Search Results (527)

Tailings backfilling (TB) is widely recognized as an environmentally friendly and engineering safe technique to enhance mining efficiency. However, the heterogeneous particle distribution in TB slurry, also-named the segregation phenomenon, can significantly affect the mechanical strength of the backfill, especially under high goaf conditions. Therefore, elucidating the spatial distribution characteristics of particles during high-goaf filling has become a crucial research focus for improving the mechanical behavior of tailings backfill. A systematic experimental investigation was conducted in this study, incorporating the similarity principle, to analyze the migration behavior of backfill slurry particles and to clarify how the different backfill heights influence the spatial distribution of fine, medium, and coarse particles. The results indicate a clear vertical variation in PSD. Based on statistical analysis of samples collected from different backfill height experiments, coarse particle content increased progressively from the upper to lower layers (median: 16.2%, 23.6%, and 25.0%), while medium-sized particles remained relatively stable (37.0%, 37.3%, 37.0%). Fine particles dominated overall but decreased with layers (45.6%, 38.8%, 38.3%). Coarse particles tended to settle downward due to gravitational forces, whereas fine particles migrated upward. The distribution of medium-sized particles remained largely homogeneous. Fine and coarse particles were subjected to opposing driving forces. Meanwhile, particles maintained an approximately symmetrical distribution in the horizontal direction. Moreover, when the backfill height exceeded 800 mm, a notable intensification of stratification occurred, indicating a strong height-dependent transition in segregation behavior. In contrast, in the horizontal direction, the PSD showed no clear dependence on backfill height. These findings provide new insights into the mechanisms of particle segregation within backfill materials, offering a theoretical foundation and experimental support for optimizing PSD within the backfill body and elucidating the collapse mechanisms of high goafs. Full article

This paper investigates the effectiveness of a coal mine methane drainage system in hard coal mining, with particular emphasis on coal seam 501 at the Staszic–Wujek coal mine (Polska Grupa Górnicza S.A., Katowice, Poland) in the Upper Silesian Coal Basin (USCB), Poland. The study evaluates methane drainage efficiency considering geo-mechanical conditions governing the optimal location of drainage boreholes. Conventional and long directional boreholes are analyzed. Opposite to conventional static analytical approaches, the proposed integrated analysis framework incorporates multi-physics processes, improving forecasting accuracy and enabling dynamic optimization of methane control in deep coal mines. The framework reproduces the geometry of the mining system and the mechanical properties of the surrounding rock mass, allowing the influence of geo-mechanical processes on methane drainage efficiency to be assessed. The methane content of coal seam 501 and methane sorption kinetics on representative coal samples are analyzed together with key characteristics of the mine ventilation system, including air and pressure distribution in workings and goafs and migration paths of methane–air mixtures within coal panel II/C. Full article

Spontaneous combustion in goaf areas poses a significant threat to coal mine safety. Traditional safety management systems, reliant on passive response and single-indicator thresholds, often suffer from delayed warnings and lack cognitive decision support. To address this challenge, this study proposes a big-data-driven cognitive computing framework for dynamic risk prediction of goaf spontaneous combustion, based on a “Cloud-Edge-End” collaborative architecture. The method leverages multi-sensor big data streams (CO, C₂H₄, O₂, etc.) and deploys a lightweight Radial Basis Function (RBF) neural network on underground edge computing nodes (STM32) for real-time analytics. The model demonstrates excellent predictive performance on imbalanced datasets, with a PR-AUC of 0.910 and a recall of 99.7%. The edge-deployed RBF model achieves a single-pass inference time of only 0.62 ms, enabling real-time cognitive risk mapping. Field application at Z Coal Mine validated the system’s effectiveness, providing an average pre-warning time of 48.5 h, achieving zero spontaneous combustion accidents, and reducing the Total Recordable Injury Rate (TRIR) by 15.2%. This work illustrates how edge-based cognitive computing can transform safety management from passive response to proactive prevention, offering a scalable and interpretable framework for intelligent mine safety. Full article

To address the challenges of rapid water loss and insufficient long-term inhibition efficiency of conventional inhibitors in the high-temperature environments of deep goafs, a novel, environmentally friendly Deep Eutectic Inhibitor (DEI) was synthesized. This DEI utilizes citric acid (Ca) and proline (Pr) as the hydrogen bond donor and acceptor, respectively, with ascorbic acid (VC) and propyl gallate (PG) serving as antioxidants. A moisture retention evaluation model based on Fick’s law of diffusion was established to systematically investigate the liquid-domain stability of the DEI across a temperature range of 30 °C to 120 °C. The results demonstrate that the DEI exhibits superior moisture retention capabilities under high-temperature conditions, with the relative moisture retention peaking in the 80–110 °C range. Mechanistically, the formation of a robust hydrogen bond network effectively counteracts moisture evaporation driven by thermal kinetic energy. Furthermore, the DEI demonstrated significant inhibition effects on four coal samples with varying degrees of metamorphism. Tests on oxidative heat release characteristics revealed that DEI treatment delayed the initial oxidation temperature of the coal. Kinetic analysis further indicated that during the critical oxidation stage (200–300 °C), the apparent activation energy of the treated coal samples increased by 10.28–18.9 kJ/mol, effectively suppressing the spontaneous combustion process. This study contributes to the development of high-efficiency and eco-friendly fire prevention materials for coal mines. Full article

As an effective technical approach for ecological environment protection in mining areas and coal resource recovery under buildings, railways and water bodies, solid backfill coal mining technology has been widely applied. When gangue was used as backfill material and placed into the goaf, its compression characteristics and crushing behavior were found to directly affect the control effect of overlying strata deformation. In this study, combined with the compression characteristics of gangue solid waste backfill materials, eight kinds of gangue solid waste backfill materials with different particle size gradations were adopted as research objects. From the perspectives of stress–strain compaction characteristics, the coupling relationship between internal crushing and acoustic emission (AE), relative density in the compacted state and particle size distribution, the hierarchical crushing behavior, and the AE response characteristics of gangue solid waste backfill materials under different gradation schemes were systematically revealed, and the optimal gradation parameters for different layers were determined. The results showed that the compaction process of gangue solid waste backfill materials could be divided into three stages: initial compression, rapid compaction and plastic compaction. During the compaction process, internal crushing was mainly concentrated in the middle layer. In the initial stage of the test, the AE intensity of the middle layer was measured to be higher than 78%, and the AE intensity remained above 50% in the compacted state. When the specimen was compressed to 220 mm, all eight gradation schemes exhibited the characteristic that the proportion of locating points and energy level in the middle layer were much higher than those in the upper and lower layers. With the continuous increase in axial pressure, the intensive area of crushing events was observed to migrate in the order of middle layer → upper layer → lower layer. With the continuous increase in axial pressure, the intensive area of crushing events was observed to migrate in the order of middle layer → upper layer → lower layer. The findings obtained in this study have provided a theoretical basis and experimental support for the gradation optimization of gangue solid waste backfill materials and roof deformation control in solid backfill coal mining engineering. Full article

To address the potential threat of surface subsidence caused by coal mining to the safe operation of buried gas pipelines in goaf collapse areas, this study investigates the geological conditions of the Mugu Coal Mine in Shanxi Province, China, and a gas pipeline passing through its surface mining area. Using a combination of numerical simulations and physical analog modeling, the mechanical response and deformation characteristics of the pipeline under mining-induced influences were systematically analyzed from three perspectives: the failure mechanisms of surface soil, the pipe–soil interaction behavior, and the damage evolution of the pipeline within the goaf. The research reveals a separation-induced failure pattern of the gas pipeline in mining-affected areas, referring to the mechanism in which differential settlement causes pipe–soil detachment, leading to unsupported bending deformation and stress concentration. Results show that the subsidence basin expands rapidly when the working face advances between 150 m and 210 m. Before this stage, the pipeline and surface soil deform synergistically with a symmetric subsidence curve centered on the goaf and uniformly distributed loads, showing no significant damage. During this stage, non-synergistic deformation occurs, leading to separation between the pipeline and soil. The maximum subsidence point shifts away from the center, destroying symmetry and causing stress concentration at the mining boundary, the advancing working face, and the goaf center, resulting in severe bending and rapid failure. After this stage, the pipe–soil interaction restabilizes with reduced separation height and extent, though pipeline deformation and damage continue to increase gradually. These findings provide a theoretical basis for engineering design optimization, targeted reinforcement measures, and monitoring strategies for gas pipelines in similar goaf collapse areas. Full article

There are significant safety risks associated with the construction and operation of wind turbines in goaf sites. Investigating the catastrophic mechanisms underlying wind turbine foundations is crucial for addressing these scientific challenges. This study employs the empirical formula method to quantitatively evaluate and analyze the stability of a goaf site. Additionally, the disaster mechanisms of wind turbine foundations in these areas are examined through similar model tests and numerical simulations. The findings indicate that the settlement deformation of the wind turbine foundation is closely related to the magnitude of the applied load. Upon completion of the loading, the maximum settlement of the foundation under rated and extreme wind speed conditions was recorded at 0.16 mm and 0.26 mm, respectively, while the maximum inclination angles were 0.04° and 0.18°, respectively. At the conclusion of the loading process, the soil pressure differences between the leeward and windward sides of the base were measured at 95.3 kPa and 139 kPa under rated and extreme wind speed conditions, respectively. This data suggests that extreme wind speeds significantly influence the distribution of base pressure, resulting in an increased uneven settlement of the foundation. Full article

To investigate how dynamic fluctuations in oxygen concentration—induced by air leakage flow in the goaf—affect the oxidation and spontaneous combustion behavior of residual coal along the airflow path, particularly considering the catalytic and inhibitory roles of CO and CO₂ generated during coal oxidation, a series-connected dual coal sample tank experimental system was developed. Experiments were conducted under controlled thermal conditions: isothermal operation in the upstream coal sample tank and programmed temperature ramping in the downstream tank. Coal oxidation indicators—including O₂ consumption rate, CO/CO₂ generation profiles, heat release rate, and apparent activation energy—were systematically quantified under dynamically varying atmospheric conditions and benchmarked against those obtained under fresh air and fixed-O₂ reference conditions. The results reveal that under dynamic atmospheres—characterized by declining O₂ concentration coupled with accumulating CO and CO₂—coal oxidation deviates markedly from behavior observed under stable, high-O₂ conditions. Crucially, CO and CO₂ are not merely passive oxidation products; they actively modulate reaction kinetics. Specifically, they suppress the dominant chain-propagation reactions of low-temperature oxidation, thereby reducing both oxygen consumption and heat release rates relative to fixed-O₂ controls at equivalent initial O₂ levels. Concurrently, they accelerate the CO-producing pathway, resulting in disproportionately elevated CO yields, even under thermally mild conditions. This decoupling between thermal activity and gaseous hazard implies a heightened risk of CO poisoning and combustible gas accumulation, potentially preceding detectable temperature rise. Accordingly, conventional single-parameter risk assessment frameworks—especially those relying solely on temperature or O₂ depletion—are insufficient for early hazard identification in such complex, transient airflow environments. We recommend integrating real-time CO concentration monitoring as a critical, proactive parameter in spontaneous combustion early-warning systems. Full article

Particle Flow Code (PFC) numerical simulations were adopted to simulate the mining process and the process of goaf collapse and to predict the residual subsidence of abandoned goafs in steeply inclined multi-seam coal mines, taking the No. 101 Coal Mine in the Xishan Mining Area of Urumqi, China, as an example. Scaled physical simulations were also employed to simulate the evolution of voids in the coal–rock mixture in the goaf. The results show that after mining, the roof of shallow coal seams becomes unstable and collapses in the anti-dip direction, causing the materials within the unconsolidated layer to fall and backfill the goaf, which further leads to ground subsidence. The mining of deep coal seams is also accompanied by the overall movement of overlying strata along the dip direction of the coal seams and surface subsidence. The content of voids within the broken coal–rock mass in the goaf tends to decrease with increasing pressure, showing a negative exponential correlation. Based on the observed relationship between displacement and void content obtained from the simulation experiments, it is inferred that the residual displacement under the current conditions of the study area accounts for approximately 10.5% of the total displacement. Combining the results of the PFC simulation and the evolution law of void content, the residual subsidence of the goaf in the study area since mine closure is predicted to range from 0 to 1 m, with a high-value zone distributed in the northeastern part of the study area. Deep goafs within the B₇–B_11–12 and B₁₄–B₁₈ coal seam groups mainly contribute to the residual subsidence. The distribution of goaf collapse pits, as revealed by field investigation, also verifies the reliability of the prediction results. Full article

Longwall top coal caving is one of the most effective methods for extracting steeply inclined and ultra-thick coal seams. To investigate the influence of caving ratio (the proportion between mining height and top coal thickness) on top coal recovery behavior and ground pressure characteristics, this study employs both the Particle Flow Code (PFC) discrete element method and a coupled FLAC^3D–PFC^3D numerical simulation approach. The effects of different caving ratios (1:3, 1:3.2, and 1:3.4) on the top coal recovery ratio, stress distribution, and gangue accumulation characteristics were analyzed. The results show that the caving ratio has a significant impact on top coal recovery. At a caving ratio of 1:3.2, adopting a two-cut-one-cave interval resulted in a top coal recovery ratio as high as 94.8%. A stress-relief zone with an arch-like distribution formed above the goaf, while a stress concentration zone developed ahead of the coal wall, where the coal–rock mass underwent compression and failure. The roof displacement exhibited an arch-shaped distribution, while the floor displacement was asymmetrical, with greater heaving observed at the lower end. As the working face advanced, the horizontal development of the plastic zone expanded rapidly, while the vertical extent changed only slightly. Throughout the caving process, the top coal demonstrated favorable caving behavior with good flowability and accumulation characteristics. These findings provide theoretical support for achieving high mining recovery in thick coal seam operations and offer practical guidance for optimizing caving process parameters in practice. Full article

Interconnected fractures induced by coal mining, known as water-conducting fracture zones (WCFZs), form a fractured zone where water from overlying aquifers flows into the goaf. Substantial findings have been established on the development height of WCFZs; however, these analyses have been based on intact structures or rock masses. Research on how primary fissures or other water-conducting structures influence the development of WCFZs remains limited. The mining seam of the Gaojiapu Coal Mine in the Ordos Basin, China, is overlaid by a gigantic and highly confined Cretaceous aquifer. Additionally, the primary fissures of the overlying strata are highly developed. Geophysical inversion of the primary fissures and vertical and horizontal drilling were undertaken in order to systematically investigate the characteristics of WCFZ development in the overlying strata. The results show that a dense network of primary fissures is connected with the middle and lower Cretaceous aquifer developed in Mining Zone 1. These fissures are prone to connecting with mining-induced fractures to form the highly developed WCFZs observed and verified in this study. A grouting engineering approach was adopted at the Gaojiapu Coal Mine to block the primary fissures in advance, as this can effectively control the abnormal development of the WCFZs and decrease the discharge of mine water, ultimately protecting the water resources of the Cretaceous aquifer. Our research clarifies the significant role of primary fissures in the development of water-conducting fracture zones, and provides important theoretical guidance for the accurate prediction and prevention of mine roof water hazards in areas with similar mining conditions. Full article

Due to the constraints of early mining conditions in some coal mines in China, a large number of pillar-type coal pillars remain in the mined-out areas. During the upward mining above the underlying pillar-type goaf, it is usually necessary to backfill the underlying goaf to form a backfill–coal pillar synergistic bearing structure, which jointly bears the load during the upward mining process. In this paper, a combination of laboratory mechanical tests and numerical simulations is used to study the failure characteristics of coal pillars, stress–strain curve characteristics, force chain transmission characteristics, and the number and distribution of fractures under the influence of backfill strength and filling ratio. The critical strength and critical filling ratio of coal pillars with different widths under the coordinated action of different backfill strengths and filling ratios are analyzed. The results show that the composite with a backfill filling ratio of 90% exhibits a stepwise change after coal pillar failure, while the composites with filling ratios of 70% and 50% show a cliff-like drop after coal pillar failure. The composite with a filling ratio of 50% completely loses its bearing capacity after coal pillar failure; the backfill is limited by its height and cannot bear the load repeatedly with the failed coal pillar, and the bearing stage lacks the common bearing stage in which the backfill wraps the failed coal pillar. The number of fractures in the coal pillar decreases with the increase in backfill strength. High-strength backfill can provide higher lateral restraint for the coal pillar through its own anti-deformation capacity. Increasing the backfill filling ratio can reduce the propagation rate of internal fractures in the coal pillar, slow down the deformation time of the coal pillar, and prevent the coal pillar from impact failure. When the coal pillar width is 8 m, the critical filling ratio of the backfill decreases from 84% to 70% as the backfill strength increases from 2 MPa to 6 MPa; when the coal pillar width is 11 m, the critical filling ratio decreases from 69% to 62%; when the coal pillar width is 14 m, the critical filling ratio decreases from 58% to 55%. The research results provide important on-site guiding significance for the safe implementation of upward mining. Full article

To address the recurring issue of excessive carbon monoxide (CO) concentrations at the return corner of fully mechanized mining faces under goaf conditions, this study investigated the elimination of CO at ambient temperature and pressure using deep eutectic solvents (DESs). CO, a colorless, odorless, and highly toxic gas, is notoriously difficult to remove under conventional conditions. A series of DESs were prepared and screened, revealing that the ethanol-modified system [Emim]Cl-CuCl-1.0E exhibited optimal CO elimination performance under conditions of 298.15 K and atmospheric pressure. Further investigations measured the viscosity-temperature relationship and thermal stability of this system while systematically examining the effects of temperature, CO contact time, and storage duration on its elimination efficiency. Analysis by FTIR and Raman spectroscopy indicated that Cu(I) ions play a crucial role in the CO absorption process. The introduction of ethanol significantly enhanced the activity of the Cu(I) ions, thereby effectively improving the CO elimination capacity of the system. This study proposes a novel potential method for managing CO in goaf areas and provides an experimental foundation for the application of DESs in the field of gas purification. Full article

Coal mining has generated a large amount of underground space, which has traditionally been reused mostly as mine wastewater storage. Given the excellent thermal insulation properties of these mine reservoirs, their potential for seasonal energy storage is considerable. However, research on cross-seasonal thermal energy storage utilizing coal mine underground reservoirs remains limited, and the thermal storage characteristics of such systems throughout their entire operational cycle are not yet fully understood. This study employs numerical simulation methods to analyze the thermal storage performance of a cross-seasonal thermal storage system based on a coal mine underground reservoir throughout a fully operation cycle. Based on the actual geological conditions of the Daliuta Coal Mine in the Shendong Mining Area, we established a thermal-fluid coupling model for a coal mine underground reservoir. Using this model, we analyzed the entire process of the heat injection stage, heat storage stage, and heat production stage within the cross-seasonal thermal energy storage system. Based on the model, the feasibility of utilizing a coal mine underground reservoir for cross-seasonal thermal energy storage was evaluated, and the system’s thermal storage performance was assessed. Results indicate that under current geological conditions of the Daliuta Coal Mine and designed operating parameters, the effective heat storage rate of the cross-seasonal system can reach 78.16%. Through investigation of the thermal storage process, the distribution evolution of hot water and heat dissipation mechanisms were thoroughly analyzed. This study identified the heat storage phase as the primary stage controlling heat loss and discussed key influencing factors affecting the thermal storage process. These findings provide novel insights for utilizing coal mine goafs and residual underground spaces, offering a reference for developing and designing novel energy storage facilities. Full article

Close-distance multi-seam mining frequently induces secondary surface deformation and subsidence. Extracting a lower coal seam beneath an existing goaf repeatedly disturbs the overburden, often leading to roof collapse and the expansion of vertical water-conducting fractures that connect the working face to aquifers. Furthermore, the overlying goaf increases the risk of water inrush into active lower workings. This study investigates the mechanisms of strata reactivation and fracturing within an overlying goaf during lower seam extraction at a mine in Northwest China. Using theoretical analysis, numerical simulation, and microseismic monitoring, the research examines the secondary fracture mechanisms of the goaf roof and the resulting water-inrush potential. Research Findings: Strata Instability: Analysis of the key sandstone strata indicates that subsidence (W) of the key rock blocks satisfies 3.17 < W₁ = 4.61 m < 18 m for the lower seam and 3.17 m < W₂ = 5.31 m < 69.6 m for the 3-1# seam. These values confirm that key rock blocks in the basic roof undergo “reactivated” instability following fracture during lower seam mining. Pressure Relief and Fluid Dynamics: Mining-induced fracture initiation and propagation trigger strata reactivation. As the distance to the center of the goaf decreases, the subsidence of the overburden increases, ultimately resulting in a “trapezoidal” bending deformation pattern. Due to secondary activation, the roof subsidence 30 m above the 221 coal seam increased from 1.89 m to 5.475 m. The layers of high-strength, medium-grained sandstone and siltstone overlying the 317 coal seam and beneath the 221 goaf serve as high-strength material for the overlying rock formations. This suppresses the development of the caving zone and fracture zone, leading to subsidence failing to reach the sum of the heights of the two coal seams (6.8 m) and only reaching a value of 5.475 m. During extraction, the stress field undergoes a distinct evolution: it transitions from an initial “regular triangular” pressure-relief zone into a tripartite “weak–strong–strong” distribution. Furthermore, fluid discharge in the overlapping zone between the 317 working face and the 221 goaf increased sequentially, displaying an “alternating” pattern of peak vector variations as the face advanced. Microseismic Activity: Monitoring within the 300–500 m range identified frequent low-energy events and high-magnitude events (10⁴ J, 10⁵ J). These findings demonstrate that secondary excavation directly impacts the aquifer, creating a significant water-inrush hazard for the active working face. Full article