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The scope of the experimental research embraces velocities of elastic waves in rock samples before and after formation of a horizontal main crack. In undamaged samples, there is no essential change in the elastic wave velocity as the axial pressure increases from 0 to 20 MPa. The main crack having its surfaces approaching gradually leads to the increase in the elastic wave velocity. Aimed to improve sensibility of kinematic ultrasonic parameters relative to mechanical stresses, the coda wave interferometry algorithm is implemented as an analysis of times of the first arrivals of multiply scattered waves. With the mentioned algorithm, sensibility of the ultrasonic control grows considerably even in uniform samples.

The article describes the decision-making concept for the systemic blasting in open pit mining at structurally complex mineral deposits. The authors discuss approaches to determining allowable seismic impact in rocks having different strength characteristics.

The article describes semi-commercial testing of different technologies and facilities which ensure the required level of mining efficiency and quality of diamond-bearing ore. The use of the column charge explosives with radial clearance and air-split emulsion explosives allows stress state control in rock mass and reduces zones of high risk of crystal damage. The chain charge explosives appear to be a clever engineering idea for difficult mining conditions. The authors review the modern methods of drilling-and-blasting at mining sites of ALROSA.

The seismic activity in undermined rock mass in a mine at the Khibiny Massif is analyzed over the period from 2008 to 2020. The influences on deformation, tensile fracturing and caving in undermined rock mass are revealed. Three zones of deformation of different nature and velocity are identified in undermined rock mass in Kirov Mine: the zone at the juncture of underground and opencast mining; the zone of overhanging rocks; the zone of two- and three-side buttress at the edges of operating deposits. It is found that mining with head-on fronts, with formation of a support pillar and with overhanging of an uncaved rock mass beam is adverse. The pillar collapses later on and deformation of the pillar-supported rock mass during breaking of the butt section on sublevels occurs in the dynamic mode with high seismic activity both in terms of the number of seismic events and their energy emission. It is found that the width of the seismic activity band and the caving pitch of the overhang depend on the height of undermined rock mass.

The authors review the application range and parameters of internal dumping in open pit mining of brachysyncline-type coalfields. Specifics of the technology is described. The factors that govern the volume of internal dumping are identified. The possible ways of increasing the volume of internal dumping are shown. The methods and means for increasing the intake capacity of internal dumps are revealed. The ecological and economic advantages of internal dumping are discussed.

For structurally complex orebodies in weak zones of enclosing rock mass, a variant of the sublevel stoping technology with cemented paste backfill is proposed. On the ground of the in-situ data, the analytical relations are constructed to determine stability of artificial roof and sidewalls in stopes. It is found that backfill possessing the uniaxial compressive strength of 3 MPa preserves stability in the course of extraction of ore from adjacent stopes and in mining on the lower lying level. The recommendations on backfilling are given.

The article highlights the urgency of studying processes of deformation, displacement and collapse of undermined strata at rockburst-hazardous deposits of the Khibiny Massif with regard to geomechanical and geodynamic risks. The authors analyze failure specifics in undermined strata under the action of tectonic stresses, which consists in impeding of fracturing due to subhorizontal compression. It is found that as the thickness of ore bodies decreases and their dip angle grows at great depths, the pitch of failure increases. The problems to be solved to continue extraction of apatite-nepheline ore at minimized induced risks and at the preserved economic efficiency are listed.

The authors investigate thermal processes in an electromagnetic percussion assembly of a downhole pulse vibration exciter at the rated energy mode in the naturally cooled air environment and at different methods of heat energy transmission from the coil to the body. The interrelation is found between the coil and body temperature, external cooling, duty cycle and the coil-body expansion gap when it is filled with air or oil. Based on the obtained results, the duty cycle of the vibration exciter in a well is calculated when the body of the electromagnetic percussion assembly is cooled with flow water.

The authors discuss concentration of fluorite from waste at Yaroslavskaya Mining Company. The waste accumulated in the tailings storage for the long operating period contain 11.6-20.7% of fluorite. Old tailings have specific process properties because the initial ore has experienced certain physicochemical treatment during primary processing, and owing to long storage. The package of balanced effects which ensure selective recovery of fluorite is substantiated. The obtained concentrates contain up to 95% CaF₂. Production of fluorite concentrates at maximal removal of silicon dioxide, which is a strictly restricted impurity, is discussed. The ways of improving the processing circuit are proposed, and the efficiency of electrochemical treatment of the pulp fluid phase at the final stages of recleaning is proved. It is found to be possible to reduce the silicon dioxide content of the concentrates to 1.25-0.99%.

The article describes the studies into the process of upward mass transfer in flotation tailings with water solutions. The swift-flowing geological process is investigated using the magnetic resonance imaging. The kinetics of water-soluble minerals as well as the structure and substance transformations in the body of tailings are studied for substantiating in-situ formation of the target concentration zones at the tailings surface.