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The article addresses a critical and timely issue: improving safety in underground coal mining. The primary objective of the paper was to develop a research methodology based on modelling studies to identify and assess the state of methane hazards during mining operations. To achieve this, structural modelling of the physical and chemical phenomena occurring in mining regions was conducted using Computational Fluid Dynamics. The core research was performed using the finite volume method on a real longwall exploitation site ventilated by a Y-system. This approach enabled the determination of methane and oxygen concentration distributions in the mining region and goafs, treated as a porous and permeable medium. Based on these findings, potential fire and/or methane explosion hazard zones were identified in the goaf. The model test results underwent a validation process, comparing them with actual measurements. The determined errors were within an acceptable range, confirming the accuracy of the developed model of the mining region and the phenomena within it. Furthermore, the model was used to predict the locations of zones at risk of fire and/or methane explosion in the goafs, particularly in areas with potentially increased gas emissions. The results clearly demonstrate the significant potential of using model studies to diagnose and forecast methane hazards in underground mining operations. Identifying these potential danger zones allows for the implementation of preventive measures to reduce the likelihood of dangerous incidents. [ABSTRACT FROM AUTHOR]

To ensure the construction and operational safety of tunnel undercrossing multi-situational goafs, the Huaying Mountain High-Speed Rail Tunnel, a critical section of the Xi'an-Chongqing High-Speed Railway, was taken as a case study. Based on a three-dimensional finite difference numerical simulation platform, twelve situations were established to analyze the effects of three factors: distance, scale, and angle. The stability analysis was conducted by examining the displacement and deformation characteristics of the surrounding rock, stress changes, and axial forces of the initial support for each situation. The results show that in tunnel undercrossing multi-situational goafs, the vertical deformation, horizontal convergence of the surrounding rock, and the maximum axial force of initial support are all affected. Within a certain range, changes in distance significantly impact subsidence and settlement deformation of the surrounding rock. However, as the distance increases, the horizontal and vertical displacements of the tunnel and the axial force of the initial support tend to decrease. Conversely, the scale and angle of the goaf have an opposite effect on the surrounding rock: as the scale and angle increase, the stability of the surrounding rock deteriorates. In this case study, when the distance exceeds 1.13 times the tunnel span, the influence of the goaf on the stability of the surrounding rock gradually decreases. When the angle exceeds 45°, vertical displacement decreases, and the increasing trend of horizontal displacement gradually diminishes. The conclusions of this paper can provide guidance for designing reinforcement schemes for tunnels crossing through multi-situational goafs. The findings provide valuable insights and guidance for similar engineering projects. [ABSTRACT FROM AUTHOR]

Copyright of Coal Science & Technology (0253-2336) is the property of Coal Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Air leakage between goaf and working face increases the risk of spontaneous combustion in goaf, posing a threat to production safety in the working face. The study uses CFD software to simulate the impact of wind speed and goaf depth on the distribution of air leakage, oxygen concentration, and carbon monoxide concentration. It was found that as wind speed increases, the air leakage plume and CO gas concentration move towards the return air side, and the air leakage speed at the working face boundary and tases with depth, and the range of CO distribution and the range of oxygen distribution on the intake side decrease. Based on this, a dynamic measurement method for air leakage is proposed. The error of wind resistance value comparison is within ±5%, indicating the feasibility of dynamic quantitative measurement of the air leakage flow field at the working face, which can improve the accuracy of air leakage measurement in the working face. Then the method was applied in the 509 working face of Ma Di Liang coal mine. The results show that the average air leakage volume in the goaf of the 509 working face is 152.19 m3/min, and the average air leakage velocity is 0.41 m/s. [ABSTRACT FROM AUTHOR]

As the conventional inert gas, it is used for the prevention and control of coal's spontaneous combustion, mainly N2 and CO2. However, there is limited research focusing on the inerting effect of composite inert gas. This paper studied the impact of using a premixed inert gas (N2 accounted for 50%, 60%, 70%, and 80%) instead of CO2 on the inerting effect of nearly horizontal and gently inclined goaf by building a physical similarity simulation experiment platform. The experimental results showed that the inerting effect of premixed inert gas was better than that of CO2. For instance, in a nearly horizontal goaf, the inerting effect of the premixed inert gas was optimal when the N2 accounted for 70%. The average O2 concentration in the monitored area decreased from 9.7% with CO2 to 6.4%. In addition, in the gently inclined goaf, the premixed inert gas exhibited an accumulation state similar to CO2, primarily occurring in the lower part region adjacent to the working face. Furthermore, the accumulation state of premixed inert gas was inversely proportional to its inerting effect. This study has important reference significance for applying inert gas fire prevention and extinguishing technology in mines. [ABSTRACT FROM AUTHOR]

Copyright of Railway Construction Technology is the property of Railway Construction Technology Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Abstract Abandoned coal mine goaf is affected by air leakages and prone to spontaneous combustion, resulting in environmental pollution and geological disasters. Haizhou Open-pit Mine adopts both underground and open-pit mining methods. During the long-term mining process, the original stable stratum structure is constantly destroyed, and the slope slides, increasing cracks and severe air leakage around the goaf and roadway. The spontaneous combustion of coal is particularly prominent after the mine shut down. At present, there is no suitable indirect monitoring method to effectively explore the spontaneous combustion area in goaf. The study developed an all-weather monitoring plan and conducted multi-point continuous long-term measurements of the spontaneous combustion state in one abandoned coal mine goaf located in the eastern part of the Haizhou Open-pit Mine. We evaluated the dynamic correlation between surface CO2 flux (SCF) and changes in the underground fire areas, determined the scope and evolution trend of the fire areas, and identified the distribution and change laws of SCF. The results show a significant positive correlation between SCF and soil temperature; moreover, the SCF value was found to reflect the CO2 emission intensity of the goaf. The high SCF in the test area showed month-wise expansion and increase, while the CO2 emission gradually increased monthly, and the calculated annual total emission was approximately 7017 t. Hence, the study can further provide guidance for the monitoring of spontaneous combustion in shallow coal seams, goaf and the assessment of CO2 emissions from underground coal fires through the on-site monitoring and analysis results.

The success of gangue support in roof cutting and retaining roadway depends on the evolution process of gangue side and its lateral pressure distribution. Based on the engineering background of Xinghua Coal Mine, this paper analyzes the mechanical characteristics of gangue compaction, the roof caving process, and the gangue side evolution process through indoor experiments and similar simulations. The mechanical model is established through theoretical analysis, and the impact of different factors on the lateral pressure of the gangue side is analyzed. The numerical simulation gives the distribution law of the overburden pressure and the lateral pressure of the gangue side at the boundary of the goaf and gives the gangue side support scheme from the perspective of gangue side lateral pressure influencing factors. The research results show that : ①The lateral pressure of the gangue side is related to the evolution process of the gangue in the goaf. In the self-organizing adjustment stage of the gangue, the lateral pressure of the gangue side is mainly generated by the self-weight of the gangue, and the lateral pressure depends on the accumulated height. In the passive compaction stage of gangue, the gangue body is repeatedly compacted under periodic roof pressure, and the lateral pressure of the gangue side gradually increases. In the stable stage of gangue, the gangue body is compacted at this stage, which plays an obvious supporting role in the overburdened rock. The stable value of the overburden pressure is 3.81 MPa, and the stable value of the gangue side lateral pressure is 2.12 MPa. ②From the position of the roof of the roadway to the position of the floor, the lateral pressure of the gangue side gradually increases. ③From the perspective of the external environment, the lateral pressure of the gangue side has a significant positive correlation with the roof overburden pressure and a significant negative correlation with the roof cutting angle. From the perspective of the gangue’s mechanical properties, the gangue side’s lateral pressure and the gangue’s internal friction angle show a significant positive correlation. Consequently, the “bag + net + u-shaped steel + inclined support monomer” gangue retaining support scheme is proposed, and the field application effect is good. This study may provide a reference for similar engineering conditions of gangue support.

Loess has unique physical, hydrodynamic and mechanical properties, which are influenced by both internal and external geological processes, as well as human engineering activities. Consequently, surface disasters are especially prevalent in the Loess region of China. The study area is situated in the middle part of Lüliang Mountain in the middle part of the Loess Plateau, which is characterised by a typical loess landform with a complex system of gullies and hill ridges. According to current theory, the cracking boundary of the goaf profile is a straight line. However, these surface disasters are actually caused by the shear action of the deep rock layer and the original vertical joint structure of the loess. By analysing the cracking process of the ‘Goaf-Overburden-Loess’ section in the study area, it can be found that the boundary of the movement basin section presents a broken line shape, which has important implications for the accurate estimation of the area affected by loess-type surface subsidence.

In order to study the “three zones” of spontaneous combustion in gob under different gas treatment conditions of high gas prone to spontaneous combustion and the change law of temperature field distribution, combined with the actual conditions of a high gas prone to spontaneous combustion working surface, a physical model of spontaneous ignition in goaf with “one face and four lanes” was constructed. The oxidation oxygen consumption and heat release parameters of coal samples obtained from temperature programmed experiment were applied to numerical simulation. The influence of different air supply, low and high pumping flow on the “three zones” of spontaneous combustion and temperature field distribution in goaf was studied. The variation of parameters such as maximum width of oxidation zone, area of oxidation zone and maximum temperature point of goaf with air supply, low and high pumping flow was quantitatively analyzed. The results show that in the range of simulation test, increasing air supply, low pumping flow and high pumping flow will cause the increase of air leakage in goaf, which is not conducive to the prevention and control of spontaneous combustion of coal left in goaf. The maximum temperature point does not change significantly (only within the range of 1K), and the influence of the change of high pumping flow rate on the width and area of the oxidation zone and the maximum temperature of the goaf is greater than that of the air supply volume and low pumping flow rate. The maximum width of oxidation zone increases with the increase of air supply, and the maximum temperature of goaf and the area of oxidation zone decrease with the increase of air supply. When the air supply increases from 1600 m3/min to 1900 m3/min, the maximum width of oxidation zone increases by 2 m (74−76 m), and the maximum temperature decreases by 0.1 K (315.38−315.28 K). The oxidation zone area decreased by 180.08 m2 (8 669.49−8 489.41 m2). The maximum width of oxidation zone increases with the increase of low extraction flow rate, the maximum temperature of goaf and the area of oxidation zone increase with the increase of extraction flow rate. When the low extraction flow rate increases from 200 m3/min to 300 m3/min, the maximum width of oxidation zone increases by 2 m (75−77 m). The maximum temperature increased by 0.152 K (315.34−315.492 K), and the oxidation zone area expanded by 51.56 m2 (8 553.79−8 605.35 m2). When the high pumping rate increased from 80 m3/min to 240 m3/min, the maximum width of the oxidation zone remained at about 75 m, and the maximum temperature increased by 0.76 K (315.13−315.89 K).

Abstract The compaction characteristics and bearing capacity of dry filling materials in goaf have a significant influence on stope control and surface stability. Through acoustic emission monitoring and mechanical model analysis, a series of confined compression tests were conducted on crushed waste with varying particle sizes and Talbot coefficients. The deformation, fragmentation, and acoustic emission characteristics under corresponding working conditions were determined. The results indicate that the stress–strain curves of crushed stone with different particle sizes and Talbot coefficients exhibit similar nonlinear behavior during confined compression. However, the strain response varies with changing stress levels. By analyzing the slope change rate of the stress–strain curve, the lateral uniaxial compression process of waste rock can be divided into three deformation stages: rapid compression, stable crushing, and slow compaction. The compressive deformation characteristics of gravel differ based on particle size and Talbot coefficient. Specimens with a higher Talbot coefficient demonstrate stronger compressive resistance and weaker deformation resistance during initial compaction loading. Notably, the internal pressure structure strength is influenced by factors such as maximum particle size D, grading coefficient n, and particle size distribution continuity, rather than solely by the proportion of large particles. The evolution of acoustic emission signals and energy-time curve during waste rock confined axial compression synchronizes with the compaction process. Overall, compaction plays a critical role in maintaining the stability of goaf in dry crushed waste filling.

In order to explore the characteristics of surface deformation caused by supercritical CO2 injection into abandoned goaf, the general characteristics and evolution process of surface deformation were studied by FLAC3D simulation. The effects of porosity, CO2 injection rate and storage depth on surface deformation characteristics were discussed from five aspects, such as deformation range and deformation amount. The results show that the surface deformation caused by CO2 injection into the abandoned goaf is in the form of “inverted bowl” uplift, and experiences the evolution process of incubation stage, active stage and stable stage. As the surface point is far away from the goaf, the proportion of its displacement in the incubation stage and the stable stage gradually increases. The surface deformation range decreases significantly with the increase of CO2 storage depth, and is less affected by the change of porosity and CO2 injection rate. The surface displacement gradually decreases with the increase of porosity and CO2 storage depth, and is less affected by the change of CO2 injection rate. The duration of surface deformation is positively correlated with porosity and CO2 injection rate, and negatively correlated with CO2 storage depth. The proportion of the displacement of the surface point in the incubation stage and the stable stage is positively correlated with the number of time steps required and the porosity and storage depth, and negatively correlated with the CO2 injection rate.

In the process of coal mining, small faults can lead to the accumulation of gas in the goaf, forming a gas enrichment zone, which poses a great threat to production safety. Therefore, it is necessary to study the gas migration law in the goaf under the influence of small faults. By using UDEC software to numerically simulate the failure process of the overlying strata in the goaf, the porosity of the overlying strata under the influence of small faults is calculated, and FLUENT software is used to numerically simulate the gas migration law in the goaf considering the influence of small faults during the mining process. Research has shown that: ① the working face is 20 m away from the small fault, and the sliding phenomenon first appears from the top of the small fault, and the displacement of the overlying rock layer in the goaf begins to be affected by the fault; When the working face reaches the fault, due to the sliding of the fault, the hanging wall rock mass undergoes a rotation phenomenon on the fault surface, supporting the rock strata in the goaf. The displacement of the overlying rock collapses significantly, and the rock strata collapse lags behind; The influence range of small faults is limited, and after the working face passes through the small fault for 60 m, the displacement law of the overlying strata in the goaf gradually returns to normal. ② By analyzing the displacement characteristics of the overlying strata in the goaf containing small faults, the displacement of the overlying strata in the goaf and its fitting formula were obtained. The three-dimensional porosity distribution law was calculated: within the range of the caving zone, the porosity of the overlying strata is the highest at four corner positions, and there is also an increase in porosity near the inlet and outlet air tunnels of the faults; Within the fracture zone, except for the position where the fault is close to the inlet and return air roadway, the porosity is relatively low and the change is not significant in other positions. ③ Obtained the gas migration law in the goaf under the influence of small faults: At a distance of 50 m from the fault in the working face, the gas migration in the goaf is almost not affected by the fault; When the working face advances to the fault, the gas migrates along the advantageous escape channel generated by the high porosity overlying rock near the fault towards the deep part of the goaf. At the same time, the gas in the hanging wall also transfers towards the deep part, causing a large amount of gas to accumulate in the lower wall of the fault, which may cause the gas to flow into the working face and return air roadway with the leakage air; When the working face passes through a fault of 50 m, the gas in the goaf continues to transfer towards the vicinity of the upper corner; When the working face passes through a fault of 100 m, the gas migration in the overlying strata of the goaf shows a turning phenomenon, and the gas concentration in the upper corner and lower wall caving zones is high.

In view of the challenges posed by the goaf at the pile tip to the design of rock-socketed piles (such as load-bearing performance and long-term service performance), a scaled model test was conducted using the rock-socketed piles in the goaf of the Dujiashan Super Bridge as a prototype. A scaled model test was conducted to study the bearing capacity of single pile at different distances from the goaf to the pile tip and whether the goaf was grouted or not. The scaled parameters were calculated and appropriate test materials were selected for model construction. Through multi-level load tests, the changing characteristics of pile top settlement, pile axial force, pile tip resistance and pile side friction at different distances from the goaf to the pile tip and after grouting were obtained. And the bearing characteristics of rock-socketed piles without goaf were comparatively analyzed. The results show that as the distance from the goaf to the pile tip decreases, the bearing capacity of the model pile tip bearing layer decreases, which is not conducive to the bearing capacity of the model pile. After grouting, the bearing capacity of the pile tip bearing layer is significantly increased, resulting in a significant reduction in pile top settlement of the model pile and a significant increase in bearing capacity. [ABSTRACT FROM AUTHOR]

Existing goaves (e.g., shafts and roadways) in mines represent important hidden dangers during the production of underlying coal seams. In this view, the accurate identification, analysis, and delimitation of the scope of goaves have become important in the 3D seismic exploration of mines. In particular, an accurate identification of the boundary swing position of goaves for 3D seismic data volumes within a certain depth interval is key and difficult at the same time. Here, a wide-band and wide-azimuth observation system was used to obtain high-resolution 3D seismic data. The complex structure of a mine was analyzed, and a seismic double processing system was applied to verify the fine processing effect of a goaf and improve the resolution of the 3D seismic data. Based on the seismic attribute identification characteristics of the goaf structure, we decided to adopt multi-attribute comprehensive identification and data fusion technologies to accurately determine the position of the goaf and of its boundary. Combining this information with the mine roadway engineering layout, we verified the accurateness and correctness of the goaf boundary location. Our study provides a good example of the accurate identification of the 3D seismic data of a roadway goaf. [ABSTRACT FROM AUTHOR]

To explore the impact of the goaf formed by steep coal mining on the safe operation of the overlying gas transmission pipeline, a three-dimensional numerical model was established for the goaf of a coal seam based on FLAC 3D software. The characteristics of geological settlement and pipeline displacement for the actual coal mine goaf were explored. In addition, the impact of steep coal seams with different dip angles and mining depths on the deformation of the overlying gas transmission pipeline was also studied. The results show that an collapse area above the coal seam slope with the largest depth of 1. 54 m is formed after mining for 100 m to the five steep coal seams in the coal mine area. The soil and rock in the collapse area mainly move horizontally and vertically downward towards the coal seam. The vertical displacement of the pipeline near the goaf is greater than the horizontal displacement, while the horizontal displacement of the pipeline far away from the goaf is greater. With the decrease of dip angle of steep seam and the increase of mining depth, the downward settlement of the pipeline increases significantly, and the position where the maximum settlement occurs gradually approaches the direction of the seam. [ABSTRACT FROM AUTHOR]

The utilization of oil shale ash in developing environmentally sustainable filling materials for subterranean mines presents a promising ecological approach, albeit with typically low ash content. In this study, the filling material was prepared by adding oil shale ash and slag. The study examines the physical and mechanical properties of filling materials predominantly composed of oil shale ash slag, sourced from the Baoming open-pit mine in Jimusar, Xinjiang. Comprehensive testing and analysis are conducted to examine the chemical composition, mineral composition, and particle grading of oil shale ash, cement, and fly ash. The research prepared 45 cubic specimens measuring 50 mm × 50 mm × 50 mm and analyzed their mechanical responses under uniaxial compression conditions, employing varying dosages of ash, cementitious materials, and water as critical variables. The results indicate that the primary constituents of oil shale ash are silica (SiO2) and aluminum trioxide (Al2O3). When the oil shale ash content ranges from 60 to 70%, with a cement-fly ash ratio of 7:1 and a water content of 11%, the filling material attains its highest average compressive strength of 16.37 MPa at 28 days. Furthermore, increased cement content in the cementitious material correlates with higher compressive strength in the filling material. This research underscores the potential of oil shale ash–based green mining filling materials to restore goaf. [ABSTRACT FROM AUTHOR]

Considering the importance of calculating surface deformation based on monitoring data, this paper proposes a method for calculating horizontal deformation based on horizontal displacement monitoring data. This study first analyzes the characteristics of horizontal displacement monitoring data, then proposes a scheme for obtaining the surface horizontal displacement field through corresponding discrete point interpolation. Subsequently, the calculation method for surface horizontal strain is introduced, along with relevant examples. The study also systematically summarizes the calculation methods for surface curvature and surface tilt deformation values, forming a set of surface deformation calculation methods based on monitoring data. The research results indicate that when there is a large number of on-site monitoring points, effective monitoring points can be selected based on the direction of horizontal displacement. When interpolating the surface horizontal displacement field, the interpolation accuracy of the radial basis function method is slightly higher than that of ordinary Kriging. The form of coordinate expression has a significant impact on interpolation accuracy. The accuracy of interpolation using horizontal displacement vectors expressed in polar coordinates is higher than that using vectors expressed in Cartesian coordinates. The calculated surface horizontal strain has effective upper and lower limits, with lower-limit strain on the contour line conforming to the typical surface deformation patterns around mined-out areas. [ABSTRACT FROM AUTHOR]

The evaluation and classification of goaf stability are fuzzy and random. To address this problem, a new classification method is proposed. A cavity monitoring system is used to detect the goaf, 3DMine and FLAC3D software are used to conduct the 3D visual modeling of the scanning results, and numerical simulation analysis is performed on the goaf. According to the analysis results, the stability classification standard of the goaf is constructed, and the characteristics of each classification are described. The evaluation indicator system of goaf stability is constructed in accordance with similar engineering experience, and the evaluation indicator is weighted by using the analytic hierarchy process. The cloud–element coupling evaluation model is built, the field measured values of indicators are collected, the cloud correlation degree of goafs belonging to each stability level is calculated, the stability level is evaluated according to the principle of maximum membership degree, and the results are compared with the numerical simulation to analyze the reasons for the differences in the stability evaluation results obtained by the two methods and to improve the accuracy of the evaluation of goaf stability. The pillar stress and surrounding rock deformation are monitored in Room 1# of the inclined mining area of Shirengou Iron Mine. The monitoring results are consistent with the evaluation results, which proves the accuracy of the proposed goaf stability classification method. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Remote Sensing is the property of Editorial Office of Journal of Remote Sensing & Science Publishing Co. and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Underground backfilling stands out as a crucial technological strategy for the eco-friendly and effective management of solid waste in mining operations. However, existing backfilling techniques have led to increased production processes at the working face, resulting in a reduction in coal extraction efficiency. Addressing the temporal and spatial interference between mine solid waste backfilling and coal mining is essential. To overcome this challenge, this study introduces a novel post-mining spatial gangue slurry backfilling method. Radar detection was employed to ascertain the typical characteristics of the subsequent space collapse roof shape. Stress monitoring and compaction experiments were conducted to establish the relationship between stress and the bulking coefficient of the overlying rock mass, identifying subsequent spatial void structure characteristics. The development of a CO2 mineralized coal-based solid waste filling material, utilizing conventional low-calcium fly ash under normal temperature and pressure conditions, was presented. This paper provides a comprehensive understanding of the post-mining spatial gangue slurry backfilling method, outlines the spatial layout approach for the corresponding system, and analyzes research challenges associated with gangue slurry backfilling materials and the technology of slurry injection borehole layout. The research aims to innovate an efficient underground disposal model for gangue, contributing to the refinement of the technical system for the comprehensive disposal and utilization of gangue. [ABSTRACT FROM AUTHOR]

Copyright of Coal Geology & Exploration is the property of Xian Research Institute of China Coal Research Institute and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Coal Science & Technology (0253-2336) is the property of Coal Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Spontaneous combustion of residual coal in the goaf is one of the main disasters in coal mines. Understanding the law of spontaneous combustion of residual coal can effectively prevent coal mine fires. This paper establishes a dynamic evolution model of overburden caving and porosity in the goaf using PFC numerical simulation software, and compares and analyzes the dynamic changes in porosity and the spontaneous combustion zone at advancing distances of 50 m, 70 m, and 100 m. The results show that when the working face advances 100 m, the porosity in the caving zone of the goaf decreases from 0–0.6 to 0.16–0.3. The range of the spontaneous combustion zone on the return air side expands from 42m-50 m to 39m–61 m, and on the inlet side, it expands from 0 to 22m–50 m. With increased exposure time, the spontaneous combustion zone range shifts slightly forward to 32m–55 m on the inlet side and 21m–49 m on the return side. This study reveals the dynamic evolution law of the spontaneous combustion zone in the goaf under the influence of different advancing distances and exposure times, which can assist in preventing goaf fires.

China is rich in mineral resources, and problems of goaf formed in the process of resource exploitation are serious obstacle to the development of China's economic, so it is of great significance for the assessment and management of goafs. This paper introduces emerging dung beetle optimizer (DBO) algorithm and establishes DBO-BP (back-propagation) model, at the same time, it is compared with a series of heuristic algorithms coupled with BP neural network models: PSO (particle swarm optimization) - BP model, WOA (whale optimization algorithm) - BP model, and SSA (sparrow search algorithm) - BP model. Then they are applied to evaluate the hazard of goafs, the result shows that the DBO-BP model gets the highest train set accuracy, which is at least 2.7 % higher than other models, while the DBO-BP model obtains the highest test set accuracy, meanwhile its effectiveness and stability have also been proven. Finally we apply the established DBO-BP model to evaluate the hazard of the tungsten mine goaf of Yaogangshan in Hunan Province, and its excellent practicability was confirmed. This paper may provide a reference for the solution of nonlinear engineering problems.

As an important negative carbon technology to solve the carbon emission problem in the coal industry, the CO2 sequestration in the mine goaf has a wide application prospect in the secondary utilization of waste resources in the goaf and the capture and storage of CO2. In this study, the influence of different temperatures and pressures, formation water salinity and cationic solution type on the interfacial tension (IFT) of CO2-formation water system was investigated by using in-situ interfacial tension meter. The gas-liquid interface diffusion effect of CO2 injection into water-bearing coal rock mass was clarified. The equation of state (SAFT-LJ equation of state) based on statistical association theory combined with the Lanner-Jones potential energy model and density gradient theory (DGT) were combined to predict the theoretical value of IFT. Using a self-developed geological sequestration and geochemical reaction simulation experimental platform, various exploratory experiments were conducted to investigate the solubility of CO2 under the same conditions. The characteristics of CO2 solubility variation in the reservoir environment of the goaf were obtained, and the corresponding theoretical values of CO2 solubility were calculated using the D-S model. The experimental results show that when the ambient temperature is constant, the reservoir pressure in the goaf is linearly negatively correlated with the IFT value. As the reservoir temperature increases, the IFT value increases correspondingly, but the change range is small. Under constant temperature and pressure conditions, there is a positive correlation between salinity and IFT value. Within the scope of this experiment, low pressure, high temperature, and high salinity promote an increase in the IFT value. The IFT values between CO2-salt solutions show an increasing trend with the increasing valence of cations (K+ < Na+ < Ca2+ < Mg2+). The pressure of the depleted reservoir is positively correlated with the CO2 solubility. When the temperature is 25 °C and under conditions of pure water, as the pressure increases from 0.5 MPa to 2.5 MPa, the corresponding CO2 solubility increases from 0.1627 mol/kg to 0.7141 mol/kg. The CO2 solubility decreases with the increases of temperature and salinity. Under the same concentration, monovalent cation solutions (NaCl, KCl) can dissolve more CO2 than divalent cation solutions (CaCl2, MgCl2). The free phase CO2 injected into the goaf overcomes the interfacial tension and breaks the geochemical balance of the goaf strata through diffusion and dissolution mass transfer. By clarifying the influence of reservoir temperature and pressure conditions and goaf water environment on IFT value and CO2 solubility, the gas-liquid interface effect and dissolution mass transfer mechanism of CO2-formation water are clarified, so as to provide a theoretical basis for the safety and evaluation of CO2 sequestration in the closed mine goaf.

Relative to conventional coal pillar retention mining technology (the 121 mining method), gob-side entry retaining by cutting roof (the 110 mining method), a non-pillar mining technique, efficiently addresses issues like poor coal resource recovery and significant rock burst damage. Nonetheless, the open-type goaf created by 110 mining techniques suffers from complex and significant air leaks, increasing the likelihood of coal spontaneous combustion (CSC) within the gob area. To address the CSC problem caused by complex air leakage within the goaf of gob-side entry retaining by roof cutting, this study takes the 17202 working face of Dongrong Second Coal Mine as the object of study. Field tests and simulation calculations are conducted to research the features of air leakage and the distribution of the oxidation zone within the goaf. Subsequently, plugging technology with varying plugging lengths is proposed and implemented. The tests and simulations reveal that the airflow migration within the goaf follows an L-shaped pattern, while air leakage primarily originates from gaps found in the gob-side entry retaining wall. The amount of air leaking into the gob-side entry retaining section is 171.59 m3/min, which represents 7.3% of the overall airflow. The maximum oxidation zone within the goaf ranges from 58.7 m to 151.8 m. After the air leakage is blocked, the airflow migration route within the goaf is transformed into a U-shaped distribution, and the maximum oxidation zone range changes from 42.8 m to 80.7 m. Engineering practice demonstrates that after air leakage plugging, the total air leakage volume within the gob-side entry retaining section significantly reduces to 20.59 m3/min, representing only 0.78% of the total airflow volume. This research provides reference on how to prevent the occurrence of CSC in similar mine goafs. [ABSTRACT FROM AUTHOR]

A three-dimensional geological model integrating real ground topography, ore bodies, and tunnels was established by 3Dmine and UAV. Combined with Rhino6-FLAC3D, a numerical calculation model for ore body extraction was developed. The impact of rock movement and surface deformation was simulated and analyzed. The effectiveness of simulation results was verified through InSAR monitoring. The results indicate that the simulation results are consistent with InSAR monitoring, indicating that the research method combining monitoring and simulation is effective. For the goaf left by open-pit mining, dry filling can limit the damage of surrounding rock and filling body. The stability of shallow filled mining areas might be affected by deep operations in the mining area, and there is a negative correlation between the severity of disturbance and the distance from deep work areas. According to InSAR monitoring and numerical simulation, the impact of goaf destruction and mining disturbance on the surface subsidence is weak. [ABSTRACT FROM AUTHOR]

The geological conditions of the karst terrace of synclinore are complicated. Geological disasters such as water inrush and mud outburst often occur when the tunnel crosses it. The Anping Tunnel was taken as an example. In the early stage of the design of the tunnel route, from the geological perspective, five main geological problems and possible geological disaster risks within the scope of the tunnel route were analyzed and evaluated one by one. And the concept of geological route selection of avoidance without disturbance was used. The route avoidance scheme was selected according to the evaluation results and the horizontal and vertical design indicators were determined. The research results have certain reference significance for geological route selection and route design of tunnels on the karst terrace under similar complicated geological conditions. [ABSTRACT FROM AUTHOR]

Increased effectiveness of methane drainage from sealed post-mining goaves in hard coal mines contributes to reduced methane emission from goaves into the mine ventilation system. This paper focuses on issues concerning the assessment of the additional amount of methane released from the goaf into mine workings during periods of atmospheric pressure drops, which can be captured with a methane drainage system. Thanks to the solutions presented in the paper, it is possible to control the efficiency of the goaf drainage system, which in turn leads to the reduction of methane emission from the mine ventilation air into Earth's atmosphere. These solutions are of great added value for both the environment and coal mines as they reduce the costs arising from greenhouse gas emissions that are incurred by mining companies, increasing the efficiency of methane capture and its use in gas engines or district heating systems. The paper uses relationships relating to the influence of atmospheric pressure changes on the process of gas release from the goaf according to the hysteresis loop of methane release during atmospheric pressure changes, which was developed based on conducted research. The analysis and conclusions presented in this paper may facilitate the development of strategies aimed at reducing methane emissions from a mine's ventilated air into Earth's atmosphere. [ABSTRACT FROM AUTHOR]

Copyright of Railway Construction Technology is the property of Railway Construction Technology Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Nonferrous Metals (Mining Section) is the property of Beijing Research Institute of Mining & Metallurgy Technology Group and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

To ensure the safety of construction and operation of the tunnel near the goaf. Based on dynamic numerical analysis, three-dimensional finite difference numerical simulation software was developed by FISH programming. Then, on basis of the construction of practical engineering, the safety distance and energy evolution mechanism in an underlying mining goaf area of deep tunnel are studied. The results show that according to the different safe distance in an underlying mining goaf area of deep tunnel, the tunnel structure is divided into danger zone, influence zone and safe zone. The relationship between the cumulative horizontal energy and stress ratio can be divided into three stages: acceleration, average stability, and deceleration. The energy evolution of the three stages can also better reflect the damage and failure mechanism inside the surrounding rock mass. The measured field curve shows that when the safety distance is 12 m, the goaf has limited influence on the stability of the tunnel, and the construction in an underlying mining goaf area of deep tunnel is stable overall and meets the safety requirements. The best safe distance between the tunnel and goaf is about one time of the tunnel span. [ABSTRACT FROM AUTHOR]

The inerting technology is a common means to prevent fires in goaf of coal mine, in which adsorption capacity is the key index to measure the inerting effect. Therefore, this paper obtained the coal spontaneous combustion (CSC) stage of Qianyingzi coal mine through programmed heating experiments, and determined the physical adsorption stage temperature (below 323.15 K) matching the actual environment. The oxidation characteristics of coal samples with different adsorption degrees were further studied by adsorption experiment and TG-DSC test. The results indicate that the combustion activation energy of coal samples follows the sequence of second-stage adsorption coal > dried coal > raw coal > first-stage adsorption coal. This implies that the CO2 saturated adsorption can exert a specific inhibitory impact on coal combustion. Therefore, the index of the saturation adsorption capacity (SAC) was proposed to evaluate the inerting effect. We further studied the adsorption capacity of coal at different ratios of CO2/N2 by molecular simulation under different pressures (0–5 MPa). The results show that CO2 dominates in both single-component adsorption and competitive saturated adsorption. The average of ratios (AOR) and average of differences (AOD) threshold are determined. The priority of SAC is obtained in the order of single-component (CS), CO2/N2 mixture ratio at 4:6 (C4:6), CO2/N2 mixture ratio at 2:8 (C2:8) from largest to smallest. Furthermore, a fuzzy optimization method for injection ratio of CO2/N2 under different pressures was established. During dynamic changes in environmental pressure, it is appropriate to inject CO2 separately at 0.2–2.5 MPa. At 3 MPa, a mixture of CO2/N2 at a ratio of 2:8 is the best for prevent fires in goaf. Similarly, an inert gas with a CO2/N2 ratio of 4:6 is injected at 3–5 MPa.

The characteristics of deformation and failure of coal pillar under goaf water infiltration and overburden load is complex. In order to study the deformation characteristics of coal pillar under the action of lateral permeation-axial load, a unilateral hydraulic loading device for the permeability test of cylindrical specimens was used to carry out compression tests of coal samples under different lateral permeation pressures and to study the failure characteristics and permeability characteristics of coal samples. The results show that: the deformation and failure of coal samples under lateral permeation-axial load can be divided into five stages: compaction, elasticity, stable fracture expansion, unstable fracture expansion and post-peak failure. With the increasing of lateral water pressure, the peak strength of coal samples gradually decreases, and the axial strain corresponding to the stable fracture expansion stage decreases. The water energy enters the inner void of coal sample under small axial strain, resulting in increased brittleness of coal sample and accelerated failure of coal sample.

To accurately explore distribution of a historical small coal mine goaf in Hami, Xinjiang, integrated application of microtremor and transient electromagnetic is used for goaf exploration researching. This work use different physical properties data into lithology, use microtremor exploration to determine the goaf position and use transient electromagnetic exploration identify goaf water. Two methods can complement each other, verify each other, and effectively reduce the wrong results of single geophysical method. Which also provides a reference for the selection and application of geophysical exploration means in small mine goaf exploration.

Abstract The large-scale extraction of coal resources in the western mining areas of China has resulted in a significant loss of water resources, which is a challenge for coordinating resource extraction with ecological preservation in the mining areas. Although underground reservoir technology can effectively solve this problem, measuring the storage capacity of underground reservoirs through engineering experiments is costly and time-consuming. Currently, there is a lack of accurate, reliable, and low-cost theoretical calculation solutions, which greatly restricts the promotion and application of underground reservoir technology. The theoretical calculation methods for underground reservoir capacity were studied based on parameters from the Shendong mining area in China. A water storage structure model for coal mine underground water reservoirs was established, taking into account the settlement boundaries of the bedrock and loose layers in shallow coal seams, based on the key layer theory and the spatial structure model of the mining roof. The mathematical expression for the load on the coal-rock mass in the goaf was derived considering the rock breaking characteristics of the mining roof. The model determined the range of each water storage area, including the zone of loose body, zone of gradual load, and the compacted zone, based on the strength of the water storage capacity. The key parameters for calculating the water storage capacity were determined using a modified model for shallow thick loose layers and thin bedrock movement. Finally, a calculation method for the storage capacity was obtained. Based on the real data from the 22,615 working face of a mine in the Shendong mining area, the water storage capacity of the underground reservoir in the goaf was jointly calculated using FLAC3D, Surfer 12.0 and the proposed calculation method. The calculated water storage capacity was approximately 1.0191 million m3. Although this result was 2.20% smaller than the on-site water pumping experiment data, it still verifies the feasibility of the above calculation method for determining the water storage capacity of underground water reservoirs.

The change of regional hydrodynamic field caused by coal mining process affects the multi-field process of the formation and evolution of mine water quality, which may lead to the pollution of the water environment in the coal mining area. Research on the driving mechanism of the hydrodynamic field and the method of quantitative calculation of key parameters is the premise of quantitative description on the multi-field effects of site pollution in the coal mining areas and its corresponding pollution control. Taking the Menkeqing Coal Mine as the geological background, this paper clarifies the evolution mechanism of the hydrodynamic field of goaf water. According to the difference in the flow path of the hydrodynamic field, it is divided into the stages of water level recovery and filling-up. It reveals the complex process of the formation and evolution of water quality in the goaf, with the hydrodynamic field as the main driving force, and the synergistic effects of multiple fields such as the hydrochemical field and the microbial field. Then the concept model of the water level recovery stage and filling-up stage and the theoretical calculation model of the analytical solution of the key parameters (permeability coefficient, water level, and water volume) of the hydrodynamic field are proposed. The measured data of the similar material simulation test and the three-dimensional box simulation test are compared with the model calculation results. The theoretical calculation of the permeability coefficient and the curve of goaf water level with time and the experimental measurement error are about 13.2% and 22.5%, respectively. The reliability of the theoretical calculation model is verified. Finally, on the basis of the equations of the hydrodynamic field, and the hydrochemical field and the microbial field under the influence of the hydrodynamic field in the goaf, a multi-field coupling effect model dominated by the hydrodynamic field is constructed. The constitutive model provides an inspiration for exploring the formation and evolution of coal mine water quality driven by the coupling of hydrodynamic field. This study supplements and expands the theory of coal mine water pollution prevention and control.

Gas extraction is one of the commonly used methods for controlling the mine disasters. But during the extraction process, it will increase the amount of air leakage in the goaf, thereby increasing the risk of coal spontaneous combustion and directly affecting the distribution of coal spontaneous combustion dangerous areas in the goaf. Taking the 30503 working face of Tashan Coal Mine of China Coal Datong Energy Co., Ltd. as the research object, according to the actual situation of the goaf, a geometric model is established. The numerical simulation methods is used to analyze the impact of different buried pipe extraction positions and extraction negative pressure on the dangerous area of coal spontaneous combustion in the goaf. The results show the following points. ① With the deepening of the extraction position of the buried pipe on the inlet side, the oxygen volume fraction on the return side shows an increasing trend. The width of the oxidation zone does not change much. The overall oxygen volume fraction on the inlet side shows a decreasing trend, and the width of the oxidation zone first decreases and then increases. The oxidation zone area in the goaf first decreases and then increases. ② In the inlet side of the fixed buried pipe extraction position, the change of the negative pressure of extraction has a greater effect on the oxygen distribution on the inlet side of the extraction zone, while it has almost no effect on the return side. ③ As the negative pressure of extraction increases, the width of the oxidation zone on the inlet side first decreases and then increases, while the width of the oxidation zone on the return side remains almost unchanged. The area of the oxidation zone in the goaf first decreases and then increases. The relationship between the oxidation zone area and the extraction negative pressure is a quadratic function. ④ The optimal position for buried pipe extraction is at a distance of 20 m from the air inlet side of the goaf to the working face. The optimal negative pressure for extraction is 5 000 Pa. At this time, the oxidation zone area of the goaf is the smallest, that is, the coal spontaneous combustion danger area is the smallest.

To ensure the construction and operational safety of tunnel undercrossing multi-situational goafs, the Huaying Mountain High-Speed Rail Tunnel, a critical section of the Xi’an-Chongqing High-Speed Railway, was taken as a case study. Based on a three-dimensional finite difference numerical simulation platform, twelve situations were established to analyze the effects of three factors: distance, scale, and angle. The stability analysis was conducted by examining the displacement and deformation characteristics of the surrounding rock, stress changes, and axial forces of the initial support for each situation. The results show that in tunnel undercrossing multi-situational goafs, the vertical deformation, horizontal convergence of the surrounding rock, and the maximum axial force of initial support are all affected. Within a certain range, changes in distance significantly impact subsidence and settlement deformation of the surrounding rock. However, as the distance increases, the horizontal and vertical displacements of the tunnel and the axial force of the initial support tend to decrease. Conversely, the scale and angle of the goaf have an opposite effect on the surrounding rock: as the scale and angle increase, the stability of the surrounding rock deteriorates. In this case study, when the distance exceeds 1.13 times the tunnel span, the influence of the goaf on the stability of the surrounding rock gradually decreases. When the angle exceeds 45°, vertical displacement decreases, and the increasing trend of horizontal displacement gradually diminishes. The conclusions of this paper can provide guidance for designing reinforcement schemes for tunnels crossing through multi-situational goafs. The findings provide valuable insights and guidance for similar engineering projects.

As the conventional inert gas, it is used for the prevention and control of coal’s spontaneous combustion, mainly N2 and CO2. However, there is limited research focusing on the inerting effect of composite inert gas. This paper studied the impact of using a premixed inert gas (N2 accounted for 50%, 60%, 70%, and 80%) instead of CO2 on the inerting effect of nearly horizontal and gently inclined goaf by building a physical similarity simulation experiment platform. The experimental results showed that the inerting effect of premixed inert gas was better than that of CO2. For instance, in a nearly horizontal goaf, the inerting effect of the premixed inert gas was optimal when the N2 accounted for 70%. The average O2 concentration in the monitored area decreased from 9.7% with CO2 to 6.4%. In addition, in the gently inclined goaf, the premixed inert gas exhibited an accumulation state similar to CO2, primarily occurring in the lower part region adjacent to the working face. Furthermore, the accumulation state of premixed inert gas was inversely proportional to its inerting effect. This study has important reference significance for applying inert gas fire prevention and extinguishing technology in mines.

An abandoned gypsum mine has been discovered beneath the route of a highway construction in Hunan province, south China. Due to the highway construction and operations safety, there is an urgent need for a comprehensive stability analysis of the abandoned mining area. The 3D laser scanning detection technique has been adopted, and over 400 drillholes were strategically placed near the highway to capture the spatial information of the abandoned gypsum mine. The ore body has an average mining thickness of about 3 m, and the depth of the mining roof ranges from 40 to 60 m, with an average span of 16 m. Based on the research achievements in the engineering geological investigation, rock mass quality assessment, and geometry information, a simplified numerical model has been established for stability analysis. The numerical model employed the IMASS rock mass constitutive model to conduct a stability analysis of the abandoned gypsum mine during the excavation process and in the medium to long term. The IMASS constitutive model can effectively reflect the entire process of rock mass from microscopic damage to macroscopic instability, and the numerical simulation of current and long-term stages provides a much greater understanding of the mining room stability and the effect of various geo-mechanical parameters not considered in traditional empirical methods. The abandoned gypsum mine stability is guaranteed in the mining and current stages. However, the numerical results showed that a 0.4 m spalling thickness of the sidewalls can cause an overall instability and failure of the abandoned mine, and reinforcement measures must be taken for long-term safety. The stability of the abandoned gypsum mine with filling solutions was also evaluated numerically. [ABSTRACT FROM AUTHOR]

Copyright of Railway Investigation & Surveying is the property of Railway Investigation & Surveying Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Railway Investigation & Surveying is the property of Railway Investigation & Surveying Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of CT Theory & Applications is the property of Editorial Department of CT Theory & Applications and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Railway Construction Technology is the property of Railway Construction Technology Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The diffusion characteristics of fine-grained gangue slurry are significant for gangue consumption and ecological environment protection, especially in underground mines. Therefore, based on the theory of porous medium transportation, this paper establishes a 3D caving zone model, proposes methods for reconstructing, statistical, and analytical voids, characterizes the distribution of voids in the caving zone and the diffusion characteristics of gangue slurry, and explores the influencing factors of the distribution of voids and the diffusion characteristics of gangue slurry. The diffusion rate and depth of the gangue slurry were calculated using Df and DT parameters. Finally, a fluidization filling method for gangue was proposed, providing a theoretical basis for solid waste treatment and environmental protection in coal mines. [ABSTRACT FROM AUTHOR]