Vol 55, No 4 (2019)

A method is proposed for solving inverse problems characterized by a set of parameters, which uses a system of singular integral equations connecting the boundary values of stress and displacement components and excluding regularization. The calculation involves specifying the static, kinematic and dynamic aspects and adapting them to the conditions of mining a specific seam. The static aspect is understood as classical calculation of the stress-strain state in the vicinity of a stope, the kinematic one takes into account the dead weight of rocks, and the dynamic one considers mining the seam and damage accumulation in enclosing rocks.

Synchronized acoustic emission and strain measurements were carried out in rock salt samples subjected simultaneously to different levels of uniaxial mechanical and incrementally increasing temperature effects. Methodological and hardware support of such measurements is described. Experimental dependences are obtained, which reflect changes in shear strains and acoustic emission activity of samples as functions of time and temperature for different axial stresses. As the stresses increase, rock salt transits to the stage of progressive creep at lower temperatures. The transition to each subsequent stage of the temperature effect is accompanied by an increase in the steepness of shear strains and activity-average acoustic emission. The patterns of changes in these parameters at the stages of steady and progressive creep of rock salt are analyzed. The advantages of using acoustic emission measurements to predict rock salt failure due to progressive creep, as well as their importance for solving the problem on estimating salt rocks properties in real thermobaric conditions for the construction and operation of underground gas storages are noted.

The interaction of an open pipe with an internal soil plug according to the Coulomb’s law of dry friction is investigated. Different soil and pipe models are considered. For all models, finite-difference solutions are obtained, for some—analytical solutions describing the process of elastic interaction of a pipe and a plug. Good agreement between numerical and analytical solutions is shown. The results of numerical calculations for different models are compared and the applicability limits of the models are determined. The effect of Coulomb dry friction on the process of pipe and plug movement is studied.

The preparation mechanism for gas-dynamic fracture of outburst-hazardous coal band during an explosive effect on a coal seam is considered. The conditions for crack formation in the zone farthest from the blasthole are studied, as well as simulation of induced cracks filling with methane, which was initially in coal in a dissolved state, and estimation of the start time for crack development due to the pressure of free methane. It is found that, depending on the mechanical and diffusion parameters of coal, the start time for crack development can vary from tens of seconds to many hours. The study results can be useful in developing a theory of explosive effect on a coal seam in a set of measures to reduce the risk of sudden outbursts of coal and gas.

The purpose of this paper was to observe the generation, development, and extent impact of rock fissures under the blasting process; the failure process of rock under the gases expansion pressure. The latest high-speed camera, producing about 30,000 frames per second (each grid was 32 µs, and exposure time 4 µs), was used to capture the failure process of rock in blasting concrete specimens. The types of cracks and the rate of extended development in a quantitative way were recorded for observation, analysis, and verification of the failure mechanism of induced by blasting. The results showed that the gas expansion rate after blasting reached the maximum of about 200 µs and then gradually attenuated. As to the development rate of the fragmentation of rock after blasting, it reached the maximum of about 130 µs, and the attenuation then became gradual. It is concluded that high-speed photography provides meaningful scientific basis for study of the detonation theory of explosives, rock blasting fracture mechanism, analysis of blast effects, etc. Further improvement and research can be done on the control of the synchronous operation of blasting and photography, and the three-dimensional spatial analysis of the rock blasting process.

The geomechanical conditions of the mined and commissioned ore deposits are determined and systematized on the basis of their typification according to geological and structural features, which are characterized by a commonality of the patterns of stress distribution in an undisturbed rock mass. The area and maximum depth for applying certain geotechnologies in the framework of geomechanical models of the geomedium are established.

The article presents one of the possibilities of using a bucket wheel excavator technology (with a daily capacity of over 100,000 m³) when removing an overburden on the stabilised front in the opencast lignite mine. The influence of excavator manoeuvring movements on the choice of parameters of operational floors is discussed. The assessment of the efficiency of the work process was made, among other things, while maintaining the required safety conditions and geometric parameters of the working front. It has been shown that in the bucket wheel excavator’s over-elevation work with variable variants of vertical and horizontal division (for a given floor height), the length of manoeuvring roads on the operational front is more favourable than the working technology of the entire height of the floor.

The stability of convective air motion in mine shafts after disactivating the draft source is investigated. Based on numerical simulation, it is found that the mine ventilation with natural draft is violated by the formation of air vortices extended along the shaft depth. The transverse profiles of motion velocity and air temperature are determined in approximation of a plane-parallel laminar flow of an incompressible medium with a vertical temperature gradient in the gravity field. Analytical calculations of the stability of the found flow to plane long-wave perturbations are carried out, as a result of which the value of critical Rayleigh parameter is obtained. A correction to the coefficient of air volume expansion allowing taking the hydrostatic compressibility of air into account is simulated. The dependence of the critical value of air temperature vertical gradient in the shaft, the excess of which leads to the formation of convective vortices and violation of through ventilation, is calculated.

Using the methods of X-ray phase analysis, analytical scanning electron microscopy and inductively coupled plasma mass spectrometry, the influence of preliminary energy effects on transformations of eudialyte concentrate base minerals during nitric acid leaching, their micromorphology and phase composition of the surface is studied. It is found that preliminary mechanical activation of the concentrate provides a 34–45% increase in the recovery of zirconium and the sum of rare-earth metal oxides into pregnant solution. Electrochemical processing of mineral suspension during nitric acid leaching and, to a greater extent, ultrasound effects contribute to an additional increase in the recovery of these elements into pregnant solution by 12–23% due to the cleaning of mineral grain surface from amorphous phases and formation of structural inhomogeneities.

The study results of gold leaching using the products of humic acids, as well as stage-by-stage fractionation of parent and gold-containing substances of these acids are presented. The gold content in the pregnant solution was up to 14–30 mg/l. Chemical analysis of the supernatant obtained by a stepwise change in pH of the solution and subsequent centrifugation determined that gold-bearing acids contain both organic and dissolved gold, which is stable to precipitation at pH 2. Fractionation of the original humic acids and subsequent leaching of gold by its individual fractions slows down the dissolution kinetics, and the fractions distinguished at different pH vary significantly in their activity. The most active is the fraction obtained by centrifugation at pH value of 4.6. The spectrum is presented, and the kinetics of gold dissolution by these acids modified by the cyanide complex is shown.

The moisture-retaining properties of rocks in the rock mass are considered at ascending capillary leaching. The dependences of the moisture capacity of disperse material of flotation tailings at ascending motion of solutions are found. The dependence of specific moisture capacity and specific moisture-yielding ability of finely dispersed material at water, pH-neutral, and capillary filtration on the grain size and level of feeding water solutions to the rock mass is revealed. Based on a laboratory experiment, the specific parameters of capillary ascending filtration for the tailing dump are calculated with regard to moisture-capacity properties of the rock mass.

The software and hardware tools for the instrumental estimation and control of the geomechanical state of engineering facilities are presented. A description of the proposed technique for measuring radial and longitudinal displacements of check borehole contour is given. A research methodology and interpretation of experimental data with analysis and monitoring of the stress-strain state of engineering facilities are proposed. The results of testing the developed software and hardware in the conditions of industrial enterprises are presented.