Ziwei Ding

Coal seam drilling for pressure relief is one of the most widely adopted measures to mitigate rock bursts. However, conventional drilling methods exhibit limited effectiveness in hard coal seams and may compromise the integrity of roadway support structures. To optimize traditional pressure relief drilling parameters, this study investigated the influence of coal seam strength and borehole diameter on pressure relief efficiency based on elastoplastic mechanics theory. A novel mechanical reaming technology for pressure relief and rock burst prevention in hard coal seams was developed and subjected to field trials. Multiple monitoring techniques were employed to evaluate its performance in terms of both pressure relief and support stability. The conclusion was drawn that: (1) The higher the strength of the coal seam, the smaller the radius of the plastic zone of the borehole; therefore, the pressure relief effect of the borehole in the hard coal seam is poor. After increasing the diameter of the borehole, the radius of the plastic zone increases, but when the diameter of the borehole increases to 300 mm, the increasing trend of the radius of the plastic zone weakens. Thus, only increasing the diameter of the borehole cannot improve the pressure relief effect of the borehole without limit. (2) An innovative hard coal seam pressure relief and anti-impact technology, termed support, deep pressure relief, unloading-support coupling, the elastic energy accumulated in the coal body through a deep large borehole while utilizing a shallow small borehole to maintain the bearing capacity of the support structure, thereby achieving a balance between pressure relief and support. (3) In comparison to conventional drilling areas, the volume of coal seam drilling powder in the mechanical reaming area has increased by 3.1 times, and the number of per meter has risen by 70%, significantly enhancing the pressure relief effect. Additionally, the anchoring force of the roof anchor cable in the mechanical reaming area has decreased by up to 29%, the variation in tension of the anchor cable on the sides has been reduced by up to 51.8%, the convergence of the two sides of the roadway has diminished by up to 63%, the convergence between the roof and floor has decreased by up to 51%, and both the stress on the support structure and the deformation of the surrounding rock have been significantly reduced. These research findings provide a theoretical foundation and technical support for the prevention and control of rock bursts in similar hard coal seam mining roadways.

This study investigates the relationship between anchor cable drilling parameters and roadway roof strata properties. The goal is to enable rapid and accurate rock type identification. Field-measured drilling data were processed using data cleaning and wavelet transform noise reduction. Four recognition models were developed and compared: LSTM (Long Short-Term Memory), BiLSTM (Bidirectional Long Short-Term Memory), DBO-LSTM (Dung Beetle Optimizer), and DBO-BiLSTM. The results demonstrate a strong correlation between vibration, pressure signals and rock strength, enabling the effective differentiation of rock types. All models performed exceptionally for coal seams with distinct features, achieving 100% accuracy, precision, recall, and F1 scores. Model performance improved with increased complexity for strata with subtle differences, such as sandstone and mudstone. The DBO-BiLSTM model outperformed others, showing significant improvements in accuracy, recall, and F1 score compared to LSTM, BiLSTM, and DBO-LSTM models. Specifically, accuracy improved by up to 9%, recall by 12.48%, and F1 score by 13.06%. These findings highlight the DBO-BiLSTM model’s superior recognition capability for roof strata drilling signals. This method provides a robust technical foundation for lithology identification in Measurement While Drilling (MWD) systems. It supports more precise and efficient roadway design in complex geological conditions.

To study the response relationship between drilling signal and rock mass geomechanical parameters, accurately and quickly perceive and predict the strength of coal and rock mass, guide the optimization of drilling control parameters and the design of the support scheme, and improve the efficiency of roadway excavation, the prediction of rock uniaxial compressive strength based on drilling signal was carried out. Based on the 112,206 return air chute in the Xiaobaodang No.1 Coal Mine as the engineering background, through the drilling data obtained from the roof anchor cable support, data processing, and feature selection, this paper establishes a coal and rock mass strength prediction model based on the AdaBoost integrated algorithm, optimizes the hyperparameter of the model, and analyzes and evaluates the prediction results. The results show that in the AdaBoost integration model, the R² of SVM is the highest, 0.972, and the values of RMSE, MAE, MAPE, and other error indicators are the lowest. The prediction accuracies of the SVM model, tree model, and linear model are 98.8%, 85.4%, and 75.6%, respectively. The experimental results show that the AdaBoost integrated algorithm using a based learning machine has higher prediction accuracy. At the same time, compared with the current advanced model, it further verifies the effectiveness of the model in the coal mine.

Hard coal seams are important geological feature of rockburst in the Ordos region. In response to the poor pressure relief effect of conventional drilling in hard coal seams in the Ordos region, as well as the problems of high-density and multi round pressure relief and support failure, a non equal pressure stress field model for drilling was established. The mechanical analysis of the plastic zone radius in drilling was derived. This analysis revealed how the coal seam strength and drilling diameter affect the pressure relief effect of drilling. A "shallow support and deep pressure relief" hard coal seam unloading support coupling and expanding pressure relief technology was proposed. A 70m comparative industrial test was conducted on site, and the pressure relief and support effect was tested using methods such as coal powder monitoring, coal gun monitoring, stress monitoring, and surrounding rock deformation monitoring. The conclusion was drawn that: (1) The radius of the plastic zone in drilling is primarily influenced by coal seam strength and drilling deformation. The drilling diameter affects the strength of the coal seam. A smaller plastic zone radius is associated with a larger drilling diameter, while a larger plastic zone radius corresponds to a larger diameter as well. However, the increase in pressure relief effect diminishes as the diameter increases. Therefore, simply increasing the drilling diameter cannot indefinitely improve the pressure relief effect. (2) In terms of the pressure relief effect, the amount of coal powder produced in the expanded pressure relief zone has increased by 3.1 times compared to conventional drilling. The "coal cannon" events are concentrated in the 7-14m section of the coal wall, which can significantly release the accumulated elastic energy inside the coal body; After unloading, the peak stress of the coal body decreases, and the recovery rate becomes slower, which has a significant unloading effect on the concentrated static load area. (3) In terms of the support effect, during and after the pressure relief period of borehole expansion, the stress on the roof of the roadway and the anchor cables on the front wall is stable, and the stress on the anchor cables is lower than that of conventional drilling; In the course of the expansion and pressure relief phase, the maximum observed reduction in the lateral movement of the tunnel's two sides was 63%, while the maximum reduction in the vertical movement of the top and bottom plates reached 51%. The efficacy of this method in mitigating the deformation of the surrounding rock in the tunnel significantly surpasses that achieved through traditional large-diameter drilling techniques. (4) We have developed a complete set of anti-erosion technology and equipment based on mechanical drilling and pressure relief, forming an engineering demonstration. The research results can provide theoretical basis and engineering reference for mines with similar conditions in the Ordos region. (Fund Project: Project supported and financed by the Shaanxi Provincial Natural Science Foundation (Grant No. 2024JC-YBMS-261); Corresponding author: DING Zi-wei; Corresponding author at: Xi 'an University of Science and Technology, Xi 'an, Shaanxi 710054, China. Tel: +86 13991812828. Email address of the corresponding author: zwding@xust.edu.cn.)

The synthesis of γ–Al₂O₃ using coal-bearing kaolinite as the aluminum source involves a multi-step process consisting of four main stages: (1) Preparation of metakaolinite, (2) Preparation of sodium aluminate solution, (3) Preparation of aluminum hydroxide, and (4) Preparation of γ-Al₂O₃ through high-temperature heat treatment. To thoroughly characterize the prepared γ-Al₂O₃, various analytical techniques were employed, including x-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, and Brunauer–Emmett–Teller (BET) surface area measurements and pore size distributions. The results of the characterization studies revealed that the synthesized γ-Al₂O₃ exhibits several notable features. The material is lightweight, has a non-crystalline structure, and appears as white porous solids. The primary particle size of the γ-Al₂O₃ is generally < 50 nm, and these nanoparticles form a three-dimensional network structure, leading to a highly porous material. The BET surface area of the γ-Al₂O₃ was determined to be 248.92 m²/g, indicating a high specific surface area that can provide ample active sites for catalytic reactions. Furthermore, the pore size distribution, as determined by the Barrett–Joyner–Halenda method, revealed that the diameters of the pores inside the particles primarily range from 2 to 10 nm, confirming its mesoporous nature. These unique properties make the prepared γ-Al₂O₃ a promising material for various applications in catalysis and other fields where a large surface area and controlled pore size are crucial for optimizing the performance of the material.

Slurry filling technology has been increasingly adopted in coal mines in the northwest region. However, due to the complexity of slurry transport pipelines, blockages remain a frequent issue. These blockages can reduce operational efficiency, with different blockage types causing varying levels of damage. Despite the significance of this issue, there is limited in-depth analysis in the literature, especially regarding the role of pressure in pipeline blockages. This study utilizes FLUENT 2020R2 (the fluid simulation software) for computational fluid dynamics simulations of slurry pipeline blockages, focusing on the impact of blockage morphology, location, and extent on slurry transport pressure distribution. The results indicate that the greater the blockage extent, the more pronounced the pressure loss along the pipeline. Furthermore, blockage morphology also has a varying effect on pressure drop. At lower blockage levels, the pressure drop variation across the three blockage types is relatively minor. However, when the blockage exceeds 50%, sedimentation-type blockages (B-blockage) cause the most significant harm. The study identifies the underlying causes of this and provides recommendations to mitigate sedimentation-type blockages. Within 1 m downstream of the blockage, the flow velocity rapidly decreases to near zero, creating a stagnant zone that accelerates the deposition of gangue particles, thereby worsening the blockage. After a sudden blockage, the location of the blockage has minimal impact on pressure drop. The influence on slurry pressure is ranked as follows: sedimentation-type blockage (B-blockage) > composite blockage (C-blockage) > attachment-type blockage (A-blockage).

To analyze the mechanical characteristics of damaged coal bodies and the mechanisms of evolution and degradation of internal pore and fracture defects under cyclic loads, raw coal containing original pore and fracture materials was selected as the research material. This study investigates the impact of cyclic loading on the mechanical properties of damaged coal and the evolution of flaw structures, such as pores and cracks, within the coal. A micro-fracture size judgment index (C_i) was defined based on fracture volume to determine the dominant macroscopic failure mode in coal bodies. The results indicate that a “hysteresis loop” forms in the loading and unloading curves of each cycle due to cyclic loading. During the cyclic loading and unloading phase, both the loading elastic modulus and the damage parameters of coal samples increase proportionally with the level of loading and the number of cycles. In the constant amplitude cyclic loading and unloading phase, there is minimal variation in the loading elastic modulus and damage parameters of coal samples, indicating their stability. As micro-scale fractures evolve within the coal body, pores with a volume less than 10⁹ μm³ decrease with increasing cyclic loading and unloading during amplification cycles but remain relatively stable during equal amplitude cyclic loading phases. The contribution rate of damage to fractures with a volume between 10⁹ and 10¹¹ μm³ increases with higher load levels and cyclic loading/unloading during both amplification and equal amplitude cycles. The minimum order of magnitude for fracture volume that dominates macroscopic failure in the coal body is determined to be 10⁹ and 10¹⁰ μm³.

Slurry filling technology has gradually been adopted in coal mines in the northwest region. However, due to the complexity of slurry transport pipelines, blockages remain a frequent issue. Pipeline blockages can adversely impact production, reducing operational efficiency, with different blockage types causing varying degrees of harm. Despite the significance of this issue, there is limited in-depth analysis in the literature, especially regarding the role of pressure in pipeline blockages. This study utilizes FLUENT software for computational fluid dynamics (CFD) simulations of slurry pipeline blockages, focusing on the impact of blockage morphology, location, and extent on slurry transport pressure distribution. The results indicate that the greater the blockage extent, the more pronounced the pressure loss along the pipeline. Furthermore, blockage morphology also has a varying effect on pressure drop. At lower blockage levels, the pressure drop variation across the three blockage types is relatively minor. However, when the blockage exceeds 50%, sedimentation-type blockages cause the most significant harm. The study analyzes the reasons behind this and offers recommendations to mitigate sedimentation-type blockages. Within 1 meter downstream of the blockage, the flow velocity rapidly decreases to near zero, creating a stagnant zone that accelerates the deposition of gangue particles, thereby worsening the blockage. After an instantaneous blockage occurs, the location of the blockage has little effect on the pipeline's pressure drop. Among the three blockage types, the impact on slurry pressure in the pipeline is ranked as follows: sedimentation-type blockage > composite blockage > attachment-type blockage.

Taking the specific production geological conditions of the auxiliary transportation lane in the west area of Gaojiabao coal mine of Shaanxi Zhengtong Coal Industry as the research background, based on the anchorage support theory and the characteristics of the TBM digging process, numerical simulation, theoretical analysis, and other research methods were used to investigate the depth of the destruction of the plastic zone of the surrounding rock of the roadway to form the reasonable support parameters of a large cross-section of hard rock roadway suitable for TBM digging and to propose an intelligent digging and support process of the TBM corresponding to the on-site practice. The proposed intelligent tunneling support technology corresponds to a field practice of TBM. The study shows that: combined with the field industrial test and adjusted by the peripheral rock deformation and damage law, the anchor diameter of 20 mm, the length of 2500 mm left-hand threaded steel anchors, row spacing of 1100 mm, spacing of 1200 mm, and the anchor diameter of Φ21.8 mm, the length of 6200 mm left-handed threaded steel anchors, row spacing of 1100 mm, spacing of 1200 mm are the most reasonable solutions, which can ensure the control of the tunnel peripheral rock. The program is the most economically efficient in ensuring the control of deformation of the roadway perimeter rock and maintaining normal use.