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The article describes the lab-scale tests of permeability of long-flame coal from the Mokhovsky Coal Mine in Kuzbass depending on the intensity of cyclic treatment of coal with liquid nitrogen. The freezing effect on jointing was assessed by a change in the gas flow and in the ultrasound velocity. It is found that permeability of the test coal in compression rises up to commercially significant values. To reach this effect, it is sufficient to implement three-four cycles of treatment with liquid nitrogen. The treatment decreases the ultrasonic P-wave velocity by up to 6%, which points at the increase in the volumetric density of microcracks.

The accomplished review of the geological and geomechanical conditions at the Tashtagol and Sheregesh deposits shows that the operating mine fields contain small- and medium-amplitude fractures, faults, dikes and ore-rock interfaces. It is revealed that during heading and stoping, geodynamic phenomena arise mostly in the neighborhood of these planes of weakness. The mathematical modeling was used for the stress-strain analysis of rock mass at different slope angles of faults approached by the development headings. It is found that in case of a fault 1 to 3 m wide, the shear of the fault edges along the fault plane at the fault slope angle of 65° can happen when an approaching roadway is at a distance not less than 10 m, at the slope angle of 45°-at a distance not less than 20 m and at the slope angle of 15°-at a distance not less than 40 m. For the faults 5 to 10 m wide, at the fault slope angle of 65°, no shearing takes place, at the slope angle of 45°, shearing can happen when a roadway approaches the fault at a distance not less than 5 m and at the slope angle of 15°-not less than 30 m.

The authors revealed the dependence of the dehydrating activation energy parameters in rocks on the phase ratio of β-quartz to α-quartz. In rocks with the predomination of β-quartz (β-quartz / α-quartz > 1), rockfalls are observed and the ratio of the dehydrating activation energies of crystallization water (chemically bound) and adsorbed water (physically bound) is less than 1. This is reflective of the build-up of free and physically bound water which penetrates defects in rocks due to the phase transition of quartz, and leads to an increase in their dehydrating energy.

The authors reviewed the known methodical approaches to the determination of strength characteristics of rocks using their testing results. Some shortages of the approaches are revealed, and the common shortage is their empirical nature consisting in reduction of strength of rock mass in proportion to degradation of its quality. The proposed procedure to determine rock mass strength takes into account the rheological alteration of rock mass. The procedure better represents physical processes in mine openings due to rock pressure.

The article describes the lab test data on the structure and permeability of sand reinforced with elastic polyurethane. The electron microscopy reveals the spatial patterns of hard polyurethane, voids and mineral particles in reinforced sand. The permeability of the test samples is investigated under conditions of uniform triaxial compression. The response of permeability of reinforced rock to freeze-thaw is analyzed depending on moisture content, specific consumption of chemical reagents and reinforcement method. The stability values of the insulating properties of sand are compared for the cases of sand reinforcement by its mixing with polyurethane resin and through creation of a low-permeable inclusion (injection simulation). The advantage of injection over mixing is shown-the consumption of polymer composition is lower and the stability to seasonal temperature fluctuations is higher.

The article describes the method to estimate sensitivity of local seismic monitoring networks in two underground mines at the Khibiny Massif: Kirovsk and Rasvumchorr. The method uses empirical data of induced seismicity monitoring. At each monitoring station, based on the behavior of seismic waves and the distance to epicenters of seismic events, detection probability diagrams were plotted for seismic events and different ranges of seismic energies. The diagrams were used for plotting the probability of detection maps for a seismic event and a certain energy range. This approach has a few advantages. First, the input data may be records of production blasts and other sources rather than natural seismic events. Second, the method allows using the averaged probability diagrams for the decision-making on deployment and expansion of monitoring networks in mines. It is shown that monitoring networks ensure reliable recording probability (95%) only for the events with an energy higher than 10⁴ J; however, there is a potential of increasing the sensitivity and reliability of recoding events with an energy of 10² J in case of inclusion of additional monitoring stations.

The article studies a mining system with stoping under open pit bodies at steeply dipping ore bodies of small and medium thickness using rubble concrete and dirt fill as ground control. The technology assumes upward mining on the levels at the total downward sequence of stoping. The limit variant of stoping in various geomechanical conditions is studied for a geotechnical situation of mining on three levels including two mined-out levels. The mining system parameters are substantiated using 3D FWEM-based mathematical stress-strain modeling. The dependence is revealed between the geotechnology parameters and the stress behavior, and between the stability of rocks in the structural components of mining and in adjacent rock mass. The areas of possible rock fracture are identified. The safety of the mining system is governed by the integrity of rubble concrete pillars and by the stability of the crown pillar.

The authors present the results of development of a powered roof support control system included in the machine group of top coal caving to a longwall conveyor. The methods of measurement of the conveyor loading by a swinging feeder, recording of changes in the quantity of dirt in total rock mass, as well as the integration of the newly developed system in the powered roof support control are described. For determining loading of the longwall conveyor by the swinging feeder, it is proposed to use the algorithms and methods of machine vision, added with a camera of projection of light marker net on the rock mass surface. The method of detection of variation in composition of rock flow is proposed to be implemented through automated measurement of gamma radiation in rock flow and comparison of the measurement with the control value. The concept of a versatile adapter is developed, and the control system architecture and automated operation algorithm are presented for the longwall top coal caving technology.

Some criteria are justified for selecting coal waste dumps suitable for heat recovery as a case-study of solid mine waste accumulated in the Donbas. These criteria involve geodynamics-position of a dump relative to the boundaries of an active geodynamic zone, as well as air dynamics-gas permeability of rocks in this zone and methane concentration in air entering the dump. It is shown that young and medium-age dumps situated within the boundaries of closed unflooded mines can contain mixture of air and gas with an explosive concentration of methane. The model of changing the role of mine methane in generation of the heat field in a self-heating dump is described. The model uses the idea that methane can both reduce the oxidation rate in coal waste and intensify their combustion efficiency. It is proposed to undertake geodynamic and gas dynamic ranking of coal dumps to determine their suitability as heat generators. The justified criteria can be used to develop a heat recovery technology for coal dumps.

The authors discuss the influence exerted by reagents-regulators on selective modification of spectral-kinetic characteristics of unrecoverable diamonds with anomalous luminosity to ensure their complete and selective recovery in X-ray luminescence separation. The parameters of kinetic stability are determined in emulsions of luminophore-bearing modifiers, and the reagents-regulators that cause no worsening of attachment of the modifiers at the surface of diamonds are found. It is shown that reagents-regulators of different classes (derivatives of alkyl/aryl phosphonates, aliphatic alcohols, bifunctionally modified derivatives of carboxymethyl cellulose, ionic and non-ionic nitrogen-bearing polymers, short-chain aliphatic amines, complex reagents) substantially decrease attachment of luminophores at the surface of hydrophobic minerals of kimberlite and prevent thereby their recovery to separation concentrate. The influence of reagents-regulators on the spectral-kinetic characteristics of the applied luminophore-bearing modifiers and treated diamonds is determined. The reagents-regulators suitable for the use in the modification technology without subsequent unwanted correction of spectral characteristics of diamonds are selected.