Home – Home – Jornals – Journal of Mining Sciences 2019 number 1

Numerical modeling results on growth of axially symmetric hydraulic fracture new free surface in isotropic poroelastic medium are presented. The problem was solved using extended finite element method based on phantom nodes and cohesion model of failure. Trajectories of the fracture are calculated for different distances from free surface under injection of certain volume of working fluid with regard to the fluid leakage. The influence of impermeable boundary on the hydraulic fracture growth is analyzed.

Based on the uniform strength and minimized stress intensity factor, the maximum strength shape of an opening in rock mass is theoretically analyzed. The criterion and solution method are proposed for the problem on prevention of failure in rock mass with opening under the action of tectonic forces and gravity. The constructed closed system of algebraic equations enables minimization of stress intensity factors depending on mechanical and geometrical parameters of rock mass.

The results of numerical modeling of intense shock wave propagation after explosion in a mine opening with permeable barrier are presented. The problem is solved in the equilibrium inviscid formulation without regard to chemical reactions and with averaged composition of mine air. It is shown that for a screen composed of four similar permeable barriers arranged as a labyrinth, the incoming shock wave has a strongest impact on the first barrier. As a consequence of weakening of the shock wave front on the first barrier, the rest barriers experience much less loading. In order to decrease peak loads on a load-bearing metal structure, it is necessary to reduce areas of their flat front surfaces.

In order to meet the increasing demand to coal, longwalls having large working heights up to 7.3 m are being operated worlwide. As the working heights increase, the load-bearing capacities of powered roof supports used at such longwalls are to be raised too. From a powered roof support it is expected that it safelybears the roof loads and transmits them to the footwall at different working heights. This article presents the results of numerical analyses on roof stresses at different longwall working heights. In order to determine the most suitable longwall working height, average stress distributions that occur on roof and gob zones are calculated for different longwall working heights. For this purpose, numerical models are built up and the procedure is applied to a real-life underground coal mine. Six distinct longwalls are modeled considering rock mass properties and working heights. In conclusion, the most suitable longwall working height for the mine under study is determined considering stresses occurring on roof strata and the gob zone.

The determination of the grain size distribution of blasted rock exceeds the capability of an analytical sieving machine which only gives reliable results within a range of 63 µm to 125 mm. Other sophisticated methods are often not available for particle size measurement in coarse-grained applications in medium scale mining. Therefore, an alternative low cost method to investigate the grain sizes of blasted rock is introduced which can cover a range from 63 µm at the lower end without an upper limit. Three different options to examine blasted dolomite grains are investigated and combined with sieve analysis to determine a complete sieving equivalent grain size distribution. Comparison with results of a technical sieving shows that this method gives a good approximation of the size distribution, improving the possibilities for design of mineral processing equipment.

Accuracy of breakstone grain-size analysis using digital images in the initial method and its modification based on algorithm proposed by Rubin is compared. A modification with averaging of features over all directions and the method with a classification feature represented by difference of intensity distribution functions of fragment projections are described. The results obtained using these methods in a series of tests on grading of five breakstone fractions measured in a certified laboratory. It is shown that the modified method by Rubin with averaging over all directions provides the highest accuracy.

In a transportation fleet in open-pit mines, the match factor is defined between loading and dumping vehicles. This factor helps in indicating the number of vehicles that depend on each other. In this study, a new parameter termed the “detailed match factor” is developed to improve the transportation fleet and relationships are deduced to control the production and grade. A transportation fleet model was simulated for a typical iron ore mine and was solved using both the detailed match factor and ant-colony algorithm methods. The detailed match factor helped in increasing the production by 10.6%

Using inverse distance weighting (IDW), the model of a coal seam with distributed geological and geomechanical characteristics is developed. The hyperbolic dependences of the cutter-loader advance feed and capacity on the coal seam thickness are found. Influence of coal face spalling on cutter-loader capacity is assessed. Using the specialized library of MTSS, the integrated model of process flows in coal face area is developed. It is found that there exists cutter-loader capacity maximum at the increasing dependence of coal cuttability on longwall length.

Backfilling mixture preparation technology using a cement-slag binder is developed for Artem mine. It is shown that backfill with granulated blast-furnace slag reaches project strength when slag is to 80% milled down to 80 μm. The authors analyze influence of milling fineness of granulated blast-furnace slag from different manufacturers on strength and rheological properties of backfill. The economic analysis of cost of binder in formation of load-bearing layer of backfill prepared using fly ash and milled granulated blast-furnace slag is performed.

Various-rank tectonic structures are distinguished in the Norilsk Region. The first-order block structure is formed by intersection of rank I geodynamically active faults: Khatanga, Imangda-Kystykhtakh, Norislk, Fokin-Tangaralakh and other. Rank II faults are the Norilsk-Kharaelakh fault, which intersects the mine field, and other 7 structures. Using geological sections and boring records obtained within the mining lease, dip slips and oblique-slip faults of rank III, represented by ridges in the terrain, are plotted in the satellite image. In the rockburst-hazardous high-grade ore sites in Glubokaya mine, it is recommended to make safe zone by advance boring of destressing holes in underground openings in zone of rank III faults.

Predicting the consequences of changes in a system such as the system of exploitation and consumption of limestone is a problem that requires an adequate analytical approach and encompasses all the limiting factors, their performance, dependence, desirable and non-desirable changes, and completion of the set goal or multiple goals. Without forming the mathematical model and applying the adequate solving method, it is not possible to solve the problem on the optimal level. This paper shows the linear model of location exploitation optimization and consumption of limestone in Macedonia, with 29 production entities - open-pit mines, and two options of consumption entities, with 15 and 16 lime consumers. By changing one of the starting presumptions, the number of consumers, the research shows that mathematical model approach with adequate sensitivity to changes of relative parameters is necessary for a complete and reliable overview of system behavior.

The resource-saving technology is proposed for mining watered lignite deposits in the Kansk-Achinsk basin without drying of productive strata. The expediency of accumulation of all water inflows in mined-out area of the open-pit mine for the subsequent use in the closed production cycle is substantiated. Effectiveness of hydromechanization in selective stripping of incompetent overburden rocks with solid inclusions is determined. Parameters of a hydraulic fill placed in the mined-out area of the open pit are presented.

Slope stability is “the heart” of open pit mining operations. Pit slope monitoring is an important undertaking requiring collection of structural data for geotechnical characterization and stability analysis. Challenges exist with conventional field data collection methods including time, safety, and data accuracy and reliability. In this paper, 3D laser scanning, photogrammetry and Split FX are integrated to investigate open pit slopes in highly geologically altered materials using a case study from the Melbur Pit slopes in Cornwall, United Kingdom. A 3D laser scanner is applied to scan structures from the slope face and to create a 3D point cloud database. Photogrammetry is applied to capture images for processing. 3D images are draped onto the point cloud to give a visual representation of the slope face. The kinematic analysis indicates that the integrated approach enhances the identification of structural discontinuity sets and their orientations. An integration of emerging digital technologies thus provides a comprehensive and reasonably reliable structural database for slope stability analysis during open pit mining.

The procedure is developed for modification of diamond surface by luminophore-containing organic compositions. The compositions are composed of an organic luminophore-anthracene, inorganic luminophore K-35 and cetane. Indication compositions are synthesized based on the selected luminophores and organic liquids and tested using pilot separator POLYUS-M. Spectral-kinetic characteristic of luminophopre-containing organic-mineral compositions, treated weakly luminous diamond crystals and kimberlite minerals are determined. The compositions ensuring better spectral-kinetic characteristics and higher extraction of diamonds during H-ray luminescence separation are selected.

The operating and promising apatite deposits in the Murmansk Regions, holding 70% of Russia’s phosphate ore reserves being unique feedstock for the production of mineral fertilizers are reviewed. The causes of reduction in P₂O₅ content of produced ore, which lead to higher cost of concentrate production and to increased volume of waste, are shown. It is found that it is efficient to stabilize the processing feed through preconcentration of apatite ore by means of coarse X-ray luminescence separation that elevates P₂O₅ content of process flow owing to removal to 20% of material with P₂O₅ content to 2%. The semi-commercial tests reveal destabilizing factors which lower the separation circuit efficiency. Elimination of these factors by adjusting velocity and motion path of coarse ore between the zones of measurement and separation allows minimization of useful mineral loss in waste by more than 2 times, which improves selectivity of X-ray luminescence separation and increases extraction of P₂O₅ in concentrate.

The process of fluid mass transfer and formation of concentration zones on evaporation barrier in rock mass are studied. A series of experiments is carried out on a special testing plant in order to examine the process of settling-down on evaporation barrier and to determine parameters of vertical zonality in settling-down of simple and complex water-soluble nonferrous metal salts. The experimentation procedure is described. The regular patterns are found in the change in content in the direction toward the surface across the whole zone of aeration from the groundwater table. The higher salt concentration is observed on the rock mass surface, in the upper salt crust. This distribution law is typical either of simple or complex salts. The main parameters of settling kinetics and evaporation rate on the barrier are revealed and evaluated.

The process of wet magnetic separation of oxidized ore from the deposit of Abail, Republic of Kazakhstan, is studied. Kinetics of roasted product milling is analyzed, and the optimal size is recommended for the fist stage of milling as -0.071 mm at the content of 55-60%. The accomplished magnetic analysis of different size products shows that the decrease in size causes no increment of iron in the magnetic product and iron is at the level of 63.0 mass%. The scanning electron microscopy reveals that the roasted and magnetic products contain floccules of gangue and magnetite particles which ass into magnetic fraction and worsen its quality. Two schemes are proposed for decomposition of floccules: multistage desliming with regard to sedimentation velocity in liquid medium and attrition with deffloculation agent. It is recommended to apply two two-stage circuit with milling, desliming and wet magnetic separation, which allows production of iron concentrate with iron content of 67% at recovery of 76.5%.

The results of the mineralogical examination if of old sulphide and oxidized gold ore tailings of a mining and processing plant in the Krasnoyarsk Territory are presented. Secondary mineral forms of antimony, namely, antimony bloom Sb₂O₃ and tripuhyite FeSBO₄, as well as iron are found. Gypsum in the waste is a newly formed phase, undetected in the initial ore, revealed in sulphide and mixed ore tailings and is absent in oxidized ore tailings. The key valuable component is gold represented by fine accretions in arsenopyrite, free gold size is not more than a few first microns.

Modeling of heat exchange processes in water-saturated rock mass during shafting with artificial freezing is performed. The problem of adjusting thermophysical properties of rock layers by the experimental measurements of temperature in the check thermal wells spaced from the freezing perimeter is analyzed. In terms of the abuilding shafts at Nezhinsky Mining and Processing Plant, significance of adjusting the the thermophysial parameters borrowed from the geological engineering survey data is illustrated. The number of independent adjustment parameters is determined from the analysis of the system of equations in two-dimensional two-phase Stefan problem in the dimensionless form. An inverse Stefan problem is formulated for a horizontal layer of rocks. The numerical algorithm is proposed for the inverse Stefan problem solution based on the gradient descent method. The algorithm minimizes functional of discrepancies between the model and measurement temperatures at the locations of the check wells. The functional of discrepancies in the phase space of the thermophysical properties and the algorithm convergence are analyzed.

A review of various real time temperature devices available for use in underground coal mines in Queensland was conducted. To investigate the fit-for-purpose of the intrinsically safe (IS) instrument, laboratory experiments were performed. The obtained results were compared to the calibrated reference instrument readings and sling psychrometer data under variation in air flow velocity, moisture content and dust content.