Working Face Of Mine Research Articles

Effect of Thick–Hard Main Roof Fracturing on the Spatiotemporal Evolution of Overburden Fractures

Gas gushing and the co-mining of coal and gas outbursts are common disasters in coal mines. The weakening of thick–hard main roof fracturing can effectively alleviate the gas overrun in the initial mining stage. Four numerical simulation schemes were designed to determine the optimal fracturing treatment scheme for the gas overrun problem in the initial mining stage of the 6505# working face in the Huanghou Coal Mine. Compared with the scheme of the non-fracturing main roof, the weakening of the main roof fracturing could alleviate the concentration of advanced abutment stress. The fissure ratio of the overburden was solved by the binary method, and the dominant channels of gas migration and their morphological evolution under different fracturing schemes were obtained. On this basis, the permeability model of “permeability–fissure ratio–fractal dimension” was established. The results show that the overburden fracture network of the horizontal fracturing scheme has a larger fractal dimension, indicating that the overburden fracture under the scheme is more fully developed and more conducive to gas migration. The research results provide valuable reference for the design of the gas extraction scheme.

Research on Occurrence Law and the Prevention of Rockbursts in Main Roadways Affected by Mining Activities: Two Case Studies from Gaojiapu and Cuimu Coal Mines, Shaanxi, China

Rockburst, one of the leading types of disaster in mining and rock engineering causing serious injuries and the loss of property, frequently occurs, involving various features and complex evolutionary mechanisms. Compared to rockbursts occurring at mining faces, those occurring in main roadways cause more serious problems for mine production. This paper first analyzes the characteristics of rockbursts in main roadways using two case studies involving the Gaojiapu and Cuimu coal mines. The causes of rockbursts in main roadways were studied using microseismic monitoring, energy density cloud maps, and seismic velocity tomography. During the mining of the 22306 working face in the Cuimu coal mine, targeted measures, such as deep-hole blasting of the roof strata and deep-hole blasting of the coal seam, were implemented to prevent rockbursts in the main roadways. The effectiveness of these measures was verified through long-term analysis of tremor activities. The study found that the influence of mining at two working faces on both sides of main roadways was significantly greater than that from a single-sided working face. The intensity of the tremor activities occurring near the main roadways was correlated with the distance from the working face to the main roadways. The closer the working face was to the main roadways, the stronger the tremor activities were near the main roadways. According to the distribution range of the tremors, the influence area of working face mining exceeded 800 m, with tremors distributed linearly along the main roadways. Even five months after the completion of working face mining, there were still a large number of tremors near the main roadways, which gradually disappeared after another five months. Mining activities were the main reason for the occurrence of main roadway rockbursts and the stress concentration within the main roadways themselves was another reason for the occurrence of rockbursts. The influence of working face mining could be reduced by deep-hole blasting of roof strata and the stress concentration within main roadways themselves could be reduced by large-diameter drilling. Those joint preventive measures effectively prevented the occurrence of rockbursts in main roadways. This study is of important theoretical and practical significance for further studies of rockburst mechanisms and prevention in regard to main roadways in coal mines, and the findings are significant in terms of the enhancement of safety in coal mines.

Coal mining activities driving the changes in bacterial community

The mechanism of the difference in bacterial community composition caused by environmental factors in the underground coal mine is unclear. In order to reveal the influence of coal mining activities on the characteristics of bacterial community structure in coal seam, 16S rRNA gene amplicon sequencing technology was used to determine the species abundance, biodiversity, and gene abundance of bacterial community in a coal mine in Shanxi Province, and the environmental factors such as metal elements, non-metal elements, pH value, and gas concentration of coal samples were determined. The results showed that environmental factors and bacterial communities had obvious regional characteristics. Mining activities greatly affected the α diversity of bacterial communities, mining working face > main airway > roadway roof > unexposed coal seam > tunneling roadway. The bacterial community composition of each sample point is also very different. The main airway, roadway roof, and unexposed coal seam are dominated by Actinobacteria while the mining working face and tunneling roadway are dominated by Proteobacteria. Among the gene abundances of metabolic pathways in each site, Citrate cycle had the greatest difference, followed by glycine, serine and threonine metabolism, and oxidative phosphorylation and methane metabolism had little difference. RDA analysis showed that the environmental factors affecting the bacterial community were mainly cadmium, oxygen, hydrogen, and gas content. CCA analysis divided the bacterial community into three categories. Degradation functional bacteria are located in mining working face, bacteria that tolerate poor environments are located in main airway and tunneling roadway, and human pathogens are mostly located in roadway roof and unexposed coal seam. The research results would provide support for realizing green and safe mining in coal mines.

Design of gas control lane of 9# coal seam in Wuhushan Mine based on layer layout optimization

In order to address the issue of gas over limit in the upper corner of the working face of the 9# coal seam in Wuhushan Mine, a series of theoretical and numerical simulation analyses were conducted to evaluate the optimal configuration for the gas control lane of the 9# coal seam. In accordance with the "O" circle theory and the lithology of the overlying rock strata of the 9# coal seam, the height range of the fallout zone and fissure zone in the working face mining area was determined by employing empirical formulas. The change rule and distribution characteristics of the porosity of the fissure zone and the fall zone in the mining area were analyzed based on the characteristics of rock movement and fall. The determination method was also provided. The numerical simulation software was employed to simulate and analyze the gas concentration field in the air-mining zone under conditions of no extraction and six distinct layer positions of the gas control lane. The optimal layer position of the gas control lane in the 9# coal seam was determined and subsequently implemented in the field. The results demonstrate that the overlying rock layer in the 9# coal seam exhibits a height range of 6.86 ~ 11.26 m, while the fissure zone displays a height range of 30.11 ~ 41.31 m. When the gas control road is situated in close proximity to the working face, the gas concentration field exhibits a markedly low concentration. When the distance between the gas control lane and the return airway of the working face is 20 m and the distance from the top of the coal seam is 20 m, the gas concentration in the upper corner and the return airway is 0.35% and 0.26%, respectively. These values are close to the lowest concentration observed in the layout scheme. Additionally, the gas extraction concentration and the pure volume of the gas control lane are 23.7% and 38.3 m3 min−1, respectively. These values represent the highest concentrations observed in the various layout schemes. The application of the gas management lane in the field, based on the numerical simulation results, demonstrated a successful extraction effect, which was consistent with the numerical simulation results. This effectively managed the issue of an over-limit of gas in the upper corner of the working face of the 9# coal seam.

Time Series Prediction of Gas Emission in Coal Mining Face Based on Optimized Variational Mode Decomposition and SSA-LSTM.

The accurate prediction of gas emissions has important guiding significance for the prevention and control of gas disasters in order to further improve the prediction accuracy of gas emissions in the mining face. According to the absolute gas emission monitoring data of the 1417 working face in a coal mine in Shaanxi Province, a GA-VMD-SSA-LSTM gas emission prediction model (GVSL) based on genetic algorithm (GA)-optimized variational mode decomposition (VMD) and sparrow search algorithm (SSA)-optimized long short-term memory (LSTM) is proposed. Firstly, a VMD evaluation standard for evaluating the amount of decomposition loss is proposed. Under this standard, the GA is used to find the optimal parameters of the VMD. Then, the SSA is used to optimize the key parameters of the LSTM to establish a GVSL prediction model. The model predicts each component and finally superimposes the prediction results for each component to obtain the final gas emission result. The results show that the accuracy of the evaluation indexes of the GVSL model and VMD-LSTM model, as well as the SSA-LSTM model and Gaussian process regression (GPR) model, are compared and analyzed horizontally and vertically under three scenarios with prediction sets of 121,94 and 57 groups. The GVSL model has the best prediction effect, and its fitting degree R2 values are 0.95, 0.96, and 0.99, which confirms the effectiveness of the proposed GVSL model for the time series prediction of gas emission in the mining face.

Optimizing Methane Control in Composite Goaf Areas: Insights from Multisource Emission Analysis and Numerical Modeling in the Tongxin Coal Mine.

Coal mine methane poses a threat to both coal production and the well-being of workers. This study investigates the complex challenge of managing methane emissions from multiple sources in coal mines prone to gas. Coal mining creates multiple air leakage channels in the mine goaf, increasing the risk of gas explosions. Tracer SF6 measurements were employed to identify multiple air leakage channels. A comprehensive numerical model, incorporating multiple air leakage channels, was developed to simulate methane distribution in the goaf and upper corner. By adjusting the combination of gas drainage rate (U) and working face ventilation flux (Q), the concentration of methane at the upper corner is expected to be decrease, ensuring safe production at the Tongxin mine. A total of 48 simulation cases were conducted, determining that U = 1080 m3/min and Q = 2250 m3/min are recommended for the 8201 working face in the Tongxin coal mine. This combination provides not only an effective solution but also a cost-efficient one for methane control. The findings offer a new insight into effective methane control providing a foundation for improving mine safety.

Development Law of Water-Conducting Fracture Zones in Overburden above Fully Mechanized Top-Coal Caving Face: A Comprehensive Study

Although it is of great significance to master the height of the water-conducting fracture zone (WCFZ) to prevent coal mine disasters and ensure safe production, the most important thing is to predict the height and range of the WCFZ ahead of the working face design before coal mining. Therefore, the 150313 fully mechanized top-coal caving working face of the Yinying coal mine was taken as the engineering background. The development laws of WCFZ were studied using comprehensive research methods, including similar simulation experiments, key strata theory, the experience formula, the numerical simulation, etc. The results show that the WCFZ evolution stage is “goaf–caving zone–fracture zone” and the developing pattern is in a non-isosceles trapezoid gradually developing upward and forward. The height of the WCFZ in the 150313 working face is 89.36 m, and the fracture/mining ratio is 12.46, which is consistent with the actual production. Apparently, the set of indoor research methods in this paper is feasible to predict the height and scope of the WCFZ. The research results can provide a scientific reference for safe mining of the 15# coal seam in Shanxi Province and the prevention and control of roof water hazards.

Stress Evolution and Rock Burst Prevention in Triangle Coal Pillars under the Influence of Penetrating Faults: A Case Study

The occurrence of rock bursts due to penetrating faults are frequent in China, thereby limiting the safe production of coal mines. Based on the engineering background of a 501 working face in a TB coal mine, this paper investigates stress and energy evolution during the excavation of this working face due to multiple penetrating faults. Utilizing both theoretical analysis and numerical simulations, this study reveals the rock burst mechanism within the triangular coal pillar influenced by the penetrating faults. Based on the evolution of stress within the triangular coal pillar, a stress index has been devised to categorize both the rock burst danger regions and the levels of rock burst risks associated with the triangular coal pillar. Furthermore, targeted stress relief measures are proposed for various energy accumulation areas within the triangular coal pillar. The results demonstrate that: (1) the superimposed tectonic stress resulting from the T6 and T5 penetrating faults exhibits asymmetric distribution and has an influence range of about 90 m in the triangular coal pillar, reaching a peak value of 11.21 MPa at a distance of 13 m from the fault plane; (2) affected by the barrier effect of penetrating faults, the abutment stress of the working face is concentrated in the triangular coal pillar, and the magnitude of the abutment stress is positively and negatively correlated with the fault plane barrier effect and the width of the triangular coal pillar, respectively; (3) the exponential increase in abutment stress and tectonic stress as the width of the triangular coal pillar decreases leads to a high concentration of static stress, which induces pillar burst under the disturbance of dynamic stress from fault activation; (4) the numerical simulation shows that when the working face is 150 m away from the fault, the static stress and accumulated energy in the triangle coal pillar begins to rise, reaching the peak at 50 m away from the fault, which is consistent with the theoretical analysis; (5) the constructed stress index indicates that the triangular coal pillar exhibits moderate rock burst risks when its width is between 73 to 200 m, and exhibits high rock burst risks when the width is within 0 to 73 m. The energy accumulation pattern of the triangular coal pillar reveals that separate stress relief measures should be implemented within the ranges of 50 to 150 m and 0 to 50 m, respectively, in order to enhance the effectiveness of stress relief. Blasting stress relief measures for the roof and coal are proposed, and the effectiveness of these measures is subsequently verified.

Predictive model for the instability of flexible formwork concrete wall in secondary mining of non-pillar coal mining

The secondary mining movement in non-pillar coal extraction causes significant overrun damage to flexible formwork concrete walls, leading to extensive deformation of roadway roof and bottom plates. This adversely affects working face efficiency and safety. The engineering context focuses on the non-pillar gob-side retaining walls in the 1315 working face of Zhaozhuang Coal Mine and the 23107 working face of Xiegou Coal Mine. Through on-site investigation, numerical simulation, theoretical analysis, and testing, we explore the stress migration law and destabilizing mechanism of the flexible formwork concrete wall influenced by the secondary mining movement of the coal-free pillar along the hollow wall. The research results showed that: (1) During the mining back process, the concrete wall formed with flexible formwork may experience stress concentration, leading to excessive damage and compromising mining safety. (2) Developing a predictive stress model for the concrete wall with flexible formwork is essential. If the stress surpasses the ultimate compressive strength during mining back, reinforcement becomes necessary.3) The length of damage overrun in the flexible formwork concrete wall exhibits two distinct stages as the distance back to mining increases. The first stage shows nearly linear growth, while the second stage indicates a decreasing growth rate, ultimately stabilizing. The application of Z6 concrete reinforcing agent effectively strengthens the flexible formwork concrete wall.

Surface damage reduction effect of ultra-high working face in Shangwan coal mine

Green mining is the basic background of high-quality mining, and source reduction is the most important part, among which the optimization of working face height and length is the most active. How to control the working face parameters, reasonably evaluate the surface subsidence characteristics of the super-long working face, and identify the limit working face length and the surface discontinuous deformation threshold is particularly important. In order to solve the problem of irreversible damage to the surface caused by the mining process of the working face, this paper discusses the whole process of surface movement in the 8.8 m super-large mining height working face of Shangwan Coal Mine through field investigation, the maximum subsidence is 6.20 m, with a subsidence coefficient of 0.72. Combined with the inflection point trajectory, advancing degree and subsidence coefficient, the 0.9 coefficient of the working face subsidence basin boundary and the loss reduction strategy far from the limit working face threshold are proposed. The results show that the subsidence basin of 12,401 working face accounts for 34%, the continuous deformation area of surface accounts for 64%, and the influence area of discontinuous deformation area is within 10 times of mining height. With the help of borehole detection verification, the caving zone height within the coal seam overburden to be between 33.2 and 33.25 m and the fracture zone height between 118.08 and 132.83 m. Therefore, the caving ratio is about 3.8, and the fracture ratio is about 13–15, which provides a strong basis for the optimization design of working face and the timing of surface ecological management.

DRA-UNet for Coal Mining Ground Surface Crack Delineation with UAV High-Resolution Images.

Coal mining in the Loess Plateau can very easily generate ground cracks, and these cracks can immediately result in ventilation trouble under the mine shaft, runoff disturbance, and vegetation destruction. Advanced UAV (Unmanned Aerial Vehicle) high-resolution mapping and DL (Deep Learning) are introduced as the key methods to quickly delineate coal mining ground surface cracks for disaster prevention. Firstly, the dataset named the Ground Cracks of Coal Mining Area Unmanned Aerial Vehicle (GCCMA-UAV) is built, with a ground resolution of 3 cm, which is suitable to make a 1:500 thematic map of the ground crack. This GCCMA-UAV dataset includes 6280 images of ground cracks, and the size of the imagery is 256 × 256 pixels. Secondly, the DRA-UNet model is built effectively for coal mining ground surface crack delineation. This DRA-UNet model is an improved UNet DL model, which mainly includes the DAM (Dual Dttention Dechanism) module, the RN (residual network) module, and the ASPP (Atrous Spatial Pyramid Pooling) module. The DRA-UNet model shows the highest recall rate of 77.29% when the DRA-UNet was compared with other similar DL models, such as DeepLabV3+, SegNet, PSPNet, and so on. DRA-UNet also has other relatively reliable indicators; the precision rate is 84.92% and the F1 score is 78.87%. Finally, DRA-UNet is applied to delineate cracks on a DOM (Digital Orthophoto Map) of 3 km2 in the mining workface area, with a ground resolution of 3 cm. There were 4903 cracks that were delineated from the DOM in the Huojitu Coal Mine Shaft. This DRA-UNet model effectively improves the efficiency of crack delineation.

Assessing open-pit mining impacts on semi-arid grassland: A framework for boundary and intensity quantification

Coal mining in northern China's grasslands faces significant environmental challenges due to the fragile semi-arid ecosystem and the abundance of mineral resources. However, current research lacks clarity in both theoretical understanding and effective quantification of its impacts. Insufficient distinction between direct and indirect environmental effects, the oversight of interactions from neighboring activities, and inaccurate measurements of impact intensity all hinder a comprehensive understanding. These limitations also prevent the precise delineation of ecological protection compensation areas. In this study, we developed a comprehensive framework utilizing Landsat time-series images (1989–2017) and field sampling data (228 sample locations in 2017) to assess the boundaries and intensities of mining impacts. First, the k-means clustering algorithm was applied to identify the Normalized Difference Vegetation Index (NDVI) time-series trajectories and map the spatial information of direct impacts. Then, a buffer zone was established and an amplitude model was proposed for determined the cross-impacts and their intensities based on the volatility of NDVI trajectories. Accordingly, a Trend-thresholds model was proposed to automatically extract the indirect impacts boundary of mining-dominated on vegetation under varying intensities. The Soil Quality Index (SQI) ∼ distance curves were fitted and a derivative model was employed for determine the boundary of indirect impacted on soil. We applied this assess framework in Baorixile coalfield (i.e., Baorixile coal mine (BM), DongMing coal mine (DM), Shunxing coal mine (SX)) a typical semi-arid grassland mining area, and quantified three types of impacts: direct, indirect, and cross-impacts. Findings reveal negative coal mining impacts primarily confined to permitted mining areas and decreasing over time. Direct impacts boundary limited in the mining sites and its impact intensity shows a dual nature, with a negative weakening and a positive strengthening trend. Widespread negative indirect impacts exist outward the mining area displays spatial heterogeneity, and its intensity attenuation with distances. In there, the very severe effect (D1) is predominantly focusing on the grassland where near by the mining work face (BM maximum range 1.2 km, DM maximum range 0.55 km, SX maximum range 0.4 km). Moreover, our study indicated that vegetation and soil exhibited consistent responses to coal mining impacts within 1 km, demonstrating the feasibility of using remote sensing data to qualify the impact boundary on the grassland environment. Besides, we further identify significant cross-impacts surrounding the mining areas, characterized by strong negative effects, particularly in the southeastern region of BM. This research offers valuable insights for effective ecological compensation governance and scientific environmental management in similar global contexts.

Energy Evolution Characteristics and Hydraulic Fracturing Roof Cutting Technology for Hard Roof Working Face during Initial Mining: A Case Study

In the process of mining, a large area of hard roof will be exposed above a goaf and may suddenly break. This can easily induce rock burst and has a significant impact on production safety. In this study, based on the engineering background of the hard roof of the 2102 working face in the Balasu coal mine, the spatial and temporal characteristics of the strain energy of the roof during the initial mining process were explored in depth. Based on a theoretical calculation, it is proposed that hydraulic fracturing should be carried out in the medium-grained sandstone layer that is 4.8–22.43 m above the roof, and that the effective fracturing section in the horizontal direction should be within 30.8 m of the cutting hole of the working face. The elastic strain energy fish model was established in FLAC3D to analyze the strain energy accumulation of the roof during the initial mining process. The simulation and elastic strain energy results show that, as the working face advances to 70–80 m, the hard roof undergoes significant bending deformation. The energy gradient increases with the rapid accumulation of strain energy to a peak value of 140.54 kJ/m3. If the first weighting occurs at this moment in time, the sudden fracture of the roof will be accompanied by the release of elastic energy, which will induce rock burst. Therefore, it is necessary to implement roof cutting and pressure relief before reaching the critical step of 77 m. To this end, the comprehensive hydraulic fracturing technology of ‘conventional short drilling + directional long drilling’ is proposed. A field test shows that the hydraulic fracturing technology effectively weakens the integrity of the rock layer. The first weighting interval is 55 m, and it continues until the end of the pressure at the 70 m position. The roof collapses well, and the mining safety is improved. This study provides an important reference for hard roof control.

Research on the evolutionary patterns and control of surrounding rock superimposed stress field local area loading in double-layer Island face main roadway

Double-layer island working face main roadway coal pillars are affected by complex mining stress superposition, when different coal pillar width combinations, the surrounding rock stress field will produce different degrees of regional loading increase effect; the study of the surrounding rock stress field regional superposition loading increase law is meaningful to explaining the failure mode of the roadway and determining the critical control area. This study combines numerical simulation with on-site monitoring and other methods and draws the following conclusions: The superimposed loading increase law (“decreasing” → “increasing”) of the abutment pressure and deviatoric stress in the lower coal seam of the double-layer island working face during the mining; the type of the principal stress deflection in the advance working face region; and by obtaining the three types of development morphology of the deviatoric stress peak zone of the roadway and its corresponding nine evolution modes (one type of circular tube → four types of inverse hyperbolic body → four types of hyperbolic body) in the double-layered island working face mining. Indicated the critical reinforcement area corresponding to the main roadway when at different combinations of coal pillar widths; determined the main track roadway protective coal pillars width for 40 m and the shape of the roadway peak deviatoric stress zone is the inverse class hyperbolic body mode; according to the evolution mode of the peak deviatoric stress zone, determined the synergistic failure control program for the asymmetric critical zone of the roadway surrounding rock which is a targeted scientific support method; after the feedback of on-site monitoring and, the support program is reasonable and effective.

Development of a Graded Early Warning Index System and Identification of Critical Temperatures for Coal Spontaneous Combustion Using Composite Gas Characteristics.

Conventional single gas alarm method and coal spontaneous combustion three-stage alarm method have become increasingly inadequate to meet complex underground conditions. To address this issue, this study focuses on the coal in the goaf of the Z109 working face in the Donggucheng Mine as the research object. Through program-controlled heating experiments, the production of carbon monoxide and hydrocarbon gases during the coal oxidation process was determined, and the variation characteristics of gas ratios with temperature were further analyzed. The coal spontaneous combustion process was subdivided into seven small stages, and a quantitative composite parameter coal spontaneous combustion grading warning system was formulated. Based on its characteristics, measures to be taken under different warning levels were proposed, and it was determined that 120, 140, and 160 °C are the key temperatures for coal spontaneous combustion prevention and control in the Z109 working face of Donggucheng Mine. By using numerical simulation, the optimal nitrogen injection position for the working face was determined and the on-site fire prevention and extinguishing measures were optimized, providing insights into the establishment of a coal mine spontaneous combustion warning system.

Floor failure behavior and water disaster prevention system of ultra-wide opposite pulling working face mining on confined aquifer

The floor failure depth of the ultra-wide opposite pulling working face (OPWF) mining on the confined aquifer is larger, and the risk of water inrush is higher. Based on the engineering background of Binhu Coal Mine (BHCM) in North China Coalfield, this paper analyzes the distribution rule of floor support pressure in OPWF mining, carries out numerical simulation before and after roof cutting, and microseismic-electrical joint dynamic monitoring. The results show that the failure depth, vertical stress, maximum principal stress, maximum shear stress, and pore water pressure of floor after roof cutting are decreased by 28.6 %, 15.5 %, 12.1 %, 30.9 %, and 41.7 %, respectively, the stress concentration coefficient is also decreased by 19.5 %. Roof cutting blocks the propagation path of mining stress, reduces the mine pressure concentration and controls the floor failure depth. Using the optimal univariate function between the floor failure depth and mining width, mining depth, mining height, roof cutting height, working face stagger distance, a multi-factor prediction model for the floor failure depth of the OPWF mining is established, and the accuracy of the model is more than 90 %. Combined with the methods of exploration, treatment, and monitoring, the water disaster prevention technical guarantee system in the ultra-wide OPWF mining on the confined aquifer is constructed, which provides a new method for the prevention and control of floor water disasters during mining.

Study on the early warning of cracking and water inrush risk of coal mine roof and floor

Microseismic monitoring has proven to be an effective approach for detecting and preempting water inrush incidents within mining operations. However, challenges persist, particularly in terms of relying on a singular early warning index and the complexities involved in quantification. In response to these obstacles, a dedicated investigation was undertaken against the backdrop of mining activities at the 11,023 working face of Paner Coal Mine. Primarily, a novel methodology for categorizing the roof and floor into distinct zones was established based on the vertical distribution of microseismic events. Furthermore, this study delves into the dynamic evolution of key source parameters, such as microseismic energy, apparent stress, and apparent volume, amidst mining disturbances, enabling a comprehensive evaluation of the risk associated with roof and floor cracking, as well as potential water inrush incidents. A groundbreaking approach to early warning was proposed, operating on three pivotal dimensions: the depth of fractures, the intensity of fractures, and the likelihood of water inrush. Through rigorous validation during mining operations at the 11,023 working face, the efficacy was substantiated. Ultimately, the achievements offer invaluable insights and practical guidance for the advancement and implementation of water inrush early warning systems in coal mining contexts.

Research on CO Migration Patterns in Shallowly Buried Coal Seam Composite Goafs.

To address the issue of CO exceedance in the close-range composite goaf, this paper focuses on the composite goaf of the Shaping Mine as the research subject and investigated the migration dynamics of CO within shallowly buried composite goaf areas. Sulfur hexafluoride gas (SF6) tracer experiments were conducted at the 13103 working face in Shaping Mine to assess surface fissures and air leakage, yielding insights into the distribution patterns of air leakage channels and facilitating the identification of critical areas for channel sealing. Programmed heating and oxidation experiments were conducted on coal seams 8# and 13# to determine the CO generation patterns during coal oxidation. The results show that higher concentrations of O2 corresponded to elevated CO production at equivalent temperatures. Subsequent data analysis unveiled exponential relationships between the O2 consumption rate and CO production rate within the goaf area, offering a theoretical framework for understanding CO migration patterns. Through numerical simulations, the study analyzed the CO migration patterns in the composite goaf area, observing downward diffusion of CO emanating from coal oxidation in the overlying goaf areas followed by dispersion toward the working face and roadways. Driven by airflow dynamics, CO accrued in the return air corner of the working face. Building upon these insights, comprehensive CO management strategies were implemented, resulting in sustained reductions of temperatures and CO concentrations to safe levels within the original high-temperature, high-concentration CO zones. Notably, CO concentrations at the return air corner of the working face continued to decline over the management period, reaching below 24 ppm within 10 to 15 days, highlighting the effectiveness of the management measures in ensuring safe underground production.

Study on the instability mechanism and control technology of narrow coal pillar in double-roadway layout of Changping mine

To address the issue of roadway support failure in narrow coal pillars under dual-lane layout, this study takes the 4309 working face of Changping Coal Mine as the engineering background and employs theoretical calculations, numerical simulations, and on-site monitoring to investigate the instability mechanisms of narrow coal pillars under dual-lane conditions and to optimize technical solutions. The results indicate that the internal stress distribution within the coal pillar is influenced by the advanced support stress, and as the working face advances, the gradually increasing advanced support pressure causes the vertical stress peak within the coal pillar to shift away from the goaf area. Computational analysis reveals that the vertical stress in the top region of a 6 m narrow coal pillar is 38% higher than that in the bottom region, with an average stress of 16 MPa in the coal pillar. The asymmetric high-level stress concentration within the coal pillar significantly affects its stability. A UDEC (Universal Distinct Element Code) model was established to compare four simulation schemes with cut-off angles of 0°, 5°, 10°, and 15°. Based on the analysis of damage parameters and fracture distribution in the narrow coal pillar roadway, it was concluded that the stability is best when the cut-off angle is 10°. The dense drilling cut-off unloading technology was applied to the 4309 working face of the Changping Mine based on the aforementioned research. On-site monitoring results show that the relative deformation of the roof and bottom plates and the two sides of the test section were controlled within 267 mm and 198 mm, respectively, effectively resolving the deformation and instability issues of the narrow coal pillars.

Study on Fracture Evolution and Water-Conducting Fracture Zone Height beneath the Sandstone Fissure Confined Aquifer

Studying the evolution law of overlying rock fissures and predicting the development height of water-conducting fissure zones is the key to preventing roof water damage, protecting mine water resources, and realizing the safe and sustainable development of the mine. To study the overburden fracture evolution law of coal mining under aquifer conditions, the 1402 working face of Longwangzhuang Mine in Shaanmian Coalfield serves as the engineering background based on the Fractal Theory and similar simulation technology; this paper analyzes the fracture evolution of overburden rock and the development law of Water-Conducting Fracture Zone (WCFZ) during the advancing of working face, and further puts forward a model for the location discrimination of overburden fracture based on plate theory. The results indicate that post-mining, overburden rock failure assumes a trapezoidal shape, and fractures around the cutting hole and the side of the working face fully develop, while those in the middle of the goaf tend to compact. The distribution of the fracture network of mining strata at different advancing distances has good self-similarity, and the fractal dimension of the fracture network of overlying rock can be divided into three stages: ascending dimension, decreasing dimension, and stable phase. The II 1 coal seam fracture does not spread to the Sandstone Fissure Confined Aquifer. These findings provide strategic guidance for protecting mine aquifer water resources, preventing and controlling roof water inrush, and ensuring safe and sustainable production within the study area.