Analysis of the top coal stability of the large section open-off cut under the gob in thick seams slicing mining.

The reserved thickness of top coal has an important influence on the stability of a large section open-off cut under gob in the thick seams slicing mining. The destabilization extremum conditions of the open-off cut top coal were derived from by elastic-plastic theory, and the optical fibre sensing technology was utilized to monitor the top coal deformation law with different thicknesses (3, 3.5, and 4 m) in the physical similar simulation experiment in the paper. The results show that the top coal thickness is greater than 3.4 m without tension cracks. In the vertical direction, the top coal of the large open-off cut is divided into mining and excavation disturbance zones under the influence of the upper slice coal mining and the excavation disturbance. In the direction of the span of the top coal can be divided into the roof fall risk zone and the warning zone. The deformation changes from exponential to linear to logarithmic in the roof fall risk zone, and it changes from linear to logarithmic in the roof fall warning zone as the number of excavations increases. The sinking amount in the two zones is smaller as the thickness of the top coal becomes larger. It is comprehensively determined that the thickness of the top coal of open-off cut is set as 3.5 m, the stability is moderate, and the field application shows that the integrity of the top coal is good after support, and the maximum off-layer value is 6 mm, which can satisfy the production requirements.

Accumulation of microplastics in fugu (Takifugu bimaculatus): A comparative study between fishing grounds and aquafarms.

Microplastics (MPs) in fish have attracted attention recently, for their ecological and food safety risks. However, knowledge gaps still exist regarding MPs in fugu, a special poisonous but precious seafood, especially that accumulated in its tissues. Accordingly, this study investigated the characteristics of MPs in cultured Takifugu bimaculatus which raised on three aquafarms and in wild individuals from three fishing grounds. More than 98.85 % of T. bimaculatus were contaminated by MPs and the average MPs abundance in wild fugu (4.25 ± 2.63 items/individual) was lower than that of cultured fugu (7.91 ± 2.16 items/individual). The abundance of MPs in fugu's tissues under different life patterns shows significant differences. There were marked differences in size of MPs presented in various tissues. This study adds to the knowledge on MPs accumulation in the tissues of wild and cultured fugu, providing warnings about its transmission and ecological risks in the food chain.

Study on Quantitative Characterization of Coupling Effect between Mining-Induced Coal-Rock Mass and Optical Fiber Sensing.

The monitoring of mine pressure, division of vertical zoning of the overburden, discrimination of key stratum structure of the overburden and monitoring of advanced abutment pressure are still the main research problems in the field of coal mining. Therefore, the promotion of development of a monitoring technology of mining-induced rock mass deformation has important research value in the mining field. There are many problems to be solved in the application of optical fiber sensing (OFS) to deformation monitoring, such as the corresponding relationship between actual deformation and optical parameters, the coupling relationship between the optical fiber and rock mass and the reasonable division of vertical zoning of the overburden. In this study, a quantitative index of coupling action between the mining rock mass and optical fiber is put forward, and the coupling coefficient of different vertical zonings is quantitatively analyzed and discussed. Based on this, five different media in contact with optical fiber are proposed. The relationship between the strain curve form, the development height of the fracture zone and the activity of key stratum is established. It is of great academic value and research significance to establish a characterization system of displacement, deformation and structural evolution of overlying strata based on optical fiber sensing technology.

Improved virtual extensometer measurement method in complex multi-fracture situation.

To overcome the limitation of the virtual extensometer method in measuring the crack opening displacement (COD) in the process of complex multi-crack propagation of rock, the measurement error of Digital Image Correlation (DIC) local deformation is theoretically analyzed. An improved virtual extensometer method for measuring the COD is proposed, which considers the temporal and spatial characteristics of crack development in the process of complex crack propagation. The accuracy of the proposed method is verified by the strain localization band numerical simulation test and indoor single crack simulation test. Furthermore, the method is applied to the two-dimensional similarity simulation test of simulating complex multi-fractures in rock stratum. The COD obtained by the traditional and improved methods is compared with the measured COD. The results show that in the case of multiple complex cracks, to obtain the COD accurately, the relative distance between the virtual extensometer measuring point and the crack should be greater than half of the sum of the width of the crack strain localization zone and the subset size. With the development of the crack, the relative distance between the virtual extensometer measuring point and the crack should increase with the increase of the width of the crack strain localization zone. The error of the COD measured by the traditional method increases with fracture development, and the maximum is 21.20%. The maximum relative error between the COD measured by the improved method and the measured crack opening is 3.61%. The research results improve the accuracy of the virtual extensometer in measuring the COD under complex multi-crack conditions.

Microplastics in different tissues of wild crabs at three important fishing grounds in China.

Crabs are an indispensable component of the benthic ecosystem and represent a type of seafood that is easily obtained and frequently eaten by humans. However, little is known about microplastic (MP) accumulation in different tissues of crabs in important fishing areas. In this study, the abundances and characteristics of MPs in different tissues of four species of wild crabs (Portunus trituberculatus, Charybdis japonica, Dorippe japonica, and Matuta planipes) were investigated across 9 sites at three important fishing grounds (Haizhou Bay, Lvsi and Yangtze River Estuary fishing grounds) in China. Crabs from all sites were found to contain MPs, with a total detection rate of 89.34%. The MP abundance in crabs from all sites ranged from 2.00 ± 2.00 to 9.81 ± 8.08 items/individual and 0.80 ± 1.09 to 22.71 ± 24.56 items/g wet weight. The abundance of MPs exponentially increased with decreasing MP size. The MPs were dominated by fibers in terms of shape, black-gray and blue-green in terms of color and cellophane in terms of composition. MPs were found in the gills and guts of the crabs, but not in the muscles. The abundance and size of the MPs in the guts were significantly higher than those in the gills, but there was no significant difference in color or shape. In addition, crab eating patterns have a significant impact on the abundance of MPs in different species. The abundance of MPs in the saprophytic crabs was significantly higher than that in the predatory crabs. MP contamination in crabs is worthy of attention for human health and the stability of marine ecosystems.