Home – Home – Jornals – Journal of Mining Sciences 2020 number 6

The fluid flow modeling procedure used ABAQUS environment and the extended finite element method. The procedure is meant for calculating pore pressure distribution and gas and fluid flow directions in rock mass in the course of solid mineral mining using hydraulic fracturing. The authors discuss the standard model and case-studies of the procedure-based calculation of gas flow rates in coal seam drainage using boreholes and fractures of different orientation.

The authors discuss a mathematical model of rock mass with regard to accumulation and release of stored energy. Self-balancing stresses are described using internal variables introduced. The type of a closed system of equations is examined. An algorithm is proposed for the numerical modeling of softening jumps within a quasi-static problem. The problem on deformation of rock mass around a tunnel is solved using the finite element method. Under certain conditions, self-balancing stresses can be unbalanced, which causes disastrous dynamic phenomena associated with confining pressure.

The authors propose a mathematical model of the effect exerted by a blast-induced seismic wave on nonuniform (multi-layer) enclosing rock mass around a tunnel. The developed numerical algorithm implements the Godunov splitting method, and a computer system is constructed. The numerical calculations determine safe drilling and blasting parameters to preserve integrity of underground structures.

The article presents the analytical model and calculation results on fracture growth in layered rock mass during blasting and hydraulic fracturing in oil reservoirs. The stress state of fractured elastic rock mass is found using 3D boundary element method. The influence of strength characteristics of layered rock mass on the shape, size and area of radial fractures is determined. The presence of a stronger layer in rock mass restrains cross sectional growth of induced fractures as compared with the existing fractures in surrounding rock mass, i.e. nonuniform fracture of rock mass along boreholes and probable oversizes are prevented in this case. It is possible to adjust the shape of fractures by changing distribution of an explosive along the borehole. During hydraulic fracturing, fractures propagate chiefly along a softer rock layer if present.

The article presents a case-study of change in the seismic energy absorption coefficient with changing mining and geological conditions during the exploitation of one of the longwalls at the Polish coal mine Ruda. Several stages of longwall excavation exploitation, differing in stress conditions, were selected for the analysis. The results obtained show that low attenuation occurs in areas of high stress concentration and, conversely, high attenuation is associated with the weakening of the rock mass.

The study focuses on the theory of zonal disintegration in gas-bearing coal seams and gas-dynamic phenomena in underground structures. The concept of unstable geomechanical behavior of coal seams is conditioned by instability of deformation during micro-cracking and macro-cracking. In the zone of disintegration in a gas-bearing coal seam, occluded methane releases from coal substance. As a result of increasing pressure of free methane, a zone of damaged coal and gas appears deep in the coal seam and can induce such gas-dynamic events as blower, sloughing and outbursting. The obtained values and relations of geomechanical and gas-dynamic parameters agree with the actual practice data.

Underground mining of hard coal seams is carried out in the Polish part of the Upper Silesian Coal Basin with an increasing level of rockburst hazard. This hazard is combated by the application of active rockburst prevention, where long-hole destress blasts take an important role. The seismic energy of the provoked tremors can be a determinant of blast effectiveness. To estimate blast effectiveness according to the seismic energy of a provoked tremor, the seismic effect method, developed for hard coal mines in the Czech part of the Upper Silesian Coal Basin, can be applied. A classification system for the evaluation of seismic effect is determined for the assigned colliery with the use of statistical analysis, in which the energy of provoked tremors and the mass of the explosives used is taken into consideration. This method can be applied not only for long-hole destress blasting, but also for other analogous types of blasting, which may initiate geomechanical processes in the rock mass, e.g. blasting for roof rock falling. In this article, an analysis of the effectiveness of both the long-hole destress blasting and blasting for roof rock falling, performed during longwall mining of coal seam no. 408 in a mine in the Polish part of the Upper Silesian Coal Basin, was carried out. The effectiveness of blasting for roof falling was verified directly in situ. The seismic effects of blasts, after which roof falling was confirmed, were classified according to the adopted scale as, mainly, very good, extremely good and excellent. It can be assumed that the analogous effects of the long-hole destress blasting indicate the occurrence of additional processes, as a result of which the rock mass reaches a new and favourable stress-strain equilibrium state.

The article describes preparation and implementation of experimental research into strength, deformation and acoustic characteristics of physical models of frame and honeycomb underground structures designed at the Research Center for Applied Geomechanics and Convergent Technologies in Mining at NUST MISIS College of Mining. An integrated test bench for physical and optical modeling of geophysical processes in the secondary stress fields, an installation and a special test bench for 3D physical modeling of any complexity are manufactured. The standard variants of physical modeling of the advanced frame and honeycomb underground structures are developed. The authors present the test data on strength, deformation and acoustic characteristics obtained on a model of a frame structure variant. The tests show that honeycomb underground structures exhibit higher stability when they contain more circular openings of smaller diameter.

The author presents the mathematical model of an autooscillating one-way action and positive-displacement system with two piston arresters. The dynamic criteria of similarity are determined, including: stiffness ratio of springs of the accumulator and percussion assembly; proportional value of the ratio between potential energy of the accumulator and kinetic energy of the piston at the preset parameters of power source; dimensionless coordinates of the piston when the positions of the distributor and the second arrester of the piston, as well as the pre-tension of the spring between the piston and the percussion assembly housing change; velocity recovery coefficient of the piston. Numerical calculations are performed in the space of the similarity criteria. The nomograms of isolines of the integral output parameters of the system and the oscillograms of dynamic characteristics are plotted. Dynamics of the system is analyzed, and its behavioral features are revealed in a wide range of input parameters. In the space of the similarity criteria, the boundaries are determined for the domains of single-blow, double-blow and multi-blow limit cycles.

The review of copper ore processing flow charts in application at ore mills in Russia and abroad is presented. The scope of the analysis embraced the reagent regimes and flotation performance. Brief information about collecting agents, frothers and depressants is given. The influence of actuation medium in flotation of copper-nickel ore is studied in terms of bulk copper-nickel concentration. The tests were carried out with production of a rougher concentrate in the acid and alkaline media with its further scavenging.

The authors study dynamics of heavy particle attached to the surface of free air bubble in liquid. The bubble with its surface vibrations and the particle are considered as a single mechanical system with geometric constraint. It is assumed that the main forces to govern interaction of these objects are the inertia force due to surface vibration of the bubble and the capillary adhesion force. The stability conditions of particle-bubble flotation aggregate at various initial surface vibrations of the bubble and at different masses of the particle are described. The velocities of the surface vibration modes are governed by the energy of turbulent pulsations in liquid.

The theoretical and experimental research is aimed to improve pretreatment and concentration of rebellious ore from the Rubtsovsk deposit. Radiation modification of lead-zinc ore properties stimulates milling efficiency and enhances processing efficiency. After radiation modification, percentage of free grains of galenite and wurtzite in milled product increased from 40.7 and 65.7% to 66.4 and 71.5%, respectively, in treatment by accelerated electrons at radiation dose of 5 kGr. As a result, the increment in zinc and lead recovery in rougher flotation concentrate made 4.74 and 9.50%, respectively.

The removal of heavy metals from the wastewater solution using a novel zeolitic material was conceived and experimentally probed. The natural zeolite was ground in a planetary ball mill to increase negative surface charge and amorphization of the material as well as a conventional ball mill. The ground materials were used for the removal of heavy metals from the wastewater solution. The maximum removals were found to be 78% for Pb, 67% for Ni and 54% for Cd by using the conventional milled natural zeolitic material at pH 11. However, 93% of Pb, 72% of Ni and 57% of Cd were removed at pH 9 with the novel zeolitic material milled by a planetary ball mill. It was revealed that the novel zeolitic material produced by a planetary ball mill increased the absorption capacity of the heavy metals and reduced the alkali requirement for pH adjustment. The removal order of heavy metals with the novel zeolitic material is determined as follows: Pb> Ni>Cd.

The mathematical methods of structural design optimization using the optimality criteria are reviewed. The resultant and nearly optimal design of a fan bade ensures the design goals at the selected criterion. The optimal design based on topology optimization was carried out in ANSYS. The optimization problem solution provided optimal distribution of the impeller blade mass for axial mine fans. It is validated to be possible to decrease the the blade mass by 60% as compared with a monolithic blade at the preserved rotation speed and ratio of flow path diameters.

The aerothermodynamic parameters of air are studied in shafts of mines of NorNickel’s Polar Division. The total pressure and temperature measurements, as well as the air density calculations in KS-2, GS and VC-4 shafts in Oktyabrsky Mine show the linear total pressure dependence on the shaft depth and the essentially nonlinear dependence of air temperature and density on the depth of shafts at intersections with ventilation channels and horizons. The lengths of sections of leveling of air parameters behind the intersections are estimated. The authors propose a new method to determine aerodynamic drag coefficients in mine shafts and calculate ADC for 28 mine shafts in the Norilsk Region. The calculation results are used in mathematical modeling of mine ventilation networks and in ventilation designs for new mine sites.

The article presents the analytical research data on the convective motion dynamics and air temperature variation in a mine tunnel after cutoff of a drag source during fire. The single-valued prediction is only possible based on the stability theory of convection currents. The mathematical modeling of advection currents of counter air flows in a tunnel is performed at longitudinal gradient of temperature. The analytical formulas are obtained to calculate advection vortex and air flow velocity in vortex as function of burning time and temperature at the source. The range of hot airflow weakly depends on the burning temperature, insignificantly grows within a day and makes 850 m at the temperature of 1000 °С. The developed procedure allows evaluating the fire size and duration, as well as the air flow velocities in tunnels after the drag source cutoff.

The authors put forward a concept of modeling objects within a mining technology. The concept integrates the technology content and state change of an object, and allows processing and storage of temporal data on digital mine twin. A set of such models shapes a joint dynamic model of evolution of all mine objects in the course of mineral mining. Using this approach, the time-variable vector, triangulation and block models can be synchronized via transactions in data bases, and can be used to describe the life cycles of individual objects or their sets within a mining technology. Implementation of this concept can help handle problems connected with digital twining of mines.

The article presents the manufacturing procedure and the test results for a synthetic layered and jointed medium with a preset internal structure and the pronounced anisotropy of properties. The test bench for hydraulic fracturing of large-size cubic models under independent triaxial loading, the test bench hydraulics and the measurement-and-recording equipment are described.

Results of modernisation of an on-line X-ray fluorescent analyser are presented, and its new capabilities are considered when investigating the composition of materials on the conveyor. The metrological characteristics of the analyser are improved owing to the use of modern electronic components in the instrument part and new analytical software.