Home – Home – Jornals – Journal of Mining Sciences 2024 number 5

This article describes a method to detect and control low-velocity intercalations in rock mass in neighborhood of tunnels and underground mine workings using calculated phase velocities of surface seismic waves. Initial data are synthetic seismograms from numerical modeling of radially symmetric propagation of seismic waves along a mine working. It is shown that overlapping of a low-velocity heterogeneity in rock mass by a higher velocity layer brings no obstacles to the identification of the heterogeneity by the proposed method. Observations over phase velocities of surface seismic waves make it possible to assess rock mass adjacent to underground structures, which is a relevant result from the practical point of view.

The limitations of traditional methods of rock mass classification are reviewed. A modification is proposed for the Hoek-Brown failure criterion, with the compression strength of rocks presented in an explicit form. An approach to the compression strength assessment is taken on the ground of generalized results obtained by Kim in experiments with model block structures made of equivalent materials. An approach to determination of scale effects on strength, deformation modulus, creep and internal friction angle is described. The constant of creep is introduced, and the correlation dependences are obtained to find the creep constant in four types of rocks. It is found that the ratio of displacement at the boundary of a mine opening to displacements in the plastic strain zone can be approximated by a function of the internal friction angle only. This concept is used to calculate internal friction angles in rocks from the analysis of field measurements. The author puts forward two hypotheses and makes an attempt to substantiate them. Hypothesis A supposes that a scale effect in similar structure rock mass depends on the compression strength, and weaker scale effects are typical of hard and brittle rocks as against softer and plastic rocks. Hypothesis B supposes that time of stress and strain relaxation increases in a larger rock mass volume while the strain rate decreases.

The author calculates initial stress state generated under the action of gravity and temperature which changes linearly with depth in stratified rock mass. It is shown that the dominant influence is exerted on the initial stress distribution by the parameter δ which is a ratio of products of triaxial compression moduli and linear expansion factors of rock layers. In two-layer rock mass, when δ calculated as a ratio of thermomechanical characteristics of the upper and lower layers is higher than one, the temperature effect results that the tensile vertical stresses are induced in the lower layer; when suchwise calculated δ is lower than one, the compressive vertical stresses arise in the lower layer. In case of a great divergence of δ from one, in the lower layer, the initial vertical and horizontal stresses increase jump-wise, and the stress pattern resembles a hydrostatic stress distribution. The author performed mathematical modeling of thermal stress field redistribution during advancing undercut-and-fill operations. The software used in the calculations took into account the backfill sequence. The features of stresses in enclosing rock mass and in backfill were revealed.

The article describes the calculated temporal development of the stress-strain behavior for the tubing support-concrete lining-rock mass using a finished 3D numerical model. The model passed verification with the help of laser scanning data on tubing support in two shafts. The factors of safety are obtained in terms of compressive stresses and strains. The authors make recommendations on using tubing of certain sizes in shafts 7 and 8 m in diameter at different depths.

The framework of the research are Bridgmen’s and Farbman’s models for viscosity of powders. The article reports the uniaxial compression test data for ground materials. The authors give examples of calculation of viscosity for coal, quartz, sandstone and sandy shale.

The shear creep failure mechanism of jointed soft rocks is a critical issue in geotechnical engineering. Using the discrete element method, a numerical model of jointed soft rocks was constructed to simulate shear creep under varying joint roughness, normal stress and shear directions. The effects of multiple factors on the creep deformation of soft rocks were then analyzed. Results indicate that the amount of creep deformation in soft rocks significantly decreases with an increase in joint roughness and with an increase in normal stress. However, the influence of shear direction on creep deformation is relatively minor. This study lays a foundation for further research into the creep behavior of soft rocks.

The article describes experimental studies on water saturation of samples of major rock types typical of Donbass. The alterations of deformation properties of moist rocks are generalized. The procedure of modeling with regard to the effect of flooding on displacement parameters in different rocks is presented. Using laboratory data, a finite-element model of activation of geomechanical processes initiated by rock mass undermining and flooding is constructed. It is found how rock mass lithology influences displacement parameters in flooding of underground roadways in coal mines being closed. The research results can help improve effective regulatory documents on ground surface displacement prediction in coal mining and mine closure through lithological analysis of coal-rock mass.

To investigate the slip mechanism of the slope with weak interlayer, the location of the weak interlayer within the slope was determined by on-site monitoring using the Hequ open pit mine as the engineering background, and a three-dimensional numerical model was established based on this, and the study of the potential slip surface and key units of the slope containing weak interlayer was carried out. The potential slip surface inside the slope with weak interlayers is determined from the perspective of displacement contour and maximum shear strain increment. The principle and method of key unit identification for the slope with weak interlayer is proposed. The initial key unit on the potential slip surface of the slope with weak interlayers is identified, and the dynamic breaking path of the key unit on the potential slip surface of the slope with weak interlayers is determined.

The difference in energy accumulation in coal and rock under the same stress level is analyzed, and it is found that the difference of energy accumulation of coal rock under the same stress level mainly depends on the elastic modulus of coal rock material. Based on the structural characteristics and mechanical properties of coal-rock, the mechanical model of combined coal-rock body was constructed and analyzed, and the calculation formula of partition energy storage of combined coal-rock body was deduced. The axial compression test of combined coal-rock body under different loading rates was designed and carried out. Finally, the differential energy instability model of the combined coal-rock body was constructed. An evaluation index of the impact tendency of the combined coal-rock body considering the elastic energy difference and the release time is proposed, which provides a multi-scale criterion for accurately evaluating the impact propensity of the combined body.

The authors design and estimate a room-and-pillar method for mining inclined orebodies with combination of two approaches to ground control: through natural stability of rock mass and by means of overlying rock caving. It is shown that in rock mass under tectonic stresses, it is safe to extract ore reserves from rooms and from temporal ore pillar under protection of rock overhang. Due to inclination of an ore body, rocks in the pillar and in the block bottom fail mostly by way of shearing. The efficient ratios of a minimal width of a temporal ore pillar to a span of a stope are determined.

Fundamental considerations like drillability and tool wear may be pondered for development of deep well drilling for oil and gas, and tunneling projects. Careful considerations of key parameters may enhance the advance rate, operational costs, activity completion timeline and inventory control for spares. NTNU/SINTEF developed drilling rate index (DRI), bit wear index (BWI) and cutter life index (CLI) to quantify drilling and TBM related parameters. Until now, most of the research work has been carried out to develop models in order to recognize the effects of rock properties on drillability. However, very little if no studies have been conducted on the prediction of bit wear using BWI. This work deals with the effects of different geo-mechanical parameters of rocks on the drillability and the bit wear. The work shows that both drillability and bit wear are affected by physical and strength parameters of rocks. Moreover, various statistical models (with R² ≥ 0.83) have been developed through simple linear regression analysis (SLRA) and multiple linear regression analysis (MLRA) for the prediction of NTNU/SINTEF indices (DRI and BWI).

The authors propose an approved integrated approach to assessing influence of coal-rock mass on coal faces by a gas-based criterion through the isotope analysis of coalbed methane. The quantitative ratios of carbon isotopes of methane are determined in coal samples and in mine air samples from seven operating mines in Kuzbass. The geometrical parameters of such zones are assessed, and the maximal methane volume capable to affect a coal face during its operation is found. It is emphasized that the gas volumes and the methane migration zone parameters differ greatly when found using a traditional method and the integrated approach with the carbon isotopic analysis of methane in mine air and in coal.

Gas emission during destruction of coal samples in a mill is measured experimentally. Using the Skochinsky Institute’s procedure, emmitable gas amount is calculated as function of coal particles. Coal samples for the tests were taken in an outburst-hazardous seam. It is found that the decrease in the size of coal particles to 0.1 mm increases gas emission by several times. The authors developed a model of force interaction between methane molecules in micro-porous coal structure and surface of coal macro-molecule, and a calculation procedure for gas emission in coal as function of its degree of breakdown.

The authors developed a resource-saving and energy-efficient technology for integrated processing of eudialyte concentrate. It is found that the main losses of valuable components (Zr and REE) are associated with leaching cake. The effective methods and modes of processing of pregnant solution are determined to ensure high recovery of Zr and REE owing to conversion of silica gel and thanks to successive extraction of zirconium phosphate and rare earth carbonates from pregnant solution. The proposed complimentary methods of regeneration of reagents and shutting off of water circuits ensure recovery of zirconium and rare earths from eudialyte concentrate. The developed technology provides additional marketable products (sodium metasilicate and ammonium nitrate), as well as economic expediency and improved ecological safety of eudialyte concentrate processing due to regeneration of calcium carbonate.

The research focuses on the specificity of flotation of carbonate-fluorite ore waste at Yaroslavskaya Mining Company. The waste composition and process properties are examined. Fluorite in the test waste occurs in mineral concretions and in slime. The problems in flotation of old mining and processing waste are governed by specific surface properties of particles, film coatings and structural transformations. The promising methods to induce conversion of components in flotation pulp are discussed. It is found that ultrasonic and electrochemical treatment of waste components promote selectivity of their separation. The indicators of processes at fixed time intervals and under special effects are analyzed. Flotation with ultrasonic and electrochemical pre-treatment of pulp substantially increases fluorite concentration in froth and enhances selectivity of fluorite separation from calcite. Recovery of fluorite in concentrates with CaF₂ content more than 94% rises by 2.97-4.58%. It is demonstrated that it is possible to reduce mass fraction of silicon dioxide in concentrates by 0.3-0.5%.

The studies on vanadium production are generalized, and the promising nature of flotation is demonstrated in this regard. The prognostic selection of fulvic acid FulvAc as a selective collecting agent relative to vanadium occurred as vanadyl VO²⁺ in acidic pregnant solutions is justified. The analysis of chemical reactivity studied the mechanism of vanadyl extraction and concentration using chelating agent FulvAc. Computer modeling is performed for a flotation system representing a slightly soluble metal complex of vanadyl fulvat [VO²⁺ - FulvAc]_n . Efficiency of FulvAc is proved by lab-scale flotation tests with recovery of vanadyl not less than 92%. Vanadium oxisols are demandable by different industries, and [VO²⁺ - FulvAc]_n is usable as complex mineral supplements for fertilizing mixtures for urban greening.

The authors analyzed some reagent regimes in flotation of nepheline from loparite ore tailings: mixture of tall oils, hydroxamic acids in combination with distilled tall oil; mix of tall oils with addition of polyalkyl benzene sulfonic acids or amine-containing collectors. The nepheline concentrate produced in the optimized reagent regime contained Al₂O₃ 27.18-27.57%. With addition of tall oil polyalkyl benzene sulfonic acid, activity of the collecting mixture reduced, and the produced concentrate quality lowered to Al₂O₃ 26.33%. Two methods to bring flotation concentrates to a standard quality are discussed. The use of magnetic separation allowed production of nepheline concentrate with Al₂O₃ 28.0-28.3% at the recovery of 72-76% compared to the initial product. Direct cationic flotation with agent Flotigam-2835 in an acidic medium with рН 4.5, created by sodium silicofluoride, produced nepheline concentrate with Al₂O₃ 29.63% at the recovery of 65.9% compared to the initial product.