Home – Home – Jornals – Journal of Mining Sciences 2016 number 4

The article reports data of a lab test of directional hydraulic fracturing carried out on a block made of organic glass. A fracture across a hole is created by means of additional shearing stress applied to the hole walls within the interval of the fracture. It is found that seismic emission under hydraulic fracturing has no bearing on destruction of the model material but appears after the fracture completion.

The theoretically evaluated multi-disciplinary approach enables determination of stress state of a coal-rock mass in the area of coal cutting using a package of geomechanical and geophysical information. The approach is based on successive solutions of two inverse problems in the framework of a geomechanical model: coal-bed tomography and assessment of horizontal components of external stress field. The numerical experiments demonstrate resolvability of the inverse problems given appropriate monitoring system ensures sufficient seismic coverage of a coal-bed in the domain of steep spatial gradients of elastic waves and the presence of regular composition in the frequency range of the order of hundreds of hertz in the sounding signal generated by a cutter-loader and/or other coal-face work machinery.

The approach to numerical modeling of physical specimen loading considered by the authors using the discrete element method enables describing ability of rocks to accumulate and release elastic energy. The model specimen is a package of particles characterized by viscoelastic interaction with dry friction. The outer layer particles are connected by elastic springs. On the whole, the model specimen is an element of a medium capable of accumulating a part of energy of deformation in the form of internal self-balanced stresses. Numerical modeling of the specimen compression is performed, and the accumulated energy is assessed. It is shown that clusters form in the medium, and sliding along the boundaries of these clusters causes discontinuities in deformation curve. Also, the discontinuities are possible under stress relaxation after unitary dynamic effect on the specimen. There is a good agreement between the numerical and experimental results.

The scope of the studies embraces statistical and mechanical properties of surface of different kind crystals of salt rocks. Fractal dimension, hardness and elasticity moduli of such crystals are determined. The article gives estimates of fracture toughness and wettability of salt rock crystals as function of fractal dimension of the crystal surface microrelief.

Under computational investigation is the process of sequential growth of hydrofractures under conditions of plane strain. The working fluid is perfect and viscous. The authors analyze influence exerted on parameters and trajectories of growing fractures by spacing of the fractures, external compression field, fluid flow rate, fluid viscosity and leakage flow rate.

The process of crack propagation in coal face area is considered as an informative sign of coal and gas outburst hazard. In the known condition of crack growth at a certain distance from coal face, it is suggested to replace mechanical parameters by geophysical data through application of different evaluation approaches: actual stresses-by spectral-acoustic method relative to amplitudes of high-frequency and low-frequency components of acoustic signal generated by mining machines in coal face area; formation pressure-by analysis of methane concentration in mine air in coal face area; strength of the most folded coal bed-by measuring strength based on penetration depth of a steel cone. The author analyzes the influence of acoustic, strength and permeability and porosity properties of coal face area on limit value of geophysical pre-outburst crack propagation criterion.

Loading causes stress concentration around defects in rocks, which induces initiation and propagation of cracks. Physically, external loading shows itself in rocks as acoustic and electromagnetic emission, included infrared radiation. Experimentally, it is found that in specimens of geomaterials under uniaxial tension, temperature is minimum; under uniaxial compression, temperature grows; under triaxial stress, temperature is maximum. It has been succeeded to derive equations for temperature prediction in a material in the zone of main crack as function of failure load. The method to estimate stress state based on the data on infrared radiation in materials is developed.

Based on the experimental data on separation of stone blocks from rock mass, the author has developed an approximate analytical model to find energy input required to initiate main crack depending on mechanical properties of rocks, geometry of bench, diameter of drillholes and meterage drilled.

Under discussion is soil transport by negative pressure generated in horizontal rotating pipeline. Based on the relations between soil batch velocity, soil batch mass and diameter of the pipeline, the authors have developed procedure to determine the limit pipeline length. The rotary velocity of the pipeline is related with its diameter. Reliability of the proposed procedure results is experimentally proved.

Coordination of heating energy sector performance and legal regulations and standards in the area of air protection from toxic substances involves opportunity analysis of limestone supply as limestone is used as deoxidant in the process of sulfur removal from smoke fuses. The problem of supplying heat power plants with limestone reduces to location identification, i.e. selection of an open pit mine offering the lowest cost of transportation. The authors present a single-phase local model for evaluation of decision-making in management of limestone supply to heat energy sector plants in Serbia.

The presented geological and technical factors make it possible to differentiate coal reserves in South Yakutia based on their property of washability. The authors have constructed algorithm for processing of data of float-and-sink analysis and evaluated coal reserves differentiation criteria. The article describes model of optimization of concentrate yield and quality management and proposes matrix of composition of marketable products based on the market requirements.

The analytical results are given for application of stripping with direct dumping in open pit mines in Kuzbass. It is emphasized that this most productive and the least power-consuming technology loses its weight in the overall content of overburden stripping. The authors propose a method to determine rational boundaries for application area of stripping with direct dumping using slice re-excavation coefficient. The scope of the discussion comprises potential trends of the technology and use of draglines towards enhancement of open pit mining efficiency.

The authors inspect operation of ventilation system in a double-line subway tunnel. It is found that air flow rates required for tunnels and passenger stations differ greatly. For routine operation modes in subway tunnels, the authors evaluate longitudinal ventilation flow chart without station-to-station air chambers, which considerably decreases construction cost of subway ventilation infrastructure. Static pressure fluctuations on outside faces of trains that move in a tunnel in opposite directions are determined. For emergency operation modes of subway tunnel ventilation, under train fire in a tunnel, the authors evaluate a fore-and-aft chart of smoke removal. Toxic emission concentration due to smoke fumes on the way of a breakdown train evacuation is determined. It is proposed to install longitudinal screens in tunnels to ensure safe concentrations of carbon monoxide and carbon dioxide on either way from a breakdown train to a station.

The authors have revealed analytical dependences for the length of a longwall and the background methane emission from a coal bed, mined-out void and wall rocks during a maintenance shift. The actual values of methane release in Kotinskaya Mine and methane concentration in a breakage heading of Kostromovskaya Mine, Belon, measured using air-and-gas control equipment are presented. The authors evaluate theoretical relationships for the cyclical behavior of methane release during a work shift in a production heading of a coal mine.

The article gives a report on integrated experimental research into targeted change of chemical and phase composition of surface and increase in contrast of physicochemical, electrical and electrochemical properties of tantalite, columbite and zircon under treatment by acid product of water electrolysis-anolyte (pH < 5) and by muriatic solution (HCl, pH 3-3.5). The X-ray photoelectron spectroscopy, high resolution spectroscopy and chemical and electrophysical techniques reveal the mechanism of structural-chemical surface transformation of tantalite, columbite, zircon and feldspar under leaching in acid solutions; this surface transformation mechanism consists in activation of dissolving of iron- and silicate-containing surface films and high-rate oxidation of iron atoms in surface layer of tantalite and columbite, with transition of Fe(II) in Fe(III) and surface destruction of zircon, with formation of acid-vacant defects of the type of SiO₃^2-, SiO₂⁰ under influence of anolyte.

Monomineral and compound fractions, ore material and concentrates are used to study effect of basic processing factors on mineral separation. The key criteria are determined to choose a method of selective extraction of minerals and their species in various cycles of a process flow chart. Such key criteria include: degree of activating effect of copper minerals on other sulfides; multifunction role of iron compounds; medium pH values; combination and concentration of depressing ions of modifying reagents; ratios of selective collectors in their combinations; scientific principles of flow chart designing; principles of concentration and recovery of minerals in different processes of dressing.

The data of experimental research into mechanical properties of limestone, hornfels and sandstone cores after treatment by accelerated electrons show that the irradiation changes the strength and deformation characteristics of the tested rocks. In limestone and hornfels, uniaxial compression strength and elasticity modulus decrease, and ratio of P- and S- wave velocities changes; in sandstone, tension strength decreases, while uniaxial compression strength, P- and S-wave velocities and dynamic Young’s modulus grow. Modification of the minerals after accelerated electron irradiation opens ways of creating efficient energy-saving technologies for pre-treatment and processing of composite ore.

The research is aimed at revealing optimum physicochemical conditions for waste processing at coal-firing heat-power plants. The efficient technology has been developed for integrated extraction of amorphous silica, alumina, English red and other useful components.

The development of a new approach to a distributed information system for bio-diversity appraisal in mining regions, with the use of data storage technologies, cloud computing services and mental processing and analysis of multivariable data is in process. It is suggested to adhere to a cardinally new solution in such system engineering and to add the architecture of such system with NoSQL MongoDB and GeoNetwork components that essentially offload the geoinformation system when retrying special calculations and user requests.

The three-component polyurethane composition is developed to create impervious screens in rock mass by hydraulic fracturing technique. Formulas for working fluids and their injection charts are given. The article describes a lab test and the test data on polymer setting time versus activator concentration and on effect of the fluid composition on the permeability of a porous medium at the limited flow rate of reagent per unit area of the screen.