This study investigates the evolution of coal permeability under mining-induced stress and gas extraction,a key factor for safe and efficient coal seam gas recovery.A simplified triaxial stress path incorporating axia...This study investigates the evolution of coal permeability under mining-induced stress and gas extraction,a key factor for safe and efficient coal seam gas recovery.A simplified triaxial stress path incorporating axial stress,confining stress,and pore pressure was applied to simulate stress relief and gas drainage in protective seam mining.Laboratory experiments on intact and fractured coal samples from the Huainan mining area were conducted using a gas-flow and stress-controlled loading system.Results indicate that coal permeability is strongly dependent on loading history and fracture morphology.The first unloading cycle produced the largest fracture volume reduction(29%in vertically fractured coal,23%in horizontally fractured coal,and 20%—21%in intact coal).Irreversible permeability loss correlated with initial porosity,while the third cycle yielded the greatest permeability increase due to cumulative damage and new fracture formation.Decreasing pore pressure amplified its influence on permeability,with intact coal showing higher stress sensitivity and fractured coal exhibiting a declining trend under cyclic loading.Unlike previous studies that focused primarily on monotonic loading or single fracture orientations,this work systematically reveals the fracture-dependent,cyclic nature of permeability evolution under coupled mining stress and gas drainage conditions.These findings highlight the nonlinear,fracture-dependent nature of coal permeability evolution and provide guidance for optimizing gas drainage,enhancing methane recovery,and improving safety in deep coal mining.展开更多
The occurrence of overlying coal pillar(OCP)exerts a strong effect on the stress and strain distribution of the surrounding rock in the stope.In this paper,the stress distribution characteristics are analyzed via the ...The occurrence of overlying coal pillar(OCP)exerts a strong effect on the stress and strain distribution of the surrounding rock in the stope.In this paper,the stress distribution characteristics are analyzed via the numerical calculation with the account of OCP presence or absence.In addition,this study revealed the joint effect of side pressure relief area of the goaf and stress concentration in OCP on the final stress distribution.Furthermore,the rules of abutment stress distribution affected by three influencing factors,namely horizontal-vertical distances between OCP and working face and buried depth of OCP,are analyzed.The functional model linking the peak stress of surrounding rock with the above influencing factors is developed.The field application of the above results proved that the rib spalling and deformation of a 2.95 m-high and 5.66 m-wide roadway could be efficiently controlled by rationally adjusting working states of the support,and adopting the hydraulic prop coordinated with the p type metal beam and anchor cable to strengthen the surrounding rock of working face and roadway,respectively.The proposed measures are considered appropriate to satisfy the safe operation requirements.展开更多
Fault is a common geological structure that has been revealed in the process of underground coal excavation and mining.The nature of its discontinuous structure controls the deformation,damage,and mechanics of the coa...Fault is a common geological structure that has been revealed in the process of underground coal excavation and mining.The nature of its discontinuous structure controls the deformation,damage,and mechanics of the coal or rock mass.The interaction between this discontinuous structure and mining activities is a key factor that dominates fault reactivation and the coal burst it can induce.This paper first summarizes investigations into the relationships between coal mining layouts and fault occurrences,along with relevant conceptual models for fault reactivation.Subsequently,it proposes mechanisms of fault reactivation and its induced coal burst based on the superposition of static and dynamic stresses,which include two kinds of fault reactivations from:mining-induced quasi-static stress(FRMSS)-dominated and seismic-based dynamic stress(FRSDS)-dominated.These two kinds of fault reactivations are then validated by the results of experimental investigations,numerical modeling,and in situ microseismic monitoring.On this basis,monitoring methods and prevention strategies for fault-induced coal burst are discussed and recommended.The results show that fault-induced coal burst is triggered by the superposition of high static stress in the fault pillar and dynamic stress from fault reactivation.High static stress comes from the interaction of the fault and the roof structure,and dynamic stress can be ascribed to FRMSS and FRSDS.The results in this paper could be of great significance in guiding the monitoring and prevention of fault-induced coal bursts.展开更多
Aiming to address the following major engineering issues faced by the Pingdingshan No. 12 mine:(1) difficulty in implementing auxiliary lifting because of its depth(i.e., beyond 1000 m);(2) highly gassy main coal seam...Aiming to address the following major engineering issues faced by the Pingdingshan No. 12 mine:(1) difficulty in implementing auxiliary lifting because of its depth(i.e., beyond 1000 m);(2) highly gassy main coal seam with low permeability;(3) unstable overlying coal seam without suitable conditions for implementing conventional mining techniques for protective coal seam; and(4) predominant reliance on ‘‘under three" coal resources to ensure production output. This study proposes an integrated, closed-cycle mining-dressing-gas draining-backfilling-mining(MDGBM) technique. The proposed approach involves the mining of protective coal seam, underground dressing of coal and gangue(UDCG), pressure relief and gas drainage before extraction, and backfilling and mining of the protected coal seam. A system for draining gas and mining the protective seam in the rock stratum is designed and implemented based on the geological conditions. This system helps in realizing pressure relief and gas drainage from the protective seam before extraction. Accordingly, another system, which is connected to the existing production system, is established for the UDCG based on the dense medium-shallow trough process. The mixed mining workface is designed to accommodate both solid backfill and conventional fully mechanized coal mining, thereby facilitating coal mining, USCG, and backfilling. The results show that: The mixed mining workface length for the Ji15-31010 protected seam was 220 m with coal production capacity 1.2 million tons per year, while the backfill capacity of gangue was 0.5 million tons per year. The gas pressure decreased from 1.78 to 0.35 MPa, and the total amount of safely mined coal was 1.34 million tons. The process of simultaneously exploiting coal and draining gas was found to be safe, efficient, and green.This process also yielded significant economic benefits.展开更多
Reduction of energy consumption in comminution is of significant importance in mining industry. To reduce such energy consumption the energy efficiency in an individual operation such as blasting must be increased. By...Reduction of energy consumption in comminution is of significant importance in mining industry. To reduce such energy consumption the energy efficiency in an individual operation such as blasting must be increased. By using both new investigations and previous experimental results, this paper demonstrates that (1) kinetic energy carried by moving fragments in rock fracture is notable and it increases with an increasing loading rate;(2) this kinetic energy can be well used in secondary fragmentation in crushing and blasting. Accordingly, part of the muck pile from previous blast should be left in front of new(bench) face in either open pit or underground blasting. If so, when new blast occurs, the fragments from the new blast will collide with the muck pile left from the previous blast, and the kinetic energy carried by the moving fragments will be partly used in their secondary fragmentation.展开更多
<正>For environment protection in mining areas in northwest China,we developed a CTSRM(comprehensive test system by radon measurement) to measure radon radioactivity and detect dynamic evolution characteristics ...<正>For environment protection in mining areas in northwest China,we developed a CTSRM(comprehensive test system by radon measurement) to measure radon radioactivity and detect dynamic evolution characteristics of mining-induced fractures in overlying strata.It was used to simulate the relationship between the dynamic evolution characteristics and radon concentrations of 33201~# coalface at Bulianta coal mine in Inner Mongolia,and feasibility of the method was validate.展开更多
Rock failure process as a natural response to mining activities is associated with seismic events, which can pose a potential hazard to mine operators, equipment and infrastructures. Mining-induced seismicity has been...Rock failure process as a natural response to mining activities is associated with seismic events, which can pose a potential hazard to mine operators, equipment and infrastructures. Mining-induced seismicity has been found to be internally correlated in both time and space domains as a result of rock fracturing during progressive mining activities. Understanding the spatio-temporal(ST) correlation of mininginduced seismic events is an essential step to use seismic data for further analysis, such as rockburst prediction and caving assessment. However, there are no established methods to perform this critical task. Input parameters used for the prediction of seismic hazards, such as the time window of past data and effective prediction distance, are determined based on site-specific experience without statistical or physical reasons to support. Therefore, the accuracy of current seismic prediction methods is largely constrained, which can only be addressed by quantitively assessing the ST correlations of mininginduced seismicity. In this research, the ST correlation of seismic event energy collected from a study mine is quantitatively analysed using various statistical methods, including autocorrelation function(ACF), semivariogram and Moran’s I analysis. In addition, based on the integrated ST correlation assessment, seismic events are further classified into seven clusters, so as to assess the correlations within individual clusters. The correlation of seismic events is found to be quantitatively assessable, and their correlations may vary throughout the mineral extraction process.展开更多
In fully mechanized solid backfilling mining(FMSBM),the loose gangues backfill body(LGBB)that filled into the goaf becomes the main body of bearing the overburden load.The deformation resistance of LGBB is critical fo...In fully mechanized solid backfilling mining(FMSBM),the loose gangues backfill body(LGBB)that filled into the goaf becomes the main body of bearing the overburden load.The deformation resistance of LGBB is critical for controlling overburden movement and surface subsidence.During the process of load bearing,LGBB will experience grain crushing,which has a significant effect on its deformation resistance.Gangues block will be accompanied with obvious acoustic emissions(AE)features in process of slipping,flipping and damaging.Under confined compression test,monitoring the AE parameters of LGBB can reveal the impact mechanism of grain crushing on LGBB deformation.The study is of great significance for obtaining an in-depth understanding of the mechanical properties of LGBB,and providing guidance to the engineering practice of FMSBM.In order to study the rules of acoustic emissions(AE)of graded Loose gangues backfill body(LGBB)in confined compression test,this article introduces the AE systems to conventional confined compression test to monitor AE signals resulted from the friction and fragmentation among LGBB.The test results show that in the process of LGBB compaction,AE parameters are highly correlated with the strain-stress curve.AE events of balanced-sized graded gangues are more inactive than other two graded samples in different compression stages,AE events of large-particle-dominated graded gangues are most active.In the spatial distribution,AE events are the most active on the edges and the middle part of test samples and the phenomenon of grain crushing is the most obvious in these positions.展开更多
The fractured rocks distributed near the structural surface of coal roadway heading face can easily cause water or air conduits,ultimately resulting in accidents that threaten production safety,such as mine flooding,g...The fractured rocks distributed near the structural surface of coal roadway heading face can easily cause water or air conduits,ultimately resulting in accidents that threaten production safety,such as mine flooding,gas leakage,or supporting failure.Therefore,successful detection of fissures is crucial to mine safety.Despite the rising popularity of computer vision in accurate fissures detection,it fails to satisfy the demand of engineering practice.To address this problem,this paper first establishes a 1000-image database of fissures of coal roadway heading face based on data collection,cleaning,and annotation.Then,a framework for fissure detection and segmentation is constructed with deep convolutional neural network(DCNN)named DeepLabv3+ serving as the overall architecture,and a lightweight MobileNetV2,instead of the original Xception,as the main feature extraction network.The database is then employed to train and test the neural network model.Finally,the robustness and adaptability of the model under the common jamming environment in coal mines are evaluated.According to the results,the deep learning algorithm,which performs favorably in identifying various fissures in the coal roadway heading face,is immune to interference such as low illumination,wire mesh,multi-scale edge,cutting mark,and concentrated light beams.Notably,the performance of such method is on par with,or better than,humans in performing individual image segmentation.The approach performs higher segmentation accuracy and calculation speed than the traditional image identification algorithm,thus realizing rapid identification of fissures in coal mines in batch.This study can provide a reference for image semantic segmentation of fissure traces under similar conditions.展开更多
This study is focused on the prediction of mining subsidence and its impact on the environment in the Hongqi mining area. The study was carried out by means of a probability integral model based, in first instance bas...This study is focused on the prediction of mining subsidence and its impact on the environment in the Hongqi mining area. The study was carried out by means of a probability integral model based, in first instance based on field surveys and the analysis of data collected from this area. Isolines of mining sub- sidence were then drawn and the impact caused by mining subsidence on the environment was analyzed quantitatively by spatial analysis with Geographic Information System （GIS）. The results indicate that the subsidence area of the first working-mine can be as large as 2.54 km2, the maximum subsidence is 3440 mrn which will cause 1524 houses to be relocated. The entire subsidence area of the mine can reach 8.09 km2, with a maximum subsidence of 3590 ram. Under these circumstances the value of the loss of ecosystem services Will reach 5.371 million Yuan and the cost of relocating buildings will increase to 6.858 million Yuan.展开更多
This paper proposes a digital image processing-based detection algorithm for cross joint traces of coal roadway heading face.Initially,the acquired images were preprocessed,i.e.,adaptive correction was conducted for n...This paper proposes a digital image processing-based detection algorithm for cross joint traces of coal roadway heading face.Initially,the acquired images were preprocessed,i.e.,adaptive correction was conducted for non-uniform illumination images based on the 2D gamma function.The edge detection algorithm was then applied to extract the edges of the structural plane,followed by the filtration of the non-structural plane noises.Moreover,the Hough transform algorithm was applied to extract the linear edges;finally,the edges were locally connected in accordance with the angle and distance criteria.The experimental results show that this algorithm can be used to reduce the noise caused by non-uniform illumination and avoid the mutual interference of multi-scale edges,so as to effectively extract the traces of the cross joint.Furthermore,Q-system and rock mass rating(RMR),were applied to conduct a quantitative evaluation on the stand-up time of unsupported roof in the four test images.The Q-system quality scores are 26.7,43.3,3.1,and 6.7,and the RMR quality scores are 56.84,58.73,48.42,and 51.42,respectively.The stand-up time of unsupported roofs with a span of 4.6 m are 30,36,7.7 and 14 d,respectively.展开更多
At present,non-pillar entry protection in longwall mining is mainly achieved through either the gob-side entry retaining(GER)procedure or the gob-side entry driving(GED)procedure.The GER procedure leads to difficultie...At present,non-pillar entry protection in longwall mining is mainly achieved through either the gob-side entry retaining(GER)procedure or the gob-side entry driving(GED)procedure.The GER procedure leads to difficulties in maintaining the roadway in mining both the previous and current panels.A narrow coal pillar about 5-7 m must be left in the GED procedure;therefore,it causes permanent loss of some coal.The gob-side pre-backfill driving(GPD)procedure effectively removes the wasting of coal resources that exists in the GED procedure and finds an alternative way to handle the roadway maintenance problem that exists in the GER procedure.The FLAC^(3D) software was used to numerically investigate the stress and deformation distributions and failure of the rock mass surrounding the previous and current panel roadways during each stage of the GPD procedure which requires"twice excavation and mining".The results show that the stress distribution is slightly asymmetric around the previous panel roadway after the"primary excavation".The stronger and stiffer backfill compared to the coal turned out to be the main bearing body of the previous panel roadway during the"primary mining".The highest vertical stresses of 32.6 and 23.1 MPa,compared to the in-situ stress of 10.5 MPa,appeared in the backfill wall and coal seam,respectively.After the"primary mining",the peak vertical stress under the coal seam at the floor level was slightly higher(18.1 MPa)than that under the backfill(17.8 MPa).After the"secondary excavation",the peak vertical stress under the coal seam at the floor level was slightly lower(18.7 MPa)than that under the backfill(19.8 MPa);the maximum floor heave and maximum roof sag of the current panel roadway were 252.9 and 322.1 mm,respectively.During the"secondary mining",the stress distribution in the rock mass surrounding the current panel roadway was mainly affected by the superposition of the front abutment pressure from the current panel and the side abutment pressure from the previous panel.The floor heave of the current panel roadway reached a maximum of 321.8 mm at 5 m ahead of the working face;the roof sag increased to 828.4 mm at the working face.The peak abutment pressure appeared alternately in the backfill and the coal seam during the whole procedure of"twice excavation and mining"of the GPD procedure.The backfill provided strong bearing capacity during all stages of the GPD procedure and exhibited reliable support for the roadway.The results provide scientific insight for engineering practice of the GPD procedure.展开更多
Based on radon gas properties and its existing projects applications, we firstly attempted to apply geo- physical and chemical properties of radon gas in the field of mining engineering, and imported radioac- tive mea...Based on radon gas properties and its existing projects applications, we firstly attempted to apply geo- physical and chemical properties of radon gas in the field of mining engineering, and imported radioac- tive measurement method to detect the development process of the overlying strata mining-induced fractures and their contained water quality in underground coal mining, which not only innovates a more simple-fast-reliable detection method, but also further expands the applications of radon gas detection technology in mining field. A 3D simulation design of comprehensive testing system for detecting strata mining-induced fractures on surface with radon gas (CTSR) was carried out by using a large-scale 3D solid model design software Pro/Engineer (Pro/E), which overcame three main disadvantages of ''static design thought, 2D planar design and heavy workload for remodification design'' on exiting design for mining engineering test systems. Meanwhile, based on the simulation design results of Pro/E software, the sta- bility of the jack-screw pressure bar for the key component in CTSR was checked with a material mechan- ics theory, which provided a reliable basis for materials selection during the latter machining process.展开更多
To study the influence of coal mining on the stability of river levees,a mechanical model of mining-induced river levee deformation was established.This was based on the mining-induced deformation characteristics of r...To study the influence of coal mining on the stability of river levees,a mechanical model of mining-induced river levee deformation was established.This was based on the mining-induced deformation characteristics of river levees and the application of a typical surface subsidence function.Meanwhile,a failure criterion was proposed for river levees.Using some examples,the deformation of,and stress distribution through,river levees under the influence of mining were obtained:the maximum tensile stress on the bottom of the river levee was less than the tensile strength,under which circumstance the river levee remained undamaged.Meanwhile,this research analyzed the influence of three factors including the maximum surface subsidence wmax,half-length of surface subsidence basin L,and foundation coefficient k on the stability of river levees.Results showed that reducing the mining height of the working face and the foundation co-efficient,and increasing the strike length of the working face could reduce the influence of mining on river levees.These results provided a theoretical basis for predicting the mining-induced deformation and failure of river levees.展开更多
It is difficult to accurately calculate the lump coal rate in a fully mechanized mining face.Therefore,a numerical simulation of the coal wall cutting process,which revealed the crack expansion,development,evolution i...It is difficult to accurately calculate the lump coal rate in a fully mechanized mining face.Therefore,a numerical simulation of the coal wall cutting process,which revealed the crack expansion,development,evolution in the coal body and the corresponding lump coal formation mechanism,was performed in PFC2D.Moreover,a correlation was established between the cutting force and lump coal formation,and a statistical analysis method was proposed to determine the lump coal rate.The following conclusions are drawn from the results:(1)Based on a soft ball model,a coal wall cutting model is established.By setting the roller parameters based on linear bonding and simulating the roller cutting process of the coal body,the coal wall cutting process is effectively simulated,and accurate lump coal rate statistics are provided.(2)Under the cutting stress,the coal body in the working face underwent three stages—microfracture generation,fracture expansion,and fracture penetration—to form lump coal,in which the fracture direction is orthogonal to the cutting pressure chain.Within a certain range from the roller,as the cutting depth of the roller increased,the number of new fractures in the coal body first increases and then stabilizes.(3)Under the cutting stress,the fractured coal body is locally compressed,thereby forming a compact core.The formation and destruction of the compact core causes fluctuations in the cutting force.The fluctuation amplitude is positively related to the coal mass.(4)Because the simulation does not consider secondary damage in the coal,the simulated lump coal rate is larger than the actual lump coal rate in the working face;this deviation is mainly concentrated in large lump coal with a diameter greater than 300 mm.展开更多
With annually increased coal mining depth,gas extraction becomes more and more problematic.The gas extraction efect depends on coal seam permeability,which,in turn,is afected by many factors,including loading and unlo...With annually increased coal mining depth,gas extraction becomes more and more problematic.The gas extraction efect depends on coal seam permeability,which,in turn,is afected by many factors,including loading and unloading stresses and strains in the coal seam.Stresses induce internal cracks,resulting in cleats and gas emission channels,the coal seam permeability permanently changes accordingly.To clarify the stress-induced efects on coal seam permeability,this survey summarized the available approaches used to link the stress path and seepage law in the coal body seepage law,which can be classifed into two design methods:single load variation and combined feld mining method.The characterization methods used to observe the surface of coal samples and three-dimensional reconstruction include electron microscopy,CT scanning,and Nuclear Magnetic Resonance(NMR).According to the stress paths designed by the above two approaches,the seepage laws and similarities of three kinds of coal samples with the fractured structure were summarized in this paper.The following directions are recommended to study the seepage law of coal bodies with three kinds of fractured structures under stress.Firstly,the stress path of the experimental coal body should be designed by the combined feld mining method.The stressed environment of a deep coal seam is complicated,and the axial and confning pressures change simultaneously.Therefore,one cannot fully refect the real situation on-site by studying permeability evolution alone.Secondly,during the coal seam mining,the stressed state changes from time to time,and the development of coal seam fractures is afected by mining.When studying the stress efect on seepage of coal samples,the fractured structure of coal samples should be considered.Finally,the available structural characterization methods of coal samples can be combined with the 3D printing technology,which would produce artifcial samples with the fractured structure characteristics of natural coal.展开更多
The control and management of mining-induced seismic hazards have attracted ever-rising attention,especially in underground longwall coal mines,where continuous mining activities dynamically alter the stress states an...The control and management of mining-induced seismic hazards have attracted ever-rising attention,especially in underground longwall coal mines,where continuous mining activities dynamically alter the stress states and induce seismic events.In this work,the Epidemic Type Aftershock Sequence(ETAS)model was applied to formulate the aftershock catalogue of mining-induced seismicity and investigate the formation of event triggering associated with longwall mining.The conventional Baiesi and Paczuski method(2004)was used to separate longwall mining-induced seismic events into triggered and nontriggered catalogues.The latter catalogue contains both non-triggering(NT)-isolated events that do not trigger subsequent events and NT-parent events of the former catalogue.Statistical properties of triggered events were analysed spatially and temporally.The temporal triggering sequence follows the Omori-Utsu law,where the temporal decay of aftershocks is influenced by the magnitude of NT-parent events in mining-induced seismicity.The spatial distribution of aftershocks follows an inverted U-shaped relationship with distance to their corresponding NT-parent events.The quantitative forecasting of triggered events was performed based on the nonhomogeneous Poisson distribution,which achieved a good consistency with their NT-parent events.Amongst the non-triggered catalogue,NT-isolated events are concentrated ahead of NT-parent events,potentially acting as foreshocks for the latter.展开更多
Nowadays,additive manufacturing,or 3D printing(3DP),though not a new technology in many industrial fields,is still relatively novel in mining engineering.This study explored the application of 3D metal printing,3D pol...Nowadays,additive manufacturing,or 3D printing(3DP),though not a new technology in many industrial fields,is still relatively novel in mining engineering.This study explored the application of 3D metal printing,3D polylactic acid/acrylonitrile butadiene styrene printing,and 3D concrete printing in coal mining.Some examples of physical models established via 3DP technologies were studied in detail,namely,3DP bolts,3DP steel ladder beams,3DP face plates,and 3DP metal arches,which were installed in scaled 3DP concrete prototype models of coal mine excavation.Through the comprehensive laboratory loading tests,the models could simulate the damage scenario highly similar to the real failures.The results show that the 3D printed physical models greatly improved the accuracy and reliability of experiments.On this basis,the conceptual design of a 3DP machine for physical models was proposed,which had the potential of resembling the strata deformation/collapse in natural scenarios.Through assessing the applicability of the additive manufacturing technology in mining engineering,this study aimed to further explore its potential applicability in other engineering contexts such as slope controlling,large underground engineering,and underground space stability.展开更多
To investigate the effect of saturation on the storage-dissipation properties and failure characteristics of red sandstone,as well as the energy mechanism of rockburst prevention by water,a series of uniaxial compress...To investigate the effect of saturation on the storage-dissipation properties and failure characteristics of red sandstone,as well as the energy mechanism of rockburst prevention by water,a series of uniaxial compression and uniaxial loading–unloading tests were conducted under five saturation levels.The effect of saturation on the mechanical properties and elastic energy density was analyzed,and a method for obtaining peak energy density was proposed.The effect of saturation on the energy evolution was examined,and the energy mechanism of water in preventing rockburst was revealed.The results indicate that an increase in saturation of red sandstone decreases the input energy density,elastic energy density,dissipated energy density,peak strength and peak strain;the compaction phase of the stress–strain curve becomes shorter;the failure mode transitions from X-conjugate oblique shear to single oblique shear;the variation in the debris ejection trajectory is as follows:radiation→X-ray→oblique upward parabola→horizontal parabola→oblique downward parabola;the degree of failure intensity and fragmentation is decreased gradually.Elastic energy density is interconnected with both saturation and stress but independent of the loading path.Saturation exhibits a dual effect on the energy storage property,i.e.,increasing saturation increases the energy storage efficiency and reduces the energy storage capacity.The ratio of peak elastic energy density to peak input energy density remains constant irrespective of saturation levels.Water prevents rockburst by decreasing the energy storage capacity of surrounding rock,alleviating the stress of surrounding rock to reduce energy storage,and elevating the energy release threshold of high-energy surrounding rock.The findings of this study contribute to understanding the effect of water on rock failure from an energy perspective,as well as provide theoretical guidance for rockburst prevention by water in deep tunnels.展开更多
Dense-array ambient noise tomography is a powerful tool for achieving high-resolution subsurface imag-ing,significantly impacting geohazard prevention and control.Conventional dense-array studies,how-ever,require simu...Dense-array ambient noise tomography is a powerful tool for achieving high-resolution subsurface imag-ing,significantly impacting geohazard prevention and control.Conventional dense-array studies,how-ever,require simultaneous observations of numerous stations for extensive coverage.To conduct a comprehensive karst feature investigation with limited stations,we designed a new synchronous-asyn-chronous observation system that facilitates dense array observations.We conducted two rounds of asynchronous observations,each lasting approximately 24 h,in combination with synchronous backbone stations.We achieved wide-ranging coverage of the study area utilizing 197 nodal receivers,with an average station spacing of 7 m.The beamforming results revealed distinct variations in the noise source distributions between day and night.We estimated the source strength in the stationary phase zone and used a weighting scheme for stacking the cross-correlation functions(C ^(1) functions)to suppress the influ-ence of nonuniform noise source distributions.The weights were derived from the similarity coefficients between multicomponent C^(1)functions related to Rayleigh waves.We employed the cross-correlation of C ^(1) functions(C^(2)methods)to obtain the empirical Green’s functions between asynchronous stations.To eliminate artifacts in C ^(2) functions from higher-mode surface waves in C^(1)functions,we filtered the C^(1)functions on the basis of different particle motions linked to multimode Rayleigh waves.The dispersion measurements of Rayleigh waves obtained from both the C^(1)and C^(2)functions were utilized in surface wave tomography.The inverted three-dimensional(3D)shear-wave(S-wave)velocity model reveals two significant low-velocity zones at depths ranging from 40 to 60 m,which align well with the karst caves found in the drilling data.The method of short-term synchronous-asynchronous ambient noise tomography shows promise as a cost-effective and efficient approach for urban geohazard investigations.展开更多
基金supported by the National Natural Science Foundation of China(52174129)the Guizhou Provincial Key Technology R&D Program([2024]034,[2023]337)the Independent Research Project of State Key Laboratory of Coal Resources and Safe Mining,CUMT(SKLCRSM22X006).
文摘This study investigates the evolution of coal permeability under mining-induced stress and gas extraction,a key factor for safe and efficient coal seam gas recovery.A simplified triaxial stress path incorporating axial stress,confining stress,and pore pressure was applied to simulate stress relief and gas drainage in protective seam mining.Laboratory experiments on intact and fractured coal samples from the Huainan mining area were conducted using a gas-flow and stress-controlled loading system.Results indicate that coal permeability is strongly dependent on loading history and fracture morphology.The first unloading cycle produced the largest fracture volume reduction(29%in vertically fractured coal,23%in horizontally fractured coal,and 20%—21%in intact coal).Irreversible permeability loss correlated with initial porosity,while the third cycle yielded the greatest permeability increase due to cumulative damage and new fracture formation.Decreasing pore pressure amplified its influence on permeability,with intact coal showing higher stress sensitivity and fractured coal exhibiting a declining trend under cyclic loading.Unlike previous studies that focused primarily on monotonic loading or single fracture orientations,this work systematically reveals the fracture-dependent,cyclic nature of permeability evolution under coupled mining stress and gas drainage conditions.These findings highlight the nonlinear,fracture-dependent nature of coal permeability evolution and provide guidance for optimizing gas drainage,enhancing methane recovery,and improving safety in deep coal mining.
基金supported by the Special Funding Projects of Sanjin Scholars” Supporting Plan (No. 2050205)the National Key Research Projects (No. 2016YFC0600701)Ordinary University Graduate Student Scientific Research Innovation Projects of Jiangsu Province of China (No. KYLX16_0564)
文摘The occurrence of overlying coal pillar(OCP)exerts a strong effect on the stress and strain distribution of the surrounding rock in the stope.In this paper,the stress distribution characteristics are analyzed via the numerical calculation with the account of OCP presence or absence.In addition,this study revealed the joint effect of side pressure relief area of the goaf and stress concentration in OCP on the final stress distribution.Furthermore,the rules of abutment stress distribution affected by three influencing factors,namely horizontal-vertical distances between OCP and working face and buried depth of OCP,are analyzed.The functional model linking the peak stress of surrounding rock with the above influencing factors is developed.The field application of the above results proved that the rib spalling and deformation of a 2.95 m-high and 5.66 m-wide roadway could be efficiently controlled by rationally adjusting working states of the support,and adopting the hydraulic prop coordinated with the p type metal beam and anchor cable to strengthen the surrounding rock of working face and roadway,respectively.The proposed measures are considered appropriate to satisfy the safe operation requirements.
基金This research was carried out by the following funded projects:National Natural Science Foundation of China(51604270,51874292,and 51804303)Fundamental Research Funds for the Central Universities(2017QNA26)+2 种基金Natural Science Foundation of Jiangsu Province(BK20180643)Independent Research Projects of State Key Laboratory of Coal Resources and Safe Mining,China University of Mining and Technology(SKLCRSM15X04)The first author also acknowledges the China Postdoctoral Council International Postdoctoral Exchange Fellowship Program(20170060).
文摘Fault is a common geological structure that has been revealed in the process of underground coal excavation and mining.The nature of its discontinuous structure controls the deformation,damage,and mechanics of the coal or rock mass.The interaction between this discontinuous structure and mining activities is a key factor that dominates fault reactivation and the coal burst it can induce.This paper first summarizes investigations into the relationships between coal mining layouts and fault occurrences,along with relevant conceptual models for fault reactivation.Subsequently,it proposes mechanisms of fault reactivation and its induced coal burst based on the superposition of static and dynamic stresses,which include two kinds of fault reactivations from:mining-induced quasi-static stress(FRMSS)-dominated and seismic-based dynamic stress(FRSDS)-dominated.These two kinds of fault reactivations are then validated by the results of experimental investigations,numerical modeling,and in situ microseismic monitoring.On this basis,monitoring methods and prevention strategies for fault-induced coal burst are discussed and recommended.The results show that fault-induced coal burst is triggered by the superposition of high static stress in the fault pillar and dynamic stress from fault reactivation.High static stress comes from the interaction of the fault and the roof structure,and dynamic stress can be ascribed to FRMSS and FRSDS.The results in this paper could be of great significance in guiding the monitoring and prevention of fault-induced coal bursts.
基金supported by the Qing Lan Project Foundation of Jiangsu Province in 2014,Foundation for Distinguished professor of Jiangsu Province in 2015,Science Fund for Creative Research Groups of the National Natural Science Foundation of China(No.51421003)Project funded by China Postdoctoral Science Foundation(2016M601915)National Key Basic Research Program of China(No.2013CB227905)
文摘Aiming to address the following major engineering issues faced by the Pingdingshan No. 12 mine:(1) difficulty in implementing auxiliary lifting because of its depth(i.e., beyond 1000 m);(2) highly gassy main coal seam with low permeability;(3) unstable overlying coal seam without suitable conditions for implementing conventional mining techniques for protective coal seam; and(4) predominant reliance on ‘‘under three" coal resources to ensure production output. This study proposes an integrated, closed-cycle mining-dressing-gas draining-backfilling-mining(MDGBM) technique. The proposed approach involves the mining of protective coal seam, underground dressing of coal and gangue(UDCG), pressure relief and gas drainage before extraction, and backfilling and mining of the protected coal seam. A system for draining gas and mining the protective seam in the rock stratum is designed and implemented based on the geological conditions. This system helps in realizing pressure relief and gas drainage from the protective seam before extraction. Accordingly, another system, which is connected to the existing production system, is established for the UDCG based on the dense medium-shallow trough process. The mixed mining workface is designed to accommodate both solid backfill and conventional fully mechanized coal mining, thereby facilitating coal mining, USCG, and backfilling. The results show that: The mixed mining workface length for the Ji15-31010 protected seam was 220 m with coal production capacity 1.2 million tons per year, while the backfill capacity of gangue was 0.5 million tons per year. The gas pressure decreased from 1.78 to 0.35 MPa, and the total amount of safely mined coal was 1.34 million tons. The process of simultaneously exploiting coal and draining gas was found to be safe, efficient, and green.This process also yielded significant economic benefits.
文摘Reduction of energy consumption in comminution is of significant importance in mining industry. To reduce such energy consumption the energy efficiency in an individual operation such as blasting must be increased. By using both new investigations and previous experimental results, this paper demonstrates that (1) kinetic energy carried by moving fragments in rock fracture is notable and it increases with an increasing loading rate;(2) this kinetic energy can be well used in secondary fragmentation in crushing and blasting. Accordingly, part of the muck pile from previous blast should be left in front of new(bench) face in either open pit or underground blasting. If so, when new blast occurs, the fragments from the new blast will collide with the muck pile left from the previous blast, and the kinetic energy carried by the moving fragments will be partly used in their secondary fragmentation.
基金Supported by the National Natural Science Foundation of China(50904063 and 51004101)the Fundamental Research Funds for the Central Universities (2010ZDP02B02)the State Key Laboratory of Coal Resources and Safe Mining(SKLCRSM08X02)
文摘<正>For environment protection in mining areas in northwest China,we developed a CTSRM(comprehensive test system by radon measurement) to measure radon radioactivity and detect dynamic evolution characteristics of mining-induced fractures in overlying strata.It was used to simulate the relationship between the dynamic evolution characteristics and radon concentrations of 33201~# coalface at Bulianta coal mine in Inner Mongolia,and feasibility of the method was validate.
文摘Rock failure process as a natural response to mining activities is associated with seismic events, which can pose a potential hazard to mine operators, equipment and infrastructures. Mining-induced seismicity has been found to be internally correlated in both time and space domains as a result of rock fracturing during progressive mining activities. Understanding the spatio-temporal(ST) correlation of mininginduced seismic events is an essential step to use seismic data for further analysis, such as rockburst prediction and caving assessment. However, there are no established methods to perform this critical task. Input parameters used for the prediction of seismic hazards, such as the time window of past data and effective prediction distance, are determined based on site-specific experience without statistical or physical reasons to support. Therefore, the accuracy of current seismic prediction methods is largely constrained, which can only be addressed by quantitively assessing the ST correlations of mininginduced seismicity. In this research, the ST correlation of seismic event energy collected from a study mine is quantitatively analysed using various statistical methods, including autocorrelation function(ACF), semivariogram and Moran’s I analysis. In addition, based on the integrated ST correlation assessment, seismic events are further classified into seven clusters, so as to assess the correlations within individual clusters. The correlation of seismic events is found to be quantitatively assessable, and their correlations may vary throughout the mineral extraction process.
文摘In fully mechanized solid backfilling mining(FMSBM),the loose gangues backfill body(LGBB)that filled into the goaf becomes the main body of bearing the overburden load.The deformation resistance of LGBB is critical for controlling overburden movement and surface subsidence.During the process of load bearing,LGBB will experience grain crushing,which has a significant effect on its deformation resistance.Gangues block will be accompanied with obvious acoustic emissions(AE)features in process of slipping,flipping and damaging.Under confined compression test,monitoring the AE parameters of LGBB can reveal the impact mechanism of grain crushing on LGBB deformation.The study is of great significance for obtaining an in-depth understanding of the mechanical properties of LGBB,and providing guidance to the engineering practice of FMSBM.In order to study the rules of acoustic emissions(AE)of graded Loose gangues backfill body(LGBB)in confined compression test,this article introduces the AE systems to conventional confined compression test to monitor AE signals resulted from the friction and fragmentation among LGBB.The test results show that in the process of LGBB compaction,AE parameters are highly correlated with the strain-stress curve.AE events of balanced-sized graded gangues are more inactive than other two graded samples in different compression stages,AE events of large-particle-dominated graded gangues are most active.In the spatial distribution,AE events are the most active on the edges and the middle part of test samples and the phenomenon of grain crushing is the most obvious in these positions.
基金We acknowledge the funding support from the National Natural Science Foundation of China(Grant Nos.52034007 and 52274101).
文摘The fractured rocks distributed near the structural surface of coal roadway heading face can easily cause water or air conduits,ultimately resulting in accidents that threaten production safety,such as mine flooding,gas leakage,or supporting failure.Therefore,successful detection of fissures is crucial to mine safety.Despite the rising popularity of computer vision in accurate fissures detection,it fails to satisfy the demand of engineering practice.To address this problem,this paper first establishes a 1000-image database of fissures of coal roadway heading face based on data collection,cleaning,and annotation.Then,a framework for fissure detection and segmentation is constructed with deep convolutional neural network(DCNN)named DeepLabv3+ serving as the overall architecture,and a lightweight MobileNetV2,instead of the original Xception,as the main feature extraction network.The database is then employed to train and test the neural network model.Finally,the robustness and adaptability of the model under the common jamming environment in coal mines are evaluated.According to the results,the deep learning algorithm,which performs favorably in identifying various fissures in the coal roadway heading face,is immune to interference such as low illumination,wire mesh,multi-scale edge,cutting mark,and concentrated light beams.Notably,the performance of such method is on par with,or better than,humans in performing individual image segmentation.The approach performs higher segmentation accuracy and calculation speed than the traditional image identification algorithm,thus realizing rapid identification of fissures in coal mines in batch.This study can provide a reference for image semantic segmentation of fissure traces under similar conditions.
基金Support for this work, provided by the Science and Technology Project of the Land and Resources Department of Henan Province (No.0979)
文摘This study is focused on the prediction of mining subsidence and its impact on the environment in the Hongqi mining area. The study was carried out by means of a probability integral model based, in first instance based on field surveys and the analysis of data collected from this area. Isolines of mining sub- sidence were then drawn and the impact caused by mining subsidence on the environment was analyzed quantitatively by spatial analysis with Geographic Information System （GIS）. The results indicate that the subsidence area of the first working-mine can be as large as 2.54 km2, the maximum subsidence is 3440 mrn which will cause 1524 houses to be relocated. The entire subsidence area of the mine can reach 8.09 km2, with a maximum subsidence of 3590 ram. Under these circumstances the value of the loss of ecosystem services Will reach 5.371 million Yuan and the cost of relocating buildings will increase to 6.858 million Yuan.
基金supported by the National Natural Scieince Foundation of China(Nos.52004204 and 52034007).
文摘This paper proposes a digital image processing-based detection algorithm for cross joint traces of coal roadway heading face.Initially,the acquired images were preprocessed,i.e.,adaptive correction was conducted for non-uniform illumination images based on the 2D gamma function.The edge detection algorithm was then applied to extract the edges of the structural plane,followed by the filtration of the non-structural plane noises.Moreover,the Hough transform algorithm was applied to extract the linear edges;finally,the edges were locally connected in accordance with the angle and distance criteria.The experimental results show that this algorithm can be used to reduce the noise caused by non-uniform illumination and avoid the mutual interference of multi-scale edges,so as to effectively extract the traces of the cross joint.Furthermore,Q-system and rock mass rating(RMR),were applied to conduct a quantitative evaluation on the stand-up time of unsupported roof in the four test images.The Q-system quality scores are 26.7,43.3,3.1,and 6.7,and the RMR quality scores are 56.84,58.73,48.42,and 51.42,respectively.The stand-up time of unsupported roofs with a span of 4.6 m are 30,36,7.7 and 14 d,respectively.
基金This research was supported by the National Natural Science Foundation of China(51604126,51974293)the Natural Science Foundation of Jiangsu Province(BK20180658),and the Distinguished Foreign Expert Talent Program funding from the Chinese Government and the Jiangxi Province.
文摘At present,non-pillar entry protection in longwall mining is mainly achieved through either the gob-side entry retaining(GER)procedure or the gob-side entry driving(GED)procedure.The GER procedure leads to difficulties in maintaining the roadway in mining both the previous and current panels.A narrow coal pillar about 5-7 m must be left in the GED procedure;therefore,it causes permanent loss of some coal.The gob-side pre-backfill driving(GPD)procedure effectively removes the wasting of coal resources that exists in the GED procedure and finds an alternative way to handle the roadway maintenance problem that exists in the GER procedure.The FLAC^(3D) software was used to numerically investigate the stress and deformation distributions and failure of the rock mass surrounding the previous and current panel roadways during each stage of the GPD procedure which requires"twice excavation and mining".The results show that the stress distribution is slightly asymmetric around the previous panel roadway after the"primary excavation".The stronger and stiffer backfill compared to the coal turned out to be the main bearing body of the previous panel roadway during the"primary mining".The highest vertical stresses of 32.6 and 23.1 MPa,compared to the in-situ stress of 10.5 MPa,appeared in the backfill wall and coal seam,respectively.After the"primary mining",the peak vertical stress under the coal seam at the floor level was slightly higher(18.1 MPa)than that under the backfill(17.8 MPa).After the"secondary excavation",the peak vertical stress under the coal seam at the floor level was slightly lower(18.7 MPa)than that under the backfill(19.8 MPa);the maximum floor heave and maximum roof sag of the current panel roadway were 252.9 and 322.1 mm,respectively.During the"secondary mining",the stress distribution in the rock mass surrounding the current panel roadway was mainly affected by the superposition of the front abutment pressure from the current panel and the side abutment pressure from the previous panel.The floor heave of the current panel roadway reached a maximum of 321.8 mm at 5 m ahead of the working face;the roof sag increased to 828.4 mm at the working face.The peak abutment pressure appeared alternately in the backfill and the coal seam during the whole procedure of"twice excavation and mining"of the GPD procedure.The backfill provided strong bearing capacity during all stages of the GPD procedure and exhibited reliable support for the roadway.The results provide scientific insight for engineering practice of the GPD procedure.
基金support for this work provided by the Fundamental Research Funds for the Central Universities(China University of Mining & Technology) (No. 2010ZDP02B02)the State Key Laboratory of Coal Resources and Safe Mining(No. SKLCRSM08X02)
文摘Based on radon gas properties and its existing projects applications, we firstly attempted to apply geo- physical and chemical properties of radon gas in the field of mining engineering, and imported radioac- tive measurement method to detect the development process of the overlying strata mining-induced fractures and their contained water quality in underground coal mining, which not only innovates a more simple-fast-reliable detection method, but also further expands the applications of radon gas detection technology in mining field. A 3D simulation design of comprehensive testing system for detecting strata mining-induced fractures on surface with radon gas (CTSR) was carried out by using a large-scale 3D solid model design software Pro/Engineer (Pro/E), which overcame three main disadvantages of ''static design thought, 2D planar design and heavy workload for remodification design'' on exiting design for mining engineering test systems. Meanwhile, based on the simulation design results of Pro/E software, the sta- bility of the jack-screw pressure bar for the key component in CTSR was checked with a material mechan- ics theory, which provided a reliable basis for materials selection during the latter machining process.
文摘To study the influence of coal mining on the stability of river levees,a mechanical model of mining-induced river levee deformation was established.This was based on the mining-induced deformation characteristics of river levees and the application of a typical surface subsidence function.Meanwhile,a failure criterion was proposed for river levees.Using some examples,the deformation of,and stress distribution through,river levees under the influence of mining were obtained:the maximum tensile stress on the bottom of the river levee was less than the tensile strength,under which circumstance the river levee remained undamaged.Meanwhile,this research analyzed the influence of three factors including the maximum surface subsidence wmax,half-length of surface subsidence basin L,and foundation coefficient k on the stability of river levees.Results showed that reducing the mining height of the working face and the foundation co-efficient,and increasing the strike length of the working face could reduce the influence of mining on river levees.These results provided a theoretical basis for predicting the mining-induced deformation and failure of river levees.
基金The funding was supported by National Natural Science Foundation of China(No.51974294).
文摘It is difficult to accurately calculate the lump coal rate in a fully mechanized mining face.Therefore,a numerical simulation of the coal wall cutting process,which revealed the crack expansion,development,evolution in the coal body and the corresponding lump coal formation mechanism,was performed in PFC2D.Moreover,a correlation was established between the cutting force and lump coal formation,and a statistical analysis method was proposed to determine the lump coal rate.The following conclusions are drawn from the results:(1)Based on a soft ball model,a coal wall cutting model is established.By setting the roller parameters based on linear bonding and simulating the roller cutting process of the coal body,the coal wall cutting process is effectively simulated,and accurate lump coal rate statistics are provided.(2)Under the cutting stress,the coal body in the working face underwent three stages—microfracture generation,fracture expansion,and fracture penetration—to form lump coal,in which the fracture direction is orthogonal to the cutting pressure chain.Within a certain range from the roller,as the cutting depth of the roller increased,the number of new fractures in the coal body first increases and then stabilizes.(3)Under the cutting stress,the fractured coal body is locally compressed,thereby forming a compact core.The formation and destruction of the compact core causes fluctuations in the cutting force.The fluctuation amplitude is positively related to the coal mass.(4)Because the simulation does not consider secondary damage in the coal,the simulated lump coal rate is larger than the actual lump coal rate in the working face;this deviation is mainly concentrated in large lump coal with a diameter greater than 300 mm.
基金supported by the National Natural Science Foundation of China(52174129,52104155,51704274)Independent Research Project of State Key Laboratory of Coal Resources and Safe Mining,CUMT(SKLCRSM22X006)Jiangsu Province Scientifc Research and Practice Innovation Project(KYCX21_2390).
文摘With annually increased coal mining depth,gas extraction becomes more and more problematic.The gas extraction efect depends on coal seam permeability,which,in turn,is afected by many factors,including loading and unloading stresses and strains in the coal seam.Stresses induce internal cracks,resulting in cleats and gas emission channels,the coal seam permeability permanently changes accordingly.To clarify the stress-induced efects on coal seam permeability,this survey summarized the available approaches used to link the stress path and seepage law in the coal body seepage law,which can be classifed into two design methods:single load variation and combined feld mining method.The characterization methods used to observe the surface of coal samples and three-dimensional reconstruction include electron microscopy,CT scanning,and Nuclear Magnetic Resonance(NMR).According to the stress paths designed by the above two approaches,the seepage laws and similarities of three kinds of coal samples with the fractured structure were summarized in this paper.The following directions are recommended to study the seepage law of coal bodies with three kinds of fractured structures under stress.Firstly,the stress path of the experimental coal body should be designed by the combined feld mining method.The stressed environment of a deep coal seam is complicated,and the axial and confning pressures change simultaneously.Therefore,one cannot fully refect the real situation on-site by studying permeability evolution alone.Secondly,during the coal seam mining,the stressed state changes from time to time,and the development of coal seam fractures is afected by mining.When studying the stress efect on seepage of coal samples,the fractured structure of coal samples should be considered.Finally,the available structural characterization methods of coal samples can be combined with the 3D printing technology,which would produce artifcial samples with the fractured structure characteristics of natural coal.
基金support from Australian Research Council(Grant No.LP200301404)support from the Fundamental Research Funds for the Central Universities(Grant No.2020CXNL02)is also much appreciated.
文摘The control and management of mining-induced seismic hazards have attracted ever-rising attention,especially in underground longwall coal mines,where continuous mining activities dynamically alter the stress states and induce seismic events.In this work,the Epidemic Type Aftershock Sequence(ETAS)model was applied to formulate the aftershock catalogue of mining-induced seismicity and investigate the formation of event triggering associated with longwall mining.The conventional Baiesi and Paczuski method(2004)was used to separate longwall mining-induced seismic events into triggered and nontriggered catalogues.The latter catalogue contains both non-triggering(NT)-isolated events that do not trigger subsequent events and NT-parent events of the former catalogue.Statistical properties of triggered events were analysed spatially and temporally.The temporal triggering sequence follows the Omori-Utsu law,where the temporal decay of aftershocks is influenced by the magnitude of NT-parent events in mining-induced seismicity.The spatial distribution of aftershocks follows an inverted U-shaped relationship with distance to their corresponding NT-parent events.The quantitative forecasting of triggered events was performed based on the nonhomogeneous Poisson distribution,which achieved a good consistency with their NT-parent events.Amongst the non-triggered catalogue,NT-isolated events are concentrated ahead of NT-parent events,potentially acting as foreshocks for the latter.
基金National Natural Science Foundation of China,Grant/Award Number:51804296China Scholarship Council Grant,Grant/Award Number:CSC#202006425019。
文摘Nowadays,additive manufacturing,or 3D printing(3DP),though not a new technology in many industrial fields,is still relatively novel in mining engineering.This study explored the application of 3D metal printing,3D polylactic acid/acrylonitrile butadiene styrene printing,and 3D concrete printing in coal mining.Some examples of physical models established via 3DP technologies were studied in detail,namely,3DP bolts,3DP steel ladder beams,3DP face plates,and 3DP metal arches,which were installed in scaled 3DP concrete prototype models of coal mine excavation.Through the comprehensive laboratory loading tests,the models could simulate the damage scenario highly similar to the real failures.The results show that the 3D printed physical models greatly improved the accuracy and reliability of experiments.On this basis,the conceptual design of a 3DP machine for physical models was proposed,which had the potential of resembling the strata deformation/collapse in natural scenarios.Through assessing the applicability of the additive manufacturing technology in mining engineering,this study aimed to further explore its potential applicability in other engineering contexts such as slope controlling,large underground engineering,and underground space stability.
基金supported by the National Natural Science Foundation of China(52104133,52304227)the Natural Science Foundation of Hunan Province(2021JJ40465,2023JJ40548)the Opening Foundation of the State Key Laboratory of Mining Response and Disaster Prevention and Control in Deep Coal Mines(SKLMRDPC20KF03).
文摘To investigate the effect of saturation on the storage-dissipation properties and failure characteristics of red sandstone,as well as the energy mechanism of rockburst prevention by water,a series of uniaxial compression and uniaxial loading–unloading tests were conducted under five saturation levels.The effect of saturation on the mechanical properties and elastic energy density was analyzed,and a method for obtaining peak energy density was proposed.The effect of saturation on the energy evolution was examined,and the energy mechanism of water in preventing rockburst was revealed.The results indicate that an increase in saturation of red sandstone decreases the input energy density,elastic energy density,dissipated energy density,peak strength and peak strain;the compaction phase of the stress–strain curve becomes shorter;the failure mode transitions from X-conjugate oblique shear to single oblique shear;the variation in the debris ejection trajectory is as follows:radiation→X-ray→oblique upward parabola→horizontal parabola→oblique downward parabola;the degree of failure intensity and fragmentation is decreased gradually.Elastic energy density is interconnected with both saturation and stress but independent of the loading path.Saturation exhibits a dual effect on the energy storage property,i.e.,increasing saturation increases the energy storage efficiency and reduces the energy storage capacity.The ratio of peak elastic energy density to peak input energy density remains constant irrespective of saturation levels.Water prevents rockburst by decreasing the energy storage capacity of surrounding rock,alleviating the stress of surrounding rock to reduce energy storage,and elevating the energy release threshold of high-energy surrounding rock.The findings of this study contribute to understanding the effect of water on rock failure from an energy perspective,as well as provide theoretical guidance for rockburst prevention by water in deep tunnels.
基金supported by the National Natural Science Foundation of China(41830103)the Project of Nanjing Center of China Geological Survey(DD20190281).
文摘Dense-array ambient noise tomography is a powerful tool for achieving high-resolution subsurface imag-ing,significantly impacting geohazard prevention and control.Conventional dense-array studies,how-ever,require simultaneous observations of numerous stations for extensive coverage.To conduct a comprehensive karst feature investigation with limited stations,we designed a new synchronous-asyn-chronous observation system that facilitates dense array observations.We conducted two rounds of asynchronous observations,each lasting approximately 24 h,in combination with synchronous backbone stations.We achieved wide-ranging coverage of the study area utilizing 197 nodal receivers,with an average station spacing of 7 m.The beamforming results revealed distinct variations in the noise source distributions between day and night.We estimated the source strength in the stationary phase zone and used a weighting scheme for stacking the cross-correlation functions(C ^(1) functions)to suppress the influ-ence of nonuniform noise source distributions.The weights were derived from the similarity coefficients between multicomponent C^(1)functions related to Rayleigh waves.We employed the cross-correlation of C ^(1) functions(C^(2)methods)to obtain the empirical Green’s functions between asynchronous stations.To eliminate artifacts in C ^(2) functions from higher-mode surface waves in C^(1)functions,we filtered the C^(1)functions on the basis of different particle motions linked to multimode Rayleigh waves.The dispersion measurements of Rayleigh waves obtained from both the C^(1)and C^(2)functions were utilized in surface wave tomography.The inverted three-dimensional(3D)shear-wave(S-wave)velocity model reveals two significant low-velocity zones at depths ranging from 40 to 60 m,which align well with the karst caves found in the drilling data.The method of short-term synchronous-asynchronous ambient noise tomography shows promise as a cost-effective and efficient approach for urban geohazard investigations.
