The aim of the paper is to select and substantiate stable shapes of crown pillars through determining regularities of rock pressure impacts on their stability depending on the crown shapes, mining depths and iron ore hardness.Methods. Stress and strain calculations are performed by the ANSYS 16.0 finite element analysis. Triangulation of the 3D model with a 2 m side is conducted to build stress and strain diagrams. In accordance with the conditions of the experiment, the models were created for horizontal, tent, arched and inclined stope crowns with the dip varying within a wide range. The assumed values of rock pressure on the ore massif conform to mining conditions of the Kryvyi Rih basin deposits at the depths of 1200 to 1700 m. Findings.The obtained values of maximum stresses in stope crowns were calculated in respect to mining depth, rock pressure, crown dip, iron ore hardness and relative curvature radius of the arched crowns. It was determined that vertical and inclined compensating rooms should be used in mining rich iron ores at great depths by sublevel caving systems. In case of the room-and-pillar systems used in mining rich iron ores at great depths, a key requirement is to apply tent and arched crowns which provide maximum stability under high rock pressure.Originality. The research proves that the integrated index of maximum stresses in crown pillars varies from -10 to +32 MPa at depths of over 1200 m and is in polynomial and logarithmic dependence on physical and mechanical properties of the ore mass. It also depends on the crown geometry and, in case of the arched crown, acquires minimal values allowing for stable crown pillar exposures at depths reaching 2000 m. Practical implications.The research results allowed to compile the methodological manual "Choice and substantiation of stable crown shapes in deep-level iron ore mining" for the underground mines of the PJSC "Sukha Balka" and "Rodina" mine of the PJSC "Kryvbaszalizrudkom".
Purpose. To determine the qualitative composition of the equivalent material of a laboratory model representing Kryvyi Rih iron-ore basin ground, as well as to develop a method to determine its quantitative composition for the study of the rock mass stability in the laboratory conditions with the geometric scale of similarity 1:200. Methods.Laboratory studies on models with geometric scale of similarity 1:200 allowed to establish the dependence of the initial stress changes on the percentage of the components comprising the equivalent material. Findings.As a result, the study found that it is expedient in laboratory conditions to replace the full-size model by the sand and paraffin-based equivalent material consisting of granite chips, cast iron, silica sand, mica and paraffin wax. It was established that the quantitative composition of the equivalent material mixture simulating rocks of Kryvyi Rih iron-ore basin consists of cast iron and granite chips (34%) and silica sand, mica and paraffin (66%).Originality. For the first time, the empirical dependence of initial stress occurring in the equivalent material on the percentage of paraffin and iron has been set. Initial stress in the equivalent material depend directly on the amount of cast iron in the mixture and vary according to the polynomial dependence, and the amount of paraffin in the mixture varies according to the quadratic dependence. Practical implications.The obtained results of laboratory tests can be used with sufficient accuracy for physical modeling of processes occurring in rocks during underground mining, and the resulting values of modeling can be used in the design of stopes to be developed.
Selective mining of complex structured ore bodies will enable increased iron content in the mined ore mass in underground mining at Kryvyi Rih iron ore basin applying the existing mining systems. The article determines the way the grade changes in a mine block of a complex structured ore body when applying bulk and selective mining as well as factors influencing indices of extracting ore mass from the block. The investigation results prove that it is reasonable to mine complex structured ore deposits with barren inclusions applying selective mining if the iron content in the block varies from 64 to 67% and horizontal thickness of the barren inclusion makes 4 – 12 m. At that, the thickness ratio should not exceed 0.3. Stoping methods should be applied to receive high indices of ore mass extraction. There is determined an ore/barren inclusion-to-ore body thickness ratio considering the dilution factor that confirms practicability of selective mining of complex structured ore bodies. Selective mining of complex structured ore deposits of Kryvyi Rih iron ore basin applying open stoping enables increasing the mined ore mass quality without considerable capital and operating costs and, consequently, staying on the market and enhancing the environmental situation in the region.
Determining the qualitative composition of the equivalent material for simulation of Kryvyi rih iron ore basin rocKs purpose. To develop a model of composition of Kryvyi Rih iron ore basin through laboratory investigation of equivalent material. methodology. Methods of mathematic simulation and experimental research are used. findings. Conditions of model and prototype similarity are determined; dependencies of physical and mechanical properties of equivalent material rocks on percentage ratio of its components are developed. As a result of the research, it is established that while simulating rocks of Kryvyi Rih iron ore basin in laboratory conditions it is reasonable to use the equivalent material based on a sand-paraffin mixture containing granite chips, fine cast iron, quartz sand, mica and paraffin. The quantitative composition of the mixture is found to be similar to rocks of Kryvyi Rih iron ore basin in the following proportions: cast iron and granite chips-34 %, quartz sand, mica and paraffin-66 %. Approximation of the dependencies results in empirical equations of Poisson's ratio and the horizontal stress of the equivalent material which depend directly on the percentage of cast iron, granite chips and paraffin. Poisson's ratio and the horizontal stress of the equivalent material are proved to grow with the increasing percentage of paraffin in the equivalent material. originality. For the first time, there have been determined empirical dependencies of Poisson's ratio and ultimate strength of the material on the percentage of paraffin and cast iron. Poisson's ratio and the coefficient of the horizontal stress of the sand-paraffin based equivalent material depend on proportions of paraffin and cast iron and are described by the power function. practical value. The results of the laboratory investigations enable creation of a sufficiently precise rock mass model to investigate processes in rocks at underground development of iron ore deposits over time.
Choosing an effective method for performing the mine surveying of the objects at mining enterprise based on the implementation of practical and analytical work. Particular attention is focused on the use of modern technologies for performing field and cameral work, which, in turn, enable to determine the most effective tools and methods for per-forming survey work in open pits, dumps, in collapse zones, and the like. At the same time, one of the priorities when creating graphic material in the form of a mine surveying plan or other mining-graphic documentation is strict compliance with the requirements for the quality of the drawn up documents. Methods. Analysis of the experimental data obtained as a result of the survey work: the mine territory, where the earth's surface collapsed; open pit flank where displacement is observed; open pit area, where reclamation is conducted. The photographic survey from the ground and from the air is made with digital cameras with different specifications for matrices and lenses. When surveying from the ground, photography from a tripod is used, and when surveying from the air, the camera is carried by an unmanned aerial vehicle. Findings. The qualitative characteristics of the images have been obtained, created by different cameras in various photographic survey conditions. The dependence of the accuracy in determining the points coordinates from the digital images on the quality characteristics of the survey equipment has been obtained, which is used when photographing from the ground or installed on unmanned aerial vehicle. Originality. Patterns have been obtained between the accuracy of the data, measured from the research object images, and the metric characteristics of digital cameras and lenses that are used to obtain them. Practical implications. A method has been developed for performing highly efficient photographic surveys of open pits, dumps and other facilities of mining enterprises. Practical data have been obtained and analysed for the use of various types of cameras and lenses to them. The analysis of the measurement characteristics of the images makes it possible to conclude that further research in this direction is necessary in order to improve the existing methods for performing ground and air photography of open pits and other objects of mining enterprises.
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