Search Results (281)

The construction of stochastic models and the use of stochastic simulations for their analysis constitute research methods used in the analysis of stochastic processes. These methods can be applied to processes carried out in underground mines. For mining processes, carried out, e.g., in hard coal mines, it is noticed that the influence of factors generally referred to as geological–mining and technical–organizational may cause a given process to be treated as not fully defined (not necessarily in terms of the process technology, but, e.g., taking into account the time taken for its implementation). This article draws attention to the possibilities of reducing the stochastic model based on the use of the properties of the convolution of probability density functions. Functions that were considered appropriate for describing the processes discussed based on time-based studies were presented. The mechanism of operation of the proposed model reduction was discussed. Reduction carried out in this way eliminates the need to analyze these parts of the model, e.g., using the stochastic simulation method. This reduction leads to simplification of the model and the calculations, which translates into the effectiveness of the research. Full article

Addressing the stability control challenges of roadways with composite roofs in the No. 34 coal seam of Donghai Mine under high-strength mining conditions, this study employed integrated methodologies including laboratory experiments, numerical modeling, and field trials. It investigated the mechanical response characteristics of the composite roof and developed a synergistic control system, validated through industrial application. Key findings indicate significant differences in mechanical behavior and failure mechanisms between individual rock specimens and composite rock masses. A theoretical “elastic-plastic-fractured” zoning model for the composite roof was established based on the theory of surrounding rock deterioration, elucidating the mechanical mechanism where the cohesive strength of hard rock governs the load-bearing capacity of the outer shell, while the cohesive strength of soft rock controls plastic flow. The influence of in situ stress and support resistance on the evolution of the surrounding rock zone radii was quantitatively determined. The FLAC^3D strain-softening model accurately simulated the post-peak behavior of the surrounding rock. Analysis demonstrated specific inherent patterns in the magnitude, ratio, and orientation of principal stresses within the composite roof under mining influence. A high differential stress zone (σ₁/σ₃ = 6–7) formed within 20 m of the working face, accompanied by a deflection of the maximum principal stress direction by 53, triggering the expansion of a butterfly-shaped plastic zone. Based on these insights, we proposed and implemented a synergistic control system integrating high-pressure grouting, pre-stressed cables, and energy-absorbing bolts. Field tests demonstrated significant improvements: roof-to-floor convergence reduced by 48.4%, rib-to-rib convergence decreased by 39.3%, microseismic events declined by 61%, and the self-stabilization period of the surrounding rock shortened by 11%. Consequently, this research establishes a holistic “theoretical modeling-evolution diagnosis-synergistic control” solution chain, providing a validated theoretical foundation and engineering paradigm for composite roof support design. Full article

To address the low drilling efficiency of the composite rod drill in gas extraction boreholes, key drilling parameters are optimized using coal-seam hardness grading tests and response surface methodology. By conducting mechanical tests on coal samples from the Sangshuping, Zhangcun, and Wangzhuang coal mines, the coal seams are classified into three categories: soft (Pus coefficient 0.87), medium–hard (2.16), and hard (3.47). Multi-factor and multi-level field tests were then performed at different working faces, using Design Expert software to analyze the response surface of three factors: pump pressure, flow rate, and feed pressure. The response surface method was used to determine the influence of drilling factors on drilling time under different coal-seam hardness conditions and the optimal drilling parameters. The results indicate that the technology is not suitable for soft coal seams due to frequent bit jamming. The optimal parameters for medium–hard coal seams are a pump pressure of 4 MPa, a flow rate of 180 L/min, and a feed pressure of 6 MPa (time per 100 m: 62 min 33 s). For hard coal seams, the optimal parameters are a pump pressure of 6 MPa, a flow rate of 200 L/min, and a feed pressure of 8 MPa (time per 100 m: 55 min 27 s). This study provides a theoretical basis for efficient coal seam drilling. Full article

Ensuring employee safety is a top priority for every enterprise, and it is especially critical in high-risk industries like coal mining. To achieve this goal, it is essential to focus efforts on identifying existing hazards and thoroughly assessing the associated risks. Accurate identification and detailed characterization of occupational hazards play a pivotal role in the occupational risk assessment process, providing the foundation for effective safety strategies. This article presents an analysis of the process of identifying occupational hazards in hard coal mining, based on applicable legal regulations and a review of the relevant literature. The analysis reveals, on the one hand, a diversity of approaches to hazard classification, and on the other, a limited use of the characteristic features of hazards in classification processes. The findings of this review form the basis for proposing a systematic classification of occupational hazards in hard coal mining, taking into account the specific features of hazards in relation to their sources and potential consequences. The proposed classification not only categorizes hazards but also describes the specifics of hazard sources, such as environmental conditions, machinery, chemicals, and human factors, as well as the possible outcomes of these hazards, including physical injury, health impacts, and even fatalities. The aim of this article is to present a proposed classification of occupational hazards in hard coal mining and to provide a detailed characterization of these hazards based on the description of their sources and potential consequences. The proposed approach, grounded in the identification of characteristic features of hazards, facilitates the effective selection of preventive measures that can be implemented to reduce risk and improve workplace safety. Due to the presence of the full spectrum of natural hazards in Polish hard coal mining, the analysis draws on available statistical data, focusing on those hazards that contribute most significantly to fatal accidents and serious injuries. In conclusion, the article emphasizes the importance of a structured and systematic approach to identifying and assessing occupational hazards in the coal mining industry. By drawing on legal and literature-based insights, it aims to contribute to the development of more effective safety practices that protect workers and minimize the occurrence of workplace accidents and illnesses. Full article

Investigating the microstructural damage and mechanical properties of coal under deep mine hygrothermal conditions is essential for ensuring the safe and efficient extraction of coal resources. In this study, X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and nanoindentation techniques were employed to examine the surface morphology and microscale mechanical properties of coal samples exposed to four environmental conditions, initial, humidified, heated, and coupled hygrothermal, under a peak indentation load of 70 mN. The results indicate that humidification led to the formation of dissolution pores and localized surface softening, resulting in a 15.9% increase in the peak indentation depth and reductions in the hardness and elastic modulus by 29.53% and 17.14%, respectively. Heating caused localized disintegration and the collapse of the coal surface, accompanied by surface hardening, with a slight 0.4% decrease in the peak indentation depth and increases in hardness and the elastic modulus by 1.32% and 1.56%, respectively. Under the coupled hygrothermal condition, numerous fine dissolution pores and microcracks developed on the coal surface, and the mechanical properties exhibited intermediate values between those observed in the humidified and heated states. Notably, the elevated temperature suppressed the moisture penetration into the coal matrix to some extent in the hygrothermal environment. A positive correlation was found between the hardness and elastic modulus, independent of the coal sample condition. The mineralogical composition significantly influenced the microscale mechanical behavior, with hard quartz minerals corresponding to lower peak indentation depths and a higher hardness, whereas soft kaolinite showed the opposite trend. Full article

In order to make the anchor bolt support prestress field fully diffuse in the composite rock stratum, improve the overall bearing capacity of surrounding rock, and give full play to the role of active support of the anchor bolt, a self-made 1:1-scale composite rock stratum similarity simulation test bed was used to compare and analyze the distribution of the anchor bolt support prestress field using different anchoring surrounding rock lithology and anchorage lengths, and the principle for optimum selection of anchoring parameters of composite rock stratum was proposed based on the test results. Considered from the point of view of stress diffusion, the effect of prestress diffusion of end anchorage bolts is better than that of lengthening anchorage; at the same time, the anchorage section should be preferentially arranged in hard rock, and the area of anchorage section near the free section should avoid the structural plane of surrounding rock. In conclusion, an industrial test was carried out under the conditions of a deep composite roof of the 2# coal seam in Qinyuan Mining Area, which determined a reasonable anchoring method and position of the composite roof under different conditions and achieved good results. Full article

Underground longwall mining conducted in the vicinity of the barrier pillars in the KWK ROW Ruch Marcel mine has led to volume changes in the rock mass. As the longwalls progressed, a gradual increase in stress occurred in the goaf overburden, as a result of which this part of the rock mass increased in density in relation to the surrounding strata. Seismic events occurring during mining as a result of elastic energy accumulation led to the relaxation of the medium and local decreases in its bulk density. The microgravimetric method is sensitive to variations in this physical parameter of rock. The most transparent effects of the differences in rock mass density can be observed by performing periodic local gravity field surveys and analysing their spatial and temporal variability. This paper analyses the relationship between ground deformations and the spatial and temporal gravity field distribution changes observed on the surface in the context of the safety of barrier pillars F1 and F2 in Marklowice (the GSB-GFO testing ground of project EPOS-PL+). Relative gravimetric surveys, referenced to the determined absolute values of g, were performed in 7 series over the period of 2021–2023. The collected data made it possible to chart differential maps of gravity field changes and anomalies with Bouguer reduction. The differential anomaly distributions between successive survey series and the reference series were analysed. This served as the basis for assessing the safety of the barrier pillars maintained by the mine and the possibility of ground deformation occurrence on the surface. Full article

The hanging of hard roofs in coal seams poses a significant threat to the safe mining of coal. Hydraulic fracturing is an important method to achieve the pre-weakening of coal seam roofs. Clarifying the scope of hydraulic fracturing in coal seam roofs and its influencing factors is a prerequisite for ensuring the effectiveness of the pre-weakening process. In this paper, we developed a fluid–structure coupling numerical simulation model for hydraulic fracturing based on the element damage theory, and have systematically examined the effects of both engineering parameters and geological factors on the hydraulic fracture propagation behavior of the segmented fracturing of coal seam roofs. Results indicate that increasing the injection rate can significantly enhance fracture propagation length. A larger stress difference directs fractures along the maximum principal stress direction and effectively extends their length. Additionally, increasing the spacing between fracture stages reduces stress interference between clusters, leading to a transition from asymmetric to uniform fracture propagation. To validate the numerical simulation results, we conducted a field test on the hydraulic fracturing of the coal seam roof, and monitored the affected area by using transient electromagnetic and microseismic monitoring techniques. Monitoring results indicated that the effective impact range of field hydraulic fracturing was consistent with the numerical simulation results. Through the systematic monitoring of support resistance and coal body stress, the supporting resistance in the fractured zone decreased by 25.10%, and the coal seam stress in the fractured zone exhibited a 1 MPa reduction. Observations demonstrate the significant effectiveness of hydraulic fracturing in regional control of the coal seam roof. This study combines numerical simulation with engineering practice to investigate hydraulic fracturing performance under varying operational conditions, with the findings providing robust technical support for safe and efficient mining production. Full article

To address the issue of rockburst in deep return airways caused by thick, hard sandstone roofs in the Hulusu Coal Mine, this study proposes a deep borehole pressure relief technique based on hydraulic fracturing. The goal is to proactively weaken the hard roof structure and effectively mitigate rockburst hazards. The research integrates numerical modeling, theoretical analytics, and field application to systematically delve into the unstable mechanism of deep hard rock and determine the crack propagation patterns and optimal borehole parameters. Engineering validation was carried out at the 21,103 mining face. Results indicate that when the borehole inclination is 45°, the spacing is 15 m, the diameter is 65 mm, the borehole depth is 24 m over the coal pillar (CP) and 30 m on the operating face, the pressure relief effect is optimal. This configuration effectively forms a pressure relief zone in the roof, significantly reduces surrounding rock stress concentration, and enhances structural stability. Field monitoring shows that the roof energy is released stably through crack propagation, effectively reducing the risk of rockburst. The proposed technique provides theoretical and engineering support for rockburst prevention in deep hard rock mining conditions. Full article

Underground coal mines face increasing challenges in the scheduling of Electric Rubber-Tired Vehicles (ERTVs) due to confined spaces, dynamic production demands, and the need to coordinate multiple constraints such as complex roadway topologies, strict time windows, and limited charging resources in the context of clean energy transitions. This study presents a Constraint Programming (CP)-based optimization framework that integrates Virtual Charging Station Mapping (VCSM) and sensor fusion positioning to decouple spatiotemporal charging conflicts and applies a dynamic topology adjustment algorithm to enhance computational efficiency. A novel RFID–vision fusion positioning system, leveraging multi-source data to mitigate signal interference in underground environments, provides real-time, reliable spatiotemporal coordinates for the scheduling model. The proposed multi-objective model systematically incorporates hard time windows, load limits, battery endurance, and roadway regulations. Case studies conducted using real-world data from a large-scale Chinese coal mine demonstrate that the method achieves a 17.6% reduction in total transportation mileage, decreases charging events by 60%, and reduces vehicle usage by approximately 33%, all while completely eliminating time window violations. Furthermore, the computational efficiency is improved by 54.4% compared to Mixed-Integer Linear Programming (MILP). By balancing economic and operational objectives, this approach provides a robust and scalable solution for sustainable ERTV scheduling in confined underground environments, with broader applicability to industrial logistics and clean mining practices. Full article

The selection of mining cutting tools used on the cutting heads of roadheaders and shearers in hard coal mines is primarily based on the uniaxial compressive strength (UCS) of the rock. However, selecting cutting tools solely on the basis of a single parameter characterizing the rock has proven to be insufficient. Therefore, the aim of the presented study was to develop guidelines for the selection of cutting tools with appropriate protective coatings on the working parts, based not only on the mechanical strength properties of rocks, but also on their abrasivity. For the study, twelve rock samples were collected from five different Polish hard coal mines. For each rock type, the UCS (uniaxial compressive strength), BTS (Brazilian tensile strength), and chemical composition (determined using wavelength-dispersive X-ray fluorescence, WD-XRF) were measured, along with the rock abrasivity index Wz, determined using a proprietary method developed at the AGH University of Krakow. The test results were compared with the calculated specific pick wear, defined as the number of picks consumed (replaced) per 1000 m³ of excavated material. As a result, a classification of rocks based on their UCS and abrasivity was developed, along with recommendations for selecting conical picks with suitable protective coatings on the working parts. Full article

Based on the engineering conditions of the 1303 working face in Zhaoxian Coal Mine, this study investigates the characteristics of mine pressure behavior and the stress-relief mechanism of advanced presplit blasting in a working face with a thick and hard roof in an extra-thick coal seam. Through a combination of numerical simulations and field experiments, the effects of advanced presplit blasting on stress distribution, roadway stability, and microseismic activity are analyzed. Corresponding mitigation measures and optimization strategies are proposed. The results indicate that the primary cause of deformation in the gob-side roadway is the superposition of lateral abutment pressure from the goaf and the front abutment pressure of the advancing working face. Advanced presplit blasting effectively reduces the magnitude of front abutment stress, inhibits its transmission, decreases the hanging area of the goaf roof, and alleviates vertical stress on the roadway side adjacent to the goaf. Furthermore, both the daily average and peak microseismic energy levels decrease as the working face approaches the advanced blasting zone. The implementation of advanced presplit blasting technology in working faces with thick and hard roofs within extra-thick coal seams significantly mitigates rockburst hazards, enhances roadway stability, and improves overall mining safety. Full article

The water-conducting fracture zone (WCFZ) is a critical geological structure formed by the destruction of overburden during coal mining operations. Accurately predicting the height of the water-conducting fractured zone (HWCFZ) is essential for ensuring safe coal production. Based on more than 150 measured heights of fractured water-conducting zone samples from various mining areas in China, this study investigates the influence of five primary factors on the height: mining thickness, mining depth, length of the panel, coal seam dip, and the proportion coefficient of hard rock. The correlation degrees and relative weights of each factor are determined through grey relational analysis and principal component analysis. All five factors exhibit strong correlations with the height of the fractured water-conducting zone, with correlation degrees exceeding 0.79. Mining thickness is found to have the highest weight (0.256). A multiple nonlinear coordinated regression equation was constructed through regression analysis of the influencing factors. The prediction accuracy was compared with three other predictive models: the multiple nonlinear additive regression model, the BP neural network model, and the GA-BP neural network model. Among these models, the multiple nonlinear coordinated regression model was found to achieve the lowest error rate (7.23%) and the highest coefficient of determination (R² = 87.42%), indicating superior accuracy and reliability. The model’s performance is further validated using drill hole data and numerical simulations at the B-1 drill hole in the Fuda Coal Mine. Predictive results for the entire Fuda Coal Mine area indicate that as the No. 15 coal seam extends northwestward, the height of the fractured water-conducting zone increases from 52.1 m to 73.9 m. These findings have significant implications for improving mine safety and preventing geological hazards in coal mining operations. Full article

The return roadway in Limin Coal Mine experiences strong mine pressure during the mining work of the I030902 working face, which poses potential safety hazards to production and management. Therefore, hydraulic fracturing is used to relieve pressure on the free coal pillar roof. Hydraulic fracture simulation tests using gelatin materials were conducted, and the propagation of the hydraulic fracturing cracks in gelatin simulating different key strata was obtained, which led to the design of the hydraulic fracturing used in the I030902 working face at Limin Coal Mine. According to the analysis of the on-site tests, after fracturing, the roof pressure decreased by 17.8%, the average pressure step distance reduced by 18.0%, the average daily rate of the roof and floor convergence decreased by 63.86%, and the average daily rate of the roof and floor convergence was reduced by 72.4%. Therefore, the feasibility of the hydraulic fracturing in weak structure formation in hard roof strata and roadway deformation control has been verified, providing a theoretical foundation and on-site date for the relief of free roadway roof pressure. Full article

During coal resource mining, hard roof mining is prone to causing rock-burst disasters because traditional blasting–cutting roof technology has the disadvantages of low efficiency and high cost. This article studies the theoretical basis and engineering application of fracturing technology with a static expansion agent (SCA). The influences of borehole diameter and spacing on the fracturing effect of a rock mass are studied through theoretical analysis and simulation. Rock mass models of a cantilever beam for a single rock layer and multiple layers were established, and the mechanical properties of the roof strata under three working conditions were analyzed. The research results show that the maximum annular stress value occurs along the drill hole wall between the adjacent drill holes, and the annular stress at the center line between two drill holes is the smallest. As the spacing between the holes increases, the annular stress at the center line decreases; however, the annular stress at the center of the drill line becomes larger with the increase in hole diameter. The degree of stress concentration increases sharply with the decrease in distance f from the borehole center to the free surface. Relative to the cantilever beam model of a single rock layer, the combined rock layers can effectively control the displacement and deformation of the cantilever roof. Based on the above research results, a drilling method with a 75 mm diameter and a 10° inclination angle is used, demonstrating that the suspended roof area can be reduced to below 20 m² using the fracturing technology with a static expansion agent, allowing the roof strata to fall simultaneously during mining. Full article