Vol 55, No 2 (2019)

Features of stress state and jointing as well as their effect on hydraulic fracture propagation direction in coal seams are considered. The flow resistance in drainage areas is analyzed depending on hydrofracture orientation, thickness of seams and spacing of holes. The comparison of one-stage and multi-stage hydrofractures created in-plane and orthogonally to hole axes is given. In simulated reservoir conditions, permeability of dense coal is studied without a fracture and with a through propped fracture subjected to confining pressure. The recommendations are developed for improving efficiency of gas drainage in coal seams based on in-mine hydraulic fracturing.

An approach is proposed to connecting strength data of different-size rock samples by the linear shear-to-normal stress dependence. The data are presented by Mohr’s circles. The key moment is the determination of centroids for uniaxial compression and tensions areas enveloped by Mohr’s semi-circles. Using coordinates of the centroids, the shear stress–normal stress curves are plotted. Thereupon, the model estimate of missing data (ultimate compression and tension strengths) is constructed for rock samples. The missing ultimate strengths are estimated in terms of meta-siltstone.

Knowledge of the state of stress regime is important to the mine designers for deciding the method of mining and for strategic design in virgin areas. This knowledge helps them in deciding the mining sequence and rock reinforcement for extraction of ores economically and safely. Generally, as excavation progresses to deeper levels, the stress tensors are also equally affected. Elevated stress regime results in concomitant increase in rock fracturing and mining induced deformations. Rock failure in the periphery of the excavation is somewhat stress related, and it is therefore important to ascertain the extent of stress levels within a given rock formation. The role of stress regime in pre- and post-mining stages is discussed. The research is based on the in-situ stress measurements conducted at deeper levels in mines. The authors also tried to ascertain the redistribution of the stresses due to mining and detect any re-orientation of the stresses due to various other geological factors.

The monitoring results on earthquake loads from blasting in the Shakhtau open-pit mine in 2016–2017 are presented. The integrated model of influence exerted by the parameters of drilling-and-blasting and the environment on the surface earthquake loading is developed, which allows high-precision prediction of the seismic effect value at any point of a study area. The estimates of the short-blasting initiation errors are given. It is concluded on the promising nature of continuous blasting monitoring in difficult geotechnical conditions when reliability of standard seismic effect valuation procedures is insufficient.

The geomechanical model of the powered roof support-top coal-roof rock system is developed. For investigation of disintegration processes in top coal of thick seam, numerical modeling with finite element discretization of a study domain is carried out using the authors’ original code. The computational experiment reveals stress distribution in rock mass, as well as evaluates position, shape and size on uncontrolled caving zones in top coal.

The studies aimed to evaluate longwall productivity in the Talda-Zapadnaya 1 Mine are carried out with regard to the technological parameters of the drum shearer and capacity of the armored face conveyor in mining thick methane-bearing coal seam. It is found that methane release reduces with increasing output of the shearer, and allowable longwall length and capacity by the gas criterion are determined. The length of longwall 6605 is optimized by the maximum annual profit of the mine.

Drmno open pit mine with the annual yield of 9 million tons of coal is one of the main providers of the primary energy source in company Elektroprivreda Srbije. Due to the immediate vicinity of two rivers, the Mlava and the Danube, water abundance in the working environment is high and the problem of protecting the open pit from infiltration of underground waters is relevant to the execution of exploitation works. This paper is focused on the multi-attribute check of the preference of one of the two projected variants of the modification of the system for protecting Drmno open pit mine against the infiltration of groundwater. The outcome of the analysis confirms the signification and justification of applying a multiattribute or multi-criteria analysis for examining such problems.

Air resistances are classified depending on their locality in underground mines. Three groups of local resistances are distinguished: shaft and mining horizon intersections; shaft and air channel intersections; stope and ventilation duct intersections in blind drifts. Influence of each group of the local resistances on the mine depression is evaluated as function of geometry and aerodynamics of underground openings. The criteria are proposed for estimating percentage influence of each group on the total mine depression are proposed. The calculation methods are determined for each group to be advisably used in quantitative analysis of air distribution in underground mine ventilation networks under the ventilation mode change.

Adsorption of IM-50 and tall oil fatty acid (ZHKTM) on cassiterite is for the first time determined using the electron and laser microscopy. The micro images of cassiterite polished sections treated with the collecting agents show newly formed phases of an organic matter, the X-ray spectra of the phases feature the increased carbon content. When cassiterite interacts with IM-50 and ZHKTM, the mineral surface is modified by stable metal-absorbent systems, which promotes efficient tin recovery from tin sulphide ore. By the change in the surface relief parameters of cassiterite, the adsorption layer of IM-50 and ZHKTM agents is qualitatively and quantitatively assessed. The comparative flotation tests of cassiterite and quartz fractions prove high collecting ability of IM-50 and ZHKTM relative to tin. It is found that ZHKTM efficiently floats cassiterite in neutral and alkaline environments while IM-50 is used at higher consumption.

—The research results on deep concentration of basic mineralogical variety of natural rich ore to obtain high-quality iron ore product for metallization are presented. The main methods of mineral dressing (selective crushing, magnetic separation in weak and strong fields, gravity separation and flotation) are tested in the technological experiments. It is shown that high-quality iron ore product can be obtained from natural rich ore using a simple technology. The simple technology should be applied at the first stage of processing for maximum possible extraction of high-quality product. Wet separation processes should be used at the later stage as they unavoidably result in high loss of marketable product, as well as bring difficulties connected with dewatering and drying.

The regular patterns are revealed in the influence exerted by the absorbed dose on the elastic wave velocity in granite after radiation exposure. It is shown that the major change in velocity of P-and S-waves in the treated cores of granite is observed when the absorbed dose is 10 kGy. The energy consumption in breaking and crushing can be estimated in the tests of uniaxial compression up to failure. Radiation exposure of granite cores to the dose of 10 kGy reduces energy consumption from 7.68 to 3.06 J in uniaxial compression up to failure and from 700.4 to 470.88 J in crushing. The obtained result is important for improvement of ore pretreatment processes.

The methodical basis is given for the macroecological rough-draught mapping of mining and processing industry zones at a local and regional scale by the key indices and numerical values of geoecological indicators reflecting the real biota response from the results of remote sensing of vegetation cover, with description of contamination sources and production infrastructure. Judged from the functional purpose of maps, the rough-draught maps provide an assessment of current state and quality of the natural environment using the relevant standards and ratings with regard to a human being and the biota as a whole as the principal ecological subject.