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This paper's goal is to investigate if a gob-side entry retention technique combined with a surrounding rock support system is feasible in three soft coal seams. Field engineering confirmed the results of numerical simulation tests and similar simulation tests, which were conducted in accordance with the actual geological conditions of Zhaojiazhai Mine. The following conclusions are reached after studying the technology and process parameter of the gob-side entry retaining in three soft coal seams in conjunction with theoretical calculations: the coal seam of Zhaojiazhai Coal Mine's 12 209 working face is a part of the soft coal seam, and its loose circle is approximately 1.8 m. The expansion roadway size is 3.5 m, and the potential loose circle range is 1.32 m, according to the same model and numerical simulation test. The support scheme after the expansion of the road working face is determined to be the "anchor rod + anchor cable + hydraulic lifting shed" support method. Furthermore, this article suggests a building method for the reinforcement and enlargement of gob-side entry retaining in three-soft thick coal seam by theoretical analysis and numerical simulation. Roadway shotcrete, advance grouting, building of a large deformation anchor cable and continuous resistance, single column lifting shed, hydraulic lifting shed, and roadway enlargement in advance are all steps in the procedure. Furthermore, an analysis is conducted on the deformation features of the surrounding rock in gob-side entry retention. The study highlights the significance of actively supporting the surrounding rock, fortifying the roof support, guaranteeing the stiffness compatibility between the shoulder filling body and the surrounding rock on the roof, boosting the wall's strength and stability, and enhancing the roadway's stability. [ABSTRACT FROM AUTHOR]

As an innovative technology for the stimulation of coalbed methane, liquid nitrogen cold soaking can produce more fractures in coal body and effectively increase the permeability of coal seam. The pore structure distribution of coal affects the permeability of coal and determines the flow and occurrence state of coalbed methane and other fluids in coal. This paper carries out a number of nuclear magnetic resonance tests on coal samples with different coal qualities treated by liquid nitrogen cold soaking and studies the influence law of liquid nitrogen soaking on coal pore structures. It is found that the liquid nitrogen makes the T2 spectral peak shifts to the right, and the anthracite changes from interval T2 spectrum to type T2. It indicates that liquid nitrogen cold soaking in the transformation of pore size to large size improves the pore connectivity and leads to more pore structures. With an increase in times of liquid nitrogen cold soaking, the size and number of coal pore structures gradually increase, and the increasing size is on the order of anthracite > bituminous > lignite. There is a positive correlation between the peak area and the times of liquid nitrogen cold soaking. The porosity and permeability of each coal sample increase with the times of liquid nitrogen cold soaking. From the MRI images of coal samples, it can be found that the liquid nitrogen cold soaking makes the microcracks extend and forms a crack network with other cracks, thereby causing macroscopic damage. The research results are helpful to further reveal the microscopic mechanism of liquid nitrogen cold soaking on coal damage. [ABSTRACT FROM AUTHOR]

The characteristics of hollow cathode discharge are investigated by using two-dimensional fluid model combined with a transport model for metastable atoms (F-M model) in argon. It shows that the stepwise ionization is one of main important mechanism for electrons production. The distribution of electric potential, density of electrons, ions, and metastable atoms are calculated with a pressure of 10 Torr and a voltage of 250 V. The peak density of electron and ion is 1.2×1013 cm-3, and the peak density of metastable atoms is 3.5×1013 cm-3. The results obtained in F-M model are compared with that in fluid model (without metastable atoms involved). Metastable atoms are found to play an important role in the discharge. In addition, with the increase of pressure and voltage, the percentage of stepwise ionization in the total ionization increase, and the difference of discharge characteristics simulated by these two kinds of models rises. [ABSTRACT FROM AUTHOR]