Search Results (32)

Clarifying the dynamic mechanism of rock pillar fracture and its rock burst-inducing mechanism is fundamental for the prevention and control of rock burst disasters in steeply inclined extra-thick coal seam groups. In this study, field monitoring, theoretical analysis, and numerical simulation were combined to investigate the rebound vibration behavior and rock burst-inducing mechanism of fractured rock pillars, and corresponding mitigation measures for rock pillar-induced rock bursts were proposed. The results indicate that instantaneous rock pillar fracture induces reciprocating rebound vibration behavior within the coal seam rock pillar, causing the velocity, displacement, and strain energy density of the rock pillar to remain in a persistent fluctuation state. Meanwhile, periodic mutual conversion between strain energy and kinetic energy occurs throughout the vibration process. During any vibration cycle, the rock pillar cannot recover to its initial equilibrium position, resulting in a sharp increase in the loads acting on the floor side of the B3–6 coal seam and a significant decrease in the loads acting on the roof side of the B1–2 coal seam. Consequently, the B3–6 coal seam remains subjected to transient dynamic loading, whereas the B1–2 coal seam experiences transient unloading after rock pillar fracture. This asymmetric transient loading mechanism is identified as the intrinsic reason for the higher rock burst proneness of the B3–6 coal seam. Based on the dynamic response characteristics of the stope coal rock system, staggered-level mining of the B1–2 and B3–6 coal seams and slotting presplitting in the B3 roadway were proposed as mitigation measures for rock pillar-induced rock bursts. When the stagger distance of the working face increases from 25 m to 100 m, the stress drop of the B3–6 coal seam is 22.9%~28.7%. When the slotting depth of the rock pillar increases from 25 m to 80 m, the stress of the B3–6 coal seam decreases by 9.88%~24.1%. These findings provide theoretical support and engineering guidance for rock burst prevention and control in steeply inclined coal seam. Full article

Accurate characterization of underground geological conditions is essential for gas control, geological hazard assessment, and safe coal mining operations. However, conventional geological interpretation methods often suffer from limited spatial accuracy due to borehole deviation, sparse geological control, and insufficient integration of multi-source borehole data. To address these limitations, this study proposes an integrated geological characterization framework combining resistivity-based image logging, borehole trajectory correction, and BIM-based three-dimensional geological modeling using 135 gas extraction boreholes from the Coal Seam 15-21050 working face of Pingdingshan No. 8 Coal Mine, China. Multi-parameter logging data, including natural gamma, apparent resistivity, natural potential, and borehole image observations, were used to identify coal seam lithology, stratigraphic interfaces, and structural characteristics. Borehole trajectory analysis revealed systematic deviation patterns controlled by borehole inclination, lithological heterogeneity, and drilling conditions, highlighting the necessity of trajectory correction for accurate spatial positioning. Trajectory-corrected borehole coordinates were subsequently integrated into a BIM-based three-dimensional geological reconstruction workflow using spatial interpolation methods. The resulting model successfully reproduced coal seam geometry, interburden distribution, and localized concealed structural anomalies. Coal Seam 15 exhibited thicknesses ranging from 2.69 to 3.47 m, while Coal Seam 16–17 ranged from 1.51 to 2.38 m. The proposed workflow improved the reliability of geological interpretation and the accuracy of spatial characterization, providing an effective technical basis for gas drainage optimization, geological hazard assessment, and intelligent underground coal mining. Full article

Mining coal seams with shallow, thick, and hard roofs often results in extensive roof suspension. This issue poses significant challenges regarding stratum control and mitigation of strong mining pressure, especially within the confined working space of a mining face. This study focuses on the 13101 working face of Shengfu Coal Mine. Through field observations, theoretical analysis, and numerical simulations, the characteristics of support resistance and microseismic activity were investigated. This research elucidates the mechanism behind the strong mining pressure driven by the structural coupling and synergistic breakage of two key strata, highlighting how their interaction dictates weighting intensity. A small-aperture hydraulic fracturing technology, specifically designed for inter-support spaces, was developed. The results indicate that the working face exhibits alternating “minor weighting” and “major weighting” events. Minor weighting occurs at an average interval of 12.38 m with a dynamic load factor of 1.14, while major weighting occurs at 41.07 m with a factor of 1.56. The roof structure was found to form a combination of an “inclined stepped rock beam” and a “voussoir beam.” Field applications demonstrate that the proposed technology reduces the major weighting interval by 41.46% and total microseismic energy release by 35.01%. This study provides a theoretical and technical basis for preventing roof disasters under similar geological conditions. Full article

Coal and gas outbursts remain one of the most critical dynamic hazards in underground coal mining, driven by complex interactions among geological, gas-related, and structural factors. In this study, a dataset comprising 90 documented coal and gas outbursts occurred in Zonguldak Coal Basin was analyzed using the Decision-Making Trial and Evaluation Laboratory (DEMATEL) method. Hierarchical levels of significance among key controlling factors were formed and the relative influence levels of the parameters were comparatively evaluated to determine their contribution to the outburst risk mechanism. The study focuses on prominence-based interpretation supported by total influence matrix heatmap rather than conventional cause–effect diagrams. The results indicate that the prominence index provides a clear hierarchy of factor importance reflecting a structurally symmetric interaction pattern among the selected variables. Mining depth, gas content, and moisture content together account for more than 70% of total system importance, identifying them as the dominant drivers of coal–gas outbursts. Fault distance shows a secondary influence, whereas seam thickness and inclination exhibit comparatively minor contributions. The results indicate that the interaction structure of outburst risk factors is balanced, and that risk is primarily governed by their combined influence. Therefore, prominence-based evaluation and heatmap visualization provide a more reliable and practical basis for identifying critical factors and prioritizing risk control strategies. The results provide practical guidance for risk prioritization and preventive planning in deep and gas-rich coal mines. Full article

Coal is the primary energy source in China and has long dominated energy consumption, serving as both the cornerstone for safeguarding national energy security and the backbone of stable energy supply. Despite the gradual improvement in the level of fully mechanized and intelligent mining in recent years, as well as the remarkable progress achieved in safe and efficient mining technologies, significant challenges are still encountered in the horizontal slicing mining of steeply inclined coal seams. This study was conducted against the engineering backdrop of the steeply inclined extra-thick coal seam in the Yimen Coal Mine, Sichuan Province. A combination of theoretical analysis, FLAC3D numerical simulation, and on-site monitoring was employed to investigate the support technology for mining roadways. Considering the geological occurrence conditions, roadway dimensions, and service life, the bolt (cable) + steel strip + metal mesh system was selected as the basic support method, with shed supports supplemented for reinforcement in areas with special geological structures or fractured surrounding rock. A non-uniform roadway support technology for horizontal slicing mining of steeply inclined extra-thick coal seams was proposed. The optimal support parameters of the roadways were determined through numerical simulation, and favorable support effects were verified by field measurements. 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

In response to the complex challenges posed by gob-side entry retaining in medium-thick coal seams—specifically, severe stress concentrations and unstable surrounding rock under composite roof structures—this study presents a comprehensive field–numerical investigation centered on the 5-200 working face of the Dianping Coal Mine, China. A three-dimensional coupled stress–displacement model was developed using FLAC3D to systematically evaluate the mechanical behavior of surrounding rock under varying roof cutting configurations. The parametric study considered roof cutting heights of 6 m, 8 m, and 10 m and cutting angles of 0°, 15°, and 25°, respectively. The results indicate that a roof cutting height of 8 m combined with a 15° inclination provides optimal stress redistribution: the high-stress zone within the coal rib is displaced 2–3 m deeper into the coal body, and roof subsidence is reduced from 2500 mm (no cutting) to approximately 200–300 mm. Field measurements corroborate these findings, showing that on the return airway side with roof cutting, initial and periodic weighting intervals increased by 4.0 m and 5.5 m, respectively, while support resistance was reduced by over 12%. These changes suggest a delayed main roof collapse and decreased dynamic loading on supports, facilitating safer roadway retention. Furthermore, surface monitoring reveals that roof cutting significantly suppresses mining-induced ground deformation. Compared to conventional longwall mining at the adjacent 5-210 face, the roof cutting approach at 5-200 resulted in notably narrower (0.05–0.2 m) and shallower (0.1–0.4 m) surface cracks, reflecting effective attenuation of stress transmission through the overburden. Taken together, the proposed roof cutting and pressure relief strategy enables both stress decoupling and energy dissipation in the overlying strata, while enhancing roadway stability, reducing support demand, and mitigating surface environmental impact. This work provides quantitative validation and engineering guidance for intelligent and low-impact coal mining practices in high-stress, geologically complex settings. Full article

The dip angle and thickness of coal seams are key geological determinants in mine system engineering. Roadways excavated in steeply inclined or thick coal seams typically exhibit significant deformation, with the combined geological configuration of steeply inclined thick seams thus presenting heightened support demands. Therefore, taking the 1502 level roadway in the Dayuan Coal Industry—situated in a steeply inclined thick coal seam—as an engineering case, mechanical models of roadways with different cross-sectional shapes are established, and the deformation and failure mechanisms of surrounding rock under different coal seam dip angles are analyzed. Based on this analysis, an asymmetric support technology scheme is proposed, followed by surrounding rock deformation monitoring and a support effectiveness evaluation. Key findings include the following: (1) in steeply inclined thick coal seam roadways with different cross-sectional shapes, the stress distribution and plastic zone development of surrounding rock follow a descending sequence, inclined roof trapezoidal section > rectangular section > arched section. Among these, the arched section is identified as the optimal roadway cross-sectional shape for this engineering context. (2) The stress-concentration area in the arch roadway aligns with the inclined direction of the coal seam, forming asymmetric stress concentration patterns. Specifically, as the coal seam dip angle increases, stress increases at the arch shoulder of the upper sidewall and the wall foundation of the lower sidewall. Concurrently, such stress concentration induces shear failure in the surrounding rock, which serves as the primary mechanism causing asymmetric deformation and failure in steeply inclined thick coal seam roadways. (3) In the 1502 level roadway, the asymmetric support technology with dip-oriented reinforcement was implemented. Compared to the original support scheme, roof deformation and sidewall convergence decreased by 46.17% and 46.8%, respectively. The revealed failure mechanisms of steeply inclined thick coal seam roadways and the proposed asymmetric support technology provide technical and engineering references for roadway support in similar mining conditions. Full article

Steeply inclined coal seams, characterized by their significant inclination angles and complex storage conditions, are globally recognized as challenging seams to mine. An orthogonal test was conducted to study the influence of four key factors, including burial depth, inclination angle, lateral pressure coefficient, and maximum horizontal principal stress direction angle, on the force on the top slab of the sharply inclined extra-thick coal seam. The research findings indicate the following: The normal stress in the hollow area above the working face increases with greater burial depth, and the normal stress in the mining hollow area above the working face increases with an increase in the lateral pressure coefficient. Within the range of 4 m from the top edge of the seam, the normal stress distribution is approximately linear, and the influence of each factor on the average value of normal stress is in the following order: inclination angle > depth of burial > angle between the maximum horizontal principal stress and the strike angle of the seam > lateral pressure coefficient; outside the range of 4 m from the top edge of the seam, the distribution of normal stress is approximately linear, and the influence of each factor on the average value of normal stress is in the following order: angle between the maximum horizontal principal stress and the strike of the formation > inclination angle > depth of burial > lateral pressure coefficient. Full article

Hard roof top-cutting and gob-side roadway retention is an effective way to improve the panel recovery ratio and reduce ground pressure. Based on the condition of Pingmei No.2 Mine, this paper establishes a stability mechanics model for the roof in a trapezoidal top-cutting roadway with inclined coal seam, in order to analyze the factors influencing the stability of the roof. This paper studies the deformation characteristics and control mechanism of the surrounding rock in a trapezoidal top-cutting roadway, and proposes targeted stability control technologies for the surrounding rock. The results showed that: (1) in a trapezoidal top-cutting roadway in the hard roof with inclined coal seam, the tensile stress of the uncut roof was inversely proportional to the coal seam dip angle, roof thickness and top-cutting height, while it was proportional to the top-cutting angle. According to actual engineering conditions, the top-cutting angle and height of the roof of the 21,100-panel were determined to be 10° and 5.0 m, respectively; (2) the special structure of the trapezoidal roadway led to asymmetric stress distribution in the surrounding rock, especially in the roof and rib. Using top-cutting, the pressure relief reduced the roof stress from 6.73 MPa to 2.04 MPa, the high stress zone moved to the inside of the solid coal, and the roof slid and deformed along the top line, showing characteristics of a “large deformation on the top side”; and (3) high-strength long anchor cables were used to reinforce the roof on the cut top side. Telescopic U-shaped steel and windshield cloth were used to block gangue and prevent wind leakage in the roadway. The on-site industrial test measured the maximum subsidence of the roof at 120 mm, and the maximum layer separation was 29 mm. Relative to non-top-cutting methods, the roof and sides showed significantly reduced deformation throughout the mining operations, which verified the reliability of the control technology. Full article

Understanding and predicting floor failure depth is crucial for both mitigating mine water inrush hazards and safeguarding groundwater resources. Mining activities can significantly disturb the geological strata, leading to shifts and damage that may result in floor cracks. These disruptions can extend to confined aquifers, thereby increasing the risk of water inrushes. Such events not only pose a threat to the safety of mining operations but also jeopardize the sustainability of surrounding groundwater systems. Therefore, accurately predicting floor failure depth to take effective coal seam floor management measures is the key to reducing the impact of coal seam mining on water resources. Seventy-eight sets of data on coal seam floor failure depth in China were collected, and the main controlling factors were considered: mining depth (D1), working face inclination length (D2), coal seam inclination (D3), and mining thickness (D4). Firstly, the distance evaluation function based on Euclidean distance was constructed as the clustering effectiveness index, and the optimal cluster number K = 3 was determined. The collected data were clustered into three categories using the K-means clustering algorithm. It was found that the clustering results were positively correlated with the size of D1, indicating that D1 played a dominant role in the clustering. The D1 dividing points of the three types of samples were between 407.7~414.9 m and 750~900 m. On this basis, the grey correlation analysis method was used to analyze the order of the influence weights of the main controlling factors of coal seam floor failure depth. For the first group, the order was D2 > D1 > D3 > D4, while, in the other two, it was D1 > D2 > D3 > D4. D1 emerged as the most influential factor, surpassing D2. Therefore, D1 between 407.7 and 414.9 m could be used as the boundary, the first group could be classified as shallow mining, and the second and third groups could be classified as deep mining. Based on this boundary, CatBoost prediction models for the depth of coal seam floor failure in deep and shallow parts were constructed and the prediction results of the model test set were compared with the calculation results of the empirical formula. These models exhibited superior accuracy with a lower mean squared error (MSE) and mean absolute error (MAE) and a higher R-squared (R²) compared to the empirical formula. This study helps to enhance the understanding of coal seam floor behavior, guide floor management, and protect groundwater resources by defining deep and shallow mining to accurately predict floor failure depth. Full article

Thick coal seams recorded abundant petrological, geochemical, and mineralogical information regarding their formation, which in turn can reflect the characteristics of the coal-forming environments, provenance attributes, paleoclimate, and so on. In order to explore the geochemical and lead isotope characteristics of thick coal seams, the No. 7 coal seam in the Datun mining area, Jiangsu Province of China, was selected as the research object. In this work, 29 samples (including coal, roof, and floor rock samples) were collected from three coal mines in the Datun mining area. Through an analysis of the mineral composition and element geochemical characteristics in the coal samples, the enrichment degree of trace elements and modes of rare earth elements were determined. The genetic mechanism of abnormal enrichment of enriched elements is discussed, especially the modes of occurrence and isotope characteristics of Pb. The results showed the following: (1) The main minerals in the coal samples include quartz, potassium feldspar, plagioclase, calcite, dolomite, pyrite, gypsum, and clay minerals, with clay minerals, calcite, quartz, and dolomite being the most common. (2) The major element oxides in coal mainly include SiO₂, Al₂O₃, Fe₂O₃, MgO, CaO, Na₂O, K₂O, TiO₂, P₂O₅, and FeO. In the vertical direction, the variation of SiO₂, Al₂O₃, Fe₂O₃, MgO, K₂O, and FeO in coal samples from the three coal mines is consistent. The average value of Al₂O₃/TiO₂ in the samples of Kongzhuang, Longdong, and Yaoqiao coal mines is 28.09–50.52, which basically locates the samples in the felsic source area, such that the sediment source is considered to be felsic source rock. (3) Elements U, La, Pb, and other elements are more enriched in Kongzhuang coal mine samples; elements Th, U, La, Pb, and other elements are more enriched in the Longdong coal mine samples; and elements Th, U, La, Pb, and other elements are more enriched in the Yaoqiao coal mine samples. Furthermore, W is enriched in Yaoqiao mine samples and is highly enriched in Longdong mine samples. The mining area is generally rich in the elements U, La, and Pb. The distribution curves of rare earth elements in the three mines are inclined to the right, with negative Eu anomalies. The enrichment is of the light rare earth enrichment type. (4) Pb isotope data show that the samples from the three mines are mainly distributed in the orogenic belt and the subduction zone lead source areas, where the upper crust and the mantle are mixed, with individual sample points distributed in the mantle and upper crust lead source areas. Full article

In addressing the issue of a low drawing rate in a steeply inclined and extremely thick coal seam, this study focused on the engineering background of the +575 horizontal working faces in the Wudong Coal Mine. By utilizing physical similarity simulation experiments, research was carried out on the top-coal-drawing rate and the gangue ratio at different coal-drawing intervals in horizontal segment mining for steeply inclined and thick coal seams, in which the relationships between the top-coal-drawing law and the drawing interval and technologies were revealed. The discrete element method was used to establish a numerical simulation model for the horizontal segment mining of steeply inclined and thick coal seams, and the roof-drawing law in the cases of the three-interval-group-of-support and drawing-once-every-two-support methods were analyzed before finally obtaining the optimal drawing technology. Through field practice, the coal-drawing effect of the technology was verified. The results indicated that the logarithmic functional relationship between the top-coal-drawing rate and the gangue ratio was established, and the optimal control indicator for top coal drawing was reached when the gangue ratio reached from 13% to 18%. The top-coal-drawing rate for the three-interval-group-of-support approach was higher than that of the method for drawing once every two supports. It was determined that the optimal mining technology was using a one-web-cutting-with-one-drawing approach for a three-interval-group-of-support method at a top-coal-drawing rate of 69.14%, which was 10.86% higher than that of the original technology. The research results further enriched the theory of top coal drawing in steeply inclined and extremely thick coal seams, thereby providing a reference and guidance for such mining operations. Full article

To study the law of gas transportation in mining areas, Fluent numerical simulation software was applied to examine the influence of different pseudo-slope lengths (PSL) on gas concentration in a U-ventilated working area under no-extraction conditions. Based on this, numerical simulation experiments were conducted on the buried pipe extraction arrangement parameters. The simulation found that when there was no extraction, the PSL had an impact on the airflow in the extraction area, which caused the airflow in the extraction area to be disordered, causing gas to accumulate locally at the working area. When the buried pipe depths (BPDs) and PSLs of the working area worked together, the gas concentration of the working area was lower when the inlet air influence zone and the extraction influence zone were through; otherwise, gas concentration accumulation occurred at the working area. The research results showed that when the PSL was at 25 m and BPD was at 20 m, the gas concentration at the working area was not abnormal, and the gas concentration in the upper corner was lower. By adjusting the PSL and BPD of the test working area, the maximum gas concentration in the upper corner was reduced to 0.46% and the maximum gas concentration in the return air outlet was reduced to 0.41%. The experimental and practical results provide important reference values for coal and gas co-mining. Full article

In Sichuan Province, China, most coal seams that are mined are steeply inclined; their roadways’ surrounding rocks are asymmetric, with non-equilibrium deformations and unstable anchorage structures, thus making major safety hazards highly likely. Using field observations and a universal distinct element code (UDEC) numerical simulation method, this paper analyzed the time-dependent failure of the ventilation roadway of Working Face 1961 of the Zhaojiaba Mine, revealing the preconditions for such damage and a bidirectional deterioration mechanism for the deformation as well as stress of surrounding rocks. Moreover, this paper built an anchorage mechanical model for the thick layer of the roadway roof and proposed a cross-boundary anchor-grouting (CBAG) differential support technique. Calculations proved that the new support was particularly effective in restraining the expansion of tension cracks, thus preventing the slipping and dislocation deformations of rock masses on the curved roof side. The feedback of engineering applications showed that the maximum development depths of cracks in the arc roof and straight inclined roof of the roadway 150 m behind the working face are only 1.5 m and 1.10 m, decreasing by 61.3% and 47.6%, respectively, compared with the primary support. The proposed technology offers an overall thick-layer bearing structure for the surrounding rocks of roadways, effectively restraining the non-equilibrium large deformations of roadways in steeply inclined coal seams. Full article