Mine dust is one of the main disasters that threatens the safety of coal mine production, deteriorates the underground working environment and induces various occupational diseases. Based on the harm of mine dust identified and the current domestic and foreign dust-proof technology, the technical research of the foam dust reduction is reviewed; the advantages and disadvantages of foam dust reduction are also discussed. According to the experimental exploration and the study of foam flow characteristics, the process of foam device and foam nozzle separation was adopted, and some site tests were conducted in fully mechanized mining and excavation working faces in Zhangcun, Shanjiaoshu and Jinjia coal mines. The foam technology led to a 59.5% dust removal efficiency in Zhangcun coal mine, which is much higher than the dust removal efficiency of the water spray dust reduction. The efficiency of total mine dust in Shanjiaoshu coal mine reached as high as 72%, and the efficiency of respirable mine dust reached 67%. Compared with the circumstance with no dust-control measure, the average density of the total mine dust in Jinjia coal mine decreased by 22.75~32.95% using foam technology. The results show that the use of the foam to inhibit the transformation of mine dust from the source of dust production to the floating state and the efficiency of dust control is greatly improved. This method can effectively reduce the mine dust density in underground mining and excavation working faces, clean the working environments, and guarantee the health of miners. The research results are of great significance for improving the production conditions of mining and excavating face and building green mines and standardized mines. Moreover, foam technology for dust control has been widely used in coal mines.

The zoning of the coal seam gas is zonal, which has a significant impact on the prominent prediction indicators, resulting in different prediction results for the same prominent prediction indicators in the same coal seam soft and hard coal. In this paper, the hard coal and soft coal in the coal seam are highlighted. The adsorption and desorption rules of the soft coal and hard coal in the outburst coal seam and its influence on the sensitivity of the outstanding prediction index are studied. The results show that: (1) the initial desorption of soft coal is larger than that of hard coal; (2) the outstanding prediction index has an exponential function relationship with gas pressure; (3) the sensitivity of prediction indicators is different. And concluded that: (1) the initial desorption rate of soft coal is faster than that of hard coal; (2) the outburst prediction index K₁ and Δh₂ increase with the increase of gas adsorption equilibrium pressure; (3) outburst prediction index K₁ is more reliable than Δh₂.

Understanding the stress‐cracks‐permeability evolution law inside coal body under cyclic loading is significant to optimize the gas extraction technology and gas disasters prevention technology. In order to explore the influence of mining cyclic stress on the mechanical behavior and permeability variation of gas‐bearing seams, the experiments on permeability evolution, deformation law, and acoustic emission (AE) characteristics of coal samples under cyclic loading with different loading stress level and different loading frequency were carried out. These results indicate that the higher loading stress level, the shorter the fatigue life of coal sample. With the increase of the loading stress level, the change rate of permeability became higher and the relation curves between permeability and loading cycles developed from “U” to “V,” which can be defined and divided into three stages, for example, decrease stage, stable stage, and increase stage. And the permeability in the decrease stage can be modeled as a power function of the loading cycles, while the permeability in the increase stage can be modeled as an exponential function of the loading cycles. Besides, the loading stress level has a significant on the permeability, while the loading frequency has little impact on the permeability evolution. In the process of coal deformation under cyclic loading, the strain development of strain coal samples was in the shape of inverted “S,” while the variation of the peak values of corresponding AE ring counts presented “U” type. In addition, there was a good correlation between the permeability and the AE parameters of coal samples, which provide a new sight into the dynamic variation process of the stress‐cracks‐permeability evolution inside coal body under cyclic loading.

With mining technology and mechanization degree being improving, fully mechanized caving mining technology (FCM) has become a main method for thick coal seam extraction in China. However, roof‐coal caving characteristics in turn restrict its recovery efficiency, especially for the coal seam with complicated structure (CCS), that is, the coal seam comprises hard or soft coal and gangue. In order to explore the key factors influencing the roof‐coal caving and recovery characteristics, related research work has been conducted as follows: firstly, a mechanical model of CCS has been established, which indicates the strength of the coal and gangue will directly affect the roof‐coal recovery. Meanwhile, based on the geological settings of Qinyuan coal mine, numerical simulation on roof‐coal caving law under different thicknesses of hard or soft coal and gangue has been performed using UDEC software. The results show that the maximum principal stress will increase with the increase of mining depth, making the roof‐coal to break easily. Furthermore, the range of the plastic zone of the top coal and the damage degree of the top coal increase with the increase of mining depth. Physical modeling results show that when an extraction‐caving ratio is 1, the number of times the coal arch forms is 0.43 at every caving, up to a maximum of 3; the number of times coal arch forms with an extraction‐caving ratio of 2 is 4.65 times larger than that with an extraction‐caving ratio of 1. The probability of coal arch formation with an extraction‐caving ratio of 3 is minimal, about 0.4, which is due to that the arch span is large and the curvature is small, so it is difficult to form a stable arch structure. According to the mechanical characteristics of roof‐coal in Qinyuan coal mine, deep‐hole blasting technique has been used to reduce the fragments of roof‐coal crushed. The results show that this technique can effectively improve the recovery of roof‐coal.

The prediction of dangerous hazards in working faces is an important link to prevent coal and gas outbursts. Improving the accuracy of predictive indicators is of great significance for reducing the phenomenon of being prominently below the critical value and ensuring safe production. The fixed-size desorption index K₁ is one of the important indicators for coal face and gas outburst prediction. Based on the diffusion theory and the physical meaning of fixed-size coal samples, the mathematical expression of K₁ is established by the self-developed high/low temperature pressure swing adsorption-desorption experimental system. According to the equation, the effects of gas pressure, loss time, coal particle size and diffusion coefficient on K₁ are studied. The results show that the K₁ index is logarithmically related to the gas pressure. Under the same conditions, the longer the loss time is, the smaller the measured K₁ is, and the smaller the particle sizes of the drill cuttings are, the more notable the performance is; the diffusion coefficient represents the ability of gas to bypass micropores and the coal matrix. The greater the ability to bypass the matrix is, the larger the diffusion coefficient under the same conditions is, and the larger K₁ is; the coal particle size has a greater influence on K₁, and the smaller the size is, the more likely it is that the phenomenon of being prominently below the critical value occurs. Therefore, the particle size composition of coal during on-site measurements is crucial for obtaining the true K₁ and the exact critical values.