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This study investigates the fracture evolution patterns of overlying strata under the mining conditions of close-distance coal seams.Taking the 9305 working face of Anshun Coal Mine as the research object, this study probed into the evolution of displacement field and strain field during the mining process of close-distance coal seams through physical similarity simulation test.The results show that ①with the continuous advancement of distance from the working face, the overburden strata first form separation cracks and longitudinal cracks, and then the middle part of the goaf is gradually compacted.②The displacement field is asymmetrically distributed in the advancing direction of the working face, The displacement of the overlying rock on the side of the working face is obviously smaller than that on the left side of the goaf, and the peak displacement is mainly concentrated in the middle of the goaf.③The maximum principal strain concentration position is asymmetrically transferred from the middle of the goaf to the open-off cut side and the working face side.The concentration degree of the open-off cut side is significantly higher than that of the working face side.This reveals that a potential correlation exists between the maximum principal strain concentration position and the gas enrichment area.

Abstract Affect gas extraction efficiency to find out the optimum well location parameters, based on the gray correlation analysis of borehole diameter, borehole spacing, and extraction pressure three boreholes parameters that influence efficiency of gas extraction from the design of orthogonal experiment, using COMSOL simulate the effective radius of extraction under different experiments, and the effective radius of extraction for optimizing index quantitative gas extraction efficiency. The results showed that: factors affecting the gas extraction efficiency of the correlation between high and low aperture drilling, borehole spacing, and extraction from extraction negative pressure, it is concluded that the influence parameters of optimal layout parameter values, respectively, borehole diameter 8 cm and 3 m borehole spacing, extraction pressure 50 kPa, combined with the numerical simulation analysis using the optimal layout of gas drilling extraction from about 30 days. The decrease in gas pressure is about 45%, which basically meets the extraction standard, and the decreasing trend of gas pressure is obviously slowed down when the extraction time is longer than 30 days. The engineering experiment is carried out in the 9306 transport lane of a mine in Guizhou Province, and the results are basically consistent with the simulation results, which verify the rationality of the gray correlation analysis method to optimize the drilling parameters, and provide a theoretical basis for the optimization of drilling parameters.

This paper introduces the research results of the main coal mine roadway excavation technologies in recent years. The technologies include cantilever roadheader comprehensive excavation technology, continuous shearer tunneling technology, and integrated excavation technology. The applicability and promotion value of these three main roadway excavation technologies in China is analyzed. The following points are pointed out. ① The comprehensive excavation technology of the cantilever roadheader can only 'excavate before anchoring'. The excavation and support processes cannot be carried out simultaneously, which limits the excavation efficiency. ② The continuous shearer tunneling technology can only be carried out in near horizontal coal seam conditions. It has certain requirements for the stability of the roof. The applicability is weak. ③ The integrated excavation technology is only suitable for rapid excavation of single roadways with large cross-sections. The integrated excavation and anchoring machine used is large and expensive. The machine has certain requirements for the stability of the bottom plate of the excavated roadways. Compared to the continuous mining machine excavation technology, the integrated excavation technology has a good application prospect in China. Expanding the excavation function of the original roadheader to the function of excavation and support can promote the research and application of integrated excavation and anchoring technology. The study analyzes the research achievements of intelligent cutting, remote intelligent monitoring, and intelligent collaborative control in the robotized intelligent excavation technology of coal mine roadways in recent years. The following points are concluded. ① Intelligent cutting technology mainly focuses on the research of adaptive recognition of coal and rock. ② Remote intelligent monitoring technology has evolved from remote real-time monitoring to remote visual monitoring. The development of virtual simulation technology visualizes the situation of underground excavation roadways on the ground. And it feeds back control signals to the excavation working face to remotely synchronize and control the excavation working face roadheader unit. This becomes an important symbol of the current intelligent remote monitoring of roadway excavation. ③ There is currently limited research on intelligent collaborative control technology. This study explores the development directions of intelligent coal mine roadway excavation. The directions include strengthening the integration and collaboration of excavation equipment, modular combination of equipment, 5G mining wireless network equipment, remote intelligent monitoring system for excavation, and research on difficult and slow excavation roadway excavation engineering.

This study focuses on the issue of gas overflow encountered during the mining of coal seams at the Anshun coal mine. Initially, a mechanical model is constructed to analyze the displacement and vertical stress distribution in the upper neighboring coal seam following the mining of the protective seam in the field. Subsequently, similar indoor simulation experiments, utilizing the digital image correlation method, are conducted to examine the evolution characteristics of the overlying rock strain during the back mining process of the lower protective seam. Numerical simulation is then employed to analyze the plastic zone, stress distribution, and evolution characteristics of the overlying coal seam during the recovery of the lower protective layer. The study finally investigates the unloading effect of the top plate and the permeability characteristics of the protected layer. The results demonstrate that the maximum main strain concentration area in the overlying rock increases as the working face progresses, transferring asymmetrically from the middle of the mining area to the cuthole side and the working face side, with the concentration on the cuthole side being notably larger. As the lower protective layer advances, the unloading range, unloading height, stress concentration area, peak value, and unloading coefficient are observed to increase gradually before stabilizing. The numerical simulation reveals a predominance of shear damage around the mining area, where high permeability facilitates gas flow. Additionally, the collapsed gangue in the mining area's center is recompacted, leading to reduced porosity and permeability. Stress concentration is noted on both sides of the coal seam, resulting in high stress at both ends and low stress in the middle of the unloading area. Furthermore, the permeability coefficient growth rate diminishes with the advancement of the lower protection layer, exhibiting negative growth in some areas, while the permeability coefficient in the unloading area remains high at the late stage of workface recovery, thereby constituting an efficient gas extraction zone. This study provides a theoretical foundation for the safe and efficient mining of protruding coal seams in southwest China. [ABSTRACT FROM AUTHOR]

This study investigates the fracture evolution patterns of overlying strata under the mining conditions of close-distance coal seams. Taking the 9305 working face of Anshun Coal Mine as the research object,this study probed into the evolution of displacement field and strain field during the mining process of close-distance coal seams through physical similarity simulation test. The results show that ©with the continuous advancement of distance from the working face,the overburden strata first form separation cracks and longitudinal cracks,and then the middle part of the goaf is gradually compacted. ©The displacement field is asymmetrically distributed in the advancing direction of the working face,The displacement of the overlying rock on the side of the working face is obviously smaller than that on the left side of the goaf,and the peak displacement is mainly concentrated in the middle of the goaf. ©The maximum principal strain concentration position is asymmetrically transferred from the middle of the goaf to the open-off cut side and the working face side. The concentration degree of the open-off cut side is significantly higher than that of the working face side. This reveals that a potential correlation exists between the maximum principal strain concentration position and the gas enrichment area. [ABSTRACT FROM AUTHOR]

Borehole destabilization damage is an important factors affecting gas extraction efficiency. To derive the fracture development law, strain, and energy evolution characteristics of different borehole diameters, uniaxial compression experiments were conducted on prefabricated rock specimens with different borehole diameters. The results showed that the elastic energy and dissipation energy of the specimens with different pore diameters changed with the compression process, and the energy distribution inside the specimens. The results show that as the pore size of the specimen increases, the strain area damaged by tensile fracture gradually decreases and the strain area damaged by shear fracture gradually increases, and the damage of the dominant specimen gradually evolves from tensile fracture as the dominant factor to tensile fracture and shear fracture together as the dominant factor and finally to shear fracture as the dominant factor. For the whole compression process of pore size rock specimens, the total energy curve shows a nonlinear growth trend, and the elastic energy curve shows a nonlinear growth trend before the specimen damage and a cliff‐type decrease after the specimen damage. From the perspective of energy distribution, the elastic energy storage limit of the specimen decreases with the increase of the specimen pore size, the energy distribution law inside the rock specimen with pores changes, and the total energy absorbed from the outside gradually changes to the dissipated energy, resulting in an increasing proportion of dissipated energy, indicating that the larger the pore size, the larger the plastic deformation, and the more obvious ductile damage characteristics of the specimen with pores will be shown. The research analyzes the causes of destabilization of rock samples with different hole diameters and provides some theoretical guidance for the study of gas extraction drilling stability. [ABSTRACT FROM AUTHOR]

Background: Signaling lymphocytic activation molecule family-7 (SLAMF7) functions as an immune checkpoint molecule on macrophages in antitumor immunity. However, its role in bacterial infection remains largely unknown.Methods: Bone marrow-derived macrophages (BMDMs) isolated from wild-type (WT) or SLAMF7 knockout (KO) mice were infected with bacteria or treated with lipopolysaccharide/interferon-γ to investigate the expression and function of SLAMF7 in macrophage polarization. A Pseudomonas aeruginosa keratitis murine model was established to explore the effect of SLAMF7 on P. aeruginosa keratitis using WT vs SLAMF7 KO mice, or recombinant SLAMF7 vs phosphate-buffered saline-treated mice, respectively.Results: SLAMF7 expression was enhanced on M1-polarized or bacterial-infected macrophages, and infiltrating macrophages in P. aeruginosa-infected mouse corneas. SLAMF7 promoted M2 polarization by inducing STAT6 activation. In vivo data showed that SLAMF7 KO aggravated, while treatment with recombinant SLAMF7 alleviated, corneal inflammation and disease severity. In addition, blockage of M2 polarization by Arg-1 inhibitor abrogated the effect of recombinant SLAMF7 in disease progression.Conclusions: SLAMF7 expression in macrophages was induced upon M1 polarization or bacterial infection and alleviated corneal inflammation and disease progression of P. aeruginosa keratitis by promoting M2 polarization. These findings may provide a potential strategy for the treatment of P. aeruginosa keratitis. [ABSTRACT FROM AUTHOR]