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

Based on the previously developed numerical analytic method for the description of the input/output parameters of a multidimensional dynamic object for a given set of admissibility (Part I), a method for optimal estimation of the values of continuous linear functionals (numerical characteristics) of the measured parameters is considered in this paper based on incorrect data containing both the fluctuation error and singular noise (Part II). The method ensures the maximum possible decomposition of computational procedures; it does not require performing traditional linearization operations and selecting an initial approximation; moreover, it does not need calculating the spectral ratios in finite linear combinations (with specified basis functions) that describe the cumulative curves of the differential equation, measured parameters, and singular noise. The random and systematic errors are analyzed; an illustrative example and recommended practice for the results obtained are provided.

Designs of a warm (uncooled) aperture diaphragm in a gas-filled cryostat with a matrix photodetector sensitive in the infrared spectral range are studied numerically and experimentally. It is shown that the matrix photodetector with a format of 384 × 288 pixels is cooled with liquid nitrogen to operating temperatures (85 K) in less than 40 seconds if the chosen design of a warm aperture diaphragm is used and in 15 seconds in the case with a throttle microcooler, while maintaining the standard sensitivity of photodetectors based on mercury-cadmium-tellurium (MCT) structures.

A simple way for measuring the radial clearances with controlled accuracy due to reducing random error components is considered. Quantitative estimates of the accuracy, speed, and efficiency of the proposed method are provided. The method is stochastic, is based on the characteristics of the random errors and impeller rotation process periodicity, and makes it possible to perform measurements with the same accuracy over the entire range of rotation speeds of the rotor of a turbo machine. The method considered in the study allows avoiding the procedure of approximation of digital samples.

An algorithm for solving the optimal control problem with terminal constraints is developed. An optimal control problem with terminal constraints and constraints on the control parameter is formulated. A numerical algorithm for solving the problem based on the penalty method and genetic algorithms is described. A computational experiment for the reaction of obtaining phthalic anhydride to achieve the maximum yield of the reaction product in the presence of terminal constraints is performed. The optimal temperature regime and optimal concentrations of reagents were obtained.

Shock wave travel in a roadway with impermeable safety barriers is modeled numerically in the equilibrium and non-viscous formulation. Inclined and arched barriers are studied at the varied porosity in a range from 0 to 0.8. The inclined and arched barriers decrease the load exerted on the barrier structure by the shock wave owing to formation of a reflected wave which is oblique, or radial in case of the arched barrier. An increase in porosity of the barrier can additionally weaken the shock wave effect but barriers with high penetrability make the defensive screen inefficient, which is confirmed by the higher differential pressure at the shock wave front after passing the barrier.

The article describes the experimental studies into hydraulic fracturing of thick-walled cylinders with a circular hole and made of cement-based GF-177 mixture. Limiting stresses are determined in four types of stress state of the bodies: uniaxial compression and tension, Brazilian Test and hydraulic fracturing. The data of the Brazilian Test and compression of rectangular parallelepipeds and circular cylinders were used to determine limiting pressure in hydraulic fracturing. The critical stress intensity factor is found. The calculated limiting pressures are compared with the values found analytically from the Lamé solution and with the test data. The influence of the storage interval on the strength is described.

The thermal and mechanical tests of different porosity limestone show that an increase in the axial load results in the higher velocities of elastic waves while elevation of temperature decreases them. Higher temperatures act to raise velocities of P- and S-waves with increasing mechanical load, which enhances acoustic strain-sensitivity of rock. The spectral analysis of the recorded signals shows that higher temperature shifts spectrum maxima to lower frequency region. It is found that size of pores has influence on attenuation frequency of ultrasonic signals. The authors describe new approaches to acoustic strain-sensitivity control in rocks and to stress measurement reliability enhancement toward stability of underground structures.

The research methodology for anisotropic permeability of geomaterials due to nonuniform stress state is theoretically justified and tested on a laboratory scale. The poroperm properties of fine grain sand and cryogel are investigated in diametral compression tests of cylindrical specimens with a center hole. The time-independent flow rate is measured in various areas of side surfaces of the specimens. The inverse coefficient problem on empirical permeability-effective stress relationship is formulated, and its solvability is demonstrated.

The author solves the problem connected with determination of shape of pillars which remain stable under any compression due to barrel distortion. The analysis of cylindrical structures uses the known Leibenson-Ishlinsky stability criterion. The boundary conditions of the problem and its solution are obtained: elasticity in the form of the critical load dependence on the height/radius ratio of pillars. The found asymptote to the curves is associated with the optimized shape of pillars.

In hydraulic fracturing of producing formations in oil and gas reservoir engineering, as well as in coal gas drainage, hydraulic fractures are propped by solid particles-proppant that prevents closure of fractures under the action of compressive stresses in rocks. It is shown that alongside with lateral earth pressure, the compressive stresses in fractures are governed by additional compression generated by fracturing and by compression of rock in depression zone formed in the reservoir fluid inflow to the fracture. The compressive effect in the depression zone can be adjusted by reducing the rate of depression growth in time. This method of compression decrease in fractures is the most efficient in reservoir engineering and in shallow coal seam gas drainage. The compressive stresses in the depression zone are comparable with the lateral earth pressure, thus, the differential pressure step-up can make it possible to keep the stress-strain behavior of rock in the neighborhood of a hydraulic fracture within the limits of elastic deformation and to prevent the fracture closure with irreversible pressing-in of proppant in rock.

The article describes the long-term in-situ observations and inspection of concrete lining in air inlet shaft No. 3 in Uralkali’s mine, which reveal the main causes of the lining failure at intersections with horizontal tunnels and in the areas of instable rocks. Numerical modeling of rock creeping and damage areas in lining at intersections with tunnels is performed in the axially symmetric and three-dimensional formulations. The calculations agree with the observation data, which proves efficiency of mathematical modeling in estimation of deformation and failure of concrete lining during shaft design and operation. Prediction of damage evolution in concrete lining in shaft No. 3 is carried out for the next 10 years.

The slope stability evaluation using the generalized Hoek-Brown criterion and with regard to the scale effect has been implemented in terms of the Chaarat gold project. Furthermore, the probabilistic assessment and sensitivity analysis are performed. Landslide probabilities are determined, and the slope stability factors are obtained as functions of the slope height and angle. The slope stability estimation procedure synthesizing classical approaches with regard to the scale effect, including GSI and probabilistic analysis is tested in rock ground. Slope stability is mainly governed by variability of the Geological Strength Index related with the scale effect.

The authors discuss the mechanism of breaking coal by blasting with a view to optimizing this method of dynamic treatment of coal and improving drilling-and-basting performance. A combination model of high gassy coal is used to describe the connection between coal breaking by blasting and subsequent gas liberation. This model and the smoothed-particle hydrodynamics method are used to study evolution of damage zones and stress-strain behavior of coal in the neighborhood of a blasthole after explosion. The research findings help predict coal response to the dynamic impact.

The authors present a new rock fracability evaluation procedure using the cluster analysis of log data on petrophysical properties of facies. The effect of the physical and mechanical properties of rocks on the fracability evaluation results is analyzed in combination with the geophysical log data. The triaxial compression tests of cores are carried out to determine their brittleness indices. An entry-level classification of petrophysical properties of rock facies is implemented by the cluster analysis of the geophysical log curves. A new classification procedure is proposed for the petro facies analysis using the permeability index and brittleness index of rocks, and the profile of rock fracablity index is obtained. Application of the procedure is illustrated using core data from a reservoir in China. The fracability index of cores sampled in a horizontal well correlates well with the calculated profile of fracability index.

In this study, Time Domain Reflectometry (TDR) is engaged to observe coaxial cable deformity caused by slope movements. Laboratory shear tests were executed to measure the deformity magnitude caused by shear failure using two coaxial cables-RG-6 and RG-213. Two assessments are performed in laboratory testing, to determine the deformity magnitude-shear test and Open-Cast (OC) model. For shear test, two regression methods are computed-linear and quadratic regression. The quadratic regression results show more effective positive correlation with shear deformity as compared to linear regression results. For RG-6 and RG-213 cables, the average highest magnitude of coaxial cable deformity by shear failure is 11 mm and 14 mm, respectively, which are equivalent to Reflection Coefficient (RC) of 0.49 and 0.050 for RG-6 and RG-213, respectively, beyond which the cable breached. Field tests are also performed which concluded that TDR is the most preferable technique to monitor slopes of OC mines.

This paper describes the development of statistical models for assessing the boulder count resulting from the limestone quarry blasting. A database of three hundred blasts was created for the development of the model. The database consists of number of holes per row, number of rows, average spacing, average burden, average depth, average stemming, explosive type, total charge fired in one round and the boulder count. All the variables in the database are ratio type except the type of the explosive which is a nominal variable. Hence two distinct statistical models have been developed for the ANFO and the SME blasts. The models have been developed in SPSS 20.0. The Student’s T-Tests and Fisher’s Exact Tests have been carried out on the models to identify the significant variables. It is further found that the prediction capability of the statistical models is strong and it provides an easy option to the field engineers to assess the blast design for the boulder-count. The developed statistical models are suitable for practical use at the limestone quarries having similar geotechnical set up.

The author addresses a method of creating directional conjugated fractures in a solid medium, integrating features of interaction of fractures and holes, specifics of fracturing by plastic materials and the use of holes as the front guides and limiters of created fractures. This method can be used to enhance efficiency of open pit and underground mining, as well as for creation of closed impermeable envelopes for advancement of slot mining technologies without construction of underground mines.

The authors analyze gas control readings obtained in Butovskaya Mine, Kemerovo Region, in step-down phase of seismicity and after blasting operations. It is estimated how seismic waves induced by blasting influences methane drainage in coal seams. It is found that methane release from coal seam to roadways increases after seismic impact.

It is technologically and economically advisable to optimize grading of low-quality fine and very fine sand with increased content of clay and dust particles used in preparation of cemented backfill mixtures by adding blast-furnace granular slag screenings 0-5 mm in size without preliminary treatment. The relationships of the size modulus, specific grain area and clay/dust particle content of sand and the percentage of slag in the composite aggregate are obtained. It is found that with increasing percentage of slag in the composite aggregate, water demand lowers owing to the higher size modulus of the aggregate and due to the decreased content of clay particles in it. This allows production of cemented backfill mixtures at the decreased consumption of cement while the strength and flowability of the mixtures are preserved.

Modern heavy-duty shearers cut coal with high production of dust particles. The screen tests of coal from Zarechnaya Mine are reported. Methane flow rate is theoretically calculated as function of dispersion phase in coal from Zarechnaya Mine at different particle size distribution of coal. It is found that methane flow rate reaches its maximum in fine coal 0-25 mm in size.

Advancement of wave action stimulation and cross-well seismic imaging in mineral mining governs the need for downhole sources of elastic vibrations. The presented periodic electromagnetic seismic source is equipped with a mechanical-hydraulic drive for fixturing in a hole and for impulse transition to rock, and an electromagnetic impactor for pressure pulse generation. This article presents the experimental studies into the operation of the seismic source of three structural layouts. The features of the operation are discussed. The supply voltage dependences of the main parameters of the seismic source are obtained, and the practical application recommendations are formulated.

The experimental studies into stimulation of chemical and electrochemical leaching of gold from rebellious concentrates by ultrasound are presented. From the assessed efficiency of saturation of chloride solutions with electrochemically activated chlorine and the analysis of change in the surface morphology and in the composition of elements, phases and particle sizes in concentrates, the leaching stimulation mechanism is determined and the efficient ultrasonic treatment parameters are found for a mineral suspension to ensure higher gold recovery by 39% in 5 h.

It is suggested to improve selective milling and disintegration of mineral associations of mining waste by means of stage-wise increase in destructive energy. It is found that relative frequency of opposite rotation of rotors and the number of pass cycles of waste through disintegrator can be of use in optimization of separation of preset size fraction at minimized loss of spodumene owing to the reduction in slurrying. The flow chart is developed for the stage-wise disintegration of spodumene-bearing mining waste with obtaining of product of flotation size - 0.16 + 0.02 mm at minimal yield (6.0%) of slime fraction - 0.02 mm. The proposed flow chart efficiency is proved by the flotation concentration results.

Dispersiveness of emulsion composed of oily reagents is estimated using the method of laser diffraction in experimental and in-process tests of flotation of slurry coal. Effect of agitation level in emulsification on emulsion dispersiveness and on flotation of different size coal of two grades is described. It is found that emulsification of oily reagents has influence on flotation efficiency. Increased dispersiveness of thermal gasoil and waste motor oil emulsion exerts a beneficial influence on flotation of coarse and fine coal of the both grades while flotation quality with waste motor oil emulsion worsens. It is possible that selectivity of separation of coarse and less hydrophobic coal also decreases.

In this study, the changes in the specific rate of breakage and breakage distribution function of the nepheline syenite sample were investigated by using alloy steel ball in five different sizes. Specific rate of breakage and breakage distribution function values were obtained from the particle size distributions acquired after the grinding periods. As a result of grinding tests, an increase in rate of breakage is observed due to the increase in ball diameter.

The authors discuss artificial freezing of water-saturated rock mass during construction of mine shafts in terms of a simplified case of a single freezing pipe. The ice growing and holding stages are examined. Maintenance of a constant thickness frozen wall is simulated using the coolant temperature sensor model. The multi-criterion numerical modeling of freezing is implemented, and the time dependences are obtained for the coolant temperature at the ice holding stage. It is found that maintenance of the constant thickness of frozen wall requires that the coolant temperature in ice holding is exponentially grown at the power around - 0.2. The ice growing stage temperature has no influence on the total energy efficiency of the freezing system.

The authors describe the structure, features and application of a software using the extended finite element method in ABAQUS. The software is meant for modeling hydraulic fracturing of permeable rock mass with fracture path tracing in nonuniform stress field.

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.