The mining height of a coal seam is a critical factor influencing the detachment,collapse,and formation of the collapse angle of the strata during strata movement.To clarify the mechanism by which mining height affect...The mining height of a coal seam is a critical factor influencing the detachment,collapse,and formation of the collapse angle of the strata during strata movement.To clarify the mechanism by which mining height affects strata movement characteristics,a physical model experiment was conducted based on the geological conditions of the Panel 122104 in Caojiatan Coal Mine in Shaanxi.The experiment examined strata movement at mining heights of 1 m and 10 m,identifying differences in detachment,collapse behavior,and collapse angles under these two conditions.The results indicate the following:Delamination range directly governs collapse patterns,with higher stress concentration accelerating delamination initiation and expanding affected zones.1 m mining height exhibits a“superposed fixed beam”structure with lower strength compared to the“fixed beam+cantilever beam”configuration under 10 m height.A model estimating collapse step shows 9.13%average error.Strata structure dictates collapse angle mechanisms:Pseudo-plastic deformation under 1 m height determines collapse angle through vertical tensile stress boundaries,whereas 10 m height exhibits brittle fracture behavior with collapse angles approximating fracture angles.Periodic collapse volume above working face directly correlates with mine pressure intensity and is positively correlated with the caving step distance,collapse angle,and caving range.These parameters show higher values under 10 m mining height,resulting in more pronounced mine pressure manifestations compared to 1 m conditions.展开更多
Rockburst represents a very dangerous phenomenon in deep underground mining in unfavourable conditions such as great depth, high horizontal stress, proximity of important tectonic structures, and unmined pillars. The ...Rockburst represents a very dangerous phenomenon in deep underground mining in unfavourable conditions such as great depth, high horizontal stress, proximity of important tectonic structures, and unmined pillars. The case study describes a recorded heavy rockburst in the Czech part of the Upper Silesian Coal Basin, which occurred during longwall mining near the protective pillar. The artificial dividing of geological blocks and creation of mining protective pillars(shaft pillars, crosscut pillars etc.) is a dangerous task in light of rockbursts occurring mainly due to overstressing of remaining pillars. A simple model of this situation is presented. Natural and mining conditions are analysed and presented in detail as well as registered seismicity during longwall mining in the area. Recorded rockbursts in the area of interest are described and their causes discussed. Many rockbursts near protective pillars were recorded in this mining region. Methodical instructions for rockburst prevention in proximity of protective pillars as well as for gates driving were devised based on the evaluation of rockburst causes. The paper presents these principles for prevention.展开更多
The evolution of mining-induced stress field in longwall panel is closely related to the fracture field and the breaking characteristics of strata.Few laboratory experiments have been conducted to investigate the stre...The evolution of mining-induced stress field in longwall panel is closely related to the fracture field and the breaking characteristics of strata.Few laboratory experiments have been conducted to investigate the stress field.This study investigated its evolution by constructing a large-scale physical model according to the in situ conditions of the longwall panel.Theoretical analysis was used to reveal the mechanism of stress distribution in the overburden.The modelling results showed that:(1)The major principal stress field is arch-shaped,and the strata overlying both the solid zones and gob constitute a series of coordinated load-bearing structures.The stress increasing zone is like a macro stress arch.High stress is especially concentrated on both shoulders of the arch-shaped structure.The stress concentration of the solid zone in front of the gob is higher than the rear solid zone.(2)The characteristics of the vertical stress field in different regions are significantly different.Stress decreases in the zone above the gob and increases in solid zones on both sides of it.The mechanical analysis show that for a given stratum,the trajectories of principal stress are arch-shaped or inverselyarched,referred to as the‘‘principal stress arch’’,irrespective of its initial breaking or periodic breaking,and determines the fracture morphology.That is,the trajectories of tensile principal stress are inversely arched before the first breaking of the strata,and cause the breaking lines to resemble an inverted funnel.In case of periodic breaking,the breaking line forms an obtuse angle with the advancing direction of the panel.Good agreement was obtained between the results of physical modeling and the theoretical analysis.展开更多
This study considered the role of coal as China’s basic energy source and examines the development of the coal industry.We focused on the intelligent development of coal mines,and introduced the“Chinese mode”of int...This study considered the role of coal as China’s basic energy source and examines the development of the coal industry.We focused on the intelligent development of coal mines,and introduced the“Chinese mode”of intelligent mining in underground coal mines,which uses complete sets of technical equipment to propose classifcation and grading standards.In view of the basic characteristics and technical requirements of intelligent coal mine systems,we established a digital logic model and propose an information entity and knowledge map construction method.This involves an active information push strategy based on a knowledge demand model and an intelligent portfolio modeling and distribution method for collaborative control of coal mines.The top-level architecture of 5G+intelligent coal mine systems combines intelligent applications such as autonomous intelligent mining,human–machine collaborative rapid tunneling,unmanned auxiliary transportation,closed-loop safety control,lean collaborative operation,and intelligent ecology.Progress in intelligent mining technology was described in terms of a dynamic modifed geological model,underground 5G network and positioning technology,intelligent control of the mining height and straightness of the longwall working face,and intelligent mining equipment.The development of intelligent coal mines was analyzed in terms of its imbalances,bottlenecks,and the compatibility of large-scale systems.Implementation ideas for promoting the development of intelligent coal mines were proposed,such as establishing construction standards and technical specifcations,implementing classifcation and grading standards according to mining policy,accelerating key technology research,and building a new management and control model.展开更多
In the Upper Silesian Coal Basin(USCB),coal seams are exploited under progressively more difficult geological and mining conditions(greater depth,higher horizontal stress,more frequent occurrence of competent rock lay...In the Upper Silesian Coal Basin(USCB),coal seams are exploited under progressively more difficult geological and mining conditions(greater depth,higher horizontal stress,more frequent occurrence of competent rock layers,etc.).Mining depth,dislocations and mining remnants in coal seams are the most important factors responsible for the occurrence of rockburst hazards.Longwall mining next to the mining edges of neighbouring coal seams is particularly disadvantageous.The levels of rockburst hazards are minimised via the use of rockburst prevention methods.One active prevention method is torpedo blasting in roof rocks.Torpedo blastings are performed in order to decrease local stress concentrations in rock masses and to fracture the roof rocks to prevent or minimise the impact of high-energy tremors on excavations.The estimation of the effectiveness of torpedo blasting is particularly important when mining is under difficult geological and mining conditions.Torpedo blasting is the main form of active rockburst prevention in the assigned colliery in the Polish part of the USCB.The effectiveness of blasting can be estimated using the seismic effect method,in which the seismic monitoring data and the mass of explosives are taken into consideration.The seismic effect method was developed in the Czech Republic and is always being used in collieries in the Czech part of the coal basin.Now,this method has been widely adopted for our selected colliery in the Polish part of the coal basin.The effectiveness of torpedo blastings in the faces and galleries of the assigned longwall in coal seam 506 has been estimated.The results show that the effectiveness of torpedo blastings for this longwall was significant in light of the seismic effect method,which corresponds to the in situ observations.The seismic effect method is regularly applied to estimating the blasting effectiveness in the selected colliery.展开更多
The four-track walking mining vehicle can better cope with the complex terrain of cobalt-rich crusts on the seabed.To explore the influence of different parameters on the obstacle-crossing ability of mining vehicles,t...The four-track walking mining vehicle can better cope with the complex terrain of cobalt-rich crusts on the seabed.To explore the influence of different parameters on the obstacle-crossing ability of mining vehicles,this paper took a certain type of mine vehicle as an example and establish a mechanical model of the mine vehicle.Through this model,the vehicle's traction coefficient variation could be analyzed during the obstacle-crossing process.It also reflected the relationship between the obstacle-crossing ability and the required traction coefficient.Many parameters were used for this analysis including the radius of the guide wheel radius,ground clearance of the driving wheel,the dip angle of the approaching angular and the position of centroid.The result showed that the ability to cross the obstacles requires adhesion coefficient as support.When the ratio between obstacle height and ground clearance of the guide wheel was greater than 0.7,the required adhesion coefficient increased sharply.The ability to cross obstacles will decrease,if the radius of the guide wheel increases,the height of the driving wheel increases or the dip angle of the approaching angular increases.It was most beneficial to cross the obstacle when-the ratio of the distance between the center of mass and the front driving wheel to the wheelbase is between 0.450.48.The results of this paper could provide reference for structural parameter design and performance research for mining vehicles.展开更多
The wide pillars are generally popular due to the high productivity and efficiency in Northwest China.The distribution of lateral abutment pressure in coal pillars is important for mining safety.To reveal the effect o...The wide pillars are generally popular due to the high productivity and efficiency in Northwest China.The distribution of lateral abutment pressure in coal pillars is important for mining safety.To reveal the effect of the first mining on the lateral abutment pressure distribution and evolution in wide pillars,an in-situ experiment,theoretical analysis and numerical simulation were performed.First,the field monitoring of lateral abutment pressure was conducted from the perspective of time and space in the Chahasu Coal Mine,Huangling No.2 Coal Mine and Lingdong Coal Mine during the first mining.Based on the field monitoring stress,a theoretical model was proposed to reveal the lateral abutment pressure distribution.The methodology was demonstrated through a case study.Aiming at the distribution mechanism,a numerical experiment was conducted through the finite-discrete element method(FDEM).Last,field observations of borehole fractures were performed to further study the damage distribution.In addition,two types of lateral abutment pressure evolution with mining advance were discussed.Suggestions on the stress monitoring layout were proposed as well.The results could provide foundations for strata control and disaster prevention in wide pillars in underground coal mines.展开更多
The complex stress environment in deep roadways,often exacerbated by thick and hard strata,frequently precipitates coal bursts,posing significant safety hazards.This paper investigates the mechanisms and preventive me...The complex stress environment in deep roadways,often exacerbated by thick and hard strata,frequently precipitates coal bursts,posing significant safety hazards.This paper investigates the mechanisms and preventive methods for coal bursts in the gob-side roadway floor(GSRF)under thick and hard roof in the Ordos region,China.First,the stress-distributing characters of GSRF were analyzed then a stress calculation formula was derived.A mechanical model was developed to determine the critical stress for buckling failure of the roadway floor strata.Criteria for the bursting instability of GSRF were then established.The lateral static load from the adjacent gob,the advancing static load from the working face,and the disturbance load from overlying thick and hard roof fractures combine to transmit high loads and energy to the roadway floor via the“roof→rib→floor”pathway,causing increased stress concentration and energy accumulation.When the conditions satisfy the criteria for bursting instability,coal bursts can occur on the roadway floor.To mitigate dynamic load disturbances,the paper proposes roof regional fracturing and abrasive water jet axial roof cutting.Hydraulic reaming of gutters in the roadway ribs and deep hole blasting at the roadway bottom corners are offered to alleviate the static loads on the surrounding rock.The implementation of targeted prevention measures for dynamic and static loads effectively reduces coal bursts in GSRF.These findings offer an example of preventing and controlling coal bursts in other mines of the Ordos region with comparable geological conditions.展开更多
Aiming at mitigating the high risks associated with conventional explosive blasting,this study developed a safe directional fracturing technique,i.e.instantaneous expansion with a single fracture(IESF),using a coal-ba...Aiming at mitigating the high risks associated with conventional explosive blasting,this study developed a safe directional fracturing technique,i.e.instantaneous expansion with a single fracture(IESF),using a coal-based solid waste expanding agent.First,the mechanism of directional fracturing blasting by the IESF was analyzed,and the criterion of directional crack initiation was established.On this basis,laboratory experiments and numerical simulations were conducted to systematically evaluate the directional fracturing blasting performance of the IESF.The results indicate that the IESF presents an excellent directional fracturing effect,with average surface undulation differences ranging from 8.1 mm to 22.7 mm on the fracture surfaces.Moreover,during concrete fracturing tests,the stresses and strains in the fracturing direction are measured to be 2.16-3.71 times and 8 times larger than those in the nonfracturing direction,respectively.Finally,the IESF technique was implemented for no-pillar mining with gob-side entry retaining through roof cutting and pressure relief in an underground coal mine.The IESF technique effectively created directional cracks in the roof without causing severe roadway deformation,achieving an average cutting rate and maximum roadway deformation of 94%and 197 mm,respectively.These on-site test results verified its excellent directional rock fracturing performance.The IESF technique,which is safe,efficient,and green,has considerable application prospects in the field of rock mechanics and engineering.展开更多
The influence of rockbolt pretension on bolting has not been well addressed,despite its critical importance in drift support systems.In this study,laboratory and numerical simulations of gravel bolting are conducted t...The influence of rockbolt pretension on bolting has not been well addressed,despite its critical importance in drift support systems.In this study,laboratory and numerical simulations of gravel bolting are conducted to investigate the effects of varying rockbolt pretensions.The simulations are developed using the particle flow code(PFC3D),enabling detailed analysis of contact forces between gravel particles under low and high rockbolt pretensions.The results indicate that bolted gravel can maintain stability even without pretension,though bearing capacity is significantly enhanced under high pretension.Two distinct bolting behaviors are identified:a pressure arch structure is formed under low pretension,while high pretension creates a compression zone characterized by intensified particle interlocking and superior load-bearing capacity.Based on these findings,a concept for drift support is proposed,integrating rockbolts and cables to stabilize both shallow and deep rocks.This study advances our understanding of bolting behaviors and provides theoretical guidance for designing effective drift support systems in practical applications.展开更多
Coal and rock dynamic disasters are always major hidden dangers threatening mine safety production.Many researchers use cement concrete material as filling and energy-absorption materials.However,the current material ...Coal and rock dynamic disasters are always major hidden dangers threatening mine safety production.Many researchers use cement concrete material as filling and energy-absorption materials.However,the current material toughness is not sufficient to meet the requirements of mine disaster prevention.Based on this,in order to find the optimal-ratio material that combines strength and toughness,the synergistic mechanism of lithium slag(LS),ethylene-vinyl acetate(EVA)copolymer,and polyvinyl alcohol(PVA)fiber mixtures in improving the mechanical properties of cement concrete,as well as the mechanism of microscopic phase evolution,was analyzed through macroscopic experiments,mesoscopic characterization,microscopic analysis,theoretical calculations,and comprehensive evaluation.The stress-strain curves obtained from the uniaxial compressive strength tests of specimens with different admixtures and fibers were investigated,and the characteristics of different stages were analyzed.The mechanical properties of different admixtures and fiber-reinforced materials,including their advantages and disadvantages,were compared through weighted comprehensive evaluation.The entire process of material failure,ranging from pore compaction,crack initiation,crack propagation,specimen instability to crack penetration,was explained via macroscopic fracture morphology,and the mechanical mechanism of how different admixtures affect the mechanical properties of concrete materials was revealed.The microscopic mechanism and the phase-evolution process of how the admixture affects concrete properties were elucidated using X-ray diffraction(XRD),hydration reaction theory,and Fourier transform infrared spectroscopy(FTIR).Furthermore,scanning electron microscopy-energy dispersive spectroscopy(SEM-EDS)was used to reveal the interfacial pore state and element distribution of the internal microstructure of concrete.The results show that PVA fiber bars can play the role of a“skeleton bridge”to improve the toughness of materials.LS can effectively promote the hydration process and cooperate with PVA fiber bars to enhance the mechanical properties of the material.EVA will inhibit the hydration reaction and degrade the material’s mechanical properties through the“organic isolation”effect.In addition,the on-site application has proven that the R3-group materials in this study can effectively inhibit the deformation of the roadway and possess strong reliability.Finally,the advantages and feasibility of LS-and-fiber-reinforced concrete were discussed from four perspectives:environmental protection,economy,disaster prevention,and development.This paper is expected to provide technical reference for the large-scale disposal of solid waste LS,the performance-optimization direction of concrete materials,and the prevention and control of coal and rock dynamic disasters.展开更多
In this study,a coupled loading method combining three-dimensional static loading with graded cyclic impacts was developed to simulate the stress environment of the surrounding rock under impact ground pressure caused...In this study,a coupled loading method combining three-dimensional static loading with graded cyclic impacts was developed to simulate the stress environment of the surrounding rock under impact ground pressure caused by cyclic disturbances.The mechanical behavior and energy dissipation of coal under this loading method were studied using a split Hopkinson pressure bar(SHPB).The results showed that the pre-applied cyclic low-pressure impacts deteriorated the coal sample's resistance to external loads.Under both cyclic low-pressure impacts and single high-pressure impacts,the dynamic peak stress and secant modulus decreased with increasing impact cycles,exhibiting dynamic fatigue characteristics.The dynamic secant modulus of the sample decreased by 4.14%-6.67%after each impact.The dissipated energy for coal fragmentation samples increased with the number of impacts,averaging 28%under cyclic low-pressure impacts and 29%under single high-pressure impacts.The efficiency of dissipated energy for coal fragmentation initially increased and then decreased as the wave impedance ratio between the coal sample and the bar increased,reaching a maximum of 43.3%when the ratio was 0.06.Based on the defined damage variable,the damage to coal samples from high-pressure impacts was found to be 12 times greater than that under low-pressure conditions.The degree of coal fragmentation was positively correlated with the maximum damage increment.With increasing maximum damage increment,the failure mode of the coal sample evolved from tensile failure to tensile-compressive-shear composite failure.展开更多
The geostress and rock blasting in underground engineering may greatly affect the stress thresholds of surrounding rock.In this study,pre-damage impact tests were first conducted on granite under varying confining pre...The geostress and rock blasting in underground engineering may greatly affect the stress thresholds of surrounding rock.In this study,pre-damage impact tests were first conducted on granite under varying confining pressures(5,10 and 15 MPa)and numbers of impacts(1,5,10 and 15 impacts).Then,uniaxial compression tests were undertaken on the pre-damaged granite to study the evolution of stress thresholds using the crack volume strain method and acoustic emission method.The crack damage stresses determined by the two methods were compared.Additionally,based on the rise time amplitude and average frequency,the evolution law of microcracks inside rock specimens was revealed,and an improved acoustic emission method was proposed.The results indicated that as the number of impacts increased,the crack closure stress,crack damage stress,and peak stress of granite specimens initially rose and then declined,while they continuously increased with the confining pressure.The proportion of shear cracks first declined and then rose with greater number of impacts and decreased with higher confining pressure,and that of tensile cracks showed the opposite trend.The improved acoustic emission method was more accurate in identifying the crack damage stress.展开更多
Coal bursts pose significant safety and operational challenges in deep mining environments,necessitating effective mitigation strategies to address high-stress concentrations and dynamic failure risks.This study evalu...Coal bursts pose significant safety and operational challenges in deep mining environments,necessitating effective mitigation strategies to address high-stress concentrations and dynamic failure risks.This study evaluated the efficacy of hydraulic fracturing as a preconditioning tool at a longwall face of the Mengcun coal mine with strong coal bursts,Shaanxi Province.The program involved the systematic creation of a fracture network through high-pressure fluid injection,monitored via microseismic arrays,stress measurements,and hydrological sensors.Results demonstrated that hydraulic fracturing effectively redistributed in-situ stresses,reducing high-stress concentrations by up to 30%,lowering the frequency of high-energy microseismic events,and enhancing the stability of fractured zones.However,the presence of unfractured blind spots and interactions with pre-existing faults highlighted the need for optimized well placement and adaptive fracturing designs.These findings underscore the potential of hydraulic fracturing as a critical preconditioning tool in high-stress mining operations,which could provide a framework for improving safety and efficiency in similar geological and operational settings.展开更多
The effect of vanadium(V)element on the microstructure and mechanical properties of anchor steel was explored by microstructural characterization and mechanical property tests of anchor steels with different V content...The effect of vanadium(V)element on the microstructure and mechanical properties of anchor steel was explored by microstructural characterization and mechanical property tests of anchor steels with different V contents.The results indicated that the trace addition of V element can generate dispersed VC nanoparticles in the anchor steel and then refine microstructure by inhibiting austenite grain growth.The increase in V content leads to the formation of a larger amount of smaller VC nanoparticles and more refined microstructure.Moreover,the increasing V content in anchor steel causes the volume fraction of ferrite to increase and that of pearlite to decrease continuously,and even leads to the formation of bainite.Accompanied by the microstructure change,the V-treated anchor steels exhibit higher strength compared with the anchor steel without V addition.However,the increased hardness difference between ferrite and pearlite results in poor coordination of deformation between them,leading to a decrease in their plasticity.The impact toughness of anchor steel first increases but then significantly decreases with the increase in V content.The improvement in impact toughness of trace V-treated anchor steel benefits from the enhancement in the band structure after hot rolling,which consumes more energy during the vertical crack propagation process.However,when the V content further increases,the hard and brittle bainite in the anchor steel can facilitate crack initiation and propagation,ultimately resulting in a reduced toughness.展开更多
Multiphase flow in porous rock is of great importance in the application of many industrial processes,including reservoir delineation,enhanced oil recovery,and CO_(2) sequestration.However,previous research typically ...Multiphase flow in porous rock is of great importance in the application of many industrial processes,including reservoir delineation,enhanced oil recovery,and CO_(2) sequestration.However,previous research typically investigated the dispersive behaviors when rock saturated with single or two-phase fluids and conducted limited studies on three-phase immiscible fluids.This study investigated the seismic dispersion,attenuation,and reflection features of seismic waves in three-phase immiscible fluidsaturated porous rocks.First,we proposed the calculation formulas of effective fluid modulus and effective fluid viscosity of multiphase immiscible fluids by taking into account the capillary pressure,reservoir wettability,and relative permeability simultaneously.Then,we analysed the frequencydependent behaviors of three-phase immiscible fluid-saturated porous rock under different fluid proportion cases using the Chapman multi-scale model.Next,the seismic responses are analysed using a four-layer model.The results indicate that the relative permeability,capillary pressure parameter,and fluid proportions are all significantly affect dispersion and attenuation.Comparative analyses demonstrate that dispersion and attenuation can be observed within the frequency range of seismic exploration for a lower capillary parameter a3 and higher oil content.Seismic responses reveal that the reflection features,such as travel time,seismic amplitude,and waveform of the bottom reflections of saturated rock and their underlying reflections are significantly dependent on fluid proportions and capillary parameters.For validation,the numerical results are further verified using the log data and real seismic data.This numerical analysis helps to further understand the wave propagation characteristics for a porous rock saturated with multiphase immiscible fluids.展开更多
The Grey Wolf Optimization(GWO)algorithm is acknowledged as an effective method for rock acoustic emission localization.However,the conventional GWO algorithm encounters challenges related to solution accuracy and con...The Grey Wolf Optimization(GWO)algorithm is acknowledged as an effective method for rock acoustic emission localization.However,the conventional GWO algorithm encounters challenges related to solution accuracy and convergence speed.To address these concerns,this paper develops a Simplex Improved Grey Wolf Optimizer(SMIGWO)algorithm.The randomly generating initial populations are replaced with the iterative chaotic sequences.The search process is optimized using the convergence factor optimization algorithm based on the inverse incompleteГfunction.The simplex method is utilized to address issues related to poorly positioned grey wolves.Experimental results demonstrate that,compared to the conventional GWO algorithm-based AE localization algorithm,the proposed algorithm achieves a higher solution accuracy and showcases a shorter search time.Additionally,the algorithm demonstrates fewer convergence steps,indicating superior convergence efficiency.These findings highlight that the proposed SMIGWO algorithm offers enhanced solution accuracy,stability,and optimization performance.The benefits of the SMIGWO algorithm extend universally across various materials,such as aluminum,granite,and sandstone,showcasing consistent effectiveness irrespective of material type.Consequently,this algorithm emerges as a highly effective tool for identifying acoustic emission signals and improving the precision of rock acoustic emission localization.展开更多
Coal wall stability is a critical factor influencing coal mining efficiency and threatens the safety of working faces,where irregular coal wall surfaces significantly affect the contact and support effectiveness of th...Coal wall stability is a critical factor influencing coal mining efficiency and threatens the safety of working faces,where irregular coal wall surfaces significantly affect the contact and support effectiveness of the support plate,thereby impacting stability.Through a combination of theoretical analysis,mechanical testing,and numerical simulations,this study establishes a mechanical model of irregular coal wall surfaces to investigate the effects of the undulation period and undulation height on coal wall failure characteristics.This research reveals the mechanical response mechanisms of irregular coal wall surfaces and proposes an innovative method to enhance coal wall stability by improving the supporting cushion material of the support plate,which was validated through numerical simulations.The results show that the undulation height and undulation period significantly influence the macroscopic mechanical parameters of the samples,with the undulation height exerting a more pronounced effect.The strength of the samples with undulating surfaces is approximately 50%-60% that of the samples with flat surfaces.The failure mode under uniaxial compression is predominantly tensile,resulting in long and slender block fragments with a characteristic“Ⅲ”-shaped tensile fracture pattern.During the loading process,samples with undu-lating surfaces dissipate energy at all stages,with a greater proportion of energy dissipation occurring during the early loading stage because of structural damage and the formation of internal cracks.The surface compressive and tensile stresses are correlated with the curvature radius of the convex surface and the elastic modulus of the supporting plate.Reducing the elastic modulus of the supporting plate material can effectively alleviate the stress concentration at convex locations and increase the peak strength.This study provides theoretical foundations and technical references for the prevention and control of coal wall spalling in deep thick coal seam mining.展开更多
This paper reviews the major achievements in terms of mechanical behaviors of coal measures,mining stress distribution characteristics and ground control in China’s deep underground coal mining.The three main aspects...This paper reviews the major achievements in terms of mechanical behaviors of coal measures,mining stress distribution characteristics and ground control in China’s deep underground coal mining.The three main aspects of this review are coal measure mechanics,mining disturbance mechanics,and rock support mechanics.Previous studies related to these three topics are reviewed,including the geo-mechanical properties of coal measures,distribution and evolution characteristics of mining-induced stresses,evolution characteristics of mining-induced structures,and principles and technologies of ground control in both deep roadways and longwall faces.A discussion is made to explain the structural and mechanical properties of coal measures in China’s deep coal mining practices,the types and dis-tribution characteristics of in situ stresses in underground coal mines,and the distribution of mining-induced stress that forms under different geological and engineering conditions.The theory of pre-tensioned rock bolting has been proved to be suitable for ground control of deep underground coal roadways.The use of combined ground control technology(e.g.ground support,rock mass modification,and destressing)has been demonstrated to be an effective measure for rock control of deep roadways.The developed hydraulic shields for 1000 m deep ultra-long working face can effectively improve the stability of surrounding rocks and mining efficiency in the longwall face.The ground control challenges in deep underground coal mines in China are discussed,and further research is recommended in terms of theory and technology for ground control in deep roadways and longwall faces.展开更多
To evaluate the coal burst proneness more precisely,a new energy criterion namely the residual elastic energy index was proposed.This study begins by performing the single-cyclic loading-unloading uniaxial compression...To evaluate the coal burst proneness more precisely,a new energy criterion namely the residual elastic energy index was proposed.This study begins by performing the single-cyclic loading-unloading uniaxial compression tests with five pre-peak unloading stress levels to explore the energy storage characteristics of coal.Five types of coals from different mines were tested,and the instantaneous destruction process of the coal specimens under compression loading was recorded using a high speed camera.The results showed a linear relationship between the elastic strain energy density and input energy density,which confirms the linear energy storage law of coal.Based on this linear energy storage law,the peak elastic strain energy density of each coal specimen was obtained precisely.Subsequently,a new energy criterion of coal burst proneness was established,which was called the residual elastic energy index(defined as the difference between the peak elastic strain energy density and post peak failure energy density).Considering the destruction process and actual failure characteristics of coal specimens,the accuracy of evaluating coal burst proneness based on the residual elastic energy index was examined.The results indicated that the residual elastic energy index enables reliable and precise evaluations of the coal burst proneness.展开更多
文摘The mining height of a coal seam is a critical factor influencing the detachment,collapse,and formation of the collapse angle of the strata during strata movement.To clarify the mechanism by which mining height affects strata movement characteristics,a physical model experiment was conducted based on the geological conditions of the Panel 122104 in Caojiatan Coal Mine in Shaanxi.The experiment examined strata movement at mining heights of 1 m and 10 m,identifying differences in detachment,collapse behavior,and collapse angles under these two conditions.The results indicate the following:Delamination range directly governs collapse patterns,with higher stress concentration accelerating delamination initiation and expanding affected zones.1 m mining height exhibits a“superposed fixed beam”structure with lower strength compared to the“fixed beam+cantilever beam”configuration under 10 m height.A model estimating collapse step shows 9.13%average error.Strata structure dictates collapse angle mechanisms:Pseudo-plastic deformation under 1 m height determines collapse angle through vertical tensile stress boundaries,whereas 10 m height exhibits brittle fracture behavior with collapse angles approximating fracture angles.Periodic collapse volume above working face directly correlates with mine pressure intensity and is positively correlated with the caving step distance,collapse angle,and caving range.These parameters show higher values under 10 m mining height,resulting in more pronounced mine pressure manifestations compared to 1 m conditions.
基金the project of the Institute of Clean Technologies for Mining and Utilisation of Raw Materials for Energy Use–Sustainability Programme of Czech Republic (No.LO1406)supported by a project for the long-term conceptual development of research organisations (No.RVO:68145535)
文摘Rockburst represents a very dangerous phenomenon in deep underground mining in unfavourable conditions such as great depth, high horizontal stress, proximity of important tectonic structures, and unmined pillars. The case study describes a recorded heavy rockburst in the Czech part of the Upper Silesian Coal Basin, which occurred during longwall mining near the protective pillar. The artificial dividing of geological blocks and creation of mining protective pillars(shaft pillars, crosscut pillars etc.) is a dangerous task in light of rockbursts occurring mainly due to overstressing of remaining pillars. A simple model of this situation is presented. Natural and mining conditions are analysed and presented in detail as well as registered seismicity during longwall mining in the area. Recorded rockbursts in the area of interest are described and their causes discussed. Many rockbursts near protective pillars were recorded in this mining region. Methodical instructions for rockburst prevention in proximity of protective pillars as well as for gates driving were devised based on the evaluation of rockburst causes. The paper presents these principles for prevention.
基金This work was supported by the National Natural Science Foundation of China(NSFC,Grant No.51874175)the China Coal Technology&Engineering Group Foundation(Grant Nos.2018RC001,KJ-2018-TDKCZL-02).Comments from two anonymous reviewers and the editor are also greatly appreciated.
文摘The evolution of mining-induced stress field in longwall panel is closely related to the fracture field and the breaking characteristics of strata.Few laboratory experiments have been conducted to investigate the stress field.This study investigated its evolution by constructing a large-scale physical model according to the in situ conditions of the longwall panel.Theoretical analysis was used to reveal the mechanism of stress distribution in the overburden.The modelling results showed that:(1)The major principal stress field is arch-shaped,and the strata overlying both the solid zones and gob constitute a series of coordinated load-bearing structures.The stress increasing zone is like a macro stress arch.High stress is especially concentrated on both shoulders of the arch-shaped structure.The stress concentration of the solid zone in front of the gob is higher than the rear solid zone.(2)The characteristics of the vertical stress field in different regions are significantly different.Stress decreases in the zone above the gob and increases in solid zones on both sides of it.The mechanical analysis show that for a given stratum,the trajectories of principal stress are arch-shaped or inverselyarched,referred to as the‘‘principal stress arch’’,irrespective of its initial breaking or periodic breaking,and determines the fracture morphology.That is,the trajectories of tensile principal stress are inversely arched before the first breaking of the strata,and cause the breaking lines to resemble an inverted funnel.In case of periodic breaking,the breaking line forms an obtuse angle with the advancing direction of the panel.Good agreement was obtained between the results of physical modeling and the theoretical analysis.
基金supported by the National Natural Science Foundation of China(Grant Numbers 51834006 and 51874174).
文摘This study considered the role of coal as China’s basic energy source and examines the development of the coal industry.We focused on the intelligent development of coal mines,and introduced the“Chinese mode”of intelligent mining in underground coal mines,which uses complete sets of technical equipment to propose classifcation and grading standards.In view of the basic characteristics and technical requirements of intelligent coal mine systems,we established a digital logic model and propose an information entity and knowledge map construction method.This involves an active information push strategy based on a knowledge demand model and an intelligent portfolio modeling and distribution method for collaborative control of coal mines.The top-level architecture of 5G+intelligent coal mine systems combines intelligent applications such as autonomous intelligent mining,human–machine collaborative rapid tunneling,unmanned auxiliary transportation,closed-loop safety control,lean collaborative operation,and intelligent ecology.Progress in intelligent mining technology was described in terms of a dynamic modifed geological model,underground 5G network and positioning technology,intelligent control of the mining height and straightness of the longwall working face,and intelligent mining equipment.The development of intelligent coal mines was analyzed in terms of its imbalances,bottlenecks,and the compatibility of large-scale systems.Implementation ideas for promoting the development of intelligent coal mines were proposed,such as establishing construction standards and technical specifcations,implementing classifcation and grading standards according to mining policy,accelerating key technology research,and building a new management and control model.
文摘In the Upper Silesian Coal Basin(USCB),coal seams are exploited under progressively more difficult geological and mining conditions(greater depth,higher horizontal stress,more frequent occurrence of competent rock layers,etc.).Mining depth,dislocations and mining remnants in coal seams are the most important factors responsible for the occurrence of rockburst hazards.Longwall mining next to the mining edges of neighbouring coal seams is particularly disadvantageous.The levels of rockburst hazards are minimised via the use of rockburst prevention methods.One active prevention method is torpedo blasting in roof rocks.Torpedo blastings are performed in order to decrease local stress concentrations in rock masses and to fracture the roof rocks to prevent or minimise the impact of high-energy tremors on excavations.The estimation of the effectiveness of torpedo blasting is particularly important when mining is under difficult geological and mining conditions.Torpedo blasting is the main form of active rockburst prevention in the assigned colliery in the Polish part of the USCB.The effectiveness of blasting can be estimated using the seismic effect method,in which the seismic monitoring data and the mass of explosives are taken into consideration.The seismic effect method was developed in the Czech Republic and is always being used in collieries in the Czech part of the coal basin.Now,this method has been widely adopted for our selected colliery in the Polish part of the coal basin.The effectiveness of torpedo blastings in the faces and galleries of the assigned longwall in coal seam 506 has been estimated.The results show that the effectiveness of torpedo blastings for this longwall was significant in light of the seismic effect method,which corresponds to the in situ observations.The seismic effect method is regularly applied to estimating the blasting effectiveness in the selected colliery.
基金Supported by National Ocean Key Special Funds in 12th Five-Year Plan of China (Grant No.DY125-11-T-01)National Natural Science Foundation of China (Grant No.52074294)。
文摘The four-track walking mining vehicle can better cope with the complex terrain of cobalt-rich crusts on the seabed.To explore the influence of different parameters on the obstacle-crossing ability of mining vehicles,this paper took a certain type of mine vehicle as an example and establish a mechanical model of the mine vehicle.Through this model,the vehicle's traction coefficient variation could be analyzed during the obstacle-crossing process.It also reflected the relationship between the obstacle-crossing ability and the required traction coefficient.Many parameters were used for this analysis including the radius of the guide wheel radius,ground clearance of the driving wheel,the dip angle of the approaching angular and the position of centroid.The result showed that the ability to cross the obstacles requires adhesion coefficient as support.When the ratio between obstacle height and ground clearance of the guide wheel was greater than 0.7,the required adhesion coefficient increased sharply.The ability to cross obstacles will decrease,if the radius of the guide wheel increases,the height of the driving wheel increases or the dip angle of the approaching angular increases.It was most beneficial to cross the obstacle when-the ratio of the distance between the center of mass and the front driving wheel to the wheelbase is between 0.450.48.The results of this paper could provide reference for structural parameter design and performance research for mining vehicles.
基金We gratefully acknowledge financial support from the National Natural Science Foundation of China(NSFC)(No.51704097)Science Foundation of Henan Polytechnic University(No.J2021–2)+1 种基金Key Research and Development Program of Henan Province,China(No.202102310244)“Science and Technology to Help the Economy 2020”Key Project(No.SQ2020YFF0426364).
文摘The wide pillars are generally popular due to the high productivity and efficiency in Northwest China.The distribution of lateral abutment pressure in coal pillars is important for mining safety.To reveal the effect of the first mining on the lateral abutment pressure distribution and evolution in wide pillars,an in-situ experiment,theoretical analysis and numerical simulation were performed.First,the field monitoring of lateral abutment pressure was conducted from the perspective of time and space in the Chahasu Coal Mine,Huangling No.2 Coal Mine and Lingdong Coal Mine during the first mining.Based on the field monitoring stress,a theoretical model was proposed to reveal the lateral abutment pressure distribution.The methodology was demonstrated through a case study.Aiming at the distribution mechanism,a numerical experiment was conducted through the finite-discrete element method(FDEM).Last,field observations of borehole fractures were performed to further study the damage distribution.In addition,two types of lateral abutment pressure evolution with mining advance were discussed.Suggestions on the stress monitoring layout were proposed as well.The results could provide foundations for strata control and disaster prevention in wide pillars in underground coal mines.
基金financially supported by the National Key Research and Development Program of China(2022YFC3004604)National Natural Science Foundation of China(U23B2093).
文摘The complex stress environment in deep roadways,often exacerbated by thick and hard strata,frequently precipitates coal bursts,posing significant safety hazards.This paper investigates the mechanisms and preventive methods for coal bursts in the gob-side roadway floor(GSRF)under thick and hard roof in the Ordos region,China.First,the stress-distributing characters of GSRF were analyzed then a stress calculation formula was derived.A mechanical model was developed to determine the critical stress for buckling failure of the roadway floor strata.Criteria for the bursting instability of GSRF were then established.The lateral static load from the adjacent gob,the advancing static load from the working face,and the disturbance load from overlying thick and hard roof fractures combine to transmit high loads and energy to the roadway floor via the“roof→rib→floor”pathway,causing increased stress concentration and energy accumulation.When the conditions satisfy the criteria for bursting instability,coal bursts can occur on the roadway floor.To mitigate dynamic load disturbances,the paper proposes roof regional fracturing and abrasive water jet axial roof cutting.Hydraulic reaming of gutters in the roadway ribs and deep hole blasting at the roadway bottom corners are offered to alleviate the static loads on the surrounding rock.The implementation of targeted prevention measures for dynamic and static loads effectively reduces coal bursts in GSRF.These findings offer an example of preventing and controlling coal bursts in other mines of the Ordos region with comparable geological conditions.
基金supported by the National Natural Science Foundation of China(Grant No.52404155)State Key Laboratory of Mining Disaster Prevention and Control(Shandong University of Science and Technology)+1 种基金Ministry of Education(Grant No.JMDPC202402)supported by the opening project of State Key Laboratory of Explosion Science and Safety Protection(Beijing Institute of Technology).The opening project number is KFJJ24-20M.
文摘Aiming at mitigating the high risks associated with conventional explosive blasting,this study developed a safe directional fracturing technique,i.e.instantaneous expansion with a single fracture(IESF),using a coal-based solid waste expanding agent.First,the mechanism of directional fracturing blasting by the IESF was analyzed,and the criterion of directional crack initiation was established.On this basis,laboratory experiments and numerical simulations were conducted to systematically evaluate the directional fracturing blasting performance of the IESF.The results indicate that the IESF presents an excellent directional fracturing effect,with average surface undulation differences ranging from 8.1 mm to 22.7 mm on the fracture surfaces.Moreover,during concrete fracturing tests,the stresses and strains in the fracturing direction are measured to be 2.16-3.71 times and 8 times larger than those in the nonfracturing direction,respectively.Finally,the IESF technique was implemented for no-pillar mining with gob-side entry retaining through roof cutting and pressure relief in an underground coal mine.The IESF technique effectively created directional cracks in the roof without causing severe roadway deformation,achieving an average cutting rate and maximum roadway deformation of 94%and 197 mm,respectively.These on-site test results verified its excellent directional rock fracturing performance.The IESF technique,which is safe,efficient,and green,has considerable application prospects in the field of rock mechanics and engineering.
基金supported by the National Natural Science Foundation of China(Grant Nos.52274124,52274123)funding of the Coal Mining and Designing Department,Tiandi Science&Technology Co.,Ltd.(Grant No.2022-2-TD-QN008).
文摘The influence of rockbolt pretension on bolting has not been well addressed,despite its critical importance in drift support systems.In this study,laboratory and numerical simulations of gravel bolting are conducted to investigate the effects of varying rockbolt pretensions.The simulations are developed using the particle flow code(PFC3D),enabling detailed analysis of contact forces between gravel particles under low and high rockbolt pretensions.The results indicate that bolted gravel can maintain stability even without pretension,though bearing capacity is significantly enhanced under high pretension.Two distinct bolting behaviors are identified:a pressure arch structure is formed under low pretension,while high pretension creates a compression zone characterized by intensified particle interlocking and superior load-bearing capacity.Based on these findings,a concept for drift support is proposed,integrating rockbolts and cables to stabilize both shallow and deep rocks.This study advances our understanding of bolting behaviors and provides theoretical guidance for designing effective drift support systems in practical applications.
基金supported by the National Natural Science Foundation of China(Nos.U23B2093 and 52034009)the National Key R&D Program of China(No.2024YFC3013801)the Fundamental Research Funds for the Central Universities(Ph.D.Top Innovative Talents Fund of CUMTB)(No.BBJ2025001).
文摘Coal and rock dynamic disasters are always major hidden dangers threatening mine safety production.Many researchers use cement concrete material as filling and energy-absorption materials.However,the current material toughness is not sufficient to meet the requirements of mine disaster prevention.Based on this,in order to find the optimal-ratio material that combines strength and toughness,the synergistic mechanism of lithium slag(LS),ethylene-vinyl acetate(EVA)copolymer,and polyvinyl alcohol(PVA)fiber mixtures in improving the mechanical properties of cement concrete,as well as the mechanism of microscopic phase evolution,was analyzed through macroscopic experiments,mesoscopic characterization,microscopic analysis,theoretical calculations,and comprehensive evaluation.The stress-strain curves obtained from the uniaxial compressive strength tests of specimens with different admixtures and fibers were investigated,and the characteristics of different stages were analyzed.The mechanical properties of different admixtures and fiber-reinforced materials,including their advantages and disadvantages,were compared through weighted comprehensive evaluation.The entire process of material failure,ranging from pore compaction,crack initiation,crack propagation,specimen instability to crack penetration,was explained via macroscopic fracture morphology,and the mechanical mechanism of how different admixtures affect the mechanical properties of concrete materials was revealed.The microscopic mechanism and the phase-evolution process of how the admixture affects concrete properties were elucidated using X-ray diffraction(XRD),hydration reaction theory,and Fourier transform infrared spectroscopy(FTIR).Furthermore,scanning electron microscopy-energy dispersive spectroscopy(SEM-EDS)was used to reveal the interfacial pore state and element distribution of the internal microstructure of concrete.The results show that PVA fiber bars can play the role of a“skeleton bridge”to improve the toughness of materials.LS can effectively promote the hydration process and cooperate with PVA fiber bars to enhance the mechanical properties of the material.EVA will inhibit the hydration reaction and degrade the material’s mechanical properties through the“organic isolation”effect.In addition,the on-site application has proven that the R3-group materials in this study can effectively inhibit the deformation of the roadway and possess strong reliability.Finally,the advantages and feasibility of LS-and-fiber-reinforced concrete were discussed from four perspectives:environmental protection,economy,disaster prevention,and development.This paper is expected to provide technical reference for the large-scale disposal of solid waste LS,the performance-optimization direction of concrete materials,and the prevention and control of coal and rock dynamic disasters.
基金supported by the Youth Fund of the CCTEG Coal Mining Research Institute(Grant No.KCYJY-2023-QN-01)the National Natural Science Foundation of China(Grant No.52174080)the Science Foundation of Tiandi Technology Co.,Ltd.(Grant No.2022-2-TD-ZD016).
文摘In this study,a coupled loading method combining three-dimensional static loading with graded cyclic impacts was developed to simulate the stress environment of the surrounding rock under impact ground pressure caused by cyclic disturbances.The mechanical behavior and energy dissipation of coal under this loading method were studied using a split Hopkinson pressure bar(SHPB).The results showed that the pre-applied cyclic low-pressure impacts deteriorated the coal sample's resistance to external loads.Under both cyclic low-pressure impacts and single high-pressure impacts,the dynamic peak stress and secant modulus decreased with increasing impact cycles,exhibiting dynamic fatigue characteristics.The dynamic secant modulus of the sample decreased by 4.14%-6.67%after each impact.The dissipated energy for coal fragmentation samples increased with the number of impacts,averaging 28%under cyclic low-pressure impacts and 29%under single high-pressure impacts.The efficiency of dissipated energy for coal fragmentation initially increased and then decreased as the wave impedance ratio between the coal sample and the bar increased,reaching a maximum of 43.3%when the ratio was 0.06.Based on the defined damage variable,the damage to coal samples from high-pressure impacts was found to be 12 times greater than that under low-pressure conditions.The degree of coal fragmentation was positively correlated with the maximum damage increment.With increasing maximum damage increment,the failure mode of the coal sample evolved from tensile failure to tensile-compressive-shear composite failure.
基金Project(2023YFC2907400)by the National Key Research and Development Program of China-2023 Key Special ProjectProject(51974043)supported by the National Natural Science Foundation of China+2 种基金Project(SKLCRKF1908)supported by the Open Fund of the State Key Laboratory of Coal Resources in Western China,Xi’an University of Science and Technology,ChinaProject(2023JJ10072)suupported by the Hunan Provincial Natural Science Foundation for Distinguished Young ScholarsProject(2022RC1173)supported by the Science and Technology Innovation Program of Hunan Province,China。
文摘The geostress and rock blasting in underground engineering may greatly affect the stress thresholds of surrounding rock.In this study,pre-damage impact tests were first conducted on granite under varying confining pressures(5,10 and 15 MPa)and numbers of impacts(1,5,10 and 15 impacts).Then,uniaxial compression tests were undertaken on the pre-damaged granite to study the evolution of stress thresholds using the crack volume strain method and acoustic emission method.The crack damage stresses determined by the two methods were compared.Additionally,based on the rise time amplitude and average frequency,the evolution law of microcracks inside rock specimens was revealed,and an improved acoustic emission method was proposed.The results indicated that as the number of impacts increased,the crack closure stress,crack damage stress,and peak stress of granite specimens initially rose and then declined,while they continuously increased with the confining pressure.The proportion of shear cracks first declined and then rose with greater number of impacts and decreased with higher confining pressure,and that of tensile cracks showed the opposite trend.The improved acoustic emission method was more accurate in identifying the crack damage stress.
基金supported by the National Natural Science Foundation of China(52274085).
文摘Coal bursts pose significant safety and operational challenges in deep mining environments,necessitating effective mitigation strategies to address high-stress concentrations and dynamic failure risks.This study evaluated the efficacy of hydraulic fracturing as a preconditioning tool at a longwall face of the Mengcun coal mine with strong coal bursts,Shaanxi Province.The program involved the systematic creation of a fracture network through high-pressure fluid injection,monitored via microseismic arrays,stress measurements,and hydrological sensors.Results demonstrated that hydraulic fracturing effectively redistributed in-situ stresses,reducing high-stress concentrations by up to 30%,lowering the frequency of high-energy microseismic events,and enhancing the stability of fractured zones.However,the presence of unfractured blind spots and interactions with pre-existing faults highlighted the need for optimized well placement and adaptive fracturing designs.These findings underscore the potential of hydraulic fracturing as a critical preconditioning tool in high-stress mining operations,which could provide a framework for improving safety and efficiency in similar geological and operational settings.
基金supported by the National Natural Science Foundation of China(Nos.52101165,52031013 and 52071322).
文摘The effect of vanadium(V)element on the microstructure and mechanical properties of anchor steel was explored by microstructural characterization and mechanical property tests of anchor steels with different V contents.The results indicated that the trace addition of V element can generate dispersed VC nanoparticles in the anchor steel and then refine microstructure by inhibiting austenite grain growth.The increase in V content leads to the formation of a larger amount of smaller VC nanoparticles and more refined microstructure.Moreover,the increasing V content in anchor steel causes the volume fraction of ferrite to increase and that of pearlite to decrease continuously,and even leads to the formation of bainite.Accompanied by the microstructure change,the V-treated anchor steels exhibit higher strength compared with the anchor steel without V addition.However,the increased hardness difference between ferrite and pearlite results in poor coordination of deformation between them,leading to a decrease in their plasticity.The impact toughness of anchor steel first increases but then significantly decreases with the increase in V content.The improvement in impact toughness of trace V-treated anchor steel benefits from the enhancement in the band structure after hot rolling,which consumes more energy during the vertical crack propagation process.However,when the V content further increases,the hard and brittle bainite in the anchor steel can facilitate crack initiation and propagation,ultimately resulting in a reduced toughness.
基金supported in part by the National Natural Science Foundation of China under Grant 41874143 and Grant 42374163in part by the Key Program of Natural Science Foundation of Sichuan Province of China under Grant 2023NSFSC0019in part by the Central Funds Guiding the Local Science and Technology Development under Grant 2024ZYD0124.
文摘Multiphase flow in porous rock is of great importance in the application of many industrial processes,including reservoir delineation,enhanced oil recovery,and CO_(2) sequestration.However,previous research typically investigated the dispersive behaviors when rock saturated with single or two-phase fluids and conducted limited studies on three-phase immiscible fluids.This study investigated the seismic dispersion,attenuation,and reflection features of seismic waves in three-phase immiscible fluidsaturated porous rocks.First,we proposed the calculation formulas of effective fluid modulus and effective fluid viscosity of multiphase immiscible fluids by taking into account the capillary pressure,reservoir wettability,and relative permeability simultaneously.Then,we analysed the frequencydependent behaviors of three-phase immiscible fluid-saturated porous rock under different fluid proportion cases using the Chapman multi-scale model.Next,the seismic responses are analysed using a four-layer model.The results indicate that the relative permeability,capillary pressure parameter,and fluid proportions are all significantly affect dispersion and attenuation.Comparative analyses demonstrate that dispersion and attenuation can be observed within the frequency range of seismic exploration for a lower capillary parameter a3 and higher oil content.Seismic responses reveal that the reflection features,such as travel time,seismic amplitude,and waveform of the bottom reflections of saturated rock and their underlying reflections are significantly dependent on fluid proportions and capillary parameters.For validation,the numerical results are further verified using the log data and real seismic data.This numerical analysis helps to further understand the wave propagation characteristics for a porous rock saturated with multiphase immiscible fluids.
基金support from the National Science Foundation of China(52304137,5192780752274124,52325403)Tiandi Science and Technology Co.,Ltd.(2022-2-TDMS012 and SKLIS202417)Sichuan University(SKHL2215).
文摘The Grey Wolf Optimization(GWO)algorithm is acknowledged as an effective method for rock acoustic emission localization.However,the conventional GWO algorithm encounters challenges related to solution accuracy and convergence speed.To address these concerns,this paper develops a Simplex Improved Grey Wolf Optimizer(SMIGWO)algorithm.The randomly generating initial populations are replaced with the iterative chaotic sequences.The search process is optimized using the convergence factor optimization algorithm based on the inverse incompleteГfunction.The simplex method is utilized to address issues related to poorly positioned grey wolves.Experimental results demonstrate that,compared to the conventional GWO algorithm-based AE localization algorithm,the proposed algorithm achieves a higher solution accuracy and showcases a shorter search time.Additionally,the algorithm demonstrates fewer convergence steps,indicating superior convergence efficiency.These findings highlight that the proposed SMIGWO algorithm offers enhanced solution accuracy,stability,and optimization performance.The benefits of the SMIGWO algorithm extend universally across various materials,such as aluminum,granite,and sandstone,showcasing consistent effectiveness irrespective of material type.Consequently,this algorithm emerges as a highly effective tool for identifying acoustic emission signals and improving the precision of rock acoustic emission localization.
基金the National Key Research and Development Program of China(Nos.2023YFC2907501 and 2023YFC2907503)the National Natural Science Foundation of China(Nos.52374106 and 52274154)the Fundamental Research Funds for the Central Universities(No.2023YQTD02).
文摘Coal wall stability is a critical factor influencing coal mining efficiency and threatens the safety of working faces,where irregular coal wall surfaces significantly affect the contact and support effectiveness of the support plate,thereby impacting stability.Through a combination of theoretical analysis,mechanical testing,and numerical simulations,this study establishes a mechanical model of irregular coal wall surfaces to investigate the effects of the undulation period and undulation height on coal wall failure characteristics.This research reveals the mechanical response mechanisms of irregular coal wall surfaces and proposes an innovative method to enhance coal wall stability by improving the supporting cushion material of the support plate,which was validated through numerical simulations.The results show that the undulation height and undulation period significantly influence the macroscopic mechanical parameters of the samples,with the undulation height exerting a more pronounced effect.The strength of the samples with undulating surfaces is approximately 50%-60% that of the samples with flat surfaces.The failure mode under uniaxial compression is predominantly tensile,resulting in long and slender block fragments with a characteristic“Ⅲ”-shaped tensile fracture pattern.During the loading process,samples with undu-lating surfaces dissipate energy at all stages,with a greater proportion of energy dissipation occurring during the early loading stage because of structural damage and the formation of internal cracks.The surface compressive and tensile stresses are correlated with the curvature radius of the convex surface and the elastic modulus of the supporting plate.Reducing the elastic modulus of the supporting plate material can effectively alleviate the stress concentration at convex locations and increase the peak strength.This study provides theoretical foundations and technical references for the prevention and control of coal wall spalling in deep thick coal seam mining.
基金This work has been supported by the National Key Research and Development Program(Grant No.2017YFC0603000)which was jointly completed by the Coal Mining Research Branch of CCRI,China University of Mining and Technology(Xuzhou and Beijing),Henan Polytechnic UniversityXinji Energy Company Limited of China Coal Energy Group.This work was also supported by the National Natural Science Foundation of China(Grant No.51927807)。
文摘This paper reviews the major achievements in terms of mechanical behaviors of coal measures,mining stress distribution characteristics and ground control in China’s deep underground coal mining.The three main aspects of this review are coal measure mechanics,mining disturbance mechanics,and rock support mechanics.Previous studies related to these three topics are reviewed,including the geo-mechanical properties of coal measures,distribution and evolution characteristics of mining-induced stresses,evolution characteristics of mining-induced structures,and principles and technologies of ground control in both deep roadways and longwall faces.A discussion is made to explain the structural and mechanical properties of coal measures in China’s deep coal mining practices,the types and dis-tribution characteristics of in situ stresses in underground coal mines,and the distribution of mining-induced stress that forms under different geological and engineering conditions.The theory of pre-tensioned rock bolting has been proved to be suitable for ground control of deep underground coal roadways.The use of combined ground control technology(e.g.ground support,rock mass modification,and destressing)has been demonstrated to be an effective measure for rock control of deep roadways.The developed hydraulic shields for 1000 m deep ultra-long working face can effectively improve the stability of surrounding rocks and mining efficiency in the longwall face.The ground control challenges in deep underground coal mines in China are discussed,and further research is recommended in terms of theory and technology for ground control in deep roadways and longwall faces.
基金This work was supported by the National Natural Science Foundation of China(No.41877272)the Fundamental Research Funds for the Central Universities of Southeast University(No.2242021R10080).
文摘To evaluate the coal burst proneness more precisely,a new energy criterion namely the residual elastic energy index was proposed.This study begins by performing the single-cyclic loading-unloading uniaxial compression tests with five pre-peak unloading stress levels to explore the energy storage characteristics of coal.Five types of coals from different mines were tested,and the instantaneous destruction process of the coal specimens under compression loading was recorded using a high speed camera.The results showed a linear relationship between the elastic strain energy density and input energy density,which confirms the linear energy storage law of coal.Based on this linear energy storage law,the peak elastic strain energy density of each coal specimen was obtained precisely.Subsequently,a new energy criterion of coal burst proneness was established,which was called the residual elastic energy index(defined as the difference between the peak elastic strain energy density and post peak failure energy density).Considering the destruction process and actual failure characteristics of coal specimens,the accuracy of evaluating coal burst proneness based on the residual elastic energy index was examined.The results indicated that the residual elastic energy index enables reliable and precise evaluations of the coal burst proneness.
