International Journal of Coal Science & Technology最新文献

The microstructure and adhesion force between dust particles determine the dust starting and migration to a certain extent. By use of scanning electron microscopy, the BET method, and the abruption technique, the microstructure and adhesion force of dust on the soil pavement of an open-pit mine were examined. The results indicate that the dust shape of soil pavement is mainly irregular quadrilateral, pentagonal and circular. The adhesion of dust particles in soil pavement reduces as particle size and temperature increase. When the particle size grows from 22 to 30 μm and the ambient temperature rises from 25 to 30 ℃, the adhesion force of dust particles in soil pavement drops dramatically. The adhesion force of dust particles in the soil pavement of open-pit mine increases as environmental humidity and pressure rise. When the environmental humidity exceeds 70% and pressure exceeds 24.79 kPa, the adhesion of dust particles increases dramatically. On the basis of the multiple regression method, a prediction model for the dust adhesion force of open-pit mines’ soil pavement has been developed. However, its accuracy needs to be further enhanced.

To rationalize the setting of joint parameters, model size, and initial value of vertical stress in simulation of mining of steeply inclined coal seams, a fault tree analysis method of discrete element numerical simulation was used and a mathematical model was proposed. A method of eliminating the influences of size-effect errors on the parameters of coal and rock samples was obtained based on previous work. Furthermore, the constitutive equation and eigenvalue determination formula of a joint discontinuity surface were established, and a method of determination of the joint parameters was proposed, forming the complete “coupling chain” between parameters for numerical simulation. In addition, a formula for the initial value of vertical stress was constructed by way of the compression and shear model of the element body. Also, the minimum dimension was determined by means of strength factor analysis of fracture mechanics. Taking the research literature as an example, the model size and initial value of vertical stress were calculated. On this basis, the physical parameters of coal samples, the physical parameters of coal rocks considering the influence of the size effect and the calculated coal rock joint parameters considering the influence of size effect were directly used to comparatively analyze the displacement and stress fields, thus verifying the reasonability and correctness of the mathematical model.

Coal gangue is one of China’s main industrial solid wastes, which contains various harmful heavy metal elements, such as lead (Pb). The long-term accumulation of coal gangue causes Pb to migrate to the surrounding environment due to weathering and rain erosion, eventually endangering human life and health with its continuous accumulation in the food chain. This review discusses the migration and transformation process of Pb in coal gangue under different conditions and summarizes the available forms and mechanisms of Pb in coal gangue. The current prevention and control and comprehensive utilization methods of Pb in coal gangue are comprehensively reviewed, and the characteristics of each method are discussed. In order to realize the economical, efficient, and high resource utilization of coal gangue, this paper provides favorable suggestions and support for subsequent in-depth research and the implementation of heavy metal prevention and control measures.

Coal mining under the geological conditions of a loose layer will lead to the intensification of surface movement and deformation, and mining under the geological conditions of a fault will lead to the living slip of a fault. Mining under both conditions will have a great impact on the safety of coal production. To reveal the evolution law of the coupling mechanism of loose layer and fault on the multi-physical fields of overburden, the numerical simulation method is used to simulate the coupling of loose layer and fault with different thicknesses, analyze the changes of vertical stress on the key strata, the changes of surface subsidence, the evolution of elastic energy on the fault zone and the changes of activated slip area of the fault zone. The simulation analysis shows that the vertical stress change trend of the key strata gradually changes from the "V" shape to the "W" shape at the beginning of mining, and the vertical stress concentration will occur at the fault. The loose layer will promote surface subsidence, and the fault will hinder the surface subsidence to a certain extent. The loose layer and the fault alternately affect the surface subsidence. The elastic energy accumulation on the key strata is mainly concentrated on both sides of the goaf. The elastic energy in the center of the goaf is dissipated. The elastic energy accumulation in the fault zone starts from the shallowly buried fault and gradually develops to the deeply buried fault. The instability of fault activation has gone through the initial stage of activation—the intensification stage of activation—the stable stage of activation. Under the working conditions of no loose layer, thin loose layer, and thick loose layer, the fault zone is the first to undergo living slip, and under the action of an extra-thick loose layer, there is a certain lag in the activation slip of the fault zone.

A comprehensive evaluation method is proposed to analyze dust pollution generated in the production process of mines. The method employs an optimized image-processing and deep learning framework to characterize the gray and fractal features in dust images. The research reveals both linear and logarithmic correlations between the gray features, fractal dimension, and dust mass, while employing Chauvenel criteria and arithmetic averaging to minimize data discreteness. An integrated hazardous index is developed, including a logarithmic correlation between the index and dust mass, and a four-category dataset is subsequently prepared for the deep learning framework. Based on the range of the hazardous index, the dust images are divided into four categories. Subsequently, a dust risk classification system is established using the deep learning model, which exhibits a high degree of performance after the training process. Notably, the model achieves a testing accuracy of 95.3%, indicating its effectiveness in classifying different levels of dust pollution, and the precision, recall, and F1-score of the system confirm its reliability in analyzing dust pollution. Overall, the proposed method provides a reliable and efficient way to monitor and analyze dust pollution in mines.

Among all methods for investigating the complex phenomenon of the coal and gas outburst, numerical modelling is the most comprehensive one that can consider all involved parameters and simulate the complex multi-physical phenomenon. The main aim of this paper is to review recent numerical modelling studies concerning this disastrous phenomenon observed in coal mining. The paper aims to analyse these studies comprehensively and identify any existing research gaps that could be addressed in future research endeavours. To this end, the concepts and equations that have been used in previous studies to simulate the solid and fluid behaviour during outburst initiation and how these equations are coupled to consider multiphysical interactions were reviewed. Both strengths and deficiencies in past outburst modelling work were highlighted. Finally, potential research topics for future studies were discussed in three categories; looking into the outburst phenomenon in the scale of the particles which is mostly focused on the discrete element method, conservation of the energy as a method to quantitively assess outburst initiation, and the application of statistics in both applying the heterogeneity in the models and assessing the possibility of the outburst occurrence.

Traditional dense large-diameter borehole stress load-off techniques reduce the stress levels in the shallow surrounding rock, weaken the bearing capacity of the shallow surrounding rock, and greatly deteriorate the shallow surrounding rock strength and supporting structure, which is not conducive to maintaining the long-term stability of the roadway. Therefore, to address the control problem for the pronounced extrusion deformation in the two sides of a roadway and the overall outward movement of the shallow surrounding rock supported by the sides bolts and anchor cables, as well as to comprehensively consider the on-site construction conditions of the two sides of a test roadway, stress load-off technology for asymmetric hole construction on the two sides of a roadway is proposed. The asymmetric stress load-off technique is a new method; while the shallow surrounding rock of the roadway sides is strongly anchored via a full anchor cable support form, a group of large stress load-off holes near the deep stress peak line of the roadway sides is excavated to relieve pressure and protect the roadway. This technology can transfer the peak stress area of the roadway side deeper into f the surrounding rock without deteriorating the shallow surrounding rock strength and damaging the supporting structure. A numerical simulation analysis of asymmetric stress load-off on the two sides of the roadway was performed, the stress load-off effect evaluation index was established, and the optimal field construction parameters were obtained. The stress load-off parameters obtained from the study are applicable to field engineering practice. Mine pressure data reveal that the test roadway remains intact and stable during the use period when the asymmetric stress load-off technique is adopted.

This study examines the fracture mechanism of cracks and the final blasting effects on defective rock masses under blasting loads. The failure processes of jointed rock with two prefabricated joints are investigated through numerical simulations using a two-dimensional finite element method. Subsequently, simulations are performed to analyze the blasting of granite specimens with various joint arrangements, focusing on the influence of front joint length, inclination angle, and blast hole distance on failure patterns, displacement, velocity, and stress at the joint ends. The numerical results provide a comprehensive summary of various typical failure modes near blast holes and joints for the first time. Specifically, the simulation successfully captures the characteristics of the ring crack zone, wing cracks, and main crack deflection affected by the front joint. Moreover, the results highlight the shielding effect of the front joint, which enhances damage in the medium between the borehole and the joint while exhibiting the opposite effect behind the joint in terms of stress wave propagation. Overall, this study offers objective insights into the mechanics and failure characteristics of jointed rock masses under blasting loads and serves as a valuable reference for the design and optimization of blasting operations.

The gas pressure in front area of heading face is essential to dynamically evaluate coal and gas outburst during coal mining. In this work, a novel inversion model of gas pressure in front area of the heading face was established on premise of the hypothesis that a time-dependent zone of steady flow exists within newly exposed face. The key parameters in the inversion model were obtained based on the gas emission models and field data of gas emission rate in different times, which were used to calculate the volumes of gas emission from different sources. The results show that the percentage of gas emission from the heading face, coal wall and collapsed coal ranges from 7% to 47%, 47% to 82% and 2% to 11%, respectively. Based on the calculated volumes of gas emission and gas pressure inversion model, the gas pressure was obtained and transformed to the gas content. The absolute errors between the gas content tested and transformed in every hour is 0.4%–33%, which proved the rationality of gas pressure inversion model. Furthermore, the daily drifting footage, the radius of gas pressure boundary and the gas permeability coefficient of coal seam were confirmed to have a great effect on the result of gas pressure inversion. The inversion results verify that the speedy excavation can increase the risk of coal and gas outburst. This work produces a useful method for gas disaster prevention and control that converts the gas emission rate to an index of gas pressure within coal seam.