The rock mass rating (RMR) has been used across the geotechnical industry for half a century. In contrast, the coal mine roof rating (CMRR) was specifically introduced to underground coal mines two decades ago to link geological characterization with geotechnical risk mitigation. The premise of CMRR is that strength properties of mine roof rock are influenced by defects typical of coal measures stratigraphy. The CMRR has been used in longwall pillar design, roof support methods, and evaluation of extended cuts, but is rarely evaluated. Here, the RMR and CMRR are applied to a longwall coal mine. Roof rock mass classifications were undertaken at 67 locations across the mine. Both classifications showed marked spatial variability in terms of roof conditions. Normal and reverse faulting occur across the mine, and while no clear relationships exist between rock mass character and faulting, a central graben zone showed heterogeneous rock mass properties, and divergence between CMRR and RMR. Overall, the CMRR data fell within the broad envelope of results reported for extended cuts at Australian and U.S. coal mines. The corollary is that the CMRR is useful, and should not be used in isolation, but rather as a component of a strata control programme.
Anticorrosion and adsorption behaviour of synthesized carbohydrazide Schiff bases, namely (Z)-N'-(4-hydroxy-3-methoxybenzylidene)-6-methyl-2-oxo-4-phenyl-1,2,3,4-tetrahydropyrimidine-5-carbohydrazide(MBTC) and (Z)-N'-(3,4-dichlorobenzylidene)-6-methyl-2-oxo-4-phenyl-1,2,3,4-tetrahydropyrimidine-5-carbohydrazide (CBTC) was examined for mild steel (MS) in 15% HCl medium. The corrosion inhibition study was performed by using gravimetric, thermodynamic, electrochemical and theoretical studies including density functional theory (DFT), molecular dynamic simulation (MDS) and Monte Carlo simulations (MCS). The outcomes in terms of corrosion inhibition efficiency using electrochemical impedance spectroscopy (EIS) method at 303 K and 150 ppm concentration were 96.75% for MBTC and 95.14% for CBTC. Both inhibitors adsorbed on the MS surface through physical as well as chemical adsorption and followed the Langmuir isotherm. The mixed-type nature of both inhibitors was identified by polarization results. Surface analysis was done using FESEM, EDX, AFM and XPS studies and results showed that a protective layer of inhibitor molecules was developed over the surface of MS. The results of DFT, MCS and MDS are in accordance with experimental results obtained by weight loss and electrochemical methods.
Gas drainage has been the most common technique for gas management in underground coal mines. This method involves drilling holes into a virgin coal seam to allow the gas bleed off from the coal into the drainage holes. A major problem with the underground gas drainage is the air leakage around the gas drainage hole that cannot be blocked off by the sealing material. The air leakage will cause the low concentration of the drained gas and decrease the efficiency of the gas drainage hole, which may further lead to many other risks, such as spontaneous combustion, gas combustion and gas explosions. A thin spray-on liner is defined as a chemical-based layer or coating (3–5 mm) that is sprayed onto the rock surface to support mining excavations. Since their introduction, thin spray-on liners have received some success as a ground support tool for underground mining. Besides ground support, thin spray-on liners also show some potential to be used as a gas management tool in underground coal mines due to their relatively low permeability. This paper describes a field trial of using thin spray-on liners for enhancing the gas drainage efficiency by blocking the fractures around the drainage holes. The project involves spraying a thin spray-on liner onto the area surrounding gas drainage holes whereby the thin spray-on liner acts as a thin membrane decreasing the permeability of coal. This restricts the air migrating through the coal seam and diluting the gas from the drainage holes. The key benefits associated with the application of TSLs are the increase in the methane purity and the decrease in the air contamination. In-situ adhesion tests were conducted in parallel with the gas tests, and the results revealed that the TSL tested could be implemented for underground coal mine applications as the main failure mode is the internal failure of the coal substrate.
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