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The in-situ monitoring technology for overburden movement in mining has the features of adapting to complex geological conditions in deep shaft high pressure water and thick coal seam mining, multi layer dynamic monitoring, and high-precision remote real-time online transmission. It provides effective data support for mining enterprises to carry out roof disaster prevention and control. Starting from the practical background of coal mining application, this paper systematically reviews the development process, technological progress, and application effects of in-situ monitoring technology for overburden movement in mining. Based on the development history of mining pressure theory and overburden movement monitoring technology in China, this paper comprehensively introduces the important stages of in-situ monitoring technology for overburden movement in mining. It elaborates on the theoretical innovation and technological breakthroughs achieved by this technology in three aspects: multidimensional real-time collaborative monitoring, unmanned online monitoring, and deep rock movement monitoring. Based on the monitoring engineering examples of coal mines such as Bulianta Coal Mine, Tongxin Coal Mine, and Gaojiabao Coal Mine, the effectiveness of in-situ monitoring technology for overburden movement in mining is demonstrated in practical engineering applications. The application prospects of this technology in different types of mining areas and research fields are discussed. It is pointed out that the development trend of in-situ monitoring technology for overburden movement in mining is precision, intelligence, and integration, namely optimizing sensor performance and layout plans to improve monitoring precision and accuracy, using artificial intelligence, big data, and Internet of things technology to achieve automatic analysis and prediction, combining the in-situ monitoring technology with other technologies to form a complete monitoring system.

The mining of extremely thick coal seam form a large space stope, the fracture disturbance of hard roof spreads to a wide range, the working face weighting has the characteristic of “strong mine pressure”, it is obviously different from rock burst, especially when the coal seam roof “square” mining period, the stope mine pressure is more intense. Based on this, the disturbance height of overburden and fracture characteristics of hard roof in extremely thick coal seam mining are discussed by field measurement and 3D physical similarity simulation. Firstly, the fracturing law of overburden was analyzed based on the field measurement, the results showed that the hard roof was fractured advance the working face during the extra thick coal seams mining. The initial movement of the roof mainly revolved around the base point near the fault line and sinking, behind the working face for a certain distance. The observation results of ground sinking showed that the strata formed a roof groups and moved combined of extra thick coal seams, and there is a step phenomenon during strata movement. The study shows that the disturbance height of overburden in extremely thick coal seam mining is large and the fracture of hard roof has steering characteristics. With the advance of coal seam mining, the transverse “O-X” fracture of low roof layer gradually turns to the longitudinal “O-X” fracture of the high hard rock. The critical position of fracture turning of hard roof in extremely thick coal seam is the so-called “square” area of coal seam mining, which reasonably explains the phenomenon of “square” pressure in working face mining. The large longitudinal fracture size of the high roof and the wide range of disturbance influence are the main factors inducing the strong mine pressure in the stope. The rationality of the “low-medium-high” layer structure of the overburden in extremely thick coal seam after mining is determined, which provides a basis for the accurate interpretation of the large space stope size cycle and the strong mine pressure.

The current fully mechanized mining equipment removal plan during sequencing working face mainly depends on manual preparation. The large workload and low efficiency lead to the extension of the construction period. The quick removal mainly depends on a high degree of mechanized operations. There is little research on optimizing the fully mechanized mining equipment removal plan during sequencing working face between different mines or different working faces in the same mine. In order to solve this problem, by investigating the mining conditions of Shendong Group's fully mechanized mining equipment in recent three years, the key parameters such as working face, equipment, personnel, and time are defined, which characterize the fully mechanized mining equipment removal during sequencing working face. Taking minimizing the maximum completion time as the objective function, a mathematical model for the fully mechanized mining equipment removal planning during sequencing working face is established. A genetic algorithm is designed to solve the mathematical model. The three-segment coding method considering the selection of working face, fully mechanized mining equipment and construction team is adopted, and the fitness function is built. The chromosomes of working face, fully mechanized mining equipment and construction team are selected, crossed and mutated. Considering the latest mining time, the legitimacy of chromosomes is judged and adjusted. By setting the number of iterations, search process of the algorithm is terminated and outputs the results. Based on the genetic algorithm for the fully mechanized mining equipment removal planning during sequencing working face, a management system of the fully mechanized mining equipment removal plan during sequencing working face based on B/S architecture is developed. It has realized the functions of basic information management of fully mechanized working face removal during sequence working face, and fully mechanized mining equipment removal planning during sequencing working face. The example shows that the application of genetic algorithm can shorten the construction period of fully mechanized mining equipment removal of 11 fully mechanized working faces in Shendong Group in 2021 from 103 days to 91 days. The method effectively improves the fully mechanized mining equipment removal planning efficiency and engineering efficiency.

The problem of strong mine pressure during the mining of the near goaf working face in Datong coalfield is more serious than that of the first mining face. In order to study the overlying strata movement law under the full mining conditions of extra-thick coal seam, the overlying strata movement of 8202 working face in Tongxin Coal Mine is monitored and analyzed by using a wireless remote monitoring system for internal strata movement of overlying strata under mining condition and borehole TV observing technology. The results show that in the early stage of large space mining of extra-thick coal seam, the overlying strata will be deformed and damaged from top to bottom in the advance working face, and then the layer group will break down and move normally from bottom to top. The overlying strata deformation and destruction in the mining site shows the change characteristics of stage step-up jump, which has a consistent correspondence with the location of the key strata, indicating that the key strata play the main control role in the strata movement. Under the condition of full mining, the overlying strata movement appears linkage subsidence phenomenon. Through physical simulation experiments, this paper further studies the nature of the whole-strata linkage subsidence of the overlying strata during full mining. The results show that before the initial breaking of the main key stratum, the grouped layered movement trend of each key layer is more obvious. After the main key stratum breaks for the first time, affected by the periodic breaking length of each key stratum and the compound breaking law of the upper and lower rock layers, the overlying strata subsidence and movement is more likely to show the whole-stratum linkage phenomenon.

The closed thermal power system employs the combustion of Li/SF6 as the heat source, which can provide power for UUV (Underwater Unmanned Vehicle). The startup and operation stability of the system can be significantly optimized by evaluating the combustion characteristics. Using the visual experimental system, the Li/SF6 combustion process is distinctly observed to be dominated by gas-phase combustion, and the flame is observed to be bright pink. The ignition temperature of Li/SF6 is 473.39 ± 2.00°C in the gaseous atmosphere for an initial pressure of 0.120 MPa and SF6 volume fraction of 75%. Furthermore, a computational model established by adopting the theory of minimum Gibbs free energy is used to estimate the combustion products of Li/SF6. Finally, the gaseous atmosphere of ignition of Li/SF6 is studied. O2 and N2 are not suitable to participate as combustion-supporting gases in the ignition of Li/SF6. Appropriately increasing the initial pressure can effectively reduce the ignition temperature of Li/SF6. To ensure the controlled combustion and safe operation of the closed thermal power system, the recommended initial SF6 volume fraction of the closed thermal power system is 75%. [ABSTRACT FROM AUTHOR]

In view of mining method of pier column backfilling of No.4 thin coal seam in the seventh mining area of Wangzhuang Coal Mine, key technical parameters of the pier column backfilling mining were researched with FLAC3D numerical simulation method, influences of the technical parameters of interval, cover depth and mining height on long-term stability of the pier column backfilling body were analyzed, and conclusions were obtained that stability of the pier column backfilling are decreased with increasing of all the three influence factors. Combining with test condition of working face of the seventh mining area in Wangzhuang Coal Mine, a backfilling mining scheme was determined with elastic nuclear area proportion to define critical safe value and through interior vertical stress change to test it, namely the pier column backfilling size is 6 m×6 m and column interval is 4 m. The practical application result shows that the scheme of pier column backfilling makes goaf filling rate reduce to 30%, and the maximum surface subsidence is only 48 mm, which can effectively control surface subsidence and realize safe mining.