Vol 53, No 5 (2017)

The results of physical modeling of geomechanical processes in outer zones of coal beds with the main roof caveable with difficulty. The scope of the modeling embraces the inlfuence seams on gas release by gas temperature and pressure variation during stage-wise outlet of gas from a pressure bomb, which simulates cyclical mechanical impact on a coal seam in the zones of a gas pocket. It is found that the low-frequency (2.0–4.5 Hz) attenuating vibrations generated in the main roof can induce both secondary rock mass disintegration as well as methane desorption and decomposition of gas hydrates (if present) accompanied by an increases in gas pressure and in number of gas-dynamic events in outer zones of coal beds.

Сhanges in acoustic emission spectra of coal samples from the Kuznetsk and Pechora Basins are experimentally studied in uniaxial and triaxial (Karman-type) compression tests. It is shown that the acoustic emission spectral patterns change considerably at the pre-failure stage in the samples under uniaxial compression: the amplitudes of low-frequency components grow while those of high frequencies reduce. Under the Karman-type compression, the amplitudes of low-frequency signals grow while the high-frequency amplitudes do not change much, because lateral hydrostatic pressure impedes opening of vertical fractures.

The object of the numerical study is the travel of pendulum waves in a blocky medium under nonstationary impact of deep-seated charge blasting on the surface of the expansion chamber. The blocky model is simulated by a two-dimensional lattice of masses connected by elastic springs along the axes and diagonals. The displacements and velocities of the masses at different half-space points are calculated using the finite-difference method.

Fracturing efficiency of fluids in specific mining processes depends on reliability of data on structure and state of rocks, on pre-setting the location of fracturing origin, on choice of a fluid and its injection regime, as well as on the accepted engineering solutions. Fracturing by fluids are the processes that alter properties, structure, composition and state of rocks. Investigation of such processes offers a deeper insight into the multi-phase media (earth crust) and promotes advancement in nonconventional mining technologies.

In focus of the studies is the influence exerted by the radial displacement of the hammering unit on the air distribution in the air hammer with the ring-shaped elastic valve. The minimal allowable volume of the backstroke chamber at the frontmost position of the hammering unit when it contacts the anvil is calculated with regard to the limited maximum pressure in the impact stroke chamber at the moment of the blow. In the capacity of the air hammer efficiency criterion, it is suggested to use the length of the powered closure of the elastic valve, that compensates rotation of the hammering unit in the body when the radial clearance between these parts grows. The parameters of the air distribution system are estimated for all standard sizes of air hammers with the ring-shape elastic valves.

The analysis is presented for explosion examination materials in mining gently dipping and inclined coal seams with mechanized equipment. It is shown that the most probable cause of explosion origin is methane-and-air mixture inflammation and subsequent blasts initiated by coal self-ignition foci in the mined-out space. In this case, burning gas is brought to stoping face and adjacent mine workings by blast wave, which causes explosions of coal dust. The mechanism of coal self-ignition in the edge parts of pillars between longwalls being under effect of rock pressure is described.

The methods and means of overburden dumping at open pit coal mines in Kuzbass are reviewed. Specific features of dumping are highlighted, and the dependence of dump stability on geological conditions and physical properties of overburden is determined. The priority lines of development in the dumping technology are aimed at efficient utilization of mined-out areas in open pits and idle hydraulic fills. The issues of the environmental safety of dumping are addressed.

The article gives test data on the influence exerted by energy impacts (ultrasonic, electrochemical and thermal) on the recovery of zirconium and rare earth elements from eudialyte concentrate to leach solution in acid leaching. An original installation is developed for the implementation of leaching. Based on the research findings on the kinetics of acid leaching of eudialyte concentrate and on the change in the concentrate micro-structure and phase composition, the mechanism for the influence of integrated energy effects on the efficiency of recovery of zirconium and rare earths into leach solution is substantiated.

The experimental research into intensification of copper–nickel ore concentration by flotation and magnetic separation shows that pretreatment of ore before milling by accelerated electrons results in the increased yield of –0.071 mm size and in enhanced recovery of useful components in the concentrate. Magnetic separation improves comprehensive utilization of mineral raw materials.

The article describes features of ore reserves and development of processing technologies at Mikhailovsky MPP. New approaches to disintegration of ore and to improvement of dry magnetic separation of unoxidized ferruginous quartzite are evaluated. The scope of the discussion embraces the process of finishing magnetite concentrate, extracted from unoxidized ferruginous quartzite by wet magnetic separation, using the flotation flow chart in the closed and open circuits, as well as with the reverse cation flotation of hematite concentrate from tailings of wet magnetic separation. The authors present engineering solutions aimed at designing energy-efficient horizontal-grate calcinator MOK-1-592 and the technologies to produce different-purpose iron ore pellets.

A Stefan problem is analyzed for the case of rock freezing during shaft sinking. It is shown that the rate of thermal diffusion in rock mass is comparable with the velocity of the boundary between different phases. The Stefan problem is solved for a single shaft using the finite difference method. The procedure for generalizing the calculation data on thickness of the frozen wall in a single shaft for the case of many shafts is improved. The frozen wall thickness forming around freezing pipes is calculated in terms of shaft 1 in the mine of Petrikovsky Mining and Processing Plant of Belaruskali.

The authors propose to assess air pollution in mining regions using the integrated instrumental monitoring, calculation and remote sensing. The algorithms for experimental data processing for the calculation and remote monitoring of snow cover pollution as a universal indicator of the pollution distribution in air are substantiated. The article presents the integrated monitoring data on the induced load in the air in the large mining industry cluster in Kuzbass.

The article presents the installation meant for the determination of gas permeability of rock specimens placed in a testing cell with the adjustable axial and lateral compression. The installation includes a measurement system for the automated long-term investigation of rock permeability in accordance with the preset program. It is also possible to test specimens with a fracture filled with a propping material. The reported data of the permeability tests of porous quartz-containing material and coal demonstrate the capacity of the installation and the experimentation specificity.

The method of the empirical mode decomposition and its application to the analysis of data obtained using a laser strain meter is described. The issues of adaptation of the method to real data are discussed. The method enables identification of a monotone trend and a slow component of deformation process much more efficiently than the conventional techniques. The method shows reliable operation in cleaning of signals from noise and high frequencies.

Due to a technical error volume 53, issue 4, 2017 has been published online with an incorrect cover data. The issue has erroneously been distributed with the cover date July 2018. The correct caver date for volume 53, issue 4 should be July 2017.