When the expressway crosses the goafs inevitably,the design is generally to build the road on coal pillars as much as possible.However,the existing coal pillars are often unable to meet relevant requirements of highwa...When the expressway crosses the goafs inevitably,the design is generally to build the road on coal pillars as much as possible.However,the existing coal pillars are often unable to meet relevant requirements of highway construction.Combining three-dimensional physical model tests,numerical simulations and field monitoring,with the Urumqi East Second Ring Road passing through acute inclined goafs as a background,the deformation and failure mechanism of the overlying rock and coal pillars in acute inclined goafs under expressway load were studied.And in accordance with construction requirements of subgrade,comprehensive consideration of the deformation and instability mechanism of acute inclined goafs,the treatment measures and suggestions for this type of geological disasters were put forward.The research results confirmed the rationality of coal pillars in acute inclined goafs under the expressway through grouting.According to the ratio of diff erent overlying rock thickness to coal pillar height,the change trend and value of the required grouting range were summarized,which can provide reference for similar projects.展开更多
The stability and fracture behavior of a goaf roof beneath an open-pit bench are critical concerns,especially under impact loading.However,the effect of the thickness-to-span ratio on dynamic failure modes remains lar...The stability and fracture behavior of a goaf roof beneath an open-pit bench are critical concerns,especially under impact loading.However,the effect of the thickness-to-span ratio on dynamic failure modes remains largely unexplored,as existing research focuses mainly on static stability.Energy dissipation and instability evolution under impact loading require further study.To address this gap,this study conducts drop-weight impact experiments on specimens with circular perforations,complemented by numerical simulations.By integrating dimensional analysis,cusp catastrophe theory,and strength reduction techniques,the dynamic instability mechanism of goaf roofs with varying thickness-to-span ratios is revealed.Results show that the thickness-to-span ratio significantly influences energy accumulation and dissipation during roof failure.A higher ratio increases both the magnitude and rate of energy dissipation,particularly during crack initiation and stable propagation,while its impact diminishes in the final failure stage.Optimizing the thickness-to-span ratio within a critical range enhances structural stability,improving the safety factor by up to 83%.However,beyond a certain threshold,additional thickness yields diminishing benefits.This study provides new insights into the energy-based instability mechanism of goaf roofs under impact loads,establishing a theoretical foundation for early warning systems and optimized safety design.展开更多
China has a long history of coal mining,among which open-pit coal mines have a large number of small coal mine goafs underground.The distribution,shape,structure and other characteristics of goafs are isolated and dis...China has a long history of coal mining,among which open-pit coal mines have a large number of small coal mine goafs underground.The distribution,shape,structure and other characteristics of goafs are isolated and discontinuous,and there is no definite geological law to follow,which seriously threatens the safety of coal mine production and personnel life.Conventional ground geophysical methods have low accuracy in detecting goaf areas affected by mechanical interference from open-pit mines,especially for waterless goaf areas,which cannot be detected by existing methods.This article proposes the use of high-frequency electromagnetic waves for goaf detection.The feasibility of using drilling radar to detect goaf was theoretically analyzed,and a goaf detection model was established.The response characteristics of different fillers in the goaf under different frequencies of high-frequency electromagnetic waves were simulated and analyzed.In a certain open-pit mine in Inner Mongolia,100MHz high-frequency electromagnetic waves were used to detect the goaf through directional drilling on the ground.After detection,excavation verification was carried out,and the location of one goaf detected was verified.The results of engineering practice show that the application of high-frequency electromagnetic waves in goaf detection expands the detection radius of boreholes,has the advantages of high efficiency and accuracy,and has important theoretical and practical significance.展开更多
China,as the world’s largest coal producer and consumer,faces increasingly severe challenges from coal mine goaf areas formed through decades of intensive mining.These underground voids,resulting from exhausted resou...China,as the world’s largest coal producer and consumer,faces increasingly severe challenges from coal mine goaf areas formed through decades of intensive mining.These underground voids,resulting from exhausted resources or technical limitations,not only cause environmental issues like land subsidence and groundwater contamination but also pose critical safety risks for ongoing mining operations,including water inrushes,gas outbursts,and roof collapses.Conventional geophysical methods such as seismic surveys and electromagnetic detection demonstrate limited effectiveness in complex geological conditions due to susceptibility to electrical heterogeneity,electromagnetic interference,and interpretation ambiguities.This study presents an innovative integrated approach combining the Audio-Frequency Electrical Transillumination(AFET)method with multi-parameter borehole logging to establish a three-dimensional detection system.The AFET technique employs 0.1–10 kHz electromagnetic waves to identify electrical anomalies associated with goafs,enabling extensive horizontal scanning.This is complemented by vertical high-resolution profiling through borehole measurements of resistivity,spontaneous potential,and acoustic velocity.Field applications in Shanxi Province’s typical coal mines achieved breakthrough results:Using a grid-drilling pattern(15 m spacing,300 m depth),the method successfully detected three concealed goafs missed by conventional approaches,with spatial positioning errors under 0.5 m.Notably,it accurately identified two un-collapsed water-filled cavities.This surface-borehole synergistic approach overcomes single-method limitations,enhancing goaf detection accuracy to over 92%.The technique provides reliable technical support for safe mining practices and represents significant progress in precise detection of hidden geological hazards in Chinese coal mines,offering valuable insights for global mining geophysics.展开更多
Coal is an essential component of global energy;however,the processes of coal mining and utilization produce significant amounts of coal mine goafs,accompanied by coal-based solid wastes and emitted CO_(2),resulting i...Coal is an essential component of global energy;however,the processes of coal mining and utilization produce significant amounts of coal mine goafs,accompanied by coal-based solid wastes and emitted CO_(2),resulting in severe ecological and environmental challenges.In response to this issue,this study pro-poses a novel approach for filling coal mine goafs using cementitious materials prepared by coal-based solid wastes mineralized with CO_(2)(15%in concentration).The CO_(2) sequestration capacities of individual solid wastes are ranked as follows:carbide slag(CS)>red mud(RM)>fly ash(FA).The performance of filling material prepared from composite solid waste(FA-CS-RM)mineralized with CO_(2) meets the filling requirements of goaf.The filling material(F60C20R20)obtained by CO_(2) mineralization was 14.9 MPa in maximum compressive strength,increasing by 32.2%compared to the non-mineralized material.The prepared filling material exhibits excellent CO_(2) sequestration capacity(i.e.,14.4 kg·t^(−1) in maximum amount of CO_(2) sequestration).According to the analysis of carbon sequestration potential,in China,the annual production of FA,CS,and RM is approximately 899,30,and 107 Mt,respectively in the year of 2023.The utilization of FA,CS,and RM individually can achieve carbon emission reductions of 3.42,10.78,and 0.61 Mt,respectively.The composite solid waste(FA-CS-RM)mineralized with CO_(2) can achieve 1.23 Mt in carbon emissions reduction.Additionally,taking Yellow River Basin of China as a case study,the total volume of underground space in coal mine goafs from 2016 to 2030 is estimated at 8.16 Gm3,indicating that this technology can sequester 0.18 Gt of CO_(2).This approach offers a promising solution for large-scale flue gas CO_(2) sequestration,recycling coal-based solid wastes,and remediating coal mine goafs,contributing to green utilization of coal and the emission reduction of carbon.展开更多
In order to reduce the risk of spontaneous combustion in goaf during goaf excavation process, polymer modified cement mortar spraying material was used to spray and seal the roadway surface. The experimental applicati...In order to reduce the risk of spontaneous combustion in goaf during goaf excavation process, polymer modified cement mortar spraying material was used to spray and seal the roadway surface. The experimental application was carried out in the upper channel 2304 of a mine in Henan Province. The test results showed that polymer modified cement mortar spraying material could effectively support the roadway and greatly reduce the deformation rate of the roadway. The best spraying thickness is 5 mm. Through the monitoring of tunnel air leakage, it is concluded that the polymer modified cement mortar spraying material can reduce the tunnel air leakage and play a better sealing effect.展开更多
A Bayes discriminant analysis method to identify the risky of complicated goaf in mines was presented. Nine factors influencing the stability of goaf risky, including uniaxial compressive strength of rock, elastic mod...A Bayes discriminant analysis method to identify the risky of complicated goaf in mines was presented. Nine factors influencing the stability of goaf risky, including uniaxial compressive strength of rock, elastic modulus of rock, rock quality designation （RQD）, area ratio of pillar, ratio of width to height of pillar, depth of ore body, volume of goaf, dip of ore body and area of goal, were selected as discriminant indexes in the stability analysis of goal. The actual data of 40 goals were used as training samples to establish a discriminant analysis model to identify the stability of goaf. The results show that this discriminant analysis model has high precision and misdiscriminant ratio is 0.025 in re-substitution process. The instability identification of a metal mine was distinguished by using this model and the identification result is identical with that of practical situation.展开更多
An integration processing system of three-dimensional laser scanning information visualization in goaf was developed. It is provided with multiple functions, such as laser scanning information management for goaf, clo...An integration processing system of three-dimensional laser scanning information visualization in goaf was developed. It is provided with multiple functions, such as laser scanning information management for goaf, cloud data de-noising optimization, construction, display and operation of three-dimensional model, model editing, profile generation, calculation of goaf volume and roof area, Boolean calculation among models and interaction with the third party soft ware. Concerning this system with a concise interface, plentiful data input/output interfaces, it is featured with high integration, simple and convenient operations of applications. According to practice, in addition to being well-adapted, this system is favorably reliable and stable.展开更多
In order to simulate field distribution rules,mathematical models for 3-D air flows and gas transfer in the goaf of the coal mining are established,based on theories of permeability and dynamic dispersion through poro...In order to simulate field distribution rules,mathematical models for 3-D air flows and gas transfer in the goaf of the coal mining are established,based on theories of permeability and dynamic dispersion through porous media. A gas dispersion equation in a 3-D field is calculated by use of numerical method on a weighted upstream multi-element balance. Based on data of an example with a U type ventilation mode,surface charts of air pressure distribution and gas concentration are drawn by Graphtool software. Finally,a comparison between actually measured results in the model test and the numerical simulation results is made to proves the numerical implementation feasible.展开更多
CFD models have been developed to investigate the Iongwall goaf gas flow patternsunder different mining and geological control conditions.The Iongwall goaf wastreated as porous regions and gas flow was modelled as a m...CFD models have been developed to investigate the Iongwall goaf gas flow patternsunder different mining and geological control conditions.The Iongwall goaf wastreated as porous regions and gas flow was modelled as a momentum sink added to themomentum equation.Gas desorption from the caved goaf and destressed coal seamswithin the mining disturbed area was modelled as additional mass sources in the continuityequation.These CFD models were developed according to specific Iongwall layoutsand calibrated against field monitoring data.Two case studies were presented demonstratingthe application of CFD modelling of goaf gas flow characteristics for improved goafgas capture and the reduction of oxygen ingress into the goaf areas for self-heating prevention.Results from the case studies indicate that the optimum goaf drainage strategywould be a combination of shallow (near the face) and deep holes to improve the overalldrainage efficiency and gas purity.For gassy Iongwall faces retreating against the seam dip,it is recommended to conduct cross-measure roof hole drainage targeting the fracturedzones overlying the return corner,rather than high capacity surface goaf drainage deep inthe goaf.展开更多
An approach which combines particle swarm optimization and support vector machine(PSO–SVM)is proposed to forecast large-scale goaf instability(LSGI).Firstly,influencing factors of goaf safety are analyzed,and followi...An approach which combines particle swarm optimization and support vector machine(PSO–SVM)is proposed to forecast large-scale goaf instability(LSGI).Firstly,influencing factors of goaf safety are analyzed,and following parameters were selected as evaluation indexes in the LSGI:uniaxial compressive strength(UCS)of rock,elastic modulus(E)of rock,rock quality designation(RQD),area ration of pillar(Sp),the ratio of width to height of the pillar(w/h),depth of ore body(H),volume of goaf(V),dip of ore body(a)and area of goaf(Sg).Then LSGI forecasting model by PSO-SVM was established according to the influencing factors.The performance of hybrid model(PSO+SVM=PSO–SVM)has been compared with the grid search method of support vector machine(GSM–SVM)model.The actual data of 40 goafs are applied to research the forecasting ability of the proposed method,and two cases of underground mine are also validated by the proposed model.The results indicated that the heuristic algorithm of PSO can speed up the SVM parameter optimization search,and the predictive ability of the PSO–SVM model with the RBF kernel function is acceptable and robust,which might hold a high potential to become a useful tool in goaf risky prediction research.展开更多
The research about subsurface characteristics by using transient electromagnetic method（TEM） and high density resistivity method（HDRM） were already conducted in Ordos. The objective of this research is to detect c...The research about subsurface characteristics by using transient electromagnetic method（TEM） and high density resistivity method（HDRM） were already conducted in Ordos. The objective of this research is to detect coalmine goaf areas based on rock resistivity. The data processing using wavelet transform, three point smoothing, RES2 DINV and Maxwell processing software to obtain 2D resistivity structure. The results showed that the layers with maximum resistivity values（30e33 U m on Line 1, 30e31 U m on Line 2, 32e40 U m on Line3） are founded at station 1e7, and 14e20 on Line 1,13e18 on Line 2, and 8e13 and 16e20 on Line 3 which is predicted as goaf layer, and the minimum resistivity values（20e26 U m of TEM, 45e75 U m of HDRM） at the other layers. This resistivity difference was caused by the geology and characteristics of the study area which is located close by the cleugh with rich coal, so the goaf area distinguishable with aquifer layer and coal seam. The results were also significant accidents and serious destruction of ecological environment.展开更多
While the fully-mechanized longwall mining technology was employed in a shallow seam under a room mining goaf and overlained by thin bedrock and thick loose sands, the roadway pillars in the abandoned room mining goaf...While the fully-mechanized longwall mining technology was employed in a shallow seam under a room mining goaf and overlained by thin bedrock and thick loose sands, the roadway pillars in the abandoned room mining goaf were in a stress-concentrated state, which may cause abnormal roof weighting, violent ground pressure behaviours, even roof fall and hydraulic support crushed(HSC) accidents. In this case,longwall mining safety and efficiency were seriously challenged. Based on the HSC accidents occurred during the longwall mining of 3-1-2 seam, which locates under the intersection zone of roadway pillars in the room mining goaf of 3-1-1 seam, this paper employed ground rock mechanics to analyse the overlying strata structure movement rules and presented the main influence factors and determination methods for the hydraulic support working resistance. The FLAC3 D software was used to simulate the overlying strata stress and plastic zone distribution characteristics. Field observation was implemented to contrastively analyse the hydraulic support working resistance distribution rules under the roadway pillars in strike direction, normal room mining goaf, roadway pillars in dip direction and intersection zone of roadway pillars. The results indicate that the key strata break along with rotations and reactions of the coal pillars deliver a larger concentrated load to the hydraulic support under intersection zone of roadway pillars than other conditions. The ‘‘overburden strata-key strata-roadway pillars-immediate roof" integrated load has exceeded the yield load that leads to HSC accidents. Findings in HSC mechanism provide a reasonable basis for shallow seam mining, and have important significance for the implementation of safe and efficient mining.展开更多
The full-space transient electromagnetic response of water-filled goaves in coal mines were numerically modeled. Traditional numerical modeling methods cannot be used to simulate the underground full-space transient e...The full-space transient electromagnetic response of water-filled goaves in coal mines were numerically modeled. Traditional numerical modeling methods cannot be used to simulate the underground full-space transient electromagnetic field. We used multiple transmitting loops instead of the traditional single transmitting loop to load the transmitting loop into Cartesian grids. We improved the method for calculating the z-component of the magnetic field based on the characteristics of full space. Then, we established the full- space 3D geoelectrical model using geological data for coalmines. In addition, the transient electromagnetic responses of water-filled goaves of variable shape at different locations were simulated by using the finite-difference time-domain （FDTD） method. Moreover, we evaluated the apparent resistivity results. The numerical modeling results suggested that the resistivity differences between the coal seam and its roof and floor greatly affect the distribution of apparent resistivity, resulting in nearly circular contours with the roadway head at the center. The actual distribution of apparent resistivity for different geoelectrical models of water in goaves was consistent with the models. However, when the goal water was located in one side, a false low-resistivity anomaly would appear on the other side owing to the full-space effect but the response was much weaker. Finally, the modeling results were subsequently confirmed by drilling, suggesting that the proposed method was effective.展开更多
Underground gassy longwall mining goafs may suffer potential gas explosions during the mining process because of the irregularity of gas emissions in the goaf and poor ventilation of the working face,which are risks d...Underground gassy longwall mining goafs may suffer potential gas explosions during the mining process because of the irregularity of gas emissions in the goaf and poor ventilation of the working face,which are risks difficult to control.In this work,the 3235 working face of the Xutuan Colliery in Suzhou City,China,was researched as a case study.The effects of air quantity and gas emission on the three-dimensional distribution of oxygen and methane concentration in the longwall goaf were studied.Based on the revised Coward’s triangle and linear coupling region formula,the coupled methane-oxygen explosive hazard zones(CEHZs)were drawn.Furthermore,a simple practical index was proposed to quantitatively determine the gas explosion risk in the longwall goaf.The results showed that the CEHZs mainly focus on the intake side where the risk of gas explosion is greatest.The CEHZ is reduced with increasing air quantity.Moreover,the higher the gas emission,the larger the CEHZ,which moves towards the intake side at low goaf heights and shifts to the deeper parts of the goaf at high heights.In addition,the risk of gas explosion is reduced as air quantities increase,but when gas emissions increase to a higher level(greater than 50 m3/min),the volume of the CEHZ does not decrease with the increase of air quantity,and the risk of gas explosion no longer shows a linear downward trend.This study is of significance as it seeks to reduce gas explosion accidents and improve mine production safety.展开更多
The ultimately exposed roof area(UERA)of goaf is crucial to the safety and economics of underground mining.The prediction models do not consider the mechanical weakness of rock mass and ignore the influence of the joi...The ultimately exposed roof area(UERA)of goaf is crucial to the safety and economics of underground mining.The prediction models do not consider the mechanical weakness of rock mass and ignore the influence of the joint damage factor,causing a large predicted exposure area with a high roof falling risk.This work adopted joint damage factor to derive a new UERA prediction model.The relationships between the UERA(S)and the span ratio(m),the density(k)and the diameter of fracture(d)were analysed by the new prediction model.The results showed that the exposed area S and the span ratio m have a U-shaped curve relationship.The S decreases with the increase of m and then increases when m is beyond 2.The exposed roof area S is in an inversely proportional power-law relationship with the fracture surface density k,and the curvature of the S-k relationship curve decreases when d=0.5 and k>7,and S is close to 0.There is a negative correlation between S and the fracture surface diameter d,the curvature of the S-d curve decreases with the increase of d and k,and the variation rate increases first and then decreases with the increase of d;when k=0.5 and d>9,S is close to 0.The predicted values of the UERA prediction model are 119.3,112.8,and 114.6 m2 with different joint damage parameters,which are slightly smaller than the actual critical exposure area of a roof(S=120 m2).The case study shows that the alternative prediction model is reasonable and acceptable and provides new theoretical support for the underground mining safety of sedimentary bauxite ore.展开更多
In exploiting shallow coal resources in western China, conservation of water resources is often subjugated to considerations of safety and production in coal mines. In order to maintain a sustainable development in th...In exploiting shallow coal resources in western China, conservation of water resources is often subjugated to considerations of safety and production in coal mines. In order to maintain a sustainable development in the Shenfu-Dongsheng coalfield, we propose a technology of constructing groundwater reservoirs in goafs in shallow coalfields to protect fragile ecological environments. Given the premise of safe production, we selected an appropriate goaf as the site for constructing a groundwater reservoir and used a mine water recharge technique in combination with other related techniques for effective water conservation. Then filtering and purification techniques were used to purify the mine water given the physical and chemical properties of mine water and its filling material, ,thereby greatly reducing suspended matter, calcium and other harmful ions in the water. With the potential of widely application, the research result has been successfully applied in the Daliuta coal mine, to great economic and ecological effect. Therefore, this achievement provides a new way for mine water conservation in shallow coal resources in western China.展开更多
Based on the classical static theory and static numerical simulation,the static method could not accurately reflect the stability of goaf where the rocks on the pillar and roof are influenced by Theological and blasti...Based on the classical static theory and static numerical simulation,the static method could not accurately reflect the stability of goaf where the rocks on the pillar and roof are influenced by Theological and blasting disturbance for a long time.According to the test from the site,an experimental study was made in Theological and dynamic disturbance.After that,on the basis of variable rock mechanics parameters from the experimental data,numerical simulation was used to analyze the vertical stress distribution of goaf,vertical displacement and plastic area of roof in the "deterioration" caused by Theological and blasting,which shows that the mechanics properties of the rock were greatly influenced by Theological,and dynamic disturbance.The results of the experimental study and numerical simulation show that the mechanics properties of rock are greatly influenced by Theological and dynamic disturbance.As a result,the stability of goaf is greatly reduced.Finally,by comparing golf monitoring results with the analysis of theoretical calculation,it was found that the results were approximately the same,which testifies the reliability of the method.This method provides a new way of studying the stability of goaf as well as laying a basic foundation for future safety management.展开更多
The concept of the carbon cycle in the old goaf of a coal mine based on CO_(2)utilization and storage was put forward adhering to the principle of low-carbon development,utilization of space resources in old goafs,and...The concept of the carbon cycle in the old goaf of a coal mine based on CO_(2)utilization and storage was put forward adhering to the principle of low-carbon development,utilization of space resources in old goafs,and associated gas resources development.Firstly,the evolution characteristics of overburden fissures in the goaf of the case was studied using a two-dimensional physical similarity simulation test,the sealing performance of the caprocks after stabilization was analyzed,and the fissures were counted and classi-fied.Then,the process of gaseous CO_(2)injection in the connected fissure was simulated by Ansys Fluent software,and the migration law and distribution characteristics of CO_(2)under the condition of gaseous CO_(2)injection were analyzed.Finally,the estimation models of free CO_(2)storage capacity in the old goaf were constructed considering the proportion of connected fissure and the effectiveness of CO_(2)injection.The CO_(2)storage capacity in the old goaf of the case coal mine was estimated.The results showed that a caprock group of“hard-thickness low-permeability hard-thickness”was formed after the caprock-fissures system in the goaf of the case tended to be stable vertically.The connected fissure,occlude cracks,and micro-fractures in the goaf accounted for 85.5%,8.5%,and 6%of the total fissures,respectively.Gaseous CO_(2)first migrated to the bottom of the connected fissure after CO_(2)was injected into the goaf,then spread horizontally along the bottom of the connected fissure after reaching the bottom,and finally spread longitudinally after filling the bottom of the entire connected fissure.The theoretical and effective storage capacities of free CO_(2)at normal temperature and pressure in the old goaf of the case were 9757 and 7477 t,respectively.The effective storage capacity of free CO_(2)at normal temperature and pressure in the old goaf after all minefield mined was 193404 t.The research can provide some reference for the coal mining industry to help the goal of“carbon peaking and carbon neutrality”.展开更多
In order to precisely predict the hazard degree of goaf(HDG), the RS-TOPSIS model was built based on the results of expert investigation. To evaluate the HDG in the underground mine, five structure size factors, i.e. ...In order to precisely predict the hazard degree of goaf(HDG), the RS-TOPSIS model was built based on the results of expert investigation. To evaluate the HDG in the underground mine, five structure size factors, i.e. goaf span, exposed area, goaf height, goaf depth, and pillar width, were selected as the evaluation indexes. And based on rough dependability in rough set(RS)theory, the weights of evaluation indexes were identified by calculating rough dependability between evaluation indexes and evaluation results. Fourty goafs in some mines of western China, whose indexes parameters were measured by cavity monitoring system(CMS), were taken as evaluation objects. In addition, the characteristic parameters of five grades' typical goafs were built according to the interval limits value of single index evaluation. Then, using the technique for order preference by similarity to ideal solution(TOPSIS), five-category classification of HDG was realized based on closeness degree, and the HDG was also identified.Results show that the five-category identification of mine goafs could be realized by RS-TOPSIS method, based on the structure-scale-effect. The classification results are consistent with those of numerical simulation based on stress and displacement,while the coincidence rate is up to 92.5%. Furthermore, the results are more conservative to safety evaluation than numerical simulation, thus demonstrating that the proposed method is more easier, reasonable and more definite for HDG identification.展开更多
基金Science and Technology Major Project of Xinjiang Uygur Autonomous Region(2020A03003-7)Fundamental Research on Natural Science Program of Shaanxi Province(2021JM-180)+2 种基金Fundamental Research Funds for the Central Universities,CHD(Project for Leading Talents)(300102211302)Tianshan Cedar Plan of Science and Technology Department of Xinjiang Uygur Autonomous Region(2017XS13)Shaanxi Province Young Talent Lifting Program(CLGC202219).
文摘When the expressway crosses the goafs inevitably,the design is generally to build the road on coal pillars as much as possible.However,the existing coal pillars are often unable to meet relevant requirements of highway construction.Combining three-dimensional physical model tests,numerical simulations and field monitoring,with the Urumqi East Second Ring Road passing through acute inclined goafs as a background,the deformation and failure mechanism of the overlying rock and coal pillars in acute inclined goafs under expressway load were studied.And in accordance with construction requirements of subgrade,comprehensive consideration of the deformation and instability mechanism of acute inclined goafs,the treatment measures and suggestions for this type of geological disasters were put forward.The research results confirmed the rationality of coal pillars in acute inclined goafs under the expressway through grouting.According to the ratio of diff erent overlying rock thickness to coal pillar height,the change trend and value of the required grouting range were summarized,which can provide reference for similar projects.
基金support from the Natural Science Foundation of Jiangsu Province(Grant No.BK20242059)the Collaborative Innovation Center for Prevention and Control of Mountain Geological Hazards of Zhejiang Province(PCMGH-2023-02)the opening fund of State Key Laboratory of Coal Mine Disaster Dynamics and Control(2011DA105827-FW202209)are gratefully acknowledged.
文摘The stability and fracture behavior of a goaf roof beneath an open-pit bench are critical concerns,especially under impact loading.However,the effect of the thickness-to-span ratio on dynamic failure modes remains largely unexplored,as existing research focuses mainly on static stability.Energy dissipation and instability evolution under impact loading require further study.To address this gap,this study conducts drop-weight impact experiments on specimens with circular perforations,complemented by numerical simulations.By integrating dimensional analysis,cusp catastrophe theory,and strength reduction techniques,the dynamic instability mechanism of goaf roofs with varying thickness-to-span ratios is revealed.Results show that the thickness-to-span ratio significantly influences energy accumulation and dissipation during roof failure.A higher ratio increases both the magnitude and rate of energy dissipation,particularly during crack initiation and stable propagation,while its impact diminishes in the final failure stage.Optimizing the thickness-to-span ratio within a critical range enhances structural stability,improving the safety factor by up to 83%.However,beyond a certain threshold,additional thickness yields diminishing benefits.This study provides new insights into the energy-based instability mechanism of goaf roofs under impact loads,establishing a theoretical foundation for early warning systems and optimized safety design.
文摘China has a long history of coal mining,among which open-pit coal mines have a large number of small coal mine goafs underground.The distribution,shape,structure and other characteristics of goafs are isolated and discontinuous,and there is no definite geological law to follow,which seriously threatens the safety of coal mine production and personnel life.Conventional ground geophysical methods have low accuracy in detecting goaf areas affected by mechanical interference from open-pit mines,especially for waterless goaf areas,which cannot be detected by existing methods.This article proposes the use of high-frequency electromagnetic waves for goaf detection.The feasibility of using drilling radar to detect goaf was theoretically analyzed,and a goaf detection model was established.The response characteristics of different fillers in the goaf under different frequencies of high-frequency electromagnetic waves were simulated and analyzed.In a certain open-pit mine in Inner Mongolia,100MHz high-frequency electromagnetic waves were used to detect the goaf through directional drilling on the ground.After detection,excavation verification was carried out,and the location of one goaf detected was verified.The results of engineering practice show that the application of high-frequency electromagnetic waves in goaf detection expands the detection radius of boreholes,has the advantages of high efficiency and accuracy,and has important theoretical and practical significance.
文摘China,as the world’s largest coal producer and consumer,faces increasingly severe challenges from coal mine goaf areas formed through decades of intensive mining.These underground voids,resulting from exhausted resources or technical limitations,not only cause environmental issues like land subsidence and groundwater contamination but also pose critical safety risks for ongoing mining operations,including water inrushes,gas outbursts,and roof collapses.Conventional geophysical methods such as seismic surveys and electromagnetic detection demonstrate limited effectiveness in complex geological conditions due to susceptibility to electrical heterogeneity,electromagnetic interference,and interpretation ambiguities.This study presents an innovative integrated approach combining the Audio-Frequency Electrical Transillumination(AFET)method with multi-parameter borehole logging to establish a three-dimensional detection system.The AFET technique employs 0.1–10 kHz electromagnetic waves to identify electrical anomalies associated with goafs,enabling extensive horizontal scanning.This is complemented by vertical high-resolution profiling through borehole measurements of resistivity,spontaneous potential,and acoustic velocity.Field applications in Shanxi Province’s typical coal mines achieved breakthrough results:Using a grid-drilling pattern(15 m spacing,300 m depth),the method successfully detected three concealed goafs missed by conventional approaches,with spatial positioning errors under 0.5 m.Notably,it accurately identified two un-collapsed water-filled cavities.This surface-borehole synergistic approach overcomes single-method limitations,enhancing goaf detection accuracy to over 92%.The technique provides reliable technical support for safe mining practices and represents significant progress in precise detection of hidden geological hazards in Chinese coal mines,offering valuable insights for global mining geophysics.
基金supported by the National Natural Science Foundation of China(U21A20321 and 22378241)Research Project Supported by Shanxi Scholarship Council of China(2024-015).
文摘Coal is an essential component of global energy;however,the processes of coal mining and utilization produce significant amounts of coal mine goafs,accompanied by coal-based solid wastes and emitted CO_(2),resulting in severe ecological and environmental challenges.In response to this issue,this study pro-poses a novel approach for filling coal mine goafs using cementitious materials prepared by coal-based solid wastes mineralized with CO_(2)(15%in concentration).The CO_(2) sequestration capacities of individual solid wastes are ranked as follows:carbide slag(CS)>red mud(RM)>fly ash(FA).The performance of filling material prepared from composite solid waste(FA-CS-RM)mineralized with CO_(2) meets the filling requirements of goaf.The filling material(F60C20R20)obtained by CO_(2) mineralization was 14.9 MPa in maximum compressive strength,increasing by 32.2%compared to the non-mineralized material.The prepared filling material exhibits excellent CO_(2) sequestration capacity(i.e.,14.4 kg·t^(−1) in maximum amount of CO_(2) sequestration).According to the analysis of carbon sequestration potential,in China,the annual production of FA,CS,and RM is approximately 899,30,and 107 Mt,respectively in the year of 2023.The utilization of FA,CS,and RM individually can achieve carbon emission reductions of 3.42,10.78,and 0.61 Mt,respectively.The composite solid waste(FA-CS-RM)mineralized with CO_(2) can achieve 1.23 Mt in carbon emissions reduction.Additionally,taking Yellow River Basin of China as a case study,the total volume of underground space in coal mine goafs from 2016 to 2030 is estimated at 8.16 Gm3,indicating that this technology can sequester 0.18 Gt of CO_(2).This approach offers a promising solution for large-scale flue gas CO_(2) sequestration,recycling coal-based solid wastes,and remediating coal mine goafs,contributing to green utilization of coal and the emission reduction of carbon.
文摘In order to reduce the risk of spontaneous combustion in goaf during goaf excavation process, polymer modified cement mortar spraying material was used to spray and seal the roadway surface. The experimental application was carried out in the upper channel 2304 of a mine in Henan Province. The test results showed that polymer modified cement mortar spraying material could effectively support the roadway and greatly reduce the deformation rate of the roadway. The best spraying thickness is 5 mm. Through the monitoring of tunnel air leakage, it is concluded that the polymer modified cement mortar spraying material can reduce the tunnel air leakage and play a better sealing effect.
基金Project (2010CB732004) supported by the National Basic Research Program of China
文摘A Bayes discriminant analysis method to identify the risky of complicated goaf in mines was presented. Nine factors influencing the stability of goaf risky, including uniaxial compressive strength of rock, elastic modulus of rock, rock quality designation （RQD）, area ratio of pillar, ratio of width to height of pillar, depth of ore body, volume of goaf, dip of ore body and area of goal, were selected as discriminant indexes in the stability analysis of goal. The actual data of 40 goals were used as training samples to establish a discriminant analysis model to identify the stability of goaf. The results show that this discriminant analysis model has high precision and misdiscriminant ratio is 0.025 in re-substitution process. The instability identification of a metal mine was distinguished by using this model and the identification result is identical with that of practical situation.
基金Project(51274250)supported by the National Natural Science Foundation of ChinaProject(2012BAK09B02-05)supported by the National Key Technology R&D Program during the 12th Five-year Plan of China
文摘An integration processing system of three-dimensional laser scanning information visualization in goaf was developed. It is provided with multiple functions, such as laser scanning information management for goaf, cloud data de-noising optimization, construction, display and operation of three-dimensional model, model editing, profile generation, calculation of goaf volume and roof area, Boolean calculation among models and interaction with the third party soft ware. Concerning this system with a concise interface, plentiful data input/output interfaces, it is featured with high integration, simple and convenient operations of applications. According to practice, in addition to being well-adapted, this system is favorably reliable and stable.
基金Projects 50534090 and 50674090 supported by the National Natural Science Foundation of China2005CB221503 by the National Key Basic ResearchDevelopment Program (973 Program)
文摘In order to simulate field distribution rules,mathematical models for 3-D air flows and gas transfer in the goaf of the coal mining are established,based on theories of permeability and dynamic dispersion through porous media. A gas dispersion equation in a 3-D field is calculated by use of numerical method on a weighted upstream multi-element balance. Based on data of an example with a U type ventilation mode,surface charts of air pressure distribution and gas concentration are drawn by Graphtool software. Finally,a comparison between actually measured results in the model test and the numerical simulation results is made to proves the numerical implementation feasible.
文摘CFD models have been developed to investigate the Iongwall goaf gas flow patternsunder different mining and geological control conditions.The Iongwall goaf wastreated as porous regions and gas flow was modelled as a momentum sink added to themomentum equation.Gas desorption from the caved goaf and destressed coal seamswithin the mining disturbed area was modelled as additional mass sources in the continuityequation.These CFD models were developed according to specific Iongwall layoutsand calibrated against field monitoring data.Two case studies were presented demonstratingthe application of CFD modelling of goaf gas flow characteristics for improved goafgas capture and the reduction of oxygen ingress into the goaf areas for self-heating prevention.Results from the case studies indicate that the optimum goaf drainage strategywould be a combination of shallow (near the face) and deep holes to improve the overalldrainage efficiency and gas purity.For gassy Iongwall faces retreating against the seam dip,it is recommended to conduct cross-measure roof hole drainage targeting the fracturedzones overlying the return corner,rather than high capacity surface goaf drainage deep inthe goaf.
基金supported by the National Basic Research Program Project of China(No.2010CB732004)the National Natural Science Foundation Project of China(Nos.50934006 and41272304)+2 种基金the Graduated Students’ResearchInnovation Fund Project of Hunan Province of China(No.CX2011B119)the Scholarship Award for Excellent Doctoral Student of Ministry of Education of China and the Valuable Equipment Open Sharing Fund of Central South University(No.1343-76140000022)
文摘An approach which combines particle swarm optimization and support vector machine(PSO–SVM)is proposed to forecast large-scale goaf instability(LSGI).Firstly,influencing factors of goaf safety are analyzed,and following parameters were selected as evaluation indexes in the LSGI:uniaxial compressive strength(UCS)of rock,elastic modulus(E)of rock,rock quality designation(RQD),area ration of pillar(Sp),the ratio of width to height of the pillar(w/h),depth of ore body(H),volume of goaf(V),dip of ore body(a)and area of goaf(Sg).Then LSGI forecasting model by PSO-SVM was established according to the influencing factors.The performance of hybrid model(PSO+SVM=PSO–SVM)has been compared with the grid search method of support vector machine(GSM–SVM)model.The actual data of 40 goafs are applied to research the forecasting ability of the proposed method,and two cases of underground mine are also validated by the proposed model.The results indicated that the heuristic algorithm of PSO can speed up the SVM parameter optimization search,and the predictive ability of the PSO–SVM model with the RBF kernel function is acceptable and robust,which might hold a high potential to become a useful tool in goaf risky prediction research.
基金supported by the Institute of Seismology Foundation, China Earthquake Administration (201326126)
文摘The research about subsurface characteristics by using transient electromagnetic method（TEM） and high density resistivity method（HDRM） were already conducted in Ordos. The objective of this research is to detect coalmine goaf areas based on rock resistivity. The data processing using wavelet transform, three point smoothing, RES2 DINV and Maxwell processing software to obtain 2D resistivity structure. The results showed that the layers with maximum resistivity values（30e33 U m on Line 1, 30e31 U m on Line 2, 32e40 U m on Line3） are founded at station 1e7, and 14e20 on Line 1,13e18 on Line 2, and 8e13 and 16e20 on Line 3 which is predicted as goaf layer, and the minimum resistivity values（20e26 U m of TEM, 45e75 U m of HDRM） at the other layers. This resistivity difference was caused by the geology and characteristics of the study area which is located close by the cleugh with rich coal, so the goaf area distinguishable with aquifer layer and coal seam. The results were also significant accidents and serious destruction of ecological environment.
基金financially supported by the Fundamental Research Funds for the Central Universities of China(NO.2015XKMS002)the Priority Academic Program Development of Jiangsu Higher Education Institutions of Chinagratefully acknowledge financial support of the above-mentioned agencies
文摘While the fully-mechanized longwall mining technology was employed in a shallow seam under a room mining goaf and overlained by thin bedrock and thick loose sands, the roadway pillars in the abandoned room mining goaf were in a stress-concentrated state, which may cause abnormal roof weighting, violent ground pressure behaviours, even roof fall and hydraulic support crushed(HSC) accidents. In this case,longwall mining safety and efficiency were seriously challenged. Based on the HSC accidents occurred during the longwall mining of 3-1-2 seam, which locates under the intersection zone of roadway pillars in the room mining goaf of 3-1-1 seam, this paper employed ground rock mechanics to analyse the overlying strata structure movement rules and presented the main influence factors and determination methods for the hydraulic support working resistance. The FLAC3 D software was used to simulate the overlying strata stress and plastic zone distribution characteristics. Field observation was implemented to contrastively analyse the hydraulic support working resistance distribution rules under the roadway pillars in strike direction, normal room mining goaf, roadway pillars in dip direction and intersection zone of roadway pillars. The results indicate that the key strata break along with rotations and reactions of the coal pillars deliver a larger concentrated load to the hydraulic support under intersection zone of roadway pillars than other conditions. The ‘‘overburden strata-key strata-roadway pillars-immediate roof" integrated load has exceeded the yield load that leads to HSC accidents. Findings in HSC mechanism provide a reasonable basis for shallow seam mining, and have important significance for the implementation of safe and efficient mining.
基金supported by the National Key Scientific Instrument and Equipment Development Project(No.2011YQ03013307)the Project Funded by the Priority Academic Program Development of Jiangsu Higher Education InstitutionsKey Laboratory of Coal Resources Exploration and Comprehensive Utilization,Ministry of Land and Resources
文摘The full-space transient electromagnetic response of water-filled goaves in coal mines were numerically modeled. Traditional numerical modeling methods cannot be used to simulate the underground full-space transient electromagnetic field. We used multiple transmitting loops instead of the traditional single transmitting loop to load the transmitting loop into Cartesian grids. We improved the method for calculating the z-component of the magnetic field based on the characteristics of full space. Then, we established the full- space 3D geoelectrical model using geological data for coalmines. In addition, the transient electromagnetic responses of water-filled goaves of variable shape at different locations were simulated by using the finite-difference time-domain （FDTD） method. Moreover, we evaluated the apparent resistivity results. The numerical modeling results suggested that the resistivity differences between the coal seam and its roof and floor greatly affect the distribution of apparent resistivity, resulting in nearly circular contours with the roadway head at the center. The actual distribution of apparent resistivity for different geoelectrical models of water in goaves was consistent with the models. However, when the goal water was located in one side, a false low-resistivity anomaly would appear on the other side owing to the full-space effect but the response was much weaker. Finally, the modeling results were subsequently confirmed by drilling, suggesting that the proposed method was effective.
基金the National Key Research and Development Program of China(No.2018YFC0808100)the Fundamental Research Funds for the Central Universities(No.2652018098)the Cultivation Fund from the Key Laboratory of Deep Geodrilling Technology,Ministry of Natural Resources(No.PY201902).
文摘Underground gassy longwall mining goafs may suffer potential gas explosions during the mining process because of the irregularity of gas emissions in the goaf and poor ventilation of the working face,which are risks difficult to control.In this work,the 3235 working face of the Xutuan Colliery in Suzhou City,China,was researched as a case study.The effects of air quantity and gas emission on the three-dimensional distribution of oxygen and methane concentration in the longwall goaf were studied.Based on the revised Coward’s triangle and linear coupling region formula,the coupled methane-oxygen explosive hazard zones(CEHZs)were drawn.Furthermore,a simple practical index was proposed to quantitatively determine the gas explosion risk in the longwall goaf.The results showed that the CEHZs mainly focus on the intake side where the risk of gas explosion is greatest.The CEHZ is reduced with increasing air quantity.Moreover,the higher the gas emission,the larger the CEHZ,which moves towards the intake side at low goaf heights and shifts to the deeper parts of the goaf at high heights.In addition,the risk of gas explosion is reduced as air quantities increase,but when gas emissions increase to a higher level(greater than 50 m3/min),the volume of the CEHZ does not decrease with the increase of air quantity,and the risk of gas explosion no longer shows a linear downward trend.This study is of significance as it seeks to reduce gas explosion accidents and improve mine production safety.
基金This work is supported by the National Natural Science Foundation of China(51974135,51704094)the National Key Research and Development Program of China(2016YFC0600802).
文摘The ultimately exposed roof area(UERA)of goaf is crucial to the safety and economics of underground mining.The prediction models do not consider the mechanical weakness of rock mass and ignore the influence of the joint damage factor,causing a large predicted exposure area with a high roof falling risk.This work adopted joint damage factor to derive a new UERA prediction model.The relationships between the UERA(S)and the span ratio(m),the density(k)and the diameter of fracture(d)were analysed by the new prediction model.The results showed that the exposed area S and the span ratio m have a U-shaped curve relationship.The S decreases with the increase of m and then increases when m is beyond 2.The exposed roof area S is in an inversely proportional power-law relationship with the fracture surface density k,and the curvature of the S-k relationship curve decreases when d=0.5 and k>7,and S is close to 0.There is a negative correlation between S and the fracture surface diameter d,the curvature of the S-d curve decreases with the increase of d and k,and the variation rate increases first and then decreases with the increase of d;when k=0.5 and d>9,S is close to 0.The predicted values of the UERA prediction model are 119.3,112.8,and 114.6 m2 with different joint damage parameters,which are slightly smaller than the actual critical exposure area of a roof(S=120 m2).The case study shows that the alternative prediction model is reasonable and acceptable and provides new theoretical support for the underground mining safety of sedimentary bauxite ore.
基金Projects NCET-05-0480 supported by the New Century Excellent Talents in University50904063 by the National Natural Science Foundation of China+1 种基金07KF09 by the Research Fund of the State Key Laboratory of Coal Resources and Mine Safety of China University of Mining & Technology2008A003 and 2005B002 by the Scientific Research Foundation of China University of Mining & Technology
文摘In exploiting shallow coal resources in western China, conservation of water resources is often subjugated to considerations of safety and production in coal mines. In order to maintain a sustainable development in the Shenfu-Dongsheng coalfield, we propose a technology of constructing groundwater reservoirs in goafs in shallow coalfields to protect fragile ecological environments. Given the premise of safe production, we selected an appropriate goaf as the site for constructing a groundwater reservoir and used a mine water recharge technique in combination with other related techniques for effective water conservation. Then filtering and purification techniques were used to purify the mine water given the physical and chemical properties of mine water and its filling material, ,thereby greatly reducing suspended matter, calcium and other harmful ions in the water. With the potential of widely application, the research result has been successfully applied in the Daliuta coal mine, to great economic and ecological effect. Therefore, this achievement provides a new way for mine water conservation in shallow coal resources in western China.
文摘Based on the classical static theory and static numerical simulation,the static method could not accurately reflect the stability of goaf where the rocks on the pillar and roof are influenced by Theological and blasting disturbance for a long time.According to the test from the site,an experimental study was made in Theological and dynamic disturbance.After that,on the basis of variable rock mechanics parameters from the experimental data,numerical simulation was used to analyze the vertical stress distribution of goaf,vertical displacement and plastic area of roof in the "deterioration" caused by Theological and blasting,which shows that the mechanics properties of the rock were greatly influenced by Theological,and dynamic disturbance.The results of the experimental study and numerical simulation show that the mechanics properties of rock are greatly influenced by Theological and dynamic disturbance.As a result,the stability of goaf is greatly reduced.Finally,by comparing golf monitoring results with the analysis of theoretical calculation,it was found that the results were approximately the same,which testifies the reliability of the method.This method provides a new way of studying the stability of goaf as well as laying a basic foundation for future safety management.
基金the financial support from the National Natural Science Foundation of China(No.52074217)the Natural Science Basic Research Program of Shaanxi Province(No.2021JLM-26).
文摘The concept of the carbon cycle in the old goaf of a coal mine based on CO_(2)utilization and storage was put forward adhering to the principle of low-carbon development,utilization of space resources in old goafs,and associated gas resources development.Firstly,the evolution characteristics of overburden fissures in the goaf of the case was studied using a two-dimensional physical similarity simulation test,the sealing performance of the caprocks after stabilization was analyzed,and the fissures were counted and classi-fied.Then,the process of gaseous CO_(2)injection in the connected fissure was simulated by Ansys Fluent software,and the migration law and distribution characteristics of CO_(2)under the condition of gaseous CO_(2)injection were analyzed.Finally,the estimation models of free CO_(2)storage capacity in the old goaf were constructed considering the proportion of connected fissure and the effectiveness of CO_(2)injection.The CO_(2)storage capacity in the old goaf of the case coal mine was estimated.The results showed that a caprock group of“hard-thickness low-permeability hard-thickness”was formed after the caprock-fissures system in the goaf of the case tended to be stable vertically.The connected fissure,occlude cracks,and micro-fractures in the goaf accounted for 85.5%,8.5%,and 6%of the total fissures,respectively.Gaseous CO_(2)first migrated to the bottom of the connected fissure after CO_(2)was injected into the goaf,then spread horizontally along the bottom of the connected fissure after reaching the bottom,and finally spread longitudinally after filling the bottom of the entire connected fissure.The theoretical and effective storage capacities of free CO_(2)at normal temperature and pressure in the old goaf of the case were 9757 and 7477 t,respectively.The effective storage capacity of free CO_(2)at normal temperature and pressure in the old goaf after all minefield mined was 193404 t.The research can provide some reference for the coal mining industry to help the goal of“carbon peaking and carbon neutrality”.
基金Project(51074178)supported by the National Natural Science Foundation of ChinaProject(2011ssxt274)supported by the Graduated Students’ Research and Innovation Foundation of Central South University of China+1 种基金Project(2011QNZT087)supported by the Graduated Students’ Free Exploration Foundation of Central South University of ChinaProject(1343-76140000011)supported by Scholarship Award for Excellent Doctoral Student granted by Ministry of Education,China
文摘In order to precisely predict the hazard degree of goaf(HDG), the RS-TOPSIS model was built based on the results of expert investigation. To evaluate the HDG in the underground mine, five structure size factors, i.e. goaf span, exposed area, goaf height, goaf depth, and pillar width, were selected as the evaluation indexes. And based on rough dependability in rough set(RS)theory, the weights of evaluation indexes were identified by calculating rough dependability between evaluation indexes and evaluation results. Fourty goafs in some mines of western China, whose indexes parameters were measured by cavity monitoring system(CMS), were taken as evaluation objects. In addition, the characteristic parameters of five grades' typical goafs were built according to the interval limits value of single index evaluation. Then, using the technique for order preference by similarity to ideal solution(TOPSIS), five-category classification of HDG was realized based on closeness degree, and the HDG was also identified.Results show that the five-category identification of mine goafs could be realized by RS-TOPSIS method, based on the structure-scale-effect. The classification results are consistent with those of numerical simulation based on stress and displacement,while the coincidence rate is up to 92.5%. Furthermore, the results are more conservative to safety evaluation than numerical simulation, thus demonstrating that the proposed method is more easier, reasonable and more definite for HDG identification.
