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
Coal is an essential fossil fuel in China; however, coal mining and its utilization are being under the increasing pressure from ecological and environmental protection. Therefore, the consulting project "Technic...Coal is an essential fossil fuel in China; however, coal mining and its utilization are being under the increasing pressure from ecological and environmental protection. Therefore, the consulting project "Technical Revolution in Ecological and Efficient Coal Mining and Utilization & Intelligence and Diverse Coordination of Coal-based Energy System," initiated by Chinese Academy of Engineering, puts forward three stages(3.0, 4.0 and 5.0) of China's coal industry development strategy. Aimed at "reduced staff,ultra-low ecological damage, and emission level near to natural gas," breakthroughs should be achieved in the following three key technologies during the China Coal Industry 3.0 stage(2016–2025): including intelligent coal mining, ecological mining, ultra-low emission and environmental protection. This paper focuses on the development trends of the China Coal Industry 3.0 and its support for China Coal Industry 4.0 and 5.0 is analyzed and prospected as well, which may offer technical assistance and strategy orientation for realizing the transformation from traditional coal energy to clean energy.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
In this article an attempt to determine the influence of mining factors on the seismic activity during the longwall mining of the upper layer of coal seam no.405/2 in one of the Polish hard coal mines in the Upper Sil...In this article an attempt to determine the influence of mining factors on the seismic activity during the longwall mining of the upper layer of coal seam no.405/2 in one of the Polish hard coal mines in the Upper Silesian Coal Basin was conducted.Two longwall panels were mined in analogous geological conditions and based on the same mining system and technology.However,there was significant difference with regards to the mining factors,which was reflected in the observed seismic activity.Some tools used in mining seismology were applied to illustrate the aforementioned influence of mining factors,e.g.the frequency-energy distribution,the frequency-magnitude distribution,the 2 D distribution of released seismic energy,the relationship between released seismic energy and the volume of mined coal,the Benioff strain release,and the Gutenberg-Richter(GR)b coefficient distribution(b is the proportion between high and low energy tremors).Concerning the Benioff strain release,a new solution,based on the slope of a fitted line in a moving time window,is proposed.展开更多
Methods of exploitation drainage, which is presently applied in polish hard coal mines in Upper Silesian Coal Basin(Poland), are not effective enough, high risk of methane hazard can be observed, and production capaci...Methods of exploitation drainage, which is presently applied in polish hard coal mines in Upper Silesian Coal Basin(Poland), are not effective enough, high risk of methane hazard can be observed, and production capacity of the mining plant is not fully used. Methane hazard, which may occur during planned coal exploitation, is presented in this paper. Following parameters are taken into consideration in the forecasts: coal extraction parameters, geological and mining conditions, deposit's methane saturation degree and impact of coal exploitation on the degasification coefficient of the seams, which are under the influence of relaxation zone. This paper presents the results of the analysis aiming to verify applicability of drainage ahead of mining of the coal seams by using surface directional wells. Based on the collected data(coal seams' structural maps, profiles of the exploratory wells, geological cross-sections), the lab tests of drilling cores and direct wells' tests, static model of the deposit was constructed and suitable grid of directional wells from the surface was designed. Comparison of forecasted methane emission volume between the two methods is investigated. The results indicated the necessity of performing appropriate deposit's stimulations in order to increase effectiveness of drainage ahead of mining.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
Mining-induced seismicity is a reflection of rock geomechanical evolution of geological environment in the natural and man-made systems and in the mining-technical systems. In order to predict and prevent mining-induc...Mining-induced seismicity is a reflection of rock geomechanical evolution of geological environment in the natural and man-made systems and in the mining-technical systems. In order to predict and prevent mining-induced seismicity, it is necessary to research geodynamics and stress state of intact rock mass, to determine possible deformations and additional stresses as a result of large-scale rock extraction, conditions of accumulated energy release. For that a geodynamical monitoring is required on every stage of deposit development and a closing. The report considers principal influencing factors of preparation and occurrence of mining-induced earthquakes. Also it estimates precursors and indicators of rock mass breaking point, and experience concerning prediction and prevention of mining-induced seismicity in the Khibiny apatite mines in the Murmansk region, which is the largest mining province.展开更多
This study demonstrates a practical cycle time analysis of dump truck haulage system of “Ukhaa Khudag” open-pit coal mine located in Umnugobi Province, Mongolia. It examines the possibility of minimizing the cycle t...This study demonstrates a practical cycle time analysis of dump truck haulage system of “Ukhaa Khudag” open-pit coal mine located in Umnugobi Province, Mongolia. It examines the possibility of minimizing the cycle time of the haulage system as well as factors impacting the speed of the dump truck. The current study divides the open pit mine road for the dump trucks into five sections which are bench road, ramp, surface road, dump road uphill, and dump road. Meanwhile, it investigates the influence of the length, the grade, and the rolling resistance of the road section on the cycle time. The data is analyzed using mathematical regression methods via Microsoft Excel program. For each of the five road sections, we compare the statistical calculations of three regression models: linear, quadratic and exponential;thus, a total of thirty regression models are obtained in this research. Accordingly, the cycle time for each road section is predicted by the most accountable model. The loaded and empty direction of the movement is measured and calculated for each road section, and it appears that the difference between the calculated mean value and the actual cycle time of the models is 0.82 seconds with a relative error of 2.51 percent.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 article presents the results of in-kind measurements and numerical modeling of the formation of water characteristics in the Kama River,which is used for technical water supply in the production of potash fertiliz...The article presents the results of in-kind measurements and numerical modeling of the formation of water characteristics in the Kama River,which is used for technical water supply in the production of potash fertilizers.In the warm season,risks arise that threaten the sustainability of the water supply.It was found that in the summer,when the studied section of the Kama River is backed up by the KamaHydroelectric Power Station,there is a significant decrease in flow rates,which leads to vertical stratification of water properties.This,in turn,significantly limits the possibilities of using water fromthe bottom zone.Under conditions of significant water discharge from the reservoir,this section has river conditions with significantly higher flow rates.Under such conditions,intense vertical mixing of water masses occurs,which improves the consumer properties of water necessary for sustainable water supply.The results of numerical modeling carried out within the framework of the three-dimensional approach confirmed this conclusion.It is shown that with an increase in the flow rate in the channel near thewater intake,the concentration of salts decreases,which is an important factor in ensuring high-quality water supply.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
Jerada coal mining generates extensive coal mine waste rock(CMWR)piles rich in valuable minerals,posing environmental challenges and economic opportunities.This study examines reprocessing feasibility through 3D geome...Jerada coal mining generates extensive coal mine waste rock(CMWR)piles rich in valuable minerals,posing environmental challenges and economic opportunities.This study examines reprocessing feasibility through 3D geometallurgical characterization.Sampling used down the hole hammer drilling technique(DTH)and drone surveys for topographical precision.Over 620 samples from(T01,T02,T08)underwent comprehensive analyses including particle size distribution,x-ray fluorescence(XRF),total sulfur/carbon analysis(S/C),and inductively coupled plasma mass spectrometry(ICP-MS)for physical-chemical characterization.Mineralogical aspects were explored via optical microscopy(OM),X-ray diffraction(XRD),scanning electron microscopy(SEM),electron probe microanalysis(EPMA),and laser ablation inductively coupled plasma mass spectrometry(LA-ICP-MS).Quantitative mineral evaluation by scanning electron microscope(QEMSCAN)provided mineral insights.Chemical data was used in a 3D block model to quantify residual coal.Results for the three examined CMWR piles(T01,T02,and T08)showed varying D80 from 160 to 300μm,notable carbon content averaged 12.5 wt%(T01),16 wt%(T02),and 8.5 wt%(T08).Sulfur presence exceeded 1 wt%in T08,and potential environmental concerns due to iron sulfides.Anthracite liberation was below 30 wt%.3D modeling estimated a total volume of 7 Mm3,mainly from T08,equaling 11.2 Mt.With its high carbon content and substantial tonnages,re-exploitation or alternative applications could minimize these CMWR piles environmental impact.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 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
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
Geo-monitoring provides quantitative and reliable information to identify hazards and adopt appropriate measures timely.However,this task inherently exposes monitoring staff to hazardous environments,especially in und...Geo-monitoring provides quantitative and reliable information to identify hazards and adopt appropriate measures timely.However,this task inherently exposes monitoring staff to hazardous environments,especially in underground settings.Since 2000s,robots have been widely applied in various fields and many studies have focused on establishing autonomous mobile robotic systems as well as solving the issue of underground navigation and mapping.However,only a few studies have conducted quantitative evaluations of these methods,and almost none have provided a systematic and comprehensive assessment of the suitability of mapping robots for underground geo-monitoring.In this study,a methodology for objective and quantitative assessment of the applicability of SLAM methods in underground geo-monitoring is proposed.This involves the development of an underground test field and some specific metrics,which allow detailed local accuracy analysis of point measurements,line segments,and areas using artificial targets.With this proposed methodology,a series of repeated experimental measurements has been performed with an autonomous driving robot and the selected LiDAR-and visual-based SLAM methods.The resulting point cloud was compared with the reference data measured by a total station and a terrestrial laser scanner.The accuracy and precision of the selected SLAM methods as well as the verifiability and reliability of the results are evaluated and discussed by analysing quantities such as the deviations of the control points coordinates,cloudto-cloud distances between the test and reference point cloud,normal vector,centre point coordinates and area of the planar objects.The results demonstrate that the HDL Graph SLAM achieves satisfactory precision,accuracy,and repeatability with a mean cloud-to-cloud distance of 0.12 m(with a standard deviation of 0.13 m)in an 80 m closed-loop measurement area.Although RTAB-Map exhibits better plane-capturing capabilities,the measurement results reveal instability and inaccuracies.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supported by the Major State Basic Research Development Program of China (No. 2014CB046302)
文摘Coal is an essential fossil fuel in China; however, coal mining and its utilization are being under the increasing pressure from ecological and environmental protection. Therefore, the consulting project "Technical Revolution in Ecological and Efficient Coal Mining and Utilization & Intelligence and Diverse Coordination of Coal-based Energy System," initiated by Chinese Academy of Engineering, puts forward three stages(3.0, 4.0 and 5.0) of China's coal industry development strategy. Aimed at "reduced staff,ultra-low ecological damage, and emission level near to natural gas," breakthroughs should be achieved in the following three key technologies during the China Coal Industry 3.0 stage(2016–2025): including intelligent coal mining, ecological mining, ultra-low emission and environmental protection. This paper focuses on the development trends of the China Coal Industry 3.0 and its support for China Coal Industry 4.0 and 5.0 is analyzed and prospected as well, which may offer technical assistance and strategy orientation for realizing the transformation from traditional coal energy to clean energy.
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.
文摘In this article an attempt to determine the influence of mining factors on the seismic activity during the longwall mining of the upper layer of coal seam no.405/2 in one of the Polish hard coal mines in the Upper Silesian Coal Basin was conducted.Two longwall panels were mined in analogous geological conditions and based on the same mining system and technology.However,there was significant difference with regards to the mining factors,which was reflected in the observed seismic activity.Some tools used in mining seismology were applied to illustrate the aforementioned influence of mining factors,e.g.the frequency-energy distribution,the frequency-magnitude distribution,the 2 D distribution of released seismic energy,the relationship between released seismic energy and the volume of mined coal,the Benioff strain release,and the Gutenberg-Richter(GR)b coefficient distribution(b is the proportion between high and low energy tremors).Concerning the Benioff strain release,a new solution,based on the slope of a fitted line in a moving time window,is proposed.
文摘Methods of exploitation drainage, which is presently applied in polish hard coal mines in Upper Silesian Coal Basin(Poland), are not effective enough, high risk of methane hazard can be observed, and production capacity of the mining plant is not fully used. Methane hazard, which may occur during planned coal exploitation, is presented in this paper. Following parameters are taken into consideration in the forecasts: coal extraction parameters, geological and mining conditions, deposit's methane saturation degree and impact of coal exploitation on the degasification coefficient of the seams, which are under the influence of relaxation zone. This paper presents the results of the analysis aiming to verify applicability of drainage ahead of mining of the coal seams by using surface directional wells. Based on the collected data(coal seams' structural maps, profiles of the exploratory wells, geological cross-sections), the lab tests of drilling cores and direct wells' tests, static model of the deposit was constructed and suitable grid of directional wells from the surface was designed. Comparison of forecasted methane emission volume between the two methods is investigated. The results indicated the necessity of performing appropriate deposit's stimulations in order to increase effectiveness of drainage ahead of mining.
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.
文摘Mining-induced seismicity is a reflection of rock geomechanical evolution of geological environment in the natural and man-made systems and in the mining-technical systems. In order to predict and prevent mining-induced seismicity, it is necessary to research geodynamics and stress state of intact rock mass, to determine possible deformations and additional stresses as a result of large-scale rock extraction, conditions of accumulated energy release. For that a geodynamical monitoring is required on every stage of deposit development and a closing. The report considers principal influencing factors of preparation and occurrence of mining-induced earthquakes. Also it estimates precursors and indicators of rock mass breaking point, and experience concerning prediction and prevention of mining-induced seismicity in the Khibiny apatite mines in the Murmansk region, which is the largest mining province.
文摘This study demonstrates a practical cycle time analysis of dump truck haulage system of “Ukhaa Khudag” open-pit coal mine located in Umnugobi Province, Mongolia. It examines the possibility of minimizing the cycle time of the haulage system as well as factors impacting the speed of the dump truck. The current study divides the open pit mine road for the dump trucks into five sections which are bench road, ramp, surface road, dump road uphill, and dump road. Meanwhile, it investigates the influence of the length, the grade, and the rolling resistance of the road section on the cycle time. The data is analyzed using mathematical regression methods via Microsoft Excel program. For each of the five road sections, we compare the statistical calculations of three regression models: linear, quadratic and exponential;thus, a total of thirty regression models are obtained in this research. Accordingly, the cycle time for each road section is predicted by the most accountable model. The loaded and empty direction of the movement is measured and calculated for each road section, and it appears that the difference between the calculated mean value and the actual cycle time of the models is 0.82 seconds with a relative error of 2.51 percent.
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the Government of the Perm Territory within the Framework of Scientific Project No.S-26/828the Ministry of Science and High Education of Russia(Theme No.121031700169-1).
文摘The article presents the results of in-kind measurements and numerical modeling of the formation of water characteristics in the Kama River,which is used for technical water supply in the production of potash fertilizers.In the warm season,risks arise that threaten the sustainability of the water supply.It was found that in the summer,when the studied section of the Kama River is backed up by the KamaHydroelectric Power Station,there is a significant decrease in flow rates,which leads to vertical stratification of water properties.This,in turn,significantly limits the possibilities of using water fromthe bottom zone.Under conditions of significant water discharge from the reservoir,this section has river conditions with significantly higher flow rates.Under such conditions,intense vertical mixing of water masses occurs,which improves the consumer properties of water necessary for sustainable water supply.The results of numerical modeling carried out within the framework of the three-dimensional approach confirmed this conclusion.It is shown that with an increase in the flow rate in the channel near thewater intake,the concentration of salts decreases,which is an important factor in ensuring high-quality water supply.
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financial support from the International Research Chairs Initiativea program funded by the International Development Research Centre,Canada(IDRC)facilitated by the Canadian Research Chairs Program(108469-001 and 109418-006).
文摘Jerada coal mining generates extensive coal mine waste rock(CMWR)piles rich in valuable minerals,posing environmental challenges and economic opportunities.This study examines reprocessing feasibility through 3D geometallurgical characterization.Sampling used down the hole hammer drilling technique(DTH)and drone surveys for topographical precision.Over 620 samples from(T01,T02,T08)underwent comprehensive analyses including particle size distribution,x-ray fluorescence(XRF),total sulfur/carbon analysis(S/C),and inductively coupled plasma mass spectrometry(ICP-MS)for physical-chemical characterization.Mineralogical aspects were explored via optical microscopy(OM),X-ray diffraction(XRD),scanning electron microscopy(SEM),electron probe microanalysis(EPMA),and laser ablation inductively coupled plasma mass spectrometry(LA-ICP-MS).Quantitative mineral evaluation by scanning electron microscope(QEMSCAN)provided mineral insights.Chemical data was used in a 3D block model to quantify residual coal.Results for the three examined CMWR piles(T01,T02,and T08)showed varying D80 from 160 to 300μm,notable carbon content averaged 12.5 wt%(T01),16 wt%(T02),and 8.5 wt%(T08).Sulfur presence exceeded 1 wt%in T08,and potential environmental concerns due to iron sulfides.Anthracite liberation was below 30 wt%.3D modeling estimated a total volume of 7 Mm3,mainly from T08,equaling 11.2 Mt.With its high carbon content and substantial tonnages,re-exploitation or alternative applications could minimize these CMWR piles environmental impact.
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(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 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 by the German Academic Scholarship Foundation,the Deutsche Forschungsgemeinschaft(DFG,German Research Foundation,Project number 422117092)the Saxon Ministry of Science and Arts.
文摘Geo-monitoring provides quantitative and reliable information to identify hazards and adopt appropriate measures timely.However,this task inherently exposes monitoring staff to hazardous environments,especially in underground settings.Since 2000s,robots have been widely applied in various fields and many studies have focused on establishing autonomous mobile robotic systems as well as solving the issue of underground navigation and mapping.However,only a few studies have conducted quantitative evaluations of these methods,and almost none have provided a systematic and comprehensive assessment of the suitability of mapping robots for underground geo-monitoring.In this study,a methodology for objective and quantitative assessment of the applicability of SLAM methods in underground geo-monitoring is proposed.This involves the development of an underground test field and some specific metrics,which allow detailed local accuracy analysis of point measurements,line segments,and areas using artificial targets.With this proposed methodology,a series of repeated experimental measurements has been performed with an autonomous driving robot and the selected LiDAR-and visual-based SLAM methods.The resulting point cloud was compared with the reference data measured by a total station and a terrestrial laser scanner.The accuracy and precision of the selected SLAM methods as well as the verifiability and reliability of the results are evaluated and discussed by analysing quantities such as the deviations of the control points coordinates,cloudto-cloud distances between the test and reference point cloud,normal vector,centre point coordinates and area of the planar objects.The results demonstrate that the HDL Graph SLAM achieves satisfactory precision,accuracy,and repeatability with a mean cloud-to-cloud distance of 0.12 m(with a standard deviation of 0.13 m)in an 80 m closed-loop measurement area.Although RTAB-Map exhibits better plane-capturing capabilities,the measurement results reveal instability and inaccuracies.
