The pore characteristics of coal have an important influence on the dynamic disaster of coal mine. Considering the disaster caused by large deformation of coal-rock mass, the influence of pore deformation and pore distribution also needs further study simultaneously. In this paper, the pore characteristics of gas outburst coal and bursting liability coal are analyzed and compared. The pore structure, the pore volume, and the pore compressibility associated with different dynamic disasters were comprehensively analyzed. The experimental data of mercury intrusion were corrected by liquid nitrogen adsorption experiment data, and the distribution of pore volume was obtained. Moreover, the fractal dimension of partial micropore was calculated, and the pore compressibility of coal was determined according to the fractal dimension. The results show that there are great differences in the pore characteristics between outburst coal and impact proneness coal, which are also one of the factors leading to different disasters in coal mine.
Highlights • NMR cryoporometry was adopted to the characterization pore size distribution in coal. • NMR intensity result for the coal was calibrated to get reliable pore size distribution. • NMR cryoporometry yields a higher pore volume magnitude, compared to low-temperature liquid nitrogen adsorption and desorption (LTNAD). • Pore size distribution can be directly obtained by NMR cryoporometry, based on the linear relation between pore volume and signal intensity and the relationship between the melting point and pore size. Abstract The characterization of coal pore structure is extremely important to coalbed methane exploitation and the prevention of gas disaster in coal mines. Various techniques have been employed to characterize the pore size distribution (PSD) in coals. Nuclear magnetic resonance (NMR) cryoporometry is a relative new technique that can be applied to obtain PSD of porous materials. However, seldom works has been done on coals by NMR cryoporometry. In this paper, PSD of six coal samples ranges from medium to high rank are measured by NMR cryoporometry. Low-temperature liquid N 2 adsorption and desorption (LTNAD) experiments are also carried out on the same samples for the comparison analysis. NMR cryoporometry can directly obtain the PSD from the linear relation between pore volume and signal intensity and the relationship between the melting point and pore size. It was also found that there is a good correlation between the results obtained by NMR cryoporometry and LTNAD. It was found that NMR cryoporometry yields higher pore volume value than LTNAD. Drying induced pores shrinkage/collapse in LTNAD measurement is the main reason causing pore volume measured by NMR cryoporometry is larger than by LTNAD. We also found the difference between NMR and LTNAD correlated with the coal moisture content. Based on the obtained experimental data, it is found that the influence of moisture content on the difference between these two techniques decreases with the increase of pore specific volume.
Abstract Coal bump refers to a sudden catastrophic failure of coal seam and usually can cause serious damages to underground mining facilities and staff. In this circumstance, this paper focuses on the recent achievements in the mechanism and prevention techniques of coal bumps over the past five years in China. Based on theoretical analysis, laboratory experiment, numerical simulation and field test, the characteristics of coal bumps occurrence in China's coal mines were described, and the difference between coal bumps and rockbursts was also discussed. In addition, three categories of coal bumps induced by “material failure” were introduced, i.e. hard roof, floor strata and tectonic structures, in which the mechanism of coal bumps induced by geological structures was analyzed. This involves the bump liability and microstructure effects on bump-prone coal failure, the mechanism of coal bumps in response to fault reactivation, island face mining or hard roof failure. Next, the achievements in the monitoring and controlling methods of coal bumps were reviewed. These methods involve the incorporated prediction system of micro-seismicity and mining-induced pressure, the distributed micro-seismic monitoring system, energy absorption support system, bolts with constant resistance and large elongation, and the “multi-stage” high-performance support. Finally, an optimal mining design is desirable for the purpose of coal bump mitigation.
Abstract A test system was developed to understand the sliding mechanism of coal-rock structure. The test system was composed by a double-shear testing model and an acousto-optic monitoring system in association with a digital camera and an acoustic emission (AE) instrument. The tests can simulate the movement of activated faults and the sliding in coal-rock structure. In this regard, instable sliding conditions of coal-rock samples, sliding types under different conditions, displacement evolution law, and AE characteristics during sliding process were investigated. Several sliding types were monitored in the tests, including unstable continuous sliding, unstable discontinuous sliding, and stable sliding. The sliding types have close relation with the axial loads and loading rates. Larger axial load and smaller loading rate mean that unstable sliding is less likely to occur. The peak shear stress was positively correlated with the axial load when sliding occurred, whereas the displacement induced by unstable sliding was uncorrelated with the axial load. A large number of AE events occurred before sliding, and the AE rate decreased after stable sliding. The results show that the tests can well simulate the process of structural instability in a coal bump, and are helpful in the understanding of fault activation and the physical processes during squeezing process of roof and floor.
Abstract This paper takes No. 52 return uphill roadway of Yangquhe coal mine as a research project. Based on the research, especially its geological condition, indoor experiments, numerical simulation and theoretical analysis were employed to determine the difficult coefficients of Yangquhe project. By using these means, the difficult coefficients of the deep rock engineering were determined. From a study of the effects of crustal stress and the roof mechanism on roadway stability, the transformation mechanism in Yangquhe coal mine has been determined. As a result of this research, the interactive support technology of pre-stressed cable mesh was developed and the technology tested in mining engineering, which proved to be feasible.
Abstract Dynamic indirect tensile tests were carried out by using a Split Hopkinson Pressure Bar (SHPB) for coal sampled from the Datong mine in China. The principal purpose was to explore the influence of bedding structure in the coal on its dynamic indirect tensile strength. However, to resolve some contradictions, X-ray micro CT, high speed optical imaging and a discrete element based modelling approach were combined to analyze the test results. The X-ray micro CT was used to detect the actual bedding structure in the coal; the high speed imaging captured failure patterns of the specimens with different bedding directions; and the numerical modelling was utilized to investigate the influence of different bedding structures on dynamic strength. The SHPB and numerical results illustrate that dynamic indirect tensile strength reliably correlates with impact velocity. In addition, the dynamic indirect tensile strength is not only influenced by the bedding direction but also by the roughness and discontinuity of the bedding. Based on these findings, a method is developed to further process the test data including a model to describe the dynamic indirect tensile strength of Datong coal. Highlights • Dynamic indirect tensile tests of coal were carried out by using a Split Hopkinson Pressure Bar. • X-ray CT and discrete element approach were combined to analyze the results. • The strength was found to be reliably correlated with impact velocity. • The strength is influenced by the bedding direction, roughness and discontinuity.
Highlights • Metal-organic frameworks (MOFs) represent a newborn family of hybrid materials. • MOFs have already shown promise in a number of biological applications. • The biological applications of MOFs raise concerns for potential cytotoxicity. • Substantial information about MOF's neurotoxicity is still quite scarce. • This study reveals for the first time the interaction of MOFs with neural cells. Abstract Metal-organic frameworks (MOFs) possess unique properties desirable for delivery of drugs and gaseous therapeutics, but their uncharacterized interactions with cells raise increasing concerns of their safety in such biomedical applications. We evaluated the adverse effects of zinc nanoscale MOFs on the cell morphology, cytoskeleton, cell viability and expression of neurotrophin signaling pathway-associated GAP-43 protein in rat pheochromocytoma PC12 cells. At the concentration of 25 μg/ml, zinc MOFs did not significantly affect morphology, viability and membrane integrity of the cells. But at higher concentrations (over 100 μg/ml), MOFs exhibited a time- and concentration-dependent cytotoxicity, indicating their entry into the cells via endocytosis where they release Zn 2+ into the cytosol to cause increased intracellular concentration of Zn 2+ . We demonstrated that the toxicity of MOFs was associated with a disrupted cellular zinc homeostasis and down-regulation of GAP-43 protein, which might be the underlying mechanism for the improved differentiation in PC12 cells. These findings highlight the importance of cytotoxic evaluation of the MOFs before their biomedical application.
An investigation was undertaken to study the characteristics of large roadway deformation and driving force of roof fall in a geologically complex zone at Huangyanhui underground coal mine, Shanxi Province, China, and to determine the main factors contributing to a roof fall accident that occurred in this mine. A series of field tests were conducted in the mine to study the geological structures, in situ stress, excavation-damaged zones of the roadway, roof-to-floor and sidewall convergences, roof separation, bolts loading and island coal pillar stress. The results of these tests have revealed that the driving force of the large roadway deformation and roof fall was not the activation of the karst collapsed pillars or concentration stress in island coal pillar, but high levels of horizontal tectonic stress and fault slip were induced by mining activities.