Vol 52, No 2 (2016)

The article focuses on efficient analysis and test methods to determine nano- and micromechanical properties of rocks and crystals. A modification of the classical elastic problems of contact mechanics implemented using the mathematical apparatus of fractional integro-differentiation is proposed. The authors build new models and algorithms aimed to advance the studies into properties and states of geomaterials based on the atomic-force microscopy techniques, and describe testing of the new approaches in calculation of the elastic modulus for hydrocarbons with nano-additives.

The article offers in situ test methods for cohesion and internal friction angle in rocks and at joints. Technologies and instrumentation for shearing of rock wedges in an open pit mine and for laser scanning and digital imaging of local falls and breaks of inaccessible rock blocks in pitwalls have been developed and approved for constructing a limit equilibrium equation and for calculation of strength properties of rocks and joints. Rock wedges for the tests are prepared using various design drill rigs, the rock wedges are sheared using a 40-t jack placed in a special metal housing with an electric hydraulic pump. Exploration of inaccessible local falls in pitwalls uses electronic tachometers and 3D mine scanner. The tests and approval of the described exploration techniques have been carried out in open pits in Kazakhstan and Kirgizia.

Presence of rock bridges in rock masses would increase the bearing capacity of non-persistent discontinuities. This increase is because of the cohesion and friction angle of the internal support system rendered by the rock bridges. In this article the effect of the number, area and configuration of the rock bridges on their shear properties are investigated. A total of 36 various models with dimensions of 30×30×30 cm of plaster specimens were fabricated simulating the open joints possessing 1, 2, 3 rock bridges respectively. The introduced rock bridges were of longitudinal and latitudinal configuration. The area of these rock bridges were 300, 450 and 600 cm² out of the total fixed area of 900 cm² respectively. The fabricated specimens were subjected to shear tests under 4 different normal loads (20, 30, 40 and 50 kg/cm²) in order to investigate the shear parameters. The results shows that, shear failure occur in longitudinal rock bridge under these normal loads. But tensile failure occur in latitudinal rock bridge when rock bridge continuity was low and shear failure occurs in latitudinal rock bridge when rock bridge area was high. This behavior occurs in each configuration and normal load. The results were indicating that the cohesion of the longitudinal rock bridges is higher than those of the latitudinal rock bridge for similar areas. It was also noticed that in the fixed area of the longitudinal rock bridges the cohesion remains constant with the change in the number of bridges. But the cohesion of the latitudinal rock bridges increase with the increase of the number of rock bridges (under fixed area of the rock bridges). The friction angel was behaved constant all through the tests carried out for various models. In the final section of this article, two equations are introduced for determining the cohesion strength in longitudinal and latitudinal rock bridges.

The solution to a hydraulic fracture problem for the model of Khristianovich–Geertsma–de Klerk is obtained on the basis of the modified formulation of the problem, which, in contrast with the conventional approach, employs the particle velocity rather than the flux. This served to complement the system of ordinary differential equations, resulting after spatial discretization, with the speed equation. The complete system is solved by the Runge–Kutta method for arbitrary initial conditions. The decaying influence of the initial conditions on key characteristics of a fracture (opening and length) at the end of a treatment, is established and numerically analyzed.

The article gives the results of simulated propagation of electromagnetic signals in stratified and damaged dielectric solid model structures exposed to pulsed acoustic treatment. It is shown that the acoustoelectric transformations in such structures result in transition of energy of acoustic pulses to energy of electromagnetic responses in double electric layers. The amplitude–frequency parameters of electromagnetic signals are connected with the characteristics of the determinate acoustic effects and with the charge state of the stratified and damaged structures.

It has been found that gold mine waste in the Amur River Area (Priamurye, Russian Far East) contains associated minerals of gold, belonging in the group of useful components. In view of the complicated nature of the mine waste, it is decided on the appraisal and recovery of the associated useful components with the help of rational technologies.

This research studies the effect of gravel pack size on sand production by designing and manufacturing a machine and a numerical model to simulate sand and gravel pack. This machine and the numerical model make it possible to test different rock along with various fluids under different stress in order to simulate the production of sand and gravel pack.PFC^3D software is applied to create this numerical model. The numerical model consists of sand from 0.22 to 1.1 mm and gravel pack from 3.5 to 4.76, 4.76 to 9.9 to 12.6 and 12.6 to 16.8 mm and the physical model holds gravel from 9 to 4.76 and 4.76 to 9.25. The results from modeling demonstrated that sand is produced the least in the numerical model using gravel from 3.5 to4.76 mm and sand is produced less in the physical model containing gravel pack ranging from 4.76 to 9 mm and the fluid left more output discharge. Moreover, the outcomes from physical modeling proved that as time drags on, the fluid production rate got reduced and then reached to a fixed amount after placing gravel pack. So, it is suggested that gravel pack from 9mm to 4.76mm is more suitable from the viewpoints of fluid production rate and prevention of sand production. Based on dimensional analysis and the results from numerical modeling in a condition without gravel pack, a relation is concluded to estimate sand production rate.

The authors analyze feasibility of voltage stabilization for permanent magnet synchronous generators in independent variable-frequency power networks. The method of voltage stabilization is based on series connection of the generator and a semiconductor converter generating wattless power. Basic energy characteristics of the semiconductor converter and synchronous generator are analytically defined, frequency constraints of the proposed method are found, and rational frequency range and overall power of the system are determined.

The article gives new experimental data on spectral characteristics of photoluminescence of natural diamonds extracted from deep horizons of Mir and Internatsionalnaya Pipes, Republic of Sakha (Yakutia) depending on composition of basic and additional optically active structural defects in crystals and on temperature during spectrum recording, considering kinetics of luminescence. It is hypothesized on applicability of low-temperature effects to enhance efficiency of photoluminescence separation of diamond crystals.

Air bubble and pyrite grain attachment is studied. It is found that mineralization area on an air bubble depends on pulp agitation time, potassium butyl xanthate concentration and pyrite grain size. The authors show the relation between mineralization area of air bubble and weight of mineral load. Using experimental data, it is calculated how many pyrite grains from a narrow size range attach to an air bubble during pulp agitation time, and the weight of these grains is estimated. Physical forces on mineral loading exerted by pyrite grains of–0.1 + 0.071,–0.071 + 0.044 and–0.044 + 0 mm in size at an air bubble at different pulp agitation times, as well as the absolute and specific retention forces are calculated, as well.

The article describes theoretical and experimental data on dearsenation of gold-containing scorodite ore in water vapor. It is shown that roasting of scorodite with pyrite in super-heated vapor enables complete removal of arsenic and sulfur in the form of sulfides from the original material and exposes noble metals.

The author performs the comparative analysis of the international standards on determination of elastic properties of rocks from uniaxial compression tests, with benefits and shortcomings of the standards presented. The measurement data on lateral and transverse strains obtained in rocks and model metal samples under compression using different type extensometers are reported. The scope of the analysis embraces applicability of extensometers to the determination of elasticity modulus and Poisson’s ratio in rocks under variation in temperature. Examples of estimating elastic properties in thawed and frozen rocks are given in terms of enclosing rocks at Botuobinskaya diamond pipe.

The authors prove relevance of digital space data to be used for regional and local operational quantitative estimation of nature in the area of mineral mining and processing. The research findings are analyzed in terms of environmental appraisal made for the area of an open pit mine at Gusevogorskoe deposit of titano-magnetite ore with vanadium admixture (Sverdlovsk Region, Russia).

The methodological approach to rehabilitation of disturbed lands in mining areas in accordance with the evolutionary program of soil formation on mineral substrates by generating biologically active medium has been substantiated and approved based on the data of many-years monitoring at various objects.