios exhibit significant differences.To clarify the intrinsic relationship between the water-cement ratio and the performance of mine ultra-fine cement systems,ultra-fine cement-based grouting materials(UPCGM)were prepared by incorporating superplasticizers,expanding agents,and accelerators into ultra-fine silicate cement.Using various macro-and micro-testing methods,the effects of the water-cement ratio(0.45-0.80)on the performance of UPCGM slurry,mechanical properties,and microstructure of the hardened body were explored,and the underlying hydration mechanisms were analyzed in depth.The results indicated:①The water-cement ratio was positively correlated with the slurry flowability and setting time of UPCGM,while it was negatively correlated with the volume expansion rate of the hardened body.②As the water-cement ratio increased,the mechanical strength of UPCGM initially increased and then decreased.At a water-cement ratio of 0.50,the hardened body exhibited the best mechanical performance,with a compressive strength of 33.70 MPa at 3 days,an increase of 298.82%to 466.39%compared to water-cement ratios of 0.60 to 0.80.The 28 days compressive strength(50.70 MPa)and flexural strength(8.50 MPa)increased by 18.18%to 85.71%and 50.44%to 95.85%,respectively.③Thermodynamic modeling,XRD,FTIR,and SEM confirmed that changes in the water-cement ratio affected the hydration degree,hydration products,pore structure,and compactness of UPCGM,with the content and size of AFt increasing as the water-cement ratio increased.④Compared with the mine inorganic reinforced composite mortar(KWJG-1),UPCGM showed slightly lower flowability,early compressive strength,and flexural strength,but had significantly enhanced slurry stability,early setting properties,and later compressive strength.At water-cement ratios of 0.50 and 0.80,the 28 days compressive strength was 14.50%and 35.48%higher than that of KWJG-1,respectively,indicating potential applications in the field of roadway surrounding rock grouting reinforcement.

Abstract:The mechanism of strong mining pressure of thick coal seam under dual key strata conditions mining is unclear,making the prediction of weighting intervals and disaster control difficult.Taking the 11223 working face in the Huainan mining area as an engineering case,the overburden migration patterns and dynamic force chain transfer mechanism under synergistic fracture of dual key strata were investigated by integrating discrete element numerical simulation,theoretical analysis and field practice.A support-surrounding rock bearing model for dual key strata fracture was established.The results demonstrate that the lower key stratum Ⅰ,directly affected by mining disturbances,exhibits periodic fracturing with an average interval of 25 m,forming a"cantilever-step rock beam"composite structure that triggers minor periodic weighting.In contrast,the upper key stratum Ⅱ,influenced by stress transfer hysteresis,breaks at an interval of 40 m with a fracture angle of 73°.Its instability induces transfer amplitude of kinetic energy up to 4.2 times the initial value,causing the peak abutment stress to surge to 48 MPa(28％exceeding the rated support resistance),which is identified as the primary cause of major periodic intense mining pressure.The fracture of dual key strata governs stress field evolution through force chain network reconstruction.Fracture of key stratum Ⅰ forms a localized"pressure arch"structure,while fracture of key stratum Ⅱ triggers asymmetric tension-compression alternation,driving the stress field through a three-stage evolution of"local unloading,regional transfer,and global reconstruction".A deep-hole pre-splitting blasting weakening scheme was proposed based on dynamic load superposition mechanisms.After field implementation,periodic weighting intervals decreased from 25 m to 16 m,the dynamic load coefficient of supports decreased from 1.5 to 1.3,and the peak roof pressure recuded by 46.7％.These findings provide theoretical and practical insights strong mining pressure control in deep multi-key strata coal mines.

Abstract:For coal mine strata control,comprehensive disposal of coal-based solid waste and carbon sequestration/reduction,a systematic approach was designed involving coal-based solid waste pretreatment,material production,and gas sequestration units.Coal gangue,fly ash,and other coal-based solid wastes were crushed and sieved.A three-dimensional(3D)in-situ crosslinked polymer network using a four-arm crosslinker(pentaerythritol glycidyl ether)to immobilize CO2 was developed,thereby establishing an in-situ crosslinking network-based carbon sequestration method.The influence of the in-situ crosslinked polymer network structure on the slurry properties,mechanical characteristics,hydration products,microstructure and carbon sequestration efficiency of solid waste-based carbon sequestration grouting/filling materials was investigated using various characterization techniques.The coupling mechanism of the in-situ crosslinked polymer network structure in these materials was elucidated.Experimental results demonstrate that the in-situ crosslinked network structure enhanced the CO2 immobilization capacity from 1.29 mg/g to 2.17 mg/g,achieving highly efficient carbon fixation.Additionally,the in-situ crosslinked network accelerated the hydration rate,promoted the hydration process,and significantly improved mechanical strength,with flexural strength increasing by 128.8%and compressive strength by 118.4%.Field tests further confirmed that the performance of the developed solid waste-based carbon sequestration grouting material in rock reinforcement,high-efficiency carbon sequestration and solid waste disposal.

Abstract:Gangue particle size and mass concentration have an important influence on the performance of backfilling materials.The size grading of gangue was characterized by the fine gangue content(the percentage of 0-5 mm gangue in the total gangue),and the influence of the fine gangue content,concentration and their interaction on the flow performance,rheological properties,mechanical properties,ultrasonic wave velocity and microstructure of backfill was analyzed.The results show that with the increase of fine gangue content and concentration,the slurry flow,bleeding rate and the total porosity decreased,while the rheological parameters,uniaxial compressive strength,modulus of elasticity,splitting tensile strength and ultrasonic wave velocity increased,making the backfill more compact.The slurry belonged to Bingham fluid,and the fluctuation of slurry shear stress curve decreased and the homogeneity became better with the increase of fine gangue content.In the interaction of two factors on the rheological parameters and mechanical properties,the increase of one factor promoted the enhancement of the other factor,but the influence of concentration was greater than that of fine gangue content.The response surface of each property to the interaction term could be fitted as parabola function surface.The splitting tensile strength was mainly 0.11-0.12 times of uniaxial compressive strength,and a significant linear positive correlation lied between them.The uniaxial compressive strength was positively correlated with ultrasonic wave velocity and the content of micropores and capillary pores,but negatively correlated with total porosity and the content of large pores and multi-damaged pores,with the fitting degree greater than 0.9.The findings demonstrate that the performance of acoustic wave velocity and microstructure in describing the influencial mechanism of these two factors on backfill strength.

Abstract:To investigate the confinement effect of carbon fiber-reinforced polymer(CFRP)sheets on the mechanical properties and energy damage behavior of coal samples,uniaxial compression tests were conducted on coal samples with varying layers of CFRP sheets.The stress-strain changes during the four stages of crack compaction,linear elasticity,yield and post-peak failure were analyzed,and the influence of CFRP sheets on the energy input,accumulation,dissipation,and release processes in coal samples was studied.The results show that the crack closure stress and crack initiation stress of coal samples first increased and then decreased with the increase in CFRP layers,but still higher than that in the unconfined state,demonstrating a significant confining effect and a marginal diminishing feature.The CFRP sheets effectively constrained the internal crack propagation in coal,improved stress distribution,made the failure process slower and more orderly,significantly enhanced the load-bearing capacity and ductility,and reduced the post-peak stress drop phenomenon.The CFRP sheets enhanced the energy input and distribution uniformity of coal samples,reduced the energy release rate,and improved the energy distribution and failure process.CFRP confinement significantly improved the mechanical properties and energy dissipation characteristics of coal samples.The proposed dissipated energy damage factor model verified the effectiveness of CFRP sheets in delaying damage accumulation and crack propagation.A mathematical relationship was derived between the layers of CFRP sheets and the equivalent coal cylindrical sleeve thickness.The research advances the understanding of coal pillar reinforcement mechanism and provides an economical and efficient new perspective for improving the recovery rate of residual coal resources in room-and-pillar mining.

Abstract:To investigate the variation laws of gas seepage in creeping coal rock under mining disturbance at different stress states,triaxial creep disturbance seepage tests were conducted using the self-developed RRTS-Ⅳ Rock Creep Disturbance Effect Test System.Based on a Burgers creep model and considering disturbance-induced damage and an improved accelerated creep component,a coal rock creep model was established,and a stress-permeability relationship formula was further derived.The experimental results show that when gas pressure is constant,an increase in confining pressure reduces permeability,while permeability increases rapidly after the axial pressure exceeds a stress threshold.This threshold lies between the stable and accelerated creep stages and is lower than the long-term strength.When confining pressure is constant,the initial permeability of the coal sample decreases with increasing initial gas pressure.At this stage,the influence of stress on permeability is weaker than the effect of desorption and adsorption on the internal swelling deformation of the coal sample.However,the effect of effective stress becomes dominant as effective stress increases.Under constant static stress,continuous disturbance causes damage and eventual failure of the coal,undergoing three stages:decelerating creep,stable creep,and accelerated creep.The level of static stress affects the initial creep state and anti-disturbance ability.Based on the creep disturbance tests,a damage-containing stress-permeability model(creep model)was established by connecting the Burgers model in series with an improved accelerated creep component,considering disturbance damage,and combining it with the permeability-strain relationship.Comparison of fitted data showed R2 values all above 0.9,validating the model.

Abstract:Hydraulic fracturing(HF)is a key technology for stress relief in surrounding rock of coal mine roadways.Optimizing its parameters is crucial for achieving effective pressure relief and stress transfer in surrounding rock.Taking a fully-mechanized mining face in a specific mine as the engineering background,the stress evolution laws of the floor and coal pillar under HF was investigated using integrated physical similarity model tests and UDEC discrete element numerical simulation.The pressure relief mechanism of HF by weakening the pressure arch to regulate mining-induced stresses was revealed.Furthermore,the influences of the HF horizon height and the rock mass damage degree in the HF-affected zone on the pressure relief effect were analyzed.The results show that when the HF fracture propagation zone is located above the high-stress zone of the coal mass,the peak vertical stress in the high-stress area of floor and shallow coal mass decreases by 10.8%-12.1%,while that in the deep low-stress zone increases by only 1.1%.When HF fractures distribute along the high-stress transfer path of the pressure arch,the load-bearing capacity of the roof in this area is significantly weakened,promoting the transfer of high stress to deeper regions.This results in a characteristic distribution featuring significant pressure relief within a shallow limited zone and slight pressure increase across a large deep zone.This elucidates the pressure relief mechanism whereby HF regulates the stress transfer path by weakening the pressure arch structure.The pressure relief effect is closely related to the HF horizon height and the rock mass damage degree in the HF-affected zone.Increasing the vertical horizon extends the pressure relief range deeper and elevates the stress in the shallow coal mass.An increase in damage degree of rock mass within the HF-affected zone significantly enhances the pressure relief magnitude in the high-stress area,further inhibiting the ability of the damaged zone to transmit the high stress of the pressure arch,thereby promoting the transfer of high stress to deeper rock mass.Field implementation demonstrates that HF significantly reduces coal pillar stress and enhances surrounding rock stability.The research findings provide theoretical bases for optimizing HF parameters to weaken hard roofs,prevent rock bursts,and de-stress in roadways subjected to intense mining-induced stresses.

Abstract:To predict deformation and locate damaged areas of roadways,a numerical model for the surrounding rock in a roadway with multiple disturbances on the floor was established.A dataset of roof deformation of the bottom drainage roadway with different geological parameters,such as surrounding rock strength and lateral pressure coefficient,and mining parameters,such as roadway section,drainage borehole and support strength was obtained.Machine learning algorithms,such as random forest,extremely randomized trees,GBDT and XGBoost were used to establish single-based learner roadway deformation prediction models respectively.With the elastic net algorithm as the meta-learner and using the Stacking fusion method,the output models of different based learners were fused to construct a fusion prediction model for surrounding rock deformation of the bottom drainage roadway under multiple disturbances.The inhibiting or promoting effects of various characteristic factors on roadway deformation were evaluated,and the dominant controlling factors affecting the stability of the surrounding rock in the bottom drainage roadway were identified.The bottom drainage roadway of the transportation roadway No.14040 in Zhaogu No.2 Mine was chosen as the engineering background.Using the established roadway deformation prediction model,with the actual production geological conditions and mining parameters of the roadway as input,the recommended support strength for the roadway was determined through reverse calculation by setting the desired roadway deformation,which guided the on-site roadway support design and key parameter determination.After field implementation of the recommended support strength,the roadway deformaitn is controlled within the allowable deformation range as specified by the decision-making model.The roof deformation is only 52%of the original support,effectively controlling the large deformation of surrounding rock in roadways.The roadway deformation prediction model established based on machine learning provides a new approach for roadway stability maintenance,promoting the development of intelligent operation and maintenance technology for coal mine roadways.

Abstract:To evaluate the stability of the residual coal pillars-roof system in room and pillar mining goaf,a three-dimensional thin platemechanical model of elastic foundation for the system was established considering the difference in the interaction relationship between coal pillars and roof at different positions.The chain instability mechanism of this system was revealed from the three-dimensional spatial structure perspective,and the influence of coal pillar spalling under time effect was considered.An evaluation method for the chain instability of this system was established.The results show that the load borne by a single coal pillar at different positions and the remaining coal pillars stability and roof deflection response characteristics caused by its instability are different.The deflection of the four-side fixed roof is smaller than that of the four-side simply supported roof under the same coal pillars conditions.After the instability of a certain coal pillar,the load increase of the remaining coal pillars during the four-side fixed roof is greater than that of the four-side simply supported roof.The spalling of coal pillars over time leads to a gradual decrease in their effective bearing size and bearing capacity,indicating the signicance of considering the coal pillar spalling due to time effect.Simplifying the roof into a thin plate and applying the energy variational method can obtain its approximate bending solution,thereby optimizing the roof fracture criterion with smaller errors.The chain instability of coal pillars-roof system is a dynamic process of"overall stability-local instability-instability diffusion-overall instability".By integrating a modified single coal pillar instability criterion and an optimized roof fracture criterion,the developed dynamic evaluation method can effectively evaluate the chain stability of coal pillars-roof system.

Abstract:Filling the gob directly with gangue generated during underground mining can not only reduce the ground land occupation,but also effectively control the stability of the gob roof.However,under the influence of time effect,the gangue will weaken the support of the roof due to load-bearing deformation,and then lead to surface collapse.To investigate the particle size gradation characteristics of underground gangue and its load-bearing deformation rule,image information extraction technology was used to obtain the particle size gradation of gangue,and gangue samples consistent with the distribution of gangue gradation were allocated according to the principle of equal scaling.The load-bearing deformation law of gangue samples under the same loading time of 24 hours and different constant loading of 5,10,15 and 20 MPa was studied by using the load-bearing deformation test apparatus.The particle size distribution of the underground gob pile exhibits a trend where smaller-sized waste rock particles predominate in quantity,decreasing as size increases.In terms of mass,smaller particles contribute less,showing an initial increase and then a decrease as particle size increases.The compression process of the gob sample comprises two stages:loading and constant load.With the increase of the constant load,the proportion of deformation occurring during the loading stage shows an increasing trend.The constant load stage can be further subdivided into rapid deformation and slow deformation phases.For the same duration of constant load,samples subjected to lower constant load settings produce greater strain.During compressive deformation,the proportion of smaller-sized particles continuously increases while larger-sized particles decrease.Waste rock particles in the 10-15 mm size range are identified as the stable particle size.Under a specific constant load,the degree of damage to typical waste rock particles gradually decreases as their layer's distance from the load application surface increases.Similarly,the vertical compression of a gob layer diminishes with increasing distance from the load application surface.Furthermore,under different constant load settings,the vertical pressure borne by the gob sample consistently exhibits a gradual decreasing trend as the distance of the layer from the load application surface increases.The vertical load transfer attenuation effect within the gob sample is verified from three aspects:particle breakage,deformation,and stress distribution.